bluuebunny/crossref_metadata_2025 huggingface dataset:
A three‐dimensional crustal seismic velocity model for southern California from a composite event method
Authors: Lin Guoqing , Shearer Peter M. , Hauksson Egill , Thurber Clifford H.
Published: November 2007

We present a new crustal seismic velocity model for southern California derived from P and S arrival times from local earthquakes and explosions. To reduce the volume of data and ensure a more uniform source distribution, we compute “composite event” picks for 2597 distributed master events that include pick information for other events within spheres of 2 km radius. The approach reduces random picking error and maximizes the number of S wave picks. To constrain absolute event locations and shallow velocity structure, we also use times from controlled sources, including both refraction shots and quarries. We implement the SIMULPS tomography algorithm to obtain three‐dimensional (3‐D) Vp and Vp/Vs structure and hypocenter locations of the composite events. Our new velocity model in general agrees with previous studies, resolving low‐velocity features at shallow depths in the basins and some high‐velocity features in the midcrust. Using our velocity model and 3‐D ray tracing, we relocate about 450,000 earthquakes from 1981 to 2005. We observe a weak correlation between seismic velocities and earthquake occurrence, with shallow earthquakes mostly occurring in high P velocity regions and midcrustal earthquakes occurring in low P velocity regions. In addition, most seismicity occurs in regions with relatively low Vp/Vs ratios, although aftershock sequences following large earthquakes are often an exception to this pattern.
Global budget of CO, 1988–1997: Source estimates and validation with a global model
Authors: Duncan B. N. , Logan J. A. , Bey I. , Megretskaia I. A. , Yantosca R. M. , Novelli P. C. , Jones N. B. , Rinsland C. P.
Published: November 2007

We present a model study of carbon monoxide for 1988–1997 using the GEOS‐Chem 3‐D model driven by assimilated meteorological data, with time‐varying emissions from biomass burning and from fossil fuel and industry, overhead ozone columns, and methane. The hydroxyl radical is calculated interactively using a chemical parameterization to capture chemical feedbacks. We document the inventory for fossil fuels/industry and discuss major uncertainties and the causes of differences with other inventories that give significantly lower emissions. We find that emissions hardly change from 1988 to 1997, as increases in Asia are offset by decreases elsewhere. The model reproduces the 20% decrease in CO at high northern latitudes and the 10% decrease in the North Pacific, caused primarily by the decrease in European emissions. The model compares well with observations at sites impacted by fossil fuel emissions from North America, Europe, and east Asia suggesting that the emissions from this source are reliable to 25%, and we argue that bottom‐up emission estimates are likely to be too low rather than too high. The model is too low at the seasonal maximum in spring in the southern tropics, except for locations in the Atlantic Ocean. This problem may be caused by an overestimate of the frequency of tropical deep convection, a common problem in models that use assimilated meteorological data. We argue that the yield of CO from methane oxidation is near unity, contrary to some other studies, based on removal rates of intermediate species.
Effects of tropospheric ozone pollution on net primary productivity and carbon storage in terrestrial ecosystems of China
Authors: Ren Wei , Tian Hanqin , Liu Mingliang , Zhang Chi , Chen Guangsheng , Pan Shufen , Felzer Benjamin , Xu Xiaofeng
Published: November 2007

We investigated the potential effects of elevated ozone (O3) along with climate variability, increasing CO2, and land use change on net primary productivity (NPP) and carbon storage in China's terrestrial ecosystems for the period 1961–2000 with a process‐based Dynamic Land Ecosystem Model (DLEM) forced by the gridded data of historical tropospheric O3 and other environmental factors. The simulated results showed that elevated O3 could result in a mean 4.5% reduction in NPP and 0.9% reduction in total carbon storage nationwide from 1961 to 2000. The reduction of carbon storage varied from 0.1 Tg C to 312 Tg C (a decreased rate ranging from 0.2% to 6.9%) among plant functional types. The effects of tropospheric O3 on NPP were strongest in east‐central China. Significant reductions in NPP occurred in northeastern and central China where a large proportion of cropland is distributed. The O3 effects on carbon fluxes and storage are dependent upon other environmental factors. Therefore direct and indirect effects of O3, as well as interactive effects with other environmental factors, should be taken into account in order to accurately assess the regional carbon budget in China. The results showed that the adverse influences of increasing O3 concentration across China on NPP could be an important disturbance factor on carbon storage in the near future, and the improvement of air quality in China could enhance the capability of China's terrestrial ecosystems to sequester more atmospheric CO2. Our estimation of O3 impacts on NPP and carbon storage in China, however, must be used with caution because of the limitation of historical tropospheric O3 data and other uncertainties associated with model parameters and field experiments.
Chemical characteristics of water‐soluble organic carbon in the Asian outflow
Authors: Miyazaki Yuzo , Kondo Yutaka , Han Sunghee , Koike Makoto , Kodama Daisuke , Komazaki Yuichi , Tanimoto Hiroshi , Matsueda Hidekazu
Published: November 2007

