2,892 research outputs found
Surface polaritons on left-handed cylinders: A complex angular momentum analysis
We consider the scattering of electromagnetic waves by a left-handed cylinder
-- i.e., by a cylinder fabricated from a left-handed material -- in the
framework of complex angular momentum techniques. We discuss both the TE and TM
theories. We emphasize more particularly the resonant aspects of the problem
linked to the existence of surface polaritons. We prove that the long-lived
resonant modes can be classified into distinct families, each family being
generated by one surface polariton propagating close to the cylinder surface
and we physically describe all the surface polaritons by providing, for each
one, its dispersion relation and its damping. This can be realized by noting
that each surface polariton corresponds to a particular Regge pole of the
matrix of the cylinder. Moreover, for both polarizations, we find that there
exists a particular surface polariton which corresponds, in the large-radius
limit, to the surface polariton which is supported by the plane interface.
There exists also an infinite family of surface polaritons of
whispering-gallery type which have no analogs in the plane interface case and
which are specific to left-handed materials.Comment: published version. v3: reference list correcte
R-modes in Neutron Stars with Crusts: Turbulent Saturation, Spin-down, and Crust Melting
Rossby waves (r-modes) have been suggested as a means to regulate the spin
periods of young or accreting neutron stars, and also to produce observable
gravitational wave radiation. R-modes involve primarily transverse,
incompressive motions of the star's fluid core. However, neutron stars gain
crusts early in their lives: therefore, r-modes also imply shear in the fluid
beneath the crust. We examine the criterion for this shear layer to become
turbulent, and derive the rate of dissipation in the turbulent regime. Unlike
dissipation from a viscous boundary layer, turbulent energy loss is nonlinear
in mode energy and can therefore cause the mode to saturate at amplitudes
typically much less than unity. This energy loss also reappears as heat below
the crust. We study the possibility of crust melting as well as its
implications for the spin evolution of low-mass X-ray binaries. Lastly, we
identify some universal features of the spin evolution that may have
observational consequences.Comment: 12 pages, 4 figures, submitted to Ap
Qudit Quantum State Tomography
Recently quantum tomography has been proposed as a fundamental tool for
prototyping a few qubit quantum device. It allows the complete reconstruction
of the state produced from a given input into the device. From this
reconstructed density matrix, relevant quantum information quantities such as
the degree of entanglement and entropy can be calculated. Generally orthogonal
measurements have been discussed for this tomographic reconstruction. In this
paper, we extend the tomographic reconstruction technique to two new regimes.
First we show how non-orthogonal measurement allow the reconstruction of the
state of the system provided the measurements span the Hilbert space. We then
detail how quantum state tomography can be performed for multi qudits with a
specific example illustrating how to achieve this in one and two qutrit
systems.Comment: 6 pages, 4 figures, submitted to PR
Strain-induced kinetics of intergrain defects as the mechanism of slow dynamics in the nonlinear resonant response of humid sandstone bars
A closed-form description is proposed to explain nonlinear and slow dynamics
effects exhibited by sandstone bars in longitudinal resonance experiments.
Along with the fast subsystem of longitudinal nonlinear displacements we
examine the strain-dependent slow subsystem of broken intergrain and
interlamina cohesive bonds. We show that even the simplest but
phenomenologically correct modelling of their mutual feedback elucidates the
main experimental findings typical for forced longitudinal oscillations of
sandstone bars, namely, (i) hysteretic behavior of a resonance curve on both
its up- and down-slopes, (ii) linear softening of resonant frequency with
increase of driving level, and (iii) gradual recovery (increase) of resonant
frequency at low dynamical strains after the sample was conditioned by high
strains. In order to reproduce the highly nonlinear elastic features of
sandstone grained structure a realistic non-perturbative form of strain
potential energy was adopted. In our theory slow dynamics associated with the
experimentally observed memory of peak strain history is attributed to
strain-induced kinetic changes in concentration of ruptured inter-grain and
inter-lamina cohesive bonds causing a net hysteretic effect on the elastic
Young's modulus. Finally, we explain how enhancement of hysteretic phenomena
originates from an increase in equilibrium concentration of ruptured cohesive
bonds that are due to water saturation.Comment: 5 pages, 3 figure
A phenomenological approach to normal form modeling: a case study in laser induced nematodynamics
An experimental setting for the polarimetric study of optically induced
dynamical behavior in nematic liquid crystal films has allowed to identify most
notably some behavior which was recognized as gluing bifurcations leading to
chaos. This analysis of the data used a comparison with a model for the
transition to chaos via gluing bifurcations in optically excited nematic liquid
crystals previously proposed by G. Demeter and L. Kramer. The model of these
last authors, proposed about twenty years before, does not have the central
symmetry which one would expect for minimal dimensional models for chaos in
nematics in view of the time series. What we show here is that the simplest
truncated normal forms for gluing, with the appropriate symmetry and minimal
dimension, do exhibit time signals that are embarrassingly similar to the ones
found using the above mentioned experimental settings. The gluing bifurcation
scenario itself is only visible in limited parameter ranges and substantial
aspect of the chaos that can be observed is due to other factors. First, out of
the immediate neighborhood of the homoclinic curve, nonlinearity can produce
expansion leading to chaos when combined with the recurrence induced by the
homoclinic behavior. Also, pairs of symmetric homoclinic orbits create extreme
sensitivity to noise, so that when the noiseless approach contains a rich
behavior, minute noise can transform the complex damping into sustained chaos.
