bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of Thin Single-Crystal Gold Films
Authors: Catlin Avery , Walker Walter P.
Published: April 2005

Single-crystal gold films were grown by vacuum deposition on heated (375°C) sodium chloride substrate blanks. Completely oriented films with thicknesses between 1000 and 3000 A were obtained, with the plane of the film being the {100} crystallographic plane. A small hole was drilled through the substrate with a water jet, and the mechanical properties were determined by stressing the unsupported film over this hole. The films were observed to undergo considerable plastic deformation, accompanied by the appearance and growth of mechanical twin bands as the stress was increased. X-ray diffraction studies were made to determine the twin orientation. Both the ultimate tensile stress and the elastic modulus were found to increase as the thickness of the films was reduced.
Experimental Investigations of the Cesium Plasma Cell
Authors: Ranken W. A. , Grover G. M. , Salmi E. W.
Published: April 2005

Some aspects of the performance of a cesium plasma cell with tantalum emitter are evaluated in terms of experimental determinations of the effects of variations in such parameters as cesium vapor pressure, emitter temperature, and emitter-collector separation distance. Experiments relating to the effect of collector serrations and to the feasibility of radiation shielding are described. Voltage-current characteristics are presented for several emitter temperatures and for a wide range of cesium vapor pressure.
Correlation of Low-Temperature Caloric and Magnetic Effects in TiFe
Authors: Schröder K. , Cheng C. H.
Published: April 2005

Magnetic measurements by Nevitt on TiFe can be interpreted on the assumption that his specimen is superparamagnetic. It is possible to calculate from his measurements approximate values of the size and number of ferromagnetic clusters. The magnetization vector of these clusters oscillates at very low temperatures within directions given by the energy of crystal anisotropy. This gives rise to the term Ccl in the specific heat at low temperatures, due to the clusters, which is to be added to the lattice and electronic terms. The calculation gives reasonable agreement of Ccl with experimental values found in specific heat measurements.
Effects of Irradiation on the Thermal Conductivity of Synthetic Sapphire
Authors: Berman R. , Foster E. L. , Schneidmesser B. , Tirmizi S. M. A.
Published: April 2005

The thermal conductivity between 2° and 100°K has been measured on synthetic sapphire single crystals and on sintered alumina, before and after reactor and γ-ray irradiations. Reactor irradiation appears to introduce two types of thermal resistivity-producing defects, one of which is dominant at low temperatures. The only effect of γ irradiation is an extra thermal resistivity at low temperatures which saturates for quite small doses. This saturation value seems to depend on the initial perfection of the crystal and is increased by reactor produced damage. At present, detailed information about the defects cannot be derived from thermal conductivity measurements alone.
Measurement of Thermal Conductivity by Utilization of the Peltier Effect. II. Correction for Wire Radiation and Determination of Specimen Radiation Emissivity
Authors: Simon R. , Bate R. T. , Lougher E. H.
Published: April 2005

The analysis in the first article on measurement of thermal conductivity by utilization of the Peltier effect [T. C. Harman, J. H. Cahn, and M. J. Logan, J. Appl. Phys. 30, 1351 (1959)] is extended to correct for radiation of heat from the lead wires. It is shown how the radiation emissivity of the semiconductor specimen can also be determined from the measured temperatures.
Determination of Electrode Shapes for Axially Symmetric Electron Guns
Authors: Harker Kenneth J.
Published: April 2005

The determination of the electrode shapes for an electron gun involves solving Laplace's equation subject to specified boundary values of voltage and normal field on an open curve. Past attempts to solve this problem for the case of axial symmetry by mathematical methods have met with considerable difficulties because the problem is improperly set and leads to unstable solutions. Following Garabedian, we have reformulated the problem in such a manner that it becomes properly set, and have applied it to a curvilinear space-charge limited flow gun. First, a conformal transformation is made which maps the beam boundary into a coordinate axis. The second step, which constitutes the essence of the method, is accomplished by making an analytic continuation of Laplace's equation and its boundary values into a fictitious complex domain. Laplace's equation, which is elliptic in the real domain, is thereby converted into a set of hyperbolic equations. This leads to a stable scheme of computation by finite differences. This method should find particular application to curvilinear flow guns, where the use of analogs, such as the electrolytic tank, requires the use of involved experimental techniques. The method is very general, however, being applicable to any configuration where the boundary conditions are given through analytic functions. If one desires, these specifications for the boundary conditions may be given implicitly, as, for example, through a set of differential equations.
Multiple Tube Collimator for Gas Beams
Authors: Hanes G. R.
Published: April 2005

A multiple tube gas collimator is described which consists of a bundle of tubes with 20-μ radii, made by electrolytic removal of copper wires from the plastic matrix in which they were embedded. Details of construction are given, as well as measurements of the angular distribution of gas flow from the collimator, which are determined with a helium mass spectrometer leak detector. The theory of flow through multiple tube sources is discussed, and a figure of merit giving relative values of beam intensity for fixed collimator area and flow rate is derived. The collimator described in this paper compares favorably with those used by previous workers.
Corbino Disk
Authors: Kleinman D. A. , Schawlow A. L.
Published: April 2005

