bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of the Leeuwin Current on phytoplankton biomass and production off Southwestern Australia
Authors: Koslow J. Anthony , Pesant Stephane , Feng Ming , Pearce Alan , Fearns Peter , Moore Thomas , Matear Richard , Waite Anya
Published: July 2008

Unlike most eastern boundary currents, the Leeuwin Current off the west coast of Australia flows poleward and is therefore warm, nutrient‐poor and suppresses upwelling. As a result, the waters off Western Australia are relatively oligotrophic. Primary productivity and concentrations of chlorophyll are particularly low in summer, when the water column is stratified and most chlorophyll is concentrated in a layer above the nutricline at approximately 100 m depth. The phytoplankton blooms in late autumn and winter, coinciding with the period of strongest Leeuwin flow. The bloom in winter is maintained by cooling and storms, which promote convective mixing of the upper water column and a shoaling of the nutricline and chlorophyll maximum layer. However, the late autumn bloom coincides with the initial intensification of the Leeuwin Current. Eddies and meanders spin up just beyond the shelf break, and Leeuwin Current water was observed at this time to destratify the water column and flood the shelf with relatively nutrient‐rich water. Several potential sources for the nutrients are proposed: upwelling by the eddies and meanders as they induce cross‐shelf motions; advection from the north, where the nutricline is shallower; and seasonal cooling.
Inferred influence of nutrient availability on the relationship between Sun‐induced chlorophyll fluorescence and incident irradiance in the Bering Sea
Authors: Schallenberg Christina , Lewis Marlon R. , Kelley Dan E. , Cullen John J.
Published: July 2008

This study examines variability in the relationship between Sun‐induced chlorophyll fluorescence and incident solar irradiance as a potential diagnostic of the nutritional status of phytoplankton. The study site is the Bering Sea, where two optical drifters were caught for more than 100 days in an anticyclonic eddy, while two others provided data from adjacent waters. Estimates of fluorescence emission normalized to the absorption of light by pigments were analyzed as a function of irradiance to describe variability of the quantum yield of fluorescence. Yields in bright sunlight and under lower light varied by a factor of 5 or more on the scale of days to weeks. For the one drifter that remained in the high‐velocity region of the eddy, there was a lagged correlation between the eddy rotation period and fluorescence parameters, with higher fluorescence yields in both low and high irradiance associated with slower rotation. Since nutrient input to the photic zone may increase with increasing shear of the eddy flow, this is consistent with the established suggestion that Sun‐induced fluorescence increases with nutrient stress in phytoplankton. Independent measurements of variable fluorescence (Fv/Fm, an indicator of photosynthetic efficiency) further support this interpretation. However, modeling shows that the established hypothesis of competition between photosynthesis and fluorescence for absorbed photons (i.e., photochemical quenching), with high fluorescence yields reflecting photosynthetic debility, does not apply near the sea surface, where photosynthesis is saturated, and dissipation of excess absorbed radiation by nonphotochemical quenching is the dominant influence on fluorescence yield.
Testing an ocean carbon model with observed sea surface pCO2 and dissolved inorganic carbon in the tropical Pacific Ocean
Authors: Christian James R. , Feely Richard A. , Ishii Masao , Murtugudde Ragu , Wang Xiujun
Published: July 2008

A basin‐scale carbon model for the tropical Pacific has been tested against in situ observations of CO2 partial pressure (pCO2) and dissolved inorganic carbon. Best agreement between model and observations occurs when gas exchange is enhanced at low wind speeds and when frictional smoothing as a parameterization of mesoscale eddy stirring/mixing is minimal. However, different realizations of the biological pump are not equally sensitive to the friction parameters, and it is not possible to completely isolate the effects of physics and biology. The model ocean shows substantial interannual variability in pCO2 and CO2 flux which is strongly correlated with the Multivariate ENSO Index. Interannual variability is similar to other models and suggests a relatively small role for the ocean in interannual variability of atmospheric CO2 growth. There are significant areas where CO2 remained supersaturated throughout the 1997–1998 El Niño and there was net outgassing from the “Wyrtki Box” at all times, but the net flux from the full model domain was near zero at the peak of the event. Testing the model against ship‐based observations produces a credible four‐dimensional field of the tropical ocean carbon system. Sampling this field with methods analogous to those used in empirical reconstructions of CO2 flux suggests that those methods can underestimate the interannual variability by up to a factor of ∼2.5 depending on the grid resolution used. Models and observations are not currently adequate to state with confidence that undersampled mesoscale variability does not affect the variability of the regional aggregate flux.
Rapid development and persistence of a massive Antarctic sea ice tongue
Authors: Rintoul Stephen R. , Sokolov Serguei , Massom Robert A.
Published: July 2008

