bluuebunny/crossref_metadata_2025 huggingface dataset:
Storm‐time configuration of the inner magnetosphere: Lyon‐Fedder‐Mobarry MHD code, Tsyganenko model, and GOES observations
Authors: Huang Chia‐Lin , Spence Harlan E. , Lyon John G. , Toffoletto Frank R. , Singer Howard J. , Sazykin Stanislav
Published: November 2006

We compare global magnetohydrodynamic (MHD) simulation results with an empirical model and observations to understand the magnetic field configuration and plasma distribution in the inner magnetosphere, especially during geomagnetic storms. The physics‐based Lyon‐Fedder‐Mobarry (LFM) code simulates Earth's magnetospheric topology and dynamics by solving the equations of ideal MHD. Quantitative comparisons of simulated events with observations reveal strengths and possible limitations and suggest ways to improve the LFM code. Here we present a case study that compares the LFM code to both a semiempirical magnetic field model and to geosynchronous measurements from GOES satellites. During a magnetic cloud event, the simulation and model predictions compare well qualitatively with observations, except during storm main phase. Quantitative statistical studies of the MHD simulation shows that MHD field lines are consistently under‐stretched, especially during storm time (Dst < −20 nT) on the nightside, a likely consequence of an insufficient representation of the inner magnetosphere current systems in ideal MHD. We discuss two approaches for improving the LFM result: increasing the simulation spatial resolution and coupling LFM with a ring current model based on drift physics (i.e., the Rice Convection Model (RCM)). We show that a higher spatial resolution LFM code better predicts geosynchronous magnetic fields (not only the average Bz component but also higher‐frequency fluctuations driven by the solar wind). An early version of the LFM/RCM coupled code, which runs so far only for idealized events, yields a much‐improved ring current, quantifiable by decreased field strengths at all local times compared to the LFM‐only code.
Simulations of OH nightglow emission in the occurrence of sprites
Authors: Huang Tai‐Yin
Published: November 2006

Recent observations on sprites have revealed that the electron energies in the luminous lightning discharge channels above thundercloud tops could be in the range of a few electron volts. Sprites are transient luminous flashes, and each flash lasts from a few to tens of milliseconds. Because some chemical reaction rates are highly dependent on temperature, it is speculated that sprites might have a significant effect on the chemistry of the atmosphere. This study is aimed to investigate how OH nightglow emission in the MLT region is affected when sprites occur. Simulations of OH nightglow emission at temperatures of ∼200 K and 400 K were performed; the former represents the normal temperature in the absence of sprites, while the latter is the assumed temperature when sprites occur. The simulation results, ignoring dynamical effects, indicate that the number density of atomic O in the nightglow region is not very sensitive to a higher temperature but that of HO2 and O3 is reduced by 45% and 0.5%, respectively, while the production of OH is enhanced by a factor of 2.6. The column‐integrated OH brightness shows a significant 16% increase when the temperature is at 400 K. The study indicates that sprites should produce a measurable effect on the OH brightness in the mesosphere.
Non‐self‐similar scaling of plasma sheet and solar wind probability distribution functions of magnetic field fluctuations
Authors: Weygand J. M. , Kivelson M. G. , Khurana K. K. , Schwarzl H. K. , Walker R. J. , Balogh A. , Kistler L. M. , Goldstein M. L.
Published: November 2006

Solar wind magnetometer and plasma data and magnetometer data acquired by Cluster in the magnetospheric plasma sheet are employed to construct probability distribution functions (PDFs) of magnetic field fluctuations over various temporal and spatial scales. This technique, often used in analysis of laboratory plasmas, is used to look for intermittent plasma turbulence and non‐self‐similar properties in the fluctuations. We examine the distribution of the magnetic field fluctuations for a single spacecraft and between pairs of correlated spacecraft time series data in both the plasma sheet and the solar wind (fast and slow speed streams). We demonstrate that the plasma sheet fluctuations have a distribution consistent with intermittent turbulence and that they scale non‐self‐similarly using two different methods (Sorriso‐Valvo et al., 1999; Hnat et al., 2002). In the solar wind both methods show that the fast solar wind magnetic field fluctuations have a PDF consistent with intermittent turbulence and scale non‐self‐similarly, but the two methods give conflicting results for the slow solar wind scaling properties. Finally, we use the results of the two methods as well as kurtosis versus scale size to roughly determine the turbulent eddy scale size in both types of solar wind (about 500 RE) and the magnetospheric plasma sheet (between 0.9 and 1.5 RE).
Constraints on the global structure of magnetic clouds: Transverse size and curvature
Authors: Liu Y. , Richardson J. D. , Belcher J. W. , Wang C. , Hu Q. , Kasper J. C.
Published: November 2006

