bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcareous phytoplankton response to the half century of interannual climatic variability in Santa Barbara Basin (California)
Authors: De Bernardi Bianca , Ziveri Patrizia , Erba Elisabetta , Thunell Robert C.
Published: June 2008

A high‐resolution study of calcareous phytoplankton in a box core from the Santa Barbara Basin (SBB) reveals floral assemblage fluctuations which can be related to climatic and paleoceanographic changes during the last half century (1940–1996). In particular, Gephyrocapsa oceanica production increased during El Niño periods, in response to high temperatures, silica depletion, and increased iron availability. Conversely, Helicosphaera carteri flux increases in conjunction with lower surface temperatures associated with La Niña episodes. Increasing abundances of Florisphaera profunda and Umbilicosphaera sibogae after 1970 reflect a warming trend and increased stratification within the basin associated with the warm phase of the Pacific Decadal Oscillation (PDO). Conversely, increased abundances of Coccolithus pelagicus and Calcidiscus leptoporus before 1970 mark the cold phase of PDO. These coccolithophore production rate data are consistent with instrumental records of surface and thermocline temperatures monitored since 1950. This is the first study to document the response of calcareous phytoplankton to surface water warming occurring in SBB since 1970.
Comparison of instantaneous and constant‐rate stream tracer experiments through non‐parametric analysis of residence time distributions
Authors: Payn Robert A. , Gooseff Michael N. , Benson David A. , Cirpka Olaf A. , Zarnetske Jay P. , Bowden W. Breck , McNamara James P. , Bradford John H.
Published: June 2008

Artificial tracers are frequently employed to characterize solute residence times in stream systems and infer the nature of water retention. When the duration of tracer application is different between experiments, tracer breakthrough curves at downstream locations are difficult to compare directly. We explore methods for deriving stream solute residence time distributions (RTD) from tracer test data, allowing direct, non‐parametric comparison of results from experiments of different durations. Paired short‐ and long‐duration field experiments were performed using instantaneous and constant‐rate tracer releases, respectively. The experiments were conducted in two study reaches that were morphologically distinct in channel structure and substrate size. Frequency‐ and time domain deconvolution techniques were used to derive RTDs from the resulting tracer concentrations. Comparisons of results between experiments of different duration demonstrated few differences in hydrologic retention characteristics inferred from short‐ and long‐term tracer tests. Because non‐parametric RTD analysis does not presume any shape of the distribution, it is useful for comparisons across tracer experiments with variable inputs and for validations of fundamental transport model assumptions.
Diagnostic analysis of water balance variability: A comparative modeling study of catchments in Perth, Newcastle, and Darwin, Australia
Authors: Samuel Jos M. , Sivapalan Murugesu , Struthers Iain
Published: June 2008

A comparative study is performed to explore interactions between climate variability and landscape factors that control water balance variability in three diverse regions of Australia: Perth (temperate with distinct dry summers); Newcastle (temperate with no distinct dry season); and Darwin (tropical region affected by monsoons). This comparative analysis is carried out through adoption of a common conceptual model. The similarity and differences between the three catchments are explored through evaluation of signatures of streamflow and soil moisture variability, and systematic sensitivity analysis with respect to parameters representing various landscape characteristics. The results of the analysis show that the biggest contributor to the differences between the catchments is the distribution of soil depth and the soil's drainage characteristics. The second factor is climate, as exemplified by the (annual) climatic dryness index and the intra‐annual (seasonal) variability of both rainfall and potential evaporation, and associated rainfall intensity patterns, and their interactions with the soil properties (i.e., soil depth and the soil's drainage characteristics). In Perth and Darwin, climate seasonality is responsible for a seasonal switching on/off of subsurface stormflow at the start/end of the wet season, respectively. In Newcastle, where soil moisture contents hover near the field capacity value throughout the year, subsurface stormflow occurs frequently throughout the year, with event‐based switching on/off in response to individual storms of moderate magnitude and temporal clustering of small storms. In addition, in rare circumstance, surface runoff is triggered in response to extreme storm events and temporal clustering of moderate to large storm events.
Simulating the formation of Hurricane Katrina (2005)
Authors: Jin Yi , Peng Melinda S. , Jin Hao
Published: June 2008

The formation of Hurricane Katrina (2005) is simulated using COAMPS® with high resolution (27 km, 9 km and 3 km grid spacing). Whereas most Atlantic hurricanes form in conjunction with easterly waves, no clear synoptic‐scale tropical disturbance was evident as a precursor for Katrina. The triply‐nested simulation, initialized 66 h before Katrina was identified as a tropical depression, successfully predicts the location and timing of Katrina's formation in the 3 km domain. The organization of the cyclone is associated with concentrated precipitation resolved with microphysics in the southeast part of the circulation. The storm does not form in the 9 km domain when the Kain‐Fritsch cumulus scheme and the microphysics are used. However, a separate simulation using microphysics alone in the 9 km domain captures Katrina's formation, though with less organized structure. This study suggests that explicitly resolving clouds in high‐resolution models holds promise for predicting tropical cyclone (TC) formation.
Variations of surface water extent and water storage in large river basins: A comparison of different global data sources
Authors: Papa F. , Güntner A. , Frappart F. , Prigent C. , Rossow W. B.
Published: June 2008

