WorldWideScience

Sample records for surface lattice oxygen

  1. Lattice dynamics in solid oxygen

    International Nuclear Information System (INIS)

    Kobashi, K.; Klein, M.L.; Chandrasekharan, V.

    1979-01-01

    Lattice dynamical calculations for the bulk α, β, and γ phases of solid O 2 and for the monolayer α and β phases have been made in the harmonic approximation. In the α and β phases, atom-atom 6-12 potentials are employed. In the γ phase, effective potentials are used between molecular centers and only the translational lattice vibrations are calculated. It is found that Laufer and Leroi's potential parameters give two k=O frequencies at 42.7 and 43.6 cm -1 in the bulk α-O 2 , and at 40.7 cm -1 for the degenerate k=0 modes in the β phase. The observed Raman lines for α-O 2 at 43 and 79 cm -1 , which are both known to exhibit isotope shifts, are thus tentatively assigned to an accidentally degenerate line and a two-phonon band, respectively, In view of the possible contribution from anharmonic effects, the agreement of the calculation with experiment (48-51 cm -1 ) in β-O 2 may be better than it seems. For the bulk γ-O 2 , a discrepancy is observed between the calculated elastic constants and those derived from Brillouin scattering experiments. This discrepancy may be due to the neglect of translation-rotation coupling. In the monolayer O 2 , Raman active modes at 28.3 and 40.6 cm -1 for the α phase, and 31.9 cm -1 for the β phase are predicted

  2. Orientation-Dependent Oxygen Evolution on RuO2 without Lattice Exchange

    DEFF Research Database (Denmark)

    Stoerzinger, Kelsey A.; Diaz-Morales, Oscar; Kolb, Manuel

    2017-01-01

    RuO2 catalysts exhibit record activities toward the oxygen evolution reaction (OER), which is crucial to enable efficient and sustainable energy storage. Here we examine the RuO2 OER kinetics on rutile (110), (100), (101), and (111) orientations, finding (100) the most active. We assess...... the potential involvement of lattice oxygen in the OER mechanism with online electrochemical mass spectrometry, which showed no evidence of oxygen exchange on these oriented facets in acidic or basic electrolytes. Similar results were obtained for polyoriented RuO2 films and particles, in contrast to previous...... work, suggesting lattice oxygen is not exchanged in catalyzing OER on crystalline RuO2 surfaces. This hypothesis is supported by the correlation of activity with the number of active Ru-sites calculated by density functional theory, where more active facets bind oxygen more weakly. This new...

  3. Electronic Origin and Kinetic Feasibility of the Lattice Oxygen Participation During the Oxygen Evolution Reaction on Perovskites.

    Science.gov (United States)

    Yoo, Jong Suk; Liu, Yusu; Rong, Xi; Kolpak, Alexie M

    2018-04-05

    Density functional theory is employed to investigate the electronic origin and feasibility of surface lattice oxygen (O surf ) participation during the oxygen evolution reaction (OER) on perovskites. O surf participation occurs via the nonelectrochemical pathway in which adsorbed atomic oxygen (O*) diffuses from the transition-metal site to the oxygen site, and then O surf shifts out of the surface plane to react with O* to form O surf -O* and a surface oxygen vacancy. The different thermodynamic driving forces of O surf participation on LaMO 3-δ (M = Ni, Co, and Cu) are explained by the changes in the oxidation state of the transition-metal site throughout the reaction. We show that O surf participation on LaNiO 3 cannot be hindered by O surf protonation in the OER potential range. By including the coverage effect and utilizing the implicit solvent model, we finally show that lattice oxygen mechanism is more feasible than the conventional mechanism for OER on LaNiO 3 .

  4. Multiplexed infrared plasmonic surface lattice resonances

    Science.gov (United States)

    Gutha, Rithvik R.; Sadeghi, Seyed M.; Sharp, Christina; Wing, Waylin J.

    2018-01-01

    We demonstrate that arrays of flat gold nanodisks with rectangular lattices can support a tunable hybrid frequency gap formed by the surface lattice resonances in the substrate ((+1, 0)sub) and the superstrate ((-1, 0)sup). For a certain polarization, rotation of the arrays reduces this gap, forming a band crossing (degenerate state) wherein both surface lattice resonances happen around a single wavelength (˜1300 nm). This highlights a situation wherein hybridization of the Rayleigh anomaly with localized surface plasmon resonances with different multipolar natures happens around the same wavelength. We demonstrate that for a different polarization of the incident light the arrays support the formation of a photonic-plasmonic state at about 1650 nm. Our results show that as the projection of the wave vector of the incident light on the planes of the nanodisk arrays increases, within a given wavelength range, the (+1, 0) mode of this state becomes amplified. Under this condition, this mode can undergo a significant blue shift without broadening, while its amplitude increases.

  5. Kählerian K3 surfaces and Niemeier lattices. I

    International Nuclear Information System (INIS)

    Nikulin, V V

    2013-01-01

    Using the results obtained in [1], Remark 1.14.7, we clarify the relation between Kählerian K3 surfaces and Niemeier lattices. We emphasize that all 24 Niemeier lattices are important in the description of K3 surfaces, not only the one related to the Mathieu group

  6. Self-avoiding and planar random surfaces on the lattice

    International Nuclear Information System (INIS)

    Durhuus, B.; Froehlich, J.

    1983-01-01

    We study models of self-avoiding (SARS) and of planar (PRS) random surfaces on a (hyper-) cubic lattice. If Nsub(γ)(A) is the number of such surfaces with given boundary γ and area A, then Nsub(γ)(A)=exp(β 0 A+o(A)), where β 0 is independent of γ. We prove that, for β>β 0 , the string tension is finite for the SARS model and strictly positive for the PRS model and that in both models the correlation length (inverse mass) is positive and finite. We discuss the possibility of the existence of a critical point and of a roughening transition. Estimates on intersection proabilities for random surfaces and connections with lattice gauge theories are sketched. (orig.)

  7. Interaction of oxygen with zirconia surface

    International Nuclear Information System (INIS)

    Ivankiv, L.I.; Ketsman, I.V.

    1999-01-01

    The influence of surface heat treatment, electron (50-800) eV irradiation and UV (180-300) nM illumination of adsorption system on the state of oxygen adsorbed on zirconia surface have been investigated. On the basis of experimental results obtained by investigation of photon emission accompanying oxygen adsorption (AL) and TPD data existence of adsorption sites on the surface is suggested on which irreversible dissociative adsorption of oxygen occurs. These very sites are associated with emission processes Conclusion is made that the only type of adsorption sites connected with anion vacancy is present on zirconia surface and this is its charge state that determines the state of adsorbed oxygen. One of the important mechanisms by which the electron and UV photon excitation affects the adsorption interaction is the change of the charge state of the adsorption site

  8. Surface-layer lattices as patterning element for multimeric extremozymes.

    Science.gov (United States)

    Ferner-Ortner-Bleckmann, Judith; Gelbmann, Nicola; Tesarz, Manfred; Egelseer, Eva M; Sleytr, Uwe B

    2013-11-25

    A promising new approach for the production of biocatalysts comprises the use of surface-layer (S-layer) lattices that present functional multimeric enzymes on their surface, thereby guaranteeing most accurate spatial distribution and orientation, as well as maximal effectiveness and stability of these enzymes. For proof of concept, a tetrameric and a trimeric extremozyme are chosen for the construction of S-layer/extremozyme fusion proteins. By using a flexible peptide linker, either one monomer of the tetrameric xylose isomerase XylA from the thermophilic Thermoanaerobacterium strain JW/SL-YS 489 or, in another approach, one monomer of the trimeric carbonic anhydrase from the methanogenic archaeon Methanosarcina thermophila are genetically linked to one monomer of the S-layer protein SbpA of Lysinibacillus sphaericus CCM 2177. After isolation and purification, the self-assembly properties of both S-layer fusion proteins as well as the specific activity of the fused enzymes are confirmed, thus indicating that the S-layer protein moiety does not influence the nature of the multimeric enzymes and vice versa. By recrystallization of the S-layer/extremozyme fusion proteins on solid supports, the active enzyme multimers are exposed on the surface of the square S-layer lattice with 13.1 nm spacing. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Simulating condensation on microstructured surfaces using Lattice Boltzmann Method

    Science.gov (United States)

    Alexeev, Alexander; Vasyliv, Yaroslav

    2017-11-01

    We simulate a single component fluid condensing on 2D structured surfaces with different wettability. To simulate the two phase fluid, we use the athermal Lattice Boltzmann Method (LBM) driven by a pseudopotential force. The pseudopotential force results in a non-ideal equation of state (EOS) which permits liquid-vapor phase change. To account for thermal effects, the athermal LBM is coupled to a finite volume discretization of the temperature evolution equation obtained using a thermal energy rate balance for the specific internal energy. We use the developed model to probe the effect of surface structure and surface wettability on the condensation rate in order to identify microstructure topographies promoting condensation. Financial support is acknowledged from Kimberly-Clark.

  10. Disordering of two-dimensional oxyxgen lattices on Mo(011) initiated by electron transitions in oxygen and molybdenum atoms

    International Nuclear Information System (INIS)

    Zasimovich, I.N.; Klimenko, E.V.; Naumovets, A.G.

    1988-01-01

    The first observation of electron-induced disordering (EID) of the submonolayer film of heavier adsorbate-oxygen is reported. The investigation of energy dependence of the effective cross section of this process, which points to the fact that EID can be initiated by the electron transitions not only in adatoms, but in the substrate, is also presented. When irradiating by electrons, the sample surface cooled up to 77 K, intensity of diffraction reflects of the (2x2) and (6x2) structures decreases rather quickly, but the reflects of more dense (6x1) lattice do not practically attenuate. The conclusions are made that the knowledge of physical factors, determining the probability of radiation defect formation in an adfilm, gives the possibility either to avoid disordering, if it is undesirable, or to use it to control the surface properties

  11. Late Archean Surface Ocean Oxygenation (Invited)

    Science.gov (United States)

    Kendall, B.; Reinhard, C.; Lyons, T. W.; Kaufman, A. J.; Anbar, A. D.

    2009-12-01

    Oxygenic photosynthesis must have evolved by 2.45-2.32 Ga, when atmospheric oxygen abundances first rose above 0.001% present atmospheric level (Great Oxidation Event; GOE). Biomarker evidence for a time lag between the evolution of cyanobacterial oxygenic photosynthesis and the GOE continues to be debated. Geochemical signatures from sedimentary rocks (redox-sensitive trace metal abundances, sedimentary Fe geochemistry, and S isotopes) represent an alternative tool for tracing the history of Earth surface oxygenation. Integrated high-resolution chemostratigraphic profiles through the 2.5 Ga Mt. McRae Shale (Pilbara Craton, Western Australia) suggest a ‘whiff’ of oxygen in the surface environment at least 50 M.y. prior to the GOE. However, the geochemical data from the Mt. McRae Shale does not uniquely constrain the presence or extent of Late Archean ocean oxygenation. Here, we present high-resolution chemostratigraphic profiles from 2.6-2.5 Ga black shales (upper Campbellrand Subgroup, Kaapvaal Craton, South Africa) that provide the earliest direct evidence for an oxygenated ocean water column. On the slope beneath the Campbellrand - Malmani carbonate platform (Nauga Formation), a mildly oxygenated water column (highly reactive iron to total iron ratios [FeHR/FeT] ≤ 0.4) was underlain by oxidizing sediments (low Re and Mo abundances) or mildly reducing sediments (high Re but low Mo abundances). After drowning of the carbonate platform (Klein Naute Formation), the local bottom waters became anoxic (FeHR/FeT > 0.4) and intermittently sulphidic (pyrite iron to highly reactive iron ratios [FePY/FeHR] > 0.8), conducive to enrichment of both Re and Mo in sediments, followed by anoxic and Fe2+-rich (ferruginous) conditions (high FeT, FePY/FeHR near 0). Widespread surface ocean oxygenation is suggested by Re enrichment in the broadly correlative Klein Naute Formation and Mt. McRae Shale, deposited ~1000 km apart in the Griqualand West and Hamersley basins

  12. Axisymmetric Lattice Boltzmann Model of Droplet Impact on Solid Surfaces

    Science.gov (United States)

    Dalgamoni, Hussein; Yong, Xin

    2017-11-01

    Droplet impact is a ubiquitous fluid phenomena encountered in scientific and engineering applications such as ink-jet printing, coating, electronics manufacturing, and many others. It is of great technological importance to understand the detailed dynamics of drop impact on various surfaces. The lattice Boltzmann method (LBM) emerges as an efficient method for modeling complex fluid systems involving rapidly evolving fluid-fluid and fluid-solid interfaces with complex geometries. In this work, we model droplet impact on flat solid substrates with well-defined wetting behavior using a two-phase axisymmetric LBM with high density and viscosity contrasts. We extend the two-dimensional Lee and Liu model to capture axisymmetric effect in the normal impact. First we compare the 2D axisymmetric results with the 2D and 3D results reported by Lee and Liu to probe the effect of axisymmetric terms. Then, we explore the effects of Weber number, Ohnesorge number, and droplet-surface equilibrium contact angle on the impact. The dynamic contact angle and spreading factor of the droplet during impact are investigated to qualitatively characterize the impact dynamics.

  13. Origami lattices with free-form surface ornaments

    NARCIS (Netherlands)

    Janbaz, S.; Noordzij, N.; Widyaratih (student), Dwisetya Safirna; Hagen, C.W.; Fratila-Apachitei, E.L.; Zadpoor, A.A.

    2017-01-01

    Lattice structures are used in the design of metamaterials to achieve unusual physical, mechanical, or biological properties. The properties of such metamaterials result from the topology of the lattice structures, which are usually three-dimensionally (3D) printed. To incorporate advanced

  14. The determination of oxygen in molybdenum and tungsten monocrystals taking into account the surface oxygen contribution

    International Nuclear Information System (INIS)

    Aleksandrov, V.D.; Egiazarov, B.G.; Polyakova, I.S.; Sel'dyakov, Yu.P.; Chernyavskij, V.T.

    1977-01-01

    The method has been developed for determining oxygen content in molybdenum and tungsten usign the neutron activation analysis. The sensitivity is 1.6X10 -5 and 1.3x10 -3 wt.% for molybdenum and tungsten, respectively. The density of oxygen distribution in surface layers has been experimentally evaluated. It is shown that the oxygen presence in a surface layer of molybdenum and tungsten does not impede oxygen determination in the bulk of the sample, when the oxygen content is >5x10 -5 wt.%. If oxygen content is -3 wt.%, the presence of oxygen in the surface layer should be taken into account

  15. Sulfatide Preserves Insulin Crystals Not by Being Integrated in the Lattice but by Stabilizing Their Surface

    DEFF Research Database (Denmark)

    Buschard, Karsten; Bracey, Austin W.; McElroy, Daniel L.

    2016-01-01

    of sulfatide does not reveal ordered occupancy representing sulfatide in the crystal lattice, suggesting that sulfatide does not permeate the crystal lattice but exerts its stabilizing effect by alternative interactions such as on the external surface of insulin crystals. Conclusions. Sulfatide is known...

  16. The surface chemistry of metal-oxygen interactions

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Baroni, Stefano

    1997-01-01

    We report on a computational study of the clean and oxygen-covered Rh(110) surface, based on density-functional theory within the local-density approximation. We have used plane-wave basis sets and Vanderbilt ultra-soft pseudopotentials. For the clean surface, we present results for the equilibrium...... structure, surface energy and surface stress of the unreconstructed and (1 x 2) reconstructed structures. For the oxygen-covered surface we have performed a geometry optimization at 0.5, 1, and 2 monolayer oxygen coverages, and we present results for the equilibrium configurations, workfunctions and oxygen...

  17. On Mordell-Weil lattices for non-hyperelliptic fibrations on surfaces with zero geometric genus and irregularity

    International Nuclear Information System (INIS)

    Khac, V Nguyen; Saito, M.-H.

    2002-01-01

    We study Mordell-Weil lattices for non-hyperelliptic fibrations on surfaces with zero geometric genus and irregularity. We prove theorems on the structure and uniqueness of such lattices in the maximal case

  18. Surface deformation caused by the Abrikosov vortex lattice

    Czech Academy of Sciences Publication Activity Database

    Lipavský, Pavel; Morawetz, K.; Koláček, Jan; Brandt, E. H.

    2008-01-01

    Roč. 77, č. 18 (2008), 184509/1-184509/7 ISSN 1098-0121 R&D Projects: GA ČR GA202/08/0326; GA AV ČR IAA100100712 Grant - others:GA ČR(CZ) GA202/07/0597 Institutional research plan: CEZ:AV0Z10100521 Keywords : superconductivity * magneto-elastic effect * vortex lattice Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.322, year: 2008

  19. Two-dimensional lattice model for the surface states of topological insulators

    Science.gov (United States)

    Zhou, Yan-Feng; Jiang, Hua; Xie, X. C.; Sun, Qing-Feng

    2017-06-01

    The surface states in three-dimensional (3D) topological insulators can be described by a two-dimensional (2D) continuous Dirac Hamiltonian. However, there exists the fermion doubling problem when putting the continuous 2D Dirac equation into a lattice model. In this paper, we introduce a Wilson term with a zero bare mass into the 2D lattice model to overcome the difficulty. By comparing with a 3D Hamiltonian, we show that the modified 2D lattice model can faithfully describe the low-energy electrical and transport properties of surface states of 3D topological insulators. So this 2D lattice model provides a simple and cheap way to numerically simulate the surface states of 3D topological-insulator nanostructures. Based on the 2D lattice model, we also establish the wormhole effect in a topological-insulator nanowire by a magnetic field along the wire and show the surface states being robust against disorder. The proposed 2D lattice model can be extensively applied to study the various properties and effects, such as the transport properties, Hall effect, universal conductance fluctuations, localization effect, etc. So, it paves a way to study the surface states of the 3D topological insulators.

  20. Thermochemical Properties of the Lattice Oxygen in W,Mn-Containing Mixed Oxide Catalysts for the Oxidative Coupling of Methane

    Science.gov (United States)

    Lomonosov, V. I.; Gordienko, Yu. A.; Sinev, M. Yu.; Rogov, V. A.; Sadykov, V. A.

    2018-03-01

    Mixed NaWMn/SiO2 oxide, samples containing individual components (Na, W, Mn) and their double combinations (Na-W, Na-Mn, W-Mn) supported on silica were studied by temperature programmed reduction (TPR) and desorption (TPD), and heat flow calorimetry during their reoxidation with molecular oxygen in pulse mode. The NaWMn/SiO2 mixed oxide was shown to contain two different types of reactive lattice oxygen. The weakly-bonded oxygen can be reversibly released from the oxide in a flow of inert gas in the temperature range of 575‒900°C, while the strongly-bonded oxygen can be removed during the reduction of the sample with hydrogen at 700-900°C. The measured thermal effect of oxygen consumption for these two oxygen forms are 185 and 350 kJ/mol, respectively. The amount of oxygen removed at reduction ( 443 μmol/g) considerably exceeded the amount desorbed in an inert gas flow ( 56 μmol/g). The obtained results suggest that the reversible oxygen desorption is due to the redox process in which manganese ions are involved, while during the temperature programmed reduction, mainly oxygen bonded with tungsten is removed.

