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  • 1990-1994  (3,511)
  • 1985-1989  (2,861)
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  • Ultrastructure
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  • 1
    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.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Virchows Archiv 425 (1994), S. 93-99 
    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
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Virchows Archiv 425 (1994), S. 305-313 
    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.
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  • 4
    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.
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  • 5
    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.
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  • 6
    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.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 55 (1994), S. 180-189 
    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.
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  • 8
    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.
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  • 9
    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.
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  • 10
    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.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 88 (1994), S. 222-227 
    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.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 88 (1994), S. 222-227 
    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.
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  • 13
    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.
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  • 14
    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.
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  • 15
    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.
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  • 16
    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.
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 190 (1994), S. 461-468 
    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.
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 190 (1994), S. 439-444 
    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.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 190 (1994), S. 583-590 
    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.
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  • 20
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    Archives of microbiology 162 (1994), S. 267-271 
    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.
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  • 21
    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.
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  • 22
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    Archives of microbiology 162 (1994), S. 267-271 
    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.
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  • 23
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    Mycopathologia 125 (1994), S. 33-39 
    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.
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  • 24
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    European archives of oto-rhino-laryngology and head & neck 251 (1994), S. 267-270 
    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.
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  • 25
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    Mycopathologia 128 (1994), S. 181-192 
    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.
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  • 26
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    Methods in cell science 16 (1994), S. 109-115 
    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.
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  • 27
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    Hydrobiologia 292-293 (1994), S. 137-142 
    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.
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  • 28
    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.
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  • 29
    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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  • 30
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    Medical molecular morphology 27 (1994), S. 1-7 
    ISSN: 1860-1499
    Keywords: Medulloblastoma ; Primitive glioma ; Differentiation ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To increase our understanding of the differentiation potential and cytogenesis of embryonal tumors in the brain, 12 medulloblastomas and 10 primitive gliomas were studied by electron microscopy. Of the medulloblastomas, 6 cases were undifferentiated tumors that demonstrated fine processes similar to microspikes. The remaining 6 cases were poorly-differentiated tumors. Axon-like processes were seen in 4 of these cases, including one with dense core vesicles. Astroglial processes were seen in 4 cases. Of the primitive gliomas, there were 2 undifferentiated tumors and 8 poorly-differentiated tumors. Some of the undifferentiated tumor cells had broad cytoplasmic processes. Of the 8 poorly-differentiated gliomas, there were groupings of junctional complexes in 7, microvilli in 4 and bundles of intermediate filaments in 5. It is concluded that medulloblastomas have both neuronal and glial differentiation potentials and that primitive gliomas have only glial differentiation potential. The origin of medulloblastomas may be from the remnants of cell nests with a multipotential differentiation capacity, and the origin for primitive gliomas may be from remnants of glial precursor cells.
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  • 31
    ISSN: 1860-1499
    Keywords: Ultrastructure ; Transferrin receptor ; Oral malignant melanoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A rare variety of malignant melanoma in the maxilla was studied by electron microscopic observation and an immunohistochemical investigation of the transferrin receptor (TfR). A number of low-stage melanosomes were seen, and the TfR was found in both the cell membrane and the cytoplasm.
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  • 32
    ISSN: 1860-1499
    Keywords: Vasoactive intestinal polypeptide (VIP) ; Intestinal ischemia ; Immunohistochemistry ; Ganglionic cells ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Alterations in the distribution of vasoactive intestinal polypeptide (VIP) in normal and ischemic small intestines of dogs were studied by using conventional transmission electron microscope, and immunohistochemistry for light and electron microscopy. At the light microscopic level, immunoreactivity was evident in the intestinal ganglionic cells of control segments. At the electron microscopic level using a pre-embedding method, the entire cytoplasm of the ganglionic cells in the control segments was filled with VIP immunoreactive products, while the post-embedding experiment showed positive reactions only within the VIP granules and Golgi vesicles. After 30 min of ischemia, immunoreactivity was greatly decreased in the ganglionic cells and a large amount of VIP immunoreactive product appeared in the striated border of epithelial cells and in nerve fibers of the subepithelial layer. These results suggest that intestinal ischemia might lead to the release of VIP, which seems to bind to the microvillus membrane of epithelial cells. The relationship between the changes in VIP distribution and its protecting mechanisms of ischemic damage is discussed.
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  • 33
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    Medical molecular morphology 27 (1994), S. 113-122 
    ISSN: 1860-1499
    Keywords: Breast cancer ; Apocrine carcinoma ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Three cases of apocrine carcinoma of the breast were investigated by light and electron microscopy. Histologically, the tumor cells were shown to have eosinophilic granular cytoplasm and occasional cytoplasmic snouts protruding into the lumen. Ultrastructurally, light and dark tumor cells were identified, and there were many lysosome-like dense bodies of various sizes and small dense granules grouped in the subapical region. Many mitochondria with incomplete cristae and numerous small vacuoles were distributed in the cytoplasm. Occasionally, intracytoplasmic lumen were visible in the tumor cells. These ultrastructural findings are quite similar to those found in normal apocrine sweat glands. However, the presence of an intraductal component of carcinoma suggests the origin to be mammary epithelial cells.
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  • 34
    ISSN: 1860-1499
    Keywords: Human T-lymphotropic virus type I (HTLV-I) ; Ultrastructure ; Basedow's disease ; Lymphocyte ; Thyroid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Thyroid tissue from a patient with Basedow's disease and immunopositive for HTLV-I was examined. Histopathological and immunohistochemical studies revealed that follicular-epithelial cells (FEC) had papillary projections reaching into the follicular lumina which were associated with diffuse T, but not B, lymphocyte infiltration and occasionally formed aggregations intermingled with T and B lymphocytes. Ultrastructurally, infiltrated lymphocytes possessing round or irregularly indented nuclei were detected in the capillary lumen, stroma and, also, FEC layers. The lymphocytes extended irregular processes, attached to long thin processes of FEC and infiltrated into FEC layers. Cocultivation of minced thyroid tissue with normal lymphocytes resulted in the establishment of a type-C virus-producing T-cell line.
