2,136 research outputs found
Collective librations of water molecules in the crystal lattice of rubidium bromide: experiment and simulation
Terahertz spectroscopy of RbBr reveals four prominent absorption lines at room temperature and a further 15 lines at 10 K. Via density-functional-theory (DFT) numerical modelling using the PBE0 hybrid GGA functional, all the absorptions are identified as correlated librations of water molecules in the RbBr lattice. Each libration mode is a combination of rocking, wagging and twisting motions of the water molecules. The number of libration lines and numerical modelling show that the C2v symmetry of water in RbBr is broken. Our modelling shows that the distribution of libration amplitudes and phases for different water molecules in the RbBr unit cell varies greatly between the different modes. All librational lines red-shift with increasing temperature. The rate of change for most lines is in the range 60â90 MHz Kâ1 (or (2â3) Ă 10â3 cmâ1 Kâ1). Two lines shift more rapidly with temperature, at rates of 240 and 300 MHz Kâ1 (or (8 and 10) Ă 10â3 cmâ1 Kâ1), respectively. Furthermore, the temperature dependence of the linewidth distinguishes two groups of lines. For one group, with weak linear temperature dependence of linewidth, cubic anharmonic terms in the RbBr crystal field are significant. This group is mainly associated with fully symmetric correlated librations. For the second group, with strong non-linear temperature dependence of the linewidth, quartic anharmonic terms in the RbBr crystal field are significant. However, the distribution of libration amplitudes, as well as the type of libration modes, influence the temperature dependence of the red shift, the linewidth, and the intensity, as well. Our combined experimental and theoretical investigation confirms the necessity of obtaining low-temperature data to observe all the calculated modes; moreover, the richness of detail in the temperature dependence of the data invites further modelling spanning a range of temperatures
Quantum-classical correspondence on compact phase space
We propose to study the -norm distance between classical and quantum
phase space distributions, where for the latter we choose the Wigner function,
as a global phase space indicator of quantum-classical correspondence. For
example, this quantity should provide a key to understand the correspondence
between quantum and classical Loschmidt echoes. We concentrate on fully chaotic
systems with compact (finite) classical phase space. By means of numerical
simulations and heuristic arguments we find that the quantum-classical fidelity
stays at one up to Ehrenfest-type time scale, which is proportional to the
logarithm of effective Planck constant, and decays exponentially with a maximal
classical Lyapunov exponent, after that time.Comment: 26 pages. 9 figures (31 .epz files), submitted to Nonlinearit
Transport critical current of Solenoidal MgB2/Cu Coils Fabricated Using a Wind-Reaction In-situ Technique
In this letter, we report the results of transport Jc of solenoid coils upto
100 turns fabricated with Cu-sheathed MgB2 wires using a wind-reaction in-situ
technique. Despite the low density of single core and some reaction between Mg
and Cu-sheath, our results demonstrate the decrease in transport Jc with
increasing length of MgB2 wires is insignificant. Solenoid coils with diameter
as small as 10 mm can be readily fabricated using a wind-reaction in-situ
technique. The Jc of coils is essentially the same as in the form of straight
wires. A Jc of 133,000 A/cm2 and 125,000 A/cm2 at 4 K and self field has been
achieved for a small coil wound using Cu-sheathed tape and Cu-sheathed wire
respectively. These results indicate that the MgB2 wires have a great potential
for lage scale applicationsComment: 6 pages, 4 figures, 1 tabl
The bends on a quantum waveguide and cross-products of Bessel functions
A detailed analysis of the wave-mode structure in a bend and its
incorporation into a stable algorithm for calculation of the scattering matrix
of the bend is presented. The calculations are based on the modal approach. The
stability and precision of the algorithm is numerically and analytically
analysed. The algorithm enables precise numerical calculations of scattering
across the bend. The reflection is a purely quantum phenomenon and is discussed
in more detail over a larger energy interval. The behaviour of the reflection
is explained partially by a one-dimensional scattering model and heuristic
calculations of the scattering matrix for narrow bends. In the same spirit we
explain the numerical results for the Wigner-Smith delay time in the bend.Comment: 34 pages, 21 figure
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
Regular and quasi black hole solutions for spherically symmetric charged dust distributions in the Einstein-Maxwell theory
Static spherically symmetric distributions of electrically counterpoised dust
(ECD) are used to construct solutions to Einstein-Maxwell equations in
Majumdar--Papapetrou formalism. Unexpected bifurcating behaviour of solutions
with regard to source strength is found for localized, as well as for the
delta-function ECD distributions. Unified treatment of general ECD
distributions is accomplished and it is shown that for certain source strengths
one class of regular solutions approaches Minkowski spacetime, while the other
comes arbitrarily close to black hole solutions.Comment: LaTeX (IOP style) 17 pages, 10 figure
Dynamical approach to chains of scatterers
Linear chains of quantum scatterers are studied in the process of
lengthening, which is treated and analysed as a discrete dynamical system
defined over the manifold of scattering matrices. Elementary properties of such
dynamics relate the transport through the chain to the spectral properties of
individual scatterers. For a single-scattering channel case some new light is
shed on known transport properties of disordered and noisy chains, whereas
translationally invariant case can be studied analytically in terms of a simple
deterministic dynamical map. The many-channel case was studied numerically by
examining the statistical properties of scatterers that correspond to a certain
type of transport of the chain i.e. ballistic or (partially) localised.Comment: 16 pages, 7 figure
Scalar field propagation in the phi^4 kappa-Minkowski model
In this article we use the noncommutative (NC) kappa-Minkowski phi^4 model
based on the kappa-deformed star product, ({*}_h). The action is modified by
expanding up to linear order in the kappa-deformation parameter a, producing an
effective model on commutative spacetime. For the computation of the tadpole
diagram contributions to the scalar field propagation/self-energy, we
anticipate that statistics on the kappa-Minkowski is specifically
kappa-deformed. Thus our prescription in fact represents hybrid approach
between standard quantum field theory (QFT) and NCQFT on the kappa-deformed
Minkowski spacetime, resulting in a kappa-effective model. The propagation is
analyzed in the framework of the two-point Green's function for low,
intermediate, and for the Planckian propagation energies, respectively.
Semiclassical/hybrid behavior of the first order quantum correction do show up
due to the kappa-deformed momentum conservation law. For low energies, the
dependence of the tadpole contribution on the deformation parameter a drops out
completely, while for Planckian energies, it tends to a fixed finite value. The
mass term of the scalar field is shifted and these shifts are very different at
different propagation energies. At the Planckian energies we obtain the
direction dependent kappa-modified dispersion relations. Thus our
kappa-effective model for the massive scalar field shows a birefringence
effect.Comment: 23 pages, 2 figures; To be published in JHEP. Minor typos corrected.
Shorter version of the paper arXiv:1107.236
Pulsar velocities due to a violation of the equivalence principle by neutrinos
We consider the pulsar velocity problem and relate it to some unconventional
neutrino oscillation mechanisms based on a violation of the equivalence
principle by neutrinos. We show that the observed pulsar velocities may be
explained by violations at the level from 10^{-9} to 10^{-10} in the case of a
non-universal tensor neutrino-gravity coupling, whereas there is no solution in
the case of a non-universal scalar neutrino-gravity coupling. Neutrinos may
remain massless and the requisite magnetic field strength is similar to that in
the conventional mass oscillation mechanism.Comment: 6 pages, minor changes, to appear in Mod. Phys. Let
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