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  • 1990-1994  (3,661)
  • 1970-1974  (2,247)
  • 1920-1924
  • 1905-1909
  • Chemical Engineering  (5,088)
  • Ultrastructure  (820)
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  • 1
    Electronic Resource
    Electronic Resource
    Ultrastructural evidence of GABA-ergic inhibition and glutamatergic excitation in the pacemaker nucleus of the gymnotiform electric fish, Hypopomus (1994)
    Springer
    Journal of comparative physiology 174 (1994), S. 267-280 
    Details
    ISSN: 1432-1351
    Keywords: Electric fish ; Pacemaker ; GABA ; Glutamate ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The medullary pacemaker nucleus of Hypopomus triggers each electric organ discharge (EOD) by a single command pulse. It consists of electrotonically coupled ‘pacemaker’ cells, which generate the rhythm, and ‘relay’ cells, which follow the pacemaker cells and excite the spinal motoneurons of the electric organ. The pacemaker cells receive two inputs from the complex of the diencephalic prepacemaker nucleus (PPn), a GABA-ergic inhibition and a glutamatergic excitation. Relay cells, on the other hand, receive two glutamatergic inputs, one from a subnucleus of the PPn, the PPn-C, and a second from the sublemniscal prepacemaker nucleus (SPPn). We have labelled afferents to the pacemaker nucleus by injecting HRP to specific sites of the prepacemaker complex. By using immunogold-labelled antibodies and en-grid staining techniques, we demonstrated GABA and glutamate immunoreactivity in labelled synaptic profiles of ultra-thin sections of the pacemaker nucleus. The two types of synapses were interspersed on the surfaces of pacemaker cells, with GABA-immunoreactive synapses apparently representing the GABA-mediated input of the ‘PPn-I’, an inhibitory subdivision of the PPn, and glutamate-immunoreactive synapses representing the input of the ‘PPn-G’, an excitatory subdivision of the PPn. Only glutamate-immunoreactive synapses were found on relay cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00240210
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrastructural alterations in thrombocytes of the snake Waglerophis merremii after Activation by ADP (1994)
    Springer
    Comparative clinical pathology 4 (1994), S. 226-231 
    Details
    ISSN: 1433-2981
    Keywords: ADP ; Snake ; Thrombocyte ; Ultrastructure ; Waglerophis merremii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The ultrastructure of the resting thrombocytes of the snake Waglerophis merremii and the process of ADP aggregation are studied. These thrombocytes are nucleate, ellipsoidal, and contain a marginal band. Endoplasmic reticulum and ribosomes are few. An open canalicular system, Golgi complex, granules resembling the alpha-granules in human platelets, and structures similar to secondary lysosomes are also present. The activation response of W. merremii thrombocytes to ADP is examined and compared to the morphological alterations in human platelets. The thrombocytes, normally ellipitical in shape, become spheroid with cytoplasmic protrusions, and adhere to one another. The open canalicular system undergoes dilation and the granules cluster at the centre of the thrombocytes. The release reaction of these granules occurs after stimulation by ADP, similar to what happens in human platelets. This similarity may suggest a process of evolutional specialization since thrombocytes in the majority of non-mammal vertebrates are not aggregated by ADP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185178
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  • 3
    Electronic Resource
    Electronic Resource
    Combined sellar gangliocytoma and pituitary adenoma in acromegaly or Cushing's disease (1994)
    Springer
    Virchows Archiv 425 (1994), S. 93-99 
    Details
    ISSN: 1432-2307
    Keywords: Pituitary adenoma ; Sellar gangliocytoma ; Immunohistology ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Three cases of a composite sellar tumour composed of a gangliocytoma and an adenoma are presented. Two patients who showed acromegaly and hyperprolactinaemia had a gangliocytoma and a growth hormone (GH)-prolactin cell adenoma in close proximity. The gangliocytoma contained growth hormone-releasing hormone (GHRH) by immunohistochemistry. At the electron microscopical level, the gangliocytoma was characterized by numerous synaptic vesicles. The third patient, a child with Cushing's disease, presented a corticotropin-releasing hormone (CRH)-positive gangliocytoma in close contact with an adrenocorticotropic hormone (ACTH) secreting adenoma, the latter a typical densely granulated ACTH cell adenoma. Ultrastructurally, the gangliocytoma revealed synaptic vesicles and sparse secretory granules. The results suggest that gangliocytomas may promote the development of pituitary adenomas by hypersecretion of releasing hormones. Whereas 20 cases of sellar GHRH producing gangliocytomas in acromegaly are reported in the literature, the combination of a CRH-positive gangliocytoma and an ACTH cell adenoma in Cushing's disease is apparently the first case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00193956
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  • 4
    Electronic Resource
    Electronic Resource
    Immunocytochemical and ultrastructural heterogeneities of normal and glibenclamide stimulated pancreatic beta cells in the rat (1994)
    Springer
    Virchows Archiv 425 (1994), S. 305-313 
    Details
    ISSN: 1432-2307
    Keywords: Rat ; Pancreatic beta cells ; Immunocytochemistry ; Ultrastructure ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract When studied morphologically in semi-thin sections in the rat in vivo, pancreatic beta cells displayed heterogeneous immunoreactivities for insulin and amylin, depending on the islet size and the intra-islet position of the beta cells. In larger islets, cortical beta cells (beta cells with contacts with all islet cell types and with the exocrine parenchyma) which are located in the periphery were more densely immunostained for insulin and amylin than medullary beta cells (beta cells with contacts only with other beta cells) which are located in the centre of the islet. Ultrastructurally, these findings were accompanied by differences in the number of secretory granules and mitochondria. Beta cells in small islets and at extra-islet sites exhibited a dense immunoreactivity. After administration of glibenclamide, immunoreactivities for insulin and amylin were diminished in a time-dependent manner, decreasing first in medullary and thereafter in cortical beta cells of larger islets. Ultrastructurally, the beta cells exhibited the typical signs of stimulation. A minority of beta cells in small islets and all beta cells in extra-islet locations remained unchanged. Thus pancreatic beta cells under basal and stimulatory conditions in vivo exhibit heterogeneity in hormone content and in ultrastructural features. These differences may represent the basis for a functional heterogeneity of the insulin secretory response of the individual beta cell both in vivo and in vitro in states of normal and impaired insulin secretion. As heterogeneity was observed only among beta cells in islets, while single beta cells surrounded by acinar cells exhibited no changes in insulin immunoreactivity, interactions between beta cells as well as between beta cells and other endocrine cells may be critical for expression of heterogeneity within the beta cell population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196154
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrastructural study of mast cells stimulated with compound 48/80 as revealed by quick-freezing method (1994)
    Springer
    Virchows Archiv 424 (1994), S. 287-294 
    Details
    ISSN: 1432-2307
    Keywords: Mast cell ; Compound 48/80 ; Ultrastructure ; Quick-freezing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The ultrastructure of mast cells stimulated with compound 48/80 was examined by quick-freezing and deep-etching (QF-DE) or freeze-substitution (QF-FS) methods. Peritoneal cells including mast cells of adult male rats were stimulated in vitro with compound 48/80 at 17° C for 0, 10, 30, 60 or 180 s. The QF-DE replicas revealed that the mast cells stimulated with compound 48/80 for 30 s decreased filamentous actin around secretory granules. In the QF-FS specimens, perigranular membranes in mast cells stimulated for 60 s formed pentalaminar structures between adjacent granules in their cytoplasm prior to degranulation. These findings suggest that preparatory states for degranulation occur in the whole cytoplasm of stimulated mast cells at early stages. Moreover, both QF-FS specimens and QF-DE replicas revealed a compact morphological appearance of discharged granules in the extra-cellular space, indicating the existence of considerable content within the granules. Skeletal structures in the granules were also demonstrated on QF-DE replicas prepared after extracting soluble elements from the cytoplasm. It is suggested that the granular contents associated with the skeletal structures are gradually detached from the discharged granules to ensure local concentration in the tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194613
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of active immunization against gonadotropin-releasing hormone on the ultrastructure of the rat ventral prostate (1994)
    Springer
    Urological research 22 (1994), S. 107-113 
    Details
    ISSN: 1434-0879
    Keywords: GnRH-DT vaccine ; Testosterone ; Ultrastructure ; Rat ; Prostate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To evaluate the effects of active immunization against gonadotropin-releasing hormone (GnRH) on the ultrastructure of the rat ventral prostate, male Sprague-Dawley rats received three consecutive intramuscular injections of 10 μg/100g body weight (D-Lys6)-GnRH-diphtheria toxoid conjugate (GnRH-DT vaccine). Following immunization, test animals developed sufficiently high antibody titres to block the pituitary gonadal axis. Consequently testosterone values dropped to the levels in castrates. This therapy leads to atrophy of the prostate. Following immunization a strong immunological response, indicating the presence of considerable amounts of a GnRH-like peptide, was observed in the ventral prostates as early as 14 days after the first injection of GnRH-DT. Immunoneutralisation of GnRH-like activity may contribute to the effects observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00311001
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  • 7
    Electronic Resource
    Electronic Resource
    Aflatoxin B1-induced ultrastructural alterations in matureZea mays embryos (1994)
    Springer
    Mycopathologia 128 (1994), S. 181-192 
    Details
    ISSN: 1573-0832
    Keywords: Aflatoxin B1 ; Embryo ; Mature ; Ultrastructure ; Zea mays L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mature maize (Zea mays L.) embryos were exposed to aflatoxin B1 (AFB1) concentrations ranging from 0.1 to 25 µg/ml for 9 days. With increasing toxin concentration above 2 µg/ml, primary root elongation of germinated embryos was progressively inhibited, to reach a maximum value of 81% at 25 µ/ml toxin. An ultrastructural investigation of the subcellular alterations induced following toxin exposure provided evidence of deteriorative changes in several compartments of the plant cell. Alteration in membrane integrity (e.g., the tonoplast, plasmalemma and inner mitochondrial membrane) was a frequent feature of many cells. Apparent fusion of vacuoles, incorporation of cytoplasmic components into vacuoles and intravacuolar membrane whorls might be interpreted as deteriorative alterations. The results are discussed in the light of ultrastructural findings for other plant systems exposed to similar AFB1 concentrations, as well as findings for animal systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01138481
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  • 8
    Electronic Resource
    Electronic Resource
    Primary osteosarcoma of the cerebrum with immunohistochemical and ultrastructural studies: report of a case (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 384-388 
    Details
    ISSN: 1432-0533
    Keywords: Key words Extraskeletal osteosarcoma ; Brain neoplasms ; Ultrastructure ; Multinucleated giant cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 57-year-old woman with primary intracerebral osteosarcoma is reported. The tumor was identified by computed tomography as a mass with hemorrhage in the right parietal lobe. The surgical and pathological examinations confirmed an osteosarcoma of intracerebral origin. She suffered from repeated local recurrence of the tumor and died about 1 year after the onset. The pathological findings showed features of osteoblastic osteosarcoma with numerous osteoclast-like multinucleated giant cells. Immunohistochemically, tumor cells were positive for vimentin, and partially for actin. Multinucleated giant cells were reactive with vimentin and CD68 antibodies. Ultrastructurally, tumor cells were rich with rough endoplasmic reticulum. These findings are consistent with the histological features of skeletal or extraskeletal osteosarcoma. This is the third case of primary intracerebral osteosarcoma reported in the literature and the first one analyzed ultrastructurally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310384
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  • 9
    Electronic Resource
    Electronic Resource
    Neuronal vacuole formation in the rat posterior cingulate/retrosplenial cortex after treatment with the N-methyl-d-aspartate (NMDA) antagonist MK-801 (dizocilpine maleate) (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 511-519 
    Details
    ISSN: 1432-0533
    Keywords: Vacuolization ; Neurotoxicity ; Neuropathology ; Electron microscopy ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cytoplasmic vacuoles appear in neurons of the posterior cingulate/retrosplenial cortex (PC/RS) of rats after treatment with N-methyl-d-aspartate (NMDA) receptor antagonists. Prominent dilatation of mitochondria and endoplasmic reticulum has been described within 2 h; however, the ultrastructural features of vacuole formation are unknown. To investigate this, the present study examined the PC/RS cortex of male rats (age 60–70 days) at 15, 30, 45, 60, 90, and 120 min after subcutaneous treatment with 1 mg/kg of the noncompetitive NMDA antagonist MK-801 (dizocilpine maleate, 5-methyl-10, 11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine). Subtle mitochondrial dilatation was identified in a few neurons as early as 15 min postdose (MPD). By 30 MPD, dilatation was more pronounced in mitochondria and also involved the endoplasmic reticulum and perinuclear space. Ribosomal disaggregation and degranulation were also evident by 30 MPD. At all subsequent time points, dilatation of mitochondria and endoplasmic reticulum progressed in severity. Although the relative involvement of mitochondria and endoplasmic reticulum varied, glia were not involved. These ultrastructural data suggest that after treatment with MK-801, mitochondrial dilatation precedes involvement of endoplasmic reticulum in vacuolization of susceptible PC/RS cortical neurons. The early mitochondrial effects identified in this study suggest an initial metabolic insult that rapidly progresses to affect endoplasmic reticulum and ribosomes. This strengthens the relationship between the ability of certain NMDA antagonists to induce energy perturbations and neuronal vacuoles in the same region of the rat cerebral cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296487
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  • 10
    Electronic Resource
    Electronic Resource
    Corticobasal degeneration: etiopathological significance of the cytoskeletal alterations (1994)
    Springer
    Acta neuropathologica 87 (1994), S. 545-553 
    Details
    ISSN: 1432-0533
    Keywords: Corticobasal degeneration ; Ultrastructure ; Tau ; Glial inclusions ; Progressive supranuclear palsy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have studied brain tissues from three patients with corticobasal degeneration (CBD) histologically, ultrastructurally and immunohistochemically. Ballooned neurons in the cerebral cortex and severe degeneration of the substantia nigra were observed in them all and weakly basophilic neurofibrillary tangles (NFTs) were distributed widely in the basal ganglia and brain stem. Ultrastructural examination demonstrated that the NFTs comprised characteristic 15-nm-wide straight tubules, which showed positive immunohistochemical staining with an antibody against tau, but not ubiquitin. Tau-immunoreactive neuronal cell bodies without NFTs also were found in the cerebral cortex and subcortical nuclei, predominantly in the brain stem, and the greatest number of tau-positive glial inclusions occurred in the cerebral gray and white matter of the pre- and post-central gyri. These inclusions comprised tubular structures with diameters of about 15 nm and were localized in the oligodendroglial cellular cytoplasm and processes. These findings indicate that there is a close cytoskeletal pathological relationship between CBD and progressive supranuclear palsy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00293314
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  • 11
    Electronic Resource
    Electronic Resource
    Synapse loss in anterior horn neurons in amyotrophic lateral sclerosis (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 222-227 
    Details
    ISSN: 1432-0533
    Keywords: Amyotrophic lateral sclerosis ; Anterior horn neuron ; Synapse ; Active zone ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This report deals with an ultrastructural investigation of the synapses of anterior horn neurons in the lumbar spinal cords of five patients with amyotrophic lateral sclerosis (ALS) who had mild neuronal depletion. Specimens from five age-matched, neurologically normal individuals served as controls. In each instance, the autopsy was performed within 3 h after death. A statistically significant decrease in cell body area, number of synapses and total synaptic length was found in the normal-appearing neurons of the ALS patients. The alterations were more pronounced in neurons with central chromatolysis. However, despite an approximately 20% reduction in the number of synapses, the length of the active synaptic zone of the normal-appearing neurons in the ALS patients was not diminished. This observation may be accounted for by a plasticity to the loss of synapses which maintained the active zone of the remaining synapses to increase synaptic efficiency. It is suggested that when the plasticity of the active zone reaches its limit, the continuing loss of synapses may lead to functional impairment. The capacity of the active synaptic zone to respond to progressive denervation of the anterior horn neurons may preserve motor function or slow the development of motor deficits in the early stage of degeneration of the lower motor neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00293397
