bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of diurnal K1 internal tide in the Luzon Strait and its influence on surface tide in the South China Sea
Authors: Jan Sen , Chern Ching‐Sheng , Wang Joe , Chao Shenn‐Yu
Published: June 2007

The predominance of diurnal surface tides over semidiurnal surface tides in the South China Sea (SCS) has been attributed to the near‐resonance response of the former in the SCS. Recent observations further revealed vigorous internal tides in the northern SCS. Conceivably, internal tides generated in the Luzon Strait could modify the surface tide in the SCS. We use a three‐dimensional tide model of the East Asian seas to address this issue. With a typical summertime stratification of the SCS as the initial condition, energy budget indicates that one third of the incident K1 surface tide energy is converted to the baroclinic energy over topographic ridges in the Luzon Strait. In comparison with a global tidal model [Matsumoto et al., 2000], our numerical experiments that annihilated or reduced the K1 internal tide in the Luzon Strait led to up to 50% amplification of the simulated K1 surface tide in the SCS. This suggests that the baroclinic energy conversion substantially reduces the amplitude of K1 surface tide in the SCS. The simulated phases in the SCS differ little from those calculated from Matsumoto’s tide model, suggesting that the modification is primarily on the amplitude. Two‐dimensional surface tidal models lack baroclinic energy conversion in the Luzon Strait; the consequent overestimation of surface K1 tide can be reduced only through precise prescription of sea levels in the Luzon Strait or assimilation of sea level data.
Atmospheric acetylene and its relationship with CO as an indicator of air mass age
Authors: Xiao Yaping , Jacob Daniel J. , Turquety Solene
Published: June 2007

Acetylene (C2H2) and CO originating from combustion are strongly correlated in atmospheric observations, offering constraints on atmospheric dilution and chemical aging. We examine here the C2H2‐CO relationships in aircraft observations worldwide, and interpret them with simple models as well as with a global chemical transport model (GEOS‐Chem). A C2H2 global source of 6.6 Tg yr−1 in GEOS‐Chem simulates the ensemble of global C2H2 observations without systematic bias, and captures most seasonal and regional features. C2H2/CO concentration ratios decrease from continental source regions to the remote atmosphere in a manner consistent between the observations and the model. However, the dC2H2/dCO slope from the linear regression does not show such a systematic decrease, either in the model or in the observations, reflecting variability in background air. The slope β = dlog[C2H2]/dlog[CO] of the linear regression of concentrations in log space offers information for separating the influences of dilution and chemical aging. We find that a linear mixing model with constant dilution rate and background is successful in fresh continental outflow but not in remote air. A diffusion model provides a better conceptual framework for interpreting the observations, where the value of β relative to the square root of the ratio of C2H2 and CO chemical lifetimes (1.7–1.9) measures the relative importance of dilution and chemistry. We thus find that dilution dominates in fresh outflow but chemical loss dominates in remote air. This result is supported by GEOS‐Chem sensitivity simulations with modified OH concentrations, and suggests that the model overestimates OH in the southern tropics.
Geophysical identification of permafrost in Livingston Island, maritime Antarctica
Authors: Hauck Christian , Vieira Gonçalo , Gruber Stephan , Blanco Juanjo , Ramos Miguel
Published: June 2007

The current permafrost distribution on Livingston Island, South Shetland Islands, maritime Antarctic, was investigated using electrical resistivity tomography, refraction seismics, and shallow borehole temperatures. The field sites include different geological and geomorphological settings, including ice cored moraines and bedrock sites with debris covers of different thickness. Two‐dimensional geophysical inversion schemes were used to analyze spatial heterogeneity at field sites and to detect isolated occurrences of ground ice. Results confirm that permafrost is widespread on Livingston Island, with high ice content in ice cored moraines and little in the cracks and fissures of frozen bedrock. Specific electrical resistivity values range from 10,000–40,000 ohm‐m (frozen unconsolidated material) to 1500–10,000 ohm‐m (frozen quartzite/shale). Combining seismic P wave velocities and specific electrical resistivities, a typical “roof‐type” distribution was found with maximum resistivities coinciding with P wave velocities around 3000 m/s and decreasing resistivities for both increasing and decreasing velocities.
Potential effects of regional pumpage on groundwater age distribution
Authors: Zinn Brendan A. , Konikow Leonard F.
Published: June 2007

Groundwater ages estimated from environmental tracers can help calibrate groundwater flow models. Groundwater age represents a mixture of traveltimes, with the distribution of ages determined by the detailed structure of the flow field, which can be prone to significant transient variability. Effects of pumping on age distribution were assessed using direct age simulation in a hypothetical layered aquifer system. A steady state predevelopment age distribution was computed first. A well field was then introduced, and pumpage caused leakage into the confined aquifer of older water from an overlying confining unit. Large changes in simulated groundwater ages occurred in both the aquifer and the confining unit at high pumping rates, and the effects propagated a substantial distance downgradient from the wells. The range and variance of ages contributing to the well increased substantially during pumping. The results suggest that the groundwater age distribution in developed aquifers may be affected by transient leakage from low‐permeability material, such as confining units, under certain hydrogeologic conditions.
Large‐time solutions for groundwater flow problems using the relationship of small p versus large t
Authors: Yeh Hund‐Der , Wang Chih‐Tse
Published: June 2007

