Action at a distance in classical uniaxial ferromagnetic arrays

We examine in detail the theoretical foundations of striking long-range couplings emerging in arrays of fluid cells connected by narrow channels by using a lattice gas (Ising model) description of a system. We present a reexamination of the well known exact determination of the two-point correlation function along the edge of a channel using the transfer matrix technique and a new interpretation is provided. The explicit form of the correlation length is found to grow exponentially with the cross section of the channels at the bulk two-phase coexistence. The aforementioned result is recaptured by a refined version of the Fisher-Privman theory of first order phase transitions in which the Boltzmann factor for a domain wall is decorated with a contribution stemming from the point tension originated at its endpoints. The Boltzmann factor for a domain wall together with the point tension is then identified exactly thanks to two independent analytical techniques, providing a critical test of the Fisher-Privman theory. We then illustrate how to build up the network model from its elementary constituents, the cells and the channels. Moreover, we are able to extract the strength of the coupling between cells and express them in terms of the length and width and coarse grained quantities such as surface and point tensions. We then support our theoretical investigation with a series of corroborating results based on Monte Carlo simulations. We illustrate how the long range ordering occurs and how the latter is signaled by the thermodynamic quantities corresponding to both planar and three-dimensional Ising arrays.Comment: 36 pages, 19 figure

Structure of interfaces at phase coexistence. Theory and numerics

We compare results of the exact field theory of phase separation in two dimensions with Monte Carlo simulations for the q-state Potts model with boundary conditions producing an interfacial region separating two pure phases. We confirm in particular the theoretical predictions that below critical temperature the surplus of non-boundary colors appears in drops along a single interface, while for q > 4 at critical temperature there is formation of two interfaces enclosing a macroscopic disordered layer. These qualitatively different structures of the interfacial region can be discriminated through a measurement at a single point for different system sizes

Sleep patterns over 15-day period in rats with spinal cord injury

Study design: Experimental, controlled trial.Objectives: the purpose of this study was to evaluate over a 15-day period alterations in sleep pattern of rats after spinal cord injury (SCI).Setting: Federal University of São Paulo, Department of Psychobiology.Methods: in total, 20 male Wistar rats were used. the rats were divided in two groups: SHAM and SCI. the rats were submitted to the following procedures: electrode insertion surgery, 24 h duration baseline sleep recording, SCI (level T9) and subsequent sleep recording for 15 consecutive days.Results: the results showed a reduction in sleep efficiency in the light period for Days 1-3, 5, 10 and 12 after SCI in relation to the SHAM group, with alterations in total waking time and sleep stages. Limb movements were observed 4 days after SCI.Conclusion: the present findings suggest that SCI may be heavily involved in altering sleep pattern in SCI subjects and that the inactivity caused by SCI may be exacerbating this altered sleep pattern.Universidade Federal de São Paulo, Dept Psychobiol, BR-04020060 São Paulo, BrazilUniversidade Federal de São Paulo, Ctr Psychobiol & Exercise Res, BR-04020060 São Paulo, BrazilSanta Casa, Dept Pathol, São Paulo, BrazilUniversidade Federal de São Paulo, Dept Psychobiol, BR-04020060 São Paulo, BrazilUniversidade Federal de São Paulo, Ctr Psychobiol & Exercise Res, BR-04020060 São Paulo, BrazilWeb of Scienc

Numerical multilevel investigation for evaluation of pressure distribution in EHL circular contacts from film thickness measurements

In this paper an analysis of the Elastohydrodynamic lubricated circular contact through a hybrid technique is presented. In particular the attention is focused on the pressure distribution calculation. A versatile code has been developed, able to evaluate the pressure distribution starting from 3-D film thickness maps obtained from the analysis of the interferometric images. The code is developed in C++ and is based on Multigrid Technique. This hybrid technique has a basic advantage with respect to the full numerical approach: the pressure is obtained without making any assumption about the lubricant itself. The main disadvantage of the method is that high resolution of the interferometric images is requested

Interfaces and wetting transition on the half plane. Exact results from field theory

We consider the scaling limit of a generic ferromagnetic system with a continuous phase transition, on the half plane with boundary conditions leading to the equilibrium of two different phases below criticality. We use general properties of low-energy two-dimensional field theory to determine exact asymptotics of the magnetization profile perpendicular to the boundary, to show the presence of an interface with endpoints pinned to the boundary, and to determine its passage probability. The midpoint average distance of the interface from the boundary grows as the square root of the distance between the endpoints, unless the reflection amplitude of the bulk excitations on the boundary possesses a stable bound state pole. The contact angle of the phenomenological wetting theory is exactly related to the location of this pole. Results available from the lattice solution of the Ising model are recovered as a particular case