16,499 research outputs found
XYZ-polarisation analysis of diffuse magnetic neutron scattering from single crystals
Studies of diffuse magnetic scattering largely benefit from the use of a
multi-detector covering wide scattering angles. Therefore, the different
contributions to the diffuse scattering that originate from magnetic, nuclear
coherent, and nuclear spin-incoherent scattering can be separated by the
so-called XYZ-polarization analysis. In the past this method has been
successfully applied to the analysis of diffuse scattering by polycrystalline
samples of magnetic disordered materials. Single crystal studies that exploit
the vector properties of spin correlations are of particular interest for
furthering our understanding of frustration effects in magnetism. Based on the
symmetry properties of polarised scattering a suitable extension of the
conventional XYZ method has been derived, which allows for the complete
separation and the analysis of features of diffuse magnetic scattering from
single crystals.Comment: 6 pages 2 figures, revised as published, one Eq. removed, minor
corrections, typos correcte
Characterization of a Second Bovine Rotavirus Serotype
Bovine rotavirus (BRV) V 1005 was characterized by two-way cross-neutralization tests as a second serotype of BRV. Virions and inner shell particles of 65 nm and 55 nm diameter respectively, and empty capsids of 65 nm and 55 nm diameter were separated by density gradient centrifugation. Three polypeptides of molecular weight 60,000, 36,000 and 28,000 (minor protein) could be identified in the outer shell of virions and in the larger empty capsids. Inner shell particles contained three polypeptides of molecular weight 105,000, 83,000 and 43,000. Both sizes of empty capsids showed two polypeptides of molecular weight 75,000 and 55,000 not found in virions. Pulse-labelling of infected cells revealed eight major and three minor intracellular viral polypeptides. Viral polypeptide synthesis started at about 6 hours p.i. and correlated in time with double-stranded RNA synthesis. As soon as viral polypeptide synthesis was detectable, newly synthesized viral polypeptides were incorporated into intracellular viral particles. Radioactive viral polypeptides appeared without a longer lag period in extracellular viruses from 6 hours p.i. onward
Band-aid for information loss from black holes
We summarize, simplify and extend recent work showing that small deviations
from exact thermality in Hawking radiation, first uncovered by Kraus and
Wilczek, have the capacity to carry off the maximum information content of a
black hole. This goes a considerable way toward resolving a long-standing
"information-loss paradox"
Single-Particle Momentum Distribution of an Efimov trimer
Experimental progress in the study of strongly interacting ultracold atoms
has recently allowed the observation of Efimov trimers. We study theoretically
a non-conventional observable for these trimer states, that may be accessed
experimentally, the momentum distribution n(k) of the constitutive bosonic
particles. The large momentum part of the distribution is particularly
intriguing: In addition to the expected 1/k^4 tail associated to contact
interactions, it exhibits a subleading tail 1/k^5 which is a hall-mark of
Efimov physics and leads to a breakdown of a previously proposed expression of
the energy as a functional of the momentum distribution.Comment: This is a subpart of the (too long to be published) work
arXiv:1001.0774. This subpart has 11 pages and 2 figures. Revised version
correcting minor error
A non-pulsating neutron star in the supernova remnant HESS J1731-347 / G353.6-0.7 with a carbon atmosphere
Context: The CCO candidate in the center of the supernova remnant shell HESS
J1731-347 / G353.6-0.7 shows no pulsations and exhibits a blackbody-like X-ray
spectrum. If the absence of pulsations is interpreted as evidence for the
emitting surface area being the entire neutron star surface, the assumption of
the measured flux being due to a blackbody emission translates into a source
distance that is inconsistent with current estimates of the remnant's distance.
