Arc Width Research Articles

Effect of Blunt Chamfers on Contact Pressure Distribution and Elastic Limit

The interfacial pressure profile is derived analytically, and the elastic load limit is evaluated numerically, for plane strain frictionless elastic contact between a flat surface and a symmetric trapezoidal body whose obtuse corners are replaced by tangent circular arcs. The shape of the pressure distribution depends only on plateau and arc widths. The results enable design of radiused chamfers to give peak-to-mean pressure ratios as low as 1.2 and elastic mean pressure limits up to 1.5 times the yield stress. Conversely, the pressure peak and elastic limit can be predicted for any microscopically blunt chamfer.

Numerical simulation of global formation of auroral arcs

Global simulation of auroral arcs is performed, based on the feedback theory of auroral arcs (Sato, 1978), for a three‐dimensionally coupled ionosphere‐magnetosphere system which includes two pairs of large‐scale Birkeland currents, large‐scale polar cap electric fields, and a day‐night asymmetry of the electron density distribution. Simulation results have shown that auroral arcs are formed in the dark sector of the auroral oval, more preferentially in the evening sector. They usually appear in multiples with a shape elongating in the east‐west direction, each arc being a couple of thousand kilometers in length and 10 to 40 km in width. A pair of small‐scale, upward and downward, Birkeland currents is associated with each arc, the density of which becomes 10 to 200 µA/m² at 110‐km height, and the intensity of the associated electrojet reaches 5 to 20 kA. Each arc is strongly polarized in the direction of the large‐scale north‐south current so that the electric field inside the arc is reduced considerably from its ambient value. What controls the formation of auroral arcs (growing speed, locations, arc width, etc.) is examined in detail. For example, the arc width becomes sharper, as the bounce time of the Alfvén wave decreases. The overall structure of auroras is largely dependent upon the large‐scale Birkeland current, the electric field, and the electron density distribution in the auroral oval.

High resolution measurements of the widths of narrow auroral arcs in the atomic oxygen green line and N 2+ first negative emissions

The anomalous inequality in the spatial extents of the OI 557.7 nm and N 2 + 391.4 nm emissions in auroral arcs was investigated by means of a ground-based low-light T.V. system. First reported in 1967 by Romick and Belon, this anomalous distribution has been the source of some controversy and also subsequent attempts to observe it have produced conflicting results. It is shown that for a simplified geometrical situation, when sufficient spatial and temporal resolution is used, the anomaly is not seen.

Atmospheric spreading of protons in auroral arcs

A model is developed to calculate the effect of atmospheric spreading on the flux and angular distribution of protons in homogeneous auroral arcs. An expression is derived that indicates the angular distribution in the atmosphere as a function of distance from arc center, neutral scale height, arc width, and initial angular distribution. The results of the model agree favorably with those based on Monte-Carlo calculations. From these results the enhancement factors needed to compute the original proton current above the atmosphere are obtained. A technique is indicated for determining the incident angular distribution from rocket-based measurements of the arc width and angular distribution.

Problems of the Irradiation of the Pelvis Cancers in Obese Patients

The irradiation of the pelvis in obese patients meets biological and technical difficulties sometimes considered insuperable. Chiefly when it is necessary to irradiate a very large volume of tissues (for instance, in the case of the irradiation of the pelvis in uterus and ovary cancers) radiotherapy is sometimes considered unsuitable because of considerations concerning the integral dose to be reached, the acute or late reactions expected, difficulties in the choice of the irradiation technique and the execution itself of the therapy. Actually the irradiation of the pelvis in obese patients is clinically possible: it has been performed without complications by the author up to integral doses of 6 × 107 grads in 50 days. The most important problem is the correct choice of treatment technique: when Co 60 gamma rays are employed, obese patients must be irradiated by means of moving beam techniques. The author brings into evidence that obese women, bearing uterus carcinomas, can be irradiated by means of biaxial pendular techniques, employing the same parameters (field at axis, arc width, position of the axis) as in normal subjects. In effect the pelvis in obese subjects is in the center of the corporal section, as in thin subjects. The shape of isodoses in pendular axial irradiations, for Co 60, does not dipend from the dimensions of the body irradiated. The properties of high voltage moving beam radiotherapy turn to the advantage of obese patients. Technical difficulties, which are not negligible, may always be overcome with proper devise.

Sex Characteristics of Black-Tailed Deer Hooves

Measurements of hooves of 106 freshly killed black-tailed deer (Odocoileus hemionus) indicated that sexual differences exist in hooves, and hence tracks. Total length and arc width (width across the toe on an arc described at one-third of the total length from the tip) were measured to the nearest 0.5 millimeter. Deer were aged by tooth replacement and wear. No significant differences existed between sexes in fawns, but arc width differences in yearlings were significant at the 5 percent level. In adults both length and arc width differences between the sexes were significant at the 5 percent level, with ranges for arc width hardly overlapping. Thus tracks of most adult males, as well as the larger yearling males, can be told with a high degree of certainty. The results have not been extended to other Odocoileus species or subspecies. The argument between sportsmen and biologists over whether or not the sex of a deer can be determined from its tracks has persisted despite frequent denials by the biologists. The objective of this study was to determine if such differences do indeed exist in hooves (and hence tracks) and to express such differences in quantitative terms. The investigation was prompted by con-

The Stanford microwave spectroheliograph antenna, a microsteradian pencil beam interferometer

A pencil beam interferometer has been constructed at Stanford, Calif., with multiple beams of 3.1 minutes of arc width to half power (0.8 microsteradian). It is composed of two equatorially-mounted, 16-element, Christiansen arrays of 3-m paraboloids, each 375 feet long (1255 wavelengths at a wavelength of 9.1 cm). The half power beamwidth of the fan beam of a single array is 2.3 minutes of arc. To form the pencil beam, the two arrays are switched together as in a Mills cross. Frequency range is from 2700 to 3350 Mc. Phase adjustment and monitoring are handled by a new technique of modulated, weakly reflecting gas-discharges maintained at the focus of the paraboloids. Television-type scanning yields maps of the sun (spectroheliograms) revealing fine details of the microwave source regions in the chromosphere and corona. All the transient bursts and a large fraction of the steady solar emission at 9.1 cm prove to originate in a small number of highly compact centers, whose brightness temperatures may exceed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5 /times 10^{5}/deg</tex> K. The sensitivity of the instrmnent also allows the thermal emission from the moon ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">250/deg</tex> K) and a number of galactic and extragalactic sources to be studied with high angular resolution. Illumination of the moon by terrestrial radar can be detected. The pencil beam interferometer furnishes the finest beams currently available from pencil beam antennas of any type. Examination of the fundamentals of extracting high resolution details of a source from its radiation field indicates the fitness of pencil beam interferometers, incorporating steerable multielement arrays, for future development to higher resolving power. Adequate technique of phase preservation over wide spacings is available.