bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Superconducting Properties of Ti–Nb–Ta Ternary Alloys
Authors: Suenaga M. , Ralls K. M.
Published: February 2004

Superconducting properties of the ternary system Ti–Nb–Ta were measured. Critical temperatures were found to decrease with increasing amount of Ta in the alloys from those of Ti–Nb binary alloys. However, a broad plateau of high critical fields (above 120 kG) was observed in the region around the composition 63 at.% Ti-31 at.% Nb-6 at.% Ta. This plateau is discussed in relationship with the corrected Abrikosov upper critical field and with the Maki upper critical field which includes the effects of Pauli paramagnetism and spin-orbit scattering. Critical current density data are also reported for one alloy.
Superconducting Origin of Spikes in the Differential Conductance of p-n and Point Contact Tunnel Junctions
Authors: Shaw Roger W.
Published: February 2004

Structure consisting of pairs of negative-going spikes in differential conductance vs bias voltage are reported for GaAs p-n junctions and for superconducting point contacts against a variety of conductors, including semiconductors. The spike pairs are symmetrically positioned about zero bias as in the previous observations of such structure by Shewchun and Williams and by Esaki and Stiles. Superconductivity is demonstrated to be essential to the phenomenon. A detailed model is discussed involving Josephson tunneling between microscopic particles within the semiconductor or point contact tunneling region. Temperature and low magnetic field data (H < 3 kOe) are in excellent agreement with the model while at higher fields the full interference pattern expected of a Josephson junction is not observed.
Magnetic-Anisotropy and Magnetostriction Constants of Substituted Lithium Ferrites at 300°K
Authors: Dionne Gerald F.
Published: February 2004

Room-temperature measurements of magnetic-anisotropy constants K1 and K2 and magnetostriction constants λ100 and λ111 on single-crystal lithium ferrites containing Al, Ti, Ga, Zn, In, Co, and Mn have been carried out by means of ferrimagnetic-resonance techniques at 5.8 GHz. From the measurements of K1, it appears that only cobalt has a significant effect on anisotropy, in accord with earlier works on other spinels. From the magnetostriction measurements, it is concluded that manganese has a significant effect on λ100 and λ111, where changes in the signs of both constants occur as the amount of substitution is increased. This effect of manganese substitutions is shown to also exist in the yttrium-iron garnet system.
Interaction of Capacitor-Bank-Produced Megagauss Magnetic Field with Small Single-Turn Coil
Authors: Shearer J. W.
Published: February 2004

Experiments on the production of high magnetic fields in single-turn coils by means of high-voltage capacitor banks are described. Fields as high as 3.5 megagauss have been produced. Numerical analysis of the interaction of this field with the metal wall shows that magnetic diffusion and wall compression are the principal interaction phenomena. In addition, experimental and theoretical evidence are presented for the emission of a vapor cloud by the wall into the magnetic-field volume. Finally, a simple approximate method for calculating the early time history of the magnetic field and coil motion is shown to give reasonable agreement with experiment.
Mössbauer Spectra of Some Magnetic Iron Hydroxides Precipitated by Porous Silica
Authors: Greenblatt S. , King F. T.
Published: February 2004

Mössbauer spectra of iron hydroxide complexes precipitated by a high surface porous silica have been obtained. In the presence of porous silica, oxidation of metallic iron results in the formation of γ-FeOOH and a noncrystalline magnetic oxide. Heating at 350°C in air converts both of the substances to δ-FeOOH. The decomposition of iron salts in the absence of silica does not give the same products. These differences may reflect the greater freedom from foreign ions characteristic of the preparation.
Faraday Rotation and Dichroism of Bismuth Calcium Vanadium Iron Garnet
Authors: Buhrer Carl F.
Published: February 2004

The magneto-optic properties of garnet single crystals close to the compensated composition BiCa2Fe4VO12 were measured in the region from 0.6 to 1.2 μ. The magnetic Faraday rotation, circular dichroism, and absorption are given as functions of wavelength. The rotation is several times greater than that of other garnets, and a figure of merit of 5°/dB is reached near 0.8 μ. Rotation measurements on two other compositions in this system show that the sign of the Faraday effect is opposite that of other compensated garnets and indicate that the origin of the large effect may be the bismuth ion.
Plastic Deformation of Alkali Halide Crystals at High Pressure: Work-Hardening Effects
Authors: Davis L. A. , Gordon R. B.
Published: February 2004

The influence of hydrostatic pressure on the plastic deformation of alkali halide single crystals at large strain has been observed. The rates of work hardening in stages I and II are approximately independent of pressure in LiF, NaCl, and KCl, but both are doubled at 4.3 kbar in KI. In stage II the fractional increase of plastic flow stress at high pressure in an interrupted compression test, δσ/σ, is accounted for by the pressure-induced increase in elastic constants in all the alkali halides examined. Evidently, the strength in stage II is controlled by elastic interactions. The stress at the onset of stage III, σIII, in the deformation of NaCl at 4.3 kbar is about half that at 1 atm; it is reduced slightly in KCl and is unchanged in KI. Deformation proceeds at lower stresses in stage III in NaCl and KCl under 4.3 kbar, and if compression at 1 atm in this stage is interrupted and reinitiated at 4.3 kbar, pronounced work softening is observed. The dependence of flow stress on pressure in stage III at constant structure, (δσ/σ)s, is small and less than that expected from the pressure-induced change of elastic constants. The negative pressure dependence of σIII and the small (δσ/σ)s in stage III may be explained in terms of thermally activated cross slip of screw dislocations when stacking faults on the primary slip plane cause a strong local dilation of the lattice.
Fatigue Mechanism in Iron at Ultrasonic Frequency
Authors: Wood W. A. , Mason W. P.
Published: February 2004

