bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining species composition in mixed-species marks: an example from the New Zealand hoki (Macruronus novaezelandiae) fishery
Authors: O'Driscoll Richard L
Published: June 2003

A model-based method has been developed for partitioning acoustic backscatter from mixed-species marks. This method uses catch-composition data to partition the echo integral, but allows for differences in trawl catchability and acoustic vulnerability between species. It was applied to estimate the biomass of New Zealand hoki (Macruronus novaezelandiae) from trawl and acoustic surveys on the Chatham Rise and Campbell Plateau in 2001. Mixed-species layers containing up to 20 different species were present in both survey areas. A total of 224 bottom-trawl surveys (123 on Chatham Rise and 101 on Campbell Plateau) were carried out to determine the species composition and relative densities. Simultaneous acoustic recordings made during each of these trawls were used to estimate vulnerability ratios for the two methods, i.e. acoustic as opposed to trawl surveys, (acoustic:trawl) by non-negative, least-squares minimization. The best-fit model for each survey attributed 14–22% of the backscatter in mixed layers within 10 m of the bottom to hoki. This produced hoki biomass estimates 1.3–1.8 times higher than the standard approach, which divides the echo integral in proportion to the catch assuming equal trawl catchability. The precision of the estimated acoustic:trawl vulnerability ratios depended on the contrast in trawl catch composition, and the ratios for the same species differed between areas. A major problem on the Chatham Rise was the acoustic contribution of small mesopelagic species, which are not caught by the bottom trawl. Despite these difficulties, the model-based approach has good potential for determining the biomass of the target species in a mixed-species mark when the different species cannot be discriminated acoustically.
Autonomous underwater vehicles: future platforms for fisheries acoustics
Authors: Fernandes Paul G , Stevenson Pete , Brierley Andrew S , Armstrong Frederick , Simmonds E.John
Published: June 2003

Autonomous underwater vehicles (AUVs) are unmanned submersibles that can be pre-programmed to navigate in three dimensions under water. The technological advances required for reliable deployment, mission control, performance, and recovery of AUVs have developed considerably over the past 10 years. Currently, there are several vehicles operating successfully in the offshore industries as well as in the applied and academic oceanographic sciences. This article reviews the application of AUVs to fisheries- and plankton-acoustics research. Specifications of the main AUVs currently in operation are given. Compared to traditional platforms for acoustic instruments, AUVs can sample previously impenetrable environments such as the sea surface, the deep sea, and under-sea ice. Furthermore, AUVs are typically small, quiet, and have the potential to operate at low cost and be unconstrained by the vagaries of weather. Examples of how these traits may be utilized in fisheries-acoustics science are given with reference to previous work in the North Sea and Southern Ocean and to potential future applications. Concurrent advances in multi-beam sonar technology and species identification, using multi-frequency and broadband sonars, will further enhance the utility of AUVs for fisheries acoustics. However, before many of the more prospective applications can be accomplished, advances in power-source technology are required to increase the range of operation. The paper ends by considering developments that may turn AUVs from objects sometimes perceived as science fiction into instruments used routinely to gather scientific facts.
Macrobubble clouds produced by breaking wind waves: A laboratory study
Authors: Kalvoda Peter M. , Xu Lilun , Wu Jin
Published: June 2003

Clouds of large air bubbles produced by breaking wind waves have been studied in a laboratory tank. Temporal evolutions of these macrobubble clouds, including their length scales, aspect ratios, area scales, and velocities, are presented; the bubble concentration and void ratio within the cloud are also found. The initial downwind velocity of the cloud is about one half, but can reach about two thirds, the phase velocity of the breaking wave. The maximum penetrating depth of the cloud is about one half the breaking wave height. All these geometric and kinematic characteristics of the cloud are also associated with those of the breaking wave.
Improved simulations of snow extent in the second phase of the Atmospheric Model Intercomparison Project (AMIP‐2)
Authors: Frei Allan , Miller James A. , Robinson David A.
Published: June 2003

Simulations of snow‐covered area (SCA) over Northern Hemisphere lands by a suite of general circulation models (GCMs) are evaluated. Results from GCM experiments submitted by an international array of research groups participating in the second phase of the Atmospheric Model Intercomparison Project (AMIP‐2) are compared to a data set derived primarily from visible band satellite imagery provided by the United States National Oceanic and Atmospheric Administration. At continental to hemispheric scales we find improvements over AMIP‐1 models, including the elimination of temporal and spatial biases in simulations of the seasonal cycle of SCA, as well as improved simulations of the magnitude of interannual variability. At regional spatial scales, while no consistent model biases are identified over North America, regions over Eurasia are identified where models consistently either underestimate or overestimate SCA at the southern boundary of the seasonal snowpack. The region of greatest model bias is eastern Asia. While SCA biases are associated with temperature and precipitation biases, over only one region do we find a relationship between the magnitudes of SCA biases and the magnitudes of temperature and/or precipitation biases.
Evidence for a dominant native source of carbon monoxide in Comet C/1996 B2 (Hyakutake)
Authors: DiSanti Michael A. , Mumma Michael J. , Dello Russo Neil , Magee‐Sauer Karen , Griep David M.
Published: June 2003

