Critical properties of the XXZ model with long-range interactions on the double chain

The $XXZ$ model $(s = 1/2)$ in a transverse field on a double chain with a uniform long-range interaction among the $z$ components of the spins is considered. The nearest-neighbour interactions are restricted to the components in the $xy$ plane and to the spins within the same chain leg, such that the Hamiltonian is given by $H = -\sum_{m=1}^{2} J_{m} \sum_{j=1}^{N}(S_{m,j}^{x}S_{m, j+1}^{x} + S_{m,j}^{y}S_{m,j+1}^{y}) - \frac{I}{N}\sum_{m,n=1}^{2} \sum_{j,k=1}^{N}S_{m,j}^{z}S_{n,k}^{z}-h\sum_{m=1}^{2} \sum_{j=1}^{N}S_{m,j}^{z}$, where $N$ is the number of sites of the lattice and $m,n$ $(m,n = 1, 2)$ label the chain legs. The model is solved exactly by introducing the Jordan-Wigner and integral Gaussian transformations, which map the Hamiltonian in a non-interacting fermion system and corresponds to an extension of the model recently studied by the authors for a single chain. The equation of state is obtained in closed form, and the critical classical (at $T > 0$) and quantum (at $T = 0$) behaviours can be determined exactly. The quantum critical surface is determined in the space generated by the transverse field and interaction parameters, and the crossover lines separating the different critical regimes are also obtained. It is also shown that, differently from the results obtained for the single chain, the system can present multiple quantum transitions.Comment: 02 pages, 02 figures, to appear in JMMM (Proceedings of ICM2006

The XY model on the one-dimensional superlattice: static properties

The XY model (s=1/2) on the one-dimensional alternating superlattice (closed chain) is solved exactly by using a generalized Jordan-Wigner transformation and the Green function method. Closed expressions are obtained for the excitation spectrum, the internal energy, the specific heat, the average magnetization per site, the static transverse susceptibility and the two-spin correlation function in the field direction at arbitrary temperature. At T=0 it is shown that the system presents multiple second order phase transitions induced by the transverse field, which are associated to the zero energy mode with wave number equal to 0 or $\pi$. It is also shown that the average magnetization as a function of the field presents, alternately, regions of plateaux (disordered phases) and regions of variable magnetization (ordered phases). The static correlation function presents an oscillating behaviour in the ordered phase and its period goes to infinity at the critical point.Comment: 16 pages, 16 figure

A comparative analysis of thermophysical properties correlations for n-paraffins to be used in wax precipitation modeling

The performance of a thermodynamic wax precipitation model strongly depends upon the n-paraffin thermophysical properties used. In order to estimate them, several correlations have been proposed, and their values have a great impact on both calculated wax disappearance temperature (WDT) and amount of wax precipitated at each temperature (WPC). The main goal of this work is to evaluate the correlations available for the relevant thermophysical properties aiming at achieving a reliable wax precipitation modeling. The methodology used involves the direct comparison of the correlations with the values of pure n-paraffin properties, and indirect evaluation by their use in the estimation of wax disappearance temperatures, the amount of wax precipitated at each temperature, and DSC experimental curves. This study contemplates two thermodynamic approaches for paraffin precipitation: the solid solution (SS), which considers the formation of one solid solution; and the multisolid phase model (MS), that assumes that each solid phase consists of a pure component.publishe

The one-dimensional XXZ model with long-range interactions

The one-dimensional XXZ model (s=1/2, N sites) with uniform long-range interactions among the transverse components of the spins is considered. The Hamiltonian of the model is explicitly given by $H=J\sum_{j=1}^{N}(s_{j}^{x}s_{j+1}^{x}+s_{j}^{y}s_{j+1}^{y}) -(I/N)\sum_{j,k=1}^{N}s_{j}^{z}s_{k}^{z}-h\sum_{j=1}^{N}s_{j}^{z},$ where the $s^{x,y,z}$ are half the Pauli spin matrices. The model is exactly solved by applying the Jordan-Wigner fermionization, followed by a Gaussian transformation. In the absence of the long-range interactions (I=0), the model, which reduces to the isotropic XY model, is known to exhibit a second-order quantum phase transition driven by the field at zero temperature. It is shown that in the presence of the long-range interactions (I different from 0) the nature of the transition is strongly affected. For I>0, which favours the ordering of the transverse components of the spins, the transition is changed from second- to first-order, due to the competition between transverse and xy couplings. On the other hand, for I<0, which induces complete frustration of the spins, a second-order transition is still present, although the system is driven out of its usual universality class, and its critical exponents assume typical mean-field values.Comment: 5 pages, 1 figure, presented at ICM2000, to be published in the Proceedings (Journal of Magnetism & Magnetic Materials

Cissus Sicyoides: Pharmacological Mechanisms Involved In The Anti-inflammatory And Antidiarrheal Activities

