690 research outputs found
Quasielastic Electron Scattering from Nuclei: Random-Phase vs. Ring Approximations
We investigate the extent to which the nuclear transverse response to
electron scattering in the quasielastic region, evaluated in the random-phase
approximation can be described by ring approximation calculations. Different
effective interactions based on a standard model of the type g'+V_pi+V_rho are
employed. For each momentum transfer, we have obtained the value of g'_0
permitting the ring response to match the position of the peak and/or the
non-energy weighted sum rule provided by the random-phase approach has been
obtained. It is found that, in general, it is not possible to reproduce both
magnitudes simultaneously for a given g'_0 value.Comment: 7 pages, 4 Postscript figures, to appear in Physical Review
Aharonov-Bohm effect in a singly connected point contact
We report the discovery of an oscillation in the low-temperature magnetoresistance of a point contact in the two-dimensional electron gas of a GaAs-AlxGa1âxAs heterostructure. The oscillation is periodic in the magnetic field and is reminiscent of the Aharonov-Bohm effect in rings, although the geometry is singly connected. A possible mechanism for this quantum interference effect is tunneling between edge states across the point contact at the potential step at the entrance and the exit of the constriction
Extended Superscaling of Electron Scattering from Nuclei
An extended study of scaling of the first and second kinds for inclusive
electron scattering from nuclei is presented. Emphasis is placed on the
transverse response in the kinematic region lying above the quasielastic peak.
In particular, for the region in which electroproduction of resonances is
expected to be important, approximate scaling of the second kind is observed
and the modest breaking of it is shown probably to be due to the role played by
an inelastic version of the usual scaling variable.Comment: LaTeX, 36 pages including 5 color postscript figures and 4 postscript
figure
Meson-exchange currents and quasielastic neutrino cross sections in the SuperScaling Approximation model
We evaluate the quasielastic double differential neutrino cross sections
obtained in a phenomenological model based on the superscaling behavior of
electron scattering data. We compare our results with the recent experimental
data for neutrinos of MiniBooNE and estimate the contribution of the vector
meson-exchange currents in the 2p-2h sector.Comment: 6 pages, 4 figure
A forage-only diet alters the metabolic response of horses in training
Most athletic horses are fed a high-starch diet despite the risk of health problems. Replacing starch concentrate with high-energy forage would alleviate these health problems, but could result in a shift in major substrates for muscle energy supply from glucose to short-chain fatty acids (SCFA) due to more hindgut fermentation of fibre. Dietary fat inclusion has previously been shown to promote aerobic energy supply during exercise, but the contribution of SCFA to exercise metabolism has received little attention.
This study compared metabolic response with exercise and lactate threshold (VLa4) in horses fed a forage-only diet (F) and a more traditional high-starch, low-energy forage diet (forageâconcentrate diet - FC). The hypothesis was that diet F would increase plasma acetate concentration and increase VLa4 compared with diet FC. Six Standardbred geldings in race training were used in a 29-day change-over experiment. Plasma acetate, non-esterified fatty acids (NEFA), lactate, glucose and insulin concentrations and
venous pH were measured in samples collected before, during and after a treadmill exercise test (ET, day 25) and muscle glycogen concentrations before and after ET. Plasma acetate concentration was higher before and after exercise in horses on diet F compared with diet FC, and there was a tendency ( P50.09) for increased VLa4 on diet F. Venous pH and plasma glucose concentrations during exercise were higher in horses on diet F than diet FC, as was plasma NEFA on the day after ET. Plasma insulin and muscle glycogen concentrations were lower for diet F, but glycogen utilisation was similar for the two diets. The results show that a high-energy, forage-only diet alters the metabolic response to exercise and, with the exception of lowered glycogen stores, appears to have positive rather than negative effects on performance traits
Relativistic pionic effects in quasielastic electron scattering
The impact of relativistic pionic correlations and meson-exchange currents on
the response functions for electromagnetic quasielastic electron scattering
from nuclei is studied in detail. Results in first-order perturbation theory
are obtained for one-particle emission electronuclear reactions within the
context of the relativistic Fermi gas model. Improving upon previous analyses
where non-relativistic reductions of the currents were performed, here a fully
relativistic analysis in which both forces and currents are treated
consistently is presented. Lorentz covariance is shown to play a crucial role
in enforcing the gauge invariance of the theory. Effects stemming uniquely from
relativity in the pionic correlations are identified and, in particular, a
comprehensive study of the self-energy contributions and of the currents
associated with the pion is presented. First- and second-kind scaling for high
momentum transfer is investigated.Comment: 43 pages, 21 figure
Hamiltonian dynamics and spectral theory for spin-oscillators
We study the Hamiltonian dynamics and spectral theory of spin-oscillators.
