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Abstract: Local thermal and chemical equilibration is studied for central AqA collisions at 10.7 160 AGeV in the Ultrarelativis- . tic Quantum Molecular Dynamics model UrQMD . The UrQMD model exhibits strong deviations from local equilibrium at the high density hadron string phase formed during the early stage of the collision. Equilibration of the hadron resonance matter is established in the central cell of volume Vs125 fm3 at later stages, tG10 fmrc, of the resulting quasi-isentropic expansion. The thermodynamical functions in the cell and their time evolution are presented. Deviations of the UrQMD quasi-equilibrium state from the statistical mechanics equilibrium are found. They increase with energy per baryon and lead to a strong enhancement of the pion number density as compared to statistical mechanics estimates at SPS energies. PACS: 25.75.-q; 24.10.Lx; 24.10.Pa; 64.30.qt
To fulfil the requirements of ESS on beam transmission and emittance growth a detailed knowledge of the physics of beam formation as well as the interaction of the H- with the residual gas is substantial. Space charge compensated beam transport using solenoids for ion optics is in favour for the Low Energy Beam Transport (LEBT) between ion source and the first RFQ. Space charge compensation reduces the electrical self fields and beam radii and therefore emittance growth due to aberrations and redistribution. Transport of H- near the ion source is negatively influenced by the dipole fields required for beam extraction and e--dumping and the high gas pressure. The destruction of the rotational symmetry together with the space charge forces causes emittance growth and particle losses within the extraction system. High residual gas pressure near the extractor together with the high cross section for stripping will influence the transmission as well as space charge compensation. Therefore a detailed knowledge of the interaction of the residual gas with the beam and the influence of the external fields on the distribution of the compensation particles is necessary to reduce particle losses and emittance growth. Preliminary experiments using positive hydrogen ions for reference already show the influence of dipole fields on beam emittance. First measurements with H- confirm these results. Additional information on the interactions of the residual gas with the beam ions have been gained from the measurements using the momentum and energy analyser.
A LEBT system consisting of an ion source, two solenoids, and a diagnostic section has been set up to investigate the space charge compensation process due to residual gas ionization [1] and to study experimentally the rise of compensation. To gain the radial beam potential distribution time resolved measurements of the residual gas ion energy distribution were carried out using a Hughes Rojanski analyzer [2,3]. To measure the radial density profile of the ion beam a CCD-camera performed time resolved measurements, which allow an estimation the rise time of compensation. Further the dynamic effect of the space charge compensation on the beam transport was shown. A numerical simulation under assumption of selfconsistent states [4] of the beam plasma has been used to determine plasma parameters such as the radial density profile and the temperature of the electrons. The acquired data show that the theoretical estimated rise time of space charge compensation neglecting electron losses is shorter than the build up time determined experimentally. An interpretation of the achieved results is given.
We calculate the shadowing of sea quarks and gluons and show that the shadowing of gluons is not simply given by the sea quark shadowing, especially at small x. The calculations are done in the lab frame approach by using the generalized vector meson dominance model. Here the virtual photon turns into a hadronic fluctuation long before the nucleus. The subsequent coherent interaction with more than one nucleon in the nucleus leads to the depletion sigma(gamma*A )< A*sigma(gamma * N) known as shadowing. A comparison of the shadowing of quarks to E665 data for 40Ca and 207Pb shows good agreement.
