Equation of state and transport processes in self--similar spheres

We study the effect of transport processes (diffusion and free--streaming) on a collapsing spherically symmetric distribution of matter in a self--similar space--time. A very simple solution shows interesting features when it is matched with the Vaidya exterior solution. In the mixed case (diffusion and free--streaming), we find a barotropic equation of state in the stationary regime. In the diffusion approximation the gravitational potential at the surface is always constant; if we perturb the stationary state, the system is very stable, recovering the barotropic equation of state as time progresses. In the free--streaming case the self--similar evolution is stationary but with a non--barotropic equation of state.Comment: 9 pages, 2 figure

Self-similar and charged spheres in the diffusion approximation

We study spherical, charged and self--similar distributions of matter in the diffusion approximation. We propose a simple, dynamic but physically meaningful solution. For such a solution we obtain a model in which the distribution becomes static and changes to dust. The collapse is halted with damped mass oscillations about the absolute value of the total charge.Comment: 15 pages, 7 figure

Controlling Physical Systems with Symmetries

Symmetry properties of the evolution equation and the state to be controlled are shown to determine the basic features of the linear control of unstable orbits. In particular, the selection of control parameters and their minimal number are determined by the irreducible representations of the symmetry group of the linearization about the orbit to be controlled. We use the general results to demonstrate the effect of symmetry on the control of two sample physical systems: a coupled map lattice and a particle in a symmetric potential.Comment: 6 page

Why does gravitational radiation produce vorticity?

We calculate the vorticity of world--lines of observers at rest in a Bondi--Sachs frame, produced by gravitational radiation, in a general Sachs metric. We claim that such an effect is related to the super--Poynting vector, in a similar way as the existence of the electromagnetic Poynting vector is related to the vorticity in stationary electrovacum spacetimes.Comment: 9 pages; to appear in Classical and Quantum Gravit

Correlation equalities and upper bounds for the transverse Ising model

Starting from an exact formal identity for the two-state transverse Ising model and using correlation inequalities rigorous upper bounds for the critical temperature and the critical transverse field are obtained which improve effective results.Comment: 8 pages, 1 figur

The Kinematically Measured Pattern Speeds of NGC 2523 and NGC 4245

We have applied the Tremaine-Weinberg continuity equation method to derive the bar pattern speed in the SB(r)b galaxy NGC 2523 and the SB(r)0/a galaxy NGC 4245 using the Calcium Triplet absorption lines. These galaxies were selected because they have strong inner rings which can be used as independent tracers of the pattern speed. The pattern speed of NGC 2523 is 26.4 $\pm$ 6.1 km s$^{-1}$ kpc$^{-1}$, assuming an inclination of 49.7$^{\circ}$ and a distance of 51.0 Mpc. The pattern speed of NGC 4245 is 75.5 $\pm$ 31.3 km s$^{-1}$ kpc$^{-1}$, assuming an inclination of 35.4$^{\circ}$ and a distance of 12.6 Mpc. The ratio of the corotation radius to the bar radius of NGC 2523 and NGC 4245 is 1.4 $\pm$ 0.3 and 1.1 $\pm$ 0.5, respectively. These values place the bright inner rings near and slightly inside the corotation radius, as predicted by barred galaxy theory. Within the uncertainties, both galaxies are found to have fast bars that likely indicate dark halos of low central concentration. The photometric properties, bar strengths, and disk stabilities of both galaxies are also discussed.Comment: Accepted for publication in The Astronomical Journal, 11 figures, 2 table

Identificação através de PCR dos genes Cryl de cepas de Bacillus thuringiensis Berliner eficientes contra a lagarta do cartucho, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae).

Fall armyworm, Spodoptera frugiperda (J.E. Smith), is the most important maize insect pest in Brazil and its damage can reduce yield up to 34%. The objective of this work was to utilize the PCR technique to identify Bacillus thuringiensis (B.t) strains that control S. frugiperda in maize crops. Biossays showed that 16 strains were very effective against S. frugiperda, 15 of them collected from soil samples and one (T09) obtained at the Institute Pasteur. The DNA of these strains were probed with cryl general primers and their proteins were analyzed by SDS-PAGE eletrophoresis. All strains present positive results for cryl genes. To further characterize these strains, specific cryl primers were empolyed. PCR technique showed that some strains harbour the same cryl genes. The only difference was the amplification of an unexpected fragment of approximately 160bp when a mixture of cry1B and cry1D specific primers was used. Analysis by phase contrast microscope showed that crystal proteins produced by these strains were all bipyramidal crystals. Also, eltrophoretic analysis of proteins by SDS-PAGE showed the same protein banding pattern for most of the strains

Bondian frames to couple matter with radiation

A study is presented for the non linear evolution of a self gravitating distribution of matter coupled to a massless scalar field. The characteristic formulation for numerical relativity is used to follow the evolution by a sequence of light cones open to the future. Bondian frames are used to endow physical meaning to the matter variables and to the massless scalar field. Asymptotic approaches to the origin and to infinity are achieved; at the boundary surface interior and exterior solutions are matched guaranteeing the Darmois--Lichnerowicz conditions. To show how the scheme works some numerical models are discussed. We exemplify evolving scalar waves on the following fixed backgrounds: A) an atmosphere between the boundary surface of an incompressible mixtured fluid and infinity; B) a polytropic distribution matched to a Schwarzschild exterior; C) a Schwarzschild- Schwarzschild spacetime. The conservation of energy, the Newman--Penrose constant preservation and other expected features are observed.Comment: 20 pages, 6 figures; to appear in General Relativity and Gravitatio