bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical speciation of organic aerosol during the International Consortium for Atmospheric Research on Transport and Transformation 2004: Results from in situ measurements
Authors: Williams Brent J. , Goldstein Allen H. , Millet Dylan B. , Holzinger Rupert , Kreisberg Nathan M. , Hering Susanne V. , White Allen B. , Worsnop Douglas R. , Allan James D. , Jimenez Jose L.
Published: March 2007

We report the first ever hourly in situ measurements of speciated organic aerosol composition. Measurements were made during July and August 2004 at Chebogue Point, Nova Scotia, using a novel thermal desorption aerosol GC/MS‐FID (TAG) instrument as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT). Hourly time resolution measurements of organic marker compounds were used to define several different source types contributing to the aerosols observed, including two aged anthropogenic sources from the United States, oxidized biogenic aerosols from Maine and Canada, local biogenic contributions to secondary organic aerosol (SOA), local anthropogenic contributions to hydrocarbon‐like organic aerosol (HOA), and a potential marine or dairy source. These TAG‐defined sources were used to separate aerosol mass spectrometer (AMS) measurements of total organics, SO42−, NO3−, and NH4+, along with total aerosol black carbon (BC) into several distinct particle types. Average organic aerosol mass ranged from 33% of the total aerosol mass during anthropogenic U.S. outflow events to 81% of total aerosol mass during biogenic oxidation events arriving from Maine and Canada during 26 July to 15 August 2004.
Cyclic AMP signalling in Dictyostelium: G‐proteins activate separate Ras pathways using specific RasGEFs
Authors: Kae Helmut , Kortholt Arjan , Rehmann Holger , Insall Robert H , Van Haastert Peter J M , Spiegelman George B , Weeks Gerald
Published: March 2007

In general, mammalian Ras guanine nucleotide exchange factors (RasGEFs) show little substrate specificity, although they are often thought to regulate specific pathways. Here, we provide in vitro and in vivo evidence that two RasGEFs can each act on specific Ras proteins. During Dictyostelium development, RasC and RasG are activated in response to cyclic AMP, with each regulating different downstream functions: RasG regulates chemotaxis and RasC is responsible for adenylyl cyclase activation. RasC activation was abolished in a gefA− mutant, whereas RasG activation was normal in this strain, indicating that RasGEFA activates RasC but not RasG. Conversely, RasC activation was normal in a gefR− mutant, whereas RasG activation was greatly reduced, indicating that RasGEFR activates RasG. These results were confirmed by the finding that RasGEFA and RasGEFR specifically released GDP from RasC and RasG, respectively, in vitro. This RasGEF target specificity provides a mechanism for one upstream signal to regulate two downstream processes using independent pathways.
Nanoscale electrical characterization of Si-nc based memory metal-oxide-semiconductor devices
Authors: Porti M. , Avidano M. , Nafría M. , Aymerich X. , Carreras J. , Jambois O. , Garrido B.
Published: March 2007

In this work, standard and nanoscale experiments have been combined to investigate the electrical properties of metal-oxide-semiconductor (MOS) memory devices with silicon nanocrystals (Si-nc) embedded in the gate oxide. The nanometer scale analysis has been performed with a conductive atomic force microscope (C-AFM) which, thanks to its high lateral resolution, allows the study of areas of only few hundreds of nm2. Therefore, with this technique, a very reduced number of Si-nc can be investigated. We have studied the conduction mechanisms, the retention time, and the amount of charge stored in the Si-nc of these structures. The results have demonstrated that Si-nc enhance the gate oxide electrical conduction due to trap assisted tunneling. On the other hand, Si-nc can act as trapping sites. The amount of charge stored in Si-nc has been estimated through the change induced in the barrier height measured from the current-voltage (I-V) curves (at the nanoscale, with C-AFM) and from the flat band voltage shift determined from the capacitance-voltage (C-V) characteristics measured on polygated structures. Both procedures have shown an occupation level of ∼20% of the Si-nc. The retention times, estimated at the nanoscale and from standard electrical characterization, are consistent. Moreover, contrary to standard characterization techniques, C-AFM allows the mesurement of lateral leakage currents in memories based on high density trapping sites. All these results allow one to conclude that C-AFM is a very suitable tool in performing a detailed investigation of the performance of memory devices based on MOS structures with Si-nc at the nanoscale.
Effects of pretreatment processes on improving the formation of ultrananocrystalline diamond
Authors: Chen Li-Ju , Tai Nyan-Hwa , Lee Chi-Young , Lin I-Nan.
Published: March 2007

Effects of pretreatment on the nuclei formation of ultrananocrystalline diamond (UNCD) on Si substrates were studied. Either precoating a thin layer of titanium (∼400nm) or ultrasonication pretreatment using diamond and titanium mixed powder (D&T process) enhances the nucleation process on Si substrates markedly, and the UNCD nuclei formed and fully covered the Si substrate, when deposition was processed using the microwave-plasma-enhanced chemical-vapor deposition process for 10min. In contrast, during the same period, ultrasonication pretreatment using diamond powders (D process) can only form large UNCD clusters, which were scarcely distributed on Si substrates. The analyses using x-ray diffractometer, secondary ion mass spectroscopy, and electron spectroscopy for chemical analysis reveal that the titanium layer reacted with carbon species in the plasma, forming crystalline TiC phase, which facilitates the subsequent formation of UNCD nuclei. The beneficial effect of Ti layer on enhancing the nucleation of UNCD is presumably owing to high solubility and high diffusivity of carbon species in Ti materials, as compared with those of Si materials.
Rayleigh wave interaction with surface-breaking cracks
Authors: Jian X. , Dixon S. , Guo N. , Edwards R.
Published: March 2007

