bluuebunny/crossref_metadata_2025 huggingface dataset:
Photometric Determination of the Electron Ionization Frequency in Dry Air
Authors: Mentzoni Michael H.
Published: February 2004

The photometric method has been proven successful in the measurement of the ionization frequency vi in dry air in the field range 40≤Eeff/p≤132 V/cm Torr. The ionizing agent was a 9.361-GHz rectangular pulse which traversed a fused quartz breakdown cell enclosed in a cylindrical waveguide. As in previous studies, the electron collision frequency was selected according to the value vc=5.3p×109 sec−1. The pressures chosen ranged from 0.5 to 36 Torr. The measurements were confined to the last half portion of the formative time lag (FTL) interval but always before manifestation of breakdown occurred as seen by abrupt changes in reflection and transmission signal pulses. The vi/p versus Eeff/p curve thus found ran reasonably parallel to the curve obtained by other workers who used the FTL-method. Compared to their results, however, the present curve was shifted towards higher vi/p values by as much as a factor of 1.8 in the lower one-half portion of the Eeff/p-range.
Potential of a Charged Axially Symmetric Conductor Inside a Cylindrical Tube
Authors: Chang I. C. , Dee Chang I.
Published: February 2004

The problem of a charged axially symmetric body inside a cylindrical tube is studied by using the method of matched asymptotic expansions. The shape of the body is assumed arbitrary. It is found that when the body dimension a is small compared with the tube radius R a simple approximate formula for the capacitance of the system is given by C=Co [1−(γCo /4πε0R)]−1+0(a2/R2),where Co is the capacitance of the isolated charged body, and γ is a universal constant, independent of the body shape, and approximately equal to 0.87.
Bolometer for Detecting Heat Pulses in a Magnetic Field
Authors: Wigmore J. K.
Published: February 2004

The bolometer depends on the rapid temperature variation of the current in an avalanching semiconductor. Typically, at 1.7°K, it has a sensitivity of 0.05 V W−1, a response time of 2×10−7 sec, and a noise equivalent power of 10−7 W Hz−1/2. The rapid response is possible because only a thin damaged layer at the surface of the semiconductor is involved in the detection process. We have used the device to detect heat pulses in magnetic fields up to 30 kOe.
Thermally Stimulated Currents in Mylar, High-Temperature Low-Field Case
Authors: Lilly A. C. , Stewart L. L. , Henderson Rosemary M.
Published: February 2004

The thermally stimulated current method has been applied to the study of thermally activated depolarization of Mylar thermoelectrets. The band arising from the depolarization is broad and sometimes multistructured. It is, in general, centered at approximately 400°K. The peak current is linear with the applied electric polarizing field up to at least 240 kV cm−1. The linearity is taken as evidence that the polarization is due to dipole orientation.
Phase Diagram of Bismuth at Low Temperatures
Authors: Compy Elvin M.
Published: February 2004

The phase diagram of bismuth has been studied from 4.2° to 300°K at pressures up to 50 kbar. Pressure was generated using a piston-cylinder apparatus with AgCl as the pressure transmitting medium. Phase transitions were detected by observing the accompanying discontinuities in electrical resistance. The phase diagram thus determined is in fair agreement with previously published results of other authors. However, the new low-temperature phase of bismuth reported by Il'ina and Itskevich was not observed.
Mass-Spectrometric Studies of a Sealed CO2 Laser
Authors: Karube Norio , Yamaka Eiso
Published: February 2004

Short-term phenomena taking place in a sealed CO2 laser have been treated mass spectrometrically. Their influences upon laser action and life have been examined in detail. Gas heating is observed to be proportional to the input power and in a water-cooled laser at 250 W input power is ΔT/T=0.24, resulting in the power decrease by the factor 0.72 at the relaxation time of the order of milliseconds. Decomposition of CO2 molecules is found to obey the equation CO2⇌CO+½O2 which is always at the equilibrium determined by the discharge parameters. The fraction of decomposed molecules is 60% for dc 10 mA and increases slightly with increasing current. The decrease of oxygen during the discharge is the cause of the long-term shift of equilibrium, which can be suppressed considerably by initial CO filling. These results have been interpreted in terms of the microscopic theory of chemical physics. The proper features in the decomposition mechanism by the discharge have also been given special considerations.
Zinc-Diffused GaAs Electroluminescent Diodes with Long Operating Life
Authors: Konnerth K. L. , Marinace J. C. , Topalian J. C.
Published: February 2004

It is found that the operating lives of Zn-diffused GaAs electroluminescent diodes depend principally upon the donor concentration. Diodes produced from wafers having 1−2×1018 donors/cm3 have longer operating lives than diodes produced from wafers having 1−2×1017 donors/cm3. To a lesser extent, operating lives depend upon the Zn-diffusion cycle. Optimum results are obtained by carrying out the diffusion at 750°C for four hours followed at 850°C for 45 min. Apparently there is little or no dependence of operating life upon the donor type (Sn or Si), the crystalline orientation of the wafers, or upon epoxy potting of the wafers. Under continuous operation, light output decreases 5%–10% during the first few hours, and then remains approximately constant thereafter (the maximum test duration was 22 500 h). These diffused diodes are relatively simple to fabricate, have efficiencies of the order of 1% and room temperature risetimes of about 10 nsec.
Effects of Dipolar Interactions on the Exchange Resonance
Authors: Gehring G. A.
Published: February 2004

