bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal Interfaces. Part I. Semi-Infinite Crystals
Authors: Van Der Merwe J. H.
Published: April 2005

This paper presents a calculation of the stresses and energies for interfaces between different crystals. Only simple cases corresponding to interfacial dislocations of pure screw or edge type are treated. The difference between the two crystals is expressed in terms of different elastic constants and variable interfacial bondings. Two kinds of interfacial forces appear: tangential forces with a periodic character and normal forces. The latter are induced by different normal displacements of the two contact surfaces of the crystals due to the equal and opposite tangential interfacial forces and are accounted for by assuming a linear relation between force and relative displacement. By using a periodic parabolic model to represent the periodic potential associated with the tangential forces, it is shown that the contribution of the normal force to the interfacial energies is negligible for the approximation used. When these normal forces are neglected, the Peierls-Nabarro representation of the interfacial forces yields simple results in terms of an interfacial rigidity modulus μ and an effective elastic constant λ+ defined by 1/λ+=1/λa+1/λb=(1−σa)μa+(1−σb)/μb, where σ is Poisson's ratio and the two crystals are designated by a and b. It is seen that ½λa≤λ+≤λa, where λa is the smaller of λa and λb. Apart from being proportional to μc, the interfacial energy E depends only on a parameter β=2π(c/p)(λ+/μ), where p is the dislocation spacing and the lattice constant c of the reference lattice is given by 2/c=1/a+1/b. The dependence on β is such that below a poorly defined value of the order of unity the variation of E is very rapid while beyond this it remains practically constant. It is further shown that the elastic energies stored in the two crystals are in the ratio λa/λb and that less than 2% of these energies is stored at distances from the interface greater than half the distance between dislocations. Similar results are shown to hold for simple twist and tilt boundaries.
Single, Temperature-Dependent Stress-Strain Law for the Dynamic Plastic Deformation of Annealed Face-Centered Cubic Metals
Authors: Bell James F.
Published: April 2005

Large amplitude wave propagation in annealed aluminum is studied experimentally to within 70°C of the melting point of the metal. The strain-rate-independent, finite amplitude wave theory is found to apply at all temperatures. The governing stress-strain law in each instance is parabolic. The coefficient of the parabolic stress-strain law varies linearly with the absolute temperature.

The annealed, face-centered cubic metals of aluminum, copper, lead, gold, and silver are all found to have the same parabolic stress-strain law at absolute zero.

Thus, from experiments using the author's diffraction grating technique, a single stress-strain law is found which is applicable at any temperature to any of these annealed metals whose melting point is specified.
Surface Features of Alkali Halide Crystals Pulled from the Melt
Authors: Sampson J. L. , McCarthy K. A.
Published: April 2005

An examination of sodium chloride and potassium chloride single crystals pulled from the melt by a method based on that of Czochralski reveals facets, stepped surfaces, and ridges on the surfaces of the crystals. By growing crystals of various axial orientations under different conditions, an empirical rule has been formulated and tested. This rule predicts the occurrence of the three types of surfaces. It is shown that facets, which appear to result from growth under conditions of thermal equilibrium, can occur when the major portion of the crystal is growing under nonequilibrium conditions. An explanation in terms of forces associated with the meniscus and of thermal effects is proposed. Photographs of three crystals are included.
Sputtering Experiments with 1- to 5-keV Ar+ Ions
Authors: Southern A. L. , Willis William R. , Robinson Mark T.
Published: April 2005

Sputtering yields have been determined with 1- to 5-keV Ar+ ions normally incident upon targets of type 304 stainless steel, three different types of polycrystalline Cu, a wide variety of Cu monocrystals, and monocrystals of Si and Ge. Ejection patterns have been recorded from these targets and from a monocrystal of InSb. The sputtering yield of polycrystalline Cu depends on the source of the metal, apparently due to variations in preferred orientation. The yield from Cu monocrystals is strongly dependent on orientation, the effect becoming more pronounced as the energy is increased. A simple model is presented which accounts for this behavior in terms of the variation with direction of the initial mean free path of the incident ion. The ejection patterns leave little doubt that focusing collision chains are primarily responsible for the transport of momentum to the surfaces of close-packed metals.
Elastic Constants of Synthetic Sapphire at 27°C
Authors: Bernstein B. T.
Published: April 2005

The six elastic stiffness constants of synthetic sapphire were independently determined by pulse-echo and continuous-wave (cw) resonance measurements at a frequency of 15 Mc. The values obtained from the pulse-echo measurements are C11=4.902, C33=4.902, C44=1.454, C12=1.654, C13=1.130, C14=−0.232, in units of 1012 dyn/cm2. The results obtained from the cw resonance measurements are C11=4.920, C33=4.920, C44=1.468, C12=1.684, C13=1.164, C14=−0.234, in units of 1012 dyn/cm2. The results of the present investigation are compared with recent resonance measurements in the kc frequency range and with earlier work in the Mc range.
Mechanism of Spall in Lucite
Authors: Keller Donald V. , Trulio John G.
Published: April 2005