When a disk with concentric inner and outer electrical contacts is placed in a magnetic field parallel to its axis, and current is made to flow through the disk, the lines of current flow have a spiral shape. This spiral current flow produces its own magnetic field, which interferes constructively or destructively with the applied field, depending upon whether the carriers spiral inward or outward, respectively. For ordinary conductors and ordinary currents the effect of the self-field of the current is very small. But the effect should be large in materials of very high mobility such as has been recently reported for bismuth at 4.2°K. In this paper the theory of the effect is given for the case in which the mean free path of the carriers is small compared to the inner radius of the disk. The analysis shows that the disk behaves as a rectifier. The easy direction of flow corresponds to outward spiraling of the carriers, which at large currents results in the explusion of the magnetic field from the disk. In the hard direction of flow the magnetic field at the center of the disk may be several orders of magnitude larger than the applied field. It is suggested that the corbino disk may be a useful rectifier in applications requiring extremely low impedance. It may also be a useful voltage regulator in a very low-voltage high-current power supply. A device consisting of the disk and a coil to provide the magnetic field is discussed in some detail. The static characteristics when the coil is connected through a suitable resistance in parallel with the disk exhibits a negative resistance. This negative resistance is useful in ac operation if a condenser is also connected in series with the coil. The equations and boundary conditions which determine the electrical properties of the disk in the time-dependent case are formulated. In the small-signal approximation the complex impedance is obtained for the limiting cases of low and high frequency. At low frequency the reactance is that of a negative inductance (-iωL). At high frequencies there is a skin effect on the tangential component of current, which causes most of the signal current to be radial and causes the impedance to reduce to the resistance of the disk.
Prediction of Fatigue Life
Authors: Freudenthal A. M.
Published: April 2005

On the basis of the relation between the ``reliability-function'' (probability of surviving beyond age N in cycles or t in time) and the ``risk'' of failure (as a function of age), the physical interpretation of the latter can be used to extrapolate the former beyond the range of possible observation. It is shown that the asymptotic distribution of smallest values is compatible with the physical concept of (dynamic or static) fatigue, while the logarithmic-normal distribution is not.
Electron Microscope Observations of Fission Fragment Tracks in Thin Films of UO2
Authors: Noggle T. S. , Stiegler J. O.
Published: April 2005

Electron microscope studies of the tracks produced by fission fragments in thin films of UO2 have established a 100% detection efficiency for fission events in films 100 A or less in thickness. A background texture decreases the efficiency in thicker films. The tracks register in the films primarily as a result of a redistribution of surface material arising from the disturbance produced by the continuous loss of energy of the fragment by electron excitation and ionization. The minimum rate of energy loss which registers as a track in the film is on the order of 1000 ev/A. Track length distributions, however, suggest that as yet unrecognized free surface effects may also contribute to the track registration.
Direct Measurements of the Surface Energies of Crystals
Authors: Gilman John J.
Published: April 2005

By means of quantitative cleavage experiments, the surface energies of several simple crystals have been measured at −196°C. The crystals and their cleavage planes are: LiF (100), MgO (100), CaF2 (111), BaF2 (111), CaCO3 (1010), Si (111), and Zn (0001). Measured values of their respective surface energies (ergs/cm2) are: 340, 1200, 450, 280, 230, 1240, and 105. The measured values for LiF and MgO are in good agreement with simple ionic lattice theory. Values for the other crystals seem consistent with their binding energies.

Under irreversible conditions an effective surface energy is measured. This quantity increases rapidly with increasing temperature for the metallic crystals, Zn and Fe (3% Si). The increase correlates with increasing plastic flow in these crystals. In contrast, the effective surface energy of LiF and MgO is only moderately dependent on temperature.

A small amount of cadmium (0.1 at.%) markedly increases the cleavage surface energy of zinc.
Production of Dislocation Loops by a Combined Climb and Glide Mechanism
Authors: Fourie J. T. , Wilsdorf H. G. F.
Published: April 2005

Studies of dislocations in elongated aluminum crystals by diffraction electron microscopy revealed narrow dislocation loops lying parallel to 〈112〉. These loops formed only behind screw dislocations, their long parts then having edge character. Four mechanisms have been proposed to account for the formation and stabilization of the narrow loops through the condensation of point defects.
Electron Microscope Studies of Colloids in KCl
Authors: Simon R. E. , Sproull R. L.
Published: April 2005

Electron microscope studies were made of surfaces of potassium chloride crystals containing excess potassium. The crystals were cleaved in a vacuum and the surfaces replicated in the same vacuum. Large potassium colloids were observed with distinctive shapes and orientations determined by the host lattice.
Velocity Behavior of a Growing Crack
Authors: Dulaney E. N. , Brace W. F.
Published: April 2005

An expression for the velocity behavior of a growing crack in a plate of brittle material is obtained by a mathematical refinement of the Mott energy balance around a moving crack. Crack velocity ċ is given by ċ=VT(1−c0/c),where VT is terminal crack velocity, c is instantaneous half-crack length, and c0 is initial half-crack length. This predicts that velocity makes a hyperbolic asymtotic approach to terminal velocity. Growing cracks in large sheets of polymethyl methacrylate approach terminal velocity over three-quarters of their length as predicted by this theory but as though from an initial crack larger than the actual initiating crack. This is interpreted as due to energy losses at the very beginning of crack growth not included in the Mott energy balance.
X-Ray Measurement of Grain Size
Authors: Warren B. E.
Published: April 2005

