bluuebunny/crossref_metadata_2025 huggingface dataset:
Source region of the 18 November 2003 coronal mass ejection that led to the strongest magnetic storm of cycle 23
Authors: Srivastava Nandita , Mathew Shibu K. , Louis Rohan E. , Wiegelmann Thomas
Published: March 2009

The superstorm of 20 November 2003 was associated with a high‐speed coronal mass ejection (CME) which originated in the NOAA AR 10501 on 18 November. This coronal mass ejection had severe terrestrial consequences leading to a geomagnetic storm with Dst index of −472 nT, the strongest of the current solar cycle. In this paper, we attempt to understand the factors that led to the coronal mass ejection on 18 November. We have also studied the evolution of the photospheric magnetic field of NOAA AR 10501, the source region of this coronal mass ejection. For this purpose, the Michelson Doppler Imager line‐of‐sight magnetograms and vector magnetograms from Solar Flare Telescope, Mitaka, obtained during 17–19 November 2003 were analyzed. In particular, quantitative estimates of the temporal variation in magnetic flux, energy, and magnetic field gradient were estimated for the source active region. The evolution of these quantities was studied for the 3‐day period with an objective to understand the preflare configuration leading up to the moderate flare which was associated with the geoeffective coronal mass ejection. We also examined the chromospheric images recorded in Hα from Udaipur Solar Observatory to compare the flare location with regions of different magnetic field and energy. Our observations provide evidence that the flare associated with the CME occurred at a location marked by high magnetic field gradient which led to release of free energy stored in the active region.
Relative intensities of middle atmosphere waves
Authors: Offermann D. , Gusev O. , Donner M. , Forbes J. M. , Hagan M. , Mlynczak M. G. , Oberheide J. , Preusse P. , Schmidt H. , Russell J. M.
Published: March 2009

Climatologies of gravity waves, quasi‐stationary planetary waves, and tides are compared in the upper stratosphere, mesosphere, and lower thermosphere. Temperature standard deviations from zonal means are used as proxies for wave activity. The sum of the waves is compared to directly measured total temperature fluctuations. The resulting difference is used as a proxy for traveling planetary waves. A preliminary climatology for these waves is proposed. A ranking of the four wave types in terms of their impact on the total wave state of the atmosphere is achieved, which is dependent on altitude and latitude. At extratropical latitudes, gravity waves mostly play a major role. Traveling planetary waves are found to play a secondary role. Quasi‐stationary planetary waves and tides yield a lesser contribution there. Vertical profiles of total temperature fluctuations show a sharp vertical gradient change (“kink” or “bend”) in the mesosphere. This is interpreted in terms of a change of wave damping, and the concept of a “wave turbopause” is suggested. The altitude of this wave turbopause is found to be mostly determined by the relative intensities of gravity waves and planetary waves. The turbopause is further analyzed, including earlier mass spectrometer data. It is found that the wave turbopause and the mass spectrometer turbopause occur rather close together. The turbopause forms a layer about 8 km thick, and the data suggest an additional 3 km mixing layer on top.
Estimates of the information provided by GPS slant data observed in Germany regarding tomographic applications
Authors: Bender M. , Dick G. , Wickert J. , Ramatschi M. , Ge M. , Gendt G. , Rothacher M. , Raabe A. , Tetzlaff G.
Published: March 2009

The observation of GPS slant delays from ground GPS networks can be used to reconstruct spatially resolved humidity fields in the troposphere by means of tomographic techniques. Tomography is always related to the solution of inverse problems which are very sensitive to the quality of the input data. Prior to a tomographic reconstruction, it is therefore necessary to quantify the information provided by a given set of GPS slant delay data. This work describes the properties and the information content of more than two million GPS slant delays taken in March 2006 by a continuously operating German GPS network. The temporal and spatial distribution of the slant paths in the atmosphere and their angular distribution in the local system of the GPS station is given. These distributions depend on the satellite orbits and show some characteristic pattern. The available information is estimated by investigating the distribution of intersection points between the slant paths. From these data it is possible to identify regions that are well covered by GPS slant paths and to evaluate the applicability of the existing German GPS stations for continuous atmosphere sounding.
Maritime Aerosol Network as a component of Aerosol Robotic Network
Authors: Smirnov A. , Holben B. N. , Slutsker I. , Giles D. M. , McClain C. R. , Eck T. F. , Sakerin S. M. , Macke A. , Croot P. , Zibordi G. , Quinn P. K. , Sciare J. , Kinne S. , Harvey M. , Smyth T. J. , Piketh S. , Zielinski T. , Proshutinsky A. , Goes J. I. , Nelson N. B. , Larouche P. , Radionov V. F. , Goloub P. , Krishna Moorthy K. , Matarrese R. , Robertson E. J. , Jourdin F.
Published: March 2009

The paper presents the current status of the Maritime Aerosol Network (MAN), which has been developed as a component of the Aerosol Robotic Network (AERONET). MAN deploys Microtops handheld Sun photometers and utilizes the calibration procedure and data processing (Version 2) traceable to AERONET. A web site dedicated to the MAN activity is described. A brief historical perspective is given to aerosol optical depth (AOD) measurements over the oceans. A short summary of the existing data, collected on board ships of opportunity during the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project is presented. Globally averaged oceanic aerosol optical depth (derived from island‐based AERONET measurements) at 500 nm is ∼0.11 and Angstrom parameter (computed within spectral range 440–870 nm) is calculated to be ∼0.6. First results from the cruises contributing to the Maritime Aerosol Network are shown. MAN ship‐based aerosol optical depth compares well to simultaneous island and near‐coastal AERONET site AOD.
Revisiting the COP9 signalosome as a transcriptional regulator
Authors: Chamovitz Daniel A
Published: March 2009

