Dynamical Evolution of a Cylindrical Shell with Rotational Pressure

We prepare a general framework for analyzing the dynamics of a cylindrical shell in the spacetime with cylindrical symmetry. Based on the framework, we investigate a particular model of a cylindrical shell-collapse with rotational pressure, accompanying the radiation of gravitational waves and massless particles. The model has been introduced previously but has been awaiting for proper analysis. Here the analysis is put forward: It is proved that, as far as the weak energy condition is satisfied outside the shell, the collapsing shell bounces back at some point irrespective of the initial conditions, and escapes from the singularity formation. The behavior after the bounce depends on the sign of the shell pressure in the z-direction. When the pressure is non-negative, the shell continues to expand without re-contraction. On the other hand, when the pressure is negative (i.e. it has a tension), the behavior after the bounce can be more complicated depending on the details of the model. However, even in this case, the shell never reaches the zero-radius configuration.Comment: To appear in Phys. Rev.

Characterization of InGaN and InAlN epilayers by microdiffraction X-Ray reciprocal space mapping

We report a study of InGaN and InAlN epilayers grown on GaN/Sapphire substrates by microfocused three-dimensional X-ray Reciprocal Space Mapping (RSM). The analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused X-ray beam, allows us to gain uniquely valuable information about the microstructure of III-N alloy epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain free. This indicates that the growth of InGaN epilayers follows the Volmer-Weber mechanism with nucleation of “seeds” on strain fields generated by the a-type dislocations which are responsible for the twist of underlying GaN mosaic blocks. In the case of InAlN epilayer formation of composition gradient was observed at the beginning of the epitaxial growth

Chemical Potential and the Nature of the Dark Energy: The case of phantom

The influence of a possible non zero chemical potential $\mu$ on the nature of dark energy is investigated by assuming that the dark energy is a relativistic perfect simple fluid obeying the equation of state (EoS), $p=\omega \rho$ ($\omega <0, constant$). The entropy condition, $S \geq 0$, implies that the possible values of $\omega$ are heavily dependent on the magnitude, as well as on the sign of the chemical potential. For $\mu >0$, the $\omega$-parameter must be greater than -1 (vacuum is forbidden) while for $\mu < 0$ not only the vacuum but even a phantomlike behavior ($\omega <-1$) is allowed. In any case, the ratio between the chemical potential and temperature remains constant, that is, $\mu/T=\mu_0/T_0$. Assuming that the dark energy constituents have either a bosonic or fermionic nature, the general form of the spectrum is also proposed. For bosons $\mu$ is always negative and the extended Wien's law allows only a dark component with $\omega < -1/2$ which includes vacuum and the phantomlike cases. The same happens in the fermionic branch for $\mu 0$ are permmited only if $-1 < \omega < -1/2$. The thermodynamics and statistical arguments constrain the EoS parameter to be $\omega < -1/2$, a result surprisingly close to the maximal value required to accelerate a FRW type universe dominated by matter and dark energy ($\omega \lesssim -10/21$).Comment: 7 pages, 5 figure

Produção de abelhas rainha européias (Apis mellifera), utilizando diferentes métodos de manejo em Captain Cook, Havai, EUA.

Objetivou-se verificar a influencia do uso de diferentes métodos de manejo nas colmeias recria, na aceitação de larvas para produção de abelhas rainha (Apis melífera ligustica). O trabalho foi conduzido durante o mês de agosto de 2008, na Hawaiian Queen CO, cidade de Captain Cook, estado do Havaí, EUA. Foi utilizado o método proposto por Doolittle (1899), utilizando-se cúpulas de acrílico. Os tratamentos foram: T1- colmeia recria com rainha composta por um ninho, tela excluidora e sobreninho (recria); T2- colmeia Recria com rainha composta por ninho, sobreninho 1, tela excluidora e sobreninho 2 (recria); T3- Introdução das larvas transferidas para ambiente com abelhas operárias órfãs e transferência para uma colmeia recria com rainha composta por um ninho, tela excluidora e sobreninho (recria); T4- Introdução das larvas transferidas para ambiente com abelhas operárias órfãs e transferência para uma colmeia recria com rainha composta por um ninho, sobreninho, tela excluidora e sobreninho (recria). Após execução do teste da normalidade de Shapiro-Wilk, foi executado o teste t para amostras independentes e Mann-Whitney. Verificou-se significância ao nível de 5% de probabilidade entre os tratamentos, ou seja, os tratamentos 1, 3 e 4 mostraram-se mais eficientes para aceitação das larvas e produção de rainhas