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The transverse mass spectra of J/psi and psi' mesons and Omega hyperons produced in central Au+Au collisions at RHIC energies are discussed within a statistical model used successfully for the interpretation of the SPS results. The comparison of the presented model with the future RHIC data should serve as a further crucial test of the hypothesis of statistical production of charmonia at hadronization. Finally, in case of validity, the approach should allow to estimate the mean transverse flow velocity at the quark gluon plasma hadronization.
The transverse mass spectra of Omega, J/psi and psi' in Pb+Pb collisions at 158 AGeV are studied within a hydrodynamical model of the quark gluon plasma expansion and hadronization. The model reproduces the existing data with the common hadronization parameters: temperature T=T_H = 170 MeV and average collective transverse velocity v_T = 0.2.
Results of the production of Xi and Xi-bar hyperons in central Pb+Pb interactions at 158 GeV/c per nucleon are presented. This analysis utilises a global reconstruction procedure, which allows a measurement of 4pi integrated yields to be made for the first time. Inverse slope paramters, which are determined from an exponential fit to the transverse mass spectra, are shown. Central rapidity densities are found to be 1.49 +- 0.08 and 0.33 +- 0.04 per event per unit of rapidity for Xi and Xi-bar respectively. Yields integrated to full phase space are 4.12 +- 0.02 and 0.77 +- 0.04 for Xi and Xi-bar. The ratio of Xi-bar/Xi at mid-rapidity is 0.22 +- 0.03.
Quantitative evaluation of parsers has traditionally centered around the PARSEVAL measures of crossing brackets, (labeled) precision, and (labeled) recall. However, it is well known that these measures do not give an accurate picture of the quality of the parsers output. Furthermore, we will show that they are especially unsuited for partial parsers. In recent years, research has concentrated on dependencybased evaluation measures. We will show in this paper that such a dependency-based evaluation scheme is particularly suitable for partial parsers. TüBa-D, the treebank used here for evaluation, contains all the necessary dependency information so that the conversion of trees into a dependency structure does not have to rely on heuristics. Therefore, the dependency representations are not only reliable, they are also linguistically motivated and can be used for linguistic purposes.
We review the representation problem based on factoring and show that this problem gives rise to alternative solutions to a lot of cryptographic protocols in the literature. And, while the solutions so far usually either rely on the RSA problem or the intractability of factoring integers of a special form (e.g., Blum integers), the solutions here work with the most general factoring assumption. Protocols we discuss include identification schemes secure against parallel attacks, secure signatures, blind signatures and (non-malleable) commitments.
The high E(T) drop of J / psi to Drell-Yan ratio from the statistical c anti-c coalescence model
(2002)
The dependence of the J/psi yield on the transverse energy ET in heavy ion collisions is considered within the statistical c¯c coalescence model. The model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the high-ET region (ET >< 100 GeV). Here ET -fluctuations and ET -losses in the dimuon event sample naturally create the celebrated drop in the J/psi to Drell-Yan ratio.
Strange particle production in A+A interactions at 158 AGeV is studied by the CERN experiment NA49 as a function of system size and collision geometry. Yields of charged kaons, phi and Lambda are measured and compared to those of pions in central C+C, Si+Si and centrality-selected Pb+Pb reactions. An overall increase of relative strangeness production with the size of the system is observed which does not scale with the number of participants. Arguing that rescattering of secondaries plays a minor role in small systems the observed strangeness enhancement can be related to the space-time density of the primary nucleon-nucleon collisions.
We address the production of black holes at LHC in space times with compactified space-like large extra dimensions (LXD). Final state black hole production leads to suppression of high-PT jets, i.e. a sharp cut-o in (pp!jet+X). This signal is compared to the jet plus missing energy signature due to graviton production in the final state as proposed by the ATLAS collaboration. Time evolution and lifetimes of the newly created black holes are calculated based on the micro- canonical formalism. It is demonstrated that previous lifetime estimates of micro black holes have been dramatically underestimated. The creation of a large number of quasi-stable black holes is predicted with life times of hundred fm/c at LHC. Medium modifications of the black holes evaporation rate due to the quark gluon plasma in relativistic heavy ion collisions as well as provided by the cosmic fluid in the early universe are studied
Motivation: The topic of this paper is the estimation of alignments and mutation rates based on stochastic sequence-evolution models that allow insertions and deletions of subsequences ("fragments") and not just single bases. The model we propose is a variant of a model introduced by Thorne, Kishino, and Felsenstein (1992). The computational tractability of the model depends on certain restrictions in the insertion/deletion process; possible effects we discuss.
