bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of a fast analytic ground state potential energy surface for the N(2D)+H2 reaction
Authors: Ho Tak-San , Rabitz Herschel , Aoiz F. Javier , Bañares Luis , Vázquez Saulo A. , Harding Lawrence B.
Published: July 2003

A new implementation is presented for the potential energy surface (PES) of the 1 2A″ state of the N(2D)+H2 system based on a set of 2715 ab initio points resulting from the multireference configuration interaction (MRCI) calculations. The implementation is carried out using the reproducing Kernel Hilbert Space interpolation method. Range parameters, via bond-order-like coordinates, are properly chosen to render a sufficiently short-range three-body interaction and a regularization procedure is invoked to yield a globally smooth PES. A fast algorithm, with the help of low-order spline reproducing kernels, is implemented for the computation of the PES and, particularly, its gradients, whose fast evaluation is essential for large scale quasi-classical trajectory calculations. It is found that the new PES can be evaluated more than ten times faster than that of an existing (old) PES based on a smaller number (1141) of data points resulting from the same MRCI calculations and a similar interpolation procedure. Although there is a general good correspondence between the two surfaces, the new PES is in much better agreement with the ab initio calculations, especially in key stationary point regions including the C2v minimum, the C2v transition state, and the N–H–H linear barrier. Moreover, the new PES is free of spurious small scale features. Analytic gradients are made available in the new PES code to further facilitate quasiclassical trajectory calculations, which have been performed and compared with the results based on the old surface.
Direct dynamics study of energy transfer and collision-induced dissociation: Effects of impact energy, geometry, and reactant vibrational mode in H2CO+–Ne collisions
Authors: Liu Jianbo , Song Kihyung , Hase William L. , Anderson Scott L.
Published: July 2003

Quasiclassical, direct dynamics trajectories, calculated at the B3LYP/6-31G** level of the theory, have been used to study the energy transfer dynamics and collision-induced dissociation (CID) of formaldehyde cation in collisions with Ne. Effects of varying collision energy were probed for ground state H2CO+, and H2CO+ with excitation in three different vibrational modes: ν6+ (in-plane CH2 rock), ν4+ (out-of-plane bend), and ν5+ (asym. CH stretch). The trajectories are in excellent agreement with an earlier detailed experimental study of state-selected H2CO+ CID. Energy disposal branching between product recoil, vibrational energy, and rotational excitation is found to vary with collision energy, vibrational state, impact parameter, and orientation. An analysis of the trajectories illustrates how mode-specific vibrational excitation effects the efficiency of translational-to-vibrational (T→V) energy transfer to promote CID.
Laser wakefield and self-modulation of driving pulse
Authors: Lin Hai , Xu Zhizhan , Chen Li-Ming , Kieffer J. C.
Published: July 2003

A self-consistent theory of plasma response to a single laser beam is proposed. The driving pump is not viewed as invariant during its interaction with the plasmas. Its modulation by the plasmas has an obvious influence on the strength of the wakefield behind the pulse. This suggests that the compression of the low-intensity pulse by the plasmas might be a possible way to excite large-amplitude wakefield.
Collective plasma effects in scattering of radiation in astrophysical plasmas
Authors: Bingham R. , Tsytovich V. N. , de Angelis U. , Forlani A. , Mendonça J. T.
Published: July 2003

The contribution to the radiative transport due to collective scattering in astrophysical plasmas and a generalization of the Kompaneets equation is obtained. Both the stimulated and spontaneous scattering and the contribution of scattering on electrons and ions are taken into account and shown to be important over a broad range of frequencies ωpe<ω<ωpec/vTe (ωpe is the plasma frequency, c is the light velocity and vTe is the electron thermal velocity). A new expression for the Eddington luminosity including collective effects is derived. In the transport cross section the scattering on ions starts to contribute for ω⩽3ωpec/vTe while in the generalized Kompaneets equation the scattering on ions dominate for ω⩽ωpe(c/vTe)(me/mi)1/4. It is shown that the contribution related to the change of frequency during the stimulated and spontaneous scattering modifies the structure of the transport equation. A new transport equation is derived which contains a derivative of the intensity with respect to the frequency and in general such an equation does not allow the use of the concept of opacity as normally defined.
Topological phenomena in the real periodic sine-Gordon theory
Authors: Grinevich P. G. , Novikov S. P.
Published: July 2003

The set of real finite-gap sine-Gordon solutions corresponding to a fixed spectral curve consists of several connected components. A simple explicit description of these components obtained by the authors recently is used to study the consequences of this property. In particular this description allows to calculate the topological charge of solutions (the averaging of the x-derivative of the potential) and to show that the averaging of other standard conservation laws is the same for all components.
Topics in quantum integrable systems
Authors: Hikami Kazuhiro , Wadati Miki
Published: July 2003

