bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Calculation of Absolute Bremsstrahlung Intensity for a Fully Ionized Fully Dissociated Hydrogenic Gas
Authors: Janes G. Sargent , Koritz H.
Published: April 2005

By using the approximate relationships of Kirkpatrick and Weidmann [Phys. Rev. 67, 321 (1945)] for bremsstrahlung intensities, numerical calculations have been made on the IBM 650 at the Avco-Everett Research Laboratory for a fully ionized, fully dissociated hydrogenic gas. The intensities are given in terms of a quantity having the units ergs/sec/unit frequency interval/steradian/cm3 as a function of hv, (from 0.5 to 4.0 ev) and kT (from 4 to 200 ev). A calibration method has been devised for measurement of absolute bremsstrahlung intensities which continually compensates for the errors present in most calibration procedures.
Effect of Fast Neutron Bombardment at Various Temperatures upon the Young's Modulus and Internal Friction of Copper
Authors: Thompson D. O. , Paré V. K.
Published: April 2005

Studies have been made of the variations of internal friction and elastic modulus during irradiation of pure copper crystals at a number of temperatures in the range 90°K to 300°K. The results are interpreted in terms of pinning of dislocation lines by radiation defects migrating from their points of origin. In terms of the room temperature value the dislocation pinning rate is 2.5×10−2 in the range 100°K to 140°K and (from previous measurements) of the order of 2.5×10−5 at 20°K. On slowly warming the sample after the irradiation, it is found that at 260°K the modulus and decrement begin to move rapidly toward their ``saturation'' values. Presumably, defects ``stored'' in the sample due to a lack of thermal mobility at the irradiation temperature become mobile at this temperature and move to the dislocation lines.
Low Angle X-Ray Diffraction of Fibrous Polyethylene
Authors: Posner A. S. , Mandelkern L. , Worthington C. R. , Diorio A. F.
Published: April 2005

Highly axially oriented fibers of linear polyethylene are shown to display four orders of well defined, meridionally directed diffraction maxima corresponding to a fundamental spacing of 408 A. An interpretation of the low angle x-ray pattern is given in terms of the fiber morphology and the Hess-Kiessig postulate as to the origin of the periodic variation in electron density. The relative macroscopic length of the fibers was systematically altered both by thermal treatment and by crosslinking, melting, and recrystallization. The magnitude of the spacings observed does not bear any direct relation to the change in length incurred, but reflects the change in crystallite size that develops because of annealing, partial melting or the introduction of crosslinks. It is also shown that in a completely shrunken fiber, where wide-angle x-ray diffraction shows that the crystallites are randomly arranged relative to one another, discrete diffraction maxima are observed at about 255 A. These maxima are, however, circular in shape. Intermediate types of line shapes are also observed, which depend solely on the crystallite orientation and not on the method by which the orientation is developed.
Reflection of Sound from Randomly Rough Surfaces
Authors: Proud J. M. , Beyer R. T. , Tamarkin Paul
Published: April 2005

A study of the reflection of underwater sound from nonperiodic, pressure release surfaces is reported. The Eckart theory for wave reflection from rough surfaces has been adapted (with some modifications) to the experimental work. A portion of the investigation was directed toward a study of the dependence of the intensity reflected in the specular direction on angle of incidence, radiation wave number and the statistics of the reflecting surface. Secondly, a method is illustrated for determination of the rms amplitude and the correlation function of the reflecting surface from an analysis of the reflected intensity distribution. The radiation wavelength, in this case, must be much larger than the rms roughness amplitude.
Effect of Temperature on Photovoltaic Solar Energy Conversion
Authors: Wysocki Joseph J. , Rappaport Paul
Published: April 2005

Photovoltaic solar energy conversion is investigated theoretically over a temperature range of 0–400°C using semiconductor materials with band gaps varying from 0.7 to 2.4 ev. Three cases are considered. In Case I, the junction current is the ideal current. In Case II, the junction current is the ideal plus a recombination current; and in Case III, a recombination current. The best conversion performance is obtained for the ideal current; the worst, for the recombination current. The maximum conversion efficiency occurs in materials with higher band gap as the temperature is increased. GaAs is close to the optimum material for temperatures below 200°C. Experimental measurements are presented on Si, GaAs, and CdS cells. The measurements on Si and GaAs agree with theoretical expectations as far as the gross behavior is concerned. The CdS cell behaves anomalously as if it were made from a material with band gap of 1.1 ev.
Penetration of Rotating Shaped Charges
Authors: Singh Sampooran
Published: April 2005

This paper presents an attempt to correlate theoretically the depth of penetration and the angular velocity of the liner in a rotating shaped charge. Each element of the rotating liner imparts an angular velocity to the corresponding jet element, and this results in a continuous increase of the cross-sectional area of the jet element as it travels in space and a corresponding decrease in the depth of penetration. In order to check the theory, numerical evaluations have been carried out in case of standard M9A1 steel cones. The theoretical results seem to explain the scanty published experimental data of the rotating shaped charges.
Production of Very High Magnetic Fields by Implosion
Authors: Fowler C. M. , Garn W. B. , Caird R. S.
Published: April 2005

