bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of preamorphization on the structural properties of ultrashallow arsenic implants in silicon
Authors: Capello L. , Metzger T. H. , Werner M. , van den Berg J. A. , Servidori M. , Ottaviano L. , Bongiorno C. , Mannino G. , Feudel T. , Herden M. , Holý V.
Published: December 2006

Continuous downscaling of complementary metal-oxide semiconductor devices requires the manufacture of highly doped ultrashallow junctions. A preamorphizing implant (PAI) is commonly used in industrial processing in order to avoid unfavorable profile broadening and channeling tails during dopant atom implant in the ultralow energy regime (<5keV). In this work, we report about a detailed characterization of the structural changes induced by xenon PAI treatment on ultralow energy arsenic-implanted (001) silicon. Combined x-ray scattering methods, medium energy ion scattering, and transmission electron microscopy are applied to obtain as comprehensive picture as possible of the reordering processes occurring during the postimplantation annealing treatment. Evidence is found that end-of-range defects, present after implant below the amorphous-to-crystalline interface, transform from small Si interstitial clusters to dislocation loops during annealing depending on the implant conditions. Simultaneously, As atoms redistribute by moving to the substitutional sites of the freshly regrown Si lattice without inducing a local residual strain field. The remaining fraction of electrically inactive dopants cumulates in a subnanometer-thick layer beneath the surface oxide.
Domain walls on the surface of q-stars
Authors: Prikas Athanasios
Published: December 2006

We study domain wall networks on the surface of q-stars in asymptotically flat or anti de Sitter spacetime. We provide numerical solutions for the whole phase space of the stable field configurations and find that the mass, radius, and particle number of the star is larger but the scalar field, responsible for the formation of the soliton, acquires smaller values when a domain wall network is entrapped on the star surface.
Depth dependence of elastic grain interaction and mechanical stress: Analysis by x-ray diffraction measurements at fixed penetration/information depths
Authors: Kumar A. , Welzel U. , Mittemeijer E. J.
Published: December 2006

Gradients of the type of elastic grain interaction and the (residual) internal state of stress were determined. This was possible by the application of x-ray diffraction stress measurements at various fixed penetration/information depths. The analysis was applied to nickel films of thicknesses 2 and 4μm. Surface anisotropy was considered as source of direction-dependent (anisotropic) elastic grain interaction. It was found that only a small gradient of the state of stress, but a pronounced gradient of the grain interaction constraints, prevails in the investigated specimens. Thereby the evidence for the depth dependence of the so-called surface anisotropy was obtained.
Hydrogen-bond vibrations in the S1↔S spectra of a nucleobase pair analog: A mixed dimer between 2-pyridone and formamide
Authors: Hazra Montu K. , Samanta Amit K. , Chakraborty Tapas
Published: December 2006

The vibronically resolved electronic spectra for S1↔S0 transitions of a mixed dimer between 2-pyridone (2PY) and formamide have been measured in a supersonic free jet expansion using laser-induced fluorescence spectroscopy. Quantum chemistry method at different levels of theory has been used to optimize the geometries of the dimer for the S0 and S1 electronic states and also to calculate the normal vibrational modes. Assignments for the vibronic bands observed in the dispersed fluorescence spectrum of the 000 band have been suggested with the aid of the ground state frequencies calculated by density functional theoretical method. Spectral analysis reveals that electronic excitation causes extensive mixing of the low-frequency intermolecular vibrational modes of the dimer with some of the intramolecular modes of the 2PY moiety. This spectral behavior is consistent with the complete active space self-consistent field theoretical prediction that with respect to a number of geometrical parameters the dimer geometry in S1 is significantly distorted from the geometry of the S0 state.
Design and nonlinear modeling of a large-displacement XYZ flexure parallel mechanism with decoupled kinematic structure
Authors: Tang Xueyan , Chen I-Ming , Li Qing
Published: December 2006

This article proposes an XYZ flexure parallel mechanism (FPM) with large displacement and decoupled kinematic structure. The motion range of the large-displacement FPM using notch hinges is more than 1mm and is achieved by assembling the typical large-displacement prismatic joints and a new large-displacement prismatic joint proposed in this article. Moreover, the decoupled XYZ stage has small cross-axis error and small parasitic rotation. An exact nonlinear modeling method for the typical prismatic joint and the new type of prismatic joint is presented. Using the proposed nonlinear method, the stiffness and dynamics of the XYZ FPM are studied. Comparison between the pseudo-rigid-body and the proposed nonlinear methods is performed on the prismatic joints and the XYZ FPM. To verify the proposed nonlinear modeling method, experiments are conducted to study the linear stiffness of the prismatic joint. The stiffness and the natural frequency of the XYZ FPM are also obtained from the experimental data. The cross-axis error and the parasitic rotation of the XYZ FPM are measured. The experimental results show that the proposed XYZ FPM achieves large displacement and decoupled motion, and the proposed nonlinear method is valid for the flexure mechanism.
Novel design for zonal flow probe arrays in the HL-2A tokamak
Authors: Yan Longwen , Hong Wenyu , Zhao Kaijun , Dong Jiaqi , Cheng Jun , Qian Jun , Yu Deliang , Luo Cuiwen , Xu Zhengyu , Huang Yuan , Yang Qingwei , Ding Xuantong
Published: December 2006

