bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave dielectric constant measurements on lossy static and flowing liquids: B×v effects
Authors: Folen V. J. , Krebs J. J. , Gingerich M. E.
Published: February 2004

A technique is described for the measurement of the refractive index n of static or flowing lossy polar liquids in the 10-GHz region and in the presence of magnetic fields H. Measurements of n as a function of H were performed on static and flowing H2O containing various concentrations of ionic impurities. The application of H (up to 7300 Oe) to liquids flowing with velocities v (up to 200 cm/sec) yielded the following result: Δn/n ≤6×10−4 for all concentrations. This result indicates that Umanskii's observed change in dielectric constant ε′ (roughly 100% change in ε′ for H = 1500 Oe and v = 50 cm/sec) is probably a spurious instrumental effect.
Electrohydrodynamic heat pipe experiments
Authors: Jones Thomas B. , Perry Michael P.
Published: February 2004

Experiments with two electrohydrodynamic heat pipes are reported. Both devices employ an electromechanical flow structure for axial liquid flow and a capillary wicking structure for (i) collection of condensed liquid at the cooled end and (ii) distribution of this liquid at the heated end. One device has circumferential grooving for the capillary structure and the other has feltmetal wicking. The experiments successfully demonstrate the electrohydrodynamic heat pipe concept. Compatibility of the two circumferential wick structures with an axial electromechanical flow structure is also demonstrated. A significant mismatch of the capillary groove and electrohydrodynamic pumping capabilities results in severe hydrodynamic burn-out limiting in the first heat pipe. Both devices have very poor over-all thermal conductances of the order of 1–2 W/°C, reflecting the generally poor heat-transfer properties of the dielectric working fluids required in electrohydrodynamic heat pipes.
Low-temperature specific heat of Li2O·Al2O3·nSiO2 glasses and keatite-phase glass ceramics
Authors: Bohn R. G.
Published: February 2004

The specific heat of Li2O·Al2O3·nSiO2 glasses and keatite-phase glass ceramics, with n=4,6,8,10,12 has been measured between 1.5 and 6 K. The temperature dependence of the specific heat was determined by using several least-squares fits to the data and found to be of the form C=C1T+C3T3. Generally, for a given composition, the magnitude of C3 for the glass ceramic is larger than the value for the corresponding glass. For a given structure, C3 also shows a composition dependence. Estimates for C1 show a dependence on both composition and structure. The results are compared to those obtained for vitreous silica.
Helium, deuterium, and neon migration in a common borosilicate glass
Authors: Shelby J. E.
Published: February 2004

Helium, deuterium, and neon permeability, diffusivity, and solubility have been measured for CGW-7740 glass. The results indicate that gas migration occurs primarily through the silica-rich phase. Reaction of deuterium with the glass structure is evident at temperatures exceeding 300°C. The activation energy associated with this reaction is approximately 15 kcal/mole, which is the same as that for hydroxyl formation in vitreous silica.
Geometrical properties of random particles and the extraction of photons from electroluminescent diodes
Authors: Joyce W. B. , Bachrach R. Z. , Dixon R. W. , Sealer D. A.
Published: February 2004

A confined random-particle flux (such as photons in an electroluminescent diode, integrating sphere, or room, music or other phonons in an auditorium, gas molecules in an imperfect vacuum chamber, neutrons in a reactor, etc.) is analyzed, and simple expressions are shown to exist for the mean path length, transit time, surface transmissivity, projected area, absorption rate, etc., that arise in its description. The results are applied to a theoretical and experimental analysis of the coupling of photons from their source within an indirect-band-gap electroluminescent diode (or within a sufficiently transparent heterostructure direct-band-gap diode) into the ambient or into a multimode optical fiber. We find that about two-thirds of the internally generated photons will reach air from an encapsulated rough-sawed red-emitting GaP(Zn,O) electroluminescent diode of reasonably high purity and contact reflectivity, whereas in a comparable green-emitting GaP(N) diode only about one-fourth of the photons escape while three-fourths are absorbed within the diode bulk and at its contacts.
Formation of PtO films by reactive sputtering
Authors: Westwood W. D. , Bennewitz C. D.
Published: February 2004

An oxide phase which is isostructural with PdO has been obtained as a thin film by reactive dc diode sputtering of Pt in argon-oxygen mixtures. Films in which this is the only crystalline phase observed have been prepared; they have a density of 13.5±1.0 g/cm3. The oxide phase is unstable at temperatures above 500 °C, and the film is converted to platinum. Thermogravimetric analysis of the films indicates that the original composition is close to PtO. Mixtures of PtO and Pt can also be obtained and the temperature coefficient of resistance of the films becomes more negative with increasing PtO content; values between +1800 and −25 000 ppm/°C have been measured.
Some electrode charge-transfer effects in solid ionic materials
Authors: Macdonald J. Ross
Published: February 2004

Recent work on electrode polarization effects in ionic conductors is discussed and extended. Contrary to a recent suggestion, analysis of the ac conduction and electrode processes occurring in such materials should involve effectively mobile charged species of both signs, not just a single mobile species. Special consideration of likely charge-transfer reactions in solid materials such as β-alumina with platinum electrodes leads to a new specific result for the Warburg impedance appropriate for such situations. The over-all impedance of the system involves a very high parallel capacitance showing ω−m frequency response, with 0.5≤m ≤1.5, of the type very frequently found experimentally.
Comment on ``Interpretation of Pt3Co FIM images as investigated with an atom probe''
Authors: Southworth H. N.
Published: February 2004

