bluuebunny/crossref_metadata_2025 huggingface dataset:
High-pulse-rate glow-discharge stabilization by gas flow
Authors: Dzakowic G. S. , Wutzke S. A.
Published: February 2004

When a transverse-discharge CO2 laser with forced flow is pulsed rapidly, the minimum time between arc-free pulses is substantially greater than the time predicted by the ratio of electrode width to gas velocity. The maximum pulse rate is predicted accurately by flow-model solutions that determine the time required to remove the glow-discharge products from the interelectrode space. The predictions were experimentally verified to a maximum pulse rate of 1 kHz using planar electrodes in a closed-cycle wind tunnel.
Neutron diffraction studies of ThNi2 Co3 and ThNi3 Co2 at 5–297°K
Authors: Atoji M. , Atoji I. , Do-Dinh C. , Wallace W. E.
Published: February 2004

Neutron powder diffraction measurements of ThNi2 Co3 and ThNi3 Co2 show that, in the 5°–297°K range covering both the ordered and disordered magnetic phases, the Ni and Co atoms are distributed in (c); (1/3, 2/3, 0) and (g); (1/2, 0, 1/2), (0, 1/2, 1/2), (1/2, 1/2, 1/2) of D6h1 −P(6/m) mm with the following occupancy distribution: In (c), 1.10 Ni + 0.90 Co and 1.50 Ni + 0.50 Co; in (g), 0.90 Ni + 2.10 Co and 1.50 Ni + 1.50 Co, in ThNi2 Co3 and ThNi3 Co2, respectively. Hence, the numbers of the Co atoms in (c) and (g) in ThNi5−5x Co5x (0≤ × ≤1) are likely given by the interpolation formulas, (5x2+3x)/4 and (−5x2 + 17x)/4, respectively. This implies that the atomic concentration of the larger moment carrier, e.g., Co, is higher in (g) than in (c) at any given x for 0<×<1. A reversed relation was postulated by van Diepen et al. for the isostructural ternaries ThCo5−5x Fe5x and ThNi5−5x Fe5x; thus in these materials, Co and Ni preferentially occupy the 3g sites. The spontaneous ordered ferromagnetic moments of our systems are too small to give rise to the detectable magnetic intensity. Nevertheless, the diffraction effect due to the torque-induced preferential alignment of the powder particles in the external magnetic field verified that the moment direction is the c axis in both ThNi2 Co3 and ThNi3 Co2. The field-induced ferromagnetic moment above the Curie temperature aligns also in the c direction and is particularly large in ThNi2 Co3.
Statistical properties of intensity-modulated coherent radiation. Theoretical and experimental aspects
Authors: Bendjaballah Chérif , Perrot Franc̊oise
Published: February 2004

This paper is concerned with the study of statistical properties of various optical fields obtained by several types of laser intensity modulation from the stationary random point process point of view. We essentially consider intensity correlations and time intervals distributions (TID). A generalization of the already known TID is given: It is the probability distribution (MTID) of the time interval between one photoelectron and the n th following photoelectron. Some theoretical and experimental results are presented in the general case (the time intervals considered are not necessarily small compared to the coherence time of the field). The modulation effect can be characterized by the photoelectron bunching effect. The TID and the MTID are significantly dependent upon the spectral profile of the field, if the used time scale is of the order of the coherence time. On the other hand, the MTID can be interpreted as the probability of the sum over time intervals between two successive photoelectrons. We treat two cases: If the variables of this sum are uncorrelated, we verify the central-limit theorem; if the variables are correlated we study the influence of the correlations when the number of summed variables becomes large.
Cerenkov radiation as a source of ultraviolet radiation
Authors: Piestrup M. A. , Pantell R. H. , Puthoff H. E. , Rothbart G. B.
Published: February 2004

The Cerenkov effect is considered as a source for far and vacuum ultraviolet radiation. Power per unit wavelength compares favorably with synchrotron emission, and the radiation is well collimated and confined to a small solid angle. The absence of spectral lines in the emission provides a source that is useful for certain types of spectroscopic studies.
Revision of the ``dielectric constant'' of ice in the millimeter-wave spectrum
Authors: Perry John W. , Straiton A. W.
Published: February 2004

This communication describes recent measurements of the complex permittivity of ice at 96.5 GHz. The relative premittivity ε′ is more nearly 3 than the previously reported value of 2. Better temperature control of the ice samples resulted in a more accurate measure of the dielectric loss of ice at this frequency.
Arc motion reversal in crossed electric and magnetic fields in an argon atomosphere from 200 to 900 Torr
Authors: Carter Richard P. , Murphree David L.
Published: February 2004

Steady retrograde motion of an argon arc discharge has been obtained at pressures up to 760 Torr, arc currents to 600 A, magnetic field strengths to 6500 G, and electrode spacing of 1.65 cm. This is at a significantly higher current and electrode gap spacing than employed for previously reported retrograde movement of an arc discharge. Erratic retrograde motion at 900 Torr was also observed. Photographs of the arc show the typical vacuum environment retrograde arc shape at pressures above atmospheric.
Influence of environment on the mobility of near-surface dislocations in ionic crystals
Authors: Westwood A. R. C. , Huntington R. D. , Macmillan N. H.
Published: February 2004

