bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Susceptibility Tensor in Ferrites
Authors: Artman J. O. , Tannenwald P. E.
Published: April 2005

Experimental techniques for measuring the magnetic susceptibility tensor components in microwave cavities are described. General expressions for the perturbation of microwave cavities by the magnetic properties of ferrites are developed. Experimental results are given for Ferramic 1331 measured at 9165 Mcps. Since these results indicate that both the real and imaginary parts of the tensor components χ and κ are approximately equal to each other in the resonance region, only measurement of the diagonal components may suffice to specify the complete tensor. However, whenever the small differences between χ and κ are desired, measurement of the tensor susceptibility in a degenerate cavity will be necessary. An attempt has been made to compare the experimental results with the Bloch-Bloembergen magnetic resonance theory as applied to circularly polarized excitation.
Dislocations in Germanium
Authors: Ellis S. G.
Published: April 2005

A light microscope study of etched germanium crystals has shown the dislocation distribution in them. The dislocations form a network in the crystal.

The formation of small angle grain boundaries is discussed.

Screw dislocations with large Burgers vectors have been found in some germanium crystals.
Positive-Ion Drainage in Magnetically Focused Electron Beams
Authors: Hines M. E. , Hoffman G. W. , Saloom J. A.
Published: April 2005

In electron tubes utilizing long electron beams ionization of residual gases can produce a positive space charge which can partially or wholly neutralize the negative space charge of the beam. Such neutralization has, under special conditions, been successfully utilized in focusing electron beams. In certain electron devices requiring long electron beams, this type of focusing is inadequate and an axial magnetic field is employed to focus the electron beam. However, when magnetic focusing is used, the assumption is usually made that the electronic space-charge fields of the beam are not neutralized by positive ions. Measurements have been made on a magnetically focused electron beam yielding information on (a) the longitudinal drainage of positive ions from the electron beam and (b) the degree of positive-ion neutralization of the electron beam. It is pointed out that localized ion traps may be present in the beam if the beam diameter varies periodically along its length because of the applied magnetic field.
Internal Friction Peak Associated with Precipitation in an Al–Ag Alloy
Authors: Damask A. C. , Nowick A. S.
Published: April 2005

Internal friction and elastic aftereffect measurements have been made on wire specimens of an Al-20% Ag alloy at various stages in the precipitation process. A specimen quenched from the solid solution region and aged at 155°C shows an internal friction peak at 140°C for a vibration frequency of 0.25 cps. The relaxation strength associated with the peak is about 0.02. The peak is not greatly affected by further anneals although these anneals completely change the character of the precipitate from the initial spherical clusters of solute atoms to the plate-like transition (γ′) precipitate. In the temperature range in which clusters redissolve (reversion), however, the internal friction shows a temperature hysteresis. The activation energy associated with the internal friction peak falls in the range 25–27 kcal/mole, depending on the state of precipitation. A mechanism is suggested whereby the peak originates in a stress-induced change in the local extent of precipitation. This behavior results from the interaction of the applied stress with the internal stresses about precipitate particles. In terms of this mechanism one can account qualitatively for the principal experimental observations.
Yield of Photoneutrons from U235 Fission Products in Beryllium and Deuterium
Authors: Bernstein S. , Ergen W. K. , Talbott F. L. , Leslie J. K. , Stanford C. P.
Published: April 2005

The yield of photoneutrons from a sample of U235 fission products at the center of a 9-in. diameter Be sphere was measured. Samples of U235 were exposed to neutrons in the reactor for periods of 15 min, 6 hr, and 74 hr. The photoneutrons created by the fission product gamma rays acting upon the Be nuclei were observed from 0.3 sec to about 4 weeks after the end of the exposure. Curves showing the photoneutron yield as a function of time, relative to the delayed neutron yield, are given for these exposure and observation times. The attempt was made to account for the observed yields from Be in this experiment, and the yield from D2O observed in an earlier experiment, in terms of known fission product gamma emitters.
Two Distinct Types of Short Arcs
Authors: Germer L. H. , Boyle W. S.
Published: April 2005

Short field emission arcs are of two types, those which vaporize metal predominantly from the anode by electron bombardment, and those in which the metal of the arc is supplied from the cathode largely by the melting of points by the field emission currents flowing through them. These are appropriately called ``anode arcs'' and ``cathode arcs.'' A single anode arc erodes a pit in the anode and leaves a corresponding roughened area on the cathode. A single cathode arc, on the other hand, leaves on the cathode a widely dispersed array of individual pits which tend strongly to lie along scratch lines; in many cases no mark at all can be found on the anode after an arc of this type. Anode and cathode arcs differ in arc voltage, which is higher for cathode arcs than for anode arcs, and in other ways. Both types of arcs have been observed for many metals, but the data reported here are for palladium only. For clean surfaces of palladium all arcs are of the cathode type at a striking potential of 400 volts, but at 300 volts and at lower voltages anode arcs are observed also, becoming more frequent as the voltage is lowered. For surfaces activated by carbonaceous material only arcs of the cathode type occur at all striking potentials. In an anode arc, metal is transferred in both directions, as measured by radioactive tracers, but the net transfer is from anode to cathode. A cathode arc transfers metal from cathode to anode only, and the magnitude per unit of arc energy is less than the transfer in an anode arc.
Effect of Neutron Irradiation on the Precipitation-Hardening Reaction in Alloys Containing Beryllium
Authors: Kernohan R. H. , Billington D. S. , Lewis A. B.
Published: April 2005