Because of their rich structure, spin-oscillators display fairly general
properties of integrable systems with two degrees of freedom. Spin-oscillators
have infinitely many transversally elliptic singularities, exactly one
elliptic-elliptic singularity and one focus-focus singularity. The most
interesting dynamical features of integrable systems, and in particular of
spin-oscillators, are encoded in their singularities. In the first part of the
paper we study the symplectic dynamics around the focus-focus singularity. In
the second part of the paper we quantize the coupled spin-oscillators systems
and study their spectral theory. The paper combines techniques from
semiclassical analysis with differential geometric methods.Comment: 32 page
Impact of leptin deficiency on male tibia and vertebral body 3D bone architecture independent of changes in body weight
Leptin an adipokine with potent effects on energy balance and body weight plays an important role in defining bone architecture in growing mammals. However, major changes in body weight can also influence morphology of trabecular and cortical bone. Therefore, we examined the impact of leptin deficiency on tibia and vertebral body 3D bone architecture independent of changes in body weight. Furthermore, advances in computational 3D image analysis suggest that average morphological values may mask regional specific differences in trabecular bone thickness. The study utilized leptin-deficient Ob/Ob mice (nâ=â8) weight-paired to C57BL/6 (C57) control mice (nâ=â8) which were split into either lean or obese groups for 24â±â2âweeks. Whole tibias and L3 vertebrae were fixed before high resolution microcomputed tomography (ÎŒCT) scanning was performed. Leptin deficiency independent of body weight reduced tibia cortical bone volume, trabecular bone volume/tissue volume, number, and mineral density. Mean tibia trabecular thickness showed no significant differences between all groups; however, significant changes in trabecular thickness were found when analyzed by region. This study demonstrates that leptin deficiency significantly impacts tibia and vertebral body trabecular and cortical bone 3D architecture independent of changes in body weight
Superscaling of Inclusive Electron Scattering from Nuclei
We investigate the degree to which the concept of superscaling, initially
developed within the framework of the relativistic Fermi gas model, applies to
inclusive electron scattering from nuclei. We find that data obtained from the
low energy loss side of the quasielastic peak exhibit the superscaling
property, i.e., the scaling functions f(\psi') are not only independent of
momentum transfer (the usual type of scaling: scaling of the first kind), but
coincide for A \geq 4 when plotted versus a dimensionless scaling variable
\psi' (scaling of the second kind). We use this behavior to study as yet poorly
understood properties of the inclusive response at large electron energy loss.Comment: 33 pages, 12 color EPS figures, LaTeX2e using BoxedEPSF macros; email
to [email protected]
Inclusive electron scattering in a relativistic Green function approach
A relativistic Green function approach to the inclusive quasielastic (e,e')
scattering is presented. The single particle Green function is expanded in
terms of the eigenfunctions of the nonhermitian optical potential. This allows
one to treat final state interactions consistently in the inclusive and in the
exclusive reactions. Numerical results for the response functions and the cross
sections for different target nuclei and in a wide range of kinematics are
presented and discussed in comparison with experimental data.Comment: 12 pages, 7 figures, REVTeX
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