Observed Polarization Effects Research Articles

Advances in CdTe Gamma-Ray Detectors

Performance of halogen-doped CdTe gamma - ray detectors has been improved significantly by the development of new device fabrication methods. In particular, these detectors do not exhibit any of the previously observed polarization effects. Room temperature resolution of 7% at 122 keV has been achieved using applied fields of less than 50 V/mm for detectors up to 100 mm3 in volume.

Enhanced heat flux in non-uniform electric fields

Heat transfer by convection from a thin wire to a liquid was very appreciably increased by the application of a non-uniform electric field of several hundred kilovolts per centimetre which was confocal with the temperature field. This enhancement of the heat flux was much larger in a polar, slightly conducting liquid than in a practically ion-free liquid; the behaviour of a non-polar liquid which contained traces of a polar impurity was intermediate between the two. The polarity of the electric field affected the magnitude of the enhancement of the heat flux in the polar liquid and to a lesser extent also in the non-polar liquid which had a slight content of a polar contamination, but the direction of the field had no influence what­-soever on the enhancement of the heat flux in the ion-free liquid. With each of these three liquids the electrostatic field delayed and even suppressed the transition to nucleate boiling and therefore reduced the risk of ‘burn-out'. It appears that dielectrophoresis is primarily responsible for the increased convection, but that an ion transport phenomenon can make a further significant contribution. The observed polarity effects, in the presence of a minute concentration of ions, suggest that this could be an ion wind. For large values of the elec­trical number ( El ) the incremental increase of the Nusselt number ( Nu ) by dielectrophoresis can be of the order of one hundred.

Polarized positron annihilation in ferromagnetic gadolinium

Abstract Measurements of the angular correlation of positron annihilation radiation in ferromagnetic Gd are presented, and observed polarization effects are attributed to anisotropic spin alignment of the conduction band.

Crystalline Reflectance Spectra of Ion—Radical Salts at Room Temperature, at 77°, and at 4.2°K. I. Wurster's Blue Perchlorate

Polarized reflectance spectra of crystalline Wurster's blue (WB) perchlorate are reported at temperatures above and below the reported phase transition at 190°K of the ion—radical salt. The spectral evidence indicates the position of the first π—π* transition in the solid and uncovers an electronic band associated with the low-temperature phase of the solid in the near-infrared spectral range at approximately 11 000 cm−1. By comparing these spectra with the solution dimer spectrum of WB perchlorate of Hausser and Murrell and by observing the unique polarization of the band in the solid, arguments are advanced in favor of a ``dimer'' model for the solid in the low-temperature phase. Further implications of the observed polarization effects are discussed.

Genetic Polarity in Bacteria

The major genetic apparatus of the enteric bacteria, Escherichia coli and Salmonella typhimurium, appears at first glance to be poor material for creating phenomena which would reflect polarity. Genetically it consists of a single linkage group or chromosome forming a circle (Jacob and Wollman, 1958; Taylor and Thoman, 1964; Sanderson and Demerec, 1965). Physically it consists of DNA, a Watson-Crick (Watson and Crick, 1953) double helix (see Cavalieri and Rosenberg, 1963; Thomas, 1963; Baldwin, 1964) formed into a circle with no free ends (Cairns, 1963). The two strands of the double helix have opposite chemical polarities, and the resulting symmetry eliminates an important possible structural basis for polarity. Most polarity phenomena are those which result from the sequential nature of the functioning of the genetic material. Functioning can be considered at two levels: the sequential replication of the chromosome and the expression (transcription and translation) of the genes. This discussion will be limited to the latter. Observed polarity effects upon gene function can generally be ascribed to the fact that the genetic information consists of a linear sequence of nucleotides and that the mechanisms which transcribe the information into messenger RNA and translate the messenger RNA into the final chain of amino acids do so in a sequential manner. As a consequence, there is a beginning and an endpoint to the linear sequence of purine and pyrimidine bases which make up a gene. This polarity is reinforced at the level of translation since the messenger RNA, being a single strand, possesses a chemical polarity.

An approximation for nucleon-nucleus polarization effects

A simple, approximate method of incorporating the effects of a nuclear spin-orbit potential in the wave function has been developed. When used with the appropriate optical-model wave function for the central potential, it permits closed-form solutions for polarizations and cross sections that are about as simple to obtain as the Born-approximation solutions. Its application is discussed in two types of problems: the elastic scattering of nucleous by nuclei, and the “direct” interaction type of nuclear rearrangement collision. In this latter problem it is found that the elastic scattering of initial and final state particles from the nuclear spin-orbit potential is primarily responsible for the observed polarization effects.

Characteristics of Radio Echoes from Meteor Trails IV: Polarization Effects

Observations have been made of radio echoes from meteor trails at 55 Mc/s in order to test the theoretical estimates by Kaiser and Closs of plasma resonance effects. The aerial array consisted of two Yagis mounted with mutually perpendicular planes of polarization on a common axis. The polarization effects observed are in good agreement with prediction for both short and long duration echoes, but some unexpected results were obtained for meteor trails with line densities in the transition region of 1012 electrons cm-1. Some calculations have been made of the effect of the finite meteor velocity upon observed polarization effects, and are in good agreement with observation.