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  • 1970-1974  (541)
  • 1972  (541)
  • Chemical Engineering  (368)
  • Engineering General  (100)
  • Rat  (73)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 336 (1972), S. 249-262 
    ISSN: 1432-2013
    Schlagwort(e): Diphosphate ; Rat ; Vitamin D Metabolism ; Intestinal Calcium ; Absorption ; Bone Mineralization ; Renal Functions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The metabolism and the organ distribution of double labelled vitamin D3 (1,2-3H-4-14C-cholecalciferol) has been studied in rats in which the bone mineralization and the intestinal calcium absorption have been inhibited by a large pose (10 mg P/kg s.c. for 7–14 days) of disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP). The most striking difference found was a reduced accumulation of radioactive cholecalciferol and its metabolites in the kidney of EHDP-treated rats. It is unlikely that this effect was due to an unspecific alteration of the functional renal tissue since blood urea, glomerular filtration rate and renal plasm a flow remained unaltered by this dose of EHDP. The EHDP-treated rats were able to form the metabolite eluted with peak IV of the silicic acid chromatographic system, that is 25-hydroxycholecalciferol. In these vitamin D repleted rats fed a high calcium diet, the tritium deficient metabolite eluted with peak V (1,25-dihydroxycholecalciferol) was only found in the intestinal mucosa of both control and EHDP groups three days after the injection of radioactive cholecalciferol, and this in a very small amount. Therefore no definitive conclusion can be drawn as to a possible interference of EHDP treatment on the production of 1,25-dihydroxycholecalciferol. The change in the renal metabolism of vitamin D in rats treated with a rachitogenic dose of EHDP may be caused by the modifications of the calcium metabolism brought about by the diphosphonate. Its relation, if any, with the decreased calcium absorption remains to be established.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 272 (1972), S. 369-377 
    ISSN: 1432-1912
    Schlagwort(e): Trimethoprim ; Placental Transfer ; Distribution ; Elimination ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary After a single i.v. administration of 50 mg/kg of Trimethoprim (TM) to rats in late pregnancy, a diffusion equilibrium of the folic acid inhibitor in the foetal organs is reached after 30–60 min. The TM levels in maternal as well as in foetal organs can have an inhibitory effect on folic acid reductase activity. The elimination of TM is lower in pregnant than in non-pregnant animals. The TM elimination of the foeti is dependent on the elimination capacity of the mother. Three-days-old rats eliminate TM some four times slower than mature animals owing to their reduced kidney development.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 272 (1972), S. 417-436 
    ISSN: 1432-1912
    Schlagwort(e): Intestinal Blood Flow ; Instestinal Absorption ; Tritiated Water-Solvent Drag ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary 1. Jejunal loops of anaesthetized rats were perfused with hypo-, iso-, and hypertonic buffered solutions containing tritiated water. The blood flow, the disapperance rate (from the intestinal lumen), and the appearance rate (in the intestinal venous blood) were determined simultaneously. 2. A decrease of the blood flow from about 1.7 to 0.2 ml min−1g−1 wet tissue weight diminished the appearance and disappearance rate of tritiated water. An increase of the blood flow caused the reversed results. The appearance rate was almost completely determined by the blood flow indicating that the intestinal absorption of tritiated water is blood flow limited. Therefore the absorption rate of tritiated water characterizes badly the diffusive water permeability of the intestinal epithelium. 3. A water net flux directed towards the blood accelerated and towards the intestinal lumen retarded the intestinal absorption of tritiated water at low, intermediate, and high blood flow values. 4. The data were analysed by a modified four-compartment-model considering the variation of blood flow and water net flux. The water net flux influences the absorption of tritiated water during the penetration through the epithelium by solvent drag (sieving coefficient 1-σ=1.54±0.19) as well as by changing the blood flow rate through capillaries near the epithelium.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 274 (1972), S. 357-374 
    ISSN: 1432-1912
    Schlagwort(e): Intestinal Blood Flow ; Blood-to-Lumen Flux ; Tritiated Water ; Solvent Drag ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary 1. Anaesthetized rats were loaded with tritiated water and a jejunal loop was perfused with hypo-, iso-, and hypertonic buffered saline solutions. The blood flow, the disappearance rate (from the blood), and the appearance rate (in the intestinal lumen) were determined simultaneously. 2. A decrease of the blood flow from about 1.7 to 0.2 ml min−1g−1 wet tissue weight diminished both the appearance rate and the disappearance rate of tritiated water. An increase of the blood flow caused the reversed results; however, at high blood flow the appearance and disappearance rate did not reach the value measured in the experiments with decreasing blood flow. 3. A water net flux directed towards the blood retarded and towards the intestinal lumen accelerated the blood-to-lumen flux of tritiated water at low, intermediate, and high blood flow values. 4. The data were analysed by a modified four-compartment-model considering the variation of blood flow and water net flux. The water net flux influences the blood-to-lumen flux of tritiated water by solvent drag during the penetration through the epithelium and by changing the luminal concentration (e.g. dilution) as well as the blood flow rate in the capillaries near the epithelium.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 273 (1972), S. 352-365 
    ISSN: 1432-1912
    Schlagwort(e): Calcium Transport ; Small Intestine ; Rat ; in vitro ; in vivo
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Intestinal calcium (Ca) transport was studied in the rat jejunum by the in vitro perfusion technique of Fisher and Parsons and in the tied loop in vivo. Mucosal uptake and absorption of Ca was examined under the following conditions: rising intraluminal Ca-concentrations (0.5–128 meq/l); inhibition of energy dependent metabolism (2,4-dinitrophenol, N2, low temperature); net water flow, out of or into the intestinal lumen; addition of strontium (Sr); pretreatment with low Ca-diet and with 6-methyl-prednisolone. The concentration-dependent Ca absorption curve rose steeply at low Ca-concentrations but changed to a slowly rising straight line above 16 meq/l Ca++. In contrast, Ca uptake into the intestinal wall was directly related to Ca concentration, was linear from the beginning and paralleled the straight part of the absorption curve. Ca absorption was decreased by inhibition of energy dependent metabolism, addition of Sr and pretreatment with prednisolone. Pretreatment with low Ca diet increased Ca absorption and direction of net water flow (“solvent drag”) had no effect on it. Mucosal uptake of Ca was similar to Ca absorption except that metabolic inhibition increased Ca uptake but decreased Ca absorption. These results are compatible with the concept of a passive mucosal uptake and of an active absorption of Ca at low intraluminal Ca concentrations with additional passive component at high Ca concentrations.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 274 (1972), S. 91-106 
    ISSN: 1432-1912
    Schlagwort(e): Choline ; Blood-Brain-Barrier ; Brain ; Rat ; Lecithin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In the rat brain the concentration of choline increases with a velocity of 20.5 nMol/g×min immediately after decapitation. This is not due to postmortal disintegration of the tissue but to persisting biochemical reactions in the absence of blood flow. This rise of choline must be considered if the concentration of choline in the living animal is to be established. Taking this fact into account one arrives at a value of 27.5±1.7 nMol Choline/g wet weight. From the arterio-venous difference of choline concentrations it has been postulated that there is an efflux of 7.2±1.5 nMol/g×min from the brain into the blood. After i.v. injection of labelled choline the peak of the specific radioactivity of choline in the brain is reached in less than 1 min but amounts to only one tenth of the specific activity of choline in blood-plasma. The specific activities in both compartments decline in parallel. Thus it can be concluded a) that choline penetrates easily through the blood-brain barrier, but the concentration gradient is directed from brain to blood; and b) that choline is continuously formed in the brain, which process permanently dilutes the quantity of labelled choline and prevents the specific activities in blood and brain from becoming equal. The calculations of turnover-rates in the different reactions leading to the choline containing glycerophosphatides are based on the data obtained. On the basis of these findings it is proposed that in the brain phosphorylated derivatives of ethanolamine (phosphorylethanolamine, cytidinediphosphate-ethanolamine) can be methylated to form the respective choline derivatives.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 10 (1972), S. 238-251 
    ISSN: 1432-0827
    Schlagwort(e): Growth ; Bone ; Rat ; Tetracycline
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Beschreibung / Inhaltsverzeichnis: Résumé La vitesse de croissance normale en longueur de la métaphyse proximale du tibia est déterminée chez le rat Sprague-Dawley entre les âges de 20 et 100 jours, en utilisant la méthode à la tétracycline. Le taux de croissance ne varie que légèrement dans les groupes d'âges différents. Il est plus élevé chez les animaux jeunes et décroit considérablement en fonction de l'augmentation de l'âge. Les rats mâles présentent une croissance plus élevée que les femelles. Cette étude a pour but de mettre au point une méthode permettant de déterminer les facteurs expérimentaux, liés à la croissance en longueur du rat.
    Kurzfassung: Zusammenfassung Die normale Längenwachstums-Geschwindigkeit der proximalen Wachstumsplatte der Tibia wurde bei Sprague-Dawley-Ratten in einem Alter zwischen 20 und 100 Tagen mittels der Tetracyclinmethode gemessen. Die Wachstumsgeschwindigkeit variierte nur wenig innerhalb der einzelnen Altersgruppen. Die Geschwindigkeit war bei jungen Tieren am höchsten und nahm mit zunehmendem Alter beträchtlich ab. Männliche Ratten wuchsen schneller als weibliche. Diese Arbeit dient als Grundlage, um die experimentelle Beeinflussung des Längenwachstums der Ratte abschätzen zu können.
    Notizen: Abstract The rate of normal growth in length from the proximal growth plate of the tibia in the Sprague-Dawley rat was measured between 20 and 100 days of age using the tetracycline method. The growth rate varied only slightly within different age groups. The rate was highest in young animals and decreased considerably with increasing age. Male rats grew faster than female. This study is intended to provide a base for an evaluation of experimental influence on the growth in length of the rat.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Archives of toxicology 30 (1972), S. 29-38 
    ISSN: 1432-0738
    Schlagwort(e): Dichlorvos ; Teratology ; Inhalation ; Rat ; Rabbit ; Dichlorvos ; Teratologie ; Inhalation ; Ratte ; Kaninchen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung An Kaninchen und Ratten wurde die teratogene Wirkung von inhaliertem Dichlorvos untersucht. Im Versuch waren primipare Kaninchenweibchen der Rasse “Dutch” mit einem Anfangsgewicht von 2 bis 3 kg und primipare Rattenweibchen vom Stamm “Carworth Farm E“ mit einem Anfangsgewicht von 200 bis 300 g. Die Tiere wurden während der gesamten Trächtigkeit folgenden Konzentrationen in der Atemluft ausgesetzt: 0,25, 1,25 und 6,25 μg Dichlorvos pro Liter Luft. Ein zusätzliches Experiment am Kaninchen wurde mit 2 und 4 μg Dichlorvos pro Liter Luft durchgeführt. Die Behandlung wirkte weder beim Kaninchen noch bei der Ratte teratogen. Selbst Konzentrationen, die für die Kaninchen tödlich waren, und die eine deutliche Cholinesterasehemmung in Plasma, Erythrocyten und Gehirn der Ratten und Kaninchen hervorriefen, wurden ohne Schädigung für die Feten vertragen.
