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  • American Institute of Physics (AIP)  (29)
  • Periodicals Archive Online (PAO)  (7)
  • 1990-1994
  • 1985-1989  (36)
  • 1915-1919
  • 1989  (36)
  • 1
    Electronic Resource
    Electronic Resource
    Mean and Gaussian curvatures of randomly decorated Voronoi and cubic tesselations (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3246-3251 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is now generally accepted that some midrange microemulsions are bicontinuous, i.e., continuous in both oil and water simultaneously. The first model of the microstructure of microemulsion that could account for a progression from discrete to bicontinuous was the Talmon–Prager or "randomly decorated Voronoi'' model. Space is tessellated into Voronoi polyhedra and the polyhedra are randomly decorated with oil and water. In variations of the model DeGennes and Taupin and Widom decorate a cubic tesselation of space. At first glance it might appear that the decorated Voronoi and cubic tessellations are zero-mean-curvature models, since they are constructed from polyhedra with planar faces. However, the edges of the polyhedra are concentrations of mean curvature, and the vertices are concentrations of Gaussian curvature. The area-averaged mean and Gaussian curvatures of the oil–water interface in the randomly decorated Voronoi and cubic models are calculated. The area-averaged mean curvatures of the two models are linear functions of oil volume fraction, change sign at a volume fraction of 0.5, and are within 0.2% of one another in magnitude. The area-averaged Gaussian curvature of the Voronoi model varies quadratically with volume fraction, and is negative for oil volume fractions from 0.18 to 0.82 (oil and water are bicontinuous for volume fractions ranging from 0.135 to 0.865). The area-averaged Gaussian curvature of the randomly decorated cubic model is a sixth-order polynomial function of oil volume fraction and is negative for volume fractions ranging from 0.23 to 0.77 (oil and water are bicontinuous over the volume fraction range 0.25 to 0.75). As an additional application, the model results are used to interpret curvature aspects of the bilayer theory of the L3 phase of surfactant solutions presented recently by Cates et al. [Europhys. Lett. 5, 733 (1988)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456899
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular dynamics for discontinuous potential. IV. Lennard-Jonesium (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4307-4313 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Argon, represented as a Lennard-Jones fluid, is simulated using a discontinuous version of the potential. The effect of discretization is thoroughly investigated in terms of the number of discontinuities and the cutoff diameter. Radial distribution functions, pressure, energy, self-diffusion coefficients, and velocity autocorrelation functions are used in order to evaluate this effect. A reduction of five times on computing time can be achieved by varying the cutoff radius and the number of discontinuities without much departure from the physical representation of Lennard-Jonesium atoms. The results indicate that discontinuous molecular dynamics is a viable alternative method to Monte Carlo and continuous molecular dynamics in simulating the properties of simple fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456811
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  • 3
    Electronic Resource
    Electronic Resource
    The statistical mechanics of inhomogeneous hard rod mixtures (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7136-7145 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The exact statistical mechanical solution to the problem of an equilibrium inhomogeneous classical one-dimensional mixture of hard rods is presented. From the solution, thermodynamic properties, density profiles, and correlation functions of hard rod fluids confined to small regions (micropores) can be calculated. The theory is applied to investigate microstructure, pore pressures, and pore adsorption selectivity of micropores in equilibrium with binary hard rod mixtures. A prescription is suggested for generalizing the one-dimensional results to higher dimensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457329
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular theories of confined fluids (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2422-2436 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density profiles and normal pressures predicted by three different approximate density functional free energy theories and the Fischer–Methfessel approximation to the Yvon–Born–Green (YBG) equation are compared with computer simulation results for fluids confined between planar walls. All models require as input a homogeneous fluid equation of state. Comparisons are made using two mean-field equations of state, one based on a Clausius hard-sphere reference fluid and the other based on a Carnahan/Starling hard-sphere reference fluid. The simplest and oldest of the models, the generalized van der Waals model, becomes unphysical at high mean pore densities. The Carnahan/Starling version of Tarazona model agrees best overall with the simulations. This model represents a systematic improvement on the generalized van der Waals model and is computationally the most complicated of all models examined. The YBG and generalized hard-rod models are not as accurate as the Tarazona model, but they capture the qualitative trends observed in the simulations. Both of these models are intuitive extensions of the exact theory of one-dimensional hard rods, and are computationally much simpler than the Tarazona model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455985
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  • 5
    Electronic Resource
    Electronic Resource
