bluuebunny/crossref_metadata_2025 huggingface dataset:
Recurrence plots of experimental data: To embed or not to embed?
Authors: Iwanski Joseph S. , Bradley Elizabeth
Published: July 2002

A recurrence plot is a visualization tool for analyzing experimental data. These plots often reveal correlations in the data that are not easily detected in the original time series. Existing recurrence plot analysis techniques, which are primarily application oriented and completely quantitative, require that the time-series data first be embedded in a high-dimensional space, where the embedding dimension dE is dictated by the dimension d of the data set, with dE⩾2d+1. One such set of recurrence plot analysis tools, recurrence quantification analysis, is particularly useful in finding locations in the data where the underlying dynamics change. We have found that for certain low-dimensional systems the same results can be obtained with no embedding.
Global sensitivity analysis of a nonlinear system using animated basins of attraction
Authors: Cusumano Joseph P. , Lin Derchyan , Morooney Kevin , Pepe Louis J.
Published: July 2002

A computer program is described that allows the effect of parameter changes on the global behavior of a nonlinear system to be studied. Steady-state motions and their basins of attraction can be rapidly obtained and visualized for given parameter values. The program is applied to the study of a differential equation modeling a nonlinear oscillator forced parametrically through its bifurcation parameter. The algorithm used in our program is based on the Interpolated Cell Mapping (ICM) method developed by Tongue [B. H. Tongue, Physica D 28(3), 401–408 (1987)]. It is shown how this method, when implemented on a vector/parallel architecture machine, can be combined with animation to perform global sensitivity analyses of nonlinear systems. A high-resolution (1152×900 pixel) animation is created which shows the evolution of the basins of attraction for a specific pair of periodic solutions as the forcing frequency and forcing amplitude are varied over a closed path in the parameter space. The movie consists of 720 pictures, each of which requires 518 400 separate simulations. In order to accomplish this task, the basic algorithm is modified, using IBM Parallel Fortran, to exploit the architecture of the IBM 3090-600S. Of particular interest is the way the animation reveals phenomena that are difficult or impossible to see in the still images. Detailed benchmarks are presented which show the performance of different configurations of the code in a typical university supercomputing environment.
Learning dynamical behaviors with explorer
Authors: Fromont Bruno , Beaufumé Pascale
Published: July 2002

This paper presents Explorer, a neural-network-based learning system, which combines Artificial Intelligence techniques with classical numerical methods to classify the dynamical behavior of a set of experiments or simulations. Explorer is easy to use and to modify, and allows one to perform qualitative studies of dynamical models at a low cost. This new tool can be adapted to many different situations because it does not require any prior theoretical background about the model being studied. Explorer first stores the relevant knowledge under the user’s supervision. Then it is used in stand-alone mode to perform an automatic exploration of a predefined domain of parameters. Explorer is used to study a complex nonlinear dynamical model, the Beasts’ model, associated with a class of physical problems known as ‘‘percolative transport.’’ The exploration map obtained allows one to visualize the distribution of the behavioral regimes in the chosen parameter space, and to point out the role played by each parameter: One parameter leads the system to chaos as it increases, while the other acts to bring the system back to a converging trajectory.
Monte Carlo simulations of quantum systems on massively parallel supercomputers
Authors: Ding Hong Q.
Published: July 2002

An efficient Monte Carlo algorithm for two-dimensional quantum spins or boson systems was implemented on two massively parallel distributed memory supercomputers: Intel Delta and iPSC/860. The algorithm uses a multispin coding technique which allows significant data compactification and efficient vectorization of Monte Carlo updates. Two data decompositions, corresponding naturally to different Monte Carlo updating processes and observable measurements, are devised such that only nearest neighbor communications are needed within a given decomposition. The algorithm dynamically switches between the two decompositions using a simple pipe along the one-dimensional ring of processing nodes of the parallel computer. In this two-decomposition scheme, the entire algorithm uses only two communication routines (exchange and broadcast); this simplification makes the code easily portable to other computers. On a 128-node Intel Delta, this algorithm updates 183 million spins per second (21 on CM-2 and 6.2 on Cray YMP). A systematic performance analysis shows a better than 90% efficiency in the parallel implementation. Several new physics results on the magnetic properties of the high temperature superconductors obtained in the simulations will be discussed.
Data acquisition and control system for the neutron time-of-flight spectrometer MIBEMOL
Authors: Wegener W. , D’Hooghe P. , De Boeck W.
Published: July 2002

An inexpensive high-performance data acquisition and control system for the neutron time-of-flight spectrometer MIBEMOL is described. The hardware for this six-chopper instrument consists of CAMAC modules and the combination of a PC-AT with an on-board computer containing a Motorola 68000 processor. The software is written in C and runs under the UNIX-like operating system OS-9. It performs in a user-friendly way tasks as menu driven communication with the apparatus, running experiments according to given options, accumulating time-of-flight spectra for up to 64 scattering angles simultaneously, organizing data output, and monitoring the instrument. The PC-AT serves as terminal. Data stored on its hard disk can be sent to a workstation for data analysis.
A new algorithm for computation of SU3 Clebsch–Gordon coefficients
Authors: Williams H. T. , Wynne Colin J.
Published: July 2002

