bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ electrical transport during isothermal annealing of nanocrystalline gold films
Authors: Ederth J. , Kish L. B. , Olsson E. , Granqvist C. G.
Published: July 2002

Advanced gas deposition was used to produce nanocrystalline gold films under conditions giving four different deposition rates. Grain growth and structural modification of the grain boundaries were probed during annealing by use of in situ electrical transport measurements. Time dependent resistivity data were fitted to a relaxation model whose activation energy went up upon increased isothermal annealing temperature. The grain boundary transmission coefficient for the samples scaled, up to a certain limit, with the deposition rate; this is believed to be due to a higher concentration of pores, or a wider grain boundary region containing a disordered structure, in samples prepared at low deposition rates. Such samples also displayed enhanced thermal stability with negligible grain growth up to 773 K upon annealing in vacuum for 2 h. Samples prepared above this limit, at the highest deposition rate, exhibited a decreased grain boundary transmission coefficient.
Nanoporous structure of sputter-deposited silicon oxide films characterized by positronium annihilation spectroscopy
Authors: Kobayashi Y. , Zheng W. , Chang T. B. , Hirata K. , Suzuki R. , Ohdaira T. , Ito Kenji
Published: July 2002

Positronium annihilation was applied to characterize the nanoporous structure of thin silicon oxide films sputter-deposited at different argon pressures ranging from 0.1 to 2.0 Pa. At higher argon pressures, the 3γ decay probability of ortho-positronium (o-Ps) was substantially enhanced. A comparison of this result with that obtained for capped samples indicated that: (a) 3γ annihilation is due to the intrinsic decay of o-Ps diffusing out from the film into vacuum and (b) films deposited at high argon pressures contain highly connected, open pores. Positron lifetime spectroscopy measurements on the capped films showed that the characteristic size of the pores can be as large as 2.6 nm, depending on the argon pressure.
Analytic gradients for the coupled-cluster singles, doubles, and triples (CCSDT) model
Authors: Gauss Jürgen , Stanton John F.
Published: July 2002

The first implementation of analytic gradients for the coupled-cluster singles, doubles, triples (CCSDT) model is described. The relevant theoretical expressions are given in a diagrammatic form together with the corresponding algebraic formulas. The computational requirements of CCSDT gradient calculations are discussed and their applicability demonstrated by performing benchmark calculations for molecular geometries with large correlation-consistent basis sets. A statistical analysis of the data reveals that CCSDT and CCSD(T) in most cases perform equally well. The CCSDT calculations thus provide further evidence for the high accuracy of the CCSD(T) approach.
Dynamics of polar solvation in acetonitrile–benzene binary mixtures: Role of dipolar and quadrupolar contributions to solvation
Authors: Luther Bradley M. , Kimmel Joel R. , Levinger Nancy E.
Published: July 2002

While dynamics of polar solvation have been tabulated for a wide range of pure polar solvents, substantially less is known about the dynamic response of solvent mixtures. Here, results for polar solvation dynamics are presented for the nonassociating mixture of a dipolar solvent, acetonitrile, and a quadrupolar solvent, benzene. The solvation response observed is sensitive to the mixing of the pure solvents, affecting both the inertial and diffusive components of the solvation response function. Addition of acetonitrile to benzene increases the amplitude of the inertial response. At high benzene mole fractions, the diffusive relaxation reveals a slow component attributed to translational diffusion of the acetonitrile.
Saddle points and dynamics of Lennard-Jones clusters, solids, and supercooled liquids
Authors: Doye Jonathan P. K. , Wales David J.
Published: July 2002

The properties of higher-index saddle points have been invoked in recent theories of the dynamics of supercooled liquids. Here we examine in detail a mapping of configurations to saddle points using minimization of |∇E|2, which has been used in previous work to support these theories. The examples we consider are a two-dimensional model energy surface and binary Lennard-Jones liquids and solids. A shortcoming of the mapping is its failure to divide the potential energy surface into basins of attraction surrounding saddle points, because there are many minima of |∇E|2 that do not correspond to stationary points of the potential energy. In fact, most liquid configurations are mapped to such points for the system we consider. We therefore develop an alternative route to investigate higher-index saddle points and obtain near complete distributions of saddles for small Lennard-Jones clusters. The distribution of the number of stationary points as a function of the index is found to be Gaussian, and the average energy increases linearly with saddle point index in agreement with previous results for bulk systems.
Screening beneficial dopants to Cu interconnects by modeling
Authors: Liu Chun-Li
Published: July 2002

We present the results of first-principles simulations of dopant segregation to grain boundaries (GBs), dopant bulk diffusion, dopant and Cu self-diffusion at the GB, and the effect of the presence of a dopant on Cu diffusion at the GB for advanced Cu alloy interconnects. Several dopants that inhibit Cu GB diffusion were identified. Two primary mechanisms were found, namely, dopant blocking and dopant dragging. Early experimental results have confirmed model predictions for one of the several dopants (carbon) identified so far. The mean time to failure has increased more than 60% with a carbon concentration in Cu as low as 0.01 at. % and the resulting resistivity increase can be controlled below 15% compared to undoped Cu.
High-energy-resolution monochromator for Kr83 nuclear resonant scattering
Authors: Zhao J. Y. , Toellner T. S. , Hu M. Y. , Sturhahn W. , Alp E. E. , Shen G. Y. , Mao H. K.
Published: July 2002