We present direct evidence that magnetic clouds (MCs) have highly flattened and curved cross section resulting from their interaction with the ambient solar wind. Lower limits on the transverse size are obtained for three MCs observed by ACE and Ulysses from the latitudinal separation between the two spacecraft, ranging from 40° to 70°. The cross‐section aspect ratio of the MCs is estimated to be no smaller than 6:1. We offer a simple model to extract the radius of curvature of the cross section, based on the elevation angle of the MC normal distributed over latitude. Application of the model to Wind observations from 1995 to 1997 (close to solar minimum) shows that the cross section is bent concavely outward by a structured solar wind with a radius of curvature of ∼0.3 AU. Near solar maximum, MCs tend to be convex outward in the solar wind with a uniform speed; the radius of curvature is proportional to the heliographic distance of MCs, as demonstrated by Ulysses observations between 1999 and 2003. These results improve our knowledge of the global morphology of MCs in the pre‐Stereo era, which is crucial for space weather prediction and heliosphere studies.
High throughput measurements of soft x-ray impurity emission using a multilayer mirror telescope
Authors: Stutman D. , Tritz K. , Delgado-Aparicio L. , Finkenthal M. , Suliman G. , Roquemore L. , Kaita R. , Kugel H. , Johnson D. , Tamura N. , Sato K. , Sudo S. , Tarrio C.
Published: November 2006

A 4in. multilayer mirror telescope has been tested on National Spherical Torus Experiment (NSTX) for high throughput measurements of the beam excited soft x-ray impurity emission. The design is aimed at imaging low-k turbulent fluctuations in the plasma core. The test device used curved and planar Mo∕Si mirrors to focus with ≈15% optical transmission and few angstrom bandwidths, the 135Å Lyα line from injected Li III atoms, or the n=2–4 line from intrinsic C VI ions. As test detectors we used 1cm2 absolute extreme ultraviolet diodes, equipped with 400kHz bandwidth, low noise preamplifiers. With the available view on NSTX the telescope successfully detected small impurity density fluctuations associated with 1∕1 modes rotating at midradius, indicating that a high signal to noise ratio and cost effective core turbulence diagnostic is feasible based on this concept.
On the microconvective instability in optically induced gratings
Authors: Mezulis A. , Blums E.
Published: November 2006

In the present work, attention is paid to some significant effects (phenomena) in forced Rayleigh scattering (FRS) experiments with an applied magnetic field, ∇T∥H, which have not been analyzed before. In the work we deal with an idea that the experimentally observed effects are caused by microconvection [M. Igonin, Magnetohydrodynamics 37, 3 (2001); A. Cebers and M. Igonin, Magnetohydrodynamics 38, 265 (2002)]. The dimensionless numbers Cm and Rm, which are responsible for the onset of microconvection, are calculated from experiments as well as from the linear stability analysis in a Hele-Shaw approximation [M. Igonin, Magnetohydrodynamics 37, 3 (2001)]. The problem of the definition of the true values of diffusion and Soret coefficients from experiments and their field dependence, which are not affected by the assumed microconvection, is solved by original data processing. Visual observation of the FRS experiment provides additional information, applicable for a further analysis.
High-brightness, high-spatial-resolution, 6.151keV x-ray imaging of inertial confinement fusion capsule implosion and complex hydrodynamics experiments on Sandia’s Z accelerator (invited)
Authors: Bennett G. R. , Sinars D. B. , Wenger D. F. , Cuneo M. E. , Adams R. G. , Barnard W. J. , Beutler D. E. , Burr R. A. , Campbell D. V. , Claus L. D. , Foresi J. S. , Johnson D. W. , Keller K. L. , Lackey C. , Leifeste G. T. , McPherson L. A. , Mulville T. D. , Neely K. A. , Rambo P. K. , Rovang D. C. , Ruggles L. E. , Porter J. L. , Simpson W. W. , Smith I. C. , Speas C. S.
Published: November 2006

When used for the production of an x-ray imaging backlighter source on Sandia National Laboratories’ 20MA, 100ns rise-time Z accelerator [M. K. Matzen et al., Phys. Plasmas 12, 055503 (2005)], the terawatt-class, multikilojoule, 526.57nm Z-Beamlet laser (ZBL) [P. K. Rambo et al., Appl. Opt. 44, 2421 (2005)], in conjunction with the 6.151keV, Mn–Heα curved-crystal imager [D. B. Sinars et al., Rev. Sci. Instrum. 75, 3672 (2004)], is capable of providing a high quality x radiograph per Z shot for various high-energy-density physics experiments. Enhancements to this imaging system during 2005 have led to the capture of inertial confinement fusion capsule implosion and complex hydrodynamics images of significantly higher quality. The three main improvements, all leading effectively to enhanced image plane brightness, were bringing the source inside the Rowland circle to approximately double the collection solid angle, replacing direct exposure film with Fuji BAS-TR2025 image plate (read with a Fuji BAS-5000 scanner), and generating a 0.3–0.6ns, ∼200J prepulse 2ns before the 1.0ns, ∼1kJ main pulse to more than double the 6.151keV flux produced compared with a single 1kJ pulse. It appears that the 20±5μm imaging resolution is limited by the 25μm scanning resolution of the BAS-5000 unit, and to this end, a higher resolution scanner will replace it. ZBL is presently undergoing modifications to provide two temporally separated images (“two-frame”) per Z shot for this system before the accelerator closes down in summer 2006 for the Z-refurbished (ZR) upgrade. In 2008, after ZR, it is anticipated that the high-energy petawatt (HEPW) addition to ZBL will be completed, possibly allowing high-energy 11.2224 and 15.7751keV Kα1 curved-crystal imaging to be performed. With an ongoing several-year project to develop a highly sensitive multiframe ultrafast digital x-ray camera (MUDXC), it is expected that two-frame HEPW 11 and 16keV imaging and four-frame ZBL 6.151keV curved-crystal imaging will be possible. MUDXC will be based on the technology of highly cooled silicon and germanium photodiode arrays and ultrafast, radiation-hardened integrated circuitry.
Reflectometer sensing of rf waves in front of the high harmonic fast wave antenna on NSTX
Authors: Wilgen J. B. , Ryan P. M. , Hanson G. R. , Swain D. W. , Bernabei S. I. , Greenough N. , DePasquale S. , Phillips C. K. , Hosea J. C. , Wilson J. R.
Published: November 2006