Neutron irradiation effects in the precipitation hardening alloy, nickel-beryllium, were measured using the ferromagnetic Curie temperature as an index of the amount of precipitate formed. Effects found previously in a similar precipitation hardening alloy, copper-beryllium, were not found upon irradiation at approximately room temperature. However, an irradiation for an integrated fast flux of 4×1017 n/cm2 at a temperature of 300°C showed that 1.3 atomic percent more beryllium in the form of the compound Ni–Be precipitated from a supersaturated solid solution than from a similar specimen held at 300°C but not irradiated.
Photovoltaic Noise in Silicon Broad Area p-n Junctions
Authors: Gianola U. F.
Published: April 2005

This paper discusses certain of the noise characteristics of silicon broad area junctions which have been developed for use for solar energy conversion. Under constant illumination the photovoltaic output of these junctions has been found to show fluctuations which are characteristic of a 1/f noise power spectrum. For varying illumination the magnitude of the photovoltaic noise voltage has been found to vary considerably, and in fact passes through a pronounced maximum. A plausible explanation of this effect is obtained by assuming that fluctuations are produced in the primary photocurrent as a result of traversing the junction. The assumption of a current dependent noise mechanism is justified by an independent experiment.
Dynamic Method for Measuring the Pyroelectric Effect with Special Reference to Barium Titanate
Authors: Chynoweth A. G.
Published: April 2005

A dynamic method has been developed for the study of the pyroelectric effect. Transient currents produced in single crystals of barium titanate when subjected to flashes of light are shown to be pyroelectric in origin. The illumination results in a small change in the temperature of the crystal which, in turn, causes the polarization to change. This change is recorded as a current in the external circuit. It is shown that from room temperature up to the Curie point, the pyroelectric current is consistent with the polarization as a function of temperature, as determined from hysteresis loop measurements. The technique proves to be a sensitive and nondestructive method for studying the state of polarization of a crystal.

The technique is used to study the pyroelectric effect induced by applied static electric fields at temperatures above the Curie point. The results are consistent with Devonshire's theory of the ferroelectricity of BaTiO3, and they confirm that the Curie point transition is of the first order.
Impact Phenomena at High Speeds
Authors: Van Valkenburg M. E. , Clay Wallace G. , Huth J. H.
Published: April 2005

A study of high speed, metal-to-metal impact in the velocity range 1 to 5 mm/μsec using ⅛-inch diameter spherical pellets is described. Pellet materials include aluminum, magnesium, steel, brass, lead, and zinc. Experiments relating to the mechanisms of cratering and the perforation of thin targets are presented. For the ⅛-in. diameter spherical pellets, it is found that the volume of the crater per unit energy of the impacting pellet is essentially constant for each material and that the penetration is proportional to the velocity of the pellet so long as the pellet velocity is less than the velocity of sound in the target material. An attempt to model very high speed impact by using soft wax targets in which the sonic velocity is less than the impacting velocity is outlined.
Perturbations of a Satellite's Orbit Due to the Earth's Oblateness
Authors: Blitzer Leon , Weisfeld Morris , Wheelon Albert D.
Published: April 2005

The free-flight motion of a satellite around a spherical earth is investigated neglecting atmospheric deceleration. This treatment is then extended by recognizing the earth's oblateness, which is represented by an additional quadrupole field. For nearly circular orbits, one finds that perturbations of the usual planar motion may be described analytically. These are characterized by a precession of the orbit plane around the equator, that is, a regression of the nodes, amounting to as much as forty miles per revolution. The large magnitude of these effects indicates that one may exploit a satellite's motion, as measured by conventional radio techniques, to determine the earth's oblateness to a new precision.
New Mechanism for the Generation of Flicker Noise in Tubes with Oxide-Coated Cathodes
Authors: Lindemann W. W. , Van Der Ziel A.
Published: April 2005

Evidence is presented which seems to indicate that a major part of the flicker noise in tubes with oxide-coated cathodes is generated in a thin surface layer of the coating. The effect is shown to be caused by the fact that a dc voltage drop and a noise voltage fluctuation are generated in the surface layer. In tubes with a porous cathode coating this noise voltage modulates the current coming out of the surface pores, thus leading to a true fluctuation in the current. In tubes with a nonporous cathode coating this noise voltage modulates the emission current, thus leading to a true fluctuation in the emission.
Copper Precipitation on Dislocations in Silicon
Authors: Dash W. C.
Published: April 2005

