bluuebunny/crossref_metadata_2025 huggingface dataset:
Walking the Path: A New Journey to Explore and Discover Through Visual Analytics
Authors: Wong Pak Chung , Rose Stuart J , Chin George , Frincke Deborah A , May Richard , Posse Christian , Sanfilippo Antonio , Thomas Jim
Published: December 2006

Under the leadership of the US Department of Homeland Security (DHS), researchers at the Pacific Northwest National Laboratory (PNNL) established a research center focusing on the discipline of visual analytics in 2004. A year later, the center led a multidisciplinary panel representing academia, industry, and government to formally define directions and priorities for future research and development (R&D) for visual analytics tools. The R&D agenda, Illuminating the Path, defines the term visual analytics as ‘the science of analytical reasoning facilitated by interactive visual interfaces’. This article describes our progress to date in walking that path. We briefly describe the background of the subject, present major professional activities and accomplishments of its community, and highlight some of the ongoing R&D efforts being carried out by researchers at PNNL to fulfill the requirements and missions of a new discipline that promises to change the way we deal with today's information.
Nature-Inspired Visualisation of Similarity and Relationships in Human Systems and Behaviours
Authors: Beale Russell , Hendley Robert J , Pryke Andy , Wilkins Barry
Published: December 2006

Visualisations of complex interrelationships have the potential to be complex and require a lot of cognitive input. We have drawn analogues from natural systems to create new visualisation approaches that are more intutive and easier to work with. We use nature-inspired concepts to provide cognitive amplification, moving the load from the user's cognitive to their perceptual systems and thus allowing them to focus their cognitive resources where they are most appropriate. Two systems are presented: one uses a physical-based model to construct the visualisation, while the other uses a biological inspiration. Their application to four visualisation tasks is discussed: the structure of information browsing on the internet; the structure of parts of the web itself; to aid the refinement of queries to a digital library; and to compare different documents for similar content.
In situ transmission electron microscopy of ion irradiated Fe–Pt alloy thin films
Authors: Morgan N. W. , Birtcher R. C. , Thompson G. B.
Published: December 2006

We report the microstructural evolution during irradiation of FePt and FePt 25at.% thin films sputter deposited onto electron transparent silicon monoxide substrates. The films were studied in situ for 500keV Kr+ irradiation up to a fluence of 1015ions∕cm2 or 4displacements∕atom (dpa). Upon irradiation to approximately 1dpa, the initial disconnected granular morphology became continuous. In particular, for FePt, accelerated grain growth was observed once the continuous morphology was achieved during ambient temperature irradiation. No atomistic (chemical) ordering from the as-deposited A1 phase into either the L10 FePt or L12 Fe3Pt phases was observed during ambient temperature irradiation. After irradiation, the specimens were then in situ annealed. The intermetallic ordering temperature, compared to that of an unirradiated film, was lowered by ≈200°C for FePt 25at.%. No decrease in the ordering temperature was observed for irradiated FePt. The rate of FePt grain growth during annealing was very similar for both irradiated and unirradiated films over the 25–650°C temperature range investigated.
Design and characterization of silicon carbide photoconductive switches for high field applications
Authors: Kelkar K. S. , Islam N. E. , Fessler C. M. , Nunnally W. C.
Published: December 2006

Characteristics of a silicon carbide photoconductive switch designed for high field applications have been studied. Analyses show that premature breakdown occurs primarily due to impact ionization and subsequent charge accumulation near the anode. For the shallow donor, deep-acceptor-type compensated material, a p+ layer next to the cathode results in field homogenization in the bulk. As a result, the blocking or hold off voltage of the switch could increase beyond the experimentally determined value of 18kV (0.45MV∕cm). Simulations also show that a minimum thickness, equivalent to a diffusion length, of the p+ layer is necessary to avoid premature breakdown. Following illumination, the photocurrent rise time of the switch would also improve by about 25% with the p+ layer near the cathode.
Effect of oxygen on the thermomechanical behavior of tantalum thin films during the β–α phase transformation
Authors: Knepper Robert , Stevens Blake , Baker Shefford P.
Published: December 2006

Tantalum thin films were prepared in the metastable β phase, and their thermomechanical behaviors were investigated in situ in an ultrahigh vacuum environment. Controlled levels of oxygen were incorporated into the films either during deposition, by surface oxidation after deposition, or during thermomechanical testing. The transformation from the β phase to the stable α phase takes place in conjunction with a distinct increase in tensile stress. The thermomechanical behavior is strongly affected by the amount of oxygen to which the film is exposed and the method of exposure. Increasing oxygen content inhibits the phase transformation, requiring higher temperatures to reach completion. It is shown that the phase transformation takes place by a nucleation and growth process that is limited by growth. Changes in the activation energy for the phase transformation due to solute drag are estimated as a function of oxygen content and the mechanisms behind the stress evolution are elucidated.
Fractional Israel layers
Authors: Krisch J. P.
Published: December 2006

A fractional Lie derivative, valid in the thin shell limit, is developed. The nonlocal nature of the fractional derivative allows the inclusion of shell thickness in the stress energy description of zero thickness Israel layers. The method is applied to several examples.
Exciton recurrence motion in aggregate systems in the presence of quantized optical fields
Authors: Nakano Masayoshi , Ohta Suguru , Kishi Ryohei , Nate Masahito , Takahashi Hideaki , Furukawa Shin-Ichi , Nitta Hiroya , Yamaguchi Kizashi
Published: December 2006