Magnetic fields are produced in the 10–15 megagauss range by use of high explosives which compress the flux obtained from initial fields of approximately a hundred thousand gauss. The fields described here occupy a cylindrical volume and are essentially axial. A typical field might have these general characteristics: Peak field 14 megagauss; 2 μsec duration from 10–14 megagauss; field volume around peak, 6 mm diameter, 50 mm estimated length.
Growth of Gallium Arsenide by Horizontal Zone Melting
Authors: Richards J. L.
Published: April 2005

The growth of single crystals of GaAs is discussed with reference to the horizontal zone melt technique. The crystalline perfection and polarity of grown crystals can be determined from a study of edge dislocations revealed on {111} by an HF, H2O2 etchant. Evidence of good thermal control during crystal growth is found from a correlation between the incidence of dislocations and the shape of the freezing interface. Dislocation densities can be reduced to a very low order by careful control of growth conditions.
Evidence for Dislocation Reactions in Copper
Authors: Young F. W. , Noggle T. S.
Published: April 2005

Observations of slip lines and etch pits at dislocations on a copper crystal hardened by irradiation and deformed by bending are interpreted in terms of dislocation reactions.
Dislocation Multiplication in Lithium Fluoride Crystals
Authors: Johnston W. G. , Gilman J. J.
Published: April 2005

Experimental observations are presented of dislocation multiplication, of the defect structure left behind by a moving dislocation, and of cross-glide of individual dislocations in LiF crystals. New dislocation loops form at many different sites in the wake of a moving dislocation. These loops have the same Burgers vector as the parent dislocation but do not, in general, lie on the same atomic plane. The rate of formation of new loops depends upon the magnitude of the applied stress. Such creation of new loops leads eventually to the formation of a wide glide band.

A moving screw dislocation trails many line defects behind it that lie parallel to its direction of motion. The existence and nature of these trails and the observed dislocation multiplication can be explained in terms of a mechanism which involves the formation, by cross-glide, of jogs on a screw dislocation. This cross-glide multiplication mechanism was originally proposed by Orowan and by Koehler. It is demonstrated that cross glide occurs easily in LiF, so that this mechanism is plausible. Some interesting complications arise when jogs are formed that are longer than several atomic spacings but less than several hundred. The defect trails exert a dragging of the screw dislocations that is not negligible compared to the yield stress of a crystal.
Elastic Constants of Yttrium Single Crystals in the Temperature Range 4.2–400°K
Authors: Smith J. F. , Gjevre J. A.
Published: April 2005

The five independent elastic constants for yttrium single crystals have been determined by the pulse-echo technique over the temperature range, 4.2–400°K. The experimental values extrapolated to 0°K are: C11=8.34±0.02, C33=8.01±0.02, C44=2.690±0.006, C12=2.91±0.03, and C13=1.9±0.4 in units of 1011 d/cm2. The degree of elastic anisotropy is low throughout the entire temperature range. The curves illustrating the temperature dependence of the elastic constants show several inflections, and the curve for C11 crosses that for C33 near 390°K. The behavior is somewhat unusual, and is probably explicable on the basis that the degree of band overlap in yttrium is quite sensitive to interatomic spacing. Such a sensitivity has previously been postulated to explain the temperature dependence of the Hall coefficient.
Optical Absorption by Free Carriers in a Semiconductor Containing a Dispersed Colloidal Phase
Authors: Gossick B. R.
Published: April 2005

The optical absorption by free carriers in a semiconductor containing a dispersed colloidal phase is treated, taking into account the dipolar diffusion of minority carriers about the particles.
Solutions of the Equations of Space Charge Flow for Radial Flow between Concentric Spherical Electrodes
Authors: Itzkan I.
Published: April 2005

The solutions of the equations of space charge flow of electron beams for radial flow between concentric spherical electrodes are formulated in such a manner as to permit the introduction of arbitrary initial conditions. This allows one to solve a variety of physical problems with the aid of a table of Airy functions. A particular case, which exhibits a potential minimum between electrodes, is presented as an illustrative example.
Motion of 180° Domain Walls in Metal Electroded Barium Titanate Crystals as a Function of Electric Field and Sample Thickness
Authors: Miller Robert C. , Savage Albert
Published: April 2005

The domain dynamics of polarization reversal in metal electroded BaTiO3 single crystals have not been adequately described in the literature. The present paper contains quantitative measurements of the velocity of the sidewise motion of 180° domain-walls in BaTiO3 crystals, most of which were electroded with 200-A thick films of Au. The wall velocity has been measured as a function of several variables including the applied electric field, the crystal thickness and the impurity content added to the crystal growth melts.