The environment-sensitive mobility of near-surface edge and screw dislocations around indentations in LiF, MgO, and NaCl has been studied. It is demonstrated that, contrary to recent reports, adsorbed species can markedly affect dislocation mobility in the absence of either surface step formation or significant reductions in surface free energy. The mechanistic significance of this is discussed.
Conduction of magnetic flux along ferromagnetic wires and ferrite rods
Authors: Cecchetti A. , Ferrari G. , Ronconi F.
Published: February 2004

The applicability of magnetostatic theory to magnetic flux conduction in ferromagnetic wires and ferrite rods is studied. The various causes of deviation of the experimental results from the theory are analyzed. Such an analysis leads to the conclusion that every accord between theory and experimental results can be considered only as a consequence of a combination of the different effects which are not expected in magnetostatic theory.
Voltage modulation of CdS phonon masers
Authors: Vrba J. , Haering R. R.
Published: February 2004

We have investigated the voltage tuning of b-axis CdS phonon masers. Voltage modulation is found to be a fairly complex phenomenon involving amplitude as well as frequency modulation of the phonon maser output. Near threshold, the frequency modulation is typically of the order of 10 kHz/V. The response is flat up to frequencies of the order of the reciprocal of the acoustic transit time. At the higher driving voltages, the tuning is reduced. The device appears promising as a FM communications transmitter.
Normal spectral emissivity of near-stoichiometric single-crystal nickel oxide in the red and in the green
Authors: Madjid A. H. , Martinez J. M.
Published: February 2004

The normal spectral emissivity of an indirectly heated wafer of single-crystal NiO has been measured for λ = 0.645 μm and λ = 0.546 μm. The NiO was characterized by a room-temperature resistivity of 7 × 1010 Ω cm, and the measurements were made using a thermal equivalent of an electrical potentiometer consisting of an incandescent NiO surface as the ``unknown'', a tantalum blackbody furnace as the ``standard'', and a thermoprobe as a ``comparison device'' with which the surface temperatures of the ``unknown'' and the ``standard'' may be compared. This arrangement is useful for the determination of emissivities of substances which are not readily fashioned into blackbodies. It is found that NiO is a very good emitter having an emissivity which ranges from about 0.94 to 0.90 as the temperature is varied from 1100 to 1500°K; and that the emissivity in the red is almost identical to the emissivity in the green. These results permit the speculation that NiO may well radiate as an almost black graybody over the red-green range within the temperature interval stated. The effects of the temperature gradients normal to the surface, which occur as a consequence of the indirect method of heating the wafer, have been examined in detail, but the influence of these nonisothermal conditions was found to be negligible when compared to the limits of error except around the highest temperatures used for the measurements in the green. The intrinsic isothermal emissivities of NiO in the red and in the green were found to be ε0.645 μm = − 691 (5) × 10−8 T + 1.001 (7) and ε0.546 μm = − 959 (2) × 10−8T + 1.033 (1), respectively.
Transient phase gratings in ZnO induced by two-photon absorption
Authors: Dean D. R. , Collins R. J.
Published: February 2004

The light diffracted from transient holographic phase gratings has been used to investigate free-carrier and thermal effects in ZnO. The gratings were optically induced by two-photon absorption of two interfering optical beams. A sequential appearance of two gratings was observed: one from free carriers and the other from lattice heating. Diffraction efficiencies varied with the fourth power of the intensity of the interfering beams and reached ≈ 10% at the highest intensities.
Electron trapping levels in cadmium selenide single crystals
Authors: Manfredotti C. , Rizzo A. , Vasanelli L. , Galassini S. , Ruggiero L.
Published: February 2004

Measurements of space-charge-limited currents have been performed on CdSe single crystals between 77 and 400 °K. Four groups of electron trapping levels have been found at 0.64, 0.49, 0.35, and 0.167 eV, with densities ranging from 5 × 1010 to 1013 cm−3. A check of the results with photocurrent vs light intensity and thermally stimulated currents measurements is presented. The origin and the nature of these centers is discussed and correlated with mobility values measured in the crystals investigated. Finally, contacts and geometry considerations are reported.
Beam divergence of the emission from double-heterostructure injection lasers
Authors: Casey H. C. , Panish M. B. , Merz J. L.
Published: February 2004

Far-field emission patterns of GaAs–AlxGa1-xAs double-heterostructure lasers have been measured to determine the dependence of the beam divergence as a function of active layer thickness d and composition x. The beam divergence in the plane of the junction θ∥ is ∼ 10°, while the beam divergence perpendicular to the junction plane θ⊥ is considerably larger and depends strongly on d and x. Curves are given for θ⊥ and the confinement factor Γ as a function of d between 0.05 and 2.0 μ for x = 0.1, 0.2, 0.3, and 0.4. These curves were calculated by considering the laser as a dielectric waveguide with a refractive index step between GaAs and AlxGa1−xAs.
Calculation of thermoluminescence glow curves by an analog computer
Authors: Razdan K. N. , Wiatrowski W. G. , Brennan W. D.
Published: February 2004