One-dimensional impulsive loading experiments have been carried out on Lucite to determine whether the spall occurs instantaneously upon the attainment of a critical tensile stress, or if there is a time delay between the attainment of a given tensile stress and spallation. The experiments involve the collision of two flat Lucite plates: a driver and a target. The velocity of the driver is adjusted until the threshold velocity for spall of the target is obtained. The experiment is repeated but the thicknesses of the two plates scaled by some factor (α). The maximum tension is then unchanged, but the time over which it acts is changed by the factor (α). In this manner the duration of tension required to spall Lucite was varied from 2×10−7 to 5×10−6 sec. The threshold velocity for spall remained constant (60 m/sec) indicating that, over this time scale, the spall mechanism for Lucite is time-independent and that a critical tensile stress exists (∼1 kbar).
Interferometric Study of the Microtopography Arising out of 90° Domain Walls in Single Crystals of Barium Titanate
Authors: Bhide V. G. , Bapat N. J.
Published: April 2005

The surface structure caused by 90° domain walls on barium titanate crystals in the ferroelectric tetragonal state has been studied as a function of temperature employing optical and interferometric techniques. It has been shown that the c-domain surfaces are inclined against the a domains at an angle tan−1 (c−a)/a. The observed stepladder structure of alternating `a' and `c' domains shows head-to-tail coupling of the dipoles. Special cases of 90° wall configuration with head-to-head or tail-to-tail orientation have also been observed.
Penetration by Shaped Charge Jets of Nonuniform Velocity
Authors: Abrahamson G. R. , Goodier J. N.
Published: April 2005

The simple hydrodynamic theory of penetration by shaped charge jets is extended to include nonuniform jet velocity distributions and stand-off distance. The penetration of a jet with an initial linear velocity distribution is compared to an ideal upper limit and is found to be close to the maximum obtainable in practice. The conclusions concern idealized jets, without regard to the performance limitations which break-up and waver impose on real jets.
Solution of Gases in Polyethylene Terephthalate
Authors: Michaels Alan S. , Vieth Wolf R. , Barrie James A.
Published: April 2005

The solubilities of helium, nitrogen, oxygen, argon, methane, carbon dioxide, and ethane in glassy amorphous and crystalline polyethylene terephthalate have been studied by time-lag and/or static sorption methods. Solubilities of all the gases but ethane were also determined in the rubbery crystalline polymer. The only deviations from Henry's law were displayed by ethane at 25°C and carbon dioxide at 25° and 40° C in the glassy polymer. Correlation of solubility constants for oxygen and nitrogen obtained by the static sorption method with values obtained dynamically indicate that the glassy crystalline polymer is an isotropic diffusion medium. Sorption in the glassy amorphous and crystalline polymers generally takes place by two processes operating concurrently: ordinary dissolution plus ``hole-filling.'' The ``hole-filling'' process obeys a Langmuir expression and dissolution obeys Henry's law for sorption of carbon dioxide in the amorphous polymer at 25°C. Crystallinity reduces gas solubility in the glassy polymer, but not generally in direct proportion to the decrease in amorphous volume. An exception is helium, which appears to obey the simple law, k=k*α. The glassy state of the partially crystalline polymer extends to about 80–85°C where a transition region is noted on a van't Hoff plot for solubility constants. The other extremity of this region (about 95°C) marks the onset of rubber-like behavior in the polymer. Heats of sorption in the glassy crystalline polymer are more exothermic than in the rubbery crystalline polymer, characteristic of the transition from sorption by dissolution and void-filling processes to dissolution alone. The heat of solution of helium is slightly positive in both the glassy and rubbery states of the crystalline polymer, with no evidence of a break at Tg. It appears that the major contribution to helium sorption in either state of the crystalline polymer is ordinary dissolution. In both the glassy and rubbery states, carbon dioxide shows evidence of a polar interaction with the polymer. Solubility constants are correlated with gas force constants ε/k̄ in both the glassy amorphous and rubbery crystalline polymers.
Retarding Field Technique for Measuring Sublimation from Dispenser and Oxide Cathodes
Authors: Florio John V.
Published: April 2005

A retarding field technique for measuring the instantaneous evaporation rate of barium and barium oxide from dispenser and oxide cathodes is described. The method is based upon measuring the time rate of change of the anode work function caused by the deposition of sublimate from the cathode surface. A simple planar diode, employing a molybdenum anode, is used. In contrast to the typical curve for barium films on molybdenum, showing a minimum work function at approximately a monolayer coverage, the results for barium oxide films indicate a similar decrease in work function up to a monolayer coverage; further deposition leads to a still lower work function.
Investigation of Polarization Processes and Electric-Field Distribution in Photoconducting Insulators
Authors: Peled S. , Harnik E. , Ben-Sira M. Y. , Pratt B.
Published: April 2005

Polarization processes in partially illuminated photoconducting insulators were further investigated with a view to elucidating some discrepancies between experiment and theory. Experiments performed on single crystals of NaCl which had been colored by x-ray irradiation only inside a well-defined strip showed that the theory previously proposed was correct. The distribution of the electric field along the sample, at various stages of the polarization process, was recorded by means of a moving light-probe scanning method. The results showed that the deviations from theory observed when the whole sample was colored were associated with the distortion of the electric-field distribution outside the directly illuminated strip, as a result of extraneous carrier generation by scattered light.
Free Vibration Experiment in the Theory of Linear Viscoelasticity
Authors: Markovitz Hershel
Published: April 2005