A metallographic study compares the fatigue mechanism in low-carbon iron subjected on the one hand to cycles of strain at an ultrasonic frequency of 17 000 Hz and on the other to 1700 cpm, the relative low order employed in usual engineering tests. It is found that the ultrasonic frequency can produce fatigue cracks at strain amplitudes much smaller than those which up to now have been regarded as safe at low frequency. Further, whereas small amplitudes at low frequency spread abnormal deformation primarily in grain boundaries, those at ultrasonic frequency concentrate it in a relatively few isolated slip bands thereby, it is suggested, heightening their damaging effects.
Optical Constants of Copper Measured with a Polarimetric Method
Authors: Stoll M. Ph.
Published: February 2004

The principle of a polarimetric method for the study of the optical properties of metals is given. Only changes in the azimuth of polarization of the reflected beam are involved. The measurements are performed with a high-sensitivity photoelectric spectropolarimeter which allows the determination of the optical constants in a range of photon energies extending from 0.52 to 3.31 eV (0.375 to 2.40 μ) and in a temperature range extending from 77° to 600°K. The method is illustrated with measurements on copper; the results are in good agreement with previously reported values.
Experimental Study of Tonks-Dattner Resonances in Rare-Gas Plasmas
Authors: Hart D. A. , Oleson N. L.
Published: February 2004

Tonks-Dattner resonances were studied in active discharges of neon, argon, and xenon in the milliTorr pressure region where self-excited moving striations are also present. The observed resonance peaks are fewer and broader than have been reported for mercury vapor discharges. The broadening is considerably greater than expected from Landau damping and Coulomb collisions and is attributed to electron density variations associated with moving striations. Direct measurements of electron densities and electron temperatures under resonance conditions permit comparison with the theory of Nickel, Parker, and Gould with no adjustable parameters. The agreement is satisfactory for argon and xenon but the high operating pressure required for stable operation of the neon plasma invalidates the use of the free fall hypothesis and the experimental resonance frequency peaks in this case lie appreciably above the predictions of the theory.
Electrostatic-Probe Studies in a Flame Plasma
Authors: Clements R. M. , Smy P. R.
Published: February 2004

Simple theoretical considerations have yielded an approximate formula for the ion current per unit length Ii to a cylindrical probe (radius rp, bias voltage V) immersed in a collision-dominated moving plasma (subsonic velocity=vf, electron density=ne, ion mobility=μi). Ii=2(πμiε0)1/3(neevfV)2/3[log(Ii/2neevfrp)]2/3 (mks)where e is the electronic charge. This relation has been checked with a propane/air flame and a moving probe; it is found to be correct within ±50% over several decades of probe voltage, probe-flame velocity and flame ionization. A more favorable choice of μi in the above expression improves the agreement between theory and experiment to ±30%. Measurements of sheath thickness obtained from the mutual interference of two adjacent probes support the basic tenets of the theoretical model. It is concluded that, in many instances of probe measurements in flames and other collision-dominated plasmas, the velocity-dependent approach adopted in this paper will be necessary since very large errors can arise if the usual static continuum plasma formulas are used. (Errors of up to a factor of 100 have been reported.)
Carrier Heating or Cooling in a Strong Built-in Electric Field
Authors: Stratton R.
Published: February 2004

A recently published calculation for the effective carrier mobility in a semiconductor space charge region with a strong built-in field is shown to lead to an unphysical result. A method for deriving the volt-current characteristic for small perturbations from equilibrium is presented.
Optical Properties of n-Type GaAs. II. Formation of Efficient Hole Traps during Annealing in Te-Doped GaAs
Authors: Hwang C. J.
Published: February 2004

The photoluminescence intensity of the near gap emission from Te-doped GaAs crystals decreases greatly after annealing at temperatures ranging from 600° to 1000°C while at the same time the intensity increases in the 1.22-eV band. The decrease in the near gap emission is less for samples annealed at higher temperatures for durations equal to the equilibrium annealing times. These results are shown here to be due to the creation of efficient hole traps whose concentration is proportional to the decrease in concentration of Te donors during annealing. The formation kinetics of these traps follows the form Nx(t)=Nx(∞){1−exp[−(t/R)0.44]}where Nx(t) and Nx(∞) are, respectively, the trap densities at annealing time t and at equilibrium, and R is the time constant for the formation process. This process is characterized by an activation energy of about 0.8 eV in the temperature range studied. The above facts when coupled with the observed increase of the 1.22-eV band emission lead to an identification of the traps as Te donor-Ga vacancy complexes which are identical to those responsible for the 1.22-eV band.
Optical Properties of n-Type GaAs. III. Relative Band-Edge Recombination Efficiency of Si- and Te-Doped Crystals before and after Heat Treatment
Authors: Hwang C. J.
Published: February 2004