Results: The process of fragment insertion and deletion in the sequence-evolution model induces a hidden Markov structure at the level of alignments and thus makes possible efficient statistical alignment algorithms. As an example we apply a sampling procedure to assess the variability in alignment and mutation parameter estimates for HVR1 sequences of human and orangutan, improving results of previous work. Simulation studies give evidence that estimation methods based on the proposed model also give satisfactory results when applied to data for which the restrictions in the insertion/deletion process do not hold.
Availability: The source code of the software for sampling alignments and mutation rates for a pair of DNA sequences according to the fragment insertion and deletion model is freely available from www.math.uni-frankfurt.de/~stoch/software/mcmcsalut under the terms of the GNU public license (GPL, 2000).
Die Sprachsituation der deutschen Schweiz, wo die Mundarten den großen Teil der gesprochenen Sprachrealität darstellen, bietet ein weites Feld für Erforschung der gesprochenen Sprache. Die starke Position der Mundarten und die weitgehend mündliche Überlieferung machen sie für die Sprachwandelforschung interessant. Nachdem die Erforschung von Sprachwandel lange auf der Rekonstruktion gesprochener Sprache aus Schriftzeugnissen beschränkt war, kann seit dem wissenschaftlich reflektierten Festhalten gesprochener Sprache in Transkripten und seit der Möglichkeit zur Tonarchivierung auf historische Zeugnisse gesprochener Sprache zurückgegriffen werden. So kann die primäre Sprachform berücksichtigt werden. Denn obwohl Lautwandel lange der zentrale Bereich der Sprachgeschichtsschreibung war und die Sprachgeschichtsschreibung weitgehend vom "Primat des Sprechens" (Sonderegger 1979, 11) ausgegangen war, musste sie sich lange mit Schriftzeugnissen abfinden, die nur Reflexe gesprochener Sprache darstellten.
The space-time dynamics and pion-HBT radii in central heavy ion-collisions at CERN-SPS and BNL-RHIC are investigated within a hydrodynamic simulation. The dependence of the dynamics and the HBT-parameters on the EoS is studied with different parametrizations of a chiral SU(3) sigma omega model. The selfconsistent collective expansion includes the e ects of e ective hadron masses, generated by the nonstrange and strange scalar condensates. Different chiral EoS show di erent types of phase transitions and even a crossover. The influence of the order of the phase transition and of the latent heat on the space-time dynamics and pion-HBT radii is studied. A small latent heat, i.e. a weak first-order chiral phase transition, or a smooth crossover lead to distinctly di erent HBT predictions than a strong first order phase transition. A quantitative description of the data, both at SPS energies as well as at RHIC energies, appears di cult to achieve within the ideal hydrodynamic approach using the SU(3) chiral EoS. A strong first-order quasi-adiabatic chiral phase transition seems to be disfavored by the pion-HBT data from CERN-SPS and BNL-RHIC.
Experiment NA49 at the Cern SPS uses a large acceptance detector for a systematic study of particle yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results for Pb+Pb collisions at 40, 80 and 158 A*GeV beam energy are shown and compared to measurements at lower and higher energies.
The large acceptance and high momentum resolution as well as the significant particle identification capabilities of the NA49 experiment at the CERN SPS allow for a broad study of fluctuations and correlations in hadronic interactions. In the first part recent results on event-by-event charge and p_t fluctuations are presented. Charge fluctuations in central Pb+Pb reactions are investigated at three different beam energies (40, 80, and 158 AGeV), while for the p_t fluctuations the focus is put on the system size dependence at 158 AGeV. In the second part recent results on Bose Einstein correlations of h-h- pairs in minimum bias Pb+Pb reactions at 40 and 158 AGeV, as well as of K+K+ and K-K- pairs in central Pb+Pb collisions at 158 AGeV are shown. Additionally, other types of two particle correlations, namely pi p, Lambda p, and Lambda Lambda correlations, have been measured by the NA49 experiment. Finally, results on the energy and system size dependence of deuteron coalescence are discussed.
Qualifizierung zum eProf? : Medienkompetenz und Qualifizierungsstrategien für Hochschullehrende
(2002)
Welche Kompetenzen benötigen Hochschullehrende, um neuen Medien in der Lehre einzusetzen? In diesem Beitrag soll beleuchtet werden, o welche Rolle haben Hochschullehrende beim Einsatzes neuer Medien in der Lehre, o welche Aufgaben und Anforderungen kommen in diesem Kontext auf sie zu und o welche Qualifizierungs- und Beratungsangebote sind dabei geeignet? Zur Beantwortung dieser Fragen wurde an verschiedenen Hochschulen untersucht, welche Aufgaben beim dem Einsatz neuer Medien bei den Lehrenden verbleiben und welche von internen und externen Anbietern (auch Rechen- und Medienzentren) übernommen werden sowie welche Qualifikationen Lehrende benötigen, um diesen Prozess zu steuern, entsprechende Entscheidungen treffen und Konzepte entwickeln zu können, um das medial gestützte Lehrangebot zu pflegen und zu betreuen. Dieser Beitrag stellt die Ergebnisse der Untersuchung zusammen.