This paper investigates Rayleigh wave interaction with simulated, surface breaking cracks using a finite element method, in which the scattered wave modes giving rise to the in-plane and out-of-plane displacements are presented. By looking at the contribution from all of the transmitted, reflected, and mode-converted signals at the crack, the magnitude of signal enhancement in the near field and the mechanism by which this occurs can be fully explained. Furthermore, oscillations in the Rayleigh wave reflection and transmission coefficients with crack depth in the far field can be explained by means of multiple reflected and transmitted wave modes at the crack, whose relative amplitudes are dependent on the crack depth. Results agree with previously published experimental measurements.
Nonlocal effects in a bounded low-temperature plasma with fast electrons
Authors: DeJoseph C. A. , Demidov V. I. , Kudryavtsev A. A.
Published: March 2007

Effects associated with nonlocality of the electron energy distribution function (EEDF) in a bounded, low-temperature plasma containing fast electrons, can lead to a significant increase in the near-wall potential drop, leading to self-trapping of fast electrons in the plasma volume, even if the density of this group is only a small fraction (∼0.001%) of the total electron density. If self-trapping occurs, the fast electrons can substantially increase the rate of stepwise excitation, supply additional heating to slow electrons, and reduce their rate of diffusion cooling. Altering the source terms of these fast electrons will, therefore, alter the near-wall sheath and, through modification of the EEDF, a number of plasma parameters. Self-trapping of fast electrons is important in a variety of plasmas, including hollow-cathode discharges and capacitive rf discharges, and is especially pronounced in an afterglow plasma, which is a key phase of any pulse-modulated discharge. In the afterglow, the electron temperature is less than a few tenths of an electron volt, and the fast electrons will have energies typically greater than an electron volt. It is shown that in the afterglow plasma of noble gases, fast electrons, arising from Penning ionization of metastable atoms, can lead to the above condition and significantly change the plasma and sheath properties. Similar effects can be important in technologically relevant electronegative gas plasmas, where fast electrons can arise due to electron detachment in collisions of negative ions with atomic species. Both experimental and modeling results are presented to illustrate these effects.
On the stability of laser wakefield electron accelerators in the monoenergetic regime
Authors: Mangles S. P. D. , Thomas A. G. R. , Lundh O. , Lindau F. , Kaluza M. C. , Persson A. , Wahlström C.-G. , Krushelnick K. , Najmudin Z.
Published: March 2007

The effects of plasma density and laser energy on the stability of laser produced monoenergetic electron beams are investigated. Fluctuations in the principal beam parameters, namely, electron energy, energy-spread, charge, and pointing, are demonstrated to be minimized at low densities. This improvement in stability is attributed to the reduced time for pulse evolution required before self-injection occurs; i.e., that the pulse is closest to the matched conditions for these densities. It is also observed that electrons are only consistently produced above a density-dependent energy threshold. These observations are consistent with there being a threshold intensity (a0≳3) required for the occurrence of self-injection after accounting for pulse compression.
Secondary instabilities in two- and three-dimensional magnetic reconnection in fusion relevant plasmas
Authors: Grasso D. , Borgogno D. , Pegoraro F.
Published: March 2007

The fast collisionless reconnection process typical of fusion relevant plasma regimes is analyzed with both two-dimensional and three-dimensional models. The vorticity and current density layers, which typically form in these regimes, are followed during all the phases of their dynamical evolution. Here, these structures are shown to be unstable in the cold electron case to secondary Kelvin-Helmholtz-like instabilities not only in the two-dimensional approximation but also in the full three-dimensional setting.
Target design for high fusion yield with the double Z-pinch-driven hohlraum
Authors: Vesey R. A. , Herrmann M. C. , Lemke R. W. , Desjarlais M. P. , Cuneo M. E. , Stygar W. A. , Bennett G. R. , Campbell R. B. , Christenson P. J. , Mehlhorn T. A. , Porter J. L. , Slutz S. A.
Published: March 2007

A key demonstration on the path to inertial fusion energy is the achievement of high fusion yield (hundreds of MJ) and high target gain. Toward this goal, an indirect-drive high-yield inertial confinement fusion (ICF) target involving two Z-pinch x-ray sources heating a central secondary hohlraum is described by Hammer et al. [Phys. Plasmas 6, 2129 (1999)]. In subsequent research at Sandia National Laboratories, theoretical/computational models have been developed and an extensive series of validation experiments have been performed to study hohlraum energetics, capsule coupling, and capsule implosion symmetry for this system. These models have been used to design a high-yield Z-pinch-driven ICF target that incorporates the latest experience in capsule design, hohlraum symmetry control, and x-ray production by Z pinches. An x-ray energy output of 9MJ per pinch, suitably pulse-shaped, is sufficient for this concept to drive 0.3–0.5GJ capsules. For the first time, integrated two-dimensional (2D) hohlraum/capsule radiation-hydrodynamics simulations have demonstrated adequate hohlraum coupling, time-dependent radiation symmetry control, and the successful implosion, ignition, and burn of a high-yield capsule in the double Z-pinch hohlraum. An important new feature of this target design is mode-selective symmetry control: the use of burn-through shields offset from the capsule that selectively tune certain low-order asymmetry modes (P2,P4) without significantly perturbing higher-order modes and without a significant energy penalty. This paper will describe the capsule and hohlraum design that have produced 0.4–0.5GJ yields in 2D simulations, provide a preliminary estimate of the Z-pinch load and accelerator requirements necessary to drive the system, and suggest future directions for target design work.
Resistive wall mode stabilization by slow plasma rotation in DIII-D tokamak discharges with balanced neutral beam injection
Authors: Strait E. J. , Garofalo A. M. , Jackson G. L. , Okabayashi M. , Reimerdes H. , Chu M. S. , Fitzpatrick R. , Groebner R. J. , In Y. , LaHaye R. J. , Lanctot M. J. , Liu Y. Q. , Navratil G. A. , Solomon W. M. , Takahashi H. ,   the DIII-D Team
Published: March 2007

