bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymptotic Spherical Shock Decay
Authors: Tannenwald L. M.
Published: April 2005

It is shown that the description of viscous and heat conductive effects in asymptotic spherical shock decay can be reduced to the solution of an ordinary first-order differential equation relating shock strength and radius. The derivation of this equation is based, to a considerable extent, on a well-justified quasi-stationary approximation. Computational work required for handling specific situations is outlined.
Noise in One-Dimensional Electron Beams
Authors: Haus Hermann A.
Published: April 2005

A generalized theory of noise in one-dimensional electron beams is developed with the aid of the theory of four-terminal networks. No specific assumptions are made as to the input noise velocity and current modulations and their correlation at the potential minimum. The ensuing theory is simpler and more general than the corresponding theories used in the past. Transformations are discussed of the standing wave of the mean-square noise current in drift regions by means of ``lossless beam transducers.'' It is shown that such transformations can be reduced to the formalism of conventional impedance transformations. Expressions are derived for the minimum obtainable noise figures of a velocity-jump amplifier, a klystron, and a traveling-wave tube. It is proved that these expressions present an ultimate limit for the noise figures of the respective tubes with regard to transformations by beam transducers with and without loss.
Arcing at Electrical Contacts on Closure. Part VI. The Anode Mechanism of Extremely Short Arcs
Authors: Boyle W. S. , Germer L. H.
Published: April 2005

The erosion at the anode of a short arc has been studied as a function of the arc duration and the magnitude of the arc current. With the current maintained at a constant value the anode pit grows continuously in diameter up to a critical value of the order of 10 microns; when this size is reached, a new arc is initiated and a new pit starts to develop. The process may be repeated. Consideration of the heat loss from the anode shows that for a constant arc power the pressure of metal vapor between the electrodes is very sensitive to the area covered by the arc. An order of magnitude estimate of the minimum metal vapor pressure required to maintain the arc (∼100 atmospheres) yields a value of the maximum pit diameter in good agreement with the experimental observations. It is evident that the steady-state short arc does not exist, and quantities such as the metal transfer, ion to electron current ratio, and pressure in the arc are dependent on the time since the initiation of the arc.
Impossible Behavior of Nonlinear Networks
Authors: Duffin R. J.
Published: April 2005

Networks of nonlinear inductors, nonlinear capacitors, nonlinear resistors, and direct current generators are considered. If the resistors are of quasi-linear type it is shown that such networks cannot generate alternating current or serve as power amplifiers.
Noise at the Potential Minimum in the High-Frequency Diode
Authors: Watkins D. A.
Published: April 2005

Noise quantities at the potential minimum in the high-frequency diode are analyzed by means of a relatively simple model which assumes that the transit angle from the cathode to the potential minimum is small and that the transit angle from the potential minimum to the anode is large. The mean-square convection current is found to be about half full shot noise for a typical case and the mean-square velocity is found to be the same as in the temperature-limited case. Application of this result to an analysis of the minimum obtainable noise figure of klystrons and traveling-wave tubes using velocity-jump noise reduction shows that their noise figure can be reduced without theoretical limit by increasing the current density at the cathode.
Noise Measurements in Semiconductors at Very Low Frequencies
Authors: Firle T. E. , Winston H.
Published: April 2005

The low-frequency noise spectra of germanium and silicon rectifiers have been determined. Two methods were employed: a numerical analysis according to the Wiener-Khintchine relationship, and a frequency translation photo playback method. No evidence of a deviation from a 1/fa(a>1) noise power law was found down to frequencies as low as 6×10−5 cps.
Calculation of the Space Charge, Electric Field, and Free Carrier Concentration at the Surface of a Semiconductor
Authors: Kingston Robert H. , Neustadter Siegfried F.
Published: April 2005

In the study of the surface properties of semiconductors, it is valuable to know the relation between carrier density at the surface and the shift in electrostatic potential from the bulk to the surface. By a solution of Poisson's equation utilizing Boltzmann statistics, the space charge, electric field, and change in free carrier concentration have been calculated for a semiconductor surface. The results are expressed as a function of the deviations of the Fermi energy from its intrinsic value in the bulk and at the surface. The calculated curves may be used for any nondegenerate semiconductor at any temperature, provided that the donor and acceptor levels are completely ionized. Numerical values are given for germanium and silicon at room temperature.
X-Ray Measurements of Particle Size and Strain Distribution in Cold Worked Silver
Authors: Schoening F. R. L. , Van Niekerk J. N.
Published: April 2005

X-ray diffraction profiles from filed solid silver specimens were measured with a Geiger counter spectrometer using crystal-reflected Cu Kα radiation. It is shown that for values of n>7, the assumption of a Gauss strain distribution fits the observed Fourier coefficients far better than a Cauchy distribution. The results obtained from solid specimens are consistent with those previously measured for silver filings. The influence of background errors is discussed.
Viscoelasticity of Poly Methacrylates
Authors: Bueche F.
Published: April 2005

This paper presents an intensive study of the viscous and elastic properties of the poly methacrylates. Variation of these properties is studied as a function of temperature in the range 60<T<160°C, as a function of molecular weight in the range 5×103<M<5×106, and as a function of plasticizer concentration over the range 0–100 percent. Capillary viscometers were used in the low-viscosity systems and tensile creep and recovery measurements under very small loads were used to study the less fluid systems. Principal effort was confined to polymethyl methacrylate but enough work was done using the butyl and decyl esters to show that the whole series of these polymers fits into a relatively simple picture. Consequently, given a certain minimum amount of data, it is now possible to predict the viscoelastic behavior of these polymers in the range of variables given above.

