22,827 research outputs found
The Black Hole Binary Nova Scorpii 1994 (GRO J1655-40): An improved chemical analysis
The chemical analysis of secondary stars of low mass X-ray binaries provides
an opportunity to study the formation processes of compact objects, either
black holes or neutron stars. Following the discovery of overabundances of
-elements in the HIRES/Keck spectrum of the secondary star of Nova
Scorpii 1994 (Israelian et al. 1999), we obtained UVES/VLT high-resolution
spectroscopy with the aim of performing a detailed abundance analysis of this
secondary star. Using a -minimization procedure and a grid of synthetic
spectra, we derive the stellar parameters and atmospheric abundances of O, Mg,
Al, Ca, Ti, Fe and Ni, using a new UVES spectrum and the HIRES spectrum.The
abundances of Al, Ca, Ti, Fe and Ni seem to be consistent with solar values,
whereas Na, and especially O, Mg, Si and S are significantly enhanced in
comparison with Galactic trends of these elements. A comparison with
spherically and non-spherically symmetric supernova explosion models may
provide stringent constraints to the model parameters as mass-cut and the
explosion energy, in particular from the relative abundances of Si, S, Ca, Ti,
Fe and Ni. Most probably the black hole in this system formed in a hypernova
explosion of a 30--35 \Msun progenitor star with a mass-cut in the range 2--3.5
\Msun. However, these models produce abundances of Al and Na almost ten times
higher than the observed values.Comment: New Accepted version for publication in Astronomy and Astrophysics
Table 2: Correcte
A Search for Pulsation in Very Low-mass Stars and Brown Dwarfs
Brown dwarfs and very low-mass stars constitute a crucial link between the intertwined processes of star formation and planet formation. To date, however, observational methods to uncover their formation mechanism or determine important properties such as mass and age have been lacking. Pulsation powered by deuterium burning in brown dwarfs and very low-mass stars is a newly suggested phenomenon that offers unprecedented opportunities to probe the interiors and evolution of these objects. We report on a photometric campaign to search for low-amplitude pulsations among young star-cluster members using a number of telescopes
Topographic hub maps of the human structural neocortical network
Hubs within the neocortical structural network determined by graph theoretical analysis play a crucial role in brain function. We mapped neocortical hubs topographically, using a sample population of 63 young adults. Subjects were imaged with high resolution structural and diffusion weighted magnetic resonance imaging techniques. Multiple network configurations were then constructed per subject, using random parcellations to define the nodes and using fibre tractography to determine the connectivity between the nodes. The networks were analysed with graph theoretical measures. Our results give reference maps of hub distribution measured with betweenness centrality and node degree. The loci of the hubs correspond with key areas from known overlapping cognitive networks. Several hubs were asymmetrically organized across hemispheres. Furthermore, females have hubs with higher betweenness centrality and males have hubs with higher node degree. Female networks have higher small-world indices
Anomalous dispersion of optical phonons at the neutral-ionic transition: Evidence from diffuse X-ray scattering
Diffuse X-ray data for mixed stack organic charge-transfer crystals
approaching the neutral-ionic phase transition can be quantitatively explained
as due to the softening of the optical phonon branch. The interpretation is
fully consistent with vibrational spectra, and underlines the importance of
electron-phonon coupling in low-dimensional systems with delocalized electrons.Comment: 4 pages, 4 figure
Three-point correlations for quantum star graphs
We compute the three point correlation function for the eigenvalues of the
Laplacian on quantum star graphs in the limit where the number of edges tends
to infinity. This extends a work by Berkolaiko and Keating, where they get the
2-point correlation function and show that it follows neither Poisson, nor
random matrix statistics. It makes use of the trace formula and combinatorial
analysis.Comment: 10 pages, 2 figure
Aggregation of frictional particles due to capillary attraction
Capillary attraction between identical millimeter sized spheres floating at a
liquid-air interface and the resulting aggregation is investigated at low
Reynolds number. We show that the measured capillary forces between two spheres
as a function of distance can be described by expressions obtained using the
Nicolson approximation at low Bond numbers for far greater particle sizes than
previously assumed. We find that viscous hydrodynamics interactions between the
spheres needs to be included to describe the dynamics close to contact. We then
consider the aggregates formed when a third sphere is added after the initial
two spheres are already in contact. In this case, we find that linear
superposition of capillary forces describes the observed approach qualitatively
but not quantitatively. Further, we observe an angular dependence of the
structure due to a rapid decrease of capillary force with distance of
separation which has a tendency to align the particles before contact. When the
three particles come in contact, they may preserve their shape or rearrange to
form an equilateral triangle cluster - the lowest energy state - depending on
the competition between attraction between particles and friction. Using these
observations, we demonstrate that a linear particle chain can be built from
frictional particles with capillary attraction.Comment: accepted for Physical Review
State estimation in quantum homodyne tomography with noisy data
In the framework of noisy quantum homodyne tomography with efficiency
parameter , we propose two estimators of a quantum state whose
density matrix elements decrease like , for
fixed known and . The first procedure estimates the matrix
coefficients by a projection method on the pattern functions (that we introduce
here for ), the second procedure is a kernel estimator of the
associated Wigner function. We compute the convergence rates of these
estimators, in risk
Switching barrier scaling near bifurcation points for non-Gaussian noise
We study noise-induced switching of a system close to bifurcation parameter
values where the number of stable states changes. For non-Gaussian noise, the
switching exponent, which gives the logarithm of the switching rate, displays a
non-power-law dependence on the distance to the bifurcation point. This
dependence is found for Poisson noise. Even weak additional Gaussian noise
dominates switching sufficiently close to the bifurcation point, leading to a
crossover in the behavior of the switching exponent
Estimating the Costs and the Disease Burden Associated With Campylobacter Infections and Sequelae in the Netherlands
Campylobacter infections pose an important public health problem in the Netherlands. Approximately 79,000 persons per year are estimated to experience symptoms of acute gastroenteritis. Further annually some 1400 ReA cases, 60 GBS cases and 11 IBD cases are associated with a previous Campylobacter infection. Using a stochastic simulation model the disease burden and the cost-of-illness of Campylobacter infections and its sequelae were estimated. Estimates of the Campylobacter-associated disease burden and costs-of-illness were 1185 DALYs (90% C.I. 693 - 1845 DALYs) per year and some 21 million E (90% C.I. 10 - 38 million E) per year respectively.Campylobacter, sequelae, cost-of-illness, disease burden, Netherlands, Food Consumption/Nutrition/Food Safety,
Models of electrolyte solutions from molecular descriptions: The example of NaCl solutions
We present a method to derive implicit solvent models of electrolyte
solutions from all-atom descriptions; providing analytical expressions of the
thermodynamic and structural properties of the ions consistent with the
underlying explicit solvent representation. Effective potentials between ions
in solution are calculated to perform perturbation theory calculations, in
order to derive the best possible description in terms of charged hard spheres.
Applying this method to NaCl solutions yields excellent agreement with the
all-atom model, provided ion association is taken into account.Comment: 4 pages, 5 figure
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