Radiative decay times for thermal pertubations in a nongray medium

The radiative decay time of harmonic thermal perturbations in a nongray medium of infinite extent is obtained in closed form for two specific band absorption models. These models are the frequently used gray band and the exponential band, the latter being considered more realistic for molecular gases. It is found that the decay time at the boundary of a semi-infinite medium can be obtained in terms of that in an infinite medium. The decay time for combined thermal radiation and conduction is also discussed. The difference in radiative decay rates for a medium with gray bands and one with exponential-tailed bands is marked; in an infinite medium at large Bouguer number, the former falls to zero while the latter rises to a maximum.     

The theory of pure operations

This paper continues the study started in [13] where classes of operations were investigated in the partially ordered vector space approach to the theory of statistical physical systems. In this approach the set of states is represented by a norm closed generating coneK in a complete base norm space (V, K, B) and the set of operations is represented by the setP of positive norm non-increasing linear operators onV. In actual physical experiments it is usually the case that only certain subsets ofK are available and it is supposed that the set (K) of such subsets is the set of split faces ofK. The properties of two important classes of operation are examined. The first classP of strong operations has the property that each member leaves every element of (K) invariant and therefore can be measured in every restricted situation. The second classP _P of pure operations has the property above and also sends pure states into pure states. A study is made, in terms of the structure of (K), of when such operations are physically relevant. The paper ends with an examination of (K),P, P _P in the Von Neumann algebra model.     

Constructive approach to symmetrized two-particle expansions

A complete set of boundary conditions (exchange operators) which follow from the symmetrization postulate for a wave function of a bifermion cluster system is given. The commutation relations of bifermion operators and properties of exchange operators are investigated. For arbitrary bifermion operators the projected Hamiltonian is examined.     

Solvent effects in ligand substitutions of square planar complexes

Data on solvent effects in ligand substitution in square planar complexes are reviewed. In view of the fact that solvent effects for reactions of the planar complexes are quite different from those observed for saturated carbon substrates, it is felt that previous explanations for protic-dipolar aprotic solvent effects may have to be reconsidered.     

Search for charm production in neutron interactions near 250 GeV/c

We have searched for narrow two-body enhancements produced in the forward direction in n-Be interactions near 250 GeV/c. We find no significant signal in any channel and report upper limits for charm production times branching rate to be 200–1000 nb/nucleon for masses in the range 1.7 ? m ? 3.5 GeV/c².     

Slab band absorptance for molecular gas radiation

Nongray molecular gas radiation can be formulated in terms of slab band absorptance, which can be calculated from correlations of laboratory-measured values of band absorption. Slab-band absorptance is not only useful for obtaining the emissivity or mean beam length but also for the formulation of the radiant flux in a nonisothermal gas. Effects of nongray self-absorption by cold boundary layers can then be readily estimated. Illustrative results are presented for gas in a channel with simple straight-line boundary layer profiles at the walls and constant temperature in the center.     

High field magnetoresistance of orientedcrystallites of AuPb2

High field magnetoresistance measurements have been made on samples of AuPb₂, which consist of islands of oriented AuPb₂ surrounded by eutectic mixture. The results obtained are very similar to what would be expected for single crystal samples. Open orbits are observed in 〈100〉, 〈110〉, 〈101〉, 〈112〉 and 〈211〉 and [001] directions. The results are consistent with predictions of the Nearly Free Electron Model.     

A non-perturbative approach to hyperfine splitting

A hyperfine energy splitting for atomic hydrogen is calculated in a non-perturbative manner for a finite width contact interaction. A close agreement between this result and first order perturbation theory is obtained.     

Power requirement for the mixing of thixotropic liquids

A procedure has recently been proposed by Godfrey et al. [1] for the calculation of the variation of power consumption with time when a thixotropic liquid is agitated from rest using an impeller which rotates at constant speed. This procedure requires a knowledge of the power requirement for Newtonian and time-independent non-Newtonian liquids together with viscometric data for the thixotropic liquid obtained under constant shear rate conditions.Experimental work to test the procedure has been carried out in a 0.126-m-diameter cylindrical vessel with anchor, helical ribbon and helical screw impellers. Power consumption data were obtained for a range of Newtonian and time-independent non-Newtonian liquids and this was then used to make predictions of the measured power input to the thixotropic liquids: salad cream, tomato ketchup, yoghurt, paint and Laponite solutions.The agreement between experiment and theory was usually better than 10%. However, for the case of the helical screws rotating in Laponite it was observed that regions existed close to the vessel wall where there was no fluid circulation. In such cases, the predicted power input was greatly in excess of the measured value. This is not a serious limitation of the predictive procedure since efficient industrial mixers would keep the entire fluid in circulation.