A new, operator-based algorithm for the calculation of Clebsch–Gordon coefficients for the group SU3 is introduced, and an ansi c program for its implementation is described. The algorithm involves the use of raising and lowering operators in analogy to a standard pedagogical approach to the more familiar SU2 Clebsch–Gordon coefficients. The nature of the approach makes the sign conventions utilized and the rules for resolution of the outer degeneracy explicit, and therefore allows straightforward changes to adapt the program to other choices. The program is written to allow its execution on personal computers of modest memory size, but also to take advantage of available memory allowing more complex results to be obtained on larger computing systems.
Fast dynamo action in spherical geometry: Numerical calculations using parallel virtual machines
Authors: Hollerbach Rainer
Published: July 2002

I present a numerical code designed to solve the magnetic induction equation in spherical geometry. I demonstrate how to use the message-passing software package parallel virtual machine to distribute this code over a cluster of workstations, and consider how the parallel efficiency depends upon the ratio of communication to computation. I demonstrate that by estimating these quantities in advance, one can very accurately predict the parallel efficiency that will result when the code is distributed over a cluster of given communication and computation speeds. It is suggested that such estimates would be extremely useful in deciding in advance whether or not it would be worthwhile to implement distributed versions of other codes. © 1995 American Institute of Physics.
Photochemical hole-burning study of 1,4-dihydroxyanthraquinone doped in amorphous silica prepared by alcoholate method
Authors: Tani Toshiro , Namikawa Hiroshi , Arai Kazuo , Makishima Akio
Published: July 2002

Preparation of amorphous silica doped with organic dye molecules, 1,4-dihydroxyanthraquinone, and the observation of the amorphous structure of this system by photochemical hole burning using the dye molecules as a spectral probe are reported. The various kinds of organic molecule-doped inorganic glassy materials are obtained with the alcoholate method. The appearance of the photochemical hole in this system shows the molecular dispersion of the dye molecules in the matrix without cracking or decomposition. The burning yield, 1.2×10−4, is the same as that observed in organic glasses. The intrinsic holewidth, 0.9 cm−1 at zero burning time limit, the burning-time dependence and the annealing effects on the hole profile were observed and compared with those in the alcoholic organic glass. It is suggested that the nearest-neighbor structures around quinizarin molecules consist of some hydroxyl groups. The matrix cages seem to be fairly tight and rigid in comparison with those of the alcoholic glass. The possibility that the quinizarin molecule or molecules are embedded within the pore of amorphous SiO2 with some amount of solvent molecules, mainly ethanol or water, seems to be excluded. The annealing effects of the burned hole indicate that there exist two kinds of mechanisms which dominate the temperature dependence of the holewidth in the present system. One is already dominant below about 27 K which gives rise to the reversible behavior in the holewidth with temperature, and the other becomes effective above 27 K and is irreversible with temperature cycling. Some discussions are given on the origin of these relaxation mechanisms in this system which are inherent in the structure of amorphous materials.
Second-order optical susceptibility of strained GeSi/Si superlattices
Authors: Friedman Lionel , Soref Richard A.
Published: July 2002

A strain-induced ordered phase has been observed recently in the alloy layers of a GeSi/Si strained-layer superlattice in which the ordered unit cell is noncentrosymmetric. Using the bond-charge model of Jha and Bloembergen [Phys. Rev. 171, 891 (1968)], the second-order susceptibility and the linear electro-optic (Pockels) coefficient of the GeSi layers are calculated and are found to be comparable in magnitude to those of GaAs.
Magnetically insulated ion diode with a gas-breakdown plasma anode
Authors: Greenly J. B. , Ueda M. , Rondeau G. D. , Hammer D. A.
Published: July 2002

An active anode plasma source has been developed for use in a magnetically insulated ion diode operated on a 1010-W pulsed power generator. This source uses an inductive voltage from a single turn coil to beak down an annular gas puff produced by a supersonic nozzle. The resulting plasma is magnetically driven toward the radial insulating magnetic field in the diode accelerating gap and stagnates at a well-defined surface after about 300 ns to form a plasma anode layer defined by magnetic flux surfaces. An ion beam is then extracted from this plasma layer by applying a 150-kV, 1-μs pulse to the accelerating gap. Optimization of the timing of the gas puff, the plasma production discharge, and the high voltage pulse has resulted in 1-μs duration 75–150-keV ion beam pulses with >100-A/cm2 peak ion current density over an area of about 400 cm2. Up to 5 J/cm2 has been collected by a 4-cm2 calorimeter. The diode impedance history can be varied so that rising, flat, and falling voltage pulse waveforms can be produced. Streak photographs of beamlets impinging on a scintillator and time integrated targets both show beam divergence angles ≤3°. However, under certain operating conditions, large excursions (∼25°) in mean aiming angle on time scales of 20–200 ns are observed.
A new gated system for two-photon holographic recording in the near infrared
Authors: Lougnot D. J. , Ritzenthaler D. , Carre C. , Fouassier J. P.
Published: July 2002

