ISSN:0021-8979    

DOI:10.1063/1.1721451

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Electron microscopic evidence is presented in support of the hypothesis that black carbon resulting from pyrolysis of gaseous hydrocarbons is produced through the intermediate formation of droplets of complex hydrocarbons. Electron diffraction studies further confirm this hypothesis if, as has been found for particles of carbon blacks, the droplets consist in part of graphitic nuclei arranged with their basal planes tangential to the droplet surface. The carbonization of small solid spherules of highly cross‐linked organic polymers is described, and it is shown that the morphology of the carbonization products is wholly analogous to those for pyrolytic carbon and carbon blacks. It is suggested, therefore, that the formation of carbon by the carbonization of solids and by deposition from the gas phase occurs through similar mechanisms and that the two processes are simply two extremes in an infinite series of processes which are all fundamentally alike.

ISSN:0021-8979    

DOI:10.1063/1.1721452

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The presence of stiffness in a stretched string vibrating between fixed supports raises all the natural frequencies over those for a perfectly flexible string. The presence of nonuniformity in cross‐sectional area along the string changes some or all of the frequencies from those for a perfectly uniform string, the amount and direction of change depending on the form of the nonuniformity. These changes in frequency may introduce error into the calculation of the average cross‐sectional area of a fiber by means of the vibroscopic technique, wherein the mechanical resonance of a stretched fiber is observed under oscillating mechanical or electrostatic forces. In this paper the natural frequencies are calculated with both the stiffness and the nonuniformity taken into account to first‐order terms. The relation between the average cross‐sectional area and the natural frequencies is analyzed. Consideration is given to the manner in which the changes in frequency and shifts of the nodes, due to nonuniformity, determine the detailed form of the area variation. The characterization of nonuniformities in terms of certain arbitrary parameters is shown to lead to the possibility of calculating the average area by measuring the natural frequencies in only the first and second modes and of calculating the maximum or minimum area by measuring also the nodal shift in the second mode.

ISSN:0021-8979    

DOI:10.1063/1.1721453

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

It is shown that in many cases the measurement of the relative humidity at which a hygroscopic particle becomes liquid can be used to establish the chemical composition of the particle. An apparatus is described which produces a stream of air of constant temperature and variable humidity. Using this apparatus the phase‐transition point was determined for particles collected on spider webs. These particles were sampled in the Sydney area on the ground and from an aircraft, and it is shown that the measured values of relative humidity for the solid‐liquid phase transition agreed with the hypothesis that the hygroscopic particles were composed of sea salt. Direct microscopic observation was used to follow the behavior of the particles; the technique was capable of dealing with particles down to 10−12g.

ISSN:0021-8979    

DOI:10.1063/1.1721454

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The summation of series involving the roots of certain transcendental equations having real roots is achieved by elementary considerations. The method is illustrated by several examples representative of those which may arise in applications. In addition to summing series, the method can be used to obtain the least positive root of the transcendental equation to any desired accuracy with but little computation.

ISSN:0021-8979    

DOI:10.1063/1.1721455

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

It was shown earlier that plastic grating‐replicas mounted upon eighth‐inch specimen screens were practical internal standards and that they could be accurately calibrated independently by spectroscopic means. Metallic replicas of diffraction gratings have been made by a direct‐stripped method. These can still be direct‐stripped easily and without damage to the original grating, and the optical quality of these pre‐shadowed all‐metal replicas is better than that of the plastic replicas. Because of their superior optical properties, the spacing can be determined spectroscopically more conveniently and with greater accuracy. In addition, the metal‐gratings are more stable than the plastic ones. The electron microscopy of the metallic replicas and the accuracy and constancy of their magnification measurement is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721456

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A process is described in which radioactive radiation traverses a solid dielectric medium to charge a collector electrode. This process offers a simple method of studying effects of radiation on matter such as bombardment‐induced conductivity, secondary emission, charge soakage, and radiation absorption. Typical data are given. Possible application of this process for the construction of a current or voltage source for use in electronic devices is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721457

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The paper is concerned in the main with a Maxwell material, which corresponds to a model having a spring and dashpot in series. The equation for longitudinal wave propagation in rods is shown to be equivalent to the telegraph equation, and solutions of transient wave problems are treated briefly in the Appendix using the Laplace transform technique. Impact on a semi‐infinite rod is considered in detail in the report. A method of superposition of images is discussed to use this solution to solve boundary value problems for finite rods. The resulting stress distributions are discussed and contrasted with those for an elastic rod. The natural grouping of problems is discussed according to the relative magnitude of the duration of interest, the relaxation time, and the wave traverse time. The influence of the idealization involved in the Maxwell model is briefly touched upon.

ISSN:0021-8979    

DOI:10.1063/1.1721458

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

It has been shown that an approximate solution for the diffraction of an electromagnetic wave by an aperture in a plane conducting screen can be obtained from a single component of the Hertz vector and that the results can be applied to calculating the field of apertures which are sufficiently large as compared to the wavelength of the incident radiation. The solution rests upon an evaluation of an inhomogeneous scalar boundary‐value problem. An infinitesimal wavelength approximation leads to a simple Kirchhoff‐like formula which is found to be identical to that obtained by Neugebauer who derived it from geometrical optics as first approximation. The special case of diffraction by a circular aperture is treated in detail, and experimental measurements by which the theory was checked are cited.

ISSN:0021-8979    

DOI:10.1063/1.1721459

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

This paper presents a new method for the measurement of surface stress. By the use of test pieces plated with copper, the stress is measured by observing the flecks on the surface produced by cyclic stress. The variation in the appearance of flecks which is due to the change of load is very sensitive at a proper load, so an accurate determination of the surface stress is feasible.The stress concentration factor in torsion is obtained experimentally by the method described for circular shafts with a circumferential notch in each. The results are compared with theoretical values, calculated from two different formulas previously derived by the author and Sonntag, respectively. It is confirmed that the experimental results obtained here are in good agreement with those calculated by the author's formula.

ISSN:0021-8979    

DOI:10.1063/1.1721460

出版商:AIP    

年代:1953

数据来源: AIP