32,958 research outputs found
Notes on the Two-brane Model with Variable Tension
Motivated by possible extensions of the braneworld models with two branes, we
investigate some consequences of a variable brane tension using the well
established results on consistency conditions. By a slight modification of the
usual stress-tensor used in order to derive the braneworld sum rules, we find
out some important constraints obeyed by time dependent brane tensions. In
particular it is shown that the tensions of two Randall-Sundrum like branes
obeying, at the same time, an Eotvos law, aggravate the fine tuning problem.
Also, it is shown that if the hidden brane tension obeys an Eotvos law, then
the visible brane has a mixed behavior allowing a bouncing-like period at early
times while it is dominated by an Eotvos law nowadays. To finalize, we discuss
some qualitative characteristics which may arise in the scope of dynamical
brane tensions, as anisotropic background and branons production.Comment: 7 pages, 1 figure, accepted for publication in Physical Review
Germination and vigor of long-pepper seeds (Piper hispidinervum) as a function of temperature and light.
A pimenta longa é considerada uma espécie promissora por apresentar a perspectiva de tornar o Brasil autosuficiente na produção de safrol, importante óleo essencial usado como fixador de fragrâncias e com propriedades terapêuticas. Na implantação de áreas destinadas à cultura dessa espécie é necessário avaliar a qualidade fisiológica das sementes utilizadas na formação de mudas. O objetivo foi determinar as condições de temperatura e luminosidade para o teste de germinação e vigor em sementes de pimenta longa. Foram utilizadas sementes de quatro lotes para as seguintes determinações: teor de água (105 + 3 ºC por 24 horas), germinação (20; 25; 30 e 35 °C com fotoperíodo de 12 e 24 horas, e alternadas de 20-30 °C e 20-35 °C, com 12 horas de luz na temperatura mais alta), índice de velocidade de germinação, velocidade de germinação, matéria seca de plântulas, emergência de plântulas, índice de velocidade de emergência e freqüência relativa da germinação. O delineamento experimental foi o inteiramente casualizado e as médias comparadas por Tukey (P<0,05). A germinação de sementes de pimenta longa pode ser avaliada a 25 °C/12 h escuro - 12 h luz, 25 °C/24 h luz, 30 °C/12 h escuro - 12 h luz e 30 °C/24 h luz, e o potencial fisiológico a 30 °C/24 h luz
Gravitational Collapse of Self-Similar and Shear-free Fluid with Heat Flow
A class of solutions to Einstein field equations is studied, which represents
gravitational collapse of thick spherical shells made of self-similar and
shear-free fluid with heat flow. It is shown that such shells satisfy all the
energy conditions, and the corresponding collapse always forms naked
singularities.Comment: 34 pages, 9 figures, late
Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz
We examine the possibility of using negative refraction stemming from the
phonon response in an anisotropic crystal to create a simple slab lens with
plane parallel sides, and show that imaging from such a lens should be possible
at room temperature despite the effects of absorption that are inevitably
present due to phonon damping. In particular, we consider the case of crystal
quartz, a system for which experimental measurements consistent with all-angle
negative refraction have already been demonstrated. Furthermore, we investigate
the possibility of subwavelength imaging from such materials, and show that it
should be possible for certain configurations.Comment: 12 pages, 10 figure
Decomposition of stochastic flows with automorphism of subbundles component
We show that given a -structure on a differentiable manifold , if
the group of automorphisms of is big enough, then there exists the
quotient of an stochastic flows by , in the sense that where , the remainder has
derivative which is vertical but transversal to the fibre of . This
geometrical context generalizes previous results where is a Riemannian
manifold and is decomposed with an isometric component, see Liao
\cite{Liao1} and Ruffino \cite{Ruffino}, which in our context corresponds to
the particular case of an SO(n)-structure on .Comment: To appear in Stochastics and Dynamics, 201
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