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  • 1
    Electronic Resource
    Electronic Resource
    Self diffusion of nuclear spins in a porous medium with a periodic microstructure (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3041-3054 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Fourier approach is developed for evaluating the diffusion eigenstates and the diffusion propagator of a periodic, fluid filled porous medium, and is applied to the calculation of the pulsed-field-gradient-spin-echo amplitude M(k,t). The method is most effective for long times t, but works quite well down to times that are short enough so that asymptotic short time approximations of the diffusion process are still valid. The main advantage of the method is that it is applicable regardless of the value of the porosity or the shape of the periodic pore space. It is used to calculate M(k,t) for a number of examples of periodic porous media with porosities as low as 10%. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468614
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  • 2
    Electronic Resource
    Electronic Resource
    Quasi-static electrical resonances and optical bistability in periodic composite materials (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4263-4273 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A variational approach is used to examine the possibility of bistable behavior in a two-component metal-dielectric composite medium with a periodic microstructure where one component has a Kerr- type field dependent part in the dielectric constant ε while the field independent part of ε in both materials is in general complex. It is shown that under certain conditions bistable behavior can occur even though the field dependent nonlinearity is weak everywhere. This is achieved by operating the material sufficiently close to one of its sharp quasi-static, microgeometric electrical resonances. The physical characteristics of the threshold intensity are worked out and considerations made on how to optimize the chances for observing optical bistability in such a material. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359483
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  • 3
    Electronic Resource
    Electronic Resource
    Field-induced tuning of the optical properties of nonlinear composites near resonance (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1431-1435 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bulk effective dielectric function of metal-dielectric composites has a series of poles in the vicinity of which it is extremely sensitive to small changes in the properties of the components. It is possible to induce such a change in the nonlinear component of a composite, containing at least one nonlinear component, by applying an external electric field at a similar frequency. This causes a tuning of the effective dielectric function and a continuous alteration of the optical properties of the medium. We propose a general framework for calculating this effect in two component composites and also calculate it in a few three component microgeometries. It is found that the optical transmittance of a thin film of this kind can be changed from zero up to 80% using moderate electric fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357747
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular diffusion in periodic porous media (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 1704-1711 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusion of fluid through a porous medium was modeled for a periodic array. The time dependent bulk effective diffusion coefficient D(t) was calculated using Bloch type eigenfunctions. The calculations were made for periodic media composed of octahedron-like obstacles which ranged from completely separated to highly overlapping obstacles (porosity of 3%). The calculation of D(t) involves evaluation of the nuclear magnetic resonance pulsed field gradient spin echo amplitude M(k,t), which is a measurable quantity. The method, which is most effective for long times, produces results which also agree with short time asymptotics. This method is applicable for any periodic microgeometry and virtually any porosity. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372081
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  • 5
    Electronic Resource
    Electronic Resource
    Enhancement of thermoelectric power factor in composite thermoelectrics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 8205-8216 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The analytical properties of macroscopic transport coefficients of two-component composites are first used to discuss the thermoelectric power factor of such a composite. It is found that the macroscopic power factor can sometimes be greater than the power factors of both of the pure components, with the greatest enhancement always achieved in a parallel slabs microstructure with definite volume fractions for the two components. Some interesting examples of actual mixtures are then considered, where the components are a "high quality thermoelectric" and a "benign metal," leading to the conclusion that considerable enhancement of the power factor is often possible, with but a modest reduction in the thermoelectric figure of merit, compared to those of the high quality thermoelectric component. Two possibilities for fabricating real composites with such improved thermoelectric properties emerge from this study: a parallel slabs microstructure of benign metal and high quality thermoelectric, and a sintered collection of benign metal grains, each of them coated by a thin shell of high quality thermoelectric. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370660
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  • 6
    Electronic Resource