The theory of viscoelasticity previously given has been extended so as to take account of the effects of chain entanglements and distributions in molecular weight. Moderately good agreement is found between theory and experiment.
Experimental Examination of the Statistical Theory of Rubber Elasticity. Low Extension Studies
Authors: Baldwin F. P. , Ivory J. E. , Anthony R. L.
Published: April 2005

An experimental study was made of the behavior of two rubbers, Butyl (GR-I-18) and Paracril-35, in the low extension region (0 to 15 percent), at temperatures ranging from −40°C to +60°C. The results have been compared with the Guth-James theory of rubber elasticity. In general, good agreement with theory was observed. Two effects predicted by the theory have been confirmed, namely, the nonlinear dependence of stress upon temperature at constant extended length, and the shift of the thermoelastic inversion extension to higher values with increasing temperature. Small deviations, which increased with increasing extension and with decreasing temperature, were observed.
Numerical Solutions of Spherical Blast Waves
Authors: Brode Harold L.
Published: April 2005

The strong-shock, point-source solution and spherical isothermal distributions were used as initial conditions for a numerical integration of the differential equations of gas motion in Lagrangean form. The von Neumann-Richtmyer artificial viscosity was employed to avoid shock discontinuities. The solutions were carried from two thousand atmospheres to less than one-tenth atmospheres peak overpressure. Results include overpressure, density, particle velocity, and position as functions of time and space. The dynamic pressure, the positive and negative impulses of both dynamic pressure and static overpressure, positive and negative durations of pressure and velocity, and shock values of all quantities are also described for various times and radial distances. Analytical approximations to the numerical results are provided.
Vibroscope Measurements of the Elastic Moduli of Nylon 66 and Dacron Filaments of Various Draw Ratios
Authors: Wakelin J. H. , Voong E. T. L. , Montgomery D. J. , Dusenbury J. H.
Published: April 2005

By use of the electrostatic vibroscope method, dynamic measurements have been made of the Young's modulus derived from bending and the torsional modulus of nylon 66 and Dacron filaments ranging in draw ratio from one (undrawn) to six. Quasistatic measurements have also been made to obtain the Young's modulus derived from extension. The dynamic values of the Young's modulus increase from draw ratio one to draw ratio six by a factor of 3.5 for nylon 66 and 5.8 for Dacron. The torsional moduli of both filament types exhibit no appreciable changes with increasing draw ratio.

The ratio of the Young's modulus to three times the torsional modulus, which ratio is unity for a homogeneous isotropic material with a Poisson's ratio of ½, is about three for nylon 66 and greater than five for Dacron at a draw ratio of six. These results, along with those obtained at lower draw ratios, indicate that both filaments become progressively anisotropic with drawing, the extent of the anisotropy reflecting mainly the changes in the Young's modulus. As a check on the experimental procedures, the elastic moduli have also been measured for a 1-mil drawn tungsten wire.
Effect of Molecular Weight Distribution on the Creep Behavior of Cellulose Acetate
Authors: Swanson D. L. , Williams J. W.
Published: April 2005

Creep measurements were carried out at 80°C on cellulose acetate fractions characterized as to molecular weight distribution by the equilibrium ultracentrifuge. Stress levels were low enough that linear viscoelastic behavior was observed. Although the effect of molecular weight was not marked, the presence of low molecular weight material in a sample decreased the amount of permanent set and increased the recoverable deformation. In all cases, more than half of the recoverable deformation occurred in less than 10 sec. The results suggest that there was present some sort of a network, although no direct x-ray evidence for crystallinity could be seen.
Effect of Pressure on Sound Propagation in Water
Authors: Litovitz T. A. , Carnevale E. H.
Published: April 2005

Measurements of the ultrasonic absorption of water have been made up to pressures of 2000 kg/cm2. The data show that both the shear and compressional losses decrease as the pressure is raised. Comparison of these results with the values predicted by Hall's theory of sound absorption in water shows that the theory must be modified to be in agreement with the experimental data. The modification consists of assuming that the open or ice type of packing is associated with the higher free-energy state. If this modification is made, the observed data is in excellent agreement with theory. This result leads to the conclusion that even at 0°C less than 30 percent of the molecules in water are arranged in the ice type of packing. The results also indicate that the free-energy difference between the two states of packing in water is temperature dependent.
A Rheological Equation of State which Predicts Non-Newtonian Viscosity, Normal Stresses, and Dynamic Moduli
Authors: DeWitt T. W.
Published: April 2005

An equation of state is formulated from the classical Maxwell assumptions of superposition of the effects due to strain and rate of deformation in a strained fluid. Except for the form of the time derivative, these assumptions result in the usual expression for a Maxwell element. The time derivative of the stress, however, is computed with respect to a set of axes in the fluid which are rotating (with respect to fixed axes) at a rate measured by the vorticity of the assumed velocity distribution. The usual transformation between rotating and fixed reference axes introduces cross terms between the stress and vorticity components.

