摘要:

Other factors being equal, the integrated intensity of a powder diffraction reflection is a function of the geometry of the source, collimator, and sample. By means of a geometrical and algebraic analysis one can predict the relative intensities to be expected with pinhole or slit collimators of different dimensions. Important gains in intensity can be obtained by replacing pinholes with slits, and the advantage is about the same if the x‐ray focal spot is viewed either longitudinally or laterally through slits of sufficient length. These results confirm experimental results reported by other investigators and also re‐emphasize the potential value of the ``side'' windows of x‐ray tubes, which are commonly neglected.

ISSN:0021-8979    

DOI:10.1063/1.1699757

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

According to Guinier the low angle x‐ray scattering of particles should disappear when they are immersed in a fluid of equal electron density. This furnishes a way of measuring the electron density of powders, providing a suitable impregnating fluid can be found. Experiments of this type have been carried out with carbon black. A method of calculating the low angle scattering coefficient defined by Warren is given for impregnated samples. Measurements of the total low angle scattering intensity were made using a double crystal spectrometer and Geiger counter. No liquid was found that would give complete matching but approximate matching was obtained with phosphoric acid solution. The data extrapolate to show an electron density of 1.1N±0.1NwhereN=Avogadro's number. This compares with a value of 0.99Nas calculated from the helium immersion mass density measurement on the same sample.

ISSN:0021-8979    

DOI:10.1063/1.1699758

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A removable intermediate lens is described which extends the range of magnification of a conventional instrument to 25:1 without sacrificing the accessibility of the objective and projection lens polepieces. The distortion, sensitivity to changes in accelerating potential and reproducibility of calibration are studied and found to be equal to, or better than in the standard arrangement. The system provides two values of the magnification which are essentially independent of the accelerating potential.

ISSN:0021-8979    

DOI:10.1063/1.1699759

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The quenching distance between plane parallel plates has been measured for propane‐air flames at eight pressures ranging from 0.0832 to 2.77 atmos., and air‐propane ratios ranging from 11 to 24. Other tests have been made at atmospheric pressure in which (a) the temperature of the quenching plates has been varied from 80° to 715°F, (b) the temperatures both of the inlet gas and the quenching plates have been varied from 80° to 545°F, and (c) a series of six different solid surfaces was tested. The minimum quenching distance is found to occur at an air‐propane ratio between 13.5 and 14.0, and is proportional to the minus 0.91 power of pressure. Lean mixtures are found to be slightly less pressure‐sensitive. When both the inlet gas and plates are heated, the minimum quenching distance is found to be proportional to the minus 0.5 power of absolute temperature. The quenching effect appears to be independent of the nature of the surface.

ISSN:0021-8979    

DOI:10.1063/1.1699760

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Maxwell's equations are solved for a perfectly conducting conical wave guide and the propagation coefficients of this guide are discussed. The field at the mouth of a finite conical horn is estimated and the radiation therefrom is calculated in integral form. These integrals are solved in series form for horns of small flare angle and moderate length and the results compared with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1699761

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Diffraction patterns of radar waves have been measured about the edge of a perfectly conducting wedge. Theoretical patterns have been calculated using an asymptotic solution suggested by Pauli. Good agreement is observed between experimental and calculated patterns. The thin wedge tested showed much similarity in diffracting properties to a suitable semi‐infinite conducting screen. The results may have application to diffraction effects about wedge‐shaped wings on high speed aircraft and missiles.

ISSN:0021-8979    

DOI:10.1063/1.1699762

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The solidification behavior of small metal (10 to 100 micron diameter) droplets has been observed on a high temperature microscope stage. An abrupt change in surface appearance and in the case of high melting metals a sudden brightening (``blick'') accompanies solidification. The solidification temperatures observed for a collection of droplets may be widely distributed, but a significant, usually the major, fraction of the droplets supercool some maximum amount (&Dgr;T‐)maxthat is reproducible and characteristic of the metal. For many metals (&Dgr;T‐)max≈0.18 times the absolute melting temperature. (&Dgr;T‐)maxis not much changed by wide variations in the cooling rate and droplet size. The growth rate of metal crystals is very great so that the solidification rate of the droplets is controlled by the nucleation frequency.

ISSN:0021-8979    

DOI:10.1063/1.1699763

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Mass spectrometric techniques have been utilized to study sublimation characteristics of materials used in electron tubes. Exploratory experiments and methods are described. Preliminary results concerning general processes induced by heat and by electron bombardment are discussed. Photographs are shown of mass spectrometer traces which demonstrate the effects described. Phenomena noted include (1) the inefficiency of electron bombardment for producing material transport from solids, (2) the thermal evaporation of alkali metal atoms and ions from bare nickel alloys, but no such evaporation from oxide cathodes formed on the same materials, (3) the complex thermal evaporation of oxide cathode constituents, (4) absence of positive ion evaporation from oxide cathodes, (5) the confirmation of mechanisms for negative ion formation in vacuum systems, and (6) the liberation of molecular oxygen from oxide cathodes which increases with electron emission drawn.

ISSN:0021-8979    

DOI:10.1063/1.1699764

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An extensive study of the charge and size distribution of particles from 0.5 to 30 microns radius in dust clouds of diverse exemplary types dispersed in air under a variety of conditions ranging from blowing with minimum of turbulence to conditions of violent and maximum impact with various types of surfaces was made using adaptations of the Hopper and Laby modification of the oil drop experiment. It was observed that all dusts, including homogeneous dusts with no impacts on solid surfaces, were charged. In homogeneous systems the charges of opposite sign were equal, nonetcharge resulting, the number of particles of similar size with opposite charges being about the same. The magnitude of charges increased somewhat less rapidly than the surface of the particle. There was no correlation between size and sign of charge. There is strong evidence that charging occurs on separation of the contacts between particles in the dispersion of the cloud. Humidity did not affect the charging. Studies of heterogeneous systems making contact with solid walls of different composition from the powder gave consistent asymmetry of charge of varying degrees depending on the proportion of particles striking the surfaces relative to those just separated.

ISSN:0021-8979    

DOI:10.1063/1.1699765

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The interaction of small particles suspended in air with the ions normally produced in the air is discussed. The neutralization of highly charged dust particles, if suspended in air, is treated in detail. The result is found to be in qualitative agreement with experiment. The special case of final equilibrium is investigated. It is found that multiply charged particles should be present in appreciable number in coarse aerosols at all times. This is confirmed by experiments both for initially charged quartz dust and for initially neutral ammonium chloride smoke. The general nature of an equilibrium charge distribution is presented. Charges up to ten electron units are found to be not uncommon.

ISSN:0021-8979    

DOI:10.1063/1.1699766

出版商:AIP    

年代:1950

数据来源: AIP