bluuebunny/crossref_metadata_2025 huggingface dataset:
A new path for the Denmark Strait overflow water from the Iceland Sea to Denmark Strait
Authors: Jonsson Steingrimur , Valdimarsson Hedinn
Published: February 2004

Denmark Strait overflow water (DSOW) is one of the main components of the thermohaline circulation. There has been no consensus on where it is formed and by which way it is brought to the Denmark Strait. It is shown here that it is brought to the sill by a hitherto unknown current that is traced from the sill back into the Iceland Sea north of Iceland. The transport of this current is sufficient to account for a major part of the transport of DSOW as it has been measured at the sill if some entrainment of ambient water is assumed. This supports theories suggesting that the Iceland Sea is the main source for the DSOW and this has consequences for the way in which climate change affects the thermohaline circulation.
Relativistic cyclotron resonance condition as applied to Type II interplanetary radio emission
Authors: Farrell W. M. , Kaiser M. L. , Bale S. D. , Desch M. D. , Fitzenreiter R. J. , Goetz K. , Bougeret J.‐L.
Published: February 2004

We demonstrate that energy from energetic electrons upstream of interplanetary (IP) shocks are able to couple directly to the o‐mode radio branch via the relativistic cyclotron harmonic resonance interaction, thereby creating the Type II radiation observed from IP shocks. The conditions required for the electron/wave resonance are that the wave frequency, f, lies near the local plasma frequency, fp, and near (but not exactly at) the cyclotron harmonics, mfc, where m is the cyclotron harmonic number. We compare the details of this relativistic electron cyclotron harmonic theory with observations in a Type II source region, with good agreement in many areas including the prediction of “Zeeman” splitting of the Type II emission. Based on the character of the high‐resolution emission spectrum, we can narrow the Type II source location to the IP shock foot region and place some general conditions on shock topology required for Type II emission.
Modeling a space weather event from the Sun to the Earth: CME generation and interplanetary propagation
Authors: Manchester Ward B. , Gombosi Tamas I. , Roussev Ilia , Ridley Aaron , De Zeeuw Darren L. , Sokolov I. V. , Powell Kenneth G. , Tóth Gábor
Published: February 2004

We present a three‐dimensional (3‐D) numerical ideal magnetohydrodynamics (MHD) model describing the time‐dependent expulsion of a coronal mass ejection (CME) from the solar corona propagating to 1 astronomical unit (AU). The simulations are performed using the Block Adaptive Tree Solar‐Wind Roe Upwind Scheme (BATS‐R‐US) code. We begin by developing a global steady‐state model of the corona that possesses high‐latitude coronal holes and a helmet streamer structure with a current sheet at the equator. The Archimedean spiral topology of the interplanetary magnetic field is reproduced along with fast and slow speed solar wind. Within this model system, we drive a CME to erupt by the introduction of a Gibson‐Low magnetic flux rope that is anchored at both ends in the photosphere and embedded in the helmet streamer in an initial state of force imbalance. The flux rope rapidly expands and is ejected from the corona with maximum speeds in excess of 1000 km/s. Physics‐based adaptive mesh refinement (AMR) allows us to capture the structure of the CME focused on a particular Sun‐Earth line with high spatial resolution given to the bow shock ahead of the flux rope as well as to the current sheet behind. The CME produces a large magnetic cloud at 1 AU (>100 R⊙) in which Bz undergoes a full rotation from north to south with an amplitude of 20 nT. In a companion paper, we find that the CME is very effective in generating strong geomagnetic activity at the Earth in two ways. First, through the strong sustained southward Bz (lasting more than 10 hours) and, second, by a pressure increase associated with the CME‐driven shock that compresses the magnetosphere.
Ground observations of chorus following geomagnetic storms
Authors: Smith A. J. , Horne R. B. , Meredith N. P.
Published: February 2004

It has been suggested that whistler mode chorus waves play a role in acceleration and loss of radiation belt electrons during geomagnetic storms. In this paper we present data from a complete solar cycle (1992–2002) of nearly continuous (>95%) VLF/ELF observations from the VLF/ELF Logger Experiment (VELOX) instrument at Halley station, Antarctica (76°S, 27°W, L = 4.3), to determine whether there is statistical evidence for enhanced whistler mode chorus waves during geomagnetic storms. The data comprise 1 s resolution measurements of ELF/VLF wave power in eight frequency bands from 500 Hz to 10 kHz. The variations in chorus activity during several storms, including the well‐studied Bastille Day event (14 July 2000), show enhanced wave power but are variable from event to event. The average behavior has been found from a superposed epoch analysis using 372 storms with minimum Dst less than −50 nT, including 82 large storms with minimum Dst less than −100 nT. Compared with average prestorm levels, the chorus intensity decreases in the storm main phase but is enhanced in the recovery phase, typically maximizing a day after the storm onset. At 1 kHz the enhancement is independent of storm severity, suggesting a saturation effect, whereas larger storms produce larger wave intensities at higher frequencies in the chorus band (e.g., 3 kHz), which is interpreted as the effect of a chorus source region located on lower L shells than for weaker storms. The storm chorus enhancement maximizes at postdawn local times, leading to a 24 hour recurrence effect. A long‐enduring depression in wave intensities, of 10 days or more, is found near the top of the normal chorus band (∼5 kHz). We suggest that this is due to precipitation from enhanced relativistic particle fluxes affecting the subionospheric propagation of spherics from nearby thunderstorm regions across the L = 2–4 zone.
Measurement and prediction of wave‐generated suborbital ripples
Authors: Williams J. J. , Bell P. S. , Thorne P. D. , Metje N. , Coates L. E.
Published: February 2004

