1,479 research outputs found
Group Importance Sampling for Particle Filtering and MCMC
Bayesian methods and their implementations by means of sophisticated Monte
Carlo techniques have become very popular in signal processing over the last
years. Importance Sampling (IS) is a well-known Monte Carlo technique that
approximates integrals involving a posterior distribution by means of weighted
samples. In this work, we study the assignation of a single weighted sample
which compresses the information contained in a population of weighted samples.
Part of the theory that we present as Group Importance Sampling (GIS) has been
employed implicitly in different works in the literature. The provided analysis
yields several theoretical and practical consequences. For instance, we discuss
the application of GIS into the Sequential Importance Resampling framework and
show that Independent Multiple Try Metropolis schemes can be interpreted as a
standard Metropolis-Hastings algorithm, following the GIS approach. We also
introduce two novel Markov Chain Monte Carlo (MCMC) techniques based on GIS.
The first one, named Group Metropolis Sampling method, produces a Markov chain
of sets of weighted samples. All these sets are then employed for obtaining a
unique global estimator. The second one is the Distributed Particle
Metropolis-Hastings technique, where different parallel particle filters are
jointly used to drive an MCMC algorithm. Different resampled trajectories are
compared and then tested with a proper acceptance probability. The novel
schemes are tested in different numerical experiments such as learning the
hyperparameters of Gaussian Processes, two localization problems in a wireless
sensor network (with synthetic and real data) and the tracking of vegetation
parameters given satellite observations, where they are compared with several
benchmark Monte Carlo techniques. Three illustrative Matlab demos are also
provided.Comment: To appear in Digital Signal Processing. Related Matlab demos are
provided at https://github.com/lukafree/GIS.gi
Thermal Giant Gravitons
We study the giant graviton solution as the AdS_5 X S^5 background is heated
up to finite temperature. The analysis employs the thermal brane probe
technique based on the blackfold approach. We focus mainly on the thermal giant
graviton corresponding to a thermal D3-brane probe wrapped on an S^3 moving on
the S^5 of the background at finite temperature. We find several interesting
new effects, including that the thermal giant graviton has a minimal possible
value for the angular momentum and correspondingly also a minimal possible
radius of the S^3. We compute the free energy of the thermal giant graviton in
the low temperature regime, which potentially could be compared to that of a
thermal state on the gauge theory side. Moreover, we analyze the space of
solutions and stability of the thermal giant graviton and find that, in
parallel with the extremal case, there are two available solutions for a given
temperature and angular momentum, one stable and one unstable. In order to
write down the equations of motion, action and conserved charges for the
thermal giant graviton we present a slight generalization of the blackfold
formalism for charged black branes. Finally, we also briefly consider the
thermal giant graviton moving in the AdS_5 part.Comment: v1: 32 pages + 11 pages appendices, 13 figures, v2: typos fixed in
Sec.2 and other misprints, references adde
Structural and Functional Evolution of Glucose Transporter 4 (GLUT4): A Look at GLUT4 in Fish
The insulin-responsive glucose transporter GLUT4 was first described in 1988 as a result of
studies on the regulation of glucose metabolism by insulin [1]. Soon after the discovery of
GLUT4, several groups cloned GLUT4 in the human [2], rat [3,4] and mouse [5]. Since its
discovery, GLUT4 has received, together with GLUT1, more experimental attention than any
other single membrane transport protein. Structurally, GLUT4 follows the predicted model
for class I glucose transporters. GLUT4 has a high affinity for glucose, with a Km of
approximately 5 mM [6], and also transports mannose, galactose, dehydroascorbic acid and
glucosamine [7-10]. In mammals, GLUT4 is mainly expressed in cardiac and skeletal muscle,
brown and white adipose tissue, and brain [6,11,12]. GLUT4 plays a pivotal role in whole
body glucose homeostasis, mediating the uptake of glucose regulated by insulin [13,14].
GLUT4 is responsible for the reduction in the postprandial rise in plasma glucose levels [6].
Insulin acts by stimulating the translocation of specific GLUT4-containing vesicles from
intracellular stores to the plasma membrane (PM) resulting in an immediate increase in
glucose transport [6,15]. The disruption of GLUT4 expression has been extensively associated
with pathologies of impaired glucose uptake and insulin resistance such as type 2 diabetes
and obesity [13,16-18]..
Entropy of the self-dual string soliton
We compute the entropy and the corresponding central charge of the self-dual
string soliton in the supergravity regime using the blackfold description of
the fully localized M2-M5 intersection.Comment: 15 pages, 1 figure, harvma
Machine-learned cloud classes from satellite data for process-oriented climate model evaluation
Clouds play a key role in regulating climate change but are difficult to
simulate within Earth system models (ESMs). Improving the representation of
clouds is one of the key tasks towards more robust climate change projections.