A novel design of three-step Langmuir probe (TSLP) array has been developed for zonal flow (ZF) studies in the HL-2A tokamak. Three TSLP arrays are used to determine three-dimensional (3D) features of the ZFs. Two TSLP arrays are located in the same poloidal plane at a 6.5cm separation, while the third TSLP array is separated toroidally by 80cm. A fourth TSLP array driven by pneumatically reciprocating system is applied for boundary parameter profile measurements within 8cm. The TSLP structure is described in detail. The measured 3D properties of the geodesic acoustic mode (GAM) ZFs are described and the poloidal and toroidal mode numbers (m<2,n∼0) are simultaneously determined in the HL-2A tokamak for the first time. The radial wave vector at the GAM frequency is estimated as 2.6±0.2cm−1, corresponding to radial scale length of 2.4cm.
Sample cell for powder x-ray diffraction at up to 500bars and 200°C
Authors: Jupe Andrew C. , Wilkinson Angus P.
Published: December 2006

A low cost sample cell for powder diffraction at high pressure and temperature that employs either sapphire or steel pressure tubes is described. The cell can be assembled rapidly, facilitating the study of chemically reacting systems, and it provides good control of both pressure and temperature in a regimen where diamond anvil cells and multianvil apparatus cannot be used. The design provides a relatively large sample volume making it suitable for the study of quite large grain size materials, such as hydrating cement slurries. However, relatively high energy x rays are needed to penetrate the pressure tube.
Measurements of electron and proton heating temperatures from extreme-ultraviolet light images at 68eV in petawatt laser experiments
Authors: Gu Peimin , Zhang B. , Key M. H. , Hatchett S. P. , Barbee T. , Freeman R. R. , Akli K. , Hey D. , King J. A. , Mackinnon A. J. , Snavely R. A. , Stephens R. B.
Published: December 2006

A 68eV extreme-ultraviolet light imaging diagnostic measures short pulse isochoric heating by electrons and protons in petawatt laser experiments. Temperatures are deduced from the absolute intensities and comparison with modeling using a radiation hydrodynamics code.
Effect of non-Maxwellian particle trapping and dust grain charging on dust acoustic solitary waves
Authors: Rubab N. , Murtaza G. , Mushtaq A.
Published: December 2006

The role of adiabatic trapped ions on a small but finite amplitude dust acoustic wave, including the effect of adiabatic dust charge variation, is investigated in an unmagnetized three-component dusty plasma consisting of electrons, ions and massive micron sized negatively charged dust particulates. We have assumed that electrons and ions obey (r,q) velocity distribution while the dust species is treated fluid dynamically. It is found that the dynamics of dust acoustic waves is governed by a modified r dependent Korteweg-de Vries equation. Further, the spectral indices (r,q) affect the charge fluctuation as well as the trapping of electrons and ions and consequently modify the dust acoustic solitary wave.
Construction of basis functions for the spin-cluster expansion of the magnetic energy on the atomic scale in rotationally invariant systems
Authors: Singer R. , Fähnle M.
Published: December 2006

The recently introduced spin-cluster expansion (SCE) is a powerful tool to represent on the atomic scale the adiabatic magnetic energy for each magnetic configuration of a system with N sites. In the present paper the theory is worked out for the very important case of rotationally invariant magnets. Appropriate basis functions for this SCE are rotationally invariant and exhibit time-reversal symmetry, are real, and constitute a complete orthonormal set for the representation of any rotationally invariant observable. It is also shown how generalized Heisenberg-type models of the magnetic energy of an isotropic magnet are represented in this symmetry-adapted SCE basis.
Ion implanted Si:P double dot with gate tunable interdot coupling
Authors: Chan V. C. , Buehler T. M. , Ferguson A. J. , McCamey D. R. , Reilly D. J. , Dzurak A. S. , Clark R. G. , Yang C. , Jamieson D. N.
Published: December 2006

We report on milli-Kelvin charge sensing measurements of a silicon double-dot system fabricated by phosphorus ion implantation. An aluminum single-electron transistor is capacitively coupled to each of the implanted dots enabling the charging behavior of the double-dot system to be studied independent of current transport. Using an electrostatic gate, the interdot coupling can be tuned from weak to strong coupling. In the weak interdot coupling regime, the system exhibits well-defined double-dot charging behavior. By contrast, in the strong interdot coupling regime, the system behaves as a single dot.
Design, growth, fabrication, and characterization of InAs∕GaAs 1.3μm quantum dot broadband superluminescent light emitting diode
Authors: Ray S. K. , Groom K. M. , Alexander R. , Kennedy K. , Liu H. Y. , Hopkinson M. , Hogg R. A.
Published: December 2006

In this paper we discuss a technique for broadening the emission and gain spectra of 1.3μm quantum dot superluminescent light emitting diodes (SLEDs). By incorporating different amounts of indium in different wells of a multi-dot-in-well stack we are able to tailor the emission and gain spectra of the devices. This technique allows us to overlap the ground state of one dot-in-well (DWELL) with the excited state of another to achieve broader and flatter emission spectra compared to a SLED design comprising DWELL layers of constant indium composition. Due to the low internal loss of these structures, this broadening is achieved without a significant reduction in the output power of the devices.
Dimensional reduction of Seiberg-Witten monopole equations, N=2 noncommutative supersymmetric field theories and Young diagrams
Authors: Sako Akifumi , Suzuki Toshiya
Published: December 2006