The objective of this study was to evaluate the pharmacological mechanisms involved in anti-inflammatory and antidiarrheal actions of hydroalcoholic extract obtained from the leaves of Cissus sicyoides (HECS). The anti-inflammatory effect was evaluated by oral administration of HECS against acute model of edema induced by xylene, and the mechanisms of action were analysed by involvement of arachidonic acid (AA) and prostaglandin E2 (PGE2). The antidiarrheal effect of HECS was observed and we analyzed the motility and accumulation of intestinal fluid. We also analyzed the antidiarrheal mechanisms of action of HECS by evaluating the role of the opioid receptor, α2 adrenergic receptor, muscarinic receptor, nitric oxide (NO) and PGE2. The oral administration of HECS inhibited the edema induced by xylene and AA and was also able to significantly decrease the levels of PGE2. The extract also exhibited significant anti-diarrheal activity by reducing motility and intestinal fluid accumulation. This extract significantly reduced intestinal transit stimulated by muscarinic agonist and intestinal secretion induced by PGE2. Our data demonstrate that the mechanism of action involved in the anti-inflammatory effect of HECS is related to PGE2. The antidiarrheal effect of this extract may be mediated by inhibition of contraction by acting on the intestinal smoothmuscle and/or intestinal transit. © 2016 by the authors; licensee MDPI, Basel, Switzerland.17

Quantum phase-space description of light polarization

We present a method to characterize the polarization state of a light field in the continuous-variable regime. Instead of using the abstract formalism of SU(2) quasidistributions, we model polarization in the classical spirit by superposing two harmonic oscillators of the same angular frequency along two orthogonal axes. By describing each oscillator by a $s$-parametrized quasidistribution, we derive in a consistent way the final function for the polarization. We compare with previous approaches and discuss how this formalism works in some relevant examples.Comment: 17 pages, 4 eps color figure

NEOPLASIA MALIGNA DA PROSTATA FRENTE A SEUS FATORES DE RISCO E RASTREAMENTO

A neoplasia maligna de próstata é uma das doenças que mais acometem os homens, tendo uma alta morbidade e uma alta incidência. Esse estudo é uma revisão de literatura do tipo transversal que busca conceituar os principais fatores de risco dessa doença, como também oferecer esclarecimentos sobre o rastreamento em homens que não apresentam sintomas, aumentando a gama de informações sobre o assunto e ajudando profissionais de saúde em geral. No resultado encontramos a discussão dos fatores de risco, sendo eles a idade, a etnia, fatores nutricionais e fatores hereditários e genéticos. Temos posteriormente o rastreamento, que inclui o toque retal, que julga o tamanho, a forma e a textura da próstata, e o exame de sangue para a aferição do Antígeno Prostático Especifico (PSA). Segundo os principais artigos utilizados, esse rastreamento não reduz a mortalidade causada pela doença, ocasionando muitas vezes resultados não confiáveis. Diante dos resultados revelados podemos observar que ainda há muito a se pesquisar sobre fatores que podem predispor a neoplasia de próstata. Como uma alternativa ao rastreamento desse câncer, temos o controle da doença com a capacitação dos profissionais, organização da assistência e diagnóstico e tratamento rápido, eficaz e qualificado dos enfermos

Adubos verdes e seus efeitos no rendimento da cana-de-açúcar em sistema de plantio direto.

O objetivo deste trabalho foi avaliar adubos verdes e seus efeitos no rendimento da cana-de-açúcar em sistema de plantio direto (SPD). O trabalho foi realizado em Campos dos Goytacazes (RJ), no período de dezembro de 2003 a julho de 2005. O delineamento experimental foi em blocos casualizados, com quatro repetições. Os tratamentos foram: feijão-de-porco (Canavalia ensiformis), mucuna-preta(Mucuna aterrimum), crotalária (Crotalária juncea) em plantio direto e vegetação espontânea em preparo convencional (testemunha). Com crotalária aos 35 dias após emergência (DAE) houve maior taxa de cobertura do solo – 87% – e, aos 92 DAE produziu 17.852 kg ha-1 de matéria seca, respectivamente, 41%, 78% e 407% superior ao feijão-de-porco, mucuna e vegetação espontânea, além de superá-las em acúmulos de K, Mg, S, Zn e Fe. O feijão-de-porco e a mucuna proporcionaram o maior teor de N na parte aérea. Com feijão-de-porco, os teores de P e Ca foram maiores que a crotalária e a mucuna. Com vegetação espontânea, o maior teor de K foi na parte aérea. As leguminosas acumularam maiores quantidades de N e Cu do que a vegetação espontânea. A crotalária e o feijão-de-porco acumularam 66% a mais de P na parte área que a mucuna. O SPD utilizando a adubação verde contribuiu significativamente para a maior produtividade de cana-de-açúcar, 135.863 kg ha-1, sendo 37% superior ao PC com a vegetação espontânea