An approximate solution is useful if the corresponding analytical solution is complicated and difficult to accurately evaluate. In the past, the relationship of small p versus large t was commonly applied to the Laplace domain solution and could successfully obtain a large‐time solution in the groundwater area. The large‐time solution usually has a simpler form than the analytical solution and is much easier for estimating the transient behavior of the groundwater flow system. However, Chen and Stone (1993) pointed out that the use of this relationship might fail to yield the correct solution in calculating the wellbore flux for the constant head test problem. Later, Mathias and Zimmerman (2003) indicated that a poor result was obtained by Gerke and van Genuchten (1993) when using the relationship of small p versus large t to derive the water transfer coefficient for the dual‐porosity media problem. This note is to show the detailed mathematical derivations involved in the issues that Chen and Stone (1993) and Gerke and van Genuchten (1993) addressed and to ensure that the relationship of small p versus large t is correct to obtain a large‐time solution for transient groundwater flow problems.
Sub‐seasonal variance of surface meteorological parameters in buoy observations and reanalyses
Authors: Serra Yolande L. , Cronin Meghan F. , Kiladis George N.
Published: June 2007

Tropical Atmosphere Ocean (TAO)/Triangle Trans‐Ocean Buoy Network (TRITON) and Eastern Pacific Investigation of Climate (EPIC) moorings across the equatorial Pacific are used to evaluate the mean climate and sub‐seasonal variance in surface meteorological variables in the NCEP/NCAR, NCEP/DOE, and ERA40 reanalyses. This study focuses on the June–November time period when tropical storms are most frequent in the region. For the mean fields, the reanalysis surface products compare better with the moorings than the 1000 hPa products. In contrast, the variance in the 1000 hPa ERA40 state variables is in best agreement with the mooring variance. As long as these disparities exist, air‐sea interaction studies and our ability to drive ocean models with observed fluxes will be limited.
BASS, an alternative to ETAS
Authors: Turcotte D. L. , Holliday J. R. , Rundle J. B.
Published: June 2007

The epidemic type aftershock sequence (ETAS) model has been widely used to model the statistics of seismicity. An essential feature of the ETAS model is the concept of generations of aftershocks. A mainshock has primary aftershocks, the primary aftershocks have secondary aftershocks, and so forth. In this paper, we introduce the branching aftershock sequence (BASS) model as an alternative to ETAS. The BASS model is fully self‐similar whereas the ETAS model is not. Furthermore, the ETAS model requires the specification of branching (parent‐daughter) ratios, while the BASS model instead utilizes Båth's law. We also show that the branching statistics in the BASS model are identical to the self‐similar Tokunaga statistics of drainage networks.
[11C]Flumazenil PET in Temporal Lobe Epilepsy: Do We Need an Arterial Input Function or Kinetic Modeling?
Authors: Hammers Alexander , Panagoda Prasan , Heckemann Rolf A , Kelsch Wolfgang , Turkheimer Federico E , Brooks David J , Duncan John S , Koepp Matthias J
Published: June 2007

Reduced signal on [11C]]flumazenil (FMZ) positron emission tomography (PET) is associated with epileptogenic foci. Linear correlations within individuals between parametric and nonparametric images of FMZ binding have been shown, and various methods have been used, without comparison of diagnostic usefulness. Using hippocampal sclerosis (HS) as a test case, we formally compare the diagnostic yield of parametric images obtained either with a parent tracer arterial plasma input function and spectral analysis (yielding volume-of-distribution (VD) images), or with an image-based input function and the simplified reference tissue model (binding potential images, BP-SRTM) with the diagnostic yield of semiquantitative-integrated (ADD) images from 10 to 20 or 20 to 40 mins (ADD1020 and ADD2040). Dynamic 90-min [11C]FMZ PET datasets and arterial plasma input functions were available for 15 patients with medically refractory medial temporal lobe epilepsy (TLE) and histologically verified unilateral HS and for 13 control subjects. SPM2 was used for analysis. ADD1020 and ADD2040 images showed decreased FMZ uptake ipsilateral to the epileptogenic hippocampus in 13/15 cases; 6/13 had bilateral decreases in the ADD1020 analysis and 5/13 in the ADD2040 analysis. BP-SRTM images detected ipsilateral decreases in 12/15 cases, with bilateral decreases in three. In contrast, VD images showed ipsilateral hippocampal decreases in all 15 patients, with bilateral decreases in three patients. Bilateral decreases in the ADD images tended to be more symmetrical and in one case were more marked contralaterally. Full quantification with an image-independent input should ideally be used in the evaluation of FMZ PET; at least in TLE, intrasubject correlations do not predict equivalent clinical usefulness.
Missing Steps in the STAIR Case: A Translational Medicine Perspective on the Development of NXY-059 for Treatment of Acute Ischemic Stroke
Authors: Feuerstein Giora Z , Zaleska Margaret M , Krams Michael , Wang Xinkang , Day Mark , Rutkowski Julia L , Finklestein Seth P , Pangalos Menelas N , Poole Michael , Stiles Gary L , Ruffolo Robert R , Walsh Frank L
Published: June 2007

