Volume 24, Issue 1, 01 January 1953

Radiation from a Horizontal Dipole in a Semi‐Infinite Dissipative Medium
View Description Hide DescriptionExpressions 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.

Ultrasonic‐Wave Study of Swollen Buna‐N Rubber
View Description Hide DescriptionThe 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.

The Elastic Constants of Cu—4 Percent Si
View Description Hide DescriptionThe elastic constants of a Cu—4 atom percent Si crystal have been determined by the pulsed ultrasonic method to be C _{11}=1.62, C _{12}=1.20, and C _{44}=0.755, all in units of 10^{12} dyne cm^{−2}. The changes in the fundamental shear constants C _{44} and ½(C _{11}–C _{12}) 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.

Forces Acting on Superconductors in Magnetic Fields
View Description Hide DescriptionThe 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 ½ρv ^{2} by (⅛π)μH ^{2}. 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.

Reverse Characteristics of High Inverse Voltage Point Contact Germanium Rectifiers
View Description Hide DescriptionA theory of the reverse characteristic of high inverse voltagegermanium 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 as V ^{½} and in the latter as V ^{2} approximately.
Current‐voltage curves of the predicted forms have been found experimentally using short rectangular pulses varying in length from 2 to 10 μsec 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.

Diffraction Patterns in Circular Apertures Less Than One Wavelength in Diameter
View Description Hide DescriptionMeasurements 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.

Metrization of Phase Space and Nonlinear Servo Systems
View Description Hide DescriptionBy introducing a proper distance function, the phase space for a servomechanism is completely metrized. A new approach is developed to study servosystems 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 servosystems.

The Transmission of Hydrogen through Palladium by Electrolysis
View Description Hide DescriptionWhenever 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.

Free Surface Properties of Explosive‐Driven Metal Plates
View Description Hide DescriptionA 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.

Thermionic Emission from Oxide‐Coated Tungsten Filaments
View Description Hide DescriptionA 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 an A value of 0.048 amp/cm^{2}‐deg^{2}. 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^{−6} meter.

X‐Ray Study of Cold Work in Thoriated Tungsten
View Description Hide DescriptionSpectrometer measurements were made of the x‐ray diffraction peaks for cold‐worked filings of thoriated tungsten: 99.25 tungsten, 0.75 thoria. A Fourier analysis was made of the peak shapes, and the instrumental broadening corrected by using the peaks of annealedmaterial. When the particle size and the distortion effects were separated, it was found that the particle size broadening corresponded to a size L̄=200A. This value is to be interpreted as the size of the coherently diffracting domains, and is a measure of the distance between layers of slip planes or layers of dislocations. The coherent distortion broadening indicated that strains in this material vary appreciably over distances of 25A or less. Strain distribution curves were obtained from a Fourier transform of the experimental coefficients. There is an indication that strains are smaller in the larger coherent regions. The measured root mean square strain corresponds to an elastic energy of 0.18 cal/g. Within experimental accuracy the integrated intensities are the same for the cold‐worked or the annealed samples.

Theory of the Single‐Wire Transmission Line
View Description Hide DescriptionEquations are derived for the current induced in an infinitely long, thin, straight wire of nonzero surface impedance when the wire is connected to a flanged coaxial line. Also, radiation field patterns are computed and the input conductance determined. It is found that the current (and likewise the input conductance) can be separated into two components, one of which is a propagating or modal current. Graphs are presented from which the efficiency of excitation of the propagating current can be computed.
A second structure consisting of a single wire between perfectly conducting parallel plates is solved as a boundary‐value problem. The solution is used in the discussion of the physical behavior of a finite single‐wire transmission line. In particular it is found that the usual transmission line concepts are valid under certain restricting conditions.

Electric Fields within Cyclotron Dees
View Description Hide DescriptionFormulas for the electric field strength parallel to and perpendicular to the magnetic field for an idealized cyclotron dee system are derived by use of the Schwarz‐Christoffel transformation. A convenient method for computing numerical values for any geometry characterized by the ratio of dee gap to dee height is presented and applied.

