bluuebunny/crossref_metadata_2025 huggingface dataset:
Approximate Solution for the Strain-Induced Deviation of the Magnetization from Saturation in Polycrystalline Cubic Ferrites
Authors: Bartel L. C.
Published: February 2004

The strain-induced uniaxial magnetic anisotropy can cause a deviation in the magnetization from saturation along the applied magnetic field. An approximate variational solution is found for the necessary threshold strain or stress and for the amplitude of this deviation in thick, semi-infinite slabs of cubic polycrystalline ferro- or ferrimagnetic materials. The resulting solutions are compared to solutions obtained from the linearized Brown's equations for equilibrium. Specific calculations are made for nickel ferrite, YIG, and magnetite.
Ferromagnetic Resonance in Si-Doped YIG
Authors: Hartwick T. S. , Smit J.
Published: February 2004

The magnetocrystalline anisotropy of Fe2+ ions in YIG has been studied by means of FMR at 10 and 30 GHz at temperatures between 4° and 400°K. Below 50°K strong magnetic anneal occurs. Anneal fields were in the [100], [111], and [110] directions. The g factor is 1.98 at 4.2°K and 1.96 at 290°K. At low temperature the resonance field HR is less than ω/γ by as much as 2000 Oe for all orientations in the (110) plane. The HR versus angle curves are explained quantitatively by taking into account canting of the spins around the Fe2+ ions as well as perturbing electrostatic fields of the neighboring Si ions. The correct temperature dependence and anisotropy of the linewidth ΔH also follow from the model calculation.
Effect of Processing on Permanent Magnet Materials Containing Rare-Earth Metals
Authors: Nesbitt E. A. , Chin G. Y. , Sherwood R. C. , Wernick J. H.
Published: February 2004

It is established that the new rare-earth permanent magnet alloys containing copper show precipitation effects during heat treatment. Alloys drastically quenched from a high temperature had a comparatively low value of coercive force which increased substantially upon aging at a lower temperature. Also, upon aging, it was observed optically that a precipitate formed. These effects permit considerable latitude in the heat treatment of the alloys. Experiments on coarse powders showed that useful permanent magnet properties can be obtained with alloys in this form. Oriented coarse powder compacts which are stable in air having intrinsic coercive forces at 17 000 Oe have been made.
Hertzian Fracture Experiments on Abraded Glass Surfaces as Definitive Evidence for an Energy Balance Explanation of Auerbach's Law
Authors: Langitan F. B. , Lawn B. R.
Published: February 2004

The question of the physical interpretation of Auerbach's law, that the critical load for production of a Hertzian cone fracture is proportional to the radius of the indenting sphere, has aroused interest in recent years (i) because of its implications concerning the validity of certain brittle fracture criteria and (ii) because of its potential use as a means for measuring fracture surface energies. Two distinct schools of thought, one based on a flaw statistical model and the other on an energy balance concept, have emerged as a result of various attempts to account for this law. This paper describes a theoretical and experimental study aimed at testing the validity of each of these two approaches. Whereas quantitative Hertzian fracture tests have hitherto been extensively made only on surfaces of carefully handled specimens, such as commercial plate glass in the as-received state, in the present case they are made on plate glass surfaces treated by an abrasion process. With as-received surfaces the obscure nature of the distribution of surface flaws, from which the cone cracks initiate, largely precludes a conclusive comparison between the two theoretical approaches, while for abraded surfaces the experimentally justifiable assumption that the flaw distribution is ``uniform'' leads to simple but widely conflicting predictions from the two approaches, thus providing the basis for a definitive experiment. According to a flaw statistical argument, in conjunction with an empirical critical stress criterion for fracture, Auerbach's law is predicted to break down for tests on uniformly damaged surfaces, with the critical load for cone fracture becoming a sensitive function of the depth of the damage layer. On the other hand, a stepwise application of Griffith's energy balance criterion for fracture to the growth of a cone crack through the inhomogeneous Hertzian stress field predicts strict adherence to Auerbach's law within limits of indenter size, with the Auerbach constant of proportionality in this law being independent of flaw statistics. Static and impact tests, made with steel balls ranging from 0.08 to 1.9 cm in radius on plate glass surfaces abraded with slurries of Nos. 240, 320, 400, and 600 SiC abrasive powder, confirm the essential constancy of Auerbach's law, thereby providing strong evidence for the energy balance explanation. Moreover, it is found that the abrasion treatment leads to a drastic reduction in the scatter in results; as a result variations of less than 10% in the fracture surface energy, which is proportional to the Auerbach constant, should be detectable in experiments performed on a given material under different test conditions.
Strain-Rate Dependence of the Tensile Failure of a Polycrystalline Material at Elevated Temperatures
Authors: Wray P. J.
Published: February 2004

A general discussion is presented of the failure modes which can occur in uniaxial tensile tests of a polyphase, polycrystalline material at various strain rates at elevated temperatures. Specific results in the temperature range 0.56–0.70Tm are given using Type 316 stainless steel as a representative material. The intrinsic plastic failure is determined solely by plastic deformation, leading first to necking and concluding by separation at a point. However, this intrinsic plastic failure may be interrupted at relatively high strain rates by the formation of cracks at inclusions within the neck. At low strain rates the onset of appreciable necking is postponed and the whole failure process is determined by intergranular crack formation. At intermediate strain rates intergranular cracks form within the neck, and a shear mode of failure is possible. Some conclusions regarding future studies are included.
Preparation of SmCo5 Permanent Magnets
Authors: Buschow K. H. J. , Naastepad P. A. , Westendorp F. F.
Published: February 2004

