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  • 1
    Electronic Resource
    Electronic Resource
    Ca2+/Calmodulin-Dependent Protein Kinase II and Protein Kinase C Phosphorylate a Synthetic Peptide Corresponding to a Sequence That Is Specific for the γ2L Subunit of the GABAA Receptor (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The γ2 subunit of the GABAA receptor (GABAA-R) is alternatively spliced. The long variant (γ2L) contains eight additional amino acids that possess a consensus sequence site for protein phosphorylation. Previous studies have demonstrated that a peptide or fusion protein containing these eight amino acids is a substrate for protein kinase C (PKC), but not cyclic AMP-dependent protein kinase A (PKA)-stimulated phosphorylation. We have examined the ability of PKA, PKC, and Ca2+/calmodulin-dependent protein kinase (CAM kinase II) to phosphorylate a synthetic peptide corresponding to residues 336–351 of the intracellular loop of the γ2L subunit and inclusive of the alternatively spliced phosphorylation consensus sequence site. PKC and CAM kinase II produced significant phosphorylation of this peptide, but PKA was ineffective. The Km values for PKC-and CAM kinase II-stimulated phosphorylation of this peptide were 102 and 35 μM, respectively. Maximal velocities of 678 and 278 nmol of phosphate/min/mg were achieved by PKC and CAM kinase II, respectively. The phosphorylation site in the eight-amino-acid insert of the γ2L subunit has been shown to be necessary for ethanol potentiation of the GABAA-R. Thus, our results suggest that PKC, CAM kinase II, or both may play a role in the effects of ethanol on GABAergic function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb03582.x
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  • 2
    Electronic Resource
    Electronic Resource
    Inhibition of Cyclic AMP Accumulation in Intact NCB-20 Cells as a Direct Result of Elevation of Cytosolic Ca2+ (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 59 (1992), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Earlier studies established that adenylyl cyclase in NCB-20 cell plasma membranes is inhibited by concentrations of Ca2+ that are achieved in intact cells. The present studies were undertaken to prove that agents such as bradykinin and ATP, which elevate the cytosolic Ca2+ concentration ([Ca2+]i) from internal stores in NCB-20 cells, could inhibit cyclic AMP (cAMP) accumulation as a result of their mobilization of [Ca2+]i and not by other mechanisms. Both bradykinin and ATP transiently inhibited [3H]cAMP accumulation in parallel with their transient mobilization of [Ca2+]i. The [Ca2+]i rise stimulated by bradykinin could be blocked by treatment with thapsigargin; this thapsigargin treatment precluded the inhibition of cAMP accumulation mediated by bradykinin (and ATP). A rapid rise in [Ca2+]i, as elicited by bradykinin, rather than the slow rise evoked by thapsigargin was required for inhibition of [3H]cAMP accumulation. Desensitization of protein kinase C did not modify the inhibitory action of bradykinin on [3H]cAMP. Effects of Ca2+ on phosphodiesterase were also excluded in the present studies. The accumulated data are consistent with the hypothesis that hormonal mobilization of [Ca2+]i leads directly to the inhibition of cAMP accumulation in these cells and presumably in other cells that express the Ca2+-inhibitable form of adenylyl cyclase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1992.tb10992.x
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  • 3
    Electronic Resource
    Electronic Resource
    Synapsin II Phosphorylation and Catecholamine Release in Bovine Adrenal Chromaffin Cells: Additive Effects of Histamine and Nicotine (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 58 (1992), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Primary cultures of bovine adrenal medullary chromaffin cells can be stimulated with nicotine, which mimics the cholinergic stimulus from the splanchnic nerve. Histamine also stimulates catecholamine release in a time-and dose-dependent manner. We have previously shown that nicotine stimulates incorporation of 32Pi into the vesicle-associated phosphoprotein synapsin II. We report here that histamine, too, stimulates an increase in 32Pi incorporation into synapsin II, which is blocked by the H1-histamine receptor-specific antagonist pyrilamine. The time course of histamine-stimulated synapsin II phosphorylation closely paralleled that of histamine-stimulated catecholamine release. Interestingly, histamine and nicotine produced an additive increase in both catecholamine release and synapsin II phosphorylation, suggesting that these two secretogogues stimulate the phenomena via independent mechanisms. When we investigated the dependence of these two agonists on extracellular calcium, we found that nicotine-stimulated release and synapsin II phosphorylation were reduced to basal levels at low calcium concentrations. However, the histamine-stimulated effects remained significantly elevated. This suggests that calcium arising from two separate pools can stimulate catecholamine release and synapsin II phosphorylation in bovine chromaffin cells. Taken together, these data support the hypothesis that synapsin II phosphorylation is a component of the secretory response from these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1992.tb09741.x