We have built a high-energy-resolution monochromator for nuclear resonant scattering from the 9.4 keV nuclear transition of Kr83. The monochromator consists of two highly asymmetric silicon single crystals arranged in a dispersive geometry and produces an energy bandwidth of 2.3 meV. This monochromator has been successfully used for a study of nuclear forward scattering and nuclear resonant inelastic scattering from a Kr83 sample that was solidified in a diamond anvil cell at 2.15 GPa and room temperature.
High-current electron beam generation by a pulsed hollow cathode
Authors: Gleizer J. Z. , Krokhmal A. , Krasik Ya. E. , Felsteiner J.
Published: July 2002

In this paper the parameters of a hollow-cathode electron source and the generated electron beam are presented. A gas puff valve is used to provide a sharp pressure gradient between the cathode cavity and the accelerating gap. To produce the plasma inside the hollow cathode we used a pulse forming network (10 kV, 5–10 μs, 5 Ω). Generation of a high-current electron beam was achieved under an accelerating voltage of 20-kV amplitude and 500-ns pulse duration. The parameters of the He gas and the plasma inside the cathode and the accelerating gap were studied by electrical and optical diagnostics for different gas pressures and discharge current amplitudes. It was found that the operation of the hollow cathode is characterized by a negative anode potential fall and that the plasma density and temperature inside the hollow cathode do not exceed 5×1012 cm−3 and 14 eV, respectively. The parameters of the electron beam were studied for different discharge current amplitudes and anode grid cell sizes. It was shown that efficient electron beam generation with a beam current amplitude of up to 300 A is achieved without significant increase of the plasma potential. Space-charge neutralization processes in the accelerating gap explain the excess of the electron current density above its space-charge-limited value, in agreement with the measured potential distribution in the accelerating gap. The results of computer simulations of the hollow-cathode operation are in satisfactory agreement with the obtained experimental data.
Temperature dependence of magnetically induced strain in single crystal samples of Ni–Mn–Ga
Authors: Pasquale Massimo , Sasso Carlo Paolo , Besseghini Stefano , Villa Elena , Chernenko Volodymyr
Published: July 2002

We investigate the effect of temperature and applied magnetic field on the strain behavior of oriented single crystal samples of Ni2MnGa. It is shown that the martensite twins can be partially oriented by the application of a magnetic field during cooling from the austenite state, observing a strain of the order of 1%. Depending on the final cooling temperature, a different value of magnetically induced strain is observed in the martensite phase, an effect due to the irreversible alignment of a fraction of the martensite twins to the magnetic field direction. The results are discussed with reference to different experimental procedures and the shape memory characteristics of the alloy.
Absorption edge determination of thick GaAs wafers using surface photovoltage spectroscopy
Authors: Sharma T. K. , Porwal S. , Kumar R. , Kumar Shailendra
Published: July 2002

A procedure for choosing the appropriate chopping frequency (f) for the surface photovoltage spectroscopy (SPS) measurements in order to obtain the absorption related features is presented. We could obtain the absorption edge of thick n+ GaAs wafer (thickness ≈700 μm) by performing SPS measurements at f⩾1 kHz at room temperature (300 K). The similar information for semi-insulating (SI) GaAs could not be obtained due to the carrier trapping at deep levels or surface states at 300 K. However, we could obtain the absorption edge of SI-GaAs by performing SPS measurements at 395 K at f=3 kHz. Here, we demonstrate the capability of the SPS technique to measure large absorption coefficient (α) values for thick wafers by performing SPS measurements and normalizing this with the reported α value at one wavelength in the above band gap region. For comparison, we also perform quasisimultaneous SPS and transmission spectroscopy (TS) measurements. The SPS technique could provide α values up to 104 cm−1 for 700-μm-thick GaAs wafers, whereas TS could only measure α values up to about 15 cm−1. An improved design of the sample holder for measuring the surface photovoltage in the chopped light geometry, which increases the signal strength by reducing the gap between the top electrode and the wafer in a controlled manner, is presented. This ensures that there is no sample damage or contamination.
Kinetic instabilities during the NOx reduction with hydrogen on Pt crystals studied with field emission on the nanoscale
Authors: Visart de Bocarmé Thierry , Kruse Norbert
Published: July 2002

