1,425 research outputs found
Colloidal charge reversal: Dependence on the ionic size and the electrolyte concentration
Extensive Monte Carlo simulations and scaling arguments are used to study the
colloidal charge reversal. The critical colloidal surface charge density
at which the reversal first appears is found to depend strongly on
the ionic size. We find that has an inflection point as a function
of the electrolyte concentration. The width of the plateau region in the
vicinity of the inflection point depends on the temperature and the ionic
radius . In agreement with the theoretical predictions it is found that the
critical colloidal charge above which the electrophoretic mobility becomes
reversed diverges as in the limit .Comment: 5 pages, 4 figure
Ions at the air-water interface: An end to one hundred year old mystery?
Availability of highly reactive halogen ions at the surface of aerosols has
tremendous implications for the atmospheric chemistry. Yet neither simulations,
experiments, nor existing theories are able to provide a fully consistent
description of the electrolyte-air interface. In this paper a new theory is
proposed which allows us to explicitly calculate the ionic density profiles,
the surface tension, and the electrostatic potential difference across the
solution-air interface. Predictions of the theory are compared to experiments
and are found to be in excellent agreement. The theory also sheds new light on
one of the oldest puzzles of physical chemistry -- the Hofmeister effect
Counterion correlations and attraction between like-charged macromolecules
A simple model is presented for the appearance of attraction between two like
charged polyions inside a polyelectrolyte solution. The polyions are modeled as
rigid cylinders in a continuum dielectric solvent. The strong electrostatic
interactions between the polyions and the counterions results in counterion
condensation. If the two polyions are sufficiently close to each other their
layers of condensed counterions can become correlated resulting in attraction
between the macromolecules. To explore the counterion induced attraction we
calculate the correlation functions for the condensed counterions. It is found
that the correlations are of very short range. For the parameters specific to
the double stranded DNA, the correlations and the attraction appear only when
the surface-to-surface separation is less than 7 /AA.Comment: 6 pages, 8 eps figures, RevTeX with epsfi
Introduction
La reprĂ©sentation politique ne sâĂ©puise pas dans les actions des reprĂ©sentants politiques, dans leurs prises de dĂ©cision ni dans la traduction des droits des reprĂ©sentĂ©s dans lâespace dĂ©libĂ©ratif du gouvernement reprĂ©sentatif. Il suffit dâobserver les bĂątiments publics, les monuments commĂ©moratifs, les symboles et rituels institutionnels â ou encore la communication politique des gouvernants â pour prendre la mesure des aspects
proprement symboliques de la représentation politique. [Premier paragraphe]Titre du Cahier : Paula Diehl et Alexandre Escudier (dir.), La « Représentation » du politique : histoire, concepts, symbole
La « Représentation » du politique:Histoire, concepts, symboles
La question de la « reprĂ©sentation » politique ne se rĂ©sume pas Ă
l'espace délibératif du gouvernement représentatif. Il suffit
d'observer les bùtiments publics, les monuments commémoratifs, les
symboles et rituels institutionnels -- ou encore la communication
politique des gouvernants -- pour prendre la mesure des aspects
proprement « symboliques » de la représentation politique. Le présent
numéro des /Cahiers du Cevipof/ propose d'explorer plus avant lesdits
aspects (trop souvent négligés par la science politique) et tente
ainsi d'ouvrir quelques pistes afin de re-problématiser le concept
usuel de « représentation politique ». Se trouvent ainsi croisées et
mises en discussion (Allemagne, France, recherches anglo-saxonnes)
diverses théories et approches conceptuelles du problÚme de la
« représentation politique », depuis le tournant du « gouvernement
représentatif » à la fin du XVIIIe siÚcle. Nous reconsidérons pour ce
faire différents aspects de la représentation proprement symbolique du
politique (esthétisation, mise en scÚne, ritualisation, visualisation,
etc.) et proposons de les articuler à une théorie de la démocratie
Phase behavior of the Lattice Restricted Primitive Model with nearest-neighbor exclusion
The global phase behavior of the lattice restricted primitive model with
nearest neighbor exclusion has been studied by grand canonical Monte Carlo
simulations. The phase diagram is dominated by a fluid (or charge-disordered
solid) to charge-ordered solid transition that terminates at the maximum
density, and reduced temperature . At
that point, there is a first-order phase transition between two phases of the
same density, one charge-ordered and the other charge-disordered. The
liquid-vapor transition for the model is metastable, lying entirely within the
fluid-solid phase envelope.Comment: 6 pages, color. submitted to J. Chem. Phy
Isothermal adsorption of polyampholytes on charged nanopatterned surfaces
We investigate the adsorption of neutral polyampholytes on charged nanopatterned surfaces. The surfaces have charged domains but are overall neutral. To perform efficient simulations, we use an approach which combines the explicit form of the interaction potential between the polyampholyte monomers and the surface with a 3d Ewald summation method. We observe that the amount of adsorption and the structure of the adsorbed polyampholytes depend strongly on the surface pattern, the relative size of the surface domains, and the charge distribution along the polyampholyte backbone
Phase diagrams in the lattice RPM model: from order-disorder to gas-liquid phase transition
The phase behavior of the lattice restricted primitive model (RPM) for ionic
systems with additional short-range nearest neighbor (nn) repulsive
interactions has been studied by grand canonical Monte Carlo simulations. We
obtain a rich phase behavior as the nn strength is varied. In particular, the
phase diagram is very similar to the continuum RPM model for high nn strength.
Specifically, we have found both gas-liquid phase separation, with associated
Ising critical point, and first-order liquid-solid transition. We discuss how
the line of continuous order-disorder transitions present for the low nn
strength changes into the continuum-space behavior as one increases the nn
strength and compare our findings with recent theoretical results by Ciach and
Stell [Phys. Rev. Lett. {\bf 91}, 060601 (2003)].Comment: 7 pages, 10 figure
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