Recent experiments in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] show that the resistive wall mode (RWM) can be stabilized by smaller values of plasma rotation than previously reported. Stable discharges have been observed with beta up to 1.4 times the no-wall kink stability limit and ion rotation velocity (measured from CVI emission) less than 0.3% of the Alfvén speed at all integer rational surfaces, in contrast with previous DIII-D experiments that indicated critical values of 0.7%–2.5% of the local Alfvén speed. Preliminary stability calculations for these discharges, using ideal magnetohydrodynamics with a drift-kinetic dissipation model, are consistent with the new experimental results. A key feature of these experiments is that slow plasma rotation was achieved by reducing the neutral beam torque. Earlier experiments with strong neutral beam torque used “magnetic braking” by applied magnetic perturbations to slow the rotation, and resonant effects of these perturbations may have led to a larger effective rotation threshold. In addition, the edge rotation profile may have a critical role in determining the RWM stability of these low-torque plasmas.
Spectroscopic determination of H, He, and H2 temperatures in a large-scale microwave plasma source
Authors: Tatarova E. , Dias F. M. , Ferreira C. M. , Puač N.
Published: March 2007

Emission spectroscopy was used for the diagnostic of a large-scale, slot antenna excited microwave plasma source operating in pure hydrogen and in helium-hydrogen and argon-hydrogen mixtures at low pressures (p=0.3mbar) and microwave power ranging from 600to900W. No evidence was found for excessive broadening of the Hα line under the present operating conditions, even though this line was found to be broader than the helium singlet line at 667.8nm. The Doppler temperatures corresponding to this helium line (400–900K) are close to the rotational temperatures (300–800K) determined from the Q branch of the Fulcher-α band under the same conditions. The kinetic temperature of H atoms corresponding to the Doppler broadening of the Hα line varies spatially between 3100 and 3400K (95% He–5% H2, p=0.3mbar, and P=900W) and between 3350 and 3900K (95% Ar–5% H2, p=0.3mbar, and P=600W) keeping constant the mixture composition, pressure, and microwave power. The rotational H2 temperature in argon-hydrogen mixtures varies from 330to400K under the same conditions. Therefore, the results presented here indicate that the kinetic temperature of H atoms is higher than the background gas temperature.
Multifolded torus chaotic attractors: Design and implementation
Authors: Yu Simin , Lu Jinhu , Chen Guanrong
Published: March 2007

This paper proposes a systematic methodology for creating multifolded torus chaotic attractors from a simple three-dimensional piecewise-linear system. Theoretical analysis shows that the multifolded torus chaotic attractors can be generated via alternative switchings between two basic linear systems. The theoretical design principle and the underlying dynamic mechanism are then further investigated by analyzing the emerging bifurcation and the stable and unstable subspaces of the two basic linear systems. A novel block circuit diagram is also designed for hardware implementation of 3-, 5-, 7-, 9-folded torus chaotic attractors via switching the corresponding switches. This is the first time a 9-folded torus chaotic attractor generated by an analog circuit has been verified experimentally. Furthermore, some recursive formulas of system parameters are rigorously derived, which is useful for improving hardware implementation.
Highly efficient and stable red phosphorescent organic light-emitting device using bis[2-(2-benzothiazoyl)phenolato]zinc(II) as host material
Authors: Kanno Hiroshi , Ishikawa Kaori , Nishio Yoshitaka , Endo Ayataka , Adachi Chihaya , Shibata Kenichi
Published: March 2007

The red-emitting phosphorescent organic light-emitting device employing Bis[2-(2-benzothiazoyl)phenolato]zinc(II) (Zn(BTP)2) as a host material has been demonstrated. The device generates saturated red emission with Commission Internationale de l’Eclairage coordinates of (0.67, 0.33), characterized by a low driving voltage of 3.2V and high external quantum efficiency of 10.3% at 10mA∕cm2. Moreover, the efficiency and lifetime are improved by using 30% NPB-doped Zn(BTP)2 host in the emitting layer, where NPB is 4,4′-bis(N-phenyl-1-naphthyl-amino)biphenyl. The maximum external quantum efficiency of the device reaches 12.6% at 1.7mA∕cm2. The device has exhibited excellent stability. The half-luminance lifetime is 240h at 80mA∕cm2 (initial luminance of 6070cd∕m2). The relationship between the employed host material and device performance is discussed.
Energy-consistent relativistic pseudopotentials and correlation consistent basis sets for the 4d elements Y–Pd
Authors: Peterson Kirk A. , Figgen Detlev , Dolg Michael , Stoll Hermann
Published: March 2007

