735 research outputs found
Absorption lines from magnetically-driven winds in X-ray binaries
High resolution X-ray spectra of black hole X-ray binaries (BHBs) show
blueshifted absorption lines from disk winds which seem to be equatorial. Winds
occur in the Softer (disk-dominated) states of the outburst and are less
prominent or absent in the Harder (power-law dominated) states. We use
self-similar magneto-hydrodynamic (MHD) accretion-ejection models to explain
the disk winds in BHBs. In our models, the density at the base of the outflow
from the accretion disk is not a free parameter, but is determined by solving
the full set of dynamical MHD equations. Thus the physical properties of the
outflow are controlled by the global structure of the disk. We studied
different MHD solutions characterized by different values of (a) the disk
aspect ratio () and (b) the ejection efficiency (). We use two
kinds of MHD solutions depending on the absence (cold solution) or presence
(warm solution) of heating at the disk surface. Such heating could be from e.g.
dissipation of energy due to MHD turbulence in the disk or from illumination.
We use each of these MHD solutions to predict the physical parameters of an
outflow; put limits on the ionization parameter (), column density and
timescales, motivated by observational results; and thus select regions within
the outflow which are consistent with the observed winds. The cold MHD
solutions cannot account for winds due to their low ejection efficiency. But
warm solutions can explain the observed physical quantities in the wind because
they can have sufficiently high values of (, implying larger
mass loading at the base of the outflow). Further from our thermodynamic
equilibrium curve analysis for the outflowing gas, we found that in the Hard
state a range of is thermodynamically unstable, and had to be excluded.
This constrain made it impossible to have any wind at all, in the Hard state.Comment: 16 Pages, 10 figures in the main body and 4 figures in the appendix.
Accepted for publication in A&
A solvable model of the genesis of amino-acid sequences via coupled dynamics of folding and slow genetic variation
We study the coupled dynamics of primary and secondary structure formation
(i.e. slow genetic sequence selection and fast folding) in the context of a
solvable microscopic model that includes both short-range steric forces and and
long-range polarity-driven forces. Our solution is based on the diagonalization
of replicated transfer matrices, and leads in the thermodynamic limit to
explicit predictions regarding phase transitions and phase diagrams at genetic
equilibrium. The predicted phenomenology allows for natural physical
interpretations, and finds satisfactory support in numerical simulations.Comment: 51 pages, 13 figures, submitted to J. Phys.
Multi-tasking Sulf1/Sulf2 enzymes do not only facilitate extracellular cell signalling but also participate in cell cycle related nuclear events
This study demonstrates highly dynamic spatial and temporal pattern of SULF1/SULF2 expression in a number of neuronal cell types growing in normal culture medium that included their transient nuclear mobilisation. Their nuclear translocation became particularly apparent during cell proliferation as both SULF1/SULF2 demonstrated not only cell membrane associated expression, their known site of function but also transient nuclear mobilisation during nuclear cell division. Nuclear localisation was apparent not only by immunocytochemical staining but also confirmed by immunoblotting staining of isolated nuclear fractions of C6, U87 and N2A cells. Immunocytochemical analysis demonstrated rapid nuclear exit of both SULF1/SULF2 following cell division that was slightly delayed but not blocked in a fraction of the polyploid cells observed in C6 cells. The overexpression of both Sulf1 and Sulf2 genes in C6 and U87 cells markedly promoted in vitro growth of these cells accompanied by nuclear mobilisation while inhibition of both these genes inhibited cell proliferation with little or no nuclear SULF1/SULF2 mobilisation. SULF1/SULF2 activity in these cells thus demonstrated a clear co-ordination of extracellular cell signalling with nuclear events related to cell proliferation
A unified accretion-ejection paradigm for black hole X-ray binaries. III. Spectral signatures of hybrid disk configurations
It has been suggested that the cycles of activity of X-ray Binaries (XrB) are
triggered by a switch in the dominant disk torque responsible for accretion
(paper I). As the disk accretion rate increases, the disk innermost regions
would change from a jet-emitting disk (JED) to a standard accretion disk (SAD).
While JEDs have been proven to successfully reproduce hard states (paper II),
the existence of an outer cold SAD introduces an extra non local cooling term.
We investigate the thermal structure and associated spectra of such a hybrid
disk configuration. We use the 2T plasma code elaborated in paper II, allowing
to compute outside-in the disk local thermal equilibrium with self-consistent
advection and optically thin-to-thick transitions, in both radiation and gas
supported regimes. The non-local inverse Compton cooling introduced by the
external soft photons is computed by the BELM code. This additional term has a
profound influence on JED solutions, allowing a smooth temperature transition
from the outer SAD to the inner JED. We explore the full parameter space in
disk accretion rate and transition radius, and show that the whole domain in
X-ray fluxes and hardness ratios covered by standard XrB cycles is well
reproduced by such hybrid configurations. Precisely, a reasonable combination
of these parameters allows to reproduce the 3-200 keV spectra of five canonical
XrB states. Along with X-ray signatures, JED-SAD configurations also naturally
account for the radio emission whenever it is observed. By varying only the
transition radius and the accretion rate, hybrid disk configurations combining
an inner JED and an outer SAD are able to reproduce simultaneously the X-ray
spectral states and radio emission of X-ray binaries during their outburst.
Adjusting these two parameters, it is then possible to reproduce a full cycle.
