bluuebunny/crossref_metadata_2025 huggingface dataset:
A Resonance Effect in the Synchrotron
Authors: Courant E. D.
Published: January 2005

The effect of the resonance occurring at n=−d(logH)/d(logr)=¾ between the second harmonic of the frequency of radial oscillations and the frequency of revolution of the particles in a synchrotron is analyzed. It is shown that this resonance will lead to an increase in the amplitude of the radial oscillations if the first Fourier coefficient of the azimuthal variation of n is too large. The effect may occur even if the value of n at the equilibrium orbit is different from ¾, because the orbit will drift back and forth periodically due to the phase oscillations and may cross the place where n=¾.

A criterion is derived for the condition that the increase in the amplitude of the oscillations per unit time due to this resonance be less than the decrease in the amplitude due to the magnetic damping, i.e. that there be a net damping effect. It turns out that this condition reduces to the requirement that the first Fourier component of the azimuthal inhomogeneities of the magnetic field be less than about 10−3. If this condition is not satisfied the resonance effect will reduce the intensity of the beam unless the equilibrium value of n is sufficiently far from ¾.
On the Design of Networks for Constant Time Delay
Authors: Hebb M. H. , Horton C. W. , Jones F. B.
Published: January 2005

Design formulae for five low pass electrical networks are obtained. These design formulae are based on the concept of ``group delay time'' which represents the delay for a signal composed of a narrow band of frequencies. The dependence on the circuit parameters of the deviation of the group delay time from a constant value is investigated for a simple L-C line, an m-derived section, a type B compensating network, and for two other networks. The relative performance of these networks is discussed, and the properties of the image impedance are summarized briefly.
An Apparatus to Depict the Load-Elongation Diagram of Yarn at Five Cycles per Second
Authors: Breazeale Francis , Whisnant John
Published: January 2005

An apparatus is described which presents on a cathode-ray oscilloscope the load-elongation hysteresis diagram, loading and unloading, of a length of yarn. The frequency may be adjusted from 1.7 to 5 cycles per second, the constant minimum load per cycle at any value from several grams to several thousand grams, and the percent extension per cycle from several percent down to several tenths of one percent. The growth of the sample as a function of time is automatically plotted, and, in addition, the stretch modulus of the sample at any time may be determined from the setting of an amplifier dial.

As way of illustration of the type of data which may be obtained with this apparatus, there are shown both the absolute and percent energy losses exhibited by tire cords of widely different constructions. For the somewhat arbitrary condition of load increment 2 kilograms over a minimum load of 0.6 kilogram, at a frequency of 5 cycles/second, both the percent and absolute energy losses increase very rapidly with increasing twist in the plies, less rapidly with increasing twist in the cord. Of interest, also, is the extremely high energy losses shown by cords which are made by plying together two plies of originally zero twist, thus giving a cord whose ply and cord twist are approximately the same, and in the same direction. Some other interesting features regarding energy losses in cords are pointed out.
Compressibility Effects in Two-Phase Flow
Authors: Tangren R. F. , Dodge C. H. , Seifert H. S.
Published: January 2005

A gas-water mixture, when expanded through a de Laval nozzle, acts as a compressible fluid. A general expression for the flow process in an idealized mixture is developed. The general thermo-hydrodynamic relations for flow through a de Laval nozzle are developed. The magnitude of the velocity of an energy pulse or signal through the mixture is determined and is compared with the velocity of flow. Experimental results are compared with those predicted using the equations developed.
Fluid Flow Patterns
Authors: Birkhoff Garrett , Caywood Thomas E.
Published: January 2005

A new photographic technique is described, for observing velocity fields in water, induced by the entry of solid missiles. The results of a number of observations are given, and compared with theoretical formulas. The corrections involved in the method are analyzed theoretically, and the theory of the corrections confirmed experimentally. It appears that the method is well adapted to velocity fields 5–100 feet per second, created by objects several inches or more in diameter, but may lead to troublesome corrections at other speeds or with smaller objects.
Dust—An Active Meteorological Factor in the Atmosphere of Northern Africa
Authors: El-Fandy M. G.
Published: January 2005

In subtropical Africa dust is shown to be an active meteorological element, particularly below the T-inversions common at 2000–3000 feet under Etesian conditions. Actual instability of the lower atmosphere is then not necessary for dust to rise, and mere mechanical stirring by day by winds of about 20 miles per hour or more is sufficient to produce severe sand storms over desert areas under such conditions.

A dust particle suspended in the atmosphere has been assumed to possess an ``air-pocket'' or ``surrounding eddy'' of its own. The radius of the ``air-pocket'' of a particle of radius ``a'' cm (less than 5 micron) is shown to be about 10a cm. It is doubtful whether one can assume the persistence of one and the same ``eddy,'' but with such an assumption made the average radius of the ``eddy'' is found to be 6a by observation, but on rejecting the assumption there appears to be a close agreement between theory and observation. The particles also share their excess of heat with their environment in a very small time, of the order of 10−2–10−3 second.