An idealized free-vibration experiment is analyzed on the basis of the theory of infinitesimal linear viscoelasticity. The resulting motion can be expressed as a sum of terms, of which some are damped sinusoidal waves while others are negative exponentials in time. For some three parameter models of viscoelastic behavior, the results of this theory are compared with those of the usual treatment which leads to a simple damped sinusoidal wave.
Scattering of Light by Heterogeneous Spheres
Authors: Stein R. S. , Wilson P. R. , Stidham S. N.
Published: April 2005

The theory for the scattering of light by homogeneous spheres satisfying the Rayleigh-Gans approximation is extended to include the effect of heterogeneous density within the spheres. These internal heterogeneities are described by a Debye-type exponential correlation function. The resulting scattering consists of a sum of two terms: one representing the homogeneous sphere scattering contribution and the second representing the additional contribution to scattered intensity arising from the internal heterogeneities. The predicted scattering patterns bear similarities to the experimentally observed scattering patterns obtained for spherulites of high polymers.
Determination of Fracture Surface Energies by the Cleavage Technique
Authors: Berry J. P.
Published: April 2005

The fracture surface energy of a material can be obtained by the cleavage technique, in which a crack is propagated along the median plane of a strip sample by forces applied at the free ends. Unfortunately, the stress distribution in a conventional sample is such that the crack tends to deviate from its original direction, so that, for isotropic materials, external constraints must be imposed to overcome this tendency. To interpret the data, relations have been derived, based on the assumption that simple beam theory can be applied to the system; this assumption is not strictly valid. The use of the constraints can be avoided by machining fine slots along the opposing faces of the sample, and the system can then be analyzed by a direct and unambiguous method. The modified technique has been applied to the glassy polymers poly(methyl methacrylate) and polystyrene for which comparative data are available from both tensile and cleavage experiments.
Nuclear Magnetic Resonance Studies of Molecular Motion in Natural Rubber
Authors: Slichter W. P. , Davis D. D.
Published: April 2005

Nuclear magnetic resonance measurements have been made on natural rubber to examine how frequency, temperature, and crystallinity influence the nuclear relaxation. Molecular motions were studied by observing NMR linewidths and spin-lattice relaxation times at temperatures between −100° and 100°C, and at radio frequencies between 2 and 60 Mc. The influence of crystallinity was seen in measurements on stark rubber. The relation between frequency and temperature in the spin-lattice relaxation process is examined in terms of the Arrhenius equation and the WLF expression. The importance of using frequency as a variable in NMR studies of molecular motion is stressed.
Effect of a Small Stokes Shift on the Operation of Three-Level Masers
Authors: Warter Peter J.
Published: April 2005

Small differences between the emission and absorption spectra of three-level maser centers can have a pronounced effect on maser operation. This paper considers the effects of a Stokes shift, the simplest and most probable difference. If there is a Stokes shift which is large compared to the linewidth, the operation of the maser will be essentially four level. If there is a small Stokes shift (some fraction of the linewidth) the operation will still be three level, but the Stokes shift will significantly affect the operation of the maser. The principal effects will be a shift of the maser line from the peak in the fluorescent emission line (away from the absorption peak) and a reduction in the upper level population required to reach the threshold of oscillation.

The evidence is not conclusive as to whether there is a Stokes shift in the ruby R1 line, but if there is a shift it is at most a small fraction of the fluorescent linewidth at room temperature. Shifts of the ruby maser line to the red have been observed by D'Haenens and Asawa and have been attributed to large temperature changes. It is likely that the temperature shift, while important, will not explain the shift which has been observed. Gires and Mayer have found the lower state population of an operating ruby maser to be approximately 75% of the unexcited population rather than approximately 50% and have suggested a Stokes shift as a possible cause of the reduction in the upper state population at threshold. This paper considers the effect of such a small Stokes shift on the operation of an otherwise ideal three-level maser.
Nonlinear rf Behavior of Electron Beams with Velocity Distribution. I. General Analysis
Authors: Yu S. P. , Mihran T. G.
Published: April 2005

The disk model of an electron beam, generalized to allow a distribution of dc velocities, leads to a set of equations that include space charge and accurately describe the nonlinear behavior of a multivelocity electron beam in a drift region. Difference equations are obtained which are suitable for solution on a digital computer. Excellent agreement is obtained at small-signal levels with linearized theory. Available for the first time as a result of the validity of the present analysis for nonlinear conditions are: (1) harmonic behavior at small-signal levels and (2) fundamental and harmonic behavior at large-signal levels.
Nonlinear rf Behavior of Electron Beams with Velocity Distribution. II. Application to Rectangular Velocity Distribution
Authors: Mihran T. G. , Yu S. P.
Published: April 2005

The nonlinear disk electron analysis in Part I is applied to a practical example. Two changes are imposed on the analysis to decrease the computer running time. Electron trajectories and the first three components of current are calculated for a beam with a rectangular velocity distribution that is simulated by eight dc velocity classes. Excellent agreement is obtained with a linear theory for small values of initial density modulation. Periodic variation of the space-charge parameter leads to the equivalent of scalloped beam amplification in a multivelocity beam.