  1. Surface solitons of four-wave mixing in an electromagnetically induced lattice

    International Nuclear Information System (INIS)

    Zhang, Yanpeng; Yuan, Chenzhi; Zhang, Yiqi; Zheng, Huaibin; Chen, Haixia; Li, Changbiao; Wang, Zhiguo; Xiao, Min

    2013-01-01

    By creating lattice states with two-dimensional spatial periodic atomic coherence, we report an experimental demonstration of generating two-dimensional surface solitons of a four-wave mixing signal in an electromagnetically induced lattice composed of two electromagnetically induced gratings with different orientations in an atomic medium, each of which can support a one-dimensional surface soliton. The surface solitons can be well controlled by different experimental parameters, such as probe frequency, pump power, and beam incident angles, and can be affected by coherent induced defect states. (letter)

  2. Free surface entropic lattice Boltzmann simulations of film condensation on vertical hydrophilic plates

    DEFF Research Database (Denmark)

    Hygum, Morten Arnfeldt; Karlin, Iliya; Popok, Vladimir

    2015-01-01

    A model for vapor condensation on vertical hydrophilic surfaces is developed using the entropic lattice Boltzmann method extended with a free surface formulation of the evaporation–condensation problem. The model is validated with the steady liquid film formation on a flat vertical wall. It is sh...

  3. Boundary Slip and Surface Interaction: A Lattice Boltzmann Simulation

    International Nuclear Information System (INIS)

    Yan-Yan, Chen; Hua-Bing, Li; Hou-Hui, Yi

    2008-01-01

    The factors affecting slip length in Couette geometry flows are analysed by means of a two-phase mesoscopic lattice Boltzmann model including non-ideal fluid-fluid and fluid-wall interactions. The main factors influencing the boundary slip are the strength of interactions between fluid-fluid and fluid-wall particles. Other factors, such as fluid viscosity, bulk pressure may also change the slip length. We find that boundary slip only occurs under a certain density (bulk pressure). If the density is large enough, the slip length will tend to zero. In our simulations, a low density layer near the wall does not need to be postulated a priori but emerges naturally from the underlying non-ideal mesoscopic dynamics. It is the low density layer that induces the boundary slip. The results may be helpful to understand recent experimental observations on the slippage of micro flows

  4. Effect of surface strain on oxygen adsorption on Zr (0001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xing [Univ. of Wisconsin-Madison, Madison, WI (United States). Dept. of Engineering Physics; Khafizov, Marat [Idaho National Laboratory (INL), Idaho Falls, ID (United States); Szlufarska, Izabela [Univ. of Wisconsin-Madison, Madison, WI (United States). Dept. of Engineering Physics; Univ. of Wisconsin-Madison, Madison, WI (United States). Dept. of Materials Science and Engineering

    2014-02-01

    The effect of surface strain on oxygen adsorption on Zr (0 0 0 1) surface is investigated by density functional theory (DFT) calculations. It is demonstrated that both surface strain and interactions between oxygen adsorbates influence the adsorption process. Oxygen binding to zirconium becomes stronger as the strain changes from compressive to tensile. When oxygen coverage is low and the oxygen interactions are negligible, surface face-centered cubic sites are the most stable for O binding. At high coverage and under compression, octahedral sites between second and third Zr layers become most favorable because the interactions between adsorbates are weakened by positive charge screening. Calculations with both single-layer adsorption model and multiple-layer adsorption model demonstrate that compressive strain at the Zr/oxide interface will provide a thermodynamic driving force for oxygen to incorporate from the surface into the bulk of Zr, while binding oxygen to the Zr surface will be easier when tensile strain is applied.

  5. Operator formalism for self-dual lattice compactification on Riemann surfaces

    International Nuclear Information System (INIS)

    Koh, I.G.; Shin, H.J.

    1988-01-01

    The authors apply the universal Grassmannian manifold approach to the heterotic string theory compactified on self-dual lattice. The generating functions on higher genus Riemann surfaces are explicitly constructed starting from that of non-chiral bosonic theory and adding the contributions of instanton sectors. The modular transformation property and its equivalent fermionic formulation of the generating function are also discussed

  6. The dissociation and recombination rates of CH4through the Ni(111) surface: The effect of lattice motion.

    Science.gov (United States)

    Wang, Wenji; Zhao, Yi

    2017-07-28

    Methane dissociation is a prototypical system for the study of surface reaction dynamics. The dissociation and recombination rates of CH 4 through the Ni(111) surface are calculated by using the quantum instanton method with an analytical potential energy surface. The Ni(111) lattice is treated rigidly, classically, and quantum mechanically so as to reveal the effect of lattice motion. The results demonstrate that it is the lateral displacements rather than the upward and downward movements of the surface nickel atoms that affect the rates a lot. Compared with the rigid lattice, the classical relaxation of the lattice can increase the rates by lowering the free energy barriers. For instance, at 300 K, the dissociation and recombination rates with the classical lattice exceed the ones with the rigid lattice by 6 and 10 orders of magnitude, respectively. Compared with the classical lattice, the quantum delocalization rather than the zero-point energy of the Ni atoms further enhances the rates by widening the reaction path. For instance, the dissociation rate with the quantum lattice is about 10 times larger than that with the classical lattice at 300 K. On the rigid lattice, due to the zero-point energy difference between CH 4 and CD 4 , the kinetic isotope effects are larger than 1 for the dissociation process, while they are smaller than 1 for the recombination process. The increasing kinetic isotope effect with decreasing temperature demonstrates that the quantum tunneling effect is remarkable for the dissociation process.

  7. The surface morphology of retinal breaks and lattice retinal degeneration. A scanning electron microscopic study.

    Science.gov (United States)

    Robinson, M R; Streeten, B W

    1986-02-01

    In 14 of 110 eye bank eyes, lesions characteristic of peripheral retinal surface pathology were examined by scanning electron microscopy (SEM). These included operculated and flap tears, trophic round holes, lattice degeneration with holes, and paravascular retinal "pitting" degeneration. By SEM, the edges of the retinal breaks were covered by smooth cellular membranes, merging peripherally with a meshwork of vitreous fibrils. The membrane cells had poorly defined borders, a pitted surface, and variable numbers of microvilli consistent with glia. Lattice surfaces and foci of paravascular retinal degeneration were covered by similar membrane, but showed characteristic differences. It appears that breaks in the internal limiting membrane always stimulate proliferation of preretinal glial membranes. Similar cellular morphology of the membranes associated with breaks is consistent with a common cell of origin. Limited proliferation of these membranes suggests that surface gliosis is normally inhibited when the cells contact either intact basement membrane or vitreous.

  8. Extending the basic function of lattice oxygen in lepidocrocite titanate - The conversion of intercalated fatty acid to liquid hydrocarbon fuels

    Science.gov (United States)

    Maluangnont, Tosapol; Arsa, Pornanan; Sooknoi, Tawan

    2017-12-01

    We report herein the basicity of the external and internal lattice oxygen (OL) in lepidocrocite titanates with respect to CO2 and palmitic acid, respectively. Several compositions have been tested with different types of the metal M aliovalently (co)substituted for Ti, K0.8[MyTi2-y]O4 (M = Li, Mg, Fe, Co, Ni, Cu, Zn, Cu/Ni and Cu/Zn). The low CO2 desorption peak temperature (70-100 °C) suggests that the external OL sites are weakly basic similar to TiO2. However, the internal OL sites are sufficiently basic to deprotonate palmitic acid, forming the intercalated potassium palmitate at the interlayer spaces. The latter serves as a two-dimensional (2D) molecular reactor for the production of liquid hydrocarbon fuels via deoxygenation under atmospheric N2. A relationship has been observed between the yield of the liquid products vs the partial charge of the lattice oxygen (δO). Since the deoxygenation pathway is highly dependent on the metal substitution, the redox-active sites might also play some roles. The co-substituted K0.8[Cu0.2Ni0.2]Ti1.6O4 produced 68.0% yield of the liquid products, with 51% saturated and 15% unsaturated C15 hydrocarbons at 350 °C.

  9. Formation of oxygen complexes in controlled atmosphere at surface ...

    Indian Academy of Sciences (India)

    The effects of boron and phosphorus incorporation in phenolic resin precursor to the oxidation resistance of glassy carbon have been studied. In order to reveal the nature and composition of the oxygen complexes formed at the surface of doped glassy carbon, under controlled atmosphere, the surface of the samples was ...

  10. Formation of oxygen complexes in controlled atmosphere at surface ...

    Indian Academy of Sciences (India)

    Abstract. The effects of boron and phosphorus incorporation in phenolic resin precursor to the oxidation resistance of glassy carbon have been studied. In order to reveal the nature and composition of the oxygen complexes formed at the surface of doped glassy carbon, under controlled atmosphere, the surface of the ...

  11. Oxygen surface exchange and oxidative dehydrogenation on oxide ion conductors

    NARCIS (Netherlands)

    Song, C.

    2012-01-01

    The research described in this thesis mainly aims at investigation of the rate of oxygen exchange at the surface of oxide ion conductors. The introduction is given in Chapter 1. A fast and simple method, referred to as pulse 18O-16O isotopic exchange (PIE), for measurement of the rate of surface

  12. Universality in Oxygen Evolution Electrocatalysis on Oxide Surfaces

    DEFF Research Database (Denmark)

    Man, Isabela Costinela; Su, Hai-Yan; Vallejo, Federico Calle

    2011-01-01

    Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated by applying standard density functional theory in combination with the c......Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated by applying standard density functional theory in combination...... that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the oxygen evolution activity, which suggests a fundamental limitation on the maximum oxygen evolution activity of planar oxide catalysts....

  13. Interaction of hydrogen and oxygen with bulk defects and surfaces of metals

    International Nuclear Information System (INIS)

    Besenbacher, F.

    1994-05-01

    The thesis deals with the interaction of hydrogen with defects in metals and the interaction of hydrogen and oxygen with metal surfaces studied by ion-beam techniques and scanning tunneling microscopy (STM), respectively. The first part of the thesis discusses the interaction of hydrogen with simple defects in transition metals. The trap-binding enthalpies and the lattice location of hydrogen trapped to vacancies have been determined, and an extremely simple and versatile picture of the hydrogen-metal interaction has evolved, in which the trap strength is mainly determined by the local electron density. Any dilution of the lattice will lead to a trap, vacancies and voids being the strongest trap. It is found that hydrogen trapped to vacancies in fcc metals is quantum-mechanically delocalized, and the excitation energies for the hydrogen in the vacancy potential are a few MeV only. The interaction of hydrogen with metal surfaces is studied by the transmission channeling (TC) technique. It is found that hydrogen chemisorbs in the highest-coordinated sites on the surfaces, and that there is a direct relationship between the hydrogen-metal bond length and the coordination number for the hydrogen. In the final part of the thesis the dynamics of the chemisorption process for oxygen and hydrogen on metal surfaces is studied by STM, a fascinating and powerful technique for exploring the atomic-scale realm of surfaces. It is found that there is a strong coupling between the chemisorption process and the distortion of the metal surface. The adsorbates induce a surface reconstruction, i.e. metal-metal bond breaks and metal-adsorbate bounds form. Whereas hydrogen interacts weakly with the metals and induces reconstructions where only nnn metals bonds are broken, oxygen interacts strongly with the metal, and the driving force for the O-induced reconstructions appears to be the formation of low-coordinated metal-O rows, formed by breaking of nn metal bonds. Finally it is shown

  14. Density-waves instability and a skyrmion lattice on the surface of strong topological insulators

    Science.gov (United States)

    Baum, Yuval; Stern, Ady

    2012-11-01

    In this work we analyze the instability conditions for spin-density-wave (SDW) formation on the surface of strong topological insulators. We find that for a certain range of Fermi energies and strength of interactions the SDW state is favored compared to the unmagnetized and the uniform-magnetization states. We also find that the SDWs are of spiral nature and, for a certain range of parameters, a Skyrmion lattice may form on the surface. We show that this phase may have a nontrivial Chern number even in the absence of an external magnetic field.

  15. Sulfatide Preserves Insulin Crystals Not by Being Integrated in the Lattice but by Stabilizing Their Surface

    Directory of Open Access Journals (Sweden)

    Karsten Buschard

    2016-01-01

    Full Text Available Background. Sulfatide is known to chaperone insulin crystallization within the pancreatic beta cell, but it is not known if this results from sulfatide being integrated inside the crystal structure or by binding the surface of the crystal. With this study, we aimed to characterize the molecular mechanisms underlying the integral role for sulfatide in stabilizing insulin crystals prior to exocytosis. Methods. We cocrystallized human insulin in the presence of sulfatide and solved the structure by molecular replacement. Results. The crystal structure of insulin crystallized in the presence of sulfatide does not reveal ordered occupancy representing sulfatide in the crystal lattice, suggesting that sulfatide does not permeate the crystal lattice but exerts its stabilizing effect by alternative interactions such as on the external surface of insulin crystals. Conclusions. Sulfatide is known to stabilize insulin crystals, and we demonstrate here that in beta cells sulfatide is likely coating insulin crystals. However, there is no evidence for sulfatide to be built into the crystal lattice.

  16. Sulfatide Preserves Insulin Crystals Not by Being Integrated in the Lattice but by Stabilizing Their Surface

    Science.gov (United States)

    Buschard, Karsten; Bracey, Austin W.; McElroy, Daniel L.; Magis, Andrew T.; Osterbye, Thomas; Atkinson, Mark A.; Bailey, Kate M.; Posgai, Amanda L.; Ostrov, David A.

    2016-01-01

    Background. Sulfatide is known to chaperone insulin crystallization within the pancreatic beta cell, but it is not known if this results from sulfatide being integrated inside the crystal structure or by binding the surface of the crystal. With this study, we aimed to characterize the molecular mechanisms underlying the integral role for sulfatide in stabilizing insulin crystals prior to exocytosis. Methods. We cocrystallized human insulin in the presence of sulfatide and solved the structure by molecular replacement. Results. The crystal structure of insulin crystallized in the presence of sulfatide does not reveal ordered occupancy representing sulfatide in the crystal lattice, suggesting that sulfatide does not permeate the crystal lattice but exerts its stabilizing effect by alternative interactions such as on the external surface of insulin crystals. Conclusions. Sulfatide is known to stabilize insulin crystals, and we demonstrate here that in beta cells sulfatide is likely coating insulin crystals. However, there is no evidence for sulfatide to be built into the crystal lattice. PMID:26981544

  17. Anatomy of topological surface states: Exact solutions from destructive interference on frustrated lattices

    Science.gov (United States)

    Kunst, Flore K.; Trescher, Maximilian; Bergholtz, Emil J.

    2017-08-01

    The hallmark of topological phases is their robust boundary signature whose intriguing properties—such as the one-way transport on the chiral edge of a Chern insulator and the sudden disappearance of surface states forming open Fermi arcs on the surfaces of Weyl semimetals—are impossible to realize on the surface alone. Yet, despite the glaring simplicity of noninteracting topological bulk Hamiltonians and their concomitant energy spectrum, the detailed study of the corresponding surface states has essentially been restricted to numerical simulation. In this work, however, we show that exact analytical solutions of both topological and trivial surface states can be obtained for generic tight-binding models on a large class of geometrically frustrated lattices in any dimension without the need for fine-tuning of hopping amplitudes. Our solutions derive from local constraints tantamount to destructive interference between neighboring layer lattices perpendicular to the surface and provide microscopic insights into the structure of the surface states that enable analytical calculation of many desired properties including correlation functions, surface dispersion, Berry curvature, and the system size dependent gap closing, which necessarily occurs when the spatial localization switches surface. This further provides a deepened understanding of the bulk-boundary correspondence. We illustrate our general findings on a large number of examples in two and three spatial dimensions. Notably, we derive exact chiral Chern insulator edge states on the spin-orbit-coupled kagome lattice, and Fermi arcs relevant for recently synthesized slabs of pyrochlore-based Eu2Ir2O7 and Nd2Ir2O7 , which realize an all-in-all-out spin configuration, as well as for spin-ice-like two-in-two-out and one-in-three-out configurations, which are both relevant for Pr2Ir2O7 . Remarkably, each of the pyrochlore examples exhibit clearly resolved Fermi arcs although only the one

  18. Chemical Recognition of Active Oxygen Species on the Surface of Oxygen Evolution Reaction Electrocatalysts.

    Science.gov (United States)

    Yang, Chunzhen; Fontaine, Olivier; Tarascon, Jean-Marie; Grimaud, Alexis

    2017-07-17

    Owing to the transient nature of the intermediates formed during the oxygen evolution reaction (OER) on the surface of transition metal oxides, their nature remains largely elusive by the means of simple techniques. The use of chemical probes is proposed, which, owing to their specific affinities towards different oxygen species, unravel the role played by these species on the OER mechanism. For that, tetraalkylammonium (TAA) cations, previously known for their surfactant properties, are introduced, which interact with the active oxygen sites and modify the hydrogen bond network on the surface of OER catalysts. Combining chemical probes with isotopic and pH-dependent measurements, it is further demonstrated that the introduction of iron into amorphous Ni oxyhydroxide films used as model catalysts deeply modifies the proton exchange properties, and therefore the OER mechanism and activity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Late Quaternary changes in surface productivity and oxygen ...

    Indian Academy of Sciences (India)

    Changes in the abundance of selected planktic foraminiferal species and some sedimentological parameters at ODP site 728A were examined to understand the fluctuations in the surface productivity and deep sea oxygenation in the NW Arabian Sea during last ∼540 kyr. The increased relative abundances of high fertility ...

  20. Oxygen surface exchange kinetics of erbia-stabilized bismuth oxide

    NARCIS (Netherlands)

    Yoo, C.-Y.; Boukamp, Bernard A.; Bouwmeester, Henricus J.M.

    2011-01-01

    The surface oxygen exchange kinetics of bismuth oxide stabilized with 25 mol% erbia (BE25) has been studied in the temperature and pO2 ranges 773–1,023 K and 0.1– 0.95 atm, respectively, using pulse-response 18O–16O isotope exchange measurements. The results indicate that BE25 exhibits a

  1. Oxygen Evolution at Hematite Surfaces: The Impact of Structure and Oxygen Vacancies on Lowering the Overpotential

    NARCIS (Netherlands)

    Zhang, X.; Klaver, P.; van Santen, R.; van de Sanden, M. C. M.; Bieberle, A.