    Notizen: Abstract The teratogenic potential of inhaled dichlorvos vapour for rabbits and rats was investigated on the offspring of primiparous female Dutch rabbits weighing 2 to 3 kg and primiparous female Carworth E strain rats weighing 200 to 300 g. The animals were exposed throughout pregnancy at concentrations of 0.25, 1.25 and 6.25 μg dichlorvos per litre of air. In an additional experiment pregnant rabbits were exposed to concentrations of 2 and 4 μg dichlorvos per litre of air. The results gave no indication that dichlorvos vapour is teratogenic in rabbits or rats even at exposure concentrations resulting in maternal deaths in rabbits, and causing depression of plasma, erythrocyte and brain cholinesterase activities in pregnant animals of both species.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Archives of toxicology 30 (1972), S. 9-18 
    ISSN: 1432-0738
    Schlagwort(e): 2,2-Dichlorvinyl Dimethyl Phosphate ; Dichlorvos ; Vapona ; Metabolism ; Man ; Rat ; Mouse ; Hamster ; 2,2-Dichlorvinyl-dimethylphosphat ; Dichlorvos ; Vapona® ; Stoffwechsel ; Mensch ; Ratte ; Maus ; Hamster
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung An Mäusen und Hamstern wurde die Exkretion und Retention der Radioaktivität nach Fütterung mit [1-14C-Vinyl]-Dichlorvos bestimmt. Außerdem wurde beim Menschen die Exkretion und Exhalation gemessen und die erhaltenen Werte mit den tierexperimentellen Daten von Rattenversuchen verglichen. Die Ergebnisse zeigen einen schnellen Stoffwechsel von Dichlorvos bei allen vier untersuchten Species. Die Dealkylierung zu Desmethyldichlorvos spielt bei der Biotransformation eine untergeordnete Rolle. Eine gewisse Ausnahme zeigen die Mäuse, bei denen 18,5 % der zugeführten Radioaktivität als Desmethyldichlorvos aufgefunden werden konnte. Bei allen Species kam es zu einer hydrolytischen Spaltung zu Dichloracetaldehyd, der weiter zu Dichloraetbanol reduziert wird. Der weitere Weg führt über die Ausscheidung als Glucuronid mit dem Harn. Ein Teil wird dechloriert und das14C-Atom als14CO2 oder14C-Hippursäure im Harn ausgeschieden. Im menschlichen Harn konnte Dichloraethanol nach Inkubation mitβ-Glucuronidase nachgewiesen werden, wenn hohe Dichlorvoskonzentrationen (38 μg/l) eingeatmet wurden. Auf dieser Basis könnte eine Überwachungsmethode gegen die Inhalation von zu hohen Dichlorvoskonzentrationen ausgearbeitet werden.
    Notizen: Abstract The routes of excretion and retention of radioactivity following the ingestion of [1-14C-vinyl]dichlorvos by mice and hamsters have been determined. The excretion of radioactivity in urine and exhaled air of man has also been measured. The data have been compared with those for rats. The results indicate that metabolism is rapid in the four species. Dealkylation to desmethyldichlorvos is a minor route of biotransformation, except in the mouse, where desmethyldichlorvos constitutes at least 18.5 % of the administered radioactivity. Hydrolytic metabolism of dichlorvos occurs in all species and leads presumably to dichloroacetaldehyde which is further metabolized by (i) reduction to dichloroethanol and excretion in the urine as the glucuronide and (ii) dechlorination followed by incorporation of the carbon atoms into endogenous biosyntheses and excretion as [14C]carbon dioxide and [14C]hippuric acid in the urine. Dichloroethanol can be detected inβ-glucuronidase-treated urine after exposure of a human subject to high air concentrations (38 μg/l) of non-radioactive dichlorvos. This may form the basis of a method of monitoring the exposure of humans to high concentrations of dichlorvos.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Archives of toxicology 28 (1972), S. 39-45 
    ISSN: 1432-0738
    Schlagwort(e): Ferrihexacyanoferrate (II) ; Rat ; Thallium ; Toxicity ; Metabolism ; Ferrihexacyanoferrat(II) ; Ratte ; Thllium ; Toxicität ; Stoffwechsel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Verabfolgung einer 2% igen kolloidalen Lösung von Ferrihexacyanoferrat (II) (FHCF) als Trinkwasser erhöht bei der Ratte die Ausscheidungsrate von intravenös injiziertem Tl2SO4 (mit 204Tl markiert) aus Leber, Nieren und Muskulatur auf das 2,8fache. Dieser Effekt ist zeitunabhängig. Die LD 50/30 d von intravenös injiziertem Tl2SO4 wird durch FHCF-Behandlung um das 2,3fache erhöht. Für diesen Schutzeffekt ist allerdings nur das während der ersten 24 Std verabfolgte FHCF verantwortlich. Diese Befunde weisen darauf hin, daß die Schäden bei der akuten Tl-Intoxikation sehr schnell irreversibel werden.
    Notizen: Abstract The administration of a 2% colloidal solution of ferrihexacyano ferrate (II) (FHCF) as drinking water increases in the rat the excretion of intravenously injected Tl2SO4 (labelled by 204Tl) from liver, kidneys and muscles by a factor of 2.8. This effect is independant of time. FHCF-treatment increases the LD 50/30 d of intravenously injected Tl2SO4 by a factor of 2.3. This protection, however, is provided by FHCF only if administered during the first 24 hours. These findings suggest that the damage resulting from acute Tl-intoxication quickly becomes irreversible.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 137 (1972), S. 301-316 
    ISSN: 1432-0568
    Schlagwort(e): Monoamines ; Brain ; Ontogeny ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The early ontogeny of the monoamine neuron systems in the rat brain has been analysed using Falck-Hillarp fluorescence histochemistry. Serial sagittal sections of embryos with a crown rump length between 7 and 13 mm, approximately corresponding to gestational days 12 to 15 were obtained from mothers treated with a monoamine oxidase inhibitor given in order to increase the monoamine levels of the embryos. 5-hydroxytryptamine (5-HT)-neurons made their first appearance in the 8 mm embryo, dopamine (DA)-neurons in the 9 mm embryo, and noradrenaline (NA)-neurons in the 11 mm embryo. Small, rounded, weakly fluorescent cell bodies forming sparse aggregations appeared first. Fluorescent processes of two types soon appeared. Short processes from the cell bodies were running perpendicular to the long axis of the brain stem within the cell groups, while long slender axon bundles could be traced ascending through the met- and mesencephalon and into the prosencephalon as well as descending in the myelencephalon andspinal cord. In the 12 mm embryo the primordial DA cell formation of the substantia nigra with its striatal projections, the 5-HT neuron formations of the caudal mesencephalon, met- and myelencephalon as well as the NA neurons of the met- and myelencephalon are relatively well developed. It is concluded that the monoamine-neurons develop mechanisms for synthesis and storage of amines at a very early stage during ontogeny, thus recapitulating the phylogeny of these old systems. Likewise, monoamine oxidase is present early. The presence of neurotransmitters specifying the different developing neurons long before development of their nerve terminal areas and therefore before the establishment of normal synaptic function may indicate a role of these substances during ontogeny other than transmission of nerve impulses.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 135 (1972), S. 301-306 
    ISSN: 1432-0568
    Schlagwort(e): Rat ; Cold ; Pineal gland ; Synaptic vesicles ; Zinc iodide-osmium tetroxide (ZIO) reaction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In den synaptischen Bläschen der Nervenendigungen der Epiphyse von Ratten, welche 2 und 4 Tage einer Temperatur von −6° bis −8°C ausgesetzt worden waren, hat man eine signifikante Vermehrung des Zinkjodid-Osmiumtetroxyd (ZIO) reaktiven Materials festgestellt. Der durchschnittliche Durchmesser der ZIO-positiven synaptischen Vesiculae betrug bei den Kontrollratten 234 Å und bei den Ratten, welche 2 und 4 Tage unter der Kälte gelebt hatten, 380 Å, bzw. 379 Å. Die ZIO-Reaktion war bei den Kontrollratten in 49,3% der synaptischen Vesiculae positiv, nach zweitägiger Kälteeinwirkung waren 58,7% und nach viertägiger Kälteeinwirkung 72,1% der synaptischen Vesiculae ZIO-positiv. Auf Grund der vorliegenden Arbeit war es jedoch nicht möglich zu entscheiden, ob die Vermehrung des ZIO-reaktiven Materials mit einer gleichzeitigen Zunahme der biogenen Amine verbunden ist.
    Notizen: Summary In the synaptic vesicles of pineal nerve endings of Wistar rats exposed for 2 and 4 days to a temperature of −6° to −8° C, a significant increase of the zinc iodide-osmium tetroxide (ZIO) reactive material was observed. The mean diameter of ZIO reactive synaptic vesicles of control rats was 234 Å; in rats exposed to cold for 2 and 4 days it was 380 Å, respectively 379 Å. In control rats the ZIO reaction was positive in 49,3% of the synaptic vesicles. The reactivity increased to 58,7% in rats exposed to cold for 2 days, and to 72,1% in rats exposed to cold for 4 days. However, the results of the present study do not permit to conclude if an increase of ZIO reactive material is accompanied by a simultaneuos increase of biogenic amines.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 137 (1972), S. 1-29 
    ISSN: 1432-0568
    Schlagwort(e): Corticotropin-Releasing Factor ; Median eminence ; Rat ; Histology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In der Zona externa infundibuli der normalen Ratte kommen geringe Mengen „Gomori-positiver” Granula vor. Nach bilateraler Adrenalektomie erfolgt eine Vermehrung der Granula, die sich durch Gabe von Hydrocortison einschränken oder verhindern läßt. Dieser Befund hat zu der Annahme geführt, daß die Granula das morphologische Äquivalent des Corticotropin-releasing factor (CRF) darstellen. Morphometrische Untersuchungen an 160 weiblichen Wistarratten zeigen, daß die Menge der nach bilateraler Adrenalektomie in der Zona externa infundibuli nachweisbaren „Gomori-positive” Granula von der postoperative Überlebensdauer abhängt. Die Granulamenge nimmt zunächst bis zum 14. Tag p.o. zu und fällt dann wieder ab. Substitution bilateral adrenalektomierter Ratten mit Hydrocortisonacetat-Kristallsuspension bewirkt eine dosisabhängige Verminderung der Granulamenge, wenn die Behandlung am Operationstag begonnen wird. Applikation von Hydrocortisonacetat-Kristallsuspension vom 14.–21. Tag p.o. führt dagegen zu einer gesteigerten Granulavermehrung. Auch bei stärkster Vermehrung sind die Granula stets nur im Infundibulum und nicht in anderen Bereichen des Hypothalamus nachweisbar. Sie besitzen bei bilateral adrenalektomierten Tieren ein charakteristisches Verteilungsmuster mit besonders hohen Konzentrationen in den paramedianen Abschnitten des rostralen Infundibulumdrittels. Aus der Art und Weise ihrer Verteilung ist zu vermuten, daß die Granula 2 Nervenfaserzügen angehören und ein Neurosekret darstellen. Nach den vorliegenden Untersuchungen besteht zwischen dem Verhalten der „Gomori-positiven” Granula in der Zona externa infundibuli und dem aus pharmakologischen Untersuchungen bekannten Verhalten des Corticotropin-releasing factor eine weitgehende Parallelität. Sie legt nahe, die Menge der Granula als Parameter der CRF-Aktivität zu verwenden.