The ability to measure rf driven waves in the edge of the plasma can help to elucidate the role that surface waves and parametric decay instabilities (PDIs) play in rf power losses on NSTX. A microwave reflectometer has recently been modified to monitor rf plasma waves in the scrape-off layer in front of the 30MHz high harmonic fast wave antenna array on NSTX. In rf heated plasmas, the plasma-reflected microwave signal exhibits 30MHz sidebands, due primarily to the modulation of the cutoff layer by the electrostatic component of the heating wave. Similarly, electrostatic parametric decay waves (when present) are detected at frequencies below the heating frequency, near 28, 26,…MHz, separated from the heating frequency by harmonics of the local ion cyclotron frequency of about 2MHz. In addition, a corresponding frequency matched set of decay waves is also detected near the ion cyclotron harmonics at 2, 4,…MHz. The rf plasma-wave sensing capability is useful for determination of the PDI power threshold as a function of antenna array phasing (including toroidal wavelength), outer gap spacing, and various plasma parameters such as the magnetic field and the plasma current.
Neutron source images and spectra to guide neutron diagnostics specifications for the National Ignition Facility
Authors: Sweezy J. E. , Wilson D. C. , Bradley P. A. , Grim G. P. , Choi C. K. , Coggeshall J. C. , Wilde C. H. , Forster R. A. , Russell R. D.
Published: November 2006

Both neutron images and spectra will diagnose ignition implosions at the National Ignition Facility. From the integrated Hohlraum and capsule calculations of copper-doped beryllium capsules using ∼1MJ of laser energy we have postprocessed neutron spectra and both energy-gated and time integrated neutron images displaying the observable consequences of two-dimensional Hohlraum asymmetries. If low signal precludes multiple down scattered images, we suggest a 6–12MeV gate. With asymmetries, it is noted that the neutron yield, spectra, and images vary with observation direction. The yield varies only several percent when observed at different angles. Since most asymmetries are expected about the Hohlraum axis, a perpendicular view has the highest priority. The next most informative view would be along the Hohlraum axis, but may be precluded by target chamber structures. We present images at the available port angles and discuss their utility. To facilitate detailed diagnostic simulations with real pinhole geometries or penumbral apertures, we offer a compact disk containing neutron spectra and gated images from various integrated calculations.
Numerical study of turbulent bubbly downflows in a vertical channel
Authors: Lu Jiacai , Tryggvason Gretar
Published: November 2006

Direct numerical simulations are used to study turbulent bubbly downflows in a vertical channel. All flow scales, including the bubbles and the flow around them, are fully resolved using a front-tracking/finite-volume method. The turbulent bubbly channel flow is driven downward by an imposed constant pressure gradient, and the friction Reynolds number of the flow, based on the friction velocity and half-width of the channel, is 127.3, corresponding to a bulk Reynolds number of 3786 for a flow without bubbles. Three cases with several nearly spherical bubbles are examined. The bubble diameter is 31.8 wall units for all cases but the number of bubbles is varied, giving average void fractions of 1.5%, 3%, and 6%. The lift force on the bubbles drives them away from the walls until the mixture in the center of the channel is in hydrostatic equilibrium. Thus, the flow consists of a core region where the average void fraction and the mean vertical velocity are approximately constant and a bubble-free wall layer. The vertical velocity fluctuations in the wall layer decrease as the void fraction increases and the width of the wall layer decreases, but in the bubble-rich core the velocity fluctuations are higher than for a corresponding single-phase turbulent flow.
Double layer based electronic nanodevices fabricated on silicon nanoneedles
Authors: Joshkin V. , Lagally M. , van der Weide D.
Published: November 2006

For many years science and industry have exploited the transport properties of electrons in different apparatus called electronic devices. We suggested and investigated the nanodevices based on the proton’s ability to carry a charge. The electrochemical model of the device has been presented and verified by experiments. The device comprises a Schottky nanodiode, which is formed by two electrodes immersed in electrolyte (one of the electrodes is a metal film and another is a silicon nanoneedle directed perpendicular to the first electrode), and two double layer capacitors that surround these electrodes. The oppositely charged double layers create a transition region localized at the nanoneedle tip where the layers touch each other. Analysis of the experimental data reveals that the curvature of the nanoneedle electrode and the width of the transition region effect a proton current, which is a major electrical current component in the electrolyte applied, and determine a “built-in” variation of the Gibbs free energy of ionic carriers across the transition region. Different types of soft and liquid electrolytes have been investigated. We show that the suggested device can be used as a sensitive infrared photodiode, memory cell, and an electronic driven hydrogen ion device.
A compact equivalent circuit for the dark current-voltage characteristics of nonideal solar cells
Authors: Pallarès J. , Cabré R. , Marsal L. F. , Schropp R. E. I.
Published: November 2006