A new two-photon method for recording holograms is presented. It is based on the fact that a first photon produces singlet oxygen by a photosensitization process; this species oxidizes a specific trap to produce a carbonyl compound. This latter is used as a conventional polymerization initiator and produces active species after the absorption of a second photon. The feasibility of this general process is demonstrated by using Methylene Blue (photosensitizer), diphenylisobenzofuranne (singlet oxygen trap), and a mixture of acrylamides (polymerizable compound). Finally, diffraction efficiencies higher than 2% are easily achieved with such systems. The influence of different experimental parameters was studied with a view to extending the sensitivity of the system to the infrared.
Optical properties and microstructure of reactively sputtered indium nitride thin films
Authors: Sullivan Brian T. , Parsons R. R. , Westra K. L. , Brett M. J.
Published: July 2002

The optical properties of reactively sputtered InN thin films were measured in the spectral region 2.5–5.5 eV using spectroscopic ellipsometry. The measured pseudodielectric function data of the InN films were found to vary with deposition power. The effective medium approximation theory, which describes a random aggregate microstructure, was able to relate the differences in the measured optical properties to the surface microroughness and porosity of the InN films. The relationship between microstructure and deposition power was subsequently verified by scanning electron microscopy. The analysis and electron microscopy indicate that the film deposited at 90 W was most representative of InN.
Persistent photoconductivity in II-VI and III-V semiconductor alloys and a novel infrared detector
Authors: Jiang H. X. , Brown G. , Lin J. Y.
Published: July 2002

Persistent photoconductivity (PPC) mechanisms, as well as the similarities and the differences of PPC properties in II-VI and III-V semiconductor alloys have been investigated. The potential applications based on PPC phenomenon in these two kinds of materials are discussed. We have observed that PPC induced in a II-VI mixed crystal by visible (above band gap) illumination can be quenched by long wavelength infrared radiation even at room temperature, which further supports our interpretation that PPC in II-VI mixed crystals is caused by random local potential fluctuations induced by compositional fluctuations. A newly developed infrared detector based on the PPC infrared quenching property of II-VI semiconductor alloys is also reported.
Modeling ferroelectric capacitor switching with asymmetric nonperiodic input signals and arbitrary initial conditions
Authors: Miller S. L. , Schwank J. R. , Nasby R. D. , Rodgers M. S.
Published: July 2002

The switching behavior of ferroelectric capacitors experiencing arbitrary time-dependent electric fields and arbitrary initial conditions is investigated both theoretically and experimentally. A general approach for modeling incomplete dipole switching in ferroelectric capacitors is used to derive equations describing the electrical behavior of a simple characterization circuit with arbitrary initial conditions and arbitrary time-dependent applied voltages. The equations include four experimentally determined parameters: the remanent and spontaneous polarizations, the coercive field, and the ferroelectric dielectric constant. Once these model parameters are determined from a single high-frequency sinusoidal hysteresis loop, model predictions are made with no adjustable parameters. The circuit behavior for both sinusoidal and trapezoidal input signals is computed, including asymmetric and nonperiodic signals as well as several different initial conditions. The accuracy of the model predictions is quantitatively verified with experimental data. The approach is also utilized to model the switching behavior of a ferroelectric capacitor containing a sheet of space charge. It is found that hysteresis loop distortions resulting from ionizing radiation resemble those caused by a sheet of space charge. This quantitative modeling capability facilitates the optimization of the design of ferroelectric memory circuits by minimizing the amount of required electrical testing and characterization. It can also be used to facilitate the identification and understanding of degradation mechanisms occurring in ferroelectric thin films.
Surface effects on carrier dynamics: photoconductivity studies on Si (111)
Authors: Hsu J. W. P. , Bahr C. C. , vom Felde A. , Downey S. W. , Higashi G. S. , Cardillo M. J.
Published: July 2002

We correlate photoconductivity with surface characterization in order to probe the influence of different surface properties of Si (111) on electron-hole dynamics. Photoconductivity data show that the carrier recombination is influenced strongly by surface structure and chemistry as well as by trace imperfections which are undetectable by conventional surface characterization techniques. Results on the Si(111):As (1×1) surface indicate carrier recombination at this surface is negligible, in contrast to the (7×7) reconstructed surface, where surface recombination is fast, with a surface recombination velocity measured to be ≥2×106 cm/s. We also investigate the effect of sputter induced disorder and compare our finding with results from other techniques. Combining our results and the present understanding of the (7×7) electronic structure, we estimate the carrier capture cross section for dangling bonds to be ∼10−15 cm2.
Experimental study of laser-induced plasma in welding conditions with continuous CO2 laser
Authors: Poueyo-Verwaerde A. , Fabbro R. , Deshors G. , de Frutos A. M. , Orza J. M.
Published: July 2002