For the period 2003–2004 and for six large river basins, the present study compares monthly time series of multi‐satellite‐derived surface water extent with other independent global data sets related to land water dynamics, such as water mass variations monitored by GRACE, simulated surface and total water storage from WGHM, water levels from altimetry, and GPCP precipitation estimates. In general, the datasets show a strong agreement with each other at seasonal timescale. In particular, over the Amazon and the Ganges basins, analysis of seasonal phase differences and hysteresis behavior between surface water extent, water level and storage reveal the complex relations between water extent and storage variations and the different effects of water transport processes within large river basins. The results highlight the value of combining multi‐satellite techniques for retrieving surface water storage dynamics.
Alignment of Linear Biochemical Pathways Using Protein Structural Classification
Authors: Hariharaputran Sridhar , Töpel Thoralf , Oberwahrenbrock Timm , Hofestädt Ralf
Published: June 2008

Metabolic, signaling and regulatory pathways form the basis of biological processes and are important for the analysis of cellular behavior and evolution. This paper presents an approach of aligning biochemical pathways on the basis of the structure of involved proteins and their classification. The suitable information is retrieved from an integrated database system.SIGNALIGN is available at: http://agbi.techfak.uni-bielefeld.de/signalign/index.jsp
Local Monte Carlo for electrostatics in anisotropic and nonperiodic geometries
Authors: Thompson David , Rottler Jörg
Published: June 2008

We present an implementation of a local Monte Carlo algorithm for simulating charged particles in anisotropic and nonperiodic geometries. Specifically, we consider a quasi-two-dimensional periodic slab geometry with an either infinite or finite third dimension. For the infinite case, we show that the method generates accurate electrostatics equivalent to standard two-dimensional Ewald formulas. We then implement constant charge or constant potential (Dirichlet) boundary conditions, which frequently occur in experimental studies of charged complex fluids or polyelectrolytes. As a demonstration of the versatility of the approach, we compute ion density profiles in front of oppositely charged surfaces (the electric double layer) and find excellent agreement with theory in known analytic limits.
Time reversal duality of magnetohydrodynamic shocks
Authors: Goedbloed J. P.
Published: June 2008

The shock conditions in magnetohydrodynamics (MHD) are reduced to their most concise, three-parameter, distilled form by consistent use of the scale independence of the MHD equations and of the de Hoffmann–Teller transformation. They then exhibit a distinct time reversal duality between entropy-allowed shocks and entropy-forbidden jumps. This yields a new classification of MHD shocks by means of the monotonicity properties with respect to upstream and downstream Alfvén Mach numbers, it exhibits the central role of intermediate discontinuities, and permits straightforward construction of all relevant dimensionless quantities of the shocks. An exhaustive overview is presented of solutions in the different parameter regimes.
Turbulence and heat exchange in condensing vapor-liquid flow
Authors: Lakehal Djamel , Fulgosi Marco , Banerjee Sanjoy , Yadigaroglu George
Published: June 2008

Turbulence and heat exchange during condensation of a vapor stream countercurrently flowing to a subcooled liquid stream in a slightly inclined channel has been investigated by direct numerical simulation (DNS). Condensation rates and imposed pressure gradients have been varied, and capillary-gravity waves have been allowed to develop at the (deformable) vapor-liquid interface. These simulations extend our previous DNS of turbulence and scalar exchange in stratified gas-liquid flows without condensation. The previous studies indicated that for conditions in which the gas-liquid interface remained continuous, i.e., did not “break,” scalar exchange rates on both the gas and liquid sides were largely determined by sweeps which brought high momentum fluid from the bulk flow to the interface. As sweep frequencies were found to scale with interfacial friction velocities, scalar exchange coefficients could be parametrized with a surface renewal theory. The issue addressed in the current work is how these findings are altered by condensation which acts somewhat like suction through a wall on the vapor side and injection through a wall on the liquid side. Both suction and injection have been found to affect shear stresses, turbulence characteristics, and scalar exchange rates, and hence similar effects might be expected during condensation. The present simulations indicate that the turbulence characteristics in both phases are affected, with turbulence intensities and Reynolds stresses being enhanced on the vapor side and attenuated on the liquid side. For a given imposed pressure gradient, the interfacial shear stress decreases as a result of the interfacial momentum exchange due to condensation. Interfacial waves are also found to be damped by condensation and the streamwise vortical structures on the liquid side are attenuated. The frequencies of sweeps and ejections, however, do scale with the interfacial friction velocity, reduced due to condensation, as does the liquid-side heat transfer coefficient. The simulations indicate that the scaling relationship between the interfacial friction velocity and the liquid-side heat transfer coefficient is similar to that in the absence of condensation, although the interfacial friction velocity itself is different, being dependent on condensation rates. As condensation rates depend in turn on the liquid-side heat transfer, their prediction becomes a coupled problem. A procedure for determining condensation rates as a function of imposed pressure gradient and liquid subcooling is derived from the simulations.
Weight growth due to resonant simulation particles and a modified δf algorithm with smooth switching between δf and total-f methods
Authors: Qin Hong , Davidson Ronald C. , Startsev Edward A.
Published: June 2008