The resulting equation of state predicts non-Newtonian behavior and the simultaneous appearance of normal stresses. It reduces to the Newtonian case for low rates of shear (or for small relaxation times) and, if the cross terms are sufficiently small (but not otherwise), to the usual Maxwell element expression in the dynamic case. A common origin is thus assigned to these several phenomena. Reduced variable and distribution function procedures, at least in principle, should be as applicable to the viscosity and pressure phenomena as to dynamic data.
Maximum Superheating of Water as a Measure of Negative Pressure
Authors: Briggs Lyman J.
Published: April 2005

Water superheated to the limit in an open tube develops an internal negative pressure Pn (tending to tear the molecules apart) equal to the saturation vapor at that temperature, less one atmosphere. Kendrick, Gilbert, and Wisner heated water in an open thin-walled capillary U-tube to 270°C for 5 sec before it exploded (Pn=53 atmos). Using their method, the writer heated three tubes to 264°, 266°, and 267°C for 5 sec or more before explosion occurred (Pn=48 to 51 atmos). The cohesive strength of water is thus sufficient to withstand an internal negative pressure of over 51 atmos at 267°C. At this temperature an additional negative pressure (applied externally through centrifugal force) would rupture the water column. It has been predicted from van der Waals' equation that the external negative pressure which the system could withstand would vanish at 273°C, in fair agreement with experiment.
Slowing Down of Neutrons by Hydrogenous Moderators
Authors: Hurwitz H. , Zweifel P. F.
Published: April 2005

Methods of treating the Boltzmann equation for the case of a sinusoidally distributed source of fast neutrons in a material containing hydrogen are discussed and compared. The effects of the simplifying assumptions commonly employed in reactor calculations are analyzed. A technique which is particularly suitable for accurate numerical integration of the Boltzmann equation in the above case is described. Numerical results are being obtained by this method, and will be presented and compared with results obtained from other approximate methods in a subsequent paper.
Similarity Solution for a Spherical Shock Wave
Authors: Latter Richard
Published: April 2005

The point-source, spherical shock wave moving into a constant density γ-law gas is considered in the limit of infinite shock strength from the point of view of the Richtmyer-von Neumann viscosity technique. A similarity solution of this problem is shown to exist and is obtained for various boundary conditions with γ=1.4. The solutions are obtained analytically in that part of the flow field not involving viscosity, and numerically in the other parts of the flow field. It is found that whereas all discontinuities of the physical parameters are removed by the viscosity there remain discontinuities in the slopes of these parameters at the shock front. It is indicated, moreover, that the complete flow field depends upon the form and magnitude of the viscosity.
X-Ray Path through Calcite in Laue Diffraction
Authors: Rogosa George L. , Schwarz Guenter
Published: April 2005

The position and width of the x-ray beam transmitted through calcite in Laue diffraction has been measured. For the extinction case, the transmitted beam has the same position and width as the incident beam. For the anomalous transmission case, the transmitted beam widens showing that the radiation propagates through the crystal along the diffracting planes. These results are in general accord with the theoretical calculations of von Laue.
Domain Configurations and Crystallographic Orientation in Grain-Oriented Silicon Steel
Authors: Paxton W. S. , Nilan T. G.
Published: April 2005

The magnetic domain structure of polycrystalline grain-oriented 3¼% silicon steel has been investigated by the magnetic-powder-pattern technique and the orientation of individual grains determined by the etchpit optical-goniometer technique. A semiquantitative relationship has been found between the domain patterns and crystalline orientation. The observed powder patterns can be grouped into five types, depending upon the angle, φ, between the rolling plane and the <100> direction lying closest to the rolling plane. When the rolling direction is known and φ is <10°, semiquantitative grain-by-grain orientation information can be obtained solely from the domain patterns.