The COP9 signalosome (CSN) is a highly conserved protein complex that was originally described as a repressor of light‐dependent growth and transcription in Arabidopsis. The most studied CSN function is the regulation of protein degradation, which occurs primarily through the removal of the ubiquitin‐like modifier Nedd8 from cullin‐based E3 ubiquitin ligases. This activity can regulate transcription‐factor stability and, therefore, transcriptional activity. Recent data suggest that the CSN also regulates transcription on the chromatin by mechanisms that are not yet clearly understood. Furthermore, the CSN subunits CSN5 and CSN2 seem to act as transcriptional coactivators and corepressors, respectively. Here, I re‐evaluate the mechanisms by which the CSN acts as a transcriptional regulator, and suggest that they could extend beyond the regulation of protein stability.
Current and shot noise measurements in a carbon nanotube-based spin diode (invited)
Authors: Merchant Christopher A. , Marković Nina
Published: March 2009

Low-temperature measurements of asymmetric carbon nanotube (CNT) quantum dots are reported. The CNTs are end-contacted with one ferromagnetic and one normal-metal electrode. The measurements show a spin-dependent rectification of the current caused by the asymmetry of the device. This rectification occurs for gate voltages for which the normal-metal lead is resonant with a level of the quantum dot. At the gate voltages at which the current is at the maximum current, a significant decrease in the current shot noise is observed.
Electron holography observation of in-plane domain structure in writer pole for perpendicular recording heads
Authors: Hirata K. , Ishida Y. , Kim J. J. , Kasai H. , Shindo D. , Takahashi M. , Tonomura A.
Published: March 2009

A direct observation of the in-plane domain structure of the writer pole of a perpendicular recording head was performed by electron holography in order to investigate the cause of pole erasure due to the instability of the domain wall behavior. The instability of domain structure of the writer pole generated a stray field on the air bearing surface of the writer pole. The domain wall trapping at the pole tip was found quite effective to form a stable domain structure in the remanent state, and it reflected domain wall energy change and initial domain structure of the writer pole.
Magnetic markers detection using PCB fluxgate array
Authors: Janosek M. , Ripka P. , Platil A.
Published: March 2009

We used an array of race-track fluxgate sensors, manufactured with printed circuit board (PCB) technology, forming a sensor head for detection of ferromagnetic and paramagnetic markers. The sensors were arranged perpendicularly to the measuring plane and we measured the difference of their output, giving us the horizontal gradient of normal component of the measured field. Due to the close match of the sensor’s parameters, subtraction of the fluxgate output signals could be done directly at the input of a lock-in amplifier, increasing the signal-to-noise ratio for small gradients. When moving the sensor head, we were able to map field gradients smaller than 6 nT/mm, which was verified while measuring the magnetic markers on a dollar bill, while suppressing the background field by a factor of 5. In a line-scanning mode, we scanned a marker formed by a 0.2 mm diameter Permalloy wire in a distance of up to 10 mm. With the help of perpendicular ac excitation at 30 Hz, we were able to detect a 0.1 ml Endorem iron-oxide superparamagnetic marker at 2 mm; volume of 0.6 ml was detectable at 10 mm.
The rewritable effects of bonded magnet for large starting torque and high efficiency in the small power single-phase written pole motor
Authors: Choi Jae-Hak , Lee Sung-Ho
Published: March 2009

This paper presents a single-phase written pole motor using a bonded ring magnet for the small power home application. The motor has an exciter pole structure inside the stator and hybrid characteristics of an induction motor and permanent magnet motor. The design parameters and operating characteristics of the hybrid concept motor are investigated to increase starting torque and efficiency, which is most important for the small power home application. Larger starting torque and higher efficiency than those of the conventional induction motor could be obtained by using the rewritable characteristics of bonded magnet on the starting and running conditions.
Nonmagnetic carbon nanotubes
Authors: Lipert Kamil , Kretzschmar Florian , Ritschel Manfred , Leonhardt Albrecht , Klingeler Rüdiger , Büchner Bernd
Published: March 2009

We have synthesized by chemical vapor deposition (CVD) single-, double-, and multiwalled carbon nanotubes without magnetic impurities. In particular, we have applied a rhenium-based CVD technique yielding nonmagnetic carbon nanotubes with diamagnetic Re particles. In addition, carbon nanotubes prepared with iron as catalyst particles are annealed at very high temperatures in which the catalyst material is completely vaporized, while the carbon nanotubes are structurally preserved. Detailed magnetic studies show for both approaches a clear diamagnetic behavior typical for pure carbon nanotubes but no indication of ferromagnetic or paramagnetic material.
Interaction between buoyancy and diffusion-driven instabilities of propagating autocatalytic reaction fronts. II. Nonlinear simulations
Authors: D’Hernoncourt J. , Merkin J. H. , De Wit A.
Published: March 2009