This paper presents a compact electrical equivalent circuit which describes the dark current-voltage characteristics of nonideal p-n junction solar cells in a wide range of temperatures. The model clearly separates the voltage drop in the junction and bulk regions. It is based on the combination of two exponential mechanisms, shunt and series resistances and space-charge limited current. In order to increase the accuracy of the parameter extraction process, both ln(I-V) and its derivative plots are fitted simultaneously. From the temperature dependence of the extracted parameters, the conduction mechanisms governing the I-V characteristics can be obtained without assuming dominating terms. In addition, the extracted parameters can be related to other electrical magnitudes obtained from such independent measurements as capacitance-voltage measurements (diffusion potential) and illuminated current-voltage characteristics (series resistance and open-circuit voltage). To exemplify the application, a p+ a-SiC:H∕n c-Si solar cell is studied and a number of major physical aspects derived from the analysis of the fitting values are discussed.
Nitrogen-substituted nanotubes and nanojunctions: Conformation and electronic properties
Authors: Carvalho A. C. M. , dos Santos M. C.
Published: November 2006

We present a theoretical study on the structural and electronic modifications caused by random nitrogen substitution in carbon tubular and branched nanostructures. Finite cluster calculations with hydrogen saturation of the tube ends were performed. Geometry optimizations were carried out through semiempirical quantum chemical calculations. Densities of states (DOS) were calculated by the density functional theory. The energy associated with nitrogen incorporation was obtained. Some tubular structures undergo a length shortening as a consequence of N substitution. DOS analysis is consistent with the shift of the electronic spectrum to lower energies and a more metallic character of the tubes upon nitrogen doping due to the emergence of nitrogen-induced states close to the conduction band. The defective regions of junctions and bends were built including five-, seven-, and eight-membered rings in the otherwise hexagonal network of carbon bonds. In order to reduce the stress caused by the curvature, a chemical doping through nitrogen substitution is proposed. Results are consistent with the shortening of bonds within the junctions and bends and an increased chemical stability of the defects.
Carrier distribution and its dependence on barrier thickness in InGaAsP∕InP asymmetric multiple quantum well lasers
Authors: Wang Huiling , Vandermeer Aaron D. , Cassidy Daniel T.
Published: November 2006

The carrier distribution and its dependence on barrier thickness were investigated experimentally using the transition cavity length method and the temperature varying photoluminescence (PL) spectra for the mirror image asymmetric multiple quantum well structures. The carriers were found to be richer in the long wavelength wells rather than in the p-side wells, and the nonuniformity of the carrier distribution depends on the barrier thickness. A rate equation model was developed to simulate the room-temperature PL spectra and it was found that the carrier distribution is very sensitive to the ratio of the capture times among different quantum wells and to the diffusion time across the barrier while the escape time plays a minor role on the carrier distribution. The large sensitivity of the carrier distribution on the diffusion time explains the dependence of the carrier distribution on the barrier thickness.
Ferromagnetic resonance and stress anisotropy in a ferromagnetic/antiferromagnetic bilayer
Authors: Rong Jian Hong , Yun Guo Hong , Narsu B. , Sprung D. W. L.
Published: November 2006

We study the ferromagnetic resonance (FMR) on a system consisting of a ferromagnetic (FM) film and an antiferromagnetic film. The FMR frequency and its linewidth were derived analytically and calculated numerically as a function of applied magnetic field and its angle, exchange anisotropy, strength, and angle of the stress anisotropy for single crystal FM films with, respectively, uniaxial or cubic magnetocrystalline anisotropies. The results show that the system with an applied or residual stress anisotropy has some symmetrical, or equivalent, directions of the hard and easy axes. This property is always destroyed by the asymmetrical shift caused by the exchange anisotropy. This fact will be helpful to the experimentalist in distinguishing between the stress and the exchange anisotropies.
Flow induced by a sphere settling in an aging yield-stress fluid
Authors: Gueslin B. , Talini L. , Herzhaft B. , Peysson Y. , Allain C.
Published: November 2006

We have studied the flow induced by a macroscopic spherical particle settling in a Laponite suspension that exhibits a yield stress, thixotropy, and shear thinning. We show that the fluid thixotropy (or aging) induces an increase with time of both the apparent yield stress and shear-thinning properties but also a breaking of the flow fore-aft symmetry predicted in Hershel-Bulkley fluids (yield-stress, shear-thinning fluids with no thixotropy). We have also varied the stress exerted by the particles on the fluid by using particles of different densities. Although the stresses exerted by the particles are of the same order of magnitude, the velocity field presents utterly different features: whereas the flow around the lighter particle shows a confinement similar to the one observed in shear-thinning fluids, the wake of the heavier particle is characterized by an upward motion of the fluid (“negative wake”), whatever the fluid’s age. We compare the features of this negative wake to the one observed in viscoelastic shear-thinning fluids (polymeric or micelle solutions). Although the flows around the two particles strongly differ, their settling behaviors display no apparent difference which constitutes an intriguing result and evidences the complexity of the dependence of the drag factor on flow field.
Phase behavior of weakly polydisperse sticky hard spheres: Perturbation theory for the Percus-Yevick solution
Authors: Fantoni Riccardo , Gazzillo Domenico , Giacometti Achille , Sollich Peter
Published: November 2006