    2016-01-01

    Simulations of the oxygen evolution reaction (OER) are essential for understanding the limitations of water splitting. Most research has focused so far on the OER at flat metal oxide surfaces. The structure sensitivity of the OER has, however, recently been highlighted as a promising research

  2. Surface oxygen vacancy and oxygen permeation flux limits of perovskite ion transport membranes

    KAUST Repository

    Hunt, Anton

    2015-09-01

    © 2015 Elsevier B.V. The mechanisms and quantitative models for how oxygen is separated from air using ion transport membranes (ITMs) are not well understood, largely due to the experimental complexity for determining surface exchange reactions at extreme temperatures (>800°C). This is especially true when fuels are present at the permeate surface. For both inert and reactive (fuels) operations, solid-state oxygen surface vacancies (δ) are ultimately responsible for driving the oxygen flux, JO2. In the inert case, the value of δ at either surface is a function of the local PO2 and temperature, whilst the magnitude of δ dictates both the JO2 and the inherent stability of the material. In this study values of δ are presented based on experimental measurements under inert (CO2) sweep: using a permeation flux model and local PO2 measurements, collected by means of a local gas-sampling probe in our large-scale reactor, we can determine δ directly. The ITM assessed was La0.9Ca0.1FeO3-δ (LCF); the relative resistances to JO2 were quantified using the pre-defined permeation flux model and local PO2 values. Across a temperature range from 825°C to 1056°C, δ was found to vary from 0.007 to 0.029 (<1%), safely within material stability limits, whilst the permeate surface exchange resistance dominates. An inert JO2 limit was identified owing to a maximum sweep surface δ, δmaxinert. The physical presence of δmaxinert is attributed to a rate limiting step shift from desorption to associative electron transfer steps on the sweep surface as PO2 is reduced. Permeate surface exchange limitations under non-reactive conditions suggest that reactive (fuel) operation is necessary to accelerate surface chemistry for future work, to reduce flux resistance and push δpast δmaxinert in a stable manner.

  3. Strong asymmetry for surface modes in nonlinear lattices with long-range coupling

    International Nuclear Information System (INIS)

    Martinez, Alejandro J.; Vicencio, Rodrigo A.; Molina, Mario I.

    2010-01-01

    We analyze the formation of localized surface modes on a nonlinear cubic waveguide array in the presence of exponentially decreasing long-range interactions. We find that the long-range coupling induces a strong asymmetry between the focusing and defocusing cases for the topology of the surface modes and also for the minimum power needed to generate them. In particular, for the defocusing case, there is an upper power threshold for exciting staggered modes, which depends strongly on the long-range coupling strength. The power threshold for dynamical excitation of surface modes increases (decreases) with the strength of long-range coupling for the focusing (defocusing) cases. These effects seem to be generic for discrete lattices with long-range interactions.

  4. Extrapolated renormalization group calculation of the surface tension in square-lattice Ising model

    International Nuclear Information System (INIS)

    Curado, E.M.F.; Tsallis, C.; Levy, S.V.F.; Oliveira, M.J. de

    1980-06-01

    By using self-dual clusters (whose sizes are characterized by the numbers b=2, 3, 4, 5) within a real space renormalization group framework, the longitudinal surface tension of the square-lattice first-neighbour 1/2-spin ferromagnetic Ising model is calculated. The exact critical temperature T sub(c) is recovered for any value of b; the exact assymptotic behaviour of the surface tension in the limit of low temperatures is analytically recovered; the approximate correlation length critical exponents monotonically tend towards the exact value ν=1 (which, at two dimensions, coincides with the surface tension critical exponent μ) for increasingly large cells; the same behaviour is remarked in what concerns the approximate values for the surface tension amplitude in the limit T→T sub(c). Four different numerical procedures are developed for extrapolating to b→infinite the renormalization group results for the surface tension, and quite satisfactory agreement is obtained with Onsager's exact expression (error varying from zero to a few percent on the whole temperature domain). Furthermore the set of RG surface tensions is compared with a set of biased surface tensions (associated to appropriate misfit seams), and find only fortuitous coincidence among them. (Author) [pt

  5. Modelling and investigation of partial wetting surfaces for drop dynamics using lattice Boltzmann method

    Science.gov (United States)

    Pravinraj, T.; Patrikar, Rajendra

    2017-07-01

    Partial wetting surfaces and its influence on the droplet movement of micro and nano scale being contemplated for many useful applications. The dynamics of the droplet usually analyzed with a multiphase lattice Boltzmann method (LBM). In this paper, the influence of partial wetting surface on the dynamics of droplet is systematically analyzed for various cases. Splitting of droplets due to chemical gradient of the surface is studied and analyses of splitting time for various widths of the strips for different Weber numbers are computed. With the proposed model one can tune the splitting volume and time by carefully choosing a strip width and droplet position. The droplet spreading on chemically heterogeneous surfaces shows that the spreading can be controlled not only by parameters of Weber number but also by tuning strip width ratio. The transportation of the droplet from hydrophobic surface to hydrophilic surface due to chemical gradient is simulated and analyzed using our hybrid thermodynamic-image processing technique. The results prove that with the progress of time the surface free energy decreases with increase in spreading area. Finally, the transportation of a droplet on microstructure gradient is demonstrated. The model explains the temporal behaviour of droplet during the spreading, recoiling and translation along with tracking of contact angle hysteresis phenomenon.

  6. Effective Wettability of Heterogenous Fracture Surfaces Using the Lattice-Boltzmann Method

    Science.gov (United States)

    E Santos, J.; Prodanovic, M.; Landry, C. J.

    2017-12-01

    Fracture walls in the subsurface are often structured by minerals of different composition (potentially further altered in contact with fluids during hydrocarbon extraction or CO2 sequestration), this yields in a heterogeneous wettability of the surface in contact with the fluids. The focus of our work is to study how surfaces presenting different mineralogy and roughness affect multiphase flow in fractures. Using the Shan-Chen model of the lattice-Boltzmann method (LBM) we define fluid interaction and surface attraction parameters to simulate a system of a wetting and a non-wetting fluid. In this work, we use synthetically created fractures presenting different arrangements of wetting and non-wetting patches, and with or without roughness; representative of different mineralogy, similar workflow can be applied to fractures extracted from X-ray microtomography images of fractures porous media. The results from the LBM simulations provide an insight on how the distribution of mineralogy and surface roughness are related with the observed macroscopic contact angle. We present a comparison between the published analytical models, and our results based on surface areas, spatial distribution and local fracture aperture. The understanding of the variables that affect the contact angle is useful for the comprehension of multiphase processes in naturally fractured reservoirs like primary oil production, enhanced oil recovery and CO2 sequestration. The macroscopic contact angle analytical equations for heterogeneous surfaces with variable roughness are no longer valid in highly heterogeneous systems; we quantify the difference thus offering an alternative to analytical models.

  7. Microstructural and surface modifications and hydroxyapatite coating of Ti-6Al-4V triply periodic minimal surface lattices fabricated by selective laser melting.

    Science.gov (United States)

    Yan, Chunze; Hao, Liang; Hussein, Ahmed; Wei, Qingsong; Shi, Yusheng

    2017-06-01

    Ti-6Al-4V Gyroid triply periodic minimal surface (TPMS) lattices were manufactured by selective laser melting (SLM). The as-built Ti-6Al-4V lattices exhibit an out-of-equilibrium microstructure with very fine α' martensitic laths. When subjected to the heat treatment of 1050°C for 4h followed by furnace cooling, the lattices show a homogenous and equilibrium lamellar α+β microstructure with less dislocation and crystallographic defects compared with the as-built α' martensite. The as-built lattices present very rough strut surfaces bonded with plenty of partially melted metal particles. The sand blasting nearly removed all the bonded metal particles, but created many tiny cracks. The HCl etching eliminated these tiny cracks, and subsequent NaOH etching resulted in many small and shallow micro-pits and develops a sodium titanate hydrogel layer on the surfaces of the lattices. When soaked in simulated body fluid (SBF), the Ti-6Al-4V TPMS lattices were covered with a compact and homogeneous biomimetic hydroxyapatite (HA) layer. This work proposes a new method for making Ti-6Al-4V TPMS lattices with a homogenous and equilibrium microstructure and biomimetic HA coating, which show both tough and bioactive characteristics and can be promising materials usable as bone substitutes. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. The Role of Lattice Vibrations in Adatom Diffusion at Metal Stepped Surfaces

    International Nuclear Information System (INIS)

    Durakanoglu, S.

    2004-01-01

    Diffusion of a single atom on metal surfaces remains a subject of continuing interest in the surface science community because of the important role it plays in several technologically important phenomena such as thin-film and eptaxial growth, catalysis and chemical reactions. Except for a few studies, most of theoretical works, ranging from molecular dynamic simulations to first principle electronic structure calculations, are devoted to determination of the characteristics of the diffusion processes and the energy barriers, neglecting the contribution of lattice vibrations in adatom diffusion. However, in a series of theoretical works on self-diffusion on the flat surfaces of Cu(100), Ag(100) and Ni(100), Ulrike et al.[1-3], showed that the vibrational contributions are important and should be included in any complete description of the temperature dependence of the diffusion coefficient. In this work, it is our aim to examine the role of lattice vibrations in adatom diffusion at stepped surfaces of Cu(100) and Ni(100) within the framework of transition state theory. Ehrlich-Shwoebel energy barriers for an adatom diffusing over a step-edge are calculated through the inclusion of vibrational internal energy. Local vibrational density of states, main ingredient to the vibrational thermodynamic functions, are calculated in the harmonic approximation, using real space Green's function method with the force constants derived from interaction potentials based on the embedded atom method. We emphasize the sensitivity of the local vibrational density of states to the local atomic environment. We, furthermore, discuss the contribution of thermodynamic functions calculated from local vibrational density of states to the prefactors in diffusion coefficient

  9. Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

    International Nuclear Information System (INIS)

    Zbiri, Mohamed; Rols, Stephane; Schober, Helmut; Johnson, Mark R; Mittal, Ranjan; Su, Yixi; Brueckel, Thomas; Xiao, Yinguo; Chaplot, Samrath L; Chatterji, Tapan; Inoue, Yasunori; Matsuishi, Satoru; Hosono, Hideo

    2010-01-01

    To shed light on the role of magnetism on the superconducting mechanism of the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering on phonon dynamics in the low-temperature orthorhombic parent compounds, which present a spin density wave. The study covers both the 122 (AFe 2 As 2 ; A = Ca, Sr, Ba) and 1111 (AFeAsF; A = Ca, Sr) phases. We extend our recent work on the Ca (122 and 1111) and Ba (122) cases by treating, computationally and experimentally, the 122 and 1111 Sr compounds. The effect of magnetic ordering is investigated through detailed non-magnetic and magnetic lattice dynamical calculations. The comparison of the experimental and calculated phonon spectra shows that the magnetic interactions/ordering have to be included in order to reproduce well the measured density of states. This highlights a spin-correlated phonon behavior which is more pronounced than the apparently weak electron-phonon coupling estimated in these materials. Furthermore, there is no noticeable difference between phonon spectra of the 122 Ba and Sr, whereas there are substantial differences when comparing these to CaFe 2 As 2 originating from different aspects of structure and bonding.

  10. Lattice Boltzmann modeling of self-propelled Leidenfrost droplets on ratchet surfaces

    Science.gov (United States)

    Li, Qing; Kang, Q. J.; Francois, M. M.; Hu, A. J.

    In this paper, the self-propelled motion of Leidenfrost droplets on ratchet surfaces is numerically investigated with a thermal multiphase lattice Boltzmann model with liquid-vapor phase change. The capability of the model for simulating evaporation is validated via the D2 law. Using the model, we first study the performances of Leidenfrost droplets on horizontal ratchet surfaces. It is numerically shown that the motion of self-propelled Leidenfrost droplets on ratchet surfaces is owing to the asymmetry of the ratchets and the vapor flows beneath the droplets. It is found that the Leidenfrost droplets move in the direction toward the slowly inclined side from the ratchet peaks, which agrees with the direction of droplet motion in experiments [Linke et al., Phys. Rev. Lett., 2006, 96, 154502]. Moreover, the influences of the ratchet aspect ratio are investigated. For the considered ratchet surfaces, a critical value of the ratchet aspect ratio is approximately found, which corresponds to the maximum droplet moving velocity. Furthermore, the processes that the Leidenfrost droplets climb uphill on inclined ratchet surfaces are also studied. Numerical results show that the maximum inclination angle at which a Leidenfrost droplet can still climb uphill successfully is affected by the initial radius of the droplet.

  11. A lattice Boltzmann model for substrates with regularly structured surface roughness

    Science.gov (United States)

    Yagub, A.; Farhat, H.; Kondaraju, S.; Singh, T.

    2015-11-01

    Superhydrophobic surface characteristics are important in many industrial applications, ranging from the textile to the military. It was observed that surfaces fabricated with nano/micro roughness can manipulate the droplet contact angle, thus providing an opportunity to control the droplet wetting characteristics. The Shan and Chen (SC) lattice Boltzmann model (LBM) is a good numerical tool, which holds strong potentials to qualify for simulating droplets wettability. This is due to its realistic nature of droplet contact angle (CA) prediction on flat smooth surfaces. But SC-LBM was not able to replicate the CA on rough surfaces because it lacks a real representation of the physics at work under these conditions. By using a correction factor to influence the interfacial tension within the asperities, the physical forces acting on the droplet at its contact lines were mimicked. This approach allowed the model to replicate some experimentally confirmed Wenzel and Cassie wetting cases. Regular roughness structures with different spacing were used to validate the study using the classical Wenzel and Cassie equations. The present work highlights the strength and weakness of the SC model and attempts to qualitatively conform it to the fundamental physics, which causes a change in the droplet apparent contact angle, when placed on nano/micro structured surfaces.

  12. Binding of oxygen on vacuum fractured pyrite surfaces: Reactivity of iron and sulfur surface sites

    Science.gov (United States)

    Berlich, A. G.; Nesbitt, H. W.; Bancroft, G. M.; Szargan, R.

    2013-05-01

    Synchrotron radiation excited photoelectron spectroscopy (SXPS) has been used to study the interaction of oxygen with vacuum fractured pyrite surfaces. Especially valence band spectra obtained with 30 eV photon energy were analyzed to provide a mechanism of the incipient steps of pyrite oxidation. These spectra are far more sensitive to the oxidation than sulfur or iron core level spectra. It is shown that oxygen is adsorbed on Fe(II) surface sites restoring the octahedral coordination of the Fe(II) sites. This process leads to the removal of two surface states in the valence band which are located at the low and high binding energy sides of the outer valence band, respectively. The existence of these surface states which have been proposed by calculations is experimentally proven. Furthermore, it is shown, that the sulfur sites are more reactive than expected. Sulfite like species are already formed after the lowest oxygen exposure of 10 L. This oxidation occurs at sulfur sites neighboring the Fe(II) surface sites. Oxidation of the S2 - surface sites which were considered as the most reactive species in former studies is second. No iron(III) oxides are formed during oxygen exposure, supporting the assumption that water plays an important role in the oxidation mechanism of pyrite surfaces.

  13. Evaluation of hydrogen and oxygen impurity levels on silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kenny, M.J.; Wielunski, L.S.; Netterfield, R.P.; Martin, P.J.; Leistner, A. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), Lindfield, NSW (Australia). Div. of Applied Physics

    1996-12-31

    This paper reports on surface analytical techniques used to quantify surface concentrations of impurities such as oxygen and hydrogen. The following analytical techniques were used: Rutherford and Backscattering, elastic recoil detection, time-of-flight SIMS, spectroscopic ellipsometry, x-ray photoelectron spectroscopy. The results have shown a spread in thickness of oxide layer, ranging from unmeasurable to 1.6 nm. The data must be considered as preliminary at this stage, but give some insight into the suitability of the techniques and a general idea of the significance of impurities at the monolayer level. These measurements have been carried out on a small number of silicon surfaces both semiconductor grade <111> crystalline material and silicon which has been used in sphere fabrication. 5 refs., 1 fig.

  14. Lattice Boltzmann model for free-surface flow and its application to filling process in casting

    CERN Document Server

    Ginzburg, I

    2003-01-01

    A generalized lattice Boltzmann model to simulate free-surface is constructed in both two and three dimensions. The proposed model satisfies the interfacial boundary conditions accurately. A distinctive feature of the model is that the collision processes is carried out only on the points occupied partially or fully by the fluid. To maintain a sharp interfacial front, the method includes an anti-diffusion algorithm. The unknown distribution functions at the interfacial region are constructed according to the first-order Chapman-Enskog analysis. The interfacial boundary conditions are satisfied exactly by the coefficients in the Chapman-Enskog expansion. The distribution functions are naturally expressed in the local interfacial coordinates. The macroscopic quantities at the interface are extracted from the least-square solutions of a locally linearized system obtained from the known distribution functions. The proposed method does not require any geometric front construction and is robust for any interfacial ...

  15. Existence of several surface-reconstructed phases in a two-dimensional lattice model

    Science.gov (United States)

    Huckaby, Dale A.; Rys, Franz S.

    1992-03-01

    The zero-temperature phase diagram is rigorously obtained for a two-dimensional lattice model with four energy parameters. It is shown that the parameter space can be divided into regions, together with their boundaries, such that in each region the ground-state configurations are of one of seven different types. These types include one which is nondegenerate, four which are doubly degenerate, one which is infinitely degenerate but with no residual entropy, and one which is infinitely degenerate and has a nonzero residual entropy. The Pirogov-Sinai extension of the Peierls argument is used to establish the existence at low temperatures of four different types of ordered surface-reconstructed phases.

  16. Modulating Protein Adsorption on Oxygen Plasma Modified Polysiloxane Surfaces

    International Nuclear Information System (INIS)

    Marletta, G.

    2006-01-01

    In the present paper we report the study on the adsorption behaviour of three model globular proteins, Human Serum Albumin, Lactoferrin and Egg Chicken Lysozyme onto both unmodified surfaces of a silicon-based polymer and the corresponding plasma treated surfaces. In particular, thin films of hydrophobic polysiloxane (about 90 degree of static water contact angle, WCA) were converted by oxygen plasma treatment at reduced pressure into very hydrophilic phases of SiOx (WCA less than 5 degree). The kinetics of protein adsorption processes were investigated by QCM-D technique, while the chemical structure and topography of the protein adlayer have been studied by Angular resolved-XPS and AFM respectively. It turned out that Albumin and Lysozyme exhibited the opposite preferential adsorption respectively onto the hydrophobic and hydrophilic surfaces, while Lactoferrin did not exhibit significant differences. The observed protein behaviour are discussed both in terms of surface-dependent parameters, including surface free energy and chemical structure, and in terms of protein-dependent parameters, including charge as well as the average molecular orientation in the adlayers. Finally, some examples of differential adsorption behaviour of the investigated proteins are reported onto nanopatterned polysiloxane surfaces consisting of hydrophobic nanopores surrounded by hydrophilic (plasma-treated) matrix and the reverse

  17. Surface oxygen effects in 14 MeV neutron activation analysis of oxygen in metals

    International Nuclear Information System (INIS)

    Janczyszyn, J.; Sztwiertnia, K.; Tarczanowski, S.