The amount of heat that can be directly supplied to the lower atmosphere by baked dust blown in a dust storm may, by itself, be sufficient to produce convection up to a height of 3000 feet or more. The same range of height of convection is also attainable in a cloud of dust by the absorption of solar radiation scattered or diffusely reflected within the cloud. In this respect it is suggested, though not fully verified, that the effect of suspended dust should be taken into account when discussing problems of upper-layer instability in subtropical Africa.

It has also been observed that in the special cases of ``squalls'' the intensity of the storm, notably the poorness of visibility, is proportional to the time during which the squall reaches its maximum. The feature has been given a mathematical explanation.

The conclusion is that owing to increased absorption of solar radiation within dusty atmospheres, or to direct heating of the air by baked dust that may be blown by day in the warm season of the region, dust is found to play a part that cannot be ignored in modifying the processes of water vapor and heat transfer, by altering turbulent and radiative processes, and in modifying the properties of air masses invading the deserts.
Some Factors Affecting the Rate of Precipitation Hardening in Cu-Be Alloys
Authors: Beck Paul A.
Published: January 2005

It was found that the lower peak hardness and faster overaging of a Co-containing Cu-Be alloy quenched from a low solution treating temperature is associated with a large amount of grain boundary precipitation. A similarly large amount of grain boundary precipitation, coupled with low peak hardness value, is obtained if the alloy contains a small amount of Cr impurity, even if the quenching temperature is normal. The grain boundary reaction resulting from the Cr impurity can be eliminated by using high solution treating temperatures.
Thermionic Emission from Sintered Cathode of Thoria and Tungsten Mixture
Authors: Fan H. Y.
Published: January 2005

To obtain suitable conductivity for direct heating, tungsten powder is added to sintered thoria cathodes. The thermionic properties of a cathode, sintered from a mixture of 67 percent thoria and 33 percent tungsten, were investigated. Emission constants were determined and the emission was found to be somewhat lower than that of cathodes sintered from pure thoria.

Change of cathode activity with temperature was observed and studied in detail. The cathode showed high activity at temperatures which would bring about deactivation of ordinary thoriated tungsten and decreased its activity when the temperature was lowered to the range where thoriated tungsten would be activated. A theory is proposed for the mechanism of the change in activity, involving the production of free thorium due to reduction of thoria by tungsten, diffusion and evaporation of thorium from thoria. Evaporation of thorium as well as thoria was proved by the use of a tungsten filament probe which detected evaporation of materials from the cathode by the change of its own emission. The energy of evaporation of free thorium from thoria is estimated from the experiments to be 46600 cal./g-atom. The energy of evaporation of thoria is found to be 184000 cal./g-molecule. The behavior of the cathode is satisfactorily explained by the proposed theory.
High Temperature Furnace for Electron Diffraction Studies of Thin Films
Authors: Alessandrini Eileen I.
Published: January 2005

A furnace has been designed which enables one to carry out electron diffraction studies of thin films at high temperatures. Electron diffraction patterns are obtainable at temperatures up to 1100°C. It is possible to bring the furnace up to 1500°C, but at temperatures over 1100°C the photographic plates are fogged by light emitted from the furnace. With the use of this furnace, recrystallizations and phase changes in thin metal and alloy films can be studied at the temperatures where these phenomena occur.
A Method of Equivalent Linearization for Non-Linear Oscillatory Systems with Large Non-Linearity
Authors: Ludeke Carl A.
Published: January 2005

This paper introduces a method, based partially on existing non-linear theory and partially on experimental results, for transforming a non-linear oscillatory system into an equivalent linear one, regardless of the amount of non-linearity in the original system.
The Illuminating System of the Electron Microscope
Authors: Hillier James , Ellis S. G.
Published: January 2005

Using a self-biased electron gun the current arriving at the specimen, the current density at the specimen, and the area of illumination of the specimen have been determined for different values of the filament height. The variation of current density at the specimen with angular aperture of illumination has been determined and the results compared with those for the zero-biased gun. The performance of the self-biased gun is assessed and some of the factors involved in its operation and maintenance are discussed.
Point-to-Plane Corona Onsets
Authors: English William N. , Loeb Leonard B.
Published: January 2005

The effect of point material and point radius of curvature on positive and negative intermittent corona onset potentials has been studied with a point-to-plane gap in air at atmospheric pressure. The negative Trichel pulse onset strangely is independent of point material but does depend on point history and radius. This surprising result is shown to come from the circumstance that the Trichel pulse onset depends on current densities needed to condition the point surface and yield a higher value of the second Townsend coefficient to give the increased currents. Trichel pulse onset thus does not mark the onset of a self-sustaining discharge. The self-sustaining discharge initiates at lower potentials and leads to currents of a low order until the cathode spot cleans up.
Magnetic Properties of Iron Compacts in Relation to Sintering Temperature
Authors: Steinitz Robert
Published: January 2005

Previous experiments have indicated that the magnetic permeability of sintered iron compacts is to a large extent determined by the final density of the compact. The permeability of five different iron powders has proved to be independent of the origin of the powder, if the compacts were sintered at the same temperature. The results were compared with the theory of Polder and Van Santen and agreed very well with their predicted curve, if the residual pores were assumed to be flat disks. It could be expected that at higher sintering temperatures, the disk-shaped pores would change into a more equiaxed or spherical shape.