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  • 12
    Electronic Resource
    Electronic Resource
    Structural and ultrastructural characteristics of human pineal gland, and pineal parenchymal tumors (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 334-348 
    Details
    ISSN: 1432-0533
    Keywords: Key words Human pineal gland ; Pineal parenchymal tumors ; Ultrastructure ; Chromogranin A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have studied 20 pineal parenchymal tumors (PPT) and 4 normal or cystic pineal glands both by light and electron microscopy and immunohistochemistry with antibodies against glial markers [glial fibrillary acidic protein (GFAP) and protein S-100] or neural/neuroendocrine markers [neurofilaments (NF), synaptophysin and chromogranin A]. Light microscopy revealed the cellular organization of pinealocytes in the normal gland and in different morphological types of pineal tumors (typical pineocytomas, PPT with intermediate differentiation, mixed PPT exhibiting elements of both pineocytoma and pineoblastoma and pineoblastomas). Immunohistochemistry showed the presence of GFAP and protein S-100 in interstitial cells in non-neoplastic pineal gland. Cell processes were labeled with anti-synaptophysin and anti-NF antibodies. No immunoreactivity was found for chromogranin A in non-neoplastic pineal gland. In pineocytomas, GFAP and protein S-100 were observed in interstitial cells. Synaptophysin and NF were present in the large rosettes of pineocytomas. Synaptophysin, NF and chromogranin A were present in pineocytomas with a lobular arrangement of cells. Anti-chromogranin A immunoreactivity was also seen in lobular areas of some PPT with intermediate differentiation. Analysis of normal human pineal gland by electron microscopy showed the presence of vesicle-crowned rodlets (VCR or synaptic ribbons), fibrous filaments (F), paired twisted filaments but few dense-core vesicles (DCV) in normal pinealocytes. Tumoral pineal cells appeared to differentiate either towards a neurosensory pathway characterized by the presence of sensory cells elements (VCR and F), or towards a neuroendocrine pathway, with the occurrence of many DCV. Immunogold labeling demonstrated the presence of chromogranin A in neurosecretory granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310377
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  • 13
    Electronic Resource
    Electronic Resource
    Structural and ultrastructural characteristics of human pineal gland, and pineal parenchymal tumors (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 334-348 
    Details
    ISSN: 1432-0533
    Keywords: Human pineal gland ; Pineal parenchymal tumors ; Ultrastructure ; Chromogranin A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have studied 20 pineal parenchymal tumors (PPT) and 4 normal or cystic pineal glands both by light and electron microscopy and immunohistochemistry with antibodies against glial markers [glial fibrillary acidic protein (GFAP) and protein S-100] or neural/neuroendocrine markers [neurofilaments (NF), synaptophysin and chromogranin A]. Light microscopy revealed the cellular organization of pinealocytes in the normal gland and in different morphological types of pineal tumors (typical pineocytomas, PPT with intermediate differentiation, mixed PPT exhibiting elements of both pineocytoma and pineoblastoma and pineoblastomas). Immunohistochemistry showed the presence of GFAP and protein S-100 in interstitial cells in nonneoplastic pineal gland. Cell processes were labeled with anti-synaptophysin and anti-NF antibodies. No immunoreactivity was found for chromogranin A in non-neoplastic pineal gland. In pineocytomas, GFAP and protein S-100 were observed in interstitial cells. Synaptophysin and NF were present in the large rosettes of pineocytomas. Synaptophysin, NF and chromogranin A were present in pineocytomas with a lobular arrangement of cells. Anti-chromogranin A immuno-reactivity was also seen in lobular areas of some PPT with intermediate differentiation. Analysis of normal human pineal gland by electron microscopy showed the presence of vesicle-crowned rodlets (VCR or synaptic ribbons), fibrous filaments (F), paired twisted filaments but few dense-core vesicles (DCV) in normal pinealocytes. Tumoral pineal cells appeared to differentiate either towards a neurosensory pathway characterized by the presence of sensory cells elements (VCR and F), or towards a neuroendocrine pathway, with the occurrence of many DCV. Immunogold labeling demonstrated the presence of chromogranin A in neurosecretory granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310377
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  • 14
    Electronic Resource
    Electronic Resource
    Primary osteosarcoma of the cerebrum with immunohistochemical and ultrastructural studies: report of a case (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 384-388 
    Details
    ISSN: 1432-0533
    Keywords: Extraskeletal osteosarcoma ; Brain neoplasms ; Ultrastructure ; Multinucleated giant cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 57-year-old woman with primary intracerebral osteosarcoma is reported. The tumor was identified by computed tomography as a mass with hemorrhage in the right parietal lobe. The surgical and pathological examinations confirmed an osteosarcoma of intracerebral origin. She suffered from repeated local recurrence of the tumor and died about 1 year after the onset. The pathological findings showed features of osteoblastic osteosarcoma with numerous osteoclastlike multinucleated giant cells. Immunohistochemically, tumor cells were positive for vimentin, and partially for actin. Multinucleated giant cells were reactive with vimentin and CD68 antibodies. Ultrastructurally, tumor cells were rich with rough endoplasmic reticulum. These findings are consistent with the histological features of skeletal or extraskeletal osteosarcoma. This is the third case of primary intracerebral osteosarcoma reported in the literature and the first one analyzed ultrastructurally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310384
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  • 15
    Electronic Resource
    Electronic Resource
    Ultrastructural features of secretory cells in the bovine oviduct epithelium (1994)
    Springer
    Anatomy and embryology 190 (1994), S. 583-590 
    Details
    ISSN: 1432-0568
    Keywords: Cattle ; Epithelium ; Oviduct ; Secretion ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The non-ciliated (NC) cells of the bovine oviduct epithelium, have been shown to release embryotrophic substances to the oviduct lumen. The aim of the present study was to investigate the ultrastructure, focusing on aspects of the secretory machinery, of NC cells in different segments of the oviduct during and after transoviduct migration of zygotes and embryos. Dairy heifers (n=8) were superovulated with an ECG/cloprostenol regimen, and the time of ovulation was estimated by ultrasound scanning. Samples from the infundibulum, ampulla, isthmus and uterotubal-junction of the oviduct were surgically collected from animals at 19–96 h and 7 1/2; –8 1/2 days after ovulation and processed for transmission electron microscopy, following standard procedures. The NC cells contained characteristic membrane-bound secretory granules composed of a lamellar cortex encaging an amorphous medulla. The two components could still be recognized during extrusion of the granule content into the oviduct lumen by exocytosis. During granulogenesis, small maturing granules without the lamellar structure were observed, but distinct condensing vacuoles were absent. An abundance of granules was found in the early versus the late group. In both groups the uterotubual junction was almost free of granules. This segment, on the contrary, was characterized by the presence of primary and secondary lysosome-like bodies. In the early group the intracellular location of the granules varied between oviduct segments. In the infundibulum they were placed in the supranuclear cytoplasm, in the isthmus they were found in the most apical part of the cells, while in the ampulla an intermediate granule position was noticed. In both groups the uterotubal junction was almost free of granules. This segment, on the contrary, was characterized by the presence of primary and secondary lysosome-like bodies. Cytoplasmic protrusions, often containing nuclei, were more frequent in the late than in the early group. This phenomenon may represent epithelial renewal. In conclusion, the NC cell of the bovine oviduct epithelium possesses an extensive capacity for protein synthesis and secretion. The numbers and location of secretory granules show cyclic and segmental variations. Most granules are present in the infundibulum and ampulla during the period of transoviduct migration of zygote and embryo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190108
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  • 16
    Electronic Resource
    Electronic Resource
    Neuronal vacuole formation in the rat posterior cingulate/retrosplenial cortex after treatment with the N -methyl-D-aspartate (NMDA) antagonist MK-801 (dizocilpine maleate) (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 511-519 
    Details
    ISSN: 1432-0533
    Keywords: Key words Vacuolization ; Neurotoxicity ; Neuropathology ; Electron microscopy ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cytoplasmic vacuoles appear in neurons of the posterior cingulate/retrosplenial cortex (PC/RS) of rats after treatment with N-methyl-D-aspartate (NMDA) receptor antagonists. Prominent dilatation of mitochondria and endoplasmic reticulum has been described within 2 h; however, the ultrastructural features of vacuole formation are unknown. To investigate this, the present study examined the PC/RS cortex of male rats (age 60 – 70 days) at 15, 30, 45, 60, 90, and 120 min after subcutaneous treatment with 1 mg/kg of the noncompetitive NMDA antagonist MK-801 (dizocilpine maleate, 5-methyl-10, 11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine). Subtle mitochondrial dilatation was identified in a few neurons as early as 15 min postdose (MPD). By 30 MPD, dilatation was more pronounced in mitochondria and also involved the endoplasmic reticulum and perinuclear space. Ribosomal disaggregation and degranulation were also evident by 30 MPD. At all subsequent time points, dilatation of mitochondria and endoplasmic reticulum progressed in severity. Although the relative involvement of mitochondria and endoplasmic reticulum varied, glia were not involved. These ultrastructural data suggest that after treatment with MK-801, mitochondrial dilatation precedes involvement of endoplasmic reticulum in vacuolization of susceptible PC/RS cortical neurons. The early mitochondrial effects identified in this study suggest an initial metabolic insult that rapidly progresses to affect endoplasmic reticulum and ribosomes. This strengthens the relationship between the ability of certain NMDA antagonists to induce energy perturbations and neuronal vacuoles in the same region of the rat cerebral cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296487
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  • 17
    Electronic Resource
    Electronic Resource
    Synapse loss in anterior horn neurons in amyotrophic lateral sclerosis (1994)
    Springer
    Acta neuropathologica 88 (1994), S. 222-227 
    Details
    ISSN: 1432-0533
    Keywords: Key words Amyotrophic lateral sclerosis ; Anterior horn neuron ; Synapse ; Active zone ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This report deals with an ultrastructural investigation of the synapses of anterior horn neurons in the lumbar spinal cords of five patients with amyotrophic lateral sclerosis (ALS) who had mild neuronal depletion. Specimens from five age-matched, neurologically normal individuals served as controls. In each instance, the autopsy was performed within 3 h after death. A statistically significant decrease in cell body area, number of synapses and total synaptic length was found in the normal-appearing neurons of the ALS patients. The alterations were more pronounced in neurons with central chromatolysis. However, despite an approximately 20  % reduction in the number of synapses, the length of the active synaptic zone of the normal-appearing neurons in the ALS patients was not diminished. This observation may be accounted for by a plasticity to the loss of synapses which maintained the active zone of the remaining synapses to increase synaptic efficiency. It is suggested that when the plasticity of the active zone reaches its limit, the continuing loss of synapses may lead to functional impairment. The capacity of the active synaptic zone to respond to progressive denervation of the anterior horn neurons may preserve motor function or slow the development of motor deficits in the early stage of degeneration of the lower motor neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00293397
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  • 18
    Electronic Resource
    Electronic Resource
    Oocyte structure in dominant and subordinate follicles in zebu cattle (Bos indicus) (1994)
    Springer
    Anatomy and embryology 190 (1994), S. 461-468 
    Details
    ISSN: 1432-0568
    Keywords: Oocyte ; Ultrastructure ; Zebu ; Nucleolus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The objective of the study was to investigate the light and ultrastructural morphology of dominant and subordinate oocytes from zebu (Bos indicus) cattle. Healthy cycling animals, which had a well-developed corpus luteum as judged by rectal palpation, were administered cloprostenol to induce luteolysis and therefore ovulation. The animals were slaughtered at days 3–11 post-ovulation, but those slaughtered at days 8–11 received a second injection of cloprostenol at day 7. Cumulus-oocyte complexes were aspirated from the largest (dominant) and the second largest (subordinate) follicles, and processed for transmission electron microscopy. Up to day 7, the dominant oocyte presented a peripherally located spherical oocyte nucleus with a compact dense fibrillar nucleolus. After day 7, the nuclear envelope became undulated and the nucleolus vacuolated. The nuclei contained an average of four nucleoli. In addition to vesicles, mitochondria, smooth endoplasmic reticulum, Golgi complexes and cortical granules, the ooplasm contained annulate lamellae and microtubules. Moreover, mitochondrial granules and pleomorphic forms of mitochondria were commonly observed. Some subordinate oocytes exhibited advanced stages of meiotic maturation. It is concluded that (1) the dominant oocyte undergoes certain prematurational changes, including nucleolus vacuolation, in the period from luteolysis up to the presumptive occurrence of the LH peak and (2) subordinate oocytes may undergo meiotic maturation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235493
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  • 19
    Electronic Resource
    Electronic Resource
    Chick gonadogenesis following early surgical bursectomy (1994)
    Springer
    Anatomy and embryology 190 (1994), S. 439-444 
    Details
    ISSN: 1432-0568
    Keywords: Chick embryo ; Bursectomy ; Female gonads ; Steroidogenic cells ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We examined the ultrastructural characteristics of the medullary steroidogenic cells in left and right female gonads of surgically bursectomized chick embryos killed on the 17th day of incubation. The steroidogenic cells of the bursectomized embryos have a more developed system of cisternae in the smooth endoplasmic reticulum than controls, and their mitochondria show some alterations in the density of the matrix and in the shape of the cristae. On the basis of these results, an enhancement of the steroidogenic activity in both gonads is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235490
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  • 20
    Electronic Resource
    Electronic Resource
    The loci of mineral in turkey leg tendon as seen by atomic force microscope and electron microscopy (1994)
    Springer
    Calcified tissue international 55 (1994), S. 180-189 
    Details
    ISSN: 1432-0827
    Keywords: Collagen ; Crystal habit ; Ultrastructure ; Turkey leg tendon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Transmission electron micrographs of fully mineralized turkey leg tendon in cross-section show the ultrastructure to be more complex than has been previously described. The mineral is divided into two regions. Needlelike-appearing crystallites fill the extrafibrillar volume whereas only platelike crystallites are found within the fibrils. When the speciment is tilted through a large angle, some of the needlelike-appearing crystallites are replaced by platelets, suggesting that the needlelike crystallites are platelets viewed on edge. If so, these platelets have their broad face roughly parallel to the fibril surface and thereby the fibril axis, where the intrafibrillar platelets are steeply inclined to the fibril axis. The projection of the intrafibrillar platelets is perpendicular to the fibril axis. The extrafibrillar volume is at least 60% of the total, the fibrils occupying 40%. More of the mineral appears to be extrafibrillar than within the fibrils. Micrographs of the mineralized tendon in thickness show both needlelike-appearing and platelet crystallites. Stereoscopic views show that the needlelike-appearing crystallites do not have a preferred orientation. From the two-dimensional Fourier transform of a selected area of the cross-sectional image, the platelike crystallites have an average dimension of 58 nm. The needlelike-appearing crystallites have an average thickness of 7 nm. The maximum length is at least 90 nm. Atomic force microscopy (AFM) of unstained, unmineralized turkey leg tendon shows collagen fibrils very much like shadow replicas of collagen in electron micrographs. AFM images of the mineralized tendon show only an occasional fibril. Mineral crystallites are not visible. Because the collagen is within the fibrils, the extrafibrillar mineral must be embedded in noncollagenous organic matter. When the tissue is demineralized, the collagen fibrils are exposed. The structure as revealed by the two modalities is a composite material in which each component is itself a composite. Determination of the properties of the mineralized tendon from the properties of its elements is more difficult than considering the tendon to be just mineral-filled collagen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425873
