24,657 research outputs found
Macroclumping as solution of the discrepancy between H{\alpha} and P v mass loss diagnostics for O-type stars
Recent studies of O-type stars demonstrated that discrepant mass-loss rates
are obtained when different diagnostic methods are employed - fitting the
unsaturated UV resonance lines (e.g. P v) gives drastically lower values than
obtained from the H{\alpha} emission. Wind clumping may be the main cause for
this discrepancy. In a previous paper, we have presented 3-D Monte-Carlo
calculations for the formation of scattering lines in a clumped stellar wind.
In the present paper we select five O-type supergiants (from O4 to O7) and test
whether the reported discrepancies can be resolved this way. In the first step,
the analyses start with simulating the observed spectra with Potsdam Wolf-Rayet
(PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit best
to the observed H{\alpha} emission lines. For the unsaturated UV resonance
lines (i.e. P v) we then apply our 3-D Monte-Carlo code, which can account for
wind clumps of any optical depths, a non-void inter-clump medium, and a
velocity dispersion inside the clumps. The ionization stratifications and
underlying photospheric spectra are adopted from the PoWR models. From fitting
the observed resonance line profiles, the properties of the wind clumps are
constrained. Our results show that with the mass-loss rates that fit H{\alpha}
(and other Balmer and He II lines), the UV resonance lines (especially the
unsaturated doublet of P v) can also be reproduced without problem when
macroclumping is taken into account. There is no need to artificially reduce
the mass-loss rates, nor to assume a sub-solar phosphorus abundance or an
extremely high clumping factor, contrary to what was claimed by other authors.
These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared
to the mass-loss rate recipe from Vink et al. Macroclumping resolves the
previously reported discrepancy between H{\alpha} and P v mass-loss
diagnostics.Comment: 18 pages, 14 figures, 5 tables, accepted for publication in
Astrononomy & Astrophysic
Gravitational memory of natural wormholes
A traversable wormhole solution of general scalar-tensor field equations is
presented. We have shown, after a numerical analysis for the behavior of the
scalar field of Brans-Dicke theory, that the solution is completely
singularity--free. Furthermore, the analysis of more general scalar field
dependent coupling constants indicates that the gravitational memory phenomenon
may play an important role in the fate of natural wormholes.Comment: 14 pages revtex, 1 ps figur
The , , , , and as dynamically generated states from vector meson - vector meson interaction
We report on some recent developments in understanding the nature of the
low-lying mesonic resonances , , ,
, and . In particular we show that these five
resonances can be dynamically generated from vector meson--vector meson
interaction in a coupled-channel unitary approach, which utilizes the
phenomenologically very successful hidden-gauge Lagrangians to produce the
interaction kernel between two vector mesons, which is then unitarized by the
Bethe-Salpeter-equation method. The data on the strong decay branching ratios,
total decay widths, and radiative decay widths of these five states, and on
related decay processes can all be well described by such an approach.
We also make predictions, compare them with the results of earlier studies, and
highlight observables that if measured can be used to distinguish different
pictures of these resonances.Comment: 9 pages; Invited talk at workshop CHIRAL'10, Valencia (Spain), June
21-24, 201
Spatio-temporal vortex beams and angular momentum
We present a space-time generalization of the known spatial (monochromatic)
wave vortex beams carrying intrinsic orbital angular momentum (OAM) along the
propagation direction. Generic spatio-temporal vortex beams are polychromatic
and can carry intrinsic OAM at an arbitrary angle to the mean momentum.
Applying either (i) a transverse wave-vector shift or (ii) a Lorentz boost to a
monochromatic Bessel beam, we construct a family of either (i) time-diffracting
or (ii) non-diffracting spatio-temporal Bessel beams, which are exact solutions
of the Klein-Gordon wave equations. The proposed spatio-temporal OAM states are
able to describe either photon or electron vortex states (both relativistic and
nonrelativistic), and can find applications in particle collisions, optics of
moving media, quantum communications, and astrophysics.Comment: 9 pages, 6 figures, to appear in Phys. Rev.
