4,472 research outputs found
On attributes of a Rotating Neutron star with a Hyperon core
We study the effect of rotation on global properties of neutron star with a
hyperon core in an effective chiral model with varying nucleon effective mass
within a mean field approach. The resulting gross properties of the rotating
compact star sequences are then compared and analyzed with other theoretical
predictions and observations from neutron stars. The maximum mass of the
compact star predicted by the model lies in the range at
Kepler frequency , which is consistant with recent observation of
high mass stars thereby reflecting the sensitivity of the underlying nucleon
effective mass in the dense matter EoS. We also discuss the implications of the
experimental constraints from the flow data from heavy-ion collisions on the
global properties of the rotating neutron stars.Comment: 11 Pages, 10 Figures and 2 Table
Differential Rotation in Neutron Stars: Magnetic Braking and Viscous Damping
Diffferentially rotating stars can support significantly more mass in
equilibrium than nonrotating or uniformly rotating stars, according to general
relativity. The remnant of a binary neutron star merger may give rise to such a
``hypermassive'' object. While such a star may be dynamically stable against
gravitational collapse and bar formation, the radial stabilization due to
differential rotation is likely to be temporary. Magnetic braking and viscosity
combine to drive the star to uniform rotation, even if the seed magnetic field
and the viscosity are small. This process inevitably leads to delayed collapse,
which will be accompanied by a delayed gravitational wave burst and, possibly,
a gamma-ray burst. We provide a simple, Newtonian, MHD calculation of the
braking of differential rotation by magnetic fields and viscosity. The star is
idealized as a differentially rotating, infinite cylinder consisting of a
homogeneous, incompressible conducting gas. We solve analytically the simplest
case in which the gas has no viscosity and the star resides in an exterior
vacuum. We treat numerically cases in which the gas has internal viscosity and
the star is embedded in an exterior, low-density, conducting medium. Our
evolution calculations are presented to stimulate more realistic MHD
simulations in full 3+1 general relativity. They serve to identify some of the
key physical and numerical parameters, scaling behavior and competing
timescales that characterize this important process.Comment: 11 pages. To appear in ApJ (November 20, 2000
Coalescing binary systems of compact objects: Dynamics of angular momenta
The end state of a coalescing binary of compact objects depends strongly on
the final total mass M and angular momentum J. Since gravitational radiation
emission causes a slow evolution of the binary system through quasi-circular
orbits down to the innermost stable one, in this paper we examine the
corresponding behavior of the ratio J/M^2 which must be less than 1(G/c) or
about 0.7(G/c) for the formation of a black hole or a neutron star
respectively. The results show cases for which, at the end of the inspiral
phase, the conditions for black hole or neutron star formation are not
satisfied. The inclusion of spin effects leads us to a study of precession
equations valid also for the calculation of gravitational waveforms.Comment: 22 pages, AASTeX and 13 figures in PostScrip
Charm quenching in heavy-ion collisions at the LHC
D-meson suppression in Pb-Pb collisions at the LHC due to charm quark
in-medium energy loss is estimated within a model that describes the available
quenching measurements at RHIC. The result is compared to that previously
published by the author. The expected sensitivity of the ALICE experiment for
studying charm energy loss via fully-reconstructed D^0-meson decays is also
presented.Comment: 8 pages, 3 figures. To appear in the proceedings of Hot Quarks 2004:
Workshop for Young Scientists on the Physics of Ultrarelativistic
Nucleus-Nucleus Collisions, Taos Valley, New Mexico, 18-24 July 2004.
Submitted to J. Phys.
Evaluation of Alternative Rations for Feeding Guinea Pigs in the Growth-fattening Stages
The objective of the research was to evaluate the use of alternative rations for feeding guinea pigs in the growth-fattening stages. The experimental units were made up of a total of 80 guinea pigs, 40 males and 40 females. A completely random design was applied in a combinatorial arrangement of factors, where factor A: alternative rations had 4 levels and factor B: sex had 2 levels (males and females), and carrying out the evaluation of different variables such as initial weight, final weight, weight gain, total feed intake, feed conversion, carcass weight, carcass yield, all this in addition to the mortality variable, these measurements had an evaluation period of 75 days, the same as the investigation lasted. For the statistical analysis, the experimental results were subjected to an analysis of Variance (ADEVA) and separation of means according to Tukey’s methodology at a significance level (P ≤ 0.05), resulting in significant differences in the feed conversion variable. While for the rest of the variables we found highly significant differences. It was concluded that the best treatment is that of the male guinea pigs that were fed with T2 since they contribute to improving the feed conversion rates without affecting the productive behavior of the livestock. As per the results obtained from this investigation, it is recommended to disseminate to small and medium producers of guinea pigs.
