994 research outputs found
Pulsar timing irregularities and the imprint of magnetic field evolution
(Abridged) The rotational evolution of isolated neutron stars is dominated by
the magnetic field anchored to the solid crust of the star. Assuming that the
core field evolves on much longer timescales, the crustal field evolves mainly
though Ohmic dissipation and the Hall drift, and it may be subject to
relatively rapid changes with remarkable effects on the observed timing
properties. We investigate whether changes of the magnetic field structure and
strength during the star evolution may have observable consequences in the
braking index, which is the most sensitive quantity to reflect small variations
of the timing properties that are caused by magnetic field rearrangements. By
performing axisymmetric, long-term simulations of the magneto-thermal evolution
of neutron stars with state-of-the-art microphysical inputs, we find that the
effect of the magnetic field evolution on the braking index can be divided into
three qualitatively different stages depending on the age and the internal
temperature: a first stage that may be different for standard pulsars (with
n~3) or low field neutron stars that accreted fallback matter during the
supernova explosion (systematically n<3); in a second stage, the evolution is
governed by almost pure Ohmic field decay, and a braking index n>3 is expected;
in the third stage, at late times, when the interior temperature has dropped to
very low values, Hall oscillatory modes in the neutron star crust result in
braking indices of high absolute value and both positive and negative signs.
Models with strong (1e14 G) multipolar or toroidal components, even with a weak
(~1e12 G) dipolar field are consistent with the observed trend of the timing
properties.Comment: 7 pages, 5 figures, accepted for publication in Astronomy &
Astrophysics (submitted July 24, 2012
RAMESES publication standards: realist syntheses
PMCID: PMC3558331This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
PSR J0007+7303 in the CTA1 SNR: New Gamma-ray Results from Two Years of Fermi-LAT Observations
One of the main results of the Fermi Gamma-Ray Space Telescope is the
discovery of {\gamma}-ray selected pulsars. The high magnetic field pulsar, PSR
J0007+7303 in CTA1, was the first ever to be discovered through its
{\gamma}-ray pulsations. Based on analysis of 2 years of LAT survey data, we
report on the discovery of {\gamma}-ray emission in the off-pulse phase
interval at the ~ 6{\sigma} level. The flux from this emission in the energy
range E \geq 100 MeV is F_100 = (1.73\pm0.40)\times10^(-8) photons/cm^2/s and
is best fitted by a power law with a photon index of {\Gamma} = 2.54\pm0.14.
The pulsed {\gamma}-ray flux in the same energy range is F_100 =
(3.95\pm0.07)\times10^(-7) photons/cm^2/s and is best fitted by an
exponentially-cutoff power-law spectrum with a photon index of {\Gamma} = 1.41
\pm 0.23 and a cutoff energy E_c = 4.04 \pm 0.20 GeV. We find no flux
variability neither at the 2009 May glitch nor in the long term behavior. We
model the {\gamma}-ray light curve with two high-altitude emission models, the
outer gap and slot gap, and find that the model that best fits the data depends
strongly on the assumed origin of the off-pulse emission. Both models favor a
large angle between the magnetic axis and observer line of sight, consistent
with the nondetection of radio emission being a geometrical effect. Finally we
discuss how the LAT results bear on the understanding of the cooling of this
neutron star.Comment: Submitted to the Astrophysical Journa
Paramagnetism in color superconductivity and compact stars
It is quite plausible that color superconductivity occurs in the inner
regions of neutron stars. At the same time, it is known that strong magnetic
fields exist in the interior of these compact objects. In this paper we discuss
some important effects that can occur in the color superconducting core of
compact stars due to the presence of the stars' magnetic field. In particular,
we consider the modification of the gluon dynamics for a color superconductor
with three massless quark flavors in the presence of an external magnetic
field. We show that the long-range component of the external magnetic field
that penetrates the color-flavor locked phase produces an instability for field
values larger than the charged gluons' Meissner mass. As a consequence, the
ground state is restructured forming a vortex state characterized by the
condensation of charged gluons and the creation of magnetic flux tubes. In the
vortex state the magnetic field outside the flux tubes is equal to the applied
one, while inside the tubes its strength increases by an amount that depends on
the amplitude of the gluon condensate. This paramagnetic behavior of the color
superconductor can be relevant for the physics of compact stars.Comment: To appear in J. Phys. A: Math. Theor. 40 (2007) 1 (Corrected
references
Global distribution of two fungal pathogens threatening endangered sea turtles
This work was supported by grants of Ministerio de Ciencia e Innovación, Spain (CGL2009-10032, CGL2012-32934). J.M.S.R was supported by PhD fellowship of the CSIC (JAEPre 0901804). The Natural Environment Research Council and the Biotechnology and Biological Sciences Research Council supported P.V.W. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Thanks Machalilla National Park in Ecuador, Pacuare Nature Reserve in Costa Rica, Foundations Natura 2000 in Cape Verde and Equilibrio Azul in Ecuador, Dr. Jesus Muñoz, Dr. Ian Bell, Dr. Juan Patiño for help and technical support during samplingPeer reviewedPublisher PD
Hemocyanin facilitates lignocellulose digestion by wood-boring marine crustaceans
Woody (lignocellulosic) plant biomass is an abundant renewable feedstock, rich in polysaccharides that are bound into an insoluble fiber composite with lignin. Marine crustacean woodborers of the genus Limnoria are among the few animals that can survive on a diet of this recalcitrant material without relying on gut resident microbiota. Analysis of fecal pellets revealed that Limnoria targets hexose-containing polysaccharides (mainly cellulose, and also glucomannans), corresponding with the abundance of cellulases in their digestive system, but xylans and lignin are largely unconsumed. We show that the limnoriid respiratory protein, hemocyanin, is abundant in the hindgut where wood is digested, that incubation of wood with hemocyanin markedly enhances its digestibility by cellulases, and that it modifies lignin. We propose that this activity of hemocyanins is instrumental to the ability of Limnoria to feed on wood in the absence of gut symbionts. These findings may hold potential for innovations in lignocellulose biorefining
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