The wall velocity as a function of the field E is described by v∞ exp (−δ/E) where δ and v∞ are constants over several decades of velocity. The quantities δ and v∞ are the activation field and extrapolated wall velocity for E=∞, respectively. This field dependence of the wall velocity is the same as that reported previously for liquid electroded specimens. The thickness dependence of the wall velocity, which is through δ, is very pronounced and similar to that observed in measurements of other variables under different experimental conditions. The present data are explained in terms of a surface layer estimated to be of the order of 100-A thick. It is suggested that high fields within the surface layer may give rise to electron field emission and the electroluminescence which is observed during polarization reversal. Effects on the wall motion which persist for times of the order of minutes are ascribed to dielectric relaxation phenomena. The observed dependence of the wall motion on the impurity content of the cyrstal, and several other parameters, may result from changes in the characteristics of the surface layer.
Formation and Initial Growth of Single-Asperity Solid-State Bonds
Authors: Holden F. C. , Melehan J. B. , Ogden H. R. , Jaffee R. I.
Published: April 2005

A gold needle point in contact with a gold flat has been used to study the formation and initial growth of single-asperity solid-state bonds. In the absence of external pressure, the growth of the bonded area can be expressed analytically by a diffusion-controlled rate equation. Values for the coefficient of self-diffusion determined from these experiments are in reasonable agreement with those given in the recent literature.
A Dynamic Hard Sphere Model
Authors: Turnbull D. , Cormia R. L.
Published: April 2005

A simple two-dimensional model, in which uniform hard spheres are made to move steadily and apparently nearly at random, is described. At low sphere density the model exhibits ``gas-like'' behavior. As the density is increased the behavior becomes more ``liquid-like'' and then ``crystallization'' occurs. Many dynamic atomic phenomena, believed to occur in the gas, liquid, or solid state, are illustrated by the model.
On the Yield and Energy Distribution of Secondary Positive Ions from Metal Surfaces
Authors: Stanton Henry E.
Published: April 2005

The kinetic energy distribution of secondary positive ions liberated from a solid metallic target of beryllium under bombardment by positive ions was measured in a mass spectrometer provided with an energy analyzer. In conformity with earlier investigations, it was found that an appreciable fraction of the ions was liberated with energies less than 5−10 ev, although some secondary ions of more than 200 ev were found. The distributions appeared to be at least partially Maxwellian in character. Although errors in measurement were large, there appeared to be little dependence of the yield of secondary ions on the mass of the bombarding ion.
Origin of the ``First-Order Structure'' of CP4-Etched Ge Surfaces
Authors: Bonfiglioli G. , Ferro A. , Mojoni A.
Published: April 2005

The present paper briefly reports about the results of examinations of surfaces of CP4-etched Ge. The origin of the so called ``1st-order structure'' observed on the micrographs is discussed. It is shown that while etching proceeds, the ending points of some dislocations are reached, or some of them become passivated. In both cases, the etch pits no longer grow and their traces give origin to the 1st-order structure.
Analysis of Composite X-Ray Diffraction Profiles
Authors: Slade J. J. , Nanni L. F.
Published: April 2005

The irregular line profiles associated with crystals that have a random structure which is coarse relative to the irradiated area are regarded as the result of the composition of a characteristic distribution and a set of broadening and translating processes.

The inversion of this composition is expressed operationally. A differential operator associated with the transform of the intrinsic distribution is introduced. This operator reduces the line profile to the set of broadening and translating elements. The operations are such as may be performed by an analogue computer. Preliminary experiments show that it may be possible to obtain the desired resolution. The effects of ``noise'' and distortion are investigated.
Precipitation in Silicon Crystals Containing Aluminum
Authors: Bullough R. , Newman R. C. , Wakefield J. , Willis J. B.
Published: April 2005

Silicon crystals containing aluminum have been annealed at various temperatures within the range 700° to 1350°C, particular emphasis being given to the range 1200° to 1300°C. Precipitation, which occurs during the heat treatment in the bulk crystal and on various structural defects, has been detected by transmission optical microscopy. A lowering of the aluminum concentration in the neighborhood of the precipitate particles after heating at 1250°C has been revealed at the surface by a novel technique involving the etching of crystals which also contain phosphorus, where internal cylindrical and planar p-n junctions are formed round individual dislocations and grain boundaries, respectively. At this temperature, no precipitation is observed on dislocations in plastically deformed crystals. The precipitation of aluminum is interpreted in terms of a chemical reaction involving the coprecipitation of oxygen and possibly carbon.
Efficiency of the Plasma Thermocouple
Authors: Lewis H. W. , Reitz J. R.
Published: April 2005

The efficiency of a thermionic converter containing cesium ions is calculated for the regime, in which the plasma density is sufficiently high so that the random current density, nev̄/4, is large compared to the actual current density. Under these circumstances, positive space charge barriers are set up at the electrodes, and the plasma region is many free paths in length. The output voltage V is determined for various currents by a consistent solution of the electrical and thermal conduction problems. The efficiency of the thermocouple is then deduced from the calculated current-voltage characteristic and the appropriate electron temperature distribution. Overall efficiencies up to 32% are predicted for a typical thermocouple circuit.
Effect of Viscosity on the Splash Caused by a Drop of Water Falling into a Mixture of Glycerol and Water
Authors: Davis Philip A. G.
Published: April 2005