The technology of making SmCo5 magnets with energy products of 20 × 106 GOe is described. This technology consists of the preparation of a powder by grinding, aligning the powder particles in a magnetic field, and cold pressing by applying a uniaxial deformation at 20 kbar. The permanent magnetic properties of the SmCo5 powders are shown to vary appreciably with various applied chemical treatments and with the composition of the alloy. The intrinsic coercive force appears to decrease with time but remains so large that the demagnetization of the induction is hardly affected. Some properties of the magnets are discussed.
Perturbation of the Refractive Index of Absorbing Media by a Pulsed Laser Beam
Authors: Longaker P. R. , Litvak M. M.
Published: February 2004

The effects on the index of refraction of various media due to energy absorbed from a long-pulsed and a Q-switched Nd-doped glass laser are investigated with a Mach-Zehnder interferometer. These effects are reasonably well predicted from the temperature coefficient of the index and the heat capacity of the media. Sonic waves generated by the Q-switched laser are observed in cases for which either heating or electro-striction is dominant.
Parametric Tuning of Laser-Stokes Sum Frequencies
Authors: McCray J. A. , Bunkenburg J.
Published: February 2004

The angular dependence of one-dimensional first (OOE) and second (OEE) index matching has been investigated for optical parametric mixing of Nd:glass laser and SRS Stokes beams from a CS2 or nitrobenzene Raman cell in a room-temperature KDP crystal. The laser and Stokes electric vectors are decomposed in the nonlinear crystal into their ordinary and extraordinary components and the various components are mixed to produce a sum frequency extraordinary wave at the predicted index-matching angles. Seven sum frequencies in the visible have been obtained for the case of CS2 at 512, 531, 550, 571, 594, 618, and 644 nm. The laser-Stokes optical parametric mixer has been found to be a simple, noncritical, discretely tunable laser source in the visible.
Scattering of Coherent Light from Nematic Liquid Crystals in the Dynamic Scattering Mode
Authors: Deutsch Ch. , Keating P. N.
Published: February 2004

Measurements of the scattering of laser light by anisylidene-para-amino-phenylacetate (APAPA) in the ``dynamic scattering'' mode associated with the passage of electric current have been made. The results have been interpreted by means of a model in which the light scattering is due to amplitude and phase modulation resulting from orientation fluctuations induced by the current flow. Coherence distances for the liquid crystal film are derived which are expected to give an inverse measure of the turbulence in it. The coherence distances are found to depend very strongly on the polarization of both incident and scattered light and to decrease markedly with either increased applied voltage or increased thickness; these results are explained in terms of the theoretical model.
Some New Considerations Concerning an Accelerated Superconducting Solenoid
Authors: Baum P. J.
Published: February 2004

An idea by Winterberg to accelerate a superconducting solenoid to hypervelocities in a magnetic traveling-wave accelerator is examined in more detail. Approximate calculations are done to determine the relative importance of diamagnetic effects as compared to fixed magnetic moment effects due to a persistent current in a type II superconductor. It is concluded that fixed magnetic moment effects predominate at very high magnetic field gradients. For the particular configuration considered the accelerator length must be increased about 5% or 3% depending on whether the diamagnetic and fixed magnetic moments are parallel or anti-parallel, respectively.
Pulsed Langmuir Probe Measurements in a Helium Afterglow Plasma
Authors: Blue E. , Stanko J. E.
Published: February 2004

The electron-temperature history and density decay rate of a 1 Torr pulsed helium afterglow plasma has been studied with electrostatic probes. The plasma was repetitively formed by electrodeless rf break-down at 21 MHz. A cylindrical double probe was positioned at the center of the plasma and, in addition, two large metal electrodes were mounted on the inner cylindrical walls of the plasma container. The arrangement of electrodes allowed for both symmetric double-probe measurements and single-probe measurements. A new pulsed probe technique was developed which makes it possible to limit the plasma depletion by the probe to that of a floating probe. At early times in the afterglow (0≤t≤2 msec) the electron energy distribution was found to be non-Maxwellian with two energy groups of electrons. At late times in the afterglow the electron energy distribution was found to be Maxwellian with a temperature corresponding to the ambient temperature. In the case of the single-probe measurements the accuracy of the temperature determination is a new result which indicates that a correct collisional probe model must predict a linear region in the semi-logarithmic plot of the probe characteristic.
Radiation Characteristics of an Electric Dipole in a Warm, Anisotropic Plasma
Authors: Chen Hollis C.
Published: February 2004

By means of the dyadic Green's function method, a formula is derived for the impedance matrix of an electric-current source immersed in a warm plasma under the influence of an external static magnetic field. A dispersion equation is given. The results are expressed in terms of the components of the compressivity and the permittivity tensors. It is shown that the power radiated by an electric dipole in such a medium can be written as the Hermitian form associated with the impedance matrix. Some numerical results are also included.
Standing Shock in a Dipole Field
Authors: Ben-Yosef N. , Rubin A. G.
Published: February 2004