When the number of crystals contributing to a powder pattern peak is small, changes in the position and orientation of the sample produce statistical variations in the measured integrated intensity. The statistics are those of a Poisson distribution, and the effect can be utilized in a very simple way for an absolute determination of grain size. Only relative intensity measurements are required. Grain sizes down to about one or two microns can be measured by this method. There is an interesting possibility of varying the experimental conditions in such a way as to distinguish between the sizes of grains and subgrains.
Field-Effect Modulation of Photoconductance in a Quasi-Intrinsic Semiconductor
Authors: Bockemuehl R. R.
Published: April 2005

The field-effect modulation of conductance in a dark-insulating photoconductor is strongly dependent on the properties of carriers of both signs. An analysis of the equilibrium space charge density resulting from electron-hole pair generation in a ``depletion layer'' and the resulting influence on the terminal characteristics of a photoconductive field-effect transistor is presented. The derived relationships explain the optical and frequency response behavior of CdS field-effect modulation of photoconductance to be observed, and provide a method for evaluating the drift mobility of holes and other carrier properties in a quasiintrinsic quasi-intrinsic semiconductor.
Uniform Avalanche Effect in Silicon Three-Layer Diodes
Authors: Goetzberger A.
Published: April 2005

Interaction of current gain and avalanche multiplication in three-layer diodes is utilized to produce uniform avalanche effect, indicated by uniform light emission over the area of a junction. Proof that the effect is caused by the three-layer action is furnished by removing the emitter layer, which changes the light emission to the usually observed microplasma pattern.
Theoretical and Experimental Study of the Backscattering Cross Section of an Infinite Ribbon
Authors: Macrakis Michael S.
Published: April 2005

The geometrical optics approximation is derived for the backscattering cross section per unit length of an infinite ribbon. A comparison is made with the exact theory, the approximate theory of Sommerfeld, the variational method, and with experimental results obtained through the space-separation method for the measurement of backscattering cross sections in a parallel-plate region.
Observation of Domains in Iron Whiskers Under High Fields
Authors: Fowler C. A. , Fryer E. M. , Treves David
Published: April 2005

An improved instrument utilizing the longitudinal Kerr magneto-optic effect is used to observe the magnetic domain development in iron whiskers undergoing a magnetization cycle. It is found that domains persist at the tip of the whisker even under conditions for which the crystal is usually assumed to be saturated. Under applied fields of a few thousand oersteds these persistent domains at the tip, in all of the specimens observed, are magnetized perpendicular to the axis of the whisker and in the same sense around its lateral faces. It is proposed that these domains are caused by the high fields localized near the sharp corners and edges of the crystal.
Changes in Macroscopic Shape, Lattice Parameter, and Density in Crystals Due to Point Defects
Authors: Balluffi R. W. , Simmons R. O.
Published: April 2005

It is demonstrated that a crystal of arbitrary shape filled with a fine random distribution of centers of dilatation will dilate homogeneously. No elastic approximations are made, and the results should hold for strains of any magnitude. By use of an average and perfect reference lattice embedded in the strained crystal, it is then shown that the lattice dilatation as measured by x-ray lattice parameter measurements and by macroscopic dimensional measurements should be the same along any direction when the number of substitutional atomic sites remains constant. Perturbing effects due to x-ray diffuse scattering should cause negligible error in determining the positions of the Laue-Bragg maxima under usual conditions. All results should apply also to the case of thermal dilatation at temperatures up to the melting point. The use of density measurements in the determination of point defect concentrations is discussed. Experimental data are reviewed.
Angular Distribution and Polarization of the Radiation Emitted by Electrons Accelerated in a Synchrotron
Authors: Bedo D. E. , Tomboulian D. H. , Rigert J. A.
Published: April 2005

The paper presents evaluations of the angular distribution of the synchrotron radiation for a high-energy accelerator. The investigation indicates that the peak power, at wavelengths in excess of a certain critical value, does not occur in the orbital plane but at some angle above or below this plane. Expressions are given for the intensity components of the radiation polarized at right angles to, and in the plane of the orbit, respectively. The radiation emitted by a monoenergetic electron is, in general, elliptically polarized, the ratio between the major and minor axes depending on the angle ψ between the direction of observation and the orbital plane. For ψ=0 the radiation is linearly polarized, and approaches circular polarization with increasing values of ψ.
High-Temperature Discharges in Ferroelectric Ceramics
Authors: Northrip John W.
Published: April 2005

