5,051 research outputs found
The role of strain hardening in the transition from dislocation-mediated to frictional deformation of marbles within the Karakoram Fault Zone, NW India
The onset of frictional failure and potentially seismogenic deformation in carbonate rocks undergoing exhumation within fault zones depends on hardening processes that reduce the efficiency of aseismic dislocation-mediated deformation as temperature decreases. However, few techniques are available for quantitative analysis of dislocation slip system activity and hardening in natural tectonites. Electron backscatter diffraction maps of crystal orientations offer one such approach via determination of Schmid factors, if the palaeostress conditions can be inferred and the critical resolved shear stresses of slip systems are constrained. We analyse calcite marbles deformed in simple shear within the Karakoram Fault Zone, NW India, to quantify changes in slip system activity as the rocks cooled during exhumation. Microstructural evidence demonstrates that between ∼300 °C and 200–250 °C the dominant deformation mechanisms transitioned from dislocation-mediated flow to twinning and frictional failure. However, Schmid factor analysis, considering critical resolved shear stresses for yield of undeformed single crystals, indicates that the fraction of grains with sufficient resolved shear stress for glide apparently increased with decreasing temperature. Misorientation analysis and previous experimental data indicate that strain-dependent work hardening is responsible for this apparent inconsistency and promoted the transition from dislocation-mediated flow to frictional, and potentially seismogenic, deformation.David Wallis and Lars Hansen acknowledge support from the Natural Environment Research Council grant NE/M000966/1
Fine-structure diagnostics of neutral carbon toward HE 0515-4414
New high-resolution high signal-to-noise spectra of the damped Lyman
(DLA) system toward the quasi-stellar object HE 0515-4414 reveal
absorption lines of the multiplets 2 and 3 in \ion{C}{i}. The resonance lines
are seen in two components with total column densities of
and , respectively. The comparision of theoretical
calculations of the relative fine-structure population with the ratios of the
observed column densities suggests that the \ion{C}{i} absorbing medium is
either very dense or exposed to very intense UV radiation. The upper limit on
the local UV energy density is 100 times the galactic UV energy density, while
the upper limit on the \ion{H}{i} number density is 110 cm. The
excitation temperatures of the ground state fine-structure levels of
and K, respectively, are consistent with the temperature-redshift
relation predicted by the standard Friedmann cosmology. The cosmic microwave
background radiation (CMBR) is only a minor source of the observed
fine-structure excitation.Comment: 5 pages, 5 figures, uses A&A macro package, gzipped tar archive,
accepted by A&
GNFactor: Multi-Task Real Robot Learning with Generalizable Neural Feature Fields
It is a long-standing problem in robotics to develop agents capable of
executing diverse manipulation tasks from visual observations in unstructured
real-world environments. To achieve this goal, the robot needs to have a
comprehensive understanding of the 3D structure and semantics of the scene. In
this work, we present , a visual behavior cloning agent for
multi-task robotic manipulation with eneralizable eural
feature ields. GNFactor jointly optimizes a generalizable neural
field (GNF) as a reconstruction module and a Perceiver Transformer as a
decision-making module, leveraging a shared deep 3D voxel representation. To
incorporate semantics in 3D, the reconstruction module utilizes a
vision-language foundation model (, Stable Diffusion) to distill
rich semantic information into the deep 3D voxel. We evaluate GNFactor on 3
real robot tasks and perform detailed ablations on 10 RLBench tasks with a
limited number of demonstrations. We observe a substantial improvement of
GNFactor over current state-of-the-art methods in seen and unseen tasks,
demonstrating the strong generalization ability of GNFactor. Our project
website is https://yanjieze.com/GNFactor/ .Comment: CoRL 2023 Oral. Website: https://yanjieze.com/GNFactor
Analysis of V2X Sidelink Positioning in sub-6 GHz
Radio positioning is an important part of joint communication and sensing in
beyond 5G communication systems. Existing works mainly focus on the mmWave
bands and under-utilize the sub-6 GHz bands, even though it is promising for
accurate positioning, especially when the multipath is uncomplicated, and
meaningful in several important use cases. In this paper, we analyze V2X
sidelink positioning and propose a new performance bound that can predict the
positioning performance in the presence of severe multipath. Simulation results
using ray-tracing data demonstrate the possibility of sidelink positioning, and
the efficacy of the new performance bound and its relation with the complexity
of the multipath
V2X Sidelink Positioning in FR1: Scenarios, Algorithms, and Performance Evaluation
In this paper, we investigate sub-6 GHz V2X sidelink positioning scenarios in
5G vehicular networks through a comprehensive end-to-end methodology
encompassing ray-tracing-based channel modeling, novel theoretical performance
bounds, high-resolution channel parameter estimation, and geometric positioning
using a round-trip-time (RTT) protocol. We first derive a novel, approximate
Cram\'er-Rao bound (CRB) on the connected road user (CRU) position, explicitly
taking into account multipath interference, path merging, and the RTT protocol.
