bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebral Metabolic Response to Low Blood Flow: Possible Role of Cytochrome Oxidase Inhibition
Authors: Gjedde Albert , Johannsen Peter , Cold Georg E , Østergaard Leif
Published: April 2005

The reactions of cerebral metabolism to imposed changes of cerebral blood flow (CBF) are poorly understood. A common explanation of the mismatched CBF and oxygen consumption (CMRO2) during neuronal excitation holds that blood flow rises more than oxygen consumption to compensate for an absent oxygen reserve in brain mitochondria. The claim conversely implies that oxygen consumption must decline when blood flow declines. As the prevailing rate of reaction of oxygen with cytochrome c oxidase is linked to the tension of oxygen, the claim fails to explain how oxygen consumption is maintained during moderate reductions of CBF imposed by hyperventilation (hypocapnia) or cyclooxygenase (COX) inhibition. To resolve this contradiction, we extended the previously published oxygen delivery model with a term allowing for the adjustment of the affinity of cytochrome c oxidase to a prevailing oxygen tension. The extended model predicted constant oxygen consumption at moderately reduced blood flow. We determined the change of affinity of cytochrome c oxidase in the extended model by measuring CBF in seven, and CMRO2 in five, young healthy volunteers before and during COX inhbition with indomethacin. The average CBF declined 35%, while neither regional nor average CMRO2 changed significantly. The adjustment of cytochrome c oxidase affinity to the declining oxygen delivery could be ascribed to a hypothetical factor with several properties in common with nitric oxide.
Atypical Hemispheric Dominance for Attention: Functional MRI Topography
Authors: Flöel Agnes , Jansen Andreas , Deppe Michael , Kanowski Martin , Konrad Carsten , Sommer Jens , Knecht Stefan
Published: April 2005

The right hemisphere is predominantly involved in tasks associated with spatial attention. However, left hemispheric dominance for spatial attention can be found in healthy individuals, and both spatial attention and language can be lateralized to the same hemisphere. Little is known about the underlying regional distribution of neural activation in these ‘atypical’ individuals. Previously a large number of healthy subjects were screened for hemispheric dominance of visuospatial attention and language, using functional Doppler ultrasonography. From this group, subjects were chosen who were ‘atypical’ for hemispheric dominance of visuospatial attention and language, and their pattern of brain activation was studied with functional magnetic resonance imaging during a task probing spatial attention. Right-handed subjects with the ‘typical’ pattern of brain organization served as control subjects. It was found that subjects with an inverted lateralization of language and spatial attention (language right, attention left) recruited left-hemispheric areas in the attention task, homotopic to those recruited by control subjects in the right hemisphere. Subjects with lateralization of both language and attention to the right hemisphere activated an attentional network in the right hemisphere that was comparable to control subjects. The present findings suggest that not the hemispheric side, but the intrahemispheric pattern of activation is the distinct feature for the neural processes underlying language and attention.
Zirconium oxidation under high-energy heavy-ion irradiation
Authors: Bérerd N. , Chevarier A. , Moncoffre N. , Jaffrézic H. , Balanzat E. , Catalette H.
Published: April 2005

This paper concerns the study of zirconium oxidation under irradiation with high energetic Xe ions. The irradiations were performed on the IRRadiation SUD (IRRSUD) beam line at Grand Accélérateur National d’Ions Lourds of Caen. The oxygen partial pressure was fixed at 10−3Pa and two temperature conditions were used, either 480°C reached by Joule effect heating or 280°C due to Xe energy deposition. Zirconia was fully characterized by Rutherford backscattering spectrometry, scanning electron microscopy, and grazing angle x-ray diffraction. Apparent diffusion coefficients of oxygen in ZrO2 were determined from these experiments by using a model which takes into account a surface exchange between oxygen gas and the ZrO2 surface. These results are compared with thermal oxidation data.
A method to determine deep level profiles in highly compensated, wide band gap semiconductors
Authors: Armstrong A. , Arehart A. R. , Ringel S. A.
Published: April 2005

A lighted capacitance–voltage (LCV) method for spatially profiling defect levels in wide band gap, highly compensated materials is presented. Combined with deep level optical spectroscopy, the optical nature of the LCV profiling technique enables the quantitative study of lower bounds of concentrations for multiple deep and midgap levels. Unlike many other approaches to measuring large deep level concentrations in resistive semiconductors, this LCV method requires no constant-capacitance feedback circuit and is applicable to wide band gap materials such as GaN and SiC. To demonstrate this technique, deep levels at Ec−3.0 and 3.28eV are spatially profiled in heavily compensated GaN:C:Si Schottky diodes. Comparison of the profiles with conventional constant-capacitance and constant-voltage approaches for calculating deep level concentrations shows good agreement between the methods and demonstrates the validity of the technique.
Learning about coronal heating from solar wind observations
Authors: Gary S. Peter , Skoug Ruth M. , Smith Charles W.
Published: April 2005

