bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixed layer depth variability in the tropical boundary of the California Current, 1997–2007
Authors: Jeronimo Gilberto , Gomez‐Valdes Jose
Published: May 2010

The variability of the mixed layer depth (MLD) is examined over a decade (1997–2007) for the tropical boundary of the California Current (24–32°N), using conductivity‐temperature‐depth observations collected by quarterly survey cruises. Results indicate that salinity gradients control MLD rather than temperature gradients. The mean state of the upper ocean indicates that contours of constant MLD are parallel to the coast, with mixed layer thickness decreasing toward the coastal zone. The deepest (∼70 m) thickness is reached in January and the shallowest (∼15 m) occurs in July. The warmer conditions (summer) are reproduced for a simple thermal energy equation. The rest of the seasons are reproduced for a one‐dimensional momentum balance for the upper ocean, which includes Ekman dynamics and stratification. This comparison indicates that the variability of MLD is mainly due to wind‐driven phenomena except during the heating period. In particular, seasonal and interannual variability of the MLD are correlated with offshore Ekman transport. An abrupt MLD change occurs between January 1998 and January 2000 associated with the strong El Niño‐La Niña cycle shift that occurred in this period.
On the recurrent Ulva prolifera blooms in the Yellow Sea and East China Sea
Authors: Hu Chuanmin , Li Daqiu , Chen Changsheng , Ge Jianzhong , Muller‐Karger Frank E. , Liu Junpeng , Yu Feng , He Ming‐Xia
Published: May 2010

A massive bloom of the green macroalgae Ulva prolifera (previously known as Enteromorpha prolifera) occurred in June 2008 in the Yellow Sea (YS), resulting in perhaps the largest “green tide” event in history. Using a novel index (Floating Algae Index) and multiresolution remote sensing data from MODIS and Landsat, we show that U. prolifera patches appeared nearly every year between April and July 2000–2009 in the YS and/or East China Sea (ECS), which all originated from the nearshore Subei Bank. A finite volume numerical circulation model, driven by realistic forcing and boundary conditions, confirmed this finding. Analysis of meteorological/environmental data and information related to local aquaculture activities strongly supports the hypothesis that the recurrent U. prolifera in the YS and ECS resulted from aquaculture of the seaweed Porphyra yezoensis (or nori) conducted along the 200 km shoreline of the Subei Bank north of the Changjiang (Yangtze) River mouth. Given the continuous growth in aquaculture efforts in the region, similar macroalgae bloom events, such as the summer 2008 event, are likely to occur in the future, particularly between May and July. This was confirmed by the 2009 bloom event in the same regions and the same period. The profit of the local P. yezoensis aquaculture industry (∼16,000 Ha in 2007) is estimated as U.S. $53 million, yet the cost to manage the impact of the summer 2008 U. prolifera bloom exceeded U.S. $100 million. Therefore, better strategies are required to balance the economic benefit of seaweed aquaculture and the costs of environmental impacts.
Observations of supercooling and frazil ice formation in the Laptev Sea coastal polynya
Authors: Dmitrenko Igor A. , Wegner Carolyn , Kassens Heidemarie , Kirillov Sergey A. , Krumpen Thomas , Heinemann Günther , Helbig Alfred , Schröder David , Hölemann Jens A. , Klagge Torben , Tyshko Konstantin P. , Busche Thomas
Published: May 2010

This paper examines a hydrographic response to the wind‐driven coastal polynya activity over the southeastern Laptev Sea shelf for April–May 2008, using a combination of Environmental Satellite (Envisat) advanced synthetic aperture radar (ASAR) and TerraSAR‐X satellite imagery, aerial photography, meteorological data, and SBE‐37 salinity‐temperature‐depth and acoustic Doppler current profiler land‐fast ice edge‐moored instruments. When ASAR observed the strongest end‐of‐April polynya event with frazil ice formation, the moored instruments showed maximal acoustical scattering within the surface mixed layer, and the seawater temperatures were either at or 0.02°C below freezing. We also find evidence of the persistent horizontal temperature and salinity gradients across the fast ice edge to have the signature of geostrophic flow adjustment as predicted by polynya models.
Multisensor snow data assimilation at the continental scale: The value of Gravity Recovery and Climate Experiment terrestrial water storage information
Authors: Su Hua , Yang Zong‐Liang , Dickinson Robert E. , Wilson Clark R. , Niu Guo‐Yue
Published: May 2010

This investigation establishes a multisensor snow data assimilation system over North America (from January 2002 to June 2007), toward the goal of better estimation of snowpack (in particular, snow water equivalent and snow depth) via incorporating both Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage (TWS) and Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover fraction (SCF) information into the Community Land Model. The different properties associated with the SCF and TWS observations are accommodated through a unified approach using the ensemble Kalman filter and smoother. Results show that this multisensor approach can provide significant improvements over a MODIS‐only approach, for example, in the Saint Lawrence, Fraser, Mackenzie, Churchill & Nelson, and Yukon river basins and the southwestern rim of Hudson Bay. At middle latitudes, for example, the North Central and Missouri river basins, the inclusion of GRACE information preserves the advantages (compared with the open loop) shown in the MODIS‐only run. However, in some high‐latitude areas and given months the open loop run shows a comparable or even better performance, implying considerable room for refinements of the multisensor algorithm. In addition, ensemble‐based metrics are calculated and interpreted domainwide. They indicate the potential importance of accurate representation of snow water equivalent autocovariance in assimilating TWS observations and the regional and/or seasonal dependence of GRACE’s capability to reduce ensemble variance. These analyses contribute to clarifying the effects of GRACE’s special features (e.g., a vertical integral of different land water changes, coarse spatial and temporal resolution) in the snow data assimilation system.
Impact origin for the Martian crustal dichotomy: Half emptied or half filled?
Authors: Reese C. C. , Orth C. P. , Solomatov V. S.
Published: May 2010