A study of the effect of annealing upon the efficiency of edge emission in heavily Si-doped GaAs crystals reveals a substantially different behavior from that observed in Te-doped GaAs crystals of comparable doping level. Essentially no change in the edge emission intensity at 77°K and a decrease of only a factor of two at 300°K is found for GaAs:Si after annealing in contrast to a decrease of a factor of 10 at 77°K and a factor of five at 300°K for GaAs:Te. The intensity of the 1.2-eV band in GaAs:Si decreases after annealing while the same band increases in intensity in GaAs:Te. From the hole diffusion length and hole lifetime analysis, it is concluded that annealing GaAs:Si reduces SiVGa (Si-donor-Ga-vacancy complex) centers but at the same time creates other unknown defects, both of which have smaller concentrations than some other compensating acceptors. These compensating acceptors are shown to be present only in GaAs:Si and are presumably Si acceptors. It is also demonstrated that the hole capture rates at SiVGa acceptors, at defects created during annealing, and at the compensating acceptors are all competitive in GaAs:Si after annealing, but only the hole capture rate at TeVGa is important in GaAs:Te. Although the 77°K hole lifetime is smaller for unannealed GaAs:Si than for GaAs:Te, the 77°K edge emission efficiency is approximately the same for both dopants if the crystals have the same room temperature carrier concentration. This result is due to the less steep absorption edge of Si-doped crystals and the shift of the absorption edge to the lower energy. Similar behavior is also found for the 300°K case and is mainly due to the less steep absorption edge of GaAs:Si.
Electric Current in a Semiconductor Space-Charge Region
Authors: Goldberg Colman
Published: February 2004

An equation for the electric current in a semiconductor space-charge region such as a p-n junction is derived. At low currents the equation has the usual form i=neμ*E−(q/e) μ*kTL∂n/∂x but the effective mobility μ* is shown to have a strong dependence on position and may be infinite or negative. This spatial dependence arises because the deviation of the average carrier energy from its equilibrium value has a first-order dependence on the current.
Approximate Theory of Emitter-Push Effect
Authors: Hu S. M. , Yeh T. H.
Published: February 2004

An approximate theory of the emitter-push effect is presented. The rate of vacancy generation during emitter diffusion is formulated using Prussin's model of dislocation distribution. A time and space average rate 〈R〉 is defined, and a quasi-steady state approximation of vacancy distribution is obtained. It is shown that the ratio of the effective to the intrinsic base diffusivities, which is also equal to the local supersaturation of vacancies in the vicinity of the base—collector junction, is given by Db/Db*=(Cv/Cv*)xjb≈16π−1/2a−3β{1−√π ierfc[xr/2(Dt)1/2]} C0D(CsDs*)−1+1,where Db is the base diffusivity, Cv is the vacancy concentration, the asterisk denotes the condition of an intrinsic semiconductor with vacancy at thermal equilibrium, a is the lattice unit cell dimension, β is the coefficient of lattice contraction, xr is the dislocation penetration depth, D is the emitter diffusivity, C0 the emitter surface concentration, Cs the concentration of lattice sites, and Ds the self-diffusivity. It is also shown that the amount of enhanced collector junction movement δ is given by δ≈2Dbtλ−2xj−1ln(Cb0/CB)[(Db/Db*)−1],where λ is a constant (=0 73), xj is the collector junction depth, Cb0 is the base surface concentration, and CB is the bulk concentration.
Analysis of Carrier Transport in Vacuum-Evaporated Epitaxial Films of Silicon on Spinel
Authors: Hasegawa Shinichi , Kaminaka Nobuyuki , Nakamura Tohru , Itoh Tadatsugu
Published: February 2004

An attempt has been made to explain the anomalous behavior of carrier mobilities in vacuum-evaporated heteroepitaxial films of silicon on spinel by taking the reciprocal of the sum of reciprocals of three kinds of mobilities, i.e., dislocation-scattering mobility, space-charge scattering mobility, and bulk silicon mobility. This treatment provides a comparatively good fit to the observed values of the film mobilities in the experiment conducted from 77°K to room temperature. It is likely that the dislocation scattering and the space-charge scattering are the dominant mechanisms in limiting the carrier mobilities, in particular, electron mobilities in the films below the mobilities in bulk silicon, the dislocation scattering being dominant below about 100°K, while the space-charge scattering is dominant above about 200°K.
Cluster Growth and Saturation Island Densities in Thin-Film Growth
Authors: Halpern V.
Published: February 2004

An analysis of the appropriate two-dimensional random walk is used in calculating the probability that an adsorbed atom at a given point on a substrate will eventually reach a specified set of capture sites. From this, a formula is derived for the rate at which critical or stable clusters of atoms will grow when atoms are deposited on the substrate at a fixed rate. These results are applied to a calculation of the nucleation rate and of the saturation density of islands when a thin film is grown by the deposition of atoms from a vapor beam, for substrate temperatures appropriate to the region of incomplete condensation. It is found that this saturation density is usually an increasing function of the substrate temperature at low temperatures, but reaches a maximum and then always decreases, the rate of decrease becoming more rapid if the size of the critical nucleus increases. These results, and the calculated dependence of this saturation density on the various binding energies and on the deposition rate, are in good qualitative agreement with experimental observations.
Thermal Expansion of Lithium Tantalate and Lithium Niobate Single Crystals
Authors: Kim Y. S. , Smith R. T.
Published: February 2004