We investigate the Seiberg-Witten monopole equations on noncommutative (N.C.) R4 at the large N.C. parameter limit, in terms of the equivariant cohomology. In other words, N=2 supersymmetric U(1) gauge theories with a hypermultiplet on N.C.R4 are studied. It is known that after topological twisting partition functions of N>1 supersymmetric theories on N.C. R2D are invariant under the N.C. parameter shift; then the partition functions can be calculated by its dimensional reduction. At the large N.C. parameter limit, the Seiberg-Witten monopole equations are reduced to ADHM equations with the Dirac equation reduced to the 0 dimension. The equations are equivalent to the dimensional reduction of non-Abelian U(N) Seiberg-Witten monopole equations in N→∞. The solutions of the equations are also interpreted as a configuration of a brane antibrane system. The theory has global symmetries under torus actions originated in space rotations and gauge symmetries. We investigate the Seiberg-Witten monopole equations reduced to the 0 dimension and the fixed point equations of the torus actions. We show that the Dirac equation reduced to the 0 dimension is automatically satisfied when the fixed point equations and the ADHM equations are satisfied. Then, we find that the Seiberg-Witten equations reduced to the 0 dimension and fixed point equations of the torus action are equivalent to just the ADHM equations with the fixed point equations. For finite N, it is known that the fixed points of the ADHM data are isolated and are classified by the Young diagrams. We also give a new proof of this statement by solving the ADHM equations and the fixed point equations concretely and by giving graphical interpretations of the field components and these equations.
Modeling multidimensional effects in the propagation of radiative shocks
Authors: Leygnac Sébastien , Boireau Laurent , Michaut Claire , Lanz Thierry , Stehlé Chantal , Clique Christine , Bouquet Serge
Published: December 2006

Radiative shocks (also called supercritical shocks) are high Mach number shock waves that photoionize the medium ahead of the shock front and give rise to a radiative precursor. They are generated in the laboratory using high-energy or high-power lasers and are frequently present in a wide range of astronomical objects. Their modelization in one dimension has been the subject of numerous studies, but generalization to three dimensions is not straightforward. We calculate analytically the absorption of radiation in a gray uniform cylinder and show how it decreases with χR, the product of the opacity χ and of the cylinder radius R. Simple formulas, whose validity range increases when χR diminishes, are derived for the radiation field on the axis of symmetry. Numerical calculations in three dimensions of the radiative energy density, flux, and pressure created by a stationary shock wave show how the radiation decreases with R. Finally, the bidimensional structures of both the precursor and the radiation field are calculated with time-dependent radiation hydrodynamics numerical simulations and the influence of two-dimensional effects on the electron density, the temperature, the shock velocity, and the shock geometry are exhibited. These simulations show how the radiative precursor shortens, cools, and slows down when R is decreased.
Relativistic description of electron Bernstein waves
Authors: Decker Joan , Ram Abhay K.
Published: December 2006

The application of the extraordinary and ordinary electron cyclotron waves for heating and current drive in overdense, magnetized plasmas is restricted. For frequencies near low harmonics of the electron cyclotron frequency these waves are cutoff near the edge of the plasma. For higher frequencies the interaction of the waves with electrons is weak leading to very low absorption of wave power. However, electron Bernstein waves provide means for heating and current drive in overdense plasmas since they have no density cutoffs and are strongly damped near harmonics of the electron cyclotron resonance. This paper discusses properties of electron Bernstein waves that make them an attractive means for delivering energy and momentum to electrons. An approximate analytical model for electrostatic waves in the weakly relativistic and weak damping limits is developed. From this model the propagation and damping characteristics of electron Bernstein waves and their dependence on plasma parameters are derived. It is found that relativistic effects are necessary to properly describe the resonant interaction of electron Bernstein waves with electrons. The characteristics of electron Bernstein wave propagation and damping are very different depending on whether the electron cyclotron harmonic resonance is approached from the low- or high-field side. The results from the analytical model and the associated analysis agree well with the results from the exact numerical calculations. This validates the physics of the simplifying assumptions on which the model is based. The electron Bernstein waves are completely damped well before the electron cyclotron resonance due to the Doppler shift. Within the damping region the waves interact with suprathermal electrons thereby having the potential for efficient current drive.
Enhanced oxygen diffusion in highly doped p-type Czochralski silicon
Authors: Murphy J. D. , Wilshaw P. R. , Pygall B. C. , Senkader S. , Falster R. J.
Published: December 2006

