1,021 research outputs found
Low Luminosity States of the Black Hole Candidate GX 339-4. I. ASCA and Simultaneous Radio/RXTE Observations
We discuss a series of observations of the black hole candidate GX 339-4 in
low luminosity, spectrally hard states. We present spectral analysis of three
separate archival Advanced Satellite for Cosmology and Astrophysics (ASCA) data
sets and eight separate Rossi X-ray Timing Explorer (RXTE) data sets. Three of
the RXTE observations were strictly simultaneous with 843 MHz and 8.3-9.1 GHz
radio observations. All of these observations have (3-9 keV) flux approximately
< 10^{-9} ergs s^{-1} cm^{-2}. The ASCA data show evidence for an 6.4 keV Fe
line with equivalent width 40 eV, as well as evidence for a soft excess that is
well-modeled by a power law plus a multicolor blackbody spectrum with peak
temperature 150-200 eV. The RXTE data sets also show evidence of an Fe line
with equivalent widths 20-140 eV. Reflection models show a hardening of the
RXTE spectra with decreasing X-ray flux; however, these models do not exhibit
evidence of a correlation between the photon index of the incident power law
flux and the solid angle subtended by the reflector. `Sphere+disk'
Comptonization models and Advection Dominated Accretion Flow (ADAF) models also
provide reasonable descriptions of the RXTE data. The former models yield
coronal temperatures in the range 20-50 keV and optical depths of \tau ~ 3. The
model fits to the X-ray data, however, do not simultaneously explain the
observed radio properties. The most likely source of the radio flux is
synchrotron emission from an extended outflow of size greater than O(10^7
GM/c^2).Comment: 18 pages in latex emulateapj.sty. Accepted for publication in the
Astrophysical Journa
Modeling of association effects in mixtures of carboxylic acids with associating and non-associating components
http://apps.isiknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=6&SID=V21Di6PajaHLPoM3@AJ&page=1&doc=1&colname=WOSThe group contribution with association equation of state GCA-EOS has been applied to calculate thermodynamic properties of
pure compounds and mixtures of carboxylic acids with paraffins, alcohols, water and gases, at low and high pressures. Two associating groups, OH and COOH, were defined. Self- and cross-association in
these mixtures were quantified through two parallel COOH/COOH and OH/OH associations. The validity of this approach is supported by an excellent representation of pure compound properties (vapor pressures and compressibility factors) and phase equilibria in mixtures of (associating + inert) and (associating + associating) components at low and high pressures
L(h, 1, 1)-labeling of outerplanar graphs
An L(h, 1, 1)-labeling of a graph is an assignment of labels from the set of integers {0, . . . , lambda} to the nodes of the graph such that adjacent nodes are assigned integers of at least distance h a parts per thousand yen 1 apart and all nodes of distance three or less must be assigned different labels. The aim of the L(h, 1, 1)-labeling problem is to minimize lambda, denoted by lambda (h, 1, 1) and called span of the L(h, 1, 1)-labeling. As outerplanar graphs have bounded treewidth, the L(1, 1, 1)-labeling problem on outerplanar graphs can be exactly solved in O(n (3)), but the multiplicative factor depends on the maximum degree Delta and is too big to be of practical use. In this paper we give a linear time approximation algorithm for computing the more general L(h, 1, 1)-labeling for outerplanar graphs that is within additive constants of the optimum values
The extended gca-eos model for mixtures of fatty oils and derivatives
The Group Contribution Equation of State GC-EOS has been satisfactory applied
to the modeling of high-pressure phase equilibria of supercritical gases (CO2, propane, ethane, dimethylether) with pure triglycerides and natural vegetable oils. The GC-EOS model size-related parameter, i.e. the critical hard sphere diameter, of the high molecular weight compounds were determined by fitting infinite dilution activity coefficients of n-alkanes
in these heavy compounds. In this way the GC-EOS model was able to correlate
and predict vapor-liquid (VLE) and liquid-liquid (LLE) equilibria of these mixtures, using a unique set of parameters, in good agreement with experimental data. In this work the application of the model is extended to mixtures containing fatty oil derivatives, such as fatty acids, fatty acids esters, mono - and diglycerides. The associating effects between molecules are described using an upgraded version of the model, the Group Contribution Associating - EOS. Satisfactory correlation and prediction of experimental VLE, LLE and ginfinite data in binary and ternary mixtures of these products with supercritical gases are
obtained
Dynamic Evolution of Permeability in Response to Chemo‐Mechanical Compaction
