508 research outputs found
Control of gradient-driven instabilities using shear Alfv\'en beat waves
A new technique for manipulation and control of gradient-driven instabilities
through nonlinear interaction with Alfv\'en waves in a laboratory plasma is
presented. A narrow field-aligned density depletion is created in the Large
Plasma Device (LAPD), resulting in coherent unstable fluctuations on the
periphery of the depletion. Two independent kinetic Alfv\'en waves are launched
along the depletion at separate frequencies, creating a nonlinear beat-wave
response at or near the frequency of the original instability. When the
beat-wave has sufficient amplitude, the original unstable mode is suppressed,
leaving only the beat-wave response at a different frequency, generally at
lower amplitude.Comment: Submitted for Publication in Physical Review Letters. Revision 2
reflects changes suggested by referees for PRL submission. One figure
removed, several major changes to another figure, and a number of major and
minor changes to the tex
Wallerian degeneration: gaining perspective on inflammatory events after peripheral nerve injury
In this review, we first provide a brief historical perspective, discussing how peripheral nerve injury (PNI) may have caused World War I. We then consider the initiation, progression, and resolution of the cellular inflammatory response after PNI, before comparing the PNI inflammatory response with that induced by spinal cord injury (SCI)
Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6
The superconductor YB6 has the second highest critical temperature Tc among
the boride family MBn. We report measurements of the specific heat,
resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K,
using a single crystal with Tc = 7.2 K. The superconducting gap is
characteristic of medium-strong coupling. The specific heat, resistivity and
expansivity curves are deconvolved to yield approximations of the phonon
density of states, the spectral electron-phonon scattering function and the
phonon density of states weighted by the frequency-dependent Grueneisen
parameter respectively. Lattice vibrations extend to high frequencies >100 meV,
but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of
yttrium ions in oversized boron cages, appears to provide most of the
superconducting coupling and gives rise to an unusual temperature behavior of
several observable quantities. A surface critical field Hc3 is also observed.Comment: 29 pages, 5 tables, 17 figures. Accepted for publication in Phys.
Rev.
Quantum interference and electron-electron interactions at strong spin-orbit coupling in disordered systems
Transport and thermodynamic properties of disordered conductors are
considerably modified when the angle through which the electron spin precesses
due to spin-orbit interaction (SOI) during the mean free time becomes
significant. Cooperon and Diffusion equations are solved for the entire range
of strength of SOI. The implications of SOI for the electron-electron
interaction and interference effects in various experimental settings are
discussed.Comment: 4 pages, REVTEX, 1 eps.figure Submitted to Phys. Rev. Let
Машинный перевод: к проблеме постредактирования
В исследовании проведен опыт постредактирования романа Лоис Лоури «The Silent Boy», первая глава которого переведена на русский язык тремя автоматическими системами: Яндекс.Переводчиком, Google Translate и DeepL Translate. Даны практические рекомендации по усовершенствованию работы постредакторов.This research is an experience of post-editing the novel “The Silent Boy” by Lois Lowry, its first chapter having been translated into Russian by three automatic systems: Yandex Translate, Google Translate and DeepL Translate. There are provided practical recommendations for improving post-editors’ work
Effects of gabapentin on muscle spasticity and both induced as well as spontaneous autonomic dysreflexia after complete spinal cord injury
We recently reported that the neuropathic pain medication, gabapentin (GBP; Neurontin), significantly attenuated both noxious colorectal distension (CRD)-induced autonomic dysreflexia (AD) and tail pinch-induced spasticity compared to saline-treated cohorts 2–3 weeks after complete high thoracic (T4) spinal cord injury (SCI). Here we employed long-term blood pressure telemetry to test, firstly, the efficacy of daily versus acute GBP treatment in modulating AD and tail spasticity in response to noxious stimuli at 2 and 3 weeks post-injury. Secondly, we determined whether daily GBP alters baseline cardiovascular parameters, as well as spontaneous AD events detected using a novel algorithm based on blood pressure telemetry data. At both 14 and 21 days after SCI, irrespective of daily treatment, acute GBP given 1 h prior to stimulus significantly attenuated CRD-induced AD and pinch-evoked tail spasticity; conversely, acute saline had no such effects. Moreover, daily GBP did not alter 24 h mean arterial pressure (MAP) or heart rate (HR) values compared to saline treatment, nor