This paper reviews field emission studies of kinetic instabilities occurring during the catalytic reduction of nitric oxide (NO) and nitrogen dioxide (NO2) by hydrogen on three-dimensional platinum crystals. Emphasis is placed on revealing that both field ion microscopy (FIM) and field electron microscopy (FEM) can image such instabilities under truly in situ reaction conditions with a lateral resolution on the nanoscale. In particular, oscillatory behavior with rapid ignition from a state of low to a state of high catalytic activity is demonstrated for both NO and NO2 reduction. Results of a local chemical probing during FIM studies of the NO+H2 reaction are also shown and provide clear evidence for the oscillatory behavior of water (detected as H2O+ and H3O+) formation and for diffusion supply of NO into surface regions emptied during the stage of high catalytic activity. The rapid ignition (“surface explosion”) of the catalytic cycle is discussed on the basis of an autocatalytic mechanism of the NO decomposition. On the (001) plane of the Pt crystal small island formation is seen to occur during the low-activity state of the catalytic cycle. Islands have a size equivalent to ∼3 nm, move independently from each other, and do not merge when colliding. A tentative model is discussed associating islands with patches of hydroxyl groups. Very regular oscillatory behavior is demonstrated for the NO2 reduction using FEM. Advantages as well as shortcomings of the FEM/FIM experimental approach are discussed and an outlook on future studies using local chemical probing will be given wherever appropriate.
The molecular origins of the two-dimensional Raman spectrum of an atomic liquid. I. Molecular dynamics simulation
Authors: Ma Ao , Stratt Richard M.
Published: July 2002

As complex as it may seem, a two-dimensional (fifth-order) nonresonant Raman spectrum may provide one of the simplest ways to get at the character of intermolecular dynamics in liquids. Its status as an echo spectroscopy means that it should not only permit us to survey the intermolecular vibrations, it should allow us to ascertain the extent of their coherence. Arriving at a microscopic interpretation of those spectra, however, poses some genuine theoretical challenges. We describe here the first complete molecular dynamics simulation of such a spectrum. By using classical dynamics and focusing on liquid Xe, we find that we are able to produce a spectrum strikingly similar to the experimentally reported (nonmagic-angle) spectra of liquid CS2. We observe, in particular, that there is no discernable echo, suggesting that the dynamics is strongly homogeneously broadened. We turn, in a companion paper, to the implications of these results for instantaneousnormal-mode models of liquids.
In-plane reversal mechanisms in circular Co dots
Authors: Prejbeanu I. L. , Natali M. , Buda L. D. , Ebels U. , Lebib A. , Chen Y. , Ounadjela K.
Published: July 2002

The reversal process of polycristalline circular Co dots is investigated for dot sizes for which the vortex state corresponds to the ground state configuration. Using magneto-optic Kerr magnetometry and magnetic force microscopy imaging, it is found that during the reversal of the magnetization, the system does not necessarily pass through its ground state configuration. For large dot diameters and thickness, the reversal occurs via nucleation, propagation, and expulsion of a single vortex, whereas for a dot thickness below 20 nm the reversal process may occur by a coherent rotation of the quasi-single-domain configuration. Furthermore, a double-vortex state formation has been evidenced for 1000-nm-large dots.
Two-color three pulse photon echo peak shift spectroscopy
Authors: Agarwal Ritesh , Prall Bradley S. , Rizvi Abbas H. , Yang Mino , Fleming Graham R.
Published: July 2002

Two-color three pulse photon echo peak shift spectroscopy (2C3PEPS) has been used to probe correlation in electronic transitions in two different regions of the electronic spectrum of a chromophore in the condensed phase. The 2C3PEPS can be done in an “uphill” or a “downhill” sense, where the first two interactions are of lower (higher) frequency than the final interaction with the radiation field. In both cases no correlation between the two spectral regions is observed at very short times. Different parts of the spectrum gain correlation owing to ultrafast solvent motion and the accompanying Stokes shift. We propose a model for the spectral shift that incorporates a conditional probability distribution for transition frequencies in the two spectral regions. The model qualitatively reproduces all the features of complete numerical simulations. Our results show that memory is partially conserved during the spectral diffusion process from the pump to the probe region. The downhill difference peak shift is very sensitive to the time scale of the inertial component of solvation and seems very promising for an accurate determination of this time scale.
Retardation and transitions of dilute and dense granular flows in a vertical pipe induced by electric fields
Authors: Chen Wei , Hou Meiying , Lu Kunquan , Jiang Zehui , Lam Lui
Published: July 2002

Granular flow of nickel particles down a vertical pipe from a hopper is shown to be retarded by a horizontal ac electric field applied to a local region along the pipe. The particles are released from the hopper by pulling out a stopper in the hopper. Two sequences of experiments with different initial flow conditions are performed. In the first sequence, a dilute flow in the pipe is created after a fixed voltage V (⩽4.8 kV) is applied across two short, vertical copper electrodes. The steady-state flow rate Q remains practically constant for VV1, the flow becomes dense; Q decreases with a power law, Q∼V−1. In the second sequence of experiments, V is first set at 4.8 kV; the flow is allowed to start, and soon becomes a dense flow; then, V is reduced to the desired voltage. The new, steady-state Q vs V curve coincides with the previous Q(V) curve of the first sequence, except for V2<VV2) to a dilute flow (V<V2). Our results show that a large enough ac electric field can decrease the flow rate of a dilute or dense flow; the critical voltage that can reduce a dense flow, V2, is less than that for the dilute flow, V1.
Native defects and self-diffusion in GaSb
Authors: Hakala M. , Puska M. J. , Nieminen R. M.
Published: July 2002