Carbon monoxide was measured in C/1996 B2 (Hyakutake) on four preperihelion dates, UT 1996 March 24.5 and April 10.2–12.2, using CSHELL at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. These observations provided the first secure ground‐based detection of cometary CO at infrared wavelengths. The rotational temperatures retrieved for CO are consistent with a heliocentric dependence Trot = 63 Rh−1.06 K over the range Rh = 1.06–0.64 AU. From long‐slit analysis we distinguish native and distributed sources of CO, and we infer the relative abundance of native to total CO to be 0.773 ± 0.054 on April 12.2. If this ratio is constant on UT April 11.2 and 12.2, the mean mixing ratios (relative to water) are 0.149 ± 0.019 for native CO and 0.191 ± 0.022 for the sum of native and extended sources. These mixing ratios are based on direct measurements of H2O made on the same dates with the same instrument and analyzed with the same data processing algorithms. The observed spatial scale for complete development of the extended source on UT 1996 April 12.2 was consistent with that observed for C/1995 O1 (Hale‐Bopp) on UT 1997 January 21, after taking into account differences in outflow velocity and heliocentric distance assuming insolation‐limited release. This may suggest similar progenitor material in these two comets.
A Born‐Oppenheimer photolysis model of N2O fractionation
Authors: Blake Geoffrey A. , Liang Mao‐Chang , Morgan Christopher G. , Yung Yuk L.
Published: June 2003

The isotopically light N2O produced by microbial activity is thought to be balanced by the return of heavy stratospheric nitrous oxide. The Yung and Miller [1997] method that first explained these trends yields photolytic fractionation factors ∼half those observed by experiment or predicted quantum mechanically, however. To address these issues, we present here a Born‐Oppenheimer photolysis model that uses only commonly available spectroscopic data. The predicted fractionations quantitatively reproduce laboratory data, and have been incorporated into zonally averaged atmospheric simulations. Like McLinden et al. [2003], who employ a three‐dimensional chemical transport model with cross sections scaled to match laboratory data, we find excellent agreement between predictions and stratospheric measurements; additional processes that contribute to the mass independent anomaly in N2O can only account for a fraction of its global budget.
Cross‐correlation between length and position in real fracture networks
Authors: Darcel C. , Bour O. , Davy P.
Published: June 2003

By analyzing local geometrical properties of a dense multiscale fracture pattern, we characterized statistically the correlations between length and position of a fracture. Apart from some resolution effects, we show that the mean distance between a fracture center and its nearest neighbor is correlated to its length l such as d ∼ l0.3. Likewise, the average area around each fracture center within which no other fracture portion is lying has an ellipsoidal shape whose factor of anisotropy is correlated to l. The long axis, along fracture strike, is correlated to l such as d ∼ l0. 25–0.3. The short axis remains invariant, about equal to the equivalent distance in a random fractal. At small scale (i.e., less than 1 m which is bed thickness) the shield area is isotropic. In addition to refining of geometrical model of fracture networks, such observations place some constraints on the stress interactions that prevail during fracture growth.
Regulation of membrane-type 1 matrix metalloproteinase activity by vacuolar H+-ATPases
Authors: MAQUOI Erik , PEYROLLIER Karine , NOËL Agnès , FOIDART Jean-Michel , FRANKENNE Francis
Published: June 2003

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is a key enzyme in normal development and malignant processes. The regulation of MT1-MMP activity on the cell surface is a complex process involving autocatalytic processing, tissue inhibitor of MMPs (TIMP) binding and constitutive internalization. However, the fate of internalized MT1-MMP is not known. Acidification of intracellular vacuolar compartments is essential for membrane trafficking, protein sorting and degradation. This acidification is controlled by vacuolar H+-ATPases, which can be selectively inhibited by bafilomycin-A1. Here, we treated human tumour cell lines expressing MT1-MMP with bafilomycin-A1, and analysed its effects on MT1-MMP activity, internalization and processing. We show that the activity of MT1-MMP on the cell surface is constitutively down-regulated through a vacuolar H+-ATPase-dependent degradation process. Blockade of this degradation caused the accumulation of TIMP-free active MT1-MMP molecules on the cell surface, although internalization was not affected. As a consequence of this impaired degradation, pro-MMP-2 activation was strongly enhanced. This study demonstrates that the catalytic activity of MT1-MMP on the cell surface is regulated through a vacuolar H+-ATPase-dependent degradation process.
Visualizing Geographic Information: VisualPoints vs CartoDraw
Authors: Keim Daniel A. , North Stephen C. , Panse Christian , Schneidewind Jörn
Published: June 2003

Cartograms are a well-known technique for showing geography-related statistical information, such as population demographics and epidemiological data. The basic idea is to distort a map by resizing its regions according to a statistical parameter, but in a way that keeps the map recognizable. In this paper, we deal with the problem of making continuous cartograms that strictly retain the topology of the input mesh. We compare two algorithms that solve the continuous cartogram problem. The first one uses an iterative relocation of vertices based on scanlines. This algorithm explicitly accounts for induced shape error. The second one is based on the Gridfit technique, which uses pixel-based distortion based on a quadtree-like data structure. The basic idea is to insert pixels, the number of which corresponds to a statistical parameter, into the data structure and distort the pixels such that every pixel obtains a unique, nonoverlapping position. Relocation of vertices of the map are positioned using the same distortion. We discuss the results obtained from both methods, compare their shape and area trade-offs as well as their efficiency, and show results from different applications.
Structural and thermal properties of silicon-doped fullerenes
Authors: Marcos P. A. , Alonso J. A. , Molina L. M. , Rubio A. , López M. J.
Published: June 2003