    1976-01-01

    To examine possible ways of reduction of the signal originating from the sample surface, the etching before and after activation and/or nitrogen transport were applied. The efficiency of post activation etching was confirmed. This procedure removes quantity of oxygen equivalent to 45μg/g for aluminium and 6μg/g for copper samples. The nitrogen transport without etching removes as much as 4μg/g in case of copper, however it turned out to be inefficient for aluminium samples. (author)

  18. Chemical analysis of surface oxygenated moieties of fluorescent carbon nanoparticles

    Science.gov (United States)

    Huang, Jie; Deming, Christopher P.; Song, Yang; Kang, Xiongwu; Zhou, Zhi-You; Chen, Shaowei

    2012-01-01

    Water-soluble carbon nanoparticles were prepared by refluxing natural gas soot in concentrated nitric acid. The surface of the resulting nanoparticles was found to be decorated with a variety of oxygenated species, as suggested by spectroscopic measurements. Back potentiometric titration of the nanoparticles was employed to quantify the coverage of carboxylic, lactonic, and phenolic moieties on the particle surface by taking advantage of their vast difference of acidity (pKa). The results were largely consistent with those reported in previous studies with other carbonaceous (nano)materials. Additionally, the presence of ortho- and para-quinone moieties on the nanoparticle surface was confirmed by selective labelling with o-phenylenediamine, as manifested in X-ray photoelectron spectroscopy, photoluminescence, and electrochemical measurements. The results further supported the arguments that the surface functional moieties that were analogous to 9,10-phenanthrenequinone were responsible for the unique photoluminescence of the nanoparticles and the emission might be regulated by surface charge state, as facilitated by the conjugated graphitic core matrix.

  19. Chemical analysis of surface oxygenated moieties of fluorescent carbon nanoparticles.

    Science.gov (United States)

    Huang, Jie; Deming, Christopher P; Song, Yang; Kang, Xiongwu; Zhou, Zhi-You; Chen, Shaowei

    2012-02-07

    Water-soluble carbon nanoparticles were prepared by refluxing natural gas soot in concentrated nitric acid. The surface of the resulting nanoparticles was found to be decorated with a variety of oxygenated species, as suggested by spectroscopic measurements. Back potentiometric titration of the nanoparticles was employed to quantify the coverage of carboxylic, lactonic, and phenolic moieties on the particle surface by taking advantage of their vast difference of acidity (pK(a)). The results were largely consistent with those reported in previous studies with other carbonaceous (nano)materials. Additionally, the presence of ortho- and para-quinone moieties on the nanoparticle surface was confirmed by selective labelling with o-phenylenediamine, as manifested in X-ray photoelectron spectroscopy, photoluminescence, and electrochemical measurements. The results further supported the arguments that the surface functional moieties that were analogous to 9,10-phenanthrenequinone were responsible for the unique photoluminescence of the nanoparticles and the emission might be regulated by surface charge state, as facilitated by the conjugated graphitic core matrix. This journal is © The Royal Society of Chemistry 2012

  20. Work function modifications of graphite surface via oxygen plasma treatment

    Science.gov (United States)

    Duch, J.; Kubisiak, P.; Adolfsson, K. H.; Hakkarainen, M.; Golda-Cepa, M.; Kotarba, A.

    2017-10-01

    The surface modification of graphite by oxygen plasma was investigated experimentally (X-ray diffraction, nanoparticle tracking analysis, laser desorption ionization mass spectrometry, thermogravimetry, water contact angle) and by molecular modelling (Density Functional Theory). Generation of surface functional groups (mainly sbnd OHsurf) leads to substantial changes in electrodonor properties and wettability gauged by work function and water contact angle, respectively. The invoked modifications were analyzed in terms of Helmholtz model taking into account the theoretically determined surface dipole moment of graphite-OHsurf system (μ = 2.71 D) and experimentally measured work function increase (from 0.75 to 1.02 eV) to determine the sbnd OH surface coverage (from 0.70 to 1.03 × 1014 groups cm-2). Since the plasma treatment was confined to the surface, the high thermal stability of the graphite material was preserved as revealed by the thermogravimetric analysis. The obtained results provide a suitable quantitative background for tuning the key operating parameters of carbon electrodes: electronic properties, interaction with water and thermal stability.

  1. Osteoblast response to oxygen functionalised plasma polymer surfaces

    CERN Document Server

    Kelly, J M

    2001-01-01

    Thin organic films with oxygen-carbon functionalities were deposited from plasmas containing vapour of the small organic compounds: allyI alcohol, methyl vinyl ketone and acrylic acid with octadiene. Characterisation of the deposits was carried out using X-ray photoelectron spectroscopy, in conjunction with chemical derivatisation, and this showed that plasma polymers retained high levels of original monomer functionality when the plasmas were sustained at low power for a given monomer vapour flow rate. High levels of attachment of rat osteosarcoma (ROS 17/2.8) cells were observed on surfaces that had high concentrations of hydroxyl and carbonyl functionalities and intermediate concentrations of carboxyl functionality. Cells did not attach to the octadiene plasma polymer. Cell attachment to carboxyl and methyl functionalised self-assembled monolayers increased with increasing concentration of surface carboxyl groups. Adsorption of the extracellular matrix protein fibronectin to acrylic acid/octadiene plasma c...

  2. Surface-assisted DNA self-assembly: An enzyme-free strategy towards formation of branched DNA lattice.

    Science.gov (United States)

    Bhanjadeo, Madhabi M; Nayak, Ashok K; Subudhi, Umakanta

    2017-04-01

    DNA based self-assembled nanostructures and DNA origami has proven useful for organizing nanomaterials with firm precision. However, for advanced applications like nanoelectronics and photonics, large-scale organization of self-assembled branched DNA (bDNA) into periodic lattices is desired. In this communication for the first time we report a facile method of self-assembly of Y-shaped bDNA nanostructures on the cationic surface of Aluminum (Al) foil to prepare periodic two dimensional (2D) bDNA lattice. Particularly those Y-shaped bDNA structures having smaller overhangs and unable to self-assemble in solution, they are easily assembled on the surface of Al foil in the absence of ligase. Field emission scanning electron microscopy (FESEM) analysis shows homogenous distribution of two-dimensional bDNA lattices across the Al foil. When the assembled bDNA structures were recovered from the Al foil and electrophoresed in nPAGE only higher order polymeric bDNA structures were observed without a trace of monomeric structures which confirms the stability and high yield of the bDNA lattices. Therefore, this enzyme-free economic and efficient strategy for developing bDNA lattices can be utilized in assembling various nanomaterials for functional molecular components towards development of DNA based self-assembled nanodevices. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. Elucidation of the Oxygen Surface Kinetics in a Coated Dual-Phase Membrane for Enhancing Oxygen Permeation Flux.

    Science.gov (United States)

    Na, Beom Tak; Park, Jeong Hwan; Park, Jong Hyuk; Yu, Ji Haeng; Joo, Jong Hoon

    2017-06-14

    The dual-phase membrane has received much attention as the solution to the instability of the oxygen permeation membrane. It has been reported that the oxygen flux of the dual-phase membrane is greatly enhanced by the active coating layer. However, there has been little discussion about the enhancement mechanism by surface coating in the dual-phase membrane. This study investigates the oxygen flux of the Ce 0.9 Gd 0.1 O 2-δ -La 0.7 Sr 0.3 MnO 3±δ (GDC 80 vol %/LSM 20 vol %) composite membrane depending on the oxygen partial pressure (P O 2 ) to elucidate the mechanism of enhanced oxygen flux by the surface modification in the fluorite-rich phase dual-phase membrane. The oxygen permeation resistances were obtained from the oxygen flux as a function of P O 2 using the oxygen permeation model. The surface exchange coefficient (k) and the bulk diffusion coefficient (D) were calculated from these resistances. According to the calculated k and D values, we concluded that the active coating layer (La 0.6 Sr 0.4 CoO 3-δ ) significantly increased the k value of the membrane. Furthermore, the surface exchange reaction on the permeate side was more sluggish than that at the feed side under operating conditions (feed: 0.21 atm/permeate side: 4.7 × 10 -4 atm). Therefore, the enhancement of the oxygen surface exchange kinetics at the permeate side is more important in improving the oxygen permeation flux of the thin film-based fluorite-rich dual-phase membrane. These results provide new insight about the function of the surface coating to enhance the oxygen permeation flux of the dual-phase membrane.

  4. 2D surface optical lattice formed by plasmon polaritons with application to nanometer-scale molecular deposition.

    Science.gov (United States)

    Yin, Yanning; Xu, Supeng; Li, Tao; Yin, Yaling; Xia, Yong; Yin, Jianping

    2017-08-10

    Surface plasmon polaritons, due to their tight spatial confinement and high local intensity, hold great promises in nanofabrication which is beyond the diffraction limit of conventional lithography. Here, we demonstrate theoretically the 2D surface optical lattices based on the surface plasmon polariton interference field, and the potential application to nanometer-scale molecular deposition. We present the different topologies of lattices generated by simple configurations on the substrate. By explicit theoretical derivations, we explain their formation and characteristics including field distribution, periodicity and phase dependence. We conclude that the topologies can not only possess a high stability, but also be dynamically manipulated via changing the polarization of the excitation laser. Nanometer-scale molecular deposition is simulated with these 2D lattices and discussed for improving the deposition resolution. The periodic lattice point with a width resolution of 33.2 nm can be obtained when the fullerene molecular beam is well-collimated. Our study can offer a superior alternative method to fabricate the spatially complicated 2D nanostructures, with the deposition array pitch serving as a reference standard for accurate and traceable metrology of the SI length standard.

  5. Return polynomials for non-intersecting paths above a surface on the directed square lattice

    Energy Technology Data Exchange (ETDEWEB)

    Brak, R. [Deartment of Mathematics, University of Melbourne, Parkville, VIC (Australia)]. E-mail: r.brak@ms.unimelb.edu.au; Essam, J.W. [Department of Mathematics, Royal Holloway College, University of London, Egham, Surrey (United Kingdom)]. E-mail: j.essam@alpha1.rhul.ac.uk

    2001-12-14

    We enumerate sets of n non-intersecting, t-step paths on the directed square lattice which are excluded from the region below the surface y=0 to which they are initially attached. In particular we obtain a product formula for the number of star configurations in which the paths have arbitrary fixed endpoints. We also consider the 'return' polynomial, R-'{sup W}{sub t}(y;k)={sigma}{sub m{>=}}{sub 0}r-'{sup W}{sub t}(y;m)k{sup m} where r-'{sup W}{sub t}(y;m) is the number of n-path configurations of watermelon type having deviation {gamma} for which the path closest to the surface returns to the surface m times. The 'marked return' polynomial is defined by u-'{sup W}{sub t}(y;k{sub 1}){identical_to}R-'{sup W}{sub 1}(y;k{sub 1}+l)={sigma}{sub m{>=}}{sub 0}u-'{sup W}{sub t}(y;m)k{sub 1}{sup m} where u-'{sup W}{sub t}(y;m) is the number of marked configurations having at least m returns, just m of which are marked. Both r-'{sup W}{sub t}(y;m) and u-'{sup W}(y;m) are expressed in terms of the numbers of paths ignoring returns but introducing a suitably modified endpoint condition. This enables u-'{sup W}{sub t}(y;m) to be written in product form for arbitrary y, but for r-'{sup W}{sub t}(y;m) this can only be done in the case y=0. (author)

  6. Continuous surface force based lattice Boltzmann equation method for simulating thermocapillary flow

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Lin, E-mail: lz@njust.edu.cn [School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Zheng, Song [School of Mathematics and Statistics, Zhejiang University of Finance and Economics, Hangzhou 310018 (China); Zhai, Qinglan [School of Economics Management and Law, Chaohu University, Chaohu 238000 (China)

    2016-02-05

    In this paper, we extend a lattice Boltzmann equation (LBE) with continuous surface force (CSF) to simulate thermocapillary flows. The model is designed on our previous CSF LBE for athermal two phase flow, in which the interfacial tension forces and the Marangoni stresses as the results of the interface interactions between different phases are described by a conception of CSF. In this model, the sharp interfaces between different phases are separated by a narrow transition layers, and the kinetics and morphology evolution of phase separation would be characterized by an order parameter via Cahn–Hilliard equation which is solved in the frame work of LBE. The scalar convection–diffusion equation for temperature field is resolved by thermal LBE. The models are validated by thermal two layered Poiseuille flow, and two superimposed planar fluids at negligibly small Reynolds and Marangoni numbers for the thermocapillary driven convection, which have analytical solutions for the velocity and temperature. Then thermocapillary migration of two/three dimensional deformable droplet are simulated. Numerical results show that the predictions of present LBE agreed with the analytical solution/other numerical results. - Highlights: • A CSF LBE to thermocapillary flows. • Thermal layered Poiseuille flows. • Thermocapillary migration.

  7. Continuous surface force based lattice Boltzmann equation method for simulating thermocapillary flow

    International Nuclear Information System (INIS)

    Zheng, Lin; Zheng, Song; Zhai, Qinglan

    2016-01-01

    In this paper, we extend a lattice Boltzmann equation (LBE) with continuous surface force (CSF) to simulate thermocapillary flows. The model is designed on our previous CSF LBE for athermal two phase flow, in which the interfacial tension forces and the Marangoni stresses as the results of the interface interactions between different phases are described by a conception of CSF. In this model, the sharp interfaces between different phases are separated by a narrow transition layers, and the kinetics and morphology evolution of phase separation would be characterized by an order parameter via Cahn–Hilliard equation which is solved in the frame work of LBE. The scalar convection–diffusion equation for temperature field is resolved by thermal LBE. The models are validated by thermal two layered Poiseuille flow, and two superimposed planar fluids at negligibly small Reynolds and Marangoni numbers for the thermocapillary driven convection, which have analytical solutions for the velocity and temperature. Then thermocapillary migration of two/three dimensional deformable droplet are simulated. Numerical results show that the predictions of present LBE agreed with the analytical solution/other numerical results. - Highlights: • A CSF LBE to thermocapillary flows. • Thermal layered Poiseuille flows. • Thermocapillary migration.

  8. Solid Oxide Fuel Cell Cathodes. Unraveling the Relationship Between Structure, Surface Chemistry and Oxygen Reduction

    Energy Technology Data Exchange (ETDEWEB)

    Gopalan, Srikanth [Boston Univ., MA (United States)

    2013-03-31

    In this work we have considered oxygen reduction reaction on LSM and LSCF cathode materials. In particular we have used various spectroscopic techniques to explore the surface composition, transition metal oxidation state, and the bonding environment of oxygen to understand the changes that occur to the surface during the oxygen reduction process. In a parallel study we have employed patterned cathodes of both LSM and LSCF cathodes to extract transport and kinetic parameters associated with the oxygen reduction process.

  9. Near Surface CO2 Triple Oxygen Isotope Composition

    Directory of Open Access Journals (Sweden)

    Sasadhar Mahata

    2016-02-01

    Full Text Available The isotopic composition of carbon dioxide in the atmosphere is a powerful tool for constraining its sources and sinks. In particular, the 17O oxygen anomaly [Δ17O = 1000 × ln(1 + δ17O/1000 - 0.516 × 1000 × ln(1 + δ18O/1000], with a value > 0.5‰ produced in the middle atmosphere, provides an ideal tool for probing the exchange of carbon dioxide between the biosphere/hydrosphere and atmosphere. The biosphere/hydrosphere and anthropogenic emissions give values ≤ 0.3‰. Therefore, any anomaly in near surface CO2 would reflect the balance between stratospheric input and exchange with the aforementioned surface sources. We have analyzed Δ17O values of CO2 separated from air samples collected in Taipei, Taiwan, located in the western Pacific region. The obtained mean anomaly is 0.42 ± 0.14‰ (1-σ standard deviation, in good agreement with model prediction and a published decadal record. Apart from typically used δ13C and δ18O values, the Δ17O value could provide an additional tracer for constraining the carbon cycle.

  10. Synthesis of Graphite Oxide with Different Surface Oxygen Contents Assisted Microwave Radiation

    Directory of Open Access Journals (Sweden)

    Adriana Ibarra-Hernández

    2018-02-01

    Full Text Available Graphite oxide is synthesized via oxidation reaction using oxidant compounds that have lattice defects by the incorporation of unlike functional groups. Herein, we report the synthesis of the graphite oxide with diverse surface oxygen content through three (B, C, D different modified versions of the Hummers method assisted microwave radiation compared with the conventional graphite oxide sample obtained by Hummers method (A. These methods allow not only the production of graphite oxide but also reduced graphene oxide, without undergoing chemical, thermal, or mechanical reduction steps. The values obtained of C/O ratio were ~2, 3.4, and ~8.5 for methodologies C, B, and D, respectively, indicating the presence of graphite oxide and reduced graphene oxide, according to X-ray photoelectron spectroscopy. Raman spectroscopy of method D shows the fewest structural defects compared to the other methodologies. The results obtained suggest that the permanganate ion produces reducing species during graphite oxidation. The generation of these species is attributed to a reversible reaction between the permanganate ion with π electrons, ions, and radicals produced after treatment with microwave radiation.

  11. Ion implantation method for preparing polymers having oxygen erosion resistant surfaces

    Science.gov (United States)

    Lee, Eal H.; Mansur, Louis K.; Heatherly, Jr., Lee

    1995-01-01

    Hard surfaced polymers and the method for making them are generally described. Polymers are subjected to simultaneous multiple ion beam bombardment, that results in a hardening of the surface, improved wear resistance, and improved oxygen erosion resistance.

  12. Plasma-Engraved Co3 O4 Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction.

    Science.gov (United States)

    Xu, Lei; Jiang, Qianqian; Xiao, Zhaohui; Li, Xingyue; Huo, Jia; Wang, Shuangyin; Dai, Liming

    2016-04-18

    Co3 O4 , which is of mixed valences Co(2+) and Co(3+) , has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co(2+) /Co(3+) ratio in Co3 O4 could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co3 O4 -based OER electrocatalyst by a plasma-engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co3 O4 surface with more Co(2+) formed. The increased surface area ensures the Co3 O4 has more sites for OER, and generated oxygen vacancies on Co3 O4 surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co3 O4 , the engraved Co3 O4 exhibits a much higher current density and a lower onset potential. The specific activity of the plasma-engraved Co3 O4 nanosheets (0.055 mA cm(-2) BET at 1.6 V) is 10 times higher than that of pristine Co3 O4 , which is contributed by the surface oxygen vacancies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. A Lattice Boltzmann Approach to Multi-Phase Surface Reactions with Heat Effects

    NARCIS (Netherlands)

    Kamali, M.R.