A linear force-taper correction is derived and its stabilizing effect is shown. Its use is suggested for improving the accuracy of monovelocity disk electron calculations.

The interpretation of space-charge wave decay in multivelocity electron beams as spatial Landau damping of the fast wave is questioned. It is suggested that damping is due to multidimensional effects not taken into account by present linear and nonlinear one-dimensional theories.
Behavior of Film Conductance during Vacuum Deposition
Authors: Learn Arthur J. , Spriggs R. Spencer
Published: April 2005

The electrical conductance was measured during vacuum deposition of tin and lead films to gain information concerning the scattering of conduction electrons at the film boundaries and the diffusion of atoms on the substrate surface during the initial stages of growth. Deposition rates varied from hundredths of angstroms per second to a hundred per second on substrates held at 300°, 255°, 195°, and 77°K and at pressures no greater than 10−6 Torr. Generally, the initial portions of the conductance curves suggest formation of larger grains at higher substrate temperatures or at lower deposition rates. In the latter case, grains again become small when the rates of arrival of residual gas atoms and vapor atoms are comparable. From the thickness for onset of electrical conduction, activation energies for the agglomeration of tin and lead films were calculated. From earlier measurements by other investigators the same quantity was calculated for mercury and copper. There is good correlation between this activation energy and heats of vaporization. Although no detailed theoretical model can be offered, the experimental values appear to be compatible with activation energies for surface diffusion. For films much thicker than the electron mean free path, and for films deposited at rates greater than a few angstroms per second so that residual gases do not play a predominant role, surface scattering of the conduction electrons is found to be more spectral the higher the substrate temperature during deposition or the lower the deposition rate. For films deposited or annealed at 300°K the electron scattering is almost entirely spectral. Interpretation is aided by electron microscope examination of the films.
Generation of Microwave Elastic Vibrations in a Disk by Ferromagnetic Resonance
Authors: Comstock R. L. , LeCraw R. C.
Published: April 2005

A calculation is presented of the generation of microwave elastic waves by the uniform precession resonance in ferromagnets. The excitation of the thickness shear modes in a normally magnetized ferromagnetic disk is treated. For uniform precession the elastic modes are driven only on the surfaces of the disk. The effects of long wavelength spin waves magnetostrictively driven by the elastic waves can be included in the analysis by a change in the elastic modulus. The coupling out of the elastic energy by bonding the disk to a non-magnetic delay medium is considered for arbitrary values of the elastic impedances of the two media. An equivalent electrical circuit for transducers is presented; the efficiency and bandwidth of disk transducers are calculated for a disk placed in a matched one port resonant cavity. A figure of merit for such transducers is defined, and calculated for yttrium iron garnet. Due to interference between the elastic waves generated on the two disk surfaces, the realizable bandwidth of the transducer is restricted by the thickness of the disk. By bonding two disks together or by using a rod, this restriction may be reduced.
Precipitation and Superconductivity in Lead-Tin and Lead-Cadmium Alloys
Authors: Livingston J. D.
Published: April 2005

The effects of precipitation from solid solution on the superconducting properties of lead-tin and lead-cadmium alloys have been studied by magnetization measurements at 4.2°K. Microstructural changes have been followed by optical and electron microscopy. These alloys as-quenched are superconductors of the second kind, their upper critical fields enhanced by quenched-in solute. At various stages in the precipitation process, the upper critical field continues to be determined primarily by the remanent solute. Magnetic hysteresis and trapped flux result from the interaction between precipitates and the flux filaments of the mixed state, a given precipitate distribution causing much more flux trapping if the matrix is a superconductor of the second kind than if it is a superconductor of the first kind. Several instances are seen where superconducting magnetization measurements yield useful metallurgical information.
Harmonic Generation in Low-Field Nuclear Induction
Authors: Forman Stanley M.
Published: April 2005

The generation of second harmonics has been observed in a low-field nuclear-induction experiment with nearly coincident, constant and alternating, magnetic fields. A pair of Helmholtz coils furnishes both a constant (H0) and an alternating (amplitude ηH0) magnetic field, and a second Helmholtz pair furnishes a constant, small magnitude (hH0) field perpendicular to the first pair. Steady-state solutions of the modified Bloch equations (relaxation to the instantaneous field) that utilize the indicated field configuration (obtained by both analytic and numerical methods) indicate first, the existence of resonance when ωR, the alternating field frequency, is a subharmonic of the gyromagnetic frequency ω0(≡γH0), and, second, relatively slow variation of the magnetic-moment components as functions of η. Analysis and experiment indicate saturation of the signal with increasing h. The nuclear sample, water with a heavy concentration of Cu(NO3)2·3H2O, about 3 cm in diameter, was closely surrounded by a 1000-turn pickup coil the output of which was fed to a narrowband wave analyzer tuned to 2ωR. With H0=6.11 G, η=2, and h=0.013, the predicted and observed second-harmonic (52 kc/sec) voltage was 0.1 μV (rms).
Sublattice Magnetizations in Rare-Earth Iron Garnets
Authors: Boyd E. L. , Moruzzi V. L. , Smart J. S.
Published: April 2005