The dipolar interactions in a two sublattice ferrimagnet are shown to give rise to magnetostatic modes associated with the exchange resonance frequency. The shift in these modes due to retardation effects is calculated. The exchange resonance frequency is shown to depend on the size of the sample when dipolar and retardation effects are included.
Fracture Surface Energies and Dislocation Processes during Dynamical Cleavage of LiF. I. Theory
Authors: Burns S. J. , Webb W. W.
Published: February 2004

The theory of the motion of a cleavage crack created by wedging open the ends of a double cantilevered crystal at a constant rate has been investigated. The results are presented for use in analysis of experimental studies of fracture dynamics in lithium fluoride reported in Part II of this series. A solution of the quasistatic equations of motion of the crack including kinetic energy effects has been found from which the dynamic fracture surface energies may be deduced for a propagating crack of this geometry by observations of either the time dependence of the crack length or the profile of the fracture opening near its tip. The detailed configurations of dislocations accompanying the tip of a moving crack in alkali halides have been calculated using dislocation dynamics and continuum elasticity theory. The plastic deformation contribution to the effective fracture surface energy has been determined and some of its consequences worked out.
Response of Cracks to Impact
Authors: Steverding B. , Lehnigk S. H.
Published: February 2004

The equation of motion for cracks which are subjected to stress pulses is derived by the Lagrangian method. An asymptotic solution is used to determine terminal crack velocity. The time in which essentially constant velocity will be reached is determined. The equation is further used to formulate a dynamic stability criterion. In addition to a critical stress a critical time of stress duration is of importance. Critical time and critical stress can be combined to a critical action. From this principle, a number of conclusions are derived which are used to explain a number of experimental facts for which a theoretical explanation was lacking hitherto.
Materials Problems in Lithium-Drifted Germanium Radiation Detectors
Authors: Jindal G. R. , Faust J. W.
Published: February 2004

This paper describes some materials problems involved in the preparation of lithium-drifted germanium gamma-ray detectors. A preliminary study shows some decided differences between the characteristics of the original starting material and the characteristics of the material after various fabrication procedures.
Transition from Emission-Limited to Space-Charge-Limited Photoconductivity
Authors: Tabak Mark D. , Scharfe Merlin E.
Published: February 2004

A transition from an initial emission-limited current to a steady-state space-charge-limited current has been observed in evaporated films of amorphous selenium. A simple model of this transition has been developed which can be used to illustrate the trapping dynamics and estimate the free carrier range.
Parametric Excitation of Low Frequencies in a Bounded Plasma
Authors: Demokan O. , Hsuan H. C. S. , Lonngren K. E. , Stern R. A.
Published: February 2004

The coupling of an incident microwave signal in a Tonks-Dattner resonance to discrete low-frequency modes in a plasma column is presented both theoretically and experimentally. The necessary conditions that the incident power and frequency had to meet in order to excite these modes are also explained and experimentally tested.
Interpretation of Dimensional Changes Caused in Pyrolytic Carbon by High-Fluence Neutron Irradiation
Authors: Bokros J. C. , Koyama K.
Published: February 2004

Dimensional changes in a variety of pyrolytic carbons irradiated at 900° to 1000°C and at 1200° to 1300°C show that during the irradiation, the rate at which the specimens change dimensions accelerates. The accelerations are most pronounced in dense, isotropic carbon and are accompanied by the generation of pores in the structure, which causes a volume expansion. The data obtained at the lower irradiation temperatures (∼900°C) suggest that the accelerations are due primarily to a degradation in crystal structure that enhances the instability of the crystallites. At the higher irradiation temperatures, increases in anisotropy contribute significantly to the accelerations. The volume expansions, the degradation of the crystal structure, and changes in thermal conductivity are all less for irradiations above 1200° than at 1000°C. These observations, together with the increases in anisotropy, are believed to be manifestations of the fact that the intercrystallite irradiation creep rate is substantially higher at irradiation temperatures above 1200° than at 1000°C. High creep rates provide an effective mechanism which relaxes the stresses that are generated between adjacent, misaligned crystallites during irradiation.
Exact Analytic Solution for First-Order Fluorescent Buildup in One Dimension
Authors: Halbleib John A.
Published: February 2004

The problem of fluorescence in slab geometries is solved exactly and analytically to first order. Analytic expressions, whose direct evaluation should be faster and more accurate than current numerical methods, are derived for differential and integral dose and for differential reflection and transmission coefficients, for the single slab case. The basic expressions are then used to obtain the general solution for the dose profile of the multislab problem. The limitations of the first-order approximation are discussed and illustrated by comparison with Monte Carlo results. It is found that even in a situation especially chosen to ensure the validity of the first-order approximation, a Monte Carlo calculation reveals the presence of higher-order effects.
Small-Signal Relaxation Times for the Lattice Scattering in n-Type GaAs
Authors: Heinle W.
Published: February 2004