An extraordinary sea ice tongue developed near 85°E over a period of 30 days in April–May 2002. The ice tongue extended to the north more than 800 km from the surrounding ice edge and covered an area greater than 200,000 km2. Satellite measurements of ice extent and roughness characteristics demonstrate that the tongue persisted as a distinct feature throughout the winter. Remote sensing observations between 1978 and 2004 confirm that ice tongues occur frequently at this location, although the 2002 tongue was particularly pronounced. We show that ocean currents and winds conspire to favor the development of ice tongues at this location. Mean streamlines of the southern part of the Antarctic Circumpolar Current turn sharply to the north near 85°E after passing through the Princess Elisabeth Trough. The edge and northern limit of the ice tongue correspond well with the pattern of mean streamlines. Mean winds in April–May have a dominant southerly component in this location, favoring offshore advection of ice; year‐to‐year variability in the prominence of the tongue is largely caused by variations in the wind, with northerly (southerly) anomalies inhibiting (promoting) development of a sea ice tongue. Ice drift is strongly northward along the axis of the tongue, suggesting the feature is formed by advection of ice from the south rather than by in situ thermodynamic ice formation. The northward current and sea ice tongue at 85°E are associated with higher biomass at all trophic levels than observed elsewhere in east Antarctica.
Monitoring temporal variability of bubble release at seeps: The hydroacoustic swath system GasQuant
Authors: Greinert Jens
Published: July 2008

A lander‐based hydroacoustic swath system, GasQuant, was deployed in an intensely bubbling seep area at the shelf west of the Crimea Peninsula, Black Sea. With its horizontally oriented swath (21 beams, 63° swath angle, 180 kHz) GasQuant operates in a sonar‐like mode and monitors bubbles remotely, exploiting their strong backscattering when crossing the swath. All active seep spots were monitored simultaneously within the covered area (2075 m2). Even applying simple processing and visualization techniques (moving average for filtering, FFT for spectrum analyses; swath and trace plots) identified 17 seeps of different activity patterns that have been grouped as follows: (1) sporadically active with one to a few long bursts (up to 18 min) or randomly occurring short bursts (<200 bursts and active for <5% of the observation time); (2) regularly active seeps showing mainly short bursts of less than one minute but also longer burst of a few minutes (200–350 bursts and 5 to 20% active); (3) frequently active spots with sometimes very periodic bubble release (>350 bursts or >20% active). Studying the bubble release variability of single seeps and of the entire area allows speculation about the external and internal processes that modulate the bubble release. In the study area none of the 17 seeps was found to be permanently active. Only one was active for 75% and another one for 45% of the time monitored. The rest only released bubbles during less than 20% of the time with an overall average of only 12%. This would have strong implications for flux extrapolations if these were based on very accurate but few short‐term measurements. Both strong overestimates and underestimates are possible. High‐resolution monitoring over at least one tidal cycle as with the GasQuant system might help to get an idea of the temporal variability. Thus flux extrapolations can be corrected to better reflect the real seep activity.
Modeling mineral dust emissions from the Sahara desert using new surface properties and soil database
Authors: Laurent B. , Marticorena B. , Bergametti G. , Léon J. F. , Mahowald N. M.
Published: July 2008

The present study investigates the mineral dust emissions and the occurrence of dust emission events over the Sahara desert from 1996 to 2001. Mineral dust emissions are simulated over a region extending from 16°N to 38°N and from 19°W to 40°E with a ° × ° spatial resolution. The input parameters required by the dust emission model are surface features data (aerodynamic roughness length, dry soil size distribution and texture for erodible soils), and meteorological surface data (mainly surface wind velocity and soil moisture). A map of the aerodynamic roughness lengths is established based on a composition of protrusion coefficients derived from the POLDER‐1 surface products. Soil dry size distribution and texture are derived from measurements performed on soil samples from desert areas, and from a soil map derived from a geomorphologic analysis of desert landscapes. Surface re‐analyzed meteorological databases (ERA‐40) of the European Centre for Medium range Weather Forecasts (ECMWF) are used. The influence of soil moisture on simulated dust emissions is quantified. The main Saharan dust sources identified during the 6‐year simulated period are in agreement with the previous studies based on in situ or satellite observations. The relevance of the simulated large dust sources and point sources (“hot spots”) is tested using aerosol indexes derived from satellite observations (TOMS Absorbing Aerosol Index and Infrared Dust Difference Index Meteosat). The Saharan dust emissions simulated from 1996 to 2001 range from 585 to 759 Tg a−1. The simulations show marked seasonal cycles with a maximum in summer for the western Sahara and in spring for the eastern Sahara. The interannual variability of dust emissions is pronounced in the eastern part of the Sahara while the emissions from the western Sahara are more regular over the studied period. The soil moisture does not noticeably affect the Saharan dust emissions, their seasonal cycle or their interannual variability, but it can partly control and limit the dust emissions in some parts of the northern desert margin, where the precipitation rates are higher. Our simulations also tend to confirm that the Sahara is the major terrestrial source of mineral dust.
A Lagrangian identification of major sources of moisture over Central Brazil and La Plata Basin
Authors: Drumond Anita , Nieto Raquel , Gimeno Luis , Ambrizzi Tercio
Published: July 2008

This work examines the main sources of moisture over Central Brazil and La Plata Basin during the year through a new Lagrangian diagnosis method which identifies the humidity contributions to the moisture budget over a region. This methodology computes budgets of evaporation minus precipitation by calculating changes in the specific humidity along back‐trajectories for the previous 10 d. The origin of all air masses residing over each region was tracked during a period of 5 years (2000–2004). These regions were selected because they coincide with two centers of action of a known dipole precipitation variability mode observed in different temporal scales (from intra seasonal up to inter decadal timescales) and are related to the climatic variability of the South American Monsoon System. The results suggested the importance of the tropical south Atlantic as a moisture source for Central Brazil, and of recycling for La Plata basin. It seems that the Tropical South Atlantic plays an important role as a moisture source for Central Brazil and La Plata basin along the year, particularly during the austral summer. The north Atlantic is also an additional source for both regions during the austral summer.
Production of 15N‐depleted biomass during cyanobacterial N2‐fixation at high Fe concentrations
Authors: Zerkle Aubrey L. , Junium Christopher K. , Canfield Donald E. , House Christopher H.
Published: July 2008