A standing bow shock is produced in the flow of a plasma into a dipole magnetic field. The flow direction is perpendicular to the magnetic field. The structure of the bow shock is investigated by measurements of particle density, electron temperature, magnetic field, and magnetic field oscillations. It seems that the oscillations are generated inside the shock which are strongly damped in the upstream direction.
Energy Gap in Hg1−xCdxTe by Optical Absorption
Authors: Scott M. W.
Published: February 2004

The absorption coefficient at the fundamental absorption edge has been measured in Hg1−xCdxTe over the composition range 0.23≤x≤0.61 and at temperatures from 300° to 10°K. The energy gap, estimated from the position of the absorption edge, increases continuously with increasing CdTe content but was not linear between the values for HgTe and CdTe. The energy gap of the alloys varied approximately linearly with temperature for T>100°K, going from a positive temperature coefficient for x<0.5 to a negative temperature coefficient for x>0.5. The temperature coefficient of the gap, dEg/dT, was linear with composition and extrapolated to +5.6×10−4 eV/°K for HgTe. The expression Eg(x, T)=−0.303+1.73x+5.6×10−4(1−2x)T+0.25x4was obtained from the data and can be used to obtain the energy gap as a function of x and T over a large range of these variables.
Short-Term Annealing in 14-MeV Neutron-Irradiated Silicon
Authors: Srour J. R. , Curtis O. L.
Published: February 2004

Using pulsed sources of 14-MeV neutrons (dose ∼109 neutrons/cm2) and fission neutrons, an investigation of short-term annealing in silicon has been performed. In n-type material, for approximately equal amounts of stable damage, the amount of unstable damage at 5×10−2 sec was ∼3.0 times greater for 14 MeV than for fission-neutron irradiation. Considering that the ratio of stable damage for equal neutron fluences is ∼2.8, the total and unstable damage ratios at this same time, for equal neutron fluences, are ∼4.6 and ∼8.5. Although the available dose of 14-MeV neutrons was small, it produced about a factor-of-two change in the carrier lifetime of high quality bulk material. No differences in the annealing curves were observed for fission-neutron irradiations varying by two orders-of-magnitude in dose, suggesting that the data obtained for 14-MeV neutrons would also be valid at higher doses.
Negative Resistance in Chromium-Doped GaAs p-i-n Diodes
Authors: Selway P. R. , Nicolle Wendy M.
Published: February 2004

Gallium arsenide p-i-n diodes, made by diffusing chromium and zinc into n-type material, exhibit a stable current-controlled negative resistance at room temperature and emit recombination radiation when biased in the forward direction. The current-voltage characteristics have been measured and analysis of the results shows that the negative resistance arises as a result of the emission of light at the p-i junction, this light being reabsorbed in the semi-insulating region and causing a photoconductive effect. The electron lifetime in the chromium-diffused semi-insulating region is estimated to be about 10−8–10−7 sec and diodes with a suitable zinc diffusion have an internal efficiency for light emission of about 0.1 photons per electron.
Effects of Spatial Dependence of Recombination Centers on the I-V Characteristics of p-n Junctions
Authors: Dolocan Voicu
Published: February 2004

Effects of spatial dependence of recombination centers on the I-V characteristics of p-n junctions are calculated. The results obtained show that these effects may explain the experimental deviations from the Shockley p-n junction theory and from the theory of the carrier generation-recombination in the space-charge region. The most important result for applications is the junction in which the lifetime increases in the direction of the carrier diffusion; in this case for diffusion current, at reverse bias, a negative resistance appears.
High-Frequency Noise in Germanium-Silicon n-n Heterojunctions
Authors: Neudeck G. W. , Thompson H. W. , Schwartz R. J.
Published: February 2004

Germanium-silicon heterojunctions have been fabricated by placing bulk n-type germanium on a germanium film that has been vacuum deposited on an n-type epitaxial silicon substrate. The germanium is alloyed to the silicon in a hydrogen atmosphere with the resulting heterojunctions showing either a current saturation when forward and reverse biased or for reverse bias only, depending upon the resistivity of the bulk n-type germanium. The forward-biased conductance and capacitance is measured over a range of frequencies from 1 to 50 MHz. The forward-biased conductance and capacitance of the n-n heterojunction have variations with bias current and with frequency similar to those of a Schottky barrier device. The excess noise temperature of the device is measured over a range of bias current at 30 MHz. The theoretical excess noise temperature of the n-n heterojunction is modeled with a mean-square noise current generator in parallel with the junction conductance and capacitance; a series resistance is added to complete the model. Comparison between the theoretical and measured excess noise temperatures indicates that the junction shows nearly full shot noise at high current levels. At low current levels traps at the interface cause the junction to show less than full shot noise. In the case of the double saturating diode, a minimum excess noise temperature is observed at a current level slightly less than the saturation current. Beyond the saturating current, the onset of breakdown is evidenced by a large increase in the excess noise temperature.
Interaction between a Light Beam and a Gunn Oscillator near the Fundamental Edge of GaAs
Authors: Guétin P.
Published: February 2004