The locking of dislocations by oxygen has been investigated experimentally in Czochralski silicon (Cz-Si) with different concentrations of shallow dopants. Specimens containing well-defined arrays of dislocation half-loops were subjected to isothermal anneals in the 350–550°C temperature range, and the stress required to bring about dislocation motion at 550°C was then measured. This dislocation unlocking stress was found to increase with annealing time due to oxygen diffusion to the dislocation core. The dislocation unlocking stress was measured in n-type Cz-Si with a high antimony doping level (∼3.4×1018cm−3) and p-type Cz-Si with a low boron doping level (∼1.3×1015cm−3). An analysis of the data taking the different oxygen concentrations into account showed that the rate of increase in dislocation unlocking stress was unaffected by the high level of antimony doping. This indicates that a high antimony doping level has no significant effect on oxygen transport for the conditions used in this experiment. However, in p-type Cz-Si with a high boron doping level (∼5.4×1018cm−3), the dislocation unlocking stress was found to rise at a much faster rate than in Cz-Si with a low boron doping level or high antimony doping level. This enhancement in dislocation locking was by a factor of approximately 60 at 400°C. By performing a numerical simulation to solve the diffusion equation for oxygen transport to a dislocation, the effective diffusivity of oxygen was deduced from the dislocation unlocking data to be 2.7×10−6exp(−1.4eV∕kT)cm2s−1 in the highly boron doped Cz-Si. In the temperature range studied, the effective diffusion coefficient in the highly boron doped Cz-Si was found to be approximately 44 times higher than expected in low boron doped Cz-Si with an identical oxygen concentration.
Anomalous reflection and refraction in anisotropic metamaterial realized by periodically loaded transmission line network
Authors: Feng Yijun , Teng Xiaohua , Zhao Junming , Chen Yan , Jiang Tian
Published: December 2006

We have studied the electromagnetic wave propagation in two-dimensional anisotropic metamaterial (AMM) by realizing the AMM through periodic structure composed of anisotropically loaded transmission line (TL) network. The dispersion relation of the TL metamaterial is analyzed by rigorous periodic TL theory, which shows hyperbolic dispersion surface in phase space below certain critical frequency. Utilizing microstrip line technique, we have constructed an interface between isotropic normal medium and a particular type of AMM with properly designed normal TL mesh and the loaded TL network, respectively. The electromagnetic wave propagation in such system has been analyzed with the consideration of circuit losses using microwave circuit simulations. We directly demonstrate interesting phenomena including the total reflection with inversion of the critical angle at small incident angle as well as the oblique total transmission at large incident angle at the interface, which have good agreement with the theoretical prediction.
A mathematical description of surface texture development in laser-ablated dentin
Authors: Oliveira V. , Sivakumar M. , Vilar R.
Published: December 2006

A cone-shaped texture is observed when a transverse cross section of human dentin cut perpendicularly to the tooth axis is processed with KrF excimer laser radiation using appropriate processing parameters. In the present paper, a mathematical model describing the kinetics of cone growth as a function of the number of laser pulses is presented. It is shown that the fractional area occupied by cones is adequately described by a modified Johnson-Mehl-Avrami-Kolmogorov equation and that the boundary lines between cones define a Voronoi tessellation generated from the corresponding initial tubule location. This model allows the surface texture evolution in dentin to be predicted from the initial tubule distribution.
Mechanics of edge effects in anisotropic thin film∕substrate systems
Authors: Murray Conal E.
Published: December 2006

The mechanical response of an anisotropic, elastic substrate subjected to an edge force on its surface was used to develop simple, analytical expressions of stress distributions for selected orientations of a substrate possessing cubic symmetry. The resulting stress distributions, calculated for both (001) and (011) orientations of a Si substrate, can differ by 20% from those predicted for an elastically isotropic case. Elastic anisotropy of strained films on a Si substrate, which produce variations in the film stress, leads to a 34% increase in SiGe film stress along [01¯1] in the (011) orientation relative to the (001) orientation. Both of these effects are incorporated into a distributed-force formulation of the elastic relaxation at the edges of strained film features to model the stress distributions across SiGe features on Si.
A method of accurately determining the positions of the edges of depletion regions in semiconductor junctions
Authors: Ong Vincent K. S. , Kurniawan Oka , Moldovan Grigore , Humphreys Colin J.
Published: December 2006

The technique of electron beam induced current (EBIC) in the scanning electron microscopy can be used to extract the depletion width in a variety of materials and devices. This article reviews current methods available for identifying the positions of the edges of the depletion layer and proposes an alternative methodology that uses the first derivative of the logarithmic EBIC profile. It was found that the precision of this method is only dependent upon the accuracy in which one can determine the lateral dimension of the beam-sample interaction. The proposed method is then applied to a gallium nitride light emitting diode device to verify the practicality of the technique.
Origin of the response of nanomechanical resonators to bacteria adsorption
Authors: Ramos D. , Tamayo J. , Mertens J. , Calleja M. , Zaballos A.
Published: December 2006

Resonant microcantilevers are being actively investigated as sensitive mass sensors for biological detection. By performing experiments of adsorption of the bacteria Escherichia coli on singly clamped microcantilevers, we demonstrate that the effect of the added mass is not the only and may not be the main origin of the response of these sensors. The experiments show that the magnitude and sign of resonance frequency shift both depend critically on the distribution of the adsorbed bacterial cells on the cantilever. We relate this behavior to the added mass that shifts the resonance to lower frequencies and the higher effective flexural rigidity of the cantilever due to the bacteria stiffness that shifts the resonance to higher frequencies. Both effects can be uncoupled by positioning the cells where each effect dominates, near the free cantilever end for measuring the added mass or near the clamping for measuring the increase of flexural rigidity.
On the prediction of viscosity of glasses from optical basicity
Authors: Choudhury P. , Pal S. K. , Ray H. S.
Published: December 2006