    2013-01-01

    The aim of the present research was to explore the promises and shift the limits of the numerical framework of lattice Boltzmann (LB) for studying the physics behind multi-component two-phase heterogeneous non-isothermal reactive flows under industrial conditions. An example of such an industrially

  14. Analysis of heterogeneous oxygen exchange and fuel oxidation on the catalytic surface of perovskite membranes

    KAUST Repository

    Hong, Jongsup

    2013-10-01

    The catalytic kinetics of oxygen surface exchange and fuel oxidation for a perovskite membrane is investigated in terms of the thermodynamic state in the immediate vicinity of or on the membrane surface. Perovskite membranes have been shown to exhibit both oxygen perm-selectivity and catalytic activity for hydrocarbon conversion. A fundamental description of their catalytic surface reactions is needed. In this study, we infer the kinetic parameters for heterogeneous oxygen surface exchange and catalytic fuel conversion reactions, based on permeation rate measurements and a spatially resolved physical model that incorporates detailed chemical kinetics and transport in the gas-phase. The conservation equations for surface and bulk species are coupled with those of the gas-phase species through the species production rates from surface reactions. It is shown that oxygen surface exchange is limited by dissociative/associative adsorption/desorption of oxygen molecules onto/from the membrane surface. On the sweep side, while the catalytic conversion of methane to methyl radical governs the overall surface reactions at high temperature, carbon monoxide oxidation on the membrane surface is dominant at low temperature. Given the sweep side conditions considered in ITM reactor experiments, gas-phase reactions also play an important role, indicating the significance of investigating both homogeneous and heterogeneous chemistry and their coupling when examining the results. We show that the local thermodynamic state at the membrane surface should be considered when constructing and examining models of oxygen permeation and heterogeneous chemistry. © 2013 Elsevier B.V.

  15. Ultrafast electron, lattice and spin dynamics on rare earth metal surfaces. Investigated with linear and nonlinear optical techniques

    Energy Technology Data Exchange (ETDEWEB)

    Radu, I.E.

    2006-03-15

    This thesis presents the femtosecond laser-induced electron, lattice and spin dynamics on two representative rare-earth systems: The ferromagnetic gadolinium Gd(0001) and the paramagnetic yttrium Y(0001) metals. The employed investigation tools are the time-resolved linear reflectivity and second-harmonic generation, which provide complementary information about the bulk and surface/interface dynamics, respectively. The femtosecond laser excitation of the exchange-split surface state of Gd(0001) triggers simultaneously the coherent vibrational dynamics of the lattice and spin subsystems in the surface region at a frequency of 3 THz. The coherent optical phonon corresponds to the vibration of the topmost atomic layer against the underlying bulk along the normal direction to the surface. The coupling mechanism between phonons and magnons is attributed to the modulation of the exchange interaction J between neighbour atoms due to the coherent lattice vibration. This leads to an oscillatory motion of the magnetic moments having the same frequency as the lattice vibration. Thus these results reveal a new type of phonon-magnon coupling mediated by the modulation of the exchange interaction and not by the conventional spin-orbit interaction. Moreover, we show that coherent spin dynamics in the THz frequency domain is achievable, which is at least one order of magnitude faster than previously reported. The laser-induced (de)magnetization dynamics of the ferromagnetic Gd(0001) thin films have been studied. Upon photo-excitation, the nonlinear magneto-optics measurements performed in this work show a sudden drop in the spin polarization of the surface state by more than 50% in a <100 fs time interval. Under comparable experimental conditions, the time-resolved photoemission studies reveal a constant exchange splitting of the surface state. The ultrafast decrease of spin polarization can be explained by the quasi-elastic spin-flip scattering of the hot electrons among spin

  16. Effects of Oxygen Partial Pressure on the Surface Tension of Liquid Nickel

    Science.gov (United States)

    SanSoucie, Michael P.; Rogers, Jan R.; Gowda, Vijaya Kumar Malahalli Shankare; Rodriguez, Justin; Matson, Douglas M.

    2015-01-01

    The NASA Marshall Space Flight Center's electrostatic levitation (ESL) laboratory has been recently upgraded with an oxygen partial pressure controller. This system allows the oxygen partial pressure within the vacuum chamber to be measured and controlled, theoretically in the range from 10-36 to 100 bar. The oxygen control system installed in the ESL laboratory's main chamber consists of an oxygen sensor, oxygen pump, and a control unit. The sensor is a potentiometric device that determines the difference in oxygen activity in two gas compartments (inside the chamber and the air outside of the chamber) separated by an electrolyte, which is yttria-stabilized zirconia. The pump utilizes coulometric titration to either add or remove oxygen. The system is controlled by a desktop control unit, which can also be accessed via a computer. The controller performs temperature control for the sensor and pump, PID-based current loop, and a control algorithm. Oxygen partial pressure has been shown to play a significant role in the surface tension of liquid metals. Oxide films or dissolved oxygen may lead to significant changes in surface tension. The effects of oxygen partial pressure on the surface tension of undercooled liquid nickel will be analyzed, and the results will be presented. The surface tension will be measured at several different oxygen partial pressures while the sample is undercooled. Surface tension will be measured using the oscillating drop method. While undercooled, each sample will be oscillated several times consecutively to investigate how the surface tension behaves with time while at a particular oxygen partial pressure.

  17. Adsorption of oxygen atom on MoSi{sub 2} (110) surface

    Energy Technology Data Exchange (ETDEWEB)

    Sun, S.P., E-mail: sunshunping@jsut.edu.cn [School of Materials Engineering, Jiangsu University of Technology, Changzhou 213001 (China); Li, X.P.; Wang, H.J. [School of Materials Engineering, Jiangsu University of Technology, Changzhou 213001 (China); Jiang, Y., E-mail: yjiang@csu.edu.cn [School of Materials Science and Engineering, and Key Laboratory for Non-ferrous Materials of Ministry of Education, Central South University, Changsha 410083 (China); Yi, D.Q. [School of Materials Science and Engineering, and Key Laboratory for Non-ferrous Materials of Ministry of Education, Central South University, Changsha 410083 (China)

    2016-09-30

    Highlights: • The adsorption of oxygen atom on MoSi{sub 2} (110) surface was studied systematically. • The stability of MoSi{sub 2} low-index surfaces was also investigated. • The preference adsorption site of MoSi{sub 2} (110) surface for oxygen atom was H site. - Abstract: The adsorption energy, structural relaxation and electronic properties of oxygen atom on MoSi{sub 2} (110) surface have been investigated by first-principles calculations. The energetic stability of MoSi{sub 2} low-index surfaces was analyzed, and the results suggested that MoSi{sub 2} (110) surface had energetically stability. The site of oxygen atom adsorbed on MoSi{sub 2} (110) surface were discussed, and the results indicated that the preference adsorption site of MoSi{sub 2} (110) surface for oxygen atom was H site (hollow position). Our calculated work should help to understand further the interaction between oxygen atoms and MoSi{sub 2} surfaces.

  18. Thermopower and lattice parameters of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films as a function of oxygen content

    Energy Technology Data Exchange (ETDEWEB)

    Giraldo, J. [Departamento de Fisica, Universidad Nacional de Colombia, Apartado Aereo 67904, Santafe de Bogota, Colombia (Colombia); Pulzara, A.; Prieto, P.; Chacon, M. [Departamento de Fisica, Universidad del Valle, Apartado Aereo 25360, Cali, Colombia (Colombia)

    1998-12-31

    The stoichiometry and structure of Y 123 compounds strongly determine their physical properties. A theoretical and experimental study in oxygen-deficient YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films is presented in this report. We have measured resistivity and thermopower in a set of high quality epitaxial samples with 0< {delta} < 0.5. The c-axis lattice constant has been determined by X-ray spectroscopy. All lattice lengths have been evaluated numerically in the same range of composition using the microscopic effective medium theory. The calculated results compare well with those reported experimentally. A correlation has been undertaken among the above and other physical quantities, in particular bond lengths, T{sub c}, and the isotope effect, and some conclusions have been extracted. The main conclusion from the present work is that although the electron-phonon interaction alone is not enough to explain the peculiarities of Y 123 based compounds and its high T{sub c}, phonons yield important contributions to their thermal transport properties. (Author)

  19. A lattice Boltzmann simulation of coalescence-induced droplet jumping on superhydrophobic surfaces with randomly distributed structures

    Science.gov (United States)

    Zhang, Li-Zhi; Yuan, Wu-Zhi

    2018-04-01

    The motion of coalescence-induced condensate droplets on superhydrophobic surface (SHS) has attracted increasing attention in energy-related applications. Previous researches were focused on regularly rough surfaces. Here a new approach, a mesoscale lattice Boltzmann method (LBM), is proposed and used to model the dynamic behavior of coalescence-induced droplet jumping on SHS with randomly distributed rough structures. A Fast Fourier Transformation (FFT) method is used to generate non-Gaussian randomly distributed rough surfaces with the skewness (Sk), kurtosis (K) and root mean square (Rq) obtained from real surfaces. Three typical spreading states of coalesced droplets are observed through LBM modeling on various rough surfaces, which are found to significantly influence the jumping ability of coalesced droplet. The coalesced droplets spreading in Cassie state or in composite state will jump off the rough surfaces, while the ones spreading in Wenzel state would eventually remain on the rough surfaces. It is demonstrated that the rough surfaces with smaller Sks, larger Rqs and a K at 3.0 are beneficial to coalescence-induced droplet jumping. The new approach gives more detailed insights into the design of SHS.

  20. Lattice distortion due to surface treatment of bias sputtering revealed by extremely asymmetric X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Y.; Akimoto, K.; Emoto, T.; Kikuchi, S.; Itagaki, K.; Namita, H

    2004-07-15

    Strain fields near InGaP or GaAs surfaces due to bias sputtering (Ar plasma-ion irradiation) for surface cleaning were measured by using a strain-sensitive X-ray diffraction technique. An extremely asymmetric InGaP or GaAs 1 1 3 reflection of the sample was measured to observe strain fields. We found that strain fields near InGaP or GaAs surfaces due to bias sputtering are affected by the bias voltage (Ar plasma-ion irradiation energy) used in this surface-cleaning treatment. By comparing measured 1 1 3 rocking curves and calculated ones based on the dynamical theory of X-rays, we estimated the thickness of a strained layer and a maximum strain at the surface. Resulting estimated parameters clearly show the bias sputtering to have two effects. One should be corresponding to the surface cleaning process of removing oxides on surfaces. The other is the lattice expansion, which is thought to be caused by compositional fluctuation near the surface or peening process of Ar ion.

  1. [Study on Square Super-Lattice Pattern with Surface Discharge in Dielectric Barrier Discharge by Optical Emission Spectra].

    Science.gov (United States)

    Niu, Xue-jiao; Dong, Li-fang; Liu, Ying; Wang, Qian; Feng, Jian-yu

    2016-02-01

    Square super-lattice pattern with surface discharge consisting of central spots and dim spots is firstly observed in the mixture of argon and air by using a dielectric barrier discharge device with water electrodes. By observing the image, it is found that the central spot is located at the centriod of its surrounding four dim spots. The short-exposure image recorded by a high speed video camera shows that the dim spot results from the surface discharges (SDs). The brightness of the central spot and is quite different from that of the dim spot, which indicates that the plasma states of the central spot and the dim spot may be differentiated. The optical emission spectrum method is used to further study the several plasma parameters of the central spot and the dim spot in different argon content. The emission spectra of the N₂ second positive band (C³IIu --> B³ IIg) are measured, from which the molecule vibration temperatures of the central spot and the dim spot are calculated respectively. The broadening of spectral line 696.57 nm (2P₂-->1S₅) is used to study the electron densities of the central spot and the dim spot. It is found that the molecule vibration temperature and electron density of the dim spot are higher than those of the central spot in the same argon content The molecule vibration temperature and electron density of the central spot and the dim spot increase with the argon content increasing from 90% to 99.9%. The surface discharge induced by the volume discharge (VD) has the determinative effect on the formation of the dim spot The experimental results above play an important role in studying the formation mechanism of surface discharg&of square super-lattice pattern with surface discharge. In addition, the studies exert an influence on the application of surface discharge and volume discharge in different fields.

  2. Universality in Oxygen Reduction Electrocatalysis on Metal Surfaces

    DEFF Research Database (Denmark)

    Viswanathan, Venkatasubramanian; Hansen, Heine Anton; Rossmeisl, Jan

    2012-01-01

    In this work, we extend the activity volcano for oxygen reduction from the face-centered cubic (fcc) metal (111) facet to the (100) facet. Using density functional theory calculations, we show that the recent findings of constant scaling between OOH* and OH* holds on the fcc metal (100) facet, as...

  3. Photo-oxidation : Major sink of oxygen in the ocean surface layer

    NARCIS (Netherlands)

    Gieskes, W. W. C.; Laane, R. W. P. M.; Ruardij, P.

    2015-01-01

    Evidence is presented that the oxygen demand associated with photochemical processes in the surface layer of oceans and seas worldwide is of the same order of magnitude as the amount of oxygen released by photosynthesis of the world's marine phytoplankton. Both estimates are of necessity quite rough

  4. Photo-oxidation: Major sink of oxygen in the ocean surface layer

    NARCIS (Netherlands)

    Gieskes, W.W.C.; Laane, R.W.P.M.; Ruardij, P.

    2015-01-01

    Evidence is presented that the oxygen demand associated with photochemical processes in the surface layer of oceans and seas worldwide is of the same order of magnitude as the amount of oxygen released by photosynthesis of the world's marine phytoplankton. Both estimates are of necessity quite rough

  5. Probing adsorption phenomena on a single crystal Pt-alloy surface under oxygen reduction reaction conditions

    DEFF Research Database (Denmark)

    Bondarenko, Alexander S.; Stephens, Ifan E.L.; Bech, Lone

    2012-01-01

    The adsorption dynamics of *OH and *O species at Pt(111) and Cu/Pt(111) near-surface alloy (NSA) surfaces in oxygen-free and O2-saturated 0.1M HClO4 was investigated. Subsurface Cu modifies the electronic structure at the Pt(111) surface resulting in weaker bonding to adsorbates like *OH, *H or *...

  6. ARPES view on surface and bulk hybridization phenomena in the antiferromagnetic Kondo lattice CeRh2Si2.

    Science.gov (United States)

    Patil, S; Generalov, A; Güttler, M; Kushwaha, P; Chikina, A; Kummer, K; Rödel, T C; Santander-Syro, A F; Caroca-Canales, N; Geibel, C; Danzenbächer, S; Kucherenko, Yu; Laubschat, C; Allen, J W; Vyalikh, D V

    2016-03-18

    The hybridization between localized 4f electrons and itinerant electrons in rare-earth-based materials gives rise to their exotic properties like valence fluctuations, Kondo behaviour, heavy-fermions, or unconventional superconductivity. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the Kondo lattice antiferromagnet CeRh2Si2, where the surface and bulk Ce-4f spectral responses were clearly resolved. The pronounced 4f (0) peak seen for the Ce terminated surface gets strongly suppressed in the bulk Ce-4f spectra taken from a Si-terminated crystal due to much larger f-d hybridization. Most interestingly, the bulk Ce-4f spectra reveal a fine structure near the Fermi edge reflecting the crystal electric field splitting of the bulk magnetic 4f (1)5/2 state. This structure presents a clear dispersion upon crossing valence states, providing direct evidence of f-d hybridization. Our findings give precise insight into f-d hybridization penomena and highlight their importance in the antiferromagnetic phases of Kondo lattices.

  7. Oxygen dosing the surface of SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Dudy, L.; Scheiderer, P.; Schuetz, P.; Gabel, J.; Buchwald, M.; Sing, M.; Claessen, R. [Physikalisches Institut, Universitaet Wuerzburg (Germany); Denlinger, J.D. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94270 (United States); Schlueter, C.; Lee, T.L. [Diamond Light Source Ltd., Didcot, Oxfordshire (United Kingdom)

    2015-07-01

    The highly mobile two-dimensional electron system (2DES) on the surface of the insulating SrTiO{sub 3}(STO) offers exciting perspectives for advanced material design. This 2DES resides in a depletion layer caused by oxygen deficiency of the surface. With photoemission spectroscopy, we monitor the appearance of quasi-particle weight (QP) at the Fermi energy and oxygen vacancy induced states in the band gap (IG). Both, QP and IG weight, increase and decrease respectively upon exposure to extreme ultraviolet (XUV) light and in-situ oxygen dosing. By a proper adjustment of oxygen dosing, any intermediate state can be stabilized providing full control over the charge carrier density. From a comparison of the charge carrier concentrations obtained from an analysis of core-level spectra and the Fermi-surface volume, we conclude on a spatially inhomogeneous surface electronic structure with at least two different phases.

  8. A pore-scale approach to colloid-surface interaction in liquid using lattice Boltzmann models.

    Science.gov (United States)

    Larsen, J. D.; Schaap, M. G.

    2016-12-01

    Knowledge of colloid transport and collection efficiency is important for understanding the transport of some contaminants of emerging concern (CEC) and for developing environmental remediation systems such as geologic filters. The interaction forces between colloids and soil materials are central to colloid transport and retention or immobilization. In this study a physical modeling approach to represent colloidal transport through porous media has been developed, using the lattice Boltzmann methodology. Lattice Boltzmann models have the uncanny ability to represent pore scale fluid flow through complex structures such as geological material. A cellular approach to computing colloid forces is applied for computational efficiency, and colloids are tracked continuously through the model. Grid refinement effects are quantified to balance computational efficiency with discretization effects. Representation of physical forces including DLVO create a natural fluid solid boundary condition for colloid transport. Collector efficiencies of geologic materials and colloid distribution curves can be produced. The present work focuses on simple porous media with a single wetting fluid phase, but the approach can be extended to heterogeneous geologic materials and multiphase systems.

  9. First principles study of dissolved oxygen water adsorption on Fe (001 surfaces

    Directory of Open Access Journals (Sweden)

    Dong ZHANG

    2018-02-01

    Full Text Available In order to study the mechanism of dissolved oxygen content on the surface corrosion behavior of Fe-based heat transfer, the first principle is used to study the adsorption of O2 monomolecular, H2O monolayer and dissolved oxygen system on Fe-based heat transfer surface. The GGA/PBE approximation is used to calculate the adsorption energy, state density and population change during the adsorption process. Calculations prove that when the dissolved oxygen is adsorbed on the Fe-based surface, the water molecule tends to adsorb at the top sites, and the oxygen molecule tends to adsorb at Griffiths. When the H2O molecule adsorbs and interacts on the Fe (001 surface, the charge distribution of the interfacial double electric layer changes to cause the Fe atoms to lose electrons, resulting in the change of the surface potential. When the O2 molecule adsorbs on the Fe (001 crystal surfaces, the electrons on the Fe (001 surface are lost and the surface potential increases. O2 molecule and the surface of the Fe atoms are prone to electron transfer, in which O atom's 2p orbit for the adsorption of O2 molecule on Fe (001 crystal surface play a major role. With the increase of the proportion of O2 molecule in the dissolved oxygen water, the absolute value of the adsorption energy increases, and the interaction of the Fe-based heat transfer surface is stronger. This study explores the influence law of different dissolved oxygen on the Fe base heat exchange surface corrosion, and the base metal corrosion mechanism for experimental study provides a theoretical reference.