In this study we examine the effects of varying Fe, Mo, and P concentrations on δ15N fractionation during N2 fixation in the cyanobacterium Anabaena variabilis. We show that when grown in Fe‐enriched media ([Fe] ≥ 50 nM), this organism produces biomass up to 3‰ lower in δ15N than when grown in Fe‐limited media ([Fe] < 50 nM). A compilation of our data with previous measurements of δ15N in N2‐fixing cyanobacteria reveals a general trend toward the production of more 15N‐depleted biomass at higher Fe concentrations. We discuss our results in the context of negative δ15N values preserved in Archean and some Phanerozoic sediments, generally attributed to the production of marine organic matter with low δ15N by N2 fixation (and potentially NH4+ regeneration) during periods of fluctuating nutrient dynamics. We suggest that enhanced Fe availability during periods of widespread ocean anoxia can further stimulate the production of 15N‐depleted biomass by N2‐fixing organisms, contributing to the isotopic record.
Climate and Tectonic Changes in the Ocean Around New Zealand
Authors: Proust Jean‐Noel , Lamarche Geoffroy , Migeon Sébastien , Neil Helen
Published: July 2008

Many countries have recognized climate change due to human activities as one of the most critical issues facing the modern world. However, validating predictive models of the potential anthropogenic impact on shaping the Earth's surface requires the examination and documentation of analogous tectonic and climate changes of the past, working with the paradigm that past environmental changes are keys to understanding the future.

A France‐New Zealand research program, which also involves institutions from several other countries, aims to disentangle the impact of tectonics and climate on the landscape evolution of New Zealand over the past million years, at a very high resolution timescale—with steps as small as 100 years, i.e., relating to events such as earthquakes, tsunamis, and cyclones. The 5‐year “Matacore” program (whose name derives from the Matakaoa debris flow coring program, although the program scope is larger than that) began in January 2006 during Leg 152 of R/V Marion Dufresne. The research team collected 31 sediment cores, cumulating 600 meters of soft sediment, during a 15‐day survey around New Zealand. Preliminary results of the program show complex interactions between tectonics and climate.
2007 Editors' Citations for Excellence in Refereeing
Authors: Anonymous
Published: July 2008

The reviewers listed below have been cited by editors of AGU journals for excellence in refereeing. The editors' citations (photographs provided as available) recognize this special service to the Union, and these individuals are to be commended for consistently providing constructive and thoughtful reviews.
Occurrence of weak, sub‐micron, tropospheric aerosol events at high Arctic latitudes
Authors: O'Neill N. T. , Pancrati O. , Baibakov K. , Eloranta E. , Batchelor R. L. , Freemantle J. , McArthur L. J. B. , Strong K. , Lindenmaier R.
Published: July 2008

Numerous fine mode (sub‐micron) aerosol optical events were observed during the summer of 2007 at the High Arctic atmospheric observatory (PEARL) located at Eureka, Nunavut, Canada. Half of these events could be traced to forest fires in southern and eastern Russia and the Northwest Territories of Canada. The most notable findings were that (a) a combination of ground‐based measurements (passive sunphotometry, high spectral resolution lidar) could be employed to determine that weak (near sub‐visual) fine mode events had occurred, and (b) this data combined with remote sensing imagery products (MODIS, OMI‐AI, FLAMBE fire sources), Fourier transform spectroscopy and back trajectories could be employed to identify the smoke events.
Stratification and mixing on sloping boundaries
Authors: Lorke A. , Umlauf L. , Mohrholz V.
Published: July 2008

In lakes as well as in the ocean vertical transport is, to a large extent, controlled by localized mixing along the boundaries of the respective basin. Direct measurements of turbulent mixing and density stratification in the bottom‐boundary layer of a large and deep lake reveal the importance of cross‐slope advection near sloping boundaries for local and basin‐scale vertical transport. The periodic, internal wave driven, occurrence of up‐ and downslope directed currents results in periodic heating and cooling of the boundary layer. Cooling of the boundary layer during periods of up‐slope flow is associated with unstable stratification and turbulent diffusivities exceed those observed during periods of down‐slope flow by almost one order of magnitude. The periodic replacement of water in this layer with water from the interior of the basin maintains vertical density gradients and thus enhances the overall efficiency of the boundary mixing.
An ensemble approach for attribution of hydrologic prediction uncertainty
Authors: Wood Andrew W. , Lettenmaier Dennis P.
Published: July 2008