Semicontinuous measurements of water‐soluble organic carbon (WSOC) and organic carbon (OC) in PM2.5 were made at Gosan, Korea, in March‐April 2005. On average, the WSOC/OC mass ratio for all air masses observed at Gosan was 0.30 ± 0.12. WSOC correlated well with CO (r2 = 0.54) in Chinese outflow, suggesting that a major part of the observed WSOC and/or their precursors was of combustion origin. The relationship between the increase of WSOC and O3 suggests that the observed WSOC was mostly secondary product. To interpret the measured organic compounds, thermal analyses of organic standards were made in the laboratory. Thermograms of a single standard of water‐soluble organic species showed that carbon that evolved at high temperatures (600°–870°C) was generally associated with water‐soluble compounds having high molecular weights (MWs) on the order of hundreds, while carbon that evolved at low temperatures (<300°C) generally had MWs of less than ∼180 g mol−1. Positive matrix factorization (PMF) analysis revealed three organic compound groups (low, medium, and highly refractory compounds) based on the OC thermograms. On average, highly and low refractory compound groups accounted for 79% and 21% of the WSOC mass, respectively, at Gosan. Highly refractory compound groups significantly contributed to WSOC regardless of air mass origin. The results of the laboratory experiments imply that a large fraction of these highly refractory compound groups was likely associated with high MW compounds. For water‐insoluble organic carbon(=OC–WSOC), medium and low refractory compound groups accounted for 60% and 40%, respectively, consistent with the results of the laboratory experiments.
Functioning of outer membrane protein assembly factor Omp85 requires a single POTRA domain
Authors: Bos Martine P , Robert Viviane , Tommassen Jan
Published: November 2007

β‐Barrel proteins are present in the outer membranes of Gram‐negative bacteria, mitochondria and chloroplasts. The central component of their assembly machinery is called Omp85 in bacteria. Omp85 is predicted to consist of an integral membrane domain and an amino‐terminal periplasmic extension containing five polypeptide‐transport‐associated (POTRA) domains. We have addressed the function of these domains by creating POTRA domain deletions in Omp85 of Neisseria meningitidis. Four POTRA domains could be deleted with only slight defects in Omp85 function. Only the most carboxy‐terminal POTRA domain was essential, as was the membrane domain. Thus, similar to the mitochondrial Omp85 homologue, the functional core of bacterial Omp85 consists of its membrane domain and a single POTRA domain, that is, POTRA5.
Regulation of flowering time by the protein arginine methyltransferase AtPRMT10
Authors: Niu Lifang , Lu Falong , Pei Yanxi , Liu Chunyan , Cao Xiaofeng
Published: November 2007

In plants, histone H3 lysine methyltransferases are important in gene silencing and developmental regulation; however, the roles of histone H4 methylation in plant development remain unclear. Recent studies found a type II histone arginine methyltransferase, AtPRTM5, which is involved in promoting growth and flowering. Here, we purified a dimerized plant‐specific histone H4 methyltransferase, plant histone arginine methyltransferase 10 (PHRMT10), from cauliflower. Arabidopsis thaliana protein arginine methyltransferase 10 (AtPRMT10)—the Arabidopsis homologue of PHRMT10—was shown to be a type I PRMT, which preferentially asymmetrically methylated histone H4R3 in vitro. Genetic disruption of AtPRMT10 resulted in late flowering by upregulating FLOWERING LOCUS C (FLC) transcript levels. In addition, we show that AtPRMT10 functions genetically separate from AtPRMT5, but that each acts to fine‐tune expression of FLC. This work adds an extra layer of complexity to flowering‐time regulation and also sheds light on the importance of asymmetric arginine methylation in plant development.
Charge-dependent model for many-body polarization, exchange, and dispersion interactions in hybrid quantum mechanical∕molecular mechanical calculations
Authors: Giese Timothy J. , York Darrin M.
Published: November 2007

This work explores a new charge-dependent energy model consisting of van der Waals and polarization interactions between the quantum mechanical (QM) and molecular mechanical (MM) regions in a combined QM∕MM calculation. van der Waals interactions are commonly treated using empirical Lennard-Jones potentials, whose parameters are often chosen based on the QM atom type (e.g., based on hybridization or specific covalent bonding environment). This strategy for determination of QM∕MM nonbonding interactions becomes tedious to parametrize and lacks robust transferability. Problems occur in the study of chemical reactions where the “atom type” is a complex function of the reaction coordinate. This is particularly problematic for reactions, where atoms or localized functional groups undergo changes in charge state and hybridization. In the present work we propose a new model for nonelectrostatic nonbonded interactions in QM∕MM calculations that overcomes many of these problems. The model is based on a scaled overlap model for repulsive exchange and attractive dispersion interactions that is a function of atomic charge. The model is chemically significant since it properly correlates atomic size, softness, polarizability, and dispersion terms with minimal one-body parameters that are functions of the atomic charge. Tests of the model are examined for rare-gas interactions with neutral and charged atoms in order to demonstrate improved transferability. The present work provides a new framework for modeling QM∕MM interactions with improved accuracy and transferability.
Simulation of the motion of flexible fibers in viscous fluid flow
Authors: Lindström Stefan B. , Uesaka Tetsu
Published: November 2007

A model for flexible fibers in viscous fluid flow is proposed, and its predictions compared with experiments found in the literature. The incompressible three-dimensional Navier–Stokes equations are employed to describe the fluid motion, while fibers are modeled as chains of fiber segments, interacting with the fluid through viscous and dynamic drag forces. Fiber segments, from the same or from different fibers, interact with each other through normal, frictional, and lubrication forces. Momentum conservation is enforced on the system to capture the two-way coupling between phases. Quantitative predictions could be made, and showed good agreement with experimental data, for the period of Jeffery orbits in shear flow, as well as for the amount of bending of flexible fibers in shear flow. Simulations, using the proposed model, also successfully reproduced the different regimes of motion for threadlike particles, ranging from rigid fiber motion to complicated orbiting behavior, including coiling and self-entanglement.
Fourier transform microwave spectrum of CO-dimethyl ether
Authors: Kawashima Yoshiyuki , Morita Yasumasa , Tatamitani Yoshio , Ohashi Nobuyuki , Hirota Eizi
Published: November 2007