Precipitates formed by copper diffused into silicon crystals were studied by optical means using an infrared image tube. Linear aggregates are identified as dislocations by correlation with etch pits. Dislocations in as-grown crystals are usually curvilinear. Dislocation loops formed during plastic deformation consist of straight-line composite portions and pure screw portions, all of which lie in 〈110〉 directions. Precipitates frequently are not found on screw dislocations; when present they differ in detail from those on composites. Interactions between adjacent dislocations can be seen. Etch pits associated with either composite or screw dislocations are similar in form, indicating that the pits formed in as-grown crystals by the technique described identify all the dislocations. Dislocation loops enter from the surface upon deformation of crystals with relatively few grown-in dislocations. Dislocation loops formed entirely within the crystal in patterns consistent with operation of the Frank-Read mechanism are observed in less perfect crystals.
Equilibrium between Glass and Water Vapor at Bake-Out Temperatures
Authors: Todd B. Johnson
Published: April 2005

The diffusion of water from glass is shown to be a reversible process. The equilibrium partial pressure of water for a soda-lime glass was 10 mm (Hg) at 500°C and 12 mm (Hg) at 550°C. In a very dry atmosphere the diffusion of water from the glass proceeded as well as in vacuum.
Properties of a Coaxial-Torus Capacitor
Authors: Waters William E.
Published: April 2005

The potential distribution and capacitance in the capacitor which consists of concentric tori, or anchor rings, are calculated. The coordinate system is different from the usual toroidal coordinates; also, Laplace's equation is not separable in the product form, hence a different technique must be used to solve the problem. It is pointed out how the solution of this problem is the first step in developing design equations for a certain class of electron guns.
Comparison of X-Ray Wavelengths for Powder Diffractometry
Authors: Parrish William , Kohler T. R.
Published: April 2005

Comparative diffractometer measurements were made with several radiations and a NaI · Tl scintillation counter with pulse-height discrimination. Figures of merit for the different wavelengths based on intensity and peak-to-background ratio of a silicon powder specimen were: CuKα 100, MoKα 32, CrKα 10, and WLα 6. Several factors contributing to the figure of merit are discussed.
Discharge Mechanism of Mercury Pool Arcs
Authors: Hernqvist Karl G.
Published: April 2005

A model for the discharge mechanism of mercury pool arcs is proposed and shown to be in agreement with experiment. The conclusions drawn from this model are the following: (1) Mercury pool arcs operate in the ball of fire mode of discharge. (2) The electron emission mechanism is nonthermionic. Emitted electrons from the cathode arrive with only thermal energies in a plasma adjacent to the cathode. The potential of this plasma is equal to or slightly higher than that of the Fermi level of the cathode. The emission may be either due to a large electric field at the cathode surface (tunnel effect) or due to an effective lowering of the cathode work function. This lowering of the work function may be caused by a vapor or plasma of high density adjacent to the cathode surface.
Phase Changes in Pile-Irradiated Uranium-Base Alloys
Authors: Bleiberg M. L. , Jones L. J. , Lustman B.
Published: April 2005

Specimens of U-9, -10.5, -12, and -13.5 w/o (weight percent) Mo and U-10 w/o Nb, heat treated to retain the metastable gamma phase at room temperature and also to transform this phase to the room temperature stable phases, were irradiated in the Materials Testing Reactor (MTR) at maximum temperatures of less than 200°C. Electrical resistivity, temperature coefficient of electrical resistivity, hardness, and density measurements as well as x-ray diffraction patterns indicated that the stable phases at room temperature reverted to the metastable gamma phase during irradiation. No apparent changes in the microstructures of thermally transformed specimens were observed after irradiation. Lack of observable microstructural changes was attributed to the development of a ghost structure. X-ray line broadening measurements indicated essentially complete homogenization of thermally transformed U-Mo alloy specimens during irradiation. The mechanism of the phase reversal was explained on the basis of the displacement spike hypothesis.
Effects of Growth Rate on Crystal Perfection and Lifetime in Germanium
Authors: Kurtz A. D. , Kulin S. A. , Averbach B. L.
Published: April 2005

Effects of crystal growth rate and growth direction on the density of random dislocations and on the minority carrier lifetime have been observed. The dislocation density increases rapidly with growth rate above a rate of about 0.15 in. per minute and varies somewhat with growth direction. The capture efficiency per unit length of dislocation decreases at high growth rates and it is suggested that this effect is caused by the failure of impurity atoms to segregate at dislocations or by the clustering of dislocations.
Electrostatic Charge Separation at Metal-Insulator Contacts
Authors: Wagner Peter E.
Published: April 2005

