bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling dust and soluble iron deposition to the South Atlantic Ocean
Authors: Johnson Matthew S. , Meskhidze Nicholas , Solmon Fabien , Gassó Santiago , Chuang Patrick Y. , Gaiero Diego M. , Yantosca Robert M. , Wu Shiliang , Wang Yuxuan , Carouge Claire
Published: August 2010

The global chemical transport model GEOS‐Chem, implemented with a dust‐iron dissolution scheme, was used to analyze the magnitude and spatial distribution of mineral dust and soluble‐iron (sol‐Fe) deposition to the South Atlantic Ocean (SAO). The comparison of model results with remotely sensed data shows that GEOS‐Chem can capture dust source regions in Patagonia and characterize the temporal variability of dust outflow. For a year‐long model simulation, 22 Tg of mineral dust and 4 Gg of sol‐Fe were deposited to the surface waters of the entire SAO region, with roughly 30% of this dust and sol‐Fe predicted to be deposited to possible high nitrate low chlorophyll oceanic regions. Model‐predicted dissolved iron fraction of mineral dust over the SAO was small, on average only accounting for 0.57% of total iron. Simulations suggest that the primary reason for such a small fraction of sol‐Fe is the low ambient concentrations of acidic trace gases available for mixing with dust plumes. Overall, the amount of acid added to the deliquesced aerosol solution was not enough to overcome the alkalinity buffer of Patagonian dust and initiate considerable acid dissolution of mineral‐iron. Sensitivity studies show that the amount of sol‐Fe deposited to the SAO was largely controlled by the initial amount of sol‐Fe at the source region, with limited contribution from the spatial variability of Patagonian‐desert topsoil mineralogy and natural sources of acidic trace gases. Simulations suggest that Patagonian dust should have a minor effect on biological productivity in the SAO.
A new method to retrieve the aerosol layer absorption coefficient from airborne flux density and actinic radiation measurements
Authors: Bierwirth Eike , Wendisch Manfred , Jäkel Evelyn , Ehrlich André , Schmidt K. Sebastian , Stark Harald , Pilewskie Peter , Esselborn Michael , Gobbi Gian Paolo , Ferrare Richard , Müller Thomas , Clarke Antony
Published: August 2010

A new method is presented to derive the mean value of the spectral absorption coefficient of an aerosol layer from combined airborne measurements of spectral net irradiance and actinic flux density. While the method is based on a theoretical relationship of radiative transfer theory, it is applied to atmospheric radiation measurements for the first time. The data have been collected with the Spectral Modular Airborne Radiation Measurement System (SMART‐Albedometer), the Solar Spectral Flux Radiometer (SSFR), and the Actinic Flux Spectroradiometer (AFSR) during four field campaigns between 2002 and 2008 (the Saharan Mineral Dust Experiment (SAMUM), the Influence of Clouds on the Spectral Actinic Flux in the Lower Troposphere (INSPECTRO) project, and the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites and Aerosol, Radiation, and Cloud Processes Affecting Arctic Climate (ARCTAS/ARCPAC) projects). The retrieval algorithm is tested in a series of radiative transfer model runs and then applied to measurement cases with different aerosol species and loading. The method is shown to be a feasible approach to obtain the mean aerosol absorption coefficient across a given accessible altitude range. The results indicate that the method is viable whenever the difference of the net irradiance at the top and bottom of a layer is equal to or higher than the measurement uncertainty for net irradiance. This can be achieved by a high optical depth or a low single‐scattering albedo within the layer.
A solution for multicomponent reactive transport under equilibrium and kinetic reactions
Authors: Sanchez‐Vila Xavier , Donado Leonardo David , Guadagnini Alberto , Carrera Jesus
Published: August 2010

Analysis of the space‐time evolution of reactive solutes in porous systems is complex owing to the presence of different types of chemical reactions. The complete description of a reactive transport scenario entails calculating the spatial and temporal distribution of species concentrations and reaction rates. Here we develop an exact explicit expression for the space‐time distribution of reaction rates for a scenario where the geochemical system can be described by an arbitrary number of equilibrium (fast) reactions and one kinetic (slow) reaction, in the absence of non‐constant‐activity immobile species. The key result is that the equilibrium reaction rate is the sum of two terms representing the availability of reactants. One term involves diffusion and dispersion and represents the contribution of mixing. The other term includes the contribution of the kinetic reaction. The approach also yields the local concentrations of all dissolved species. Yet the latter are not needed for the direct computation of equilibrium reaction rates. We illustrate the approach by means of a simple reactive transport scenario, involving a common ion effect in the presence of a kinetic and an equilibrium reaction leading to precipitation and dissolution processes within a one‐dimensional fully saturated porous medium. The example highlights the highly nonlinear and nonmonotonic response of the system to the controlling input parameters.
Solute dynamics during bank storage flows and implications for chemical base flow separation
Authors: McCallum James L. , Cook Peter G. , Brunner Philip , Berhane Dawit
Published: August 2010