    Efficient molecular simulation of chemical potentials (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2370-2385 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper evaluates methods of estimating chemical potential—actually fugacity coefficient—from molecular simulations. These methods are based on formulas given by Widom, by Bennett, and by Shing and Gubbins. They are tested with molecular dynamics simulations of Lennard-Jones liquids along the isotherm kT/ε=1.2 for densities from 0.65σ−3 to 0.90σ−3. A new test molecule sampling method, excluded volume map sampling, is found to be as much as 2 orders of magnitude more efficient than uniform test molecule sampling; it is more efficient and reliable than restricted umbrella sampling proposed by Shing and Gubbins. Several difficulties of estimating the variance of the fugacity coefficient estimates are surmounted by novel application of standard statistical methods. The statistical analysis shows that Bennett's method yields estimates with the least variance and Widom's method yields estimates with the greatest variance although all methods are consistent to within statistical error. Pressure and fugacity coefficient estimates obey the Gibbs–Duhem equation along the chosen isotherm up to densities of 0.75σ−3 for 108-molecule, 0.8σ−3 for 200-molecule, and 0.9σ−3 for 500-molecule simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455979
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  • 6
    Electronic Resource
    Electronic Resource
    Coriolis induced vibration and rotation mixing in formaldehyde (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5420-5433 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of Coriolis interaction on the intramolecular dynamics of formaldehyde is investigated theoretically. Classical dynamics calculations are presented that include all seven degrees of freedom, i.e., the six vibrational modes and the rotational mode associated with K, the projection of total angular momentum on a body-fixed axis. These calculations show that vibrational modes 4 (out of plane bend) and 6 (HCO bend) can be significantly coupled due to Coriolis interaction. The qualitative features of such coupling is further understood via study of a reduced dimension model that includes just modes 4, 6, and the rotational degree of freedom. Two interesting classical consequences of Coriolis interaction are noted. First, for large K (e.g., for ||K||∼J) we find vibrational mixing can occur without significant deterioration of K. We find that this mixing is not due to the usual "Chirikov'' or pendulum picture of nonlinear resonance. Second, we find that both vibrational and rotational mixing can occur when the rotational frequency is in resonance with the difference in vibrational frequencies. In this situation, the resonances lead to a partial K mixing. Chaos about the resonances can lead to a more extensive K mixing. Quantum calculations are also performed for the reduced dimension model and the nature of the quantum eigenstates is discussed in relation to the corresponding classical dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456448
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of the 2D5/2–2D3/2 fine structure interval in metastable nitrogen atoms at 1.15 mm by laser magnetic resonance (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 628-632 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Far infrared laser magnetic resonance (LMR) spectra of metastable (2p3)2D nitrogen atoms have been measured using laser lines in carbonyl fluoride (COF2) at 1135 μm and methanol (CH3OH) at 1224 μm. The concentration of N 2D was optimized by electron paramagnetic resonance (EPR) using a hybrid EPR/LMR spectrometer. The far infrared cavity of this spectrometer was designed to oscillate at wavelengths longer than 1 mm. The LMR spectra were analyzed using g factors derived from the EPR spectrum [Radford and Evenson, Phys. Rev. 168, 70 (1968)] and yield a precise value of the 2D5/2–2D3/2 fine structure separation of −261 447.7(2) MHz, −8.720 957(7) cm−1(2σ).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456141
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  • 8
    Electronic Resource
    Electronic Resource
    Epitaxial growth of thin films of BaTiO3 using excimer laser ablation (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 112-114 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Excimer laser ablative sputtering of sintered pellets of BaTiO3 has been used to epitaxially grow thin ∼1-μm-thick films of this material of LiF substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102393
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  • 9
    Electronic Resource
    Electronic Resource
    Low-resistivity contacts to bulk high Tc superconductors (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2605-2607 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Convenient methods for obtaining extremely low resistivity contacts to bulk high Tc superconductors ( ρc in the range of 10−11–10−12 Ω cm2) are described. Three different configurations of silver contact metal in Y-Ba-Cu-O have been employed, i.e., embedded Ag wire, embedded Ag particles, and selectively patterned Ag clad on superconductor wire. In all three cases, the low-resistivity metallic contacts are formed in situ during the sintering or melt processing of the superconductor, thus eliminating the need for separate steps of contact preparation such as vacuum deposition of contact metal and additional heat treatment. The distribution and morphology of the silver contacts will be discussed. The measured contact resistivities in the present work are the lowest reported for the high Tc superconductors, and these methods may serve as a useful basis for important contact technologies needed for bulk superconductor applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101038
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular beam epitaxy growth of InSb films on GaAs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2235-2237 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InSb films have been grown by molecular beam epitaxy on GaAs substrates. The procedure incorporated a low-temperature (300 °C) growth of a thin (300 A(ring)) InSb interface layer prior to the InSb active layer growth at 380 °C. A beam equivalent pressure ratio of Sb4 to In of 4 led to samples with the highest 77 K Hall mobilities. Hall mobilities in excess of 35 000 cm2 /V s at 77 K and x-ray rocking curve widths less than 250 arcsec are routinely achieved in films 2–5 μm thick. The 77 K Hall electron mobilities are a factor of 4 greater than recently reported results. The x-ray rocking curve widths are also substantially less. Possible explanations for the improved film properties are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101134
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