One possible mechanism for Martian hemispherical dichotomy formation is excavation of the northern lowland basin in the existing crust by a single giant impact. Here we explore a related scenario in which the impact melt volume is sufficient to fill the excavated cavity, produce a thickened crust, and generate a topographic basin centered on the opposite side of the planet. We investigate this mechanism by formulating a model for viscous spreading of a partially molten layer over a spherical surface. We derive numerical solutions and calculate the final area of the spreading layer as a function of impactor size and shape of the layer boundary due to an initially asymmetric melt region. Results are compared with observations, including lowland basin size, shape of the dichotomy boundary, age difference between crustal provinces, and crustal thickness.
On the representativeness of plot size and location for scaling transpiration from trees to a stand
Authors: Mackay D. Scott , Ewers Brent E. , Loranty Michael M. , Kruger Eric L.
Published: May 2010

Scaling transpiration from trees to larger areas is a fundamental problem in ecohydrology. For scaling stand transpiration from sap flux sensors we asked if plot representativeness depended on plot size and location, the magnitude of environmental drivers, parameter needs for ecosystem models, and whether the goal was to estimate transpiration per unit ground area (EC), per unit leaf area (EL), or canopy stomatal conductance (GS). Sap flux data were collected in 108 trees with heat dissipation probes, and biometric properties were measured for 752 trees within a 1.44 ha Populus tremuloides stand along an upland‐to‐wetland gradient. EC was estimated for the stand using eight different plot sizes spanning a radius of 2.0–12.0 m. Each estimate of EC was derived from 200 plots placed randomly throughout the stand. We also derived leaf area index (L), canopy closure (PCC), and the canopy average reference stomatal conductance (GSref), which are key parameters used in modeling transpiration and evapotranspiration. With increasing plot size, EC declined monotonically but EL and GSref were largely invariant. Interplot variance of EC also declined with increasing plot size, at a rate that was independent of vapor pressure deficit. Plot representativeness was dependent on location within the stand. Scaling to the stand required three plots spanning the upland to wetland, with one to at most 10 trees instrumented for sap flux. Plots that were chosen to accurately reflect the spatial covariation of L, PCC, and GSref were most representative of the stand.
Microbial risk assessment in heterogeneous aquifers: 2. Infection risk sensitivity
Authors: Molin S. , Cvetkovic V. , Stenström T. A.
Published: May 2010

The entire chain of events of human disease transmitted through contaminated water, from pathogen introduction into the source (E. coli, rotavirus, and Hepatitis A), pathogen migration through the aquifer pathway, to ingestion via a supply well, and finally, the potential infection in the human host, is investigated. The health risk calculations are based on a relevant hazardous event with safe setback distances estimated by considering the infection risk from peak exposure in compliance with an acceptable level defined by a regulatory agency. A site‐specific hypothetical scenario is illustrated for an aquifer with similar characteristics as the Cape Cod site, Massachusetts (United States). Relatively large variation of safe distances for the three index pathogens is found; individually, none of the index pathogens could predict the safe distance under the wide range of conditions investigated. It is shown that colloid filtration theory (CFT) with spatially variable attachment‐detachment rates yields significantly different results from the effective CFT model (i.e., assuming spatially constant parameters).
Subtropical dipole mode in the Southern Hemisphere: A global view
Authors: Wang F.
Published: May 2010

A global wavenumber‐3 dipole SST mode is showed to exist in the Southern Hemisphere subtropical climate variability in austral summer. A positive (negative) phase of the mode is characterized by cool (warm) SST anomalies in the east and warm (cool) SST anomalies in the southwest of the south Indian, Pacific, and Atlantic Oceans, respectively. This coherent dipole structure is largely a response of ocean mixed layer to the atmospheric forcing characterized by migration and modulation of the subtropical high‐pressures, in which the latent heat flux play a leading role through wind‐induced evaporation, although ocean dynamics may also be crucial in forming SST anomalies attached to the continents. Exploratory analyses suggest that this mode is strongly damped by the negative heat flux feedback, with a persistence time about three months and no spectral peak at interannual to decadal time scales. As the subtropical dipole mode is linearly independent of ENSO and SAM, whether it represents an additional source of climate predictability should be further studied.
Sr‐Nd‐Hf isotopes along the Pacific Antarctic Ridge from 41 to 53°S
Authors: Hamelin Cédric , Dosso Laure , Hanan Barry , Barrat Jean‐Alix , Ondréas Hélène
Published: May 2010