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  • 35
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    Medical molecular morphology 27 (1994), S. 254-256 
    ISSN: 1860-1499
    Keywords: Gonad ; Mesonephros ; Histogenesis ; Primordial sex cord ; Folliculogenous sex cord ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The histogenesis and organogenesis of the human gonad in twelve embryos and six fetuses of ovulational ages 5 to 18 weeks was investigated by histological and ultrastructural examination, including observation of almost complete serial Epon-embedded sections of the entire gonads of 10 embryos. This investigation revealed that the main constituent cells of the gonads are derived from the mesonephros, and that the coelomic epithelium is not involved in the formation of the main component at any stage.
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  • 36
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    Medical molecular morphology 27 (1994), S. 260-263 
    ISSN: 1860-1499
    Keywords: Cellular interaction ; Follicular wall ; Granulosa cell ; Theca cell ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Bovine granulosa and theca cells were cultured on the opposite sides of a collagen membrane, and the morphological and structural effects of the interaction between theca and granulosa cells were studied. The apical surface of both granulosa and theca cells in the cocultured group appeared convex, while control cells were thin and flat. Numerous filopodia spread over the cellular surface connecting the cells. Constituents of rough endoplasmic reticulum in the cocultured cells were extended and swollen when compared with those observed in the cells cultured alone. Cocultured granulosa cells formed multilayered sheets, while granulosa cells cultured alone formed monolayered sheets. Theca cells in the cocultured group were more densely packed than cells cultured alone. These results indicate that the levels of cellular activity and intercellular communication among each type of cell are increased by the granulosa and theca cell interactions.
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  • 37
    ISSN: 1860-1499
    Keywords: X-ray microanalysis ; Freeze-drying ; Calcium ; Ultrastructure ; Isehemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract There is considerable interest of the changes in intracellular electrolytes in various pathophysiological states in cardiology. X-ray microanalysis is a useful method to measure the concentration of intracellular elements, and freeze-drying is a required technique for X-ray microanalysis to preserve elements. In this study, we utilized a new technique by which ultrathin sections were evaporated by carbon in an external freeze-dryer after freeze-drying and we were able to obtain clear electron micrographs of papillary muscles and myocytes. Calcium concentrations of mitochondria and cytosol were measured during 120 min ischemia. We showed that mitochondria played a role in intracellular calcium regulation during 30 min ischemia.
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  • 38
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    Molecular Reproduction and Development 37 (1994), S. 457-461 
    ISSN: 1040-452X
    Keywords: Canine sperm ; Pyospermia ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The red wolf (Canis rufus) is an endangered species with 194 individuals remaining in the wild and in various captive facilities. Breeding efforts at the Graham, WA site (Point Defiance Zoo and Aquarium) have involved artificial insemination with fresh or frozen semen in an effort to increase population and maximize the genetic potential of the stock. Electron microscopic observations were made in semen specimens obtained by electroejaculation from mature males prior to their use in an effort to determine semen parameters that might be useful in guiding breeding procedures. Sperm samples were either fixed immediately or treated with capacitating media and fixed after 4 to 7 hr of incubation. Many of the specimens examined were pyospermic (white cell in semen) and showed evidence of spermophagy, primarily by neutrophils. Of the six animals surveyed, only one showed little evidence of spermophagy, and three had extensive pyospermia and spermophagy but this finding was not correlated with fertility. Samples fixed immediately as well as those incubated for several hours showed evidence of spermophagy, indicating that the phagocytosis was not the result of culture. Gene pool restriction and/or captive stress may be contributing factors of reduced semen quality. © 1994 Wiley-Liss, Inc.
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  • 39
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    Microscopy Research and Technique 27 (1994), S. 145-164 
    ISSN: 1059-910X
    Keywords: Human ; Mouse ; Oocytes ; Maturation ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: This paper reviews the process of peri-ovulatory oocyte maturation and the ultrastructural organization of the human egg and compares it with that of the mouse. The main thrust of the paper is on the human, since there are several reviews on the mouse. Both preovulatory and postovulatory events at fertilization, as well as some of the aberrant features of maturation are covered. Some changes induced by oocyte culture and cooling in the human are also included. The report attempts to focus on unique features of the human oocyte and shows a variety of ultrastructural differences between human and murine oocytes, which may well reflect differences in their physiology and biochemistry. Based on these differences and further observations on the process of fertilization of both species, particularly with respect to the inheritance of paternal centrioles, it is concluded that the mouse may not be a suitable modle for the development and refinement of current procedures in human assisted reproductive technology. © 1994 Wiley-Liss, Inc.