The behavior of two of the types of patterns in an applied magnetic field is shown, and on the basis of this behavior, a three-dimensional domain configuration is proposed for one of the less complicated surface patterns.
Isothermal Viscosity-Molecular Weight Dependence for Long Polymer Chains
Authors: Fox T. G. , Loshaek S.
Published: April 2005

Evidence is given showing that the equation, logη=3.4 logZ+K, represents an empirical law of flow which holds generally for sufficiently long flexible chain molecules in bulk or in solution. Here η is the viscosity, Z is the number of atoms in the chain, and K is a constant which is dependent on the polymer type and on the temperature. All of the available data which cover wide molecular weight ranges for linear (and branched) molecules in bulk or in solution, including results on polyesters, polyamides, polystyrene, polyisobutylene, polydimethyl siloxane, and polymethyl methacrylate, support this conclusion. For chains having fewer than a critical number, Zc, of chain atoms (Zc being characteristic of the polymer species) the dependence of η on Z is less severe but more complex. These results are in semiquantitative agreement with the recent theory of F. Bueche. On the basis of this theory, values for the concentration of chain entanglements in various polymers are obtained from the observed values of Zc.
Apparatus for Making Simultaneous Stress and Birefringence Measurements on Polymers
Authors: Gurnee E. F. , Patterson L. T. , Andrews R. D.
Published: April 2005

An instrument has been constructed to allow simultaneous measurements of stress and birefringence in polymer samples to be made as a function of time and temperature. The stress is measured by attaching one end of the sample to a cantilever beam near the fulcrum; the small deflection of the beam is indicated by means of a differential transformer, which in turn is attached to an automatic recorder.

The birefringence is measured with a Senarmont compensator (quarter-wave plate method). Measurements can be made either manually or with a continuously rotating analyzer. This latter method permits the automatic recording of the birefringence and is also adaptable to the study of rapid birefringence changes. The sample is housed in a copper pipe surrounded by a thermostatically controlled liquid bath.

Some data are presented showing the use of this apparatus in measuring birefringence and stress changes during stress relaxation experiments (sample held at constant elongation), birefringence changes during creep under constant load, and stress-optical coefficients.
Small Particle X-Ray Scattering by Fibers. II. Radial Distribution of Microcrystallites
Authors: Heyn A. N. J.
Published: April 2005

Radial distribution functions of the microcrystalline particles in fibers are derived from the x-ray scattering at small angles. Particle distribution functions are obtained by application of the method of Fourier synthesis to the x-ray data, by inversion of the intensity scattered under conditions where interparticle interference plays a part.

Different distribution curves are obtained with different fibers, investigated under the same conditions.

The distribution curves obtained with the same fiber investigated under different conditions of swelling, are consistent with the wider separation of the particles at higher degrees of swelling. A quantitative explanation is thus given of the differences between the scattered intensities at different degrees of swelling.

The degree of crystallinity is calculated from the distribution curves, so obtained, in combination with the particle sizes determined in preceding papers.
Tensile Strength of Plastics above the Glass Temperature
Authors: Bueche F.
Published: April 2005

A theory is presented for the tensile strength of rubbery plastics under dynamic test conditions. It is found that a nearly universal curve may be plotted relating the tensile strength of rubbers to the time of application of the load in a simple creep test or to the shear rate in a conventional type tensile test. The dependence on chain length, degree of cross linking, and temperature is also predicted.

Experimental results for the tensile strength of poly butyl methacrylate in the range 30–95°C are presented. These are shown to agree with the theory within the experimental error. The experimental testing scale extends over a range of eight decades when use is made of a temperature—time superposition principle predicted by the theory.

By comparing the tensile creep and tensile strength curves for poly butyl methacrylate, it is possible to find the size of a segment as defined in the theory of viscoelasticity. One segment is found to contain about six monomer units.
Shock Waves in Air Produced by Waves in a Plate
Authors: Allen William A. , Mapes Joe M. , Mayfield Earle B.
Published: April 2005

A shadowgraphic technique has been used to measure surface motion of a series of steel plates while they deform under impact caused by ½-in. diameter steel cylinders fired into their back surfaces at about 2800 ft/sec. The strength of the air shock produced when an initial longitudinal wave in a plate strikes the free surface of the plate has been inferred from the measured shock wave velocity in the air. The shock strength has been related to particle velocity of the surface of the plate. The results are compared to previous work involving contact explosions of small charges on plates.
Emission from Hollow Cathodes
Authors: Poole K. M.
Published: April 2005

The results of a phenomenological study of hollow cathodes are presented. Evidence has been accumulated to show that an oxide-coated hollow cathode has two regions of emission with significantly different properties. These are believed to be the coated inner surface of the cavity and a deposit of crystalline material formed on the orifice edge by evaporation from the original coating. Measurements of the relative importance of the two sources have been made under various conditions.
Electromagnetic Suspension of a Molten Zone
Authors: Pfann W. G. , Hagelbarger D. W.
Published: April 2005

A new method of suspending a molten zone is as follows: clamp a horizontal cylindrical ingot at both ends; apply a horizontal magnetic field normal to the ingot where the zone is to be suspended; and pass a direct current through the ingot, creating an upward force equal and opposite to the gravitational force, thereby permitting the zone to be melted and suspended. It is shown theoretically that such a zone will be stable in a uniform magnetic field if its length-to-diameter ratio is less than π and if its length is less than 0.17(γ/ρ)½, where γ and ρ denote surface tension and density, respectively, in cgs units. Some experimental results and practical considerations are discussed.
Concavity of Resistance Functions
Authors: Shannon C. E. , Hagelbarger D. W.
Published: April 2005

