248 research outputs found
Accretion Processes for General Spherically Symmetric Compact Objects
We investigate the accretion process for different spherically symmetric
space-time geometries for a static fluid. We analyse this procedure using the
most general black hole metric ansatz. After that, we examine the accretion
process for specific spherically symmetric metrics obtaining the velocity of
the sound during the process and the critical speed of the flow of the fluid
around the black hole. In addition, we study the behaviour of the rate of
change of the mass for each chosen metric for a barotropic fluid.Comment: 10 pages, 15 figures, v2 accepted for publication in 'European
Physical Journal C
Porcine colonization of the Americas: a 60k SNP story.
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The extended tails of Palomar 5: A ten degree arc of globular cluster tidal debris
Using wide-field photometric data from the Sloan Digital Sky Survey (SDSS) we
recently showed that the Galactic globular cluster Palomar 5 is in the process
of being tidally disrupted. Its tidal tails were initially detected in a 2.5
degree wide band along the celestial equator. A new analysis of SDSS data for a
larger field now reveals that the tails of Pal 5 have a much larger spatial
extent and can be traced over an arc of 10 deg across the sky, corresponding to
a projected length of 4 kpc at the distance of the cluster. The number of
former cluster stars found in the tails adds up to about 1.2 times the number
of stars in the cluster. The radial profile of stellar surface density in the
tails follows approximately a power law r^gamma with -1.5 < gamma < -1.2.
The stream of debris from Pal 5 is significantly curved, which demonstrates
its acceleration by the Galactic potential. The cluster is presently near the
apocenter but has repeatedly undergone disk crossings in the inner part of the
Galaxy leading to strong tidal shocks. Our results suggest that the observed
debris originates mostly from mass loss within the last 2 Gyrs. The cluster is
likely to be destroyed after the next disk crossing, which will happen in about
100 Myr. (abridged)Comment: 44 pages, including 14 figures (Figs.1,3 & 14 with decreased
resolution), accepted for publication in the Astronomical Journa
Decoherence and entanglement degradation of a qubit-qutrit system in non-inertial frames
We study the effect of decoherence on a qubit-qutrit system under the
influence of global, local and multilocal decoherence in non-inertial frames.
We show that the entanglement sudden death can be avoided in non-inertial
frames in the presence of amplitude damping, depolarizing and phase damping
channels. However, degradation of entanglement is seen due to Unruh effect. It
is shown that for lower level of decoherence, the depolarizing channel degrades
the entanglement more heavily as compared to the amplitude damping and phase
damping channels. However, for higher values of decoherence parameters,
amplitude damping channel heavily degrades the entanglement of the hybrid
system. Further more, no ESD is seen for any value of Rob's acceleration.Comment: 16 pages, 5 .eps figures, 1 table; Quantum Information Processing,
published online, 5 July, 201
SU(3) symmetry breaking in lower fp-shell nuclei
Results of shell-model calculations for lower fp-shell nuclei show that SU(3)
symmetry breaking in this region is driven by the single-particle spin-orbit
splitting. However, even though states of the yrast band exhibit SU(3) symmetry
breaking, the results also show that the yrast band B(E2) values are
insensitive to this fragmentation of the SU(3) symmetry; specifically, the
quadrupole collectivity as measured by B(E2) transition strengths between low
lying members of the yrast band remain high even though SU(3) appears to be
broken. Results for and using the Kuo-Brown-3
two-body interaction are given to illustrate these observations.Comment: Updated to the published versio
The Stellar Content and Star Formation History of the late-type spiral galaxy NGC 300 from Hubble Space Telescope observations
We present the first WFPC2 V, I photometry for the Sculptor Group galaxy NGC
300 in four fields ranging from the centre to the outer edge. We have made the
first measurement of the star formation histories in two disk fields: the
oldest stars were born at similar epochs and formation activity increased but
at different mean rates. The main disk stellar population is predominantly old,
consisting of RGB and AGB stars, based on a synthetic colour magnitude diagram
analysis. Z is found to have been more metal poor than 0.006 (or 0.33Zsolar)
with no evidence for significant change in the mean Z value over time in both
disk fields. In the central region, we find a dearth of bright stars with
respect to the two disk fields that cannot be explained by observational
effects. Taken at face value, this finding would agree with the Davidge (1998)
report of suppressed star formation there during the past 1Gyr with respect to
his disk fields at larger radii; but the possibility of significant central
extinction affecting our finding remains. We have also determined the first
distance modulus estimate based on the tip of the red giant branch method: on
the Cepheid distance scale of Ferrarese et al. (2000) we find (m-M)o =
26.56+/-0.07 (+/-0.13) mag; and a similar value from the Cepheid-independent
empirical method by Lee et al. (1993), both in good agreement with the Cepheid
distance determined by Freedman et al. (2001). A discrepancy between this and
the theoretical calibration of the red giant branch tip magnitude method
remains. Finally, we report a newly detected young (up to about 10Myr) stellar
association of about average size (~140pc) in one of the disk fields.Comment: 47 pages, 12 figures (the quality of Figures 1 and 6 has been
degraded), Corrected minor textual errors and two reference omissions to
match the version to be published in The Astronomical Journa
Cross section measurements of 155,157Gd(n, Îł) induced by thermal and epithermal neutrons
© SIF, Springer-Verlag GmbH Germany, part of Springer Nature 2019Neutron capture cross section measurements on 155Gd and 157Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n_TOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C6D6 liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for 155Gd and 157Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181 eV and 307 eV, respectively for 155Gd and 157Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2. 01 (28) à 10 - 4 and 2. 17 (41) à 10 - 4; average total radiative width of 106.8(14) meV and 101.1(20) meV and s-wave resonance spacing 1.6(2) eV and 4.8(5) eV for n + 155Gd and n + 157Gd systems, respectively.Peer reviewedFinal Accepted Versio
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