9,941 research outputs found
Vertex Reconstruction Using a Single Layer Silicon Detector
Typical vertex finding algorithms use reconstructed tracks, registered in a
multi-layer detector, which directly point to the common point of origin. A
detector with a single layer of silicon sensors registers the passage of
primary particles only in one place. Nevertheless, the information available
from these hits can also be used to estimate the vertex position, when the
geometrical properties of silicon sensors and the measured ionization energy
losses of the particles are fully exploited. In this paper the algorithm used
for this purpose in the PHOBOS experiment is described. The vertex
reconstruction performance is studied using simulations and compared with
results obtained from real data. The very large acceptance of a single-layered
multiplicity detector permits vertex reconstruction for low multiplicity events
where other methods, using small acceptance subdetectors, fail because of
insufficient number of registered primary tracks.Comment: accepted for publication in Nucl. Instr. Meth.
Dynamics of Particle Production in Relativistic Nuclear Collisions
Saturation models for particle production in relativistic nuclear collisions
are discussed. In particular, I show that the predictions from the high density
QCD for the qualitative shape of are very sensitive to the form of the
unintegrated gluon distribution.Comment: 4 pages, 4 figures, Proceedings for Quark Matter 200
Elliptic flow of the dilute Fermi gas: From kinetics to hydrodynamics
We use the Boltzmann equation in the relaxation time approximation to study
the expansion of a dilute Fermi gas at unitarity. We focus, in particular, on
the approach to the hydrodynamic limit. Our main finding are: i) In the regime
that has been studied experimentally hydrodynamic effects beyond the
Navier-Stokes approximation are small, ii) mean field corrections to the
Boltzmann equation are not important, iii) experimental data imply that
freezeout occurs very late, that means that the relaxation time remains smaller
than the expansion time during the entire evolution of the system, iv) the
experimental results also imply that the bulk viscosity is significantly
smaller than the shear viscosity of the system.Comment: 18 pages, 6 figure
Fusion at deep subbarrier energies: potential inversion revisited
For a single potential barrier, the barrier penetrability can be inverted
based on the WKB approximation to yield the barrier thickness. We apply this
method to heavy-ion fusion reactions at energies well below the Coulomb barrier
and directly determine the inter-nucleus potential between the colliding
nuclei. To this end, we assume that fusion cross sections at deep subbarrier
energies are governed by the lowest barrier in the barrier distribution. The
inverted inter-nucleus potentials for the O +Sm and O
+Pb reactions show that they are much thicker than phenomenological
potentials. We discuss a consequence of such thick potential by fitting the
inverted potentials with the Bass function.Comment: 8 pages, 5 figures. Uses aipxfm.sty. A talk given at the FUSION08:
New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, September
22-26, 2008, Chicago, US
Involvement of fusion activity of ultraviolet light-inactivated sendai virus in formation of target antigens recognized by cytotoxic T cells
Mice inoculated with ultraviolet light-inactivated Sendai virus mount a cell- mediated immune response to the virus. Cytotoxic T cells specific for Sendai virus can be obtained by in vitro secondary stimulation of primed spleen cells with syngeneic stimulator cells coated with UV-inactivated Sendai virus. Neither in vivo nor in vitro stimulation alone is sufficient to generate specific cytotoxic T cells. Sharing of the H-2 haplotype between cytotoxic T cells and target cells is required for the Sendai virus-specific lysis to occur. The fusion (F) glycoprotein of Sendai virus has been implicated in target antigen formation (20). Ethanol treatment of Sendai virus causes complete inactivation of the cell-fusion and hemolytic activities of the envelope, but does not affect the antigenicity of the F glycoprotein; furthermore, hemagglutinin and neuraminidase activities of the envelope HANA glycoprotein are also left intact after ethanol treatment. Target cells can be prepared by coating them with various numbers of UV-inactivated Sendai virus that have been treated with ethanol or, as a control, phosphate-buffered saline (PBS). The amount of virus adsorbed to target cells during the cytotoxicity reaction time using either ethanol-treated or untreated (PBS "treated") virions is essentially identical, but target cells coated with ethanol-treated Sendai virus fail to serve as targets for cytotoxic T cells. These results indicate that fusion activity of the Sendai virus envelope is essential to the formation of the target antigen and that virus adsorption to cell surfaces without fusion of the envelope with cell membranes is not sufficient to allow killing by virus-specific cytotoxic T cells
Two-phase flow in a porous medium modeling
This research is devoted to the multiphase modeling in substances containing pores. The experimental setup is built in Comsol Multiphysics package and constitutes a soil column that deals with two substances when one of them goes from above of the column while the other one goes from below. Throughout the experiment air represents the 'upper' substance while the second one varies. The varying matter allows checking the model for its accuracy. After the check the transition to the air/oil system is done. The result of simulation is distribution of substance pressure in the laboratory column at the final time
Exact Stochastic Mean-Field dynamics
The exact evolution of a system coupled to a complex environment can be
described by a stochastic mean-field evolution of the reduced system density.
