bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Bridge Erosion of Electrical Contacts. Part I.
Authors: Lander J. J. , Germer L. H. 
Published: January 2005

Bridge erosion is the transfer of metal from one electrode to the other which occurs when an electric current is broken in a low voltage circuit which is essentially purely resistive. It is associated with the bridge of molten metal formed between the electrodes as they are pulled apart, and more specifically with the ultimate boiling of some of the metal of this bridge before the contact is finally broken. This paper is concerned with fundamental studies of this molten bridge and with empirical measurements of the transfer of metal.
From known physical constants one calculates that, when the melting point is reached at a current I, the diameter of the area of contact of two electrodes is about 1.5×10−5 I cm for silver, copper, or gold, and about 7.5×10−5 I for platinum or palladium. When the maximum temperature of the molten bridge reaches the boiling point the mean bridge diameters are roughly 4×10−5 I and 20×10−5 I respectively. Experimental tests have been made of relations entering into these calculations.
On breaking a contact about 6×10−14 I3 cm3 of metal is transferred from the positive to the negative electrode. This represents about 100 percent of the volume of the molten bridge for silver, copper, or gold, and about 0.5 percent for platinum or palladium. The amount of transfer can be decreased, and even its direction reversed, by heating the negative electrode, and by other means. Calculations have been made of temperature distributions in the neighborhood of a contact and a theory has been developed to account for the reversal of direction of transfer. The theory of the fundamental mechanism has, however, been reserved for later publication.
Energy Losses of Sound Waves in Metals Due to Scattering and Diffusion
Authors: Mason W. P. , McSkimin H. J. 
Published: January 2005

When high frequency longitudinal and transverse sound waves are sent through a multicrystalline rod of metal, attenuation losses result because of scattering and diffusion of sound waves by the grains. When the grain size is less than one-third of the wave-length, these losses are due to Rayleigh fourth power law scattering and are proportional to the grain volume. The scattering factor depends on the anisotropy of the elastic constants. Two different factors are obtained, one for shear waves and one for longitudinal waves. These factors have been evaluated for cubic and hexagonal metals. From the measured elastic constants the only metals with a low loss are aluminum, magnesium, and tungsten. The calculations indicate that the losses for aluminum and magnesium are about equal for longitudinal waves, but for shear waves magnesium has a very low shear loss. It has been found experimentally that magnesium has nearly as low a loss as fused quartz.
Experiments with higher frequencies show that when the wave-length is one-third of the grain size or less, the transmission process becomes a diffusion process similar to the propagation of a heat wave. The grain sizes determine the mean free path, and the loss becomes inversely proportional to the grain diameter. An approximate formula for diffusion losses has been obtained which agrees closely with the experimental values.
The Fracture of Liquids
Authors: Fisher John C. 
Published: January 2005

A liquid subjected to negative pressure is metastable; vapor bubbles form spontaneously and grow until the pressure of the system rises to the equilibrium vapor pressure. The rate of bubble formation is calculated from the theory of nucleation, and the negative pressure pt that gives one bubble (i.e., fracture) in t seconds is determined. pt is very nearly independent of t, and is proportional to σ32 where σ is the surface tension. Subcooled liquids such as glass also are metastable under negative pressure; cracks form spontaneously and grow until the pressure rises to the equilibrium vapor pressure. Nucleation theory leads to an expression for the fracture stress of glass that is proportional to (E2σ3)¼ where E is the elastic modulus. The transition from high temperature cavity-nucleated fracture to low temperature crack-nucleated fracture is examined.
Fracture strengths calculated from nucleation theory agree satisfactorily with the maximum experimental values, and are an order of magnitude smaller than the forces required for simultaneous separation of all atomic bonds cut by a plane surface. The frequent occurrence of premature failure is associated with the presence of pre-existing surface cracks in glass, and of positive contact-angle impurity in contact with liquids.
Velocity of the Anode Spark in Copper Sulfate Solutions Under Application of Impulsive Potential
Authors: Henry Hugh F. 
Published: January 2005