The nonlinear dynamics resulting from the interplay between diffusive and buoyancy-driven Rayleigh–Taylor (RT) instabilities of autocatalytic traveling fronts are analyzed numerically for fronts ascending or descending in the gravity field and for various values of the relevant parameters, the Rayleigh numbers Ra and Rb of the reactant A and autocatalytic product B, respectively, and the ratio D=DB/DA of the diffusion coefficients of the two key chemical species. The interaction between the coarsening dynamics characteristic of the RT instability and the fixed short wavelength dynamics of the diffusive instability leads in some parameter regimes to complex dynamics dominated by the irregular succession of birth and death of fingers. Large single convective fingers with a tip deformed by the short wavelength diffusive instability are also observed. If D is sufficiently small and the RT instability is active, the concentration of the slower diffusing species B can be convected to values above its fully reacted concentration. Experimental conditions that would allow the observation of the dynamics predicted here are described.
Temperature-induced magnetic-anisotropy crossover in a Co/MgO/Co heterostructure
Authors: Gladczuk L. , Aleshkevych P. , Szymczak R. , Dluzewski P. , Aleszkiewicz M. , Paszkowicz W. , Minikayev R. , Przyslupski P.
Published: March 2009

Phenomena occurring at the interface may significantly modify the properties of magnetic thin films. In this paper, the effect of temperature on the magnetic properties of Co(001)/MgO/Co trilayers is studied. The trilayer structure was modified by partial coverage of Co layers by Au at the Co/MgO interface. It is found that when the quantity of deposited gold is small, formation of islands at the Co/MgO interfaces takes place, which is proved by the topological surface analysis and by the x-ray reflectivity. In the investigated trilayer structure, gradual changes of the easy magnetization axis from the in-plane to the out-of-plane direction are observed during lowering the temperature from 300 to 5 K. The analysis of the ferromagnetic resonance spectra within the multiple-magnetic-layer model system indicates that the surface anisotropy provides a significant contribution to the magnetic anisotropy of complete Co(001)/MgO/Co heterostructure.
Structural properties of polymeric DNA from molecular dynamics simulations
Authors: Samanta Sudipta , Mukherjee Supti , Chakrabarti Jaydeb , Bhattacharyya Dhananjay
Published: March 2009

Most of the reported DNA structural studies are based on oligonucleotide structures, which have artifacts due to unstable terminal base pairs (bps). We have carried out molecular dynamics simulation of DNA oligonucleotides in such a manner that gives rise to properties of polymeric DNA of infinite length. Molecular dynamics simulation studies of six homo- and heteropolymeric DNA sequences are reported here to understand structural features of all ten unique dinucleotide sequences. We observe that each of these dinucleotide sequences has unique features in agreement with Calladine’s rule [C. R. Calladine, J. Mol. Biol. 161, 343 (1982)]. We noticed significant structural alternation between BI and BII forms for d(CA).d(TG) dinucleotide, where one of the strands showed frequent transitions between usual and unusual ε and ζ torsion angles associated with bp stacking geometry. In terms of the calculated bending rigidity and persistence length, pyrimidine-purine bp steps, namely, d(TA).d(TA), d(CA).d(TG), and d(CG).d(CG) are the most flexible dinucleotide bp steps. We estimated the major groove widths from our simulations. We did not observe much variation in major and minor groove widths depending on the base sequence. However, the distribution of water molecules in the minor groove shows sensitivity to the DNA sequence.
Physical and chemical effects on crystalline H2O2 induced by 20 keV protons
Authors: Loeffler M. J. , Baragiola R. A.
Published: March 2009

We present laboratory studies on radiation chemistry, sputtering, and amorphization of crystalline H2O2 induced by 20 keV protons at 80 K. We used infrared spectroscopy to identify H2O, O3, and possibly HO3, measure the fluence dependence of the fraction of crystalline and amorphous H2O2 and of the production of H2O and destruction of H2O2. Furthermore, using complementary techniques, we observe that the sputtering yield depends on fluence due to the buildup of O2 radiation products in the sample. In addition, we find that the effective cross sections for the destruction of hydrogen peroxide and the production of water are very high compared to radiation chemical processes in water even though the fluence dependence of amorphization is nearly the same for the two materials. This result is consistent with a model of fast cooling of a liquid track produced by each projectile ion rather than with the disorder produced by the formation of radiolytic products.
Shape formation of ferrofluid under external magnetic fields using level set method
Authors: Kim Young Sun , Lee Se-Hee , Choi Hong Soon , Park Il Han
Published: March 2009

The shape formation of ferrofluid under magnetic field has been considered to be one of most difficult problems to analyze. In this paper we present a numerical implementation of the level set method for the equilibrium shape calculation of ferrofluid under magnetic field. The magnetic-fluid coupled system has an extremum value of electromagnetic system energy. When the system is composed of magnetic permeable material and current sources, the system energy is a maximum at the equilibrium state. The level set method is adopted for shape capturing since it can easily handle shape variations of fluid including topological changes such as merging, splitting, and even disappearing of connected material regions. The velocity field for the level set method is calculated using a shape derivative of continuum sensitivity analysis that is derived by employing the material derivative concept. The numerical results for a model problem of some ferrofluid on a glass plate show that the level set method works well for the ferrofluid shape formation.
Noncrystalline compact packings of hard spheres of two sizes: Bipyramids and the geometry of common neighbors
Authors: Miracle D. B. , Harrowell Peter
Published: March 2009