Aims: With the best available observational data, we extended the pulse period
search down to a sub-millisecond time scale and used a carbon atmosphere model
to describe the X-ray spectrum of the CCO and to estimate geometrical
parameters of the neutron star. Methods: To search for pulsations we used data
of an observation of the source with XMM-Newton performed in timing mode. For
the spectral analysis, we used earlier XMM-Newton observations performed in
imaging mode, which permits a more accurate treatment of the background. The
carbon atmosphere models used to fit the CCO spectrum are computed assuming
hydrostatic and radiative equilibria and take into account pressure ionization
and the presence of spectral lines. Results: Our timing analysis did not reveal
any pulsations with a pulsed fraction above ~8% down to 0.2 ms. This finding
further supports the hypothesis that the emitting surface area is the entire
neutron star surface. The carbon atmosphere model provides a good fit to the
CCO spectrum and leads to a normalization consistent with the available
distance estimates of the remnant. The derived constraints on the mass and
radius of the source are consistent with reasonable values of the neutron star
mass and radius. After the CCO in Cas A, the CCO in HESS J1731-347 / G353.6-0.7
is the second object of this class for which a carbon atmosphere model provides
a consistent description of X-ray emission.Comment: 6 pages, 5 figures, accepted for publication in
Astronomy&Astrophysic
Violation of Bell's inequalities implies distillability for N qubits
We consider quantum systems composed of qubits, and the family of all
Bell's correlation inequalities for two two-valued measurements per site. We
show that if a -qubit state violates any of these inequalities, then
it is at least bipartite distillable. Indeed there exists a link between the
amount of Bell's inequality violation and the degree of distillability. Thus,
we strengthen the interpretation of Bell's inequalities as detectors of useful
entanglement.Comment: 6 pages, 3 figures, REVTEX. List of authors extended. Partially
rewritten, a rather qualitative explanation of the results. Conclusions
unchange
Ultra-High Energy Cosmic Rays: Some General Features, and Recent Developments Concerning Air Shower Computations
We present an introductory lecture on general features of cosmic rays, for
non-experts, and some recent developments concerning cascade equations for air
shower developments.Comment: invited talk, presented at the Hadron-RANP2004 worksho
The Properties of Outer Retinal Band Three Investigated With Adaptive-Optics Optical Coherence Tomography.
PurposeOptical coherence tomography's (OCT) third outer retinal band has been attributed to the zone of interdigitation between RPE cells and cone outer segments. The purpose of this paper is to investigate the structure of this band with adaptive optics (AO)-OCT.MethodsUsing AO-OCT, images were obtained from two subjects. Axial structure was characterized by measuring band 3 thickness and separation between bands 2 and 3 in segmented cones. Lateral structure was characterized by correlation of band 3 with band 2 and comparison of their power spectra. Band thickness and separation were also measured in a clinical OCT image of one subject.ResultsBand 3 thickness ranged from 4.3 to 6.4 μm. Band 2 correlations ranged between 0.35 and 0.41 and power spectra of both bands confirmed peak frequencies that agree with histologic density measurements. In clinical images, band 3 thickness was between 14 and 19 μm. Measurements of AO-OCT of interband distance were lower than our corresponding clinical OCT measurements.ConclusionsBand 3 originates from a structure with axial extent similar to a single surface. Correlation with band 2 suggests an origin within the cone photoreceptor. These two observations indicate that band 3 corresponds predominantly to cone outer segment tips (COST). Conventional OCT may overestimate both the thickness of band 3 and outer segment length
On the attractors of two-dimensional Rayleigh oscillators including noise
We study sustained oscillations in two-dimensional oscillator systems driven
by Rayleigh-type negative friction. In particular we investigate the influence
of mismatch of the two frequencies. Further we study the influence of external
noise and nonlinearity of the conservative forces. Our consideration is
restricted to the case that the driving is rather weak and that the forces show
only weak deviations from radial symmetry. For this case we provide results for
the attractors and the bifurcations of the system. We show that for rational
relations of the frequencies the system develops several rotational excitations
with right/left symmetry, corresponding to limit cycles in the four-dimensional
phase space. The corresponding noisy distributions have the form of hoops or
tires in the four-dimensional space. For irrational frequency relations, as
well as for increasing strength of driving or noise the periodic excitations
are replaced by chaotic oscillations.Comment: 9 pages, 5 figure
Central engines of Gamma Ray Bursts. Magnetic mechanism in the collapsar model
In this study we explore the magnetic mechanism of hypernovae and
relativistic jets of long duration gamma ray bursts within the collapsar
scenario. This is an extension of our earlier work [1]. We track the collapse
of massive rotating stars onto a rotating central black hole using axisymmetric
general relativistic magnetohydrodynamic code that utilizes a realistic
equation of state and takes into account the cooling associated with emission
of neutrinos and the energy losses due to dissociation of nuclei. The neutrino
heating is not included. We describe solutions with different black hole
rotation, mass accretion rate, and strength of progenitor's magnetic field.
Some of them exhibits strong explosions driven by Poynting-dominated jets with
power up to . These jets originate from the black
hole and powered via the Blandford-Znajek mechanism. A provisional criterion
for explosion is derived. A number of simulation movies can be downloaded from
http://www.maths.leeds.ac.uk/~serguei/research/movies/anim.htmlComment: 4 pages, 3 figures, GAMMA08 Heidelberg Symposiu
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