In a previous paper by Razdan, Brennan, and Grossweiner, it was shown that theoretical thermoluminescence (TL) glow curves for first-order kinetics and the temperature-independent preexponential factor can be successfully generated using an analog computer. The present work was undertaken to extend the computer program to include second-order kinetics as well as the temperature dependence of the preexponential factor in both the first- and second-order kinetics. The theoretical TL glow curves obtained with the new programs are reported here. Also reported are the details of the programs developed: the amplitude and time scaling procedures, sample calculations of the initial conditions, and potentiometer settings.
Magneto-optic Kerr rotation of bismuth-substituted iron garnets in the 2–5.2-eV spectral range
Authors: Wittekoek S. , Popma T. J. A.
Published: February 2004

In connection with the large Faraday and Kerr rotations found previously in the compounds Bi3−2xCa2xFe5−x VxO12 (CaVBIG), three series of related garnets containing bismuth have been prepared and the polar Kerr rotation spectra of polycrystalline samples of these materials have been studied. Three strong rotation peaks were observed near 2.7, 4, and 5 eV. In the first series, Y2.2−2xBi0.8Ca2xFe5−x VxO12 with x = 0−1.1, the influence of the V5+ and tetrahedral Fe3+ concentration on the three transitions was studied, in the second series, Y3−xBixFe5O12 (x = 0−1.0), the influence of Bi3+ concentration, and in the third series, Y2.0−xBi1.0CaxFe5−x ZrxO12, the influence of octahedral Fe3+. The transitions near 2.7 and 4 eV are strongly enhanced in proportion to the Bi3+ content. The transition near 2.7 eV, which is responsible for the high Faraday rotation in the visible, is proportional to the tetrahedral Fe3+ content. The effect of a small mixing of the oxygen −2p, tetrahedral iron 3d, and bismuth 6p electronic wave functions is discussed in order to explain the results. The large value of the Kerr rotations (1°) is of interest for magneto-optic applications.
High critical current densities found for thick Nb12Al3Ge superconducting deposits made by high-rate sputtering
Authors: Dahlgren S. D. , Kroeger D. M.
Published: February 2004

Superconducting critical current densities up to 5.2 × 105 A/cm2 at 75 kOe and 4.2°K, and up to 4.4 × 105 A/cm2 at 100 kOe were measured for a 66-μm-thick Nb12Al3Ge deposit made at a rate of 1 μm/min by high-rate sputtering. Current-density-vs-transverse-magnetic-field curves were either linear or nearly linear, and the current density dropped only 33% over the field range investigated (50–100 kOe). The sample that carried the highest current densities was deposited at 20°C and heat treated one day at 750°C. Current densities for another sample from the same deposit, but heat treated 20 days at 750°C, were about 14% lower than for the sample heat treated one day. The deposits were body-centered-cubic (bcc) when deposited at 20°C. Heat treatment at 750°C produced a single metastable A-15 phase containing grains of 350-Å diameter; the small grain size presumably accounted for the high current density. Current densities measured with the field perpendicular to the deposit plane were only about 14% lower than with the field parallel to the deposit plane, which indicated the A-15 phase grains formed by heat treatment at 750°C were nearly equiaxed. The high current density results and the availability of high-rate sputtering equipment encourage fabrication of practical quantities of sputter-deposited Nb–Al–Ge superconducting products. Estimated fabrication rates and costs were reasonable.
Energy spectrum of Na+ ions sputtered from NaCl crystals
Authors: Miyagawa S.
Published: February 2004

The energy spectrum of Na+ ions sputtered from NaCl crystals under 20-keV He+ ion bombardment is measured in the energy range from 1 eV to 100 eV using a time-of-flight technique. The spectrum behaves like that of neutral atoms sputtered from metals.
Effect of photocarriers on surface barrier electroreflectance in MOS capacitor configurations
Authors: Bottka N.
Published: February 2004

Photoexcited carriers redistribute the charges in the space-charge region of a semiconductor. The wavelength-dependent photoeffect is most significant at low temperatures and strongly affects the modulating electric field in surface barrier electroreflectance (SBER). This work undertakes a study of this effect on SBER by making concurrent ac capacitance and conductance measurements in the MOS configuration and comparing the results with photoconductivity theory. The relationship between photocapacitance and the effective modulating electric field is investigated, providing herewith a better understanding of SBER at low temperatures.
Local- and defect-mode infrared absorption of carbon ions implanted in silicon
Authors: Vaidyanathan K. V.
Published: February 2004

Infrared-absorption measurements on carbon-implanted silicon are reported. A localized vibrational mode for substitutional carbon has been observed in annealed samples and in samples implanted at 500°C. The results suggest that between 40 and 60% of the implanted ions occupy substitutional sites. A broad absorption band which shifts to shorter wavelength on annealing has been observed and is attributed to the formation of SiC microcrystals. Absorption bands at 1097, 750, 640, and 625 cm−1 have been observed in pulled crystals. It is suggested that these bands arise due to the presence of carbon-oxygen complexes formed during implantation.
Collisional effects on the transient response of a cylindrical electrostatic probe
Authors: Peterson E. W.
Published: February 2004

The low-frequency response characteristics of an electron-attracting cylindrical probe operating in the transition regime are presented. The analysis is applicable for probes of arbitrary ratios of radius to Debye length operating in plasmas where the collisional effects result from electron-neutral interactions. Equations which relate the probe current fluctuations to fluctuations in the plasma properties are presented with the intent of providing an explicit formulation for data interpretation. Conditions are also defined which must be satisfied if the intensity of the electron density fluctuations are to be determined directly from probe current measurements. In addition, qualitative results are presented which describe the probe transient response when collisional effects result from electron-ion interactions.
Influence of electrode configuration upon electric breakdown in electronegative gases
Authors: Crowe Robert W.
Published: February 2004