Major, trace element and Sr‐Nd‐Hf isotope data in basalts collected along the Pacific‐Antarctic Ridge (PAR) axis between 53 and 41°S, far from any hotspot influence, reveal tight coherent geochemical variations within the depleted MORB mantle. All samples are located below the Pacific reference line defining two sub‐oceanic mantle domains on each side of the Easter microplate. The data extend the PAR 66‐53°S field towards more radiogenic Sr (0.70264), less radiogenic Nd (ɛ = 7.7) and Hf (ɛ = 11.4) values. The along ridge geochemical variability is closely related to the morphological segmentation of the ridge. Anomalous geochemical features are attributed to the atypical morphology of two segments due to the presence of off‐axis magmatism. The first order ridge discontinuity defined by the Menard transform fault separates two slightly different mantle domains, each with its own history.
The role of transmembrane domain 9 in substrate recognition by the fungal high-affinity glutathione transporters
Authors: Thakur Anil , Bachhawat Anand K.
Published: May 2010

Hgt1p, a high-affinity glutathione transporter from Saccharomyces cerevisiae belongs to the recently described family of OPTs (oligopeptide transporters), the majority of whose members still have unknown substrate specificity. To obtain insights into substrate recognition and translocation, we have subjected all 21 residues of TMD9 (transmembrane domain 9) to alanine-scanning mutagenesis. Phe523 was found to be critical for glutathione recognition, since F523A mutants showed a 4-fold increase in Km without affecting expression or localization. Phe523 and the previously identified polar residue Gln526 were on the same face of the helix suggesting a joint participation in glutathione recognition, whereas two other polar residues, Ser519 and Asn522, of TMD9, although also orientated on the same face, did not appear to be involved. The size and hydrophobicity of Phe523 were both key features of its functionality, as seen from mutational analysis. Sequence alignments revealed that Phe523 and Gln526 were conserved in a cluster of OPT homologues from different fungi. A second cluster contained isoleucine and glutamate residues in place of phenylalanine and glutamine residues, residues that are best tolerated in Hgt1p for glutathione transporter activity, when introduced together. The critical nature of the residues at these positions in TMD9 for substrate recognition was exploited to assign substrate specificities of several putative fungal orthologues present in these and other clusters. The presence of either phenylalanine and glutamine or isoleucine and glutamate residues at these positions correlated with their function as high-affinity glutathione transporters based on genetic assays and the Km of these transporters towards glutathione.
Optimal solution for the viscous nonlinear dispersive wave equation
Authors: Shen Chunyu , Gao Anna
Published: May 2010

In this paper, we study the optimal control problem for the viscous nonlinear dispersive wave equation. We first prove the existence and uniqueness of a weak solution to this equation in a short interval by using the Galerkin method. Furthermore, the existence of an optimal solution to the viscous nonlinear dispersive wave equation is proved.
Resistive switching mechanism in delafossite-transition metal oxide (CuInO2–CuO) bilayer structure
Authors: Varandani Deepak , Singh Bharti , Mehta Bodh R. , Singh Mandeep , Singh Vidya Nand , Gupta Dasees
Published: May 2010

This study reports reversible and unipolar resistive switching in oxide bilayer structure due to the conversion of rectifying CuInO2–CuO semiconductor heterojunction to metal-semiconductor CuInO2–Cu Ohmic contact. High resolution transmission electron microscopy and conducting atomic force microscopy studies establish that switching occurs due to formation of conducting Cu filaments in CuO layer with CuInO2 layer remaining unaffected. The bilayer structure, with CuO layer acting as the switching element and CuInO2 layer as the resistance controlling element, exhibits improved switching parameters in comparison to single CuO layer.
Vacancy defect and carrier distributions in the high mobility electron gas formed at ion-irradiated SrTiO3 surfaces
Authors: Herranz G. , Copie O. , Gentils A. , Tafra E. , Basletić M. , Fortuna F. , Bouzehouane K. , Fusil S. , Jacquet É. , Carrétéro C. , Bibes M. , Hamzić A. , Barthélémy A.
Published: May 2010

Using a combination of advanced characterization tools (positron annihilation spectroscopy, conductive-tip atomic force microscopy, and high-field magnetotransport), we have studied the extension, origin and properties of the high mobility electron gas (HMEG) generated by etching the SrTiO3 surfaces with Ar+ ions. Contrary to previous assumptions, we show that this HMEG is not confined to nanometric thickness but extends to a few micrometer from the surface. We discuss this unanticipated large spatial extension in terms of the striking large diffusion of oxygen vacancy-related defects.
Controlling the size distribution of embedded Au nanoparticles using ion irradiation
Authors: Ramjauny Y. , Rizza G. , Perruchas S. , Gacoin T. , Botha R.
Published: May 2010