The exciton dynamics of model aggregate systems, dimer, trimer, and pentamer, composed of two-state monomers is computationally investigated in the presence of three types of quantized optical fields, i.e., coherent, amplitude-squeezed, and phase-squeezed fields, in comparison with the case of classical laser fields. The constituent monomers are assumed to interact with each other by the dipole-dipole interaction, and the two-exciton model, which takes into account both the one- and two-exciton generations, is employed. As shown in previous studies, near-degenerate exciton states in the presence of a (near) resonant classical laser field create quantum superposition states and thus cause the spatial exciton recurrence motion after cutting the applied field. In contrast, continuously applied quantized optical fields turn out to induce similar exciton recurrence motions in the quiescent region between the collapse and revival behaviors of Rabi oscillation. The spatial features of exciton recurrence motions are shown to depend on the architecture of aggregates. It is also found that the coherent and amplitude-squeezed fields tend to induce longer-term exciton recurrence behavior than the phase-squeezed field. These features have a possibility for opening up a novel creation and control scheme of exciton recurrence motions in aggregate systems under the quantized optical fields.
Thermodynamics and kinetics during pulsed laser annealing and patterning of FePt films
Authors: Buschbeck J. , Fähler S. , Weisheit M. , Leistner K. , McCord J. , Rellinghaus B. , Schultz L.
Published: December 2006

Laser annealing using 25ns pulses of a KrF excimer laser was applied to electrochemical and pulsed laser deposited FePt films of 700nm and 40 or 80nm thicknesses, respectively. The dependence of phase formation and magnetization behavior on the film thickness and the as-deposited state are studied. Models of the film heating are compared to the experimentally observed results. Furthermore a time temperature transformation (TTT) diagram for the ordering of FePt is proposed, summarizing the phase formation in dependence on annealing time and temperature. In agreement with the TTT diagram, laser annealing leads to a disordering of L10-ordered films. By only partially disordering the L10 phase, this approach provides control over the coercivity of hard magnetic FePt films. Local disordering is applied for magnetic patterning of the FePt films with dot patterns in the micrometer size range.
A semiclassical model of dielectric relaxation in glasses
Authors: Jameson John R. , Harrison Walter , Griffin P. B. , Plummer J. D. , Nishi Y.
Published: December 2006

A semiclassical double-well model of dielectric relaxation current in glasses is extended to (i) nonzero temperature, (ii) complex bias histories, and (iii) strong electric fields. At finite temperature, thermal excitation yields a contribution linear in temperature, which adds to the temperature-independent contribution from tunneling from the zero-temperature case. Both contributions vary linearly with applied field and have a time dependence of 1∕tn. Experimental measurements in three different glasses are shown to agree with this prediction, and it is shown how to use such measurements to estimate the material parameters t0 and σ0. For complex bias histories, a principle of superposition is found, as observed experimentally, if the applied fields are weak compared to the material parameter E0, estimated to be on the order of 107V∕m. For an electric field pulsed periodically from 0 to E, the current can be decomposed into a fast contribution due to particles tunneling back and forth every cycle of the field, and a slow residual contribution whose time dependence is the same as that for a continuous bias, but whose magnitude is reduced by the duty cycle of the periodic bias. For a sinusoidal electric field, thermal excitation gives a contribution to the dielectric constant that varies linearly with temperature and has a real part that varies logarithmically with frequency and an imaginary part that varies as the inverse tangent of frequency. For tunneling, both parts are independent of temperature and vary approximately as the logarithm of frequency, a dependence observed experimentally and almost indistinguishable from that suggested by the 1∕tn current response to a step voltage. For strong electric fields, the current that flows after the field is removed is found to be dominated by particles that fell forward when the field was on. Since particles fall forward quickly but tunnel back slowly, even strong fields applied for a short period of time can produce a large, long-lasting return current. These analyses lead to a number of testable predictions, and should be useful for understanding the phenomenon of dielectric relaxation and its impact on electronic devices.
Two-dimensional simulation of ac-driven microplasmas confined to 100–300μm diameter cylindrical microcavities in dielectric barrier devices
Authors: Seo Jeong Hyun , Eden J. Gary
Published: December 2006

Cylindrical microcavity plasma devices with diameters (D) in the 100–300μm range and a dielectric barrier structure similar to that described by Park et al. [J. Appl. Phys. 99, 026107 (2006)] for Al∕Al2O3 devices have been investigated numerically. A two-dimensional fluid simulation of microplasmas in Ne/7% Xe gas mixtures with pD values (where p is the total gas pressure) in the 3–9Torrcm interval yields the temporal history of the spatially resolved electron and ion number densities in response to a 250kHz bipolar excitation wave form. Calculations show two distinct regions of plasma development, along the microcavity axis and near the wall, each of which dominates the plasma characteristics in separate pD regions. For low pD values (<4Torrcm), the negative glow produced at the cavity wall extends to the microcavity axis which, in combination with the strong axial electric field, produces an intense glow discharge on axis. For 4≲pD≲6Torrcm, a weakened axial discharge is observed early in the life of the plasma but the radial variation of the electron density flattens. Further increases in the gas pressure (to the largest pD values investigated, 6–9Torrcm) result in the retreat of the negative glow to the vicinity of the microcavity wall, thereby producing a diffuse but annular discharge. Even at the higher pD values, the axial discharge appears to facilitate ignition of the negative glow. The predictions of the simulations are consistent with the behavior of Al∕Al2O3 microplasma devices for which D=100–300μm.
Highly anisotropic conductivity in organosiloxane liquid crystals
Authors: Gardiner D. J. , Coles H. J.
Published: December 2006