Ceramic disks of barium titanate and lead zirconate titanate, when heated above 100°C, exhibit current discharges which cannot be attributed to the ferroelectric polarization of the material. These discharges are largest in the temperature interval 300°–600°C and depend primarily on the electrode material and its method of application. Discharges of several millicoulombs at voltages up to one-half volt have been obtained from a ceramic disk one-half inch in diameter and 30 mils thick having a silver electrode and an indium counterelectrode. Although thermoelectric, pyroelectric, and electret effects are observed in these samples, these phenomena contribute only a very small portion of the total discharge. At constant temperature near 350°C the discharge decays with time as the sum of two exponentials, falling to half-maximum in periods of the order of one-half hour. At higher temperatures the decay rate increases, while temperature cycling produces a voltage cycling superimposed on the decay. These findings support an explanation of the effect in terms of solid state chemical activity between the metallic electrodes and the titanate lattice.
Experimental Study of Arc Stability. I
Authors: Cobine J. D. , Farrall G. A.
Published: April 2005

The stability of short arcs in gases and in metal vapors is closely related to the phenomena associated with the cathode spot. Use is made of improved techniques to study this phenomenon for a considerable range of electrode materials. The distribution of arc life for a given average current is shown to follow the survival law. These data demonstrate that a small percentage of arcs of a given current on very clean metal surfaces may have lifetimes that are extremely short or very long compared with the average life. The relation between the average life of an arc and its average current is shown generally to consist of two sharply defined sections each of the form lnt=A lnI+B. The distribution of lifetimes and the relation between average life and average current are shown for Hg, Cd, Zn, Cu2Sb, Bi, Bi-Cu, Cu-In, Ag, Cu3Sn, Al, Be, Cu, Cu-W-Th, Cu-MoC, Mo, and W. It is shown that high vapor pressure materials tend to produce more stable arcs than those having low vapor pressure.
Atom Ejection Patterns in Single-Crystal Sputtering
Authors: Anderson G. S. , Wehner G. K.
Published: April 2005

Experimental studies of the atom ejection patterns in single-crystal sputtering mostly by Hg+ ions have been made. These patterns give evidence of the anisotropic spread of energy from a collision center, and support the concept of focusing collisions in nearest and next-nearest neighbor directions. In Ge the patterns were found to be strikingly similar to those from a bcc crystal. This could be explained by assuming that under ion bombardment so many interstitials are formed near the surface that the atom arrangement of the Ge crystal resembles that of a bcc lattice.
Effect of Electron Irradiation and Subsequent Thermal Treatment on Young's Modulus of Copper
Authors: Sosin A. , Bienvenue L. L.
Published: April 2005

Measurements of Young's modulus of copper following high energy electron irradiation and subsequent heat treatment are reported. The modulus is observed to increase following short exposures at −190°C in three separate temperature regions, centered at approximately −45°C, −5°C, and +80°C. These modulus increases are discussed in terms of the various point defects created by the bombarding electrons.
Effect of Specimen Delocalization in Electron Diffraction Studies of Gas Molecules
Authors: Bartell L. S.
Published: April 2005

The effect upon a normal electron diffraction pattern of an extraneous uniform distribution of the gaseous specimen is considered quantitatively. It is shown that the delocalization of gas may lead to errors in internuclear distances of several thousandths of an Angstrom unit or more in conventional experiments. Equations are presented for the correction of experimental data.
Experimental Investigation of a High-Energy Density, High-Pressure Arc Plasma
Authors: Martin Edward A.
Published: April 2005

The underwater spark is utilized to study the fundamental parameters of a plasma at 30 000°K and 10 000 atmos pressure. The 25-kv spark is obtained by underwater discharge of capacitors having a stored energy of 1800 joules, the inertia of the water providing the confinement necessary to develop high pressures. Phenomena relating to the initiating wire (exploded wire) are discussed. Kerr cell photographs show that spherical structures are formed around both electrodes under certain conditions. A possible explanation is postulated. A detailed energy balance and particle balance are carried out. The results show that the plasma has great capability to store energy in dissociation, excitation, and ionization without a corresponding increase in temperature. The plasma is 30% ionized and the total particle density is about 2×1027 per cubic meter. At this density the plasma radiates a blackbody spectrum. Pressures are obtained by calculation based on the rate of spark channel expansion and the shock properties of water. The plasma is found to have an internal pressure of the same order of magnitude as the external pressure because of interparticle Coulomb forces. Plasma conductivity calculated from equations of Gvosdover and Spitzer and Harm agree very well with the experimental value. The study is basically experimental, with the emphasis in interpretation being placed on reliability of the conclusions rather than on refined accuracy.
Diffusion Coefficients, Solubilities, and Permeabilities for He, Ne, H2, and N2 in Vycor Glass
Authors: Leiby C. C. , Chen C. L.
Published: April 2005

The permeability of a Vycor filter (680 cm2 area and 0.25 mm thick) is given for helium at six temperatures ranging from 299°K to 723°K, for neon and hydrogen at 673°K and 723°K, and for nitrogen at 673°K. The observed values and their temperature dependences are in good agreement with corresponding values for fused quartz reported elsewhere. Values of the diffusion coefficient of these gases in Vycor also were obtained experimentally, enabling calculation of their solubilities. Helium appears to deviate from activated diffusion in Vycor somewhere between 100° and 26°C. Its permeation velocity and diffusion coefficient at 26°C are larger than expected for activated diffusion, while its solubility at 26°C is one-half its value at 100°C. These changes suggest that some structure sensitive diffusion process begins to dominate the activated or solution process at these lower temperatures. Helium flow rates through the filter as high as 2100 mm Hg (0°C)×cc/hr at a filter temperature of 450°C and a pressure difference of 35 cm Hg (0°C) were observed. On the basis of observed permeation rates for the above gases, it is estimated that the filtered helium has an impurity content of less than 1/50th of its unfiltered value.
Growth, Structure, and Properties of Graphite Whiskers
Authors: Bacon Roger
Published: April 2005

