bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Pulse-Shaping by Saturable Optical Materials
Authors: Macomber James D.
Published: January 2005

As a high-intensity monochromatic light pulse passes through a material containing two-level systems, saturable absorption or amplification of the radiation may occur. The resultant ``shaping'' of the intensity-vs-time curve as a function of distance into the sample is the subject of this paper. A theory is developed based on the Einstein rate equations, and pulse-shape functions are derived which depend on the absorption and loss coefficients of the material, the relaxation time of the systems, the input-pulse intensity and width, the initial ``state-of-pump'', and number density of absorbers in the sample.
Ordered Pt3–Co Alloy Studied in the Field-Ion Microscope
Authors: Tsong Tien Tzou , Müller Erwin W.
Published: January 2005

Atomically resolved field-ion microscope images of the {111} planes of ordered Pt3–Co confirm unambiguously our hypothesis of the invisibility of the Co atom species in Pt–Co alloys. From the known lattice structure, L12, the composition of {110} and {100} planes of ordered Pt3–Co are expected to alternate in subsequent layers between pure Pt layers and equiatomic Pt and Co layers. This is confirmed by direct observation during controlled layer-by-layer field evaporation. Antiphase domains show up clearly only when the domain boundary passes through a {110} or {100} plane, but tracing the boundary through the matrix is difficult. No sharp boundary between the ordered and the disordered phase has been observed in the partially ordered state of the alloy.
Temperature Dependence of the Ferromagnetic Resonance Linewidth in Thin Ni–Fe Films
Authors: Patton Carl E. , Wilts Charles H.
Published: January 2005

Linewidths for ferromagnetic resonance with the static magnetic field in the film plane have been measured at frequencies from 1–9 Gc/sec and temperatures from 4.2°–300°K for Ni–Fe alloy films (77% Ni) 150 to 1500 Å thick. The linewidth exhibits a maximum in the vicinity of 80°K and the effect is generally larger in thinner films. The amplitude of the linewidth temperature dependence is independent of frequency and the maximum shifts to slightly higher temperatures with increasing frequency. The amplitude can be enhanced by heating the film at 150°C in air (oxidation) and removed by a similar treatment in a hydrogen atmosphere. This enhancement-removal cycle can be repeated reproducibly. The time required for saturation of the enhancement when the oxidation treatment was slowed down by annealing in a vacuum of 10−3 Torr instead of at atmospheric pressure was observed to be independent of film thickness, indicating that a volume-diffusion process is not involved. The apparent importance of surface oxidation suggests two possible mechanisms, valence exchange and exchange anisotropy, which may contribute to the linewidth temperature dependence. The discovery of a temperature-dependent linewidth in thin films which exhibits a maximum in the vicinity of 80°K and the identification of this dependence with a surface oxidation process are the primary results of this investigation.
Normalization and Absorption Correction of Arbitrary X-Ray Scattering Intensities of Paracrystalline Substances
Authors: Ergun Sabri , Bayer James , Van Buren Wayne
Published: January 2005

A method has been developed for normalization and absorption correction of x-ray scattering intensities of paracrystalline substances, i.e., matter in a state intermediate between crystalline and amorphous states. In the method, the equation for the observed intensities is transformed into a linear form, φ(s, μT)=K[1+g(s, μT)]+Ki(s), where i(s) is the oscillatory part of the interference function. If a proper value is assigned to μT, a plot of φ vs g yields a straight line (having a slope K) modified only by the oscillations of i. When MoKα radiation is used, the period of such oscillations becomes small compared to the range of g. The mean value of i is zero in the medium- and high-angle range; therefore, a straight-line correlation of φ with g to yield a slope having a value equal to that of the intercept allows the determination of μT and K with an accuracy within the precision of measurement of the scattered intensities. The method is readily programmed for a computer.
Thermodynamic Conditions of the Test Gas in a Ballistic Compressor
Authors: Takeo Makoto , Holmes Quentin A. , Ch'en Shang Yi
Published: January 2005

The development of a free-piston compressor at the University of Oregon is described. In order to characterize the thermodynamic conditions of the test gas in the ballistic compressor, a theoretical analysis of the piston's motion is made taking into account gas leakage, viscous friction, and heat losses. The values used for the radial clearance of the piston and the heat-loss constant are chosen so that the computed peak pressure and minimum volume of the test gas agree with experiment. The predictions of this treatment are then compared with observed pressure and acceleration profiles which were taken using argon and helium as test gases over a range of peak test-gas pressures from 476 to 1660 atm and are found to be in good agreement. The acceleration profile is found to be more sensitive than the pressure profile. It is evident that the compression process is nonadiabatic due to gas leakage around the piston and heat losses to the compressor walls.
Dislocation Pinning and Temperature Dependence of Internal Friction
Authors: Baker G. S. , Carpenter S. H.
Published: January 2005

The strain amplitude-dependent dislocation damping of pure (∼5 ppm interstitials) tungsten samples has been measured as a function of temperature from −190° to +100°C. The data cannot be interpreted in terms of the sample thermally activated breakaway theory of Friedel. The data gives the wrong stress dependence and unreasonably low activation energies.
Effect of Concentration-Dependent Diffusion Coefficient on the Migration of Interphase Boundaries
Authors: Trivedi R. , Pound G. M.
Published: January 2005