In this paper, we present the conductivity and dielectric characterization of three homologous series of smectic A siloxane containing liquid crystals. The materials studied include one monomesogenic series, which consists of a 4-(ω-alkyloxy)-4′-cyanobiphenyl unit terminated by pentamethyldisiloxane, and two bimesogenic series, which consist of twin 4-(ω-alkyloxy)-4′-cyanobiphenyls joined via tetramethyldisiloxane or decamethylpentasiloxane. All of the compounds exhibit wide temperature range enantiotropic smectic A phases; the effect of the siloxane moiety is to suppress nematic morphology even in the short chain homologs. We find that these compounds exhibit a highly anisotropic conductivity: the value perpendicular to the director is to up to 200 times that parallel to the director. For the nonsiloxane analog 4-(ω-octyl)-4′-cyanobiphenyl (8CB), this value is approximately 2. It is also found that the dielectric anisotropy is reduced significantly; a typical value is ∼1 compared to 8.4 for 8CB. We propose that the origin of these unusual properties is in the smectic structure; the microphase separation of the bulky, globular siloxane moieties into liquidlike regions severely inhibits the mobility parallel to the director and across the smectic layers. Further, the inclusion of this unit acts to increase the antiparallel correlations of molecular dipoles in the aromatic and alkyloxy sublayers, reducing the dielectric anisotropy significantly compared to nonsiloxane analogs. The highly anisotropic conductivity suggests that these materials are particularly suitable for application in electro-optic effects which exploit this property, e.g., the bistable electro-optic effect in smectic A liquid crystals.
First-order perturbation solutions of embedded strained wires
Authors: Chiu C.-H. , Wang Hangyao
Published: December 2006

The paper presents the first-order perturbation solutions to the two-dimensional elasticity problems of strained wires embedded in a multilayered film-substrate system with homogeneous elastic properties. The solutions are accurate to the first order of the characteristic slope of the wires; the expressions of the solutions are concise for wires containing multiple facets; and the solutions are valid for single wire, multiple wires with different shapes, and a periodic array of identical wires. The perturbation solutions provide an efficient scheme for studying the effects of embedded wires on the stresses in the multilayered system.
Kinetics of the bcc–hcp transition in He4 off the melting curve
Authors: Birchenko A. P. , Vekhov Ye. O. , Mikhin N. P. , Polev A. V. , Rudavskii E. Ya.
Published: December 2006

The kinetics of the bcc–hcp structural phase transition in He4 is investigated by the method of precision barometry in the pressure range 25–31 bar and temperature range 1.25–1.90K. Under constant-volume conditions the kinetics of the pressure and temperature variations is recorded in the range of molar volumes Vm=20.85–21.10cm3∕mole. It is found that the process of cooling is accompanied by an unusual two-stage relaxation of the pressure: initially an exponential decrease of the pressure occurs due to thermal contraction of the supercooled bcc phase, and then the structural transition itself occurs very rapidly. The latter is accompanied by a pronounced thermal effect due to the release of the heat of the phase transition. It is shown that the inverse, hcp–bcc phase transition occurs in one stage (without a delay) and is accompanied by absorption of the heat of transition. Experimental data on the variation of the pressure are obtained in the bcc and hcp single-phase regions and along the bcc–hcp phase equilibrium line.
Blistering of implanted crystalline silicon by plasma hydrogenation investigated by Raman scattering spectroscopy
Authors: Düngen W. , Job R. , Mueller T. , Ma Y. , Fahrner W. R. , Keller L. O. , Horstmann J. T. , Fiedler H.
Published: December 2006

Czochralski silicon wafers were implanted with H+ ions at a dose of 1×1016cm−2 followed by hydrogen plasma treatments at different temperatures. The minimum hydrogen implantation dose required for silicon surface exfoliation of 3×1016H+∕cm2 without further hydrogen incorporation was reduced to one-third by subsequent plasma hydrogenation. The corresponding local vibrational modes of hydrogen molecules, vacancy-hydrogen complexes, and Si–H bonds on surfaces have been analyzed by micro-Raman scattering spectroscopy to investigate blistering and platelet formation. The surface profile has been studied by atomic force microscopy and scanning electron microscopy. The plasma treated samples were annealed to investigate the mechanism and applicability of the induced exfoliation. ⟨111⟩-platelet formation occurred below plasma hydrogenation temperatures of 350°C. At temperatures above 450°C, ⟨100⟩-platelet nucleation induced blistering.
Composition influences on the electrical and electromechanical properties of lead zirconate titanate thin films
Authors: Gerber P. , Böttger U. , Waser R.
Published: December 2006