Extensive Molecular Dynamics simulations have been performed to investigate the structural and thermal properties of Si-doped fullerenes containing one and two silicon atoms. Both, a many-body potential and ab initio Density Functional Theory (DFT) have been used to investigate the structural features of the heterofullerenes. The competition between the exohedral and the substitutional types of doping, as a function of fullerene size (both even and odd heterofullerenes have been considered) and Si concentration, is analyzed. The DFT calculations confirm the main structural trends obtained with the many-body potential. The thermal stability and the structural transformations of the heterofullerenes have been also studied as a function of temperature (T=0–5000 K). The structural transformations include, local rearrangement of atoms, isomerization transitions, diffusion of atoms, eventual destruction of the cage, and sublimation of atoms. The isomerization transition between exohedral and substitutional isomers has been observed experimentally.
Spatial and temperature dependence of the spectroscopic profile of a magnetic atom adsorbed on a metal surface—Co/Cu(111)
Authors: Shimada Yuki , Kasai Hideaki , Nakanishi Hiroshi , Agerico Diño Wilson , Okiji Ayao , Hasegawa Yukio
Published: June 2003

As a representative Kondo system, consisting of a magnetic atom adsorbed on a metal surface, we consider a Co adatom on a Cu(111) surface. We introduce general expressions for the tunneling current and the differential conductance dI/dV, and discuss the corresponding spatial and temperature dependencies of the dI/dV line shapes that can be observed when the system is probed with a scanning tunneling microscope (STM). Starting with the STM tip sufficiently far from the Co adatom, the corresponding dI/dV line shape initially has an asymmetric structure about the Fermi level, which gradually becomes symmetric with decreasing STM tip–Co adatom distance, due to the competition between first-order (direct electron tunneling from the STM tip to the metal surface) and second-order (via the magnetic adsorbate) tunneling processes. The corresponding line shape also shows a strong temperature dependence, increasing in width with increasing temperature. As an aid to studying and observing these temperature dependencies experimentally, we suggest the utility of considering the temperature dependence of the derivative of dI/dV with respect to the bias voltage V, i.e., the d2I/dV2 line shape.
Si
0.85
Ge
0.15
oxynitridation in nitric oxide/nitrous oxide ambient
Authors: Dasgupta Anindya , Takoudis Christos G. , Lei Yuanyuan , Browning Nigel D.
Published: June 2003

Low temperature, nitric oxide (NO)/nitrous oxide (N2O) aided, sub-35 Å Si0.85Ge0.15 oxynitrides have been grown at 550 and 650 °C, while the oxynitridation feed gases have been preheated to 900 and 1000 °C, respectively, before entering the reaction zone. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS) data suggest that NO-assisted oxynitridation incorporates more nitrogen than the N2O-assisted one, while there is minimal Ge segregation towards the dielectric/substrate interface in both oxynitridation processes. Moreover, SIMS results suggest that nitrogen is distributed throughout the film in contrast to high temperature Si oxynitridation, where nitrogen incorporation takes place near the dielectric/substrate interface. Z-contrast imaging with scanning transmission electron microscopy shows that the oxynitride grown in NO at 650 °C has a sharp interface with the bulk Si0.85Ge0.15, while the roughness of the dielectric/Si0.85Ge0.15 substrate interface is less than 2 Å. These results are discussed in the context of an overall mechanism of SiGe oxynitridation.
The influence of impurities on the growth of helium-induced cavities in silicon
Authors: Vishnyakov V. M. , Donnelly S. E. , Carter G.
Published: June 2003

The effects of implanted oxygen, carbon, nitrogen, and self-damage on the growth of helium-induced cavities in silicon during high-temperature annealing have been studied. Impurities and helium were implanted into silicon at room temperature. Annealing at temperatures above 1000 K converts small He-filled bubbles into larger empty voids. The mean void size after annealing for 30 min at 1173 K was significantly reduced by the presence of all three implanted impurities. In extreme cases, the mean void radius is reduced from 10 nm, for a pure He implant, to 2.8 nm in a C pre-implanted sample. On the other hand, self-ion damage, unless at or near the level sufficient to cause amorphization, does not significantly affect cavity growth during annealing. We speculate that the presence of impurities significantly reduces the movement of voids by pinning them to dislocations or impurity aggregates or by chemical reactions at the void surfaces.
Anion photoelectron spectroscopy of solvated transition state precursors
Authors: Gómez Harry , Meloni Giovanni , Madrid James , Neumark Daniel M.
Published: June 2003