The diffusion-controlled interphase-boundary migration problem is defined by a system of equations in which the boundary conditions for the diffusion equation are determined by capillarity. Numerical computer solutions to these equations were obtained for steady-state Widmanstätten ferrite plate growth. The effect of a concentration-dependent diffusion coefficient on the migration rate of some simple interphase boundary shapes was investigated. It was found that a constant diffusion coefficient corresponding to the weighted average coefficient in the matrix gave an exact growth rate.
Cycle-Dependent Fracture of Polymethyl Methacrylate
Authors: Feltner C. E.
Published: January 2005

The fatigue behavior of PMMA and its fracture surface appearance have been studied over a range of stresses giving lives from 2×103 to 3×107 cycles. It has been proved that PMMA fails in a cycle-dependent manner. However, the mechanism by which fatigue cracks are initiated in unnotched specimens remains uncertain. The appearances of the fatigue fracture surfaces of PMMA have a number of features in common with fatigue fractures in metals. Most notable is the appearance of striations or ripple markings which delineate successive positions of the fatigue crack front. As in metals, the striations are formed during stage-II crack propagation by the blunting of the crack tip on the tensile stroke followed by resharpening of the crack tip on the subsequent compressive stroke.
X-Ray Studies on Preferred Orientation in Carbon Fibers
Authors: Ruland W.
Published: January 2005

The preferred orientation in carbon fibers of cellulosic origin as a function of the temperature of heat treatment has been determined by x-ray diffraction. It is shown that the preferred orientation in the starting material is destroyed with the destruction of the cellulose structure; only a very small orientation effect remains and stays nearly constant up to a heat-treatment temperature of about 1000°C. Further heating produces a reorientation which can attain and even surpass the degree of preferred orientation in the starting material. No evidence for a direct correlation between the preferred orientation in the starting material and the carbonized product has been found.
Nickel Ferrite Thin Films: Microstructures and Magnetic Properties
Authors: Brook R. J. , Kingery W. D.
Published: January 2005

Thin films of nickel ferrite (NiFe2O4) have been prepared by a reactive-sputtering technique using an iron-nickel alloy as the cathode and oxygen-argon mixtures as the reactive gas. Electron microscopy and electron-diffraction studies indicate that films deposited on substrates at temperatures below 0°C are noncrystalline whereas films deposited at higher temperatures are polycrystalline, the size of the crystallites increasing as the temperature is increased.

Measurements of electrical conductivity and magnetic susceptibility have been made on films prepared at various temperatures, and the results are interpreted in terms of film microstructure. In particular, the noncrystalline films show paramagnetic behavior, and the micropolycrystalline films show superparamagnetic behavior; ferrimagnetism is only found in films having a grain size greater than 150 Å and prepared at 400°C and above.
Dislocation Mobility in Copper
Authors: Greenman W. Frank , Vreeland Thad , Wood David S.
Published: January 2005

The velocity of dislocations of mixed edge-screw type in copper crystals of 99.999% purity has been measured as a function of stress at room temperature. Dislocation displacements produced by torsion stress pulses of microsecond duration were detected by etch pitting {100} surfaces. A nearly linear relationship between dislocation velocity and resolved shear stress was found. Stresses from 2.8×106 to 23.1×106 dyn/cm2 produced velocities from 160 to 710 cm/sec. These data give a value of the damping constant for high-velocity dislocations of 7×10−4 dyn·sec/cm2, in good agreement with the values deduced from internalfriction measurements. The results also agree, within experimental and theoretical uncertainties, with the phonon viscosity model for the mobility of dislocations.
Effect of Particle Size on the Colloid Band in CsBr
Authors: Jensen Richard E.
Published: January 2005

The effect of particle size on the half-width of the colloid band in CsBr is discussed. Boundary scattering of electrons predominated for small particles and radiation damping for large particles, yielding broad half-widths. For intermediate-sized particles, bulk relaxation effects predominated and the half-width was a minimum. Variations in the minimum half-width in different specimens and the lack of the expected temperature dependence indicated the presence of impurities in the colloidal particles. Electron-microscope observations revealed that the particles were spherical. The colloid band occurred at 1050 nm as compared with the predicted position at 960 nm. Comparison of the observed colloid-band positions in the alkali halides with the predicted positions reveals a systematic difference, the reason for which is not known.
Hall Effect in Thin Metal Films
Authors: Chopra K. L. , Bahl S. K.
Published: January 2005

Hall coefficient RH and Hall mobility μ have been measured for annealed polycrystalline and epitaxially grown gold, silver, and copper films at 296° and 77°K. At thicknesses above about 600 Å, nearly bulk values are obtained for RH and μ. Below 600 Å, a film-thickness dependence (size effect) was observed. This dependence is weak for epitaxially grown films, indicating a predominantly specular reflection of conduction electrons. On the other hand, the dependence is marked for polycrystalline films. Results on polycrystalline gold and silver films fit a predominantly diffuse scattering behavior. Data on carefully prepared polycrystalline films of copper agree well with Sondheimer's theory for perfect diffuse scattering so that best fit mean free path values can be calculated. In general, however, contrary to the theoretical predictions, RH was found to show a slight size effect even for film thicknesses greater than the electron mean free path (t>l). This departure may be the result of an oversimplified theory. The sharper decline of the Hall mobility for t<l in polycrystalline films than is expected theoretically may be attributed to enhanced crystallite-size boundary scattering.
Plasma Acceleration in an Electrical Discharge by the Self-Induced Magnetic Field
Authors: Malliaris A. C.
Published: January 2005