    Notizen: Summary In the zona externa infundibuli (outer layer of the median eminence) of the normal rat a minute number of “Gomori-positive” granules can be detected. Following bilateral adrenalectomy their number increases. This augmentation can be restricted or inhibited by administration of hydrocortisone, a finding, which has led to the assumption that the granules are the morphological equivalent of the corticotropin-releasing factor (CRF). Morphometrical studies on 160 female Wistar rats show that following bilateral adrenalectomy the quantity of “Gomori-positive” granules is dependent on the length of the post-operative survival period. Up to the 14th day p.o. the quantity of granules increases; from then on it diminishes. Substitution of bilaterally adrenalectomized rats with hydrocortisone acetate crystal suspension results in a dose-dependent decrease in the quantity of granules if treatment is begun on the day of operation. In contrast, administration of hydrocortisone acetate crystal suspension from the 14th to the 21st day p.o. results in increased augmentation of the granules. Even when maximum augmentation of the granules is reached, they are invariably found only in the infundibulum and not in other regions of the hypothalamus. In animals that have been subjected to bilateral adrenalectomy, the granules show a characteristic pattern of distribution, with particularly high concentrations in the paramedian parts of the rostral third of the infundibulum. The manner in which the granules are distributed suggests that they are a neurosecretory substance localized in two fibre tracts. The present study points to a close parallelism between the behaviour of the “Gomori-positive” granules in the zona externa infundibuli and that of the corticotropin-releasing factor as revealed by pharmacological investigations. It would seem that the quantity of granules can be used as a parameter of CRF activity.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 138 (1972), S. 155-165 
    ISSN: 1432-0568
    Schlagwort(e): Cerebellum ; Neurogenesis ; Autoradiography ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Time of origin of various neuronal elements in the cerebellum of rat was established with the aid of tritiated-thymidine-autoradiography. The earliest nerve cells to form were the Purkinje cells, and they came into existence on days 15 and 16 of gestation. Interstitial nerve cells had their genesis on days 15, 16, 17 and 18, and the marginal cells on day 16 of the embryonic development. The Golgi cells were found to come into existence on days 17, 18 and 19 of gestation. On day 21 of gestation a number of small-medium-sized nerve cells, which were smaller than the Golgi cells but larger than the granule cells, were seen to come into existence. Finally, the earliest stock of granule, basket and stellate cells, primarily in the nodulus, flocculus and para-flocculus, were observed to have been formed on the day 21 of embryogenesis.
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Archives of toxicology 29 (1972), S. 39-49 
    ISSN: 1432-0738
    Schlagwort(e): Mouse ; Rat ; Brain ; Light-Dark-Programming ; Circadian ; Toxicity Rhythms ; Acetylcholine ; Pilocarpine ; Oxotremorine ; Carbachol ; Physostigmine ; Neostigmine ; Atropine ; Scopolamine ; Atropine Methyl Nitrate ; Maus ; Ratten ; Gehirn ; Beleuchtungsprogramm ; Circadianer Toxicitätsrhythmus ; Acetylcholin ; Piloearpin ; Oxotremorin ; Carbachol ; Physostigmin ; Neostigmin ; Atropin ; Scopolamin ; Atropin-methylnitrat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Nach Adaptation an ein Licht-Dunkelprogramm (8.00 bis 20.00 Licht, 20.00 bis 8.00 Dunkelheit) wurde der Acetylcholingehalt (ACh) im Mittelhirn und N. caudatus von Ratten sowie im Gesamthirn von Mäusen bestimmt. Die höchsten ACh-Konzentrationen wurden bei Ratten um 24.00 gefunden; die höchsten ACh-Werte bei der Maus waren nicht signifikant von den Konzentrationen um 24.00 und 12.00 verschieden. Signifikante ACh-Minima traten im Mittelhirn der Ratte um 12.00, im N. caudatus sowie im Mäusegehirn um 18.00 Uhr auf. Während der Dunkelperiode wurde die größte Toxicität gegenüber i.v. bzw. i.p. injiziertem ACh bei Mäusen gefunden. Ähnliche zeitliche Unterschiede ergaben sich für Neostigmin, Pilocarpin und Oxytremorin. Die Toxicität von Carbachol zeigte Maxima bei 12.00 und 24.00. Für Physostigmin, einen CholinesteraseHemmstoff mit einem tertiären Stickstoff, lagen sowohl die Toxicitätsmaxima als auch die Toxicitätsminima in der Dunkelperiode. Die rhythmische Schwankung der Toxicität von i.p. verabfolgtem Atropin verhielt sich umgekehrt wie die der Cholinomimetica (außer Carbachol). Auch nach i.v. Applikation von Scopolamin und N-Methylatropin war ein entsprechender rhythmischer Einfluß auf die Toxicität nachweisbar. Die Vorbehandlung mit N-Methylatropin schwächte die Toxicität zwar ab, der Toxicitätsrhythmus gegenüber ACh und Physostigmin war aber nicht verändert. Die Toxicität von Cholinomimetica zeigt ein Maximum während der höchsten ACh-Konzentrationen im Gehirn und der höchsten Stoffwechselaktivität. Bei den anticholinergen Substanzen zeigte sich ein umgekehrtes Verhältnis. Die Beziehungen zum zentralen ACh-Gehalt sind unklar.
    Notizen: Abstract Acetylcholine (ACh) levels were determined in rat midbrain and caudate nucleus and mouse whole brain in mature animals adapted 3 weeks to a programmed lighting schedule (08:00 to 20:00 h light; 20:00 to 08:00 dark). Peak ACh levels in the rat occurred at 24:00 h; in the mouse the peak at 06:00 h did not differ significantly from values obtained at 24:00 and 12:00 h. Significant trough values occurred at 12:00 h in rat midbrain and at 18:00h in rat caudate nucleus and mouse brain. In mice toxicity of I.V. and I.P. administered ACh is maximal during the dark. Neostigmine, pilocarpine and oxotremorine have toxicity patterns similar to ACh. Carbachol toxicity peaked at 12:00 and 24:00 h. With physostigmine, a tertiary anticholinesterase, peak and trough occurred during the dark. The atropine (I.P.) toxicity rhythm is a mirror image of the cholinomimetic rhythm (except for carbachol). I.V. scopolamine and atropine methyl nitrate patterns resemble atropine's but are less clear-cut. Atropine methyl nitrate pretreatment reduced ACh and physostigmine toxicity but did not alter the overall pattern. Cholinomimetic toxicity and brain ACh patterns are similar, peaking when metabolic activity is maximal. An inverse relationship holds for the anticholinergic drugs. The relationship to central ACh is uncertain.
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 15 (1972), S. 29-38 
    ISSN: 1432-1106
    Schlagwort(e): Ventromedial hypothalamus ; Single units ; Spontaneous and stimulated activity ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The relationship between mean firing rate and activity pattern was studied in 177 neurons in the ventromedial hypothalamus of rats immobilized by Remyolan. Stationary epochs of spontaneous or stimulated activity containing at least 512 interspike intervals were analyzed with the LINC computer. The most frequently encountered interval histograms (IHs) were of the exponential (35%) or gamma 2 (25%) type. The IH shape remained unchanged even if the average firing rate was varied over a wide range (from 20/sec to 2/sec) by polarization through the recording microelectrode (2–5 nA, 1–10 min) or by intracarotid injection of glucose (0.1 ml, 10–25%). The coefficient of variation (CV = SD/ mean interval) was 1.03 for the spontaneous and 0.90 or 0.95 for the activity influenced by polarization or glucose, respectively. Since according to other studies sensory stimulation decreases CV by reorganization of the synaptic input, it is suggested that polarization and glucose affect predominantly the postsynaptic elements without significantly changing the presynaptic activity pattern.
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 20 (1972), S. 248-257 
    ISSN: 1432-0533
    Schlagwort(e): Experimental CNS Tumours ; N-Nitrosomethylurea ; Ethylnitrosourea ; Cell Culture ; Clonal Growth ; Aggregation Pattern ; Transplantation ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Two sarcomas, one neurosarcoma and one polymorphous tumour of uncertain classification of the central nervous system of the rat induced by N-nitrosomethylurea or ethylnitrosourea were the source of 14 clones. The cytomorphology and the aggregation pattern of the clonesin vitro are described. The malignancy and histology were checked by homologous transplantation. All the clones formed sarcoma-like structuresin vivo, but it was difficult to decide whether these neoplasias were real sarcomas or very dedifferentiated glial tumours. The differences in cytology observedin vitro were greater than the histological differencesin vivo.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 22 (1972), S. 269-271 
    ISSN: 1432-0533
    Schlagwort(e): l-DOPA ; Neoplasm, Striatal ; Motor Behavior ; Rat ; Catecholamines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary After administration ofl-DOPA to a rat with a unilateral striatal neoplasm of the nucleus caudatus-putamen, postural asymmetries and rotating behavior were observed. These observations are discussed in relation to the activity of catecholamines within the central nervous system.
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Psychopharmacology 24 (1972), S. 449-455 
    ISSN: 1432-2072
    Schlagwort(e): Avoidance and Acquisition ; Methamphetamine ; Discrimination Learning ; CNS Stimulants ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Avoidance responses, extra responses (on avoidance lever) and wrong lever responses were measured in naive rats acquiring a discriminated avoidance in a 2 lever Skinner box, 30 min after methamphetamine (0.25, 0.5 and 1.0 mg/kg). The smallest dose was ineffective; 0.5 and 1.0 mg/kg significantly increased the number of avoidance responses. This increase was not associated with a significant increase in the two other responses studied. The progressive increase (from the first to second part of the acquisition session) in avoidance responses was not accompanied by a parallel increase in the other responses. The position discrimination and the discrimination of the presence or absence of the conditioned stimulus was observed to be better in the drug groups.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Psychopharmacology 26 (1972), S. 195-200 
    ISSN: 1432-2072
    Schlagwort(e): Forced Motility ; Motor Activity ; Brain Noradrenaline and 5-Hydroxytryptamine ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The levels of 5-HT and 5-HIAA in the rat brain were measured after 1, 6, 24 and 36 h of forced motility in a treadwheel. The results showed that 5-HT metabolism had already increased in the forebrain after 1 h of exercise but later also increased in the brain stem, especially in the mesencephalon-pons-medulla regions. These changes had almost entirely disappeared after 50 min of rest. The NA levels with and without monoamine oxidase inhibitor were measured in animals after 36 h of forced motility. The results indicated an increase in NA metabolism in the brain stem.
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  • 21
    ISSN: 1432-2072
    Schlagwort(e): Agressive Behaviour ; Apomorphine ; Testosterone ; Testes ; Hypophysis ; Adrenal Glands ; Thyroid ; Castration ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The weights of testes, prostates, adrenals, thymus and the pituitary of rats with apomorphine induced aggressiveness did not differ from those without aggressiveness. Postpubertal castration, adrenalectomy or thyroidectomy did not reduce the apomorphine induced aggressive behaviour, but a considerable reduction was found after hypophysectomy. Prepubertal castration significantly reduced, but did not completely abolish the proportion of aggressive rats, especially when castration was performed on the 5th day. Prolonged treatment of male, female and castrated rats with high doses of testosterone from the time of weaning increased the proportion of aggressive animals. Less intensive treatment and treatment of adult rats were ineffective.
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Psychopharmacology 26 (1972), S. 317-320 
    ISSN: 1432-2072
    Schlagwort(e): Oxazepam ; Conflict Behavior ; Rat ; Maze
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Rats were tested in a Lashley III maze, the floor of which was heated. The animals had to learn to negotiate it in order to gain access to the unheated goal box. In the early period of training the animals were able to find the goal box rapidly and without error. Their performance then deteriorated, in a particular way which strongly evoked a conflict behavior. This deterioration in performance was progressively reduced by oxazepam administration (8 mg/kg/day).