Experiments to check this theory have been made, and the results are in good agreement. Compared for identical densities, the permeability of different iron powders is appreciably higher if sintering is done at 1250–1350°C and for 24 hours, instead of at 1150°C for one hour. Different powders, however, now show quite different permeabilities, which could be explained by a different inclination of the powder to form spheroidal pores.

It is shown that coining after high temperature sintering brings the permeability values back to the curve of the disk-shaped flat pores. The effect of the increase in permeability at higher temperature cannot, therefore, be due to a purification process, but must be attributed to a change in the pore shape.
A Study of the e.m.f. Method
Authors: Tai C. T.
Published: January 2005

The present work contains an investigation of the e.m.f. method to determine the input impedance of a thin biconical antenna as first suggested by Schelkunoff. By considering the various components of the currents flowing on the antenna, it has been shown that the sinusoidal part is, indeed, the dominating component among all these currents. An investigation of the total current at the end of the antenna, where the lateral surface of the cone and the spherical cap meet, shows that the current is not identically zero at that point, but vanishes as the reciprocal of the square of the characteristic impedance of the cone. The two approximate expressions of the complex conjugate power used in the e.m.f. method are derived, as well as the exact expression. Computation of some integrals occurring in the formulation is also treated in detail to show the various approximations involved.
The Precision Determination of Lattice Constants by the Powder and Rotating Crystal Methods and Applications
Authors: Straumanis M. E.
Published: January 2005

A method that makes possible the attainment of a very high degree of precision in the determination of lattice constants (in some cases more than 1:200,000, even with crystals of lower symmetry) is described. The method and its applications, which has been in steady development since 1934 (in Riga, University of Latvia), tries to eliminate the errors of the Debye-Scherrer-Hull and rotating crystal methods by a careful experimental technique, based on:

(1) Very exactly built cameras of a reasonable diameter (64 mm);

(2) Elimination of all well-known errors of the powder and rotating crystal methods (e.g., elimination of film shrinkage errors by a new method of putting the film into the camera);

(3) Locating the camera in a specially constructed thermostat so that the temperature some hours before and during exposure is kept constant.

The films obtained in this way are very clear, especially in the important back-reflection region, with distinct lines (or spots) that can be measured exactly. As no standard substances are necessary and the absorption corrections are negligible (using very thin samples), the method must be regarded absolute. Of course, the sample (crystal) must be prepared, mounted, and centered under the microscope, a procedure that is not difficult.

Applications: lattice constants and expansion coefficients (even within the range of 10°C); quantitative solubility determinations; appearance of new phases and transition points; the determination of the exact value of Avogadro's number; molecular and atomic weight determinations (if the exact density values are known); statement of imperfections in crystals.
Dead Time and Non-Linearity Characteristics of the Geiger-Counter X-Ray Spectrometer
Authors: Alexander Leroy , Kummer Elizabeth , Klug Harold P.
Published: January 2005

The satisfactory use of Geiger-counter methods for the measurement of diffracted x-ray intensities demands that the observed counting rates be corrected for the non-linear response of the counter. Both the multiple foil method of calibrating the non-linearity of response and the two-source method of Beers for measuring counter dead time have been found to be unsatisfactory approaches to this problem. The experience of this laboratory indicates that electronically controlled oscillographic techniques for the direct measurement of dead time are much more satisfactory. With a knowledge of the dead time, τ, the true counting rate, N, can be calculated from the observed counting rate, No, by employing the formula N=No/(1−Noτ).

For a pulsating x-ray source the effective counting rate is faster than the observed by a factor which is characteristic of the type of rectification employed, the target material, and the voltage applied to the x-ray tube. A sufficiently accurate value of this factor can be arrived at by oscillographic observation of the pulse pattern and in some cases by mathematical analysis.
Reflection Method of Determining Preferred Orientation on the Geiger-Counter Spectrometer
Authors: Field Michael , Merchant M. Eugene
Published: January 2005

A rapid and accurate method of determining preferred orientation in the surface of thick samples was devised using a reflection technique on the Geiger-counter spectrometer. By presenting the specimen face to all possible angles with respect to the incident x-ray beam, through use of a special fixture, and recording the intensity of diffraction on a potentiometer recorder, the relative number of planes of a given set at each orientation can be determined. The change of intensity due to the positioning of the specimen face away from the Bragg angle is taken care of by a correction formula which is experimentally verified. The method is especially valuable for dealing with thin layers on thick specimens.
Influence of Magnetic Field on Recrystallization
Authors: Smoluchowski R. , Turner R. W.
Published: January 2005