An electrical discharge is considered between two electrodes arranged axisymmetrically in the absence of an external magnetic field. Discharge currents are used up to 2500 A in a steady state and in the presence of a nitrogen-flow rate of the order of a few hundred milligrams per second. The interaction of the discharge with its self-induced magnetic field is examined and the importance of magnetoplasmadynamic effects in the acceleration of plasma is determined quantitatively. After a brief consideration of the analytical background several experiments are discussed and the corresponding results are analyzed. It has been determined that the self-magnetic field makes a substantial contribution, as high as 60% or higher in certain cases, to the acceleration of plasma. The particularly effective mechanism in these experiments seems to be the self-induced compression of the plasma in the discharge in front of the cathode. Further experimental results are presented from measurements of the momentum flux and of the velocity in the plasma flow. These measurements are constructively correlated with the forces which accelerate the plasma.
Structural Dependence of the Tracer-Level Diffusion of Thorium in Pyrolytic Carbons
Authors: Lonsdale H. K. , Graves J. N.
Published: January 2005

Tracer-level diffusion studies have been carried out on laboratory-prepared samples of pyrolytic carbons of widely divergent microstructure. These samples are well characterized and contain no exposed layer-plane edges. Using a 228Th tracer, diffusion coefficients have been measured perpendicular to the plane of deposition over the temperature range 1600° to 2000°C. The diffusion coefficients were found to have a significant dependence on microstructure, the diffusion coefficient in a highly oriented, laminar pyrolytic carbon being more than an order of magnitude smaller than that in either isotropic or granular carbons. The diffusion coefficient D, in cm2/sec, of thorium perpendicular to the plane of deposition in granular, isotropic, and laminar pyrolytic carbons is given by D=7.1×104 exp(−152 000/RT)  (granular),D=15.5 exp(−114 000/RT)      (isotropic),D=1.2×104 exp(−157 000/RT)  (laminar).

The tracer-level diffusion coefficients for thorium in the laminar pyrolytic carbon were substantially smaller than the values that have been reported by others for diffusion in highly anisotropic, columnar pyrolytic carbon. Microstructural parameters, such as apparent crystallite size and anisotropy factor, are useful in correlating the present results but are of limited value in quantitatively rationalizing the large variations in diffusion coefficients.

Measurements of the tracer-level diffusion coefficient of thorium in a polycrystalline graphite were also performed.
Fast-Randomization Phenomena in an Unstable Plasma-Sac Configuration
Authors: Hoyaux M. F. , Williams E. M.
Published: January 2005

Results of a detailed experimental study of conditions in and about a plasma sac formed at a constriction in a discharge column are reported. An evolution of phenomena is initiated by the application to the discharge column of a high-current pulse, which in combination with a low steady-state pressure produces a marked depletion of neutral-gas atoms. This depletion causes a high voltage drop to develop across the double sheath which bounds the plasma sac and a resultant high acceleration of the electron gas toward the constriction. The Mach number increases; when it approaches a critical value, of the order of or slightly greater than unity, extremely rapid randomization of the electron velocities ensues. Concurrently, the Mach number is stabilized near unity over a substantial range of increase of the voltage drop which is accelerating the electrons. A tentative explanation is included.
Optical Investigation of Magnetically Induced Elastic-Wave Dispersion in YIG
Authors: Dixon R. W.
Published: January 2005

Optical beam probing techniques utilizing Bragg diffraction from elastic waves have been used to explore the phenomenon of elastic-wave dispersion in yttrium iron garnet. Rotatory dispersion (acoustic Faraday effect) two orders of magnitude larger (approx. 220 rad/cm) than previously reported was obtained. Large group-velocity dispersion has also been observed, (group velocities as slow as one-half the normal value) and combined with the Faraday rotation measurements to permit the direct, independent, determination of values of the second magnetoelastic constant and the internal magnetic field. The dependence of the latter on position along the axis of the sample is obtained without computation or knowledge of the demagnetizing fields.
Exchange Anisotropy in Oxidized Permalloy Thin Films at Low Temperatures
Authors: Hagedorn F B.
Published: January 2005

