The Levi-Civita spacetime

We consider two exact solutions of Einstein's field equations corresponding to a cylinder of dust with net zero angular momentum. In one of the cases, the dust distribution is homogeneous, whereas in the other, the angular velocity of dust particles is constant [1]. For both solutions we studied the junction conditions to the exterior static vacuum Levi-Civita spacetime. From this study we find an upper limit for the energy density per unit length $\sigma$ of the source equal ${1\over 2}$ for the first case and ${1\over 4}$ for the second one. Thus the homogeneous cluster provides another example [2] where the range of $\sigma$ is extended beyond the limit value ${1\over 4}$ previously found in the literature [3,4]. Using the Cartan Scalars technics we show that the Levi-Civita spacetime gets an extra symmetry for $\sigma={1\over 2}$ or ${1\over 4}$. We also find that the cluster of homogeneous dust has a superior limit for its radius, depending on the constant volumetric energy density $\rho_0$

Finite size effects in nonequilibrium wetting

Models with a nonequilibrium wetting transition display a transition also in finite systems. This is different from nonequilibrium phase transitions into an absorbing state, where the stationary state is the absorbing one for any value of the control parameter in a finite system. In this paper, we study what kind of transition takes place in finite systems of nonequilibrium wetting models. By solving exactly a microscopic model with three and four sites and performing numerical simulations we show that the phase transition taking place in a finite system is characterized by the average interface height performing a random walk at criticality and does not discriminate between the bounded-KPZ classes and the bounded-EW class. We also study the finite size scaling of the bKPZ universality classes, showing that it presents peculiar features in comparison with other universality classes of nonequilibrium phase transitions.Comment: 14 pages, 6figures, major change

Pulse-height-spectrum distortion in xenon gaseous detectors for soft X-rays: experimental results

The results of an experimental determination of the pulse-height distortion in soft X-ray spectra in gaseous xenon detectors are presented. The study confirms previous Monte Carlo simulation results and emphasizes the importance of the electric field in the drift region in reducing spectral degradation while the effect of a strong magnetic field in the same region is shown to be negligibleJNICT (Junta Nacional de Investigação Científica e Tecnológica) Projecto STRDA/P/CEN/422/9

Biologia da polinização da castanheira-do-brasil (Bertholletia excelsa Bonpl., LECYTHIDACEAE) em Tomé-Açu, Pará.

A castanheira-do-brasil (Bertholletia excelsa Bonpl.) é uma espécie arbórea nativa da Amazônia. Este estudo teve como objetivo investigar a biologia floral e os requerimentos de polinização dessa espécie em um Sistema Agroflorestal (SAF), em Tomé-Açu/PA, nos anos de 2010 e 2011. Chegou-se às flores através de torres de observação de 12 a 20 metros de altura. Caracterizou-se: a antese; duração da floração; receptividade de estigma; viabilidade de pólen; localização dos osmóforos; volume e % de açúcar do néctar; comportamento e identificação de visitantes florais; e o sistema reprodutivo, através de testes de polinização controlada: autopolinização espontânea (AE, n=540/1.672) e induzida (AI, n=657/1.566); xenogamia (XE, n=880/1.716) e geitonogamia (GE, n=742/1.443). O controle foi realizado por polinização livre (PL, n=564/2.343), dados de 2010/2011, respectivamente. A floração ocorreu nos meses de outubro a janeiro. A antese variou entre as árvores entre 01:00h e 05:30h. De 07:00h às 11:00h o estigma está receptivo e o pólen viável. O néctar tem maior concentração de açúcares às 8:30h e volume crescente de 06:30 às 12:30h. Registrou-se a formação de 29 frutos em 2010: AE=9; AI=7; XE=10; GE=2 e PL=1. Em 2011, apenas dois frutos: XE=1 e PL=1. Nas flores, coletou-se 64 insetos entre as ordens Hymenoptera; Hemiptera; e Coleoptera. O polinizador efetivo foi Xylocopa frontalis

Temperature inversion symmetry in the Casimir effect with an antiperiodic boundary condition

We present explicitly another example of a temperature inversion symmetry in the Casimir effect for a nonsymmetric boundary condition. We also give an interpretation for our result.Comment: 4 page