Insight into the efficient filling of space in systems of binary spheres is explored using bipyramids consisting of 3≤n≤8 tetrahedra sharing a common pair of spheres. Compact packings are sought in bipyramids consisting of larger hard spheres of unit radius and smaller hard spheres of radius 0.001≤R≤1. Seventy-seven distinct compact bipyramids are found. The number of distinct compact bipyramids increases with the number n of constituent tetrahedra. No compact bipyramids are found for R≥0.9473 and for 0.8493≥R≥0.7434. A topological instability eliminates compact packings for R≤0.1547. Pentagonal bipyramids cover a larger range in R than any other compact bipyramids studied.
A study of the fixed-node error in quantum Monte Carlo calculations of electronic transitions: The case of the singlet n→π∗ (CO) transition of the acrolein
Authors: Bouabça Thomas , Ben Amor Nadia , Maynau Daniel , Caffarel Michel
Published: March 2009

We report fixed-node diffusion Monte Carlo (FN-DMC) calculations of the singlet n→π∗ (CO) vertical transition of acrolein. The impact of the fixed-node approximation on the excitation energy is investigated. To do that, trial wave functions corresponding to various nodal patterns are used. They are constructed by using either a minimal complete-active-space self-consistent field (CASSCF) calculation involving an oxygen lone pair n and the π∗ (CO) molecular orbitals or a more complete set involving all the molecular orbitals expected to play a significant role in the excitation process. Calculations of both states have been performed with molecular orbitals optimized separately for each state via standard “state specific” CASSCF calculations or by using a common set of optimized orbitals [“state averaged” CASSCF calculations] whose effect is to introduce some important correlation between the nodal patterns of the two electronic states. To investigate the role of the basis set three different basis of increasing size have been employed. The comparative study based on the use of all possible combinations of basis sets, active spaces, and type of optimized molecular orbitals shows that the nodal error on the difference of energies is small when chemically relevant active space and state-averaged-type CASSCF wave functions are used, although the fixed-node error on the individual total energies involved can vary substantially. This remarkable result obtained for the acrolein suggests that FN-DMC calculations based on a simple strategy (use of standard ab initio wave functions and no Monte Carlo optimization of molecular orbital parameters) could be a working computational tool for computing electronic transition energies for more general systems.
Enantioselectivity of amino acids using chiral sensors based on nanotubes
Authors: Vardanega D. , Picaud F. , Girardet C.
Published: March 2009

The selective detection of amino acid enantiomers can be achieved by considering chiral nanotubes used in a resonator configuration. We show that this enantioselectivity is appreciably increased when a peptide molecule is inserted in the tube. The chiral polarization of the nanotube at the linear and nonlinear levels due to the inserted polar peptide is very sensitive to the adsorption of left- or right-handed alanine molecules. This leads to a difference in the resonance frequency of the sensor which can increase to 12 MHz when the nanotube is not chiral (instead of 0 for the bare tube) and can reach 38 MHz for a chiral tube (instead of 14 MHz for the bare tube). The influence of the various parameters which are responsible for such a differential frequency shift, i.e., the tube hyperpolarizability, the polar electric properties of the peptide, and the screening effect due to the tube on the peptide-alanine interactions, is discussed and some general rules are given regarding the optimization of the enantioselectivity of these sensors.
Light-induced charge transfer in hybrid composites of organic semiconductors and silicon nanocrystals
Authors: Dietmueller Roland , Stegner Andre R. , Lechner Robert , Niesar Sabrina , Pereira Rui N. , Brandt Martin S. , Ebbers André , Trocha Martin , Wiggers Hartmut , Stutzmann Martin
Published: March 2009

Charge transfer between silicon nanocrystals (Si-nc) and organic semiconductors has been investigated via light-induced electron spin resonance (LESR). Composites of Si-nc with the hole conductor poly(3-hexylthiophene) (P3HT) and with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been investigated. The LESR measurements allow one to quantify light-induced charge transfer between Si-nc and P3HT, which results in positive P3HT polarons. PCBM, in contrast, acts as an electron acceptor in composites with Si-nc, and after illumination, negative PCBM radicals are created. These results are discussed in terms of light-induced generation and separation of charge carriers in the hybrid composites.
Thermal detectivity enhancement of visible and near infrared thermography by using super-resolution algorithm: Possibility to generalize the method to other domains
Authors: Teyssieux Damien , Euphrasie Sebastien , Cretin Bernard
Published: March 2009

This paper reports on a method which allows a decrease in the minimal detectable temperature in visible and near infrared thermography. This original method permits an increase in the thermal sensitivity without loss of good spatial resolution. It is based on a binning operation and a super-resolution algorithm. The radiometric model and super-resolution method are presented. Measurements on two different samples show the enhancement of the thermal sensitivity and the capability of the method. Finally, the authors propose different ways in which the method can be applied.
Investigation of the reactions of small neutral iron oxide clusters with methanol
Authors: Xie Yan , Dong Feng , Heinbuch Scott , Rocca Jorge J. , Bernstein Elliot R.
Published: March 2009