Oxidized Permalloy thin films exhibit uniaxial anisotropy at room temperature, but at low temperatures develop a mixture of uniaxial and unidirectional anisotropies. Exchange coupling between the ferromagnetic permalloy and the antiferromagnetic oxide, at temperatures below the latter's Néel temperature, account for this phenomenon. New observations and interpretations of low-temperature hysteresis-loop effects in oxidized Permalloy films are reported in this paper. The initial susceptibility in the original uniaxial hard direction has been measured at 4.2°K for various combinations of Permalloy and oxide-layer thicknesses. While the results are found to be in qualitative agreement with a model based on a simple mixture of anisotropies, a semiquantitative understanding is found possible only after assuming that reversal of the Permalloy magnetization direction also reverses the spin orientations in a large fraction of the antiferromagnetic material. For very thin (∼10 Å) oxide layers, this fraction is larger than 9/10, but it drops to about ½ for 60-Å layers. The observed reduction in hysteresis loss as the oxide thickness is increased is also consistent with this model. An example is given where the unidirectional anisotropy is sufficiently large so that the magnetic structure has only one stable remanent state. This same structure is shown to exhibit a new property of ferromagnetic-antiferromagnetic coupling recently reported by Paccard et al. Finally, the temperature dependence of the hysteresis loops above 4.2°K is discussed. It is concluded that exchange anisotropy serves as a basis for understanding the many anomalous effects which have been observed.
Thermal Properties of Gold-Silicon Binary Alloy near the Eutectic Composition
Authors: Chen H. S. , Turnbull D.
Published: January 2005

We have measured the specific heat Cp and the enthalpy of Au-18.6 at.% Si alloy in some of its various forms. Cp of the liquid form falls continuously with increasing temperature from 8.38±0.05 at 563°K, corresponding to an undercooling of 73°K, to 7.90±0.05 cal/gfw·°K, and it exhibits no singular behavior at the melting temperature Tm. It exceeds the heat capacity of the eutectic solid by 1.87 cal/gfw·°K at Tm. This high specific heat in the liquid state and its decrease with increasing temperature is attributed principally to the configurational entropy, as has been suggested for the pure liquid metals. Cp of the amorphous alloy, formed by rapidly chilling the liquid, was measured for the temperature range from 208° to 278°K. It rises slowly to 225°K, then falls, and then rises again with increasing temperature. It exceeds Cp of the eutectic solid by 0.2 to 0.4 cal/gfw·°K. Cp of the metastable intermetallic crystalline phase, formed when the liquid is less rapidly chilled, falls between the values for the eutectic and the amorphous solids.

The intermetallic phase melts at 631°K, which is only a little lower than the melting point, 636°K, found for the eutectic mixture. Its heat of fusion ΔHf is 1.59 kcal/gfw, while that of the eutectic mixture is found to be 2.35±0.1 kcal/gfw. The heat and excess entropy of mixing of the liquid elements to form the liquid alloy at 1336°K are evaluated to be −1.6±0.1 kcal/gfw and 0.39±0.17 cal/gfw·°K, respectively. The especially deep-lying eutectic exhibited by this system is attributed to the tendency for unlike atoms to associate when in the metallic state, in contrast with the strong tendency for phase separation in the solid state owing to the high stability of silicon in its covalent crystalline form.
Transmuted-Center Fermi-Level Spectroscopy in Slow-Neutron-Irradiated ZnO
Authors: Lindeberg G. K.
Published: January 2005

Measurements of resistivity vs time and temperature between 70° and 300°K were made on an n-type ZnO crystal which had been irradiated in a slow neutron-integrated flux of 4.1×1020 cm−2. During the course of the measurements, the crystal was transmutation doped by the 245-day half-life decay of 65Zn to 65Cu. 69Ga was also present in the crystal, as the daughter of the shorter-lived 69Zn. The data were treated using a phenomenological theory of transmuted-center Fermi-level spectroscopy (TCFLS) based upon assumptions of sample homogeneity, electron-system equilibrium, filled transmuted acceptors, and linear relation at constant temperature between Fermi level and log10 resistivity. The data are consistent with a 69Ga-donor model, two levels of which are resolved by the TCFLS technique. The results illustrate the potentiality of TCFLS for determination of semiconductor forbidden-band state parameters, and also for carrier microscopic-mobility determination. Two model parameters, corresponding to the concentrations of the shallow forbidden-band states, were determined to within 3% standard error.
Superconductivity of Cd–Bi Eutectic Solder
Authors: Fassnacht R. E. , Dillinger J. R.
Published: January 2005

Measurements are presented which show that the superconducting transition temperature of a eutectic alloy of Cd–Bi is 0.53°K in zero magnetic field. Critical-field measurements are given from which (dHc/dT)T=Tc is found to be 91 Oe/°K. These results are discussed in terms of the phase diagram of the Cd–Bi system and in terms of the use of Cd–Bi eutectic as a solder in constructing apparatus for use at very low temperatures.
Electron Microscope Study of the Morphology of Lithium Fluoride Surfaces following Dissolution in Dilute Aqueous Solutions of Ferric Ions
Authors: Ramachandran T. R. , Ives M. B.
Published: January 2005

High-resolution replica electron microscopy has revealed a complex structure of surface ledges on {100} cleavages of lithium fluoride crystals after etching in dilute aqueous solutions of ferric chloride. Ledge heights vary from approximately 400 Å in etchant containing 0.1 ppm ferric ions and are unresolvable at greater than 2 ppm ferric ions. The ledge density is also modified with change in ferric ion content, and this has been related to previous studies of inhibitor adsorption in this system. It is proposed that the ledge structure is due to irregular inhibition by the ferric ions, and the results have been compared with recent theoretical and experimental studies of crystal dissolution.
Optical Effects in Metals: Application of a Least-Squares Method to Measurements on Gold and Silver
Authors: Meyer Erhard , Frede Heike , Knof Hans
Published: January 2005