The individual iron sublattice magnetizations in yttrium iron garnet and gadolinium iron garnet have been measured by NMR techniques as a function of temperature. The observed resonance frequencies are slightly higher for GdIG in both cases, the differences at low temperatures being about 0.67% for the octahedral sites and 0.70% for the tetrahedral sites. These differences are tentatively interpreted as due to the volume dependence of the hyperfine coupling constant A. The difference for the octahedral sites decreases slightly with increasing temperature, while that for the tetrahedral sites increases appreciably. A molecular field calculation shows that this behavior can be explained by assuming that the Gd3+ ions interact much more strongly with tetrahedral sites than with octahedral sites.
Microwave Elastic Properties of Nonmagnetic Garnets
Authors: Spencer E. G. , Denton R. T. , Bateman T. B. , Snow W. B. , Van Uitert L. G.
Published: April 2005

Investigations on cylindrical rods of yttrium iron garnet (YIG) have shown that the magnetostrictive effect at microwave frequencies makes them effective microwave acoustic transducers, and that a lower bound of the acoustic Q is of the order of 2×105 at 1 kMc/sec. This paper describes measurements of acoustic Q's of nearly this same magnitude obtained with the nonmagnetic yttrium gallium garnet (YGaG) and yttrium aluminum garnet (YAlG). A table is given of the longitudinal and shear acoustic wave velocities, elastic stiffness constants, and elastic isotropy for yttrium gallium garnet and yttrium aluminum garnet. Similar data for yttrium iron garnet by Clark and Strakna are included for reference.
Barrier Height Studies on Metal-Semiconductor Systems
Authors: Spitzer W. G. , Mead C. A.
Published: April 2005

Photovoltaic and space-charge capacitance measurements have been used to study the height of the Schottky barrier at the metal-semiconductor interface of a series of metals evaporated onto ``vacuum cleaved'' samples of n-type CdS and n- and p-type GaAs. Although the barrier heights for metal-CdS samples increase with increasing metal work function as predicted by simple theory, significant deviations were noted. The barrier heights measured on metal-GaAs samples at different temperatures show very little dependence on the metal and appear to be fixed relative to the valence band edge by surface states. The results are compatible with the model in which the photoresponse, for photon energies less than the semiconductor energy gap, arises principally from photoemission of carriers from the metal into the semiconductor; however, the results are sensitive to the method of surface preparation and comparisons with other work are difficult.
Microplasma Breakdown in Germanium
Authors: Poleshuk M. , Dowling P. H.
Published: April 2005

Interpretation of breakdown results in Ge diodes is frequently complicated by effects associated with surface excess current. When these effects are minimized, breakdown is observed within the junction at a ``breakdown center,'' starting at a definite voltage VB, and is accompanied by the onset of microplasma pulses. In any one diode, there may be a number of centers, each having its characteristic value of VB and producing characteristic microplasma pulses. The minimum value of VB determines the breakdown voltage of the diode and it is possible to increase the latter radically by etching away centers having lower values of VB.

Observations were made at temperatures from −253° to 27°C on Ge alloy junctions (n-type base resistivities from 0.54 to 5.4 Ω-cm). The properties of the pulses are discussed in some detail: the effect of raising the voltage above VB, the effect of light, and the temperature coefficient of VB. Values of the last are sufficiently high to suggest that suitable diodes can be used as cryogenic thermometers capable of reading smaller changes than 0.01°C at −253°C.

Various aspects of the microplasma breakdown are discussed: the mechanism for triggering a pulse and that for ``turning it off,'' the role of the spreading resistance, the possible role of a negative resistance at breakdown, and the effect of microplasma breakdown on the measurement of carrier multiplication at voltages in the vicinity of breakdown.
Study on Dislocation Relaxation Peaks in Gold and Copper
Authors: Okuda S.
Published: April 2005

An inverted torsion pendulum apparatus is described for the measurement of internal friction and dynamic modulus of metals over the temperature range 4° to 300°K after deformation in situ at 4°K. A detailed study of low-temperature internal friction peaks in pure gold and copper was carried out with this apparatus. By comparison of the results with other reported measurements, the activation energies for the Niblett-Wilks peak (EN-W) and for the Bordoni peak (EB) in gold and copper were deduced as follows: EN−W was 0.10 eV (for gold) and 0.045 eV (for copper);and EB was 0.19 eV (for gold) and 0.12 eV (for copper).The internal friction below 15°K was found to rise for gold specimens deformed at low temperature. This rise is discussed in detail and suggests a relaxation peak below 15°K in cold-worked gold.
Application of the Garrett Method to Calculation of Coil Geometries for Generating Homogeneous Magnetic Fields in Superconducting Solenoids
Authors: Marshall H. L. , Weaver H. E.
Published: April 2005

The design and construction of a superconducting solenoid generating a magnetic field of high homogeneity is discussed. The design is based on the Garrett mathematical description of a magnetic field produced from a set of axially symmetric coils. The experimental results for a 1.75 in. i.d. solenoid, operating at either 10 or 24 kg and possessing end-correcting coils in an arrangement determined by theory, indicate a central field homogeneity of 1/105 over about 1 in. at 10 kg and 0.75 in. at 24 kg. At approximately 9.4 kg it was possible to clearly resolve the three chemically shifted proton NMR peaks of ethyl alcohol. This result indicated a homogeneity of 1/106 over the sample at a single point in the accessible field volume.
Use of Langmuir Probes to Study Ion-Electron Recombination
Authors: Kretschmer C. B. , Petersen H. L.
Published: April 2005

Between about 0.1 and 20 mm Hg, ion concentration is related to the current collected by a negative cylindrical probe by the equation (in practical units) n=1.78×1013λe−1/2μ−5/8(Vprp)−1/4i5/8,where λe is the electron mean free path, μ is the ion mobility, Vp and rp are the probe voltage and radius, and i is the probe current per unit length. The plasma is not perturbed because the probe current is supplied by ionization occurring at the sheath boundary.