Experiments in a large‐scale wave flume using regular and irregular waves with periods between 4 s and 6 s and heights between 0.2 m and 1.55 m have examined the formation of wave‐generated ripples using sediment beds composed of four grain sizes (D50 = 0.349 mm, 0.329 mm, 0.220 mm, and 0.162 mm) in a water depth of approximately 4 m. Estimates of wave‐generated ripple height,η, and wavelength, λ, were obtained using zero down‐crossing analyses of bed profiles measured by acoustic means along a 4‐m transect normal to the ripple crests. Further information pertaining to λ was obtained from bed images obtained using scanning sonar. The analyses reported here focus on the sequence bedforms that evolved in response to stepwise increases and decreases in wave height. Results show that ripples for the most part are suborbital in nature and do not conform well to empirical equations used frequently to predict η and λ values in the field. On the basis of the present data, two new equations for prediction of η and λ are obtained and their use in field situations where hydrodynamic and sedimentary conditions favor development of suborbital bedforms is recommended.
Nannofossil carbonate fluxes during the Early Cretaceous: Phytoplankton response to nutrification episodes, atmospheric CO2, and anoxia
Authors: Erba Elisabetta , Tremolada Fabrizio
Published: February 2004

Greenhouse episodes during the Valanginian and Aptian correlate with major perturbations in the C cycle and in marine ecosystems, carbonate crises, and widespread deposition of Corg‐rich black shales. Quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the Southern Alps (northern Italy), where high‐resolution integrated stratigraphy allows precise dating of Early Cretaceous geological events. Rock‐forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean‐atmosphere system. Increased rates of volcanism during the formation of Ontong Java and Manihiki Plateaus and the Paranà‐Etendeka large igneous province (LIP) are proposed to have caused the geological responses associated with early Aptian oceanic anoxic event (OAE) 1a and the Valanginian event, respectively. Calcareous nannofloras reacted to the new conditions of higher pCO2 and fertility by drastically reducing calcification. The Valanginian event is marked by a 65% reduction in nannofossil paleofluxes that would correspond to a 2–3 times increase in pCO2 during formation of the Paranà‐Endenteka LIP. A 90% reduction in nannofossil paleofluxes, which occurred in a 1.5 myr‐long interval leading into OAE1a, is interpreted as the result of a 3–6 times increase in pCO2 produced by emplacement of the giant Ontong Java and Manihiki Plateaus. High pCO2 was balanced back by an accelerated biological pump during the Valanginian episode, but not during OAE1a, suggesting persisting high levels of pCO2 in the late Aptian and/or the inability of calcareous phytoplankton to absorb excess pCO2 above threshold values.
Effect of noise on the neutral direction of chaotic attractor
Authors: Lai Ying-Cheng , Liu Zonghua
Published: February 2004

A chaotic attractor from a deterministic flow must necessarily possess a neutral direction, as characterized by a null Lyapunov exponent. We show that for a wide class of chaotic attractors, particularly those having multiple scrolls in the phase space, the existence of the neutral direction can be extremely fragile in the sense that it is typically destroyed by noise of arbitrarily small amplitude. A universal scaling law quantifying the increase of the Lyapunov exponent with noise is obtained. A way to observe the scaling law in experiments is suggested.
A new approach to data storage using localized structures
Authors: Coullet P. , Riera C. , Tresser C.
Published: February 2004

In this paper we describe how to use the bifurcation structure of static localized solutions in one dimension to store information on a medium in such a way that no extrinsic grid is needed to locate the information. We demonstrate that these principles, deduced from the mathematics adapted to describe one-dimensional media, also allow one to store information on two-dimensional media.
Pressure Measurements in a Magnetically Driven Shock Tube
Authors: Rudderow W. H.
Published: February 2004

Measurements of total pressure and static pressure were taken in a magnetically driven shock tube at an Alfvén Mach number of M1≈0.66 in air at an initial pressure range of 50–200 μHg. Total pressure measurements ranged from 0.3–0.8 of the Newtonian pressure based on an equilibrium real gas density ratio. A small separation between the shock and drive current sheet was detected over the range of initial pressures, but was not always repeatable. The static pressure was measured and found to be approximately equal to the drive magnetic pressure.
Fast Fluorescence Measurements in Dyes
Authors: Pine Alan S.
Published: February 2004

Excited singlet lifetimes of ∼2 nsec for cryptocyanine and ∼6 nsec for chloroaluminum phthalocyanine have been measured directly from fluorescence. The fast excitation source is a mode-locked ruby laser. A model is proposed to explain these and other relaxation measurements compatible with the observed fluorescent efficiencies of the dyes.
Dislocation Pile-up in Two-Phase Materials
Authors: Kuang J. G. , Mura T.
Published: February 2004

Based on the theory of continuously distributed dislocations, the equilibrium equations for both edge-and screw-dislocation pile-ups in materials composed of soft and hard phases are formulated in terms of a singular integral equation. The integral equation is solved exactly by using the Wiener-Hopf technique with Mellin transforms.