Two sets of 32 rotational transitions were observed for the carbon monoxide–dimethyl ether (CO-DME) complex and two sets of 30 transitions for both C13O-DME and CO18-DME, in the frequency region from 3.5to25.2GHz, with J ranging from 1←0 up to 7←6, by using a Fourier transform microwave spectrometer. The splittings between the two sets of the same transition varied from 2to15MHz, and the two components were assigned to the two lowest states of the internal rotation of CO with respect to DME governed by a twofold potential. A preliminary analysis carried out separately for the two sets of the observed transition frequencies by using an ordinary asymmetric-rotor Hamiltonian indicated that the heavy-atom skeleton of the complex was essentially planar, as evidenced by the “pseudoinertial defects,” i.e., the inertial defects, which involve the contributions of the out-of-plane hydrogens of the two methyl groups, Icc−Iaa−Ibb of −5.764(23) and −5.753(16)uÅ2 for the symmetric and antisymmetric states, respectively. All of the observed transition frequencies were subsequently analyzed simultaneously, by using a phenomenological Hamiltonian which was described in a previous paper on Ar-DME and Ne-DME [Morita et al., J. Chem. Phys. 124, 094301 (2006)]. The rotational constants thus derived were analyzed to give the distance between the centers of gravity of the two component molecules, DME and CO, to be 3.682Å and the angle between the CO and the a-inertial axes to be 75.7°; the C end of the CO being closer to the DME. Most a-type transitions were observed as closely spaced triplets, which were ascribed to the internal rotation of the two methyl tops of DME. The V3 potential barrier was obtained to be 772(2)cm−1 from the first-order Coriolis coupling term between the internal rotation and overall rotation, which is about 82% of V3 for the DME monomer, whereas the second-order contribution of the coupling to the B rotational constant led to V3 of 705(3)cm−1. By assuming a Lennard-Jones-type potential, the dissociation energy was estimated to be EB=1.6kJmol−1, to be compared with 1.0 and 2.5kJmol−1 for Ne-DME and Ar-DME, respectively.
Optical properties of pentacene and perfluoropentacene thin films
Authors: Hinderhofer Alexander , Heinemeyer Ute , Gerlach Alexander , Kowarik Stefan , Jacobs Robert M. J. , Sakamoto Youichi , Suzuki Toshiyasu , Schreiber Frank
Published: November 2007

The optical properties of pentacene (PEN) and perfluoropentacene (PFP) thin films on various SiO2 substrates were studied using variable angle spectroscopic ellipsometry. Structural characterization was performed using x-ray reflectivity and atomic force microscopy. A uniaxial model with the optic axis normal to the sample surface was used to analyze the ellipsometry data. A strong optical anisotropy was observed, and enabled the direction of the transition dipole of the absorption bands to be determined. Furthermore, comparison of the optical constants of PEN and PFP thin films with the absorption spectra of the monomers in solution shows significant changes due to the crystalline environment. Relative to the monomer spectrum, the highest occupied molecular orbital to lowest unoccupied molecular orbital transition observed in PEN (PFP) thin film is reduced by 210meV (280meV). A second absorption band in the PFP thin film shows a slight blueshift (40meV) compared to the spectrum of the monomer with its transition dipole perpendicular to that of the first absorption band.
Including lateral interactions into microkinetic models of catalytic reactions
Authors: Hellman A. , Honkala K.
Published: November 2007

In many catalytic reactions lateral interactions between adsorbates are believed to have a strong influence on the reaction rates. We apply a microkinetic model to explore the effect of lateral interactions and how to efficiently take them into account in a simple catalytic reaction. Three different approximations are investigated: site, mean-field, and quasichemical approximations. The obtained results are compared to accurate Monte Carlo numbers. In the end, we apply the approximations to a real catalytic reaction, namely, ammonia synthesis.
Chiral response of single walled carbon nanotube based sensors to adsorption of amino acids: A theoretical model
Authors: Vardanega D. , Picaud F. , Girardet C.
Published: November 2007

Calculations of the interaction energy and dielectric responses of chiral single walled carbon nanotubes to the presence of amino acid enantiomers are carried out. A theoretical study is developed to show that the frequency shifts of selected nanotubes conveniently tailored to the size of the probed molecules and used in a resonator configuration can selectively detect different species of amino acids and the left- and right-handed enantiomers of these species. Criteria for an optimization of the adsorption energy and frequency response on the size and chiral angle of the nanotubes are given. It is found that a very small set of carbon tubes obeys these conditions.
Relaxation time, diffusion, and viscosity analysis of model asphalt systems using molecular simulation
Authors: Zhang Liqun , Greenfield Michael L.
Published: November 2007

