6,819 research outputs found
Implicit Finite-Size Effects in Computer Simulations
The influence of periodic boundary conditions (implicit finite-size effects)
on the anisotropy of pair correlations in computer simulations is studied for a
dense classical fluid of pair-wise interacting krypton atoms near the triple
point. Molecular dynamics simulation data for the pair distribution function of
N-particle systems, as a function of radial distance, polar angle, and
azimuthal angle are compared directly with corresponding theoretical
predictions [L. R. Pratt and S. W. Haan, J. Chem. Phys. 74, 1864 (1981)]. For
relatively small systems of N=60, 80, and 108 atoms, significant angular
variation is observed, which is qualitatively, and in several cases
quantitatively, well predicted by theory. Finite-size corrections to the
spherically-averaged radial distribution function, however, are found to be
comparable to random statistical errors for runs of 10^5 time steps.Comment: plain TeX, 14 pages + 16 postscript figures, to appear Z. Phys.
Thermodynamically Stable One-Component Metallic Quasicrystals
Classical density-functional theory is employed to study finite-temperature
trends in the relative stabilities of one-component quasicrystals interacting
via effective metallic pair potentials derived from pseudopotential theory.
Comparing the free energies of several periodic crystals and rational
approximant models of quasicrystals over a range of pseudopotential parameters,
thermodynamically stable quasicrystals are predicted for parameters approaching
the limits of mechanical stability of the crystalline structures. The results
support and significantly extend conclusions of previous ground-state
lattice-sum studies.Comment: REVTeX, 13 pages + 2 figures, to appear, Europhys. Let
Children in Immigrant Families - The U.S. and 50 States: Economic Need Beyond the Official Poverty Measure
Analyzes gaps between child poverty rates in immigrant families and native-born families based on two alternative measures that take into account the costs of housing, food, other basic necessities, transportation, taxes, child care, and early education
Children in Immigrant Families -- The U.S. and 50 States: National Origins, Language, and Early Education
Draws on new results of U.S. Census 2000 data to focus on children in immigrant families, highlighting the proportion, dispersion, national origins, language, and early education of children in newcomer families nationwide and in various states
Poisson-Boltzmann Theory of Charged Colloids: Limits of the Cell Model for Salty Suspensions
Thermodynamic properties of charge-stabilised colloidal suspensions are
commonly modeled by implementing the mean-field Poisson-Boltzmann (PB) theory
within a cell model. This approach models a bulk system by a single macroion,
together with counterions and salt ions, confined to a symmetrically shaped,
electroneutral cell. While easing solution of the nonlinear PB equation, the
cell model neglects microion-induced correlations between macroions, precluding
modeling of macroion ordering phenomena. An alternative approach, avoiding
artificial constraints of cell geometry, maps a macroion-microion mixture onto
a one-component model of pseudo-macroions governed by effective interactions.
In practice, effective-interaction models are usually based on linear screening
approximations, which can accurately describe nonlinear screening only by
incorporating an effective (renormalized) macroion charge. Combining charge
renormalization and linearized PB theories, in both the cell model and an
effective-interaction (cell-free) model, we compute osmotic pressures of highly
charged colloids and monovalent microions over a range of concentrations. By
comparing predictions with primitive model simulation data for salt-free
suspensions, and with predictions of nonlinear PB theory for salty suspensions,
we chart the limits of both the cell model and linear-screening approximations
in modeling bulk thermodynamic properties. Up to moderately strong
electrostatic couplings, the cell model proves accurate in predicting osmotic
pressures of deionized suspensions. With increasing salt concentration,
however, the relative contribution of macroion interactions grows, leading
predictions of the cell and effective-interaction models to deviate. No
evidence is found for a liquid-vapour phase instability driven by monovalent
microions. These results may guide applications of PB theory to soft materials.Comment: 27 pages, 5 figures, special issue of Journal of Physics: Condensed
Matter on "Classical density functional theory methods in soft and hard
matter
Charge Renormalization, Effective Interactions, and Thermodynamics of Deionized Colloidal Suspensions
Thermodynamic properties of charge-stabilised colloidal suspensions depend
sensitively on the effective charge of the macroions, which can be
substantially lower than the bare charge in the case of strong
counterion-macroion association. A theory of charge renormalization is
proposed, combining an effective one-component model of charged colloids with a
thermal criterion for distinguishing between free and associated counterions.
The theory predicts, with minimal computational effort, osmotic pressures of
deionized suspensions of highly charged colloids in close agreement with
large-scale simulations of the primitive model.Comment: 15 pages, 7 figure
Against the Klan: A Newspaper Pub-lisher in South Louisiana During the 1960s
Lou Major Baton Rouge: Louisiana State University Press, 2021 ISBN: 9780807175408 188 p. $29.95 (ebk
The Medieval Canon and the Renaissance Image of the Turk: A Brief Historiography of Pre-Modern European Conceptions of the Muslim World
This historiographic essay examines the scholarly debate over pre-modern European “images,” or conceptions, of the Muslim World during the Middle Ages and the Renaissance. Adopting a thematic approach, this study is guided by four themes shared by two or more works. While this essay largely revolves around the image studies of Nancy Bisaha, Norman Daniel, and Robert Schwoebel, the interpretations of additional scholars are presented as well. Though points of convergence exists between the works presented here, far more telling is the fact that the sharp contrasts between these historians aptly illustrates the challenge of determining the precise nature of the pre-modern European image of Islam, with all its abstract complexity
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