did it reduce the incidence of spontaneous AD events compared to saline over the three week assessment period. Power spectral density (PSD) analysis of the MAP signals demonstrated relative power losses in mid frequency ranges (0.2–0.8 Hz) for all injured animals relative to low frequency MAP power (0.02–0.08 Hz). However, there was no significant difference between groups over time post-injury; hence, GBP had no effect on the persistent loss of MAP fluctuations in the mid frequency range after injury. In summary, the mechanism(s) by which acute GBP treatment mitigate aberrant somatosensory and cardiophysiological responses to noxious stimuli after SCI remain unclear. Nevertheless, with further refinements in defining the dynamics associated with AD events, such as eliminating requisite concomitant bradycardia, the objective repeatability of automatic detection of hypertensive crises provides a potentially useful tool for assessing autonomic function pre- and post-SCI, in conjunction with experimental pharmacotherapeutics for neuropathic pain, such as GBP
Rare earth magnetism in CeFeAsO: A single crystal study
Single crystals of CeFeAsO, large enough to study the anisotropy of the
magnetic properties, were grown by an optimized Sn-flux technique. The high
quality of our single crystals is apparent from the highest residual
resistivity ratio, RRR = 12, reported among undoped RFeAsO compounds (R=rare
earth) as well as sharp anomalies in resistivity, specific heat, C(T), and
thermal expansion at the different phase transitions. The magnetic
susceptibility chi(T) presents a large easy-plane anisotropy consistent with
the lowest crystal electric field doublet having a dominant Gamma_6 character.
Curie-Weiss like susceptibilities for magnetic field parallel and perpendicular
to the crystallographic c-axis do not reveal an influence of a staggered field
on the Ce site induced by magnetic ordering of the Fe. Furthermore, the
standard signatures for antiferromagnetic order of Ce at T_N = 3.7 K observed
in chi(T) and C(T) are incompatible with a Zeeman splitting Delta = 10 K of the
CEF ground state doublet at low temperature due to the Fe-magnetic order as
previously proposed. Our results can be reconciled with the earlier observation
by assuming a comparatively stronger effect of the Ce-Ce exchange leading to a
reduction of this Zeeman splitting below 15 K.Comment: 15 pages, 6 figures, added section on magn. susceptibilit
Do interactions increase or reduce the conductance of disordered electrons? It depends!
We investigate the influence of electron-electron interactions on the
conductance of two-dimensional disordered spinless electrons. By using an
efficient numerical method which is based on exact diagonalization in a
truncated basis of Hartree-Fock states we are able to determine the exact
low-energy properties of comparatively large systems in the diffusive as well
as in the localized regimes. We find that weak interactions increase the d.c.
conductance in the localized regime while they decrease the d.c. conductance in
the diffusive regime. Strong interactions always decrease the conductance. We
also study the localization of single-particle excitations close to the Fermi
energy which turns out to be only weakly influenced by the interactions.Comment: final version as publsihed, 4 pages REVTEX, 6 EPS figures include
Hybrid Equation/Agent-Based Model of Ischemia-Induced Hyperemia and Pressure Ulcer Formation Predicts Greater Propensity to Ulcerate in Subjects with Spinal Cord Injury
Pressure ulcers are costly and life-threatening complications for people with spinal cord injury (SCI). People with SCI also exhibit differential blood flow properties in non-ulcerated skin. We hypothesized that a computer simulation of the pressure ulcer formation process, informed by data regarding skin blood flow and reactive hyperemia in response to pressure, could provide insights into the pathogenesis and effective treatment of post-SCI pressure ulcers. Agent-Based Models (ABM) are useful in settings such as pressure ulcers, in which spatial realism is important. Ordinary Differential Equation-based (ODE) models are useful when modeling physiological phenomena such as reactive hyperemia. Accordingly, we constructed a hybrid model that combines ODEs related to blood flow along with an ABM of skin injury, inflammation, and ulcer formation. The relationship between pressure and the course of ulcer formation, as well as several other important characteristic patterns of pressure ulcer formation, was demonstrated in this model. The ODE portion of this model was calibrated to data related to blood flow following experimental pressure responses in non-injured human subjects or to data from people with SCI. This model predicted a higher propensity to form ulcers in response to pressure in people with SCI vs. non-injured control subjects, and thus may serve as novel diagnostic platform for post-SCI ulcer formation. © 2013 Solovyev et al
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