7,120 research outputs found
Polynomial cubic splines with tension properties
In this paper we present a new class of spline functions with tension properties. These splines are composed by polynomial cubic pieces and therefore are conformal to the standard, NURBS based CAD/CAM systems
Jets and outflows in Radio Galaxies: implications for AGN feedback
One of the main debated astrophysical problems is the role of the AGN
feedback in galaxy formation. It is known that massive black holes have a
profound effect on the formation and evolution of galaxies, but how black holes
and galaxies communicate is still an unsolved problem. For Radio Galaxies,
feedback studies have mainly focused on jet/cavity systems in the most massive
and X-ray luminous galaxy clusters. The recent high-resolution detection of
warm absorbers in some Broad Line Radio Galaxies allow us to investigate the
interplay between the nuclear engine and the surrounding medium from a
different perspective. We report on the detection of warm absorbers in two
Broad Line Radio Galaxies, 3C 382 and 3C 390.3, and discuss the physical and
energetic properties of the absorbing gas. Finally, we attempt a comparison
between radio-loud and radio-quiet outflows.Comment: To be published in the proceedings of High Energy Phenomena in
Relativistic Outflows III (HEPRO III, IJMPCS). 4 pages, 2 figure
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ECRG4 regulates neutrophil recruitment and CD44 expression during the inflammatory response to injury.
The complex molecular microenvironment of the wound bed regulates the duration and degree of inflammation in the wound repair process, while its dysregulation leads to impaired healing. Understanding factors controlling this response provides therapeutic targets for inflammatory disease. Esophageal cancer-related gene 4 (ECRG4) is a candidate chemokine that is highly expressed on leukocytes. We used ECRG4 knockout (KO) mice to establish that the absence of ECRG4 leads to defective neutrophil recruitment with a delay in wound healing. An in vitro human promyelocyte model identified an ECRG4-mediated suppression of the hyaluronic acid receptor, CD44, a key receptor mediating inflammation resolution. In ECRG4 KO mouse leukocytes, there was an increase in CD44 expression, consistent with a model in which ECRG4 negatively regulates CD44 levels. Therefore, we propose a previously unidentified mechanism in which ECRG4 regulates early neutrophil recruitment and subsequent CD44-mediated resolution of inflammation
Measuring Column Densities in Quasar Outflows: VLT Observations of QSO 2359-1241
We present high resolution spectroscopic VLT observations of the outflow seen
in QSO 2359-1241. These data contain absorption troughs from five resonance Fe
II lines with a resolution of ~7 km/s and signal-to-noise ratio per resolution
element of order 100. We use this unprecedented high quality data set to
investigate the physical distribution of the material in front of the source,
and by that determine the column densities of the absorbed troughs. We find
that the apparent optical depth model gives a very poor fit to the data and
greatly underestimates the column density measurements. Power-law distributions
and partial covering models give much better fits with some advantage to
power-law models, while both models yield similar column density estimates. The
better fit of the power-law model solves a long standing problem plaguing the
partial covering model when applied to large distance scale outflow: How to
obtain a velocity dependent covering factor for an outflow situated at
distances thousands of time greater than the size of the AGN emission source.
This problem does not affect power-law models. Therefore, based on the better
fit and plausibility of the physical model, we conclude that in QSO 2359-1241,
the outflow covers the full extent of the emission source but in a
non-homogeneous way.Comment: 27 pages, 6 figures, to appear on ApJ Jul 10. The full (online)
version of figure 2 can be obtained here:
http://www.phys.vt.edu/~arav/f2_online_version.p
The inelastic hard dimer gas: a non-spherical model for granular matter
We study a two-dimensional gas of inelastic smooth hard dimers. Since the
collisions between dimers are dissipative, being characterized by a coefficient
of restitution , and no external driving force is present, the energy
of the system decreases in time and no stationary state is achieved. However,
the resulting non equilibrium state of the system displays several interesting
properties in close analogy with systems of inelastic hard spheres, whose
relaxational dynamics has been thoroughly explored. We generalise to inelastic
systems a recently method introduced [G.Ciccotti and G.Kalibaeva, J. Stat.
Phys. {\bf 115}, 701 (2004)] to study the dynamics of rigid elastic bodies made
up of different spheres hold together by rigid bonds. Each dimer consists of
two hard disks of diameter , whose centers are separated by a fixed distance
. By describing the rigid bonds by means of holonomic constraints and
deriving the appropriate collision rules between dimers, we reduce the dynamics
to a set of equations which can be solved by means of event driven simulation.
After deriving the algorithm we study the decay of the total kinetic energy,
and of the ratio between the rotational and the translational kinetic energy of
inelastic dimers. We show numerically that the celebrated Haff's homogeneous
cooling law , describing how the kinetic energy of an inelastic hard
sphere system with constant coefficient of restitution decreases in time, holds
even in the case of these non spherical particles. We fully characterize this
homogeneous decay process in terms of appropriate decay constants and confirm
numerically the scaling behavior of the velocity distributions.Comment: 21 pages, 6 figures and 2 tables, submitted to JC
Noise Rectification and Fluctuations of an Asymmetric Inelastic Piston
We consider a massive inelastic piston, whose opposite faces have different
coefficients of restitution, moving under the action of an infinitely dilute
gas of hard disks maintained at a fixed temperature. The dynamics of the piston
is Markovian and obeys a continuous Master Equation: however, the asymmetry of
restitution coefficients induces a violation of detailed balance and a net
drift of the piston, as in a Brownian ratchet. Numerical investigations of such
non-equilibrium stationary state show that the velocity fluctuations of the
piston are symmetric around the mean value only in the limit of large piston
mass, while they are strongly asymmetric in the opposite limit. Only taking
into account such an asymmetry, i.e. including a third parameter in addition to
the mean and the variance of the velocity distribution, it is possible to
obtain a satisfactory analytical prediction for the ratchet drift velocity.Comment: 6 pages, 5 figures, to be published on Europhysics Letters; some
references have been adde
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