This paper represents an effort to derive a theoretical expression which will predict the influence of electrode configuration upon the electric breakdown voltage in electronegative gases. The initial portion of the paper is involved with a presentation and discussion of the generalized condition for breakdown in all gases for an unspecified electrode configuration or structure. The equation is then applied to the particular configuration consisting of two parallel wires of infinite length. An equation is derived, from which it is possible to calculate the breakdown voltage of any gas as a function of the radius of the wire r0. Knowledge of certain parameters, characteristic of a specific gas, is the only requirement necessary to accomplish this. The results of calculations are presented for the simple gas nitrogen, which does not have a tendency to produce negative ions by electron capture. These are compared with the results of similar calculations for the highly electronegative gas C3F8. The calculations show that the breakdown voltage of nitrogen is strongly dependent upon r0, which is in agreement with the experimental observations of previous investigators. C3F8, on the other hand, showed entirely different behavior. To be more specific, the value of r0 appeared to have little if any influence upon its breakdown voltage. Furthermore, it is shown that the electrode configuration, giving rise to distortion of the electric field, does not affect the final outcome of the calculations when the gas under consideration is highly electronegative. Experimental verification of this prediction has been achieved by measuring the breakdown voltage of C3F8 in a uniform electric field, and comparing the results with those obtained with the point-to-plane configuration. For both cases, the results agree to within 10%, providing adequate verification of the conclusions derived from the theory.
Dynamic behavior of Josephson tunnel junctions in the subnanosecond range
Authors: Zappe H. H. , Grebe K. R.
Published: February 2004

Transitions from the zero-voltage to the voltage state have been directly measured on large (≃104 μm2) Josephson junctions. By adjusting the current load, the switching times (10–90%) were varied from 60 to 400 psec. Good agreement was found between theoretical and experimental results. The times required to transfer current from junctions into superconductive inductances (10−11−10−10 H) were also investigated. The switching times ranged from 300 to 550 psec and agreed basically with our simple theoretical model. To explain the details of the voltage developed during current transfer, self-pumped junction resonances had to be invoked. Although these times are expected to be smaller in miniaturized devices, they represent to our knowledge the shortest times ever reported for circuits with a dissipation of less than 10−5 W in continuous operation.
Addendum: xerographic discharge characteristics of photoreceptors. II
Authors: Chen Inan
Published: February 2004

An error in the previous paper of the same title, concerning the discharge with bulk generated carriers, has been corrected. The conclusions of the previous paper are still qualitatively correct.
Sensitive LiTaO3 pyroelectric detector
Authors: Roundy C. B. , Byer R. L.
Published: February 2004

We have constructed and tested a sensitive LiTaO3 pyroelectric detector with a measured NEP of 1.3×10−10 W/(Hz)1/2, which is in good agreement with the theoretical value. LiTaO3 has the advantages of being nonhygroscopic, relatively insensitive to ambient temperature, and has sufficient mechanical strength to polish to 10-μ-thick samples. We show that no one figure of merit is sufficient for evaluating pyroelectric materials for use in low NEP detectors.
Impact of cylinders on a rigid boundary
Authors: Wilkins Mark L. , Guinan Michael W.
Published: February 2004

An experimental procedure originally proposed by G. I. Taylor to determine the dynamic yield point of metals is studied, using high-speed computer simulations. A simple method is outlined for determining the yield strength of materials that can be described by elastic-plastic theory. Results for several metals are presented.
Instantaneous and equilibrium Grüneisen parameters for a nonlinear viscoelastic polymer
Authors: Nunziato Jace W. , Walsh Edward K.
Published: February 2004

In studying the propagation of shock waves in nonlinear viscoelastic solids, it is useful to characterize the mechanical response of the material in terms of instantaneous and equilibrium stress-strain functions. A natural extension of this concept to include thermodynamic influences leads to the consideration of instantaneous and equilibrium thermodynamic response functions for the stress and internal energy. An important factor in the thermoviscoelastic behavior concerns the stress/energy response as characterized by the Grüneisen parameter, or in the present context, an instantaneous and equilibrium parameter. An example of these parameters and their temperature dependence is given for the solid polymer, polymethyl methacrylate, based on a thermoviscoelastic constitutive model developed for predicting steady shock wave propagation.
Photoionization cross sections of holes at zinc centers in silicon
Authors: Herman J. M. , Sah C. T.
Published: February 2004

The spectral dependences of the photoionization cross sections for holes at neutral and singly ionized zinc centers are measured using photocapacitance transient techniques in n + p junctions. Lucovsky's delta function potential model fits the results well. The photoionization cross section for holes at singly ionized zinc centers is much greater than the photoionization cross section for electrons at doubly ionized zinc centers. A large electric field dependence and a small temperature dependence are observed near the absorption edge of the photoionization cross section for holes at singly ionized zinc centers. The temperature dependence indicates a possible two-step photothermal process has taken place when the center is photoionized.
Alkaline-metals-silicon Schottky barriers
Authors: Szydlo N. , Poirier R.
Published: February 2004