It is proved that any network of linearly wound potentiometers and fixed resistors has a curve of resistance versus shaft angle which is concave downward.
Gamma-Ray Dosage in Inhomogeneous Nuclear Reactors
Authors: Primak W.
Published: April 2005

Methods for estimating the gamma-ray dosage in samples undergoing irradiation in nuclear reactors are developed. They are applied to the calculation of the dosage in inhomogeneous reactors using CP-3 and X-10 as examples. The examples include a calculation of the heating which results from the absorption of gamma rays and of the chemical reaction which results from the absorption of gamma rays. The non-uniformity of the gamma-ray dosage in bodies undergoing irradiation is demonstrated and estimated. The results show that in nuclear reactors the gamma-ray dosage varies very greatly depending on the experimental arrangements and that, in particular cases, the major contribution to the dosage can arise from any of the following individual sources or some combination of them: the material being irradiated, the containers, the structural members of the irradiation facility, the moderator, or the fuel.
Experimental Test of the Theory of Penetration by Metallic Jets
Authors: Eichelberger R. J.
Published: April 2005

Experimental measurements of jet velocity and of penetration velocity as functions of depth of penetration are described for lined cavity charges fired into several types of target material and under a variety of experimental conditions. The results show that the hydrodynamic theory of penetration of Pugh and of Hill, Mott, and Pack describes very accurately the early stages of the penetration process. Strength of the target becomes an appreciable factor in the later stages, however. A simple modification of the theory is described which appears to account adequately for these strength effects. Some alterations in ideas concerning the mechanism of penetration by the jet after fracture are also described.
On the Discontinuity in the Temperature Coefficient of the Velocity of Ultrasonic Waves in Polymeric Materials
Authors: Work Richard N.
Published: April 2005

It is proposed that the discontinuity is a manifestation of the sudden change in the expansion coefficient that occurs at the glass-transition temperature. A comparison of volume-temperature data with velocity-temperature and velocity-pressure data taken from the literature gives reasonably good agreement with this explanation. Further, the dependence of velocity on density is seen to be chiefly through the strong dependence of the modulus on density and to a lesser extent through the appearance of density explicitly in the equation that relates velocity to the density and modulus.
Energy Concentration Effects in Ferrite Loaded Wave Guides
Authors: Melchor J. L. , Ayres W. P. , Vartanian P. H.
Published: April 2005

The primary objective of this study was to determine the effects of geometric parameters on microwave transmission characteristics for two counter-rotating circularly polarized waves in ferrite loaded wave guide. Ferrite rods were mounted coaxially in circular wave guide of 0.934 in. diameter. Effects of rod diameter and length were observed on reflection, phase shift or Faraday rotation, and ellipticity. Effects of frequency and applied magnetic field were observed in addition to differences in energy concentration in a ferrite for the two circular waves. A greater percentage of the microwave energy is found to be in the ferrite for one rotating component than for the other. It is shown that Faraday rotation of large diameter rods cannot be used to characterize ferrites accurately.
Thermal Flux Distribution from a Fast Neutron Line Source
Authors: Stuart G. W.
Published: April 2005

The spatial distribution of thermal neutrons originating from a fast neutron line source, with slowing down described by age theory, and thermal percolation through an infinite, isotropic medium described by diffusion theory, is presented.
Scattering Theorems for Bounded Periodic Structures
Authors: Twersky V.
Published: April 2005

Theorems relating the plane wave modes (scalar or vector) transmitted and reflected by periodic structures of lossless elements bounded by two parallel planes are derived. One special case is continuity of energy flux normal to the boundary planes, and others relate the phases, or both phases and magnitudes, of the propagating modes. These relations are essentially discrete analogs (i.e., with integrals over all angles of observation replaced by sums over propagating mode directions) of the relations for a bounded scatterer given by Saxon. The essential difference in the two situations is that by restricting the parameters so that only a few modes propagate we obtain special cases which can be treated relatively explicitly. Thus the case of one propagating mode, and the cases corresponding to Bragg reflections are discussed in some detail; here there is both conservation of magnitude and phase.
Free Fall Breakup of Large Drops
Authors: Magarvey R. H. , Taylor B. W.
Published: April 2005

The breakup of large water drops during free fall is of importance to meteorologists. Theories of precipitation lean heavily on drop multiplication resulting from the shattering of large drops. An experiment is described in which the actual breakup of large drops is observed, and data obtained from which the mechanism of break may be inferred. Drops in the various stages of disintegration have been photographed and the size distribution of fragments noted. A large drop falling freely through the air deforms, inflates somewhat in the same manner as a parachute and bursts with considerable violence. The origin of various size groups of fragments and its significance in determining the observed size distribution has been noted. An experimental arrangement is described that permits a large number of photographs to be taken of all stages of disintegration.
Limit-Periodic Dielectric Media
Authors: Redheffer Raymond
Published: April 2005

