37,918 research outputs found
Logic-controlled occlusive cuff system
An occlusive cuff system comprises a pressure cuff and a source of regulated compressed gas feeding the cuff through an electrically operated fill valve. An electrically operated vent valve vents the cuff to the ambient pressure. The fill valve is normally closed and the vent valve is normally open. In response to an external start signal, a logic network opens the fill valve and closes the vent valve, thereby starting the pressurization cycle and a timer. A pressure transducer continuously monitors the pressure in the cuff. When the transducer's output equals a selected reference voltage, a comparator causes the logic network to close the fill valve. The timer, after a selected time delay, opens the vent valve to the ambient pressure, thereby ending the pressurization cycle
Coronal mass ejections, magnetic clouds, and relativistic magnetospheric electron events: ISTP
The role of high-speed solar wind streams in driving relativistic electron acceleration within the Earth\u27s magnetosphere during solar activity minimum conditions has been well documented. The rising phase of the new solar activity cycle (cycle 23) commenced in 1996, and there have recently been a number of coronal mass ejections (CMEs) and related âmagnetic cloudsâ at 1 AU. As these CME/cloud systems interact with the Earth\u27s magnetosphere, some events produce substantial enhancements in the magnetospheric energetic particle population while others do not. This paper compares and contrasts relativistic electron signatures observed by the POLAR, SAMPEX, Highly Elliptical Orbit, and geostationary orbit spacecraft during two magnetic cloud events: May 27â29, 1996, and January 10â11, 1997. Sequences were observed in each case in which the interplanetary magnetic field was first strongly southward and then rotated northward. In both cases, there were large solar wind density enhancements toward the end of the cloud passage at 1 AU. Strong energetic electron acceleration was observed in the January event, but not in the May event. The relative geoeffectiveness for these two cases is assessed, and it is concluded that large induced electric fields (âB/ât) caused in situ acceleration of electrons throughout the outer radiation zone during the January 1997 event
Confinement: Understanding the Relation Between the Wilson Loop and Dual Theories of Long Distance Yang Mills Theory
In this paper we express the velocity dependent, spin dependent heavy quark
potential in QCD in terms of a Wilson Loop determined
by pure Yang Mills theory. We use an effective dual theory of long-distance
Yang Mills theory to calculate for large loops; i.e. for loops of
size . ( is the flux tube radius, fixed by the value of the
Higgs (monopole) mass of the dual theory, which is a concrete realization of
the Mandelstam 't Hooft dual superconductor mechanism of confinement).
We replace by , given by a functional integral
over the dual variables, which for can be evaluated by a
semiclassical expansion, since the dual theory is weakly coupled at these
distances. The classical approximation gives the leading contribution to
and yields a velocity dependent heavy quark potential which
for large becomes linear in , and which for small approaches lowest
order perturbative QCD. This latter fact means that these results should remain
applicable down to distances where radiative corrections giving rise to a
running coupling constant become important. The spin dependence of the
potential reflects the vector coupling of the quarks at long range as well as
at short range. The methods developed here should be applicable to any
realization of the dual superconductor mechanism. They give an expression
determining independent of the classical approximation, but
semi classical corrections due to fluctuations of the flux tube are not worked
out in this paper. Taking these into account should lead to an effective string
theory free from the conformal anomaly.Comment: 39 pages, latex2e, 1 figure(fig.eps
Collision of Viscoelastic Spheres: Compact Expressions for the Coefficient of Normal Restitution
The coefficient of restitution of colliding viscoelastic spheres is
analytically known as a complete series expansion in terms of the impact
velocity where all (infinitely many) coefficients are known. While beeing
analytically exact, this result is not suitable for applications in efficient
event-driven Molecular Dynamics (eMD) or Monte Carlo (MC) simulations. Based on
the analytic result, here we derive expressions for the coefficient of
restitution which allow for an application in efficient eMD and MC simulations
of granular Systems.Comment: 4 pages, 4 figure
Gamma-ray halos as a measure of intergalactic magnetic fields: a classical moment problem
The presence of weak intergalactic magnetic fields can be studied by their
effect on electro-magnetic cascades induced by multi-TeV gamma-rays in the
cosmic radiation background. Small deflections of secondary electrons and
positrons as the cascade develops extend the apparent size of the emission
region of distant TeV gamma-ray sources. These gamma-ray halos can be
resolvable in imaging atmospheric Cherenkov telescopes and serve as a measure
of the intergalactic magnetic field strength and coherence length. We present a
method of calculating the gamma-ray halo for isotropically emitting sources by
treating magnetic deflections in the cascade as a diffusion process. With this
ansatz the moments of the halo follow from a set of simple diffusion-cascade
equations. The reconstruction of the angular distribution is then equivalent to
a classical moment problem. We present a simple solution using Pade
approximations of the moment's generating function.Comment: 12 pages, 6 figure
Sky localization of complete inspiral-merger-ringdown signals for nonspinning massive black hole binaries
We investigate the capability of LISA to measure the sky position of
equal-mass, nonspinning black hole binaries, combining for the first time the
entire inspiral-merger-ringdown signal, the effect of the LISA orbits, and the
complete three-channel LISA response. We consider an ensemble of systems near
the peak of LISA's sensitivity band, with total rest mass of 2\times10^6
M\odot, a redshift of z = 1, and randomly chosen orientations and sky
positions. We find median sky localization errors of approximately \sim3
arcminutes. This is comparable to the field of view of powerful electromagnetic
telescopes, such as the James Webb Space Telescope, that could be used to
search for electromagnetic signals associated with merging massive black holes.
