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  • 1
    Electronic Resource
    Electronic Resource
    Theory of universal fast orientational dynamics in the isotropic phase of liquid crystals (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4193-4202 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical treatment is presented that demonstrates universal dynamical behavior in the isotropic phase of liquid crystals on ultrafast time scales and short distance scales. The theoretical development generates a temperature independent power law for the short time scale decay of the molecular orientational correlation function. This provides a theoretical rationale for the postulate of universal behavior based on recent experimental observations on two liquid crystal systems. A temperature independent power law decay with the identical exponent, 0.63, was observed for the two systems. First, an alternative theoretical approach reproduces the Landau de Gennes results for the long distance scale, slow time scale orientational dynamics in the isotropic phase. This approach is also capable of examining the short distance scale and short time scale dynamics, and yields a temperature independent power law decay with exponent 0.5. Then critical correlations of fluctuations and local symmetry considerations are included. The Ising model of critical systems is employed. This detailed analysis yields the experimentally observed exponent, 0.63, without recourse to adjustable parameters. Modern theories of dynamic critical phenomena like dynamic scaling theory, the kinetic Ising model and the stochastic model of Karder–Parisi–Zhang are considered as alternative approaches. While these theories can generate some of the features found in experiment, it is not possible to reproduce the observed experimental results without internal inconsistencies or unwarranted adjustable parameters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469467
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  • 2
    Electronic Resource
    Electronic Resource
    Method for producing neutral and negative hydrogen particles applicable to hot plasma diagnosis (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 2158-2162 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method is described whereby a beam of positive hydrogen ions incident at grazing angles on an array of cesium-covered tungsten foils is used to produce H0 and H− particles by negative surface ionization. The results of these experiments indicate that the method can provide diagnostic beams of particles to hot plasmas and can also energy-analyze charge exchange neutrals emerging from hot plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139979
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  • 3
    Electronic Resource
    Electronic Resource
    Electron binding energy and long-range electronic coupling: A theoretical study (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9888-9896 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic couplings in long-range electron transfer have been calculated using ab initio molecular orbital theory to investigate the effect of the binding energy of the electron on the decay of through-space and through-bond couplings. Through-space and through-bond couplings for anions and cations of the CF3 dimer and of CnH2n and CnF2n chains were calculated by ab initio molecular orbital theory. The anions and cations provide systems for which the electron binding energies, Be, differ by about a factor of 10. Through-space couplings decay exponentially, exp(−βR), with increasing distance, R, between the donor/acceptor carbon atoms. The decay coefficient β varies approximately as B1/2e. In contrast, the decay coefficients for through-bond coupling in CnF2n and CnH2n chains are not affected significantly by the binding energy of the electron. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471753
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanism of NH2+CO2 formation in OH+HNCO reaction: Rate constant evaluation via ab initio calculations and statistical theory (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9703-9707 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Portions of the [CH2NO2] potential energy surface related to the OH+HNCO reaction were calculated by means of ab initio molecular orbital theory at the QCISD(T)/6-311++G(d,p) level based on UMP2/6-31G(d,p) optimized geometries. Of all possible three channels considered, the hydrogen abstraction turns out to be the dominant reaction channel. The addition to C atom requires activation energy slightly larger than that of the abstraction but smaller than that of the N addition, in contrast to the H+HNCO reaction. The structural and energetic parameters for the channels thus characterized were further utilized for the calculation of rate constants in the framework of a quantum statistical theory (QRRK). The contributions of the individual reaction channel towards the total rate constant have been examined. Although the OH+HNCO→NH2+CO2 reaction is more exothermic than the hydrogen abstraction OH+HNCO→H2+NCO, it is confirmed that rate constant for CO2 loss is much lower than that of H2O-elimination. The standard heat of formation of the adduct HNC(OH)O is estimated to be ΔHf298=−41.1±3 kcal/mol. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474090
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  • 5
    Electronic Resource
    Electronic Resource
    Field-induced phase switching and electrically driven strains in sol-gel derived antiferroelectric (Pb,Nb)(Zr,Sn,Ti)O3 thin layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1171-1177 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tin-modified lead zirconate titanate thin layers were prepared by a sol-gel method. A room- temperature antiferroelectric (AFE) phase composition Pb0.99Nb0.02[(Zr0.58Sn0.42)0.96Ti0.04] 0.98O3 was prepared and examined for weak- and high-field dielectric properties as a function of temperature, with emphasis on field-induced AFE-ferroelectric (FE) switching characteristics. Thin layers processed with a lead oxide cover coat were found to be free of any secondary phases and showed improved properties. Room-temperature values of dielectric constant K'=390 and saturation polarization Ps=20 μC/cm2 were obtained with field-induced strains up to 0.15% in submicron grain structures. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360353