The native defects in GaSb have been studied with first-principles total-energy calculations. We report the structures and the formation energies of the stable defects and estimate the defect concentrations under different growth conditions. The most important native defect is the GaSb antisite, which acts as an acceptor. The other important defects are the acceptor-type Ga vacancy and the donor-type Ga interstitial. The Sb vacancies and interstitials are found to have much higher formation energies. A metastable state is observed for the SbGa antisite. The significantly larger concentrations of the Ga vacancies and interstitials compared to the corresponding Sb defects is in accordance with the asymmetric self-diffusion behavior in GaSb. The data supports the next-nearest-neighbor model for the self-diffusion, in which the migration occurs independently in the different sublattices. Self-diffusion is dominated by moving Ga atoms.
High resolution frequency stability measurement system
Authors: Brida G.
Published: July 2002

This article reports on the frequency stability measurement system based upon the dual-mixer time-difference scheme working at 10 MHz with 1 Hz beat note. The principle of the system is reviewed, the design approach is described, and the experimental results are presented. The measurement system shows a stability of 5.6×10−14/τ (Allan deviation) and a temperature sensitivity of some picoseconds per Kelvin. An approach to reduce crosstalk problems has been tested.
The method of characteristic for nonlinear generalized Rayleigh–Taylor instability associated with equatorial spread F: An analytical approach
Authors: Sekar R. , Kherani E. A.
Published: July 2002

An analytical method is presented for the nonlinear generalized Rayleigh–Taylor instability occurring over the night-time equatorial F region of the terrestrial ionosphere. The time and spatial domain characteristic methods are adopted to describe the evolutions of plasma density and particle flux, respectively. The analysis efficiently describes the known nonlinear features of instability as suggested by many numerical simulations. The existence of shock or steepened structures and their dynamics are discussed by studying the evolution of the characteristics.
Monte Carlo simulation of bremsstrahlung emission by electrons
Authors: Acosta E. , Llovet X. , Salvat F.
Published: July 2002

An algorithm for the simulation of bremsstrahlung emission by fast electrons using numerical cross sections is described. It is based on natural factorization of the double-differential cross section and on the fact that the intrinsic angular distribution of photons with a given energy can be very closely approximated by a Lorentz-boosted dipole distribution. The parameters of this angular distribution vary smoothly with the atomic number of the target atom and with the energies of the projectile’s electron and the photon emitted. Results from simulations of thick-target bremsstrahlung are compared with experimental data.
Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors
Authors: McHale G. , Newton M. I. , Martin F.
Published: July 2002

A model for the mass sensitivity of Love wave and layer guided shear horizontal acoustic plate mode (SH–APM) sensors is developed by considering the propagation of shear horizontally polarized acoustic waves in a three layer system. A dispersion equation is derived for this three layer system and this is shown to contain the dispersion equation for the two layer system of the substrate and the guiding layer plus a term involving the third layer, which is regarded as a perturbing mass layer. This equation is valid for an arbitrary thickness perturbing mass layer. The perturbation, Δν, of the wave speed for the two-layer system by a thin third layer of density, ρp and thickness Δh is shown to be equal to the mass per unit area multiplied by a function dependent only on the properties of the substrate and the guiding layer, and the operating frequency of the sensor. The independence of the function from the properties of the third layer means that the mass sensitivity of the bare, two-layer, sensor operated about any thickness of the guiding layer can be deduced from the slope of the numerically or experimentally determined dispersion curve. Formulas are also derived for a Love wave on an infinite thickness substrate describing the change in mass sensitivity due to a change in frequency. The consequences of the various formulas for mass sensing applications are illustrated using numerical calculations with parameters describing a (rigid) poly(methylmethacrylate) wave-guiding layer on a finite thickness quartz substrate. These calculations demonstrate that a layer-guided SH–APM can have a mass sensitivity comparable to, or higher, than that of Love waves propagating on the same substrate. The increase in mass sensitivity of the layer guided SH–APMs over previously studied SH–APM sensors is of significance, particularly for liquid sensing applications. The relevance of the dispersion curve to experiments using higher frequencies or frequency hopping and to experiments using thick guiding layers is discussed.
Tunnel injection In0.4Ga0.6As/GaAs quantum dot lasers with 15 GHz modulation bandwidth at room temperature
Authors: Bhattacharya P. , Ghosh S.
Published: July 2002

By utilizing tunnel injection of electrons, first demonstrated in quantum well lasers, we have measured enhanced small-signal modulation bandwidth, f−3dB, and reduced temperature sensitivity of the threshold current, characterized by T0, in In0.4Ga0.6As/GaAs self-organized quantum dot ridge waveguide lasers. Values of f−3dB=15 GHz at 283 K and T0=237 K for 318⩾T⩾278 are measured in these devices. The differential gain at 283 K is dg/dn≅8.5×10−14 cm2 and the gain compression factor ε=4.5×10−17 cm3.
Low-frequency quantum oscillations of the impedance of layered conductors at high magnetic field
Authors: Kirichenko O. V. , Kozlov I. V.
Published: July 2002

The propagation of electromagnetic waves in layered conductors is investigated by the method of the quantum kinetic equation. The quantum oscillations of the impedance for elastic scattering on impurities is calculated. An expression is obtained for the low-frequency oscillations of the impedance over a wide range of frequencies of the electromagnetic wave.
Modeling of the plasma jet of a stationary plasma thruster
Authors: Garrigues L. , Bareilles J. , Boeuf J. P. , Boyd I. D.
Published: July 2002

