bluuebunny/crossref_metadata_2025 huggingface dataset:
Probing potential surfaces for hydrogen bonding: Near-infrared combination band spectroscopy of van der Waals stretch (ν4) and geared bend (ν5) vibrations in (HCl)2
Authors: Fárnı́k Michal , Davis Scott , Schuder Michael D. , Nesbitt David J.
Published: July 2002

High resolution infrared spectra of the two “low” frequency intermolecular modes—van der Waals stretch (ν4) and geared bend (ν5) of (HCl)2—have been characterized in HCl-stretch excited states using a slit jet spectrometer. In a high resolution high sensitivity search covering the range between 2880 and 3070 cm−1 four (HCl)2 combination bands associated with in-plane vibrations ν4 and ν5 have been observed. The vibrational assignment of these bands is based on comparison between observed intermolecular mode energies and predictions from recent six-dimensional (6D) quantum mechanical (QM) calculations [Y. Qiu, J. Z. H. Zhang, and Z. Bačić, J. Chem. Phys. 108, 4804 (1998)], though additional confirmation is provided by ancillary spectroscopic information such as rotational constants, predissociation linewidths, and Cl35/37Cl isotopic band shifts. The experimentally observed intermolecular energies agree with theoretical predictions to ≈2–4 cm−1 out of 60–90 cm−1, suggesting that the 6D potential energy surface can describe combination band excitation in these lower frequency intermolecular coordinates fairly well. Three of the four observed combination bands arise from the upper tunneling level (B+), and all four bands are built exclusively on bound HCl stretch (ν2). To account for these striking intensity anomalies, a simple model for three-dimensional QM calculation of transition moments is introduced, which correctly reproduces the experimental trends. In this model, the propensity for ν2 based combination bands arising from upper tunneling levels can be successfully ascribed to the unusually “floppy” nature of the intermolecular vibrations, which results in a “harmonic oscillator” Δv=+1 propensity for excitations between tunneling levels along the geared bend coordinate.
A first-passage scheme for determination of overall rate constants for non-diffusion-limited suspensions
Authors: Lu Shih-Yuan , Yen Yi-Ming
Published: July 2002

A first-passage scheme is devised to determine the overall rate constant of suspensions under the non-diffusion-limited condition. The original first-passage scheme developed for diffusion-limited processes is modified to account for the finite incorporation rate at the inclusion surface by using a concept of the nonzero survival probability of the diffusing entity at entity-inclusion encounters. This nonzero survival probability is obtained from solving a relevant boundary value problem. The new first-passage scheme is validated by an excellent agreement between overall rate constant results from the present development and from an accurate boundary collocation calculation for the three common spherical arrays [J. Chem. Phys. 109, 4985 (1998)], namely simple cubic, body-centered cubic, and face-centered cubic arrays, for a wide range of P and f. Here, P is a dimensionless quantity characterizing the relative rate of diffusion versus surface incorporation, and f is the volume fraction of the inclusion. The scheme is further applied to random spherical suspensions and to investigate the effect of inclusion coagulation on overall rate constants. It is found that randomness in inclusion arrangement tends to lower the overall rate constant for f up to the near close-packing value of the regular arrays because of the inclusion screening effect. This screening effect turns stronger for regular arrays when f is near and above the close-packing value of the regular arrays, and consequently the overall rate constant of the random array exceeds that of the regular array. Inclusion coagulation too induces the inclusion screening effect, and leads to lower overall rate constants.
Fluid description of a magnetized plasma
Authors: Mahajan S. M. , Hazeltine R. D.
Published: July 2002

With the constraints of Lorentz covariance as a guide, the most general energy-momentum tensor for a plasma subject to a dominant electromagnetic force is constructed. A consistent scheme is developed to derive a closed set of fluid equations determining all the unknowns in this energy-momentum tensor. Note that knowledge of the energy-momentum tensor is sufficient to close the Maxwell equations. The new theory takes the original magnetohydrodynamics (MHD) program, a fluid theory of magnetized plasma, to its logical limit, but is distinct from MHD in several respects. Relativistic as well as the nonrelativistic (directed as well as thermal speed much smaller than the speed of light) versions of the system are displayed.
The relativistic J-matrix theory of scattering: An analytic solution
Authors: Alhaidari A. D.
Published: July 2002

The relativistic J-matrix is investigated in the case of Coulomb-free scattering for a general short-range spin-dependent perturbing potential and in two different L2 bases. The resulting recursion relation of the reference problem, in this case, has an analytic solution. The nonrelativistic limit is obtained and shown to be identical to the familiar nonrelativistic J-matrix.
Heterodyne O-mode reflectometer on the JT-60U tokamak
Authors: Oyama N. , Shinohara K.
Published: July 2002

A three-channel heterodyne O-mode reflectometer system has been developed for density fluctuation measurements on the JT-60U tokamak. The system consists of one fixed channel with a frequency of 34 GHz and two selectable frequency channels with frequencies in the range of 34–40 and 48–50 GHz in order to measure the change of fluctuation amplitude, fluctuation coherence, and movement of the cutoff layer during the discharge. The reflectometer system has now become a standard diagnostic for density fluctuation measurements on JT-60U covering both core and edge plasma regions. The capabilities of the system are illustrated for three experimental cases: edge transport barriers in H-mode plasmas, internal transport barriers in reversed shear plasmas, and fast turbulence burst at the onset of multifaceted asymmetric radiation from the edge.
Microstructure and magnetic properties of (Pr,Tb)2(Fe,Nb,Zr)14B/α-Fe nanocomposites
Authors: Jin Z. Q. , Okumura H. , Wang H. L. , Hadjipanayis G. C.
Published: July 2002