Optical constants of optically thick gold and silver films evaporated onto a quartz plate under high vacuum, were measured by the ellipse method of Drude. A least-squares method, including iteration, was applied to data obtained with the rather simple apparatus; values for the optical constants thus calculated agree with existing values obtained by more elaborate methods.
Pressure Dependence of High-Temperature Creep in Single Crystals of Indium
Authors: Chevalier G. T. , McCormick P. , Ruoff A. L.
Published: January 2005

The activation volume for the high-temperature steady-state creep of high-purity single-crystal indium in the pressure range of 0.8–5.5 kbar has been obtained using the change-of-slope method. The activation volume obtained is 12.0±0.9 cm3/mole, which corresponds to 0.76 atomic volume.
Liquid and Solid Cesium on a Rhenium Substrate
Authors: Webster Harold F.
Published: January 2005

Cesium metal has been deposited from the vapor on a large-grained rhenium substrate. Both the wetting of the substrate by the cesium and the mode of growth of solid films of cesium are dependent upon the crystal face exposed by the various grains of rhenium. The experiment was done in a sealed-off glass tube which had a residual gas pressure of 10−9 Torr before cesium was admitted. Both the wetting and the mode of film growth were dependent upon monolayer amounts of impurities. Epitaxial relationships were observed to exist between many of the rhenium grains and the deposited cesium.
Avalanche-Photodiode Frequency Response
Authors: Emmons R. B.
Published: January 2005

The short-circuit photocurrent from an avalanche photodiode is calculated using an exact solution of the differential transport equations for the multiplication region. The dc electric field and the hole and electron velocities are assumed constant in the avalanche region into which photoelectrons are injected. It is shown that the electron- and hole-ionization coefficients α and β remain constant over a practical range of multiplied photocurrents. Computer studies of the solution show that avalanche multiplication does not reduce the device bandwidth as long as the dc multiplication M0 is less than the ratio of α and β, i.e., as long as M0<α/β. The previously obtained frequency dependence of the multiplication, M(ω) = M0[1 + ω2M02τ12]−1/2, which indicates a constant-multiplication bandwidth product, is now shown to be valid only if M0>α/β. The previously unspecified ``effective'' transit time, τ1, in this equation is approximately τ1 = N(β/α)τ, where N is a number varying slowly from ⅓ to 2 as β/α varies from 1 to 10−3, and τ is the multiplication-region transit time.

The complete solution of this problem thus shows that the widely different results previously obtained for β/α = 0 and β/α = 1 are continuously joined, and provides a simple criterion for judging the ranges of validity of the two limiting cases. The results emphasize the practical importance of obtaining the required multiplication at fields such that M0<α/β where the multiplication does not affect the bandwidth. This also leads to minimum excess avalanche-region noise, and hence to the closest possible solid-state analog to the vacuum-tube photomultiplier.
Thermal and Optical Energy Gaps in Pb0.93Sn0.07Te and Pb0.85Sn0.15Te
Authors: Tauber R. N. , Cadoff I. B.
Published: January 2005

The optical absorption edge (indirect energy gap) was determined for Pb0.93Sn0.07Te and Pb0.85Sn0.15Te in the temperature range from 80° to 520°K. The variation of Eg with temperature indicated that two valence bands were operative. Below 300°K, linear variation of bandgap with temperature was observed yielding values of dEg/dT of 3.0−3.4×10−4 and 2.9−3.3×10−4 eV/°K for the Sn0.07 and Sn0.15 alloys, respectively. Above 400°K, dEg/dT was zero for both. The 0°K extrapolated values of Eg were 0.162 and 0.113 eV for the low-temperature range and about 0.28 and 0.24 eV for the high-temperature range, for Sn0.07 and Sn0.15, respectively. Electrical resistivity data obtained in the intrinsic range (above 500°K) yield thermal energy gaps of 0.30 and 0.23 eV for Sn0.07 and Sn0.15, respectively. A proposed band model for SnTe based on the compositional dependence of the energy gaps is presented.
ac Electrical Breakdown in Thin Silicon Oxide Films
Authors: Klein N. , Levanon N.
Published: January 2005

Silicon oxide capacitors were produced by vapor deposition in vacuum on glass slides. On the application of ac voltages in the frequency range 10 to 50 000 cps, single-hole breakdown, propagating breakdown, and maximum voltage breakdown events were observed. The processes in these breakdown events and the destruction were analogous to those occurring on dc. However, the peak value of the ac maximum dielectric strength, Fam, was found to be 10%–20% larger than the dc maximum dielectric strength Fdm; this is in contrast with the much larger dc strength found for thick insulations. Good agreement was found between observations and between calculated values of Fam and Fam/Fdm. Fam of the samples tested ranged from 1.75 to 6.9 MV/cm. Above 1−10 kc/sec, Fam decreased quasilinearly with frequency due to dielectric loss. At frequencies <10 cps, Fam decreased, probably due to temperature ripple. A small decrease in Fam is also caused by large series resistors.
Superparamagnetic Magnesioferrite Precipitates from Dilute Solutions of Iron in MgO
Authors: Wirtz G. P. , Fine M. E.
Published: January 2005