Chemical base flow separation is a widely applied technique in which contributions of groundwater and surface runoff to streamflow are estimated based on the chemical composition of stream water and the two end‐members. This method relies on the assumption that the groundwater end‐member can be accurately defined and remains constant. We simulate solute transport within the aquifer during and after single and multiple river flow events, to show that (1) water adjacent to the river will have a concentration intermediate between that of the river and that of regional groundwater and (2) the concentration of groundwater discharge will approach that of regional groundwater after a flow event but may take many months or years before it reaches it. In applying chemical base flow separation, if the concentration in the river prior to a flow event is used to represent the pre‐event or groundwater end‐member, then the groundwater contribution to streamflow will be overestimated. Alternatively, if the concentration of regional groundwater a sufficient distance from the river is used, then the pre‐event contribution to streamflow will be underestimated. Changes in concentration of groundwater discharge following changes in river stage predicted by a simple model of stream‐aquifer flows show remarkable similarity to changes in river chemistry measured over a 9 month period in the Cockburn River, southeast Australia. If the regional groundwater value was used as the groundwater end‐member, chemical base flow separation techniques would attribute 8% of streamflow to groundwater, as opposed to 25% if the maximum stream flow value was used.
Influence of wettability variations on dynamic effects in capillary pressure
Authors: O'Carroll Denis M. , Mumford Kevin G. , Abriola Linda M. , Gerhard Jason I.
Published: August 2010

Traditional continuum‐based multiphase simulators incorporate a capillary pressure‐saturation relationship that assumes instantaneous attainment of equilibrium following a disturbance. This assumption may not be appropriate for systems where the capillary pressure is a function of the rate of change of saturation, a phenomenon referred to as dynamic capillary pressure. Previous studies have investigated the impact of soil and fluid properties on dynamic effects in capillary pressure; however, the impact of wettability on this phenomenon has not been investigated to date. In this study, two‐phase multistep outflow (MSO) experiments conducted in chemically treated sands with different equilibrium contact angles were used to investigate the influence of wettability variations on dynamic effects in capillary pressure during displacement of water by tetrachloroethene (PCE). Data from the MSO experiments were modeled with a multiphase flow simulator that includes dynamic effects and were also analyzed through comparisons with theoretical model predictions for interface movement in a single capillary tube. Results showed that a faster approach to equilibrium, characterized by smaller fitted damping coefficients, occurred in sands with larger equilibrium contact angles. Damping coefficients for sands with an operational contact angle greater than 80° were found to be an order of magnitude smaller than those with an operational contact angle less than 65°. These results suggest that it may be possible to neglect dynamic effects in capillary pressure in systems that approach intermediate‐wet conditions but that these effects will be increasingly important in more water‐wet systems.
Spatially distributed erosion and sediment yield modeling in the upper Indus River basin
Authors: Ali Khawaja Faran , De Boer Dirk H.
Published: August 2010

Spatially distributed erosion rates and sediment yields are predicted in the mountainous upper Indus River basin with coupled models of erosion and sediment delivery. Potential erosion rates are calculated with the Thornes model in combination with a surface runoff model. Sediment delivery ratios (SDRs) are hypothesized to be a function of travel time of surface runoff from catchment cells to the nearest downstream channel. Modeled monthly erosion rates for the upper Indus River basin indicate that 87% of the annual gross erosion takes place in the three summer months. The erosion risk map suggests that the areas with the greatest erosion potential are concentrated in subbasins with high relief and a substantial proportion of glacierized area. Lower erosion rates can be explained by the arid climate and low relief on the Tibetan Plateau and by the dense vegetation and lower relief in the lower monsoon subregion. High erosion rates (>1.0 mm a−1) occur over 66.4% of the basin area. The model predicts an average annual erosion rate of 3.2 mm a−1or 868 Mt a−1, which is approximately 4.5 times the long‐term observed annual sediment yield of the basin. The predicted annual basin sediment yield is 244 Mt a−1, which compares reasonably well to the measured value of 195.1 Mt a−1. The overall sediment delivery ratio in the basin is calculated as 0.28. Model results indicate that higher delivery ratios (SDR > 0.6) are found in 18% of the basin area, mostly located in the high‐relief subbasins. The sediment delivery ratio is lower than 0.2 in 70% of the basin area. The Indus subbasins generally show an increase of sediment delivery ratio with basin area. Model evaluation based on accuracy statistics suggest “very good” to “satisfactory” performance ratings for predicted sediment yields. The presented modeling framework requires relatively few data, all of which can be derived from global data sets. It therefore can be used to predict erosion and sediment yield in other ungaged or poorly gaged drainage basins.
Hydrothermal cooling along the Eastern Lau Spreading Center: No evidence for discharge beyond the neovolcanic zone
Authors: Baker Edward T. , Martinez Fernando , Resing Joseph A. , Walker Sharon L. , Buck Nathaniel J. , Edwards Margo H.
Published: August 2010