A stratified dielectric sheet with dielectric constant ε(x), permeability μ(x) and thickness d is uniformly contracted to yield a sheet with parameters ε(nx), μ(nx), d/n. Now n of these contracted panels are stacked up to yield again a sheet of thickness d. What can be said of the limiting medium obtained in this way, as n→∞ ? If the symbol [] denotes ``mean value of,'' the results of this paper may be summarized as follows: At perpendicular polarization, the limiting medium acts like a homogeneous medium with dielectric constant, permeability and thickness given respectively by [ε][μ]−12[1/μ]−12, [μ]12[1/μ]−12, d[μ]12[1/μ]12. At parallel polarization the parameters are, respectively, [ε]12[1/ε]−12, [μ][ε]−12[1/ε]−12, d[ε]12[1/ε]12. The relevance of these results to topics of current interest is indicated. The analysis is not based on the equivalent-circuit analogues which are sometimes used to study artificial dielectrics, but is developed without approximation from Maxwell's equations.
Slippage of Water over Nonwettable Surfaces
Authors: Schnell Erhard
Published: April 2005

When water flows over glass which has been treated with the vapor of dimethyldichlorosilane and thus made water repellent, slipping on the boundary between the solid surface and the water takes place. This is is shown in capillary tubes of various diameters. The amount of slipping is small, but measurable. It disappears or becomes extremely small in case of turbulent flow.
Damping of Underwater Explosion Bubble Oscillations
Authors: Keller Joseph B. , Kolodner Ignace I.
Published: April 2005

When an explosive detonates underwater it creates a bubble of gas which performs damped radial oscillations of large amplitude. The usual theory of these oscillations treats the water as incompressible and yields undamped oscillations of constant period. We have modified this theory by taking account of the compressibility of the water. Our theory predicts damped oscillations of diminishing period. Comparison of the predicted and observed radius-time curves for one particular case shows fairly good agreement. Radius-time curves for four representative cases have been computed with a large number of periods in each case. These can be used to describe a variety of explosions.
Breakdown of Air at Microwave Frequencies
Authors: Gould Lawrence , Roberts Louis W.
Published: April 2005

A theory for uniform field breakdown in air at microwave frequencies is developed and applied with success to predicting values of breakdown over a wide range of experimental conditions. Three distinct types of breakdown are treated; c.w. (continuous wave) breakdown, single pulse breakdown, and multipulse breakdown. The conditions for breakdown are determined from a solution of the electron continuity equation for an average electron, in which electron ionization, attachment, and diffusion are the dominant mechanisms. Modulation of the electron average energy at twice the frequency of the applied field becomes important at either high pressure or low frequency and modifies the values of the breakdown field. The breakdown field strengths are shown to be determined from a single curve for each type of breakdown power, either c.w. or pulsed. These theoretical curves are in accordance with the experimental results, thus verifying the assumption and the values of the coefficients used in the theory.
Diffusion of Gold in Single Crystals of Silver
Authors: Jaumot F. E. , Sawatzky A.
Published: April 2005

The diffusion of Au in Ag has been measured in the temperature range from 650 to 950°C, using Au198 as a tracer. The data indicate that the diffusion coefficient is given by the equation D=0.26 exp(−45 500/RT) cm2/sec. The fact that the activation energy for the diffusion of Au in Ag is identical to that for self-diffusion in Ag is discussed briefly.
Physical Properties of Titanium. II. The Hall Coefficient and Resistivity
Authors: Scovil Georgiana W.
Published: April 2005

The Hall coefficient of titanium has been measured over a temperature range from 350°K to 1100°K. The coefficient is −2.0×10−11m3/coulomb near room temperature, reverses sign at (675±30)°K, and increases to a value of +3.5×10−11m3/coulomb at 1100°K. The measurements were made on titanium samples which had a purity of 99.99%. The samples were heated by direct current, and the temperatures were determined indirectly from the resistivity measurements which were made with each Hall measurement. The resistivity is 0.48 microhm m at 350°K. It increases to a maximum of 1.76 microhm m at the crystal transition temperature.
Propagation of Cleavage Cracks in Crystals
Authors: Gilman John J.
Published: April 2005

The role of crack propagation velocity in the cleavage of crystals and aggregates is emphasized in this paper. The available data on crack propagation in elastic media are summarized, showing that this phenomenon is adequately understood at present. For inelastic media, it is postulated that in addition to the Griffith Criterion two critical velocity conditions must be satisfied or crack propagation cannot occur. One critical velocity pertains to propagation through a crystal, and the other to propagation through an aggregate. The first critical velocity depends on the rate at which plastic glide can absorb energy at a crack tip and the number and size of cleavage steps that a crack front contains. These quantities are estimated. The second critical velocity accounts for the dependence of fracture stress on grain size in aggregates and interprets other experimental behaviors of aggregates which contradict previous interpretations.
On Chemical Surface Reactions in Laminar Boundary Layer Flows
Authors: Chambré Paul L. , Acrivos Andreas
Published: April 2005

The progress of an isothermal chemical reaction on a catalytic surface, which is located in a laminar hydrodynamic flow field of large Reynolds number, is analyzed. Past analytical investigations have been restricted primarily to chemical reactions in fully velocity developed flow fields subject frequently to one or both of the following approximations. (i) The actual velocity distribution is replaced by a flow of uniform velocity. (ii) The concentrations of the reactants on the catalytic surface are prescribed subject to certain hypotheses concerning the rate controlling mechanism.