The dislocation distribution function is found in explicit form. It is shown that the number of dislocations in the piled-up array can be determined directly from the Mellin transform of the distribution function without its inverse transform.
Electron-Mirror-Microscope Analysis of Surface Potentials on Ferroelectrics
Authors: English F. L.
Published: February 2004

Electron-mirror photomicrographs were taken of barium titanate single-crystal and lead zirconate-titanate polycrystalline ferroelectric materials. Electrical potential distributions were observed with the microscope on the surfaces of both materials. The domain structure of barium titanate was evident as was the transition from the ferroelectric to the paraelectric state. Lead zirconate-titanate ceramic in the unpoled and poled states appeared significantly different as did regions polarized in opposite directions. These observations are explained in terms of bound surface charges.
Radiation from High-Pressure Plasmas
Authors: Bauder U.
Published: February 2004

If the temperature dependence of the total radiation source strength and the continuum radiation source strength of a gas are known, the contribution of the line radiation can be determined. The investigation of the line factor L shows that it is independent of pressure over a wide temperature and pressure range. Therefore, to determine the total radiation source strength of a gas at high pressure, one need calculate only the continuum radiation at high pressure and use the measured or calculated line factor of the gas at atmospheric pressure. This method was applied to argon and the total radiation source strength u=F (temperature, pressure), in the range 9000≤T≤15 000°K and 1≤p≤100 atm was determined using the existing values measured at 1 atm.
Extensional Mechanical Properties of Polyester- and Polyether-Based Polyurethanes
Authors: Klosner Jerome M. , Segai Alexander , Franklin Howard N.
Published: February 2004

An investigation of the extensional mechanical properties of a polyester-based polyurethane (Texin 480 A Opaque 149004 B) and a polyether-based polyurethane is described.

Dynamic steady-state tests were performed over a frequency range of 1000–8000 Hz and a temperature range of 50°–110°F for the polyester material held at a constant elongation of 105%. The experiments on the polyether were conducted at 110% initial elongation over a range of frequency of 200–1600 Hz, and a temperature range of 50°–110°F.

The complex modulus was found for both materials and the reduced-variable concept applied. Master curves for the moduli at a reference temperature of 510°R (50°F) are presented.

Relaxation tests were performed on the same materials and the relaxation modulus determined. Finally, the relaxation spectrum was determined by using the data from the dynamic and relaxation experiments.
Internal Friction in Vibrating Granular Reeds and its Application to Vitreous Silica
Authors: Warshavsky Mordechai , Robinson Howard A.
Published: February 2004

The Zener theory of internal friction in vibrating reeds has been generalized to three dimensions and expressions derived for the case where the grained structure of the reed is smaller than the wavelength of the standing wave. The theory is applied to the experimental values of the internal friction in vitreous silica; it is shown that such internal friction in silica may be explained by the presence of small grains whose dimensions are those found in recent electron micrographs.
New Data on the Shear Stresses and Energies of ½ 〈110〉, {111} Edge Dislocations in Elastically Anisotropic fcc Metals
Authors: Duncan T. R. , Kuhlmann-Wilsdorf D. , Moore J. T.
Published: February 2004

Numerical data and curves for the shear stresses and energies of ½ 〈110〉, {111} edge dislocations in elastically anisotropic fcc and diamond-type materials are presented, based on a previously published analytical solution, to supersede those contained in the earlier paper.

The corrected data are compared with data by Foreman, by Van Hull and Weertman, and by Seeger and Wobser, and are shown to be reliable.
Energy-Transfer Mechanism and Typical Operating Characteristics for the Thermal rf Plasma Generator
Authors: Freeman M. P. , Chase J. D.
Published: February 2004

Operating characteristics of an atmospheric-pressure, rf plasma torch and of its associated 30-kW power oscillator are inferred from available instrumentation and calorimetric heat balance measurements with various working fluids in torches of two diameters. The governing equations for the arc, neglecting convection, are derived and solved analytically for the crude channel-model approximation. Material functions for argon and nitrogen are then used to predict operating characteristics for these fluids. Fair agreement indicates that at least some of the essential physical phenomena of the discharge have been resolved. The analysis serves to explain much of the ``art of operation'' with special emphasis on the concepts of coupling and impedance matching.
Electron and Hole-Capture Coefficient of Indium in Silicon at Low Temperatures
Authors: Preier Horst
Published: February 2004

This paper describes conductivity, Hall effect, and noise measurements of partially compensated In-doped Si-samples at low temperatures. The samples were p-type in the dark and became n-type when illuminated. Hole concentration of the unilluminated samples and electron concentration of the illuminated sample were determined from the Hall coefficients. Mobilities were then derived from the conductivities. Capture coefficients for holes and electrons were obtained by noise measurements as function of frequency resulting in γp=≃10−6 cm3 sec−1 and γn≃10−11 cm3 sec−1. The I-V characteristic of illuminated samples between p+-contacts was measured. Its analysis also furnished values for the electron-capture coefficient.
Electrical and Optical Properties of GaAs Injection Lasers with Closely Compensated p-Type Region
Authors: Kressel H. , Hawrylo F. Z.
Published: February 2004