The principal thermal expansion coefficients of single crystals of LiTaO3, LiNbO3 and α quartz (for reference purposes) have been determined by an x-ray diffraction technique in the temperature range 25°–500°C. All three materials crystallize in the trigonal system, the first two in class 3m and the last one in class 32, and are characterized by only two principal expansion coefficients, parallel and normal to the c or Z axis. The Bragg x-ray angle data were fitted to suitable polynomials in the temperature deviations from an arbitrary reference of 25°C, and the expansion coefficients up to second order calculated from the coefficients of these polynomials. The Z-axis expansion of LiTaO3 showed a definite maximum at about 250°C. Similar behavior was indicated in the Z-axis expansion of LiNbO3, but at a much higher temperature (at the high extreme of the measurement range). The expansion of all three crystals normal to the Z axis was quite regular.
Study of Acoustoelectric Domains in Semiconducting CdS by Optical Modulation Technique
Authors: Kumar C. S. , Hutchinson W. G.
Published: February 2004

Optical modulation produced by acoustoelectric domains in semiconducting CdS is shown to be associated with the acoustic flux, rather than the accompanying high electric field in the domain. The optical modulation effect serves as a useful technique for exploring the origin and nature of the flux, and to understand the amplification process itself.
Elastic and Photoelastic Properties of TeO2 Single Crystal
Authors: Uchida Naoya , Ohmachi Yoshiro
Published: February 2004

Elastic stiffness, acoustic absorption, and photoelastic constants of the crystal have been determined at room temperature using ultrasonic light diffraction and pulse-echo methods. Two acoustic modes have been found to be particularly useful to acousto-optical applications: One is the shear mode propagated in the [110] direction with displacement along [1̄10], which is characterized by a remarkably high acousto-optical figure of merit, M (n6p2/ρv3) = 793×10−18 sec3/g; and the other is the longitudinal mode along [001] with high figure of merit defined taking account of frequency bandwidth, M′ (n7p2/ρv) = 142×10−7 cm2·sec/g, and low acoustic loss.
Investigation of the Electrical Properties of Sr1−xBaxNb2O6 with Special Reference to Pyroelectric Detection
Authors: Glass A. M.
Published: February 2004

The dielectric constants, electrical conductivity, specific heat, and pyroelectric coefficients of ferro-electric Sr1−xBaxNb2O6 (SBN) are investigated as a function of temperature in the range 10°–500°K, and as a function of the Sr/Ba composition of the material. A simple technique for measuring absolute pyroelectric coefficients and spontaneous polarizations of ferroelectrics is described. The electric field and frequency dependence of the dielectric properties are also investigated. The theory of pyroelectric detection is discussed from a materials point of view, and the experimental data are considered in terms of the usefulness of SBN as a pyroelectric detector of electromagnetic radiation.
Three-Dimensional Electromagnetic Scattering from a Circular Tube of Finite Length
Authors: Kao Cheng C.
Published: February 2004

An electromagnetic plane wave in either E or H polarization is normally incident on a cylinder which is assumed to be an infinitely thin-walled, perfectly conducting, circular tube of finite length with complete generality both in radius and length. For either polarization both axial and transverse currents are induced. The problem is transformed into determining an infinity of Fourier components by expanding each function of θ into a Fourier series. For each Fourier component a pair of integral equations for the total currents is obtained. These are decoupled in a special sense permitting the transverse total current to be obtained first, followed by the axial total current. The diflerence current is then defined and expressed in terms of the total current, making possible the determination of the inside and the outside total current. These are experimentally measurab e quantities. The theoretical formulas for the scattered fields, the far field patterns, and the scattering cross sections are also derived in terms of the total current. Finally, sample results, both theoretical and experimental, are included.
Angular Confinement of Field Electron and Ion Emission
Authors: Swanson L. W. , Crouser L. C.
Published: February 2004

Three methods of confining the angular dispersion of a field electron beam from 〈100〉 oriented tungsten emitters are investigated; they are (1) thermal-field buildup, (2) selective work function reduction by zirconium adsorption, and (3) high-temperature field evaporation. All three methods confine the emission to a beam half-angle of less than 9° in the dc current range 0.1 to 100 μA. Method (1) results in a ∼50% reduction in beam voltage. Provided that the vacuum level is good (∼10−10 Torr), long and short term current instabilities are negligible for dc current levels below 10 μA at 300°K for each of the emitter end forms investigated. The angular dispersion and beam voltage of a field ion beam can also be reduced by method (1) as described briefly in this paper.
Restrike Channel Resistance of Thin Exploding Wires
Authors: Vlastós Antonios E.
Published: February 2004

Using simultaneous measurements of current, voltage, and radius, the resistance of the restrike channels of thin exploding wires can be determined with good accuracy. Restrikes developing at the exterior or in the interior of exploding thin constantan and copper wires were examined. The wire length was 13 cm for constantan and 13.8 cm for copper, the wire diameter was 0.005 cm and the applied voltage was 1–23 kV. The results show that restrikes developing at the exterior of the wire have higher resistances than the restrikes developing in the interior. The values of the restrike resistance were compared with the relations of Toepler and Rompe and Weizel. The latter relation seems to be better suited for the description of the restrike resistance of thin exploding wires. The conductivity of the restrikes increases with increasing applied voltage and at high voltages the conductivity reaches values of 3×104 (Ω m)−1. The conductivity seems to reach its maximum on the ledge observed on the voltage oscillograms and to fall afterwards.
Dynamic Nucleation of the Ice Phase in Supercooled Water
Authors: Gitlin Sonia N. , Lin San-San
Published: February 2004