We have examined how Gunn domains could modulate the transmission of infrared light. All the phenomena related to the free-carrier absorption cannot give an appreciable effect due to the relatively low carrier density in the devices (1014–1015 cm−3). Modulation by the linear electro-optic effect is difficult to achieve experimentally. On the other hand, the high value of the electric field inside moving domains produces a shift of the fundamental edge towards longer wavelengths (Franz-Keldysh effect). We have performed experiments using a GaAs laser as a light source, and a marked modulation was observed. The maximum value that we have observed is 66% at 9050 Å. The electric field deduced from the Franz theory is of the correct order-of-magnitude when compared to the fields inside the domain. Another effect of the illumination is to produce extra carriers in the material. Thus, each time a dipole crosses the perturbed region, the current shows a deformation. If the laser is cooled down, the domains can disappear and this provides a means of changing the frequency of the current oscillations. A frequency ratio of 6 has been obtained. The deformation shows a relatively long decay time typically of the order of 100 nsec. We discuss the marked similarity which exists between the transient changes in conductivity occurring in this experiment and those present when a sample containing a high field domain is subjected to an additional voltage pulse. We have found that the same trap level is involved in both experiments.
Theory of Wide-Band Maser Action in GaAs
Authors: Rode D. L.
Published: February 2004

A general expression for the small-signal microwave conductivity of a nonequilibrium electron plasma is derived in terms of the momentum distribution function. The dependence of conductivity upon the orientation of the microwave field with respect to a steady bias electric field is presented in detail. Carrier-phonon relaxation processes, such as those characteristic of polar semiconductors, lead to large variations of conductivity with frequency. For certain electron scattering models approximate to GaAs, the present results illustrate how a population inversion discovered by Fawcett and Rees could lead to wide band maser action at submillimeter-wave frequencies.
Cascading Explosive Generators with Autotransformer Coupling
Authors: Cummings David B.
Published: February 2004

An explosive generator offers large pulses of energy in a uniquely small, light device. These advantages cannot be fully exploited with the capacitor bank previously required for input energy. The origin and development of an efficient autotransformer concept are described. This autotransformer makes it practical to cascade explosive generators to overcome the size and weight handicap of the input energy source. Test results show an energy gain of 3.7 per stage with simple parallel-plate generators coupled with a 3 to 1 autotransformer.
Vanadium LII, III X-Ray Emission and Absorption Spectra from Metal, Oxides, Nitride, Carbide, and Boride
Authors: Fischer David W.
Published: February 2004

The vanadium LII,III x-ray emission and absorption spectra (λ∼24 Å) from pure metal, oxides, nitride, carbide, and boride have been investigated using a plane-crystal vacuum spectrometer with electron beam excitation and flow-proportional detection. Emission spectra were studied over a wide range of accelerating voltages and takeoff angles, showing that satellite emission and self-absorption effects can cause gross distortion in band shapes. A replica of the LII,III absorption spectrum can be constructed solely from emission spectra afflicted with widely different amounts of self-absorption. The LII,III emission spectra from the oxides and nitride exhibit an anamalous crossover transition from the 2p level of the anion to the LII and LIII levels of vanadium. This transition appears to be related to the degree of anion-cation orbital overlap and to the electrical properties of the material. Energy shifts of emission bands and absorption edges indicate the charge flow from vanadium to anion in the oxides and nitride. The LIII edges are used to estimate the width of the forbidden gap in V2O5. Oxygen K emission from the oxides exhibits a peculiar dependence on the dispersing crystal used and is also influenced by satellite emission and self-absorption.
Width of the 1332-cm−1 Raman Line in Diamond
Authors: Stenman Folke
Published: February 2004

The width of the 1332-cm−1 Raman line in diamond has been measured using 6328-Å He-Ne laser excitation and a double grating monochromator for analyzing the scattered light. The Raman and system line profiles were determined for various settings of the spectrograph entrance and intermediate slits. The Raman linewidth was determined for each setting using the method employed by Park [Phys. Lett. 22, 39 (1966)]. The average of the various determination is Δν=1.88±0.12 cm−1 FWHM.
Nuclear Magnetic Relaxation Time of Water in a Porous Medium with Heterogeneous Surface Wettability
Authors: Kumar J. , Fatt I. , Saraf D. N.
Published: February 2004

The nuclear magnetic relaxation time of water in porous media with heterogeneous internal surface wettability is shown to be a function of the ratio of water-wet to oil-wet internal surface area. Conventional laboratory nuclear magnetic resonance equipment is used in these studies in contrast to highly specialized apparatus used by previous workers.
Angular Dependence of the Critical Field of Quenched Thin Pb and Sn Films
Authors: Schiller Charles K. , Bulow H.
Published: February 2004

Resistive critical field measurements have been performed in quenched pure Pb and Sn films of 1900-and 650-Å thicknesses with randomly oriented crystals both following the condensation on a quartz plate at 6.2° and 4.1°K and during annealing. In particular, the dependence of the critical field of these quenched metal films on the angle between the magnetic field direction and the film surface have been investigated. The experiments show that the theory of the behavior of the critical field of thin metal films as presented by Tinkham, based on the concept of flux quantization and vortices, provides a very good description for our quenched metal films. The good agreement between experimental results and theoretical predictions for several annealing temperatures suggests, in addition, that nominal crystal size and defect concentration do not greatly affect the angular dependence of the critical field.
Theoretical Hugoniot Stress-Temperature-Strain States for Aluminum and Copper
Authors: Foltz J. V. , Grace F. I.
Published: February 2004