The effect of viscosity and velocity on splashes produced by low-velocity water drops was investigated by means of high-speed photography. Graphs have been constructed showing the effects on the time of duration of the various stages of the splash and a dimensional analysis in terms of the Reynold's number and Froude's number has been made.
Temperature-Dependence of the Electrical Resistivity of bcc Cr–Fe Alloys
Authors: Rajan N. S. , Waterstrat R. M. , Beck Paul A.
Published: April 2005

The electrical resistivity vs temperature was determined for a bcc Cr+20 at.% Fe alloy from 4.2° to 300°K. The absence of any discontinuity in this curve indicates that the very high temperature-coefficient of the linear term of the specific heat previously found at that composition is not associated with a phase transformation between room temperature and 4.2°K. For bcc Cr-alloys with Fe contents increasing from 0 to 16 at.% Fe the resistivity vs temperature anomaly shifts from approximately 308°K to progressively lower temperatures, and the anomalous resistivity increase with decreasing temperature becomes progressively larger. It is quite possible that these anomalies are connected with antiferromagnetic-paramagnetic transition in the alloys considered.
Specific Ionization Measurements and Energy Requirements for F-Center Formation
Authors: Jordan R. D. , Alger R. S.
Published: April 2005

Measurements were made of the energy required to produce F centers in pure and sensitized alkali halide crystals by bombardment with electrons and deuterons accelerated in a Van de Graaff generator. In KBr+KH exposed to 1.2-Mev electrons, 35 ev were required per F center. This value is in agreement with other published data. A value of approximately 100 ev was required with deuterons and KBr+KH. Slightly lower yields were found for several other salts. The specific ionizations of electrons, deuterons, and gamma rays were investigated and used to determine the accelerator beam size and penetration. The ranges of electrons in KBr, KCl, and NaCl were measured as a function of accelerator voltage and found to agree well with ranges predicted by the Feather rule. Energy transport and features of the specific ionization pattern are discussed in terms of the Seitz synthesis of crystal imperfections.
Studies in Partial Switching of Ferrite Cores
Authors: Tancrell Roger H. , McMahon Robert E.
Published: April 2005

The characteristics of Mg Mn ferrite cores in a partially switched state are investigated. Questions are considered relating to the percentage of flux switched at various locations within a core as well as the speed of this switching. Results show that the amplitude and duration of the set pulse has a pronounced effect on the core behavior. It has been found that most of the variation of the switching waveform among different regions is due to the geometry of the core. Models are proposed to describe the behavior observed experimentally. The operation of partially switched cores in a fast memory and the investigation of various memory schemes are discussed. Possible applications of the partially switched cores for digital computer applications are mentioned.
External Fields from Domain Walls of Cobalt Film
Authors: Kostyshyn B. , Brophy J. E. , Oi I. , Roshon D. D.
Published: April 2005

By scanning the surface with a Hall probe, domain patterns on thin cobalt films have been mapped by measuring the fringing flux normal to the film surface. The samples studied were cobalt approximately 2000A thick. At the domain boundaries, peak fields ranged in intensity from less than 0.5 to 4.5 oe. The probe to film gap was 13 μ. The sensitive area of the probe was a square of bismuth 20 μ on a side. It was observed that along specific boundaries, reversal of flux direction occurs. The boundaries exhibiting low peak fields were generally parallel to the easy direction of magnetization, whereas the boundaries exhibiting high fields were skewed relative to the easy direction of magnetization. Kerr effect and Hall probe patterns for the same domain configuration are shown to agree.
High Power Effects on Ferrimagnetic Resonance
Authors: Weiss M. T.
Published: April 2005

Ferrimagnetic resonance experiments have been performed on single-crystal spheres of manganese ferrite at high microwave power levels. The variation of susceptibility with power level is in good agreement with Suhl's recent theoretical treatment of the saturation process in which scattering of the uniform precession into spin waves caused by impurities and imperfections is taken into account. Our results show that the ratio of intrinsic to scattering decay constants is close to zero, so that the susceptibility decreases gradually at power levels substantially below the theoretical critical signal level. At very high power levels, various anomalous effects appear such as absorption line asymmetries, bistabilities, and flat-topped absorption lines.
Stable, High Density Field Emission Cold Cathode
Authors: Martin E. E. , Trolan J. K. , Dyke W. P.
Published: April 2005

The practical application of the field emission electron source has heretofore been impeded by insufficient reliability. Instability (i.e., changes in emitted current at a fixed applied voltage) results from changes in the cold cathode surface associated with contamination and sputtering. The cold clean cathode is shown to be electrically stable at dc emission densities up to 107 amp/cm2. Techniques are discussed which permitted stable operation of a single needle tungsten cathode during 1000 hr at an average beam power of 35 w (corresponding to a beam power density of 35 billion w per unit cathode area). A simple method is described which permits reconditioning of the cathode surface when required, and apparently extends life indefinitely; operating periods in excess of 12 000 hr are reported. An explanation is suggested for the small, gradual residual changes observed in the emitted current.
Electrical Stability and Life of the Heated Field Emission Cathode
Authors: Dyke W. P. , Charbonnier F. M. , Strayer R. W. , Floyd R. L. , Barbour J. P. , Trolan J. K.
Published: April 2005