The microstructure and magnetic properties of Pr2Fe14B/α-Fe nanocomposites with small amount of Tb, Nb, and Zr additions have been investigated. A c-axis texture in the 2:14:1 phase has been observed in ribbons spun at speeds below 14 m/s. Optimal magnetic properties were found in annealed samples spun at 14–17 m/s. With small additions of Nb and Zr, the coercivity significantly increases. Nb substitution leads to a poor loop squareness, which can be significantly improved with Zr addition due to a refinement in microstructure, resulting in a drastic increase in the energy product. Optimum magnetic properties with a room temperature coercivity of 8.2 kOe, and (BH)m=20.3 MGOe have been obtained in Pr7Tb1Fe87Nb0.5Zr0.5B4 ribbons. Transmission electron microscopy on this sample revealed a much finer and homogeneous microstructure with an average grain size of 20 nm.
Metal–insulator transition of VO2 thin films grown on TiO2 (001) and (110) substrates
Authors: Muraoka Y. , Hiroi Z.
Published: July 2002

The effect of uniaxial stress along the c axis on the metal–insulator transition of VO2 has been studied in the form of epitaxial thin films grown on TiO2 (001) and (110) substrates. A large reduction in the transition temperature TMI from 341 K for a single crystal to 300 K has been observed in the film on TiO2 (001) where the c-axis length is compressed owing to an epitaxial stress, while the TMI has been increased to 369 K in the film on TiO2 (110) where the c-axis length is expanded. The correlation between the c-axis length and TMI is suggested: the shorter c-axis length results in the lower TMI.
Analytic Coulomb matrix elements in the lowest Landau level in disk geometry
Authors: Tsiper E. V.
Published: July 2002

Using Darling’s theorem on products of generalized hypergeometric series, an analytic expression is obtained for the Coulomb matrix elements in the lowest Landau level in the representation of angular momentum. The result is important in the studies of fractional quantum Hall effect (FQHE) in disk geometry. Matrix elements are expressed as simple finite sums of positive terms, eliminating the need to approximate these quantities with slowly convergent series. As a by-product, an analytic representation for certain integrals of products of Laguerre polynomials is obtained.
The toroid cavity autoclave for high-pressure and variable-temperature in situ nuclear magnetic resonance studies
Authors: Niessen Heiko G. , Trautner Peter , Wiemann Sabine , Bargon Joachim , Woelk Klaus
Published: July 2002

The toroid cavity autoclave (TCA) is a coaxial nuclear magnetic resonance (NMR) resonator and high-pressure autoclave for in situ NMR studies, which combines the advantages of a toroid NMR detector with the features of a cylindrical metal pressure vessel. It is designed to fit within the limited space of a standard NMR narrow-bore cryomagnet and allows for recording high resolution NMR spectra during chemical reactions under high pressure. Compounds that, for example, initiate a reaction can be injected into the reactor through a nonreturn valve even if the TCA is already pressurized. The TCA is heated by a resistive, coaxial heating arrangement that does not generate any stray magnetic field in the sample volume. Current pressure and temperature capabilities are 0–300 bar and room temperature to 150 °C, respectively. With standard 200 MHz H1 NMR experiments, signal resolution of 0.55 Hz and signal-to-noise ratios comparable to those of standard NMR probes were achieved. In a further development, the TCA is optimized for gas/liquid reactions in which gaseous components are vigorously mixed with the liquid to obtain maximum reaction rates. Applications to parahydrogen induced polarization are shown, in which the nuclear spin polarization patterns show pairwise addition of hydrogen in both liquid organic solvents and in supercritical CO2.
Simulation of magnetic recording in media with irregular microstructures
Authors: Greaves S. J. , Miura M. , Goodman A. M.
Published: July 2002

A realistic simulation of a magnetic recording medium necessitates the use of a realistic grain microstructure. However, the calculation of the demagnetizing field for irregular structures is difficult. In this article an approach to the calculation of demagnetizing tensors is described which allows for the use of arbitrary microstructures and also allows nonmagnetic grain boundaries to be included in the model. Simulations of media with various grain size distributions are described. A narrower distribution of grain sizes results in higher signal-to-noise ratios for recorded tracks and increased resistance to stray fields.
Modification of the perpendicular magnetic anisotropy of ultrathin Co films due to the presence of overlayers
Authors: Park Sungkyun , Lee Sukmock , Falco Charles M.
Published: July 2002

In order to understand the effect of interfacial strain on perpendicular magnetic anisotropy (PMA) of ultrathin Co films, ex situ Brillouin light scattering measurements were performed for various overlayer materials. The samples were prepared by molecular beam epitaxy and Cu, Al, and Au were used as overlayer materials. We observed a decrease in PMA of the Co with the Cu and Al overlayers. In addition, we found an unexpected result that the PMA is significantly reduced when an Au overlayer of 35 Å is covered by an extra Al capping layer. The amount of this reduction depends on the thickness of the Al layer. Our results lead us to speculate that misfit strain at the interface between the Al and the Au can be propagated through the Au layer to affect the magnetic properties of Co.
Pinning phenomena near the lower critical field for superconductor
Authors: Liu Zuhan
Published: July 2002