The continued failure in approving new drugs for treatment of acute stroke has been recently set back by the failure of the NXY-059 (Stroke-Acute Ischemic NXY Treatment (SAINT) II) trial. The disappointment was heightened by the latter study being viewed as a most promising compound for stroke drug development program based on the preclinical data. Since the SAINT I/II development program included many of the STAIR (Stroke Therapy Academic Industry Round table) guidelines, yet have still failed to achieve the expected efficacy, there is a clear need to continue and analyze the path forward for stroke drug discovery. To this end, this review calls for a consortium approach including academia, government (FDA/NIH), and pharmaceutical industry partnerships to define this path. It is also imperative that more attention is given to the evolving discipline of Translational Medicine. A key issue in this respect is the need to devote more attention to the characteristics of the drug candidate nature—target interaction, and its relationship to pharmacodynamic treatment end points. It is equally important that efforts are spent to prove that phenotypic outcomes are linked to the purported mechanism of action of the compound. Development of technologies that allows a better assessment of these parameters, especially in in vivo models are paramount. Finally, rational patient selection and new outcome scales tailored in an adaptive design model must be evaluated.
Nanosecond plasma-mediated electrosurgery with elongated electrodes
Authors: Vankov Alexander , Palanker Daniel
Published: June 2007

Progress in interventional medicine is associated with the development of more delicate and less invasive surgical procedures, which requires more precise and less traumatic, yet affordable, surgical instruments. Previously we reported on the development of the pulsed electron avalanche knife for dissection of soft tissue in liquid media using the 100 ns plasma-mediated electric discharges applied via a 25 μm disk microelectrode. Cavitation bubbles accompanying explosive vaporization of the liquid medium in front of such a pointed electrode produced a series of craters that did not always merge into a continuous cut. In addition, this approach of surface ablation provided a limited depth of cutting. Application of an elongated electrode capable of cutting with its edge rather than just with its pointed apex faces a problem of nonuniformity of the electric field on a nonspherical electrode. In this article we explore dynamics of the plasma-mediated nanosecond discharges in liquid medium in positive and negative polarities and describe the geometry of an electrode that provides a sufficiently uniform electric field along an extended edge of a surgical probe. A highly enhanced and uniform electric field was obtained on very sharp (2.5 μm) exposed edges of a planar electrode insulated on its flat sides. Uniform ionization and simultaneous vaporization was obtained along the whole edge of such a blade with 100 ns pulses at 4–6 kV. A continuous cutting rate of 1 mm/s in the retina and in soft membranes was achieved at a pulse repetition rate of 100 Hz. The collateral damage zone at the edges of incision did not exceed 80 μm. Negative polarity was found advantageous due to the lower rate of electrode erosion and due to better spatial confinement of the plasma-mediated discharge in liquid.
Phosphorylation effect on the GSSS peptide conformation in water: Infrared, vibrational circular dichroism, and circular dichroism experiments and comparisons with molecular dynamics simulations
Authors: Lee Kyung-Koo , Joo Cheonik , Yang Seongeun , Han Hogyu , Cho Minhaeng
Published: June 2007

The phosphorylation effect on the small peptide conformation in water has not been clearly understood yet, despite the widely acknowledged notion that control of protein activity by phosphorylation works mainly by inducing conformational change. To elucidate the detailed mechanism, we performed infrared (IR) absorption and vibrational and electronic circular dichroism studies of both unphosphorylated and phosphorylated tetrapeptides, GSSS 1 and GSSpS 2. The solution structure of the tetrapeptide is found to be little dependent on the presence of the neutral or negatively charged phosphoryl group, and to be a mixture of extended structures including polyproline II (PII) and β-sheet conformations. The additional band at 1598cm−1 in the amide I IR spectrum of the phosphorylated peptide GSSpS at neutral pD appears to be clear spectroscopic evidence for direct intramolecular hydrogen-bonding interaction between the side chain dianionic phosphoryl group and the backbone amide proton. On the basis of amide I IR band analyses, the authors found that the probability of finding the phosphoryl group strongly H bonded to the backbone proton in GSSpS is about 43% at pD 7.0 and 37°C. Such a H-bonding interaction in GSSpS has the biological standard enthalpy and entropy of −15.1kJ∕mol and −51.2J∕Kmol, respectively. Comparisons between the experimentally measured IR and VCD spectra and the numerically simulated ones suggested that the currently available force field parameters need to be properly modified. The results in this paper may shed light on an unknown mechanism of controlling the peptide conformation by phosphorylation.
The wimple: A rippled deformation of a wetting film during its drainage
Authors: Ajaev Vladimir S. , Tsekov Roumen , Vinogradova Olga I.
Published: June 2007

