54 research outputs found
Space-time laser instabilities in homogeneously broadened dense media
We investigate the space-time dynamics of a homogeneously broadened single-mode laser when local field correction (LFC) is taken into account. We demonstrate that the Maxwell-Bloch equations modified by LFC admit travelling-wave solutions, as when LFC is not taken into account. Their stability is discussed and compared to the case without LFC
Effect of Mn Doped and Mn+Sn Co-doping on the Properties of ZnO Thin Films
Mn doped and Mn/Sn co-doped ZnO thin films nanoparticles have been successfully synthesized by Spray pyrolysis technique at 300 0C. X-ray diffraction study showed that all the films have the hexagonal wurtzite structure with the preferential orientation (002) plane. The optical measurement exhibited an increase in the average transmittance from 77% for Mn doped ZnO to 84% for Mn/Sn co-doped ZnO films in the visible region. Further the optical band gap changes from 3.18 eV for undoped ZnO films to 3.27 eV for Mn/Sn co-doped ZnO films. The electrical resistivity has decreased with incorporation of Mn and Sn ions to reach the minimum value of 11 (Ω.cm) for Mn doped ZnO film
Stabilization of space–time laser instability through the finite transverse extension of pumping
We investigate the space–time dynamics of a homogeneously broadened single-mode laser when diffraction is taken into account. It is well known that such a laser displays instability when pumping reaches the second laser threshold. We show that the laser dynamics can be stabilized by pumping in a domain of finite width. The analysis of stationary solutions to the Maxwell–Bloch equations (evanescent waves, travelling waves, localized solutions) allows the stabilization mechanism to be explained
Analyse de dynamiques spatio-temporelles d’un laser
La dynamique spatio-temporelle d’un système laser avec diffraction est étudiée. La correspondance entre la structure du portrait de phase et l’organisation relative desdéfauts topologiques dans les diagrammes spatio-temporels est clairement mise en évidence. Ainsi, une dynamique de type chaos toroïdal est associée à des défauts apparaissant périodiquement (dans l’espace et dans le temps). En revanche, il n’y a plus de périodicité des défauts sur les diagrammes spatio-temporels lorsque le régime est un chaos développé
Elastic Scattering of Pions From the Three-nucleon System
We examine the scattering of charged pions from the trinucleon system at a
pion energy of 180 MeV. The motivation for this study is the structure seen in
the experimental angular distribution of back-angle scattering for pi+ 3He and
pi- 3H but for neither pi- 3He nor pi+ 3H. We consider the addition of a double
spin flip term to an optical model treatment and find that, though the
contribution of this term is non-negligible at large angles for pi+ 3He and pi-
3H, it does not reproduce the structure seen in the experiment.Comment: 15 pages + 5 figure
Faddeev Calculations of Proton-Deuteron Radiative Capture with Exchange Currents
pd capture processes at various energies have been analyzed based on
solutions of 3N-Faddeev equations and using modern NN forces. The application
of the Siegert theorem is compared to the explicit use of - and
-like exchange currents connected to the AV18 NN interaction. Overall
good agreement with cross sections and spin observables has been obtained but
leaving room for improvement in some cases. Feasibility studies for 3NF's
consistently included in the 3N continuum and the 3N bound state have been
performed as well.Comment: Minor changes in notation, ps files for figure
The He(e, ed)p Reaction in q-constant Kinematics
The cross section for the He(e, ed)p reaction has been measured as a
function of the missing momentum in q -constant kinematics at
beam energies of 370 and 576 MeV for values of the three-momentum transfer
of 412, 504 and 604 \mevc. The L(+TT), T and LT structure functions have been
separated for = 412 and 504 \mevc. The data are compared to three-body
Faddeev calculations, including meson-exchange currents (MEC), and to
calculations based on a covariant diagrammatic expansion. The influence of
final-state interactions and meson-exchange currents is discussed. The
-dependence of the data is reasonably well described by all calculations.
However, the most advanced Faddeev calculations, which employ the AV18
nucleon-nucleon interaction and include MEC, overestimate the measured cross
sections, especially the longitudinal part, and at the larger values of .
The diagrammatic approach gives a fair description of the cross section, but
under(over)estimates the longitudinal (transverse) structure function.Comment: 17 pages, 7 figure
Lattice Simulations for Light Nuclei: Chiral Effective Field Theory at Leading Order
We discuss lattice simulations of light nuclei at leading order in chiral
effective field theory. Using lattice pion fields and auxiliary fields, we
include the physics of instantaneous one-pion exchange and the leading-order
S-wave contact interactions. We also consider higher-derivative contact
interactions which adjust the S-wave scattering amplitude at higher momenta. By
construction our lattice path integral is positive definite in the limit of
exact Wigner SU(4) symmetry for any even number of nucleons. This SU(4)
positivity and the approximate SU(4) symmetry of the low-energy interactions
play an important role in suppressing sign and phase oscillations in Monte
Carlo simulations. We assess the computational scaling of the lattice algorithm
for light nuclei with up to eight nucleons and analyze in detail calculations
of the deuteron, triton, and helium-4.Comment: 44 pages, 15 figure
Moscow-type NN-potentials and three-nucleon bound states
A detailed description of Moscow-type (M-type) potential models for the NN
interaction is given. The microscopic foundation of these models, which appear
as a consequence of the composite quark structure of nucleons, is discussed.
M-type models are shown to arise naturally in a coupled channel approach when
compound or bag-like six-quark states, strongly coupled to the NN channel, are
eliminated from the complete multiquark wave function. The role of the
deep-lying bound states that appear in these models is elucidated. By
introducing additional conditions of orthogonality to these compound six-quark
states, a continuous series of almost on-shell equivalent nonlocal interaction
models, characterized by a strong reduction or full absence of a local
repulsive core (M-type models), is generated. The predictions of these
interaction models for 3N systems are analyzed in detail. It is shown that
M-type models give, under certain conditions, a stronger binding of the 3N
system than the original phase-equivalent model with nodeless wave functions.
An analysis of the 3N system with the new versions of the Moscow NN potential
describing also the higher even partial waves is presented. Large deviations
from conventional NN force models are found for the momentum distribution in
the high momentum region. In particular, the Coulomb displacement energy for
nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H
binding energy is extrapolated to the experimental value.Comment: 23 pages Latex, 9 figures, to appear in Phys.Rev.
The Quasielastic 3He(e,e'p)d Reaction at Q^2 = 1.5 GeV^2 for Recoil Momenta up to 1 GeV/c
We have studied the quasielastic 3He(e,e'p)d reaction in perpendicular
coplanar kinematics, with the energy and momentum transferred by the electron
fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e'p)d cross section
was measured for missing momenta up to 1000 MeV/c, while the A_TL asymmetry was
extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150
MeV/c, the measured cross section is described well by calculations that use a
variational ground-state wave function of the 3He nucleus derived from a
potential that includes three-body forces. For missing momenta from 150 to 750
MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c,
the experimental cross section is more than an order of magnitude larger than
predicted by available theories. The A_TL asymmetry displays characteristic
features of broken factorization, and is described reasonably well by available
models.Comment: 5 pages, 3 figures, submitted to Physical Review Letters, v3: changed
conten
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