Results are presented of a detailed study of the electrical and optical properties of GaAs injection lasers fabricated by the liquid phase epitaxy method with heavily doped, closely compensated p regions (Zn∼1020 cm−3, Sn∼5×1019 cm−3). The effects of various heat treatment steps were investigated to elucidate the role of injection and tunneling. The optical emission of the untreated diodes is centered at ∼9600 Å (300°K) and is thus considerably displaced from the bandgap energy. Despite the fact that internal absorption should be small in these devices, the external radiative efficiency is generally low at moderate current densities. Non-radiative tunneling currents are shown to dominate charge transfer over a large range of forward bias. After heat treatment, the spontaneous efficiency improves and simultaneous stimulated emission at two wavelengths separated by 400 Å is observed at low temperatures. These emission bands are shown to originate in p-type regions adjoining the junction differing in their degree of doping and of compensation. The threshold current density for lasing in the heavily doped, closely compensated region is considerably higher than for the more lightly doped, less compensated region.
Properties of a Ferromagnetic Powder in a Nonmagnetic Matrix
Authors: Baldwin John A.
Published: February 2004

A study has been made of the magnetic properties of ferromagnetic powder suspended in a nonmagnetic matrix. The study was motivated by a desire to predict the properties of keepers employed in some fast computer memories. Expressions are obtained which give the static susceptibility and useful frequency range of such materials. The susceptibility is found to be small and relatively independent of that of the parent material. However, the useful frequency range is greatly increased.

The analysis is used to evaluate effective demagnetizing factors and interaction fields in quasiuniformly magnetized bodies. It is shown that the theory is consistent with certain experimental findings concerning polycrystalline ferrites and YIG. Finally, a suggestion is made for possible observation of domain-wall resonance.
Paramagnetic Resonance Study at Millimeter Wavelengths of an Axial Fe3+ Spectrum in Strontium Titanate
Authors: Baer Ralph , Wessel Gunter , Rubins R. S.
Published: February 2004

Paramagnetic resonance measurements have been made on an axially symmetric spectrum of Fe3+ (configuration 3d5) in SrTiO3. The SrTiO3 sample contained a nominal 0.3% Fe impurity. The results were found to be consistent with the assumption that the spin-Hamiltonian is HS=DO20+G∥·Sz+G⊥·Sx+(a/120) (O40+5O44)+(F/180) O40. From room-temperature measurements at 35.0 GHz, 65.1 GHz, 69.4 GHz, and 75.0 GHz, values are obtained for the coupling constants in the spin-Hamiltonian: 2D=(2.707±0.008) cm−1, and (5a/2+5F/3)≅0.01 cm−1. D was determined to be of positive sign in an experiment carried out at 1.2°K and 9.4 GHz. Results of between 25 and 60 G were obtained for the linewidths of some of the transitions.
Electrical Resistivity of NiAl, CoAl, NiGa, and CoGa
Authors: Yamaguchi Y. , Kiewit D. A. , Aoki T. , Brittain J. O.
Published: February 2004

The electrical resistivities of NiAl, CoAl, NiGa, and CoGa were measured at 4.2° and 297°K by the usual potentiometric method. The variations of resistivities of these intermetallic compounds with temperature and composition indicate that the compounds are metallic, although not good conductors, and that the point-defect concentration present in these materials is important in considerations of the electrical transport properties. The variations of resistivities with composition indicated that the point defects in NiAl, CoAl, and CoGa tend to cluster as the composition departs from stoichiometry.
CdTe–HgTe Heterostructures
Authors: Almasi G. S. , Smith A. C.
Published: February 2004

The heterostructures described here were prepared by solid-state diffusion from a mixture of CdTe and HgTe powders into a wafer of single-crystal CdTe. The composition profiles as measured with an electron-beam microprobe show that 100 μ wide transition regions can be achieved. These profiles are consistent with published results on diffusion between bulk HgTe and bulk CdTe. Increasing the proportion of HgTe in the powder shifts the optical absorption edge from a wavelength of 0.8 μ (the value for bulk CdTe) to beyond the 15 μ limit of the measuring instruments. The photoelectromagnetic (PEM) effect shows a fairly flat spectral sensitivity for wavelengths between 1 and 5 μ. The photovoltaic response shows an anomalous exponential dependence on the photon energy, believed to be due to an undesirable p-n junction caused by cadmium vacancy formation. Theoretical models are derived for both effects.
Mechanical Aberrations of a Magnetic Quadrupole Quadruplet Lens
Authors: Kawakatsu Hisazo , Vosburgh Kirby G. , Siegel Benjamin M.
Published: February 2004

The mechanical aberrations of a system of two or more magnetic quadrupoles have been studied. Displacement, rotation, and tilting of one quadrupole, and the effects of radial and rotational errors in alignment of one pole are considered as well as the inhomogeneity of the material used in the system. The changes in field distribution introduced by these errors are calculated and the corresponding aberration formulas are derived.