It has long been accepted that hydrodynamic pressure in a draining fluid film can cause inversion of curvature of a fluid-fluid interface, creating the so-called dimple. However, it was recently discovered that a different shape, dubbed a wimple, can be formed if a bubble/drop is initially in the field of repulsive surface forces, so that a wetting film is formed. The film profile then includes a central region in which the film remains thin, surrounded by a ring of greater film thickness and bounded at the outer edge by a barrier rim. This shape later evolves to a conventional dimple, which then drains in the usual way. Here we carry out numerical simulations of the draining film evolution that allow us to uncover the physical mechanism responsible for wimple formation. Simple analytical estimates are then obtained for characteristic times of different stages of drainage, and are shown to be in good agreement with experimental data. We demonstrate that wimpling is a general phenomenon that can be encountered in many different systems.
Binding in transition metal complexes: Reduced multireference coupled-cluster study of the MCH2+ (M=Sc to Cu) compounds
Authors: Li Xiangzhu , Paldus Josef
Published: June 2007

The recently developed reduced multireference coupled-cluster method with singles and doubles (RMR CCSD), which is perturbatively corrected for triples [RMR CCSD(T)], is employed to compute binding energies of nine transition metal ions with CH2. Unlike analogous compounds involving main-group elements, the MCH2+ (M=Sc to Cu) transition metal complexes often exhibit a non-negligible multireference character. The authors thus employ the RMR CCSD(T) method, which represents an extension of the standard single-reference (SR) CCSD(T) method and can account for multireference effects, while employing only small reference spaces. In this way the role of quasidegeneracy effects on the binding energies of these complexes can be assessed at a higher SD(T) level than is possible with the widely used ab initio methods, namely, with the standard SR CCSD(T) approach, and provide a new benchmark for these quantities. The difference between the RMR and the standard CCSD(T) methods becomes particularly evident when considering nonequilibrium geometries.
Geminal model chemistry III: Partial spin restriction
Authors: Rassolov Vitaly A. , Xu Feng
Published: June 2007

The authors define an ab initio electronic structure model that uses partial spin restriction. It is an intermediate case between the so-called spin-restricted and spin-unrestricted formulations, which are popular in electronic structure methodology. Partial spin restriction arises naturally when the wave function is represented as an antisymmetrized product of two-electron functions, as it is done in generalized valence bond and antisymmetrized product of strongly orthogonal geminal theories. The authors show that the new model is size consistent, and it improves the description of transition metal compounds.
Intermittent search process and teleportation
Authors: Bénichou O. , Moreau M. , Suet P.-H. , Voituriez R.
Published: June 2007

The authors study an intermittent search process combining diffusion and “teleportation” phases in a d-dimensional spherical continuous system and in a regular lattice. The searcher alternates diffusive phases, during which targets can be discovered, and fast phases (teleportation) which randomly relocate the searcher, but do not allow for target detection. The authors show that this alternation can be favorable for minimizing the time of first discovery, and that this time can be optimized by a convenient choice of the mean waiting times of each motion phase. The optimal search strategy is explicitly derived in the continuous case and in the lattice case. Arguments are given to show that much more general intermittent motions do provide optimal search strategies in d dimensions. These results can be useful in the context of heterogeneous catalysis or in various biological examples of transport through membrane pores.
Ab initioelectron propagators in molecules with strong electron-phonon interaction. I. Phonon averages
Authors: Dahnovsky Yuri
Published: June 2007

Ab initio electron propagators in molecular systems with strong electron-electron and electron-phonon interactions are considered to study molecular electronic properties. This research is important in electron transfer reactions where the electron transition is not considered any longer as a single electron transfer process or in temperature dependences of current-voltage characteristics in molecular wires or aggregates. To calculate electron Green’s functions, the authors apply a small polaron canonical transformation that intrinsically contains strong electron-phonon effects. According to this transformation, the excitation energies of the noninteracting Hamiltonian are shifted down by the relaxation (solvation) energy for each state. The electron-electron interaction is also renormalized by the electron-phonon coupling. For some values of the electron-phonon coupling constants, the renormalized Coulomb integrals can be negative resulting in the attraction between two electrons. Within this transformation, they develop a diagrammatic expansion for electron Green’s function in which the electron-phonon interaction is included into the multiple phonon correlation functions. The multiple phonon correlation functions are exactly found. It is pointed out that Wick’s theorem for such correlation functions is invalid. Consequently, there is no Dyson equation for electron Green’s functions. The proposed approach can be considered for future method developments for quantum chemical calculations that include strong nonadiabatic (non-Born-Oppenheimer) effects.
Tuning polymer melt fragility with antiplasticizer additives
Authors: Riggleman Robert A. , Douglas Jack F. , de Pablo Juan J.
Published: June 2007

A polymer-diluent model exhibiting antiplasticization has been developed and characterized by molecular dynamics simulations. Antiplasticizer molecules are shown to decrease the glass transition temperature Tg but to increase the elastic moduli of the polymeric material in the low-temperature glass state. Moreover, the addition of antiplasticizing particles renders the polymer melt a stronger glass-forming material as determined by changes in the characteristic temperatures of glass formation, the fragility parameter D from fits to the Vogel-Folcher-Tamman-Hesse equation, and through the observation of the temperature dependence of the size of cooperatively rearranging regions (strings) in each system. The length of the strings exhibits a weaker temperature dependence in the antiplasticized glass-forming system than in the more fragile pure polymer, consistent with the Adam-Gibbs model of glass formation. Unexpectedly, the strings become increasingly concentrated in the antiplasticizer particles upon cooling. Finally, we discuss several structural indicators of cooperative dynamics, and find that the dynamic propensity (local Debye-Waller factor ⟨u2⟩p) does seem to provide a strong correlation with local molecular displacements at long times. The authors also consider maps of the propensity, and find that the antiplasticized system exhibits larger fluctuations over smaller length scales compared to the pure polymer.
Oxygen adsorption on Mo(112) surface studied by ab initio genetic algorithm and experiment
Authors: Sierka Marek , Todorova Tanya K. , Sauer Joachim , Kaya Sarp , Stacchiola Dario , Weissenrieder Jonas , Shaikhutdinov Shamil , Freund Hans-Joachim
Published: June 2007