We study the effects of size polydispersity on the gas-liquid phase behavior of mixtures of sticky hard spheres. To achieve this, the system of coupled quadratic equations for the contact values of the partial cavity functions of the Percus-Yevick solution [R. J. Baxter, J. Chem. Phys. 49, 2770 (1968)] is solved within a perturbation expansion in the polydispersity, i.e., the normalized width of the size distribution. This allows us to make predictions for various thermodynamic quantities which can be tested against numerical simulations and experiments. In particular, we determine the leading order effects of size polydispersity on the cloud curve delimiting the region of two-phase coexistence and on the associated shadow curve; we also study the extent of size fractionation between the coexisting phases. Different choices for the size dependence of the adhesion strengths are examined carefully; the Asakura-Oosawa model [J. Chem. Phys. 22, 1255 (1954)] of a mixture of polydisperse colloids and small polymers is studied as a specific example.
State-to-state reactive differential cross sections for the H+H2→H2+H reaction on five different potential energy surfaces employing a new quantum wavepacket computer code: DIFFREALWAVE
Authors: Hankel Marlies , Smith Sean C. , Allan Robert J. , Gray Stephen K. , Balint-Kurti Gabriel G.
Published: November 2006

State-to-state differential cross sections have been calculated for the hydrogen exchange reaction, H+H2→H2+H, using five different high quality potential energy surfaces with the objective of examining the sensitivity of these detailed cross sections to the underlying potential energy surfaces. The calculations were performed using a new parallel computer code, DIFFREALWAVE. The code is based on the real wavepacket approach of Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)]. The calculations are parallelized over the helicity quantum number Ω′ (i.e., the quantum number for the body-fixed z component of the total angular momentum) and wavepackets for each J,Ω′ set are assigned to different processors, similar in spirit to the Coriolis-coupled processors approach of Goldfield and Gray [Comput. Phys. Commun. 84, 1 (1996)]. Calculations for J=0–24 have been performed to obtain converged state-to-state differential cross sections in the energy range from 0.4to1.2eV. The calculations employ five different potential energy surfaces, the BKMP2 surface and a hierarchical family of four new ab initio surfaces [S. L. Mielke, et al., J. Chem. Phys. 116, 4142 (2002)]. This family of four surfaces has been calculated using three different hierarchical sets of basis functions and also an extrapolation to the complete basis set limit, the so called CCI surface. The CCI surface is the most accurate surface for the H3 system reported to date. Our calculations of differential cross sections are the first to be reported for the A2, A3, A4, and CCI surfaces. They show that there are some small differences in the cross sections obtained from the five different surfaces, particularly at higher energies. The calculations also show that the BKMP2 performs well and gives cross sections in very good agreement with the results from the CCI surface, displaying only small divergences at higher energies.
Electronic structure and binding energy of a hydrogenic impurity in a hierarchically self-assembled GaAs∕AlxGa1−xAs quantum dot
Authors: Li Shu-Shen , Xia Jian-Bai
Published: November 2006

We calculate the electronic structures and binding energy of a hydrogenic impurity in a hierarchically self-assembled GaAs∕AlxGa1−xAs quantum dot (QD) in the framework of effective-mass envelope-function theory. The variation of the electronic structures and binding energy with the QD structure parameters and the position of the impurity are studied in detail. We find that (1) acceptor impurity energy levels depend more sensitively on the size of the QD than those of a donor impurity; (2) all impurity energy levels strongly depend on the GaAs quantum well (QW) width; (3) a donor impurity in the QD has only one binding energy level except when the GaAs QW is large; (4) an acceptor impurity in the QD has two binding energy levels, which correspond to heavy- and light-hole quantum states; (5) the binding energy has a maximum value when the impurity is located below the symmetry axis along the growth direction; and (6) the binding energy has a minimum value when the impurity is located at the top corner of the QD.
Crystallographic properties of the MnGa2Se4 compound under high pressure
Authors: Marquina J. , Power Ch. , Grima P. , Morocoima M. , Quintero M. , Couzinet B. , Chervin J. C. , Munsch P. , González J.
Published: November 2006

X-ray diffraction measurements on MnGa2Se4, a II-III2-VI4 magnetic semiconductor compound, are made as a function of pressure up to 25GPa. It is found that in the range of 0<P<12GPa the structure is a defect tetragonal; in the range between 12 and 14GPa a two phase field α+NaCl type exists. It is found that at about 14GPa a transition to the cubic NaCl-type structure occurs and it appeared that this transition is irreversible. From the analysis of the x-ray diffraction lines, lattice parameter values are determined as a function of pressure. These results allow the evaluation of the compressibility coefficients of the corresponding parameters. The observed behavior of δ, χa, and χc with pressure are explained by using the relations proposed by Abrahams and Bernstein [J. Chem. Phys. 52, 5607 (1970)]. It is found that at about 3GPa, a symmetry change, from an ordered tetragonal to a disordered tetragonal structure, occurs.
Thermopower and electrical conductivity of Mn1.68−XCu0.6+X+Y+ZCo0.24−YNi0.48−Z thin film oxides obtained through metal organic decomposition processing
Authors: Moyer Jerome G. , Kukuruznyak Dmitry A. , Nguyen Nam , Prowse Michael S. , Ohuchi Fumio S.
Published: November 2006