  10. Generalized isothermic lattices

    International Nuclear Information System (INIS)

    Doliwa, Adam

    2007-01-01

    We study multi-dimensional quadrilateral lattices satisfying simultaneously two integrable constraints: a quadratic constraint and the projective Moutard constraint. When the lattice is two dimensional and the quadric under consideration is the Moebius sphere one obtains, after the stereographic projection, the discrete isothermic surfaces defined by Bobenko and Pinkall by an algebraic constraint imposed on the (complex) cross-ratio of the circular lattice. We derive the analogous condition for our generalized isothermic lattices using Steiner's projective structure of conics, and we present basic geometric constructions which encode integrability of the lattice. In particular, we introduce the Darboux transformation of the generalized isothermic lattice and we derive the corresponding Bianchi permutability principle. Finally, we study two-dimensional generalized isothermic lattices, in particular geometry of their initial boundary value problem

  11. The effect of plutonium dioxide water surface coverage on the generation of hydrogen and oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Veirs, Douglas K. [Los Alamos National Laboratory; Berg, John M. [Los Alamos National Laboratory; Crowder, Mark L. [Savannah River National Laboratory

    2012-06-20

    The conditions for the production of oxygen during radiolysis of water adsorbed onto plutonium dioxide powder are discussed. Studies in the literature investigating the radiolysis of water show that both oxygen and hydrogen can be generated from water adsorbed on high-purity plutonium dioxide powder. These studies indicate that there is a threshold in the amount of water below which oxygen is not generated. The threshold is associated with the number of monolayers of adsorbed water and is shown to occur at approximately two monolayers of molecularly adsorbed water. Material in equilibrium with 50% relative humidity (RH) will be at the threshold for oxygen generation. Using two monolayers of molecularly adsorbed water as the threshold for oxygen production, the total pressure under various conditions is calculated assuming stoichiometric production of hydrogen and oxygen. The specific surface area of the oxide has a strong effect on the final partial pressure. The specific surface areas resulting in the highest pressures within a 3013 container are evaluated. The potential for oxygen generation is mitigated by reduced relative humidity, and hence moisture adsorption, at the oxide surface which occurs if the oxide is warmer than the ambient air. The potential for oxygen generation approaches zero as the temperature difference between the ambient air and the material approaches 6 C.

  12. Nitrogen cycling across the Peruvian oxygen minimum zone surface sediments

    Science.gov (United States)

    Sommer, S.; Bohlen, L.; Dale, A. W.; Wallmann, K.; Noffke, A.; Hensen, C.; Mosch, T.; Pfannkuche, O.

    2012-04-01

    Oxygen minimum zones (OMZ) are key regions for pelagic and benthic nitrogen turnover. During Meteor cruise M77 (Oct. - Dec. 2008) benthic nitrogen cycling along a latitudinal depth transect (85 to 1000 m) across the Peruvian OMZ at 11°S was studied involving in situ flux measurements, pore water geochemistry as well as diagenetic modeling. Along this transect bottom water oxygen levels were minor importance on the shelf and upper slope but was the dominant N sink at 1000 m. Mass balance calculations as well as modeling indicate that dissimilatory nitrate reduction to ammonium (DNRA) by sulfur bacteria and ammmonification were the main source pathways for ammonium to the bottom water, yielding release rates of up to 4.6 mmol m-2 d-1. DNRA retains DIN within the ecosystem and counteracts the removal of DIN via denitrification and/or anammox. This finding is in contrast to the current opinion that slope sediments in general represent major sinks for DIN.

  13. Simulation of dissolution in porous media in three dimensions with lattice Boltzmann, finite-volume, and surface-rescaling methods

    Science.gov (United States)

    Gray, F.; Cen, J.; Boek, E. S.

    2016-10-01

    We present a pore-scale dissolution model for the simulation of reactive transport in complex porous media such as those encountered in carbon-storage injection processes. We couple a lattice Boltzmann model for flow calculation with a finite-volume method for solving chemical transport equations, and allow the computational grid to change as mineral surfaces are dissolved according to first-order reaction kinetics. We appraise this scheme for use with high Péclet number flows in three-dimensional geometries and show how the popular first-order convection scheme is affected by severe numerical diffusion when grid Péclet numbers exceed unity, and confirm that this can be overcome relatively easily by using a second-order method in conjunction with a flux-limiter function. We then propose a surface rescaling method which uses parabolic elements to counteract errors in surface area exposed by the Cartesian grid and avoid the use of more complex embedded surface methods when surface reaction kinetics are incorporated. Finally, we compute dissolution in an image of a real porous limestone rock sample injected with HCl for different Péclet numbers and obtain dissolution patterns in concordance with theory and experimental observation. A low injection flow rate was shown to lead to erosion of the pore space concentrated at the face of the rock, whereas a high flow rate leads to wormhole formation.

  14. A modified Lattice Boltzmann model for pore-scale simulation of desorption process at surface water-groundwater interface

    Science.gov (United States)

    Zhang, Pei; Galindo Torres, Sergio; Tang, Hongwu; Scheuermann, Alexander; Jin, Guangqiu; Li, Ling

    2017-04-01

    A pore-scale numerical model is introduced to simulate the desorption process at surface water-groundwater interface. The Navier-Stokes equations for fluid and Advection-Diffusion equation for scalar transport are solved by Lattice Boltzmann Method (LBM). In previous studies, the macroscopic desorption kinetic equations are usually applied as a boundary condition. However, it may be problematic for pore-scale simulation since most desorption kinetic equations are fitted from macroscopic global variables. We avoid this problem by discretizing the particle surface into a large number of adsorption sites to mimic the microscopic desorption process. The state of each adsorption site follows the Langmuir's theory. Furthermore, benefiting from the mesoscopic inherent of the LBM, the total number of adsorbate which really contacted with the particle surface can be calculated rather than the local concentration. The predicted desorption Isotherm and concentration profile match well with theoretical solutions and experimental data. By using presented model, we find that the desorption process at surface water-groundwater interface shows a complex response to surface water flow.

  15. Improved thrombogenicity on oxygen etched Ti6Al4V surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Riedel, Nicholas A. [Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523 (United States); Smith, Barbara S. [School of Biomedical Engineering, Colorado State University, Fort Collins, CO 80523 (United States); Williams, John D. [Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523 (United States); Popat, Ketul C., E-mail: ketul.popat@colostate.edu [Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523 (United States); School of Biomedical Engineering, Colorado State University, Fort Collins, CO 80523 (United States)

    2012-07-01

    Thrombus formation on blood contacting biomaterials continues to be a key factor in initiating a critical mode of failure in implantable devices, requiring immediate attention. In the interest of evaluating a solution for one of the most widely used biomaterials, titanium and its alloys, this study focuses on the use of a novel surface oxidation treatment to improve the blood compatibility. This study examines the possibility of using oblique angle ion etching to produce a high quality oxide layer that enhances blood compatibility on medical grade titanium alloy Ti6Al4V. An X-ray photoelectron spectroscopy (XPS) analysis of these oxygen-rich surfaces confirmed the presence of TiO{sub 2} peaks and also indicated increased surface oxidation as well as a reduction in surface defects. After 2 h of contact with whole human plasma, the oxygen etched substrates demonstrated a reduction in both platelet adhesion and activation as compared to bare titanium substrates. The whole blood clotting behavior was evaluated for up to 45 min, showing a significant decrease in clot formation on oxygen etched substrates. Finally, a bicinchoninic acid (BCA) total protein assay and XPS were used to evaluate the degree of key blood serum protein (fibrinogen, albumin, immunoglobulin G) adsorption on the substrates. The results showed similar protein levels for both the oxygen etched and control substrates. These results indicate that oblique angle oxygen etching may be a promising method to increase the thrombogenicity of Ti6Al4V. - Highlights: Black-Right-Pointing-Pointer Oblique angle oxygen ion etching creates a high quality, uniform oxide surface. Black-Right-Pointing-Pointer Oxygen etched substrates showed fewer adhered platelets. Black-Right-Pointing-Pointer Platelet activation was reduced by the improved oxide surface. Black-Right-Pointing-Pointer Oxygen etched substrates exhibited increased whole blood clotting times. Black-Right-Pointing-Pointer Although clotting reductions were

  16. Crystal lattice imaging of the silica and alumina faces of kaolinite using atomic force microscopy.

    Science.gov (United States)

    Gupta, Vishal; Hampton, Marc A; Nguyen, Anh V; Miller, Jan D

    2010-12-01

    The crystal lattice images of the two faces of kaolinite (the silica face and the alumina face) have been obtained using contact-mode atomic force microscopy (AFM) under ambient conditions. Lattice resolution images reveal the hexagonal surface lattice of these two faces of kaolinite. Analysis of the silica face of kaolinite showed that the hexagonal surface lattice ring of oxygen atoms had a periodicity of 0.50±0.04nm between neighboring oxygen atoms, which is in good agreement with the surface lattice structure of the mica basal plane. The center of the hexagonal ring of oxygen atoms is vacant. Analysis of the alumina face of kaolinite showed that the hexagonal surface lattice ring of hydroxyls surround a hydroxyl in the center of the ring. The atomic spacing between neighboring hydroxyls was determined as 0.36±0.04nm. Ordering of the kaolinite particles for examination of the silica and alumina surfaces was accomplished using different substrates, a procedure previously established. Crystal lattice imaging supports previous results and independently confirms that the two faces of kaolinite have been properly identified. Copyright © 2010 Elsevier Inc. All rights reserved.

  17. Surface texturing of superconductors by controlled oxygen pressure

    Science.gov (United States)

    Chen, N.; Goretta, K.C.; Dorris, S.E.

    1999-01-05

    A method of manufacture of a textured layer of a high temperature superconductor on a substrate is disclosed. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO{sub 2} atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO{sub 2} atmosphere to cause solidification of the molten superconductor in a textured surface layer. 8 figs.

  18. Oxygen adsorption on the Al₉Co₂(001) surface: first-principles and STM study.

    Science.gov (United States)

    Villaseca, S Alarcón; Loli, L N Serkovic; Ledieu, J; Fournée, V; Gille, P; Dubois, J-M; Gaudry, E

    2013-09-04

    Atomic oxygen adsorption on a pure aluminum terminated Al9Co2(001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a 'bridge' type site between the cluster entities exposed at the (001) surface termination. The Al-O bonding between the adsorbate and the substrate presents a covalent character, with s-p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al-O distances are in agreement with those reported in Al2O and Al2O3 oxides and for oxygen adsorption on Al(111).

  19. Late Quaternary changes in surface productivity and oxygen ...

    Indian Academy of Sciences (India)

    The increased relative abundances of high fertility taxa, i.e., Globigerinita glutinata and Globigerina bulloides mainly during interglacial intervals indicate intense upwelling. Strong SW summer monsoon probably increased the upwelling in the western Arabian Sea during interglacial intervals and caused high surface ...

  20. ATOMIC POSITIONS ON OXYGEN-COVERED CU(110) SURFACES

    NARCIS (Netherlands)

    DORENBOS, G; BREEMAN, M; BOERMA, DO

    The reconstructed Cu(110)-p(2 x 1)O and Cu(110)-c(6 x 2)O surfaces were studied using low-energy ion scattering combined with time of flight. Azimuthal scans were measured with 6 keV Ar ions for recoiling O, scattered Ar and recoiling Cu atoms. Part of the scans were analysed using a newly developed

  1. Sorption of oxygen on Cu(111)-Ni surfaces and its reaction with hydrogen

    NARCIS (Netherlands)

    Mesters, C.M.A.M.; Koster, A. de; Gijzeman, O.L.J.; Geus, John W.

    1984-01-01

    The interaction of O2 with a Cu(111)-Ni alloy and the reaction of sorbed oxygen with H2 has been investigated with ellipsometry and AES. The surface alloys were prepared by dissociation of nickel carbonyl on a clean Cu(111) surface. Sorption of O2 can be described by a precursor state model for

  2. Spectroscopic ellipsometric investigation of clean and oxygen covered copper single crystal surfaces

    NARCIS (Netherlands)

    Hanekamp, L.J.; Lisowski, W.F.; Bootsma, G.A.

    1982-01-01

    Spectroscopic ellipsometric measurements (400–820 nm) have been performed on clean and oxygen covered Cu(110) and Cu(111) surfaces in an AES-LEED UHV system. The complex dielectric functions of the clean surfaces were calculated from measurements between room temperature and 600 K. In contrast with

  3. Surface analysis of long-distance oxygen plasma sterilized PTFE film

    Energy Technology Data Exchange (ETDEWEB)

    Liu Hongxia, E-mail: hxliu72@mail.xjtu.edu.cn [Department of Environmental Science and Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Zhang Huijun; Chen Jierong [Department of Environmental Science and Engineering, Xi' an Jiaotong University, Xi' an 710049 (China)

    2009-06-30

    The influence of long-distance oxygen plasma sterilization on surface properties of substrate material, i.e., medical poly(tetrafluoroethylene) (PTFE), and aging effect of these sterilized PTFE film surfaces were investigated by contact angle measurement, mass loss determination, scanning electron microscopy (SEM) as well as bacterial adhesion and platelet adhesion measurements in vitro, respectively. The changes in chemical structure of sterilized PTFE film were followed using X-ray photoelectron spectroscopy (XPS). As a result of plasma sterilization oxygen-containing functional groups (such as C=O and C=O), especially the C=O group are introduced into PTFE surfaces, and thus pronounced increases of surface free energy and surface wettability are presented when the sample positions are within 0-40 cm. The film surface wettability degrades little as the aging time continued as long as 190 days. At the same time, the minimal surface degradation and damage occur on the sterilized PTFE when the sample position is at 40 cm. Moreover, the antibacterial adhesion and blood compatibility of sterilized PTFE surface are enhanced and the optimal effects are also obtained at 40 cm. The essential reason may be due to the optimal equilibrium between surface wettability and surface damage, which is achieved at 40 cm. Overall, of the surface properties of long-distance oxygen plasma sterilized PTFE analyzed, the sterilization at 40 cm is optimal.

  4. Surface modification of polystyrene with atomic oxygen radical anions-dissolved solution

    International Nuclear Information System (INIS)

    Wang Lian; Yan Lifeng; Zhao Peitao; Torimoto, Yoshifumi; Sadakata, Masayoshi; Li Quanxin

    2008-01-01

    A novel approach to surface modification of polystyrene (PS) polymer with atomic oxygen radical anions-dissolved solution (named as O - water) has been investigated. The O - water, generated by bubbling of the O - (atomic oxygen radical anion) flux into the deionized water, was characterized by UV-absorption spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. The O - water treatments caused an obvious increase of the surface hydrophilicity, surface energy, surface roughness and also caused an alteration of the surface chemical composition for PS surfaces, which were indicated by the variety of contact angle and material characterization by atomic force microscope (AFM) imaging, field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and attenuated total-reflection Fourier transform infrared (ATR-FTIR) measurements. Particularly, it was found that some hydrophilic groups such as hydroxyl (OH) and carbonyl (C=O) groups were introduced onto the polystyrene surfaces via the O - water treatment, leading to the increases of surface hydrophilicity and surface energy. The active oxygen species would react with the aromatic ring molecules on the PS surfaces and decompose the aromatic compounds to produce hydrophilic hydroxyl and carbonyl compounds. In addition, the O - water is also considered as a 'clean solution' without adding any toxic chemicals and it is easy to be handled at room temperature. Present method may suit to the surface modification of polymers and other heat-sensitive materials potentially

  5. Evolution of Oxygen Deficiency Center on Fused Silica Surface Irradiated by Ultraviolet Laser and Posttreatment

    Directory of Open Access Journals (Sweden)

    Hai-Bing Lü

    2014-01-01

    Full Text Available Evolution of oxygen deficiency centers (ODCs on a fused silica surface irradiated using a 355 nm ultraviolet (UV laser beam in both vacuum and atmospheric conditions was quantitatively studied using photoluminescence and X-ray photoelectron spectroscopy. When the fusedsilica surface was exposed to the UV laser in vacuum, the laser damage threshold was decreased whereas the concentration of the ODCs was increased. For the fuse silica operated under the high power lasers, creation of ODCs on their surface resulted from the UV laser irradiation, and this is more severe in a high vacuum. The laser fluence and/or laser intensity have significant effects on the increase of the ODCs concentration. The ODCs can be effectively repaired using postoxygen plasma treatment and UV laser irradiation in an excessive oxygen environment. Results also demonstrated that the “gain” and “loss” of oxygen at the silica surface is a reversible and dynamic process.

  6. Surface oxygen vacancies on WO{sub 3} contributed to enhanced photothermo-synergistic effect

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yingying; Wang, Changhua; Zheng, Han; Wan, Fangxu; Yu, Fei; Zhang, Xintong, E-mail: xtzhang@nenu.edu.cn; Liu, Yichun

    2017-01-01

    Graphical abstract: WO{sub 3−x} acts as efficient and stable photothermocatalyst for detoxification of gaseous acetaldehyde. - Highlights: • WO{sub 3} was annealed under air and hydrogen atomsphere. • Phase transition from WO{sub 3} to WO{sub 2.72} to WO{sub 2} was observed after hydrogen treatment. • WO{sub 3−x} with optimized degree of oxygen deficiency displayed significant photothermocatalytic activity against degradation of acetaldehyde. • Mechanism operating in photocatalytic and thermal effects is discussed. - Abstract: Photothermooxidation has demonstrated a high efficiency in the removal of volatile organic compounds in air. Among photothermocatalysts, attention is presently focused on composites of noble metal/metal oxide or metal oxide/metal oxide. Instead, in this work, we present a case of single oxide WO{sub 3} subjected to hydrogen treatment as photothermocatalyst. With the increase of hydrogen treatment temperature, the color of WO{sub 3} changes from yellow to blue to dark blue and a phase transition from WO{sub 3} to WO{sub 2.72} to WO{sub 2} is accompanied, suggesting an increase of concentration of oxygen vacancy. Photothermocatalytic test against degradation of gaseous acetaldehyde at 60 °C under UV light shows that WO{sub 3−x} sample with low concentration of oxygen vacancy displays the most significant synergetic effect between photocatalysis and thermocatalysis. Its photothermocatalytic activity in terms of CO{sub 2} evolution rate is 5.2 times higher than that of photocatalytic activity. However, WO{sub 3}–WO{sub 2.72} and WO{sub 2} with high degree of oxygen deficiency show insignificant synergetic effect between photocatalysis and thermocatalysis. The reason for the different synergistic effect over above samples is believed to lie in balance between decreased activation energy of lattice oxygen and recombination of photogenerated electrons and holes induced by oxygen deficiency.

  7. Technologies for protection of the Space Station power system surfaces in atomic oxygen environment

    Science.gov (United States)

    Nahra, Henry K.; Rutledge, Sharon K.

    1988-01-01

    Technologies for protecting Space Station surfaces from degradation caused by atomic oxygen are discussed, stressing protection of the power system surfaces. The Space Station power system is described and research concerning the solar array surfaces and radiator surfaces is examined. The possibility of coating the solar array sufaces with a sputter deposited thin film of silicon oxide containing small concentrations of polytetrafluoroethylene is presented. Hexamethyldisiloxane coating for these surfaces is also considered. For the radiator surfaces, possible coatings include silver teflon thermal coating and zinc orthotitanate.

