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  • 1
    Electronic Resource
    Electronic Resource
    Pharmazie (1991)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 25 (1991), S. xi 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19910250213
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  • 2
    Electronic Resource
    Electronic Resource
    A highly rigid capped porphyrin (1992)
    s.l. : American Chemical Society
    The @journal of organic chemistry 57 (1992), S. 1015-1018 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00029a045
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  • 3
    Electronic Resource
    Electronic Resource
    An equation of state theory for hydrogen-bonding polymer mixtures (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 6710-6723 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100170a061
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  • 4
    Electronic Resource
    Electronic Resource
    GaInAs/InP selective area metalorganic vapor phase epitaxy for one-step-grown buried low-dimensional structures (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 560-568 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The selective area epitaxy of GaInAs/InP layers grown by low-pressure metalorganic vapor phase epitaxy through SiO2 patterned masks was investigated. The layers are found to develop mesa structures limited by {111} and (100) facets outside of the opened mask, and perfect selective epitaxy is obtained. The absence of GaInAs growth on {111} facets allows the fabrication of very narrow buried GaInAs layers in a single growth step. For both materials, the growth rates are found to depend strongly on the mask geometry owing to surface diffusion of the reactant species from the no- or low-growth SiO2 mask and {111} facets toward (100) surfaces. A detailed quantitative analysis is made to identify the critical parameters that control the growth behavior, and a model is described from which the upper limit of the growth rates for any mask design can be calculated. Low-temperature cathodoluminescence measurements show strong emission of the buried GaxIn1−xAs layers and indicate local stoichiometry variations Δx(approximately-equal-to)±5% around the x=47% lattice-matched composition that are attributed to different diffusion coefficients of the reactant species on the SiO2 mask and {111} facets. The results show that selective area metalorganic vapor phase epitaxy is a promising technique for the fabrication of one-step-grown buried quantum-well wire arrays and narrow cavity InP-based buried lasers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346829
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamic light scattering by aqueous solutions of rodlike fd-virus particles (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6284-6289 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dynamic light scattering (DLS) measurements on aqueous solutions of rodlike fd-virus particles (length=880 nm, diameter=9 nm) below and above the overlap concentration c*=1 particle/length3 are reported. In samples with screened Coulomb interaction the short-time behavior of the time correlation functions does not show a significant concentration dependence, in contrast to samples at very low ionic strength (strong Coulomb interaction), where the short-time behavior is dominated by the static structure factor S(q). In this case S(q) derived by DLS methods, using an equation that has been proved for interacting spherical particles and weakly interacting rods, is in excellent agreement with S(q) determined by static light scattering (SLS) up to a particle concentration of about 5c*. Above significant deviations are found. At very low ionic strength the existence of a distinct very long tail in the time correlation function as previously reported can be confirmed, but the new experiments suggest that this is due to dust particles and aggregates and not to the interaction between the fd particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461548
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  • 6
    Electronic Resource
    Electronic Resource
    A lattice model describing hydrogen bonding in polymer mixtures (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6166-6174 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Flory lattice model is used to obtain an expression for the free energy of mixing polymers that hydrogen bond. The derivation is based on the determination of the probability that a mixture of the nonhydrogen bonded chains would spontaneously occur in a configuration equivalent to the hydrogen bonded system. Our result has three parts. The usual contribution to the free energy from mixing covalent chains, a contribution from the hydrogen bonds that is equal to the result that would be obtained if the segments were not covalently linked, and a "correction'' term that accounts for the excess entropy of mixing introduced by the second term. A consequence of this model is that there should be no dependence of the equilibrium constants describing hydrogen bonding upon covalent chain length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458340
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  • 7
    Electronic Resource
    Electronic Resource