When applying the standard δf particle-in-cell simulation method to simulate linear and nonlinear collective instabilities with coherent structures, wave-particle interaction may result in large weight growth for resonant or nearly resonant simulation particles. In this paper, we demonstrate that the large noise associated with the large weight of nearly resonant simulation particles can produce significant error fields at the nonlinear stage of the instability. To overcome this deleterious effect, we have developed a modified δf method that contains a smooth switching algorithm between the δf and total-f methods. Before the switch, the simulation effectively makes use of the desirable low-noise feature of the δf method for small weight to accurately follow unstable mode structures. When the weight function becomes large during the nonlinear phase, the low-noise advantage of the δf method ceases to be significant and the simulation is switched to the total-f method to avoid the large noise induced by nearly resonant simulation particles. This algorithm has been successfully applied to simulation studies of the electrostatic Harris instability driven by large temperature anisotropy in high-intensity charged particle beams typical of applications in high current accelerators, including high-energy density physics and heavy ion fusion.
Electronic structure of CeF from frozen-core four-component relativistic multiconfigurational quasidegenerate perturbation theory
Authors: Tatewaki Hiroshi , Yamamoto Shigeyoshi , Watanabe Yoshihiro , Nakano Haruyuki
Published: June 2008

We have investigated the ground state and the two lowest excited states of the CeF molecule using four-component relativistic multiconfigurational quasidegenerate perturbation theory calculations, assuming the reduced frozen-core approximation. The ground state is found to be (4f1)(5d1)(6s1), with Ω=3.5, where Ω is the total electronic angular momentum around the molecular axis. The lowest excited state with Ω=4.5 is calculated to be 0.104eV above the ground state and corresponds to the state experimentally found at 0.087eV. The second lowest excited state is experimentally found at 0.186eV above the ground state, with Ω=3.5 based on ligand field theory calculations. The corresponding state having Ω=3.5 is calculated to be 0.314eV above the ground state. Around this state, we also have the state with Ω=4.5. The spectroscopic constants Re, ωe, and ν(1-0) calculated for the ground and first excited states are in almost perfect agreement with the experimental values. The characteristics of the CeF ground state are discussed, making comparison with the LaF+ and LaF molecules. We denote the d- and f-like polarization functions as d* and f*. The chemical bond of CeF is constructed via {Ce3.6+(5p6d*0.3f*0.1)F0.6−(2p5.6)}3+ formation, which causes the three valence electrons to be localized at Ce3.6+.
Solutions for turbulent buoyant plumes rising from circular sources
Authors: Michaux G. , Vauquelin O.
Published: June 2008

Analytical solutions are developed for turbulent plumes rising from circular sources of positive buoyancy in a quiescent environment of uniform density. From governing equations written in a form which encompasses both the Boussinesq and non-Boussinesq cases, we derive analytical expressions for all plume variables (radius, velocity, and density deficit) in terms of a single quantity Γ, called the plume function. For given source conditions, we then show that Γ (and, subsequently, all plume variables) can be evaluated at any height from two integral functions which are defined for lazy and forced plumes. For a practical use, these integral functions are given in tables. Moreover, exact values and locations of the maximum velocity and the plume neck are determined.
Structural, vibrational, and dielectric properties of a Ba0.5Sr0.5TiO3 thin film: Temperature and electric field dependence from Raman spectroscopy, x-ray diffraction, and microwave measurements
Authors: Bouyanfif H. , Suherman P. M. , Jackson T. J. , El Marssi M. , Hriljac J.
Published: June 2008

We present a Raman spectroscopy study of the phase transition occurring in a Ba0.5Sr0.5TiO3 thin film deposited by ablation laser on a MgO substrate. This Raman investigation is compared to x-ray diffraction studies of the temperature dependence of the structure and of the dielectric properties at microwave frequencies. These different probes evidence a diffuse phase transition in the range of 243–283K from the low temperature ferroelectric-tetragonal phase to the high temperature paraelectric cubic phase. Stabilization of the tetragonal phase in the thin film down to 83K was observed instead of the expected transition to an orthorhombic phase below 190K. This stabilization may be attributed to the tensile stress induced by the substrate. A careful analysis of the frequency dependence of the dielectric response suggested that the observed tunability and dielectric loss were determined by extrinsic effects such as charged defects and/or depletion layers.
Catalytic role of carbons in methane decomposition for CO- and CO2-free hydrogen generation
Authors: Huang Liping , Santiso Erik E. , Nardelli Marco Buongiorno , Gubbins Keith E.
Published: June 2008

Decomposition of methane is an environmentally attractive approach to CO- and CO2-free hydrogen production. Using first principles calculations at the density functional theory level, our studies demonstrate that the defective carbons can be used as catalysts for methane decomposition, without the need for other catalysts, such as transition metals or oxides, and the catalytic sites can be regenerated by the deposition of carbon decomposed from methane, to make the hydrogen production a continuous process. Additionally, since no other gases are produced in the process, the cost of CO2 sequestration and hydrogen purification from CO contamination will be dramatically reduced.
Pair correlation functions in mixtures of Lennard-Jones particles
Authors: Ben-Naim Arieh , Mountain Raymond
Published: June 2008