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  • 21
    Electronic Resource
    Electronic Resource
    Bioactive glass-ceramic containing crystalline apatite and wollastonite initiates biomineralization in bone cell cultures (1994)
    Springer
    Calcified tissue international 55 (1994), S. 458-466 
    Details
    ISSN: 1432-0827
    Keywords: In vitro ; Bioactive glass ceramic ; Mineralization ; Bone bonding mechanisms ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Rat bone cells were cultured in the presence of bioactive glass-ceramic containing crystalline apatite and wollaston te. Scanning electron microscopy observations of the surface of the seeded ceramic disks revealed that cells attached, spread, and proliferated on the material surface. Soaking in cell-free culture medium showed that no change occurred in the surface structure. However, when cultured with bone cells and observed under a transmission electron microscope, an electron-dense layer was noted initially at the surface of the material, before bone formation occurred. In addition, energy-dispersive X-ray microanalysis demonstrated the presence of calcium and phosphorus in this layer. Progressively, during the following days of culture, active osteoblasts synthetized and laid down an osteoid matrix composed of numerous collagen fibrils arranged either parallel or perpendicularly to the first-formed electron-dense layer. Mineralization initiated on the ceramic surface dispersed then along the collagenous fibrils, leading to a mineralized matrix which surrounded the ceramic particles. These results demonstrate the capacity of apatite-wollastonite glass ceramic to initiate biomineralization in osteoblast cultures and to achieve a direct bond between the surface apatite layer of the bioactive glass-ceramic and the mineralized bone matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298560
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  • 22
    Electronic Resource
    Electronic Resource
    Ultrastructural analysis of graft-to-host connections, with special reference to dopamine-neuropeptide Y interactions in the rat striatum, after transplantation of fetal mesencephalon cells (1994)
    Springer
    Experimental brain research 98 (1994), S. 84-96 
    Details
    ISSN: 1432-1106
    Keywords: Dopaminergic grafts ; Neuropeptide Y ; Ultrastructure ; Striatum ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In a previous study we demonstrated that grafted dopamine (DA) neurons are able to induce an early and widespread normalization of DA-neuropeptide Y (NPY) interactions in the host striatum previously deprived of its DA input. Since similar recoveries were found to occur in striatal areas densely or poorly reinnervated by the graft, the question was raised as to what mechanisms (synaptic or volumic release) were involved in these functional effects. Ultrastructural analysis of graft-to-host relationships was performed using single — and double — immunolabelling techniques to detect neurons containing tyrosine hydroxylase (TH) and NPY, with a view to analysing the early establishment of synaptic connectivity in various areas of the host striatum. Within 1 month of the grafting, TH-immunoreactive (TH-IR) neurons showed most of the normal intrinsic morphological features characteristic of adult rat neurons and were found to have established direct relationships with various striatal neuronal populations. TH-NPY relationships were observed only in the area most densely reinnervated by the graft, and their relative frequency was found to be roughly the same as that determined in the intact striatum. Three months after the grafting, this percentage decreased, probably owing to the further elongation in TH-IR axons resulting in a wider distribution of the TH-NPY associations over the host striatum. In the zones distal from the graft, the reinnervation was far from complete and the few TH-IR fibres projected only to some unlabelled elements, mainly of the spiny type, which have been shown to interact normally with both DA afferents and NPY cells and therefore may relay the DA action over the whole striatum on the NPY population. It can be concluded from these data that the rapid and extensive functional normalization of the TH-NPY interactions previously found to occur in the entire striatum may depend on the restoration of direct and indirect synaptic relationships. A diffuse action of DA through non-synaptic mechanisms may also account for the fact that the amine has access to broader striatal populations than to those presumably reached by DA fibres arising from the graft.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229112
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  • 23
    Electronic Resource
    Electronic Resource
    Die klinische Pathologie invertierter Papillome der Harnblase Eine komplexe morphologische und katamnestische Studie (2. Mitteilung) (1994)
    Springer
    Der Pathologe 15 (1994), S. 279-285 
    Details
    ISSN: 1432-1963
    Keywords: Schlüsselwörter Invertiertes Harnblasenpapillom ; Wachstumstypen ; Ultrastruktur ; Maligne Transformation ; Klinischer Verlauf ; Key words Inverted urinary bladder papilloma ; Growth types ; Ultrastructure ; Malignant transformation ; Clinical course
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The histopathology, ultrastructure, pathological status and clinical course are described in a total of 29 cases of inverted papilloma of the urinary bladder (IP). The IP was isolated in 16 cases and occurred in combination with a papillary urothelial carcinoma in 13 cases. Histologically, a trabecular, a glandular and a mixed type can be differentiated. The trabecular from predominates in a ratio of 4 : 1. The glandular form is further subdivided into a cystic form and an adenomatous form containing cylindrical cells. Contrary to earlier assumptions, dysplasia and malignant transformation also occur in IP. Amongst the 16 isolated IP observed, four showed slight and four showed moderate dysplasia. One isolated IP was malignant and invasive. In IP in combination with papillary urothelial carcinomas, malignant transformation is somewhat more frequent. Four malignant IP and up to 85 % dysplasias were found among the 13 cases. The ultrastructure of IP reveals two cell types: a light cell form which corresponds to a slightly dysplastic urothelium and a darker cell form with or without microvilli which is observed in the glandular type. A frequent characteristic is a thickening of the basement membrane besides abundant “tight junctions”. The immunohistochemistry is relatively uncharacteristic. This also applies to the blood group isoantigens, which showed irregular and relative uninformative results in the SCRA test. IP is observed in all age groups and the sex ratio (M/F) is 3 : 1. The average age of manifestation is 56 years, about 10 years earlier than bladder carcinoma. Just under two-thirds of IPs are in the region of the trigonum, the ureteral ostia at the neck of the bladder and the prostatic part of the urethra, and IPs rarely exceed 3 cm in size. Malignant transformation and recurrence are only rarely observed. With regard to the formal pathogenetics, there are correlations with Brunn cell clusters and with the basal urothelial cell, which can be characterized as the urothelially determinative cell.
    Notes: Zusammenfassung Auf der Basis von insgesamt 29 Fällen mit einem invertierten Harnblasenpapillom (IP), von denen bei 16 das IP isoliert vorkam und in weiteren 13 eine Kombination mit einem papillären Urothelkarzinom vorlag, wird zur Histopathologie, Ultrastruktur, Dignität und zum klinischen Verlauf Stellung genommen. Histologisch zeigen sich Wachstumstypen, die sich in einem trabekulären, glandulären und einem Mischtyp äußern. In einem Verhältnis von 4 : 1 überwiegt die trabekuläre Form. Entgegen früheren Annahmen kommen beim IP auch Dysplasien sowie eine maligne Transformation vor. Die Ultrastruktur des IP läßt 2 Zellarten erkennen: eine helle Zellform, die einem gering dysplastischen Urothel entspricht und eine dunklere Zellform mit oder ohne Mikrovilli, die beim drüsigen Typ zur Beobachtung kommt. Häufiges Merkmal ist eine Basalmembranverdickung neben reichlich „tight junction“. Die Immunhistochemie zeigt eine Differenzierung in Richtung Basalzelle, ist jedoch wenig charakteristisch, so auch die Blutgruppenisoantigene, die sich irregulär verhalten. Das IP wird in allen Altersgruppen beobachtet und überwiegt mit 3 : 1 beim männlichen Geschlecht. Durchschnittliches Manifestationsalter liegt im 56. Lebensjahr, etwa 10 Jahre früher als beim Harnblasenkarzinom. Knapp zwei Drittel sind im Bereich Trigonum, der Ureterostien des Blasenhalses und der Pars prostatica urethrae lokalisiert und überschreiten nur sehr selten die Größe von 3,0 cm. Ebenso wie die maligne Transformation werden auch Rezidive nur selten beobachtet. Formalpathogenetisch bestehen Beziehungen zu den Brunn-Zellnestern und zur basalständigen Urothelzelle, die als urotheliale Determinativzelle charakterisiert werden kann.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002920050055
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  • 24
    Electronic Resource
    Electronic Resource
    Ultrastructure of an extreme thermophilic hydrogen-oxidizing bacterium Calderobacterium hydrogenophilum (1994)
    Springer
    Archives of microbiology 162 (1994), S. 267-271 
    Details
    ISSN: 1432-072X
    Keywords: Key words     Extremely thermophilic eubacterium ; Calderobacterium hydrogenophilium ; Ultrastructure ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract       Calderobacterium hydrogenophilum is an extreme thermophilic, obligately chemoautotrophic, hydrogen-oxidizing bacterium. The cells were shown to be non-motile straight rods of average size 0.4 × 2.5 μm. After negative-staining of the whole cells, no flagella were observed. The multilayered cell wall was of type 1 and possessed a crystalline proteinaceous surface layer exhibiting p4 symmetry. The square unit cells had a lattice constant of approximately 11 nm. Cell division occurred by a constriction mechanism. C. hydrogenophilum differred from a similar hydrogen-oxidizing eubacterium, Hydrogenobacter thermophilus, by the absence of intracytoplasmic membrane structures in chemically fixed cells. However, an electron-dense intracytoplasmic hemispherical structure adhering to the inner membrane was frequently observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301849
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  • 25
    Electronic Resource
    Electronic Resource
    Ultrastructure of an extreme thermophilic hydrogen-oxidizing bacterium Calderobacterium hydrogenophilum (1994)
    Springer
    Archives of microbiology 162 (1994), S. 267-271 
    Details
    ISSN: 1432-072X
    Keywords: Extremely thermophilic eubacterium ; Calderobacterium hydrogenophilium ; Ultrastructure ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Calderobacterium hydrogenophilum is an extreme thermophilic, obligately chemoautotrophic, hydrogen-oxidizing bacterium. The cells were shown to be nonmotile straight rods of average size 0.4x2.5 μm. After negative-staining of the whole cells, no flagella were observed. The multilayered cell wall was of type 1 and possessed a crystalline proteinaceous surface layer exhibiting p4 symmetry. The square unit cells had a lattice constant of approximately 11 nm. Cell division occurred by a constriction mechanism. C. hydrogenophilum differred from a similar hydrogen-oxidizing eubacterium, Hydrogenobacter thermophilus, by the absence of intracytoplasmic membrane structures in chemically fixed cells. However, an electron-dense intracytoplasmic hemispherical structure adhering to the inner membrane was frequently observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301849
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  • 26
    Electronic Resource
    Electronic Resource
    Analog of vertebrate anionic sites in blood-brain interface of larval Drosophila (1994)
    Springer
    Cell & tissue research 277 (1994), S. 87-95 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Blood-brain barrier ; Anionic sites ; Larvae ; Septate junctions ; CNS ; Glia ; Ultrastructure ; Drosophila melanogaster (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The blood-brain barrier ensures brain function in vertebrates and in some invertebrates by maintaining ionic integrity of the extraneuronal bathing fluid. Recent studies have demonstrated that anionic sites on the luminal surface of vascular endothelial cells collaborate with tight junctions to effect this barrier in vertebrates. We characterize these two analogous barrier factors for the first time on Drosophila larva by an electron-dense tracer and cationic gold labeling. Ionic lanthanum entered into but not through the extracellular channels between perineurial cells. Tracer is ultimately excluded from neurons in the ventral ganglion mainly by an extensive series of (pleated sheet) septate junctions between perineurial cells. Continuous junctions, a variant of the septate junction, were not as efficient as the pleated sheet variety in blocking tracer. An anionic domain now is demonstrated in Drosophila central nervous system through the use of cationic colloidal gold in LR White embedment. Anionic domains are specifically stationed in the neural lamella and not noted in the other cell levels of the blood-brain interface. It is proposed that in the central nervous system of the Drosophila larva the array of septate junctions between perineurial cells is the physical barrier, while the anionic domains in neural lamella are a “charge-selective barrier” for cations. All of these results are discussed relative to analogous characteristics of the vertebrate blood-brain barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00303084
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  • 27
    Electronic Resource
    Electronic Resource
    C-PON immunoreactive neurons in the neostriatum of the hedgehog (Erinaceus europaeus): a correlated light- and electron-microscopic study (1994)
    Springer
    Cell & tissue research 277 (1994), S. 177-181 
    Details
    ISSN: 1432-0878
    Keywords: Key words: C-PON ; Neuropeptide Y ; Neostriatum ; Immunocytochemistry ; Ultrastructure ; Erinaceus europaeus (Insectivora)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The present study provides light- and electron-microscopic immunocytochemical data on the presence of neurons that are immunoreactive to the C-terminal flanking peptide of neuropeptide Y, C-PON, in the neostriatum of the hedgehog (Erinaceus europaeus). Positive neurons have mostly fusiform or round perikarya from which two to four poorly branched processes arise. Immunostained fibers and puncta are also evenly distributed throughout the neostriatum. Ultrastructurally, each neuron exhibits a deeply invaginated nucleus surrounded by abundant cytoplasm with a well-developed rough endoplasmic reticulum and Golgi apparatus. Positive neurons receive symmetric and asymmetric synapses from unlabeled terminals. The results of this study can be correlated with previous findings, as the C-PON-positive neurons of the hedgehog resemble medium-sized neostriatal neurons that are known to be local circuit neurons exhibiting C-PON in the rat. Thus, a high degree of C-PON neuronal system phylogenetic conservation and function can be postulated for the neostriatum of mammals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00303094
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  • 28
    Electronic Resource
    Electronic Resource
    Analog of vertebrate anionic sites in blood-brain interface of larval Drosophila (1994)
    Springer
    Cell & tissue research 277 (1994), S. 87-95 
    Details
    ISSN: 1432-0878
    Keywords: Blood-brain barrier ; Anionic sites ; Larvae ; Septate junctions ; CNS ; Glia ; Ultrastructure ; Drosophila melanogaster (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The blood-brain barrier ensures brain function in vertebrates and in some invertebrates by maintaining ionic integrity of the extraneuronal bathing fluid. Recent studies have demonstrated that anionic sites on the luminal surface of vascular endothelial cells collaborate with tight junctions to effect this barrier in vertebrates. We characterize these two analogous barrier factors for the first time on Drosophila larva by an electron-dense tracer and cationic gold labeling. Ionic lanthanum entered into but not through the extracellular channels between perineurial cells. Tracer is ultimately excluded from neurons in the ventral ganglion mainly by an extensive series of (pleated sheet) septate junctions between perineurial cells. Continuous junctions, a variant of the septate junction, were not as efficient as the pleated sheet variety in blocking tracer. An anionic domain now is demonstrated in Drosophila central nervous system through the use of cationic colloidal gold in LR White embedment. Anionic domains are specifically stationed in the neural lamella and not noted in the other cell levels of the blood-brain interface. It is proposed that in the central nervous system of the Drosophila larva the array of septate junctions between perineurial cells is the physical barrier, while the anionic domains in neural lamella are a “charge-selective barrier” for cations. All of these results are discussed relative to analogous characteristics of the vertebrate blood-brain barrier.
