8,534 research outputs found
Intercontinental antenna arraying by symbol stream combining at ICE Giacobini-Zinner encounter
Deep space tracking stations on different continents were arrayed during the encounter of the International Cometary Explorer (ICE) spacecraft with the comet Giacobini-Zinner during September 9 through 12, 1985. This is the first time that telemetry signals received on different continents have been combined to enhance signal to noise ratio. The arraying was done in non-real time using the method of symbol stream combining. The improvement in signal to noise ratio was typically 2 dB over the stronger of the two stations in each array
Extended Classical Over-Barrier Model for Collisions of Highly Charged Ions with Conducting and Insulating Surfaces
We have extended the classical over-barrier model to simulate the
neutralization dynamics of highly charged ions interacting under grazing
incidence with conducting and insulating surfaces. Our calculations are based
on simple model rates for resonant and Auger transitions. We include effects
caused by the dielectric response of the target and, for insulators, localized
surface charges. Characteristic deviations regarding the charge transfer
processes from conducting and insulating targets to the ion are discussed. We
find good agreement with previously published experimental data for the image
energy gain of a variety of highly charged ions impinging on Au, Al, LiF and KI
crystals.Comment: 32 pages http://pikp28.uni-muenster.de/~ducree
Cryo-FIB Machining: An Alternative to TEM Cryo-Sections Cut with Diamonds?
Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7-August 11, 201
Coherent vs incoherent interlayer transport in layered metals
The magnetic-field, temperature, and angular dependence of the interlayer
magnetoresistance of two different quasi-two-dimensional (2D) organic
superconductors is reported. For -(BEDT-TTF)I we find a
well-resolved peak in the angle-dependent magnetoresistance at (field parallel to the layers). This clear-cut proof for the coherent
nature of the interlayer transport is absent for
''-(BEDT-TTF)SFCHCFSO. This and the non-metallic
behavior of the magnetoresistance suggest an incoherent quasiparticle motion
for the latter 2D metal.Comment: 4 pages, 4 figures. Phys. Rev. B, in pres
Perturbations of nuclear C*-algebras
Kadison and Kastler introduced a natural metric on the collection of all
C*-subalgebras of the bounded operators on a separable Hilbert space. They
conjectured that sufficiently close algebras are unitarily conjugate. We
establish this conjecture when one algebra is separable and nuclear. We also
consider one-sided versions of these notions, and we obtain embeddings from
certain near inclusions involving separable nuclear C*-algebras. At the end of
the paper we demonstrate how our methods lead to improved characterisations of
some of the types of algebras that are of current interest in the
classification programme.Comment: 45 page
"Squashed Entanglement" - An Additive Entanglement Measure
In this paper, we present a new entanglement monotone for bipartite quantum
states. Its definition is inspired by the so-called intrinsic information of
classical cryptography and is given by the halved minimum quantum conditional
mutual information over all tripartite state extensions. We derive certain
properties of the new measure which we call "squashed entanglement": it is a
lower bound on entanglement of formation and an upper bound on distillable
entanglement. Furthermore, it is convex, additive on tensor products, and
superadditive in general.
Continuity in the state is the only property of our entanglement measure
which we cannot provide a proof for. We present some evidence, however, that
our quantity has this property, the strongest indication being a conjectured
Fannes type inequality for the conditional von Neumann entropy. This inequality
is proved in the classical case.Comment: 8 pages, revtex4. v2 has some more references and a bit more
discussion, v3 continuity discussion extended, typos correcte
On the Treatment of Neutrino Oscillations Without Resort to Weak Eigenstates
We discuss neutrino oscillations in the framework of the quantum field theory
without introducing the concept of neutrino weak eigenstates. The external
particles are described by wave packets and the different mass eigenstate
neutrinos propagate between the production and detection interactions, which
are macroscopically localized in space-time. The time-averaged cross section,
which is the measurable quantity in the usual experimental setting, is
calculated. It is shown that only in the extremely relativistic limit the usual
quantum mechanical oscillation probability can be factored out of the cross
section.Comment: LaTeX-18pages, JHU-TIPAC-930011,DFTT 22/9
Macroscopic Quantum Tunneling of Ferromagnetic Domain Walls
Quantum tunneling of domain walls out of an impurity potential in a
mesoscopic ferromagnetic sample is investigated. Using improved expressions for
the domain wall mass and for the pinning potential, we find that the cross-over
temperature between thermal activation and quantum tunneling is of a different
functional form than found previously. In materials like Ni or YIG, the
crossover temperatures are around 5 mK. We also find that the WKB exponent is
typically two orders of magnitude larger than current estimates. The sources
for these discrepancies are discussed, and precise estimates for the transition
from three-dimensional to one-dimensional magnetic behavior of a wire are
given. The cross-over temperatures from thermal to quantum transitions and
tunneling rates are calculated for various materials and sample sizes.Comment: 10 pages, 2 postscript figures, REVTe
NGC300 X-1 and IC10 X-1: a new breed of black hole binary?
[ABRIDGED] IC10 X-1 has recently been confirmed as a black hole (BH) +
Wolf-Rayet (WR) X-ray binary, and NGC300 X-1 is thought to be. IC10 X-1 and
NGC300 X-1 have similar X-ray properties, with luminosities ~10^38 erg/s, and
orbital periods ~30 hr. We investigate similarities between these two, as well
as differences between them and the known Galactic BH binary systems. We have
examined XMM-Newton observations of NGC300 X-1 and IC10 X-1. We extracted
lightcurves and spectra; power density spectra (PDS) were constructed from the
lightcurves, and the X-ray emission spectra were modeled. Each source exhibits
PDS that are characteristic of disc-accreting X-ray binaries (XBs) in the high
state. In this state, Galactic XBs with known BH primaries have soft, thermal
emission; however the emission spectra of our targets are predominantly
non-thermal. Furthermore, the Observation 1 spectrum of NGC300 X-1 is
strikingly similar to that of IC10 X-1. The remarkable similarity between the
behaviour of NGC300 X-1 in Observation 1 and that of IC10 X-1 lends strong
evidence for NGC300 X-1 being a (BH+WR) binary. The unusual spectra of NGC300
X-1 and IC10 X-1 may be due to these systems existing in a persistently high
state, whereas all known BH LMXBs are transient. BH XBs in a persistent high
state could retain their corona, and hence exhibit a large non-thermal
component. LMC X-1 is a BH XB that has only been observed in the high state,
and its spectrum is remarkably similar to those of our targets. We therefore
classify NGC300 X-1, IC10 X-1 and perhaps LMC X-1 as a new breed of BH XB,
defined by their persistently high accretion rates and consequent stable disc
configuration and corona. This scenario may also explain the lack of
ultraluminous X-ray sources in the canonical soft state.Comment: Approved for publication in A&A. 8 pages, 5 figure
Critical behaviour of the Rouse model for gelling polymers
It is shown that the traditionally accepted "Rouse values" for the critical
exponents at the gelation transition do not arise from the Rouse model for
gelling polymers. The true critical behaviour of the Rouse model for gelling
polymers is obtained from spectral properties of the connectivity matrix of the
fractal clusters that are formed by the molecules. The required spectral
properties are related to the return probability of a "blind ant"-random walk
on the critical percolating cluster. The resulting scaling relations express
the critical exponents of the shear-stress-relaxation function, and hence those
of the shear viscosity and of the first normal stress coefficient, in terms of
the spectral dimension of the critical percolating cluster and the
exponents and of the cluster-size distribution.Comment: 9 pages, slightly extended version, to appear in J. Phys.
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