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  • 4
    Electronic Resource
    Electronic Resource
    Surface polygonization on GaAs wafers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1468-1471 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polygonized surface structure produced by furnace annealing GaAs wafers was studied by optical and scanning electron microscopy. The surface structure was revealed by chemically etching wafers which had been implanted with silicon and subjected to a furnace annealing cycle. Cathodoluminescence micrographs demonstrate an absence of impurity segregation to the polygon boundaries. No correlation was found between growth-induced dislocations and the polygonal networks. It is proposed that the surface structure results from a vacancy-condensation process. Related surface effects were observed for rapidly annealed wafers. A correlation between the furnace annealed and rapidly annealed GaAs is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341819
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanisms of interdiffusion in copper/nickel thin-film couples (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1147-1155 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanisms of interdiffusion in copper/nickel thin-film couples have been investigated in the temperature interval 573–777 K by in situ measurement of contact resistance, Auger depth profiling (ADP), and transmission electron microscopy. Correlation between evolution of contact resistance and measured Auger concentration profiles has been established and mechanisms incorporating rapid grain boundary diffusion, followed by defect-assisted diffusion into grain interiors (Type B kinetics), are proposed to explain the accelerated reactions observed. A modified Whipple model and two independent methods, based on ADP and contact resistance measurements, are used to calculate grain boundary and intragranular diffusion coefficients, respectively. The calculated grain boundary diffusion coefficient is (0.82 cm2/s) exp(−1.48eV/kT) for nickel in copper, and approximately 4×10−13 cm2/s for copper in nickel at 673 K. An average intragranular diffusion coefficient for nickel in copper is determined to be (2.6×10−6 cm2/s) exp(−1.38 eV/kT) by both methods, whereas ADP data yield a corresponding value of (5.2×10−8 cm2/s) exp(−1.51eV/kT) for copper in nickel. It is concluded that characterization of chemical composition and microstructure, combined with in situ measurement of concomitant electrical properties, provides a reliable description of interdiffusion mechanisms in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336552
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  • 6
    Electronic Resource
    Electronic Resource
    An analysis of dislocation reduction by impurity hardening in the liquid-encapsulated Czochralski growth of 〈111〉 InP (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4383-4389 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Excessive impurity additions have been widely used to suppress dislocation generation in the liquid-encapsulated Czochralski (LEC) growth of InP. We have analyzed this approach by means of the quasi-steady-state heat transfer/thermal stress model. A strong motivation for the investigation was provided by the recent measurement of the critical resolved shear stress σCRS of InP as a function of temperature in the range 748–948 °K for several Ge and S concentrations. The experimental data were analyzed by the method of least squares via the usually accepted logarithmic dependence of σCRS on reciprocal temperature. The extrapolated values of σCRS exhibit a monotonic increase with impurity addition at temperatures near the melting point. Introducing the σCRS and realistic estimates of other physical properties (thermal diffusivity, thermal expansion coefficient, elastic constants, etc.) in the thermal stress model, the dislocation distribution pattern in a {111} substrate cut from a 〈111〉 boule was constructed. This necessitated a suitable recasting of the formalism that was previously applicable only to the {100} orientation. The computed dislocation contour maps on {111} wafers display sixfold symmetry resembling the "Star of David,'' in overall agreement with etch-pit patterns. InP crystals 2.5 cm in diameter grown in a standard high ambient temperature gradient but containing a large amount of Ge ((approximately-equal-to)1019 cm−3) are predicted and observed to be dislocation-free. On the other hand, in nominally undoped material a large density of defects is forecast, especially at the periphery, in line with the etchpit configuration. Intermediate doping levels (∼1017 cm−3 Ge, ∼1018 cm−3 S) reduce the density in the core but leave the outer edge essentially unaltered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335528
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  • 7
    Electronic Resource