The cold tungsten field cathode exhibits electrical stability and long life (12 000 hr demonstrated) at dc emission densities up to 107/cm2, when operated in vacuum tubes with a residual gas pressure below 10−12 mm Hg; with a provision for periodic reconditioning of the cathode surface by a brief flash heating, satisfactory operation of the cold cathode may be achieved at tube pressures up to about 10−9 mm Hg. Continuous heating of the field cathode is shown to yield useful electrical stability at conventional tube pressures, e.g., 10−6 mm Hg.

The theory of transport phenomena in heated metals is applied to a quantitative study of the geometrical stability of the heated field cathode. Expressions are derived for the time rate of change of cathode tip radius in the presence or absence of dc and pulsed electric fields at the cathode surface, and long-term geometrical stability of the cathode surface is predicted when the average applied field has the proper value. Large cathodes operated at high current level will only tolerate pulsed emission, and expressions are obtained for the maximum allowed duty cycle and pulse length in this case; small heated cathodes are capable of stable dc emission.

Occurrence of a vacuum arc is proposed as the cause of cathode failure. Considerations based on this assumption lead to predictions concerning the dependence of average cathode life on temperature, and to quantitative expressions for the statistical distribution and average value of life for unbiased field cathodes operated at high temperatures.

Experimental results yielded by the operation of 85 cathodes show good agreement with the theory. The heated cathode shows constant performance over a long period after which cathode failure occurs abruptly, and the statistical nature of cathode life is confirmed. The statistical distribution of cathode life and the measured effect of various parameters on average life show good agreement with theoretical predictions. Unbiased tungsten cathodes yielded an average life of 250 hr at an optimum cathode temperature of 2040°K. With the application of a suitable bias both long-term stability and an average life of 487 hr at 1970°K have been achieved, and according to the theory a substantial further increase in average life may be obtained by the use of a higher cathode temperature and of cathode materials with reduced impurity content.
Scattering of a Plane Transverse Wave by a Spherical Obstacle in an Elastic Medium
Authors: Einspruch Norman G. , Witterholt E. J. , Truell Rohn
Published: April 2005

An analysis of the scattering of transverse elastic waves by spherical obstacles is presented. The scatterer is taken to be (a) a cavity, (b) a rigid sphere, (c) a fluid-filled cavity, and (d) to consist of an elastic material with properties different from those of the surrounding material. The problems are carried as far as possible analytically without approximations and are reported as matrix equations. The solution of these equations yields the expansion coefficients that describe the waves which are scattered outward from the obstacle and which are excited within the scatterer. A general expression for the scattering cross section offered to a transverse wave has been derived. The Rayleigh approximation is then considered in detail for three of the cases.
Photoelastic Properties of Polystyrene in the Glassy State. III. Styrene Derivatives and Copolymers
Authors: Rudd J. F. , Andrews R. D.
Published: April 2005

The stress-optical coefficient, Young's modulus, and strain-optical coefficient at room temperature (27°C) have been determined for several styrene derivatives, for two copolymer systems (styrene/α-methyl styrene and styrene/methyl methacrylate) over the entire composition range, and for several copolymers of styrene with acrylates and methacrylates of varying composition. The results indicate that steric effects, particularly in the immediate neighborhood of the chain backbone, have a very important influence on the nature of the molecular motions (and, consequently, on the photoelastic behavior) during glassy distortions. The stress-optical coefficient becomes more negative (phenyl rings less free to orient) as a result of α-substitution on the chain or ortho-substitution on the phenyl ring. Substitution in the para-position of the phenyl ring, or increasing the separation of the phenyl ring from the chain backbone makes the stress-optical coefficient more positive (phenyl rings more free to orient); plasticizers (including residual monomer and solvents) or decreasing molecular weight have an effect in the same direction. Copolymer systems show nonideal mixing, photoelastically, indicating that interaction effects between neighboring monomer units along the chain are of significant magnitude. This may provide a means of studying the nature of the monomer sequences in copolymers (e.g., of block and graft copolymers), and also of observing stereospecific structure in polymers.
Orientation Density and Its Use in Quantitative Texture Studies
Authors: Dunn C. G. , Walter J. L.
Published: April 2005

An equation is derived from a definition of orientation density, Q=δζ/1.4ρ3, where Q is the average orientation density in an orientation state of size ρ centered on a particular orientation and δζ is the measured volume fraction of the sample with orientations within the orientation state. An approximate relationship between orientation density and (100) pole density for a strong single component texture is obtained, namely, Q0=1.08P032, where Q0 is the maximum orientation density and P0 is the maximum pole density. Samples that include the orientations of a large number of grains are used to illustrate the application of orientation density to the study of textures. Orientation density results are considered to be especially valuable when the texture has many components.
Regelation, Surface Diffusion, and Ice Sintering
Authors: Kingery W. D.
Published: April 2005

