341 research outputs found
A single structured light beam as an atomic cloud splitter
We propose a scheme to split a cloud of cold non-interacting neutral atoms
based on their dipole interaction with a single structured light beam which
exhibits parabolic cylindrical symmetry. Using semiclassical numerical
simulations, we establish a direct relationship between the general properties
of the light beam and the relevant geometric and kinematic properties acquired
by the atomic cloud as its passes through the beam.Comment: 10 pages, 5 figure
Comment on "Fermionic entanglement ambiguity in noninertial frames"
In this comment we show that the ambiguity of entropic quantities calculated
in Physical Review A 83, 062323 (2011) for fermionic fields in the context of
Unruh effect is not related to the properties of anticommuting fields, as
claimed in Physical Review A 83, 062323 (2011), but rather to wrong
mathematical manipulations with them and not taking into account a fundamental
superselection rule of quantum field theory.Comment: To appear in Physical Review A. Some of the problems discussed in
this comment can also be found in other previously published papers studying
the Unruh effect for fermions (in the context of quantum information theory).
An extended version of the comment can be found here
http://arxiv.org/abs/1108.555
Optical scalar beam propagation in nontrivial spacetime backgrounds
We study the propagation of structured optical scalar beams in a spacetime
background parameterized by a second-rank symmetric tensor. An analytic
expression for the Green's function in a cylindrical coordinate system is
obtained for particular choices of such a tensor. This facilitates the
numerical exploration of the propagation of apertured Gaussian beams in this
nontrivial background. Unusual focusing properties are found along with a
decrease in the Gouy phase compared to that in standard vacuum. In the case of
apertured Bessel beams, the medium allows to overcome finite aperture effects
so that the corresponding diffraction length is increased; besides, the central
spot of a zero order Bessel concentrates an increased fraction of the energy of
the beam. Multiple scenarios beyond an electromagnetic field in the presence of
an anisotropic medium could support the results reported here. They include a
bosonic field in a weak gravitational field or a nontrivial spacetime
background arising from Lorentz symmetry breaking. In particular, our results
could illustrate how optically transparent multiferroic materials offer
unprecedented opportunities to tailor structured beam propagation, as well as
to simulate nontrivial spacetime backgrounds.Comment: 15 pages, 24 figure
Rotational Effects of Twisted Light on Atoms Beyond the Paraxial Approximation
The transition probability for the emission of a Bessel photon by an atomic
system is calculated within first order perturbation theory. We derive a closed
expression for the electromagnetic potentials beyond the paraxial approximation
that permits a systematic multipole approximation . The matrix elements between
center of mass and internal states are evaluated for some specially relevant
cases. This permits to clarify the feasibility of observing the rotational
effects of twisted light on atoms predicted by the calculations. It is shown
that the probability that the internal state of an atom acquires orbital
angular momentum from light is, in general, maximum for an atom located at the
axis of a Bessel mode. For a Gaussian packet, the relevant parameter is the
ratio of the spread of the atomic center of mass wave packet to the transversal
wavelength of the photon.Comment: 10 pages, no figure
Hepatozoonosis canina
Se diagnosticó hepatozoonosis en cuatro perras de raza beagle que habían sufrido una infestación masiva por garrapatas. Se describe el cuadro clínico, protocolo laboratorial, diagnóstico diferencial, tratamiento y evolución. Tras eliminar la presencia de otros procesos patológicos, concluimos que Hepatozoon canis produce una reacción leucoeritroblástica, que remite con el tratamiento.The study diagnosed canine hepatozoonosis in four Beagles, that become infested with ticks. It describes the clinical signs, laboratory protocol, diferential diagnosis, treatment and evolution. After eliminate the presence of other pathology, we conclude what Heparozoon canis causes a leucoeritroblastic reaction, that remit with treatment
Capacities of Grassmann channels
A new class of quantum channels called Grassmann channels is introduced and