The velocity of the luminous anode spark produced in CuSO4 solutions by application of impulsive potential has been measured as a function of the interelectrode gap, input voltage, and solution normality. Determinations were made for input potentials of 15–30 kv, interelectrode gaps of 15–80 mm, and solution concentrations of 0.0125–0.0625N.
The spark velocity was found to depend upon the input potential and the interelectrode gap by the empirical equation: V=311.1(E0−11.7)/G,where V is the spark velocity in meters/sec., E0 is the input voltage in kv, and G is the interelectrode gap in cm. Qualitatively, it was observed that as the solution normality increased, the maximum breakdown distance decreased and the spark behaved more erratically.
The maximum length which the spark streamers reach may be stated empirically by the equation: Lm=2.33×10−3(E0+2.89)2/(N+0.545)(G−0.43)12,where Lm is the maximum streamer length in cm, E0 is the input potential in kv, G is the interelectrode gap in cm, and N is the normality of the solution.
The computed potential at which the spark cases its progress through the liquid, Em, was found to be proportional to the input potential but independent of the interelectrode gap and the solution concentration. The ratio Em/E0 was 0.646. The time lag in initiation of the spark was also found to depend upon the input voltage but to be independent of the interelectrode gap and the solution concentration.
The Thermodynamics of a Strained Elastomer. I. General Analysis
Authors: Mooney M. 
Published: January 2005

The thermodynamic functions of principal interest in a strained elastomer are the entropy and energy of deformation. The volume is of secondary importance, and it can be assumed, with sufficient accuracy for most purposes, that the volume is linear in the temperature and the mean pressure. The basic partial differential equations of thermodynamics can then be integrated, yielding expressions for the energy and entropy of deformation in terms of observable quantities.
In the present analysis the volume effects caused by changes in mean pressure and crystallinity are taken into account, and the effects associated with change in shape are sharply separated from those associated with change in volume. It is shown that the superelastic functions of deformation previously published (M. Mooney, J. App. Phys. 11, 582–92 (1940)) have a very general validity.
The Thermodynamics of a Strained Elastomer. II. Compressibility
Authors: Copeland L. E. 
Published: January 2005

Adiabatic compressibility coefficients were measured on a series of cured polymers of commercial types under pressures up to 5000 lb./in.2. In most cases, the second order as well as the first order coefficient could be determined from the data. The linear isothermal compressibility also was calculated from the measured linear adiabatic coefficient.
Preliminary measurements of the thermal expansion of a stretched Hevea gum stock show that there is a slight decrease in expansion at the 200 percent elongation, presumably due to partial crystallization.
The Thermodynamics of a Strained Elastomer. III. The Thermal Coefficient of Modulus and the Statistical Theory of Elasticity
Authors: Copeland L. E. , Mooney M. 
Published: January 2005

Published thermoelasticity data are critically analyzed by means of thermodynamic equations developed in the first paper of this series. Equations known to be of the proper form are fitted by least squares to the experimental data, which were first corrected to allow for the changes in shape when tested under variable temperature and constant length. If the measurements are accepted as truly reversible, the data show that several different elastomers depart considerably in some respects from the predictions of the statistical theory of elasticity.
Some thermoelasticity measurements in torsion are reported which seem to give the most reliable evidence that stress is proportional to absolute temperature.
Creep, Recovery, and Permanent Set for GR-S and Hevea
Authors: Gehman S. D. 
Published: January 2005

A study was made of creep, recovery, and permanent set for Hevea and GR-S over a 1000-hr. period and a range of elongations at 35°C. Creep for GR-S is greater than for Hevea. The stress for GR-S is considered to be supported to a greater extent by a relatively unstable secondary bond structure. This is consistent with the large creep values for GR-S at low elongations and the large ratio of primary or recoverable creep to permanent set. Hevea, in contrast, shows low creep at both high and low elongations and maximum creep at intermediate elongations for which the structure is heterogeneous, consisting of amorphous and crystalline phases.
A procedure was worked out for determining the contribution of permanent set to the observed creep. The creep curves were concave to the strain axis when plotted against logarithmic time. After correction was made for permanent set, they were found to be approximately linear, thus extending the range of application of the Tobolsky-Eyring theory of creep.
At the start of the creep test the flow appears to be due largely to the reversible yielding of relatively weak bonds which can reform under the action of the elastic network when the stress is removed. For longer periods of time, or for higher elongations, the flow involves more deep seated changes in structure. Larger units of structure are displaced or stronger bonds broken with resultant permanent molecular displacements upon removal of the stress. For Hevea at high elongations all of the flow was accounted for by permanent set.
Ionosphere Reflections Recorded Mechanically by Means of a Repetition Frequency Converter
Authors: Stoffregen W. 
Published: January 2005

A method of converting the high repetition frequency used by echo sounding to a lower value by means of a converter between the receiver and the recorder is described. The method is adapted to recordings of radio-echoes from the ionosphere, in which case the repetition frequency of 50 c/sec. of the pulse transmission after reception is converted into a repetition frequency of ½–⅕ c/sec. before being supplied to the recorder. Ionosphere echoes having a delay of the order of milliseconds and a pulse width of about 20–100 μsec. may thus be recorded mechanically.
The principle of repetition frequency conversion described here may also find applications in recording ultrasonic or radar reflections.
Quantitative X-Ray Investigations on the Crystallinity of Cellulose Fibers. A Background Analysis
Authors: Hermans P. H. , Weidinger A. 
Published: January 2005