Using this equation, the following values of the dissociative-recombination coefficient α in cm3/sec were obtained from pulse discharge afterglow measurements: argon, 3.6×10−7 for high excitation and 1.4×10−6 for moderate excitation; oxygen, 2.0×10−6; mercury, 3.5×10−6. For nitrogen α was found to be proportional to pressure and equal to 1.7×10−7 at 1 mm Hg. For cesium the above equation does not apply, and the value α = 1.7×10−7 was obtained from experimental results using conventional probe theory. The frequency of three-body conversion of atomic to molecular ions was found to be 151 sec−1 for argon and 37 sec−1 for helium.
Focusing of Neutral Particle Beams by Fictitious Force Fields
Authors: Dempsey Daniel F.
Published: April 2005

In a rotating coordinate system the Coriolis force and centrifugal force can account for the curved trajectories followed by moving particles. It is shown that particle trajectories diverging from a source fixed in the rotating system may come to a focus at another point fixed in the system. Both first- and second-order focusing are obtained and an example of each is given. Expressions are derived for velocity dispersion and for the transverse aberration at the focus.
Thermomagnetic Figure of Merit: Bismuth
Authors: Horst Rudolf B.
Published: April 2005

The asymptotic value of the isothermal thermomagnetic figure of merit is obtained for a two-band multivalleyed semiconductor or semimetal where the concentration of holes and electrons is equal. The bismuth band structure is used as a specific model. It is shown that at strong magnetic fields the isothermal Nernst coefficient Njii is independent of the magnetic field Bk. The isothermal electrical resistivity is proportional to (Njii)Bk2 and the isothermal thermal conductivity is equal to the sum of the lattice thermal conductivity κii0 and the strong field ambipolar contribution (κiii)amb, where (κiii)amb is proportional to Njii. The isothermal Ettingshausen coefficient Ejii is also obtained and it is shown that κiiiEiji = −NjiiT. The largest figure of merit is obtained when the electron and hole mobilities are large and approximately equal, when the lattice thermal conductivity is small, and when the Fermi energy is approximately equal to +kT.
Nucleation and Growth of Ferroelectric Domains in BaTiO3 at Fields from 2 to 450 kV/cm
Authors: Stadler H. L. , Zachmanidis P. J.
Published: April 2005

The nucleation and movement of 180° domain walls in BaTiO3 crystals with salt-water electrodes has been observed directly by partial switching and repeated differential etching at applied fields from 2 to 450 kV/cm. Most of the polarization was found to be reversed by sidewise growth of new domains at these fields, as it is at lower fields, but the sidewise wall velocities are higher, as high as 105 cm/sec. The nuclei are originally circular cylinders, becoming squared up by sidewise growth whose lowest velocity is along the 100 crystal axis. The sidewise wall velocity and the nucleation rate each vary as E1.4, thereby causing the known E−1.4 variation of ts. The nucleation rate dependence is not understood, but the wall-velocity dependence agrees strikingly with a previously uncalculated prediction of the Miller-Weinreich theory. This indicates that, at both high and low applied fields, the apparent sidewise motion of 180° domain walls is due to the nucleation and forward growth of knife-shaped steps on the previously existing wall.
Low-Temperature Properties of Evaporated Lead Films
Authors: Caswell H. L. , Priest J. R. , Budo Y.
Published: April 2005

Lead films have been deposited onto room-temperature substrates having low thermal expansion coefficients and the residual mechanical stresses present in these films have been determined as a function of film thickness and film purity. At room temperature no measurable stress (<5×107 dyn/cm2) was present in any film. At 78° and 4.2°K the stress σ was given by σ=α+β/d, where α is a constant dependent on temperature and d is the film thickness. A model involving surface pinning of dislocations predicts an equation of this form, but the experimental values for the stress were found to be appreciably larger than values calculated on the basis of bulk data. The experimental values were substantiated by superconducting critical temperature measurements on films of various thicknesses. Localized crystalline growth was observed in lead films after cooling to 4°K. The film material around these micron-size crystals exhibiting five- and sixfold rotational symmetry was thinned to the point that physical holes were evident in the thinner films. In addition, with repeated temperature cycling, extensive cross slip was observed.
Luminescence of GaAs Grown in Oxygen
Authors: Turner W. J. , Pettit G. D. , Ainslie N. G.
Published: April 2005