Heat transported from the mantle beneath spreading centers creates an astonishingly narrow ribbon of convective heat discharge at plate boundaries, as apparently demonstrated by exhaustive exploration for hydrothermal discharge sites over the last three decades. Recent observations and models are now challenging this assumption of exclusively axis‐centric high‐temperature venting. One example is the proposal that intense cooling along the vertical boundaries of a broad low‐velocity volume (LVV) of hot crust could generate high‐temperature fluids several kilometers off axis. To test the hypothesis that substantial hydrothermal discharge might occur beyond the LVV, we conducted a dense survey grid of the ridge and surrounding seafloor (up to ±5 km) along 175 km of the Eastern Lau Spreading Center and Valu Fa Ridge (∼1800 km of track line). Our sampling array extended from ∼50 to 400 m above bottom and included light‐scattering, oxidation‐reduction potential, and hydrographic sensors attached to the tow line and beneath the IMI120 sonar mapping system. The surveys successfully mapped plumes from several vent fields in the neovolcanic zone (∼±1.5 km about the axis) but did not detect evidence of significant discharge anywhere farther off‐axis. At a few locations on the Valu Fa Ridge, however, we did record oxidation‐reduction potential anomalies with hydrographic density signatures that imply low‐temperature hydrothermal sources on the axial flank. Although these sites are hundreds of meters deeper than the adjacent crest, they are above, not beyond, the previously mapped LVV. Our results thus do not support a simple picture of high‐temperature fluids ascending undiluted through the crust to the seafloor several kilometers off‐axis. However, we cannot exclude the possibilities that the largely unmapped LVV is narrower here than seen on other ridges, that hydrothermal fluids formed beyond the LVV are channeled to the axis, or that discharge beyond the neovolcanic zone occurs only as dispersed, very low‐temperature fluids. Our observations do demonstrate that high‐temperature discharge predominantly exits the seafloor within a narrow (∼±1.5 km) axial ribbon, regardless of the presence or absence of an axial magma chamber.
Fertilizing the Amazon and equatorial Atlantic with West African dust
Authors: Bristow Charlie S. , Hudson‐Edwards Karen A. , Chappell Adrian
Published: August 2010

Atmospheric mineral dust plays a vital role in Earth's climate and biogeochemical cycles. The Bodélé Depression in Chad has been identified as the single biggest source of atmospheric mineral dust on Earth. Dust eroded from the Bodélé is blown across the Atlantic Ocean towards South America. The mineral dust contains micronutrients such as Fe and P that have the potential to act as a fertilizer, increasing primary productivity in the Amazon rain forest as well as the equatorial Atlantic Ocean, and thus leading to N2 fixation and CO2 drawdown. We present the results of chemical analysis of 28 dust samples collected from the source area, which indicate that up to 6.5 Tg of Fe and 0.12 Tg of P are exported from the Bodélé Depression every year. This suggests that the Bodélé may be a more significant micronutrient supplier than previously proposed.
Eastern boreal North American wildfire risk of the past 7000 years: A model‐data comparison
Authors: Hély Christelle , Girardin Martin P. , Ali Adam A. , Carcaillet Christopher , Brewer Simon , Bergeron Yves
Published: August 2010

We present here a 7000‐year wildfire reconstruction based on sedimentary charcoal series from five lakes located south of Hudson Bay in eastern boreal North America. The reconstruction shows a significant downward trend in the frequency of large fires from 0.0061 fire·yr−1ca. 5000 cal yr BP to 0.0033 fire·yr−1 at present. Simulations of fire‐season climate based on UK Universities Global Atmospheric Modelling Programme output and reconstructions based on proxy data both indicate a shift toward increasing available moisture in the region between the mid‐Holocene and today. We infer that the diminishing trend in wildfire activity was ultimately caused by the steady orbitally driven reduction in summer insolation. Future higher temperatures not compensated for by significant precipitation increases will bring fire frequency back toward its upper limit, recorded between 6000 and 2000 cal yr BP.
Large variations in travel times of mantle‐sensitive seismic waves from the South Sandwich Islands: Is the Earth's inner core a conglomerate of anisotropic domains?
Authors: Tkalčić Hrvoje
Published: August 2010

Cylindrical anisotropy in Earth's inner core has been invoked to account for travel times of PKP core‐sensitive seismic waves, such as from the South Sandwich Islands (SSI) earthquakes observed in Alaska, which depart from predictions. Newly collected travel‐time residuals from seismic waves from the SSI region that sample only Earth's mantle (PcP and P waves) have a comparable range to the PKP differential travel‐time residuals, yet they are insensitive to core structure. This observation suggests that mantle structure affects PKP travel time residuals more than previously acknowledged and challenges the existing conceptual framework of a uniform inner core anisotropy. The inner core could be a conglomerate of anisotropic domains, and the PKP travel times are most likely influenced by the geometry of inner core sampling and inhomogeneous mantle structure. This concept reconciles observed complexities in travel times while preserving a net inner core anisotropy that is required by observations of Earth's free oscillations.
Decadal changes in tropical convection suggest effects on stratospheric water vapor
Authors: Tselioudis George , Tromeur Eric , Rossow William B. , Zerefos C. S.
Published: August 2010

Analysis of satellite observations of tropical Weather States derived from a cluster analysis of ISCCP cloud property retrievals, shows that the deep convection Weather State increased in frequency from 1983 to about 2000 and remained at a nearly constant level after that. The sharpest deep convection increase occurred between 1993 and 2000. This convection variability is driven by changes that occur in the Indian Ocean and the Western‐Central Pacific regions, which are the regions where the majority of deep tropical convection occurs. Analysis modifications to account for satellite coverage changes during the period under examination do not alter these findings. Previous studies showed that stratospheric water vapor increased from 1980 to 2000 and dropped after that to lower levels that persist until today, and that this change could explain part of the recent global temperature variability. Since tropical deep convection is an important mechanism affecting stratospheric water vapor concentrations, the observed decadal changes in tropical deep convection could explain in part the stratospheric water vapor variability patterns.
Testing a theory for the effect of latitude on the persistence of eddy‐driven jets using CMIP3 simulations
Authors: Barnes Elizabeth A. , Hartmann Dennis L.
Published: August 2010