Laser-induced plasmas obtained during a welding process have been studied. Spectroscopic diagnostics and an integrating sphere collecting the reflected CO2 light are the principal diagnostics used in order to determine the spatial variations of the microscopic parameters such as electron density and temperature, and the energy absorption during this process. For several experimental processing conditions of shielding gases, the main perturbing effects such as absorption and refraction of the CO2 laser radiation are quantified. Several possibilities for reducing these perturbing effects are then discussed.
Performance analysis of a new metal-insulator-semiconductor capacitor incorporated with Pt-SnOx catalytic layers for the detection of O2 and CO gases
Authors: Kang W. P. , Kim C. K.
Published: July 2002

The integration of the catalytic properties of platinum (Pt) and tin oxide (SnOx) in the Pt-SnOx-Si3N4-SiO2-Si metal-insulator-semiconductor (MIS) capacitor allows the detection of oxygen (O2) and carbon monoxide (CO) gases at a much lower operating temperature than that of the conventional solid-state gas detectors. The operation characteristics of the device for the detection of O2 and CO are described as a function of the gas pressure and temperature ranging from 27 to 100 °C. Repeatability of the device for CO detection in an open air ambient is also presented. A model based on adsorption/reaction of oxygen ions at the Pt-SnOx interface of the MIS capacitor is proposed for oxygen/carbon monoxide detection. The physical and chemical mechanisms responsible for the gas sensing behaviors are discussed. The detection mechanisms explain the device behaviors and account for the following experimental observations and reaction kinetic analysis of the experimental data: (1) the dependence of the reaction kinetics on the square root of the O2 partial pressure, (2) the requirement of oxygen as a constituent of the background gas for CO detection, (3) the inverse proportional relationship of the reaction kinetics to CO partial pressure, and (4) the need of Pt and SnOx as the catalytic layers in the MIS capacitor for gas detection.
The chemical oxidation of hydrogen-terminated silicon (111) surfaces in water studied in situ with Fourier transform infrared spectroscopy
Authors: Boonekamp E. P. , Kelly J. J. , van de Ven J. , Sondag A. H. M.
Published: July 2002

The chemical oxidation of hydrogen-terminated silicon (111) surfaces in water was studied in situ with Fourier transform IR spectroscopy in the multiple total internal reflection mode. On the basis of measurements of the absorbance of the Si-H and Si-O-Si vibrations as a function of time it is concluded that reactions involving the oxidation of silicon hydride and the formation of silicon oxide are coupled. The decrease in the hydride coverage and increase in the oxide coverage are linear functions of ln(t). The time dependence of oxide growth is explained in terms of electrostatic and mechanical changes at the Si/water interface.
Oxidation of polycrystalline silver films by hyperthermal oxygen atoms
Authors: Oakes D. B. , Krech R. H. , Upschulte B. L. , Caledonia G. E.
Published: July 2002

Results of the oxidation of polycrystalline silver films with hyperthermal (8–12 km/s) oxygen atoms are presented. The oxidation process is monitored using two techniques. The mass gain of a silver film is measured with a quartz crystal microbalance (QCM) and the resistance of a thin strip of the polycrystalline film is monitored during the oxidation process. These silver film monitors are to be used in atomic oxygen flux measurements. We have found the QCM to be the more reliable monitor of hyperthermal atomic oxygen for reasons discussed herein. Mass uptake measurements of films with a known silver mass loading in addition to x-ray diffraction analysis of the resulting oxides have identified the oxide as Ag2O2. The reaction probability of 8 km/s oxygen atoms with the silver films is shown to be greater than 0.5. No oxygen atom velocity dependence was observed for the oxidation rate over the range 8–12 km/s, nor was a temperature dependence observed between 0 and 85 °C. Oxidation is shown to be diffusion limited after an oxide layer of ∼250 Å thick has formed.
Hybrid Monte Carlo-fluid model of a direct current glow discharge
Authors: Bogaerts A. , Gijbels R. , Goedheer W. J.
Published: July 2002

A self-consistent hybrid Monte Carlo-fluid model for a direct current glow discharge is presented. The Monte Carlo part simulates the fast electrons while the fluid part describes the ions and slow electrons. Typical results of the model include collision rates of the fast electrons, energy distributions of these electrons, fluxes and densities of the different plasma species, the electric field and the potential distribution, all as a function of position from the cathode. The influence of the negative glow on the calculations in the cathode dark space is studied. Moreover the influence of three-dimensional scattering instead of forward scattering and the incorporation of side wall effects is investigated. Calculations are carried out for a range of voltages and pressures in order to study their influence on the calculated quantities. Comparison was made between total electrical currents calculated in the model and experimentally measured ones to check the validity of the model.
Polarization effects of a high-power CO2 laser beam on aluminum alloy weldability
Authors: Sato Shunichi , Takahashi Kunimitsu , Mehmetli Bülent
Published: July 2002