Samples composted of chemically synthesized Au nanoparticles (NPs) (16.0±2.0 nm) embedded within a planar silica film are used as model system to investigate the evolution of a second phase under irradiation when the temperature and the ion stopping power are changed. Samples are irradiated with 4 MeV Au2+ ions and 4 MeV Br2+ ions for temperature ranging from 30 °C up to 800 °C and for fluences up to 8×1016 cm−2. We show that at room temperature the complete dissolution of the NPs leads to the formation of smaller precipitates with a narrower size distribution, i.e., 2.0±0.3 nm. However, when the temperature is increased and/or the nuclear stopping power is decreased, a reduction in the dissolution rate was observed. This leads to the formation of a bimodal size distribution. Finally, the evolution of the density of the precipitates with the temperature is discussed in term of the thermal stability of the irradiation-induced defects within the silica matrix.
Modulation of electronic properties of hexagonal boron nitride bilayers by an electric field: A first principles study
Authors: Yang Zailin , Ni Jun
Published: May 2010

The electronic structures of hexagonal boron nitride (BN) bilayers are studied by first principles calculations. The stabilities of BN bilayers with various stackings are determined. We find that an external electric field could significantly modulate the energy gaps of BN bilayers. By a relatively small adjustment of interlayer distance near the equilibrium position, we show that the direct band gaps can be obtained in a wide energy range when an external electric field is applied. These results suggest potential applications of BN bilayers in light emitting devices.
Finite element analysis of the effect of electrodes placement on accurate resistivity measurement in a diamond anvil cell with van der Pauw technique
Authors: Wu Baojia , Huang Xiaowei , Han Yonghao , Gao Chunxiao , Peng Gang , Liu Cailong , Wang Yue , Cui Xiaoyan , Zou Guangtian
Published: May 2010

The van der Pauw technique is widely used to determine resistivity of materials. In diamond anvil cell the compressed sample will make the contact placement change under high pressure. Using finite element analysis, we study the effect of contact placement error induced by pressure on the resistivity measurement accuracy of van der Pauw method. The results show the contact placement has a significant effect on determination accuracy. This method can provide accurate determination of sample resistivity when the spacing b between the contact center and sample periphery is less than D/9 (sample diameter). And the effect of contact placement error on accuracy rapidly increases as the contact location is closing to the sample center. For the same contact placement, the contact size error has a more obvious effect on the semiconductor sample.
Up-conversion luminescence of Mn2+ ions in Zn1−xMgxS:Mn2+ nanoparticles
Authors: Zhang Yong , Wang Bo , Liu Xiong , Wang Yunjun , Xiao Min
Published: May 2010

The up-conversion luminescence of Zn1−xMgxS:Mn2+ nanoparticles fabricated by an inorganic precipitation method is studied by using a near-infrared femtosecond laser. The up-converted luminescence is blueshifted when increasing the Mg composition because of weaker crystal field effect. Comparing with thin films, the luminescence of Zn1−xMgxS:Mn2+ nanoparticles shifts several nanometers to the red side due to quantum confinement effect and site-selected Mn2+ excitation. The measured power dependence shows that a second-order absorption process is responsible for the up-conversion luminescence. The up-conversion luminescence peak of the Zn1−xMgxS:Mn2+ nanoparticles does not change when the excitation wavelength is tuned between 750 to 790 nm.
The role of magnetic field in the transition to streaming ablation in wire arrays
Authors: Martin M. R. , Seyler C. E. , Greenly J. B.
Published: May 2010

In wire array Z-pinches, the magnetic field configuration and the global field penetration of individual wires play a key role in the ablation plasma dynamics. Knowledge of the magnetic field configuration is necessary to understand the ablation plasma acceleration process near the wires. Two-dimensional resistive magnetohydrodynamics simulations show that a change in the global magnetic field configuration is critical to initiating inward flow of the ablation plasma. Analysis of these simulations show that the initially compressive J×B force around a wire in its vacuum field configuration undergoes a transition to a configuration in which the Lorentz force can accelerate plasma toward the array axis. This transition is achieved through a low magnetic Reynolds number diffusive flow in which the plasma and the magnetic field are decoupled. The plasma current follows the expanding plasma toward the array axis and, after traveling a critical distance scaling with the array radius divided by the wire number, the global magnetic field threads the wire core, thereby allowing J×B coronal acceleration into ablation streams.
The lower hybrid wave cutoff: A case study in eikonal methods
Authors: Richardson A. S. , Bonoli P. T. , Wright J. C.
Published: May 2010

Eikonal, or ray tracing, methods are commonly used to estimate the propagation of radio frequency fields in plasmas. While the information gained from the rays is quite useful, an approximate solution for the fields would also be valuable, e.g., for comparison to full wave simulations. Such approximations are often difficult to perform numerically because of the special care which must be taken to correctly reconstruct the fields near reflection and focusing caustics. In this paper, we compare the standard eikonal method for approximating fields to a method based on the dynamics of wave packets. We compare the approximations resulting from these two methods to the analytical solution for a lower hybrid wave reflecting from a cutoff. The algorithm based on wave packets has the advantage that it can correctly deal with caustics, without any special treatment.
Effect of ultraviolet and x-ray radiation on the work function of TiO2 surfaces
Authors: Gutmann S. , Wolak M. A. , Conrad M. , Beerbom M. M. , Schlaf R.
Published: May 2010