The freezing together of ice particles when they are brought into contact, originally described by Faraday and called regelation, is shown to occur not only at the freezing point, but also at temperatures as low as −25°C. It is shown that pressure melting is not essential to the process, nor is the presence of any unique liquid film. The welding together of ice particles occurs as a result of surface diffusion, as indicated by the time dependence and particle size dependence for the process. Surface diffusion of H2O molecules over an ice surface is found to be rapid. Equations for the kinetics of the process are closely related to those derived for sintering phenomena, but a quantitative derivation of the surface diffusion coefficient is not obtained.
Etching of Surfaces with 8-Kev Argon Ions
Authors: Cunningham R. L. , Haymann P. , Lecomte C. , Moore W. J. , Trillat J. J.
Published: April 2005

Methods of optical and electron microscopy were used to study the effects on solid surfaces of bombardment with argon ions of 8-kev energy. The targets were crystals of aluminum, zinc and α-corundum, and polycrystalline gold and aluminum. At oblique ionic incidence, etch hillocks were formed that were invariably oriented along the surface component of the direction of the ionic beam. Crystals were etched by ionic bombardment while being heated at elevated temperatures; this technique revealed dislocations widely spaced along the direction of growth in aluminum crystals.
Explosively Loaded Metallic Cylinders. I
Authors: Allison F. E. , Watson R. W.
Published: April 2005

Recent experiments using thin-walled metal cylinders internally loaded with high explosives have been performed in an effort to show that the casing velocity vector bisects the angle formed by the expanding cylinder and the undisturbed portion. This relation, which was first derived by Sir Geoffrey Taylor, can be expressed by the equation δ=θ/2, where δ is the angle between the velocity vector and the normal to the undisturbed casing, and θ is the angle formed by the normals to the moving and undisturbed portions of the casing. Although this relation forms a part of most theories pertaining to the acceleration of thin liners by high explosives, direct experimental verification of the relation has been difficult. In an attempt to verify Taylor's relation, values of δ were determined by inspecting the fragmentation patterns produced on cylindrical witness targets surrounding the charges. The values of δ determined in this manner are within the range of recent measurements by Singh using similar charges. Values of θ were independently determined from Kerr Cell photographs of the expanding cylinders. The experimental observations are in good agreement with the relation δ=θ/2.
Explosively Loaded Metallic Cylinders. II
Authors: Allison F. E. , Schriempf J. Thomas
Published: April 2005

High-speed oscillographic pin technique was used to determine the radial displacement as a function of time for thin-walled copper cylinders internally loaded with high explosive (60RDX/40TNT). The results were compared with theoretical calculations based on G. I. Taylor's model for the expansion of an incompressible cylinder and on the additional assumption that the detonation products behaved as an adiabatically expanding polytropic gas. Theoretical calculations and experimental measurements were made for cylinders having a 0.500-in. inside diameter and seven different wall thicknesses ranging from 0.030 in. to 0.122 in. Although the experimental results agree with the calculated velocities at the larger radii, the data do not follow the theory in detail. During the initial expansion, the measurements show that the cylinder does not behave as an incompressible fluid, but is accelerated in a step-wise fashion characteristic of motion produced by shock waves.
Thermal Positive Ion Emission and the Anomalous Flicker Effect
Authors: Datz S. , Minturn R. E. , Taylor E. H.
Published: April 2005

The correlation between the anomalous flicker effect in space charge limited diodes and the positive ion pulses which generate it is studied in the light of recent measurements of the size and shape of thermal positive ion pulses from tungsten filaments. It is shown that the positive ion pulses, although smaller than the electron pulses, have similar duration times, and that the periodic structure of the electron pulses may be quantitatively explained by reflection of the positive ion bursts back and forth through the region of maximum space charge.
Bounds on the Elements of the Equivalent Network for Scattering in Waveguides. I. Theory
Authors: Spruch Larry , Bartram Ralph
Published: April 2005

For a few particular waveguide problems, standard variational expressions have previously been shown to be upper or lower bounds on the quantities of interest. However, bounds have not previously been obtained for any truly three-dimensional problem; that is, where the fields cannot be derived from a single scalar potential. An example is a three-dimensional obstacle which contacts only one waveguide surface. As one consequence, no straightforward procedure exists for improving the approximations. Recently, Kato devised a rather general method for bounding the cotangent of the phase shift for a given angular momentum in a quantum mechanical central potential scattering problem. This method should be applicable whenever a system can be analyzed in terms of uncoupled standing waves each characterizable by one real phase shift. The method is here adapted to waveguides, including truly three-dimensional problems. The obstacle must be symmetric about a plane perpendicular to the waveguide axis, with certain exceptions only one mode should propagate, and the system should be lossless. Analysis is then possible in terms of ηe and η0, the real uncoupled phase shifts associated with the even and odd standing waves, respectively. The bounds obtained on cotηe and cotη0 determine bounds on the equivalent network elements.
Bounds on the Elements of the Equivalent Network for Scattering in Waveguides. II. Application to Dielectric Obstacles
Authors: Bartram Ralph , Spruch Larry
Published: April 2005