A controversy exists over whether the nonimaging of the cobalt atoms in field ion images from ordered alloys of cobalt and platinum is due to their preferential evaporation or simply to their invisibility due to selective ionization. Recent atom probe results are held to support the latter theory. It is shown that these results have been misinterpreted and that they in fact support the former theory instead.
Electron microscope study of silver colloids in KCl : Ag
Authors: Jain S. C. , Arora N. D. , Chaudhary K. L.
Published: February 2004

Transmission electron microscope studies of the colloids of silver in KCl : Ag crystals show that the colloidal particles are spherical in shape and have a size distribution among them. Using the observed size distribution and modified optical constants for small metal particles by the Kawabata-Kubo method and Mie's theory, the calculated shapes of the optical bands agree well with the observed band shape.
Effect of antiphase boundary energy on mutual cross slip of unlike dislocations
Authors: Marcinkowski M. J. , Sadananda K.
Published: February 2004

A detailed numerical analysis has been made with respect to the cross slip behavior of a pair of passing screw-type superlattice dislocations on parallel slip planes in a simple B2-type superlattice. It is found that below some critical interplanar spacing, cross slip will always occur with mutual annihilation of the two dislocations. This critical spacing in turn establishes the maximum stress required to pass both dislocations past one another (i.e., the maximum strengthening). It is found that the maximum passing stress increases linearly with increasing antiphase boundary energy.
Plasma-induced field emission and the characteristics of high-current relativistic electron flow
Authors: Parker R. K. , Anderson Richard E. , Duncan Charles V.
Published: February 2004

The results of a comprehensive diode study conducted using a pulsed high-current electron accelerator are reported. Time-dependent analysis of right-cylindrical graphite cathodes has shown evidence of the field emission character of the cold-cathode diode. The effects of cathode whiskers or microprojections on the diode response have been observed. Within a few nanoseconds after the voltage is applied to the diode, the whiskers explode to form cathode flares. The observed diode perveance throughout the remainder of the pulse can be explained in terms of the expansion of the plasma cathode formed by the merger of many cathode flares. Cathode plasma velocities ranged from approximately 2 to 3 cm/μsec. The observed diode behavior was consistent with that predicted by previous studies of high-voltage vacuum breakdown.
Microwave propagation in magnetized ferrite-dielectric composite transmission lines
Authors: Wu You-Sun , Rosenbaum F. J.
Published: February 2004

Analytical results have been derived for the lossless infinite parallel-plane waveguide inhomogeneously loaded with a ferrite-dielectric composite medium. It is found that the existing mode is a hybrid mode composed of all six field components. The magnetic property of ferrite in this composite medium is masked by the presence of a dielectric. It has been shown that this study represents a good approximation for the complicated microstrip transmission lines fabricated out of this composite medium.
Two-dimensional current density distribution within three-terminal semiconductor devices
Authors: Hu Shih-Pei , Rabinovici Benjamin M.
Published: February 2004

To understand fully the operating mechanism of three-terminal semiconductor devices, it is important to know the minority-carrier, electric field, potential, and current-density distributions within the device as a function of the spatial variables. This paper presents the formulation and closed-form solution of the two-dimensional dependency of the minority-carrier distribution within a three-terminal semiconductor device and in particular as it applies to the thyristor. Boundary conditions to obtain the solution were chosen so as to conform to realistic devices being manufactured and to the physical properties of their surfaces. The general solution was derived starting from the basic diffusion equation, and family of curves of the solution for the static case of typical thyristors were obtained with the aid of a digital computer. This was done for the forward blocking and forward conducting states with and without gate current. Experimental results were carried out and good correlation with analytical calculations were obtained.
Optical absorption in ion-bombarded magnetic garnet films
Authors: Seman J. A. , Wemple S. H. , North J. C.
Published: February 2004

Optical absorption measurements are reported for the damaged surface layers produced by proton and neon bombardment of iron-garnet liquid-phase-epitaxial films. The excess optical absorption is shown to be an absorption tail on O(2p)→Fe(3d) charge-transfer bands centered near 4 eV with about 10% contributed by higher-energy optical transitions. The distribution of states for Ne bombardment is different from that for H bombardment, and in the case of Ne the state distribution depends on the dose. Saturation at a photon energy of 2.2 eV occurs at an absorption coefficient of ∼2×104 cm−1. The average damage density over the damaged layer thickness is observed to increase with decreasing H energy, in agreement with hard-bubble-suppression data and nuclear stopping power considerations. Based on optical absorption and hard-bubble-suppression results it is estimated that the dose window for hard bubble suppression corresponds roughly to an average disorder range from ∼3–30% amorphous (amorphous defined optically). Annealing studies show that no simple activation energy description applies to the damaged material. Deep states anneal out more rapidly than shallow states for both H and Ne bombardment.
Effects of low-temperature fast-neutron irradiation on ac losses in NbTi
Authors: Brown B. S. , Freyhardt H. C. , Blewitt T. H.
Published: February 2004