Superparamagnetic magnesioferrite particles were precipitated from MgO containing approximately 1 cation % Fe, by aging at 700° and 800°C. The composition was determined to be Mg1.2Fe1.8O3.9 and the spontaneous magnetization at 0°K was 330 emu cm−3. The cation distribution and Curie temperatures were found to depend only on aging temperature, and not on aging time or solution-treating temperature. Curie temperatures of 520° and 490°K were measured on samples aged at 700° and 800°C, and the fraction of iron ions on tetrahedral sites within the precipitate was 0.36 and 0.35, respectively. The saturation magnetization is higher, the Curie temperature is lower, and the fraction of iron ions on tetrahedral sites is less than in bulk stoichiometric MgFe2O4.
Magnetoelastic-Elastic Wave Scattering
Authors: Comstock R. L. , Kusnezov N.
Published: January 2005

The scattering of plane-circularly polarized magnetoelastic and elastic waves from a discontinuity surface is analyzed. The magnetic and elastic boundary conditions at the surface of a ferromagnetic medium used in the scattering analysis are discussed. The theory is used to explain certain echos observed in magnetoelastic-elastic delay lines, and new experiments are described in which magnetoelastic waves propagating in a YIG cylinder are scattered to elastic waves propagating in a rutile cylinder.
Formulas for Phase Velocity and Damping of Longitudinal Waves in Thick-Walled Viscoelastic Tubes
Authors: Klip Willem , Van Loon Pieter , Klip Dorothea A.
Published: January 2005

The frequency equation for longitudinal waves in a viscoelastic tube of infinite length filled with a viscous fluid is solved for the complex wavenumber, k(=k1+ik2). Thus for two modes, Young's mode and Lamb's mode, an explicit expression for k is obtained which yields the phase velocity c(=ω/k1, ω=radial frequency) and the damping constant k2. The formulas for k, c, and k2 are valid for wall thicknesses up to the size of the inner radius of the tube. The approximation as compared with results obtained numerically with an IBM 7040 digital computer from the original frequency equation involves an error which in almost all cases is considerably less than 1.5%. For Lamb's mode, as it was found earlier for the torsional mode, an increase of the fluid viscosity increases the damping at the higher frequencies but decreases the damping at the lower frequencies. The theoretical results are compared with those of experiments in which the longitudinal waves are generated in the fluid and the fluid in its turn moves the wall. The experimental curves thus obtained show the pattern of Young waves, and the agreement with the Young curves obtained from the formulas mentioned above is satisfactory. For torsional waves, formulas for k, c, and k2 analogous to these for longitudinal waves are given.
Nucleation Rate of Vacancy Clusters in Aluminum
Authors: Davis T. L.
Published: January 2005

A small disk of vacancies is used as the critically sized cluster for the formation of dislocation loops in quenched aluminum. Application of steady-state nucleation theory to this model yields a coherent description for the nucleation of single and multiple loops which is in agreement with several different sets of experimental data. It also defines the important variables and predicts their effect in the nucleation process.
Ion Cyclotron Resonance Line Broadening at High E/P
Authors: Wobschall Darold C. , Fluegge Robert A. , Graham John R.
Published: January 2005

Observations were made of ion cyclotron resonance absorption linewidths and shapes at values of E/P up to 400 V/cm·Torr. Three methods of heating the ions are compared. If the detector rf electric field is used to heat the ions, the line shapes are distorted and not well suited for simple interpretation. With the dc heating method, the line shapes are close to Lorentzian and the collision cross section as a function of E/P can be determined from the increase in linewidth as a function of pressure. For He+ in He at E/P = 100 V/cm·Torr, the cross section is 30 Å2, in fair agreement with previous studies. By heating with a separate oscillator fixed at the cyclotron frequency, similar line broadening is observed, but a dip appears at the center of the absorption line. This dip is attributed to a nonlinear dependence of collision frequency on electric field, and is enhanced by the strong dependence of the ion concentration on collision frequency under steady-state diffusion conditions.
The uv Absorption Edge of Tin Oxide Thin Films
Authors: Spence Wendell
Published: January 2005

The absorption edge spectrum of thin films of SnO2 has been obtained at room temperature using unpolarized light. The dependence of the absorption coefficient upon film resistivity has been noted and an impurity peak at about 3.4 eV has been observed. The measurements suggest an indirect edge near 2.7 eV and a direct edge near 4.3 eV.
Ultrasonic Attenuation in Ge–Si Alloys
Authors: Keller K. R.
Published: January 2005

Measurements of the ultrasonic attenuation of 0.64- and 3.1-GHz compressional waves in Ge–Si alloys show a decrease in the attenuation with alloying. Simple theory predicts that the ultrasonic attenuation of compressional waves in insulators is proportional to thermal conductivity. In Ge–Si alloys, there is a large reduction in the thermal conductivity with alloying. However, the observed reduction in attenuation is appreciably smaller than the decrease in thermal conductivity. When the Ge–Si alloys are doped with Fe beyond the solubility limit, a peak in the attenuation-vs-temperature curve is observed at low temperatures. This peak is attributed to the presence of excess Fe, which is precipitated out in planes arranged in a near-periodic fashion.
Pressure and Temperature Effects on the Viscosity of Liquids
Authors: Frisch David , Eyring Henry , Kincaid John F.
Published: January 2005