Density functional theory in combination with genetic algorithm is applied to determine the atomic models of p(1×2) and p(1×3) surface structures observed upon oxygen adsorption on a Mo(112) surface. The authors’ simulations reveal an unusual flexibility of Mo(112) resulting in oxygen-induced reconstructions and lead to more stable structures than any suggested so far. Comparison of the stabilities of the predicted models shows that different p(1×2) and p(1×3) structures may coexist over a wide range of oxygen pressures. A pure p(1×2) structure can be obtained only in a narrow region of oxygen pressures. In contrast, a pure p(1×3) structure cannot exist as a stable phase. The results of simulations are fully supported by a multitude of experimental data obtained from low energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy.
Growth kinetics of carbon nanowall-like structures in low-temperature plasmas
Authors: Levchenko I. , Ostrikov K. , Rider A. E. , Tam E. , Vladimirov S. V. , Xu S.
Published: June 2007

The results of a hybrid numerical simulation of the growth kinetics of carbon nanowall-like nanostructures in the plasma and neutral gas synthesis processes are presented. The low-temperature plasma-based process was found to have a significant advantage over the purely neutral flux deposition in providing the uniform size distribution of the nanostructures. It is shown that the nanowall width uniformity is the best (square deviations not exceeding 1.05) in high-density plasmas of 3.0×1018m−3, worsens in lower-density plasmas (up to 1.5 in 1.0×1017m−3 plasmas), and is the worst (up to 1.9) in the neutral gas-based process. This effect has been attributed to the focusing of ion fluxes by irregular electric field in the vicinity of plasma-grown nanostructures on substrate biased with −20V potential, and differences in the two-dimensional adatom diffusion fluxes in the plasma and neutral gas-based processes. The results of our numerical simulations are consistent with the available experimental reports on the effect of the plasma process parameters on the sizes and shapes of relevant nanostructures.
Envelope pulsed ultrasonic distance measurement system based upon amplitude modulation and phase modulation
Authors: Huang Y. P. , Wang J. S. , Huang K. N. , Ho C. T. , Huang J. D. , Young M. S.
Published: June 2007

A novel microcomputer-based ultrasonic distance measurement system is presented. This study proposes an efficient algorithm which combines both the amplitude modulation (AM) and the phase modulation (PM) of the pulse-echo technique. The proposed system can reduce error caused by inertia delay and amplitude attenuation effect when using the AM and PM envelope square wave form (APESW). The APESW ultrasonic driving wave form causes a phase inversion phenomenon in the relative wave form of the receiver. The phase inversion phenomenon sufficiently identifies the “measurement pulse” in the received wave forms, which can be used for accurate time-of-flight (TOF) measurement. In addition, combining a countertechnique to compute the phase shifts of the last cycle for TOF, the presented system can obtain distance resolution of 0.1% of the wavelength corresponding to the 40kHz frequency of the ultrasonic wave. The standard uncertainty of the proposed distance measurement system is found to be 0.2mm at a range of 50–500mm. The APESW signal generator and phase detector of this measuring system are designed on a complex programmable logic device, which is used to govern the TOF measurement and send the data to a personal computer for distance calibration and examination. The main advantages of this APESW system are high resolution, low cost, narrow bandwidth requirement, and ease of implementation.
Structural, magnetic, and transport properties of Fe3O4∕Si(111) and Fe3O4∕Si(001)
Authors: Boothman Catherine , Sánchez Ana M. , van Dijken Sebastiaan
Published: June 2007

Carrier transport across Fe3O4∕Si interfaces has been studied for two different Si substrate orientations. The Fe3O4 films exhibit a (111) texture on both (111)- and (001)-oriented substrates and field-cooling experiments show the characteristic step in film magnetization at the Verwey transition temperature of magnetite. Current-voltage measurements indicate the formation of high-quality Schottky barriers with an ideality factor of about n=1.06. Fits to the transport data using the thermionic emission/diffusion model yield Schottky barrier heights of 0.52 and 0.65eV for Fe3O4∕Si(111) and Fe3O4∕Si(001) structures, respectively. The interface between the magnetite films and silicon substrates consists of a crystalline iron silicide/amorphous oxide bilayer with reduced magnetic moment.
Origin of green luminescence of ZnO powders reacted with carbon black
Authors: Hu Yi , Chen H.-J.
Published: June 2007

