Dynamics of Multifragmentation in Heavy Ion Collisions

We review multifragmentation data obtained at the SIS/GSI accelerator using heavy ion beams with (0.1-1)A GeV together with the ALADIN and FOPI experimental setups.Comment: 25 pages, with 38 included figures; invited talk at the Nishinomiya-Yukawa Symposium on Frontiers of Nuclear Collision Dynamics, Japan (nov.18-19); to be published in Progress of Theoretical Physic

Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies

The classical dynamical model for reactions induced by weakly-bound nuclei at near-barrier energies is developed further. It allows a quantitative study of the role and importance of incomplete fusion dynamics in asymptotic observables, such as the population of high-spin states in reaction products as well as the angular distribution of direct alpha-production. Model calculations indicate that incomplete fusion is an effective mechanism for populating high-spin states, and its contribution to the direct alpha production yield diminishes with decreasing energy towards the Coulomb barrier. It also becomes notably separated in angles from the contribution of no-capture breakup events. This should facilitate the experimental disentanglement of these competing reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the author), Accepted in Journal of Physics

Medium mass fragments production due to momentum dependent interactions

The role of system size and momentum dependent effects are analyzed in multifragmenation by simulating symmetric reactions of Ca+Ca, Ni+Ni, Nb+Nb, Xe+Xe, Er+Er, Au+Au, and U+U at incident energies between 50 MeV/nucleon and 1000 MeV/nucleon and over full impact parameter zones. Our detailed study reveals that there exist a system size dependence when reaction is simulated with momentum dependent interactions. This dependence exhibits a mass power law behavior.Comment: 5 figure

Re-evaluating Moodie's Opisthotonic-Posture Hypothesis in Fossil Vertebrates Part I: Reptiles—the taphonomy of the bipedal dinosaurs Compsognathus longipes and Juravenator starki from the Solnhofen Archipelago (Jurassic, Germany)

More or less complete and articulated skeletons of fossil air-breathing vertebrates with a long neck and tail often exhibit a body posture in which the head and neck are recurved over the back of the animal. Additionally, the tail is typically drawn over the body, while the limbs have a rigid appearance. In palaeontological literature, this "opisthotonic posture” of such fossils still requires a causal interpretation in an etiological context. According to this hypothesis, there is a presumption of a cerebral disorder generating perimortem muscle spasms that are preserved by rapid burial or other sequestration of a skeleton in the fossil record. We re-evaluate this "opisthotonic posture hypothesis” by analysing the non-avian theropods Compsognathus longipes and Juravenator starki from the famous South Franconian plattenkalks of the Upper Jurassic Solnhofen Archipelago. Decay experiments with the extant domestic fowl Gallus gallus L. and analysis of the theropods' constructional morphological constraints reveal that the opisthotonic posture is not a peri- but a postmortem phenomenon. By analysing the timeline of decomposition, it is possible to recognise different stages of decay, depending on the varying decay resistance of soft tissues. Adipocere formation must have blocked further decay until embedding was completed by minimal sedimentation. Analyses of the palaeoenvironment of the basins of the Solnhofen Archipelago show that the conditions of deposition of individual basins cannot be considered to be similar, even inside the same time frame. Therefore, a generalised approach of looking at the depositional setting must be excluded. Assumptions by Faux and Padian (2007) that the accepted palaeoenvironmental reconstruction of the Solnhofen Fossillagerstätte has to be questioned in the light of the opisthotonic posture hypothesis enforce the need for a review of palaeoecological factors of the Franconian Plattenkalks from a taphonomic perspectiv

Transverse flow of nuclear matter in collisions of heavy nuclei at intermediate energies

The Quantum Molecular Dynamics Model (IQMD) is used to investigate the origin of the collective transverse velocity observed in heavy ion experiments. We find that there are three contributions to this effect: initial-final state correlations, potential interactions and collisions. For a given nuclear equation of state (eos) the increase of the transverse velocity with increasing beam energy is caused by the potential part. For a given beam energy the collective transverse velocity is independent of the nuclear eos but the relative contributions of potential and collisions differ. In view of the importance of the potential interactions between the nucleons it is not evident that the similarity of the radial velocities measured for fragments at beam energies below 1 AGeV and that for mesons at beam energies above 2 AGeV is more than accidental.Comment: 5 pages, 5 figures, revtex, OASIS ref PLB1700

First record of the leptonectid ichthyosaur Eurhinosaurus longirostris from the Early Jurassic of Switzerland and its stratigraphic framework

An incomplete skull of the leptonectid ichthyosaur Eurhinosaurus longirostris found in the Rietheim Member (previously "Posidonienschiefer”; Toarcian, Early Jurassic) of Staffelegg, Canton Aargau, is the first record from Switzerland of this taxon and supports the status of Eurhinosaurus longirostris as a palaeobiogeographic very widespread ichthyosaur species in the Early Toarcian of Western Europe. Being from either the Bifrons or Variabilis zone, it is one of the youngest records of Eurhinosaurus and one of the few diagnostic ichthyosaur finds from this time interval. The partial skull is well articulated and preserved three-dimensionally in a carbonate concretion. Both the mode of preservation of the ichthyosaur and an associated ammonoid (Catacoeloceras raquinianum) provided the age of the concretion, which had been collected from scree. Taphocoenosis and taphonomy show the C. raquinianum to be one of few non re-worked fossils recorded from the Early to Late Toarcian boundary (Bifrons/Variabilis zone) of northern Switzerland in general and of this ammonite species in particular. The Toarcian section at Staffelegg differs from other localities where strata of the same age are exposed with respect to facies variations of the Rietheim Member (previously "Posidonienschiefer”, Early Toarcian) and the extraordinarily high thickness of the Gross Wolf Member (previously "Jurensis-Mergel”, Late Toarcian

Directed and Elliptic Flow in 158 AGeV Pb+Pb Collisions

Directed and elliptic flow of protons and positively charged pions has been studied in the target fragmentation region using the Plastic Ball detector in the WA98 experiment. The results exhibit a strong dependence on centrality, rapidity, and transverse momentum. The rapidity dependence can be described by a Gaussian distribution. The model comparisons reveal a large discrepancy of the flow strength obtained from the data and the simulations.Comment: 4 pages, 4 eps figures, talk at Quark Matter 99, see also http://qgp.uni-muenster.de/WA98/qm99/flo