Linearly polarized CO2 laser beams have been used to investigate the effects of polarization on aluminum alloy weldability. Bead-on-plate welding tests have been performed on A5083 (AlMg4.5Mn0.7) alloy plates with quasi-TEM00-mode beams whose polarization direction is parallel or perpendicular to the welding direction, referred to as the parallel or the perpendicular polarization beam, respectively. Comparison of the fusion zone shapes between the two cases shows that deeper penetration, and hence more efficient optical energy coupling to the work can be obtained with the parallel polarization beam. This effect can be interpreted as being due to the higher Fresnel absorption at the keyhole front wall for the parallel polarization beam than for the perpendicular polarization beam. It is also found that the polarization effect is much more evident in the case of He gas shielding than in the case of Ar gas shielding. The weaker polarization effects observed in the case of Ar may be due to more densely formed laser-induced plume or plasma because of lower ionization potential and much smaller thermal conductivity of Ar when compared with those of He. Under such conditions the energy coupling may be dominated by plasma absorption (the inverse bremsstrahlung absorption). It has so far been considered that in aluminum welding, the energy coupling is dominated by the plasma absorption, because relatively strong plasma is observed in aluminum welding. But our results indicate that the Fresnel absorption process has an important role on the energy coupling mechanism under certain conditions.
An experimental investigation of electromechanical responses in a polyurethane elastomer
Authors: Zhang Q. M. , Su J. , Kim Chy Hyung , Ting R. , Capps Rodger
Published: July 2002

The electromechanical response of a polyurethane elastomer was investigated at room temperature and in the temperature range near its glass transition. It was found that the Maxwell stress contribution to the strain response can be significant at temperatures higher than the glass transition temperature. In addition, the material exhibits a very high electrostrictive coefficient Q, about two orders of magnitude higher than that of polyvinylidene fluoride. It was also found that in a polymeric material, the chain segment motions can be divided into those related to the polarization response and those related to the mechanical response and the overlap between the two yields the electromechanical response of the material. In general, the activation energies for different types of motion can be different, resulting in different relaxation times in the dielectric, the elastic compliance, and the electrostrictive data, as observed in the polyurethane elastomer investigated. The experimental results indicate that at the temperatures investigated, the activation energy for the mechanical related segment motions is higher than that of nonmechanical related segment motions.
Photon recycling and Shockley’s diode equation
Authors: Martı́ A. , Balenzategui J. L. , Reyna R. F.
Published: July 2002

The Shockley’s diode equation predicts a current-voltage characteristic different from that used by Shockley and Queisser to compute the limiting efficiency of photovoltaic energy conversion under the assumptions of the detailed balance theory. The reasons for such discrepancy are discussed being the neglect of photon recycling effects in Shockley’s diode equation the main cause. This interpretation is crucial to understand the fundamentals on which the computation of the limiting efficiency of solar cells is based. Without photon recycling effects, it can be concluded that the limiting efficiency (one sun) of a gallium arsenide solar cell is 26.8% (with the sun assumed as blackbody at 6000 K) while the true figure is 30.7%, 38.7% as long as the angle of emission of photons from the cell is fully restricted.
Determination of vacancy concentrations in the bulk of silicon wafers by platinum diffusion experiments
Authors: Jacob M. , Pichler P. , Ryssel H. , Falster R.
Published: July 2002

Diffusion of platinum at low temperatures is a convenient way to characterize vacancy profiles in silicon. This article summarizes the experiments performed to find a standard procedure, discusses the pitfalls and limitations, and shows the applicability of the method. The results of experiments with float-zone and Czochralski-grown samples in the temperature range from 680 to 842 °C were found to disagree with the predictions of models published in the literature. Therefore, parameters governing the diffusion of point defects and platinum in silicon were determined for this temperature range.
Piezoelectrically forced vibrations of rectangular SC-cut quartz plates
Authors: Lee P. C. Y. , Lin W. S.
Published: July 2002

A system of two-dimensional first-order equations for piezoelectric crystal plates with general symmetry and with electroded faces was recently deduced from the three-dimensional equations of linear piezoelectricity. Solutions of these equations for AT-cut plates of quartz were shown to give accurate dispersion curves without corrections, and the resonances predicted agree closely with the experimental data of Koga and Fukuyo [I. Koga and H. Fukuyo, J. Inst. Electr. Commun. Eng. Jpn. 36, 59 (1953)] and that of Nakazawa, Horiuchi, and Ito (M. Nakazawa, K. Horiuchi, and H. Ito, Proceedings of the 1990 IEEE Ultrasonics Symposium, pp. 547–555). In this article, these equations are employed to study the free as well as the forced vibrations of doubly rotated quartz plates. Solutions of straight-crested vibrational modes varying in the x1 and x3 directions of SC-cut quartz plates of infinite extent are obtained and from which dispersion curves are computed. Comparison of those dispersion curves with those from the three-dimensional equations shows that the agreement is very close without any corrections. Resonance frequencies for free vibrations and capacitance ratios for piezoelectrically forced vibrations are computed and examined for various length-to-thickness or width-to-thickness ratios of rectangular SC-cut quartz plates. The capacitance ratio as a function of forcing frequency is computed for a rectangular AT-cut quartz and compared with the experimental data of Seikimoto, Watanabe, and Nakazawa (H. Sekimoto, Y. Watanabe, and M. Nakazawa, Proceedings of the 1992 IEEE Frequency Control Symposium, pp. 532–536) and is in close agreement.
Store–restore operation of flux quanta in coplanar type high Tc superconductive quantum interference devices
Authors: Fuke Hiroyuki , Saitoh Kazuo , Utagawa Tadashi , Enomoto Youichi
Published: July 2002

