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Correlation functions by cluster variation method for Ising model with NN, NNN, and plaquette interactions
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A new approach to organic solvent detection: High-reflectivity Bragg reflectors based on a gold nanoparticle/teflon-like composite material
No full textA new sensing element for organic solvents based on a polymeric distributed Bragg reflector (DBR) is presented. The periodic stack consists of alternating Teflon-like and gold nanoparticle/Teflon-like layers, and shows high reflectivity in the optical telecommunications spectral range. Sensing properties are due to the peculiar absorbing behavior of composite layers, which swell in the presence of organic vapors, causing DBR periodicity change and consequently the high reflectivity window shift (see Figure)
High reflectivity Bragg reflectors based on a gold nanoparticle/Teflon-like composite material as a new approach to organic solvent detection
No full textWe report on the properties of a new optical sensing element for organic solvents based on polymeric distributed Bragg reflector (DBR), which can be easily interfaced with optical fibers. The DBR is a periodic stack of alternating Teflon-like and gold nanoparticle/Teflon-like composite layers showing high reflectivity in the optical telecommunication spectral range and sensing proper-ties due to the peculiar absorbing properties of the composite layers. The swelling of the composite layers in presence of organic vapors causes a DBR periodicity change and this results in the shift of the high reflectivity window. (C) 2004 Elsevier B.V. All rights reserved
Persistence Exponent in Superantiferromagnetic Quenching
No full textWe measure the persistence exponent in a phase separating two-dimensional spin system with non-conserved dynamics quenched in a region with four coexisting stripe phases. The system is an Ising model with nearest neighbor, next-to-the-nearest neighbor and plaquette interactions. Due the particular nature of the ground states, the order parameter is defined in terms of blocks of spins. Our estimate of the persistence exponent, ` = 0:42, differs from those of the two-dimensional Ising and four state Potts models. Our procedure allows the study of persistence properties also at finite temperature T : our results are compatible with the hypothesis that ` does not depend on T below the critical point. PACS numbers: 02.50.-r, 05.40.+j, 05.20.-y Typeset using REVT E X Corresponding author I. INTRODUCTION When a system is quenched from a disordered phase into a multiphase coexistence region, ordered domains form randomly and grow in a self-similar way [ 1]. The kinetics of coarsening domai..
Homogenization of a reaction-diffusion problem with large nonlinear drift and robin boundary data
No full textWe study the periodic homogenization of a reaction -diffusion problem with large nonlinear drift and Robin boundary condition posed in an unbounded perforated domain. The nonlinear problem is associated with the hydrodynamic limit of a totally asymmetric simple exclusion process (TASEP) governing a population of interacting particles crossing a domain with obstacle. We are interested in deriving rigorously the upscaled model equations and the corresponding effective coefficients for the case when the microscopic dynamics are linked to a particular choice of characteristic length and time scales that lead to an exploding nonlinear drift. The main mathematical difficulty lies in proving the two -scale compactness and strong convergence results needed for the passage to the homogenization limit. To cope with the situation, we use the concept of two -scale compactness with drift, which is similar to the more classical two -scale compactness result but it is defined now in moving coordinates. We provide as well a strong convergence result for the corrector function, starting this way the search for the order of the convergence rate of the homogenization process for our target nonlinear drift problem
Renormalization Group results for lattice surface models.
Full text linkWe study the phase diagram of statistical systems of closed and open interfaces built on a cubic lattice. Interacting closed interfaces can be written as Ising models, while open surfaces as Z(2) gauge systems. When the open surfaces reduce to closed interfaces with few defects, also the gauge model can be written as an Ising spin model. We apply the lower bound renormalization group (LBRG) transformation introduced by Kadanoff (Phys. Rev. Lett. 34, 1005 (1975)) to study the Ising models describing closed and open surfaces with few defects. In particular, we have studied the Ising-like transition of self-avoiding surfaces between the random-isotropic phase and the phase with broken global symmetry at varying values of the mean curvature. Our results are compared with previous numerical work. The limits of the LBRG transformation in describing regions of the phase diagram where not ferromagnetic ground-states are relevant are also discussed. PACS number: 68.10.-m (Fluid surfaces and flu..
Anisotropic dynamical scaling in a spin model with competing interactions
Full text linkResults are presented for the kinetics of domain growth of a two-dimensional Ising spin model with competing interactions quenched from a disordered to a striped phase. The domain growth exponents are beta=1/2 and beta=1/3 for single-spin-flip and spin-exchange dynamics, as found in previous simulations. However, the correlation functions measured in the direction parallel and transverse to the stripes are different as suggested by the existence of different interface energies between the ground states of the model. In the case of single-spin-flip dynamics an anisotropic version of the Ohta-Jasnow-Kawasaki theory for the pair scaling function can be used to fit our data
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