The complex magnetic permeability of Nb-44 at.% Ti has been measured using a modified Hartshorn ac bridge and a lock-in amplifier. The out-of-phase signal can be directly related to the energy losses, and critical current can be calculated using the Bean model. Samples were irradiated in a fission neutron spectrum to a dose of 3.2×1018 neutron/cm2. All measurements were taken in situ at approximately 4.5 °K in an external magnetic field continuously swept to 6.7 kOe while applying ac magnetic fields at 88 Hz with amplitudes between 8 and 500 Oe. Irradiations and measurements were performed on an annealed and a cold-worked sample of the alloy. For the annealed sample, no changes were observed in VL and thus in Jc after 8.2×1017 neutron/cm2 and after an anneal to 320 °K. A decrease of approximately 8% was observed in Jc for the cold-worked sample after 3.2×1018 neutron/cm2. One-half of this decrease was recovered by 270 °K.
Saturation magnetization of gallium-substituted yttrium iron garnet
Authors: Hansen P. , Röschmann P. , Tolksdorf W.
Published: February 2004

The saturation magnetization of gallium-substituted yttrium iron garnet single crystals of composition Y3[Fe2−x Gax](Fe3−y Gay) O12 with 0≤x+y≤1.5 has been investigated in the temperature range 4.2≤T≤Tc. The magnetization values are below most data of previous investigations on this system. From the fit of the molecular field theory to the experimental results at T=4.2 K the fraction of the tetrahedral gallium ions ft=y/(x+y) could be deduced and are found to range between 1 and 0.91 for 0≤x+y≤1.5. The compensation temperature occurring for x+y>1 has been studied as a function of the gallium distribution.
Thermomagnetic writing on thin-film MnBi using an electron beam
Authors: Heyworth R. C. F. , Hoffman G. R.
Published: February 2004

Thermomagnetic writing of small areas on MnBi thin films using an electron beam has been demonstrated both on unheated films and on films maintained at an elevated temperature during the writing procedure. Experiments in which the incident energy of the beam was varied have allowed a safe writing region to be established. Factors which influence the written spot diameter are discussed.
Lateral spread of ion-implanted impurities in silicon
Authors: Pan E. , Fang F. F.
Published: February 2004

A technique for measuring the overlaps of the gate electrodes of field-effect structures is described. Ion-implanted self-aligned gate FET structures were used to evaluate the lateral spread of low-energy (RP<0.1 μm) high-dosage (5×1015/cm2) phosphorus and boron implantations and was found to be less than 10−5 cm. Sheet resistance of the implanted region can also be evaluated by this technique. Some series resistance effects associated with inadequate annealing as well as two-dimensional field aspects on the threshold voltage associated with short channel devices in this experiment were observed.
Test of a semiempirical equation describing laser beam divergence
Authors: Bates Harry E. , Phillips Robert W. , Sasser Thurman
Published: February 2004

A semiempirical equation describing laser beam divergence for a flat-flat laser resonator taking into consideration the resonator Q is tested. This equation describing beam divergence consists of two parts: a contribution due to diffraction and distortion in the resonator material and a term which accounts for cavity geometry and photon lifetime. Good agreement is obtained with experiment.
Control of nonlinear effects in acoustic surface waves
Authors: Nakagawa Yasuhiko , Yamanouchi Kazuhiko , Shibayama Kimio
Published: February 2004

Theoretical and experimental investigations are made of nonlinear effects in acoustic surface waves with and without velocity dispersion. First, the results of the investigation of nonlinear effects in surface-wave devices are reported. Second, it is shown that the nonlinear effects in acoustic surface waves can be controlled by velocity dispersion; namely, when the velocity dispersion of acoustic surface waves is increased, the nonlinear effects are reduced, and when the acoustic surface waves are free from velocity dispersion, the nonlinear effects are increased. The experiment was conducted with specimens of a 131°-rotated Y-cut X-propagating LiNbO3, and the fundamental frequency was about 300 MHz.
Electron lifetime and diffusion constant in germanium-doped gallium arsenide
Authors: Acket G. A. , Nijman W. , 't Lam H.
Published: February 2004

The lifetime of electrons in Ge-doped p-type GaAs grown by liquid phase epitaxy has been determined as a function of doping level using an optical phase-shift technique. The internal radiative efficiency of this material is found to be high even at room temperature. Furthermore, the electron lifetime τ has been measured in Ge-doped samples compensated with Sn donors. Data are presented both for 300°K and 77°K. Measurements of the diffusion length on the same samples are also presented. From the combined results the diffusion constant of the electrons is obtained as a function of doping level both for the Ge-doped and the Ge-doped Sn-compensated samples. In GaAs doped with Ge only, τ at 300°K is inversely proportional to the hole concentration p; at this temperature partial compensation with Sn donors has only an effect at higher hole concentrations. At 77°K, the τ values depend more strongly on the degree of compensation. Conclusions regarding the influence of band tailing are presented.
Force on domain wall due to perturbation of current in a magnetoresistive overlayer
Authors: Carr W. J.
Published: February 2004