In order to gain additional information about the origin of preferred orientation of recrystallized grains, the influence of a magnetic field on recrystallization of iron-cobalt alloys is being studied. Preliminary results indicate a change of the texture which can be qualitatively accounted for by considering the magnetostrictive properties of the alloy and their influence on the stability of the recrystallization centers.
The Morphology of Carbon Black Particles in Shadow-Cast Specimens
Authors: Watson John H. L.
Published: January 2005

Observations are given which favor a reticulate chain structure for carbon black. The discovery of ``hollow'' particles in carbon black dispersions of P-33 and Thermax is reported along with possible explanations for the observed image intensities which give rise to the interpretation of hollowness. Striated surfaces strongly suggestive of a laminar structure and serrated edges which conform in orientation with these plateaus have been detected. Rough areas arranged both in lines and at random are observed over the surfaces of some particles. Shape variations away from the spheroidal and the occurrence of straight-edged images are stressed again.
Coexistence Relations of n+1 Phases in n-Component Systems
Authors: Pepper Paul M.
Published: January 2005

In an investigation of the coexistence relationships of n+1 phases in the isothermic-isobaric sections of n-component systems, Paul A. Beck found that there are at most two coexistence patterns possible. Furthermore, theoretically, only a well-chosen sample need be examined for the phases it contains in order to clarify the phase coexistence relationships of the n+1 phases whose compositions are already known. The present paper gives formulas for calculating the composition of the ``well-chosen sample.'' Supplementary formulas are given for the range of coexistence, in the composition space, for any n phases known to coexist.
A Method for the Instantaneous Measurement of Velocity and Temperature in High Speed Air Flow
Authors: Marlow D. G. , Nisewanger C. R. , Cady W. M.
Published: January 2005

A beam of ultrasonic sound waves is projected across an air stream the velocity and temperature of which are required. From the known ultrasonic frequency and the measured wave-length, the temperature may be determined; and from the slope of the beam boundary, an approximate Mach number may be obtained. The method is applicable to steady-flow problems as in wind tunnels or to transient-flow problems such as the study of shock waves.
Some Properties of the Ba2SiO4 Oxide Cathode Interface
Authors: Eisenstein A.
Published: January 2005

Oxide cathodes prepared on a Si-Ni alloy base metal have an interface of barium orthosilicate. The thickness of this layer is measured by means of an x-ray method and found to increase with the life of the cathode and to be of the order of 10−3 cm. Measurements of the effective, specific electrical conductivity were made and compared with the conductivity of the coating, (BaSr)O. Both materials exhibit a conductivity-temperature variation characteristic of semiconductors; however, the conductivity of the interface was always less than that of the coating. The interface layer influences the thermionic emission characteristics of the cathode due to an interface voltage developed by the flow of emission current. A retarding-potential method is developed for determining this voltage.
Fields from Fluid Flow Mappers
Authors: Moore A. D.
Published: January 2005

Fluid flow within the streamline (viscous) range, made visible by appropriate means, may be made to simulate fields occurring in electrostatic, magnetic, electric current, heat flow, chemical diffusion, and other situations. Simple, reliable, and inexpensive techniques for setting up the desired fluid flow situations have been worked out, and are described herein.

Two-dimensional fields with one, several, or many non-distributed sources (or sinks) may usually be made up and operated with ease. Techniques for the simulation of certain three-dimensional fields with axes of symmetry have also been developed.

Through the invention of the ``sandbed'' feature, the fluid flow method has been greatly extended: fields due to distributed sources can be simulated, not only outside the sources, but inside them as well.

Numerous photographs of fluid mappers in operation, illustrating all of the foregoing types of cases, are included.
High Inverse Voltage Germanium Rectifiers
Authors: Benzer S.
Published: January 2005

Rectifying current-voltage characteristics going up to several hundred volts inverse have been observed in metal-germanium point contact rectifiers. A reproducible negative differential resistance region occurs in the inverse characteristic. Certain impurities are desirable in producing high voltage material. Surface treatment, e.g., by etching, is very important. The metal used as a whisker has little effect. Increasing the force of contact increases greatly the current of low voltages but has less effect on the high voltage curve. Pronounced improvement of rectification can be effected by treatment of the contact with large currents.

Variation with temperature is very marked, especially for crystals of large inverse resistance; the variation of the inverse peak with temperature indicates that contact heating is responsible for the negative resistance. Time lags in the inverse negative resistance region of the order of 10−5 second occur.

When contact is made between two Ge crystals, typical inverse characteristics are observed in both directions. Photoelectric effects are observed and indicate that the barrier thickness is greater the higher the inverse peak voltage.
The Aerodynamics of Golf Balls
Authors: Davies John M.
Published: January 2005

The aerodynamic forces on golf balls were studied by dropping spinning balls through the horizontal wind stream of the B. F. Goodrich wind tunnel. The lift, L, and drag, D, were calculated from the drift of the balls, rotating at speeds, N, up to 8000 r.p.m. while falling through a wind stream having a velocity of 105 feet per second. For a standard dimple or mesh golf ball weighing 0.1 lb., the lift varied with the rotational speed as L=0.064 ×[1−exp(−0.00026N)], with a maximum observed value of 0.055 lb. or more than half the weight of the ball. The drag increased nearly linearly from about 0.06 lb. for no spin to about 0.1 lb. at 8000 r.p.m.