The Schottky barrier heights at the interface between metallic alkaline metals and vacuum-cleaved n-type Si have been found to be 0.46±0.03 and 0.43±0.03 eV, respectively, for potassium and cesium. The Cs-p-Si contact has presented a barrier height of 0.57±0.03 eV. The barrier height was determined from measurements of the reverse or forward current-voltage characteristic of Schottky diodes in a vacuum of 10−7 or 10−6 Torr and at 283 or 273°K.
Brewster-angle method of thin-film index measurement
Authors: Watts R. K.
Published: February 2004

An experimental test is proposed for distinguishing between Brewster's angle and interference anomalies in measuring the refractive index of a thin film by Abelès,s method.
Equivalent circuit and equipartition theorem in lossy dielectric or ferroelectric capacitors
Authors: van der Ziel A.
Published: February 2004

A simple model for a lossy dielectric is investigated involving a material with two time constants τ and τ1, where τ≪τ1, and the noise between the device terminals due to these losses is evaluated. The reason for an apparent violation of the equipartition law is pointed out. The discussion is valid for relatively small losses. The results are applied to ferroelectric capacitors used as pyroelectric detectors.
Inhibition of radiation blistering in tin bombarded by protons and alpha particles
Authors: Mikkelson R. C. , Miller J. W. , Holland R. E. , Gemmell D. S.
Published: February 2004

Tin monocrystals have been bombarded with large doses ([inverted lazy s]5×1017 particles/cm2) of 1.5–4-MeV ions of H and He. Proton irradiations above 225 °C produce neither visible surface damage nor degradation of the ability of a crystal to channel the incident particles. Room-temperature irradiations by H or He ions produce little observable damage near the crystal surfaces unless followed by post-irradiation anneals to 220 °C or above. After such anneals, however, channeling measurements show permanent deterioration and the surfaces may show deformations such as swelling, blistering, and effervescence.
Nanosecond surface discharge study by using Dust figure techniques
Authors: Murooka Y. , Koyama S.
Published: February 2004

The developing mechanisms of the positive and negative corona streamers on the insulation surface have been studied by using the Dust figure technique together with a line pulser. The present method has the advantage of measuring the velocity of corona discharge development and the discharge mechanism, because the distributions of the positive and negative charges in the discharge figure can be colorfully separated and recorded. By applying shorter time pulses from 10- to 920-nsec duration to a needle point where a glass plate is sandwiched in between the needle and plate electrodes, the diameter of the recorded discharge and the charge quantities and their distributions against the pulse duration were obtained. The observed average velocities of the developing corona streamers at a voltage of 12.0 kV were 2.05×108 cm/sec in the positive and 0.63×108 cm/sec in the negative, respectively. Moreover, when the negative pulse voltage was applied to the needle point the formation time lag of the cathode fall was about 10 nsec and the resulting high densities of the positive and the negative charges induced a back discharge.
Partial trapping of a low-density plasma by an rf quasipotential well
Authors: Johnson Curtis D.
Published: February 2004

A study is made of plasma trapping by the radio frequency (rf) quasipotential well of a cylindrical resonant cavity operating in the TM011 mode. This is done by injecting a plasma into the cavity with continuous rf excitation and observing the subsequent plasma decay. The experiment is conducted in such a way that the potential well appears only during the plasma decay. A significant delay in decay time is observed, and calculations indicate this to be due to partial trapping of the plasma by the quasipotential well. This trapping is observed experimentally at an electron density ne[inverted lazy s]109cm−3 for a plasma with an electron temperature Te[inverted lazy s]2.5 eV. Trapping is noted by an increase in decay time for an average rf quasipotential well energy <8 eV. For higher well energy, an anomalous loss of plasma is observed as indicated by a marked decrease in decay time.
Spectral analysis of the signal from the Laser Doppler Velocimeter: turbulent flows
Authors: Edwards R. V. , Angus J. C. , Dunning John W.
Published: February 2004

A method for prediction and analysis of the spectrum of the signal from the Laser Doppler Velocimeter is presented. The results relate the heterodyne spectrum of the signal to the space-time correlation fuction for the turbulent transport of tracer particles in the fluid and to the characteristics of the optical system.
Distribution function of forces exerted by defects on domain walls in 50–50% NiFe
Authors: Baldwin John A. , Milstein Frederick
Published: February 2004

Defects in ferromagnetic materials can exert forces on domain walls. For a given defect there is a maximum force fm which it can exert. For any greater force, the wall snaps free of the defect. At this point the average wall position has moved past the defect a distance z0, called the range of the defect. There is a linear relation between fm and z0 given by fm=k z0, where k is a spring constant. There is a distribution function n(z0) of defect ranges such that n(z0) dz0 gives the number of defects per unit volume having a range between z0 and z0+dz0. The number of defects per unit volume which can exert a maximum force between fm and fm+dfm is n(fm/k) (dfm/k). The distribution function for a particular sample (a tape-wound core of grain-oriented 50–50% NiFe) has been determined. It is given by n(z0)=z0−1Nexp(−z0/Z), where N≃1.6×1012 m−3 and Z=average range ≃ 70 μ. The spring constant k≃5×10−3 N/m. The maximum force averaged over the distribution is fm≃3.5×10−7 N. The total number of defects with which a steadily moving wall interacts at any one time is finite and is N0≃104. The defect density is estimated to be ≃2×1013 m−3. The results are checked by comparison with independent experimental and theoretical results and are found to be in satisfactory agreement provided that some experimental results are reinterpreted in the light of other experiments which observe the wall configuration rather than assuming it.
Magnetic bubble detection using waveguide fiber optics
Authors: Borrelli N. F.
Published: February 2004