The pair correlation functions for a mixture of two Lennard–Jones particles were computed by both the Percus–Yevick equations and by molecular dynamics. The changes in the pair correlation function resulting from changes in the composition of the mixtures are quite unexpected. Essentially, identical changes are obtained from the Percus–Yevick equations and from molecular dynamics simulations. The molecular reason for this unexpected behavior is discussed.
A general statistical test for correlations in a finite-length time series
Authors: Hanson Jeffery A. , Yang Haw
Published: June 2008

The statistical properties of the autocorrelation function from a time series composed of independently and identically distributed stochastic variables has been studied. Analytical expressions for the autocorrelation function’s variance have been derived. It has been found that two common ways of calculating the autocorrelation, moving-average and Fourier transform, exhibit different uncertainty characteristics. For periodic time series, the Fourier transform method is preferred because it gives smaller uncertainties that are uniform through all time lags. Based on these analytical results, a statistically robust method has been proposed to test the existence of correlations in a time series. The statistical test is verified by computer simulations and an application to single-molecule fluorescence spectroscopy is discussed.
Fabrication and magnetism of Fe65Co35-MgF2 granular films for high frequency application
Authors: Yao Dongsheng , Ge Shihui , Zhang Bangmin , Zuo Huaping , Zhou Xueyun
Published: June 2008

A series of (Fe65Co35)x(MgF2)1−x films with different metal volume fraction x was fabricated by magnetron sputtering. High resolution transmission electron micrographs show that the film consists of bcc Fe65Co35 particles uniformly embedded in an amorphous insulating MgF2 matrix with particle size around a few nanometers. The research results reveal that high sputtering power (200 W) leads to the occurrence of FeCo fluorides, which are harmful to soft magnetic properties. For the samples fabricated using 60 W, good soft magnetic properties have been obtained in a wide x range (x=0.9−0.55), with Hc not exceeding 10 Oe, along with high resistivity. In particular, for the sample with x=0.62, coercivities in hard and easy axes are 0.6 and 7.2 Oe, respectively, 4πMs=11.5 kG, and ρ reaches 2.53 mΩ cm. The dependence of complex permeability μ=μ′−jμ″ on frequency shows that the real part μ′ is more than 100 below 1.0 GHz and ferromagnetic resonance frequency reaches 2.35 GHz. The excellent soft magnetic property is ascribed to the exchange coupling among magnetic granules.
A generalized, periodic nonlinearity-reduced interferometer for straightness measurements
Authors: Wu Chien-ming
Published: June 2008

Periodic nonlinearity is a systematic error limiting the accuracy of displacement measurements at the nanometer level. However, an interferometer with a displacement measurement accuracy of less than 1nm is required in nanometrology and in fundamental scientific research. To meet this requirement, a generalized, periodic nonlinearity-reduced interferometer, based on three construction principles has been developed for straightness measurements. These three construction principles have resulted in an interferometer with a highly stable design with reduced periodic nonlinearity. Verifications by a straightness interferometer have demonstrated that the periodic nonlinearity was less than 40pm. The results also demonstrate that the interferometer design is capable of subnanometer accuracy and is useful in nanometrology.
Electron-phonon scattering in amorphous In2O3–ZnO films
Authors: Funaki Makoto , Makise Kazumasa , Shinozaki Bunjyu , Yano Koki , Utsuno Futoshi , Inoue Kazuyoshi , Nakamura Hiroaki
Published: June 2008

For amorphous transparent conductive oxide In2O3–ZnO films over a wide range of resistivities ρ, the temperature dependences of ρ and Hall coefficient RH have been measured in the temperature range of 2.0–300 K. The low-resistivity films show a metallic characteristic (dρ/dT>0), although high-resistivity films show an insulating behavior (dρ/dT<0). Even in metallic films, however, the resistivity slightly increases with decreasing temperature below 20 K because of the term ρquanta(T) due to quantum effects. Through a careful analysis, we have found that the ρ(T) of metallic films changes in the form of ρ(T)−ρ0−ρquanta∝ρ0T2 at temperatures below ∼100 K. This temperature dependence can be explained by the interference term ρel-imp-ph between the impurity scattering and the electron-phonon scattering. At temperatures of 20–300 K, it has been found that ρ(T) agrees well with the sum of the Grüneisen–Bloch term ρel-ph(T)=βel-phF(T,Θd) and the term ρel-imp-ph(T)=Bel-imp-phG(T,Θd). From analyses, with the coefficients βel-ph and Bel-imp-ph and the Debye temperature Θd as fitting parameters, we have obtained Θd≃1013±13 K and the longitudinal sound velocity uℓ≃13 500 m/s under some assumptions.
Study of tunneling mechanism of Au nanocrystals in HfAlO matrix as floating gate memory
Authors: Chan K. C. , Lee P. F. , Dai J. Y.
Published: June 2008

A floating gate memory structure containing HfAlO control gate, self-organized Au nanocrystals (NCs), and a HfAlO tunnel layer has been fabricated by pulsed-laser deposition. Owing to the charging effects of Au NCs, a significant threshold voltage shift has been obtained and the memory window up to 10.0V and stored charge density up to 1×1014∕cm2 has been achieved. Fowler–Nordheim tunneling mechanism is used to analyze the capacitance-voltage characteristics of the trilayer memory structure, and it is found that higher density and smaller size of the Au NCs result in a higher tunneling coefficient and a larger memory window.
Monolithic rare-earth doped sol-gel tapered rib waveguide laser
Authors: Peled A. , Chiasera A. , Nathan M. , Ferrari M. , Ruschin S.
Published: June 2008