Recent developments in the theory of quantum integrable particle systems in one-dimension with inverse square interactions are reviewed. First the Yangian symmetry is introduced and the energy spectra of the related spin models are discussed. The character of the su(n)1 WZNW theory is shown to be closely related with the Rogers–Szegö polynomial. Second, the infinite dimensional representation for solutions of the Yang–Baxter equation and the reflection equation is given. Based on the representation, the Dunkl operators associated with the classical root systems are constructed. The Macdonald polynomial and its generalization are discussed in connection with the eigenstates for the trigonometric case. Finally, some results on short-range interacting systems are mentioned.
Ultraviolet and infrared spectroscopy for effluent analysis in a molten salt electrochemical cell
Authors: Moore J. F. , Pellin M. J. , Calaway W. F. , Hryn J. N.
Published: July 2003

An apparatus that combines gas phase spectroscopy over two wavelength ranges for analysis of effluent from a molten salt electrochemical cell is described. The cell is placed in a quartz tube that is sealed at the top with a cap containing feedthrus for power, thermometry, and gas flow. A resistance furnace brings the cell assembly to the desired temperature while the cap remains cooled by water. Inert gas continually purges the cell headspace carrying effluent from the electrolysis sequentially through two gas cells, one in a Fourier transform infrared (FTIR) spectrometer and one in a fiber-optic coupled ultraviolet visible spectrometer. Strong vibrational absorptions in the IR can easily identify common effluent components such as HCl, CO, CO2, and H2O. Electronic bands can identify IR-inactive molecules of importance including Cl2 and O2. Since the absorptivity of all of these species is known, determinations of the gas concentration can be made without using standards. Spectra from the electrolysis of molten MgCl2 are shown and discussed, as well as the limit of detection and inherent time resolution of the apparatus as implemented.
Actively stabilized optical feedback scheme for very stable, high sensitivity shear-force measurement
Authors: Jeong Heeseong , Kwak Noh-Min , Huh Hyeongjun , Cho Kyuman
Published: July 2003

We present here an active feedback control scheme which can maintain the distance between a laterally vibrating tapered optical fiber tip (TOFT) and a one facet of a laser diode (LD) at optimum value to measure the vibration amplitude of the TOFT in an optical feedback shear-force measurement scheme. Extremely good sensitivity for measuring the vibration amplitude, 9.58×10−2 pm/√Hz for a metal coated TOFT, can be maintained for at least 6 h by use of an active stablization scheme. Using a linearized lasing model of the LD in the presence of optical feedback, we are able to determine the vibration amplitude and effective reflection coefficient of the TOFT.
Microrheology: Structural evolution under static and dynamic conditions by simultaneous analysis of confocal microscopy and diffusing wave spectroscopy
Authors: Nicolas Yves , Paques Marcel , Knaebel Alexandra , Steyer Alain , Munch Jean-Pierre , Blijdenstein Theo B. J. , van Aken George A.
Published: July 2003

An oscillatory shear configuration was developed to improve understanding of structural evolution during deformation. It combines an inverted confocal scanning laser microscope (CSLM) and a special sample holder that can apply to the sample specific deformation: oscillatory shear or steady strain. In this configuration, a zero-velocity plane is created in the sample by moving two plates in opposite directions, thereby providing stable observation conditions of the structural behavior under deformation. The configuration also includes diffusion wave spectroscopy (DWS) to monitor the network properties via particle mobility under static and dynamic conditions. CSLM and DWS can be performed simultaneously and three-dimensional images can be obtained under static conditions. This configuration is mainly used to study mechanistic phenomena like particle interaction, aggregation, gelation and network disintegration, interactions at interfaces under static and dynamic conditions in semisolid food materials (desserts, dressings, sauces, dairy products) and in nonfood materials (mineral emulsions, etc.). Preliminary data obtained with this new oscillatory shear configuration are described that demonstrate their capabilities and the potential contribution to other areas of application also.
Spectral analytical system for measuring time-resolved spectra of materials under shock
Authors: Peng Qixian , Hu Shaolou , Tang Jingyou
Published: July 2003

A spectral analytical system has been developed for measuring the time-resolved spectra of a transient emission. In this system, a special optical splitter-delay generator converts the time-distribution spectra into the space-distribution spectra, and the time-dependent spectra are recorded by a two-dimensional charge coupled device, accompanied with a multichannel plate intensifier. The time resolution of 20 ns and the recording time of 120 ns have been achieved in the experiment for argon emission shocked to 12 000 K.
Development of an all-optical infrared modulator and its application to fiber optic thermometry
Authors: Saito Mitsunori , Nishikawa Takashi , Shishido Mitsunobu
Published: July 2003

In some fiber optic sensors, effective noise reduction is achievable by modulating signal radiation at the fiber input end. A small durable modulator is required if a fiber probe is to be inserted in a narrow hazardous environment. The use of plasma absorption in semiconductors is helpful in the development of an all-optical compact modulator that is compatible with various hazardous environments. Since the carrier recombination time in Si (∼0.5 ms) is longer than that in other semiconductors, Si is suitable for the 10–1000 Hz modulation required for sensitive infrared detection. Infrared light modulation at 1 kHz was demonstrated in the 2–12 μm wavelength range by Nd:YAG laser irradiation. This modulation technique was used in infrared fiber optic thermometry, and it successfully eliminated the effects of fiber temperature variation, formerly a serious problem in conventional thermometry.
Laser-based speed of sound measurements in water and aqueous D, L, and DL alanine solutions
Authors: Fischer Andrew T. , Compton Robert N.
Published: July 2003