The influences of the Zr content on the structural, electrical, and electromechanical properties of Pb[Zr(x),Ti(1−x)]O3 [PZT(x∕1−x)] thin films are investigated in detail. Additionally to measuring all major characteristics of the samples, the electromechanical large-signal behavior is modeled. Raising the Zr content increases the unit cell size and forces the preferred phase to become rhombohedral above the morphotropic phase boundary (MPB). The increased unit cell size changes the switching behavior and increases the intrinsic behavior of the unit cells. The intrinsic behavior is reduced by the phase change, which also introduces non-180° domain wall motion, improving the large-signal strain. Additionally, the domain configuration in saturation is more stable further away from the MPB. Finally, the most suitable materials will be selected for different applications.
Influence of long-range substrate roughness on disorder in V-groove quantum wire structures
Authors: Reichardt H. , Leifer K. , Pelucchi E. , Karlsson K. F. , Weman H. , Rudra A. , Kapon E.
Published: December 2006

The observation and the interpretation of line splitting in photoluminescence and cathodoluminescence spectra of GaAs∕AlGaAs V-groove quantum wires (QWRs) are reported. The QWR emission line splits into two peaks whose intensities oscillate systematically along the axis of the wire. Combining atomic force microscopy and cathodoluminescence measurements, we show a clear correlation between the surface topography of the V-groove and the individual peak intensities. We elucidate the relationship between the V-groove sidewall roughness and the shape at its bottom, and explain their impact on the QWR formation using a two-dimensional growth model accounting for self-limited growth in each V-groove domain. The influence of the long-range substrate roughness on the QWR spectral features is thus clarified. The study provides guidelines for improving QWR uniformity in order to achieve near-ideal model systems for one-dimensional semiconductors.
Existence and uniqueness for the reflection and transmission problem in stratified electromagnetic media
Authors: Berti Alessia
Published: December 2006

The reflection-transmission problem of time-harmonic waves in a stratified electromagnetic medium is investigated. The waves are sent from upward or downward with oblique incidence. By means of the energy flux, up-going and down-going waves are distinguished and the reflection and transmission matrices are introduced. When the solid occupies a strip between two homogeneous media, the existence and uniqueness of the reflected and transmitted waves are proved. The same conclusions are obtained for a dielectric without memory extended in the whole space.
Investigation of the leakage mechanism in Sr–Ta–O and Bi–Ta–O thin film capacitors
Authors: Goux L. , Wouters D. J.
Published: December 2006

In this work, we studied the leakage mechanism at different temperatures in Pt∕Sr–Ta–O∕Pt and Pt∕Bi–Ta–O∕Pt thin film capacitors. The dielectrics were deposited by metal-organic chemical vapor deposition at 360°C as amorphous layers, and the complete process flow of the capacitors was kept below 500°C. Conduction is governed by Poole-Frenkel emission down to ∼15 and ∼20nm for Sr–Ta–O and Bi–Ta–O, respectively. From the Poole-Frenkel plots, we extracted an index of refraction of ∼2.1 for Sr–Ta–O and ∼2.5 for Bi–Ta–O, and an energy of ∼0.8eV from involved trap centers to the conduction band for both dielectrics.
Solid-liquid interfacial energy of pyrene
Authors: Akbulut S. , Ocak Y. , Böyük U. , Erol M. , Keşlioğlu K. , Maraşlı N.
Published: December 2006

The equilibrated grain boundary groove shapes for commercial purity pyrene (PY) were directly observed by using a temperature gradient stage. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient and solid-liquid interfacial energy of PY have been determined to be (8.9±0.9)×10−8Km and (21.9±3.3)×10−3Jm−2 with the present numerical model and Gibbs-Thomson equation, respectively. The grain boundary energy of PY phase has been determined to be (42.8±7.3)×10−3Jm−2 from the observed grain boundary groove shapes. Thermal conductivity ratio of liquid phase to solid phase has also been measured to be 0.89.
Plasma oscillations in two-dimensional electron channel of a ring diode
Authors: Heidari Semiromi E. , Ebrahimi F. , Bagheri M.
Published: December 2006

We present an analytical approach based on the boundary conditions and complete set of orthonormal functions applied to Poisson’s equation coupled with the hydrodynamic electron transport equations for calculating the spectra of the plasma oscillations in two-dimensional electron channel diodes with slot and ring geometries.
Design and construction of a compact vacuum furnace for scientific research
Authors: Lee Chin C. , Wang David T. , Choi Won S.
Published: December 2006

The design, construction, and measurement of a compact vacuum furnace are reported. This type of furnace has many scientific applications in material processing and growth research. One example is the fluxless bonding process, where elevated temperature is needed to melt the solder and vacuum environment is required to inhibit solder oxidation. The primary objective of the furnace design is to keep the vacuum enclosure cool using only natural convection while allowing the heating platform to reach high temperature. This characteristic is necessary to enable us to seal the vacuum chamber using O-rings. To achieve this, the platform was designed to be thermally isolated from the chamber enclosure. Heat losses from the platform by conduction, convection, and radiation were analyzed. The dominating loss was found to be caused by the blackbody radiation, which can thus be used to estimate the relationship between platform temperature and the drive power needed. With a graphite platform of 75×75×25mm3, only 270W of power is needed to drive the platform to 400°C. At this temperature, the temperature of the furnace enclosure is below 55°C, allowing O-rings to be used to seal the vacuum chamber. Using a mechanical pump, the furnace can be pumped down to 40mTorr, which is low enough for our fluxless bonding processes. With a temperature controller, the platform temperature can be controlled within 1%. The heat-up time to 400°C is only 7min.
Simulations of the dynamics of thermal undulations in lipid bilayers in the tensionless state and under stress
Authors: Shkulipa S. A. , den Otter W. K. , Briels W. J.
Published: December 2006

