12,746 research outputs found
Classical versus Quantum Structure of the Scattering Probability Matrix. Chaotic wave-guides
The purely classical counterpart of the Scattering Probability Matrix (SPM)
of the quantum scattering matrix is defined for 2D
quantum waveguides for an arbitrary number of propagating modes . We compare
the quantum and classical structures of for a waveguide
with generic Hamiltonian chaos. It is shown that even for a moderate number of
channels, knowledge of the classical structure of the SPM allows us to predict
the global structure of the quantum one and, hence, understand important
quantum transport properties of waveguides in terms of purely classical
dynamics. It is also shown that the SPM, being an intensity measure, can give
additional dynamical information to that obtained by the Poincar\`{e} maps.Comment: 9 pages, 9 figure
Top quark physics in hadron collisions
The top quark is the heaviest elementary particle observed to date. Its large
mass makes the top quark an ideal laboratory to test predictions of
perturbation theory concerning heavy quark production at hadron colliders. The
top quark is also a powerful probe for new phenomena beyond the Standard Model
of particle physics. In addition, the top quark mass is a crucial parameter for
scrutinizing the Standard Model in electroweak precision tests and for
predicting the mass of the yet unobserved Higgs boson. Ten years after the
discovery of the top quark at the Fermilab Tevatron top quark physics has
entered an era where detailed measurements of top quark properties are
undertaken. In this review article an introduction to the phenomenology of top
quark production in hadron collisions is given, the lessons learned in Tevatron
Run I are summarized, and first Run II results are discussed. A brief outlook
to the possibilities of top quark research a the Large Hadron Collider,
currently under construction at CERN, is included.Comment: 84 pages, 32 figures, accepted for publication by Reports on Progress
in Physic
Delivering genetic education and genetic counseling for rare diseases in rural Brazil
Brazil is the largest country in Latin America, with an ethnically diverse, Portuguese-speaking and predominantly Roman Catholic population of some 194 million. Universal health care is provided under the Federal Unified Health System (Sistema Único de Saúde) but, as in many other middle and low income countries, access to medical genetics services is limited in rural and remote regions of the country. Since there is no formally recognized Genetic Counseling profession, genetic counseling is provided by physicians, trained either in medical genetics or a related clinical discipline. A comprehensive medical genetics program has been established in Monte Santo, an inland rural community located in the state of Bahia in Northeast Brazil, with high prevalences of a number of autosomal recessive genetic disorders, including non-syndromic deafness, phenyketonuria, congenital hypothyroidism and mucopolysaccharidosis VI (Maroteaux-Lamy syndrome). Genetic education, counseling and treatment are locally provided, with a neonatal screening program for MPSVI currently under trial
Open Charm Production at STAR
We present the open charm spectra at mid-rapidity from direct reconstruction
of D0, D* and D+/- in d+Au collisions at sqrt(sNN)=200 GeV using the STAR
detector at RHIC. The indirect electron/positron measurements via charm
semileptonic decays in p+p and d+Au collisions are also reported. The total
c\bar(c) cross section per nucleon-nucleon collision is extracted from both
direct and indirect measurements and are consistent with each other. By
combining the D0 and semileptonic measurements together, the cross section of
1.4+/-0.2+/-0.4 mb is higher than expectations from PYTHIA and other pQCD
calculations. The open charm pT distribution from direct measurements covers
the pT range up to ~10 GeV/c and follows a power-law distribution.Comment: 7 pages, 4 figures, proceedings for Hot Quark 04 Conference.
submitted to J. Phys. G: Nucl. Phy
Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR
We study the nature of the quasiinvariants in nematic 5CB and measure their
relaxation times by encoding the multiple quantum coherences of the states
following the JB pulse pair on two orthogonal bases, Z and X. The experiments
were also performed in powder adamantane at 301 K which is used as a reference
compound having only one dipolar quasiinvariant. We show that the evolution of
the quantum states during the build up of the quasi-equilibrium state in 5CB
prepared under the S condition is similar to the case of adamantane and that
their quasi-equilibrium density operators have the same tensor structure. In
contrast, the second constant of motion, whose explicit operator form is not
known, involves a richer composition of multiple quantum coherences on the X
basis of even order, in consistency with the truncation inherent in its
definition. We exploited the exclusive presence coherences 4, 6, 8, besides 0
and 2 under the W condition to measure the spin-lattice relaxation time T_{W}
accurately, so avoiding experimental difficulties that usually impair dipolar
order relaxation measurement such as Zeeman contamination at high fields, and
also superposition of the different quasiinvariants. This procedure opens the
possibility of measuring the spin-lattice relaxation of a quasiinvariant
independent of the Zeeman and S reservoirs, so incorporating a new relaxation
parameter useful for studying the complex molecular dynamics in mesophases. In
fact, we report the first measurement of T_{W} in a liquid crystal at high
magnetic fields. The comparison of the obtained value with the one
corresponding to a lower field (16 MHz) points out that the relaxation of the
W-order strongly depends on the intensity of the external magnetic field,
similarly to the case of the S reservoir, indicating that the relaxation of the
W-quasiinvariant is also governed by the cooperative molecular motions.Comment: 7 figures. http://www.famaf.unc.edu.ar/series/AFis2005.ht
Ground-based near-IR observations of the secondary eclipse of CoRoT-2b
We present the results of a ground-based search for the secondary eclipse of
the 3.3 Mjup transiting planet CoRoT-2b. We performed near infrared photometry
using the LIRIS instrument on the 4.2 m William Herschel Telescope, in the H
and K_s filters. We monitored the star around two expected secondary eclipses
in two nights under very good observing conditions. For the depth of the
secondary eclipse we find in H-band a 3 sigma upper limit of 0.17%, whereas we
detected a tentative eclipse with a depth of 0.16+-0.09% in the K_s-band. These
depths can be translated into brightness temperatures of T_H<2250 K and T_{K_s}
= 1890(+260-350) K, which indicate an inefficient re-distribution of the
incident stellar flux from the planet's dayside to its nightside. Our results
are in agreement with the CoRoT optical measurement (Alonso et al. 09) and with
Spitzer 4.5 and 8 micron results (Gillon et al. 09c).Comment: Astronomical Journal, accepte
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