For a superconductive quantum interference device (SQUID) with rather large loop inductance for a single flux quantum, store–restore operation of flux quanta has been examined by external current pulses. To sense the stored flux quanta, the device includes another directly coupled SQUID as a magnetometer. Both of the coplanar type dc SQUIDs have been composed of Josephson junctions made by the narrow-focused ion beam irradiation technique in single-layer NdBa2Cu3O7−δ superconducting films. The SQUID has a critical current of 375 μA and an inductive parameter (βL) of 32. The number of stored flux quanta is controlled by the pulse signal height and the input terminal, but not by the number of pulses.
Difference in the behavior of oxygen deficient defects in Ge-doped silica optical fiber preforms under ArF and KrF excimer laser irradiation
Authors: Essid M. , Brebner J. L. , Albert J. , Awazu K.
Published: July 2002

Photobleaching of optical absorption bands in the 5 eV region and the creation of others at higher and lower energy have been examined in the case of ArF (6.4 eV) and KrF (5 eV) excimer laser irradiation of 3GeO2:97SiO2 glasses. We report a difference in the transformation process of the neutral oxygen monovacancy and also of the germanium lone pair center (GLPC) into electron trap centers associated with fourfold coordinated Ge ions and Ge-E′ centers when we use one or the other laser. Correlations between absorption bands and electron spin resonance signals were made after different steps of laser irradiation. It was found that the KrF laser generates twice as many Ge-E′ centers as the ArF laser for the same dose of energy delivered. The main reason for this difference is found to be the more efficient bleaching of the GLPC (5.14 eV) by the KrF laser compared to that by the ArF laser.
A few remarks on the electrostriction of elastomers
Authors: Krakovský I. , Romijn T. , Posthuma de Boer A.
Published: July 2002

The electromechanical behavior of isotropic dielectrics with emphasis on cross-linked polymers (elastomers) as a special case is briefly discussed. Errors often committed in the derivation of expressions used in interpretation of experimental results are pointed out.
Microstructure and domain structures of Sm0.56GdxDy0.44−x(Co0.68Fe0.22Cu0.08Zr0.02)7.22 magnets with low temperature coefficients
Authors: Yang Jinbo , Ji Changguo , Mao Weihua , Yang Yingchang , Xu Hai , Han Baoshan , Li Wei , Yu Xiaojun
Published: July 2002

The microstructure and domain structures of high performance temperature-compensated sintered magnets with composition of Sm0.56GdxDy0.44−x(TM)7.22 (TM=Co0.68Fe0.22Cu0.08Zr0.02)7.22 (0.0⩽x⩽0.4) have been investigated by using electron microscopy and magnetic force microscopy. Both microstructure and magnetic properties of these magnets show a significant dependence on the content of heavy rare earth Gd and Dy. The intrinsic coercive force increases significantly with increasing Gd content. It is found that there are two different types of grains in the magnets, which show different domain structures. The larger magnetocrystalline anisotropy, larger cell size, and coarser grain boundary region give rise to a higher coercivity in the Gd-rich magnets.
Effects of phase separation and decomposition on the minority carrier diffusion length in AlxGa1−xN films
Authors: Cremades A. , Albrecht M. , Krinke J. , Dimitrov R. , Stutzmann M. , Strunk H. P.
Published: July 2002

Combined electron beam induced current and transmission electron microscopy (TEM) measurements have been performed on both undoped and Si-doped AlGaN epitaxial films with aluminum contents x ranging from x=0 to x=0.79, in order to correlate the electrical and structural properties of the films. The diffusion length of holes in the films ranges between 0.3 and 15.9 μm, and the estimated lifetime of holes for doped samples varies between 0.2 ns and 16 μs. Different effects contribute to the observed increase in the diffusion length with increasing aluminum content. Among others, dislocations seem to be active as nonradiative recombination sites, and phase separation and decomposition as observed by TEM in Al-rich alloys lead to the formation of a spatially indirect recombination path due to the piezoelectric field in the films. Potential fluctuations associated with these phase irregularities could also give rise to electron induced persistent conductivity contributing to the increase of the diffusion length. From our experimental observations, we conclude that the silicon dopants are partially activated in Al-rich alloys, and do not influence significantly the values of the diffusion length of holes in these samples.
Charge control and mobility in AlGaN/GaN transistors: Experimental and theoretical studies
Authors: Zhang Yifei , Smorchkova I. P. , Elsass C. R. , Keller Stacia , Ibbetson James P. , Denbaars Steven , Mishra Umesh K. , Singh Jasprit
Published: July 2002