An investigation has been made of the electrostatic charge produced in vacuum on several inorganic insulators when they are put into rolling contact with nickel, platinum, and copper surfaces. The primary role of relative motion is to increase the area on the insulator that ultimately undergoes contact, thereby increasing the total charge separated. With quartz, all evidence favors electron transfer which occurs because the nonconductor has a higher effective work function than the metal. Field emission-induced back leakage of electrons during separation of the charged surfaces is considered to reduce the charge originally separated to that actually measured. Little difference is seen between the charging properties of quartz cleaned chemically in room air and quartz subsequently outgassed at 700°C in vacuo better than 10−8 mm Hg. No difference in electron affinity is found between fused and monocrystalline quartz. No evidence directly supporting electron transfer is found for the other insulators tested, synthetic single crystals of Al2O3, MgO, NaCl, KCl, KBr, and KI; and the possibility of ion transfer is considered. All charge against nickel much less vigorously and less reproducibly than does quartz. The alkali halides and MgO which contains excess Mg or O as a bulk impurity charge positively, while stoichiometric MgO charges negatively. With Al2O3, there is a strong dependence of charge density on crystallographic orientation. Alteration of charging properties by surface and/or bulk conduction is found to be negligible for all insulators tested, within the reproducibility of the charging measurements.
On the Minimum of Magnetization Reversal Time
Authors: Kikuchi Ryoichi
Published: April 2005

A modified Landau-Lifshitz equation is solved for a single-domain sphere and an infinitely-wide thin single-domain sheet of ferromagnetic material neglecting anisotropy. The external magnetic field is switched from one direction to its opposite instantaneously at the initial time and the behavior of the magnetization vector is investigated thereafter. It is shown that there is a critical value of the damping constant corresponding to the minimum value of the (repetitive) magnetization reversal time. If the damping constant is larger than the critical value, the magnetization vector moves slower; if it is smaller, the magnetization vector moves faster but oscillates so that it takes longer time until it comes to a rest at the final position. The critical values of the Landau-Lifshitz damping constant λ are γM for the sphere and 0.013γM for the thin sheet, where γ and M are the gyromagnetic ratio and the magnetization, respectively. The computed minimum switching time for the thin sheet of 4–79 molybdenum Permalloy is of the order of 10−9 sec.
Method for Measurement of the Rate of Drying of Surface Coatings
Authors: Jenness James R.
Published: April 2005

By observation of rolling friction effects, the rate of drying of paints, varnishes, and other surface coatings can be evaluated more precisely than by previous methods. The time of descent of a ball rolling down a coated incline has been proposed as an index of surface condition. The basic physical phenomenon involved, however, is rolling friction, so the coefficient of rolling friction would be preferable for use as a standard. A metric analogous to Brinell hardness can be defined from the coefficient of rolling friction. The ratio between the coefficient of rolling friction and the radius of the test ball is proposed as an index of surface condition.
Uses of Carbon Replicas in Electron Microscopy
Authors: Bradley D. E.
Published: April 2005

Some of the early techniques for the preparation of carbon films and replicas for the electron microscope are compared with the method of vacuum evaporation developed by the author. The basic techniques for the production of replicas from evaporated carbon are described, and the high resolution obtainable is demonstrated and discussed. Some properties of evaporated carbon replicas are mentioned.

Descriptions are given of the carbon replica methods used in metallurgy and some applications are illustrated. Applications of carbon replicas in the following fields of research are also described: microbiology, biology, botany, entomology, chemistry, and industrial applications including the study of fibers.

It is concluded that evaporated carbon can be used as the final replica in any multistage replica process, and that it can be applied with advantage in almost every field of research in which the electron microscope is employed.
Xenon Arc Transients, Electrical and Optical
Authors: LeCompte George W. , Edgerton Harold E.
Published: April 2005

The growth of the luminous area of a high current discharge in an electronic xenon-filled flashtube has been studied by means of a sequence of timed short-exposure photographs taken with a magneto-optic shutter. Electrical measurements show that the tube conductance is approximately proportional to the luminous area of the arc channel. The ionized gas has a volume conductivity of about 90 mho/cm averaged over the luminous path during the buildup for the conditions investigated.
Lifetime Measurements of Excess Carriers in Semiconductors
Authors: Harrick N. J.
Published: April 2005

A technique is described whereby bulk carrier lifetimes in semiconductors can be measured over a wide range of injection level without making any electrical connections to the sample. The excess carriers are created by visible light and their distribution is measured by absorption of infrared radiation. The most important advantage of this technique is that the electric field term can be neglected in the continuity equation which describes the carrier distribution and the diffusion length can thus be determined directly. It appears that this technique may be used even in the presence of trapping. Some measurements are described for germanium where it is found that the carrier lifetime may increase or decrease with injection level. This is consistent with the Hall-Shockley-Read theory of carrier recombination.
Some Statistical Properties of Signal Plus Narrow Band Noise Integrated over a Finite Time Interval
Authors: Maximon L. C. , Ruina J. P.
Published: April 2005

