53,307 research outputs found
K X-Ray Energies and Transition Probabilities for He-, Li- and Be-like Praseodymium ions
Theoretical transition energies and probabilities for He-, Li- and Be-like
Praseodymium ions are calculated in the framework of the multi-configuration
Dirac-Fock method (MCDF), including QED corrections. These calculated values
are compared to recent experimental data obtained in the Livermore SuperEBIT
electron beam ion trap facility
Radial distribution function of penetrable sphere fluids to second order in density
The simplest bounded potential is that of penetrable spheres, which takes a
positive finite value if the two spheres are overlapped, being 0
otherwise. In this paper we derive the cavity function to second order in
density and the fourth virial coefficient as functions of (where is the Boltzmann constant and is the
temperature) for penetrable sphere fluids. The expressions are exact, except
for the function represented by an elementary diagram inside the core, which is
approximated by a polynomial form in excellent agreement with accurate results
obtained by Monte Carlo integration. Comparison with the hypernetted-chain
(HNC) and Percus-Yevick (PY) theories shows that the latter is better than the
former for only. However, even at zero temperature (hard sphere
limit), the PY solution is not accurate inside the overlapping region, where no
practical cancelation of the neglected diagrams takes place. The exact fourth
virial coefficient is positive for , reaches a minimum
negative value at , and then goes to zero from below as
for high temperatures. These features are captured qualitatively,
but not quantitatively, by the HNC and PY predictions. In addition, in both
theories the compressibility route is the best one for , while
the virial route is preferable if .Comment: 10 pages, 2 figures; v2: minor changes; to be published in PR
Evidence that the degree of band 3 phosphorylation modulates human erythrocytes nitric oxide efflux – in vitro model of hyperfibrinogenemia
© 2011 – IOS Press and the authors. All rights reservedRecent evidence has shown that plasma fibrinogen, a major cardiovascular risk factor, interacts with the erythrocyte membrane and acts to influence blood flow via erythrocyte nitric oxide (NO) modulation. In the present pioneer in-vitro study, whole blood samples were harvested from healthy subjects and aliquots were incubated in the absence (control aliquots) and presence of fibrinogen at different degrees of band 3 phosphorylation, and the levels of NO, nitrite, nitrate and S-nitroglutathione (GSNO) were determined.
Hyperfibrinogenemia interferes with erythrocyte NO mobilization without changing its efflux in a way that seems to be dependent of the degree of band 3 phosphorylation. In presence of higher fibrinogen concentrations the NO efflux is reinforced when band 3 is phosphorylated (p < 0.001). Higher levels of nitrite, nitrate and GSNO were documented (p < 0.05). However, the mechanisms by which fibrinogen signalling modulates erythrocyte function remain to be clarified and are currently under study. These conditions may be considered an approach to be followed in blood storage for transfusions.This study was supported by grants from the FCT - Fundação para a Ciência e a Tecnologia (project reference PTDC/SAU-OSM/73449/2006
Topological Defects in Contracting Universes
We study the behaviour and consequences of cosmic string networks in
contracting universes. They approximately behave during the collapse phase as a
radiation fluids. Scaling solutions describing this are derived and tested
against high-resolution numerical simulations. A string network in a
contracting universe, together with the gravitational radiation it generates,
can affect the dynamics of the universe both locally and globally, and be an
important source of radiation, entropy and inhomogeneity. We discuss possible
implications for bouncing and cyclic models.Comment: Shorter version of astro-ph/0206287. To appear in Phys. Rev. Let
Telluric correction in the near-infrared: Standard star or synthetic transmission?
Context. The atmospheric absorption of the Earth is an important limiting
factor for ground-based spectroscopic observations and the near-infrared and
infrared regions are the most affected. Several software packages that produce
a synthetic atmospheric transmission spectrum have been developed to correct
for the telluric absorption; these are Molecfit, TelFit, and TAPAS. Aims. Our
goal is to compare the correction achieved using these three telluric
correction packages and the division by a telluric standard star. We want to
evaluate the best method to correct near-infrared high-resolution spectra as
well as the limitations of each software package and methodology. Methods. We
applied the telluric correction methods to CRIRES archival data taken in the J
and K bands. We explored how the achieved correction level varies depending on
the atmospheric T-P profile used in the modelling, the depth of the atmospheric
lines, and the molecules creating the absorption. Results. We found that the
Molecfit and TelFit corrections lead to smaller residuals for the water lines.
The standard star method corrects best the oxygen lines. The Molecfit package
and the standard star method corrections result in global offsets always below
0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O
lines and around 1% for the O2 lines. All methods and software packages result
in a scatter between 3% and 7% inside the telluric lines. The use of a tailored
atmospheric profile for the observatory leads to a scatter two times smaller,
and the correction level improves with lower values of precipitable water
vapour. Conclusions. The synthetic transmission methods lead to an improved
correction compared to the standard star method for the water lines in the J
band with no loss of telescope time, but the oxygen lines were better corrected
by the standard star method.Comment: 18 pages, 13 figures, Accepted to A&
Dark Matter directional detection: comparison of the track direction determination
Several directional techniques have been proposed for a directional detection
of Dark matter, among others anisotropic crystal detectors, nuclear emulsion
plates, and low-pressure gaseous TPCs. The key point is to get access to the
initial direction of the nucleus recoiling due to the elastic scattering by a
WIMP. In this article, we aim at estimating, for each method, how the
information of the recoil track initial direction is preserved in different
detector materials. We use the SRIM simulation code to emulate the motion of
the first recoiling nucleus in each material. We propose the use of a new
observable, D, to quantify the preservation of the initial direction of the
recoiling nucleus in the detector. We show that in an emulsion mix and an
anisotropic crystal, the initial direction is lost very early, while in a
typical TPC gas mix, the direction is well preserved.Comment: 9 pages, 5 figure
Impact of micro-telluric lines on precise radial velocities and its correction
Context: In the near future, new instruments such as ESPRESSO will arrive,
allowing us to reach a precision in radial-velocity measurements on the order
of 10 cm/s. At this level of precision, several noise sources that until now
have been outweighed by photon noise will start to contribute significantly to
the error budget. The telluric lines that are not neglected by the masks for
the radial velocity computation, here called micro-telluric lines, are one such
noise source. Aims: In this work we investigate the impact of micro-telluric
lines in the radial velocities calculations. We also investigate how to correct
the effect of these atmospheric lines on radial velocities. Methods: The work
presented here follows two parallel lines. First, we calculated the impact of
the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum
by synthetic atmospheric spectra and evaluated the effect created by the
presence of the telluric lines. Then, we divided HARPS spectra by synthetic
atmospheric spectra to correct for its presence on real data and calculated the
radial velocity on the corrected spectra. When doing so, one considers two
atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS.
Results: We find that the micro-telluric lines can induce an impact on the
radial velocities calculation that can already be close to the current
precision achieved with HARPS, and so its effect should not be neglected,
especially for future instruments such as ESPRESSO. Moreover, we find that the
micro-telluric lines' impact depends on factors, such as the radial velocity of
the star, airmass, relative humidity, and the barycentric Earth radial velocity
projected along the line of sight at the time of the observation.Comment: Accepted in A&
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