The work functions of nanocrystalline anatase (TiO2) thin films and a rutile single crystal were measured using photoemission spectroscopy (PES). The nanocrystalline titanium dioxide films were deposited in-vacuum using electrospray thin film deposition. A comparison between ultraviolet photoemission spectroscopy (UPS) and low intensity x-ray photoemission spectroscopy (LIXPS) work function measurements on these samples revealed a strong, immediate, and permanent work function reduction (>0.5 eV) caused by the UPS measurements. Furthermore, it was found that regular XPS measurements also reduce the work function after exposure times ranging from seconds to minutes. These effects are similar in magnitude to artifacts seen previously on indium tin oxide (ITO) substrates characterized with XPS and UPS, and are likely related to the formation of a surface dipole through the photochemical hydroxylation of oxygen vacancies present on the TiO2 surface.
The properties of small Ag clusters bound to DNA bases
Authors: Soto-Verdugo Víctor , Metiu Horia , Gwinn Elisabeth
Published: May 2010

We study the binding of neutral silver clusters, Agn (n=1–6), to the DNA bases adenine (A), cytosine (C), guanine (G), and thymine (T) and the absorption spectra of the silver cluster-base complexes. Using density functional theory (DFT), we find that the clusters prefer to bind to the doubly bonded ring nitrogens and that binding to T is generally much weaker than to C, G, and A. Ag3 and Ag4 make the stronger bonds. Bader charge analysis indicates a mild electron transfer from the base to the clusters for all bases, except T. The donor bases (C, G, and A) bind to the sites on the cluster where the lowest unoccupied molecular orbital has a pronounced protrusion. The site where cluster binds to the base is controlled by the shape of the higher occupied states of the base. Time-dependent DFT calculations show that different base-cluster isomers may have very different absorption spectra. In particular, we find new excitations in base-cluster molecules, at energies well below those of the isolated components, and with strengths that depend strongly on the orientations of planar clusters with respect to the base planes. Our results suggest that geometric constraints on binding, imposed by designed DNA structures, may be a feasible route to engineering the selection of specific cluster-base assemblies.
Langmuir wave dispersion relation in non-Maxwellian plasmas
Authors: Ouazene M. , Annou R.
Published: May 2010

The Langmuir wave dispersion relation is derived in partially ionized plasmas, where free electrons are confined to move in a nearest neighbor ions’ potential well. The equilibrium velocity distribution function experiences then, a departure from Maxwell distribution function. The effect of the non-Maxwellian character of the distribution function on the Langmuir phase and group velocities as well as the phase matching conditions and the nonlinear growth rate of decay instability is investigated. The proposed Langmuir wave dispersion relation is relevant to dense and cryogenic plasmas.
Three dimensional character of whistler turbulence
Authors: Ganguli Gurudas , Rudakov Leonid , Scales Wayne , Wang Joseph , Mithaiwala Manish
Published: May 2010

It is shown that the dominant nonlinear effect makes the evolution of whistler turbulence essentially three dimensional in character. Induced nonlinear scattering due to slow density perturbation resulting from ponderomotive force triggers energy flux toward lower frequency. Anisotropic wave vector spectrum is generated by large angle scatterings from thermal plasma particles, in which the wave propagation angle is substantially altered but the frequency spectrum changes a little. As a consequence, the wave vector spectrum does not indicate the trajectory of the energy flux. There can be conversion of quasielectrostatic waves into electromagnetic waves with large group velocity, enabling convection of energy away from the region. We use a two-dimensional electromagnetic particle-in-cell model with the ambient magnetic field out of the simulation plane to generate the essential three-dimensional nonlinear effects.
Molecular dynamics simulations of the chain dynamics in monodisperse oligomer melts and of the oligomer tracer diffusion in an entangled polymer matrix
Authors: Durand M. , Meyer H. , Benzerara O. , Baschnagel J. , Vitrac O.
Published: May 2010

The apparent analogy between the self-diffusion of linear oligomers in monodisperse systems, 2 up to 32 monomers, and their tracer diffusion in an entangled polymer matrix of length 256 is investigated by molecular dynamics simulations at constant pressure. Oligomers and polymers are represented by the same coarse-grained (bead-spring) model. An analysis based on the Rouse model is presented. The scaling relationship of the self-diffusion coefficient D with the chain length N written as D∝N−α is analyzed for a wide range of temperatures down to the glass transition temperature Tg. Near Tg, the heterogeneous dynamics is explored by the self-part of the van Hove distribution function and various non-Gaussian parameters. For the self-diffusion in a monodisperse system a scaling exponent α(T)>1 depending on temperature is found, whereas for the tracer diffusion in an entangled matrix α=1 is obtained at all temperatures, regardless of the oligomer length. The different scaling behavior between both systems is explained by a different monomer mobility, which depends on chain length for monodisperse systems, but is constant for all tracers in the polymer matrix.
Plasma column displacement measurements by modified Rogowski sine-coil and Biot–Savart/magnetic flux equation solution on IR-T1 tokamak
Authors: Razavi M. , Mollai M. , Khorshid P. , Nedzelskiy I. , Ghoranneviss M.
Published: May 2010