A 0.65-eV luminescence peak has been observed in GaAs crystals grown in oxygen. The strength of the peak increases with increasing oxygen pressure during crystal growth. The 0.93-eV peak previously reported from electroluminescence measurements on GaAs diodes is observed in photoluminescence to decrease with increasing oxygen pressure and is absent in samples grown under high oxygen pressure. The 0.65-eV emission is not found in GaAs crystals pulled from AlN crucibles or in crystals grown in quartz without added oxygen. These two luminescence emissions appear to be related to the levels observed in optical absorption and photoconductivity measurements on n-type GaAs.
Modulation Broadening of NMR and ESR Line Shapes
Authors: Wilson G. V. H.
Published: April 2005

An analysis is made of the phase sensitive detection of magnetic resonances at various harmonics of the modulation frequency. The results are applicable to any experiment in which phase sensitive detection is employed. A mathematical treatment of modulation broadening is developed. Unlike the Taylor expansion method this is applicable in all practical cases. Signal amplitude and line shape of Lorentz and Gaussian resonances are calculated for the first three harmonics as functions of the modulation amplitude.

Expressions which relate the Fourier coefficients of a modulation-broadened resonance line shape to those of the true integrated line shape are derived. The use of these expressions in correcting observed line shapes for modulation broadening is compared with that of another method involving the summation of a convergent series.
Mutual Interaction between Microplasmas in Silicon p-n Junctions
Authors: Ruge Ingolf , Keil Günter
Published: April 2005

Mutual interaction between microplasmas in silicon p-n junctions was found to be present if the conducting time of microplasmas reaches the magnitude of 10−7−10−6 sec. Then a conducting microplasma may trigger the conduction of others. The resulting pulses show multistable levels. Several examples of such a pulse form, caused by the trigger process, are given.

Measurements have shown that the microplasmas investigated do not lie close together and that a cluster form for microplasmas is not a necessary condition for a mutual interaction.

A simultaneous, independent operation of several microplasmas was found to be very improbable if one or more of the working microplasmas reach pulse lengths of the order of 10−4−10−3 sec.
Pulse Excitation Studies of Gain and Trapping in Photoconductors
Authors: Bube Richard H.
Published: April 2005

Excitation of photoconductors by single pulses of monoenergetic photons shows that the integrated gain over one pulse event is approximately equal to the steady-state gain, except in materials for which the steady-state gain itself is a function of photon flux. Measurement of the peak pulse current as a function of pulse length permits the determination of trap density in a simple manner, which agrees well with values measured independently by thermally stimulated conductivity. A model based on a quasiuniform trap distribution is shown to be capable of predicting the observed dependence of peak pulse current on pulse length without the use of any adjustable parameters. Changes in trap density by several orders of magnitude with variations in ambient atmosphere are demonstrated for certain cadmium sulfide crystals.
Field-Emission Microscopy of Twins in Vapor-Grown fcc Whiskers
Authors: Melmed Allan J.
Published: April 2005

Twins have been found by field-emission microscopy in vapor-grown whiskers of Au and Pt. Evidence is presented to show that the twinning occurs during whisker growth, and possible twinning mechanisms are discussed. A mounting technique is described for making observations of the whisker growth ends.
Extension of Unoriented Nylon 66 Filaments
Authors: Bender Malcolm F. , Williams Malcolm L.
Published: April 2005

The orientation of nylon 66 filaments usually occurs by a cold-drawing process. This process has previously been described, in phenomenological terms, by the adiabatic theory of cold drawing of Muller and Jackel and Marshall and Thompson. To explain the process in structural terms, tensile creep experiments under low loads have been performed in an atmosphere of controlled temperature and humidity. The extension first increases uniformly with log time; then there is a rather sharp yield point where the extension quickly increases by a large amount. The location of the yield point on the log time scale is quite sensitive to environmental conditions. Phenomenologically, the behavior is similar to the propagation of Lüder's bands in metals. These results are not consonant with the adiabatic theory; therefore, the recent crystal defect model of nylon 66 proposed by Zaukelies has been used to suggest a qualitative explanation in terms of dislocations.
Cleavage Surface Energy of {100} Magnesium Oxide
Authors: Westwood A. R. C. , Goldheim D. L.
Published: April 2005

The modification of the Gilman cleavage technique described recently by Westwood and Hitch has been used to determine the surface energy γ0 of {100} MgO at 298°K. The value 1150±80 ergs/cm2 is in good agreement with previous experimental estimates of γ0, but somewhat lower than theoretical estimates. Metallographic studies were made of the plastic relaxation that occurs in the vicinity of the crack tip when cleavage cracks are repropagated, and a correlation between the extent of plastic relaxation, crack length, and the measured cleavage surface energy was observed.
Ice Interface Morphology and Texture Developed during Freezing
Authors: Harrison J. D. , Tiller W. A.
Published: April 2005

The freezing of pure water and several aqueous solutions has been studied by a direct observation technique. The solid-liquid interface morphology and crystal texture produced during the freezing of water were studied. For the aqueous solutions two families of knife-edged cells formed, one parallel to the basal plane and one parallel to the c axis. Two preferred crystal textures were observed, corresponding to the two cell families being aligned with the direction of heat flow. For the freezing of pure water, the same two textures were observed; however, the explanation for their occurrence is quite different. Theoretical explanations have been given for all of the texture results and the differences between these results and those found by other investigators.
Diffusion-Damped Domain-Wall Motion
Authors: Janak James F.
Published: April 2005

