Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution

NASA Astrophysics Data System (ADS)

Liu, Yuanyue; Wu, Jingjie; Hackenberg, Ken P.; Zhang, Jing; Wang, Y. Morris; Yang, Yingchao; Keyshar, Kunttal; Gu, Jing; Ogitsu, Tadashi; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M.; Wood, Brandon C.; Yakobson, Boris I.

2017-09-01

Low-cost, layered transition-metal dichalcogenides (MX2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX2 surfaces, and leverage the understanding to report group-5 MX2 (H-TaS2 and H-NbS2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm-2 current density at an overpotential of ˜50-60 mV with a loading of 10-55 μg cm-2, surpassing other reported MX2 candidates without any performance-enhancing additives.

Edge reactivity and water-assisted dissociation on cobalt oxide nanoislands

DOE PAGES

Fester, J.; García-Melchor, M.; Walton, A. S.; ...

2017-01-30

Here, transition metal oxides show great promise as Earth-abundant catalysts for the oxygen evolution reaction in electrochemical water splitting. However, progress in the development of highly active oxide nanostructures is hampered by a lack of knowledge of the location and nature of the active sites. Here we show, through atom-resolved scanning tunnelling microscopy, X-ray spectroscopy and computational modelling, how hydroxyls form from water dissociation at under coordinated cobalt edge sites of cobalt oxide nanoislands. Surprisingly, we find that an additional water molecule acts to promote all the elementary steps of the dissociation process and subsequent hydrogen migration, revealing the importantmore » assisting role of a water molecule in its own dissociation process on a metal oxide. Inspired by the experimental findings, we theoretically model the oxygen evolution reaction activity of cobalt oxide nanoislands and show that the nanoparticle metal edges also display favourable adsorption energetics for water oxidation under electrochemical conditions.« less

Formation of RNA oligomers on montmorillonite: site of catalysis

NASA Technical Reports Server (NTRS)

Ertem, G.; Ferris, J. P.

1998-01-01

Certain montmorillonites catalyze the self condensation of the 5'-phosphorimidazolide of nucleosides in pH 8 aqueous electrolyte solutions at ambient temperatures leading to formation of RNA oligomers. In order to establish the nature of the sites on montmorillonite responsible for this catalytic activity, oligomerization reactions were run with montmorillonites which had been selectively modified (I) at the edges by (a) fluoride treatment, (b) silylation, (c) metaphosphate treatment of the anion exchange sites (II) in the interlayer by (a) saturation with quaternary alkylammonium ions of increasing size, (b) aluminum polyoxo cations. High pressure liquid chromatography, HPLC, analysis of condensation products for their chain lengths and yields indicated that modification at the edges did not affect the catalytic activity to a significant extent, while blocking the interlayer strongly inhibited product formation.

Revealing the Double-Edged Sword Role of Graphene on Boosted Charge Transfer versus Active Site Control in TiO2 Nanotube Arrays@RGO/MoS2 Heterostructure.

PubMed

Quan, Quan; Xie, Shunji; Weng, Bo; Wang, Ye; Xu, Yi-Jun

2018-05-01

Charge separation/transfer is generally believed to be the most key factor affecting the efficiency of photocatalysis, which however will be counteracted if not taking the active site engineering into account for a specific photoredox reaction. Here, a 3D heterostructure composite is designed consisting of MoS 2 nanoplatelets decorated on reduced graphene oxide-wrapped TiO 2 nanotube arrays (TNTAs@RGO/MoS 2 ). Such a cascade configuration renders a directional migration of charge carriers and controlled immobilization of active sites, thereby showing much higher photoactivity for water splitting to H 2 than binary TNTAs@RGO and TNTAs/MoS 2 . The photoactivity comparison and mechanistic analysis reveal the double-edged sword role of RGO on boosted charge separation/transfer versus active site control in this composite system. The as-observed inconsistency between boosted charge transfer and lowered photoactivity over TNTAs@RGO is attributed to the decrease of active sites for H 2 evolution, which is significantly different from the previous reports in literature. The findings of the intrinsic relationship of balanced benefits from charge separation/transfer and active site control could promote the rational optimization of photocatalyst design by cooperatively manipulating charge flow and active site control, thereby improving the efficiency of photocatalysis for target photoredox processes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Factors Affecting Soil Fauna Feeding Activity in a Fragmented Lowland Temperate Deciduous Woodland

PubMed Central

Simpson, Jake E.; Slade, Eleanor; Riutta, Terhi; Taylor, Michele E.

2012-01-01

British temperate broadleaf woodlands have been widely fragmented since the advent of modern agriculture and development. As a result, a higher proportion of woodland area is now subject to edge effects which can alter the efficiency of ecosystem functions. These areas are particularly sensitive to drought. Decomposition of detritus and nutrient cycling are driven by soil microbe and fauna coactivity. The bait lamina assay was used to assess soil fauna trophic activity in the upper soil horizons at five sites in Wytham Woods, Oxfordshire: two edge, two intermediate and one core site. Faunal trophic activity was highest in the core of the woodland, and lowest at the edge, which was correlated with a decreasing soil moisture gradient. The efficiency of the assay was tested using four different bait flavours: standardised, ash (Fraxinus excelsior L.), oak (Quercus robur L.), and sycamore (Acer pseudoplatanus L.). The standardised bait proved the most efficient flavour in terms of feeding activity. This study suggests that decomposition and nutrient cycling may be compromised in many of the UK's small, fragmented woodlands in the event of drought or climate change. PMID:22235311

Factors affecting soil fauna feeding activity in a fragmented lowland temperate deciduous woodland.

PubMed

Simpson, Jake E; Slade, Eleanor; Riutta, Terhi; Taylor, Michele E

2012-01-01

British temperate broadleaf woodlands have been widely fragmented since the advent of modern agriculture and development. As a result, a higher proportion of woodland area is now subject to edge effects which can alter the efficiency of ecosystem functions. These areas are particularly sensitive to drought. Decomposition of detritus and nutrient cycling are driven by soil microbe and fauna coactivity. The bait lamina assay was used to assess soil fauna trophic activity in the upper soil horizons at five sites in Wytham Woods, Oxfordshire: two edge, two intermediate and one core site. Faunal trophic activity was highest in the core of the woodland, and lowest at the edge, which was correlated with a decreasing soil moisture gradient. The efficiency of the assay was tested using four different bait flavours: standardised, ash (Fraxinus excelsior L.), oak (Quercus robur L.), and sycamore (Acer pseudoplatanus L.). The standardised bait proved the most efficient flavour in terms of feeding activity. This study suggests that decomposition and nutrient cycling may be compromised in many of the UK's small, fragmented woodlands in the event of drought or climate change.

Platinum nanoparticle during electrochemical hydrogen evolution: Adsorbate distribution, active reaction species, and size effect

DOE PAGES

Tan, Teck L.; Wang, Lin -Lin; Zhang, Jia; ...

2015-03-02

For small Pt nanoparticles (NPs), catalytic activity is, as observed, adversely affected by size in the 1–3 nm range. We elucidate, via first-principles-based thermodynamics, the operation H* distribution and cyclic voltammetry (CV) during the hydrogen evolution reaction (HER) across the electrochemical potential, including the underpotential region (U ≤ 0) that is difficult to assess in experiment. We consider multiple adsorption sites on a 1 nm Pt NP model and show that the characteristic CV peaks from different H* species correspond well to experiment. We next quantify the activity contribution from each H* species to explain the adverse effect of size.more » From the resolved CV peaks at the standard hydrogen electrode potential (U = 0), we first deduce that the active species for the HER are the partially covered (100)-facet bridge sites and the (111)-facet hollow sites. Upon evaluation of the reaction barriers at operation H* distribution and microkinetic modeling of the exchange current, we find that the nearest-neighbor (100)-facet bridge site pairs have the lowest activation energy and contribute to ~75% of the NP activity. Edge bridge sites (fully covered by H*) per se are not active; however, they react with neighboring (100)-facet H* to account for ~18% of the activity, whereas (111)-facet hollow sites contribute little. As a result, extrapolating the relative contributions to larger NPs in which the ratio of facet-to-edge sites increases, we show that the adverse size effect of Pt NP HER activity kicks in for sizes below 2 nm.« less

Mapping Catalytically Relevant Edge Electronic States of MoS2

PubMed Central

2018-01-01

Molybdenum disulfide (MoS2) is a semiconducting transition metal dichalcogenide that is known to be a catalyst for both the hydrogen evolution reaction (HER) as well as for hydro-desulfurization (HDS) of sulfur-rich hydrocarbon fuels. Specifically, the edges of MoS2 nanostructures are known to be far more catalytically active as compared to unmodified basal planes. However, in the absence of the precise details of the geometric and electronic structure of the active catalytic sites, a rational means of modulating edge reactivity remain to be developed. Here we demonstrate using first-principles calculations, X-ray absorption spectroscopy, as well as scanning transmission X-ray microscopy (STXM) imaging that edge corrugations yield distinctive spectroscopic signatures corresponding to increased localization of hybrid Mo 4d states. Independent spectroscopic signatures of such edge states are identified at both the S L2,3 and S K-edges with distinctive spatial localization of such states observed in S L2,3-edge STXM imaging. The presence of such low-energy hybrid states at the edge of the conduction band is seen to correlate with substantially enhanced electrocatalytic activity in terms of a lower Tafel slope and higher exchange current density. These results elucidate the nature of the edge electronic structure and provide a clear framework for its rational manipulation to enhance catalytic activity. PMID:29721532

Direct Visualization of Catalytically Active Sites at the FeO–Pt(111) Interface

DOE PAGES

Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; ...

2015-05-31

Within the area of surface science, one of the “holy grails” is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O 2 andmore » CO environments revealed catalytic activity occurring at the FeO–Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO–Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. As a result, the presented STM results are in accord with DFT+U calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.« less

Effects of Edge on-Site Potential in a Honeycomb Topological Magnon Insulator

NASA Astrophysics Data System (ADS)

Pantaleón, Pierre A.; Xian, Yang

2018-06-01

While the deviation of the edge on-site potential from the bulk values in a magnonic topological honeycomb lattice leads to the formation of edge states in a bearded boundary, this is not the case for a zigzag termination, where no edge state is found. In a semi-infinite lattice, the intrinsic on-site interactions along the boundary sites generate an effective defect and this gives rise to Tamm-like edge states. If a nontrivial gap is induced, both Tamm-like and topologically protected edge states appear in the band structure. The effective defect can be strengthened by an external on-site potential, and the dispersion relation, velocity and magnon density of the edge states all become tunable.

Engineering Ni-Mo-S Nanoparticles for Hydrodesulfurization.

PubMed

Bodin, Anders; Christoffersen, Ann-Louise N; Elkjær, Christian F; Brorson, Michael; Kibsgaard, Jakob; Helveg, Stig; Chorkendorff, Ib

2018-06-13

Nanoparticle engineering for catalytic applications requires both a synthesis technique for the production of well-defined nanoparticles and measurements of their catalytic performance. In this paper, we present a new approach to rationally engineering highly active Ni-Mo-S nanoparticle catalysts for hydrodesulfurization (HDS), i.e., the removal of sulfur from fossil fuels. Nanoparticle catalysts are synthesized by the sputtering of a Mo 75 Ni 25 metal target in a reactive atmosphere of Ar and H 2 S followed by the gas aggregation of the sputtered material into nanoparticles. The nanoparticles are filtered by a quadrupole mass filter and subsequently deposited on a planar substrate, such as a grid for electron microscopy or a microreactor. By varying the mass of the deposited nanoparticles, it is demonstrated that the Ni-Mo-S nanoparticles can be tuned into fullerene-like particles, flat-lying platelets, and upright-oriented platelets. The nanoparticle morphologies provide different abundances of Ni-Mo-S edge sites, which are commonly considered the catalytically important sites. Using a microreactor system, we assess the catalytic activity of the Ni-Mo-S nanoparticles for the HDS of dibenzothiophene. The measurements show that platelets are twice as active as the fullerene-like particles, demonstrating that the Ni-Mo-S edges are more active than basal planes for the HDS. Furthermore, the upright-standing orientation of platelets show an activity that is six times higher than the fullerene-like particles, demonstrating the importance of the edge site number and accessibility to reducing, e.g., sterical hindrance for the reacting molecules.

Surface properties and graphitization of polyacrylonitrile based fiber electrodes affecting the negative half-cell reaction in vanadium redox flow batteries

NASA Astrophysics Data System (ADS)

Langner, J.; Bruns, M.; Dixon, D.; Nefedov, A.; Wöll, Ch.; Scheiba, F.; Ehrenberg, H.; Roth, C.; Melke, J.

2016-07-01

Carbon felt electrodes for vanadium redox flow batteries are obtained by the graphitization of polyacrylonitrile based felts at different temperatures. Subsequently, the surface of the felts is modified via thermal oxidation at various temperatures. A single-cell experiment shows that the voltage efficiency is increased by this treatment. Electrode potentials measured with reference electrode setup show that this voltage efficiency increase is caused mainly by a reduction of the overpotential of the negative half-cell reaction. Consequently, this reaction is investigated further by cyclic voltammetry and the electrode activity is correlated with structural and surface chemical properties of the carbon fibers. By Raman, X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy the role of edge sites and oxygen containing functional groups (OCFs) for the electrochemical activity are elucidated. A significant activity increase is observed in correlation with these two characteristics. The amount of OCFs is correlated with structural defects (e.g. edge sites) of the carbon fibers and therefore decreases with an increasing graphitization degree. Thus, for the same thermal oxidation temperature carbon fibers graphitized at a lower temperature show higher activities than those graphitized at a higher temperature.

Measuring the Edge Recombination Velocity of Monolayer Semiconductors.

PubMed

Zhao, Peida; Amani, Matin; Lien, Der-Hsien; Ahn, Geun Ho; Kiriya, Daisuke; Mastandrea, James P; Ager, Joel W; Yablonovitch, Eli; Chrzan, Daryl C; Javey, Ali

2017-09-13

Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS 2 monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on the material's optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ effective , as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination. Accordingly, we introduce a metric called edge recombination velocity (ERV) to characterize the impact of 2D material edges on nonradiative carrier recombination. The unpassivated WS 2 monolayer disks yield an ERV ∼ 4 × 10 4 cm/s. This work quantifies the nonradiative recombination edge effects in monolayer semiconductors, while simultaneously establishing a practical characterization approach that can be used to experimentally explore edge passivation methods for 2D materials.

Contact formation during fibroblast locomotion: involvement of membrane ruffles and microtubules

PubMed Central

1988-01-01

We have correlated the motility of the leading edge of fibroblasts, monitored by phase-contrast cinematography, with the relative distributions of several cytoskeletal elements (vinculin, tubulin, and actin) as well as with the contact patterns determined by interference reflection microscopy. This analysis has revealed the involvement of both ruffles and microspikes, as well as microtubules in the initiation of focal contact formation. Nascent vinculin sites within the leading edge or at its base, taken as primordial cell-substrate contacts, were invariably colocalized with sites that showed a history of transient, prolonged, or cyclic ruffling activity. Extended microspike structures, often preceded the formation of ruffles. Immunofluorescent labeling indicated that some of these primordial contacts were in close apposition to the ends of microtubules that penetrated into the leading edge. By fluorescence and electron microscopy short bundles of actin filaments found at the base of the leading edge were identified as presumptive, primordial contacts. It is concluded that ruffles and microspikes, either independently or in combination, initiate and mark the sites for future contact. Plaque proteins then accumulate (within 10-30 s) at the contract site and, beneath ruffles, induce localized bundling of actin filaments. We propose that all primordial contacts support traction for leading edge protrusion but that only some persist long enough to nucleate stress fiber assembly. Microtubules are postulated as the elements that select, stabilize, and potentiate the formation of these latter, long-lived contacts. PMID:3126193

Resource selection by black-footed ferrets in South Dakota and Montana

USGS Publications Warehouse

Jachowski, D.S.; Millspaugh, J.J.; Biggins, D.E.; Livieri, T.M.; Matchett, M.R.; Rittenhouse, C.D.

2011-01-01

The black-footed ferret (Mustela nigripes), once extinct in the wild, remains one of the most critically endangered mammals in North America despite 18 years of reintroduction attempts. Because black-footed ferrets are specialized predators of prairie dogs (Cynomys sp.), a better understanding of how black-footed ferrets select resources might provide insight into how best to identify and manage reintroduction sites. We monitored ferret resource selection at two reintroduction sites with different densities of prairie dog populations-one that contained a high density of prairie dogs (Conata Basin, South Dakota) and one that was lower (UL Bend, Montana). We evaluated support for hypotheses about ferret resource selection as related to the distribution of active burrows used by black-tailed prairie dogs (Cynomys ludovicianus), interactions between ferrets, and habitat edge effects. We found support for all three factors within both populations; however, they affected ferret resource selection differently at each site. Ferrets at Conata Basin tended to select areas with high prairie dog burrow density, closer to the colony edge, and that overlapped other ferret ranges. In contrast, ferrets at UL Bend tended not to select areas of high active prairie dog burrow density, avoided areas close to edge habitat, and females avoided areas occupied by other ferrets. The differences observed between the two sites might be best explained by prairie dog densities, which were higher at Conata Basin (119.3 active burrows per ha) than at UL Bend (44.4 active burrows per ha). Given the positive growth of ferret populations at Conata Basin, management that increases the density of prairie dogs might enhance ferret success within natural areas. To achieve long-term recovery of ferrets in the wild, conservationists should increasingly work across and outside natural area boundaries to increase prairie dog populations.

Comparisons of shear-wave slowness in the Santa Clara Valley, California using blind interpretations of data from invasive and noninvasive methods

USGS Publications Warehouse

Boore, D.M.; Asten, M.W.

2008-01-01

Many groups contributed to a blind interpretation exercise for the determination of shear-wave slowness beneath the Santa Clara Valley. The methods included invasive methods in deep boreholes as well as noninvasive methods using active and passive sources, at six sites within the valley (with most investigations being conducted at a pair of closely spaced sites near the center of the valley). Although significant variability exists between the models, the slownesses from the various methods are similar enough that linear site amplifications estimated in several ways are generally within 20% of one another. The methods were able to derive slownesses that increase systematically with distance from the valley edge, corresponding to a tendency for the sites to be underlain by finer-grained materials away from the valley edge. This variation is in agreement with measurements made in the boreholes at the sites.

Defining the origins of electron transfer at screen-printed graphene-like and graphite electrodes: MoO2 nanowire fabrication on edge plane sites reveals electrochemical insights.

PubMed

Rowley-Neale, Samuel J; Brownson, Dale A C; Banks, Craig E

2016-08-18

Molybdenum (di)oxide (MoO2) nanowires are fabricated onto graphene-like and graphite screen-printed electrodes (SPEs) for the first time, revealing crucial insights into the electrochemical properties of carbon/graphitic based materials. Distinctive patterns observed in the electrochemical process of nanowire decoration show that electron transfer occurs predominantly on edge plane sites when utilising SPEs fabricated/comprised of graphitic materials. Nanowire fabrication along the edge plane sites (and on edge plane like-sites/defects) of graphene/graphite is confirmed with Cyclic Voltammetry, Scanning Electron Microscopy (SEM) and Raman Spectroscopy. Comparison of the heterogeneous electron transfer (HET) rate constants (k°) at unmodified and nanowire coated SPEs show a reduction in the electrochemical reactivity of SPEs when the edge plane sites are effectively blocked/coated with MoO2. Throughout the process, the basal plane sites of the graphene/graphite electrodes remain relatively uncovered; except when the available edge plane sites have been utilised, in which case MoO2 deposition grows from the edge sites covering the entire surface of the electrode. This work clearly illustrates the distinct electron transfer properties of edge and basal plane sites on graphitic materials, indicating favourable electrochemical reactivity at the edge planes in contrast to limited reactivity at the basal plane sites. In addition to providing fundamental insights into the electron transfer properties of graphite and graphene-like SPEs, the reported simple, scalable, and cost effective formation of unique and intriguing MoO2 nanowires realised herein is of significant interest for use in both academic and commercial applications.

Theoretical investigation of the role of clay edges in prebiotic peptide bond formation. II - Structures and thermodynamics of the activated complex species

NASA Technical Reports Server (NTRS)

Collins, Jack R.; Loew, Gilda H.; Luke, Brian T.; White, David H.

1988-01-01

Molecular orbital calculations are used to study amino acid activation by anhydride formation in neutral phosphates and in tetrahedral silicate and aluminate sites on clay edges. The results agree with previous ab initio studies of Luke et al. (1984) on the reactant species. Relative heats of formation of the anhydrides indicate the extent of anhydride formation to be the greatest for Al and the least for phosphate, which is the same order as the stability of hydrolysis.

Hydrothermal fabrication of few-layer MoS2 nanosheets within nanopores on TiO2 derived from MIL-125(Ti) for efficient photocatalytic H2 evolution

NASA Astrophysics Data System (ADS)

Ye, Fei; Li, Houfen; Yu, Hongtao; Chen, Shuo; Quan, Xie

2017-12-01

Protons tend to bond strongly with unsaturated-coordinate S element located at the edge of nano-MoS2 and are consequently reduced to H2. Therefore, increasing the active S atoms quantity will be a feasible approach to enhance hydrogen evolution. Herein we developed a porous TiO2 derived from metal organic frameworks (MOFs) as scaffold to restrict the growth and inhibit the aggregation of MoS2 nanosheets. As a result, the thickness of the prepared MoS2 nanosheets was less than 3 nm (1-4 layers), with more edges and active S atoms being exposed. This few-layer MoS2-porous TiO2 exhibits a H2 evolution rate of 897.5 μmol h-1 g-1, which is nearly twice as much as free-stand MoS2 nanosheets and twenty times more than physical mixture of MoS2 with porous TiO2. The high performance is attributed to that more active edge sites in few-layer MoS2-porous TiO2 are exposed than pure MoS2. This work provides a new method to construct MOFs derived porous structures for controlling MoS2 to expose active sites for HER.

Edge states in a ferromagnetic honeycomb lattice with armchair boundaries

NASA Astrophysics Data System (ADS)

Pantaleón, Pierre A.; Xian, Y.

2018-02-01

We investigate the properties of magnon edge states in a ferromagnetic honeycomb lattice with armchair boundaries. In contrast with fermionic graphene, we find novel edge states due to the missing bonds along the boundary sites. After introducing an external on-site potential at the outermost sites we find that the energy spectra of the edge states are tunable. Additionally, when a non-trivial gap is induced, we find that some of the edge states are topologically protected and also tunable. Our results may explain the origin of the novel edge states recently observed in photonic lattices. We also discuss the behavior of these edge states for further experimental confirmations.

Electronic structure of transition metal-cysteine complexes from X-ray absorption spectroscopy.

PubMed

Leung, Bonnie O; Jalilehvand, Farideh; Szilagyi, Robert K

2008-04-17

The electronic structures of HgII, NiII, CrIII, and MoV complexes with cysteine were investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory. The covalency in the metal-sulfur bond was determined by analyzing the intensities of the electric-dipole allowed pre-edge features appearing in the XANES spectra below the ionization threshold. Because of the well-defined structures of the selected cysteine complexes, the current work provides a reference set for further sulfur K-edge XAS studies of bioinorganic active sites with transition metal-sulfur bonds from cysteine residues as well as more complex coordination compounds with thiolate ligands.

Unravelling Site-Specific Photo-Reactions of Ethanol on Rutile TiO2(110)

PubMed Central

Hansen, Jonas Ø.; Bebensee, Regine; Martinez, Umberto; Porsgaard, Soeren; Lira, Estephania; Wei, Yinying; Lammich, Lutz; Li, Zheshen; Idriss, Hicham; Besenbacher, Flemming; Hammer, Bjørk; Wendt, Stefan

2016-01-01

Finding the active sites of catalysts and photo-catalysts is crucial for an improved fundamental understanding and the development of efficient catalytic systems. Here we have studied the photo-activated dehydrogenation of ethanol on reduced and oxidized rutile TiO2(110) in ultrahigh vacuum conditions. Utilizing scanning tunnelling microscopy, various spectroscopic techniques and theoretical calculations we found that the photo-reaction proceeds most efficiently when the reactants are adsorbed on regular Ti surface sites, whereas species that are strongly adsorbed at surface defects such as O vacancies and step edges show little reaction under reducing conditions. We propose that regular Ti surface sites are the most active sites in photo-reactions on TiO2. PMID:26915303

ERK-MAPK drives lamellipodia protrusion by activating the WAVE2 regulatory complex.

PubMed

Mendoza, Michelle C; Er, E Emrah; Zhang, Wenjuan; Ballif, Bryan A; Elliott, Hunter L; Danuser, Gaudenz; Blenis, John

2011-03-18

Cell movement begins with a leading edge protrusion, which is stabilized by nascent adhesions and retracted by mature adhesions. The ERK-MAPK (extracellular signal-regulated kinase-mitogen-activated protein kinase) localizes to protrusions and adhesions, but how it regulates motility is not understood. We demonstrate that ERK controls protrusion initiation and protrusion speed. Lamellipodial protrusions are generated via the WRC (WAVE2 regulatory complex), which activates the Arp2/3 actin nucleator for actin assembly. The WRC must be phosphorylated to be activated, but the sites and kinases that regulate its intermolecular changes and membrane recruitment are unknown. We show that ERK colocalizes with the WRC at lamellipodial leading edges and directly phosphorylates two WRC components: WAVE2 and Abi1. The phosphorylations are required for functional WRC interaction with Arp2/3 and actin during cell protrusion. Thus, ERK coordinates adhesion disassembly with WRC activation and actin polymerization to promote productive leading edge advancement during cell migration. Copyright © 2011 Elsevier Inc. All rights reserved.

ERK-MAPK Drives Lamellipodia Protrusion by Activating the WAVE2 Regulatory Complex

PubMed Central

Mendoza, Michelle C.; Emrah, E.; Zhang, Wenjuan; Ballif, Bryan A.; Elliott, Hunter L.; Danuser, Gaudenz; Blenis, John

2011-01-01

Summary Cell movement begins with a leading edge protrusion, which is stabilized by nascent adhesions and retracted by mature adhesions. The ERK-MAPK (extracellular signal regulated kinasemitogen-activated protein kinase) localizes to protrusions and adhesions, but how it regulates motility is not understood. We demonstrate ERK controls protrusion initiation and protrusion speed. Lamellipodial protrusions are generated via the WRC (WAVE2 Regulatory Complex), which activates the Arp2/3 actin nucleator for actin assembly. The WRC must be phosphorylated to be activated, but the sites and kinases that regulate its intermolecular changes and membrane recruitment are unknown. We show ERK co-localizes with the WRC at lamellipodial leading edges and directly phosphorylates two WRC components: WAVE2 and Abi1. The phosphorylations are required for functional WRC interaction with Arp2/3 and actin during cell protrusion. Thus, ERK coordinates adhesion disassembly with WRC activation and actin polymerization to promote productive leading edge advancement during cell migration. PMID:21419341

Controlling the Active Sites of Sulfur-Doped Carbon Nanotube-Graphene Nanolobes for Highly Efficient Oxygen Evolution and Reduction Catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Sawy, Abdelhamid M.; Mosa, Islam M.; Su, Dong

Controlling active sites of metal-free catalysts is an important strategy to enhance activity of the oxygen evolution reaction (OER). We made many attempts have been made to develop metal-free catalysts, but the lack of understanding of active-sites at the atomic-level has slowed the design of highly active and stable metal-free catalysts. We also developed a sequential two-step strategy to dope sulfur into carbon nanotube–graphene nanolobes. This bidoping strategy introduces stable sulfur–carbon active-sites. Fluorescence emission of the sulfur K-edge by X-ray absorption near edge spectroscopy (XANES) and scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) mapping and spectra confirm thatmore » increasing the incorporation of heterocyclic sulfur into the carbon ring of CNTs not only enhances OER activity with an overpotential of 350 mV at a current density of 10 mA cm -2, but also retains 100% of stability after 75 h. Furthermore, the bidoped sulfur carbon nanotube–graphene nanolobes behave like the state-of-the-art catalysts for OER but outperform those systems in terms of turnover frequency (TOF) which is two orders of magnitude greater than (20% Ir/C) at 400 mV overpotential with very high mass activity 1000 mA cm -2 at 570 mV. Moreover, the sulfur bidoping strategy shows high catalytic activity for the oxygen reduction reaction (ORR). Stable bifunctional (ORR and OER) catalysts are low cost, and light-weight bidoped sulfur carbon nanotubes are potential candidates for next-generation metal-free regenerative fuel cells.« less

Controlling the Active Sites of Sulfur-Doped Carbon Nanotube-Graphene Nanolobes for Highly Efficient Oxygen Evolution and Reduction Catalysis

DOE PAGES

El-Sawy, Abdelhamid M.; Mosa, Islam M.; Su, Dong; ...

2015-12-03

Controlling active sites of metal-free catalysts is an important strategy to enhance activity of the oxygen evolution reaction (OER). We made many attempts have been made to develop metal-free catalysts, but the lack of understanding of active-sites at the atomic-level has slowed the design of highly active and stable metal-free catalysts. We also developed a sequential two-step strategy to dope sulfur into carbon nanotube–graphene nanolobes. This bidoping strategy introduces stable sulfur–carbon active-sites. Fluorescence emission of the sulfur K-edge by X-ray absorption near edge spectroscopy (XANES) and scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) mapping and spectra confirm thatmore » increasing the incorporation of heterocyclic sulfur into the carbon ring of CNTs not only enhances OER activity with an overpotential of 350 mV at a current density of 10 mA cm -2, but also retains 100% of stability after 75 h. Furthermore, the bidoped sulfur carbon nanotube–graphene nanolobes behave like the state-of-the-art catalysts for OER but outperform those systems in terms of turnover frequency (TOF) which is two orders of magnitude greater than (20% Ir/C) at 400 mV overpotential with very high mass activity 1000 mA cm -2 at 570 mV. Moreover, the sulfur bidoping strategy shows high catalytic activity for the oxygen reduction reaction (ORR). Stable bifunctional (ORR and OER) catalysts are low cost, and light-weight bidoped sulfur carbon nanotubes are potential candidates for next-generation metal-free regenerative fuel cells.« less

An Automated Method of Scanning Probe Microscopy (SPM) Data Analysis and Reactive Site Tracking for Mineral-Water Interface Reactions Observed at the Nanometer Scale

NASA Astrophysics Data System (ADS)

Campbell, B. D.; Higgins, S. R.

2008-12-01

Developing a method for bridging the gap between macroscopic and microscopic measurements of reaction kinetics at the mineral-water interface has important implications in geological and chemical fields. Investigating these reactions on the nanometer scale with SPM is often limited by image analysis and data extraction due to the large quantity of data usually obtained in SPM experiments. Here we present a computer algorithm for automated analysis of mineral-water interface reactions. This algorithm automates the analysis of sequential SPM images by identifying the kinetically active surface sites (i.e., step edges), and by tracking the displacement of these sites from image to image. The step edge positions in each image are readily identified and tracked through time by a standard edge detection algorithm followed by statistical analysis on the Hough Transform of the edge-mapped image. By quantifying this displacement as a function of time, the rate of step edge displacement is determined. Furthermore, the total edge length, also determined from analysis of the Hough Transform, combined with the computed step speed, yields the surface area normalized rate of the reaction. The algorithm was applied to a study of the spiral growth of the calcite(104) surface from supersaturated solutions, yielding results almost 20 times faster than performing this analysis by hand, with results being statistically similar for both analysis methods. This advance in analysis of kinetic data from SPM images will facilitate the building of experimental databases on the microscopic kinetics of mineral-water interface reactions.

Silver-Coated Nylon Dressing Plus Active DC Microcurrent for Healing of Autogenous Skin Donor Sites

DTIC Science & Technology

2013-08-01

of contact dermatitis induced by 1,2-dinitrochlorobenzene, Nadworny et al demonstrated that Acticoat induced apoptosis of inf lammatory cells in the...activity of nanocrys- talline silver in a porcine contact dermatitis model. Nanomedicine. 2008;4:241Y251. 14. Atiyeh BS, Costagliola M, Hayek SN, et...good skin contact , and these electrodes were replaced when necessary. The edges of the donor site were inspected for evidence of healing or infection

Formation of Stone-Wales edge: Multistep reconstruction and growth mechanisms of zigzag nanographene.

PubMed

Dang, Jing-Shuang; Wang, Wei-Wei; Zheng, Jia-Jia; Nagase, Shigeru; Zhao, Xiang

2017-10-05

Although the existence of Stone-Wales (5-7) defect at graphene edge has been clarified experimentally, theoretical study on the formation mechanism is still imperfect. In particular, the regioselectivity of multistep reactions at edge (self-reconstruction and growth with foreign carbon feedstock) is essential to understand the kinetic behavior of reactive boundaries but investigations are still lacking. Herein, by using finite-sized models, multistep reconstructions and carbon dimer additions of a bared zigzag edge are introduced using density functional theory calculations. The zigzag to 5-7 transformation is proved as a site-selective process to generate alternating 5-7 pairs sequentially and the first step with largest barrier is suggested as the rate-determining step. Conversely, successive C 2 insertions on the active edge are calculated to elucidate the formation of 5-7 edge during graphene growth. A metastable intermediate with a triple sequentially fused pentagon fragment is proved as the key structure for 5-7 edge formation. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Patched bimetallic surfaces are active catalysts for ammonia decomposition.

PubMed

Guo, Wei; Vlachos, Dionisios G

2015-10-07

Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core-shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core-shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

Patched bimetallic surfaces are active catalysts for ammonia decomposition

NASA Astrophysics Data System (ADS)

Guo, Wei; Vlachos, Dionisios G.

2015-10-01

Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core-shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core-shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

Oxygen reduction reaction activity and structural stability of Pt-Au nanoparticles prepared by arc-plasma deposition.

PubMed

Takahashi, Shuntaro; Chiba, Hiroshi; Kato, Takashi; Endo, Shota; Hayashi, Takehiro; Todoroki, Naoto; Wadayama, Toshimasa

2015-07-28

The oxygen reduction reaction (ORR) activity and durability of various Au(x)/Pt100 nanoparticles (where x is the atomic ratio of Au against Pt) are evaluated herein. The samples were fabricated on a highly-oriented pyrolytic graphite substrate at 773 K through sequential arc-plasma depositions of Pt and Au. The electrochemical hydrogen adsorption charges (electrochemical surface area), particularly the characteristic currents caused by the corner and edge sites of the Pt nanoparticles, decrease with increasing Au atomic ratio (x). In contrast, the specific ORR activities of the Au(x)/Pt100 samples were dependent on the atomic ratios of Pt and Au: the Au28/Pt100 sample showed the highest specific activity among all the investigated samples (x = 0-42). As for ORR durability evaluated by applying potential cycles between 0.6 and 1.0 V in oxygen-saturated 0.1 M HClO4, Au28/Pt100 was the most durable sample against the electrochemical potential cycles. The results clearly showed that the Au atoms located at coordinatively-unsaturated sites, e.g. at the corners or edges of the Pt nanoparticles, can improve the ORR durability by suppressing unsaturated-site-induced degradation of the Pt nanoparticles.

Active-Optical Sensors Using Red NDVI Compared to Red Edge NDVI for Prediction of Corn Grain Yield in North Dakota, U.S.A.

PubMed Central

Sharma, Lakesh K.; Bu, Honggang; Denton, Anne; Franzen, David W.

2015-01-01

Active-optical sensor readings from an N non-limiting area standard established within a farm field are used to predict yield in the standard. Lower yield predictions from sensor readings obtained from other parts of the field outside of the N non-limiting standard area indicate a need for supplemental N. Active-optical sensor algorithms for predicting corn (Zea mays, L.) yield to direct in-season nitrogen (N) fertilization in corn utilize red NDVI (normalized differential vegetative index). Use of red edge NDVI might improve corn yield prediction at later growth stages when corn leaves cover the inter-row space resulting in “saturation” of red NDVI readings. The purpose of this study was to determine whether the use of red edge NDVI in two active-optical sensors (GreenSeeker™ and Holland Scientific Crop Circle™) improved corn yield prediction. Nitrogen rate experiments were established at 15 sites in North Dakota (ND). Sensor readings were conducted at V6 and V12 corn. Red NDVI and red edge NDVI were similar in the relationship of readings with yield at V6. At V12, the red edge NDVI was superior to the red NDVI in most comparisons, indicating that it would be most useful in developing late-season N application algorithms. PMID:26540057

Active-Optical Sensors Using Red NDVI Compared to Red Edge NDVI for Prediction of Corn Grain Yield in North Dakota, U.S.A.

PubMed

Sharma, Lakesh K; Bu, Honggang; Denton, Anne; Franzen, David W

2015-11-02

Active-optical sensor readings from an N non-limiting area standard established within a farm field are used to predict yield in the standard. Lower yield predictions from sensor readings obtained from other parts of the field outside of the N non-limiting standard area indicate a need for supplemental N. Active-optical sensor algorithms for predicting corn (Zea mays, L.) yield to direct in-season nitrogen (N) fertilization in corn utilize red NDVI (normalized differential vegetative index). Use of red edge NDVI might improve corn yield prediction at later growth stages when corn leaves cover the inter-row space resulting in "saturation" of red NDVI readings. The purpose of this study was to determine whether the use of red edge NDVI in two active-optical sensors (GreenSeeker™ and Holland Scientific Crop Circle™) improved corn yield prediction. Nitrogen rate experiments were established at 15 sites in North Dakota (ND). Sensor readings were conducted at V6 and V12 corn. Red NDVI and red edge NDVI were similar in the relationship of readings with yield at V6. At V12, the red edge NDVI was superior to the red NDVI in most comparisons, indicating that it would be most useful in developing late-season N application algorithms.

Design and Preparation of Supported Au Catalyst with Enhanced Catalytic Activities by Rationally Positioning Au Nanoparticles on Anatase.

PubMed

Wang, Liang; Wang, Hong; Rice, Andrew E; Zhang, Wei; Li, Xiaokun; Chen, Mingshu; Meng, Xiangju; Lewis, James P; Xiao, Feng-Shou

2015-06-18

A synergistic effect between individual components is crucial for increasing the activity of metal/metal oxide catalysts. The greatest challenge is how to control the synergistic effect to obtain enhanced catalytic performance. Through density functional theory calculations of model Au/TiO2 catalysts, it is suggested that there is strong interaction between Au nanoparticles and Ti species at the edge/corner sites of anatase, which is favorable for the formation of stable oxygen vacancies. Motivated by this theoretical analysis, we have rationally prepared Au nanoparticles attached to edge/corner sites of anatase support (Au/TiO2-EC), confirmed by their HR-TEM images. As expected, this strong interaction is well characterized by Raman, UV-visible, and XPS techniques. Very interestingly, compared with conventional Au catalysts, Au/TiO2-EC exhibits superior catalytic activity in the oxidations using O2. Our approach to controlling Au nanoparticle positioning on anatase to obtain enhanced catalytic activity offers an efficient strategy for developing more novel supported metal catalysts.

Empirical calibration of uranium releases in the terrestrial environment of nuclear fuel cycle facilities.

PubMed

Pourcelot, Laurent; Masson, Olivier; Saey, Lionel; Conil, Sébastien; Boulet, Béatrice; Cariou, Nicolas

2017-05-01

In the present paper the activity of uranium isotopes measured in plants and aerosols taken downwind of the releases of three nuclear fuel settlements was compared between them and with the activity measured at remote sites. An enhancement of 238 U activity as well as 235 U/ 238 U anomalies and 236 U are noticeable in wheat, grass, tree leaves and aerosols taken at the edge of nuclear fuel settlements, which show the influence of uranium chronic releases. Further plants taken at the edge of the studied sites and a few published data acquired in the same experimental conditions show that the 238 U activity in plants is influenced by the intensity of the U atmospheric releases. Assuming that 238 U in plant is proportional to the intensity of the releases, we proposed empirical relationships which allow to characterize the chronic releases on the ground. Other sources of U contamination in plants such as accidental releases and "delayed source" of uranium in soil are also discussed in the light of uranium isotopes signatures. Copyright © 2017 Elsevier Ltd. All rights reserved.

Edge-Driven Block Rotations Interpreted From New GPS Results: Papua New Guinea

NASA Astrophysics Data System (ADS)

Wallace, L.

2001-12-01

An ongoing discussion in plate tectonics involves whether microplate motions are driven by plate edge forces or by flow at the base of the lithosphere. We present results from a GPS network of 40 sites spanning much of the mainland of Papua New Guinea (PNG). Most of the sites are concentrated in the region of the active Finisterre arc-continent collision and have been observed on multiple campaigns from 1993-2001. Significant portions of the Ramu-Markham fault are locked, which has implications for seismic hazard assessment in the Markham Valley region. Additionally, we find that out-of-sequence thrusting is important in emplacement of the Finisterre arc terrane onto the PNG mainland. Site velocities derived from these GPS data have helped to delineate the major tectonic blocks in the region. We model site velocities by simultaneously dealing with rigid block rotation and elastic strain. We find that the mainland of PNG consists of four distinct tectonic plates: the Australian, South Bismarck and Woodlark plates (in agreement with previous studies), and a previously unrecognized New Guinea Highlands plate. The relative rotation poles for at least two of these plate pairs plot on their respective boundaries, indicating that microplate motion in PNG may be dominantly edge-driven, as predicted for this region by Schouten and Benes (1993).

X-ray absorption near-edge spectroscopy in bioinorganic chemistry: Application to M–O2 systems

PubMed Central

Sarangi, Ritimukta

2012-01-01

Metal K-edge X-ray absorption spectroscopy (XAS) has been extensively applied to bioinorganic chemistry to obtain geometric structure information on metalloprotein and biomimetic model complex active sites by analyzing the higher energy extended X-ray absorption fine structure (EXAFS) region of the spectrum. In recent years, focus has been on developing methodologies to interpret the lower energy K-pre-edge and rising-edge regions (XANES) and using it for electronic structure determination in complex bioinorganic systems. In this review, the evolution and progress of 3d-transition metal K-pre-edge and rising-edge methodology development is presented with particular focus on applications to bioinorganic systems. Applications to biomimetic transition metal–O2 intermediates (M = Fe, Co, Ni and Cu) are reviewed, which demonstrate the power of the method as an electronic structure determination technique and its impact in understanding the role of supporting ligands in tuning the electronic configuration of transition metal–O2 systems. PMID:23525635

Out-of-plane spin polarization of edge currents in Chern insulator with Rashba spin-orbit interaction

NASA Astrophysics Data System (ADS)

Chen, Tsung-Wei; Hsiao, Chin-Lun; Hu, Chong-Der

2016-07-01

We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at the site-I and site-II atoms, and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increases the number of Dirac points and the band-touching phenomenon can be generated by tuning the on-site potential in the non-zero Haldane phase. By using the Pontryagin winding number and numerical Berry curvature methods, we find that the Chern number pattern is {+2, -1, 0} and {-2, +1, 0} for the positive and negative Haldane phase, respectively. A non-zero Chern number is called a Chern-insulating phase. We discovered that changes in both the Haldane phase and on-site potential leads to a change in the orientation of the bulk spin polarization of site-I and site-II atoms. Interestingly, in a ribbon with a zigzag edge, which naturally has site-I atoms at one outer edge and site-II atoms at the opposite outer edge, the spin polarization of the edge states approximately obeys the properties of bulk spin polarization regardless of the change in the Chern number. In addition, even when the Chern number changes from  +2 to  -1 (or  -2 to  +1), by tuning the strength of the on-site potential, the sign of the spin polarization of the edge states persists. This approximate bulk-edge correspondence of the spin polarization in the Haldane-Rashba system would play an important role in spintronics, because it enables us to control the orientation of the spin polarization in a single Chern-insulating phase.

Out-of-plane spin polarization of edge currents in Chern insulator with Rashba spin-orbit interaction.

PubMed

Chen, Tsung-Wei; Hsiao, Chin-Lun; Hu, Chong-Der

2016-07-13

We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at the site-I and site-II atoms, and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increases the number of Dirac points and the band-touching phenomenon can be generated by tuning the on-site potential in the non-zero Haldane phase. By using the Pontryagin winding number and numerical Berry curvature methods, we find that the Chern number pattern is {+2, -1, 0} and {-2, +1, 0} for the positive and negative Haldane phase, respectively. A non-zero Chern number is called a Chern-insulating phase. We discovered that changes in both the Haldane phase and on-site potential leads to a change in the orientation of the bulk spin polarization of site-I and site-II atoms. Interestingly, in a ribbon with a zigzag edge, which naturally has site-I atoms at one outer edge and site-II atoms at the opposite outer edge, the spin polarization of the edge states approximately obeys the properties of bulk spin polarization regardless of the change in the Chern number. In addition, even when the Chern number changes from  +2 to  -1 (or  -2 to  +1), by tuning the strength of the on-site potential, the sign of the spin polarization of the edge states persists. This approximate bulk-edge correspondence of the spin polarization in the Haldane-Rashba system would play an important role in spintronics, because it enables us to control the orientation of the spin polarization in a single Chern-insulating phase.

Iron L2,3-Edge X-ray Absorption and X-ray Magnetic Circular Dichroism Studies of Molecular Iron Complexes with Relevance to the FeMoco and FeVco Active Sites of Nitrogenase

PubMed Central

2017-01-01

Herein, a systematic study of a series of molecular iron model complexes has been carried out using Fe L2,3-edge X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopies. This series spans iron complexes of increasing complexity, starting from ferric and ferrous tetrachlorides ([FeCl4]−/2–), to ferric and ferrous tetrathiolates ([Fe(SR)4]−/2–), to diferric and mixed-valent iron–sulfur complexes [Fe2S2R4]2–/3–. This test set of compounds is used to evaluate the sensitivity of both Fe L2,3-edge XAS and XMCD spectroscopy to oxidation state and ligation changes. It is demonstrated that the energy shift and intensity of the L2,3-edge XAS spectra depends on both the oxidation state and covalency of the system; however, the quantitative information that can be extracted from these data is limited. On the other hand, analysis of the Fe XMCD shows distinct changes in the intensity at both L3 and L2 edges, depending on the oxidation state of the system. It is also demonstrated that the XMCD intensity is modulated by the covalency of the system. For mononuclear systems, the experimental data are correlated with atomic multiplet calculations in order to provide insights into the experimental observations. Finally, XMCD is applied to the tetranuclear heterometal–iron–sulfur clusters [MFe3S4]3+/2+ (M = Mo, V), which serve as structural analogues of the FeMoco and FeVco active sites of nitrogenase. It is demonstrated that the XMCD data can be utilized to obtain information on the oxidation state distribution in complex clusters that is not readily accessible for the Fe L2,3-edge XAS data alone. The advantages of XMCD relative to standard K-edge and L2,3-edge XAS are highlighted. This study provides an important foundation for future XMCD studies on complex (bio)inorganic systems. PMID:28653855

Formation, Migration, and Reactivity of Au CO Complexes on Gold Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jun; McEntee, Monica; Tang, Wenjie

2016-01-12

Here, we report experimental as well as theoretical evidence that suggests Au CO complex formation upon the exposure of CO to active sites (step edges and threading dislocations) on a Au(111) surface. Room-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, transmission infrared spectroscopy, and density functional theory calculations point to Au CO complex formation and migration. Room-temperature STM of the Au(111) surface at CO pressures in the range from 10^ 8 to 10^ 4 Torr (dosage up to 10^6 langmuir) indicates Au atom extraction from dislocation sites of the herringbone reconstruction, mobile Au CO complex formation and diffusion, and Aumore » adatom cluster formation on both elbows and step edges on the Au surface. The formation and mobility of the Au CO complex result from the reduced Au Au bonding at elbows and step edges leading to stronger Au CO bonding and to the formation of a more positively charged CO (CO +) on Au. These studies indicate that the mobile Au CO complex is involved in the Au nanoparticle formation and reactivity, and that the positive charge on CO increases due to the stronger adsorption of CO at Au sites with lower coordination numbers.« less

Active star formation in NGC 2264

NASA Technical Reports Server (NTRS)

Schwartz, P. R.; Thronson, H. A., Jr.; Odenwald, S. F.; Glaccum, W.; Loewenstein, R. F.; Wolf, G.

1985-01-01

The region of NGC 2264 near the cone nebula is the site of active star formation in a rotating ring seen nearly edge on as a two lobed source. Allen's infrared source (IRS 1) surrounds a B3V star still embedded in the southern lobe of the cloud. The northern lobe, IRS 2, also probably contains young stars.

Patched bimetallic surfaces are active catalysts for ammonia decomposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Wei; Vlachos, Dionisios G.

In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-Hmore » bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.« less

Patched bimetallic surfaces are active catalysts for ammonia decomposition

DOE PAGES

Guo, Wei; Vlachos, Dionisios G.

2015-10-07

In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-Hmore » bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.« less

Node-based measures of connectivity in genetic networks.

PubMed

Koen, Erin L; Bowman, Jeff; Wilson, Paul J

2016-01-01

At-site environmental conditions can have strong influences on genetic connectivity, and in particular on the immigration and settlement phases of dispersal. However, at-site processes are rarely explored in landscape genetic analyses. Networks can facilitate the study of at-site processes, where network nodes are used to model site-level effects. We used simulated genetic networks to compare and contrast the performance of 7 node-based (as opposed to edge-based) genetic connectivity metrics. We simulated increasing node connectivity by varying migration in two ways: we increased the number of migrants moving between a focal node and a set number of recipient nodes, and we increased the number of recipient nodes receiving a set number of migrants. We found that two metrics in particular, the average edge weight and the average inverse edge weight, varied linearly with simulated connectivity. Conversely, node degree was not a good measure of connectivity. We demonstrated the use of average inverse edge weight to describe the influence of at-site habitat characteristics on genetic connectivity of 653 American martens (Martes americana) in Ontario, Canada. We found that highly connected nodes had high habitat quality for marten (deep snow and high proportions of coniferous and mature forest) and were farther from the range edge. We recommend the use of node-based genetic connectivity metrics, in particular, average edge weight or average inverse edge weight, to model the influences of at-site habitat conditions on the immigration and settlement phases of dispersal. © 2015 John Wiley & Sons Ltd.

Atomic layer deposition overcoating: tuning catalyst selectivity for biomass conversion.

PubMed

Zhang, Hongbo; Gu, Xiang-Kui; Canlas, Christian; Kropf, A Jeremy; Aich, Payoli; Greeley, Jeffrey P; Elam, Jeffrey W; Meyers, Randall J; Dumesic, James A; Stair, Peter C; Marshall, Christopher L

2014-11-03

The terraces, edges, and facets of nanoparticles are all active sites for heterogeneous catalysis. These different active sites may cause the formation of various products during the catalytic reaction. Here we report that the step sites of Pd nanoparticles (NPs) can be covered precisely by the atomic layer deposition (ALD) method, whereas the terrace sites remain as active component for the hydrogenation of furfural. Increasing the thickness of the ALD-generated overcoats restricts the adsorption of furfural onto the step sites of Pd NPs and increases the selectivity to furan. Furan selectivities and furfural conversions are linearly correlated for samples with or without an overcoating, though the slopes differ. The ALD technique can tune the selectivity of furfural hydrogenation over Pd NPs and has improved our understanding of the reaction mechanism. The above conclusions are further supported by density functional theory (DFT) calculations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A PKC-MARCKS-PI3K regulatory module links Ca2+ and PIP3 signals at the leading edge of polarized macrophages.

PubMed

Ziemba, Brian P; Falke, Joseph J

2018-01-01

The leukocyte chemosensory pathway detects attractant gradients and directs cell migration to sites of inflammation, infection, tissue damage, and carcinogenesis. Previous studies have revealed that local Ca2+ and PIP3 signals at the leading edge of polarized leukocytes play central roles in positive feedback loop essential to cell polarization and chemotaxis. These prior studies showed that stimulation of the leading edge Ca2+ signal can strongly activate PI3K, thereby triggering a larger PIP3 signal, but did not elucidate the mechanistic link between Ca2+ and PIP3 signaling. A hypothesis explaining this link emerged, postulating that Ca2+-activated PKC displaces the MARCKS protein from plasma membrane PIP2, thereby releasing sequestered PIP2 to serve as the target and substrate lipid of PI3K in PIP3 production. In vitro single molecule studies of the reconstituted pathway on lipid bilayers demonstrated the feasibility of this PKC-MARCKS-PI3K regulatory module linking Ca2+ and PIP3 signals in the reconstituted system. The present study tests the model predictions in live macrophages by quantifying the effects of: (a) two pathway activators-PDGF and ATP that stimulate chemoreceptors and Ca2+ influx, respectively; and (b) three pathway inhibitors-wortmannin, EGTA, and Go6976 that inhibit PI3K, Ca2+ influx, and PKC, respectively; on (c) four leading edge activity sensors-AKT-PH-mRFP, CKAR, MARCKSp-mRFP, and leading edge area that report on PIP3 density, PKC activity, MARCKS membrane binding, and leading edge expansion/contraction, respectively. The results provide additional evidence that PKC and PI3K are both essential elements of the leading edge positive feedback loop, and strongly support the existence of a PKC-MARCKS-PI3K regulatory module linking the leading edge Ca2+ and PIP3 signals. As predicted, activators stimulate leading edge PKC activity, displacement of MARCKS from the leading edge membrane and increased leading edge PIP3 levels, while inhibitors trigger the opposite effects. Comparison of the findings for the ameboid chemotaxis of leukocytes with recently published findings for the mesenchymal chemotaxis of fibroblasts suggests that some features of the emerging leukocyte leading edge core pathway (PLC-DAG-Ca2+-PKC-MARCKS-PIP2-PI3K-PIP3) may well be shared by all chemotaxing eukaryotic cells, while other elements of the leukocyte pathway may be specialized features of these highly optimized, professional gradient-seeking cells. More broadly, the findings suggest a molecular mechanism for the strong links between phospho-MARCKS and many human cancers.

The Design, Synthesis, and Characterization of Open Sites on Metal Clusters

NASA Astrophysics Data System (ADS)

Nigra, Michael Mark

Coordinatively unsaturated corner and edge atoms have been hypothesized to have the highest activity of sites responsible for many catalytic reactions on a metal surface. Recent studies have validated this hypothesis in varied reaction systems. However, quantification of different types of coordinatively unsaturated sites, and elucidation of their individual catalytic rates has remained a largely unresolved challenge when understanding catalysis on metal surfaces. Yet such structure-function knowledge would be invaluable to the design of more active and selective metal-surface catalysts in the future. I investigated the catalytic contributions of undercoordinated sites such as corner and edge atoms are investigated in a model reaction system using organic ligands bound to the gold nanoparticle surface. The catalyst consisted of 4 nm gold nanoparticles on a metal oxide support, using resazurin to resorufin as a model reaction system. My results demonstrate that in this system, corner atom sites are the most undercoordinated sites, and are over an order of magnitude more active when compared to undercoordinated edge atom sites, while terrace sites remain catalytically inactive for the reduction reaction of resazurin to resorufin. Catalytic activity has been also demonstrated for calixarene-bound gold nanoparticles using the reduction of 4-nitrophenol. With the 4-nitrophenol reduction reaction, a comparative study was undertaken to compare calixarene phosphine and calixarene thiol bound 4 nm gold particles. The results of the study suggested that a leached site was responsible for catalysis and not sites on the original gold nanoparticles. Future experiments with calixarene bound gold clusters could investigate ligand effects in reactions where the active site is not a leached or aggregated gold species, possibly in oxidation reactions, where electron-rich gold is hypothesized to be a good catalyst. The results that emphasize the enhanced catalytic activity of undercoordinated sites led me to synthesize small gold clusters consisting of a high fraction of coordinatively unsaturated open sites. This was enabled through an approach that utilized bulky calix[4]arene ligands that are bound to a gold core. Since the size of the calix[4]arene ligand is commensurate with the size of the gold cluster core, the calix[4]arene ligand does not pack closely together on the gold cluster surface. This in turn results in areas of accessible gold atom sites between ligands. Additionally, these calix[4]arene ligands prevent cluster aggregation and electronically tune the gold core in a manner conceptually similar to enzymes affecting reactivity through organic side-chains acting as ligands. I quantified the number of open sites that result from this packing problem on the gold cluster surface, using fluorescence probe chemisorption experiments. The results of these chemisorption measurements support the mechanical model of accessibility whereby accessibility is not dependent on the identity of the functional group, whether it be calixarene phosphines or N-heterocyclic carbenes, bound to the gold surface, but rather to the relative radii of curvature of bound ligands and the gold cluster core. Additional materials characterization was completed with transmission electron microscopy in both bright-field imaging of zeolites, in MCM-22 and delaminated ITQ-2 and UCB-1 materials, and in dark field imaging of glucan coatings on oxide particles. These materials could prove to be interesting materials as to use as supports for the calixarene-bound metal clusters described above or for other metal clusters.

Highly Enhanced Gas Adsorption Properties in Vertically Aligned MoS2 Layers.

PubMed

Cho, Soo-Yeon; Kim, Seon Joon; Lee, Youhan; Kim, Jong-Seon; Jung, Woo-Bin; Yoo, Hae-Wook; Kim, Jihan; Jung, Hee-Tae

2015-09-22

In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS2 compared to that of the conventional basal plane exposed MoS2 films. To compare the effect of the alignment of MoS2 on the gas adsorption properties, we synthesized three distinct MoS2 films with different alignment directions ((1) horizontally aligned MoS2 (basal plane exposed), (2) mixture of horizontally aligned MoS2 and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS2 (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS2 film shows about 5-fold enhanced sensitivity to NO2 gas molecules compared to horizontally aligned MoS2 film. Vertically aligned MoS2 has superior resistance variation compared to horizontally aligned MoS2 even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO2 binding energies are computed for multiple configurations near the edge sites of MoS2, which verifies that electrical response to target gas molecules (NO2) correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. We believe that this observation extends to other 2D TMD materials as well as MoS2 and can be applied to significantly enhance the gas sensor performance in these materials.

Groundlayer vegetation gradients across oak woodland canopy gaps

USGS Publications Warehouse

Pavlovic, N.B.; Grundel, R.; Sluis, W.

2006-01-01

Frequency of groundlayer plants was measured across oak woodland canopy gaps at three sites in northwest Indiana to examine how vegetation varied with gap size, direction along the gap edge, and microhabitat. Microhabitats were defined as under the canopy adjacent to the gap, along the gap edge, and within the gap. Gap-sites consisted of gaps plus adjacent tree canopy. Gaps were classified as small (16 ± 1 m2), medium (97 ± 8), and large (310 ± 32). Neither richness nor diversity differed among microhabitats, gap sizes, or edges. Similarity between microhabitats wthin a gap-site increased as the distance between plots decreased and as the difference in PAR decreased, the latter explaining twice the variation in percent dissimilarity compared to Mg concentration, A horizon depth, and litter cover. Diervilla lonicera, Frageria virginiana, Helianthus divaricatus, Polygonatum pubescens, Quercus velutina, Smilacena stellata, and Tradescantia ohiensis decreased, whileTephrosia virginiana and legumes increased in frequency, from canopy to gap, and C4 grasses peaked at the gap edge, independent of gap size. Additional species frequency varied across the microhabitat gradient within specific sites. Sorghastrum nutans was three times more frequent in gaps at large sites than elsewhere. The vegetation in medium-sized gap-sites was more variable than within small and large gap-sites, suggesting greater environmental heterogeneity at that scale. Within gap-sites, vegetation was more heterogeneous within edges and canopies than in gaps. Edges were more similar in composition to gaps than to canopy groundlayer within gap-sites. Few species varied significantly in frequency around the gap edge. The oak woodland groundlayer on sandy substrates can be characterized as a mosaic of forb dominated vegetation that varies across light gradients associated with canopy gaps, transitioning to islands of grassland vegetation when gaps exceed 160 m2.

Nanoscale electrochemical patterning reveals the active sites for catechol oxidation at graphite surfaces.

PubMed

Patel, Anisha N; McKelvey, Kim; Unwin, Patrick R

2012-12-19

Graphite-based electrodes (graphite, graphene, and nanotubes) are used widely in electrochemistry, and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. In the present work, this model was tested directly for the first time using scanning electrochemical cell microscopy reactive patterning and shown to be incorrect. For the electro-oxidation of dopamine as a model process, the reaction rate was measured at high spatial resolution across a surface of highly oriented pyrolytic graphite. Oxidation products left behind in a pattern defined by the scanned electrochemical cell served as surface-site markers, allowing the electrochemical activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochemical measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochemically active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of carbon-based biosensors, and the results are additionally important for understanding electrochemical processes on related sp(2)-hybridized materials such as pristine graphene and nanotubes.

Refining As-cast β-Ti Grains Through ZrN Inoculation

NASA Astrophysics Data System (ADS)

Qiu, Dong; Zhang, Duyao; Easton, Mark A.; St John, David H.; Gibson, Mark A.

2018-03-01

The columnar-to-equiaxed transition and remarkable refinement of β-Ti grains occur in an as-cast Ti-13Mo alloy when a new grain refiner, ZrN, was inoculated at a nitrogen level as low as 0.4 wt pct. The grain refining effect is attributed to in situ-formed TiN particles that provide active nucleation sites and solute Zr that promotes constitutional supercooling. Reproducible orientation relationships were identified between TiN nucleants and β-Ti matrix, and well explained by the edge-to-edge matching model.

A PKC-MARCKS-PI3K regulatory module links Ca2+ and PIP3 signals at the leading edge of polarized macrophages

PubMed Central

Ziemba, Brian P.

2018-01-01

The leukocyte chemosensory pathway detects attractant gradients and directs cell migration to sites of inflammation, infection, tissue damage, and carcinogenesis. Previous studies have revealed that local Ca2+ and PIP3 signals at the leading edge of polarized leukocytes play central roles in positive feedback loop essential to cell polarization and chemotaxis. These prior studies showed that stimulation of the leading edge Ca2+ signal can strongly activate PI3K, thereby triggering a larger PIP3 signal, but did not elucidate the mechanistic link between Ca2+ and PIP3 signaling. A hypothesis explaining this link emerged, postulating that Ca2+-activated PKC displaces the MARCKS protein from plasma membrane PIP2, thereby releasing sequestered PIP2 to serve as the target and substrate lipid of PI3K in PIP3 production. In vitro single molecule studies of the reconstituted pathway on lipid bilayers demonstrated the feasibility of this PKC-MARCKS-PI3K regulatory module linking Ca2+ and PIP3 signals in the reconstituted system. The present study tests the model predictions in live macrophages by quantifying the effects of: (a) two pathway activators—PDGF and ATP that stimulate chemoreceptors and Ca2+ influx, respectively; and (b) three pathway inhibitors—wortmannin, EGTA, and Go6976 that inhibit PI3K, Ca2+ influx, and PKC, respectively; on (c) four leading edge activity sensors—AKT-PH-mRFP, CKAR, MARCKSp-mRFP, and leading edge area that report on PIP3 density, PKC activity, MARCKS membrane binding, and leading edge expansion/contraction, respectively. The results provide additional evidence that PKC and PI3K are both essential elements of the leading edge positive feedback loop, and strongly support the existence of a PKC-MARCKS-PI3K regulatory module linking the leading edge Ca2+ and PIP3 signals. As predicted, activators stimulate leading edge PKC activity, displacement of MARCKS from the leading edge membrane and increased leading edge PIP3 levels, while inhibitors trigger the opposite effects. Comparison of the findings for the ameboid chemotaxis of leukocytes with recently published findings for the mesenchymal chemotaxis of fibroblasts suggests that some features of the emerging leukocyte leading edge core pathway (PLC-DAG-Ca2+-PKC-MARCKS-PIP2-PI3K-PIP3) may well be shared by all chemotaxing eukaryotic cells, while other elements of the leukocyte pathway may be specialized features of these highly optimized, professional gradient-seeking cells. More broadly, the findings suggest a molecular mechanism for the strong links between phospho-MARCKS and many human cancers. PMID:29715315

First-principles study of adsorption-desorption kinetics of aqueous V2+/V3+ redox species on graphite in a vanadium redox flow battery.

PubMed

Jiang, Zhen; Klyukin, Konstantin; Alexandrov, Vitaly

2017-06-14

Vanadium redox flow batteries (VRFBs) represent a promising solution to grid-scale energy storage, and understanding the reactivity of electrode materials is crucial for improving the power density of VRFBs. However, atomistic details about the interactions between vanadium ions and electrode surfaces in aqueous electrolytes are still lacking. Here, we examine the reactivity of the basal (0001) and edge (112[combining macron]0) graphite facets with water and aqueous V 2+ /V 3+ redox species at 300 K employing Car-Parrinello molecular dynamics (CPMD) coupled with metadynamics simulations. The results suggest that the edge surface is characterized by the formation of ketonic C[double bond, length as m-dash]O functional groups due to complete water dissociation into the H/O/H configuration with surface O atoms serving as active sites for adsorption of V 2+ /V 3+ species. The formation of V-O bonds at the surface should significantly improve the kinetics of electron transfer at the edge sites, which is not the case for the basal surface, in agreement with the experimentally hypothesized mechanism.

Switchgrass growth and pine-switchgrass interactions in established intercropping systems

DOE PAGES

Tian, Shiying; Cacho, Julian F.; Youssef, Mohamed A.; ...

2016-06-22

Intercropping switchgrass ( Panicum virgatum L.) with loblolly pine ( Pinus taeda L.) has been proposed for producing bioenergy feedstock in the southeastern United States. This study investigated switchgrass growth and pine–switchgrass interactions at two established experimental fields (7-year-old Lenoir site and 5-year-old Carteret site) located on the coastal plain of eastern United States. Position effects (edge and center of switchgrass alley in intercropping plots) and treatment effects (intercropping vs. grass-only) on above ground switchgrass growth were evaluated. Interspecific interactions with respect to capturing resources (light, soil water, and nitrogen) were investigated by measuring photosynthetically active radiation (PAR) above grassmore » canopy, soil moisture, and soil mineral nitrogen contents. Switchgrass growth was significantly (P = 0.001) affected by treatments in Lenoir and by position (P < 0.0001) in both study sites. Relative to the center, PAR above grass canopy at edge in both sites was about 48% less during the growing season. Soil water content during the growing season at the edge of grass alley was significantly (P = 0.0001) lower by 23% than at the center in Lenoir, while no significant (P = 0.42) difference was observed in Carteret, in spite of more grass growth at center at both sites. Soil mineral nitrogen content at the center of intercropping plots in Lenoir (no fertilization during 2015) was significantly (P < 0.07) lower than at the edge during the peak of growing season (June, July, and August), but not during early and late parts of growing season (May, September, and November). Position effects on soil water and mineral nitrogen were less evident under conditions with higher external inputs (rainfall and fertilization) and lower plant uptake during nongrowing seasons. Here, results from this study contributed to a better understanding of above- and belowground pine–switchgrass interactions which is necessary to properly manage this new cultivation system for bioenergy production in the southeastern United States.« less

A biosensor generated via high throughput screening quantifies cell edge Src dynamics

PubMed Central

Gulyani, Akash; Vitriol, Eric; Allen, Richard; Wu, Jianrong; Gremyachinskiy, Dmitriy; Lewis, Steven; Dewar, Brian; Graves, Lee M.; Kay, Brian K.; Kuhlman, Brian; Elston, Tim; Hahn, Klaus M.

2011-01-01

Fluorescent biosensors for living cells currently require laborious optimization and a unique design for each target. They are limited by the availability of naturally occurring ligands with appropriate target specificity. Here we describe a biosensor based on an engineered fibronectin monobody scaffold that can be tailored to bind different targets via high throughput screening. This Src family kinase (SFK) biosensor was made by derivatizing a monobody specific for activated SFK with a bright dye whose fluorescence increases upon target binding. We identified sites for dye attachment and alterations to eliminate vesiculation in living cells, providing a generalizable scaffold for biosensor production. This approach minimizes cell perturbation because it senses endogenous, unmodified target, and because sensitivity is enhanced by direct dye excitation. Automated correlation of cell velocities and SFK activity revealed that SFK are activated specifically during protrusion. Activity correlates with velocity, and peaks 1–2 microns from the leading edge. PMID:21666688

Protonation state of the Cu4S2 CuZ site in nitrous oxide reductase: redox dependence and insight into reactivity

PubMed Central

Johnston, Esther M.; Dell’Acqua, Simone; Pauleta, Sofia R.; Moura, Isabel; Solomon, Edward I.

2015-01-01

Spectroscopic and computational methods have been used to determine the protonation state of the edge sulfur ligand in the Cu4S2 CuZ form of the active site of nitrous oxide reductase (N2OR) in its 3CuICuII (1-hole) and 2CuI2CuII (2-hole) redox states. The EPR, absorption, and MCD spectra of 1-hole CuZ indicate that the unpaired spin in this site is evenly delocalized over CuI, CuII, and CuIV. 1-hole CuZ is shown to have a μ2-thiolate edge ligand from the observation of S-H bending modes in the resonance Raman spectrum at 450 and 492 cm−1 that have significant deuterium isotope shifts (−137 cm−1) and are not perturbed up to pH 10. 2-hole CuZ is characterized with absorption and resonance Raman spectroscopies as having two Cu-S stretching vibrations that profile differently. DFT models of the 1-hole and 2-hole CuZ sites are correlated to these spectroscopic features to determine that 2-hole CuZ has a μ2-sulfide edge ligand at neutral pH. The slow two electron (+1 proton) reduction of N2O by 1-hole CuZ is discussed and the possibility of a reaction between 2-hole CuZ and O2 is considered. PMID:26417423

How strong is the edge effect in the adsorption of anticancer drugs on a graphene cluster?

PubMed

Rungnim, Chompoonut; Chanajaree, Rungroj; Rungrotmongkol, Thanyada; Hannongbua, Supot; Kungwan, Nawee; Wolschann, Peter; Karpfen, Alfred; Parasuk, Vudhichai

2016-04-01

The adsorption of nucleobase-analog anticancer drugs (fluorouracil, thioguanine, and mercaptopurine) on a graphene flake (C54H18) was investigated by shifting the site at which adsorption occurs from one end of the sheet to the other end. The counterpoise-corrected M06-2X/cc-pVDZ binding energies revealed that the binding stability decreases in the sequence thioguanine > mercaptopurine > fluorouracil. We found that adsorption near the middle of the sheet is more favorable than adsorption near the edge due to the edge effect. This edge effect is stronger for the adsorption of thioguanine or mercaptopurine than for fluorouracil adsorption. However, the edge effect reduces the binding energy of the drug to the flake by only a small amount, <5 kcal/mol, depending on the adsorption site and the alignment of the drug at this site.

Effects of fragmentation on the spatial ecology of the California Kingsnake (Lampropeltis californiae)

USGS Publications Warehouse

Anguiano, Michael P.; Diffendorfer, James E.

2015-01-01

We investigated the spatial ecology of the California Kingsnake (Lampropeltis californiae) in unfragmented and fragmented habitat with varying patch sizes and degrees of exposure to urban edges. We radiotracked 34 Kingsnakes for up to 3 yr across four site types: interior areas of unfragmented ecological reserves, the urbanized edge of these reserves, large habitat fragments, and small habitat fragments. There was no relationship between California Kingsnake movements and the degree of exposure to urban edges and fragmentation. Home range size and movement patterns of Kingsnakes on edges and fragments resembled those in unfragmented sites. Average home-range size on each site type was smaller than the smallest fragment in which snakes were tracked. The persistence of California Kingsnakes in fragmented landscapes may be related directly to their small spatial movement patterns, home-range overlap, and ability to use urban edge habitat.