Hydrologic prediction errors arise from uncertainty in initial moisture states (mainly snowpack and soil moisture), in boundary forcings (primarily future precipitation and temperature), and from model structure and parameter uncertainty. We evaluate the relative importance of initial condition and boundary forcing uncertainties using a hindcast‐based framework that contrasts Ensemble Streamflow Prediction (ESP) with an approach that we term “reverse‐ESP”. In ESP, a hydrologic model with assumed perfect initial conditions (ICs) is forced by a forecast ensemble resampled from observed meteorological sequences; whereas reverse‐ESP combines an ensemble of resampled ICs with a perfect meteorological forecast. The framework shows that in northern California, US, ICs yield streamflow prediction skill for up to 5 months during the transition between the wet and dry seasons, whereas during the reverse transition, climate forecast information is critical. In southern Colorado, IC knowledge outweighs climate prediction skill for shorter periods due to a more uniform precipitation regime.
Ground surface temperature reconstructions: Using in situ estimates for thermal conductivity acquired with a fiber‐optic distributed thermal perturbation sensor
Authors: Freifeld B. M. , Finsterle S. , Onstott T. C. , Toole P. , Pratt L. M.
Published: July 2008

We have developed a borehole methodology to estimate formation thermal conductivity in situ with a spatial resolution of one meter. In parallel with a fiber‐optic distributed temperature sensor (DTS), a resistance heater is deployed to create a controlled thermal perturbation. The transient thermal data is inverted to estimate the formation's thermal conductivity. We refer to this instrumentation as a Distributed Thermal Perturbation Sensor (DTPS), given the distributed nature of the DTS measurement technology. The DTPS was deployed in permafrost at the High Lake Project Site (67°22′N, 110°50′W), Nunavut, Canada. Based on DTPS data, a thermal conductivity profile was estimated along the length of a wellbore. Using the thermal conductivity profile, the baseline geothermal profile was then inverted to estimate a ground surface temperature history (GSTH) for the High Lake region. The GSTH exhibits a 100‐year long warming trend, with a present‐day ground surface temperature increase of 3.0 ± 0.8°C over the long‐term average.
Magnetic coupling of the ring current and the radiation belt
Authors: Ebihara Y. , Fok M.‐C. , Blake J. B. , Fennell J. F.
Published: July 2008

The magnetic influence of the storm time ring current on high‐energy particles is demonstrated by using a simulation of the ring current incorporating self‐consistent magnetic and electric fields. Observations by the Polar satellite show that the magnetic field is occasionally depressed by 50% or more near the equatorial plane at <6 RE. We call them equatorially magnetic depression events (EMDEs) and focus on the most intense EMDE observed during an intense storm on 22 October 1999. The simulation predicts that under a strong convection electric field, the magnetic field strength is highly depressed around L = 5 by newly injected ions of energy 80 keV or less. The depressed magnetic field causes a significant adiabatic decrease in the high‐energy ion flux at pitch angles near 90° to conserve the first adiabatic invariant. A more tail‐like (shortened) magnetic field line causes an enhancement of the flux at pitch angles near 0° and 180° to conserve the second adiabatic invariant. Consequently, a butterfly‐like pitch angle distribution (PAD) is formed, which agrees with the Polar observation. We propose that the adiabatic process could have acted not only on the high‐energy component of the protons but also on relativistic electrons in the outer radiation belt. This notion is supported by simultaneous Polar observation of relativistic electron fluxes that show a decrease at pitch angles near 90° and a slight increase at pitch angles near 0° and 180°. PADs of protons and electrons can be used to distinguish nonadiabatic processes acting selectively on electrons from adiabatic ones.
Comparative methods in R hackathon
Authors: O’Meara Brian , Alfaro Michael , Bell Charles , Bolker Benjamin , Butler Marguerite , Cowan Peter , de Vienne Damien , Desper Richard , Felsenstein Joseph , Harmon Luke , Heibl Christoph , Hipp Andrew , Hunt Gene , Jombart Thibaut , Kembel Steve , Lapp Hilmar , Loarie Scott , Maddison Wayne , Midford Peter , Orme David , Paradis Emmanuel , Price Sam , Rabosky Dan , Sidlauskas Brian , Smith Stacey , Swofford Dave , Vision Todd , Waddell Peter , Zanne Amy , Zwickl Derrick
Published: July 2008

The R statistical analysis package has emerged as a popular platform for implementation of powerful comparative methods to understand the evolution of organismal traits and diversification. A hackathon was organized to bring together active R developers as well as end-users working on the integration of comparative phylogenetic methods within R to actively address issues of data exchange standards, code interoperability, usability, documentation quality, and the breadth of functionality for comparative methods available within R. Outcomes included a new base package for phylogenetic trees and data, a public wiki with tutorials and overviews of existing packages, code to allow Mesquite and R to interact, improvement of existing packages, and increased interaction within the community.
MAP1 structural organization in Drosophila: in vivo analysis of FUTSCH reveals heavy- and light-chain subunits generated by proteolytic processing at a conserved cleavage site
Authors: Zou Beiyan , Yan Huaru , Kawasaki Fumiko , Ordway Richard W.
Published: July 2008

The MAP1 (microtubule-associated protein 1) family is a class of microtubule-binding proteins represented by mammalian MAP1A, MAP1B and the recently identified MAP1S. MAP1A and MAP1B are expressed in the nervous system and thought to mediate interactions of the microtubule-based cytoskeleton in neural development and function. The characteristic structural organization of mammalian MAP1s, which are composed of heavy- and light-chain subunits, requires proteolytic cleavage of a precursor polypeptide encoded by the corresponding map1 gene. MAP1 function in Drosophila appears to be fulfilled by a single gene, futsch. Although the futsch gene product is known to share several important functional properties with mammalian MAP1s, whether it adopts the same basic structural organization has not been addressed. Here, we report the identification of a Drosophila MAP1 light chain, LCf, produced by proteolytic cleavage of a futsch-encoded precursor polypeptide, and confirm co-localization and co-assembly of the heavy chain and LCf cleavage products. Furthermore, the in vivo properties of MAP1 proteins were further defined through precise MS identification of a conserved proteolytic cleavage site within the futsch-encoded MAP1 precursor and demonstration of light-chain diversity represented by multiple LCf variants. Taken together, these findings establish conservation of proteolytic processing and structural organization among mammalian and Drosophila MAP1 proteins and are expected to enhance genetic analysis of conserved MAP1 functions within the neuronal cytoskeleton.
Regulation of gene expression by hypoxia
Authors: Kenneth Niall Steven , Rocha Sonia
Published: July 2008