Scalar-relativistic pseudopotentials and corresponding spin-orbit potentials of the energy-consistent variety have been adjusted for the simulation of the [Ar]3d10 cores of the 4d transition metal elements Y–Pd. These potentials have been determined in a one-step procedure using numerical two-component calculations so as to reproduce atomic valence spectra from four-component all-electron calculations. The latter have been performed at the multi-configuration Dirac-Hartree-Fock level, using the Dirac-Coulomb Hamiltonian and perturbatively including the Breit interaction. The derived pseudopotentials reproduce the all-electron reference data with an average accuracy of 0.03eV for configurational averages over nonrelativistic orbital configurations and 0.1eV for individual relativistic states. Basis sets following a correlation consistent prescription have also been developed to accompany the new pseudopotentials. These range in size from cc-pVDZ-PP to cc-pV5Z-PP and also include sets for 4s4p correlation (cc-pwCVDZ-PP through cc-pwCV5Z-PP), as well as those with extra diffuse functions (aug-cc-pVDZ-PP, etc.). In order to accurately assess the impact of the pseudopotential approximation, all-electron basis sets of triple-zeta quality have also been developed using the Douglas-Kroll-Hess Hamiltonian (cc-pVTZ-DK, cc-pwCVTZ-DK, and aug-cc-pVTZ-DK). Benchmark calculations of atomic ionization potentials and 4dm−25s2→4dm−15s1 electronic excitation energies are reported at the coupled cluster level of theory with extrapolations to the complete basis set limit.
Magnetism in coaxial palladium nanowires
Authors: Stewart D. A.
Published: March 2007

While bulk palladium is nonmagnetic, several recent studies have shown that magnetism can occur in hcp Pd films, fcc twinned Pd nanoparticles, and Pd atomic strands. These studies show that small changes in Pd atomic configurations can induce magnetic properties. This raises the question of whether nanoscale Pd structures in general are magnetic. In this work, we examine coaxial palladium nanowires in an effort to determine the most stable configurations and their magnetic properties. Relaxed nanowire structures are found using density functional calculations in the plane wave basis. In several metallic systems such as gold, coaxial nanowires have proven to be the lowest energy configurations for ultrathin (⩽1nm) nanowires. We consider magnetism in these structures as a function of diameter and coaxial configuration. These results are also compared to fcc and hcp Pd nanowires of comparable diameters. We find that the (6, 0) coaxial nanowire provides the most stable structure and exhibits a magnetic moment of 0.278μB∕at.
High-pressure high-temperature synthesis and magnetic properties of ordered perovskite Sr2Cu(Re0.69−xWxCa0.31)O6 (0⩽x⩽0.6)
Authors: Balamurugan S. , Isobe M. , Takayama-Muromachi E.
Published: March 2007

We report the synthesis and magnetic properties of polycrystalline Sr2Cu(Re0.69−xWxCa0.31)O6 samples with x=0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6, which were prepared by high-pressure high-temperature synthesis technique. These phases had ordered cubic perovskite structures. The pristine compound (x=0) underwent a ferromagnetic (ferrimagnetic) transition with TC∼460K. The ferromagnetism was suppressed by the W substitution and disappears almost completely for x=0.6. Mechanism of the suppression of the magnetism is discussed assuming a localized electron system.
Exchange bias in a nanocolumnar Ni80Fe20∕α-Fe2O3 thin film
Authors: van Lierop J. , Lin K.-W. , Guo Z.-Y. , Ko P.-H. , Ouyang H.
Published: March 2007

A Ni80Fe20∕α-Fe2O3 thin film has been deposited using a dual ion-beam deposition technique where the α-Fe2O3 is formed in situ by O2 bombardment of pure Fe. AC susceptibility results indicate moment fluctuations at temperatures above 150K. This behavior combined with the thermal fluctuation driven temperature dependence of the negative field coercivity indicates that the α-Fe2O3 nanocolumnar crystallite magnetism evolves from static single domain moments to superparamagnetic moments with warming. 25kOe field cooling establishes exchange bias with an onset temperature of 50K. The positive (Hc2) and negative (Hc1) field coercivities exhibit very different temperature dependencies, with Hc1(T) well described by a thermally activated coherent domain wall reversal model, while Hc2(T) is essentially constant except for the lowest temperatures. These results point towards different domain reversal mechanisms in positive and negative fields.
Bonding-site dependence of surface resistivity: CO on epitaxial Cu(100) films
Authors: Liu Chang , Tobin R. G.
Published: March 2007

The authors have measured the contribution of CO adsorbed on different bonding sites to the resistivity of epitaxial Cu(100) films. Through an analysis of the correlation between surface resistivity and temperature-programed desorption measurements, CO on terraces is found to affect the resistance much more strongly than CO on defect sites. Two possible explanations are considered: a reduced scattering cross section of defect CO owing to the different local electronic structure at defect sites or strong scattering by the bare defect that is not significantly affected by the adsorption of CO.
Magneto-optic properties of CoFe2−xGaxO4
Authors: Lee S. J. , Song S. H. , Lo C. C. , Aldini S. T. , Jiles D. C.
Published: March 2007

Research on cobalt ferrite based composites has increased recently due to their potential applications such as noncontact magnetoelastic stress or torque sensors and erasable magneto-optic recording media. We report a study of the polar Kerr rotation spectra for CoFe2−xGaxO4 (with x=0.4 and x=0.8). Each of the spectra consists of two peaks of negative Kerr rotation in the measured photon energy range of 1.5–3.0eV. For x=0.4, one peak occured at 1.8eV and the other at 2.25eV. For x=0.8, the first peak shifted to a higher energy of about 1.9eV, while the second peak remained at 2.25eV. The origin of the peaks in the polar Kerr spectra and the observed shift of peak position resulting from Ga substitution can be explained by the intervalence charge-transfer transition, in which an electron from a metallic cation is transferred to a neighboring cation through an optical excitation.
High magnetic field properties of yttrium-substituted Ho6Fe23 alloys and deuterides
Authors: Ostoréro J. , Guillot M.
Published: March 2007

