10,318 research outputs found
Platelets and their chemokines in atherosclerosis-clinical applications
The concept of platelets as important players in the process of atherogenesis has become increasingly accepted due to accumulating experimental and clinical evidence. Despite the progress in understanding the molecular details of atherosclerosis, particularly by using animal models, the inflammatory and thrombotic roles of activated platelet s especially in the human system remain difficult to dissect, as often only the complications of atherosclerosis, i.e., stroke and myocardial infarction are definable but not the plague burden. Platelet indices including platelet count and mean platelet volume (MPV) and soluble mediators released by activated platelets are associated with atherosclerosis. The chemokine CXCL4 has multiple atherogenic activities, e.g., altering the differentiation of T cells and macrophages by inhibiting neutrophil and monocyte apoptosis and by increasing the uptake of oxLDL and synergizing with CCL5. CCL5 is released and deposited on endothelium by activated platelets thereby triggering atherogenic monocyte recruitment, which can be attenuated by blocking the corresponding chemokine receptor CCR5. Atheroprotective and plague stabilizing properties are attributed to CXCL12, which plays an important role in regenerative processes by attracting progenitor cells. Its release from luminal attached platelets accelerates endothelial healing after injury. Platelet surface molecules GPIIb/IIIa, GP1b alpha, P-selectin, JAM-A and the CD40/CD40L dyade are crucially involved in the interaction with endothelial cells, leukocytes and matrix molecules affecting atherogenesis. Beyond the effects on the arterial inflammatory infiltrate, platelets affect cholesterol metabolism by binding, modifying and endocytosing LDL particles via their scavenger receptors and contribute to the formation of lipid laden macrophages. Current medical therapies for the prevention of atherosclerotic therapies enable the elucidation of mechanisms linking platelets to inflammation and atherosclerosis
The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
Aims. A large number of Calcium Infrared Triplet (IRT) spectra are expected
from the GAIA- and CARMENES missions. Conversion of these spectra into known
activity indicators will allow analysis of their temporal evolution to a better
degree. We set out to find such a conversion formula and to determine its
robustness.
Methods. We have compared 2274 Ca II IRT spectra of active main-sequence F to
K stars taken by the TIGRE telescope with those of inactive stars of the same
spectral type. After normalizing and applying rotational broadening, we
subtracted the comparison spectra to find the chromospheric excess flux caused
by activity. We obtained the total excess flux, and compared it to established
activity indices derived from the Ca II H & K lines, the spectra of which were
obtained simultaneously to the infrared spectra.
Results. The excess flux in the Ca II IRT is found to correlate well with
and , as well as , if the
-dependency is taken into account. We find an empirical conversion formula
to calculate the corresponding value of one activity indicator from the
measurement of another, by comparing groups of datapoints of stars with similar
B-V.Comment: 16 pages, 15 figures. Accepted for publication in Astronomy &
Astrophysic
From Cooper Pairs to Composite Bosons: A Generalized RPA Analysis of Collective Excitations
The evolution of the ground state and the excitation spectrum of the two and
three dimensional attractive Hubbard model is studied as the system evolves
from a Cooper pair regime for weak attraction to a composite boson regime for a
strong attraction.Comment: 20 pages RevTex, 7 figures on reques
Slicing the Torus: Obscuring Structures in Quasars
Quasars and Active Galactic Nuclei (AGNs) are often obscured by dust and gas.
It is normally assumed that the obscuration occurs in an oblate "obscuring
torus", that begins at the radius at which the most refractive dust can remain
solid. The most famous form of this torus is a donut-shaped region of molecular
gas with a large scale-height. While this model is elegant and accounts for
many phenomena at once, it does not hold up to detailed tests. Instead the
obscuration in AGNs must occur on a wide range of scales and be due to a
minimum of three physically distinct absorbers. Slicing the "torus" into these
three regions will allow interesting physics of the AGN to be extracted.Comment: 8 pages, 1 figure. To appear in the proceedings of the conference
"The central kiloparsec in Galactic Nuclei:Astronomy at High Angular
Resolution 2011", open access Journal of Physics: Conference Series (JPCS),
published by IOP Publishin
The Magnetic Properties of an L Dwarf Derived from Simultaneous Radio, X-ray, and H-alpha Observations
We present the first simultaneous, multi-wavelength observations of an L
dwarf, the L3.5 candidate brown dwarf 2MASS J00361617+1821104, conducted with
the Very Large Array, the Chandra X-ray Observatory, and the Kitt Peak 4-m
telescope. We detect strongly variable and periodic radio emission (P=3 hr)
with a fraction of about 60% circular polarization. No X-ray emission is
detected to a limit of L_X/L_{bol}<2e-5, several hundred times below the
saturation level observed in early M dwarfs. Similarly, we do not detect
H-alpha emission to a limit of L_{H-alpha}/L_{bol}<2e-7, the deepest for any L
dwarf observed to date. The ratio of radio to X-ray luminosity is at least four
orders of magnitude in excess of that observed in a wide range of active stars
(including M dwarfs) providing the first direct confirmation that late-M and L