Vlasov theory describing the interaction of Alfvén-cyclotron fluctuations and ions in the collisionless solar wind predicts that alpha particles should be strongly scattered perpendicular to the background magnetic field when the alpha/proton relative velocity vαp is negative or has a sufficiently small positive value relative to the Alfvén speed vA. This theory also predicts that, if vαp∕vA is positive and sufficiently large, it is the protons which are scattered in the perpendicular direction, although less strongly. Here proton and alpha particle anisotropies measured in the solar wind near 1AU (AU, astronomical unit) by the plasma and magnetic field instruments on the Advanced Composition Explorer spacecraft are reported which are consistent with these predicted signatures. This indicates that Alfvén-cyclotron heating of ions is active in the solar wind; by using this medium to study this fundamental process, a greater understanding may be obtained of how Alfvén-cyclotron scattering contributes to heating of ions in the solar corona.
Density profile control in a large diameter, helicon plasma
Authors: Cluggish B. P. , Anderegg F. A. , Freeman R. L. , Gilleland J. , Hilsabeck T. J. , Isler R. C. , Lee W. D. , Litvak A. A. , Miller R. L. , Ohkawa T. , Putvinski S. , Umstadter K. R. , Winslow D. L.
Published: April 2005

Plasmas with peaked radial density profiles have been generated in the world’s largest helicon device, with plasma diameters of over 70 cm. The density profiles can be manipulated by controlling the phase of the current in each strap of two multistrap antenna arrays. Phase settings that excite long axial wavelengths create hollow density profiles, whereas settings that excite short axial wavelengths create peaked density profiles. This change in density profile is consistent with the cold-plasma dispersion relation for helicon modes, which predicts a strong increase in the effective skin depth of the rf fields as the wavelength decreases. Scaling of the density with magnetic field, gas pressure, and rf power is also presented.
Air boring and nonvacuum electron beam welding with a plasma window
Authors: Hershcovitch Ady , Team Acceleron
Published: April 2005

The plasma window is a novel apparatus that utilizes a stabilized plasma arc as interface between vacuum and atmosphere or pressurized targets without solid material. Additionally, the plasma has a lensing effect on charged particles. This feature enables beam focusing to very small spot sizes and overcoming beam dispersion due to scattering by atmospheric atoms and molecules. Recently, the plasma window was mated to a conventional electron beam welder. And, electron beam welding in atmosphere was accomplished with electron beams of unprecedented low power and energy. Weld quality for the nonvacuum plasma window electron beam welding approached the quality of in-vacuum electron beam welding, without the use of helium as process gas. Weld widths were independent of stand-off distance for up to 5cm, which along with visual observations suggest that pinched beam propagation might have been achieved with 6–25mA, 90–150KeV electron beams. That may explain the better than expected welding results. By comparison previously demonstrated self-pinched propagation used kA MeV electron beams.
Implicit solution of the four-field extended-magnetohydrodynamic equations using high-order high-continuity finite elements
Authors: Jardin S. C. , Breslau J. A.
Published: April 2005

Here we describe a technique for solving the four-field extended-magnetohydrodynamic (MHD) equations in two dimensions. The introduction of triangular high-order finite elements with continuous first derivatives (C1 continuity) leads to a compact representation compatible with direct inversion of the associated sparse matrices. The split semi-implicit method is introduced and used to integrate the equations in time, yielding unconditional stability for arbitrary time step. The method is applied to the cylindrical tilt mode problem with the result that a nonzero value of the collisionless ion skin depth will increase the growth rate of that mode. The effect of this parameter on the reconnection rate and geometry of a Harris equilibrium and on the Taylor reconnection problem is also demonstrated. This method forms the basis for a generalization to a full extended-MHD description of the plasma with six, eight, or more scalar fields.
Active and fast particle driven Alfvén eigenmodes in Alcator C-Mod
Authors: Snipes J. A. , Basse N. , Boswell C. , Edlund E. , Fasoli A. , Gorelenkov N. N. , Granetz R. S. , Lin L. , Lin Y. , Parker R. , Porkolab M. , Sears J. , Sharapov S. , Tang V. , Wukitch S.
Published: April 2005

Alfvén eigenmodes (AEs) are studied to assess their stability in high density reactor relevant regimes where Ti≈Te and as a diagnostic tool. Stable AEs are excited with active magnetohydrodynamics antennas in the range of the expected AE frequency. Toroidal Alfvén eigenmode (TAE) damping rates between 0.5%<γ∕ω<4.5% have been observed in diverted and limited Ohmic plasmas. Unstable AEs are excited with a fast ion tail driven by H minority ion cyclotron radio frequency (ICRF) heating with electron densities in the range of n¯e=0.5–2×1020m−3. Energetic particle modes or TAEs have been observed to decrease in frequency and mode number with time up to a large sawtooth collapse, indicating the role fast particles play in stabilizing sawteeth. In the current rise phase, unstable modes with frequencies that increase rapidly with time are observed with magnetic pick-up coils at the wall and phase contrast imaging density fluctuation measurements in the core. Modeling of these modes constrains the calculated safety factor profile to be very flat or with slightly reversed shear. AEs are found to be more stable for an inboard than for central or outboard ICRF resonances in qualitative agreement with modeling.
Propagation of electromagnetic waves in the plasma near electron cyclotron resonance: Undulator-induced transparency
Authors: Shvets G. , Tushentsov M. , Tokman M. D. , Kryachko A.
Published: April 2005