It is shown that the small-signal behavior of n-type GaAs can be described in the approximation of displaced Maxwellian distribution functions in terms of five field-dependent relaxation constants Γk which are defined as the eigenvalues of the matrix controlling the change with time of the electron temperatures, the drift velocities, and the population ratio. For the frequency dependence of these quantities and the mobility, expressions of the form ∑ k=15Ckiω−Γkresult, where the Ck depend only on the bias field. Hence the frequency limit for negative differential mobility is derived, having a maximum value of 200 GHz. Furthermore the frequencies of the plasma modes are calculated as a function of the bias field and the electron concentration. Two of the six plasma modes are oscillatory (especially for large electron density); one of the relaxation-type modes (the soft mode) is shown to give rise for current-controlled instability of the infinitely extended semiconductor for bias fields which belong to negative slope of the static characteristic.
Improved Aging and Switching of Lead Zirconate-Lead Titanate Ceramics with Indium Electrodes
Authors: Fraser D. B. , Maldonado J. R.
Published: February 2004

After repeated switching, ferroelectric ceramic plates will exhibit aging evident in hysteresis loops as a marked decrease in remanent polarization (Pr) and an increase in coercive field (Ec). A hot-pressed ceramic having a composition of 65% lead zirconate-35% lead titanate with 2 at.% lanthanum and having a grain size 2 μ or less was used to study the effects of various electrode materials. The source disks were polished down to a thickness of 25, 37, or 63 μ and square plates 2.5 mm on edge were cut for testing. Prior to the application of the electrodes, the square plates were annealed in air at 700°C for 10 min and cooled slowly to room temperature. Electrodes were then applied as opposing disks 1.5 mm in diameter on the surfaces of the plates. A Sawyer-Tower circuit was used to observe hysteresis loops formed on an oscilloscope at a frequency of 60 Hz, and occasionally at 600 Hz. Maximum applied voltage corresponded to approximately 3Ec. Results were obtained for vapor plated electrodes of Al, Cr–Au, Pb, PbO–Ag, Sn–Ag, Ag, Ga, and In. For all but the In electrodes, a large decrease of Pr was evident by 107 cycles. The In electrodes yielded lower values of Ec (approximately 8 kV/cm) and the value of Ec did not increase appreciably over the test period. After 109 cycles, Pr had decreased by only 14% for the In electrodes.
Photoemission of Holes and Electrons from Aluminum into Aluminum Oxide
Authors: Goodman Alvin M.
Published: February 2004

The photoemission of both electrons and holes from aluminum into thin layers of ``plasma-grown'' aluminum oxide has been observed. The threshold energies for these processes are found to be 2.0±0.2 eV for electrons and 3.1±0.2 eV for holes. An approximate energy band diagram of the Al–Al2O3 interface based on these values is presented.
Double Injection Currents in Long p-i-n Diodes with One Trapping Level
Authors: Deuling H. J.
Published: February 2004

An exact uniform theory is given for the I-V characteristic of long p-i-n diodes with one trapping level. This theory does not assume a constant recombination lifetime or quasi-neutrality, as did all previous treatments of this problem. As limiting cases, the theory gives the cube law at high injection levels, the square law for the semiconductor regime and the Ashley—Milnes regime. The theory is applied to the acceptor level of Au in Si for which case numerical solutions are given.
Surface Study of Anodized Indium Antimonide
Authors: Hung Roland Y. , Yon Eugene T.
Published: February 2004

The surface properties of the anodized oxide/InSb system have been studied using metal-oxide-semi-conductor structures. It was found that the surface state charges are negative in general. This negative surface charge comes from the following two sources: the acceptor-type surface state on the real InSb surface and the positively charged trap levels in the oxide. There is also evidence that two sets of trap levels exist in the oxide, with relaxation time as the characteristic difference. The Electron Microprobe Analyzer was employed in this investigation to evaluate the chemical composition in the oxide as well as in the surface layer of InSb. This was achieved by regulating the accelerating voltage to control the depth of electron penetration.
Interpretation of Equilibrium and Steady-State Hall and Thermoelectric Effects in Inhomogeneous Materials
Authors: Blount George H. , Bube Richard H. , Robinson Arthur L.
Published: February 2004

Consideration of simple variations of a basic resistive-network model for an inhomogeneous material shows that a wide variety of experimentally observed effects can be described with respect to equilibrium or steady-state Hall and thermoelectric measurements. The correlation between these macroscopic Hall and thermoelectric measurements and the microscopic electrical and geometrical properties of the material is derived. A suitable combination of both Hall and thermoelectric measurements on the same sample makes it possible to determine the dominant average microscopic and geometric parameters of the system. Although developed under the stimulus of research into the photoconductivity mechanism in chemically deposited lead sulfide layers, the results of the consideration may have a wider application.
Amorphous versus Crystalline GeTe Films. III. Electrical Properties and Band Structure
Authors: Bahl S. K. , Chopra K. L.
Published: February 2004