Keywords: alternative rations, corn, broccoli leaf, guinea pig, fattening growth stage
Resumen
El objetivo de la investigación fue evaluar la utilización de raciones alternativas para la alimentación de cuyes en las etapas crecimiento-engorde. Las unidades experimentales estuvieron conformadas por un total de 80 cuyes de los cuales 40 fueron machos y 40 hembras. Se aplicó un diseño completamente al azar, en arreglo combinatorio de factores, donde el factor A: raciones alternativas teniendo 4 niveles y el factor B: sexo con 2 niveles (machos y hembras), y llevándose a cabo la evaluación de diferentes variables como son: peso inicial, peso final ganancia de peso, consumo total de alimento, conversión alimenticia, peso a la canal, rendimiento a la canal todo esto en y la variable mortalidad, estas mediciones tuvieron un periodo de evaluación de 75 dÃas mismos que duro la investigación. Para el análisis estadÃstico los resultados experimentales fueron sometidos a un análisis de Varianza (ADEVA) y separación de medias de acuerdo a la metodologÃa de Tukey a un nivel de significancia (P≤0,05) dando como resultado diferencias significativas en la variable conversión alimenticia mientras que para el resto de variables encontramos diferencias altamente significativas. Se concluye que el mejor tratamiento es el de los cuyes machos que fueron alimentados con T2 ya que contribuyen a mejorar los Ãndices de conversión alimenticia sin afectar el comportamiento productivo de los semovientes. Se recomienda difundir a pequeños y medianos productores de cuyes, los resultados obtenidos de la presente investigación.
Palabras Clave: Raciones alternativas, MaÃz, Hoja de brócoli, Cuyes, Etapa crecimiento-engord
Relativistic precession around rotating neutron stars: Effects due to frame-dragging and stellar oblateness
General relativity predicts that a rotating body produces a frame-dragging
(or Lense-Thirring) effect: the orbital plane of a test particle in a
non-equatorial orbit precesses about the body's symmetry axis. In this paper we
compute the precession frequencies of circular orbits around rapidly rotating
neutron stars for a variety of masses and equations of state. The precession
frequencies computed are expressed as numerical functions of the orbital
frequency observed at infinity. The post-Newtonian expansion of the exact
precession formula is examined to identify the relative magnitudes of the
precession caused by the Lense-Thirring effect, the usual Newtonian quadrupole
effect and relativistic corrections. The first post-Newtonian correction to the
Newtonian quadrupole precession is derived in the limit of slow rotation. We
show that the post-Newtonian precession formula is a good approximation to the
exact precession close to the neutron star in the slow rotation limit (up to
\sim 400 Hz in the present context).
The results are applied to recent RXTE observations of neutron star low-mass
X-ray binaries, which display kHz quasi-periodic oscillations and, within the
framework of beat frequency models, allow the measurement of both the neutron
star spin frequency and the Keplerian frequency of the innermost ring of matter
in the accretion disk around it. For a wide range of realistic equations of
state, we find that the predicted precession frequency of this ring is close to
one half of the low-frequency (\sim 20 - 35 Hz) quasi-periodic oscillations
seen in several Atoll sources.Comment: 35 pages including 10 figures and 6 tables. To appear in the
Astrophysical Journa
Induced scalarization in boson stars and scalar gravitational radiation
The dynamical evolution of boson stars in scalar-tensor theories of gravity
is considered in the physical (Jordan) frame. We focus on the study of
spontaneous and induced scalarization, for which we take as initial data
configurations on the well-known S-branch of a single boson star in general
relativity. We show that during the scalarization process a strong emission of
scalar radiation occurs. The new stable configurations (S-branch) of a single
boson star within a particular scalar-tensor theory are also presented.Comment: 18 pages, 11 figures. Minor changes to match the published versio
The bar-mode instability in differentially rotating neutron stars: Simulations in full general relativity
We study the dynamical stability against bar-mode deformation of rapidly
spinning neutron stars with differential rotation. We perform fully
relativistic 3D simulations of compact stars with , where is
the total gravitational mass and the equatorial circumferential radius. We
adopt an adiabatic equation of state with adiabatic index . As in
Newtonian theory, we find that stars above a critical value of (where is the rotational kinetic energy and the gravitational
binding energy) are dynamically unstable to bar formation. For our adopted
choices of stellar compaction and rotation profile, the critical value of
is , only slightly smaller than the
well-known Newtonian value for incompressible Maclaurin spheroids.
The critical value depends only very weakly on the degree of differential
rotation for the moderate range we surveyed. All unstable stars form bars on a
dynamical timescale. Models with sufficiently large subsequently form
spiral arms and eject mass, driving the remnant to a dynamically stable state.
Models with moderately large do not develop spiral
arms or eject mass but adjust to form dynamically stable ellipsoidal-like
configurations. If the bar-mode instability is triggered in supernovae collapse
or binary neutron star mergers, it could be a strong and observable source of
gravitational waves. We determine characteristic wave amplitudes and
frequencies.Comment: 17 pages, accepted for publication in AP
Energy Dependence of the Cronin Effect from Non-Linear QCD Evolution
The non-linear evolution of dense partonic systems has been suggested as one
of the novel physics mechanisms relevant to the dynamics of hadron-nucleus and
nucleus-nucleus collisions at collider energies. Here we study to what extent
the description of Cronin enhancement in the framework of this non-linear
evolution is consistent with the recent observation in 200 AGeV d--Au
collisions at the Relativistic Heavy Ion Collider. We solve the
Balitsky-Kovchegov evolution equation numerically for several initial
conditions encoding Cronin enhancement. We find that the properly normalized
nuclear gluon distribution is suppressed at all momenta relative to that of a
single nucleon. Calculating the resulting spectrum of produced gluons in p-A
and A-A collisions, we establish that the nonlinear QCD evolution is unable to
generate a Cronin type enhancement, and that it quickly erases any such
enhancement which may be present at lower energies.Comment: 4 pages, Latex, 3 eps-figure
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