In this paper, we prove that for fields close to the lower critical field, minimizers of the Ginzburg–Landau functional of an inhomogeneous superconductor have a number of vortices bounded independently from the Ginzburg–Landau parameter. We also locate the vortices.
Magnetic properties and critical behavior of the pure and diluted two-dimensional weak ferromagnet (CH3NH3)2Mn1−xCdxCl4
Authors: Paduan-Filho A. , Becerra C. C.
Published: July 2002

The compound (CH3NH3)2MnCl4 had for a long time been considered a good example of a quasi-two-dimensional Heisenberg antiferromagnet, however, it is a weak ferromagnet with a nearly quadratic layer structure. In this work we measure the magnetization of (CH3NH3)2MnCl4 and the diluted with cadmium compound (CH3NH3)2Mn0.95Cd0.05Cl4. The Néel temperature for the pure sample was determined as TN=44.75 K and a weak-ferromagnetic moment was observed within the nearly quadratic layer (perpendicular to the easy axis). From the measured weak magnetic moment, we estimate a canting angle for the sublattices magnetizations θ∼0.07° from the easy axis. The overall temperature dependence of the weak magnetic moment is the same as that previously measured for the sublattice magnetization in neutron diffraction experiments (as expected). However, close to TN the critical exponent β of the magnetization changes from β1=0.17±0.02 [0.01<(1−T/TN)<0.1] to β2=0.23±0.02 [0.001<(1−T/TN)<0.01] in the immediate neighborhood of TN. In the diluted compound (TN=41.0±0.5 K) and below 0.9TN the magnetization due to the weak component follows the same behavior found for the pure system but closer to TN an almost linear dependence of the magnetization with temperature is observed.
Influence of sample shape on the production of intrinsic localized modes in an antiferromagnetic lattice
Authors: Sato M. , English L. Q. , Hubbard B. E. , Sievers A. J.
Published: July 2002

The formation of intrinsic localized modes (ILMs) via the uniform mode instability is considered for different crystal geometries for a layered quasi-1D antiferromagnet (C2H5NH3)2CuCl4. By varying the sample shape and hence the demagnetization factor, it is possible to tune the frequency of the uniform mode with respect to the long-wavelength spin wave frequencies. Molecular dynamics simulations predict that the smaller the difference between the two frequencies, the easier to create ILMs from the large amplitude uniform mode. High power nonlinear experiments on samples of different shapes confirm this prediction.
In situ determination of Nd–Fe–B crystallization pathways
Authors: Kramer M. J. , Yang N. , McCallum R. W. , Dennis K. W. , Lewis L. H.
Published: July 2002

In order to understand the effect of solute additions on the crystallization behavior and to directly measure the crystallization pathways, a series of high temperature x-ray diffraction (HTXRD) experiments were performed on rapidly-solidified Nd2Fe14B alloys from room temperature to 1073 K using high-energy synchrotron radiation and a Debye–Scherrer geometry. The relative phase fractions of crystalline and amorphous material and changes in lattice parameters were determined as a function of temperature using Rietveld analysis. The effect of solute additions on the lattice parameters of the Nd2Fe14B unit cell was clearly evident. As-quenched samples measured at room temperature consist of predominantly glassy Nd–Fe–B (up to 90 wt. %), 8–9 wt. % crystalline Nd2Fe14B and the remainder α-Fe. From room temperature up to the Curie temperature (Tc) for Nd2Fe14B, the unit cell volume contracts primarily due to contraction in the basal plane. From 600 K up to the crystallization temperature the thermal expansion is linear with a positive slope. There is a second inflection in the thermal expansion at the crystallization temperature. This inflection is indicative of solute ejection from the devitrified structure while the negative thermal expansion found for T<600 K is a result of spontaneous magnetostriction which reflects the local anisotropies in the Nd2Fe14B structure.
Vibrational spectroscopy and photodissociation of jet-cooled ammonia
Authors: Bach Andreas , Hutchison J. Matthew , Holiday Robert J. , Crim F. Fleming
Published: July 2002

Vibrationally mediated photodissociation action spectroscopy provides rotation-vibration spectra of jet-cooled ammonia in the 2.3 μm and 3.0 μm regions by detecting the emission of electronically excited NH2(Ã 2A1) produced by the photodissociation of the vibrationally excited molecules. Vibrational excitation changes the relative photofragmentation yield of NH2(Ã 2A1) markedly. Isoenergetic photolysis of ammonia molecules with one quantum of antisymmetric N–H stretching excitation (ν3) or two quanta of bend (2ν4) yields three times more excited state NH2(Ã 2A1) than photolysis of NH3 with a quantum of symmetric N–H stretch excitation (ν1). By contrast, the relative yield is insensitive to initial vibrational excitation of the combination bands ν1+ν2 and ν2+ν3 that contain the umbrella (inversion) motion ν2. The vibrational mode dependence of the NH2(Ã 2A1) photofragment yield arises from either enhanced Franck–Condon factors for electronic excitation or from an increased probability for the competing nonadiabatic dissociation to form the ground state NH2(X̃ 2B1) product.
Ce concentration dependence on the magnetic and transport properties of Ce doped Si epitaxial films prepared by molecular beam epitaxy
Authors: Yokota T. , Fujimura N. , Wada T. , Hamasaki S. , Ito T.
Published: July 2002