A calculation is made of the force on a cylindrical domain in the presence of a current-carrying magnetoresistive overlay. The force results from the perturbation produced by the field of the domain on the current in the overlay. When the force exceeds the coercive force, the domain should propagate. For a Permalloy overlay a rough estimate of the magnitude of the effective magnetic field gives a value of 0.01 Oe for a current of 10 A/cm width in the overlay.
Annealing behavior and temperature dependence of the growth-induced magnetic anisotropy in epitaxial Sm-YIGG
Authors: Hagedorn F. B.
Published: February 2004

The annealing behavior and temperature dependence of the growth-induced magnetic anisotropy in epitaxial films of Y2.6Sm0.4Ga1.2Fe3.8O12 have been investigated. This garnet composition is presently being widely used for magnetic bubble domain device work. Decay times for the anisotropy are tens of hours at 1250°C and several hours at 1325°C. This rapid decrease in annealing time with increasing annealing temperature can be understood by postulating that oxygen vacancies play a significant role in determining the diffusion rate and that the oxygen vacancy concentration increases rapidly with increasing temperature. From these considerations, a lower limit of 2.8×107 yr is estimated for the decay time of the anisotropy at 100°C, based on an assumed activation energy of 1 eV. By using torque magnetometer measurements, the anisotropy has been found to vary by about an order of magnitude over the temperature range −10 to 110°C. Only two different kinds of temperature dependences were observed among films grown on four differently oriented substrates, in agreement with predictions of the site-preference model for growth-induced anisotropy. Also described is a new torque magnetometer technique for measuring the effective anisotropy field in magnetic materials which support bubble domains.
Monte Carlo approach to the spatial deposition of energy by electrons in molecular hydrogen
Authors: Heaps M. G. , Green A. E. S.
Published: February 2004

The Monte Carlo (MC) and continuous slowdown approximation (CSDA) approaches to the spatial depostition of energy by electrons are compared using the same detailed atomic cross section (DACS). It is found that the CSDA method overestimates the amount of energy that is deposited near the end of the path for electrons above a few hundred electron volts. The MC results are in approximate agreement with experimental data in such a way as to be relatively independent of the actual gas used. Our MC results are extended to obtain the three-dimensional deposition of energy by sub-keV electrons in molecular hydrogen.
Magnetic insulation of an intense relativistic electron beam
Authors: Golden J. , Orzechowski T. J. , Bekefi G.
Published: February 2004

A magnetic field is used as an insulator, preventing electrons from crossing the gap of a pulsed field-emission diode subjected to voltages of 100–250 kV. The diode is comprised of two concentric cylinders with a variable gap separation ranging from 2 to 6 mm. A pulsed magnetic field up to 15 kG is applied along the diode axis. When the magnetic field exceeds a certain critical value, the electron current (which is typically 10–30 kA) is reduced by approximately two orders of magnitude. The desired magnetic insulation lasts over the full 50-nsec voltage pulse.
Reply to ``Comment on `Glide systems and Peierls stresses in fcc and bcc metals from phonon energies' ''
Authors: Boffi S. , Caglioti G. , Rizzi G. , Rossitto F.
Published: February 2004

It is shown in this reply that the work done in the original paper was relevant within the frame of the Frenkel-Kontorova-Hobart model. It is recognized that there are indeed limitations of the above model to predicting yield stress of bcc metals.
Lattice relaxation in α-iron containing small xenon-vacancy clusters
Authors: Drentje S. A. , Ekster J.
Published: February 2004

Binding energies and atomic configurations for small xenon-vacancy clusters in α-iron have been computed using a model based on a two-body potential between the interacting atoms. Various clusters were placed near the center of a sphere containing about 150 iron atoms initially at regular positions in bcc configuration. The results of these calculations are of importance for the interpretation of hyperfine interaction measurements on implanted radioactive sources.
Extinction in mosaic crystals
Authors: Werner S. A.
Published: February 2004

Exact formal solutions of the transport equations which govern the flow of current in a mosaic crystal set at a Bragg condition are given. These solutions are applied to a crystal cut in the shape of a parallelepiped. A formula is derived for the extinction coefficient for this crystal shape. We call this result the ``AB-extinction formula''. It will provide the experimentalist with an approximate method to correct for anisotropic extinction resulting from a crystal shape anisotropy. It is suggested that the exact results of the dynamical diffraction theory for slabs should be used to correct for primary extinction. The mathematical and conceptual errors in the theory given by Zachariasen are pointed out.
Interdependence of strain, precipitation, and dislocation formation in epitaxial Se-doped GaAs
Authors: Abrahams M. S. , Blanc J. , Buiocchi C. J.
Published: February 2004

The defect morphology of Se-doped GaAs grown by CVD on undoped 100-oriented GaAs substrates has been studied by transmission electron microscopy. Two types of samples are discussed: The first is nearly saturated, n ≅ NSe ≅ 4 × 1018 cm−3; the second is supersaturated, n ≅ 1.5 × 1019 cm−3, NSe ≅ 4 × 1019 cm−3. The nearly saturated samples exhibit an array of small features (probably Frank loops) near the original interface and have a density of misfit relieving dislocations ≲103 cm−1. The supersaturated samples show a large number of Frank loops, whose density decreases monotonically with distance away from the original interface while their diameter increases in this direction. The loops seem to be invariably connected with one or more very small precipitate particles of Ga2Se3. Most of the Frank loops are of the intrinsic type; these are sometimes accompanied by closely neighboring loops of extrinsic nature. Pure edge misfit relieving dislocations with a density ≅ 104 cm−1 are observed at the interface, running in one of the 〈011〉 directions, but not in the orthogonal direction. A model is proposed to explain these results. Among the ingredients of this model are the notions (i) that misfit dislocations are asymmetrically introduced well away from the original interface and climb to that interface; (ii) that the solubility of Se in GaAs is a function of the imposed strain; and (iii) that the precipitation of Ga2Se3 in GaAs is accompanied by the formation of both As vacancies and interstitial Ga in the matrix.
Excitation of monofilar and bifilar modes on a transmission line in a circular tunnel
Authors: Hill David A. , Wait James R.
Published: February 2004