Three-dimensional WS2 nanosheet networks for H2O2 produced for cell signaling

NASA Astrophysics Data System (ADS)

Tang, Jing; Quan, Yingzhou; Zhang, Yueyu; Jiang, Min; Al-Enizi, Abdullah M.; Kong, Biao; An, Tiance; Wang, Wenshuo; Xia, Limin; Gong, Xingao; Zheng, Gengfeng

2016-03-01

Hydrogen peroxide (H2O2) is an important molecular messenger for cellular signal transduction. The capability of direct probing of H2O2 in complex biological systems can offer potential for elucidating its manifold roles in living systems. Here we report the fabrication of three-dimensional (3D) WS2 nanosheet networks with flower-like morphologies on a variety of conducting substrates. The semiconducting WS2 nanosheets with largely exposed edge sites on flexible carbon fibers enable abundant catalytically active sites, excellent charge transfer, and high permeability to chemicals and biomaterials. Thus, the 3D WS2-based nano-bio-interface exhibits a wide detection range, high sensitivity and rapid response time for H2O2, and is capable of visualizing endogenous H2O2 produced in living RAW 264.7 macrophage cells and neurons. First-principles calculations further demonstrate that the enhanced sensitivity of probing H2O2 is attributed to the efficient and spontaneous H2O2 adsorption on WS2 nanosheet edge sites. The combined features of 3D WS2 nanosheet networks suggest attractive new opportunities for exploring the physiological roles of reactive oxygen species like H2O2 in living systems.Hydrogen peroxide (H2O2) is an important molecular messenger for cellular signal transduction. The capability of direct probing of H2O2 in complex biological systems can offer potential for elucidating its manifold roles in living systems. Here we report the fabrication of three-dimensional (3D) WS2 nanosheet networks with flower-like morphologies on a variety of conducting substrates. The semiconducting WS2 nanosheets with largely exposed edge sites on flexible carbon fibers enable abundant catalytically active sites, excellent charge transfer, and high permeability to chemicals and biomaterials. Thus, the 3D WS2-based nano-bio-interface exhibits a wide detection range, high sensitivity and rapid response time for H2O2, and is capable of visualizing endogenous H2O2 produced in living RAW 264.7 macrophage cells and neurons. First-principles calculations further demonstrate that the enhanced sensitivity of probing H2O2 is attributed to the efficient and spontaneous H2O2 adsorption on WS2 nanosheet edge sites. The combined features of 3D WS2 nanosheet networks suggest attractive new opportunities for exploring the physiological roles of reactive oxygen species like H2O2 in living systems. Electronic supplementary information (ESI) available: Additional figures. See DOI: 10.1039/c5nr09236a

Unique active site promotes error-free replication opposite an 8-oxo-guanine lesion by human DNA polymerase iota

PubMed Central

Kirouac, Kevin N.; Ling, Hong

2011-01-01

The 8-oxo-guanine (8-oxo-G) lesion is the most abundant and mutagenic oxidative DNA damage existing in the genome. Due to its dual coding nature, 8-oxo-G causes most DNA polymerases to misincorporate adenine. Human Y-family DNA polymerase iota (polι) preferentially incorporates the correct cytosine nucleotide opposite 8-oxo-G. This unique specificity may contribute to polι’s biological role in cellular protection against oxidative stress. However, the structural basis of this preferential cytosine incorporation is currently unknown. Here we present four crystal structures of polι in complex with DNA containing an 8-oxo-G lesion, paired with correct dCTP or incorrect dATP, dGTP, and dTTP nucleotides. An exceptionally narrow polι active site restricts the purine bases in a syn conformation, which prevents the dual coding properties of 8-oxo-G by inhibiting syn/anti conformational equilibrium. More importantly, the 8-oxo-G base in a syn conformation is not mutagenic in polι because its Hoogsteen edge does not form a stable base pair with dATP in the narrow active site. Instead, the syn 8-oxo-G template base forms the most stable replicating base pair with correct dCTP due to its small pyrimidine base size and enhanced hydrogen bonding with the Hoogsteen edge of 8-oxo-G. In combination with site directed mutagenesis, we show that Gln59 in the finger domain specifically interacts with the additional O8 atom of the lesion base, which influences nucleotide selection, enzymatic efficiency, and replication stalling at the lesion site. Our work provides the structural mechanism of high-fidelity 8-oxo-G replication by a human DNA polymerase. PMID:21300901

Mechanisms of the oxygen reduction reaction on B- and/or N-doped carbon nanomaterials with curvature and edge effects.

PubMed

Zou, Xiaolong; Wang, Luqing; Yakobson, Boris I

2018-01-18

Despite recent increased research interest in hetero-atom (B and/or N) doping effects on the oxygen reduction reaction (ORR) performance of carbon nanomaterials, microscopic understanding of active catalytic sites and effects of B and/or N doping has not been conclusively reached. Here, through comparative first-principles simulations between BN codoping and isolated B or N doping in both graphene nanoribbons (GNRs) and carbon nanotubes (CNTs), we not only identify active sites in these doped carbon nanomaterials, but elucidate the underlying mechanism of ORR processes. While the distortion of C-C bonds in CNTs leads to strong binding of O 2 , spin density distribution along the edges plays a key role in enhancing the adsorption strength of O 2 on GNRs. The effective adsorption of O 2 facilitates the following elementary reduction reactions. Based on thermodynamic analyses, O 2 adsorption as well as the electron and proton transfer to O atom are identified as key rate-determining steps. For CNTs, a good linear scaling is found between the adsorption energies of key intermediate products and that of atomic O, and thus the latter serves as a good descriptor for ORR activities. Further, N-doped high-quality CNTs are shown to exhibit best performance. For GNRs, due to edge effects, the linear relationship is broken, which promotes the catalytic activities in the BN codoping case. These findings resolve the long-standing controversy on the synergetic effects of B and N codoping, which deepens our understanding of the reaction mechanism. This work might further facilitate the optimization of the doping strategies for high-efficiency carbon-based ORR catalysts.

Arsenic Removal from Drinking Water by Adsorptive Media - U.S. EPA Demonstration Project at Goffstown, NH, Final Performance Evaluation Report

EPA Science Inventory

This report documents the activities performed and the results obtained from the arsenic removal treatment technology demonstration project at the Orchard Highlands Subdivision site in Goffstown, NH. The main objective of the project was to evaluate the effectiveness of AdEdge T...

Morphology and mixing of black carbon particles collected in central California during the CARES field study

DOE PAGES

Moffet, Ryan C.; O'Brien, Rachel E.; Alpert, Peter A.; ...

2016-11-23

Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California Central Valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using scanning transmission X-ray microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles, highlighting the importance ofmore » highly aged particles at urban sites during periods of high photochemical activity. Based on the observation of thick coatings and more convex BC inclusion morphology, either the aging was rapid or the contribution of fresh BC emissions at the urban site was relatively small compared to background concentrations. Most particles were observed to have the BC inclusion close to the center of the host. However, host particles containing inorganic rich inclusions had the BC inclusion closer to the edge of the particle. Furthermore, these measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes.« less

Morphology and mixing of black carbon particles collected in central California during the CARES field study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moffet, Ryan C.; O'Brien, Rachel E.; Alpert, Peter A.

Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California Central Valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using scanning transmission X-ray microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles, highlighting the importance ofmore » highly aged particles at urban sites during periods of high photochemical activity. Based on the observation of thick coatings and more convex BC inclusion morphology, either the aging was rapid or the contribution of fresh BC emissions at the urban site was relatively small compared to background concentrations. Most particles were observed to have the BC inclusion close to the center of the host. However, host particles containing inorganic rich inclusions had the BC inclusion closer to the edge of the particle. Furthermore, these measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes.« less

Investigating Catalyst–Support Interactions To Improve the Hydrogen Evolution Reaction Activity of Thiomolybdate [Mo 3 S 13 ] 2– Nanoclusters

DOE PAGES

Hellstern, Thomas R.; Kibsgaard, Jakob; Tsai, Charlie; ...

2017-09-22

Molybdenum sulfides have been identified as promising materials for catalyzing the hydrogen evolution reaction (HER) in acid, with active edge sites that exhibit some of the highest turnover frequencies among nonpreciousmetal catalysts. The thiomolybdate [Mo 3S 13] 2- nanocluster catalyst contains a structural motif that resembles the active site of MoS 2 and has been reported to be among the most active forms of molybdenum sulfide. Herein, we improve the activity of the [Mo 3S 13] 2- catalysts through catalyst-support interactions. We synthesize [Mo 3S 13] 2- on gold, silver, glassy carbon, and copper supports to demonstrate the ability tomore » tune the hydrogen binding energy of [Mo 3S 13] 2- using catalyst-support electronic interactions and optimize HER activity.« less

Investigating Catalyst–Support Interactions To Improve the Hydrogen Evolution Reaction Activity of Thiomolybdate [Mo 3 S 13 ] 2– Nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hellstern, Thomas R.; Kibsgaard, Jakob; Tsai, Charlie

Molybdenum sulfides have been identified as promising materials for catalyzing the hydrogen evolution reaction (HER) in acid, with active edge sites that exhibit some of the highest turnover frequencies among nonpreciousmetal catalysts. The thiomolybdate [Mo 3S 13] 2- nanocluster catalyst contains a structural motif that resembles the active site of MoS 2 and has been reported to be among the most active forms of molybdenum sulfide. Herein, we improve the activity of the [Mo 3S 13] 2- catalysts through catalyst-support interactions. We synthesize [Mo 3S 13] 2- on gold, silver, glassy carbon, and copper supports to demonstrate the ability tomore » tune the hydrogen binding energy of [Mo 3S 13] 2- using catalyst-support electronic interactions and optimize HER activity.« less

K- and L-edge X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) determination of differential orbital covalency (DOC) of transition metal sites

DOE PAGES

Baker, Michael L.; Mara, Michael W.; Yan, James J.; ...

2017-02-09

Continual advancements in the development of synchrotron radiation sources have resulted in X-ray based spectroscopic techniques capable of probing the electronic and structural properties of numerous systems. This review gives an overview of the application of metal K-edge and L-edge X-ray absorption spectroscopy (XAS), as well as Kα resonant inelastic X-ray scattering (RIXS), to the study of electronic structure in transition metal sites with emphasis on experimentally quantifying 3d orbital covalency. The specific sensitivities of K-edge XAS, L-edge XAS, and RIXS are discussed emphasizing the complementary nature of the methods. L-edge XAS and RIXS are sensitive to mixing between 3dmore » orbitals and ligand valence orbitals, and to the differential orbital covalency (DOC), that is, the difference in the covalencies for different symmetry sets of the d orbitals. Both L-edge XAS and RIXS are highly sensitive to and enable separation of σ and π donor bonding and π back bonding contributions to bonding. Applying ligand field multiplet simulations, including charge transfer via valence bond configuration interactions, DOC can be obtained for direct comparison with density functional theory calculations and to understand chemical trends. Here, the application of RIXS as a probe of frontier molecular orbitals in a heme enzyme demonstrates the potential of this method for the study of metal sites in highly covalent coordination sites in bioinorganic chemistry.« less

K- and L-edge X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) determination of differential orbital covalency (DOC) of transition metal sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Michael L.; Mara, Michael W.; Yan, James J.

Continual advancements in the development of synchrotron radiation sources have resulted in X-ray based spectroscopic techniques capable of probing the electronic and structural properties of numerous systems. This review gives an overview of the application of metal K-edge and L-edge X-ray absorption spectroscopy (XAS), as well as Kα resonant inelastic X-ray scattering (RIXS), to the study of electronic structure in transition metal sites with emphasis on experimentally quantifying 3d orbital covalency. The specific sensitivities of K-edge XAS, L-edge XAS, and RIXS are discussed emphasizing the complementary nature of the methods. L-edge XAS and RIXS are sensitive to mixing between 3dmore » orbitals and ligand valence orbitals, and to the differential orbital covalency (DOC), that is, the difference in the covalencies for different symmetry sets of the d orbitals. Both L-edge XAS and RIXS are highly sensitive to and enable separation of σ and π donor bonding and π back bonding contributions to bonding. Applying ligand field multiplet simulations, including charge transfer via valence bond configuration interactions, DOC can be obtained for direct comparison with density functional theory calculations and to understand chemical trends. Here, the application of RIXS as a probe of frontier molecular orbitals in a heme enzyme demonstrates the potential of this method for the study of metal sites in highly covalent coordination sites in bioinorganic chemistry.« less

Edge-terminated molybdenum disulfide with a 9.4-Å interlayer spacing for electrochemical hydrogen production

DOE PAGES

Gao, Min -Rui; Chan, Maria K. Y.; Sun, Yugang

2015-07-03

In this study, layered molybdenum disulfide has demonstrated great promise as a low-cost alternative to platinum-based catalysts for electrochemical hydrogen production from water. Research effort on this material has focused mainly on synthesizing highly nanostructured molybdenum disulfide that allows the exposure of a large fraction of active edge sites. Here we report a promising microwave-assisted strategy for the synthesis of narrow molybdenum disulfide nanosheets with edge-terminated structure and a significantly expanded interlayer spacing, which exhibit striking kinetic metrics with onset potential of -103 mV, Tafel slope of 49 mV per decade and exchange current density of 9.62 × 10 -3more » mA cm -2, performing among the best of current molybdenum disulfide catalysts. Besides benefits from the edge-terminated structure, the expanded interlayer distance with modified electronic structure is also responsible for the observed catalytic improvement, which suggests a potential way to design newly advanced molybdenum disulfide catalysts through modulating the interlayer distance.« less

Edge-terminated molybdenum disulfide with a 9.4-Å interlayer spacing for electrochemical hydrogen production

PubMed Central

Gao, Min-Rui; Chan, Maria K.Y.; Sun, Yugang

2015-01-01

Layered molybdenum disulfide has demonstrated great promise as a low-cost alternative to platinum-based catalysts for electrochemical hydrogen production from water. Research effort on this material has focused mainly on synthesizing highly nanostructured molybdenum disulfide that allows the exposure of a large fraction of active edge sites. Here we report a promising microwave-assisted strategy for the synthesis of narrow molybdenum disulfide nanosheets with edge-terminated structure and a significantly expanded interlayer spacing, which exhibit striking kinetic metrics with onset potential of −103 mV, Tafel slope of 49 mV per decade and exchange current density of 9.62 × 10−3 mA cm−2, performing among the best of current molybdenum disulfide catalysts. Besides benefits from the edge-terminated structure, the expanded interlayer distance with modified electronic structure is also responsible for the observed catalytic improvement, which suggests a potential way to design newly advanced molybdenum disulfide catalysts through modulating the interlayer distance. PMID:26138031

Fourier transform inequalities for phylogenetic trees.

PubMed

Matsen, Frederick A

2009-01-01

Phylogenetic invariants are not the only constraints on site-pattern frequency vectors for phylogenetic trees. A mutation matrix, by its definition, is the exponential of a matrix with non-negative off-diagonal entries; this positivity requirement implies non-trivial constraints on the site-pattern frequency vectors. We call these additional constraints "edge-parameter inequalities". In this paper, we first motivate the edge-parameter inequalities by considering a pathological site-pattern frequency vector corresponding to a quartet tree with a negative internal edge. This site-pattern frequency vector nevertheless satisfies all of the constraints described up to now in the literature. We next describe two complete sets of edge-parameter inequalities for the group-based models; these constraints are square-free monomial inequalities in the Fourier transformed coordinates. These inequalities, along with the phylogenetic invariants, form a complete description of the set of site-pattern frequency vectors corresponding to bona fide trees. Said in mathematical language, this paper explicitly presents two finite lists of inequalities in Fourier coordinates of the form "monomial < or = 1", each list characterizing the phylogenetically relevant semialgebraic subsets of the phylogenetic varieties.

Ethylene dissociation on flat and stepped Ni(1 1 1): A combined STM and DFT study

NASA Astrophysics Data System (ADS)

Vang, Ronnie T.; Honkala, Karoliina; Dahl, Søren; Vestergaard, Ebbe K.; Schnadt, Joachim; Lægsgaard, Erik; Clausen, Bjerne S.; Nørskov, Jens K.; Besenbacher, Flemming

2006-01-01

The dissociative adsorption of ethylene (C 2H 4) on Ni(1 1 1) was studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM studies reveal that ethylene decomposes exclusively at the step edges at room temperature. However, the step edge sites are poisoned by the reaction products and thus only a small brim of decomposed ethylene is formed. At 500 K decomposition on the (1 1 1) facets leads to a continuous growth of carbidic islands, which nucleate along the step edges. DFT calculations were performed for several intermediate steps in the decomposition of ethylene on both Ni(1 1 1) and the stepped Ni(2 1 1) surface. In general the Ni(2 1 1) surface is found to have a higher reactivity than the Ni(1 1 1) surface. Furthermore, the calculations show that the influence of step edge atoms is very different for the different reaction pathways. In particular the barrier for dissociation is lowered significantly more than the barrier for dehydrogenation, and this is of great importance for the bond-breaking selectivity of Ni surfaces. The influence of step edges was also probed by evaporating Ag onto the Ni(1 1 1) surface. STM shows that the room temperature evaporation leads to a step flow growth of Ag islands, and a subsequent annealing at 800 K causes the Ag atoms to completely wet the step edges of Ni(1 1 1). The blocking of the step edges is shown to prevent all decomposition of ethylene at room temperature, whereas the terrace site decomposition at 500 K is confirmed to be unaffected by the Ag atoms. Finally a high surface area NiAg alloy catalyst supported on MgAl 2O 4 was synthesized and tested in flow reactor measurements. The NiAg catalyst has a much lower activity for ethane hydrogenolysis than a similar Ni catalyst, which can be rationalized by the STM and DFT results.

On the Preferred Active Sites of Promoted MoS 2 for Hydrodesulfurization with Minimal Organonitrogen Inhibition

DOE PAGES

Rangarajan, Srinivas; Mavrikakis, Manos

2016-12-14

Hydrodesulfurization is a process to produce ultralow-sulfur diesel fuel. Although promoted molybdenum sulfide (MoS 2) catalysts have been used industrially for several decades, the active site requirements for selective hydrodesulfurization of organosulfur compounds with minimal inhibition by organonitrogen constituents of a real gasoil feed has not been resolved. By using molecular binding energy descriptors derived from plane wave density functional theory calculations for comparative adsorption of organosulfur and organonitrogen compounds, we analyzed more than 20 potential sites on unpromoted and Ni- and Co-promoted MoS 2. We also found that hydrogen sulfide and ammonia are simple descriptors of adsorption of stericallymore » unhindered organosulfur and organonitrogen compounds such as dibenzothiophene and acridine, respectively. Further, organonitrogen compounds in gasoil bind more strongly than organosulfur compounds on all sites except on sites with exposed metal atoms on the corner and sulfur edges of promoted MoS 2. Consequently, these sites are proposed as required for maximum-hydrodesulfurization minimum-inhibition catalysis.« less

Sorption selectivity of birnessite particle edges: a d-PDF analysis of Cd(ii) and Pb(ii) sorption by δ-MnO2 and ferrihydrite.

PubMed

van Genuchten, Case M; Peña, Jasquelin

2016-08-10

Birnessite minerals (layer-type MnO2), which bear both internal (cation vacancies) and external (particle edges) metal sorption sites, are important sinks of contaminants in soils and sediments. Although the particle edges of birnessite minerals often dominate the total reactive surface area, especially in the case of nanoscale crystallites, the metal sorption reactivity of birnessite particle edges remains elusive. In this study, we investigated the sorption selectivity of birnessite particle edges by combining Cd(ii) and Pb(ii) adsorption isotherms at pH 5.5 with surface structural characterization by differential pair distribution function (d-PDF) analysis. We compared the sorption reactivity of δ-MnO2 to that of the nanomineral, 2-line ferrihydrite, which exhibits only external surface sites. Our results show that, whereas Cd(ii) and Pb(ii) both bind to birnessite layer vacancies, only Pb(ii) binds extensively to birnessite particle edges. For ferrihydrite, significant Pb(ii) adsorption to external sites was observed (roughly 20 mol%), whereas Cd(ii) sorption was negligible. These results are supported by bond valence calculations that show comparable degrees of saturation of oxygen atoms on birnessite and ferrihydrite particle edges. Therefore, we propose that the sorption selectivity of birnessite edges follows the same order of that reported previously for ferrihydrite: Ca(ii) < Cd(ii) < Ni(ii) < Zn(ii) < Cu(ii) < Pb(ii).

RESEARCH STUDIES AT THE GILT EDGE MINE SUPERFUND SITE

EPA Science Inventory

A collaborative effort is being implemented at the Gilt Edge Mine Superfund site near Lead, SD. The partnerships involves the Mine Waste Technology Program (MWTP) with the USEPA's NRMRL, Region VIII Superfund program, the DOE, MSE Technology Application, Inc (MSE) and CDM Federal...

Structural characterization of cup-stacked-type nanofibers with an entirely hollow core

NASA Astrophysics Data System (ADS)

Endo, M.; Kim, Y. A.; Hayashi, T.; Fukai, Y.; Oshida, K.; Terrones, M.; Yanagisawa, T.; Higaki, S.; Dresselhaus, M. S.

2002-02-01

Straight long carbon nanofibers with a large hollow core obtained by a floating reactant method show a stacking morphology of truncated conical graphene layers, which in turn exhibit a large portion of open edges on the outer surface and also in the inner channels. Through a judicious choice of oxidation conditions, nanofibers with increased active edge sites are obtained without disrupting the fiber's morphology. A graphitization process induces a morphological change from a tubular type to a reversing saw-toothed type and the formation of loops along the inner channel of the nanofibers, accompanied by a decrease in interlayer spacing.

Mesembrinellinae (Diptera: Calliphoridae) to edge effects in the Tinguá Biological Reserve, Rio de Janeiro, Brazil.

PubMed

Gadelha, B Q; Silva, A B; Ferraz, A C P; Aguiar, V M

2015-11-01

In this study we describe the diversity of Mesembrinelinae in a biological reserve in the city of Nova Iguaçu, State of Rio de Janeiro. Traps containing sardines were distributed seasonally, at four sites: Site A (22° 58.788' S, 43° 43.459' W), in a forest edge, and sites B (22° 58.523' S, 43° 44.540' W), C (22° 58.350' S, 43° 44.678' W), and D (22° 34.865' S, 43° 27.063' W), located 1,000 m, 500 m, and 2,000 m respectively, inwards from the edge. A total of 2,150 individuals of Mesembrinellinae were collected, representing ten species. Laneela nigripes Guimarães, 1977 was the most abundant species, followed by Mesembrinella bellardiana Aldrich, 1922, Eumesembrinella cyaneicincta (Surcouf, 1919) and Mesembrinella semihyalina Mello, 1967. These species were common and constant during the study period. Mesembrinella batesi Aldrich, 1922, Eumesembrinella quadrilineata (Fabricius, 1805) and Huascaromusca aeneiventris (Wiedmann, 1830) were the less abundant flies, being considered rare and accidental. Eumesembrinella besnoiti (Seguy, 1925) was rare and accessory. Eumesembrinella cyaneicincta, M. bellardiana, M. semihyalina and M. bicolor were mostly collected in site B, while L. nigripes was mostly collected in site C. The edge effect was not evident since the four sites showed similar populations. Site B showed a strong positive relationship between abundance and richness, in site C the correlation was positive and weak, and there was no correlation in A and D. The highest abundance of specimens was recorded during autumn and winter. These flies occurred from the edge up to 2,000 m inside the forest.

Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu exchange sites under different conditions

DOE PAGES

Zhang, Renqin; Helling, Kathy; McEwen, Jean-Sabin

2016-03-29

Copper-exchanged SAPO-34 (Cu-SAPO-34) provides excellent catalytic activity and hydrothermal sta-bility in the selective catalytic reduction (SCR) of NOxby using NH3as a reductant. Here, we find that the6-membered ring (6MR) site is the most energetically favorable for a Cu+ion while the 8-memberedring (8MR) sites are less favorable by about 0.5 eV with respect to the 6MR site in Cu-SAPO-34. Uponadsorption of molecular species (H2O, O, OH, O2), the energy differences between Cu in the 8MR and 6MRsites decreases and almost disappears. Further, a thermodynamic phase diagram study shows that a Cu+ion bound to a single H2O molecule is the most stablemore » species at low oxygen potential values while aCu2+ion bound to 2 OH species is more stable when the oxygen chemical potential is sufficiently high. Bycomparing Cu K-edge XANES between Cu-SSZ-13 and Cu-SAPO-34 with Cu in different oxidation states,we conclude that it is difficult to differentiate the simulated XANES of Cu in these structures at a givenoxidation state. By studying the Cu K-edge XANES of several favorable structures in Cu-SAPO-34 in thepresence of adspecies, the simulated XANES results capture the real trend of the edge shift with oxidationstate and gives new insights into the experimentally determined XANES of Cu-SAPO-34 obtained understandard SCR conditions.« less

Ticks and Borrelia in urban and peri-urban green space habitats in a city in southern England.

PubMed

Hansford, Kayleigh M; Fonville, Manoj; Gillingham, Emma L; Coipan, Elena Claudia; Pietzsch, Maaike E; Krawczyk, Aleksandra I; Vaux, Alexander G C; Cull, Benjamin; Sprong, Hein; Medlock, Jolyon M

2017-03-01

Ticks are becoming increasingly recognised as important vectors of pathogens in urban and peri-urban areas, including green space used for recreational activities. In the UK, the risk posed by ticks in such areas is largely unknown. In order to begin to assess the risk of ticks in urban/peri-urban areas in southern England, questing ticks were collected from five different habitat types (grassland, hedge, park, woodland and woodland edge) in a city during the spring, summer and autumn of 2013/2014 and screened for Borrelia burgdorferi sensu lato. In addition, seasonal differences in B. burgdorferi s.l. prevalence were also investigated at a single site during 2015. Ixodes ricinus presence and activity were significantly higher in woodland edge habitat and during spring surveys. DNA of Borrelia burgdorferi s.l. was detected in 18.1% of nymphs collected across the 25 sites during 2013 and 2014 and two nymphs also tested positive for the newly emerging tick-borne pathogen B. miyamotoi. Borrelia burgdorferi s.l. prevalence at a single site surveyed in 2015 were found to be significantly higher during spring and summer than in autumn, with B. garinii and B. valaisiana most commonly detected. These data indicate that a range of habitats within an urban area in southern England support ticks and that urban Borrelia transmission cycles may exist in some of the urban green spaces included in this study. Sites surveyed were frequently used by humans for recreational activities, providing opportunity for exposure to Borrelia infected ticks in an urban/peri-urban space that might not be typically associated with tick-borne disease transmission. Crown Copyright © 2017. Published by Elsevier GmbH. All rights reserved.

Sorption of uranium (VI) on homoionic sodium smectite experimental study and surface complexation modeling.

PubMed

Korichi, Smain; Bensmaili, Aicha

2009-09-30

This paper is an extension of a previous paper where the natural and purified clay in the homoionic Na form were physico-chemically characterized (doi:10.1016/j.clay.2008.04.014). In this study, the adsorption behavior of U (VI) on a purified Na-smectite suspension is studied using batch adsorption experiments and surface complexation modeling (double layer model). The sorption of uranium was investigated as a function of pH, uranium concentration, solid to liquid ratio, effect of natural organic matter (NOM) and NaNO(3) background electrolyte concentration. Using the MINTEQA2 program, the speciation of uranium was calculated as a function of pH and uranium concentration. Model predicted U (VI) aqueous speciation suggests that important aqueous species in the [U (VI)]=1mg/L and pH range 3-7 including UO(2)(2+), UO(2)OH(+), and (UO(2))(3)(OH)(5)(+). The concentration of UO(2)(2+) decreased and that of (UO(2))(3)(OH)(5)(+) increased with increasing pH. The potentiometric titration values and uptake of uranium in the sodium smectite suspension were simulated by FITEQL 4.0 program using a two sites model, which is composed of silicate and aluminum reaction sites. We compare the acidity constants values obtained by potentiometric titration from the purified sodium smectite with those obtained from single oxides (quartz and alpha-alumina), taking into account the surface heterogeneity and the complex nature of natural colloids. We investigate the uranium sorption onto purified Na-smectite assuming low, intermediate and high edge site surfaces which are estimated from specific surface area percentage. The sorption data is interpreted and modeled as a function of edge site surfaces. A relationship between uranium sorption and total site concentration was confirmed and explained through variation in estimated edge site surface value. The modeling study shows that, the convergence during DLM modeling is related to the best estimation of the edge site surface from the N(2)-BET specific surface area, SSA(BET) (thus, total edge site concentrations). The specific surface area should be at least 80-100m(2)/g for smectite clays in order to reach convergence during the modeling. The range of 10-20% SSA(BET) was used to estimate the values of edge site surfaces that led to the convergence during modeling. An agreement between the experimental data and model predictions is found reasonable when 15% SSA(BET) was used as edge site surface. However, the predicted U (VI) adsorption underestimated and overestimated the experimental observations at the 10 and 20% of the measured SSA(BET), respectively. The dependence of uranium sorption modeling results on specific surface area and edge site surface is useful to describe and predict U (VI) retardation as a function of chemical conditions in the field-scale reactive transport simulations. Therefore this approach can be used in the environmental quality assessment.

Resonant inelastic x-ray scattering probes the electron-phonon coupling in the spin liquid κ -(BEDT-TTF)2Cu2(CN) 3

NASA Astrophysics Data System (ADS)

Ilakovac, V.; Carniato, S.; Foury-Leylekian, P.; Tomić, S.; Pouget, J.-P.; Lazić, P.; Joly, Y.; Miyagawa, K.; Kanoda, K.; Nicolaou, A.

2017-11-01

Resonant inelastic x-ray scattering at the N K edge reveals clearly resolved harmonics of the anion plane vibrations in the κ -(BEDT-TTF) 2Cu2 (CN) 3 spin-liquid insulator. Tuning the incoming light energy at the K edge of two distinct N sites permits us to excite different sets of phonon modes. The cyanide (CN) stretching mode is selected at the edge of the ordered N sites which are more strongly connected to the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecules, while positionally disordered N sites show multimode excitation. Combining measurements with calculations on an anion plane cluster permits us to estimate the site-dependent electron-phonon coupling of the modes related to nitrogen excitation.

Atomic-scale distortion of optically activated Sm dopants identified with site-selective X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Ishii, Masashi; Crowe, Iain F.; Halsall, Matthew P.; Hamilton, Bruce; Hu, Yongfeng; Sham, Tsun-Kong; Harako, Susumu; Zhao, Xin-Wei; Komuro, Shuji

2013-10-01

The local structure of luminescent Sm dopants was investigated using an X-ray absorption fine-structure technique with X-ray-excited optical luminescence. Because this technique evaluates X-ray absorption from luminescence, only optically active sites are analyzed. The Sm L3 near-edge spectrum contains split 5d states and a shake-up transition that are specific to luminescent Sm. Theoretical calculations using cluster models identified an atomic-scale distortion that can reproduce the split 5d states. The model with C4v local symmetry and compressive bond length of Sm-O of a six-fold oxygen (SmO6) cluster is most consistent with the experimental results.

Sorption selectivity of birnessite particle edges: a d-PDF analysis of Cd( ii ) and Pb( ii ) sorption by δ-MnO 2 and ferrihydrite

DOE Office of Scientific and Technical Information (OSTI.GOV)

van Genuchten, Case M.; Peña, Jasquelin

2016-01-01

Birnessite minerals (layer-type MnO2), which bear both internal (cation vacancies) and external (particle edges) metal sorption sites, are important sinks of contaminants in soils and sediments. Although the particle edges of birnessite minerals often dominate the total reactive surface area, especially in the case of nanoscale crystallites, the metal sorption reactivity of birnessite particle edges remains elusive. In this study, we investigated the sorption selectivity of birnessite particle edges by combining Cd(II) and Pb(II) adsorption isotherms at pH 5.5 with surface structural characterization by differential pair distribution function (d-PDF) analysis. We compared the sorption reactivity of δ-MnO2 to that ofmore » the nanomineral, 2-line ferrihydrite, which exhibits only external surface sites. Our results show that, whereas Cd(II) and Pb(II) both bind to birnessite layer vacancies, only Pb(II) binds extensively to birnessite particle edges. For ferrihydrite, significant Pb(II) adsorption to external sites was observed (roughly 20 mol%), whereas Cd(II) sorption was negligible. These results are supported by bond valence calculations that show comparable degrees of saturation of oxygen atoms on birnessite and ferrihydrite particle edges. Therefore, we propose that the sorption selectivity of birnessite edges follows the same order of that reported previously for ferrihydrite: Ca(II) < Cd(II) < Ni(II) < Zn(II) < Cu(II) < Pb(II).« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fester, Jakob; Bajdich, Michal; Walton, Alex S.

Here, metal oxide nanostructures and thin films grown on metallic substrates have attracted strong attention as model catalysts and as interesting inverse catalyst systems in their own right. In this study, we investigate the role of metal support in the growth and stabilization of cobalt oxide nanostructures on the three related (111) surfaces of Au, Pt and Ag, as investigated by means of high-resolution scanning tunneling microscopy and DFT calculations. All three substrates promote the growth of crystalline CoO x (x = 1–2) islands under oxidative conditions, but we find several noteworthy differences in the occurrence and stabilization of fourmore » distinct cobalt oxide island phases: Co–O bilayers, O–Co–O trilayers, Co–O–Co–O double bilayers and O–Co–O–Co–O multilayers. Using atom-resolved images combined with analysis of defect lines in bilayer islands on Au and Pt, we furthermore unambiguously determine the edge structure. Interestingly, the island shape and abundances of edge types in bilayers change radically from mixed Co/O edge terminations on Au(111) to a predominance of Co terminated edges (~91 %) on Pt(111) which is especially interesting since the Co metal edges are expected to host the most active sites for water dissociation.« less

Change Observed in Martian Sand Dune

NASA Image and Video Library

2015-11-16

This animation flips back and forth between views taken in 2010 and 2014 of a Martian sand dune at the edge of Mount Sharp, documenting dune activity. The images are from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. They cover an area about 740 feet (about 225 meters) wide, showing a site called "Dune 2" in the "Bagnold Dunes" dune field. NASA's Curiosity Mars rover will observe this dune up close on the rover's route up Mount Sharp. North is toward the top. The edge of the dune at the crescent-shaped slip face on the south edge advances slightly during the four-year period between the dates of the images. Figure A is an annotated version with an arrow indicating the location of this change. The lighting angle is different in the two images, resulting in numerous changes in shadows. http://photojournal.jpl.nasa.gov/catalog/PIA20161

Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vjunov, Aleksei; Wang, Meng; Govind, Niranjan

We report the structural changes induced by Brønsted acidic site deprotonation in a zeolite with MFI structure as a function of temperature up to 430°C using in situ Al K-edge X-ray absorption fine structure spectroscopy (XAFS). At ambient conditions, the protons are present as hydrated hydronium ions (H3O+(H2O)n) that are ion-paired to the anionic, Al tetrahedral (T) site. At elevated temperatures, loss of water molecules hydrating the hydronium ions leads to an unstable free hydronium ion that disso-ciates to form the hydroxylated T-site. The formation of this (-O3)-Al-(OH-) species leads to the elongation of one of the four Al-O bondsmore » and causes significant distortion of the tetrahedral symmetry about the Al atom. This distortion leads to the appearance of new pre-edge features in the Al K-edge X-ray absorption near edge structure (XANES) spectra. The pre-edge peak assignment is confirmed by time-dependent density functional theory calculation of the XANES spectrum. The XANES spectra are also sensitive to solutes or solvent that are in proximity to the T-site. A second structural transition occurs at about the same temperature, namely the conversion of a minor fraction of extra-framework octahedral Al present in the sample at ambient conditions to a tetrahedral species through the de-coordination of H2O-ligands. Both IR spectroscopy and thermogravimetric analysis (TGA) are further used to confirm the overall chemical transformation of the T-site.« less

Summer behavior of adult radio-equipped woodcock in central Maine

USGS Publications Warehouse

Owen, R.B.; Morgan, J.W.

1975-01-01

The behavior of 26 adult American woodcock (Philohela minor) was studied in central Maine during the summers of 1971-73 using radiotelemetry. Adults used diurnal covers and nocturnal sites that were similar to those previously recorded for immature woodcock. The adults, however, were more active during the daylight hours and moved to nocturnal sites later in the evening. Adult woodcock seemed to be less susceptible than immatures to capture by banding crews at night, because adults walked more often between diurnal and nocturnal sites and remained close to the brushy edges at night. Adult birds occupied a smaller composite summer range than the immatures, did not move as far from their capture sites dunng the observation penods, and traveled shorter distances between diurnal and nocturnal sites.

The role of electronic coupling between substrate and 2D MoS2 nanosheets in electrocatalytic production of hydrogen.

PubMed

Voiry, Damien; Fullon, Raymond; Yang, Jieun; de Carvalho Castro E Silva, Cecilia; Kappera, Rajesh; Bozkurt, Ibrahim; Kaplan, Daniel; Lagos, Maureen J; Batson, Philip E; Gupta, Gautam; Mohite, Aditya D; Dong, Liang; Er, Dequan; Shenoy, Vivek B; Asefa, Tewodros; Chhowalla, Manish

2016-09-01

The excellent catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial efforts towards increasing the edge concentration. The 2H basal plane is less active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Here we show that the activity of the 2H basal planes of monolayer MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. Phase-engineered low-resistance contacts on monolayer 2H-phase MoS2 basal plane lead to higher efficiency of charge injection in the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ∼-0.1 V and ∼50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two-dimensional MoS2 nanosheet catalysts for the HER.

Fast detection and low power hydrogen sensor using edge-oriented vertically aligned 3-D network of MoS2 flakes at room temperature

NASA Astrophysics Data System (ADS)

Agrawal, A. V.; Kumar, R.; Venkatesan, S.; Zakhidov, A.; Zhu, Z.; Bao, Jiming; Kumar, Mahesh; Kumar, Mukesh

2017-08-01

The increased usage of hydrogen as a next generation clean fuel strongly demands the parallel development of room temperature and low power hydrogen sensors for their safety operation. In this work, we report strong evidence for preferential hydrogen adsorption at edge-sites in an edge oriented vertically aligned 3-D network of MoS2 flakes at room temperature. The vertically aligned edge-oriented MoS2 flakes were synthesised by a modified CVD process on a SiO2/Si substrate and confirmed by Scanning Electron Microscopy. Raman spectroscopy and PL spectroscopy reveal the signature of few-layer MoS2 flakes in the sample. The sensor's performance was tested from room temperature to 150 °C for 1% hydrogen concentration. The device shows a fast response of 14.3 s even at room temperature. The sensitivity of the device strongly depends on temperature and increases from ˜1% to ˜11% as temperature increases. A detail hydrogen sensing mechanism was proposed based on the preferential hydrogen adsorption at MoS2 edge sites. The proposed gas sensing mechanism was verified by depositing ˜2-3 nm of ZnO on top of the MoS2 flakes that partially passivated the edge sites. We found a decrease in the relative response of MoS2-ZnO hybrid structures. This study provides a strong experimental evidence for the role of MoS2 edge-sites in the fast hydrogen sensing and a step closer towards room temperature, low power (0.3 mW), hydrogen sensor development.

Electrostatic properties of graphene edges for electron emission under an external electric field

NASA Astrophysics Data System (ADS)

Gao, Yanlin; Okada, Susumu

2018-04-01

Electronic properties of graphene edges under a lateral electric field were theoretically studied in regard to their edge shapes and terminations to provide a theoretical insight into their field emission properties. The work function and potential barrier for the electron emission from the graphene edges are sensitive to their shape and termination. We also found that the hydrogenated armchair edge shows the largest emission current among all edges studied here. The electric field outside the chiral edges is spatially modulated along the edge because of the inhomogeneous charge density at the atomic sites of the edge arising from the bond alternation.

Distance from forest edge affects bee pollinators in oilseed rape fields.

PubMed

Bailey, Samantha; Requier, Fabrice; Nusillard, Benoît; Roberts, Stuart P M; Potts, Simon G; Bouget, Christophe

2014-02-01

Wild pollinators have been shown to enhance the pollination of Brassica napus (oilseed rape) and thus increase its market value. Several studies have previously shown that pollination services are greater in crops adjoining forest patches or other seminatural habitats than in crops completely surrounded by other crops. In this study, we investigated the specific importance of forest edges in providing potential pollinators in B. napus fields in two areas in France. Bees were caught with yellow pan traps at increasing distances from both warm and cold forest edges into B. napus fields during the blooming period. A total of 4594 individual bees, representing six families and 83 taxa, were collected. We found that both bee abundance and taxa richness were negatively affected by the distance from forest edge. However, responses varied between bee groups and edge orientations. The ITD (Inter-Tegular distance) of the species, a good proxy for bee foraging range, seems to limit how far the bees can travel from the forest edge. We found a greater abundance of cuckoo bees (Nomada spp.) of Andrena spp. and Andrena spp. males at forest edges, which we assume indicate suitable nesting sites, or at least mating sites, for some abundant Andrena species and their parasites (Fig. 1). Synthesis and Applications. This study provides one of the first examples in temperate ecosystems of how forest edges may actually act as a reservoir of potential pollinators and directly benefit agricultural crops by providing nesting or mating sites for important early spring pollinators. Policy-makers and land managers should take forest edges into account and encourage their protection in the agricultural matrix to promote wild bees and their pollination services.

Distance from forest edge affects bee pollinators in oilseed rape fields

PubMed Central

Bailey, Samantha; Requier, Fabrice; Nusillard, Benoît; Roberts, Stuart P M; Potts, Simon G; Bouget, Christophe

2014-01-01

Wild pollinators have been shown to enhance the pollination of Brassica napus (oilseed rape) and thus increase its market value. Several studies have previously shown that pollination services are greater in crops adjoining forest patches or other seminatural habitats than in crops completely surrounded by other crops. In this study, we investigated the specific importance of forest edges in providing potential pollinators in B. napus fields in two areas in France. Bees were caught with yellow pan traps at increasing distances from both warm and cold forest edges into B. napus fields during the blooming period. A total of 4594 individual bees, representing six families and 83 taxa, were collected. We found that both bee abundance and taxa richness were negatively affected by the distance from forest edge. However, responses varied between bee groups and edge orientations. The ITD (Inter-Tegular distance) of the species, a good proxy for bee foraging range, seems to limit how far the bees can travel from the forest edge. We found a greater abundance of cuckoo bees (Nomada spp.) of Andrena spp. and Andrena spp. males at forest edges, which we assume indicate suitable nesting sites, or at least mating sites, for some abundant Andrena species and their parasites (Fig. 1). Synthesis and Applications. This study provides one of the first examples in temperate ecosystems of how forest edges may actually act as a reservoir of potential pollinators and directly benefit agricultural crops by providing nesting or mating sites for important early spring pollinators. Policy-makers and land managers should take forest edges into account and encourage their protection in the agricultural matrix to promote wild bees and their pollination services. PMID:24634722

Mesenchymal chemotaxis requires selective inactivation of Myosin II at the leading edge via a non-canonical PLCγ/PKCα pathway

PubMed Central

Asokan, Sreeja B.; Johnson, Heath E.; Rahman, Anisur; King, Samantha J.; Rotty, Jeremy D.; Lebedeva, Irina P.; Haugh, Jason M.; Bear, James E.

2014-01-01

Summary Chemotaxis, migration towards soluble chemical cues, is critical for processes such as wound healing and immune surveillance, and is exhibited by various cell types from rapidly-migrating leukocytes to slow-moving mesenchymal cells. To interrogate the mechanisms involved in mesenchymal chemotaxis, we observed cell migration in microfluidic chambers that generate stable gradients of the chemoattractant PDGF. Surprisingly, we found that pathways implicated in amoeboid chemotaxis, such as PI3K and mTOR signaling, are dispensable for chemotaxis to PDGF. Instead, we find that local inactivation of Myosin IIA, through a non-canonical Ser1/2 phosphorylation of the regulatory light chain, is essential. This site is phosphorylated by PKCα, which is activated by an intracellular gradient of diacylglycerol generated by PLCγ. Using a combination of TIRF imaging and gradients of activators/inhibitors in the microfluidic chambers, we demonstrate that this signaling pathway and subsequent inhibition of Myosin II activity at the leading edge is required for mesenchymal chemotaxis. PMID:25482883

High-performance transition metal-doped Pt 3Ni octahedra for oxygen reduction reaction

DOE PAGES

Huang, Xiaoqing; Zhao, Zipeng; Cao, Liang; ...

2015-06-11

Bimetallic platinum-nickel (Pt-Ni) nanostructures represent an emerging class of electrocatalysts for oxygen reduction reaction (ORR) in fuel cells, but practical applications have been limited by catalytic activity and durability. We surface-doped Pt 3Ni octahedra supported on carbon with transition metals, termed M-Pt 3Ni/C, where M is vanadium, chromium, manganese, iron, cobalt, molybdenum (Mo), tungsten, or rhenium. The Mo-Pt 3Ni/C showed the best ORR performance, with a specific activity of 10.3 mA/cm2 and mass activity of 6.98 A/mgPt, which are 81- and 73-fold enhancements compared with the commercial Pt/C catalyst (0.127 mA/cm 2 and 0.096 A/mg Pt). In conclusion, theoretical calculationsmore » suggest that Mo prefers subsurface positions near the particle edges in vacuum and surface vertex/edge sites in oxidizing conditions, where it enhances both the performance and the stability of the Pt3Ni catalyst.« less

Edge effects and beta diversity in ground and canopy beetle communities of fragmented subtropical forest

PubMed Central

Catterall, Carla P.; Stork, Nigel E.

2018-01-01

Clearing of dry forests globally creates edges between remnant forest and open anthropogenic habitats. We used flight intercept traps to evaluate how forest beetle communities are influenced by distance from such edges, together with vertical height, spatial location, and local vegetation structure, in an urbanising region (Brisbane, Australia). Species composition (but not total abundance or richness) differed greatly between ground and canopy. Species composition also varied strongly among sites at both ground and canopy levels, but almost all other significant effects occurred only at ground level, where: species richness declined from edge to interior; composition differed between positions near edges (<10 m) and interiors (> 50 m); high local canopy cover was associated with greater total abundance and richness and differing composition; and greater distances to the city centre were associated with increased total abundances and altered composition. Analyses of individual indicator species associated with this variation enabled further biological interpretations. A global literature synthesis showed that most spatially well-replicated studies of edge effects on ground-level beetles within forest fragments have likewise found that positions within tens of metres from edges with open anthropogenic habitats had increased species richness and different compositions from forest interior sites, with fewer effects on abundance. Accordingly, negative edge effects will not prevent relatively small compact fragments (if >10–20 ha) from supporting forest-like beetle communities, although indirect consequences of habitat degradation remain a threat. Retention of multiple spatially scattered forest areas will also be important in conserving forest-dependent beetles, given high levels of between-site diversity. PMID:29494680

Edge effects and beta diversity in ground and canopy beetle communities of fragmented subtropical forest.

PubMed

Stone, Marisa J; Catterall, Carla P; Stork, Nigel E

2018-01-01

Clearing of dry forests globally creates edges between remnant forest and open anthropogenic habitats. We used flight intercept traps to evaluate how forest beetle communities are influenced by distance from such edges, together with vertical height, spatial location, and local vegetation structure, in an urbanising region (Brisbane, Australia). Species composition (but not total abundance or richness) differed greatly between ground and canopy. Species composition also varied strongly among sites at both ground and canopy levels, but almost all other significant effects occurred only at ground level, where: species richness declined from edge to interior; composition differed between positions near edges (<10 m) and interiors (> 50 m); high local canopy cover was associated with greater total abundance and richness and differing composition; and greater distances to the city centre were associated with increased total abundances and altered composition. Analyses of individual indicator species associated with this variation enabled further biological interpretations. A global literature synthesis showed that most spatially well-replicated studies of edge effects on ground-level beetles within forest fragments have likewise found that positions within tens of metres from edges with open anthropogenic habitats had increased species richness and different compositions from forest interior sites, with fewer effects on abundance. Accordingly, negative edge effects will not prevent relatively small compact fragments (if >10-20 ha) from supporting forest-like beetle communities, although indirect consequences of habitat degradation remain a threat. Retention of multiple spatially scattered forest areas will also be important in conserving forest-dependent beetles, given high levels of between-site diversity.

Calculation of optical and K pre-edge absorption spectra for ferrous iron of distorted sites in oxide crystals

NASA Astrophysics Data System (ADS)

Vercamer, Vincent; Hunault, Myrtille O. J. Y.; Lelong, Gérald; Haverkort, Maurits W.; Calas, Georges; Arai, Yusuke; Hijiya, Hiroyuki; Paulatto, Lorenzo; Brouder, Christian; Arrio, Marie-Anne; Juhin, Amélie

2016-12-01

Advanced semiempirical calculations have been performed to compute simultaneously optical absorption and K pre-edge x-ray absorption spectra of Fe2 + in four distinct site symmetries found in minerals. The four symmetries, i.e., a distorted octahedron, a distorted tetrahedron, a square planar site, and a trigonal bipyramidal site, are representative of the Fe2 + sites found in crystals and glasses. A particular attention has been paid to the definition of the p -d hybridization Hamiltonian which occurs for noncentrosymmetric symmetries in order to account for electric dipole transitions. For the different sites under study, an excellent agreement between calculations and experiments was found for both optical and x-ray absorption spectra, in particular in terms of relative intensities and energy positions of electronic transitions. To our knowledge, these are the first calculations of optical absorption spectra on Fe2 + placed in such diverse site symmetries, including centrosymmetric sites. The proposed theoretical model should help to interpret the features of both the optical absorption and the K pre-edge absorption spectra of 3 d transition metal ions and to go beyond the usual fingerprint interpretation.

Highly dispersed buckybowls as model carbocatalysts for C–H bond activation

DOE PAGES

Soykal, I. Ilgaz; Wang, Hui; Park, Jewook; ...

2015-03-19

Buckybowl fractions dispersed on mesoporous silica constitute an ideal model for studying the catalysis of graphitic forms of carbon since the dispersed carbon nanostructures contain a high ratio of edge defects and curvature induced by non-six-membered rings. Dispersion of the active centers on an easily accessible high surface area material allowed for high density of surface active sites associated with oxygenated structures. This report illustrates a facile method of creating model polycyclic aromatic nano-structures that are not only active for alkane C-H bond activation and oxidative dehydrogenation but also can be practical catalysts to be eventually used in industry.

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonitemore » edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites (‘spillover’ effect).« less

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

DOE PAGES

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.; ...

2017-10-06

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonitemore » edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites (‘spillover’ effect).« less

Density functional theory study the effects of oxygen-containing functional groups on oxygen molecules and oxygen atoms adsorbed on carbonaceous materials.

PubMed

Qi, Xuejun; Song, Wenwu; Shi, Jianwei

2017-01-01

Density functional theory was used to study the effects of different types of oxygen-containing functional groups on the adsorption of oxygen molecules and single active oxygen atoms on carbonaceous materials. During gasification or combustion reactions of carbonaceous materials, oxygen-containing functional groups such as hydroxyl(-OH), carbonyl(-CO), quinone(-O), and carboxyl(-COOH) are often present on the edge of graphite and can affect graphite's chemical properties. When oxygen-containing functional groups appear on a graphite surface, the oxygen molecules are strongly adsorbed onto the surface to form a four-member ring structure. At the same time, the O-O bond is greatly weakened and easily broken. The adsorption energy value indicates that the adsorption of oxygen molecules changes from physisorption to chemisorption for oxygen-containing functional groups on the edge of a graphite surface. In addition, our results indicate that the adsorption energy depends on the type of oxygen-containing functional group. When a single active oxygen atom is adsorbed on the bridge site of graphite, it gives rise to a stable epoxy structure. Epoxy can cause deformation of the graphite lattice due to the transition of graphite from sp2 to sp3 after the addition of an oxygen atom. For quinone group on the edge of graphite, oxygen atoms react with carbon atoms to form the precursor of CO2. Similarly, the single active oxygen atoms of carbonyl groups can interact with edge carbon atoms to form the precursor of CO2. The results show that oxygen-containing functional groups on graphite surfaces enhance the activity of graphite, which promotes adsorption on the graphite surface.

Density functional theory study the effects of oxygen-containing functional groups on oxygen molecules and oxygen atoms adsorbed on carbonaceous materials

PubMed Central

Song, Wenwu; Shi, Jianwei

2017-01-01

Density functional theory was used to study the effects of different types of oxygen-containing functional groups on the adsorption of oxygen molecules and single active oxygen atoms on carbonaceous materials. During gasification or combustion reactions of carbonaceous materials, oxygen-containing functional groups such as hydroxyl(-OH), carbonyl(-CO), quinone(-O), and carboxyl(-COOH) are often present on the edge of graphite and can affect graphite’s chemical properties. When oxygen-containing functional groups appear on a graphite surface, the oxygen molecules are strongly adsorbed onto the surface to form a four-member ring structure. At the same time, the O-O bond is greatly weakened and easily broken. The adsorption energy value indicates that the adsorption of oxygen molecules changes from physisorption to chemisorption for oxygen-containing functional groups on the edge of a graphite surface. In addition, our results indicate that the adsorption energy depends on the type of oxygen-containing functional group. When a single active oxygen atom is adsorbed on the bridge site of graphite, it gives rise to a stable epoxy structure. Epoxy can cause deformation of the graphite lattice due to the transition of graphite from sp2 to sp3 after the addition of an oxygen atom. For quinone group on the edge of graphite, oxygen atoms react with carbon atoms to form the precursor of CO2. Similarly, the single active oxygen atoms of carbonyl groups can interact with edge carbon atoms to form the precursor of CO2. The results show that oxygen-containing functional groups on graphite surfaces enhance the activity of graphite, which promotes adsorption on the graphite surface. PMID:28301544

Laboratory and field investigations of marsh edge erosion

USDA-ARS?s Scientific Manuscript database

This chapter presents the laboratory experiments and field observations of marsh edge erosion. The marsh retreat rate in a field study site in Terrebonne Bay, Louisiana, was measured using GPS systems and aerial photographs. The wave environment was also measured in order to correlate the marsh edge...

Comparative analysis of cobalt oxide nanoisland stability and edge structures on three related noble metal surfaces: Au(111), Pt(111) and Ag(111)

DOE PAGES

Fester, Jakob; Bajdich, Michal; Walton, Alex S.; ...

2016-09-12

Here, metal oxide nanostructures and thin films grown on metallic substrates have attracted strong attention as model catalysts and as interesting inverse catalyst systems in their own right. In this study, we investigate the role of metal support in the growth and stabilization of cobalt oxide nanostructures on the three related (111) surfaces of Au, Pt and Ag, as investigated by means of high-resolution scanning tunneling microscopy and DFT calculations. All three substrates promote the growth of crystalline CoO x (x = 1–2) islands under oxidative conditions, but we find several noteworthy differences in the occurrence and stabilization of fourmore » distinct cobalt oxide island phases: Co–O bilayers, O–Co–O trilayers, Co–O–Co–O double bilayers and O–Co–O–Co–O multilayers. Using atom-resolved images combined with analysis of defect lines in bilayer islands on Au and Pt, we furthermore unambiguously determine the edge structure. Interestingly, the island shape and abundances of edge types in bilayers change radically from mixed Co/O edge terminations on Au(111) to a predominance of Co terminated edges (~91 %) on Pt(111) which is especially interesting since the Co metal edges are expected to host the most active sites for water dissociation.« less

The active site structure of tetanus neurotoxin resolved by multiple scattering analysis in X-Ray absorption spectroscopy.

PubMed Central

Meneghini, C; Morante, S

1998-01-01

A detailed study of the x-ray absorption spectrum of tetanus neurotoxin in the K-edge EXAFS region of the zinc absorber is presented that allows the complete identification of the amino acid residues coordinated to the zinc active site. A very satisfactory interpretation of the experimental data can be given if multiple scattering contributions are included in the analysis. Comparing the absorption spectrum of tetanus neurotoxin to that of two other structurally similar zinc-endopeptidases, thermolysin and astacin, in which the zinc coordination mode is known from crystallographic data, we conclude that in tetanus neurotoxin, besides a water molecule, zinc is coordinated to two histidines and a tyrosine. PMID:9746536

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Hyun You; Liu, Ping

Mixed metal oxides have attracted considerable attention in heterogeneous catalysis due to the unique stability, reactivity, and selectivity. Here, the activity and stability of the CuTiO x monolayer film supported on Cu(111), CuTiO x/Cu(111), during CO oxidation was explored using density functional theory (DFT). The unique structural frame of CuTiO x is able to stabilize and isolate a single Cu + site on the terrace, which is previously proposed active for CO oxidation. Furthermore, it is not the case, where the reaction via both the Langmuir–Hinshelwood (LH) and the Mars-van Krevelen (M-vK) mechanisms are hindered on such single Cu +more » site. Upon the formation of step-edges, the synergy among Cu δ+ sites, TiO x matrix, and Cu(111) is able to catalyze the reaction well. Depending on temperatures and partial pressure of CO and O 2, the surface structure varies, which determines the dominant mechanism. In accordance with our results, the Cu δ+ ion alone does not work well for CO oxidation in the form of single sites, while the synergy among multiple active sites is necessary to facilitate the reaction.« less

Complex catalytic behaviors of CuTiO x mixed-oxide during CO oxidation

DOE PAGES

Kim, Hyun You; Liu, Ping

2015-09-21

Mixed metal oxides have attracted considerable attention in heterogeneous catalysis due to the unique stability, reactivity, and selectivity. Here, the activity and stability of the CuTiO x monolayer film supported on Cu(111), CuTiO x/Cu(111), during CO oxidation was explored using density functional theory (DFT). The unique structural frame of CuTiO x is able to stabilize and isolate a single Cu + site on the terrace, which is previously proposed active for CO oxidation. Furthermore, it is not the case, where the reaction via both the Langmuir–Hinshelwood (LH) and the Mars-van Krevelen (M-vK) mechanisms are hindered on such single Cu +more » site. Upon the formation of step-edges, the synergy among Cu δ+ sites, TiO x matrix, and Cu(111) is able to catalyze the reaction well. Depending on temperatures and partial pressure of CO and O 2, the surface structure varies, which determines the dominant mechanism. In accordance with our results, the Cu δ+ ion alone does not work well for CO oxidation in the form of single sites, while the synergy among multiple active sites is necessary to facilitate the reaction.« less

Local and landscape scale factors influencing edge effects on woodland salamanders.

PubMed

Moseley, Kurtis R; Ford, W Mark; Edwards, John W

2009-04-01

We examined local and landscape-scale variable influence on the depth and magnitude of edge effects on woodland salamanders in mature mixed mesophytic and northern hardwood forest adjacent to natural gas well sites maintained as wildlife openings. We surveyed woodland salamander occurrence from June-August 2006 at 33 gas well sites in the Monongahela National Forest, West Virginia. We used an information-theoretic approach to test nine a priori models explaining landscape-scale effects on woodland salamander capture proportion within 20 m of field edge. Salamander capture proportion was greater within 0-60 m than 61-100 m of field edges. Similarly, available coarse woody debris proportion was greater within 0-60 m than 61-100 m of field edge. Our ASPECT model, that incorporated the single variable aspect, received the strongest support for explaining landscape-scale effects on salamander capture proportion within 20 m of opening edge. The ASPECT model indicated that fewer salamanders occurred within 20 m of opening edges on drier, hotter southwestern aspects than in moister, cooler northeastern aspects. Our results suggest that forest habitat adjacent to maintained edges and with sufficient cover still can provide suitable habitat for woodland salamander species in central Appalachian mixed mesophytic and northern hardwood forests. Additionally, our modeling results support the contention that edge effects are more severe on southwesterly aspects. These results underscore the importance of distinguishing among different edge types as well as placing survey locations within a landscape context when investigating edge impacts on woodland salamanders.

Evaluation of nekton use and habitat characteristics of restored Louisiana marsh

USGS Publications Warehouse

Thom, C.S.B.; Peyre, M.K.G.L.; Nyman, J.A.

2004-01-01

Marsh terracing and coconut fiber mats are two wetland restoration techniques implemented at Sabine National Wildlife Refuge, Louisiana, USA. Using nekton as an indicator of habitat quality, nekton community assemblages were compared between terraced, coconut-matted, unmanaged marsh (restoration goal), and open water (pre-restoration) habitats. Using a throw trap and a 3 m ?? 2 m straight seine, 192 nekton samples were collected over four dates in 2001 and 2002 at all habitats. Nekton abundance was similar at unmanaged marsh (restoration goal), coconut mat, and terrace edge, and significantly higher than at open water (pre-restoration) sites (P < 0.05). Coconut-matted habitat and unmanaged marsh edges had significantly higher numbers of benthic dependent species than terrace edges (P < 0.05), potentially because of differences in substrate. Terraced sites had lower organic matter and siltier substrate as compared to unmanaged marsh sites. At Sabine NWR, terracing increased nekton use as compared to pre-restoration conditions (open water samples) by providing marsh edge habitat, but failed to support a nekton community similar to unmanaged marsh (restoration goals) or coconut-matted sites. Future restoration projects may evaluate the combined use of coconut mats with terracing projects in order to enhance habitat for benthic dependent nekton.

Site response, shallow shear-wave velocity, and wave propagation at the San Jose, California, dense seismic array

USGS Publications Warehouse

Hartzell, S.; Carver, D.; Williams, R.A.; Harmsen, S.; Zerva, A.

2003-01-01

Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are compared. These spectra show surface waves generated/ scattered at the edges of the Santa Clara Valley and possibly within the valley at the western edge of the Evergreen basin.

Reactivity and Characterization of Solid State Hydrodesulfurization Catalysts.

NASA Astrophysics Data System (ADS)

Lindner, James Henry

1990-01-01

The identification of the phase responsible for hydrodesulfurization (HDS) activity has been the subject of extensive research. In this study, model solid state catalysts prepared from elemental starting materials were synthesized, characterized, and then used to desulfurize thiophene at temperatures ranging from 200-400 ^circC and a pressure of one atmosphere. The results of this work indicate that an increased HDS activity can be correlated with the presence of a poorly crystalline molybdenum sulfide-like phase detected by XRD, HREM, or AEM. The formation of this sulfur-deficient, non-stoichiometric phase could be accomplished by either removing sulfur directly from the catalyst synthesis mixture to yield a non-stoichiometric MoS_{ rm 2-x} moiety, or by introducing a transition metal promoter such as Fe, Co, Ni, or Cu into the system. The promoter atoms induced structural changes in the molybdenum sulfide edge planes by effectively scavenging sulfur during catalyst synthesis to form promoter sulfide species, which enhanced the formation of a non-stoichiometric, highly active molybdenum sulfide. This morphological effect was the primary function of the promoter in this system. All model catalysts displayed similar structure in the (0002) basal plane of MoS_2; however, only the catalytically active samples showed a high concentration of defects and disorder in the (1010), (1011), and (1012) edge planes. The HREM images obtained from these edge planes and their correlation with HDS activity dramatically illustrated the importance of the often-discussed edge plane structure of MoS_2 and its significance on HDS catalysis. Normalization of the HDS activities for the solid state models and a commercial catalyst with O_2 or CO chemisorption uptakes suggested that a similarity may exist between the catalytically active sites of these materials. In-situ XPS revealed that increasing promoter atom concentrations resulted in a more complete reduction of the promoter atom; but this shift to lower binding energies could not necessarily be correlated with activity. However, it was observed that the more active catalysts all exhibited the ability to dissociate H_2 and remove oxygen from their surface. This H_2 spillover or activation may also influence catalyst performance.

Energetics of edge oxidization of graphene nanoribbons

NASA Astrophysics Data System (ADS)

Yasuma, Airi; Yamanaka, Ayaka; Okada, Susumu

2018-06-01

On the basis of the density functional theory, we studied the geometries and energetics of O atoms adsorbed on graphene edges for simulating the initial stage of the edge oxidization of graphene. Our calculations showed that oxygen atoms are preferentially adsorbed onto the graphene edges with the zigzag portion, resulting in a large adsorption energy of about 5 eV. On the other hand, the edges with armchair shape are rarely oxidized, or the oxidization causes substantial structural reconstructions, because of the stable covalent bond at the armchair edge with the triple bond nature. Furthermore, the energetics sensitively depends on the edge angles owing to the inhomogeneity of the charge density at the edge atomic sites.

Metallic 1T-LixMoS2 Cocatalyst Significantly Enhanced the Photocatalytic H2 Evolution over Cd0.5Zn0.5S Nanocrystals under Visible Light Irradiation.

PubMed

Du, Hong; Guo, Hong-Li; Liu, Ya-Nan; Xie, Xiao; Liang, Kuang; Zhou, Xiao; Wang, Xin; Xu, An-Wu

2016-02-17

In the present work, metallic 1T-LixMoS2 is utilized as a novel cocatalyst for Cd0.5Zn0.5S photocatalyst. The obtained LixMoS2/Cd0.5Zn0.5S hybrids show excellent photocatalytic performance for H2 generation from aqueous solution containing Na2S and Na2SO3 under splitting visible light illumination (λ ≥ 420 nm) without precious metal cocatalysts. It turns out that a certain amount of intercalating Li(+) ions ultimately drives the transition of MoS2 crystal from semiconductor triagonal phase (2H phase) to metallic phase (1T phase). The distinct properties of 1T-LixMoS2 promote the efficient separation of photoexcited electrons and holes when used as cocatalyst for Cd0.5Zn0.5S photocatalyst. As compared to 2H-MoS2 nanosheets only having edge active sites, photoinduced electrons not only transfer to the edge sites of 1T-LixMoS2, but also to the plane active sites of 1T-LixMoS2 nanosheets. The content of LixMoS2 in hybrid photocatalysts influences the photocatalytic activity. The optimal 1T-LixMoS2 (1.0 wt %)/Cd0.5Zn0.5S nanojunctions display the best activity for hydrogen production, achieving a hydrogen evolution rate of 769.9 μmol h(-1), with no use of noble metal loading, which is about 3.5 times higher than that of sole Cd0.5Zn0.5S, and 2 times higher than that of 2H-MoS2 (1.0 wt %)/Cd0.5Zn0.5S samples. Our results demonstrate that Li(+)-intercalated MoS2 nanosheets with high conductivity, high densities of active sites, low cost, and environmental friendliness are a prominent H2 evolution cocatalyst that might substitute for noble metal for potential hydrogen energy applications.

Flutter suppression and gust alleviation using active controls

NASA Technical Reports Server (NTRS)

Nissim, E.

1975-01-01

Application of the aerodynamic energy approach to some problems of flutter suppression and gust alleviation were considered. A simple modification of the control-law is suggested for achieving the required pitch control in the use of a leading edge - trailing edge activated strip. The possible replacement of the leading edge - trailing edge activated strip by a trailing edge - tab strip is also considered as an alternate solution. Parameters affecting the performance of the activated leading edge - trailing edge strip were tested on the Arava STOL Transport and the Westwind Executive Jet Transport and include strip location, control-law gains and a variation in the control-law itself.

Edge effect on post-dispersal artificial seed predation in the southeastern Amazonia, Brazil.

PubMed

Penido, G; Ribeiro, V; Fortunato, D S

2015-05-01

This paper evaluates the post-dispersal artificial seed predation rates in two areas of the southeastern Amazon forest-savanna boundary, central Brazil. We conducted the survey in a disturbance regime controlled research site to verify if exists an edge effect in these rates and if the disturbance (in this case annual fire and no fire) affects seed predation. We placed 800 peanuts seeds in each area at regular distance intervals from the fragment`s edge. Data were analyzed by a likelihood ratio model selection in generalized linear models (GLM). The complete model (with effects from edge distance and site and its interaction) was significative (F3=4.43; p=0.005). Seeds had a larger predation rates in fragment's interior in both areas, but in the controlled area (no disturbance) this effect was less linear. This suggests an edge effect for post-dispersal seed predation, and that disturbances might alter these effects. Even if we exclude the site effect (grouping both areas together) there is still a strong edge effect on seed predation rates (F3=32.679; p>0.001). We did not verify predator's species in this study; however, the presence of several species of ants was extremely common in the seeds. The detection of an edge effect in only a short survey time suggests that there is heterogeneity in predation rates and that this variation might affect plant recruitment in fragmented areas of the Amazon forest. Henceforth, this seed predation should be taken in consideration in reforestation projects, where the main source of plants species is from seed distribution.

Edge disturbance drives liana abundance increase and alteration of liana-host tree interactions in tropical forest fragments.

PubMed

Campbell, Mason J; Edwards, Will; Magrach, Ainhoa; Alamgir, Mohammed; Porolak, Gabriel; Mohandass, D; Laurance, William F

2018-04-01

Closed-canopy forests are being rapidly fragmented across much of the tropical world. Determining the impacts of fragmentation on ecological processes enables better forest management and improves species-conservation outcomes. Lianas are an integral part of tropical forests but can have detrimental and potentially complex interactions with their host trees. These effects can include reduced tree growth and fecundity, elevated tree mortality, alterations in tree-species composition, degradation of forest succession, and a substantial decline in forest carbon storage. We examined the individual impacts of fragmentation and edge effects (0-100-m transect from edge to forest interior) on the liana community and liana-host tree interactions in rainforests of the Atherton Tableland in north Queensland, Australia. We compared the liana and tree community, the traits of liana-infested trees, and determinants of the rates of tree infestation within five forest fragments (23-58 ha in area) and five nearby intact-forest sites. Fragmented forests experienced considerable disturbance-induced degradation at their edges, resulting in a significant increase in liana abundance. This effect penetrated to significantly greater depths in forest fragments than in intact forests. The composition of the liana community in terms of climbing guilds was significantly different between fragmented and intact forests, likely because forest edges had more small-sized trees favoring particular liana guilds which preferentially use these for climbing trellises. Sites that had higher liana abundances also exhibited higher infestation rates of trees, as did sites with the largest lianas. However, large lianas were associated with low-disturbance forest sites. Our study shows that edge disturbance of forest fragments significantly altered the abundance and community composition of lianas and their ecological relationships with trees, with liana impacts on trees being elevated in fragments relative to intact forests. Consequently, effective control of lianas in forest fragments requires management practices which directly focus on minimizing forest edge disturbance.

Architecture of Allosteric Materials and Edge Modes

NASA Astrophysics Data System (ADS)

Yan, Le; Ravasio, Riccardo; Brito, Carolina; Wyart, Matthieu

Allostery, a long-range elasticity-mediated interaction, remains the biggest mystery decades after its discovery in proteins. We introduce a numerical scheme to evolve functional materials that can accomplish a specified mechanical task. In this scheme, the number of solutions, their spatial architectures and the correlations among them can be computed. As an example, we consider an ``allosteric'' task, which requires the material to respond specifically to a stimulus at a distant active site. We find that functioning materials evolve a less-constrained trumpet-shaped region connecting the stimulus and active sites and that the amplitude of the elastic response varies non-monotonically along the trumpet. As previously shown for some proteins, we find that correlations appearing during evolution alone are sufficient to identify key aspects of this design. Finally, we show that the success of this architecture stems from the emergence of soft edge modes recently found to appear near the surface of marginally connected materials. Overall, our in silico evolution experiment offers a new window to study the relationship between structure, function, and correlations emerging during evolution. L.Y. was supported in part by the National Science Foundation under Grant No. NSF PHY11-25915. M.W. thanks the Swiss National Science Foundation for support under Grant No. 200021-165509 and the Simons Foundation Grant (#454953 Matthieu Wyart).

Dual-Native Vacancy Activated Basal Plane and Conductivity of MoSe2 with High-Efficiency Hydrogen Evolution Reaction.

PubMed

Gao, Daqiang; Xia, Baorui; Wang, Yanyan; Xiao, Wen; Xi, Pinxian; Xue, Desheng; Ding, Jun

2018-04-01

Although transition metal dichalcogenide MoSe 2 is recognized as one of the low-cost and efficient electrocatalysts for the hydrogen evolution reaction (HER), its thermodynamically stable basal plane and semiconducting property still hamper the electrocatalytic activity. Here, it is demonstrated that the basal plane and edges of 2H-MoSe 2 toward HER can be activated by introducing dual-native vacancy. The first-principle calculations indicate that both the Se and Mo vacancies together activate the electrocatalytic sites in the basal plane and edges of MoSe 2 with the optimal hydrogen adsorption free energy (ΔG H* ) of 0 eV. Experimentally, 2D MoSe 2 nanosheet arrays with a large amount of dual-native vacancies are fabricated as a catalytic working electrode, which possesses an overpotential of 126 mV at a current density of 100 mV cm -2 , a Tafel slope of 38 mV dec -1 , and an excellent long-term durability. The findings pave a rational pathway to trigger the activity of inert MoSe 2 toward HER and also can be extended to other layered dichalcogenide. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Observation of the origin of d0 magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

NASA Astrophysics Data System (ADS)

Singh, Shashi B.; Wang, Yu-Fu; Shao, Yu-Cheng; Lai, Hsuan-Yu; Hsieh, Shang-Hsien; Limaye, Mukta V.; Chuang, Chen-Hao; Hsueh, Hung-Chung; Wang, Hsaiotsu; Chiou, Jau-Wern; Tsai, Hung-Ming; Pao, Chih-Wen; Chen, Chia-Hao; Lin, Hong-Ji; Lee, Jyh-Fu; Wu, Chun-Te; Wu, Jih-Jen; Pong, Way-Faung; Ohigashi, Takuji; Kosugi, Nobuhiro; Wang, Jian; Zhou, Jigang; Regier, Tom; Sham, Tsun-Kong

2014-07-01

Efforts have been made to elucidate the origin of d0 magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region. The intensity of O K-edge STXM-XANES in the impurity region is more predominant in ZnO NCs than in NWs. The increase in the unoccupied (occupied) density of states at/above (at/below) the conduction-band minimum (valence-band maximum) or the Fermi level is related to the population of defects at the O sites, as revealed by comparing the ZnO NCs to the NWs. The results of O K-edge and Zn L3,2-edge X-ray magnetic circular dichroism demonstrated that the origin of magnetization is attributable to the O 2p orbitals rather than the Zn d orbitals. Further, the local density approximation (LDA) + U verified that vacancies in the form of dangling or unpaired 2p states (due to Zn vacancies) induced a significant local spin moment in the nearest-neighboring O atoms to the defect center, which was determined from the uneven local spin density by analyzing the partial density of states of O 2p in ZnO.Efforts have been made to elucidate the origin of d0 magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region. The intensity of O K-edge STXM-XANES in the impurity region is more predominant in ZnO NCs than in NWs. The increase in the unoccupied (occupied) density of states at/above (at/below) the conduction-band minimum (valence-band maximum) or the Fermi level is related to the population of defects at the O sites, as revealed by comparing the ZnO NCs to the NWs. The results of O K-edge and Zn L3,2-edge X-ray magnetic circular dichroism demonstrated that the origin of magnetization is attributable to the O 2p orbitals rather than the Zn d orbitals. Further, the local density approximation (LDA) + U verified that vacancies in the form of dangling or unpaired 2p states (due to Zn vacancies) induced a significant local spin moment in the nearest-neighboring O atoms to the defect center, which was determined from the uneven local spin density by analyzing the partial density of states of O 2p in ZnO. Electronic supplementary information (ESI) available: Scanning photoelectron microscopy (SPEM) results of ZnO NCs and NWs. Computational details and calculated total and partial density of states (PDOS) of bulk wurtzite ZnO with oxygen anion vacancies (VO). See DOI: 10.1039/c4nr01961j

The differential effects of halothane and isoflurane on electroencephalographic responses to electrical microstimulation of the reticular formation.