The magnetic properties of the Ho6−xYxFe23Dz (x=0, 0.5, 1 and z=0, 16) deuterides and of the parent alloys are studied under high dc magnetic field (230kOe) on samples oriented parallel and perpendicular to the external field in the 4.2–300K temperature range. All compounds that retain the cubic Fm3m crystallographic structure present canted ferrimagnetic structure. For most of the samples, field-induced transitions characterized by a linear variation of M above the transition field are found. Upon deuteration drastic changes of the magnetic properties are observed and the main “magnetic parameters” are then determined. In the alloys the exchange interaction Ho–Fe increases when the yttrium content increases but decreases in the deuterides. For all alloys the Curie temperature remains close to 510K.
A phase diagram for the Bose-Einstein condensation of magnons
Authors: Bennett L. H. , Della Torre E. , Johnson P. R. , Watson R. E.
Published: March 2007

Evidence has recently been given for the Bose-Einstein condensation (BEC) of magnons in nanostructures. This behavior occurs for nanoparticles some tens of nanometers in size (having some millions of atoms in a nanoparticle). Here we explore the effect of particle size on the BEC critical temperature and the blocking temperature. These considerations lead to a proposed phase diagram for magnetic behavior in nanoparticles, with distinct BEC, superparamagnetic, and ferromagnetic phases.
Growth, spectral properties, and laser demonstration of Yb3+:BaGd2(MoO4)4 cleavage crystal
Authors: Zhu Haomiao , Chen Yujin , Lin Yanfu , Gong Xinghong , Tan Qiguang , Luo Zundu , Huang Yidong
Published: March 2007

Detailed polarized spectral properties of a 3.6 at. % Yb3+:BaGd2(MoO4)4 (Yb3+:BGM) cleavage crystal grown by the Czochralski method have been investigated, including the absorption cross section, the emission cross-section, and the fluorescence lifetime. The evaluation of the laser potentiality shows that the Yb3+:BGM crystal is promising for tunable and ultrashort laser generations around 1 μm. The room temperature quasi-CW laser operation of an unprocessed 3.6 at. % Yb3+:BGM cleavage plate has been demonstrated with diode pumping. The results indicate that the Yb3+:BGM crystal is a good candidate for microchip laser gain medium by cleavage technique.
Magnetic probe array with high sensitivity for fluctuating field
Authors: Kanamaru Yuki , Gota Hiroshi , Fujimoto Kayoko , Ikeyama Taeko , Asai Tomohiko , Takahashi Tsutomu , Nogi Yasuyuki
Published: March 2007

A magnetic probe array is constructed to measure precisely the spatial structure of a small fluctuating field included in a strong confinement field that varies with time. To exclude the effect of the confinement field, the magnetic probes consisting of figure-eight-wound coils are prepared. The spatial structure of the fluctuating field is obtained from a Fourier analysis of the probe signal. It is found that the probe array is more sensitive to the fluctuating field with a high mode number than that with a low mode number. An experimental demonstration of the present method is attempted using a field-reversed configuration plasma, where the fluctuating field with 0.1% of the confinement field is successfully detected.
Fermi resonance in CO2: A combined electronic coupled-cluster and vibrational configuration-interaction prediction
Authors: Rodriguez-Garcia Valerie , Hirata So , Yagi Kiyoshi , Hirao Kimihiko , Taketsugu Tetsuya , Schweigert Igor , Tasumi Mitsuo
Published: March 2007

The authors present a first-principles prediction of the energies of the eight lowest-lying anharmonic vibrational states of CO2, including the fundamental symmetric stretching mode and the first overtone of the fundamental bending mode, which undergo a strong coupling known as Fermi resonance. They employ coupled-cluster singles, doubles, and (perturbative) triples [CCSD(T) and CCSDT] in conjunction with a range of Gaussian basis sets (up to cc-pV5Z, aug-cc-pVQZ, and aug-cc-pCVTZ) to calculate the potential energy surfaces (PESs) of the molecule, with the errors arising from the finite basis-set sizes eliminated by extrapolation. The resulting vibrational many-body problem is solved by the vibrational self-consistent-field and vibrational configuration-interaction (VCI) methods with the PESs represented by a fourth-order Taylor expansion or by numerical values on a Gauss-Hermite quadrature grid. With the VCI, the best theoretical estimates of the anharmonic energy levels agree excellently with experimental values within 3.5cm−1 (the mean absolute deviation). The theoretical (experimental) anharmonic frequencies of the Fermi doublet are 1288.9 (1285.4) and 1389.3 (1388.2)cm−1.
Void growth by dislocation-loop emission
Authors: Ahn D. C. , Sofronis P. , Kumar M. , Belak J. , Minich R.
Published: March 2007