  8. Surface Oxidation of AuNi Heterodimers to Achieve High Activities toward Hydrogen/Oxygen Evolution and Oxygen Reduction Reactions.

    Science.gov (United States)

    Ni, Bing; He, Peng; Liao, Wenxin; Chen, Shuangming; Gu, Lin; Gong, Yue; Wang, Kai; Zhuang, Jing; Song, Li; Zhou, Gang; Wang, Xun

    2018-04-01

    Although much attention has been paid to the exploration of highly active electrocatalysts, especially catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), the development of multifunctional catalysts remains a challenge. Here, we utilize AuNi heterodimers as the starting materials to achieve high activities toward HER, OER and ORR. The HER and ORR activities in an alkali environment are similar to those of Pt catalysts, and the OER activity is very high and better than that of commercial IrO 2 . Both the experimental and calculated results suggest that the surface oxidation under oxidative conditions is the main reason for the different activities. The NiO/Ni interface which exists in the as-synthesized heterodimers contributes to high HER activity, the Ni(OH) 2 -Ni-Au interface and the surface Ni(OH) 2 obtained in electrochemical conditons gives rise to promising ORR and OER activities, respectively. As a comparison, a Au@Ni core-shell structure is also synthesized and examined. The core-shell structure shows lower activities for HER and OER than the heterodimers, and reduces O 2 selectively to H 2 O 2 . The work here allows for the development of a method to design multifunctional catalysts via the partial oxidation of a metal surface to create different active centers. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Effects of atomic oxygen irradiation on the surface properties of phenolphthalein poly(ether sulfone)

    International Nuclear Information System (INIS)

    Pei Xianqiang; Li Yan; Wang Qihua; Sun Xiaojun

    2009-01-01

    To study the effects of low earth orbit environment on the surface properties of polymers, phenolphthalein poly(ether sulfone) (PES-C) blocks were irradiated by atomic oxygen in a ground-based simulation system. The surface properties of the pristine and irradiated blocks were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM). It was found that atomic oxygen irradiation induced the destruction of PES-C molecular chains, including the scission and oxidation of PES-C molecular chains, as evidenced by FTIR and XPS results. The scission of PES-C molecular chains decreased the relative concentration of C in the surface, while the oxidation increased the relative concentration of O in the surface. The changes in surface chemical structure and composition also changed the surface morphology of the block, which shifted from smooth structure before irradiation to 'carpet-like' structure after irradiation

  10. Effects of atomic oxygen irradiation on the surface properties of phenolphthalein poly(ether sulfone)

    Energy Technology Data Exchange (ETDEWEB)

    Pei Xianqiang [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, No. 18, Tianshui Middle Road, Lanzhou 730000 (China); Li Yan [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, No. 18, Tianshui Middle Road, Lanzhou 730000 (China); Graduate school of the Chinese Academy of Sciences, Beijing 100039 (China); Wang Qihua [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, No. 18, Tianshui Middle Road, Lanzhou 730000 (China)], E-mail: Wangqh@lzb.ac.cn; Sun Xiaojun [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, No. 18, Tianshui Middle Road, Lanzhou 730000 (China)

    2009-03-15

    To study the effects of low earth orbit environment on the surface properties of polymers, phenolphthalein poly(ether sulfone) (PES-C) blocks were irradiated by atomic oxygen in a ground-based simulation system. The surface properties of the pristine and irradiated blocks were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM). It was found that atomic oxygen irradiation induced the destruction of PES-C molecular chains, including the scission and oxidation of PES-C molecular chains, as evidenced by FTIR and XPS results. The scission of PES-C molecular chains decreased the relative concentration of C in the surface, while the oxidation increased the relative concentration of O in the surface. The changes in surface chemical structure and composition also changed the surface morphology of the block, which shifted from smooth structure before irradiation to 'carpet-like' structure after irradiation.

  11. Effects of atomic oxygen irradiation on the surface properties of phenolphthalein poly(ether sulfone)

    Science.gov (United States)

    Pei, Xianqiang; Li, Yan; Wang, Qihua; Sun, Xiaojun

    2009-03-01

    To study the effects of low earth orbit environment on the surface properties of polymers, phenolphthalein poly(ether sulfone) (PES-C) blocks were irradiated by atomic oxygen in a ground-based simulation system. The surface properties of the pristine and irradiated blocks were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM). It was found that atomic oxygen irradiation induced the destruction of PES-C molecular chains, including the scission and oxidation of PES-C molecular chains, as evidenced by FTIR and XPS results. The scission of PES-C molecular chains decreased the relative concentration of C in the surface, while the oxidation increased the relative concentration of O in the surface. The changes in surface chemical structure and composition also changed the surface morphology of the block, which shifted from smooth structure before irradiation to "carpet-like" structure after irradiation.

  12. Feasibility Analysis of Liquefying Oxygen Generated from Water Electrolysis Units on Lunar Surface

    Science.gov (United States)

    Jeng, Frank F.

    2009-01-01

    Concepts for liquefying oxygen (O2) generated from water electrolysis subsystems on the Lunar surface were explored. Concepts for O2 liquefaction units capable of generating 1.38 lb/hr (0.63 kg/hr) liquid oxygen (LOX) were developed. Heat and mass balance calculations for the liquefaction concepts were conducted. Stream properties, duties of radiators, heat exchangers and compressors for the selected concepts were calculated and compared.

  13. Surface-Selective Preferential Production of Reactive Oxygen Species on Piezoelectric Ceramics for Bacterial Killing

    OpenAIRE

    Tan, Guoxin; Wang, Shuangying; Zhu, Ye; Zhou, Lei; Yu, Peng; Wang, Xiaolan; He, Tianrui; Chen, Junqi; Mao, Chuanbin; Ning, Chengyun

    2016-01-01

    Reactive oxygen species (ROS) can be used to kill bacterial cells, and thus the selective generation of ROS from material surfaces is an emerging direction in antibacterial material discovery. We found the polarization of piezoelectric ceramic causes the two sides of the disk to become positively and negatively charged, which translate into cathode and anode surfaces in an aqueous solution. Because of the microelectrolysis of water, ROS are preferentially formed on the cathode surface. Conseq...

  14. Electron spin-lattice relaxation of the S0 state of the oxygen-evolving complex in photosystem II and of dinuclear manganese model complexes.

    Science.gov (United States)

    Kulik, L V; Lubitz, W; Messinger, J

    2005-07-05

    The temperature dependence of the electron spin-lattice relaxation time T1 was measured for the S0 state of the oxygen-evolving complex (OEC) in photosystem II and for two dinuclear manganese model complexes by pulse EPR using the inversion-recovery method. For [Mn(III)Mn(IV)(mu-O)2 bipy4]ClO4, the Raman relaxation process dominates at temperatures below 50 K. In contrast, Orbach type relaxation was found for [Mn(II)Mn(III)(mu-OH)(mu-piv)2(Me3 tacn)2](ClO4)2 between 4.3 and 9 K. For the latter complex, an energy separation of 24.7-28.0 cm(-1) between the ground and the first excited electronic state was determined. In the S0 state of photosystem II, the T1 relaxation times were measured in the range of 4.3-6.5 K. A comparison with the relaxation data (rate and pre-exponential factor) of the two model complexes and of the S2 state of photosystem II indicates that the Orbach relaxation process is dominant for the S0 state and that its first excited state lies 21.7 +/- 0.4 cm(-1) above its ground state. The results are discussed with respect to the structure of the OEC in photosystem II.

  15. Fluorine-Terminated Diamond Surfaces as Dense Dipole Lattices: The Electrostatic Origin of Polar Hydrophobicity.

    Science.gov (United States)

    Mayrhofer, Leonhard; Moras, Gianpietro; Mulakaluri, Narasimham; Rajagopalan, Srinivasan; Stevens, Paul A; Moseler, Michael

    2016-03-30

    Despite the pronounced polarity of C-F bonds, many fluorinated carbon compounds are hydrophobic: a controversial phenomenon known as "polar hydrophobicity". Here, its underlying microscopic mechanisms are explored by ab initio calculations of fluorinated and hydrogenated diamond (111) surfaces interacting with single water molecules. Gradient- and van der Waals-corrected density functional theory simulations reveal that "polar hydrophobicity" of the fully fluorinated surfaces is caused by a negligible surface/water electrostatic interaction. The densely packed C-F surface dipoles generate a short-range electric field that decays within the core repulsion zone of the surface and hence vanishes in regions accessible by adsorbates. As a result, water physisorption on fully F-terminated surfaces is weak (adsorption energies Ead 0.2 eV) that is dominated by electrostatic interactions. The suppression of electrostatic interactions also holds for perfluorinated molecular carbon compounds, thus explaining the prevalent hydrophobicity of fluorocarbons. In general, densely packed polar terminations do not always lead to short-range electric fields. For example, surfaces with substantial electron density spill-out give rise to electric fields with a much slower decay. However, electronic spill-out is limited in F/H-terminated carbon materials. Therefore, our ab initio results can be reproduced and rationalized by a simple classical point-charge model. Consequently, classical force fields can be used to study the wetting of F/H-terminated diamond, revealing a pronounced correlation between adsorption energies of single H2O molecules and water contact angles.

  16. Adsorption of atomic nitrogen and oxygen on [Formula: see text] surface: a density functional theory study.

    Science.gov (United States)

    Breedon, M; Spencer, M J S; Yarovsky, I

    2009-04-08

    The adsorption of atomic nitrogen and oxygen on the ([Formula: see text]) crystal face of zinc oxide (ZnO) was studied. Binding energies, workfunction changes, vibrational frequencies, charge density differences and electron localization functions were calculated. It was elucidated that atomic oxygen binds more strongly than nitrogen, with the most stable [Formula: see text] structure exhibiting a binding energy of -2.47 eV, indicating chemisorption onto the surface. Surface reconstructions were observed for the most stable minima of both atomic species. Positive workfunction changes were calculated for both adsorbed oxygen and nitrogen if the adsorbate interacted with zinc atoms. Negative workfunction changes were calculated when the adsorbate interacted with both surface oxygen and zinc atoms. Interactions between the adsorbate and the surface zinc atoms resulted in ionic-type bonding, whereas interactions with oxygen atoms were more likely to result in the formation of covalent-type bonding. The positive workfunction changes correlate with an experimentally observed increase in resistance of ZnO conductometric sensor devices.

  17. Surface recombination of oxygen atoms in O2 plasma at increased pressure: II. Vibrational temperature and surface production of ozone

    Science.gov (United States)

    Lopaev, D. V.; Malykhin, E. M.; Zyryanov, S. M.

    2011-01-01

    Ozone production in an oxygen glow discharge in a quartz tube was studied in the pressure range of 10-50 Torr. The O3 density distribution along the tube diameter was measured by UV absorption spectroscopy, and ozone vibrational temperature TV was found comparing the calculated ab initio absorption spectra with the experimental ones. It has been shown that the O3 production mainly occurs on a tube surface whereas ozone is lost in the tube centre where in contrast the electron and oxygen atom densities are maximal. Two models were used to analyse the obtained results. The first one is a kinetic 1D model for the processes occurring near the tube walls with the participation of the main particles: O(3P), O2, O2(1Δg) and O3 molecules in different vibrational states. The agreement of O3 and O(3P) density profiles and TV calculated in the model with observed ones was reached by varying the single model parameter—ozone production probability (\\gamma_{O_{3}}) on the quartz tube surface on the assumption that O3 production occurs mainly in the surface recombination of physisorbed O(3P) and O2. The phenomenological model of the surface processes with the participation of oxygen atoms and molecules including singlet oxygen molecules was also considered to analyse \\gamma_{O_{3}} data obtained in the kinetic model. A good agreement between the experimental data and the data of both models—the kinetic 1D model and the phenomenological surface model—was obtained in the full range of the studied conditions that allowed consideration of the ozone surface production mechanism in more detail. The important role of singlet oxygen in ozone surface production was shown. The O3 surface production rate directly depends on the density of physisorbed oxygen atoms and molecules and can be high with increasing pressure and energy inputted into plasma while simultaneously keeping the surface temperature low enough. Using the special discharge cell design, such an approach opens up the

  18. Surface recombination of oxygen atoms in O2 plasma at increased pressure: II. Vibrational temperature and surface production of ozone

    International Nuclear Information System (INIS)

    Lopaev, D V; Malykhin, E M; Zyryanov, S M

    2011-01-01

    Ozone production in an oxygen glow discharge in a quartz tube was studied in the pressure range of 10-50 Torr. The O 3 density distribution along the tube diameter was measured by UV absorption spectroscopy, and ozone vibrational temperature T V was found comparing the calculated ab initio absorption spectra with the experimental ones. It has been shown that the O 3 production mainly occurs on a tube surface whereas ozone is lost in the tube centre where in contrast the electron and oxygen atom densities are maximal. Two models were used to analyse the obtained results. The first one is a kinetic 1D model for the processes occurring near the tube walls with the participation of the main particles: O( 3 P), O 2 , O 2 ( 1 Δ g ) and O 3 molecules in different vibrational states. The agreement of O 3 and O( 3 P) density profiles and T V calculated in the model with observed ones was reached by varying the single model parameter-ozone production probability (γ O 3 ) on the quartz tube surface on the assumption that O 3 production occurs mainly in the surface recombination of physisorbed O( 3 P) and O 2 . The phenomenological model of the surface processes with the participation of oxygen atoms and molecules including singlet oxygen molecules was also considered to analyse γ O 3 data obtained in the kinetic model. A good agreement between the experimental data and the data of both models-the kinetic 1D model and the phenomenological surface model-was obtained in the full range of the studied conditions that allowed consideration of the ozone surface production mechanism in more detail. The important role of singlet oxygen in ozone surface production was shown. The O 3 surface production rate directly depends on the density of physisorbed oxygen atoms and molecules and can be high with increasing pressure and energy inputted into plasma while simultaneously keeping the surface temperature low enough. Using the special discharge cell design, such an approach opens up

  19. Crystalline and lattice matched Ba0.7Si0.3O layers on plane and vicinal Si(001) surfaces

    International Nuclear Information System (INIS)

    Zachariae, J.

    2006-01-01

    In this work the low temperature growth conditions of epitaxial and lattice-matched Ba 0.7 Sr 0.3 O layers on Si(100) were investigated using the combination of low energy electron diffraction (LEED), x-ray photoemission (XPS) and electron energy loss spectroscopy (EELS). With these methods crystallinity, stoichiometry and electronic structure of both occupied and unoccupied levels were studied as a function of layer thickness. Oxide layers were generated by evaporating the metals in oxygen ambient pressure with the sample at room temperature. Perfect crystallinity and lattice matching was only obtained starting with a preadsorbed monolayer (ML) of Sr or Ba at a concentration close to one monolayer. The XPS analysis shows that Ba 0.7 Sr 0.3 O as a high-K gate dielectric offers an adequate band gap, an appropriate band alignment and a atomically sharp interface to the Si(001) substrate. No silicide and silicate species, or SiO 2 formation at the interface after oxidation were found. To show that Ba 0.7 Sr 0.3 O is really appropriate to replace SiO 2 as a gate dielectric, first C-V and I-V curves of MOS-diodes with SrO, BaO and Ba 0.7 Sr 0.3 O as gateoxide were measured under ambient conditions. Besides other results, it turns out that the measured dielectric constant of Ba 0.7 Sr 0.3 O conforms with the expected value of ε ∼ 25 - 30. Exploring ways for self-organized structuring of insulating films, the possibility to produce replicas of step trains, given by a vicinal Si(001)-4 [110] surface, in layers of crystalline and perfectly lattice matched Ba 0.7 Sr 0.3 O were investigated. For this purpose high-resolution spot profile analyses in low-energy electron diffraction (SPA-LEED) both on flat Si(001) and on vicinal Si(001)-4 [110] were carried out. The G(S) analysis of these mixed oxide layers reveals a strong influence of local compositional fluctuations of Sr and Ba ions and their respective scattering phases, which appears as an unphysically large variation

  20. Atomic Oxygen Treatment for Non-Contact Removal of Organic Protective Coatings from Painting Surfaces

    Science.gov (United States)

    Rutledge, Sharon K.; Banks, Bruce A.; Cales, Michael

    1994-01-01

    Current techniques for removal of varnish (lacquer) and other organic protective coatings from paintings involve contact with the surface. This contact can remove pigment, or alter the shape and location of paint on the canvas surface. A thermal energy atomic oxygen plasma, developed to simulate the space environment in low Earth orbit, easily removes these organic materials. Uniform removal of organic protective coatings from the surfaces of paintings is accomplished through chemical reaction. Atomic oxygen will not react with oxides so that most paint pigments will not be affected by the reaction. For paintings containing organic pigments, the exposure can be carefully timed so that the removal stops just short of the pigment. Color samples of Alizarin Crimson, Sap Green, and Zinc White coated with Damar lacquer were exposed to atomic oxygen. The lacquer was easily removed from all of the samples. Additionally, no noticeable change in appearance was observed after the lacquer was reapplied. The same observations were made on a painted canvas test sample obtained from the Cleveland Museum of Art. Scanning electron microscope photographs showed a slight microscopic texturing of the vehicle after exposure. However, there was no removal or disturbance of the paint pigment on the surface. It appears that noncontact cleaning using atomic oxygen may provide a viable alternative to other cleaning techniques. It is especially attractive in cases where the organic protective surface cannot be acceptably or safely removed by conventional techniques.

  1. Water Induced Surface Reconstruction of the Oxygen (2x1) covered Ru(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Maier, Sabine; Cabrera-Sanfelix, Pepa; Stass, Ingeborg; Sanchez-Portal, Daniel; Arnau, Andres; Salmeron, Miquel

    2010-08-06

    Low temperature scanning tunneling microscopy (STM) and density functional theory (DFT) were used to study the adsorption of water on a Ru(0001) surface covered with half monolayer of oxygen. The oxygen atoms occupy hcp sites in an ordered structure with (2x1) periodicity. DFT predicts that water is weakly bound to the unmodified surface, 86 meV compared to the ~;;200 meV water-water H-bond. Instead, we found that water adsorption causes a shift of half of the oxygen atoms from hcp sites to fcc sites, creating a honeycomb structure where water molecules bind strongly to the exposed Ru atoms. The energy cost of reconstructing the oxygen overlayer, around 230 meV per displaced oxygen atom, is more than compensated by the larger adsorption energy of water on the newly exposed Ru atoms. Water forms hydrogen bonds with the fcc O atoms in a (4x2) superstructure due to alternating orientations of the molecules. Heating to 185 K results in the complete desorption of the water layer, leaving behind the oxygen honeycomb structure, which is metastable relative to the original (2x1). This stable structure is not recovered until after heating to temperatures close to 260K.