A procedure for estimation of viscosity from the optical basicity of glass melts is reported for the first time. SCIGLASS data for four silicate glass systems are chosen to develop the method proposed. The temperature corresponding to a particular viscosity value decreases exponentially with the increase of the optical basicity of a melt. Study of the dependence of viscosity on optical basicity leads to a viscosity-temperature relation which is a modified form of the well-known Vogel-Fulcher-Tamman equation [H. Vogel, Phys. Z. 22, 645 (1921); G. S. Fulcher, J. Am. Chem. Soc. 8, 339 (1925)].
Space charge field and dynamics of the grating formation in a photorefractive polymer-dispersed liquid crystal based on a photoconducting polysiloxane
Authors: Paelke Lutz , Kitzerow Heinz-S.
Published: December 2006

A photorefractive system composed of liquid crystal droplets dispersed in a photoconducting polymer is characterized by means of two-beam coupling. The amplitudes and phases of the spatial variations of the refractive index and the absorption coefficient are measured using the moving grating technique. Dynamic measurements indicate that the phase of the refractive index modulation is nearly constant while the amplitude increases gradually. The maximum value of the internal space charge field can be estimated from the amplitude of the phase grating and is found to be of the order of one-hundredth of the external bias field.
Growth of Au–TiO2 nanocomposite thin films by a dual-laser, dual-target system
Authors: György E. , Sauthier G. , Figueras A. , Giannoudakos A. , Kompitsas M. , Mihailescu I. N.
Published: December 2006

Nanocomposite thin films formed by gold nanoparticles embedded in a titanium dioxide matrix have been synthesized by pulsed laser deposition. Two synchronized laser sources, an ArF* excimer (λ=193nm, τFWHM∼12ns) laser and a frequency tripled Nd:yttrium aluminium garnet (λ=355nm, τFWHM∼10ns) laser, were used for the simultaneous ablation of the titanium dioxide and gold targets. The optical absorption characteristics of the obtained nanocomposites were investigated as a function of laser parameters used for the ablation of the gold target. The obtained results proved the possibility of tuning the optical properties of gold–titanium dioxide nanocomposites with the proper choice of laser irradiation parameters. Band gap narrowing and absorption in the visible spectral region induced by the incorporation of gold enable the design of nanostructured thin films to be achieved for photocatalysts and solar energy converters.
Dynamics of an interface with adsorption layer between two fluids
Authors: Felderhof B. U.
Published: December 2006

The dynamics of a flat interface with adsorption layer between two viscous fluids is studied on the basis of the linearized Navier-Stokes equations. The dispersion equation for interfacial waves involves surface tension and elasticity moduli of the interface, besides gravitational acceleration. The displacement of the interface due to a force density applied at the interface is characterized by a susceptibility tensor. Wave excitation due to a monochromatic plane wave source or a monochromatic line source located at some distance from the interface is discussed.
Spatially distributed stochastic systems: Equation-free and equation-assisted preconditioned computations
Authors: Qiao Liang , Erban Radek , Kelley C. T. , Kevrekidis Ioannis G.
Published: December 2006

Spatially distributed problems are often approximately modeled in terms of partial differential equations (PDEs) for appropriate coarse-grained quantities (e.g., concentrations). The derivation of accurate such PDEs starting from finer scale, atomistic models, and using suitable averaging is often a challenging task; approximate PDEs are typically obtained through mathematical closure procedures (e.g., mean field approximations). In this paper, we show how such approximate macroscopic PDEs can be exploited in constructing preconditioners to accelerate stochastic computations for spatially distributed particle-based process models. We illustrate how such preconditioning can improve the convergence of equation-free coarse-grained methods based on coarse timesteppers. Our model problem is a stochastic reaction-diffusion model capable of exhibiting Turing instabilities.
A time-dependent analytical sheath model for dual-frequency capacitively coupled plasma
Authors: Jiang Wei , Mao Ming , Wang You-Nian
Published: December 2006

The time-dependent model of the ion motion is used to study characteristics of dual-frequency (DF) capacitive sheaths. The model assumes that both the ion density and velocity vary with time, but time-derivative terms are neglected. Analytical expressions of the instantaneous electron sheath edge and the sheath potential are obtained with the assumption of a step-like electron density profile. It is shown that the present model can give monotonic spatial distributions of the sheath potential and ion density within the DF sheath. The dependence of the maximum sheath thickness and sheath voltage on the ratio of two frequencies or currents is also discussed.
Self-similar magnetohydrodynamic model for direct current discharge fireball experiments
Authors: Tsui K. H. , Navia C. E. , Robba M. B. , Carneiro L. T. , Emelin S. E.
Published: December 2006

Ball lightning models and corresponding laboratory efforts in generating fireballs are briefly summarized to give an overview of the current status. In particular, emphasis is given to direct current discharge experiments at atmospheric pressure such as capillary discharge with a plasma plume in front of the anode opening [Emelin et al., Tech. Phys. Letters 23, 758 (1997)] and water resistor discharge with fluttering fireball overhead [Egorov and Stepanov, Tech. Phys. 47, 1584 (2002)]. These fireballs are interpreted as laboratory demonstrations of the self-similar magnetohydrodynamic (MHD) model of ball lightning [Tsui, Phys. Plasmas 13, 072102 (2006)].
Dipolar coupling in closely packed pseudo-spin-valve nanowire arrays
Authors: Goolaup S. , Adeyeye A. O. , Singh N.
Published: December 2006