A finite strain deformation formalism developed in the literature can be used to calculate Hugoniot states for isotropic materials. In the present paper, terms in the free-energy function are retained to third order, enabling temperature-stress-strain relations to be determined for uniaxial shock loading for stresses up to 150 kbar in metals. Coefficients of these terms are expressed as functions of the elastic constants of the material. The theoretical Hugoniot stress-strain curve for copper and aluminum agrees satisfactorily with experiment when the elastic constants are sufficiently accurate.
Terminal-Group Association in Carboxy- and Carboxylate-Terminated Polybutadiene
Authors: Otocka E. P. , Hellman M. Y. , Blyler L. L.
Published: February 2004

The viscosity of carboxylic-acid-terminated polybutadiene increases markedly upon neutralization with mono- and divalent bases. These viscosity increases are related to apparent molecular weight, considering the association of the terminal salts as ``polymerizing'' the difunctional prepolymer. For the monovalent alkali-metal salts, simple end-group dimerization seems to occur with an average ΔH of ∼−25 kcal/mole. Neutralization with ions of higher valency leads to materials with higher viscosities.
Effects of Hydrostatic Pressure on the Mechanical Behavior of Polyethylene and Polypropylene
Authors: Mears D. R. , Pae K. D. , Sauer J. A.
Published: February 2004

An apparatus has been designed and constructed that will allow determination of the mechanical behavior of polymer specimens subject to applied tensile and compressive loading, while the sample is simultaneously subject to a hydrostatic pressure environment. The moduli of high-density polyethylene and polypropylene determined from compressive tests show a significant increase with pressure. Tensile nominal stress-strain curves have been obtained at various pressures up to 100 000 psi. These show that the yield stress also increases significantly with increasing pressure for both materials. The nature of yielding and fracture is found to be quite different for the two polymers studied. Polyethylene tends to deform more by shear, and the necked region at high pressures reduces to a fine point before separation. In polypropylene, fracture occurs by plastic tearing across the cross section. An attempt is made to account for the experimental results by use of yield criteria that includes a hydrostatic pressure component. Consideration is also given to the effect of finite deformation theory on the increase in modulus of elasticity under a high pressure environment. The specific nature of the effects produced by the high pressure is found to depend strongly on the molecular structure of the polymer.
Plastic Deformation of Polypropylene. III. Small-Angle X-Ray Scattering in the Neck Region
Authors: Peterlin A. , Baltá-Calleja F. J.
Published: February 2004

The small-angle x-ray scattering (SAXS) pattern of polypropylene (PP) drawn at various temperatures (Td = 20°, 100°, and 135°C) was investigated in a range of very closely spaced draw ratio (λ) values through the neck region. In the zone before the neck starts (λ = 1.05–1.1) the uniform diffraction ring due to microspherulitic material with a long period L0 changes into a four-point diagram superposed onto an elliptical halo. At the beginning of the neck (λ = 1.3–2.5) two meridional maxima arising from a new fibrous structure with a limiting long period LT appear. Irrespective of whether L0>LT or L0<LT the transition between L0 and LT is discontinuous. The four-point pattern reminiscent of the spherulitic structure remains observable up to the end of the neck. In the same manner as in the case of PE, stacks of lamellae exhibiting the most favorable orientation for chain tilt and slip start being plastically deformed and finally break into folded-chain blocks which are incorporated into microfibrils. The fracture occurs in a thin destruction zone which separates the new microfibrils from the not yet transformed stack of original lamellae. Because of the morphological inhomogeneity of the spherulitic sample, the destruction zones and, hence, the starting points of the microfibrils are rather randomly scattered in the neck region and do not merge into one single layer extending over the whole cross section of the sample.
Stress-Optical Properties of PVC above the Glass Transition
Authors: Andrews R. D. , Chatre V.
Published: February 2004

Studies of the photoelastic behavior of a PVC homopolymer film have been carried out in the rubbery state above the glass transition (up to 160°C) to complement studies already carried out in the glassy state. Some measurements were also made on the same samples in the glassy state for completeness. Step-loading experiments were used, as in previous experiments in the glassy state. The results obtained are somewhat complex, indicating that this polymer is considerably different in nature from a simple amorphous polymer such as polystyrene. There is a progressive shift in the zero load values of birefringence (when the sample is unloaded from increasing stress levels), indicating that a progressive structure change is taking place as load level is increased. This could be a result of progressive plastic yield or breaking and reforming of stress-sensitive crosslinks. Below the glass transition this shift takes place in two stages, which may be related to the secondary beta transition and major glass transition of the polymer. The stress-optical coefficient changes from small negative values to large positive values as temperature is increased through the glass transition; a zero value is observed at 80°C. In addition to the abrupt change of SOC at the glass transition, a second abrupt change is observed at 145°C which is the temperature of annealing of the film; annealing conditions may therefore be playing a very important role in determining the solid-state structure of the polymer.
Composite Acoustic Delay Medium with a Zero Temperature Coefficient of Delay
Authors: Fraser D. B. , Egerton L. , Thomson J.
Published: February 2004

