Charge fluctuations in Au+Au collisions at RHIC energy

A hadron and string cascade model, JPCIAE, together with the corresponding Monte Carlo event generator, has been employed in this paper to investigate further the charge fluctuations in Au+Au collisions at Snn = 130 GeV. The default JPCIAE calculations are in good agreement with PHENIX and STAR data. We found that the thermal predictions for the π gas, the resonance π gas and quark matter deviate, respectively, from the corresponding dynamical simulations from the JPCIAE model. The discrepancies were also found between the π charge fluctuations and the charge fluctuations of all species of hadrons. However the charge fluctuations for "π from ρ and ω decay" and for all the hadrons from resonance decay are close to each other, indicating the correlation between positively and negatively charged hadrons is not sensitive to the species of hadrons. This work shows further that it is questionable to use the charge fluctuations as a signature of QGP.     

The effect of transcrystallinity on the behavior of fibers in polymer matrices

Single copper fibers embedded in a polypropylene matrix along part of their length will, on application of a tensile load, break in the absence of transcrystallinity adjacent to the fiber, or pull out of the polymer matrix in the presence of a transcrystalline zone. It is shown that the transcrystalline zone allows thinning of the fiber in the matrix up to the point at which compressive forces created by the shrinkage of the polymer around the fiber on cooling are removed and fiber pullout occurs.     

Anomalous freezing point depression of solvents in a swollen homogeneous rubber network

The freezing point depression of a solvent, imbibed by crosslinked polyisoprene networks, was studied. It is argued that in a swollen vulcanizate, polymer chains subdivide the solvent, creating zones too small for nucleation on cooling to occur at the normal freezing point of the solvent. The freezing point of the solvent is identified with the temperature at which nuclei can form in the swollen network. A linear relationship between freezing point and the volume fraction of rubber in the swollen gel is predicted for a uniformly crosslinked network. Such a relationship is shown to hold for gamma-irradiated polyisoprene, but not for peroxide-cured samples, where deviations from linearity are interpreted as indicative of nonuniformity in the network. © 1993 John Wiley & Sons, Inc.     

A martingale characterisation of the Brownian excursion compensator

Summary The note concerns the structure of the Brownian excursion filtration ( ^x , xR). This filtration, indexed by the space variable, has infinite martingale dimension. We show how it can be characterised by the martingale properties of the reflecting Brownian local time.     

Critical parameters affecting dynamic mechanical analysis using a du Pont 981 analyser

The parameters affecting Young's modulus and the glass transition temperature have been investigated. Sample dimensions as well as the sample clamping have been shown to be critical. For analysis at non-ambient temperatures the gas flow rate as well as the position of the sample thermocouple, are also important.

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Zusammenfassung Es wurden die den Young Modulus und die Glasübergangstemperatur beeinflussenden Parameter untersucht. Die Probengröße und die Packungsdichte der Probe erwiesen sich als kritisch. Für Analysen oberhalb der Raumtemperatur sind die Geschwindigkeit der Gasströmung und die Lage des Thermoelements in der Probe besonders wichtig.

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We wish to thank the South African C. S. I. R. for financial assistance.     

A contribution to the theory of accelerated sulphur vulcanization of natural rubber and polybutadiene BR with tetramethyl thiuram disulphide and bis(2-benzothiazolyl) disulphide

A number of simple natural rubber (NR) and polybutadiene (BR) formulations were vulcanized in a differential scanning calorimeter. From the shapes of the exothermal cure curves the interaction of curatives can be examined. It is suggested that polysulphidic-accelerator-terminated pendent groups could either crosslink, or be chelated with zinc ions. The latter reaction allows interaction with accelerator molecules to reform the unchelated pendent group, and a zinc accelerator complex, that, in turn, can react with sulphur and rubber molecules to give pendent groups. Differences in the behavior of NR and BR are attributed to the relative rates of these two reactions in the elastomers. Bis(2-benzothiazolyl) disulphide does not react with zinc, and it is suggested that it coordinates with the zinc dithiolate accelerator complex, increasing its activity.     

Photolysis of poly(ethyl acrylate) and poly(n–butyl acrylate) in vacuo

Thin films of poly(ethyl acrylate) and poly(n-butyl acrylate) were decomposed in vacuo by means of a high pressure Hg lamp, and the rate of development of volatile products was measured. The main gaseous products were CO, CO₂, and the alcohol, aldehyde, alkane, and formate derived from the respective ester groups. In addition poly(ethyl acrylate) evolved acetal as well as ethyl propionate, while n-butyl valerate was evolved from poly(n-butyl acrylate) only after prolonged exposure. All products and the principal features of the decomposition are discussed.