Hypoxia induces profound changes in the cellular gene expression profile. The discovery of a major transcription factor family activated by hypoxia, HIF (hypoxia-inducible factor), and the factors that contribute to HIF regulation have greatly enhanced our knowledge of the molecular aspects of the hypoxic response. However, in addition to HIF, other transcription factors and cellular pathways are activated by exposure to reduced oxygen. In the present review, we summarize the current knowledge of how additional hypoxia-responsive transcription factors integrate with HIF and how other cellular pathways such as chromatin remodelling, translation regulation and microRNA induction, contribute to the co-ordinated cellular response observed following hypoxic stress.
The evolution of Ga and As core levels in the formation of Fe∕GaAs (001): A high resolution soft x-ray photoelectron spectroscopic study
Authors: Thompson Jamie D. W. , Neal James R. , Shen Tiehan H. , Morton Simon A. , Tobin James G. , Dan Waddill G. , Matthew Jim A. D. , Greig Denis , Hopkinson Mark
Published: July 2008

A high resolution soft x-ray photoelectron spectroscopic study of Ga and As 3d core levels has been conducted for Fe∕GaAs (001) as a function of Fe thickness. This work has provided unambiguous evidence of substrate disrupting chemical reactions induced by the Fe overlayer—a quantitative analysis of the acquired spectra indicates significantly differing behavior of Ga and As during Fe growth, and our observations have been compared with existing theoretical models. Our results demonstrate that the outdiffusing Ga and As remain largely confined to the interface region, forming a thin intermixed layer. Whereas at low coverages Fe has little influence on the underlying GaAs substrate, the onset of substrate disruption when the Fe thickness reaches 3.5Å results in major changes in the energy distribution curves (EDCs) of both As and Ga 3d cores. Our quantitative analysis suggests the presence of two additional As environments of metallic character: one bound to the interfacial region and another which, as confirmed by in situ oxidation experiments, surface segregates and persists over a wide range of overlayer thickness. Analysis of the corresponding Ga 3d EDCs found not two, but three additional environments—also metallic in nature. Two of the three are interface resident whereas the third undergoes outdiffusion at low Fe coverages. Based on the variations of the integrated intensities of each component, we present a schematic of the proposed chemical makeup of the Fe∕GaAs (001) system.
X-ray conversion efficiency of high-Z hohlraum wall materials for indirect drive ignition
Authors: Dewald E. L. , Rosen M. , Glenzer S. H. , Suter L. J. , Girard F. , Jadaud J. P. , Schein J. , Constantin C. , Wagon F. , Huser G. , Neumayer P. , Landen O. L.
Published: July 2008

The conversion efficiency of 351nm laser light to soft x rays (0.1–5keV) was measured for Au, U, and high Z mixture “cocktails” used as hohlraum wall materials in indirect drive fusion experiments. For the spherical targets in a direct drive geometry, flattop laser pulses and laser smoothing with phase plates are employed to achieve constant and uniform laser intensities of 1014 and 1015W∕cm2 over the target surface that are relevant for the future ignition experiments at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)]. The absolute time and spectrally resolved radiation flux is measured with a multichannel soft x-ray power diagnostic. The conversion efficiency is then calculated by dividing the measured x-ray power by the incident laser power from which the measured laser backscattering losses are subtracted. After ∼0.5ns, the time resolved x-ray conversion efficiency reaches a slowly increasing plateau of 95% at 1014W∕cm2 laser intensity and of 80% at 1015W∕cm2. The M-band flux (2–5keV) is negligible at 1014W∕cm2 reaching ∼1% of the total x-ray flux for all target materials. In contrast, the M-band flux is significant and depends on the target material at 1015W∕cm2 laser intensity, reaching values between 10% of the total flux for U and 27% for Au. LASNEX simulations [G. B. Zimmerman and W. L. Kruer, Comm. Plasma Phys. Contr. Fusion 2, 51 (1975)] show good agreement in conversion efficiency and radiated spectra with data when using XSN atomic physics model and a flux limiter of 0.15, but they underestimate the generated M-band flux.
Localized dynamic subgrid closure for simulation of magnetohydrodynamic turbulence
Authors: Miki Kenji , Menon Suresh
Published: July 2008