The relaxation processes of height undulations and density fluctuations in a membrane have been studied by molecular dynamics simulations of a coarse grained amphiphilic bilayer model. We observe a double exponential decay in their time correlations, with relaxation rates in good quantitative agreement with the theory by Seifert and Langer [Europhys. Lett. 23, 71 (1993)]. Intermonolayer friction due to slippage between the two monolayers is shown to be the dominant dissipative mechanism at the high wave numbers, q>10μm−1, typically encountered in computer simulations. We briefly discuss the ramifications of the slow undulatory relaxation process for the calculation of bending rigidities from the static undulation structure factors. The relaxation rates are sensitive to the surface tension, and at high elongations an oscillatory contribution is observed in the time correlation of the undulations.
The dynamics of an isolated plasma filament at the edge of a toroidal device
Authors: Ryutov D. D.
Published: December 2006

The dynamics of an isolated plasma filament (an isolated blob) in the far scrape-off layer (SOL) of a toroidal device is described, with a proper averaging of the geometrical parameters as well as plasma parameters along the filament. The analysis is limited to the magnetohydrodynamic description. The effects of the electrical contact of the filament end with the limiter and of the finite plasma resistivity are also discussed.
Density-functional theory with effective potential expressed as a direct mapping of the external potential: Applications to atomization energies and ionization potentials
Authors: Glushkov Vitaly N. , Fesenko Sergey I.
Published: December 2006

In this paper the authors further develop and apply the direct-mapping density functional theory to calculations of the atomization energies and ionization potentials. Single-particle orbitals are determined by solving the Kohn-Sham [Phys. Rev. A. 140, 1133 (1965)] equations with a local effective potential expressed in terms of the external potential. A two-parametric form of the effective potential for molecules is proposed and equations for optimization of the parameters are derived using the exchange-only approximation. Orbital-dependent correlation functional is derived from the second-order perturbation theory in its Møller-Plesset-type zeroth-order approximation based on the Kohn-Sham orbitals and orbital energies. The total atomization energies and ionization potentials computed with the second-order perturbation theory were found to be in agreement with experimental values and benchmark results obtained with ab initio wave mechanics methods.
Exploring DNA groove water dynamics through hydrogen bond lifetime and orientational relaxation
Authors: Pal Subrata , Maiti Prabal K. , Bagchi Biman
Published: December 2006

Dynamics of water molecules in the grooves of DNA are of great interest both for practical (functionality of DNA) and fundamental (as examples of confined systems) interest. Here the authors employ atomistic molecular dynamics simulations to understand varying water dynamics at the minor and the major grooves of a 38 base-pair long DNA duplex in water. In order to understand and quantify the diversity in the nature of hydrogen bond due to many hydrogen bond donors and acceptors present in the four bases, they have undertaken study of hydrogen bond lifetime (HBLT) correlation functions of all the specific hydrogen bonds between the base atoms and water molecules. They find that the HBLT correlation functions are in general multiexponential, with the average lifetime depending significantly on the specificity and may thus be biologically relevant. The average hydrogen bond lifetime is longer in the minor groove than that in the major groove by almost a factor of 2. Analysis further shows that water hydrogen bonds with phosphate oxygen have substantially shorter lifetimes than those with the groove atoms. They also compute two different orientational time correlation functions (OTCFs) of the water molecules present at the major and the minor grooves and attempt to correlate OTCF with HBLT correlation function. The OTCFs in the minor groove exhibit three time scales, with the time constant of the slowest component one to two orders of magnitude longer than what is observed for bulk water. A slow component is also present for the major groove water but with shorter time constant. Interestingly, correlation between reformations allowed HBLT correlation function [CHB(t)] and the OTCF markedly deviates from each other in the grooves, indicating enhanced rigidity of water molecules in the grooves.
Phase-sensitive stimulated Raman adiabatic passage in dipolar extended lambda systems
Authors: Marx Christoph A. , Jakubetz Werner
Published: December 2006

The authors investigate the possible phase-sensitive behavior of (multiphoton) stimulated Raman adiabatic passage population transfer in extended lambda systems, if more than one state of an anharmonic progression of target levels is accessible in transitions of different photonicities. They use a minimal model four-level system (4LS) with one initial state separated from two target states by an apex state. The parameters of the 4LS are adapted from the bend states of the HCN-HNC system. Using a dressed-state analysis within the rotating wave approximation (RWA), the authors identify phase-dependent diabatic transitions between the two dressed states contributing to the state vector as the mechanism leading to phase-sensitive target populations. The essential features giving rise to the phase dependence are found to be different (non-zero-) diagonal elements of the dipole matrix, i.e., permanent dipole moments, and the presence of a direct two-photon overtone coupling between the apex state and the lower target state which formally enters the RWA Hamiltonian upon inclusion of permanent dipole moments. Among the parameters controlling the extent of the effect are the anharmonic properties of the target progression and the absolute values of the field frequencies, so that in view of the requirement to tune the driving fields into the vicinity of resonance, details of the level structure are of importance. A comparative numerical study executed without invoking RWA shows that qualitatively there are similar trends in the appearance of phase sensitivity, although the effects are considerably more pronounced in the full treatment. In the full treatment the authors also explore off-resonance conditions and discuss the signatures of phase sensitivity in the target populations.
Development of a pulsed-biasing system and temperature measurement techniques for transient heating experiments on plasma-material interactions
Authors: Hanna J. , Doerner R. , Hernandez R. , Seraydarian R. , Pugno R.
Published: December 2006