Experimental results from spall tests on aluminum reveal the presence of a dense dislocation structure in an annulus around a void that grew under the tensile pulse when a shock wave was reflected at the free surface of the specimen. The proposition is that dislocation emission from the void surface under load is a viable mechanism for void growth. To understand void growth in the absence of diffusive effects, the interstitial-loop emission mechanism under tensile hydrostatic stress is investigated. First, the micromechanics of pile-up formation when interstitial loops are emitted from a void under applied macroscopic loading is reviewed. Demand for surface energy expenditure upon void-surface change is taken into consideration. It is demonstrated that in face-centered cubic metals loop emission from voids with a radius of ∼10 nm is indeed energetically possible in the hydrostatic stress environment generated by shock loading. On the other hand, the levels of hydrostatic stress prevalent in common structural applications are not sufficient to drive loops at equilibrium positions above a ∼10 nm void. However, for voids larger than about 100 nm, the energetics of loop emission are easily met as a necessary condition even under the low stress environment prevalent in structural applications.
Kinetic Alfvén waves in a homogeneous dusty magnetoplasma with dust charge fluctuation effects
Authors: Zubia K. , Rubab N. , Shah H. A. , Salimullah M. , Murtaza G.
Published: March 2007

Kinetic Alfvén waves with finite Larmor radius effects have been examined rigorously in a uniform dusty plasma in the presence of an external/ambient magnetic field. Two-potential theory has been applied for these electromagnetic waves and the dispersion relation is derived which shows a cutoff frequency at the dust-lower-hybrid frequency due to the hybrid motion of magnetized ions and cold and unmagnetized dust dynamics. The dust charge fluctuation effect was analyzed for finding the damping of the electromagnetic kinetic Alfvén waves, which arises on account of the electrostatic parallel component of the waves. The dust charge fluctuation damping is seen to be contributed dominantly by the perpendicular motion of electrons and ions in the dusty magnetoplasma.
Barkhausen noise in variable thickness amorphous finemet films
Authors: Puppin Ezio , Pinotti Ermanno , Brenna Massimiliano
Published: March 2007

We measured the statistical properties of Barkhausen noise in finemet films with nominal composition Fe73.5Cu1Nb3Si22.5B4 and variable thickness between 25 and 1000nm. Films have been sputtered on glass substrates and their structure is amorphous. The critical exponents of the power-law distributions for the jumps amplitude show a remarkable stability over the whole thickness range, whereas the other macroscopic magnetic properties undergo strong variations. The value of the critical exponent is about 0.8 between 50 and 500nm with a small increase up to 1.0 at 1000nm. These values are similar to those observed with the same experimental technique in other two-dimensional (2D) systems, but definitely smaller with respect to the values observed in truly three-dimensional (3D) systems. Our data therefore indicate that, in the investigated thickness range, the behavior remains typical of 2D systems. The small increase of the critical exponent at 1000nm might be an indication of a starting transition toward a 3D behavior.
Pressure driven flow of polymer solutions in nanoscale slit pores
Authors: Millan Jaime A. , Jiang Wenhua , Laradji Mohamed , Wang Yongmei
Published: March 2007

Polymer solutions subject to pressure driven flow and in nanoscale slit pores are systematically investigated using the dissipative particle dynamics approach. The authors investigated the effect of molecular weight, polymer concentration, and flow rate on the profiles across the channel of the fluid and polymer velocities, polymer density, and the three components of the polymers radius of gyration. They found that the mean streaming fluid velocity decreases as the polymer molecular weight and/or polymer concentration is increased, and that the deviation of the velocity profile from the parabolic profile is accentuated with increase in polymer molecular weight or concentration. They also found that the distribution of polymers conformation is highly anisotropic and nonuniform across the channel. The polymer density profile is also found to be nonuniform, exhibiting a local minimum in the center plane followed by two symmetric peaks. They found a migration of the polymer chains either from or toward the walls. For relatively long chains, as compared to the thickness of the slit, a migration toward the walls is observed. However, for relatively short chains, a migration away from the walls is observed.
On the turbulent structure in the wake of Taylor bubbles rising in vertical pipes
Authors: Shemer L. , Gulitski A. , Barnea D.
Published: March 2007

The development of gas-liquid slug flow along pipes is governed by the interaction between consecutive elongated bubbles. It is commonly accepted that the trailing bubble’s shape and velocity are affected by the flow field in the liquid phase ahead of it. Particle image velocimetry (PIV) measurements of the velocity field in the wake of an elongated Taylor bubble are performed for different pipe diameters and various Reynolds numbers. Experiments are carried out in both laminar and turbulent background flows. Ensemble-averaged quantities in the frame of reference moving with the Taylor bubble are calculated. Peculiarities regarding the variation of the mean velocity distributions, as well as of the normal and shear Reynolds stresses, with the distance from the Taylor bubble bottom are discussed.
The low-temperature photochromic and photorefractive response of bismuth germanium oxide doped with molybdenum
Authors: Wood Adam W. , Hunt C. A. , Martin J. J.
Published: March 2007