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  • 40
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    Microscopy Research and Technique 29 (1994), S. 411-431 
    ISSN: 1059-910X
    Keywords: Corrosion casts ; LM ; SEM ; TEM ; Microvasculature ; Ultrastructure ; Absorption ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The aim of the present study was to provide a comprehensive morphological analysis of the porcine epididymis in view of the specific functions being performed in different regions of this organ. Blood supply and microvasculature of efferent ductules and epididymal duct were investigated by means of corrosion casts which were analysed macroscopically and by scanning electron microscopy. This revealed blood supply to the testis and epididymis to be closely related. The capillary pattern was typical for the efferent ductules, the caput, corpus, and distal cauda epididymidis, respectively. Corrosion casts were also used to visualize the course of the efferent ductules themselves. Tissue samples from different regions of the efferent ductules and epididymal duct were examined by light microscopy and both scanning and transmission electron microscopy, with special attention being payed to transitional areas. Morphological criteria allowed the distinction of three segments within the efferent ductules and of the initial segment, proximal caput, distal caput, corpus, proximal cauda, and distal cauda regions of the epididymal duct. Components of the endocytic apparatus of efferent ductule principal cells were identified by ferritin uptake. Ultrastructural evidence of absorption in the epididymal duct was particularly prominent in proximal and distal caput. Extensive cisternae of rough endoplasmic reticulum and a well-developed Golgi apparatus were indicative of active protein synthesis and secretion especially in the distal caput and corpus regions. However, assignment of various organelles in principal cells of the epididymal duct to either absorptive or secretory pathways still remains tentative. © 1994 Wiley-Liss, Inc.
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  • 41
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    Molecular Reproduction and Development 38 (1994), S. 421-430 
    ISSN: 1040-452X
    Keywords: Cumulus ; Oocyte ; Zona pellucida ; SEM ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Surface characteristics of the bovine oocyte and its investments before, during, and after maturation, and fertilization in vitro were evaluated by scanning electron microscopy (SEM). Oocyte diameters were also measured during SEM analysis of the oocyte. The cumulus cells manifested a compact structure with minimal intercellular spaces among them in the immature oocytes. These became fully expanded with increased intercellular spaces after maturation in vitro, but contracted again after fertilization. The zona pellucida (ZP) showed a fibrous, open mesh-like structure in the maturing and matured oocytes. The size and number of meshes on the ZP decreased dramatically after fertilization. The vitelline surface of immature oocytes was characterized by distribution of tongue-shaped protrusions (TSPs) varying in density. After 10 and 22 hr of maturation incubation, oocyte surface microvilli (MV) increased to become the predominant surface structure, and TSPs decreased substantially. The vitelline surface of fertilized oocytes (at 6 and 20 hr) was similar to that of the matured oocytes, but unfertilized oocytes had less dense MV than did fertilized oocytes (at 20 hr). The diameter of the oocytes decreased from 99 to 80 μm during maturation and increased to 106 μm after insemination (P 〈 0.05). Membrane maturation was characterized by surface changes from a TSP-predominant pattern to a MV-predominant pattern. Thus, the bovine oocyte maturation process was found to involve the expansion of cumulus cells and the maturation of the ZP, which changes dramatically upon fertilization. Also, volumetric changes occurred in ooplasm processed for SEM following oocyte maturation and insemination. © 1994 Wiley-Liss, Inc.
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  • 42
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    Microscopy Research and Technique 29 (1994), S. 169-176 
    ISSN: 1059-910X
    Keywords: Celiac ganglion ; Chromaffin cells ; Autonomic nervous system ; Ultrastructure ; Guinea pig ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Utilizing electron microscopic observation, several contacts between small, granule-containing cells (SGC) and postganglionic neurons (PGN) in the celiac ganglion of the guinea pig have been observed. A SGC in very close association with a PGN was seen to receive a distinct synaptic contact that contained many vesicles with dense cores. This contact was morphologically unlike cholinergic synapses previously reported on chromaffin cells. Because the SGC and PGN were clearly separated by a thin rim of satellite cell cytoplasm mutual to both cells, it is not known how or if the SGC would possibly exert a synaptic or paracrine effect on the PGN. Also, intraganglion SGC existed as large well-vascularized islands within the celiac ganglion. These intraganlion clusters sometimes contained more than 50 cells and perhaps could be considered to function as localized neuroendocrine components within the ganglion by secreting granule products into the nearby blood vessels for local or distant effects, although this certainly is not known. This work reports a unique synaptic ending upon a single-occurring SGC, which, in turn, closely approximates a ganglion neuron in a soma-somatic relationship. In addition, a very close association (but no actual contact) was observed between granule-containing processes, presumably emanating from the intraganglion clusters, and PGN. Whatever the function of ganglionic SGC may be, the exact relationship between SGC and PGN presumably would be of great interest and potential importance. © 1994 Wiley-Liss, Inc.
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  • 43
    ISSN: 1059-910X
    Keywords: Sinus afferent pathway ; SP interneurons ; Double immunocytochemistry ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The ultrastructure of substance P-containing nerve terminals synapsing on catecholamine neurons in the rat commissural subnucleus of the nucleus tractus solitarii (NTScom) was studied using a double immunocytochemical labeling technique. Although there were numerous tyrosine hydroxylase-immunoreactive (TH-I) somata present, substance P immunoreactive (SP-I) cell bodies were only occasionally found in the NTScom. At the light microscopic level, many SP-I terminals were seen closely associated with TH-I dendrites and somata. At the electron microscopic level, SP-I terminals synapsing on TH-I structures were also readily encountered. SP-I terminals contained small, clear, and predominantly spherical vesicles (32 ± 4 nm diameter), as well as large dense-cored vesicles approximately 100 nm in diameter. Postsynaptic TH-I dendritic profiles of various calibers and somata were encountered. These postsynaptic TH-I structures often showed postsynaptic densities. The morphological features of the SP-TH synapses in the present study, that is, the size of synaptic vesicles and the presence of postsynaptic densities, are quite different from those of central carotid sinus afferent synapses reported in our previous study [Chen et al. (1992), J. Neurocytol., 21:137-147]. Therefore, most of the SP terminals of the SP-TH synapses in the NTScom appear not to originate from the carotid sinus afferents. SP-I second-order neurons of the carotid sinus afferent pathway [Chen et al. (1991), J. Auton. Nerv. Syst., 33:97-98] may be one of the possible sources of such terminals. © 1994 Wiley-Liss, Inc.