This will be shown in a forthcoming paper (paper IV).Comment: Accepted for publication in A&
The outflow in Mrk 509: A method to calibrate XMM-Newton EPIC-pn and RGS
We have analyzed three XMM-Newton observations of the Seyfert 1 galaxy Mrk
509, with the goal to detect small variations in the ionized outflow
properties. Such measurements are limited by the quality of the
cross-calibration between RGS, the best instrument to characterize the
spectrum, and EPIC-pn, the best instrument to characterize the variability. For
all three observations we are able to improve the relative calibration of RGS
and pn consistently to 4 %. In all observations we detect three different
outflow components and, thanks to our accurate cross-calibration we are able to
detect small differences in the ionization parameter and column density in the
highest ionized component of the outflow. This constrains the location of this
component of the outflow to within 0.5 pc of the central source. Our method for
modeling the relative effective area is not restricted to just this source and
can in principle be extended to other types of sources as well.Comment: 11 pages, 9 figure
A natural orbital functional for the many-electron problem
The exchange-correlation energy in Kohn-Sham density functional theory is
expressed as a functional of the electronic density and the Kohn-Sham orbitals.
An alternative to Kohn-Sham theory is to express the energy as a functional of
the reduced first-order density matrix or equivalently the natural orbitals. In
the former approach the unknown part of the functional contains both a kinetic
and a potential contribution whereas in the latter approach it contains only a
potential energy and consequently has simpler scaling properties. We present an
approximate, simple and parameter-free functional of the natural orbitals,
based solely on scaling arguments and the near satisfaction of a sum rule. Our
tests on atoms show that it yields on average more accurate energies and charge
densities than the Hartree Fock method, the local density approximation and the
generalized gradient approximations
Multiwavelength Campaign on Mrk 509 X. Lower limit on the distance of the absorber from HST COS and STIS spectroscopy
Active Galactic Nuclei often show evidence of photoionized outflows. A major
uncertainty in models for these outflows is the distance () to the gas from
the central black hole. In this paper we use the HST/COS data from a massive
multi-wavelength monitoring campaign on the bright Seyfert I galaxy Mrk 509, in
combination with archival HST/STIS data, to constrain the location of the
various kinematic components of the outflow. We compare the expected response
of the photoionized gas to changes in ionizing flux with the changes measured
in the data using the following steps: 1) We compare the column densities of
each kinematic component measured in the 2001 STIS data with those measured in
the 2009 COS data; 2) We use time-dependent photionization calculations with a
set of simulated lightcurves to put statistical upper limits on the hydrogen
number density that are consistent with the observed small changes in the ionic
column densities; 3) From the upper limit on the number density, we calculate a
lower limit on the distance to the absorber from the central source via the
prior determination of the ionization parameter. Our method offers two
improvements on traditional timescale analysis. First, we account for the
physical behavior of AGN lightcurves. Second, our analysis accounts for the
quality of measurement in cases where no changes are observed in the absorption
troughs. The very small variations in trough ionic column densities (mostly
consistent with no change) between the 2001 and 2009 epochs allow us to put
statistical lower limits on the distance between 100--200 pc for all the major
UV absorption components at a confidence level of 99%. These results are mainly
consistent with the independent distance estimates derived for the warm
absorbers from the simultaneous X-ray spectra.Comment: Accepted to A&A (06 APR 2012
Evidence for the Decay Sigma+ -> p mu+ mu-
We report the first evidence for the decay Sigma+ -> p mu+ mu- from data
taken by the HyperCP experiment(E871) at Fermilab. Based on three observed
events, the branching ratio is B(Sigma+ -> p,mu+,mu-) = [8.6 +6.6,-5.4(stat)
+/-5.5(syst)] x 10**-8. The narrow range of dimuon masses may indicate that the
decay proceeds via a neutral intermediate state, Sigma+ -> p P0, P0 -> mu+ mu-,
with a P0 mass of 214.3 +/- 0.5 MeV/c**2 and branching ratio B(Sigma+ -> p P0;
P0 -> mu+ mu-) = [3.1 +2.4,-1.(stat) +/-1.5(syst)] x 10**-8.Comment: As published in PR
A critical assessment of the Self-Interaction Corrected Local Density Functional method and its algorithmic implementation
We calculate the electronic structure of several atoms and small molecules by
direct minimization of the Self-Interaction Corrected Local Density
Approximation (SIC-LDA) functional. To do this we first derive an expression
for the gradient of this functional under the constraint that the orbitals be
orthogonal and show that previously given expressions do not correctly
incorporate this constraint. In our atomic calculations the SIC-LDA yields
total energies, ionization energies and charge densities that are superior to
results obtained with the Local Density Approximation (LDA). However, for
molecules SIC-LDA gives bond lengths and reaction energies that are inferior to
those obtained from LDA. The nonlocal BLYP functional, which we include as a
representative GGA functional, outperforms both LDA and SIC-LDA for all ground
state properties we considered.Comment: 14 pages, 5 figure
Structural and Electronic Properties of Small Neutral (MgO)n Clusters
Ab initio Perturbed Ion (PI) calculations are reported for neutral
stoichiometric (MgO)n clusters (n<14). An extensive number of isomer structures
was identified and studied. For the isomers of (MgO)n (n<8) clusters, a full
geometrical relaxation was considered. Correlation corrections were included
for all cluster sizes using the Coulomb-Hartree-Fock (CHF) model proposed by
Clementi. The results obtained compare favorably to the experimental data and
other previous theoretical studies. Inclusion of correlaiotn is crucial in
order to achieve a good description of these systems. We find an important
number of new isomers which allows us to interpret the experimental magic
numbers without the assumption of structures based on (MgO)3 subunits. Finally,
as an electronic property, the variations in the cluster ionization potential
with the cluster size were studied and related to the structural isomer
properties.Comment: 24 pages, LaTeX, 7 figures in GIF format. Accepted for publication in
Phys. Rev.
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