We consider the excitation of monofilar and bifilar modes on a transmission line in a circular tunnel by a short dipole antenna. As expected, the monofilar mode is excited more strongly by an antenna placed in the tunnel, but the bifilar mode has lower attenuation. The excessive losses in the monofilar or coaxial mode are attributed to the return current flow along the tunnel walls. In the bifilar or transmission-line mode the fields are more confined to the region of the wire conductors.
Characteristics of organic colorants transferred by laser scanning
Authors: Braudy Robert S.
Published: February 2004

This paper discusses two characteristics necessary for efficient laser-induced transfer of organic colorants. Results analyzed on a scanning electron microscope and scanning microdensitometer suggest that the material transfer is caused by melting and vaporization.
Molecular-field coefficients of Ti4+- and Zn2+- substituted lithium ferrites
Authors: Dionne Gerald F.
Published: February 2004

By empirical methods similar to those outlined previously for the iron garnets, molecular-field coefficients are reported for the complicated LiTiZn ferrite system. As in the case of the garnets, the intrasublattice coefficients NAA and NBB are linearly dependent on the Ti4+ and Zn2+ concentrations, but the intersublattice coefficient NAB has a quadratic dependence on the Ti4+ substitutions. Where possible, the computed results are compared with experiment, and the agreement is found to be good over the ranges 0≤t≤0.9 and 0≤z≤0.4.
Current-induced magnetic-flux structures in a type-I superconducting constriction
Authors: Watson H. L. , Kampwirth R. T. , Huebener R. P.
Published: February 2004

We have studied the current-induced magnetic-flux structures in type-I superconducting constrictions using a high-resolution magneto-optical method. The samples were Pb films 60–100 μm thick with a single constriction of 0.5–1.0 mm width, similar to the Anderson-Dayem bridge geometry. In the resistive state, moving flux-tube trains are nucleated at both sample edges, at first precisely at the narrowest portion of the constriction. With increasing current, the flux-tube trains extend more and more into the outlying regions performing a curved path. From the resistive voltage and our magneto-optical observations the flux-tube nucleation rate for a flux-tube train is estimated using the Josephson relation.
Kerr-effect enhancement and improvement of readout characteristics in MnBi film memory
Authors: Egashira K. , Yamada T.
Published: February 2004

Enhancement of the Kerr effect was studied to assess its effectiveness in improving readout characteristics of a magneto-optical memory utilizing MnBi films. SiO was used to enhance the Kerr effect by coating it on magnetic films. The coating results in a change, not only in the Kerr rotation but also in the ellipticity and reflectivity of the films. Changes of these quantities were calculated as a function of the SiO thickness, using optical constants of both MnBi and SiO, i.e., the refractive indices n2 and n3 of SiO and MnBi, respectively, and the off-diagonal element ε′ of the dielectric tensor of MnBi. The optical constants determined in this work were n2=(2.0±0.02)−(0.02±0.02)i, n3=3.1−3.5i, and ε′ = −1.2−0.4i at a wavelength of 6328 Å. The Kerr rotation and the reflectivity were measured for various SiO thicknesses and were compared with the results of theoretical calculations. Experimental and theoretical results agreed well with each other. The readout signal-to-noise ratio, which is a function of the Kerr rotation, ellipticity, and reflectivity, is expected to be improved by a factor of more than 2, when SiO is coated on the MnBi film surface.
Effect of nonellipsoidal nonparabolic band structure on longitudinal magnetoresistance in bismuth
Authors: Wu Chhi-Chong , Tsai Jensan
Published: February 2004

Adopting the Cohen nonellipsoidal nonparabolic (NENP) model as the energy band of bismuth, calculations of the conductivity tensor in the presence of ultrasound propagating parallel to a dc magnetic field are performed by using a quantum-mechanical treatment which is valid at high frequencies and in strong magnetic fields. It is found that the longitudinal resistivity oscillates with the dc magnetic field. However, these ``giant quantum oscillations'' will be diminished by increasing the sound frequency. This dependence of the longitudinal resistivity on the dc magnetic field arises from the nonlinear effect of the energy bands owing to the NENP band structure of bismuth.
Effect of electrical-conductivity variations on the characteristics of arc discharges
Authors: Whitman Alan M. , Cohen Ira M.
Published: February 2004

Algebraically calculated current-voltage characteristics of arc discharges are obtained with a canal model for planar and cylindrical arcs and electrical conductivity given as a power of the heat-flux potential. For slower than linear variation, the current-voltage characteristic has a distinct minimum, whereas for faster than linear variation the arc electric field tends to zero as current increases without limit.
Weak-field magnetoresistance in Czochralski-grown Pb1−xSnxTe
Authors: Hoff G. F. , Jensen J. D.
Published: February 2004