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  • 44
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    Numerical Linear Algebra with Applications 1 (1994), S. 105-105 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 45
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    Numerical Linear Algebra with Applications 1 (1994), S. 151-154 
    ISSN: 1070-5325
    Keywords: Linear systems ; Singular systems ; Iterative methods ; Convergent methods ; Index of the iteration operator ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Equivalence is shown between different conditions for convergence of iterative methods for consistent singular systems of linear equations on Banach spaces. These systems appear in many applications, such as Markov chains and Markov processes. The conditions considered relate the range and null spaces of different operators.
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  • 46
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    Numerical Linear Algebra with Applications 1 (1994), S. 211-212 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 47
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    Numerical Linear Algebra with Applications 1 (1994), S. 179-210 
    ISSN: 1070-5325
    Keywords: Linear system solvers ; Conjugate gradients ; Iteration number estimates ; Explicit preconditionings ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Instead of the standard estimate in terms of the spectral condition number we develop a new CG iteration number estimate depending on the quantity B = 1/ntr M/(det M)1/n, where M is an n × n preconditioned matrix. A new family of iterative methods for solving symmetric positive definite systems based on B-reducing strategies is described. Numerical results are presented for the new algorithms and compared with several well-known preconditioned CG methods.
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  • 48
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    Numerical Linear Algebra with Applications 1 (1994), S. 155-177 
    ISSN: 1070-5325
    Keywords: Preconditioning ; Diagonal compensation ; Eigenvalue bounds ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: When solving linear algebraic equations with large and sparse coefficient matrices, arising, for instance, from the discretization of partial differential equations, it is quite common to use preconditioning to accelerate the convergence of a basic iterative scheme. Incomplete factorizations and sparse approximate inverses can provide efficient preconditioning methods but their existence and convergence theory is based mostly on M-matrices (H-matrices). In some application areas, however, the arising coefficient matrices are not H-matrices. This is the case, for instance, when higher-order finite element approximations are used, which is typical for structural mechanics problems. We show that modification of a symmetric, positive definite matrix by reduction of positive offdiagonal entries and diagonal compensation of them leads to an M-matrix. This diagonally compensated reduction can take place in the whole matrix or only at the current pivot block in a recursive incomplete factorization method. Applications for constructing preconditioning matrices for finite element matrices are described.
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  • 49
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    Numerical Linear Algebra with Applications 1 (1994) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 50
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    Numerical Linear Algebra with Applications 1 (1994), S. 237-245 
    ISSN: 1070-5325
    Keywords: Korovkin theorem ; Heat conduction equation ; Lax theorem ; Difference scheme ; Convergence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Sufficient conditions are obtained for the convergence of difference schemes for the numerical solution of the Cauchy problem for a heat conduction equation in two space variables. The sufficient conditions are derived in a form similar to those for the convergence of a sequence of linear positive operators in the Korovkin theorem. As an application it is shown that difference schemes that are widely used in practice can easily be checked for convergence by these conditions.
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  • 51
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    Numerical Linear Algebra with Applications 1 (1994), S. 213-236 
    ISSN: 1070-5325
    Keywords: Optimal order preconditioners ; Algebraic multilevel ; Chebyshev polynomial approximation ; Diagonal compensation ; Approximate inverses ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The numerical solution of elliptic selfadjoint second-order boundary value problems leads to a class of linear systems of equations with symmetric, positive definite, large and sparse matrices which can be solved iteratively using a preconditioned version of some algorithm. Such differential equations originate from various applications such as heat conducting and electromagnetics. Systems of equations of similar type can also arise in the finite element analysis of structures.We discuss a recursive method constructing preconditioners to a symmetric, positive definite matrix. An algebraic multilevel technique based on partitioning of the matrix in two by two matrix block form, approximating some of these by other matrices with more simple sparsity structure and using the corresponding Schur complement as a matrix on the lower level, is considered.The quality of the preconditioners is improved by special matrix polynomials which recursively connect the preconditioners on every two adjoining levels. Upper and lower bounds for the degree of the polynomials are derived as conditions for a computational complexity of optimal order for each level and for an optimal rate of convergence, respectively.The method is an extended and more accurate algebraic formulation of a method for nine-point and mixed five- and nine-point difference matrices, presented in some previous papers.
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  • 52
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    Numerical Linear Algebra with Applications 1 (1994) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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    Topics: Mathematics
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  • 53
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    Numerical Linear Algebra with Applications 1 (1994), S. 1-1 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 54
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    Numerical Linear Algebra with Applications 1 (1994), S. 33-44 
    ISSN: 1070-5325
    Keywords: Rank revealing QR factorization ; Column pivoting ; Numerical rank ; Subset selection ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Rank revealing factorizations are used extensively in signal processing in connection with, for example, linear prediction and signal subspace algorithms. We present an algorithm for computing rank revealing QR factorizations of low-rank matrices. The algorithm produces tight upper and lower bounds for all the largest singular values, thus making it particularly useful for treating rank deficient problems by means of subset selection, truncated QR, etc. The algorithm is similar in spirit to an algorithm suggested earlier by Chan for matrices with a small nullity, and it can also be considered as an extension of ordinary column pivoting.
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  • 55
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    Numerical Linear Algebra with Applications 1 (1994), S. 571-581 
    ISSN: 1070-5325
    Keywords: GMRES ; GMRES(m) ; Large-scale nonsymmetric linear systems ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The generalized minimal residual (GMRES) method is widely used for solving very large, nonsymmetric linear systems, particularly those that arise through discretization of continuous mathematical models in science and engineering. By shifting the Arnoldi process to begin with Ar0 instead of r0, we obtain simpler Gram-Schmidt and Householder implementations of the GMRES method that do not require upper Hessenberg factorization. The Gram-Schmidt implementation also maintains the residual vector at each iteration, which allows cheaper restarts of GMRES(m) and may otherwise be useful.
