3,394 research outputs found

    Fluctuations of a driven membrane in an electrolyte

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    We develop a model for a driven cell- or artificial membrane in an electrolyte. The system is kept far from equilibrium by the application of a DC electric field or by concentration gradients, which causes ions to flow through specific ion-conducting units (representing pumps, channels or natural pores). We consider the case of planar geometry and Debye-H\"{u}ckel regime, and obtain the membrane equation of motion within Stokes hydrodynamics. At steady state, the applied field causes an accumulation of charges close to the membrane, which, similarly to the equilibrium case, can be described with renormalized membrane tension and bending modulus. However, as opposed to the equilibrium situation, we find new terms in the membrane equation of motion, which arise specifically in the out-of-equilibrium case. We show that these terms lead in certain conditions to instabilities.Comment: 7 pages, 2 figures. submitted to Europhys. Let

    On U_q(SU(2))-symmetric Driven Diffusion

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    We study analytically a model where particles with a hard-core repulsion diffuse on a finite one-dimensional lattice with space-dependent, asymmetric hopping rates. The system dynamics are given by the \mbox{Uq_{q}[SU(2)]}-symmetric Hamiltonian of a generalized anisotropic Heisenberg antiferromagnet. Exploiting this symmetry we derive exact expressions for various correlation functions. We discuss the density profile and the two-point function and compute the correlation length ξs\xi_s as well as the correlation time ξt\xi_t. The dynamics of the density and the correlations are shown to be governed by the energy gaps of a one-particle system. For large systems ξs\xi_s and ξt\xi_t depend only on the asymmetry. For small asymmetry one finds ξtξs2\xi_t \sim \xi_s^2 indicating a dynamical exponent z=2z=2 as for symmetric diffusion.Comment: 10 pages, LATE

    Meandering instability of curved step edges on growth of a crystalline cone

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    We study the meandering instability during growth of an isolated nanostructure, a crystalline cone, consisting of concentric circular steps. The onset of the instability is studied analytically within the framework of the standard Burton-Cabrera-Frank model, which is applied to describe step flow growth in circular geometry. We derive the correction to the most unstable wavelength and show that in general it depends on the curvature in a complicated way. Only in the asymptotic limit where the curvature approaches zero the results are shown to reduce to the rectangular case. The results obtained here are of importance in estimating growth regimes for stable nanostructures against step meandering.Comment: 4 pages, 3 figures, RevTe

    Information transport by sine-Gordon solitons in microtubules

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    We study the problem of information propagation in brain microtubules. After considering the propagation of electromagnetic waves in a fluid of permanent electric dipoles, the problem reduces to the sine-Gordon wave equation in one space and one time dimensions. The problem of propagation of information is thus set.Comment: 3 page

    Magic Islands and Barriers to Attachment: A Si/Si(111)7x7 Growth Model

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    Surface reconstructions can drastically modify growth kinetics during initial stages of epitaxial growth as well as during the process of surface equilibration after termination of growth. We investigate the effect of activation barriers hindering attachment of material to existing islands on the density and size distribution of islands in a model of homoepitaxial growth on Si(111)7x7 reconstructed surface. An unusual distribution of island sizes peaked around "magic" sizes and a steep dependence of the island density on the growth rate are observed. "Magic" islands (of a different shape as compared to those obtained during growth) are observed also during surface equilibration.Comment: 4 pages including 5 figures, REVTeX, submitted to Physical Review

    An interacting spin flip model for one-dimensional proton conduction

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    A discrete asymmetric exclusion process (ASEP) is developed to model proton conduction along one-dimensional water wires. Each lattice site represents a water molecule that can be in only one of three states; protonated, left-pointing, and right-pointing. Only a right(left)-pointing water can accept a proton from its left(right). Results of asymptotic mean field analysis and Monte-Carlo simulations for the three-species, open boundary exclusion model are presented and compared. The mean field results for the steady-state proton current suggest a number of regimes analogous to the low and maximal current phases found in the single species ASEP [B. Derrida, Physics Reports, {\bf 301}, 65-83, (1998)]. We find that the mean field results are accurate (compared with lattice Monte-Carlo simulations) only in the certain regimes. Refinements and extensions including more elaborate forces and pore defects are also discussed.Comment: 13pp, 6 fig

    Long-Term Potentiation: One Kind or Many?

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    Do neurobiologists aim to discover natural kinds? I address this question in this chapter via a critical analysis of classification practices operative across the 43-year history of research on long-term potentiation (LTP). I argue that this 43-year history supports the idea that the structure of scientific practice surrounding LTP research has remained an obstacle to the discovery of natural kinds

    Speciesistic Veganism: An Anthropocentric Argument

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    The paper proposes an anthropocentric argument for veganism based on a speciesistic premise that most carnists likely affirm: human flourishing should be promoted. I highlight four areas of human suffering promoted by a carnistic diet: (1) health dangers to workers (both physical and psychological), (2) economic dangers to workers, (3) physical dangers to communities around slaughterhouses, and (4) environmental dangers to communities-at-large. Consequently, one could ignore the well-being of non-human animals and nevertheless recognize significant moral failings in the current standard system of meat production
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