552 research outputs found
Giant Octupole Resonance Simulation
Using a pseudo-particle technique we simulate large-amplitude isoscalar giant
octupole excitations in a finite nuclear system. Dependent on the initial
conditions we observe either clear octupole modes or over-damped octupole modes
which decay immediately into quadrupole ones. This shows clearly a behavior
beyond linear response. We propose that octupole modes might be observed in
central collisions of heavy ions
Nonlinear relaxation field in charged systems under high electric fields
The influence of an external electric field on the current in charged systems
is investigated. The results from the classical hierarchy of density matrices
are compared with the results from the quantum kinetic theory. The kinetic
theory yields a systematic treatment of the nonlinear current beyond linear
response. To this end the dynamically screened and field-dependent
Lenard-Balescu equation is integrated analytically and the nonlinear relaxation
field is calculated. The classical linear response result known as Debye -
Onsager relaxation effect is only obtained if asymmetric screening is assumed.
Considering the kinetic equation of one specie the other species have to be
screened dynamically while the screening with the same specie itself has to be
performed statically. Different other approximations are discussed and
compared.Comment: language correction
The radial defocusing energy-supercritical cubic nonlinear wave equation in R^{1+5}
In this work, we consider the energy-supercritical defocusing cubic nonlinear
wave equation in dimension d=5 for radially symmetric initial data. We prove
that an a priori bound in the critical space implies global well-posedness and
scattering. The main tool that we use is a frequency localized version of the
classical Morawetz inequality, inspired by recent developments in the study of
the mass and energy critical nonlinear Schr\"odinger equation.Comment: AMS Latex, 20 page
In-medium two-nucleon properties in high electric fields
The quantum mechanical two - particle problem is considered in hot dense
nuclear matter under the influence of a strong electric field such as the field
of the residual nucleus in heavy - ion reactions. A generalized
Galitskii-Bethe-Salpeter equation is derived and solved which includes
retardation and field effects. Compared with the in-medium properties in the
zero-field case, bound states are turned into resonances and the scattering
phase shifts are modified. Four effects are observed due to the applied field:
(i) A suppression of the Pauli-blocking below nuclear matter densities, (ii)
the onset of pairing occurs already at higher temperatures due to the field,
(iii) a field dependent finite lifetime of deuterons and (iv) the imaginary
part of the quasiparticle self-energy changes its sign for special values of
density and temperatures indicating a phase instability. The latter effect may
influence the fragmentation processes. The lifetime of deuterons in a strong
Coulomb field is given explicitly.Comment: ps file + 7 figures (eps
Conductivity in quasi two-dimensional systems
The conductivity in quasi two-dimensional systems is calculated using the
quantum kinetic equation. Linearizing the Lenard-Balescu collision integral
with the extension to include external field dependences allows one to
calculate the conductivity with diagrams beyond the GW approximation including
maximally crossed lines. Consequently the weak localization correction as an
interference effect appears here from the field dependence of the collision
integral (the latter dependence sometimes called intra-collisional field
effect). It is shown that this weak localization correction has the same origin
as the Debye-Onsager relaxation effect in plasma physics. The approximation is
applied to a system of quasi two-dimensional electrons in hetero-junctions
which interact with charged and neutral impurities and the low temperature
correction to the conductivity is calculated analytically. It turns out that
the dynamical screening due to charged impurities leads to a linear temperature
dependence, while the scattering from neutral impurities leads to the usual
Fermi-liquid behavior. By considering an appropriate mass action law to
determine the ratio of charged to neutral impurities we can describe the
experimental metal-insulator transition at low temperatures as a Mott-Hubbard
transition.Comment: 7 pages 7 pages appendix 11 figure
Uniform Decay of Local Energy and the Semi-Linear Wave Equation on Schwarzchild Space
We provide a uniform decay estimate of Morawetz type for the local energy of
general solutions to the inhomogeneous wave equation on a Schwarzchild
background. This estimate is both uniform in space and time, so in particular
it implies a uniform bound on the sup norm of solutions which can be given in
terms of certain inverse powers of the radial and advanced/retarded time
coordinate variables. As a model application, we show these estimates give a
very simple proof small amplitude scattering for nonlinear scalar fields with
higher than cubic interactions.Comment: 24 page
Ginzburg-Landau theory of superconducting surfaces under electric fields
A boundary condition for the Ginzburg-Landau wave function at surfaces biased
by a strong electric field is derived within the de Gennes approach. This
condition provides a simple theory of the field effect on the critical
temperature of superconducting layers.Comment: 4 pages, 1 figur
The concept of correlated density and its application
The correlated density appears in many physical systems ranging from dense
interacting gases up to Fermi liquids which develop a coherent state at low
temperatures, the superconductivity. One consequence of the correlated density
is the Bernoulli potential in superconductors which compensates forces from
dielectric currents. This Bernoulli potential allows to access material
parameters. Though within the surface potential these contributions are largely
canceled, the bulk measurements with NMR can access this potential. Recent
experiments are explained and new ones suggested. The underlying quantum
statistical theory in nonequilibrium is the nonlocal kinetic theory developed
earlier.Comment: 14 pages, CMT30 proceeding
Boundary condition for Ginzburg-Landau theory of superconducting layers
Electrostatic charging changes the critical temperature of superconducting
thin layers. To understand the basic mechanism, it is possible to use the
Ginzburg-Landau theory with the boundary condition derived by de Gennes from
the BCS theory. Here we show that a similar boundary condition can be obtained
from the principle of minimum free energy. We compare the two boundary
conditions and use the Budd-Vannimenus theorem as a test of approximations.Comment: 6 pages, 4 figure
Virial corrections to simulations of heavy ion reactions
Within QMD simulations we demonstrate the effect of virial corrections on heavy ion reactions. Unlike in standard codes, the binary collisions are treated as non-local so that the contribution of the collision flux to the reaction dynamics is covered. A comparison with standard QMD simulations shows that the virial corrections lead to a broader proton distribution bringing theoretical spectra closer towards experimental values. Complementary BUU simulations reveal that the non-locality enhances the collision rate in the early stage of the reaction. It suggests that the broader distribution appears due to an enhanced pre-equilibrium emission of particles
- …