Propagation of electromagnetic waves in magnetized plasma near the electron cyclotron frequency can be strongly modified by adding a weak magnetic undulator. For example, both right- and left-hand circularly polarized waves can propagate along the magnetic field without experiencing resonant absorption. This effect of entirely eliminating electron cyclotron heating is referred to as the undulator-induced transparency (UIT) of the plasma, and is the classical equivalent of the well-known quantum mechanical effect of electromagnetically induced transparency. The basics of UIT are reviewed, and various ways in which UIT can be utilized to achieve exotic propagation properties of electromagnetic waves in plasmas are discussed. For example, UIT can dramatically slow down the waves’ group velocity, resulting in the extreme compression of the wave energy in the plasma. Compressed waves are polarized along the propagation direction, and can be used for synchronous electron or ion acceleration. Strong coupling between the two wave helicities are explored to impart the waves with high group velocities ∂ω∕∂k for vanishing wave numbers k. Cross-helicity coupling for realistic density and magnetic field profiles are examined using a linearized fluid code, particle-in-cell simulations, and ray-tracing WKB calculations.
Commuting flows and conservation laws for noncommutative Lax hierarchies
Authors: Hamanaka Masashi
Published: April 2005

We discuss commuting flows and conservation laws for Lax hierarchies on noncommutative spaces in the framework of the Sato theory. On commutative spaces, the Sato theory has revealed essential aspects of the integrability for wide class of soliton equations which are derived from the Lax hierarchies in terms of pseudodifferential operators. Noncommutative extension of the Sato theory has been already studied by the author and Toda, and the existence of various noncommutative Lax hierarchies are guaranteed. In this paper, we present conservation laws for the noncommutative Lax hierarchies with both space–space and space–time noncommutativities and prove the existence of infinite number of conserved densities. We also give the explicit representations of them in terms of Lax operators. Our results include noncommutative versions of KP, KdV, Boussinesq, coupled KdV, Sawada-Kotera, modified KdV equation and so on.
Raman study for E2 phonon of ZnO in Zn1−xMnxO nanoparticles
Authors: Wang J. B. , Zhong H. M. , Li Z. F. , Lu Wei
Published: April 2005

Raman scattering at room temperature is reported in Zn1−xMnxO nanoparticles for the range of 0⩽x⩽0.15. The effect of compositional disorder is obtained by analyzing the broadening and asymmetry of the first-order E2(high) phonon mode. It is found that the Raman line shapes for the ZnO E2(high) phonon in Zn1−xMnxO alloys can be well described by the spatial correlation model. It is shown that the substitutional disorder can introduce changes in the linewidth, line center position, and asymmetry of the first-order E2(high) phonon mode in Zn1−xMnxO nanoparticles.
Electronic transport properties of a bismuth microwire array in a magnetic field
Authors: Hasegawa Yasuhiro , Ishikawa Yoshiaki , Morita Hiroyuki , Komine Takashi , Shirai Hajime , Nakamura Hiroaki
Published: April 2005

The magneto-Seebeck coefficient and magnetoresistivity of a polycrystalline bismuth microwire array were measured under magnetic fields of 0–2T and at temperatures of 50–300K. To avoid the influence of contact resistance between the wire array and the electrodes, bulk bismuth was used for the electrodes. In the absence of a magnetic field, the Seebeck coefficient and resistivity were −76μV∕K and 1.8μΩm at 300K, respectively. The magneto-Seebeck coefficient for the wire array increased with the application of an external magnetic field, attributable to the precise control of impurities and carrier scattering process in the fabrication of the wire array. The phonon drag effect was observed below 100K, with a corresponding increase in the magneto-Seebeck coefficient under high magnetic fields. However, the magnetoresistivity was also raised under higher magnetic fields, detracting from the thermoelectric properties. Through analysis of the power factor, the optimum magnetic field was determined for each temperature, revealing a trend for the optimum magnetic field to increase with temperature. The power factor was improved by a maximum factor of 1.12, achieved at 200K and 0.25T. Further improvements appear to be possible by eliminating the bulk bismuth employed for the electrodes.
Ion cyclotron range of frequency mode conversion physics in Alcator C-Mod: Experimental measurements and modeling
Authors: Wukitch S. J. , Lin Y. , Parisot A. , Wright J. C. , Bonoli P. T. , Porkolab M. , Basse N. , Edlund E. , Hubbard A. , Lin L. , Lynn A. , Marmar E. , Mossessian D. , Phillips P. , Schilling G.
Published: April 2005

In ion cyclotron range of frequency experiments, we have simultaneously measured the incident fast wave and the mode converted waves in the mode conversion region in D(He3) plasmas using an upgraded phase contrast imaging diagnostic in the Alcator C-Mod tokamak [I. H. Hutchinson, R. Boivin, F. Bombarida et al., Phys. Plasmas 1, 1511 (1994)]. To experimentally validate the full wave TORIC [M. Brambilla, Nucl. Fusion 38, 1805 (1998)] physics kernel, the simulated power deposition and line integrated perturbed density profiles were compared with experimental profiles and are found to be in remarkably good agreement with the experimentally determined profiles. This suggests the physics model and computation algorithm used in TORIC, particularly for the mode converted waves, model the mode conversion physics well. We also report results from initial mode conversion current drive experiments where the modification of the sawtooth period was clearly observed and was shown to depend on antenna phasing suggesting the presence of a localized driven current.
Segregation and enhanced diffusion of nitrogen in silicon induced by low energy ion bombardment
Authors: Stoddard N. , Duscher G. , Karoui A. , Stevie F. , Rozgonyi G.
Published: April 2005