Reactions of neutral iron oxide clusters (FemOn, m=1–2, n=0–5) with methanol (CH3OH) in a fast flow reactor are investigated by time of flight mass spectrometry. Detection of the neutral iron oxide cluster distribution and reaction intermediates and products is accomplished through single photon ionization by a 118 nm (10.5 eV) VUV laser. Partially deuterated methanol (CD3OH) is employed to distinguish reaction products and reaction mechanisms. Three major reactions are identified experimentally: CH3OH association with FeO; methanol dehydrogenation on FeO1,2 and Fe2O2–5; and (CH2O)Fe formation. Density functional theory calculations are carried out to identify reaction products, and to explore the geometric and electronic structures of the iron oxide clusters, reaction intermediates, and transition states, and to evaluate reaction pathways. Neutral formaldehyde is calculated to be formed on FeO1,2 and Fe2O2–5 clusters. Hydrogen transfer from methanol to iron oxide clusters occurs first from the O–H moiety of methanol, and is followed by a hydrogen transfer from the C–H moiety of methanol. Computational results are in good agreement with experimental observations and reveal reaction mechanisms for neutral iron oxide clusters taking methanol to formaldehyde through various reaction intermediates. Based on the experimental results and the calculated reaction mechanisms and pathways, complete catalytic cycles are suggested for the heterogeneous reaction of CH3OH to CH2O facilitated by an iron oxide catalyst.
Understanding two-pulse phase-modulated decoupling in solid-state NMR
Authors: Scholz Ingo , Hodgkinson Paul , Meier Beat H. , Ernst Matthias
Published: March 2009

A theoretical description of the two-pulse phase-modulated (TPPM) decoupling sequence in magic-angle spinning NMR is presented using a triple-mode Floquet approach. The description is formulated in the radio-frequency interaction-frame representation and is valid over the entire range of possible parameters leading to the well-known results of continuous-wave (cw) decoupling and XiX decoupling in the limit of a phase change of 0° and 180°, respectively. The treatment results in analytical expressions for the heteronuclear residual coupling terms and the homonuclear spin-diffusion terms. It also allows the characterization of all resonance conditions that can contribute in a constructive or a destructive way to the residual linewidth. Some of the important resonance conditions are described for the first time since they are not accessible in previous treatments. The combination of the contributions from the residual couplings and the resonance conditions to the effective Hamiltonian, as obtained in a Floquet description, is shown to be required to describe the decoupling behavior over the full range of parameters. It is shown that for typical spin system and experimental parameters a C13 linewidth of approximately 12Hz can be obtained for TPPM decoupling in an organic solid or a protein. This is a major contribution to the experimentally observed linewidths of around 20Hz and indicates that decoupling techniques are still one of the limiting factors in the achievable linewidths.
A Hamiltonian electromagnetic gyrofluid model
Authors: Waelbroeck F. L. , Hazeltine R. D. , Morrison P. J.
Published: March 2009

An isothermal truncation of the electromagnetic gyrofluid model of Snyder and Hammett [Phys. Plasmas 8, 3199 (2001)] is shown to be Hamiltonian. The corresponding noncanonical Lie–Poisson bracket and its Casimir invariants are presented. The invariants are used to obtain a set of coupled Grad–Shafranov equations describing equilibria and propagating coherent structures.
Simulation of electron thermal transport in H-mode discharges
Authors: Rafiq T. , Pankin A. Y. , Bateman G. , Kritz A. H. , Halpern F. D.
Published: March 2009

Electron thermal transport in DIII-D H-mode tokamak plasmas [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] is investigated by comparing predictive simulation results for the evolution of electron temperature profiles with experimental data. The comparison includes the entire profile from the magnetic axis to the bottom of the pedestal. In the simulations, carried out using the automated system for transport analysis (ASTRA) integrated modeling code, different combinations of electron thermal transport models are considered. The combinations include models for electron temperature gradient (ETG) anomalous transport and trapped electron mode (TEM) anomalous transport, as well as a model for paleoclassical transport [J. D. Callen, Nucl. Fusion 45, 1120 (2005)]. It is found that the electromagnetic limit of the Horton ETG model [W. Horton et al., Phys. Fluids 31, 2971 (1988)] provides an important contribution near the magnetic axis, which is a region where the ETG mode in the GLF23 model [R. E. Waltz et al., Phys. Plasmas 4, 2482 (1997)] is below threshold. In simulations of DIII-D discharges, the observed shape of the H-mode edge pedestal is produced when transport associated with the TEM component of the GLF23 model is suppressed and transport given by the paleoclassical model is included. In a study involving 15 DIII-D H-mode discharges, it is found that with a particular combination of electron thermal transport models, the average rms deviation of the predicted electron temperature profile from the experimental profile is reduced to 9% and the offset to −4%.
Controlled growth of one-dimensional clusters of molybdenum atoms using double-walled carbon nanotube templating
Authors: Tao Yousheng , Muramatsu Hiroyuki , Hayashi Takuya , Kim Yoong Ahm , Shimamoto Daisuke , Endo Morinobu , Kaneko Katsumi , Terrones Mauricio , Dresselhaus Mildred S.
Published: March 2009

We report the controlled growth of one-dimensional clusters of molybdenum atoms inside the inner cores of double-walled carbon nanotubes. A combined characterization including high resolution transmission electron microscopy, nitrogen adsorption measurement at 77 K, x-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis reveals that the growth of one-dimensional Mo clusters can be controlled by varying the reaction conditions. The products have specific surface areas of 360–480 m2 g−1, and their characteristic properties are attributed to the presence of Mo cluster, which affect the electronic structure and can be exploited for the development of nanotube electronic devices.
Electric field of Ions in solution probed by hyper-Rayleigh scattering
Authors: Shelton David P.
Published: March 2009