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Psychopharmacology 25 (1972), S. 218-228 
    ISSN: 1432-2072
    Schlagwort(e): Fighting ; Delta-9-Tetrahydrocannabinol ; Chlordiazepoxide ; Fixed-Interval ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The frequency with which electric shock to the feet elicited fighting in five pairs of albino rats was not altered significantly by intraperitoneal injections of delta-9-tetrahydrocannabinol (THC) in doses ranging from 0.064–6.4 mg/kg, although chlordiazepoxide reduced the frequency of such fighting in a dose-related manner. This finding held true despite manipulations of THC vehicle, injection-test interval, and the previous drug experience of the subjects. In contrast, doses of 4.0 mg/kg produced a striking reduction in lever-pressing maintained by an FI 60″ schedule of food reinforcement.
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Psychopharmacology 23 (1972), S. 171-179 
    ISSN: 1432-2072
    Schlagwort(e): Reserpine ; Neonatal Treatment ; Sexual Behaviour ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract To investigate whether reserpine given in the critical period of sexual differentiation of the rat brain affects adult sexual behaviour, female and male rats were given a single injection of reserpine on the fourth day after birth, and their sexual behaviour was tested at maturity. In the 11 consecutive daily tests for spontaneous sexual behaviour the reserpine treated female animals showed fewer regular behavioural and vaginal oestrous cycles than the control animals. 19 % of the reserpinized and none of the control animals had prolonged oestrous behaviour without a coincident prolonged vaginal cycle. The reseptivity quotients of the reserpine treated animals were reduced. In the tests for hormone induced sexual behaviour after ovariectomy no statistically significant differences between the number of animals responding or between the receptivity quotients occurred. The tests for spontaneous sexual behaviour in males showed that the reserpinized animals needed fewer intromissions to ejaculate than the controls. The significance of these findings is discussed.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Psychopharmacology 26 (1972), S. 347-360 
    ISSN: 1432-2072
    Schlagwort(e): Chronic Nicotine ; Attention Task ; Arousal ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Male, Holtzman rats were trained extensively on an attention task which required them to respond with a single lever-press to a very short, variably presented stimulus for food reinforcement, but which also required them to inhibit inappropriate responses. After performance had stabilized, two groups were treated with either nicotine base (100 Μg/kg, s.c., t.i.d.) or saline for 4 weeks. The groups were crossed-over so that the first received saline and the second nicotine for an additional 4 weeks. A 3-week saline recovery period followed. Rats were tested on the attention task daily through all periods. Analysis of the data indicated that independent of the treatment-order, rats performed more efficiently under nicotine treatment than under saline conditions. The improvement in performance was most notable in the reduction of inappropriate responding during chronic nicotine treatment. The significance of the behavioral changes in relation to proposed nicotine-induced neurophysiological changes and the two-arousal hypothesis are discussed.
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  • 26
    ISSN: 1432-2013
    Schlagwort(e): Cardiac Output ; Blood O2 Dissociation Curve ; High Altitude ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In rats adapted to a simulated altitude of 3500 m cardiac output measured at hypoxia by the direct Fick principle was significantly lower than in the control animals (mean values 54.3 ml/min and 69.8 ml/min, resp.). The decrease of cardiac output was accompanied by an increase of arterio-venous O2 difference and a decrease of stroke volume in the adapted rats. It is suggested that the decrease of cardiac output might be related to the increase of hematocrit. The adapted rats also showed higher arterial and mixed-venous O2 content (both at hypoxia) and increased O2 capacity. Arterial O2 saturation of the animals previously exposed to simulated high altitude hypoxia was significantly higher (67.3% as against 61.2% in the controls). The standard O2 dissociation curve showed lower oxygen affinity in the blood of the adapted animals but no physiological advantage concerning the transport of O2 to the tissues was found. In another group of animals the Bohr factor was estimated and no difference was found between rat and human blood.
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 335 (1972), S. 198-212 
    ISSN: 1432-2013
    Schlagwort(e): Intestinal Absorption ; Medium Chain Fatty Acids ; Kinetics ; Active Transport ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary 1. The transport of14C-octanoate by rat small intestine was determined in vitro by a modification of the method of Semenza and Mühlhaupt, and in vivo by using isolated segments or a perfusion technique in conscious rats (Haberichet al., 1968). 2. The absorption capacity of14C-octanoate in the distal ileum was significantly lower than in the proximal jejunum. 3. 14C-octanoate injected into a jejunal segment appeared rapidly in portal venous blood reaching its maximal concentration 4 min after the injection. 4. The transport of octanoate showed a saturation effect with increasing concentrations after an incubation of 4 min. However, with constant concentrations of octanoate in the medium, the transport rate was constant for 8–10 min. A similar saturation effect was also demonstrated in vivo. Values for maximal absorption rate (V max) and the half-saturation constant (K m), calculated from the Lineweaver-Burk plot, were 1.0 μMol/min and 17.7 mM, respectively. 5. Accumulation of octanoate in tissue water was demonstrated. For example, after incubation for 40 min in a medium concentration of 0.1 mM, the tissue/ medium ratio was 2.75:1. 6. Cyanide (2×10−4 M) markedly diminished the absorption rate of octanoate. 7. The absorption of octanoate was competitively inhibited by caproic acid (C6) in vitro. The inhibition constant (K i), calculated from the Dixon plot, was 47 mM. 8. Simultaneous administration of glucose and octanoate in vivo did not affect the absorption rate of the fatty acid. 9. These results suggest that the intestinal absorption of octanoate is an energy-dependant active process.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 334 (1972), S. 293-302 
    ISSN: 1432-2013
    Schlagwort(e): Lactate Turnover ; l-Lactate14C (U) ; Hypoxaemia ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary 1. Lactate turnover was measured in 24 anesthetized rats using14C-U-(l) Lactate with the priming dose-infusion technique. 2. 14C Lactate in blood was determined with a specific radio-enzymatic micromethod. 3. Lactate turnover increases with blood lactate concentration in the range 0.5 to 3 mM. In a steady state system this relationship means that a new equilibrium may be achieved at a higher pool level, between lactate production and utilization. 4. Comparing available data in four mammalian species lactate turnover at normal lactate levels was found to be approximately constant when computed on a body surface unit basis.
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  • 29
    ISSN: 1432-2013
    Schlagwort(e): Cardiac Hypertrophy ; Diffusion Distance ; High Altitude ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In growing rats adapted to a simulated altitude of 3500 m for about 4 weeks and in their controls the evolution of cardiac ventricular weight was followed. The increase of total ventricular weight found in the adapted animals can be attributed exclusively to the increase of right ventricular weight. In other adapted and control animals cardiac capillary densities, muscle fiber diameter and external capillary radius were estimated and fiber—capillary ratio and diffusion distance were calculated. There was an increase of capillary density together with a decrease of muscle fiber density, fiber-capillary ratio and diffusion distance in the right but not in the left ventricle of the adapted rats. The muscle fiber diameters, however, were larger in both heart ventricles of the rats exposed to a simulated high altitude, especially in the right ventricle. This indicates that true hypertrophy of the muscle fibers is mainly responsible for the increase of right ventricular weight. In the left ventricle, however, a hypertrophy of the muscle fibers together with a decrease of stroma components is demonstrated. The physiological importance of the shorter diffusion distance in the right ventricle of the high altitude adapted rats is discussed and it is suggested that the shorter diffusion distance may help to keep the tissue O2 partial pressure above the critical value, mainly also in extreme situations with high myocardial O2 consumption.
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 331 (1972), S. 357-364 
    ISSN: 1432-2013
    Schlagwort(e): Thoracic Aorta ; Complex Dynamic Young's Modulus ; Age ; Serum Lipids ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In 2 groups of male albino rats (wistar-strain), 6 months and 18 months of age, dynamic Young's moduli in longitudinal direction were measured, at 5 different frequencies between 1 and 5 Hz. Each group consisted of 10 animals. Measurements were made at the natural length and at 1.2 times this length. From each animal several serum lipids were determined. It was found that: 1. measured at the natural length and 1.2 times this length, no significant difference of dynamic Young's moduli between both age groups could be demonstrated 2. concerning the dynamic Young's moduli there is significant interaction between stretch level and age 3. retraction was significantly smaller in the old rats than in the young ones 4. the old animals had a significantly higher serum lipid content than the young rats 5. no correlation between serum lipids and Young's moduli could be demonstrated.
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 337 (1972), S. 71-79 
    ISSN: 1432-2013
    Schlagwort(e): Rat ; Hypothalamus ; Prolactin ; LH
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Plasma levels of prolactin and LH were measured by radioimmunoassay following electrochemical stimulation of the medial preoptic area (MPO) or the arcuate nucleus (Arc.N.) in pentobarbital anesthetized proestrous rats. Differences in the secretion pattern of prolactin and LH were observed when stimulated by means of acutely or chronically implanted electrodes. Acute implantation and stimulation of the MPO resulted in no change in serum prolactin levels, whereas stimulation by means of chronically implanted electrodes evoked a marked increase in serum prolactin. The general observation was that electrostimulation in the acute experiments causes a less sharp but more prolonged prolactin and LH release from pituitary than stimulation through chronically implanted electrodes.
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  • 32
    ISSN: 1432-2013
    Schlagwort(e): Pulmonary Diffusing Capacity ; Alveolar-arterial O2 Pressure Difference ; High Altitude ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Steady-state pulmonary diffusing capacity for CO and alveolar-arterial O2 pressure differences were measured at hypoxia in growing rats adapted to a simulated altitude of 3500 m. The pulmonary diffusing capacity was significantly higher and the alveolar-arterial gradients were significantly lower in the adapted animals as compared with the controls exposed to hypoxia for the first time. The increased diffusing capacity could be explained entirely by the increase of blood O2 and CO capacity whereas the decrease of gradients might be explained by the increase of blood O2 capacity together with an increase of the arterio-venous O2 difference.
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Journal of neurology 202 (1972), S. 21-36 
    ISSN: 1432-1459
    Schlagwort(e): Hydrocephalus, Experimental ; Ethylnitrosourea ; Experimental Hydrocephalus ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung 25 mg/kg Äthylnitrosoharnstoff wurden am 9 1/2. Tag der Schwangerschaft SD-JCL-Ratten injiziert. Die Feten wurden am Termin excidiert und mit dem Stereomikroskop untersucht. 78% der Feten zeigten einen Hydrocephalus. Die histologische Untersuchung in Stufenschnitten des Gehirns zeigte eine Stenose des Aquädukts ohne subependymale Gliose, ödematöse Plexus chorioidei mit prallgefüllten Gefäßen, spärlichem Bindegewebe und geschwollenen Epithelzellen, Verdünnung der telencephalen Wandungen mit schwach entwickelter granulärer Schicht und in der ependymalen Zone verbleibenden Neuroblasten. Die Entwicklung der jungen Ratten wurde studiert. 75% der neugeborenen Ratten zeigten klinisch gewisse Hinweise auf den Hydrocephalus. Stark betroffene Tiere wurden zunehmend somnolent und/oder gelähmt und starben meist vor Ende der 4. Woche. Der Eiweißgehalt des Liquors war nennenswert vermehrt. Es wurden subdurale, subarachnoidale und intraventrikuläre Blutungen beobachtet und als wahrscheinliche Todesursache angesehen. Die histologische Untersuchung der hydrocephalen Jungtiere ergab eine Abflachung der Ependymzellschicht und pralle Füllung corticaler Gefäße von der 2. Woche an. In späteren Stadien wurde eine Dickenabnahme der periventrikulären weißen Substanz, im besonderen im Bereiche des Occipitalhornes nachgewiesen. Im verdünnten Pallium waren Vacuolenbildungen des perineuralen Gewebes zu sehen, Verbreiterung der Virchow-Robinschen Räume und eine dem Status spongiosus ähnliche Degeneration. Verschiedene Formen ependymaler Wucherung wurden gesehen. Die vorliegende Studie stellt die erste postnatale Beobachtung von transplacentar verursachtem kongenitalem Hydrocephalus in der Ratte dar. Die hier beschriebene Technik erwies sich als einfaches und reproduzierbares Mittel, um einen kongenitalen Hydrocephalus in der Ratte zu erzeugen.