Diluted magnetic semiconductors, Si:Ce thin films with the Ce concentration below 1.5 at. %, were prepared by solid source molecular beam epitaxy. Magnetization curves (M-H) for all the samples show superparamagnetic behaviors at least up to 300 K. Temperature dependence of the magnetic susceptibility (χ-T) has a cusp, which is ascribed to the spin glass. Temperature dependence of resistivity (ρ-T) also has a cusp at around the cusp temperature in χ-T curves. As the amount of substituted Ce in Si estimated from the lattice constant increases, the cusp temperature also increases. The amount of substituted Ce in Si is considered to play an important role for the anomalous magnetic and transport properties.
Diffuse interface electron scattering in epitaxial Co/Cu bilayers
Authors: Keavney David J. , Park Sungkyun , Falco Charles M.
Published: July 2002

We have examined the origin of diffuse electron scattering at Co/Cu interfaces using in situ resistance measurements and scanning tunneling microscopy (STM) on a model system consisting of epitaxial (111)-oriented Co on Cu and Cu on Co. We grew epitaxial Co/Cu bilayers on 40 Å Cu(111)/Si(111) substrates, and monitored the resistance and surface morphology during the initial stages of growth for both Co on Cu and Cu on Co. For the case of Co on Cu, the resistance initially increases by 10% at submonolayer coverage, and then drops after 1–1.5 ML coverage. In situ STM topographs taken at similar stages of growth reveal that 20–30 Å Co islands initially nucleate above Cu step edges at submonolayer coverage and then grow inward to cover the Cu terraces. These islands introduce new steps at the surface, dramatically reduce the lateral correlation length of the surface profile, and consequently increase its contribution to the surface scattering resistance. We find that the nucleation and percolation of these islands is strongly correlated with the resistance behavior. In contrast, for Cu deposited on Co, we observe no island nucleation, and no corresponding resistance increase.
Spin injection from a ferromagnetic metal into a semiconductor
Authors: Jaffrès H. , Fert A.
Published: July 2002

We calculate the spin polarization of electrons injected from a ferromagnetic metal (F) into a semiconductor (SC) or a two-dimensional semiconductor electron gas (2-DEG) and the resulting magnetoresistance (MR) of a F/SC/F structure. Due to the conductivity mismatch between F and SC, efficient spin-injection can be obtained only by inserting a tunnel junction at the F/N interfaces. We find that a F1/SF/F2 structure can present a nonzero MR if the junction resistance is chosen in a relatively narrow range determined by the spin-diffusion length and resistivity of F and SC, the distance between the ferromagnets and the width of the conduction channels. The case of a 2-DEG is particularly favorable.
Effect of exchange coupling in nanocrystalline CoPt bulk magnets
Authors: Xiao Q. F. , Brück E. , Zhang Z. D. , de Boer F. R. , Buschow K. H. J.
Published: July 2002

The effect of the atomic disorder–order transformation on remanence enhancement and coercivity in isotropic CoPt magnets has been studied by isothermal annealing at 675 °C, well below the transformation temperature, for 10–80 min after quenching from 900 °C. The results of x-ray diffraction, alternating-current susceptibility, and magnetization measurements indicate that the strong remanence enhancement effect originates from exchange coupling between the face-centered-tetragonal ordered hard-magnetic precipitated phase and the face-centered-cubic disordered soft-magnetic matrix phase during the initial ordering transformation. The nonuniform distribution of the magnetic anisotropy results in a lower reversibility, unlike the so-called exchange spring magnet.
Experimental study of magnetic interactions between colloidal particles in magnetic fluids
Authors: Taketomi Susamu , Shull Robert D.
Published: July 2002

In order to clarify whether or not there is any magnetic interaction between the magnetic colloidal particles in magnetic fluids (MFs), we present a method for comparing the magnetization curve of a mother MF with that of a few-thousand-fold diluted solution. For a MF which showed clusters of colloidal particles in an optical microscope under an applied magnetic field, the hysteresis loops for the mother MF and its few-thousand-fold dilution displayed different shapes for weak fields. We conclude from this result that strong magnetic interactions exist between the particles in this MF. On the contrary for a MF which showed no clusters under optical microscopy, no differences in shapes of the hysteresis loops for the mother MF and its few-thousand-fold dilution were observed in the weak field region. However, differences were observed for the field region above 80 kA/m.
Strain-induced magnetic anisotropies in ultrathin epitaxial NixPd1−x alloy films
Authors: Matthes F. , Seider M. , Schneider C. M.
Published: July 2002

We studied the influence of alloy composition and thickness on the magnetic properties of ultrathin NixPd1−x alloy films epitaxially grown on Cu(100) and Cu3Au(100) substrates. Our experiments show that the magnetoelastic anisotropy plays a seminal role in the competition of the different contributions to the magnetic anisotropy. Its magnitude and sign can be adjusted via the film strain that in turn depends on the alloy composition. At a fixed thickness of 9 monolayers and a Ni concentration of 87% for Cu(100) and of 50% for Cu3Au(100) we observe an inverse spin reorientation transition (iSRT). The occurrence of the iSRT is attributed to the fact that the magnetoelastic anisotropy overcompensates all other contributions to the effective anisotropy Eeff.
Data driven function approximation models for simulating magnetic hysteresis
Authors: Sun M. , Fujiwara H.
Published: July 2002