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    URL: http://dx.doi.org/10.1007/BF00303084
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  • 29
    Electronic Resource
    Electronic Resource
    Odontoclastic resorption of the superficial nonmineralized layer of predentine in the shedding of human deciduous teeth (1994)
    Springer
    Cell & tissue research 277 (1994), S. 19-26 
    Details
    ISSN: 1432-0878
    Keywords: Odontoclasts ; Resorption ; Predentine ; Ultrastructure ; Histochemistry ; TR-ACPase (tartrateresistant acid phosphatase) ; Deciduous teeth ; Shedding ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Resorption by odontoclasts of a superficial nonmineralized layer of predentine that occurs in prior to the shedding of human deciduous teeth was studied by light and electron microscopy. As resorption of the tooth roots neared completion, multinucleate cells appeared on the predentine surface of the coronal dentine between the degenerated odontoblasts, excavated characteristic resorption lacunae in the nonmineralized predentine. These multinucleate cells had the same ultrastructural characteristics as odontoclasts and histochemical demonstration of tartrate-resistant acid phosphatase activity in the multinucleate cells revealed intense staining in numerous small granules identified as lysosomes. Occasionally, the multinucleate cells simultaneously resorbed both nonmineralized and calcospherite-mineralized matrix in the predentine. The study demonstrates that multinucleate odontoclasts can resorb nonmineralized predentine matrix in vivo, probably in the same way as they resorb demineralized organic matrix in the resorption zone underlying their ruffled border.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00303076
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  • 30
    Electronic Resource
    Electronic Resource
    C-PON immunoreactive neurons in the neostriatum of the hedgehog (Erinaceus europaeus): a correlated light- and electron-microscopic study (1994)
    Springer
    Cell & tissue research 277 (1994), S. 177-181 
    Details
    ISSN: 1432-0878
    Keywords: C-PON ; Neuropeptide Y ; Neostriatum ; Immunocytochemistry ; Ultrastructure ; Erinaceus europaeus (Insectivora)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The present study provides light- and electronmicroscopic immunocytochemical data on the presence of neurons that are immunoreactive to the C-terminal flanking peptide of neuropeptide Y, C-PON, in the neostriatum of the hedgehog (Erinaceus europaeus). Positive neurons have mostly fusiform or round perikarya from which two to four poorly branched processes arise. Immunostained fibers and puncta are also evenly distributed throughout the neostriatum. Ultrastructurally, each neuron exhibits a deeply invaginated nucleus surrounded by abundant cytoplasm with a well-developed rought endoplasmic reticulum and Golgi apparatus. Positive neurons receive symmetric and asymmetric synapses from unlabeled terminals. The results of this study can be correlated with previous findings, as the C-PON-positive neurons of the hedgehog resemble medium-sized neostriatal neurons that are known to be local circuit neurons exhibiting C-PON in the rat. Thus, a high degree of C-PON neuronal system phylogenetic conservation and function can be postulated for the neostriatum of mammals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00303094
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  • 31
    Electronic Resource
    Electronic Resource
    Occurrence of unusual tubular invaginations of the plasma membrane in smooth muscle cells of the lamprey, Lampetra japonica (1994)
    Springer
    Cell & tissue research 276 (1994), S. 51-59 
    Details
    ISSN: 1432-0878
    Keywords: Sarcolemma ; Surface tubules ; Smooth muscle ; Endothelial cells ; Fibroblasts ; Ultrastructure ; Lamprey, Lampetra japonica (Cyclostomata)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Numerous tubular structures were observed in the surface region of smooth muscle cells making up the vascular walls in the lamprey, Lampetra japonica; they were designated as surface tubules. The limiting membrane of the surface tubules was connected to the plasma membrane, allowing communication of the lumen of the tubule with the extracellular space. Tannic acid reacted with osmium, serving as an extracellular marker, penetrated into the tubules but not into the intracellular organelles, such as the endoplasmic reticulum and the Golgi complex. The surface tubules were grouped in longitudinal parallel rows, separated from each other by tubule-free areas where dense plaques were present. Each tubule was fairly cylindrical (approximately 60 nm in diameter) and often ramified into two or three branches with a blind end. Occasionally, these tubules were encircled by the sarcoplasmic reticulum which was located immediately beneath the plasma membrane. Similar tubules were also observed in the surface region of vascular endothelial cells and fibroblasts in the adventitial connective tissue. The possibility that the surface tubules in the present observations are analogous to the smooth muscle caveolae or the striated muscle T-tubule is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354784
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  • 32
    Electronic Resource
    Electronic Resource
    Glucagon-like peptide 1 immunoreactivity in gastroentero-pancreatic endocrine tumors: a light- and electron-microscopic study (1994)
    Springer
    Cell & tissue research 276 (1994), S. 571-580 
    Details
    ISSN: 1432-0878
    Keywords: Glucagon-like peptide 1 ; Endocrine tumors ; Immunohistochemistry ; Ultrastructure ; Multiple endocrine neoplasia type 1 ; Co-localization ; Man
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The preproglucagon gene encodes, in addition to glucagon, two smaller peptides with structural similarity: glucagon-like peptides 1 and 2. Glucagon-like peptide 1 (GLP-1) 7–36 amide is the most powerful incretin candidate. In the present study, GLP-1 immunoreactivity was investigated in tissue specimens of various types of gastroenteropancreatic tumors, and the serum-levels of GLP-1 were assayed. Immunohistochemical staining of 88 tumors revealed GLP-1 immunoreactivity in 17 neoplasias (19.3 %), viz., in 7 out of 33 non-functioning tumors, 4 out of 20 gastrinomas, 4 out of 13 insulinomas, 1 out of 3 vasoactive-intestinal-polypeptide (VIP)omas and 1 adrenocorticotropic-hormone (ACTH)-producing tumor. In these tumors, GLP-1-immunoreactive cells were distributed either diffusely, arranged in clusters, or as single cells. All GLP-1-positive tumors were immunoreactive for glucagon or glicentin, 10 tumors were immunoreactive for pancreatic polypeptide, and 8 tumors for insulin. Ultrastructural analysis of 8 GLP-1-positive tumors, with the immunogold technique, demonstrated GLP-1 immunoreactivity mainly in cells resembling the A-cells of the pancreas or the L-cells of the gut. Of the 17 GLP-1-immunoreactive tumors, 15 were primarily located in the pancreas. Additionally, 2 non-functioning tumors of the rectum were GLP-1 immunoreactive. Five tumors were GLP-1 immunoreactive from 9 patients with multiple endocrine neoplasia I syndrome. Patients with GLP-1-immunoreactive tumors were characterized by a significantly lower rate of distant metastases (P〈0.01) and a higher rate of curative resections (P〈0.05). In 2 out of 22 patients, elevated serum-levels of GLP-1 were found: one patient with a vasoactive-intestinal-polypeptide (VIP)oma and 1 patient with a non-functioning tumor. This indicates that GLP-1 might be secreted at least by a few gastroenteropancreatic endocrine tumors.
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    URL: http://dx.doi.org/10.1007/BF00343955
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    Electronic Resource
    Immunogold labelling of serotonin-like and FMRFamide-like immunoreactive material in neurohaemal areas on abdominal nerves of Rhodnius prolixus (1994)
    Springer
    Cell & tissue research 278 (1994), S. 145-151 
    Details
    ISSN: 1432-0878
    Keywords: Abdominal nerve neurohaemal area ; FMRFamide ; Immunogold-labelling ; Serotonin ; Ultrastructure ; Rhodnius prolixus (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The ultrastructure of neurohaemal areas on abdominal nerves of the blood-sucking bug Rhodnius prolixus was investigated. Four types of axon terminals were found, distinguished by the morphology of their neurosecretory granules. By use of post-embedding immunogold labelling, granules in Type I axon terminals were shown to contain serotonin-like immunoreactive material, and granules in Type II axon terminals were shown to contain FMRFamide-like immunoreactive material. There was no colocalization of these materials. It is suggested that Type III terminals contain peptidergic diuretic hormone, which has previously been reported to be present in electron-dense neurosecretory granules in this neurohaemal area. The identity of material in Type IV terminals is unknown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00305786
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  • 34
    Electronic Resource
    Electronic Resource
    Immunogold labelling of serotonin-like and FMRFamide-like immunoreactive material in neurohaemal areas on abdominal nerves of Rhodnius prolixus (1994)
    Springer
    Cell & tissue research 278 (1994), S. 145-151 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Abdominal nerve neurohaemal area ; FMRFamide ; Immunogold-labelling ; Serotonin ; Ultrastructure ; Rhodnius prolixus (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The ultrastructure of neurohaemal areas on abdominal nerves of the blood-sucking bug Rhodnius prolixus was investigated. Four types of axon terminals were found, distinguished by the morphology of their neurosecretory granules. By use of post-embedding immunogold labelling, granules in Type I axon terminals were shown to contain serotonin-like immunoreactive material, and granules in Type II axon terminals were shown to contain FMRFamide-like immunoreactive material. There was no colocalization of these materials. It is suggested that Type III terminals contain peptidergic diuretic hormone, which has previously been reported to be present in electron-dense neurosecretory granules in this neurohaemal area. The identity of material in Type IV terminals is unknown.
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    URL: http://dx.doi.org/10.1007/BF00305786
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  • 35
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    Electronic Resource
    Regulation of secretory granule formation in chronically hypersecretory melanotrophs in the rat pituitary (1994)
    Springer
    Cell & tissue research 275 (1994), S. 339-344 
    Details
    ISSN: 1432-0878
    Keywords: Secretory granules ; Golgi apparatus ; Haloperidol ; Ultrastructure ; Pituitary gland, pars intermedia ; Rat (Sprague Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The formation of secretory granules in chronically hypersecretory melanotrophs in the rat pituitary was studied. Hypersecretion was induced by treatment with the dopamine antagonist haloperidol (1.5 mg/kg daily for 7 days), which releases the normal neural dopaminergic inhibition of secretion from the melanotroph. Morphometric analysis showed a 100% increase in the volume fraction of granular endoplasmic reticulum after haloperidol treatment, while the volume fractions of electron-dense granules, electron-lucent granules and the Golgi apparatus were unaltered. The mean diameter of the mature secretory granules was increased by 10%, indicating a 30% increase in mean granule volume. A similar increase in diameter was observed in condensing granules within the Golgi area. With earlier results on the effect of chronic inhibition the study shows that a main adaptive response of the melanotroph to altered secretory conditions is a change in the volume of the secretory granules, regulated by a mechanism that operates at an early stage of granule formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319432
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  • 36
    Electronic Resource
    Electronic Resource
    Cellular responses of the skin of carp (Cyprinus carpio) exposed to acidified water (1994)
    Springer
    Cell & tissue research 275 (1994), S. 481-492 
    Details
    ISSN: 1432-0878
    Keywords: Skin ; Ultrastructure ; Endogenous peroxidase ; Water acidification ; Cyprinus carpio (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The skin of carp was examined after exposure to acidified water. Degenerative cells were common in the upper epidermal layers. During the first days most of these cells exhibited signs of necrosis. Later on the incidence of necrosis decreased and that of apoptosis increased. In the acid-exposed fish, the upper filament cells and pavement cells produced secretory vesicles of high electron density, some of which showed peroxidase activity. This enzyme activity was also present in the glycocalyx covering these cells, and in the cytoplasm of apoptotic cells. Mitotic figures and newly differentiating mucous cells were common in the outer epidermal layers. Mucous cells became elongated and produced mucosomes of high electron density. Mucosomes with peroxidase activity were also found. Club cells increased in number. Chloride cells and solitary chemo-sensory cells, not seen in the controls, appeared in the upper epithelial layer. The skin was invaded by many leucocytes and by pigment-containing cytoplasmic extensions of melanocytes. Some leucocytes apparently penetrated into the club cells. These structural observations reflect the complexity of the physiological response of the skin to acid water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318817
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  • 37
    Electronic Resource
    Electronic Resource
    Ultrastructure of an identified array of growth cones and possible substrates for guidance in the embryonic medicinal leech, Hirudo medicinalis (1994)
    Springer
    Cell & tissue research 276 (1994), S. 281-293 
    Details
    ISSN: 1432-0878
    Keywords: Comb cell ; Growth cone ; Motility ; Substrate ; Basement membrane ; Ultrastructure ; Hirudo medicinalis (Annelida)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The oblique muscle organizer (Comb- or C-cell) in the embryonic medicinal leech, Hirudo medicinalis, provides an amenable situation to examine growth cone navigation in vivo. Each of the segmentally iterated C-cells extends an array of growth cones through the body wall along oblique trajectories. C-cell growth cones undergo an early, relatively slow period of extension followed by later, protracted and rapid directed outgrowth. During such transitions in extension, guidance might be mediated by a number of factors, including intrinsic constraints on polarity, spatially and temporally regulated cell and matrix interactions, physical constraints imposed by the environment, or guidance along particular cells in advance of the growth cones. Growth cones and their environment were examined by transmission electron microscopy to define those factors that might play a significant role in migration and guidance in this system. The ultrastructural examination has made the possibility very unlikely that simple, physical constraints play a prominent role in guiding C-cell growth cones. No anatomically defined paths or obliquely aligned channels were found in advance of these growth cones, and there were no identifiable physical boundaries, which might constrain young growth cones to a particular location in the body wall before rapid extension. There were diverse associations with many matrices and basement membranes located above, below, and within the layer in which growth cones appear to extend at the light level. Additionally, a preliminary examination of myocyte assembly upon processes proximal to the growth cones further implicates a role for matrix-associated interactions in muscle histogenesis as well as process outgrowth during embryonic development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306114
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  • 38
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    Electronic Resource
    Ontogeny of the endocrine pancreas in sea bass (Dicentrarchus labrax): an ultrastructural study. I. The primordial cord and the primitive, single and primordial islets (1994)
    Springer
    Cell & tissue research 276 (1994), S. 309-322 
    Details
    ISSN: 1432-0878
    Keywords: Endocrine pancreas ; Ontogeny ; Ultrastructure ; Dicentrarchus labrax (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The primordial cord and the primitive, single and primordial islets present in the 3 earliest stages of the developing endocrine pancreas of sea bass were studied ultrastructurally. The primordial cord consisted of type I and II cells and was included in the gut. Besides these cell types, X cells were seen in the primitive islet. The single islet was made up of type I, II, III and IV cells. A correlation between these endocrine cell-types and cells previously identified immunocytochemically, was established. Type I, II, III and IV cells, correlated respectively with SST-25-, insulin-, SST-14- and glucagon-immunoreactive cells, and could be related to the D1, B, D2 and A cells, respectively, of older larvae and adult sea bass. Each cell type shows characteristic secretory granules from its first appearance. A progressive development of the organelles and an increase in the number and size of the secretory granules, whose ultrastructure also varied, was observed in the endocrine cells of the primordial cord and the succeeding islets. In 25-day-old larvae at the beginning of the fourth developmental stage, the primordial islet, the first ventral islet found, was close to a pancreatic duct and blood vessel, and consisted of type I and II cells whose ultrastructure was similar to that of the type I and II cells in the primordial cord. These data suggest a ductular origin for the pancreatic endocrine cells in the ventral pancreas. It is suggested that although endocrine cells undergo mitosis, their increase in number during the earliest development stages is principally due to the differentiation of surrounding cells.
