559 research outputs found
Techniques complexes d'étude d'E.D.O
We relate some properties of complexifications of real analytic foliations with problems such that existence of first integrals or convergent normalizations. Holomorphic diffeomorphisms having an invariant real foliation play a crucial role
Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions
In this paper we address the adequacy of various approximate methods of
including Coulomb distortion effects in (e,e') reactions by comparing to an
exact treatment using Dirac-Coulomb distorted waves. In particular, we examine
approximate methods and analyses of (e,e') reactions developed by Traini et al.
using a high energy approximation of the distorted waves and phase shifts due
to Lenz and Rosenfelder. This approximation has been used in the separation of
longitudinal and transverse structure functions in a number of (e,e')
experiments including the newly published 208Pb(e,e') data from Saclay. We find
that the assumptions used by Traini and others are not valid for typical (e,e')
experiments on medium and heavy nuclei, and hence the extracted structure
functions based on this formalism are not reliable. We describe an improved
approximation which is also based on the high energy approximation of Lenz and
Rosenfelder and the analyses of Knoll and compare our results to the Saclay
data. At each step of our analyses we compare our approximate results to the
exact distorted wave results and can therefore quantify the errors made by our
approximations. We find that for light nuclei, we can get an excellent
treatment of Coulomb distortion effects on (e,e') reactions just by using a
good approximation to the distorted waves, but for medium and heavy nuclei
simple additional ad hoc factors need to be included. We describe an explicit
procedure for using our approximate analyses to extract so-called longitudinal
and transverse structure functions from (e,e') reactions in the quasielastic
region.Comment: 30 pages, 8 figures, 16 reference
Transformations isotropes des germes de feuilletages holomorphes
AbstractGiven Fω a germ of holomorphic singular foliation at the origin of Cn defined by an equation ω=0 (with ω∧dω=0), we are interested in describing the group of isotropic transformations of Fω, i.e., the group of those germs Φ of diffeomorphisms at the origin of Cn that satisfy Φ∗ω∧ω=0
y scaling in electron-nucleus scattering
Data on inclusive electron scattering from A = 4, 12, 27, 56, 197 nuclei at large momentum transfer are presented and analyzed in terms of y scaling. We find that the data do scale for y 1), and we study the convergence of the scaling function with the momentum transfer Q^2 and A
Sum Rules and Moments of the Nucleon Spin Structure Functions
The nucleon has been used as a laboratory to investigate its own spin
structure and Quantum Chromodynamics. New experimental data on nucleon spin
structure at low to intermediate momentum transfers combined with existing high
momentum transfer data offer a comprehensive picture of the transition region
from the {\it confinement} regime of the theory to its {\it asymptotic freedom}
regime. Insight for some aspects of the theory is gained by exploring lower
moments of spin structure functions and their corresponding sum rules (i.e. the
Gerasimov-Drell-Hearn, Bjorken and Burkhardt-Cottingham). These moments are
expressed in terms of an operator product expansion using quark and gluon
degrees of freedom at moderately large momentum transfers. The sum rules are
verified to a good accuracy assuming that no singular behavior of the structure
functions is present at very high excitation energies. The higher twist
contributions have been examined through the moments evolution as the moments
evolution as the momentum transfer varies from higher to lower values.
Furthermore, QCD-inspired low-energy effective theories, which explicitly
include chiral symmetry breaking, are tested at low momentum transfers. The
validity of these theories is further examined as the momentum transfer
increases to moderate values. It is found that chiral perturbation calculations
agree reasonably well with the first moment of the spin structure function
at momentum transfer of 0.1 GeV but fail to reproduce the neutron
data in the case of the generalized polarizability .Comment: 21 pages, 4 figures, review for Modern Physics Letters A. Minor
modifications in text and improved quality for one figure. Corrected mistakes
in section
Density effect in Cu K-shell ionization by 5.1-GeV electrons
We have made an absolute measurement of the Cu K-shell impact ionization cross section by 5.1-GeV electrons, which demonstrates directly a density effect predicted by Fermi in 1940. By determining the ratio of the K x-ray yield from a thin front and back layer of the target by a novel grazing emission method, we have verified the effect of transition radiation on the x-ray production, suggested by Sorensen and reported by Bak et al
Plasmonic terahertz detection by a double-grating-gate field-effect transistor structure with an asymmetric unit cell
Plasmonic terahertz detection by a double-grating gate field-effect
transistor structure with an asymmetric unit cell is studied theoretically.
Detection responsivity exceeding 8 kV/W at room temperature in the photovoltaic
response mode is predicted for strong asymmetry of the structure unit cell.
This value of the responsivity is an order of magnitude greater than reported
previously for the other types of uncooled plasmonic terahertz detectors. Such
enormous responsivity can be obtained without using any supplementary antenna
elements because the double-grating gate acts as an aerial matched antenna that
effectively couples the incoming terahertz radiation to plasma oscillations in
the structure channel.Comment: Submitted to APL, 8 pages, 2 figure
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
- …