We investigate several data driven function approximation models to learn the hysteretic behavior of ferromagnetic materials. They include neural networks, linear least squares models based on radial basis functions, and low order polynomial functions. When properly trained, they are capable of predicting major features of magnetization and torque loops.
A novel method for the study of slider-disk interaction in high performance disk drives
Authors: Man Yijun , Liu Bo , Ma Yansheng
Published: July 2002

This work reports a novel method for the visualization of slider-disk or slider-particle-disk interactions. The method is based on a special testing disk which is same as the conventional magnetic disk media except using a layer of magneto-optical (MO) material to replace the magnetic layer of the magnetic disk media. The magnetization in the MO layer will be switched by a small external field applied if the temperature generated by the interactions is higher than the Curie temperature of the MO material. The proposed method and corresponding setup were used successfully in the experimental study of slider-disk and slider-particle-disk interactions.
Temperature, density, and pressure dependence of relaxation times in supercooled liquids
Authors: Alba-Simionesco Christiane , Kivelson Daniel , Tarjus Gilles
Published: July 2002

We have examined experimental and simulation data on the relaxation times (τα) and the viscosities in liquids and supercooled liquids as functions of temperature (T), density (ρ), and pressure (p). We achieve a data collapse by placing the data on master curves that depend only on a single density- and species-dependent (but T independent) effective interaction energy, E∞(ρ).
Quantitative analysis method for the vapor phase concentration
Authors: Kim J. U. , Suk H. , Kim G. H.
Published: July 2002

In order to understand fuel vaporization and fuel–air mixing phenomena, methods for determining the concentration of fuel vapor and liquid are necessary. Previously, the vapor phase concentration was normally calculated from the absorption measurement. However, the absorption coefficient of vapor is a characteristic of the solute and depends on the wavelength of the excitation light, the solvent, and the temperature. Therefore it may require that each parameter be correctly determined, and the overall accuracy depends on the accuracy of separate parameters. In this study a direct measurement of the vapor pressure and temperature was conducted and those results were compared with the results from the absorption measurement. The method used in the direct pressure measurement is much closer to an estimate based on the Clausius–Clapeyron equation. Based on this argument, it is believed that the direct pressure measurement method is preferred for accurate measurement of the vapor phase concentration to apply to the quantitative analysis in fuel spray study.
Extremely wide speed range measurement system
Authors: Prokin Milan
Published: July 2002

The speed measurement system is based on an advanced single buffered method utilizing both the pulse counting and the period measurement. The extremely wide speed range from 5×10−5 to 1830 rpm is independent of the sampling time, chosen between 100 μs and 22 ms. The maximum static relative error is limited to 6.67×10−4 for 1 ms or 6.67×10−3 for 100 μs sampling time. This method is useful for a real-time control and an off-line speed analysis.
Spin-polarized current induced magnetization switch: Is the modulus of the magnetic layer conserved? (invited)
Authors: Wegrowe J.-E. , Hoffer X. , Guittienne Ph. , Fábián A. , Gravier L. , Wade T. , Ansermet J.-Ph.
Published: July 2002

The direct effect of spin-polarized current on magnetization states is studied on various electrodeposited single contacted nanowires (diameter about 60 nm). Three kinds of samples have been studied: (1) Homogeneous Ni nanowires, (2) nanowires composed of both a homogeneous Ni part and a multilayered Co(10 nm)/Cu(10 nm) part, (3) pseudospin-valve pillars Co(30 nm)/Cu(10 nm)/Co(10) electrodeposited in Cu wires. The magnetization reversal due to the current injection is observed in the three cases. The effect is observed with using different experimental protocols, including current activated after-effect measurements. The results obtained suggest that two different mechanisms are able to account for the magnetization reversal: exchange torque and spin transfer. We propose a definition of the two mechanisms based on the conservation or nonconservation of the magnetic moment of the ferromagnetic nanostructure.
Design optimization of a permanent magnet synchronous motor by the response surface methodology
Authors: Fujishima Y. , Wakao S. , Yamashita A. , Katsuta T. , Matsuoka K. , Kondo M.
Published: July 2002

This article proposes an effective computational approach to design optimization of an outer-rotor type permanent magnet synchronous motor. As usual, because of the complicated rotor configuration and the complex magnetic saturation effects, it is difficult to design the lightweight permanent magnet synchronous motor structure that makes good use of reluctance torque within an acceptable CPU time. In this article, we adopt the finite element method as a magnetic field analysis method and the genetic algorithms as a search method. Furthermore, the response surface methodology, which enables us to evaluate the objective physical quantities in a much shorter time, is introduced into the above methods in the proposed approach. This optimization approach results in an overall increase in the optimization speed, that is, substantial CPU time reduction in comparison with the case of a conventional one. Some numerical results that demonstrate the validity of the proposed approach are also presented.
Edge ion heating and parametric decay during injection of ion cyclotron resonance frequency power on the Alcator C-Mod tokamak
Authors: Rost J. C. , Porkolab M. , Boivin R. L.
Published: July 2002