PubMed

Orth, Mashawn; Bravo, Emigdio; Barter, Linda; Carstens, Earl; Antognini, Joseph F

2006-06-01

Isoflurane and halothane cause electroencephalographic (EEG) depression and neuronal depression in the reticular formation, a site critical to consciousness. We hypothesized that isoflurane, more than halothane, would depress EEG activation elicited by electrical microstimulation of the reticular formation. Rats were anesthetized with either halothane or isoflurane and stimulating electrodes were positioned in the reticular formation. In a crossover design, anesthetic concentration was adjusted to 0.8 and 1.2 minimum alveolar concentration (MAC) of halothane or isoflurane and electrical microstimulation was performed and the EEG responses were recorded. Microstimulation increased the spectral edge and median edge frequencies 2-2.5 Hz at 0.8 MAC for halothane and isoflurane and 1.2 MAC halothane. At 1.2 MAC isoflurane, burst suppression occurred and microstimulation decreased the period of isoelectricity (24% +/- 19% to 8% +/- 7%; P < 0.05), whereas the spectral edge and median edge frequencies were unchanged. At anesthetic concentrations required to produce immobility, the cortex remains responsive to electrical microstimulation of the reticular formation, although the EEG response is depressed in the transition from 0.8 to 1.2 MAC. These data indicate that cortical neurons remain responsive to synaptic input during isoflurane and halothane anesthesia.

DFT Insights into the Competitive Adsorption of Sulfur- and Nitrogen-Containing Compounds and Hydrocarbons on Co-Promoted Molybdenum Sulfide Catalysts

DOE PAGES

Rangarajan, Srinivas; Mavrikakis, Manos

2016-04-07

The adsorption of 20 nitrogen-/sulfur-containing and hydrocarbon compounds on the sulfur edge of cobalt-promoted molybdenum sulfide (CoMoS) catalyst was studied using density functional theory, accounting for van der Waals interactions, to elicit comparative structure–property trends across different classes of molecules relevant to hydrotreating. Unhindered organosulfur compounds preferentially adsorb on a “CUS-like” site formed by the dimerization of two neighboring sulfur atoms on the edge to create a vacancy. Nitrogen-containing compounds and 4,6-dimethyldibenzothiophene, however, prefer the brim sites. Binding energy trends indicate that nitrogen-containing compounds will inhibit hydrodesulfurization on the brim sites and, relatively weakly, on the CUS-like sites. Edge vacanciesmore » are,thus, likely to be essential for hydrodesulfurization of unhindered organosulfur compounds. Furthermore, van der Waals forces contribute significantly to the binding energy of compounds (up to 1.0 eV for large compounds such as alkyl-substituted acridines) on CoMoS.« less

Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co

DOE PAGES

Pendyala, Venkat Ramana Rao; Jacobs, Gary; Ma, Wenping; ...

2016-07-23

The effect of co-fed hydrogen chloride (HCl) in syngas on the performance of iron and cobalt-based Fischer-Tropsch (FT) catalysts was investigated in our earlier studies [ACS Catal. 5 (2015) 3124-3136 and DOE final report 2011; Catal. Lett. 144 (2014) 1127-1133]. For an iron catalyst, lower HCl concentrations (< 2.0 ppmw of HCl)) in syngas did not significantly affect the activity, whereas rapid deactivation occurred at higher concentrations (~20 ppmw). With cobalt catalysts, even low concentrations of HCl (100 ppbw) caused catalyst deactivation, and the deactivation rate increased with increasing HCl concentration in the syngas. The deactivation of the catalysts ismore » explained by the chloride being adsorbed on the catalyst surface to (1) block the active sites and/or (2) electronically modify the sites. In this study, XANES spectroscopy was employed to investigate HCl poisoning mechanism on the iron and cobalt catalysts. Cl K-edge normalized XANES results indicate that Cl is indeed present on the catalyst following HCl poisoning and exhibits a structure similar to the family of compounds MCl; two main peaks are formed, with the second peak consisting of a main peak and a higher energy shoulder. At the Co K and Fe K edges, the white line was observed to be slightly increased relative to the same catalyst under clean conditions. There is then the additional possibility that Cl adsorption may act in part to intercept electron density from the FT metallic function (e.g.,cobalt or iron carbide). If so, this would result in less back-donation and therefore hinder the scission of molecules such as CO.« less

First-principles investigation of armchair boron nitride nanoribbons for sensing PH3 gas molecules

NASA Astrophysics Data System (ADS)

Srivastava, Pankaj; Jaiswal, Neeraj K.; Sharma, Varun

2014-09-01

The present work exhibits density functional theory (DFT) based first-principles calculations to explore the sensing properties of bare armchair boron nitride nanoribbons (ABNNR) for PH3 gas molecules. Edges of the ribbon were considered as the sites of possible adsorption with two different configurations i.e. adsorption at one edge and adsorption at both edges of the ribbon. It is revealed that B atoms of the ribbons are more energetically favorable sites for the adsorption of PH3 molecules as compared with N atoms. The adsorption of PH3 affects the electronic properties of nanoribbons. One edge PH3 adsorbed ribbons are metallic whereas in both edges PH3 adsorption, the band gap is decreased than that of bare ribbon. The changes in electronic properties caused by PH3 adsorption are further supported by the current-voltage (I-V) characteristics of the considered configurations. The results show that ABNNR can serve as a potential candidate for PH3 sensing applications.

Full multiple-scattering calculations on silicates and oxides at the Al K edge

NASA Astrophysics Data System (ADS)

Cabaret, Delphine; Sainctavit, Philippe; Ildefonse, Philippe; Flank, Anne-Marie

1996-05-01

We present full multiple-scattering calculations at the aluminium K edge that we compare with experiments for four crystalline silicates and oxide minerals. In the different minerals aluminium atoms are either fourfold or sixfold coordinated to oxygen atoms in Al sites that are poorly symmetric. The calculations are based on different choices of one-electron potentials according to aluminium coordinations and crystallographic structures of the compounds. Hence it is possible to determine how the near-edge spectral features are a sensitive probe of the effective potential seen by the photoelectron in the molecular environment. The purpose of this work is to determine on the one hand the relation between Al K-edge spectral features and the geometrical arrangements around the aluminium sites, and on the other hand the electronic structure of the compounds.

Monitoring changes in landscape pattern: use of Ikonos and Quickbird images.

PubMed

Alphan, Hakan; Çelik, Nil

2016-02-01

This paper aimed to analyze short-term changes in landscape pattern that primarily results from building development in the east coast of Mersin Province (Turkey). Three sites were selected. Ikonos (2003) and Quickbird (2009) images for these sites were classified, and land cover transformations were quantitatively analyzed using cross-tabulation of classification results. Changes in landscape structure were assessed by comparing the calculated values of area/edge and shape metrics for the earlier and later dates. Area/edge metrics included percentage of land and edge density, while shape metrics included perimeter-area ratio, fractal dimension, and related circumscribing circle (RCC) metrics. Orchards and buildings were dominating land cover classes. Variations in patch edge, size, and shapes were also analyzed and discussed. Degradation of prime agricultural areas due to building development and implications of such development on habitat fragmentation were highlighted.

A Combined Probe-Molecule, Mössbauer, Nuclear Resonance Vibrational Spectroscopy, and Density Functional Theory Approach for Evaluation of Potential Iron Active Sites in an Oxygen Reduction Reaction Catalyst

DOE PAGES

Kneebone, Jared L.; Daifuku, Stephanie L.; Kehl, Jeffrey A.; ...

2017-07-06

While non-precious metal M-N-C (M = Fe or Co) catalysts have been developed that are effective for the oxygen reduction reaction in polymer electrolyte fuel cells, no consensus has yet been reached regarding the nature of the M sites in these heterogeneous catalysts that are responsible for reaction with dioxygen (O 2). While multiple studies have developed correlations between Fe distributions in as-prepared catalysts and ORR activity, the direct identification of sites reactive towards O 2 or O 2-analog molecules remains a significant challenge. In the present study, we demonstrate a new approach to identifying and characterizing potential Fe activemore » sites in complex ORR catalysts that combines an effective probe molecule (NO (g)) Mössbauer spectroscopy and nuclear resonance vibrational spectroscopy (NRVS) with density functional theory (DFT) calculations. Mössbauer spectroscopic studies demonstrate that NO (g) treatment of electrochemically reduced PANI-57Fe-C leads to selective reaction with only a sub-set of the Fe species present. Nuclear resonance vibrational spectroscopic studies identified new Fe-ligand vibrations associated with the site reactive towards NO (g). DFT calculations of vibrational properties of a small selection of previously proposed active site structures suggest that graphene zig-zag edge hosted Fe-N structures may be responsible for the observed vibrational behavior with NO (g) probe molecules. Moreover, such sites are likely also reactive to O 2, possibly serving as the ORR active sites in the synthesized materials.« less

A Combined Probe-Molecule, Mössbauer, Nuclear Resonance Vibrational Spectroscopy, and Density Functional Theory Approach for Evaluation of Potential Iron Active Sites in an Oxygen Reduction Reaction Catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kneebone, Jared L.; Daifuku, Stephanie L.; Kehl, Jeffrey A.

While non-precious metal M-N-C (M = Fe or Co) catalysts have been developed that are effective for the oxygen reduction reaction in polymer electrolyte fuel cells, no consensus has yet been reached regarding the nature of the M sites in these heterogeneous catalysts that are responsible for reaction with dioxygen (O 2). While multiple studies have developed correlations between Fe distributions in as-prepared catalysts and ORR activity, the direct identification of sites reactive towards O 2 or O 2-analog molecules remains a significant challenge. In the present study, we demonstrate a new approach to identifying and characterizing potential Fe activemore » sites in complex ORR catalysts that combines an effective probe molecule (NO (g)) Mössbauer spectroscopy and nuclear resonance vibrational spectroscopy (NRVS) with density functional theory (DFT) calculations. Mössbauer spectroscopic studies demonstrate that NO (g) treatment of electrochemically reduced PANI-57Fe-C leads to selective reaction with only a sub-set of the Fe species present. Nuclear resonance vibrational spectroscopic studies identified new Fe-ligand vibrations associated with the site reactive towards NO (g). DFT calculations of vibrational properties of a small selection of previously proposed active site structures suggest that graphene zig-zag edge hosted Fe-N structures may be responsible for the observed vibrational behavior with NO (g) probe molecules. Moreover, such sites are likely also reactive to O 2, possibly serving as the ORR active sites in the synthesized materials.« less

The effect of site geometry, Ti content and Ti oxidation state on the Ti K-edge XANES spectrum of synthetic hibonite

NASA Astrophysics Data System (ADS)

Doyle, P. M.; Berry, A. J.; Schofield, P. F.; Mosselmans, J. F. W.

2016-08-01

The Al-rich oxide hibonite (CaAl12O19) is modeled to be the second mineral to condense from a gas of solar composition and is found within calcium-aluminum-rich inclusions and the matrix of chondritic meteorites. Both Ti3+ and Ti4+ are reported in meteoritic hibonite, so hibonite has been proposed as a single mineral oxybarometer that could be used to elucidate conditions within the first 0.2 Myrs of the Solar System. Synthetic hibonites with Ti3+/(Ti3+ + Ti4+) (hereafter Ti3+/ΣTi) ranging between 0 and 1 were prepared as matrix-matched standards for meteoritic hibonite. The largest yield of both Ti-free and Ti-bearing hibonite at ∼1300 and ∼1400 °C was obtained by a single sinter under reducing conditions. In situ micro-beam Ti K-edge X-ray absorption near edge structure (XANES) spectra were recorded from the synthetic hibonites, as well as from terrestrial hibonite. Spectral features in the post-crest region were shown to correlate with the Ti4+ content. Furthermore, Ti4+ on the M2 trigonal bipyramidal and the adjoining M4 octahedral sites appears to cause variability in the post-crest region as a function of orientation. For this suite of synthetic hibonites it was observed that the pre-edge peak region is not influenced by orientation, but is controlled by Ti3+/ΣTi, site geometry and/or Ti concentration. In particular, the pre-edge peak intensities reflect Ti coordination environment and distortion of the M4 octahedral site. Therefore, although pre-edge peak intensities have previously been used to determine Ti3+/ΣTi in meteoritic minerals, we excluded use of the pre-edge peak intensities for quantifying Ti valence states in hibonite. The energy of the absorption edge at a normalized intensity of 0.8 (E0.8) and the energy of the minimum between the pre-edge region and the absorption edge (Em1) were found to vary systematically with Ti3+/ΣTi. Ti3+/ΣTi in hibonite as a function of Em1 was modeled by a quadratic function that may be used to quantify Ti3+/ΣTi in meteoritic hibonite when the synthetic hibonite standards are crystal-chemically matched to the natural samples and are measured during the same analytical session as the meteoritic hibonites.

Plume Delineation in the BC Cribs and Trenches Area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rucker, Dale F.; Sweeney, Mark D.

2004-11-30

HydroGEOPHYSICS, Inc. and Pacific Northwest National Laboratory (PNNL) were contracted by Fluor Hanford Group, Inc. to conduct a geophysical investigation in the area of the BC Cribs and Trenches (subject site) at the Hanford Site in Richland, Washington. The BC Cribs and Trenches are located south of the 200 East Area. This document provides the details of the investigation to identify existing infrastructure from legacy disposal activities and to delineate the edges of a groundwater plume that contains radiological and heavy metal constituents beneath the 216-B-26 and 216-B-52 Trenches, and the 216-B-14 through 216-B-19 Cribs.

The aqueous electrochemistry of carbon-based surfaces-investigation by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Mühl, T.; Myhra, S.

2007-04-01

Electro-oxidation of carbon-based materials will lead to conversion of the solid to CO2/CO at the anode, with H2 being produced at the cathode. Recent voltammetric investigations of carbon nano-tubes and single crystal graphite have shown that only edge sites and other defect sites are electrochemically active. Local oxidation of diamond-like carbon films (DLC) by an STM tip in moist air followed by imaging allows correlation of topographical change with electro-chemical conditions and surface reactivity. The results may have implications for lithographic processing of carbon surfaces, and may have relevance for electrochemical H2 production.

Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite.

PubMed

Zougrou, I M; Katsikini, M; Brzhezinskaya, M; Pinakidou, F; Papadopoulou, L; Tsoukala, E; Paloura, E C

2016-08-01

Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite

NASA Astrophysics Data System (ADS)

Zougrou, I. M.; Katsikini, M.; Brzhezinskaya, M.; Pinakidou, F.; Papadopoulou, L.; Tsoukala, E.; Paloura, E. C.

2016-08-01

Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

Lunar Roving Vehicle photographed against lunar background during EVA

NASA Image and Video Library

1971-08-01

AS15-88-11901 (31 July-2 Aug. 1971) --- The Lunar Roving Vehicle (LRV) is photographed alone against the desolate lunar background during the third Apollo 15 lunar surface extravehicular activity (EVA) at the Hadley-Apennine landing site. This view is looking north. The west edge of Mount Hadley is at the upper right edge of the picture. Mount Hadley rises approximately 4,500 meters (about 4,765 feet) above the plain. The most distant lunar feature visible is approximately 25 kilometers (about 15.5 statute miles) away. While astronauts David R. Scott, commander; and James B. Irwin, lunar module pilot, descended in the Lunar Module (LM) "Falcon" to explore the moon, astronaut Alfred M. Worden, command module pilot, remained with the Command and Service Modules (CSM) in lunar orbit.

Sulfur K-edge XAS of WV=O vs. MoV=O Bis(dithiolene) Complexes: Contributions of Relativistic Effects to Electronic Structure and Reactivity of Tungsten Enzymes†

PubMed Central

Tenderholt, Adam L.; Szilagyi, Robert K.; Holm, Richard H.; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.

2009-01-01

Molybdenum- or tungsten-containing enzymes catalyze oxygen atom transfer reactions involved in carbon, sulfur, or nitrogen metabolism. It has been observed that reduction potentials and oxygen atom transfer rates are different for W relative to Mo enzymes and the isostructural Mo/W complexes. Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations on [MoVO(bdt)2]− and [WVO(bdt)2]−, where bdt = benzene-1,2-dithiolate(2−), have been used to determine that the energies of the half-filled redox-active orbital, and thus the reduction potentials and M=O bond strengths, are different for these complexes due to relativistic effects in the W sites. PMID:17720249

Resonant inelastic X-ray scattering on ferrous and ferric bis-imidazole porphyrin and cytochrome c: Nature and role of the axial methionine-Fe bond

DOE PAGES

Kroll, Thomas; Hadt, Ryan G.; Wilson, Samuel A.; ...

2014-12-04

Axial Cu–S(Met) bonds in electron transfer (ET) active sites are generally found to lower their reduction potentials. An axial S(Met) bond is also present in cytochrome c (cyt c) and is generally thought to increase the reduction potential. The highly covalent nature of the porphyrin environment in heme proteins precludes using many spectroscopic approaches to directly study the Fe site to experimentally quantify this bond. Alternatively, L-edge X-ray absorption spectroscopy (XAS) enables one to directly focus on the 3d-orbitals in a highly covalent environment and has previously been successfully applied to porphyrin model complexes. However, this technique cannot be extendedmore » to metalloproteins in solution. Here, we use metal K-edge XAS to obtain L-edge like data through 1s2p resonance inelastic X-ray scattering (RIXS). It has been applied here to a bis-imidazole porphyrin model complex and cyt c. The RIXS data on the model complex are directly correlated to L-edge XAS data to develop the complementary nature of these two spectroscopic methods. Comparison between the bis-imidazole model complex and cyt c in ferrous and ferric oxidation states show quantitative differences that reflect differences in axial ligand covalency. The data reveal an increased covalency for the S(Met) relative to N(His) axial ligand and a higher degree of covalency for the ferric states relative to the ferrous states. These results are reproduced by DFT calculations, which are used to evaluate the thermodynamics of the Fe–S(Met) bond and its dependence on redox state. Furthermore, these results provide insight into a number of previous chemical and physical results on cyt c.« less

Interactions between bacterial carbon monoxide and hydrogen consumption and plant development on recent volcanic deposits.

PubMed

King, Gary M; Weber, Carolyn F

2008-02-01

Patterns of microbial colonization and interactions between microbial processes and vascular plants on volcanic deposits have received little attention. Previous reports have shown that atmospheric CO and hydrogen contribute significantly to microbial metabolism on Kilauea volcano (Hawaii) deposits with varied ages and successional development. Relationships between CO oxidation and plant communities were not clear, however, since deposit age and vegetation status covaried. To determine plant-microbe interactions in deposits of uniform ages, CO and hydrogen dynamics have been assayed for unvegetated tephra on a 1959 deposit at Pu'u Puai (PP-bare), at the edge of tree 'islands' within the PP deposit (PP-edge) and within PP tree islands (PP-canopy). Similar assays have been conducted for vegetated and unvegetated sites on a 1969 Mauna Ulu (MU) lava flow. Net in situ atmospheric CO uptake was highest at PP-edge and PP-bare sites (2.2+/-0.5 and 1.3+/-0.1 mg CO m(-2) day(-1), respectively), and least for PP-canopy (-3.2+/-0.9 mg CO m(-2) day(-1), net emission). Respiration rates, microbial biomass and maximum CO uptake potential showed an opposing pattern. Comparisons of atmospheric CO uptake and CO(2) production rates indicate that CO contributes significantly to microbial metabolism in PP-bare and MU-unvegetated sites, but negligibly where vegetation is well developed. Nonetheless, maximum potential CO uptake rates indicate that CO oxidizer populations increase with increasing plant biomass and consume CO actively. Some of these CO oxidizers may contribute to elevated nitrogen fixation rates (acetylene reduction) measured within tree islands, and thus, support plant successional development.

Unified mechanism of alkali and alkaline earth catalyzed gasification reactions of carbon by CO2 and H2O

USGS Publications Warehouse

Chen, S.G.; Yang, R.T.

1997-01-01

From molecular orbital calculations, a unified mechanism is proposed for the gasification reactions of graphite by CO2 and H2O, both uncatalyzed and catalyzed by alkali and alkaline earth catalysts. In this mechanism, there are two types of oxygen intermediates that are bonded to the active edge carbon atoms: an in-plane semiquinone type, Cf(O), and an off-plane oxygen bonded to two saturated carbon atoms that are adjacent to the semiquinone species, C(O)Cf(O). The rate-limiting step is the decomposition of these intermediates by breaking the C-C bonds that are connected to Cf(O). A new rate equation is derived for the uncatalyzed reactions, and that for the catalyzed reactions is readily available from the proposed mechanism. The proposed mechanism can account for several unresolved experimental observations: TPD and TK (transient kinetics) desorption results of the catalyzed systems, the similar activation energies for the uncatalyzed and catalyzed reactions, and the relative activities of the alkali and alkaline earth elements. The net charge of the edge carbon active site is substantially changed by gaining electron density from the alkali or alkaline earth element (by forming C-O-M, where M stands for metal). The relative catalytic activities of these elements can be correlated with their abilities of donating electrons and changing the net charge of the edge carbon atom. As shown previously (Chen, S. G.; Yang, R. T. J. Catal. 1993, 141, 102), only clusters of the alkali compounds are active. This derives from the ability of the clusters to dissociate CO2 and H2O to form O atoms and the mobility of the dissociated O atoms facilitated by the clusters.

Nano-targeted induction of dual ferroptotic mechanisms eradicates high-risk neuroblastoma.

PubMed

Hassannia, Behrouz; Wiernicki, Bartosz; Ingold, Irina; Qu, Feng; Van Herck, Simon; Tyurina, Yulia Y; Bayır, Hülya; Abhari, Behnaz A; Angeli, Jose Pedro Friedmann; Choi, Sze Men; Meul, Eline; Heyninck, Karen; Declerck, Ken; Chirumamilla, Chandra Sekhar; Lahtela-Kakkonen, Maija; Van Camp, Guy; Krysko, Dmitri V; Ekert, Paul G; Fulda, Simone; De Geest, Bruno G; Conrad, Marcus; Kagan, Valerian E; Berghe, Wim Vanden; Vandenabeele, Peter; Berghe, Tom Vanden

2018-06-25

High-risk neuroblastoma is a devastating malignancy with very limited therapeutic options. Here, we identify withaferin A (WA) as a natural ferroptosis-inducing agent in neuroblastoma, which acts through a novel double-edged mechanism. WA dose-dependently either activates the nuclear factor-like 2 pathway through targeting of Kelch-like ECH-associated protein 1 (noncanonical ferroptosis induction) or inactivates glutathione peroxidase 4 (canonical ferroptosis induction). Noncanonical ferroptosis induction is characterized by an increase in intracellular labile Fe(II) upon excessive activation of heme oxygenase-1, which is sufficient to induce ferroptosis. This double-edged mechanism might explain the superior efficacy of WA as compared with etoposide or cisplatin in killing a heterogeneous panel of high-risk neuroblastoma cells, and in suppressing the growth and relapse rate of neuroblastoma xenografts. Nano-targeting of WA allows systemic application and suppressed tumor growth due to an enhanced accumulation at the tumor site. Collectively, our data propose a novel therapeutic strategy to efficiently kill cancer cells by ferroptosis.

Reproducible nucleation sites for flux dendrites in MgB 2

NASA Astrophysics Data System (ADS)

Johansen, T. H.; Shantsev, D. V.; Olsen, Å. A. F.; Roussel, M.; Pan, A. V.; Dou, S. X.

2007-12-01

Magneto-optical imaging was used to study dendritic flux penetration in films of MgB 2. By repeating experiments under the same external conditions, reproducible features were seen in the pattern formation; dendrites tend to nucleate from fixed locations along the edge. However, their detailed structure deeper inside the film is never reproduced. The reproducibility in nucleation sites is explained as a result of edge roughness causing field hot spots.

Activating and optimizing MoS 2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies

DOE PAGES

Li, Hong; Tsai, Charlie; Koh, Ai Leen; ...

2015-11-09

As a promising non-precious catalyst for the hydrogen evolution reaction, molybdenum disulphide (MoS 2) is known to contain active edge sites and an inert basal plane. Activating the MoS 2 basal plane could further enhance its HER activity but is not often a strategy for doing so. Herein, we report the first activation and optimization of the basal plane of monolayer 2H-MoS 2 for HER by introducing sulphur (S) vacancies and strain. Our theoretical and experimental results show that the S-vacancies are new catalytic sites in the basal plane, where gap states around the Fermi level allow hydrogen to bindmore » directly to exposed Mo atoms. The hydrogen adsorption free energy (ΔG H) can be further manipulated by straining the surface with S-vacancies, which fine-tunes the catalytic activity. Furthermore, proper combinations of S-vacancy and strain yield the optimal ΔG H = 0 eV, which allows us to achieve the highest intrinsic HER activity among molybdenum-sulphide-based catalysts.« less

Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes.

PubMed

Sun, Chia-Liang; Pao, Chih-Wen; Tsai, Huang-Ming; Chiou, Jau-Wern; Ray, Sekhar C; Wang, Houng-Wei; Hayashi, Michitoshi; Chen, Li-Chyong; Lin, Hong-Ji; Lee, Jyh-Fu; Chang, Li; Tsai, Min-Hsiung; Chen, Kuei-Hsien; Pong, Way-Faung

2013-08-07

The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.

4d Electronic structure analysis of ruthenium in the perovskite oxides by Ru K- and L-edge XAS.

PubMed

Kim, J Y; Hwang, S H; Kim, S J; Demazeau, G; Choy, J H; Shimada, H

2001-03-01

The 4d electronic structure of ruthenium in the perovskite oxides, La2MRuIVO6 (M = Zn, Mg, and Li) and Ba2YRuVO6, has been investigated by the Ru K-and L-edge XANES and EXAFS analyses. Such X-ray absorption spectroscopic results clarify that the RuIV (d4) and RuV (d3) ions are stabilized in nearly regular Oh site. Comparing the Ru L-edge XANES spectra of perovskites containing isovalent ruthenium, it has been found that the t2g state is mainly influenced by A site cation, whereas the eg is mainly affected by neighboring B site cation. The experimental EXAFS spectra in the range of R < or = approximately 4.5 A are well reproduced by ab-initio calculation based on crystallographic data, which supports the long-range structure presented by Rietveld refinement.

Adsorption of xenon on vicinal copper and platinum surfaces

NASA Astrophysics Data System (ADS)

Baker, Layton

The adsorption of xenon was studied on Cu(111), Cu(221), Cu(643) and on Pt(111), Pt(221), and Pt(531) using low energy electron diffraction (LEED), temperature programmed desorption (TPD) of xenon, and ultraviolet photoemission of adsorbed xenon (PAX). These experiments were performed to study the atomic and electronic structure of stepped and step-kinked, chiral metal surfaces. Xenon TPD and PAX were performed on each surface in an attempt to titrate terrace, step edge, and kink adsorption sites by adsorption energetics (TPD) and local work function differences (PAX). Due to the complex behavior of xenon on the vicinal copper and platinum metal surfaces, adsorption sites on these surfaces could not be adequately titrated by xenon TPD. On Cu(221) and Cu(643), xenon desorption from step adsorption sites was not apparent leading to the conclusion that the energy difference between terrace and step adsorption is minuscule. On Pt(221) and Pt(531), xenon TPD indicated that xenon prefers to bond at step edges and that the xenon-xenon interaction at step edges in repulsive but no further indication of step-kink adsorption was observed. The Pt(221) and Pt(531) TPD spectra indicated that the xenon overlayer undergoes strong compression near monolayer coverage on these surfaces due to repulsion between step-edge adsorbed xenon and other encroaching xenon atoms. The PAX experiments on the copper and platinum surfaces demonstrated that the step adsorption sites have lower local work functions than terrace adsorption sites and that higher step density leads to a larger separation in the local work function of terrace and step adsorption sites. The PAX spectra also indicated that, for all surfaces studied at 50--70 K, step adsorption is favored at low coverage but the step sites are not saturated until monolayer coverage is reached; this observation is due to the large entropy difference between terrace and step adsorption states and to repulsive interactions between xenon atoms adsorbed at step edges (on the platinum surfaces). The results herein provide several novel observations regarding the adsorptive behavior of xenon on vicinal copper and platinum surfaces.

Spread dynamics of perennial pepperweed (Lepidium latifolium) in two seasonal wetland areas

USGS Publications Warehouse

Renz, Mark J.; Steinmaus, Scott J.; Gilmer, David S.; DiTomaso, Joseph M.

2012-01-01

Perennial pepperweed is an invasive plant that is expanding rapidly in several plant communities in the western United States. In California, perennial pepperweed has aggressively invaded seasonal wetlands, resulting in degradation of habitat quality. We evaluated the rate and dynamics of population spread, assessed the effect of disturbance on spread, and determined the biotic and abiotic factors influencing the likelihood of invasion. The study was conducted at eight sites within two wetland regions of California. Results indicate that in undisturbed sites, spread was almost exclusively through vegetative expansion, and the average rate of spread was 0.85 m yr−1 from the leading edge. Spread in sites that were disked was more than three times greater than in undisturbed sites. While smaller infestations increased at a faster rate compared with larger populations, larger infestations accumulated more newly infested areas than smaller infestations from year to year. Stem density was consistently higher in the center of the infestations, with about 2.4 times more stems per square meter compared with the leading edge at the perimeter of the population. The invasion by perennial pepperweed was positively correlated with increased water availability but was negatively correlated with the cover of perennial and annual species. Thus, high cover of resident vegetation can have a suppressive effect on the rate of invasion, even in wetland ecosystems. On the basis of these results, we recommend that resident plant cover not be disturbed, especially in wet areas adjacent to areas currently infested with perennial pepperweed. For infested areas, management efforts should be prioritized to focus on controlling satellite populations as well as the leading edge of larger infestations first. This strategy could reduce the need for costly active restoration efforts by maximizing the probability of successful re-establishment of resident vegetation from the adjacent seedbank.

Research for preparation of cation-conducting solids by high-pressure synthesis and other methods

NASA Technical Reports Server (NTRS)

Goodenough, J. B.; Hong, H. Y. P.; Kafalas, J. A.; Dwight, K., Jr.

1975-01-01

It was shown that two body-centered-cubic skeleton structures, the Im3 KSbO3 phase and the defect-pyrochlore phase A(+)B2X6, do exhibit fast Na(+)-ion transport. The placement of anions at the tunnel intersection sites does not impede Na(+)-ion transport in (NaSb)3)(1/6 NaF), and may not in (Na(1+2x)Ta2 5F)(Ox). The activation energies are higher than those found in beta-alumina. There are two possible explanations for the higher activation energy: breathing of the bottleneck (site face or edge) through which the A(+) ions must pass on jumping from one site to another may be easier in a layer structure and/or A(+)-O bonding may be stronger in the cubic structures because the O(2-) ion bonds with two (instead of three) cations of the skeleton. If the former explanation is dominant, a lower activation energy may be achieved by optimizing the lattice parameter. If the latter is dominant, a new structural principle may have to be explored.

Silica-supported isolated gallium sites as highly active, selective and stable propane dehydrogenation catalysts† †Electronic supplementary information (ESI) available: Experimental details, material characterization data, catalytic measurement details and crystallographic details. CCDC 1499756. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc05178b Click here for additional data file. Click here for additional data file.

PubMed Central

Searles, Keith; Siddiqi, Georges; Safonova, Olga V.

2017-01-01

Single-site gallium centers on the surface of silica are prepared via grafting of [Ga(OSi(OtBu)3)3(THF)] on SiO2–700 followed by a thermolysis step. The resulting surface species corresponds to well-defined tetra-coordinate gallium single-sites, [( 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 SiO)3Ga(XOSi)] (X = –H or Si) according to IR, X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis. These gallium sites show high activity, selectivity and stability for propane dehydrogenation with an initial turnover frequency of 20 per h per gallium center, propylene selectivity of ≥93% and remarkable stability over 20 h. The stability of the catalyst probably results from site-isolation of the active site on a non-reducible support such as silica, diminishing facile reduction typical of Ga2O3-based catalysts. PMID:28553501

Electrochemical generation of sulfur vacancies in the basal plane of MoS2 for hydrogen evolution

PubMed Central

Tsai, Charlie; Li, Hong; Park, Sangwook; Park, Joonsuk; Han, Hyun Soo; Nørskov, Jens K.; Zheng, Xiaolin; Abild-Pedersen, Frank

2017-01-01

Recently, sulfur (S)-vacancies created on the basal plane of 2H-molybdenum disulfide (MoS2) using argon plasma exposure exhibited higher intrinsic activity for the electrochemical hydrogen evolution reaction than the edge sites and metallic 1T-phase of MoS2 catalysts. However, a more industrially viable alternative to the argon plasma desulfurization process is needed. In this work, we introduce a scalable route towards generating S-vacancies on the MoS2 basal plane using electrochemical desulfurization. Even though sulfur atoms on the basal plane are known to be stable and inert, we find that they can be electrochemically reduced under accessible applied potentials. This can be done on various 2H-MoS2 nanostructures. By changing the applied desulfurization potential, the extent of desulfurization and the resulting activity can be varied. The resulting active sites are stable under extended desulfurization durations and show consistent HER activity. PMID:28429782

Electrochemical generation of sulfur vacancies in the basal plane of MoS2 for hydrogen evolution

DOE PAGES

Tsai, Charlie; Li, Hong; Park, Sangwook; ...

2017-04-21

Recently, sulfur (S)-vacancies created on the basal plane of 2H-molybdenum disulfide (MoS 2) using argon plasma exposure exhibited higher intrinsic activity for the electrochemical hydrogen evolution reaction than the edge sites and metallic 1T-phase of MoS 2 catalysts. But, a more industrially viable alternative to the argon plasma desulfurization process is needed. In this work, we introduce a scalable route towards generating S-vacancies on the MoS 2 basal plane using electrochemical desulfurization. We found that they can be electrochemically reduced under accessible applied potentials, even though sulfur atoms on the basal plane are known to be stable and inert. Thismore » can be done on various 2H-MoS 2 nanostructures. Furthermore, by changing the applied desulfurization potential, the extent of desulfurization and the resulting activity can be varied. The resulting active sites are stable under extended desulfurization durations and show consistent HER activity.« less

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

NASA Astrophysics Data System (ADS)

Xu, Wei; Li, Yani; Yu, Bo; Yang, Jindou; Zhang, Ying; Chen, Xi; Zhang, Guofang; Gao, Ziwei

2015-01-01

A successive anchoring of Ti(NMe2)4, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1‧-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, 13C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands.

The use of time and space by the Panamanian tamarin, Saguinus oedipus.

PubMed

Dawson, G A

1979-01-01

Tamarin activity patterns and habitat utilization strategies in the Tropical Dry Forest of the Panama Canal Zone were monitored quantitatively using radio-location telemetry. The daily tamarin activity pattern differed from that of other Neotropical primates in that early morning and late afternoon activity normally did not occur. Total daily activity time averaged 676 +/- 62 min. Sleeping trees, and behaviors associated with their use, were documented. Daily path length averaged 2,061 +/- 402 m. Mean travel distance was 468 +/- 66 m. Approximately one-third of the home range was utilized on a given day. Wet season home ranges for two social groups were 26 and 32 ha in area. Areas of low brush, forest edge, and vine-entangled second growth were heavily used by foraging tamarins. Large shade trees, particularly evergreens, were important as refuges from solar radiation. Open-canopy forest types and areas of grass were avoided. Social groups on resource-stable lowland sites defended territories; those on unstable upland sites used a system of time-space segregation. Upland groups became seminomadic during the dry season. Suitability of home range site may affect social group stability, natality, and infant survivorship.

Astronaut John Young stands at ALSEP deployment site during first EVA

NASA Technical Reports Server (NTRS)

1972-01-01

Astronaut John W. Young, commander of the Apollo 16 lunar landing mission, stands at the Apollo Lunar Surface Experiments Package (ALSEP) deployment site during the first Apollo 16 extravehicular activity (EVA-1) at the Descartes landing site. The components of the ALSEP are in the background. The lunar surface drill is just behind and to the right of Young. The drill's rack and bore stems are to the left. The three sensor Lunar Surface Magnetometer is beyond the rack. The dark object in the right background is the Radioisotope Thermoelectric Generator (RTG). Between the RTG and the drill is the Heat Flow Experiment. A part of the Central Station is at the right center edge of the picture. This photograph was taken by Astronaut Charles M. Duke Jr., lunar module pilot.

Plant/soil concentration ratios of SSWRa for contrasting sites around an active U mine-mill

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibrahim, S.A.; Whicker, F.W.

Concentrations of 226Ra were determined in native vegetation and underlying substrate (soil and tailings) at various sites around a conventional open-pit, acid leach U production operation in Wyoming. Plant/soil concentration ratios (CRs) for 226Ra were estimated for various sites, including weathered tailings; a tailings impoundment shoreline; downwind from exposed tailings; a mine overburden reclamation area; and several background locations. Radium-226 concentrations for vegetation and substrate and CR values from the perturbed sites were elevated above background. The highest vegetation concentration (1.3 Bq g-1) was found in a grass which had invaded exposed, weathered tailings. Levels of 226Ra in soil andmore » vegetation and CR values decreased with distance from the tailings impoundment edge. CR values varied significantly among sites, but few differences were found between plant species groups. The observed CR values ranged from 0.07 at the background and reclamation areas to 0.4 downwind from the tailings area. Average CR values for plants growing on exposed tailings and within one meter from the impoundment edge were 0.15 and 0.3, respectively. CR values of 226Ra for plants on tailings substrates were comparatively low in contrast to other radionuclides in the U chain. We speculate that in the case of sulfuric acid leached tailings-derived material, 226Ra is sequestered as sulfate, which is highly insoluble relative to the sulfates of the other elements (e.g., U and Th) resulting in reduced availability for plant uptake.« less

The contact mechanics and occurrence of edge loading in modular metal-on-polyethylene total hip replacement during daily activities.

PubMed

Hua, Xijin; Li, Junyan; Jin, Zhongmin; Fisher, John

2016-06-01

The occurrence of edge loading in hip joint replacement has been associated with many factors such as prosthetic design, component malposition and activities of daily living. The present study aimed to quantify the occurrence of edge loading/contact at the articulating surface and to evaluate the effect of cup angles and edge loading on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR) during different daily activities. A three-dimensional finite element model was developed based on a modular MoP bearing system. Different cup inclination and anteversion angles were modelled and six daily activities were considered. The results showed that edge loading was predicted during normal walking, ascending and descending stairs activities under steep cup inclination conditions (≥55°) while no edge loading was observed during standing up, sitting down and knee bending activities. The duration of edge loading increased with increased cup inclination angles and was affected by the cup anteversion angles. Edge loading caused elevated contact pressure at the articulating surface and substantially increased equivalent plastic strain of the polyethylene liner. The present study suggested that correct positioning the component to avoid edge loading that may occur during daily activities is important for MoP THR in clinical practice. Copyright © 2016. Published by Elsevier Ltd.

Modified edge-to-edge technique for correction of congenital mitral regurgitation in infants and children.

PubMed

Zhang, Gang; Zhang, Fusheng; Zhu, Mei; Zhang, Wenlong; Fan, Quanxin; Zou, Chengwei; Wang, Anbiao

2011-10-01

Since 2008, 28 patients with congenital mitral regurgitation have undergone mitral valve repair with a modified edge-to-edge technique at our institution. The regurgitant mitral leaflet was sutured with a pledget-reinforced, horizontal mattress suture with No. 4-0 polypropylene on the ventricle side and a pledget-reinforced mattress suture with Gore-Tex sutures (W.L. Gore & Associates, Flagstaff, AZ) and Dacron pledgets (Chest, Shanghai) placed on the anterior and posterior annulus corresponding to the edge-to-edge suturing site. Early results are encouraging, but a longer follow-up is needed. Copyright © 2011 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.

Surface complexation modeling of zinc sorption onto ferrihydrite.

PubMed

Dyer, James A; Trivedi, Paras; Scrivner, Noel C; Sparks, Donald L

2004-02-01

A previous study involving lead(II) [Pb(II)] sorption onto ferrihydrite over a wide range of conditions highlighted the advantages of combining molecular- and macroscopic-scale investigations with surface complexation modeling to predict Pb(II) speciation and partitioning in aqueous systems. In this work, an extensive collection of new macroscopic and spectroscopic data was used to assess the ability of the modified triple-layer model (TLM) to predict single-solute zinc(II) [Zn(II)] sorption onto 2-line ferrihydrite in NaNO(3) solutions as a function of pH, ionic strength, and concentration. Regression of constant-pH isotherm data, together with potentiometric titration and pH edge data, was a much more rigorous test of the modified TLM than fitting pH edge data alone. When coupled with valuable input from spectroscopic analyses, good fits of the isotherm data were obtained with a one-species, one-Zn-sorption-site model using the bidentate-mononuclear surface complex, (triple bond FeO)(2)Zn; however, surprisingly, both the density of Zn(II) sorption sites and the value of the best-fit equilibrium "constant" for the bidentate-mononuclear complex had to be adjusted with pH to adequately fit the isotherm data. Although spectroscopy provided some evidence for multinuclear surface complex formation at surface loadings approaching site saturation at pH >/=6.5, the assumption of a bidentate-mononuclear surface complex provided acceptable fits of the sorption data over the entire range of conditions studied. Regressing edge data in the absence of isotherm and spectroscopic data resulted in a fair number of surface-species/site-type combinations that provided acceptable fits of the edge data, but unacceptable fits of the isotherm data. A linear relationship between logK((triple bond FeO)2Zn) and pH was found, given by logK((triple bond FeO)2Znat1g/l)=2.058 (pH)-6.131. In addition, a surface activity coefficient term was introduced to the model to reduce the ionic strength dependence of sorption. The results of this research and previous work with Pb(II) indicate that the existing thermodynamic framework for the modified TLM is able to reproduce the metal sorption data only over a limited range of conditions. For this reason, much work still needs to be done in fine-tuning the thermodynamic framework and databases for the TLM.

Camera identity from minute film-edge mark characteristics.

PubMed

Kuppuswamy, R

2003-07-08

A case is presented in which a camera recovered from a site of bomb blast was linked to some incriminating film negatives by the characteristic markings existing along a small portion of the edge of the film negatives.

Local structure investigation of Ga and Yb dopants in Co 4 Sb 12 skutterudites

DOE PAGES

Hu, Yanyun; Chen, Ning; Clancy, J. P.; ...

2017-12-29

We report our x-ray absorption spectroscopy studies at both Ga K-edge and Yb L 2-edge to elucidate the local structure of Ga and Yb dopants in Yb xGa yCo 4Sb 12. Our extended x-ray absorption fine structure (EXAFS) data confirm that Ga atoms occupy two crystallographic sites: one is the 24g site replacing Sb, and the other is the 2a site in the off-center void position. We find that the occupancy ratio of these two sites varies significantly as a function of the filling fraction of additional Yb, which exclusively occupies the 2a on-center site. At low concentrations of Yb,more » Ga 24g and Ga 2a dopants coexist and they form a charge-compensated compound defect proposed by Qiu et al. [Adv. Mater. 23, 3194 (2013)]. The Ga 24g occupancy increases gradually with increasing Yb concentration, and almost all Ga occupies the 24g site for the highest Yb concentration (x = 0.4). In addition to the local crystal structure evidence provided by our EXAFS data, we also present x-ray absorption near-edge structure (XANES) spectra, which show a small Ga K-edge energy shift as a function of Yb concentration consistent with the change from predominantly Ga 2a to Ga 24g states. Our result suggests that the increased solubility of Yb in Yb-Ga co-doped Co 4Sb 12 skutterudites is due to the increased Ga 24g electron acceptor, and thus provides an important strategy to optimize the carrier concentration in partially filled skutterudites.« less

Local structure investigation of Ga and Yb dopants in Co4Sb12 skutterudites

NASA Astrophysics Data System (ADS)

Hu, Yanyun; Chen, Ning; Clancy, J. P.; Salvador, James R.; Kim, Chang-Yong; Shi, Xiaoya; Li, Qiang; Kim, Young-June

2017-12-01

We report comprehensive x-ray absorption spectroscopy studies at both the Ga K edge and Yb L2 edge to elucidate the local structure of Ga and Yb dopants in YbxGayCo4Sb12 . Our extended x-ray absorption fine structure (EXAFS) data confirm that Ga atoms occupy two crystallographic sites: one is the 24 g site replacing Sb, and the other is the 2 a site in the off-center void position. We find that the occupancy ratio of these two sites varies significantly as a function of the filling fraction of additional Yb, which exclusively occupies the 2 a on-center site. At low concentrations of Yb, Ga24 g and Ga2 a dopants coexist and they form a charge-compensated compound defect proposed by Qiu et al. [Adv. Funct. Mater. 23, 3194 (2013), 10.1002/adfm.201202571]. The Ga24 g occupancy increases gradually with increasing Yb concentration, and almost all Ga occupies the 24 g site for the highest Yb concentration studied (x =0.4 ). In addition to the local structural evidence provided by our EXAFS data, we also present x-ray absorption near-edge structure (XANES) spectra, which show a small Ga K -edge energy shift as a function of Yb concentration consistent with the change from predominantly Ga2 a to Ga24 g states. Our result suggests that the increased solubility of Yb in Yb-Ga co-doped Co4Sb12 skutterudites is due to the increased Ga24 g electron acceptor, and thus provides an important strategy to optimize the carrier concentration in partially filled skutterudites.

Local structure investigation of Ga and Yb dopants in Co 4 Sb 12 skutterudites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Yanyun; Chen, Ning; Clancy, J. P.

We report our x-ray absorption spectroscopy studies at both Ga K-edge and Yb L 2-edge to elucidate the local structure of Ga and Yb dopants in Yb xGa yCo 4Sb 12. Our extended x-ray absorption fine structure (EXAFS) data confirm that Ga atoms occupy two crystallographic sites: one is the 24g site replacing Sb, and the other is the 2a site in the off-center void position. We find that the occupancy ratio of these two sites varies significantly as a function of the filling fraction of additional Yb, which exclusively occupies the 2a on-center site. At low concentrations of Yb,more » Ga 24g and Ga 2a dopants coexist and they form a charge-compensated compound defect proposed by Qiu et al. [Adv. Mater. 23, 3194 (2013)]. The Ga 24g occupancy increases gradually with increasing Yb concentration, and almost all Ga occupies the 24g site for the highest Yb concentration (x = 0.4). In addition to the local crystal structure evidence provided by our EXAFS data, we also present x-ray absorption near-edge structure (XANES) spectra, which show a small Ga K-edge energy shift as a function of Yb concentration consistent with the change from predominantly Ga 2a to Ga 24g states. Our result suggests that the increased solubility of Yb in Yb-Ga co-doped Co 4Sb 12 skutterudites is due to the increased Ga 24g electron acceptor, and thus provides an important strategy to optimize the carrier concentration in partially filled skutterudites.« less

40 CFR 228.5 - General criteria for the selection of sites.

Code of Federal Regulations, 2013 CFR

2013-07-01

... levels or to undetectable contaminant concentrations or effects before reaching any beach, shoreline..., designate ocean dumping sites beyond the edge of the continental shelf and other such sites that have been...

40 CFR 228.5 - General criteria for the selection of sites.

Code of Federal Regulations, 2014 CFR

2014-07-01

... levels or to undetectable contaminant concentrations or effects before reaching any beach, shoreline..., designate ocean dumping sites beyond the edge of the continental shelf and other such sites that have been...

40 CFR 228.5 - General criteria for the selection of sites.

Code of Federal Regulations, 2011 CFR

2011-07-01

... levels or to undetectable contaminant concentrations or effects before reaching any beach, shoreline..., designate ocean dumping sites beyond the edge of the continental shelf and other such sites that have been...

40 CFR 228.5 - General criteria for the selection of sites.

Code of Federal Regulations, 2010 CFR

2010-07-01

... levels or to undetectable contaminant concentrations or effects before reaching any beach, shoreline..., designate ocean dumping sites beyond the edge of the continental shelf and other such sites that have been...

40 CFR 228.5 - General criteria for the selection of sites.

Code of Federal Regulations, 2012 CFR

2012-07-01

... levels or to undetectable contaminant concentrations or effects before reaching any beach, shoreline..., designate ocean dumping sites beyond the edge of the continental shelf and other such sites that have been...

Assessment of AVIRIS data from vegetated sites in the Owens Valley, California

NASA Technical Reports Server (NTRS)

Rock, B. N.; Elvidge, Christopher D.; Defeo, N. J.

1988-01-01

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data were acquired from the Bishop, CA area, located at the northern end of the Owens Valley, on July 30, 1987. Radiometrically-corrected AVIRIS data were flat-field corrected, and spectral curves produced and analyzed for pixels taken from both native and cultivated vegetation sites, using the JPS SPAM software program and PC-based spreadsheet programs. Analyses focussed on the chlorophyll well and red edge portions of the spectral curves. Results include the following: AVIRIS spectral data are acquired at sufficient spectral resolution to allow detection of blue shifts of both the chlorophyll well and red edge in moisture-stressed vegetation when compared with non-stressed vegetation; a normalization of selected parameters (chlorophyll well and near infrared shoulder) may be used to emphasize the shift in red edge position; and the presence of the red edge in AVIRIS spectral curves may be useful in detecting small amounts (20 to 30 pct cover) of semi-arid and arid vegetation ground cover. A discussion of possible causes of AVIRIS red edge shifts in respsonse to stress is presented.

Hooded Warbler Nesting Success Adjacent to Group-selection and Clearcut Edges in a Southeastern Bottomland Forest

Treesearch

Christopher E. Moorman; David C. Guynn; John C. Kilgo

2002-01-01

During the 1996, 1997, and 199X breeding seasons, WC located and monitored Hooded Warbler (Wilsonia citrina) nests in a bottomland forest and examined the effects of edge proximity, edge type, and nest-site vegetation on nesting success. SW- cessful Hooded Warbler nests were more concealed from below and were located in nest patches with a greater...

Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

DOE PAGES

Getsoian, Andrew "Bean"; Das, Ujjal; Camacho-Bunquin, Jeffrey; ...

2016-06-13

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order tomore » better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. Furthermore, these findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.« less

Survey of techniques for reduction of wind turbine blade trailing edge noise.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barone, Matthew Franklin

2011-08-01

Aerodynamic noise from wind turbine rotors leads to constraints in both rotor design and turbine siting. The primary source of aerodynamic noise on wind turbine rotors is the interaction of turbulent boundary layers on the blades with the blade trailing edges. This report surveys concepts that have been proposed for trailing edge noise reduction, with emphasis on concepts that have been tested at either sub-scale or full-scale. These concepts include trailing edge serrations, low-noise airfoil designs, trailing edge brushes, and porous trailing edges. The demonstrated noise reductions of these concepts are cited, along with their impacts on aerodynamic performance. Anmore » assessment is made of future research opportunities in trailing edge noise reduction for wind turbine rotors.« less

Subalpine Conifer Seedling Demographics: Species Responses to Climate Manipulations Across an Elevational Gradient at Niwot Ridge, Colorado

NASA Astrophysics Data System (ADS)

Castanha, C.; Germino, M. J.; Torn, M. S.; Ferrenberg, S.; Harte, J.; Kueppers, L. M.

2010-12-01

The effect of climate change on future ranges of treeline species is poorly understood. For example, it is not known whether trees will recruit into the alpine, above the current treeline, and whether population-level differences in trees will mediate range shifts. At Niwot Ridge, Colorado, we used common gardens and climate manipulations to test predictions that warming will lead to greater recruitment at and beyond the cold edge of these species ranges, and will reduce recruitment at the warm edge. Seed from local populations of limber pine and Englemann spruce was harvested and reciprocally planted in 3 experimental sites spanning an elevation gradient from lower subalpine forest (10,000’), to the upper subalpine treeline ecotone (11,000’), to the alpine tundra (11,300’). In Fall 2009 seeds were sown into 20 plots at each site. Overhead infrared heaters targeted increases in growing season surface soil temperature of 4-5°C. The heating treatment, which began in October 2009, was crossed with manual watering, which was initiated following snowmelt in 2010. Over the 2010 growing season, we surveyed seedling germination and mortality weekly. Germination began in early May at the forest site, in early June at the krummholz site, and in early July at the alpine site. Depending on the site and plot, heating accelerated germination by 1 to 4 weeks. Seed source elevation, species, and site all affected germination, with effects for the two species also depending on site. At all sites, lower elevation, warm-edge populations had higher germination rates than high-elevation, cool-edge populations, indicating a potential bottleneck for germination of the high elevation seed sources in the adjacent alpine tundra. At all sites, survival was generally higher for pine than for spruce. Watering tended to enhance pine germinant survival while heating tended to depress spruce germinant survival. Our results indicate that the alpine tundra, generally considered an inhospitable environment, was not favorable for Englemann spruce, even with warming. In contrast, once seeds were introduced, the alpine tundra proved favorable to limber pine germination, irrespective of the climate manipulation.

Molecular Dynamics Simulation of Resin Adsorption at Kaolinite Edge Sites: Effect of Surface Deprotonation on Interfacial Structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeitler, T. R.; Greathouse, J. A.; Cygan, R. T.

Low-salinity water flooding, a method of enhanced oil recovery, consists of injecting low ionic strength fluids into an oil reservoir in order to detach oil from mineral surfaces in the underlying formation. Although highly successful in practice, the approach is not completely understood at the molecular scale. Molecular dynamics simulations have been used to investigate the effect of surface protonation on the adsorption of an anionic crude oil component on clay mineral edge surfaces. A set of interatomic potentials appropriate for edge simulations has been applied to the kaolinite (010) surface in contact with an aqueous nanopore. Decahydro-2-napthoic acid inmore » its deprotonated form (DHNA –) was used as a representative resin component of crude oil, with monovalent and divalent counterions, to test the observed trends in low-salinity water flooding experiments. Surface models include fully protonated (neutral) and deprotonated (negative) edge sites, which require implementation of a new deprotonation scheme. The surface adsorptive properties of the kaolinite edge under neutral and deprotonated conditions have been investigated for low and high DHNA – concentrations with Na + and Ca 2+ as counterions. The tendency of DHNA – ions to coordinate with divalent (Ca 2+) rather than monovalent (Na +) ions greatly influences adsorption tendencies of the anion. Additionally, the formation of net positively charged surface sites due to Ca 2+ at deprotonated sites results in increased DHNA – adsorption. Divalent cations such as Ca 2+ are able to efficiently bridge surface sites and organic anions. Replacing those cations with monovalent cations such as Na + diminishes the bridging mechanism, resulting in reduced adsorption of the organic species. As a result, a clear trend of decreased DHNA – adsorption is observed in the simulations as Ca 2+ is replaced by Na + for deprotonated surfaces, as would be expected for oil detachment from reservoir formations following a low-salinity flooding event.« less

Molecular Dynamics Simulation of Resin Adsorption at Kaolinite Edge Sites: Effect of Surface Deprotonation on Interfacial Structure

DOE PAGES

Zeitler, T. R.; Greathouse, J. A.; Cygan, R. T.; ...

2017-10-05

Low-salinity water flooding, a method of enhanced oil recovery, consists of injecting low ionic strength fluids into an oil reservoir in order to detach oil from mineral surfaces in the underlying formation. Although highly successful in practice, the approach is not completely understood at the molecular scale. Molecular dynamics simulations have been used to investigate the effect of surface protonation on the adsorption of an anionic crude oil component on clay mineral edge surfaces. A set of interatomic potentials appropriate for edge simulations has been applied to the kaolinite (010) surface in contact with an aqueous nanopore. Decahydro-2-napthoic acid inmore » its deprotonated form (DHNA –) was used as a representative resin component of crude oil, with monovalent and divalent counterions, to test the observed trends in low-salinity water flooding experiments. Surface models include fully protonated (neutral) and deprotonated (negative) edge sites, which require implementation of a new deprotonation scheme. The surface adsorptive properties of the kaolinite edge under neutral and deprotonated conditions have been investigated for low and high DHNA – concentrations with Na + and Ca 2+ as counterions. The tendency of DHNA – ions to coordinate with divalent (Ca 2+) rather than monovalent (Na +) ions greatly influences adsorption tendencies of the anion. Additionally, the formation of net positively charged surface sites due to Ca 2+ at deprotonated sites results in increased DHNA – adsorption. Divalent cations such as Ca 2+ are able to efficiently bridge surface sites and organic anions. Replacing those cations with monovalent cations such as Na + diminishes the bridging mechanism, resulting in reduced adsorption of the organic species. As a result, a clear trend of decreased DHNA – adsorption is observed in the simulations as Ca 2+ is replaced by Na + for deprotonated surfaces, as would be expected for oil detachment from reservoir formations following a low-salinity flooding event.« less

Simulation of clustering and anisotropy due to Co step-edge segregation in vapor-deposited CoPt3

NASA Astrophysics Data System (ADS)

Maranville, B. B.; Schuerman, M.; Hellman, F.

2006-03-01

An atomistic mechanism is proposed for the creation of structural anisotropy and consequent large perpendicular magnetic anisotropy in vapor-deposited films of CoPt3 . Energetic considerations of bonding in Co-Pt suggest that Co segregates to step edges due to their low coordination, for all film orientations, while Pt segregates to the two low index surfaces. Coalescence of islands during growth cause these Co-rich step edges to become flat thin Co platelets in a Pt rich matrix, giving rise to the experimentally observed magnetic anisotropy. This proposed model is tested with kinetic Monte Carlo simulation of the vapor deposition growth. A tight-binding, second-moment approximation to the interatomic potential is used to calculate the probability of an atom hopping from one surface site to another, assuming an Arrhenius-like activation model of surface motion. Growth is simulated by allowing many hopping events per adatom. The simulated as-grown films show an asymmetry in Co-Co bonding between the in-plane and out-of-plane directions, in good agreement with experimental data. The growth temperature dependence found in the simulations is strong and similar to that seen in experiments, and an increase in Co edge segregation with increasing temperature is also observed.

Edge-enriched, porous carbon-based, high energy density supercapacitors for hybrid electric vehicles.

PubMed

Kim, Yong Jung; Yang, Cheol-Min; Park, Ki Chul; Kaneko, Katsumi; Kim, Yoong Ahm; Noguchi, Minoru; Fujino, Takeshi; Oyama, Shigeki; Endo, Morinobu

2012-03-12

Supercapacitors can store and deliver energy by a simple charge separation, and thus they could be an attractive option to meet transient high energy density in operating fuel cells and in electric and hybrid electric vehicles. To achieve such requirements, intensive studies have been carried out to improve the volumetric capacitance in supercapacitors using various types and forms of carbons including carbon nanotubes and graphenes. However, conventional porous carbons are not suitable for use as electrode material in supercapacitors for such high energy density applications. Here, we show that edge-enriched porous carbons are the best electrode material for high energy density supercapacitors to be used in vehicles as an auxiliary powertrain. Molten potassium hydroxide penetrates well-aligned graphene layers vertically and consequently generates both suitable pores that are easily accessible to the electrolyte and a large fraction of electrochemically active edge sites. We expect that our findings will motivate further research related to energy storage devices and also environmentally friendly electric vehicles. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hanguang; Hwang, Sooyeon; Wang, Maoyu

To significantly reduce the cost of proton exchange membrane (PEM) fuel cells, current Pt must be replaced by platinum-metal-group (PGM)-free catalysts for the oxygen reduction reaction (ORR) in acid. We report here a new class of high-performance atomic iron dispersed carbon catalysts through controlled chemical doping of iron ions into zinc-zeolitic imidazolate framework (ZIF), a type of metal-organic framework (MOF). The novel synthetic chemistry enables accurate size control of Fe-doped ZIF catalyst particles with a wide range from 20 to 1000 nm without changing chemical properties, which provides a great opportunity to increase the density of active sites that ismore » determined by the particle size. We elucidated the active site formation mechanism by correlating the chemical and structural changes with thermal activation process for the conversion from Fe-N4 complex containing hydrocarbon networks in ZIF to highly active FeNx sites embedded into carbon. A temperature of 800oC was identified as the critical point to start forming pyridinic nitrogen doping at the edge of the graphitized carbon planes. Further increasing heating temperature to 1100oC leads to increase of graphitic nitrogen, generating possible synergistic effect with FeNx sites to promote ORR activity. The best performing catalyst, which has well-defined particle size around 50 nm and abundance of atomic FeNx sites embedded into carbon structures, achieve a new performance milestone for the ORR in acid including a half-wave potential of 0.85 V vs RHE and only 20 mV loss after 10,000 cycles in O2 saturated H2SO4 electrolyte. The new class PGM-free catalyst with approaching activity to Pt holds great promise for future PEM fuel cells.« less

Modeling CH 4 and CO 2 cycling using porewater stable isotopes in a thermokarst bog in Interior Alaska: results from three conceptual reaction networks

DOE PAGES

Neumann, Rebecca B.; Blazewicz, Steven J.; Conaway, Christopher H.; ...

2015-12-16

Quantifying rates of microbial carbon transformation in peatlands is essential for gaining mechanistic understanding of the factors that influence methane emissions from these systems, and for predicting how emissions will respond to climate change and other disturbances. In this study, we used porewater stable isotopes collected from both the edge and center of a thermokarst bog in Interior Alaska to estimate in situ microbial reaction rates. We expected that near the edge of the thaw feature, actively thawing permafrost and greater abundance of sedges would increase carbon, oxygen and nutrient availability, enabling faster microbial rates relative to the center ofmore » the thaw feature. We developed three different conceptual reaction networks that explained the temporal change in porewater CO2, CH4, δ13C-CO2 and δ13C-CH4. All three reaction-network models included methane production, methane oxidation and CO2 production, and two of the models included homoacetogenesis — a reaction not previously included in isotope-based porewater models. All three models fit the data equally well, but rates resulting from the models differed. Most notably, inclusion of homoacetogenesis altered the modeled pathways of methane production when the reaction was directly coupled to methanogenesis, and it decreased gross methane production rates by up to a factor of five when it remained decoupled from methanogenesis. The ability of all three conceptual reaction networks to successfully match the measured data indicate that this technique for estimating in-situ reaction rates requires other data and information from the site to confirm the considered set of microbial reactions. Despite these differences, all models indicated that, as expected, rates were greater at the edge than in the center of the thaw bog, that rates at the edge increased more during the growing season than did rates in the center, and that the ratio of acetoclastic to hydrogenotrophic methanogenesis was greater at the edge than in the center. In both locations, modeled rates (excluding methane oxidation) increased with depth. A puzzling outcome from the effort was that none of the models could fit the porewater dataset without generating “fugitive” carbon (i.e., methane or acetate generated by the models but not detected at the field site), indicating that either our conceptualization of the reactions occurring at the site remains incomplete or our site measurements are missing important carbon transformations and/or carbon fluxes. This model–data discrepancy will motivate and inform future research efforts focused on improving our understanding of carbon cycling in permafrost wetlands.« less

Variation in Ground Shaking on the Fraser River Delta (Greater Vancouver, Canada)

NASA Astrophysics Data System (ADS)

Cassidy, J. F.; Rogers, G. R.

2003-04-01

The thick, soft soils of the Fraser River delta, just south of Vancouver, Canada, are home to critical infrastructure such as one of North America's busiest port facilities, Canada's second busiest airport, and key transportation and power-transmission facilities for 2-3 million people. This area is also one of the most seismically active regions in Canada. We have utilised recent three-component, digital records of recent moderate (1996 M=5.1 at 200 km distance, 1997 M=4.3 at 40 km distance) and large (2001 M=6.8 at 300 km distance) earthquakes to examine the response to seismic shaking in the greater Vancouver, region, with an emphasis on the site response of the Fraser River delta. These suites of accelerograms have relatively low amplitudes (maximums of 0.015g for the 1996 records, 0.024g for the 1997 records, and 0.035g for the 2001 records). The 1997 data set is significant as it contains the first three-component recordings made on bedrock in greater Vancouver, and the 2001 data set is significant as it contains long-period signal (1-10 second energy). Using the method of spectral ratios, we estimate the site response for each of the strong motion instrument soil sites. Our results show frequency-dependent amplification, with factors of up to 12 times (relative to competent bedrock) near the edge of the delta. Here, the amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period). Near the centre of the delta(where the soft soils are thickest) peak amplification of 4-10 times(relative to competent bedrock) is measured. Relative to firm soil, the peak amplification ranges from 2-5 for the thick soil delta centre sites, and 2-6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation is observed. The more distant earthquakes (200-300 km) present a simpler and more predictable picture of ground motion variation than that of the 1997 earthquake (40 km distant). The Geological Survey of Canada is currently deploying a demonstration dense urban seismograph network (~1km spacing) which crosses the northern edge of the Fraser delta in the greater Vancouver area to address varying site response in more detail.

Interactions on External MOF Surfaces: Desorption of Water and Ethanol from CuBDC Nanosheets.

PubMed

Elder, Alexander C; Aleksandrov, Alexandr B; Nair, Sankar; Orlando, Thomas M

2017-10-03

The external surfaces of metal-organic framework (MOF) materials are difficult to experimentally isolate due to the high porosities of these materials. MOF surface surrogates in the form of copper benzenedicarboxylate (CuBDC) nanosheets were synthesized using a bottom-up approach, and the surface interactions of water and ethanol were investigated by temperature-programmed desorption (TPD). A method of analysis of diffusion-influenced TPD was developed to measure the desorption properties of these porous materials. This approach also allows the extraction of diffusion coefficients from TPD data. The transmission Fourier transform infrared spectra, powder X-ray diffraction patterns, and TPD data indicate that water desorbs from CuBDC nanosheets with activation energies of 44 ± 2 kJ/mol at edge sites and 58 ± 1 kJ/mol at external surface and internal and pore sites. Ethanol desorbs with activation energies of 58 ± 1 kJ/mol at internal pore sites and 66 ± 0.4 kJ/mol at external surface sites. Co-adsorption of water and ethanol was also investigated. The presence of ethanol was found to inhibit the desorption of water, resulting in a water desorption process with an activation energy of 68 ± 0.7 kJ/mol.

Differences in mobility at the range edge of an expanding invasive population of Xenopus laevis in the west of France.

PubMed

Louppe, Vivien; Courant, Julien; Herrel, Anthony

2017-01-15

Theoretical models predict that spatial sorting at the range edge of expanding populations should favor individuals with increased mobility relative to individuals at the center of the range. Despite the fact that empirical evidence for the evolution of locomotor performance at the range edge is rare, data on cane toads support this model. However, whether this can be generalized to other species remains largely unknown. Here, we provide data on locomotor stamina and limb morphology in individuals from two sites: one from the center and one from the periphery of an expanding population of the clawed frog Xenopus laevis in France where it was introduced about 30 years ago. Additionally, we provide data on the morphology of frogs from two additional sites to test whether the observed differences can be generalized across the range of this species in France. Given the known sexual size dimorphism in this species, we also test for differences between the sexes in locomotor performance and morphology. Our results show significant sexual dimorphism in stamina and morphology, with males having longer legs and greater stamina than females. Moreover, in accordance with the predictions from theoretical models, individuals from the range edge had a greater stamina. This difference in locomotor performance is likely to be driven by the significantly longer limb segments observed in animals in both sites sampled in different areas along the range edge. Our data have implications for conservation because spatial sorting on the range edge may lead to an accelerated increase in the spread of this invasive species in France. © 2017. Published by The Company of Biologists Ltd.

Unveiling the water-associated conformational mobility in the active site of ascorbate peroxidase.

PubMed

Chao, Wei-Chih; Lin, Li-Ju; Lu, Jyh-Feng; Wang, Jinn-Shyan; Lin, Tzu-Chieh; Chen, Yi-Han; Chen, Yi-Ting; Yang, Hsiao-Ching; Chou, Pi-Tai

2018-03-01

We carried out comprehensive spectroscopic studies of wild type and mutants of ascorbate peroxidase (APX) to gain understanding of the conformational mobility of the active site. In this approach, three unnatural tryptophans were applied to replace the distal tryptophan (W41) in an aim to probe polarity/water environment near the edge of the heme-containing active site. 7-azatryptophan ((7-aza)Trp) is sensitive to environment polarity, while 2,7-azatryptophan ((2,7-aza)Trp) and 2,6-diazatryptophan ((2,6-aza)Trp) undergo excited-state water-catalyzed double and triple proton transfer, respectively, and are sensitive to the water network. The combination of their absorption, emission bands and the associated relaxation dynamics of these fluorescence probes, together with the Soret-band difference absorption and resonance Raman spectroscopy, lead us to unveil the water associated conformational mobility in the active site of APX. The results are suggestive of the existence of equilibrium between two different environments surrounding W41 in APX, i.e., the water-rich and water-scant forms with distinct fluorescence relaxation. Our results thus demonstrate for the first time the power of integrating multiple sensors (7-aza)Trp, (2,7-aza)Trp and (2,6-aza)Trp in probing the water environment of a specifically targeted Trp in proteins. Copyright © 2017 Elsevier B.V. All rights reserved.

Influence of point defects on the near edge structure of hexagonal boron nitride

NASA Astrophysics Data System (ADS)

McDougall, Nicholas L.; Partridge, Jim G.; Nicholls, Rebecca J.; Russo, Salvy P.; McCulloch, Dougal G.

2017-10-01

Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor with applications including gate insulation layers in graphene transistors, far-ultraviolet light emitting devices and as hydrogen storage media. Due to its complex microstructure, defects in hBN are challenging to identify. Here, we combine x-ray absorption near edge structure (XANES) spectroscopy with ab initio theoretical modeling to identify energetically favorable defects. Following annealing of hBN samples in vacuum and oxygen, the B and N K edges exhibited angular-dependent peak modifications consistent with in-plane defects. Theoretical calculations showed that the energetically favorable defects all produce signature features in XANES. Comparing these calculations with experiments, the principle defects were attributed to substitutional oxygen at the nitrogen site, substitutional carbon at the boron site, and hydrogen passivated boron vacancies. Hydrogen passivation of defects was found to significantly affect the formation energies, electronic states, and XANES. In the B K edge, multiple peaks above the major 1 s to π* peak occur as a result of these defects and the hydrogen passivated boron vacancy produces the frequently observed doublet in the 1 s to σ* transition. While the N K edge is less sensitive to defects, features attributable to substitutional C at the B site were observed. This defect was also calculated to have mid-gap states in its band structure that may be responsible for the 4.1-eV ultraviolet emission frequently observed from this material.

Comparison between infaunal communities of the deep floor and edge of the Tonga Trench: Possible effects of differences in organic matter supply

NASA Astrophysics Data System (ADS)

Leduc, Daniel; Rowden, Ashley A.; Glud, Ronnie N.; Wenzhöfer, Frank; Kitazato, Hiroshi; Clark, Malcolm R.

2016-10-01

Hadal trenches are characterised by environmental conditions not found in any other environment, thereby providing new opportunities to understand the processes that shape deep-sea benthic communities. Technological advances have led to an increase in the number of investigations in hadal trenches over the last two decades. However, more quantitative samples including the deepest parts of trenches is needed to better understand trends in benthic diversity, abundance, biomass and community structure in these extreme habitats, and how these may be shaped by environmental and/or evolutionary factors. In this study, we describe and compare the abundance, biomass, vertical distribution in the sediment, diversity, and community structure of nematodes and other infauna in sediments from the Horizon Deep ( 10 800 m) in the Tonga Trench and a site on the edge of the trench ( 6250 m). Mean nematode abundance was six times greater at the Horizon Deep site (387 ind. 10 cm-2) than at the trench edge site (65 ind. 10 cm-2). A similar pattern was observed for biomass (15 vs 2 μgDW 10 cm-2, respectively), which likely resulted from elevated organic matter supply at the Horizon Deep site. There was no significant difference in nematode species richness between the two sites, but diversity measured using rarefaction was significantly greater at the trench edge site than at the Horizon Deep site [ES(20); 13.8 vs 7.8]. Dominance was much more pronounced in the Horizon Deep, which may be due to competitive exclusion by a small number of opportunistic species. Nematode community structure differed significantly both between sites and among sediment depth layers. The presence of subsurface peaks in pigment concentrations, bacteria abundance, and nematode abundance at the Horizon Deep site is consistent with a recent turbidite event, and may also reflect high rates of bioturbation by larger fauna resulting from high food availability. Determining the relative influences of different environmental factors on hadal trench benthic communities will require further investigation based on quantitative samples encompassing the trench axis as well as the oceanic and continental slopes.

