1,315 research outputs found
Optical properties of small polarons from dynamical mean-field theory
The optical properties of polarons are studied in the framework of the
Holstein model by applying the dynamical mean-field theory. This approach
allows to enlighten important quantitative and qualitative deviations from the
limiting treatments of small polaron theory, that should be considered when
interpreting experimental data. In the antiadiabatic regime, accounting on the
same footing for a finite phonon frequency and a finite electron bandwidth
allows to address the evolution of the optical absorption away from the
well-understood molecular limit. It is shown that the width of the multiphonon
peaks in the optical spectra depends on the temperature and on the frequency in
a way that contradicts the commonly accepted results, most notably in the
strong coupling case. In the adiabatic regime, on the other hand, the present
method allows to identify a wide range of parameters of experimental interest,
where the electron bandwidth is comparable or larger than the broadening of the
Franck-Condon line, leading to a strong modification of both the position and
the shape of the polaronic absorption. An analytical expression is derived in
the limit of vanishing broadening, which improves over the existing formulas
and whose validity extends to any finite-dimensional lattice. In the same
adiabatic regime, at intermediate values of the interaction strength, the
optical absorption exhibits a characteristic reentrant behavior, with the
emergence of sharp features upon increasing the temperature -- polaron
interband transitions -- which are peculiar of the polaron crossover, and for
which analytical expressions are provided.Comment: 16 pages, 6 figure
Peripartum hysterectomy: a five year review at a tertiary care centre
Background: Peripartum hysterectomy is a life-saving procedure resorted to when conservative measures fail to control obstetric haemorrhage. Several predisposing factors, suboptimal care and lack of infrastructure may lead to this emergency procedure. We wanted to find out factors associated with peripartum hysterectomy and the adverse maternal outcomes at our centre.Methods: A retrospective case series analysis of 40 cases of peripartum hysterectomy performed over a period of 5 years from January 2010 to December 2014 at Government Medical College Hospital, Thrissur, Kerala was done.Results: The incidence of peripartum hysterectomy was 0.29%. The most common indication for peripartum hysterectomy was hysterectomy was uterine atony (50%). Thirty-five women (88%) were between 20 and 35 years. Most of the subjects were unbooked. There were two maternal deaths (case fatality rate of 5%) following peripartum hysterectomy during this period. All the subjects required blood transfusion.Conclusions: Prompt performance hysterectomy before the patient’s clinical condition deteriorates is the key to success. The incidence of adherent placenta is increasing, so every effort should be taken to reduce the caesarean section rates globally.
The Forcing Geodetic Cototal Domination Number of a Graph
Let be a geodetic cototal domination set of . A subset is called a forcing subset for if is the unique minimum geodetic cototal domination set containing . The minimum cardinality T is the forcing geodetic cototal domination number of S is denotedby , is the cardinality of a minimum forcing subset of S. The forcing geodetic cototal domination number of ,denoted by , is , where the minimum is takenover all -sets in . Some general properties satisfied by this concept arestudied. It is shown that for every pair of integers with ,there exists a connected graph such that and . where isthe geodetic cototal dominating number of
MOA-2011-BLG-293Lb: First Microlensing Planet possibly in the Habitable Zone
We used Keck adaptive optics observations to identify the first planet
discovered by microlensing to lie in or near the habitable zone, i.e., at
projected separation AU from its host, being the highest microlensing mass definitely identified.
The planet has a mass , and could in principle
have habitable moons. This is also the first planet to be identified as being
in the Galactic bulge with good confidence: kpc. The
planet/host masses and distance were previously not known, but only estimated
using Bayesian priors based on a Galactic model (Yee et al. 2012). These
estimates had suggested that the planet might be a super-Jupiter orbiting an M
dwarf, a very rare class of planets. We obtained high-resolution images
using Keck adaptive optics to detect the lens and so test this hypothesis. We
clearly detect light from a G dwarf at the position of the event, and exclude
all interpretations other than that this is the lens with high confidence
(95%), using a new astrometric technique. The calibrated magnitude of the
planet host star is . We infer the following probabilities
for the three possible orbital configurations of the gas giant planet: 53% to
be in the habitable zone, 35% to be near the habitable zone, and 12% to be
beyond the snow line, depending on the atmospherical conditions and the
uncertainties on the semimajor axis.Comment: Accepted by ApJ, 21 pages, 4 figure
Microlensing with advanced contour integration algorithm: Green's theorem to third order, error control, optimal sampling and limb darkening
Microlensing light curves are typically computed either by ray-shooting maps
or by contour integration via Green's theorem. We present an improved version
of the second method that includes a parabolic correction in Green's line
integral. In addition, we present an accurate analytical estimate of the
residual errors, which allows the implementation of an optimal strategy for the
contour sampling. Finally, we give a prescription for dealing with
