10,828 research outputs found
Evidence for a Massive Neutron Star from a Radial-Velocity Study of the Companion to the Black Widow Pulsar PSR B1957+20
The most massive neutron stars constrain the behavior of ultra-dense matter,
with larger masses possible only for increasingly stiff equations of state.
Here, we present evidence that the black widow pulsar, PSR B1957+20, has a high
mass. We took spectra of its strongly irradiated companion and found an
observed radial-velocity amplitude of K_obs=324+/-3 km/s. Correcting this for
the fact that, due to the irradiation, the center of light lies inward relative
to the center of mass, we infer a true radial-velocity amplitude of K_2=353+/-4
km/s and a mass ratio q=M_PSR/M_2=69.2+/-0.8. Combined with the inclination
i=65+/-2 deg inferred from models of the lightcurve, our best-fit pulsar mass
is M_PSR=2.40+/-0.12 M_sun. We discuss possible systematic uncertainties, in
particular in the lightcurve modeling. Taking an upper limit of i<85 deg based
on the absence of radio eclipses at high frequency, combined with a
conservative lower-limit to the motion of the center of mass, K_2>343 km/s
(q>67.3), we infer a lower limit to the pulsar mass of M_PSR>1.66 M_sun.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ;
revision includes more detail on the spectral classification and discussion
of other recent high neutron-star masse
Translocating the blood-brain barrier using electrostatics
Copyright © 2012 Ribeiro,Domingues,
Freire,Santos and Castanho. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.Mammalian cell membranes regulate homeostasis, protein activity, and cell signaling. The charge at the membrane surface has been correlated with these key events. Although mammalian cells are known to be slightly anionic, quantitative information on the membrane charge and the importance of electrostatic interactions in pharmacokinetics and pharmacodynamics remain elusive. Recently, we reported for the first time that brain endothelial cells (EC) are more negatively charged than human umbilical cord cells, using zeta-potential measurements by dynamic light scattering. Here, we hypothesize that anionicity is a key feature of the blood-brain barrier (BBB) and contributes to select which compounds cross into the brain. For the sake of comparison, we also studied the membrane surface charge of blood components—red blood cells (RBC), platelets, and peripheral blood mononuclear cells (PBMC).To further quantitatively correlate the negative zeta-potential values with membrane charge density, model membranes with different percentages of anionic lipids were also evaluated. From all the cells tested, brain cell membranes are the most anionic and those having their lipids mostly exposed, which explains why lipophilic cationic compounds are more prone to cross the blood-brain barrier.Fundação para a Ciência e Tecnologia — Ministério da Educação e Ciência (FCT-MEC, Portugal) is acknowledged for funding (including fellowships SFRH/BD/42158/2007 to Marta M.B. Ribeiro, SFRH/BD/41750/2007 to Marco M. Domingues and SFRH/BD/70423/2010 to João M. Freire) and project PTDC/QUI-BIQ/119509/2010. Marie Curie Industry-Academia Partnerships and Pathways (European Commission) is also acknowledged for funding (FP7-PEOPLE-2007-3-1-IAPP, Project 230654)
Young Radio Pulsars in Galactic Globular Clusters
Currently three isolated radio pulsars and one binary radio pulsar with no
evidence of any previous recycling are known in 97 surveyed Galactic globular
clusters. As pointed out by Lyne et al., the presence of these pulsars cannot
be explained by core-collapse supernovae, as is commonly assumed for their
counterparts in the Galactic disk. We apply a Bayesian analysis to the results
from surveys for radio pulsars in globular clusters and find the number of
potentially observable non-recycled radio pulsars present in all clusters to be
< 3600. Accounting for beaming and retention considerations, the implied birth
rate for any formation scenario for all 97 clusters is < 0.25 pulsars per
century assuming a Maxwellian distribution of velocities with a dispersion of
10 km s^{-1}. The implied birth rates for higher velocity dispersions are
substantially higher than inferred for such pulsars in the Galactic disk. This
suggests that the velocity dispersion of young pulsars in globular clusters is
significantly lower than those of disk pulsars. These numbers may be
substantial overestimates due to the fact that the currently known sample of
young pulsars is observed only in metal-rich clusters. We propose that young
pulsars may only be formed in globular clusters with metallicities with
log[Fe/H] > -0.6. In this case, the potentially observable population of such
young pulsars is 447^{+1420}_{-399} (the error bars give the 95% confidence
interval) and their birth rate is 0.012^{+0.037}_{-0.010} pulsars per century.
The mostly likely creation scenario to explain these pulsars is the electron
capture supernova of a OMgNe white dwarf.Comment: 13 Pages, 6 Figures, 4 Tables, to appear in Ap
Confining potential in a color dielectric medium with parallel domain walls
We study quark confinement in a system of two parallel domain walls
interpolating different color dielectric media. We use the phenomenological
approach in which the confinement of quarks appears considering the QCD vacuum
as a color dielectric medium. We explore this phenomenon in QCD_2, where the
confinement of the color flux between the domain walls manifests, in a scenario
where two 0-branes (representing external quark and antiquark) are connected by
a QCD string. We obtain solutions of the equations of motion via first-order
differential equations. We find a new color confining potential that increases
monotonically with the distance between the domain walls.Comment: RevTex4, 5 pages, 1 figure; version to appear in Int. J. Mod. Phys.
Production, breeding and potential of cowpea crop in Brazil.
About 50 years ago cowpea was reported as a relatively minor tropical legume. However, in the last years, it has been emerging as one of the most important food legume of the 21st century (SINGH, 2010). Brazil is not out of this panorama. Brazilian agriculture is undergoing major technological changes and, in addition, globalization in agribusiness has caused impacts on the production chain of several crops, particularly those heavily dependent on the use of a large volume of agricultural inputs, mainly fertilizers and pesticides. Such crops have had a higher production cost each year. On the other hand, this situation has brought new opportunities. Business farmers have sought new alternatives for their production arrangements. In this context cowpea constitutes one of the best options.bitstream/item/85620/1/Doc-216-Production.pd
Participação no XI Met-Encontro nacional sobre metodologias de laboratório.
bitstream/CNPA/18316/1/DOC161.pd
Can we see pulsars around Sgr A*? - The latest searches with the Effelsberg telescope
Radio pulsars in relativistic binary systems are unique tools to study the
curved space-time around massive compact objects. The discovery of a pulsar
closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr
A*, would provide a superb test-bed for gravitational physics. To date, the
absence of any radio pulsar discoveries within a few arc minutes of Sgr A* has
been explained by one principal factor: extreme scattering of radio waves
caused by inhomogeneities in the ionized component of the interstellar medium
in the central 100 pc around Sgr A*. Scattering, which causes temporal
broadening of pulses, can only be mitigated by observing at higher frequencies.
Here we describe recent searches of the Galactic centre region performed at a
frequency of 18.95 GHz with the Effelsberg radio telescope.Comment: 3 pages, 2 figures, Proceedings of IAUS 291 "Neutron Stars and
Pulsars: Challenges and Opportunities after 80 years", 201
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