A magnetic bubble domain was detected optically by the Faraday effect using a single-mode optical waveguide structure and a photomultiplier. The light source was a 20-mW He–Ne laser. The optical waveguide having a 5-μ core diameter was placed 5 μ from a garnet film which supported 8-μ bubble domains; the bubble motion was produced by the action of a conducting gold strip evaporated onto the garnet film. It is suggested that detection of bubble domains of the order of 1 μ could be made by the method with the appropriate waveguide with no loss of signal.
Magnetization of hysteretic superconductors for complete field penetration and a critical-state model with Jc(H)=α/H
Authors: Ohmer Melvin C. , Heinrich John P.
Published: February 2004

A critical-state model with Jc(H)=α/H has been developed for cylindrical geometries. It qualitatively describes the shape of magnetization curves obtained on multifilamentary superconducting wire and it accurately predicts the hysteretic loss. The size dependence of the hysteretic loss for this model is essentially the same as the Bean-London model result. However the maximum magnetization for this model is proportional to R1/2. The temperature dependence of the hysteretic loss and α have been determined from magnetization data for NbTi wire.
Dynamics of elliptical magnetic bubbles
Authors: Wanas M. A.
Published: February 2004

Domain-wall anisotropy forces cylindrical domains (magnetic bubbles) to deviate from circular to elliptical geometry. Dynamics of elliptical bubbles are considered. It is found that the magnitude of the damping and coercive forces experienced by a moving eliptical bubble depends upon the direction of bubble motion. Bubbles suffer less damping and less coercion if moved along the wall-preferred direction.
Domain walls in bubble films. I. General theory of static properties
Authors: Schlömann Ernst
Published: February 2004

The magnetic field due to surface charge distorts the internal structure of domain walls in films as compared to those in an infinite medium. In the midplane of the film the wall magnetization is parallel to the wall plane (for stationary walls), but near the film surface it is ``twisted'' into a direction that can be almost perpendicular to the wall plane. The width and energy of such walls and the twist angle have been calculated by a variational method for uniaxial anisotropy and stationary plane walls. For very thick films (film thickness » wall width in an infinite medium) the reciprocal wall width and the wall energy are smaller than the values for an untwisted wall by approximately a factor of (1−0.65σ)1/2, where σ=4πM0/Ha, M0 is the saturation magnetization, and Ha the uniaxial anisotropy field. For very thin films they are smaller by a factor of (1−σ)1/2.
Note on shock-wave velocity in high-speed liquid-solid impact
Authors: Huang Yen C. , Hammitt F. G. , Mitchell T. M.
Published: February 2004

A better relationship between the shock-wave and impact velocities in high-speed water-solid impact is determined from the fundamental equations of continuity, momentum, and state. A second-order relationship is hypothesized and the necessary coefficients then found using the Tait equation of state. Very good agreement is found with available experimental data for water.
``Secondary'' dynamic scattering in negative nematic liquid crystal films
Authors: Chang Roger
Published: February 2004

Experimental microstructural evidence is presented to show that the intervortex spacing decreases monotonically with increasing applied voltage beyond the ``secondary'' hydrodynamic threshold for all doped negative nematic liquid crystal films.
Volume-diffusion-controlled shrinkage of an isolated grain-boundary pore
Authors: Markworth Alan J.
Published: February 2004

An analytical study is presented of the quasistationary volume-diffusion-controlled shrinkage kinetics of an isolated spherical pore situated on an otherwise infinite planar grain boundary. The vacancy concentration along the boundary is taken to be everywhere constant, whereas that in the solid along the pore surface is assumed to be a function of position. An exact solution of the Laplace equation is used to evaluate the current of vacancies from the pore to the boundary. As expected, it is found that the ratio of the instantaneous vacancy current emanating from a pore situated on a grain boundary to that associated with an intragranular pore having the same size, but located far from any boundaries, is generally greater than unity. A quantitative description is given of the dependence of this ratio upon the nature of the vacancy concentration assumed to exist in the solid along the surface of the grain-boundary pore.
Photosensitivity in superconducting tunnel junctions with a cadmium selenide barrier
Authors: Rissman Paul
Published: February 2004

Photosensitivity is observed in superconducting tunnel junctions with a cadmium selenide barrier. This supports the conclusion that the important factor in determining photosensitivity is the predominance of trap levels of only one type, in this case hole trap levels.
Optical properties of SiAs single crystals
Authors: Kunioka Akio , Ho K. K. , Sakai Yoshio
Published: February 2004

Single crystals of silicon arsenide have been grown by the Bridgman technique. SiAs was found to have an optical energy gap of 2.18±0.05 eV at room temperature and seemed to exhibit a direct optical transition. The temperature coefficient of the energy gap was about −(2.8±0.5)×10−4 eV/K. From the multiple interference fringes of some SiAs samples, the refractive index was calculated. Over a wavelength equal to infinity, it had a value of 3.1±0.1, thus leading to a value of 9.6±0.6 for the high-frequency dielectric constant. The extinction coefficient near the absorption edge has also been deduced.
Secondary electron emission from a Fe(110) single crystal
Authors: Koshikawa T. , Shimizu R. , Goto K. , Ishikawa K.
Published: February 2004