For application in un-thermostated delay lines a delay medium possessing a low acoustic loss, a zero temperature coefficient of delay and a zero or low aging rate is required. Present isopaustic glasses meet these requirements satisfactorily with the exception of aging which is found to be dependent upon thermal history to a degree that causes difficulty in some applications. This paper reports a new approach to forming a zero temperature coefficient delay medium consisting of the combination in a hot pressed ceramic, with grain size much less than the acoustic wavelength, of two individually stable materials possessing temperature coefficients opposite in sign. Three mixtures have been prepared with different mass ratios of vitreous SiO2 and powdered crystalline MgF2 by pressing at temperatures of 900°–1120°C and at pressures of 7000–20 000 psi. A zero temperature coefficient is found at 41°C for a mixture with a mass ratio (SiO2/MgF2) of 0.360, a positive coefficient is found for a mixture with mass ratio of 0.306 and a negative coefficient for a mass ratio of 0.419. The internal friction of the mixtures near 1.5 MHz is comparable to and even lower than that of typical isopaustic glasses, though the frequency dependence of the loss is higher. For the mixture with mass ratio of 0.360 the attenuation coefficient depends on frequency as f2.3. Tests have shown no measurable room temperature aging over an eight week period following a mild heating to 110°C.
Crossed-Field Acoustic Amplification in Extrinsic, High-Mobility, Nondegenerate Semiconductors
Authors: Weller K. P. , Van Duzer T.
Published: February 2004

A theory, based on Chambers' solution to the classical Boltzmann equation, is developed for the acoustic gain in a high-mobility (μ), nondegenerate, extrinsic semiconductor subjected to crossed dc electric (E0) and magnetic (B0) fields with the wave vector k in the E0×B0 direction. The theory does not restrict the cyclotron radius Rc to a value much less than acoustic wavelength; previous theory based on the phenomenological semiconductor equations requires kRc≪1 for validity. Simple approximations to the general result are developed for the cases of kRc≲1 and kRc≫1, where Rc is the cyclotron radius. The theory is found to explain recent experimental measurements in the regime kRc≲1 where the simpler theory has failed. A lowering of the maximum attainable gain at a given frequency occurs with decreasing B0. Cyclotron resonance peaks in the acoustic gain occur in the regime kRc≫1 when the Doppler-shifted frequency is an integral multiple of the cyclotron frequency. The anomalous behavior in the threshold curve of acoustoelectric current oscillation in InSb is qualitatively explained on the basis of the theory.
Branching and Bending of Dislocations in Sodium Chloride Crystals
Authors: Babu V. Hari , Bansigir K. G.
Published: February 2004

Discrepancies arising in the number and positions of the etch pits on the opposite cleavage faces when cleavage takes place at different positions from the branching and bending points have been discussed. Experimental evidence for these discrepancies is presented by the help of a new etchant consisting of methanol as solvent and CdCl2 as poison developed for NaCl crystals. Using this etchant which has the unique property of producing etch pits associated with beaks at the aged dislocations, actual branching of dislocations occurring inside the crystal, shift in the positions of the corresponding etch pits on the opposite cleavage faces due to bending of dislocations near the cleavage plane, etch pits associated with wings, and solution channels arising due to dislocation half-loops have been recorded.
Dislocation Dynamics and Steady Plastic Wave Profiles in 6061-T6 Aluminum
Authors: Johnson J. N. , Barker L. M.
Published: February 2004

Under certain conditions, plastic wave profiles in 6061-T6 aluminum may achieve a constant wave velocity and steady shape within a few millimeters from the impact surface in a plate-impact experiment. The finite rise time of the steady plastic wave is assumed to be controlled by the motion of dislocations within the solid. The theory of steady-propagating waves is presented and theoretically determined wave profiles are compared with those measured experimentally by means of laser interferometry. These studies provide information on dislocation velocity and multiplication under conditions of shock-wave compression. In particular, if the mobile dislocation density is assumed to be a function of plastic strain alone, the dislocation velocity is found to be proportional to (τ−τ0)n, where τ is the applied shear stress, τ0 is a back stress, and n is a constant approximately equal to 2. Thus, it appears that a linear relationship between dislocation velocity and shear stress, which has been found to apply for strain rates less than 10−2 μsec−1 in aluminum, may not be sufficient to describe rate-dependent behavior at strain rates greater than 10−2 μsec−1, which are achieved in shock-wave compression.
Pyroelectric Effect in Barium Titanate Ceramic
Authors: Lang Sidney B. , Rice Lynn H. , Shaw Steven A.
Published: February 2004

The pyroelectric coefficient (at constant stress) of a 95 wt% BaTiO3, 5 wt% CaTiO3 ceramic composition (Clevite Ceramic B) was measured over the temperature range from 4.9° to 400°K. Extrema in the pyroelectric coefficient were observed at the rhombohedral-orthorhombic transition point (150°–170°K), the orthorhombic-tetragonal transition point (240°–260°K), and the tetragonal-cubic transition point (Curie point, at 387°K). The pyroelectric coefficient showed no anomalous behavior below 150°K. A spontaneous polarization curve derived from the pyroelectric results is compared with published single-crystal measurements. The ceramic results can be completely interpreted by means of a model describing switching of domain orientations at phase transitions.
Characterization of Piezoelectric Transducers Used in Ultrasonic Devices Operating Above 0.1 GHz
Authors: Meitzler A. H. , Sittig E. K.
Published: February 2004