Molecular dynamics simulation was used to calculate rotational relaxation time, diffusion coefficient, and zero-shear viscosity for a pure aromatic compound (naphthalene) and for aromatic and aliphatic components in model asphalt systems over a temperature range of 298–443 K. The model asphalt systems were chosen previously to represent real asphalt. Green–Kubo and Einstein methods were used to estimate viscosity at high temperature (443.15 K). Rotational relaxation times were calculated by nonlinear regression of orientation correlation functions to a modified Kohlrausch–Williams–Watts function. The Vogel–Fulcher–Tammann equation was used to analyze the temperature dependences of relaxation time, viscosity, and diffusion coefficient. The temperature dependences of viscosity and relaxation time were related using the Debye–Stokes–Einstein equation, enabling viscosity at low temperatures of two model asphalt systems to be estimated from high temperature (443.15 K) viscosity and temperature-dependent relaxation time results. Semiquantitative accuracy of such an equivalent temperature dependence was found for naphthalene. Diffusion coefficient showed a much smaller temperature dependence for all components in the model asphalt systems. Dimethylnaphthalene diffused the fastest while asphaltene molecules diffused the slowest. Neat naphthalene diffused faster than any component in model asphalts.
Helical instability of a rotating viscous liquid jet
Authors: Kubitschek J. P. , Weidman P. D.
Published: November 2007

Vertical rotating viscous liquid jet experiments show a clear preference for helical instabilities that evolve from initially planar disturbances at large rotation rates for fixed fluid properties. The laboratory setup for the experiments described herein was chosen as the nearest earth-based equivalent to a uniformly rotating viscous liquid column in the absence of gravity. In the ideal situation with stress-free boundaries, the preferred modes of linear temporal instability are theoretically known over the entire physical domain spanned by the Hocking parameter L=γ∕ρa3Ω2 and the rotational Reynolds number Re=a2Ω∕ν, where a is the column radius, Ω is its uniform angular velocity, and ρ, ν, and γ are, respectively, the fluid density, kinematic viscosity, and surface tension. The theoretical results show that instability in L-Re parameter space is dominated by three mode types: The axisymmetric mode, the n≥2 planar modes, and the first n=1 spiral mode. Experiments reveal that, in the L-Re region for which the uniformly rotating liquid column is dominated by planar modes of instability, the rotating liquid jet spontaneously gives rise to planar disturbances of mode n≥2 that rapidly evolve into helical instabilities. However, these observed instabilities are not the spiral normal modes that exist for n≥1 as posited in linear stability theory. In spite of obvious fundamental differences between the rotating liquid jet and the uniformly rotating liquid column, some remarkable similarities associated with initial growth rates, angular frequencies, and mode transitions between the two systems are found.
Frequency dependence of phase-synchronization time in nonlinear dynamical systems
Authors: Park Kwangho , Lai Ying-Cheng , Krishnamoorthy Satish
Published: November 2007

It has been found recently that the averaged phase-synchronization time between the input and the output signals of a nonlinear dynamical system can exhibit an extremely high sensitivity to variations in the noise level. In real-world signal-processing applications, sensitivity to frequency variations may be of considerable interest. Here we investigate the dependence of the averaged phase-synchronization time on frequency of the input signal. Our finding is that, for typical nonlinear oscillator systems, there can be a frequency regime where the time exhibits significant sensitivity to frequency variations. We obtain an analytic formula to quantify the frequency dependence, provide numerical support, and present experimental evidence from a simple nonlinear circuit system.
Dissociative recombination of H+(H2O)3 and D+(D2O)3 water cluster ions with electrons: Cross sections and branching ratios
Authors: Öjekull J. , Andersson P. U. , Någård M. B. , Pettersson J. B. C. , Marković N. , Derkatch A. M. , Neau A. , Al Khalili A. , Rosén S. , Larsson M. , Semaniak J. , Danared H. , Källberg A. , Österdahl F. , af Ugglas M.
Published: November 2007

Dissociative recombination (DR) of the water cluster ions H+(H2O)3 and D+(D2O)3 with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H+(H2O)3 in the energy range of 0.001–0.8eV, and relative cross sections have been measured for D+(D2O)3 in the energy range of 0.001–1.0eV. The DR cross sections for H+(H2O)3 are larger than previously observed for H+(H2O)n (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H+(H2O)3 mainly results in the formation of 3H2O+H (probability of 0.95±0.05) and with a possible minor channel resulting in 2H2O+OH+H2 (0.05±0.05). The dominating channels for DR of D+(D2O)3 are 3D2O+D (0.88±0.03) and 2D2O+OD+D2 (0.09±0.02). The branching ratios are comparable to earlier DR results for H+(H2O)2 and D+(D2O)2, which gave 2X2O+X (X=H,D) with a probability of over 0.9.
Charge storage characteristics of Au nanocrystals embedded in high-k gate dielectrics on Si
Authors: Wang Chen-Chan , Wu Jyun-Yi , Chiou Yan-Kai , Chang Che-Hao , Wu Tai-Bor
Published: November 2007

The charge storage characteristics of metal-oxide-semiconductor structures containing Au nanocrystals in atomic-layer-deposited high-k gate dielectrics were studied. Cross-sectional high-resolution transmission electron microscopy reveals that the Au nanocrystals are self-assembled in the high-k dielectric matrix after high temperature annealing in N2 ambient. The memory effect was observed from capacitance-voltage (C-V) relations and a satisfactory charge retention characteristic was obtained in the sample using Al2O3 as the gate dielectric than in the one using Hf2AlOx. Moreover, a saturation of electron storage in the metal-oxide-semiconductor capacitors was also observed.
Optimal control of the viscous Degasperis-Procesi equation
Authors: Tian Lixin , Shen Chunyu
Published: November 2007

This paper studies the problem for optimal control of the viscous Degasperis-Procesi equation. The existence and uniqueness of weak solution to the equation are proved in a short interval. The optimal control of the viscous Degasperis-Procesi equation under boundary condition is given and the existence of optimal solution to the equation is proved.
On the properties of electrostatic drift and sound modes in radially and axially inhomogeneous bounded plasmas
Authors: Vranjes J. , Poedts S.
Published: November 2007