Electronic structure of Cr doped Fe3O4 thin films by X-ray absorption near-edge structure spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Chi-Liang; Dong, Chung-Li; Asokan, Kandasami; Chern, G.; Chang, C. L.

2018-04-01

Present study reports the electronic structures of Cr doped Fe3O4 (Fe3-xCrxO4 (0 ≤ x ≤ 3) grown on MgO (100) substrates in the form of thin films fabricated by a plasma-oxygen assisted Molecular Beam Epitaxy (MBE). X-ray absorption near-edge structure (XANES) spectra at Cr & Fe L-, and O K-edges were used to understand the electronic structure: changes in the bonding nature, valence states, and site occupancies. Cr doping in Fe3O4 results in the change of charge transfer, crystal structure, and selective occupation of ions in octahedral and tetrahedral sites. Such change modifies the electrical and magnetic properties due to the covalency of Cr ions. The physical and chemical properties of ferrites are strongly dependent on the lattice site, ion size of dopant, and magnetic nature present at different structural symmetry of the spinel structure.

Spectroscopic and computational insight into the activation of O2 by the mononuclear Cu center in polysaccharide monooxygenases.

PubMed

Kjaergaard, Christian H; Qayyum, Munzarin F; Wong, Shaun D; Xu, Feng; Hemsworth, Glyn R; Walton, Daniel J; Young, Nigel A; Davies, Gideon J; Walton, Paul H; Johansen, Katja Salomon; Hodgson, Keith O; Hedman, Britt; Solomon, Edward I

2014-06-17

Strategies for O2 activation by copper enzymes were recently expanded to include mononuclear Cu sites, with the discovery of the copper-dependent polysaccharide monooxygenases, also classified as auxiliary-activity enzymes 9-11 (AA9-11). These enzymes are finding considerable use in industrial biofuel production. Crystal structures of polysaccharide monooxygenases have emerged, but experimental studies are yet to determine the solution structure of the Cu site and how this relates to reactivity. From X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopies, we observed a change from four-coordinate Cu(II) to three-coordinate Cu(I) of the active site in solution, where three protein-derived nitrogen ligands coordinate the Cu in both redox states, and a labile hydroxide ligand is lost upon reduction. The spectroscopic data allowed for density functional theory calculations of an enzyme active site model, where the optimized Cu(I) and (II) structures were consistent with the experimental data. The O2 reactivity of the Cu(I) site was probed by EPR and stopped-flow absorption spectroscopies, and a rapid one-electron reduction of O2 and regeneration of the resting Cu(II) enzyme were observed. This reactivity was evaluated computationally, and by calibration to Cu-superoxide model complexes, formation of an end-on Cu-AA9-superoxide species was found to be thermodynamically favored. We discuss how this thermodynamically difficult one-electron reduction of O2 is enabled by the unique protein structure where two nitrogen ligands from His1 dictate formation of a T-shaped Cu(I) site, which provides an open coordination position for strong O2 binding with very little reorganization energy.

Tuning the Selectivity of Single-Site Supported Metal Catalysts with Ionic Liquids

DOE PAGES

Babucci, Melike; Fang, Chia -Yu; Hoffman, Adam S.; ...

2017-09-11

1,3-Dialkylimidazolium ionic liquid coatings act as electron donors, increasing the selectivity for partial hydrogenation of 1,3-butadiene catalyzed by iridium complexes supported on high-surface-area γ-Al 2O 3. High-energy-resolution fluorescence detection X-ray absorption near-edge structure (HERFD XANES) measurements quantify the electron donation and are correlated with the catalytic activity and selectivity. Furthermore, the results demonstrate broad opportunities to tune electronic environments and catalytic properties of atomically dispersed supported metal catalysts.

Recording and labeling at a site along the cochlea shows alignment of medial olivocochlear and auditory nerve tonotopic mappings

PubMed Central

2016-01-01

Medial olivocochlear (MOC) neurons provide an efferent innervation to outer hair cells (OHCs) of the cochlea, but their tonotopic mapping is incompletely known. In the present study of anesthetized guinea pigs, the MOC mapping was investigated using in vivo, extracellular recording, and labeling at a site along the cochlear course of the axons. The MOC axons enter the cochlea at its base and spiral apically, successively turning out to innervate OHCs according to their characteristic frequencies (CFs). Recordings made at a site in the cochlear basal turn yielded a distribution of MOC CFs with an upper limit, or “edge,” due to usually absent higher-CF axons that presumably innervate more basal locations. The CFs at the edge, normalized across preparations, were equal to the CFs of the auditory nerve fibers (ANFs) at the recording sites (near 16 kHz). Corresponding anatomical data from extracellular injections showed spiraling MOC axons giving rise to an edge of labeling at the position of a narrow band of labeled ANFs. Overall, the edges of the MOC CFs and labeling, with their correspondences to ANFs, suggest similar tonotopic mappings of these efferent and afferent fibers, at least in the cochlear basal turn. They also suggest that MOC axons miss much of the position of the more basally located cochlear amplifier appropriate for their CF; instead, the MOC innervation may be optimized for protection from damage by acoustic overstimulation. PMID:26823515

Recording and labeling at a site along the cochlea shows alignment of medial olivocochlear and auditory nerve tonotopic mappings.

PubMed

Brown, M Christian

2016-03-01

Medial olivocochlear (MOC) neurons provide an efferent innervation to outer hair cells (OHCs) of the cochlea, but their tonotopic mapping is incompletely known. In the present study of anesthetized guinea pigs, the MOC mapping was investigated using in vivo, extracellular recording, and labeling at a site along the cochlear course of the axons. The MOC axons enter the cochlea at its base and spiral apically, successively turning out to innervate OHCs according to their characteristic frequencies (CFs). Recordings made at a site in the cochlear basal turn yielded a distribution of MOC CFs with an upper limit, or "edge," due to usually absent higher-CF axons that presumably innervate more basal locations. The CFs at the edge, normalized across preparations, were equal to the CFs of the auditory nerve fibers (ANFs) at the recording sites (near 16 kHz). Corresponding anatomical data from extracellular injections showed spiraling MOC axons giving rise to an edge of labeling at the position of a narrow band of labeled ANFs. Overall, the edges of the MOC CFs and labeling, with their correspondences to ANFs, suggest similar tonotopic mappings of these efferent and afferent fibers, at least in the cochlear basal turn. They also suggest that MOC axons miss much of the position of the more basally located cochlear amplifier appropriate for their CF; instead, the MOC innervation may be optimized for protection from damage by acoustic overstimulation. Copyright © 2016 the American Physiological Society.

Astronaut John Young stands at ALSEP deployment site during first EVA

NASA Image and Video Library

1972-04-21

AS16-114-18388 (21 April 1972) --- Astronaut John W. Young, commander of the Apollo 16 lunar landing mission, stands at the Apollo Lunar Surface Experiments Package (ALSEP) deployment site during the first Apollo 16 extravehicular activity (EVA) at the Descartes landing site. The components of the ALSEP are in the background. The lunar surface drill is just behind and to the right of astronaut Young. The drill's rack and bore stems are to the left. The three-sensor Lunar Surface Magnetometer is beyond the rack. The dark object in the right background is the Radioisotope Thermoelectric Generator (RTG). Between the RTG and the drill is the Heat Flow Experiment. A part of the Central Station is at the right center edge of the picture. This photograph was taken by astronaut Charles M. Duke Jr., lunar module pilot.

Breeding biology of an afrotropical forest understory bird community in northeastern Tanzania

USGS Publications Warehouse

Mkongewa, Victor J.; Newmark, William D.; Stanley, Thomas R.

2013-01-01

Many aspects of the breeding biology of Afrotropical forest birds are poorly known. Here we provide a description based on the monitoring of 1461 active nests over eight breeding seasons about one or more aspects of the breeding biology for 28 coexisting understory bird species on the Amani Plateau in the East Usambara Mountains, Tanzania. Mean nest height and mean distance of nest from forest edge varied widely among species with most species constructing nests across a broad vertical and forest edge to interior gradient. However, there were important exceptions with all sunbird species and several dove and waxbill species constructing nests in close proximity to the forest edge. For 17 common species for which we recorded two or more active nests, mean clutch size across species was 1.9 eggs per clutch, the lowest site-specific mean clutch size yet reported for a tropical forest bird community. For nine bird species, a subset of the 17 common species, length of breeding season, defined as the difference between the earliest and latest recorded incubation onset date, ranged from 88–139 days. Most of these nine species displayed a unimodal distribution in incubation onset dates across a breeding season which extended from the end of August through middle January. In summary, a wide variation exists in most aspects of the breeding biology within an understory forest bird community in the East Usambara Mountains.

A high pressure La K-edge X-ray absorption fine structure spectroscopy investigation of La1/3NbO3

NASA Astrophysics Data System (ADS)

Marini, C.; Joseph, B.; Noked, O.; Shuker, R.; Kennedy, B. J.; Mathon, O.; Pascarelli, S.; Sterer, E.

2018-01-01

La K-edge X-ray absorption spectroscopy has been used to elucidate the changes in the local electronic and lattice structure that occur in the A-site deficient double perovskite La?NbO? up to 6 GPa. The pressure evolution of the oxygen dodecahedrum around the A-site has been examined. XANES (X-ray absorption near edge structure) data show modifications ascribed to the increase of bands overlapping as a consequence of the bond distance contraction, which has been directly probed by EXAFS (extended x-ray absorption fine structure) spectra. The La-O Debye Waller factors (DWFs) tend to increase whereas the La-Nb bond DWFs show only a tendency to decrease indicating the robustness of the crystal lattice structure, even in presence of the oxygen disordering. This permits the system to reverse back to its original conditions in this pressure range as evident from the measurements upon pressure release. The present results have been interpreted in the light of charge transfer related to the two-step reduction mechanism acting at the Nb site (with niobium ions passing from Nb? to Nb?) which also results in the elongation of the Nb-O bond distances in the octahedra, in agreement with the Nb K-edge results reported earlier.

Effective rate constants for nanostructured heterogeneous catalysts

NASA Astrophysics Data System (ADS)

Hendy, Shaun; Gaston, Nicola; Zhang, Philip; Lund, Nat

2012-02-01

There is currently a high level of interest in the use of nanostructured materials for catalysis. For instance, gold, which is largely inert in the bulk, can exhibit strong catalytic activity when in nanoparticle form. With precious metal catalysts such as Pt and Pd in high demand, the use of these materials in nanoparticle form can also substantially reduce costs by exposure of more surface area for the same volume of material. When reactants are plentiful, the effective activity of a nanoparticulate catalyst will increase roughly with its surface area. However, under diffusion-limited conditions, the reactant must diffuse to active sites on the catalyst, so a high surface area and a high density of active sites may bring diminishing returns if reactant is consumed faster than it arrives. Here we apply a mathematical homogenisation approach to derive simple expressions for the effective reactivity of a nanostructured catalyst under diffusion limited conditions that relate the intrinsic rate constants of the surfaces presented by the catalyst to an effective rate constant. When highly active catalytic sites, such as step edges or other defects are present, we show that distinct limiting cases emerge depending on the degree of overlap of the reactant depletion zone about each site. In gases, the size of this depletion zone is approximately the mean free path, so the effective reactivity will depend on the structure of the catalyst on that scale. We discuss implications for the optimal design of nanoparticle catalysts.

Simulation of Sentinel-2A Red Edge Bands with RPAS Based Multispectral Data

NASA Astrophysics Data System (ADS)

Davids, Corine; Storvold, Rune; Haarpaintner, Jorg; Arnason, Kolbeinn

2016-08-01

Very high spatial and spectral resolution multispectral data was collected over the Hallormstađur test site in eastern Iceland using a fixed wing remotely piloted aerial system as part of the EU FP7 project North State (www.northstatefp7.eu). The North State project uses forest variable estimates derived from optical and radar satellite data as either input or validation for carbon flux models. The RPAS data from the Hallormsstađur forest test site in Iceland is here used to simulate Landsat and Sentinel-2A data and to explore the advantages of the new Sentinel-2A red edge bands for forest vegetation mapping. Simple supervised classification shows that the inclusion of the red edge bands improves the tree species classification considerably.

Molecular dynamics simulations of cesium adsorption on illite nanoparticles.

PubMed

Lammers, Laura N; Bourg, Ian C; Okumura, Masahiko; Kolluri, Kedarnath; Sposito, Garrison; Machida, Masahiko

2017-03-15

The charged surfaces of micaceous minerals, especially illite, regulate the mobility of the major radioisotopes of Cs ( 134 Cs, 135 Cs, 137 Cs) in the geosphere. Despite the long history of Cs adsorption studies, the nature of the illite surface sites remains incompletely understood. To address this problem, we present atomistic simulations of Cs competition with Na for three candidate illite adsorption sites - edge, basal plane, and interlayer. Our simulation results are broadly consistent with affinities and selectivities that have been inferred from surface complexation models. Cation exchange on the basal planes is thermodynamically ideal, but exchange on edge surfaces and within interlayers shows complex, thermodynamically non-ideal behavior. The basal planes are weakly Cs-selective, while edges and interlayers have much higher affinity for Cs. The dynamics of NaCs exchange are rapid for both cations on the basal planes, but considerably slower for Cs localized on edge surfaces. In addition to new insights into Cs adsorption and exchange with Na on illite, we report the development of a methodology capable of simulating fully-flexible clay mineral nanoparticles with stable edge surfaces using a well-tested interatomic potential model. Copyright © 2016 Elsevier Inc. All rights reserved.

The binuclear nickel center in the A-cluster of acetyl-CoA synthase (ACS) and two biomimetic dinickel complexes studied by X-ray absorption and emission spectroscopy

NASA Astrophysics Data System (ADS)

Schrapers, P.; Mebs, S.; Ilina, Y.; Warner, D. S.; Wörmann, C.; Schuth, N.; Kositzki, R.; Dau, H.; Limberg, C.; Dobbek, H.; Haumann, M.

2016-05-01

Acetyl-CoA synthase (ACS) is involved in the bacterial carbon oxide conversion pathway. The binuclear nickel sites in ACS enzyme and two biomimetic synthetic compounds containing a Ni(II)Ni(II) unit (1 and 2) were compared using XAS/XES. EXAFS analysis of ACS proteins revealed similar Ni-N/O/S bond lengths and Ni-Ni/Fe distances as in the crystal structure in oxidized ACS, but elongated Ni-ligand bonds in reduced ACS, suggesting more reduced nickel species. The XANES spectra of ACS and the dinickel complexes showed overall similar shapes, but less resolved pre-edge and edge features in ACS, attributed to more distorted square-planar nickel sites in particular in reduced ACS. DFT calculation of pre-edge absorption and Kβ2,5 emission features reproduced the experimental spectra of the synthetic complexes, was sensitive even to the small geometry differences in 1 and 2, and indicated low-spin Ni(II) sites. Comparison of nickel sites in proteins and biomimetic compounds is valuable for deducing structural and electronic differences in response to ligation and redox changes.

Boundaries in ground beetle (Coleoptera: Carabidae) and environmental variables at the edges of forest patches with residential developments

PubMed Central

Davis, Doreen E.

2018-01-01

Background Few studies of edge effects on wildlife objectively identify habitat edges or explore non-linear responses. In this paper, we build on ground beetle (Coleoptera: Carabidae) research that has begun to address these domains by using triangulation wombling to identify boundaries in beetle community structure and composition at the edges of forest patches with residential developments. We hypothesized that edges are characterized by boundaries in environmental variables that correspond to marked discontinuities in vegetation structure between maintained yards and forest. We expected environmental boundaries to be associated with beetle boundaries. Methods We collected beetles and measured environmental variables in 200 m by 200 m sampling grids centered at the edges of three forest patches, each with a rural, suburban, or urban context, in Charlotte, North Carolina, USA. We identified boundaries within each grid at two spatial scales and tested their significance and overlap using boundary statistics and overlap statistics, respectively. We complemented boundary delineation with k-means clustering. Results Boundaries in environmental variables, such as temperature, grass cover, and leaf litter depth, occurred at or near the edges of all three sites, in many cases at both scales. The beetle variables that exhibited the most pronounced boundary structure in relation to edges were total species evenness, generalist abundance, generalist richness, generalist evenness, and Agonum punctiforme abundance. Environmental and beetle boundaries also occurred within forest patches and residential developments, indicating substantial localized spatial variation on either side of edges. Boundaries in beetle and environmental variables that displayed boundary structure at edges significantly overlapped, as did boundaries on either side of edges. The comparison of boundaries and clusters revealed that boundaries formed parts of the borders of patches of similar beetle or environmental condition. Discussion We show that edge effects on ground beetle community structure and composition and environmental variation at the intersection of forest patches and residential developments can be described by boundaries and that these boundaries overlap in space. However, our results also highlight the complexity of edge effects in our system: environmental boundaries were located at or near edges whereas beetle boundaries related to edges could be spatially disjunct from them; boundaries incompletely delineated edges such that only parts of edges were well-described by sharp transitions in beetle and/or environmental variables; and the occurrence of boundaries related to edges was apparently influenced by individual property management practices, site-specific characteristics such as development geometry, and spatial scale. PMID:29333346

Boundaries in ground beetle (Coleoptera: Carabidae) and environmental variables at the edges of forest patches with residential developments.

PubMed

Davis, Doreen E; Gagné, Sara A

2018-01-01

Few studies of edge effects on wildlife objectively identify habitat edges or explore non-linear responses. In this paper, we build on ground beetle (Coleoptera: Carabidae) research that has begun to address these domains by using triangulation wombling to identify boundaries in beetle community structure and composition at the edges of forest patches with residential developments. We hypothesized that edges are characterized by boundaries in environmental variables that correspond to marked discontinuities in vegetation structure between maintained yards and forest. We expected environmental boundaries to be associated with beetle boundaries. We collected beetles and measured environmental variables in 200 m by 200 m sampling grids centered at the edges of three forest patches, each with a rural, suburban, or urban context, in Charlotte, North Carolina, USA. We identified boundaries within each grid at two spatial scales and tested their significance and overlap using boundary statistics and overlap statistics, respectively. We complemented boundary delineation with k -means clustering. Boundaries in environmental variables, such as temperature, grass cover, and leaf litter depth, occurred at or near the edges of all three sites, in many cases at both scales. The beetle variables that exhibited the most pronounced boundary structure in relation to edges were total species evenness, generalist abundance, generalist richness, generalist evenness, and Agonum punctiforme abundance. Environmental and beetle boundaries also occurred within forest patches and residential developments, indicating substantial localized spatial variation on either side of edges. Boundaries in beetle and environmental variables that displayed boundary structure at edges significantly overlapped, as did boundaries on either side of edges. The comparison of boundaries and clusters revealed that boundaries formed parts of the borders of patches of similar beetle or environmental condition. We show that edge effects on ground beetle community structure and composition and environmental variation at the intersection of forest patches and residential developments can be described by boundaries and that these boundaries overlap in space. However, our results also highlight the complexity of edge effects in our system: environmental boundaries were located at or near edges whereas beetle boundaries related to edges could be spatially disjunct from them; boundaries incompletely delineated edges such that only parts of edges were well-described by sharp transitions in beetle and/or environmental variables; and the occurrence of boundaries related to edges was apparently influenced by individual property management practices, site-specific characteristics such as development geometry, and spatial scale.

Coexisting oak species, including rear-edge populations, buffer climate stress through xylem adjustments.

PubMed

Granda, E; Alla, A Q; Laskurain, N A; Loidi, J; Sánchez-Lorenzo, A; Camarero, J J

2018-02-01

The ability of trees to cope with climate change is a pivotal feature of forest ecosystems, especially for rear-edge populations facing warm and dry conditions. To evaluate current and future forests threats, a multi-proxy focus on the growth, anatomical and physiological responses to climate change is needed. We examined the long-term xylem adjustments to climate variability of the temperate Quercus robur L. at its rear edge and the sub-Mediterranean Quercus pyrenaica Willd. Both species coexist at a mesic (ME, humid and warmer) and a xeric (XE, dry and cooler) site in northern Spain, the latter experiencing increasing temperatures in recent decades. We compared xylem traits at each site and assessed their trends, relationships and responses to climate (1960-2008). Traits included basal area increment, earlywood vessel hydraulic diameter, density and theoretical-specific hydraulic conductivity together with latewood oxygen (δ18O) stable isotopes and δ13C-derived water-use efficiency (iWUE). Quercus robur showed the highest growth at ME, likely through enhanced cambial activity. Quercus pyrenaica had higher iWUE at XE compared with ME, but limited plasticity of anatomical xylem traits was found for the two oak species. Similar physiological performance was found for both species. The iWUE augmented in recent years especially at XE, likely explained by stomatal closure given the increasing δ18O signal in response to drier and sunnier growing seasons. Overall, traits were more correlated at XE than at ME. The iWUE improvements were linked to higher growth up to a threshold (~85 μmol mol-1) after which reduced growth was found at XE. Our results are consistent with Q. pyrenaica and Q. robur coexisting at the central and dry edge of the climatic species distribution, respectively, showing similar responses to buffer warmer conditions. In fact, the observed adjustments found for Q. robur point towards growth stability of similar rear-edge oak populations under warmer climate conditions. © The Author(s) 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Pd@Pt core-shell concave decahedra: A class of catalysts for the oxygen reduction reaction with enhanced activity and durability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xue; Vera, Madeline; Chi, Miaofang

Here, we report a facile synthesis of multiply twinned Pd@Pt core shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 degrees C, naturally generating a core shell structure covered by concave facets. The nonuniformity inmore » the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm 2 pt) and mass (1.60 A/mg/ 2 pt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm 2 pt and 0.32 A/mg pt, respectively). After 10 000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mg pt, more than twice that of the pristine Pt/C catalyst.« less

Pd@Pt core-shell concave decahedra: A class of catalysts for the oxygen reduction reaction with enhanced activity and durability

DOE PAGES

Wang, Xue; Vera, Madeline; Chi, Miaofang; ...

2015-11-13

Here, we report a facile synthesis of multiply twinned Pd@Pt core shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 degrees C, naturally generating a core shell structure covered by concave facets. The nonuniformity inmore » the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm 2 pt) and mass (1.60 A/mg/ 2 pt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm 2 pt and 0.32 A/mg pt, respectively). After 10 000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mg pt, more than twice that of the pristine Pt/C catalyst.« less

Electrochemical maps and movies of the hydrogen evolution reaction on natural crystals of molybdenite (MoS2): basal vs. edge plane activity.

PubMed

Bentley, Cameron L; Kang, Minkyung; Maddar, Faduma M; Li, Fengwang; Walker, Marc; Zhang, Jie; Unwin, Patrick R

2017-09-01

Two dimensional (2D) semiconductor materials, such as molybdenum disulfide (MoS 2 ) have attracted considerable interest in a range of chemical and electrochemical applications, for example, as an abundant and low-cost alternative electrocatalyst to platinum for the hydrogen evolution reaction (HER). While it has been proposed that the edge plane of MoS 2 possesses high catalytic activity for the HER relative to the "catalytically inert" basal plane, this conclusion has been drawn mainly from macroscale electrochemical (voltammetric) measurements, which reflect the "average" electrocatalytic behavior of complex electrode ensembles. In this work, we report the first spatially-resolved measurements of HER activity on natural crystals of molybdenite, achieved using voltammetric scanning electrochemical cell microscopy (SECCM), whereby pixel-resolved linear-sweep voltammogram (LSV) measurements have allowed the HER to be visualized at multiple different potentials to construct electrochemical flux movies with nanoscale resolution. Key features of the SECCM technique are that characteristic surface sites can be targeted and analyzed in detail and, further, that the electrocatalyst area is known with good precision (in contrast to many macroscale measurements on supported catalysts). Through correlation of the local voltammetric response with information from scanning electron microscopy (SEM) and atomic force microscopy (AFM) in a multi-microscopy approach , it is demonstrated unequivocally that while the basal plane of bulk MoS 2 (2H crystal phase) possesses significant activity, the HER is greatly facilitated at the edge plane ( e.g. , surface defects such as steps, edges or crevices). Semi-quantitative treatment of the voltammetric data reveals that the HER at the basal plane of MoS 2 has a Tafel slope and exchange current density ( J 0 ) of ∼120 mV per decade and 2.5 × 10 -6 A cm -2 (comparable to polycrystalline Co, Ni, Cu and Au), respectively, while the edge plane has a comparable Tafel slope and a J 0 that is estimated to be more than an order-of-magnitude larger (∼1 × 10 -4 A cm -2 ). Finally, by tracking the temporal evolution of water contact angle (WCA) after cleavage, it is shown that cathodic polarization has a 'self-cleaning' effect on the surface of MoS 2 , consistent with the time-independent ( i.e. , time after cleavage) HER voltammetric response.

Arp2/3 complex–dependent actin networks constrain myosin II function in driving retrograde actin flow

PubMed Central

Yang, Qing; Zhang, Xiao-Feng; Pollard, Thomas D.

2012-01-01

The Arp2/3 complex nucleates actin filaments to generate networks at the leading edge of motile cells. Nonmuscle myosin II produces contractile forces involved in driving actin network translocation. We inhibited the Arp2/3 complex and/or myosin II with small molecules to investigate their respective functions in neuronal growth cone actin dynamics. Inhibition of the Arp2/3 complex with CK666 reduced barbed end actin assembly site density at the leading edge, disrupted actin veils, and resulted in veil retraction. Strikingly, retrograde actin flow rates increased with Arp2/3 complex inhibition; however, when myosin II activity was blocked, Arp2/3 complex inhibition now resulted in slowing of retrograde actin flow and veils no longer retracted. Retrograde flow rate increases induced by Arp2/3 complex inhibition were independent of Rho kinase activity. These results provide evidence that, although the Arp2/3 complex and myosin II are spatially segregated, actin networks assembled by the Arp2/3 complex can restrict myosin II–dependent contractility with consequent effects on growth cone motility. PMID:22711700

WAVE2 is regulated by multiple phosphorylation events within its VCA domain

PubMed Central

Pocha, Shirin M; Cory, Giles O

2009-01-01

The (Wiskott-Aldrich Syndrome Protein)-family verprolin homologous protein (WAVE) family of proteins occupies a pivotal position in the cell, converting extracellular signals into the formation of branched filamentous (F) actin structures. WAVE proteins contain a verprolin central acidic (VCA) domain at their C-terminus, responsible for binding to and activating the Arp2/3 complex, which in-turn nucleates the formation of new actin filaments. Here we identify five Casein Kinase 2 (CK2) phosphorylation sites within the VCA domain of WAVE2, serines 482, 484, 488, 489, and 497. Phosphorylation of these sites is required for a high affinity interaction with the Arp2/3 complex. Phosphorylation of ser 482 and 484 specifically inhibits the activation of the Arp2/3 complex by the WAVE2 VCA domain, but has no effect on the affinity for the Arp2/3 complex when the other phosphorylation sites are occupied. We demonstrate phosphorylation of all five sites on endogenous WAVE2 and show that their mutation to non-phosphorylatable alanine residues inhibits WAVE2 function in vivo, inhibiting cell ruffling and disrupting the integrity of the leading edge of migrating cells. Cell Motil. Cytoskeleton 2008. © 2008 Wiley-Liss, Inc. PMID:19012317

WAVE2 is regulated by multiple phosphorylation events within its VCA domain.

PubMed

Pocha, Shirin M; Cory, Giles O

2009-01-01

The (Wiskott-Aldrich Syndrome Protein)-family verprolin homologous protein (WAVE) family of proteins occupies a pivotal position in the cell, converting extracellular signals into the formation of branched filamentous (F) actin structures. WAVE proteins contain a verprolin central acidic (VCA) domain at their C-terminus, responsible for binding to and activating the Arp2/3 complex, which in-turn nucleates the formation of new actin filaments. Here we identify five Casein Kinase 2 (CK2) phosphorylation sites within the VCA domain of WAVE2, serines 482, 484, 488, 489, and 497. Phosphorylation of these sites is required for a high affinity interaction with the Arp2/3 complex. Phosphorylation of ser 482 and 484 specifically inhibits the activation of the Arp2/3 complex by the WAVE2 VCA domain, but has no effect on the affinity for the Arp2/3 complex when the other phosphorylation sites are occupied. We demonstrate phosphorylation of all five sites on endogenous WAVE2 and show that their mutation to non-phosphorylatable alanine residues inhibits WAVE2 function in vivo, inhibiting cell ruffling and disrupting the integrity of the leading edge of migrating cells. (c) 2008 Wiley-Liss, Inc.

Edge-Cracking Behavior of CoCrFeMnNi High-Entropy Alloy During Hot Rolling

NASA Astrophysics Data System (ADS)

Won, Jong Woo; Kang, Minju; Kwon, Heoun-Jun; Lim, Ka Ram; Seo, Seong Moon; Na, Young Sang

2018-05-01

This work investigated edge-cracking behavior of equiatomic CoCrFeMnNi high-entropy alloy during hot rolling at rolling temperatures 500 ≤ T R ≤ 1000 °C. Edge cracks did not form in the material rolled at 500 °C, but widened and deepened into the inside of plate as T R increased from 500 °C. Edge cracks were most severe in the material rolled at 1000 °C. Mn-Cr-O type non-metallic inclusion and oxidation were identified as major factors that caused edge cracking. The inclusions near edge region acted as preferential sites for crack formation. Connection between inclusion cracks and surface cracks induced edge cracking. Rolling at T R ≥ 600 °C generated distinct inclusion cracks whereas they were not serious at T R = 500 °C, so noticeable edge cracks formed at T R ≥ 600 °C. At T R = 1000 °C, significant oxidation occurred at the crack surface. This accelerated edge crack penetration by embrittling the crack tip, so severe edge cracking occurred at T R = 1000 °C.

Elemental analyses of hypervelocity micro-particle impact sites on interplanetary dust experiment sensor surfaces

NASA Technical Reports Server (NTRS)

Simon, Charles G.; Hunter, J. L.; Griffis, D. P.; Misra, V.; Ricks, D. R.; Wortman, Jim J.

1992-01-01

The Interplanetary Dust Experiment (IDE) had over 450 electrically active ultra-high purity metal-oxide-silicon impact detectors located on the six primary sides of the Long Duration Exposure Facility (LDEF). Hypervelocity micro-particles that struck the active sensors with enough energy to breakdown the 0.4 to 1.0 micron thick SiO2 insulator layer separating the silicon base (the negative electrode), and the 1000 A thick surface layer of aluminum (the positive electrode) caused electrical discharges that were recorded for the first year of orbit. These discharge features, which include 50 micron diameter areas where the aluminum top layer has been vaporized, facilitate the location of the impacts. The high purity Al-SiO2-Si substrates allow detection of trace (ppm) amounts of hypervelocity impactor residues. After sputtering through a layer of surface contamination, secondary ion mass spectrometry (SIMS) is used to create two-dimensional elemental ion intensity maps of micro-particle impact sites on the IDE sensors. The element intensities in the central craters of the impacts are corrected for relative ion yields and instrumental conditions and then normalized to silicon. The results are used to classify the particles' origins as 'manmade', 'natural' or 'indeterminate'. The last classification results from the presence of too little impactor residue (a frequent occurrence on leading edge impacts), analytical interference from high background contamination, the lack of information on silicon residue, the limited usefulness of data on aluminum in the central craters, or a combination of these circumstances. Several analytical 'blank' discharges were induced on flight sensors by pressing down on the sensor surface with a pure silicon shard. Analyses of these blank discharges showed that the discharge energy blasts away the layer of surface contamination. Only Si and Al were detected inside the discharge zones, including the central craters, of these features. A total of 35 impacts on leading edge sensors and 22 impacts on trailing edge sensors were analyzed.

21 CFR 882.5900 - Preformed craniosynostosis strip.

Code of Federal Regulations, 2010 CFR

2010-04-01

... bone edges of craniectomy sites (sites where the skull has been cut) to prevent the bone from regrowing in patients whose skull sutures are abnormally fused together. (b) Classification. Class II...

Complexation of iron hexacyanides by cytochrome c. Evidence for electron exchange at the exposed heme edge.

PubMed

Stellwagen, E; Cass, R D

1975-03-25

Electrostatic binding of at least two anionic iron hexacyanides to cationic horse heart cytochrome c was demonstrated by equilibrium dialysis measurements. No binding was detected following trifluoroacetylation of all of the 19 lysine residues. Replacement of the natural heme iron ligand methionine 80 by the alternative intrinsic ligand lysine 79 but not the extrinsic ligand imidazole resulted in the loss of one hexacyanide binding site. It is proposed that this site is located at the exposed heme edge and is functional in electron exchange.

Effects of clay minerals on transport of graphene oxide in saturated porous media.

PubMed

Lu, Taotao; Xia, Tianjiao; Qi, Yu; Zhang, Chengdong; Chen, Wei

2017-03-01

The presence of kaolinite, montmorillonite, and illite in packed quartz sand inhibited the transport of graphene oxide to different degrees. Transport inhibition was exerted mainly by the presence of positively charged sites on clay edges (which served as favorable deposition sites), whereas the effects on the overall particle-collector interaction energy and flow path were small. Kaolinite exhibited the most significant transport-inhibition effects because of its high percentage of edge area. Environ Toxicol Chem 2017;36:655-660. © 2016 SETAC. © 2016 SETAC.

Creation of forest edges has a global impact on forest vertebrates

PubMed Central

Peres, CA; Banks-Leite, C; Wearn, OR; Marsh, CJ; Butchart, SHM; Arroyo-Rodríguez, V; Barlow, J; Cerezo, A; Cisneros, L; D’Cruze, N; Faria, D; Hadley, A; Harris, S; Klingbeil, BT; Kormann, U; Lens, L; Medina-Rangel, GF; Morante-Filho, JC; Olivier, P; Peters, SL; Pidgeon, A; Ribeiro, DB; Scherber, C; Schneider-Maunory, L; Struebig, M; Urbina-Cardona, N; Watling, JI; Willig, MR; Wood, EM; Ewers, RM

2017-01-01

Summary Forest edges influence more than half the world’s forests and contribute to worldwide declines in biodiversity and ecosystem functions. However, predicting these declines is challenging in heterogeneous fragmented landscapes. We assembled an unmatched global dataset on species responses to fragmentation and developed a new statistical approach for quantifying edge impacts in heterogeneous landscapes to quantify edge-determined changes in abundance of 1673 vertebrate species. We show that 85% of species’ abundances are affected, either positively or negatively, by forest edges. Forest core species, which were more likely to be listed as threatened by the IUCN, only reached peak abundances at sites farther than 200-400 m from sharp high-contrast forest edges. Smaller-bodied amphibians, larger reptiles and medium-sized non-volant mammals experienced a larger reduction in suitable habitat than other forest core species. Our results highlight the pervasive ability of forest edges to restructure ecological communities on a global scale. PMID:29088701

L-edge sum rule analysis on 3d transition metal sites: from d10 to d0 and towards application to extremely dilute metallo-enzymes.

PubMed

Wang, Hongxin; Friedrich, Stephan; Li, Lei; Mao, Ziliang; Ge, Pinghua; Balasubramanian, Mahalingam; Patil, Daulat S

2018-03-28

According to L-edge sum rules, the number of 3d vacancies at a transition metal site is directly proportional to the integrated intensity of the L-edge X-ray absorption spectrum (XAS) for the corresponding metal complex. In this study, the numbers of 3d holes are characterized quantitatively or semi-quantitatively for a series of manganese (Mn) and nickel (Ni) complexes, including the electron configurations 3d 10 → 3d 0 . In addition, extremely dilute (<0.1% wt/wt) Ni enzymes were examined by two different approaches: (1) by using a high resolution superconducting tunnel junction X-ray detector to obtain XAS spectra with a very high signal-to-noise ratio, especially in the non-variant edge jump region; and (2) by adding an inert tracer to the sample that provides a prominent spectral feature to replace the weak edge jump for intensity normalization. In this publication, we present for the first time: (1) L-edge sum rule analysis for a series of Mn and Ni complexes that include electron configurations from an open shell 3d 0 to a closed shell 3d 10 ; (2) a systematic analysis on the uncertainties, especially on that from the edge jump, which was missing in all previous reports; (3) a clearly-resolved edge jump between pre-L 3 and post-L 2 regions from an extremely dilute sample; (4) an evaluation of an alternative normalization standard for L-edge sum rule analysis. XAS from two copper (Cu) proteins measured using a conventional semiconductor X-ray detector are also repeated as bridges between Ni complexes and dilute Ni enzymes. The differences between measuring 1% Cu enzymes and measuring <0.1% Ni enzymes are compared and discussed. This study extends L-edge sum rule analysis to virtually any 3d metal complex and any dilute biological samples that contain 3d metals.

Determination and prioritization of MoDOT geotechnical related problems with emphasis on effectiveness of design for bridge approach slabs and pavement edge drains

DOT National Transportation Integrated Search

2003-01-01

Surveys, interviews and site visits were used to identify, observe and document geotechnical-related problems in Missouri DOT infrastructure. Documented issues were evaluated and prioritized. Additional attention was focused on Pavement Edge Drains a...

Uncovering the Atomistic Mechanism for Calcite Step Growth

DOE PAGES

De La Pierre, Marco; Raiteri, Paolo; Stack, Andrew G.; ...

2017-04-13

Determining a complete atomic-level picture of how minerals grow from aqueous solution remains a challenge as macroscopic rates can be a convolution of many reactions. For the case of calcite (CaCO 3) in water, computer simulations have been used in this paper to map the complex thermodynamic landscape leading to growth of the two distinct steps, acute and obtuse, on the basal surface. The carbonate ion is found to preferentially adsorb at the upper edge of acute steps while Ca 2+ only adsorbs after CO 3 2-. In contrast to the conventional picture, ion pairs prefer to bind at themore » upper edge of the step with only one ion, at most, coordinated to the step and lower terrace. Finally, migration of the first carbonate ion to a growth site is found to be rate-limiting for kink nucleation, with this process having a lower activation energy on the obtuse step.« less

Assessing the feasibility of the Effectiveness of Discontinuing Bisphosphonates trial: a pilot study.

PubMed

Wright, N C; Foster, P J; Mudano, A S; Melnick, J A; Lewiecki, M E; Shergy, W J; Curtis, J R; Cutter, G R; Danila, M I; Kilgore, M L; Lewis, E C; Morgan, S L; Redden, D T; Warriner, A H; Saag, K G

2017-08-01

The Effectiveness of Discontinuing Bisphosphonates (EDGE) study is a planned pragmatic clinical trial to guide "drug holiday" clinical decision making. This pilot study assessed work flow and feasibility of such a study. While participant recruitment and treatment adherence were suboptimal, administrative procedures were generally feasible and minimally disrupted clinic flow. The comparative effectiveness of continuing or discontinuing long-term alendronate (ALN) on fractures is unknown. A large pragmatic ALN discontinuation study has potential to answer this question. We conducted a 6-month pilot study of the planned the EDGE study among current long-term ALN users (women aged ≥65 with ≥3 years of ALN use) to determine study work flow and feasibility including evaluating the administrative aspects of trial conduct (e.g., time to contract, institutional review board (IRB) approval), assessing rates of site and participant recruitment, and evaluating post-randomization outcomes, including adherence, bisphosphonate-associated adverse events, and participant and site satisfaction. We assessed outcomes 1 and 6 months after randomization. Nine sites participated, including seven community-based medical practices and two academic medical centers. On average (SD), contract execution took 3.4 (2.3) months and IRB approval took 13.9 (4.1) days. Sites recruited 27 participants (13 to continue ALN and 14 to discontinue ALN). Over follow-up, 22% of participants did not adhere to their randomization assignment: 30.8% in the continuation arm and 14.3% in the discontinuation arm. No fractures or adverse events were reported. Sites reported no issues regarding work flow, and participants were highly satisfied with the study. Administrative procedures of the EDGE study were generally feasible, with minimal disruption to clinic flow. In this convenience sample, participant recruitment was suboptimal across most practice sites. Accounting for low treatment arm adherence, a comprehensive recruitment approach will be needed to effectively achieve the scientific goals of the EDGE study.

Aluminium X-ray absorption Near Edge Structure in model compounds and Earth's surface minerals

NASA Astrophysics Data System (ADS)

Ildefonse, P.; Cabaret, D.; Sainctavit, P.; Calas, G.; Flank, A.-M.; Lagarde, P.

Aluminium K-edge X-ray absorption near edge spectra (XANES) of a suite of silicate and oxides minerals consist of electronic excitations occurring in the edge region, and multiple scattering resonances at higher energies. The main XANES feature for four-fold Al is at around 2 eV lower energy than the main XANES feature for six-fold Al. This provides a useful probe for coordination numbers in clay minerals, gels, glasses or material with unknown Al-coordination number. Six-fold aluminium yields a large variety of XANES features which can be correlated with octahedral point symmetry, number of aluminium sites and distribution of Al-O distances. These three parameters may act together, and the quantitative interpretation of XANES spectra is difficult. For a low point symmetry (1), variations are mainly related to the number of Al sites and distribution of Al-O distances: pyrophyllite, one Al site, is clearly distinguished from kaolinite and gibbsite presenting two Al sites. For a given number of Al-site (1), variations are controlled by changes in point symmetry, the number of XANES features being increased as point symmetry decreases. For a given point symmetry (1) and a given number of Al site (1), variations are related to second nearest neighbours (gibbsite versus kaolinite). The amplitude of the XANES feature at about 1566 eV is a useful probe for the assessment of AlIV/Altotal ratios in 2/1 phyllosilicates. Al-K XANES has been performed on synthetic Al-bearing goethites which cannot be studied by 27Al NMR. At low Al content, Al-K XANES is very different from that of α-AlOOH but at the highest level, XANES spectrum tends to that of diaspore. Al-K XAS is thus a promising tool for the structural study of poorly ordered materials such as clay minerals and natural alumino-silicate gels together with Al-subsituted Fe-oxyhydroxides.

Protection of fish spawning habitat for the conservation of warm-temperature reef-fish fisheries of shelf-edge reefs of Florida

USGS Publications Warehouse

Koenig, Christopher C.; Coleman, Felicia C.; Grimes, Churchill B.; Fitzhugh, Gary R.; Scanlon, Kathryn M.; Gledhill, Christopher T.; Grace, Mark

2000-01-01

We mapped and briefly describe the surficial geology of selected examples of shelf-edge reefs (50–120 m deep) of the southeastern United States, which are apparently derived from ancient Pleistocene shorelines and are intermittently distributed throughout the region. These reefs are ecologically significant because they support a diverse array of fish and invertebrate species, and they are the only aggregation spawning sites of gag (Mycteroperca microlepis), scamp (M. phenax), and other economically important reef fish. Our studies on the east Florida shelf in the Experimental Oculina Research Reserve show that extensive damage to the habitat-structuring coral Oculina varicosa has occurred in the past, apparently from trawling and dredging activities of the 1970s and later. On damaged or destroyed Oculina habitat, reef-fish abundance and diversity are low, whereas on intact habitat, reef-fish diversity is relatively high compared to historical diversity on the same site. The abundance and biomass of the economically important reef fish was much higher in the past than it is now, and spawning aggregations of gag and scamp have been lost or greatly reduced in size. On the west Florida shelf, fishers have concentrated on shelf-edge habitats for over 100 yrs, but fishing intensity increased dramatically in the 1980s. Those reefs are characterized by low abundance of economically important species. The degree and extent of habitat damage there is unknown. We recommend marine fishery reserves to protect habitat and for use in experimentally examining the potential production of unfished communities.

Speciation and distribution of copper in a mining soil using multiple synchrotron-based bulk and microscopic techniques.

PubMed

Yang, Jianjun; Liu, Jin; Dynes, James J; Peak, Derek; Regier, Tom; Wang, Jian; Zhu, Shenhai; Shi, Jiyan; Tse, John S

2014-02-01

Molecular-level understanding of soil Cu speciation and distribution assists in management of Cu contamination in mining sites. In this study, one soil sample, collected from a mining site contaminated since 1950s, was characterized complementarily by multiple synchrotron-based bulk and spatially resolved techniques for the speciation and distribution of Cu as well as other related elements (Fe, Ca, Mn, K, Al, and Si). Bulk X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that soil Cu was predominantly associated with Fe oxides instead of soil organic matter. This agreed with the closest association of Cu to Fe by microscopic X-ray fluorescence (U-XRF) and scanning transmission X-ray microscopy (STXM) nanoanalysis, along with the non-occurrence of photoreduction of soil Cu(II) by quick Cu L3,2-edge XANES spectroscopy (Q-XANES) which often occurs when Cu organic complexes are present. Furthermore, bulk-EXAFS and STXM-coupled Fe L3,2-edge nano-XANES analysis revealed soil Cu adsorbed primarily to Fe(III) oxides by inner-sphere complexation. Additionally, Cu K-edge μ-XANES, L3,2-edge bulk-XANES, and successive Q-XANES results identified the presence of Cu2S rather than radiation-damage artifacts dominant in certain microsites of the mining soil. This study demonstrates the great benefits in use of multiple combined synchrotron-based techniques for comprehensive understanding of Cu speciation in heterogeneous soil matrix, which facilitates our prediction of Cu reactivity and environmental fate in the mining site.

Silicon K-edge XANES spectra of silicate minerals

NASA Astrophysics Data System (ADS)

Li, Dien; Bancroft, G. M.; Fleet, M. E.; Feng, X. H.

1995-03-01

Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measured using synchrotron radiation (SR). The spectra are qualitatively interpreted based on MO calculation of the tetrahedral SiO{4/4-}cluster. The Si K-edge generally shifts to higher energy with increased polymerization of silicates by about 1.3 eV, but with considerable overlap for silicates of different polymerization types. The substitution of Al for Si shifts the Si K-edge to lower energy. The chemical shift of Si K-edge is also sensitive to cations in more distant atom shells; for example, the Si K-edge shifts to lower energy with the substitution of Al for Mg in octahedral sites. The shifts of the Si K-edge show weak correlation with average Si-O bond distance (dSi-O), Si-O bond valence (sSi-O) and distortion of SiO4 tetrahedra, due to the crystal structure complexity of silicate minerals and multiple factors effecting the x-ray absorption processes.

Edge effects on growth and biomass partitioning of an Amazonian understory herb (Heliconia acuminata; Heliconiaceae).

PubMed

Bruna, Emilio M; de Andrade, Ana Segalin

2011-10-01

After deforestation, environmental changes in the remaining forest fragments are often most intense near the forest edge, but few studies have evaluated plant growth or plasticity of plant growth in response to edge effects. In a 2-year common garden experiment, we compared biomass allocation and growth of Heliconia acuminata with identical genotypes grown in 50 × 35 m common gardens on a 25-year-old edge and in a forest interior site. Genetically identical plants transplanted to the forest edge and understory exhibited different patterns of growth and biomass allocation. However, individuals with identical genotypes in the same garden often had very different responses. Plants on forest edges also had higher growth rates and increased biomass at the end of the experiment, almost certainly due to the increased light on the forest edge. With over 70000 km of forest edge created annually in the Brazilian Amazon, phenotypic plasticity may play an important role in mediating plant responses to these novel environmental conditions.

Temperature dependence of pre-edge features in Ti K-edge XANES spectra for ATiO₃ (A = Ca and Sr), A₂TiO₄ (A = Mg and Fe), TiO₂ rutile and TiO₂ anatase.

PubMed

Hiratoko, Tatsuya; Yoshiasa, Akira; Nakatani, Tomotaka; Okube, Maki; Nakatsuka, Akihiko; Sugiyama, Kazumasa

2013-07-01

XANES (X-ray absorption near-edge structure) spectra of the Ti K-edges of ATiO3 (A = Ca and Sr), A2TiO4 (A = Mg and Fe), TiO2 rutile and TiO2 anatase were measured in the temperature range 20-900 K. Ti atoms for all samples were located in TiO6 octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre-edge and post-edge. After the AIIP, amplitudes damped due to Debye-Waller factor effects with temperature. Amplitudes in the pre-edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre-edge peaks in various titanium compounds over a wide temperature range.

Chromium speciation in oxide-type compounds: application to minerals, gems, aqueous solutions and silicate glasses

NASA Astrophysics Data System (ADS)

Farges, François

2009-09-01

Cr K-edge XANES spectra were obtained for a variety of Cr-bearing model compounds containing Cr(II), Cr(III), Cr(IV), Cr(V) and Cr(VI), in which the Cr-site symmetry is D4h, Oh and Td. The centroid position of the pre-edge feature is a better indicator of the Cr valence than the edge position. In Cr-rich oxides, higher-energy transitions must be excluded in order to refine a robust valence for Cr. The pre-edge for chromates is not unique and varies as a function of the CrO4 2- moiety distortion, which is often related to Cr-polymerization (monochromate vs. dichromate). Both the analogy with the Mn K-pre-edge information and ab initio FEFF calculations of the pre-edge feature for Cr(III) and Cr(VI) confirm the experimental trends. This methodology is applied to the Cr K-edge pre-edge feature collected in gems (emerald, spinel and ruby), the layered minerals fuchsite and kämmererite, two Cr-bearing aqueous solutions and a set of sodo-calcic silicate glasses used for bottling sparkling white wine. In emerald and fuchsite, the Cr-site is differently distorted than its ruby or spinel counterpart. In a Cr(III)-bearing aqueous solution and sodo-calcic glass, no evidence for Cr(III) with Td and C3v symmetry is detected. However, minor amounts of chromate moieties (most likely monomeric) are detected in a glass synthesized in air. Preliminary spectra for the wine bottle glass suggest that only trace amounts of chromates might possibly be present in these glasses.

a Study of Electrical Structures of Shanchiao Fault in Taiwan Using Audio-Frequency Magnetotelluric (amt) Method

NASA Astrophysics Data System (ADS)

Yang, C.; Liu, H.

2007-12-01

The Shanchiao normal fault is located in the western edge of Taipei basin in an N-E to S-W direction. Since the fault crosses through the Tertiary basement of Taipei basin, it is classified as an active fault. The overburden of the fault is sediments with a thickness around few tenth meters to several hundred meters. No detailed studies related to the Shanchiao fault in the western side of Taipei Basin are reported. In addition, there are no outcrops which have been found on the surface. This part of fault seems to be a potential source of disaster for the development of western Taipei basin. The audio-frequency magnetotelluric (AMT) method is a technique used to find the vertical resistivity distribution of formation and to characterize a fault structure through the ground surface based measurement. Based on the geological investigation and lithogic information from wells, the AMT data from six soundings at Wugu site, nine soundings at XinZhuang site and eight sounding at GuanDu site were collected on a NE-SW profile, approximately perpendicular to the prospective strike of the Shanchiao fault. AMT data were then inverted for two- dimension resistivity models (sections). The features of all resistivity sections are similar; an apparent drop in resistivity was observed at the position correlates to the western edge of Taipei basin. The predicted location of Shanchiao fault matches was verified by the lithologic sections of boreholes nearby. It indicates that the Shanchiao normal fault may associate with the subsidence of Taipei basin. The basement is clearly detected as a geoelectrical unit having resistivity less than 250 . It has a trend of increasing its depth toward S-E. The uplift of layers in the east of resistivity sections may affect by the XinZhuang thrust fault from the east. As with each site, the calculated resistivity may affect by cultural interference. However, the AMT survey still successfully delineates the positions and features of the Shanchiao fault and western edge of Taipei basin. Keywords¡GCSAMT, RIP, Shanchiao fault

21 CFR 882.5900 - Preformed craniosynostosis strip.

Code of Federal Regulations, 2012 CFR

2012-04-01

... craniosynostosis strip. (a) Identification. A preformed craniosynostosis strip is a plastic strip used to cover bone edges of craniectomy sites (sites where the skull has been cut) to prevent the bone from regrowing...

21 CFR 882.5900 - Preformed craniosynostosis strip.

Code of Federal Regulations, 2014 CFR

2014-04-01

... craniosynostosis strip. (a) Identification. A preformed craniosynostosis strip is a plastic strip used to cover bone edges of craniectomy sites (sites where the skull has been cut) to prevent the bone from regrowing...

21 CFR 882.5900 - Preformed craniosynostosis strip.

Code of Federal Regulations, 2013 CFR

2013-04-01

... craniosynostosis strip. (a) Identification. A preformed craniosynostosis strip is a plastic strip used to cover bone edges of craniectomy sites (sites where the skull has been cut) to prevent the bone from regrowing...

21 CFR 882.5900 - Preformed craniosynostosis strip.

Code of Federal Regulations, 2011 CFR

2011-04-01

... craniosynostosis strip. (a) Identification. A preformed craniosynostosis strip is a plastic strip used to cover bone edges of craniectomy sites (sites where the skull has been cut) to prevent the bone from regrowing...

Enhancement of spin polarization induced by Coulomb on-site repulsion between localized pz electrons in graphene embedded with line defects.

PubMed

Ren, Ji-Chang; Wang, Zhigang; Zhang, Rui-Qin; Ding, Zejun; Van Hove, Michel A

2015-11-11

It is well known that the effect of Coulomb on-site repulsion can significantly alter the physical properties of the systems that contain localized d and/or f electrons. However, little attention has been paid to the Coulomb on-site repulsion between localized p electrons. In this study, we demonstrated that Coulomb on-site repulsion between localized pz electrons also plays an important role in graphene embedded with line defects. It is shown that the magnetism of the system largely depends on the choice of the effective Coulomb on-site parameter Ueff. Ueff at the edges of the defect enhances the exchange splitting, which increases the magnetic moment and stabilizes a ferromagnetic state of the system. In contrast, Ueff at the center of the defect weakens the spin polarization of the system. The behavior of the magnetism is explained with the Stoner criterion and the charge accumulation at the edges of the defect. Based on the linear response approach, we estimate reasonable values of Ueff to be 2.55 eV (2.3 eV) at the center (edges) of the defects. More importantly, using a DFT+U+J method, we find that exchange interactions between localized p electrons also play an important role in the spin polarization of the system. These results imply that Coulomb on-site repulsion is necessary to describe the strong interaction between localized pz electrons of carbon related materials.

Capacity improvement of the carbon-based electrochemical capacitor by zigzag-edge introduced graphene

NASA Astrophysics Data System (ADS)

Tamura, Naoki; Tomai, Takaaki; Oka, Nobuto; Honma, Itaru

2018-01-01

The electrochemical properties of graphene edge has been attracted much attention. Especially, zigzag edge has high electrochemical activity because neutral radical exits on edge. However, due to a lack of efficient production method for zigzag graphene, the electrochemical properties of zigzag edge have not been experimentally demonstrated and the capacitance enhancement of carbonaceous materials in energy storage devices by the control in their edge states is still challenge. In this study, we fabricated zigzag-edge-rich graphene by a one-step method combining graphene exfoliation in supercritical fluid and anisotropic etching by catalytic nanoparticles. This efficient production of zigzag-edge-rich graphene allows us to investigate the electrochemical activity of zigzag edge. By cyclic voltammetry, we revealed the zigzag edge-introduced graphene exhibited unique redox reaction in aqueous acid solution. Moreover, by the calculation on the density function theory (DFT), this unique redox potential for zigzag edge-introduced graphene can be attributed to the proton-insertion/-extraction reactions at the zigzag edge. This finding indicates that the graphene edge modification can contribute to the further increase in the capacitance of the carbon-based electrochemical capacitor.

Graphite carbon nitride/boron-doped graphene hybrid for efficient hydrogen generation reaction.

PubMed

Yang, Liang; Wang, Xin; Wang, Juan; Cui, Guomin; Liu, Daoping

2018-08-24

Metal-free carbon materials, with tuned surface chemical and electronic properties, hold great potential for the hydrogen evolution reaction (HER). We designed and synthesized a CN/BG hybrid electrocatalytic system with a porous and active graphite carbon nitride (CN) layer on boron-doped graphene (BG). A porous CN layer on graphene could provide exposed defects and edges that act as active sites for proton adsorption and reduction. The composition, structure, surface electronics, and chemical properties of this CN/BG hybrid system were tuned to obtain excellent HER activity and stability. Detailed surface chemical, morphological, and structural analyses demonstrated the synergetic effect arising from the electronic interaction between CN and BG, which contributed to the enhanced electrocatalytic performances.

Impact of Zeolite Aging in Hot Liquid Water on Activity for Acid-Catalyzed Dehydration of Alcohols.

PubMed

Vjunov, Aleksei; Derewinski, Miroslaw A; Fulton, John L; Camaioni, Donald M; Lercher, Johannes A

2015-08-19

The location and stability of Brønsted acid sites catalytically active in zeolites during aqueous phase dehydration of alcohols were studied on the example of cyclohexanol. The catalytically active hydronium ions originate from Brønsted acid sites (BAS) of the zeolite that are formed by framework tetrahedral Si atom substitution by Al. Al K-edge extended X-ray absorption fine structure (EXAFS) and (27)Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopies in combination with density functional theory (DFT) calculations are used to determine the distribution of tetrahedral Al sites (Al T-sites) both qualitatively and quantitatively for both parent and HBEA catalysts aged in water prior to catalytic testing. The aging procedure leads to partial degradation of the zeolite framework evidenced from the decrease of material crystallinity (XRD) as well as sorption capacity (BET). With the exception of one commercial zeolite sample, which had the highest concentration of framework silanol-defects, there is no evidence of Al coordination modification after aging in water. The catalyst weight-normalized dehydration rate correlated best with the sum of strong and weak Brønsted acidic protons both able to generate the hydrated hydronium ions. All hydronium ions were equally active for the acid-catalyzed reactions in water. Zeolite aging in hot water prior to catalysis decreased the weight normalized dehydration reaction rate compared to that of the parent HBEA, which is attributed to the reduced concentration of accessible Brønsted acid sites. Sites are hypothesized to be blocked due to reprecipitation of silica dissolved during framework hydrolysis in the aging procedure.

Interaction of size-selected gold nanoclusters with dopamine

NASA Astrophysics Data System (ADS)

Montone, Georgia R.; Hermann, Eric; Kandalam, Anil K.

2016-12-01

We present density functional theory based results on the interaction of size-selected gold nanoclusters, Au10 and Au20, with dopamine molecule. The gold clusters interact strongly with the nitrogen site of dopamine, thereby forming stable gold-dopamine complexes. Our calculations further show that there is no site specificity on the planar Au10 cluster with all the edge gold atoms equally preferred. On the other hand, in the pyramidal Au20 cluster, the vertex metal atom is the most active site. As the size increased from Au10 to Au20, the interaction strength has shown a declining trend. The effect of aqueous environment on the interaction strengths were also studied by solvation model. It is found that the presence of solvent water stabilizes the interaction between the metal cluster and dopamine molecule, even though for Au10 cluster the energy ordering of the isomers changed from that of the gas-phase.

Mutations close to a hub residue affect the distant active site of a GH1 β-glucosidase.

PubMed

Souza, Valquiria P; Ikegami, Cecília M; Arantes, Guilherme M; Marana, Sandro R

2018-01-01

The tertiary structure of proteins has been represented as a network, in which residues are nodes and their contacts are edges. Protein structure networks contain residues, called hubs or central, which are essential to form short connection pathways between any pair of nodes. Hence hub residues may effectively spread structural perturbations through the protein. To test whether modifications nearby to hub residues could affect the enzyme active site, mutations were introduced in the β-glycosidase Sfβgly (PDB-ID: 5CG0) directed to residues that form an α-helix (260-265) and a β-strand (335-337) close to one of its main hub residues, F251, which is approximately 14 Å from the Sfβgly active site. Replacement of residues A263 and A264, which side-chains project from the α-helix towards F251, decreased the rate of substrate hydrolysis. Mutation A263F was shown to weaken noncovalent interactions involved in transition state stabilization within the Sfβgly active site. Mutations placed on the opposite side of the same α-helix did not show these effects. Consistently, replacement of V336, which side-chain protrudes from a β-strand face towards F251, inactivated Sfβgly. Next to V336, mutation S337F also caused a decrease in noncovalent interactions involved in transition state stabilization. Therefore, we suggest that mutations A263F, A264F, V336F and S337F may directly perturb the position of the hub F251, which could propagate these perturbations into the Sfβgly active site through short connection pathways along the protein network.

Evidence for Weakly Correlated Oxygen Holes in the Highest-Tc Cuprate Superconductor HgBa2 Ca2 Cu3 O8 +δ

NASA Astrophysics Data System (ADS)

Chainani, A.; Sicot, M.; Fagot-Revurat, Y.; Vasseur, G.; Granet, J.; Kierren, B.; Moreau, L.; Oura, M.; Yamamoto, A.; Tokura, Y.; Malterre, D.

2017-08-01

We study the electronic structure of HgBa2 Ca2 Cu3 O8 +δ (Hg1223; Tc=134 K ) using photoemission spectroscopy (PES) and x -ray absorption spectroscopy (XAS). Resonant valence band PES across the O K edge and Cu L edge identifies correlation satellites originating in O 2 p and Cu 3 d two-hole final states, respectively. Analyses using the experimental O 2 p and Cu 3 d partial density of states show quantitatively different on-site Coulomb energy for the Cu site (Ud d=6.5 ±0.5 eV ) and O site (Up p=1.0 ±0.5 eV ). Cu2 O7 -cluster calculations with nonlocal screening explain the Cu 2 p core level PES and Cu L -edge XAS spectra, confirm the Ud d and Up p values, and provide evidence for the Zhang-Rice singlet state in Hg1223. In contrast to other hole-doped cuprates and 3 d -transition metal oxides, the present results indicate weakly correlated oxygen holes in Hg1223.

Site Transfer Functions of Three-Component Ground Motion in Western Turkey

NASA Astrophysics Data System (ADS)

Ozgur Kurtulmus, Tevfik; Akyol, Nihal; Camyildiz, Murat; Gungor, Talip

2015-04-01

Because of high seismicity accommodating crustal deformation and deep graben structures, on which have, urbanized and industrialized large cities in western Turkey, the importance of site-specific seismic hazard assessments becomes more crucial. Characterizing source, site and path effects is important for both assessing the seismic hazard in a specific region and generation of the building codes/or renewing previous ones. In this study, we evaluated three-component recordings for micro- and moderate-size earthquakes with local magnitudes ranging between 2.0 and 5.6. This dataset is used for site transfer function estimations, utilizing two different spectral ratio approaches 'Standard Spectral Ratio-(SSR)' and 'Horizontal to Vertical Spectral Ratio-(HVSR)' and a 'Generalized Inversion Technique-(GIT)' to highlight site-specific seismic hazard potential of deep basin structures of the region. Obtained transfer functions revealed that the sites located near the basin edges are characterized by broader HVSR curves. Broad HVSR peaks could be attributed to the complexity of wave propagation related to significant 2D/3D velocity variations at the sediment-bedrock interface near the basin edges. Comparison of HVSR and SSR estimates for the sites located on the grabens showed that SSR estimates give larger values at lower frequencies which could be attributed to lateral variations in regional velocity and attenuation values caused by basin geometry and edge effects. However, large amplitude values of vertical component GIT site transfer functions were observed at varying frequency ranges for some of the stations. These results imply that vertical component of ground motion is not amplification free. Contamination of HVSR site transfer function estimates at different frequency bands could be related to complexities in the wave field caused by deep or shallow heterogeneities in the region such as differences in the basin geometries, fracturing and fluid saturation along different propagation paths. The results also show that, even if the site is located on a horst, the presence of weathered zones near the surface could cause moderate frequency dependent site effects.

Shelfal sediment transport by undercurrents forces turbidity current activity during high sea level, Chile continental margin

NASA Astrophysics Data System (ADS)

Bernhardt, Anne; Hebbeln, Dierk; Regenberg, Marcus; Lückge, Andreas; Strecker, Manfred. R.

2016-04-01

Understanding the links between terrigenous sediment supply and marine transport and depositional processes along tectonically active margins is essential to decipher turbidite successions as potential archives of climatic and seismic forcings and to comprehend timing and quantity of marine clastic deposition. Sequence stratigraphic models predict coarse-grained terrigenous sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine clastic deposition during periods of transgression and highstand has been attributed to the continued geomorphic connectivity between terrestrial sediment sources and marine sinks (e.g., rivers connected to submarine canyons) often facilitated by narrow shelves, high sediment supply causing delta migration to the shelf edge, and/or abrupt increases in sediment supply due to climatic variability or catastrophic events. To decipher the controls on Holocene highstand turbidite deposition, we analyzed twelve sediment cores of spatially disparate, coeval Holocene turbidite systems along the Chile margin (29-40°S) with changing climatic and geomorphic characteristics but uniform changes of sea level. Intraslope basins in north-central Chile (29-33°S) offshore a narrow to absent shelf record a shut-off of turbidite activity during the Holocene. In contrast, core sites in south-central Chile (36-40°S) offshore a wide continental shelf have repeatedly experienced turbidite deposition during sea-level highstand conditions, even though most of the depocenters are not connected via canyons to sediment sources. The interplay of stable high sediment supply related to strong onshore precipitation in combination with a wide shelf, over which undercurrents move sediment towards the shelf edge, appears to control Holocene turbidite sedimentation and sediment export to the deep sea.

A first-principles based study of ns2 containing ternary iodides and their possibility of scintillation

NASA Astrophysics Data System (ADS)

Kang, Byungkyun; Fang, C. M.; Biswas, Koushik

2016-10-01

A recently investigated scintillator material CsBa2I5 showed promising properties when activated with ns2 ions In+, Tl+ or the lanthanide Eu2+. This sparked our interest in an analogous group of materials, e.g. InBa2I5 or TlBa2I5 where the ns2 ion is part of the crystal framework, replacing the alkali ion. Many of these compounds of the type AB2X5 (X  =  halogen) have been previously synthesized and have interesting stereochemical activity. Using density functional calculations we have studied the stable monoclinic phase of the aforementioned ns2 containing iodides. One objective is to explore them as scintillators where the ns2 ions, now appearing as part of the crystal, play a central role. Compared to CsBa2I5, their reduced fundamental band gap and possibility of higher light yield may be attributed to an induced degree of covalency in the ns2-I bonds. The valence and conduction band edges have discernible contributions from the ns2 ions’ s and p orbitals which is crucial in carrier localization. The antibonding Ga or In s sates near valence edge may be a favored site for a hole trap, as against a {{V}k} center. Additional differences among the ns2 compounds lead to qualitatively different self-trapped excitons that may fundamentally affect luminescence. The possibility of fast electron capture at the ns2 sites and the prospect of self-activated scintillation via ns2-p  →  {{V}k} or ns2-p  →  ns2-s transitions may draw interest in related applications.

ANCHOR HILL PIT LAKE IN SITU TREATMENT, GILT EDGE MINE SUPERFUND SITE, S. DAKOTA, USA - A RETROSPECTIVE

EPA Science Inventory

The EPA Region VII Superfund office and the EPA National Risk Management Research Laboratory (NRMRL) Mine Waste Technology Program (MWTP)have been conducting a field scale technology demonstration of an in situ treatment of the Anchor Hill Pit Lake at the Gilt Edge Mine Superfund...

PICNIC PAVILION JUST BEYOND THE WESTERN EDGE OF THE BOTANIC ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

PICNIC PAVILION JUST BEYOND THE WESTERN EDGE OF THE BOTANIC GARDEN. THIS PAVILION IS ROUGHLY LOCATED ON THE SITE OF "BARTRAM HALL," ANDREW EASTLAKE'S ITALIANATE VILLA DESIGNED BY NOTED PHILADELPHIA ARCHITECT SAMUEL SLOAN AND CONSTRUCTED IN 1850-1851 - John Bartram House & Garden, 54th Street & Lindbergh Boulevard, Philadelphia, Philadelphia County, PA

A study of the effects of Reynolds number and Mach number on constant pressure coefficient jump for shock-induced trailing-edge separation

NASA Technical Reports Server (NTRS)

Cunningham, Atlee M., Jr.; Spragle, Gregory S.

1987-01-01

The influence of Mach and Reynolds numbers as well as airfoil and planform geometry on the phenomenon of constant shock jump pressure coefficient for conditions of shock induced trailing edge separation (SITES) was studied. It was demonstrated that the phenomenon does exist for a wide variety of two and three dimensional flow cases and that the influence of free stream Mach number was not significant. The influence of Reynolds number was found to be important but was not strong. Airfoil and planform geometric characteristics were found to be very important where the pressure coefficient jump was shown to vary with the sum of: (1) airfoil curvature at the upper surface crest, and (2) camber surface slope at the trailing edge. It was also determined that the onset of SITES could be defined as a function of airfoil geometric parameters and Mach number normal to the leading edge. This onset prediction was shown to predict the angle of onset to within + or - 1 deg accuracy or better for about 90% of the cases studied.

Habitat edges have weak effects on duck nest survival at local spatial scales

USGS Publications Warehouse

Raquel, Amelia J; Ringelman, Kevin M.; Ackerman, Joshua T.; Eadie, John M.

2015-01-01

Edge effects on nesting success have been documented in breeding birds in a variety of contexts, but there is still uncertainty in how edge type and spatial scale determine the magnitude and detectability of edge effects. Habitat edges are often viewed as predator corridors that surround or penetrate core habitat and increase the risk of predation for nearby nests. We studied the effects of three different types of potential predator corridors (main perimeter roads, field boundaries, and ATV trails within fields) on waterfowl nest survival in California. We measured the distance from duck nests to the nearest edge of each type, and used distance as a covariate in a logistic exposure analysis of nest survival. We found only weak evidence for edge effects due to predation. The best supported model of nest survival included all three distance categories, and while all coefficient estimates were positive (indicating that survival increased with distance from edge), 85% coefficient confidence intervals approached or bounded zero indicating an overall weak effect of habitat edges on nest success. We suggest that given the configuration of edges at our site, there may be few areas far enough from hard edges to be considered ‘core’ habitat, making edge effects on nest survival particularly difficult to detect.

Atomic Oxygen Durability of Second Surface Silver Microsheet Glass Concentrators

NASA Technical Reports Server (NTRS)

deGroh, Kim K.; Jaworske, Donald A.; Smith, Daniela C.; Mroz, Thaddeus S.

1996-01-01

Second surface silver microsheet glass concentrators are being developed for potential use in future solar dynamic space power systems. Traditional concentrators are aluminum honeycomb sandwich composites with either aluminum or graphite epoxy face sheets, where a reflective aluminum layer is deposited onto an organic leveling layer on the face sheet. To protect the underlying layers, a SiO2 layer is applied on top of the aluminum reflective layer. These concentrators may be vulnerable to atomic oxygen degradation due to possible atomic oxygen attack of the organic layers at defect sites in the protective and reflective coatings. A second surface microsheet glass concentrator would be inherently more atomic oxygen durable than these first surface concentrators. In addition, a second surface microsheet glass concentrator design provides a smooth optical surface and allows for silver to be used as a reflective layer, which would improve the reflectivity of the concentrator and the performance of the system. A potential threat to the performance of second surface microsheet glass concentrators is atomic oxygen attack of the underlying silver at seams and edges or at micrometeoroid and debris (MMD) impacts sites. Second surface silver microsheet glass concentrator samples were fabricated and tested for atomic oxygen durability. The samples were iteratively exposed to an atomic oxygen environment in a plasma asher. Samples were evaluated for potential degradation at fabrication seams, simulated MMD impact sites, and edges. Optical microscopy was used to evaluate atomic oxygen degradation. Reflectance was obtained for an impacted sample prior to and after atomic oxygen exposure. After an initial atomic oxygen exposure to an effective fluence of approx. 1 x 10(exp 21) atoms/cm(exp 2), oxidation of the silver at defect sites and edges was observed. Exposure to an additional approx. 1 x 10(exp 21) atoms/cm(exp 2) caused no observed increase in oxidation. Oxidation at an impact site caused negligible changes in reflectance. In all cases oxidation was found to be confined to the vicinity of the seams, impact sites, edges or defect sites. Asher to in-space atomic oxygen correlation issues will be addressed.

Transient habitats limit development time for periodical cicadas.

