33,527 research outputs found
Performance of a First-Level Muon Trigger with High Momentum Resolution Based on the ATLAS MDT Chambers for HL-LHC
Highly selective first-level triggers are essential to exploit the full
physics potential of the ATLAS experiment at High-Luminosity LHC (HL-LHC). The
concept for a new muon trigger stage using the precision monitored drift tube
(MDT) chambers to significantly improve the selectivity of the first-level muon
trigger is presented. It is based on fast track reconstruction in all three
layers of the existing MDT chambers, made possible by an extension of the
first-level trigger latency to six microseconds and a new MDT read-out
electronics required for the higher overall trigger rates at the HL-LHC. Data
from -collisions at is used to study the
minimal muon transverse momentum resolution that can be obtained using the MDT
precision chambers, and to estimate the resolution and efficiency of the
MDT-based trigger. A resolution of better than is found in all sectors
under study. With this resolution, a first-level trigger with a threshold of
becomes fully efficient for muons with a transverse momentum
above in the barrel, and above in the
end-cap region.Comment: 6 pages, 11 figures; conference proceedings for IEEE NSS & MIC
conference, San Diego, 201
In-Situ Dual-Port Polarization Contrast Imaging of Faraday Rotation in a High Optical Depth Ultracold 87Rb Atomic Ensemble
We study the effects of high optical depth and density on the performance of
a light-atom quantum interface. An in-situ imaging method, a dual-port
polarization contrast technique, is presented. This technique is able to
compensate for image distortions due to refraction. We propose our imaging
method as a tool to characterize atomic ensembles for high capacity spatial
multimode quantum memories. Ultracold dense inhomogeneous Rubidium samples are
imaged and we find a resonant optical depth as high as 680 on the D1 line. The
measurements are compared with light-atom interaction models based on
Maxwell-Bloch equations. We find that an independent atom assumption is
insufficient to explain our data and present corrections due to resonant
dipole-dipole interactions
Semiclassical universality of parametric spectral correlations
We consider quantum systems with a chaotic classical limit that depend on an
external parameter, and study correlations between the spectra at different
parameter values. In particular, we consider the parametric spectral form
factor which depends on a scaled parameter difference . For
parameter variations that do not change the symmetry of the system we show by
using semiclassical periodic orbit expansions that the small expansion
of the form factor agrees with Random Matrix Theory for systems with and
without time reversal symmetry.Comment: 18 pages, no figure
Neutrino oscillation signatures of oxygen-neon-magnesium supernovae
We discuss the flavor conversion of neutrinos from core collapse supernovae
that have oxygen-neon-magnesium (ONeMg) cores. Using the numerically calculated
evolution of the star up to 650 ms post bounce, we find that, for the normal
mass hierarchy, the electron neutrino flux in a detector shows signatures of
two typical features of an ONeMg-core supernova: a sharp step in the density
profile at the base of the He shell and a faster shock wave propagation
compared to iron core supernovae. Before the shock hits the density step (t ~
150 ms), the survival probability of electron neutrinos is about 0.68, in
contrast to values of 0.32 or less for an iron core supernova. The passage of
the shock through the step and its subsequent propagation cause a decrease of
the survival probability and a decrease of the amplitude of oscillations in the
Earth, reflecting the transition to a more adiabatic propagation inside the
star. These changes affect the lower energy neutrinos first; they are faster
and more sizable for larger theta_13. They are unique of ONeMg-core supernovae,
and give the possibility to test the speed of the shock wave. The time
modulation of the Earth effect and its negative sign at the neutronization peak
are the most robust signatures in a detector.Comment: 14 pages, 10 figures (16 figure files). Text and graphics added for
illustration and clarification; Results unchanged. Version accepted for
publication in Physical Review
Test of constancy of speed of light with rotating cryogenic optical resonators
A test of Lorentz invariance for electromagnetic waves was performed by
comparing the resonance frequencies of two optical resonators as a function of
orientation in space. In terms of the Robertson-Mansouri-Sexl theory, we obtain
, a ten-fold improvement compared to
the previous best results. We also set a first upper limit for a so far unknown
parameter of the Standard Model Extension test theory,
.Comment: 4 pages, 2 figures, accepted for publication Phys. Rev. A (2005
Combined cerebellar and bilateral cervical posterior spinal artery stroke demonstrated on MRI