A sample of nitrogen-doped, single crystal Czochralski silicon was subjected to several different surface preparations. Secondary ion mass spectrometry depth profiling has shown that prolonged glancing-angle bombardment by 3–5kV Ar+ ions significantly increases the nitrogen concentration in the near surface by up to an order of magnitude over the bulk value. Concentrations are observed to be elevated over the bulk value to a depth up to 25μm. Nitrogen-implanted samples and samples with a 1nm surface nitride did not exhibit nitrogen segregation under the same conditions, but a sample with 100nm of surface nitride did exhibit ion bombardment induced drive-in. In nitride-free samples, the source of the nitrogen is indicated to be a nitrogen-rich layer in the first micron of material. The diffusion behavior of nitrogen in silicon is discussed and the Crowdion mechanism for diffusion is suggested as the enabling mechanism for the enhanced low temperature diffusion.
Ionization potentials of transparent conductive indium tin oxide films covered with a single layer of fluorine-doped tin oxide nanoparticles grown by spray pyrolysis deposition
Authors: Fukano Tatsuo , Motohiro Tomoyoshi , Ida Takashi , Hashizume Hiroo
Published: April 2005

Indium tin oxide (ITO) films deposited with single layers of monodispersive fluorine-doped tin oxide (FTO) nanoparticles of several nanometers in size were grown on glass substrates by intermittent spray pyrolysis deposition using conventional atomizers. These films have significantly higher ionization potentials than the bare ITO and FTO films grown using the same technique. The ITO films covered with FTO particles of 7nm in average size show an ionization potential of 5.01eV, as compared with ∼4.76 and ∼4.64eV in ITO and FTO films, respectively, which decreases as the FTO particle size increases. The ionization potentials are practically invariant against oxidation and reduction treatments, promising a wide application of the films to transparent conducting oxide electrodes in organic electroluminescent devices and light-emitting devices of high efficiencies.
Epitaxial growth of CuScO2 thin films on sapphire a-plane substrates by pulsed laser deposition
Authors: Kakehi Yoshiharu , Satoh Kazuo , Yotsuya Tsutom , Nakao Satoru , Yoshimura Takeshi , Ashida Atsushi , Fujimura Norifumi
Published: April 2005

An epitaxial film of CuScO2, a transparent oxide semiconductor with a delafossite structure, was grown on an α−Al2O3(112¯0) substrate by a pulsed laser deposition method using a single-phase Cu2Sc2Oδ target. A two-dimensional x-ray reciprocal space mapping measurement revealed that the film was single phase with a rhombohedral crystal structure. The film showed six-fold rotational symmetry in the basal plane, indicating that the film had a twinned domain structure. The epitaxial growth of CuScO2[3R](0001) thin films on α−Al2O3(112¯0) substrates is caused by the uniaxial locked epitaxy mechanism along the ⟨1¯21¯0⟩ direction of the film, and the orientation relationships of the film with respect to the substrate were CuScO2[3R](0001)∕∕α−Al2O3(112¯0) and CuScO2[3R][1¯21¯0]∕∕α−Al2O3[88¯01]. The optical transmittance of the film was larger than 65% in the visible/near-infrared regions, while the energy gap for direct allowed transition was estimated as 3.7 eV. The resistivity of the film, 9.3×106Ωcm at room temperature, significantly decreased to 4.0 Ωcm after both substituting Mg2+ ions for Sc3+ and intercalating excess oxygen. The Mg-doped CuScO2+X(0001) thin film showed optical transmittance of larger than 65% in the visible region, and the Seebeck coefficient was positive, indicating a p-type conductivity.
Intermolecular self-interaction energies of magic clusters MAu4 (M=Ti and Zr)
Authors: Han Young-Kyu
Published: April 2005

Two TiAu4 (or ZrAu4) clusters are known to bind to each other with unusually high (∼5–7eV) interaction energies at the Møller–Plesset second-order perturbation theory (MP2) level [T. K. Ghanty et al., J. Chem. Phys.120, 11363 (2004)]. Our MP2 calculations also show very high interaction energies of about 8eV for (TiAu4)2 and (ZrAu4)2. However, the strong MP2 bindings are found to be partly ascribable to large basis set superposition error (BSSE). The BSSE-corrected interaction energies are 4.63 and 4.25eV for (TiAu4)2 and (ZrAu4)2, respectively. We also found that there are Hartree–Fock wave function instabilities for the systems, implying that the restricted MP2 descriptions are potentially inadequate. High-level calculations are needed to draw clear conclusions.
Charge transport in metal oxides: A theoretical study of hematite α-Fe2O3
Authors: Iordanova N. , Dupuis M. , Rosso K. M.
Published: April 2005

