37,227 research outputs found
Long-Range Order and Dynamic Structure Factor of a Nematic under a Thermal Gradient
We use a fluctuating hydrodynamic approach to calculate the orientation
fluctuations correlation functions of a thermotropic nematic liquid crystal in
a nonequilibrium state induced by a stationay heat flux. Since in this
nonequilibrium stationary state the hydrodynamic fluctuations evolve on three
widely separated times scales, we use a time-scale perturbation procedure in
order to partially diagonalize the hydrodynamic matrix. The wave number and
frequency dependence of these orientation correlation functions is evaluated
and their explicit functional form on position is also calculated analytically
in and out of equilibrium. We show that for both states these correlactions are
long-ranged. This result shows that indeed, even in equilibrium there is
long-range orientational order in the nematic, consistently with the well known
properties of these systems.We also calculate the dynamic structure of the
fluid in both states for a geometry consistent with light scattering
experiments experiments. We find that as with isotropic simple fluids, the
external temperature gradient introduces an asymmetry in the spectrum shifting
its maximum by an amount proportional to the magnitude of the gradient. This
effect may be of the order of 7 per cent. Also, the width at half height may
decrease by a factor of about 10 per cent. Since to our knowledge there are no
experimental results available in the literature to compare with, the
predictions of our model calculation remains to be assessed.Comment: 11 pages, 3 figures, presented at the 3rd NEXT-SigmaPhi International
Conference (13-18 August 2005, Kolymbari CRETE
Polydispersity Effects in the Dynamics and Stability of Bubbling Flows
The occurrence of swarms of small bubbles in a variety of industrial systems
enhances their performance. However, the effects that size polydispersity may
produce on the stability of kinematic waves, the gain factor, mean bubble
velocity, kinematic and dynamic wave velocities is, to our knowledge, not yet
well established. We found that size polydispersity enhances the stability of a
bubble column by a factor of about 23% as a function of frequency and for a
particular type of bubble column. In this way our model predicts effects that
might be verified experimentally but this, however, remain to be assessed. Our
results reinforce the point of view advocated in this work in the sense that a
description of a bubble column based on the concept of randomness of a bubble
cloud and average properties of the fluid motion, may be a useful approach that
has not been exploited in engineering systems.Comment: 11 pages, 2 figures, presented at the 3rd NEXT-SigmaPhi International
Conference, 13-18 August, 2005, Kolymbari, Cret
Equation of state of hard oblate ellipsoids by replica exchange Monte Carlo
We implemented the replica exchange Monte Carlo technique to produce the
equation of state of hard 1:5 aspect-ratio oblate ellipsoids for a wide density
range. For this purpose, we considered the analytical approximation of the
overlap distance given by Bern and Pechukas and the exact numerical solution
given by Perram and Wertheim. For both cases we capture the expected
isotropic-nematic transition at low densities and a nematic-crystal transition
at larger densities. For the exact case, these transitions occur at the volume
fraction 0.341, and in the interval , respectively.Comment: 4 pages, 2 figure
Angular momenta, helicity, and other properties of dielectric-fiber and metallic-wire modes
Spin and orbital angular momenta (AM) of light are well studied for
free-space electromagnetic fields, even nonparaxial. One of the important
applications of these concepts is the information transfer using AM modes,
often via optical fibers and other guiding systems. However, the
self-consistent description of the spin and orbital AM of light in optical
media (including dispersive and metallic cases) was provided only recently
[K.Y. Bliokh et al., Phys. Rev. Lett. 119, 073901 (2017)]. Here we present the
first accurate calculations, both analytical and numerical, of the spin and
orbital AM, as well as the helicity and other properties, for the full-vector
eigenmodes of cylindrical dielectric and metallic (nanowire) waveguides. We
find remarkable fundamental relations, such as the quantization of the
canonical total AM of cylindrical guided modes in the general nonparaxial case.
