bluuebunny/crossref_metadata_2025 huggingface dataset:
Faraday rotation data analysis with least-squares elliptical fitting
Authors: White Adam D. , McHale G. Brent , Goerz David A. , Speer Ron D.
Published: October 2010

A method of analyzing Faraday rotation data from pulsed magnetic field measurements is described. The method uses direct least-squares elliptical fitting to measured data. The least-squares fit conic parameters are used to rotate, translate, and rescale the measured data. Interpretation of the transformed data provides improved accuracy and time-resolution characteristics compared with many existing methods of analyzing Faraday rotation data. The method is especially useful when linear birefringence is present at the input or output of the sensing medium, or when the relative angle of the polarizers used in analysis is not aligned with precision; under these circumstances the method is shown to return the analytically correct input signal. The method may be pertinent to other applications where analysis of Lissajous figures is required, such as the velocity interferometer system for any reflector (VISAR) diagnostics. The entire algorithm is fully automated and requires no user interaction. An example of algorithm execution is shown, using data from a fiber-based Faraday rotation sensor on a capacitive discharge experiment.
Global potential energy surfaces for O(P3)+H2O(A11) collisions
Authors: Conforti Patrick F. , Braunstein Matthew , Braams Bastiaan J. , Bowman Joel M.
Published: October 2010

Global analytic potential energy surfaces for O(P3)+H2O(A11) collisions, including the OH+OH hydrogen abstraction and H+OOH hydrogen elimination channels, are presented. Ab initio electronic structure calculations were performed at the CASSCF+MP2 level with an O(4s3p2d1f)/H(3s2p) one electron basis set. Approximately 105 geometries were used to fit the three lowest triplet adiabatic states corresponding to the triply degenerate O(P3)+H2O(A11) reactants. Transition state theory rate constant and total cross section calculations using classical trajectories to collision energies up to 120 kcal mol−1 (∼11 km s−1 collision velocity) were performed and show good agreement with experimental data. Flux-velocity contour maps are presented at selected energies for H2O collisional excitation, OH+OH, and H+OOH channels to further investigate the dynamics, especially the competition and distinct dynamics of the two reactive channels. There are large differences in the contributions of each of the triplet surfaces to the reactive channels, especially at higher energies. The present surfaces should support quantitative modeling of O(P3)+H2O(A11) collision processes up to ∼150 kcal mol−1.
National Ignition Facility neutron time-of-flight measurements (invited)
Authors: Lerche R. A. , Glebov V. Yu. , Moran M. J. , McNaney J. M. , Kilkenny J. D. , Eckart M. J. , Zacharias R. A. , Haslam J. J. , Clancy T. J. , Yeoman M. F. , Warwas D. P. , Sangster T. C. , Stoeckl C. , Knauer J. P. , Horsfield C. J.
Published: October 2010

The first 3 of 18 neutron time-of-flight (nTOF) channels have been installed at the National Ignition Facility (NIF). The role of these detectors includes yield, temperature, and bang time measurements. This article focuses on nTOF data analysis and quality of results obtained for the first set of experiments to use all 192 NIF beams. Targets produced up to 2×1010 2.45 MeV neutrons for initial testing of the nTOF detectors. Differences in neutron scattering at the OMEGA laser facility where the detectors were calibrated and at NIF result in different response functions at the two facilities. Monte Carlo modeling shows this difference. The nTOF performance on these early experiments indicates that the nTOF system with its full complement of detectors should perform well in future measurements of yield, temperature, and bang time.
Spectroscopic measurement of ion temperature and ion velocity distributions in the flux-coil generated FRC
Authors: Gupta D. , Bolte N. , Gota H. , Hayashi R. , Kiyashko V. , Marsili P. , Morehouse M. , Primavera S. , Roche T. , Wessel F.
Published: October 2010

One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.
Tiltable magnetic anisotropy in oblique-deposited Fe arrays using nanoporous anodic aluminum oxides
Authors: Huang Kai-Tze , Kuo Po-Cheng , Lin Ger-Pin , Shen Chih-Lung , Yao Yeong-Der
Published: October 2010

Tiltable magnetic anisotropy of self-assembled Fe arrays on nanoporous anodic aluminum oxide has been obtained via oblique evaporation. The rims of the pores, which induce a stacking variation to the stacked atoms, obstructed on the top and shadowed on the inner-wall, aid the formation of isolated arrays with extended “sterns.” The sterns, formed perpendicularly on the unshadowed inner-wall inducing out-of-plane shape anisotropy, dominate the magnetic anisotropy via the coupling to the magnetization of the topmost single-domain array. High perpendicular magnetic anisotropy (1.38×107 ergs/cm3) is induced by the stern at a nominal thickness of 16 nm via 50°-oblique deposition, and capable of tilting with a decrease in shape anisotropy as a result of the decreased oblique angle and increased nominal thickness. The 45°-tilted magnetic anisotropy with independent magnetization reversal is obtained at an oblique angle of about 27.6°.
Cation order–disorder phase transitions in LiGaO2: Observation of the pathways of ternary wurtzite under high pressure
Authors: Lei Li , Irifune Tetsuo , Shinmei Toru , Ohfuji Hiroaki , Fang Leiming
Published: October 2010