Piezoelectric transducers for ultrasonic devices operating at frequencies above 100 MHz are presently being made either by thin-film deposition techniques or by bonding thin plates to the substrate and lapping them to the required thickness. In either case the performance of the transducers cannot be evaluated separated from the device, and the evaluation is complicated by the presence of intermediate layers and spurious circuit elements. This paper uses Mason's equivalent circuit to critically appraise the validity of methods used to evaluate transducer performance from loss and admittance measurements made under these circumstances. Computed families of curves are presented, spanning the practically important range of mechanical impedances and coupling factors. Experimental data from a ZnO film and a LiNbO3 thin-plate transducer on fused quartz substrates are presented to demonstrate the application of equivalent circuit descriptions to obtain the coupling factors.
Elastic and Piezoelectric Constants of Ba2NaNb5O15
Authors: Warner A. W. , Coquin G. A. , Fink J. L.
Published: February 2004

The elastic, piezoelectric, and dielectric constants of Ba2NaNb5O15 have been measured. The experimental techniques used involve mostly thickness-mode measurements made on small plate-shaped samples of various crystallographic orientations. As reported previously, the z-cut plate has a thickness longitudinal mode coupling factor of 0.57, which makes this material attractive for application as a high-frequency longitudinal mode transducer. However, from the measured constants and the theory of piezoelectric plate vibrations, it is determined that no crystallographic orientation other than the z-cut has properties suitable for ultrasonic transducer applications.
Sputter Machining of Piezoelectric Transducers
Authors: Beecham D.
Published: February 2004

This paper demonstrates that sputter machining can be used to obtain fundamental mode transducers or resonators for the frequency range above 100 MHz where mechanical methods of thickness reduction have low yields. Material is removed by bombarding the specimen with high-energy ions drawn from a gaseous plasma. Experimental results are given for the sputter machining of sputter-deposited zinc oxide, Y-cut lithium niobate, and Y-cut quartz. The highest fundamental resonant frequency attained was 1.8 GHz using lithium niobate, corresponding to a thickness of about 2 μ.
Grain Boundary Self-Diffusion in Nickel
Authors: Canon R. F. , Stark J. P.
Published: February 2004

High-purity nickel bicrystals with controlled grain boundary misorientations have been grown from the melt using an electron beam floating-zone technique. These bicrystals have symmetrical tilt grain boundaries with 10° misorientation between {111} planes tilted about a 〈112〉 axis, and 10° twist about a {111} axis. The diffusion of nickel-63 in these boundaries and similar sintered grain boundaries has been studied over the temperature range 600°–970°C using high-resolution contact autoradiography. Using the dislocation pipe model for low-angle grain boundaries, edge and screw dislocations were found to have similar activation energies of 40.7 and 44.9 kcal/mole, respectively. The value for the tilt boundaries is shown to agree well with recent work on isolated edge dislocations in nickel. It is concluded that the low-angle tilt boundaries are composed of 〈112〉 {111} edge dislocation arrays which exhibit the same diffusion behavior as isolated edge dislocations formed by plastic deformation. Also, the higher value of the activation energy for 〈112〉 tilt boundaries as compared to previously reported results on 〈100〉 tilt grain boundaries in nickel points out a basic difference in the energy required for the mass transport process in the two types of dislocation structures found in 〈100〉 and 〈112〉 tilt boundaries. A theoretical explanation of this activation energy difference is consistent with an assumed vacancy mechanism for dislocation pipe self-diffusion.
Diffusion of Nickel in Amorphous Silicon Dioxide and Silicon Nitride Films
Authors: Ghoshtagore R. N.
Published: February 2004

Nickel-59 radiotracer has been used to determine nickel diffusion coefficients in amorphous silicon dioxide and silicon nitride films between 1100° and 1490°K. Nickel distribution has been found to be Fickian with the calculated diffusivities obeying Arrhenius equation. Long diffusion times have been found to produce anomalous diffusivities in silicon nitride.
Effect of Large Electric Fields on the Electron Energy Distribution and Ionization Rate in a Cesium Discharge
Authors: Shaw D. T. , Margolis S. G.
Published: February 2004

The Boltzmann equation with the electric field and the collision terms is solved numerically for a spatially uniform, steady-state, cesium thermionic plasma. The collision terms includes the elastic, inelastic, and electron-electron Coulomb interactions. The Fokker-Plank approximation of the Coulomb collision is used in the present study. The effects of non-Saha population on the electron energy distribution and ionization rate near the emitter are discussed.
Photoemission from Cesium Oxide Covered GaInAs
Authors: Klein Wolfgang
Published: February 2004

