Anisotropic superconducting properties of aligned MgB2 crystallites

Samples of aligned MgB2 crystallites have been prepared, allowing for the first time the direct identification of an upper critical field anisotropy Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40 A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background signal was identified, possibly related to the raw materials purity.Comment: 4 pages, 4 figures; Revised version to appear in Phys. Rev. Let

Irreversible magnetization under rotating fields and lock-in effect on ErBa_2Cu_3O_7 single crystal with columnar defects

We have measured the irreversible magnetization M_i of an ErBa_2Cu_3O_7 single crystal with columnar defects (CD), using a technique based on sample rotation under a fixed magnetic field H. This method is valid for samples whose magnetization vector remains perpendicular to the sample surface over a wide angle range - which is the case for platelets and thin films - and presents several advantages over measurements of M_L(H) loops at fixed angles. The resulting M_i(\Theta) curves for several temperatures show a peak in the CD direction at high fields. At lower fields, a very well defined plateau indicative of the vortex lock-in to the CD develops. The H dependence of the lock-in angle \phi_L follows the H^{-1} theoretical prediction, while the temperature dependence is in agreement with entropic smearing effects corresponding to short range vortex-defects interactions.Comment: 7 pages, 6 figures, to be published in Phys. Rev.

Avaliação da relação entre soja e produção de biodiesel.

O objetivo deste estudo foi avaliar a importância da producão de soja para o desenvolvimento do biodiesel no Brasil e o que representa o biocombustível para o mercado da oleaginosa. A análise de oferta e demanda por biodiesel revelou que as empresas apresentam capacidade produtiva para atender ao B5 e que as usinas da região sul são as mais eficientes, em relação às vendas. O estudo da expansão da produção de soja revelou que o seu cultivo está imerso em um contexto cercado por grandes movimentos e pressões por sustentabilidade ambiental. Embora o Brasil seja um grande exportador de soja ?in natura?, a tendência aponta para a evolução do volume produzido de óleo, o que, em grande parte, se deve ao aumento na produção do grão. Verificou-se que a dispersão do cultivo da soja em diferentes regiões do país, com escala de produção suficiente para atender à produção de volumes significativos de biodiesel, possibilitou combater os crônicos problemas logísticos existentes no agronegócio nacional. Por fim, a análise do Programa Nacional de Produção e Uso do Biodiesel confirmou que o óleo de soja é a matéria-prima que supre quase 80% da produção de biodiesel no Brasil. O desenvolvimento de outras fontes para a diversificação de matéria-prima para a produção de biodiesel, tais como sebo bovino, gordura de frango, algodão e mamona, possibilitará diminuir a pressão sobre a soja e tornar o negócio mais competitivo. Evaluation of the relationship between soybean and biodiesel production. Abstract. The objective of this study was to evaluate the importance of soybean production for the biodiesel development in Brazil and what the biofuel represents to the oilseed market. The analysis of biodiesel?s supply and demand has shown that companies have production capacity to attend B5 and that the plants of the south region are the most efficient in terms of sales. The study about soybean production revealed that its cultivation is immersed in an environment surrounded by great changes and pressures for environmental sustainability. Although Brazil is a great soybean exporter, the trend points to the evolution of the volume of oil producing, what, in the most, occurs due to the increase in the production of grain. It was found that the spread of soybean cultivation in different regions of the country, with sufficient production scale to attend the significant volumes of biodiesel production, became possible to combat the chronic problems in national agribusiness logistics. Finally, the analysis of the National Production and Use of Biodiesel showed that soybean oil is the raw material that supplies almost 80% of biodiesel production in Brazil. The development of other sources for diversification of feedstock for biodiesel production, such as beef tallow, chicken fat, cotton and castor beans, will allow to reduce the pressure on soybeans and to make the business more competitive

Extreme events of precipitation in the rainy season of the state of Bahia.