A population of suprathermal ions has been observed in the scrape off layer during injection of power in the ion cyclotron frequency range on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. These ions generated energetic neutrals which were measured with a charge exchange neutral particle analyzer. In the hydrogen minority heating regime, fast particles were generated only when the injected power was above 500 kW. Fast particles were observed at a low level of injected power when the rf was a multiple of the ion cyclotron frequency in the scrape off layer. The power deposited in the edge was always less than five percent of the injected power and did not increase impurity levels. The theoretical threshold of parametric decay instabilities for decay of the pump wave in the antenna near field into an ion Bernstein wave and an ion cyclotron quasimode matches the observed threshold for fast ion production under a variety of conditions.
The direct simulation Monte Carlo of flows composed of asymmetric potential scatterers
Authors: Alves Nuno , Stark John
Published: July 2002

Predicted fluid transport properties are dictated by the assumed interaction-potential model between molecules. The direct simulation Monte Carlo (DSMC) method has been developed principally for those potentials that may be included efficiently in computational terms. In this paper nonisotropic scattering models are investigated for the Couette flow, with both shear stress and heat flux being calculated; the results are then compared to those predicted by the variable hard sphere (VHS) and the variable soft sphere (VSS) models. The same procedure is then repeated for a shock wave flow case. It is concluded that, even when extreme post-collision directionality is modeled, statistically similar results to VHS and VSS models are obtained if the total collision cross section and its variation with temperature are appropriately normalized. This demonstrates the important result that to achieve convergence with the measured transport properties of heat flux and viscosity, as well as with shock flow structures then highly precise molecular models are not required for DSMC. Conversely, the adoption of different scattering models, attempting to simulate specific features of the underlying physics of a collision, may not always be achieved using the DSMC method. Variation of the total cross section with temperature is a well-recognized phenomenon included in all successful models for molecular processes. Of itself, however, this variation does not determine the post-collision partners, rather it influences the rate at which processes can occur. As a result it is contributive to, rather than the determinant of, the physical outcome from a collision.
Data acquisition and control system for large volume plasma device
Authors: Patel G. B. , Srivastava P. K. , Awasthi L. M. , Anitha V. P. , Ravi G. , Patel P. J. , Baruah U. K. , Mattoo S. K.
Published: July 2002

This article describes hardware and software solutions to a need which is comprised of (i) acquisition of a large volume of high speed data with multiple time scales, (ii) control of various operational parameters of device and diagnostics, and (iii) processing and management of the acquired data for a large volume plasma device. The solution relies on the base of a VXI bus and uses a standard PC with a Windows 98/NT operating system and C as the programming language. The system is networked with the existing network with the result of allowing a large data storage space of processing facilities from any terminal in the laboratory.
Three-phase, voltage controlled sinusoidal oscillator
Authors: Bayard J.
Published: July 2002

A method allowing the making of any multiphase, voltage-controlled, sinusoidal signal generator is presented. To prove its feasibility, a three-phase, voltage controlled, sine wave signal generator was built. The differences between the three phase sine waves are kept precisely at 120° and a perfect matching of the signal magnitudes is obtained whatever the frequency value. A very low distortion rate and a wide frequency range can be obtained. The described circuit is particularly attractive to build low or ultralow frequency multiphase sinusoidal oscillators.
Dielectric and piezoelectric properties of the Mn-substituted Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystal
Authors: Priya Shashank , Uchino Kenji
Published: July 2002

In this article, we report the dielectric and piezoelectric properties of Mn modified 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 (PZNT) single crystals. The crystals were grown by the modified-flux method. Mn substitution resulted in enhanced mechanical quality factor, Qm, and a moderate increment in the rhombohedral to tetragonal phase transition temperature with increasing Mn composition. Investigation of the role of Mn in PZNT was performed on the basis of dielectric, piezoelectric and polarization versus electric hysteresis measurements. It was found that the improved Qm is obtained because of the induction of the “hard” characteristics into the PZNT single crystal. High Qm piezocrystals are being developed for high power applications.
Lagrangian averages, averaged Lagrangians, and the mean effects of fluctuations in fluid dynamics
Authors: Holm Darryl D.
Published: July 2002

We begin by placing the generalized Lagrangian mean (GLM) equations for a compressible adiabatic fluid into the Euler–Poincaré (EP) variational framework of fluid dynamics, for an averaged Lagrangian. This is the Lagrangian averaged Euler–Poincaré (LAEP) theorem. Next, we derive a set of approximate small amplitude GLM equations (glm equations) at second order in the fluctuating displacement of a Lagrangian trajectory from its mean position. These equations express the linear and nonlinear back-reaction effects on the Eulerian mean fluid quantities by the fluctuating displacements of the Lagrangian trajectories in terms of their Eulerian second moments. The derivation of the glm equations uses the linearized relations between Eulerian and Lagrangian fluctuations, in the tradition of Lagrangian stability analysis for fluids. The glm derivation also uses the method of averaged Lagrangians, in the tradition of wave, mean flow interaction. Next, the new glm EP motion equations for incompressible ideal fluids are compared with the Euler-alpha turbulence closure equations. An alpha model is a GLM (or glm) fluid theory with a Taylor hypothesis closure. Such closures are based on the linearized fluctuation relations that determine the dynamics of the Lagrangian statistical quantities in the Euler-alpha equations. Thus, by using the LAEP theorem, we bridge between the GLM equations and the Euler-alpha closure equations, through the small-amplitude glm approximation in the EP variational framework. We conclude by highlighting a new application of the GLM, glm, and α-model results for Lagrangian averaged ideal magnetohydrodynamics.
A comparison of self-assembly in lattice and off-lattice model amphiphile solutions
Authors: Bedrov Dmitry , Smith Grant D. , Freed Karl F. , Dudowicz Jacek
Published: July 2002