Transport of conduction electrons and holes through the lattice of α-Fe2O3 (hematite) is modeled as a valence alternation of iron cations using ab initio electronic structure calculations and electron transfer theory. Experimental studies have shown that the conductivity along the (001) basal plane is four orders of magnitude larger than the conductivity along the [001] direction. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus’ theory. The calculation of the electronic coupling followed the generalized Mulliken–Hush approach using the complete active space self-consistent field method. Our findings demonstrate an approximately three orders of magnitude anisotropy in both electron and hole mobility between directions perpendicular and parallel to the c axis, in good accord with experimental data. The anisotropy arises from the slowness of both electron and hole mobilities across basal oxygen planes relative to that within iron bilayers between basal oxygen planes. Interestingly, for elementary reaction steps along either of the directions considered, there is only less than one order of magnitude difference in mobility between electrons and holes, in contrast to accepted classical arguments. Our findings indicate that the most important quantity underlying mobility differences is the electronic coupling, albeit the reorganization energy contributes as well. The large values computed for the electronic coupling suggest that charge transport reactions in hematite are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron spin coupling within the Fe–Fe donor-acceptor pair, while the reorganization energy is essentially independent of the electron spin coupling.
Probabilistic transport models for plasma transport in the presence of critical thresholds: Beyond the diffusive paradigm
Authors: Sánchez R. , van Milligen B. Ph. , Carreras B. A.
Published: April 2005

It is argued that the modeling of plasma transport in tokamaks may benefit greatly from extending the usual local paradigm to accommodate scale-free transport mechanisms. This can be done by combining Lévy distributions and a nonlinear threshold condition within the continuous time random walk concept. The advantages of this nonlocal, nonlinear extension are illustrated by constructing a simple particle density transport model that, as a result of these ideas, spontaneously exhibits much of nondiffusive phenomenology routinely observed in tokamaks. The fluid limit of the system shows that the kind of equations that are appropriate to capture these dynamics are based on fractional differential operators. In them, effective diffusivities and pinch velocities are found that are dynamically set by the system in response to the specific characteristics of the fueling source and external perturbations. This fact suggests some dramatic consequences for the extrapolation of these transport properties to larger size systems.
Simulation of spheromak evolution and energy confinement
Authors: Cohen B. I. , Hooper E. B. , Cohen R. H. , Hill D. N. , McLean H. S. , Wood R. D. , Woodruff S. , Sovinec C. R. , Cone G. A.
Published: April 2005

Simulation results are presented that illustrate the formation and decay of a spheromak plasma driven by a coaxial electrostatic plasma gun, and model the plasma energy confinement. The physics of magnetic reconnection during formation is also illuminated. The simulations are performed with the three-dimensional, time-dependent, resistive magnetohydrodynamic NIMROD code [C. R. Sovinec, A. H. Glasser, T. A. Gianakon, D. C. Barnes, R. A. Nebel, S. E. Kruger, D. D. Schnack, S. J. Plimpton, A. Tarditi, and M. S. Chu, J. Comput. Phys. 195, 355 (2004)]. The simulation results are compared to data from the Sustained Spheromak Physics Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)]. The simulation results are tracking SSPX with increasing fidelity (e.g., improved agreement with measured magnetic fields, fluctuation amplitudes, and electron temperature) as the simulation has been improved in its representations of the experimental geometry, the magnetic bias coils, and the detailed time dependence of the current source driving the plasma gun, and uses realistic parameters. The simulations confirm that controlling the magnetic fluctuations is influenced by the current drive history and by matching the gun current in sustainment approximately to the value corresponding to the eigenvalue in the flux-conserver for the parallel current in a force-free equilibrium.
Isotopic variation of experimental lifetimes for the lowest Πu1 states of N2
Authors: Sprengers J. P. , Ubachs W. , Baldwin K. G. H.
Published: April 2005

Lifetimes of several Πu1 states of the three natural isotopomers of molecular nitrogen, N214,N14N15, and N215, are determined via linewidth measurements in the frequency domain. Extreme ultraviolet (XUV)+UV two-photon ionization spectra of the bΠu1(v=0–1,5–7) and c3Πu1(v=0) states of N214,bΠu1(v=0–1,5–6) and c3Πu1(v=0) states of N14N15, and bΠu1(v=0–7),c3Πu1(v=0), and oΠu1(v=0) states of N215 are recorded at ultrahigh resolution, using a narrow band tunable XUV-laser source. Lifetimes are derived from the linewidths of single rotationally resolved spectral lines after deconvolution of the instrument function. The observed lifetimes depend on the vibrational quantum number and are found to be strongly isotope dependent.
Levitation mechanism of a single steel ball under moderate magnetic fields provided by a Ne–Fe–B ring magnet
Authors: Sakai M. , Takabayashi Y. , Sugawara K. , Shibayama T. , Shimomura Y. , Orikasa T. , Kamishima K. , Hirastuka N.
Published: April 2005

Mechanism for magnetic levitation of a steel ball in a plastic box [S. Sasaki, I. Yagi, and M. Murakami, J. Appl. Phys. 95, 2090 (2004)] was investigated quantitatively based on measurement of the magnetic moments of the steel ball and ring magnet used in levitation experiment. The two-dimensional potential energy calculated in terms of magnetic dipole-dipole interactions gives rise to a stable equilibrium position approximately in agreement with the levitating position observed in our study. The role of the diamagnetic characteristic of the plastic plates was also discussed quantitatively.
Experimental investigation of domain switching criterion for soft lead zirconate titanate piezoceramics under coaxial proportional electromechanical loading
Authors: Zhou Dayu , Wang Zhenggui , Kamlah Marc
Published: April 2005

