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  • Atomic, Molecular and Optical Physics  (3)
  • Life and Medical Sciences  (3)
  • 1980-1984  (6)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 17 (1980), S. 1191-1200 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dans le present article on considére un nouveau modèle pour le transport moléculaire à travers des membranes, qui a été introduit antérieurement par Hosur. Dans ce modèle, la membrane est assimilée à une barrière de potentiel, en déterminant le flux matériel à travers de la měme partant dès le coefficient de transmission de la barrière, en supposant l'existence d'une différence d'énergie parmi les molécules qui appartiennent à les fluides d'une et d'autre cǒté de la membrane. On obtient ainsi, une expression pour le flux dans le cas de pétites différences d'énergie, qui a été particularisée au cas ou la difference d'énergie est due à un gradient de température, un gradient de concentration ou à tous les deux gradients agissant ensemble. Dans tous les cas, sous certaines conditions, on obtient des equations qui sont formellement identiques à celles obtenues par la thermodynamique des processus irréversibles.
    Abstract: In vorliegendem Artikel wird ein von Hosur eingeführtes Modell für Transport durch Membranen untersucht. In diesem Modell wird die Membran mit einer Potentialschwelle assimiliert, und der Materialfluss durch die Membran wird vom Transmissionskoeffizient der Schwelle bestimmt, wobei es wird angenommen, dass ein Energieunterschied unter den Molekülen an den beiden Seiten der Membran existiert. Für den Fall wo dieser Energieunterschied klein ist wird eine Gleichung für den Transport erhalten. Diese wird spezialisiert zu den Fallen wo der Energieunterschied von einem Temperatur-oder Konzentrationsgradient oder beiden zusammen verursacht wird. In allen Fallen werden-mit gewissen Begrenzungen-Gleichungen erhalten, die mit denen der Thermodynamik irreversibler Prozesse formal identisch sind.
    Notes: In the present paper a new model for the transport through membranes, introduced previously by Hosur, is considered. In this model, the membrane is assimilated to a potential barrier, and the material flow through the membrane is determined from the transmission coefficient of the barrier, assuming the existence of an energy difference among the molecules placed at both sides of the membrane. An equation for the transport, in the case of small energy differences, is obtained, which is particularized to the cases that the energy difference is caused by a temperature gradient, a concentration gradient, and both gradients acting together. In all cases, under certain limitations, formally identical equations to those of the thermodynamics of irreversible processes are obtained.
    Additional Material: 1 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 595-600 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analysis of nonadditive effects in small palladium clusters via LCAO-MO-SCF calculations using the nonempirical pseudopotential model is presented. The results are tentatively correlated with previous studies on various metal clusters (Li, Be, Mg, etc.) for which a good knowledge of multibody terms has provided a valuable guide for understanding the cluster stabilities and their chemisorption capacity.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 83-93 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Classically every physical thing has some geometry or other, but in the quantum theory the notions of spatial structure, shape, and size seem to become hazy if not outright inapplicable. In particular, elementary entities are by definition structureless and seem to have no size or shape other than those imposed by their environmént - as represented, e.g., by the boundary conditions. However, this does not entail that systems of interacting components, such as molecules, lack a geometry as well, as has been argued in recent times. The purpose of this paper is to investigate this claim. Since the solution to the problem whether a quantum-mechanical system possesses a geometry depends critically upon the definition of the latter, we elucidate the notions of extension, shape, and spatial configuration of a system. We do so first classically in terms of the energy density, then quantum mechanically in terms of a suitably constructed position distribution function that depends upon the spatial coordinates (and is thus a field quantity) rather than on the particle coordinates. In this way we construct both classical and quantal concepts of the geometry of a system. We also define the notions of spatial structure and chemical structure of a quantal system. Our quantum-mechanical concepts are quite general and constitute smooth extensions of the corresponding classical concepts. The upshot of this investigation is that a quantal system does have a geometry, albeit not as clearcut a one as a classical system, that is primarily determined by the interactions among its components. (Thus, physics determines geometry of physical systems, not the other way around.) This conclusion is obtained within nonrelativistic quantum mechanics without adding any extra assumptions. Our result vindicates the ball-and-spoke models of molecules and thus shows once again that quantum chemistry, although different from classical chemistry, stays close to the chemist's work bench.
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  • 4
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In this work, we have completed a study of the development of the ovoviviparous lizard Liolaemus tenuis tenuis. Ovoviviparity in this lizard is a condition in which eggs are retained within the reproductive duct for about 60 days. During this period the phases of segmentation, gastrulation, neurulation, presomitic, and somitic embryos transpire. During the months of December and January the eggs are laid, and at this time the embryos are comparable to stage 27 Liolaemus gravenhorsti lizard embryos, or to stage 29 Calotes versicolor lizard embryos. Differentiation of the facial region occurs between Days 12 and 42 after egg laying. Limbs develop rapidly between the 8th and 23rd days. By 53 days the appendicular skeleton is completely formed. After 36 days the mesonephros begins to degenerate, and its function is gradually taken over by the developing metanephros. Newborn lizards do not possess an egg caruncle. During the period up to hatching, there is a great increase of liquid within the egg, presumably amniotic fluid. Cracks develop in the leathery shell shortly before hatching and are, perhaps, the first sign of the onset of hatching. Increase of liquid in the egg during postlaying development accounts for its increase in weight and change in shape. Weight of the embryo at hatching does not exceed 32% of the total weight of the egg.
    Additional Material: 27 Ill.
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  • 5
    ISSN: 0730-2312
    Keywords: phosphatidylinositol ; human platelets ; alpha catecholamines ; clonidine ; yohimbine ; prazosin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Epinephrine and adenosine diphosphate (ADP) stimulated 3H-glycerol uptake into phosphatidylinositol of human platelets. Yohimbine, an alpha-2 adrenoceptor antagonist, markedly reduced epinephrine-stimulated 3H-glycerol uptake into phosphatidylinositol; while prazosin, an alpha-1 antagonist, was without effect. Likewise, yohimbine, but not prazosin, blocked epinephrine-induced platelet aggregation. Furthermore, clonidine, a specific agonist for alpha-2 adrenoceptors, stimulated incorporation of-3H-glycerol into phosphatidylinositol and promoted platelet aggregation in the presence of low concentrations of ADP. These studies indicate that the effects of epinephrine on platelet aggregation and phosphatidylinositol synthesis are mediated through alpha-2 adrenoceptors. Further, since the stimulation of phosphatidylinositol synthesis seen with epinephrine was also observed with ADP, this suggests that the increased 3H-glycerol labeling is an indirect result of platelet aggregation.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 4 (1983), S. 315-326 
    ISSN: 0197-8462
    Keywords: Drosophila ; ELF electromagnetic effects ; oviposition ; development ; viability ; magnetic fields ; DC magnetic fields ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Drosophila flies placed in a habitat with two lateral boxes demonstrated sensitivity to magnetic fields: Oviposition decreased by exposure to pulsated extremely low frequency (ELF) (100)Hz, 1.76 miliTesla (mT) and sinusosidal fields (50 Hz, 1 mT), while there was no initial effect of exposure to a static magnetic field (4.5 mT). Drosophila eggs treated for 48 h with the above described fields showed that (1) mortality of eggs was lower in controls than in eggs exposed to all tested magnetic fields; (2) mortality of larvae increased when a permanent magnet was used; (3) mortality of pupae was highest when a permanent magnet was used; and (4) general adult viability was highest in controls (67%) and diminished progressively when eggs were exposed to pulsated (55%), sinusoidal (45%), and static (35%) magnetic fields.
    Additional Material: 2 Ill.
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