PubMed

Karban, Richard

2014-01-01

Periodical cicadas (Magicicada spp.) mature in 13 or 17 years, the longest development times for any non-diapausing insects. Selection may favor prolonged development since nymphs experience little mortality and individuals taking 17 years have been shown to have greater fecundity than those taking 13 years. Why don't periodical cicadas take even longer to develop? Nymphs feed on root xylem fluid and move little. Ovipositing females prefer fast-growing trees at forest edges. I hypothesized that (1) adults emerging at edges would be heavier than those from forest interiors and (2) habitat changes could limit development time. I collected newly eclosed females that had neither fed as adults nor moved from their site of development. For M. septendecim, females from edges were 4.9% heavier than those from the interior. I assumed that emergence density indicated habitat quality and measured density at eight sites in 1979, 1996, and 2013. Over three generations, variation in densities was great; densities at two sites crashed, and at one site they exploded to 579/m2 Habitat transience may limit development time because only adults can reassess habitats and reposition offspring. In conclusion, cicadas are affected by habitat characteristics, habitats change over 17 years, and cicadas may emerge, mate, and redistribute their offspring to track habitat dynamics.

Population ecology of the gulf ribbed mussel across a salinity gradient: recruitment, growth and density

USGS Publications Warehouse

Honig, Aaron; Supan, John; LaPeyre, Megan K.

2015-01-01

Benthic intertidal bivalves play an essential role in estuarine ecosystems by contributing to habitat provision, water filtration, and promoting productivity. As such, changes that impact population distributions and persistence of local bivalve populations may have large ecosystem level consequences. Recruitment, growth, mortality, population size structure and density of the gulf coast ribbed mussel, Geukensia granosissima, were examined across a salinity gradient in southeastern Louisiana. Data were collected along 100-m transects at interior and edge marsh plots located at duplicate sites in upper (salinity ~4 psu), central (salinity ~8 psu) and lower (salinity ~15 psu) Barataria Bay, Louisiana, U.S.A. Growth, mortality and recruitment were measured in established plots from April through November 2012. Mussel densities were greatest within the middle bay (salinity ~8) regardless of flooding regime, but strongly associated with highest stem densities of Juncus roemerianus vegetation. Mussel recruitment, growth, size and survival were significantly higher at mid and high salinity marsh edge sites as compared to all interior marsh and low salinity sites. The observed patterns of density, growth and mortality in Barataria Bay may reflect detrital food resource availability, host vegetation community distribution along the salinity gradient, salinity tolerance of the mussel, and reduced predation at higher salinity edge sites.

Hydraulic properties and fine root mass of Larix sibirica along forest edge-interior gradients

NASA Astrophysics Data System (ADS)

Chenlemuge, Tselmeg; Dulamsuren, Choimaa; Hertel, Dietrich; Schuldt, Bernhard; Leuschner, Christoph; Hauck, Markus

2015-02-01

At its southernmost distribution limit in Inner Asia, the boreal forest disintegrates into forest fragments on moist sites (e.g. north-facing slopes), which are embedded in grasslands. This landscape mosaic is characterized by a much higher forest edge-to-interior ratio than in closed boreal forests. Earlier work in the forest-steppe ecotone of Mongolia has shown that Larix sibirica trees at forest edges grow faster than in the forest interior, as the more xeric environment at the edge promotes self-thinning and edges are preferentially targeted by selective logging and livestock grazing. Lowered stand density reduces competition for water in these semi-arid forests, where productivity is usually limited by summer drought. We studied how branch and coarse root hydraulic architecture and xylem conductivity, fine root biomass and necromass, and fine root morphology of L. sibirica respond to sites differing in water availability. Studying forest edge-interior gradients in two regions of western Mongolia, we found a significant reduction of branch theoretical (Kp) and empirical conductivity (Ks) in the putatively more drought-affected forest interior in the Mongolian Altai (mean precipitation: 120 mm yr-1), while no branch xylem modification occurred in the moister Khangai Mountains (215 mm yr-1). Kp and Ks were several times larger in roots than in branches, but root hydraulics were not influenced by stand density or mean annual precipitation. Very low fine root biomass: necromass ratios at all sites, and in the forest interior in particular, suggest that L. sibirica seeks to maintain a relatively high root conductivity by producing large conduits, which results in high root mortality due to embolism during drought. Our results suggest that L. sibirica is adapted to the semi-arid climate at its southernmost distribution limit by considerable plasticity of the branch hydraulic system and a small but apparently dynamic fine root system.

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1991-01-01

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using X-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1991-01-01

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using x-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Chemical Insights into the Design and Development of Face-Centered Cubic Ruthenium Catalysts for Fischer-Tropsch Synthesis.

PubMed

Li, Wei-Zhen; Liu, Jin-Xun; Gu, Jun; Zhou, Wu; Yao, Si-Yu; Si, Rui; Guo, Yu; Su, Hai-Yan; Yan, Chun-Hua; Li, Wei-Xue; Zhang, Ya-Wen; Ma, Ding

2017-02-15

Ruthenium is a promising low-temperature catalyst for Fischer-Tropsch synthesis (FTS). However, its scarcity and modest specific activity limit its widespread industrialization. We demonstrate here a strategy for tuning the crystal phase of catalysts to expose denser and active sites for a higher mass-specific activity. Density functional theory calculations show that upon CO dissociation there are a number of open facets with modest barrier available on the face-centered cubic (fcc) Ru but only a few step edges with a lower barrier on conventional hexagonal-closest packed (hcp) Ru. Guided by theoretical calculations, water-dispersible fcc Ru catalysts containing abundant open facets were synthesized and showed an unprecedented mass-specific activity in the aqueous-phase FTS, 37.8 mol CO ·mol Ru -1 ·h -1 at 433 K. The mass-specific activity of the fcc Ru catalysts with an average size of 6.8 nm is about three times larger than the previous best hcp catalyst with a smaller size of 1.9 nm and a higher specific surface area. The origin of the higher mass-specific activity of the fcc Ru catalysts is identified experimentally from the 2 orders of magnitude higher density of the active sites, despite its slightly higher apparent barrier. Experimental results are in excellent agreement with prediction of theory. The great influence of the crystal phases on site distribution and their intrinsic activities revealed here provides a rationale design of catalysts for higher mass-specific activity without decrease of the particle size.

Switchable Hydrolase Based on Reversible Formation of Supramolecular Catalytic Site Using a Self-Assembling Peptide.

PubMed

Zhang, Chunqiu; Shafi, Ramim; Lampel, Ayala; MacPherson, Douglas; Pappas, Charalampos G; Narang, Vishal; Wang, Tong; Maldarelli, Charles; Ulijn, Rein V

2017-11-13

The reversible regulation of catalytic activity is a feature found in natural enzymes which is not commonly observed in artificial catalytic systems. Here, we fabricate an artificial hydrolase with pH-switchable activity, achieved by introducing a catalytic histidine residue at the terminus of a pH-responsive peptide. The peptide exhibits a conformational transition from random coil to β-sheet by changing the pH from acidic to alkaline. The β-sheet self-assembles to form long fibrils with the hydrophobic edge and histidine residues extending in an ordered array as the catalytic microenvironment, which shows significant esterase activity. Catalytic activity can be reversible switched by pH-induced assembly/disassembly of the fibrils into random coils. At higher concentrations, the peptide forms a hydrogel which is also catalytically active and maintains its reversible (de-)activation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Creation of forest edges has a global impact on forest vertebrates.

PubMed

Pfeifer, M; Lefebvre, V; Peres, C A; Banks-Leite, C; Wearn, O R; Marsh, C J; Butchart, S H M; Arroyo-Rodríguez, V; Barlow, J; Cerezo, A; Cisneros, L; D'Cruze, N; Faria, D; Hadley, A; Harris, S M; Klingbeil, B T; Kormann, U; Lens, L; Medina-Rangel, G F; Morante-Filho, J C; Olivier, P; Peters, S L; Pidgeon, A; Ribeiro, D B; Scherber, C; Schneider-Maunoury, L; Struebig, M; Urbina-Cardona, N; Watling, J I; Willig, M R; Wood, E M; Ewers, R M

2017-11-09

Forest edges influence more than half of the world's forests and contribute to worldwide declines in biodiversity and ecosystem functions. However, predicting these declines is challenging in heterogeneous fragmented landscapes. Here we assembled a global dataset on species responses to fragmentation and developed a statistical approach for quantifying edge impacts in heterogeneous landscapes to quantify edge-determined changes in abundance of 1,673 vertebrate species. We show that the abundances of 85% of species are affected, either positively or negatively, by forest edges. Species that live in the centre of the forest (forest core), that were more likely to be listed as threatened by the International Union for Conservation of Nature (IUCN), reached peak abundances only at sites farther than 200-400 m from sharp high-contrast forest edges. Smaller-bodied amphibians, larger reptiles and medium-sized non-volant mammals experienced a larger reduction in suitable habitat than other forest-core species. Our results highlight the pervasive ability of forest edges to restructure ecological communities on a global scale.

Creation of forest edges has a global impact on forest vertebrates

NASA Astrophysics Data System (ADS)

Pfeifer, M.; Lefebvre, V.; Peres, C. A.; Banks-Leite, C.; Wearn, O. R.; Marsh, C. J.; Butchart, S. H. M.; Arroyo-Rodríguez, V.; Barlow, J.; Cerezo, A.; Cisneros, L.; D'Cruze, N.; Faria, D.; Hadley, A.; Harris, S. M.; Klingbeil, B. T.; Kormann, U.; Lens, L.; Medina-Rangel, G. F.; Morante-Filho, J. C.; Olivier, P.; Peters, S. L.; Pidgeon, A.; Ribeiro, D. B.; Scherber, C.; Schneider-Maunoury, L.; Struebig, M.; Urbina-Cardona, N.; Watling, J. I.; Willig, M. R.; Wood, E. M.; Ewers, R. M.

2017-11-01

Forest edges influence more than half of the world’s forests and contribute to worldwide declines in biodiversity and ecosystem functions. However, predicting these declines is challenging in heterogeneous fragmented landscapes. Here we assembled a global dataset on species responses to fragmentation and developed a statistical approach for quantifying edge impacts in heterogeneous landscapes to quantify edge-determined changes in abundance of 1,673 vertebrate species. We show that the abundances of 85% of species are affected, either positively or negatively, by forest edges. Species that live in the centre of the forest (forest core), that were more likely to be listed as threatened by the International Union for Conservation of Nature (IUCN), reached peak abundances only at sites farther than 200-400 m from sharp high-contrast forest edges. Smaller-bodied amphibians, larger reptiles and medium-sized non-volant mammals experienced a larger reduction in suitable habitat than other forest-core species. Our results highlight the pervasive ability of forest edges to restructure ecological communities on a global scale.

Vanadium K-edge X-ray absorption spectroscopy of bromoperoxidase from Ascophyllum nodosum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arber, J.M.; de Boer, E.; Garner, C.D.

Bromoperoxidase from Ascophyllum nodusum was the first vanadium-containing enzyme to be isolated. X-ray absorption spectra have now been collected in order to investigate the coordination of vanadium in the native, native plus bromide, native plus hydrogen peroxide, and dithionite-reduced forms of the enzyme. The edge and X-ray absorption near-edge structures show that, in the four samples studied, it is only on reduction of the native enzyme that the metal site is substantially altered. In addition, these data are consistent with the presence of vanadium(IV) in the reduced enzyme and vanadium(V) in the other samples. Extended X-ray absorption fine structure datamore » confirm that there are structural changes at the metal site on reduction of the native enzyme, notably a lengthening of the average inner-shell distance, and the presence of terminal oxygen together with histidine and oxygen-donating residues.« less

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wei; Li, Yani; Yu, Bo

2015-01-15

A successive anchoring of Ti(NMe{sub 2}){sub 4}, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, {sup 13}C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-sitemore » silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, {sup 13}C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated.« less

Towards ALD thin film stabilized single-atom Pd 1 catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piernavieja-Hermida, Mar; Lu, Zheng; White, Anderson

Supported precious metal single-atom catalysts have shown interesting activity and selectivity in recent studies. However, agglomeration of these highly mobile mononuclear surface species can eliminate their unique catalytic properties. In this paper, we study a strategy for synthesizing thin film stabilized single-atom Pd 1 catalysts using atomic layer deposition (ALD). The thermal stability of the Pd 1 catalysts is significantly enhanced by creating a nanocavity thin film structure. In situ infrared spectroscopy and Pd K-edge X-ray absorption spectroscopy (XAS) revealed that the Pd 1 was anchored on the surface through chlorine sites. The thin film stabilized Pd 1 catalysts weremore » thermally stable under both oxidation and reduction conditions. The catalytic performance in the methanol decomposition reaction is found to depend on the thickness of protecting layers. While Pd 1 catalysts showed promising activity at low temperature in a methanol decomposition reaction, 14 cycle TiO 2 protected Pd 1 was less active at high temperature. Pd L 3 edge XAS indicated that the low reactivity compared with Pd nanoparticles is due to the strong adsorption of carbon monoxide even at 250 °C. Lastly, these results clearly show that the ALD nanocavities provide a basis for future design of single-atom catalysts that are highly efficient and stable.« less

Towards ALD thin film stabilized single-atom Pd 1 catalysts

DOE PAGES

Piernavieja-Hermida, Mar; Lu, Zheng; White, Anderson; ...

2016-07-27

Supported precious metal single-atom catalysts have shown interesting activity and selectivity in recent studies. However, agglomeration of these highly mobile mononuclear surface species can eliminate their unique catalytic properties. In this paper, we study a strategy for synthesizing thin film stabilized single-atom Pd 1 catalysts using atomic layer deposition (ALD). The thermal stability of the Pd 1 catalysts is significantly enhanced by creating a nanocavity thin film structure. In situ infrared spectroscopy and Pd K-edge X-ray absorption spectroscopy (XAS) revealed that the Pd 1 was anchored on the surface through chlorine sites. The thin film stabilized Pd 1 catalysts weremore » thermally stable under both oxidation and reduction conditions. The catalytic performance in the methanol decomposition reaction is found to depend on the thickness of protecting layers. While Pd 1 catalysts showed promising activity at low temperature in a methanol decomposition reaction, 14 cycle TiO 2 protected Pd 1 was less active at high temperature. Pd L 3 edge XAS indicated that the low reactivity compared with Pd nanoparticles is due to the strong adsorption of carbon monoxide even at 250 °C. Lastly, these results clearly show that the ALD nanocavities provide a basis for future design of single-atom catalysts that are highly efficient and stable.« less

78 FR 51796 - Self-Regulatory Organizations; NYSE Arca, Inc.; Notice of Filing and Immediate Effectiveness of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-21

... change is available on the Exchange's Web site at www.nyse.com , at the principal office of the Exchange... forms of alternative trading systems (``ATSs''), including dark pools and electronic communication... and Direct Edge. Today, BATS and Direct Edge provide certain market data at no charge on their Web...

Porous Carbon-Hosted Atomically Dispersed Iron-Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Shaofang; Zhu, Chengzhou; Su, Dong

As one of the alternatives to replace precious metal catalysts, transition-metal–nitrogen–carbon (M–N–C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M–N–C catalysts can achieve good electrochemical perfor-mances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. In this work, metal–organic frameworks derived porous single-atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further posttreatment. Combining the X-ray absorption near-edge spectroscopy and electrochemical measure-ments, the SAEs have been identified with superior oxygen reduction reaction (ORR) activity and stability compared with Pt/C catalysts in alkaline condition.more » More impressively, the SAEs also show excellent ORR electrocatalytic perfor-mance in both acid and neutral media. This study of nonprecious catalysts provides new insights on nanoengineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yanli; Sheng, Gang; Juranek, Stefan

The slicer activity of the RNA-induced silencing complex is associated with argonaute, the RNase H-like PIWI domain of which catalyses guide-strand-mediated sequence-specific cleavage of target messenger RNA. Here we report on the crystal structure of Thermus thermophilus argonaute bound to a 5'-phosphorylated 21-base DNA guide strand, thereby identifying the nucleic-acid-binding channel positioned between the PAZ- and PIWI-containing lobes, as well as the pivot-like conformational changes associated with complex formation. The bound guide strand is anchored at both of its ends, with the solvent-exposed Watson-Crick edges of stacked bases 2 to 6 positioned for nucleation with the mRNA target, whereas twomore » critically positioned arginines lock bases 10 and 11 at the cleavage site into an unanticipated orthogonal alignment. Biochemical studies indicate that key amino acid residues at the active site and those lining the 5'-phosphate-binding pocket made up of the Mid domain are critical for cleavage activity, whereas alterations of residues lining the 2-nucleotide 3'-end-binding pocket made up of the PAZ domain show little effect.« less

Porous Carbon-Hosted Atomically Dispersed Iron–Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Shaofang; Zhu, Chengzhou; Su, Dong

2018-02-01

As one of the alternatives to replace precious metal catalysts, transition-metal–nitrogen–carbon (M–N–C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M–N–C catalysts can achieve good electrochemical perfor-mances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. In this work, metal–organic frameworks derived porous single-atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further posttreatment. Combining the X-ray absorption near-edge spectroscopy and electrochemical measure-ments, the SAEs have been identified with superior oxygen reduction reaction (ORR) activity and stability compared with Pt/C catalysts in alkaline condition.more » More impressively, the SAEs also show excellent ORR electrocatalytic perfor-mance in both acid and neutral media. This study of nonprecious catalysts provides new insights on nanoengineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.« less

Crystal field splitting and spin states of Co ions in cobalt ferrite with composition Co1.5Fe1.5O4 using magnetization and X-ray absorption spectroscopy measurements

NASA Astrophysics Data System (ADS)

Sinha, A. K.; Singh, M. N.; Achary, S. N.; Sagdeo, A.; Shukla, D. K.; Phase, D. M.

2017-08-01

Structural, magnetic and electronic properties of partially inverted Cobalt Ferrite with composition Co1.5Fe1.5O4 is discussed in the present work. Single phase (SG: Fd3m) sample is synthesized by co-precipitation technique and subsequent air annealing. The values of saturation magnetization obtained from careful analysis of approach to saturation in initial M(H) curves are used to determine spin states of Co ions in tetrahedral (TH) and octahedral (OH) sites. Spin states of Co3+ ions in TH sites, which has not been reported in literature, were found to be in high spin state. Temperature variation of magnetic parameters has been studied. The sample shows magneto-crystalline anisotropy with two clearly distinct pinning centers. Oxygen K-edge and Fe as well as Co L2,3-edge X-ray absorption (XAS) spectra have been used as complementary measurements to study crystal field splitting and core hole effects on transition metal (TM) 3d orbitals. The ratio of intensities of t2g and eg absorption bands in O-K edge XAS spectrum is used to estimate the spin states of Co ions at OH and TH sites. The results are in agreement with those obtained from magnetization data, and favors Co3+ ions in TH sites in high spin states. Normalized areas of the satellite peaks in TM L2,3-edge XAS spectra have been used to estimate 3dn+1L contribution in ground state wave function and the contributions were found to be significant.

Habitat selection in a rocky landscape: experimentally decoupling the influence of retreat site attributes from that of landscape features.

PubMed

Croak, Benjamin M; Pike, David A; Webb, Jonathan K; Shine, Richard

2012-01-01

Organisms selecting retreat sites may evaluate not only the quality of the specific shelter, but also the proximity of that site to resources in the surrounding area. Distinguishing between habitat selection at these two spatial scales is complicated by co-variation among microhabitat factors (i.e., the attributes of individual retreat sites often correlate with their proximity to landscape features). Disentangling this co-variation may facilitate the restoration or conservation of threatened systems. To experimentally examine the role of landscape attributes in determining retreat-site quality for saxicolous ectotherms, we deployed 198 identical artificial rocks in open (sun-exposed) sites on sandstone outcrops in southeastern Australia, and recorded faunal usage of those retreat sites over the next 29 months. Several landscape-scale attributes were associated with occupancy of experimental rocks, but different features were important for different species. For example, endangered broad-headed snakes (Hoplocephalus bungaroides) preferred retreat sites close to cliff edges, flat rock spiders (Hemicloea major) preferred small outcrops, and velvet geckos (Oedura lesueurii) preferred rocks close to the cliff edge with higher-than-average sun exposure. Standardized retreat sites can provide robust experimental data on the effects of landscape-scale attributes on retreat site selection, revealing interspecific divergences among sympatric taxa that use similar habitats.

One-pot synthesis of CdS nanocrystals hybridized with single-layer transition-metal dichalcogenide nanosheets for efficient photocatalytic hydrogen evolution.

PubMed

Chen, Junze; Wu, Xue-Jun; Yin, Lisha; Li, Bing; Hong, Xun; Fan, Zhanxi; Chen, Bo; Xue, Can; Zhang, Hua

2015-01-19

Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition-metal dichalcogenides (TMDs) showed outstanding performance as co-catalysts for the hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one-pot wet-chemical method is developed to prepare MS2-CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4-10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2-CdS nanohybrids possess a large number of edge sites in the MS2 layers, which are active sites for the HER. The photocatalytic performances of WS2-CdS and MoS2-CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS2-CdS nanohybrids showed enhanced stability after a long-time test (16 h), and 70% of catalytic activity still remained. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Remediation System Evaluation, Savage Municipal Water Supply Superfund Site (PDF)

EPA Pesticide Factsheets

The Savage Municipal Water Supply Superfund Site, located on the western edge of Milford, New Hampshire, consists of a source area and an extended plume that is approximately 6,000 feet long and 2,500 feet wide.

An X-ray absorption spectroscopic study of the metal site preference in Al1-xGaxFeO3

NASA Astrophysics Data System (ADS)

Walker, James D. S.; Grosvenor, Andrew P.

2013-01-01

Magnetoelectric materials have potential for being introduced into next generation technologies, especially memory devices. The AFeO3 (Pna21; A=Al, Ga) system has received attention to better understand the origins of magnetoelectric coupling. The magnetoelectric properties this system exhibits depend on the amount of anti-site disorder present, which is affected by the composition and the method of synthesis. In this study, Al1-xGaxFeO3 was synthesized by the ceramic method and studied by X-ray absorption spectroscopy. Al L2,3-, Ga K-, and Fe K-edge spectra were collected to examine how the average metal coordination number changes with composition. Examination of XANES spectra from Al1-xGaxFeO3 indicate that with increasing Ga content, Al increasingly occupies octahedral sites while Ga displays a preference for occupying the tetrahedral site. The Fe K-edge spectra indicate that more Fe is present in the tetrahedral site in AlFeO3 than in GaFeO3, implying more anti-site disorder is present in AlFeO3.

L-edge sum rule analysis on 3d transition metal sites: from d 10 to d 0 and towards application to extremely dilute metallo-enzymes

DOE PAGES

Wang, Hongxin; Friedrich, Stephan; Li, Lei; ...

2018-02-13

According to L-edge sum rules, the number of 3d vacancies at a transition metal site is directly proportional to the integrated intensity of the L-edge X-ray absorption spectrum (XAS) for the corresponding metal complex. In this study, the numbers of 3d holes are characterized quantitatively or semi-quantitatively for a series of manganese (Mn) and nickel (Ni) complexes, including the electron configurations 3d 10 → 3d 0. In addition, extremely dilute (<0.1% wt/wt) Ni enzymes were examined by two different approaches: (1) by using a high resolution superconducting tunnel junction X-ray detector to obtain XAS spectra with a very high signal-to-noisemore » ratio, especially in the non-variant edge jump region; and (2) by adding an inert tracer to the sample that provides a prominent spectral feature to replace the weak edge jump for intensity normalization. In this publication, we present for the first time: (1) L-edge sum rule analysis for a series of Mn and Ni complexes that include electron configurations from an open shell 3d0 to a closed shell 3d 10; (2) a systematic analysis on the uncertainties, especially on that from the edge jump, which was missing in all previous reports; (3) a clearly-resolved edge jump between pre-L 3 and post-L 2 regions from an extremely dilute sample; (4) an evaluation of an alternative normalization standard for L-edge sum rule analysis. XAS from two copper (Cu) proteins measured using a conventional semiconductor X-ray detector are also repeated as bridges between Ni complexes and dilute Ni enzymes. The differences between measuring 1% Cu enzymes and measuring <0.1% Ni enzymes are compared and discussed. As a result, this study extends L-edge sum rule analysis to virtually any 3d metal complex and any dilute biological samples that contain 3d metals.« less

L-edge sum rule analysis on 3d transition metal sites: from d 10 to d 0 and towards application to extremely dilute metallo-enzymes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hongxin; Friedrich, Stephan; Li, Lei

According to L-edge sum rules, the number of 3d vacancies at a transition metal site is directly proportional to the integrated intensity of the L-edge X-ray absorption spectrum (XAS) for the corresponding metal complex. In this study, the numbers of 3d holes are characterized quantitatively or semi-quantitatively for a series of manganese (Mn) and nickel (Ni) complexes, including the electron configurations 3d 10 → 3d 0. In addition, extremely dilute (<0.1% wt/wt) Ni enzymes were examined by two different approaches: (1) by using a high resolution superconducting tunnel junction X-ray detector to obtain XAS spectra with a very high signal-to-noisemore » ratio, especially in the non-variant edge jump region; and (2) by adding an inert tracer to the sample that provides a prominent spectral feature to replace the weak edge jump for intensity normalization. In this publication, we present for the first time: (1) L-edge sum rule analysis for a series of Mn and Ni complexes that include electron configurations from an open shell 3d0 to a closed shell 3d 10; (2) a systematic analysis on the uncertainties, especially on that from the edge jump, which was missing in all previous reports; (3) a clearly-resolved edge jump between pre-L 3 and post-L 2 regions from an extremely dilute sample; (4) an evaluation of an alternative normalization standard for L-edge sum rule analysis. XAS from two copper (Cu) proteins measured using a conventional semiconductor X-ray detector are also repeated as bridges between Ni complexes and dilute Ni enzymes. The differences between measuring 1% Cu enzymes and measuring <0.1% Ni enzymes are compared and discussed. As a result, this study extends L-edge sum rule analysis to virtually any 3d metal complex and any dilute biological samples that contain 3d metals.« less

Electron distributions in the plasma sheet boundary layer - Time-of-flight effects

NASA Technical Reports Server (NTRS)

Onsager, T. G.; Thomsen, M. F.; Gosling, J. T.; Bame, S. J.

1990-01-01

The electron edge of the plasma sheet boundary layer lies lobeward of the ion edge. Measurements obtained near the electron edge of the boundary layer reveal low-speed cutoffs for earthward and tailward-flowing electrons. These cutoffs progress to lower speeds with deeper penetration into the boundary layer, and are consistently lower for the earthward-directed electrons than for the tailward-direction electrons. The cutoffs and their variation with distance from the edge of the boundary layer can be consistently interpreted in terms of a time-of-flight effect on recently reconnected magnetic field lines. The observed cutoff speeds are used to estimate the downtail location of the reconnection site.

The non-receptor tyrosine kinase Lyn controls neutrophil adhesion by recruiting the CrkL–C3G complex and activating Rap1 at the leading edge

PubMed Central

He, Yuan; Kapoor, Ashish; Cook, Sara; Liu, Shubai; Xiang, Yang; Rao, Christopher V.; Kenis, Paul J. A.; Wang, Fei

2011-01-01

Establishing new adhesions at the extended leading edges of motile cells is essential for stable polarity and persistent motility. Despite recent identification of signaling pathways that mediate polarity and chemotaxis in neutrophils, little is known about molecular mechanisms governing cell–extracellular-matrix (ECM) adhesion in these highly polarized and rapidly migrating cells. Here, we describe a signaling pathway in neutrophils that is essential for localized integrin activation, leading edge attachment and persistent migration during chemotaxis. This pathway depends upon Gi-protein-mediated activation and leading edge recruitment of Lyn, a non-receptor tyrosine kinase belonging to the Src kinase family. We identified the small GTPase Rap1 as a major downstream effector of Lyn to regulate neutrophil adhesion during chemotaxis. Depletion of Lyn in neutrophil-like HL-60 cells prevented chemoattractant-induced Rap1 activation at the leading edge of the cell, whereas ectopic expression of Rap1 largely rescued the defects induced by Lyn depletion. Furthermore, Lyn controls spatial activation of Rap1 by recruiting the CrkL–C3G protein complex to the leading edge. Together, these results provide novel mechanistic insights into the poorly understood signaling network that controls leading edge adhesion during chemotaxis of neutrophils, and possibly other amoeboid cells. PMID:21628423

Bird productivity and nest predation in agricultural grasslands

USGS Publications Warehouse

Ribic, Christine; Guzy, Michael J.; Anderson, Travis J.; Sample, David W.; Nack, Jamie L.

2012-01-01

Effective conservation strategies for grassland birds in agricultural landscapes require understanding how nesting success varies among different grassland habitats. A key component to this is identifying nest predators and how these predators vary by habitat. We quantified nesting activity of obligate grassland birds in three habitats [remnant prairie, cool-season grass Conservation Reserve Program (CRP) fields, and pastures) in southwest Wisconsin, 2002-2004. We determined nest predators using video cameras and examined predator activity using track stations. Bobolink (Dolichonyx oryzivorus) and Henslow's Sparrow (Ammodramus henslowii) nested primarily in CRP fields, and Grasshopper Sparrow (A. savannarum) in remnant prairies. Eastern Meadowlark (Sturnella magna) nested evenly across all three habitats. Daily nest survival rate for Eastern Meadowlark varied by nesting stage alone. Daily nest survival rate for Grasshopper Sparrow varied by nest vegetation and distance to the nearest woody edge; nest survival was higher near woody edges. In CRP fields, most predators were grassland-associated, primarily thirteen-lined ground squirrels (Ictidomys tridecemlineatus). In pastures, one-third of the nest predators were grassland-associated (primarily thirteen-lined ground squirrels) and 56% were associated with woody habitats (primarily raccoons, Procyon lotor). Raccoon activity was greatest around pastures and lowest around prairies; regardless of habitat, raccoon activity along woody edges was twice that along non-woody edges. Thirteen-lined ground squirrel activity was greater along prairie edges than pastures and was greater along nonwoody edges compared to woody edges. In CRP fields, raccoon activity was greater along edges compared to the interiors; for ground squirrels these relationships were reversed. Using video camera technology to identify nest predators was indispensable in furthering our understanding of the grassland system. The challenge is to use that knowledge to develop management actions for both birds and predators.

Sulfur K-edge X-ray absorption spectroscopy and density functional theory calculations on monooxo Mo(IV) and bisoxo Mo(VI) bis-dithiolenes: insights into the mechanism of oxo transfer in sulfite oxidase and its relation to the mechanism of DMSO reductase.

PubMed

Ha, Yang; Tenderholt, Adam L; Holm, Richard H; Hedman, Britt; Hodgson, Keith O; Solomon, Edward I

2014-06-25

Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of two complexes [Mo(IV)O(bdt)2](2-) and [Mo(VI)O2(bdt)2](2-) (bdt = benzene-1,2-dithiolate(2-)) that relate to the reduced and oxidized forms of sulfite oxidase (SO). These are compared with those of previously studied dimethyl sulfoxide reductase (DMSOr) models. DFT calculations supported by the data are extended to evaluate the reaction coordinate for oxo transfer to a phosphite ester substrate. Three possible transition states are found with the one at lowest energy, stabilized by a P-S interaction, in good agreement with experimental kinetics data. Comparison of both oxo transfer reactions shows that in DMSOr, where the oxo is transferred from the substrate to the metal ion, the oxo transfer induces electron transfer, while in SO, where the oxo transfer is from the metal site to the substrate, the electron transfer initiates oxo transfer. This difference in reactivity is related to the difference in frontier molecular orbitals (FMO) of the metal-oxo and substrate-oxo bonds. Finally, these experimentally related calculations are extended to oxo transfer by sulfite oxidase. The presence of only one dithiolene at the enzyme active site selectively activates the equatorial oxo for transfer, and allows facile structural reorganization during turnover.

Seismic site characterization of an urban dedimentary basin, Livermore Valley, California: Site tesponse, basin-edge-induced surface waves, and 3D simulations

USGS Publications Warehouse

Hartzell, Stephen; Leeds, Alena L.; Ramirez-Guzman, Leonardo; Allen, James P.; Schmitt, Robert G.

2016-01-01

Thirty‐two accelerometers were deployed in the Livermore Valley, California, for approximately one year to study sedimentary basin effects. Many local and near‐regional earthquakes were recorded, including the 24 August 2014 Mw 6.0 Napa, California, earthquake. The resulting ground‐motion data set is used to quantify the seismic response of the Livermore basin, a major structural depression in the California Coast Range Province bounded by active faults. Site response is calculated by two methods: the reference‐site spectral ratio method and a source‐site spectral inversion method. Longer‐period (≥1  s) amplification factors follow the same general pattern as Bouguer gravity anomaly contours. Site response spectra are inverted for shallow shear‐wave velocity profiles, which are consistent with independent information. Frequency–wavenumber analysis is used to analyze plane‐wave propagation across the Livermore Valley and to identify basin‐edge‐induced surface waves with back azimuths different from the source back azimuth. Finite‐element simulations in a 3D velocity model of the region illustrate the generation of basin‐edge‐induced surface waves and point out strips of elevated ground velocities along the margins of the basin.

Shape-Dependent Electrocatalytic Reduction of CO2 to CO on Triangular Silver Nanoplates.

PubMed

Liu, Subiao; Tao, Hongbiao; Zeng, Li; Liu, Qi; Xu, Zhenghe; Liu, Qingxia; Luo, Jing-Li

2017-02-15

Electrochemical reduction of CO 2 (CO 2 RR) provides great potential for intermittent renewable energy storage. This study demonstrates a predominant shape-dependent electrocatalytic reduction of CO 2 to CO on triangular silver nanoplates (Tri-Ag-NPs) in 0.1 M KHCO 3 . Compared with similarly sized Ag nanoparticles (SS-Ag-NPs) and bulk Ag, Tri-Ag-NPs exhibited an enhanced current density and significantly improved Faradaic efficiency (96.8%) and energy efficiency (61.7%), together with a considerable durability (7 days). Additionally, CO starts to be observed at an ultralow overpotential of 96 mV, further confirming the superiority of Tri-Ag-NPs as a catalyst for CO 2 RR toward CO formation. Density functional theory calculations reveal that the significantly enhanced electrocatalytic activity and selectivity at lowered overpotential originate from the shape-controlled structure. This not only provides the optimum edge-to-corner ratio but also dominates at the facet of Ag(100) where it requires lower energy to initiate the rate-determining step. This study demonstrates a promising approach to tune electrocatalytic activity and selectivity of metal catalysts for CO 2 RR by creating optimal facet and edge site through shape-control synthesis.

Acidity of edge surface sites of montmorillonite and kaolinite

NASA Astrophysics Data System (ADS)

Liu, Xiandong; Lu, Xiancai; Sprik, Michiel; Cheng, Jun; Meijer, Evert Jan; Wang, Rucheng

2013-09-01

Acid-base chemistry of clay minerals is central to their interfacial properties, but up to now a quantitative understanding on the surface acidity is still lacking. In this study, with first principles molecular dynamics (FPMD) based vertical energy gap technique, we calculate the acidity constants of surface groups on (0 1 0)-type edges of montmorillonite and kaolinite, which are representatives of 2:1 and 1:1-type clay minerals, respectively. It shows that tbnd Si-OH and tbnd Al-OH2OH groups of kaolinite have pKas of 6.9 and 5.7 and those of montmorillonite have pKas of 7.0 and 8.3, respectively. For each mineral, the calculated pKas are consistent with the experimental ranges derived from fittings of titration curves, indicating that tbnd Si-OH and tbnd Al-OH2OH groups are the major acidic sites responsible to pH-dependent experimental observations. The effect of Mg substitution in montmorillonite is investigated and it is found that Mg substitution increases the pKas of the neighboring tbnd Si-OH and tbnd Si-OH2 groups by 2-3 pKa units. Furthermore, our calculation shows that the pKa of edge tbnd Mg-(OH2)2 is as high as 13.2, indicating the protonated state dominates under common pH. Together with previous adsorption experiments, our derived acidity constants suggest that tbnd Si-O- and tbnd Al-(OH)2 groups are the most probable edge sites for complexing heavy metal cations.

1. VIEW OF THE WILBURWOMBLE MILL SITE, LOOKING NORTHEAST FROM ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. VIEW OF THE WILBUR-WOMBLE MILL SITE, LOOKING NORTHEAST FROM LITTLE JOHNS CREEK. THE THREE CONCRETE MORTAR BLOCKS MARK THE LOCATION OF THE STAMP BATTERIES - Wilbur-Womble Mill, Southern Edge Of Salt Spring Valley, Copperopolis, Calaveras County, CA

Active edge maps for medical image registration

NASA Astrophysics Data System (ADS)

Kerwin, William; Yuan, Chun

2001-07-01

Applying edge detection prior to performing image registration yields several advantages over raw intensity- based registration. Advantages include the ability to register multicontrast or multimodality images, immunity to intensity variations, and the potential for computationally efficient algorithms. In this work, a common framework for edge-based image registration is formulated as an adaptation of snakes used in boundary detection. Called active edge maps, the new formulation finds a one-to-one transformation T(x) that maps points in a source image to corresponding locations in a target image using an energy minimization approach. The energy consists of an image component that is small when edge features are well matched in the two images, and an internal term that restricts T(x) to allowable configurations. The active edge map formulation is illustrated here with a specific example developed for affine registration of carotid artery magnetic resonance images. In this example, edges are identified using a magnitude of gradient operator, image energy is determined using a Gaussian weighted distance function, and the internal energy includes separate, adjustable components that control volume preservation and rigidity.

Occupancy and abundance of wintering birds in a dynamic agricultural landscape

USGS Publications Warehouse

Miller, Mark W.; Pearlstine, Elise V.; Dorazio, Robert M.; Mazzotti, Frank J.

2011-01-01

Assessing wildlife management action requires monitoring populations, and abundance often is the parameter monitored. Recent methodological advances have enabled estimation of mean abundance within a habitat using presence–absence or count data obtained via repeated visits to a sample of sites. These methods assume populations are closed and intuitively assume habitats within sites change little during a field season. However, many habitats are highly variable over short periods. We developed a variation of existing occupancy and abundance models that allows for extreme spatio-temporal differences in habitat, and resulting changes in wildlife abundance, among sites and among visits to a site within a field season. We conducted our study in sugarcane habitat within the Everglades Agricultural Area southeast of Lake Okeechobee in south Florida. We counted wintering birds, primarily passerines, within 245 sites usually 5 times at each site during December 2006–March 2007. We estimated occupancy and mean abundance of birds in 6 vegetation states during the sugarcane harvest and allowed these parameters to vary temporally or spatially within a vegetation state. Occupancy and mean abundance of the common yellowthroat (Geothlypis trichas) was affected by structure of sugarcane and uncultivated edge vegetation (occupancy=1.00 [95%CĪ=0.96–1.00] and mean abundance=7.9 [95%CĪ=3.2–19.5] in tall sugarcane with tall edge vegetation versus 0.20 [95%CĪ=0.04–0.71] and 0.22 [95%CĪ=0.04–1.2], respectively, in short sugarcane with short edge vegetation in one half of the study area). Occupancy and mean abundance of palm warblers (Dendroica palmarum) were constant (occupancy=1.00, 95%CĪ=0.69–1.00; mean abundance=18, 95%CĪ=1–270). Our model may enable wildlife managers to assess rigorously effects of future edge habitat management on avian distribution and abundance within agricultural landscapes during winter or the breeding season. The model may also help wildlife managers make similar management decisions involving other dynamic habitats such as wetlands, prairies, and even forested areas if forest management or fires occur during the field season.

Occupancy and abundance of wintering birds in a dynamic agricultural landscape

USGS Publications Warehouse

Miller, M.W.; Pearlstine, E.V.; Dorazio, R.M.; Mazzotti, F.J.

2011-01-01

Assessing wildlife management action requires monitoring populations, and abundance often is the parameter monitored. Recent methodological advances have enabled estimation of mean abundance within a habitat using presence-absence or count data obtained via repeated visits to a sample of sites. These methods assume populations are closed and intuitively assume habitats within sites change little during a field season. However, many habitats are highly variable over short periods. We developed a variation of existing occupancy and abundance models that allows for extreme spatio-temporal differences in habitat, and resulting changes in wildlife abundance, among sites and among visits to a site within a field season. We conducted our study in sugarcane habitat within the Everglades Agricultural Area southeast of Lake Okeechobee in south Florida. We counted wintering birds, primarily passerines, within 245 sites usually 5 times at each site during December 2006-March 2007. We estimated occupancy and mean abundance of birds in 6 vegetation states during the sugarcane harvest and allowed these parameters to vary temporally or spatially within a vegetation state. Occupancy and mean abundance of the common yellowthroat (Geothlypis trichas) was affected by structure of sugarcane and uncultivated edge vegetation (occupancy = 1.00 [95%C?? = 0.96-1.00] and mean abundance = 7.9 [95%C?? = 3.2-19.5] in tall sugarcane with tall edge vegetation versus 0.20 [95%C?? = 0.04-0.71] and 0.22 [95%C?? = 0.04-1.2], respectively, in short sugarcane with short edge vegetation in one half of the study area). Occupancy and mean abundance of palm warblers (Dendroica palmarum) were constant (occupancy = 1.00, 95%C?? = 0.69-1.00; mean abundance = 18, 95%C?? = 1-270). Our model may enable wildlife managers to assess rigorously effects of future edge habitat management on avian distribution and abundance within agricultural landscapes during winter or the breeding season. The model may also help wildlife managers make similar management decisions involving other dynamic habitats such as wetlands, prairies, and even forested areas if forest management or fires occur during the field season. ?? 2011 The Wildlife Society.

Long- and Short-Range Structure of Ferrimagnetic Iron-Chromium Maghemites.

PubMed

García-Guaderrama, Marco; Montero-Cabrera, María E; Morán, Emilio; Alario-Franco, Miguel A; Fuentes-Cobas, Luis E; Macías-Ríos, Edgar; Esparza-Ponce, Hilda E; Fuentes-Montero, María E

2015-12-07

Maghemite-like materials containing Fe(3+) and Cr(3+) in comparable amounts have been prepared by solution-combustion synthesis. The conditions of synthesis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure iron maghemite since their maghemite-hematite transformation takes place at about ∼ 700 °C instead of ∼ 300 °C, as usually reported. These materials were studied by synchrotron radiation X-ray diffraction (XRD) and by X-ray absorption fine structure (XAFS) of the K-absorption edge of two elements. High-resolution XRD patterns were processed by means of the Rietveld method. Thus, maghemites were studied by XAFS in both Fe and Cr K-edges to clarify the short-range structure of the investigated systems. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure transitions were performed. The extended X-ray absorption fine structure (EXAFS) spectra were fitted considering the facts that the central atom of Fe is able to occupy octahedral and tetrahedral sites, each with a weight adjustment, while Cr occupies only octahedral sites. Interatomic distances were determined for x = 1, by fitting simultaneously both Fe and Cr K-edges average EXAFS spectra. The results showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO3).

National Program of Inspection of Non-Federal Dams, Tennessee. Glady Hollow Dam (OFDBA Site 41-1) (Inventory Number TN 13113), Obion River Basin, near Lassiter Corner, Tennessee, Obion County, Tennessee. Phase I Investigation Report.

DTIC Science & Technology

1981-09-01

collection pipes wrapped in filter cloth. The dam is situated near the edge of the loess bluffs in northwest Tennessee that overlooks Reelfoot Lake ...roughly six miles west of Hornbeak, in Obion County, Tennessee. The site is located near the edge of the loess bluff overlooking Reelfoot Lake to the...feet long with a crest width of 15 feet. It is in the small size and high hazard potential category. The structure impounds a 5.5 acre lake used for

Contribution of planktonic and benthic food sources to the diet of the reef-forming vermetid gastropod Dendropoma petraeum in the western Mediterranean

NASA Astrophysics Data System (ADS)

Vizzini, Salvatrice; Colombo, Francesca; Costa, Valentina; Mazzola, Antonio

2012-01-01

In the Mediterranean Sea, the vermetid Dendropoma petraeum (Monterosato, 1884) forms highly biodiverse reefs that have received increasing attention in recent years although very little is known about the food habit of this species. The main goal of this study was to describe the trophic role of planktonic and benthic food sources for D. petraeum. Specimens from three morphological zones of the reef (inner edge, cuvette and outer edge) at two sites with different wave exposure along the north-western coast of Sicily (Italy; western Mediterranean) were compared for δ 13C and δ 15N. Isotopic determinations were also carried out on potential food sources identified in epilithon, reef macroalgae and suspended particulate organic matter. δ 13C for D. petraeum showed significantly more depleted values in the more exposed conditions (i.e. the site with higher wave exposure and outer edge of the reef), while δ 15N did not differ appreciably. These results suggest greater exploitation of benthic sources in the sheltered than in the exposed site and reveal diet shift and trophic flexibility at a small spatial scale for the reef-former D. petraeum.

The influence of the membrane-polymer interface on colloidal membrane dynamics and phase behavior

NASA Astrophysics Data System (ADS)

Zakhary, Mark J.

A primary challenge in the field of self-assembly is to identify simple interactions that produce well-defined, complex, and controllable materials. A large part of this task is to creatively engineer appropriate assembly components with such suitable interactions built-in. Here, we demonstrate that rod-like subunits, experimentally modeled by fd bacteriophage viruses, with simple and predictable hard-core repulsive interactions, exhibit a great wealth of fascinating self-assembly behavior. These rods form two-dimensional liquid crystalline colloidal membranes consisting of monolayers of aligned particles owing purely to entropic considerations. Due to surface tension, rods near the edge of the monolayers twist, resulting in an elastic nematic ring surrounding the fluid-like membrane interior, and it is the rich phenomena rooted in the interplay between the edge and the interior that is the subject of this thesis. The chiral nature of the fd subunits causes a symmetry breaking at the membrane edge, which leads to chiral control of interfacial tension and resultantly a controllable, reversible morphological transition between membranes and one-dimensional twisted ribbons. Using optical microscopic and optical tweezer techniques, we show that a nucleation barrier exists in association with the membrane-ribbon transition, and investigate this barrier using fluctuation analysis as well as highly controlled force-extension experiments. The finite bending rigidity of the membrane edge is studied, and we show that long filamentous polymers spontaneously adhere to the edge, introducing the concept of geometrical edge-active agents. By analyzing the suppressed edge fluctuations of filament-bound membranes, it is found that the edge bending rigidity varies by up to an order of magnitude in a predictable and controllable way. Finally, we study the effect of the monolayer edge on the membrane coalescence, and observe two types of stable liquid crystalline defects that form at the coalescence site due to chiral incompatibility and frustration. By observing the fluctuations of these structures under various sample conditions, we quantify physical parameters associated with the defects, as well as their respective regions of stability. Optical tweezers are used to easily effect controllable membrane self-coalescence, which allows for imprinting defect networks, transforming between defect types, and imparting irreversible topological alterations to defects.

Localized Ras signaling at the leading edge regulates PI3K, cell polarity, and directional cell movement

PubMed Central

Sasaki, Atsuo T.; Chun, Cheryl; Takeda, Kosuke; Firtel, Richard A.

2004-01-01

During chemotaxis, receptors and heterotrimeric G-protein subunits are distributed and activated almost uniformly along the cell membrane, whereas PI(3,4,5)P3, the product of phosphatidylinositol 3-kinase (PI3K), accumulates locally at the leading edge. The key intermediate event that creates this strong PI(3,4,5)P3 asymmetry remains unclear. Here, we show that Ras is rapidly and transiently activated in response to chemoattractant stimulation and regulates PI3K activity. Ras activation occurs at the leading edge of chemotaxing cells, and this local activation is independent of the F-actin cytoskeleton, whereas PI3K localization is dependent on F-actin polymerization. Inhibition of Ras results in severe defects in directional movement, indicating that Ras is an upstream component of the cell's compass. These results support a mechanism by which localized Ras activation mediates leading edge formation through activation of basal PI3K present on the plasma membrane and other Ras effectors required for chemotaxis. A feedback loop, mediated through localized F-actin polymerization, recruits cytosolic PI3K to the leading edge to amplify the signal. PMID:15534002

Waterbird nest-site selection is influenced by neighboring nests and island topography

USGS Publications Warehouse

Hartman, Christopher; Ackerman, Joshua T.; Takekawa, John Y.; Herzog, Mark

2016-01-01

Avian nest-site selection is influenced by factors operating across multiple spatial scales. Identifying preferred physical characteristics (e.g., topography, vegetation structure) can inform managers to improve nesting habitat suitability. However, social factors (e.g., attraction, territoriality, competition) can complicate understanding physical characteristics preferred by nesting birds. We simultaneously evaluated the physical characteristics and social factors influencing selection of island nest sites by colonial-nesting American avocets (Recurvirostra americana) and Forster's terns (Sterna forsteri) at 2 spatial scales in San Francisco Bay, 2011–2012. At the larger island plot (1 m2) scale, we used real-time kinematics to produce detailed topographies of nesting islands and map the distribution of nests. Nesting probability was greatest in island plots between 0.5 m and 1.5 m above the water surface, at distances <10 m from the water's edge, and of moderately steep (avocets) or flat (terns) slopes. Further, avocet and tern nesting probability increased as the number of nests initiated in adjacent plots increased up to a peak of 11–12 tern nests, and then decreased thereafter. Yet, avocets were less likely to nest in plots adjacent to plots with nesting avocets, suggesting an influence of intra-specific territoriality. At the smaller microhabitat scale, or the area immediately surrounding the nest, we compared topography, vegetation, and distance to nearest nest between nest sites and paired random sites. Topography had little influence on selection of the nest microhabitat. Instead, nest sites were more likely to have vegetation present, and greater cover, than random sites. Finally, avocet, and to a lesser extent tern, nest sites were closer to other active conspecific or heterospecific nests than random sites, indicating that social attraction played a role in selection of nest microhabitat. Our results demonstrate key differences in nest-site selection between co-occurring avocets and terns, and indicate the effects of physical characteristics and social factors on selection of nesting habitat are dependent on the spatial scale examined. Moreover, these results indicate that islands with abundant area between 0.5 m and 1.5 m above the water surface, within 10 m of the water's edge, and containing a mosaic of slopes ranging from flat to moderately steep would provide preferred nesting habitat for avocets and terns. © 2016 The Wildlife Society.

A Novel Wound Retractor Combining Continuous Irrigation and Barrier Protection Reduces Incisional Contamination in Colorectal Surgery.

PubMed

Papaconstantinou, Harry T; Ricciardi, Rocco; Margolin, David A; Bergamaschi, Roberto; Moesinger, Robert C; Lichliter, Warren E; Birnbaum, Elisa H

2018-03-09

Surgical site infection (SSI) remains a persistent and morbid problem in colorectal surgery. Key to its pathogenesis is the degree of intraoperative bacterial contamination at the surgical site. The purpose of this study was to evaluate a novel wound retractor at reducing bacterial contamination. A prospective multicenter pilot study utilizing a novel wound retractor combining continuous irrigation and barrier protection was conducted in patients undergoing elective colorectal resections. Culture swabs were collected from the incision edge prior to device placement and from the exposed and protected incision edge prior to device removal. The primary and secondary endpoints were the rate of enteric and overall bacterial contamination on the exposed incision edge as compared to the protected incision edge, respectively. The safety endpoint was the absence of serious device-related adverse events. A total of 86 patients were eligible for analysis. The novel wound retractor was associated with a 66% reduction in overall bacterial contamination at the protected incision edge compared to the exposed incision edge (11.9 vs. 34.5%, P < 0.001), and 71% reduction in enteric bacterial contamination (9.5% vs. 33.3%, P < 0.001). The incisional SSI rate was 2.3% in the primary analysis and 1.2% in those that completed the protocol. There were no adverse events attributed to device use. A novel wound retractor combining continuous irrigation and barrier protection was associated with a significant reduction in bacterial contamination. Improved methods to counteract wound contamination represent a promising strategy for SSI prevention (NCT 02413879).

Geologic and Site Survey Setting for JIP Gulf of Mexico Gas Hydrate Drilling

NASA Astrophysics Data System (ADS)

Hutchinson, D. R.; Snyder, F.; Hart, P. E.; Ruppel, C. D.; Pohlman, J.; Wood, W. T.; Coffin, R. B.; Edwards, K. M.

2005-12-01

The JIP Gulf of Mexico drilling program targeted two contrasting geologic settings to understand natural gas hydrates: a salt-withdrawal minibasin and a mound/seep site, both at mid-slope water depths of about 1300 m. The minibasin site (lease block Keathley Canyon 151) contains a Bottom Simulating Reflection (BSR) that deepens from 260 m below the sea floor near the edge of the basin to 500 mbsf towards the center of the basin. Drilling was conducted at a site in which the BSR is about 415 mbsf. Seismic stratigraphy of the minibasin consists of continuous laminated sequences of variable thicknesses alternating with more massive units of discontinuous reflections. These sequences represent uniform hemipelagic deposition, which drapes the basin, and turbidite deposition, which pinches out along the basin edges. The BSR crosses several of these sequences. A map of amplitude values at the BSR shows a strong banding pattern indicative of the layering, with the highest amplitudes interpreted to be trapped gas in the coarser-grained units. Prior to drilling, piston-core data indicated extensive shallow mass wasting near the edges of the minibasin. Heat flow data indicated thermal gradients that in general predicted a BSR deeper than observed in the seismic data. Full-waveform inversion of 3D multichannel data indicated a probable thick zone of low-saturation hydrate immediately above the BSR. There is little coherent seismic stratigraphy at the mound/seep site in the Mississippi Canyon (lease blocks Atwater Valley 13/14), as the canyon fill is dominated by a complex mix of turbidite and mass-wasting deposits. Hints of a possible BSR that is warped upwards beneath the mound can be seen in both 3D and 2D multichannel seismic data, but it cannot be traced laterally away from the mound with any certainty. A seismic pull-down pseudo-structure beneath the mound suggests the presence of a free-gas low-velocity zone at shallow depths. Pore-water analyses from shallow piston cores and closely-spaced heat-flow data indicate the mound is a site of probable fluid venting. A transect of bottom photographs crosses a possible mud flow and numerous bacterial mats, consistent with features seen in fluid venting at other sites in the Gulf. Prestack inversion of the multichannel data did not predict significant gas hydrate at the site on the edge of the mound. However, at the control site off the mound, predictions were more favorable for low hydrate saturations in the deeper part of the drill hole.

Active Control of Separation From the Flap of a Supercritical Airfoil

NASA Technical Reports Server (NTRS)

Melton, La Tunia Pack; Yao, Chung-Sheng; Seifert, Avi

2003-01-01

Active flow control in the form of periodic zero-mass-flux excitation was applied at several regions on the leading edge and trailing edge flaps of a simplified high-lift system t o delay flow separation. The NASA Energy Efficient Transport (EET) supercritical airfoil was equipped with a 15% chord simply hinged leading edge flap and a 25% chord simply hinged trailing edge flap. Detailed flow features were measured in an attempt to identify optimal actuator placement. The measurements included steady and unsteady model and tunnel wall pressures, wake surveys, arrays of surface hot-films, flow visualization, and particle image velocimetry (PIV). The current paper describes the application of active separation control at several locations on the deflected trailing edge flap. High frequency (F(+) approx.= 10) and low frequency amplitude modulation (F(+)AM approx.= 1) of the high frequency excitation were used for control. Preliminary efforts to combine leading and trailing edge flap excitations are also reported.

Continuous multi-component geophysical experiment on LUSI mud edifice: What can we learn from it?

NASA Astrophysics Data System (ADS)

Mauri, Guillaume; Husein, Alwi; Karyono, Karyono; Hadi, Soffian; Mazzini, Adriano; Collignon, Marine; Faubert, Maïté; Miller, Stephen A.; Lupi, Matteo

2016-04-01

The Lusi eruption is located in East Java, Indonesia, and is ongoing since May 29th, 2006. In the framework of joined international projects, several joint geophysical studies focussing on seismic monitoring, spatial investigation over the mud edifice and its surroundings are being conducted. Here we present freshly acquired data from a test site to investigate: (1) potential change in the natural electrical self-potential generation over time (2) potential change in gravity field associated to change in mass or volume, (3) if the geysering activity generates disruption on either the electrical or gravity field. We selected a location ˜200m to the NE of the active Lusi crater. The experiment site covers an area of 60m x 80m, crossing the boundaries between the soft and the solid walkable mud. The western edge of the study area was less than 100m away from the rim of the crater site. A self-potential array made of 6 Pb-PbCl2 electrodes was deployed over the site. The electrodes were positioned inside active seeps, on dry unaltered zones and close to the mud stream that flushes the water erupted from the crater site. All the electrodes were connected to a single Pb-PbCl2 electrode reference. A second array of 7 thermometers was installed positioning 5 of them next to SP electrodes, one to measure atmospheric temperature and another P/T probe to monitor the stream water. In addition a seismometer coupled with a HD video camera, a thermal camera and a gravimeter recorded on site for several days monitoring visual and seismic activity of the crater. The collected data allows us to 1) monitor and define the different geysering activities ongoing at the crater, 2) define the delay existing between the recorded seismicity and the visual observations, 3) verify if the crater activity triggers perturbations that are transmitted to e.g. the thousands of satellite seeps distributed in the 7 square kilometers zone inside the embankment; 4) how significant is the delay between the crater activity and the water streamed out.

Enhanced electrocatalytic activity of MoS(x) on TCNQ-treated electrode for hydrogen evolution reaction.

PubMed

Chang, Yung-Huang; Nikam, Revannath D; Lin, Cheng-Te; Huang, Jing-Kai; Tseng, Chien-Chih; Hsu, Chang-Lung; Cheng, Chia-Chin; Su, Ching-Yuan; Li, Lain-Jong; Chua, Daniel H C

2014-10-22

Molybdenum sulfide has recently attracted much attention because of its low cost and excellent catalytical effects in the application of hydrogen evolution reaction (HER). To improve the HER efficiency, many researchers have extensively explored various avenues such as material modification, forming hybrid structures or modifying geometric morphology. In this work, we reported a significant enhancement in the electrocatalytic activity of the MoSx via growing on Tetracyanoquinodimethane (TCNQ) treated carbon cloth, where the MoSx was synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)2MoS4) precursor at 170 °C. The pyridinic N- and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formation of Mo(5+) and S2(2-) species in the MoSx, especially with S2(2-) serving as an active site for HER. In addition, the smaller particle size of the MoSx grown on TCNQ-treated carbon cloth reveals a high ratio of edge sites relative to basal plane sites, indicating the richer effective reaction sites and superior electrocatalytic characteristics. Hence, we reported a high hydrogen evolution rate for MoSx on TCNQ-treated carbon cloth of 6408 mL g(-1) cm(-2) h(-1) (286 mmol g(-1) cm(-2) h(-1)) at an overpotential of V = 0.2 V. This study provides the fundamental concepts useful in the design and preparation of transition metal dichalcogenide catalysts, beneficial in the development in clean energy.

Mitigation of EMU Cut Glove Hazard from Micrometeoroid and Orbital Debris Impacts on ISS Handrails

NASA Technical Reports Server (NTRS)

Ryan, Shannon; Christiansen, Eric L.; Davis, Bruce A.; Ordonez, Erick

2009-01-01

Recent cut damages sustained on crewmember gloves during extravehicular activity (ISS) onboard the International Space Station (ISS) have been caused by contact with sharp edges or a pinch point according to analysis of the damages. One potential source are protruding sharp edged crater lips from micrometeoroid and orbital debris (MMOD) impacts on metallic handrails along EVA translation paths. A number of hypervelocity impact tests were performed on ISS handrails, and found that mm-sized projectiles were capable of inducing crater lip heights two orders of magnitude above the minimum value for glove abrasion concerns. Two techniques were evaluated for mitigating the cut glove hazard of MMOD impacts on ISS handrails: flexible overwraps which act to limit contact between crewmember gloves and impact sites, and; alternate materials which form less hazardous impact crater profiles. In parallel with redesign efforts to increase the cut resilience of EMU gloves, the modifications to ISS handrails evaluated in this study provide the means to significantly reduce cut glove risk from MMOD impact craters

Scalable Low-Cost Fabrication of Disposable Paper Sensors for DNA Detection

PubMed Central

2015-01-01

Controlled integration of features that enhance the analytical performance of a sensor chip is a challenging task in the development of paper sensors. A critical issue in the fabrication of low-cost biosensor chips is the activation of the device surface in a reliable and controllable manner compatible with large-scale production. Here, we report stable, well-adherent, and repeatable site-selective deposition of bioreactive amine functionalities and biorepellant polyethylene glycol-like (PEG) functionalities on paper sensors by aerosol-assisted, atmospheric-pressure, plasma-enhanced chemical vapor deposition. This approach requires only 20 s of deposition time, compared to previous reports on cellulose functionalization, which takes hours. A detailed analysis of the near-edge X-ray absorption fine structure (NEXAFS) and its sensitivity to the local electronic structure of the carbon and nitrogen functionalities. σ*, π*, and Rydberg transitions in C and N K-edges are presented. Application of the plasma-processed paper sensors in DNA detection is also demonstrated. PMID:25423585

Scalable Low-Cost Fabrication of Disposable Paper Sensors for DNA Detection

DOE PAGES

Gandhiraman, Ram P.; Nordlund, Dennis; Jayan, Vivek; ...

2014-11-25

Controlled integration of features that enhance the analytical performance of a sensor chip is a challenging task in the development of paper sensors. A critical issue in the fabrication of low-cost biosensor chips is the activation of the device surface in a reliable and controllable manner compatible with large-scale production. Here, we report stable, well-adherent, and repeatable site-selective deposition of bioreactive amine functionalities and biorepellant polyethylene glycol-like (PEG) functionalities on paper sensors by aerosol-assisted, atmospheric-pressure, plasma-enhanced chemical vapor deposition. This approach requires only 20 s of deposition time, compared to previous reports on cellulose functionalization, which takes hours. We presentmore » a detailed analysis of the near-edge X-ray absorption fine structure (NEXAFS) and its sensitivity to the local electronic structure of the carbon and nitrogen functionalities. σ*, π*, and Rydberg transitions in C and N K-edges. Lastly, application of the plasma-processed paper sensors in DNA detection is also demonstrated.« less

Quenched dynamics and spin-charge separation in an interacting topological lattice

NASA Astrophysics Data System (ADS)

Barbiero, L.; Santos, L.; Goldman, N.

2018-05-01

We analyze the static and dynamical properties of a one-dimensional topological lattice, the fermionic Su-Schrieffer-Heeger model, in the presence of on-site interactions. Based on a study of charge and spin correlation functions, we elucidate the nature of the topological edge modes, which, depending on the sign of the interactions, either display particles of opposite spin on opposite edges, or a pair and a holon. This study of correlation functions also highlights the strong entanglement that exists between the opposite edges of the system. This last feature has remarkable consequences upon subjecting the system to a quench, where an instantaneous edge-to-edge signal appears in the correlation functions characterizing the edge modes. Besides, other correlation functions are shown to propagate in the bulk according to the light cone imposed by the Lieb-Robinson bound. Our study reveals how one-dimensional lattices exhibiting entangled topological edge modes allow for a nontrivial correlation spreading, while providing an accessible platform to detect spin-charge separation using state-of-the-art experimental techniques.

Differences in breeding bird assemblages related to reed canary grass cover cover and forest structure on the Upper Mississippi River

USGS Publications Warehouse

Kirsch, Eileen M.; Gray, Brian R.

2017-01-01

Floodplain forest of the Upper Mississippi River provides habitat for an abundant and diverse breeding bird community. However, reed canary grass Phalaris arundinacea invasion is a serious threat to the future condition of this forest. Reed canary grass is a well-known aggressive invader of wetland systems in the northern tier states of the conterminous United States. Aided by altered flow regimes and nutrient inputs from agriculture, reed canary grass has formed dense stands in canopy gaps and forest edges, retarding tree regeneration. We sampled vegetation and breeding birds in Upper Mississippi River floodplain forest edge and interior areas to 1) measure reed canary grass cover and 2) evaluate whether the breeding bird assemblage responded to differences in reed canary grass cover. Reed canary grass was found far into forest interiors, and its cover was similar between interior and edge sites. Bird assemblages differed between areas with more or less reed canary grass cover (.53% cover breakpoint). Common yellowthroat Geothlypis trichas, black-capped chickadee Parus atricapillus, and rose-breasted grosbeak Pheucticus ludovicianus were more common and American redstart Setophaga ruticilla, great crested flycatcher Myiarchus crinitus, and Baltimore oriole Icterus galbula were less common in sites with more reed canary grass cover. Bird diversity and abundance were similar between sites with different reed canary grass cover. A stronger divergence in bird assemblages was associated with ground cover ,15%, resulting from prolonged spring flooding. These sites hosted more prothonotary warbler Protonotaria citrea, but they had reduced bird abundance and diversity compared to other sites. Our results indicate that frequently flooded sites may be important for prothonotary warblers and that bird assemblages shift in response to reed canary grass invasion.

Bird use of reforestation sites: Influence of location and vertical structure

USGS Publications Warehouse

Twedt, Daniel J.; Cooper, Robert

2005-01-01

In the Lower Mississippi Valley, more than 300,000 acres of agricultural land have been reforested in the last 10 years. Planning decisions on how and where to restore forest are complex and usually reflect landowner objectives. However, initial planning decisions may have a large influence on the value of restored stands for birds and other wildlife.Reforestation of small, isolated tracts will likely result in mature forests where reproductive output of breeding birds does not compensate for adult mortality (sink habitats). This may be due to factors such as lower reproductive success near edges (edge effects), insufficient area of habitat to attract colonizing birds (area effects), or restricted population mixing and mating opportunities because of limited dispersal among tracts (isolation effects).Conversely, reforestation adjacent to existing forest increases contiguous forest area and provides areas buffered from agricultural or urban habitats (interior forest core).Bottomland reforestation has historically focused on planting relatively slow-growing tree species, particularly oaks (Quercus spp.). Thus, restoration sites are often dominated by grasses and forbs for up to a decade after tree planting. Grassland birds are the first birds to colonize reforested sites. However, abundance and productivity of grassland birds is generally poor on sites associated with woody vegetation, such as sites adjacent to mature forest.As woody vegetation develops on reforested sites, birds preferring shrub-scrub habitat displace grassland species (Twedt et al. 2002) (fig. 1). Planting faster-growing trees compresses the time for colonization by shrub-scrub birds and the increased vertical stature of these trees attracts forest birds (Twedt and Portwood 1996). Additionally, planting next to existing mature forests creates transitional edges that reduce the detrimental effects of abrupt forest-agriculture interfaces.

Localization and mobility edges in one-dimensional deterministic potentials

NASA Astrophysics Data System (ADS)

Tong, Peiqing

1994-10-01

In this paper, we study the localization properties of the wave function of a one-dimensional tight-binding electron moving in an asymptotic periodic potential, Vn=λ cos(2πQn+παnν), where n is the site index and 0<ν<1. For Q rational, the electronic energy band consists of many subbands, and the number of subbands is determined by Q. For λ<2, there are two mobility edges where the eigenstates at the subband center are all extended, whereas the subband-edge states are all localized in every subband. We develop some heuristic arguments to calculate exactly the mobility edges for this model and carry out numerical work to study the localization properties of the model. Our theoretical results are essentially in exact agreement with the numerical results. We calculate the critical exponents δ and β at mobility edges. We also study the nature of the localized, extended eigenstates and mobility edges of this system as a function of λ, α, and ν.

Sorption of Metal Ions on Clay Minerals.

PubMed

Schlegel; Charlet; Manceau

1999-12-15

The mechanism of Co uptake from aqueous solution onto hectorite (a magnesian smectite) and its impact on the stability of this clay mineral were investigated as a function of Co concentration (TotCo = 20 to 200 µM, 0.3 M NaNO(3)) and ionic strength (0.3 and 0.01 M NaNO(3), TotCo = 100 µM) by combining kinetics measurements and Co K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The morphology of the sorbent phase was characterized by atomic force microscopy (AFM) and consists of lath-type particles bounded by large basal planes and layer edges. At low ionic strength (0.01 M NaNO(3)), important Co uptake occurred within the first 5 min of reaction, consistent with Co adsorption on exchange sites of hectorite basal planes. Thereafter, the sorption rate dramatically decreased. In contrast, at high ionic strength (0.3 M NaNO(3)), Co uptake rate was much slower within the first 5 min and afterward higher than at 0.01 M NaNO(3), consistent with Co adsorption on specific surface sites located on the edges of hectorite. Time-dependent isotherms for Co uptake at high ionic strength indicated the existence of several sorption mechanisms having distinct equilibration times. The dissolution of hectorite was monitored before and after Co addition. A congruent dissolution regime was observed prior to Co addition. Just after Co addition, an excess release of Mg relatively to congruent dissolution rates occurred at both high and low ionic strengths. At high ionic strength, this excess release nearly equaled the amount of sorbed Co. The dissolution rate of hectorite then decreased at longer Co sorption times. EXAFS spectra of hectorite reacted with Co at high and low ionic strengths and for reaction times longer than 6 h, exhibited similar features, suggesting that the local structural environments of Co atoms are similar. Spectral simulations revealed the occurrence of approximately 2 Mg and approximately 2 Si neighboring cations at interatomic distances characteristic of edge-sharing linkages between Co and Mg octahedra and corner-sharing linkages between Co octahedra and Si tetrahedra, respectively. This local structure is characteristic of inner sphere mononuclear surface complexes at layer edges of hectorite platelets. The occurrence of these complexes even at low ionic strength apparently conflicts with kinetics results, as exchangeable divalent cations are known to form outer sphere surface complexes. To clarify this issue, the amount of Co adsorbed on exchange sites was calculated from the solute Co concentration, assuming that cation exchange was always at equilibrium. These calculations showed that sorbed Co was transferred within 48 h from exchange sites to edge sorption sites. Copyright 1999 Academic Press.

Radon emanation from the moon - Spatial and temporal variability.

NASA Technical Reports Server (NTRS)

Gorenstein, P.; Golub, L.; Bjorkholm, P.

1973-01-01

Observations of Rn-222 and Po-210 on the lunar surface with the orbiting Apollo alpha particle spectrometer reveal a number of features in their spatial distribution and indicate the existence of time variations in lunar radon emission. Localized Rn-222 or Po-210 around the craters Aristarchus and Grimaldi and the edges of virtually all maria indicates time varying radon emission and suggests a correlation between alpha 'hot spots' and sites of transient optical events observed from the earth. In a gross sense, the slower variations of Rn-222 seem to correlate with the distribution of gamma activity.

Supporting Faculty Learning About Teaching: The On the Cutting Edge Website

NASA Astrophysics Data System (ADS)

Fox, S.; Iverson, E. A.; Manduca, C. A.; Kirk, K. B.; McDaris, J. R.; Ormand, C. J.; Bruckner, M. Z.

2011-12-01

The On the Cutting Edge website captures information about teaching geoscience from workshop participants and leaders. Designed to both support workshop participants in making use of ideas developed at the workshop and to allow a broader audience to access these ideas, the site includes more than 4900 pages of content in 39 topical collections with more than 1400 community-contributed teaching activities. The site is well used: in 2010, 850,000 visitors made more than one million visits to the site viewing more than 2.1 million pages. To obtain a more detailed understanding of site use within our target population, we interviewed a sample of 30 geoscience faculty. Five primary uses were described repeatedly and in depth: finding ideas for teaching, understanding what colleagues are doing in specific teaching situations, learning about methods, tools, or topic in education or geoscience, finding visualizations, and networking or career planning. Interviewees could describe particular instances where they made use of teaching materials and could cite reasons why they believed this improved student learning. To understand how these uses are manifest in the weblogs, a sample of 73 sessions that lasted at least 10 minutes, and viewed 10 or more pages were selected from March 2009 logs. Sessions were selected to sample heavy use of one or more topical collections, and to sample the diversity of log characteristics. The sessions were described qualitatively and the resulting descriptions categorized. Four recognizable use patterns emerged: activity browsing in some cases combined with study of a pedagogic method, browsing visualizations and associated topical content, digging deep within a particular topical collection, and cross-site browsing. These patterns seem consistent with the uses reported in the interviews. An analysis of characteristics of all sessions in 2008 viewing 10 or more pages indicate that the major uses described in the interview study by 30 faculty are in fact widespread among the 16,000 users seeing 10 or more pages. The most widespread identifiable use is finding teaching activities or finding out what colleagues are doing in a particular teaching situation (20-40% of use). Roughly 30% of use appears to be related to seeking visualizations for class. Another 20% of use includes learning about pedagogic methods, though that may not be the users' intention when they enter the site. As in the interview study, use associated with finding career information is significant though less common (10% of use). The relative distribution of page views across modules is well aligned with the reported uses, and offers further confirmation that these uses are widely represented in the deep sessions.