Various transport studies have been carried out on amorphous and crystalline GeTe films of 80 Å to 10 μ thickness. Crystalline GeTe has a low resistivity (∼10−4 Ω·cm at 300°K) which increases with temperature slowly and nearly linearly at low temperatures (below ∼300°K) and rapidly at higher temperatures. The hole concentration (N∼1010−1021 cm−3) increases only slightly with temperature. Mobility varies as N−4/3. These results in conjunction with the tunnel-spectroscopy and optical data show that crystalline GeTe is a degenerate (and thus metallic conduction), p-type narrow band gap (∼0.1–0.2 eV) semiconductor with Fermi level ∼0.3–0.5 eV inside the valence band. The linear increase of the susceptibility mass with hole concentration, the constancy of the Hall coefficient up toωLτ=0.35 (ωL=Larmor frequency, τ=collision relaxation time), and the monotonic increase of thermopower with temperature indicate that conduction takes place only in a single valence band. Amorphous GeTe films exhibit activated conduction. The dc resistivity varies from 410° to 77°K as ρ0 exp (Eg/2kT), where Eg is about 0.8 eV and ρ0 is the resistivity of crystalline GeTe films. Ac resistivity decreases with frequency (ω) as ω−n, where n lies between 0.5 and 1.0, depending on the temperature. The activation energy for ac conduction decreases rapidly from the dc value to zero with decreasing temperature as well as increasing frequency. The capacitance of amorphous GeTe at 77°K varies as ω−0.2 while the loss factor is independent of the frequency. With increasing dc field, the linear dependence of current on voltage changes to a power relation Vn, where n varies rapidly from ∼3 to 6 or more in a small range of the applied field. At very high fields, I ∝expβF1/2 (β=constant) is observed. These results, together with the tunnel-spectroscopy, and optical data suggest that amorphous GeTe may be represented as a p-type semiconductor with band gap ∼0.8 eV with exponential tailing of the bands and a continum of localized states in the vicinity (both sides) of the band edges. Conduction takes place by two parallel processes of intrinsic excitation across the band gap, and thermally and/or field-assisted hopping from one localized (trapping) state to another. Dc conduction by hopping at low fields is negligible. At higher fields, trap modified space-charge-limited current flow and Poole-Frenkel effect determine the nonlinear field dependence of current.
Dependence of Resolving Power of an Aperiodic Radio-Frequency Mass Spectrometer on the Waveform of the rf Signal
Authors: Lall H. B.
Published: February 2004

This work deals with the effect of radio-frequency waveform on the resolving power of an aperiodic rf mass spectrometer. The expressions for the energy-gain function and resolution from one- to five-stage analyzer configurations have been obtained with five different waveforms of the rf signal. The improvement of the resolving power obtained with square-wave over sine wave excitation has been illustrated graphically for all the five configurations of the analyzer assembly. The effect of adding second harmonic to the sine wave, on the resolving power, has been investigated. The influence of inaccuracies in the grid-positioning on the resolving power with sine and square-wave operations has been discussed.
Piezoelectric Surface Waves in Cubic Crystals
Authors: Tseng C.-C.
Published: February 2004

The existence of a piezoelectric surface wave, which does not arise in nonpiezoelectric materials has recently been reported in hexagonal crystals by Bleustein and Gulyaev. It is shown that similar waves can exist in cubic crystals of 4̄3m and 23 classes, along [110] direction on the (1̄10) plane and their equivalent orientations. Velocity equations for the piezoelectric surface wave and the elastic surface wave are derived and their characteristics discussed.
Fundamental and Higher-Order Mode Surface Wave Propagation on Layered Anisotropic Substrates—Gold on Lithium Niobate
Authors: Waldner M. , Pedinoff M. E. , Jones W. R. , Campbell J. J.
Published: February 2004

Calculations for the phase velocity of acoustic surface waves on lithium niobate with a contiguous gold layer have been carried out for the fundamental and higher-order modes of propagation. The anisotropy of the substrate leads to a prediction that the first higher-order mode has a low-frequency cutoff. In some cases the phase velocity dispersion curves for various modes have crossing points. Theoretical calculations and experimental evidence of the position of the crossing points for the first two modes and the phase velocity characteristics of the dominant mode above and below the crossing points as a function of the frequency-film thickness product are given.
Sampled-cw Study of ``Inhomogeneous'' Ultrasonic Responses in Solids
Authors: Miller J. G. , Bolef D. I.
Published: February 2004

The ``propagating wave'' analysis of an ultrasonic resonator is extended to include some effects of nonparallelism, guided wave phenomena, and electrical loading. Each of these effects contributes an ``inhomogeneous'' broadening to the continuous wave frequency domain response and an ``inhomogeneous'' damping to the time domain decay. Experimental verification for ultrasound propagating in both thin and bulk solid specimens is obtained by utilizing the sampled-continuous wave ultrasonic spectrometer. Quantitative evaluation of interference effects among harmonic and inharmonic responses is achieved using the spectrometer in the time domain mode of observation.
Spectral Investigation of Acoustoelectric Domains in n-GaAs by Microwave Emission Studies
Authors: Zoroglu Demir S. , Chang I-C.
Published: February 2004

Microwave emission from n-GaAs crystals, under conditions of current instability with propagating acoustoelectric domains, was detected and analyzed for various stages of the total acoustic flux level in such domains. Frequency range covered extended from 0.2 to 4.5 GHz. Diagnostic experiments indicate that the emission is due to the electromechanical conversion of the acoustic flux as the propagating domain hits the anode. The frequency spectrum of the emission shows various peaks that can be identified as sub-harmonics and sum frequencies. The experimental result is consistent with the theory of parametric conversions.
Observation of CO2 Laser Induced Acoustical Waves in CO2
Authors: Brinkschulte Hermann W.
Published: February 2004