Weak-field magnetoresistance measurements were made on Pb1−xSnxTe Czochralski-grown crystals for x=0.17. These crystals have compositional striations that are a result of the variation in the Pb/Sn ratio along the growth axis. The electrical measurements were made for the sample current parallel and perpendicular to the growth axis. The results demonstrate that the electrical properties are dependent on how the crystal is oriented relative to the compositional striations.
Laser-induced plasma perturbation studies of energy transfer in CO2 glow-discharge lasers
Authors: Gower M. C. , Carswell A. I.
Published: February 2004

V-V and V-T energy transfer mechanisms have been investigated in CO2 glow discharges using a pulsed laser plasma perturbation method. The appropriate rate equations are presented, the solutions of which were found to adequately describe the observed induced spontaneous emission and discharge current changes. From the spontaneous emission studies, it is possible to observe directly intermolecular V-V pumping between CO2(ν3) and both CO and N2, while the temporal variations in discharge current permitted measurements to be made of the V-T rates for the (1000) and (0001) levels. New data for the deactivation of the (1000) level in the discharge is presented along with quenching rates of (0110) by H2O and CO. In addition, both radial and longitudinal acoustic waves were found to propagate in the discharge following amplification or absorption of the 10.6-μm laser pulse.
NO spectroscopy by pulsed PbS1−x Sex diode lasers
Authors: Preier H. , Riedel W.
Published: February 2004

Laser properties of PbS0.615Se0.385 diodes emitting at about 5.4 μm are described. The wavelength shift during the application of a current pulse has been studied in detail. Its application for the detection of NO in a gas at atmospheric pressure is presented.
On the growth of single crystals of ammonium chloride from vapor-phase techniques
Authors: Sharma S. D. , Kumar Krishna
Published: February 2004

Kinetics of growth of ammonium chloride single crystals have been studied employing vapor-phase techniques. The crystals grown by the Piper-Polich technique were found polycrystalline in nature. Single crystals of ammonium chloride 1–2 mm wide and 5–7 mm long have been grown below its transformation temperature employing sublimation techniques. A possible growth mechanism has been suggested.
Elastic constant increases upon crystallization of a sputter-deposited amorphous alloy
Authors: Merz M. D. , Allen R. P. , Dahlgren S. D.
Published: February 2004

A 0.2-in.-thick amorphous samarium-cobalt alloy (Sm2Co17) was prepared by sputter deposition. Increases in shear and bulk moduli were measured before and after crystallization with an ultrasonic technique. The shear modulus increased 45% and the bulk modulus increased 7% upon crystallization. Density increases were less than 2%. The increases were in accord with theoretical predictions.
Stripe domains in arbitrarily oriented fields
Authors: Yang Mou-Hsin , Muller M. W.
Published: February 2004

We have calculated the width of stripe domains in uniaxial magnetic films in a static uniform applied field of arbitrary magnitude and orientation. The results are in good agreement with reported experimental results.
He–Li+ Interaction Energy at Small Internuclear Distances
Authors: Fischer C. R.
Published: February 2004

A single configuration MO-SCF calculation of the He-Li+ interaction energy in the Born-Oppenheimer approximation for internuclear separations between 0.1 and 0.7 Å is found to be in diasgreement with the same interaction deduced by Zehr and Berry from atomic scattering data. The calculated/experimental ratio for the energy is approximately 1.4 for 0.21 Å < r <0.74 Å . The MO-SCF potential may be presented to within 10% by the Born-Mayer form as V (r) = 580 exp ( − 5.4r) eV with r in Å. It is shown that the discrepancy cannot be accounted for by the neglect of correlation energy associated with the single configuration MO type of calculation.
Medium Effects on the NMR and Thermodynamic Properties of 1,1,2,2-Tetrabromofluoroethane
Authors: Govil G. , Bernstein H. J.
Published: February 2004

Chemical shifts, coupling constant, free energy, and free energy of activation for 1,1,2,2-tetrabromofluoroethane have been found to depend on temperature and solvent. The results can be explained qualitatively using the “reaction-field” model. Vapor-phase values for the different thermodynamic and NMR properties of the molecule have been estimated. Theory for calculating NMR spectra of two exchanging AX systems has been presented.
Improvement of Molecular Gaussian Wavefunctions
Authors: Bishop David M.
Published: February 2004

Gaussian electronic wavefunctions for H, H2+, and H2 are presented and it is shown how they may be improved by, in each case, adding to the basis set a function of the form χ = (ρ − r)lfor r≤ρ = 0 for r>ρ, centered on each nucleus, where r is the distance from the nucleus and ρ and l are parameters which may be chosen to minimize the electronic energy. Such improvement is shown to be greater than that which would be obtained by adding a further Gaussian function to the basis set.
Internuclear Separation Derivatives of the Energy of a Diatomic Molecule
Authors: Kim Hojing
Published: February 2004

