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  • 1
    Electronic Resource
    Electronic Resource
    Surface Phosphorylation by Ecto-Protein Kinase C in Brain Neurons: A Target for Alzheimer's β-Amyloid Peptides (1995)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 65 (1995), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The powerful regulatory machinery of protein phosphorylation operates in the extracellular environment of the brain. Enzymatic activity with the catalytic specificity of protein kinase C (PKC) was detected on the surface of brain neurons, where it can serve as a direct target for neurotrophic and neurotoxic substances that control neuronal development and cause neurodegeneration. This activity fulfilled all the criteria required of an ectoprotein kinase (ecto-PK). Detailed analysis of surface protein phosphorylation in cultured brain neurons using specific exogenous substrates (casein, histones, and myelin basic protein), inhibitors (PKC-pseudosubstrate 19–36; K252b) and antibodies (anti-PKC catalytic region M.Ab.1.9, antibodies to the carboxy-terminus of eight PKC isozymes) revealed several types of ecto-PK activity, among them ecto-PKs with catalytic specificity of the PKC isozymes ζ and δ. The activity of the neuronal ecto-PKC is constitutive and not stimulated by phorbol esters. The phosphorylation of a 12K/13K surface protein duplex by ecto-PKC-δ was found to be developmentally regulated, with peak activity occurring during the onset of neuritogenesis. Alzheimer's amyloid peptides β1–40 and β25–35 applied at neurotrophic concentrations stimulated the phosphorylation of endogenous substrates of ecto-PKC activity in brain neurons but inhibited specifically this surface phosphorylation activity with the same dose-response relationships that cause neurodegeneration. As may be expected from a relevant pathophysiological activity, β-amyloid peptide 1–28 did not inhibit this surface phosphorylation. The discovery that ecto-PKC-mediated protein phosphorylation serves as a target for β-amyloid peptides at the very site they operate, i.e., at the neuronal cell surface, opens a new research direction in the investigation of molecular events that play a role in the etiology of developmental disabilities and neurodegenerative disorders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1995.65052022.x
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  • 2
    Electronic Resource
    Electronic Resource
    Scanning tunneling microscopy theory for an adsorbate: Application to adenine adsorbed on a graphite surface (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 7814-7824 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An expression is obtained for the current in scanning tunneling microscopy (STM) for a single adsorbate molecule. For this purpose the "Newns–Anderson'' treatment (a "discrete state in a continuum'' treatment) is used to obtain wave functions and other properties of the adsorbate/substrate system. The current is expressed in terms of the adsorbate–tip matrix elements, and an effective local density of states of the adsorbate/substrate system, at the adsorbate. As an example, the treatment is applied to the STM image of adenine adsorbed on a graphite surface, and the results are compared with experiment. The dependence of the image on the position of adenine with respect to the underlying graphite is considered. A discussion is given of the type of experimental STM data needed for suitable comparison of theory and experiment. In an analysis of the calculations, the role of each atom, its neighbors, next nearest neighbors, etc., in an adsorbed molecule is considered. The need for using in the present calculation more orbitals than only the HOMO and the LUMO of the adsorbate is also noted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466824
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  • 3
    Electronic Resource
    Electronic Resource
    Room-temperature optical transitions in Mg-doped cubic GaN/GaAs(100) grown by metalorganic chemical vapor deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2064-2066 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of room-temperature optical transitions in a Mg-doped cubic GaN epilayer grown on GaAs(100) by metalorganic chemical vapor deposition has been investigated. By examining the dependence of photoluminescence on the excitation intensity (which varied over four orders) at room temperature, four different emissions with different origins were identified. A blue emission at ∼3.037 eV was associated with a shallow Mg acceptor, while three different lower-energy emissions at ∼2.895, ∼2.716, and ∼2.639 eV were associated with a deep Mg complex. In addition to a shallow acceptor at E≅0.213 eV, three Mg-related deep defect levels were also found at around 215, 374, and 570 meV (from the conduction band). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372139
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  • 4
    Electronic Resource
    Electronic Resource
    A theoretical model of scanning tunneling microscopy: Application to the graphite (0001) and Au(111) surfaces (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7565-7573 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An expression for the scanning tunneling microscopy (STM) current between the tip and sample is presented using first-order perturbation theory for a two-Hamiltonian formalism ("reactants'' and "products''). The calculated STM current depends on the square of the sample-tip matrix elements, averaged over a selection of random points in wave vector space. In the limit of low voltage and temperature, this averaging is over the Fermi surface of the sample. The model is applied to the graphite (0001) and Au(111) surfaces using a simple model (chain) of a tungsten tip and the tight-binding approximation. Comparisons with experiments and with the result for graphite obtained by Tersoff and Lang using a molybdenum tip are given. The theory is applied elsewhere to STM of adsorbates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464696
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  • 5
    Electronic Resource
    Electronic Resource
