摘要:

Shadow projection permits higher resolution and simpler operation than other methods of x‐ray microscopy. A point source, less than 1&mgr; in diameter, is obtained by the use of magnetic electron lenses and used for projecting shadow images at a primary magnification up to 100× with an exposure time in the order of minutes. The use of a metal foil as target and tube window insures high intensity at the specimen, which is in air. A resolving power little short of the best optical performance has been obtained with an accelerating voltage of 10 kv. The practical limitations to resolution, contrast, and exposure time are discussed in detail. A resolution of 100A should be practicable, but only with longer x‐rays and an exposure of the order of 1 hour.

ISSN:0021-8979    

DOI:10.1063/1.1721338

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The internal friction and Young's modulus of single crystals of copper were measured as a function of strain amplitude after they were subjected to various amounts of cold work and different annealing treatments. It was found that the position of the peak in the internal frictionversuscold‐work curve was dependent upon the strain amplitude of the measurement. No minimum in the Young's modulusversuscold‐work curve was found as contrasted with Lawson's result for polycrystalline copper. A minimum was found in the internal frictionversusannealing time curve, and a maximum was found in the corresponding Young's modulus curve. The results are semiquantitatively explained using a dislocation model.

ISSN:0021-8979    

DOI:10.1063/1.1721339

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The presence of tungsten as a major impurity in the base metal of an oxide‐coated cathode leads to the formation of the interface Ba3WO6. If silicon is also present, but as a minor impurity, this element gradually replaces tungsten in the interface to form Ba2SiO4. Similar reactions between titanium and aluminum with other known interface compounds were examined.

ISSN:0021-8979    

DOI:10.1063/1.1721340

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The spectral emissivities of graphite and carbon have been determined at a wavelength of 0.653&mgr; in the temperature range of 1285 to 2035°K and have been found to be temperature dependent in accordance with a prediction from a relation between reflectivity and resistivity. For polished graphite of high purity having a resistivity of about 1120 microhm‐cm the value obtained is 0.78; the value obtained for a polished high density graphite having a resistivity of 1740 microhm‐cm is 0.78; and that for polished spectroscopic carbon having a resistivity of 5080 microhm‐cm is 0.79. If graphite is sublimed from a polished surface, the latter becomes roughened, so that the emissivity increases. In one particular experiment it attained a value of 0.90.

ISSN:0021-8979    

DOI:10.1063/1.1721341

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Complete integrated solutions have been found in terms of elementary functions for the motion of an electron on the axis of a progressive wave linear accelerator with a constant wave speed, &bgr;=1. The character of the solutions has been discussed and asymptotic relations found.Calculations have been made for the third section of the Purdue linear accelerator, in which the curves for the first two sections where &bgr;<1 have been extended. The energy distribution of the emergent beam was computed. It was found possible to design a linear accelerator with constant wave speed sections which, without preliminary bunching, would produce a beam of greater homogeneity in energy than might have been expected.

ISSN:0021-8979    

DOI:10.1063/1.1721342

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

This theoretical paper deals with the low frequency permittivity (&egr;) of a dilute suspension (conductivity &sgr;, volume concentration &rgr;), in a conducting medium (conductivity &sgr;s, permittivity &egr;s), of ellipsoidal particles (major axis 2a) each composed of a conducting core covered with a nonconducting surface membrane (thicknesst, permittivity &egr;m). The quantity[&egr;−(&sgr;/&sgr;s)&egr;s]/(&rgr;a&egr;m/t)is expressed in terms of Weierstrass' elliptic functions of the axial ratios, for parallel and random arrangement of the ellipsoidal axis. A table of its numerical values is given.

ISSN:0021-8979    

DOI:10.1063/1.1721343

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The solution is given for the total power flow from an oscillating magnetic dipole, situated above a flat homogeneous conducting ground and oriented in the vertical direction. The result is employed to derive an expression for the radiation resistance of a small wire loop whose axis is perpendicular to the ground. It is pointed out that for a finitely conducting ground that the radiation resistance is very large when the height of the small loop or dipole is a small fraction of a wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1721344

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Values of complex shear compliance (and rigidity) have been obtained for a sample of polyisobutylene of viscosity‐average molecular weight 1.35×106at 22 temperatures from −45 to 100°C and at about 20 frequencies from 30 to 5000 cps. Measurements were made by means of the transducer method of Fitzgerald and Ferry with a precision of ±2 percent and are estimated to be accurate to within ±3 percent as evidenced by agreement obtained between 7 different samples of widely varying dimensions. Values of the real part of the complex shear complianceJ′ vary from 3.1×10−7cm2/dyne at 99.9°C to 1.0×10−10cm2/dyne at −44.6°C. The frequency dependence of the loss tangentJ″/J′ indicates the presence of a low, broad maximum of 1.7 at −10 to −5°C and a second, smaller maximum at lower temperatures. This second maximum is also evident in a plot ofJ″/J′ at a fixed frequency against temperature. The wide temperature and frequency ranges of the measurements have provided an essentially complete experimental description of the dispersion region in polyisobutylene corresponding to the transition from a rubber‐like elasticity to that of a hard glass.

ISSN:0021-8979    

DOI:10.1063/1.1721345

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A procedure for calibrating photographic emulsions has been devised which measures the deviation from linearity of the curve relating electron exposure to optical density. The experimental application of this procedure is found to give results consistent with a very simple model of the exposure process. It is also noted that the sensitivity of a photographic plate increases with increasing distance from the center of the plate. Measurements of this effect are given.

ISSN:0021-8979    

DOI:10.1063/1.1721346

出版商:AIP    

年代:1953

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721348

出版商:AIP    

年代:1953

数据来源: AIP