18,920 research outputs found
Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes
We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric
nuclear matter which are based on improved approximations schemes. The
potential matrix elements have been adapted for isospin asymmetric nuclear
matter in order to account for the proton-neutron mass splitting in a more
consistent way. The proton properties are particularly sensitive to this
adaption and its consequences, whereas the neutron properties remains almost
unaffected in neutron rich matter. Although at present full Brueckner
calculations are still too complex to apply to finite nuclei, these
relativistic Brueckner results can be used as a guidance to construct a density
dependent relativistic mean field theory, which can be applied to finite
nuclei. It is found that an accurate reproduction of the
Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of
these coupling functions.Comment: 34 pages, 9 figures, submitted to Eur. Phys. J.
Dilepton production at HADES: theoretical predictions
Dileptons represent a unique probe for nuclear matter under extreme
conditions reached in heavy-ion collisions. They allow to study meson
properties, like mass and decay width, at various density and temperature
regimes. Present days models allow generally a good description of dilepton
spectra in ultra-relativistic heavy ion collision. For the energy regime of a
few GeV/nucleon, important discrepancies between theory and experiment, known
as the DLS puzzle, have been observed. Various models, including the one
developed by the T\"{u}bingen group, have tried to address this problem, but
have proven only partially successful. High precision spectra of dilepton
emission in heavy-ion reactions at 1 and 2 GeV/nucleon will be released in the
near future by the HADES Collaboration at GSI. Here we present the predictions
for dilepton spectra in C+C reactions at 1 and 2 GeV/nucleon and investigate up
to what degree possible scenarios for the in-medium modification of vector
mesons properties are accessible by the HADES experiment.Comment: 12 pages, 4 figures; submitted to Phys.Lett.
Non--Newtonian viscosity of interacting Brownian particles: comparison of theory and data
A recent first-principles approach to the non-linear rheology of dense
colloidal suspensions is evaluated and compared to simulation results of
sheared systems close to their glass transitions. The predicted scenario of a
universal transition of the structural dynamics between yielding of glasses and
non-Newtonian (shear-thinning) fluid flow appears well obeyed, and calculations
within simplified models rationalize the data over variations in shear rate and
viscosity of up to 3 decades.Comment: 6 pages, 2 figures; J. Phys. Condens. Matter to be published (Jan.
2003
Criteria for Continuous-Variable Quantum Teleportation
We derive an experimentally testable criterion for the teleportation of
quantum states of continuous variables. This criterion is especially relevant
to the recent experiment of Furusawa et al. [Science 282, 706-709 (1998)] where
an input-output fidelity of was achieved for optical coherent
states. Our derivation demonstrates that fidelities greater than 1/2 could not
have been achieved through the use of a classical channel alone; quantum
entanglement was a crucial ingredient in the experiment.Comment: 12 pages, to appear in Journal of Modern Optic
Remote coupling of air lines
Bullseye coupler is projected pneumatically from one railroad car at the second car's point of connection. System depends on assumption that inaccuracies in relative position of cars do not exceed certain limits. System is usefull to oil drilling, marine rescue and salvage, nuclear work and chemical plant operations
Glass transitions and shear thickening suspension rheology
We introduce a class of simple models for shear thickening and/ or `jamming'
in colloidal suspensions. These are based on schematic mode coupling theory
(MCT) of the glass transition, having a memory term that depends on a density
variable, and on both the shear stress and the shear rate. (Tensorial aspects
of the rheology, such as normal stresses, are ignored for simplicity.) We
calculate steady-state flow curves and correlation functions. Depending on
model parameters, we find a range of rheological behaviours, including
`S-shaped' flow curves, indicating discontinuous shear thickening, and
stress-induced transitions from a fluid to a nonergodic (jammed) state, showing
zero flow rate in an interval of applied stress. The shear thickening and
jamming scenarios that we explore appear broadly consistent with experiments on
dense colloids close to the glass transition, despite the fact that we ignore
hydrodynamic interactions. In particular, the jamming transition we propose is
conceptually quite different from various hydrodynamic mechanisms of shear
thickening in the literature, although the latter might remain pertinent at
lower colloid densities. Our jammed state is a stress-induced glass, but its
nonergodicity transitions have an analytical structure distinct from that of
the conventional MCT glass transition.Comment: 33 pages; 19 figure
Mathematical theory of the Goddard trajectory determination system
Basic mathematical formulations depict coordinate and time systems, perturbation models, orbital estimation techniques, observation models, and numerical integration methods
Model independent study of the Dirac structure of the nucleon-nucleon interaction
Relativistic and non-relativistic modern nucleon-nucleon potentials are
mapped on a relativistic operator basis using projection techniques. This
allows to compare the various potentials at the level of covariant amplitudes
were a remarkable agreement is found. In nuclear matter large scalar and vector
mean fields of several hundred MeV magnitude are generated at tree level. This
is found to be a model independent feature of the nucleon-nucleon interaction.Comment: 5 pages, 2 figures, results for V_lowk added, to appear in PR
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