1,603 research outputs found
Intrinsic Dynamic Shape Prior for Fast, Sequential and Dense Non-Rigid Structure from Motion with Detection of Temporally-Disjoint Rigidity
While dense non-rigid structure from motion (NRSfM) has been extensively studied from the perspective of the reconstructability problem over the recent years, almost no attempts have been undertaken to bring it into the practical realm. The reasons for the slow dissemination are the severe ill-posedness, high sensitivity to motion and deformation cues and the difficulty to obtain reliable point tracks in the vast majority of practical scenarios. To fill this gap, we propose a hybrid approach that extracts prior shape knowledge from an input sequence with NRSfM and uses it as a dynamic shape prior for sequential surface recovery in scenarios with recurrence. Our Dynamic Shape Prior Reconstruction (DSPR) method can be combined with existing dense NRSfM techniques while its energy functional is optimised with stochastic gradient descent at real-time rates for new incoming point tracks. The proposed versatile framework with a new core NRSfM approach outperforms several other methods in the ability to handle inaccurate and noisy point tracks, provided we have access to a representative (in terms of the deformation variety) image sequence. Comprehensive experiments highlight convergence properties and the accuracy of DSPR under different disturbing effects. We also perform a joint study of tracking and reconstruction and show applications to shape compression and heart reconstruction under occlusions. We achieve state-of-the-art metrics (accuracy and compression ratios) in different scenarios
Optical Response of SrRuO Reveals Universal Fermi-liquid Scaling and Quasiparticles Beyond Landau Theory
We report optical measurements demonstrating that the low-energy relaxation
rate () of the conduction electrons in SrRuO obeys scaling
relations for its frequency () and temperature () dependence in
accordance with Fermi-liquid theory. In the thermal relaxation regime,
1/\tau\propto (\hbar\omega)^2 + (p\pi\kB T)^2 with , and
scaling applies. Many-body electronic structure calculations using dynamical
mean-field theory confirm the low-energy Fermi-liquid scaling, and provide
quantitative understanding of the deviations from Fermi-liquid behavior at
higher energy and temperature. The excess optical spectral weight in this
regime provides evidence for strongly dispersing "resilient" quasiparticle
excitations above the Fermi energy
A New Limit on Signals of Lorentz Violation in Electrodynamics
We describe the results of an experiment to test for spacetime anisotropy
terms that might exist from Lorentz violations. The apparatus consists of a
pair of cylindrical superconducting cavity-stabilized oscillators operating in
the TM_{010} mode with one axis east-west and the other vertical. Spatial
anisotropy is detected by monitoring the beat frequency at the sidereal rate
and its first harmonic. We see no anisotropy to a part in 10^{13}. This puts a
comparable bound on four linear combinations of parameters in the general
Standard Model extension, and a weaker bound of <4 x 10^{-9} on three others.Comment: 4 pages, 3 figures, 2 table
Hybridization gap and anisotropic far-infrared optical conductivity of URu2Si2
We performed far-infrared optical spectroscopy measurements on the heavy
fermion compound URu 2 Si 2 as a function of temperature. The light's
electric-field was applied along the a-axis or the c-axis of the tetragonal
structure. We show that in addition to a pronounced anisotropy, the optical
conductivity exhibits for both axis a partial suppression of spectral weight
around 12 meV and below 30 K. We attribute these observations to a change in
the bandstructure below 30 K. However, since these changes have no noticeable
impact on the entropy nor on the DC transport properties, we suggest that this
is a crossover phenomenon rather than a thermodynamic phase transition.Comment: To be published in Physical Review
Na2IrO3 as a spin-orbit-assisted antiferromagnetic insulator with a 340 meV gap
We study Na2IrO3 by ARPES, optics, and band structure calculations in the
local-density approximation (LDA). The weak dispersion of the Ir 5d-t2g
manifold highlights the importance of structural distortions and spin-orbit
coupling (SO) in driving the system closer to a Mott transition. We detect an
insulating gap {\Delta}_gap = 340 meV which, at variance with a Slater-type
description, is already open at 300 K and does not show significant temperature
dependence even across T_N ~ 15 K. An LDA analysis with the inclusion of SO and
Coulomb repulsion U reveals that, while the prodromes of an underlying
insulating state are already found in LDA+SO, the correct gap magnitude can
only be reproduced by LDA+SO+U, with U = 3 eV. This establishes Na2IrO3 as a