We have developed a two-dimensional hybrid fluid – particle-in-cell Monte Carlo collisions (PIC- MCC) model to study the plume of a stationary plasma thruster. The model is based on a fluid description of the electrons (the electron density follows a Boltzmann distribution) and a particle description of the ion and neutral transport. Collisions between heavy species are taken into account with a Monte Carlo method. The electric field is obtained from Poisson's equation or from the quasineutrality assumption. We first show that the results from the PIC-MCC model are close to the results of a more time-consuming direct simulation Monte Carlo approach. We then compare the model predictions of the plume density and ion energy distribution with experimental measurements. Finally, we present a brief discussion on the assumptions of the model and on its ability to give reliable predictions on important issues such as the flux of ions backscattered to the satellite.
Single-fundamental-mode photonic-crystal vertical-cavity surface-emitting lasers
Authors: Song Dae-Sung , Kim Se-Heon , Park Hong-Gyu , Kim Chang-Kyu , Lee Yong-Hee
Published: July 2002

A photonic-crystal vertical-cavity surface-emitting laser (PC-VCSEL) is proposed and demonstrated. The 850-nm-PC-VCSEL shows single-mode continuous-wave operation in the entire current range. The side-mode suppression ratio is 35–40 dB for the sample with the hole pitch (Λ) 5 μm and the hole diameter (a) 3.5 μm. The guiding effect of the single-defect triangular-lattice two-dimensional photonic crystal structure is experimentally observed and is explained by the effective index model.
Chaos in a multimode solid-state laser system
Authors: Bracikowski C. , Roy Rajarshi
Published: July 2002

When a nonlinear crystal is placed within a multimode solid-state laser cavity, deterministic fluctuations are induced in the output intensity. In this paper, the results of our studies of the intensity noise in a diode pumped, intracavity frequency doubled Nd:YAG (neodymium doped yttrium aluminum garnet) laser will be presented. First, a novel technique to eliminate these fluctuations is described. Second, the observation of antiphase states in the laser output is discussed. These states are characterized by a cyclic periodic pulsing of the individual longitudinal mode intensities. Finally, the statistical properties of chaotic intensity fluctuations are characterized. It is be demonstrated that it is possible to accurately model the laser dynamics by a system of globally coupled, nonlinear oscillators.
Dynamical properties of a ferroelectric capacitor observed through nonlinear time series analysis
Authors: Hegger Rainer , Kantz Holger , Schmüser Frank , Diestelhorst Martin , Kapsch Ralf-Peter , Beige Horst
Published: July 2002

By data analysis the ordinary differential equation for the description of an experimental electric resonance circuit with nonlinear capacitor is derived. Triglycine sulfate (TGS) was used as nonlinear dielectric material. This is the most thoroughly investigated ferroelectric with a second order phase transition. Its static dielectric small signal behavior is well described in the framework of the Landau theory, yielding a Duffing-type ordinary differential equation as a model equation of the circuit. Data analysis allows us to check carefully the validity of this model and to determine required corrections of this simplified equation.
Scale and space localization in the Kuramoto–Sivashinsky equation
Authors: Wittenberg Ralf W. , Holmes Philip
Published: July 2002

We describe a wavelet-based approach to the investigation of spatiotemporally complex dynamics, and show through extensive numerical studies that the dynamics of the Kuramoto–Sivashinsky equation in the spatiotemporally chaotic regime may be understood in terms of localized dynamics in both space and scale (wave number). A projection onto a spline wavelet basis enables good separation of scales, each with characteristic dynamics. At the large scales, one observes essentially slow Gaussian dynamics; at the active scales, structured “events” reminiscent of traveling waves and heteroclinic cycles appear to dominate; while the strongly damped small scales display intermittent behavior. The separation of scales and their dynamics is invariant as the length of the system increases, providing additional support for the extensivity of the spatiotemporally complex dynamics claimed in earlier works. We show also that the dynamics are spatially localized, discuss various correlation lengths, and demonstrate the existence of a characteristic interaction length for instantaneous influences. Our results motivate and advance the search for localized, low-dimensional models that capture the full behavior of spatially extended chaotic partial differential equations.
The nature of chaos in two systems of ordinary nonlinear differential equations
Authors: Pachner J.
Published: July 2002

When a suitable method is applied for the numerical integration of systems of ordinary differential equations with one (Rössler) or two (Lorenz) nonlinear terms, the integral curve is always smooth, without any trace of chaotic motion, and the numerical results are supported by a simple analysis of the equations and by Poincaré’s qualitative theory of the ordinary nonlinear differential equations. It is also demonstrated that a degenerate system with two nonlinear terms can be integrated analytically. The system is reduced to the differential equation for a harmonic oscillator (an electric LC circuit), where the only difference lies in the fact that the independent variable is not the time variable but an exponential function of time. For a certain set of constants the integral of the Lorenz system is asymptotically, very fast, approaching an integral of the degenerate system. The results of numerical integration by two methods discussed in the paper are compared with the analytical solution. They show that the methods are stable and accurate.
Scalar invariants of the radiating Kerr–Newman metric: A simple application of GRTensor
Authors: Musgrave Peter , Lake Kayll
Published: July 2002