A systematic study of the effects of lateral magnetostatic coupling of closely packed pseudo-spin-valve Ni80Fe20(10nm)∕Cu(tCu)∕Ni80Fe20(80nm) nanowire arrays with varied Cu film thicknesses is investigated. Nanowire arrays with a width of 185nm and edge-to-edge spacings of 35 and 185nm, respectively, were fabricated using deep ultraviolet lithography at 248nm exposing wavelength. When the Cu spacer layer thickness is comparable to the edge-to-edge spacing of the closely packed wires, marked changes in the magnetization reversal process are observed for the nanowire array with edge-to-edge spacing of 35nm, due to the competition between the dipolar coupling between the neighboring nanowires and interlayer magnetostatic coupling between the thick and thin Ni80Fe20 layers.
Ab initio prediction of half-metallic properties for the ferromagnetic Heusler alloys Co2MSi (M=Ti,V,Cr)
Authors: Chen Xing-Qiu , Podloucky R. , Rogl P.
Published: December 2006

By means of density functional calculations, the magnetic and electronic properties and phase stabilities of the Heusler compounds Co2MSi (with M=Ti,V,Cr,Mn,Fe,Co,Ni) were investigated. Based on the calculated results, we predict the ferromagnetic phases of the compounds Co2TiSi, Co2VSi, and Co2CrSi to be half metals. Of particular interest is Co2CrSi because of its high density of majority-spin states at Fermi energy in combination with a reasonably high estimated Curie temperature of 747K. The compounds Co2TiSi and Co2VSi are thermodynamically stable, whereas Co2CrSi is of a metastable phase which might be stabilized by suitable experimental techniques.
Final state problem for Korteweg–de Vries type equations
Authors: Hayashi Nakao , Naumkin Pavel I.
Published: December 2006

We study the final state problem for the Korteweg–de Vries type equations: ut−1∕ρ∣∂x∣ρ−1ux=λu2ux, (t,x)∊R+×R,∥u(t)−FS(t)∥L2→0 as t→∞, where λ∊R, the function FS(t) we call a final state, defined by the final data u+. We show that there does not exist a nontrivial solution of this equation in the case of FS(t)=U(t)u+, where U(t) is the free evolution group of this equation. We construct the modified wave operator for the Korteweg–de Vries type equations under the conditions that the final data u+ arc real-valued functions and the Fourier transform û+(ξ) vanishes at the origin.
Proton hydration in aqueous solution: Fourier transform infrared studies of HDO spectra
Authors: Śmiechowski Maciej , Stangret Janusz
Published: December 2006

This paper attempts to elucidate the number and nature of the hydration spheres around the proton in an aqueous solution. This phenomenon was studied in aqueous solutions of selected acids by means of Fourier transform infrared spectroscopy of semiheavy water (HDO), isotopically diluted in H2O. The quantitative version of difference spectrum procedure was applied for the first time to investigate such systems. It allowed removal of bulk water contribution and separation of the spectra of solute-affected HDO. The obtained spectral data were confronted with ab initio calculated structures of small gas-phase and polarizable continuum model (PCM) solvated aqueous clusters, H+(H2O)n, n=2–8, in order to help in establishing the structural and energetic states of the consecutive hydration spheres of the hydrated proton. This was achieved by comparison of the calculated optimal geometries with the interatomic distances derived from HDO band positions. The structure of proton hydration shells outside the first hydration sphere essentially follows the model structure of other hydrated cations, previously revealed by affected HDO spectra. The first hydration sphere complex in diluted aqueous solutions was identified as an asymmetric variant of the regular Zundel cation [The Hydrogen Bond: Recent Developments in Theory and Experiments, edited by P. Schuster, G. Zundel, and C. Sandorfy (North-Holland, Amsterdam, 1976), Vol. II, p. 683], intermediate between the ideal Zundel and Eigen structures [E. Wicke et al., Z. Phys. Chem. Neue Folge 1, 340 (1954)]. Evidence was found for the existence of strong and short hydrogen bonds, with oxygen-oxygen distance derived from the experimental affected spectra equal 2.435Å on average and in the PCM calculations about 2.41–2.44Å. It was also evidenced for the first time that the proton possesses four well-defined hydration spheres, which were characterized in terms of hydrogen bonds’ lengths and arrangements. Additionally, an outer hydration layer, shared with the anion, as well as loosely bound water molecules interacting with free electron pairs of the central complex were detected in the affected spectra.
A generalized Petschek magnetic reconnection rate
Authors: Arber T. D. , Haynes M.
Published: December 2006

Simple physical arguments show that a generalization of the basic Petschek reconnection rate allows it to be extended to the Hall magnetohydrodynamic (MHD) rate. This result is confirmed by direct numerical simulations of the compressible fluid equations. To ensure that Petschek reconnection is obtained we specify a localized resistivity. The new generalized reconnection rate therefore gives an accurate estimate of the unforced Petschek reconnection rate for both MHD and Hall MHD. Since the Hall Petschek rate does not vanish in the limit of zero resistivity this generalized rate may also give the collisionless Hall Petschek reconnection rate.
Basic properties of the current-current correlation measure for random Schrödinger operators
Authors: Hislop Peter D. , Lenoble Olivier
Published: December 2006

