Energetics of ion competition in the DEKA selectivity filter of neuronal sodium channels

The energetics of ionic selectivity in the neuronal sodium channels is studied. A simple model constructed for the selectivity filter of the channel is used. The selectivity filter of this channel type contains aspartate (D), glutamate (E), lysine (K), and alanine (A) residues (the DEKA locus). We use Grand Canonical Monte Carlo simulations to compute equilibrium binding selectivity in the selectivity filter and to obtain various terms of the excess chemical potential from a particle insertion procedure based on Widom's method. We show that K$^{+}$ ions in competition with Na$^{+}$ are efficiently excluded from the selectivity filter due to entropic hard sphere exclusion. The dielectric constant of protein has no effect on this selectivity. Ca$^{2+}$ ions, on the other hand, are excluded from the filter due to a free energetic penalty which is enhanced by the low dielectric constant of protein.Comment: 14 pages, 7 figure

Magnetization and susceptibility of ferrofluids

A second-order Taylor series expansion of the free energy functional provides analytical expressions for the magnetic field dependence of the free energy and of the magnetization of ferrofluids, here modelled by dipolar Yukawa interaction potentials. The corresponding hard core dipolar Yukawa reference fluid is studied within the framework of the mean spherical approximation. Our findings for the magnetic and phase equilibrium properties are in quantitative agreement with previously published and new Monte Carlo simulation data.Comment: 8 pages including 4 figure

The Dynamics of Interethnic Friendships and Negative Ties in Secondary School:The Role of Peer-Perceived Ethnicity

This study examines ethnic integration in secondary school. Social identity theory suggests that perception of relevant individual attributes plays a crucial role in defining ingroups and outgroups, contributing to befriending, and disliking others. Therefore, we analyze the role of peer-perceived ethnicity in social ties. Networks of friendship, dislike, and perceived ethnicity were modeled together using dynamic stochastic actor-oriented models, separating the effect of perceived ethnicity on social ties from that of social ties on perceived ethnicity. Data came from a Hungarian sample of 12 school classes with one minority group: the Roma. Treating friendship and dislike as mutually exclusive and comparing them to neutral relations, we found evidence for the role of perceived ethnicity in dislike-majority students disliked those they perceived as minority peers. However, we saw no direct effect of ethnicity on the friendship network. Implications of the joint modeling of mutually exclusive relationship aspects are discussed

Spontaneous polarisation of the neutral interface for valence asymmetric coulombic systems

In this paper, we discuss the phenomenon of a spontaneous polarisation of a neutral hard planar interface for valence asymmetric coulombic systems. Within a field theoretical description, we account for the existence of non trivial charge density and electric potential profiles. The analysis of the phenomenon shows that the effect is related to combinatorics in relation with the existence of the two independent species cations and anions. This simple and basic feature is related to the quantum mechanical properties of the system. The theoretical results are compared with numerical simulations data and are shown to be in very good agreement, which a fortiori justifies our physical interpretation.Comment: 12 pages, 11 figure

A Balaton környéki kisvízfolyások makroszkópikus gerinctelen faunája | On the macroinvertebrate fauna of inflows of lake Balaton

A Balaton környéki kisvízfolyások makroszkópikus gerinctelen faunája kevéssé ismert. Habár számos faunisztikai jellegű gyűjtést végeztek ezen a területen, ezekben a publikációkban csak szórványos adatok találhatók. Dolgozatunkban átfogó irodalmi áttekintést adunk a Balaton környéki patakok makrogerinctelen faunájáról, illetve saját, 2006-ban végzett faunisztikai felmérésünk eredményeit mutatjuk be. | The aquatic macroinvertebrate fauna of streams in the catchment area of Lake Balaton is poorly known. Although there were carried out many faunistical investigation in this area, only sporadic data can be found in the literature. In this paper a compilation is given on the macroinvertebrate fauna of streams of Lake Balaton, and the results of own faunistical investigations carried out in 2006 are presented

Correspondence on rajyaguru et al

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Phase transitions and ordering of confined dipolar fluids

We apply a modified mean-field density functional theory to determine the phase behavior of Stockmayer fluids in slitlike pores formed by two walls with identical substrate potentials. Based on the Carnahan-Starling equation of state, a fundamental-measure theory is employed to incorporate the effects of short-ranged hard sphere - like correlations while the long-ranged contributions to the fluid interaction potential are treated perturbatively. The liquid-vapor, ferromagnetic liquid - vapor, and ferromagnetic liquid - isotropic liquid first-order phase separations are investigated. The local orientational structure of the anisotropic and inhomogeneous ferromagnetic liquid phase is also studied. We discuss how the phase diagrams are shifted and distorted upon varying the pore width.Comment: 15 pages including 8 figure

A simulational and theoretical study of the spherical electrical double layer for a size-asymmetric electrolyte: the case of big coions

Monte Carlo simulations of a spherical macroion, surrounded by a size-asymmetric electrolyte in the primitive model, were performed. We considered 1:1 and 2:2 salts with a size ratio of 2 (i.e., with coions twice the size of counterions), for several surface charge densities of the macrosphere. The radial distribution functions, electrostatic potential at the Helmholtz surfaces, and integrated charge are reported. We compare these simulational data with original results obtained from the Ornstein-Zernike integral equation, supplemented by the hypernetted chain/hypernetted chain (HNC/HNC) and hypernetted chain/mean spherical approximation (HNC/MSA) closures, and with the corresponding calculations using the modified Gouy-Chapman and unequal-radius modified Gouy-Chapman theories. The HNC/HNC and HNC/MSA integral equations formalisms show good concordance with Monte Carlo "experiments", whereas the notable limitations of point-ion approaches are evidenced. Most importantly, the simulations confirm our previous theoretical predictions of the non-dominance of the counterions in the size-asymmetric spherical electrical double layer [J. Chem. Phys. 123, 034703 (2005)], the appearance of anomalous curvatures at the outer Helmholtz plane and the enhancement of charge reversal and screening at high colloidal surface charge densities due to the ionic size asymmetry.Comment: 11 pages, 7 figure