General formulas for the higher-order derivatives of the energy with respect to the internuclear separation of a diatomic molecule are derived from the Hellmann-Feynman theorem and the integral Hellmann-Feynman theorem. The phenomenon of the cancellation of terms involving the charge density and its derivatives, which has been observed for the second-order derivative by Salem, is shown to prevail for third-and higher-order derivatives. On this basis an approximate working formula is suggested. A new condition under which an approximate wavefunction satisfies the Hellmann-Feynman theorem rigorously is given. With such an approximate wavefunction, the formulas for the general derivatives of the energy derived are also shown to be valid.
Corrections to the Kinetic Theory of Fluid Diffusion
Authors: Dymond J. H. , Alder B. J.
Published: February 2004

The measured diffusion coefficients of methane along the liquid branch of the liquid-vapor coexistence curve at temperatures from the critical down to near the normal boiling temperature can be quantitatively predicted on the basis of hard-sphere diffusion theory. This constitutes an experimental verification of the van der Waals theory of transport, and furthermore, it shows the practical importance of the contribution of correlated events to hard sphere diffusion, recently observed in computer experiments.
Stark Effect in Electronic Spectra: The Asymmetric Rotor
Authors: Lombardi John R.
Published: February 2004

Qualitative and quantitative analysis is made of the information obtainable from an electronic spectrum of an asymmetric rotor in an electric field. The most general case is considered where the Stark effect may be smaller, larger, or approximately equal to the asymmetry doubling. A method is described to obtain Stark-asymmetric rotor energies and wavefunctions and from these determine the expected Stark-effect patterns in optical spectra. It is shown that from these spectra one may obtain all three components of an excited-state dipole moment, and its direction relative to the ground-state moment. In addition, it is shown how the Stark effect may be used as an aid in the assignment of asymmetric rotor spectra.
Potential of Average Force for Macroions of Rigid-Sphere Potentials
Authors: Isihara A. , Aono O.
Published: February 2004

A method to evaluate the potential of average force between macroions of rigid-sphere potentials is presented. It is based on evaluating the pair distribution function in a chain diagram approximation using the pseudopotential method. The result is given by a screened Coulomb potential with hard core effects and is confirmed by an alternative classical method which also does not use the Poisson-Blotzmann equation.
Motional Effects in the Electron Spin Resonance Absorption Spectrum of CO2– Molecule-Ions in Single-Crystal Calcite
Authors: McMillan J. A. , Marshall S. A.
Published: February 2004

The electron spin resonance absorption spectrum of CO2– molecule-ion in single-crystal calcite has been reinvestigated as a function of temperature. Between 77° and 250°K the spectrum exhibits orthorhombic symmetry and from the manner in which the widths of the spectral components behave, it is concluded that in this temperature range the CO2– molecule-ion hops from one to another of three equivalent configurations each being rotationally displaced from the other two by  ± 2π / 3 radians in the (111) plane. Such hops involve the crossing of one of three equivalent potential wells whose depths are estimated to be 0.165 eV and whose widths are not more than 0.1 radians. At 250°K the spectrum associated with the (111) plane is wiped out. Above this temperature an axially symmetric spectrum appears whose parameters are simply related to those of the low-temperature spectrum, and from the manner in which the widths depend upon temperature, it is concluded that in this temperature region the CO2– molecule-ion undergoes hindered rotations about the [111] direction.
Quantum Oscillations in the Shape of Pressure-Broadened Atomic Lines
Authors: Mies Frederick H.
Published: February 2004

Oscillatory or bandlike structure is predicted to occur in the wings of pressure-broadened atomic lines when the interaction potential between the emitting atom M* and the perturbing atom A is deeply attractive compared to kT and the interaction in the final state is repulsive. The oscillations in intensity arise from quantum effects and are associated with the nodal structure of the continuum wavefunction which describes the dissociated state of the diatomic molecule (A + M*). The number of maxima in the line shape is a measure of the number of bound states which can be supported in the potential while the amplitude and resolution of the oscillations depend on the long-range behavior of the potential. The bandlike structure, which may extend over thousands of cm−1 on the long-wavelength side of the atomic emission line, is resolvable as long as kT < ∼ 1 / 10 the vibrational quantum ℏωe of the AM* molecule. This is a generalization of similar bandlike structure which has been calculated and observed to occur in the collision-induced radiation of helium metastable atoms and which is merely a special case of pressure broadening involving forbidden lines. Specific calculations are presented for the broadening of the hydrogen Lyman-α line by H(1s), and the visible absorption spectra of H(1s) in the presence of free protons. The quantum theory of line shape which is employed here was first developed by Jablonski but then neglected due to difficulties involved in evaluating essentially the band strength for continuum–continuum transitions of diatomic molecules. Jablonski introduced the WKB and other approximations into his theory which reduced it to the classical statistical theory. These approximations are compared to exact quantum-mechanical calculations. The WKB approximation is shown to be quite valid in the special case of attractive–replusive transitions, but Jablonski then improperly averaged over those very quantum oscillations of interest here. This structure offers a unique and extremely sensitive method of studying interaction potentials involving excited states of atoms.
Valence-Bond Studies of Contact Nuclear Spin–Spin Coupling. I. A Truncated Matrix Sum Method
Authors: Barfield Michael
Published: February 2004

