260,845 research outputs found
Field theory for size- and charge asymmetric primitive model of electrolytes. Mean-field stability analysis and pretransitional effects
The primitive model of ionic systems is investigated within a field-theoretic
description for the whole range of size-, \lambda, and charge, Z, ratios of the
two ionic species. Two order parameters (OP) are identified, and their
relations to physically relevant quantities are described for various values of
\lambda and Z. Instabilities of the disordered phase associated with the two
OP's are determined in the mean-field approximation.
A gas-liquid separation occurs for any Z and \lambda different from 1. In
addition, an instability with respect to various types of periodic ordering of
the two kinds of ions is found
Monte Carlo study of gating and selection in potassium channels
The study of selection and gating in potassium channels is a very important
issue in modern biology. Indeed such structures are known in all types of cells
in all organisms where they play many important functional roles. The mechanism
of gating and selection of ionic species is not clearly understood. In this
paper we study a model in which gating is obtained via an affinity-switching
selectivity filter. We discuss the dependence of selectivity and efficiency on
the cytosolic ionic concentration and on the typical pore open state duration.
We demonstrate that a simple modification of the way in which the selectivity
filter is modeled yields larger channel efficiency
Electrostatic model of atomic ordering in complex perovskite alloys
We present a simple ionic model which successfully reproduces the various
types of compositional long-range order observed in a large class of complex
insulating perovskite alloys. The model assumes that the driving mechanism
responsible for the ordering is simply the electrostatic interaction between
the different ionic species. A possible new explanation for the anomalous
long-range order observed in some Pb relaxor alloys, involving the proposed
existence of a small amount of Pb^4+ on the B sublattice, is suggested by an
analysis of the model.Comment: 4 pages, two-column style with 1 postscript figure embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#lb_orde
Silver as antibacterial toward Listeria monocytogenes
Listeria monocytogenes is a serious foodborne pathogen that can contaminate food during processing and can grow during food shelf-life. New types of safe and effective food contact materials embedding antimicrobial agents, like silver, can play an important role in the food industry. The present work aimed at evaluating the in vitro growth kinetics of different strains of L. monocytogenes in the presence of silver, both in its ionic and nano form. The antimicrobial effect was determined by assaying the number of culturable bacterial cells, which formed colonies after incubation in the presence of silver nanoparticles (AgNPs) or silver nitrate (AgNO(3)). Ionic release experiments were performed in parallel. A different reduction of bacterial viability between silver ionic and nano forms was observed, with a time delayed effect exerted by AgNPs. An association between antimicrobial activity and ions concentration was shown by both silver chemical forms, suggesting the major role of ions in the antimicrobial mode of action
Self-consistent field theory of polymer-ionic molecule complexation
A self-consistent field theory is developed for polymers that are capable of binding small ionic molecules (adsorbates). The polymer-ionic molecule association is described by Ising-like binding variables, C_(i)^(a)(kΔ)(= 0 or 1), whose average determines the number of adsorbed molecules, nBI. Polymer gelation can occur through polymer-ionic molecule complexation in our model. For polymer-polymer cross-links through the ionic molecules, three types of solutions for nBI are obtained, depending on the equilibrium constant of single-ion binding. Spinodal lines calculated from the mean-field free energy exhibit closed-loop regions where the homogeneous phase becomes unstable. This phase instability is driven by the excluded-volume interaction due to the single occupancy of ion-binding sites on the polymers. Moreover, sol-gel transitions are examined using a critical degree of conversion. A gel phase is induced when the concentration of adsorbates is increased. At a higher concentration of the adsorbates, however, a re-entrance from a gel phase into a sol phase arises from the correlation between unoccupied and occupied ion-binding sites. The theory is applied to a model system, poly(vinyl alcohol) and borate ion in aqueous solution with sodium chloride. Good agreement between theory and experiment is obtaine
Thermal and structural properties of ionic fluids
The electrostatic interaction in ionic fluids is well-known to give rise to a
characteristic phase behavior and structure. Sometimes its long range is
proposed to single out the electrostatic potential over other interactions with
shorter ranges. Here the importance of the range for the phase behavior and the
structure of ionic fluids is investigated by means of grandcanonical Monte
Carlo simulations of the lattice restricted primitive model (LRPM). The
long-ranged electrostatic interaction is compared to various types of
short-ranged potentials obtained by sharp and/or smooth cut-off schemes.
Sharply cut off electrostatic potentials are found to lead to a strong
dependence of the phase behavior and the structure on the cut-off radius.
However, when combined with a suitable additional smooth cut-off, the
short-ranged LRPM is found to exhibit quantitatively the same phase behavior
and structure as the conventional long-ranged LRPM. Moreover, the
Stillinger-Lovett perfect screening property, which is well-known to be
generated by the long-ranged electrostatic potential, is also fulfilled by
short-ranged LRPMs with smooth cut-offs. By showing that the characteristic
phase behavior and structure of ionic fluids can also be found in systems with
short-ranged potentials, one can conclude that the decisive property of the
electrostatic potential in ionic fluids is not the long range but rather the
valency dependence
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