The behavior of electrostatic drift and ion sound waves is discussed in plasmas with an equilibrium density gradient both perpendicular and parallel to the ambient magnetic field. In spatially unlimited plasmas, and in Cartesian geometry, the mode amplitude is calculated for several profiles of the equilibrium density. Exact analytical solutions are found. Cylindric plasmas bounded in the radial direction and bounded or unbounded in the axial direction are also investigated in the presence of equilibrium density gradients in both the radial and axial directions. Exact analytical solutions are found in terms of the Kummer confluent hypergeometric functions, describing standing oscillatory patterns in the radial and axial directions, associated with the drift mode propagating in the poloidal (θ) direction.
Atomic force microscopy: Loading position dependence of cantilever spring constants and detector sensitivity
Authors: Vakarelski Ivan U. , Edwards Scott A. , Dagastine Raymond R. , Chan Derek Y. C. , Stevens Geoffrey W. , Grieser Franz
Published: November 2007

A simple and accurate experimental method is described for determining the effective cantilever spring constant and the detector sensitivity of atomic force microscopy cantilevers on which a colloidal particle is attached. By attaching large (approximately 85μm diameter) latex particles at various positions along the V-shaped cantilevers, we demonstrate how the normal and lateral spring constants as well as the sensitivity vary with loading position. Comparison with an explicit point-load theoretical model has also been used to verify the accuracy of the method.
Investigation of the roundtrip cavity loss in laser diode pumped erbium:ytterbium-phosphate glass microchip lasers
Authors: Liu Shujing , Song Feng , Cai Hong , Li Teng , Zhang Xin , Wu Zhaohui , Tian Jianguo
Published: November 2007

We present a method for determination of the roundtrip cavity loss in the laser diode pumped erbium:ytterbium-codoped phosphate glass microchip laser. Slope efficiency and laser threshold were measured in the experiment and their dependencies on roundtrip cavity loss were derived through rate equations. According to the energy levels, cumulative upconversion and cooperative upconversion are taken into consideration to ensure the accuracy of the derivation. Roundtrip cavity losses in different cavity configurations were investigated.
Microstrip resonator for microwaves with controllable polarization
Authors: Mayer Alegre T. P. , Torrezan A. C. , Medeiros-Ribeiro G.
Published: November 2007

In this work, the authors implemented a resonator based on microstrip cavities that permit the generation of microwaves with arbitrary polarization. Design, simulation, and implementation of the resonators were performed using standard printed circuit boards. The electric field distribution was mapped using a scanning probe cavity perturbation technique. Electron spin resonance using a standard marker was carried out in order to verify the polarization control from linear to circular.
Nanocubic boron nitride/nanodiamond multilayer structures
Authors: Li H. Q. , Leung K. M. , Ma K. L. , Ye Q. , Chong Y. M. , Zou Y. S. , Zhang W. J. , Lee S. T. , Bello I.
Published: November 2007

Nanocubic boron nitride/nanodiamond (N-cBN/ND) multilayer structures with each alternating layer being ∼100nm thick have been prepared by magnetron sputter and microwave plasma enhanced chemical vapor depositions. These multilayers exhibit remarkable properties, in particular, the mechanical properties. The multilayer structure is characteristic with (i) extreme hardness (82GPa) considerably surpassing the values of the individual materials from which the multilayer is composed, (ii) high surface smoothness, (iii) significantly reduced film stress when compared with a single cBN layer of equivalent thickness, and (iv) great chemical stability. The N-cBN/ND multilayers developed have therefore important implications in mechanical and chemically resistant applications.
High energy pulsed inductive thruster modeling operating with ammonia propellant
Authors: Mikellides Pavlos G. , Villarreal James K.
Published: November 2007

Numerical modeling of the pulsed inductive thruster operating with ammonia propellant at high energy levels, utilized a time-dependent, two-dimensional, and axisymmetric magnetohydrodynamics code to provide bilateral validation of experiment and theory and offer performance insights for improved designs. The power circuit model was augmented by a plasma voltage algorithm that accounts for the propellant’s time-dependent resistance and inductance to properly account for plasma dynamics and was verified using available analytic solutions of two idealized plasma problems. Comparisons of the predicted current waveforms to experimental data exhibited excellent agreement for the initial half-period, essentially capturing the dominant acceleration phase. Further validation proceeded by comparisons of the impulse for three different energy levels, 2592, 4050, and 4608J and a wide range of propellant mass values. Predicted impulse captured both trends and magnitudes measured experimentally for nominal operation. Interpretation of the modeling results in conjunction to experimental observations further confirm the critical mass phenomenon beyond which efficiency degrades due to elevated internal energy mode deposition and anomalous operation.
Anisotropic magnetoresistance in colossal magnetoresistive La1−xSrxMnO3 thin films
Authors: Yau Jeng-Bang , Hong X. , Posadas A. , Ahn C. H. , Gao W. , Altman E. , Bason Y. , Klein L. , Sidorov M. , Krivokapic Z.
Published: November 2007