The theory developed in the companion article for obtaining rigorous bounds on cotη, where η the phase shift, is applied to scattering by dielectric obstacles in rectangular waveguides. For the obstacles considered here, bounds are also obtained on the phase shifts directly and on the elements of the equivalent T network. The exact solution for a dielectric slab of finite length, which extends to the conducting boundaries of the waveguide and completely encloses the obstacle, is introduced as a convenient trial function. The permittivity of the slab is retained as a parameter which is varied to improve the bounds. In the expressions for the bounds on cotηe and cotη0, the particular obstacle configuration appears only in certain integrals of relatively simple form. Numerical results are obtained for large and small obstacles of various shapes, including some truly three-dimensional cases. The upper and lower bounds on the phase shifts and on the elements of the equivalent circuit are found to be quite close to one another. In one case, the bounds obtained by using the simple trial function are compared with the bounds obtained by using the trial function which generates the Schwinger integral variational principle.
Recovery of Internal Friction in Aluminum after Plastic Deformation
Authors: Holwech Ivar
Published: April 2005

The internal friction in polycrystalline, super purity aluminum has been measured during and after creep under constant load by the ultrasonic pulse method. The increase of internal friction was found to be independent of frequency in the measured range (2.5 to 12 Mc). The room temperature recovery of internal friction after unloading could be described by the formula: Δα=C1/ (t+C2)C3. Typical values of the constants C2 and C3 are 10 sec. and 0.6, respectively. The experimental results are discussed in terms of the Weertman-Salkovitz theory of low-amplitude internal friction.
Positive Column Formation in Ion Sources Employing Surface Ionization
Authors: Auer P. L. , Hurwitz H.
Published: April 2005

In order to gain some insight in the problem of space charge neutralization of ion beams we make use of a previous calculation to discuss the unidimensional flow of positive ions in a tube where both ions and electrons issue from an emitter surface but only ion current is collected by means of an accelerating electrode. The resulting ion flow can be neutralized to varying degrees by the electrons present. We find that even in the absence of collisional interactions the potential distribution in the tube may closely resemble the electrode sheath and positive column structure familiar to glow discharges. This is the situation to be expected whenever the ion current has values far in excess of that predicted from a zero degree of neutralization space charge limited theory.
Measurement of Elastic Constants of RbBr, RbI, CsBr, and CsI by an Ultrasonic cw Resonance Technique
Authors: Bolef D. I. , Menes M.
Published: April 2005

An ultrasonic cw resonance technique for the measurement of the velocity of sound in solids is described. The end correction due to the presence of the transducer and coupling film can be calculated from consideration of a transmission-line equivalent circuit. An experimental comparison is made of the cw and two pulse techniques over the frequency range 5 to 45 Mc. Application of the cw resonance technique is made to the measurement of the room-temperature adiabatic elastic constants of single crystals of RbBr, RbI, CsBr, and CsI. A tabulation of the important elastic properties of these crystals is presented.
Mechanism of Inert Gas Cleanup in a Gaseous Discharge
Authors: Blodgett K. B. , Vanderslice T. A.
Published: April 2005

An investigation has been made of the cleanup of inert gases by a gas discharge. The cleanup of rare gases in a tube in which metal is being sputtered is governed largely by two factors. First, the rate at which the metal is sputtered, and second, the potential of the surface on which the metal lands. At small negative or positive potentials on the surface collecting sputtered metal there is a slow cleanup rate caused by uncharged species being buried by sputtered metal. At more negative potentials burial of ions becomes important, and cleanup is much more rapid. Recovery has been effected by heating to the evaporation temperatures of the metal. As the metal evaporates the buried gas is liberated. Hundreds of equivalent monolayers of argon have been cleaned up with only a total recovery of about one equivalent monolayer by heating at 1500°C. This shows that even with a forced ``solubility'' of the order of one per cent we find no evidence for significant diffusion of argon in metals. An electrode collecting ions at a uniform current density over the surface will have a net cleanup rate of zero on that surface after the initial cleanup of a small amount of gas. After the initial disappearance of some gas, resputtering will occur liberating the cleaned up gas as fast as it is being cleaned up.
Beta Particle Transmission Currents in Solid Dielectrics
Authors: Gross Bernhard , Bradley Arthur , Pinkerton Arthur P.
Published: April 2005

The current from a beta particle source measured through a thin dielectric cannot be predicted simply from the absorption curve. A model is considered in which the space charge formation in the medium results in a component of current in addition to that of the betas transmitted. Calculations developed from this model give a close approximation to experimental results.
Single-Crystal Magnetic Anisotropy and Magnetostriction Studies in Iron-Base Alloys
Authors: Hall R. C.
Published: April 2005