Acoustical waves have been observed in CO2, at initial pressures between 2 and 25 Torr, caused by sudden heating from incident CO2 laser pulses. The effect was observed by monitoring the temperature increase of the window of the absorption cell due to the incident sound wave. Results indicate that the influence of a high-power laser beam upon the penetrated atmosphere—and the feedback of the disturbed atmosphere on the propagation of the laser beam—may be conveniently studied under simulated laboratory conditions.
Effect of Particle Size and Shape on the Infrared Absorption Spectra of Barium Titanate and Strontium Titanate Powders
Authors: Luxon J. T. , Montgomery D. J. , Summitt R.
Published: February 2004

Effects of particle size and particle shape have been studied in the infrared absorption spectra of BaTiO3 and SrTiO3 powders to determine whether previously developed methods to treat such effects are applicable to crystals having high dielectric constant and ``soft'' lattice modes. The spectrum of both materials exhibits three absorption bands (BaTiO3: 545, 400, and 180 cm−1; SrTiO3: 605, 400, and 175 cm−1) that are considerably removed from the TO-mode frequencies computed from bulk single-crystal reflection data (BaTiO3: 510, 183, and 33.8 cm−1; SrTiO3: 546, 178, and 87.5 cm−1). These frequencies were successfully correlated with the bulk-crystal frequencies by use of classical electromagnetic scattering theory and an extension of Fröhlich's method. The low-frequency ``soft'' modes of both crystals were found to have an unusually large dependence on particle shape with the consequence that the powders absorb radiation at the corresponding LO-mode frequency.
Accurate Orientation Method for dHvA Data
Authors: Mueller F. M. , Windmiller L. R. , Ketterson J. B.
Published: February 2004

A new technique for improving the accuracy of the angular orientation of nonsymmetry plane dHvA data on cubic systems by an order of magnitude (from 2.0° to 0.2°) has been developed. The extension of this technique to orienting dHvA data in noncubic crystallographic systems, or to orienting data for other types of experiments, viz. neutron scattering, should be straightforward.
Growth of High-Quality LiNbO3 Crystals from the Congruent Melt
Authors: Byer R. L. , Young J. F. , Feigelson R. S.
Published: February 2004

The use of LiNbO3 crystals in nonlinear optical experiments has been limited by the lack of long, high-quality crystals. We have shown that crystals grown from a congruent composition melt are significantly less susceptible to birefringence variations which in the past have limited the useful phase-matchable lengths of LiNbO3 crystals. Both a birefringence test which directly measures the spatial birefringence of the crystal and a second harmonic generation test were used to evaluate crystals grown from melts of various compositions. Crystals with less than 10−5 variation in birefringence over a length of 4 cm have been obtained repeatably when grown from congruent melts.
Mechanical Hysteresis and Dislocation-Dislocation Interactions in Copper Crystals
Authors: Dralla J. , Bilello J. C.
Published: February 2004

Half-cycle mechanical hysteresis loops, at positive stress bias, representing damping frequencies in the range of ≈10−1 Hz were performed on copper crystals at room temperature. The hysteretic character and stability of the dislocation structure were explored by repetitive stress cycling at constant stress amplitude. It was found that the decrement decreased with continued stress cycling and eventually reached a saturation value. Changes in the decrement, with cycling, provided an extremely sensitive way of detecting dislocation rearrangements at low stress levels. Sectioning and etch pitting of the crystals was performed in order to reveal quantitatively both the forest and primary dislocation structures associated with the hysteresis behavior. Correlation of the damping and etch-pit data indicated that low-frequency mechanical hysteresis could be attributed to ``pinning'' of primary dislocations at forest dislocation junctions.
Observation of Grain Boundaries with the Field-Ion Microscope
Authors: Fortes M. A. , Smith D. A.
Published: February 2004

The information which can be gained from field-ion micrographs showing grain boundaries is considered critically. An attempt is made to quantify the factors governing the ``ring'' configuration across both low-angle and high-angle grain boundaries. It is shown that spiral configurations can be generated in the absence of grain boundary dislocations. Some potential applications of the grain boundary contrast theory are indicated.
Mechanism of Thermal Annihilation of Stacking Faults in GaAs
Authors: Abrahams M. S. , Buiocchi C. J.
Published: February 2004

Epitaxial layers of GaAs grown from the liquid phase have been studied by transmission electron microscopy. The layers were grown on mechanically polished substrates and contain intrinsic stacking faults bounded by Shockley partial dislocations. Near each end of most of these grown-in faults, there are three overlapping intrinsic faults. The two faults which overlap the grown-in fault form by vacancy migration during growth and are bounded by Frank partials. Unfaulting of these three-layer defects was observed on annealing and is accomplished by the nucleation and motion of Shockley partials. These unfaulting Shockley partials have been observed for the first time. The final state is one in which the total faulted structure is eliminated.
Thermal Currents from Corona Charged Mylar
Authors: Creswell Robert A. , Perlman Martin M.
Published: February 2004