Compositional variations of spinel oxides to a reference composition Mn1.68−XCu0.6+X+Y+ZCo0.24−YNi0.48−ZO4 (x and z=0.2, 0.4 and y=+∕−0.1) are made. Thermopower and electrical conductivity of these materials are measured in thin film forms obtained through metal organic decomposition. This low-temperature fabrication technique allows the concentration of metastable Mn4+ and Cu1+ ions, which are essential to charge transport in the oxide spinel, to be controlled. All compositions have n-type behavior, and the conduction occurs via polaron hopping between neighboring Mn3+oct and Mn4+oct sites. Compositional variations alter the Mn and Cu oxidation state concentrations, and modify the conductivity and thermopower. Charge balance models are used in some cases to interpret the influences that doping and fluctuating oxygen content have on the variable valence Mn and Cu. After accounting for changes in oxygen concentration, we found that replacing portions of Co with Cu raise both the conductivity and thermopower magnitude, and substituting small amounts of Cu for Ni reduces these thermoelectric factors. Surprisingly, the effects of doping show parallel rises or declines in conductivity and thermopower magnitude. This implies that conductivity is more strongly impacted by the activated carrier mobility than by the number of charge carriers in these oxides.
Elucidation of the annealing process required in the preparation of the thermoluminescence phosphor of CaSO4:Tm
Authors: Shinsho Kiyomitsu , Watanabe Eiji , Urushiyama Akio
Published: November 2006

The thermoluminescence phosphor of CaSO4:Tm was subjected to physicochemical studies. Careful thermo mass spectrometry and thermogravimetry/differential thermal analysis studies for a solid sample prepared by 200°C evaporation of a sulfuric acid medium without annealing by an extremely slow speed of temperature elevation were carried out. The data revealed, along with an initial weight loss corresponding to a small, nonstoichiometric amount of crystal water at 200°C, evidence for reaction with H2O vapor in air between 300 and 500°C and a 550°C and a subsequent release of SOx at higher temperatures until the beginning of bursting decomposition of CaSO4 bulk above 700°C. H1 NMR study revealed a broad signal at 9.9ppm, which was easily assigned to the crystal water involved. This initial solid has no thermostimulated luminescence (TL) efficiency. The first signal at 9.9ppm disappeared at 200°C. A new signal appeared at 13.1ppm by annealing from 300°C and increased significantly in intensity during annealing up to 600°C, which could be assigned to the intermediate produced by the reaction with H2O vapor in air. The intensity of this signal in turn was reduced by annealing at temperatures higher than 600°C and almost disappeared at 800°C. The solid by annealing at 700°C has the best TL efficiency. Several lines of the present physicochemical evidence suggest that the energy trap on irradiation of ionizing radiation is related to the concentration of O2− produced by the decomposition of SO42− during the annealing process in the course of the preparation of CaSO4:RE.
Coupling induced subband structures and collective single electron behavior in a single layer Si quantum dot array
Authors: Yu L. W. , Chen K. J. , Wu L. C. , Xu J. , Li W. , Huang X. F.
Published: November 2006

We report a study on the coupling induced subband structures and the collective single electron behavior in a single layer Si quantum dot (Si-QD) array, which is fabricated by a layer-by-layer technique using hydrogen diluted silane gas in plasma enhanced chemical vapor deposition system. Unique peak structures are observed in both the I-V and the capacitance-voltage (C-V) characteristics. The total number of electrons charged into the Si-QD array is found to be the same as the number of coupled quantum dots under the electrode. This phenomenon originates from a collective charging behavior of electrons into the subband structures in the Si-QD array, which evolved from the discrete energy levels in the individual Si QDs due to the weak interdot coupling. The different coupling and retention properties for the s-state and p-state subbands as well as the mechanisms for the charging and redistribution of electrons among the subbands are analyzed and discussed.
The vibrational structures of furan, pyrrole, and thiophene cations studied by zero kinetic energy photoelectron spectroscopy
Authors: Yang Jie , Li Juan , Mo Yuxiang
Published: November 2006

The vibrational structures of the electronic ground states (X̃A22) of furan, pyrrole, and thiophene cations have been studied by zero kinetic energy (ZEKE) photoelectron spectroscopic method. In addition to the strong excitations of the symmetric a1 vibrational modes, other three symmetric vibrational modes (a2, b1, and b2) have been observed unambiguously. These results which cannot be explained by the Franck-Condon principle illustrate that the vibronic coupling and the Coriolis coupling may play important roles in understanding the vibrational structures of the five-membered heterocycle cations. The vibrationally resolved ZEKE spectra are assigned with the assistance of the density function theory calculations, and the fundamental frequencies for many vibrational modes have been determined for the first time. The first adiabatic ionization energies for furan, pyrrole, and thiophene were determined as 8.8863, 8.2099, and 8.8742eV, respectively, with uncertainties of 0.0002eV.
Development of a wall shear stress integral measurement and analysis system for two-phase flow boundary layers
Authors: Dominguez-Ontiveros Elvis E. , Estrada-Perez Carlos E. , Ortiz-Villafuerte Javier , Hassan Yassin A.
Published: November 2006

