11,068 research outputs found
The Persistence of Memory, or How the X-Ray Spectrum of SNR 0509-67.5 Reveals the Brightness of its Parent Type Ia Supernova
We examine the dynamics and X-ray spectrum of the young Type Ia supernova
remnant 0509-67.5 in the context of the recent results obtained from the
optical spectroscopy of its light echo. Our goal is to estimate the kinetic
energy of the supernova explosion using Chandra and XMM-Newton observations of
the supernova remnant, thus placing the birth event of 0509-67.5 in the
sequence of dim to bright Type Ia supernovae. We base our analysis on a
standard grid of one-dimensional delayed detonation explosion models, together
with hydrodynamic and X-ray spectral calculations of the supernova remnant
evolution. From the remnant dynamics and the properties of the O, Si, S, and Fe
emission in its X-ray spectrum we conclude that 0509-67.5 was originated ~400
years ago by a bright, highly energetic Type Ia explosion similar to SN 1991T.
Our best model has a kinetic energy of 1.4x10E51 erg and synthesizes 0.97 Msun
of 56Ni. These results are in excellent agreement with the age estimate and
spectroscopy from the light echo. We have thus established the first connection
between a Type Ia supernova and its supernova remnant based on a detailed
quantitative analysis of both objects.Comment: 10 pages, 9 figures, plus an exclusive astro-ph-only Appendix; ApJ in
press, companion paper to Rest et al. 0
L. Thommen, Das Volkstribunat der späten römischen Republik (Historia. Einzelschriften- Heft. 59), Stuttgart. Franz Steiner Verlag. 1989. 287 pp.
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The impact of chemical differentiation of white dwarfs on thermonuclear supernovae
Gravitational settling of 22Ne in cooling white dwarfs can affect the outcome
of thermonuclear supernovae. We investigate how the supernova energetics and
nucleosynthesis are in turn influenced by this process. We use realistic
chemical profiles derived from state-of-the-art white dwarf cooling sequences.
The cooling sequences provide a link between the white dwarf chemical structure
and the age of the supernova progenitor system. The cooling sequence of a 1
M_sun white dwarf was computed until freezing using an up-to-date stellar
evolutionary code. We computed explosions of both Chandrasekhar mass and
sub-Chandrasekhar mass white dwarfs, assuming spherical symmetry and neglecting
convective mixing during the pre-supernova carbon simmering phase to maximize
the effects of chemical separation. Neither gravitational settling of 22Ne nor
chemical differentiation of 12C and 16O have an appreciable impact on the
properties of Type Ia supernovae, unless there is a direct dependence of the
flame properties (density of transition from deflagration to detonation) on the
chemical composition. At a fixed transition density, the maximum variation in
the supernova magnitude obtained from progenitors of different ages is ~0.06
magnitudes, and even assuming an unrealistically large diffusion coefficient of
22Ne it would be less than ~0.09 mag. However, if the transition density
depends on the chemical composition (all other things being equal) the oldest
SNIa can be as much as 0.4 magnitudes brighter than the youngest ones (in our
models the age difference is 7.4 Gyr). In addition, our results show that 22Ne
sedimentation cannot be invoked to account for the formation of a central core
of stable neutron-rich Fe-group nuclei in the ejecta of sub-Chandrasekhar
models, as required by observations of Type Ia supernovae.Comment: 8 pages, 8 figures, 3 tables, accepted for Astronomy and
Astrophysics. Revised version with corrected typo
Higher order correction to the neutrino self-energy in a medium and its astrophysical applications
We have calculated the 1/M^4 (M the vector boson mass) order correction to
the neutrino self-energy in a medium. The possible application of this higher
order contribution to the neutrino effective potential is considered in the
context of the Early Universe hot plasma and of the cosmological Gamma Ray
Burst fireball. We found that, depending on the medium parameters and on the
neutrino properties (mixing angle and mass square difference) the resonant
oscillation of active to active neutrinos is possible.Comment: 10 pages, revtex style, uses axodraw.sty, 1 figur
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Glucocorticoid-regulated localization of cell surface glycoproteins in rat hepatoma cells is mediated within the Golgi complex.
Glucocorticoid hormones regulate the post-translational maturation and sorting of cell surface and extracellular mouse mammary tumor virus (MMTV) glycoproteins in M1.54 cells, a stably infected rat hepatoma cell line. Exposure to monensin significantly reduced the proteolytic maturation and externalization of viral glycoproteins resulting in a stable cellular accumulation of a single 70,000-Mr glycosylated polyprotein (designated gp70). Cell surface- and intracellular-specific immunoprecipitations of monensin-treated cells revealed that gp70 can be localized to the cell surface only in the presence of 1 microM dexamethasone, while in uninduced cells gp70 is irreversibly sequestered in an intracellular compartment. Analysis of oligosaccharide processing kinetics demonstrated that gp70 acquired resistance to endoglycosidase H with a half-time of 65 min in the presence or absence of hormone. In contrast, gp70 was inefficiently galactosylated after a 60-min lag in uninduced cells while rapidly acquiring this carbohydrate modification in the presence of dexamethasone. Furthermore, in the absence or presence of monensin, MMTV glycoproteins failed to be galactosylated in hormone-induced CR4 cells, a complement-selected sorting variant defective in the glucocorticoid-regulated compartmentalization of viral glycoproteins to the cell surface. Since dexamethasone had no apparent global effects on organelle morphology or production of total cell surface-galactosylated species, we conclude that glucocorticoids induce the localization of cell surface MMTV glycoproteins by regulating a highly selective step within the Golgi apparatus after the acquisition of endoglycosidase H-resistant oligosaccharide side chains but before or at the site of galactose attachment
Tratamiento de elementos rectos y curvos de sección variable por métodos matriciales
En este trabajo se presenta la formulación necesaria para el tratamiento de elementos
de directriz recta o circunferencial con características geométricas e imerciales variables según la directriz, así como de las cargas equivalentes, dentro del ámbito del Análisis Matricial de Estructuras.Peer Reviewe
Tratamiento de elementos rectos y curvos de sección variable por métodos matriciales
En este trabajo se presenta la formulación necesaria para el tratamiento de elementos
de directriz recta o circunferencial con características geométricas e imerciales variables según la directriz, así como de las cargas equivalentes, dentro del ámbito del Análisis Matricial de Estructuras.Peer Reviewe
Exit, Punishment and Rewards in Commons Dilemmas: An Experimental Study
Commons dilemmas are interaction situations where a common good is provided or exploited by a group of individuals so that optimal collective outcomes clash with private interests. Although in these situations, social norms and institutions exist that might help individuals to cooperate, little is known about the interaction effects between positive and negative incentives and exit options by individuals. We performed a modified public good game experiment to examine the effect of exit, rewards and punishment, as well as the interplay between exit and rewards and punishment. We found that punishment had a stronger effect than rewards on cooperation if considered by itself, whereas rewards had a stronger effect when combined with voluntary participation. This can be explained in terms of the ‘framing effect’, i.e., as the combination of exit and rewards might induce people to attach higher expected payoffs to cooperative strategies and expect better behaviour from others
Avance sobre un nuevo bronce romano hallado en Montealegre (Valladolid): Tessera hospitalis del 134 d. C.
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