Photoelectron (PE) spectra have been collected for the clustered bihalide anions XHX−•(M) (X=Br, I) and BrHI−•(M), where M=H2O, HBr, and HI, in order to probe the effects of strongly solvating species on the PE spectra of transition state precursor anions. The PE spectra of the XHX−•(H2O) ions show similar vibrational progressions as the spectra of the bare BrHBr− and IHI− anions, indicating that photodetachment of the bare and hydrated ions accesses similar XHX transition state geometries on the X+HX reaction potential energy surfaces. These results are consistent with electronic structure calculations that predict a double hydrogen-bonded XHX−•(H2O) structure in which the symmetry of the strong XHX− hydrogen bond is largely preserved. In contrast, PE spectra of BrHBr−(HBr)1,2 and IHI−(HI)1,2 indicate that the addition of a single HBr or HI disrupts the symmetric XHX− bond, resulting in structures of the form X−•(HX)n, and altering the geometry of the Franck–Condon region accessed on the neutral potential energy surfaces. Similarly, PE spectra of BrHI−•(HI) and BrHI−•(HBr) suggest anion structures of the form I−•(HBr)HI and I−•(HBr)2, respectively.
Study of excitonic ground state energies in coupled three-quantum dot systems for far-infrared laser applications
Authors: Lai Z. Y. , Shen W. Z.
Published: June 2003

Effective mass theory and variation method are used to calculate the ground state energies of excitons in coupled three-quantum dot (3-QD) systems. To calculate multicenter integrals involving two particle wave functions, a series of spheres are used to cover the coordinate space and further approximation has been made when the radii of the integral spheres are suitably selected around the three spherical QDs in near equal radius. The results obtained from the calculation of In0.5Ga0.5As/GaAs and GaAs/Al0.2Ga0.8As coupled 3-QD systems are basically in agreement with the experiments. Based on the energy level schemes in these systems, we make suggestions for the application of far-infrared and/or terahertz sources.
Photoionization and ab initio study of trichloromethylsilane
Authors: Lu K. T. , Ma C. I. , Chiang S. Y. , Chen J. M.
Published: June 2003

Dissociative ionization of Si(CH3)Cl3 has been investigated by photoionization mass spectrometry and calculations of molecular electronic structure. From the photoionization efficiency spectra of ions measured over an energy range 9–30 eV, we determined appearance energies of the parent cation and various fragment cations. The ionization energy of Si(CH3)Cl3 is 11.18 eV. A fragment SiCl3+ appears at 11.77 eV and a second fragment Si(CH3)Cl2+ at 12.02 eV. Molecular electronic calculations of structures and energies of the Si(CH3)Cl3+ radical cation and various fragment cations are made with GAUSSIAN-2 and GAUSSIAN-3 in the GAUSSIAN 98 package. Reaction energies for various fragmentation processes are computed, in satisfactory agreement with experimental data for dissociation. Results of these calculations are applied to establish dissociative photoionization channels of Si(CH3)Cl3 near the ionization threshold.
Combinatorial preparation and infrared screening of hydrogen sorbing metal alloys
Authors: Olk C. H. , Tibbetts G. G. , Simon D. , Moleski J. J.
Published: June 2003

We introduce the use of thin-film combinatorial methods to synthesize Mg-based hydrogen storage alloys and demonstrate the use of spatially resolved infrared imaging as a high throughput hydrogen storage candidate screening technique. Using a combination of pulsed laser deposition and magnetron sputtering, multicompositional samples were produced for hydrogen sorption studies. Analysis is presented of a sample that consists of 16 separate Mg–Ni–Fe ternary pads and 32 Mg–Ni or Mg–Fe binary pads. Hydrogen sorption related emissivity changes observed indicate a substantial decrease in hydriding temperatures, which sensitively depends on composition.
A quantitative theory and computational approach for the vibrational Stark effect
Authors: Brewer Scott H. , Franzen Stefan
Published: June 2003

Density functional theory (DFT) has been used to calculate the vibrational Stark tuning rates of a variety of nitriles and carbonyls in quantitative agreement with experimental values with a correction factor of f=1.1 for the local electric field. These calculations show that the vibrational Stark tuning rate has an anharmonic contribution and a contribution due to geometric distortions caused in the molecules due to the applied electric field. The anharmonic and geometric distortion components of the vibrational Stark tuning rate were calculated by the frequency dependence of the CN or CO stretching mode with varying applied electric fields by using the optimized structure in zero applied field or allowing the structure to optimize in the applied electric field, respectively. The changes in the calculated frequency of the CN or CO stretching mode, bond length, and dipole moment of this bond with varying applied electric fields are shown. The transition polarizability and the difference polarizability were also calculated by DFT for comparison to the experimental data on nitriles and carbonyls. The DFT calculations suggest that the sign of the transition polarizability is negative and this result in turn has an effect on the experimental data analysis since the sign of the transition polarizability is not determined by experiment.
Adsorption of methylchloride on Si(100) from first principles
Authors: Romero Aldo H. , Sbraccia Carlo , Silvestrelli Pier Luigi , Ancilotto Francesco
Published: June 2003

The chemisorption of methylchloride (CH3Cl) on Si(100) is studied from first principles. We find that, among a number of possible adsorption configurations, the lowest-energy structure is one in which the methylchloride molecule is dissociated into CH3 and Cl fragments which are bound to the two Si atoms of the same surface dimer. Our calculations show that dissociative chemisorption of methylchloride on Si(100) may proceed along different reaction paths characterized by different energy barriers that the system must overcome: some dissociation processes are mediated by a molecular precursor state and, at least in one case, we find that the dissociation process is nonactivated, in agreement with recent experimental findings. We have also generated, for many possible adsorption structures, theoretical scanning tunneling microscopy images which could facilitate the interpretation of experimental measurements.
Microstructure of thin tantalum films sputtered onto inclined substrates: Experiments and atomistic simulations
Authors: Dalla Torre J. , Gilmer G. H. , Windt D. L. , Kalyanaraman R. , Baumann F. H. , O’Sullivan P. L. , Sapjeta J. , Dı́az de la Rubia T. , Djafari Rouhani M.
Published: June 2003