    Notizen: Summary SD-JCL rats were injected with 25 mg/kg of ethylnitrosourea on day 9 1/2 of gestation. Fetuses were excised near term and examined under dissecting microscope. 78% of viable fetuses were found to be hydrocephalic. On the histologic study of the serial sections of the brain, a stenosis of the Sylvian aqueduct without subependymal gliosis, edematous choroid plexus with engorged vessels, scanty connective tissue and swollen epithelium, thinning of the telencephalic wall with poorly developed granular layers and the neuroblasts remaining in the ependymal zone, were the characteristic findings in the hydrocephalic fetuses. The natural course of the treated young rats was studied. 75% of the newborn rats showed some clinical evidence of hydrocephalus. Severely affected rats became progressively lethargic and/or paralytic, and died usually before the end of 4th week. Protein content of the cerebrospinal fluid was significantly increased. Subdural, subarachnoid and intraventricular hemorrhages were observed and suspected to be the cause of death. On the histological examination of hydrocephalic youngs, flattening of the ependymal cells and engorgement of the cortical vessels were observed as early as in 2-week-old youngs. In more advanced stages, there was noted the thinning of the periventricular white matter, especially around the occipital horn. The thin pallium showed vacuolization of the perineural tissue, enlargement of the Virchow-Robin space and the status spongiosus-like degeneration. Various types of ependymal proliferation was seen. The present study represents the first postnatal observation of the transplacentally induced congenital hydrocephalus in the rat. The present technique proved to be a simple and reproducible model of producing a congenital hydrocephalus in the rat.
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Research in experimental medicine 159 (1972), S. 114-123 
    ISSN: 1433-8580
    Schlagwort(e): Scalds ; Local cooling ; Rat ; Quantity of leucocytes ; Verbrühung ; Lokale Kühlung ; Ratte ; Verhalten der Leukocyten
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Untersuchungen an Ratten ergaben folgende Befunde: 1. Sofortige lokale Kühlung nach der Verbrühung beeinflußt bei der Ratte im untersuchten Zeitraum von 15 Tagen den Verlauf der Erkrankung gemessen am Parameter der Leukocytenzahl. 2. Die Kühlungszeit muß ausreichend lang sein. 3. Die Kühlung muß früh genug einsetzen, beim Versuchstier Ratte innerhalb 5 min nach Verbrühung. 4. Bei verspätetem Kühlungsbeginn läßt sich auch durch Verlängerung der Kühlungsdauer das Verhalten der Leukocytenzahl im Ablauf des Krankheitsgeschehens nach Verbrühung nicht beeinflussen.
    Notizen: Summary Following results are obtained in experiments with rats: Immediate local cooling after scald had a significant influence on progress of “burn-disease”. Time for local cooling must be long enough, onset of local cooling early enough. It is not possible to restore the consequences of a late onset by prolongation of cooling.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 34-40 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This paper describes the use of an electron microprobe for characterizing filler and polymer dispersios in polymer composites. Examples described are: filler distribution in sisal reinforced polyester; aggregation of titanium dioxide in glassreinforced polyester; mixing behavior in a blend of silicone rubber, natural rubber, and titanium dioxide; and distribution of silica in a low-gloss paint on an ABS plastic surface. The limitations of electron microprobe analyses for qualitative and quantitative studies, the use of back scattered electrons for surface topography, and techniques for preparing specimens are mentioned.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 36
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The processing of polymers and other solids, such as waxes and acids, often requires the melting of a bulk or granular charge before its introduction into a process stream. Two approximate techniques for relating heat transfer and melting rates are presented here and the shielding effect of the melt formation is considered. The heat available for melting is sometimes remarkably decreased by the heat carried away by the flowing melt. Means are presented for quantitatively determining the shielding or sensible heat effect of the film. The thermal efficiency of the phase transformation process is discussed, and the effects of heat loss to both increased bulk temperature of the flowing melt and conduction in the solid are demonstrated. A comparison with experiment is made using temperature and melt flow data for polyethylene and polyoxymethylene. Heat transfer coefficients and melting correlations useful in practice are presented.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 37
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 101-108 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Interpenetrating polymer networks (IPN's) of polybutadiene (PB) and polystyrene (PS) were prepared using both random (containing 36% cis, 55% trans, and 9% 1,2 vinyl) PB and high-cis PB. For both series, a wide range of PB/PS compositions were synthesized. Using samples stained with osmium tetroxide, electron microscope studies revealed an irregular cellular structure of a few hundred Ångstrom diameter with the first component, PB, making up the cell walls. The size of the cells was found to depend on the PB crosslink density for the random materials. Modulus-temperature data revealed two distinct glass transitions, confirming the microscopy finding of two phases. However, the transition temperature and transition slope varied with composition, and with the microstructure of the polybutadiene, giving evidence of significant molecular mixing. Stress-strain data on the IPN's showed that materials rich in PB behave like self-reinforced elastomers. Charpy impact resistance experiments on materials rich in PS indicated values of 5 ft-lb/in. of notch, which compares well with graft-type polyblends of similar PB/PS composition. The results were interpreted in the light of the recent theoretical work of Bragaw, who considered the importance of the distances between domain boundaries with respect to crack acceleration mechanics. Although the IPN's considered herein exhibited somewhat less than the predicted optimum phase dimensions, the arrangement of the domains is different from ordinary impact resistant plastics.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 193-198 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The rapid increase in the rate of application of thermoplastics in engineering design problems and the interest in the structural use of these materials have resulted in the requirement of comprehensive information about the behaviour of thermoplastics when subjected to cyclic loading conditions. In addition to the “total fatigue life” data already available for many materials, attempts have been made to analyse the crack initiation and steady crack growth processes and determine the effects of parameters such as mean load, frequency and crack geometry on the rate of crack propagation. The results of an investigation of these aspects of fatigue crack growth in a brittle thermoplastic, polymethylmethacrylate (PMMA), have already been reported. In this paper, the results of a test program devised to study the behaviour, at room temperature and in air, of a polycarbonate, (PC), under similar loading conditions, are presented. Fracture Mechanics concepts have been used to analyse the results. It was found that a relationship of the form ȧN = β λn already shown to predict the cyclic fatigue crack propagation rate in PMMA, is also applicable to polycarbonate. However, when the effects of frequency and loading rate were studied, it was found that after the magnitude of parameter K̇( = ΔK/half the periodic time) exceeded 4000 lbf in. -3/2 s-1, the influence of the mean level of stress intensity factor, Km, became negligible in comparison to the effect of ΔK.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 39
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effect of rubber particle size on the tensile properties of rolled and unrolled acrylonitrile-butadiene-styrene has been studied by considering model systems consisting of mixtures of a small particle (0.1 micron diam) rubber, S, and a large particle (0.56 micron diam) rubber, L, in an SAN matrix. Before rolling, tensile toughness is characterized by crazing. While both rubber induce matrix crazing, ABS systems containing only the S rubber exhibits early failure due to crack formation, before crazing is propagated very far along the tensile axis. The inefficiency of the small particle rubber is interpreted in terms of high composite yield stress and insufficient distance between particles to allow craze branching. The efficiency of the small particle rubber is improved via the addition of a small amount of large particle, L, rubber to the composite or by a slight degree of cold rolling, both of which enhance craze propagation in the tensile direction. With further rolling, the tensile deformation mode changes from one of localized crazing, which is propagated, to one of uniform deformation, which occurs without crazing.
    Zusätzliches Material: 7 Ill.
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  • 40
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 317-322 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The dependence of true stress on the extension ratio of PVC threads has been determined for a wide range of extension rates. Since the polymer subjected to deformation was in the high-elastic state (at temperatures from 90 to 160°), the deformations were predominantly high-elastic. The dependence of true stress on the amount of high-elastic deformation is described by the Mooney-Rivlin equation.Relaxation moduli have been found on the basis of measurements of stress relaxation at constant deformation after various extension ratios were attained at different rates. Within the limits of deformation regimes at which the true stress is an increasing function of extension ratio the relaxation moduli do not depend on extension ratio and rate of extension. This enables one to arrive at a master curve of the relaxation modulus versus relaxation time with the reservation indicated above concerning the increasing character of the dependence of true stress on extension ratio. The relaxation spectrum represented by the high-elasticity plateau has been determined from the relaxation moduli according to the first approximation.The experimental data for a very wide range of deformation regimes and temperatures are presented in the form of an invariant dependence of the ratio of true stress to the rate of deformation on the product of deformation time by extension ratio.The ultimate strength of the specimens frozen rapidly after the attainment of definite extension ratios is determined by the accumulated high-elastic deformation.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 41
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A procedure has been developed for analyzing the elongation of a specimen in a tensile test for the elastic, anelastic, and plastic components of strain. The procedure was applied to bisphenol-A polycarbonate, which showed the division between the anelastic and plastic components to be justified and gave the following results. First, the elastic modulus was found to be essentially constant, independent of stress up to at least 7,000 psi. Second, the strain accumulated at the yield point was found to be mainly anelastic and recoverable with release of the stress. Third, plastic or non-recoverable strain was mainly accumulated only beyond the yield point. These latter two results suggest that anelasticity is important for ductility. The relatively large anelastic response at low stresses that contribute to the ductility of polycarbonate probably arises from both the large size of the moving segment and the large low temperature loss process.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 42
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 459-463 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Melt capillary flow and extrudate swelling for low density polyethylenes (LDPE), differing in ease of heavy-duty, blownfilm extrusion, have been employed as processability criteria. LDPE of good processability is characterized by a unique combination of melt fluidity, temperature, shear rate dependence and melt elasticity. These characteristics of flow are correlated with LDPE film blowing process variables such as maximum take-up speed, film thickness scatter, and extruder temperatures profile. Intuitively, these melt flow criteria should be extended to Trouton's viscosity and the tensile strength of the melt. The limited development of the elongation viscometry techniques, however, has limited their application.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 59-63 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The melting of solids under shear conditions is an important operation in the processing of most thermoplastics. In this study, solid blocks of high density polyethylene were melted on a hot, moving surface over a range of surface temperatures and velocities. The conservation equations for mass, momentum, and energy were applied to the molten layer and then simplified by an order of magnitude analysis. A general model that included all significant terms gave rates of melting that agreed closely with the measured rates. A simpler model that was analogous to present extruder models predicted melting rates that were ten to twenty-five percent lower than the experimental values. Models for polymers with low to moderate crystallinity should be modified to account for physical removal of amorphous material by shear forces.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 44
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 81-90 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Rheological behavior of dispersed two-phase polymer melts has been investigated by means of a capillary rheometer. The two-phase systems chosen for study were blends of two polymers: high-density polyethylene and polystyrene, which are incompatible in the molten state. In order to investigate the state of dispersion, photographs were taken of the microstructure of extrudate samples, showing that the polystyrene forms long fibers or droplets as a discrete phase dispersed in the polyethylene which forms a continuous phase. Measurements were made of the axial pressure distributions of the two-phase molten polymers flowing through circular tubes, which permit one, according to the theory advanced by Han, to determine viscous and elastic properties of the melts. Also measured was melt die swell ratio. It has been found from the two independent experimental techniques that there exist a maximum and/or minimum elastic property at a certain blending ratio, and that the elastic property decreases first with L/D ratio of a capillary and then levels off.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
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  • 45
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 120-124 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Kinetic parameters (reaction rate constant, activation energy, and frequency factor) were determined by differential scanning calorimetry using a linearly rising temperature program for the polymerization of diallyl phthalate monomer catalyzed with dicumyl peroxide. Cure times for specific degrees of cure at constant temperature were calculated and found to agree with the degree of cure measured by infrared spectroscopy. The relationship between non-isothermal and isothermal cure cycles is discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 46
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 47
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 30-33 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The progress of interfacial debonding caused by the diffusion of boiling water to glass fibre/polyester resin interfaces has been followed by shining a He-Ne laser beam along fibres and recording the changes in intensity of the emergent beam. Compared with measurements of electical conductivity arising from the presence of diffused water at the interface, it is concluded that the laser beam method provides more certain evidence of debonding.The glass/resin interface has also been investigated in partially cured composites and in filled composites, during exposure to boiling water.