limb-darkened sources reaching arbitrary accuracy. These optimizations lead to
a substantial speed-up of contour integration codes along with a full mastery
of the errors.Comment: 34 pages, 11 figure
Evolutionary algorithm-based analysis of gravitational microlensing lightcurves
A new algorithm developed to perform autonomous fitting of gravitational
microlensing lightcurves is presented. The new algorithm is conceptually
simple, versatile and robust, and parallelises trivially; it combines features
of extant evolutionary algorithms with some novel ones, and fares well on the
problem of fitting binary-lens microlensing lightcurves, as well as on a number
of other difficult optimisation problems. Success rates in excess of 90% are
achieved when fitting synthetic though noisy binary-lens lightcurves, allowing
no more than 20 minutes per fit on a desktop computer; this success rate is
shown to compare very favourably with that of both a conventional (iterated
simplex) algorithm, and a more state-of-the-art, artificial neural
network-based approach. As such, this work provides proof of concept for the
use of an evolutionary algorithm as the basis for real-time, autonomous
modelling of microlensing events. Further work is required to investigate how
the algorithm will fare when faced with more complex and realistic microlensing
modelling problems; it is, however, argued here that the use of parallel
computing platforms, such as inexpensive graphics processing units, should
allow fitting times to be constrained to under an hour, even when dealing with
complicated microlensing models. In any event, it is hoped that this work might
stimulate some interest in evolutionary algorithms, and that the algorithm
described here might prove useful for solving microlensing and/or more general
model-fitting problems.Comment: 14 pages, 3 figures; accepted for publication in MNRA
Probing the Galactic Potential with Next-Generation Observations of Disk Stars
Near-future surveys promise a dramatic improvement in the number and
precision of astrometric, photometric and spectroscopic measurements of stars
in the Milky Way's disk. We examine the impact of such surveys on our
understanding of the Galaxy by "observing" particle realizations of
non-axisymmetric disk distributions orbiting in an axisymmetric halo with
appropriate errors and then attempting to recover the underlying potential
using a Markov Chain Monte Carlo (MCMC) approach. We demonstrate that the
azimuthally averaged gravitational force field in the Galactic plane--and
hence, to a lesser extent, the Galactic mass distribution--can be tightly
constrained over a large range of radii using a variety of types of surveys so
long as the error distribution of the measurements of the parallax, proper
motion and radial velocity are well-understood and the disk is surveyed
globally. One advantage of our method is that the target stars can be selected
non-randomly in real or apparent-magnitude space to ensure just such a global
sample without biasing the results. Assuming we can always measure the
line-of-sight velocity of a star with at least 1 km/s precision, we demonstrate
that the force field can be determined to better than ~1% for Galactocentric
radii in the range R=4-20 kpc We conclude that near-future surveys, like SIM
Lite, Gaia, and VERA, will provide the first precise mapping of the
gravitational force field in the region of the Galactic disk.Comment: 41 pages and 10 figures, accepted for publication in Ap
Dynamics of conflicts in Wikipedia
In this work we study the dynamical features of editorial wars in Wikipedia
(WP). Based on our previously established algorithm, we build up samples of
controversial and peaceful articles and analyze the temporal characteristics of
the activity in these samples. On short time scales, we show that there is a
clear correspondence between conflict and burstiness of activity patterns, and
that memory effects play an important role in controversies. On long time
scales, we identify three distinct developmental patterns for the overall
behavior of the articles. We are able to distinguish cases eventually leading
to consensus from those cases where a compromise is far from achievable.
Finally, we analyze discussion networks and conclude that edit wars are mainly
fought by few editors only.Comment: Supporting information adde
Self-trapped Exciton and Franck-Condon Spectra Predicted in LaMnO
Because the ground state has cooperative Jahn-Teller order, electronic
excitations in LaMnO are predicted to self-trap by local rearrangement of
the lattice. The optical spectrum should show a Franck-Condon series, that is,
a Gaussian envelope of vibrational sidebands. Existing data are reinterpreted
in this way. The Raman spectrum is predicted to have strong multiphonon
features.Comment: 5 pages with two embedded postscript figure
A frozen super-Earth orbiting a star at the bottom of the Main Sequence
We observed the microlensing event MOA-2007-BLG-192 at high angular
resolution in JHKs with the NACO adaptive optics system on the VLT while the
object was still amplified by a factor 1.23 and then at baseline 18 months
later. We analyzed and calibrated the NACO photometry in the standard 2MASS
system in order to accurately constrain the source and the lens star fluxes. We
detect light from the host star of MOA-2007-BLG-192Lb, which significantly
reduces the uncertainties in its char- acteristics as compared to earlier
analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late
type M-dwarf (0.084 [+0.015] [-0.012] M\odot) at a distance of 660 [+100] [-70]
pc orbited by a 3.2 [+5.2] [-1.8] M\oplus super-Earth at 0.66 [+0.51] [-0.22]
AU. We then discuss the properties of this cold planetary system.Comment: published version A&A 540, A78 (2012) A&A, 10 pages, 7 Figure
- …