摘要:

By applying Stokes' Fourier transform method for the analysis of diffraction maxima it is shown that the pure diffraction contour generated by a crystallite size distribution is apt to be approximated rather closely by the function 1/(1+k2&phgr;2). In the case of the x‐ray spectrometer this pure diffraction contour is broadened significantly by the action of the following five geometrical factors: (I) the x‐ray source width, (II) flat rather than curved sample surface, (III) vertical divergence of the x‐ray beam, (IV) penetration of the sample by the beam, and (V) the receiving slit width.The broadening of the pure diffraction contour due to the action of each of the five factors and the breadth of the final contour generated by the instrument can be deduced by employing the convolution approach suggested by Spencer. The effect of each instrumental factor is expressed by a convolution equation of the formfi(&phgr;)=−∞+∞Wi(&zgr;)fi−1(&phgr;−&zgr;)d&zgr;,in which &phgr; is the angular displacement from twice the ideal Bragg angle, 2&thgr;,fi−1is the contour before the action of theith geometrical factor,Wiis the form of theith geometrical factor, andfiis the contour after the action ofWionfi−1. Starting with a pure diffraction contour of the form 1/(1+k2&phgr;2), generalized broadening curves are derived for the effect of each of the five geometrical factors. Using these curves it is possible to predict the breadth of the final diffraction contour generated by the spectrometer from an initial contour of any breadth.

ISSN:0021-8979    

DOI:10.1063/1.1699611

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The accuracy of the Scherrer crystallite size equation is limited in part by the uncertainty in &bgr;, the experimentally deduced pure diffraction broadening. Currently used procedures for estimating &bgr; from the observed breadth of a Debye‐Scherrer line are not, in general, applicable to the x‐ray spectrometer.By making use of a scheme of convolution analysis for analyzing the effect of geometrical factors in broadening the pure diffraction contour, a correction curve is developed for determining &bgr; from the experimentally measured line breadthsbandB(Jones' notation). The degree of reliability of this correction procedure is ascertained by applying Stokes' direct Fourier transform procedure for determining the form of the pure diffraction contour free of instrumental effects.Suggestive procedures are given for crystallite size determination with the x‐ray spectrometer in different size ranges, and several examples are described.

ISSN:0021-8979    

DOI:10.1063/1.1699612

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A mass spectrometer tube using velocity selection is described. The tube has parallel plane grids made with knitted wire nets with a large percentage of open area. The grids are arranged in groups of three, and radiofrequency alternating potential is applied to the middle grid of each group. Stopping potentials are used to turn back all ions except those with the selected mass. The spectrometer has sufficient resolution for ordinary gas analysis requirements and is simpler, more compact, and more rugged than magnetic beam deflection devices.

ISSN:0021-8979    

DOI:10.1063/1.1699613

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A method has been developed for the study of grain boundary migration in high purity aluminum, which allows positive determination of thedirectionof grain boundary movements. By means of this method it was confirmed that the migration of grain boundaries resulting from surface energy takes place in the direction toward the centers of curvature of the boundaries. On the other hand, strain induced grain boundary migration, such as occurs in recrystallization, proceeds in a direction away from the centers of curvature of the moving boundaries. It was also found that certain strained grains serve as nuclei for strain‐free grains of the same orientation which grow at the expense of neighboring strained grains. Most of the strain‐free grains formed during the annealing of high purity aluminum cold rolled up to about 40 percent are produced by this mechanism of strain‐induced boundary migration, without the formation of new nuclei.

ISSN:0021-8979    

DOI:10.1063/1.1699614

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Expressions are derived for the external field produced by a slot of arbitrary shape in the wall of a circular wave guide (of infinite extent and infinite conductivity), the tangential components of the electric field in the slot being assumed to have been prescribed. This is accomplished by matching a Fourier representation of the external field, built up by superposition of basic sets of cylindrical waves, to a Fourier expansion of the prescribed field over the surface of the cylindrical wave guide. The far‐zone field is obtained by applying the method of steepest descent to the Fourier integrals that constitute the coefficients in the expansion for the external field. The results satisfy the radiation conditions for far‐zone fields.

ISSN:0021-8979    

DOI:10.1063/1.1699615

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

It is demonstrated on simple dynamic principles that a supersonic airfoil under certain conditions exhibits the same drag and the same lift slope regardless of whether it flies forward or backward.

ISSN:0021-8979    

DOI:10.1063/1.1699616

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

This paper presents an approximate method of determining the pressure distribution during impact on the surface of a body which strikes a horizontal water surface at an arbitrary angle.The effect of the splash is neglected and the pressure on the free boundary is assumed proportional to the potential, as if the process were an impulse. The shape of the submerged portion of the striking body is approximated by a semi‐ellipse (two dimensions), by a hemisphere, half an ellipsoid of revolution and half a general ellipsoid. Under those conditions, explicit results for the pressure distribution are found. As a special example, the impact pressures on a sphere striking at 45° angle are computed in detail.

ISSN:0021-8979    

DOI:10.1063/1.1699617

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Contrary to current belief, cavitation has been found responsible for the depolymerizing effect of intense ultrasonic waves. This was demonstrated by irradiating two portions of a 1 percent polystyrene solution in toluene under conditions identical except for the following. The first portion was given no special prior treatment, showed many cavitation bubbles during irradiation, and decreased in molecular weight (as measured by the intrinsic viscosity) to about one‐tenth of the initial value. The second portion was given a preliminary treatment of degassing by boiling under vacuum, showed no cavitation bubbles during the irradiation, and underwent no appreciable change in molecular weight.Similar experiments with solutions of hydroxyethyl cellulose in water showed that, in this case also, cavitation is necessary for depolymerization. The opposite conclusion of earlier investigators is attributed to their inadequate method for eliminating cavitation.Oxidants known to be produced by ultrasonic waves in solutions containing dissolved oxygen or nitrogen cannot be responsible for the degradation, because substantially the same amount of depolymerization occurs even when helium is the only gas present.

ISSN:0021-8979    

DOI:10.1063/1.1699618

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An electron microscope is described in which a range of magnifications between 1000 and 100,000 times can be covered continuously. This is achieved through the use of an intermediate projector lens.The principles of design are briefly discussed and the construction of the microscope and the high frequency‐operated 100‐kv power unit is dealt with in some detail. The instrument is provided with objective apertures to enhance image contrast and to permit operation with dark field illumination.Data is given relating to the electron optical system and it is shown how the instrument can be used to obtain electron diffraction patterns characteristic of small areas of a specimen under microscopic observation. The alignment procedure is briefly described and some typical micrographs are shown.

ISSN:0021-8979    

DOI:10.1063/1.1699619

出版商:AIP    

年代:1950

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1699620

出版商:AIP    

年代:1950

数据来源: AIP