Capitalizing on tensor decomposition and ESPRIT methods, we propose
high-resolution channel parameter estimation algorithms specifically tailored
to dense multipath V2X sidelink environments, designed to detect multipath
components (MPCs) and extract line-of-sight (LoS) parameters. Finally, using
realistic ray-tracing data and antenna patterns, comprehensive simulations are
conducted to evaluate channel estimation and positioning performance,
indicating that sub-meter accuracy can be achieved in sub-6 GHz V2X with the
proposed algorithms
Dichlorido(η6-toluene)[tris(4-methoxyphenyl)phosphine]ruthenium(II)
In the title compound, [RuCl2(C7H8)(C21H21O3P)], the RuII atom possesses a pseudo-octahedral geometry and the metrical parameters around the metallic core compare well with those of similar three-legged-piano-stool complexes
Molecular dynamics simulations of oscillatory Couette flows with slip boundary conditions
The effect of interfacial slip on steady-state and time-periodic flows of
monatomic liquids is investigated using non-equilibrium molecular dynamics
simulations. The fluid phase is confined between atomically smooth rigid walls,
and the fluid flows are induced by moving one of the walls. In steady shear
flows, the slip length increases almost linearly with shear rate. We found that
the velocity profiles in oscillatory flows are well described by the Stokes
flow solution with the slip length that depends on the local shear rate.
Interestingly, the rate dependence of the slip length obtained in steady shear
flows is recovered when the slip length in oscillatory flows is plotted as a
function of the local shear rate magnitude. For both types of flows, the
friction coefficient at the liquid-solid interface correlates well with the
structure of the first fluid layer near the solid wall.Comment: 31 pages, 11 figure
The formation of the eccentric-orbit millisecond pulsar J1903+0327 and the origin of single millisecond pulsars
The millisecond pulsar J1903+0327 is accompanied by an ordinary G-dwarf star
in an unusually wide (\,days) and eccentric () orbit. The standard model for producing MSPs fails to explain the
orbital characteristics of this extraordinary binary, and alternative binary
models are unable to explain the observables. We present a triple-star model
for producing MSPs in relatively wide eccentric binaries with a normal
(main-sequence) stellar companion. We start from a stable triple system
consisting of a Low-Mass X-ray Binary (LMXB) with an orbital period of at least
1 day, accompanied by a G-dwarf in a wide and possibly eccentric orbit.
Variations in the initial conditions naturally provide a satisfactory
explanation for the unexplained triple component in the eclipsing soft X-ray
transient 4U~2129+47 or the cataclysmic variable EC 19314-5915. The best
explanation for J1903, however, results from the expansion of the orbit of the
LMXB, driven by the mass transfer from the evolving donor star to its neutron
star companion, which causes the triple eventually to becomes dynamically
unstable. Using numerical computations we show that, depending on the precise
system configuration at the moment the triple becomes dynamically unstable, the
ejection of each of the three components is possible. If the donor star of the
LMXB is ejected, a system resembling J1903, will result. If the neutron star is
ejected, a single MSP results. This model therefore also provides a
straightforward mechanism for forming single MSP in the Galactic disk. We
conclude that the Galaxy contains some 30--300 binaries with characteristics
similar to J1903, and about an order of magnitude fewer single millisecond
pulsars produced with the proposed triple scenario.Comment: ApJ accepted for publicatio
Diagnosis and management of subcutaneous implantable cardioverter‐defibrillator infections based on process mapping
Background: Infection is a well‐recognized complication of cardiovascular implantable electronic device (CIED) implantation, including the more recently available subcutaneous implantable cardioverter‐defibrillator (S‐ICD). Although the AHA/ACC/HRS guidelines include recommendations for S‐ICD use, currently there are no clinical trial data that address the diagnosis and management of S‐ICD infections. Therefore, an expert panel was convened to develop consensus on these topics. /
Methods: A process mapping methodology was used to achieve a primary goal – the development of consensus on the diagnosis and management of S‐ICD infections. Two face‐to‐face meetings of panel experts were conducted to recommend useful information to clinicians in individual patient management of S‐ICD infections. /
Results: Panel consensus of a stepwise approach in the diagnosis and management was developed to provide guidance in individual patient management. /
Conclusion: Achieving expert panel consensus by process mapping methodology in S‐ICD infection diagnosis and management was attainable, and the results should be helpful in individual patient management
Non-Perturbative Renormalization Group for Simple Fluids
We present a new non perturbative renormalization group for classical simple
fluids. The theory is built in the Grand Canonical ensemble and in the
framework of two equivalent scalar field theories as well. The exact mapping
between the three renormalization flows is established rigorously. In the Grand
Canonical ensemble the theory may be seen as an extension of the Hierarchical
Reference Theory (L. Reatto and A. Parola, \textit{Adv. Phys.}, \textbf{44},
211 (1995)) but however does not suffer from its shortcomings at subcritical
temperatures. In the framework of a new canonical field theory of liquid state
developed in that aim our construction identifies with the effective average
action approach developed recently (J. Berges, N. Tetradis, and C. Wetterich,
\textit{Phys. Rep.}, \textbf{363} (2002))
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