We investigate the way in which parameter errors decrease with measurement
time, focusing specifically on the additional information provided during the
merger-ringdown segment of the signal. We find that this information improves
all parameter estimates directly, rather than through diminishing correlations
with any subset of well- determined parameters. Although we have employed the
baseline LISA design for this study, many of our conclusions regarding the
information provided by mergers will be applicable to alternative mission
designs as well.Comment: 9 pages, 5 figures, submitted to Phys. Rev.
Gradual diffusion and punctuated phase space density enhancements of highly relativistic electrons: Van Allen Probes observations
Abstract The dual-spacecraft Van Allen Probes mission has provided a new window into mega electron volt (MeV) particle dynamics in the Earth\u27s radiation belts. Observations (up to E ~10 MeV) show clearly the behavior of the outer electron radiation belt at different timescales: months-long periods of gradual inward radial diffusive transport and weak loss being punctuated by dramatic flux changes driven by strong solar wind transient events. We present analysis of multi-MeV electron flux and phase space density (PSD) changes during March 2013 in the context of the first year of Van Allen Probes operation. This March period demonstrates the classic signatures both of inward radial diffusive energization and abrupt localized acceleration deep within the outer Van Allen zone (L ~4.0 ± 0.5). This reveals graphically that both competing mechanisms of multi-MeV electron energization are at play in the radiation belts, often acting almost concurrently or at least in rapid succession. Key Points Clear observations to higher energy than ever before Precise detection of where and how acceleration takes place Provides new eyes on megaelectron Volt
Lattice Monte Carlo calculations for unitary fermions in a finite box
We perform lattice Monte Carlo simulations for up to 66 unitary fermions in a
finite box using a highly improved lattice action for nonrelativistic spin 1/2
fermions. We obtain a value of for the Bertsch
parameter, defined as the energy of the unitary Fermi gas measured in units of
the free gas energy in the thermodynamic limit. In addition, for up to four
unitary fermions, we compute the spectrum of the lattice theory by exact
diagonalization of the transfer matrix projected onto irreducible
representations of the octahedral group for small to moderate size lattices,
providing an independent check of our few-body simulation results. We compare
our exact numerical and simulation results for the spectrum to benchmark
studies of other research groups, as well as perform an extended analysis of
our lattice action improvement scheme, including an analysis of the errors
associated with higher partial waves and finite temporal discretization.Comment: Significant revisions from previous version. Included data at a
larger volume and performed an infinite volume extrapolation of the Bertsch
parameter. Published versio
Kinetic cross coupling between non-conserved and conserved fields in phase field models
We present a phase field model for isothermal transformations of two
component alloys that includes Onsager kinetic cross coupling between the
non-conserved phase field and the conserved concentration field. We also
provide the reduction of the phase field model to the corresponding macroscopic
description of the free boundary problem. The reduction is given in a general
form. Additionally we use an explicit example of a phase field model and check
that the reduced macroscopic description, in the range of its applicability, is
in excellent agreement with direct phase field simulations. The relevance of
the newly introduced terms to solute trapping is also discussed
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