As a particular case, the mechanical aberrations of a quadruplet projector, are computed. The construction tolerances are estimated for an allowable image defect (magnification error) of 3% in the radial and rotatinoal directions. The calculations indicate that the projector system can be used in an electron microscope without excessive image defects. The image is most sensitive to rotational misalignment with a required tolerance of ±2×10−3 rad.
Rotation of Isolated Spherical Ferromagnetic Single Domains Subjected to Varying Magnetic Field and Strain
Authors: Abrams M. D. , Gillott D. H.
Published: February 2004

This paper develops a limited model representative of ferromagnetic materials employing the ferromagnetic domain as the basic building block. The effects of the magnetostatic field, magnetocrystalline anisotropy, and magnetoelastic stress on domain rotation are considered. The process of domain rotation from an unstable state to a stable one is included in the model. The model is simulated by a computer program, and representative sets of hysteresis loops are obtained. Previous investigations are briefly discussed and contrasted with the present study.
Precipitation of Iron Carbides in Tempered Martensite
Authors: Ron Moshe , Shechter Hanan , Niedzwiedz S.
Published: February 2004

The precipitation of carbides in 0.7 wt%-carbon steel as a function of tempering temperature has been studied through the Mössbauer effect, magnetic measurements, and x-ray observations.

The magnetic behavior of the extracted precipitates is discussed. The tiny clusters obtained by extraction after the early stages of tempering (up to 250°C) show the relation of these clusters to martensitic bct cells (``Johnson clusters'').

The results obtained by further stages of tempering (250–500°C) show a decrease in the relative amount of the Johnson clusters, followed by a precipitation of ferromagnetic carbides. The behavior of the internal field, the TC and θD, as a function of the tempering temperature suggests a decrease of the relative carbon content with the increasing tempering temperatures. The Fe3C is formed toward 550°C.
Electrical Properties of Sulfur-Doped Gallium Phosphide
Authors: Hara Tohru , Akasaki Isamu
Published: February 2004

Sulfur-doped n-type GaP crystals with carrier concentrations in the range between 6.0×1016 and 5.7×1018 cm−3 have been grown by an epitaxial-growth technique. Hall measurements on these crystals have been carried out over the temperature range from 4.2°–400°K. The room temperature electron mobility in GaP depends weakly upon the donor concentration. The temperature dependence of electron mobility in the higher temperature region indicates that polar mode lattice scattering is dominant. In the lower temperature region, ionized impurity scattering does not play an important role. Impurity conduction is observed below about 60°K. The impurity conduction process changes from hopping to metallic form with increasing doping level. This critical transition concentration is 2.1×1018 cm−3 in GaP.
Analysis of the Leonard and Ramey Method of Determining the Thickness of Thin Metallic Films
Authors: Marsocci V. A. , Siegel P.
Published: February 2004

The method of determining the thickness of thin metallic films from measurements of the conductivity and the isothermal Hall voltage is examined with a detail made feasible by implementing the analysis as a portion of a computer program designed for the reduction of the measured data. It is observed that the deviation of the computed data points from the values obtained by direct measurement of the thicknesses of the films, is not due predominantly to errors in the assumed values of the bulk mean free path for electrons. It is demonstrated that errors in the measurement of the geometry of the films will produce the same type of deviation in the results but to a larger extent than does the error in the electronic mean free path.
Elastic Precursor Decay in Quartzite for Cylindrical and Spherical Flow
Authors: Johnson James N.
Published: February 2004

When a shear-yielding solid is subjected to impact or explosive loading, the propagating disturbance may consist of two distinct wavefronts. The first is the elastic precursor and the second is the plastic wave, which carries the material to the final stress. In solids which exhibit rate-dependent stress-strain behavior the precursor amplitude is not constant, but decreases with propagation distance. For plane shock waves this decay is due entirely to the rate-dependent property of the material. However, for cylindrical and spherical shock waves there is additional attenuation due to geometrical divergence. The decay of the elastic shock wave in Sioux quartzite is calculated for plane, cylindrical, and spherical flow. If r0 is the radius of the cavity in which the disturbance is initiated, the equations of plane flow can be used with negligible error when r0 > 50 cm for a cylindrical cavity, and r0 > 100 cm for a spherical cavity. For an initial stress of 0.100 Mbar and a cavity radius of 5 cm, the precursor amplitudes at 5 cm from the cavity surface are approx 0.058, 0.041, and 0.030 Mbar for plane, cylindrical, and spherical flow, respectively.
Structures for the Measurement of High-Frequency Properties of Point-Contact Josephson Junctions
Authors: McCumber D. E.
Published: February 2004

Others have demonstrated that superconductor point-contact Josephson junctions interact with electromagnetic fields having free-space wavelengths as short as several hundred microns. To lay a theoretical foundation for more quantitative measurements of junction properties, we have undertaken an analysis of electromagnetic properties of three closed point-contact structures and have computed how those structures influence a point-contact junction described by a simple but plausible model. The analysis is in part an exercise in antenna theory; the conductors, superconductors, and dielectrics making up the structure act as an antenna for the intrinsically nonlinear Josephson junction.
Stimulated Brillouin Scattering in Piezoelectric Semiconductors
Authors: Gordon R. L.
Published: February 2004