We derive the relativistic quantum transport equation for the pion distribution function based on an effective Lagrangian of the QHD-II model. The closed-time-path Green s function technique and the semiclassical, quasiparticle, and Born approximations are employed in the derivation. Both the mean field and collision term are derived from the same Lagrangian and presented analytically. The dynamical equation for the pions is consistent with that for the nucleons and Delta's which we developed before. Thus, we obtain a relativistic transport model which describes the hadronic matter with N,Delta, and pi degrees of freedom simultaneously. Within this approach, we investigate the medium effects on the pion dispersion relation as well as the pion absorption and pion production channels in cold nuclear matter. In contrast to the results of the nonrelativistic model, the pion dispersion relation becomes harder at low momenta and softer at high momenta as compared to the free one, which is mainly caused by the relativistic kinetics. The theoretically predicted free piN->Delta cross section is in agreement with the experimental data. Medium effects on the piN->Delta cross section and momentum-dependent Delta-decay width are shown to be substantial. PACS-numbers: 24.10.Jv, 13.75.Cs, 21.65.1f, 25.75.2q
Time resolved measurements of the biased disk effect at an Electron Cyclotron Resonance Ion Source
(1999)
First results are reported from time resolved measurements of ion currents extracted from the Frankfurt 14 GHz Electron Cyclotron Resonance Ion Source with pulsed biased-disk voltage. It was found that the ion currents react promptly to changes of the bias. From the experimental results it is concluded that the biased disk effect is mainly due to improvements of the extraction conditions for the source and/or an enhanced transport of ions into the extraction area. By pulsing the disk voltage, short current pulses of highly charged ions can be generated with amplitudes significantly higher than the currents obtained in continuous mode.
We study J/psi suppression in AB collisions assuming that the charmonium states evolve from small, color transparent configurations. Their interaction with nucleons and nonequilibrated, secondary hadrons is simulated using the microscopic model UrQMD. The Drell-Yan lepton pair yield and the J/psi Drell-Yan ratio are calculated as a function of the neutral transverse energy in Pb+Pb collisions at 160 GeV and found to be in reasonable agreement with existing data.
Time-resolved Fourier transform infrared difference spectra of the phosphoenzyme conversion and Ca(2+) release reaction (Ca(2)E(1)-P --> E(2)-P) of the sarcoplasmic reticulum Ca(2+)-ATPase were recorded at pH 7 and 1 degrees C in H(2)O and (2)H(2)O. In the amide I spectral region, the spectra indicate backbone conformational changes preserving conformational changes of the preceding phosphorylation step. beta-sheet or turn structures (band at 1685 cm(-1)) and alpha-helical structures (band at 1653 cm(-1)) seem to be involved. Spectra of the model compound EDTA for Ca(2+) chelation indicate the assignment of bands at 1570, 1554, 1411 and 1399 cm(-1) to Ca(2+) chelating Asp and Glu carboxylate groups partially shielded from the aqueous environment. In addition, an E(2)-P band at 1638 cm(-1) has been tentatively assigned to a carboxylate group in a special environment. A Tyr residue seems to be involved in the reaction (band at 1517 cm(-1) in H(2)O and 1515 cm(-1) in (2)H(2)O). A band at 1192 cm(-1) was shown by isotopic replacement in the gamma-phosphate of ATP to originate from the E(2)-P phosphate group. This is a clear indication that the immediate environment of the phosphoenzyme phosphate group changes in the conversion reaction, altering phosphate geometry and/or electron distribution.
The effect of a single site mutation of Arg-54 to methionine in Paracoccus denitrificans cytochrome c oxidase was studied using a combination of optical spectroscopy, electrochemical and rapid kinetics techniques, and time-resolved measurements of electrical membrane potential. The mutation resulted in a blue-shift of the heme a alpha-band by 15 nm and partial occupation of the low-spin heme site by heme O. Additionally, there was a marked decrease in the midpoint potential of the low-spin heme, resulting in slow reduction of this heme species. A stopped-flow investigation of the reaction with ferrocytochrome c yielded a kinetic difference spectrum resembling that of heme a(3). This observation, and the absence of transient absorbance changes at the corresponding wavelength of the low-spin heme, suggests that, in the mutant enzyme, electron transfer from Cu(A) to the binuclear center may not occur via heme a but that instead direct electron transfer to the high-spin heme is the dominating process. This was supported by charge translocation measurements where Deltapsi generation was completely inhibited in the presence of KCN. Our results thus provide an example for how the interplay between protein and cofactors can modulate the functional properties of the enzyme complex.
Noneequilibrium models (three-fluid hydrodynamics and UrQMD) use to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions. It is demonstrated that these two models - although they do treat the most interesting early phase of the collisions quite differently(thermalizing QGP vs. coherent color fields with virtual particles) - both yields a reasonable agreement with a large variety of the available heavy ion data.