Two new high-pressure phases of LiGaO2 have been discovered by direct compression of orthorhombic wurtzite-type LiGaO2 at pressures between 7 and 22 GPa and the temperatures of 25–2000 °C by means of the multianvil apparatus. The new intermediate phase recovered above 13 GPa at room temperature has been determined as a cation-disordered tetragonal structure with lattice parameters a=0.287 63(36) nm and c=0.419 29(117) nm, space group I4/m. The new high-pressure phase recovered above 16 GPa and 1400 °C has been refined as a cation-disordered cubic structure with lattice parameter of a=0.411 34(16) nm, space group Fm-3m. Powder x-ray diffraction and Raman scattering spectra observations reveal that besides the previously described polymorphic hexagonal phase, the tetragonal and cubic new phases of LiGaO2 are found to have rocksalt-related structures. Their structures can be labeled as layered-rocksalt-type, deformed-rocksalt-type, and disordered-rocksalt-type, respectively. The relationships between polymorphs of LiGaO2 provide some new insights into the pathways of ternary wurtzite-type semiconductors under high pressure.
Range-dependent adiabatic connections
Authors: Teale A. M. , Coriani S. , Helgaker T.
Published: October 2010

Recently, we have implemented a scheme for the calculation of the adiabatic connection linking the Kohn–Sham system to the physical, interacting system. This scheme uses a generalized Lieb functional, in which the electronic interaction strength is varied in a simple linear fashion, keeping the potential or the density fixed in the process. In the present work, we generalize this scheme further to accommodate arbitrary two-electron operators, allowing the calculation of adiabatic connections following alternative paths as outlined by Yang [J. Chem. Phys. 109, 10107 (1998)]. Specifically, we examine the error-function and Gaussian-attenuated error-function adiabatic connections. It is shown that while the error-function connection displays some promising features, making it amenable to the possible development of new exchange-correlation functionals by modeling the adiabatic connection integrand, the Gaussian-attenuated error-function connection is less promising. We explore the high-density and strong static correlation regimes for two-electron systems. Implications of this work for the utility of range-separated schemes are discussed.
Effects of Ag on the Kirkendall void formation of Sn–xAg/Cu solder joints
Authors: Kim Sunghwan , Yu Jin
Published: October 2010

Binary Sn–Ag solders with varying amounts of Ag (0.5, 2.0, and 3.5 wt %) were reacted with Cu under bump metallurgy (UBM) which was electroplated with bis-sodium sulfopropyl-disulfide additive, and the characteristics of Kirkendall void formation at the solder joints were investigated. The results indicate that the propensity to form Kirkendall voids at the solder joint decreased with the Ag content. Subsequent Auger electron spectroscopy analyses showed that Ag dissolved in the Cu UBM reduced the segregation of S to the Cu3Sn/Cu interface, which suppressed the nucleation of Kirkendall voids at the interface.
High accuracy wavelength calibration for a scanning visible spectrometer
Authors: Scotti Filippo , Bell Ronald E.
Published: October 2010

Spectroscopic applications for plasma velocity measurements often require wavelength accuracies ≤0.2 Å. An automated calibration, which is stable over time and environmental conditions without the need to recalibrate after each grating movement, was developed for a scanning spectrometer to achieve high wavelength accuracy over the visible spectrum. This method fits all relevant spectrometer parameters using multiple calibration spectra. With a stepping-motor controlled sine drive, an accuracy of ∼0.25 Å has been demonstrated. With the addition of a high resolution (0.075 arc sec) optical encoder on the grating stage, greater precision (∼0.005 Å) is possible, allowing absolute velocity measurements within ∼0.3 km/s. This level of precision requires monitoring of atmospheric temperature and pressure and of grating bulk temperature to correct for changes in the refractive index of air and the groove density, respectively.
Ultrabroadband sensitization of near infrared emission through energy transfer from Pb to Yb ions in LiYbMo2O8:Pb
Authors: Ye S. , Yu D. C. , Huang X. Y. , Yang Z. M. , Zhang Q. Y.
Published: October 2010

Ultrabroadband sensitization of near infrared emission through energy transfer from Pb to Yb ions in LiYbMo2O8:Pb has been achieved upon ultraviolet (UV)-blue light excitation varying from 300 to 450 nm. The excitation band at 300–370 nm can be assigned to the charge transfer state of MoO42− groups, while the band at 370–450 nm could be mainly ascribed to charge transfer from Pb2+ to Yb3+ with a possible additional partial absorption contribution of Pb3+. Application of these phosphors in silicon-based solar cells might enhance its UV-blue response via spectrum modification.
Backscatter measurements for NIF ignition targets (invited)
Authors: Moody J. D. , Datte P. , Krauter K. , Bond E. , Michel P. A. , Glenzer S. H. , Divol L. , Niemann C. , Suter L. , Meezan N. , MacGowan B. J. , Hibbard R. , London R. , Kilkenny J. , Wallace R. , Kline J. L. , Knittel K. , Frieders G. , Golick B. , Ross G. , Widmann K. , Jackson J. , Vernon S. , Clancy T.
Published: October 2010

Backscattered light via laser-plasma instabilities has been measured in early NIF hohlraum experiments on two beam quads using a suite of detectors. A full aperture backscatter system and near backscatter imager (NBI) instrument separately measure the stimulated Brillouin and stimulated Raman scattered light. Both instruments work in conjunction to determine the total backscattered power to an accuracy of ∼15%. In order to achieve the power accuracy we have added time-resolution to the NBI for the first time. This capability provides a temporally resolved spatial image of the backscatter which can be viewed as a movie.
The use of Bayesian inversion to resolve plasma equilibrium
Authors: Hole M. J. , von Nessi G. , Pretty D. , Howard J. , Blackwell B. , Svensson J. , Appel L. C.
Published: October 2010

