A nucleation theory for the anomalous freezing point depression of solvents in swollen rubber gels

It is shown that, on cooling, solvent present at the surface of swollen vulcanizates freezes before the onset of freezing in the gel solvent, causing gel solvent to diffuse to the sample surface where it adds to existing crystalline areas. At the freezing point of the gel solvent a liquid-solid equilibrium does not exist, and a theory is postulated to account for the freezing point depression observed in swollen gels in terms of the conditions required for the formation of crystalline nuclei within the gel solvent. The theory is shown to apply to the freezing of cyclohexane and benzene in vulcanized and unvulcanized natural rubber. In line with the theory the presence of carbon black does not alter the solvent freezing point, but vacuole formation around nonreinforcing fillers leads to lower freezing point depressions.     

Exciton capture cross sections of indium and boron impurities in silicon

Measurements have been made of the decay rates and intensity ratios of photoluminescence lines from Si:In, B. We deduce values for the In and B exciton capture cross sections in the temperature range 3.6 ? 5.9 K. The large difference between the In and B cross sections is discussed in terms of excited states of the In bound exciton.     

Production and marketing decisions with multiple objectives in a competitive environment

This paper presents an application of the mathematical program which has been called the Fritz John problem to a situation in applied economics. A model is presented which enables a firm to maximize profit, subject to constraints on maintenance of market share in the face of collusive action by competitors and subject to resource constraints. An example problem is formulated and solved.The authors wish to acknowledge comments and suggestions offered by J. W. Blankenship and R. E. Kuenne.     

Low lying excited states of the bound exciton in a spherical model

We report the calculation of the S-like excited states of the bound exciton produced by exciting the outer particle. We find that in spherical model for all but very small (?0.03) and very large (?10) mass ratios these states are unbound. We have tentatively identified some of the excited states as being those observed for the donor bound exciton in Gap.     

Simple relation between lidar multiple scattering and depolarization for water clouds

An empirical relationship is derived between the multiple-scattering fraction and the linear depolarization ratio by using Monte Carlo simulations of water clouds measured by backscatter lidar. This relationship is shown to hold for clouds having a wide range of extinction coefficients, mean droplet sizes, and droplet size distribution widths. The relationship is also shown to persist for various instrument fields of view and for measurements made within broken cloud fields. The results obtained from the Monte Carlo simulations are verified by using multiple-field-of-view lidar measurements. For space-based lidars equipped to measure linear depolarization ratios, this new relationship can be used to accurately assess signal perturbations due to multiple scattering within nonprecipitating water clouds.