    Rheological properties of suspensions of interacting rodlike FD-virus particles (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4920-4928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low shear (γ(overdot)=1 s−1) and shear rate dependent (1 s−1〈γ(overdot)〈100 s−1) viscosity measurements on aqueous suspensions of rodlike FD-virus particles (length=880 nm, diameter=9 nm) below and above the overlap concentration c* =1 particle/length3 are presented. Properties like intrinsic viscosity [η], the virus concentration and shear rate dependence of η are studied in deionized ("saltfree'') suspensions and in the presence of NaCl, where the Coulomb interaction between the particles is totally screened. In the latter case, [η] is in excellent agreement with theoretical predictions [A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); R. M. Davis and W. B. Russel, Macromolecules 20, 518 (1987)]. As a function of the virus concentration, η follows certain power laws in c. The observed exponents depend here on the applied shear rate. In the low shear region, η(c) can be described by the well known Huggins behavior. An attempt to fit the data by the popular stretched exponential form failed. The variation of η with shear rate is compared with available theories [M. Doi and S. F. Edwards, The Theory of Polymer Dynamics (Clarendon, Oxford, 1986); A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); J. S. Dahler, S. Fesciyan, and N. Xystris, Macromolecules 16, 1673 (1983)]. A theory of Hess [Z. Naturforsch. Teil A 35, 915 (1980)] allows us to evaluate the concentration dependent values of the rotational diffusion constant Drot from the η(γ(overdot)) data which are found to be in very good agreement with the values of Drot, obtained by electric or magnetic birefringence [H. Kramer, M. Deggelmann, C. Graf, M. Hagenbüchle, C. Johner, and R. Weber, Macromolecules 25, 4325 (1992); J. F. Maguire and J. P. McTague, Phys. Rev. Lett. 45, 1891 (1980); H. Nakamura and K. Okano, Phys. Rev. Lett. 50, 186 (1983)]. For strong Coulomb interaction among the suspended viruses no adequate theory is available. Therefore, the data achieved under these conditions are interpreted in terms of the corresponding results of the non-Coulomb interacting samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464947
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  • 8
    Electronic Resource
    Electronic Resource
    High-temperature ovens (1700 °C) for a wide range of oxygen gas pressures (10−6–2×103 bar): A new two-chamber autoclave (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3829-3833 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the construction of four different systems used for annealing samples in oxygen. The gas pressure can be controlled over nine decades (10−6–2×103 bar). The maximum temperature, 1700 °C, is limited by the ceramic materials used for thermal insulation and for the crucibles. The low-pressure furnaces (10−6–1 bar) have an external heating system and incorporate an active regulation of a small gas flow. The intermediate pressure furnaces (1–150 bar) are heated either by a special resistive wire or by rf heating with a Pt-20%Rh susceptor, both in the pressurized gas chamber. Quenching is possible in the latter. For the kbar range, we designed a double-chamber autoclave with separate heater and sample spaces, filled with Ar and O2. The gas pressures are balanced in a cold, separate vessel by means of a silicon hose. The temperature is measured with a thermocouple feeding into the hot, pressurized oxygen environment very close to the sample. The construction problems of this new autoclave have been solved with particular emphasis on the safety requirements. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145215
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  • 9
    Electronic Resource
    Electronic Resource
    Ischemia-Induced Accumulation of Extracellular Amino Acids in Cerebral Cortex, White Matter, and Cerebrospinal Fluid (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: In a global model of brain ischemia, accumulation of amino acids was studied in the extracellular space of the auditory cortex and the internal capsule using microdialysis, and in CSF of halothane anesthetized cats. In both brain regions, blood flow determined by hydrogen clearance decreased below 10 ml/100 g/min after extracranial multiple-vessel occlusion, and extracellular potassium activity (Ke) measured in the dialysate increased significantly. A delayed rise in Ke was observed in CSF. In contrast, ischemic amino acid accumulation differed markedly between the two brain regions investigated. In cortex, transmitter amino acids glutamate, aspartate, and γ-aminobutyric acid (GABA) rose almost immediately after onset of ischemia, and increased 30-, 25-, and 250-fold, respectively, after 2 h of ischemia. The nontransmitter amino acids taurine, alanine, and serine increased 10-, seven-, and fourfold, respectively, whereas glutamine and essential amino acids (valine, phenylalanine, isoleucine, and leucine) increased only 1.5-fold. In the internal capsule, increases in amino acids, if any, were delayed and much smaller than in cortex. The largest alteration was a fivefold elevation of GABA. In CSF, changes in amino acids were small and comparable to those in the internal capsule. Our results demonstrate that ischemia-induced extracellular amino acid accumulation is a well localized phenomenon restricted to gray matter structures that possess release and reuptake systems for these substances. We assume that amino acids diffuse slowly into adjacent white matter structures, and into CSF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb05823.x
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  • 10
    Electronic Resource
    Electronic Resource
    Evidence of biogenic greigite (ferrimagnetic Fe3S4) in soil (1994)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The occurrence of greigite (Fe3S4) in soils is reported for the first time. It forms irregularly-shaped aggregations within plant cells in the Gr2 horizon of a gley soil developed from colluvial material. Greigite was identified by X-ray diffraction and magnetic measurements and was investigated by optical and transmission electron microscopy. Biogenic formation is proposed, based on the elongated shape of single greigite crystals, and sulphur isotope analyses, which showed a depletion in 34S relative to the soil-water sulphate. The cell-edge length of 0.98639±0.00003 nm is significantly smaller than values reported for sedimentary greigite. The mean coherence length of 27 nm agrees with TEM observations and indicates that the single greigite crystals lie in the superparamagnetic region. However, the fine aggregates show magnetically single-domain behaviour. Greigite is the only carrier of a stable magnetic remanence in the soil profile studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.1994.tb00490.x
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