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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 689-690 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1607-1613 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Random sequential addition is a process that generates nonequilibrium configurations of hard objects. The corresponding spatial pair correlations are investigated via a Percus–Yevick (PY)-like integral equation. Numerical solutions are obtained in one, two, and three dimensions. Comparison with exact results in one dimension and with Monte Carlo data in higher dimensions shows that the PY-like integral equation provides an accurate description of the structure, except close to the jamming limit, where the logarithmic divergence of the correlation function at contact is not reproduced. Using diagrammatic expansions, we show that in one dimension, contrary to its equilibrium counterpart, this equation is only exact up to the second order in density. © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4256-4260 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the Green–Bogoliubov method, we derive an expression for the thermodynamic pressure or grand potential density for a molecular model of a fluid confined in a disordered porous matrix. The expression is equivalent to the virial equation derived previously via the replica method [Rosinberg et al., J. Chem. Phys. 100, 5172 (1994)] but differs from an expression recently derived from the condition of mechanical equilibrium. It is concluded that the condition of mechanical equilibrium does not yield information about the thermodynamics of these systems. The thermodynamic pressure can be obtained from experiment indirectly by integrating the Gibbs adsorption isotherm and, in principle, by direct measurement. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9164-9180 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of two-dimensional configurations of spherocylinders (discorectangles) generated by random sequential adsorption (RSA) is analyzed via the circular harmonic expansion of the pair distribution function and compared to that of equilibrium fluids at the same density. The structural differences are minimal for short particles but become more pronounced as the aspect ratio of the particles increases. An analysis of the correlations between particles which adsorb at high coverage with their nearest neighbors in saturated RSA configurations, reveals that the most probable relative orientation for particles with aspect ratio α≈2 is perpendicular. This observation helps to explain the maximum in saturation coverage as a function of particle elongation near the aspect ratio α=2.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5172-5177 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the replica method, we derive the thermodynamic relations for a fluid in equilibrium with a quenched porous matrix. In particular, the appropriate Gibbs–Duhem equation is obtained as well as the equivalence between grand canonical and canonical ensembles. The exact compressiblity and virial equations are derived. Whereas the compressibility equation remains a direct and practical way to obtain the adsorption isotherm, the virial equation involves terms which do not relate easily to the properties of the fluid/matrix system. This explains the inconsistency between previous theoretical predictions and computer simulation results.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 803-809 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented to study the exchange broadening of isotropic Raman bands due to ultrarapid proton-transfer reactions. It represents a generalization of standard theories of Raman band profiles of nonreactive liquids. The variables describing the reaction are assumed to represent a dichotomic Markovian process. The spectral behavior of various AH/H2O mixtures is studied as a function of the exchange rate and the interplay of various band shaping mechanisms is discussed in detail. Finally, the potentialities of the Raman spectroscopy as a tool to measure the rate constant are critically assessed.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 11289-11298 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical study of the phase diagram and the structure of a fluid adsorbed in high-porosity aerogels by means of an integral-equation approach combined with the replica formalism. To simulate a realistic gel environment, we use an aerogel structure factor obtained from an off-lattice diffusion-limited cluster–cluster aggregation process. The predictions of the theory are in qualitative agreement with the experimental results, showing a substantial narrowing of the gas–liquid coexistence curve (compared to that of the bulk fluid), associated with weak changes in the critical density and temperature. The influence of the aerogel structure (nontrivial short-range correlations due to connectedness, long-range fractal behavior of the silica strands) is shown to be important at low fluid densities. © 2001 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9296-9303 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a computer simulation and theoretical study of a ballistic deposition process in which spheres are incident on a planar surface. Each incoming sphere follows a path of steepest descent which may involve rolling over the surface of preadsorbed spheres. All particles reaching a stable, elevated position are removed. The frequency of the various rolling mechanisms are evaluated as a function of coverage. The addition mechanism generates clusters of connected spheres by accretion and coalescence. We evaluate the dependence of the cluster size distribution and coalescence probability on coverage. Various peaks in the radial distribution function of the deposited layer provide a signature for the deposition mechanism. The asymptotic approach to saturation is shown to be of the form θ∞−θ(t) ∝exp[−(4/π)Smt]/t2, where Sm=(square root of)3/2 is the smallest possible target area. The expression is shown to be consistent with the simulation results. Interpolants, which accurately describe the time-dependent coverage over the entire coverage range, are developed based on the exact expressions for the asymptotic and low coverage kinetics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5212-5218 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the random sequential adsorption (RSA) of unoriented anisotropic objects onto a flat uniform surface, for various shapes (spherocylinders, ellipses, rectangles, and needles) and elongations. The asymptotic approach to the jamming limit is shown to follow the expected algebraic behavior, θ(∞)−θ(t)∼t−1/3, where θ is the surface coverage; this result is valid for all shapes and elongations, provided the objects have a nonzero proper area. In the limit of very small elongations, the long-time behavior consists of two successive critical regimes: The first is characterized by Feder's law, t−1/2, and the second by the t−1/3 law; the crossover occurs at a time that scales as ε−1/2 when ε→0, where ε is a parameter of anisotropy. The influence of shape and elongation on the saturation coverage θ(∞) is also discussed. Finally, for very elongated objects, we derive from scaling arguments that when the aspect ratio α of the objects becomes infinite, θ(∞) goes to zero according to a power law α−p, where p=1/(1+2(square root of)2). The fractal dimension of the system of adsorbed needles is also discussed.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5219-5228 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the kinetics of random sequential adsorption (RSA) of anisotropic bodies (rectangles, ellipses, spherocylinders or, more precisely, discorectangles, and needles) at low-to-intermediate coverages. In this regime, the adsorption probability can be expressed as a power series in the coverage. We calculate numerically the second- and third-order coefficients of the series and compare the results to simulation data. The results for the low-coverage kinetics are then combined with the asymptotic results of Paper I [J. Chem. Phys. 97, xxxx (1992)] to construct approximate equations for the adsorption probability over the entire coverage range. While the equations provide a reasonably good description of the RSA kinetics, they produce unsatisfactory estimates of the saturation coverages. The effect of particle shape on the adsorption kinetics and surface structure is discussed. Finally, the available surface function is compared with that corresponding to equilibrium configurations of the adsorbed particles.
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