The effect of latitude on the persistence of north–south shifts in the position of the jet is investigated in 37 CMIP3 integrations over four forcing scenarios. The persistence of the Southern Annular Mode (SAM) decreases when the mean jet is located closer to the pole. An asymmetry is shown whereby the equatorward‐shifted jet is more persistent than the poleward‐shifted jet. The sphericity of the earth inhibits wave breaking on the poleward flank of the jet which decreases the feedback between the eddies and the mean‐flow and yields a wider, less self‐sustaining jet. The results suggest a decrease in e‐folding time of the SAM of 3 days per degree of poleward shift of the jet. The mechanism described explains why models with jets too far equatorward relative to observations over‐predict the timescale of the SAM and suggests that these models will also exaggerate poleward shifts of jets associated with global warming.
A new generation mechanism of butterfly pitch angle distributions of energetic ions: Multiple pitch angle scattering in the stretched magnetic field
Authors: Shibahara K. , Nosé M. , Fritz T. A. , Niehof J.
Published: August 2010

A new generation mechanism of a butterfly pitch angle distribution (PAD) of energetic ions is demonstrated by a test particle simulation in the stretched magnetic field. The Polar satellite detected some events of the butterfly PADs of the energetic protons (≳80 keV) in the outer ring current region around midnight near the equatorial plane. They were observed at relatively disturbed time in the inner magnetosphere and the ring current appeared to be developed; that is, magnitude of the magnetic field at the Polar satellite was highly depressed and the adiabaticity of the protons were expected to be violated. To reproduce the butterfly PAD, we perform a test particle simulation in which the first adiabatic invariant μ can be changed. When the radius of the field line becomes almost comparable to the Larmor radius of a proton, it suffers significant scattering of pitch angle (α) due to change of μ. This μ‐scattering process causes reform of the PADs. Owing to cumulative μ‐scattering, the flux of the protons ends to have a peak at α ∼ 40° (or 140°) and collapses at α ∼ 0° (or 180°) and 90°, which is a butterfly PAD. The reproduced PAD resembles the butterfly PADs observed by the Polar satellite. We suggest that the nonadiabatic effect is important for not only the generation mechanisms of the butterfly PAD but also the development of the storm‐time ring current.
Giant impacts, core stratification, and failure of the Martian dynamo
Authors: Arkani‐Hamed Jafar , Olson Peter
Published: August 2010

The close timing of the giant impacts and the cessation of the core dynamo of Mars at around 4 Ga suggest a possible causal relationship between these two events. We study the shock heating of the Martian interior caused by the impact that created Utopia basin, the largest of the 20 giant impact basins formed on Mars around 4 Ga. Using empirical scaling laws connecting the diameters of the basin and the projectile, we calculate the shock pressure distribution in Mars on the basis of Pierazzo et al.'s (1997) formula, which is then used to estimate the impact‐induced temperature increase in the Martian mantle and core, adopting the “ordinary” and “foundering” shock heating mechanisms proposed by Watters et al. (2009) and impact velocities of 10 and 15 km/s. It is shown that the reduction of the heat flux out of the core due to impact heating of the overlying mantle is on the order of 0.03%–0.3% of the preimpact heat flux of the core (15 mW/m2), indicating that the impact heating of the mantle has insignificant effect on the thermal convection of the core. However, the shock waves that penetrate into the core directly and differentially heat the core in only a few minutes, which causes stable thermal stratification of the core within about a few years and diminishes the core convection and the thermally driven core dynamo within a few thousand years. Exhaustion of the impact heat and removal of the stratification is necessary to reestablish a superadiabatic temperature gradient and reactivate convection in the core. As the impact heat becomes concentrated in the upper parts of the core, the stratified part of the core first cools by conduction to the mantle and then later with a contribution from penetrative convection below the core‐mantle boundary and by conduction into the deeper parts of the core. Depending on the impact velocity and the shock heating mechanisms, tens of millions of years may be needed to fully exhaust the core heat to the mantle, during which time global core convection is suppressed and a thermally driven core dynamo is problematic.
Dissociation between Vascular Endothelial Growth Factor Receptor-2 and Blood Vessel Density in the Caudate Nucleus after Chronic Hydrocephalus
Authors: Deshpande Abhishek , Dombrowski Stephen M , Leichliter Anna , Krajcir Natalie , Zingales Nicholas , Inoue Masahiro , Schenk Soren , Fukamachi Kiyotaka , Luciano Mark G
Published: August 2010

Correction to: Journal of Cerebral Blood Flow & Metabolism (2009) 29, 1806–1815; doi:10.1038/jcbfm.2009.98; published online 15 July 2009

Following the publication of this article, the authors noted the following error:

Figure 4E (Bar graph illustrating total density of GFAP astrocytes) is to be replaced by the following graph. The original bar graph submitted is for the density of VEGF (vascular endothelial growth factor) + GFAP (glial fibrilliary acidic protein) cells and not for the total density of GFAP cells.