Doping the photorefractive material bismuth germanium oxide, Bi12GeO20 (BGO), with the 4d atom molybdenum introduces only a small shift to lower energy in the absorption cutoff in as-grown or well-annealed samples. Exposing a Mo-doped sample to blue-green light at 80K superimposes an additional well-resolved photochromic absorption band at 1.22eV and a possible weak band at 1.75eV upon the regular photochromic spectrum of undoped BGO. The 1.22eV band has a major anneal stage in the 125–140K range, which is accompanied by a smaller decrease in the regular photochromic bands. Similar to undoped BGO the remaining photochromic spectrum anneals when the sample is warmed above 200K and completely disappears above 250K. The photosensitivity of the additional bands is the same as that of the regular photochromic bands in undoped BGO. Since undoped BGO is an n-type photoconductor the bands are most likely due to an electron trapped at the Mo defect. A simple possible defect would be a Mo substituting for a Ge in the sillenite structure. An electron trapped at such a MoGe center could act as a small polaron and give rise to the bands. The photorefractive response of Mo-doped BGO was measured at 514nm as a function of temperature down to 116K. Doping with Mo causes a significant slowing of the grating growth rate. The growth rate slowed as the temperature was lowered. The diffraction efficiency of the gratings in Mo-doped BGO increased significantly as the sample was cooled down to 216K. Below that temperature the growth rate was so slow that the gratings did not reach saturation for the 1s “write” time. In undoped BGO the growth rate of the gratings slowed as the temperature was lowered. However, they remained much faster than in the Mo-doped samples and they continued to reach saturation down to the lowest temperatures studied. The dark decay of index gratings in Mo-doped BGO was also modified. At room temperature the dark decay was much faster than in undoped BGO. The dark decay slowed as the sample was cooled and for temperatures below about 200K is nearly the same as that of undoped BGO.
Finite element analysis of resistivity measurement with four point probe in a diamond anvil cell
Authors: Huang Xiaowei , Gao Chunxiao , Li Ming , He Chunyuan , Hao Aimin , Zhang Dongmei , Yu Cuiling , Wang Yue , Sang Chong , Cui Xiaoyan , Zou Guangtian
Published: March 2007

Using finite element analysis, we studied the steady current field distribution under the configuration of four point probe method for resistivity measurement in a diamond anvil cell (DAC). Based on the theoretical analysis, we made a correction to the formula by Valdes [L. B. Valdes, Proc IRE, 42, 420 (1958)]. The results show that our formula provides more accurate determination of sample resistivity, especially when the sample thickness is less than the probe spacing. We found that finite size of the electrode could lead to significant errors in resistivity measurement for semiconducting samples. We also found that the probe spacing is a key factor in the resistivity measurement accuracy for samples in DAC. When the sample thickness t is close to the probe spacing s, the error becomes larger and reaches a maximum.
Development of a liquid tin microjet target for an efficient laser-produced plasma extreme ultraviolet source
Authors: Higashiguchi Takeshi , Hamada Masaya , Kubodera Shoichi
Published: March 2007

A regenerative tin liquid microjet target was developed for a high average power extreme ultraviolet (EUV) source. The diameter of the target was smaller than 160 μm and good vacuum lower than 0.5 Pa was maintained during the operation. A maximum EUV conversion efficiency of 1.8% at the Nd:yttrium-aluminum-garnet laser intensity of around 2×1011 W∕cm2 with a spot diameter of 175 μm (full width at half maximum) was observed. The angular distribution of the EUV emission remained almost isotropic, whereas suprathermal ions mainly emerged toward the target normal.
Global analytic first integrals for the real planar Lotka-Volterra system
Authors: Llibre Jaume , Valls Clàudia
Published: March 2007

We provide the complete classification of all Lotka-Volterra systems of the form ẋ=x(ax+by+c) and ẏ=y(Ax+By+C) in R2 having a global analytic first integral.
Magnetoelectric effect in laminate composites of Tb1−xDyxFe2−y and Fe-doped BaTiO3
Authors: Zhang Ning , Fan Junfeng , Rong Xiaofang , Cao Hongxia , Wei Jianjun
Published: March 2007

Fe-doped BaTiO3 has been synthesized with sol-gel technique. Its transformation point of ferroelectric to paraelectric and the latent heat of the transformation were observed at 103.27 °C and 169.9 J/mol, respectively. They are a little less than those for pure BaTiO3. Bonded layered composites Tb1−xDyxFe2−y/BaTi0.99Fe0.01O3 have been fabricated. Their magnetoelectric (ME) effect has been investigated. The transverse ME voltage coefficient for the bilayer Tb1−xDyxFe2−y–BaTi0.99Fe0.01O3 and the trilayer Tb1−xDyxFe2−y–BaTi0.99Fe0.01O3–Tb1−xDyxFe2−y can reach 578 (mv Oe−1 cm−1) and 2100 (mv Oe−1 cm−1), respectively, under a bias magnetic field of 350 Oe at room temperature. Those are about 50% larger than those for the bilayer and trilayer composed by pure BaTiO3. It suggests that the doped BaTiO3 can be a new choice of piezoelectrics to compose ME composites.
Dynamics of magnetic-field-induced clustering in ionic ferrofluids from Raman scattering
Authors: Heinrich D. , Goñi A. R. , Thomsen C.
Published: March 2007

Using Raman spectroscopy, the authors have investigated the aggregation/disgregation of magnetic nanoparticles in dense ionic ferrofluids (IFF) into clusters due to the action of an inhomogeneous external magnetic field. Evidence for changes in particle density and/or effective cluster size were obtained from the variation of the Raman intensity in a time window from 10sto10min for magnetic fields up to 350mT and at a temperature of 28°C. Clustering sets in already at very low fields (>15mT) and the IFF samples exhibit a clear hysteresis in the Raman spectra after releasing the magnetic field, which lasts for many hours at room temperature. The authors determined the characteristic times of the two competing processes, that of field-induced cluster formation and, at room temperature, that of thermal-activated dissociation, to range from 100to150s.
Gamma-ray detection efficiency of the microchannel plate installed as an ion detector in the low energy particle instrument onboard the GEOTAIL satellite
Authors: Tanaka Y. T. , Yoshikawa I. , Yoshioka K. , Terasawa T. , Saito Y. , Mukai T.
Published: March 2007

