摘要:

A slab with one surface cut and etched parallel to (100) crystallographic planes formed the cathode in a low power electron microscope. The electron image of the cathode was formed on a fluorescent screen with a small hole at the center. An electron collector placed behind the hole permitted a measure of the electron current passing through the hole as a function of the temperature of the cathode as measured with an optical pyrometer.The most probable value of the work function, &phgr;, obtained after 2400 hours of outgassing in a sealed‐off, gettered tube is 4.59±0.02 ev. This may be compared with 4.56 ev obtained previously by Nichols for the work function in the [100] direction of a tungsten single crystal wire.

ISSN:0021-8979    

DOI:10.1063/1.1699413

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The exact theory of the rate of growth of spherical precipitate particles has previously been developed for the initial stage where the individual precipitate particles do not interfere with one another. In the present paper this theory is carried one stage further to include their mutual interference. It is found that in the particular case of a very dilute solution this interference may be accounted for in a relatively simple manner. The applicability of the theory has been tested by new observations upon the precipitation of carbon from &agr;‐iron. Good agreement is found up to 95 percent completion of precipitation.

ISSN:0021-8979    

DOI:10.1063/1.1699422

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

For a linear system, steady‐state response to sinusoidal stress cannot have a unique dynamic modulus and phase shift, but these quantities must be related to rate of creep; particularly they cannot be independent of external frequency.A proof is given that such linear system is always equivalent to a viscoelastic system. Finally the discrepancy between the relations deduced and experimental results of various authors is pointed out and discussed.

ISSN:0021-8979    

DOI:10.1063/1.1699431

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Developments have been made in the use of spraying methods in the preparation of specimens for examination in the electron microscope. At the same time, two wholly volatile diluents, containing electrolytes and adjusted to normalpH, have been developed for use in forming the spray drops. The use of volatile electrolytes makes it unnecessary to wash the specimen after the droplet patterns have been formed on the specimen screens.There are several qualitative and quantitative uses and advantages of the spray technique as described. The qualitative ones are these: (1) the brief drying time of the droplets helps to preserve the shapes of particles upon drying, and also allows studies to be made of rapidly reacting systems; (2) since the drop patterns are reproducibly representative samples of the suspension under investigation, qualitative assays of the particulate composition of the suspension can be made, and a comparison of the particulate composition of two closely similar suspensions can be made under ideal control conditions; (3) the droplet patterns are discretely bounded by blank areas of substrate film, and this fact makes practicable the detection of small and subtle differences between the fine structure of the specimen material and that of the substrate.The quantitative uses of the spray technique are: (1) by use of reference particles of known numbers in a suspension it is readily possible to determine the volumes of droplets issuing from a spray‐making device; (2) by use of reference particles it is also possible to make an assay of the number of other particles, such as a virus, per unit volume of mixed suspension; (3) if a suspension is highly purified, the particle weight of the material in suspension can be determined. Experiments involving the counting of about 10,000 particles show that the quantitative precision is as good as would be expected from the statistics of random sampling.The construction and use of a spray gun are described, as well as the characteristics of two volatile diluents: ammonium acetate and ammonium carbonate.

ISSN:0021-8979    

DOI:10.1063/1.1699411

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The diffraction patterns of radar waves about a semi‐infinite copper screen have been measured. The measurements were made by revolving a bisectoral horn in a circle of radius 15″ or 30″ about the diffracting edge. Measurements were made at three positions along the edge, one of which coincided with the corner of the screen so that the pattern obtained was actually that of a quarter‐infinite plane. Measurements were made for two orientations of the screen corresponding to angles of incidence of 0° and −22½°. Theoretical patterns have been calculated for the entire 360° of rotation and these agree well with the experimental patterns. A comparison is made between the theory, measurements, and the equivalent optical measurements.

ISSN:0021-8979    

DOI:10.1063/1.1699412

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Measurements made of the surface temperature of evaporating water drops are in agreement with the requirements of the theory ennunciated by Fuchs which states that the temperature is determined by the difference between the ambient and saturated vapor density of the drop.

ISSN:0021-8979    

DOI:10.1063/1.1699414

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

X‐ray diffraction methods have been used to measure long‐ and short‐range order parameters for single crystals of the alloy Cu3Au held at elevated temperatures. It is shown that short‐range order parameters may be obtained by a three‐dimensional Fourier analysis of the ``scattering power'' for the diffuse background scattering of x‐rays, expressed as a function of reciprocal lattice coordinates. Appropriate experimental and computational procedures are outlined. Intensity measurements have been made with a special arrangement of a bent‐crystal monochromator and a Geiger‐counter spectrometer. Short‐range parameters are given for the first ten shells of atoms surrounding a given atom for three temperatures above the critical temperature of Cu3Au. These results, and those for the long‐range order parameter agree well with theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1699415

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Three of the alkali halides, LiF, KBr, and NaCl were examined as integrating detectors for high energy photons and particles. Dosage measurements were based on the number of color centers formed in single crystals under x‐ and cathode‐ray bombardment. Exposures of 20 to 104r (30‐kv x‐rays) were measured photoelectrically and 105to 107r (3 Mev x‐ and cathode rays) were measured optically. The crystals have advantages in measurements where wide range, high absorption, small size, and simplicity are desirable; however, their use is restricted by the length of the bleaching period required between exposures.

ISSN:0021-8979    

DOI:10.1063/1.1699416

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An experimental investigation of the thermionic emission from oxide‐coated cathodes is presented in which the applied voltage range extends from the retarding potential region through zero field and up to an average accelerating field of 50,000 volts per cm. The retarding potential range yields information concerning the energy distribution of the electrons emitted, and indicates an excellent agreement between theory and experiment for high retarding fields. Near zero field, cathode inhomogeneity or patch effect may be responsible for the deviations found. Consideration is given to the influence of a possible reflection effect, but theoretical calculation indicates that with the large area cathode used, the simultaneous reflection at the emitter and the collector surfaces so alter the observed current voltage relationship, that the existence or non‐existence of a reflection effect cannot be determined by the experiment. Results shown in the accelerating field region up to 50,000 volts per cm are accounted for on the bases of two assumptions which are (1) patch effect for small accelerating fields and (2), the intensification of the field at sharp points expected in view of the inherent roughness of the cathodes studied. The deviation of the experimental results from those predicted by the Schottky mirror image theory is explained over the whole range of observation by these two assumptions.

ISSN:0021-8979    

DOI:10.1063/1.1699417

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

High velocity flames in half‐open tubes produced by placing a grid augmenter in the path of an advancing flame are described. High speed schlieren motion pictures and instantaneous pressure measurements are used to study flame structure and accompanying flow in the tube. It is found that the grid augmenter causes a mixing of burning and unburned gases, resulting in an increase in reaction surface. As a result the total amount of reaction per unit time per unit volume is increased, thus leading to the observed high velocities.

ISSN:0021-8979    

DOI:10.1063/1.1699418

出版商:AIP    

年代:1950

数据来源: AIP