Single crystals of a number of binary iron-base alloys were grown, fabricated, and tested for magnetic anisotropy (K1) and magnetostriction (λ100 and λ111). The additions made to iron included vanadium, molybdenum, germanium, chromium, titanium, and tin. The anisotropy of iron was lowered by the addition elements with the possible exception of tin. On the other hand, λ100 of iron was generally raised by these addition elements. Only titanium and tin lowered λ100; however, titanium had limited solublilty in iron and tin caused embrittlement.
Electron Probe Measurements of Evaporated Metal Films
Authors: Sweeney W. E. , Seebold R. E. , Birks L. S.
Published: April 2005

Calibration curves of X-ray intensity vs specimen thickness have been prepared for the electron probe microanalyzer by using evaporated films of Cr, Mn, Zn, and Au in the 0–5000 A range. For each element, the x-ray intensity increased almost linearly with thickness; for a given thickness, the x-ray intensity increased (but not linearly) with atomic number. Using previously published data on electron excitation efficiency to calculate expected x-ray intensities, the measured values from Cr, Mn, and Au were about 0.75 to 0.85 times the calculated value whereas Zn was about 1.25 times the calculated value. The variations are thought to result from some undetermined parameter such as density or internal strain.
On the Theory of the Close-Spaced Impregnated Cathode Thermionic Converter
Authors: Rittner E. S.
Published: April 2005

The tables associated with the exact Langmuir space charge theory have been represented to a maximum relative error of 0.01% by approximation formulas which are suitable for use with digital computers. Application of the exact theory to a thermionic converter comprising two close-spaced planar impregnated cathodes has permitted a critical evaluation of the approximate space charge theory of Nottingham. The influence of the electrode separation, the emitter and collector work functions and of the emitter temperature has been investigated. Spectral emittance measurements on a cathode surface at two wavelength has resulted in a more firmly based estimate of the radiation heat transfer between two impregnated cathodes and of the maximum efficiency of an ideal design.
Etch Pits at Dislocations in Copper
Authors: Livingston J. D.
Published: April 2005

A modification of an etch discovered by Lovell and Wernick has been shown to be a reliable means of revealing dislocations as etch pits on (111) faces of copper crystals. The etch has been employed to study dislocation distributions in as-grown, annealed, and deformed crystals.

A high-temperature anneal is found to lower the dislocation density of melt-grown crystals. A ``double-etch'' technique is employed to observe the motion of dislocations, and to show that the dislocations initially present in these crystals are mobile at low stresses. Subboundaries are numerous in these crystals and are found capable of hindering dislocation movement. Observations of the dislocation structure of crystals deformed in bending and in tension are reported, including the appearance of ``glide polygonization'' after room-temperature deformation.
Theory of Dislocation Climb in Metals
Authors: Lothe Jens
Published: April 2005

An estimate of the climb motion of dislocation jogs is given, which takes into account the fact that dislocations are pipes of easy diffusion. The climb of dislocations under near-equilibrium conditions is then discussed. A new estimate is made of the jog concentration, for which vacancy equilibrium will be established along the entire dislocation. It is argued that the dislocation line tension is an important driving force both in high-temperature creep and in whisker dekinking. Under quench conditions it must be expected that a great number of jogs are nucleated at the nodes of the dislocation network.
Tensile Properties of Thin, Evaporated Gold Films
Authors: Neugebauer C. A.
Published: April 2005

Evaporated gold films in the 500–15 000 A thickness range were prepared on rocksalt substrates. Depending on the temperature of the substrate during deposition, the films were completely, partially, or randomly oriented with respect to the (100) plane of the rocksalt, as determined by x-ray diffraction. The stress-strain curve of the free films was investigated and was found to be quite steep up to very high stresses, but plastic deformation and creep were observed even at relatively low stresses. The ultimate tensile strength of the films is from 2 to 4 times that of the annealed bulk material and is not a function of film thickness. The Young's moduli are found to be normal. Comparing the stress-strain behavior of evaporated films with that of whiskers suggests that the former owe their high strength to a high concentration of defects which were uniformly quenched in during the evaporation process, and which greatly impede dislocation motion and multiplication, and not to an abnormally high stress required to nucleate dislocations which is commonly observed in whiskers.
Properties ofp-Type GaAs Prepared by Copper Diffusion
Authors: Rosi F. D. , Meyerhofer D. , Jensen R. V.
Published: April 2005

Purification of arsenic by hydrogen sublimation and gallium by vacuum annealing resulted in the preparation of high resistivity (∼106 ohm-cm), n-type GaAs crystals by the horizontal Bridgman technique. Conversion of this material to p-type was accomplished by the inward diffusion of copper from the crystal surface. Measurements of Hall mobility as a function of hole concentration in the range, 2×1016 cm−3 to 3×1017 cm−3, at room temperature showed a dependence which is consistent with theory. The analysis suggests a lattice mobility for holes of 450 cm2 V−1 sec−1 at 300°K. The mobility varied approximately as T−2.3 in the range 76°–300°K. At the low temperatures the number of ionized impurities ranged from 2×1015 cm−3. The energy levels associated with copper in GaAs are 0.023 ev and 0.15 ev above the valence band.