Lattice Monte Carlo and off-lattice molecular dynamics simulations of h1t4 and h4t1 (head/tail) amphiphile solutions have been performed as a function of surfactant concentration and temperature. The lattice and off-lattice systems exhibit quite different self-assembly behavior at equivalent thermodynamic conditions. We found that in the weakly aggregating regime (no preferred-size micelles), all models yield similar micelle size distributions at the same average aggregation number, albeit at different thermodynamic conditions (temperatures). In the strongly aggregating regime, this mapping between models (through temperature adjustment) fails, and the models exhibit qualitatively different micellization behavior.
Effect of atomic disorder or chain length on the stability of photoinduced polarization inversion
Authors: Wang Lu-xia , Liu De-sheng , Wei Jian-hua , Xie Shi-jie , Han Sheng-hao , Mei Liang-mo
Published: July 2002

The effect of atomic disorder or chain length on the stability of photoinduced polarization inversion has been studied. The atomic disorder was simulated by square-random or Gaussian-random model. It was found that for the square-random distribution case, photoinduced polarization inversion remains steadily when atomic disorder is less than 18a (a is the lattice constant of polyacetylene), the reversion polarization disappears and gets into normal polarized state when the disorder is stronger than over 18a. The reason of a normal polarization resulted from the strong lattice disorder was discussed. The relationship between the reverse polarization of biexciton state and the confinement constant te as well as the variation of chain length was also studied.
Air-gap capacitance cell for the investigation of porous or solvent containing dielectric films
Authors: Schwödiauer Reinhard , Bauer Siegfried
Published: July 2002

An air-gap capacitance cell is presented, designed for temperature dependent dielectric spectroscopy on materials that cannot be contacted with surface electrodes: materials such as porous foams and membranes or solvent containing polymer resins. The capability of the system is demonstrated with measurements up to 300 °C, performed on a 60 μm porous poly(tetrafluoroethylene) (PTFE) and on a precured hybrid system of a porous PTFE, soaked with the low-k aromatic ether polymer: poly(1,1,1-triphenyl ethane perfluorocyclobutylether). The measurement system allows recording of the dielectric loss spectra with high resolution, barely influenced by thermal expansion or ionic conductivity.
Infrared–microwave double resonance spectroscopy of OCS in pure He4 and mixed He4/He3 clusters
Authors: Kunze M. , Markwick P. R. L. , Pörtner N. , Reuss J. , Havenith M.
Published: July 2002

We have performed microwave–infrared double resonance measurements on OCS in pure He4 and mixed He4/He3 clusters. In contrast to our previous study on OCS in pure He4 cluster, where an asymmetric inhomogeneous linewidth increasing with rotational quantum number j was observed [S. Grebenev, M. Havenith, F. Madeja, J. P. Toennies, and A. F. Vilesov, J. Chem. Phys. 113, 9060 (2000)], we find the lines in the mixed helium cluster to be much narrower, showing a symmetric, probably homogeneous line width. The spectra indicate a significant difference in the rotational relaxation of OCS in mixed clusters as compared to pure He4 cluster. We have applied the model of Lehmann [K. K. Lehmann, Mol. Phys. 97, 645 (1999)], describing the interaction of a molecule with the helium cluster, and modified it in order to describe particle in a box states of OCS in mixed helium clusters. The calculations indicate while in the mixed cluster the OCS is confined to the inner He4 core, the energy of the particle in the box states is increased as compared to the pure He4 cluster. Relaxation mechanisms via these particle in the box states and surface excitations (ripplons) of the cluster are discussed in the text.
Chemical origin of the yellow luminescence in GaN
Authors: Kucheyev S. O. , Toth M. , Phillips M. R. , Williams J. S. , Jagadish C. , Li G.
Published: July 2002

The influence of ion-beam-produced lattice defects as well as H, B, C, N, O, and Si, introduced by ion implantation, on the luminescence properties of wurtzite GaN is studied by cathodoluminescence spectroscopy. Results indicate that intrinsic lattice defects produced by ion bombardment mainly act as nonradiative recombination centers and do not give rise to the yellow luminescence (YL) of GaN. Experimental data unequivocally shows that C is involved in the defect-impurity complex responsible for YL. In addition, C-related complexes appear to act as efficient nonradiative recombination centers. Implantation of H produces a broad luminescent peak which is slightly blueshifted with respect to the C-related YL band in the case of high excitation densities. The position of this H-related YL peak exhibits a blueshift with increasing excitation density. Based on this experimental data and results reported previously, the chemical origin of the YL band is discussed.
Phosphorous trapped within buckminsterfullerene
Authors: Larsson J. A. , Greer J. C. , Harneit W. , Weidinger A.
Published: July 2002

Under normal circumstances, when covalent molecules form, electrons are exchanged between atoms to form bonds. However, experiment and theoretical computations reveal exactly the opposite effect for the formation of group V elements nitrogen and phosphorous encapsulated within a buckminsterfullerene molecule. The C60 carbon cage remains intact upon encapsulation of the atom, whereas the electronic charge cloud of the N or P atom contracts. We have studied the chemical, spin, and thermodynamic properties of endohedral phosphorous (P@C60) and have compared our results with earlier findings for N@C60. From a combined experimental and theoretical vantage, we are able to elucidate a model for the interaction between the trapped group V atom and the fullerene cage. A picture emerges for the electronic structure of these complexes, whereby an atom is trapped within a fullerene, and interacts weakly with the molecular orbitals of the C60 cage.
Thermoelectron-enhanced micrometer-scale plasma generation
Authors: Ito Tsuyohito , Terashima Kazuo
Published: July 2002