The modified Rogowski sine-coil (MRSC) has been designed and implemented for the plasma column horizontal displacement measurements on small IR-T1 tokamak. MRSC operation has been examined on test assembly and tokamak. Obtained results show high sensitivity to the plasma column horizontal displacement and negligible sensitivity to the vertical displacement; linearity in wide, ±0.1 m, range of the displacements; and excellent, 1.5%, agreement with the results of numerical solution of Biot–Savart and magnetic flux equations.
Full electromagnetic Vlasov code simulation of the Kelvin–Helmholtz instability
Authors: Umeda Takayuki , Miwa Jun-ichiro , Matsumoto Yosuke , Nakamura Takuma K. M. , Togano Kentaro , Fukazawa Keiichiro , Shinohara Iku
Published: May 2010

Recent advancement in numerical techniques for Vlasov simulations and their application to cross-scale coupling in the plasma universe are discussed. Magnetohydrodynamic (MHD) simulations are now widely used for numerical modeling of global and macroscopic phenomena. In the framework of the MHD approximation, however, diffusion coefficients such as resistivity and adiabatic index are given from empirical models. Thus there are recent attempts to understand first-principle kinetic processes in macroscopic phenomena, such as magnetic reconnection and the Kelvin–Helmholtz (KH) instability via full kinetic particle-in-cell and Vlasov codes. In the present study, a benchmark test for a new four-dimensional full electromagnetic Vlasov code is performed. First, the computational speed of the Vlasov code is measured and a linear performance scaling is obtained on a massively parallel supercomputer with more than 12 000 cores. Second, a first-principle Vlasov simulation of the KH instability is performed in order to evaluate current status of numerical techniques for Vlasov simulations. The KH instability is usually adopted as a benchmark test problem for guiding-center Vlasov codes, in which a cyclotron motion of charged particles is neglected. There is not any full electromagnetic Vlasov simulation of the KH instability; this is because it is difficult to follow E⃗×B⃗ drift motion accurately without approximations. The present first-principle Vlasov simulation has successfully represented the formation of KH vortices and its secondary instability. These results suggest that Vlasov code simulations would be a powerful approach for studies of cross-scale coupling on future Peta-scale supercomputers.
Cooperative microexcitations in 2+1D chain-bundle dusty plasma liquids
Authors: Io Chong-Wai , Chan Chia-Ling , I Lin
Published: May 2010

Through direct visualization at the discrete level, the microexcitations in cold 2+1D dusty plasma liquids formed by negatively charged dusts suspended in low pressure gaseous discharges were experimentally investigated, in which the downward ion flow wake field induces strong vertical coupling and chain bundle structure. It is found that the horizontal structure and motion are similar to those of the two-dimensional liquid. Different types of basic cooperative chain excitations: straight vertical chains with small amplitude jittering, chain tilting-restraightening, bundle twisting-restraightening, and chain breaking-reconnection, are observed. The region with good (poor) horizontal structural order prefers the straight (tilted or broken) chains with little (large) titling and tilting rate.
Structure of Ce1−xSnxO2 and its relation to oxygen storage property from first-principles analysis
Authors: Gupta Asha , Kumar Anil , Hegde M. S. , Waghmare U. V.
Published: May 2010

CeO 2 – SnO 2 solid solution has been reported to possess high oxygen storage/release property which possibly originates from local structural distortion. We have performed first-principles based density functional calculations of Ce1−xSnxO2 structure (x=0, 0.25, 0.5, 1) to understand its structural stability in fluorite in comparison to rutile structure of the other end-member SnO2, and studied the local structural distortion induced by the dopant Sn ion. Analysis of relative energies of fluorite and rutile phases of CeO2, SnO2, and Ce1−xSnxO2 indicates that fluorite structure is the most stable for Ce1−xSnxO2 solid solution. An analysis of local structural distortions reflected in phonon dispersion show that SnO2 in fluorite structure is highly unstable while CeO2 in rutile structure is only weakly unstable. Thus, Sn in Ce1−xSnxO2-fluorite structure is associated with high local structural distortion whereas Ce in Ce1−xSnxO2-rutile structure, if formed, will show only marginal local distortion. Determination of M–O (M=Ce or Sn) bond lengths and analysis of Born effective charges for the optimized structure of Ce1−xSnxO2 show that local coordination of these cations changes from ideal eightfold coordination expected of fluorite lattice to 4+4 coordination, leading to generation of long and short Ce–O and Sn–O bonds in the doped structure. Bond valence analyses for all ions show the presence of oxygen with bond valence ∼1.84. These weakly bonded oxygen ions are relevant for enhanced oxygen storage/release properties observed in Ce1−xSnxO2 solid solution.
Electron-acoustic vortices in multicomponent magnetoplasma
Authors: Haque Q. , Mirza Arshad M. , Nargis Shahida
Published: May 2010

Linear and nonlinear properties of electron-acoustic waves in a multicomponent magnetoplasma comprising of cold and beam electrons and two species of thermal unmagnetized ions are investigated here. It is found that the electron beam velocity, electron Debye length, electron Larmor radius, and concentration of the cold and beam electrons affect the linear dispersion characteristics of electron-acoustic wave. It is also found that such a multicomponent plasma admits dipolar and vortex street type structures for the normalized electrostatic potential Φ<1. The relevance of this investigation in laboratory as well as in space plasmas such as in auroral region, geomagnetic tail, etc. is also pointed out.
Toroidal kinetic ηi-mode study in reversed-field pinch plasmas
Authors: Liu Songfen , Guo S. C. , Dong J. Q.
Published: May 2010