The structure in the σ (Ep) and η (Ep) curves obtained from a Fe (110) single crystal were studied for primary energies, 40 eV ∼ 2.0 keV. The characteristics of σθ(Ep) and ηθ(Ep) and the fine structures of σEp (θ) and ηEp (θ) are shown to play complementary roles. The features in the structure become broader with increasing Ep. This effect seems to correspond to the fact that the dependence of the diffraction effect on Ep becomes less sensitive with the increase of primary energy Ep.
Experimental properties of injection lasers. III. Current dependence of polarization
Authors: Sommers H. S. , Lockwood H. F.
Published: February 2004

The power distribution function which describes the shape and current dependence of the lateral beam is applied to a phenomenological model of weakly polarized injection lasers. It predicts that the polarization of coherent power should drop rapidly from an infinite value at threshold to near unity at high drive. Careful measurement of polarization of a laser representative of the model, with especial attention to rejection of the spontaneous emission, supports this conclusion. The form of the power distribution function used in the analysis implies that lasers with strong polarization at high drive have large threshold differences of the two polarizations, suggesting that present theories of the source of polarization are inadequate. The difficulty of interpreting the present results in terms of spatial hole burning or inhomogeneities is pointed out.
Random walk models of semiconductor noise
Authors: Alberding N.
Published: February 2004

The ensemble averages of the spectral densities appropriate to various types of random walk are evaluated using a Monte Carlo method. The results are compared with theory. It is shown that a ``drifting'' walk cannot in itself explain the occurrence of 1/f noise in semiconductors.
Surface layers of Nb–Al compounds on niobium
Authors: Dickey J. M. , Garcia N. , Strongin Myron
Published: February 2004

Thin layers of Nb–Al compounds on a Nb substrate have been produced. An initial deposit of 200 Å of Al yielded samples with transition temperatures of 14°K after suitable heat treatment, and it appears that Nb3Al is formed.
Photoconductivity of chromium-compensated GaAs after irradiation by 0.8-MeV electrons
Authors: O'Brien J. K. , Corelli J. C.
Published: February 2004

The photoconductive response to infrared light of high-resistivity chromium-compensated GaAs is examined before and after irradiation (at 300°K) with 0.8-MeV electrons. The typical spectrum of this material is observed for the unirradiated case. After irradiation two induced levels were observed; a deep trap at Ec − 1.32 eV and a level at Ec − 0.54 eV. For high fluences the band gap exhibits striking changes and infrared response was no longer seen at energies below 0.52 eV. Isochronal anneals to 350°C restored the photoconductivity spectrum to a semblance of the unirradiated case.
Transverse surface waves on a piezoelectric material carrying a metal layer of finite thickness
Authors: Curtis R. G. , Redwood M.
Published: February 2004

Theory of the propagation of a surface wave related both to Bleustein-Gulyaev waves and Love waves is developed. The wave has unidirectional particle motion perpendicular to the direction of propagation and parallel to the surface of a piezoelectric material which is covered with a finite-thickness layer of an isotropic conducting material. An equation relating phase velocity to material costants is solved in closed form for a piezoelectric material of class 6mm, and conditions for the existence of various modes are presented. Piezoelectricity allows a nonleaky but dispersive wave to exist under conditions is which no love wave is possible, namely, when the shear wave velocity in the layer is greater than that in the substrate. Numerical results are presented for aluminium, gold, and zinc layers on PZT 4 ceramic.
Controlled thermonuclear reactor first wall sputtering and wall life estimates
Authors: Laegreid N. , Dahlgren S. D.
Published: February 2004

Equations and graphs are developed for rapid estimation of sputtering rates at the first wall of controlled thermonuclear reactors (CTR). High-energy particle sputtering yield data and potential particle fluxes are presently not readily available for most materials and many reactor designs, thus the equations were set up to provide rapid estimation of sputtering effects when data become available. Limiting wall sputtering-yield-particle-flux products were determined according to the equation ΣSμφμ < Kd(t′)/t′, where Sμ and φμ are the sputtering yield (atoms/particle) and flux (particles/cm2 sec) of bombarding species μ, d(t′) is the allowable wall thickness removal (in cm) in t′ years, and K is a material constant. K varied little (from 1.36×1015 to 3.28×1015) for the wall materials considered (V, Mo, Nb, Ta, Zr, stainless steel, and Al2O3), so that a conservative estimate for the limiting sputtering-yield-particle-flux product is 1015 times the allowable sputtering rate in cm/yr. The sputtering yield in molecules per particle given for compounds such as Al2O3 must be multiplied by the number of atoms in the molecule to satisfy this relationship. Use of the equations to estimate wall sputtering of pulsed (high-β) and steady-state (low-β) reactors indicated that sputtering rates will be sufficiently high that they cannot be ignored. Factors reducing sputtering erosion rates, such as surface roughness, impurity effects, and sputtered material redeposition, are discussed.
Wave-packet spreading on a random transmission line
Authors: Besieris Ioannis M. , Tappert Frederick D.
Published: February 2004