The use of thermoelectrons allowed easy generation of a micrometer-scale very high-frequency plasma (thermoelectron-enhanced micrometer-scale plasma) in a fine capillary, with an inner diameter of approximately 120 μm. A tungsten wire, whose diameter was 25 μm, inserted into the region was used to provide thermoelectrons. Approximately 5 W of power was sufficient to sustain this plasma. The plasma was very stable and the discharge continued for at least 60 min.
Temperature and doping-dependent resistivity of Ti/Au/Pd/Au multilayer ohmic contact to n-GaN
Authors: Lu Changzhi , Chen Hongnai , Lv Xiaoliang , Xie Xuesong , Mohammad S. Noor
Published: July 2002

The temperature (both measurement temperature and annealing temperature) and doping dependence of specific contact resistivity of Ti/Au/Pd/Au multilayer ohmic contact have been studied. The metallization for the contact involves the deposition of the composite metal layer Ti/Au/Pd/Au (200 Å/600 Å/400 Å/500 Å) on n-GaN. When the contacts were annealed at 800 °C for 30 s in air it was observed that the contact resistivity decreases with increasing doping concentration of the n-GaN, but increases with increasing measurement temperature of the contact. Within the framework of the transmission line measurement method, the specific contact resistivity for doping ND=6×1017 cm−3 was ρS=1.0×10−4 Ω cm2, and for doping ND=1020 cm−3 was ρS=2.38×10−9 Ω cm2. The resistivity ρS=1.0×10−4 Ω cm2 for ND=6×1017 cm−3 decreased to ρS≈8×10−7 Ω cm2 after a second annealing. Thus annealing, some times more than once, appears to play an important role in shaping the best value of the resistivity. The physical cause underlying the realization of doping and temperature dependence of the contact involves the diffusion of much of Pd and Au deep into n-GaN leaving Ti on the surface and allowing Ti to react with GaN to form TiN. The work functions of TiN and GaN are close; also TiN has a very narrow band-gap metallic character. Both of these are important for yielding good ohmic contact to n-GaN. Nitrogen vacancies which behave as donor atoms are also formed. They enhance the quality of the contact resistivity.
Symplectic quaternion scheme for biophysical molecular dynamics
Authors: Miller T. F. , Eleftheriou M. , Pattnaik P. , Ndirango A. , Newns D. , Martyna G. J.
Published: July 2002

Massively parallel biophysical molecular dynamics simulations, coupled with efficient methods, promise to open biologically significant time scales for study. In order to promote efficient fine-grained parallel algorithms with low communication overhead, the fast degrees of freedom in these complex systems can be divided into sets of rigid bodies. Here, a novel Hamiltonian form of a minimal, nonsingular representation of rigid body rotations, the unit quaternion, is derived, and a corresponding reversible, symplectic integrator is presented. The novel technique performs very well on both model and biophysical problems in accord with a formal theoretical analysis given within, which gives an explicit condition for an integrator to possess a conserved quantity, an explicit expression for the conserved quantity of a symplectic integrator, the latter following and in accord with Calvo and Sanz-Sarna, Numerical Hamiltonian Problems (1994), and extension of the explicit expression to general systems with a flat phase space.
Using the Hall effect to measure interface trap densities in silicon carbide and silicon metal-oxide-semiconductor devices
Authors: Saks N. S. , Ancona M. G. , Rendell R. W.
Published: July 2002

A technique is presented for measuring the density of interface traps versus energy DIT(E) using the Hall effect in metal-oxide-semiconductor samples. Good agreement is obtained between this Hall approach and standard C–V techniques in both SiC and silicon test devices. DIT(E) is found to be much higher in 4H–SiC compared to 6H devices oxidized at the same time. DIT(E) in both SiC poly types increases exponentially with energy approaching the conduction bandedge.
Nonlinear dynamics of an interface in an inclined channel
Authors: Zhang J. , Miksis M. J. , Bankoff S. G. , Tryggvason G.
Published: July 2002

Here we consider the gravity-driven dynamics of two superposed, incompressible, immiscible, viscous fluids flowing in a parallel-wall channel. The fluids are governed by the Navier–Stokes equations with surface tension along the interface. We use the front tracking numerical method to determine the solutions. Both stable and unstable solutions are obtained. The unstable solutions are characterized by a finger of lower fluid rising into the upper fluid. Our results are consistent with the predictions of linear stability theory. In addition, we attempt to characterize the growth of the unstable solutions as a function of the Reynolds and the Bond number.
Temporally resolved Raman backscattering diagnostic of high intensity laser channeling
Authors: Jones T. G. , Krushelnick K. , Ting A. , Kaganovich D. , Moore C. I. , Morozov A.
Published: July 2002

The implementation of an innovative technique for measuring the propagation of intense laser pulses through plasma channels is described. At high laser intensities, temporally resolved stimulated Raman backscattering can be used to diagnose both the electron density and the laser intensity inside the plasma channel, observations which are not possible using other techniques. This diagnostic is demonstrated in experiments using an open-ended capillary in which a plasma channel was created. The plasma channel was generated using either an electrical discharge or laser ablation by a second laser pulse.