This study introduces a new machine-learning based framework relying on
satellite observations to improve understanding of the representation of clouds
and their relevant processes in climate models. The proposed method is capable
of assigning distributions of established cloud types to coarse data. It
facilitates a more objective evaluation of clouds in ESMs and improves the
consistency of cloud process analysis. The method is built on satellite data
from the MODIS instrument labelled by deep neural networks with cloud types
defined by the World Meteorological Organization (WMO), using cloud type labels
from CloudSat as ground truth. The method is applicable to datasets with
information about physical cloud variables comparable to MODIS satellite data
and at sufficiently high temporal resolution. We apply the method to
alternative satellite data from the Cloud\_cci project (ESA Climate Change
Initiative), coarse-grained to typical resolutions of climate models. The
resulting cloud type distributions are physically consistent and the horizontal
resolutions typical of ESMs are sufficient to apply our method. We recommend
outputting crucial variables required by our method for future ESM data
evaluation. This will enable the use of labelled satellite data for a more
systematic evaluation of clouds in climate models.Comment: Main Paper 16 pages, 11 figures. Supporting material 7 Pages, 8
figures. This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Anisotropy of Magnetic Field and Velocity Fluctuations in the Solar Wind
We present a large statistical study of the fluctuation anisotropy in minimum variance (MV) frames of the magnetic field and solar wind velocity. We use 2, 10, 20, and 40 minute intervals of simultaneous magnetic field (the Wind spacecraft) and velocity (the Spektr-R spacecraft) observations. Our study confirms that magnetic turbulence is a composite of fluctuations varying along the mean magnetic field and those changing in the direction perpendicular to the mean field. Regardless of the length scale within the studied range of spacecraft-frame frequencies, ≈90% of the observed magnetic field fluctuations exhibit an MV direction aligned with the mean magnetic field, ≈10% of events have the MV direction perpendicular to the background field, and a negligible portion of fluctuations has no preferential direction. On the other hand, the MV direction of velocity fluctuations tends to be distributed more uniformly. An analysis of magnetic compressibility and density fluctuations suggests that the fluctuations resemble properties of Alfvénic fluctuations if the MV direction is aligned with background magnetic field whereas slow-mode-like fluctuations have the MV direction perpendicular to the background field. The proportion between Alfvénic and slow-mode-like fluctuations depends on plasma β and length scale: the dependence on the solar wind speed is weak. We present 3D numerical MHD simulations and show that the numerical results are compatible with our experimental results
Electric field inversion asymmetry: Rashba and Stark effects for holes in resonant tunneling devices
We report experimental evidence of excitonic spin-splitting, in addition to
the conventional Zeeman effect, produced by a combination of the Rashba
spin-orbit interaction, Stark shift and charge screening. The
electric-field-induced modulation of the spin-splitting are studied during the
charging and discharging processes of p-type GaAs/AlAs double barrier resonant
tunneling diodes (RTD) under applied bias and magnetic field. The abrupt
changes in the photoluminescence, with the applied bias, provide information of
the charge accumulation effects on the device.Comment: 4 pages, 2 figure
One-Dimensional Approximation of Viscous Flows
Attention has been paid to the similarity and duality between the
Gregory-Laflamme instability of black strings and the Rayleigh-Plateau
instability of extended fluids. In this paper, we derive a set of simple
(1+1)-dimensional equations from the Navier-Stokes equations describing thin
flows of (non-relativistic and incompressible) viscous fluids. This
formulation, a generalization of the theory of drop formation by Eggers and his
collaborators, would make it possible to examine the final fate of
Rayleigh-Plateau instability, its dimensional dependence, and possible
self-similar behaviors before and after the drop formation, in the context of
fluid/gravity correspondence.Comment: 17 pages, 3 figures; v2: refs & comments adde
A systematic review and meta-analysis on the effectiveness of xenograft to prevent periodontal defects after mandibular third molar extraction.
Background: To evaluate the use of guided bone regeneration with xenograft to prevent periodontal defect in the distal aspect of the second molar after the surgical removal of the mandibular third molar.Material and Methods: Three electronic databases (Pubmed, Cochrane Library and Scopus) were searched in April 2020. Randomized clinical trials in non-smokers and healthy patients, with at least six months follow-up, comparing periodontal probing depth, clinical attachment level, alveolar bone level and adverse events were selected by two independent investigators. The risk of bias assessment of the selected studies was evaluated by means of the Cochrane Collaboration's Tool. Finally, a meta-analysis of the outcomes of interest was performed.Results: Despite 795 articles were found in the initial search, only three randomized controlled clinical trials were included. Pooled results favoured the use of the xenograft plus collagen membrane over the spontaneous healing in terms of periodontal probing depth gain (MD=2.36; 95% CI 0.69 to 4.03; P=0.005) and clinical attachment level gain (MD=2.52; 95% CI 0.96 to 4.09; P=0.002). No other statistically significant differences were found. Conclusions: Within the limitations of the present review, the xenograft plus collagen membrane exhibited better periodontal results than spontaneous healing without increasing postoperative complications. However, future well-designed studies with larger samples are required to confirm our result
Black Brane Viscosity and the Gregory-Laflamme Instability
We study long wavelength perturbations of neutral black p-branes in
asymptotically flat space and show that, as anticipated in the blackfold
approach, solutions of the relativistic hydrodynamic equations for an effective
p+1-dimensional fluid yield solutions to the vacuum Einstein equations in a
derivative expansion. Going beyond the perfect fluid approximation, we compute
the effective shear and bulk viscosities of the black brane. The values we
obtain saturate generic bounds. Sound waves in the effective fluid are
unstable, and have been previously related to the Gregory-Laflamme instability
of black p-branes. By including the damping effect of the viscosity in the
unstable sound waves, we obtain a remarkably good and simple approximation to
the dispersion relation of the Gregory-Laflamme modes, whose accuracy increases
with the number of transverse dimensions. We propose an exact limiting form as
the number of dimensions tends to infinity.Comment: 16 pages, 3 figures. v2: minor corrections and refs adde
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