Experiments were carried out in which cavitating bubbles were produced by impact and by fast-travelling rods, and filmed by high speed photography. The experiments showed that cavitation is a necessary but not a sufficient condition for dynamic nucleation of the ice phase in the liquid. A temperature dependence was confirmed from nucleation threshold measurements. No attempt was made to confirm or disprove the various mechanisms proposed in the literature to explain freezing induced by cavitation.
Kinetic Model for the Iodine Photodissociation Laser
Authors: O'Brien Dennis E. , Bowen J. Ray
Published: February 2004

A kinetic model for the four level iodine laser is presented which includes pumping, radiative, and collisional transfer between levels. Numerical results obtained are shown to be in good agreement with available experimental data. The model correctly predicts the influence of pressure level and flash lamp parameters on the laser output and the occurrence of spiked pulses.
Frequency Response of the 6328-Å Helium-Neon Laser Interferometer
Authors: Potter I. C.
Published: February 2004

The speed of response of a 6328-Å helium-neon laser interferometer has been investigated under various conditions of operation. The laser oscillated in a small number of modes (all TEM00). At low output levels, the bandwidth of the interferometer was proportional to the output power, and except very close to threshold was not unduly affected by variation of the output spectrum. For values of the excitation parameter η (the ratio of unsaturated line-center gain-to-loss) between 1.0 and 1.25, the bandwidth f0 was approximately f0≃[(η−1)/1.7η](J/2π),where J is the fraction of the radiation energy lost per second from the cavity. The observations are interpreted in terms of loss modulation, taking into account the coupling between the intensities in the various modes of oscillation. The results obtained are equally applicable to other examples of loss modulation.
Atomically Clean Surfaces by Pulsed Laser Bombardment
Authors: Bedair S. M. , Smith Harold P.
Published: February 2004

It is shown that high power, Q-spoiled lasers offer an interesting method for obtaining clean surfaces in vacuum. However, complete removal of oxygen and sulfur contamination from nickel surfaces by laser bombardment at 100 MW/cm2 produced irreparable surface damage that is attributed to filamentizing of the laser beam and/or to nonuniform surface reflectivity. On the other hand, application of the technique at 30 MW/cm2 successfully removed the (7×7) satellite structure from (111) silicon surfaces without surface damage.
Evaluation of Current-Produced Two-Dimensional Magnetic Fields
Authors: Beth Richard A.
Published: February 2004

Formulas are developed for the two-dimensional magnetic field (and its derivatives of all orders) produced by a long straight conductor of uniform current density. These formulas are independent of whether the field point lies inside or outside the conductor and avoid ambiguities due to multiple values of the complex logarithm. Evaluation of the formulas can be done numerically, with the arbitrary conductor boundary approximated by a polygon, or graphically, or mechanically.
Magnetic Anisotropy in Dysprosium
Authors: Bly P. H. , Corner W. D. , Taylor K. N. R.
Published: February 2004

Torque measurements have been made on single-crystal dysprosium. The constant K1 was determined in the paramagnetic region, and also in the antiferromagnetic region, where the transition to ferromagnetism appeared as a large distortion in the torque curves. From the data in the paramagnetic region the saturation value of K1 is predicted as 1.1×108 ergs g−1. The constant K4 was determined in the ferromagnetic region, and changes in sign were observed at field strengths close to the critical value. The changes in easy direction for magnetization are compared with the behavior of the magnetostriction of dysprosium.
Internal Friction Phenomena Connected with Either Edge or Screw Dislocations in Germanium
Authors: Calzecchi F. , Gondi P. , Mantovani S.
Published: February 2004

Internal friction measurements were carried out on germanium specimens with either edge or screw dislocations. The Kessler peak and logarithmic trend were checked with the edge character specimens. The screw character specimens showed two new peaks and another logarithmic stage, all characterized by low activation energies. A logarithmic dependence of the peak temperature on the dislocation density was also observed. Under certain conditions, regarding the kink distance dependence on dislocation density and on pinning lengths, the results concerning the screw dislocations may be interpreted in terms of smooth kink-free motion while the edge dislocation phenomena can be explained on the basis of damping mechanisms depending on interactions between either kinks and dragging points or point defects and dislocations.
Some Combinations of Third-Order Elastic Constants for Strontium Titanate Single Crystals
Authors: Mackey James E. , Arnold R. T.
Published: February 2004