A power switching system has been developed to reverse the voltage polarity on the sample holder of PISCES-B from negative to positive potential in the microsecond time scale. Positive biasing draws electrons from the steady-state plasma through the sample, creating Ohmic heating on the surface. This pulsed biasing is used to replicate the transient heat loads that will be seen on plasma facing components during transient events, such as edge localized modes, in a device such as ITER. Surface temperatures are measured using two pyrometry techniques, a fast two-color system and a slower, more sensitive spectral system.
Entropy changes associated with the first-order magnetic transition in LaFe13−xSix
Authors: Jia L. , Liu G. J. , Sun J. R. , Zhang H. W. , Hu F. X. , Dong C. , Rao G. H. , Shen B. G.
Published: December 2006

Entropy changes accompanying a first-order magnetic transition have been studied for the intermetallic alloys LaFe13−xSix. An expression of the entropy change due to lattice expansion/contraction is derived based on the general thermodynamics theory. Combining it with the structural/magnetic measurements, and the mean-field-theory analyses, changes in magnetic, lattice, and electronic entropies are estimated. It is found that although magnetic entropy change is dominant, lattice entropy change is comparably large and cancels out most of the magnetic one. In contrast, electronic entropy change is negligibly small.
On passage through resonances in volume-preserving systems
Authors: Vainchtein D. L. , Neishtadt A. I. , Mezic I.
Published: December 2006

Resonance processes are common phenomena in multiscale (slow-fast) systems. In the present paper we consider capture into resonance and scattering on resonance in 3D volume-preserving multiscale systems. We propose a general theory of those processes and apply it to a class of kinematic models inspired by viscous Taylor-Couette flows between two counter-rotating cylinders. We describe the phenomena during a single passage through resonance and show that multiple passages lead to the chaotic advection and mixing. We calculate the width of the mixing domain and estimate a characteristic time of mixing. We show that the resultant mixing can be described using a diffusion equation with a diffusion coefficient depending on the averaged effect of the passages through resonances.
Combined density functional/polarizable continuum model study of magnetochiral birefringence: Can theory and experiment be brought to agreement?
Authors: Jansík Branislav , Rizzo Antonio , Frediani Luca , Ruud Kenneth , Coriani Sonia
Published: December 2006

The magnetic-field-induced axial birefringence (magnetochirality) of five closed-shell chiral molecules (three substituted oxiranes, carvone, and limonene) is studied at the density functional theory level using Becke’s 3-parameter Lee-Yang-Parr functional and frequency-dependent quadratic response theory. The influence of the environment and the conformational distribution on the property is also studied. The environment effects are described by the polarizable continuum model in its integral-equation formulation. The effect of the conformational distribution is investigated by performing calculations on several conformers—for carvone and limonene—followed by Boltzmann averaging. The calculated values for the magnetochiral birefringence are compared to previous ab initio results and experimental data where available. The refined model presented here brings the ab initio values closer to experiment. Still, disagreements remain in some cases and it appears difficult to resolve these discrepancies.
The relativistic complete active-space second-order perturbation theory with the four-component Dirac Hamiltonian
Authors: Abe Minori , Nakajima Takahito , Hirao Kimihiko
Published: December 2006

The relativistic complete active-space second-order perturbation theory (CASPT2) is developed for the four-component relativistic Hamiltonian. The present method can describe the near-degenerated and dissociated electronic states of molecules involving atoms of heavy elements. The present approach is less expensive than the relativistic multireference configuration interaction method. The ground and low-lying excited states of TlH, Tl2, and PtH molecules are calculated with the Dirac-Coulomb (DC) CASPT2 method and their spectroscopic constants are obtained. These spectroscopic constants are compared with experimental findings and previous theoretical work. For all the molecules, the spectroscopic constants of DC-CASPT2 show good agreement with the experimental or previous theoretical spectroscopic constants. The present theory provides accurate descriptions of bonding or dissociation states and of ground and excited states in a well-balanced way.
Extreme ultraviolet diagnostics of preformed plasma in laser-driven proton acceleration experiments
Authors: Ragozin Eugene N. , Pirozhkov Alexander S. , Yogo Akifumi , Ma Jinglong , Ogura Koichi , Orimo Satoshi , Sagisaka Akito , Mori Michiaki , Li Zhong , Nishiuchi Mamiko , Daido Hiroyuki
Published: December 2006