We report the design, fabrication, and characterization of a monolithic tapered rib waveguide laser made of Nd doped silica hafnia sol-gel. The laser has a 604nm thick guiding layer. CW pumping was coupled in via a grating which also coupled out the lasing signal output, while reflection gratings supported the feedback. A lasing threshold of 20mW and an output power of 2.45mW were measured in a 3cm long device.
Crystal-field study of Yb3+ doped LuVO4
Authors: Jandl S. , Lévesque Y. , Nekvasil V. , Bettinelli M.
Published: June 2008

Raman active phonons of Yb doped LuVO4 ranging from 0.25% to 30% are detected and analyzed at low temperature in order to determine the doping effects on the crystalline quality and the phonon contribution to the crystal-field vibronics. Also, Yb3+ ion F7∕22 and F5∕22 crystal-field energy levels are measured as a function of doping by infrared absorption and luminescence. The appropriate crystal-field Hamiltonian parameters are determined and the presence of Yb3+–Yb3+ magnetically interacting pairs, which play an important role in cooperative emission, is confirmed.
Chemical and physical interface studies of the atomic-layer-deposited Al2O3 on GaAs substrates
Authors: Shahrjerdi D. , Garcia-Gutierrez D. I. , Tutuc E. , Banerjee S. K.
Published: June 2008

In this work, we study the chemical and physical properties of the interface between Al2O3 and GaAs for different surface treatments of GaAs. The interfacial layer between the high-κ layer and GaAs substrate was studied using x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The reduction in native oxide layer was observed upon atomic layer deposition of Al2O3 on nontreated GaAs using trimethyl aluminum precursor. It was also observed that the sulfide treatment effectively mitigates the formation of the interfacial layer as compared to the surface hydroxylation using NH4OH. The electrical characteristics of GaAs capacitors further substantiate the XPS and TEM results.
Anisotropy of crystal-melt interfacial free energy of silicon by simulation
Authors: Apte Pankaj A. , Zeng X. C.
Published: June 2008

We extend the cleaving wall method to a nonpairwise additive potential. Using this method, we compute the anisotropy of crystal-melt interfacial free energy γ for Stillinger–Weber potential of silicon [F. H. Stillinger and T. A. Weber, Phys. Rev. B 31, 5262 (1985)]. The calculated γ for (100), (111), and (110) orientations are 0.42±0.02, 0.34±0.02, and 0.35±0.03J∕m2, respectively. The anisotropy in γ we found is consistent with the experimental observation that Si(100)-melt interface develops (111) facets and also helps in explaining a higher undercooling observed for Si(111)-melt interface in Czochralski method.
Fiber Bragg grating tether used to measure drag forces in neutral buoyancy flow tank tests
Authors: Wade S. A. , Jolley W. , Fouras A.
Published: June 2008

The drag exerted on neutrally buoyant tethered spheres in a flow tank was measured as a function of flow rate. A unique solution to the problem was achieved using an optical fiber including a Bragg grating sensor as part of the tether. Measurements of the strain on the tether taken at flow rates between 0.14 and 0.33m∕s, were used to determine drag forces for spheres with diameters ranging from 40to100mm. Vortex-induced vibration was observed in tests performed at Reynolds numbers from 5×103to4.5×104. The drag coefficients for these tests were found to range from 0.51 to 0.77.
An optical pump-probe technique for measuring the thermal conductivity of liquids
Authors: Schmidt Aaron , Chiesa Matteo , Chen Xiaoyuan , Chen Gang
Published: June 2008

We present a pump-probe optical technique for measuring the thermal conductivity of liquids. The technique uses a reflective geometry which does not depend on the optical properties of the liquid and requires as little as a single droplet to produce a result. An analytical solution is given for bidirectional heat flow in layered media, including the effects of radial heat flow from coaxial Gaussian laser spots, thermal interface resistances, and the accumulation of multiple laser pulses. In addition, several experimental improvements over previous pump-probe configurations are described, resulting in an improved signal to noise ratio and smaller errors at long stage delay times. The technique is applied to a range of liquids and solids. Results are in good agreement with literature values.
Surface resistivity estimation by scanning surface potential microscopy
Authors: Rakocevic Z. , Popovic N. , Bogdanov Z. , Goncic B. , Strbac S.
Published: June 2008

Nickel was sputter deposited on a glass with a thin film thickness of 600nm under either in an argon atmosphere or under a partial pressure of nitrogen of either 1.3×10−4 or 4×10−4mbar. Atomic force microscopy and scanning surface potential microscopy (SSPM) were used to study the morphology and to estimate the surface resistivity of the obtained Ni thin films taking into account surface-roughness effects. For the three samples investigated, the surface resistivity values as estimated using SSPM were in good agreement with the results obtained by standard four-point probe measurements.
Simplest nontoxic double-layered cuprate Ba2CaCu2O4(O,F)2 superconductor with a transition temperature of 108K
Authors: Shirage P. M. , Shivagan D. D. , Tanaka Y. , Kodama Y. , Kito H. , Iyo A.
Published: June 2008