Three linear combinations of the six adiabatic third-order elastic constants in cubic crystals can be determined by use of the ultrasonic second-harmonic generation technique. The combinations which are obtained are designated K3[100], K3[110], and K3[111]. In the work reported here, room-temperature values of the K3's have been measured for strontium titanate single crystals. The reported values are (in units of 1012 dyn/cm2): K3[100]=C111=−49.6±4.3K3[110]=14(C111+3C112+12C166=−27.3±3.2K3[111]=19(C111+6C112+12C144+24C166+2C123+16C456=−27.9±2.6.The data have been compared with the theoretical values of K3 for the alkali halide crystals, and it has been observed that the ratio of | C111 |/C11 for strontium titanate agrees with the corresponding ratio for many of the NaCl type crystals. In order to estimate the six third-order elastic constants of strontium titanate, it has been assumed that the Cauchy relations extended to third-order elastic constants hold.
Hydrostatic Pressure and the Mechanism of Creep in Aluminum
Authors: McCormick Paul G. , Ruoff Arthur L.
Published: February 2004

Hydrostatic pressure has been used as a tool in the study of creep in aluminun to show that there is a change of mechanism associated with the drop of activation energy for creep found as the temperature decreases below about 0.6Tm. Moreover, this change occurs, while the argument of the sinh (Abσ/kT) term in the usual lattice diffusion controlled theories of creep is still small with respect to one, i.e., before any sizeable vacancy supersaturation is build up.
Temperature Dependence of the Elastic Constants of Tin Telluride
Authors: Beattie A. G.
Published: February 2004

The temperature dependence of the elastic constants of SnTe has been measured between 1.2 and 300 K. A change was found in the slope of C44 around 135 K in crystals with a carrier concentration of 6×1020 carriers/cm3. No indication of a low temperature phase transition was seen. The 0°K Debye temperature for this carrier concentration is 192.2±0.4 K.
Structure of Amorphous Ni–Pd–P and Fe–Pd–P Alloys
Authors: Maitrepierre P. L.
Published: February 2004

Ternary alloys of nickel-palladium-phosphorus and iron-palladium-phosphorus containing 15–20 at.% phosphorus were rapidly quenched from the liquid state. The structures of the quenched alloys were investigated by x-ray diffraction. Broad maxima in the diffraction patterns, indicative of a glass-like structure, were obtained for 13–73 at.% nickel and 13–44 at.% iron, with palladium and phosphorus adding up to 100%. The interference functions were evaluated from the coherent x-ray scattering and used to compute the electronic radial distribution functions for these alloys. Average interatomic distances and coordination numbers were obtained from the radial distribution functions. A linear relationship between interatomic distances and composition, similar to Vegard's law in crystalline systems, was shown for these metallic glasses. The structure of the quenched Ni–Pd–P and Fe–Pd–P alloys could be explained in terms of structural units analogous to those existing in the metal-rich phosphides. A quasi-crystalline model based on the Pd3P structure, with nickel or iron substituting for palladium, was shown to give a very satisfactory approximation of the amorphous structure of the Ni–Pd–P and Fe–Pd–P alloys. Such a model was also in good agreement with electrical and magnetic properties measured for these metallic glasses.
Nonlinear Absorption Behavior of Indanthrone Dyes: Comparison of Optical Saturation and Photochemical Processes
Authors: Huff L. , DeShazer L. G.
Published: February 2004

The nonlinear absorption of ruby laser radiation by indanthrone dyes resulted in significant temporal shaping of the transmitted laser pulse at incident flux densities greater than 30 MW/cm2. This behavior and the observation that aggregation of the dye molecules is associated with the nonlinear response indicates that photochemical processes may be responsible for the effect. Models involving such processes were analyzed and the results compared to the experimental data.
Parametric Image Conversion: Part I
Authors: Firester Arthur H.
Published: February 2004

We consider frequency-doubling image conversion of a brilliant object by self-interaction of its radiation within a nonlinear material. We have demonstrated that by placing the nonlinear material in the image plane of a lens, high-resolution, three-dimensional image conversion can be achieved, whereas for other positions of the nonlinear material crosstalk noise can be so severe as to make the resultant image unrecognizable. We have developed a theory of this type of image conversion which uses the formalism of Fourier optics. This theory is applied to a case which is very similar to more general image converters and this case is experimentally demonstrated.
Decomposition of Gamma-Phase Manganese Copper Alloys
Authors: Smith J. H. , Vance E. R.
Published: February 2004

The decomposition of γ-Mn–Cu alloys containing more than 60 at.% Mn to the mixed (α+γ) phase has been studied using x-ray and neutron diffractometry and measurements of electrical resistance and Young's modulus of elasticity. There is strong evidence that manganese-enriched clusters having the γ-phase structure are produced prior to the precipitation of α-Mn. When γ-phase alloys were aged at 450°C for increasing periods of time, they remained single phase, but developed long-range antiferromagnetic order associated with a tetragonal (c/a<1) lattice distortion, and with a corresponding rise of the Néel temperature to an asymptotic value of ∼470°K for all compositions. The effects of aging at other temperatures, and the behavior of furnace-cooled alloys are discussed in terms of the pre-precipitation of manganese-rich clusters.
Microwave Diagnostics of a Transient Plasma with an Active Fabry-Perot Resonator
Authors: Ajmera R. C. , Lashinsky H.
Published: February 2004

A technique is described for microwave diagnostics of a transient plasma that makes use of an active Fabry-Perot resonator, in which a positive-feedback loop is to provide gain. The experimental results indicate that the technique is attractive from the point of view of sensitivity, dynamic range, time resolution and convenience of readout.
Simple Circuit for Obtaining the Electron Energy Distribution in a Plasma
Authors: Alexeff E. , Howell D. F.
Published: February 2004