    Zusätzliches Material: 5 Ill.
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  • 48
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 53-58 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Evidence is presented of the main steps in the physical breakdown of glass-fiber reinforced polyester (GRP) composites on outdoor weathering. The chronological sequence is fiber ridging, rupture of the resin layer covering ridging fibers or fibers running close to the surface, spalling of the resin at the site of failure and subsequent erosion, fiber prominence and formation of a network of microcracks. Breakdown is believed to be caused by a type of stress fatigue imposed on the composite by cyclic variation of humidity and temperature in conjunction with solar radiation, and by the action of water and oxygen. The under side of the exposed GRP sheeting shows only incipient breakdown, indicating that solar radiation is an important factor. Countermeasures suggested to reduce breakdown include techniques to keep fibers away from the surface, use of resins with better thermal and moisture characteristics, and use of resin formulations with the best light stability.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 64-73 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Practical extrusion processes often involve geometrically complex dies. Such dies are usually tapered, or streamlined, to achieve maximum output rate under conditions of laminar flow. These converging flows may be analysed in terms of their extensional and simple shear components to calculate the relationships between volume flow rate, pressure drop, and post extrusion swelling. The analysis can also be extended to cover the free convergence as fluid flows from a reservior into a die. Comparisons between predicted and observed data for a series of coni-cylindrical dies suggest that using this approach the pressure drop/flow rate relationship can be predicted within ±20% and the swell ratio/flow rate relationship within ±10%. Similar treatments have been in use for the last three years in solving such complex flow problems as radial flow in injection moulding and two-dimensional annular convergence in blow moulding dies.
    Zusätzliches Material: 4 Ill.
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  • 50
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 109-111 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A new method for removal of thin films of photoresist polymers has been found. When polymeric films are exposed to ultraviolet light in the presence of air, the material can be removed leaving an extremely clean surface, free of carbonaceous material. This process has been examined for a variety of photoresist polymers as well as on nonphotoresist polymers and on a variety of substrates. The process offers a new method of photoresist removal.
    Zusätzliches Material: 4 Ill.
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  • 51
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 204-208 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Thermal conductivity measurements were made on polyethylene samples which had been crystallized at different temperatures in order to vary density and lamellar crystal thickness. Tests were also made on polyethylenes which were oriented by mechanical shearing and by crystallization in a temperature gradient. The thermal conductivity increased linearly by 50% as the density went from 0.96 to 0.99 gm/cc. By orientation the conductivity was increased ten fold in the direction of molecular orientation and decreased two fold in the perpendicular direction. For samples oriented by deformation at different temperatures, the conductivity apparently correlates with birefringence.
    Zusätzliches Material: 5 Ill.
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  • 52
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 335-339 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Recently, rotational molding engineers, concerned with warpage and uneven cooling in parts, have been “pre-cooling” the mold in forced draft air after removal from the oven and prior to water quenching to removal temperature. In this paper, we analyze some of the factors that influence the rate of heat removal from an amorphous plastic in a metal mold. We find that mold thickness and thermal diffusivity, convection heat transfer coefficient of the cooling fluid, the thermal properties of the plastic and the initial, final and “freezing” temperatures of the plastic influence this cooling rate and the corresponding rate of volumetric shrinkage. We illustrate our analysis with several examples and discuss some guidelines in detail.
    Zusätzliches Material: 3 Ill.
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  • 53
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 358-363 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The birefringences of injection molded plates and the birefringence during steady, isothermal shear flow were compared for some amorphous polymers. The materials studied were a polystyrene, a “toughened” polystyrene and an acrylonitrile-butadiene-styrene copolymer. The birefringence of the plates, notably the maximum value for the average over the thickness was found to be related to the shear stress at the cavity wall that had occurred during the mold filling process. This relationship was independent of temperature. To a good approximation, it was also the same as the relationship between the flow birefringence and the shear stress at the wall in isothermal channel flow. It thus appears that the anisotropy of injection molded objects is dominated by the shear stresses during the mold filling process regardless of the temperature and of the macroscopic rate of deformation.
    Zusätzliches Material: 12 Ill.
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  • 54
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 55
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 402-408 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Energy transport to molten, flowing polymer has been studied. Experimental temperature profiles were determined at various axial lengths. These data are both precise and reproducible. Viscous dissipation was found to be a significant factor in these systems. In addition, sizable thermal expansion cooling effects were noted. It was also shown that the effect of viscous dissipation on Nusselt number was a function of Graetz number. At high Graetz numbers viscous dissipation had a sizable effect that declined to negligible proportions at Graetz values of 7 or less. Prior theoretical treatment of temperature profile development is shown to be only qualitatively correct.
    Zusätzliches Material: 9 Ill.
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  • 56
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 387-395 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A theoretical model was developed for the newly-defined delay zone of the plasticating screw extruder. The delay zone starts at the end of the solids conveying zone, i.e. at the point where the solid plug surface contacting the barrel melts and forms a film of melt up to where the steady state melting mechanism starts to operate. The model permits the film thickness and pressure profiles in this zone to be calculated. Published results were used to support the validity of the model. The results indicate that the film thickness at the end of the delay zone is several times the flight clearance. Finally, a criteria, based on the final value of the film thickness, is suggested to calculate the length of the delay zone.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 57
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 416-419 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The melt flow of emulsion polymerized polystyrene has been investigated in accordance with the particle flow concepts developed by Berens and Folt. Particles were found to be present in the extrudate up to 210°C and resins with larger particles were found to have lower viscosities. The molecular weight appears to have no significant effect on the melt viscosity above a certain molecular weight. The energy of activation for viscous flow at 190°C and at shear stress of 5 × 105 dynes/cm2 was found to be 29-33 kcal/mol depending on type of resin.
    Zusätzliches Material: 7 Ill.
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  • 58
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 395-395 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 59
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 397-401 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An improved apparatus for studying temperature profiles in molten, flowing polymers has been developed. The apparatus incorporates modifications and improvements of earlier temperature profile devices. In addition, this unit made it possible to study temperature profile development as a function of axial flow length. Data taken with the apparatus were found not only to be precise and highly reproducible but also to show the proper trends with respect to physical behavior.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 420-424 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Creep tests up to 106 seconds in tension and compression were conducted on polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polypropylene (PP). Measurements of longitudinal and lateral strain provided values for tension and compression strain ratio. These increased with time and stress for PMMA and PVC from about 0.38 to 0.44. The results for PP increased from 0.44 to above 0.5 in. tension and showed a decreasing ratio in compression, which suggested a time and stress dependent structural change. Volumetric strain was computed from the linear strains and plotted against stress and axial strain. Except at 102 seconds, the relationships were non-linear up to volumetric strains of about 0.3% and in the cases of PMMA and PVC there were greater changes of volume in tension than compression.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 61
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 444-449 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An activation energy theory of yielding in glassy polymers has been proposed by Starita and Keaton. It predicts a linear relation between energy to yield and test temperature. This concept was tested and found valid for five amorphous polymers; poly(methyl methacrylate), polycarbonate, polyarylsulfone, polysulfone and poly(vinyl chloride), in uniaxial extension at temperatures from 25°C to the glass transition. For extenstion rates of 0.2 in/min, yield energy was found to go to zero at Tg, as commonly determined by thermodynamic methods like dilatometry or scanning calorimetry. The effect of other extension rates, plasticizer and molecular weight appears to affect only the intercept much as Tg is affected by the same changes. The slope, or the ratio of thermal to mechanical energy efficiency in overcoming the flow activation barrier, is largely unchanged.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 25-29 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Dynamical mechanical relaxation spectra of a number of polyurethane-polyether block copolymers have been studied as a function of composition, temperature and frequency. At low temperatures these copolymers are characterized by a high glass-like modulus which decreases to a much lower typically elastomeric value in a narrow temperature range. The latter is a function in certain cases of the composition of the polymer. The rubbery plateau is maintained up to at least 140°C. In addition, a secondary relaxation is observed around -130°C. These observations can be interpreted in terms of an overall structure consisting of a polyether matrix containing segregated polyurethane domains, the latter serving as physical crosslinks in the system at ambient temperatures and above.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 63
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 184-192 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The phenomenon of extrudate distortion, which is called melt fracture, was studied for polystyrene samples of narrow and broad molecular weight distribution, and commerical samples of polypropylene and linear and branched polyethylene. It was experimentally found that the shear stress at the onset of melt fracture (τcr) is of the order of 106 dynes/cm2 and independent of the distribution of molecular weights. As the weight average molecular weight increases the shear stress τcr decreases. For polystyrene extruded at τcr the recoverable shear strain, which is defined to be half the ration (first normal stress difference/shear stress), was found proportional to the factor MzMz+1/Mw2 which represents the distrubution of molecular weights. The proportionality is expected to hold for other polymer systems. The polymer behavior at the onset of melt fracture was explained in terms of Graessley's entanglement theory and his correlation between true and Rouse shear compliance.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 209-212 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polymeric films deposited from the vapor of C4Cl6 by the surface-photopolymerization technique are electrically and mechanically continuous on various substrates when very thin. The thickness of the films depends upon irradiation time with wavelengths in the region 2000-3000Å. Re-irradiation in oxygen (air) of the polymeric films with light of these low wavelengths leads to patterned removal of the films. Since films 500Å thick and less can resist etchants for various substrates, a new and extremely thin positive photoresist system is possible. Resolution of etched substrates to lines a few microns wide has been demonstrated. If the polymeric films from C4Cl6 are deposited from the monomeric vapor at lower substrate temperatures they are soluble in various solvents. Re-irradiation with UV light with the films in vacuum produces a patterned fixing of the polymer with respect to acetone. A negative photoresist system is therefore possible. Again, films of thickness 500Å and less can resist various etchants such that substrates can be etched to high resolution.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 224-235 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This experimental study of suspension-chlorinated linear polyethylenes (CPE), (degree of chlorination 25 to 48% Cl), covers dynamic mechancial behavior at 3.5 and 110 Hz in the temperature range - 100 to 120°C. The semicrystalline samples, with a maximum degree of crystallinity of 25%, showed the main relaxations α and β. The effect of thermal treatment was examined. In the amorphous specimens, in addition to the Tg relaxation, other low temperature damping peaks were observed. The mechancial spectra indicate structure heterogeneity and increasing stiffness with increasing chlorine substitution. For the most prominent β relaxation, the apparent activation energy was determined from the frequency shift of tan δ and E″ maxima. The effect of structure, crystallinity and frequency on Young's moduli are also discussed. For the amorphous γ ray-Crosslinked elastomeric samples the photoelastic properties were examined at near equilibrium conditions between 30° and 80°C at various degrees of crosslinking. The polarizability anisotropy of the optical link and the Mooney-Rivlin elasticity constants were determined and an attempt was made to relate the result to the specimens' structure. A compatibility study was also made for a 42% Cl, CPE/high cis polybutadiene polyblend. The damping mechanical spectra indicate a noninteracting system whose Young's moduli can be correlated with those of the pure components using a phenomenological model proposed by Takayanagi.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 272-276 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This paper presents results obtained by the experimental technique of photoelastic stress analysis and by finite or discrete element analysis, applied to the case of buckling of a single, axially-loaded metal fiber embedded in a plastic matrix. The program was conducted utilizing a mild steel fiber embedded in an epoxy resin system. The fiber was loaded axially with an increasing compressive force until buckling occurred. Along with determination of the critical load for the fiber, the maximum shearing stress at any point in the epoxy matrix was determined using two-dimension photoelastic stress analysis. In the analytical study, the fiber was modeled by a series of bending elements and the matrix by an assemblage of constant-strain triangular elements. The total system was thus modeled by the two types of elements connected at common nodal points. The instability was solved as a standard eigenvalue problem and the stress tensor was obtained by finite element stress analysis.