A local dynamic kinetic energy model (LDKM) for large-eddy simulation (LES) of magnetohydrodynamic (MHD) turbulence is proposed. The proposed MHD turbulence model evaluates all model coefficients locally and dynamically without any ad hoc averaging. This model also does not assume low magnetic Reynolds numbers. The turbulent residual-helicity effect (α-effect) appearing in the magnetic induction equation is successfully modeled. For validation, high-Re decaying isotropic decay turbulence with and without a mean magnetic field are studied using LES. The effect of rotation is also studied. For the case without rotation, it is observed that the energy spectrum follows a k−5∕3 law. For the case with rotation, it is shown that two mechanisms, phase scrambling due to frame rotation and Joule dissipation, are competing, and two distinct regimes with respect to rotation rate are observed. There is a critical rotation rate at which the energy decays most in MHD turbulence. It is also shown that this MHD-LDKM model is applicable to wide variety of high/low magnetic Reynolds number applications.
Microstructural evolution in H ion induced splitting of freestanding GaN
Authors: Moutanabbir O. , Scholz R. , Senz S. , Gösele U. , Chicoine M. , Schiettekatte F. , Süßkraut F. , Krause-Rehberg R.
Published: July 2008

We investigated the microstructural transformations during hydrogen ion-induced splitting of GaN thin layers. Cross-sectional transmission electron microscopy and positron annihilation spectroscopy data show that the implanted region is decorated with a high density of 1–2nm bubbles resulting from vacancy clustering during implantation. These nanobubbles persist up to 450°C. Ion channeling data show a strong dechanneling enhancement in this temperature range tentatively attributed to strain-induced lattice distortion. The dechanneling level decreases following the formation of plateletlike structures at 475°C. Extended internal surfaces develop around 550°C leading to the exfoliation of GaN thin layer.
Surface potential and magnetic properties of La0.7Sr0.3MnO3 periodic arrays fabricated by direct electron beam writing
Authors: Wu Ming-Chung , Wu Yi-Jen , Huang Yu-Ching , Chuang Chih-Min , Cheng Kuo-Chung , Lin Ching-Fuh , Chen Yang-Fang , Su Wei-Fang
Published: July 2008

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La0.7Sr0.3MnO3 electron beam resist. Two unique features of our approach are (1) the patterned La0.7Sr0.3MnO3 resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the dosage of electron beam. The mechanism of the dual function characteristic of the resist was studied using Kelvin probe microscope. The surface potential of patterned La0.7Sr0.3MnO3 resist increases with increasing electron beam dosage due to the changes of resist composition. The formations of periodic magnetic arrays were confirmed by the studies of scanning electron microscope and magnetic force microscope. The magnetization of La0.7Sr0.3MnO3 can be enhanced by postsintering the sample at 900 °C after electron beam irradiation. We have therefore provided a one-step, simple, and convenient alternative technique for the fabrication of nanoscale magnetic patterns, which form the building blocks for the study of physical properties in periodic magnetic arrays.
Experimental verification of standing-wave plasmonic resonances in split-ring resonators
Authors: Chen Chia-Yun , Wu Shich-Chuan , Yen Ta-Jen
Published: July 2008

We experimentally demonstrate multiple resonances in split-ring resonators (SRRs) from direct electric excitations in midinfrared and near infrared regions. The ratio of the entire length of SRRs to the resonance modes and wavelengths presents a clear linear relationship. Such expression validates in both cases of electric and magnetic responses in SRRs excited by electric field and is further confirmed by examining the SRRs with different lengths. Therefore, our quantitative observations indicate that the multiple resonances can be interpreted by the standing-wave plasmonic resonances and further facilitate to design the desired operation frequencies and responses of SRRs for practical applications.
Localized surface plasmon polaritons in Ag∕SiO2∕Ag plasmonic thermal emitter
Authors: Ye Yi-Han , Jiang Yu-Wei , Tsai Ming-Wei , Chang Yi-Tsung , Chen Chia-Yi , Tzuang Dah-Ching , Wu Yi-Ting , Lee Si-Chen
Published: July 2008

The reflection dispersion relation and emission spectra of Ag∕SiO2∕Ag trilayer plasmonic thermal emitters with different lattice constant and Ag line width were investigated. The top Ag film is perforated with parallel line-shape hole array. The induced Ag∕SiO2 surface plasmons at both top and bottom Ag∕SiO2 interface are found coupled together. The coupling effect results in the localized surface plasmon polaritons confined at the top Ag∕SiO2 interface which exhibit the Fabry–Pérot resonance. The thermal emission peak position coincides with the reflection minimum in the dispersion relation and shifts to long wavelength as the Ag line width increases, which proves that the emission is due to the excitation of localized surface plasmon polaritons. Moreover, the emitted light is polarized perpendicular to the parallel metal lines.
Quantum conditions on dynamics and control in open systems
Authors: Wu Lian-Ao , Bharioke Arjun , Brumer Paul
Published: July 2008

Quantum conditions on the control of dynamics of a system coupled to an environment are obtained. Specifically, consider a system initially in a system subspace H0 of dimensionality M0, which evolves to populate system subspaces H1, H2 of dimensionalities M1, M2. Then, there always exists an initial state in H0 that does not evolve into H2 if M0>dM2, where 2⩽d⩽(M0+M1+M2)2 is the number of operators in the Kraus representation. Note, significantly, that the maximum d can be far smaller than the dimension of the bath. If this condition is not satisfied, then dynamics from H0 that avoids H2 can only be attained physically under stringent conditions. An example from molecular dynamics and spectroscopy, i.e., donor to acceptor energy transfer, is provided.
Repeated epitaxial growth and transfer of arrays of patterned, vertically aligned, crystalline Si wires from a single Si(111) substrate
Authors: Spurgeon Joshua M. , Plass Katherine E. , Kayes Brendan M. , Brunschwig Bruce S. , Atwater Harry A. , Lewis Nathan S.
Published: July 2008