dwarfs violate the radio/X-ray correlation. The radio emission is due to
gyrosynchrotron radiation in a large-scale magnetic field of about 175 G, which
is maintained on timescales longer than three years. The detected 3-hour period
may be due to (i) the orbital motion of a companion at a separation of about
five stellar radii, similar to the configuration of RS CVn systems, (ii) an
equatorial rotation velocity of about 37 km/s and an anchored, long-lived
magnetic field, or (iii) periodic release of magnetic stresses in the form of
weak flares. In the case of orbital motion, the magnetic activity may be
induced by the companion, possibly explaining the unusual pattern of activity
and the long-lived signal. We conclude that fully convective stars can maintain
a large-scale and stable magnetic field, but the lack of X-ray and H-alpha
emission indicates that the atmospheric conditions are markedly different than
in early-type stars and even M dwarfs. [abridged]Comment: Submitted to ApJ; 26 pages, 15 figure
Vortex State and Field-Angle Resolved Specific Heat Oscillation for H // ab in d-Wave Superconductors
When magnetic field is applied parallel to the ab plane in d_{x^2-y^2}-wave
superconductors, the transition of stable vortex lattice structure, spatial
structure of local density of states, and specific heat oscillation by rotation
of magnetic field orientation are investigated by quantitative calculations
based on the selfconsistent Eilenberger theory. We estimate how the vortex
state changes depending on the relative angle between the node-direction of the
superconducting gap and magnetic field orientation. To reproduce the
sign-change of specific heat oscillation observed in CeCoIn_5, our study is
done by including strong paramagnetic effect. The quantitative theoretical
calculations give decisive information to analyze the experimental data on the
field-angle dependence, and establish the angle-resolved specific heat
experiment as a spectroscopic means to identify the node-position of the
superconducting gap.Comment: 9 pages, 13 figure
Probing the interplay between lattice dynamics and short-range magnetic correlations in CuGeO3 with femtosecond RIXS
Investigations of magnetically ordered phases on the femtosecond timescale
have provided significant insights into the influence of charge and lattice
degrees of freedom on the magnetic sub-system. However, short-range magnetic
correlations occurring in the absence of long-range order, for example in
spin-frustrated systems, are inaccessible to many ultrafast techniques. Here,
we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is
capable of probing such short-ranged magnetic dynamics in a charge-transfer
insulator through the detection of a Zhang-Rice singlet exciton. Utilizing
trRIXS measurements at the O K-edge, and in combination with model
calculations, we probe the short-range spin-correlations in the frustrated spin
chain material CuGeO3 following photo-excitation, revealing a strong coupling
between the local lattice and spin sub-systems
Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers
Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. Since one of the most limiting factors in performing Large Eddy Simulation (LES) of real combustors is estimating the adequate grid, the effects of mesh resolution are investigated by computing full annular LES of a realistic helicopter combustion chamber on three grids, respectively made of 38, 93 and 336 million elements. Results are compared in terms of mean and fluctuating fields. LES captures self-established azimuthal modes. The presence and structure of the modes is discussed. This study therefore highlights the potential of LES for studying combustion instabilities in annular gas turbine combustors
Coherent Potential Approximation for `d - wave' Superconductivity in Disordered Systems
A Coherent Potential Approximation is developed for s-wave and d-wave
superconductivity in disordered systems. We show that the CPA formalism
reproduces the standard pair-breaking formula, the self-consistent Born
Approximation and the self-consistent T-matrix approximation in the appropriate
limits. We implement the theory and compute T_c for s-wave and d-wave pairing
using an attractive nearest neighbor Hubbard model featuring both binary alloy
disorder and a uniform distribution of scattering site potentials. We determine
the density of states and examine its consequences for low temperature heat
capacity. We find that our results are in qualitative agreement with
measurements on Zn doped YBCO superconductors.Comment: 35 pages, 23 figures, submitted to Phys Rev.
Uniaxial pressure induced stripe order rotation in La1.88Sr0.12CuO4
Static stripe order is detrimental to superconductivity. Yet, it has been proposed that transverse stripe fluctuations may enhance the inter-stripe Josephson coupling and thus promote superconductivity. Direct experimental studies of stripe dynamics, however, remain difficult. From a strong-coupling perspective, transverse stripe fluctuations are realized in the form of dynamic “kinks”—sideways shifting stripe sections. Here, we show how modest uniaxial pressure tuning reorganizes directional kink alignment. Our starting point is La1.88Sr0.12CuO4 where transverse kink ordering results in a rotation of stripe order away from the crystal axis. Application of mild uniaxial pressure changes the ordering pattern and pins the stripe order to the crystal axis. This reordering occurs at a much weaker pressure than that to detwin the stripe domains and suggests a rather weak transverse stripe stiffness. Weak spatial stiffness and transverse quantum fluctuations are likely key prerequisites for stripes to coexist with superconductivity
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