Complete experiments in pseudoscalar photoproduction

Necessary and sufficient conditions are derived for three double polarisation measurements to complement cross section and single polarisation measurements in pseudoscalar meson photoproduction to enable amplitudes to be determined up to discrete ambiguities. Rules for choosing two further measurements to resolve the discrete ambiguities are given and practical applications of the rules to particular reactions are discussed.     

The ordered dispersal of point defects over cubic lattices: Application to fluorite-related structures

Superlattices, formed by ordering one kind of defect among the sites of a cubic lattice, may be generated by the repetition of an octahedral unit which has a defect at its center and six more defects at its vertices. The superlattices are severely restricted in number by requiring the vertices of the unit to be equidistant from the center at a radius, R, and mutually separated by at least the same distance, R. Such a restriction applies to cation superlattices in pyrochlores, type-C sesquioxides, and UY₆O₁₂, and to the formal anion vacancies which relate UY₆O₁₂ to fluorite. At each value of R, several superlattices may be possible, involving different fractions, 1/n, of the cubic sites, and these are catalogued for R values less than (14)^1/2a_A (where a_A is the cell edge of the cubic lattice). Parallel defect-rich rows may occur for the highest values of 1/n at a given R, but in most cases the restriction disperses defects efficiently, i.e., tends to satisfy repulsions between defects, as is demonstrated by computed electrostatic potentials. The stability of such ordered dispersals of defects (relative to their randomized alternatives) decreases as n increases, except where an increment in n involves an increase in R. Variations in the stability of superlattice phases in PrO_x may be of this type. Site potentials in the superlattices are related empirically to n^1/3 using reduced variables involving R. High symmetry is not essential to the efficient dispersal of point defects.     

Balance equations for high field transport in the finite collision duration regime

Modifications of the balance equations obtained in the displaced Maxwellian approach for treating high electric field transport are developed for the case where the collision duration is non-negligible. The first-order corrections require the collision induced changes to be averaged over an effective collision duration.     

Effects in polarography attributable to specific adsorption of depolarizers

Summary Some effects in polarography produced by specific adsorption of the oxidised form of the depolarizer are discussed. It is suggested that this adsorption may lead to maxima in d.c. polarography when the depolarizer concentration is small and the solution has a high electrical conductivity. In normal pulse polarography specific adsorption of the oxidised form of the depolarizer may produce a maximum on the polarographic wave which is not basically due to streaming of the solution. Specific adsorption also leads to an increase in sensitivity in a.c. polarography and in R.F. polarography it produces asymmetry in the wave. Experimental results for lead ion in HClO₄ solutions containing varying amounts of Br^– ion suggest that as the concentration of Br^– increases, although the adsorbed species is probably at first PbBr⁺, eventually undissooiated PbBr₂ is strongly adsorbed.

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Zusammenfassung Die Wirkung der spezifischen Adsorption der oxydierten Form des Depolarisators auf polarographische Bestimmungen wird erörtert. Diese Adsorption kann bei der Gleichstrompolarographie Maxima verursachen, wenn die Depolarisationskonzentration niedrig ist und die Lösung eine hohe elektrische Leitfähigkeit besitzt. Bei der normalen Pulspolarographie kann die spezifische Adsorption der oxydierten Form des Depolarisators auch ein Maximum verursachen, daß grundsätzlich nicht von einer Strömung der Lösung herrührt. Bei der Wechselstrompolarographie führt die spezifische Adsorption auch zu einer Zunahme der Empfindlichkeit und bei der Radiofrequenzpolarographie wird eine Asymmetrie der Stufen hervorgerufen. Versuche mit Bleiionen in perchlorsauren Lösungen mit verschiedenen Gehalten an Bromid zeigten, daß bei steigenden Br^–-Konzentrationen anfangs wahrscheinlich PbBr⁺, schließlich jedoch undissoziiertes PbBr₂ stark adsorbiert wird.

     

HE(I) Photoelectron spectra of 1,2-ethanediol in the liquid and gas phases

Nine bands in the He(I) gas-phase photoelectron spectrum of 1,2-ethanediol are assigned by means of ab initio calculation and by comparison with the sp     

Field-dependence of carrier screening in non-linear transport theory

Modifications to the high-field Boltzmann transport equation are obtained to include ab initio self-consistent non-equilibrium free-carrier screening of the scattering rates. For quasi-static homogeneous fields the screening involves a Lindhard-like dielectric function which is field-dependent via the carrier distribution function and the carrier energetics.     

The post-post-Newtonian problem in classical electromagnetic theory

We find the Lagrangian to order c^?4 for two charged bodies (with $\text{e}{}_1\text{m}{}_1\text{=}\text{e}{}_2\text{m}{}_2$) in electromagnetic theory. This Lagrangian contains acceleration terms in its final form and we show why it is incorrect to eliminate these terms by using the equationsof motion in the Lagrangian as was done by Golubenkov and Smorodinskii, and by Landau and Lifshitz. We find the center of inertia and show that the potential energy term does not split equally between particles 1 and 2 as it does in the Darwin Lagrangian (Lagrangian to order c^?2). In addition to the infinite self-energy terms in the electromagnetic energy-momentum tensor, which are eliminated using Gupta's method, some new type of divergent terms are found in the moment of electromagnetic field energy and in the electromagnetic field momentum which cancel in the final conservation law for the center of inertia.