In this experimental work, “soft” lead zirconate titanate specimens in an initially unpoled state were subjected to combined electromechanical loading, in which a compressive stress and a parallel, proportional electric field were applied simultaneously. By changing the ratio of stress to the electric field between tests, a series of nonlinear polarization and strain responses were obtained. An attempt has been made to explain the experimental findings by simultaneously taking into account the contributions of dielectric response, elastic deformation, piezoeffects, and irreversible domain switching. Initial domain switching surfaces in the biaxial stress and electric field space were determined based on an offset method. Several switching conditions existing in the literature were summarized and compared with the experimental data obtained in this work. Such an investigation may serve to calibrate and validate existing constitutive models concerning the large-signal nonlinear behavior of piezoceramics.
Role of ceramic supports on microwave heating of materials
Authors: Basak Tanmay , Priya A. Shanthi
Published: April 2005

A detailed analysis has been carried out to study efficient heating due to microwaves for one-dimensional samples placed on ceramic supports (Al2O3, SiC). The greater effects on microwave heating of samples have been illustrated via average power within a sample versus sample thickness diagram for various cases. The maxima in power, also termed as “resonances,” is observed for specific sample thicknesses and the two consecutive maxima in average power are termed as R1 and R2 modes. The greater heating effects leading to hot spots would occur in water samples during both-sides incidence when the sample is kept on Al2O3 support. SiC support may be recommended for water samples due to uniform heating throughout the sample. In contrast, SiC support could cause local hot spots or thermal runaway for oil samples. The localized hot spots are more pronounced for the samples exposed to microwaves on both faces. The choice of support may not be trivial due to the complex dielectric response of sample-support assembly. Current analysis has been illustrated for low- and high-dielectric materials (water and oil) and a representative case study has also been shown for beef samples. Based on such observations, a generalized heating strategy for materials due to uniform plane waves has been derived.
Edge ion heating by launched high harmonic fast waves in the National Spherical Torus Experiment
Authors: Biewer T. M. , Bell R. E. , Diem S. J. , Phillips C. K. , Wilson J. R. , Ryan P. M.
Published: April 2005

A new spectroscopic diagnostic on the National Spherical Torus Experiment (NSTX) [J. Spitzer, M. Ono, M. Peng, D. Bashore, T. Bigelow, A. Brooks, J. Chrzanowaki, H. M. Fan, P. Heitzenroeder, T. Jarboe et al., Fusion Technol2. 30, 1337 (1996)] measures the velocity distribution of ions in the plasma edge simultaneously along both poloidal and toroidal views. An anisotropic ion temperature is measured during high power high harmonic fast wave (HHFW) rf heating in helium plasmas, with the poloidal ion temperature roughly twice the toroidal ion temperature. Moreover, the measured spectral distribution suggests that two populations of ions are present and have temperatures of typically 500eV and 50eV with rotation velocities of −50km∕s and −10km∕s, respectively (predominantly perpendicular to the local magnetic field). This bimodal distribution is observed in both the toroidal and poloidal views (for both He+ and C2+ ions), and is well correlated with the period of rf power application to the plasma. The temperature of the hot component is observed to increase with the applied rf power, which was scanned between 0 and 4.3MW. The 30MHz HHFW launched by the NSTX antenna is expected and observed to heat core electrons, but plasma ions do not resonate with the launched wave, which is typically at >10th harmonic of the ion cyclotron frequency in the region of observation. A likely ion heating mechanism is parametric decay of the launched HHFW into an ion Bernstein wave (IBW). The presence of the IBW in NSTX plasmas during HHFW application has been directly confirmed with probe measurements. IBW heating occurs in the perpendicular ion distribution, consistent with the toroidal and poloidal observations. Calculations of IBW propagation indicate that multiple waves could be created in the parametric decay process, and that most of the IBW power would be absorbed in the outer 10–20cm of the plasma, predominantly on fully stripped ions. These predictions are in qualitative agreement with the observations and must be accounted for when calculating the energy budget of the plasma.
Light emission and charge trapping in Er-doped silicon dioxide films containing silicon nanocrystals
Authors: Nazarov A. , Sun J. M. , Skorupa W. , Yankov R. A. , Osiyuk I. N. , Tjagulskii I. P. , Lysenko V. S. , Gebel T.
Published: April 2005

The processes of electro- (EL) and photoluminescence (PL) and charge trapping in Er-implanted SiO2 containing silicon nanoclusters have been studied. It is shown that in Er-doped SiO2 with an excess of silicon nanoclusters of 10 at. %, a strong energy transfer from silicon nanoclusters results in a ten-fold increase of the PL peak at 1540 nm from Er luminescent centers, whereas the EL is strongly quenched by the excess silicon nanoclusters. It is further shown that the implantation of Er creates in the oxide positive charge traps with a giant cross section (σh0>10−13cm2). Introducing subsequent silicon nanocrystals in the oxide leads to the formation of negative charge traps of a giant cross section (σe0>10−13cm2). The possible reason for the EL quenching in the Er-doped SiO2 by silicon nanoclusters is discussed.
Structure and magnetic properties of Mn-doped ZnO nanoparticles
Authors: Luo J. , Liang J. K. , Liu Q. L. , Liu F. S. , Zhang Y. , Sun B. J. , Rao G. H.
Published: April 2005