A laser-based method for determining the speed of sound in liquids is presented in which the second harmonic (532 nm) of a pulsed Nd:YAG laser is focused into a liquid to produce a spherical sound wave pulse. A well-collimated He:Ne laser beam is positioned at a known and variable distance from the laser focus in order to determine the time-of-transit of the sound pulse. Measurements of the slope of distance versus time produces absolute values of the speed of sound in pure water within 0.06% agreement with presently accepted values. Using this method, the speed of sound in alanine/water mixtures are compared for D, L, and DL concentrations from 0 to 1.80 (saturation) molar. Isentropic compressibilities for all three solutions were determined from the measurement of sound velocity and no differences between the DL and D or L are observed, at all densities. The method is totally passive and could be used to determine sound velocities under extreme temperature or chemical conditions.
Quartz crystal resonators with atomically smooth surfaces for use in contact mechanics
Authors: Berg Steffen , Ruths Marina , Johannsmann Diethelm
Published: July 2003

A quartz crystal shear resonator was modified by gluing a thin piece of mica on one surface to obtain an acoustic sensor with a macroscopic atomically smooth area. Contact mechanics experiments with this resonator touching a half-spherical mica surface were performed at high shear rate by integrating it into a surface forces apparatus, which provides simultaneous load control and interferometric measurement of the real contact area and surface separation. The procedures for gluing mica on a quartz resonator without significant loss of its sensitivity and gluing a half-spherical mica surface are described in detail. Sensitivity issues and overtone order dependence are discussed. Although our work focuses on contact mechanics experiments, the technique is also relevant for quartz crystal microbalance applications.
Switching current measurements of large area Josephson tunnel junctions
Authors: Wallraff A. , Lukashenko A. , Coqui C. , Kemp A. , Duty T. , Ustinov A. V.
Published: July 2003

We have developed a scheme for high resolution measurements of the switching current distribution of a current-biased Josephson tunnel junction using a timing technique. In the measurement setup digital control and read-out electronics are galvanically isolated from the analog sample bias electronics by an optical fiber link. We have successfully used this technique to investigate thermal activation and macroscopic quantum tunneling of the phase in a high-quality 5×5 μm2 Nb–Al/AlOx–Nb Josephson tunnel junction with a critical current of Ic≈325 μA. At temperatures above the cross over temperature of T★≈280 mK the escape is dominated by thermal activation. Due to the high quality factor of the junction (Q≈95), the escape temperature is noticeably affected by the thermal prefactor. At temperatures below T★, the value of which agrees well with the theoretical predictions, the escape of the phase by quantum mechanical tunneling is observed. The presented technique can be employed to characterize current-biased Josephson tunnel junctions for applications in quantum information processing.
Power law kinetics in reversible enzyme-catalyzed reaction due to diffusion
Authors: Paul Sujata , Gangopadhyay Gautam
Published: July 2003

The effect of diffusion on the reversible enzyme-catalyzed reaction is investigated. The kinetic scheme of the enzyme-catalyzed reaction is considered with a little generalization of Michaelis–Menten mechanism where the last step is taken as reversible. By using a fluctuation theory approach we have considered the relaxation mechanism where the quadratic nonlinearity of the equation of fluctuation around the equilibrium acts as a small perturbation. In three dimensions, the effect of diffusion is reflected through the relaxation kinetics of the reaction as a power law asymptotics, t−3/2, when the system approaches equilibrium.
Isotropic–nematic transition of long, thin, hard spherocylinders confined in a quasi-two-dimensional planar geometry
Authors: Cosentino Lagomarsino Marco , Dogterom Marileen , Dijkstra Marjolein
Published: July 2003

We present computer simulations of long, thin, hard spherocylinders in a narrow planar slit. We observe a transition from the isotropic to a nematic phase with quasi-long-range orientational order upon increasing the density. This phase transition is intrinsically two-dimensional and of the Kosterlitz–Thouless type. The effective two-dimensional density at which this transition occurs increases with plate separation. We qualitatively compare some of our results with experiments where microtubules are confined in a thin slit, which gave the original inspiration for this work.
A multimode vibronic treatment of absorption, resonance Raman, and hyper-Rayleigh scattering of excitonically coupled molecular dimers
Authors: Myers Kelley Anne
Published: July 2003

The linear absorption spectra, resonance Raman excitation profiles and depolarization dispersion curves, and hyper-Rayleigh scattering profiles are calculated for excitonically coupled homodimers of a model electron donor–acceptor “push–pull” conjugated chromophore as a function of dimer geometry. The vibronic eigenstates of the dimer are calculated by diagonalizing the matrix of transition dipole couplings among the vibronic transitions of the constituent monomers. The absorption spectra show the usual red- or blueshifted transitions for J-type or H-type dimers, respectively. When the electronic coupling is large compared with the vibronic width of the monomer spectrum, the dimer absorption spectra exhibit simple Franck–Condon progressions having reduced vibronic intensities compared with the monomer, and the resonance Raman excitation profiles are shifted but otherwise only weakly perturbed. When the coupling is comparable to the vibronic width, the H-dimer absorption spectra exhibit irregular vibronic frequency spacings and intensity patterns and the effects on the Raman excitation profiles are larger. There is strong dispersion in the Raman depolarization ratios for dimer geometries in which both transitions carry oscillator strength. The first hyperpolarizabilities are somewhat enhanced in J-dimers and considerably reduced in H-dimers. These effects on the molecular β will amplify the effects of dimerization on the ground-state dipole moment in electro-optic materials formed from chromophore-doped polymers that must be electric field poled to obtain the net alignment needed for a macroscopic χ(2).
Effects of charge–charge interactions on dimensions of unfolded proteins: A Monte Carlo study
Authors: Kundrotas Petras J. , Karshikoff Andrey
Published: July 2003