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  • 56
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    Numerical Linear Algebra with Applications 1 (1994), S. 555-570 
    ISSN: 1070-5325
    Keywords: Linear system of equations ; Iterative method ; Fast algorithm ; Arnoldi process ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new iterative scheme is described for the solution of large linear systems of equations with a matrix of the form A = ρU + ζI, where ρ and ζ are constants, U is a unitary matrix and I is the identity matrix. We show that for such matrices a Krylov subspace basis can be generated by recursion formulas with few terms. This leads to a minimal residual algorithm that requires little storage and makes it possible to determine each iterate with fairly little arithmetic work. This algorithm provides a model for iterative methods for non-Hermitian linear systems of equations, in a similar way to the conjugate gradient and conjugate residual algorithms. Our iterative scheme illustrates that results by Faber and Manteuffel [3,4] on the existence of conjugate gradient algorithms with short recurrence relations, and related results by Joubert and Young [13], can be extended.
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  • 57
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    Numerical Linear Algebra with Applications 1 (1994), S. 583-587 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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    Topics: Mathematics
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  • 58
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    Numerical Linear Algebra with Applications 1 (1994), S. 45-63 
    ISSN: 1070-5325
    Keywords: Conjugate gradients ; Convergence ; Linear systems ; Acceleration of conjugate gradients ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The solution of linear systems has considerable importance for the computation of problems resulting from engineering, physics, chemistry, computer science, mathematics, medicine and economics. The calculation of costly and time-consuming problems, e.g. crash tests, simulation of the human lung and skin, calculation of electrical and magnetical fields, thermal analysis and fluid dynamics, to name only a few, has become possible with the recent developments of advanced computer architectures and iterative solvers. Generalized conjugate gradient (CG) methods are the most important iterative solvers because they converge very quickly under certain conditions. Therefore they are widely used and in a rapid further development.The purpose of this paper is to present new results for the convergence of generalized CG methods. A convergence result for non-symmetric and non-positive definite matrices is given that includes the classical theory for symmetric, positive definite matrices as a special case.The norm of the residuals resulting from CG methods may oscillate heavily. Different remedies for smoothing this sequence have been proposed, for example by van der Vorst. Schönauer introduced in the 1980s a smoothing algorithm to get a norm nonincreasing function of the iteration index. For this algorithm a complete theoretical analysis is given. A surprising result is obtained showing that the smoothing algorithm is in a sense optimal. Convergence estimates are derived therefrom. A geometric interpretation of the smoothing algorithm is given showing the propagation of the errors.It should be stressed that a smooth convergence of the residuals is not equivalent to a smooth convergence of the errors which is the proper aim. A class of error minimizing methods can be easily derived from the theory.
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  • 59
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    Numerical Linear Algebra with Applications 1 (1994), S. 107-128 
    ISSN: 1070-5325
    Keywords: Incomplete factorization ; Preconditioning ; Linear elasticity problems ; Displacement decomposition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Two preconditioning techniques for the numerical solution of linear elasticity problems are described and studied. Both techniques are based on spectral equivalence approach. The first technique consists in an incomplete factorization of the separate displacement component part of the stiffness matrix. The second technique uses an incomplete factorization of the isotropic approximation to the stiffness matrix. Results concerning existence, stability and efficiency of these preconditioning techniques are presented. The efficiency and robustness of the described techniques are illustrated by numerical experiments.
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  • 60
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    Numerical Linear Algebra with Applications 1 (1994), S. 129-139 
    ISSN: 1070-5325
    Keywords: Conjugate gradient method ; Nonsymmetric linear system ; Krylov subspace method ; Conjugate residual method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Yserentant's and Bramble/Pasciak/Xu's hierarchical preconditioners only require the hierarchical node connection of a finite element grid. So they could be applied to nonsymmetric FE-systems too, having a symmetric preconditioner. We investigate the question whether this fact could be useful in the CG-like iterative methods. The main key is the consideration of an appropriate choice of the inner product defined in the N-vector space. It is shown, how the inner product influences the formulas of the methods, the rate of convergence and some other properties.
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  • 61
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    Numerical Linear Algebra with Applications 1 (1994), S. 141-150 
    ISSN: 1070-5325
    Keywords: Invariant manifolds ; Error estimates ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Many processes in the sciences and in engineering are modelled by dynamical systems and - in discretized version - by nonlinear maps. To understand the often complicated dynamical behaviour it is a well established tool to use the concept of invariant manifolds of the system. In this way it is often possible to reduce the dimension of the system considerably. In this paper we propose a new method to calculate numerically invariant manifolds near fixed points of maps. We prove convergence of our procedure and provide an error estimation. Finally, the application of the method is illustrated by examples.
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  • 62
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    Numerical Linear Algebra with Applications 1 (1994), S. 335-335 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 63
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    Numerical Linear Algebra with Applications 1 (1994), S. 369-386 
    ISSN: 1070-5325
    Keywords: GMRES ; Unsymmetric linear systems ; Iterative solver ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Recently Eirola and Nevanlinna have proposed an iterative solution method for unsymmetric linear systems, in which the preconditioner is updated from step to step. Following their ideas we suggest variants of GMRES, in which a preconditioner is constructed per iteration step by a suitable approximation process, e.g., by GMRES itself. Our numerical experiments indicate that this may lead to considerable savings in CPU-time and memory requirements in typical CFD applications.