ZnO powders were synthesized by a precipitation method and annealed with carbon black. Electron paramagnetic resonance (EPR) and photoluminescence spectroscopies were conducted to study the characteristics of the ZnO powders. The g factor of the EPR signal shifted to lower value for the samples annealed with carbon black. These signals are assigned to singly ionized oxygen vacancy composed of VO• complex and isolated VO• defects. The transition from VO• complex to isolated VO• is proposed to explain the shift of the EPR signals. In conclusion, a transition of an electron from VO• to VO•• at the surface of the ZnO particles is responsible for the green emission peak at 528nm from current results.
Sub-wavelength resolution in linear arrays of plasmonic particles
Authors: Simovski Constantin R. , Viitanen Ari J. , Tretyakov Sergei A.
Published: June 2007

Recently, we suggested the idea of an optical superlens based on the extraordinary dispersion properties of plasmonic nanochains. In the present paper we discuss the results of numerical simulations of the imaging of point sources in this superlens. The simulations show that sub-wavelength resolution can be obtained in much thicker structures than usual. A distance of nearly λ/2 between the source and the image plane is achieved. In addition the effects of stochastic deviations in geometrical parameters are studied.
A strong reduction in the density of near-interface traps at the SiO2∕4H-SiC interface by sodium enhanced oxidation
Authors: Allerstam F. , Ólafsson H. Ö. , Gudjónsson G. , Dochev D. , Sveinbjörnsson E. Ö. , Rödle T. , Jos R.
Published: June 2007

This paper demonstrates how sodium enhanced oxidation of Si face 4H-SiC results in removal of near-interface traps at the SiO2∕4H-SiC interface. These detrimental traps have energy levels close to the SiC conduction band edge and are responsible for low electron inversion channel mobilities (1–10cm2∕Vs) in Si face 4H-SiC metal-oxide-semiconductor field effect transistors. The presence of sodium during oxidation increases the oxidation rate and suppresses formation of these near-interface traps resulting in high inversion channel mobility of 150cm2∕Vs in such transistors. Sodium is incorporated by using carrier boats made of sintered alumina during oxidation or by deliberate sodium contamination of the oxide during the formation of the SiC∕SiO2 interface.
Carbon dioxide reforming of methane by pulsed glow discharge at atmospheric pressure: The effect of pulse compression
Authors: Ghorbanzadeh A. M. , Modarresi H.
Published: June 2007

Methane reforming by carbon dioxide in pulsed glow discharge at atmospheric pressure is examined. The plasma pulse is compressed to less than 50ns. This compression enables one to work at higher frequencies, over 3kHz, without glow-arc transition. The main products of the reaction are synthetic gases (H2, CO) and C2 hydrocarbons. Approximately 42% of plasma energy goes to the chemical dissociation, when the reactant ratio is CO2∕CH4=1. At this point, the energy expense is less than 3.8eV per converted molecule while reactant conversions are relatively high reaching to 55% (CH4) and 42% (CO2). The reactor energy performance even gets better at higher CO2∕CH4 ratios. While energy efficiency reached about 45%, at feed ratio of CO2∕CH4=5, the conversions of about 65% and 45% were obtained for methane and carbon dioxide, respectively. A model describing dissociation through molecular vibrations is introduced. According to the model, the high nonequilibrium state of vibrational energy at short pulses leads to this improvement, especially in carbon dioxide.
Optimized pulsed laser deposition by wavelength and static electric field control: The case of tetrahedral amorphous carbon films
Authors: Patsalas P. , Kaziannis S. , Kosmidis C. , Papadimitriou D. , Abadias G. , Evangelakis G. A.
Published: June 2007

We report on the application of a static (dc) electric field in the plume region during the pulsed Nd doped yttrium aluminum garnet laser deposition (PLD) of tetrahedral amorphous carbon (ta-C) films in vacuum ambient (pressure=10−4–10−3Pa), where the working pressure is exclusively due to ablation vapor. This approach is strikingly different from the plasma- or ion-beam-assisted PLD because the mean free path at this pressure is by far longer than the target to substrate distance. Thus, the electric field interacts with individual ionized species invoking ion acceleration and gas-phase reactions among different ionized species. These phenomena are clearly dependent on the laser wavelength (first, second, or third harmonic, λ=1064, 532, and 355nm, respectively) used for the ablation. We found that the application of the electric field causes surface smoothing (the roughness decreases from about 1to0.4nm) and faster deposition rate (from about 2to7nm∕min) for the second and third harmonics. In addition, the phenomena are less intense in the case of the first harmonic due to the low concentration of ionized species in the plume. In addition, in the case of PLD using λ=532nm, the electric field improves the film’s density (from 2.60to2.95g∕cm3). The correlations found are discussed in terms of the ablated species and the deposition mechanisms of the ta-C.
Thermodynamic stability of type-I and type-II clathrate hydrates depending on the chemical species of the guest substances
Authors: Miyoshi Tatsuya , Imai Masatoshi , Ohmura Ryo , Yasuoka Kenji
Published: June 2007