Stennis Space Center Verification & Validation Capabilities

NASA Technical Reports Server (NTRS)

Pagnutti, Mary; Ryan, Robert E.; Holekamp, Kara; ONeal, Duane; Knowlton, Kelly; Ross, Kenton; Blonski, Slawomir

2005-01-01

Scientists within NASA s Applied Sciences Directorate have developed a well-characterized remote sensing Verification & Validation (V&V) site at the John C. Stennis Space Center (SSC). This site enables the in-flight characterization of satellite and airborne high spatial and moderate resolution remote sensing systems and their products. The smaller scale of the newer high resolution remote sensing systems allows scientists to characterize geometric, spatial, and radiometric data properties using a single V&V site. The targets and techniques used to characterize data from these newer systems can differ significantly from the techniques used to characterize data from the earlier, coarser spatial resolution systems. Scientists are also using the SSC V&V site to characterize thermal infrared systems and active lidar systems. SSC employs geodetic targets, edge targets, radiometric tarps, atmospheric monitoring equipment, and thermal calibration ponds to characterize remote sensing data products. The SSC Instrument Validation Lab is a key component of the V&V capability and is used to calibrate field instrumentation and to provide National Institute of Standards and Technology traceability. This poster presents a description of the SSC characterization capabilities and examples of calibration data.

Scanned gate microscopy of inter-edge channel scattering in the quantum Hall regime

NASA Astrophysics Data System (ADS)

Woodside, Michael T.; Vale, Chris; McEuen, Paul L.; Kadow, C.; Maranowski, K. D.; Gossard, A. C.

2000-03-01

Novel scanned probe techniques have recently been used to study in detail the microscopic properties of 2D electron gases in the quantum Hall regime [1]. We report local measurements of the scattering between edge states in a quantum Hall conductor with non-equilibrium edge state populations. Using an atomic force microscope (AFM) tip as a local gate to perturb the edge states, we find that the scattering is dominated by individual, microscopic scattering sites, which we directly image and characterise. The dependence of the scattering on the AFM tip voltage reveals that it involves tunneling both through quasi-bound impurity states and through disorder-induced weak links between the edge states. [1] S. H. Tessmer et al., Nature 392, 51 (1998); K. L. McCormick et al., Phys. Rev. B 59, 4654 (1999); A. Yacoby et al., Solid State Comm. 111, 1 (1999).

Injection current minimization of InAs/InGaAs quantum dot laser by optimization of its active region and reflectivity of laser cavity edges

NASA Astrophysics Data System (ADS)

Korenev, V. V.; Savelyev, A. V.; Zhukov, A. E.; Maximov, M. V.

2015-11-01

The ways to optimize key parameters of active region and edge reflectivity of edge- emitting semiconductor quantum dot laser are provided. It is shown that in the case of optimal cavity length and sufficiently large dispersion lasing spectrum of a given width can be obtained at injection current up to an order of magnitude lower in comparison to non-optimized sample. The influence of internal loss and edge reflection is also studied in details.

A facile top-down etching to create a Cu2O jagged polyhedron covered with numerous {110} edges and {111} corners with enhanced photocatalytic activity.

PubMed

Shang, Yang; Sun, Du; Shao, Yiming; Zhang, Dongfeng; Guo, Lin; Yang, Shihe

2012-11-05

Cutting edge: A Cu(2)O jagged polyhedron, with numerous {110} edges and {111} corners, has been developed through a top-down selective oxidative etching process at the expense of the original {111} facet (see figure). The as-prepared nanocrystals exhibited higher photocatalytic activities for the degradation of methylene orange, which may be primarily ascribed to the increased edges and corners. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A statistical model of expansion in a colony of black-tailed prairie dogs

Treesearch

R. P. Cincotta; Daniel W. Uresk; R. M. Hansen

1988-01-01

To predict prairie dog establishment in areas adjacent to a colony we sample: (1) VISIBILITY through the vegetation using a target, (2) POPULATION DENSITY at the cology edge, (3) DISTANCE from the edge to the potential site of settlement, and (4) % FORB COVER. Step-wise regression analysis indicated that establishment of prairie dogs in adjacent prairie was most likely...

Chronophin coordinates cell leading edge dynamics by controlling active cofilin levels

PubMed Central

Delorme-Walker, Violaine; Seo, Ji-Yeon; Gohla, Antje; Fowler, Bruce; Bohl, Ben; DerMardirossian, Céline

2015-01-01

Cofilin, a critical player of actin dynamics, is spatially and temporally regulated to control the direction and force of membrane extension required for cell locomotion. In carcinoma cells, although the signaling pathways regulating cofilin activity to control cell direction have been established, the molecular machinery required to generate the force of the protrusion remains unclear. We show that the cofilin phosphatase chronophin (CIN) spatiotemporally regulates cofilin activity at the cell edge to generate persistent membrane extension. We show that CIN translocates to the leading edge in a PI3-kinase–, Rac1-, and cofilin-dependent manner after EGF stimulation to activate cofilin, promotes actin free barbed end formation, accelerates actin turnover, and enhances membrane protrusion. In addition, we establish that CIN is crucial for the balance of protrusion/retraction events during cell migration. Thus, CIN coordinates the leading edge dynamics by controlling active cofilin levels to promote MTLn3 cell protrusion. PMID:26324884

Surface modification study of borate materials from B K-edge X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Kasrai, Masoud; Fleet, Michael E.; Muthupari, Swaminathan; Li, D.; Bancroft, G. M.

The B K-edge X-ray absorption near-edge structure (XANES) spectra of two borates with tetrahedrally-coordinated B [[4]B; natural danburite (CaB2Si2O8) and synthetic boron phosphate (BPO4)] have been recorded in total electron yield (TEY) and fluorescence yield (FY) modes to investigate the surface and bulk structure of these materials. The TEY XANES measurement shows that danburite is susceptible to surface damage involving conversion of [4]B sites to [3]B sites by reaction with moisture and/or mechanical abrasion (grinding, polishing, etc.). The bulk of the mineral is essentially unaffected. Commercial boron phosphate powder exhibits more extensive surface and bulk damage, which increases with air exposure but is recovered on heating at 650°C. In contrast to ELNES, the XANES technique is not affected by beam damage and when collected in the FY mode is capable of yielding meaningful information on the coordination and intermediate-range structure of B in borate and borosilicate materials.

Optimal Shape of a Gamma-ray Collimator: single vs double knife edge

NASA Astrophysics Data System (ADS)

Metz, Albert; Hogenbirk, Alfred

2017-09-01

Gamma-ray collimators in nuclear waste scanners are used for selecting a narrow vertical segment in activity measurements of waste vessels. The system that is used by NRG uses tapered slit collimators of both the single and double knife edge type. The properties of these collimators were investigated by means of Monte Carlo simulations. We found that single knife edge collimators are highly preferable for a conservative estimate of the activity of the waste vessels. These collimators show much less dependence on the angle of incidence of the radiation than double knife edge collimators. This conclusion also applies to cylindrical collimators of the single knife edge type, that are generally used in medical imaging spectroscopy.

Mosaic of Apollo 16 Descartes landing site taken from TV transmission

NASA Technical Reports Server (NTRS)

1972-01-01

A 360 degree field of view of the Apollo 16 Descartes landing site area composed of individual scenes taken from a color transmission made by the color RCA TV camera mounted on the Lunar Roving Vehicle. This panorama was made while the LRV was parked at the rim of North Ray crater (Stations 11 and 12) during the third Apollo 16 lunar surface extravehicular activity (EVA-3) by Astronauts John W. Young and Charles M. Duke Jr. The overlay identifies the directions and the key lunar terrain features. The camera panned across the rear portion of the LRV in its 360 degree sweep. Note Young and Duke walking along the edge of the crater in one of the scenes. The TV camera was remotely controlled from a console in the Mission Control Center.

A study of microseismicity in northern Baja California, Mexico

NASA Technical Reports Server (NTRS)

Johnson, T. L.; Koczynski, T.; Madrid, J.

1976-01-01

Five microearthquake instruments were operated for 2 months in 1974 in a small mobile array deployed at various sites near the Agua Blanca and San Miguel faults. An 80-km-long section of the San Miguel fault zone is presently active seismically, producing the vast majority of recorded earthquakes. Very low activity was recorded on the Agua Blanca fault. Events were also located near normal faults forming the eastern edge of the Sierra Juarez suggesting that these faults are active. Hypocenters on the San Miguel fault range in depth from 0 to 20 km although two-thirds are in the upper 10 km. A composite focal mechanism showing a mixture of right-lateral and dip slip, east side up, is similar to a solution obtained for the 1956 San Miguel earthquake which proved consistent with observed surface deformation.

Landscape changes and colony site dynamics: How gull-billed terns cope at the sea's edge

USGS Publications Warehouse

Erwin, R.M.; Williams, B.; Watts, B.; Truitt, B.; Stotts, D.; Eyler, B.

1996-01-01

Gull-billed Terns have declined dramatically in coastal Virginia over the past 20 years, with apparently low reproductive success. They nest, usually in mixed-species colonies, in two discrete habitat types: large, sandy barrier islands or shell/sandbars on the edges of marsh islands in the lagoon systems. The smaller shell/sandbars seem to provide more consistent nestling habitat and predation pressures than do barrier islands among years. We hypothesize that colony site turnover (between years) should be higher in the more uncertain barrier island habitats than among the shell/sandbar colonies. Our results do not corroborate the prediction. We postulate that social (and other) factors may explain these differences.

Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

PubMed

Marini, C; Noked, O; Kantor, I; Joseph, B; Mathon, O; Shuker, R; Kennedy, B J; Pascarelli, S; Sterer, E

2016-02-03

Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa.

Theory of K-edge resonant inelastic x-ray scattering and its application for La0.5Sr1.5MnO4

NASA Astrophysics Data System (ADS)

Seman, T. F.; Liu, X.; Hill, J. P.; van Veenendaal, M.; Ahn, K. H.

2013-03-01

We present a formula based on tight-binding approach for the calculation of K-edge resonant inelastic x-ray scattering spectrum for transition metal oxides, by extending the previous result [K. H. Ahn, A. J. Fedro, and M. van Veenendaal, Phys. Rev. B 79, 045103 (2009).] to include explicit momentum dependence and a basis with multiple core hole sites. We apply this formula to layered charge, orbital, and spin ordered manganites, La0.5Sr1.5MnO4. The K-edge RIXS spectrum is found not periodic with respect to the actual reciprocal lattice, but approximately periodic with respect to the reciprocal lattice for the hypothetical unit cell with one core hole site. With experimental strcuture and reasonable tight-binding parameters, we obtain good agreement with experimental data, in particular, with regards to the large variation of the intensity with momentum. We find that the screening in La0.5Sr1.5MnO4 is highly localized around the core hole site and demonstrate the potential of K-edge RIXS as a probe for the screening dynamics in materials. Work supported by US.DOE Contr. DE-AC02-98CH10886 (X.L.,J.H.), US.DOE Award DE-FG02-03ER46097 (M.v.V.), CMCSN under Grants DE-FG02-08ER46540 & DE-SC0007091 (T.S.,K.A.,M.v.V.), Argonne XSD Visitor Prog.(K.A.), US.DOE Contr. DE-AC02-06CH11357 (X.L.,J.H).

The transportation and environmental impacts of infill versus greenfield development: a comparative case study analysis.

DOT National Transportation Integrated Search

1999-10-01

This paper tries to answer the question of which site provides more efficient or better transportation services to a new residential or commercial development - an urban infill site or a suburban edge/greenfield? In order to answer this question, the...

Fine-Tuning the Activity of Metal–Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhanyong; Peters, Aaron W.; Platero-Prats, Ana E.

Few-atom cobalt-oxide clusters, when dispersed on a Zr-based metal–organic framework (MOF) NU-1000, have previously been shown to be active for the oxidative dehydrogenation (ODH) of propane at low temperatures (< 230 °C), affording a selective and stable propene production catalyst. In our current work, a series of promoter ions with varying Lewis acidity, including Ni(II), Zn(II), Al(III), Ti(IV) and Mo(VI), are anchored as metal-oxide,hydroxide clusters to NU-1000 via SIM (solvothermal deposition within MOFs–specifically the nodes) followed by incorporation of Co(II) ions via vapor-phase AIM (atomic layer deposition (ALD) in MOFs). This process yields a series of NU-1000-supported bimetallic-oxo,hydroxo,aqua clusters. Usingmore » difference envelope density (DED) analyses, the spatial locations of the promoter ions and catalytic cobalt ions are determined. For all samples the SIM-anchored promoter ions are sited between pairs of Zr 6 nodes along the MOF c-axis (channel-aligned axis) whereas the location of the AIM-anchored cobalt ions varies depending on the identity of promoter metal ion. With Ni(II)-, Al(III)-, or Ti(IV)-containing clusters as promoters, the oxy-cobalt species are sited atop the promoter sites; with Mo(VI) they grow exclusively on the MOF nodes sites (hexa-Zr(IV)- oxo,hydroxo,aqua units); with Zn(II) they grow on both the node and promoter. The NU-1000- supported bimetallic-oxide clusters are active for propane ODH after thermal activation under O 2 to open a cobalt coordination site and to oxidize Co(II) to Co(III), as evidenced by operando Xray absorption spectroscopy at the Co K-edge. The cobalt component is exclusively responsible for the observed catalysis. In accord with the decreasing Lewis acidity of the promoter ion, catalytic activity increases in the order: Mo(VI)« less

Fine-Tuning the Activity of Metal–Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane

DOE PAGES

Li, Zhanyong; Peters, Aaron W.; Platero-Prats, Ana E.; ...

2017-10-04

Few-atom cobalt-oxide clusters, when dispersed on a Zr-based metal–organic framework (MOF) NU-1000, have previously been shown to be active for the oxidative dehydrogenation (ODH) of propane at low temperatures (< 230 °C), affording a selective and stable propene production catalyst. In our current work, a series of promoter ions with varying Lewis acidity, including Ni(II), Zn(II), Al(III), Ti(IV) and Mo(VI), are anchored as metal-oxide,hydroxide clusters to NU-1000 via SIM (solvothermal deposition within MOFs–specifically the nodes) followed by incorporation of Co(II) ions via vapor-phase AIM (atomic layer deposition (ALD) in MOFs). This process yields a series of NU-1000-supported bimetallic-oxo,hydroxo,aqua clusters. Usingmore » difference envelope density (DED) analyses, the spatial locations of the promoter ions and catalytic cobalt ions are determined. For all samples the SIM-anchored promoter ions are sited between pairs of Zr 6 nodes along the MOF c-axis (channel-aligned axis) whereas the location of the AIM-anchored cobalt ions varies depending on the identity of promoter metal ion. With Ni(II)-, Al(III)-, or Ti(IV)-containing clusters as promoters, the oxy-cobalt species are sited atop the promoter sites; with Mo(VI) they grow exclusively on the MOF nodes sites (hexa-Zr(IV)- oxo,hydroxo,aqua units); with Zn(II) they grow on both the node and promoter. The NU-1000- supported bimetallic-oxide clusters are active for propane ODH after thermal activation under O 2 to open a cobalt coordination site and to oxidize Co(II) to Co(III), as evidenced by operando Xray absorption spectroscopy at the Co K-edge. The cobalt component is exclusively responsible for the observed catalysis. In accord with the decreasing Lewis acidity of the promoter ion, catalytic activity increases in the order: Mo(VI)« less

Aqueous solubility diagrams for cementitious waste stabilization systems. 3. Mechanism of zinc immobilizaton by calcium silicate hydrate.

PubMed

Tommaseo, C E; Kersten, M

2002-07-01

Zinc oxide was added during hydration of alite (C3S) as an analogue for solidification/stabilization by cement of metal-bearing hazardous waste. Curing of samples was stopped at various intervals between 8 h and 100 d, and the reaction products were analyzed by both X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS at Zn, Ca, and Si K-edges). Calcium zincate hydrate (CaZn2(OH)6 x 2H2O) initially formed together with calcium silicate hydrate (CSH) vanishes from X-ray diffractograms after 14 d, and no other crystalline Zn-bearing phase could be detected thereafter. EXAFS Zn K-edge data analysis reveals that Zn(O,OH)4 tetrahedra continue to determine the first shell coordination. However, a new Zn-Si bond appears in the second coordination shell as indicated by both Zn K-edge and Si K-edge EXAFS. Together with the Ca-Zn and Ca-Ca shells derived from the Ca K-edge EXAFS spectra, a structural model for the site occupation of Zn in CSH is proposed, whereby the Zn(O,OH)4 tetrahedra are bound in layer rather than interlayer positions substituting for the silicate bridging tetrahedra and/or at terminal silicate chain sites. This structural model enables ultimately the formulation of a thermodyamic Lippmann model to predict the aqueous solubility of Zn in solid solution with a CSH phase of a Ca/Si ratio fixed to unity.

Tectonic Setting of NGHP-1 Site 17, Andaman Forearc

NASA Astrophysics Data System (ADS)

Cochran, J. R.

2008-12-01

The National Gas Hydrate Program (NGHP) Expedition 1 was an 'IODP-like' coring and logging program to investigate gas hydrate occurrences along the margins of India. Although most sites were located along the east coast of India, Site NGHP-01-17 was located near 10° 45'N on the Andaman forearc approximately 50 km east of Little Andaman Island in a water depth of 1325 m. Seismic lines across the site show an anomalously deep bottom simulating reflector (BSR) at a depth of about 600 mbsf. Coring and logging results confirmed that the BSR does mark the base of the gas hydrate stability zone. The age of the sediments at the base of the hole was estimated as 12.3 Ma. The Andaman Sea is an extensional basin resulting from strain partitioning during oblique subduction at the Sunda trench. The site is located within the eastern portion of the Andaman-Nicobar outer arc accretionary ridge on a long sliver of crust between the Eastern Margin Fault and the Diligent Fault. They are both down-to-the-east normal faults that form the eastern edge of the accretionary prism. The West Andaman Fault (WAF), which forms the principal active plate boundary between the Sumatra Fault and the Andaman Spreading Center, is located about 45 km further east along the eastern side of Invisible Bank. The Eastern Margin Fault forms the eastern edge of the block containing Little Andaman Island and extends northward for at least 100 km along the eastern side of South Andaman Island where it appears to die out. It can be traced south to about 8° 20'N where it dies out east of Tarasa Island. The Diligent Fault extends south to about 9° N where it apparently merges with the WAF. It forms the eastern edge of the accretionary prism northward to at least to 13° N and most likely to the Mynamar shelf at 14° N. It probably continues on to join the Kabaw Fault, which marks the eastern boundary of the accretionary prism in Myanmar. Although there is a significant vertical offset across both faults near the NGDP-1-17 site, the Diligent Fault appears to have also experienced strike-slip faulting at some point, probably prior to formation of the Andaman Spreading Center at about 4 Ma. At that time the situation may have been similar to that now found between about 7° N and 4° N where the northern motion of the sliver plate is concentrated at two locations, a fault system along the landward margin of the accretionary prism and another system further landward that forms the main plate boundary.

Edge-Related Activity Is Not Necessary to Explain Orientation Decoding in Human Visual Cortex.

PubMed

Wardle, Susan G; Ritchie, J Brendan; Seymour, Kiley; Carlson, Thomas A

2017-02-01

Multivariate pattern analysis is a powerful technique; however, a significant theoretical limitation in neuroscience is the ambiguity in interpreting the source of decodable information used by classifiers. This is exemplified by the continued controversy over the source of orientation decoding from fMRI responses in human V1. Recently Carlson (2014) identified a potential source of decodable information by modeling voxel responses based on the Hubel and Wiesel (1972) ice-cube model of visual cortex. The model revealed that activity associated with the edges of gratings covaries with orientation and could potentially be used to discriminate orientation. Here we empirically evaluate whether "edge-related activity" underlies orientation decoding from patterns of BOLD response in human V1. First, we systematically mapped classifier performance as a function of stimulus location using population receptive field modeling to isolate each voxel's overlap with a large annular grating stimulus. Orientation was decodable across the stimulus; however, peak decoding performance occurred for voxels with receptive fields closer to the fovea and overlapping with the inner edge. Critically, we did not observe the expected second peak in decoding performance at the outer stimulus edge as predicted by the edge account. Second, we evaluated whether voxels that contribute most to classifier performance have receptive fields that cluster in cortical regions corresponding to the retinotopic location of the stimulus edge. Instead, we find the distribution of highly weighted voxels to be approximately random, with a modest bias toward more foveal voxels. Our results demonstrate that edge-related activity is likely not necessary for orientation decoding. A significant theoretical limitation of multivariate pattern analysis in neuroscience is the ambiguity in interpreting the source of decodable information used by classifiers. For example, orientation can be decoded from BOLD activation patterns in human V1, even though orientation columns are at a finer spatial scale than 3T fMRI. Consequently, the source of decodable information remains controversial. Here we test the proposal that information related to the stimulus edges underlies orientation decoding. We map voxel population receptive fields in V1 and evaluate orientation decoding performance as a function of stimulus location in retinotopic cortex. We find orientation is decodable from voxels whose receptive fields do not overlap with the stimulus edges, suggesting edge-related activity does not substantially drive orientation decoding. Copyright © 2017 the authors 0270-6474/17/371187-10$15.00/0.

Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

DOE PAGES

Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

2016-04-08

Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less

Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less

Activating without Inhibiting: Left-Edge Boundary Tones and Syntactic Processing

ERIC Educational Resources Information Center

Roll, Mikael; Horne, Merle; Lindgren, Magnus

2011-01-01

Right-edge boundary tones have earlier been found to restrict syntactic processing by closing a clause for further integration of incoming words. The role of left-edge intonation, however, has received little attention to date. We show that Swedish left-edge boundary tones selectively facilitate the on-line processing of main clauses, the…

WIDEFIELD SPECTRAL-DOMAIN OPTICAL COHERENCE TOMOGRAPHY IMAGING OF PERIPHERAL ROUND RETINAL HOLES WITH OR WITHOUT RETINAL DETACHMENT.

PubMed

Casswell, Edward J; Abou Ltaif, Sleiman; Carr, Thomas; Keane, Pearse A; Charteris, David G; Wickham, Louisa

2018-03-02

To describe the widefield spectral-domain optical coherence tomography features of peripheral round retinal holes, with or without associated retinal detachment (RD). Retrospective, observational study of 28 eyes with peripheral round retinal holes, with and without RD. Patients underwent imaging with a widefield 50-degree spectral-domain optical coherence tomography (Heidelberg Engineering, Germany) and Optos ultra-widefield imaging systems (Optos, United Kingdom). Vitreous attachment at the site of the retinal hole was detected in 27/28 (96.4%) cases. Cases were split into three groups: RHs with RD (n = 12); RHs with subretinal fluid (n = 5), and flat RHs (n = 11), with minimal or no subretinal fluid. 91.6% retinal holes associated with subretinal fluid or RD had vitreous attachment at the site of the hole. Eighty percent had vitreous attachment at both edges of the retinal hole, in a U-shape configuration, which appeared to exert traction. By contrast, flat retinal holes had visible vitreous attachment only at one edge of the retinal hole in 45.4%. Vitreous attachment was commonly seen at the site of round retinal holes. Vitreous attachment at both edges of the retinal hole in a U-shape configuration was more commonly seen at holes associated with subretinal fluid or RD.

Marshes on the Move: Testing effects of seawater intrusion on ...

EPA Pesticide Factsheets

The Northeastern United States is a hotspot for sea level rise (SLR), subjecting coastal salt marshes to erosive loss, shifts in vegetation communities, and altered biogeochemistry due to seawater intrusion. Salt marsh plant community zonation is driven by tradeoffs in stress tolerance and interspecific interactions. As seawater inundates progressively higher marsh elevations, shifts in marsh vegetation communities landward may herald salt marsh “migration”, which could allow continuity of marsh function and ecosystem service provision. To elucidate possible effects of seawater intrusion on marsh-upland edge plant communities, a space-for-time approach was replicated at two Rhode Island salt marshes. At each site, peat blocks (0.5 m x 0.5 m x 0.5 m, n=6) with intact upland-marsh edge vegetation were transplanted downslope into the regularly-inundated mid-marsh. Procedural controls (n=3) were established at each elevation by removing and replacing peat blocks, and natural controls (n=3) consisted of undisturbed plots. During peak productivity, each plot was assessed for species composition, percent cover and average height. Results demonstrate stunting of marsh-upland edge vegetation in response to increased inundation, and the beginnings of colonization of the transplanted plots by salt marsh species. The extent of colonization differed between the two sites, suggesting that site-specific factors govern vegetation responses to increased inundation.

76 FR 68301 - Airworthiness Directives; Bell Helicopter Textron, Inc. (Bell), Model 205A-1, 205B, 210, and 212...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-04

... the inspection area for any edge delamination, as indicated by a dark line located along any bond line... docket Web site, you can find and read the comments to any of our dockets, including the name of the... indicated by a dark line located along any bond line, or a crack in the paint finish. An edge delamination...

Trace elements and rare earth elements in wet deposition of Lijiang, Mt. Yulong region, southeastern edge of the Tibetan Plateau.

PubMed

Guo, Junming; Kang, Shichang; Huang, Jie; Sillanpää, Mika; Niu, Hewen; Sun, Xuejun; He, Yuanqing; Wang, Shijing; Tripathee, Lekhendra

2017-02-01

In order to investigate the compositions and wet deposition fluxes of trace elements and rare earth elements (REEs) in the precipitation of the southeastern edge of the Tibetan Plateau, 38 precipitation samples were collected from March to August in 2012 in an urban site of Lijiang city in the Mt. Yulong region. The concentrations of most trace elements and REEs were higher during the non-monsoon season than during the monsoon season, indicating that the lower concentrations of trace elements and REEs observed during monsoon had been influenced by the dilution effect of increased precipitation. The concentrations of trace elements in the precipitation of Lijiang city were slightly higher than those observed in remote sites of the Tibetan Plateau but much lower than those observed in the metropolises of China, indicating that the atmospheric environment of Lijiang city was less influenced by anthropogenic emissions, and, as a consequence, the air quality was still relatively good. However, the results of enrichment factor and principal component analysis revealed that some anthropogenic activities (e.g., the increasing traffic emissions from the rapid development of tourism) were most likely important contributors to trace elements, while the regional/local crustal sources rather than anthropogenic activities were the predominant contributors to the REEs in the wet deposition of Lijiang city. Our study was relevant not only for assessing the current status of the atmospheric environment in the Mt. Yulong region, but also for specific management actions to be implemented for the control of atmospheric inputs and the health of the environment for the future. Copyright © 2016. Published by Elsevier B.V.

Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential

NASA Astrophysics Data System (ADS)

Tournassat, C.; Tinnacher, R. M.; Grangeon, S.; Davis, J. A.

2018-01-01

The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonite edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites ('spillover' effect). A series of U(VI) - Na-montmorillonite batch adsorption experiments was conducted as a function of pH, with variable U(VI), Ca, and dissolved carbonate concentrations. Based on the experimental data, a new type of surface complexation model (SCM) was developed for montmorillonite, that specifically accounts for the spillover effect using the edge surface speciation model by Tournassat et al. (2016a). The SCM allows for a prediction of U(VI) adsorption under varying chemical conditions with a minimum number of fitting parameters, not only for our own experimental results, but also for a number of published data sets. The model agreed well with many of these datasets without introducing a second site type or including the formation of ternary U(VI)-carbonato surface complexes. The model predictions were greatly impacted by utilizing analytical measurements of dissolved inorganic carbon (DIC) concentrations in individual sample solutions rather than assuming solution equilibration with a specific partial pressure of CO2, even when the gas phase was laboratory air. Because of strong aqueous U(VI)-carbonate solution complexes, the measurement of DIC concentrations was even important for systems set up in the 'absence' of CO2, due to low levels of CO2 contamination during the experiment.

Porous Carbon-Hosted Atomically Dispersed Iron-Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Shaofang; Zhu, Chengzhou; Su, Dong

As one of the alternatives to replace precious metal catalysts, transition metal-nitrogen-carbon (M-N-C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M-N-C catalysts can achieve good electrochemical performances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. Thus, M-N-C’s stability and selectivity have not been comparable to their noble metal counterparts. In this work, metal-organic frameworks (MOFs)-derived porous single-atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further post-treatment. Combining the X-ray absorption near-edge spectroscopy (XANES) and electrochemical measurements, the SAEs have been identifiedmore » with superior ORR activity and stability compared with Pt/C catalysts in alkaline condition. More impressively, the SAEs also show excellent ORR electrocatalytic performance in both acid and neutral media. Furthermore, this study of nonprecious catalysts provides new insights on nano-engineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.« less

Porous Carbon-Hosted Atomically Dispersed Iron-Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

DOE PAGES

Fu, Shaofang; Zhu, Chengzhou; Su, Dong; ...

2018-02-12

As one of the alternatives to replace precious metal catalysts, transition metal-nitrogen-carbon (M-N-C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M-N-C catalysts can achieve good electrochemical performances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. Thus, M-N-C’s stability and selectivity have not been comparable to their noble metal counterparts. In this work, metal-organic frameworks (MOFs)-derived porous single-atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further post-treatment. Combining the X-ray absorption near-edge spectroscopy (XANES) and electrochemical measurements, the SAEs have been identifiedmore » with superior ORR activity and stability compared with Pt/C catalysts in alkaline condition. More impressively, the SAEs also show excellent ORR electrocatalytic performance in both acid and neutral media. Furthermore, this study of nonprecious catalysts provides new insights on nano-engineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.« less

Structurally tailored graphene nanosheets as lithium ion battery anodes: an insight to yield exceptionally high lithium storage performance

NASA Astrophysics Data System (ADS)

Li, Xifei; Hu, Yuhai; Liu, Jian; Lushington, Andrew; Li, Ruying; Sun, Xueliang

2013-11-01

How to tune graphene nanosheets (GNSs) with various morphologies has been a significant challenge for lithium ion batteries (LIBs). In this study, three types of GNSs with varying size, edge sites, defects and layer numbers have been successfully achieved. It was demonstrated that controlling GNS morphology and microstructure has important effects on its cyclic performance and rate capability in LIBs. Diminished GNS layer number, decreased size, increased edge sites and increased defects in the GNS anode can be highly beneficial to lithium storage and result in increased electrochemical performance. Interestingly, GNSs treated with a hydrothermal approach delivered a high reversible discharge capacity of 1348 mA h g-1. This study demonstrates that the controlled design of high performance GNS anodes is an important concept in LIB applications.How to tune graphene nanosheets (GNSs) with various morphologies has been a significant challenge for lithium ion batteries (LIBs). In this study, three types of GNSs with varying size, edge sites, defects and layer numbers have been successfully achieved. It was demonstrated that controlling GNS morphology and microstructure has important effects on its cyclic performance and rate capability in LIBs. Diminished GNS layer number, decreased size, increased edge sites and increased defects in the GNS anode can be highly beneficial to lithium storage and result in increased electrochemical performance. Interestingly, GNSs treated with a hydrothermal approach delivered a high reversible discharge capacity of 1348 mA h g-1. This study demonstrates that the controlled design of high performance GNS anodes is an important concept in LIB applications. Electronic supplementary information (ESI) available: SEM morphologies of GNS-I-III at low magnification, the TEM image of GNSs hydrothermally treated with urea in a ratio of 1 : 0, XPS survey, and SEM morphology changes of the three GNS anodes at low magnification after 100 charge-discharge cycles. See DOI: 10.1039/c3nr04823c

Photograph of Apollo 17 lunar landing site location

NASA Technical Reports Server (NTRS)

1972-01-01

A photographic illustration of a full Moon showing the location of the Apollo 17 landing site on the lunar nearside. The black dot pinpointing the landing site is in the Taurus-Littrow area at the southeastern edge of the Sea of Serenity. The coordinates of the landing point are 30 degrees 44 minutes 38 seconds east longitude and 20 degrees 9 minutes 50 seconds north latitude.

The effects of patch shape on indigo buntings. Evidence for an ecological trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weldon, Aimee J.; Haddad, Nick M.

2005-01-01

Weldon, Aimee, J., and Nick M. Haddad. 2005. The effect of patch shape on indigo buntings: Evidence for an ecological trap. Ecology 86(6):1422-1431. Abstract. Habitat loss and fragmentation have led to a widespread increase in the proportion of edge habitat in the landscape. Disturbance-dependent bird species are widely assumed to benefit from these edges. However, anthropogenic edges may concentrate nest predators while retaining habitat cues that birds use to select breeding habitat. This may lead birds to mistakenly select dangerous habitat a phenomenon known as an ecological trap. We experimentally demonstrated how habitat shape, and thus amount of edge, canmore » adversely affect nest site selection and reproductive success of a disturbance-dependent bird species, the Indigo Bunting (Passerina cyanea). We did so within a landscape-scale experiment composed of equal-area habitat patches that differed in their amount of edge. Indigo Buntings preferentially selected edgy patches, which contained 50% more edge than more compact rectangular patches. Further, buntings fledged significantly fewer young per pair in edgy patches than in rectangular patches. These results provide the first experimental evidence that edges can function as ecological traps.« less

Stand development on reforested bottomlands in the Mississippi Alluvial Valley

USGS Publications Warehouse

Twedt, D.J.

2004-01-01

Reforestation of bottomland hardwood sites in the southeastern United States has markedly increased in recent years due, in part, to financial incentives provided by conservation programs. Currently > 250,000 ha of marginal farmland have been returned to hardwood forests. I observed establishment of trees and shrubs on 205 reforested bottomlands: 133 sites were planted primarily with oak species (Quercus spp.), 60 sites were planted with pulpwood producing species (Populus deltoides, Liquidambar styraciflua, or Platanus occidentalis), and 12 sites were not planted (i.e., passive regeneration). Although oak sites were planted with more species, sites planted with pulpwood species were more rapidly colonized by additional species. The density of naturally colonizing species exceeded that of planted species but density of invaders decreased rapidly with distance from forest edge. Trees were shorter in height on sites planted with oaks than on sites planted with pulpwood species but within a site, planted trees attained greater heights than did colonizing species. Thus, planted trees dominated the canopy of reforested sites as they matured. Planted species acted in concert with natural invasion to influence the current condition of woody vegetation on reforested sites. Cluster analysis of species importance values distinguished three woody vegetation conditions: (1) Populus deltoides stands (2) oak stands with little natural invasion by other tree species, and (3) stands dominated by planted or naturally invading species other than oaks. Increased diversity on reforested sites would likely result from (a) greater diversity of planted species, particularly when sites are far from existing forest edges and (b) thinning of planted trees as they attain closed canopies.

High-Lift System for a Supercritical Airfoil: Simplified by Active Flow Control

NASA Technical Reports Server (NTRS)

Melton, LaTunia Pack; Schaeffler, Norman W.; Lin, John C.

2007-01-01

Active flow control wind tunnel experiments were conducted in the NASA Langley Low-Turbulence Pressure Tunnel using a two-dimensional supercritical high-lift airfoil with a 15% chord hinged leading-edge flap and a 25% chord hinged trailing-edge flap. This paper focuses on the application of zero-net-mass-flux periodic excitation near the airfoil trailing edge flap shoulder at a Mach number of 0.1 and chord Reynolds numbers of 1.2 x 10(exp 6) to 9 x 10(exp 6) with leading- and trailing-edge flap deflections of 25 deg. and 30 deg., respectively. The purpose of the investigation was to increase the zero-net-mass-flux options for controlling trailing edge flap separation by using a larger model than used on the low Reynolds number version of this model and to investigate the effect of flow control at higher Reynolds numbers. Static and dynamic surface pressures and wake pressures were acquired to determine the effects of flow control on airfoil performance. Active flow control was applied both upstream of the trailing edge flap and immediately downstream of the trailing edge flap shoulder and the effects of Reynolds number, excitation frequency and amplitude are presented. The excitations around the trailing edge flap are then combined to control trailing edge flap separation. The combination of two closely spaced actuators around the trailing-edge flap knee was shown to increase the lift produced by an individual actuator. The phase sensitivity between two closely spaced actuators seen at low Reynolds number is confirmed at higher Reynolds numbers. The momentum input required to completely control flow separation on the configuration was larger than that available from the actuators used.

Syntheses, Characterization and Kinetics of Nickel-Tungsten Nitride Catalysts for Hydrotreating of Gas Oil

NASA Astrophysics Data System (ADS)

Botchwey, Christian

This thesis summarizes the methods and major findings of Ni-W(P)/gamma-Al 2O3 nitride catalyst synthesis, characterization, hydrotreating activity, kinetic analysis and correlation of the catalysts' activities to their synthesis parameters and properties. The range of parameters for catalyst synthesis were W (15-40 wt%), Ni (0-8 wt%), P (0-5 wt%) and nitriding temperature (TN) (500-900 °C). Characterization techniques used included: N2 sorption studies, chemisorption, elemental analysis, temperature programmed studies, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray, infrared spectroscopy, transmission electron microscopy and x-ray absorption near edge structure. Hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) were performed at: temperature (340-380 °C), pressure (6.2-9.0 MPa), liquid hourly space velocity (1-3 h-1) and hydrogen to oil ratio (600 ml/ml, STP). The predominant species on the catalyst surface were Ni3N, W2N and bimetallic Ni2W3N. The bimetallic Ni-W nitride species was more active than the individual activities of the Ni3N and W2N. P increased weak acid sites while nitriding temperature decreased amount of strong acid sites. Low nitriding temperature enhanced dispersion of metal particles. P interacted with Al 2O3 which increased the dispersion of metal nitrides on the catalyst surface. HDN activity increased with Ni and P loading but decreased with increase in nitriding temperature (optimum conversion; 60 wt%). HDS and HDA activities went through a maximum with increase in the synthesis parameters (optimum conversions; 88. wt% for HDS and 47 wt% for HDA). Increase in W loading led to increase in catalyst activity. The catalysts were stable to deactivation and had the nitride structure conserved during hydrotreating in the presence of hydrogen sulfide. The results showed good correlation between hydrotreating activities (HDS and HDN) and the catalyst nitrogen content, number of exposed active sites, catalyst particle size and BET surface area. HDS and HDN kinetic analyses, using Langmuir-Hinshelwood models, gave activation energies of 66 and 32 kJ/mol, respectively. There were no diffusion limitations in the reaction process. Two active sites were involved in HDS reaction while one site was used for HDN. HDS and HDN activities of the Ni-W(P)/gamma-Al 2O3 nitride catalysts were comparable to the corresponding sulfides.

Magnesium K-edge XANES spectroscopy of geological standards.

PubMed

Yoshimura, Toshihiro; Tamenori, Yusuke; Iwasaki, Nozomu; Hasegawa, Hiroshi; Suzuki, Atsushi; Kawahata, Hodaka

2013-09-01

Magnesium K-edge X-ray absorption near-edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg-bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.

Determination of interstitial oxygen atom position in U2N3+xOy by near edge structure study

NASA Astrophysics Data System (ADS)

Jiang, A. K.; Zhao, Y. W.; Long, Z.; Hu, Y.; Wang, X. F.; Yang, R. L.; Bao, H. L.; Zeng, R. G.; Liu, K. Z.

2018-06-01

The determination of interstitial oxygen atom site in U2N3+xOy film could facilitate the understanding of the oxidation mechanism of α-U2N3 and the effect of U2N3+xOy on anti-oxidation. By comparing the similarities and variances between N K edge and O K edge electron energy loss spectra (EELS) for oxidized α-U2N3 and UO2, the present work looks at the local structure of nitrogen and oxygen atoms in U2N3+xOy film, identifying the most possible position of interstitial O atom.

The local environment of Cu+ in Cu-Y zeolite and its relationship to the synthesis of dimethyl carbonate.

PubMed

Drake, Ian J; Zhang, Yihua; Briggs, Daniel; Lim, Bomyi; Chau, Tanguy; Bell, Alexis T

2006-06-22

Cu-exchanged Y zeolite was investigated in order to determine the location of the copper cations relative to the zeolite framework and to determine which Cu cations are active for the oxidative carbonylation of methanol to dimethyl carbonate (DMC). Cu-Y zeolite was prepared by vapor-phase exchange of H-Y with CuCl. The oxidation state, local coordination, and bond distances of Al and Cu were determined using Al K-edge and Cu K-edge X-ray absorption spectroscopy (XAS). Complimentary information was obtained by H2 temperature-programmed reduction and by in-situ infrared spectroscopy. Cu-Y has a Cu/Al ratio of unity and very little occluded CuCl. The average Al-O and Al-Cu bond distances are 1.67 angstroms and 2.79 angstroms, respectively, and the average Cu-O and Cu-Si(Al) bond distances are 1.99 angstroms and 3.13 angstroms, respectively. All of the Cu exchanged is present as Cu+ in sites I', II, and III'. Cu-Y is active for the oxidative carbonylation of methanol, and at low reactant contact time produces DMC as the primary product. With increasing reactant contact time, DMC formation decreases in preference to the formation of dimethoxy methane (DMM) and methylformate (MF). The formation of DMM and MF is attributed to the hydrogenation of DMC and the hydrogenolysis of DMM, respectively. Observation of the catalyst under reaction conditions reveals that most of the copper cations remain as Cu+, but some oxidation of Cu+ to Cu2+ does occur. It is also concluded that only those copper cations present in site II and III' positions are accessible to the reactants, and hence are catalytically active. The dominant adsorbed species on the surface are methoxy groups, and adsorbed CO is present as a minority species. The relationship of these observations to the kinetics of DMC synthesis is discussed.

Numerical Analysis of Edge Over Coating and Baffle Effect on Hot-Dip Galvanizing

NASA Astrophysics Data System (ADS)

Bao, Chengren; Kang, Yonglin; Li, Yan

2017-06-01

In hot-dip galvanizing process, air jet wiping control is so crucial to determine the coating thickness and uniformity of the zinc layer on the steel strip. A numerical simulation of gas-jet wiping in hot-dip galvanizing was conducted to minimize the occurrence of edge over coating (EOC). The causes of EOC were identified by contrasting and analyzing the airflow fields on the strip edge with and without a baffle. The factors influencing the airflow field on the strip edge during the change in the gap between the baffle and the strip edge were also analyzed. The effect of the distance between the air knife and the strip was evaluated. Technological parameters with on-site guidance role were obtained by combining them with the actual production to elucidate the role of the baffle in restraining the occurrence of EOC. The uniform distribution of pressure and coating thickness on the strip is achieved when the distance of the baffle from the strip edge is about 0.3 times of the jetting distance.

Comparable Monoterpene emission from pine forests across 500 mm precipitation gradient in the semi-arid transition zone

NASA Astrophysics Data System (ADS)

Seco, Roger; Karl, Thomas; Turnipseed, Andrew; Greenberg, Jim; Guenther, Alex; Llusia, Joan; Penuelas, Josep; Dicken, Uri; Rotenberg, Eyal; Rohatyn, Shani; Preisler, Yakir; Yakir, Dan

2014-05-01

Atmospheric volatile organic compounds (VOCs) have key environmental and biological roles, and can affect atmospheric chemistry, secondary aerosol formation, and as a consequence also climate. At the same time, global changes in climate arising from human activities can modify the VOC emissions of vegetation in the coming years. Monoterpene emission fluxes were measured during April 2013 at two forests in the semi-arid climate of Israel. Both forests were dominated by Pinus halepensis trees of similar age, but differed in the amount of annual average precipitation received (~276 and ~760 mm at the Yatir and Birya sites, respectively). Measurements performed included leaf-level sampling and gas exchange, as well as canopy-level flux calculations. Leaf level monoterpene emissions were sampled from leaf cuvettes with adsorbent cartridges and later analyzed by GC-MS. Canopy scale fluxes were calculated with the Disjunct Eddy Covariance technique by means of a Quadrupole PTRMS and eddy-covariance system. We report the differences observed between the two forests in terms of photosynthetic activity and monoterpene emissions, aiming to see the effect of the different climatic regimes at each location. Significantly higher emission rates of monoterpenes were observed in the wetter site during mid-day, in both the leaf scale and canopy scale measurements. Remarkably, however, normalized to 30C and corrected for tree density differences between the sites indicated comparable emission rates for both sites, with higher emission rated in the evening hours in the dry site at the edge of the Negev Desert. Modeling the monoterpene emission rates using MEGAN v2.1 indicated better agreement with observations in the wetter site then in the dry site, especially with respect to fluxes during the evening hours.

Activities in a social networking-based discussion group by endoscopic retrograde cholangiopancreatography doctors.

PubMed

Kang, Xiaoyu; Zhao, Lina; Liu, Na; Wang, Xiangping; Zhang, Rongchun; Liu, Zhiguo; Liang, Shuhui; Yao, Shaowei; Tao, Qin; Jia, Hui; Pan, Yanglin; Guo, Xuegang

2017-10-01

Online social networking is increasingly being used among medical practitioners. However, few studies have evaluated its use in therapeutic endoscopy. Here, we aimed to analyze the shared topics and activities of a group of endoscopic retrograde cholangiopancreatography (ERCP) doctors in a social networking-based endoscopic retrograde cholangiopancreatography discussion group (EDG). Six ERCP trainers working in Xijing Hospital and 48 graduated endoscopists who had finished ERCP training in the same hospital were invited to join in EDG. All group members were informed not to divulge any private information of patients when using EDG. The activities of group members on EDG were retrospectively extracted. The individual data of the graduated endoscopists were collected by a questionnaire. From June 2014 to May 2015, 6924 messages were posted on EDG, half of which were ERCP related. In total, 214 ERCP-related topics were shared, which could be categorized into three types: sharing experience/cases (52.3%), asking questions (38.3%), and sharing literatures/advances (9.3%). Among the 48 graduated endoscopists, 21 had a low case volume of less than 50 per year and 27 had a high volume case volume of 50 or more. High-volume graduated endoscopists posted more ERCP-related messages (P=0.008) and shared more discussion topics (P=0.003) compared with low-volume graduated endoscopists. A survey showed that EDG was useful for graduated endoscopists in ERCP performance and management of post-ERCP complications, etc. A wide range of ERCP-related topics were shared on the social networking-based EDG. The ERCP-related behaviors on EDG were more active in graduated endoscopists with an ERCP case volume of more than 50 per year.

Ergosterol and Water Changes in Tricholoma matsutake Soil Colony during the Mushroom Fruiting Season

PubMed Central

Lee, Dong-Hee; Park, Young-Woo; Lee, Young-Nam; Ka, Kang-Hyun; Park, Hyun; Bak, Won-Chull

2009-01-01

The purpose of this study is to understand spatio-temporal changes of active fungal biomass and water in Tricholoma matsutake soil colonies during the mushroom fruiting season. The active fungal biomass was estimated by analyzing ergosterol content at four different points within four replicated locations in a single circular T. matsutake colony at Ssanggok valley in the Sogri Mt. National Park in Korea during 2003 to 2005. The four points were the ahead of the colony, the front edge of the colony and 20 cm and 40 cm back from the front edge of the colony. Ergosterol content was 0.0 to 0.7 µg per gram dried soil at the ahead, 2.5 to 4.8 µg at the front edge, 0.5 to 1.8 µg at the 20 cm back and 0.3 to 0.8 µg at the 40 cm back. The ergosterol content was very high at the front edge where the T. matsutake hyphae were most active. However, ergosterol content did not significantly change during the fruiting season, September to October. Soil water contents were lower at the front edge and 20 cm back from the front edge of the colony than at the ahead and 40 cm back during the fruiting season. Soil water content ranged from 12 to 19% at the ahead, 10 to 11% at the edge, 9 to 11% at the 20 cm back and 11 to 15% at the 40 cm back. Our results suggest that the active front edge of the T. matsutake soil colony could be managed in terms of water relation and T. matsutake ectomycorrhizal root development. PMID:23983500

Soil Moisture Retrieval Through Changing Corn Using Active/Passive Microwave Remote Sensing

NASA Technical Reports Server (NTRS)

ONeill, P. E.; Joseph, A.; DeLannoy, G.; Lang, R.; Utku, C.; Kim, E.; Houser, P.; Gish, T.

2003-01-01

An extensive field experiment was conducted from May-early October, 2002 at the heavily instrumented USDA-ARS (U.S. Dept. of Agriculture-Agricultural Research Service) OPE3 (Optimizing Production Inputs for Economic and Environmental Enhancement) test site in Beltsville, MD to acquire data needed to address active/passive microwave algorithm, modeling, and ground validation issues for accurate soil moisture retrieval. During the experiment, a tower-mounted 1.4 GHz radiometer (Lrad) and a truck-mounted dual-frequency (1.6 and 4.75 GHz) radar system were deployed on the northern edge of the site. The soil in this portion of the field is a sandy loam (silt 23.5%, sand 60.3%, clay 16.1%) with a measured bulk density of 1.253 g/cu cm. Vegetation cover in the experiment consisted of a corn crop which was measured from just after planting on April 17, 2002 through senescence and harvesting on October 2. Although drought conditions prevailed during the summer, the corn yield was near average, with peak biomass reached in late July.

Clusterization Effects in III-V Nitrides: Nitrogen Vacancies, and Si and Mg Impurities in Aluminum Nitride and Gallium Nitride

NASA Astrophysics Data System (ADS)

Gubanov, V. A.; Pentaleri, E. A.; Boekema, C.; Fong, C. Y.; Klein, B. M.

1997-03-01

We have investigated clusterization of nitrogen vacancies and Si and Mg doping impurities in zinc-blende aluminum nitride (c-AlN) and gallium nitride (c-GaN) by the tight-binding LMTO technique. The calculations used 128-site supercells. Si and Mg atoms replacing ions in both the cation and anion sublattices of the host lattices of the host crystals have been considered. The Mg impurity at cation sites is found to form partially occupied states at the valence-band edge, and may result in p-type conductivity. When Si substitutes for Ga, the impurity band is formed at the conduction-band edge, resulting in n-type conductivity. Si impurities at cation sites, and Mg impurity at anion sites are able to form resonance states in the gap. The influence of impurity clusterization in the host lattice and interstitial sites on electronic properties of c-AlN and c-GaN crystals are modeled. The changes in vacancy- and impurity-state energies, bonding type, localization, density of states at the Fermi level in different host lattices, their dependence on impurity/vacancy concentration are analyzed and compared with the experimental data.

Diversity of Cyclic Di-GMP-Binding Proteins and Mechanisms

PubMed Central

2015-01-01

ABSTRACT Cyclic di-GMP (c-di-GMP) synthetases and hydrolases (GGDEF, EAL, and HD-GYP domains) can be readily identified in bacterial genome sequences by using standard bioinformatic tools. In contrast, identification of c-di-GMP receptors remains a difficult task, and the current list of experimentally characterized c-di-GMP-binding proteins is likely incomplete. Several classes of c-di-GMP-binding proteins have been structurally characterized; for some others, the binding sites have been identified; and for several potential c-di-GMP receptors, the binding sites remain to be determined. We present here a comparative structural analysis of c-di-GMP-protein complexes that aims to discern the common themes in the binding mechanisms that allow c-di-GMP receptors to bind it with (sub)micromolar affinities despite the 1,000-fold excess of GTP. The available structures show that most receptors use their Arg and Asp/Glu residues to bind c-di-GMP monomers, dimers, or tetramers with stacked guanine bases. The only exception is the EAL domains that bind c-di-GMP monomers in an extended conformation. We show that in c-di-GMP-binding signature motifs, Arg residues bind to the O-6 and N-7 atoms at the Hoogsteen edge of the guanine base, while Asp/Glu residues bind the N-1 and N-2 atoms at its Watson-Crick edge. In addition, Arg residues participate in stacking interactions with the guanine bases of c-di-GMP and the aromatic rings of Tyr and Phe residues. This may account for the presence of Arg residues in the active sites of every receptor protein that binds stacked c-di-GMP. We also discuss the implications of these structural data for the improved understanding of the c-di-GMP signaling mechanisms. PMID:26055114

Habitat use and foraging behavior of Townsend's big-eared bat (Corynorhinus townsendii) in coastal California

USGS Publications Warehouse

Fellers, Gary M.; Pierson, Elizabeth D.

2002-01-01

Radiotracking studies of Townsend's big-eared bat (Corynorhinus townsendii) were conducted in grazed grassland and coastal forest (California bay, Douglas-fir, and redwood) at Point Reyes National Seashore in coastal central California. Radiotagged bats were used to determine the foraging patterns of both female and male bats and to locate alternate roost sites. The animals showed considerable loyalty to their primary roost sites even though the study was conducted after the nursery period had ended, when the bats would normally be dispersing for the season. Foraging patterns differed between male and female bats, with females traveling greater distances than males. Males consistently stayed close to the maternity colony both during day and night. Both sexes flew in the immediate vicinity of vegetation, both when foraging and when traveling from the roost to foraging areas. Foraging activity was concentrated primarily along the edges of riparian vegetation.

Effect of aluminum on the local structure of silicon in zeolites as studied by Si K edge X-ray absorption near-edge fine structure: spectra simulation with a non-muffin tin atomic background.

PubMed

Bugaev, Lusegen A; Bokhoven, Jeroen A van; Khrapko, Valerii V

2009-04-09

Experimental Si K edge X-ray absorption near-edge fine structure (XANES) of zeolite faujasite, mordenite, and beta are interpreted by means of the FEFF8 code, replacing the theoretical atomic background mu(0) by a background that was extracted from an experimental spectrum. To some extent, this diminished the effect of the inaccuracy introduced by the MT potential and accounted for the intrinsic loss of photoelectrons. The agreement of the theoretical and experimental spectra at energies above the white lines enabled us to identify structural distortion around silicon, which occurs with increasing aluminum content. The Si K edge XANES spectra are very sensitive to slight distortions in the silicon coordination. Placing an aluminum atom on a nearest neighboring T site causes a distortion in the silicon tetrahedron, shortening one of the silicon-oxygen bonds relative to the other three.

Femtosecond time-resolved X-ray absorption spectroscopy of anatase TiO2 nanoparticles using XFEL

PubMed Central

Obara, Yuki; Ito, Hironori; Ito, Terumasa; Kurahashi, Naoya; Thürmer, Stephan; Tanaka, Hiroki; Katayama, Tetsuo; Togashi, Tadashi; Owada, Shigeki; Yamamoto, Yo-ichi; Karashima, Shutaro; Nishitani, Junichi; Yabashi, Makina; Suzuki, Toshinori; Misawa, Kazuhiko

2017-01-01

The charge-carrier dynamics of anatase TiO2 nanoparticles in an aqueous solution were studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser in combination with a synchronized ultraviolet femtosecond laser (268 nm). Using an arrival time monitor for the X-ray pulses, we obtained a temporal resolution of 170 fs. The transient X-ray absorption spectra revealed an ultrafast Ti K-edge shift and a subsequent growth of a pre-edge structure. The edge shift occurred in ca. 100 fs and is ascribed to reduction of Ti by localization of generated conduction band electrons into shallow traps of self-trapped polarons or deep traps at penta-coordinate Ti sites. Growth of the pre-edge feature and reduction of the above-edge peak intensity occur with similar time constants of 300–400 fs, which we assign to the structural distortion dynamics near the surface. PMID:28713842

Ca K-Edge XAS as a Probe of Calcium Centers in Complex Systems

DOE PAGES

Martin-Diaconescu, Vlad; Gennari, Marcello; Gerey, Bertrand; ...

2014-12-10

Calcium K-edge pre-edges coupled with TD-DFT theoretical calculation of spectra provide a powerful approach for the characterization of complex calcium centers in inorganic and bioinorganic chemistry. Herein, Ca K-edge X-ray absorption spectroscopy (XAS) is developed as a means to characterize the local environment of calcium centers. The spectra for six, seven, and eight coordinate inorganic and molecular calcium complexes were analyzed and determined to be primarily influenced by the coordination environment and site symmetry at the calcium center. The experimental results are closely correlated to time-dependent density functional theory (TD-DFT) calculations of the XAS spectra. The applicability of this methodologymore » to complex systems was investigated using structural mimics of the oxygen-evolving complex (OEC) of PSII. It was found that Ca K-edge XAS is a sensitive probe for structural changes occurring in the cubane heterometallic cluster due to Mn oxidation. Future applications to the OEC are discussed.« less

Wait for the Bus: How Lowcountry School Site Selection and Design Deter Walking to School and Contribute to Urban Sprawl.

ERIC Educational Resources Information Center

Kouri, Christopher

This paper presents a study on how the South Carolina school site selection process can affect the quality of the students' experience and access to their schools. Focusing on students options for getting to school, e.g., hazards that prevent students from walking to school and the size of school sites that place schools on the edge of…

Photograph of Apollo 17 lunar landing site location

NASA Image and Video Library

1972-07-01

S72-01718 (July 1972) --- A photographic illustration of a full moon showing the location of the Apollo 17 landing site on the lunar nearside. The black dot pinpointing the landing site is in the Taurus-Littrow area at the southeastern edge of the Sea of Serenity. The coordinates of the landing point are 30 degrees 44 minutes 58 seconds east longitude and 20 degrees 9 minutes 50 seconds north latitude.

KSC-04PD-1544

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Media tour the Orbiter Processing Facility (OPF) housing the Space Shuttle Discovery at KSC. During this event, they received the latest information on Discoverys processing and viewed workers preparing the vehicle for its safe return to flight scheduled for a launch planning window of March 2005. Kicking off the activities at the Press Site Auditorium, technical experts led two workshops addressing Reinforced Carbon- Carbon and vehicle instrumentation. Later, reporters toured the OPF to see work in progress on Discovery, including reinstallation of the Reinforced Carbon-Carbon panels on the Shuttle's wing leading edge, wiring inspections and instrumentation updates being completed for Return to Flight.

KSC-04pd1544

NASA Image and Video Library

2004-07-23

KENNEDY SPACE CENTER, FLA. - Media tour the Orbiter Processing Facility (OPF) housing the Space Shuttle Discovery at KSC. During this event, they received the latest information on Discovery’s processing and viewed workers preparing the vehicle for its safe return to flight scheduled for a launch planning window of March 2005. Kicking off the activities at the Press Site Auditorium, technical experts led two workshops addressing Reinforced Carbon-Carbon and vehicle instrumentation. Later, reporters toured the OPF to see work in progress on Discovery, including reinstallation of the Reinforced Carbon-Carbon panels on the Shuttle's wing leading edge, wiring inspections and instrumentation updates being completed for Return to Flight.

Insights into the Vitis complex in the Danube floodplain (Austria).

PubMed

Arnold, Claire; Bachmann, Olivier; Schnitzler, Annik

2017-10-01

European grapevine populations quickly disappeared from most of their range, massively killed by the spread of North American grapevine pests and diseases. Nowadays taxonomic pollution represents a new threat. A large Vitis complex involves escaped cultivars, rootstocks, and wild grapevines. The study aimed to provide insight into the Vitis complex in the Danube region through field and genetic analyses. Among the five other major rivers in Europe which still host wild grapevine populations, the Danube floodplain is the only one benefiting from an extensive protected forest area (93 km²) and an relatively active dynamic flood pulse. The Donau-Auen National Park also regroups the largest wild grapevine population in Europe. Ninety-two percent of the individuals collected in the park were true wild grapevines, and 8% were hybrids and introgressed individuals of rootstocks, wild grapevines, and cultivars. These three groups are interfertile acting either as pollen donor or receiver. Hybrids were established within and outside the dykes, mostly in anthropized forest edges. The best-developed individuals imply rootstock genes. They establish in the most erosive parts of the floodplain. 42% of the true wild grapevines lived at the edges of forest/meadow, 33.3% at the edges forest/channels, and 23.9% in forest gaps. DBH (Diameter Breast Height) varied significantly with the occurrence of flooding. Clones were found in both true wild and hybrids/introgressed grapevines. The process of cloning seemed to be prevented in places where flooding dynamics is reduced. The current global distribution of true wild grapevines shows a strong tendency toward clustering, in sites where forestry practices were the most extensive. However, the reduced flooding activity is a danger for long-term sustainability of the natural wild grapevine population.

Multi-site evaluation of APEX for crop and grazing land in the Heartland region of the US

USDA-ARS?s Scientific Manuscript database

The Agricultural and Policy Environmental Extender (APEX) is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of management practices. Current practice is to fully calibrate the model for each site simulation, which requires ...

1. VIEW, LOOKING WEST, AT THE SITE OF THE PINE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. VIEW, LOOKING WEST, AT THE SITE OF THE PINE LOG MILL. THE STONE RETAINING WALL ON THE RIGHT MARKS THE LOCATION OF THE 1896 20-STAMP FACILITY, EXPANDED SOUTH TO INCLUDE 20 ADDITIONAL STAMPS BY 1899 - Pine Log Mill, Southern Edge of Salt Spring Valley, Copperopolis, Calaveras County, CA

Report: American Recovery and Reinvestment Act Site Visit of the Diversion Ditch Repair Project at the Gilt Edge Mine Superfund Site, Lawrence County, South Dakota

EPA Pesticide Factsheets

Report #12-R-0601, July 25, 2012. PWT did not have adequate controls to ensure that its subcontractors and vendors complied with the Buy American and Davis-Bacon Act (DBA) provisions of the Recovery Act.

A model for managing edge effects in harvest scheduling using spatial optimization

Treesearch

Kai L. Ross; Sándor F. Tóth

2016-01-01

Actively managed forest stands can create new forest edges. If left unchecked over time and across space, forest operations such as clear-cuts can create complex networks of forest edges. Newly created edges alter the landscape and can affect many environmental factors. These altered environmental factors have a variety of impacts on forest growth and structure and can...

A theoretical study on reaction mechanisms and kinetics of thiophene hydrodesulfurization over MoS 2 catalysts

DOE PAGES

Jin, Qiu; Chen, Biaohua; Ren, Zhibo; ...

2018-02-10

In the present study, thiophene hydrodesulphurization (HDS) over the Mo-edge, the S-edge, and the Mo-S connection edge of MoS 2 catalyst with 50% sulfur coverage was studied using first-principles based microkinetic modeling. Two parallel HDS routes, i.e., direct desulfurization (DDS) and hydrogenation (HYD) were taken into account. It has been found that the major reaction route of thiophene HDS on the Mo- and the Mo-S edges is temperature dependent. In the low temperature range of 500–600 K, the HYD route is dominant, leading to the C 4H 8 formation. As the temperature increases, the DDS route becomes competitive with themore » HYD route. At the temperature above 650 K, the DDS route will be the dominant HDS reaction route on the Mo- and the Mo-S edges. The DDS route leading to the formation of C 4H 6 is the major thiophene HDS reaction route on the S-edge in the entire temperature range of 500–750 K. The microkinetic modeling results show the overall HDS activity on the S-edge is lower than it on the Mo- and the Mo-S edges. The Mo-S edge also provides a preferential reaction pathway, which facilitates 2-hydrothiophene migration from the Mo-edge to the S-edge, followed by remaining elementary steps with lower activation barriers in the DDS route.« less

A theoretical study on reaction mechanisms and kinetics of thiophene hydrodesulfurization over MoS 2 catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Qiu; Chen, Biaohua; Ren, Zhibo

In the present study, thiophene hydrodesulphurization (HDS) over the Mo-edge, the S-edge, and the Mo-S connection edge of MoS 2 catalyst with 50% sulfur coverage was studied using first-principles based microkinetic modeling. Two parallel HDS routes, i.e., direct desulfurization (DDS) and hydrogenation (HYD) were taken into account. It has been found that the major reaction route of thiophene HDS on the Mo- and the Mo-S edges is temperature dependent. In the low temperature range of 500–600 K, the HYD route is dominant, leading to the C 4H 8 formation. As the temperature increases, the DDS route becomes competitive with themore » HYD route. At the temperature above 650 K, the DDS route will be the dominant HDS reaction route on the Mo- and the Mo-S edges. The DDS route leading to the formation of C 4H 6 is the major thiophene HDS reaction route on the S-edge in the entire temperature range of 500–750 K. The microkinetic modeling results show the overall HDS activity on the S-edge is lower than it on the Mo- and the Mo-S edges. The Mo-S edge also provides a preferential reaction pathway, which facilitates 2-hydrothiophene migration from the Mo-edge to the S-edge, followed by remaining elementary steps with lower activation barriers in the DDS route.« less

Dynamic Edge Effects in Small Mammal Communities across a Conservation-Agricultural Interface in Swaziland

PubMed Central

Hurst, Zachary M.; McCleery, Robert A.; Collier, Bret A.; Fletcher, Robert J.; Silvy, Nova J.; Taylor, Peter J.; Monadjem, Ara

2013-01-01

Across the planet, high-intensity farming has transformed native vegetation into monocultures, decreasing biodiversity on a landscape scale. Yet landscape-scale changes to biodiversity and community structure often emerge from processes operating at local scales. One common process that can explain changes in biodiversity and community structure is the creation of abrupt habitat edges, which, in turn, generate edge effects. Such effects, while incredibly common, can be highly variable across space and time; however, we currently lack a general analytical framework that can adequately capture such spatio-temporal variability. We extend previous approaches for estimating edge effects to a non-linear mixed modeling framework that captures such spatio-temporal heterogeneity and apply it to understand how agricultural land-uses alter wildlife communities. We trapped small mammals along a conservation-agriculture land-use interface extending 375 m into sugarcane plantations and conservation land-uses at three sites during dry and wet seasons in Swaziland, Africa. Sugarcane plantations had significant reductions in species richness and heterogeneity, and showed an increase in community similarity, suggesting a more homogenized small mammal community. Furthermore, our modeling framework identified strong variation in edge effects on communities across sites and seasons. Using small mammals as an indicator, intensive agricultural practices appear to create high-density communities of generalist species while isolating interior species in less than 225 m. These results illustrate how agricultural land-use can reduce diversity across the landscape and that effects can be masked or magnified, depending on local conditions. Taken together, our results emphasize the need to create or retain natural habitat features in agricultural mosaics. PMID:24040269

28. AERIAL VIEW LOOKING EAST AT THE WEST GATE IN ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

28. AERIAL VIEW LOOKING EAST AT THE WEST GATE IN 1978. SHOWN IS BUILDING 100, THE MAIN ENTRANCE POINT TO THE SITE FROM 1969 UNTIL 1985. DURING THIS TIME EACH AUTOMOBILE THAT ENTERED THE SITE WAS SEARCHED. IN 1985, BUILDING 120 WAS BUILT AT THE OUTERMOST WEST EDGE OF THE SITE. THERE WERE 29 FACILITIES AROUND THE SITE DEDICATED TO SECURITY (5/4/78). - Rocky Flats Plant, Bounded by Indiana Street & Routes 93, 128 & 72, Golden, Jefferson County, CO

Active edge control in the precessions polishing process for manufacturing large mirror segments

NASA Astrophysics Data System (ADS)

Li, Hongyu; Zhang, Wei; Walker, David; Yu, Gouyo

2014-09-01

The segmentation of the primary mirror is the only promising solution for building the next generation of ground telescopes. However, manufacturing segmented mirrors presents its own challenges. The edge mis-figure impacts directly on the telescope's scientific output. The `Edge effect' significantly dominates the polishing precision. Therefore, the edge control is regarded as one of the most difficult technical issues in the segment production that needs to be addressed urgently. This paper reports an active edge control technique for the mirror segments fabrication using the Precession's polishing technique. The strategy in this technique requires that the large spot be selected on the bulk area for fast polishing, and the small spot is used for edge figuring. This can be performed by tool lift and optimizing the dell time to compensate for non-uniform material removal at the edge zone. This requires accurate and stable edge tool influence functions. To obtain the full tool influence function at the edge, we have demonstrated in previous work a novel hybrid-measurement method which uses both simultaneous phase interferometry and profilometry. In this paper, the edge effect under `Bonnet tool' polishing is investigated. The pressure distribution is analyzed by means of finite element analysis (FEA). According to the `Preston' equation, the shape of the edge tool influence functions is predicted. With this help, the multiple process parameters at the edge zone are optimized. This is demonstrated on a 200mm crosscorners hexagonal part with a result of PV less than 200nm for entire surface.

Gallbladder shape extraction from ultrasound images using active contour models.

PubMed

Ciecholewski, Marcin; Chochołowicz, Jakub

2013-12-01

Gallbladder function is routinely assessed using ultrasonographic (USG) examinations. In clinical practice, doctors very often analyse the gallbladder shape when diagnosing selected disorders, e.g. if there are turns or folds of the gallbladder, so extracting its shape from USG images using supporting software can simplify a diagnosis that is often difficult to make. The paper describes two active contour models: the edge-based model and the region-based model making use of a morphological approach, both designed for extracting the gallbladder shape from USG images. The active contour models were applied to USG images without lesions and to those showing specific disease units, namely, anatomical changes like folds and turns of the gallbladder as well as polyps and gallstones. This paper also presents modifications of the edge-based model, such as the method for removing self-crossings and loops or the method of dampening the inflation force which moves nodes if they approach the edge being determined. The user is also able to add a fragment of the approximated edge beyond which neither active contour model will move if this edge is incomplete in the USG image. The modifications of the edge-based model presented here allow more precise results to be obtained when extracting the shape of the gallbladder from USG images than if the morphological model is used. © 2013 Elsevier Ltd. Published by Elsevier Ltd. All rights reserved.

A Spatial-Spectral Approach for Visualization of Vegetation Stress Resulting from Pipeline Leakage.

PubMed

Van derWerff, Harald; Van der Meijde, Mark; Jansma, Fokke; Van der Meer, Freek; Groothuis, Gert Jan

2008-06-04

Hydrocarbon leakage into the environment has large economic and environmental impact. Traditional methods for investigating seepages and their resulting pollution, such as drilling, are destructive, time consuming and expensive. Remote sensing is an efficient tool that offers a non-destructive investigation method. Optical remote sensing has been extensively tested for exploration of onshore hydrocarbon reservoirs and detection of hydrocarbons at the Earth's surface. In this research, we investigate indirect manifestations of pipeline leakage by way of visualizing vegetation anomalies in airborne hyperspectral imagery. Agricultural land-use causes a heterogeneous landcover; variation in red edge position between fields was much larger than infield red edge position variation that could be related to hydrocarbon pollution. A moving and growing kernel procedure was developed to normalzie red edge values relative to values of neighbouring pixels to enhance pollution related anomalies in the image. Comparison of the spatial distribution of anomalies with geochemical data obtained by drilling showed that 8 out of 10 polluted sites were predicted correctly while 2 out of 30 sites that were predicted clean were actually polluted.

A Spatial-Spectral Approach for Visualization of Vegetation Stress Resulting from Pipeline Leakage

PubMed Central

van der Werff, Harald; van der Meijde, Mark; Jansma, Fokke; van der Meer, Freek; Groothuis, Gert Jan

2008-01-01

Hydrocarbon leakage into the environment has large economic and environmental impact. Traditional methods for investigating seepages and their resulting pollution, such as drilling, are destructive, time consuming and expensive. Remote sensing is an efficient tool that offers a non-destructive investigation method. Optical remote sensing has been extensively tested for exploration of onshore hydrocarbon reservoirs and detection of hydrocarbons at the Earth's surface. In this research, we investigate indirect manifestations of pipeline leakage by way of visualizing vegetation anomalies in airborne hyperspectral imagery. Agricultural land-use causes a heterogeneous landcover; variation in red edge position between fields was much larger than infield red edge position variation that could be related to hydrocarbon pollution. A moving and growing kernel procedure was developed to normalzie red edge values relative to values of neighbouring pixels to enhance pollution related anomalies in the image. Comparison of the spatial distribution of anomalies with geochemical data obtained by drilling showed that 8 out of 10 polluted sites were predicted correctly while 2 out of 30 sites that were predicted clean were actually polluted. PMID:27879905

Contribution of insectivorous avifauna to top down control of Lindera benzoin herbivores at forest edge and interior habitats

NASA Astrophysics Data System (ADS)

Skoczylas, Daniel R.; Muth, Norris Z.; Niesenbaum, Richard A.

2007-11-01

Predation of herbivorous Lepidoptera larvae by insectivorous avifauna was estimated on Lindera benzoin in edge and interior habitats at two sites in eastern Pennsylvania (USA). Clay baits modeled after Epimecis hortaria (Geometridae) larvae, the primary herbivore of L. benzoin at our study sites, were used to estimate predation by birds. In both habitat types, models were placed on uninjured L. benzoin leaves as well as on leaves that had prior insect herbivore damage. Rates of model attack were greater, and model longevity reduced, in forest edge plots compared to interiors. Naturally occurring herbivore damage on L. benzoin was greater in forest interiors. However, model attack was not significantly greater on leaves with prior herbivory damage, suggesting that birds do not effectively use this type of leaf damage as a cue in their foraging. Our findings are consistent with a contribution of bird predation towards top-down control of herbivory in this system. We further discuss these results in a broader context considering the possible effects of habitat type on leaf quality, leaf defense, and herbivore performance.

Extensive hydrothermal activity in the NE Lau basin revealed by ROV dives

NASA Astrophysics Data System (ADS)

Embley, R. W.; Resing, J. A.; Tebo, B.; Baker, E. T.; Butterfield, D. A.; Chadwick, B.; Davis, R.; de Ronde, C. E. J.; Lilley, M. D.; Lupton, J. E.; Merle, S. G.; Rubin, K. H.; Shank, T. M.; Walker, S. L.; Arculus, R. J.; Bobbitt, A. M.; Buck, N. J.; Caratori Tontini, F.; Crowhurst, P. V.; Mitchell, E.; Olson, E. J.; Ratmeyer, V.; Richards, S.; Roe, K. K.; Kenner-Chavis, P.; Martinez-Lyons, A.; Sheehan, C.; Brian, R.