Recently, Bayesian probability theory has been used at a number of experiments to fold uncertainties and interdependencies in the diagnostic data and forward models, together with prior knowledge of the state of the plasma, to increase accuracy of inferred physics variables. A new probabilistic framework, MINERVA, based on Bayesian graphical models, has been used at JET and W7-AS to yield predictions of internal magnetic structure. A feature of the framework is the Bayesian inversion for poloidal magnetic flux without the need for an explicit equilibrium assumption. Building on this, we discuss results from a new project to develop Bayesian inversion tools that aim to (1) distinguish between competing equilibrium theories, which capture different physics, using the MAST spherical tokamak, and (2) test the predictions of MHD theory, particularly mode structure, using the H-1 Heliac. Specifically, we report on correction of the motional Stark effect, pickup coils, flux-loop constrained Bayesian inferred equilibrium for varying toroidal flux.
Time-resolved spectra of dense plasma focus using spectrometer, streak camera, and CCD combination
Authors: Goldin F. J. , Meehan B. T. , Hagen E. C. , Wilkins P. R.
Published: October 2010

A time-resolving spectrographic instrument has been assembled with the primary components of a spectrometer, image-converting streak camera, and CCD recording camera, for the primary purpose of diagnosing highly dynamic plasmas. A collection lens defines the sampled region and couples light from the plasma into a step index, multimode fiber which leads to the spectrometer. The output spectrum is focused onto the photocathode of the streak camera, the output of which is proximity-coupled to the CCD. The spectrometer configuration is essentially Czerny–Turner, but off-the-shelf Nikon refraction lenses, rather than mirrors, are used for practicality and flexibility. Only recently assembled, the instrument requires significant refinement, but has now taken data on both bridge wire and dense plasma focus experiments.
Matrix isolation ESR and theoretical studies of metal phosphides
Authors: Fuller Rebecca O. , Chandler Graham S. , Davis Jeffrey R. , McKinley Allan J.
Published: October 2010

The ZnP, Z67nP, CdP, C111dP, and C113dP radicals have been formed by laser ablation of the metal with GaP pressed into the metal surface, isolated in an inert neon matrix at 4.3 K and their electronic structure was established using electron spin resonance spectroscopy. The following magnetic parameters were determined experimentally for ZnP/Z67nP, g⊥=1.9982(2), A⊥(P)=111(6) MHz, A⊥(Z67n)=160(2) MHz, and D=−29 988(3) MHz and estimates were made for the following ZnP/Z67nP magnetic parameters: g∥=1.9941(2), A∥(P)=−5(6) MHz, and A∥(Z67n)=180(50) MHz. The following magnetic parameters for CdP/C111dP/C113dP were determined experimentally: g⊥=1.9963(2), A⊥(P)=97(3) MHz, A⊥(C111d)=862(3) MHz, and A⊥(C113d)=902(3) MHz. Evidence for the formation of the MgP radical was also obtained and an approximate hyperfine coupling constant of A⊥(P)=157(6) MHz was determined. The low-lying electronic states of ZnP and MgP were also investigated using the multiconfigurational self-consistent field technique. Potential energy surfaces, binding energies, optimized bond lengths, energy separations, and dissociation energies have been determined. Both radicals are found to have Σ4− ground states with a leading configuration at re of 10σ211σ25π15π112σ1 for ZnP and 7σ28σ23π13π19σ1 for MgP. Significant mixing to this state is calculated for MgP.
Imaging of the magnetic field structure in megagauss plasmas by combining pulsed polarimetry with an optical Kerr effect shutter technique
Authors: Smith R. J.
Published: October 2010

Pulsed polarimetry in combination with a high speed photographic technique based on the optical Kerr effect is described. The backscatter in a pulsed polarimeter is directed through a scattering cell and photographed using an ∼1 ps shutter, essentially freezing the intensity pattern. The image provides both the local electron density and magnetic field distributions along and transverse to the laser sightline. Submillimeter spatial resolution is possible for probing wavelengths in the visible due to the high densities and strong optical activity. Pulsed polarimetry is thereby extended to centimeter-sized plasmas with ne>1019−1020 cm−3 and B>20–100 T (MG) produced by multiterawatt, multimega-ampere electrical drivers, wire Z pinches, and liner imploded magnetized plasmas.
Development of a spatially resolving x-ray crystal spectrometer for measurement of ion-temperature (Ti) and rotation-velocity (v) profiles in ITER
Authors: Hill K. W. , Bitter M. , Delgado-Aparicio L. , Johnson D. , Feder R. , Beiersdorfer P. , Dunn J. , Morris K. , Wang E. , Reinke M. , Podpaly Y. , Rice J. E. , Barnsley R. , O’Mullane M. , Lee S. G.
Published: October 2010