We report the crystal structure and magnetic properties of the Zn1−xMnxO compounds synthesized by a combustion method. The Zn1−xMnxO compounds with x=0–0.1 crystallize in the wurtzite ZnO structure. The lattice parameters a and c of Zn1−xMnxO increase linearly with the Mn content, indicating that Mn2+ ions substitute for Zn2+ ions. Scanning electron microscopy shows that the average particle radius of Zn0.95Mn0.05O is about 40 nm. From the Curie–Weiss behavior of susceptibility at high temperature, it was found that the Mn–Mn interaction is dominated by antiferromagnetic coupling with effective nearest-neighbor exchange constant J about −32 K and the large negative value of the Curie–Weiss temperature.
Vibrational dependence of the H2–H2 C6 dispersion coefficients
Authors: Hinde Robert J.
Published: April 2005

We use the sum-over-states formalism to compute the imaginary-frequency dipole polarizabilities for H2, as a function of the H–H bond length, at the full configuration interaction level of theory using atom-centered d-aug-cc-pVQZ basis sets. From these polarizabilities, we obtain isotropic and anisotropic C6 dispersion coefficients for a pair of H2 molecules as functions of the two molecules’ bond lengths.
Density functional study of the interaction of chlorine atom with small neutral and charged silver clusters
Authors: Zhao Shuang , Li Zhen-Hua , Wang Wen-Ning , Fan Kang-Nian
Published: April 2005

Chlorine adsorption on small neutral, anionic, and cationic silver clusters Agn(n=2–7) has been studied using the PW91PW91 density functional method. It was found that the adsorption of chlorine on the lowest-energy bare clusters does not always produce the lowest-energy complexes. In addition, the binding of chlorine can greatly change the geometries of the silver clusters in some cases. Among various possible adsorption sites, bridge site is energetically preferred for the neutral Agn while top site is energetically more preferred for the anionic Agn with n⩽6. For cationic clusters, adsorptions on bridge and face sites have similar binding energies, which are much larger than those on top sites. Natural bond orbital analyses show that irrespective of charge state, electrons always transfer from silver atoms to adsorbate and silver acts like alkali metals in the interaction with chlorine atom. Significant odd-even alternation patterns in the properties of the complexes have been observed: Even-electron clusters often have higher ionization energies, lower electron affinities, and higher dissociation energies than their odd-electron neighbors. It was also found that chlorine atoms bind more strongly with odd-electron bare clusters than with even-electron bare clusters. These patterns reveal that even-electron clusters are more stable than odd-electron clusters.
Counterion condensation and release in micellar solutions
Authors: Hsiao Chin Chieh , Wang Tzu-Yu , Tsao Heng-Kwong
Published: April 2005

Counterion condensation and release in micellar solutions are investigated by direct measurement of counterion concentration with ion-selective electrode. Monte Carlo simulations based on the cell model are also performed to analyze the experimental results. The degree of counterion condensation is indicated by the concentration ratio of counterions in the bulk to the total ionic surfactant added, α⩽1. The ionic surfactant is completely dissociated below the critical micelle concentration (cmc). However, as cmc is exceeded, the free counterion ratio α declines with increasing the surfactant concentration and approaches an asymptotic value owing to counterion condensation to the surface of the highly charged micelles. Micelle formation leads to much stronger electrostatic attraction between the counterion and the highly charged sphere in comparison to the attraction of single surfactant ion with its counterion. A simple model is developed to obtain the true degree of ionization, which agrees with our Monte Carlo results. Upon addition of neutral polymer or monovalent salts, some of the surfactant counterions are released to the bulk. The former is due to the decrease of the intrinsic charge (smaller aggregation number) and the degree of ionization is increased. The latter is attributed to competitive counterion condensation, which follows the Hefmeister series. This consequence indicates that the specific ion effect plays an important role next to the electrostatic attraction.
Comparison of experimental time-of-flight spectra of the HF products from the F+H2 reaction with exact quantum mechanical calculations
Authors: Rusin Lev Yu. , Sevryuk Mikhail B. , Toennies J. Peter
Published: April 2005

High resolution HF product time-of-flight spectra measured for the reactive scattering of F atoms from n-H2(p-H2) molecules at collision energies between 69 and 81meV are compared with exact coupled-channel quantum mechanical calculations based on the Stark–Werner ab initio ground state potential energy surface. Excellent agreement between the experimental and computed rotational distributions is found for the HF product vibrational states v′=1 and v′=2. For the v′=3 vibrational state the agreement, however, is less satisfactory, especially for the reaction with p-H2. The results for v′=1 and v′=2 confirm that the reaction dynamics for these product states is accurately described by the ground electronic state 1A′2 potential energy surface. The deviations for HF(v′=3,j′⩾2) are attributed to an enhancement of the reaction resulting from the 25% fraction of excited (P1∕22) fluorine atoms in the reactant beam.
Semiclassical states for NLS equations with magnetic potentials having polynomial growths
Authors: Cingolani Silvia , Secchi Simone
Published: April 2005

We prove existence of standing wave solutions for a nonlinear Schrödinger equation on R3 under the influence of an external magnetic field B. In particular we deal with the physically meaningful case of a constant magnetic field B=(0,0,b) having source in the potential A(x)=(b∕2)(−x2,x1,0) corresponding to the Lorentz gauge.
Molecular dynamics simulations of polymer transport in nanocomposites
Authors: Desai Tapan , Keblinski Pawel , Kumar Sanat K.
Published: April 2005