A classical theory of Stimulated Brillouin Scattering (SBS) in piezoelectric semiconductors is presented. It is shown that, to a first approximation, acoustoelectric interactions act to change the inverse absorption length of sound from a value α = αs, where αs is the absorption coefficient in the absence of acoustoelectric phenomena, to α = αs+αw+ikβ, where αw is the ultrasonic attenuation and β is the relative change in sound velocity due to piezoelectric stiffening, both as derived by White. Calculations based on a solution obtained with simple boundary conditions indicate that the threshold for SBS can be significantly reduced when the scattering process takes place in the presence of ultrasonic amplification. Results indicate that the threshold may be reduced to a flux in the neighborhood of 106 W/m2, a value attainable with currently available cw lasers.
Large-Signal Effects in Self-Locked Lasers
Authors: Tang C. L. , Statz H.
Published: February 2004

Most past studies of mode locking are concerned with conditions near laser threshold. In this paper we use numerical analysis to study large-signal conditions. Specifically, we restrict ourselves to a traveling wave cavity, a homogeneously broadened line, and a small spatial extent of the medium. The density matrix equations characterizing the medium and Maxwell's equations are solved by computer. It is found for small pump power that mode locking and spike formation occur as previously predicted by the small-signal theory. As the pump intensity is increased, the spike amplitude increases to a certain critical level and then upon further increasing the pump power, the spike repetition frequency increases discontinuously to twice, three times, four times, etc., its original value. The critical spike amplitudes are not simply related to 180° pulses.
Electrical Properties of n-Type Silicon Doped with Gold
Authors: Bullis W. Murray , Strieter F. J.
Published: February 2004

Gold was diffused into arsenic-doped silicon slices with initial resistivity of 0.3 or 5 Ω·cm at temperatures between 850° and 1250°C for times sufficiently long that the gold concentration was essentially constant, except for a very thin surface region which had a much larger concentration. The gold concentration was determined by means of neutron activation analysis. It was found that the gold concentrations were lower than would be expected from published solubility data when diffusion occurred at temperatures below 1100°C. Several surface treatments were found to result in similar gold concentrations when an evaporated gold film was used as the source. The measured room-temperature resistivity was found to be in fair agreement with computations using accepted values for the various silicon parameters and the gold energy levels. Although refinements in the calculations and improved experimental techniques are both still necessary, it has been shown that the qualitative features of the model on which the calculations are based are certainly correct. It has also been shown that gold diffusions in silicon with a moderate dislocation density can be carried out satisfactorily in an oxidizing atmosphere.
Density Changes in Atomic-Pile-Irradiated Polyacrylonitrile
Authors: Beevers R. B.
Published: February 2004

X-ray measurements on polyacrylonitrile which has been irradiated in an atomic pile at dosages up to 3×108 rad show a relatively small amount of change in the scattering diagrams. Samples were examined in the form of compressed disks and dosages calculated from viscosity measurements on Perspex solutions in chloroform. Density measurements showed a linear relationship with dosage and provide a relatively simple and sensitive new dosimetry system.
Shock-Wave Compression of Barium Titanate and 95/5 Lead Zirconate Titanate
Authors: Doran Donald G.
Published: February 2004

The shock compression of the ceramics BaTiO3(5%CaTiO3) and Pb(Zr0.95Ti0.05)O3(1 wt%Nb2O5) was measured in the ranges 5–200 kbar and 2–140 kbar, respectively. Barium titanate exhibits a two-wave structure above 30 kbar; the first wave has a velocity of 6.27 mm/μsec. The cusp in the Hugoniot at 30 kbar is interpreted as a dynamic elastic limit. Comparison of the first wave velocity with the measured longitudinal sound speeds of the tetragonal (ferroelectric) and cubic (paraelectric) phases (5.4 and ∼6.2 mm/μsec, respectively) suggests, as does other evidence, that the material begins to transform to the cubic phase in the neighborhood of 7 kbar. Below 7 kbar, subsonic velocities are observed and it is speculated that this phenomenon is associated with domain reorientation.

The particular lead zirconate composition studied has a two-wave structure above about 40 kbar; the position of the cusp in the Hugoniot depends sensitively on initial density. This cusp is presumably the Hugoniot elastic limit. A weak cusp is also observed at about 2 kbar. The wave velocity is essentially sonic below 2 kbar and subsonic above 2 kbar, increasing to about sonic in the neighborhood of 40 kbar.
Thermal Conductivities of He, Ne, Ar, and of their Mixtures
Authors: Burge Harland L. , Robinson Lawrence Baylor
Published: February 2004

The use of a line-source transient-heat-transfer technique to determine the thermal conductivities of He, Ne, Ar, and of their mixtures is reported along with results. The method employs existing rigorous analytical theory for a finite line source possessing heat capacity. The experimental and analytical techniques minimize the effects of instrument size, radiation, free convection, and thermal separation of the mixtures. The linesource diameter was 0.00763 cm with a central 0.00203-cm nickel temperature sensing coil to provide temperature data. Experimental times of 270 msec or less and total temperature rises of less than 10°C were used to minimize radiation, free convection, and thermal separation effects. The data show excellent agreement with existing data and an internal consistency and accuracy believed to demonstrate elimination of undesirable effects upon over-all thermal-conductivity determinations.
Impact Ionization and Charge Transport in GaAs: GaP 50% Alloy
Authors: Williams Richard
Published: February 2004