Imaging x-ray crystal spectrometer (XCS) arrays are being developed as a US-ITER activity for Doppler measurement of Ti and v profiles of impurities (W, Kr, and Fe) with ∼7 cm (a/30) and 10–100 ms resolution in ITER. The imaging XCS, modeled after a prototype instrument on Alcator C-Mod, uses a spherically bent crystal and 2D x-ray detectors to achieve high spectral resolving power (E/dE>6000) horizontally and spatial imaging vertically. Two arrays will measure Ti and both poloidal and toroidal rotation velocity profiles. The measurement of many spatial chords permits tomographic inversion for the inference of local parameters. The instrument design, predictions of performance, and results from C-Mod are presented.
Determination of free polaron lifetime in organic bulk heterojunction solar cells by transient time analysis
Authors: Li Kejia , Shen Yang , Majumdar Nabanita , Hu Chong , Gupta Mool C. , Campbell Joe C.
Published: October 2010

A transient response technique that is widely used to measure the minority carrier lifetime in inorganic semiconductors is proposed to measure the lifetime of free polarons in a polymer:fullerene bulk heterojunction (BHJ) solar cell. A numerical model that can be used to describe the transient behavior of BHJ devices has been developed. Using the proposed method, the lifetime of free polarons in poly (3-hexylthiophene) and [6, 6]-phenyl C61-butyric acid methyl ester blend film is estimated to be in the range of 300–400 ns.
Magnetic order, aging, and spin frustration in a percolating spin system, LiNi0.8Co0.1Mn0.1O2
Authors: Wikberg J. M. , Dahbi M. , Saadoune I. , Gustafsson T. , Edström K. , Svedlindh P.
Published: October 2010

Structural and magnetic properties of the Li layered oxide, LiNi0.8Co0.1Mn0.1O2, have been studied by means of x-ray diffraction, dc magnetization, ac linear, and nonlinear susceptibility as well as by magnetic aging and temperature cycling experiments. A percolating spin system interacting via antiferromagnetic and ferromagnetic superexchange interactions of different strength induce a ferrimagnetic quasilong-range order with a transition temperature Tc≈70 K, a Weiss temperature of −25 K and an effective magnetic moment of 2.07 μB. On cooling below Tc the two-dimensional (2D) triangular lattice built up of edge-sharing metal oxide octahedras first exhibits a 2D spin glass like behavior followed by complete spin frustration in three dimensions below 30 K. The findings correlate well with expectations for a ferrimagnetic reentrant cluster glass system as well as with predictions of the percolating cluster model.
Electric field assisted charge carrier photogeneration in poly(spirobifluorene-co-benzothiadiazole)
Authors: Devizis A. , Serbenta A. , Peckus D. , Thiessen A. , Alle R. , Meerholz K. , Hertel D. , Gulbinas V.
Published: October 2010

The dynamics of charge carrier generation in poly(spirobifluorene-co-benzothiadiazole) was investigated by electric field-induced fluorescence quenching and differential absorption measurements. Three different time domains of carrier generation have been identified: an ultrafast phase, a subnanosecond phase, and an entire lifetime phase. The charge generation efficiencies during the first and second phases were found to be almost independent of temperature, being about 25% and 10%, respectively, at an applied electric field of 1.3×106 V/cm, while the generation efficiency during the third phase increases from 2% at 80 K to 10% at room temperature. The results of transient spectroscopy measurements and quantum chemical calculations suggest an intramolecular charge transfer for about 1 ps from the alkoxy-substituted fluorene side group to the benzothiadiazole subunit of the main chain. The formation and evolution of the resulting charge transfer states determine the way of charge carrier generation.
High pressure x-ray diffraction and extended x-ray absorption fine structure studies on ternary alloy Zn1−xBexSe
Authors: Bhalerao Gopalkrishna M. , Polian Alain , Gauthier Michel , Itié Jean-Paul , Baudelet François , Ganguli Tapas , Deb Sudip K. , Mazher Javed , Pagès Olivier , Firszt Franciszek. , Paszkowicz Wojciech
Published: October 2010

The ternary semiconductor alloy Zn1−xBexSe has been studied under high pressure by x-ray diffraction and extended x-ray absorption fine structure (EXAFS) at the Zn and Se K-edge in order to determine the bulk and bond-specific elastic properties. Our measurements on samples with x=0.06–0.55 show pressure induced phase transformation from zinc blende to NaCl. The phase transformation pressure increases linearly with x. Murnaghan equation of state fitting to the data yields the unit cell volume at ambient pressure and bulk modulus, both of which follow the Vegard’s law. Nearest neighbor bond distances derived from EXAFS do not show sharp phase transition except for x=0.06. Bond modulus derived for the Zn–Se bonds shows them to be apparently stiffer than the bulk alloy, which is nontrivial. This tendency increases with increasing x and a strong positive bowing from the Vegard’s law is observed. We attribute the observed anomalies to the contrastingly different properties of the two components ZnSe and BeSe.
Effect of strong electrostatic interactions of microparticles on the dust acoustic waves
Authors: Yaroshenko V. V. , Nosenko V. , Morfill G. E.
Published: October 2010

It is shown that strong electrostatic interaction of highly charged microparticles (which is common for many laboratory experiments) can significantly modify the behavior of dust acoustic waves in a complex plasma giving rise to their transition, at large wave numbers, into a new regime similar to the dust thermal mode. Examples of the dispersion curves are calculated for realistic complex plasma parameters and a comparison with a recent experiment is presented. Excellent agreement is found between the theory and the experiment.
Scaling studies with the dual crystal spectrometer at the OMEGA-EP laser facility
Authors: Szabo C. I. , Workman J. , Flippo K. , Feldman U. , Seely J. F. , Hudson L. T. , Henins A.
Published: October 2010