The free energy of activation for viscous flow is related to an entropy and energy of activation by the same equations as any equilibrium. This, for the theory of viscosity is perfectly general and independent of the mechanism. The rolling over each other of pairs of molecules lying in adjoining layers is the mechanism which appears to be the most probable, and the equations for this bimolecular flow process are developed here. At low pressures the heat of activation for viscous flow is about one-third the energy of vaporization, but as the pressure is raised, it increases rapidly because of the work term, P V/n′. Here P is the external pressure, V is molal volume and V/n′ is the extra volume required before the flow process can take place. Calculations made for n-pentane, ether, benzene, iso-pentane, water, and mercury over as extended a temperature and pressure range as the data permit are found to agree satisfactorily with the experimental viscosity. The results are interpreted in terms of the liquid structure and the mechanism of viscous flow. The results of applying our theory to the liquids for which the necessary data is available show that the effect of pressure on viscosity can be calculated a priori, with thermodynamic data only, with reasonable success.
Cuprous-Cupric Oxide Films on Copper
Authors: Cruzan C. G. , Miley H. A.
Published: January 2005

The influence of film thickness on the formation of cupric oxide in cuprous oxide films on an abraded copper surface was studied from measurements obtained by the electrolytic reduction method. The critical thickness value for the formation of cupric oxide in the films appeared to be near 600A for a commercial copper, and the critical thickness range was found to be approximately 400 to 800A. The thicknesses resulting from heating specimens in different atmospheres, for a given time, increase with the oxygen concentration. The time required to produce films of a given thickness decreases as the oxygen concentration increases. Murison's observations concerning the conditions favorable to the formation of cupric oxide in the films at a higher temperature were extended to include the proper period of heating and film thickness as well as oxygen concentration. Dunholter and Kersten's electron diffraction analyses of copper oxide films on mirror-like surfaces were considered to be in satisfactory agreement with the present results.
On the Resistance to the Uniform Motion of a Solid Through a Viscous Liquid
Authors: Block Raymond B.
Published: January 2005

This paper is a report on an experimental investigation of the resistance to the uniform motion of a solid through a viscous liquid, the results of which appear to indicate that the liquid slipped on the surface of the solid. The apparatus was a straight, closed, glass tube containing a steel ball and the liquid being studied. The tube was arranged so that it could be inclined at various angles with the horizontal, and the only motion of the ball that was considered in working up the observations was one of pure rolling. The liquids employed were mixtures of glycerine and methyl alcohol. The analysis of the data is based upon Stokes' and Oseen's forms of Rayleigh's law of resistance, and the results of the investigation are interpreted in the light of theories due to A. B. Basset and to H. Brillié.
Preparation of High Melting Alloys with the Aid of Electron Bombardment
Authors: Hultgren Ralph , Pakkala M. H.
Published: January 2005

An electron bombardment furnace was constructed for high temperature melting. The temperature attainable is limited only by the refractoriness of the crucible; a tantalum cup (m.p. 2850°C) was melted with the expenditure of only 700 watts. Degassing of sample and surroundings causes gas discharge if the rate of heating is too rapid. Metals volatile at their melting point cannot be melted, but this applies to only a few metals such as manganese and palladium. Alloys of platinum with tungsten, molybdenum, and cobalt are now being successfully prepared for x-ray investigation. The tendency of some metals to react with available refractory crucibles needs further study before their alloys can be prepared.
The Measurement of Solid Friction of Plastics
Authors: Gemant Andrew
Published: January 2005

In view of the increasing importance of synthetic plastic materials, a method is developed to measure their vibrational damping in a wide range of temperature up to fairly high plasticity. The method and its results should be useful both from a physical and technical standpoint.
The Dielectric Properties of the Rutile Form of TiO2
Authors: Berberich L. J. , Bell M. E.
Published: January 2005

Three specimens of rutile were prepared and the dielectric properties studied over a range of frequency and temperature. A dielectric constant of approximately 100 was found which remained substantially constant through the highest radiofrequencies, falling off only in the infra-red region. The dielectric losses are low, particularly at the higher frequencies. The dielectric constant decreases with increasing temperature, having an average temperature coefficient of −8.2×10−4/°C. An exponential relationship between conductivity and the reciprocal of the absolute temperature holds for rutile in the higher temperature region. Mixtures of rutile powder with other dielectric materials obey a logarithmic mixture formula. Two mechanisms which have been proposed to explain the high dielectric constant of rutile are discussed. A simple mechanism based on the Clausius-Mosotti equation is described.
Notes on the Power Factor Testing of Long Lengths of Cables
Authors: Walker Eric A.
Published: January 2005

The ratio of watts to volt-amperes does not give the power factor of long cables because of the resistance of the conductor and sheath. The error involved varies as the length squared and might be quite appreciable at lengths of 10,000 feet. Correction factors are given involving the use of an infinite series for exact results and a simple algebraic formula for approximate results.
Stress Analysis by Three-Dimensional Photoelastic Methods
Authors: Drucker Daniel C. , Mindlin Raymond D.
Published: January 2005

