1,250 research outputs found
Pediatric epstein-barr virus carriers with or without tonsillar enlargement may substantially contribute to spreading of the virus
BACKGROUND: Human-to-human transmission of the persistent infection establishing Epstein-Barr virus (EBV) occurs via saliva. Tonsils act as important portal of entry and exit of EBV. The contagiousness of pediatric EBV carriers and the role played by tonsillar enlargement (TE) are not known. METHODS: We compared EBV shedding in mouthwash samples from pediatric EBV carriers with or without TE to that in mouthwash samples from pediatric patients with infectious mononucleosis (IM), the symptomatic form of primary infection if delayed after the age of 5 years. EBV DNA was quantified by polymerase chain reaction, and contagiousness was assessed using the cord lymphocyte transformation assay. RESULTS: EBV carriers with TE shed EBV DNA at an almost similar frequency (although in lower amounts) as pediatric patients with acute IM but more frequently (P <.001) and in higher amounts (P = .038) than EBV carriers without TE. EBV DNA levels in mouthwash samples from EBV carriers with TE mirrored levels in tonsils and gradually declined after tonsillectomy. Almost half of the mouthwash samples from pediatric EBV carriers contained infectious EBV. CONCLUSIONS: Pediatric EBV carriers--in particular, those with TE-may considerably contribute to the spreading of EBV in industrialized countries
A multi-detector array for high energy nuclear e+e- pair spectrosocopy
A multi-detector array has been constructed for the simultaneous measurement
of energy- and angular correlation of electron-positron pairs produced in
internal pair conversion (IPC) of nuclear transitions up to 18 MeV. The
response functions of the individual detectors have been measured with
mono-energetic beams of electrons. Experimental results obtained with 1.6 MeV
protons on targets containing B and F show clear IPC over a wide
angular range. A comparison with GEANT simulations demonstrates that angular
correlations of pairs of transitions in the energy range between 6 and
18 MeV can be determined with sufficient resolution and efficiency to search
for deviations from IPC due to the creation and subsequent decay into
of a hypothetical short-lived neutral boson.Comment: 20 pages, 8 figure
Critical behavior of the long-range Ising chain from the largest-cluster probability distribution
Monte Carlo simulations of the 1D Ising model with ferromagnetic interactions
decaying with distance as are performed by applying the
Swendsen-Wang cluster algorithm with cumulative probabilities. The critical
behavior in the non-classical critical regime corresponding to is derived from the finite-size scaling analysis of the largest cluster.Comment: 4 pages, 2 figures, in RevTeX, to appear in Phys. Rev. E (Feb 2001
Criticality in one dimension with inverse square-law potentials
It is demonstrated that the scaled order parameter for ferromagnetic Ising
and three-state Potts chains with inverse-square interactions exhibits a
universal critical jump, in analogy with the superfluid density in helium
films. Renormalization-group arguments are combined with numerical simulations
of systems containing up to one million lattice sites to accurately determine
the critical properties of these models. In strong contrast with earlier work,
compelling quantitative evidence for the Kosterlitz--Thouless-like character of
the phase transition is provided.Comment: To appear in Phys. Rev. Let
Z_2-gradings of Clifford algebras and multivector structures
Let Cl(V,g) be the real Clifford algebra associated to the real vector space
V, endowed with a nondegenerate metric g. In this paper, we study the class of
Z_2-gradings of Cl(V,g) which are somehow compatible with the multivector
structure of the Grassmann algebra over V. A complete characterization for such
Z_2-gradings is obtained by classifying all the even subalgebras coming from
them. An expression relating such subalgebras to the usual even part of Cl(V,g)
is also obtained. Finally, we employ this framework to define spinor spaces,
and to parametrize all the possible signature changes on Cl(V,g) by
Z_2-gradings of this algebra.Comment: 10 pages, LaTeX; v2 accepted for publication in J. Phys.
Explosive nucleosynthesis in core-collapse supernovae
The specific mechanism and astrophysical site for the production of half of
the elements heavier than iron via rapid neutron capture (r-process) remains to
be found. In order to reproduce the abundances of the solar system and of the
old halo stars, at least two components are required: the heavy r-process
nuclei (A>130) and the weak r-process which correspond to the lighter heavy
nuclei (A<130). In this work, we present nucleosynthesis studies based on
trajectories of hydrodynamical simulations for core-collapse supernovae and
their subsequent neutrino-driven winds. We show that the weak r-process
elements can be produced in neutrino-driven winds and we relate their
abundances to the neutrino emission from the nascent neutron star. Based on the
latest hydrodynamical simulations, heavy r-process elements cannot be
synthesized in the neutrino-driven winds. However, by artificially increasing
the wind entropy, elements up to A=195 can be made. In this way one can mimic
the general behavior of an ejecta where the r-process occurs. We use this to
study the impact of the nuclear physics input (nuclear masses, neutron capture
cross sections, and beta-delayed neutron emission) and of the long-time
dynamical evolution on the final abundances.Comment: 10 pages, 8 figures, invited talk, INPC 2010 Vancouver, Journal of
Physics: Conference Serie
Spin-charge gauge approach to metal-insulator crossover and transport properties in High-T cuprates
The spin-charge gauge approach to consider the metal-insulator crossover
(MIC) and other anomalous transport properties in High-T cuprates is
briefly reviewed. A U(1) field gauging the global charge symmetry and an SU(2)
field gauging the global spin-rotational symmetry are introduced to study the
two-dimensional model in the limit . The MIC as a clue to the
understanding of the ``pseudogap'' (PG) phase, is attributed to the competition
between the short-range antiferromagnetic order and dissipative motion of
charge carriers coupled to the slave-particle gauge field. The composite
particle formed by binding the charge carrier (holon) and spin excitation
(spinon) via the slave particle gauge field exhibits a number of peculiar
properties, and the calculated results are in good agreement with experimental
data for both PG and ``strange metal'' phases. Connections to other gauge field
approaches in studying the strong correlation problem are also briefly
outlined.Comment: 32 pages, to appear in the special issue on "Correlated Electrons" of
J. Phys.: Condens. Mat
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