The dual crystal spectrometer (DCS) is an approved diagnostic at the OMEGA and the OMEGA-EP laser facilities for the measurement of high energy x-rays in the 11–90 keV energy range, e.g., for verification of the x-ray spectrum of backlighter targets of point projection radiography experiments. DCS has two cylindrically bent transmission crystal channels with image plate detectors at distances behind the crystals close to the size of the respective Rowland circle diameters taking advantage of the focusing effect of the cylindrically bent geometry. DCS, with a source to crystal distance of 1.2 m, provides the required energy dispersion for simultaneous detection of x-rays in a low energy channel (11–45 keV) and a high-energy channel (19–90 keV). A scaling study is described for varied pulse length with unchanged laser conditions (energy, focusing). The study shows that the Kα line intensity is not strongly dependent on the length of the laser pulse.
Progress of development of Thomson scattering diagnostic system on COMPASS
Authors: Bilkova P. , Melich R. , Aftanas M. , Böhm P. , Sestak D. , Jares D. , Weinzettl V. , Stöckel J. , Hron M. , Panek R. , Scannell R. , Walsh M. J.
Published: October 2010

A new Thomson scattering diagnostic system has been designed and is being built now on the COMPASS tokamak at the Institute of Plasma Physics ASCR in Prague (IPP Prague) in the Czech Republic. This contribution focuses on design, development, and installation of the light collection and detection system. High spatial resolution of 3 mm will be achieved by a combination of design of collection optics and connected polychromators. Imaging characteristics of both core and edge plasma collection objectives are described and fiber backplane design is presented. Several calibration procedures are discussed. The operational deployment of the Thomson scattering diagnostic is planned by the end of 2010.
Comparative electron temperature measurements of Thomson scattering and electron cyclotron emission diagnostics in TCABR plasmas
Authors: Alonso M. P. , Figueiredo A. C. A. , Borges F. O. , Elizondo J. I. , Galvão R. M. O. , Severo J. H. F. , Usuriaga O. C. , Berni L. A. , Machida M.
Published: October 2010

We present the first simultaneous measurements of the Thomson scattering and electron cyclotron emission radiometer diagnostics performed at TCABR tokamak with Alfvén wave heating. The Thomson scattering diagnostic is an upgraded version of the one previously installed at the ISTTOK tokamak, while the electron cyclotron emission radiometer employs a heterodyne sweeping radiometer. For purely Ohmic discharges, the electron temperature measurements from both diagnostics are in good agreement. Additional Alfvén wave heating does not affect the capability of the Thomson scattering diagnostic to measure the instantaneous electron temperature, whereas measurements from the electron cyclotron emission radiometer become underestimates of the actual temperature values.
Frozen density embedding with hybrid functionals
Authors: Laricchia S. , Fabiano E. , Della Sala F.
Published: October 2010

The Kohn–Sham equations with constrained electron density are extended to hybrid exchange-correlation (XC) functionals. We derive the frozen density embedding generalized Kohn–Sham (FDE-GKS) scheme which allows to treat the nonlocal exact-exchange in the subsystems. For practical calculations we propose an approximated version of the FDE-GKS in which the nonadditive exchange potential is computed at a semilocal level. The proposed method is applied to compute the ground-state electronic properties of small test systems and selected DNA base pairs. The results of calculations employing the hierarchy of XC functionals BLYP/B3LYP/BHLYP and PBE/PBE0 are presented, in order to analyze the effect of nonlocal exchange contributions, and compared with reference coupled-cluster singles and doubles results. We find that the use of hybrid functionals leads to a significant improvement in the description of ground-state electronic properties of the investigated systems. The semilocal version of the FDE-GKS correctly reproduces the dipole and the electron density distribution of the exact GKS supramolecular system, with errors smaller than the ones obtained using conventional semilocal XC functionals.
Calibration of a flat field soft x-ray grating spectrometer for laser produced plasmas
Authors: Park J. , Brown G. V. , Schneider M. B. , Baldis H. A. , Beiersdorfer P. , Cone K. V. , Kelley R. L. , Kilbourne C. A. , Magee E. W. , May M. J. , Porter F. S.
Published: October 2010

We have calibrated the x-ray response of a variable line spaced grating spectrometer, known as the VSG, at the Fusion and Astrophysics Data and Diagnostic Calibration Facility at the Lawrence Livermore National Laboratory (LLNL). The VSG has been developed to diagnose laser produced plasmas, such as those created at the Jupiter Laser Facility and the National Ignition Facility at LLNL and at both the Omega and Omega EP lasers at the University of Rochester’s Laboratory for Laser Energetics. The bandwidth of the VSG spans the range of ∼6–60 Å. The calibration results presented here include the VSG’s dispersion and quantum efficiency. The dispersion is determined by measuring the x rays emitted from the hydrogenlike and heliumlike ions of carbon, nitrogen, oxygen, neon, and aluminum. The quantum efficiency is calibrated to an accuracy of 30% or better by normalizing the x-ray intensities recorded by the VSG to those simultaneously recorded by an x-ray microcalorimeter spectrometer.
Note: A robust low-cost high-sensitivity subangstrom bidirectional displacement sensor
Authors: Armitage P. R. , Wright C. D.
Published: October 2010