Proton acceleration experiments involving a 5μm thick Ti foil target irradiation are carried out with the femtosecond Ti:sapphire laser JLITE-X. The plasma emission at 13.5nm is recorded employing concave multilayer mirrors, which image the front- and rear-side plasmas onto the sensitive surfaces of a fast x-ray photodiode and a backside-illuminated charge coupled device. Online time-of-flight fast-particle measurements are performed simultaneously with the extreme ultraviolet (XUV) measurements. A strong correlation is observed between the energetic proton signal and the spatiotemporal behavior of the XUV plasma emission. In particular, the longer duration of the prepulse-produced XUV plasma emission indicates a lowering of the maximum proton energy. This allows using the XUV emission for the diagnostics of the high-intensity laser–solid-target interaction.
Experimental study of two-dimensional, monodisperse, frictional-collisional granular flows down an inclined chute
Authors: Bi Weitao , Delannay Renaud , Richard Patrick , Valance Alexandre
Published: December 2006

In this study, positions, velocities, and rotations of monodisperse disks confined two-dimensionally in a glass-walled chute are measured using a high-speed camera. Steady, fully developed granular flows (SFD) down bumpy inclines are systematically investigated in the frictional-collisional (dense, rapid) regime. Three bottoms with different effective roughness heights and roughness distributions are studied to evaluate the influence of the bottom condition. The granular flows are shallow, having a typical depth of ten disk diameters. In the range of flow rates and inclination angles where SFD flows occur, the mean discharge velocity is approximately proportional to the flow depth. The surface solid fractions slightly decrease from the bottom to the free surface. The streamwise velocity profiles are close to the linear profile at small inclination angles, whereas at large inclination angles, they are best approximated by the Bagnold profile. The mean angular velocity is equal to the half shear rate everywhere in the flow except near the free surface and the bottom. At large inclination angles, relatively deep SFD flows exhibit an S-shaped granular temperature profile, but in the core, the temperature is far from scaling linearly with the square shear rate. The streamwise and crosswise translational temperatures are slightly different from each other, whereas the rotational temperature is only half of the crosswise translational temperature. The rough bottoms have complex influences on the granular flows as revealed by the velocity and temperature profiles.
Trenched epitaxial lateral overgrowth of fast coalesced a-plane GaN with low dislocation density
Authors: Wang Te-Chung , Lu Tien-Chang , Ko Tsung-Shine , Kuo Hao-Chung , Yu Min , Wang Sing-Chung , Chuo Chang-Cheng , Lee Zheng-Hong , Chen Hou-Guang
Published: December 2006

The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on trenched a-plane GaN buffer layers. Not only the threading dislocation density but also the difference of anisotropic in-plane strain between orthogonal crystal axes can be mitigated by using trenched epitaxial lateral overgrowth (TELOG). The low threading dislocation density investigated by the cross-sectional transmission electron microscopy was estimated to be 3×107cm−2 on the N-face GaN wing. On the other hand, the Ga-face GaN wing with a faster lateral overgrowth rate could be influenced by the thin GaN layer grown on the bottom of the trenches, resulting in higher dislocation density generated. As a result, the authors concluded that a narrower stripped GaN seeds and deeper stripped trenches etched into the surface of sapphire could derive a better quality a-plane GaN film. Finally, they demonstrated the fast coalescence process of TELOG GaN films below 10μm thick.
Time-dependent density-functional theory beyond the adiabatic approximation: Insights from a two-electron model system
Authors: Ullrich C. A.
Published: December 2006

Most applications of time-dependent density-functional theory (TDDFT) use the adiabatic local-density approximation (ALDA) for the dynamical exchange-correlation potential Vxc(r,t). An exact (i.e., nonadiabatic) extension of the ground-state LDA into the dynamical regime leads to a Vxc(r,t) with a memory, which causes the electron dynamics to become dissipative. To illustrate and explain this nonadiabatic behavior, this paper studies the dynamics of two interacting electrons on a two-dimensional quantum strip of finite size, comparing TDDFT within and beyond the ALDA with numerical solutions of the two-electron time-dependent Schrödinger equation. It is shown explicitly how dissipation arises through multiple particle-hole excitations, and how the nonadiabatic extension of the ALDA fails for finite systems but becomes correct in the thermodynamic limit.
Icosahedral quasicrystals by optical interference holography
Authors: Tam Wing Yim
Published: December 2006

Optical interference holography has been proven to be a useful technique in fabricating periodic photonic crystals in which electromagnetic waves are forbidden in certain frequency band gaps. Compared to periodic crystals, quasicrystals, having higher point group symmetry, are more favorable in achieving complete band gaps. In this letter, we propose two seven-beam optical interference configurations based on the reciprocal vector space representation to fabricate icosahedral quasicrystals. Interference simulations for the quasicrystals exhibit the full symmetry of an icosahedron. The result paves the way for the fabrication of photonic quasicrystals using holographic lithography.
Bragg reflector based gate stack architecture for process integration of excimer laser annealing
Authors: Fortunato G. , Mariucci L. , Cuscunà M. , Privitera V. , La Magna A. , Spinella C. , Magrì A. , Camalleri M. , Salinas D. , Simon F. , Svensson B. , Monakhov E.
Published: December 2006