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    URL: http://dx.doi.org/10.1007/BF00306116
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  • 39
    Electronic Resource
    Electronic Resource
    Ontogeny of the endocrine pancreas in sea bass (Dicentrarchus labrax): an ultrastructural study. II. The big and secondary islets (1994)
    Springer
    Cell & tissue research 276 (1994), S. 323-331 
    Details
    ISSN: 1432-0878
    Keywords: Endocrine pancreas ; Ontogeny ; Ultrastructure ; Dicentrarchus labrax (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The big and secondary islets of sea bass larvae were characterized ultrastructurally from, 25 to 60 days after hatching. From the 25th day, big islets consisted of inner type II and III, external type I and peripheral type IV cells. From the 55th day, type V cells appeared in limited peripheral areas. Secondary islets, first found in 32-day-old larvae, were made up of inner type II and III, external type I, and peripheral either type IV and V cells (type I islets), or only type V cells (type II islets). Type I cells contained secretory granules with a fine granular, low-medium electron-dense material, whereas the secretory granules of type II cells were smaller and had a high electron-dense core with diffused limits; needle and rod-like crystalloid contents were occasionally found. Type III secretory granules posessed a homogeneous, high or medium electron-dense material with or without a clear halo. Type IV cells had secretory granules with a polygonal dense core embedded in a granular matrix and granules containing a high or medium electron-dense material. Type V cells had secretory granules with a fine granular, high or medium electron-dense content. These cell-types correlated with cells previously identified immuno-cytochemically, as regards to their distribution in the islets, and related to those characterized ultrastructurally in adult specimens. Thus, types I, II, III, IV and V correspond to D1, B, D2, A and PP cells, respectively. From the 32nd day onwards, endocrine cells of all the different types were found grouped, type V cells also being observed in isolation close to pancreatic ducts and/or blood vessels. Small groups consisting of type I and II cells were found in 40-day-old larvae. A mitotic centroacinar ductular cell containing some secretory granules similar to those of type I cells, was seen adjacent to a type I cell. As the larvae grew older, the endoplasmic reticulum developed, the number of free ribosomes decreased, and the number and size of the secretory granules increased. Dark type I, II, III, IV and V cells were found in the islets and cell clusters from the 55th day onwards.
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    URL: http://dx.doi.org/10.1007/BF00306117
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  • 40
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    Electronic Resource
    Storage lesion of human platelets as revealed by ultrathin sections and freeze-fracture replicas (1994)
    Springer
    Cell & tissue research 276 (1994), S. 477-483 
    Details
    ISSN: 1432-0878
    Keywords: Platelets ; Storage ; Ultrastructure ; Freeze fracture ; Transmission electron microscopy ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We report the ultrastructural changes occurring in human platelets during eight days of storage. Extension of pseudopodia is frequently observed, but a concentration of organelles in the centre of the platelets is found only in a minor fraction (∼5%). Striking changes can be observed in both the granules and the open canalicular system. In fresh platelets, the latter often has the form of stacked membranes that have no lumen, but these membranes separate and spread with increasing storage time. However, the openings of this system on the outer surface of the platelet remain unchanged. Some of these features differ from the morphological description of platelets activated by thrombin or ADP, and suggest that the storage lesion is the result of a prolonged weak activation that leads to an incomplete release reaction within the first five days.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00343945
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  • 41
    Electronic Resource
    Electronic Resource
    Three-dimensional architecture of the tubular endocytic apparatus and paramembranous networks of the endoplasmic reticulum in the rat visceral yolk-sac endoderm (1994)
    Springer
    Cell & tissue research 278 (1994), S. 353-361 
    Details
    ISSN: 1432-0878
    Keywords: Yolk sac ; Tubular endosomes ; Smooth endoplasmic reticulum ; Ultrastructure ; Endocytosis ; Rat (Wistar)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The three-dimensional architecture of the tubular endocytic apparatus and the endoplasmic reticulum in the rat yolk-sac endoderm was investigated after loading with horseradish peroxidase-conjugated concanavalin A by intrauterine administration. After 30 min, small vesicles (50–150 nm in diameter), small tubules (80–100 nm in diameter) and large vacuoles (0.2–1.0 μm in diameter) in the apical cytoplasm were labeled with the tracer, but lysosomes (1.0–3.5 μm in diameter) in the supranuclear cytoplasm were not labeled until 60 min after loading. Stereo-viewing of the labeled small tubules in thick sections revealed that they were not isolated structures but formed three-dimensional anastomosing networks, which were also confirmed by scanning electron microscopy after maceration with diluted osmium tetroxide. Their earlier labeling with the endocytic tracer, localization in the apical cytoplasm and three-dimensional network formation indicated that the labeled small tubules represented tubular endosomes (tubular endocytic apparatus). These well-developed membranous networks provided by the tubular endosomes are suggested to facilitate the receptor-mediated endocytosis and transcytosis of the maternal immunoglobulin in the rat yolk-sac endoderm. Scanning electron microscopy further revealed lace-like networks of the smooth endoplasmic reticulum near the lateral plasma membrane. Their possible involvement in transport of small molecules or electrolytes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414178
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  • 42
    Electronic Resource
    Electronic Resource
    Ultrastructure and ontogeny of a new type of eyespot in dinoflagellates (1994)
    Springer
    Protoplasma 179 (1994), S. 142-150 
    Details
    ISSN: 1615-6102
    Keywords: Dinoflagellate ; Eyespot ; Gymnodinium natalense ; Ontogeny ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Ultrastructure and ontogeny of a new type of eyespot in dinoflagellates is described. A marine tidal poolGymnodinium natalense is found to possess a highly organized eyespot whose structure is unique among dinoflagellates. The eyespot is rectangular in ventral view, C-shaped in apical view, and is located posterior to the sulcus. The eyespot is independent of the chloroplast and consists of several (typically six) layers of hemi-cylindrical walls which are concentrically arranged with narrow spacing between them. Each hemicylindrical wall is enclosed by a single unit membrane and is composed of many regularly arranged rectangular crystalline bricks. These crystalline bricks are produced in small vesicles which are formed in the invaginations of the chloroplast. The vesicles containing newly formed crystalline bricks are then transported to the sulcal area to assemble the eyespot. The crystalline bricks are arranged in a neat row within the vesicle termed “eyespot forming vesicle” (EFV), which is located near the sulcus. The hemi-cylindrical wall is constructed within the EFV. Based on the structure of the eyespot, viz. consisting of concentric multi-layered walls, the eyespot is thought to act as a quarter-wave stack antenna.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403952
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  • 43
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    Electronic Resource
    Induction and formation ofCochliobolus sativus appressoria (1994)
    Springer
    Protoplasma 178 (1994), S. 34-47 
    Details
    ISSN: 1615-6102
    Keywords: Appressorium ; Cochliobolus sativus ; Electron microscopy ; Thigmotropism ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary GerminatingCochliobolus sativus spores were induced to form appressoria on a variety of artificial surfaces, including replicas of the barley leaf surface. Evidence was obtained for the involvement of chemical and topographic signals during induction of appressorium formation inC. sativus. Germ tube thigmotropism was also observed in vitro. Ultrastructure relevant to appressorium formation was observed, including the germ tube apex, apical swelling of the germ tube apex prior to appressorium formation, the appressorium with associated septation and the penetration peg. Cytochemical probes applied to germlings at the electron microscope level failed to detect α-D-mannan, α-D-glucan, β-D-galactan, D-glcNAc or D-galNAc polymers in the extracellular mucilage associated with the fungal germlings. The ultrastructure of hyphal apices from germlings grown under different nutritional conditions differed with respect to Spitzenkörper morphology, apex shape and in the quantity of associated extracellular mucilage. Experimental findings are discussed relative to current understanding of appressorium induction in more extensively studied systems.
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    URL: http://dx.doi.org/10.1007/BF01404119
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  • 44
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    Electronic Resource
    Isolation and characterization of aleurone protoplasts from a malting variety of barley (Hordeum vulgare L.) (1994)
    Springer
    Protoplasma 177 (1994), S. 132-143 
    Details
    ISSN: 1615-6102
    Keywords: α-Amylase ; (1-3, l-4)-β-Glucanase ; Hormones ; Monensin ; Transfection ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A procedure has been developed to isolate protoplasts from mature aleurone layers of the malting variety Alexis and four other barley genotypes. It combines induction of endogenous cell wall degrading enzymes together with use of Onuzuka cellulase R 10 and driselase and results in better yields for two varieties than can be obtained with the huskless variety Himalaya. The viability of the freshly isolated protoplasts is greater than 90% and in spite of the presence of gibberellic acid during isolation procedures, most of the protoplasts are at an early developmental stage, as judged by ultrastructure. Gibberellic acid-induced changes in protoplast structure resemble those reported for Himalaya protoplasts. The protoplasts secrete both α-amylase (EC 3.2.1.1) and (1-3, 1-4)-β-glucanase (EC 3.2.1.73) into the surrounding medium. Transfection studies using a low pI α-amylase promoter to direct chloramphenicol acetyltransferase expression in aleurone protoplasts from Alexis and Himalaya revealed significant differences in their hormone responsiveness. In the absence of hormones, low levels of expression of the reporter enzyme were obtained in Alexis protoplasts, while high levels were characteristic for Himalaya protoplasts. An 8-fold increase in the expression of the reporter gene was induced by supplying the transfected Alexis protoplasts with gibberellin A3, whereas expression in Himalaya protoplasts remained unchanged. When Himalaya protoplasts were isolated from aleurone layers that had not been incubated with GA3 during the initial stages of protoplasting (the classical procedure), the hormone response of the promoter was 2.5-fold. It is thus possible to optimize the aleurone protoplast isolation procedure for different barley genotypes and mutants of interest in studies of transgenic gene expression and hormone induced secretion of proteins from this unique secretory plant tissue.
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    URL: http://dx.doi.org/10.1007/BF01378987
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  • 45
    Electronic Resource
    Electronic Resource
    Structure of Golgi apparatus (1994)
    Springer
    Protoplasma 180 (1994), S. 14-28 
    Details
    ISSN: 1615-6102
    Keywords: Golgi apparatus ; Dictyosome ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Golgi apparatus (GA) of eukaryotic cells consist of one or more stacks of flattened saccules (cisternae) and an array of fenestrae and tubules continuous with the peripheral edges of the saccules. Golgi apparatus also are characterized by zones of exclusion that surround each stack and by an assortment of vesicles (or vesicle buds) associated with both the stacks and the peripheral tubules of the stack cisternae. Each stack (sometimes referred to as Golgi apparatus, Golgi complex, or dictyosome) is structurally and functionally polarized, reflecting its role as an intermediate between the endoplasmic reticulum, the cell surface, and the lysosomal system of the cell. There is probably only one GA per cell, and all stacks of the GA appear to function synchronously. All Golgi apparatus are involved in the generation and movement of product and membrane within the cell or to the cell exterior, and these functions are often reflected as structural changes across the stacks. For example, in plants, both product and membrane appear to maturate from the cis to the trans poles of the stacks in a sequential, or serial, manner. However, there is also strong ultrastructural evidence in plants for a parallel input to the stack saccules, probably through the peripheral tubules. The same modes of functioning probably also occur in animal GA; although here, the parallel mode of functioning almost surely predominates. In some cells at least, GA stacks give rise to tubular-vesicular structures that resemble the trans Golgi network. Rudimentary GA, consisting of tubular-vesicular networks, have been identified in fungi and may represent an early stage of GA evolution.
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    URL: http://dx.doi.org/10.1007/BF01379220
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  • 46
    Electronic Resource
    Electronic Resource
    Actin associated with plasmodesmata (1994)
    Springer
    Protoplasma 180 (1994), S. 169-184 
    Details
    ISSN: 1615-6102
    Keywords: Actin ; Cell-cell communication ; Plasmodesmata ; Regulation ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have used several methods to localise actin associated with plasmodesmata. In meristematic plant material fixed in 0.1% glutaraldehyde/1% paraformaldehyde and embedded in LR White resin, actin was localised (in TEM using 5 nm gold-labelled secondary antibody to C4 anti-actin primary antibody) in the neck region by the plasma membrane and endoplasmic reticulum, and also down the length of the plasmodesma, deep in the cell wall. When the chemical fixation was replaced by rapid freezing in liquid propane (without cryoprotectants) and substitution in acetone, the plasmodesmata were labelled in similar positions, but with less background label on sections. While only 8–20% of plasmodesmata were labelled, the label was 10 to 100 fold denser over plasmodesmata than over the surrounding wall indicating specific association with plasmodesmata. We presume the apparent extracellular location of some label was due to the size of the antibodies between the site of attachment and the observed position of the gold particle. Gold label was found in similar locations in material fixed in 3% paraformaldehyde, infiltrated with sucrose, frozen, sectioned (10–12 μm thick), then labelled with antibodies before resin embedding. Furthermore, cell walls in epidermal peels stained with rhodamine-phalloidin showed localised patches of fluorescence, presumably at the site of plasmodesmata (or primary pit-fields), which were connected on either side to fluorescent strands of actin in the cytoplasm. Suspension cultured cells ofNicotiana plumbaginifolia similarly stained showed very faint, narrow fluorescent strands crossing the walls of sister cells, which may indicate actin associated with individual plasmodesmata, shown in TEM to be sparsely distributed in these walls. In addition, the neck regions of cytochalasin-treated plasmodesmata were greatly enlarged and lacked the normal extracellular ring of particles. We propose that actin associated with plasmodesmata stabilizes the neck region and possibly also the cytoplasmic sleeve, and may be actively involved in regulating cell-to-cell transport.
