7,926 research outputs found
A Study of a Mini-drift GEM Tracking Detector
A GEM tracking detector with an extended drift region has been studied as
part of an effort to develop new tracking detectors for future experiments at
RHIC and for the Electron Ion Collider that is being planned for BNL or JLAB.
The detector consists of a triple GEM stack with a small drift region that was
operated in a mini TPC type configuration. Both the position and arrival time
of the charge deposited in the drift region were measured on the readout plane
which allowed the reconstruction of a short vector for the track traversing the
chamber. The resulting position and angle information from the vector could
then be used to improve the position resolution of the detector for larger
angle tracks, which deteriorates rapidly with increasing angle for conventional
GEM tracking detectors using only charge centroid information. Two types of
readout planes were studied. One was a COMPASS style readout plane with 400
micron pitch XY strips and the other consisted of 2x10mm2 chevron pads. The
detector was studied in test beams at Fermilab and CERN, along with additional
measurements in the lab, in order to determine its position and angular
resolution for incident track angles up to 45 degrees. Several algorithms were
studied for reconstructing the vector using the position and timing information
in order to optimize the position and angular resolution of the detector for
the different readout planes. Applications for large angle tracking detectors
at RHIC and EIC are also discussed.Comment: Submitted to the IEEE Transactions on Nuclear Scienc
On the Tail of the Overlap Probability Distribution in the Sherrington--Kirkpatrick Model
We investigate the large deviation behavior of the overlap probability
density in the Sherrington--Kirkpatrick model from several analytical
perspectives. First we analyze the spin glass phase using the coupled replica
scheme. Here generically
, and we compute the first correction to the expansion of \A
in powers of . We study also the case, where is know
exactly. Finally we study the paramagnetic phase, where exact results valid for
all 's are obtained. The overall agreement between the various points of
view is very satisfactory. Data from large scale numerical simulations show
that the predicted behavior can be detected already on moderate lattice sizes.Comment: 18 pages including ps figure
Nonequilibrium dynamics of a simple stochastic model
We investigate the low-temperature dynamics of a simple stochastic model,
introduced recently in the context of the physics of glasses. The slowest
characteristic time at equilibrium diverges exponentially at low temperature.
On smaller time scales, the nonequilibrium dynamics of the system exhibits an
aging regime. We present an analytical study of the scaling behaviour of the
mean energy, of its local correlation and response functions, and of the
associated fluctuation-dissipation ratio throughout the regime of low
temperature and long times. This analysis includes the aging regime, the
convergence to equilibrium, and the crossover behaviour between them.Comment: 36 pages, plain tex, 7 figures, to be published by Journal of Physics
Dirac quasiparticles in the mixed state
Energies and wave functions are calculated for d-wave quasiparticles in the
mixed state using the formalism of Franz and Tesanovic for the low-lying energy
levels. The accuracy of the plane-wave expansion is explored by comparing
approximate to exact results for a simplified one-dimensional problem, and the
convergence of the plane- wave expansion to the two-dimensional case is
studied. The results are used to calculate the low-energy tunneling density of
states and the low-temperature specific heat, and these theoretical results are
compared to semiclassical treatments and to the available data. Implications
for the muon spin resonance measurements of vortex core size are also
discussed.Comment: 13 pages, 15 figures, RevTeX. References corrected. A factor of 2 in
the results has been corrected, and the conclusions have been update
Damage spreading in the mode-coupling equations for glasses
We examine the problem of damage spreading in the off-equilibrium mode
coupling equations. The study is done for the spherical -spin model
introduced by Crisanti, Horner and Sommers. For we show the existence of
a temperature transition well above any relevant thermodynamic transition
temperature. Above the asymptotic damage decays to zero while below
it decays to a finite value independent of the initial damage. This transition
is stable in the presence of asymmetry in the interactions. We discuss the
physical origin of this peculiar phase transition which occurs as a consequence
of the non-linear coupling between the damage and the two-time correlation
functions.Comment: 5 pages, 2 figures, Revtex fil
Phase coexistence and finite-size scaling in random combinatorial problems
We study an exactly solvable version of the famous random Boolean
satisfiability problem, the so called random XOR-SAT problem. Rare events are
shown to affect the combinatorial ``phase diagram'' leading to a coexistence of
solvable and unsolvable instances of the combinatorial problem in a certain
region of the parameters characterizing the model. Such instances differ by a
non-extensive quantity in the ground state energy of the associated diluted
spin-glass model. We also show that the critical exponent , controlling
the size of the critical window where the probability of having solutions
vanishes, depends on the model parameters, shedding light on the link between
random hyper-graph topology and universality classes. In the case of random
satisfiability, a similar behavior was conjectured to be connected to the onset
of computational intractability.Comment: 10 pages, 5 figures, to appear in J. Phys. A. v2: link to the XOR-SAT
probelm adde
Modeling microevolution in a changing environment: The evolving quasispecies and the Diluted Champion Process
Several pathogens use evolvability as a survival strategy against acquired
immunity of the host. Despite their high variability in time, some of them
exhibit quite low variability within the population at any given time, a
somehow paradoxical behavior often called the evolving quasispecies. In this
paper we introduce a simplified model of an evolving viral population in which
the effects of the acquired immunity of the host are represented by the
decrease of the fitness of the corresponding viral strains, depending on the
frequency of the strain in the viral population. The model exhibits evolving
quasispecies behavior in a certain range of its parameters, ans suggests how
punctuated evolution can be induced by a simple feedback mechanism.Comment: 15 pages, 12 figures. Figures redrawn, some additional clarifications
in the text. To appear in Journal of Statistical Mechanics: Theory and
Experimen
Theory of vortex lattice effects on STM spectra in d-wave superconductors
Theory of scanning tunneling spectroscopy of low energy quasiparticle (QP)
states in vortex lattices of d-wave superconductors is developed taking account
of the effects caused by an extremely large extension of QP wavefunctions in
the nodal directions and the band structure in the QP spectrum. The oscillatory
structures in STM spectra, which correspond to van Hove singularities are
analysed. Theoretical calculations carried out for finite temperatures and
scattering rates are compared with recent experimental data for high
temperature cuprates.Comment: 4 pages, 3 eps figures, M2S-HTSC-VI conference paper, using Elsevier
style espcrc2.st
Kob-Andersen model: a non-standard mechanism for the glassy transition
We present new results reflecting the analogies between the Kob-Andersen
model and other glassy systems. Studying the stability of the blocked
configurations above and below the transition we also give arguments that
supports their relevance for the glassy behaviour of the model.
However we find, surprisingly, that the organization of the phase space of
the system is different from the well known organization of other mean-field
spin glasses and structural glasses.Comment: New reference added and one update
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