novel type of Mott-like correlated insulator in which Coulomb and relativistic
effects have to be treated on an equal footing.Comment: Accepted in Physical Review Letters. Auxiliary and related material
can be found at:
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.htm
Lessons to be learned from the coherent photoproduction of pseudoscalar mesons
We study the coherent photoproduction of pseudoscalar mesons---particularly
of neutral pions---placing special emphasis on the various sources that put
into question earlier nonrelativistic-impulse-approximation calculations. These
include: final-state interactions, relativistic effects, off-shell ambiguities,
and violations to the impulse approximation. We establish that, while
distortions play an essential role in the modification of the coherent cross
section, the uncertainty in our results due to the various choices of
optical-potential models is relatively small (of at most 30%). By far the
largest uncertainty emerges from the ambiguity in extending the many
on-shell-equivalent representations of the elementary amplitude off the mass
shell. Indeed, relativistic impulse-approximation calculations that include the
same pionic distortions, the same nuclear-structure model, and two sets of
elementary amplitudes that are identical on-shell, lead to variations in the
magnitude of the coherent cross section by up to factors of five. Finally, we
address qualitatively the assumption of locality implicit in most
impulse-approximation treatments, and suggest that the coherent reaction
probes---in addition to the nuclear density---the polarization structure of the
nucleus.Comment: Manuscript is 27 pages long and includes 11 eps figure
Pion-nucleus optical potential valid up to the DELTA-resonance region
We present in this article an optical potential for the -nucleus
interaction that can be used in various studies involving -nucleus
channels. Based on earlier treatments of the low energy -nucleus optical
potential, we have derived a potential expression applicable from threshold up
to the -resonance region. We extracted the impulse approximation form
for this potential from the scattering amplitude and then added to it
kinematical and physical corrections. The kinematic corrections arise from
transforming the impulse approximation expression from the center of
mass frame to the -nucleus center of mass frame, while the physical
corrections arise mostly from the many-body nature of the -nucleus
interaction. By taking advantage of the experimental progress in our knowledge
of the process, we have updated earlier treatments with parameters
calculated from state-of-the-art experimental measurements.Comment: 23 pages, 12 figures. Accepted for publication in Physical Review
Recent Technological Developments on LGAD and iLGAD Detectors for Tracking and Timing Applications
This paper reports the last technological development on the Low Gain
Avalanche Detector (LGAD) and introduces a new architecture of these detectors
called inverse-LGAD (iLGAD). Both approaches are based on the standard
Avalanche Photo Diodes (APD) concept, commonly used in optical and X-ray
detection applications, including an internal multiplication of the charge
generated by radiation. The multiplication is inherent to the basic n++-p+-p
structure, where the doping profile of the p+ layer is optimized to achieve
high field and high impact ionization at the junction. The LGAD structures are
optimized for applications such as tracking or timing detectors for high energy
physics experiments or medical applications where time resolution lower than 30
ps is required. Detailed TCAD device simulations together with the electrical
and charge collection measurements are presented through this work.Comment: Keywords: silicon detectors, avalanche multiplication, timing
detectors, tracking detectors. 8 pages. 8 Figure
Detection and classification of buried dielectric anomalies using a separated aperture sensor and a neural network discriminator
Includes bibliographical references.The problem of detection and classification of buried dielectric anomalies using a separated aperture microwave sensor and an artificial neural network discriminator was considered. Several methods for training and data representation were developed to study the trainability and generalization capabilities of the networks. The effect of the architectural variation on the network performance was also studied. The principal component method was used to reduce the volume of the data and also the dimension of the weight space. Simulation results on two types of targets were obtained which indicated superior detection and classification performance when compared with the conventional methods
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