The design of a simple, robust, low-cost, and bidirectional displacement sensor with subangstrom resolution is described. A small gold plate is attached to the object, whose displacement is to be measured, and a small gold tip is brought into contact with the plate, establishing a reference current between the two. Movements of the gold plate away from the tip lead to a change in the tip-plate current; the reference current is then re-established by moving the tip using a simple magnetic actuator. The resolution of the sensor has been calibrated using an interferometer and was shown to be as high as 0.3 Å per system count. Potential applications of the sensor are numerous, including microbar air pressure measurement, motion and infrasound detection, thermal sensing, and gravitational field and relativistic gravity wave measurement.
Development of a short duration backlit pinhole for radiography on the National Ignition Facility
Authors: Huntington C. M. , Krauland C. M. , Kuranz C. C. , Drake R. P. , Park H.-S. , Kalantar D. H. , Maddox B. R. , Remington B. A. , Kline J.
Published: October 2010

Experiments on the National Ignition Facility (NIF) will require bright, short duration, near-monochromatic x-ray backlighters for radiographic diagnosis of many high-energy density systems. This paper details a vanadium pinhole backlighter producing (1.8±0.5)×1015 x-ray photons into 4π sr near the vanadium He-like characteristic x-ray energy of 5.18 keV. The x-ray yield was quantified from a set of Ross filters imaged to a calibrated image plate, with the Dante diagnostic used to confirm the quasimonochromatic nature of the spectrum produced. Additionally, an x-ray film image shows a source-limited image resolution of 26 μm from a 20 μm diameter pinhole.
Modeling the noble metal/TiO2 (110) interface with hybrid DFT functionals: A periodic electrostatic embedded cluster model study
Authors: Ammal Salai Cheettu , Heyden Andreas
Published: October 2010

The interaction of Aun and Ptn (n=2,3) clusters with the stoichiometric and partially reduced rutile TiO2 (110) surfaces has been investigated using periodic slab and periodic electrostatic embedded cluster models. Compared to Au clusters, Pt clusters interact strongly with both stoichiometric and reduced TiO2 (110) surfaces and are able to enhance the reducibility of the TiO2 (110) surface, i.e., reduce the oxygen vacancy formation energy. The focus of this study is the effect of Hartree–Fock exchange on the description of the strength of chemical bonds at the interface of Au/Pt clusters and the TiO2 (110) surface. Hartree–Fock exchange helps describing the changes in the electronic structures due to metal cluster adsorption as well as their effect on the reducibility of the TiO2 surface. Finally, the performance of periodic embedded cluster models has been assessed by calculating the Pt adsorption and oxygen vacancy formation energies. Cluster models, together with hybrid PBE0 functional, are able to efficiently compute reasonable electronic structures of the reduced TiO2 surface and predict charge localization at surface oxygen vacancies, in agreement with the experimental data, that significantly affect computed adsorption and reaction energies.
Pair interaction potentials of colloids by extrapolation of confocal microscopy measurements of collective suspension structure
Authors: Iacovella Christopher R. , Rogers Reginald E. , Glotzer Sharon C. , Solomon Michael J.
Published: October 2010

A method for measuring the pair interaction potential between colloidal particles by extrapolation measurement of collective structure to infinite dilution is presented and explored using simulation and experiment. The method is particularly well suited to systems in which the colloid is fluorescent and refractive index matched with the solvent. The method involves characterizing the potential of mean force between colloidal particles in suspension by measurement of the radial distribution function using 3D direct visualization. The potentials of mean force are extrapolated to infinite dilution to yield an estimate of the pair interaction potential, U(r). We use Monte Carlo simulation to test and establish our methodology as well as to explore the effects of polydispersity on the accuracy. We use poly-12-hydroxystearic acid-stabilized poly(methyl methacrylate) particles dispersed in the solvent dioctyl phthalate to test the method and assess its accuracy for three different repulsive systems for which the range has been manipulated by addition of electrolyte.
O
3
-based atomic layer deposition of hexagonal La2O3 films on Si(100) and Ge(100) substrates
Authors: Lamagna L. , Wiemer C. , Perego M. , Volkos S. N. , Baldovino S. , Tsoutsou D. , Schamm-Chardon S. , Coulon P. E. , Fanciulli M.
Published: October 2010

The hexagonal phase of La2O3 is obtained upon vacuum annealing of hydroxilated La2O3 films grown with atomic layer deposition at 200 °C using La(PirCp)3 and O3. A dielectric constant value of 24±2 and 22±1 is obtained on Si-based and Ge-based metal-oxide-semiconductor capacitors, respectively. However, the relatively good La2O3 dielectric properties are associated with significant interface reactivity on both semiconductor substrates. This leads to the identification of a minimum critical thickness that limits the scaling down of the equivalent oxide thickness of the stack. These findings are explained by the spontaneous formation of lanthanum silicate and germanate species which takes place during the growth and also upon annealing. Although the ultimate film thickness scalability remains an unsolved concern, the use of an O3-based process is demonstrated to be a suitable solution to fabricate La2O3 films that can be successfully converted into the high-k hexagonal phase.
Ultrasensitive nanoparticle detection using a portable whispering gallery mode biosensor driven by a periodically poled lithium-niobate frequency doubled distributed feedback laser
Authors: Shopova S. I. , Rajmangal R. , Nishida Y. , Arnold S.
Published: October 2010