Graphite whiskers have been grown in a dc arc under a pressure of 92 atmospheres of argon and at 3900°K. They are embedded in a solid matrix of graphite which builds up by diffusion of carbon vapor from the positive to the negative electrode. Diameters range from a fraction of a micron to over five microns, with recoverable lengths up to 3 cm. They consist of one or more concentric tubes, each tube being in the form of a scroll, or rolled-up sheet of graphite layers, extending continuously along the length of the whisker, with the c axis exactly perpendicular to the whisker axis. They exhibit a high degree of flexibility, tensile strengths up to 2000 kg-mm−2, Young's modulus in excess of 7×1012 dyne-cm−2, and values of room-temperature resistivity of around 65 μohm-cm, which approximates the single crystal value.
Photoelectronic Analysis of High Resistivity Crystals: (a) GaAs, (b) Sb2S3
Authors: Bube Richard H.
Published: April 2005

A series of photoelectronic measurements has been used to obtain information about the following basic properties of high resistivity crystals: (1) majority carrier lifetime, (2) band gap, (3) activation energy for dark conductivity, and (4) activation energies and densities of trapping centers for carriers. Such measurements have been made on representative high resistivity n-type crystals of GaAs and Sb2S3. The results are reported here together because both crystals show evidence for trapping of photoexcited carriers by compensated donor centers of the same type as those which uncompensated give rise to the normal dark conductivity. Additional data on Sb2S3, together with other results on similar crystals, suggest that these same uncompensated donor centers may play an important role in the recombination process.
Thermal Initiation of Explosives
Authors: Zinn John , Mader Charles L.
Published: April 2005

Numerical solutions have been obtained for the nonlinear heat conduction equations arising in the theory of thermal explosions. Explosion times are calculated for externally heated spheres, cylinders, and slabs of several explosive materials, and the results are shown to agree with experiment.
Single Crystal Tungstates for Resonance and Emission Studies
Authors: Van Uitert L. G. , Soden R. R.
Published: April 2005

A number of single crystal tungstates have been prepared for paramagnetic resonance and emission studies. Compositions such as monoclinic MgWO4, ZnWO4, CdWO4, and tetragonal CaWO4, SrWO4, and BaWO4 containing paramagnetic ions of the transition and rare earth series have been prepared. They were grown by dissolving the constituent oxides into an equimolar mixture of Na2WO4 and WO3 at 1100 to 1250°C and cooling at 2 to 3°C per hour to 700°C.

These crystals offer the advantages of one environment for the paramagnetic ions present, freedom from strain (hardness equal to that of iron), absence of random ordering effects, minimal effects from nuclear magnetic moments, and chemical stability. Large zero field splitting are observed in the monoclinic crystals, making them of interest for studies at high microwave frequencies. The tetragonal compositions are promising at the lower microwave frequencies and have shown very narrow resonance lines. Line widthṡ as low as 1.5 Mc have been obtained in CaWO4:Mn.

Na0.5Y0.5WO4 crystals, which have the scheelite structure, were also grown. Random ordering effects of monovalent sodium and trivalent yttrium, however, result in a nonhomogeneous electrostatic environment throughout the crystals and hence cause broad paramagnetic resonance lines.
Effect of Oxide Layers on the Diffusion of Phosphorus into Silicon
Authors: Allen R. B. , Bernstein H. , Kurtz A. D.
Published: April 2005

The diffusion of phosphorus from the vapor phase into single crystal silicon has been studied. The experimental data are analyzed in terms of a two-layer diffusion model, leading to the determination of a diffusion constant for phosphorus in the oxide. The resulting diffusion constant at 1150°C is found to be 2.1×10−15 cm/sec2 with an activation energy of 1.4 ev.
Observations on MnBi Films during Heat Treatment
Authors: Mayer Ludwig
Published: April 2005

Observations of magnetic surface phenomena, which were made during the vacuum heat treatment necessary to develop ferromagnetic MnBi films from their nonmagnetic constituents, are described. A vacuum hot stage for a metallurgical microscope was constructed in order to accomplish by means of the Kerr magneto-optic effect this visual observation of incipient ferromagnetism. MnBi films with some areas already magnetic were first observed. The phenomena occurring during evolution of the magnetic state in the areas adjacent to the already magnetic areas could be observed readily and the experiments could be reproduced consistently. Attempts to nucleate this transformation in the vacuum hot stage were only partly successful because reproducibility could not be achieved. Growth of a new magnetic area on MnBi film manifests itself first as an essentially structureless area. This structureless area then becomes an area of antiparallel domains. The size of the domains depends mainly on the duration of the existence of the structureless state. Large domains tend to develop if the structureless state is kept in existence for a short time and vice versa. In addition to the immediate practical goal of improving reproducibility in the preparation of MnBi films such visual observation of the nascent state of ferromagnetism may also be of general interest to the physics of magnetism.
Detailed Study of Switching Current in Barium Titanate
Authors: Drougard M. E.
Published: April 2005