Thermal currents have been obtained from corona-charged Mylar. The results are interpreted in terms of electron and/or ion trapping and subsequent release upon reheating. A theory is developed for thermal release of these ``near surface'' charged specimens when no external field is applied. A new method is presented to obtain energies for a series of peaks present in complex thermal current spectra. The trapping parameters are also determined using both the initial rise analysis of Garlick and Gibson, and the curve fitting technique of Cowell and Woods. The results are consistent with four discrete traps in Mylar at depths of 0.55, 0.85, 1.4 and 2.2 (all ±0.1) eV. The 0.55- and 0.85-eV traps are electronic, that at 1.4 eV is either an electronic trap with a Coulomb barrier, or ionic. The 2.2-eV trap is either ionic, interfacial, or involves dissociation of a complex with subsequent release of an electron to the conduction band. Assuming that the traps empty under monomolecular conditions, analysis of the thermal-current peaks yields trap densities of the order of 1016/cm3, an electron mobility—lifetime product of about 10−10 cm2/V, and escape probabilities that agree with those determined from isothermal charge decay.
Radiation from a Localized Source in a Gyromagnetic Medium
Authors: Vasile C. F. , Felsen L. B.
Published: February 2004

While wave propagation in gyromagnetic media has been investigated extensively in the technical literature, little attention has been given to the excitation of such waves by a prescribed source. This problem is treated in the present paper. To render the analysis tractable, the source function is taken as a time-harmonic line source of electric currents with a rapidly varying phase, embedded in an infinite homogeneous gyromagnetic medium whose axis of magnetization is perpendicular to the source direction. For further simplification, the operating frequency is taken to be near gyromagnetic resonance. The resulting model incorporates relevant anomalies of the radiation process, and also serves as a prototype for more practical thin slab configurations. The analysis is performed for permeability tensors in which spin exchange effects are ignored and included. In the former case, the refractive index surface may have open branches and gives rise to an infinity in the total radiated power (infinity catastrophe); this anomaly is removed when spin exchange is accounted for. Detailed study of the radiation fields and radiated power densities shows that except for certain initial directions, the outward power flow is almost entirely in the electromagnetic waves, and the total radiated power in the electromagnetic waves far exceeds that in the spin exchange waves, even when the source dimensions tend to zero. These results imply that a localized electromagnetic current source does not strongly excite the spin exchange waves.
Axial Electromagnetic Modes and Self-Resonance in LSA Diodes
Authors: Rode D. L.
Published: February 2004

Electromagnetic modes in a semiconductor cylinder are described for cases of negative and positive conductivity. These modes, with purely axial electric field orientation, exist only for nonzero conductivity. Formulas for the radiated power, quality factor, and field distributions are presented. The idealized model approximates the LSA mode of a microwave oscillator. For such a cylindrical diode oscillator, a self-resonance condition determines the frequency×diameter product, f×D=2.4×109 cm/sec, and doping concentration/frequency ratio, n/f=6×104 sec/cm3. The latter result is coincident with that derived previously from a space-charge control criterion. The electric field amplitude is uniform to within 16% over the cross section of the self-resonant diode.
Shock-Induced Phase-Transition Pressures in Fe–Cr and Fe–Cr–Ni Alloys
Authors: Gust W. H. , Royce E. B.
Published: February 2004

The variation of shock-induced phase-transition pressure with alloy composition has been observed for several Fe–Cr and Fe–Cr–Ni alloys through use of the inclined-mirror technique. It was found that transition pressures for Fe–Cr alloys varied continuously from the known 130-kbar value for pure iron to 230 kbar for 30% Cr content. Alloys of the Fe–Cr–8% Ni series exhibited almost linear decrease in transition pressure from 120 to 80 kbar as Cr was increased from zero to 18%; no transition was observed for an 8% Ni–22% Cr alloy up to 124-kbar. Further systematic decreases in phase-transition pressures were observed for Fe–Cr–12% Ni and Fe–Cr–16% Ni alloys.
Superconducting NBTI Microwave Cavity
Authors: Soumpasis D. , Lüders K.
Published: February 2004

We have investigated the properties of a rectangular cavity made of ``hard'' superconducting Nb0.52Ti0.48 alloy and resonating in the TE-101 mode at 9.125 GHz. Preliminary results in fields up to 10 kG show that such a device could be very useful in applications where high Q's in the presence of strong magnetic fields are desirable.
Theory of the DeBlois Experiment. III. Effect of Neighboring Imperfections
Authors: Aharoni Amikam
Published: February 2004

The assumption of an infinite coil, used so far for the study of the effect of surface roughness on the nucleation field, is relieved and a finite coil is introduced taking into account the correct fall-off of its field. The demagnetizing field caused by surface roughness on an iron whisker is approximated (as before) by the field, on the axis of symmetry, of a straight-cut cylindrically symmetric irregularity, on the surface of an infinite circular cylinder. Unlike the case of an infinite coil, here the effect of the defect can be studied as a function of its distance from the center of the coil, which allows a subtraction of the effect of the neighboring defects from the apparent nucleation field at the particular defect under study. The values computed for the nucleation field due to a defect at the center of the coil are closer to the experimental values than nucleation fields computed before for an infinite coil, but the approximation is still a rather crude one.
Analysis of Exchange-Coupled Magnetic Thin Films
Authors: Hagedorn F. B.
Published: February 2004