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    URL: http://dx.doi.org/10.1007/BF01507853
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  • 47
    Electronic Resource
    Electronic Resource
    Production and modifications of extracellular structures during development of chytridiomycetes (1994)
    Springer
    Protoplasma 181 (1994), S. 123-141 
    Details
    ISSN: 1615-6102
    Keywords: Carbohydrates ; Chytridiomycetes ; Extracellular material ; Membranes ; Ultrastructure ; Zoospores
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In development of the primitive fungi, chytridiomycetes, unwalled zoospores bearing single, posterior flagella are transformed into walled, round-cells which elaborate the thallus. Production, structural modification, or release of extracellular material are involved with each transition of developmental stage. This article reviews the variety and developmental changes of extracellular materials found at the cell surface of chytridiomycetes. A cell coat, produced from Golgi-derived vesicles during zoosporogenesis, is visible around free swimming zoospores of some chytridiomycetes. How the zoospore surface receives and transduces signals is not widely explored, but it is known that fenestrated cisternae and simple cisternae, which are integrated into the microbody-lipid globule complex, are spatially and structurally associated with the plasma membrane and flagellar apparatus. This spatial association, as well as the cytochemical localization of calcium in fenestrated cisternae, suggest a mechanism for signal transduction and for regulation of zoospore motility. Zoospores become encased in a new layer of extracellular material as the zoospore encysts. Among some chytrids the source of this material is preexisting vesicles which fuse with the plasma membrane. Among other zoospores, a readily identifiable population of encystment vesicles is not apparent, demonstrating that there is no single pattern or mechanism for zoospore encystment in chytridiomycetes. Encysted zoospores developing into thalli, typically produce cell walls with a microfibrillar substructure. Ultrastructural analysis of walls reveals distinctive architecture and remarkable sculpturing which have been used in systematics of some members of chytridiomycetes. Nothing is known as to underlying controls of cytoskeletal elements and plasma membrane enzyme complexes in wall biogenesis. Many changes in cell surface structures accompany thallus maturation. Septa, many traversed with plasmodesmata, are produced in most chytrid thallus types. As sporangia and resting spores prepare for the production and release of zoospores, additional extracellular layers of material are frequently produced. Polarized deposits of extracellular material become discharge plugs, discharge vesicles, or endoopercula. Interstitial material is also released into cleavage furrows. Circumscissile or localized digestion of walls produce operculate or inoperculate exit ports for zoospore release. Cryofixation preserves more extensive extracellular material than does conventional chemical fixation, and broader application of cryofixation may radically alter our current view of cell surface structure. Thus chytridiomycetes exhibit a range in patterns for the occurrence and subsequent modifications of extracellular materials, even for members within the same order. The most universally recognized role for these extracellular materials is protection. Although there is a reasonable view of the types of extracellular material involved in chytridiomycete development, we have only limited understandings of their biogenesis or roles in regulation and communication, areas awaiting more investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666392
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    Characterization of zoospore and cyst surface structure in saprophytic and fish pathogenicSaprolegnia species (oomycete fungal protists) (1994)
    Springer
    Protoplasma 181 (1994), S. 142-163 
    Details
    ISSN: 1615-6102
    Keywords: Saprolegnia ; Lectins ; Concanavalin A ; Wheat germ agglutinin ; Monoclonal antibodies ; Ultrastructure ; Pathogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The importance of the surface structure and chemistry in zoospores and cysts of oomycetes is briefly reviewed and the organelle systems associated with encystment described. The surface structure and chemistry of primary and secondary zoospores and cysts ofSaprolegnia diclina (a representative saprophytic species) andS. parasitica (a representative salmonid fish pathogen) were explored using the lectins concanavilin A (Con A) and wheat germ agglutinin (WGA) and monoclonal antibodies (MAbs) raised against a mixed zoospore and cyst suspension ofS. parasitica. The binding of lectins and antibodies to spores was determined using immunofluorescence microscopy with fluorescein isothiocyanate-labelled probes and with electron microscopy with gold-conjugated probes applied to spore suspensions post-fixation. In both species Con A, which is specific for glucose and mannose sugars, bound to both the surface of primary and secondary zoospores (the surface glycocalyx) and their cyst coats and readily induced zoospore encystment. The binding to the cysts appeared to be mainly associated with the matrix material released from the primary and secondary encystment vesicles and which appeared to diminish with time. No binding to germ tube walls was observed with this lectin. The MAb labelling showed a generally similar binding pattern to the primary and secondary cysts to that observed with Con A, although the binding to zoospores was more variable. Primary zoospores bound the antibodies but secondary zoospores appeared less reactive. It is suggested that the MAbs share a common epitope with one or more of the Con A-binding components. In both species WGA, which is specific for amongst other things the sugar N-acetyl glucosamine, bound to localised apical patches on the primary zoospores. This lectin also binds to the ventral groove region of secondary zoospores ofS. diclina, which were induced to encyst by this lectin. In contrast secondary zoospores ofS. parasitica were not induced to encyst by the addition of WGA and showed a patchy dorsal binding with this lectin. WGA also binds to both the inner wall of discharged primary cysts and the young germ tube walls of both species. These observations are discussed both in relation to other oomycete spores and to their possible functional and ecological significance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666393
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    Observations on the flagellar apparatus of a coccolithophorid,Cruciplacolithus neohelis (Prymnesiophyceae) (1994)
    Springer
    Journal of plant research 107 (1994), S. 53-62 
    Details
    ISSN: 1618-0860
    Keywords: Coccolithophorid ; Cruciplacolithus neohelis ; Flagellar apparatus ; Haptophyceae ; Prymnesiophyceae ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The flagellar apparatus ofCruciplacolithus neohelis (McIntyre and Bé) Reinhardt including its transition region is described. The transition region contains a hat-shaped structure, which is suggested to be one of the common features of the Prymnesiophyceae. Its flagellar root system resembles that of most coccolithophorids examined so far, except that only one vestigial crystalline root is present associated with root 1. Two well-developed crystalline roots associated with roots 1 and 2, respectively, appear in the preprophase of nuclear division, suggesting conversion to a mitotic spindle. The taxonomic and evolutionary significance of the flagellar apparatus is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02344530
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  • 50
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    Ultrastructural changes in murine lymphocytes induced by aflatoxin B1 (1994)
    Springer
    Mycopathologia 125 (1994), S. 33-39 
    Details
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Lymphocytes ; Mice ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This investigation sought to determine whether splenic lymphocytes obtained from Balb/C mice exposed to aflatoxin B1 (AFB1) showed any ultrastructural changes which could account for the immunodysfunction attributable to aflatoxins. Lymphocytes obtained from Balb/C mice administered aflatoxin B1 in olive oil daily for three weeks were studied using both transmission and scanning electron microscopy. The lymphocytes demonstrated ultrastructural changes primarily in the mitochondria where marked internal dissociation of the cristae was revealed by transmission electron microscopy. All other cellular organelles were unaffected. No significant alterations in external structure were observed under scanning electron microscopy. The findings of this study indicate that AFB1 administration does not affect the surface topography of lymphocytes, but AFB1, by causing extensive mitochondrial damage, may affect the way in which these cells function. This could be a possible explanation for the immunodysfunction associated with AFB1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01103973
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    Normal and neoplastic Schwann cells in fish (1994)
    Springer
    Methods in cell science 16 (1994), S. 109-115 
    Details
    ISSN: 1573-0603
    Keywords: Animal model ; Neurofibroma ; Schwann cell ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Peripheral nerve sheath (PNS) neoplasms, primarily neurofibromas, schwannomas and maliganant schwannomas, are among the most common tumors in fishes. Model systems involving PNS tumors in fishes are also valuable because mammalian models of PNS tumors are rare. Schwann cells, the primary cell type suspected of neoplastic transformation in these tumors, have been difficult to culture. We describe techniques for culturing normal and neoplastic Schwann cells from fish. We also present methods for preparing cells on culture dishes for electron microscopy which are especially useful when specific cells in a culture must be located for ultrastructural examination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01404819
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    Kinocilia in the developing stria vascularis of the rat pup (1994)
    Springer
    European archives of oto-rhino-laryngology and head & neck 251 (1994), S. 267-270 
    Details
    ISSN: 1434-4726
    Keywords: Cochlea ; Ultrastructure ; Stria vascularis ; Development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mammalian stria vascularis undergoes certain developmental changes in the postnatal rat. The present study was designed to examine the ultrastructure of the stria vascularis in rat pups from immediately after birth to 20 days postpartum. The cochlea were removed with the animals under xylazine (Rompun) anesthesia and were prepared for transmission electron microscopy. Each of the three cell types in the stria were found to contain kinocilia up until 12–17 days of age. The presence of kinocilia in the intermediate and basal cells has not been previously described. Findings suggest that these organelles may serve a motile and/or sensory function to assist in the maturation of cell functions, particularly ion transport, during early stages of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00181882
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    The integumental ultrastructure of Parathalestris harpactoides (Claus, 1863) (copepoda, harpacticoida) (1994)
    Springer
    Hydrobiologia 292-293 (1994), S. 137-142 
    Details
    ISSN: 1573-5117
    Keywords: Ultrastructure ; morphology ; integument ; copepoda ; crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The integument of Parathalestris harpactoides (Claus, 1863) is studied by scanning and transmission electron microscopy. The general structure of the integument conforms to the common pattern known from Copepoda. Emphasis is given to the structural variation of the cuticle in different regions of the body. The cuticle measures about 6 µm in most parts of the body, and shows a laminate appearance. The epicuticle is about 60 nm thick. Numerous pore canals containing muscular tonofilaments penetrate the procuticular layer of the integument. A peculiar feature is the presence of a ‘honeycombed’ layer in the outermost zone of the cuticle of some parts of the body. The epidermal layer, muscle insertions and integumental pores are of common type. The cuticle of some specimens, both males and females, is covered with microorganisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229933
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    Polyspirodilactam: A new family of high temperature polymers (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 6-11 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new class of materials based on a spirodilactam structure has been recently synthesized as part of research into new polymeric materials. Not only is the spirodilactam structure novel, but it was not even the intended product in the synthesis as originally designed. The polymerization process discovered by the reaction of 4-ketopimelic acid or its corresponding spirodilactone with primary amines opened a new field of polysprodilactam chemistry. This paper describes the chemistry leading to the discovery of spirodilactam-based polymers and initial applications in the area of thermoplastics and thermosets. Most recent developments to be covered include aromatic spirodilactams and isomeric spirodilactams.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340105
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    High temperature thermosets based on the cocuring of a novel spirodilactam bisallylether and bismaleimide (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 12-16 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Spirodilactam bisallylether is a new high temperature performance monomer. It melts at 154°C, and is thermally inactive in forming a homopolymer. However, it reacts readily with a bismaleimide via “ene” reaction. Therefore, it could be used as a comonomer and an effective toughening modifier for bismaleimide. The properties of the blends of spirodilactam bisallylether and 4,4'-bismaleimidodiphenyl-methane were studied. The cocured resins have high glass transition temperature, 〉 300°C. By adding 30 to 40 mole % of the bisallylether, the compact tension toughness of the bismaleimide was improved to 0.7 MPa-m1/2. Therefore, the resins have a combination of high glass transition temperature and toughness. They also showed good flexural properties. Despite the high water absorption, 5 to 7%, the resins retained high hot/wet flexural properties because of the high glass transition.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340106
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    Compatibilization of immiscible blends with a mutually miscible third polymer (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 59-68 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Four immiscible blend systems, styrene-maleic anhydride/styrene-acrylonitrile (SMA/SAN). styrene-maleic anhydride/acrylonitrile-butadiene-styrene (SMA/ABS), poly(vinylidene fluoride)/SAN (PVF2/SAN), and PVF2/ABS, were investigated. The effect of adding up to about 10 wt% of a third polymer that is miscible with each blend component, poly(methylmethacrylate) (PMMA), was determined. In every case, the addition of PMMA led to the improvement of properties such as tensile strength, tensile elongation, and notched impact strength. Furthermore, the addition of PMMA resulted in finer, more uniform dispersions of the primary blend components. The experimental results are interpreted in terms of interfacial activity of the common phase component, PMMA.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340111
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    A thermoanalytical study on solid-state cure of poly(p-phenylene sulfide) (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 81-85 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Differential scanning calorimetry (DSC) was used to investigate the solid-state cure process of poly(phenylene sulfide)(PPS) resin. Virgin PPS resin in an open sample pan was cured in DSC cell. Either air or oxygen was used as a curing atmosphere. Cure temperatures were in the range of 200 and 250 °C, which are below the melting point of PPS resin. Cure temperature as well as atmospheric condition influenced the cure behavior of PPS in the solid state. Both the rate and the amount of cure increased with increasing cure temperature. On the other hand, the time to reach the maximum cure rate was independent of cure temperature. Changing the atmosphere from air to oxygen increased both the cure rate and the amount of cure. The size effect of PPS particles on the cure reaction was also discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340202
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    The anisotropy of slow crack growth in polyethylene pipes (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 109-115 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Slow crack growth was measured in the perpendicular and parallel directions relative to the extrusion direction of the pipe. For five pipes from different manufacturers, the anisotropy factor, the lifetime to fracture in the perpendicular direction divided by lifetime in the parallel direction, varied from 1.2 to 4.7 for complete fracture and 1.4 to 4.0 for crack initiation. The degree of molecular orientation was determined by measuring the shrinkage that occured when a pipe specimen was heated near its melting point. The amount of shrinkage correlated with the anisotropy factor for slow crack growth. The shape change after shrinkage was related to the flow pattern of the resin during extrusion and the cooling rate after extrusion.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340206
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  • 59
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    Viscoelasticity of some engineering plastics analyzed with the modified stress-optical rulePart 7 of the series “Birefringence of Amorphous Polymers.” (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 135-140 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), of poly(ether sulfone) (PES), polysulfone (PSF), and polyethermide (PEI), were measured over the frequency range 1 to 130 Hz. The data were analyzed with a modified stress-optical rule: The Young's modulus was decomposed into two complex functions, EG*(ω) and ER*(ω); the modified stress-optical coefficient, CR and CG, associated with the rubber (R) and glass (G) components, respectively, were determined. The results for six polymers, including polystyrene, poly(α-methyl styrene), and bisphenol A polycarbonate were compared with each other. One of the coefficients, CR, equivalent to the stress-optical coefficient in melts, mainly depended on the way in which phenyl groups were connected to the chain. The other, CG, was in the range of 20 to 40 Brewsters, and did not strongly depend on the details of polymer structure. The component function, EG*(ω), which was located in the glassy region and originated from the high glassy modulus, was almost the same in shape when plotted against ω with double logarithmic scales. The R component, ER*(ω), located at the long time end of the glass-to-rubber transition zone, was slightly sensitive to the molecular structure of polymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340210
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    A closer look at the MWD-viscosity transform (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 159-165 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: While there is abundant evidence that the molecular weight distribution (MWD) of a linear polymer has an influence on the shape of the viscosity function, the ability to convert the viscosity function to an MWD has been questioned. Using strictly numerical techniques, we have shown that the viscosity function can be transformed to the MWD, but always with some distortion. However, distinct bimodality can be qualitatively preserved through both the MWD-viscosity and viscocity-MWD transforms.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340213
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    A model for the unfoamed skin on microcellular foams (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 169-173 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In microcellular plastics, an unfoamed skin that is integral with the foamed core can be created by allowing the nucleating gas to diffuse from the surfaces of a gas saturated specimen prior to foaming. In this paper, a semi-empirical model is proposed that predicts the skin thickness variation in microcellular foams as a function of gas desorption time. The model shows good agreement with experimental results on the polycarbonate-carbon dioxide system.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340302
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  • 62
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    Kinematics and deformation characteristics as a mixing measure in the screw extrusion process (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 174-189 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The present paper proposes “Deformation Characteristics” (DC) as a new deformation measure of screw extrusion processes, based on the Green deformation tensor. In contrast to previous strain measures heuristically proposed by Mohr, et al., Mckelvey, and Pinto and Tadmor, the new DC can naturally incorporate the demixing phenomena and systematically take into account the three-dimensional circulatory flow with the screw flight effect. Therefore, DC can be regarded as an improved strain measure. “Weighted Average Deformation characteristics” (WADC) is also proposed to indicate the overall deformation characteristics as a quantitative measure to the “goodness of mixing” of the extrusion process. The present paper includes discussion on delicate differences between DC and several other strain measures in case of the two-dimensional velocity approximation, and on the application of DC into a general three-dimensional velocity field obtained by a quasi-three-dimensional finite element analysis of extrusion processes. In determining WADC in the three-dimensional application, the residence time distribution function, including the three-dimensional circulatory flow effect, is used.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340303
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    Simulation of non-isothermal flow in modular co-rotating twin screw extrusion (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 229-237 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Non-isothermal flow is simulated in the screw and kneading disc elements in a modular co-rotating twin screw extruder. Methods of calculating mean temperature rises for individual elements are discussed and results are presented. The implications of non-isothermal operation for scale-up is discussed. A method is then described for making calculations in a modular co-rotating machine, that contains many different elements. Example calculations are given showing the tendency of larger machines to buildup greater temperatures when viscous heating is included.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340309
