576 research outputs found
Properties of the Ising magnet confined in a corner geometry
No full textThe properties of Ising square lattices with nearest neighbor ferromagnetic exchange confined in a corner geometry, are studied by means of Monte Carlo simulations. Free boundary conditions at which boundary magnetic fields +/- h are applied, i.e., at the two boundary rows ending at the lower left corner a field +h acts, while at the two boundary rows ending at the upper right corner a field -h acts. For temperatures T less than the critical temperature T-c of the bulk, this boundary condition leads to the formation of two domains with opposite orientation of the magnetization direction, separated by an interface which for T larger than the filling transition temperature T-f(h) runs from the upper left corner to the lower right corner, while for T T-f(h) it scales as w proportional to root L. The distribution P(l) of the interface position l (measured along the z-direction from the corners) decays exponentially for T T-f(h). Unlike the findings for critical wetting in the thin film geometry of the Ising model, the Monte Carlo results for corner wetting are in very good agreement with the theoretical predictions. (C) 2007 Elsevier B.V. All rights reserved
Paroxetine treatment improves motor symptoms in patients with multiple system atrophy
No full textPurpose: In view of the putative role of serotonergic neurotransmission in basal ganglia circuitry we investigated the effects of paroxetine (PXT) as a selective serotonin reuptake inhibitor (SSRI) on the motor performance in n = 19 patients clinically diagnosed as MSA using a double-blind placebo-controlled randomized study design. In addition, we assessed the effects on the psychopathological status of the patients. Results: The short-term add-on treatment with PXT up to 30mg tid for two weeks resulted in a significant improvement of the motor abilities of the upper limbs and speech when compared to placebo. The treatment with PXT was generally well tolerated. The degree of depressive symptoms was not significantly influenced by PXT or placebo during the observation period. Conclusions: Previous observations suggest that serotonergic projections may modulate the neuronal excitability of the mesolimbic system and cerebellar system. The observed effects of PXT on motor performance may therefore be due to a direct action of the drug on the motor system. However, these results should be regarded as preliminary, and further research is suggested to evaluate the long-term outcome and clinical relevance of SSRI co-medication in MSA. (c) 2006 Elsevier Ltd. All rights reserved
Single-chain simulation of Ising density functional theory for weak polyelectrolytes
No full textConventional theories of weak polyelectrolytes are either computationally prohibitive to account for the multidimensional inhomogeneity of polymer ionization in a liquid environment or oversimplistic in describing the coupling effects of ion-explicit electrostatic interactions and long-range intrachain correlations. To bridge this gap, we implement the Ising density functional theory (iDFT) for ionizable polymer systems using the single-chain-in-mean-field algorithm. The single-chain-in-iDFT (sc-iDFT) shows significant improvements over conventional mean-field methods in describing segment-level dissociation equilibrium, specific ion effects, and long-range intrachain correlations. With an explicit consideration of the fluctuations of polymer configurations and the position-dependent ionization of individual polymer segments, sc-iDFT provides a faithful description of the structure and thermodynamic properties of inhomogeneous weak polyelectrolyte systems across multiple length scales.Directorate for Mathematical and Physical Sciences 10.13039/100000086Deutsche Forschungsgemeinschaft 10.13039/501100001659Division of Graduate Education 10.13039/10000008
Genomewide association scan of suicidal thoughts and behaviour in major depression
No full textBACKGROUND: Suicidal behaviour can be conceptualised as a continuum from suicidal ideation, to suicidal attempts to completed suicide. In this study we identify genes contributing to suicidal behaviour in the depression study RADIANT. METHODOLOGY/PRINCIPAL FINDINGS: A quantitative suicidality score was composed of two items from the SCAN interview. In addition, the 251 depression cases with a history of serious suicide attempts were classified to form a discrete trait. The quantitative trait was correlated with younger onset of depression and number of episodes of depression, but not with gender. A genome-wide association study of 2,023 depression cases was performed to identify genes that may contribute to suicidal behaviour. Two Munich depression studies were used as replication cohorts to test the most strongly associated SNPs. No SNP was associated at genome-wide significance level. For the quantitative trait, evidence of association was detected at GFRA1, a receptor for the neurotrophin GDRA (p = 2e-06). For the discrete trait of suicide attempt, SNPs in KIAA1244 and RGS18 attained p-values of <5e-6. None of these SNPs showed evidence for replication in the additional cohorts tested. Candidate gene analysis provided some support for a polymorphism in NTRK2, which was previously associated with suicidality. CONCLUSIONS/SIGNIFICANCE: This study provides a genome-wide assessment of possible genetic contribution to suicidal behaviour in depression but indicates a genetic architecture of multiple genes with small effects. Large cohorts will be required to dissect this further.Alexandra Schosser, Amy W. Butler, Marcus Ising, Nader Perroud, Rudolf Uher, Mandy Y. Ng, Sarah Cohen-Woods, Nick Craddock, Michael J. Owen, Ania Korszun, Lisa Jones, Ian Jones, Michael Gill, John P. Rice, Wolfgang Maier, Ole Mors, Marcella Rietschel, Susanne Lucae, Elisabeth B. Binder, Martin Preisig, Julia Perry, Federica Tozzi, Pierandrea Muglia, Katherine J. Aitchison, Gerome Breen, Ian W. Craig, Anne E. Farmer, Bertram Müller-Myhsok, Peter McGuffin and Cathryn M. Lewi