We report synthesis and properties of the simplest double-layered cuprate superconductor Ba2CaCu2O4(O,F)2. A superconducting transition temperature (Tc) has been achieved as high as 108K for a sample with a nominal fluorine content y=1.6 in Ba2CaCu2O6−yFy. The Tc is the highest among double-layer cuprates that are free of toxic elements such as Hg, Tl, and Pb so that the nontoxic Ba2CaCu2O4(O,F)2 will be promising for application. As y decreases from approximately 2, the a-axis length decreases and the Tc increases from 40to108K. The material is underdoped at large y and as y decreases, the doping moves toward an optimally doped state.
Trap-controlled space-charge-limited current mechanism in resistance switching at Al∕Pr0.7Ca0.3MnO3 interface
Authors: Harada T. , Ohkubo I. , Tsubouchi K. , Kumigashira H. , Ohnishi T. , Lippmaa M. , Matsumoto Y. , Koinuma H. , Oshima M.
Published: June 2008

Well-defined metal-insulator-metal trilayered structures composed of epitaxial Pr0.7Ca0.3MnO3 insulator layers, epitaxial LaNiO3 bottom electrodes, and Al metal top electrodes were fabricated on LaAlO3 (100) substrates. The I-V characteristics of the trilayer structures show electric-field-induced resistance switching. The resistance switching ratio of the heterostructures was up to 100 when positive and negative pulsed voltages were applied. Detailed I-V analysis indicates the importance of both trap-controlled space-charge-limited current and Poole–Frenkel effect in resistance switching at Al∕Pr0.7Ca0.3MnO3 interfaces.
Generation of a squeezing vacuum at a telecommunication wavelength with periodically poled LiNbO3
Authors: Feng Jinxia , Tian Xiutao , Li Yongmin , Zhang Kuanshou
Published: June 2008

A continuous-wave squeezed vacuum at a telecommunication wavelength was reported. Using an Er-doped fiber amplifier seeded by a single-frequency laser diode as the pump laser source, via a frequency doubler and an optical parametric oscillator based on periodically poled LiNbO3, the squeezed vacuum of 2.4±0.1dB below the shot noise limit at 1560nm was observed (the inferred initial squeezing is about 6.4±0.5dB). This system is compatible with standard telecommunication optical fiber, and will be useful for long-distance quantum communication and distributed quantum computing.
A phase feature extraction technique for terahertz reflection spectroscopy
Authors: Zhong Hua , Zhang Cunlin , Zhang Liangliang , Zhao Yuejin , Zhang Xi-Cheng
Published: June 2008

We present a feature extraction technique for identification of explosive and biological materials using terahertz reflection time-domain spectroscopy (RTDS). The absorption signatures of the materials are extracted directly from the second-order derivative of the phase of the sample beam with respect to frequency. This technique provides a straightforward and fast solution to solve the phase-retrieval problem in RTDS and will benefit the future development of a standoff, large-size focal-plane terahertz sensing and imaging system.
An ab initio study on energy gap of bilayer graphene nanoribbons with armchair edges
Authors: Lam Kai-Tak , Liang Gengchiau
Published: June 2008

Dependency of energy bandgap (Eg) of bilayer armchair graphene nanoribbons (AGNRB) on their widths, interlayer distance (D), and edge doping concentration of boron/nitrogen was investigated using local density approximation and compare to the results of monolayer graphene nanoribbons (AGNRM). Although Eg of AGNRB, in general, is smaller than that of AGNRM, of AGNRB exhibits two distinct groups, metal and semiconductor, while AGNRM displays purely semiconducting behavior. Moreover, Eg of AGNRB is highly sensitive to D, indicating a possible application in tuning Eg by varying D. Finally, edge doping of both AGNR systems reduces Eg by 11%–17%/4%–10% for AGNRM∕AGNRB, respectively.
Morphotropic phase boundary in (1−x)Bi0.5Na0.5TiO3–xK0.5Na0.5NbO3 lead-free piezoceramics
Authors: Kounga Alain Brice , Zhang Shan-Tao , Jo Wook , Granzow Torsten , Rödel Jürgen
Published: June 2008

The electromechanical behavior of (1−x)Bi0.5Na0.5TiO3–xK0.5Na0.5NbO3 (BNT-KNN) lead free piezoelectric ceramics is investigated for 0⩽x⩽0.12 to gain insight into the antiferroelectric-ferroelectric (AFE-FE) phase transition on the basis of the giant strain recently observed in BNT-based systems. At x≈0.07, a morphotropic phase boundary (MPB) between a rhombohedral FE phase and a tetragonal AFE phase is found. While the piezoelectric coefficient is largest at this MPB, the total strain further increases with increasing KNN content, indicating the field-induced AFE-FE transition as the main reason for the large strain.
Genetic effects of radio-frequency, atmospheric-pressure glow discharges with helium
Authors: Li Guo , Li He-Ping , Wang Li-Yan , Wang Sen , Zhao Hong-Xin , Sun Wen-Ting , Xing Xin-Hui , Bao Cheng-Yu
Published: June 2008

