878 research outputs found
Thermal Dileptons from Coarse-Grained Transport as Fireball Probes at SIS Energies
Utilizing a coarse-graining method to convert hadronic transport simulations
of Au+Au collisions at SIS energies into local temperature, baryon and pion
densities, we compute the pertinent radiation of thermal dileptons based on an
in-medium spectral function that describes available spectra at
ultrarelativistic collision energies. In particular, we analyze how far the
resulting yields and slopes of the invariant-mass spectra can probe the
lifetime and temperatures of the fireball. We find that dilepton radiation sets
in after the initial overlap phase of the colliding nuclei of about 7 fm/c, and
lasts for about 13 fm/c. This duration closely coincides with the development
of the transverse collectivity of the baryons, thus establishing a direct
correlation between hadronic collective effects and thermal EM radiation, and
supporting a near local equilibration of the system. This fireball "lifetime"
is substantially smaller than the typical 20-30 fm/c that naive considerations
of the density evolution alone would suggest. We furthermore find that the
total dilepton yield radiated into the invariant-mass window of
GeV/, normalized to the number of charged pions, follows a relation to
the lifetime found earlier in the (ultra-) relativistic regime of heavy-ion
collisions, and thus corroborates the versatility of this tool. The spectral
slopes of the invariant-mass spectra above the mass provide a
thermometer of the hottest phases of the collision, and agree well with the
maximal temperatures extracted from the coarse-grained hadron spectra.Comment: 9 pages, 6 figures; v2: extended discussion, matches the version
accepted for publicatio
Internationale Kapitalgeber und Bildungsinvestition in der sogenannten Dritten Welt: Die Beispiele Namibia und Senegal
Model Continuity in Discrete Event Simulation: A Framework for Model-Driven Development of Simulation Models.
Most of the well known modeling and simulation methodologies state the importance of conceptual modeling in simulation studies and they suggest the use of conceptual models during the simulation model development process. However, only a limited number of methodologies refers to howto move from a conceptual model to an executable simulation model. Besides, existing modeling and simulation methodologies do not typically provide a formal method for model transformations between the models in different stages of the development process. Hence, in the current M&S practice, model continuity is usually not fulfilled. In this article, a model driven development framework for modeling and simulation is in order to bridge the gap between different stages of a simulation study and to obtain model continuity. The applicability of the framework is illustrated with a prototype modeling environment and a case study in the discrete event simulation domain
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