Finite-size, magnetic and chemical-potential effects on first-order phase transitions

We perform a study about effects of an applied magnetic field and a finite chemical potential on the size-dependent phase structure of a first-order transition. These effects are introduced by using methods of quantum fields defined on toroidal spaces, and we study in particular the case of two compactified dimensions, imaginary time and a spatial one (a heated film). It is found that for any value of the applied field, there is a minimal size of the system, independent of the chemical potential, below which the transition disappears.Comment: 19 pages, 3 figures, version accepted for publication in Phys. Lett.

Time series forecasting with the WARIMAX-GARCH method

It is well-known that causal forecasting methods that include appropriately chosen Exogenous Variables (EVs) very often present improved forecasting performances over univariate methods. However, in practice, EVs are usually difficult to obtain and in many cases are not available at all. In this paper, a new causal forecasting approach, called Wavelet Auto-Regressive Integrated Moving Average with eXogenous variables and Generalized Auto-Regressive Conditional Heteroscedasticity (WARIMAX-GARCH) method, is proposed to improve predictive performance and accuracy but also to address, at least in part, the problem of unavailable EVs. Basically, the WARIMAX-GARCH method obtains Wavelet “EVs” (WEVs) from Auto-Regressive Integrated Moving Average with eXogenous variables and Generalized Auto-Regressive Conditional Heteroscedasticity (ARIMAX-GARCH) models applied to Wavelet Components (WCs) that are initially determined from the underlying time series. The WEVs are, in fact, treated by the WARIMAX-GARCH method as if they were conventional EVs. Similarly to GARCH and ARIMA-GARCH models, the WARIMAX-GARCH method is suitable for time series exhibiting non-linear characteristics such as conditional variance that depends on past values of observed data. However, unlike those, it can explicitly model frequency domain patterns in the series to help improve predictive performance. An application to a daily time series of dam displacement in Brazil shows the WARIMAX-GARCH method to remarkably outperform the ARIMA-GARCH method, as well as the (multi-layer perceptron) Artificial Neural Network (ANN) and its wavelet version referred to as Wavelet Artificial Neural Network (WANN) as in [1], on statistical measures for both in-sample and out-of-sample forecasting

Temporary use of a coastal ecosystem by the fish, Pomadasys corvinaeformis (Perciformes: Haemulidae), at Guaratuba Bay, Brazil

Pomadasys corvinaeformis is Qne ofthe most abundant species found in Guaratuba Bay, an Atlantic coastal, estuarine ecosystem in Paraná, Brazil. We tested whether this species comprises a resident or migratorial population. Abundance, size distribution, and gonad development of individuaIs captured during the year show that pre-adults enter the system when salinities are greater (autumn and early winter). During this time, they are mostly associated with mangroves and adjacent areas. When salinities begin to fall (late spring and summer) these now maturing individuaIs return to the sea where they spawn. Thus, P. corvinaeformis is migratorial and estuarine-dependent and uses this area prior to sexual maturity. During the period in this bay, P. corvinaeformis presents a great plasticity of feeding habits, that include inainly Crustacea, MoIlusca and Thaliacea.Pomadasys corvinaeformis é uma das espécies de maior representatividade na ictiofauna da Baía de Guaratuba, litoral do Estado do Paraná. Este trabalho investigou se a espécie compõe ali uma população permanente, residente no sistema, ou se é migratória, fteqüentando-o apenas em épocas determinadas. Resultados de 12 meses sobre variações de abundância, distribuição de tamanho e aspectos reprodutivos indicam que indivíduos subadultos ingressam no sistema quando a salinidade é maior (outono, começo de inverno). Nesta época, os indivíduos utilizam a área de manguezal e suas adjacências. Quanto a salinidade começa a cair (final de primavera, verão), estes indivíduos agora em maturação gonadal retomam para o mar, onde desovam. P. corvinaeformis é, portanto, uma espécie migratória e estuarino-dependente que utiliza a Baía em período anterior ao de maturidade gonadal. Ali, apresenta uma dieta muito variada, constituída basicamente de Crustacea, MoIlusca e Thaliacea

Canonical transformation for stiff matter models in quantum cosmology

In the present work we consider Friedmann-Robertson-Walker models in the presence of a stiff matter perfect fluid and a cosmological constant. We write the superhamiltonian of these models using the Schutz's variational formalism. We notice that the resulting superhamiltonians have terms that will lead to factor ordering ambiguities when they are written as operators. In order to remove these ambiguities, we introduce appropriate coordinate transformations and prove that these transformations are canonical using the symplectic method.Comment: Revtex4 Class, 3 pages, No Figure

Comportamento dos fluxos de N2O por dois métodos de quantificação: câmaras estáticas e micrometeorológico.

O objetivo do trabalho consistiu em comparar os fluxos de óxido nitroso (N2O) obtidos pelo método da câmara estática com um método micrometeorológico (gradiente de fluxo) em área consolidada com sistema de integração lavoura-pecuária, fase pastagem.Pôster - pós-graduação