A quantitative investigation of the intensity of scattered radiation in a series of native and regenerated cellulosic objects, including bacterial cellulose and fibers transformed into cellulose IV, is offered. The technique used involves the use of copper radiation monochromatized by reflection, specimens with randomized orientation of equal size and density, rotation of the plane film, and measurement of primary beam intensity by means of a device introduced by Goppel.
The procedure of evaluation consists of measuring integrated intensities of the crystalline peaks and that of the diffuse background. After correction of the latter for radiation scattered by air and for the background components due to Compton radiation and thermal scattering, as derived from exposures of sugar crystals and diamond, the diffuse background is represented by a curve exhibiting a flat maximum.
The height of this maximum was assumed to be a correct relative measure of the disordered portion and the total intensity of the coherently diffracted radiation of the crystalline peaks as a relative measure of the crystalline portion.
Within the series of native specimens the ordered and disordered fractions are found to be equal in cotton, cotton linters, ramie, and flax fibers. In woodpulp the disordered fraction is slightly higher and in bacterial cellulose considerably higher.
Within a series of rayons, including slightly and highly orientated viscose rayons, Cellophane, Lilienfeld rayon, and cuprammonium rayon, the ordered and disordered fractions were also found to be equal. Slightly less disordered substance is found in Fortisan, in mercerized ramie and in specimens where cellulose II has been transformed in cellulose IV by a heat treatment.
It is shown that the relative proportions of the fractions of disordered substance, for all objects investigated, are in satisfactory quantitative agreement with those deduced from the sorptive capacity for water vapor.
The absolute percentage of the crystalline portion calculated from the experimental data is 70±2 percent for the native fibers and 39±3 percent for the rayons. These figures are in reasonable agreement with those previously estimated from sorption isotherms (68 percent and 35 percent), from density determinations (60 percent and 25 percent), from birefringence and x-ray orientation measurements in regenerated fibers (≤40 percent for rayon), and from recrystallization of amorphous cellulose powder (∼35 percent for rayon).
The observed relative intensities of the principal crystalline interferences give rise to a discussion of the limited scope of the concept ``crystallinity'' in cellulose fibers, and it is argued that the concept ``degree of lateral order'' may be preferable.
Comparison of observed relative line intensities with the theoretically calculated ones, reveals another marked difference between native and regenerated fibers, pointing to the fact that certain states of lateral order prevalent in the latter may be absent in the former.
Universal Curves for Dielectric-Filled Wave Guides and Microwave Dielectric Measurement Methods for Liquids
Authors: Surber W. H. 
Published: January 2005

The characteristics of wave guides containing a non-ideal dielectric medium are expressed in terms of a dissipation factor, D, the effect of which is analogous to that of the loss tangent of the medium, tanδ, for coaxial or two-conductor transmission lines. A set of universal curves may then be constructed for the variation of the wave-guide parameters as functions of the dielectric loss factor in terms of D. These curves are independent of the dielectric constant, ε′, and of the frequency and mode of operation.
An experimental method is described for the measurement of the dielectric constants of medium and high loss liquids using a variable length of liquid dielectric column contained in a section of wave guide or coaxial line and terminated by a perfectly reflecting plane. Either a unidirectional coupler or slotted line may be used to observe the variation of the magnitude of the reflection coefficient with the dielectric sample length. An exact analytical expression is given for the determination of the constants of the medium using the dielectric constant, ε′, and the dissipation factor, D, as the primary independent parameters instead of ε′ and tanδ. A graphical method of solution is also given.
Explosives with Lined Cavities
Authors: Birkhoff Garrett , MacDougall Duncan P. , Pugh Emerson M. , Taylor Sir Geoffrey 
Published: January 2005

Explosives detonated in contact with thick steel plates produce much deeper holes in the steel when there is a cavity in the explosive in contact with the plate. While this phenomenon has been known for more than 150 years, the enormous increase in penetrating power that can be produced by lining the explosive cavity with thin metal has been discovered only recently. During the war a number of light, low velocity, antitank weapons (e.g., the rocket-propelled Bazooka) were developed which made use of this phenomenon to perforate thick armor plate.
A fairly complete mathematical theory of this essentially new phenomenon is presented together with some of the experimental data that aided in the formulation and testing of the theory. The process is separated into two phases: first, the formation of part of the metal liner into a long thin jet traveling longitudinally at very high velocities (30,000 ft./sec.) and, second, the forcing aside of the target material by the extremely high pressures (0.3-million atmos.) produced by the impact of the high speed jet.
The theories of both of these phases are based upon the classical hydrodynamics of perfect fluids, which is applicable because the strength of the metals involved can be neglected at the high pressures encountered.
Irradiation of Biological Materials by High Energy Roentgen Rays and Cathode Rays
Authors: Trump J. G. , Van De Graaff R. J. 
Published: January 2005