Due to low gas temperatures and high densities of active species, atmospheric-pressure glow discharges (APGDs) would have potential applications in the fields of plasma-based sterilization, gene mutation, etc. In this letter, the genetic effects of helium radio-frequency APGD plasmas with the plasmid DNA and oligonucleotide as the treated biomaterials are presented. The experimental results show that it is the chemically active species, instead of heat, ultraviolet radiation, intense electric field, and/or charged particles, that break the double chains of the plasmid DNA. The genetic effects depend on the plasma operating parameters, e.g., power input, helium flow rate, processing distance, time, etc.
Polarization-dependent confocal Raman microscopy of an individual ZnO nanorod
Authors: Chien Chih-Tao , Wu Ming-Chung , Chen Chun-Wei , Yang Hung-Hsien , Wu Jih-Jen , Su Wei-Fang , Lin Chauo-Sung , Chen Yang-Fang
Published: June 2008

In this study, polarized-Raman scattering measurements of an individual ZnO nanorod were carried out by using a confocal microscope together with a high-resolution piezoelectric stage. A predominant A1 (TO) mode at 378cm−1 in the parallel polarization (E∥) configuration and a predominant E2 (high) mode at 438cm−1 in the perpendicular polarization (E⊥) configuration demonstrate the strong polarization dependent Raman scattering signals of an individual ZnO nanorod. The Raman intensity images of the individual ZnO nanorods with different orientation configurations can also be obtained, which reflect the interplay between the local phonon behavior and geometric anisotropy.
Ordering of fullerene and carbon nanotube thin films under energetic ion impact
Authors: Kumar Amit , Avasthi D. K. , Pivin J. C. , Koinkar P. M.
Published: June 2008

We report the ordering of carbon nanostructures under energetic ion irradiation at low fluence (<5×1011ions∕cm2). Fullerene thin films and multiwalled carbon nanotube (MWCNT) films were irradiated with 200MeV Au and 60MeV Ni ions at different ion fluences, respectively. The changes in the irradiated films have been investigated by means of Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, and Raman spectroscopy. FTIR and Raman spectroscopy show the improvement of vibration strength in low fluence irradiated fullerene and MWCNT films. X-ray diffraction analysis on low fluence irradiated fullerene films revealed the structural order along the (220) atomic planes.
Spatial evolution of an ion beam created by a geometrically expanding low-pressure argon plasma
Authors: Corr C. S. , Boswell R. W. , Charles C. , Zanger J.
Published: June 2008

The spatial distribution of an ion beam—created at the interface of a small diameter plasma source and much larger diameter diffusion chamber—is studied in a low-pressure inductively coupled plasma using a retarding field energy analyzer. It is found that the ion beam density decays axially and radially in the diffusion chamber following the expansion of the plasma from the source region. The radial distribution of the ion beam indicates that the acceleration region has a convex shape and is located just outside the source exit, giving rise to a hemispherical plasma expansion into the diffusion chamber.
Ionization gas sensing of the ion flow current in a microtripolar electrode system with carbon nanotubes
Authors: Hou Zhongyu , Cai Bingchu , Xu Dong
Published: June 2008

We report the tests of a tripolar on-chip microelectrode system with carbon nanotubes, where the ion flow current (Ii) and the partial discharge current produced by the field ionization process of gaseous molecules can be measured to characterize the gas species and concentration. A theoretical account is given regarding the underlying differences between their sensing mechanisms. Further, comparative analysis of these two outputs in response to the concentration dynamic changes of ethanol/acetone in N2 demonstrates the explicit cases of improved sensitivity and selectivity of the Ii measurement.
Dark current in multilayer amorphous selenium x-ray imaging detectors
Authors: Mahmood S. A. , Kabir M. Z. , Tousignant O. , Mani H. , Greenspan J. , Botka P.
Published: June 2008

A theoretical model for describing the bias-dependent transient behavior of dark current in multilayer (n-i-p) amorphous selenium (a-Se) detectors has been developed. The transient dark currents in these detectors are measured and are compared to the proposed dark current model. It has been found that the dark current is mainly controlled by Schottky emission of holes from the metal/a-Se contact. The initial and steady state dark currents are mainly controlled by the barrier height and the trap centers in the n layer, respectively.
Microwave probed photoconductivity spectroscopy of deep levels in Ni doped Ge
Authors: Gaubas E. , Uleckas A. , Grigonis R. , Sirutkaitis V. , Vanhellemont J.
Published: June 2008

A transient technique to simultaneously measure carrier lifetime and deep levels in semiconductors is proposed based on microwave probed photoconductivity spectroscopy in the wavelength range between 0.5 and 16μm. The application of this noncontacting technique is illustrated by a study of carrier lifetime and deep levels in Ni implanted and annealed Ge wafers. The activation energies of the deep levels are determined at room temperature and compared with those extracted by means of capacitance deep level transient spectroscopy.
Magnetic field induced extinction of light in a suspension of Fe3O4 nanoparticles
Authors: Philip John , Laskar J. M. , Raj Baldev
Published: June 2008

