39,511 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
Quasi-equilibrium binary black hole sequences for puncture data derived from helical Killing vector conditions
We construct a sequence of binary black hole puncture data derived under the
assumptions (i) that the ADM mass of each puncture as measured in the
asymptotically flat space at the puncture stays constant along the sequence,
and (ii) that the orbits along the sequence are quasi-circular in the sense
that several necessary conditions for the existence of a helical Killing vector
are satisfied. These conditions are equality of ADM and Komar mass at infinity
and equality of the ADM and a rescaled Komar mass at each puncture. In this
paper we explicitly give results for the case of an equal mass black hole
binary without spin, but our approach can also be applied in the general case.
We find that up to numerical accuracy the apparent horizon mass also remains
constant along the sequence and that the prediction for the innermost stable
circular orbit is similar to what has been found with the effective potential
method.Comment: 6 pages, 3 figures, 1 tabl
Spectral analysis of skeletal muscle changes resulting from 59 days of weightlessness in Skylab 2
During stressful exercise of the m. gastrocnemius, preflight and postflight surface electromyograms (EMG) were taken from each of the Skylab II astronauts. Measurements on the muscle were made once 5 days before launch, and four times postflight on recovery day, 4 days after recovery, 16 days after recovery and 29 days after recovery. It was hypothesized that the disused gastrocnemius would exhibit dysfunction characteristics similar to those found in laboratory studies on disuse and of pathologically astrophied muscle, and that physical stress would be associated with heightened fatigability in the muscle. Both hypotheses were sustained. The results showed significant shifts of the predominant frequency of the gastrocnemius into higher than normal bands which suggests a relationship between muscle disuse characteristics and pathologic dysfunction characteristics. It was concluded that the spectrally analyzed EMG is a sensitive measure of muscle dsyfunction that is associated with disuse. Antigravity muscles exhibit heightened susceptibility to fatigue when subjected to lengthy weightlessness
Connectedness properties of the set where the iterates of an entire function are unbounded
We investigate the connectedness properties of the set I+(f) of points where the iterates of an entire function f are unbounded. In particular, we show that I+(f) is connected whenever iterates of the minimum modulus of f tend to ∞. For a general transcendental entire function f, we show that I+(f)∪ \{\infty\} is always connected and that, if I+(f) is disconnected, then it has uncountably many components, infinitely many of which are unbounded
Coulomb Drag between One-Dimensional Wigner Crystal Rings
We consider the Coulomb drag between two metal rings in which the long range
Coulomb interaction leads to the formation of a Wigner crystal. The first ring
is threaded by an Ahranov Bohm flux creating a persistent current J_0. The
second ring is brought in close proximity to the second and due to the Coulomb
interaction between the two rings a drag current J_D is produced in the second.
We investigate this system at zero temperature for perfect rings as well as the
effects of impurities. We show that the Wigner crystal state can in principle
lead to a higher ratio of drag current to drive current J_D/J_0 than in weakly
interacting electron systems.Comment: 12 pages, 10 figure
Laser cooling and control of excitations in superfluid helium
Superfluidity is an emergent quantum phenomenon which arises due to strong
interactions between elementary excitations in liquid helium. These excitations
have been probed with great success using techniques such as neutron and light
scattering. However measurements to-date have been limited, quite generally, to
average properties of bulk superfluid or the driven response far out of thermal
equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of
superfluid excitations in real-time. Furthermore, strong light-matter
interactions allow both laser cooling and amplification of the thermal motion.
This provides a new tool to understand and control the microscopic behaviour of
superfluids, including phonon-phonon interactions, quantised vortices and
two-dimensional quantum phenomena such as the Berezinskii-Kosterlitz-Thouless
transition. The third sound modes studied here also offer a pathway towards
quantum optomechanics with thin superfluid films, including femtogram effective
masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex
interactions, and self-assembly into complex geometries with sub-nanometre
feature size.Comment: 6 pages, 4 figures. Supplementary information attache
Improved Quantum Hard-Sphere Ground-State Equations of State
The London ground-state energy formula as a function of number density for a
system of identical boson hard spheres, corrected for the reduced mass of a
pair of particles in a sphere-of-influence picture, and generalized to fermion
hard-sphere systems with two and four intrinsic degrees of freedom, has a
double-pole at the ultimate \textit{regular} (or periodic, e.g.,
face-centered-cubic) close-packing density usually associated with a
crystalline branch. Improved fluid branches are contructed based upon exact,
field-theoretic perturbation-theory low-density expansions for many-boson and
many-fermion systems, appropriately extrapolated to intermediate densities, but
whose ultimate density is irregular or \textit{random} closest close-packing as
suggested in studies of a classical system of hard spheres. Results show
substantially improved agreement with the best available Green-function Monte
Carlo and diffusion Monte Carlo simulations for bosons, as well as with ladder,
variational Fermi hypernetted chain, and so-called L-expansion data for
two-component fermions.Comment: 15 pages and 7 figure
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
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