The free energy differences are calculated for various type-I and type-II clathrate hydrates based on molecular-dynamics simulations, thereby evaluating the thermodynamic stability of the hydrates depending on the chemical species of the guest substances. The simulation systems consist of 27unit cells, that is, 1242 water molecules and 216 guest molecules for type-I hydrates, and 3672 water molecules and 648 guest molecules for type-II hydrates. The water molecules are described by TIP4P potential, while the guest molecules are described by one-site Lennard-Jones potential, U=4ε{(σ∕r)12−(σ∕r)6}, where U is the potential energy, r is the particle distance, σ is the particle diameter, and ε is the energy well depth. The optimal values of σ that yield the minimum free energy (the best thermodynamic stability) were determined to be 0.39nm for the type-I hydrates and 0.37nm for the type-II hydrates.
Field emission display device structure based on double-gate driving principle for achieving high brightness using a variety of field emission nanoemitters
Authors: Chen Jun , Dai Y. Y. , Luo J. , Li Z. L. , Deng S. Z. , She J. C. , Xu N. S.
Published: June 2007

In order to apply various cold cathode nanoemitters in a field emission display (FED) and to achieve high brightness, a FED device structure with double gates and corresponding driving method have been proposed. Individual pixel addressing can be achieved by applying proper sequence of positive or negative voltage to the lower gate and upper gate, respectively. The feasibility of the device has been demonstrated by using carbon nanotube and tungsten oxide nanowire cold emitters. Display of moving images has been demonstrated and high luminance up to 2500cd∕m2 was obtained. The reported device structure is versatile for nanoemitters regardless of substrate or preparation temperature. The results are of significance to the development of FED using nanoemitters.
The role of the defect levels in MgO in the low firing voltage, wide driving voltage margin operation of an alternate current plasma display panel
Authors: Ha Chang Hoon , Kim Joong Kyun , Whang Ki-Woong
Published: June 2007

In order to study the relationship between the discharge characteristics of an ac plasma display panel and the surface conductivity of a MgO thin film, we measured the surface current across a ring-shaped MgO film temporally induced by exposure to monochromatic vacuum ultraviolet radiation from a synchrotron radiation source whose wavelength ranges from 60 to 240 nm (5.5−25 eV). The experimental results show that the surface current begins to increase rapidly at a photon energy of about 9 eV which might correspond to the valence band edge of MgO. The differences in the surface current level correlate well with the differences in the preparation method of the MgO films and their respective discharge characteristics, such as firing, minimum sustained voltages, address voltage margins, and address discharge delay times. Surface charge measurements using the linear electro-optic effect also show consistent correlations with the surface current measurement of each MgO sample.
Temperature dependence of the thermal conductivity of different forms of diamond
Authors: Barman Saswati , Srivastava G. P.
Published: June 2007

We present a systematic theoretical investigation of the thermal conductivity of naturally abundant, isotopically enriched, fast neutron irradiated single crystals of diamond, and chemical vapor deposited diamond films of different types over a large temperature range. Existing experimental data have been analyzed using Callaway’s theoretical model [Phys. Rev. 113, 1046 (1959)] for thermal conductivity based on an isotropic continuum phonon dispersion relation and using normal and umklapp phonon-phonon relaxation times derived from the application of time-dependent perturbation theory within an anharmonic continuum model. In contrast to existing theoretical studies of the thermal conductivity of diamond, our approach considers Grüneisen’s constant as the only (semi)adjustable parameter for anharmonic phonon interactions. This work quantifies the enhancement of the thermal conductivity of diamond with isotopic purity. This work also accounts for the dip in the thermal conductivity curve for hot filament chemical vapor deposition of diamond films and neutron irradiated diamond at low temperatures and provides an estimate of the amount, type, and size of defects present in such samples. We find that the N-drift term in Callaway’s theory provides a significant contribution to the thermal conductivity of all the forms of diamond studied here.
Role of oxygen vacancies in tuning magnetic properties of Co-doped SnO2 insulating films
Authors: Liu X. F. , Sun Y. , Yu R. H.
Published: June 2007

A series of films deposited under different oxygen partial pressures and annealed under different atmospheres were prepared to investigate the role of oxygen vacancies in tuning magnetic properties of Co-doped SnO2 films. The inclusive Co in SnO2 is in the 2+ state and substitutes for the Sn4+ site. Intrinsic room temperature ferromagnetism is observed in all films, which is not carrier mediated, but coexists with the dielectric behavior. A maximum magnetic moment of 2.37 μB∕Co is achieved by vacuum annealing due to the increase and diffusion of oxygen vacancies rather than the improvement of crystallinity of the film, and the magnetic moment decreases considerably after air annealing or increasing the oxygen partial pressure during deposition. The changes of oxygen vacancy concentration and distribution are indirectly demonstrated by the relative shifts of Co 2p3∕2 peaks in XPS spectra. The band gap of Co-doped SnO2 film is larger than that of pure SnO2 film, suggesting the influence of inclusive Co on the electronic states, and further blueshift after annealing is also visible. The F-center model is modified to explain the ferromagnetism in insulating Co-doped SnO2 films.
Transition metal interaction and Ni-Fe-Cu-Si phases in silicon
Authors: Heuer M. , Buonassisi T. , Istratov A. A. , Pickett M. D. , Marcus M. A. , Minor A. M. , Weber E. R.
Published: June 2007