The polarization reversal process in ferroelectrics has, up to now, been characterized solely by the total switching time and the maximum value of the switching current. The work presented in this paper was aimed at determining how the instantaneous value of the switching current in single crystals of BaTiO3 depends on the applied field, the state of net polarization of the crystal, and possibly other factors. It has been found that the switching current density can be expressed as the product of a function of the polarization, φ(p), and a function of the electric field, exp(−α/E). The form of the function φ(p) indicates a predominance of sideways expansion of 180° domains, with an exponentially increasing domain wall velocity. This last result is shown to be in agreement with a picture of domain wall motion by nucleation of new domain wall layers. This interpretation, together with some details of the switching current pattern, suggests that a crystal, although apparently single-domain, may always retain some small domains of opposite polarization.
Decay of Wax Electrets
Authors: Perlman M. M.
Published: April 2005

The internal field within an electret can be varied by changing the spacing and arrangement of shielding electrodes (``partial shielding''). The application of this technique to rosin-wax electrets shows that the charge decay observed upon unshielding electrets is caused primarily by volume polarization due to internal field rather than by external ion collection.
Theory of Non-Newtonian Flow. III. A Method for Analyzing Non-Newtonian Flow Curves
Authors: Kim Wan Kyue , Hirai Nishio , Ree Taikyue , Eyring Henry
Published: April 2005

The historical development of the rate theory of viscosity is briefly reviewed. The Ree-Eyring equation of generalized viscosity, η= ∑ n=1m(xnβn/αn)(sinh−1βnṡ/βnṡ)is applied successfully in a variety of cases. (For the definitions of the symbols in this equation, reference is made to the text.) We develop here a new method for determining the parameters xn/αn and βn in Eq. (A). According to the method, these parameters are uniquely determined. When we used the parameters determined by the new method, the viscosities for solutions of poly-γ-benzyl-l-glutamate were calculated from Eq. (A). It is found that Eq. (A) is much superior to other frequently applied viscosity equations.

Upon calculating the Newtonian viscosities ηs for fairly concentrated solutions of polyacrylonitrile and of nitrated pine pulp, the following empirical formula is found: ηs≃KC2Mβp12. Here K is a characteristic constant for a solution; C the concentration; M the molecular weight; and βp is the ``principal'' relaxation time. In dilute solutions, Eq. (B) reduces to the form ηs≃K′CM.
Single-Velocity Equivalents for Multivelocity Electron Streams
Authors: Gray Glenn A.
Published: April 2005

Several electron beam problems which involve a distribution in electron velocities are treated. In each case the actual multivelocity stream is replaced by an equivalent single-velocity stream. Such a procedure provides a common viewpoint for the examples which are considered. For a traveling wave tube, it is found that a distribution of dc electron velocities has the same effect as an increase in the space charge parameter QC, a result which is in agreement with the earlier findings of Watkins and Rynn. Also, agreement with earlier theories is found in the cases of space charge wave propagation on a multivelocity stream, and the double-stream amplifier. In the case of noise fluctuations in high velocity beams, it is found that the time varying part of either the rms or the mean stream velocity may be used to specify the ac velocity modulation on the equivalent single-velocity beam. That is, either value should be equally valid in a first order treatment. Finally, a class of re-entrant beam devices are analyzed, and experimental results are cited as an indication of the validity of the theory.
On the Concept of Fictitious Surface Charges of an Electron Beam
Authors: Chu E. L.
Published: April 2005

The electrodynamical phenomena in the boundary strip of a sharply focused electron beam are extremely complicated. This difficulty is usually resolved by postulating a layer of surface current on the boundary of the unperturbed beam while considering the troublesome boundary strip as nonexistent. A critical examination is made of this technique with the result that, if the calculated rf power is to be the same as in the actual beam, a layer of electric dipoles must also be postulated. The discussion begins with the Jacobian and Taylor's expansion, with particular emphasis on the applicability of the latter to the boundary strip, then proceeds to the formulation of a modified problem on an equal-power basis and the specification of the surface conditions which are to be satisfied. Second-order quantities are included in all equations, so that the small-signal beam kinetic quantities can be reliably calculated.
Thermal Attenuation of Nonlinear Stress Waves
Authors: Treitel Sven
Published: April 2005

The work of Knopoff and MacDonald (1958) on the attenuation of nonlinear stress waves in solids has been extended to include thermal losses. The damping of a nonlinear stress wave is completely describable in terms of two attenuation coefficients, a ``mechanical'' coefficient α1, and a ``thermal'' coefficient α2. The latter is probably small compared to the other, but much high-precision experimental work is required to settle this point definitely.
Operating Characteristics of a Molecular-Beam Maser
Authors: Venkates H. G. , Strandberg M. W. P.
Published: April 2005