A theoretical description of contact nuclear spin–spin coupling is presented in terms of a valence-bond formalism which does not invoke the approximation of a “mean excitation energy” in the second-order perturbation sum. By explicitly including a sum over the valence-bond triplet-state wavefunctions, a general expression for the contact nuclear spin coupling constant is obtained in a theory which uses a bond diagram formalism. The relationship of this extended theory to existing valence-bond descriptions is investigated. As examples of the applicability of the method, detailed results are given for the contributions of the individual triplet states to the long-range proton coupling constants in eight electron fragments of the butadiene and allene molecules.
Valence-Bond Studies of Contact Nuclear Spin–Spin Coupling. II. Long-Range Pi-Electron Coupling between Protons
Authors: Barfield Michael
Published: February 2004

A theoretical study of long-range proton coupling is presented in terms of a semiempirical valence-bond formalism which does not invoke the approximation of a “mean excitation energy” in the second-order perturbation sum. Using the spin coupling theory which includes an explicit sum over the triplet-state valence-bond wavefunctions, π-electron contributions to long-range couplings are calculated for a large number of unsaturated molecules in which the protons are separated by four to seven bonds. The calculated results are shown to be in reasonably good agreement with the available experimental data and are of importance in discussing mechanisms of contact nuclear spin–spin coupling.
Third Virial Coefficients for Mixtures of Lennard-Jones 6–12 Molecules
Authors: Stogryn Daniel E.
Published: February 2004

The reduced third virial coefficient for arbitrary multicomponent mixtures of Lennard-Jones 6–12 molecules is obtained as a series in variables related to the well-depth parameters of the potentials. The coefficients of this series are in turn given as series in the reduced temperature. Included in the analysis is the contribution to the third virial coefficient from the pairwise nonadditive three-body interactions described by Kihara. This work makes use of an expansion of the third cluster intergral in terms of confluent hypergeometric functions, and the analytical development is carried far enough so that only singlefold numerical integrations are required to obtain the final numerical results. Appropriate tables are presented to allow calculations of the third virial coefficient.
Luminescence in MgO
Authors: Sibley W. A. , Nelson C. M. , Chen Y.
Published: February 2004

The phosphorescence and x-ray stimulated luminescence of a series of nominally pure MgO crystals has been investigated. We suggest that the series of emission peaks around 1.4eV is due to Mg(OH)2 impurity, and have presented evidence which substantiates the assignment of the 1.7-eV and 2.5-eV luminescence with Cr3+ and Ni2+, respectively. The effect of electron and neutron irradiation on the samples is also discussed.
Born–Green–Yvon and Kirkwood Hierarchies in Equilibrium
Authors: García-Colín L. S. , Braun E.
Published: February 2004

It is shown that the Born–Green–Yvon and Kirkwood hierarchies for the nth-body distribution function, in the equilibrium theory of fluids, contrary to what is usually stated, are not equivalent. The resulting integral equations for the pair correlation function, after using the superposition approximation, are different. This difference is not due to the approximation.
Solvent and Temperature Dependence of NMR Spectral Parameters in 2-Fluoropyridine Solutions
Authors: Alger T. D. , Gutowsky H. S.
Published: February 2004

Spin-echo methods have been used to measure the effects of solvent and temperature on the 14N and 19F spectral parameters (R1N, R2F0, and JNF) in several 2-fluoropyridine solutions. These effects were found to depend upon the dielectric constant ε of the solutions, while η / R1N, the ratio of visocity to spin–lattice relaxation rate, was found to be approximately constant. Also, with few exceptions η tends to increase with increasing ε. Such polarity dependence is found in the effects of temperature as well as of solvent, which supports previous suggestions that the spectral parameters are modified primarily by weak van der Waals-type molecular association. Instrumental errors are discussed.
Microwave Spectra of Methylcyclopropanes. II. Methylcyclopropane
Authors: Ford Robert G. , Beaudet Robert A.
Published: February 2004

The microwave spectrum of methylcyclopropane was observed in the range 8–38 GHz. The barrier to internal rotation of the methyl group was determined as 2860 ± 50 cal/mole from splittings of the rotational transitions. The dipole moment was found to be: μA = 0.097 ± 0.001 D, μC = 0.100 ± 0.005 D, and μtotal = 0.139 ± 0.004 D.
Virial Theorem, the Variational Principle, and Nonlinear Parameters in Quantum Mechanics: Application to the 31D and 33D States of the Helium Isoelectronic Series
Authors: Brown Robert T.
Published: February 2004

The connection between the virial theorem and the variational principle with respect to nonlinear parameters has been investigated for a system of n particles interacting through Coulomb forces. It is found that if the nonlinear parameters are chosen to be n scale parameters and considered as the components of a position vector in an n-dimensional Euclidean space, the locus of points for which the virial theorem is satisfied is a path of steepest descent on the energy surface. It is thus possible to minimize the energy along a path of steepest descent without the necessity of calculating derivatives. As an example, variational wavefunctions and energies are obtained for the 31D and 33D states of the helium isoelectronic series through Z = 30, with the trial function a 39-term configuration-interaction expansion in members of a denumerably complete basis set. The calculated energies for He and Li+ agree with observed values to within 0.000007 a.u. The agreement with energies obtained from Hylleraas-type expansions for Z ≤ 10 is of the same order, and in some cases it is the configuration-interaction energy which is lower.