Electrostatic interactions (EI) in denatured state of proteins are an important factor regulating folding/unfolding equilibria in these macromolecules. Therefore, a physically adequate model for description of EI in denatured proteins is highly desirable. For this purpose, unfolded polypeptide chains with excluded volume and charge–charge interactions taken into consideration were studied by means of Monte Carlo simulations. Charge–charge interactions were calculated using the Coulomb law both with constant, εs, and distance dependent, ε(r), dielectric permittivity. Average dimensions, in terms of radius of gyration, Rg, for chains of different lengths Nr, were obtained within a wide temperature range and for various distributions of positive and negative charges. The results suggest that unfolded proteins can adopt two distinct states, compact and expanded, depending on temperature and charge composition. The compact state is characterized by Rg close to that of native proteins, while the expanded state has Rg corresponding to a flexible homopolymer with excluded volume interactions only. A simple procedure for evaluation of Rg of unfolded proteins at different pH is proposed and the predicted Rg values are compared to the experimental data for fully unfolded states for several soluble denatured proteins.
Swelling behavior of responsive amphiphilic gels
Authors: Jarkova Elena , Lee Nam-Kyung , Vilgis Thomas A.
Published: July 2003

We study the equilibrium swelling degrees of an amphiphilic microgel which consists of two different types of constituents: hydrophobic (H) and hydrophilic (P) monomers. Using Flory-type theories, scaling arguments, and variational calculations, we investigate the influence of the number of cross links and cross-linking types on the equilibrium swelling behavior. We show that amphiphilic microgels exhibit discrete swelling degrees which are more pronounced than for homopolymer networks as the fraction of hydrophobic components in the gel changes. The heterogeneous cross links between different types of monomers prevent a complete phase separation and stabilize the gel at relatively high fraction of H monomers. Disorder in the arrangement of the monomers as well as the cross-linking positions is treated in the framework of the variational principle. The method developed here is also applied for designed networks which display well-defined conformational transitions. Such macrogels can be used for drug loading or release under specific environments. We provide scaling results for specifically constructed networks that are confirmed by our variational theory.
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multiple-quantum nuclear magnetic resonance investigations of molecular order distributions in poly(dimethylsiloxane) networks: Evidence for a linear mixing law in bimodal systems
Authors: Saalwächter Kay , Ziegler Pascal , Spyckerelle Olivier , Haidar Bassel , Vidal Alain , Sommer Jens-Uwe
Published: July 2003

We present proton–proton multiple-quantum investigations on a series of monomodal and strongly bimodal end-linked poly(dimethylsiloxane) model networks. A robust pulse sequence characterized by a well-defined double-quantum Hamiltonian along with a specific normalization approach is used to obtain double-quantum build-up curves. These curves are analyzed in terms of the spin dynamics of a local subsystem of monomer-fixed spins, where analytical fitting functions yielding residual dipole–dipole coupling constants are derived on the basis of exact solutions provided by simulations. Further employing the novel experimental strategy of double-quantum preselection of elastically active network chains, it is shown that the network response is purely heterogeneous, and that the data can be analyzed in terms of distributions of local dynamic order parameters using different models. The results yield consistent proof that local chain order in bimodal networks obeys a linear mixing law of short- and long-chain components. The order parameter distribution in a long-chain monomodal network is found to be surprisingly narrow, with a rather high average order parameter. Implications on the validity of present theories used to explain order and dynamics in networks are discussed.
Method of moments of coupled-cluster equations: The quasivariational and quadratic approximations
Authors: Pimienta Ian S. O. , Kowalski Karol , Piecuch Piotr
Published: July 2003

The method of moments of coupled-cluster equations (MMCC) and the renormalized coupled-cluster (CC) approaches [see, e.g., K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 18 (2000)] are extended to potential energy surfaces involving multiple bond breaking by introducing the new quasivariational (QV) and quadratic (Q) MMCC approximations. The QMMCC approximations retain the single-reference and noniterative character of the renormalized CC methods, while allowing us to obtain the highly accurate description of multiple bond stretching or breaking. The discussion of the general QVMMCC and QMMCC theories is augmented by the results of test calculations for the double dissociation of H2O and triple bond breaking in N2.
Charge transfer effects in molecule–negative ion complexes induced by core ionization
Authors: Streltsov A. I. , Dobrodey N. V. , Cederbaum L. S.
Published: July 2003