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    Influence of a compatibilizing agent on the phase morphology of a polyethylene-polyamide 6 blend in a modular intermeshing co-rotating twin screw extruder (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 221-228 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A study of the influence of a compatibilizing agent on phase morphology development in a 75/25 polyethylene/polyamide-6 blend in a modular co-rotating twin screw extruder is presented. The development of phase morphology along the axis of the modular screw was observed by cooling the extruder and removing the polymer from the screw channels. Changes in phase morphology due to the addition of a compatibilizer have been investigated using scanning electron microscopy. Sufficient quantities of compatibilizing agent produce significant increases in the rate of mixing and also reduce the scale of the phase morphology. Much larger quantities (5%) than actually required for interface coverage are needed for rapid mixing. This seems to be due to the high viscosity of the matrix.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340308
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    Publications by P. H. Lindenmeyer (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 251-251 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340403
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    Masthead (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340401
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    Does quantum magic impinge on polymer physics? (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 260-265 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Penrose states that quantum effects can occur even in relatively large systems when energy differences remain small. This is just the situation with polymer materials. A quantum description by Penrose of the formation of quasi-crystals can be rewritten to apply to polymer crystallization. The implications of the need to take account of quantum effects are discussed. Another approach based on the quantization of energy levels in clusters of atoms offers a possible explanation of heat setting in nylon and polyester fibers. Finally some problems of the interpretation of quantum theory are discussed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340405
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    A novel approach to a truly dynamic thermodynamicsEditor's note: Paul Lindenmeyer remained active in his retirement and left a legacy of several manuscripts in various stages of completion. We have selected one of his manuscripts as a contribution to this memorial issue. This paper presents some of the controversial issues of nonequilibrium thermodynamics that Paul was attempting to address. Professor Astarita kindly agreed to provide comments and a critique regarding the approach and ideas advocated by Paul Lindenmeyer. (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 252-259 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A novel approach to a truly dynamic thermodynamics is proposed in which equilibrium is defined in terms of explicit time, distance, and acceptable error scales. This approach involves reformulating the second law of thermodynamics in terms of an excess energy that vanishes at equilibrium instead of an entropy that assumes some unknown maximum value. Excess energy is defined mathematically as the total Legendre transform of energy with respect to an independent set of extensive variables. Excess energy is effectively the free energy functional of a nonequilibrium system and is a function of the time, distance, and acceptable error scales. Elimination of entropy from thermodynamics requires recognizing temperature as a thermal stress, proportional to the antimetric component of the stress tensor that is neglected when one assumes the validity of Cauchy's second law of motion. The inclusion of temperature as part of the stress-strain couple completes the science of thermomechanics and opens the way for a practical unification of chemistry and physics in strictly mechanical terms.The last sentence of the abstract shows how high the goals that Lindem meyer set for himself were. I personally do not agree with the idea that mechanics is the queen of all sciences, and that given deep enough probing one could achieve “a practical unification of chemistxy and physics in strictly mechanical terms”; for instance, electromagnetism has full citizenship's rights in physics, and it is hard to conceive that it could be reduced to mechanics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340404
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    Characterization of the interfacial bond in paper-polypropylene-paper laminatesDedicated to the memory of Paul H. Lindenmeyer, colleague and friend. (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 285-289 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The interfacial strength of two paper-polypropylene-paper laminates used for electrical power transmission cable insulation has been measured using a peel test after a variety of conditionings that simulate the service thermal stress conditions. Immersion in dielectric oil at 23°C causes little decrease in peel strength, but heating in the oil at 90°C causes a rapid initial loss followed by a slow loss of strength. Cyclic and static heating show that cyclic fatigue is not a factor as the initial loss of strength occurs in a time comparable to the first two test cycles and further heating causes much less loss of strength. Tensile and compressive stresses resulting from cable winding have no effect on the loss of bond strength during heating in oil. Vacuum drying of the laminate and oil (as in cable manufacture) before heating results in less decrease in peel strength than heating without prior drying. Optical and electron microscopy show minimal wetting of the paper fibrils by the polypropylene with only a few having been either normal to or at a steep angle to the polypropylene surface. That is, the fibrils appear to be parallel to the interface and only partially immersed in the polypropylene. Micrographs show little, if any, differences between the interfaces on the two sides as well as little paper on the polypropylene after delamination and vice versa. It is suggested that the bonding mechanism is a combination of weak mechanical interlocking and secondary bonds. It is also suggested that swelling of the polypropylene relative to the paper by the dielectric oil at 90°C weakens the interfacial bond.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340409
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    The effect of annealing on stretched trans-1,4-polyisoprene networks (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 290-300 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Variations of stress with temperature for stretched networks of trans-polyisoprene networks in the crystallization region are reported. Such profiles are characteristically U-shaped with the stress at lower temperatures often climbing to high levels. Valley widths of the profiles narrow as annealing temperature increases to about 50°C, then widen at yet higher temperatures. The degree of crystallization at 22°C is 37% and independent of deformation and annealing temperature. The β crystal form is overwhelmingly present with traces of other crystal forms appearing only at high deformations. The theory of stress-induced crystallization provides a good description of experimental results provided the nucleation parameter σ is dependent upon deformation. Therefore, the data provide good qualitative support for the theory in its current form.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340410
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    Thermoplastic polyheterocycles. I: Polyalkylene-benzoxazolesPresented in part at the 25th anniversary meeting of the ACS Polymer Group of the North Carolina Section of the American Chemical Society, Chapel Hill, N.C., Nov. 12, 1992. (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 301-304 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polyalkylenebenzoxazoles of high molecular weight (inherent viscosity values from 0.76 to 2.95) were prepared from 4,6-diaminoresorcinol dihydrochloride and aliphatic diacids in polyphosphoric acid by heating at 180 to 200°C for 3-5 h. Melting points of the polymers ranged from 148 to 423°C, depending on the length of the alkylene chain. Glass transition temperatures were relatively low, ranging from 50 to 100°C and did not show the pronounced odd/even effect noted for melting points. In all cases, rapid weight loss occurred above 400°C. No evidence for the formation of a molecular composite was observed in an attempt to prepare in situ a rod-like polybenzoxazole in a polyalkylenebenzoxazole.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340411
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    Masthead (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340201
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    Oligomer distribution for interfacial step growth polycondensation (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 93-101 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Low levels of oligomer molecules are generally desirable in polymeric materials. It is known that several reactor variables can affect the oligomer distribution, and therefore it is useful to have predictive models for molecular weight distribution. The normal approach of a differential equation-based model is very complex to set up if it is applied rigorously to include all the non-Flory aspects of the step growth polycondensation and in particular the interfacial polycarbonate polymerization. In this paper, simple methods based on the Monte Carlo method and Stockmayer distribution are applied to simulate the effects of mass-transfer, unequal reactivity, and the starting stoichiometry of the polycondensing functional groups on the oligomer distribution. It is shown that these parameters can have a significant effect on the oligomer weight distribution and polydispersity of the final polymer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340204
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    Mechanical properties and deformation mechanism of polyoxymethylene chain in the crystalline state (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 308-317 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The true crystallite modulus of polyoxymethylene (POM) was evaluated experimentally and thoeretically as a function of temperature. The mechanical deformation mechanism of POM was lattice-dynamically predicted and confirmed by measuring the stress-induced vibrational frequency shifts of the infrared and Raman spectra, which were interpreted on the basis of anharmonic potential field.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340413
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    Analysis of the temperature rise in the projectile and extended chain polyethylene fiber composite armor during ballistic impact and penetration (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 141-152 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The ultra-high strength/modulus, extended chain polyethylene fiber (Spectra® fiber) composite has shown great potential as a lightweight armor material with its extraordinary capability of absorbing the kinetic energy of projectiles. But the relatively low melting point of this fiber (∼ 145°C) has caused concerns regarding the effect of temperature rise during the impact/penetration process on the performance as armor material. In this article, an analysis of temperature rise in projectile and the fiber composite during the impact/penetration process is described. Combining the simulation of impact deformation by finite element analysis and the simulation of temperature rise by a finite difference approximation of the related dynamic equations, the temperature rise caused by the projectile/composite interaction was estimated. Results show that there is a significant temperature rise at the projectile/composite interface due to the friction but that the short length of time involved in the process and the low thermal conductivity of Spectra fiber composite keep the temperature rise in a very small region (in the order of 0.001 cm) around the interface during the impact/penetration process. Consequently, the volume that is affected by the temperature rise is very small, in the order of total 0.001 cm3 around the projectile, and this is too small to generate any detectable effect on the armor performance. After the projectile is stopped, however, substantial heating of fiber composite can occur under specific conditions as the result of heat flow from the hot projectile embedded in the composite. This heating of fibers, however, is a postmortem effect and hence inconsequential to the ballistic performance of the composite armor.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340211
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    Masthead (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340301
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    Analysis of a reactor with surface renewal for poly(ethylene terephthalate) synthesis (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 190-200 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model of a polycondensation reactor that can be used in the final stage for poly(ethylene terephthalate) (PET) is established and compared with experimental data obtained from a laboratory scale reactor with film renewal. Detailed side reactions are considered along with the diffusional removal of the small molecules through thin film. Among several kinetic constants, the polycondensation reaction rate constant k1(= k8) and diester group degradation reaction rate constant k7 have an influence over the degree of polymerization. The values of k1(= k8) and k7 for 0.05 wt% Sb2O3 were obtained as curve-fit values: (1) k1(= k8) = 3.4 × 106 exp(- 18.500/RT′) (L/mol-min); (2) k7 = 1.3 × 1011 exp(- 37,800/RT′) (min-1). Effects of the film exposure time, reduced pressure of vacuum, temperature, the initial terephthalic acid (TPA)/ethylene glycol (EG) mole ratio, the initial degree of polymerization, and catalysts were well explained by the model.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340304
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    Entrance effects for power-law fluid (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 209-212 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Entrance pressure losses for the creeping flow of a power-law fluid are calculated for an abrupt contraction of ratio 2, 4, 8 and ∞ for both the axisymmetric and planar cases using P2P1 and P+2P1 finite elements. Contrary to some earlier findings in the literature, the entrance pressure loss obtained by using the two different types of finite elements, both of which satisfy the Babus̆ka-Brezzi condition, are found to converge to the same results. The present results also confirm that the variational method of Duda and Vrentas gives excellent upper bounds for both the axisymmetric and planar cases with infinite contraction ratio.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340306
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    Semianalytical solution for epoxy-amine curing in the presence of nonisothermal effects (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 405-413 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The curing of epoxy-amine polymer has been modeled by the reaction of functional groups, and the mole balance of these is governed by a set of six nonlinear differential equations. In this work, we have first developed a complete analytical solution for isothermal curing. For nonisothermal curing, we have divided the domain of hydroxyl group concentration β into small increments Δβ and adopted our analytical results for this domain. In addition, we solved the energy balance equation analytically and obtained the temperature rise for Δβ. We have compared our results with those obtained from the Runge Kutta numerical solutions. We have shown that our semianalytical technique is about a thousand times more efficient and faster.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340505
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    Shear test for thermoplastic polymers (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 513-518 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A shear test is proposed as a complement to the tensile test in order to characterize the short time mechanical behavior of thermoplastic polymers. The proposed test geometry makes the test easy to perform and to evaluate and gives relevant information about anisotropy, plastic deformation, crack initiation, and propagation properties. Three different materials have been tested and the results are discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340609
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    Residual stress development in neat poly(etheretherketone) (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 500-506 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Material property models for poly(etheretherketone) (PEEK) have been combined with a residual stress model to provide a means for investigating the effect of crystallization process on the residual stress development in semicrystalline materials. The analysis shows that crystallization causes an increase in the residual stress levels. This increase is affected through an increase in the resin modulus values and through the resin modulus build-up at higher temperatures. The shrinkage due to crystallization was found to have no effect on the residual stress development in neat PEEK.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340607
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    Viscoelastic properties of a 60 mol% para-hydroxybenzoic acid/40 mol% poly(ethylene terephthalate) liquid crystalline copolyester. II: Effect of shear historyPart of this work was originally presented at the International Regional Meeting of the Polymer Processing Society in Seoul, Korea, September 26-29, 1990. (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 519-527 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Temperature sweeps of dynamic viscoelastic properties have shown that phydroxybenzoic acid (PHB)-based liquid crystalline polyesters, specifically in this case those copolymerized with poly(ethylene terephthalate) (PET), can be subjected to considerable supercooling if initial heating curves are compared to subsequent cooling curves, indicating that this type of material can be in quite different states even at the same temperature, depending on thermal history. Utilizing this supercooling behavior, viscoelastic properties of a 60 mol% PHB/40 mol% PET material produced by Unitika were monitored before and, particularly, after large-scale shear deformation to determine how potential structure changes induced by the shear are reflected in viscoelastic properties immediately, and with time. According to dynamic viscoelastic temperature sweep data four quite different initial states were employed including conditions with, as well as largely free of, crystallites. However, in all cases, post-shear monitoring showed decreased G′ and G″ values with almost no evidence of return towards initial values within approximately 25 min. These results, in addition to furthering somewhat the fundamental understanding of the flow and relaxation properties of liquid crystalline polymers, may be useful in polymer processing, where large-scale shear deformations employed in forming processes appear to be capable of changing considerably the subsequent behavior of such materials.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340610
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    Correlation for volume phase transition of polymeric gel (vinyl alcohol-sodium acrylate copolymer) in alcohol-water solutions (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 507-512 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A thermodynamic model was proposed to correlate the phase behavior of a swelling polymeric gel (vinyl alcohol-sodium acrylate copolymer) and the volume phase transition in alcohol (methanol, ethanol or propanol)-water solutions. The model is based on the Flory-Huggins formula for polymer solution coupled with the osmotic pressure by rubber elasticity proposed by Flory. The volume change behavior and the equilibrium concentrations inside and outside the gel were successfully correlated using the present model.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340608
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    Radical terpolymerization of zincacrylate, acrylonitrile, and styrene initiated by As2S3-styrene complex (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 528-531 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Terpolymerization was investigated by dilatometry for zincacrylate (ZnA2), acrylonitrile (AN), and styrene (St), radically initiated by a As2S3-styrene complex (I) in dimethyl sulphoxide (DMSO), at 90 ± 0.1°C for 1 h under inert atmosphere. The system follows non-ideal kinetics, due to primary radical termination as well as a degradative chain transfer reaction. The kinetic expression for the system is Rpα(I)0.27 (St)0.31 (AN) 0.22[ZnA2]0.12. The value for the activation energy and kp2/kt are 55 kJ mol-1 and 1.87 × 10-7 1 mol-1 s-1 respectively. The terpolymer has been characterized by IR and NMR spectroscopy. The thermal stability and solubility of the terpolymer have also been studied.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340611
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    Masthead (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340701
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    Flow field analysis of an intermeshing counterrotating twin screw extruder (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 551-558 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The intermeshing counterrotating twin screw extruder is widely used for compounding, devolatilization, blending, and reactive extrusion. A fluid dynamics analysis package-FIDAP, using the finite element method, was implemented to simulate the 3-D flow patterns in the region of conveying elements and shearing discs of a Leistritz LSM30.34 twin screw extruder. The rheological behavior of the fluid was described by a power law model. The flow fields were characterized in terms of velocity profiles, pressure distributions, shear stresses generated, and a parameter λ quantifying the elongational flow components. The influence of screw rotational speed and axial pressure difference on the flow characteristics was also analyzed. A comparison between the flow characteristics in the shearing discs operated in a corotating or counterrotating mode was also presented.