In this article we report on two dimensional sheet charge and mobility in GaN/AlGaN heterostructure field effect transistors. Both experimental and theoretical results are presented. Experimental results are reported on samples grown by metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Theoretical studies are done to examine how spontaneous polarization and piezoelectric effect control the sheet charge density. The studies also focus on how interface roughness, aluminum mole fraction in the barrier and phonon scattering influence mobility. We find that interface roughness is a dominant source of scattering in the samples reported. Due to the variation in growth techniques we find that the MBE samples have a smoother interface compared to the MOCVD samples. By carefully fitting the experimental data we present results on interface roughness parameters for MBE and MOCVD samples.
Magnetic circular dichroism of low symmetry cupric sites
Authors: Gerstman Bernard S. , Brill Arthur S.
Published: July 2002

General properties of the MCD of cupric ions in ligand fields of low symmetry are described. C terms arising from spin-orbit coupling are dominant at liquid helium temperatures If spin-orbit coupling of the excited states to the ground state is negligible compared with spin-orbit coupling of the excited states among themselves, then the C values for the transitions sum to zero. It follows that nonvanishing of the sum of the C values over all transitions is due to spin-orbit coupling with the ground state. This net rotational offset is calculated for hybrid orbital ‘‘united atom’’ models of the electronic states of the metal–ligand complexes. Simulations of C term spectra from hybrid atomic orbital models illustrate relations between MCD features and properties of low symmetry cupric sites.
Selectivity in coherent transient Raman measurements of vibrational dephasing in liquids
Authors: Loring Roger F. , Mukamel Shaul
Published: July 2002

The microscopic information content of coherent transient Raman measurements is analyzed. It is shown that for short pulses and optically thin samples the Kaiser–Laubereau pulse sequence is the Raman analog of the optical free induction decay, and that the experimental observable contains the same dynamical information as the isotropic, spontaneous Raman line shape. Under these conditions, the experiment therefore cannot be used to selectively measure the homogeneous dephasing time of a system with an inhomogeneously broadened line. The results of our analysis are at variance with the earlier results of Kaiser and Laubereau and the more recent predictions of Oxtoby. However, these experiments, under certain circumstances, may be used to obtain a nonselective line narrowing, as found by Zinth, Polland, Laubereau, and Kaiser. We also consider the situation in which the sample is optically dense, in which case laser depletion must be taken into account. The distinction between saturation of the vibrational transition and depletion of the pump pulse is discussed, and selectivity is shown to arise from the former phenomenon, rather than from the latter. This result is at variance with the predictions of George and Harris. An alternative pulse sequence, the Raman echo, is suggested as a tool to achieve selectivity. A unified theory of the Raman echo is developed, which is valid for a bath with arbitrary time scale and which interpolates between the limits of homogeneous and inhomogeneous line broadening.
Influence of the mean free path of reactant particles on the kinetics of diffusion-controlled reactions. II. Rate of bulk recombination
Authors: Tachiya M.
Published: July 2002

The rate constant of bulk recombination of neutral particles was calculated over the whole range of their mean free path l by use of Monte Carlo techniques. The results depend drastically on whether one uses the space criterion or the energy criterion for the accomplishment of reaction, especially when l→∞.
Fourth-order Mo/ller–Plessett perturbation theory in the local correlation treatment. I. Method
Authors: Saebo/ Svein , Pulay Peter
Published: July 2002

Fourth-order Mo/ller–Plesset perturbation theory (MP4) is formulated for localized internal orbitals of closed-shell systems. Unlike previous localized perturbation theories, our formulation is strictly identical with canonical MP4 theory if no further approximations are made. In the local treatment, large savings can be achieved by two techniques: (1) neglecting or treating at a lower (second order) level pair correlation between distant pairs, and (2) restricting the correlation basis to the atomic orbitals in the spatial vicinity of the correlated pair. These techniques have been used in our previous local correlation treatment for variational CI, coupled electron pair (CEPA), and approximate coupled cluster (ACCD) wave functions. The MP4 method is more economical than these techniques because of the absence of iterative cycles. Implementation with single, double, and quadruple substitutions is discussed.
Kinetics of diffusion-influenced bimolecular reactions in solution. II. Effects of the gating mode and orientation-dependent reactivity
Authors: Lee Sangyoub , Karplus Martin
Published: July 2002

The formalism presented in the preceding paper is applied to investigate the combined effects of gating modes and orientation-dependent reactivity on the rate of diffusion-influenced bimolecular reactions. A general expression for the rate coefficient is derived for reactions involving a sink function that is highly localized along the orientational and gating coordinates. For reactions involving spherical molecules, of which one species has a diffusive gating coordinate, the expression for the rate coefficient is evaluated analytically. For the general case involving arbitrarily complicated molecules, a methodology for evaluating the expression for the rate coefficient by Brownian dynamics simulations is described, and test results on two simple model reactions are presented. For these cases the present method converges more rapidly than other Brownian dynamics approaches.
A new efficient method for calculation of energy eigenvalues and eigenstates of the one-dimensional Schrödinger equation
Authors: Lindberg Bengt
Published: July 2002