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  • 64
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    Numerical Linear Algebra with Applications 1 (1994), S. 337-368 
    ISSN: 1070-5325
    Keywords: Local refinement ; Preconditioning ; Two-grid method ; Cell-centered grids ; Finite differences ; Elliptic problem ; Optimal rate of convergence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Two preconditioning techniques for solving difference equations arising in finite difference approximation of elliptic problems on cell-centered grids are studied. It is proven that the BEPS and the FAC preconditioners are spectrally equivalent to the corresponding finite difference schemes, including a nonsymmetric one, which is of higher-order accuracy. Numerical experiments that demonstrate the fast convergence of the preconditioned iterative methods (CG and GCG-LS in the nonsymmetric case) are presented.
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  • 65
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    Numerical Linear Algebra with Applications 1 (1994), S. 421-425 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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    Topics: Mathematics
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  • 66
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    Numerical Linear Algebra with Applications 1 (1994), S. 403-420 
    ISSN: 1070-5325
    Keywords: Quasi-minimal residual iteration ; Non-Hermitian matrix ; Singular linear system ; Markov chain modeling ; Krylov-subspace method ; Convergence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Recently, Freund and Nachtigal proposed the quasi-minimal residual algorithm (QMR) for solving general nonsingular non-Hermitian linear systems. The method is based on the Lanczos process, and thus it involves matrix - vector products with both the coefficient matrix of the linear system and its transpose. Freund developed a variant of QMR, the transpose-free QMR algorithm (TFQMR), that only requires products with the coefficient matrix. In this paper, the use of QMR and TFQMR for solving singular systems is explored. First, a convergence result for the general class of Krylov-subspace methods applied to singular systems is presented. Then, it is shown that QMR and TFQMR both converge for consistent singular linear systems with coefficient matrices of index 1. Singular systems of this type arise in Markov chain modeling. For this particular application, numerical experiments are reported.
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  • 67
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    Numerical Linear Algebra with Applications 1 (1994) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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    Numerical Linear Algebra with Applications 1 (1994), S. 387-402 
    ISSN: 1070-5325
    Keywords: Preconditioning ; Incomplete LU ; Threshold strategies ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this paper we describe an Incomplete LU factorization technique based on a strategy which combines two heuristics. This ILUT factorization extends the usual ILU(O) factorization without using the concept of level of fill-in. There are two traditional ways of developing incomplete factorization preconditioners. The first uses a symbolic factorization approach in which a level of fill is attributed to each fill-in element using only the graph of the matrix. Then each fill-in that is introduced is dropped whenever its level of fill exceeds a certain threshold. The second class of methods consists of techniques derived from modifications of a given direct solver by including a dropoff rule, based on the numerical size of the fill-ins introduced, traditionally referred to as threshold preconditioners. The first type of approach may not be reliable for indefinite problems, since it does not consider numerical values. The second is often far more expensive than the standard ILU(O). The strategy we propose is a compromise between these two extremes.
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    Numerical Linear Algebra with Applications 1 (1994), S. 427-447 
    ISSN: 1070-5325
    Keywords: Nonsymmetric linear systems ; Conjugate gradient type iterative methods ; GMRES ; Restarting ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The solution of nonsymmetric systems of linear equations continues to be a difficult problem. A main algorithm for solving nonsymmetric problems is restarted GMRES. The algorithm is based on restarting full GMRES every s iterations, for some integer s〉0. This paper considers the impact of the restart frequency s on the convergence and work requirements of the method. It is shown that a good choice of this parameter can lead to reduced solution time, while an improper choice may hinder or preclude convergence. An adaptive procedure is also presented for determining automatically when to restart. The results of numerical experiments are presented.
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    Communications in Numerical Methods in Engineering 10 (1994) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    Communications in Numerical Methods in Engineering 10 (1994), S. 1-9 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An iterative method is introduced for computing second-order partial derivatives (sensitivities) of eigenvalues and eigenvectors of matrices which depend on a number of real design parameters. Numerical tests confirm the viability of the method and support our theoretical analysis. Alternative methods are reviewed briefly and compared with the one proposed here.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 11-19 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the formulation of the semi-Loof element the rotation of the tangent plane is derived from the interpolation of the transverse displacement, while the rotation of the normal is interpolated separately by another set of shape functions. The geometric stiffness matrix can be formulated by use of either of the two rotation representations. It is demonstrated that the use of the tangent plane representation in the geometric stiffness matrix is far superior to the common form at present.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 21-32 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient solution to boundary-value problems may be based on the application of a suitably truncated T-complete set of Trefftz functions over individual subdomains and on linking the fields by a least-squares procedure. Although it yields a symmetric system of linear equations, this approach as originally presented by Zielinski and Zienkiewicz is not suited for implementation into FE codes. The present paper presents two equivalent formulations, which take respectively the form of the finite (FE) and non-conventional boundary-element (BE) approach. Both allow the resulting simultaneous equations to be assembled following the standard direct stiffness methods and can readily be implemented into existing FE codes.As in the conventional p-method, the accuracy may be controlled within large limits without increasing the number of elements. The present approach allows substantial saving in computer time in comparison with the so-called hybrid-Trefftz (HT) elements, though the assumed displacement fields are identical. The practical efficiency of the new T-element approach is assessed on the problem of stress concentration in a symmetrically compressed perforated panel.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 43-58 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method is presented for the solution of elliptical problems defined on general-shape multiconnected three-dimensional domains approximated by means of polyhedra. The boundary conditions may be of the Neumann type. The differential operator and the normal derivative are discretized by generalized finite-difference (GFD) methods using an orthogonal non-uniform Cartesian grid. The convergence properties are analysed and the solutions of some Poisson and biharmonic problem are presented.