    Electronic Resource
    Quasi-steady-state heat transfer/thermal stress model for dislocation generation in the vertical gradient freeze growth of GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4016-4022 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have formulated a tractable model of the vertical gradient freeze (VGF) process for GaAs, providing dislocation density contour lines in terms of geometrical and physical parameters. First, the temperature distribution in a cylindrical boule has been determined in closed form involving modified Bessel functions of the first kind, order zero (I0) by solving the quasi-steady-state partial differential equation for heat conduction. Subsequently, the principal thermoelastic stress components have been evaluated and then resolved in the {111}, 〈11¯0(approximately-greater-than) slip system which in excess of the critical resolved shear stress (CRSS) introduce dislocations by slip. We present dislocation density contour maps for 2- and 3-in.-diam undoped (100) GaAs grown by VGF under a variety of linear thermal gradients (v) imposed on the periphery of the boule. We show that for large v the dislocation distribution is similar to that observed in liquid-encapsulated Czochralski (LEC) material but lowering v effectively suppresses dislocation generation even in boules larger than 2 in. in diameter. A comparison of dislocation generation in VGF and standard LEC growth using very recent CRSS data is also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352868
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  • 8
    Electronic Resource
    Electronic Resource
    A comparison of reducing the dislocation densities in GaAs grown by the vertical gradient freeze and liquid-encapsulated Czochralski techniques (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 477-479 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have recently applied the quasi-steady state heat transfer/thermal stress model for dislocation generation to the vertical gradient freeze (VGF) process for GaAs, permitting a direct comparison with the original treatment of liquid-encapsulated Czochralski (LEC) growth. Very recent high temperature critical resolved shear stress (CRSS) data on undoped VGF and In-doped LEC specimens were used. We show that the ∼threefold increase in CRSS with In is sufficient to inhibit defect formation in the central ∼75% of 3 in. diameter LEC wafers grown in a high ambient temperature gradient, duplicating the etch-pit density (EPD) data. Undoped VGF wafers are predicted to be nearly dislocation-free. The theoretical results on 3 in. material track the low EPD counts in both the 〈100〉 and 〈110〉 directions in a 5 K/cm gradient imposed on the crystals' surface. We also discuss the origin of dislocations in regions free of thermal stresses and propose their suppression by the addition of a small amount of In in VGF experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353825
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  • 9
    Electronic Resource
    Electronic Resource
    Silicon-doping level dependent diffusion of Be in AlGaAs/GaAs quantum well lasers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4648-4654 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated Be diffusion during molecular beam epitaxial growth of GaAs/AlGaAs graded index separate confinement heterostructure laser structures using secondary ion mass spectrometry (SIMS). For growth at 700 °C we find that Be from the p-type AlGaAs cladding layer diffuses into the quantum well and beyond. As a result, the p-n junction is displaced from the heterojunction. The extent of Be diffusion is found to depend on the dopants in the graded index (GRIN) regions adjoining the GaAs active layer. When the GRIN segments are left intentionally undoped, Be diffuses through the entire p-side GRIN, the quantum well active and a significant portion of the n-side GRIN. However, when the GRIN regions are doped, respectively, with Be and Si on the p and n sides, the displacement of the p-n junction caused by Be diffusion is significantly reduced. Assuming that Be diffuses from a constant source at the surface into a n-type layer as a singly charged interstitial donor, our analysis predicts that increasing the doping of the n layer retards the diffusion of Be while that of the p layer enhances it. Further, including the electric field of the p-n junction in the model leads to peaks and inflections resembling those observed in the experimental SIMS profiles. In view of Be-related oxygen contamination and Be diffusion on the p-side GRIN region, Be should be dispensed with on the p side, however, Si addition on the n side is beneficial as it minimizes Be diffusion and p-n junction displacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352120
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of mononuclear and dinuclear bis(2,2'-bipyridine)ruthenium(II) complexes containing sulfur-donor ligands (1989)
    s.l. : American Chemical Society
    Inorganic chemistry 28 (1989), S. 912-920 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00304a023
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