Quantitative predictions are made of the spreading and attenuation of a single forward-propagating wave packet on a random, dissipative, and dispersive transmission line modeled by a generalized telegraphist's equation with slowly varying random coefficients.
Magnetogasdynamic compression of a coaxial plasma accelerator flow for micrometeoroid simulation
Authors: Igenbergs Eduard B. , Shriver Edward L.
Published: February 2004

A new configuration of coaxial plasma accelerator with self-energized magnetic compressor coil attached is described. It is shown that the circuit may be treated theoretically by analyzing an equivalent circuit mesh. The results obtained from the theoretical analysis are shown to compare favorably with the results measured experimentally. Using this accelerator configuration, glass beads of 125-μ diameter were accelerated to velocities as high as 11 km/sec, while 700-μ-diam glass beads were accelerated to velocities as high as 5 km/sec. The velocities are within the hypervelocity regime of meteroids.
Technique for studying dynamic tensile failure in liquids: application to glycerol
Authors: Carlson G. A. , Henry K. W.
Published: February 2004

A new experimental technique has been developed for the study of the dynamic tensile strength of liquids. The liquid is confined between a solid plate and a stretched aluminized Mylar film. Pulsed electron beam deposition in the plate generates a stress wave which traverses the liquid and gives a high tensile stress during reflection at the Mylar-covered free surface. Interferometric analysis of the motion of the Mylar film provides a sensitive measure of the stress-wave-liquid interaction. The technique has been used to determine a dynamic tensile strength for glycerol at room temperature of 0.6±0.1 kbar from 5 to 23 kbar/μsec. No variation of tensile strength with stress rate was found.
Diagnosis of the optical properties and structure of lanthanum hexaboride thin films
Authors: Peschmann K. R. , Calow J. T. , Knauff K. G.
Published: February 2004

The application of the typical metallic refractory compound lanthanum hexaboride as a thin-film material has been studied. Film properties are estimated by using bulk optical constants derived from a Kramers-Kronig analysis of the bulk material. Films with thicknesses of 130–2000 Å have been prepared by sputtering and electron-beam evaporation onto substrates with temperatures between 100 and 1200 °C. The effective optical constants of the films are derived by means of a computer program and used together with the modified Drude theory to give the free-electron relaxation time. Conductivity measurements give the electron mean free path. The optical and electrical film data are compared with the bulk properties of the material. The observed differences can be explained by the influence of crystal imperfections. The explanation is in qualitative agreement with information from x-ray diffractometer scans.
Microstructure of cobalt and cobalt-phosphorous thin films
Authors: Admon U. , Bar-Or A. , Treves D.
Published: February 2004

The morphology and crystallography of Co and Co(P) thin films (<500 Å), produced by electroplating, were examined by electron microscopy and diffraction. It was found that the pH of the plating solution affects phase constitution and texture as it does in thicker films. Films deposited at low pH showed appreciable proportion of fcc grains, and the hexagonal grains were oriented with their axes of easy magnetization parallel to the film plane. At high pH, the deposits were hexagonal and showed 〈00.2〉 fiber axis. A pH of 3 to 4 corresponded to the transition region. Phosphorus was co-deposited with cobalt by adding hypophosphite ion to the plating solution. It acts as grain refiner, stabilizes the hexagonal phase, and randomizes the texture. An explanation of the effect of phosphorus on magnetic properties, which enables magneto-optic recording, is suggested.
High-resolution spectroscopy of I2 using laser-molecularbeam techniques
Authors: Youmans D. G. , Hackel L. A. , Ezekiel S.
Published: February 2004

Laser-molecular-beam techniques have been used to observe the hyperfine structure of molecular I2. A 5145-Å argon laser, tuneable over 0.05 Å, is used to induce fluorescence in a molecular beam of I2. The measured width of the individual I2 transitions is 3 MHz, i.e., a resolution of 5×10−9. The natural width of the lines has been estimated to be less than 800 kHz.
Reversible floating-gate memory
Authors: Card H. C. , Worrall A. G.
Published: February 2004

Reversible memory behavior is reported for an insulated gate structure, in which charge is stored on a polysilicon gate. This gate is floating between layers of silicon dioxide (SiO2) and silicon nitride (Si3N4). The floating gate is charged negatively by hot carrier injection through the SiO2, from an avalanche plasma in the underlying silicon. This charge can then be removed by applying a positive voltage between an external gate and the silicon substrate. The positive voltage causes electrons to flow through the nitride layer. Both charge states are remembered when external bias voltages are removed. The importance of circuit configuration during charging is discussed, and improvements of injection efficiency for a favorable configuration are described.
ac losses in superconducting magnet suspensions for high-speed transportation
Authors: Tinkham M.
Published: February 2004

A rather general relation is derived between vertical accelerations of the train and cryogenic power dissipation due to ac currents induced in the superconducting suspension magnets. Our theoretical results account for the order of magnitude of the rather large losses observed in the Fuji Electric test vehicle, which used less than state-of-the-art conductors. Even with parameters estimated to represent the best commercially available materials, however, it appears that these losses may be comparable with the total heat leak due to all other causes if the accelerations are as large as permitted by subjective human ride quality considerations. Empirical data on losses under appropriate conditions of B, Ḃ, and I/Ic may be needed to ascertain whether improved materials will be required to avoid serious design constraints by cryogenic heating.