840 research outputs found
High nuclear polarization of helium-3 at low and high pressure by metastability exchange optical pumping at 1.5 Tesla
We perform metastability exchange optical pumping of helium-3 in a strong
magnetic field of 1.5 T. The achieved nuclear polarization, from 80% at 1.33
mbar to 25% at 67 mbar, shows a substantial improvement at high pressures with
respect to standard low-field optical pumping. The specific mechanisms of
metastability exchange optical pumping at high field are investigated,
advantages and intrinsic limitations are discussed. From a practical point of
view, our results open the way to alternative technological solutions for
polarized helium-3 applications and in particular for magnetic resonance
imaging of human lungs.Comment: accepted for publication in Europhysics Letter
Clues to the nature of the Delta^*(1700) resonance from pion- and photon-induced reactions
We make a study of the (pi^- p --> K^0 pi^0 Lambda), (pi^+ p --> K^+ pi^+
Lambda), (K^+\bar{K}^0 p), (K^+ pi^+ Sigma^0), (K^+ pi^0 Sigma^+), and (eta
pi^+ p) reactions, in which the basic dynamics is given by the excitation of
the Delta^*(1700) resonance which subsequently decays into (K Sigma^*(1385)) or
(Delta(1232) eta). In a similar way we also study the (gamma p --> K^0 pi^+
Lambda), (K^+ pi^- Sigma^+), (K^+ pi^+ Sigma^-), (K^0 pi^0 Sigma^+), and (eta
pi^0 p) related reactions. The cross sections are proportional to the square of
the coupling of Delta^*(1700) to (Sigma^*K), (Delta eta) for which there is no
experimental information but which is provided in the context of coupled
channels chiral unitary theory where the Delta^*(1700) is dynamically
generated. Within present theoretical and experimental uncertainties one can
claim a global qualitative agreement between theory and experiment. We provide
a list of items which need to be improved in order to make further progress
along these lines.Comment: 11 pages, 5 figure
NN coupling and two-pion photoproduction on the nucleon
Effects of non-resonant photoproductions arising from two different
couplings are investigated in the reaction. We find that
the pseudoscalar (PS) coupling is generally preferable to the
pseudovector (PV) coupling and particularly the total cross sections
are successfully described by the model with the PS coupling. In order
to see the difference between the two couplings, we also show the results of
invariant mass spectra and helicity-dependent cross sections in various isospin
channels calculated with the PS and PV couplings.Comment: 35 pages, 11 figures, minor changes and version to be published in
Phys.Rev.
Concurrent Helminthic Infection Protects Schoolchildren with Plasmodium vivax from Anemia
malaria in rural areas in the municipality of Careiro, in the Western Brazilian Amazon. (nâ=â9). In children without intestinal helminthes, a significant decrease in the hemoglobin during the malarial attack was seen as compared to the baseline concentration. In the survival analysis, no difference was seen in the time (in days) from the baseline cross-sectional to the first malarial infection, between parasitized and non-parasitized children.
Flexible construction of hierarchical scale-free networks with general exponent
Extensive studies have been done to understand the principles behind
architectures of real networks. Recently, evidences for hierarchical
organization in many real networks have also been reported. Here, we present a
new hierarchical model which reproduces the main experimental properties
observed in real networks: scale-free of degree distribution (frequency
of the nodes that are connected to other nodes decays as a power-law
) and power-law scaling of the clustering coefficient
. The major novelties of our model can be summarized as
follows: {\it (a)} The model generates networks with scale-free distribution
for the degree of nodes with general exponent , and arbitrarily
close to any specified value, being able to reproduce most of the observed
hierarchical scale-free topologies. In contrast, previous models can not obtain
values of . {\it (b)} Our model has structural flexibility
because {\it (i)} it can incorporate various types of basic building blocks
(e.g., triangles, tetrahedrons and, in general, fully connected clusters of
nodes) and {\it (ii)} it allows a large variety of configurations (i.e., the
model can use more than copies of basic blocks of nodes). The
structural features of our proposed model might lead to a better understanding
of architectures of biological and non-biological networks.Comment: RevTeX, 5 pages, 4 figure
Analysis of CLAS data on double charge pion electroproduction
Recent developments in phenomenological analysis of the CLAS data on 2
electroproduction are presented. The contributions from isobar channels and
, electrocouplings at from 0.25 to 0.6
GeV were determined from the analysis of comprehensive data on differential
and fully integrated 2 cross sections. Experiment Numbers: E94-005 Group:
Hall BComment: Paper compiled for NSTAR2007 meetin
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