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  • 1
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    Roles of bulk viscosity on Rayleigh-Taylor instability: Non-equilibrium thermodynamics due to spatio-temporal pressure fronts (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-09-07
    Description: Direct numerical simulations of Rayleigh-Taylor instability (RTI) between two air masses with a temperature difference of 70 K is presented using compressible Navier-Stokes formulation in a non-equilibrium thermodynamic framework. The two-dimensional flow is studied in an isolated box with non-periodic walls in both vertical and horizontal directions. The non-conducting interface separating the two air masses is impulsively removed at t = 0 (depicting a heaviside function). No external perturbation has been used at the interface to instigate the instability at the onset. Computations have been carried out for rectangular and square cross sections. The formulation is free of Boussinesq approximation commonly used in many Navier-Stokes formulations for RTI. Effect of Stokes’ hypothesis is quantified, by using models from acoustic attenuation measurement for the second coefficient of viscosity from two experiments. Effects of Stokes’ hypothesis on growth of mixing layer and evolution of total entropy for the Rayleigh-Taylor system are reported. The initial rate of growth is observed to be independent of Stokes’ hypothesis and the geometry of the box. Following this stage, growth rate is dependent on the geometry of the box and is sensitive to the model used. As a consequence of compressible formulation, we capture pressure wave-packets with associated reflection and rarefaction from the non-periodic walls. The pattern and frequency of reflections of pressure waves noted specifically at the initial stages are reflected in entropy variation of the system.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Colloids exposed to random potential energy landscapes: From particle number density to particle-potential and particle-particle interactions (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-07-29
    Description: Colloidal particles were exposed to a random potential energy landscape that has been created optically via a speckle pattern. The mean particle density as well as the potential roughness, i.e., the disorder strength, were varied. The local probability density of the particles as well as its main characteristics were determined. For the first time, the disorder-averaged pair density correlation function g (1) ( r ) and an analogue of the Edwards-Anderson order parameter g (2) ( r ), which quantifies the correlation of the mean local density among disorder realisations, were measured experimentally and shown to be consistent with replica liquid state theory results.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry studies of YBa2Cu3O7−δ deposited on SrTiO3 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 8272-8276 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric function ε=ε1−iε2 of the YBa2Cu3O7−δ high-Tc superconducting films grown on (100) SrTiO3 (c-axis oriented) and (110) SrTiO3 (ab-oriented) substrate was measured by spectroscopic polarization modulation ellipsometry (SPME) and changes in film orientation were studied by comparing films of various thicknesses. The films deposited on SrTiO3 (100) substrates demonstrated an isotropic ε1 that changed with film thickness. It is observed that the decrease in the metallic dielectric behavior associated with the increase in the thickness of the films grown on (100) SrTiO3 substrates is mainly due to a change in the orientation of the films. The films deposited on SrTiO3 (110) showed anisotropic dielectric behavior when the plane of polarization is parallel and perpendicular to the c-axis of the film. These studies show that for this high-temperature superconductor with anisotropic dielectric behavior, SPME is a highly sensitive technique capable of measuring small changes in the film orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347435
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  • 4
    Electronic Resource
    Electronic Resource
    Schottky diodes using poly(3-hexylthiophene) (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2957-2958 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier diodes have been fabricated using poly(3-hexylthiophene)(P3HT) as the semiconductor and indium as the metal. P3HT was doped with FeCl3 at room temperature to form a p-type semiconductor. The Schottky junctions of In on FeCl3-doped P3HT using pressure contact exhibit rectification ratios ranging from 104:1 to 106:1 at a bias of ±1 V.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355319
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  • 5
    Electronic Resource
    Electronic Resource
    Current density dependence of the activation energy in type II superconductors (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 592-595 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have conducted magnetic relaxation experiments to calculate the effective activation energy, U, as a function of critical current density. We have shown that, from the nonlinearity of U, one can explain the nonlogarithmic decay of magnetization in type II superconductors. The nonlinearity of U was considered by expanding U about a current density, J0. The coefficients of expansion were determined experimentally and were used to develop the relationship between U and J for both conventional type II superconductors (Nb3Sn filamentary) and high-Tc superconductors (YBa2Cu3O7−δ and Bi2Sr2CaCu2Oy single crystals). Both types of superconductor were observed to behave in similar fashion. We have also calculated U0 using the standard formulas and the intercepts of the tangent of the U vs M curve and have found the results to be comparable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351837
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  • 6
    Electronic Resource
    Electronic Resource
    Diatomic molecules, rotations, and path-integral Monte Carlo simulations: N2 and H2 on graphite (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6031-6051 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational motion of homonuclear diatomic molecules confined to two dimensions at finite temperatures is discussed within the framework of path-integral Monte Carlo (PIMC) techniques. For single rotators the symmetry restriction on the total wave function coupling nuclear spin and rotations of these diatomic molecules is carried over to PIMC for fermionic and bosonic diatomic molecules. Three experimentally relevant quantum statistical averages are formulated, and quantum effects due to discrete level spacing and exchange are separated with the help of these averages. The method is applied to single N2 and H2 rotators adsorbed on graphite in the frozen-in crystal field which is due to the commensurate ((square root of)3×(square root of)3)R30° "2-in'' herringbone phase. Contrary to H2, exchange effects are negligible for N2 in the relevant temperature range. The resulting sign problem for certain combinations of molecule and averaging procedure is discussed. PIMC simulations of the phase transition from the translationally (square root of)3-ordered and orientationally disordered phase to the herringbone phase were carried out for complete N2 monolayers without a symmetry restriction on the wave function. Due to dispersive quantum fluctuations, transition temperature and ground-state order parameter are depressed by roughly 10% as compared to classical MC simulations of the same realistic model. In addition, the PIMC results are compared to quasiharmonic and quasiclassical approximations. The quasiharmonic treatment yields the correct order parameter suppression, the quasiclassical simulation the lowering of the transition temperature, but only the full quantum PIMC simulations describe the entire temperature range of interest correctly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466186
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  • 7
    Electronic Resource
    Electronic Resource
    A vacuum gauge using positive temperature coefficient thermistor as the sensor (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4670-4673 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A vacuum gauge has been designed and fabricated using a new type of sensor element, the semiconducting barium titanate positive temperature coefficient (PTC) thermistor. It covers a much wider range and better resolution compared to conventional Pirani gauge and other thermistor vacuum gauges particularly in the low vacuum levels due to its extreme high temperature coefficient. The details of design criteria of the instrument and its performance characteristics have been discussed. Due to the unique autocurrent limiting and stabilizing capabilities of a PTC thermistor, the fabrication of the instrument appears to be much cheaper. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287619
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  • 8
    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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  • 9
    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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  • 10
    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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