The variance of narrow band noise plus c.w. signal after detection and integration over a finite time interval is derived. The problem is solved for Ideal, Gaussian, and High Q Single Tuned filters with square law and linear detection, the latter for large predetection signal-to-noise ratio. In addition to these filters the analysis is carried through for a model which considers the envelope of narrow band noise plus signal as a function which is constant for intervals of duration equal to the reciprocal of the noise band width and statistically independent in different intervals. Graphs of the mean square deviation divided by the mean power for noise alone are given for all filters and the model, with square law detection and predetection signal-to-noise ratios 0, 0.5, 1, 2.
Asymptotic Expansions of Solutions of the Heat Conduction Equation in Internally Bounded Cylindrical Geometry
Authors: Ritchie R. H. , Sakakura A. Y.
Published: April 2005

The formal solutions of problems involving transient heat conduction in infinite internally bounded cylindrical solids may be obtained by the Laplace transform method. Asymptotic series representing the solutions for large values of time are given in terms of functions related to the derivatives of the reciprocal gamma function. The results are applied to the case of the internally bounded infinite cylindrical medium with, (a) the boundary held at constant temperature; (b) with constant heat flow over the boundary; and (c) with the ``radiation'' boundary condition. A problem in the flow of gas through a porous medium is considered in detail.
Vapor Pressure of Plastic Materials
Authors: Jensen Niels
Published: April 2005

A method is presented of measuring the equivalent nitrogen vapor pressure of polymeric materials over a range of temperatures. It is found that, for the range of temperatures investigated (300–450°K), the vapor pressure-temperature characteristics of the polymeric materials studied are described by the empirical relation logP=A−B/T.

The values of the constants A and B in this equation are determined for a number of materials including nylon, Teflon, saran, polyethylene, and mylar.
Stability of Periodic-Field Beam Focusing
Authors: Chang K. K. N.
Published: April 2005

By taking into consideration both the effects of space-charge and large-amplitude scalloping, an analytic solution for periodic-field beam focusing is obtained through use of successive approximation and Fourier series expansion. The stability limit is then determined by studying a perturbation of the obtained solution. The perturbation results in a Hill's differential equation for the incremental beam radius. This equation yields a stability criterion for periodic-field beam focusing. It is found that instability starts at some degree of beam scalloping and ends at a higher one, and thus forms an unstable band.
Backscattering for Arbitrary Angles of Incidence of a Plane Electromagnetic Wave on a Perfectly Conducting Spheroid with Small Eccentricity
Authors: Mushiake Yasuto
Published: April 2005

The scattering of a plane electromagnetic wave by a perfectly conducting spheroid with small eccentricity is treated by a method of expanding the scattered field directly in a series of spherical vector wave functions. An expression for the first-order solution of the backscattered field is obtained for arbitrary angles of incidence of a plane wave. The numerical values of echo areas computed from the first-order expression are shown for various cases, and rough experimental results are also discussed. During this study some mathematical formulas involving the associated Legendre functions have been derived.
Phase Contrast Observations of Flames
Authors: Saunders M. J. , Smith A. G.
Published: April 2005

The phase contrast principle has been applied to a telescopic system to produce a simple instrument of high sensitivity for studying inhomogeneities in fluid media. As an example of the power of the method, the phase contrast telescope has been used to study the regions in and around premixed propane gas flames.
Emissivity of Hydrogen Atoms at High Temperatures
Authors: Aroeste Henry , Benton William C.
Published: April 2005

A method is described for making estimates of the total emissivity of hydrogen in the temperature and pressure ranges where hydrogen atoms predominate under equilibrium conditions. For a typical geometrical depth of 50 cm, and temperatures of the order of 12 500°K and higher, with pressures of the order of 100 atmos and higher, the emissivity approaches unity (ε[similar or greater-than]0.95), while for temperatures of the order of 9500°K and lower, with pressures of the order of 10 atmos and lower, the emissivity approaches zero (ε[similar or less-than]0.05). The variations of the emissivity between these approximate limits are shown graphically as functions of temperature and pressure with the geometrical depth set at 50 cm. The variation of the emissivity with geometrical depth is also shown graphically at 12 600°K and 20 atmos.
Autocorrelation Analysis of the Sliding Process
Authors: Rabinowicz Ernest
Published: April 2005

A simple model of the sliding process is developed in which the junctions are of the same size, but have different shear strengths, and, using an artificially obtained friction trace, it is shown that the size of the junctions may be deduced through a simple autocorrelation analysis. Applied to real friction traces obtained at slow sliding speeds, the technique gives an average junction diameter of 9.10−4 cm, in good agreement with previous estimates, while a different statistical method gives a value of 5.10−4 cm.
Vapor Lubrication of Graphite Sliding Contacts
Authors: Savage Robert H. , Schaefer D. L.
Published: April 2005

A fundamental study of graphite sliding contacts shows that atmospheric concentrations of only a few parts per million of the larger organic molecules are sufficient to prevent the severe wear of graphite which occurs in a dry atmosphere. The experimental results suggest roughly the empirical rule that the minimum relative ``humidity'' of a vapor for effective lubrication decreases logarithmically with chain length in the region 5 to 15 A.
Effect of Stress on the Expansion Coefficient
Authors: Rosenfield A. R. , Averbach B. L.
Published: April 2005

