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  • 1
    Electronic Resource
    Electronic Resource
    Photoinduced molecular transformations. Part 107. A versatile substitution of a carbonyl group of steroidal ketones by a heteroatom. The synthesis of aza-, oxa-, thia-, selena-, and tellurasteroids (1990)
    s.l. : American Chemical Society
    The @journal of organic chemistry 55 (1990), S. 2170-2176 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00294a035
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of defect scattering on guided electron waves in two coupled quantum wires (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2299-2311 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated how the presence of a defect in two coupled quasi-one-dimensional quantum wires influences the propagation properties of guided electron waves in the system. The defect potential in the two dimensional electron gas is modeled by a two dimensional δ function. In elastic scattering, the transfer of the electron among various eigenstates of the uncoupled quantum wires and from one wire to the other is largely affected by the defect potential. For the single mode shallow potential well system, the defect causes incomplete energy transfer between the channels. As the position of the defect varies along the channel, the characteristics of the mode amplitude functions change dramatically as the defect passes through nodes of the amplitude function of the incident waves in the channel. When the defect position is away from these nodes the amplitude functions of the transmitted waves reduce greatly due to the large reflection by the defect. And their variation never reaches zero as in the case without defect. When the defect position is near these nodes the tunneling characteristics between the two channels are as if the defect is absent since the reflection is minimal. For the strong scatterer we find a pinning effect in that the mode amplitude function of the channel where the defect is located always has one of its transmission minima pinned down to the defect. We introduce a possible way of injecting the propagating electron into a particular channel and at a given longitudinal position, by controlling the position of the defect in the structure. In the multimode deep potential well structure, the transfer from an eigenstate of the uncoupled quantum wires to the other states is greatly enhanced and the characteristics of the amplitude functions are dramatically changed by intersubband scatterings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351572
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  • 3
    Electronic Resource
    Electronic Resource
    The first-order Jahn–Teller distortion and the symmetry of the electron density in the BH+3 radical (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1232-1239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Self-consistent field (SCF) and complete active space multiconfiguration (CAS-MCSCF) calculations with extended basis sets are used to show that the electron–nuclear attraction energy is the dominant contributor to the total energy lowering associated with the Jahn–Teller distortion of BH+3. Furthermore the Jahn–Teller distortion raises the interelectronic and internuclear repulsion energies. These observations are consistent with a contraction of the molecular framework and electron cloud. In the context of the relationship between the electron distribution and the Jahn–Teller distortion direction, it is observed that the electron density associated with the canonical highest occupied molecular orbital (HOMO) of the D3h constrained BH3 radical has C2v symmetry, which corresponds to the preferred point group of the Jahn–Teller distortion in BH+3. The effect of electron correlation on the electron density distribution is shown to be inconsequential for the prediction of the direction of the Jahn–Teller distortion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462873
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  • 4
    Electronic Resource
    Electronic Resource
    Application of the thermodynamic cycle perturbation method to systems with nonadditive potentials (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2762-2768 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have extended the thermodynamic perturbation cycle approach to compute thermodynamic properties of systems with nonadditive potentials. A rapid iterative method was developed and tested by application to systems of water microclusters of alkali metal cations and halogen anions interacting by means of a model potential incorporating polarization. The perturbation cycle calculations are in agreement with the results of direct calculation as long as both initial and final microclusters are unambiguously stable. For marginally stable cationic microclusters, e.g. Rb(H2O)+6 or Cs(H2O)+5, the perturbation cycle approach appears to provide more reliable estimates of thermodynamic properties. Transmutation entropy estimates entail substantial uncertainty, even for transitions between stable microclusters. They are in fair agreement with those of other theoretical studies but differ noticeably from the experimental values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458915
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  • 5
    Electronic Resource
    Electronic Resource
    Wetting transitions in polymer blends: A Monte Carlo lattice simulation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8537-8541 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Wetting transitions of binary polymer mixtures in contact with a wall were studied using lattice models by the method of Monte Carlo simulation. First-order wetting transitions were found below the critical temperature but at a moderately high volume fraction of the polymer type favored by the wall. The transitions appear to be second order at low temperatures or for short chain lengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460087
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  • 6
    Electronic Resource
    Electronic Resource