For a smooth ball the lift was negative at all rotational speeds below 5000 r.p.m. Above this speed, the lift was positive but was less than for the standard ball. The drag for these balls was nearly constant at about 0.08 lb. Balls with shallower dimples than standard gave intermediate results. Driving tests were consistent with the wind tunnel results.

These results explain why a golfer cannot obtain long drives with a ball having a smooth surface and why the standard dimple or mesh surface gives him greater distance and better control of the ball.
The Projection of Crystal Structure Factors on the Reciprocal Lattice
Authors: McLachlan Dan , Christ C. L.
Published: January 2005

A discussion of the use of the wave addition method for making projections of the crystal structure factor, Fhko, upon the reciprocal lattice, in a fashion similar to that used in making electron density projections in real space, through the use of the ``sand machine'' and devices operating on similar principles, has been developed.
Antennas and Open-Wire Lines. Part I. Theory and Summary of Measurements
Authors: King Ronold
Published: January 2005

Theoretical models of antennas driven by hypothetical generators are contrasted with antennas driven from transmission lines. The coupling between an antenna and a two-wire line driving it, as well as end-effects on the line, are considered in their relationship to the definition of an independent impedance for the antenna. It is concluded that a physically significant impedance can be defined only outside a terminal zone near the junction of load and line. The derivation and approximate solution of generalized transmission-line equations that take account of coupling-effects and end-effects are given for (1) antenna as end-load in the plane of a two-wire line with and without a high impedance-stub support; (2) antenna as center-load in the plane of a two-wire line symmetrically driven at each end; (3) antenna as end-load in the plane perpendicular to the line with stub support. Theoretical predictions of measured impedances defined outside a terminal zone on a feeding line in these several arrangements may differ greatly from one another and from the ratio of scalar potential difference to current for an isolated antenna with gap. These differences are due primarily to capacitive end-effects and coupling-effects of which account may be taken by a lumped positive or negative capacitance across the load terminals of an ideal transmission line. Inductive effects are also involved but are relatively small. Methods for evaluating the elements in a terminal-zone network are given. The theoretical results are verified experimentally with good agreement in all cases.
Potential Functions for a Thermionic Vacuum Tube
Authors: Okress E. C.
Published: January 2005

Space charge free potential functions for a particular type of thermionic vacuum tube are derived and represented graphically for four sets of boundary conditions. The geometry under consideration comprises two spaced parallel equipotential metallic planes between which are three symmetrically interposed planes of spaced metallic strands. The strands are mutually parallel in their respective planes, though the strands in planes adjacent to the equipotential surfaces are both orthogonal to those in the central plane. This structure is divided principally into two planes, due to the orthogonal relationship between the strands in the central and adjacent planes. These two planes are each conformally transformed such that the analysis thereof yields the desired potential functions for the original structure, neglecting edge effects. Finally, the theoretical results are applied to a typical commercial thermionic vacuum tube.
Time Constants for Vacuum Gage Systems
Authors: Schaaf S. A. , Cyr R. R.
Published: January 2005

A typical system for measuring pressures in a rarefied gas consists of a vacuum gage connected to the gas by a length of tubing, usually with an orifice of diameter smaller than that of the tubing at the end. The interior surface of this system will outgas at a fairly constant rate for a long period of time so that an equilibrium state will be reached with a definite non-constant pressure distribution along the tubing. The response time constant for the system to come to equilibrium and the difference in pressure between gas and gage are functions of the outgassing rate and the geometry of the system. An analysis is made assuming molecular flow, and formulas are obtained for the response time and the pressure difference. It is shown that there is an optimum value of the tubing diameter for a given orifice diameter, gage volume, and length of tubing. This optimum is rather critical; if the diameter is too small, response time constants of the order of hours may result. Experimental work has been done and the results compared with theory. This work was done under ONR contract.
The Propagation of Electromagnetic Waves in a Tube Containing a Coaxial D.C. Discharge
Authors: Rosen Philip
Published: January 2005

The boundary value problem involved in finding the propagation characteristics of electromagnetic waves in a cylindrical tube containing a coaxial d.c. discharge is solved. Ohm's law is assumed to hold for the alternating current. This assumption has been verified theoretically for the case where the alternating electric field is small compared with the d.c. field. Curves which give the relationship between the complex propagation constant, γ, and the complex dielectric coefficient, Kc′, have been computed for the solution in which the TEM mode of the coaxial line is approached as Kc′ becomes infinite.
Magnetically Controlled Wave-Guide Attenuators
Authors: Miller Theodore
Published: January 2005