The expansion coefficients of specimens under tensile stress and after the stress has been removed have been measured for three steels (0.20, 0.40, 0.80% carbon) and for two types of Invar. If the applied stress is below the elastic limit the change in expansion coefficient α, with stress σ is shown to be given by (∂α/∂σ)T=−1/E2(∂E/∂T)σ, where E is Young's modulus and T the temperature; if the stress is removed the expansivity returns to its original value. When the applied stress exceeds the elastic limit, there is a discontinuous change in expansion coefficient, and the expansivity on unloading differs from the original value. The lattice distortion associated with the onset of even a slight plastic strain (2×10−6) appears sufficient to change the expansion coefficient both under load and after the load is removed.
Formative Time Lags in the Electric Breakdown of Liquid Hydrocarbons
Authors: Crowe R. W.
Published: April 2005

Recent investigations of the time dependence of electrical breakdown in liquid hydrocarbons have led to a disagreement regarding the influence of molecular structure upon the formative time lag. This paper represents an attempt to resolve the discrepancy, and to determine if possible the significance of the time lag in the breakdown process. The experiments involve the application of rectangular pulses of voltage of variable duration and amplitude to the liquids between hemispherical electrodes.

The results of the investigation show definitely that the formative time lag is insensitive to changes in the molecular weight of the hydrocarbon liquid. Consequently, it cannot be associated with the time required for positive ions to cross the spark gap, as has been suggested by recent investigators. Its characteristic dependence upon the electrode separation, however, suggests that it may be mainly a measure of the transit time of an electron or an electron avalanche.
Frequency Doubling in Ferrites
Authors: Ayres W. P. , Vartanian P. H. , Melchor J. L.
Published: April 2005

The torque equation for the motion of the magnetization in a magnetized ferrite yields a component along the direction of the applied dc magnetic field. The time dependent part of this component is of second order in rf quantities and has previously been neglected. With high incident powers an observable double frequency output is predicted. A high intensity microwave magnetic field and an orthogonal dc magnetic field were applied to a ferrite body. Double frequency magnetic fields were generated in the same direction as the dc magnetizing field. A primary frequency of 3175 mc was used with peak powers up to 200 watts. The peak output power at 6350 mc was found to increase linearly with the square of the peak input power over a range of 42 db. Reasonable agreement was found between theory and experiment.
Short-Range Order Coexisting with Long-Range Order in Cu3Au
Authors: Roberts B. W. , Vineyard G. H.
Published: April 2005

Diffuse x-ray scattering from a single crystal of Cu3Au was observed at T/Tc≅0.995 where the long-range order parameter S equals 0.85. By annealing at low temperatures, nearly perfect order was obtained. A difference curve yields the diffuse scattering attributable to short-range order coexisting with the long-range order state of S=0.85. Analysis of the diffuse intensity in absolute units gives values of the first three short-range order coefficients. The first coefficient is found to be close to the perfect order value: α1=0.33. Within experimental error the observed coefficients fit both the Cowley theory and a random long-range order model equally well.
On the Nature of Thermal Spikes
Authors: Tucker Charles W. , Senio Peter
Published: April 2005

Theoretical calculations suggest that the duration (10−11 sec) and smallest dimension (20 atom diameters) of thermal spikes in metals undergoing irradiation may be too small to permit the thermal nucleation and growth of crystals of a second phase even though the average ``temperature'' of the spike may be above the melting point. Experiments have been performed which show that even the very energetic fission thermal spikes are too rapid and small to permit the nucleation and growth of a second phase in uranium metal containing 2 atomic % chromium. It is suggested that the terms ``heated'' and ``melted'' are not strictly appropriate to thermal spikes. Rather the region of a thermal spike should be regarded as a highly disturbed zone in which atomic interchange can occur, but which quickly returns to the structure and orientation of the surrounding crystal with a distribution of interstitials and vacancies which may then interact with each other or with other defects possibly present in the crystal.
A Favorable Condition for Seeing Simple Molecules in a Field Emission Microscope
Authors: Becker J. A. , Brandes R. G.
Published: April 2005

The intensely bright doublets sometimes observed in field emission microscopes vary in size, shape, intensity, and resolution. It is proposed that these doublets are owing to simple small molecules adsorbed on tungsten protrusions or ridges on the tungsten tip covered with a chemisorbed layer of residual gas. The variation in the doublets is ascribed to variation in the size and shape of the protrusions as predicted by a theory developed by D. J. Rose.
Pressure Distribution on a Hydrofoil Running near the Water Surface
Authors: Parkin Blaine R. , Perry Byrne , Wu T. Yao-tsu
Published: April 2005

The effect of the free surface on the pressure distribution on the upper side of a shallow-running hydrofoil is considered from a general point of view. Previous theoretical and experimental work is reviewed in order to compare the range of flow variables for which each treatment of the surface proximity problem is valid. A qualitative theoretical expression for the pressure is developed. This result shows the relative importance of the pertinent parameters, and it is shown to agree qualitatively with previous experiments as well as with new pressure measurements made in the free surface water tunnel. The foregoing considerations reinforce the view generally held in the past, that the principles of potential theory when properly applied to hydrofoils, even at shallow submergences, may be expected to lead to valid and useful results.
Attenuation in the Shock Tube: I. Laminar Flow
Authors: Hollyer Robert N.
Published: April 2005