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of extremely fine Y2BaCuO5 precipitates on the critical current density of melt-processed YBa2Cu3Ox (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 7396-7408 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on previously developed melt processing methods, Y2BaCuO5 (211) precipitates with various size were obtained in YBa2Cu3Ox (123). In particular, a wide distribution of 211 size from 100 Å to 10 μm has been found to exist in the matrix of 123, and strongly effected the critical current density, Jc. An enhancement of Jc was always found to be associated with the presence of extremely fine 211 precipitates. The flux pinning by these precipitates can be understood by considering the interaction of flux lines with cavities. It was found that although the flux lines are strongly pinned by cavities, the effectiveness decreases with the increasing number of flux lines trapped by them. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365280
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  • 7
    Electronic Resource
    Electronic Resource
    Red shifting the intersubband response of quantum-well infrared photodetectors by thermal annealing (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4737-4740 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Selectively red shifting the photoresponse of intersubband GaAs/Al0.25Ga0.75As multiple-quantum-well (MQW) infrared photodetectors (QWIPs) by furnace and rapid thermal annealing is explored. Selective interdiffusion of the MQW is achieved by dielectric encapsulating (SiO2 or Si3N4) the surface. The high dark current of annealed QWIPs is attributed to dopant out-diffusion from the QWs into the barriers. Declining responsivities result from reduced carrier density in the QW and a red shift of the intersubband transition energy. In this work, the intersubband energy is determined by the Fourier synthesis model and compared with experimental results (further confirming the interdiffusion mechanism). Minimal dark current and responsivity degradation is observed for Si3N4-encapsulated QWIPs red shifted by 1 μm © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363456
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  • 8
    Electronic Resource
    Electronic Resource
    A Green's function approach to third-order elastic constants of disordered solids (1986)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 2807-2812 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Starting from a Lippmann–Schwinger-type equation, which is very similar to that of quantum mechanical multiple scattering theory, Zeller and Dederichs [Phys. Status Solidi B 55, 831 (1973)] have developed the effective medium theory. This theory has found wide application in understanding the mechanical behavior of disordered solids. However, unlike the problem in quantum mechanics, this equation of the random elasticity is only approximate since this is a linear response theory. So, it is proposed in this work for the first time to go beyond this approximation to treat nonlinear properties of such solids of which the third-order elastic constant is a generic. Again, so far as the nonlinear elastic behavior of these solids is concerned, no work has been done except the simple Voigt- and Reuss-type averaging. Both are extreme approximations and are, moreover, known to lead to violation of the equilibrium condition. The salient feature of the present calculation is to get an exact formal solution of the problem in terms of an appropriate Green's function in a closed form. The result obtained is quite general and may be adopted to treat nonlinearity in any tensor property of disordered materials. Finally several approximations, including a self-consistent solution, have been discussed for obtaining the effective nonlinear static mechanical susceptibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527256
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  • 9
    Electronic Resource
    Electronic Resource
    Two-dimensional turbulent boundary layers over rigid and moving swept wavy surfaces (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 964-970 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The two-dimensional, incompressible, turbulent boundary layer over a flexible wall is analyzed. The wall consists of sinusoidal waves that are swept with respect to the flow direction. The mean flow is a boundary layer with wave-induced stresses. These stresses are evaluated from the solution of the linear problem. It is found that the small mean skin friction reduction, observed for the case of zero sweep, persists. The pressure drag reduces for swept wavy wall from its value for no sweep. There is a small drag reduction for the moving wall cases even for the lowest phase speed considered. Within the assumptions of the turbulence model used, a possible drag reduction mechanism is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865691
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  • 10
    Electronic Resource
    Electronic Resource
    Improved circular polarizer for far-infrared lightpipe systems (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 5559-5562 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present an improved design for far-infrared (FIR) circular polarizers used in a lightpipe transmission system for magneto-optical experiments. A peak efficiency of nearly 100% is achieved for FIR laser radiation by reducing the multiple reflections within the polarizer system, as well as scattering from the walls of the lightpipe. Broadband low-resolution measurements are less susceptible to errors due to multiple reflections, but incorporation of these improvements is still found to reduce systematic errors due to the reflection from the sample. Also, we have measured the low temperature index of refraction of quartz and find significant disagreement with published values for frequencies below 100 cm−1. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146084
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