Presented in this paper are some new analytical results for two exchange-coupled magnetic thin films. The formulation of the problem which is used is similar to that of Goto et al., who reduced the determination of the magnetic configuration of the films in the presence of an external magnetic field to the evaluation of elliptic integrals. Derived herein is an expression for the second variation of the magnetic energy, thereby allowing an investigation of the stability of previously determined magnetic configurations. Evaluation of this expression, as well as determination of the magnetic configuration, must be done numerically, and tables giving magnetic configurations and critical fields are included for a variety of thickness combinations and magnetic parameters. In addition, new analytical results are presented for several limiting cases. Transcendental equations have been derived which give the threshold fields for arbitrary film parameters when the easy axes are mutually parallel in the two films and when the external field is either parallel or perpendicular to the common easy axis. Expressions are also developed for the critical fields in composites involving both very thin and very thick films, and the magnetic properties of a pair of very thin films are shown to be simple combinations of the constituents' magnetic properties. Finally, several discrepancies are discussed between the approximate results of Goto et al. and the exact results obtained herein.
Excitation of Longitudinal Magnetoelastic Waves in Axially Magnetized YIG Rods
Authors: Lewis M. F.
Published: February 2004

It is shown experimentally and theoretically that longitudinal magnetoelastic waves can be excited with an efficiency comparable to that of transverse magnetoelastic waves in an axially magnetized YIG rod whose axis is appropriately oriented relative to the crystallographic axes. In conjunction with a thin film piezoelectric longitudinal-wave transducer this could form the basis of a useful two-port device.
Anisotropic Susceptibility of an Antiferromagnet in Applied Field
Authors: Fairall C. W. , Swinehart D. D. , Cowen J. A.
Published: February 2004

The anisotropy in the magnetic susceptibility of a uniaxial antiferromagnet in an applied field has been calculated using a simple molecular field model and measured using a novel set of susceptibility coils. The apparatus consists of a superconducting solenoid coaxially enclosing the susceptibility coils which in turn enclose a rotor for orienting the crystal. The customary molecular field model is solved explicitly for susceptibility as a function of applied field and angle. The theoretical and experimental values agree very well for all angles and fields.
Mechanism of Energy Conversion of Magnetostatic Waves into Spin Waves in Ferrimagnetic Cylinder
Authors: Sawado Eikichi
Published: February 2004

The energy flow of the magnetostatic waves is derived from the Lagrangian intensity, and the wave impedances of the magnetostatic waves and the exchange spin waves are derived from the energy flow of those waves. It is shown in the present paper that the energy conversion of the magnetostatic waves into the spin waves is possible only when the wave impedance of two magnetic oscillating systems are equal.
Magnetic Resonance Study of Polycrystalline MnAu2 at 100 GHz
Authors: Hart L. W. , Stanford J. L.
Published: February 2004

We report the results of magnetic resonance studies at high microwave frequencies in metallic, metamagnetic, polycrystalline MnAu2. The investigation covered microwave frequencies from 95 to 119 GHz, temperatures from 4.2° to 400°K, and magnetic field intensities up to 50 kOe. No resonance was observed in the spiral magnetic phase at our frequencies. At fields above that necessary to induce a ferromagnetic component in the spiral-spin system, a temperature- and frequency-dependent peak was observed in the microwave power absorption, as a function of magnetic field applied in the plane of the disk-shaped sample. We have interpreted this absorption as ferromagnetic resonance in a system with large uni-axial magnetic anisotropy. Values of the Lande g-factor and uni-axial anisotropy constant at low temperatures are determined from the data, but with large experimental uncertainty due to severe magnetic hysteresis exhibited with field cycling.
Small-Signal Mixing and Harmonic Generation in Thin Magnetic Films
Authors: Ellis David M.
Published: February 2004

A method is developed for calculating the response of a thin magnetic film subjected to static magnetic fields and small time-varying fields. An applied field is considered small if it produces rotations, φ1 of Ms such that sin2φ1≈2φ1 and cos2φ1≈1. The measured response is the time derivative of that component of flux which arises from Ms. A component of this flux change generates a voltage in a conductor held close to the film. It is shown that this sensed voltage contains not only the frequency of the applied field but also its harmonics. Independent variables are chosen to be the magnitude and direction of the static field and the direction of the small time-varying fields. General expressions for the output voltage generated by the film at fundamental and second-haramonic frequencies are developed. Theoretically predicted signal behavior is illustrated by fixing two of the independent variables and plotting the dependence of output voltage on the remaining variable.
MnBi Films: High-Temperature Phase Properties and Curie-Point Writing Characteristics
Authors: Chen D. , Aagard R. L.
Published: February 2004

Manganese bismuth films can exist in two crystallographic phases. The Curie temperatures, magneto-optical, and magnetic properties of films prepared at the quenched high-temperature phase were measured and compared with those of the films at the normal low-temperature phase. The low Curie temperature of 180°C makes the quenched films more attractive for optical memory applications. Laser Curie-point writing experiments have been performed on both types of films at various operating temperatures. The results can be explained on the basis of the physical properties of the two phases of MnBi films.
Recovery of an Ultrasonic Second-Harmonic Amplitude in an Aluminum Crystal
Authors: Scorey C. R.
Published: February 2004

A second-harmonic wave generated by a 10-MHz compressional wave in an aluminium single crystal is found to increase in amplitude when a small static stress is applied to the crystal. The second-harmonic amplitude in the stressed crystal shows a recovery with time which is found to be thermally activated. An activation energy of 1.1 eV is measured.
Motion of Elasto-Plastic Membranes under Shock Loading
Authors: Dresner Lawrence
Published: February 2004

