22,534 research outputs found
Beyond the soft photon approximation in radiative production and decay of charged vector mesons
We study the effects of model-dependent contributions and the electric
quadrupole moment of vector mesons in the decays and
. Their interference with the amplitude originating
from the radiation due to electric charges vanishes for photons emitted
collinearly to the charged particle in the final state. This brings further
support to our claim in previous works, that measurements of the photon energy
spectrum for nearly collinear photons in those decays are suitable for a first
measurement of the magnetic dipole moment of charged vector mesons.Comment: 13 pages, 2 eps figures, Latex. Accepted for publication in Journal
of Physics G: Nuclear and Particle Physics(2001
Shadowing by non uniformly hyperbolic periodic points and uniform hyperbolicity
We prove that, under a mild condition on the hyperbolicity of its periodic
points, a map which is topologically conjugated to a hyperbolic map
(respectively, an expanding map) is also a hyperbolic map (respectively, an
expanding map). In particular, this result gives a partial positive answer for
a question done by A. Katok, in a related context
Coulomb blockade in graphene nanoribbons
We propose that recent transport experiments revealing the existence of an
energy gap in graphene nanoribbons may be understood in terms of Coulomb
blockade. Electron interactions play a decisive role at the quantum dots which
form due to the presence of necks arising from the roughness of the graphene
edge. With the average transmission as the only fitting parameter, our theory
shows good agreement with the experimental data.Comment: 4 pages, 2 figure
Long-distance radiative corrections to the di-pion tau lepton decay
We evaluate the model-dependent piece of O(alpha) long-distance radiative
corrections to tau^- \to \pi^- \pi^0\nu_{\tau} decays by using a meson
dominance model. We find that these corrections to the di-pion invariant mass
spectrum are smaller than in previous calculations based on chiral perturbation
theory. The corresponding correction to the photon inclusive rate is tiny
(-0.15%) but it can be of relevance when new measurements reach better
precision.Comment: 4 pages, 2 figures. An estimate of the shift produced in the
evaluation of the h.v.p. contribution to the muon anomalous magnetic moment
is added. Version to appear in Phys. Rev.
Clinical Dilemma in the Treatment of a Patient with Microangiopathic Haemolytic Anaemia, Thrombocytopaenia and Severe Hypertension
While haemolytic uraemic syndrome in children is predominantly associated with Shiga toxin -producing Escherichia coli (typically 0157:H7), some cases occur without associated diarrhoea, or as the manifestation of an underlying disorder other than infection.
Haemolytic uraemic syndrome is characterised
by microangiopathic anaemia, thrombocytopaenia
and renal failure, on occasion accompanied by severe hypertension. Malignant hypertension is a syndrome that sometimes exhibits the same laboratory abnormalities
as haemolytic uraemic syndrome as it may
share the same pathological findings: thrombotic microangiopathy. As clinical features of both entities overlap, the distinction between them can be very
difficult. However, differentiation is essential for the treatment decision, since early plasma exchange dramatically reduces mortality in haemolytic uraemic syndrome not associated with diarrhoea. An increasing
number of genetic causes of this pathology have been described and may be very useful in differentiating it from thrombotic microangiopathy due to other aetiologies. Despite advances in the understanding
of the pathophysiology of haemolytic uraemic
syndrome not associated with diarrhoea, the
management often remains empirical. We describe a patient with simultaneous microangiopathic haemolytic
anaemia, thrombocytopaenia and severe hypertension managed in the acute period of illness with plasma exchange
Regulating entanglement production in multitrap Bose-Einstein condensates
A system of traps is considered, each containing a large number of
Bose-condensed atoms. This ensemble of traps is subject to the action of an
external modulating field generating nonequilibrium nonground-state
condensates. When the frequency of the modulating field is in resonance with
the transition frequency between two different topological coherent modes, each
trap becomes an analog of a finite-level resonant atom. Similarly to the case
of atoms in an electromagnetic resonant field, one can create entanglement
between atomic traps subject to a common resonant modulating field generating
higher coherent modes in each of the traps. A method is suggested for
regulating entanglement production in such a system of multitrap and multimode
Bose-Einstein condensates coupled through a common resonant modulating field.
Several regimes of evolutional entanglement production, regulated by
manipulating the external field, are illustrated by numerical calculations.Comment: Latex file, 3 figure
Dirac fermions in a power-law-correlated random vector potential
We study localization properties of two-dimensional Dirac fermions subject to
a power-law-correlated random vector potential describing, e.g., the effect of
"ripples" in graphene. By using a variety of techniques (low-order perturbation
theory, self-consistent Born approximation, replicas, and supersymmetry) we
make a case for a possible complete localization of all the electronic states
and compute the density of states.Comment: Latex, 4+ page
NGC 3105: a young open cluster with low metallicity
NGC 3105 is a young open cluster hosting blue, yellow and red supergiants.
This rare combination makes it an excellent laboratory to constrain
evolutionary models of high-mass stars. It is poorly studied and fundamental
parameters such as its age or distance are not well defined. We intend to
characterize in an accurate way the cluster as well as its evolved stars, for
which we derive for the first time atmospheric parameters and chemical
abundances. We identify 126 B-type likely members within a radius of
2.70.6 arcmin, which implies an initial mass, 4100
M. We find a distance of 7.20.7 kpc for NGC 3105, placing it at
=10.01.2 kpc. Isochrone fitting supports an age of 286 Ma,
implying masses around 9.5 M for the supergiants. A high fraction of
Be stars (25 %) is found at the top of the main sequence down to
spectral type b3. From the spectral analysis we estimate for the cluster a
=+46.90.9 km s and a low metallicity,
[Fe/H]=-0.290.22. We also have determined, for the first time, chemical
abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved
stars. The chemical composition of the cluster is consistent with that of the
Galactic thin disc. An overabundance of Ba is found, supporting the enhanced
-process. NGC 3105 has a low metallicity for its Galactocentric distance,
comparable to typical LMC stars. It is a valuable spiral tracer in a very
distant region of the Carina-Sagittarius spiral arm, a poorly known part of the
Galaxy. As one of the few Galactic clusters containing blue, yellow and red
supergiants, it is massive enough to serve as a testbed for theoretical
evolutionary models close to the boundary between intermediate and high-mass
stars.Comment: 18 pages, 13 figures. Accepted for publication in A&
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