An integral system was developed for the measurement and analysis of wall shear stress data from a two-phase boundary layer flow. Three different and independent measurement techniques are incorporated in a synchronized acquisition system. The three measurement techniques are the particle tracking velocimetry, a differential pressure transducer, and an optical wall shear stress sensor. Each of these techniques provides complementary information that helps in the description and understanding of the phenomena involved in a two-phase boundary layer. The practical implementation of the integral measurement and analysis system is demonstrated with the measurement of the wall shear stress of a microbubble laden boundary layer flow in a channel. The agreement in the results of the wall shear stress from the three synchronized measurements techniques was 93% for the single-phase case and 92.8% for the two-phase flow measurements. Moreover, independent measurements with each technique show no appreciable change in the values obtained when they were all synchronized. The advantages and limitations of each individual technique are discussed for measurement and analysis of two-phase flow data, as well the advantages of having an integral system that combines the information from all measurement techniques at the same time.
Active control of the ion resonance instability by ion removing fields
Authors: Bettega G. , Cavaliere F. , Cavenago M. , De Luca F. , Illiberi A. , Pozzoli R. , Romé M.
Published: November 2006

The off-axis bulk rotation (l=1 diocotron mode) of an electron plasma column confined in a Malmberg-Penning trap is strongly destabilized by a small population of positive ions formed by energetic electron-neutral collisions. The instability, known as ion resonance instability, drives the plasma against the wall, destroying the confinement. A new experimental technique based on the static or time dependent application of low voltages to the inner conductors of the trap is shown to be effective in controlling the instability. The efficiency of the control technique is experimentally investigated by a systematic variation of the amplitudes, time duration, and periodicity of the additional potentials.
Effect of dislocations on electrical and electron transport properties of InN thin films. I. Strain relief and formation of a dislocation network
Authors: Lebedev V. , Cimalla V. , Pezoldt J. , Himmerlich M. , Krischok S. , Schaefer J. A. , Ambacher O. , Morales F. M. , Lozano J. G. , González D.
Published: November 2006

The strain-relaxation phenomena and the formation of a dislocation network in 2H-InN epilayers during molecular beam epitaxy are reported. Plastic and elastic strain relaxations were studied by reflection high-energy electron diffraction, transmission electron microscopy, and high resolution x-ray diffraction. Characterization of the surface properties has been performed using atomic force microscopy and photoelectron spectroscopy. In the framework of the growth model the following stages of the strain relief have been proposed: plastic relaxation of strain by the introduction of geometric misfit dislocations, elastic strain relief during island growth, formation of threading dislocations induced by the coalescence of the islands, and relaxation of elastic strain by the introduction of secondary misfit dislocations. The model emphasizes the determining role of the coalescence process in the formation of a dislocation network in heteroepitaxially grown 2H-InN. Edge-type threading dislocations and dislocations of mixed character have been found to be dominating defects in the wurtzite InN layers. It has been shown that the threading dislocation density decreases exponentially during the film growth due to recombination and, hence, annihilation of dislocations, reaching ∼109cm−2 for ∼2200nm thick InN films.
Calculations of nuclear quadrupole coupling in noble gas–noble metal fluorides: Interplay of relativistic and electron correlation effects
Authors: Lantto Perttu , Vaara Juha
Published: November 2006

The nuclear quadrupole coupling constants (NQCCs) of noble gas and noble metal nuclei in the recently found noble gas–noble metal fluorides (NgMF, where Ng=Ar,Kr,Xe and M=Cu,Ag,Au) are obtained theoretically by high-level ab initio calculations, where both relativistic and electron correlation effects are included, and compared to experimental results. Fully relativistic four-component Dirac-Hartree-Fock (DHF) calculations are carried out at the basis set limit for electric field gradient that couples with the electric quadrupole moment of the nucleus, and uncorrelated relativistic effects are extracted by comparing DHF results to nonrelativistic (NR) HF calculations. Electron correlation effects are investigated both at fully relativistic second-order Møller-Plesset (DMP2) and at NR MP2 levels of theory, as well as at the NR coupled-cluster singles and doubles with perturbational triples [CCSD(T)] level. The validity of the approximation where relativistic effects, on the one hand, and nonrelativistically obtained correlation effects, on the other hand, are evaluated separately and assumed to be additive, is investigated by comparison with the DMP2 results. Inclusion of relativistic effects is shown to be necessary for obtaining the correct NQCC trends as the nucleus of interest and/or its neighbors become heavier. Electron correlation treatment is needed for approaching quantitative agreement with the experimental NQCCs. The assumption of additive electron correlation and relativistic effects, corresponding to the NR correlation treatment added on top of relativistic DHF data, gives qualitatively correct noble gas NQCCs. For noble metal NQCCs, correlation treatment at the relativistic level of theory is mandatory for reaching agreement with experimental results. Current work also confirms the experimental trends of NQCCs, which have been taken as an indication of nearly covalent interaction between noble gas and noble metal in the heaviest present systems, especially in XeAuF.
Mass-dependent and non-mass-dependent isotope effects in ozone photolysis: Resolving theory and experiments
Authors: Cole Amanda S. , Boering Kristie A.
Published: November 2006