We demonstrate a significant reduction in the limit of label-free detection of individual viral-sized nanoparticles in aqueous solution through the use of a frequency doubled telecom laser constructed from a distributed feedback-periodically poled lithium-niobate (DFB-PPLN) union. By driving a whispering gallery mode biosensor near a wavelength of 650 nm with this device we have detected real-time adsorption steps for particles 36 nm in radius with a signal to noise ratio of 8. The noise equivalent detection limit is ∼20 ag (17 nm radius). This new lower limit is attributed to the ultralow resonance wavelength noise [(Δλr)rms/λr<10−9] associated with the use of the DFB-PPLN device.
Structural changes and phase stability of graphitelike BC3 under explosive shock-wave loading
Authors: de Rességuier T. , Kurakevych O. O. , Chabot A. , Petitet J. P. , Solozhenko V. L.
Published: October 2010

The response of graphitelike BC3 phases (t-BC3) to shock-wave loading has been studied using two types of high explosives, in order to investigate the possible routes to synthesize via dynamic compression superhard materials in the form of high-pressure phases such as the B-doped diamond produced recently under high static pressures and temperatures. The loading conditions resulting from wave propagation in the shock recovery setup have been determined from theoretical predictions confirmed by numerical simulations and velocity measurements. Over the explored range of shock pressure (from 10 to 30 GPa), no detectable diamond phase could be quenched, probably because of insufficient temperature, but Raman and x-ray diffraction studies of the recovered samples indicate permanent structural changes that have been compared to those observed after shorter, laser driven shock compression. These changes include local phase segregation of t-BC3 and the production of highly disordered phases.
Structure formation in the oceanic subsurface bubble layer by an internal wave field
Authors: Grimshaw R. H. J. , Khusnutdinova K. R. , Ostrovsky L. A. , Topolnikov A. S.
Published: October 2010

We model the effects of an internal wave on the structure of the oceanic subsurface bubble layer, generated by breaking surface waves. We consider two situations: when breaking is caused either by a strong sustained wind or by the direct interaction of surface waves with an internal wave. We find that the effects are twofold; bubbles are driven by the internal wave field and the injection of bubbles into the water is enhanced in downwelling areas behind the crests of the internal wave. We use an uncoupled problem formulation, substituting the solution for an internal wave in a two-layer fluid model into the equations describing the bubble dynamics. The latter equations are solved numerically, showing structure formation in the bubble layer for each of the two cases, when one of the aforementioned mechanisms dominates the other.
A connection between continuum and atomic description of interface thermal conductance
Authors: Jagannadham K.
Published: October 2010

A continuous distribution of thermal sources is used in the two phases at the interface to satisfy the boundary conditions associated with thermal conduction in a two-phase medium. The distribution of thermal sources is used to determine the temperature profile when there is an external source of thermal energy in phase 1 or when there is a step in the temperature at the interface due to finite interface thermal conductance. The thermal sources are identified with phonons present at the interface. The phonon distributions are superimposed to arrive at the temperature profile in a two-phase medium with an external source and finite interface thermal conductance. The interface thermal conductance is related to the variation in phonon distributions. Interface thermal conductance of Si/Ge interface determined from the present model is close to the value predicted by acoustic mismatch and diffuse mismatch models.
Determinant role of tunneling resistance in electrical conductivity of polymer composites reinforced by well dispersed carbon nanotubes
Authors: Yu Y. , Song G. , Sun L.
Published: October 2010

Three-dimensional Monte Carlo simulation is used to investigate the electrical conductivity of nanocomposites composing of conducting nanofillers and insulating polymer matrix. When nanofillers concentrations low and they are well dispersed in the insulating matrix, electron tunneling resistance between the nanofiller junctions is found to play the dominant role in electron transport. In addition to the tunneling resistance, there is also the resistance of the conducting nanotube segments. These two types of resistance form the resistor network for electron conductance. For composites with well dispersion, individual tubes are separated by polymer molecules and the resulted tunneling resistance can be several orders larger in magnitude than the resistance of individual tubes. Considering the two types of resistors are always linked in an alternating order in the resistor network, the much larger tunneling resistance plays the determinant role in the electrical resistance of nanocomposites. When the contribution of the intrinsic tube resistance is ignored, the number of resistors in conduction paths can be reduced by more than a half and as a result, the computation efficiency is significantly improved. With improved computation efficiency, three-dimensional cubic representative volume elements with high nanotube aspect ratios up to 1000 can be simulated. Simulation results are in good agreement with the critical behaviors predicted by the classical percolation theory, as well as the reported experimental measurements.
Dry calibration of electromagnetic flowmeters based on numerical models combining multiple physical phenomena (multiphysics)
Authors: Fu X. , Hu L. , Lee K. M. , Zou J. , Ruan X. D. , Yang H. Y.
Published: October 2010

This paper presents a method for dry calibration of an electromagnetic flowmeter (EMF). This method, which determines the voltage induced in the EMF as conductive liquid flows through a magnetic field, numerically solves a coupled set of multiphysical equations with measured boundary conditions for the magnetic, electric, and flow fields in the measuring pipe of the flowmeter. Specifically, this paper details the formulation of dry calibration and an efficient algorithm (that adaptively minimizes the number of measurements and requires only the normal component of the magnetic flux density as boundary conditions on the pipe surface to reconstruct the magnetic field involved) for computing the sensitivity of EMF. Along with an in-depth discussion on factors that could significantly affect the final precision of a dry calibrated EMF, the effects of flow disturbance on measuring errors have been experimentally studied by installing a baffle at the inflow port of the EMF. Results of the dry calibration on an actual EMF were compared against flow-rig calibration; excellent agreements (within 0.3%) between dry calibration and flow-rig tests verify the multiphysical computation of the fields and the robustness of the method. As requiring no actual flow, the dry calibration is particularly useful for calibrating large-diameter EMFs where conventional flow-rig methods are often costly and difficult to implement.
High retention of the polarization and depolarization field in polycrystalline metal/Pb(ZrTi)O3/metal capacitors
Authors: Delimova L. A. , Yuferev V. S.
Published: October 2010