2014-12-01

Dives with the QUEST 4000 ROV (Remotely Operated Vehicle) in September 2012 discovered nine hydrothermal sites in the arc and rear-arc region of the NE Lau Basin in 1150 m to 2630 m depth. These sites, originally detected by water column and seafloor surveys conducted in 2008-2011, include: (1) a paired sulfur-rich/black smoker field on the summit of a tectonically deformed magmatic arc volcano (Niua), (2) fracture-controlled black smoker venting on several small en echelon seamounts (north Matas) that lie between the magmatic arc and the backarc spreading center and (3) a magmatic degassing site on the summit of a dacite cone within a large (~12 km diameter) caldera volcano (Niuatahi). Dives at West Mata Seamount, which was undergoing strombolian volcanic activity and effusive rift-zone eruptions from 2008 to 2010, revealed a dormant volcanic phase in September 2012, with continued low-temperature diffuse venting. The high-temperature venting is likely driven by magmatic heat indicative of underlying partial melt zones and/or melt pockets distributed through the region. The occurrence of the youngest known boninite eruptions on the Mata volcanoes is consistent with subduction fluid flux melting extending into the rear-arc zone. Extension related to the transition from subduction to strike-slip motion of the northern Tonga Arc over the active Subduction-Transform Edge Propagator (STEP) fault probably contributes to the enhanced volcanism/hydrothermal activity in the NE Lau Basin. Chemosynthetic ecosystems at these sites range from mostly motile, lower diversity ecosystems at the eruptive/magmatically-degassing sites to higher diversity ecosystems with less mobile faunal components at the black-smoker systems. The wide range of fluid chemistry, water depth and geologic settings of the hydrothermal systems in this area provides an intriguing template to study the interaction of hydrothermal fluid chemistry, chemosynthetic habitats and their geologic underpinning within an arc/backarc setting.

Hyperactive hydrothermal activity in the NE Lau basin revealed by ROV dives

NASA Astrophysics Data System (ADS)

Embley, R. W.; Resing, J. A.; Tebo, B.; Baker, E. T.; Butterfield, D. A.; Chadwick, B.; Davis, R.; de Ronde, C. E.; Lilley, M. D.; Lupton, J. E.; Merle, S. G.; Rubin, K. H.; Shank, T. M.; Walker, S. L.; Arculus, R. J.; Bobbitt, A. M.; Buck, N.; Caratori Tontini, F.; Crowhurst, P. V.; Mitchell, E.; Olson, E. J.; Ratmeyer, V.; Richards, S.; Roe, K. K.; Keener, P.; Martinez Lyons, A.; Sheehan, C.; Brian, R.

2013-12-01

Dives with the QUEST 4000 ROV (Remotely Operated Vehicle) in September 2012 discovered nine hydrothermal sites in the arc and rear-arc region of the NE Lau Basin in 1150 m to 2630 m depth. These sites, originally detected by water column and seafloor surveys conducted in 2008-2011, include: (1) a paired sulfur-rich/black smoker field on the summit of a tectonically deformed magmatic arc volcano (Niua), (2) fracture-controlled black smoker venting on several small en echelon seamounts (north Matas) that lie between the magmatic arc and the backarc spreading center and (3) a magmatic degassing site on the summit of a dacite cone within a large (~12 km diameter) caldera volcano (Niuatahi). Dives at West Mata Seamount, which was undergoing strombolian volcanic activity and effusive rift-zone eruptions from 2008 to 2010, revealed a dormant volcanic phase in September 2012, with continued low-temperature diffuse venting. The high-temperature venting is likely driven by magmatic heat indicative of underlying partial melt zones and/or melt pockets distributed through the region. The occurrence of the youngest known boninite eruptions on the Mata volcanoes is consistent with subduction fluid flux melting extending into the rear-arc zone. Extension related to the transition from subduction to strike-slip motion of the northern Tonga Arc over the active Subduction-Transform Edge Propagator (STEP) fault probably contributes to the enhanced volcanism/hydrothermal activity in the NE Lau Basin. Chemosynthetic ecosystems at these sites range from mostly motile, lower diversity ecosystems at the eruptive/magmatically-degassing sites to higher diversity ecosystems with less mobile faunal components at the black-smoker systems. The wide range of fluid chemistry, water depth and geologic settings of the hydrothermal systems in this area provides an intriguing template to study the interaction of hydrothermal fluid chemistry, chemosynthetic habitats and their geologic underpinning within an arc/backarc setting.

Genotype and elevation influence Spartina alterniflora colonization and growth in a created salt marsh

USGS Publications Warehouse

Proffitt, C.E.; Travis, S.E.; Edwards, K.R.

2003-01-01

Colonization, growth, and clonal morphology differ with genotype and are influenced by elevation. Local adaptation of Spartina alterniflora to environmental conditions may lead to dominance by different suites of genotypes in different locations within a marsh. In a constructed marsh, we found reduced colonization in terms of density of clones with increasing distance from edge in a 200-ha mudflat created in 1996; however, growth in diameter was not different among three 100-m-long zones that differed in distance from site edge. Distance from edge was confounded by elevation in this comparison of natural colonization. The rate of clonal expansion in diameter was 3.1 m/yr, and clonal growth was linear over the 28 mo of the study. The area dominated by S. alterniflora in the three distance zones increased concomitantly with clonal growth. However, the lower initial clonal densities and colonization by other plant species resulted in reduced overall dominance by S. alterniflora in the two more-interior locations. Seedling recruitment was an important component of S. alterniflora colonization at all elevations and distances from edge two years after site creation. Seedlings were spatially very patchy and tended to occur near clones that probably produced them. A field experiment revealed that S. alterniflora height and total stem length varied with genotype, while stem density and flowering stem density did not. Differences between edge and center of clonal patches also occurred for some response variables, and there were also significant interactions with genotype. Differences between edge and center are interpreted as differences in clone morphology. Elevation differences over distances of a few meters influenced total stem length and flowering stem density but not other response variables. Clones that were larger in diameter also tended to have greater stem heights and total stem lengths. A number of plant morphological measures were found to vary significantly among the five genotypes and had broad-sense heritabilities ranging up to 0.71. These results indicate that S. alterniflora populations developing on new substrata colonize broadly, but growth and reproduction vary with genotype and are influenced by changes in elevation (range: 11.8 cm), and probably other environmental factors, over relatively small distances. Differences in growth and clone morphology of different genets, and the frequent occurrence of seedlings throughout the site, underscore the importance of genetic variability in natural and created populations.

Probing the Watson-Crick, wobble, and sugar-edge hydrogen bond sites of uracil and thymine.

PubMed

Müller, Andreas; Frey, Jann A; Leutwyler, Samuel

2005-06-16

The nucleobases uracil (U) and thymine (T) offer three hydrogen-bonding sites for double H-bond formation via neighboring N-H and C=O groups, giving rise to the Watson-Crick, wobble and sugar-edge hydrogen bond isomers. We probe the hydrogen bond properties of all three sites by forming hydrogen bonded dimers of U, 1-methyluracil (1MU), 3-methyluracil (3MU), and T with 2-pyridone (2PY). The mass- and isomer-specific S1 <-- S0 vibronic spectra of 2PY.U, 2PY.3MU, 2PY.1MU, and 2PY.T were measured using UV laser resonant two-photon ionization (R2PI). The spectra of the Watson-Crick and wobble isomers of 2PY.1MU were separated using UV-UV spectral hole-burning. We identify the different isomers by combining three different diagnostic tools: (1) Selective methylation of the uracil N3-H group, which allows formation of the sugar-edge isomer only, and methylation of the N1-H group, which leads to formation of the Watson-Crick and wobble isomers. (2) The experimental S1 <-- S0 origins exhibit large spectral blue shifts relative to the 2PY monomer. Ab initio CIS calculations of the spectral shifts of the different hydrogen-bonded dimers show a linear correlation with experiment. This correlation allows us to identify the R2PI spectra of the weakly populated Watson-Crick and wobble isomers of both 2PY.U and 2PY.T. (3) PW91 density functional calculation of the ground-state binding and dissociation energies De and D0 are in agreement with the assignment of the dominant hydrogen bond isomers of 2PY.U, 2PY.3MU and 2PY.T as the sugar-edge form. For 2PY.U, 2PY.T and 2PY.1MU the measured wobble:Watson-Crick:sugar-edge isomer ratios are in good agreement with the calculated ratios, based on the ab initio dissociation energies and gas-phase statistical mechanics. The Watson-Crick and wobble isomers are thereby determined to be several kcal/mol less strongly bound than the sugar-edge isomers. The 36 observed intermolecular frequencies of the nine different H-bonded isomers give detailed insight into the intermolecular force field.

Corridors promote fire via connectivity and edge effects.

PubMed

Brudvig, Lars A; Wagner, Stephanie A; Damschen, Ellen I

2012-04-01

Landscape corridors, strips of habitat that connect otherwise isolated habitat patches, are commonly employed during management of fragmented landscapes. To date, most reported effects of corridors have been positive; however, there are long-standing concerns that corridors may have unintended consequences. Here, we address concerns over whether corridors promote propagation of disturbances such as fire. We collected data during prescribed fires in the world's largest and best replicated corridor experiment (Savannah River Site, South Carolina, USA), six -50-ha landscapes of open (shrubby/herbaceous) habitat within a pine plantation matrix, to test several mechanisms for how corridors might influence fire. Corridors altered patterns of fire temperature through a direct connectivity effect and an indirect edge effect. The connectivity effect was independent of fuel levels and was consistent with a hypothesized wind-driven "bellows effect." Edges, a consequence of corridor implementation, elevated leaf litter (fuel) input from matrix pine trees, which in turn increased fire temperatures. We found no evidence for corridors or edges impacting patterns of fire spread: plots across all landscape positions burned with similar probability. Impacts of edges and connectivity on fire temperature led to changes in vegetation: hotter-burning plots supported higher bunch grass cover during the field season after burning, suggesting implications for woody/herbaceous species coexistence. To our knowledge, this represents the first experimental evidence that corridors can modify landscape-scale patterns of fire intensity. Corridor impacts on fire should be carefully considered during landscape management, both in the context of how corridors connect or break distributions of fuels and the desired role of fire as a disturbance, which may range from a management tool to an agent to be suppressed. In our focal ecosystem, longleaf pine woodland, corridors might provide a previously unrecognized benefit during prescribed burning activities, by promoting fire intensity, which may assist in promoting plant biodiversity.

The Impact of Nature-Based Tourism on Bird Communities: A Case Study in Pallas-Yllästunturi National Park

NASA Astrophysics Data System (ADS)

Huhta, Esa; Sulkava, Pekka

2014-05-01

Nature-based tourism and recreation within and close to protected areas may have negative environmental impacts on biodiversity due to urban development, landscape fragmentation, and increased disturbance. We conducted a 3-year study of disturbances of birds induced by nature-based tourism over a recreational gradient in the Pallas-Yllästunturi National Park and its surroundings in northern Finland. Bird assemblages were studied in highly disturbed areas close to the park (a ski resort, villages, and accommodation areas) and in campfire sites, along hiking routes (recreational areas) and in a forest (control area) within the park. Compared with the forest, the disturbed urbanized areas had higher abundances of human-associated species, corvid species, cavity and building nesters, and edge species. The abundances of managed forest species were higher in campfire sites than in the forest. Hiking trails and campfire sites did not have a negative impact on open-nesting bird species. The most likely reason for this outcome is that most campfire sites were situated at forest edges; this species group prefers managed forests and forest edge as a breeding habitat. The abundances of virgin forest species did not differ among the areas studied. The results of the study suggest that the current recreation pressure has not caused substantial changes in the forest bird communities within the National Park. We suggest that the abundances of urban exploiter species could be used as indicators to monitor the level and changes of urbanization and recreational pressure at tourist destinations.

The impact of nature-based tourism on bird communities: a case study in Pallas-Yllästunturi National Park.

PubMed

Huhta, Esa; Sulkava, Pekka

2014-05-01

Nature-based tourism and recreation within and close to protected areas may have negative environmental impacts on biodiversity due to urban development, landscape fragmentation, and increased disturbance. We conducted a 3-year study of disturbances of birds induced by nature-based tourism over a recreational gradient in the Pallas-Yllästunturi National Park and its surroundings in northern Finland. Bird assemblages were studied in highly disturbed areas close to the park (a ski resort, villages, and accommodation areas) and in campfire sites, along hiking routes (recreational areas) and in a forest (control area) within the park. Compared with the forest, the disturbed urbanized areas had higher abundances of human-associated species, corvid species, cavity and building nesters, and edge species. The abundances of managed forest species were higher in campfire sites than in the forest. Hiking trails and campfire sites did not have a negative impact on open-nesting bird species. The most likely reason for this outcome is that most campfire sites were situated at forest edges; this species group prefers managed forests and forest edge as a breeding habitat. The abundances of virgin forest species did not differ among the areas studied. The results of the study suggest that the current recreation pressure has not caused substantial changes in the forest bird communities within the National Park. We suggest that the abundances of urban exploiter species could be used as indicators to monitor the level and changes of urbanization and recreational pressure at tourist destinations.

Resonant inelastic X-ray scattering on synthetic nickel compounds and Ni-Fe hydrogenase protein

NASA Astrophysics Data System (ADS)

Sanganas, Oliver; Löscher, Simone; Pfirrmann, Stefan; Marinos, Nicolas; Glatzel, Pieter; Weng, Tsu-Chien; Limberg, Christian; Driess, Matthias; Dau, Holger; Haumann, Michael

2009-11-01

Ni-Fe hydrogenases are proteins catalyzing the oxidative cleavage of dihydrogen (H2) and proton reduction to H2 at high turnover rates. Their active site is a heterobimetallic center comprising one Ni and one Fe atom. To understand the function of the site, well resolved structural and electronic information is required. Such information is expected to become accessible by high resolution X-ray absorption and emission techniques, which are rapidly developing at third generation synchrotron radiation sources. We studied a number of synthetic Ni compounds, which mimic relevant features of the Ni site in hydrogenases, and the Ni site in the soluble, NAD-reducing hydrogenase (SH) from the bacterium Ralstonia eutropha by resonant inelastic X-ray scattering (RIXS) using a Rowland-type spectrometer at the ESRF. The SH is particularly interesting because its H2-cleavage reaction is highly resistant against inhibition by O2. Kα-fluorescence detected RIXS planes in the 1s→3d region of the X-ray absorption spectrum were recorded on the protein which allow to extract L3-edge type spectra Spectral features of the protein are compared to those of the model compounds.

Optimized Finite Difference Method for the Full-Potential XANES Simulations: Application to Molecular Adsorption Geometries in MOFs and Metal-Ligand Intersystem Crossing Transients.

PubMed

Guda, Sergey A; Guda, Alexander A; Soldatov, Mikhail A; Lomachenko, Kirill A; Bugaev, Aram L; Lamberti, Carlo; Gawelda, Wojciech; Bressler, Christian; Smolentsev, Grigory; Soldatov, Alexander V; Joly, Yves

2015-09-08

Accurate modeling of the X-ray absorption near-edge spectra (XANES) is required to unravel the local structure of metal sites in complex systems and their structural changes upon chemical or light stimuli. Two relevant examples are reported here concerning the following: (i) the effect of molecular adsorption on 3d metals hosted inside metal-organic frameworks and (ii) light induced dynamics of spin crossover in metal-organic complexes. In both cases, the amount of structural models for simulation can reach a hundred, depending on the number of structural parameters. Thus, the choice of an accurate but computationally demanding finite difference method for the ab initio X-ray absorption simulations severely restricts the range of molecular systems that can be analyzed by personal computers. Employing the FDMNES code [Phys. Rev. B, 2001, 63, 125120] we show that this problem can be handled if a proper diagonalization scheme is applied. Due to the use of dedicated solvers for sparse matrices, the calculation time was reduced by more than 1 order of magnitude compared to the standard Gaussian method, while the amount of required RAM was halved. Ni K-edge XANES simulations performed by the accelerated version of the code allowed analyzing the coordination geometry of CO and NO on the Ni active sites in CPO-27-Ni MOF. The Ni-CO configuration was found to be linear, while Ni-NO was bent by almost 90°. Modeling of the Fe K-edge XANES of photoexcited aqueous [Fe(bpy)3](2+) with a 100 ps delay we identified the Fe-N distance elongation and bipyridine rotation upon transition from the initial low-spin to the final high-spin state. Subsequently, the X-ray absorption spectrum for the intermediate triplet state with expected 100 fs lifetime was theoretically predicted.

Salamander abundance along road edges and within abandoned logging roads in Appalachian forests.

PubMed

Semlitsch, Raymond D; Ryan, Travis J; Hamed, Kevin; Chatfield, Matt; Drehman, Bethany; Pekarek, Nicole; Spath, Mike; Watland, Angie

2007-02-01

Roads may be one of the most common disturbances in otherwise continuous forested habitat in the southern Appalachian Mountains. Despite their obvious presence on the landscape, there is limited data on the ecological effects along a road edge or the size of the "road-effect zone." We sampled salamanders at current and abandoned road sites within the Nantahala National Forest, North Carolina (U.S.A.) to determine the road-effect zone for an assemblage of woodland salamanders. Salamander abundance near the road was reduced significantly, and salamanders along the edges were predominantly large individuals. These results indicate that the road-effect zone for these salamanders extended 35 m on either side of the relatively narrow, low-use forest roads along which we sampled. Furthermore, salamander abundance was significantly lower on old, abandoned logging roads compared with the adjacent upslope sites. These results indicate that forest roads and abandoned logging roads have negative effects on forest-dependent species such as plethodontid salamanders. Our results may apply to other protected forests in the southern Appalachians and may exemplify a problem created by current and past land use activities in all forested regions, especially those related to road building for natural-resource extraction. Our results show that the effect of roads reached well beyond their boundary and that abandonment or the decommissioning of roads did not reverse detrimental ecological effects; rather, our results indicate that management decisions have significant repercussions for generations to come. Furthermore, the quantity of suitable forested habitat in the protected areas we studied was significantly reduced: between 28.6% and 36.9% of the area was affected by roads. Management and policy decisions must use current and historical data on land use to understand cumulative impacts on forest-dependent species and to fully protect biodiversity on national lands.

Microstructural investigations of the trimmed edge of DP980 steel sheets

NASA Astrophysics Data System (ADS)

Bhattacharya, S.; Green, D. E.; Sohmshetty, R.; Alpas, A. T.

2017-10-01

In order to reduce vehicle weight while maintaining crashworthiness, advanced high strength steels (AHSSs), such as DP980, are extensively used for manufacturing automotive body components. During trimming operations, the high tensile strength of DP980 sheets tends to cause damage of the trim edge of D2 die inserts, which result in deterioration of the edge quality. The objective of this work is to study the damage microstructures at the trimmed edge of DP980 steel sheets as a function of the number of trimming cycles. A mechanical press equipped with AISI D2 tool steel inserts was used to continuously trim 1.4 mm thick sheets of DP980 at a rate of 30 strokes/min. Cross-sectional SEM images of the trimmed edges revealed that the sheared edge quality of the DP980 sheets decreased, indicated by an increase in the burr width, with an increase in the number of trims from 40,000 to 70,000. Plastic strains were estimated using the displacements of the martensite plates within plastic flow fields of ferrite. Site-specific cross-sectional TEM samples, excised from the trimmed edge using the in-situ `lift-out' technique by focused ion-beam (FIB)-milling, revealed cracking at the ferrite/martensite interfaces after 70,000 cycles indicating an increase in the depth of deformation zone possibly due to trimming with a chipped and blunted die edge.

Effects of rare-earth size on the electronic structure of La1−xLuxVO3.

PubMed

Chen, B; Laverock, J; Newby, D; McNulty, J F; Smith, K E; Glans, P-A; Guo, J-H; Qiao, R-M; Yang, W-L; Lees, M R; Tung, L D; Singh, R P; Balakrishnan, G

2015-03-18

The electronic structure of La(1-x)Lu(x)VO(3)(x = 0, 0.2, 0.6 and 1) single crystals has been investigated using soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy, and resonant soft x-ray inelastic scattering to study the effects of rare-earth size. The x-ray absorption and emission spectra at the O K-edge present a progressive evolution with R-site cation, in agreement with local spin density approximation calculations. This evolution with R, together with the temperature dependence of the O K-edge spectra, is attributed to changes in the crystal structure of La(1-x)Lu(x)VO(3). The crystal-field dd. excitations probed by resonant inelastic x-ray scattering at the V L(3)-edge exhibit an increase in energy and enhanced intensity with the decrease of R-site ionic radius, which is mainly attributed to the increased tilting magnitude of the VO(6) octahedra. Upon cooling to ~95 K, the dd* excitations are prominently enhanced in relative Intensity, in agreement with the formation of the Jahn.Teller distortion int he orbital ordering phase. Additionally, the dd* transitions of the mixed compounds are noticeably suppressed with respect to those of the pure compounds, possibly owing to the formation of C-type orbital ordering induced by large R-site size variances.

Topological Edge Modes in Active Mikado Networks

NASA Astrophysics Data System (ADS)

Zhou, Di; Zhang, Leyou; Mao, Xiaoming

Mechanical properties of disordered fiber networks are not only important in understanding a broad range of natural (such as the cytoskeleton and the extracellular matrix) and manmade materials (such as aerogels and porous media) but also exhibit interesting and rich physics. In this talk, we discuss how topological floppy edge modes can emerge from these fiber networks as a result of active driving. It is known that straight fibers in a network carries a state of self-stress and bears a bulk floppy mode. We find that, interestingly, by driving the network with a tiny perturbation, the bulk modes evolve into edge modes. We introduce a new transfer matrix formulation that can be applied to this strongly disordered system, to characterize the topological edge modes. We also discuss possible implications of these edge modes in biological processes. NSF-DMR-1609051.

Naegleria fowleri: contact-dependent secretion of electrondense granules (EDG).

PubMed

Chávez-Munguía, Bibiana; Villatoro, Lizbeth Salazar; Omaña-Molina, Maritza; Rodríguez-Monroy, Marco Aurelio; Segovia-Gamboa, Norma; Martínez-Palomo, Adolfo

2014-07-01

The free living amoeba Naegleria fowleri is pathogenic to humans but also to other mammalians. These amoebae may invade the nasal mucosa and migrate into the brain causing cerebral hemorrhagic necrosis, a rapidly fatal infection. Knowledge of the cytolytic mechanism involved in the destruction of brain tissues by Naegleria trophozoites is limited. In other amoebic species, such as Entamoeba histolytica, we have previously reported the possible lytic role of small cytoplasmic components endowed with proteolytic activities, known as electrondense granules (EDG). Using transmission electron microscopy we now report that EDG, seldom found in long term cultured N. fowleri, are present in abundance in trophozoites recovered from experimental mice brain lesions. Numerous EDG were also observed in amoebae incubated with collagen substrates or cultured epithelial cells. SDS-PAGE assays of concentrated supernatants of these trophozoites, containing EDG, revealed proteolytic activities. These results suggest that EDG may have a clear role in the cytopathic mechanisms of this pathogenic amoeba. Copyright © 2014 Elsevier Inc. All rights reserved.

Molybdenum X-Ray Absorption Edges from 200 – 20,000 eV, The Benefits of Soft X-Ray Spectroscopy for Chemical Speciation

PubMed Central

George, Simon J.; Drury, Owen B.; Fu, Juxia; Friedrich, Stephan; Doonan, Christian J.; George, Graham N.; White, Jonathan M.; Young, Charles G.; Cramer, Stephen P.

2009-01-01

We have surveyed the chemical utility of the near-edge structure of molybdenum x-ray absorption edges from the hard x-ray K-edge at 20,000 eV down to the soft x-ray M4,5-edges at ~230 eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO4 and MoS42-. We used three criteria for assessing near-edge structure of each edge: (i) the ratio of the observed chemical shift between MoO42- and MoS42- and the linewidth, (ii) the chemical information from analysis of the near-edge structure and (iii) the ease of measurement using fluorescence detection. Not surprisingly, the K-edge was by far the easiest to measure, but it contained the least information. The L2,3-edges, although harder to measure, had benefits with regard to selection rules and chemical speciation in that they had both a greater chemical shift as well as detailed lineshapes which could be theoretically analyzed in terms of Mo ligand field, symmetry, and covalency. The soft x-ray M2,3-edges were perhaps the least useful, in that they were difficult to measure using fluorescence detection and had very similar information content to the corresponding L2,3-edges. Interestingly, the soft x-ray, low energy (~230 eV) M4,5-edges had greatest potential chemical sensitivity and using our high resolution superconducting tunnel junction (STJ) fluorescence detector they appear to be straightforward to measure. The spectra were amenable to analysis using both the TT-multiplet approach and FEFF. The results using FEFF indicate that the sharp near-edge peaks arise from 3d → 5p transitions, while the broad edge structure has predominately 3d → 4f character. A proper understanding of the dependence of these soft x-ray spectra on ligand field and site geometry is necessary before a complete assessment of the utility of the Mo M4,5-edges can be made. This work includes crystallographic characterization of sodium tetrathiomolybdate. PMID:19041140

Magnetism of Nanographene-Based Microporous Carbon and Its Applications: Interplay of Edge Geometry and Chemistry Details in the Edge State

NASA Astrophysics Data System (ADS)

Enoki, Toshiaki; Kiguchi, Manabu

2018-03-01

This paper is a contribution to the Physical Review Applied collection in memory of Mildred S. Dresselhaus. Nanographenes have important edge geometry dependence in their electronic structures. In armchair edges, electron wave interference works to contribute to energetic stability. Meanwhile, zigzag edges possess an edge-localized and spin-polarized nonbonding edge state, which causes electronic, magnetic, and chemical activities. In addition to the geometry dependence, the electronic structures are seriously affected by edge chemistry details. The edge chemistry dependence together with edge geometries on the electronic structures are discussed with samples of randomly networked nanographenes (microporous activated carbon fibers) in pristine state and under high-temperature annealing. In the pristine sample with the edges oxidized in ambient atmospheric conditions, the edge state, which is otherwise unstable, can be stabilized because of the charge transfer from nanographene to terminating oxygen. Nanographene, whose edges consist of a combination of magnetic zigzag edges and nonmagnetic armchair edges, is found to be ferrimagnetic with a nonzero net magnetic moment created under the interplay between a strong intrazigzag-edge ferromagnetic interaction and intermediate-strength interzigzag-edge antiferromagnetic-ferromagnetic interaction. At heat-treatment temperatures just below the fusion start (approximately 1500 K), the edge-terminating structure is changed from oxygen-containing groups to hydrogen in the nanographene network. Additionally, hydrogen-terminated zigzag edges, which are present as the majority and chemically unstable, play a triggering role in fusion above 1500 K. The fusion start brings about an insulator-to-metal transition at TI -M˜1500 K . Local fusions taking place percolatively between nanographenes work to expand the π -bond network, eventually resulting in the development of antiferromagnetic short-range order toward spin glass in the magnetic moments of nanographenes. For applications, the edge-state spins in nanographene-based microporous carbon can be a good tool as a molecule sensor in detecting molecules having different chemical properties and sizes. The on-off magnetic switching phenomena upon the adsorption of H2O and other OH-containing molecules offers a molecule sensor. A He sensor, in which the edge-state spins is employed as a probe, is also proposed on the basis of a huge condensation of He into ultramicropores.

Project X: competitive intelligence data mining and analysis

NASA Astrophysics Data System (ADS)

Gilmore, John F.; Pagels, Michael A.; Palk, Justin

2001-03-01

Competitive Intelligence (CI) is a systematic and ethical program for gathering and analyzing information about your competitors' activities and general business trends to further your own company's goals. CI allows companies to gather extensive information on their competitors and to analyze what the competition is doing in order to maintain or gain a competitive edge. In commercial business this potentially translates into millions of dollars in annual savings or losses. The Internet provides an overwhelming portal of information for CI analysis. The problem is how a company can automate the translation of voluminous information into valuable and actionable knowledge. This paper describes Project X, an agent-based data mining system specifically developed for extracting and analyzing competitive information from the Internet. Project X gathers CI information from a variety of sources including online newspapers, corporate websites, industry sector reporting sites, speech archiving sites, video news casts, stock news sites, weather sites, and rumor sites. It uses individual industry specific (e.g., pharmaceutical, financial, aerospace, etc.) commercial sector ontologies to form the knowledge filtering and discovery structures/content required to filter and identify valuable competitive knowledge. Project X is described in detail and an example competitive intelligence case is shown demonstrating the system's performance and utility for business intelligence.

Tracking metal ions through a Cu/Ag efflux pump assigns the functional roles of the periplasmic proteins

DOE PAGES

Chacon, Kelly N.; Mealman, Tiffany D.; McEvoy, Megan M.; ...

2014-10-13

Copper is an essential nutrient for all aerobic organisms but is toxic in excess. At the host–pathogen interface, macrophages respond to bacterial infection by copper-dependent killing mechanisms, whereas the invading bacteria are thought to counter with an up-regulation of copper transporters and efflux pumps. The tripartite efflux pump CusCBA and its metallochaperone CusF are vital to the detoxification of copper and silver ions in the periplasm of Escherichia coli. However, the mechanism of efflux by this complex, which requires the activation of the inner membrane pump CusA, is poorly understood. In this paper, we use selenomethionine (SeM) active site labelsmore » in a series of biological X-ray absorption studies at the selenium, copper, and silver edges to establish a “switch” role for the membrane fusion protein CusB. We determine that metal-bound CusB is required for activation of cuprous ion transfer from CusF directly to a site in the CusA antiporter, showing for the first time (to our knowledge) the in vitro activation of the Cus efflux pump. This metal-binding site of CusA is unlike that observed in the crystal structures of the CusA protein and is composed of one oxygen and two sulfur ligands. Finally, our results suggest that metal transfer occurs between CusF and apo-CusB, and that, when metal-loaded, CusB plays a role in the regulation of metal ion transfer from CusF to CusA in the periplasm.« less

Tracking metal ions through a Cu/Ag efflux pump assigns the functional roles of the periplasmic proteins.

PubMed

Chacón, Kelly N; Mealman, Tiffany D; McEvoy, Megan M; Blackburn, Ninian J

2014-10-28

Copper is an essential nutrient for all aerobic organisms but is toxic in excess. At the host-pathogen interface, macrophages respond to bacterial infection by copper-dependent killing mechanisms, whereas the invading bacteria are thought to counter with an up-regulation of copper transporters and efflux pumps. The tripartite efflux pump CusCBA and its metallochaperone CusF are vital to the detoxification of copper and silver ions in the periplasm of Escherichia coli. However, the mechanism of efflux by this complex, which requires the activation of the inner membrane pump CusA, is poorly understood. Here, we use selenomethionine (SeM) active site labels in a series of biological X-ray absorption studies at the selenium, copper, and silver edges to establish a "switch" role for the membrane fusion protein CusB. We determine that metal-bound CusB is required for activation of cuprous ion transfer from CusF directly to a site in the CusA antiporter, showing for the first time (to our knowledge) the in vitro activation of the Cus efflux pump. This metal-binding site of CusA is unlike that observed in the crystal structures of the CusA protein and is composed of one oxygen and two sulfur ligands. Our results suggest that metal transfer occurs between CusF and apo-CusB, and that, when metal-loaded, CusB plays a role in the regulation of metal ion transfer from CusF to CusA in the periplasm.

FA(I):A(+) and FA(II):Cu(+) laser activity and photographic sensitization at the low coordinated surfaces of AgBr ab initio calculations.

PubMed

Shalabi, A S

2002-08-01

The twofold potentials of F(A)(I):Au(+) and F(A)(II)Cu(+) color centers at the low coordinated surfaces of AgBr thin films in providing tunable laser activity and photographic sensitization were investigated using ab initio methods of molecular electronic structure calculations. Clusters of variable size were embedded in simulated Coulomb fields that closely approximated the Madelung fields of the host surfaces, and the nearest neighbor ions to the F(A) defect site were allowed to relax to equilibrium in each case. Based on the calculated Stokes shifted optical transition bands and horizontal shifts along the configuration coordinate diagrams, both F(A)(I):Au(+) and F(A)(II):Cu(+) color centers were found to be laser active. The laser activity faded quickly as the bromide ion coordination decreased from 5 (flat) to 4 (edge) to 3 (corner) and as the size of the impurity cation increased from Cu(+) to Au(+). The latter relation was explainable in terms of the axial perturbation of the impurity cation. The smallest calculated Stokes-shift at the corner surface suggested that emission had the same oscillator strength as absorption. All relaxed excited states RESs of the defect containing surfaces were deep below the lower edges of the conduction bands of the defect free ground state surfaces, indicating that F(A)(I):Au(+) and F(A)(II):Cu(+) are suitable laser defects. The probability of orientational destruction of the two centers attributed to the assumed RES saddle point ion configurations along the <110> axis was found to be directly proportional to the size of the impurity cation, with activation energy barriers of about 0.655-3.294 eV for Cu(+), and about 1.887-3.404 eV for Au(+). The possibility of exciton (energy) transfer from the sites of higher coordination to those of lower coordination is demonstrated. The more laser active F(A)(II):Cu(+) center was more easily formed than the less laser active F(A)(I):Au(+) center. The Glasner-Tompkins empirical relation was generalized to include F(A) centers at the low coordinated surfaces of silver bromide thin film. As far as color photographic sensitization is concerned, the lowest unoccupied molecular orbitals of the selected dye molecules in the excited states were high enough for electron injection. F(A) defect formation and rotational diffusion of silver clusters reduced the energy gaps between the excited dye molecules and the lower edges of the conduction bands and allowed for hole injection. About 54-60% of the reduction of silver ions at the flat surface of AgBr was attributed to the host anions and F(A) defect formation, leaving about 40-46% for the reduction of photoelectrons as well as the electrons of the developer or dye molecules. The unrelaxed rotational diffusions of the central Ag(4) by 90 degrees decreased the latter percentage, but were severely hindered by activation energy barriers. Copyright 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1104-1120, 2002

Radiation Dosimetry from Intratumoral Injection of Radionuclides in Human Breast Cancer

DTIC Science & Technology

2006-07-01

receive estimated doses of 463cGy in the injection site, with a 10% isodose range of 0.02cm from the injection site edge. Based...predicted before, the radiation absorbed doses to the sentinel lymph nodes will be about one Page 12 of 66 tenth of those to the injection sites in ... on preclinical studies suggesting a total of 2% leakage of radiogallium in the form of free Ga(+3),

Spectroscopic, Computational and Kinetic Studies of the μ4-Sulfide Bridged Tetranuclear CuZ Cluster in N2O Reductase: pH Effect on the Edge Ligand and its Contribution to Reactivity

PubMed Central

Ghosh, Somdatta; Gorelsky, Serge I.; George, Serena DeBeer; Chan, Jeannine M.; Cabrito, Inês; Dooley, David M.; Moura, José J. G.; Moura, Isabel; Solomon, Edward I.

2008-01-01

A combination of spectroscopy and DFT calculations has been used to evaluate the pH effect at the CuZ site in Pseudomonas nautica (Pn) N2OR and Achromobacter cycloclastes (Ac) N2OR and its relevance to catalysis. Absorption, MCD, EPR with sulfur K-edge XAS spectra of the enzymes at high and low pH show minor changes. However, resonance Raman (rR) spectroscopy of PnN2OR at high pH shows that the 415 cm−1 Cu-S vibration (observed at low pH) shifts to higher frequency, loses intensity and obtains a 9 cm−1 18O shift, implying significant Cu-O character, demonstrating the presence of a OH− ligand at the CuICuIV edge. From DFT calculations both protonation of the OH− to H2O or the μ4-S2− to μ4-SH− would produce large spectral changes which are not observed. Alternatively, DFT calculations including a lysine residue at an H-bonding distance from the CuICuIV edge ligand show that the position of the OH− ligand depends on the protonation state of the lysine. This would change the coupling of the Cu-(OH) stretch with the Cu-S stretch, as observed in the rR spectrum. Thus the observed pH effect (pKa ~9.2) likely reflects protonation equilibrium of the lysine residue which would both raise E0 and provide a proton for lowering the barrier for the N-O cleavage and for reduction of the [Cu4S(im)7OH]2+ to the fully reduced 4CuI active form for turnover. PMID:17352474

Development and demonstration of a flutter-suppression system using active controls. [wind tunnel tests

NASA Technical Reports Server (NTRS)

Sandford, M. C.; Abel, I.; Gray, D. L.

1975-01-01

The application of active control technology to suppress flutter was demonstrated successfully in the transonic dynamics tunnel with a delta-wing model. The model was a simplified version of a proposed supersonic transport wing design. An active flutter suppression method based on an aerodynamic energy criterion was verified by using three different control laws. The first two control laws utilized both leading-edge and trailing-edge active control surfaces, whereas the third control law required only a single trailing-edge active control surface. At a Mach number of 0.9 the experimental results demonstrated increases in the flutter dynamic pressure from 12.5 percent to 30 percent with active controls. Analytical methods were developed to predict both open-loop and closed-loop stability, and the results agreed reasonably well with the experimental results.

Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

NASA Astrophysics Data System (ADS)

Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

2013-04-01

Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding defects in TM nano-grain oxides are qualitatively similar to vacant-site defects in non-crystalline SiO2 and GeO2 for ulta-thin films, < 0.2 nm thick, and yield similar performance in MOSCAPs on Ge substrates heralding applications in aggressively-scale CMOS devices.

Spectroscopic and DFT Studies of Second Sphere Variants of the Type 1 Copper Site in Azurin: Covalent and Non-Local Electrostatic Contributions to Reduction Potentials

PubMed Central

Hadt, Ryan G.; Sun, Ning; Marshall, Nicholas M.; Hodgson, Keith O.; Hedman, Britt; Lu, Yi; Solomon, Edward I.

2012-01-01

The reduction potentials (E0) of type 1 (T1) or blue copper (BC) sites in proteins and enzymes with identical first coordination spheres around the redox active copper ion can vary by ~400 mV. Here, we use a combination of low temperature electronic absorption and magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and S K-edge X-ray absorption spectroscopies to investigate a series of second sphere variants—F114P, N47S, and F114N in Pseudomonas aeruginosa azurin (Az)—which modulate hydrogen bonding to and protein derived dipoles nearby the Cu-S(Cys) bond. Density functional theory (DFT) calculations correlated to the experimental data allow for the fractionation of the contributions to tuning E0 into covalent and non-local electrostatic components. These are found to be significant, comparable in magnitude, and additive for active H-bonds, while passive H-bonds are mostly non-local electrostatic in nature. For dipoles, these terms can be additive to or oppose one another. This study provides a methodology for uncoupling covalency from non-local electrostatics, which, when coupled to X-ray crystallographic data, distinguishes specific local interactions from more long range protein/active interactions, while affording further insight into the second sphere mechanisms available to the protein to tune the E0 of electron transfer sites in biology. PMID:22985400

Challenges in initiating and conducting personalized cancer therapy trials: perspectives from WINTHER, a Worldwide Innovative Network (WIN) Consortium trial

PubMed Central

Rodon, J.; Soria, J. C.; Berger, R.; Batist, G.; Tsimberidou, A.; Bresson, C.; Lee, J. J.; Rubin, E.; Onn, A.; Schilsky, R. L.; Miller, W. H.; Eggermont, A. M.; Mendelsohn, J.; Lazar, V.; Kurzrock, R.

2015-01-01

Advances in ‘omics’ technology and targeted therapeutic molecules are together driving the incorporation of molecular-based diagnostics into the care of patients with cancer. There is an urgent need to assess the efficacy of therapy determined by molecular matching of patients with particular targeted therapies. WINTHER is a clinical trial that uses cutting edge genomic and transcriptomic assays to guide treatment decisions. Through the lens of this ambitious multinational trial (five countries, six sites) coordinated by the Worldwide Innovative Networking Consortium for personalized cancer therapy, we discovered key challenges in initiation and conduct of a prospective, omically driven study. To date, the time from study concept to activation has varied between 19 months at Gustave Roussy Cancer Campus in France to 30 months at the Segal Cancer Center, McGill University (Canada). It took 3+ years to be able to activate US sites due to national regulatory hurdles. Access to medications proposed by the molecular analysis remains a major challenge, since their availability through active clinical trials is highly variable over time within sites and across the network. Rules regarding the off-label use of drugs, or drugs not yet approved at all in some countries, pose a further challenge, and many biopharmaceutical companies lack a simple internal mechanism to supply the drugs even if they wish to do so. These various obstacles should be addressed to test and then implement precision medicine in cancer. PMID:25908602

Emission properties of Ce-doped alkaline earth borate glasses for scintillator applications

NASA Astrophysics Data System (ADS)

Torimoto, Aya; Masai, Hirokazu; Okada, Go; Kawaguchi, Noriaki; Yanagida, Takayuki

2017-11-01

We investigate the photoluminescence (PL) and X-ray-induced luminescence properties of 0.1 mol% Ce-doped MO-B2O3 (M = Ca, Sr, and Ba) glasses. We also determine the Ce3+/(Ce3++Ce4+) ratio by X-ray absorption near-edge structure analyses. The emission intensities of PL, X-ray scintillation, and thermally stimulated luminescence (TSL) depend on the host glass composition. The order of the PL intensity from highest to lowest is as follows: Ca-substituted glass, Ba-substituted glass, and Sr-substituted glass. Our results suggest that the optical absorption edge and quantum yield (QY) are influenced by the local coordination state of Ce3+, which, in turn, is likely to be affected by the optical basicity. The order of the X-ray scintillation intensity from highest to lowest is reverse of that of the PL intensity. This is probably because the interaction probability of X-rays with matter depends on the effective atomic number of the material and the effective atomic number has a stronger influence on the scintillation intensity than does the QY. Though the TSL glow curves reveal that the density and energy depth of the trap sites depend on the substituted alkaline earth oxides, we are unable to correlate the electron spin resonance (ESR) spectra with the TSL results. Therefore, it is considered that the ESR active sites are not responsible for the TSL in these systems.

The role of shock induced trailing-edge separation in limit cycle oscillations

NASA Technical Reports Server (NTRS)

Cunningham, Atlee M., Jr.

1989-01-01

The potential role of shock induced trailing edge separation (SITES) in limit cycle oscillations (LCO) was established. It was shown that the flip-flop characteristics of transition to and from SITES as well as its hysteresis could couple with wing modes with torsional motion and low damping. This connection led to the formulation of a very simple nonlinear math model using the linear equations of motion with a nonlinear step forcing function with hysteresis. A finite difference solution with time was developed and calculations were made for the F-111 TACT were used to determine the step forcing function due to SITES transition. Since no data were available for the hysteresis, a parameter study was conducted allowing the hysteresis effect to vary. Very small hysteresis effects, which were within expected bounds, were required to obtain reasonable response levels that essentially agreed with flight test results. Also in agreement with wind tunnel tests, LCO calculations for the 1/6 scale F-111 model showed that the model should have not experienced LCO.

Forest edges: Effects on vegetation, environmental gradients and local avian communities in the Sierra Juarez, Oaxaca, Mexico

NASA Astrophysics Data System (ADS)

Burcsu, Theresa Katherine

Edge effects are among the most serious threats to forest integrity because as global forest cover decreases overall, forest edge influence increases proportionally, driving habitat change and loss. Edge effects occur at the division between adjacent habitat types. Our understanding of edge effects comes mainly from tropical wet, temperate and boreal forests. Because forest structure in moisture-limited forests differs from wetter forest types, edge dynamics are likely to differ as well. Moreover, dry forests in the tropics have been nearly eliminated or exist only as forest fragments, making edge influence an important conservation and management concern for remaining dry forests. This study addresses this gap in the edge influence knowledge by examining created, regenerating edges associated with forest management in a seasonally dry pine-oak forest of Oaxaca, creating a new data point in edge effects research. In this study I used Landsat TM imagery and a modified semivariance analysis to estimate the distance of edge influence for vegetation. I also used field methods to characterize forest structure and estimate edge influence on canopy and subcanopy vegetation. To finalize the project I extended the study to bird assemblages to identify responses and habitat preferences to local-scale changes associated with regenerating edges created by group-selection timber harvest. Remote sensing analysis estimated that the distance of edge influence was 30-90 m from the edge. Vegetation analysis suggested that edge effects were weak relative to wetter forest types and that remote sensing data did not provide an estimate that was directly applicable to field-measured vegetative edge effects. The bird assemblages likewise responded weakly to habitat change associated with edge effect. Open canopy structure, simple vertical stratigraphy, and topographic variation create forest conditions in which small openings do not create a high contrast to undisturbed forest. Thus, in this seasonally dry, open forest, vegetation and bird communities respond less to small openings than they do in wetter, more closed-canopy forests. Management practices and historical land-use interact and interfere with the detectability of edge influence in our study area. These results support hypotheses proposed for open forest types and suggest that patterns in edge influence in wet forest types may not be applicable to dry sites.

Edge and area effects on the occurrence of migrant forest songbirds

USGS Publications Warehouse

Parker, T.H.; Stansberry, B.M.; Becker, C.D.; Gipson, P.S.

2005-01-01

Concerns about forest fragmentation and its conservation implications have motivated numerous studies that investigate the influence of forest patch area and forest edge on songbird distribution patterns. The generalized effects of forest patch size and forest edge on animal distributions is still debatable because forest patch size and forest edge are often confounded and because of an incomplete synthesis of available data. To fill a portion of this gap, we incorporated all available published data (33 papers) in meta-analyses of forest edge and area effects on site occupancy patterns for 26 Neotropical migrant forest-nesting songbirds in eastern North America. All reported area effects are confounded or potentially confounded by edge effects, and we refer to these as "confounded" studies. The converse, however, is not true and most reported edge effects are independent of patch area. When considering only nonconfounded studies of edge effects, only 1 of 17 species showed significant edge avoidance and 3 had significant affinity for edges. In confounded studies, 12 of 22 species showed significant avoidance of small patches and edges, and 1 had an affinity for small patches and edges. Furthermore, average effect sizes averaged across studies or species tended to be higher for confounded studies than for edge studies. We discuss three possible reasons for differences in results between these two groups of studies. First, studies of edge effects tended to be carried out in landscapes with greater forest cover than studies of confounded effects; among confounded effects studies, as forest cover increased, we observed a nonsignificant trend towards decreasing strength of small patch or edge avoidance effects. Thus, the weaker effects in edge studies may be due to the fact that these studies were conducted in forest-dominated landscapes. Second, we may have detected strong effects only in confounded studies because area effects are much stronger than edge effects on bird occurrence, and area effects drive the results in confounded studies. Third, edge and area effects may interact in such a way that edge effects become more important as forest patch size decreases; thus, both edge and area effects are responsible for results in confounded studies. These three explanations cannot be adequately separated with existing data. Regardless, it is clear that fragmentation of forests into small patches is detrimental to many migrant songbird species. ??2005 Society for Conservation Biology.

Populus tremuloides mortality near the southwestern edge of its range

Treesearch

Thomas J. Zegler; Margaret M. Moore; Mary L. Fairweather; Kathryn B. Ireland; Peter Z. Fule

2012-01-01

Mortality and crown dieback of quaking aspen (Populus tremuloides) were extensive on the Williams Ranger District, Kaibab National Forest in northern Arizona. We collected data from a random sample of 48 aspen sites to determine the relationship of predisposing site and stand factors and contributing agents to ramet mortality. Mortality of overstory (P10.1 cm DBH)...

1. VIEW, LOOKING NORTHEAST, SHOWING THE SITE OF THE EMPIRE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. VIEW, LOOKING NORTHEAST, SHOWING THE SITE OF THE EMPIRE MILL. THE ADIT IS AT TOP, ABOVE THE TERRACES FOR THE CRUSHER AND 5-STAMP MILL. REMAINS OF THE BOILER HOUSING ARE ON THE LOWER TERRACE, AT RIGHT, WITH ENGINE MOUNT TO LEFT - Empire Mill, Southern Edge of Salt Spring Valley, Copperopolis, Calaveras County, CA

Multi-site evaluation of APEX for crop and grazing land in the Heartland region of the US

USDA-ARS?s Scientific Manuscript database

The Agricultural and Policy Environmental Extender (APEX) is powerful and useful to estimate the edge-of-field impacts of management practices. A drawback is that it needs to be calibrated for each site, which requires resources and data. The objective of this study was to compare annual model perfo...

Oxygen and sulfur adsorption on vicinal surfaces of copper and silver: Preferred adsorption sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Da-Jiang; Thiel, Patricia A.

We present an extensive density functional theory (DFT) study of adsorption site energetics for oxygen and sulfur adsorbed on two vicinal surfaces of Cu and Ag, with the goal of identifying the most stable adsorption site(s), identifying trends and common themes, and comparing with experimental work in the literature where possible. We also present benchmark calculations for adsorption on the flat (111) and (100) surfaces. The first vicinal surface is the (211), and results are similar for both metals. Here, we find that the step-doubling reconstruction is favored with both adsorbates and is driven by the creation of a specialmore » stable fourfold hollow (4fh) site at the reconstructed step. Zig-zag chain structures consisting of X–M–X units (X = chalcogen, M = metal) at the step edge are considered, in which the special 4fh site is partially occupied. The zig-zag configuration is energetically competitive for oxygen but not sulfur. DFT results for oxygen agree with experiment in terms of the stability of the reconstruction, but contradict the original site assignment. The second vicinal surface is the (410), where again results are similar for both metals. For oxygen, DFT predicts that step sites are filled preferentially even at lowest coverage, followed by terrace sites, consistent with the experiment. For sulfur, in contrast, DFT predicts that terrace sites fill first. Oxygen forms O–M–O rows on the top edge of the step, where it occupies incomplete 4fh sites. This resolves an experimental ambiguity in the site assignment. Finally, for both the (211) and (410) surfaces, the interaction energy that stabilizes the X–M–X chain or row correlates with the linearity of the X–M–X unit, which may explain key differences between oxygen and sulfur.« less

Oxygen and sulfur adsorption on vicinal surfaces of copper and silver: Preferred adsorption sites

DOE PAGES

Liu, Da-Jiang; Thiel, Patricia A.

2018-03-28

We present an extensive density functional theory (DFT) study of adsorption site energetics for oxygen and sulfur adsorbed on two vicinal surfaces of Cu and Ag, with the goal of identifying the most stable adsorption site(s), identifying trends and common themes, and comparing with experimental work in the literature where possible. We also present benchmark calculations for adsorption on the flat (111) and (100) surfaces. The first vicinal surface is the (211), and results are similar for both metals. Here, we find that the step-doubling reconstruction is favored with both adsorbates and is driven by the creation of a specialmore » stable fourfold hollow (4fh) site at the reconstructed step. Zig-zag chain structures consisting of X–M–X units (X = chalcogen, M = metal) at the step edge are considered, in which the special 4fh site is partially occupied. The zig-zag configuration is energetically competitive for oxygen but not sulfur. DFT results for oxygen agree with experiment in terms of the stability of the reconstruction, but contradict the original site assignment. The second vicinal surface is the (410), where again results are similar for both metals. For oxygen, DFT predicts that step sites are filled preferentially even at lowest coverage, followed by terrace sites, consistent with the experiment. For sulfur, in contrast, DFT predicts that terrace sites fill first. Oxygen forms O–M–O rows on the top edge of the step, where it occupies incomplete 4fh sites. This resolves an experimental ambiguity in the site assignment. Finally, for both the (211) and (410) surfaces, the interaction energy that stabilizes the X–M–X chain or row correlates with the linearity of the X–M–X unit, which may explain key differences between oxygen and sulfur.« less

Mach-Zehnder interferometry using broken symmetry quantum Hall edges in graphene

NASA Astrophysics Data System (ADS)

Wei, Di; van der Sar, Toeno; Sanchez-Yamagishi, Javier; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo; Halperin, Bertrand; Yacoby, Amir

Graphene has emerged as a unique platform for studying electron optics, particularly in the presence of a magnetic field. Here, we engineer a Mach-Zehnder interferometer using quantum Hall edge states that co-propagate along a single gate-defined NP interface. We use encapsulated monolayer graphene, clean enough to lift the four-fold spin and valley degeneracy. In order to create two separate co-propagating paths, we exploit the suppression of edge state scattering along gate defined edges, and use scattering sites at the ends of the NP interface to form our beam splitters. We observe conductance oscillations as a function of magnetic and electric field indicative of coherent transport, and measure values consistent with spin-selective scattering. We can tune our interferometer to regimes of high visibility (>98 %), surpassing the values reported for GaAs quantum-well Mach-Zehnder interferometers. These results demonstrate a promising method to observe interference between fractional charges in graphene.

XANES and EXAFS study of Au-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1990-01-01

The near-edge structure (XANES) of the Au L3 and Cu K edges of YBa2Au(0.3)Cu(2.7)O(7-delta) was studied. X ray diffraction suggests that Au goes on the Cu(1) site and XANES shows that this has little effect on the oxidation state of the remaining copper. The gold L3 edge develops a white line feature whose position lies between that of trivalent gold oxide (Au2O3) and monovalent potassium gold cyanide (KAu(CN)2) and whose intensity relative to the edge step is smaller than in the two reference compounds. The L3 EXAFS for Au in the superconductor resembles that of Au2O3. However, differences in the envelope of the Fourier filtered component for the first shell suggest that the local structure of the Au in the superconductor is not equivalent to Au2O3.

Spatially Resolved Quantification of the Surface Reactivity of Solid Catalysts.

PubMed

Huang, Bing; Xiao, Li; Lu, Juntao; Zhuang, Lin

2016-05-17

A new property is reported that accurately quantifies and spatially describes the chemical reactivity of solid surfaces. The core idea is to create a reactivity weight function peaking at the Fermi level, thereby determining a weighted summation of the density of states of a solid surface. When such a weight function is defined as the derivative of the Fermi-Dirac distribution function at a certain non-zero temperature, the resulting property is the finite-temperature chemical softness, termed Fermi softness (SF ), which turns out to be an accurate descriptor of the surface reactivity. The spatial image of SF maps the reactive domain of a heterogeneous surface and even portrays morphological details of the reactive sites. SF analyses reveal that the reactive zones on a Pt3 Y(111) surface are the platinum sites rather than the seemingly active yttrium sites, and the reactivity of the S-dimer edge of MoS2 is spatially anisotropic. Our finding is of fundamental and technological significance to heterogeneous catalysis and industrial processes demanding rational design of solid catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interplay between climatic and tectonic processes in the St. Elias foreland, southern Alaska: Evolution of a glaciated convergent margin since the mid-Pleistocene

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Gulick, S. P.; Ridgway, K. R.; Jaeger, J. M.; Cowan, E. A.; Slagle, A. L.; Forwick, M.

2013-12-01

The offshore St. Elias fold-thrust belt records the complex interaction between collisional tectonics and glacial climate variability, providing insight for models of orogenesis and the evolution of glacial depocenters. Ongoing collision of the Yakutat (YAK) microplate with North America (NA) has driven orogenesis of the St. Elias Mountains and the advance of the offshore deformation front to the southeast. Glacial erosion and deposition have provided sediment that constructed the upper continental shelf, much of which has been reincorporated into the orogenic wedge through offshore faulting and folding. We integrate core and downhole logging data from IODP Expedition 341 (Sites U1420 and U1421) drilled on the Yakutat shelf and slope with high-resolution and regional seismic profiles to investigate the coupled structural and stratigraphic evolution of the St. Elias margin. Site U1420 lies on the Yakutat shelf within the Bering Trough, a shelf-crossing trough that is within primary depocenter for Bering Glacier sediments. The sub-seafloor architecture of the Bering Trough region is defined by a regional unconformity that marks the first glacial advance to the shelf edge. Below the unconformity, the shelf is constructed by multiple aggradational packages that are likely a series of pro-glacial outer shelf/slope fans. Two faults underlie the glacial packages and have been rendered inactive as the depositional environment has evolved, while faulting elsewhere on the shelf has initiated. Site U1421 lies on the current continental slope, within the backlimb of an active thrust that forms part of the modern YAK-NA deformation front. At each of these sites, we recovered glacigenic diamict (at depths up to ~1015 m at Site U1420), all of which is younger than 0.781 Ma. Preliminary age models for the Bering Trough region indicate that the entire outer shelf and shelf edge environment have been built since the Mid-Pleistocene Transition (MPT), and is possibly even younger. In stark contrast to previous interpretations, the shelf environment, in addition to the proximal deep-sea fan system, appears to be a primary glacial depocenter since the MPT, with an average accumulation rate >1.3 mm/yr. Additionally, initiation of active deformation away from the Bering Trough depocenter likely occurred since ~1 Ma. These observations suggest that possible tectonic reorganization due to mass redistribution by glacial processes occurs at time scales on the order of 100kyr-1Myr. It follows that the St. Elias orogenic system may be more sensitive to glacial-interglacial cycles than previously recognized.

Ab initio thermodynamics and kinetics for coalescence on nanoislands and nanopits on metal(100) surfaces

NASA Astrophysics Data System (ADS)

Evans, Jim; Han, Yong; Stoldt, Conrad; Thiel, Patricia

Coalescence or sintering of nanoscale features on metal(100) surfaces is mediated by periphery or edge diffusion. These processes are highly sensitive to the multiple diffusion barriers for various local edge environments. We provide an optimal strategy to determine both thermodynamics and kinetics for these systems at the ab initio level. The former requires assessing conventional interactions between adatoms at adsorption sites. The latter requires assessing unconventional interactions between the hopping atom at a bridge site transition state and other nearby atoms. KMC simulation reveals that this formulation recovers observed sintering times for Ag nanoislands on Ag(100), including a novel size dependence. The formulation also applies for nanopits where there are additional challenges to capture kinetics. Work supported by NSF Grant CHE-1507223.

Link Prediction in Evolving Networks Based on Popularity of Nodes.

PubMed

Wang, Tong; He, Xing-Sheng; Zhou, Ming-Yang; Fu, Zhong-Qian

2017-08-02

Link prediction aims to uncover the underlying relationship behind networks, which could be utilized to predict missing edges or identify the spurious edges. The key issue of link prediction is to estimate the likelihood of potential links in networks. Most classical static-structure based methods ignore the temporal aspects of networks, limited by the time-varying features, such approaches perform poorly in evolving networks. In this paper, we propose a hypothesis that the ability of each node to attract links depends not only on its structural importance, but also on its current popularity (activeness), since active nodes have much more probability to attract future links. Then a novel approach named popularity based structural perturbation method (PBSPM) and its fast algorithm are proposed to characterize the likelihood of an edge from both existing connectivity structure and current popularity of its two endpoints. Experiments on six evolving networks show that the proposed methods outperform state-of-the-art methods in accuracy and robustness. Besides, visual results and statistical analysis reveal that the proposed methods are inclined to predict future edges between active nodes, rather than edges between inactive nodes.

Corrective Action Investigation Plan for Corrective Action Unit 528: Polychlorinated Biphenyls Contamination, Nevada Test Site, Nevada, Rev. 0

DOE Office of Scientific and Technical Information (OSTI.GOV)

U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office

This Corrective Action Investigation Plan contains the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office's approach to collect the data necessary to evaluate corrective action alternatives appropriate for the closure of Corrective Action Unit (CAU) 528, Polychlorinated Biphenyls Contamination (PCBs), Nevada Test Site (NTS), Nevada, under the Federal Facility Agreement and Consent Order. Located in the southwestern portion of Area 25 on the NTS in Jackass Flats (adjacent to Test Cell C [TCC]), CAU 528 consists of Corrective Action Site 25-27-03, Polychlorinated Biphenyls Surface Contamination. Test Cell C was built to support the Nuclear Rocket Development Stationmore » (operational between 1959 and 1973) activities including conducting ground tests and static firings of nuclear engine reactors. Although CAU 528 was not considered as a direct potential source of PCBs and petroleum contamination, two potential sources of contamination have nevertheless been identified from an unknown source in concentrations that could potentially pose an unacceptable risk to human health and/or the environment. This CAU's close proximity to TCC prompted Shaw to collect surface soil samples, which have indicated the presence of PCBs extending throughout the area to the north, east, south, and even to the edge of the western boundary. Based on this information, more extensive field investigation activities are being planned, the results of which are to be used to support a defensible evaluation of corrective action alternatives in the corrective action decision document.« less

How water molecules affect the catalytic activity of hydrolases--a XANES study of the local structures of peptide deformylase.

PubMed

Cui, Peixin; Wang, Yu; Chu, Wangsheng; Guo, Xiaoyun; Yang, Feifei; Yu, Meijuan; Zhao, Haifeng; Dong, Yuhui; Xie, Yaning; Gong, Weimin; Wu, Ziyu

2014-12-12

Peptide deformylase (PDF) is a prokaryotic enzyme that catalyzes the deformylation of nascent peptides generated during protein synthesis and water molecules play a key role in these hydrolases. Using X-ray absorption near edge spectroscopy (XANES) and ab initio calculations we accurately probe the local atomic environment of the metal ion binding in the active site of PDF at different pH values and with different metal ions. This new approach is an effective way to monitor existing correlations among functions and structural changes. We show for the first time that the enzymatic activity depends on pH values and metal ions via the bond length of the nearest coordinating water (Wat1) to the metal ion. Combining experimental and theoretical data we may claim that PDF exhibits an enhanced enzymatic activity only when the distance of the Wat1 molecule with the metal ion falls in the limited range from 2.15 to 2.55 Å.

Enzyme electrokinetics: hydrogen evolution and oxidation by Allochromatium vinosum [NiFe]-hydrogenase.

PubMed

Léger, Christophe; Jones, Anne K; Roseboom, Winfried; Albracht, Simon P J; Armstrong, Fraser A

2002-12-31

The mechanism of catalytic hydrogen evolution and oxidation by Allochromatium vinosum [NiFe]-hydrogenase has been studied by protein film voltammetry (PFV) with the enzyme adsorbed at a pyrolytic graphite edge electrode. By analyzing the entire shapes of catalytic voltammograms, the energetics of the catalytic cycles (reduction potentials and acidity constants of the active states), including the detailed profiles of activity against pH and the sequences of proton and electron transfers, have been determined, and these are discussed with respect to the mechanism. PFV, which probes rates as a continuous function of the electrochemical potential (i.e., in the "potential domain"), is proven to be an invaluable tool for determining the redox properties of an active site in the presence of its substrate, at room temperature, and during turnover. This is especially relevant in the case of the active states of hydrogenase, since one of its substrates (the proton) is always present at significant levels in the titration medium at physiological pH values.

Dopant activation in Sn-doped Ga2O3 investigated by X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Siah, S. C.; Brandt, R. E.; Lim, K.; Schelhas, L. T.; Jaramillo, R.; Heinemann, M. D.; Chua, D.; Wright, J.; Perkins, J. D.; Segre, C. U.; Gordon, R. G.; Toney, M. F.; Buonassisi, T.

2015-12-01

Doping activity in both beta-phase (β-) and amorphous (a-) Sn-doped gallium oxide (Ga2O3:Sn) is investigated by X-ray absorption spectroscopy (XAS). A single crystal of β-Ga2O3:Sn grown using edge-defined film-fed growth at 1725 °C is compared with amorphous Ga2O3:Sn films deposited at low temperature (<300 °C). Our XAS analyses indicate that activated Sn dopant atoms in conductive single crystal β-Ga2O3:Sn are present as Sn4+, preferentially substituting for Ga at the octahedral site, as predicted by theoretical calculations. In contrast, inactive Sn atoms in resistive a-Ga2O3:Sn are present in either +2 or +4 charge states depending on growth conditions. These observations suggest the importance of growing Ga2O3:Sn at high temperature to obtain a crystalline phase and controlling the oxidation state of Sn during growth to achieve dopant activation.

Linking snake behavior to nest predation in a Midwestern bird community.

PubMed

Weatherhead, Patrick J; Carfagno, Gerardo L F; Sperry, Jinelle H; Brawn, Jeffrey D; Robinson, Scott K

2010-01-01

Nest predators can adversely affect the viability of songbird populations, and their impact is exacerbated in fragmented habitats. Despite substantial research on this predator-prey interaction, however, almost all of the focus has been on the birds rather than their nest predators, thereby limiting our understanding of the factors that bring predators and nests into contact. We used radiotelemetry to document the activity of two snake species (rat snakes, Elaphe obsoleta; racers, Coluber constrictor) known to prey on nests in Midwestern bird communities and simultaneously monitored 300 songbird nests and tested the hypothesis that predation risk should increase for nests when snakes were more active and in edge habitat preferred by both snake species. Predation risk increased when rat snakes were more active, for all nests combined and for two of the six bird species for which we had sufficient nests to allow separate analyses. This result is consistent with rat snakes being more important nest predators than racers. We found no evidence, however, that nests closer to forest edges were at greater risk. These results are generally consistent with the one previous study that investigated rat snakes and nest predation simultaneously. The seemingly paradoxical failure to find higher predation risk in the snakes' preferred habitat (i.e., edge) might be explained by the snakes using edges at least in part for non-foraging activities. We propose that higher nest predation in fragmented habitats (at least that attributable to snakes) results indirectly from edges promoting larger snake populations, rather than from edges directly increasing the risk of nest predation by snakes. If so, the notion of edges per se functioning as ecological "traps" merits further study.

X-ray metrology of an array of active edge pixel sensors for use at synchrotron light sources

NASA Astrophysics Data System (ADS)

Plackett, R.; Arndt, K.; Bortoletto, D.; Horswell, I.; Lockwood, G.; Shipsey, I.; Tartoni, N.; Williams, S.

2018-01-01

We report on the production and testing of an array of active edge silicon sensors as a prototype of a large array. Four Medipix3RX.1 chips were bump bonded to four single chip sized Advacam active edge n-on-n sensors. These detectors were then mounted into a 2 by 2 array and tested on B16 at Diamond Light Source with an x-ray beam spot of 2um. The results from these tests, compared with optical metrology demonstrate that this type of sensor is sensitive to the physical edge of the silicon, with only a modest loss of efficiency in the final two rows of pixels. We present the efficiency maps recorded with the microfocus beam and a sample powder diffraction measurement. These results give confidence that this sensor technology can be used effectively in larger arrays of detectors at synchrotron light sources.

Solution XAS Analysis for Exploring the Active Species in Homogeneous Vanadium Complex Catalysis

NASA Astrophysics Data System (ADS)

Nomura, Kotohiro; Mitsudome, Takato; Tsutsumi, Ken; Yamazoe, Seiji

2018-06-01

Selected examples in V K-edge X-ray Absorption Near Edge Structure (XANES) analysis of a series of vanadium complexes containing imido ligands (possessing metal-nitrogen double bond) in toluene solution have been introduced, and their pre-edge and the edge were affected by their structures and nature of ligands. Selected results in exploring the oxidation states of the active species in ethylene dimerization/polymerization using homogeneous vanadium catalysts [consisting of (imido)vanadium(V) complexes and Al cocatalysts] by X-ray absorption spectroscopy (XAS) analyses have been introduced. It has been demonstrated that the method should provide more clear information concerning the active species in situ, especially by combination with the other methods (NMR and ESR spectra, X-ray crystallographic analysis, and reaction chemistry), and should be powerful tool for study of catalysis mechanism as well as for the structural analysis in solution.

Effect of Co and O defects on ferromagnetism in Co-doped ZnO: An X-ray absorption spectroscopic investigation

NASA Astrophysics Data System (ADS)

Singhal, Rishi K.; Jakhar, Narendra; Samariya, A.; Dolia, S. N.; Kumar, Sudhish

2018-02-01

Understanding of origin of ferromagnetism in dilute magnetic oxides (DMO's) has become one of the most challenging research problems in condensed matter physics. Here we are reporting a detailed study of magnetic properties and electronic structure of two 5% Co-doped ZnO samples (the as-prepared sample Zn0.95Co0.05O and the hydrogenated sample Zn0.95Co0.05O:H). The as-prepared sample is found to be paramagnetic while through hydrogenation, we observed inducement of remarkable ferromagnetism in it. The H-mediated magnetic transition is accompanied by electronic structure modifications with no structural deviations. To get in-depth information into electronic structure correlations of the observed ferromagnetism, we have investigated their electronic properties in detail. For this purpose, we have employed the site-selective and element-sensitive X-ray-absorption spectroscopy (XAS) in the vicinity of the Cobalt L2,3 edge, the oxygen K edge, and the Zinc L3 edge using synchrotron radiation. The Co L2,3 edge spectra clearly show that Co dopants reside at the Zn sites for both these samples and that they are tetrahedrally coordinated with the ligand O atoms. Very minor changes are observed in the Zn L3 edge spectra. However, the O 1s edge spectra display dominant additional components in the ferromagnetic hydrogenated sample Zn0.95Co0.05O:H, not observed in the as-prepared non-magnetic sample Zn0.95Co0.05O. We conclude that the observed spectral features can be attributed to the presence of O vacancies and the hybridization of Co 3d states with O 2p vacancy states. These two factors together are likely to play important role in inducement of ferromagnetic ordering in this Co-doped ZnO system. However, which of these two weighs more in this mechanism, cannot be pinpointed and more studies are required in this regard.

Measurement Sets and Sites Commonly Used for Characterization

NASA Technical Reports Server (NTRS)

Pagnutti, Mary; Holekamp, Kara; Ryan, Robert; Sellers, Richard; Davis, Bruce; Zanoni, Vicki

2002-01-01

Scientists at NASA's Earth Science Applications Directorate are creating a well-characterized Verification & Validation (V&V) site at the Stennis Space Center. This site enables the in-flight characterization of remote sensing systems and the data they acquire. The data are predominantly acquired by commercial, high spatial resolution satellite systems, such as IKONOS and QuickBird 2, and airborne systems. The smaller scale of these newer high resolution remote sensing systems allows scientists to characterize the geometric, spatial, and radiometric data properties using a single V&V site. The targets and techniques used to characterize data from these newer systems can differ significantly from the techniques used to characterize data from the earlier, coarser spatial resolution systems. Scientists are also using the SSC V&V site to characterize thermal infrared systems and active LIDAR systems. SSC employs geodetic targets, edge targets, radiometric tarps, and thermal calibration ponds to characterize remote sensing data products. This paper presents a proposed set of required measurements for visible through long-wave infrared remote sensing systems and a description of the Stennis characterization. Other topics discussed include: 1) The use of ancillary atmospheric and solar measurements taken at SSC that support various characterizations; 2) Additional sites used for radiometric, geometric, and spatial characterization in the continental United States; 3) The need for a standardized technique to be adopted by CEOS and other organizations.

Measurement Sets and Sites Commonly used for Characterizations

NASA Technical Reports Server (NTRS)

Pagnutti, Mary; Holekamp, Kara; Ryan, Robert; Blonski, Slawomir; Sellers, Richard; Davis, Bruce; Zanoni, Vicki

2002-01-01

Scientists with NASA's Earth Science Applications Directorate are creating a well-characterized Verification & Validation (V&V) site at the Stennis Space Center (SSC). This site enables the in-flight characterization of remote sensing systems and the data that they require. The data are predominantly acquired by commercial, high-spatial resolution satellite systems, such as IKONOS and QuickBird 2, and airborne systems. The smaller scale of these newer high-resolution remote sensing systems allows scientists to characterize the geometric, spatial, and radiometric data properties using a single V&V site. The targets and techniques used to characterize data from these newer systems can differ significantly from the earlier, coarser spatial resolution systems. Scientists are also using the SSC V&V site to characterize thermal infrared systems and active Light Detection and Ranging (LIDAR) systems. SSC employs geodetic targets, edge targets, radiometric tarps, and thermal calibration ponds to characterize remote sensing data products. This paper presents a proposed set of required measurements for visible-through-longwave infrared remote sensing systems, and a description of the Stennis characterization. Other topics discussed inslude: 1) use of ancillary atmospheric and solar measurements taken at SSC that support various characterizations, 2) other sites used for radiometric, geometric, and spatial characterization in the continental United States,a nd 3) the need for a standardized technique to be adopted by the Committee on Earth Observation Satellites (CEOS) and other organizations.

Fundamentals and Methods of High Angle-of-Attack Flying Qualities Research

DTIC Science & Technology

1988-01-01

the subject, Carr sites the work of Ham and Gorelick (1968) (Reference (26)) which showed that additional lift could be created by rapid pitching of...the laminar boundary layer near the leading-edge. Thicker airfoils (t/c > 0. 12), 32 NADC 88020-60 representative of figure 24b, typically create ...lift-curve can result from leading-edge flow separation as shown in figure 24a. An airplance with this type of lift-curve would exhibit little or no

Enabling Colloidal Synthesis of Edge-Oriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis.