General expressions for the emitted power and the frequency pulling in an ammonia maser have been deduced. The operating characteristics of the maser have been deduced by introducing a mean-square time of flight of molecules in the cavity.
Microwave Study of Afterglow Discharge in Water Vapor
Authors: Takeda Susumu , Dougal Arwin A.
Published: April 2005

Results of a microwave investigation of decaying plasmas produced in water vapor H2O are reported. Electron loss processes prevailing in these decaying water vapor plasmas were interpreted. In the electron density range from 1010 to 108 per cm3, electron-ion recombination prevails as the dominant electron loss process with a coefficient of 10−6 to 10−5 cm3/sec. For vapor pressures up to 7.0 mm Hg, electron attachment to water vapor molecules or their derivatives was too small to be detectable, i.e., an attachment probability less than 10−7. The electron collision probability for momentum transfer collisions with water vapor molecules was measured to be 2300±500 cm−1 mm Hg−1 for electrons near thermal energies at room temperature. The collision probability steeply decreases with increasing electron energy in the low energy range. An interpretation of the de-ionization processes in TR tubes filled with admixtures of water vapor and noble gases is given.
Monoenergetic Neutron Irradiation of Germanium
Authors: Curtis O. L. , Cleland J. W.
Published: April 2005

A study has been made on 14-Mev neutron-irradiated germanium, using lifetime, Hall, and resistivity measurements to determine the nature of the radiation-induced defects and to compare the damage with that produced by neutrons from a fission spectrum. The electron removal rate in high-resistivity, n-type material is ∼8/cm−3 per incident neutron/cm2, measured at 77°K. Lifetime measurements have been made on n- and p-type material. On the basis of simple recombination theory, assuming no variation of capture probabilities with temperature, the results for n-type material indicate that a recombination level is located 0.32 ev above the valence band near the center of the energy gap. Assuming an introduction rate of recombination centers equal to one-half the electron removal rate in n-type material, the following values of recombination capture cross sections are obtained: σn=2.2×10−17 cm2; σp=6×10−15 cm2, the latter value being correct only within about a factor of two. The ratio of the cross sections, σp/σn, which is independent of the method of determining the number of recombination centers, is ∼300, indicating that the recombination centers are negatively charged. The lifetime measurements for p-type germanium are not so readily analyzed. Possible explanations for observed behavior are discussed.
Microwave Determination of Plasma Density Profiles
Authors: Wharton Charles B. , Slager Donald M.
Published: April 2005

A method for the rapid determination of the average electron density and of the spatial electron density distribution in plasmas is presented. The technique employed permits time-resolved measurements over a wide range of electron densities, introducing little or no perturbation into the gaseous discharge. The quantities measured by the described techniques have been correlated previously with other plasma measurements and show reasonably good agreement.
High-Energy Sputtering
Authors: Yonts O. C. , Normand C. E. , Harrison Don E.
Published: April 2005

Sputtering ratios for copper have been determined in the energy ranges 5–40 kev for bombardment by Ar+, He+, and D+. Argon values range from 6.48 at 5 kev to 9.25 at 27.5 kev, deuterium from 0.048 at 10 kev to 0.023 at 44 kev, and helium from 0.23 at 15 kev to 0.75 at 40 kev.

Preliminary data are included for 30-kev sputtering of copper by H+(0.011), D+(0.03), He+(0.13), N+(5.28), Ne+(3.61), Ar+(9.02), CU+(9.60), Kr+(15.15), and U+(20.9). Also included are sputtering ratios at 30 kev for Ar+ on Ta(2.7), Mo(3.31), and Al(2.38). Most of these data are the result of a single measurement, and require further verification.

A definite pressure dependence of the sputtering ratio for Ar+ on Cu was found in the range of 0.04 to 0.08 μ.
Influence of Irradiation with β Rays on the Electrification of KCl Crystals
Authors: Szaynok Anna
Published: April 2005

The measurements of electrical charges on dust clouds of crushed KCl monocrystals previously irradiated with β rays shows that the value of the mean charge depends on irradiation time. In the case of KCl irradiated with β rays, a photoelectric effect is not observed, despite the presence of F centers.
Focusing Molecular Beams of NH3
Authors: Helmer J. C. , Jacobus F. B. , Sturrock P. A.
Published: April 2005

The problem of forming molecular beams for use in ammonia masers is examined. It is shown theoretically and experimentally that through the use of a new type of parabolic focuser with a ``point source'' effuser, the molecular flow may either be reduced by a factor of 8, for the same power output, or the power output may be increased by a factor of 2 for the same molecular flow. A theory of beam formation in a multitube effuser is described. This shows that the most intense molecular beam is formed by an effuser of small overall diameter. Design considerations are discussed for parabolic, upper-state focusers, and for coaxial, lower-state focusers. The operation of a system is described, using a lower-state focuser and an ionization detector, in which lower-state molecules produced by maser oscillation may be detected.
Cratering and Shock Wave Phenomena in Steel Plates at High Impact Speeds
Authors: Mayfield Earle B. , Rogers James W.
Published: April 2005