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  • 75
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    Communications in Numerical Methods in Engineering 10 (1994), S. 59-65 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A heuristic optimization design methodology based on redesign rules for composite laminated plates is presented. It is modelled on the cyclic approach to the design process observed in designers of structural components using composites. In comparison with a simple weight minimization algorithm it gives quasioptimal ply thicknesses, but takes under ten iterations. It is thereby shown to be most suitable for initial design studies. Multiaxial combinations of in-plane loads and bending moments are considered in the design procedure.
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  • 76
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    Communications in Numerical Methods in Engineering 10 (1994), S. 33-42 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Reduction of reheating time saves on energy input and increases the production rate in the steel-making process. Reductions can be achieved by allowing the centre temperature of a steel bar to be lower than the surface temperature by a small margin, before starting with the hot rolling process. This can only be done if the temperature difference does not adversely affect the quality of the final product or the rolling equipment. The paper presents numerical simulations to investigate the savings that can be obtained for various temperature differences between surface and centre temperatures to evaluate the feasibility of the concept. The results presented include the cross-sectional temperature distribution in a typical steel bar during reheating at hourly intervals as well as the effect of various differences between centre and surface temperatures on reheating time. The reheating time predicted for various steel bar sizes as well as for various differences between surface and centre temperatures are then compared against measured reheating times. To indicate the practical applicability of the concept to the hot rolling process the detailed temperature distribution in a typical steel bar, with an initial temperature difference between the surface and centre of the bar, was simulated numerically. This was compared to a similar simulation for a well soaked steel bar for which experimental measurements are also available. The numerical method used to obtain the simulations is also presented. Boundary conditions account for radiation, convection and conduction inside the steel bar. It is concluded that the concept of allowing differences between surface and centre temperatures of a steel bar during reheating holds great potential for energy savings in the steel-making process.
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  • 77
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    Communications in Numerical Methods in Engineering 10 (1994), S. 73-80 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Standard isoparametric finite elements can be used as singular crack-tip elements in fracture mechanical computations by placing the middle nodes in the neighbourhood of the crack tip. Such elements have already been applied to several plane and three-dimensional problems, so this method can be considered as commonly well accepted. The paper shows that singularity of order r(1 - m)/m is obtained with an nth-order isoparametric element.
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  • 78
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    Communications in Numerical Methods in Engineering 10 (1994), S. 67-71 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, an iterative method of statistic linearization (IMSL) is presented to solve non-linear stochastic vibration equations. This method represents an improvement over the classical linearization method. The method uses the solution of the corresponding linear vibration equation as an initial value in an iterative procedure. To obtain information about essential statistical average values, the method uses a ‘boot-strapping’ procedure, which defines a pseudorandom process based on the statistical characteristics of the linear solution and then uses samples from the process to estimate them. For Gaussian input excitation, the statistical average values are obtained by theoretical analysis.
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  • 79
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    Communications in Numerical Methods in Engineering 10 (1994), S. 89-91 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 80
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    Communications in Numerical Methods in Engineering 10 (1994), S. 81-87 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Dynamic stress intensity factors of cracked linear viscolastic solids under conditions of plane stress are computed by the boundary-element method in conjunction with the numerical Laplace transform and the correspondence principle of linear viscoelasticity. Quadratic isoparametric conventional and quarter-point boundary elements are employed. The multidomain approach is used in cases where symmetry cannot be invoked. Dynamic stress intensity factors are computed for cracked viscoelastic rectangular plates subjected to suddenly applied loads, and comparisons are made against results obtained by other numerical methods.
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  • 81
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    Communications in Numerical Methods in Engineering 10 (1994) 
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  • 82
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    Communications in Numerical Methods in Engineering 10 (1994), S. 93-110 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new approach to constructing monotonous second-order-accurate schemes for time-dependent Navier-Stokes equations in the compressible case is suggested. Flows with shock waves and thin viscous boundary layers are considered. The approach joins two different schemes while each of them is appropriate for its own type of flow. The resulting scheme is constructed as a splitting one, and the approach is applied at the stage governed by the Euler equations in Lagrangian variables. The approach turns out to be fruitful also for parabolic equations with ‘viscous’ terms. The method is illustrated by the problem on compression of deuterium in a conical solid-body target with viscous heating of deuterium.
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  • 83
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    Communications in Numerical Methods in Engineering 10 (1994), S. 111-119 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new eigensolution reanalysis method for modified structures is developed and presented based on the usual first-order perturbation scheme and the Rayleigh quotients. By this method, the accuracies of the eigensolutions of the modified structures computed by perturbation methods are improved. A numerical example is presented and the accuracies of the usual first-order perturbation method, second-order perturbation method, William B. Bickford method and the proposed method are compared.
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  • 84
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    Communications in Numerical Methods in Engineering 10 (1994), S. 121-134 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this study a perturbation method for computing the upper and lower bounds of eigenvalues of structural vibration systems with interval parameters is presented. The eigenproblem of the uncertain (interval) structure is expressed by equations consisting of the uncertainties. If the uncertainity is small in parameters, the eigensolutions of uncertain structures can be obtained efficiently by the perturbation method presented. A numerical example is given to demonstrate the validity of the method.
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  • 85
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    Communications in Numerical Methods in Engineering 10 (1994), S. 135-148 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The performance of the univariant finite element Q1P0 and the multivariant finite elements Q1+P0 and R2+P0 are compared for simulation of three-dimensional incompressible viscous flows. Incompressible flow vortices for the R2+P0 element are presented. For the two flows simulated, the R2+P0 element is found to be not only the most accurate but also computationally the most efficient of the three types of finite element used. For one of the two flows simulated, the pressure distribution obtained by using the Q1P0 element is found to be afflicted with the checker-board spurious pressure mode. For the uniform finite-element mesh used, the checker-board pressure mode is eliminated by taking a weighted average of the pressure over the neighbouring Q1P0 elements.