PubMed

Sun, Yugang; Alimohammadi, Farbod; Zhang, Dongtang; Guo, Guangsheng

2017-03-08

By selectively promoting heterogeneous nucleation/growth of MoS 2 on graphene monolayer sheets, edge-oriented (EO) MoS 2 nanosheets with expanded interlayer spacing (∼9.4 Å) supported on reduced graphene oxide (rGO) sheets were successfully synthesized through colloidal chemistry, showing the promise in low-cost and large-scale production. The number and edge length of MoS 2 nanosheets per area of graphene sheets were tuned by controlling the reaction time in the microwave-assisted solvothermal reduction of ammonium tetrathiomolybdate [(NH 4 ) 2 MoS 4 ] in dimethylformamide. The edge-oriented and interlayer-expanded (EO&IE) MoS 2 /rGO exhibited significantly improved catalytic activity toward hydrogen evolution reaction (HER) in terms of larger current density, lower Tafel slope, and lower charge transfer resistance compared to the corresponding interlayer-expanded MoS 2 sheets without edge-oriented geometry, highlighting the importance of synergistic effect between edge-oriented geometry and interlayer expansion on determining HER activity of MoS 2 nanosheets. Quantitative analysis clearly shows the linear dependence of current density on the edge length of MoS 2 nanosheets.

Continental shelf landscapes of the southeastern United States since the last interglacial

NASA Astrophysics Data System (ADS)

Harris, M. Scott; Sautter, Leslie Reynolds; Johnson, Kacey L.; Luciano, Katherine E.; Sedberry, George R.; Wright, Eric E.; Siuda, Amy N. S.

2013-12-01

The wide, sediment-starved continental shelf and modern coastal areas of the southeastern United States retain well-preserved but scattered remnants of a submerged paleolandscape. This paper presents a conceptual model of stratigraphic deposition and landscape formation since the last interglacial on the continental shelf of South Carolina, with portions of North Carolina, Georgia, and Florida (USA). Data for this study include multibeam bathymetry surveys, sidescan sonar mosaics, high-resolution subbottom profiles, and ground-truth surveys from - 250 m to the modern tidewater region. Four bathymetric zones are recognized with eleven landforms and landform indicators. The described zones range in depths from the modern shoreline, across the shelf, and over the shelf edge to - 250 m MSL. Relative sea level curves are presented for the area and discussed in conjunction with cultural and climatic events. The potential for preservation of Paleoamerican sites is high at the shelf edge between - 130 m and - 45 m, with Archaic and later occupations likely in depths of less than - 25 m. Prominent vantage points for Paleoamericans (> 11 kya) would have existed at the shelf edge, and tidewater resources would have been available nearby for a period of almost 6 ka. Rapid transgression rates (> 60 km/ka) after the sea level rose over the shelf edge make preservation of tidewater sites less likely on the outer and middle shelf. Searches for the earliest Paleoamericans should focus on promontories at the edge of the shelf and along future discoveries of paleoincisions on the shelf. Mapping and delineating this paleolandscape and associated unconsolidated sedimentary deposits interspersed with rocky plains and ledges will continue to be a priority to marine archeologists, coastal managers, fishery scientists, and marine spatial planners over the next several decades.

Smoke-derived karrikin perception by the α/β-hydrolase KAI2 from Arabidopsis

PubMed Central

Guo, Yongxia; Zheng, Zuyu; La Clair, James J.; Chory, Joanne; Noel, Joseph P.

2013-01-01

Genetic studies in Arabidopsis implicate an α/β-hydrolase, KARRIKIN-INSENSITIVE 2 (KAI2) as a receptor for karrikins, germination-promoting butenolide small molecules found in the smoke of burned plants. However, direct biochemical evidence for the interaction between KAI2 and karrikin and for the mechanism of downstream signaling by a KAI2–karrikin complex remain elusive. We report crystallographic analyses and ligand-binding experiments for KAI2 recognition of karrikins. The karrikin-1 (KAR1) ligand sits in the opening to the active site abutting a helical domain insert but distal from the canonical catalytic triad (Ser95-His246-Asp217) of α/β-hydrolases, consistent with the lack of detectable hydrolytic activity by purified KAI2. The closest approach of KAR1 to Ser95-His246-Asp217 is 3.8 Å from His246. Six aromatic side chains, including His246, encapsulate KAR1 through geometrically defined aromatic–aromatic interactions. KAR1 binding induces a conformational change in KAI2 at the active site entrance. A crevice of hydrophobic residues linking the polar edge of KAR1 and the helical domain insert suggests that KAI2–KAR1 creates a contiguous interface for binding signaling partners in a ligand-dependent manner. PMID:23613584

Smoke-derived karrikin perception by the α/β-hydrolase KAI2 from Arabidopsis.

PubMed

Guo, Yongxia; Zheng, Zuyu; La Clair, James J; Chory, Joanne; Noel, Joseph P

2013-05-14

Genetic studies in Arabidopsis implicate an α/β-hydrolase, KARRIKIN-INSENSITIVE 2 (KAI2) as a receptor for karrikins, germination-promoting butenolide small molecules found in the smoke of burned plants. However, direct biochemical evidence for the interaction between KAI2 and karrikin and for the mechanism of downstream signaling by a KAI2-karrikin complex remain elusive. We report crystallographic analyses and ligand-binding experiments for KAI2 recognition of karrikins. The karrikin-1 (KAR1) ligand sits in the opening to the active site abutting a helical domain insert but distal from the canonical catalytic triad (Ser95-His246-Asp217) of α/β-hydrolases, consistent with the lack of detectable hydrolytic activity by purified KAI2. The closest approach of KAR1 to Ser95-His246-Asp217 is 3.8 Å from His246. Six aromatic side chains, including His246, encapsulate KAR1 through geometrically defined aromatic-aromatic interactions. KAR1 binding induces a conformational change in KAI2 at the active site entrance. A crevice of hydrophobic residues linking the polar edge of KAR1 and the helical domain insert suggests that KAI2-KAR1 creates a contiguous interface for binding signaling partners in a ligand-dependent manner.

Zinc-mediated Allosteric Inhibition of Caspase-6*

PubMed Central

Velázquez-Delgado, Elih M.; Hardy, Jeanne A.

2012-01-01

Zinc and caspase-6 have independently been implicated in several neurodegenerative disorders. Depletion of zinc intracellularly leads to apoptosis by an unknown mechanism. Zinc inhibits cysteine proteases, including the apoptotic caspases, leading to the hypothesis that zinc-mediated inhibition of caspase-6 might contribute to its regulation in a neurodegenerative context. Using inductively coupled plasma optical emission spectroscopy, we observed that caspase-6 binds one zinc per monomer, under the same conditions where the zinc leads to complete loss of enzymatic activity. To understand the molecular details of zinc binding and inhibition, we performed an anomalous diffraction experiment above the zinc edge. The anomalous difference maps showed strong 5σ peaks, indicating the presence of one zinc/monomer bound at an exosite distal from the active site. Zinc was not observed bound to the active site. The zinc in the exosite was liganded by Lys-36, Glu-244, and His-287 with a water molecule serving as the fourth ligand, forming a distorted tetrahedral ligation sphere. This exosite appears to be unique to caspase-6, as the residues involved in zinc binding were not conserved across the caspase family. Our data suggest that binding of zinc at the exosite is the primary route of inhibition, potentially locking caspase-6 into the inactive helical conformation. PMID:22891250

Antiferromagnetic interaction between A'-site Mn spins in A-site-ordered perovskite YMn3Al4O12.

PubMed

Tohyama, Takenori; Saito, Takashi; Mizumaki, Masaichiro; Agui, Akane; Shimakawa, Yuichi

2010-03-01

The A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y(3+)Mn(3+)(3)Al(3+)(4)O(2-)(12) with magnetic Mn(3+) at the A' site and non-magnetic Al(3+) at the B site. An antiferromagnetic interaction between the A'-site Mn(3+) spins is induced by the nearest neighboring Mn-Mn direct exchange interaction and causes an antiferromagnetic transition at 34.3 K.

Electronic Structure of p- and n-Type Doping Impurities in Cubic Gallium Nitride

NASA Astrophysics Data System (ADS)

Pentaleri, E. A.; Gubanov, V. A.; Fong, C. Y.; Klein, B. M.

1996-03-01

LMTO-TB calculations were performed to investigate the electronic structure of C, Be, Mg, Si, Zn, and Cd substitutional impurities in cubic GaN (c-GaN). The calculations used 128-site supercells consisting of 64-atoms. Empty spheres of two types occupied the remaining sites. Semi-core Ga 3d states were treated explicitly as valence states. Both amphoteric substitutions were considered for C and Si impurities, while only cation-site substitutions were considered for Be, Mg, Zn, and Cd. All metal impurities formed partially occupied impurity states at the VB edge, which may result in p-type conductivity. C and Si impurities substituted at anion sites form sharp resonances in the gap, and are inactive in creating either p- or n-type carriers. Likewise, cation-site C substitutions introduce to the middle of the band gap strongly localized states that are inactive in carrier formation. Cation-site Si substitutions form an impurity sub-band at the CB edge, leading to n-type conductivity. The DOS at the Fermi level for each impurity-doped c-GaN crystal is used to estimate the most effective p-type doping impurities. The wave-function composition, space, and energy localization is analyzed for different impurities via projections onto the orbital basis and atomic coordinational spheres, and by examining calculated charge-density distributions.

Preferred site occupation of 3 d atoms in NixF e4 -xN (x =1 and 3) films revealed by x-ray absorption spectroscopy and magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Takata, Fumiya; Ito, Keita; Takeda, Yukiharu; Saitoh, Yuji; Takanashi, Koki; Kimura, Akio; Suemasu, Takashi

2018-02-01

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism measurements were performed at the Ni and Fe L2 ,3 absorption edges for N ixF e4 -xN (x =1 and 3) epitaxial films. Spectral line-shape analysis and element-specific magnetic moment evaluations are presented. Shoulders at approximately 2 eV above the Ni L2 ,3 main peaks in the XAS spectrum of N i3FeN were interpreted to originate from hybridization of orbitals between Ni 3 d at face-centered (II) sites and N 2 p at body-centered sites, while such features were missing in NiF e3N film. Similar shoulders were observed at Fe L2 ,3 edges in both films. These results indicate that the orbitals of Ni atoms did not hybridize with those of N atoms in the NiF e3N film. Hence, Ni atoms preferentially occupied corner (I) sites, where the hybridization was weak because of the relatively long distance between Ni at I sites and N atoms. The relatively large magnetic moment deduced from sum-rule analysis of NiF e3N also showed a good agreement with the presence of Ni atoms at I sites.

Holistic, model-based optimization of edge leveling as an enabler for lithographic focus control: application to a memory use case

NASA Astrophysics Data System (ADS)

Hasan, T.; Kang, Y.-S.; Kim, Y.-J.; Park, S.-J.; Jang, S.-Y.; Hu, K.-Y.; Koop, E. J.; Hinnen, P. C.; Voncken, M. M. A. J.

2016-03-01

Advancement of the next generation technology nodes and emerging memory devices demand tighter lithographic focus control. Although the leveling performance of the latest-generation scanners is state of the art, challenges remain at the wafer edge due to large process variations. There are several customer configurable leveling control options available in ASML scanners, some of which are application specific in their scope of leveling improvement. In this paper, we assess the usability of leveling non-correctable error models to identify yield limiting edge dies. We introduce a novel dies-inspec based holistic methodology for leveling optimization to guide tool users in selecting an optimal configuration of leveling options. Significant focus gain, and consequently yield gain, can be achieved with this integrated approach. The Samsung site in Hwaseong observed an improved edge focus performance in a production of a mid-end memory product layer running on an ASML NXT 1960 system. 50% improvement in focus and a 1.5%p gain in edge yield were measured with the optimized configurations.

Reduction of Free Edge Peeling Stress of Laminated Composites Using Active Piezoelectric Layers

PubMed Central

Huang, Bin; Kim, Heung Soo

2014-01-01

An analytical approach is proposed in the reduction of free edge peeling stresses of laminated composites using active piezoelectric layers. The approach is the extended Kantorovich method which is an iterative method. Multiterms of trial function are employed and governing equations are derived by taking the principle of complementary virtual work. The solutions are obtained by solving a generalized eigenvalue problem. By this approach, the stresses automatically satisfy not only the traction-free boundary conditions, but also the free edge boundary conditions. Through the iteration processes, the free edge stresses converge very quickly. It is found that the peeling stresses generated by mechanical loadings are significantly reduced by applying a proper electric field to the piezoelectric actuators. PMID:25025088

Enhanced visible light photocatalytic activity in N-doped edge- and corner-truncated octahedral Cu2O

NASA Astrophysics Data System (ADS)

Zou, Mingming; Liu, Honghong; Feng, Lu; Thomas, Tiju; Yang, Minghui

2017-03-01

Edge- and corner-truncated octahedral Cu2O is successfully synthesized using an aqueous mixture of CuCl2, sodium dodecyl sulfate, NaOH, and NH2OH3·HCl. Cu2O1-xNx(150 °C, 30 min) samples are synthesized by nitridation of Cu2O using an ammonothermal process. Cu retains a formal valence state through and beyond the nitridation process. N concentration in this sample is 1.73 at%, out of which 1.08 at% is substitutional in nature. Photocatalytic activity of Cu2O1-xNx(150 °C, 30 min) sample is investigated and compared to that of pristine edge- and corner-truncated octahedral Cu2O. Results show that Cu2O1-xNx(150 °C, 30 min) sample with dominant {110} facets has a higher photocatalytic activity than the pristine Cu2O material. Higher surface energy and a greater density of the ;Cu; dangling bonds on {110} facets of edge- and corner-truncated octahedral Cu2O1-xNx is the plausible reason for the observed optimum catalytic activity. Furthermore defect states induced by nitridation results in improved visible light adsorption. And also the band edge states changes which brought about by N doping. This is an interesting result since it bypasses the usual challenge faced by pristine Cu2O which have band edge states between which transitions are normally forbidden. Selective radical quenching experiments suggest that photocatalytic activity of Cu2O1-xNx is due to formation of hydroxyl radicals in water, subsequent to photogeneration of charge carriers in the photocatalyst.

Sorption of Sr, Co and Zn on illite: Batch experiments and modelling including Co in-diffusion measurements on compacted samples

NASA Astrophysics Data System (ADS)

Montoya, V.; Baeyens, B.; Glaus, M. A.; Kupcik, T.; Marques Fernandes, M.; Van Laer, L.; Bruggeman, C.; Maes, N.; Schäfer, T.

2018-02-01

Experimental investigations on the uptake of divalent cations (Sr, Co and Zn) onto illite (Illite du Puy, Le-Puy-en-Velay, France) were carried out by three different international research groups (Institute for Nuclear Waste Disposal, KIT (Germany), Group Waste & Disposal, SCK-CEN, (Belgium) and Laboratory for Waste Management, PSI (Switzerland)) in the framework of the European FP7 CatClay project. The dependence of solid-liquid distribution ratios (Rd values) on pH at trace metal conditions (sorption edges) and on the metal ion concentration (sorption isotherms) was determined in dilute suspensions of homo-ionic Na-illite (Na-IdP) under controlled N2 atmosphere. The experimental results were modelled using the 2 Site Protolysis Non Electrostatic Surface Complexation and Cation Exchange (2SPNE SC/CE) sorption model. The sorption of Sr depends strongly on ionic strength, while a rather weak pH dependence is observed in a pH range between 3 and 11. The data were modelled with cation exchange reactions, taking into account competition with H, K, Ca, Mg and Al, and surface complexation on weak amphotheric edge sites at higher pH values. The sorption of Co on Na-IdP, however, is strongly pH dependent. Cation exchange on the planar sites and surface complexation on strong and weak amphoteric edge sites were used to describe the Co sorption data. Rd values for Co derived from in-diffusion measurements on compacted Na-IdP samples (bulk-dry density of 1700 kg m-3) between pH 5.0 and 9.0 are in good agreement with the batch sorption data. The equivalence of both approaches to measure sorption was thus confirmed for the present test system. In addition, the results highlight the importance of both major and minor surface species for the diffusive transport behaviour of strongly sorbing metal cations. While surface complexes at the edge sites determine largely the Rd value, the diffusive flux may be governed by those species bound to the planar sites, even at low fractional occupancies. The pH dependent sorption determined for trace Zn concentrations showed large Rd values across the entire pH range with almost no dependence on the background electrolyte concentration. Additional sorption experiments carried out at substantial fractional Zn loadings demonstrated that the selectivity for the exchange of Na+ for Zn2+ at the planar sites could not explain the large Rd values measured at low pH and trace Zn concentrations. This suggests that another mechanism is ruling Zn uptake under these conditions.

Structural basis for the inhibition of poly(ADP-ribose) polymerases 1 and 2 by BMN 673, a potent inhibitor derived from dihydropyridophthalazinone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aoyagi-Scharber, Mika, E-mail: maoyagi@bmrn.com; Gardberg, Anna S.; Yip, Bryan K.

2014-08-29

BMN 673, a novel PARP1/2 inhibitor in clinical development with substantial tumor cytotoxicity, forms extensive hydrogen-bonding and π-stacking in the nicotinamide pocket, with its unique disubstituted scaffold extending towards the less conserved edges of the pocket. These interactions might provide structural insight into the ability of BMN 673 to both inhibit catalysis and affect DNA-binding activity. Poly(ADP-ribose) polymerases 1 and 2 (PARP1 and PARP2), which are involved in DNA damage response, are targets of anticancer therapeutics. BMN 673 is a novel PARP1/2 inhibitor with substantially increased PARP-mediated tumor cytotoxicity and is now in later-stage clinical development for BRCA-deficient breast cancers.more » In co-crystal structures, BMN 673 is anchored to the nicotinamide-binding pocket via an extensive network of hydrogen-bonding and π-stacking interactions, including those mediated by active-site water molecules. The novel di-branched scaffold of BMN 673 extends the binding interactions towards the outer edges of the pocket, which exhibit the least sequence homology among PARP enzymes. The crystallographic structural analyses reported here therefore not only provide critical insights into the molecular basis for the exceptionally high potency of the clinical development candidate BMN 673, but also new opportunities for increasing inhibitor selectivity.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Getsoian, Andrew "Bean"; Das, Ujjal; Camacho-Bunquin, Jeffrey

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order tomore » better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. Furthermore, these findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Getsoian, Andrew “Bean”; Das, Ujjal; Camacho-Bunquin, Jeffrey

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order tomore » better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. These findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.« less

The effect of adhesive dressing edges on cutaneous irritancy and skin barrier function.

PubMed

Dykes, P J

2007-03-01

To assess the effect of repeated application and removal of adhesive edges from wound-care products on cutaneous irritancy and barrier function in normal volunteer subjects. This was a study using a 'repeat-insult patch test'. Adhesive edges from six commonly used wound-care products were applied continuously to the same site (six applications over a 14-day period) in 30 normal volunteer subjects. The test sites were assessed clinically before product reapplication using established ranking scales for cutaneous erythema. The cumulative irritancy score (CIS) for each test site was determined by adding the erythema scores at days 3, 5, 8, 10, 12 and 15. At the study end the barrier function of each test site was assessed by measuring transepidermal water loss (TEWL). The CIS showed that the products fall into two distinct groups, with Mepilex, Tielle and Allevyn giving low scores and Biatain, Comfeel and DuoDERM higher scores. Statistical analysis indicated significant differences (p < 0.05) between Mepilex and Biatain, Mepilex and Comfeel, Mepilex and DuoDERM, Tielle and Biatain, Allevyn and Biatain. The mean TEWL values also indicated that the products fall into two distinct groups: Mepilex, Tielle and Allevyn with low mean values close to that of normal adjacent back skin and Biatain, Comfeel and DuoDERM with much higher mean values. Statistical analysis indicated that Mepilex, Tielle and Allevyn were not significantly different from normal skin (p < 0.05), whereas Biatain, Comfeel and DuoDERM were significantly higher than normal skin and the other products tested. The results show clear differences between products; the clinical scores and TEWL measurements indicate that the products fall into two distinct groups. This novel approach seems able to discriminate between adhesive borders and may be useful during product development and in selecting products for clinical trials.

Radiocesium interaction with clay minerals: Theory and simulation advances Post-Fukushima.

PubMed

Okumura, Masahiko; Kerisit, Sebastien; Bourg, Ian C; Lammers, Laura N; Ikeda, Takashi; Sassi, Michel; Rosso, Kevin M; Machida, Masahiko

2018-04-14

Insights at the microscopic level of the process of radiocesium adsorption and interaction with clay mineral particles have improved substantially over the past several years, triggered by pressing social issues such as management of huge amounts of waste soil accumulated after the Fukushima Dai-ichi nuclear power plant accident. In particular, computer-based molecular modeling supported by advanced hardware and algorithms has proven to be a powerful approach. Its application can now generally encompass the full complexity of clay particle adsorption sites from basal surfaces to interlayers with inserted water molecules, to edges including fresh and weathered frayed ones. On the other hand, its methodological schemes are now varied from traditional force-field molecular dynamics on large-scale realizations composed of many thousands of atoms including water molecules to first-principles methods on smaller models in rather exacting fashion. In this article, we overview new understanding enabled by simulations across methodological variations, focusing on recent insights that connect with experimental observations, namely: 1) the energy scale for cesium adsorption on the basal surface, 2) progress in understanding the structure of clay edges, which is difficult to probe experimentally, 3) cesium adsorption properties at hydrated interlayer sites, 4) the importance of the size relationship between the ionic radius of cesium and the interlayer distance at frayed edge sites, 5) the migration of cesium into deep interlayer sites, and 6) the effects of nuclear decay of radiocesium. Key experimental observations that motivate these simulation advances are also summarized. Furthermore, some directions toward future solutions of waste soil management are discussed based on the obtained microscopic insights. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Radiocesium interaction with clay minerals: Theory and simulation advances Post–Fukushima

DOE PAGES

Okumura, Masahiko; Kerisit, Sebastien; Bourg, Ian C.; ...

2018-03-14

Insights at the microscopic level of the process of radiocesium adsorption and interaction with clay mineral particles have improved substantially over the past several years, triggered by pressing social issues such as management of huge amounts of waste soil accumulated after the Fukushima Dai–ichi nuclear power plant accident. In particular, computer–based molecular modeling supported by advanced hardware and algorithms has proven to be a powerful approach. Its application can now generally encompass the full complexity of clay particle adsorption sites from basal surfaces to interlayers with inserted water molecules, to edges including fresh and weathered frayed ones. On the othermore » hand, its methodological schemes are now varied from traditional force–field molecular dynamics on large–scale realizations composed of many thousands of atoms including water molecules to first–principles methods on smaller models in rather exacting fashion. In this article, we overview new understanding enabled by simulations across methodological variations, focusing on recent insights that connect with experimental observations, namely: 1) the energy scale for cesium adsorption on the basal surface, 2) progress in understanding the structure of clay edges, which is difficult to probe experimentally, 3) cesium adsorption properties at hydrated interlayer sites, 4) the importance of the size relationship between the ionic radius of cesium and the interlayer distance at frayed edge sites, 5) the migration of cesium into deep interlayer sites, and 6) the effects of nuclear decay of radiocesium. Key experimental observations that motivate these simulation advances are also summarized. Furthermore, some directions toward future solutions of waste soil management are discussed based on the obtained microscopic insights.« less

Radiocesium interaction with clay minerals: Theory and simulation advances Post–Fukushima

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okumura, Masahiko; Kerisit, Sebastien; Bourg, Ian C.

Insights at the microscopic level of the process of radiocesium adsorption and interaction with clay mineral particles have improved substantially over the past several years, triggered by pressing social issues such as management of huge amounts of waste soil accumulated after the Fukushima Dai–ichi nuclear power plant accident. In particular, computer–based molecular modeling supported by advanced hardware and algorithms has proven to be a powerful approach. Its application can now generally encompass the full complexity of clay particle adsorption sites from basal surfaces to interlayers with inserted water molecules, to edges including fresh and weathered frayed ones. On the othermore » hand, its methodological schemes are now varied from traditional force–field molecular dynamics on large–scale realizations composed of many thousands of atoms including water molecules to first–principles methods on smaller models in rather exacting fashion. In this article, we overview new understanding enabled by simulations across methodological variations, focusing on recent insights that connect with experimental observations, namely: 1) the energy scale for cesium adsorption on the basal surface, 2) progress in understanding the structure of clay edges, which is difficult to probe experimentally, 3) cesium adsorption properties at hydrated interlayer sites, 4) the importance of the size relationship between the ionic radius of cesium and the interlayer distance at frayed edge sites, 5) the migration of cesium into deep interlayer sites, and 6) the effects of nuclear decay of radiocesium. Key experimental observations that motivate these simulation advances are also summarized. Furthermore, some directions toward future solutions of waste soil management are discussed based on the obtained microscopic insights.« less

78 FR 48201 - Japan Lessons-Learned Project Directorate Interim Staff Guidance JLD-ISG-2013-01; Guidance for...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-07

... following the earthquake and shutdown of the operating units, however, the first large tsunami wave inundated the site, followed by additional waves. The tsunami caused extensive damage to site facilities and..., and after some period of time at the other units. Unit 6 retained the function of one air-cooled EDG...

78 FR 3039 - Japan Lessons-Learned Project Directorate Interim Staff Guidance JLD-ISG-2012-06; Performing a...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-15

... following the earthquake and shutdown of the operating units, however, the first large tsunami wave inundated the site, followed by additional waves. The tsunami caused extensive damage to site facilities and..., and after some period of time at the other units. Unit 6 retained the function of one air-cooled EDG...

Climate-induced landslide reactivation at the edge of the Most Basin (Czech Republic) - progress towards better landslide prediction

NASA Astrophysics Data System (ADS)

Burda, J.; Hartvich, F.; Valenta, J.; Smítka, V.; Rybář, J.

2013-02-01

The catastrophic landslide at Eisenberg in North Bohemia was reactivated during January 2011. This study integrates a range of geoscientific evidence in order to constrain the spatial and temporal development of this reactivation. It has investigated long-term geodetic measurements to assess the morphological development of the site over the last two decades. There is evidence to suggest that, over this period, the site had been subjected to progressive deformation caused by the collapse of an old mine gallery. However, climatic data show that the reactivation itself was triggered by a dramatic rise in the water table induced by rapid snowmelt during a period of winter warming. Furthermore, geomorphological mapping has been used to characterise the morphology of the reactivated landslide and geophysical profiling has been used to analyse its internal structure. The results show that fissures are continuing to develop above the reactivated landslide scarp while highly saturated stiff-fissured claystones provide an incipient slide plane. The application of laser scanning has shown minimal evidence for ongoing landslide activity. It is, however, clear that future landslide events will occur here due to the favourable lithological, structural, and geotechnical conditions. Finally, we propose that future landslide activity at the site may be predicted by the height of water table as this defines theoretical pore pressure at the depth of the shear plane.

Carbon Fibers Conductivity Studies

NASA Technical Reports Server (NTRS)

Yang, C. Y.; Butkus, A. M.

1980-01-01

In an attempt to understand the process of electrical conduction in polyacrylonitrile (PAN)-based carbon fibers, calculations were carried out on cluster models of the fiber consisting of carbon, nitrogen, and hydrogen atoms using the modified intermediate neglect of differential overlap (MINDO) molecular orbital (MO) method. The models were developed based on the assumption that PAN carbon fibers obtained with heat treatment temperatures (HTT) below 1000 C retain nitrogen in a graphite-like lattice. For clusters modeling an edge nitrogen site, analysis of the occupied MO's indicated an electron distribution similar to that of graphite. A similar analysis for the somewhat less stable interior nitrogen site revealed a partially localized II electron distribution around the nitrogen atom. The differences in bonding trends and structural stability between edge and interior nitrogen clusters led to a two-step process proposed for nitrogen evolution with increasing HTT.

Organochlorines in surface soil at electronic-waste wire burning sites and metal contribution evaluated using quantitative X-ray speciation

NASA Astrophysics Data System (ADS)

Fujimori, Takashi; Takigami, Hidetaka; Takaoka, Masaki

2013-04-01

Heavy metals and toxic chlorinated aromatic compounds (aromatic-Cls) such as dioxins and polychlorinated biphenyls (PCBs) are found at high concentrations and persist in surface soil at wire burning sites (WBSs) in developing countries in which various wire cables are recycled to yield pure metals. Chlorine K-edge near-edge X-ray absorption fine structure (NEXAFS) is used to detect the specific chemical form of Cl and estimate its amount using a spectrum jump in the solid phase. Quantitative X-ray speciation of Cl was applied to study the mechanisms of aromatic-Cls formation in surface soil at WBSs in Southeast Asia. Relationships between aromatic-Cls and chlorides of heavy metals were evaluated because heavy metals are promoters of the thermochemical solid-phase formation of aromatic-Cls.

Recent advances in aerodynamic energy concept for flutter suppression and gust alleviation using active controls

NASA Technical Reports Server (NTRS)

Nissim, E.

1977-01-01

Control laws are derived, by using realizable transfer functions, which permit relaxation of the stability requirements of the aerodynamic energy concept. The resulting aerodynamic eigenvalues indicate that both the trailing edge and the leading edge-trailing edge control systems can be made more effective. These control laws permit the introduction of aerodynamic damping and stiffness terms in accordance with the requirements of any specific system. Flutter suppression and gust alleviation problems can now be treated by either a trailing edge control system or by a leading edge-trailing edge control system by using the aerodynamic energy concept. Results are applicable to a wide class of aircraft operating at subsonic Mach numbers.

ERK reinforces actin polymerization to power persistent edge protrusion during motility

PubMed Central

Mendoza, Michelle C.; Vilela, Marco; Juarez, Jesus E.; Blenis, John; Danuser, Gaudenz

2016-01-01

Cells move through perpetual protrusion and retraction cycles at the leading edge. These cycles are coordinated with substrate adhesion and retraction of the cell rear. Here, we tracked spatial and temporal fluctuations in the molecular activities of individual moving cells to elucidate how extracellular regulated kinase (ERK) signaling controlled the dynamics of protrusion and retraction cycles. ERK is activated by many cell-surface receptors and we found that ERK signaling specifically reinforced cellular protrusions so that they translated into rapid, sustained forward motion of the leading edge. Using quantitative fluorescent speckle microscopy (qFSM) and cross-correlation analysis, we showed that ERK controlled the rate and timing of actin polymerization by promoting the recruitment of the actin nucleator Arp2/3 to the leading edge. Arp2/3 activity generates branched actin networks that can produce pushing force. These findings support a model in which surges in ERK activity induced by extracellular cues enhance Arp2/3-mediated actin polymerization to generate protrusion power phases with enough force to counteract increasing membrane tension and to promote sustained motility. PMID:25990957

Crystal structure of the dopamine N-acetyltransferase–acetyl-CoA complex provides insights into the catalytic mechanism

PubMed Central

Cheng, Kuo-Chang; Liao, Jhen-Ni; Lyu, Ping-Chiang

2012-01-01

The daily cycle of melatonin biosynthesis in mammals is regulated by AANAT (arylalkylamine N-acetyltransferase; EC 2.3.1.87), making it an attractive target for therapeutic control of abnormal melatonin production in mood and sleep disorders. Drosophila melanogaster Dat (dopamine N-acetyltransferase) is an AANAT. Until the present study, no insect Dat structure had been solved, and, consequently, the structural basis for its acetyl-transfer activity was not well understood. We report in the present paper the high-resolution crystal structure for a D. melanogaster Dat–AcCoA (acetyl-CoA) complex obtained using one-edge (selenium) single-wavelength anomalous diffraction. A binding study using isothermal titration calorimetry suggested that the cofactor bound to Dat first before substrate. Examination of the complex structure and a substrate-docked model indicated that Dat contains a novel AANAT catalytic triad. Site-directed mutagenesis, kinetic studies and pH-rate profiles confirmed that Glu47, Ser182 and Ser186 were critical for catalysis. Collectively, the results of the present study suggest that Dat possesses a specialized active site structure dedicated to a catalytic mechanism. PMID:22716280

Insights into electrode/electrolyte interfacial processes and the effect of nanostructured cobalt oxides loading on graphene-based hybrids by scanning electrochemical microscopy

NASA Astrophysics Data System (ADS)

Gupta, Sanju; Carrizosa, Sara B.

2016-12-01

Nanostructured cobalt oxide polymorphs (CoO and Co3O4) deposited via electrodeposition allowed optimal loading on supercapacitive graphene nanosheets producing a set of graphene-based hybrids namely, CoO/GO, CoO/ErGO, Co3O4/GO, Co3O4/rGO, and Co3O4/ErGO, as pseudocapacitive electrochemical electrodes. We gained fundamental insights into the complex physicochemical interfacial processes at electrode surfaces and electrode/electrolyte (or solid/liquid) interfaces by scanning electrochemical microscopy operating in the feedback probe approach and imaging modes while monitoring and mapping the redox probe (re)activity behavior. We determined the various experimental descriptors including diffusion coefficient, electron transfer rate, and electroactive site distribution on electrodes. We emphasize the interplay of (1) heterogeneous basal and edge plane active sites, (2) graphene surface functional moieties (conducting/semiconducting), and (3) crystalline spinel cobalt oxides (semiconducting/insulating) coated graphene, reinforcing the available electron density of states in the vicinity of the Fermi level contributing to higher electroactivity, faster interfacial diffusion, and shorter distances for electron transfer, facilitated through molecular and chemical bridges obtained by electrodeposition as compared with the physical deposition.

Active Layer Soil Carbon and Nutrient Mineralization, Barrow, Alaska, 2012

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stan D. Wullschleger; Holly M. Vander Stel; Colleen Iversen

This data set consists of bulk soil characteristics as well as carbon and nutrient mineralization rates of active layer soils manually collected from the field in August, 2012, frozen, and then thawed and incubated across a range of temperatures in the laboratory for 28 day periods in 2013-2015. The soils were collected from four replicate polygons in each of the four Areas (A, B, C, and D) of Intensive Site 1 at the Next-Generation Ecosystem Experiments (NGEE) Arctic site near Barrow, Alaska. Soil samples were coincident with the established Vegetation Plots that are located in center, edge, and trough microtopographymore » in each polygon. Data included are 1) bulk soil characteristics including carbon, nitrogen, gravimetric water content, bulk density, and pH in 5-cm depth increments and also by soil horizon, 2) carbon, nitrogen, and phosphorus mineralization rates for soil horizons incubated aerobically (and in one case both aerobically and anaerobically) for 28 days at temperatures that included 2, 4, 8, and 12 degrees C. Additional soil and incubation data are forthcoming. They will be available when published as part of another paper that includes additional replicate analyses.« less

Powered protrusion cutter

DOEpatents

Bzorgi, Fariborz M.

2010-03-09

An apparatus for clipping a protrusion of material is provided. The protrusion may, for example, be a bolt head, a nut, a rivet, a weld bead, or a temporary assembly alignment tab protruding from a substrate surface of assembled components. The apparatus typically includes a cleaver having a cleaving edge and a cutting blade having a cutting edge. Generally, a mounting structure configured to confine the cleaver and the cutting blade and permit a range of relative movement between the cleaving edge and the cutting edge is provided. Also typically included is a power device coupled to the cutting blade. The power device is configured to move the cutting edge toward the cleaving edge. In some embodiments the power device is activated by a momentary switch. A retraction device is also generally provided, where the retraction device is configured to move the cutting edge away from the cleaving edge.

Device for cutting protrusions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bzorgi, Fariborz M

An apparatus for clipping a protrusion of material is provided. The protrusion may, for example, be a bolt head, a nut, a rivet, a weld bead, or a temporary assembly alignment tab protruding from a substrate surface of assembled components. The apparatus typically includes a cleaver having a cleaving edge and a cutting blade having a cutting edge. Generally, a mounting structure configured to confine the cleaver and the cutting blade and permit a range of relative movement between the cleaving edge and the cutting edge is provided. Also typically included is a power device coupled to the cutting blade.more » The power device is configured to move the cutting edge toward the cleaving edge. In some embodiments the power device is activated by a momentary switch. A retraction device is also generally provided, where the retraction device is configured to move the cutting edge away from the cleaving edge.« less

XPD Helicase Structures And Activities: Insights Into the Cancer And Aging Phenotypes From XPD Mutations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, L.; Fuss, J.O.; Cheng, Q.J.

2009-05-18

Mutations in XPD helicase, required for nucleotide excision repair (NER) as part of the transcription/repair complex TFIIH, cause three distinct phenotypes: cancer-prone xeroderma pigmentosum (XP), or aging disorders Cockayne syndrome (CS), and trichothiodystrophy (TTD). To clarify molecular differences underlying these diseases, we determined crystal structures of the XPD catalytic core from Sulfolobus acidocaldarius and measured mutant enzyme activities. Substrate-binding grooves separate adjacent Rad51/RecA-like helicase domains (HD1, HD2) and an arch formed by 4FeS and Arch domains. XP mutations map along the HD1 ATP-binding edge and HD2 DNA-binding channel and impair helicase activity essential for NER. XP/CS mutations both impair helicasemore » activity and likely affect HD2 functional movement. TTD mutants lose or retain helicase activity but map to sites in all four domains expected to cause framework defects impacting TFIIH integrity. These results provide a foundation for understanding disease consequences of mutations in XPD and related 4Fe-4S helicases including FancJ.« less

XPD Helicase Structures and Activities: Insights into the Cancer and Aging Phenotypes from XPD Mutations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tainer, John; Fan, Li; Fuss, Jill O.

2008-06-02

Mutations in XPD helicase, required for nucleotide excision repair (NER) as part of the transcription/repair complex TFIIH, cause three distinct phenotypes: cancer-prone xeroderma pigmentosum (XP), or aging disorders Cockayne syndrome (CS), and trichothiodystrophy (TTD). To clarify molecular differences underlying these diseases, we determined crystal structures of the XPD catalytic core from Sulfolobus acidocaldarius and measured mutant enzyme activities. Substrate-binding grooves separate adjacent Rad51/RecA-like helicase domains (HD1, HD2) and an arch formed by 4FeS and Arch domains. XP mutations map along the HD1 ATP-binding edge and HD2 DNA-binding channel and impair helicase activity essential for NER. XP/CS mutations both impair helicasemore » activity and likely affect HD2 functional movement. TTD mutants lose or retain helicase activity but map to sites in all four domains expected to cause framework defects impacting TFIIH integrity. These results provide a foundation for understanding disease consequences of mutations in XPD and related 4Fe-4S helicases including FancJ.« less

Sensitivity of indentation testing to step-off edges and interface integrity in cartilage repair.

PubMed

Bae, Won C; Law, Amanda W; Amiel, David; Sah, Robert L

2004-03-01

Step-off edges and tissue interfaces are prevalent in cartilage injury such as after intra-articular fracture and reduction, and in focal defects and surgical repair procedures such as osteochondral graft implantation. It would be useful to assess the function of injured or donor tissues near such step-off edges and the extent of integration at material interfaces. The objective of this study was to determine if indentation testing is sensitive to the presence of step-off edges and the integrity of material interfaces, in both in vitro simulated repair samples of bovine cartilage defect filled with fibrin matrix, and in vivo biological repair samples from a goat animal model. Indentation stiffness decreased at locations approaching a step-off edge, a lacerated interface, or an integrated interface in which the distal tissue was relatively soft. The indentation stiffness increased or remained constant when the site of indentation approached an integrated interface in which the distal tissue was relatively stiff or similar in stiffness to the tissue being tested. These results indicate that indentation testing is sensitive to step-off edges and interface integrity, and may be useful for assessing cartilage injury and for following the progression of tissue integration after surgical treatments.

Spatial structure of correlations around a quantum impurity at the edge of a two-dimensional topological insulator

NASA Astrophysics Data System (ADS)

Allerdt, Andrew; Feiguin, A. E.; Martins, G. B.

2017-07-01

We calculate exact zero-temperature real-space properties of a substitutional magnetic impurity coupled to the edge of a zigzag silicenelike nanoribbon. Using a Lanczos transformation [A. Allerdt et al., Phys. Rev. B 91, 085101 (2015), 10.1103/PhysRevB.91.085101] and the density-matrix renormalization-group method, we obtain a realistic description of stanene and germanene that includes the bulk and the edges as boundary one-dimensional helical metallic states. Our results for substitutional impurities indicate that the development of a Kondo state and the structure of the spin correlations between the impurity and the electron spins in the metallic edge state depend considerably on the location of the impurity. More specifically, our real-space resolution allows us to conclude that there is a sharp distinction between the impurity being located at a crest or a trough site at the zigzag edge. We also observe, as expected, that the spin correlations are anisotropic due to an emerging Dzyaloshinskii-Moriya interaction with the conduction electrons and that the edges scatter from the impurity and "snake" or circle around it. Our estimates for the Kondo temperature indicate that there is a very weak enhancement due to the presence of spin-orbit coupling.

[Medical image segmentation based on the minimum variation snake model].

PubMed

Zhou, Changxiong; Yu, Shenglin

2007-02-01

It is difficult for traditional parametric active contour (Snake) model to deal with automatic segmentation of weak edge medical image. After analyzing snake and geometric active contour model, a minimum variation snake model was proposed and successfully applied to weak edge medical image segmentation. This proposed model replaces constant force in the balloon snake model by variable force incorporating foreground and background two regions information. It drives curve to evolve with the criterion of the minimum variation of foreground and background two regions. Experiments and results have proved that the proposed model is robust to initial contours placements and can segment weak edge medical image automatically. Besides, the testing for segmentation on the noise medical image filtered by curvature flow filter, which preserves edge features, shows a significant effect.

Waning habitats due to climate change: the effects of changes in streamflow and temperature at the rear edge of the distribution of a cold-water fish

NASA Astrophysics Data System (ADS)

María Santiago, José; Muñoz-Mas, Rafael; Solana-Gutiérrez, Joaquín; García de Jalón, Diego; Alonso, Carlos; Martínez-Capel, Francisco; Pórtoles, Javier; Monjo, Robert; Ribalaygua, Jaime

2017-08-01

Climate changes affect aquatic ecosystems by altering temperatures and precipitation patterns, and the rear edges of the distributions of cold-water species are especially sensitive to these effects. The main goal of this study was to predict in detail how changes in air temperature and precipitation will affect streamflow, the thermal habitat of a cold-water fish (the brown trout, Salmo trutta), and the synergistic relationships among these variables at the rear edge of the natural distribution of brown trout. Thirty-one sites in 14 mountain rivers and streams were studied in central Spain. Models of streamflow were built for several of these sites using M5 model trees, and a non-linear regression method was used to estimate stream temperatures. Nine global climate models simulations for Representative Concentration Pathways RCP4.5 and RCP8.5 scenarios were downscaled to the local level. Significant reductions in streamflow were predicted to occur in all of the basins (max. -49 %) by the year 2099, and seasonal differences were noted between the basins. The stream temperature models showed relationships between the model parameters, geology and hydrologic responses. Temperature was sensitive to streamflow in one set of streams, and summer reductions in streamflow contributed to additional stream temperature increases (max. 3.6 °C), although the sites that are most dependent on deep aquifers will likely resist warming to a greater degree. The predicted increases in water temperatures were as high as 4.0 °C. Temperature and streamflow changes will cause a shift in the rear edge of the distribution of this species. However, geology will affect the extent of this shift. Approaches like the one used herein have proven to be useful in planning the prevention and mitigation of the negative effects of climate change by differentiating areas based on the risk level and viability of fish populations.

Incremental triangulation by way of edge swapping and local optimization

NASA Technical Reports Server (NTRS)

Wiltberger, N. Lyn

1994-01-01

This document is intended to serve as an installation, usage, and basic theory guide for the two dimensional triangulation software 'HARLEY' written for the Silicon Graphics IRIS workstation. This code consists of an incremental triangulation algorithm based on point insertion and local edge swapping. Using this basic strategy, several types of triangulations can be produced depending on user selected options. For example, local edge swapping criteria can be chosen which minimizes the maximum interior angle (a MinMax triangulation) or which maximizes the minimum interior angle (a MaxMin or Delaunay triangulation). It should be noted that the MinMax triangulation is generally only locally optical (not globally optimal) in this measure. The MaxMin triangulation, however, is both locally and globally optical. In addition, Steiner triangulations can be constructed by inserting new sites at triangle circumcenters followed by edge swapping based on the MaxMin criteria. Incremental insertion of sites also provides flexibility in choosing cell refinement criteria. A dynamic heap structure has been implemented in the code so that once a refinement measure is specified (i.e., maximum aspect ratio or some measure of a solution gradient for the solution adaptive grid generation) the cell with the largest value of this measure is continually removed from the top of the heap and refined. The heap refinement strategy allows the user to specify either the number of cells desired or refine the mesh until all cell refinement measures satisfy a user specified tolerance level. Since the dynamic heap structure is constantly updated, the algorithm always refines the particular cell in the mesh with the largest refinement criteria value. The code allows the user to: triangulate a cloud of prespecified points (sites), triangulate a set of prespecified interior points constrained by prespecified boundary curve(s), Steiner triangulate the interior/exterior of prespecified boundary curve(s), refine existing triangulations based on solution error measures, and partition meshes based on the Cuthill-McKee, spectral, and coordinate bisection strategies.

Genetics Home Reference: leptin receptor deficiency

MedlinePlus

... Ferraz-Amaro I, Dattani MT, Ercan O, Myhre AG, Retterstol L, Stanhope R, Edge JA, McKenzie S, Lessan ... qualified healthcare professional . About Selection Criteria for Links Data Files & API Site Map Subscribe Customer Support USA. ...

Field site selection: getting it right first time around

PubMed Central

Malcolm, Colin A; El Sayed, Badria; Babiker, Ahmed; Girod, Romain; Fontenille, Didier; Knols, Bart GJ; Nugud, Abdel Hameed; Benedict, Mark Q

2009-01-01

The selection of suitable field sites for integrated control of Anopheles mosquitoes using the sterile insect technique (SIT) requires consideration of the full gamut of factors facing most proposed control strategies, but four criteria identify an ideal site: 1) a single malaria vector, 2) an unstructured, relatively low density target population, 3) isolation of the target population and 4) actual or potential malaria incidence. Such a site can exist in a diverse range of situations or can be created. Two contrasting SIT field sites are examined here: the desert-flanked Dongola Reach of the Nile River in Northern State, Sudan, where malaria is endemic, and the island of La Reunion, where autochthonous malaria is rare but risk is persistent. The single malaria-transmitting vector at both sites is Anopheles arabiensis. In Sudan, the target area is a narrow 500 km corridor stretching from the rocky terrain at the Fourth Cataract - just above the new Merowe Dam, to the northernmost edge of the species range, close to Egypt. Vector distribution and temporal changes in density depend on the Nile level, ambient temperature and human activities. On La Reunion, the An. arabiensis population is coastal, limited and divided into three areas by altitude and exposure to the trade winds on the east coast. Mosquito vectors for other diseases are an issue at both sites, but of primary importance on La Reunion due to the recent chikungunya epidemic. The similarities and differences between these two sites in terms of suitability are discussed in the context of area-wide integrated vector management incorporating the SIT. PMID:19917079

Elucidation of Active Sites for the Reaction of Ethanol on TiO 2 /Au(111)

DOE PAGES

Boyle, David T.; Wilke, Jeremy A.; Palomino, Robert M.; ...

2017-03-17

Obtaining a molecular-level understanding of the reaction of alcohols with heterogeneous model catalysts is critical for improving industrial catalytic processes, such as the production of H 2 from alcohols. Gold has been shown to be an excellent oxidation catalyst once oxygen is added to it. The use of reducible oxides provides a source of oxygen on Au(111) for the reaction of ethanol, which is easily regenerated in the presence of an oxygen background. In this work, ethanol operates as a probe molecule to investigate the role of Au(111), TiO 2 nanoparticles, and TiO 2/Au interfacial surface sites on the catalyticmore » properties of TiO 2/Au(111). Ultrahigh vacuum temperature-programmed desorption (TPD) studies with ethanol/Au(111) elucidate previously unreported adsorption sites for ethanol. Ethanol molecularly adsorbs to Au terrace sites, step edges, and undercoordinated kink sites with adsorption energies of -51.7, -55.8, and -65.1 kJ/mol, respectively. In a TPD coverage study of ethanol on TiO 2/Au(111) indicates ethanol undergoes dissociative adsorption to form H*(a) and CH 3CH 2O*(a) on the inverse model catalyst surface. The desorption temperature of low coverages of ethanol from TiO2/Au(111) (Tdes ≈ 235 K) is at an intermediate temperature between the desorption temperatures from bulk Au(111) and TiO 2(110), indicating both Au and TiO 2 play a role in the adsorption of ethanol. Both low-temperature adsorption and high-temperature reactions are studied and indicate that ethanol-derived products such as acetaldehyde and ethylene desorb from TiO 2/Au(111) at ~500 K. Here, we report the identification of catalytically active sites on TiO 2/Au(111) as interfacial sites between the oxide and Au(111) surface through the use of temperature-programmed desorption and infrared reflection absorption spectroscopy.« less

Elucidation of Active Sites for the Reaction of Ethanol on TiO 2 /Au(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyle, David T.; Wilke, Jeremy A.; Palomino, Robert M.

Obtaining a molecular-level understanding of the reaction of alcohols with heterogeneous model catalysts is critical for improving industrial catalytic processes, such as the production of H 2 from alcohols. Gold has been shown to be an excellent oxidation catalyst once oxygen is added to it. The use of reducible oxides provides a source of oxygen on Au(111) for the reaction of ethanol, which is easily regenerated in the presence of an oxygen background. In this work, ethanol operates as a probe molecule to investigate the role of Au(111), TiO 2 nanoparticles, and TiO 2/Au interfacial surface sites on the catalyticmore » properties of TiO 2/Au(111). Ultrahigh vacuum temperature-programmed desorption (TPD) studies with ethanol/Au(111) elucidate previously unreported adsorption sites for ethanol. Ethanol molecularly adsorbs to Au terrace sites, step edges, and undercoordinated kink sites with adsorption energies of -51.7, -55.8, and -65.1 kJ/mol, respectively. In a TPD coverage study of ethanol on TiO 2/Au(111) indicates ethanol undergoes dissociative adsorption to form H*(a) and CH 3CH 2O*(a) on the inverse model catalyst surface. The desorption temperature of low coverages of ethanol from TiO2/Au(111) (Tdes ≈ 235 K) is at an intermediate temperature between the desorption temperatures from bulk Au(111) and TiO 2(110), indicating both Au and TiO 2 play a role in the adsorption of ethanol. Both low-temperature adsorption and high-temperature reactions are studied and indicate that ethanol-derived products such as acetaldehyde and ethylene desorb from TiO 2/Au(111) at ~500 K. Here, we report the identification of catalytically active sites on TiO 2/Au(111) as interfacial sites between the oxide and Au(111) surface through the use of temperature-programmed desorption and infrared reflection absorption spectroscopy.« less

Stennis Space Center Verification & Validation Capabilities

NASA Technical Reports Server (NTRS)

Pagnutti, Mary; Ryan, Robert E.; Holekamp, Kara; O'Neal, Duane; Knowlton, Kelly; Ross, Kenton; Blonski, Slawomir

2007-01-01

Scientists within NASA#s Applied Research & Technology Project Office (formerly the Applied Sciences Directorate) have developed a well-characterized remote sensing Verification & Validation (V&V) site at the John C. Stennis Space Center (SSC). This site enables the in-flight characterization of satellite and airborne high spatial resolution remote sensing systems and their products. The smaller scale of the newer high resolution remote sensing systems allows scientists to characterize geometric, spatial, and radiometric data properties using a single V&V site. The targets and techniques used to characterize data from these newer systems can differ significantly from the techniques used to characterize data from the earlier, coarser spatial resolution systems. Scientists have used the SSC V&V site to characterize thermal infrared systems. Enhancements are being considered to characterize active lidar systems. SSC employs geodetic targets, edge targets, radiometric tarps, atmospheric monitoring equipment, and thermal calibration ponds to characterize remote sensing data products. Similar techniques are used to characterize moderate spatial resolution sensing systems at selected nearby locations. The SSC Instrument Validation Lab is a key component of the V&V capability and is used to calibrate field instrumentation and to provide National Institute of Standards and Technology traceability. This poster presents a description of the SSC characterization capabilities and examples of calibration data.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jay, Raphael M.; Norell, Jesper; Eckert, Sebastian

Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal–ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by themore » metal site occupation, whereas the ligand hole instead influences σ-donation. Here, our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.« less

Dynamic Stall Characteristics of Drooped Leading Edge Airfoils

NASA Technical Reports Server (NTRS)

Sankar, Lakshmi N.; Sahin, Mehmet; Gopal, Naveen

2000-01-01

Helicopters in high-speed forward flight usually experience large regions of dynamic stall over the retreating side of the rotor disk. The rapid variations in the lift and pitching moments associated with the stall process can result in vibratory loads, and can cause fatigue and failure of pitch links. In some instances, the large time lag between the aerodynamic forces and the blade motion can trigger stall flutter. A number of techniques for the alleviation of dynamic stall have been proposed and studied by researchers. Passive and active control techniques have both been explored. Passive techniques include the use of high solidity rotors that reduce the lift coefficients of individual blades, leading edge slots and leading edge slats. Active control techniques include steady and unsteady blowing, and dynamically deformable leading edge (DDLE) airfoils. Considerable amount of experimental and numerical data has been collected on the effectiveness of these concepts. One concept that has not received as much attention is the drooped-leading edge airfoil idea. It has been observed in wind tunnel studies and flight tests that drooped leading edge airfoils can have a milder dynamic stall, with a significantly milder load hysteresis. Drooped leading edge airfoils may not, however, be suitable at other conditions, e.g. in hover, or in transonic flow. Work needs to be done on the analysis and design of drooped leading edge airfoils for efficient operation in a variety of flight regimes (hover, dynamic stall, and transonic flow). One concept that is worthy of investigation is the dynamically drooping airfoil, where the leading edge shape is changed roughly once-per-rev to mitigate the dynamic stall.

Mourning Dove nesting habitat and nest success in Central Missouri

USGS Publications Warehouse

Drobney, R.D.; Schulz, J.H.; Sheriff, S.L.; Fuemmeler, W.J.

1998-01-01

Previous Mourning Dove (Zenaida macroura) nesting studies conducted in areas containing a mixture of edge and continuous habitats have focused on edge habitats. Consequently, little is known about the potential contribution of continuous habitats to dove production. In this study we evaluated the relative importance of these two extensive habitat types by monitoring the habitat use and nest success of 59 radio-marked doves during 1990-1991 in central Missouri. Of 83 nests initiated by our marked sample, most (81.9%) were located in edge habitats. Although continuous habitats were selected less as nest sites, the proportion of successful nests did not differ significantly from that in edge habitats. Our data indicate that continuous habitats should not be considered marginal nesting habitat. If the intensity of use and nest success that we observed are representative regionally or nationally, continuous habitats could contribute substantially to annual Mourning Dove production because of the high availability of these habitats throughout much of the Mourning Dove breeding range.

Comparison of routinely used intestinal biopsy forceps in dogs: an ex vivo histopathological approach.

PubMed

Dahan, J; Semin, M O; Monton, C; Amiriantz, S; Concordet, D; Raymond-Letron, I; Dossin, O

2017-03-01

To compare the quality of duodenal and ileal samples obtained with different biopsy forceps. Fifteen dogs were included in a prospective ex vivo study. After euthanasia, the duodenum and the ileum were sampled with four different forceps and evaluated according to a standardised scoring system. The biopsy forceps evaluated had alligator jaws or cups with smooth edge with or without a needle. The global quality of the biopsies was better in the ileum that in the duodenum regardless of the biopsy forceps. Biopsy forceps with smooth edge including a needle resulted in fewer artefacts than biopsy forceps with smooth edge but no needle in both sites and those with alligator jaws without a needle provided deeper biopsies than those with smooth edge without a needle only in the duodenum. There was no effect of the biopsy forceps type on the size of the biopsies. Our findings may aid in choosing the appropriate type of forceps for intestinal biopsy. © 2017 British Small Animal Veterinary Association.

Uranium XAFS analysis of kidney from rats exposed to uranium

PubMed Central

Kitahara, Keisuke; Numako, Chiya; Terada, Yasuko; Nitta, Kiyohumi; Homma-Takeda, Shino

2017-01-01

The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structure (µXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U L III-edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. µXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate. PMID:28244440

Uranium XAFS analysis of kidney from rats exposed to uranium.

PubMed

Kitahara, Keisuke; Numako, Chiya; Terada, Yasuko; Nitta, Kiyohumi; Shimada, Yoshiya; Homma-Takeda, Shino

2017-03-01

The kidney is the critical target of uranium exposure because uranium accumulates in the proximal tubules and causes tubular damage, but the chemical nature of uranium in kidney, such as its chemical status in the toxic target site, is poorly understood. Micro-X-ray absorption fine-structure (µXAFS) analysis was used to examine renal thin sections of rats exposed to uranyl acetate. The U L III -edge X-ray absorption near-edge structure spectra of bulk renal specimens obtained at various toxicological phases were similar to that of uranyl acetate: their edge position did not shift compared with that of uranyl acetate (17.175 keV) although the peak widths for some kidney specimens were slightly narrowed. µXAFS measurements of spots of concentrated uranium in the micro-regions of the proximal tubules showed that the edge jump slightly shifted to lower energy. The results suggest that most uranium accumulated in kidney was uranium (VI) but a portion might have been biotransformed in rats exposed to uranyl acetate.

Perception of Human-Derived Risk Influences Choice at Top of the Food Chain

PubMed Central

Cristescu, Bogdan; Stenhouse, Gordon B.; Boyce, Mark S.

2013-01-01

On human-used landscapes, animal behavior is a trade-off between maximizing fitness and minimizing human-derived risk. Understanding risk perception in wildlife can allow mitigation of anthropogenic risk, with benefits to long-term animal fitness. Areas where animals choose to rest should minimize risk from predators, which for large carnivores typically equate to humans. We hypothesize that high human activity leads to selection for habitat security, whereas low activity enables trading security for forage. We investigated selection of resting (bedding) sites by GPS radiocollared adult grizzly bears (n = 10) in a low density population on a multiple-use landscape in Canada. We compared security and foods at resting and random locations while accounting for land use, season, and time of day. On reclaimed mines with low human access, bears selected high horizontal cover far from trails, but did not avoid open (herbaceous) areas, resting primarily at night. In protected areas bears also bedded at night, in areas with berry shrubs and Hedysarum spp., with horizontal cover selected in the summer, during high human access. On public lands with substantial human recreation, bears bedded at day, selected resting sites with high horizontal cover in the summer and habitat edges, with bedding associated with herbaceous foods. These spatial and temporal patterns of selection suggest that bears perceive human-related risk differentially in relation to human activity level, season and time of day, and employ a security-food trade-off strategy. Although grizzly bears are presently not hunted in Alberta, their perceived risks associated with humans influence resting-site selection. PMID:24367549

Measurement of ground water velocity using Rhodamine WT dye near Sheffield, Illinois

USGS Publications Warehouse

Garklavs, George; Toler, L.G.

1985-01-01

Ground-water flow velocity was estimated in a tract of land adjacent to a low-level radioactive-waste disposal site near Sheffield, Illinois, by measuring the time-of-travel between two wells spaced 110 feet apart. Rhodamine WT dye was the principal tracer used in the test. The leading edge and peak concentrations of Rhodamine WT were well defined. A ground-water velocity of 6.9 feet per day (2,500 feet per year) was computed from the arrival time of the leading edge of the tracer cloud. (USGS)

Oblique along path toward structures at rear of parcel. Original ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Oblique along path toward structures at rear of parcel. Original skinny mosaic path along edge of structures was altered (delineation can be seen in concrete) path was widened with a newer mosaic to make access to the site safer. Structures (from right) edge of Round House (with "Spring Garden"), Pencil house, Shell House, School House, wood lattice is attached to chain-link fence along north (rear) property line. These structures were all damaged by the 1994 Northridge earthquake. Camera facing northeast. - Grandma Prisbrey's Bottle Village, 4595 Cochran Street, Simi Valley, Ventura County, CA

The doping sites in Eu2+-doped AIBIIPO4 phosphors and their consequence on the photoluminescence excitation spectra

NASA Astrophysics Data System (ADS)

Amer, M.; Boutinaud, P.

2018-02-01

The energy corresponding to the excitation edge in Eu2+-doped phosphate phosphors of the type AIBIIPO4 (AI = monovalent cation, BII = divalent cation) is calculated from the knowledge of two crystal-structure-related factors he(X(i)) and Fc(X(i)) which are connected respectively to the crystal field splitting (CFS) and the centroid energy (Ec) of the excited 4f65d1 electron configuration of Eu2+. The calculation is carried out for each cation site X(i) available for Eu2+ in 25 different compositions of AIBIIPO4 including NaZnPO4-Eu2+ for which the luminescence is firstly reported. Our results indicate (1) that is it possible to identify the nature of the cation site that contributes to the excitation edge of Eu2+ in AIBIIPO4 within an accuracy of±1000 cm-1 and (2) that the method can be used as a tool for the predictive design of AIBIIPO4 - Eu2+ phosphors applicable in solid state LED-based lighting.

Surface complexation model for multisite adsorption of copper(II) onto kaolinite

NASA Astrophysics Data System (ADS)

Peacock, Caroline L.; Sherman, David M.

2005-08-01

We measured the adsorption of Cu(II) onto kaolinite from pH 3-7 at constant ionic strength. EXAFS spectra show that Cu(II) adsorbs as (CuO 4H n) n-6 and binuclear (Cu 2O 6H n) n-8 inner-sphere complexes on variable-charge ≡AlOH sites and as Cu 2+ on ion exchangeable ≡X-H + sites. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed at least up to pH 6.5. Inner-sphere complexes are bound to the kaolinite surface by corner-sharing with two or three edge-sharing Al(O,OH) 6 polyhedra. Our interpretation of the EXAFS data are supported by ab initio (density functional theory) geometries of analog clusters simulating Cu complexes on the {110} and {010} crystal edges and at the ditrigonal cavity sites on the {001}. Having identified the bidentate (≡AlOH) 2Cu(OH) 20, tridentate (≡Al 3O(OH) 2)Cu 2(OH) 30 and ≡X-Cu 2+ surface complexes, the experimental copper(II) adsorption data can be fit to the reactions

Kinetic analysis of site-directed mutants of methionine synthase from Candida albicans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasannan, Priya; Suliman, Huda S.; Robertus, Jon D., E-mail: jrobertus@mail.utexas.edu

2009-05-15

Fungal methionine synthase catalyzes the transfer of a methyl group from 5-methyl-tetrahydrofolate to homocysteine to create methionine. The enzyme, called Met6p in fungi, is required for the growth of the pathogen Candida albicans, and is consequently a reasonable target for antifungal drug design. In order to understand the mechanism of this class of enzyme, we created a three-dimensional model of the C. albicans enzyme based on the known structure of the homologous enzyme from Arabidopsis thaliana. A fusion protein was created and shown to have enzyme activity similar to the wild-type Met6p. Fusion proteins containing mutations at eight key sitesmore » were expressed and assayed in this background. The D614 carboxylate appears to ion pair with the amino group of homocysteine and is essential for activity. Similarly, D504 appears to bind to the polar edge of the folate and is also required for activity. Other groups tested have lesser roles in substrate binding and catalysis.« less

Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte

DOE PAGES

Zhuang, Zhongbin; Giles, Stephen A.; Zheng, Jie; ...

2016-01-14

The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizesmore » the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Here, owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.« less

Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte

PubMed Central

Zhuang, Zhongbin; Giles, Stephen A.; Zheng, Jie; Jenness, Glen R.; Caratzoulas, Stavros; Vlachos, Dionisios G.; Yan, Yushan

2016-01-01

The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells. PMID:26762466

Active hydrogen evolution through lattice distortion in metallic MoTe2

NASA Astrophysics Data System (ADS)

Seok, Jinbong; Lee, Jun-Ho; Cho, Suyeon; Ji, Byungdo; Kim, Hyo Won; Kwon, Min; Kim, Dohyun; Kim, Young-Min; Oh, Sang Ho; Wng Kim, Sung; Lee, Young Hee; Son, Young-Woo; Yang, Heejun

2017-06-01

Engineering surface atoms of transition metal dichalcogenides (TMDs) is a promising way to design catalysts for efficient electrochemical reactions including the hydrogen evolution reaction (HER). However, materials processing based on TMDs, such as vacancy creation or edge exposure, for active HER, has resulted in insufficient atomic-precision lattice homogeneity and a lack of clear understanding of HER over 2D materials. Here, we report a durable and effective HER at atomically defined reaction sites in 2D layered semimetallic MoTe2 with intrinsic turnover frequency (TOF) of 0.14 s-1 at 0 mV overpotential, which cannot be explained by the traditional volcano plot analysis. Unlike former electrochemical catalysts, the rate-determining step of the HER on the semimetallic MoTe2, hydrogen adsorption, drives Peierls-type lattice distortion that, together with a surface charge density wave, unexpectedly enhances the HER. The active HER using unique 2D features of layered TMDs enables an optimal design of electrochemical catalysts and paves the way for a hydrogen economy.

Phosphorene Co-catalyst Advancing Highly Efficient Visible-Light Photocatalytic Hydrogen Production.

PubMed

Ran, Jingrun; Zhu, Bicheng; Qiao, Shi-Zhang

2017-08-21

Transitional metals are widely used as co-catalysts boosting photocatalytic H 2 production. However, metal-based co-catalysts suffer from high cost, limited abundance and detrimental environment impact. To date, metal-free co-catalyst is rarely reported. Here we for the first time utilized density functional calculations to guide the application of phosphorene as a high-efficiency metal-free co-catalyst for CdS, Zn 0.8 Cd 0.2 S or ZnS. Particularly, phosphorene modified CdS shows a high apparent quantum yield of 34.7 % at 420 nm. This outstanding activity arises from the strong electronic coupling between phosphorene and CdS, as well as the favorable band structure, high charge mobility and massive active sites of phosphorene, supported by computations and advanced characterizations, for example, synchrotron-based X-ray absorption near edge spectroscopy. This work brings new opportunities to prepare highly-active, cheap and green photocatalysts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-dimensional CuIn alloy nanowires as a robust and efficient electrocatalyst for selective CO2-to-CO conversion

NASA Astrophysics Data System (ADS)

Jang, Youn Jeong; Lee, Jaehyuk; Kim, Ju Hun; Lee, Byeong Jun; Lee, Jae Sung

2018-02-01

Electrical anodization of Cu foil produces one-dimensional Cu nanowires of high surface areas, which turns to CuIn alloy nanowires by indium electrodeposition replacing edge site Cu atoms. An electrochemical pre-activation forms a highly conformal amorphous In(OH)3 overlayer with oxygen vacancy on the CuIn alloy that facilitates CO2 adsorption to promote selective CO formation suppressing competing H2 adsorption. Thus the activated CuIn alloy nanowires catalyse electrochemical CO2 conversion to CO with high CO selectivity (>68.2%) and high current density (ca. -3.9 mAcm-2) at -0.6 VRHE, which represents the higher partial CO current density (ca. -2.66 mAcm-2) than that of previously reported CuIn alloy powders without nanostructuring. The performance remains stable for more than 15 h without significant degradation.

Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential

NASA Astrophysics Data System (ADS)

Kwon, Kideok D.; Newton, Aric G.

2016-10-01

The surfaces of clay minerals, which are abundant in atmospheric mineral dust, serve as an important medium to catalyze ice nucleation. The lateral edge surface of 2:1 clay minerals is postulated to be a potential site for ice nucleation. However, experimental investigations of the edge surface structure itself have been limited compared to the basal planes of clay minerals. Density functional theory (DFT) computational studies have provided insights into the pyrophyllite edge surface. Pyrophyllite is an ideal surrogate mineral for the edge surfaces of 2:1 clay minerals as it possesses no or little structural charge. Of the two most-common hydrated edge surfaces, the AC edge, (1 1 0) surface in the monoclinic polytype notation, is predicted to be more stable than the B edge, (0 1 0) surface. These stabilities, however, were determined based on the total energies calculated at 0 K and did not consider environmental effects such as temperature and humidity. In this study, atomistic thermodynamics based on periodic DFT electronic calculations was applied to examine the effects of environmental variables on the structure and thermodynamic stability of the common edge surfaces in equilibrium with bulk pyrophyllite and water vapor. We demonstrate that the temperature-dependent vibrational energy of sorbed water molecules at the edge surface is a significant component of the surface free energy and cannot be neglected when determining the surface stability of pyrophyllite. The surface free energies were calculated as a function of temperature from 240 to 600 K and water chemical potential corresponding to conditions from ultrahigh vacuum to the saturation vapor pressure of water. We show that at lower water chemical potentials (dry conditions), the AC and B edge surfaces possessed similar stabilities; at higher chemical potentials (humid conditions) the AC edge surface was more stable than the B edge surface. At high temperatures, both surfaces showed similar stabilities regardless of the water chemical potential. The equilibrium morphology of pyrophyllite crystals is also expected to be dependent on these two environmental variables. Surface defects may impact the surface reactivity. We discuss the thermodynamic stability of a possible Si cation vacancy defect which provides additional hydroxyl group on the surface.

Robust edge states in amorphous gyromagnetic photonic lattices

NASA Astrophysics Data System (ADS)

Mansha, Shampy; Chong, Y. D.

2017-09-01

We numerically study amorphous analogs of a two-dimensional photonic Chern insulator. The amorphous lattices consist of gyromagnetic rods that break time-reversal symmetry, with the lattice sites generated by a close-packing algorithm. The level of short-range order is adjustable, and there is no long-range order. The topologically nontrivial gaps of the photonic Chern insulator are found to persist into the amorphous regime, so long as there is sufficient short-range order. Strongly nonreciprocal robust transmission occurs via edge states, which are shown to propagate ballistically despite the absence of long-range order, and to be exponentially localized along the lattice edge. Interestingly, there is an enhancement of nonreciprocal transmission even at very low levels of short-range order, where there are no discernible spectral gaps.

A Semi-Automatic Method for Image Analysis of Edge Dynamics in Living Cells

PubMed Central

Huang, Lawrence; Helmke, Brian P.

2011-01-01

Spatial asymmetry of actin edge ruffling contributes to the process of cell polarization and directional migration, but mechanisms by which external cues control actin polymerization near cell edges remain unclear. We designed a quantitative image analysis strategy to measure the spatiotemporal distribution of actin edge ruffling. Time-lapse images of endothelial cells (ECs) expressing mRFP-actin were segmented using an active contour method. In intensity line profiles oriented normal to the cell edge, peak detection identified the angular distribution of polymerized actin within 1 µm of the cell edge, which was localized to lamellipodia and edge ruffles. Edge features associated with filopodia and peripheral stress fibers were removed. Circular statistical analysis enabled detection of cell polarity, indicated by a unimodal distribution of edge ruffles. To demonstrate the approach, we detected a rapid, nondirectional increase in edge ruffling in serum-stimulated ECs and a change in constitutive ruffling orientation in quiescent, nonpolarized ECs. Error analysis using simulated test images demonstrate robustness of the method to variations in image noise levels, edge ruffle arc length, and edge intensity gradient. These quantitative measurements of edge ruffling dynamics enable investigation at the cellular length scale of the underlying molecular mechanisms regulating actin assembly and cell polarization. PMID:21643526

Protection of fish spawning habitat for the conservation of warm temperate reef fish fisheries of shelf-edge reefs of Florida

USGS Publications Warehouse

Koenig, Christopher C.; Coleman, Felicia C.; Grimes, Churchill B.; Fitzhugh, Gary R.; Scanlon, Kathryn M.; Gledhill, Christopher T.; Grace, Mark

2000-01-01

We mapped and briefly describe the surficial geology of selected examples of shelfedge reefs (50–120 m deep) of the southeastern United States, which are apparently derived from ancient Pleistocene shorelines and are intermittently distributed throughout the region. These reefs are ecologically significant because they support a diverse array of fish and invertebrate species, and they are the only aggregation spawning sites of gag (Mycteroperca microlepis), scamp (M. phenax), and other economically important reef fish. Our studies on the east Florida shelf in the Experimental Oculina Research Reserve show that extensive damage to the habitat-structuring coral Oculina varicosa has occurred in the past, apparently from trawling and dredging activities of the 1970s and later. On damaged or destroyed Oculina habitat, reef-fish abundance and diversity are low, whereas on intact habitat, reef-fish diversity is relatively high compared to historical diversity on the same site. The abundance and biomass of the economically important reef fish was much higher in the past than it is now, and spawning aggregations of gag and scamp have been lost or greatly reduced in size. On the west Florida shelf, fishers have concentrated on shelf-edge habitats for over 100 yrs, but fishing intensity increased dramatically in the 1980s. Those reefs are characterized by low abundance of economically important species. The degree and extent of habitat damage there is unknown. We recommend marine fishery reserves to protect habitat and for use in experimentally examining the potential production of unfished communities.