The ion temperature gradient (ITG) driven electrostatic modes in reversed-field pinch (RFP) plasma are studied with the gyrokinetic integral equation. A systematic threshold study is carried out and the results are compared with that in tokamaks with similar geometry and reveal that the ITG modes in RFP configurations are more stable than in tokamaks. The physics mechanism for such difference is that shorter connection length in RFPs leads to stronger landau damping, which is dominant and ultimately determinant for the stability threshold. The results confirm and extend the previous conclusion obtained with the differential equation [S. C. Guo, Phys. Plasmas 13, 122510 (2008)]. In addition, the effects of magnetic gradient and curvature drifts, which induce important interaction driving the modes, are carefully investigated. The effects of safety factor, ratio of electron temperature to ion temperature, magnetic shear as well as finite Larmor radius are also studied.
Magnetic moment and local moment alignment in anionic and/or oxidized Fen clusters
Authors: Roy D. R. , Robles R. , Khanna S. N.
Published: May 2010

First principles studies on the ground state structure, binding energy, spin multiplicity, and the noncollinearity of local spin moments in Fen and Fen− clusters and their oxides, viz., FenO2 and FenO2− have been carried out within a density functional formalism. The ground states of Fen and Fen− clusters have collinear spins with a magnetic moment of around 3.0 μB per atom. The O2 molecule is found to be dissociatively absorbed and its most significant effect on spin occurs in Fe2, where Fe2O2 and Fe2O2− show antiferromagnetic and noncollinear spin arrangements, respectively. The calculated adiabatic electron affinity and the vertical transitions from the anion to the neutral species are found to be in good agreement with the available negative ion photodetachment spectra, providing support to the calculated ground states including the noncollinear ones.
Structures of neutral and anionic Au16 clusters revisited
Authors: Chen Gang , Wang Qian , Sun Qiang , Kawazoe Yoshiyuki , Jena Puru
Published: May 2010

Using the density functional theory and generalized gradient approximation for exchange and correlation potential, we have performed an extensive search to obtain the ground state geometries of both neutral and anionic Au16 cluster by considering over 200 low lying isomers. For the neutral Au16 cluster we found a new Td compact structure to be the lowest energy configuration, which is nearly degenerate in total energy with the previously reported Cs and C2v noncage structures. While the Au16− cluster, in agreement with previous calculations, is found to have a Td hollow cage structure, an isomer with a planar structure is found to be lower in energy. The photoelectron spectra from all the nine lowest energy isomers are calculated and compared with experiment to determine the possibility of their existence. Molecular dynamics simulations on both neutral and anionic Au16 clusters are carried out to provide further insight into the origin and stability of these structures. Our comprehensive study allows us to answer the following questions: (1) Why are the adiabatic and vertical detachment energies of Au16 cluster nearly identical when the lowest energy structures of the anion and the neutral are so very different? (2) How is Au16− formed? Is it born neutral and the extra electron attaches afterwards or is it born anionic and the structure evolves during the electron attachment process?
Experimental and modeling study of thermal rate coefficients and cross sections for electron attachment to C60
Authors: Viggiano Albert A. , Friedman Jeffrey F. , Shuman Nicholas S. , Miller Thomas M. , Schaffer Linda C. , Troe Jürgen
Published: May 2010

Thermal electron attachment to C60 has been studied by relative rate measurements in a flowing afterglow Langmuir probe apparatus. The rate coefficients of the attachment k1 are shown to be close to 10−6 cm3 s−1 with a small negative temperature coefficient. These results supersede measurements from the 1990s which led to much smaller values of k1 with a large positive temperature coefficient suggesting an activation barrier. Theoretical modeling of k1 in terms of generalized Vogt–Wannier capture theory shows that k1 now looks more consistent with measurements of absolute attachment cross sections σat than before. The comparison of capture theory and experimental rate or cross section data leads to empirical correction factors, accounting for “intramolecular vibrational relaxation” or “electron-phonon coupling,” which reduce k1 below the capture results and which, on a partial wave-selected level, decrease with increasing electron energy.
Lattice thermal transport in BaxREyCo4Sb12 (RE=Ce, Yb, and Eu) double-filled skutterudites
Authors: Bai S. Q. , Shi X. , Chen L. D.
Published: May 2010

We use the Debye model to investigate the phonon scattering mechanisms in BaxREyCo4Sb12 double-filled skutterudites. Filling two types of guest atoms (barium and rare-earth elements) into the voids of skutterudite introduces additional phonon point defect scattering from the extra mass fluctuation at the void site, and additional phonon resonant scattering by the fillers with different vibrational frequencies, leading to significant reduction in the lattice thermal conductivity.
Jet regime of the afterspark channel decay
Authors: Leonov S. B. , Isaenkov Y. I. , Firsov A. A. , Nothnagel S. L. , Gimelshein S. F. , Shneider M. N.
Published: May 2010