    Surface properties of solids using a semi-infinite approach and the tight-binding approximation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7405-7411 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A semi-infinite approach (rather than a slab method or finite number of layers) is used to treat surface properties such as wave functions, energy levels, and Fermi surfaces of semi-infinite solids within the tight-binding (TB) approximation. Previous single-band results for the face-centered cubic lattice with a (111) surface and for the simple cubic lattice with a (001) surface are extended to semi-infinite layers, while the extension to calculations of other surfaces is straightforward. Treatment of more complicated systems is illustrated in the calculation of the graphite (0001) surface. Four interacting bands are considered in the determination of the wave functions, energies, and Fermi surface of the graphite (0001) surface. For the TB model used, the matrix elements in the secular determinants for the semi-infinite solid and for the infinite bulk solid obey the same expressions, and the wave functions are closely related. Accordingly, the results for the bulk system can then be directly applied to the semi-infinite one. The main purpose of the present paper is to provide wave functions and other properties used elsewhere to treat phenomena such as scanning tunneling microscopy and electron transfer rates at electrodes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465096
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  • 6
    Electronic Resource
    Electronic Resource
    High p-type conductivity in cubic GaN/GaAs(113)A by using Be as the acceptor and O as the codopant (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2707-2709 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: P-type room-temperature conductivities as high as 50/Ω cm are achieved in cubic GaN layers by the concept of reactive codoping. We use Be as the acceptor species and O as the reactive donor to render isolated Coulomb scatterers into dipole scatterers. This concept allows us to achieve high hole mobilities and thus p-type conductivities. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117685
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  • 7
    Electronic Resource
    Electronic Resource
    Cubic-phase GaN light-emitting diodes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2498-2500 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The feasibility of growing device-quality cubic GaN/GaAs(001) films by metal organic chemical vapor deposition has been demonstrated. The optical quality of the GaN films was characterized by room-temperature photoluminescence measurements, which shows a full width at half maximum of 46 meV. The structural quality of the films was investigated by transmission electron microscopy. There are submicron-size grains free from threading dislocations and stacking faults. More importantly, a cubic-phase GaN blue light-emitting diode has been fabricated. The device process, which is very simple and compatible with current GaAs technology, indicates a promising future for the blue light-emitting diode. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123019
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  • 8
    Electronic Resource
    Electronic Resource
    Optimized growth conditions for the epitaxial nucleation of β-GaN on GaAs(001) by molecular beam epitaxy (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 473-475 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin (5–7 monolayers) nucleation layers of GaN are deposited on (2×4)-GaAs(001) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction applied in situ reveals these layers to be epitaxial β-GaN. Transmission electron microscopy confirms this result and reveals in addition that the layers are highly connected and have an atomically abrupt interface to the GaAs substrate. The rms roughness of these layers, as measured by atomic force microscopy, is as low as 1.4 Å. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119583
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  • 9
    Electronic Resource
    Electronic Resource
    Optical characterization of high-purity cubic GaN grown on GaAs (001) substrate by metalorganic chemical vapor deposition (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3025-3027 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical properties of cubic GaN films have been investigated in the temperature range of 10–300 K. Five peaks were observed at 10 K. From the dependence of photoluminescence emissions on the temperature and excitation intensity, we have assigned two of the five peaks (2.926 and 2.821 eV) to donor–acceptor pair (DAP) transitions. Furthermore, these two peaks were found to be related to a common shallow donor involved in the peak position previously reported at 3.150 eV. The intensities of DAP transitions were much weaker than that of excitonic emission even at low temperature, indicating a relatively high purity of our samples. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126567
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  • 10
    Electronic Resource
    Electronic Resource
    Risk Exposures and International Diversification: Evidence from iShares (2005)
    Oxford, UK; Malden, USA : Blackwell Publishing Ltd/Inc.
    Journal of business finance & accounting 32 (2005), S. 0 
    Details
    ISSN: 1468-5957
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: Abstract:  We examine the newly developed international diversification instruments–iShares traded on the American Stock Exchange. Given the fact that iShares can be created and redeemed at will, the daily price of an iShare is expected to be equal to the daily portfolio value of the underlying assets in the home-country market. Therefore, theoretically, iShare pricing should be influenced by the risk from the iShare's home-country market and not the risk from the US market, per se. We evaluate the risk exposure of iShare prices to the US market (non-fundamental effect) as well as the home-country market (the fundamental effect). We find that most iShare returns are significantly influenced by and sensitive to the US market risk. Moreover, the US market appears to be the key permanent driving factor and the home-country market is a pronounced transitory driving force for iShare prices. These findings indicate the presence of limits of international arbitrage for iShares. As a result, the international diversification benefits of iShares become questionable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0306-686X.2005.00612.x
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