Multiplicity distributions in canonical and microcanonical statistical ensembles

The aim of this paper is to introduce a new technique for the calculation of observables, in particular multiplicity distributions, in various statistical ensembles at finite volume. The method is based on Fourier analysis of the grand canonical partition function. A Taylor expansion of the generating function is used to separate contributions to the partition function in their power in volume. We employ Laplace’s asymptotic expansion to show that any equilibrium distribution of multiplicity, charge, energy, etc. tends to a multivariate normal distribution in the thermodynamic limit. A Gram–Charlier expansion additionally allows for the calculation of finite volume corrections. Analytical formulas are presented for the inclusion of resonance decay and finite acceptance effects directly into the partition function of the system. This paper consolidates and extends previously published results of the current investigation into the properties of statistical ensembles.     

Recent results from PHOBOS on particle production at high p T

A selection of experimental results from the PHOBOS Collaboration relevant for probing high-energy nuclear collisions with high transverse momentum particles is presented. The inclusive yields of charged particles and comparisons between nuclear and elementary collisions already reveal a large amount of parton energy loss in the hot and dense medium created in heavy ion collisions. Remarkable scaling and factorization features are observed, unifying the data taken at various collision energies, centralities and nuclear sizes. To further analyze the nature of the energy loss, a measurement of pseudorapidity (Δη) and azimuthal angle (Δφ) correlations between high transverse momentum charged hadrons (p _T >2.5 GeV/c) and all associated charged particles is presented at both short-range (small Δη) and long-range (large Δη) over a continuous detector acceptance covering −4<Δη<2. Various near- and away-side features of the correlation structure are discussed as a function of centrality in Au + Au collisions at  GeV. The results provide new information about the longitudinal (Δη) extent of the near-side ‘ridge’ structure, first observed by the STAR Collaboration over a narrower η range. In central Au + Au collisions the ridge structure extends to at least Δη=4, and its strength completely diminishes as collisions become more peripheral. Presenter of the paper on the 3rd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, 8–14 June 2008, Illa da Toxa (Galicia-Spain).     

Gerichtliche Blutuntersuchung

Ohne Zusammenfassung     

Fundamentals and applications of polymers designed for laser ablation

The ablation characteristics of various polymers were studied at low and high fluences for an irradiation wavelength of 308 nm. The polymers can be divided into three groups, i.e. polymers containing triazene groups, designed ester groups, and reference polymers, such as polyimide. The polymers containing the photochemically most active group (triazene) exhibit the lowest thresholds of ablation (as low as 25 mJ cm^-2) and the highest etch rates (e.g. 250 nm/pulse at 100 mJ cm^-2), followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients have a clear influence on the ablation characteristics. The different behavior of polyimide might be explained by a pronounced thermal part in the ablation mechanism. The laser-induced decomposition of the designed polymers was studied by nanosecond interferometry and shadowgraphy. The etching of the triazene polymer starts and ends with the laser pulse, indicating photochemical ablation. Shadowgraphy reveals mainly gaseous products and a pronounced shockwave in air. The designed polymers were tested for an application as the polymer fuel in laser plasma thrusters. Received: 21 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +41-56/3104-412, E-mail: thomas.lippert@psi.ch     

Syntheses and reactions of some fluorinated dienes,cyclobutenes and furans

There are many reports¹ of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically

useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed.We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described.

For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.

     

Effects of natural environmental factors on delta13C of lichens

This preliminary study was designed to determine the extent to which the carbon isotope ratio in four species of lichens was influenced by such features as humidity, rainfall, radioactivity, and air quality. The sampling sites were selected to be at a great distance from any pollution. At the time of sampling, field data (temperature, relative humidity, average monthly precipitation, and radioactivity) were recorded. delta(13)C in whole lichen specimens were determined using standard mass spectrometric techniques with a standard deviation of+/-0.3 per thousand. We have found a weak but negative correlation between delta(13)C and relative humidity, and a positive correlation between delta(13)C and average monthly precipitation at the studied sites. The effects were minor, of the order of 1.5 per thousand for all the lichens. We have examined the correlation between (137)Cs activity concentration of the studied lichens and delta(13)C of these lichens, and we have suggested that fixation of radiocesium does not alter photosynthesis rate. There was a delta(13)C variation with the altitude gradient with less negative delta(13)C values at higher altitude. It is possible that this difference is caused by the ozone and occurred at the high elevations.