It has been observed that the microwave power loss of a section of wave guide filled with iron powder material could be varied by subjecting the iron powder to an externally applied magnetic field. This paper describes some experiments performed with various kinds of iron powders. Measurements have been made with the magnetic field applied parallel to, and perpendicular to the plane of the magnetic component of the electromagnetic wave inside the guide. The possibility of ferromagnetic resonance is considered. A theoretical formula for the power loss exhibited by low conductivity iron powder attenuators is developed and compared with experimental measurements.
Effect of Strain Rate Upon Plastic Flow of Steel
Authors: Zener C. , Hollomon J. H.
Published: January 2005

An experiment has been designed to check a previously proposed equivalence of the effects of changes in strain rate and in temperature upon the stress-strain relation in metals. It is found that this equivalence is valid for the typical steels investigated. The behavior of these steels at very high rates of deformation may, therefore, be obtained by tests at moderate rates of deformation performed at low temperatures. The results of such tests are described. Aside from changing the isothermal stress-strain relation, an increase of strain rate tends to change the conditions from isothermal to adiabatic. It is found that at low temperatures, the adiabatic stress-strain relation in the plastic range is radically different from the isothermal, having an initial negative rather than a positive slope. This initial negative slope renders unstable homogeneous plastic deformation.
The Problem of Reduction of Vibrations by Use of Materials of High Damping Capacity
Authors: Gemant Andrew
Published: January 2005

This paper deals with considerations concerning the reduction in amplitude of unwanted vibrations of machinery parts through the use of materials of high damping capacity. The problem is to reconcile the requirement for high damping with that for high mechanical quality (strength, fatigue resistance, etc.). Two ways are suggested: (1) the use of a material whose decrement generally is low but rises rapidly as the stress increases; (2) the use of a material whose damping capacity is low but rises to high peaks in certain frequency ranges. It is shown by numerical computation in two instances, namely, turbine blade vibrations and crankshaft oscillations in engines, how the suggested methods would work out in practice.
The Technique of Microradiography
Authors: Maddigan S. E.
Published: January 2005

Investigations have been made of the various factors considered to influence the sensitivity of the microradiographic method for the examination of alloys. Both target element and applied voltage influenced the results. Radiographs are shown to demonstrate the effect; an explanation is given in terms of the x-ray emission curves and the absorption differential curves for the phases of the radiographed alloy. Target-specimen distance was an important factor for uncollimated rays, particularly for distances of less than 6 in. with minute inhomogeneities or with low values for the absorption differential. The size of inhomogeneity, lower limit of absorption differential, and upper limit of magnification were also studied. For investigation of the distribution of elements in inhomogeneities, it was concluded that, contrary to previous reports, both target element and applied voltage must be carefully chosen after a study of the absorption differential curves. The optimum voltage range is usually 2.5 to 3.5 times the excitation potential.
Antenna Theory and Experiment
Authors: Schelkunoff S. A.
Published: January 2005

This paper presents: (1) a comparison between several approximate theoretical formulas for the input impedance of cylindrical antennas in the light of available experimental evidence; and (2) a discussion of the local capacitance in the vicinity of the input terminals, mathematical difficulties created by its presence, and methods of overcoming these difficulties. No exact solution of the antenna problem is available at present and so far it is impossible to set definite limits for errors which may be involved in various approximations. For this reason in appraising these approximations one is forced to rely on one's judgment and on experimental evidence. It is hoped that this paper will aid in correlating theory and experiment to the advantage of both.
A Modification of Hallén's Solution of the Antenna Problem
Authors: Gray Marion C.
Published: January 2005

An alternative formula for the input impedance of a cylindrical antenna is derived from Hallén's integral equation. It is shown that the introduction of a variable parameter Z(z) in place of Hallén's Ω=log (4l2/a2) modifies the numerical results considerably, and leads to much better agreement with experimental evidence.
Exploring Stress-Strain Relations of Isotropic Plastic Solids
Authors: Prager W.
Published: January 2005

Combined torsion and tension of thin-walled tubes constitutes one of the few testing arrangements in which a fairly general state of uniform stress can be realized without too great experimental difficulties. A manner of representing graphically the results of such tests is used to discuss, in geometrical terms, some stress-strain relations of the mathematical theory of plasticity. It is shown that the theories of B. de Saint-Venant, M. Lévy, and R. v. Mises lead to physically unacceptable conclusions unless the material is supposed to be rigid as long as the stresses have not reached the yield limit. The predictions of the theories of L. Prandtl, E. Reuss, H. Hencky, and A. Nádai are compared with the results of experiments on mild steel; the possible effects of viscosity and strain hardening are discussed.
Studies in Three-Dimensional Photoelasticity Stress Concentrations in Shafts with Transverse Circular Holes in Tension Relation Between Two- and Three-Dimensional Factors
Authors: Frocht Max M.
Published: January 2005