their classical and quantum capacity is calculated. The channel class appears
in a study of the two-mode squeezing operator constructed from operators
satisfying the fermionic algebra. We compare Grassmann channels with the
channels induced by the bosonic two-mode squeezing operator. Among other
results, we challenge the relevance of calculating entanglement measures to
assess or compare the ability of bosonic and fermionic states to send quantum
information to uniformly accelerated frames.Comment: 33 pages, Accepted in Journal of Mathematical Physics; The role of
the (fermionic) braided tensor product for quantum Shannon theory, namely
capacity formulas, elucidated; The conclusion on the equivalence of Unruh
effect for bosons and fermions for quantum communication purposes made clear
and even more precis
A relativistic study of Bessel beams
We present a fully relativistic analysis of Bessel beams revealing some
noteworthy features that are not explicit in the standard description. It is
shown that there is a reference frame in which the field takes a particularly
simple form, the wave appearing to rotate in circles. The concepts of
polarization and angular momentum for Bessel beams is also reanalyzed.Comment: 11 pages, 2 fig
All-Optical Production of a Degenerate Fermi Gas
We achieve degeneracy in a mixture of the two lowest hyperfine states of
Li by direct evaporation in a CO laser trap, yielding the first
all-optically produced degenerate Fermi gas. More than atoms are
confined at temperatures below K at full trap depth, where the Fermi
temperature for each state is K. This degenerate two-component mixture
is ideal for exploring mechanisms of superconductivity ranging from Cooper
pairing to Bose condensation of strongly bound pairs.Comment: 4 pgs RevTeX with 2 eps figs, to be published in Phys. Rev. Let
Documentación y análisis arquitectónico en el País Vasco. Algunas experiencias llevadas a cabo en Álava-España
Intravenous immunoglobulin to prevent myasthenic crisis after thymectomy and other procedures can be omitted in patients with well-controlled myasthenia gravis
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was funded by a Fondo de Investigación Sanitaria (FIS-FEDER) (grants PI16-01673 and PI19/00593) and an Interlaken Research Award Programme (2012-12094537).Background: Myasthenic crisis (MC) is a potentially life-threatening complication of myasthenia gravis. Its precipitating factors include surgical procedures, particularly thymectomy. The role of preoperative intravenous immunoglobulin (IVIg) in preventing MC in patients scheduled for thymectomy and other surgery with general anaesthesia is unknown. Our objective was to test the hypothesis that preoperative IVIg is effective in preventing myasthenic crisis in patients with myasthenia gravis scheduled for surgery under general anaesthesia, including thymectomy. Methods: A prospective, randomized, double-blind, single-centre study was conducted over a 4-year period. The treatment group received IVIg, 0.4 g/kg/day preoperatively for 5 consecutive days, and the placebo group received saline solution under the same conditions. The two groups were age-matched, with similar functional status, and Myasthenia Gravis Foundation of America class. All patients had well-controlled myasthenia gravis with minimal manifestations before surgery. The primary outcome measured was MC. Intubation times, time in the recovery room, number of postoperative complications, and days of hospitalization were the secondary outcomes measured. Results: A total of 47 patients were randomized, 25 to the IVIg group and 22 to placebo. There were 19 men and 28 women, with a mean age of 58.6 years, mean body mass index of 27.8 kg/m, and mean acetylcholine receptor antibodies of 12.9 nmol/l. The mean forced vital capacity was 84.4%. The mean quantitative myasthenia gravis sum score was 6.3. Ten patients (five in each arm) had a history of MC. Thymectomy was performed in 16 patients. Only one patient in the placebo group presented with MC requiring non-invasive ventilation (but no reintubation) for 6 days. Neither differences between groups in the univariate analysis nor risk factors for MC in the multivariate analysis were found. Conclusions: Preoperative IVIg to prevent MC does not appear to be justified in well-controlled myasthenia gravis patients. This study provides class I evidence that preparation with IVIg to prevent MC is not necessary in well-controlled myasthenia gravis patients scheduled for surgery with general anaesthesia
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