In this investigation the principal aim has been to calculate the actual surface concentration in a laminar boundary layer flow without unduly sacrificing the hydrodynamic features or introducing unnecessary assumptions about the effective over-all reaction mechanism. The method presented, which is related to an analysis of convective heat transfer from a nonisothermal surface, is applicable to arbitrary catalytic reaction mechanisms in a certain class of laminar boundary layer type flow fields.
Ferrite Post in a Rectangular Wave Guide
Authors: Epstein P. S. , Berk A. D.
Published: April 2005

A thin circular ferrite post magnetized lengthwise is placed in a rectangular wave guide with its axis normal to the direction of propagation of the incident waves. The polarization is such that the electric vector is parallel to the post. The reflected and transmitted waves are calculated both with respect to their intensities and phases. The results are also applied to find the influence of a thin ferrite post upon the resonant frequency of a rectangular cavity.
Invariants in Experimental Data on Linear Kinetics and the Formulation of Models
Authors: Berman Mones , Schoenfeld Robert
Published: April 2005

A new mathematical approach for the analysis of radioactive tracer experiments on compartmentalized systems in steady states is presented. The experimental measurements of the amounts of tracer in one or more compartments are approximated by a sum of exponential functions of time. The coefficients and exponential factors of these functions are shown to represent a set of invariants of the data. These are then related in a concise matrix equation to the compartmental model parameters, which are defined as the transition probabilities per unit time per unit quantity (turn-over rates) of molecules from one compartment (or state) into another.

When measurements are incomplete, the freedom in choosing a model is expressed in turns of a minimum number of variables equal to the difference between the number of model parameters and the number of invariants found in the data. It is shown how other information regarding the model parameters or the amounts of material in steady state may be combined with the tracer data to reduce the degrees of freedom of a proposed model.

Matrix transformations are worked out to allow the mapping of all mathematically consistent models in the configuration space of the minimum variables. The boundaries in this space corresponding to the limits for physically realizable models are found. Thus, a model is expressed by a set of coordinates and the values of all the parameters are obtained by substituting the values of the coordinates. Investigation of the range of variation of each parameter over the bounded region is also possible.
Even-Order Subharmonic Oscillations
Authors: Cunningham W. J.
Published: April 2005

The generation of an even-order subharmonic, or harmonic, oscillation in a driven nonlinear resonant system described by just a cubic nonlinear term requires the simultaneous appearance of a zero-frequency component. This component effectively introduces a squared nonlinear term. A simple experiment with an electrical circuit is described, showing the presence of the zero-frequency component.
Paramagnetic Resonance of Lattice Defects in Irradiated Quartz
Authors: Weeks R. A.
Published: April 2005

Various kinds of silica glass and natural and synthetic crystals have been irradiated with fast neutrons at temperatures of ∼250°C and above 300°C. In the glasses, asymmetric paramagnetic resonance lines resulting from the irradiation have been observed with apparent g values of 2.0013±0.0006 and 2.0090±0.0007, and half-widths of ≈1.7 gauss and ≈40 gauss, respectively. Two groups of lines were found in the natural crystals and have been associated with the two lines in the glasses, the two lines in the glasses being the envelope of the lines in the crystals when they are summed over random orientations with respect to the magnetic field. On the basis of g values, absence of common impurity and of hyperfine splitting, and the thermal stability of the lines, it is concluded that the observed resonances in the silica glasses and crystals have their origin in defects in the basic SiO4 tetrahedra generated by fast neutrons and primary and secondary knockons. From preliminary optical bleaching data in neutron irradiated Corning silica it is tentatively concluded that the resonance with g=2.0013 is associated with the defect which gives rise to an optical absorption band at 2120 A. The g values of the two lines in the silica glasses suggest that one center is an electron and the other a hole.
Effect of Electron Irradiation on Young's Modulus
Authors: Dieckamp H. , Sosin A.
Published: April 2005

Young's modulus and internal friction measurements are reported on high-purity copper following electron bombardment. The modulus is observed to rise rapidly with electron flux reaching an early saturation followed by a slow decrease. The rapid saturation is attributed to dislocation pinning. The rate of saturation is temperature dependent in the range from −195°C to about 0°C suggesting defect migration at low temperatures. The slow decrease is attributed to a ``bulk effect'' due to interstitial-vacancy pairs.
Diffusion of Aluminum in Single Crystal Silicon
Authors: Miller R. C. , Savage A.
Published: April 2005

The diffusion of aluminum into silicon has been reinvestigated to clear up certain discrepancies in the existing aluminum data. The diffusion constants found in this work are in good agreement with those determined by Fuller and Ditzenberger and an order of magnitude less than those reported in another investigation. Aluminum solid solubilities in the neighborhood of 1019 atoms/cm3 have been found over the 1200 to 1400°C temperature range. These concentrations are several orders of magnitude larger than those reported in other aluminum diffusion investigations. The p-n junction penetrations and transition capacitances of the diffused samples were used to determine diffusivities and solid solubilities.
Ultrasonic Attenuation Caused by Thermoelastic Heat Flow
Authors: Lücke Kurt
Published: April 2005

Expressions for the attenuation of sound waves in a standard linear viscoelastic body have been derived and have been applied to the attenuation due to the thermoelastic effect.