Part I. General problems of technique arising in three-dimensional photoelastic analysis by means of the frozen stress pattern method are discussed. These include suggestions for loading, slicing, improvement of boundary visibility, a discussion of time stresses, and methods for the determination of the fringe order and fringe value in a model with a static or frozen stress pattern. A number of instructive three-dimensional stress patterns are shown. Part II. Stress concentration factors for shafts with ratios of r/d equal to 0.0666, 0.323, and 0.164 are determined, r being the radius of the hole, D the diameter of the shaft, and d=D−2r. Part III. A relation is established between two- and three-dimensional factors of stress concentration for a range of r/d which does not exceed 0.5, which is believed to cover the most practical cases. It is shown that the three-dimensional factors are somewhat greater than the two-dimensional factors for the same ratio of r/d.
The Magnetically Focused Radial Beam Vacuum Tube
Authors: Skellett A. M.
Published: January 2005

A new type of vacuum tube is described in which a flat radial beam of electrons in a cylindrical structure may be made to rotate about the axis. Features of the tube are the absence of an internal focusing structure and resultant simplicity of design, its small size, its low voltages, and its high beam currents. The focusing of the beams and their directional control are accomplished by a magnetic field.
Potential Nuclear Monokinetic Electron Sources
Authors: Pool M. L.
Published: January 2005

In this paper sixty-eight nuclear monokinetic electron sources are tabulated. These sources are obtained by producing designated artificial radioactive elements. The voltage of the electrons emitted in the lowest energy group is 17 kev and that in the highest is 578 kev. Applications seem possible in special radio tubes and for certain experiments with electron microscopes and electron diffraction.
Limiting Stable Current in Electron Beams in the Presence of Ions
Authors: Pierce J. R.
Published: January 2005

In electron flow, the net electronic charge may be neutralized by positive ions. In this case, for a given geometry there is a limiting current beyond which homogeneous flow is unstable. This limiting current is evaluated for flow normal to parallel plane equipotentials and for flow filling a conducting tube and constrained to motion parallel to the axis. For parallel planes at a potential V0 volts and spaced a distance L cm apart, the limiting current density in amperes/cm2 isi0=104×10−6V032/L2. For a long conducting tube the limiting current is I0=160×10−6V032. These limiting currents are roughly 6 times as great as in the absence of ions.
Electrostatic Properties of Rubber and GR-S
Authors: Havenhill R. S. , O'Brien H. C. , Rankin J. J.
Published: January 2005

A new ``electrostatic modulator'' for measuring the electrostatic charges on various materials is described in this paper. In this apparatus the electrostatic lines of force established between the charged specimen and the grid of an audiofrequency amplifier are cut or modulated at audiofrequency by a motor-driven fan. The resultant alternating current voltage is amplified and measured on a meter in the output circuit. This device, in conjunction with a mirror surfaced metal plunger system for contacting the sample, has been used to measure the contact potential of various rubber and GR-S compounds. Data are shown on both rubber and GR-S compounds, and they bear out the formulation of an ``electrostatic contact potential theory of reinforcement'' in which reinforcement is explained on the basis of contact potentials and resultant electrostatic forces set up between the rubber and the reinforcing agents. By the application of this theory, organic materials, which have a highly positive charge, such as polymerized Trimethyldihydroquinoline and Flectol H, have been found to increase the tensile of GR-S pure gum type compounds as much as fivefold and to nearly double the tensile of high zinc oxide GR-S compounds.
Speed of Retraction of Rubber
Authors: Stambaugh R. B. , Rohner Margaret , Gehman S. D.
Published: January 2005

A method of measuring the speed of retraction of rubber is described which utilizes an electronic timing circuit with photo-cell input. The results include measurements of the speed of retraction of Hevea and synthetic rubbers as a function of elongation, temperature, carbon black loading, and cure. They are discussed both from the standpoint of the new information which they give in regard to rubber structure and high elasticity as well as their practical application to evaluate quality and cure. High speed photographs are included which are of interest in showing the manner in which rubber retracts.
Some Relations Between Stress, Strain, and Temperature in a Pure-Gum Vulcanizate of GR-S Synthetic Rubber
Authors: Roth Frank L. , Wood Lawrence A.
Published: January 2005

Stress-temperature relations at constant elongation and at constant length have been studied in a pure-gum vulcanizate of GR-S. Such studies yield information useful for calculations involved in the theory of its elastic behavior, and furnish practical data regarding its tensile properties at different temperatures. The compounding recipe was: 100 parts by weight of GR-S, 2 parts of sulfur, 1 part of zinc oxide, and 0.5 part of zinc dibutyl dithiocarbamate. The specimens were first held at constant length and constant temperature for a period of ½ hour to 2 hours, after which time the effects of relaxation of stress during the observation of stress-temperature relations were negligible. The value of the stress after relaxation at each elongation was used to plot a stress-strain curve. The stress-temperature relations observed for temperatures below the relaxation temperature were linear and reproducible on successive runs of increasing and decreasing temperature. When the temperature was raised above the relaxation temperature straight lines were not obtained, since further relaxation occurred at the higher temperatures. The intercepts at 0°K for the lines obtained below the temperature of relaxation are useful in evaluating the internal energy changes. The intercepts of the lines representing the experiments at constant elongation were found to be negative. The absolute values were of the order of 10 percent of the stress after relaxation for the lowest elongations, and increased to almost 30 percent of the stress at the highest elongation.
Limiting Law of the Reinforcement of Rubber
Authors: Smallwood Hugh M.
Published: January 2005