A variety of charge transfer effects can take place as a result of core ionization of anion–molecule complexes. As specific examples we study the core ionization of Na−H2O and Cl−H2O clusters using an ab initio Green’s function method. The site-localized character of the electron distribution in the ground state of these weakly bound clusters favors a transfer of an electron from the negative atomic ion to the H2O molecular unit upon ionization of the O1s core level. The charge transferred screens the created core hole giving rise to the appearance of low-lying satellites which are completely absent in the spectrum of the isolated H2O molecule. Energies and intensities of the charge-transfer satellites are found to depend strongly on the chemical type of the atomic anion. While the bandshape of the O1s−1 spectrum of Cl−H2O is very similar to that of isolated H2O, the spectrum of Na−H2O has virtually nothing to do with the core-ionization spectrum of the water molecule. Interestingly, the charge-transfer satellites seen in the O1s core-ionization spectrum of the Cl−H2O cluster can be well related to states in the O1s core-excitation spectrum of the isolated H2O molecule. The physics of core ionization of the clusters is discussed in detail.
Analytic first derivatives for general coupled-cluster and configuration interaction models
Authors: Kállay Mihály , Gauss Jürgen , Szalay Péter G.
Published: July 2003

A general method for the analytic computation of energy gradients within coupled-cluster (CC) and configuration interaction (CI) theory is presented. The proposed algorithm is formulated in the framework of our recent string-based many-body formalism and allows to handle wave functions truncated at arbitrary excitation level or including excitations selected via a complete active space. The considered wave function classes include any single-reference as well as several multireference-type CC and CI ansätze and as a special case the full CI limit. The applicability of the proposed and implemented procedure is demonstrated by performing benchmark CC and CI gradient and property calculations up to full CI for H2O (1A1), HF (1Σ+), NH2 (2B1), and OH (2Π) as well as for the transition state of the F+H2→HF+H reaction.
Effects of Hall electric fields on the saturation of forced antiparallel magnetic field merging
Authors: Dorelli John C.
Published: July 2003

The role of Hall electric fields in flux pile-up antiparallel magnetic field merging is addressed. Analytical solutions of the resistive Hall magnetohydrodynamics (Hall-MHD) equations are obtained, describing stagnation point flows in a thin current sheet. The stagnation point flow solutions explain a number of interesting effects observed in two-dimensional resistive Hall-MHD simulations of forced magnetic reconnection. In particular, when Hall electric fields are important within the current sheet, less pile-up of magnetic energy is required upstream of the current sheet to support a given reconnection electric field. Fast electron flows transport magnetic flux into the diffusion layer without requiring a compensating drop in plasma pressure upstream of the current sheet. The maximum flux pile-up merging rate allowed by the external plasma pressure becomes independent of the Lundquist number, scaling like the square root of the ratio of the ion inertial length to the spatial scale of the stagnation point flow. Thus, Hall electric fields provide a possible solution to the problem of flux pile-up saturation in two-dimensional, resistive MHD models of forced magnetic reconnection.
Modification of the shielding and wake potentials in a streaming dusty magnetoplasma
Authors: Salimullah M. , Shukla P. K. , Nambu M. , Nitta H. , Ishihara O. , Rizwan A. M.
Published: July 2003

The effect of an external magnetic field on the Debye shielding and dynamical wake potentials has been examined analytically in a uniform dusty plasma containing equilibrium ion and dust flows. The effects of the ion polarization drift and dust particle dynamics on the strength and the effective length of the new static Debye shielding potential and the dynamical oscillatory potential are studied. It is found that for the supersonic ion flow, the modified Debye–Hückel screening length, and the effective length, L∥, of the oscillatory wake potential due to the modified dust acoustic modes [cf. Eqs. (7) and (17)] become larger by a factor of ωpi/ωci than those due to the usual dust-acoustic wave, where ωpi and ωci are the ion plasma and ion gyrofrequencies, respectively.
Theory-based modeling of particle transport in ASDEX Upgrade H-mode plasmas, density peaking, anomalous pinch and collisionality
Authors: Angioni C. , Peeters A. G. , Pereverzev G. V. , Ryter F. , Tardini G. ,   ASDEX Upgrade Team
Published: July 2003

The theoretical prediction of density profiles in tokamak plasmas plays a major role for the prediction of the plasma performance in a fusion reactor. The density peaking measured in plasmas in high confinement mode of the ASDEX Upgrade tokamak [O. Gruber, H.-S. Bosch, S. Günter et al., Nucl. Fusion 39, 1321 (1999)] is shown to decrease with increasing collisionality. This experimental behavior is explained with a theoretical fluid transport model for ion temperature gradient and trapped electron modes, GLF23, which includes a valid description of the effects of collisions on these instabilities. Collisionless reactive models, like the Weiland model, are in disagreement with the experimental observations. The difference between the predictions of the two models must be ascribed to collisionality. This has been ascertained by a detailed comparison of the physics content of the two models and by the implementation of modified, collisionless versions of the GLF23 model, which yield results analogous to those of the Weiland model and in disagreement with the experiment. It is shown that the anomalous particle pinch decreases with collisionality and the relative role of the neoclassical Ware pinch becomes important at high collisionality, that is close to the density limit in present large tokamak experiments, while it is practically negligible at low collisionality. The present results reconciliate apparently contradictory observations on the existence of an anomalous particle pinch collected so far in tokamaks.
Effect of grain size-distribution on dust acoustic solitons
Authors: Ishak-Boushaki M. , Bahamida S. , Annou R.
Published: July 2003