Pressure‐solution creep is an important fluid‐mediated deformation mechanism, causing chemo‐mechanical transformations and porosity and permeability changes in rocks. The presence of phyllosilicates, in particular, has previously been hypothesized to further reduce porosity and pore connectivity. Nevertheless, a full characterization of the spatio‐temporal evolution of permeability during this process has yet to be reported. A pure NaCl aggregate and a mixture of NaCl and biotite were deformed through pressure‐solution creep while monitoring their microstructural evolution through computed X‐ray micro‐tomography. The evolution of permeability and fluid velocity of the samples were computed by using the pore geometries from the X‐ray micro‐tomography as input for the Lattice‐Boltzmann modeling. The results indicate that, as deformation proceeds, porosity and permeability decrease in both samples. In the salt ‐biotite sample pressure solution creep causes the formation of a compaction band perpendicular to the direction of loading, forming a barrier for permeability. Along the other two directions, pore connectivity and permeability are retained in the marginal salt layers, making the sample strongly anisotropic. The presence of biotite controls the way pore coordination number evolves and hence, the connectivity of the pathways. Biotite flakes create an enhanced porosity decrease leading to compaction and reduction of pore connectivity. This reduction in porosity affects local stresses and local contact areas, reducing over time the driving force. According to a texture‐porosity process, the reduction in porosity causes salt ions to dissolve in the marginal salt and precipitate within the biotite‐bearing layer, where the bulk volume of salt grains increases over time
A new generation photodetector for astroparticle physics: the VSiPMT
The VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an innovative design we
proposed for a revolutionary photon detector. The main idea is to replace the
classical dynode chain of a PMT with a SiPM (G-APD), the latter acting as an
electron detector and amplifier. The aim is to match the large sensitive area
of a photocathode with the performance of the SiPM technology. The VSiPMT has
many attractive features. In particular, a low power consumption and an
excellent photon counting capability. To prove the feasibility of the idea we
first tested the performance of a special non-windowed SiPM by Hamamatsu (MPPC)
as electron detector and current amplifier. Thanks to this result Hamamatsu
realized two VSiPMT industrial prototypes. In this work, we present the results
of a full characterization of the VSiPMT prototype
Site-specific acetylation of ISWI by GCN5
<p>Abstract</p> <p>Background</p> <p>The tight organisation of eukaryotic genomes as chromatin hinders the interaction of many DNA-binding regulators. The local accessibility of DNA is regulated by many chromatin modifying enzymes, among them the nucleosome remodelling factors. These enzymes couple the hydrolysis of ATP to disruption of histone-DNA interactions, which may lead to partial or complete disassembly of nucleosomes or their sliding on DNA. The diversity of nucleosome remodelling factors is reflected by a multitude of ATPase complexes with distinct subunit composition.</p> <p>Results</p> <p>We found further diversification of remodelling factors by posttranslational modification. The histone acetyltransferase GCN5 can acetylate the <it>Drosophila </it>remodelling ATPase ISWI at a single, conserved lysine, K753, <it>in vivo </it>and <it>in vitro</it>. The target sequence is strikingly similar to the N-terminus of histone H3, where the corresponding lysine, H3K14, can also be acetylated by GCN5. The acetylated form of ISWI represents a minor species presumably associated with the nucleosome remodelling factor NURF.</p> <p>Conclusion</p> <p>Acetylation of histone H3 and ISWI by GCN5 is explained by the sequence similarity between the histone and ISWI around the acetylation site. The common motif RK<sup>T</sup>/<sub>S</sub>xGx(K<sup>ac</sup>)xP<sup>R</sup>/<sub>K </sub>differs from the previously suggested GCN5/PCAF recognition motif GKxxP. This raises the possibility of co-regulation of a nucleosome remodelling factor and its nucleosome substrate through acetylation of related epitopes and suggests a direct crosstalk between two distinct nucleosome modification principles.</p
Large scale simulations of H and He reionization and heating driven by stars and more energetic sources
We present simulations of cosmic reionization and reheating from to
, investigating the role of stars (emitting soft UV-photons), nuclear
black holes (BHs, with power-law spectra), X-ray binaries (XRBs, with hard
X-ray dominated spectra), and the supernova-associated thermal bremsstrahlung
of the diffuse interstellar medium (ISM, with soft X-ray spectra). We
post-process the hydrodynamical simulation Massive-Black II (MBII) with
multifrequency ionizing radiative transfer. The source properties are directly
derived from the physical environment of MBII, and our only real free parameter
is the ionizing escape fraction . We find that, among the models
explored here, the one with an escape fraction that decreases with decreasing
redshift yields results most in line with observations, such as of the neutral
hydrogen fraction and the Thomson scattering optical depth. Stars are the main
driver of hydrogen reionization and consequently of the thermal history of the
intergalactic medium (IGM). We obtain
at for all source types, with volume averaged temperatures . BHs are rare and negligible to hydrogen
reionization, but conversely they are the only sources which can fully ionize
helium, increasing local temperatures by . The thermal and
ionization state of the neutral and lowly ionized hydrogen differs
significantly with different source combinations, with ISM and (to a lesser
extent) XRBs, playing a significant role and, as a consequence, determining the
transition from absorption to emission of the 21 cm signal from neutral
hydrogen.Comment: 17 pages, 19 figures, accepted for publication in MNRA
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