摘要:

Expressions for the electric field due to an oscillating horizontal dipole placed in a semi‐infinite dissipative medium have been derived for the case when the frequency is low. The main work involves the evaluation of some complex integrals which have been reduced to forms suitable for numerical computation.

ISSN:0021-8979    

DOI:10.1063/1.1721113

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The velocity and attenuation of ultrasonic waves are measured as a function of temperature in specimens of a Buna‐N vulcanizate swollen to various degrees with methyl ethyl ketone. The frequencies are 2, 5, and 10 megacycles. The experimental method consists of determining the insertion loss and the time delay due to insertion of a flat sample in the liquid acoustic medium of a pulse‐reflection apparatus; an improved technique of observation, in which phase delay as well as envelope delay is examined, leads to more precise time data than previous applications of the method. As solvent content of the specimen increases, the position of the maximum of attenuation with respect to temperature moves to lower temperatures, and the height of the attenuation peak is reduced. It is shown that the height of the attenuation peak, when corrections are made for temperature effects according to the mechanisms of rubberlike elasticity, is proportional to the mass of polymer per unit volume in the swollen specimen; moreover, the temperature of maximum attenuation is a linear function of the ratio, for the swollen specimen, of mass of solvent to mass of polymer. The latter finding indicates, if the concept of energy of activation is applicable, that the reduction of activation energy is proportional to the number of solvent molecules associated with each polymeric ``chain segment.'' The paper contains auxiliary data on dimensional and volumetric aspects of swelling and swelling rate.

ISSN:0021-8979    

DOI:10.1063/1.1721132

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The elastic constants of a Cu—4 atom percent Si crystal have been determined by the pulsed ultrasonic method to beC11=1.62,C12=1.20, andC44=0.755, all in units of 1012dyne cm−2. The changes in the fundamental shear constantsC44and ½(C11–C12) owing to alloying have been expressed in terms of a change in electrostatic stiffness and a change in ionic stiffness, both of which are shown to be reasonable. The experimental ionic effect is interpretable in terms of the solute‐solvent ion core interaction and the local distortions around a solute atom. The previously known results for Cu—28 Zn also conform to this picture.

ISSN:0021-8979    

DOI:10.1063/1.1721124

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The forces acting on a superconducting body in a magnetic field may be obtained by analogy with hydro‐dynamics, considering the similarity of the force field around a perfect diamagnetic with the flow field of an ideal liquid past an impermeable body of the same shape. The translation is provided by replacing ½&rgr;v2by (⅛&pgr;)&mgr;H2. As a practical application of the repulsive forces acting on superconductors in a diverging magnetic field, design of two types of magnetic supports for a sphere is described. In the coil‐type support, two coils with opposed currents are necessary to provide stable equilibrium. Similarly, the permanent‐magnet‐type support requires two transversely magnetized rings with opposed polarity. The dissipation of energy in a rotating sphere by eddy currents and by viscous drag of the surrounding gas was studied. The nonexistence of any torque on a freefloating, superconducting sphere in a rotating, transverse field indicates absence of interaction between the superconducting electrons and the metallic lattice.

ISSN:0021-8979    

DOI:10.1063/1.1721125

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A theory of the reverse characteristic of high inverse voltage germanium rectifiers is developed, which takes account of the radial symmetry of the point contact and the presence of positive holes in the ``inversion region'' of the semiconductor. The field at the metal is found to consist of three components. The first component varies inversely with the radius of the contact and directly with the applied voltage for larger voltages. The second component is produced by the impurity centers and varies approximately as the cube root of the voltage. The third component is produced by the positive holes in the inversion region and is approximately constant. This last component lowers the effective barrier height for rectifiers made of very pure material. The first is the more important of the variable components and is responsible for increases in current resulting from image force and tunnel effect at high voltages. In the former case the logarithm of the current varies asV½and in the latter asV2approximately.Current‐voltage curves of the predicted forms have been found experimentally using short rectangular pulses varying in length from 2 to 10 &mgr;sec to minimize thermal effects. Where possible, barrier heights are determined by measurements over a range of temperatures and detailed numerical comparisons of theoretical and experimental data are made. The two sets of data are in remarkably good agreement thus implying that the theoretical picture is essentially correct.

ISSN:0021-8979    

DOI:10.1063/1.1721126

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Measurements were made of the diffraction patterns of circular apertures from 0.2 to 1.0 wavelength in diameter when a plane polarized electromagnetic wave was incident normally upon them. Microwaves of wavelengths 16 cm and 32 cm were employed. The intensity of radiation relative to that of the unperturbed beam was determined at points along the electric and magnetic diameters of the apertures. The data disagreed with calculations from Young's circuital form in two major ways: (1) A sharp increase in intensity was observed at the ends of the electric diameter, (2) a surprising peak in intensity at the centers of apertures near one‐half wavelength in diameter was 50 percent greater than calculations from the integral. A more complete interpretation of Young's theory of diffraction would include multiple reflections from the edges. The high intensity at the center of the aperture a half‐wavelength in diameter was qualitatively accounted for by multiple reflections from the edges near the ends of the magnetic diameter.

ISSN:0021-8979    

DOI:10.1063/1.1721127

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

By introducing a proper distance function, the phase space for a servomechanism is completely metrized. A new approach is developed to study servo systems directly on the basis of instantaneous performance under an arbitrary input function. A criterion for determining the effect of nonlinearity on performance is obtained. It will serve as basis for the design of nonlinear servo systems.

ISSN:0021-8979    

DOI:10.1063/1.1721128

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Whenever a metal is made, the cathode in a dilute sulfuric acid bath the transmission of hydrogen may be observed by means of its reaction with oxygen of the air. A more detailed study of the transmission through palladium shows that the area of the surface at which the hydrogen leaves is the principal controlling factor. Possible applications to hydrogenation studies are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721129

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A photographic technique for study of metal free surfaces under acceleration by high explosives is presented. Methods for reducing the data from the photographic record are described. Specific results using brass plates driven by Composition B explosive are cited.

ISSN:0021-8979    

DOI:10.1063/1.1721130

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A study has been made of thermionic emission from tungsten filaments cataphoretically coated with alkaline earth oxides. It was found that the emission from the oxide‐coated filament was not influenced by the variation of work‐function with crystallographic direction of the base metal. A Richardson plot of emission at zero field yielded an apparent work function of 1.3 volts and anAvalue of 0.048 amp/cm2‐deg2. In retarding potential data, the energy of thermionic electrons showed an apparent deviation from Maxwell‐Boltzmann statistics. This deviation was interpreted as due to a potential drop through the coating. Such an interpretation led to a conductivity activation‐energy of 1.3 volts. A strip theory of patches was used to explain the accelerating potential data. Satisfactory agreement with experiment was found with a patch amplitude of 0.2 volt and a period of 2×10−6meter.

ISSN:0021-8979    

DOI:10.1063/1.1721131

出版商:AIP    

年代:1953

数据来源: AIP