The investigation of dust-acoustic solitons when ions are adiabatically heated, whereas dust grains are size-distributed, is conducted. The solitary solutions are shown to undergo a transformation into snoidal ones. The Mach numbers allowing bounded oscillatory solutions are increased, but the allowed Mach numbers range becomes strongly compressed. The permeability of dust grains enhances the constraints on the existence of the above-mentioned solutions.
Novel integrable reductions in nonlinear continuum mechanics via geometric constraints
Authors: Rogers C. , Schief W. K.
Published: July 2003

The nonlinear equations that describe solitonic behavior in physical systems have, to-date, typically been derived by approximation or expansion methods. Here, by contrast, hidden integrable structure is revealed in diverse areas of nonlinear continuum mechanics through natural geometric constraints.
Implementing of a precision fast thermoelectric cooler controller using a personal computer parallel port connection and ADN8830 controller
Authors: Flaxer Eli
Published: July 2003

A complete design of a compact precision and fast thermoelectric cooler (TEC) controller with a parallel port connection to a personal computer (PC), using a pulse width modulation technique by a dedicated smart driver, and digital control designed using very high-speed integrated circuit hardware description language is presented. The design allows replacement of the PC with an “on board” embedded microcontroller. This circuit is demonstrated as a TEC controller for a high-speed electro-optical modulator.
Mode-cleaning and injection optics of the gravitational-wave detector GEO600
Authors: Goßler S. , Casey M. M. , Freise A. , Grant A. , Grote H. , Heinzel G. , Heurs M. , Husman M. E. , Kötter K. , Leonhardt V. , Lück H. , Malec M. , Mossavi K. , Nagano S. , McNamara P. W. , Plissi M. V. , Quetschke V. , Robertson D. I. , Robertson N. A. , Rüdiger A. , Schilling R. , Skeldon K. D. , Strain K. A. , Torrie C. I. , Ward H. , Weiland U. , Willke B. , Winkler W. , Hough J. , Danzmann K.
Published: July 2003

The British–German interferometric gravitational-wave detector GEO600 uses two high-finesse triangular ring cavities of 8 m optical pathlength each, as an optical mode-cleaning system. The modecleaner system is housed in an ultrahigh-vacuum environment to avoid contamination of the optics and to minimize both the influence of refractive index variations of the air and acoustic coupling to the optics. To isolate the cavities from seismic noise, all optical components are suspended as double pendulums. These pendulums are damped at their resonance frequencies at the upper pendulum stage with magnet-coil actuators. A suspended reaction mass supports three coils matching magnets bonded onto the surface of one mirror of each cavity, allowing length control of the modecleaner cavities to maintain resonance with the laser light. A fully automated control system stabilizes the frequency of the slave laser to that of the master laser, the frequency of the master laser to the length of the first modecleaner and the length of the first to the length of the second modecleaner. The control system uses the Pound–Drever–Hall sideband technique and operates autonomously over long time periods with only infrequent human interaction. The duty cycle of the system was measured to be 99.7% during an 18 day period. The throughput of the whole modecleaner system is about 50%. In this article, we give an overview of the mechanical and optical setup and the achieved performance of the double modecleaner system.
Resolution enhancement of scanning four-point-probe measurements on two-dimensional systems
Authors: Hansen Torben M. , Stokbro Kurt , Hansen Ole , Hassenkam Tue , Shiraki Ichiro , Hasegawa Shuji , Bøggild Peter
Published: July 2003

A method to improve the resolution of four-point-probe measurements of two-dimensional (2D) and quasi-2D systems is presented. By mapping the conductance on a dense grid around a target area and postprocessing the data, the resolution can be improved by a factor of approximately 50 to better than 1/15 of the four-point-probe electrode spacing. The real conductance sheet is simulated by a grid of discrete resistances, which is optimized by means of a standard optimization algorithm, until the simulated voltage-to-current ratios converges with the measurement. The method has been tested against simulated data as well as real measurements and is found to successfully deconvolute the four-point-probe measurements. In conjunction with a newly developed scanning four-point probe with electrode spacing of 1.1 μm, the method can resolve the conductivity with submicron resolution.
Tip–sample distance control for near-field scanning microwave microscopes
Authors: Kim Myung Sik , Kim Songhui , Kim Jooyoung , Lee Kiejin , Friedman Barry , Kim Jin-Tae , Lee Jaekwang
Published: July 2003