    Electronic Resource
    Fluid flow in a random porous medium: A network model and effective medium approximation (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1616-1621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fluid flow through a random porous medium is discussed in the context of a network model of a diluted array of planar cracks by an effective medium approximation. We find the threshold concentration of cracks pc above which flow occurs. It turns out to be much higher than the bond percolation threshold. The existing cracks are assumed to have a range of thicknesses. The flow permeability is found as a function of the concentration for a number of crack thickness distributions. Near the threshold, anomalous critical behavior, in the form of a nonuniversal critical exponent for the permeability, is found to occur even for a family of nonsingular thickness distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339585
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  • 7
    Electronic Resource
    Electronic Resource
    Thermoelectric properties of a composite medium (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6821-6833 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the thermoelectric properties of a composite medium. Various approximations are developed for calculating the matrix Qˆe of the bulk effective transport coefficients of the medium, including exact upper and lower bounds for Qˆe under various conditions. Results are especially detailed for two-component composites, where a field decoupling transformation is used to reduce the thermoelectric problem to two uncoupled quasi-conductivity problems. Exact bounds are then obtained for the absolute thermopower αe and the thermoelectric figure of merit Ze in two-component composites. We prove that Ze of the composite can never exceed the largest value of Z in any component. Some of these results are extended to certain classes of multicomponent composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349830
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  • 8
    Electronic Resource
    Electronic Resource
    Bose-Einstein condensation in one- and two-dimensional gases (1974)
    Springer
    Journal of statistical physics 10 (1974), S. 299-319 
    Details
    ISSN: 1572-9613
    Keywords: Bose-Einstein condensation ; phase transition ; helium thin films ; one-dimensional systems ; two-dimensional systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that the one- and two-dimensional ideal Bose gases undergo a phase transition if the temperature is lowered at constant pressure. At the pressure-dependent transition temperature Tc (P) and in their thermodynamic limit the specific heat at constant pressure cp and the particle densityn diverge, the entropyS and specific heat at constant volumec v fall off sharply but continuously to zero, and the fraction of particles in the ground state N0/N jumps discontinuously from zero to one. This Bose-Einstein condensation provides a remarkable example of a transition which has most of the properties of a second-order phase transition, except that the order parameter is discontinuous. The nature of the condensed state is described in the large but finiteN regime, and the width of the transition region is estimated. The effects of interactions in real one- and two-dimensional Bose systems and recent experiments on submonolayer helium films are discussed briefly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01012253
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  • 9
    Electronic Resource
    Electronic Resource
    Hydrodynamic theory of fourth sound in clamped conditions (1974)
    Springer
    Journal of low temperature physics 15 (1974), S. 559-576 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The hydrodynamic theory of fourth sound is developed in detail for the cases of a flat capillary and a porous superleak filled with superfluid helium whose normal fluid motion is completely clamped. The attenuation is calculated including rigorously all the thermal conduction effects in both the helium and the capillary walls. Also included in the case of the superleak are the Rayleigh scattering and the thermal effects of the resonator walls. Comparison of the superleak results with existing experiments leads to the conclusion that Q factors of fourth-sound resonators could be increased considerably.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00654627
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  • 10
    Electronic Resource
    Electronic Resource
    Effective medium approximation for strongly nonlinear media (1997)
    Springer
    Journal of statistical physics 86 (1997), S. 455-479 
    Details
    ISSN: 1572-9613
    Keywords: The effective medium theory ; nonlinear behavior ; composite medium ; strong nonlinearity ; bulk effective moduli ; bulk effective conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effective medium approximation is one of the most popular approximations used for calculating the effective coefficients of linear composite media. When the same approach is applied to the case of power-law nonlinear composite media the obtained expression contains a function whose values are unknown. In order to determine the form of this function and to calculate some coefficients related to it, we calculate the electric field for the case of a single inclusion. The numerical solution is based on the relaxation method for solving differential equations, but involves some modifications due to the nonlinearity. After the solution of the differential equation the function and the coefficients are calculated and examined. The results differ considerably from those obtained earlier by simple approximations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02199110
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