The effect of the filler upon the modulus of compounded rubber has been calculated with the aid of some simplifying assumptions. From these calculations it is found that the increase in modulus, caused by the filler, is directly proportional to the volume loading, and is independent of the particle size of the filler. The stress system in the vicinity of a spherical filler particle has also been calculated. A series of experiments has been made to check these calculations. From the results of these experiments, it has been deduced that carbon black is flocculated in rubber; and that P-33, Thermax, and Gilder's whiting are completely dispersed in rubber. These last-named fillers give increases in modulus substantially in agreement with the calculations. It has further been found that Kadox and XX zinc oxide give unusually large increases in modulus. These are ascribed to alteration of the type of cure of the rubber matrix. Catalpo clay showed excessive modulus because of high calender grain.
Stress-Temperature Relations in a Pure-Gum Vulcanizate of Natural Rubber
Authors: Wood Lawrence A. , Roth Frank L.
Published: January 2005

Stress-temperature relations at constant elongation have been studied in a pure-gum vulcanizate of natural rubber. Such studies yield information useful for calculations involved in the theory of its elastic behavior, and furnish practical data regarding its tensile properties at different temperatures. The crystallization of the rubber which occurs on stretching is a factor of considerable importance in the explanation of the results obtained. The compound contained 100 parts by weight of smoked sheet rubber, 2 parts of sulfur, 1 part of zinc oxide, and 0.5 part of zinc dibutyl dithiocarbamate (``Butyl zimate''), and it was vulcanized 40 minutes at 115°C. The stress-temperature studies were made after the specimens were stretched and allowed to relax at a constant temperature of 25°C or 70°C for about two hours. The change of stress with time at the end of two hours was small enough to be without influence on later results, except when the flow was excessive or when the stretched rubber continued to crystallize, as it did at elongations between 150 percent and 500 percent at 25°C. At elongations of 150 percent and less, no evidences whatever of crystallization were found during the time of the experiments. At elongations of 500 percent and more, the crystallization which occurred during stretching and in the first few minutes thereafter was so complete that the stress soon became independent of time. At 70°C both the upper and lower limits of the range of elongations in which continued crystallization occurred were somewhat higher. Values of the stress after relaxation have been used to plot a stress-strain curve. The stress-temperature relations obtained by lowering the temperature to about −20°C were always linear and reproducible on successive runs of increasing and decreasing temperature, except when the flow was excessive or when the stretched rubber continued to crystallize. An additional period of relaxation was required if the rubber was heated above the temperature at which the first relaxation occurred. The slopes of the stress-temperature lines and the values of the stress at any temperature depend upon the temperature at which relaxation was carried out. The stress intercepts at 0°K are small compared with the total stress for elongations up to 150 percent. At the higher elongations the intercepts take on increasingly large negative values, finally becoming approximately equal in magnitude to the total stress.
Physical Aspects of Foaming in Steam Generation
Authors: Cassel Hans M.
Published: January 2005

Vaporization of pure liquids is reviewed as a problem of heat transfer and the rate of vapor bubble creation. Applying an idea of Gibbs, the influence upon the activation energy of nucleus formation exerted by the contact angle at the vapor/liquid/solid phase boundaries as well as by the shape and size of submerged solids is quantitatively expressed by the reduction in the volume requirement of the nucleus. Possible effects of solutes in superheated liquids upon steam bubble creation and growth are discussed. The stabilization of foam in boiling electrolyte solutions is explained by the thermoelectric potential differences originating from the temperature gradient around growing bubbles. The effect of foam inhibiting agents (e.g., castor oil) is interpreted as a change in the rate of bubble creation caused by surface conditioning of heating elements and suspended particles.
X-Ray Measurement of Order in the Alloy Cu3Au
Authors: Wilchinsky Zigmond W.
Published: January 2005

X-ray diffraction theory is developed for the evaluation of long range order and short range order in the alloy Cu3Au, and experiments are described whereby each type of order was measured. Values of the long range order parameter S were found to be 0.86 for 250°C, 0.81 for 370°C, and 0.79 for 380°C, the samples being held at elevated temperatures during the x-ray exposures. At the critical temperature Tc=388°C, S suddenly dropped to zero. Above Tc short range order was found to exist, the amount present being specified by a set of parameters σi which are associated with the interatomic distances ri. The dominant short range order parameter σ1, referring to nearest neighbors, was evaluated as 0.50 for 540°C and 0.25 for 750°C.