9,951 research outputs found
Two-Body T-Matrices without Angular Momentum Decomposition: Energy and Momentum Dependencies
The two-body t-matrix is calculated directly as function of two vector
momenta for different Malfliet-Tjon type potentials. At a few hundred MeV
projectile energy the total amplitude is quite a smooth function showing only a
strong peak in forward direction. In contrast the corresponding partial wave
contributions, whose number increases with increasing energy, become more and
more oscillatory with increasing energy. The angular and momentum dependence of
the full amplitude is studied and displayed on as well as off the energy shell
as function of positive and negative energies. The behavior of the t-matrix in
the vicinity of bound state poles and resonance poles in the second energy
sheet is studied. It is found that the angular dependence of T exhibits a very
characteristic behavior in the vicinity of those poles, which is given by the
Legendre function corresponding to the quantum number either of the bound state
or the resonance (or virtual) state. This behavior is illustrated with
numerical examples.Comment: 19 pages (revtex), 15 figure
Weak antilocalization in high mobility Ga(x)In(1-x)As/InP two-dimensional electron gases with strong spin-orbit coupling
We have studied the spin-orbit interaction in a high mobility two-dimensional
electron gas in a GaInAs/InP heterostructure as a function of an applied gate
voltage as well as a function of temperature. Highly sensitive magnetotransport
measurements of weak antilocalization as well as measurements of Shubnikov--de
Haas oscillations were performed in a wide range of electron sheet
concentrations. In our samples the electron transport takes place in the strong
spin precession regime in the whole range of applied gate voltages, which is
characterized by the spin precession length being shorter than the elastic mean
free path. The magnitude of the Rashba spin-orbit coupling parameter was
determined by fitting the experimental curves by a simulated quantum
conductance correction according to a model proposed recently by Golub [Phys.
Rev. B 71, 235310 (2005)]. A comparison of the Rashba coupling parameter
extracted using this model with the values estimated from the analysis of the
beating pattern in the Shubnikov--de Haas oscillations showed a good agreement.Comment: 5 pages, 5 figures, accepted for publication in Phys.Rev.
Measuring fitness of Kenyan children with polyparasitic infections using the 20-meter shuttle run test as a morbidity metric.
BACKGROUND: To date, there has been no standardized approach to the assessment of aerobic fitness among children who harbor parasites. In quantifying the disability associated with individual or multiple chronic infections, accurate measures of physical fitness are important metrics. This is because exercise intolerance, as seen with anemia and many other chronic disorders, reflects the body's inability to maintain adequate oxygen supply (VO(2) max) to the motor tissues, which is frequently linked to reduced quality-of-life in terms of physical and job performance. The objective of our study was to examine the associations between polyparasitism, anemia, and reduced fitness in a high risk Kenyan population using novel implementation of the 20-meter shuttle run test (20mSRT), a well-standardized, low-technology physical fitness test.
METHODOLOGY/PRINCIPAL FINDINGS: Four villages in coastal Kenya were surveyed during 2009-2010. Children 5-18 years were tested for infection with Schistosoma haematobium (Sh), malaria, filaria, and geohelminth infections by standard methods. After anthropometric and hemoglobin testing, fitness was assessed with the 20 mSRT. The 20 mSRT proved easy to perform, requiring only minimal staff training. Parasitology revealed high prevalence of single and multiple parasitic infections in all villages, with Sh being the most common (25-62%). Anemia prevalence was 45-58%. Using multiply-adjusted linear modeling that accounted for household clustering, decreased aerobic capacity was significantly associated with anemia, stunting, and wasting, with some gender differences.
CONCLUSIONS/SIGNIFICANCE: The 20 mSRT, which has excellent correlation with VO(2), is a highly feasible fitness test for low-resource settings. Our results indicate impaired fitness is common in areas endemic for parasites, where, at least in part, low fitness scores are likely to result from anemia and stunting associated with chronic infection. The 20 mSRT should be used as a common metric to quantify physical fitness and compare sub-clinical disability across many different disorders and community settings
The increase of Binding Energy and Enhanced Binding in Non-Relativistic QED
We consider a Pauli-Fierz Hamiltonian for a particle coupled to a photon
field. We discuss the effects of the increase of the binding energy and
enhanced binding through coupling to a photon field, and prove that both
effects are the results of the existence of the ground state of the self-energy
operator with total momentum .Comment: 14 pages, Latex. Final version, accepted for publication in J. Math.
Phy
A new approach to the modelling of local defects in crystals: the reduced Hartree-Fock case
This article is concerned with the derivation and the mathematical study of a
new mean-field model for the description of interacting electrons in crystals
with local defects. We work with a reduced Hartree-Fock model, obtained from
the usual Hartree-Fock model by neglecting the exchange term. First, we recall
the definition of the self-consistent Fermi sea of the perfect crystal, which
is obtained as a minimizer of some periodic problem, as was shown by Catto, Le
Bris and Lions. We also prove some of its properties which were not mentioned
before. Then, we define and study in details a nonlinear model for the
electrons of the crystal in the presence of a defect. We use formal analogies
between the Fermi sea of a perturbed crystal and the Dirac sea in Quantum
Electrodynamics in the presence of an external electrostatic field. The latter
was recently studied by Hainzl, Lewin, S\'er\'e and Solovej, based on ideas
from Chaix and Iracane. This enables us to define the ground state of the
self-consistent Fermi sea in the presence of a defect. We end the paper by
proving that our model is in fact the thermodynamic limit of the so-called
supercell model, widely used in numerical simulations.Comment: Final version, to appear in Comm. Math. Phy
A Factorization Law for Entanglement Decay
We present a simple and general factorization law for quantum systems shared
by two parties, which describes the time evolution of entanglement upon passage
of either component through an arbitrary noisy channel. The robustness of
entanglement-based quantum information processing protocols is thus easily and
fully characterized by a single quantity.Comment: 4 pages, 5 figure
Structural and magnetic properties of an InGaAs/FeSi superlattice in cylindrical geometry
The structure and the magnetic properties of an InGaAs/Fe3Si superlattice in
a cylindrical geometry are investigated by electron microscopy techniques,
x-ray diffraction and magnetometry. To form a radial superlattice, a
pseudomorphic InGaAs/Fe3As bilayer has been released from its substrate
self-forming into a rolled-up microtube. Oxide-free interfaces as well as areas
of crystalline bonding are observed and an overall lattice mismatch between
succeeding layers is determined. The cylindrical symmetry of the final radial
superlattice shows a significant effect on the magnetization behavior of the
rolled-up layers
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