24,313 research outputs found
System and method for moving a probe to follow movements of tissue
An apparatus is described for moving a probe that engages moving living tissue such as a heart or an artery that is penetrated by the probe, which moves the probe in synchronism with the tissue to maintain the probe at a constant location with respect to the tissue. The apparatus includes a servo positioner which moves a servo member to maintain a constant distance from a sensed object while applying very little force to the sensed object, and a follower having a stirrup at one end resting on a surface of the living tissue and another end carrying a sensed object adjacent to the servo member. A probe holder has one end mounted on the servo member and another end which holds the probe
Novel substrates for Helium adsorption: Graphane and Graphene-Fluoride
The discovery of fullerenes has stimulated extensive exploration of the
resulting behavior of adsorbed films. Our study addresses the planar substrates
graphene-fluoride (GF) and graphane (GH) in comparison to graphene. We present
initial results concerning the potential energy, energy bands and low density
behavior of 4He and 3He films on such different surfaces. For example, while
graphene presents an adsorption potential that is qualitatively similar to that
on graphite, GF and GH yield potentials with different symmetry, a number of
adsorption sites double that on graphene/graphite and a larger corrugation for
the adatom. In the case of GF, the lowest energy band width is similar to that
on graphite but the He atom has a significantly larger effective mass and the
adsorption energy is about three time that on graphite. Implications concerning
the monolayer phase diagram of 4He are explored with the exact path integral
ground state method. A commensurate ordered state similar to the sqrt{3} x
sqrt{3} R30^o state on graphite is found the be unstable both on GF and on GH.
The ground states of submonolayer 4He on both GF and GH are superfluids with a
Bose Einstein condensate fraction of about 10%.Comment: 6 pages, 3 figures, LT26 proceedings, accepted for publication in
Journal of Physics: Conference Serie
Binary black hole spacetimes with a helical Killing vector
Binary black hole spacetimes with a helical Killing vector, which are
discussed as an approximation for the early stage of a binary system, are
studied in a projection formalism. In this setting the four dimensional
Einstein equations are equivalent to a three dimensional gravitational theory
with a sigma model as the material source. The sigma
model is determined by a complex Ernst equation. 2+1 decompositions of the
3-metric are used to establish the field equations on the orbit space of the
Killing vector. The two Killing horizons of spherical topology which
characterize the black holes, the cylinder of light where the Killing vector
changes from timelike to spacelike, and infinity are singular points of the
equations. The horizon and the light cylinder are shown to be regular
singularities, i.e. the metric functions can be expanded in a formal power
series in the vicinity. The behavior of the metric at spatial infinity is
studied in terms of formal series solutions to the linearized Einstein
equations. It is shown that the spacetime is not asymptotically flat in the
strong sense to have a smooth null infinity under the assumption that the
metric tends asymptotically to the Minkowski metric. In this case the metric
functions have an oscillatory behavior in the radial coordinate in a
non-axisymmetric setting, the asymptotic multipoles are not defined. The
asymptotic behavior of the Weyl tensor near infinity shows that there is no
smooth null infinity.Comment: to be published in Phys. Rev. D, minor correction
Quantum entanglement and teleportation in pulsed cavity-optomechanics
Entangling a mechanical oscillator with an optical mode is an enticing and
yet a very challenging goal in cavity optomechanics. Here we consider a pulsed
scheme to create Einstein-Podolsky-Rosen-type entanglement between a
traveling-wave light pulse and a mechanical oscillator. The entanglement can be
verified unambiguously by a pump-probe sequence of pulses. In contrast to
schemes that work in a steady-state regime under a continuous-wave drive, this
protocol is not subject to stability requirements that normally limit the
strength of achievable entanglement. We investigate the protocol's performance
under realistic conditions, including mechanical decoherence, in full detail.
We discuss the relevance of a high mechanical Qf product for entanglement
creation and provide a quantitative statement on which magnitude of the Qf
product is necessary for a successful realization of the scheme. We determine
the optimal parameter regime for its operation and show it to work in current
state-of-the-art systems.Comment: 10 pages, 2 figure
Age, Metallicity, and the Distance to the Magellanic Clouds From Red Clump Stars
We show that the luminosity dependence of the red clump stars on age and
metallicity can cause a difference of up to < ~0.6 mag in the mean absolute I
magnitude of the red clump between different stellar populations. We show that
this effect may resolve the apparent ~0.4 mag discrepancy between red
clump-derived distance moduli to the Magellanic Clouds and those from, e.g.,
Cepheid variables. Taking into account the population effects on red clump
luminosity, we determine a distance modulus to the LMC of 18.36 +/- 0.17 mag,
and to the SMC of 18.82 +/- 0.20 mag. Our alternate red clump LMC distance is
consistent with the value (m-M){LMC} = 18.50 +/- 0.10 adopted by the HST
Cepheid Key Project. We briefly examine model predictions of red clump
luminosity, and find that variations in helium abundance and core mass could
bring the Clouds closer by some 0.10--0.15 mag, but not by the ~0.4 mag that
would result from setting the mean absolute I-magnitude of the Cloud red clumps
equal to the that of the Solar neighborhood red clump.Comment: Accepted for publication in The Astrophysical Journal Letters, AASTeX
4.0, 10 pages, 1 postscript figur
Noble gas films on a decagonal AlNiCo quasicrystal
Thermodynamic properties of Ne, Ar, Kr, and Xe adsorbed on an Al-Ni-Co
quasicrystalline surface (QC) are studied with Grand Canonical Monte Carlo by
employing Lennard-Jones interactions with parameter values derived from
experiments and traditional combining rules. In all the gas/QC systems, a
layer-by-layer film growth is observed at low temperature. The monolayers have
regular epitaxial fivefold arrangements which evolve toward sixfold
close-packed structures as the pressure is increased. The final states can
contain either considerable or negligible amounts of defects. In the latter
case, there occurs a structural transition from five to sixfold symmetry which
can be described by introducing an order parameter, whose evolution
characterizes the transition to be continuous or discontinuous as in the case
of Xe/QC (first-order transition with associated latent heat). By simulating
fictitious noble gases, we find that the existence of the transition is
correlated with the size mismatch between adsorbate and substrate's
characteristic lengths. A simple rule is proposed to predict the phenomenon.Comment: 19 pages. 8 figures. (color figures can be seen at
http://alpha.mems.duke.edu/wahyu/ or
http://www.iop.org/EJ/abstract/0953-8984/19/1/016007/
Identifying a Two-State Hamiltonian in the Presence of Decoherence
Mapping the system evolution of a two-state system allows the determination
of the effective system Hamiltonian directly. We show how this can be achieved
even if the system is decohering appreciably over the observation time. A
method to include various decoherence models is given and the limits of this
technique are explored. This technique is applicable both to the problem of
calibrating a control Hamiltonian for quantum computing applications and for
precision experiments in two-state quantum systems. For simple models of
decoherence, this method can be applied even when the decoherence time is
comparable to the oscillation period of the system.Comment: 8 pages, 6 figures. Minor corrections, published versio
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