The electric field of dissolved ions accounts for the narrow spike at zero frequency shift, with the polarization signature of a polar longitudinal collective mode, in the high resolution hyper-Rayleigh light scattering (HRS) spectrum for liquid water and other polar solvents. This peak in the HRS spectrum probes both the structure factor and the fluctuation time for the ion charge density in solution. The experimental results for KCl–D2O solutions are consistent with the Debye–Hückel charge structure factor and determine the diffusion coefficient and static local field factor.
Near compensated half-metal in Sr2NiOsO6
Authors: Song Weiyu , Zhao Erjun , Meng Jian , Wu Zhijian
Published: March 2009

The electronic and magnetic properties of tetragonal double perovskite Sr2NiOsO6 were studied by use of the density functional theory and including the spin-orbit coupling. Compensated half-metal is found if the spin-orbit coupling is not considered. Spin-orbit coupling induces orbital moments on both Ni and Os, making Sr2NiOsO6 a near compensated half-metal. Ferromagnetic phase is slightly favored over antiferromagnetic phase (by 4 meV). The small energy difference also suggests that both phases are competitive for the ground state. At ferromagnetic phase, the calculated net magnetic moment is 3.53μB, in good agreement with experimental value of 3.44μB. At antiferromagnetic phase, the net magnetic moment is 0.69μB, in which the contribution from the net spin moment is 0.09μB.
Magnetization reversal in CoPt(111) hard/soft bilayers
Authors: Alexandrakis V. , Niarchos D. , Wolff M. , Panagiotopoulos I.
Published: March 2009

The magnetization reversal in magnetron sputtered CoPt(111) hard/soft bilayers has been studied by polarized neutron reflectometry and magnetization measurements. The stability of the hard layer is tuned by the heat-treatment conditions which are used to crystallize the chemically ordered, high anisotropy, L10 phase. All the samples show the same features in their first order reversal curves but the lateral domain size during the magnetization reversal of the soft layer differs. In samples with strong intergrain coupling it exceeds the coherence length of the neutron beam, resulting in spin-flip scattering. In contrast, the hard layer reversal occurs through the reorientation in small domains.
Terahertz-wave generation by GaP rib waveguides via collinear phase-matched difference-frequency mixing of near-infrared lasers
Authors: Saito Kyosuke , Tanabe Tadao , Oyama Yutaka , Suto Ken , Nishizawa Jun-ichi
Published: March 2009

We constructed rib waveguides from GaP material using an inductively coupled plasma reactive ion etching technique based on Ar/Cl2 gas application. We obtained a waveguide with a rib height of 200 μm. Terahertz-wave generation from the GaP-crystal rib waveguides was demonstrated via collinear phase-matched difference-frequency mixing of near-infrared light. The terahertz output peak corresponding to the fundamental modes appeared around 0.75 THz for a 1-mm-wide rib waveguide. The position of the fundamental mode shifted to 1.32 THz for a 200-μm-wide waveguide, which is attributable to the two-dimensional confinement of the terahertz waves in the waveguide. The conversion efficiency was enhanced in the rib waveguide compared to that in both slab waveguides and bulk GaP crystals.
Analysis of surface roughness of optical elements planarized by nonadiabatic optical near-field etching
Authors: Naruse Makoto , Yatsui Takashi , Nomura Wataru , Hirata Kazuya , Tabata Yoshinori , Ohtsu Motoichi
Published: March 2009

Nonadiabatic optical near-field etching is a novel way of polishing surfaces of optical elements without any mechanical contact processes. It selectively induces photochemical reactions on the surface in regions where optical near fields are excited, namely, in the vicinity of portions having fine-scale rough structures, which leads to reduced surface roughness. In this paper, we analyze the surface roughness of optical elements planarized by nonadiabatic optical near-field etching based on power spectrum-based methods. Our analysis clearly reveals the effects of the near-field etching which are otherwise concealed when using conventional roughness measures such as the roughness average (Ra). We also investigate the effect of planarization via numerical simulations using surface profiles obtained experimentally before and after the near-field etching.
Photoactive periodic media
Authors: Ben-Messaoud Tahar , Riordon Jason , Melanson Alexandre , Ashrit P. V. , Haché Alain
Published: March 2009

Photoactive (photochromic) multilayers of MoO3/SiO2 are studied optically before and after UV excitation. Enhancement in photochromic activity is observed over a wide spectrum and in particular near the photonic band edges where optical changes are up to 25 times greater than in similarly prepared bulk, nonperiodic samples. Applications to light-sensitive devices are discussed.
Photoluminescent and crystalline properties of Y3−xAl5O12:Cex3+ phosphor nanofibers prepared by electrospinning
Authors: Suryamas Adi Bagus , Munir Muhammad Miftahul , Iskandar Ferry , Okuyama Kikuo
Published: March 2009

Cerium-doped yttrium aluminum garnet (YAG:Ce3+; Y3−xAl5O12:Cex3+) phosphor nanofibers were successfully prepared using an electrospinning method followed by a heating process. Aluminum nitrate nonahydrate, yttrium nitrate hexahydrate, and cerium nitrate hexahydrate dissolved in dimethylformadide, poly(vinyl pyrrolidone), and ethanol comprised the precursor. The precursor was electrospun under atmospheric conditions to obtain the as-prepared fibers, which consisted of salts and the polymer composite. The as-prepared fibers were then heated to remove the polymer and to obtain the YAG:Ce3+ crystalline fibers. The morphology of the final fibers was homogeneous; the fibers were approximately 300 nm in diameter and several centimeters in length. The photoluminescence (PL) and crystalline properties of the fibers were studied as a function of both the doping fraction (0.005≤x≤0.4) and the heating temperature (900–1400 °C). High heating temperatures resulted in a high degree of crystallinity, crystallites that ranged from 20 to 55 nm in size, and enhanced PL intensity. A doping concentration of 1% (x=0.01) gave the highest PL intensity under excitation at 470 nm. The PL spectra were centered at 530 nm due to the transition from the 5d state to the 4f state (A21g→F25/2 and A21g→F27/2).
Influence of pressure and silane depletion on microcrystalline silicon material quality and solar cell performance
Authors: Bugnon G. , Feltrin A. , Meillaud F. , Bailat J. , Ballif C.
Published: March 2009