Leonid Shil'nikov taught us that combining global considerations and local
spectral analysis near critical points is crucial to understand the
phenomenology associated to homoclinic bifurcations. Here this helps us
construct a phenomenological approach to modeling experiments in nonlinear
dissipative contexts.Comment: 25 pages, 9 figure
High-pressure phase and transition phenomena in ammonia borane NH3BH3 from X-ray diffraction, Landau theory, and ab initio calculations
Structural evolution of a prospective hydrogen storage material, ammonia
borane NH3BH3, has been studied at high pressures up to 12 GPa and at low
temperatures by synchrotron powder diffraction. At 293 K and above 1.1 GPa a
disordered I4mm structure reversibly transforms into a new ordered phase. Its
Cmc21 structure was solved from the diffraction data, the positions of N and B
atoms and the orientation of NH3 and BH3 groups were finally assigned with the
help of density functional theory calculations. Group-theoretical analysis
identifies a single two-component order parameter, combining ordering and
atomic displacement mechanisms, which link an orientationally disordered parent
phase I4mm with ordered distorted Cmc21, Pmn21 and P21 structures. We propose a
generic phase diagram for NH3BH3, mapping three experimentally found and one
predicted (P21) phases as a function of temperature and pressure, along with
the evolution of the corresponding structural distortions. Ammonia borane
belongs to the class of improper ferroelastics and we show that both
temperature- and pressure-induced phase transitions can be driven to be of the
second order. The role of N-H...H-B dihydrogen bonds and other intermolecular
interactions in the stability of NH3BH3 polymorphs is examined.Comment: 23 pages, 7 figure
Phase space caustics in multi-component systems
As examples of quantum-"classical" coupling systems, multi-component systems
are studied by semiclassical evaluations of the Feynman kernels in the
coherent-state representation. From the observation of the phase space caustics
due to the presence of the internal degree of freedom (IDF), two phenomena are
explained in terms of the semiclassical theory: (1) The quantum oscillations of
the IDF induce quantum interference patterns in the Hushimi representation; (2)
Chaotic dynamics destroys the coherence of the quantum oscillations.Comment: 6 pages, 7 ps figures, To appear in Phys. Rev. Let
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Depression, anxiety, pain and quality of life in people living with chronic hepatitis C: A systematic review and meta-analysis
Objectives: Individuals infected with hepatitis C virus (HCV) can develop extrahepatic
conditions which may have a significant impact on life expectancy and quality of
life. We conducted a systematic review to assess the causal relationship between
HCV and extrahepatic conditions and the impact of HCV upon health-related
quality of life of people in the UK. /
Methods: HCV advocacy groups identified conditions that they thought most important to
research, and the perspectives of various stakeholders informed the scope of the
review. A comprehensive literature search of a range of electronic databases and
websites was undertaken. Screening, quality assessment and data extraction were
conducted using specialist software. The key criterion for inclusion in a synthesis
was a study’s testing of the association between HCV and either quality of life or
conditions specified as important by advocacy groups: depression, anxiety or
painful conditions. Other criteria relating to study populations, measures and
matching of study groups were also applied. Two reviewers assessed included
studies, with disagreements resolved by a third reviewer where necessary. Studies
were assessed for methodological quality using standardised appraisal tools. Metaanalyses were performed. Based on the consistency and sufficiency of research
evidence, the findings were graded as strong, promising, tentative or inconclusive. /
Results: 71 studies were included in the review’s syntheses. All studies were judged to be at
a moderate or high risk of bias. Only two UK studies met our inclusion criteria. /
Quality of life: Evidence from 22 studies indicates that people with HCV have worse quality of life
than ‘general’ or ‘healthy’ populations; meta-analysis of nine studies indicated\ud
that the physical (PCS) and mental health (MCS) domains of quality of life on the
Health-Related Quality of Life Scale were both statistically and clinically worse
among HCV-infected people (PCS: MD 5.54, 95% CI 3.73-7.35, MCS: MD 3.81, 95% CI
1.97-5.64). Evidence from seven included studies suggests that people co-infected
with HCV and HIV have worse quality of life than individuals with HIV only; metaanalysis of five studies indicated that both the physical and mental health domains
of quality of life were significantly worse among people who were co-infected
(PCS: MD 2.57, 95% CI 1.08-4.06, MCS: MD 1.88, 95% CI 0.06-3.69). /
Depression and anxiety: Evidence from 22 studies indicates that depression and anxiety are more severe,
and depression is more common among people with HCV compared to those
without it. Meta-analysis of 12 studies identified the severity of depression in
people with HCV to be significantly greater than in those without HCV (Mean difference 0.98, 95% CI 0.43-1.53). Meta-analysis of nine studies identified the
severity of clinical anxiety to be significantly greater among people with HCV
(Mean difference 0.47, 95% CI 0.09-0.86). Meta-analysis of seven studies identified
participants with HCV to be approximately three times more likely to be depressed
compared to those without HCV (OR 2.77, 95% CI 1.62-4.74). No statistically
significant evidence that anxiety is more common among people with HCV was
found. /
Pain: Evidence was appraised from 26 studies on painful conditions. A meta-analysis of
four studies indicates that people with HCV are 17% more likely to suffer from
arthralgia than those without HCV (RR 1.17, 95% CI 1.04-1.31). A meta-analysis of
five studies suggested that people with HCV are significantly more likely to suffer
from fibromyalgia; key differences across the studies in terms of the health status
(co-morbidities) of HCV patients and comparison groups mean it is not possible to
quantify the increased risk attributable to HCV. Other studies, including those on
arthritis, were not amenable to meta-analysis. /
Conclusions: Evidence suggests an association between HCV infection and
depression, anxiety, fibromyalgia, arthralgia and health-related quality of life.
However, the evidence was graded as ‘promising’ or ‘tentative’ rather than
‘strong’. More high-quality research on the association between HCV and these
conditions is needed
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