Molecular dynamics simulations on the Kremer–Grest bead-spring model of polymer melts are used to study the effect of spherical nanoparticles on chain diffusion. We find that chain diffusivity is enhanced relative to its bulk value when polymer-particle interactions are repulsive and is reduced when polymer-particle interactions are strongly attractive. In both cases chain diffusivity assumes its bulk value when the chain center of mass is about one radius of gyration Rg away from the particle surface. This behavior echoes the behavior of polymer melts confined between two flat surfaces, except in the limit of severe confinement where the surface influence on polymer mobility is more pronounced for flat surfaces. A particularly interesting fact is that, even though chain motion is strongly speeded up in the presence of repulsive boundaries, this effect can be reversed by pinning one isolated monomer onto the surface. This result strongly stresses the importance of properly specifying boundary conditions when the near surface dynamics of chains are studied.
Vibrational energies for the X̃A11, ÃB11, and B̃A11 states of SiH2∕SiD2 and related transition probabilities based on global potential energy surfaces
Authors: Tokue Ikuo , Yamasaki Katsuyoshi , Nanbu Shinkoh
Published: April 2005

Transition probabilities were evaluated for the X̃A11-ÃB11 and ÃB11-B̃A11 systems of SiH2 and SiD2 to analyze the X̃→Ã→B̃ photoexcitation. The Franck–Condon factors (FCFs) and Einstein’s B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the SiH2(X̃A11,ÃB11,B̃A11) electronic states and the electronic transition moments for the X̃-Ã, X̃-B̃, and Ã-B̃ system. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least-squares method combined with the Shepard interpolation. The obtained FCFs for the X̃-Ã and Ã-B̃ systems exhibit that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies with the three states; the barrier to linearity is evaluated to be 21 900cm−1 for the X̃ state, 6400cm−1 for the Ã state, and 230–240cm−1 for the B̃ state. The theoretical lifetimes for the pure bending levels of the Ã and B̃ states were calculated from the fluorescence decay rates for the Ã-X̃, B̃-Ã, and B̃-X̃ emissions.
Quantitative extraction of in-plane surface properties using torsional resonance mode of atomic force microscopy
Authors: Song Yaxin , Bhushan Bharat
Published: April 2005

In the torsional resonance mode of atomic force microscopy (AFM), torsional amplitude and phase shift have been used for in-plane surface property imaging. However, no quantitative relation between torsional amplitude/phase shift and surface properties has yet been established. This paper studies how lateral contact stiffness and viscosity affect the torsional vibration of the cantilever in AFM. A basic methodology to extract in-plane surface properties is described and its effectiveness is demonstrated by quantitatively extracting the lateral contact stiffnesses and viscosities of two different materials: Si(100) and epoxy.
Restitution in mapping models with an arbitrary amount of memory
Authors: Kalb Soma S. , Tolkacheva Elena G. , Schaeffer David G. , Gauthier Daniel J. , Krassowska Wanda
Published: April 2005

Restitution, the characteristic shortening of action potential duration (APD) with increased heart rate, has been studied extensively because of its purported link to the onset of fibrillation. Restitution is often represented in the form of mapping models where APD is a function of previous diastolic intervals (DIs) and/or APDs, An+1=F(Dn,An,Dn−1,An−1,…), where An+1 is the APD following a DI given by Dn. The number of variables previous to Dn determines the degree of memory in the mapping model. Recent experiments have shown that mapping models should contain at least three variables (Dn,An,Dn−1) to reproduce a restitution portrait (RP) that is qualitatively similar to that seen experimentally, where the RP shows three different types of restitution curves (RCs) [dynamic, S1–S2, and constant-basic cycle length (BCL)] simultaneously. However, an interpretation of the different RCs has only been presented in detail for mapping models of one and two variables. Here we present an analysis of the different RCs in the RP for mapping models with an arbitrary amount of memory. We determine the number of variables necessary to represent the different RCs in the RP. We also present a graphical visualization of these RCs. Our analysis reveals that the dynamic and S1–S2 RCs reside on two-dimensional surfaces, and therefore provide limited information for mapping models with more than two variables. However, constant-BCL restitution is a feature of the RP that depends on higher dimensions and can possibly be used to determine a lower bound on the dimensionality of cardiac dynamics.
Using non-Gaussian density functional fits to improve relative free energy calculations
Authors: Nanda Hirsh , Lu Nandou , Woolf Thomas B.
Published: April 2005

The accurate and reliable computation of relative free energy differences remains an important long-term goal. Major stumbling blocks for achieving this goal reflect the difficulty of sampling in a known fashion along the reaction coordinate and of maximally combining information that has been collected from the simulation along the reaction coordinate. In this paper we examine the utility of a probability density functional type fit to the distribution of work events collected during a nonequilibrium sample along the reaction coordinate. This approach can readily be generalized to equilibrium sampling and has the potential to estimate the quality of a relative free energy estimate as data are being collected. The method may have the greatest utility for nonequilibrium sampling where non-Gaussian work distributions are generally present that are strongly dominated by rare event sampling in the tail region. We believe that the approach can be used to augment the design and the error analysis of relative free energy computations thus improving the ability to reliably and with known accuracy compute a relative free energy.