The current-current correlation measure plays a crucial role in the theory of conductivity for disordered systems. We prove a Pastur-Shubin-type formula for the current-current correlation measure expressing it as a thermodynamic limit for random Schrödinger operators on the lattice and the continuum. We prove that the limit is independent of the self-adjoint boundary conditions and independent of a large family of expanding regions. We relate this finite-volume definition to the definition obtained by using the infinite-volume operators and the trace-per-unit volume.
The permanent electric dipole moments and magnetic g factors of uranium monoxide
Authors: Heaven Michael C. , Goncharov Vasiliy , Steimle Timothy C. , Ma Tongmei , Linton Colan
Published: December 2006

Permanent electric dipole moments and magnetic g factors for uranium monoxide (UO) have been determined from analyses of optical Stark and Zeeman spectra recorded at a spectral resolution that approaches the natural linewidth limit. Numerous branch features in the previously characterized [L. A. Kaledin et al., J. Mol. Spectrosc. 164, 27 (1994)] (0,0) [18403]5-X(1)4 and (0,0) [18404]5-X(1)4 electronic transitions were recorded in the presence of tunable static electric (Stark effect) or magnetic (Zeeman effect) fields. The lines exhibited unusually large Zeeman tuning effects. A ligand field model and an ab initio electronic structure calculation [R. Tyagi, Ph.D. thesis, The Ohio State University (2005)] were used to interpret the ground state properties. The results indicate that the low energy electronic states of UO are sufficiently ionic for the meaningful application of ligand field theory models. The dipole moments and g factors were distinctly different for the three electronic states examined, which implies that these properties may be used to deduce the underlying electronic state configurations.
Variational approach to Robertson–Walker spacetimes with homogeneous scalar fields
Authors: Giambò Roberto , Giannoni Fabio , Magli Giulio
Published: December 2006

Existence of solutions between prescribed configurations is proved for spatially flat Robertson–Walker spacetimes coupled with homogeneous scalar field sources, using a modified version of the Euler–Maupertuis least action variational principle. The solutions are obtained as limits of approximating variational problems, solved using the techniques originally introduced by Rabinowitz.
Rapid-thermal-processing-based internal gettering for heavily boron-doped Czochralski silicon
Authors: Fu Liming , Yang Deren , Ma Xiangyang , Tian Daxi , Que Duanlin
Published: December 2006

The effect of rapid-thermal processing (RTP) ambients on the formation of oxygen precipitates and denuded zone (DZ) in heavily boron-doped (HB) Czochralski (Cz) silicon by a low-high (L-H) two-step annealing (800°C∕4h+1000°C∕16h) has been investigated. It was found that after the L-H two-step annealing, there was a high density of bulk microdefects (BMDs) and no observable DZ was formed near the surface in HB Cz silicon wafers preannealed by the RTP in Ar ambient, while the BMD density was quite low in HB Cz silicon wafers preannealed by the RTP in O2 ambient. However, applying the preannealing of RTP sequentially in Ar and O2 ambients allowed us to obtain a high density of BMDs in combination with a sufficient DZ by the subsequent L-H two-step annealing. This approach offers a pathway to optimize internal gettering for HB Cz silicon.
On dust spin up in uniform magnetized plasma
Authors: Krasheninnikov S. I.
Published: December 2006

Two mechanisms of dust particle spin up in uniform magnetized plasma associated with ion gyromotion and j⃗×B⃗ force caused by cross-field current flowing through the grain are discussed. Estimations made for the conditions of a tokamak-edge plasma show that such mechanisms can spin up dust particles to characteristic rotation frequencies ∼106s−1.
Design and implementation of a high power rf oscillator on a printed circuit board for multipole ion guides
Authors: Mathur Raman , O’Connor Peter B.
Published: December 2006

Radio frequency (rf) oscillators are commonly used to drive electrodes of ion guides. In this article a rf oscillator circuit design and its implementation is presented. The printed circuit board for the rf oscillator is designed and fabricated. The performance of the circuit was tested to transfer ions through a hexapole in a matrix-assisted laser desorption∕ionization Fourier transform mass spectrometer. A comprehensive discussion of several aspects of printed circuit board design for high power and high frequency circuits is presented.
Detection and identification of illicit drugs using terahertz imaging
Authors: Lu Meihong , Shen Jingling , Li Ning , Zhang Yan , Zhang Cunlin , Liang Laishun , Xu Xiaoyu
Published: December 2006

We demonstrated an advanced terahertz imaging technique for detection and identification of illicit drugs by introducing the component spatial pattern analysis. As an explanation, the characteristic fingerprint spectra and refractive index of ketamine were first measured with terahertz time-domain spectroscopy both in the air and nitrogen. The results obtained in the ambient air indicated that some absorption peaks are not obvious or probably not dependable. It is necessary and important to present a more practical technique for the detection. The spatial distributions of several illicit drugs [3,4-methylenedioxymethamphetamine, methylenedioxyamphetamine, heroin, acetylcodeine, morphine, and ketamine], widely consumed in the world, were obtained from terahertz images using absorption spectra previously measured in the range from 0.2to2.6THz in the ambient air. The different kinds of pure illicit drugs hidden in mail envelopes were inspected and identified. It could be an effective method in the field of safety inspection.
The physics of rotational tunneling: hole-burning spectroscopy of methyl groups
Authors: Somoza M. M. , Friedrich J.
Published: December 2006