Diodes of 50% alloy of GaAs: GaP have been studied in which the material has been made semi-insulating by compensation with iron. An electrode of evaporated gold on this material is blocking for electrons. Electrons may be injected from a base wafer of n-type GaAs. The material is slightly p-type due to ionization of deep acceptor levels. When electrons are injected there is a space-charge-limited current in which the electron concentration is controlled by a small concentration of holes which are present. Analysis of the data gives estimates of the concentration and capture cross section for recombination centers. Using a blocking contact, impact ionization multiplication of carriers injected by light is observed. The impact ionization coefficient is measured.
Dielectric Properties of Solid Solutions of BiFeO3 with Pb(Ti, Zr)O3 at High Temperature and High Frequency
Authors: Smith Robert T. , Achenbach Gary D. , Gerson Robert , James W. J.
Published: February 2004

Solid solutions of BiFeO3 with PbTiO3, PbTi0.5Zr0.5O3, and PbZrO3 were prepared. The crystallographic data on these solutions, which are basically perovskitic, are given. The dielectric constants of the materials were determined at a frequency of 0.53 GHz and at temperatures up to 800°C. Dielectric Curie points were found in solutions containing up to 90 mole % BiFeO3. These results leave little doubt that BiFeO3 is ferroelectric or antiferroelectric. The extrapolated Curie point for BiFeO3 is above 850°C. BiFeO3 appears more likely to be ferroelectric than antiferroelectric, but the distinction between the two classifications may not be sharp.
Analysis of Domain-Wall Motion in Canted Antiferromagnets
Authors: Gyorgy E. M. , Hagedorn F. B.
Published: February 2004

The equation of motion for a domain wall in a canted, orthorhombic antiferromagnet has been solved. The analysis shows that the mobilities for Bloch and Néel walls are nearly alike for small applied fields in materials like YFeO3 and that a great similarity exists with wall motion in ordinary magnetic materials. The main difference between the present and previous expressions for wall velocity is in the functional dependence for the value of the applied field above which deviations from the simple low-field solution occur. However, this field turns out for YFeO3 to be numerically about the same that is obtained by considering the YFeO3 to be simply a weak ferromagnet.
Preparation of a Stabilized Nb3Sn-Based Superconducting Tape by a Diffusion Process
Authors: Gavaler J. R. , Patterson A. , Autler S. H.
Published: February 2004

A diffusion process has been developed for the preparation of Nb3Sn ribbon which can subsequently be stabilized to any desired level. The preparation process is described in detail with emphasis on the effect of reaction time, reaction temperature, and contamination on the critical current of the Nb3Sn. Under optimum conditions, short samples of the ribbon showed a current density of approx 105 A/cm2 in a field of 100 000 G.

The superconducting ribbon, after the diffusion reaction, is partially stabilized by a thin layer of tin which remains on the surface. To further stabilize the ribbon to any desired level, another metal can be bonded to the Nb3Sn through this layer of tin.

A small copper-stabilized test magnet was constructed to determine the degree of degradation occurring when the ribbon is wound into magnet. This magnet was found to have approximately the same current-carrying capacity as short samples of the ribbon.
Elastic-Modulus Effect in the Interaction of Point Defects with Dislocation Ribbons
Authors: Shieh W. T.
Published: February 2004

The interaction energy due to modulus differences of point defects, such as solute atoms and vacancies, with dislocations is derived, using Eshelby's theory of interaction energy of an elastic inhomogeneity in the presence of applied stress field. It is shown that the interaction may be attractive or repulsive depending on the ratio of shear moduli, μi and μ, of the point defects and solvent atoms, respectively, and the parameter ε=[(1+νi) / (1+ν)]/[(1−2νi) / (1−2ν)], where νi and ν are Poisson's ratios of point defects and solvent atoms, respectively. The energy profile for the case of screw-dislocation ribbons differs remarkably from that of edge-dislocation ribbons. The result obtained can be used to account for the annealing-out of the stacking fault of a dislocation ribbon, and the contribution to segregation or desegregation of solute atoms at the stacking fault.
Effects of Electron-Density Fluctuations on Plasma-Column Resonances
Authors: Johnson C. D. , Berry L. A. , Nickel J. C.
Published: February 2004

A theory describing the interaction between electron-density fluctuations and the main dipole resonance of the Dattner spectrum is presented. The results of the theory are compared with experiment, and it is found that the fluctuations can substantially modify the resonance shape.
The Shape of Modulation-Broadened, Unsaturated, Lorentzian Magnetic Resonance Transitions
Authors: Buckmaster H. A. , Dering J. C.
Published: February 2004

The effect of modulation broadening on the shape of unsaturated, Lorentzian absorption lines is examined. The closed, analytic expressions for the Fourier coefficients anL due to Wahlquist are employed to derive exact formulas relating the location and amplitude of the extrema, the location and amplitude of the slope extrema, the slope extrema ratio, and the location of the zeros of the observed a2L to the true half-width for arbitrary modulation amplitude [normalized modulation amplitude (1/β)]. Wahlquist's results for a1L are extended to include the location and amplitude of the slope extrema. It is shown that simultaneous measurement of a1L and a2L, when the normalized modulation amplitude is near unity, can be employed to determine if the lineshape is Lorentzian. For a Lorentzian lineshape, these measurements can be used to determine the linewidth and the number of paramagnetic spins under conditions of near-maximum sensitivity. Graphs and tables of the various results of experimental interest in making these determinations and calculations are included.
Small-Angle Scattering of X-Rays by Neutron-Irradiated Germanium
Authors: den Ouden G.
Published: February 2004