Combined cerebellar and spinal ischemic stroke is a rare, critical condition. We report a patient with combined cerebellar and bilateral posterolateral cervical spinal cord infarction due to bilateral stenosis of the vertebral arteries. MRI is the method of choice for imaging this condition; diffusion-weighted imaging of the spinal cord gives reliable results
A polarizable interatomic force field for TiO parameterized using density functional theory
We report a classical interatomic force field for TiO, which has been
parameterized using density functional theory forces, energies, and stresses in
the rutile crystal structure. The reliability of this new classical potential
is tested by evaluating the structural properties, equation of state, phonon
properties, thermal expansion, and some thermodynamic quantities such as
entropy, free energy, and specific heat under constant volume. The good
agreement of our results with {\em ab initio} calculations and with
experimental data, indicates that our force-field describes the atomic
interactions of TiO in the rutile structure very well. The force field can
also describe the structures of the brookite and anatase crystals with good
accuracy.Comment: Accepted for publication in Phys. Rev. B; Changes from v1 include
multiple minor revisions and a re-write of the description of the force field
in Section II
The effect of light assisted collisions on matter wave coherence in superradiant Bose-Einstein condensates
We investigate experimentally the effects of light assisted collisions on the
coherence between momentum states in Bose-Einstein condensates. The onset of
superradiant Rayleigh scattering serves as a sensitive monitor for matter wave
coherence. A subtle interplay of binary and collective effects leads to a
profound asymmetry between the two sides of the atomic resonance and provides
far bigger coherence loss rates for a condensate bathed in blue detuned light
than previously estimated. We present a simplified quantitative model
containing the essential physics to explain our experimental data and point at
a new experimental route to study strongly coupled light matter systems.Comment: 10 pages, 4 figure
Semiclassical approach to discrete symmetries in quantum chaos
We use semiclassical methods to evaluate the spectral two-point correlation
function of quantum chaotic systems with discrete geometrical symmetries. The
energy spectra of these systems can be divided into subspectra that are
associated to irreducible representations of the corresponding symmetry group.
We show that for (spinless) time reversal invariant systems the statistics
inside these subspectra depend on the type of irreducible representation. For
real representations the spectral statistics agree with those of the Gaussian
Orthogonal Ensemble (GOE) of Random Matrix Theory (RMT), whereas complex
representations correspond to the Gaussian Unitary Ensemble (GUE). For systems
without time reversal invariance all subspectra show GUE statistics. There are
no correlations between non-degenerate subspectra. Our techniques generalize
recent developments in the semiclassical approach to quantum chaos allowing one
to obtain full agreement with the two-point correlation function predicted by
RMT, including oscillatory contributions.Comment: 26 pages, 8 Figure
Influence of external flows on crystal growth: numerical investigation
We use a combined phase-field/lattice-Boltzmann scheme [D. Medvedev, K.
Kassner, Phys. Rev. E {\bf 72}, 056703 (2005)] to simulate non-facetted crystal
growth from an undercooled melt in external flows. Selected growth parameters
are determined numerically.
For growth patterns at moderate to high undercooling and relatively large
anisotropy, the values of the tip radius and selection parameter plotted as a
function of the Peclet number fall approximately on single curves. Hence, it
may be argued that a parallel flow changes the selected tip radius and growth
velocity solely by modifying (increasing) the Peclet number. This has
interesting implications for the availability of current selection theories as
predictors of growth characteristics under flow.
At smaller anisotropy, a modification of the morphology diagram in the plane
undercooling versus anisotropy is observed. The transition line from dendrites
to doublons is shifted in favour of dendritic patterns, which become faster
than doublons as the flow speed is increased, thus rendering the basin of
attraction of dendritic structures larger.
For small anisotropy and Prandtl number, we find oscillations of the tip
velocity in the presence of flow. On increasing the fluid viscosity or
decreasing the flow velocity, we observe a reduction in the amplitude of these
oscillations.Comment: 10 pages, 7 figures, accepted for Physical Review E; size of some
images had to be substantially reduced in comparison to original, resulting
in low qualit
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