摘要:

The decay and recovery of the pulsed emission of cathodes consisting of BaO on nickel are studied. The emission of the cathodes is measured in diodes of cylindrical geometry having water‐cooled copper anodes spaced 0.019 inch from the cathode.Most of the diodes show a decay of anode current when first put in pulse operation. Decays of 2–50 percent are observed during 150‐&mgr;s pulses. The decay tends to disappear when the tubes are aged under pulse conditions. The peak current is a linearly decreasing function of the logarithm of the duty cycle, even when there is no perceptible decay during the pulses. The rate of decrease is independent of the pulse repetition rate and decreases with cathode temperature.Current‐voltage characteristics during the pulse and recovery periods are obtained by short sampling pulses. A comparison of these characteristics with computed ideal characteristics does not discriminate unambiguously between a variation of emission and a variation of internal cathode impedance as a source of current decay. Studies to separate the contributions of these effects are in progress.

ISSN:0021-8979    

DOI:10.1063/1.1702322

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A determination was made of the ratio of the stored energy to the energy expended in cold‐working copper by twisting. Ratios of about 0.03 were found in three cylindrical samples which were cold‐worked to the extent of 8 to 12 cal/g.

ISSN:0021-8979    

DOI:10.1063/1.1702323

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

In several types of applications of microradiography, particularly for histochemical and microchemical analysis by x‐ray absorption spectroscopy, it is desirable to use monochromatic radiation of a wavelength selected specifically with reference to an absorption edge of the element of interest. An x‐ray tube having as its target a material whoseK&agr;characteristic wavelength is suitable is the most usual source of monochromatic x‐radiation. In many cases, however, an otherwise desirable target is physically unsuitable for use as a target inside a vacuum tube. Hence, the possibility of producing fluorescent characteristic radiation with intensities sufficient for microradiography becomes of interest. The very high intensity of the primary x‐ray beam made available by the newly developed beryllium‐window x‐ray tubes suggests new possibilities for the excitation of fluorescent radiation.This paper reports the results of exploratory work attempting to establish the factors governing the intensity and degree of monochromaticity of fluorescent x‐radiation. Several materials, ranging from titanium (atomic number 22) to molybdenum (42) were studied comparatively, with exciting radiations of various characteristics; titanium was studied in greater detail. It is concluded that a considerably higher degree of monochromaticity is obtainable by this method than by direct bombardment and that intensities useful for some aspects by microradiography are obtainable.

ISSN:0021-8979    

DOI:10.1063/1.1702324

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Velocity and attenuation of both transverse and longitudinal ultrasonic waves are measured in a buna‐N vulcanizate at 2, 5, and 10 megacycles, over a range of temperatures. The method involves use of solid transmission media to conduct pulsed signals into a thin flat specimen. Values of the bulk modulus and of the complex shear modulus are computed from the measurements. It is found that longitudinal‐wave losses in this particular synthetic rubber are substantially accounted for by the relaxation phenomena measured in shear, but this conclusion is subject to considerable quantitative uncertainty arising from experimental errors estimated to be as large as 5 percent for longitudinal‐wave acoustic data and 10 percent for transverse‐wave acoustic data. It is found that below approximately −25°C the shear‐modulus loss tangent becomes relatively independent of temperature and frequency in the present range.

ISSN:0021-8979    

DOI:10.1063/1.1702325

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The methods of measuring the space charge reduction factor for shot noise are briefly reviewed, and attention is drawn to the difficulties of making a similar measurement for flicker noise. An indirect qualitative test is described in which a triode is used both in normal manner and as a diode under retarding field conditions. Noise measurements at a high and a low frequency show that the effect of space charge on flicker noise exceeds that for shot noise. The diode results are used to estimate the value of the flicker noise reduction factor which is then seen to have a value less than the corresponding shot noise reduction factor at all current levels.

ISSN:0021-8979    

DOI:10.1063/1.1702326

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A study has been made by electron microscopy of the size and size distribution of 22 synthetic latices. Included are GR‐S latices Types II, III, and V, polystyrene latices, and several latices of special character.Details are given on sample preparation, measurement, application of corrections, calculation of number, volume to surface, and molecular weight average diameters, as well as the number and weight average distributions.The weight average particle size range covered was 730 to 3920A. The smallest sizes were shown by Type II latices, followed in order by Type III, polystyrene, Type V, and some of the special latices. The latices were all nonhomogeneous in size and showed size distributions both on a number and weight basis which in some instances contained single and in some cases double maxima.

ISSN:0021-8979    

DOI:10.1063/1.1702327

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The summation of Fourier series is attained by use of ordinary linear differential equations with constant coefficients having inputs that depend on certain combinations of the Dirac delta‐function. The method is illustrated by several examples representative of those series that arise in applications.

ISSN:0021-8979    

DOI:10.1063/1.1702328

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The problem of electromagnetic back‐scattering or radar response from cylindrical wires has been investigated using a variational method. The relation between this method and the induced emf method is discussed. To demonstrate the flexibility of the variational calculation different trial functions have been used to determine the numerical values of the back‐scattering cross section for the case of broadside incidence. The boundary condition regarding the currents at the ends of the wire is also carefully examined.

ISSN:0021-8979    

DOI:10.1063/1.1702329

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Data on the thermal forces acting on aerosol particles in a temperature gradient are relatively few. Measurements are reported here on droplets of paraffin oil and castor oil suspended in air, showing the effect of temperature gradient, particle size, and particle material. The thermal force is directly proportional to the temperature gradient prevailing in the gas and to the particle diameter. It is an inverse function of the thermal conductivity of the aerosol material. The agreement between the experimental data and the theory of P. S. Epstein [Z. Physik54, 537 (1929)] is satisfactory, a fortunate result in view of the approximations to the actual physical situation made in the derivation of the theoretical equation. The velocity of migration of aerosol particles in a temperature gradient can be estimated from Epstein's formula.

ISSN:0021-8979    

DOI:10.1063/1.1702330

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The aspects of free molecular flow in the sample inlet to the mass spectrometer are pointed out and the conditions under which such flow can occur are described. Methods for calculating the leak diameter and sample pressure for various flow rates are developed. These principles are illustrated by consideration of the flow characteristics in the mass spectrometer leak detector, and by an example from reaction kinetic studies.The decrease in pressure in the sample reservoir is also described. This is applied to a determination of molecular weights. The effect of the pressure decrease on apparent fragmentation patterns is pointed out and a rational expression for spectrometer sensitivity is suggested which is based on the fraction of molecules which flow through the spectrometer which appear as ions.

ISSN:0021-8979    

DOI:10.1063/1.1702331

出版商:AIP    

年代:1952

数据来源: AIP