A study has been made of neutron-irradiated germanium single crystals by measuring the small-angle scattering of x-rays. The magnitude of the observed scattering is found to be strongly dependent on the crystallographic orientation of the specimen with respect to the direction of the incident x-ray beam. The scattering can be explained in terms of double-Bragg scattering and is believed to be due to lattice strain associated with the radiation-induced defects. The results imply that the damaged regions (spikes) which in addition to point defects are produced by the bombarding neutrons have a disordered (possibly amorphous) structure with a density which differs from that of the surrounding matrix by at most a few percent. Annealing measurements reveal a distinct annealing stage centered at about 160°C in which approximately 60% of the small-angle scattering recovers. The activation energy of this stage is found to be 1.2 eV and is associated with the annihilation of either vacancies or divacancies. The annealing of the remainder of the small-angle scattering in the temperature range above 350°C is attributed to the recovery of the damaged regions.
Cesium Adsorption on Insulating Substrates
Authors: Kamins T. I.
Published: February 2004

Theoretical and experimental results are presented which clarify the nature of thin cesium layers adsorbed on insulating substrates. From a consideration of the forces acting on adsorbed Cs atoms and ions, it is found that the Cs is adsorbed in atomic form. A model based on image-force considerations predicts the ionization energy of the isolated adsorbed atom to be about 1.4 eV, and the corresponding dipole moment to be about 3 D units directed toward the substrate. As the surface coverage increases, adsorbate interactions produce an increasing ionization energy. Photoemission threshold measurements indicate that the surface coverage on a clean, smooth surface is about one monolayer for a system in thermal equilibrium with a Cs reservoir.
Electrical Properties of Cesium Adsorbed on Insulating Substrates
Authors: Kamins T. I.
Published: February 2004

Theoretical and experimental results are presented which help to clarify the nature of the electrical conductivity of thin cesium layers adsorbed on insulating substrates. A model describing the adsorption kinetics is proposed; it is postulated that most of the desorbing atoms move from a dense first layer into a dilute second layer before desorbing from the film. This model predicts a nearly constant heat of adsorption, which is consistent with experimental observations. Various conduction mechanisms are theoretically considered. It is found that the observed conduction is best described by localized charge transfer in the adsorbed film itself, rather than by metallic conduction or conduction in the substrate. The conductivity is explained on the basis of a tunneling model. A computer simulation which models the conduction between random, filled adsorption sites is described, and good agreement between theory and experimental conductance-temperature data is shown. The theory developed predicts a conductivity modulation due to a change in the number of carriers in the film when an electric field is applied normal to the substrate. Experimental observation of a 60% change in the conductance of Cs layers adsorbed on ferroelectric BaTiO3 substrates is reported. Photoemission studies confirm that the number of electrons in the adsorbed film is substantially different for the two polarizations of the BaTiO3 substrate.
Thermal Release of Inert Gases from a (100) Tungsten Surface
Authors: Kornelsen E. V. , Sinha M. K.
Published: February 2004

A clean (100) tungsten surface has been bombarded with beams of 40 eV to 5 keV ions of Ne, Ar, Kr, and Xe. Gas desorption rates, measured as the crystal was subsequently heated at 40°K/sec, show a number of fairly clearly defined peaks between 400° and 2200°K. The characteristics of these peaks with varying ion energy, mass, and direction of incidence suggest the following interpretation: (a) All peaks below 1650°K (4 for Ne, 5 for Ar, Kr, and Xe) are the result of desorption via a single activated step from sites within, at most, 10 Å of the crystal surface, and (b) the single peak above 1700°K is the result of isotropic diffusion of more deeply penetrating ions with an activation energy 104 kcal/mole, the same for all four gases.
Free Expansion of an Isolated Plasma Column
Authors: Hyman Julius
Published: February 2004

An isolated column of plasma is formed by the partial ionization of neutral argon gas with an intense, high-energy photon beam. The manner in which this plasma expands radially from its initial prescribed position is observed in a region where the plasma has no interaction with confining walls. It is shown that the expansion proceeds initially in accord with the wave equation, having a velocity of propagation u ≈ (γkTe/Mi)1/2, a value predicted theoretically by Shimony and Cahn. The driving force for the plasma expansion comes from the electrons, which are in turn cooled predominately by the adiabatic expansion.
Method of Locating the Axis of a Magnetic Field for Electron-Beam Focusing
Authors: Nishihara H. , Terada M.
Published: February 2004

A quick and accurate method of locating the axis of a magnetic field of rotational symmetry is proposed. It is shown that the deviation of the field axis in direction or in position from the axis of a reference frame (the instrument axis) is found from the angular distribution of the transverse field component. This is detected by rotating a Hall probe on the instrument axis. Formulas for locating the axis of a uniform magnetic field and that of a periodic one for electron-beam focusing are derived, and have been experimentally confirmed. The instrument for the measurement is easily constructed, and the procedures are so simple that results can be obtained in a short time. Moreover, this can be done with error of less than a few percent and with resolution of the order of 10−4 rad in direction in case of uniform fields and of 10−4 in position (ratio to the inner radius of a magnetic field device) in case of periodic fields.