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  • 86
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    Communications in Numerical Methods in Engineering 10 (1994), S. 179-181 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 87
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    Communications in Numerical Methods in Engineering 10 (1994), S. 149-154 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the use of a truncated envelope technique is discussed as a preconditioning for the conjugate gradient method for solving large linear systems of equations with symmetric positive-definite matrices. An algorithm to generate a truncated envelope is introduced. Computational experience with systems of linear equations from the Harwell-Boeing collection is presented to highlight the efficiency of this approach.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 167-178 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A sixth-order polynomial shape function is developed for BIE analysis. The function is applied over only three-noded elements, but with the support for the function extending over adjacent elements. This avoids the oscillations near the ends of the range which otherwise are characteristic of high-order polynomial interpolation. Various test problems are explored, and it is shown that results as accurate as those from conventional quadratic elements are obtained with larger nodal spacings, and thus giving the potential for significant reductions in matrix storage requirements and solution times.
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  • 89
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    Communications in Numerical Methods in Engineering 10 (1994), S. 155-166 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A finite element formulation based on superposition is proposed for a lifting aerofoil in incompressible potential flow. An accuracy improvement technique for the singularity at the aerofoil trailing edge is discussed. It is shown that the quarter-node quadrilateral element can be readily employed to simulate this singularity. It is also demonstrated that the circulation in the flow field can be easily represented by a single constraint equation rather than introducing an artificial cut line in the mesh. The influence of finite-element mesh size on solution accuracy and the correct form of the boundary condition have been investigated as well. Numerical examples are given for both steady and quasisteady Joukowski aerofoils of various thicknesses and at a range of incidences. In all test cases, good agreement is observed between the analytical solution and the numerical result.
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  • 90
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    Communications in Numerical Methods in Engineering 10 (1994) 
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    Communications in Numerical Methods in Engineering 10 (1994), S. 183-194 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An 8-node element (HMITC) for 3D non-linear analysis of solids is presented. The new element is based on an element developed by Wilson and Ibrahimbegovic, that incorporates incompatible modes, and on the method of mixed interpolation of tonsorial components. The HMITC element does not contain spurious zero energy modes and satisfies Irons' Patch Test. The numerical experimentation indicates that the HMITC has good performance even with distorted meshes.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 203-215 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper we consider an explicit finite-element method, with elements adaptively oriented in space-time, for the solution of one-dimensional conservation laws, extending previous work dealing with linear convection-diffusion and incompressible flow. In particular we consider Burgers' equation and the compressible Euler equations.
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  • 93
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    Communications in Numerical Methods in Engineering 10 (1994), S. 195-201 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A numerical method, based on neural-network-based functions, for solving partial differential equations is reported in the paper. Using a ‘universal approximator’ based on a neural network and point collocation, the numerical problem of solving the partial differential equation is transformed to an unconstrained minimization problem. The method is extremely easy to implement and is suitable for obtaining an approximate solution in a short period of time. The technique is illustrated with the aid of two numerical examples.
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  • 94
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    Communications in Numerical Methods in Engineering 10 (1994), S. 217-225 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient algorithm for consideration of axial and cyclic symmetry in the boundary-element method is presented. The appropriate transformation relationships was derived. The algorithm is then implemented in a boundary element program for the analysis of 2D elastostatic problems. Through analysis of typical problems the validity of the algorithm and its implementation is verified. A high level of accuracy and substantial reduction in computer time and storage was achieved.
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  • 95
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    Communications in Numerical Methods in Engineering 10 (1994), S. 227-235 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The diffusion of oxygen into an absorbing medium as an example of an implicit moving boundary problem has been dealt with by a number of authors using various numerical techniques, and, where appropriate, approximate analytical expressions. To evaluate the time for complete absorption, extrapolation is usually employed. An unconditionally stable explicit numerical scheme that avoids the limitations of such methods is presented and tested herein. Unlike existing schemes this method is fully numerical; it avoids the large array size, generally required for existing methods, by using a variable-length time step. The time for complete absorption emerges from the final step in the normal computing procedure with no recourse to extrapolation. Furthermore, owing to the implicit condition prevailing at the moving boundary, no iterations are needed to evaluate the time step required for the moving boundary to move a single space increment. The numerical results obtained compare very favourably with those due to earlier authors.
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  • 96
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    Communications in Numerical Methods in Engineering 10 (1994), S. 237-248 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper we have developed a new formulation for solution of structural-acoustic coupling problems by boundary elements using the multiple reciprocity method. It is assumed that the structure is composed of plate components and is excited by the external or the internal noise source. The efficiency of the proposed formulation becomes especially remarkable if the boundary-value problem is to be solved repeatedly for different values of frequency. The accuracy of the numerical computations has been compared with the analytical solution in a test example.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 257-265 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Techniques for stress- and strain-controlled in situ homogenization of inelastic periodic composites are presented. The results of homogenization computations on a specific elastoplastic composite solid are then employed to validate the form of an orthotropic elastoplasticity model with a tensorial kinematic hardening law.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 249-255 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An algorithm for evaluation of friction in general contact-impact interfaces is described. The algorithm is based on an explicit finite-element method. Coulomb's friction law is assumed. The defence node algorithm is used such that the sticking condition can be imposed with the Lagrange multiplier method even in explicit dynamic analysis. The algorithm is supposed to be applicable in general situations, including large deformations of the contact-impact bodies and large relative sliding between the contact-impact boundaries. Numerical results are presented to demonstrate the performance of the algorithm.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 275-277 
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    Keywords: Engineering ; Engineering General
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    Communications in Numerical Methods in Engineering 10 (1994) 
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    Keywords: Engineering ; Engineering General
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    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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