Long term relaxation of the photovoltaic current in poled and then short-circuited capacitors with polycrystalline Pb(ZrTi)O3 (PZT) film, where (111) oriented PZT grains are separated by ultrathin semiconductor PbO phase is studied. The quantum energy of the excitation light is lower than PZT band gap but higher than PbO band gap. The measured photovoltaic current differs entirely from well-known photovoltaic current observed in single-crystal ferroelectrics, which flows in polarization direction and originates due to asymmetry of impurity potential caused by the polarization. The photocurrent, which we measure, is always directed against the polarization and is not related to the depolarization of the film. The driving force of the measured photocurrent is the depolarization field generated by polarization charge on PZT grain boundaries [Delimova et al., Appl. Phys. Lett. 91, 112907 (2007)]. Photoexcited in PbO interlayers free carriers drift in this field toward electrodes producing the photocurrent, which can serve as a criterion of existence of the depolarization field. It is shown that the steady-state photovoltaic current in poled M/PZT/M capacitors, measured for a year without their repolarization, demonstrates only 30% decrease. This means that during the year the depolarization field has remained in the film, the polarization charge generating the depolarization field has not been compensated, thereby indicating that the polarization is also conserved. The calculation of the photocurrent, depolarization field and polarization, performed using two-dimensional phenomenological model, shows that the polarization charge on grain boundaries cannot be compensated completely neither by free carriers nor charged dopants, which confirms the experimental result.
Phase evolution and the multiple metal-insulator transitions in epitaxially shear-strained La0.67Ca0.33MnO3/NdGaO3(001) films
Authors: Huang Zhen , Wang Lingfei , Tan Xuelian , Chen Pingfan , Gao Guanyin , Wu Wenbin
Published: October 2010

The ferromagnetic-metal (FM) to antiferromagnetic-insulator (AFI) transition, near 250 K, has been induced in epitaxially shear-strained La0.67Ca0.33MnO3/NdGaO3(001) films, although they are doped for a FM ground state. We showed that for these films the phase diagram can feature the five regions of paramagnetic-insulator, FM, AFI dominated, FM dominated, and the frozen state, evolving with decreasing temperatures. And the phase instabilities in the temperature/magnetic-field regime can lead to multiple metal-insulator transitions over the various phase boundaries, in addition to a huge low-field magnetoresistance in the wide temperature range. The results underline that with the elastic-driven phase separation and consequently the complex phase evolution, this epitaxial system could be employed for further understanding of the manganites, and also for thin-film devices applications.
Low-frequency Raman scattering from acoustic vibrations of spherical CdSe/CdS nanoparticles
Authors: Chen I-Chuen , Weng Chih-Li , Lin Cheng-Hsiao , Tsai Yan-Chr
Published: October 2010

The Raman light to vibration coupling coefficients Cαβ of the l=0 and the l=2 spheroidal phonon modes of quasifree spherical CdSe/CdS core/shell nanoparticles are calculated. Based on the Lamb model, the displacement vectors of acoustic phonon modes are obtained and the Cαβ is also derived. The Raman scattering from quasifree CdSe/CdS nanoparticles with various inner radii is investigated. For the l=0 acoustic modes, the bond polarizability model is adopted to calculate Cαβ, whose peak positions shift toward lower frequencies with the increase in the inner radius. It could be accounted for by the decrease in the averaged longitudinal and transverse sound velocities. Moreover, the ratio of the coefficients Aαβγδ {Montagna and Dusi, [Phys. Rev. B 52, 10080 (1995)]} between layers characterizes behaviors of peak heights of Cαβ. For the l=2 modes based on the dipole-induced-dipole model, the behaviors of peak positions are obtained by varying values of vL and vT of materials in both layers. As we treat the core/shell nanoparticle as a whole, the behavior of Cαβ peak positions on a CdSe/CdS core/shell nanoparticle is consistent with its dependence on the averaged sound velocities of the whole nanoparticle. Meanwhile, it also agrees with the calculated results for a CdSxSe1−x one {Ristić et al., [J. Appl. Phys. 104, 073519 (2008)]}. However, we observed that some peaks reach dramatically high values for given inner radii of the CdSe/CdS nanoparticles, which occur only in the spherical core/shell nanoparticles.
Water film confined in a nanoscale gap: Surface polarity and hydration effects
Authors: Liu Shuhai , Guo Dan , Xie Guoxin
Published: October 2010

The water film nanoconfined between solid surfaces was investigated using thin film interferometry. Experimental results indicate that surface polarity and hydration effects can strongly influence on the property of water film. It is thought that water molecules strongly bind to surface containing hydrophilic groups and a preferential slip plane is created against the adjacent layer between the hydration sheath and bulk water. The slip plane dramatically weakens the entrainment effect in the inlet zone of lubrication by breaking the hydrogen-bonding network.