We demonstrate a near-field scanning microwave microscope (NSMM) which uses a tuning fork shear-force feedback method to control the distance between tip and sample. This distance control method is independent of local microwave characteristics. The probe tip for the NSMM is attached to one prong of a quartz tuning fork and directly coupled to a high-quality microstrip resonator with a dielectric resonator at an operating frequency of f=4.5–5.5 GHz. The amplitude of the tuning fork was used as a distance control parameter in the feedback system. To demonstrate the ability of the distance regulation system, we present topographic images of an uneven conducting metal sample and compare the height response and the NSMM image.
Silicon self-diffusivity measurement in thermal SiO2 by Si30/Si28 isotopic exchange
Authors: Mathiot D. , Schunck J. P. , Perego M. , Fanciulli M. , Normand P. , Tsamis C. , Tsoukalas D.
Published: July 2003

Isotopic exchange is used to measure the silicon self-diffusivity in thermal silicon dioxide. The experiments, using an isotopically enriched Si28 oxide layer, are specially designed to obtain the actual equilibrium diffusivity in the oxide. A simple Arrhenius law, with an activation energy of 5.34 eV, very nicely describes the measured diffusivities as a function of the temperature. Our values are compared with literature data, and we discuss the possible origin of the observed differences.
Transmission electron microscopy study of a defected zone in GaN on a SiC substrate grown by hydride vapor phase epitaxy
Authors: Bendersky Leonid A. , Tsvetkov Denis V. , Melnik Yuriy V.
Published: July 2003

A defected zone (DZ) in the hydride vapor phase epitaxy (HVPE)-deposited GaN located near an interface with a SiC substrate was investigated by transmission electron microscopy for both plan-view and cross-section specimens. Predominant defects in the DZ are dislocations and stacking fault-type interfaces. Analysis of the defects by a moiré contrast and high-resolution imaging has suggested that the interfaces resulted from the process of coalescence and overgrowth of three-dimensional nucleated islands. The islands differ by a translation with respect to the reference (substrate) lattice, and therefore their coalescence results in the formation of domains separated by stacking fault-type boundaries. For the HVPE process used in depositing the specimens studied, we infer that the islands adopted the shape of {112̄l}-faceted truncated pyramids. Continued coalescence and overgrowth of the nonequivalent by translation domains result in a substructure of connected (0001) and {112̄0} stacking faults and threading dislocations. The density of these defects decreases with continued coalescence as the growth of GaN progresses, and thus determines the effective thickness of the DZ. We anticipate that the extent of such defected zones depends on the nucleation frequency and anisotropic growth rate of different crystallographic facets.
Optical properties of H-band emission in single heterojunctions
Authors: Qu Fanyao , Dantas N. O. , Morais P. C. , da Silva E. C. F. , Quivy A. A. , Leite J. R.
Published: July 2003

The optical properties of n- and p-type, modulation- and delta-doped Al0.35Ga0.65As–GaAs single heterojunctions (SHs) have been studied by means of low-temperature photoluminescence measurement and self-consistent calculation. A very strong, broad, and asymmetric H-band emission was observed only in p-type delta-doped SH. When the optical excitation intensity increases by two orders of magnitude a redshift as large as 27 meV is observed in the H-band emission energy. The large redshift observed is attributed to both inefficiency of screening in the two-dimensional-hole gas and effective band-gap renormalization. It was also observed that the H-band emission strongly depends upon the doping type (n or p type) and doping profile (modulation doping or delta doping).
Probe measurements in anisotropic discharges
Authors: Malykov A. , Mijovic S. , Vuceljic M.
Published: July 2003

A current–voltage characteristic of one-side planar and cylindrical probes was considered for the use in the determination of plasma parameters when the electron velocity distribution functions (EVDFs) were significantly anisotropic. The EVDFs, space potential, and rates of inelastic process in pulse modulated and stratified discharges were obtained. The results obtained using the exact and simplified method were compared. It was also shown that only a simplified method gives satisfactory results in the wide range of discharge conditions. Some discrepancies between theoretically determined and measured potentials in homogeneous plasma were found. A procedure, which allows for exact determination of space potentials, was given.
Computationally efficient quantum-mechanical technique to calculate the direct tunneling gate current in metal-oxide-semiconductor structures
Authors: Hakim M. M. A. , Haque A.
Published: July 2003

We propose a computationally efficient, accurate and numerically stable quantum-mechanical technique to calculate the direct tunneling (DT) gate current in metal-oxide-semiconductor (MOS) structures. Knowledge of the imaginary part Γ of the complex eigenenergy of the quasi-bound inversion layer states is required to estimate the lifetimes of these states. Exploiting the numerically obtained exponential dependence of Γ on the thickness of the gate-dielectric layer even in the sub-1-nm-thickness regime, we have simplified the determination of Γ in devices where it is too small to be calculated directly. It is also shown that the MOS electrostatics, calculated self-consistently with open boundary conditions, is independent of the dielectric layer thickness provided that the other parameters remain unchanged. Utilizing these findings, a computationally efficient and numerically stable method is developed for calculating the tunneling current–gate voltage characteristics. The validity of the proposed model is demonstrated by comparing simulation results with experimental data. Sample calculations for MOS transistors with high-K gate-dielectric materials are also presented. This model is particularly suitable for DT current calculation in devices with thicker gate dielectrics and in device or process characterization from the tunneling current measurement.
Electron transit time and reliable mobility measurements from thick film hydroxyquinoline-based organic light-emitting diode
Authors: Tse S. C. , Fong H. H. , So S. K.
Published: July 2003