The original graph was inadvertently submitted for publication. The changing of the graph does not change any text in the publication or any other data or graphs already published. The change also does not influence the interpretation or the conclusions of the paper. The authors regret the error.
Identification and biophysical assessment of the molecular recognition mechanisms between the human haemopoietic cell kinase Src homology domain 3 and ALG-2-interacting protein X
Authors: Shi Xiaoli , Opi Sandrine , Lugari Adrien , Restouin Audrey , Coursindel Thibault , Parrot Isabelle , Perez Javier , Madore Eric , Zimmermann Pascale , Corbeil Jacques , Huang Mingdong , Arold Stefan T. , Collette Yves , Morelli Xavier
Published: August 2010

SFKs (Src family kinases) are central regulators of many signalling pathways. Their functions are tightly regulated through SH (Src homology) domain-mediated protein–protein interactions. A yeast two-hybrid screen using SH3 domains as bait identified Alix [ALG-2 (apoptosis-linked gene 2)-interacting protein X] as a novel Hck (haemopoietic cell kinase) SH3 domain interactor. The Alix–Hck-SH3 interaction was confirmed in vitro by a GST (glutathione transferase) pull-down assay and in intact cells by a mammalian two-hybrid assay. Furthermore, the interaction was demonstrated to be biologically relevant in cells. Through biophysical experiments, we then identified the PRR (proline-rich region) motif of Alix that binds Hck-SH3 and determined a dissociation constant of 34.5 μM. Heteronuclear NMR spectroscopy experiments were used to map the Hck-SH3 residues that interact with an ALIX construct containing the V and PRR domains or with the minimum identified interacting motif. Finally, SAXS (small-angle X-ray scattering) analysis showed that the N-terminal PRR of Alix is unfolded, at least before Hck-SH3 recognition. These results indicate that residues outside the canonical PxxP motif of Alix enhance its affinity and selectivity towards Hck-SH3. The structural framework of the Hck–Alix interaction will help to clarify how Hck and Alix assist during virus budding and cell-surface receptor regulation.
Porcine glutathione transferase Alpha 2-2 is a human GST A3-3 analogue that catalyses steroid double-bond isomerization
Authors: Fedulova Natalia , Raffalli-Mathieu Françoise , Mannervik Bengt
Published: August 2010

A primary role of GSTs (glutathione transferases) is detoxication of electrophilic compounds. In addition to this protective function, hGST (human GST) A3-3, a member of the Alpha class of soluble GSTs, has prominent steroid double-bond isomerase activity. The isomerase reaction is an obligatory step in the biosynthesis of steroid hormones, indicating a special role of hGST A3-3 in steroidogenic tissues. An analogous GST with high steroid isomerase activity has so far not been found in any other biological species. In the present study, we characterized a Sus scrofa (pig) enzyme, pGST A2-2, displaying high steroid isomerase activity. High levels of pGST A2-2 expression were found in ovary, testis and liver. In its functional properties, other than steroid isomerization, pGST A2-2 was most similar to hGST A3-3. The properties of the novel porcine enzyme lend support to the notion that particular GSTs play an important role in steroidogenesis.
State-to-state quantum dynamics of the O(P3)+OH(Π2)→H(S2)+O2(Σ3g−) reaction
Authors: Ma Jianyi , Lin Shi Ying , Guo Hua , Sun Zhigang , Zhang Dong H. , Xie Daiqian
Published: August 2010

The authors report a detailed quantum mechanical study of the state-to-state dynamics of the O+OH(vi=0, ji=0)→H+O2(vf,jf) reaction on an accurate HO2(X2A″) potential energy surface. The scattering dynamics was treated using a reactant coordinate based Chebyshev real wavepacket method with full Coriolis coupling. A total of 84 partial waves were calculated in order to achieve convergence up to the collision energy of 0.17 eV. The differential cross section is near forward-backward symmetric, consistent with the complex-forming mechanism. The O2 product was found to have a monotonically decaying vibrational distribution and highly excited and inverted rotational distributions, also consistent with the formation of the HO2 intermediate. These quantum mechanical results were compared with those obtained in earlier quasiclassical trajectory and statistical studies and it is shown that the statistical theory gives a reasonably good description of the product state distributions despite its inability to predict the total reaction cross section.
Island shape controls magic-size effect for heteroepitaxial diffusion
Authors: Wu Henry H. , Signor A. W. , Trinkle Dallas R.
Published: August 2010

Lattice mismatch of Cu on Ag(111) produces fast diffusion for “magic sizes” of islands. A size- and shape-dependent reptation mechanism is responsible for low diffusion barriers. Initiating the reptation mechanism requires a suitable island shape, not just magic sizes. Shape determines the dominant diffusion mechanism and leads to multiple clearly identifiable magic-size trends for diffusion depending on the number of atoms whose bonds are shortened during diffusion, which ultimately affects the self-assembly of islands.
Some aspects of emission variation in InAs quantum dots coupled with symmetric quantum wells
Authors: Torchynska T. V. , Stintz A.
Published: August 2010

The photoluminescence (PL), its temperature and power dependences, as well as PL inhomogeneity and x ray diffraction (XRD) has been studied in the symmetric In0.15Ga1−0.15As/GaAs quantum wells with embedded InAs quantum dots (QDs) (dot-in-a-well, DWELL) with different QD densities, obtained by the variation in QD growth temperatures. It is shown that four reasons are responsible for the difference in emission intensities, PL peak positions and PL inhomogeneity in studied QD structures: (i) the high concentration of nonradiative (NR) recombination centers in the capping In0.15Ga1−0.15As layer at low QD growth temperatures (470 °C), (ii) the QD density and size distributions for the structures with QD grown at 490–535 °C, (iii) the high concentration of NR recombination centers in the GaAs barrier at high QD growth temperatures (535 °C), and (iv) the variation nonmonotonous of elastic strain versus QD density. XRD study confirms that with decreasing density of QDs in DWELLs from 1.1×1011 cm−2 down to 1.3×1010 cm−2 at the rise of QD growth temperatures the level of compressive strain in DWELLs varies nonmonotonously. The reasons of compressive strain variation and the impact of this variation on emission parameters of DWELLs have been discussed as well.
Noncontact evaluation of the dependency of electrical conductivity on stress for various Al alloys as a function of plastic deformation and annealing
Authors: Morozov Maxim , Tian Gui Yun , Withers Philip J.
Published: August 2010