Multiple arrays of Si wires were sequentially grown and transferred into a flexible polymer film from a single Si(111) wafer. After growth from a patterned, oxide-coated substrate, the wires were embedded in a polymer and then mechanically separated from the substrate, preserving the array structure in the film. The wire stubs that remained were selectively etched from the Si(111) surface to regenerate the patterned substrate. Then the growth catalyst was electrodeposited into the holes in the patterned oxide. Cycling through this set of steps allowed regrowth and polymer film transfer of several wire arrays from a single Si wafer.
Stressed triangular lattices on microsized spherical surfaces and their defect management
Authors: Li C. R. , Dong W. J. , Gao L. , Cao Z. X.
Published: July 2008

Triangular lattices were assembled on spherical surfaces and caps via thermal stress engineering on core/shell microstructures. The lattices on a complete spherical surface, when the total number is small, contain uniquely fivefold disclinations, whereas scars consisting of pentamer-heptamer chains emerged when more vertices are available (>360). Disclination-free pattern were obtained on caps, revealing the defect management strategy in nature. All the experimental observations can be explained by numerical studies to Thomson’s problem [J. J. Thomson, Philos. Mag. 7, 237 (1904)]. These results can help understand the various patterns assembled on curved surfaces, and be of essential importance for the en masse fabrication of nanostructures on pliable substrates.
A modeling approach for the purification of group III metals (Ga and In) by zone refining
Authors: Ghosh K. , Mani V. N. , Dhar S.
Published: July 2008

An “experimental friendly” model for zone refining process is proposed which predicts effective zone length in each refining passes that would lead to maximal solute removal, thereby leading to ultrapurification of the material for use in high-end electronic applications. The effectiveness of the model is experimentally tested and validated by purifying gallium from 4N (99.99%) to 6N5 (99.99995%) purity level at 30% yield and ∼6 N at 70% yield with respect to targeted metallic impurities such as, Zn, Cu, Al, Ca, Bi, Si, Pb, Ni, Mn, and Fe, as analyzed by inductively coupled plasma optical emission spectrometry, graphite furnace atomic absorption spectrometry, and high resolution inductively coupled plasma mass spectrometry techniques. The distribution coefficient (k) of all the targeted impurities, detected in the purified gallium, was found to be less than 1. By comparing the experimentally obtained axial concentration profiles with the theoretical calculations, the k values of some detected impurities, such as Ca and Al, are determined to be ∼0.8, Pb and Bi to be 0.7, Cu to be 0.65, and Fe to be 0.68, which prove the efficiency of the proposed model in reducing the concentration of these vulnerable impurities significantly. Following the model and as evidenced from the theoretical predictions, degradation of material purification containing a mixture of impurities having k less than as well as greater than 1 was elucidated experimentally by zone refining of 4N6 indium. Only a 40% yield of 5N6 indium was obtained, thereby highlighting the intricacies and problem areas in ultrapurification of these types of material.
Dielectric properties of Ti2AlC and Ti2AlN MAX phases: The conductivity anisotropy
Authors: Haddad Noël , Garcia-Caurel Enric , Hultman Lars , Barsoum Michel W. , Hug Gilles
Published: July 2008

The optical properties of Ti2AlN and Ti2AlC were determined in the 2–80 eV energy range by electron energy loss spectroscopy and in the visible-ultraviolet range, from 1.6 to 5.5 eV, by spectroscopic ellipsometry. Both experimental techniques are angular resolved and in very good agreement over their overlapping energy range. We observe a dependence of the dielectric function as a function of the crystallographic orientation of the crystals. In particular, we notice a shift of the energy position of the plasmon absorption of Ti2AlC with respect to Ti2AlN. Moreover, a drastic change is also observed in the shape of the dielectric function as a function of the composition (or valence electron concentration). The dielectric functions are fitted to an empirical semiclassic Drude–Lorentz model to obtain physical parameters such as the relaxation times. These microscopic parameters are then used in a macroscopic model to yield the transport properties such as the static conductivity as function of the crystal orientation. Ti2AlN is found to be a better conductor than Ti2AlC in all orientations, which is consistent with experimental measurements. A comparison of the electrical and optical properties of these two compounds is made in terms of different electronic properties and interband-intraband transitions deduced from our model.
A complex x-ray characterization of heteroepitaxial silicon/insulator/silicon(111) structures
Authors: Zaumseil P. , Schroeder T.
Published: July 2008

The application of new semiconductor materials deposited on Si substrates via heteroepitaxial growth on oxide buffer layers is one possible way to improve performance and functionality of future Si-based integrated circuits. It is demonstrated how the crystallographic structure of semiconductor-insulator-semiconductor (SIS) structures consisting of a Si(111) substrate, Pr2O3 and Y2O3 insulating buffer layers, and Si cap layer can be characterized by different x-ray techniques. Especially a combination of pole figure measurement with conventional x-ray diffraction scans and reciprocal space mapping is applied to study the in-plane orientation of the oxide and epi-Si layer relative to the Si substrate, the strain state of the individual layers, and the structural perfection of the epi-Si film. Oxide and Si cap layer were grown by molecular beam epitaxy and have the same (111) lattice orientation as the substrate. It is shown that the oxide layers grow in a type B stacking orientation only, while the epilayer exhibits exclusively the same type A orientation as the substrate. Pole figure measurements reveal an unexpected orientation of a small fraction of the epi-Si lattice. This behavior was explained by microtwins as the major defect mechanism in the epi-Si layer. The proposed combination of x-ray techniques allows a relatively fast, integrated, and nondestructive analysis of the epi-Si layer.
Mössbauer study on martensite phase in Ni50Mn36.5Fe0.557Sn13 metamagnetic shape memory alloy
Authors: Umetsu R. Y. , Kainuma R. , Amako Y. , Taniguchi Y. , Kanomata T. , Fukushima K. , Fujita A. , Oikawa K. , Ishida K.
Published: July 2008

