7,782 research outputs found
A multipurpose large volume sea-water sampler
The need for large volumes of sea-water, from all depths, for radioisotope studies with carbon-14, tritium or fission-products, has resulted in the development of a variety of sampling devicesâŠ
Teleportation as a Depolarizing Quantum Channel, Relative Entropy and Classical Capacity
We show that standard teleportation with an arbitrary mixed state resource is
equivalent to a generalized depolarizing channel with probabilities given by
the maximally entangled components of the resource. This enables the usage of
any quantum channel as a generalized depolarizing channel without additional
twirling operations. It also provides a nontrivial upper bound on the
entanglement of a class of mixed states. Our result allows a consistent and
statistically motivated quantification of teleportation success in terms of the
relative entropy and this quantification can be related to a classical
capacity.Comment: Version published in Phys. Rev. Let
The Dust Content of Galaxy Clusters
We report on the detection of reddening toward z ~ 0.2 galaxy clusters. This
is measured by correlating the Sloan Digital Sky Survey cluster and quasar
catalogs and by comparing the photometric and spectroscopic properties of
quasars behind the clusters to those in the field. We find mean E(B-V) values
of a few times 10^-3 mag for sight lines passing ~Mpc from the clusters'
center. The reddening curve is typical of dust but cannot be used to
distinguish between different dust types. The radial dependence of the
extinction is shallow near the cluster center suggesting that most of the
detected dust lies at the outskirts of the clusters. Gravitational
magnification of background z ~ 1.7 sources seen on Mpc (projected) scales
around the clusters is found to be of order a few per cent, in qualitative
agreement with theoretical predictions. Contamination by different spectral
properties of the lensed quasar population is unlikely but cannot be excluded.Comment: 4 pages, 3 figure
Dephasing representation of quantum fidelity for general pure and mixed states
General semiclassical expression for quantum fidelity (Loschmidt echo) of
arbitrary pure and mixed states is derived. It expresses fidelity as an
interference sum of dephasing trajectories weighed by the Wigner function of
the initial state, and does not require that the initial state be localized in
position or momentum. This general dephasing representation is special in that,
counterintuitively, all of fidelity decay is due to dephasing and none due to
the decay of classical overlaps. Surprising accuracy of the approximation is
justified by invoking the shadowing theorem: twice--both for physical
perturbations and for numerical errors. It is shown how the general expression
reduces to the special forms for position and momentum states and for wave
packets localized in position or momentum. The superiority of the general over
the specialized forms is explained and supported by numerical tests for wave
packets, non-local pure states, and for simple and random mixed states. The
tests are done in non-universal regimes in mixed phase space where detailed
features of fidelity are important. Although semiclassically motivated, present
approach is valid for abstract systems with a finite Hilbert basis provided
that the discrete Wigner transform is used. This makes the method applicable,
via a phase space approach, e. g., to problems of quantum computation.Comment: 11 pages, 4 figure
A FUSE survey of high-latitude Galactic molecular hydrogen
Measurements of molecular hydrogen (H_2) column densities are presented for
the first six rotational levels (J=0 to 5) for 73 extragalactic targets
observed with FUSE. All of these have a final signal-to-noise ratio larger than
\snlimit, and are located at galactic latitude |b|>20 deg. The individual
observations were calibrated with the FUSE calibration pipeline CalFUSE version
2.1 or higher, and then carefully aligned in velocity. The final velocity
shifts for all the FUSE segments are listed. H_2 column densities or limits are
determined for the 6 lowest rotational (J) levels for each HI component in the
line of sight, using a curve-of-growth approach at low column densities ~16.5),
and Voigt-profile fitting at higher column densities. Detections include 73
measurements of low-velocity H_2 in the Galactic Disk and lower Halo. Eight
sightlines yield non-detections for Galactic H_2. The measured column densities
range from log N(H_2)=14 to log N(H_2)=20. Strong correlations are found
between log N(H_2) and T_01, the excitation temperature of the H_2, as well as
between log N(H_2) and the level population ratios (log (N(J')/N(J))). The
average fraction of nuclei in molecular hydrogen (f(H_2)) in each sightline is
calculated; however, because there are many HI clouds in each sightline, the
physics of the transition from HI to H_2 can not be studied. Detections also
include H2 in 16 intermediate-velocity clouds in the Galactic Halo (out of 35
IVCs). Molecular hydrogen is seen in one high-velocity cloud (the Leading Arm
of the Magellanic Stream), although 19 high-velocity clouds are intersected;
this strongly suggests that dust is rare or absent in these objects. Finally,
there are five detections of H_2 in external galaxies.Comment: Accepted for ApJ Supplement. Note: figs 7 and 8 not included because
astro-ph rejects them as too bi
A mass balance for 137Cs and 90Sr in the North Atlantic Ocean
The total inventory of 137Cs(3272 kCi) and 90Sr(2257 kCi) in the North Atlantic Ocean in 1972, as well as the subinventories in the 0 to 1000 m, 1000 to 2000 m, 2000 m to bottom layers, continental shelf waters and bottom sediments, have been estimated. We have been careful to provide reliable estimates of uncertainty for each of these values. We have also estimated the inputs of 137Cs to the Atlantic Ocean as direct fallout (2065 kCi), or as ocean current transport (240 kCi) since the start of large scale nuclear testing...
Collisions of boosted black holes: perturbation theory prediction of gravitational radiation
We consider general relativistic Cauchy data representing two nonspinning,
equal-mass black holes boosted toward each other. When the black holes are
close enough to each other and their momentum is sufficiently high, an
encompassing apparent horizon is present so the system can be viewed as a
single, perturbed black hole. We employ gauge-invariant perturbation theory,
and integrate the Zerilli equation to analyze these time-asymmetric data sets
and compute gravitational wave forms and emitted energies. When coupled with a
simple Newtonian analysis of the infall trajectory, we find striking agreement
between the perturbation calculation of emitted energies and the results of
fully general relativistic numerical simulations of time-symmetric initial
data.Comment: 5 pages (RevTex 3.0 with 3 uuencoded figures), CRSR-107
Correlations for pairs of periodic trajectories for open billiards
In this paper we prove two asymptotic estimates for pairs of closed
trajectories for open billiards similar to those established by Pollicott and
Sharp for closed geodesics on negatively curved compact surfaces. The first of
these estimates holds for general open billiards in any dimension. The more
intricate second estimate is established for open billiards satisfying the so
called Dolgopyat type estimates. This class of billiards includes all open
billiards in the plane and open billiards in satisfying some
additional conditions
MCG+00-32-16: An Irregular Galaxy Close to the Lowest Redshift Absorber on the 3C 273 Line of Sight
MCG+00-32-16 is the galaxy closest in position-velocity space to the lowest
redshift Ly absorber along the line-of-sight to the quasar 3C 273. Its
projected separation is 204 (d/19 Mpc) kpc, where d is the distance from the
Milky Way to the galaxy, and the redshift difference is only 94 km/s; HI
1225+01 is slightly closer in projected separation to the absorber, but has a
greater redshift difference. We present HI synthesis array mapping and CCD
photometry in B and R for MCG+00-32-16. The HI disk is rotating in such a way
that the side of the galaxy closer to the sight-line to the quasar has the
larger velocity difference from the absorber. The absorber may be a ``failed
dwarf'' member of a poor galaxy group of which MCG+00-32-16 and HI 1225+01 are
the only members to have formed stars.Comment: 14 pages, 9 figures, accepted by Astrophysical Journa
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