Multiterminal conductance of a floquet topological insulator
We report on simulations of the dc conductance and quantum Hall response of a Floquet topological insulator using Floquet scattering theory. Our results reveal that laser-induced edge states lead to quantum Hall plateaus once imperfect matching with the nonilluminated leads is lessened. The magnitude of the Hall plateaus, however, is not directly related to the number and chirality of all the edge states at a given energy, as usual. Instead, the plateaus are dominated by those edge states adding to the time-averaged density of states. Therefore, the dc quantum Hall conductance of a Floquet topological insulator is not directly linked to topological invariants of the full Floquet bands.publishedVersionFil: Foa Torres, Luis Eduardo Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Foa Torres, Luis Eduardo Francisco. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Pérez Piskunow, Pablo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Pérez Piskunow, Pablo Matías. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Balseiro, Carlos A. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina.Fil: Balseiro, Carlos A. Comisión Nacional de Energía Atómica. Instituto Balseiro; Argentina.Fil: Balseiro, Carlos A. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Usaj, Gonzalo. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina.Fil: Usaj, Gonzalo. Comisión Nacional de Energía Atómica. Instituto Balseiro; Argentina.Fil: Usaj, Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Física de los Materiales Condensado
Geometrothermodynamics
We present the fundamentals of geometrothermodynamics, an approach to study
the properties of thermodynamic systems in terms of differential geometric
concepts. It is based, on the one hand, upon the well-known contact structure
of the thermodynamic phase space and, on the other hand, on the metric
structure of the space of thermodynamic equilibrium states. In order to make
these two structures compatible we introduce a Legendre invariant set of
metrics in the phase space, and demand that their pullback generates metrics on
the space of equilibrium states. We show that Weinhold's metric, which was
introduced {\it ad hoc}, is not contained within this invariant set. We propose
alternative metrics which allow us to redefine the concept of thermodynamic
length in an invariant manner and to study phase transitions in terms of
curvature singularities.Comment: Revised version, to be published in Jour. Math. Phy
Estimação de parâmetros genéticos para peso ao nascer em bovinos da raça Canchim avaliados sob diferentes modelos animais.
Foram utilizadas 18.215 observações de peso ao nascer de bovinos da raça Canchim criados em todo o Brasil, para estimar parâmetros genéticos para essa caracteristica utilizando-se quatro diferentes modelos animais. Nestes modelos foram considerados os efeitos fixos de grupo de contemporâneos (fazenda, ano e época de nascimento e sexo) e as covariáveis porcentagens de Charolês no animal e na mãe e porcentagem de heterozigose na mãe (efeito linear) e idade da vaca ao parto (efeitos linear e quadrático). Os efeitos aleatórios considerados foram os efeitos genéticos aditivo direto e materno e de ambiente permanente materno em diferentes combinações. Para a estimação dos parâmetros, os dados foram analisados pelo método da máxima verossimilhança restrita livre de derivadas e o teste de razão de verossimilhança (LRT) foi utilizado para a comparação dos modelos. O modelo completo (efeitos genéticos aditivo direto e materno e de ambiente permanente) foi o mais adequado, resultando nas seguintes estimativas de parâmetros: 0,30; 0,05 e 0,05 para a herdabilidade direta, herdabilidade materna e fração da variância atribuída ao ambiente permanente, respectivamente. A correlação entre os efeitos aditivos direto e materno foi próxima de zero
Reduced ratio of protective versus proinflammatory cytokine responses to commensal bacteria in HLA-B27 transgenic rats
Germ-free HLA-B27 transgenic (TG) rats do not develop colitis, but colonization with specific pathogen-free (SPF) bacteria induces colitis accompanied by immune activation. To study host-dependent immune responses to commensal caecal bacteria we investigated cytokine profiles in mesenteric lymph node (MLN) cells from HLA-B27 TG versus nontransgenic (non-TG) littermates after in vitro stimulation with caecal bacterial lysates (CBL). Supernatants from CBL-stimulated unseparated T- or B- cell-depleted MLN cells from HLA-B27 TG and non-TG littermates were analysed for IFN-γ, IL-12, TNF, IL-10 and TGF-β production. Our results show that unfractionated TG MLN cells stimulated with CBL produced more IFN-γ, IL-12 and TNF than did non-TG MLN cells. In contrast, CBL-stimulated non-TG MLN cells produced more IL-10 and TGF-β. T cell depletion abolished IFN-γ and decreased IL-12 production, but did not affect IL-10 and TGF-β production. Conversely, neither IL-10 nor TGF-β was produced in cultures of B cell-depleted MLN. In addition, CD4+ T cells enriched from MLN of HLA-B27 TG but not from non-TG rats produced IFN-γ when cocultured with CBL-pulsed antigen presenting cells from non-TG rats. Interestingly, IL-10 and TGF-β, but not IFN-γ, IL-12 and TNF were produced by MLN cells from germ-free TG rats. These results indicate that the colitis that develops in SPF HLA-B27 TG rats is accompanied by activation of IFN-γ-producing CD4+ T cells that respond to commensal bacteria. However, B cell cytokine production in response to components of commensal intestinal microorganisms occurs in the absence of intestinal inflammation
Deformation of quantum mechanics in fractional-dimensional space
A new kind of deformed calculus (the D-deformed calculus) that takes place in
fractional-dimensional spaces is presented. The D-deformed calculus is shown to
be an appropriate tool for treating fractional-dimensional systems in a simple
way and quite analogous to their corresponding one-dimensional partners. Two
simple systems, the free particle and the harmonic oscillator in fractional-
dimensional spaces are reconsidered into the framework of the D-deformed
quantum mechanics. Confined states in a D-deformed quantum well are studied.
D-deformed coherent states are also found.Comment: 12 pages, some misprints have been corrected, two figures are adde
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