We report on magnetic field and temperature-dependent measurements of the anisotropic magnetoresistance (AMR) in epitaxial La1−xSrxMnO3 (LSMO) thin films. While in 3d ferromagnetic alloys increasing the magnetization, either by reducing the temperature or increasing the magnetic field, increases the AMR, we find that in LSMO films the AMR dependence on magnetization displays nonmonotonic behavior which becomes particularly pronounced in lightly doped compounds. We believe that this behavior is related to the inhomogeneity exhibited by these materials.
Marangoni flow on an inkjet nozzle plate
Authors: de Jong Jos , Reinten Hans , Wijshoff Herman , van den Berg Marc , Delescen Koos , van Dongen Rini , Mugele Frieder , Versluis Michel , Lohse Detlef
Published: November 2007

In piezo inkjet printing, nozzle failures are often caused by an ink layer on the nozzle plate. It is experimentally shown that the ink layer at the nozzle is formed through streamers of ink, emanating from a central ink band on the nozzle plate. The streamers propagate over a wetting nanofilm of 13nm thickness, directed toward the actuated nozzles. The motion of the front end of the streamers follows a power law in time with an exponent 12. The observations are consistent with a surface tension gradient driven flow. The origin of the Marangoni flow is an effective lower surfactant concentration of the ink around the nozzle.
A new correlation method for high sensitivity current noise measurements
Authors: Ciofi Carmine , Scandurra Graziella , Merlino Rosario , Cannatà Gianluca , Giusi Gino
Published: November 2007

The properties of a differential transconductance amplifier coupled with a four channel measurement system are exploited in order to reach a very high sensitivity in current noise measurements. In particular, it is demonstrated that, in proper conditions, the noise contributions coming from the active and passive devices that make up the transresistance amplifier can be virtually eliminated. Moreover, the proposed measurement method allows the evaluation of the impedance of the device under test from noise measurement data. Actual measurement results are also reported that demonstrate the effectiveness of the proposed approach.
Water passivation effect on polycrystalline silicon nanowires
Authors: Lin Horng-Chih , Su Chun-Jung , Hsiao Cheng-Yun , Yang Yuh-Shyong , Huang Tiao-Yuan
Published: November 2007

Defects present in the grain boundaries of polycrystalline materials are known to impede carrier transport inside the materials, and the electronic device performance having such materials as active channels will be adversely affected. In this work, dramatic improvement in device performance was observed as field-effect transistors with polycrystalline silicon nanowire (poly-SiNW) channels were exposed to a wet environment. Passivation of defects in the poly-SiNW by H+ and/or OH− contained in the aqueous solution is proposed to explain the phenomenon.
Deep levels and carrier compensation in V-doped semi-insulating 4H-SiC
Authors: Son N. T. , Carlsson P. , Gällström A. , Magnusson B. , Janzén E.
Published: November 2007

Electron paramagnetic resonance was used to study semi-insulating (SI) 4H-SiC substrates doped with vanadium (V) in the range of 5.5×1015–1.1×1017cm−3. Our results show that the electrical activation of V is low and hence only in heavily V-doped 4H-SiC, vanadium is responsible for the SI behavior, whereas in moderately V-doped substrates, the SI properties are thermally unstable and determined by intrinsic defects. We show that the commonly observed thermal activation energy Ea∼1.1eV in V-doped 4H–SiC may be related to deep levels of the carbon vacancy.
Antiferroelectric hysteresis loops with two exchange constants using the two dimensional Ising model
Authors: Misirlioglu I. B. , Pintilie L. , Boldyreva K. , Alexe M. , Hesse D.
Published: November 2007

Monte-Carlo simulations are carried out to reproduce hysteresis loops of antiferroelectric single crystals using an Ising Hamiltonian in two dimensions where pseudospin interactions are defined by two constants. It is shown that with this approach, hysteresis loops can be obtained in very good qualitative agreement with the experiments. While our approach is similar to that of Milhazes et al. [Phys. Status Solidi B 242, 1141 (2005)], we also demonstrate that the hysteresis loop shapes heavily depend on the ratio of the electrostaticlike term to the intrinsic Hamiltonian of the system.
Effect of oxygen concentration on the magnetic properties of La2CoMnO6 thin films
Authors: Guo H. Z. , Gupta A. , Zhang Jiandi , Varela M. , Pennycook S. J.
Published: November 2007

The dependence of the magnetic properties on oxygen concentration in epitaxial La2CoMnO6 thin films deposited on (100)-oriented SrTiO3 substrates has been investigated by varying the oxygen background pressure during growth using pulsed laser deposition. Two distinct ferromagnetic (FM) phases are revealed, and the relative fraction varies with the oxygen concentration. The existence of oxygen vacancies induces the local vibronic Mn3+–O–Co3+ superexchange interactions in direct competition with the static FM Mn4+–O–Co2+ interactions. This results in the appearance of a new low temperature FM phase and suppression of the high-temperature FM phase, creating two distinct magnetic phase transitions.
Effect of Yb concentration on the resistivity and lifetime of CdTe:Ge:Yb codoped crystals
Authors: Sochinskii N. V. , Abellán M. , Rodríguez-Fernández J. , Saucedo E. , Ruiz C. M. , Bermúdez V.
Published: November 2007

The resistivity and electron lifetime of CdTe:Ge:Yb crystals are reported, demonstrating that the effect of Yb concentration is crucial for accurate electrical compensation. It is also demonstrated that the codoping of CdTe with Ge as deep donor and with Yb as rare-earth element could be a promising way to obtain semiinsulating CdTe crystals with good transport properties. High resistivity (5×109Ωcm) and lifetime (9μs) were obtained, thus confirming the beneficial effect of rare-earth doping.
Ductility at the nanoscale: Deformation and fracture of adhesive contacts using atomic force microscopy
Authors: Pradeep N. , Kim D.-I. , Grobelny J. , Hawa T. , Henz B. , Zachariah M. R.
Published: November 2007