GRTensor is an interactive PC-based program for tensor analysis primarily of interest for teaching and research in general relativity. It uses either maplev or mathematica as its algebraic engine. In this paper we use GRTensor to evaluate the Ricci and Weyl invariants for the radiating Kerr–Newman metric. This includes, as a special case, all nonvanishing invariants of the Kerr metric—the archetypical black hole solution in general relativity.
Computer-assisted assessment of student understanding in physics
Authors: Lea Suzanne M. , Thacker Beth A. , Kim Eunsook , Miller Kathleen M.
Published: July 2002

A computer program that presents and grades physics problems is described. The reliability of the grading is discussed in the context of diagnostic tests. The concept of computerized testing in physics is shown to be feasible. It was found that graphics answer representations can be used to measure student understanding: students with correct graphics answers provide correct explanations and conversely. The sample problem studied did not produce any false negative results; the only false positive results were caused by incomplete explanations which are easily caught by keyword checking.
Symbolic simulation of nonlinear random resistor networks by m
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Authors: Yu K. W.
Published: July 2002

Symbolic simulation is a technique, which combines symbolic and numerical solutions of a system of linear or nonlinear algebraic equations. One parameter is left in symbolic form and all quantities of interest are computed in a series expansion with respect to this parameter. As an example of considerable current interest, the computer algebra system mathematica is used to study the effective response of a nonlinear random resistor network. A system of nonlinear circuit equations is solved and the effective response is computed as a series expansion. We also find that due to geometric effects near the percolation threshold, the ohmic region in the current–voltage characteristics shrinks. The present approach is shown to have many advantages over purely numerical techniques while the required computing effort is quite modest. Applications of symbolic simulations to other related problems and the extension to more parameters are also discussed.
A MacintoshTM-based multiparameter pulse height analyzer and multichannel scaler system for advanced teaching laboratories
Authors: Bajema J. , Ashktorab K. , Becchetti F. D. , Hotz D. , Shapiro M.
Published: July 2002

A low-cost, moderately high-speed Apple MacintoshTM-based data acquisition and analysis system has been developed based on a low-cost National Instruments■ NuBus TTL interface card with external Nuclear Instruments Module analog-to-digital converters. Features of the system include multiparameter coincident pulse height analysis and multichannel scaling in a user-friendly graphical user-interface environment of data windows, pull-down menus, and multiparameter gating. This system has been effectively used for nuclear, atomic, and modern physics experiments in the advanced undergraduate laboratory courses at the University of Michigan. It offers a cost-effective solution for numerous data acquisition needs.
Symbolic tensor calculus using index notation
Authors: Castellví P. , Jaén X. , Llanta E.
Published: July 2002

We present a Mathematica program which implements tensor calculus using index notation. Common operations, such as contractions, lowering and raising of indices, symmetrization and antisymmetrization, and covariant derivatives, are implemented in such a manner that the notation for the inputs is close to that found in textbooks. The optimization of the time to perform the calculations has been one of the main objectives when writing the code. This program has been merged with the package TTC, recently published in this journal, so the user can use both intrinsic notation and index expressions when performing tensor calculus. © 1995 American Institute of Physics.
Implementation and characterization of three-dimensional particle-in-cell codes on multiple-instruction-multiple-data massively parallel supercomputers
Authors: Lyster P. M. , Liewer P. C. , Decyk V. K. , Ferraro R. D.
Published: July 2002

A three-dimensional electrostatic particle-in-cell (PIC) plasma simulation code has been developed on coarse-grained distributed-memory massively parallel computers with message passing communications. Our implementation is the generalization to three-dimensions of the general concurrent particle-in-cell (GCPIC) algorithm. In the GCPIC algorithm, the particle computation is divided among the processors using a domain decomposition of the simulation domain. In a three-dimensional simulation, the domain can be partitioned into one-, two-, or three-dimensional subdomains (‘‘slabs,’’ ‘‘rods,’’ or ‘‘cubes’’) and we investigate the efficiency of the parallel implementation of the push for all three choices. The present implementation runs on the Intel Touchstone Delta machine at Caltech; a multiple-instruction-multiple-data (MIMD) parallel computer with 512 nodes. We find that the parallel efficiency of the push is very high, with the ratio of communication to computation time in the range 0.3%–10.0%. The highest efficiency (≳99%) occurs for a large, scaled problem with 643 particles per processing node (∼134 million particles on 512 nodes) which has a push time of about 250 ns per particle per time step. We have also developed expressions for the timing of the code which are a function of both code parameters (number of grid points, particles, etc.) and machine-dependent parameters (effective FLOP rate, and the effective interprocessor bandwidths for the communication of particles and grid points). These expressions can be used to estimate the performance of scaled problems—including those with inhomogeneous plasmas—to other parallel machines once the machine-dependent parameters are known. © 1995 American Institute of Physics.
Fast algorithms for random numbers with exponential and normal distributions
Authors: Fernández Julio F. , Rivero Juan
Published: July 2002