The motion of an infinitely long strip of foil with clamped edges has been calculated under the following circumstances: (i) pressure wave incident either head on or side on, (ii) membrane stress either constant or proportional to strain. The constant-stress case has been solved completely by the method of characteristics. The membrane profile is known, and the maximum strain is known as a function of the incident pressure, membrane thickness, membrane width, and membrane stress. A similarity solution is known for the membrane in which stress is proportional to strain for head-on incidence. It describes the early stages of membrane motion. It gives an acceptable approximation to the maximum strain as a function of incident pressure, membrane thickness, membrane width, and membrane modulus. Numerical solutions of the equations of membrane motion are described.
Kerr Effect in Substituted Aromatic Nitro Compounds
Authors: Pearson A. D. , Northover W. R. , Chandross E. A.
Published: February 2004

A method for the determination of Kerr constants of liquids is described. The effects of adding or substituting other groups into the aromatic ring of nitrobenzene are reported. The effectiveness of increasing molecular asymmetry on the Kerr effect in a series of compounds is also noted. The most effective material measured was a 1 molar solution of 2,5-dimethoxy-4′-nitro-stilbene in nitrobenzene. This solution has a Kerr constant almost eight times that of pure nitrobenzene.
Characteristics of Radiation-Dominated Electric Arcs
Authors: Lowke J. J.
Published: February 2004

Temperature profiles of arcs when radiation is the principal energy transfer process have been derived from material functions. Arcs which are optically thin are approximately isothermal or constricted depending on whether εN/σ is an increasing or decreasing function of temperature; εN is the net emission coefficient and σ the electrical conductivity. Arcs which are optically thick have a temperature profile similar to conduction dominated arcs. Theoretically predicted examples of these three types of arcs are a 2000-A arc at 30 atm in air, a low current arc in the vapor of a rare-earth metal at 20 Torr, and a 4000-A arc at 1000 atm in air. For arcs which are nearly isothermal, it is possible at any value of current and radius to make approximate calculations of (1) the temperature of the arc core, (2) the electric field strength, (3) the thickness of the outer arc sheath, and (4) the fraction of the input energy carried to the wall by conduction. Such calculations are made for arcs in air and are compared with the results of exact calculations which take into account the details of the self-absorption of radiation. Approximate calculations show that when εN/σ has a maximum as a function of temperature, multiple solutions for the temperature profile are possible for some values of arc current and radius.
Electrostatic Probe and Electronic Circuit for Low-Temperature Plasma Measurements
Authors: Musal Henry M.
Published: February 2004

The principles of operation and practical realization of a planar guard-ring probe with a floating potential electrode, and an associated electronic circuit to accomplish floating potential compensation of the probe characteristic, are described here. This configuration provides stable and reproducible measurement of the complete planar Langmuir probe characteristic in low-electron-temperature plasma, even in the presence of spurious potential fluctuations.
Eigenvalues of a Microwave Cavity Filled with a Plasma of Variable Radial Density
Authors: Shohet J. L. , Hatch Albert J.
Published: February 2004

A solution to the eigenvalue problem of a cylindrical plasma of variable radial density placed coaxially within a cylindrical cavity has been obtained. The solution is based on a model constructed by dividing the plasma into a series of concentric shells, in each of which the plasma density is assumed to be constant but not necessarily equal to that of any other shell. Maxwell's equations are solved exactly for the electro-magnetic fields in each shell. The boundary relations at the inner and outer surface of each shell and at the cavity walls result in a set of simultaneous equations which may be solved numerically for the eigenfrequencies if the cavity dimensions, number of shells, and density in each shell are specified. For a given density profile, which may be obtained from experiments, the frequency shift of the system for a given mode may be determined as a function of the density of the central shell. A 10-shell model has been used to solve for the frequencies of the first 10 modes of a cylindrical cavity.
Isochronal Resistivity Study of Defect Recovery in High-Neutron-Fluence Irradiated Molybdenum
Authors: Keys L. K. , Moteff J.
Published: February 2004

An isochronal resistivity study from ∼70° to 1200°C has been completed on molybdenum irradiated at ∼70°C to fast neutron (En≥1 MeV) fluences from 1.1×1019 n/cm2 to 1.5×1021 n/cm2. For all but the highest fluence specimen, three major recovery regions are observed at about 0.15 Tm (Stage III), 0.22 Tm, and 0.31 Tm (Stage IV). It is considered that the lowest temperature region results from the recovery of self interstitials, and that the highest temperature region represents excess-monovacancy recovery if there is an excess, with possible contributions from the recovery of defect clusters. The intermediate region could contain contributions from recovering divacancies. An anomalous saturation effect occurs at ∼5×1019 to 1020 n/cm2 (En≥1 MeV) with a drop-off in the radiation-induced resistivity increment fraction at high fluences. This drop off in resistivity appears to result from the saturation and complete irradiation annealing of the Stage III defect due to its high mobility at the relatively high homologous-irradiation temperature (0.12 Tm) leaving essentially only a large recovery in the region of Stage IV after irradiation to the highest fluence. A nonannealing residual resistivity increment observed for the highest fluence specimen is attributed to the presence of Tc (and possible Ru) formed via thermal neutron (n, γ) reactions.