    Random sequential adsorption: Series and virial expansions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8252-8257 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce an operator formalism for random sequential adsorption on lattices and in continuous space. This provides a convenient framework for deriving series expansions for the deposition rate dθ/dt in powers of t. Several specific examples—the square lattice with nearest-neighbor exclusion, and with exclusion extended to next-nearest neighbors, and disks and oriented squares on the plane—are considered in detail. Precise estimates for θ(t) and the jamming coverage are obtained via Padé approximant analysis. These are found to be in excellent agreement with simulation results. A diagrammatic expansion for dθ/dt is derived, and its relation to the equilibrium Mayer series is elucidated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460109
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  • 7
    Electronic Resource
    Electronic Resource
    The realizations of quantum groups of An−1 and Cn types in q-deformed oscillator systems at classical and quantum levels (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 3241-3245 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In the classical q-deformed oscillators system, the Poisson bracket realizations of the quantum enveloping algebras of An−1 and Cn types are given in the symplectic space (V,Ω) (without deformation). When the oscillators system is canonically quantized, the Lie bracket realizations of the quantum enveloping algebras of An−1 and Cn types are obtained. The Hopf structures of these quantum enveloping algebras are supplied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529484
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  • 8
    Electronic Resource
    Electronic Resource
    Nonlinear I–V characteristics of a mesoscopic conductor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5094-5102 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a general theoretical formulation, based on nonequilibrium Green's functions, for nonlinear dc transport in multiprobe mesoscopic conductors. The theory is gauge invariant and is useful for the predictions of current–voltage characteristics and the nonequilibrium charge pileups inside the conductor. We have provided a detailed comparison between the gauge invariant scattering matrix theory and our theory. We have also given several examples where the I–V curve can be obtained analytically. The effects of exchange and correlation have been considered explicitly. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371485
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  • 9
    Electronic Resource
    Electronic Resource
    Magnet enhanced optical falling needle/sphere rheometer (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2315-2321 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A magnet enhanced falling needle/sphere rheometer equipped with a precision optical monitor and signal feedback system has been developed. The instrument which utilized the basic features of a magnetic sphere/needle rheometer could be controlled using a PC/AT(286) computer. The important advantages of this instrument over existing falling needle/sphere viscometers are as follows: (1) An extremely large viscosity range from the usual solvent viscosity (say, ∼1.0 cP) to that of polymer melts (say, 1010 cP) is available with an experimental precision of (approximately-less-than)1%. (2) The measurement time could be reduced by about 4 orders of magnitude (e.g., from hours to seconds) for a high viscosity fluid. (3) One single needle/sphere could cover a few orders of the viscosity range and two needles with appropriate densities could cover the whole viscosity range (1 cP(approximately-less-than)η(approximately-less-than)1010 cP). (4) Only a small amount (∼4 mL with the present setup) of sample is needed. (5) The sample chamber can be sealed hermetically and is suitable for toxic fluids. (6) The instrument permits measurements of the shear rate dependence of viscosity using a single needle/sphere. (7) For nonNewtonian fluids, the viscoelastic behavior could be measured. A set of viscosity standards was used to calibrate the device. Linear calibration curves of viscosity against the reciprocal of the falling needle velocity under both natural gravity field and fixed artificial magnetic fields were obtained. A flow curve was determined for a random copolymer solution using a single needle but varying the magnetic field, showing the applicability of the device for measuring the rheological properties of polymer solutions and melts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143156
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  • 10
    Electronic Resource
    Electronic Resource
    Phosphatase Activity Toward Abnormally Phosphorylated τ: Decrease in Alzheimer Disease Brain (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: Microtubule-associated protein τ is abnormally hyperphosphorylated and aggregated in affected neurons of Alzheimer disease brain. This hyperphosphorylated τ can be dephosphorylated at some of the abnormal phosphorylated sites by purified protein phosphatase-1, 2A, and 2B in vitro. In the present study, we have developed an assay to measure protein phosphatase activity toward τ-1 sites (Ser199/Ser202) using the hyperphosphorylated τ isolated from Alzheimer disease brain as substrate. Using this assay, we have identified that in normal brain, protein phosphatase-2A and 2B and, to a lesser extent, 1 are involved in the dephosphorylation of τ. The Km values of dephosphorylation of the hyperphosphorylated τ by protein phosphatase-2A and 2B are similar. The τ phosphatase activity is decreased by ∼30% in brain of Alzheimer disease patients compared with those of age-matched controls. These findings suggest that a defect of protein phosphatase could be the cause of the abnormal hyperphosphorylation of τ in Alzheimer disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1995.65020732.x
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