We have combined experiments and atomistic modeling in order to better understand the growth and structure of metal films deposited onto sidewalls of trenches and vias. Using x-ray reflectance, atomic force microscopy, and high-resolution transmission electron microscopy to characterize the microstructure and morphology of Ta films grown by magnetron sputtering onto inclined substrates, we find that films deposited at larger incidence angles tend towards columnar microstructure with high roughness and low density. We have used a three-dimensional Monte Carlo model (ADEPT) to simulate the growth process, under conditions close to those investigated experimentally. A binary collision model is included in the Monte Carlo deposition procedure to describe the interaction of energetic particles with the surface. Examination of the film microstructure and morphology resulting from the simulations indicates that the energetic impinging particles are necessary to produce film densities comparable to those found experimentally. By including these effects, we thus find good agreement between the simulations and the experimental results.
Iron oxidation under the influence of phosphate thin films
Authors: Grosseau-Poussard J. L. , Panicaud B. , Pedraza F. , Renault P. O. , Silvain J. F.
Published: June 2003

Iron phosphate thin films have been obtained under controlled conditions by chemical conversion deposition. The films were formed on polycrystalline α-iron by immersion in acetone, as an organic solvent. After deposition, the films were investigated by x-ray photoelectron spectroscopy (XPS) and their influence on the thermal oxidation of α-iron was studied by means of in situ low incidence x-ray diffraction of synchrotron radiation. The study reveals interesting features related to the structure of both the phosphate and thermal oxide films. The XPS data suggest the iron phosphate to be constituted of long chains of phosphate groups PO43−; these groups being interconnected by Fe2+ and Fe3+ cations. X-ray diffraction measurements have shown a significant modification of the oxidation behavior of α-iron at 400 °C and atmospheric pressure, which is derived from the presence of the thin film: α-Fe2O3 formation is clearly enhanced to the detriment of Fe3O4, compared to the oxidation of pure iron in which Fe3O4 is the dominant phase. As the growth rate of the α-Fe2O3 layer is significantly reduced compared to that of Fe3O4, thus the phosphated layers may find niche applications in low-to-moderate temperature environments.
Influence of nonstoichiometry on long-range order and its measurement in (GaAs)1−xGe2x and related alloys
Authors: Holloway H.
Published: June 2003

The influence of nonstoichiometry on long-range order in metastable alloys of GaAs with Ge has been studied using Monte Carlo simulations and analytic approximations based on the Davis–Holloway stochastic growth model applied to a 〈111〉 growth direction. The results show that the direct effects of nonstoichiometry on long-range order are relatively small. However, deviations from stoichiometry comparable to those reported previously can introduce significant errors into x-ray measurements of the order parameter. It is shown that discrepancies between measured order parameters and those calculated using the growth model can be explained as arising from the unrecognized effects of nonstoichiometry on the x-ray measurements. An incidental result of the analysis is that the long-range order predicted by the Davis-Holloway model arises entirely from its prohibition of Ga-Ga nearest-neighbor pairs. Identical results are obtained with and without the additional prohibition of As-As nearest-neighbor pairs.
Shock compression of a free-electron gas
Authors: Nellis W. J.
Published: June 2003

The shock compression curve (Hugoniot) of a free-electron gas was calculated and evaluated numerically for a metal with a Fermi energy of 5 eV. Shock pressure, internal energy, and temperature were calculated as functions of compression. The Hugoniot curve has a limiting compression of fourfold of initial density and agrees with expected limiting values at small and large compressions. Above a compression of ∼3.3-fold of initial density, a shock pressure of ∼250 GPa (2.5 Mbar), and a temperature of ∼10 eV, free electrons are a nondegenerate ideal gas. Shock pressures of the free electron gas are a factor of 104 larger at all compressions than those of an ideal gas of nuclei with the same number density, indicative of the strong effect of Fermi–Dirac and Maxwell–Boltzmann statistics. This simple free-electron model calculates shock compression curves of Li and Na, which differ by ∼50% from experimental data, illustrating that interactions between electrons and nuclei must be taken into account, as expected.
Molecular gradients for the second-order generalized Van Vleck variant of multireference perturbation theory
Authors: Dudley Timothy J. , Khait Yuriy G. , Hoffmann Mark R.
Published: June 2003