This paper describes the results of an investigation and extension of the various proposed procedures and methods of analysis for the photoelastic determination of three-dimensional states of stress. Two important limitations of the previous developments are removed. A true extension to three dimensions is given by the determination of the effect on retardation of appreciable variation in the orientation of the secondary principal stresses in planes perpendicular to the wave normal (such variation being the rule rather than the exception for general states of stress). Also, methods for the analysis of whole planes are presented, thus avoiding the cumbersome and tedious point by point procedures that have been advanced. In the particular case of plane stress, these methods reduce to a purely optical technique for determining the principal stresses themselves, or more easily their sum, for the entire model.
Atomic Distribution in Aluminum-Silver Alloys During Aging
Authors: Barrett Charles S. , Geisler Alfred H.
Published: January 2005

Laue photographs of aluminum-rich aluminum-silver crystals during aging at 20° and 150°C show more or less clearly defined streaks along certain zonal ellipses, in addition to the streaks caused by thermal agitation. These have been analyzed by stereographic and reciprocal lattice projections and are found to result from two-dimensional gratings parallel to planes of the form {111}. The streaks with 20° aging are more diffuse than with 150° aging; no streaks were found with 200° aging. When the precipitate lattice is fully developed, it yields sharp spots along the streaks at positions predicted from earlier studies of the Widmanstätten structure; preceding this state there exist very thin plate-like nuclei on randomly spaced {111} planes, which govern the orientation and shape of the fully developed precipitate. These may consist of (a) clusters of silver atoms or (b) imperfect lattices caused by (111) layers of atoms shifting parallel to themselves as required for the transformation from the face-centered cubic to the hexagonal close-packed lattice but with the shifting occurring on random planes, thus destroying the lattice periodicity normal to these planes.
Studies in Lubrication IX. The Effect of the Pressure Variation of Viscosity on the Lubrication of Plane Sliders
Authors: Muskat M. , Evinger H. H.
Published: January 2005

The Reynolds theory is applied to the calculation of the lubrication properties of plane sliders—thrust bearings—of infinite width provided with lubricants whose viscosities increase exponentially with the pressure. The friction coefficient, minimum film thickness, and lubricant flow were calculated both for fixed wedge angle and pivoted sliders. The effect of the viscosity variation with pressure is determined by the magnitude of the dimensionless product of the viscosity-pressure exponent and the bearing load per unit area. The analysis shows that for each choice of this product there will be a limiting position of the pivot line of the slider or of the equivalent Sommerfeld variable at which the film pressures and friction forces will become infinite, and beyond which it will be impossible to operate the slider. Moreover this product is shown to be limited by a maximum value equal to 2, which means that the absolute maximum load per unit area which can be carried by such slider systems is equal to twice the reciprocal of the viscosity-pressure exponent. Specific calculations on the friction properties of bearings operating with lubricants of different viscosity pressure exponents give curves of friction coefficient vs. load or Sommerfeld variable quite similar to those observed in practical tests. At high loads or low values of the Sommerfeld variable the friction coefficient curves split and follow the behavior generally interpreted in terms of oiliness and boundary lubrication phenomena.
The Flow of Air Through Porous Media
Authors: Sullivan R. R. , Hertel K. L.
Published: January 2005

The values of the constant in the equation which relates permeability of a porous medium to the porosity and specific surface of the medium are determined for three cases. These experimental values are found to be consistent with the theoretical indications of Fowler and Hertel.
Spark Gaps with Short Time Lag
Authors: Slepian Joseph , Berkey W. E.
Published: January 2005

Short spark gaps (order of one mm) in air at atmospheric pressure, unless specially radiated, show large spark lag when tested at little above the sparking potential. In engineering literature this property is measured by the impulse ratio, i.e., the ratio of the voltage at which breakdown occurs under a voltage surge rising at a specified rate (about 50 kilovolts per microsecond), to the voltage at which breakdown occurs with slowly increasing impressed 60-cycle voltage. The spark lag shows statistical variations, and its mean has been shown to be nearly equal to the mean time for emission of an electron from the cathode, prior to the spark. The electron current from the cathode prior to the spark is greatly increased by the presence of a pointed projection on the cathode, so that the mean spark lag at a given voltage is greatly reduced. However, if a single pointed projection is used, of sufficient size to reduce the spark lag at a given voltage, it also reduces the 60-cycle sparking potential, so that the impulse ratio, which is the quantity important in engineering applications, is not reduced. By using a very large number of extremely small pointed projections on the cathode, the spark lag can be reduced without appreciable lowering of the 60-cycle sparking potentials. Thus impulse ratios little greater than unity can be obtained. Small particles of carborundum, rutile, alumina and porcelain, of various sizes were attached to the cathodes of spark gaps, and the impulse ratios tested. Minimum impulse ratios were obtained when the particle linear dimensions were between 2×10−3 and 15×10−3 cm.
Changes in the Absorption Spectrum of Pb and Ni Films at Low Temperatures
Authors: Squire Charles F.
Published: January 2005

The temperature dependence (298°K to 80°K) of the absorption spectrum of Ag, Cu, Cd, Al, Sn, Sb, Pb, and Ni has been studied. Only Pb and Ni showed a relative change; Pb films transmit more ultraviolet light at 80°K than at 298°K, Ni films transmit less visible light at 80°K than at 298°K.