This paper presents a method of noncontact evaluation of the anisotropic dependency of electrical conductivity of metallic specimens exposed to tensile stress. The method combines eddy current (EC) measurements using a directional probe with numerical modeling to infer the electrical conductivity longitudinal and transverse to an essentially static uniaxial applied tensile stress. The inversion method has been applied to various aluminum alloys (AA1050, AA2024, AA5083, and AA7075). The recovered changes in electrical conductivity lie within the theoretically expected range of a few percent at the yield stress. The effect of prior plastic strain and heat treatment on electrical conductivity has also been evaluated. The electrical conductivity tensor for hardenable alloys exhibit a distinct dependence on cold work compared to the nonhardenable ones. The outcomes are discussed in terms of their implications for the use of EC measurements for diagnosing the state of residual stress for aluminum alloys.
Spectroscopic study of CHBrF2 up to 9500 cm−1: Vibrational analysis, integrated band intensities, and ab initio calculations
Authors: Charmet Andrea Pietropolli , Stoppa Paolo , Tasinato Nicola , Baldan Alessandro , Giorgianni Santi , Gambi Alberto
Published: August 2010

The gas-phase infrared spectra of bromodifluoromethane, CHBrF2, have been examined at medium resolution in the range of 200–9500 cm−1. The assignment of the absorptions in terms of fundamental, overtone, combination, and hot bands, assisted by quantum chemical calculations is consistent all over the region investigated. Accurate values of integrated band intensities have also been determined for the first time in the range of 500–6000 cm−1. Structural and molecular spectroscopic properties have been calculated at high level of theory. The coupled cluster CCSD(T) method in conjunction with a hierarchical series of correlation consistent basis sets has been employed and extrapolation to complete basis set has been considered for the equilibrium geometry. Vibrational analysis based on the second order perturbation theory has been carried out with the ab initio anharmonic force constants calculated using the second order Møller–Plesset perturbation as well as coupled cluster [CCSD(T)] theory. A good agreement between the computed and the experimental data also including the integrated infrared band intensities has been obtained.
Unidirectional hopping transport of interacting particles on a finite chain
Authors: Einax Mario , Solomon Gemma C. , Dieterich Wolfgang , Nitzan Abraham
Published: August 2010

Particle transport through an open, discrete one-dimensional channel against a mechanical or chemical bias is analyzed within a master equation approach. The channel, externally driven by time-dependent site energies, allows multiple occupation due to the coupling to reservoirs. Performance criteria and optimization of active transport in a two-site channel are discussed as a function of reservoir chemical potentials, the load potential, interparticle interaction strength, driving mode, and driving period. Our results, derived from exact rate equations, are used in addition to test a previously developed time-dependent density functional theory, suggesting a wider applicability of that method in investigations of many particle systems far from equilibrium.
Ligand effect on uranium isotope fractionations caused by nuclear volume effects: An ab initio relativistic molecular orbital study
Authors: Abe Minori , Suzuki Tatsuya , Fujii Yasuhiko , Hada Masahiko , Hirao Kimihiko
Published: August 2010

We have calculated the nuclear volume term (ln Knv) of the isotope fractionation coefficient (ε) between U235–U238 isotope pairs by considering the effect of ligand coordination in a U(IV)–U(VI) reaction system. The reactants were modeled as [UO2Cl3]− and [UO2Cl4]2− for U(VI), and UCl4 for U(IV). We adopted the Dirac–Coulomb Hartree–Fock method with the Gaussian-type finite nucleus model. The result obtained was ln Knv=0.001 90 at 308 K, while the experimentally estimated value of ln Knv is 0.002 24. We also discuss how the ligand affects the value of ln Knv, especially for the various structures of different compounds, and different ligands within the halogen ion series (F, Cl, and Br).
Notes: Kinetic unfreezing of a binary alloy and configurational entropy
Authors: Johari G. P. , Aji Daisman P. B.
Published: August 2010

Analysis of the specific heat data of a partially disordered, kinetically frozen state of Mg3Cd crystal shows that, as for glass relaxation, its atomic diffusion rate is nonexponential but less nonlinear. As its state transforms on heating to an equilibrium disordered state in a time-dependent manner, the enthalpy increases by 362.8 J/mol and the entropy by 1.28 J/mol K. Increase in the vacancy population on heating raises the probability of partial disintegration of its superlattice. Kinetic-unfreezing temperature is the same in the enthalpy and entropy considerations. If that were found also for a glass, its configurational entropy would be finite.
Transferability of anharmonic force fields in simulations of molecular vibrations
Authors: Parchaňský Václav , Bouř Petr
Published: August 2010