Methyl groups are most outstanding quantum systems due to their inherent symmetry properties which cannot be destroyed by any kind of lattice disorder. We show how optical hole-burning techniques can be employed to measure rotational tunneling relaxation processes. Since the tunneling parameters are extremely sensitive to changes in the host lattice, there is a rich variety of relaxation phenomena that can be observed. Hole-burning techniques have the capability of measuring not only extremely slow processes with high precision but also rather fast processes. We exploit this possibility to show that the relaxation times at 2K change by 14 orders of magnitude if the permutation symmetry of the methyl group is destroyed by asymmetric deuterium substitution.
Spectroscopy of nanosized composites consisting of silicon-organic polymers in nanoporous silicas
Authors: Ostapenko N. , Kozlova N. , Suto S. , Watanabe A.
Published: December 2006

Fluorescence and excitation spectra (T=5–290K) of nanosized silicon-organic polymers poly(di-n-hexylsilane) and poly(methyl(phenyl)silane) incorporated into porous silica materials MCM-41 and SBA-15 have been studied with varying pore diameter from 2.8to10nm. The controlled variation of the pore diameter in a wide range (2.8–10nm) permitted us, for the first time, to investigate the optical properties of the polymers on their transition from isolated macromolecules to a film. It is found that this transition depends on polymer type and occurs via the formation of new spatially independent structures of the polymers not observed in the spectra of the film, namely, via the formation of disordered and (or) ordered conformations of polymer chains and clusters.
Comparative study of structure and photo-induced reactivity of malonaldehyde and acetylacetone isolated in nitrogen matrices
Authors: Trivella A. , Coussan S. , Chiavassa T. , Theulé P. , Roubin P. , Manca C.
Published: December 2006

The structure and reactivity of the eight enolic forms (one chelated and seven non-chelated) of malonaldehyde and acetylacetone are compared through theoretical and experimental data. Ground-state geometries, energies, and vibrational frequencies are calculated with the B3LYP∕6–311++G(2d,2p) model chemistry. The electronic delocalization as well as the cis/trans rotamer properties are analyzed. The hydrogen bond strength of the chelated forms can be estimated by the energy difference between chelated and non-chelated forms, and its enhancement due to methyl-induced electron release is estimated as 1.7kcal∙mol−1. UV- and IR-induced reactivity of molecules isolated in nitrogen matrices is studied by means of FT-IR spectrometry. Interconversion between rotamers is the main process observed for both molecules, only some among the seven non-chelated forms being created.
Fourier transform infrared studies of the N2–O2 binary system
Authors: Minenko M. , Jodl H.-J.
Published: December 2006

Solid solutions (N2)x(O2)1−x have been investigated by infrared absorption measurements mainly in the O2 and N2 stretching regions, between 60–10K, completing former similar studies by Raman scattering. We produced thermodynamically stable samples by a careful thermal treatment, followed by cooling/heating cycles over weeks, during which we took spectra. From fingerprints in the infrared spectra we deduce phase-transition and solubility lines and suggest a refined, improved T−x% phase diagram in respect to the inconsistencies between those in the literature. The spectra of N2–O2 mixtures are pretty complex, but by referring to known spectra of the pure systems N2 or O2 we were able to assign and interpret broad (∼100cm−1) phonon side bands to fundamentals and an electronic transition (O2), depending on actual temperature and concentration. Narrow features in the spectra (<10cm−1) were attributed to the vibron DOS of N2 or O2, whose bandwidth, band shape, and intensity are different and characteristic for each phase. Differences between pure and mixed systems are pointed out. The matrix isolation technique (2ppm of CO) was used to probe our mixture.
Extraordinary temperature dependence of isochoric thermal conductivity of crystalline CO2 doped with inert gases
Authors: Konstantinov V. A. , Manzhelii V. G. , Revyakin V. P. , Sagan V. V.
Published: December 2006

The isochoric thermal conductivities of the solid solutions (CO2)0.905Kr0.095 and (CO2)1−xXex (x=0.052 and 0.097) of different densities are investigated in the temperature interval from 150K to the onset of melting. An unusual effect of point defects on the thermal conductivity has been detected. In pure CO2 at T>150K the isochoric thermal conductivity decreases smoothly with increasing temperature. In contrast, the thermal conductivity of CO2∕Kr and CO2∕Xe solid solutions first decreases, passing through a minimum at 200–210K, and then starts to increase with temperature up to the onset of melting. This behavior of the isochoric thermal conductivity is attributed to the rotation of the CO2 molecules, which gain more freedom as the spherically symmetrical inert gas atoms are dissolved in the CO2.
Ionic chromophores Xep+ (p⩽4) in multishell rare-gas clusters Xem(NF3)kNe7500 (m,k⩽100) studied with fluorescence spectroscopy
Authors: Kanaev A. , Museur L. , Laarmann T. , Möller T.
Published: December 2006

We have studied fluorescence spectra of small Xem and Xem(NF3)k clusters (m,k⩽102) embedded in large host Ne7500 clusters, excited with SR excitation in the VUV spectral region above the Xe+(P1∕22) atomic limit. The IR emission bands due to ionic chromophores Xep+ (p=2,3,4) as well as UV (B–X) and visible (C–A) bands due to desorbed Xe+F− excimer molecules have been observed. The triatomic Xe2F excimer emission has only been observed under low-energy excitation close to the lowest xenon exciton absorption band. A competition between ionic and charge-transfer reaction channels is followed as a function of the cluster sizes m and k.