Recently, a revised second-order generalized Van Vleck perturbation theory (GVVPT2) for the description of molecular electronic structure has been reported [J. Chem. Phys. 117, 4133 (2002)] that is both state selective and of the “perturb-then-diagonalize” type of multireference perturbation theory (MRPT). Herein, formulas for analytic derivatives of the GVVPT2 energy with respect to nuclear perturbations are presented, as are illustrative calculations on model problems. Specifically, it is shown that the modification of the energy denominator, which addresses the so-called intruder-state problem of MRPT, is analytically differentiable with respect to nuclear perturbation and only requires use of matrices available, or directly obtainable, from the underlying multiconfigurational self-consistent field calculation. The developed formalism takes full advantage of the theoretical and computational characteristics of the GVVPT2 energy. In particular, the calculations are performed directly in a spin-adapted basis and utilize the recently introduced concept of macroconfigurations. Moreover, the full flexibility of the energy calculations with respect to arbitrariness of reference—i.e., no restriction to complete active space self-consistent field—is retained. Test calculations on N2 and O3 comparing the analytic derivatives with the results of finite-difference calculations corroborate the formulas and implementation.
Analysis procedure for calculation of electron energy distribution functions from incoherent Thomson scattering spectra
Authors: Costa i Bricha E. , Graham W. G. , Morrow T. , Steen P. G. , Thompson C. E.
Published: June 2003

Incoherent Thomson scattering (ITS) provides a nonintrusive diagnostic for the determination of one-dimensional (1D) electron velocity distribution in plasmas. When the ITS spectrum is Gaussian its interpretation as a three-dimensional (3D) Maxwellian velocity distribution is straightforward. For more complex ITS line shapes derivation of the corresponding 3D velocity distribution and electron energy probability distribution function is more difficult. This article reviews current techniques and proposes an approach to making the transformation between a 1D velocity distribution and the corresponding 3D energy distribution. Previous approaches have either transformed the ITS spectra directly from a 1D distribution to a 3D or fitted two Gaussians assuming a Maxwellian or bi-Maxwellian distribution. Here, the measured ITS spectrum transformed into a 1D velocity distribution and the probability of finding a particle with speed within 0 and given value v is calculated. The differentiation of this probability function is shown to be the normalized electron velocity distribution function.
Simulation of amplified spontaneous emission in high gain KrF laser amplifiers
Authors: Lehmberg R. H. , Giuliani J. L.
Published: June 2003

High gain KrF amplifier simulations require a realistic model of amplified spontaneous emission (ASE). We have recently developed an accurate three-dimensional time-dependent code to model ASE and parasitic oscillations in the Nike and Electra amplifiers. It currently includes arbitrary specular reflections at all of the walls and can be easily extended to nonspecular reflections. It can also simulate the ASE that would be seen by another amplifier stage or a camera located outside the amplifier module. The code approximates the ASE light by a discrete set of ordinates or quasi-plane waves whose propagation vectors represent all directions, but cluster preferentially around the amplifier axis, where the gain is highest. At each grid point, it updates the directed intensity by adding an analytic solution of the radiation transport equation within time increment Δt to the earlier intensity at a “local look-back” (LLB) point; this point is located a distance cΔt back along the ordinate’s characteristic direction. Because the LLB does not generally lie at a grid point, interpolation is required to calculate the earlier flux. Trilinear interpolation is simple and computationally fast, but it can introduce numerical spatial diffusion in the specific intensity. This diffusion is usually tolerable, but it can be a significant limitation if one attempts to treat a problem where the operating conditions or ASE viewing position favor a narrow range of directions that are not parallel to one of the Cartesian axes. For those conditions, we use an alternative interpolation scheme based on the flux-corrected transport algorithm, which previously has been used only to treat shock wave propagation in fluids. This article describes the code in detail, then shows ASE simulations illustrating the code’s capabilities and the effects of transient excitation, diffusion, and gain narrowing.
Filamentation instability in a semiconductor laser
Authors: Amrita  , Sharma A. K.
Published: June 2003

In a semiconductor laser, a perturbation in the laser intensity, transverse to the direction of laser propagation, has a tendency to grow. The regions of higher intensity cause higher stimulated emission via electron–hole recombination, hence the electron density falls and gives rise to a higher refractive index. This region attracts power from neighbors causing growth of intensity perturbation.
Phase selective synthesis of gadolinium silicide films on Si(111) using an interfacial SiO2 layer
Authors: Chung K. B. , Choi Y. K. , Jang M. H. , Noh M. , Whang C. N.
Published: June 2003

We synthesized a single phase GdSi2 film on a Si(111) substrate with an interfacial SiO2 layer. In order to take account of the role of the interfacial SiO2 layer, systematic investigations on clean and oxidized Si substrates were done by using in situ reflection of high energy electron diffraction, x-ray diffraction, and atomic force microscopy of the silicides formed with post annealing. Our result showed that the interfacial SiO2 layer enhanced the structural transformation of the initial GdSi1.7 hexagonal phase into the GdSi2 orthorhombic phase above the decomposition temperature of SiO2(∼800 °C). We proposed a reaction mechanism for the GdSi2 film formation with the help of the interfacial SiO2 layer. The measured electrical resistivity of the Gd-silicide film strongly depends on the silicide phase.
Polarity determination for GaN/AlGaN/GaN heterostructures grown on (0001) sapphire by molecular beam epitaxy
Authors: Park Y. S. , Lee H. S. , Na J. H. , Kim H. J. , Si Sang Man , Kim Hwa-Mok , Kang T. W. , Oh Jae Eung
Published: June 2003