The ideal flow predicted for an inviscid adiabatic shock tube is not realized in experiments. A correction of the ideal theory for the viscous stresses and heat losses arising from the interaction of the gas flow with the tube walls is calculated. The boundary layer is regarded as a distribution of sinks of energy and momentum. The actual distribution is approximated by that behind a constant strength shock front and is calculated for laminar flows. The change in shock strength caused by a single sink located at a fixed distance behind the shock front is determined and this result is integrated over the distribution previously calculated. Interactions between the expanding compression chamber gas and the wall are neglected. It is shown by comparison with experiment that the interactions treated account for the major part of the attenuation of the shock front. It is pointed out that more data are required to evaluate precisely the assumptions used in the calculation.
Ignition of Combustible Gases by Converging Shock Waves
Authors: Fay James A. , Lekawa Edward
Published: April 2005

Hydrogen-oxygen and hydrogen-air mixtures were ignited by converging cylindrical shock waves using the apparatus devised by Perry and Kantrowitz [J. Appl. Phys. 22, 878–886 (1951)], and the minimum strength shock wave necessary for ignition was determined. The enthalpy increase in the wake of the shock wave within a cylinder of diameter equal to the quenching distance and of unit height was calculated and found to be comparable with the minimum spark ignition energy divided by the quenching distance. An analysis of the unsteady heat conduction problem lends support to the choice of the quenching distance as the significant dimension of the region over which heat addition is effective in causing ignition.
Conduction Mechanism in Oxide-Coated Cathodes
Authors: Hensley Eugene B.
Published: April 2005

Measurements have been made on a system composed of two parallel planar cathodes so arranged that their surfaces may be pressed together or separated by a small gap. Low-field conductivity measurements show that above approximately 700°K, the conductance of the system does not depend on physical contact between the cathode surfaces. This result supports the theory that the high-temperature conductivity is a property of the electron gas in the cathode pores. The ratio of conductivity to thermionic emission was measured under conditions designed to preserve the state of activation of the cathode surface. The results agreed with the theoretically predicted ratio and demonstrate that the higher values previously reported were caused by a lower activation on the surface than in the interior of the cathode.
Polymorphism of Iron at High Pressure
Authors: Bancroft Dennison , Peterson Eric L. , Minshall Stanley
Published: April 2005

Propagation of compressive waves generated by high explosive in Armco iron may, under certain conditions, occur with three stable shocks, which are characterized by abrupt and possibly quasi-discontinuous change of pressure. The characteristics of these have been investigated experimentally and found to be consistent with the hypothesis of a polymorphic transition in iron at about 0.13 megabar. The same phenomenon has been observed in mild steel.
Some Experiments on, and a Theory of, Surface Breakdown
Authors: Garrett C. G. B. , Brattain W. H.
Published: April 2005

Experiments on surface breakdown at reverse-biased germanium n+p alloyed junctions are described, and the results related to a new model for surface breakdown that takes explicit account of semiconductor surface charge and fringing field. The experiments show (i) that surface breakdown, like body breakdown, is an avalanche process; (ii) that multiplication sets in first at a particular spot. The experiments serve also to confirm conclusions already reached from device experience: (i) that high breakdown voltage is promoted by that sign of surface charge which tends towards the formation of a ``channel'' over the material of the higher resistivity side, and low breakdown voltage by the opposite sign of surface charge; (ii) that the breakdown voltage is increased by surrounding the material by a medium of high dielectric constant. The theory accounts for all these observations and leads, when the calculations are carried out for an equivalent one-dimensional structure, to a quantitative prediction of the relation between breakdown voltage, surface charge, resistivity, and the dielectric constant of the surrounding medium. The evidence for the validity of this relation is discussed briefly.
Relationship between Small-Angle Dislocation Boundaries and Creep
Authors: Ancker Betsy , Hazlett Thomas H. , Parker Earl R.
Published: April 2005

Small-angle dislocation boundaries of controlled nature (sharp or diffuse) and density were introduced (by prestraining at room temperature and annealing at 800°C) into high-purity polycrystalline nickel prior to creep at 700°C. By this method, the shape of the creep curve was varied drastically. The initial density of small-angle boundaries ranged from an average of nearly zero per grain, to a large number which was limited by the occurrence of recrystallization. X-ray microscopic examination showed that the dislocation networks developed during creep were nearly identical and were independent of the initial density and nature. The density of small-angle boundaries developed during creep is also independent of the creep strain within the limits of 1% and 7.5%, the strain at which the most ductile specimens fractured. The near identity of the substructure developed during creep was further verified by the substantial equality of the specimens' tensile strengths after creep. The only detectable difference in the substructures was an increase of the average boundary angle with increasing total strain. The type of substructure uniquely developed during high-temperature deformation is discussed in terms of dislocation climb and the interaction of local stress fields from climbing dislocations with those in piled-up arrays.
Space Charge Effects in Dense, Velocity-Modulated Electron Beams
Authors: Weinstein M. , Von Foerster H. M.
Published: April 2005

By assuming the bunching process of electrons in the drift region of a klystron as being space periodic, rather than time periodic, it is possible to describe the debunching mechanism in a finite diameter beam on a large signal basis. It is shown that such beams have a discrete spectrum of oscillations with the plasma frequency as series limits. This makes it impossible to assign a unique bunching parameter to all electrons.

