1,953 research outputs found
Uni-directional transport properties of a serpent billiard
We present a dynamical analysis of a classical billiard chain -- a channel
with parallel semi-circular walls, which can serve as a model for a bended
optical fiber. An interesting feature of this model is the fact that the phase
space separates into two disjoint invariant components corresponding to the
left and right uni-directional motions. Dynamics is decomposed into the jump
map -- a Poincare map between the two ends of a basic cell, and the time
function -- traveling time across a basic cell of a point on a surface of
section. The jump map has a mixed phase space where the relative sizes of the
regular and chaotic components depend on the width of the channel. For a
suitable value of this parameter we can have almost fully chaotic phase space.
We have studied numerically the Lyapunov exponents, time auto-correlation
functions and diffusion of particles along the chain. As a result of a
singularity of the time function we obtain marginally-normal diffusion after we
subtract the average drift. The last result is also supported by some
analytical arguments.Comment: 15 pages, 9 figure (19 .(e)ps files
On finite--temperature and --density radiative corrections to the neutrino effective potential in the early Universe
Finite-temperature and -density radiative corrections to the neutrino
effective potential in the otherwise CP-symmetric early Universe are considered
in the real-time approach of Thermal Field Theory. A consistent perturbation
theory endowed with the hard thermal loop resummation techniques developed by
Braaten and Pisarski is applied. Special attention is focused on the question
whether such corrections can generate any nonzero contribution to the
CP-symmetric part of the neutrino potential, if the contact approximation for
the W-propagator is used.Comment: 11 pages, revtex styl
Egorov property in perturbed cat map
We study the time evolution of the quantum-classical correspondence (QCC) for
the well known model of quantised perturbed cat maps on the torus in the very
specific regime of semi-classically small perturbations. The quality of the QCC
is measured by the overlap of classical phase-space density and corresponding
Wigner function of the quantum system called quantum-classical fidelity (QCF).
In the analysed regime the QCF strongly deviates from the known general
behaviour in particular it decays faster then exponential. Here we study and
explain the observed behavior of the QCF and the apparent violation of the QCC
principle.Comment: 12 pages, 7 figure
Performance of the ATLAS Muon Drift-Tube Chambers at High Background Rates and in Magnetic Fields
The ATLAS muon spectrometer uses drift-tube chambers for precision tracking.
The performance of these chambers in the presence of magnetic field and high
radiation fluxes is studied in this article using test-beam data recorded in
the Gamma Irradiation Facility at CERN. The measurements are compared to
detailed predictions provided by the Garfield drift-chamber simulation
programme
Variable Height Step Test Provides Reliable Heart Rate Response: Virtual Cardiorespiratory Testing During COVID-19 Pandemic
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Large-Scale Production of Monitored Drift Tube Chambers for the ATLAS Muon Spectrometer
Precision drift tube chambers with a sense wire positioning accuracy of
better than 20 microns are under construction for the ATLAS muon spectrometer.
70% of the 88 large chambers for the outermost layer of the central part of the
spectrometer have been assembled. Measurements during chamber construction of
the positions of the sense wires and of the sensors for the optical alignment
monitoring system demonstrate that the requirements for the mechanical
precision of the chambers are fulfilled
Radial stability analysis of the continuous pressure gravastar
Radial stability of the continuous pressure gravastar is studied using the
conventional Chandrasekhar method. The equation of state for the static
gravastar solutions is derived and Einstein equations for small perturbations
around the equilibrium are solved as an eigenvalue problem for radial
pulsations. Within the model there exist a set of parameters leading to a
stable fundamental mode, thus proving radial stability of the continuous
pressure gravastar. It is also shown that the central energy density possesses
an extremum in rho_c(R) curve which represents a splitting point between stable
and unstable gravastar configurations. As such the rho_c(R) curve for the
gravastar mimics the famous M(R) curve for a polytrope. Together with the
former axial stability calculations this work completes the stability problem
of the continuous pressure gravastar.Comment: 17 pages, 5 figures, References corrected, minor changes wrt v1,
matches published versio
Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions
For the muon spectrometer of the ATLAS detector at the large hadron collider
(LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift
tubes are used for precision tracking covering an active area of 5000 m2 in the
toroidal field of superconducting air core magnets. The chambers have to
provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an
absolute pressure of 3 bar and gas gain of 2?104. The environment in which the
chambers will be operated is characterized by high neutron and background with
counting rates of up to 100 per square cm and second. The resolution and
efficiency of a chamber from the serial production for ATLAS has been
investigated in a 100 GeV muon beam at photon irradiation rates as expected
during LHC operation. A silicon strip detector telescope was used as external
reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m
at the highest background rate. The detection efficiency of the drift tubes is
unchanged under irradiation. A tracking efficiency of 98% at the highest rates
has been demonstrated
Resolution and Efficiency of the ATLAS Muon Drift-Tube Chambers at High Background Rates
The resolution and efficiency of a precision drift-tube chamber for the ATLAS
muon spectrometer with final read-out electronics was tested at the Gamma
Irradiation Facility at CERN in a 100 GeV muon beam and at photon irradiation
rates of up to 990 Hz/square cm which corresponds to twice the highest
background rate expected in ATLAS. A silicon strip detector telescope was used
as external reference in the beam. The pulse-height measurement of the read-out
electronics was used to perform time-slewing corrections which lead to an
improvement of the average drift-tube resolution from 104 microns to 82 microns
without irradiation and from 128 microns to 108 microns at the maximum expected
rate. The measured drift-tube efficiency agrees with the expectation from the
dead time of the read-out electronics up to the maximum expected rate
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