Accurate simulations of vibrational molecular spectra require precise molecular force fields, at least with cubic and quartic anharmonic corrections beyond the harmonic limits. Generation of such force field terms becomes computationally prohibitive for larger molecules. In this work, an alternate possibility is explored, where approximate anharmonic force field components are obtained from molecular fragments. Transferability properties of the cubic and incomplete quartic fields are discussed and tested on model oligoproline molecules. Automatic transfer schemes including cubic, two and three atomic quartic force constants are developed and implemented. The results indicate that the main vibrational interactions in molecules are local and the anharmonic constants are mostly well amendable to the transfer. Exact anharmonic normal mode force fields of larger molecules compared very well to those obtained from smaller molecular parts. The most important changes in vibrational spectra caused by the anharmonic interactions could be reproduced with two and three atomic force field terms. The transfer scheme thus provides molecular anharmonic force fields without a significant loss of accuracy and brings significant savings of computer time and memory needed to generate molecular vibrational energies and spectra.
Synchronized force and particle image velocimetry measurements on a NACA 0015 in poststall under control of time periodic electromagnetic forcing
Authors: Cierpka Christian , Weier Tom , Gerbeth Gunter
Published: August 2010

The paper shows the results of an experimental flow control investigation using periodic actuation by streamwise Lorentz forces at the leading edge of a NACA 0015 profile. Synchronized measurements of force and time resolved particle image velocimetry were performed in a sodium hydroxide channel for Reynolds numbers of Re=0.5×105 and 105. A wavelet algorithm was used to detect vortical structures and reveals the relation between these large scale structures and the observed lift and drag forces. Complementary information on vortical structures was gained by vorticity based proper orthogonal decomposition of the data. In order to minimize the energetic effort of the flow actuation, the investigation focuses on small momentum coefficients. For small angles of attack, a complete reattachment of the flow can be established by the actuation, whereas for large angles of attack, the interaction of vortical structures becomes more prominent. This paper discusses the effects of excitation frequency and wave form for two qualitatively different flow regimes. It is found that for larger angles of attack, the optimal excitation frequency in terms of lift gain is similar to the dominant frequency of the lift fluctuations observed for the unforced flow. This frequency is determined by the wake.
Self-diffusivity as a function of density and temperature in crystalline solids and compensating rules for self-diffusion parameters in carbon subgroup crystals
Authors: Papathanassiou A. N. , Sakellis I. , Grammatikakis J.
Published: August 2010

The self-diffusion coefficient of crystalline solids as a function of density and temperature may derive from thermodynamics concepts and an earlier elastic thermodynamic point defect model [Varotsos and Alexopoulos, Phys. Rev. B 15, 4111 (1977); Phys. Rev. B 18, 2683 (1978)]. Compensation laws ruling self-diffusion parameters in carbon-subgroup crystals obtained from theoretical calculations are predicted, as well.
Charge carrier separation induced by intrinsic surface strain in pristine ZnO nanowires
Authors: Kou Liangzhi , Li Chun , Zhang Zi-Yue , Chen Changfeng , Guo Wanlin
Published: August 2010

We predict by first-principles calculations a spontaneous charge carrier separation mechanism in pristine [0001]-oriented ZnO nanowires. We find that the shrinking strain induced by surface reconstruction causes electrons and holes to separate and move toward the core and surface region, respectively. Such separation can be enhanced by axially applied tensile strain as a result of the enhancement of surface strain induced by the Poisson effect, and be suppressed by compressive axial strain. Similar carrier separations are found in IIB-sulfides. This intrinsic charge separation and tensile strain induced enhancement are expected to shed light on solar cell designs.
High-resolution friction force microscopy under electrochemical control
Authors: Labuda Aleksander , Paul William , Pietrobon Brendan , Lennox R. Bruce , Grütter Peter H. , Bennewitz Roland
Published: August 2010

We report the design and development of a friction force microscope for high-resolution studies in electrochemical environments. The design choices are motivated by the experimental requirements of atomic-scale friction measurements in liquids. The noise of the system is analyzed based on a methodology for the quantification of all the noise sources. The quantitative contribution of each noise source is analyzed in a series of lateral force measurements. Normal force detection is demonstrated in a study of the solvation potential in a confined liquid, octamethylcyclotetrasiloxane. The limitations of the timing resolution of the instrument are discussed in the context of an atomic stick-slip measurement. The instrument is capable of studying the atomic friction contrast between a bare Au(111) surface and a copper monolayer deposited at underpotential conditions in perchloric acid.
Fluorine-vacancy defects in fluorine-implanted silicon studied by electron paramagnetic resonance
Authors: Umeda T. , Isoya J. , Ohshima T. , Onoda S. , Morishita N. , Okonogi K. , Shiratake S.
Published: August 2010

An electron paramagnetic resonance (EPR) study on fluorine-vacancy defects (FnVm) in fluorine-implanted silicon is demonstrated. Fluorine implantation is an important technology for Si microdevices and EPR measurements showed that this process created a variety of FnVm defects of different sizes (V2, V4, and V5). In FnVm, a Si–F bond exhibited a different chemical nature compared to a Si–H bond in hydrogen-vacancy complexes. The most primitive defect was FV2 (F0 center) and the final types were FnV5 (F1 center) and FnV2 (F2 center) which increased in annealing processes as low temperature as 200 °C.
Low-power write-once-read-many-times memory devices
Authors: Wang Jianpu , Gao Feng , Greenham Neil C.
Published: August 2010