Properties of the interface in the confined Ising magnet with competing surface fields
No full textA two-dimensional magnetic Ising system confined in an L x D geometry (L infinity, this interface undergoes a wetting transition that occurs at the critical curve T(w)(h), so that for T < T(w)(h) such an interface is bound to the walls, while for T(w)(h) <= T < T(cb) the interface is freely fluctuating around the center of the film, where T(cb) is the bulk critical temperature. By considering both short- and long-range magnetic fields acting at the walls, we study the divergence of the (equilibrated) average position of the interface when approaching the wetting critical point. Furthermore, starting from a monodomain structure with the interface bound to one wall, we also study the dynamics of the interface unbinding. (c) 2006 Elsevier B.V. All rights reserved
Stochastic domination for the Ising and fuzzy Potts models
No full textWe discuss various aspects concerning stochastic domination for the Ising model and the fuzzy Potts model. We begin by considering the Ising model on the homogeneous tree of degree , \Td. For given interaction parameters , and external field h_1\in\RR, we compute the smallest external field such that the plus measure with parameters and dominates the plus measure with parameters and for all . Moreover, we discuss continuity of with respect to the three parameters , , and also how the plus measures are stochastically ordered in the interaction parameter for a fixed external field. Next, we consider the fuzzy Potts model and prove that on \Zd the fuzzy Potts measures dominate the same set of product measures while on \Td, for certain parameter values, the free and minus fuzzy Potts measures dominate different product measures. For the Ising model, Liggett and Steif proved that on \Zd the plus measures dominate the same set of product measures while on \T^2 that statement fails completely except when there is a unique phase
Manifest Modular Invariance in the Near-Critical Ising Model
No full textUsing recent results in mathematics, I point out that free energies and
scale-dependent central charges away from criticality can be represented in
compact form where modular invariance is manifest. The main example is the
near-critical Ising model on a thermal torus, but the methods are not
restricted to modular symmetry, and apply to automorphic symmetries more
generally. One application is finite-size effects.Comment: 23 pages, 7 figure
Circle Patterns and Critical Ising Models
No full textA circle pattern is an embedding of a planar graph in which each face is inscribed in a circle. We define and prove magnetic criticality of a large family of Ising models on planar graphs whose dual is a circle pattern. Our construction includes as a special case the critical isoradial Ising models of Baxter.© The Author(s) 201
Stochastic domination for the Ising and fuzzy Potts models
No full textWe discuss various aspects concerning stochastic domination for the Ising model and the fuzzy Potts model. We begin by considering the Ising model on the homogeneous tree of degree , \Td. For given interaction parameters , and external field h_1\in\RR, we compute the smallest external field such that the plus measure with parameters and dominates the plus measure with parameters and for all . Moreover, we discuss continuity of with respect to the three parameters , , and also how the plus measures are stochastically ordered in the interaction parameter for a fixed external field. Next, we consider the fuzzy Potts model and prove that on \Zd the fuzzy Potts measures dominate the same set of product measures while on \Td, for certain parameter values, the free and minus fuzzy Potts measures dominate different product measures. For the Ising model, Liggett and Steif proved that on \Zd the plus measures dominate the same set of product measures while on \T^2 that statement fails completely except when there is a unique phase
Geometric effects on critical behaviours of the Ising model
No full textWe investigate the critical behaviour of the two-dimensional Ising model defined on a curved surface with a constant negative curvature. Finite-size scaling analysis reveals that the critical exponents for the zero-field magnetic susceptibility and the correlation length deviate from those for the Ising lattice model on a flat plane. Furthermore, when reducing the effects of boundary spins, the values of the critical exponents tend to those derived from the mean field theory. These findings evidence that the underlying geometric character is responsible for the critical properties of the Ising model when the lattice is embedded on negatively curved surfaces
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