The Néel model of diffusion aftereffect has been used to analyze the motion of 90° and 180° domain walls when the aftereffect mechanism is present. Instability occurs in the response of the 180° wall to step and ramps of applied magnetic fields. For a step of field, the response of the wall is delayed from the time of application of the field by a time which decreases with increasing step height. For a ramp of field in a finite sample, instability occurs when a minimum ramp slope is exceeded. These instabilities furnish a basis for the explanation of the recently reported phenomenon of ``dynamic squareness'' of the hysteresic loop.
Formation of Diamond-Shaped Prismatic Loops in Quenched fcc Metals
Authors: Eikum Alf , Thomas G.
Published: April 2005

The concept of dissociated prismatic dislocation loops is proposed to explain the formation of diamond-shaped loops observed in several metals after quench aging. The dissociated prismatic loop is composed of parallel segments on {111} planes having a/6 <112> Burgers vectors. It is shown that diamond-shaped loops form from either a triangular or hexagonal Frank loop, and once formed can rotate on the glide cylinder to any orientation between and including {111} and {110}.

Climb kinetics are qualitatively discussed in terms of the equilibrium separation of partials. The separation is approximately equal to the core radius (2|b|) in Al, but is large enough in Cu (∼12|b|) to be experimentally detected. These considerations may explain why large loops are not often observed in metals other than aluminum.
Proposal for a Two-Stage Semiconductor Laser through Tunneling and Injection
Authors: Wang Shyh
Published: April 2005

In the present paper, an analysis of laser action in semiconductors is made, and a condition for population inversion is established. The radiation output is found to be proportional to the deviation from the equilibrium value of the occupancy of the allowed states including the states in the conduction and valence band and also the donor and acceptor states. Possible laser levels are discussed.

Following the general analysis, a scheme is proposed for laser action in covalent semiconductors where the top of the valence band and the bottom of the conduction band do not occur at the same value of k. The scheme consists of simultaneously tunneling electrons into the (000) valley of the conduction band and injecting holes into the valence band. The outstanding feature of the proposed scheme is that it offers a definite possibility for separate amplitude and frequency modulation of the laser output. Various losses associated with the proposed scheme are also discussed.
Thermionic Studies of Various Uranium Compounds
Authors: Haas George A. , Jensen John T.
Published: April 2005

The thermionic constants of UO2, UN, USi2, USi3, UB2, UB4, UC, UC–ZrC, and evaporated films of U on W have been determined using a pulsed strong-field Schottky method within the temperature range of 1200° to 2400°K. The results are consistent with the hypothesis that a film of uranium on the surface activates all of these compounds. This surface film can be provided by a natural excess of uranium in the compound, from a chemical reduction by the base metal, or by evaporation from an external source. The resulting active state for all of the compounds can be described within a factor of 2 or 3 by the empirical Richardson constants Φ=3.0 eV, A = 10 A/cm2deg2.
Investigation of the Patch Effect in Uranium Carbide
Authors: Haas George A. , Thomas Richard E.
Published: April 2005

An electron beam scanning technique has been devised to measure variations in the surface work function. These measurements indicate a wide patch distribution in the range of 3.25 to 4.5 eV for inactive uranium carbide, which upon thermal activation becomes covered with a surface having a work function in the narrow band of 3.0 to 3.25 eV. The active surface is very sensitive to ambient gases and can be easily poisoned to a value of work function higher than was the case for the inactive state. These results support the hypothesis that a uranium film is responsible for the activation as was suggested by previous thermionic measurements. An analysis of the effect of a nonuniformity in work function on thermionic measurements, shows that experimental Richardson plots or effective work function plots can give highly erroneous results. The magnitude of this error can be determined and is expressed in terms of the spread of the patch distribution.
Fluorescence and Stimulated Emission from Trivalent Europium in Yttrium Oxide
Authors: Chang N. C.
Published: April 2005

Measurements are reported of the absorption, emission, and excitation spectra of Eu3+ in Y2O3, and also of fluorescence lifetime and quantum efficiency. An approximate level scheme is given. Conditions for laser action are calculated, and the results of a laser experiment are described. The importance of a strong ultraviolet excitation band probably corresponding to transitions from f-electron to d-electron levels is indicated.
Flow of a Rarefied Gas between Two Parallel Plates
Authors: Cercignani Carlo , Daneri Adelia
Published: April 2005

The Poiseuille flow of a rarefied gas between two parallel plates is analyzed numerically for an inverse Knudsen number ranging from 0 to 10.5. The Bhatnagar, Gross, and Krook model is used and the transport integrodifferential equation is reduced to a purely integral one, which is solved numerically by the discrete ordinate method.

The plot of the volume flow rate vs pressure is shown to have the expected minimum; besides, it fits well with experimental results and previous approximate calculations.

In particular, the results given by Takao, properly corrected, are in good agreement with ours.
Transmission Electron Microscopy of Cleaved Silicon
Authors: Frankl D. R.
Published: April 2005

Transmission electron micrographs of cleaved silicon samples show severe distortion near the cleavage marks and misorientation of the regions between marks. These results are interpreted as evidence for localized plastic deformation during cleavage.