A microchannel plate (MCP) assembly has been used as an ion detector in the low energy particle (LEP) instrument onboard the magnetospheric satellite GEOTAIL. Recently the MCP assembly has detected gamma rays emitted from an astronomical object and has been shown to provide unique information of gamma rays if they are intense enough. However, the detection efficiency for gamma rays was not measured before launch, and therefore we could not analyze the LEP data quantitatively. In this article, we report the gamma-ray detection efficiency of the MCP assembly. The measured efficiencies are 1.29%±0.71% and 0.21%±0.14% for normal incidence 60 and 662 keV gamma rays, respectively. The incident angle dependence is also presented. Our calibration is crucial to study high energy astrophysical phenomena by using the LEP.
Direct evidence of an order-disorder nature of ferroelectric phase transitions in K2MgWO2(PO4)2
Authors: Maczka Mirosław , Hanuza Jerzy , Majchrowski Andrzej , Kojima Seiji
Published: March 2007

K 2 Mg W O 2 ( P O 4 ) 2 single crystal, related to famous optical nonlinear material KTiOPO4, was investigated by micro-Brillouin scattering with a focus on the central components of the relaxation modes. A critical slowing down has been clearly observed in the vicinity of T1=436K while suppressed by the coupling with the order parameter. The temperature dependence of the relaxation time indicates that the former transition is the second order, while the latter is strongly first order. The obtained results show that disorder processes in the sublattice of potassium ions play a major role in the mechanism of these phase transitions.
Large magnetoresistance in Co∕Ni∕Co ferromagnetic single electron transistors
Authors: Liu R. S. , Pettersson H. , Michalak L. , Canali C. M. , Suyatin D. , Samuelson L.
Published: March 2007

The authors report on magnetotransport investigations of nanoscaled ferromagnetic Co∕Ni∕Co single electron transistors. As a result of reduced size, the devices exhibit single electron transistor characteristics at 4.2K. Magnetotransport measurements carried out at 1.8K reveal tunneling magnetoresistance (TMR) traces with negative coercive fields, which the authors interpret in terms of a switching mechanism driven by the shape anisotropy of the central wirelike Ni island. A large TMR of about 18% is observed within a finite source-drain bias regime. The TMR decreases rapidly with increasing bias, which the authors tentatively attribute to excitation of magnons in the central island.
Molecular dynamics simulation of diffusion and sorption of water in conducting polyaniline
Authors: Ostwal Mayur M. , Tsotsis Theodore T. , Sahimi Muhammad
Published: March 2007

Energy minimization and molecular dynamics simulations are used to develop, for the first time, atomistic models of HCl- and HBr-doped conducting polyanilines, in order to study diffusion and adsorption of water vapor in the polymers. Various morphological properties of the polymers are computed, including their pair correlation functions that are found to be in good agreement with the experimental data, and their accessible free volumes. Also computed are the sorption isotherms and effective self-diffusivity of water vapor in the polymers. The computed sorption isotherms are in quantitative agreement with the experimental data, while the diffusivities are within an order of magnitude of the data. The reasons for the differences between the computed and measured diffusivities are discussed.
Time-to-space mapping in a gas medium for the temporal characterization of vacuum-ultraviolet pulses
Authors: Cunovic S. , Müller N. , Kalms R. , Krikunova M. , Wieland M. , Drescher M. , Maltezopoulos Th. , Frühling U. , Redlin H. , Plönjes-Palm E. , Feldhaus J.
Published: March 2007

The authors introduce a method for cross correlating vacuum-ultraviolet with near-infrared femtosecond light pulses in a perpendicular geometry. Photoelectrons generated in an atomic gas by laser-assisted photoionization are used to create a two-dimensional image of the cross-correlation volume, thereby mapping time onto a space coordinate. Thus, information about pulse duration and relative timing between the pulses can be obtained without the need to scan an optical delay line. First tests using vacuum-ultraviolet pulses from the free-electron laser at the Deutsches Elektronen Synchrotron set an upper limit for their temporal jitter with respect to external optical laser pulses.
Dynamics of a two-state quantum dot laser with saturable absorber
Authors: Viktorov E. A. , Cataluna M. A. , O’Faolain L. , Krauss T. F. , Sibbett W. , Rafailov E. U. , Mandel Paul
Published: March 2007

The authors study the regime of self-pulsations in a two-state quantum dot laser with saturable absorber. Experiments demonstrate and theory explains the appearance of self-pulsations at low relaxation oscillation frequency. The system exhibits a period doubling sequence of bifurcations leading to chaos.
Improved conductivity of transparent single-wall carbon nanotube thin films via stable postdeposition functionalization
Authors: Parekh Bhavin B. , Fanchini Giovanni , Eda Goki , Chhowalla Manish
Published: March 2007

A simple postdeposition method for improving the conductivity of transparent and conducting single-wall carbon nanotube (SWNT) thin films via exposure to nitric acid and thionyl chloride is reported. A systematic study on a range of films of variable density and from different commercial sources of SWNTs is performed. The functionalized films possess sheet resistances as low as that of indium tin oxide (ITO) (∼30Ω∕◻) albeit at lower transmittance (∼50%). At 80±5% transmittance, the functionalized films have resistance values ranging from 150to300Ω∕◻. The SWNT films, however, are more flexible than ITO. The stability of the functionalized films upon annealing and processing in solvents (water, methanol, and chloroform) is also reported.