This quantization, as well as the noninteger values of the spin and orbital AM,
are determined by the generalized geometric and dynamical phases in the mode
fields. Moreover, we show that the spin AM of metallic-wire modes is
determined, in the geometrical-optics approximation, by the transverse spin of
surface plasmon-polaritons propagating along helical trajectories on the wire
surface. Our work provides a solid platform for future studies and applications
of the AM and helicity properties of guided optical and plasmonic waves.Comment: 12 pages, 4 figures, to appear in Optic
Inner and outer star forming regions over the disks of spiral galaxies. I. Sample characterization
Context. The knowledge of abundance distributions is central to understanding
the formation and evolution of galaxies. Most of the relations employed for the
derivation of gas abundances have so far been derived from observations of
outer disk HII regions, despite the known differences between inner and outer
regions. Aims. Using integral field spectroscopy (IFS) observations we aim to
perform a systematic study and comparison of two inner and outer HII regions
samples. The spatial resolution of the IFS, the number of objects and the
homogeneity and coherence of the observations allow a complete characterization
of the main observational properties and differences of the regions. Methods.
We analyzed a sample of 725 inner HII regions and a sample of 671 outer HII
regions, all of them detected and extracted from the observations of a sample
of 263 nearby, isolated, spiral galaxies observed by the CALIFA survey.
Results. We find that inner HII regions show smaller equivalent widths, greater
extinction and luminosities, along with greater values of
[NII]{\lambda}6583/H{\alpha} and [OII]{\lambda}3727/[OIII]{\lambda}5007
emission-line ratios, indicating higher metallicites and lower ionization
parameters. Inner regions have also redder colors and higher photometric and
ionizing masses, although Mion/Mphot is slighty higher for the outer regions.
Conclusions. This work shows important observational differences between inner
and outer HII regions in star forming galaxies not previously studied in
detail. These differences indicate that inner regions have more evolved stellar
populations and are in a later evolution state with respect to outer regions,
which goes in line with the inside-out galaxy formation paradigm.Comment: 16 page
Examining the structure of ideas of reference in clinical and community samples
Aims: This study addresses the psychometric properties of a Spanish validation of the REF scale of ideas of reference (IRs) in detecting and following at-risk mental states and psychosis.
Methods: A total of 9447 participants were distributed in three groups: 676 patients with various diagnoses-154 with psychotic disorders, 6291 youths aged 11 to 20, and 2480 adult participants aged 21 to 84.
Results: Youths had higher scores than adults on IRs, observing a progressive decrease and stabilization in the twenties. Exploratory factor analysis provided a structure for the overall IRs score, with five first-order dimensions and one second-order dimension. Confirmatory factor analysis supported the structure with excellent fit. The REF scale was invariant across sex and samples. The internal consistency of the complete scale was excellent and acceptable across the five first-order factors. Strong relationships were found with the positive dimension of the community assessment of psychic experience-42, as well as with aberrant salience. Low and moderate relationships were found with public self-consciousness, anxiety, and depression. Youths and patients diagnosed with schizophrenia and other psychotic disorders had a high mean IRs frequency. Male sex, greater age (among the adults), and the "causal explanations", "Songs, newspapers, books" and laughing and commenting" REF subscales showed predictive power in the diagnostic categories of schizophrenia and other psychotic disorders
New dynamical scaling universality for quantum networks across adiabatic quantum phase transitions
We reveal universal dynamical scaling behavior across adiabatic quantum phase
transitions (QPTs) in networks ranging from traditional spatial systems (Ising
model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our
findings, which lie beyond traditional critical exponent analysis and adiabatic
perturbation approximations, are applicable even where excitations have not yet
stabilized and hence provide a time-resolved understanding of QPTs encompassing
a wide range of adiabatic regimes. We show explicitly that even though two
systems may traditionally belong to the same universality class, they can have
very different adiabatic evolutions. This implies more stringent conditions
need to be imposed than at present, both for quantum simulations where one
system is used to simulate the other, and for adiabatic quantum computing
schemes.Comment: 5 pages, 3 figures, plus supplementary material (6 pages, 1 figure
Large dynamic light-matter entanglement from driving neither too fast nor too slow
A significant problem facing next-generation quantum technologies is how to
generate and manipulate macroscopic entanglement in light and matter systems.
Here we report a new regime of dynamical light-matter behavior in which a
giant, system-wide entanglement is generated by varying the light-matter
coupling at \emph{intermediate} velocities. This enhancement is far larger and
broader-ranged than that occurring near the quantum phase transition of the
same model under adiabatic conditions. By appropriate choices of the coupling
within this intermediate regime, the enhanced entanglement can be made to
spread system-wide or to reside in each subsystem separately.Comment: 7 pages, 7 figure
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