Experimental and computational analyses of jet formation at the boundary of a decaying pulse discharge in an ambient quiescent air at 1 atm are presented. High velocity jets are observed attributed to the channel curvature set during the initial breakdown phase. The general convex-to-concave jet direction is explained, and the mechanisms of jets formation are discussed.
An optimized three-dimensional linear-electric-field time-of-flight analyzer
Authors: Gilbert J. A. , Lundgren R. A. , Panning M. H. , Rogacki S. , Zurbuchen T. H.
Published: May 2010

In situ measurements of the dynamics and composition of space plasmas have greatly improved our understanding of the space environment. In particular, mass spectrometers that use a combination of electrostatic analyzers and time-of-flight systems can identify revealing dynamic and compositional characteristics of ions, and thus constrain their sources and the physical processes relevant for their transport. We demonstrate an optimized design of a linear-electric-field time-of-flight technology that can be used to obtain a high signal to noise: ions that follow an energy-isochronous oscillation within the instrument impact an emissive plate and cause secondary electrons to be sent toward the detector, triggering a high-resolution measurement. By focusing these secondary electrons to a central area on a position-sensitive anode, their signals are separated from ions and neutrals that do not experience energy-isochronous motion. Using their impact positions, the high mass resolution measurements are easily distinguished from other signals on the detector, leading to very favorable signal-to-noise ratios. This optimization provides an improvement to existing technologies without increasing the instrument size or complexity, and uses a novel time-of-flight circuit that combines timing and position information from many signals and ions.
Surface acoustic wave devices based on AlN/sapphire structure for high temperature applications
Authors: Aubert Thierry , Elmazria Omar , Assouar Badreddine , Bouvot Laurent , Oudich Mourad
Published: May 2010

AlN/sapphire layered structure has been investigated as a potential substrate for surface acoustic wave (SAW) devices operating at high temperatures up to 950 °C under air atmosphere. Frequency characterizations of the SAW delay lines based on this structure indicate a slight increase of 2 dB in the insertion losses after annealing for 30 min at 900 °C. Scanning electron and atomic force microscopy as well as x-ray diffraction measurements suggest that theses losses are due to the deterioration of the Pt/Ta electrodes and to a slight oxidation of the AlN film.
Positive temperature coefficient resistor behavior in praseodymium-doped ZnO (0001¯)∣(0001¯) boundaries
Authors: Lee Jong-Sook , Kim Yong , Shin Eui-Chol , Maier Joachim
Published: May 2010

Clear positive temperature coefficient resistor (PTCR) dc behavior has been shown in Pr-doped ZnO (0001¯)∣(0001¯) bicrystals by electrical characterization over an unprecedentedly wide temperature range between 40 and 1070 K. With subtraction of the PTCR dc, the admittance can be described by a deep trap level at 0.26 eV but no clue to the origin of the PTCR behavior is provided. Capacitance-voltage characteristics revealed a maximum in the Schottky barrier heights consistent with the PTCR behavior. The PTCR behavior in Pr-doped ZnO c-axis oriented bicrystals is thus phenomenologically analogous to that of the ferroelectric BaTiO3.
Detecting, but not affecting, nest-box occupancy
Authors: Moore Tracey , de Tores Paul , Fleming Patricia A.
Published: May 2010

Context. Nest boxes are a useful tool in the reintroduction, conservation and monitoring of many hollow-using species.
Aims. All forms of nest-box monitoring involve some form of invasion, often upsetting their continued use by occupants. We conducted a pilot study to investigate and validate the innovative use of temperature dataloggers (iButtons®) to remotely monitor nest-box use, leaving the nest-box occupants untouched.
Methods. In captivity, iButton recordings revealed the duration and time of day when each of the three nest-box designs was occupied by Pseudocheirus occidentalis (western ringtail possums); the accuracy of occupancy data was validated by unobtrusive infrared video recording. In the field, where translocated P. occidentalis and naturally occurring Trichosurus vulpecula (common brushtail possum) populations are present, hair sampling at the nest-box entrances (in addition to iButton recording) was used to identify the mammal species present.
Key results. Nest-box use by captive P. occidentalis validated iButtons as a useful remote-monitoring tool, with <5–6% error for two nest-box designs. Although there was limited use of nest boxes at the field site, our results confirmed that iButtons are useful for remote-monitoring of nest-box use in the field; iButton data revealed both short (<2 h) and long (>10 h) periods of continuous occupancy (T. vulpecula only). In addition to the convenience (to researcher and animal) of continuous (24-h) monitoring with minimal disturbance, a major advantage from using iButtons is that occupancy can be matched with environmental temperature or rainfall records, as well as other events (e.g. storms or frost).
Conclusions. iButtons are a useful remote-monitoring tool of nest boxes, and it is possible that their use in this manner may be extended to tree-hollow occupation. Most importantly, this approach can inform us as to the conditions under which the nest boxes are used by fauna, as well as preferences for different nest-box designs.
Implications. It is important to note that the criteria used for determining the presence or absence in the nest box (i.e. temperature difference, Tin– Tout, of 2°C) in the present study will not be relevant for all nest-box designs and before using these methods, the thermal properties of the nest box or tree hollow will require investigation.