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 302-308 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Experimental studies have been conducted with a 2 1/3 oz reciprocating-screw injection molding machine to check the validity of a proposed theoretical model for injection molding. A semi-circular cavity has been employed in the study to achieve spreading radial flow during the filling stage. Both high speed photography and pressure transducer measurements have been employed to obtain data on polyethylene. The photographic studies confirm the existence of spreading radial flow throughout the filling stage, and are in very good agreement with data obtained with the transducer on the progression of the melt front in the cavity. The results show that the proposed theoretical model yields predictions which are in good agreement with experimental data for all stages of the injection molding cycle with polyethylene. The model also predicts a composite pressure-time curve for the overall cycle which is similar to those reported in the literature and which satisfactorily represents the data obtained in this study. It is also possible to predict a short shot under selected molding conditions in agreement with observation. The main problems in the application of the model arise during the filling stage near the cavity entrance where viscoelastic and end effects are important and where some of the assumptions inherent in the model may not be valid.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 199-203 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: It has been recognized recently that suspension polyvinyl chloride granules consist of particles ca 1μ in diam which are linked together to form a three-dimensional, sponge-like lattice. This paper deals with the fusion process of this particulate structure of PVC resin during powder extrusion. Extrudates prepared under various extrusion conditions are investigated through the electron microscope using a methyl methacrylate (MMA) embedding method followed by ultrathin sectioning. The MMA embedding method has been proven to be an effective means of revealing the detailed structure of molded PVC. Results showed that the 1μ-particles were subjected to breakdown due to heat and shear into fibrils 100-300 Å in thickness, which were the final structure attainable by extrusion. Discussion was focused on the fibrillar structure especially in relation to the elasticity in plasticized PVC.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 219-223 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A stability analysis of fiber spinning of isothermal power-law fluids has been carried out. The analysis for purely viscous fluids indicates that the critical extension ratio increases with an increase in power-law constant q above 1. For q greater than approximately 1.5, very high values of critical extension ratio are obtained. A stability analysis in the presence of viscous and inertial forces indicates that for q 〉 1 critical extension ratio can be correlated to a quantity Rq = q - 1 + 3Re, wherein Re is the Reynolds number. For the values of Rq greather than approximately 0.5, very high values of critical extension ratios are obtained.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 70
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 288-293 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The dimensional recovery of cold-rolled polycarbonate was measured between 100 and 147°C, and compared to stress-relaxation data. The strain-recovery isotherms were superimposed to produce a master curve which could be represented by a distribution function, U(τ), termed the strain recovery spectrum. U(τ) is found to be nearly identical to the relaxation spectrum, H(τ), calculated from the stress-relaxation master curve; and the shift in U(τ) as a function of temperature, WLF shift factor, is similar to that obtained from other viscoelastic measurements on polycarbonate. For the deformations studied, 25 and 50% reduction in thickness, the recovery behavior is found to be independent of strain (linear), suggesting that nonlinearity in a polymer glass results from large stresses, and not from large strains.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 72
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 323-334 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The state of the problem of elastic turbulence is critically discussed. It is shown that the development of elastic turbulence is associated with the transition of polymer systems to the high elastic state.Model experiments with a narrow-MWD polybutadiene have been carried out. The method of vizualization of the flow in a flat slit with the aid of circular-polarized light has been used. The results of polarization-optical investigation are compared with the results of capillary viscometry and dynamic measurements at small amplitudes. It is shown, in accordance with theoretical predictions, that when a polymer passes from the fluid to the high elastic state with an increase in the shear rate, it ceases to behave as a fluid under shear. This is accompanied by various forms of flow perturbation at the duct exit and entrance and inside the duct. Perturbations at the duct entrance and exit are due to stress concentration in these zones. The transition of a polymer to the high elastic state near the walls inside the duct gives rise to the “stick-slip” process or to continuous slippage along the duct walls, depending on the velocity of polymer movement. This can be clearly traced by the changes in the interference band pattern. Still higher velocities result in an intensive process of continuity break (rupture) in the polymer and in its chaotic movement in the duct as an aggregate of irregularly shaped lumps, which, relaxing, may form a continuous body again. Attention is drawn to the significance of these observations for a quantitative description of the viscosity anomaly of polymer systems and of the relationship between the viscosity anomaly with various flow irregularities and perturbations in such systems.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 353-357 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The Brabender Plasti-Corder is shown to be an effective tool for predicting the processing characteristics of thermoplastic polymers. Procedures for determining the molding temperature range, the relative melt viscosity over a continuous temperature range, and the stability of molding and experimental curtain coating materials are presented.Molding temperature ranges can be determined by first establishing the Brabender torque which corresponds to the maximum viscosity at which a material will just fill the cavity in a particular injection system under full injection pressure and maximum injection rate. This torque is constant for any material to be molded in this system. A Brabender torque-temperature curve is then obtained on the pertinent resin and the temperature which corresponds to the torque associated with the maximum viscosity is the minimum molding temperature. Maximum molding temperature is the temperature at which the log of the torque deviates from a linear dependence on temperature.The stability of thermoplastic compositions can be shown by a Brabender torque-time curve at constant temperature. An unstable polymer shows decreasing torque with time if the decomposition predominantly consists of chain scission.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 432-436 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: High density polyethylene (PE), polycarbonate (PC), and polymethylmethacrylate (PMMA) were subjected to uniaxial tensile deformation up to the onset of instability or necking. Simultaneous readings of longitudinal extension and transverse contraction (width and thickness) were obtained continuously during the loading period. From these data, plots of longitudinal versus “average” transverse strain were produced and it was found that the trends were neither constant nor linear over the full strain range employed. Additional plots of per cent volume change versus longitudinal strain indicate that the PMMA and PC show a maximum volume increase of about 0.6% while PE shows a maximum volume decrease on the order of 2.5%. Similar volume decreases have been noted by others and it would appear that structural changes are the most likely cause of this behavior.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 75
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 454-458 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The kinetics for the thermal degradation of poly (1,4-cyclohexylenedimethylene terephthalate) (PCHDT) were evaluated by means of a melt extruder. The effects of temperature, residence time, and oxygen content of the gas blanketing the polymer during storage on degradation of PCHDT were determined. The rate of thermal degradation was measured in terms of the rate of decrease of inherent viscosity and the rate of increase of carboxyl end group concentration.Residence time, temperature, and their interaction all contributed significantly to the degradation. For the conditions investigated, the oxygen content of the blanketing gas had no measurable effect on degradation. Analysis of the kinetic data yielded equations based on a random chain scission mechanism. These equations enabled the prediction of inherent viscosity and carboxyl end group concentration as functions of temperature and residence time and the inherent viscosity and carboxyl end group concentration of the original polymer. The activation energies for decrease in inherent viscosity and increase in carboxyl end group concentration of poly (1,4-cyclohexylenedimethylene terephthalate) were determined as 38.7 kcal/mole, respectively.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 12-24 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An improved theoretical model was derived for the solids conveying zone of a plasticating extruder. The model makes possible calculations in variable channel depth section. It also allows for a bulk density which is a function of pressure and for the non-isotropic pressure distribution in the solid plug. An expression for maximum flow rate was also derived. Results simulated by the model on a computer indicate the effect of variables on extruder performance. The power consumption terms in the solids conveying zone of a plasticating extruder were also derived. Total power consumption is the sum of power consumptions on the barrel surface, screw surfaces and those due to pressure rise. Their relative importance was analyzed by computations. The effect of operating conditions and coefficients of friction on the various power terms was also analyzed.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 77
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 48-52 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The structural utility of short, glass fiber-reinforced epoxy composities is experimentally investigated for fiber volume fractions from 0.15 to 0.5. The strength and stiffness of systems with randomly oriented fibers are compared with those of similar composites with aligned fibers. The ultimate strength of both types of material increses in a reasonably linear fashion with volume fraction up to 0.5. For all volume fractions in this range, strength of the random composites is slightly higher than the longitudinal and much higher than the transverse strength of equivalent compsites with aligned fibers. The modulus of the random system is approximately two-thirds the longitudinal and twice the transverse modulus of the unidirectional material. The structural utility of the flow molded material is greatest in uniaxial, stiffness critical situations. The greater strength and planar isotropy of the random composites make them preferable in all strength limited or multiaxial applications.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 78
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 79
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 91-100 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The mechanical properties of glass bead (30 micron diameter glass spheres) filled epoxy and polyester resins have been studied as a function of volume fraction of filler and the strength of the interfacial bond. The bonding between glass and resin was varied by chemically surface treating the glass using a silicone mold release to prevent chemical bonding at one extreme and a silane coupling agent to maximize bonding at the other extreme. Theoretical predictions of the elastic modulus and tensile strength have been made utilizing a finite element method. Excellent agreement is obtained with the experimental results. Izod impact energies have been measured for these composites as a function of filler content and interface treatment.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 112-119 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The proper use of lubricants and other additives in the compounding of PVC is hampered by lack of knowledge of their interactions with the polymer. Differential scanning calorimetry has been applied to measure the effect of ingredients on the glass transition temperature of PVC. An interaction parameter, based on changes in the glass transition temperature, has been proposed which quantitatively defines the degree of compatibility and which relates to the more empirical definition of lubricants as internal or external. This study of the compatibility of compounding ingredients as a function of molecular weight and chemical structure provides fundamental information of value in formulating, compounding and processing of PVC.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 150-156 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The deep drawability of biaxially cold-rolled thermoplastic sheets has been studied using polycarbonate, polyvinyl chloride, and acrylonitrile-butadiene-styrene polymers. Each polymer was rolled to two different reductions in thickness. The deep drawability of these rolled sheets was measured by determining the limiting draw ratio using a Swift cup test. Strain ratios were measured in three directions for each of the rolled sheets in order to determine the normal and planar anisotropy of the sheets. It has been determined that the drawability of a sheet can be correlated with the normal anisotropy of the sheet and it is the increase in normal anisotropy of a sheet which increases the drawability of the sheet. It has also been shown that lubrication increases the drawability due to a reduction in punch force.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 157-166 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Plastics in solid wastes is a problem of growing concern. Recycling of wastes is currently believed to be the most acceptable form of disposal in the long run; however, this route is known to be especially difficult for plastics. Recycling would be easier if the various generic types present in solid wastes, mainly polyethylene, polystyrene and poly (vinyl chloride), could be isolated; however, this would be very difficult and expensive. This is a first report on research aimed at evaluating the potential of recycling plastics as a polymer blend of the various generic types. This approach suffers from the difficulty that the different plastics are incompatible and the blend has poor mechanical properties. The extent of this problem is documented with data on many ternary blends employing virgin polyethylene, polystyrene and poly (vinyl chloride) of numerous grades likely to be found in solid wastes. Property degradation was found to be more severe as the complexity of the blend increased, indicating that general municipal wastes could be reused only in very low grade applications, whereas certain commercial wastes might have brighter prospects. Strategies for improving blend properties are outlined.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 84