Current Flow in Cylinders
View Description Hide DescriptionThe mixed boundary value problem arising from the flow of current into a right circular cylinder of radius a through a perfectly conducting coaxial disk electrode at one end is solved approximately. The boundary conditions are met rigorously except that the electrode is not quite plane. A solution valid for all values of the disk radius is given for which in the worst case the deviation from flatness is nearly 0.01a. More exact solutions are worked out for disk radii ¼a, ½a, and ¾a and the first forty coefficients in the Bessel function series for the potential in the cylinder are tabulated. A cylinder whose diameter is eight times its length is also treated for disk radii ¼a and ½a and the first forty coefficients in the potential series are tabulated. The probable errors in the resistance formulas derived from these solutions are given.

The Statistics of Liquid Spray and Dust Electrification by the Hopper and Laby Method
View Description Hide DescriptionThe electric charges created upon individual microscopic particles of an aerosol during its generation have been determined by the Hopper and Laby oil drop method. In the spraying of nonconducting liquids, the charges produced upon droplets in the diameter range 2–50 microns are found to follow a normal distribution with the average charge zero and the mean square charge proportional to droplet volume. This result favors the electrification mechanism of statistical fluctuation of electrolytic ion concentration among the droplets rather than the more prominent Lenard mechanism. The charge distribution among clean mercurydroplets in the diameter range 1–6 microns sprayed from a glass sprayer is asymmetric because of contact effects at the mercury‐glass interface: the average droplet charge is positive, relatively large, and increases with droplet diameter. The dependence of dispersive dust charging upon particle surface roughness is illustrated by observations made with relatively smooth microscopic glass spheres and compared with data for rough crushed quartz particles.

Temperature Dependence of the Elastic Moduli and Internal Friction of Silica and Glass
View Description Hide DescriptionThe dynamic Young's moduli and the internal friction of fused quartz, Pyrex glass, and soft glass rods were measured at a frequency of 37 kilocycles, in longitudinal vibration, within the temperature range −170° to 1000°C. The moduli of Pyrex and quartz increased with rising temperature, up to the softening point of the glass, while that of soft glass decreased. All three moduli were approximately linear with respect to the temperature over most of the measurement interval. Internal friction maxima were noted at high temperatures, while at the lowest measurementtemperatures a significant increase in background damping occurred. A brief recapitulation of existing theory is given and employed to interpret the internal friction data. It is suggested that, in microscopically inhomogeneous media, the diffusionmeasurement by internal friction methods is not equivalent to the determination by other techniques.

Method of Time‐Free Solutions for Radioactive Decay and Radionuclide Production
View Description Hide DescriptionA time‐free recursion formula development for the classical radioactive decay leads to a distribution form of solution for both natural and artificial chains.

Preparation of Uniformly Dispersed Specimens of Particulate Matter for Electron Microscopy
View Description Hide DescriptionThe transfer of monolayers of proteins to solid surfaces from a liquid substrate is now a well‐established procedure. It has been found that if particulate matter is present in the protein solution from which the monolayer is to be formed, the surface streaming set up by the spreading of the protein over the surface of a liquid substrate causes the particles to be distributed uniformly throughout the available surface. They can then be transferred to a solid surface along with the proteinmonolayer. This procedure has been used in the preparation of specimens for electron microscopy by raising previously immersed collodion‐coated wire mesh screens, attached to glass microscope slides, through the interface occupied by the monolayer. Micrographs of viruses,bacteria, and other bodies mounted in this manner have been obtained. The method commends itself by virtue of the simplicity of the procedure, the uniform dispersion of the particles, the elimination of interference from extraneous dissolved substances, and the high quality of the micrographs obtained.

Tracer Diffusion in the Ground in Radioactive Leak Location
View Description Hide DescriptionThe diffusion in the ground of a radioactive tracer gas, used for locating leaks in buried pipes, has been calculated, and the results are presented in the form of graphs. It is shown how the information can be used to obtain the amount of radioactivity needed in a test for both beta‐emitters (C‐14 in carbon monoxide) and gamma‐emitters (Br‐82 in methyl bromide).

The Extinction of Predominantly Subharmonic Oscillations in Nonlinear Systems
View Description Hide DescriptionThis paper describes the use of an electromechanical analog to examine the limiting values of various parameters needed to destroy a predominantly subharmonic oscillation of order one‐third, existing in a nonlinear system. The results of the analog are then compared with the limiting values suggested by existing theory.