The impact of aluminum projectiles on steel plates for impact velocities of 2500 m/sec to 3000 m/sec and about 1100 m/sec was studied. Crater volume and penetration were measured. Shock wave velocity from the free surface was determined and the particle velocity calculated. For annealed 4130 steel plates impacted at 2750 m/sec average velocity, the average free surface particle velocity was 0.205 mm/μsec. Existing theory on cratering and penetration gave excellent agreement with the observed values.
Optical Studies of the Diffraction of Water Waves by Circular and Thin Elliptic Cylinders
Authors: Barakat Richard , Barakat Robert
Published: April 2005

By using the optical grid method the diffraction of water waves from circular and elliptic cylinders were measured and compared with theory. The scattered wave intensity S and the total energy scattered per sec per unit intensity Q were measured and the results bear out the well-known fact that for angles less than 30 deg or in the vicinity of 180 deg, one cannot separate out the scattered wave and the incident plane wave.

The optical grid method is described in detail and the advantage of its being able to measure the instantaneous field emphasized.
Parametric Amplification along Nonlinear Transmission Lines
Authors: Landauer Rolf
Published: April 2005

A pump signal propagating along a dispersionless transmission line with a distributed nonlinear capacitance is subject to deformation, since different parts of the signal move with different velocities. This process of deformation will eventually result in the formation of an electromagnetic shock wave. The deformation will affect the parametric amplification process. If a small signal consisting of a positive pulse, short compared to the pump cycle, is added to the pump signal at the input end, then it is shown that the small signal at the output must be non-negative. All other small signals, including in particular those with sinusoidal time variation, can be regarded as superpositions of these short pulses. As a consequence it is shown that, in general, a sinusoidal signal will not be increased in its fundamental frequency component, by traveling down the line together with the pump signal. There are certain exceptional frequencies, multiples of one half the pump frequency, where a suitably phased small signal may be increased at its fundamental frequency, but not by a sufficient amount to be of practical interest.
Kinetics of Sintering of Sodium Chloride in the Presence of an Inert Gas
Authors: Moser J. B. , Whitmore D. H.
Published: April 2005

Direct observations of interfacial growth and the approach of centers between spheres of sodium chloride were made in an argon atmosphere and over a temperature range of 700 to 800°C. The rate law governing the increase of the contact area between spheres, the effect of changing size scale on this rate and the absence of a change in the center-to-center distance during sintering all indicate that the rate-determining mechanism of material transport in this sintering process is evaporation-condensation. A model is presented which considers Stefan flow to occur within a thin boundary layer in the gaseous phase adjacent to the condensing surface, the sintering rate being predominantly governed by the rate at which sodium chloride vapor diffuses through this boundary layer. The marked pressure-dependence of the empirical relationship between contact area and sintering time for fixed temperature and sphere size is consistent with the proposed model.
Effect of Pressure on Phosphor Decay
Authors: Gregg D. W. , Drickamer H. G.
Published: April 2005

An apparatus has been developed to measure the effect of pressure to over 50 000 atmospheres on the decay rate of phosphors. Three manganese activated phosphors with exponential decay curves were studied. In two cases the rate of decay decreased, in the third case it increased. A tentative explanation is offered. An hexagonal ZnS:Cu phosphor showed little pressure effect to 40 000 atmospheres at which pressure it transformed irreversibly to the cubic form with a sharp increase in decay rate and a large decrease in intensity.
Low-Temperature Transport Properties of Commercial Metals and Alloys. II. Aluminums
Authors: Powell Robert L. , Hall William J. , Roder Hans M.
Published: April 2005

The thermal conductivity, electrical resistivity, Lorenz number, thermoelectric force, and thermoelectric power are given in the temperature range 4–120°K for ten aluminums and aluminum alloys: high-purity, 1100-F, 1100-O, 3003-F, 2024-T4, 5052-O, 5083-O, 5086-F, 5154-O, and 6063-T5. Four of the samples show a maximum in thermal conductivity, the others do not. For the four high-thermal conductivity samples the separate components in the electronic thermal resistivity are resolved; for the others, components in both the electronic and the lattice thermal resistivities are given. The residual electrical resistivities vary from 2.5×10−8 to 3.2×10−6 ohm cm. The Lorenz numbers for the high-conductivity samples fall considerably below the Sommerfeld value 2.44×10−8 watt-ohm/°K2; those for the low-conductivity samples are somewhat above the Sommerfeld value. The thermoelectric power of some of the the alloys is positive with respect to the high-purity sample, for others it is negative. The various properties, methods of analysis, and separation of components are discussed in detail.
On The Behavior of Thermal Vacancies in Pure Aluminum
Authors: Kuhlmann-Wilsdorf Doris , Wilsdorf H. G. F.
Published: April 2005

The results are reported of an investigation of quenched-in prismatic dislocation loops in super-purity aluminum. Some new effects have been observed: in particular, that loops tend to be grouped in clusters containing a surplus of loops of one orientation; that more than four loop orientations are realized; and that often pairs of similarly oriented and similarly shaped loops are present in the quenched material. It is concluded that vacancies aggregate into three dimensional clusters, containing from a few to a few hundred or even thousand vacancies, before being converted into prismatic loops.