Comparison of Viscosities from the Chapman-Enskog and Relaxation Time Methods

A quantitative comparison between the results of shear viscosities from the Chapman-Enskog and relaxation time methods is performed for selected test cases with specified elastic differential cross sections: (i) the non-relativistic, relativistic and ultra-relativistic hard sphere gas with angle and energy independent differential cross section, (ii) the Maxwell gas, (iii) chiral pions and (iv) massive pions. Our quantitative results reveal that the extent of agreement (or disagreement) depends very sensitively on the energy dependence of the differential cross sections employed.Comment: Submitted to Cent. Eur. J.Phy

Biologically inspired learning in a layered neural net

A feed-forward neural net with adaptable synaptic weights and fixed, zero or non-zero threshold potentials is studied, in the presence of a global feedback signal that can only have two values, depending on whether the output of the network in reaction to its input is right or wrong. It is found, on the basis of four biologically motivated assumptions, that only two forms of learning are possible, Hebbian and Anti-Hebbian learning. Hebbian learning should take place when the output is right, while there should be Anti-Hebbian learning when the output is wrong. For the Anti-Hebbian part of the learning rule a particular choice is made, which guarantees an adequate average neuronal activity without the need of introducing, by hand, control mechanisms like extremal dynamics. A network with realistic, i.e., non-zero threshold potentials is shown to perform its task of realizing the desired input-output relations best if it is sufficiently diluted, i.e. if only a relatively low fraction of all possible synaptic connections is realized

Invariance of the relativistic one-particle distribution function

The one-particle distribution function is of importance both in non-relativistic and relativistic statistical physics. In the relativistic framework, Lorentz invariance is possibly its most fundamental property. The present article on the subject is a contrastive one: we review, discuss critically, and, when necessary, complete, the treatments found in the standard literature

Het ontwikkelen, optimaliseren en beperkt valideren van voorbehandelings-, extractie-, en opwerkingsvoorschriften ten behoeve van het bepalen van organische verbindingen in de vaste matrices grond, waterbodem en bouwstoffen voor de in project V24/104 ontwikkelde GCMS-voorschriften. (Project 105 fase 1)

A restricted deskstudy is carried out to investigate the possibilities for improvement of previously developed methods for the determination of pesticides and organic contaminants in solid matrices like soil and construction materials. For the pretreatment and extraction of samples a number of methods are in principal suitable. Based on experience and in connection to existing methods a selection has been made

Genome sequences of 10 new carnation mottle virus variants

Here, we report the genome sequences of 10 Carnation mottle virus variants. Six variants originated from a single proprietary carnation cultivar, and four were derived from four different proprietary cultivars. All variants showed nucleotide differences, but the last four did not show any variation at the amino acid level

Monitoring zware metalen en organische microverontreinigingen in Nederlandse visserijproducten

In 2003 is ten behoeve van het ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) een monitoringsprogramma opgestart waarin gehalten van organische microverontreinigingen en metalen in Nederlandse visserijproducten worden gemeten. Het onderzoek is uitgevoerd naar polychloorbifenylen (PCBs), organochloor pesticiden (OCPs), tris(4-chloor)phenylmethaan en –methanol (TCPM(e)), dioxines en dioxine-achtige PCBs (beperkt aantal monsters), cadmium, lood, kwik, zink en seleen. Voornamelijk in Nederlandse viswateren gevangen en/of aangelande vis is in het onderzoek betrokken evenals enkele monsters gekweekte vis. Uit de resultaten blijkt dat gehalten van organische microverontreinigingen vooral hoog zijn in rivierpaling. De hoogst verontreinigde locaties betreffen de benedenstroomse gebieden van de grote rivieren zoals het Haringvliet en de Nieuwe Merwede. Op enkele locaties komen PCB gehalten boven de Warenwet consumptienorm