    Additional Material: 21 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340703
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    Heterogeneous suspension polymerization of vinyl chloride: Phase distribution and evolution (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 532-540 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A model for the phase distribution and evolution of the heterogeneous (suspension) polymerization of vinyl chloride is presented. Experimental information on pressure, temperature, and conversion has been obtained from a 34 liter bench reactor reproducing reaction conditions and product properties typical of industrial operation. A calculation procedure based on simple plant data is proposed for the description of the phase compositions and their evolution over the entire process. Results based on classical Flory-Huggins theory of solutions are presented and compared with existing data.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760340612
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    Multilayer extrusion: Experiments and computer simulation (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 559-569 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model is presented for the computer simulation of multilayer flow of polymer melts in coexitrusion. The proposed model can handle an arbitrary number of layers. The viscosity of each layer is shear-rate and temperature dependent. Given the material properties, die dimensions, and process conditions, the model determines the flow field throughout the die gap. Computer simulations and experimental data are presented for a three-layer polyester/EVA/polyester film coextrusion, with emphasis on the interfacial instability and its effects on optical properties of the film. The rsults are discussed in the context of the critical interfacial shear stress criterion that has been proposed by Schrenk, et al. (1) for the onset of interfacial instability. It appears that elasticity differences between layers contribute to the interfacial instability. It is conjectured that minimizing interfacial shear stress and matching elasticities of adjacent layers is an appropriate criterion in coextrusion analysis.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340704
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  • 89
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    Electronic Resource
    A unified lubrication approach for the design of a coat-hanger die (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 541-550 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A simple unified lubrication approach has been proposed to design a coat-hanger die that can deliver wide and uniform liquid sheets. This approach requires that the wall stress in the manifold be constant. With this constraint, any inelastic non-Newtonian fluid model can be used to describe the liquid motion inside the die. Fluid models that can represent the pseudoplastic or viscoplastic behavior of polymeric liquids have been selected for illustration. A general equation that can be solved to determine the effect of production variations on flow uniformity inside the die has also been derived.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340702
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  • 90
    Electronic Resource
    Electronic Resource
    Mechanism of shear modification of low density polyethylene (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 570-579 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this paper we address the aspects associated with shear modification of low density polyethylene by extrusion. By successive passes of the polymer through an extruder it can be shown that both the melt viscosity and melt elasticity are reduced by shear modification. These reversible variations are not accompanied by significant changes in molecular weight distribution. The major effects of extrusion are to decrease the amount of elastically effecitve material. Study of proton relaxation times at 150°C shows that the melt comprises regions of relatively ordered, entangled, and unentangled polymer. Shearing reduces the proportion of more ordered material. The elastically effective anchors that are reduced by shearing are regions with restricted segmental mobility rather than conventional entanglements or intermolecular knots. Successive extrusions produce a relatively small decrease in the number of such constraints to molecular motion. Repeated shearing has a diminishing effect on the proportion of more ordered material in the polyethlene melt. This parallels observations of the effects of repeated shear modification on the properties of polyethylene films and other extrudates.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340705
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  • 91
    Electronic Resource
    Electronic Resource
    Controller design and performance analysis for a reactive extrusion process (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 585-597 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper presents the design and analysis of a process control strategy for a reactive extrusion polypropylene degradation process. The primary control objective is to continuously produce polypropylene with desired properties (viscosity) despite variations in the properties of the feed material. The viscosity of the polypropylene, measured using an In-line Wedge Rheometer, is controlled by manipulating the feed concentration of the peroxide which acts as the initiator for the degradation reaction. An empirical model of the reactive degradation process is developed which describes the process dynamics and the characteristic process disturbances. Minimum variance (MV), constrained minimum variance (CMV), and pole placement (PP) controllers are first evaluated and compared in simulation. Then, a pole placement controller is implemented on the actual reactive extrusion process, with results being presented for the response of the controlled process to load disturbances due to feed material changes.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340707
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  • 92
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340801
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  • 93
    Electronic Resource
    Electronic Resource
    A sliding plate normal thrust rheometer for molten plastics (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 580-584 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A sliding plate rheometer has been developed to measure the normal thrust of a molten plastic in large amplitude oscillatory shear. The normal thrust of a molten plastic in large amplitude oscillatory shear is a significant nonlinear effect that has previously been unobtainable. Normal thrust measurements may now be used to help understand and characterize nonlinear viscoelastic behavior inherent in most molten plastics. The new rhemoeter incorporates a piezoelectric pressure transducer in a very stiff plate that minimizes compliance. Normal thrust measurements with cone and plate rheometers are made by measuring the total force on the plate (or cone) and are subject to error due to edge effects. The new rheometer measures the local pressure in the sample and is therefore unaffected by sample size or edge effects. Normal thrust measurements in large amplitude oscillatory shear are reported for both molten Phillips TR480 high density polyethylene pipe resin which contains 2% by weight of carbon black filler and IUPAC LDPE X. Crosstalk due to shear stress on the active face of the pressure transducer causes signal error which for oscillatory shear is filtered out using a discrete Fourier transform.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340706
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  • 94
    Electronic Resource
    Electronic Resource
    Influence of a core/shell rubber phase on the morphology and the impact resistance of a PC/SAN blend (75/25) (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 613-624 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: At 75/25 concentration ratio, bisphenol a polycarbonate (PC)/styreneacry-lonitrile copolymer (SAN) blend has poor impact resistance compared to PC/ABS. A rubber phase methacrylate-butadiene-styrene (MBS) of core/shell type was dispersed in PC/SAN blend. The morphology of the unmodified and modified blend was investigated. The influence of the acrylonitrile ratio in the SAN on the microstructure was studied. It clearly shows that core/shell resides at the interface between PC and SAN. It seems that core/shell particles enhance the adhesion between the different phases. Their presence influences the interface mobility; i.e., the coalescence of the dispersed phase observed in pure PC/SAN is considerably reduced when the MBS particles are added. The impact resistance of the samples was correlated with the morphology.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340802
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  • 95
    Electronic Resource
    Electronic Resource
    Modeling of polypropylene degradation during reactive extrusion with implications for process control (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 598-612 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper presents the development of a model for free radical initiated polypropylene degradation during reactive extrusion that combines a kinetic model of the polypropylene degradation reaction with a simplified model of the melting mechanism in the extruder. The free radical initiated degradation of polypropylene is characterized by a narrowing of the molecular weight distribution (MWD) and a decrease in the molecular weight averages. A high temperature SEC is used to determine MWD's for three different commercially available polypropylenes degraded at various initiator concentrations in a 1.5 inch single screw extruder (L/D = 24:1). The predictions of the kinetic model alone and the combined kinetic-melting model are compared with the experimentally determined MWD's and molecular weight averages for the degraded polypropylenes. The predictions of a modified kinetic model that includes the possibility of termination by combination are also examined. The kinetic-melting model is found to provide significantly improved predictions of the experimentally determined MWD's and molecular weight averages in comparison to the original kinetic model. A viscosity-molecular weight relationship is also developed, which is then used to determine the gain of the degradation process as a function of the initiator concentration from the molecular weight averages predicted by the kinetic-melting model. Earlier work has shown such prior knowledge of the process gain can be used to significantly improve the performance of process control schemes for the degradation process.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340708
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  • 96
    Electronic Resource
    Electronic Resource
    Rubber modified epoxy resin. I: Cure kinetics and chemorheology (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 625-631 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The curing and vitrification effect during the reaction of ATBN modified epoxy resin was studied through the dynamic differential scanning calorimetry method and a new reaction kinetic equation containing generalized WLF equation was developed to describe the reaction rate at both glassy and rubbery state. An autocatalytic mechanism was found to describe adequately the cure kinetics of the rubber modified epoxy resin and the overall order of reaction was assumed to be 2. The kinetic parameters were determined from the DSC data through the Marquardt's multivariable nonlinear regression method and Runge-Kutta integration technique. The presence of rubber indicated minor effect on the cure kinetics of epoxy resin. The Arrhenius type viscosity function was employed to establish a relationship between viscosity data measured by RMS and chemical conversion calculated from the reaction kinetic equation.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340803
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  • 97
    Electronic Resource
    Electronic Resource
    Modeling of the Dynamics of Water and R-11 blown polyurethane foam formation (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 642-649 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polyurethane foam formation involves both polymerization and expansion processes. The dynamics of the water and R-11 blown foams depend on the rates of chemical and physical blowing processes, along with the rate of viscosity increase of the reacting mixture. Experiments were carried out to study the dynamics of free rising, water and R-11 blown rigid polyurethane foams. The density and temperature change during the foam formation were monitored. A theoretical model was developed to predict the density and temperature variation with time. In the model, the physical blowing agent (R-11) evaporation process is assumed to be heat generation-controlled and the carbon dioxide generation process to be controlled by the rate of the water-isocyanate reaction. The kinetic parameters of the reactions of isocyanate with polyol and water were obtained separately and were asssumed to be independent of each other. The water-isocyanate reaction appears to follow first-order kinetics with respect to concentration of water. The theoretical predictions of the model show good agreement with the experimental data for density variation with time. The model predictions for temperature rise also match experimental data, except at the later stages of foaming when it is found to be slower than the experimental measurements. However, this deviation does not affect the dynamics of density change since it occurs after the completion of the expansion process.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340805
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  • 98
    Electronic Resource
    Electronic Resource
    A personal computer software program for coathanger die simulation (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 657-664 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A good extrusion die must distribute the polymer melt in the flow channel such that the material exits from the die with a uniform velocity and temperature. Coathanger dies are commonly used for the extrusion of plastic sheets and films. The die is usually provided with a straining bar allowing a regulation of the flowrate in the case of a poor design. But this, in turn, can affect temperature uniformity. Therefore, the design of coathanger die is a complex task which is mainly accomplished by trial and error in industry. Analyses of the flow in coathanger dies have been reported in the literature. Analytical and numerical approaches are used to solve this problem. The first one involves many simplifying assumptions: the most important ones being the unidirectional and isothermal flow of the polymer. Most numerical methods deal with a 2-D geometry, but only a few of them have considered the non-isothermal flow. A new model has been developed using a modified FAN method (Flow Analysis Network introduced by Tadmor) for the calculation of the 2-D flow, coupled with a finite-difference scheme for the calculation of temperature. The overall model can run on a PC with only a few minutes of calculation. Good agreement was obtained between experimental data and simulations.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340807
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  • 99
    Electronic Resource
    Electronic Resource
    A finite element model for complex profile calibration (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 650-656 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new finite element model named Corrected Slice Method (CSM) has been developed to cope with three-dimensional vacuum cooling calibrator problems. Such problems appear whenever the cooling channel lay-out comprises transverse channels in the calibrator. The CSM is an extension of the 2D approach (8), which takes into account the axial heat fluxes within the calibrator. The proposed model was validated by comparing the numerical results obtained on a test problem with a rigorous finite element approach. Moreover, a real complex profile-calibrator system was simulated in order to illustrate the full performance of the porposed method.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340806
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  • 100
    Electronic Resource
    Electronic Resource
    The use of flexural tests in the study of environmental stress cracking of polymers (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 665-670 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of bend testers for the determination of critical strains in the study of environmental stress cracking has been assessed. Using the combination of polystyrene in ethanol, various factors affecting the measurement of critical strains were investigated, including the strain applied during the bend testing, the time of immersion in the liquid prior to straining, the surface finish, and the extent of physical aging. It was concluded that the best determination of critical strain is the strain at which a sample just shows signs of crazing, rather than the strain at the outer edge of a band of crazes. The measured value of critical strain increases with increased prior immersion time, decreased surface roughness, and decreased physical aging time. Reasons for these variations are discussed. It is concluded that although the use of bend testers is valuable for qualitative testing, careful testing methodologies need to be adopted for it to be a useful quantitative test.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340808
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