White light photoresponse, quantum efficiency, energy distribution, work function, dark current, uniformity, and stability of the photoresponse of GaInAs were measured at room temperature. The polycrystalline, heavily doped p-type samples were polished, glow discharged, heat cleaned in an ultrahigh vacuum system and covered with cesium oxide. The photoemission up to photon energies of 1.85 eV is due to thermalized photoelectrons that diffuse in the Γ1C conduction band minimum. Their diffusion length and escape probability were evaluated. Above 1.85 eV, electrons thermalized in the X1C and L1C conduction band minima and hot electrons contributed considerably to the photoemissive yield. Work function measurements by the vibrating reed method showed that the threshold at 1.05 eV was bandgap limited. Stability and uniformity studies indicated a great potential for the application of this material as a practical photocathode.
Ion Sampling Through the Anode and Cathode of a DC Discharge
Authors: Held Herman , Gilkinson J. L. , Chanin L. M.
Published: February 2004

Measurements are reported of positive ions sampled through the anode and the cathode of a dc discharge in argon containing small concentrations of cesium. Data were obtained for argon pressures up to 3 Torr and cesium pressures as high as 4×10−3 Torr. Ions observed through the cathode were Ar+, Ar++, Ar2+, and Cs+, through the anode Ar+, Ar2+, and Cs+ were measured. Comparison is made of anode and cathode sampling measurements.
Effect of Viscosity on the Transfer of Energy in Forced Water Waves
Authors: Sen A. R.
Published: February 2004

It is known that when a localized pressure p0(x2+z2)1/2 exp(iωt)×H(t) is applied on the surface (y=0) of a deep or shallow unbounded nonviscous liquid, no energy is transmitted through the liquid for the zeroes of P0(ω2/g), P0(k) being the zero-order Hankel transform of p0(r) in r. It is explained here that the effect of viscosity is to ensure a continuous transfer of energy for all values of ω.
Temperature Distribution and Stresses in Circular Wafers in a Row During Radiative Cooling
Authors: Hu S. M.
Published: February 2004

A model is proposed in which transient temperature profiles in circular wafers in a row during cooling are analyzed. Various effects such as the number of wafers in a row, the position of the wafer in a row, the ratio of the wafer radius to the wafer spacing, multiple reflections, and the contribution of conduction are considered. It is shown that drastic radial variations of temperature can occur because of the geometrical factor affecting the efficiency of radiative transfer in various parts of a wafer. Thermal stresses thus induced in the cooling wafer can often exceed the yield stress in silicon wafers, causing plastic deformation. The phenomenon of ``thermal warping'' is briefly discussed.
Superfluorescence Limitations on the Inversion Process in Large-Aperture Laser Amplifiers
Authors: Sibert E. , Tittel F.
Published: February 2004

A Monte Carlo computation procedure has been used to study the effect of superfluorescence losses upon the design of a large-aperture disk laser system in terms of the enhanced photon flux density. This parameter is indicative of the maximum attainable population inversion. It was found that laser disks up to 6 in. in diam are capable of useful optical energy storage. The technique can also be applied to other laser geometries to estimate superfluorescence effects more readily than previous numerical integration methods.
Mode-Locked and Bandwidth-Narrowed Nd-Glass Laser
Authors: Magnante P. C.
Published: February 2004

Light pulses 0.3-nsec wide were generated from a mode-locked Nd-glass laser which had its bandwidth narrowed by spectral-mode selectors. The duration of these pulses, as measured by the two-photon fluorescence technique, corresponded to the inverse bandwidth in the frequency domain as measured with a Fabry-Perot interferometer. A fast rise-time light detector showed that more than half of the modes were phase locked.
Hamilton's Principle and the Maximum-Emission Coincidence
Authors: Schwarz S. E. , Gordon P. L.
Published: February 2004

Self-locking of frequencies in laser oscillators is considered. The equations of motion for the cavity fields are restated as an extremum principle, which is a modified form of Hamilton's principle. This extremum condition is then compared with the ``maximum-emission'' condition hypothesized by Tang and Statz. It is found that the latter is not derivable from the former, unless one assumes infinitely fast-population relaxation of the laser medium and central tuning of laser modes with respect to the atomic resonance, and performs calculations by means of third-order perturbation theory. If the requirement of third-order perturbation calculations is relaxed, the maximum-emission hypothesis leads to a statement which is different from that of Hamilton's principle, but which coincidentally has the same solutions. If either of the other two assumptions is relaxed, the maximum-emission hypothesis not only gives a statement different from that of Hamilton's principle but leads to incorrect results.
Rotary Electrical AC Generators Utilizing the Magnetic Shielding and Trapping by Superconducting Plates
Authors: Kawabe Ushio , Kudo Mitsuhiro , Hara Nobuhiro , Doi Toshio
Published: February 2004

Superconducting rotary ac generators were developed utilizing magnetic shielding and trapping between many pairs of hard superconducting plates. To show the possibilities of the proposed generators, models I and II were constructed and tested in liquid helium at 4.2°K. Two heat-treated Nb–40Zr–10Ti plates plates (40-mm diam and 8-mm thick) with three keyhole-shaped slots were used for the rotor of the model I, and sintered Nb3Sn discs (17.5-mm diam and 8.0-mm thick) embedded three by three in three 40-mm-diam bakelite plates were used for model II. When model II was operated at 1000 rpm with a resistance load in a state in which a field of 1.4 kG was trapped between disks, a maximum output power of 5.72 W was obtained with 6.5 A (rms) and 0.88 V (rms). The electrical efficiency was 89%. The total power loss was 0.72 W, 58% of which was mechanical bearing loss.