In addition to the anomalous O17 and O18 isotope effects in the three-body ozone formation reaction O+O2+M, isotope effects in the destruction of ozone by photolysis may also play a role in determining the isotopic composition of ozone and other trace gases in the atmosphere. While previous experiments on ozone photolysis at 254nm were interpreted as evidence for preferential loss of light ozone that is anomalous (or “non-mass-dependent”), recent semiempirical theoretical calculations predicted a preferential loss of heavy ozone at that wavelength that is mass dependent. Through photochemical modeling results presented here, we resolve this apparent contradiction between experiment and theory. Specifically, we show that the formation of ozone during the UV photolysis experiments is not negligible, as had been assumed, and that the well-known non-mass-dependent isotope effects in ozone formation can account for the non-mass-dependent enrichment of the heavy isotopologs of ozone observed in the experiment. Thus, no unusual non-mass-dependent fractionation in ozone photolysis must be invoked to explain the experimental results. Furthermore, we show that theoretical predictions of a mass-dependent preferential loss of the heavy isotopologs of ozone during UV photolysis are not inconsistent with the experimental data, particularly if mass-dependent isotope effects in the chemical loss reactions of ozone during the photolysis experiments or experimental artifacts enrich the remaining ozone in O17 and O18. Before the calculated fractionation factors can be quantitatively evaluated, however, further investigation of possible mass-dependent isotope effects in the reactions of ozone with O(D1), O(P3), O2(Δ1), and O2(Σ1) is needed through experiments we suggest here.
A five-dimensional potential energy surface and predicted infrared spectra for the N2O-hydrogen complexes
Authors: Zhou Yanzi , Ran Hong , Xie Daiqian
Published: November 2006

We present a five-dimensional potential energy surface for the N2O-hydrogen complex using supermolecular approach with the full counterpoise correction at the coupled-cluster singles and doubles with noniterative inclusion of connected triple level. The normal mode Q3 for the ν3 antisymmetric stretching vibration of the N2O molecule was included in the calculations of the potential energies. The radial discrete variable representation/angular finite basis representation method and Lanczos algorithm were employed to calculate the rovibrational energy levels for four species of N2O-hydrogen complexes (N2O–para-H2, –ortho-H2, –ortho-D2, and –para-D2) without separating the inter- and intramolecular vibrations. The calculated band origins are all blueshifted relative to the isolated N2O molecule and in good agreement with the experimental values. The calculated rotational spectroscopic constants and molecular structures agree well with the available experimental results. The frequencies and line intensities of the rovibrational transitions in the ν3 region of N2O for the van der Waals ground vibrational state were calculated and compared with the observed spectra. The predicted infrared spectra are consistent with the observed spectra and show that the N2O–H2 complexes are mostly a-type transitions while both a-type and b-type transitions are significant for the N2O–D2 complexes.
Stability analysis of natural convective flows in horizontal annuli: Effects of the axial and radial aspect ratios
Authors: Petrone Giuseppe , Chénier Eric , Lauriat Guy
Published: November 2006

Linear stability analyses for two-dimensional natural convection in horizontal air-filled annuli are performed for three-dimensional perturbations and radius ratios in the range 1.2⩽R⩽3. Flow transitions from moderate to large-gap annuli, which have not been reported before, are thoroughly investigated. As a result, stability diagrams are obtained for finite and for infinite length annuli. The leading disturbances and threshold values are found to agree well with experimental data and three-dimensional numerical solutions. Three-dimensional simulations were also carried out to examine the influence on the flow stability of no-slip boundary conditions at the end-walls.
Temporal evolution of ion fragment production from methylsilane by a hot tungsten wire
Authors: Yoshimura Satoru , Toh Akinori , Toyoshima Takahiro , Kiuchi Masato , Hamaguchi Satoshi
Published: November 2006

Temporal evolution of ion fragment production from gaseous methylsilane in contact with a hot tungsten wire was measured with a use of a low-energy mass analyzed ion beam system. The mechanisms of molecular fragmentation in the system are similar to those for typical catalytic chemical vapor deposition processes. The fragmentation rates vary during the process due to surface modification of the tungsten wire. The extent of surface modification depends on the tungsten temperature. When the tungsten temperature was set to 1940°C, ion fragments were produced initially but the production terminated about 1h after the start of the experiment. The termination of ion production seems to be caused by the formation of a thick 3C-SiC layer on the tungsten surface, which was identified by x-ray diffraction measurement. When the tungsten temperature was set to 2220°C, ion fragment production continued at least for 8h. In this case the layer of deposited compounds, which mainly consist of WC, W2C, C, and 4H-SiC, was relatively thin.