In order to study the formation of polarization-induced two-dimensional electron gases (2DEGs), GaN/AlGaN/GaN heterostructures with different polarity were grown on sapphire (0001) substrates by plasma-assisted molecular-beam epitaxy. The polarity of GaN layers can be changed from the normal N-polarity to a Ga-polarity surface by inserting a thin Al metal layer prior to the growth of AlN buffer layer. The surface stability of each lattice polarity film was studied by in situ reflection high-energy electron diffraction. The polarity of the films and the location of 2DEGs in the heterostructure have been evaluated by investigating the carrier concentration profiles in the GaN/AlGaN/GaN heterostructures. A simple model to explain the polarity change by a thin Al metal layer is proposed.
High-voltage multichannel rail gap switch triggered by corona discharges
Authors: Niedbalski Jorge
Published: June 2003

A simple trigger assembly designed to promote multichannel breakdown in a high-voltage low-inductance rail gap switch operating in a dc voltage hold-off mode is described. The switch is formed by two extended (rail) cylindrical electrodes, separated by spacing of 10 mm and pressurized with nitrogen or air up to about 0.5 bar. The gas breakdown in multiple sites of the interelectrode volume is initiated by preionization with ultraviolet radiation pulses simultaneously emitted from an array of circular orifices and is performed along one generatrix of the surface of a tabular electrode (cathode) which are generated in its interior by capacitively coupled (pulsed corona) discharges. The switch has been tested by discharging capacitors of 40 and 100 nF in an underdamped condition at voltages and peak currents up to 15 kV and 14 kA, respectively. The maximum energy transferred per shot was about 11 J. The trigger assembly allows one to arbitrarily select the number of channels to be formed just by varying the number of preionization sources (orifices) distributed in the cathode and as a result they are unaffected by the discharges.
Large remanent polarization of 100% polar-axis-oriented epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 thin films
Authors: Morioka Hitoshi , Asano Gouji , Oikawa Takahiro , Funakubo Hiroshi , Saito Keisuke
Published: June 2003

100% polar-axis (c-axis)-oriented epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) thin films were grown and their large remanent polarization (Pr) was directly measured. Perfectly c-axis-oriented epitaxial PZT thin films were obtained on (100)cSrRuO3//(100)SrTiO3 substrates when the deposition temperature increased to 540 °C together with a decrease in the film thickness down to 50 nm. Polarization–electric-field hysteresis loops were well saturated and had a square shape. The Pr of a 50 nm thick film saturated at 0.9 V, and its value was over 90 μC/cm2; almost independent of the measurement frequency within the range from 20 Hz to 1 kHz. This value was in good agreement with the estimated one from the a- and c-axes mixture-oriented epitaxial PZT film having the same composition taking into account the fact that only the c-axis-oriented domain contributed to the polarization. On the other hand, the coercive field value of a perfectly c-axis-oriented film was 140 kV/cm and almost the same as that of the mixture-oriented one having the same film thickness. These results show that PZT has a large Pr applicable for high-density ferroelectric random access memory.
Calculation of three-dimensional electromagnetic force field during arc welding
Authors: Kumar A. , DebRoy T.
Published: June 2003

Electromagnetic force is an important driving force for convection in the weld pool during arc welding. Accurate calculation of the electromagnetic force field requires complex numerical calculations of three-dimensional current density and magnetic flux fields. Several simplifying assumptions have been suggested to avoid the complex calculations. The resulting analytical expressions for the electromagnetic force field have been widely used without any critical evaluation of their intrinsic merit, since accurate numerical calculations were difficult in the past because of lack of fast computers. A numerical model has been developed to accurately calculate the current density and magnetic flux fields and the resulting electromagnetic force field in three dimensions in the entire weldment. The model can take into account any current distribution on the work piece surface and evaluate the effects of different arc locations and work piece geometry on the electromagnetic force field. Contributions of the electrode current, arc plasma, and current distribution inside the three-dimensional work piece to the magnetic field and the electromagnetic force field are determined. The electromagnetic force field computed from the model is compared with those obtained from the commonly used simplified expressions of electromagnetic force to examine the accuracy of the commonly used simplifying assumptions. The accuracy of the computed electromagnetic force field can be significantly improved by using the proposed numerical model.
Optical power limiting and stabilization using a two-photon absorbing neat liquid crystal in isotropic phase
Authors: He Guang S. , Lin Tzu-Chau , Prasad Paras N. , Cho Chih-Chien , Yu Liang-Jye
Published: June 2003

This letter reports on a neat liquid crystal that incorporates a two-photon-absorbing chromophore in its structure. The nonlinear optical properties including two-photon-induced fluorescence spectrum and decay behavior, as well as the effective two-photon absorption coefficient of this liquid crystal in its isotropic phase are presented. Fairly good optical limiting and stabilization performance with this nonlinear material have been achieved by using ∼815-nm and ∼5-ns laser pulses.
Delayed electroluminescence via triplet–triplet annihilation in light emitting diodes based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]
Authors: Sinha S. , Monkman A. P.
Published: June 2003

A spectroscopically resolved delayed electrofluorescence is observed from poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH–PPV) thin film at low temperature. From the measurements of the delayed fluorescence intensities at a particular delay time as well as the decay kinetics of the delayed fluorescence spectra at different temperatures, we conclude that the delayed fluorescence is generated via triplet–triplet annihilation. It is suggested that the triplet state of MEH–PPV thin film has a lifetime much shorter than that of polyfluorene thin film, which is consistent with the triplet energies of these polymers.
Protective effect of dietary nitrate on experimental gastritis in rats
Authors: Larauche Muriel , Anton Pauline M. , Garcia-Villar Rafaël , Theodorou Vassilia , Frexinos Jacques , Buéno Lionel , Fioramonti Jean
Published: June 2003

