2,963 research outputs found
Extensive population synthesis of isolated neutron stars with field decay
We perform population synthesis studies of different types of neutron stars
taking into account the magnetic field decay. For the first time, we confront
our results with observations using {\it simultaneously} the Log N -- Log S
distribution for nearby isolated neutron stars, the Log N -- Log L distribution
for magnetars, and the distribution of radio pulsars in the --
diagram. We find that our theoretical model is consistent with all sets of data
if the initial magnetic field distribution function follows a log-normal law
with and . The
typical scenario includes about 10% of neutron stars born as magnetars,
significant magnetic field decay during the first million years of a NS life.
Evolutionary links between different subclasses may exist, although robust
conclusions are not yet possible.
We apply the obtained field distribution and the model of decay to study
long-term evolution of neuton stars till the stage of accretion from the
interstellar medium. It is shown that though the subsonic propeller stage can
be relatively long, initially highly magnetized neutron stars ( G) reach the accretion regime within the Galactic lifetime if their
kick velocities are not too large. The fact that in previous studies made 10
years ago, such objects were not considered results in a slight increase of the
Accretor fraction in comparison with earlier conclusions. Most of the neutron
stars similar to the Magnificent seven are expected to become accreting from
the interstellar medium after few billion years of their evolution. They are
the main predecestors of accreting isolated neutron stars.Comment: 4 pages, conference "Astrophysics of Neutron Stars - 2010" in honor
of M. Ali Alpar, Izmir, Turke
Energy versus information based estimations of dissipation using a pair of magnetic colloidal particles
Using the framework of stochastic thermodynamics, we present an experimental
study of a doublet of magnetic colloidal particles which is manipulated by a
time-dependent magnetic field. Due to hydrodynamic interactions, each bead
experiences a state-dependent friction, which we characterize using a
hydrodynamic model. In this work, we compare two estimates of the dissipation
in this system: the first one is energy based since it relies on the measured
interaction potential, while the second one is information based since it uses
only the information content of the trajectories. While the latter only offers
a lower bound of the former, we find it to be simple to implement and of
general applicability to more complex systems.Comment: Main text: 5 pages, 4 figures. Supplementary material: 5 pages, 5
figure
Recombination dramatically speeds up evolution of finite populations
We study the role of recombination, as practiced by genetically-competent
bacteria, in speeding up Darwinian evolution. This is done by adding a new
process to a previously-studied Markov model of evolution on a smooth fitness
landscape; this new process allows alleles to be exchanged with those in the
surrounding medium. Our results, both numerical and analytic, indicate that for
a wide range of intermediate population sizes, recombination dramatically
speeds up the evolutionary advance
Fijación interna versus percutánea en fracturas diafisarias de metacarpianos: estudio de casos-controles
Objetivos: comparación de resultados clínicos de fijación interna versus fijación percutánea. Material
y Métodos: estudio retrospectivo de casos y controles de 58 fracturas de metacarpianos (43 pacientes). Se incluyeron
las fracturas diafisarias, sin afectación articular. Se excluyeron si había afectación del pulgar o de falanges, fracturas
abiertas o más de 3 fracturas en la misma mano. Un total de 26 fracturas fueron tratadas con fijación interna y
32 con percutánea. Con un seguimiento medio de 2,5 años (rango, 1-4), se valoró la función mediante movilidad activa
total (MAT), fuerza, DASH, EAV de dolor y resultado radiográfico. Resultados: con ambos tratamientos los resultados
fueron satisfactorios. El tiempo de consolidación y alineación radiográfica fueron similares. Todas las valoraciones
clínicas, objetivas y subjetivas, fueron mejores en el grupo de fijación interna, así como la tasa de retorno a
las actividades previas. En el grupo de fijación interna hubo un caso de pseudoartrosis que fue reoperado y otro de
déficit de movilidad. En el grupo percutáneo hubo 4 casos con déficit de movilidad. Discusión y conclusiones: ambas
técnicas ofrecen resultados adecuados, pero con la fijación interna se obtuvieron mejores resultados respecto a movilidad,
fuerza, mayor facilidad para realización de las actividades previas y retorno a las laborales y deportivas, a pesar
de las complicaciones inherentes a la cirugía abiertaObjectives: comparison of outcomes with internal fixation versus percutaneous fixation. Material
and Methods: retrospective case-control study of 58 metacarpal fractures (43 patients). Shaft fractures without joint
involvement were included. Exclusion criteria were involvement of the thumb or phalange, open fracture, or more
than 3 fractures in the same hand. There were 26 fractures treated with internal fixation and 32 with percutaneous
fixation. With a mean follow-up of 2,5 years (range, 1-4), functional evaluation was performed by total active motion
(TAM), strength grip, DASH, pain VAS, and radiographic results. Results: satisfactory outcomes were obtained with
both treatments. Consolidation time and radiographic alignment were similar. All clinical objective and subjective
assessments were better in the internal fixation group, as well as the rate of return to previous activities. In the internal
fixation group, there was one case with nonunion, which was reoperated, and other with lack of motion. In the
percutaneous group, there were 4 cases with mobility deficits. Discussion and conclusions: satisfactory results were
offered by both methods, but better outcomes were obtained by internal fixation with regard to motion, strength, best
facility for previous activities, and return to work and sport activities. All this was spite of the inherent complications of open surger
The influence of magnetic field geometry on magnetars X-ray spectra
Nowadays, the analysis of the X-ray spectra of magnetically powered neutron
stars or magnetars is one of the most valuable tools to gain insight into the
physical processes occurring in their interiors and magnetospheres. In
particular, the magnetospheric plasma leaves a strong imprint on the observed
X-ray spectrum by means of Compton up-scattering of the thermal radiation
coming from the star surface. Motivated by the increased quality of the
observational data, much theoretical work has been devoted to develop Monte
Carlo (MC) codes that incorporate the effects of resonant Compton scattering in
the modeling of radiative transfer of photons through the magnetosphere. The
two key ingredients in this simulations are the kinetic plasma properties and
the magnetic field (MF) configuration. The MF geometry is expected to be
complex, but up to now only mathematically simple solutions (self-similar
solutions) have been employed. In this work, we discuss the effects of new,
more realistic, MF geometries on synthetic spectra. We use new force-free
solutions in a previously developed MC code to assess the influence of MF
geometry on the emerging spectra. Our main result is that the shape of the
final spectrum is mostly sensitive to uncertain parameters of the
magnetospheric plasma, but the MF geometry plays an important role on the
angle-dependence of the spectra.Comment: 6 pages, 4 figures To appear in Proceedings of II Iberian Nuclear
Astrophysics Meeting held in Salamanca, September 22-23, 201
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