We introduce low-power write-once-read-many-times memory devices fabricated from solution. These devices are based on an electron-only structure using colloidal ZnO semiconductor nanoparticles and the doped conjugated polymer polyethylenedioxythiophene doped with polystyrene sulfonic acid (PEDOT:PSS). The conductive p-doped conjugated polymer is permanently dedoped by injected electrons, producing an insulating state. This demonstration provides a class of memory devices with the potential for extremely low-cost, low-power-consumption applications, such as radio-frequency identification tags.
Hysteresis in the resistance of a graphene device induced by charge modulation in the substrate
Authors: Brant J. C. , Leon J. , Barbosa T. C. , Araujo E. N. D. , Archanjo B. S. , Plentz F. , Alves E. S.
Published: August 2010

We have fabricated graphene devices on lightly doped Si substrates and show that pronounced changes in resistance versus gate voltage, R(Vg), characteristics of these devices at 77 K are induced by the variation in the charge distribution in substrate with both gate voltage and illumination. The R(Vg) of the graphene devices in the dark shows remarkable changes as the carriers in the underlying substrate go through accumulation, depletion, and inversion regimes. We demonstrate the possibility of using a graphene device as an optical-latch.
Mobility improvement in nanowire junctionless transistors by uniaxial strain
Authors: Raskin Jean-Pierre , Colinge Jean-Pierre , Ferain Isabelle , Kranti Abhinav , Lee Chi-Woo , Akhavan Nima Dehdashti , Yan Ran , Razavi Pedram , Yu Ran
Published: August 2010

Improvement of current drive in n- and p-type silicon junctionless metal-oxide-semiconductor-field-effect-transistors (MOSFETs) using strain is demonstrated. Junctionless transistors have heavily doped channels with doping concentrations in excess of 1019 cm−3 and feature bulk conduction, as opposed to surface channel conduction. The extracted piezoresistance coefficients are in good agreement with the piezoresistive theory and the published coefficients for bulk silicon even for 10 nm thick silicon nanowires as narrow as 20 nm. These experimental results demonstrate the possibility of enhancing mobility in heavily doped silicon junctionless MOSFETs using strain technology.
Strontium-induced ferroelectriclike relaxor behavior in Bi-based pyrochlores
Authors: Du Huiling , Shi Xiang
Published: August 2010

The dielectric properties of stoichiometric dense ceramics (Bi1.5Zn0.5−xSrx)(Ti1.5Nb0.5)O7 (BZSTN, x=0–0.5) have been investigated as a function of temperature and frequency. A significant relaxation behavior at about 250 °C is induced when moderate Sr2+ is substituted with Zn2+ in Bi1.5Zn0.5Ti1.5Nb0.5O7 (BZTN) ceramics. The observation of hysteretic behavior in the P versus E curves shows the existence of a polar state. The ferroelectriclike relaxor behavior arises mainly from the dynamic response of the micropolar clusters, which exist in the off-center ions doped paraelectric. The ultrahigh permittivity of 245 at ambient temperature could be very promising for integrated capacitors and microwave resonators.
Three-dimensional acoustic lenses with axial symmetry
Authors: Sanchis Lorenzo , Yánez Andrés , Galindo Pedro L. , Pizarro Joaquín , Pastor Juan Martínez
Published: August 2010

In this paper a technique to design three dimensional (3D) devices to focus acoustic waves composed of scattering elements is proposed. The devices are designed and optimized in two dimensions (2D) with the help of a genetic algorithm and the 2D multiple scattering formalism. The transition from 2D to 3D is made by applying a rotation operation to the optimized design, thus passing from a set of 2D circular scatters to their equivalent 3D concentric rings of circular section and finite dimensions, considerably improving its performance. The method has been applied to the design and theoretical characterization of a single-focus acoustic lens and a tunable lens capable of changing the focal length with frequency. A prototype lens was fabricated using aluminum rings clamped to a rigid frame, obtaining a good agreement between theory and experiment.
Intrinsic half-metallic BN–C nanotubes
Authors: Huang Bing , Si Chen , Lee Hoonkyung , Zhao Lu , Wu Jian , Gu Bing-Lin , Duan Wenhui
Published: August 2010

Using spin-polarized density functional theory calculations, we demonstrate that hybrid BN–C nanotubes (BN-CNTs) have diverse electronic and magnetic properties depending on their percentage of carbon and BN components. Typically, a BN-CNT is converted from a nonmagnetic semiconductor to a spin-polarized metal and then to a nonmagnetic semiconductor by increasing the ratio of BN component. The intrinsic half-metallicity could be achieved when the percentage of carbon component in the tube is within a certain ratio, and is insensitive to the tube curvature. Our findings suggest that BN-CNTs may offer unique opportunities for developing nanoscale spintronic materials.
Orientational photoreactive effects in nematic liquid crystals on silver sulfide thin films
Authors: Emoto Akira , Maeda Kazuya , Tanaka Kunihiko , Kawatsuki Nobuhiro , Ono Hiroshi
Published: August 2010

We present a highly functionalized photorefractive device consisting of fullerene (C60)-doped nematic liquid crystals (NLCs) on silver sulfide thin films. Either stable holograms or real-time holography is possible depending on the polarity of an external electric field. When certain direction of external field is applied to the device under irradiation by interference field, photoexcited charges are recombined with silver ions at the boundary between the silver sulfide and NLCs. The resulting interface structures reorient the NLC molecules and holographic gratings are stably memorized. When the polarity of the external field is reversed, normal photorefractive holographic gratings are formed.