Abstract: The increase of frequency and intensity of extreme precipitation events has generated consequences for biodiversity of natural systems, economic and life losses. In particular, the state of Bahia has been the scene of an increase of severe droughts in almost its entirety and outbreaks of floods that serve as a warning to the future. In this regard, the objective of this work was to analyze the frequency of occurrence of extreme events of precipitation between 1981 and 2010 of Bahia.Resumo em português: Eventos extremos de precipitação na estação chuvosa do estado da Bahia. SIC 2013

Structure and Subhalo Population of Halos in a Self-Interacting Dark Matter Cosmology

We study the structure of Milky Way (MW)- and cluster-sized halos in a Lambda Cold Dark Matter (CDM) cosmology with self-interacting (SI) dark particles. The cross section per unit of particle mass has the form sigma = sig_0(1/v_100)^alpha, where sig_0 is a constant in units of cm^2/gr and v_100 is the relative velocity in units of 100 km/s. Different values for sigma with alpha= 0 or 1 were used. For small values of sigma = const. (sig_0<0.5), the core density of the halos at z=0 is typically higher at a given mass for lower values of sig_0 or, at a given sig_0, for lower masses. For values of sig_0 as high as 3.0, the halos may undergo the gravothermal catastrophe before z=0. When alpha = 1, the core density of cluster- and MW-sized halos is similar. Using sigma = 0.5-1.0x(1/v_100), our predictions agree with the central densities and the core scaling laws of halos both inferred from the observations of dwarf and LSB galaxies and clusters of galaxies. The cumulative Vmax-functions of subhalos in MW-sized halos with (sig_0,alpha) = (0.1,0.0), (0.5,0.0) and (0.5,1.0) agree roughly with observations (luminous satellites) for Vmax > 30 km/s, while at Vmax = 20 km/s the functions are a factor 5-8 higher, similar to the CDM predictions. The halos with SI have slightly more specific angular momentum at a given mass shell and are rounder than their CDM counterparts. We conclude that the introduction of SI particles with sigma \propto 1/v_100 may remedy the cuspy core problem of the CDM cosmogony, while the subhalo population number remains similar to that of the CDM halos.Comment: To appear in ApJ, December 20, 2002. We added plots showing the evolution of the heat capacity profile for halos in the core expansion and gravothermal catastrophe phases. Minor changes in the text were introduce

Classificação de anos secos e chuvosos em zonas pluviometricamente homogêneas no Estado da Bahia.

O conhecimento da distribuição espaço-temporal das chuvas pode orientar a tomada de decisão sobre as medidas necessárias para minimizar os danos decorrentes da irregularidade dessa variável. Em particular, o Estado da Bahia apresenta um cenário com alta variabilidade na precipitação pluvial, decorrente da conjunção de diferentes sistemas meteorológicos que atuam nessa região, bem como, de um relevo constituído por planícies, vales, serras e montanhas (BARSOSA, 2000). As técnicas de mineração de dados são uma alternativa promissora para identificar zonas pluviométricas homogêneas e analisar o comportamento das séries temporais (HAN; KAMBER, 2011). Neste sentido, o objetivo deste trabalho foi identificar as zonas pluviometricamente homogêneas e classificar climaticamente os anos com relação à precipitação, em cada região associada com a produtividade agrícola do Estado

Método para comparar curvas de produção de ovos usando um modelo matemático.

bitstream/item/85106/1/DCOT-293.pd

Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders

The flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction, in which cases heat transfer occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. We obtain a simple linear criterion that determines whether the infinite-cylinder assumption can be employed. The curvature of the cylinders enters this linear relationship through the slope and additive constant. For a given length-to-gap aspect ratio there is a critical Rayleigh number beyond which the laminar flow in the finite system is convective and so the behaviour is entirely different from the periodic case. The criterion does not depend on the Prandtl number and appears quite robust with respect to the Reynolds number. In particular, it continues to work reasonably in the turbulent regime.Comment: 25 pages, 9 figure