We report new algorithms for the generation of pseudorandom numbers with normal and exponential distributions. No transcendental functions need to be evaluated. No tables are needed. These algorithms are inspired by some fundamental schemes of statistical physics. Our normal random number generator is an order of magnitude times faster than Box–Muller’s algorithm. Our exponential random number generator is several times faster than taking the logarithm of a uniform random deviate and than von Neumann’s algorithm. © 1996 American Institute of Physics.
Object orientation and visualization of physics in two dimensions
Authors: Burgess Mark , Haugerud Hårek , Strandlie Are
Published: July 2002

We present a generalized framework for cellular/lattice-based visualizations in two dimensions based on state-of-the-art computing abstractions. Our implementation takes the form of a library of reusable functions written in C++ that hide complex graphical programming issues from the user and mimic the algebraic structure of physics at the Hamiltonian level. Our toolkit is not just a graphics library but an object analysis of physical systems that disentangles separate concepts in a faithful analytical way. It could be rewritten in other languages such as Java and extended to three-dimensional systems straightforwardly. We illustrate the usefulness of our analysis with implementations of spin films (the two-dimensional XY model with and without an external magnetic field) and a model for diffusion through a triangular lattice. © 1998 American Institute of Physics.
Effect of the grain size distribution on the magnetization curve
Authors: Escobar M. A. , Magaña L. F. , Valenzuela R.
Published: July 2002

Using theoretical expressions for the magnetization curve of polycrystalline ferrimagnets given previously, we have considered the effect of a grain size distribution on the magnetization versus applied magnetic field curve. We have observed the effects of various theoretical probability distribution functions and compared them with an experimental curve of yttrium iron garnet, Y3Fe5O12. The best fitting was obtained with a normal logarithmic distribution function for the grain size distribution of the sample.
Crystal growth kinetics of boron oxide under pressure
Authors: Aziz Michael J. , Nygren Eric , Hays James F. , Turnbull David
Published: July 2002

We have measured the crystal growth rate u of B2O3-I in the amorphous phase, as it varied over five orders of magnitude with changes in temperature and pressure. We eliminated the crystal nucleation barrier by seeding the surface of boron oxide glass with crystals. u became measurable only when the pressure exceeded a threshold level near 10 kbar. Using the published thermodynamic information on the B2O3 system and a crude free-energy model for the crystal and glass phases, we account qualitatively for our results with the theory of crystal growth limited by the rate of two-dimensional nucleation of monolayers. The constants for the prefactor, activation energy, activation volume, and ledge tension are determined by fitting. By adjusting the thermodynamic parameters to a set of values that are well within the ranges delineated by their experimental uncertainties, we account quantitatively for the measured growth rates from 300 to 500 °C and from 0 to 30 kbar with the following relation: u(T,P)=(785 m/s)[‖ΔGm‖/(RT)]1/6 ×exp[π×3 Å(420 erg/cm2)2(28 cm3/mole)/(3 kTΔGm)]exp[−10 366 cal/mole/(RT)] ×exp[−P×16 cm3/mole/(RT)]×{1−exp[ΔGm/(RT)]}2/3, with the driving free energy given by ΔGm(T,P)=(13 cm3/mole) [PM(T)−P] and the melting curve given by PM(T)=(T−450 °C)/(42.6 K/kbar). The ‘‘B2O3 crystallization anomaly’’, that crystals have never been observed to grow at atmospheric pressure, is explained, since according to our model, the frequency of two-dimensional nucleation is negligible at all temperatures at pressures less than 10 kbar.
A perturbation theory for the acoustoelastic effect of surface waves
Authors: Husson D.
Published: July 2002

The acoustoelastic effect for surface and plate waves propagating in nonuniformly stressed media is analyzed. The theory is based on our earlier perturbation theory and normal mode technique which was used for volume waves. As with the earlier treatment, a Lagrangian description of the motion of the particles in an elastic medium is used. The results are applied to analyze the acoustoelastic effect for Rayleigh waves and Lamb waves in nonuniformly stressed media.
Thermoelastic attenuation of Rayleigh waves
Authors: Jurczyk G. K. , Klemens P. G.
Published: July 2002

Thermoelastic attenuation of Rayleigh waves is larger than that of bulk waves because heat is conducted not only in the propagation direction, but also normal to the surface. This attenuation is further enhanced if the thermal expansivity is a function of depth below the surface. Expressions are obtained for the attenuation and some experimental data on Rayleigh wave attenuation is discussed.
Velocities and emission rates of cathode-produced molybdenum macroparticles in a vacuum arc
Authors: Shalev S. , Boxman R. L. , Goldsmith S.
Published: July 2002