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 265-271 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Many industrial processes require that solids be transformed to the molten state, thus accurate correlations of heat transfer and melting rates are important in process design. The heat-balance integral type of analysis is applied here to melter systems where phase change and convection effects are of equal importance, and the appropriate parameters that govern the thermal transport process are presented. Applications of the results to both Newtonian and non-Newtonian, power-law melts are discussed, and extensions to variable property situations are outlined. Although the results herein are directly applicable to contact melting systems, the governing parameters are useful in the correlation of other melting processes as well. Acomparison is made between the theory and some experimental data for a gravity-feed contact melter. The results are directly applicable in practice to the melting of bulk and granular crystalline polymers on melting grids, tube bundles, and plates.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 277-281 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The cup drawing process of thermoplastic sheet is analyzed on the basis of small deformation theory. The drawability of thermoplastic sheets is related to material parameters which may be investigated without performing an actual drawing process. Values for the drawability which are obtained by this method agree with values which are obtained by the Swift cup test.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 86
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Torsional braid analysis has been explored as a means of providing a quantitative measure for the effectiveness of polymer additives. Quantitative determinations have been made of antioxidant activity of selected compounds when formulated with certain elastomers prone to oxidative crosslinking on heat aging. The torsional braid technique has been used to determine the time dependence of the sharp torsional modulus increase which corresponds to a change from a rubbery to a highly crosslinked state. This time dependence is taken as a measure of the rate of oxidative crosslinking in heat-aged elastomer films coated on a Fiberglas braid. In this manner an assessment of antioxidant activity can be made. The effect of concentration and aging temperature on antioxidant activity can be made also. It has been also possible to use this technique to study the effect of structural changes in an antioxidant on its resultant activity. Feasibility studies have also been made on antiozonants in natural rubber and cis-polybutadience at three temperatures. A value of 10.9 Kcal/mole was calculated for the activation energy for the oxidative crosslinking reaction of cis-polybutadiene.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 87
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 309-314 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A criterion, based on the behavior of polymer solutions, is developed and applied for the prediction of the onset of flow anomalies observed at the capillary entrance for polymer melts. It is shown that a direct correspondence exists between the flow anomalies observed for polymer solutions and polymer melts. The onset of these anomalies can be correlated with a critical Weissenberg number which is consistent with the equality of the shear wave velocity and friction velocity. This critical condition can be employed to derive expressions useful for predicting the critical recoverable shear and critical shear stress for melt fracture.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 88
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 340-345 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polymer molecular weight heterogeneity affects the rheological properties of polymer melts such as melt viscosity, fracture and die swell. These rheological properties affect the conversion of the polymer from the bulk resin state to its final usable form. In this particular study, the effect of molecular weight distribution on polyethylene blown film characteristics was studied. The effect of the molecular weight heterogeneity on the rheological characteristics of the polymer in the molten state and its effect on the film properties is presented.The properties studied included film gloss, haze, tear resistance and film impact strength.This study shows that broadening the molecular weight distribution increases haze and reduces film gloss. Further, it was shown that a linear relationship exists between film gloss and external haze. Both values are measures of surface irregularities in the film which are affected by the drawing characteristics of the polymer.A broader molecular weight distribution results in increased impact strength as measured by the Dart Drop Impact Test. This is, it is believed, a result of the increase in long chain branching of the higher molecular weight fractions of the polymer which cause a higher degree of molecular weight entanglement at the branch sites. In contrast the tear strength is reduced as the molecular weight distribution broadens because of the low molecular weight fraction in the broad spectrum material which tend to decrease resistance to tear.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 89
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 364-377 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Literature relating to the fundamental nature of the fibrous state is reviewed with the goal of illustrating evidence for the existence of a possibly fundamental morphological unit, the elemental microfiber or fibril. Following a short summary of the rather well documented situation in natural fibers, the problem of the microfiber in synthetic fibers is probed in terms of phenomena in solution and bulk polymeric systems. The reviewed literature indicates the existence of unique, elemental microfibers in synthetic fibers is largely tenuous; however, there is wide evidence of the existence of complex elongated structures axially aligned within macrofibers which future work may resolve into a central microfiber. The structural complexity appears to simplify for transformations occurring in high shear fields. This review covers articles through 1971, and it is notable that in 1971 approximately 100 articles of high relevance appeared in major journals.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 90
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 378-386 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Isothermal solids conveying theories have been developed in the past. However, due to friction, the surface temperature of the solid plug does increase. This change in temperature will strongly affect the temperature sensitive coefficients of friction and consequently also the pressure that develops. The surface temperature of the solid plug is also an important variable on its own because, when it reaches the melting point, the solids conveying zone is terminated. A mathematical model has been developed to calculate the temperature profile in the solid plug together with the strongly interacting pressure profile. Calculations indicate that high pressure in the solids conveying zone can practically be obtained only by very efficient cooling of the barrel in this zone.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 91
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 409-415 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Two engineering plastics, an acrylonitrile-butadiene-styrene resin (ABS resin, Cycolac MS) and a rigid polyvinyl chloride resin (PVC resin, Dacovin 2082) were investigated to determine the effects of cold working. In particular, the “bending under tension” stress system of a deep drawing process was considered. The object was to determine the effect of the blank-holder pressure, the ratio of the punch radius to the material thickness, the speed of deformation and the temperature of deformation. The stress-strain characteristics of the deformed and undeformed material were markedly different. Upper yield points were lower in the deformed specimens, the tensile strengths were decreased by 10 to 15% and the %-elongation at break was higher - up to double the values for underformed specimens. An analysis indicated that these effects can be attributed to non-homogeneous yielding. The results also indicated that crazing plays an important role in permitting an ABS material to permanently conform to a radius with no geometric constraints.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 437-443 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A method for measuring the unperturbed radius of gyration and the degree of long-chain branching in Gaussian-distribution polymers is proposed. Polyvinyl chloride (PVC) and polyvinyl acetate (PVAc) were selected to illustrate the method. It was observed that PVC samples prepared by homogeneous and heterogeneous polymerizations exhibit the same degree of long-chain branching. This conclusion is supported by viscometric data. The polydispersity ratios (Mw/Mn) indicate that both types of polymerizations would yield a very small amount of total branching (long chain and short chain.) The calculated unperturbed radius of gyration of linear PVC samples was found to be 0.185 \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\frac{{{\rm \dot A}^{\rm 2} {\rm mole}}}{{{\rm gm}}}} \right) $\end{document}, and that of PVAc was determined to be 0.107 \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\frac{{{\rm \dot A}^{\rm 2} {\rm mole}}}{{{\rm gm}}}} \right) $\end{document}. The value obtained for PVC is shown to be in agreement with the value determined from the viscometric method as described in our previous work.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 1-11 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The surface tension of a polymer liquid is a property of considerable practical importance. Within the past decade the experimental difficulties in accurately measuring the surface tension of viscous polymer melts have been overcome, and a considerable body of data is now available. This review discusses the measurement techniques which have proved useful, the results which have been obtained, and theoretical approaches which have been applied to them. A tabulation of surface and interfacial tension values which have been published up to mid-1971 is included.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 94
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: In a study of the transient behavior of a series of nylon 6/6 yarns differing systematically in mechanical properties, the effects of high-speed, transverse missile impact upon yarn specimens were observed by high-speed photography. The loss in missile kinetic energy was determined directly from the reduction in missile velocity and was studied as a function of yarn tenacity and missile impact velocity. The shape of the missile energy loss curves was due to the partition of missile energy into yarn kinetic energy and yarn strain energy. The missile energy losses and yarn dynamic breaking strains were compared to static breaking energies and breaking strains for these yarns. The observed trends are discussed in terms of the differing yarn tenacities and test rates.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 77-80 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An experimental study was made of melt flow instabilities in extrusion of two-phase polymer systems. For the study, blends were prepared from two polymers: polystyrene (Dow Chemical STYRON 686) and high density polyethylene (Union Carbide DMDJ 4309). The experimental technique used in the present study was the same as that described in a previous paper by the authors. The study shows that there are abrupt increases both in exit pressure and in the recoverable shear strain (defined as the ratio of the exit pressure to shear stress) at the critical flow conditions. It has also been found that an addition of a small amount of high density polythylene (2.5 wt-% and 5.0 wt-%) increases the critical shear rate of polystyrene and hence results in a higher throughput rate before extrudate distortion is actually observed. This result is explained in terms of the independently determined melt elasticity of the two-phase systems investigated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 134-139 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Two-phase polymer systems have achieved commercial importance due mainly to the improvement in impact strength brought about by the addition of dispersed rubber particles to a normally brittle glassy polymer. Rubber-reinforced polystyrene and ABS plastics are two familiar examples. An important drawback of this class of materials is their lack of transparency, caused by the scattering of light at the interface between the phases. The theory of light scattering by spherical particles indicates that the degree of scattering (turbidity) is a function of the amount of dispersed phase present, its particle size, the ratio of refractive indices of the phases, and the wavelength of light. Quantitative predictions of the effects of the above parameters on the transparency of two-phase systems can be made, providing answers to the questions “How close must the refractive indices be?” and “What size must the dispersed-phase particles be?” for a given level of transparency. Calculations for typical polymer pairs reveal that at a given dispersed-phase level, a maximum in turbidity is obtained roughly in the range of particle sizes thought to be necessary for good impact strength. Also, if the refractive indices are matched at a particular temperature, small particle sizes greatly increase the temperature range over which scattering is minimized.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 179-183 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Based upon known polymerization kinetics, the extent and rate of re-equilibration of nylon 6 have been analyzed. Relationships have been developed for the calculation of the rates of molecular weight change and monomer regeneration as functions of initial water concentration, degree of polymerization, and type and concentration of end groups. The results are in good agreement with published data.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 98
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An experimental program was conducted to study the thermochemical, flammability and toxicological characteristics of uncoated and coated polyisocyanurate foams. The coatings used were fluorinated copolymer and an intumescent material. Flammability testing methods included the XP-2 chamber smoke test, ASTM D-1692, infrared photography, Bureau of Mines penetration test, and a JP-4 fuel combustion chamber. The results of these tests are presented in a companion paper. Combustion and pyrolysis gases were analyzed by gas chromatography and mass spectrometry. The LD-50 and LD-100 tests were performed on Sprague-Dawley rats housed in an environmental chamber. The isocyanurate foam, flourinated-copolymer-coated foam, and the intumescent-coated foam were found to have excellent flammability and insulation characteristics, although smoke development was substantial. The LD-50 values for Sprague-Dawley rats, based on a two-week survival, were approximately 2.0 gm/ft3 for all three materials. Examination indicated an absence of any significant cause of death except carbon monoxide poisoning.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972) 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 100
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 167-178 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: An experimental program was conducted to study the thermochemical and flammability characteristics of an improved polyisocyanurate foam, uncoated and coated either with fluorinated copolymer or an intumescent material. Testing methods included thermal analysis; scanning electron microscopy; infrared photography; infrared spectroscopy; HLT-15, ASTM D-1692, Bureau of Mines Penetration, and XP-2 smoke chamber flammability tests; limiting oxygen index (LOI); and a moderate-scale fire simulation test. The uncoated and coated foams were found to have excellent flammability and insulation characteristics, although smoke development was substantial.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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