Hydrogenated microcrystalline silicon growth by very high frequency plasma-enhanced chemical vapor deposition is investigated in an industrial-type parallel plate R&D KAI™ reactor to study the influence of pressure and silane depletion on material quality. Single junction solar cells with intrinsic layers prepared at high pressures and in high silane depletion conditions exhibit remarkable improvements, reaching 8.2% efficiency. Further analyses show that better cell performances are linked to a significant reduction of the bulk defect density in intrinsic layers. These results can be partly attributed to lower ion bombardment energies due to higher pressures and silane depletion conditions, improving the microcrystalline material quality. Layer amorphization with increasing power density is observed at low pressure and in low silane depletion conditions. A simple model for the average ion energy shows that ion energy estimates are consistent with the amorphization process observed experimentally. Finally, the material quality of a novel regime for high rate deposition is reviewed on the basis of these findings.
Electrical relaxation in CdI2 doped silver vanadate superionic glasses
Authors: Ghosh Aloka , Dutta D. , Kabi S. , Ghosh A.
Published: March 2009

In this paper we have studied electrical relaxation in several compositions of CdI2–Ag2O–V2O5 superionic glasses in wide frequency and temperature ranges. We have used the power law formalism as well as the electric modulus formalism to analyze the experimental results. We have observed that the dc conductivity increases and the activation energy decreases with the increase of the CdI2 content in the compositions. We have also observed that the concentration of mobile Ag+ ions is not thermally activated and is almost independent of CdI2 content. The mobile ion concentration is also less than that of the total Ag+ ions present in the compositions. The conductivity is primarily determined by the mobility rather than the ion concentration. The conductivity relaxation time shows Arrhenius behavior with an activation energy, which is almost equal to that of the dc conductivity, indicating that the same ions take part in the dc and the ac conduction. The values of frequency exponent and stretching exponent are observed to be almost temperature and composition independent. The exponents are less than unity and obey the relationship proposed by Ngai.
Spatially resolved electron energy loss spectroscopy on n-type ultrananocrystalline diamond films
Authors: Arenal R. , Stephan O. , Bruno P. , Gruen D. M.
Published: March 2009

The addition of nitrogen to the synthesis gas during synthesis of ultrananocrystalline-diamond (UNCD) films results in films uniquely exhibiting very high n-type electrical conductivity even at ambient temperatures. This result is due to the formation of nanowires having elongated diamond core nanostructures and a sp2-bonded C sheath surrounding the core. The work presented here provides detailed confirmation of this important result through spatially resolved-electron energy loss spectroscopy. The direct observation of nitrogen incorporated in the sheath has been enabled. The incorporation of this nitrogen provides strong support to a plausible mechanism for the n-type conduction characteristic of the UNCD films.
Influence of electric field on saturated film boiling
Authors: Tomar G. , Biswas G. , Sharma A. , Welch S. W. J.
Published: March 2009

Electrohydrodynamic (EHD) forces enhance heat and mass transfer in fluid flows. In two-phase flows under the influence of an electric field, an EHD force acts on the interface resulting in an enhanced interfacial motion. We perform a numerical study of the effect of the application of an electric field on bubble density and heat transfer characteristics during saturated film boiling. Application of electric field results in shorter bubble separation distances, faster growth of the instability, and higher bubble release frequency. Increasing the electric-field intensity shows an increase in the space averaged Nusselt number, thus indicating the role of electric field in the enhancement of heat transfer. We perform full nonlinear simulations of saturated film boiling coupled with electrohydrodynamics using a coupled level set and volume of fluid algorithm. Simulations have been performed for water and refrigerant R123a at near critical pressures.
Transient photovoltaic behavior of air-stable, inverted organic solar cells with solution-processed electron transport layer
Authors: Kim Chang Su , Lee Stephanie S. , Gomez Enrique D. , Kim Jong Bok , Loo Yueh-Lin
Published: March 2009

The short-circuit current density of inverted organic solar cells comprising a solution-processed titania electron transport layer increases with continuous illumination in air and saturates after 10 min. On extended exposure (>2 days), the open-circuit voltage of the devices increases also. The improvement in device characteristics over short time scales is attributed to the filling of shallow electron traps in titania. With an increase in photoconductivity of titania, the short-circuit current increases accordingly. The increase in open-circuit voltage on extended exposure to air is attributed to an increase in the electrostatic field across the diodes when polythiophene is doped by oxygen.
Perpendicular spin torque promotes synchronization of magnetic tunnel junction based spin torque oscillators
Authors: Zhou Yan , Åkerman Johan
Published: March 2009