Time- and space-resolved measurements of the axial and transverse velocity components of Mo macroparticles produced in a 1-kA peak current, 30-ms duration vacuum arc were performed using laser-Doppler anemometry (LDA). Individual macroparticle velocity components in the range of 10–750 m/s were detected and average velocity components in the range of 100–400 m/s were determined. Using the results of the measurements of individual velocity components we obtain that a typical rms value of the macroparticle speed is in the range 400–700 m/s. Comparing the average values of the radial and axial components indicates that typical emission angles are at approximately 30°±5° with respect to the cathode surface. The relative time-resolved macroparticle emission rate was measured by using the LDA apparatus as a particle counter. Peak macroparticle emission occurred at a time midway between peak current and peak average cathode surface temperature. This result, together with the observation that the macroparticle emission rate could be increased by increasing the current pulse repetition rate, indicate that the macroparticle emission rate is influenced by the average cathode surface temperature as well as the instantaneous arc current.
Crystallization characteristics of late transition metal-Zr glasses around the composition M90Zr10
Authors: Altounian Z. , Batalla E. , Strom-Olsen J. O.
Published: July 2002

We report on the glass-forming ability and crystallization products of Cu-, Ni-, Co-, and Fe-Zr around the composition M90Zr10. Cu-Zr cannot be made glassy by metal spinning in this composition range and Ni-Zr only with difficulty at Ni90Zr10. Two new metastable phases are observed: Co5Zr and a bcc form of Ni.
Pressure and temperature dependence of the static dielectric constants and elastic anomalies of ZnF2
Authors: Vassiliou John K.
Published: July 2002

The static dielectric constants εa and εc of ZnF2 have been studied in the range 4–296 °K at zero pressure and in the pressure range 0–5 kbar at 296, 195, and 78 °K. εa and εc exhibit normal temperature behavior. εc decreases with pressure as is normally the case. εa, on the other hand, exhibits an anomalous increase with pressure at room temperature. This anomalous increase is reduced with decreasing temperature and by 78 °K has completely disappeared. The pressure and temperature results are combined with thermal expansion and compressibility data to evaluate the pure volume and the pure temperature dependence of the dielectric constants. The dielectric constants are described by a Clausius–Mossotti relation. The Szigeti effective charge ratios have been determined for the transverse optical (TA) modes along the [100] and c axes. These ratios are found to be rather small, being 0.44 and 0.54 for the two axes, respectively, suggesting that the bonding is partially covalent. The principal components for the Gruneisen tensor have also been determined. Below 80 °K, they are negative. This is due to the negative mode-Gruneisen parameters of the transverse acoustic (TA) modes associated with the C44 and Cs elastic constants. The possible correlation between the pressure anomaly of εa and temperature anomaly of C44 is discussed and attributed to the instability of the chains of F− octahedra.
Heating in crystalline solids due to rapid deformation
Authors: Miller P. J. , Coffey C. S. , DeVost V. F.
Published: July 2002

We present experimental evidence that during rapid deformation of at least some crystalline and polymeric solids heat is generated at unexpectedly high temperatures beginning essentially at the moment deformation begins. The heat was observed by fast infrared sensors. Both the initial infrared emissions and the apparent blackbody temperatures were far in excess of what can reasonably be accounted for by the conventional picture that distributes the energy due to deformation over the bulk of the solid. It appears that the origins of these high temperatures are associated with mechanical processes that effectively concentrate the energy of deformation into small local regions within the sample. These local hot spot regions are most likely associated with shear bands and possibly fracture sites in the deforming crystal.
Theoretical and experimental determination of deep trap profiles in semiconductors
Authors: Zhao Jian H. , Lee Jyh-Chwen , Fang Z. Q. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

A simple and accurate expression is developed for profiling deep-level traps in semiconductors using Schottky barriers and deep-level transient spectroscopy (DLTS). Through the use of computer simulations as well as the application to actual experimental results it is shown that the standard expressions which are generally employed can result in large errors in the calculated trap concentration near the metal semiconductor interface. It is also pointed out that the standard DLTS expressions will result in large differences in the calculated trap concentrations for donorlike or acceptorlike traps when the trap concentration is comparable to the shallow level concentration.
Large-signal time-domain modeling of low-pressure rf glow discharges
Authors: Barnes Michael S. , Cotler Tina J. , Elta Michael E.
Published: July 2002

Large-signal time-domain modeling (simulation) of rf glow discharges is a very useful and potentially accurate tool for the study of low-pressure (50–500-mT) gaseous electronics at high frequencies. Unfortunately, the computational limitations imposed for stability, accuracy, and efficiency can often hinder the production of useful, cost-effective results. This paper describes a self-consistent argon rf glow-discharge simulation at 13.56 MHz for equal- and unequal-area parallel-plate electrode geometries. Some of the numerical problems associated with this type of simulation are identified and the numerical methods used to overcome them are described. To illustrate the usefulness of this modeling scheme, the plasma potential and the cathode dc bias are examined as functions of electrode area ratio and rf power.
Retardation-related effects on the optical behavior of a granular surface. I. Dipolar treatment
Authors: Bosi Giulio
Published: July 2002

A critical examination of standard treatments dealing with granular systems reveals the need for a new, self-consistent treatment taking retarded fields into account. The electromagnetic problem involving dielectric spherical grains imbedded in a host medium under the influence of a plane monochromatic wave is given a general and exact solution. Formulas defining the induced dipoles are carried out explicitly: the right forms of the polarizability and of the local field are easily singled out. The effective permittivity of periodic structures is also presented and its values plotted for a number of models of granular films. These calculations show that retardation is responsible for lowering the resonance peaks and shifting them toward lower frequencies as the dipole–dipole distance increases.