摘要:

This paper is concerned with theoretical estimates of wide‐angle radiation in pencil beam antennas. In reflector‐type antennas this energy consists of direct radiation from the feed and scattered energy from the reflector. Approximate methods for the evaluation of these contributions are discussed, together with their simplifying assumptions. To get some numerical indications, calculations were made for paraboloidal reflectors of differentf/Dratios and a class of primary patterns which provide an approximate representation of a great many common feeds. The results are presented in graphical form to provide useful design information. They show the dependence of the wide‐angle radiation level on feed and dish parameters.

ISSN:0021-8979    

DOI:10.1063/1.1722063

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The effect of low‐temperature (liquid nitrogen) reactor irradiation on the white‐to‐grey tin transformation has been investigated. It was found that, compared to an unirradiated pure sample, the transformation, measured by dilatometry, is drastically accelerated by prior irradiation. The irradiation apparently eliminates the normally very long induction period. The kinetic behavior of reactor irradiated samples and of samples seeded with grey tin were found to be qualitatively similar. These results indicate that the defects introduced into white tin by reactor irradiation serve as nuclei, or at least embryos of nucleation, for the subsequent phase transformation. Whether point defects, their aggregates, or the strains surrounding the displaced atoms are responsible for the artificial ``seeding'' cannot yet be decided. Reactor irradiation appears to be a promising new tool for studying nucleation and growth processes since quite uniform artificial nucleation can be accomplished this way.

ISSN:0021-8979    

DOI:10.1063/1.1722064

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Number and energy gamma‐ray albedos have been calculated for a material ofZeff=13, corresponding to both concrete and aluminum. The Monte Carlo method was used, the calculations being performed on an IBM‐701. The single‐ and multiple‐scattered components were evaluated separately; the multiple‐scattered component was considerably the larger of the two in most cases, being as much as three times as large as the single‐scattered component. For moderately small incident angles, the emergent photons are distributed approximately proportional to the cosine of the normal angle of emergence. The spectra peak around 150–250 kev and in some cases have a second peak at higher energy; such secondary peaks move upward in energy and increase in importance as the angle of incidence increases. The average energy of the emergent photons varies from 0.33 to 1.4moc2. For the multiple‐scattered component the average energy varies from 0.30 to 0.93moc2. Buildup factors have been calculated for 2moc2gammas normally incident on aluminum of 2 and 4 mean free paths thickness.

ISSN:0021-8979    

DOI:10.1063/1.1722065

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The reverse current and carrier lifetime have been measured in a series of germanium diodes as a function of temperature between room temperature and liquid nitrogen temperature. The lifetime reaches a plateau at low temperatures, and its behavior can be explained in terms of the Hall‐Shockley‐Read recombination theory. LogiRvs1/Texhibits a break to a shallower slope at lower temperatures, which can be explained in terms of charge generation by recombination centers in the space‐charge region.

ISSN:0021-8979    

DOI:10.1063/1.1722067

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The scattering of a cylindrical TEM wave by two parallel, identical conducting circular cylinders is developed as a special case of a theoretical analysis which treats the scattering by an arbitrary array of cylinders. Only the case with the incidentE‐vector parallel to the axes of the cylinders is considered, and attention is focused on the mutual effects present when the cylinder diameter and spacing are comparable to a wavelength.The approximations made in the theory are tested experimentally using 3 cm microwaves in a parallel plate region. Significant departures from the results of the independent scattering hypothesis as predicted by the theory have been confirmed experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1722068

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A high‐speed automatic electron‐trajectory tracer was employed to study the relative loss in deflection sensitivity and linearity caused by continuous resistive helical and conventional band‐type cathode‐ray tube postdeflection accelerators. A total of 144 trajectories was traced for six different electrode configurations immersed in a wedge‐type electrolytic tank that simulated a particular tube envelope. Beam‐deflection angles of 5.5°, 13.5°, 21.5°, and 30° were employed with maximum potential differences of 0, 2.3, 4.8, 7.3, 9.8, and 12.3‐kv postdeflection acceleration and a 2.7‐kv initial electron energy. The relative error of the resultant trajectories plotted is estimated at one percent. Of the configurations tested, the performance of the continuous resistive helix was far superior in deflection sensitivity and slightly better in deflection linearity. The results also indicate that a linear, stepped voltage distribution [(V0/N)·n], although poorer than the continuous‐helix distribution, may give better performance than that resulting from a stepped, geometrical voltage distribution (V0,V0/2,V0/4, etc.).

ISSN:0021-8979    

DOI:10.1063/1.1722069

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The nonmagnetic radio‐frequency principle of mass selection appears attractive because it promises to result in a mass spectrometer of simple construction and rugged nature. Accurate evaluation of the use of this principle is difficult because of the lack of published performance data. In an effort to obtain performance data a 5‐stage Bennett‐type tube with stage separation of 5–9‐4–7 cycles has been constructed and operational variables studied theoretically and experimentally.The experimental results are encouraging. They indicate the tube is capable of sufficient stability, resolving power, and sensitivity to be used for many analytical and research problems. Electronic circuits required to achieve a reasonable stability are relatively simple.

ISSN:0021-8979    

DOI:10.1063/1.1722070

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Siliconn‐p‐njunction transistors have been made from rate‐grown single crystals. Using gallium and antimony as doping agents, single crystals ofn‐type silicon have been grown containing up to fivep‐regions from 0.0005 to 0.002 inches wide which are suitable for the production of transistors. The ohmic contact to thep‐type base region was made by alloying an aluminum wire using techniques similar to those employed in the fabrication of aluminum‐silicon diodes.The electrical evaluation ofn‐p‐ntransistors produced from these single crystals is described. Alphas in excess of 0.9 at −1 ma emitter current have been obtained, and collector saturation currents of 10−6ampere/cm2are common. With base‐layer widths of about 0.0005 inch, the alpha cutoff occurs at approximately 5 megacycles. The units (approximately 0.04×0.04×0.5 inches in size) have been operated at power levels in excess of 1.5 watts in air with no special provision for heat dissipation.

ISSN:0021-8979    

DOI:10.1063/1.1722071

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Measurements of the flux‐reversal time &tgr; as a function of the applied magnetic fieldHhave been made for ⅛‐mil, ¼‐mil, ½‐mil, and 1‐mil 4–79 molybdenum‐Permalloy tape cores. There measurements have been taken at seven temperatures, ranging from −196°C to 270°C. From these measurements, the switching coefficientSw=(H−H0)&tgr; is found, whereH0is the threshold field value for irreversible domain‐wall motion. Determination of the switching coefficient as the tape thickness is varied permits a separation of the spin‐relaxation and eddy‐current contributions to switching delay. These contributions are studied individually as functions of temperature. Upon increasing the temperature over the range considered, the eddy‐current contribution and the threshold field valueH0are approximately halved, and the spin‐relaxation contribution is reduced by 20 percent. All these factors lead to a faster flux reversal at higher temperature for a given applied field. This behavior is in agreement with theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1722072

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The one‐dimensional contact region common to shock‐tube flows is idealized by the simple model of initial step change in temperature and density at constant pressure. For weak transitions, neglect of pressure effects, and linearization of the conservation equations gives spatially monotonic temperature and density profiles with the contact region thickening as the square root of time. Experimental results are noted from shock‐tube studies of two air/air contact regions. Insofar as comparison of theory and experiment is possible, the theory for weak transitions appears reasonable.

ISSN:0021-8979    

DOI:10.1063/1.1722073

出版商:AIP    

年代:1955

数据来源: AIP