We describe a very simple technique for obtaining an instantaneous display of the electron energy distribution in a plasma. We electronically doubly differentiate the current-voltage characteristic of the Langmuir probe, following the method of Druyvesteyn. In our technique, we use operational amplifiers for differentiation. Our new contributions are: First, we have discovered where the noise is produced that formerly made operational amplifiers unsatisfactory; second, we have demonstrated that this noise can be eliminated; and third, we have produced simple techniques for cross checking our double-differentiating system to demonstrate that the noise-elimination process does not appreciably distort the desired information.
Spectroscopic Survey of Self-Compressed Electron Beam Produced Plasmas
Authors: Rizzo J. E.
Published: February 2004

The application of 1500-J self-focused 1.5-MeV electron pulses of 25-nsec duration to production of energetic plasmas has been studied by time resolved emission spectroscopy. In Ar and He at pressures of from 0.15 to 1.5 Torr a high-energy plasma is formed which continues radiating for up to 500 μsec. Under drifting electron beam conditions the He plasma appears to be doubly ionized. Measurements of excitation temperature from the relative intensities of neutral He lines fit an equilibrium model 2 μsec after the electron passage and indicate a temperature of 10 000°K falling to 5000°K by 400 μsec. A measurement of the width of the He(I)4921-Å line indicates an electron density of 1.2×1015 cm−3 at 70 μsec, falling to 3.4×1014 cm−3 by 200 μsec. Studies of an Ar plasma have shown the emission at peak excitation to be in the Ar(IV) spectrum. When the beam exceeds its critical current and is stopped by its own magnetic compression, in Ar, the quenching of the Ar(IV) emission indicates that the plasma reaches an energy which is high compared to the 145 eV necessary to four times ionize and remains above this level for 8 μsec.
Model for Radiation-Induced Charge Trapping and Annealing in the Oxide Layer of MOS Devices
Authors: Gwyn C. W.
Published: February 2004

A model is proposed to explain radiation damage and charge trapping in the oxide layer of MOS devices after exposure to ionizing radiation. This model is based upon the close similarity between radiation effects in the silicon dioxide layer and in fused silica. In addition to explaining the production of damage by ionization, the model has an advantage over other models inasmuch as the charge trapping in a relatively impurity-free silicon dioxide layer can be explained. The model explains radiation-induced charge trapping in the oxide and subsequent annealing of the charge as a function of temperature and exposure to ultraviolet radiation. In addition, the model suggests that the sensitivity of MOS devices to ionizing radiation can be reduced by decreasing the amorphous structure of the oxide.
Study of the Anisotropy of Radiation Damage Rates in n-Type Silicon
Authors: Hemment P. L. F. , Stevens P. R. C.
Published: February 2004

Consideration of the factors influencing electron radiation damage has led to the development of a computer program to predict damage rates as a function of electron beam energy and crystal orientation with respect to the beam. Experimental results using low-energy electrons (in the range 100–400 keV) are presented, which show the carrier removal rate as a function of sample orientation and electron beam energy. These measurements supplement the earlier results of Haddad and Banbury. Comparison of the calculated and experimental results enables us to make suggestions about the form of the displacement energy as a function of direction in the crystal, and to determine an effective threshold energy of 22 eV. Our model of the displacement-energy profile is justified in a simple manner from crystallographic considerations.
EPR Study of Lithium-Diffused, Mn-Doped GaAs
Authors: Title Reuben S.
Published: February 2004

An EPR study of the Mn spectra in Li-diffused Mn-doped GaAs is presented. The EPR spectra show that the symmetry at the Mn site is orthorhombic. This thus indicates association between the Mn and Li impurities. A model is proposed which is consistent with the observed symmetry at the Mn site, the donor impurities, and with the infrared absorption of the localized vibrational modes of the Li impurities as observed by Lorimor and Spitzer.
Optical Mixing of Laser Radiation Reflected from a Shock Wave
Authors: Simpson D. , Smy P. R.
Published: February 2004

A differential mixing technique is described whereby the Doppler shift of light reflected from a shock wave can be measured in the laboratory. Results are given for the application of the technique to shock waves produced in a conventional pressure-driven shock tube, and it is found that measurements of shock wave velocity can be performed with a spatial resolution ∼10−5 m, and of shock wave curvature with a resolution up to 10−1 m−1. Deliberate optimization of the various design parameters involved is expected to improve the sensitivity of either of these measurements by about an order-of-magnitude.
Luminosity and Pressure Aberrations in Detonating Nitromethane Solutions
Authors: Mallory H. Dean , Greene G. A.
Published: February 2004

Smear camera photographs of the detonation process in nitromethane and in its solutions with acetone often show dark striations and/or larger dark regions. Photographic evidence now presented leads to the conclusion that these two characteristic entities are not the same, although both may indicate local nonreaction sites. New data is presented showing the possibility of detonation buildup in large dark regions as evidenced by brightly luminous interaction figures and strong local pressure differences.
On-Line Computer Analysis and Control of Experiments
Authors: Kaplow Roy , Posen Harold
Published: February 2004

