61,623 research outputs found
Nonextensive Quantum H-Theorem
A proof of the quantum -theorem taking into account nonextensive effects
on the quantum entropy is shown. The positiveness of the time variation
of combined with a duality transformation implies that the nonextensive
parameter lies in the interval [0,2]. It is also shown that the equilibrium
states are described by quantum -power law extensions of the Fermi-Dirac and
Bose-Einstein distributions. Such results reduce to the standard ones in the
extensive limit, thereby showing that the nonextensive entropic framework can
be harmonized with the quantum distributions contained in the quantum
statistics theory.Comment: 5 pages, LaTe
Dark Matter and Dark Energy due to Photons that Attract or Repel Each Other
The Through a simple model we study the possibility of photon with mass and charge that can produce an attractive or repulsive force at galactic distances. The main source of the dark energy can be provided by the non-vanishing photon mass during the period of dark radiation of the Universe. A simple analysis shows that the non-vanishing photon mass of the order of is consistent with the current observations. For distances separating nearby galaxies dominates the force of Newtonian attraction between photonic masses (Dark Matter). For distant galaxies dominates the repulsive electrical force between photon charges (Dark Energy)
Alterations in white matter microstructure in neurofibromatosis-1.
Neurofibromatosis (NF1) represents the most common single gene cause of learning disabilities. NF1 patients have impairments in frontal lobe based cognitive functions such as attention, working memory, and inhibition. Due to its well-characterized genetic etiology, investigations of NF1 may shed light on neural mechanisms underlying such difficulties in the general population or other patient groups. Prior neuroimaging findings indicate global brain volume increases, consistent with neural over-proliferation. However, little is known about alterations in white matter microstructure in NF1. We performed diffusion tensor imaging (DTI) analyses using tract-based spatial statistics (TBSS) in 14 young adult NF1 patients and 12 healthy controls. We also examined brain volumetric measures in the same subjects. Consistent with prior studies, we found significantly increased overall gray and white matter volume in NF1 patients. Relative to healthy controls, NF1 patients showed widespread reductions in white matter integrity across the entire brain as reflected by decreased fractional anisotropy (FA) and significantly increased absolute diffusion (ADC). When radial and axial diffusion were examined we found pronounced differences in radial diffusion in NF1 patients, indicative of either decreased myelination or increased space between axons. Secondary analyses revealed that FA and radial diffusion effects were of greatest magnitude in the frontal lobe. Such alterations of white matter tracts connecting frontal regions could contribute to the observed cognitive deficits. Furthermore, although the cellular basis of these white matter microstructural alterations remains to be determined, our findings of disproportionately increased radial diffusion against a background of increased white matter volume suggest the novel hypothesis that one potential alteration contributing to increased cortical white matter in NF1 may be looser packing of axons, with or without myelination changes. Further, this indicates that axial and radial diffusivity can uniquely contribute as markers of NF1-associated brain pathology in conjunction with the typically investigated measures
Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d
The question whether ferroelectricity (FE) may coexist with a metallic or
highly conducting state, or rather it must be suppressed by the screening from
the free charges, is the focus of a rapidly increasing number of theoretical
studies and is finally receiving positive experimental responses. The issue is
closely related to the thermoelectric and multiferroic (also magnetic)
applications of FE materials, where the electrical conductivity is required or
spurious. In these circumstances, the traditional methods for probing
ferroelectricity are hampered or made totally ineffective by the free charges,
which screen the polar response to an external electric field. This fact may
explain why more than 40 years passed between the first proposals of FE metals
and the present experimental and theoretical activity. The measurement of the
elastic moduli, Young's modulus in the present case, versus temperature is an
effective method for studying the influence of doping on a FE transition
because the elastic properties are unaffected by electrical conductivity. In
this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed
by electron doping through O vacancies; only the onset temperatures are
depressed, but the magnitudes of the softenings, and hence of the piezoelectric
activity, are initially even increased
Centrifugal force induced by relativistically rotating spheroids and cylinders
Starting from the gravitational potential of a Newtonian spheroidal shell we
discuss electrically charged rotating prolate spheroidal shells in the Maxwell
theory. In particular we consider two confocal charged shells which rotate
oppositely in such a way that there is no magnetic field outside the outer
shell. In the Einstein theory we solve the Ernst equations in the region where
the long prolate spheroids are almost cylindrical; in equatorial regions the
exact Lewis "rotating cylindrical" solution is so derived by a limiting
procedure from a spatially bound system. In the second part we analyze two
cylindrical shells rotating in opposite directions in such a way that the
static Levi-Civita metric is produced outside and no angular momentum flux
escapes to infinity. The rotation of the local inertial frames in flat space
inside the inner cylinder is thus exhibited without any approximation or
interpretational difficulties within this model.
A test particle within the inner cylinder kept at rest with respect to axes
that do not rotate as seen from infinity experiences a centrifugal force.
Although the spacetime there is Minkowskian out to the inner cylinder
nevertheless that space has been induced to rotate, so relative to the local
inertial frame the particle is traversing a circular orbit.Comment: 12 pages, 2 figure
Resposta de Pinus taeda L. na aplicação de cinza de biomassa vegetal em cambissolo húmico, em vaso.
Resumo
Resposta de Pinus taeda L. à aplicação de cinza de biomassa vegetal em Cambissolo Húmico, em vaso.
Foi avaliado o efeito de doses de cinza de biomassa vegetal, equivalentes a 0; 10; 20; 40 e 80 t.ha-1, sobre caracterĂsticas quĂmicas do solo e sobre o desenvolvimento e absorção de nutrientes por mudas de Pinus taeda L., em casa-de-vegetação da Embrapa Florestas, em Colombo, PR, em Cambissolo HĂşmico, coletado na camada de 0 a 20 cm, em PiraĂ do Sul, PR. Porções da amostra do solo foram colocadas em vasos, sendo as alĂquotas de cada tratamento aplicadas na camada de 0 a 10 cm, apĂłs preencher os vasos com 20 cm de solo. Foram analisadas as acĂculas e o solo (camadas 0 a 10 cm, 10 cm a 20 cm e 20 cm a 30 cm). Avaliaram-se a altura, o diâmetro e as massas secas da parte aĂ©rea, da raiz - MSR e total. A aplicação da cinza diminuiu a acidez e o teor de Al, e aumentou os teores de Ca, Mg, K e P, com efeitos mais pronunciados na camada de 0 a 10 cm; nĂŁo houve efeito dos tratamentos no desenvolvimento das mudas; o teor de Cu nas acĂculas foi diminuĂdo com o aumento da dose de cinza
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