In this work roentgen rays and cathode rays of several million-volts energy have been applied to an investigation of their biological, photo-chemical, and germicidal effects, particularly as they are related to the processing of foods and biological materials. A constant-potential electrostatic generator, together with an acceleration tube, was used to produce continuous streams of electrons with homo-geneous and controllable energy. [R. J. Van de Graaff, K. T. Compton, and L. C. Van Atta, Phys. Rev. 43, 149 (1943).] These high energy electrons were utilized both for the production of penetrating roentgen rays and for the direct irradiation of materials. The mechanism of the biological action of both roentgen rays and cathode rays is discussed, as well as the energy considerations in their application to various absorbers. The companion paper [C. G. Dunn, W. L. Campbell, H. Fram, and A. Hutchins, J. App. Phys. 19, 605 (1948)] reports on measurements of the lethal action of these radiations on a wide variety of micro-organisms and also on the effect of the radiations on enzymes, vitamins, and certain whole food products. Both investigations have been conducted cooperatively by the Departments of Electrical Engineering and Food Technology at the Massachusetts Institute of Technology.
The systematic and quantitative study of the effects of roentgen and cathode rays on various elementary forms of living matter is regarded as an essential prelude to their possible widespread application to the preservation of foods and the sterilization of various biological materials. It was realized that the mechanisms of biological action of high energy roentgen rays and cathode rays are similar and depend closely upon the ionization energy absorbed per gram of material. The studies were begun with roentgen rays since these were immediately available and permitted quantitative measurement of the energy absorbed in the biological materials. Later, the water-cooled gold x-ray target was replaced with an aluminum cathode-ray window, and corresponding studies were begun on the direct application of high energy electrons to these materials. During the period of these biological studies the x-ray source was also used in a daily clinical program of deep cancer therapy under the medical direction of Dr. Richard Dresser and also in the investigation of the physical properties of high energy radiations. [R. Dresser, Radiology, in publication.]
Transmission Losses in 2n-Terminal Networks
Authors: Belevitch Vitold 
Published: January 2005

The semipositive character of the dissipation function of any physical 2n-terminal network imposes some restrictions on the realizability of prescribed transmission losses between the various pairs of terminals when they are connected to given impedances. These restrictions are most easily expressed in terms of elements of the efficiency matrix of the network, which is defined in the first part of this paper. Discussions of the application of matrix calculus to the solution of reactive and resistive, transformer-type, and general 2n-terminal networks are presented.
A very useful tool in solving telephone transmission problems is the conventional theory of 4-terminal transducers, often called 4-pole networks. Although this theory is sufficient for the study of most circuits, some problems involve networks with a larger number of terminals, which are often referred to as 2n-terminal, or 2n-pole networks. This paper is a contribution to their theory.
The particular point that will be considered in this paper is the restriction imposed by physical realizability on the arbitrary choice of transmission losses between various pairs of terminals connected to a given set of terminating (generator or receiver) impedances.
Carbon Film Formation and Commutator Brush-Wear As Revealed by the Electron Microscope
Authors: Fullam Ernest F. , Savage Robert H. 
Published: January 2005

The faces of carbon or graphite brushes, polished by rubbing against a rotating copper disk and subsequently examined with the electron microscope by means of surface replicas, are found to consist of many tilted ``fingers,'' which are the projecting portions of the large and irregular graphite plates composing the brush. These graphite projections show a directional overlap, which is determined by the direction of motion of the disk, and when viewed stereoscopically they are found to be inclined at various angles up to nearly 90° with reference to the plane of the rotating base. They account for a previously observed ``directional memory'' of graphited surfaces and they show that such surfaces in general cannot be regarded as consisting simply of graphite plates oriented with the hexagonal planes flat and parallel to the plane of motion.
The brush track on the rotating copper base is found to contain small islands of carbon deposited from the brush. These islands consist of large numbers of graphite wear-fragments, which are individually of very small size in comparison with the projections of the brush face. These fragments are clearly derived from the projections by a tearing apart of their edges and are packed tightly and with random arrangement into the tool marks of the copper smoothing over the irregularities of the latter. It is not determined whether this ``carbon film'' of the brush track is continuous.
The wear-dust of unlubricated graphite is found to consist of particles which are very small in average size compared with those from which brushes are manufactured. The size of these wear-fragments extends below the resolving power of the electron microscope, and this is consistent with recent data on similar particles of a size determined independently by adsorption measurements.