A method for the numerical solution of the one-dimensional Schrödinger equation based on a matrix formulation of Numerov’s method is described. Some matrix theory leading to an efficient algorithm for the slicing of the spectrum of the related eigenproblem for a pair of tridiagonal matrices is developed. Finally the application of defect correction to the discretization gives a method of order of accuracy eight. Results of example calculations are presented.
The Raman spectra of polycrystalline orthorhombic YF3, SmF3, HoF3, YbF3, and single crystal TbF3
Authors: Wilmarth W. R. , Begun G. M. , Nave S. E. , Peterson J. R.
Published: July 2002

The Raman spectra of the orthorhombic form of polycrystalline YF3, SmF3, TbF3, HoF3, and YbF3 have been recorded. Room-temperature, polarized Raman spectra of a single crystal of orthorhombic TbF3 have also been obtained. Based on these polarized Raman spectra, symmetry assignments have been made for 23 of the expected 24 Raman active phonon vibrations in TbF3. By analogy to the results from single crystal TbF3, tentative symmetry assignments of the observed phonon vibrations were also made for the other compounds included in this work.
An electron diffraction study of alkali fluoride vapors
Authors: Hartley J. G. , Fink M.
Published: July 2002

The structures of NaF, KF, RbF, and CsF in the vapor phase were determined via standard electron diffraction counting techniques with nozzle temperatures ranging from 798 to 1123 K. The reactivity of the fluorides combined with the higher temperature requirements necessitated a new nozzle design as well as modification to the oven. The data analysis yielded the structure parameters and the ratio of monomeric to dimeric compounds. The mean amplitudes of vibration of the monomeric molecules were held at values based on microwave frequencies and the harmonic potential approximation. The corrected monomer distances re agree well with microwave-spectroscopy results. Rhombic geometries with bonded dimer distances ranging from 2.08 to 2.70 Å were observed. The F–M–F bond angles were found to be nearly constant, varying only from 82.2° to 85.5°. The dimer mole fractions in the vapor were observed to vary from 5% to 18%. There were no significant amounts of any trimeric species observed in the vapor. The observed dimer mole fractions were compared with existing measurements from velocity selection experiments and found to be in excellent agreement. The dimer mole fractions were also compared with various theoretical predictions.
Relationships in the approach to criticality in fluids, including systematic differences between vapor–liquid and liquid–liquid systems
Authors: Singh Rajiv R. , Pitzer Kenneth S.
Published: July 2002

The available data on a number of vapor–liquid and liquid–liquid systems have been reexamined. The effective critical exponent is used to describe the approach to criticality for the two types of systems. The liquid–liquid critical systems have a small or zero first Wegner correction term, and are similar in this respect to the spin 1/2 Ising lattice. The gas–liquid critical systems have a much larger first Wegner term and are qualitatively similar to a high spin Ising lattice. By analyzing data for a number of fluids, we find strong support for a universal value for the first Wegner coefficient for vapor–liquid coexistence in simple fluids. The higher correction terms are substance dependent. These statements do not apply to ionic fluids which have quite different properties. The extent to which metals differ or are similar is examined briefly. The substance dependence of the leading critical amplitudes has also been examined with reference to the extensions of the corresponding states theorem. An approximate linear dependence of the amplitude on the acentric factor of the fluid is found.
A theoretical and experimental study of forces between charged mica surfaces in aqueous CaCl2 solutions
Authors: Kjellander R. , Marčelja S. , Pashley R. M. , Quirk J. P.
Published: July 2002

The interaction between two mica surfaces immersed in CaCl2 solutions has been directly measured. Accurate theoretical calculations, including the anisotropic hypernetted chain (HNC) theory used in this work, predict that at reasonably high surface charge densities the electrical double layer interactions in the presence of divalent counterions should be attractive at short surface separations (in the range 0.6–2 nm). Under most conditions investigated, the experimental results indicate that this indeed is the case. The attraction is a consequence of the correlation between the ions. In addition to the double layer interaction, in most cases the measured force contains an oscillatory contribution. At low CaCl2 concentrations and small surface separations, Ca2+ ions between the surfaces are exchanged for H3O+ ions, which decreases the oscillatory interaction and the ion-correlation attraction. At high concentrations the force is dominated by a strong hydration repulsion, which is related to the adoration of Ca2+ ions onto the mica surface. These complications are not considered in the theoretical treatment—which uses the primitive model for the electrolyte—but the ion-correlation attraction is sufficiently prominent to be detected by surface force measurements. The accuracy of the anisotropic HNC theory for 2:1 electrolytes in the primitive model has been checked by comparing calculated ionic concentration profiles with those obtained by Monte Carlo simulations for identical systems. The agreement is excellent.