Magnetic and differential scanning calorimetric measurements and Mössbauer examination were carried out to clarify the magnetic features of Ni50Mn36.5Fe0.557Sn13. The magnetic field cooling effects were observed in the thermomagnetization curves below 235K and the Curie temperature of the parent phase was near the martensitic transformation temperature. The Mössbauer spectra taken from the parent+martensite two-phase state at 312K and from the martensite single-phase state at 264K were both singlets, showing a typical paramagnetic feature. On the other hand, the Mössbauer spectra taken from the martensite phase at 199 and 80K were complicated, including some magnetic components.
Simultaneous forward and backward terahertz generations in periodically poled stoichiometric LiTaO3 crystal using femtosecond pulses
Authors: Yu N. E. , Kang C. , Yoo H. K. , Jung C. , Lee Y. L. , Kee C.-S. , Ko D.-K. , Lee J. , Kitamura K. , Takekawa S.
Published: July 2008

Forward and counterpropagated backward terahertz generations were demonstrated via difference frequency generation using a femtosecond laser. By cooling the crystal to reduce terahertz losses, we achieved the terahertz generations of 1.36 and 0.65THz. Temperature-dependent measurements showed gradual intensity increase of the terahertz pulse and red shift of the center frequency as the temperature decrease from 255to143K, although there were insignificant decreases of the spectral bandwidth.
Dispersion and interaction of waveguide modes in a relativistic electron beam with ion-channel guiding
Authors: Maraghechi Borna , Maraghechi Behrouz
Published: July 2008

A theory for the high-frequency eigenmodes of a cylindrical metallic waveguide partially filled with a relativistic electron beam and guided by an ion channel is presented. Equations that permit calculation of dispersion curves for five families of wave modes are derived. The dependence of the frequencies and the dispersion curves of azimuthally asymmetric modes on the ratio of the beam radius a to the waveguide radius R are studied in detail. The coupling of the dispersion curves of different modes is studied and illustrated for the partially filled waveguide. It was found that, in their course of interaction, HE modes cannot displace the betatron modes in a completely filled waveguide, which is different from the case of a magnetized electron beam. Physical and analytical explanations are presented for this difference.
Enhanced light extraction efficiency from AlGaInP thin-film light-emitting diodes with photonic crystals
Authors: Bergenek K. , Wiesmann Ch. , Wirth R. , O’Faolain L. , Linder N. , Streubel K. , Krauss T. F.
Published: July 2008

We investigate the use of photonic crystals for light extraction from high-brightness thin-film AlGaInP light-emitting diodes with different etch depths, lattice constants, and two types of lattices (hexagonal and Archimedean). Both simulations and experimental results show that the extraction of high order modes with a low effective index neff is most efficient. The highest external quantum efficiency without encapsulation is 19% with an Archimedean A7 lattice with reciprocal lattice constant G=1.5k0, which is 47% better than an unstructured reference device.
Application of metal nanoparticles decorated carbon nanotubes in photovoltaics
Authors: Somani Prakash R. , Somani Savita P. , Umeno M.
Published: July 2008

Carbon nanotubes decorated with metal nanoparticles are introduced to photovoltaic application. The introduction of metal nanoparticles in the organic/organic-inorganic heterojunction solar cells is expected to improve the exciton dissociation (due to strong electric field at the metal-organics interface) and hence photovoltaic action. An improved photovoltaic action is indeed observed in n-Si/poly(3-octylthiophene) heterojunction solar cells incorporating multiwalled carbon nanotubes (MWCN) decorated with platinum metal nanoparticles (Pt: 20wt%, 10–15nm) as compared to pristine MWCN. The incorporation of metal nanoparticles should provide an alternative strategy to improve the photovoltaic performance of organic/organic-inorganic solar cells.
Design of fine phosphor system for the improvement in the luminescent properties of the phosphor layer in the plasma display panel: Theoretical and experimental analysis
Authors: Cho Chae-Woong , Paik Ungyu , Park Do-Hyung , Kim Yoon-Chang , Zang Dong-Sik
Published: July 2008

Improvement in the luminescent properties of plasma display panels via phosphor size control was theoretically and experimentally investigated. From theoretical analyses of photon extraction and plasma efficiency, fine phosphor system was designed, which was compared with experimental data. The denser microstructure of finer phosphor-based layer promoted photon extraction efficiency by higher reflectivity. Also, the finer phosphor increased vacuum-ultraviolet discharge space and corresponding plasma efficiency via decrease in layer thickness. Based on the results, the phosphor size control improved the panel efficiency by the synergistic effect of improvements in photon extraction and plasma efficiency.