Fracture of nanosize contacts formed between spherical probes and flat surfaces is studied using an atomic force microscope in an ultrahigh vacuum environment. Analysis of the observed deformation during the fracture process indicates significant material extensions for both gold and silica contacts. The separation process begins with an elastic deformation followed by plastic flow of material with atomic rearrangements close to the separation. Classical molecular dynamics studies show similarity between gold and silicon, materials that exhibit entirely different fracture behavior at macroscopic scale. This direct experimental evidence suggests that fracture at nanoscale occurs through a ductile process.
Investigation of violet InGaN laser diodes with normal and reversed polarizations
Authors: Yen Sheng-Horng , Kuo Yen-Kuang , Tsai Meng-Lun , Hsu Ta-Cheng
Published: November 2007

The polarity is a special property for III-nitride materials with wurtzite structure along different orientations. The influence of normal and reversed polarizations on laser performance of the violet laser diodes with Ga-face and N-face configurations is studied numerically. Specifically, the laser performance, band diagram, carrier confinement, and emission wavelength are investigated. The results show that the threshold current is improved and emission wavelength is redshifted when the laser diode is with reversed polarization.
Superconducting microrings as magnetic pinning centers
Authors: Gillijns W. , Silhanek A. V. , Moshchalkov V. V.
Published: November 2007

The nucleation of the superconducting condensate in an Al film deposited on top of a periodic array of microsized Pb rings is investigated using transport measurements. We demonstrate that these Pb rings form tunable pinning sites which can be switched at will to repel or attract vortices in the Al film, depending on their magnetic history. After zero field cooling, a repulsive interaction between the rings and the vortices is observed, while after field cooling, the interaction becomes attractive. The flexibility of such current-induced pinning centers can lead to an enhanced control over the vortex motion.
Energy transfer boosted by photonic crystals with metal film patterns
Authors: Li Mingzhu , Liao Qing , Zhang Jianping , Jiang Lei , Song Yanlin , Zhu Daoben , Chen Dong , Tang Fangqiong , Wang Xue-Hua
Published: November 2007

An active plasmonic device is fabricated by introducing a photonic crystal structure into an energy transfer system across a metal film. It is demonstrated that the stopband of the photonic crystal plays a key role in improving the efficiency of the energy transfer. A well-designed stopband can enhance the emission intensity of the device by over ten times compared with that of a similar planar device. Active plasmonic devices based on photonic crystal structure will provide promising materials for highly efficient optic devices.
An approach to further improve piezoelectric properties of (K0.5Na0.5)NbO3-based lead-free ceramics
Authors: Du Hongliang , Zhou Wancheng , Luo Fa , Zhu Dongmei , Qu Shaobo , Pei Zhibin
Published: November 2007

An approach to further improve piezoelectric properties of (1−x)(K0.5Na0.5)NbO3–xLiNbO3 (KNLN) ceramics, i.e., the optimum poling temperatures (Tp) of KNLN ceramics should be chosen near the polymorphic phase transition temperatures, is proposed. This is contrary to conventional wisdom associated with electrical poling of ceramics. Piezoelectric constant d33 of KNLN (x=0.07) ceramics increases from 210to274pC∕N by selecting optimum Tp. This result indicates that this approach is very effective in improving piezoelectric properties of KNLN ceramics. Moreover, this approach can also be applied to other (K0.5Na0.5)NbO3 based ceramics.
Morphotropic phase boundary and piezoelectric properties of (Bi1∕2Na1∕2)TiO3–(Bi1∕2K1∕2)TiO3–KNbO3 lead-free piezoelectric ceramics
Authors: Fan Guifen , Lu Wenzhong , Wang Xiaohong , Liang Fei
Published: November 2007

The crystal structure and piezoelectric properties of ternary ceramics x(Bi1∕2Na1∕2)TiO3–y(Bi1∕2K1∕2)TiO3–zKNbO3 (abbreviated as BNT-BKT-KN100x∕100y∕100z) system have been investigated. Effects of BKT and KN on the crystalline structure were examined. The morphotropic phase boundary (MPB) phase diagram of BNT-BKT-KN ternary system was determined by x-ray diffraction patterns from sintered specimens. Near the MPB, BNT-BKT-KN82∕16∕2 ceramics had good performances with piezoelectric constant d33=215pC∕N which reached a maximum value in this ternary system and planar electromechanical coupling factor kp=35%. Besides, BNT-BKT-KN87∕10∕3 ceramics had good performances with piezoelectric constant d33=138pC∕N and electromechanical coupling factor kp=38% which attained a maximum value in this ternary system.
Polycrystalline silicon thin-film transistors on quartz fiber
Authors: Sugawara Yuta , Uraoka Yukiharu , Yano Hiroshi , Hatayama Tomoaki , Fuyuki Takashi , Nakamura Toshihiro , Toda Sadayuki , Koaizawa Hisashi , Mimura Akio , Suzuki Kenkichi
Published: November 2007