In the present article we characterize several intermetallic phases of the Cu-Ni-Fe-Si system found as precipitates in the misfit dislocation layer of intentionally contaminated and slowly cooled Si1−xGex∕Si-heterostructures. The clusters showed a characteristic phase speciation into a Cu-rich part similar to Cu3Si and an Fe-Ni-Cu-Si phase similar to NiSi2. It is suggested that the precipitate formation of the investigated intermetallic silicides involves a homogeneous precursor phase at higher temperatures that later decomposes into the observed phases. Our results indicate that chemical reactions between metals and silicon during precipitation may reduce the lattice mismatch compared to single-metal precipitates, rendering mixed-metal-silicide precipitates more stable and energetically favorable.
Alloy scattering in AlGaN and InGaN: A numerical study
Authors: Bellotti Enrico , Bertazzi Francesco , Goano Michele
Published: June 2007

Wave-vector-dependent rates of disorder-induced alloy scattering have been computed for wurtzite AlGaN and InGaN to determine the transport properties of III-nitride alloys through full band Monte Carlo simulation. Contrary to previous studies, the empirical selection of a constant alloy scattering potential has been replaced by a more fundamental approach based on detailed information about the electronic structure and the corresponding screened atomic potentials. Band structures and atomic potentials have been determined in the framework of the nonlocal empirical pseudopotential method; good agreement of the fundamental energy gap with available experimental information has been achieved over the entire composition range of the alloys with the inclusion of a disorder contribution in the pseudopotential. The calculated alloy scattering potential is in reasonable agreement with the few indirect measurements available for AlGaN. Calculations of electron steady-state velocity-field curves confirm that alloy scattering has significant effects on the transport properties of AlGaN and InGaN.
Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol
Authors: Sun Wen-Ting , Li Guo , Li He-Ping , Bao Cheng-Yu , Wang Hua-Bo , Zeng Shi , Gao Xing , Luo Hui-Ying
Published: June 2007

Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure α-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images.
Interface capacitance of La0.8Ca0.2MnO3∕Nb:SrTiO3 junctions
Authors: Chen Y. F. , Ziese M. , Esquinazi P.
Published: June 2007

The temperature, current, and magnetic field dependences of the transport properties at the interface between La0.8Ca0.2MnO3 and Nb(0.1%):SrTiO3 were studied. The striking feature in the present transport data is the appearance of a charging effect that typically occurs in RC circuits. It can be well modeled by a simple RC equivalent circuit. The results show that the interface of the present junctions has a very large capacitance with a value of the areal capacitance of 60nF∕mm2 leading to a very large time constant of the order of 100s at 100K. Both the interfacial resistance and the time constant significantly decrease with increasing temperature, current, and magnetic field, whereas the interfacial capacitance remains essentially unchanged. This phenomenon opens up the possibility for the development of a different type of current, magnetic field, and temperature sensitive capacitor.
Metal-like conductivity in transparent Al:ZnO films
Authors: Bamiduro O. , Mustafa H. , Mundle R. , Konda R. B. , Pradhan A. K.
Published: June 2007

This letter reports on the metal-like conductivity down to 125K in highly crystalline transparent (⩾85% in the visible region) Al:ZnO films grown on sapphire and glass substrates by pulsed-laser deposition technique. Significantly different surface morphologies were found on both types of films. Temperature dependent resistivity measurements of the films grown at 450°C on sapphire and glass show metal-like conductivity with electrical resistivity, ∼1.77×10−4 and ∼3.92×10−4Ωcm, respectively, at room temperature followed by either a residual conductivity or a metal-semiconductor transition at low temperature due to the localization effect caused by the defects.
Enhanced nonlinear optical properties of oxygen deficient lead-niobium-germanate film glasses
Authors: Gonzalo J. , Fernandez H. , Solis J. , Munoz-Martin D. , Fernandez-Navarro J. M. , Afonso C. N. , Fierro J. L. G.
Published: June 2007

The third order nonlinear optical properties of oxygen deficient lead-niobium-germanate film glasses with heavy metal contents beyond that of the bulk glass formation region have been investigated. Values of the nonlinear third order optical susceptibility up to ∕χ(3)∕≈1.8×10−11esu have been measured by degenerate four wave mixing at 800nm in films having large heavy metal fractions (0.93). The fast buildup and decay times (≈130fs) of the nonlinear response confirm its nonresonant character. The partial reduction of Nb5+ to Nb4+ evidenced by x-ray photoelectron spectroscopy, which is associated with the oxygen deficiency, appears to be responsible for the strong enhancement of ∕χ(3)∕.
Ring-based ultrasonic virtual point detector with applications to photoacoustic tomography
Authors: Yang Xinmai , Li Meng-Lin , Wang Lihong V.
Published: June 2007

An ultrasonic virtual point detector is constructed using the center of a ring transducer. The virtual point detector provides ideal omnidirectional detection free of any aperture effect. Compared with a real point detector, the virtual one has lower thermal noise and can be scanned with its center inside a physically inaccessible medium. When applied to photoacoustic tomography, the virtual point detector provides both high spatial resolution and high signal-to-noise ratio. It can also be potentially applied to other ultrasound-related technologies.