The formalism developed in Ref. [D.Lacroix, Phys. Rev. E77, 041126 (2008)] is
illustrated in the Caldeira-Leggett model where a harmonic oscillator is
coupled to a bath of harmonic oscillators. Similar exact reformulation could be
used to extend mean-field transport theories in Many-body systems and
incorporate two-body correlations beyond the mean-field one. The connection
between open quantum system and closed many-body problem is discussed.Comment: Proceedings series of Proceedings of "FUSION08: New Aspects of Heavy
Ion Collisions near the Coulomb Barrier", September 22-26, 2008, Chicago, US
Observation of mixed anisotropy in the critical susceptibility of an ultrathin magnetic film
Measurements of the magnetic susceptibility of Fe/W(110) films with thickness
in the range of 1.6 to 2.4 ML Fe, show that in addition to the large response
along the easy axis associated with the Curie transition, there is a much
smaller, paramagnetic hard axis response that is not consistent with the 2D
anisotropic Heisenberg model used to describe homogeneous in-plane ferromagnets
with uniaxial anisotropy. The shape, amplitude, and peak temperature of the
hard axis susceptibility, as well as its dependence upon layer completion close
to 2.0 ML, indicate that inhomogeneities in the films create a system of mixed
anisotropy. A likely candidate for inhomogeneities that are magnetically
relevant in the critical region are the closed lines of step edges associated
with the incomplete layers. According to the Harris criterion, the existence of
magnetically relevant inhomogeneities may alter the critical properties of the
films from those of a 2D Ising model. Experiments in the recent literature are
discussed in this context.Comment: 9 two-column pages, 6 figures. This replacement has a new title and
abstract, and one additional figur
Stopping and Baryon Transport in Heavy Ion Reactions
In this report I will give an experimental overview on nuclear stopping in
hadron collisions, and relate observations to understanding of baryon
transport. Baryon number transport is not only evidenced via net-proton
distributions but also by the enhancement of strange baryons near mid-rapidity.
Although the focus is on high-energy data obtained from pp and heavy ions from
RHIC, relevant data from SPS and ISR will be considered. A discussion how the
available data at higher energy relates and gives information on baryon
junction, quark-diquark breaking will be made.Comment: 8 pages, 7 figures. Invited plenary talk for the 5'th international
conference on Physics and Astrophysics of Quark Gluon Plasma, February 8-12,
2005, Salt Lake City, Kolkata, Indi
Optimal control of predictive mean-field equations and applications to finance
We study a coupled system of controlled stochastic differential equations
(SDEs) driven by a Brownian motion and a compensated Poisson random measure,
consisting of a forward SDE in the unknown process and a
\emph{predictive mean-field} backward SDE (BSDE) in the unknowns . The driver of the BSDE at time may depend not just upon the
unknown processes , but also on the predicted future
value , defined by the conditional expectation . \\ We give a sufficient and a necessary
maximum principle for the optimal control of such systems, and then we apply
these results to the following two problems:\\ (i) Optimal portfolio in a
financial market with an \emph{insider influenced asset price process.} \\ (ii)
Optimal consumption rate from a cash flow modeled as a geometric It\^ o-L\'
evy SDE, with respect to \emph{predictive recursive utility}
- …