The time delay (τd) in the transient electroluminescence (EL) signal of a bilayer organic light-emitting diode with a structure of indium-tin oxide /N,N′-diphenyl-N,N′-bis(3methylphenyl)-(1,1′-biphenyl)-4,4′-diamine /tris(8-hydroxyquinoline) aluminum (Alq3)/Al has been measured and analyzed as a function of the thickness (D) of the Alq3 layer. For a thin layer of Alq3 (D<180 nm), it is found that τd is affected by both the charging effect and carrier transit time through the Alq3 layer. For a thicker layer of Alq3 (D>200 nm), τd approaches the intrinsic electron transit time through Alq3. Electron mobility of Alq3 can be evaluated for the thick-film devices and the results are in excellent agreement with independent time-of-flight measurements. The application of transient EL in mobility measurement for C540-doped Alq3 is discussed.
Response of aluminum nitride (including a phase change) to large strains, high strain rates, and high pressures
Authors: Johnson Gordon R. , Holmquist Timothy J. , Beissel Stephen R.
Published: July 2003

This article contains a description of a computational constitutive model for brittle materials subjected to large strains, high strain rates, and high pressures. The focus of this model is to determine the response of aluminum nitride under high velocity impact conditions that produce large strains, high strain rates, and high pressures. The strength is expressed as a function of the pressure, strain rate, and accumulated damage; and it allows for strength of both intact and failed material. The pressure is primarily expressed as a function of the volumetric strain, but it also includes the effect of bulking for the failed material. For materials without a phase change this model is an extension of the previous Johnson–Holmquist models for brittle materials. The primary new feature of this model is the capability to include a phase change, and this is required for aluminum nitride. Computations are performed to illustrate the capabilities of the model, to compare computed results to experimental results, and to provide an understanding of the behavior of aluminum nitride under the conditions of high velocity impact.
Fabrication and nonlinear optical properties of nanoparticle silver oxide films
Authors: Chiu Yi , Rambabu U. , Hsu Ming-Hong , Shieh Han-Ping D. , Chen Chien-Yang , Lin Hsi-Hsiang
Published: July 2003

We report the fabrication of nanoparticle silver oxide thin films by rf magnetron sputtering and characterization of their nonlinear optical properties. The chemical decomposition and reversibility of AgOx compounds were studied by thermogravimetric analysis, differential scanning calorimetry, and x-ray diffraction. Electron spectroscopy for chemical analysis measurements revealed a 0.5 eV negative binding energy shift from AgO to Ag2O phase. The effect of particle plasmon resonance was confirmed by the absorption band shift with increased Ag2O particle size. The measured third-order nonlinear susceptibility (χ3=3.4×10−7 esu) and response time (27 ps) of the Ag2O nanoparticles makes it promising for applications in all-optical switching devices and optical data storage systems.
Lax equations scattering and KdV
Authors: Sabatier P. C.
Published: July 2003

The study of the Korteveg–de Vries (KdV) equation is considered as a special chapter of potential scattering where the dynamic scattering equation is a set of coupled “Lax” equations. With this approach, all points of view and all tools of potential scattering have their counterpart in the standard inverse scattering transform, which appears as a straightforward consequence. If the approach is transposed to the quarterplane problem, it shows a generalization to KdV of the solutions obtained by Fokas in the linearized KdV problem, but unfortunately the last step is iterative and complicated. The method can also be used to study NLS.
Thermal stability and partial dewetting of crystalline organic thin films: 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111)
Authors: Krause B. , Dürr A. C. , Schreiber F. , Dosch H. , Seeck O. H.
Published: July 2003

The thermal stability and dewetting effects of crystalline organic thin films on inorganic substrates have been investigated for a model system for organic epitaxy, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Ag(111). The thin films deposited under a variety of growth conditions have been annealed stepwise and studied by in situ x-ray diffraction and noncontact atomic force microscopy. It has been found that comparatively smooth films deposited at temperatures Tg≲350 K are metastable, while films deposited at Tg≳350 K are stable against annealing on a time scale of several hours. The thermal expansion of thin PTCDA films and bulk samples has been determined.
The role of phase in molecular Rydberg wave packet dynamics
Authors: Smith R. A. L. , Stavros V. G. , Verlet J. R. R. , Fielding H. H. , Townsend D. , Softley T. P.
Published: July 2003

The dynamics of Rydberg wave packets in NO are investigated in the regime where the electronic period is comparable with the rotational motion of the molecular ion core. The presence of a rotating molecular core manifests itself in the wave packet dynamics as a series of peaks separated by the rotational beat period TRot, but offset by ΔμTRot, where Δμ is the difference in quantum defect between the two dominant Rydberg series in the superposition. We rationalize this by treating the dynamics of a wave packet created from a coherent superposition of two interleaved Rydberg series as two separate electron wave packets, which interfere with one another when they overlap spatially. There is a periodic phase difference between the two wave packets that depends on the rotational energy of the core in each Rydberg series and also on the quantum defects. The resulting interference pattern in the Rydberg population manifests itself as peaks in the wave packet spectrum at the stroboscopic period.