357 research outputs found
Well-posedness, energy and charge conservation for nonlinear wave equations in discrete space-time
We consider the problem of discretization for the U(1)-invariant nonlinear
wave equations in any dimension. We show that the classical finite-difference
scheme used by Strauss and Vazquez \cite{MR0503140} conserves the
positive-definite discrete analog of the energy if the grid ratio is , where and are the mesh sizes of the time and space
variables and is the spatial dimension. We also show that if the grid ratio
is , then there is the discrete analog of the charge which is
conserved.
We prove the existence and uniqueness of solutions to the discrete Cauchy
problem. We use the energy conservation to obtain the a priori bounds for
finite energy solutions, thus showing that the Strauss -- Vazquez
finite-difference scheme for the nonlinear Klein-Gordon equation with positive
nonlinear term in the Hamiltonian is conditionally stable.Comment: 10 page
Recoil Studies in the Reaction of 12-C Ions with the Enriched Isotope 118-Sn
The recoil properties of the product nuclei from the interaction of 2.2
GeV/nucleon 12-C ions from Nuclotron of the Laboratory of High Energies (LHE),
Joint Institute for Nuclear Research (JINR) at Dubna with a 118-Sn target have
been studied using catcher foils. The experimental data were analyzed using the
mathematical formalism of the standard two-step vector model. The results for
12-C ions are compared with those for deuterons and protons. Three different
Los Alamos versions of the Quark-Gluon String Model (LAQGSM) were used for
comparison with our experimental data.Comment: 10 pages, 6 figures, submitted to Nucl. Phys.
CEM03 and LAQGSM03 - new modeling tools for nuclear applications
An improved version of the Cascade-Exciton Model (CEM) of nuclear reactions
realized in the code CEM2k and the Los Alamos version of the Quark-Gluon String
Model (LAQGSM) have been developed recently at LANL to describe reactions
induced by particles and nuclei for a number of applications. Our CEM2k and
LAQGSM merged with the GEM2 evaporation/fission code by Furihata have
predictive powers comparable to other modern codes and describe many reactions
better than other codes; therefore both our codes can be used as reliable event
generators in transport codes for applications. During the last year, we have
made a significant improvements to the intranuclear cascade parts of CEM2k and
LAQGSM, and have extended LAQGSM to describe photonuclear reactions at energies
to 10 GeV and higher. We have produced in this way improved versions of our
codes, CEM03.01 and LAQGSM03.01. We present a brief description of our codes
and show illustrative results obtained with CEM03.01 and LAQGSM03.01 for
different reactions compared with predictions by other models, as well as
examples of using our codes as modeling tools for nuclear applications.Comment: 12 pages, 10 figures, to be published in Journal of Physics:
Conference Series: Proc. Europhysics Conf. on New Trends in Nuclear Physics
Applications and Technologies (NPDC19), Pavia, Italy, September 5-9, 200
Spallation Residues in the Reaction 56Fe + p at 0.3, 0.5, 0.75, 1.0 and 1.5 A GeV
The spallation residues produced in the bombardment of 56}Fe at 1.5, 1.0,
0.75, 0.5 and 0.3 A GeV on a liquid-hydrogen target have been measured using
the reverse kinematics technique and the Fragment Separator at GSI (Darmstadt).
This technique has permitted the full identification in charge and mass of all
isotopes produced with cross-sections larger than 10^{-2} mb down to Z=8. Their
individual production cross-sections and recoil velocities at the five energies
are presented. Production cross-sections are compared to previously existing
data and to empirical parametric formulas, often used in cosmic-ray
astrophysics. The experimental data are also extensively compared to different
combinations of intra-nuclear cascade and de-excitation models. It is shown
that the yields of the lightest isotopes cannot be accounted for by standard
evaporation models. The GEMINI model, which includes an asymmetric fission
decay mode, gives an overall good agreement with the data. These experimental
data can be directly used for the estimation of composition modifications and
damages in materials containing iron in spallation sources. They are also
useful for improving high precision cosmic-ray measurements.Comment: Submited to Phys. Rev. C (10/2006
Variation of nonequilibrium processes in p+Ni system with beam energy
The energy and angular dependence of double differential cross sections
dsigma/dOmega dE were measured for p, d, t, 3,4He, 6,7Li, 7,9Be, and 10,11B
produced in collisions of 0.175 GeV protons with Ni target. The analysis of
measured dfferential cross sections allowed to extract total production cross
sections for ejectiles listed above. The shape of the spectra and angular
distributions indicate the presence of other nonequilibrium processes besides
the emission of nucleons from the intranuclear cascade, and besides the
evaporation of various particles from remnants of intranuclear cascade. These
nonequilibrium processes consist of coalescence of nucleons into light charged
particles during the intranuclear cascade, of the fireball emission which
contributes to the cross sections of protons and deuterons, and of the break-up
of the target nucleus which leads to the emission of intermediate mass
fragments. All such processes were found earlier at beam energies 1.2, 1.9, and
2.5 GeV for Ni as well as for Au targets, however, significant differences in
properties of these processes at high and low beam energy are observed in the
present study.Comment: 10 pages, 9 figure
Competition of coalescence and "fireball" processes in nonequilibrium emission of light charged particles from p+Au collisions
The energy and angular dependence of double differential cross sections was
measured for p,d,t,He,Li,Be, and B isotopes produced in collisions of 1.2 and
1.9 GeV protons with Au target. The shape of the spectra and angular
distributions almost does not change in the beam energy range from 1.2 to 2.5
GeV, however, the absolute value of the cross sections increases for all
ejectiles. A phenomenological model of two emitting, moving sources reproduces
very well spectra and angular distributions of intermediate mass fragments.
Double differential cross sections for light charged particles (LCP) were
analyzed in the frame of the microscopic model of intranuclear cascade (INC)
with coalescence of nucleons and statistical model for evaporation of particles
from excited residual nuclei. Energy and angular dependencies of data agree
satisfactorily neither with predictions of microscopic intranuclear cascade
calculations for protons, nor with coalescence calculations for other LCP.
Phenomenological inclusion of another reaction mechanism - emission of LCP from
a "fireball", i.e., fast and hot moving source - combined with the microscopic
model calculations of INC, coalescence and evaporation of particles leads to
very good description of the data. It was found that nonequilibrium processes
are very important for production of LCP. They exhaust 40-80% of the total
cross sections - depending on the emitted particles. Coalescence and "fireball"
emission give comparable contributions to the cross sections with exception of
3He data where coalescence clearly dominates. The ratio of sum of all
nonequilibrium processes to those proceeding through stage of statistical
equilibrium does almost not change in the beam energy range from 1.2 GeV to 2.5
GeV for all light charged particles.Comment: 14 pages, 12 figures, IV tables, \pacs{25.40.-h,25.40.Sc,25.40.Ve
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