Welches der vielen Internet-Bezahlsysteme sich am Markt durchsetzen wird, hängt entscheidend von der „gefühlten Sicherheit“ bei den Kunden ab. Dieses Fazit konnte man Ende Juni 2002 zum Abschluss des Symposiums „Digitales Geld“ im Institut für Telematik ziehen. Weitere Voraussetzungen für den wirtschaftlichen Erfolg sind einfache Bedienung, transparente und bequeme Abwicklung sowie niedrige Kosten für Verbraucher und Anbieter, waren sich die 14 Referenten aus Wissenschaft, Wirtschaft und Verbänden einig. Das Symposium zur Sicherheit von Internet-Bezahlsystemen verfolgten rund 30 Teilnehmer vor Ort und mehr als 100 durch Live-Übertragung im World Wide Web. Die technischen Probleme - so wurde klar - sind mehr oder weniger alle gelöst. Offen bleibt die Frage, wie für das Verträgeschließen und Bezahlen im Internet mehr gesellschaftliche Akzeptanz und juristische Absicherung erreicht werden kann. Nach dem übereinstimmenden Urteil der meisten Referenten sind Internet-Bezahlsysteme „selbst für die technische Avantgarde“ noch zu kompliziert zu bedienen. Verständlich sei der Wunsch nach einheitlichen Standards. Noch immer stellten für die Kunden die Überweisung nach Rechnung (fast 90% der Internet- Käufer), die Lastschriftabbuchung (über 70%) und die Nachnahme-Zahlung (rund 65%) die beliebtesten Zahlverfahren beim Online-Shopping dar, betonten Marktforscher und Verbraucherschützer. Den größten Bedarf für neue Verfahren, die sinnvollerweise auf den vorhandenen Abrechnungsmechanismen aufbauen sollten, sahen die Symposiums-Teilnehmer im Bereich der Abrechnung von Klein(st)-Beträgen, wie sie beim Kauf digitaler Güter (Software, Musik, elektronische Dokumente usw.) anfallen. Um rentabel arbeiten zu können, seien hier aber die Sicherheitsanforderungen geringer. Mobiles Bezahlen per Handy werde sich in Zukunft immer mehr durchsetzen. Das Sicherheitsproblem liege hier in der „Luftschnittstelle“, so ein Experte, denn das Abhören von Mobilfunkverkehr sei in Europa besonders weit verbreitet. In jedem Fall - so hochrangige Vertreter der Finanzwirtschaft - haben Verfahren im E- und M-Commerce dann eine Chance, wenn sie auf den weltweit bewährten Transaktionsmechanismen beruhen.
The production of multiple strange baryons in pp interactions is studied. Here one can directly probe the microscopic decay of color flux tubes, allowing to differentiate between different string models and a statistical description of the hadronization. To analyse the different stages of a heavy ion collision the time evolution of the elastic and inelastic collision rates in central Pb+Pb interactions are studied. The microscopic simulation supports the idea of separated phases (non-equilibrium -> chemical freeze-out -> kinetic freeze-out) in the evolution of the system. The spectra and abundances of Lambda(1520), K 0(892) and other resonances are used to study the break-up dynamics of the source between chemical and thermal freeze-out.
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R ~ 8 km. PACS: 26.60+c, 21.65+f, 97.60.Gb, 97.60.Jd
The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) theta - omega approach. The commonly adopted noninteracting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent e ective hadron masses and e ective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three di erent parametrizations of the model, which show di erent types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, freezing of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters di er considerably from those obtained in simple noninteracting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The in-medium masses turn out di er up to 150 MeV from their vacuum values.
We present calculations of two-pion and two-kaon correlation functions in relativistic heavy ion collisions from a relativistic transport model that includes explicitly a first-order phase transition from a thermalized quark-gluon plasma to a hadron gas. We compare the obtained correlation radii with recent data from RHIC. The predicted R_side radii agree with data while the R_out and R_long radii are overestimated. We also address the impact of in-medium modifications, for example, a broadening of the rho-meson, on the correlation radii. In particular, the longitudinal correlation radius R_long is reduced, improving the comparison to data.