These results check with a velocity-phase analysis of high-density electron beams carried out with a beam analyzer at a frequency of 3000 Mc.
Pulsed T-F Emission Electron Projection Microscopy
Authors: Dyke W. P. , Barbour J. P.
Published: April 2005

Pulse electronic techniques extend the advantages of field emission microscopy to desirable experimental conditions not attained with steady-state fields. A visually continuous ``motion picture'' emission pattern enhances the study of transient cathode mechanisms while holding negligible the adverse effects of large electrostatic forces on both cathode stability and mechanisms under study. Observation is extended to elevated cathode temperatures, to higher environmental gas pressures, and to low tensile strength cathode materials; at the same time, excellent cathode electrical stability is maintained. Several mechanisms are illustrated, including condensation, volume diffusion, surface migration, and cathode blunting.
Method for the Study of Lattice Inhomogeneities Combining X-Ray Microscopy and Diffraction Analysis
Authors: Weissmann S.
Published: April 2005

An x-ray diffraction method has been developed which establishes a direct correlation between the spot reflections on the Debye-Scherrer lines and the lattice regions on the specimen surface giving rise to these reflections. After this correlation has been accomplished an analysis of the spot reflections based on the double diffractometer principle is carried out. The method applied to the study of the substructure of metals and alloys discloses the coexistence of various orders of magnitude of substructural entities. The determination of size, disorientation, and lattice misalignment for the various orders of substructural entities is shown and the nature of the small-angle boundaries is investigated. The general applicability of the method to various research problems is briefly discussed.
Sensitivity of Ultrasonic Attenuation and Velocity Changes to Plastic Deformation and Recovery in Aluminum
Authors: Hikata Akira , Truell Rohn , Granato Andrew , Chick Bruce , Lücke Kurt
Published: April 2005

Measurements of changes in ultrasonic attenuation together with changes in ultrasonic velocity have been made concurrently with load strain measurements in tensile tests on the same specimen of aluminum. The results of such measurements taken during loading of the specimen, during relaxation or recovery at constant strain, and during unloading show a number of interesting effects. These observed effects are interpreted in terms of dislocation behavior for the various stages of the experiment. The experimental results for attenuation α and velocity change Δv/v permit the calculation of changes in dislocation density and loop length based on a dislocation damping theory developed in this laboratory to include both megacycle and kilocycle frequencies. The strain due to dislocation motion was calculated with a simple model and with dislocation loop lengths and densities obtained from the data and the theory just mentioned. The comparison of the calculated strain and the measured strain lends support to the use of this model, and while this dislocation damping model may not be entirely correct it does seem to be possible to obtain information about stress-strain behavior at low strains from sound propagation data alone.
Free Vibrations of Isotropic Cubes and Nearly Cubic Parallelepipeds
Authors: Ekstein H. , Schiffman T.
Published: April 2005

Free vibrations of isotropic cubes and nearly cubic parallelepipeds are derived by a modification of the Ritz method. The trial functions are chosen to be similar to actual modes, but simple enough to be manageable. The semidirect method of variational calculus is used to obtain some of them, others are simple solutions of somewhat different elastic problems. The resultant secular determinant of 15th degree is reduced (factored) by the use of group theory, so that the frequency equation can be solved analytically. The modes are classified according to symmetry properties. Some unexpected degeneracies are found which are not predicted by group theory.
Retarded Polarization Phenomena in BaTiO3 Crystals
Authors: Wieder H. H.
Published: April 2005

Slow polarization phenomena in BaTiO3 c-domain crystals were observed for applied electric fields smaller than 1 kv/cm. It is shown that the rate of change of polarization with time for small but constant fields implies the same phenomena observed for switching experiments performed at fields considerably larger than 1 kv/cm. No threshold field was found below which antiparallel nuclei would not propagate and complete the polarization reversal cycle.
Interfacial Waves in Viscoelastic Media
Authors: Tchen Chan-Mou
Published: April 2005

The stability of waves on the interface of two superposed semi-infinite layers of incompressible media is studied. The two uniform layers are of different densities and different viscoelastic properties. Gravity, Taylor acceleration, and surface tension are taken into consideration. The main problems considered are the dispersion, decay and growth of waves, and the formulation of a hydrodynamical foundation for the cohesive action of elasticity.