An analysis procedure and data accumulation scheme is described which allows implementation of a fully interactive, computerized ``process control'' for a general class of physical experiments in terms of derivable experimental results. The method is applicable whenever the derivable physical parameters can be expressed in terms of integrals over functions of the measured quantities and reciprocal relationships allow prediction of the measured values in terms of the derived quantities. The analysis may be most useful when the transformations are orthogonal.
Systematic Errors in Alternating Current Hall Effect Measurements
Authors: McKinzie H. L. , Tannhauser D. S.
Published: February 2004

This article discusses in the form of a table the spurious signals which can arise in a Hall effect measuring apparatus using alternating current and either an ac or a dc magnetic field. It is pointed out which of these spurious signals can simulate a Hall effect. Checking procedures to distinguish between the real Hall effect and the spurious effects are given.
Determining Polar Angles from Mössbauer Intensity Ratios
Authors: Violet C. E.
Published: February 2004

Polar angles cannot be determined in general from intensity ratios of Mössbauer hyperfine lines. However, conditions can be found that specify the polar angle as either perpendicular or parallel to the Mössbauer photon.
Measurement of Growth Rate for Sub-Visible Bubbles in a Bubble Chamber
Authors: Harigel G. , Hilke H. J. , Rogers A. , Horlitz G. , Wolff S. , Fretwurst E. , Lindström G.
Published: February 2004

Resonant absorption of high-frequency sound was tried as a new method for the determination of bubble growth. In the 85-cm bubble chamber at DESY, filled with a Ne/H2 mixture (90/10 mole%) at 29°K, the growth rate of subvisible bubbles was measured with 122-kHz ultrasonics for time intervals between 10 and 70 μsec after the passage of a particle. The results were evaluated according to the theory of Trammell and were compared with an extrapolation from optically measured values under the assumption of an R∼t1/2 dependence for the bubble radius.
Ionic Conductance of Potassium Azide in the Solid State
Authors: Maycock J. N. , Verneker V. R. Pai
Published: February 2004

New experimental results on the dc electrical conductance, between room temperature and 250°C, of potassium azide single crystals and pellets and potassium azide doped with barium azide are described. These data have been interpreted as involving cation current carrying species. Numerical values for the enthalpy of migration and enthalpy of defect pair formation are deduced. These are, respectively Δh1=0.79±0.05 and h=1.43±0.05. Isothermal dc conductance data are also presented and imply that the charge carriers are involved in the thermal decomposition processes of KN3.
Dislocation Pile-Up in Half-Space
Authors: Kuang J. G. , Mura T.
Published: February 2004

If an obstacle exists in the vicinity of the free surface of a half-space and a stress field is applied in such a manner that dislocations are pushed towards the obstacle, an array of dislocations then piles up into an equilibrium distribution against the obstacle. The distributions of dislocations are obtained by the Wiener-Hopf technique for the edge and screw dislocations. The total strength of dislocations (Burgers vector multiplied by the number of dislocations) distributed in the distance L is calculated as 0.92π(1−v)σAL/G for edge dislocations and 2σAL/G for screw dislocations, where G, v are the shear modulus and Poisson ratio respectively and σA is the applied stress. The result can be applied to crack problems. The above two numbers for the total strength of dislocations give the crack openings at the free surface for the extensional mode and the antiplane shear mode of fracture, respectively.
Measurement of the Integrated X-Ray Intensities of Ge and Si
Authors: Jennings L. D.
Published: February 2004

The integrated Bragg intensities of the (111) reflections of perfect crystal Ge and Si have been measured with a higher accuracy than heretofore. Ge was measured using x-ray wavelengths of 0.56 and 1.54 Å, and Si using 1.54 Å. Comparison of the scattering factors so obtained with those measured previously by the same method or by the Pendellösung fringe method leads us to the conclusion that there is not a systematic difference between the two methods, as has been suggested. We find that the reflectivity in the wings of the Bragg peak is much lower than the calculated value, and this effect would have to be taken into account if accuracies of the order of 0.1% are envisaged. We also measured Si (222) and found results in agreement with other reflection measurements, but not with recent transmission measurements.
Analysis of Laue Diffraction Images from Deformed Lattice Planes
Authors: Lal Krishan , Peneva S. K.
Published: February 2004

An extension of the method for calculating the shapes of diffracting planes from the shape of the observed Laue spots is described in this paper. The method can be used for determining the shapes of the Laue spots diffracted from ideally perfect and deformed sets of planes. The method has been applied for calculating the shapes of several Laue spots by considering the planes to be ideally perfect. The calculated shapes are then compared with the shapes observed on Laue photographs.
Scattering Obliquely Incident Microwaves by a Moving Plasma Column
Authors: Yeh C.
Published: February 2004

The problem of the interaction of obliquely incident microwaves with a plasma column which is moving uniformly in the axial direction is treated analytically. An arbitrary polarization for the incident plane wave is assumed. Two methods in solving this problem are presented. Extensive numerical results for the scattered energy in the backward and broadside directions and the angular distribution of the scattered energy are obtained for various interesting ranges of the parameters involved. It is found that cross-polarized field components are induced even at normal incidence when the plasma medium is moving with respect to the observer and that cross-polarized field components disappear at an incident angle θ0=sin−1(vz/c), where vz is the velocity of the moving plasma and c is the speed of light in vacuum when the plasma column is imbedded in free space.