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  • 1990-1994  (25)
  • 1955-1959  (5)
  • 1920-1924  (6)
  • 1
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 54 (1990), S. 0 
    ISSN: 1471-4159
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Abstract: Some of the enzyme choline-O-acetyltransferase (ChAT) associated with central cholinergic nerve terminals appears to be nonionically associated with membranes. In the present study, we tested the possibility that some membrane-bound ChAT might be anchored to membranes by a phosphatidylinositol linkage by incubating rat hippocampal tissue with phospholipase C (PLC) from Bacillus cereus. The PLC selectively augmented the release of ChAT; also, the glycosylphosphatidylinositol-PLC inhibitor, zinc, blocked this increase in release. When control and PLC-treated hippocampal tissues were subjected to Triton X-114 phase separation, a procedure that separates amphiphilic from hydrophilic proteins, the detergent-soluble, membrane-bound fraction of tissue ChAT appeared to be the source of the ChAT released by PLC into the incubation medium. Zinc also blocked the temperature-dependent release of ChAT, but not lactic dehydrogenase, from hippocampal tissue. Extracellular membrane-bound ChAT appeared to be the source of the ChAT released by a low exogenous concentration of PLC, as well as that released by a temperature-dependent process during tissue incubation. Phosphatidylinositol-specific PLC from Bacillus thuringiensis released ChAT, but not lactic dehydrogenase, from a crude synaptosomal fraction prepared from rat hippocampal tissue. These results suggest that some of the membrane-bound ChAT in rat hippocampal tissue may be extracellular and anchored to the membrane by phosphatidylinositol, and also that an endogenous factor in hippocampal tissue may function to remove this extracellular ChAT from the membrane.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 44 (1922), S. 216-217 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 44 (1922), S. 624-634 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 364-390 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The purpose of this paper is to provide an independent, comprehensive, critical review of the "renormalization group'' theory of turbulence developed by Yakhot and Orszag [J. Sci. Comput. 1, 3 (1986)]. The first part of the paper is a confirmation of their basic theory for the Navier–Stokes equations, followed by a discussion of approximations in the scale removal procedure. The main part of the paper examines the YO derivations of the velocity-derivative skewness and the transport equation for the energy dissipation rate E. An algebraic error in the derivation of the skewness is corrected. Several problems are identified in the derivation of the E equation which suggest that the derivation should be reformulated. The present paper has become the basis for such a reformulation, to be published separately by Yakhot and Smith.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 992-994 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In order to determine the best representation of the turbulence spectrum in the dissipation range, the dynamical equation for the rate of energy dissipation E is used, together with a model spectrum of the form E[k] = CKE2/3k−5/3 exp[ − σkm], to obtain a prediction for the velocity derivative skewness S¯ at high Reynolds number: S¯ = S¯[CK,m]. The skewness data suggest that m=2 is the best model for laboratory-scale flows.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1572-1574 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We show that the radiative efficiencies and lifetimes of photoexcited carriers in epitaxial GaAs may both be enhanced by three to four orders of magnitude by the preparation of thin n+, doped layers at the surface and substrate interfaces. Samples were prepared by organometallic vapor phase epitaxy with n− region (∼1015 cm−3) thicknesses of 3–10 μm and n+ regions Si doped to concentrations of 5×1018 cm−3. Time-resolved luminescence in such structures (25–300 K), under both surface and bulk (near-band- edge) excitation conditions, reveals band-to-band-dominated recombination spectra, with carrier lifetimes ranging from a minimum of 150 ns at 50 K to 800 ns at room temperature. This is in sharp contrast to the subnanosecond lifetimes and poor raditive efficiencies typical in conventionally prepared, bulk or epitaxial GaAs, but is comparable to the best reported for high-purity LPE GaAs/AlxGa1−xAs double heterostructures.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Analytical chemistry 31 (1959), S. 102-105 
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 687-689 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have used an electrical technique to determine the ambipolar lifetime in p-i-n GaAs/AlGaAs self-electro-optic-effect devices in which the i region consists of a multiple quantum well structure (MQW). From an analysis of the voltage drop in the i region obtained from the forward current-voltage characteristics, values for the ambipolar lifetimes are derived for diodes with different MQW. A value of 80–90 ps is determined for the ambipolar lifetime which is found not to change significantly when the AlxGa1−xAs barrier thickness or composition is reduced from 65 to 35 A(ring) or x∼0.3 to 0.2, respectively, in the MQW. Since these changes in the barrier have previously been shown to improve photoresponse efficiency of the p-i-n diode, it is inferred that the carrier escape and collection times are smaller than 80–90 ps in devices with thin (35 A(ring)) or low (x∼0.2) AlxGa1−xAs barrier.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1809-1811 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We describe symmetric self-electro-optic effect devices (S-SEEDs) with clamping diodes connected to the center node of the devices to ensure both diodes of the S-SEEDs have an electric field across them at all times. These diode-clamped S-SEEDs operate over a greater wavelength range, with greater powers before saturating, and have lower optical switching energies compared to conventional S-SEEDs. An 8×8 array of diode-clamped S-SEEDs has been built and tested. We have demonstrated bistable operation with voltage swings of only 2 V over a wavelength range of 15 nm. Required optical switching energies of 340–580 fJ were measured at input powers from 500 nW to 100 μW for devices with 10×10 μm mesas. This is the lowest reported switching energy for any SEED with acceptable bistable characteristics.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Symmetric self-electro-optic effect devices (S-SEEDs) using extremely shallow GaAs/Al0.04Ga0.96As multiple quantum wells are demonstrated. By exploiting mainly exciton ionization, rather than the usual quantum-confined Stark shift, room-temperature optical bistability is obtained with no applied bias. The extremely shallow symmetric-SEED (symmetric E-SEED) exhibits contrast ratios (CRs)(approximately-equal-to)3.5, with biasses〈5 V, demonstrating system applicability and compatability with electronics. Large system tolerances Δλ(approximately-equal-to)6 nm and maximum bistability loop width (approximately-equal-to)70% are also obtained. Moreover, due to fast carrier escape times, the symmetric E-SEED exhibits useful CRs(approximately-greater-than)2 even at continuous-wave intensities (approximately-greater-than)70 μW/μm2.
    Materialart: Digitale Medien
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