An advanced gate stack structure, which incorporates a Bragg reflector, has been developed for the integration of excimer laser annealing into the power metal-oxide semiconductor (MOS) transistor fabrication process. This advanced gate structure effectively protects the gate stack from melting, thus solving the problem related to protrusion formation. By using this gate stack configuration, power MOS transistors were fabricated with improved electrical characteristics. The Bragg reflector based gate stack architecture can be applied to other device structures, such as scaled MOS transistors, thus extending the possibilities of process integration of excimer laser annealing.
Femtosecond coherent anti-Stokes Raman scattering measurement of gas temperatures from frequency-spread dephasing of the Raman coherence
Authors: Lucht Robert P. , Roy Sukesh , Meyer Terrence R. , Gord James R.
Published: December 2006

Gas-phase temperatures and concentrations are measured from the magnitude and decay of the initial Raman coherence in femtosecond coherent anti-Stokes Raman scattering (CARS). A time-delayed probe beam is scattered from the Raman polarization induced by pump and Stokes beams to generate CARS signal; the dephasing rate of this initial coherence is determined by the temperature-sensitive frequency spread of the Raman transitions. Temperature is measured from the CARS signal decrease with increasing probe delay. Concentration is found from the ratio of the CARS and nonresonant background signals. Collision rates do not affect the determination of these quantities.
Monoclinic morphotropic phase and grain size-induced polarization rotation in Pb(Mg1∕3Nb2∕3)O3–PbTiO3
Authors: Carreaud J. , Kiat J. M. , Dkhil B. , Algueró M. , Ricote J. , Jiménez R. , Holc J. , Kosec M.
Published: December 2006

A detailed Rietveld analysis of x-ray data, collected at room temperature, was done on ceramics with controlled grain size between 100nm and 4μm for (PbMg1∕3Nb2∕3O3)0.80–(PbTiO3)0.20 (PMN-PT20), i.e., a compound at the border of the so-called morphotropic phase boundary. With size reduction the polarization rotates within the monoclinic plane from MB, i.e., Px=Py>Pz to MA, i.e., Px=Py<Pz, and finally reaches a rhombohedral phase, i.e., Px=Py=Pz, below a critical value of ∼200nm without diminishing the amplitude of the polarization. This study provides an easy way to tailor the direction of polarization of these materials.
Localized exciton luminescence in nitrogen-incorporated SnO2 thin films
Authors: Pan S. S. , Ye C. , Teng X. M. , Li L. , Li G. H.
Published: December 2006

The photoluminescence properties of nitrogen-incorporated SnO2 thin films on Si (100) substrates deposited by reactive magnetron sputtering have been studied. A strong photoluminescence band centered at 3.696eV with full width at half maximum of 0.2eV has been observed at room temperature. The peak position of the emission shifts to higher energy with increasing excitation intensity or decreasing temperature. The emission is considered due to the localized exciton recombination, and the observed exciton localization and band-tail states are believed to originate from the potential fluctuation induced by spatial distribution fluctuations of nitrogen concentration and∕or grain boundary defects in the nanocrystalline film.
Broadband reflective liquid crystalline gels due to the ultraviolet light screening made by the liquid crystal
Authors: Relaix Sabrina , Bourgerette Christian , Mitov Michel
Published: December 2006

It is shown that the natural ultraviolet light absorbing properties of the liquid crystal constituent during the photoinduced elaboration of a liquid crystalline gel induce the broadening of the reflection bandwidth. The polymer component is then included in a resin by preserving its spatial distribution, and transmission electron microscopy investigations of cross sections show the existence of a structure gradient, which is at the origin of the broadening phenomenon. Such reflectors may be of interest for reflective polarizer-free displays or smart windows for the control of solar light for which a broadband reflection is required.
Applications of NiFe2O4 nanoparticles for a hyperthermia agent in biomedicine
Authors: Bae Seongtae , Lee Sang Won , Takemura Y.
Published: December 2006

Self-heating temperature rising characteristics, cytotoxicity, and magnetic properties of NiFe2O4 nanoparticles have been investigated to confirm the effectiveness as an in vivo hyperthermia agent in biomedicine. NiFe2O4 nanoparticles showed both superparamagnetic and ferrimagnetic behaviors depending on particle sizes. The quantitative cytotoxicity test verified that both uncoated and chitosan-coated NiFe2O4 nanoparticles had noncytotoxicity. The solid state 35nm size NiFe2O4 nanoparticles first exhibited a maximum self-heating temperature of 44.2°C at H0f=5.1×108Am−1s−1. The physical nature of the self-heating was primarily thought to be due to the magnetic hysteresis loss, Neel rotations, and Brownian rotations of 35nm size NiFe2O4 nanoparticles.
Red electrophosphorescent top emission organic light-emitting device with Ca∕Ag semitransparent cathode
Authors: Lee C. J. , Pode R. B. , Han J. I. , Moon D. G.
Published: December 2006

Using a Ca (10nm)∕Ag (10nm) semitransparent cathode and efficient electron transport and/or buffer layer, red electrophosphorescent top emission organic light-emitting device has been fabricated. A low turn-on voltage of 4.6V and clean electrophosphorence peaks at 616 and 674nm are reported. X-ray photoelectron spectroscopy depth profiling measurements reveal the presence of Ca(OH)2 in Ca∕Ag bilayer cathode and the skin depth over 15nm in the visible region is determined in this structure. Results show that the compositional modification of the Ca∕Ag cathode enhances its optical transparency and final performance of the electrophosphorescent top emission device.