摘要:

The 5 elastic constants of hexagonal cobalt have been determined using pulse modulated ultrasonic waves which are reflected back and forth within the crystal. Frequencies between 10 and 30 Mc/sec were used. Values of the constants were derived from 11 measurements of wave velocities for longitudinal and shear modes in 3 crystals, using a phase comparison technique. At 25°C the constants (all in 1012dynes/cm2) are:c11=3.071±0.5 percent,c12=1.650±0.5 percent,c13=1.027±1.5 percent,c33=3.581±0.5 percent,c44=0.755±0.5 percent. These are based on a density of 8.836.

ISSN:0021-8979    

DOI:10.1063/1.1722007

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Oscillators employing phase focusing such as magnetrons have fairly well defined spokes whose rotational speed is proportional to the oscillation frequency. Each spoke is composed of a finite number of electrons having random velocities and consequently is subject to random fluctuations about a mean position. This spoke ``jitter'' leads to fluctuations in the oscillation frequency resulting in frequency modulation noise. It is the theoretical evaluation of the parameters of this noise as affecting the power spectrum of the oscillator output that is of interest here. The theoretical results compare favorably with the measured power spectrum of a voltage‐tunable magnetron. The application of the formulas require an estimate of electron temperature although no attempt is made to evaluate this temperature. Amplitude fluctuation noise appears to be relatively unimportant in continuous‐wave phase‐focused oscillators.

ISSN:0021-8979    

DOI:10.1063/1.1722008

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Two methods are described for the measurement of lifetime of minority carriers. One depends on pulse injection of carriers in a filament and detection, after a known time, at a collector. The second makes use of the decay of the conductivity modulation caused by minority carriers after injection at a single contact. Both measure the lifetime in a small region rather than the average value over a large part of the sample.

ISSN:0021-8979    

DOI:10.1063/1.1722009

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Chandrasekhar's relaxation time is applied to the electron gas in flow. By determining the relaxation time,tR, and the mean transit time,tT, two types of electron flow may be characterized: anisotropic flow iftT«tR, and isotropic flow iftR«tT. It is shown that the electron temperature along the flow decreases as the mean velocity of the electrons increases in a parallel plane diode. In the given examples, the boundary conditions are obtained for a particular model which has been recommended in the study of thermionic emission.

ISSN:0021-8979    

DOI:10.1063/1.1722010

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A source of silver iodide aerosols has been studied to determine the effect of the temperature of generation on the crystal structure of the particles in the aerosol output. Sampling was done by use of a novel thermal precipitator which gave samples in the proper form for direct analysis in a Debye‐Scherrer x‐ray diffraction camera. Patterns were obtained indicating the presence of both cubic and hexagonal modifications (ZnS and ZnO type). As the source temperature was raised, an increase of the proportion of hexagonal particles was observed, 95 percent hexagonal particles resulted when the source was operated at 800°C. An explanation of this behavior is proposed.

ISSN:0021-8979    

DOI:10.1063/1.1722011

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

This article describes the application of the Doppler principle to the measurement of detonation velocity with three‐centimeter electromagnetic radiation. The method makes use of the ionized wave front in detonation as a moving reflecting surface for electromagnetic waves. Detonation velocities for four different solid explosives were calculated from the observed Doppler frequencies and the indices of refraction, which were measured by a microwave interferometer. Complexities in the observed Doppler patterns come about because the cylindrical charges act as multimode dielectric wave guides.

ISSN:0021-8979    

DOI:10.1063/1.1722012

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The reflection of a plane wave of sound from a layer separating regions of different sound velocities, the layer itself containing a velocity variation through an extremum, is considered in terms of its dependence upon the angle of incidence, the layer thickness, and the velocity variation through the layer. It is found that the power reflection coefficient may differ significantly from its value for the corresponding abrupt or monotonic velocity transition. Numerical results are tabulated for various types of layers of thickness from zero to ten wavelengths and with a total velocity transition of ±5 and ±10 ft/sec.

ISSN:0021-8979    

DOI:10.1063/1.1722013

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Using a reproducible pulsed voltage technique, the electric strengths of liquid hexane, heptane, and tetradecane have been measured with small electrode spacings (approximately 2 to 200 microns). The electric strengths are found to change inversely with the logarithm of the separation in accord with theoretical expectation. On the basis of an approximate model of the breakdown process, the measurements on heptane yield values of 9×10−7cm for the electron mean free path in the liquid and 9 for the number of multiplications per electron required for breakdown.

ISSN:0021-8979    

DOI:10.1063/1.1722014

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The effects of pressure, temperature, and physical state on the ability of a barium getter to sorb carbon monoxide are presented. At pressures in the 10−5‐mm range, a five‐milligram getter is exhausted in about one thousand hours. Temperatures ranging from room temperature to 150°C did not affect greatly the rate of gettering or the capacities of the getters. The observed gettering rates or capacities do not obey any simple law over an extended time.

ISSN:0021-8979    

DOI:10.1063/1.1722015

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The rates of crystallization of two polymer‐diluent mixtures, poly‐(ethylene oxide)‐diphenyl ether and poly‐(decamethylene adipate)‐dimethyl formamide were studied at various temperatures ranging from 6° to 15° below the melting points of the mixtures. The various mixtures investigated encompassed a wide range of compositions; the volume fraction of the diluentv1ranged from about 0.10 to 0.70. The crystallization behavior observed was strikingly similar to that previously reported for bulk polymers in the first paper of this series. The results are interpreted by making the necessary modifications to the treatment previously employed wherein steady‐state nucleation and growth were assumed to occur simultaneously throughout the process. Agreement obtained between theory and experiment is similar to the corresponding results for the bulk polymer.

ISSN:0021-8979    

DOI:10.1063/1.1722016

出版商:AIP    

年代:1955

数据来源: AIP