The thermoelastic attenuation for sound waves has been computed for single crystals and polycrystalline materials under application of the high-frequency approximation of sound propagation. For single crystals the attenuation in the main propagation directions have been computed explicitly for cubic and hexagonal crystals taking into account the anisotropy of the elastic properties and thermal expansion.

Comparison with experiments in the megacycle region shows that the attenuation caused by heat flow between the grains of a polycrystalline specimen is usually overpowered by scattering at the grain structure. Also the computed attenuation caused by heat flow between the regions of compressions and rarefaction of the wave is for many materials much smaller than the measured values.

For single crystals of certain metals, however, the computed and the measured values have the same order of magnitude. It can be shown that in these cases the attenuation is composed of a thermoelastic component and of a component resulting from dislocations. In zinc the two components can be separated experimentally and the agreement between the measured and the computed thermoelastic damping is very good.
Magnetic Granulometry and Super-Paramagnetism
Authors: Bean C. P. , Jacobs I. S.
Published: April 2005

The magnetic technique of particle size measurement based on the work of Elmore consists of a comparison of a modified Langevin curve with the observed magnetization curve for an appropriate system of ferromagnetic particles. The average magnetic moment per particle is obtained from this analysis, and the average particle size is thus determined. The prediction by Néel of thermal relaxation in single-domain ferromagnetic particles broadens the range of applicability of the granulometry method, with special emphasis on the size range from 20 A to about 100 A. A possible objection to the method, arising from evidence for an abnormal temperature dependence of the saturation magnetization of very small magnetic particles, is re-examined experimentally and found to be invalid. Several examples are presented that demonstrate the predicted thermal relaxation and that point to a wide utilization of the granulometry technique.
Extremely Low-Frequency Electromagnetic Waves. I. Reception from Lightning
Authors: Liebermann Leonard
Published: April 2005

Extremely low-frequency (ELF) radio waves (10–500 cycles) originating in lightning were received over distances in excess of 15 000 km. Transmission conditions were equally good, day or night. Propagation distances were ascertained by analysis of higher frequency components (>1700 cycles) according to known methods. The receiving antenna employed an arrangement of grounded electrodes which uniquely determined the azimuthal direction of the source. Two distinct classes of ELF pulses are described which are attributed to different conditions of propagation.
Extremely Low-Frequency Electromagnetic Waves. II. Propagation Properties
Authors: Liebermann Leonard
Published: April 2005

Properties of electromagnetic propagation at extremely low frequencies (below 500 cycles) are deduced from analysis of pulse distortion. The source of the transmitted pulse is lightning. Two distinct transmission types are analyzed. Normal, or type I, propagation is shown to behave as if the earth's surface and ionosphere constitute a wave guide composed of two plane parallel surfaces, with one surface partially conducting. This wave guide has no low-frequency limit on progagation; attenuation formulas are given. The transmission properties of type II, or anomalous propagation, are derived and seen to be inexplicable by means of this wave-guide model. The analysis leads to a determination of the effective conductivity of the ionospheric reflector at these frequencies: the daytime reflecting layer (D layer) conductivity is 104 esu; the nighttime conductivity (E layer) is 5×104 esu; both results are far lower than deduced by other means.
Note on the Reduction of Carrier Lifetime in p-n Junction Diodes by Electron Bombardment
Authors: Miller W. , Bewig K. , Salzberg B.
Published: April 2005

Commercial encapsulated silicon p-n junction diodes were bombarded by 2 Mev electrons from a Van de Graaff generator. The reverse transient current and the static I–V characteristics of the junction were measured before and after varying intervals of the bombardment time. The time dependence of the reverse transient current is in close agreement with theory, and the reciprocal of the minority carrier lifetime, as inferred from these data, is found to be a linear function of the bombardment time. The bombardment also produced marked changes in the static I–V characteristics of the diodes. These data are not in agreement with simple p-n junction theory. A suggested explanation is that the diode behavior is generally similar to that of a p-i-n junction.
Approximate Theory on the Stability of Interfacial Waves between Two Streams
Authors: Tchen Chan-Mou
Published: April 2005

The stability of the interface of two superposed streams is studied by extending the theory of Helmholtz stability to include the viscosity and surface tension in the waves. The two uniform layers of incompressible fluids are of different densities, viscosities and stream velocities. Gravity, Taylor acceleration, and surface tension are taken into consideration. An approximate theory is developed and is valid in three ranges of wave numbers. Neutral stability, rate of growth, and rate of decay are illustrated graphically.