7,996 research outputs found
Probing the parameter space of HD 49933: a comparison between global and local methods
We present two independent methods for studying the global stellar parameter
space (mass M, age, initial chemical composition X_0, Z_0) of HD 49933 with
seismic data. Using a local minimization and an MCMC algorithm, we obtain
consistent results for the determination of the stellar properties: M = 1.1 -
1.2 M_solar, Age ~ 3.0 Gyr, Z_0 ~ 0.008. A description of the error ellipses
can be defined using Singular Value Decomposition techniques, and this is
validated by comparing the errors with those from the MCMC method.Comment: to be published in JPC
Poly(ADP-Ribose) Polymerase 1 Accelerates Single-Strand Break Repair in Concert with Poly(ADP-Ribose) Glycohydrolase
Single-strand breaks are the commonest lesions arising in cells, and defects in their repair are implicated in neurodegenerative disease. One of the earliest events during single-strand break repair (SSBR) is the rapid synthesis of poly(ADP-ribose) (PAR) by poly(ADP-ribose) polymerase (PARP), followed by its rapid degradation by poly(ADP-ribose) glycohydrolase (PARG). While the synthesis of poly(ADP-ribose) is important for rapid rates of chromosomal SSBR, the relative importance of poly(ADP-ribose) polymerase 1 (PARP-1) and PARP-2 and of the subsequent degradation of PAR by PARG is unclear. Here we have quantified SSBR rates in human A549 cells depleted of PARP-1, PARP-2, and PARG, both separately and in combination. We report that whereas PARP-1 is critical for rapid global rates of SSBR in human A549 cells, depletion of PARP-2 has only a minor impact, even in the presence of depleted levels of PARP-1. Moreover, we identify PARG as a novel and critical component of SSBR that accelerates this process in concert with PARP-1
State of Annual Paid Leave–Doctors’ Working Conditions
The article's abstract is not available.
 
Magnetic phase diagram of cubic perovskites SrMn_1-xFe_xO_3
We combine the results of magnetic and transport measurements with Mossbauer
spectroscopy and room-temperature diffraction data to construct the magnetic
phase diagram of the new family of cubic perovskite manganites SrMn_1-xFe_xO_3.
We have found antiferromagnetic ordering for lightly and heavily Fe-substituted
material, while intermediate substitution leads to spin-glass behavior. Near
the SrMn_0.5Fe_0.5O_3 composition these two types of ordering are found to
coexist and affect one another. The spin glass behavior may be caused by
competing ferro- and antiferromagnetic interactions among Mn^4+ and observed
Fe^3+ and Fe^5+ ions.Comment: 8 pages, 10 figures, revtex, accepted to Phys. Rev.
The AGASA/SUGAR Anisotropies and TeV Gamma Rays from the Galactic Center: A Possible Signature of Extremely High-energy Neutrons
Recent analysis of data sets from two extensive air shower cosmic ray
detectors shows tantalizing evidence of an anisotropic overabundance of cosmic
rays towards the Galactic Center (GC) that ``turns on'' around eV. We
demonstrate that the anisotropy could be due to neutrons created at the
Galactic Center through charge-exchange in proton-proton collisions, where the
incident, high energy protons obey an power law associated with
acceleration at a strong shock. We show that the normalization supplied by the
gamma-ray signal from EGRET GC source 3EG J1746-2851 -- ascribed to pp induced
neutral pion decay at GeV energies -- together with a very reasonable spectral
index of 2.2, predicts a neutron flux at eV fully consistent
with the extremely high energy cosmic ray data. Likewise, the normalization
supplied by the very recent GC data from the HESS air-Cerenkov telescope at
\~TeV energies is almost equally-well compatible with the eV
cosmic ray data. Interestingly, however, the EGRET and HESS data appear to be
themselves incompatible. We consider the implications of this discrepancy. We
discuss why the Galactic Center environment can allow diffusive shock
acceleration at strong shocks up to energies approaching the ankle in the
cosmic ray spectrum. Finally, we argue that the shock acceleration may be
occuring in the shell of Sagittarius A East, an unusual supernova remnant
located very close to the Galactic Center. If this connection between the
anisotropy and Sagittarius A East could be firmly established it would be the
first direct evidence for a particular Galactic source of cosmic rays up to
energies near the ankle.Comment: 57 pages, 2 figure
Chandra Observation of the Cluster Environment of a WAT Radio Source in Abell 1446
Wide-angle tail (WAT) radio sources are often found in the centers of galaxy
clusters where intracluster medium (ICM) ram pressure may bend the lobes into
their characteristic C-shape. We examine the low redshift (z=0.1035) cluster
Abell 1446, host to the WAT radio source 1159+583. The cluster exhibits
possible evidence for a small-scale cluster-subcluster merger as a cause of the
WAT radio source morphology. This evidence includes the presence of temperature
and pressure substructure along the line that bisects the WAT as well as a
possible wake of stripped interstellar material or a disrupted cool core to the
southeast of the host galaxy. A filament to the north may represent cool,
infalling gas that's contributing to the WAT bending while spectroscopically
determined redshifts of member galaxies may indicate some component of a merger
occurring along the line-of-sight. The WAT model of high flow velocity and low
lobe density is examined as another scenario for the bending of 1159+583. It
has been argued that such a model would allow the ram pressure due to the
galaxy's slow motion through the ICM to shape the WAT source. A temperature
profile shows that the cluster is isothermal (kT= 4.0 keV) in a series of
annuli reaching a radius of 400 kpc. There is no evidence of an ongoing cooling
flow. Temperature, abundance, pressure, density, and mass profiles, as well as
two-dimensional maps of temperature and pressure are presented.Comment: 40 AASTeX pages including 15 postscript figures; accepted for
publication in Ap
Antiferromagnetic Order in Disorder-Induced Insulating Phase of SrRu_{1-x}Mn_xO_3 (0.4<x<0.6)
We have performed the powder neutron diffraction measurements on the solid
solutions of SrRu_{1-x}Mn_xO_3, and found that the itinerant ferromagnetic
order observed in pure SrRuO_3 changes into the C-type antiferromagnetic (AF)
order with nearly localized d electrons in the intermediate Mn concentration
between x=0.4 and 0.6. With increasing x, the AF moment is strongly enhanced
from 1.1 mB (x=0.4) to 2.6 mB (x=0.6), which is accompanied by the elongation
of the tetragonal c/a ratio. These results suggest that the substitution of Mn
for Ru suppresses the itinerant character of the d electrons, and induces the
superexchange interaction through the compression in the c plane. We have also
found that the magnetic and transport properties observed in our tetragonal
samples are quite similar to those of recently reported orthorhombic ones.Comment: 4 pages, 4 figure
Increasing the Fine Structure Visibility of the Hinode SOT Ca II H Filtergrams
We present the improved so-called Madmax (OMC) operator selecting maxima of
convexities computed in multiple directions around each pixel rewritten in
MatLab and shown to be very efficient for pattern recognition.
The aim of the algorithm is to trace the bright hair-like features (for ex.
chromospheric thin jets or spicules) of solar ultimate observations polluted by
a noise of different origins. This popular spatial operator uses the second
derivative in the optimally selected direction for which its absolute value has
a maximum value. Accordingly, it uses the positivity of the resulting intensity
signal affected by a superposed noise. The results are illustrated using a test
artificially generated image and real SOT (Hinode) images are also used, to
make your own choice of the sensitive parameters to use in improving the
visibility of images.Comment: 12 pages, 3 figurs, submitted in Solar Physic
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