Nitrates have long been considered as harmful dietary components and judged responsible for deleterious effects on human health, leading to stringent regulations concerning their levels in food and water. However, recent studies demonstrate that dietary nitrate may have a major role in human health as a non-immune mechanism for host defence, through its metabolism to NO in the stomach. NO is a versatile molecule and although evidence exists showing that administration of low doses of exogenous NO protects against gastrointestinal inflammation, higher NO doses have been shown to exacerbate injury. So, the effect of an ingestion of nitrates in doses corresponding to a normal diet in human consumers on an experimental gastritis induced by iodoacetamide in rats was investigated. During gastritis one of the following compounds was given orally: water; KNO3; the NO donor sodium nitroprusside; the NO scavenger haemoglobin given with either water or KNO3. N(G)-nitro-L-arginine methyl ester (L-NAME), a non-specific NO synthase inhibitor, was administered with either water, iodoacetamide alone, or combined with KNO3. After killing, the stomach was resected and microscopic damage scores, myeloperoxidase and NO synthase activities were determined. Iodoacetamide-induced gastritis was significantly reduced by KNO3administration, an effect which was reproduced by sodium nitroprusside and reversed by haemoglobin. L-NAME induced gastric mucosal damage in itself, and KNO3did not prevent the gastritis induced by iodoacetamide associated with L-NAME. In conclusion, dietary nitrate exerts a protective effect against an experimental gastritis in rats by releasing NO in the stomach but such an effect requires the production of endogenous NO.
Calcium Clearance Mechanisms of Mouse Sperm
Authors: Wennemuth Gunther , Babcock Donner F. , Hille Bertil
Published: June 2003

The spermatozoon is specialized for a single vital role in fertilization. Past studies show that Ca2+ signals produced by the opening of plasma membrane entry channels initiate several events required for the sperm to reach and enter the egg but reveal little about how resting [Ca2+]i is maintained or restored after elevation. We examined these homeostatic mechanisms by monitoring the kinetics of recovery from depolarizing stimuli under conditions intended to inhibit candidate mechanisms for sequestration or extrusion of Ca2+ from the cytosol. We found that the Ca2+-ATPase pump of the plasma membrane performs the major task of Ca2+ clearance. It is essential in the final stages of recovery to achieve a low resting [Ca2+]i. With immunomethods we found a ∼130-kD plasma membrane Ca2+-ATPase protein on Western blots of whole sperm extracts and showed immunolocalization to the proximal principal piece of the flagellum. The plasma membrane Na+-Ca2+ exchanger also exports Ca2+ when [Ca2+]i is elevated. Simultaneous inhibition of both mechanisms of extrusion revealed an additional contribution to clearance from a CCCP-sensitive component, presumably sequestration by the mitochondria. Involvement of SERCA pumps was not clearly detected. Many aspects of the kinetics of Ca2+ clearance observed in the presence and absence of inhibitors were reproduced in a mathematical model based on known and assumed kinetic parameters. The model predicts that when cytosolic [Ca2+] is at 1 μM, the rates of removal by the Ca2+-ATPase, Na+-Ca2+-exchanger, mitochondrial uniporter, and SERCA pump are ∼1.0, 0.35, 0.33, and 0 μmole l−1 s−1, rates substantially slower than those reported for other cells studied by similar methods. According to the model, the Na+-Ca2+ exchanger is poised so that it may run in reverse at resting [Ca2+]i levels. We conclude that the essential functions of sperm do not require the ability to recover rapidly from globally elevated cytosolic [Ca2+].
QFD: the role of various leadership styles
Authors: Politis John D.
Published: June 2003

Quality function deployment (QFD) methodologies, as opposed to traditional quality approaches, are most often cited as essential for advancing the competitive advantage of an organisation. Unfortunately, little is known about the roles played by leadership in the process of QFD in the Arab world. A survey of 104 middle level managers from a wide variety of United Arab Emirates’ industries who are engaged in quality management programs was undertaken to investigate the relationship between different leadership style dimensions and a number of QFD methodologies. Results indicate that the leadership styles that involve human interaction and encourage participative decision making are supportive of open and collaborative QFD methodologies.
Leadership and the 80/20 revolution
Authors: Lloyd Bruce , Koch Richard
Published: June 2003

Bruce Lloyd, Professor of Strategic Management, South Bank University in discussion with Richard Koeh, author of the recent book The 80/20 Revolution. The author argues that the 80/20 Revolution is designed to encourage people to realise the power that they have as individuals, and to realise the creativity that I believe, is inherent in everyone – and that most people can develop to a much greater extent than is currently the case. The book explores the reason why things are changing and what we all need to do to keep ahead of the game; it also discusses the role of outsourcing and the changing relationship between individuals and the corporation, as well as the renewed emphasis on “The search for meaning.” The author concludes that individuals need to take more control of their lives and to recognise that we all find meaning and happiness from doing things for other people that they feel good about.