We demonstrate the fabrication of polycrystalline silicon (poly-Si) thin-film transistors (TFTs) on a thin quartz fiber for the first time. The poly-Si used in the active layer of the TFTs was prepared by excimer laser annealing of an amorphous Si thin film deposited on the fiber. Top-gated TFTs were fabricated on the fiber, and a field effect mobility of 10cm2∕Vs was obtained. The proposed TFTs on a thin quartz fiber, named fiber TFTs, have potential application in microelectronic devices using TFTs fabricated on one-dimensional substrates.
Structural and compositional investigation of yttrium-doped HfO2 films epitaxially grown on Si (111)
Authors: Yang Z. K. , Lee W. C. , Lee Y. J. , Chang P. , Huang M. L. , Hong M. , Yu K. L. , Tang M.-T. , Lin B.-H. , Hsu C.-H. , Kwo J.
Published: November 2007

Cubic phase yttrium-doped HfO2 (YDH) ultrathin films were grown on Si (111) substrates by molecular beam epitaxy. Thorough structural and morphological investigations by x-ray scattering and transmission electron microscopy reveal that the YDH thin films are epitaxially grown on the Si substrates with (111)YDH‖(111)Si and [101¯]YDH‖[11¯0]Si. The interface between YDH and Si is atomistic sharp and free of interfacial layer. We have also determined the yttrium content of YDH films to be 19% by using anomalous x-ray diffraction (AXD) across Y k edge and angle resolved x-ray photoelectron spectroscopy (AR-XPS). The agreement between the AXD and AR-XPS results manifests that the incorporated Y atoms homogeneously substitute Hf atoms in the crystalline lattice and form a substitutional solid solution.
Effects of water stress and soil type on photosynthesis, leaf water potential and yield of olive trees (Olea europaea L. cv. Chemlali Sfax)
Authors: Rouina B. Ben , Trigui A. , d'Andria R. , Boukhris M. , Chaïeb M.
Published: November 2007

In Tunisia, olives are grown under severe rain-fed, arid conditions. To determine the behaviour of olive trees (cv. Chemlali Sfax) during the severe drought affecting Tunisian arid areas in 2002, a range of physiological parameters were investigated in three adjacent orchards. Two olive orchards were rain-fed, one located on a sandy soil, and the other on a sandy-loam clay soil. A third orchard was also located on sandy soil, but received remedial irrigation (415 mm of water per year; ~40% of olive evapotranspiration). Predawn leaf water potential (Ψpd) did not fall below –1.52 MPa for irrigated olive trees. However, a large decrease in Ψpd was observed for rain-fed olive trees in the same period with Ψpd measured at about –3.2 MPa on sandy soil and –3.6 MPa on sandy-loam clay soil. At the same time, the minimal leaf water potential recorded at midday (Ψmin) decreased to –4.15 MPa and –4.71 MPa in the rain-fed trees for sandy and sandy-loam clay soil, respectively. For irrigated trees, the Ψmin was –1.95 MPa. These results were associated with relative water content, which varied from 80% for irrigated trees to 54 and 43.6%, respectively, for rain-fed trees and trees subjected to severe drought. In August, when the relative water content values were less than 50%, a progressive desiccation in the outer layer of canopy and death of terminal shoots were observed in trees, which grew on the sandy-loam clay soil. Furthermore, low soil water availability also affected (negatively) the net photosynthetic rate in rain-fed orchards (10.3 µmol/m2.s for irrigated trees v. 5.3 µmol/m2.s in rain-fed trees on sandy soil) and stomatal conductance (98.5 mmol/m2.s v. 69.3 mmol/m2.s). However, it improved water use efficiency (7.6 v. 4.7 µmol CO2/mmol H2O), which increased by more than 50% in both groups of rain-fed trees compared with the irrigated ones. We can conclude that olive trees respond to drought by showing significant changes in their physiological and biological mechanisms. These results also help our understanding of how olive trees cope with water stress in the field and how marginal soils can restrict growth and lower yields.
High nitrogen during growth reduced glucoraphanin and flavonol content in broccoli (Brassica oleracea var. italica) heads
Authors: Jones R. B. , Imsic M. , Franz P. , Hale G. , Tomkins R. B.
Published: November 2007

Broccoli (Brassica oleracea var. italica) heads are commonly consumed in the Western diet and frequent consumption is thought to help protect against certain cancers and cardiovascular disease. Broccoli heads contain relatively high levels of glucosinolates and flavonols, thought to be the key phytochemicals that contribute to the health benefits gained upon consumption. In this study, we investigated the effect of applied nitrogen (N) at either 0, 15, 30 or 60 kg/ha, or 30, 60, 90 or 150 kg/ha with applied sulfur (S) at 50 or 100 kg/ha on the glucosinolates glucoraphanin, glucobrassicin and progoitrin, and the flavonols quercetin and kaempferol in broccoli cv. Marathon florets. Trials were conducted in two sites in either heavy clay or sandy loam to also assess the effect of soil type on phytochemical content. Application rates were based around recommended N and S applications for this crop in south-east Australia. N applications over 30 kg/ha caused a decrease in the content of glucoraphanin (18–34%) and both flavonols (20–38%). Progoitrin content was not affected while glucobrassicin increased by up to 44% with N applications >30 kg/ha. S applications of 50 or 100 kg/ha had no significant effect on either glucosinolates or flavonols. Crop yield (fresh weight), however, was significantly depressed (up to 40%) by N applications below 60 kg/ha. Fresh weight was also significantly depressed in plants grown in heavy clay compared with plants grown in a sandy loam, and phytochemical content increased, possibly due to a concentration effect. Therefore, low N applications to optimise phytochemicals may be only commercially useful if growers are producing mini-broccoli heads, as levels required to optimise phytochemical content (<30 kg/ha) also caused a significant decline in yield.