We study how the perpendicular spin transfer torque term (bj), present in magnetic tunneling junctions (MTJs), affects the synchronization of serially connected MTJ-based spin torque oscillators (MTJ-STOs). We find that bj modifies the intrinsic preferred I-V phase shift in single MTJ-STO in such a way that serially connected MTJ-STOs synchronize much more readily without the need for additional circuitry to change the I-V phase. This result strongly suggests that synchronization of serially connected MTJ-STOs should be significantly more straightforward than the previously attempted serial synchronization of giant magnetoresistance based STOs (GMR-STOs).
Intense multimicrojoule high-order harmonics generated from neutral atoms of In2O3 nanoparticles
Authors: Elouga Bom L. B. , Ganeev R. A. , Abdul-Hadi J. , Vidal F. , Ozaki T.
Published: March 2009

We studied high-order harmonic generation from plasma that contains an abundance of indium oxide nanoparticles. We found that harmonics from nanoparticle-containing plasma are considerably more intense than from plasma produced on the In2O3 bulk target, with high-order harmonic energy ranging from 6 μJ (for the ninth harmonic) to 1 μJ (for the 17th harmonic) in the former case. The harmonic cutoff from nanoparticles was at the 21st order, which is lower than that observed using indium oxide solid target. By comparing the harmonic spectra obtained from solid and nanoparticle indium oxide targets, we concluded that intense harmonics in the latter case are dominantly generated from neutral atoms of the In2O3 nanoparticles.
Internal quantum efficiency and nonradiative recombination coefficient of GaInN/GaN multiple quantum wells with different dislocation densities
Authors: Dai Q. , Schubert M. F. , Kim M. H. , Kim J. K. , Schubert E. F. , Koleske D. D. , Crawford M. H. , Lee S. R. , Fischer A. J. , Thaler G. , Banas M. A.
Published: March 2009

Room-temperature photoluminescence (PL) measurements are performed on GaInN/GaN multiple-quantum-well heterostructures grown on GaN-on-sapphire templates with different threading-dislocation densities. The selective optical excitation of quantum wells and the dependence of integrated PL intensity on excitation power allow us to determine the internal quantum efficiency (IQE) as a function of carrier concentration. The measured IQE of the sample with the lowest dislocation density (5.3×108 cm−2) is as high as 64%. The measured nonradiative coefficient A varies from 6×107 to 2×108 s−1 as the dislocation density increases from 5.3×108 to 5.7×109 cm−2, respectively.
Efficient generation of energy-tunable entangled photons in a semiconductor microcavity
Authors: Oka Hisaki , Oohata Goro , Ishihara Hajime
Published: March 2009

A scheme is proposed for the generation of polarization- and frequency-entangled photons in a semiconductor planar microcavity. Photon entanglement can be achieved by converting two lower polariton branches with symmetric in-plane momenta into lower and upper polariton branches with zero in-plane momentum via a biexciton state. The phase-matching condition is satisfied for a microcavity with cavity detuning equal to the biexciton binding energy. The generation efficiency and energy control of the entangled photons are demonstrated for a CuCl microcavity as an example.
Growth of AlGaN/GaN heterojunction field effect transistors on semi-insulating GaN using an AlGaN interlayer
Authors: Chen Z. , Pei Y. , Newman S. , Chu R. , Brown D. , Chung R. , Keller S. , Denbaars S. P. , Nakamura S. , Mishra U. K.
Published: March 2009

Semi-insulating (SI) GaN layers were grown on 4H-SiC substrates by inserting an AlGaN layer between the AlN buffer and the GaN layer. Secondary ion mass spectroscopy measurements showed that the AlGaN layer prevented Si from diffusing from the substrate into the GaN layer. X-ray diffraction and atomic force microscopy analyses showed that an optimized AlGaN interlayer does not degrade the crystal quality or surface morphology of the SI GaN. The room temperature mobility of an AlGaN/GaN heterostructure using this SI GaN was 2200 cm2/V s. High electron mobility transistors (HEMTs) with 0.65 μm long gates were also fabricated on these SI GaN buffers. A power density of 19.0 W/mm with a power added efficiency of 48% was demonstrated at 10 GHz at a drain bias of 78 V. These HEMTs also exhibited sharp pinch off, low leakage, and negligible dispersion.
Visible-blind ultraviolet photodetector based on double heterojunction of n-ZnO/insulator-MgO∕p-Si
Authors: Zhang T. C. , Guo Y. , Mei Z. X. , Gu C. Z. , Du X. L.
Published: March 2009

Exploiting a double heterojunction of n-ZnO/insulator-MgO∕p-Si grown by molecular beam epitaxy, a visible-blind ultraviolet (UV) photodetector has been fabricated. The photodetector shows a rectification ratio of ∼104 at ±2V and a dark current of 0.5nA at a reverse bias of −2V.The photoresponse spectrum indicates a visible-blind UV detectivity of our devices with a sharp cut off at the wavelength of 378nm and a high UV/visible rejection ratio. The key role of the middle insulating MgO layer, as a barrier layer for minority carrier transport, has been demonstrated.
Distributed feedback all-organic microlaser based on holographic polymer dispersed liquid crystals
Authors: Criante L. , Lucchetta D. E. , Vita F. , Castagna R. , Simoni F.
Published: March 2009

An optically pumped vertically emitting all-organic laser, based on a holographic polymer dispersed liquid crystal reflection grating operating in a distributed feedback configuration, is presented. The used experimental geometry overcomes the main drawbacks characterizing similar systems, allowing virtually infinite operations and absence of damages associated with the high energy of the optical pumping.