We report magnetic field induced extinction of light in Mie regime using a magnetic nanofluid containing Fe3O4 nanoparticles of 6.7nm. At a critical applied magnetic field (HC2), the transmitted light intensity becomes extinct where the HC2 follows a power law decay with volume fraction of nanoparticles (HC2∞ϕ−x, where x=0.283) indicating a structural transition. The light transmission was reversible with the magnetic field. We discuss various possible mechanisms responsible for the extinction of light under external magnetic field. The experimental finding may have significant application in tunable light controlling devices.
Modulated terahertz responses of split ring resonators by nanometer thick liquid layers
Authors: Sun Yimin , Xia Xiaoxiang , Feng Hui , Yang Haifang , Gu Changzhi , Wang Li
Published: June 2008

The terahertz responses of planar arrays of split ring resonators with 50nm thin liquid layers introduced in the interspaces between the metal structures have been studied using the terahertz-time domain spectroscopy technique. In our experimental configuration, both the circular current driven and linear polarization induced resonances show redshifted and enhanced transmission. The dielectric functions extracted from an effective medium model indicate that the behavior of the surface and interface charge oscillations is highly sensitive to the interface environment changes. The results suggest that this kind of device may be used for sensing applications.
Vessel wall vibrations: trigger for embolism repair?
Authors: Salleo Sebastiano , Trifilò Patrizia , Lo Gullo Maria Assunta
Published: June 2008

Xylem embolism repair is preceded by starch depolymerisation in vessel-associated cells (VAC) of Laurus nobilis L. (laurel) twigs, but the primary signal triggering such a process is still unknown. We tested the hypothesis that conduit wall vibrations during cavitation may be sensed by VAC inducing starch-to-sugar conversion. Twigs of laurel from watered or stressed plants were exposed to ultrasound for 60 min to simulate acoustic waves emitted by cavitating conduits. Preliminary tests showed that ultrasound caused no damage to cell membrane integrity nor did they cause xylem embolism. The number of VAC with high starch content (HSC-cells) was estimated microscopically by counting the cells with more than 50% of their lumen filled with starch granules. Sonication had no effect on HSC-cells in twigs from watered plants while it induced a drop in the percentage HSC-cells from 80 to 40% in twigs from stressed plants, at the ultrasound source location. No effect was recorded in these twigs 20 mm from the ultrasound source. Sonication was a good simulator of cavitation in inducing starch depolymerisation which suggests a possible bio- physical nature for the signal initiating embolism repair.
Medicago truncatula as a model for understanding plant interactions with other organisms, plant development and stress biology: past, present and future
Authors: Rose Ray J.
Published: June 2008

Medicago truncatula Gaertn. cv. Jemalong, a pasture species used in Australian agriculture, was first proposed as a model legume in 1990. Since that time M. truncatula, along with Lotus japonicus (Regal) Larsen, has contributed to major advances in understanding rhizobia Nod factor perception and the signalling pathway involved in nodule formation. Research using M. truncatula as a model has expanded beyond nodulation and the allied mycorrhizal research to investigate interactions with insect pests, plant pathogens and nematodes. In addition to biotic stresses the genetic mechanisms to ameliorate abiotic stresses such as salinity and drought are being investigated. Furthermore, M. truncatula is being used to increase understanding of plant development and cellular differentiation, with nodule differentiation providing a different perspective to organogenesis and meristem biology. This legume plant represents one of the major evolutionary success stories of plant adaptation to its environment, and it is particularly in understanding the capacity to integrate biotic and abiotic plant responses with plant growth and development that M. truncatula has an important role to play. The expanding genomic and genetic toolkit available with M. truncatula provides many opportunities for integrative biological research with a plant which is both a model for functional genomics and important in agricultural sustainability.
Rangeland degradation and restoration management in China
Authors: Han J. G. , Zhang Y. J. , Wang C. J. , Bai W. M. , Wang Y. R. , Han G. D. , Li L. H.
Published: June 2008

Rangelands of China have for centuries provided forage for livestock but now their role in water, soil, and biodiversity conservation is being recognised by Governments and people. However, much of the rangelands has recently degraded and desertification is now a widespread problem. The cause of the degradation is over-grazing and over-cultivation. Climate change is exacerbating the problem. The Chinese Governments have begun to address these severe problems through policy adjustments and projects. In parallel, some research and development is taking place. There are major impediments to addressing the problem; the importance of rangelands to China and its people are generally underestimated, legislative protection is incomplete and often ineffective, little attention is paid to scientific knowledge for development of management of natural resources, there is insufficient technological support, and Governments are not able to invest sufficiently to effectively restore and develop rangeland natural resources. However, with this background we propose how the problems might be more effectively addressed in the future.
Timelines, talk and transcription
Authors: Forsyth Richard , Clarke David D. , Lam Phoenix
Published: June 2008

Linguists and other social scientists have employed many transcription conventions to exhibit the temporal interleaving of multi-speaker talk. The existence of many different systems, which are mutually incompatible, is evidence that representing spoken discourse remains problematic. This study proposes a novel orthographic transcription layout based on word timings. To test this method, the Maptask corpus (Anderson et al. 1991) is used because it contains unusually precise information on the timings of vocal events. This makes it possible to evaluate a non-standard talk-division format (TST1) in which the alternation of speakers is not imposed by a transcriber's intuition but emerges from the empirical data. It highlights the prevalence of ‘echoing’ in the joint production of dialogue. Moreover, lengths of speech segments and inter-speaker intervals as defined by this procedure show significant associations with a number of contextual and interactional variables, indicating that this approach has analytic as well as representational benefits.