  2. Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

    Science.gov (United States)

    Niaz, Shanawer; Zdetsis, Aristides D.; Koukaras, Emmanuel N.; Gülseren, Oǧuz; Sadiq, Imran

    2016-11-01

    In most of the realistic ab initio and model calculations which have appeared on the emission of light from silicon nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si29 nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated Si nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies but trends in same fashion. It is also demonstrated that within same composition, oxidizing constituent, along with their spatial distribution substantially alters binding energy, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (up to 1.48 eV) and localization of frontier orbitals.

  3. Oxygen reduction reaction over silver particles with various morphologies and surface chemical states

    Science.gov (United States)

    Ohyama, Junya; Okata, Yui; Watabe, Noriyuki; Katagiri, Makoto; Nakamura, Ayaka; Arikawa, Hidekazu; Shimizu, Ken-ichi; Takeguchi, Tatsuya; Ueda, Wataru; Satsuma, Atsushi

    2014-01-01

    The oxygen reduction reaction (ORR) in an alkaline solution was carried out using Ag powders having various particle morphologies and surface chemical states (Size: ca. 40-110 nm in crystalline size. Shape: spherical, worm like, and angular. Surface: smooth with easily reduced AgOx, defective with AgOx, and Ag2CO3 surface layer). The various Ag powders were well characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption, scanning electron microscopy, Raman spectroscopy, cyclic voltammetry, and stripping voltammetry of underpotential-deposited lead. Defective and oxidized surfaces enhanced the Ag active surface area during the ORR. The ORR activity was affected by the morphology and surface chemical state: Ag particles with defective and angular surfaces showed smaller electron exchange number between three and four but showed higher specific activity compared to Ag particles with smooth surfaces.

  4. Distinguishibility of Oxygen Desorption From the Surface Region with Mobility Dominant Effects in Nanocrystalline Ceria Films

    Energy Technology Data Exchange (ETDEWEB)

    Saraf, Laxmikant V; Shutthanandan, V; Zhang, Yanwen; Thevuthasan, Suntharampillai; Wang, Chong M; El-Azab, Anter; Baer, Donald R

    2004-11-15

    We present an investigation of oxygen (18Ο) uptake measurements in 1 μm thick nanocrystalline ceria films grown on single crystal Al₂O₃ (0001) by nuclear reaction analysis (NRA). Oxygen uptake measurements were carried out in the temperature range of 200°C-600°C at a background 18O pressure of 4.0 x 10-6 Torr. Average grain-size in the as-grown films, synthesized by sol-gel process was ~ 3 nm confirmed by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) measurements. From the diffusion depth profiles, changes in intensity and slopes in surface and interface regions indicate dominating oxygen mobility effects. Oxygen desorption is clearly distinguishable in the film surface region as a result of shift in the oxygen peak intensity. It is argued that high defect density in nanocrystalline ceria which is associated with nano-grain surface combined with intermediate temperature reducing environment triggers multiple processes like diffusion, desorption and exchange interaction. The promising nature of NRA is realized as an effective tool to acquire the depth-dependent information regarding such complex reactions that exists in nanocrystalline environment.

  5. Magnetic susceptibility of oxygen adsorbed on the surface of spherical and fibrous activated carbon.

    Directory of Open Access Journals (Sweden)

    Kiyoshi Kawamura

    2009-02-01

    Full Text Available The magnetic susceptibilities of oxygen adsorbed on the surface of bead-shaped activated carbon and activated carbon fibers were evaluated as a function of temperature between 4.2 K and 300 K, and found to exhibit a sharp peak at around 50 K. This implies that the adsorbed oxygen molecules form an antiferromagnetic state. The relation between the susceptibility and the adsorbed mass suggest that the thickness of the adsorbed oxygen is thin enough to consider a two-dimensional structure for bead–shaped activated carbon and carbon fibers across the fiber axis but thick enough to regard it as three-dimensional along the fiber axis. The result is discussed with reference to the study on one-dimensional oxygen array.

  6. Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

    Energy Technology Data Exchange (ETDEWEB)

    Niaz, Shanawer, E-mail: shanawersi@gmail.com [Department of Physics, Bilkent University, Ankara 06800 (Turkey); Molecular Engineering Laboratory, at the Department of Physics, University of Patras, Patras, GR-26500 (Greece); Zdetsis, Aristides D.; Koukaras, Emmanuel N. [Molecular Engineering Laboratory, at the Department of Physics, University of Patras, Patras, GR-26500 (Greece); Gülseren, Oǧuz [Department of Physics, Bilkent University, Ankara 06800 (Turkey); Sadiq, Imran [Centre of Excellence in Solid State Physics, University of the Punjab, Lahore (Pakistan)

    2016-11-30

    Highlights: • Understanding surface science of oxygenated silicon nanocrystals by means of their composition, stoichiometry and spatial distribution. • Drastic change observed in binding energy, localization of frontier orbitals and HOMO-LUMO gap up to 1.48 eV. • Might be a safe alternative of size dependent bandgap tunability. - Abstract: In most of the realistic ab initio and model calculations which have appeared on the emission of light from silicon nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si{sub 29} nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated Si nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies but trends in same fashion. It is also demonstrated that within same composition, oxidizing constituent, along with their spatial distribution substantially alters binding energy, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (up to 1.48 eV) and localization of frontier orbitals.

  7. Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

    International Nuclear Information System (INIS)

    Niaz, Shanawer; Zdetsis, Aristides D.; Koukaras, Emmanuel N.; Gülseren, Oǧuz; Sadiq, Imran

    2016-01-01

    Highlights: • Understanding surface science of oxygenated silicon nanocrystals by means of their composition, stoichiometry and spatial distribution. • Drastic change observed in binding energy, localization of frontier orbitals and HOMO-LUMO gap up to 1.48 eV. • Might be a safe alternative of size dependent bandgap tunability. - Abstract: In most of the realistic ab initio and model calculations which have appeared on the emission of light from silicon nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si 29 nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated Si nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies but trends in same fashion. It is also demonstrated that within same composition, oxidizing constituent, along with their spatial distribution substantially alters binding energy, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (up to 1.48 eV) and localization of frontier orbitals.

  8. Surface-Selective Preferential Production of Reactive Oxygen Species on Piezoelectric Ceramics for Bacterial Killing.

    Science.gov (United States)

    Tan, Guoxin; Wang, Shuangying; Zhu, Ye; Zhou, Lei; Yu, Peng; Wang, Xiaolan; He, Tianrui; Chen, Junqi; Mao, Chuanbin; Ning, Chengyun

    2016-09-21

    Reactive oxygen species (ROS) can be used to kill bacterial cells, and thus the selective generation of ROS from material surfaces is an emerging direction in antibacterial material discovery. We found the polarization of piezoelectric ceramic causes the two sides of the disk to become positively and negatively charged, which translate into cathode and anode surfaces in an aqueous solution. Because of the microelectrolysis of water, ROS are preferentially formed on the cathode surface. Consequently, the bacteria are selectively killed on the cathode surface. However, the cell experiment suggested that the level of ROS is safe for normal mammalian cells.

  9. Effect of Oxygen and Initiator Solubility on Admicellar Polymerization of Styrene on Silica Surfaces

    Directory of Open Access Journals (Sweden)

    Pohlee Cheah

    2017-01-01

    Full Text Available Although admicellar polymerization has been termed the surface analog of emulsion polymerization, previous reports utilizing free radical-initiated admicellar polymerization relied on high levels of the free radical initiator when compared to emulsion polymerization, likely due to the presence of oxygen in the reported admicellar polymerization systems. Admicellar polymerizations of styrene on the surface of precipitated silica initiated by either a water-soluble or a water-insoluble initiator were studied to determine the effect of dissolved oxygen and free radical initiator solubility on the kinetics, yield, and molecular weight of the polymer formed. Results show that the presence of oxygen reduces the polymer yield and limits molecular weight. The solubility of the initiator also affected the polymer formed in the admicellar polymerization of styrene. While monomer conversions and polymer yield were similar, the molecular weights of polymerizations initiated by a water-soluble initiator were higher than comparable polymerizations initiated by a water-insoluble initiator.

  10. Monte Carlo Technique Used to Model the Degradation of Internal Spacecraft Surfaces by Atomic Oxygen

    Science.gov (United States)

    Banks, Bruce A.; Miller, Sharon K.

    2004-01-01

    Atomic oxygen is one of the predominant constituents of Earth's upper atmosphere. It is created by the photodissociation of molecular oxygen (O2) into single O atoms by ultraviolet radiation. It is chemically very reactive because a single O atom readily combines with another O atom or with other atoms or molecules that can form a stable oxide. The effects of atomic oxygen on the external surfaces of spacecraft in low Earth orbit can have dire consequences for spacecraft life, and this is a well-known and much studied problem. Much less information is known about the effects of atomic oxygen on the internal surfaces of spacecraft. This degradation can occur when openings in components of the spacecraft exterior exist that allow the entry of atomic oxygen into regions that may not have direct atomic oxygen attack but rather scattered attack. Openings can exist because of spacecraft venting, microwave cavities, and apertures for Earth viewing, Sun sensors, or star trackers. The effects of atomic oxygen erosion of polymers interior to an aperture on a spacecraft were simulated at the NASA Glenn Research Center by using Monte Carlo computational techniques. A two-dimensional model was used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of the distance into a parallel-walled cavity. The model allows the atomic oxygen arrival direction, the Maxwell Boltzman temperature, and the ram energy to be varied along with the interaction parameters of the degree of recombination upon impact with polymer or nonreactive surfaces, the initial reaction probability, the reaction probability dependence upon energy and angle of attack, degree of specularity of scattering of reactive and nonreactive surfaces, and the degree of thermal accommodation upon impact with reactive and non-reactive surfaces to be varied to allow the model to produce atomic oxygen erosion geometries that replicate actual experimental results from space. The degree of

  11. Oxygen termination of homoepitaxial diamond surface by ozone and chemical methods: An experimental and theoretical perspective

    Science.gov (United States)

    Navas, Javier; Araujo, Daniel; Piñero, José Carlos; Sánchez-Coronilla, Antonio; Blanco, Eduardo; Villar, Pilar; Alcántara, Rodrigo; Montserrat, Josep; Florentin, Matthieu; Eon, David; Pernot, Julien

    2018-03-01

    Phenomena related with the diamond surface of both power electronic and biosensor devices govern their global behaviour. In particular H- or O-terminations lead to wide variations in their characteristics. To study the origins of such aspects in greater depth, different methods to achieve oxygen terminated diamond were investigated following a multi-technique approach. DFT calculations were then performed to understand the different configurations between the C and O atoms. Three methods for O-terminating the diamond surface were performed: two physical methods with ozone at different pressures, and an acid chemical treatment. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, HRTEM, and EELS were used to characterize the oxygenated surface. Periodic-DFT calculations were undertaken to understand the effect of the different ways in which the oxygen atoms are bonded to carbon atoms on the diamond surface. XPS results showed the presence of hydroxyl or ether groups, composed of simple Csbnd O bonds, and the acid treatment resulted in the highest amount of O on the diamond surface. In turn, ellipsometry showed that the different treatments led to the surface having different optical properties, such as a greater refraction index and extinction coefficient in the case of the sample subjected to acid treatment. TEM analysis showed that applying temperature treatment improved the distribution of the oxygen atoms at the interface and that this generates a thinner amount of oxygen at each position and higher interfacial coverage. Finally, DFT calculations showed both an increase in the number of preferential electron transport pathways when π bonds and ether groups appear in the system, and also the presence of states in the middle of the band gap when there are π bonds, Cdbnd C or Cdbnd O.

  12. Tunable Oxygen Functional Groups as Electrocatalysts on Graphite Felt Surfaces for All-Vanadium Flow Batteries

    Energy Technology Data Exchange (ETDEWEB)

    Estevez, Luis [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Reed, David [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Nie, Zimin [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Schwarz, Ashleigh M. [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Nandasiri, Manjula I. [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Kizewski, James P. [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Wang, Wei [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Thomsen, Edwin [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Liu, Jun [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Zhang, Ji-Guang [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Sprenkle, Vincent [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA; Li, Bin [Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland WA 99352 USA

    2016-05-17

    We decorated the surfaces of graphite felts with some oxygen-containing functional groups, such as C-OH, O=C and HO-C=O. And the mole ratios and amounts of these functional groups were effectively adjusted on the graphite surface by a particular method. The catalytic effects of amounts and mole ratio of different kinds of functional groups on VRB electrode performances were investigated in detail.

  13. Simultaneous modulation of surface composition, oxygen vacancies and assembly in hierarchical Co3O4 mesoporous nanostructures for lithium storage and electrocatalytic oxygen evolution

    DEFF Research Database (Denmark)

    Sun, Hongyu; Zhao, Yanyan; Mølhave, Kristian

    2017-01-01

    in superior electrochemical properties when used as the anode materials for lithium-ion batteries and as an electrocatalyst for the oxygen evolution reaction. The excellent electrochemical performance is attributed to the synergistic effects of novel hierarchical morphology, crystal structure of the active......We developed a facile solution reductive method to simultaneously tune the surface composition, oxygen vacancies and three dimensional assembly in Co3O4 hierarchical nanostructures. The controllable surface composition, oxygen vacancies together with hierarchical micro/nanoarchitectures resulted...... materials, the improvement of intrinsic conductivity and inner surface area induced by the oxygen vacancies. The present strategy not only provides a facile method to assemble novel hierarchical architectures, but also paves a way to control surface structures (chemical composition and crystal defects...

  14. The interaction of oxygen with Ni(100) and the reduction of the surface oxide by hydrogen

    NARCIS (Netherlands)

    Bokx, P.K. de; Labohm, F.; Gijzeman, O.L.J.; Bootsma, B.A.; Geus, John W.

    The interaction of oxygen with Ni(100) has been studied with ellipsometry, Auger electron spectroscopy and low energy electron diffraction. The observations of other workers are completely confirmed. The same techniques and procedures have been used to study the reduction of the surface oxide with

  15. Self-interacting polymer chains terminally anchored to adsorbing surfaces of three-dimensional fractal lattices

    Science.gov (United States)

    Živić, I.; Elezović-Hadžić, S.; Milošević, S.

    2018-01-01

    We have studied the adsorption problem of self-attracting linear polymers, modeled by self-avoiding walks (SAWs), situated on three-dimensional fractal structures, exemplified by 3d Sierpinski gasket (SG) family of fractals as containers of a poor solvent. Members of SG family are enumerated by an integer b (b ≥ 2), and it is assumed that one side of each SG fractal is an impenetrable adsorbing surface. We calculate the critical exponents γ1 ,γ11, and γs, which are related to the numbers of all possible SAWs with one, both, and no ends anchored to the adsorbing boundary, respectively. By applying the exact renormalization group (RG) method (for the first three members of the SG fractal family, b = 2 , 3, and 4), we have obtained specific values of these exponents, for θ-chain and globular polymer phase. We discuss their mutual relations and relations with corresponding values pertinent to extended polymer chain phase.

  16. The modification of nanocomposite hybrid polymer surfaces by exposure to oxygen containing plasmas

    Science.gov (United States)

    Figueiredo, Ashley; Zimmermann, Katherine; Augustine, Brian; Hughes, Chris; Chusuei, Charles

    2006-11-01

    The wetting properties of the surfaces of the nanocomposite hybrid polymer poly[(propylmethacryl-heptaisobutyl- polyhedral oligomeric silsequioxane)-co-(methylmethacrylate)] (POSS-PMMA)has been studied before and after exposure to plasmas containing oxygen. The contact angle of water droplets on the surface showed a substantial decrease after plasma exposure indicating an increase in the hydrophilicity of the surface. A model was developed in which the plasma preferentially removed organic material including both the PMMA backbone and isobutyl groups from the corners of the POSS cages leaving behind a surface characterized by the silicon oxide-like POSS material. Measurements of surface concentrations of oxygen, silicon, and carbon by x-ray photoelectron spectroscopy (XPS) showed an increase in the amount of oxygen and silicon compared to carbon and the appropriate chemical shifts were observed in the XPS data to support the model of Si-O enrichment on the surface. Variable angle spectroscopic ellipsometry (VASE) and atomic force microscopy (AFM) measurements also supported the model and these results will be presented.

  17. Surface characterization of the chitosan membrane after oxygen plasma treatment and its aging effect

    International Nuclear Information System (INIS)

    Wang Yingjun; Yin Shiheng; Ren Li; Zhao Lianna

    2009-01-01

    Chitosan has received considerable attention for biomedical applications in recent years because of its biocompatibility and biodegradability. In this paper, angle-resolved x-ray photoelectron spectroscopy (ARXPS) was carried out to investigate the chemical groups' spatial orientation on the chitosan membrane surface. Oxygen plasma treatment was also employed to improve the surface hydrophilicity of the chitosan membrane. The results of ARXPS revealed the distribution of surface polar groups, such as-OH and O=CNH 2 toward the membrane bulk, which was the origin of the chitosan membrane surface hydrophobicity. The contact angle measurements and XPS results indicated that oxygen plasma treatment can markedly improve the surface hydrophilicity and surface energy of the chitosan membrane by incorporating oxygen-containing polar groups. With the existence of the aging process, the influence of plasma treatment was not permanent, it faded with storage time. The ARXPS result discovered that the reorientation of polar functional groups generated by plasma treatment toward the membrane bulk was primarily responsible for the aging effect.

  18. Combustion of methane-oxygen and methane-oxygen-CFC mixtures initiated by a high-current slipping surface discharge

    International Nuclear Information System (INIS)

    Kossyi, I.A.; Silakov, V.P.; Tarasova, N.M.

    2001-01-01

    Results are presented from experimental studies of the destruction of chlorofluorocarbon (CF 2 Cl 2 ) molecules in a methane-oxygen (air) gas mixture whose combustion is initiated by a high-current slipping surface discharge. It is found that a three-component CH 4 + O 2 (air)+ CF 2 Cl 2 gas mixture (even with a considerable amount of the third component) demonstrates properties of explosive combustion involving chain reactions that are typical of two-component CH 4 + O 2 mixtures. Experiments show the high degree of destruction (almost complete decomposition) of chlorofluorocarbons contained in the mixture during one combustion event. The combustion dynamics is studied. It is shown that the combustion initiated by a slipping surface discharge has a number of characteristic features that make it impossible to identify the combustion dynamics with the formation of a combustion or detonation wave. The features of the effects observed can be related to intense UV radiation produced by a pulsed high-current surface discharge

  19. Fermi Surface of Three-Dimensional La(1-x)Sr(x)MnO3 Explored by Soft-X-Ray ARPES: Rhombohedral Lattice Distortion and its Effect on Magnetoresistance.

    Science.gov (United States)

    Lev, L L; Krempaský, J; Staub, U; Rogalev, V A; Schmitt, T; Shi, M; Blaha, P; Mishchenko, A S; Veligzhanin, A A; Zubavichus, Y V; Tsetlin, M B; Volfová, H; Braun, J; Minár, J; Strocov, V N

    2015-06-12

    Electronic structure of the three-dimensional colossal magnetoresistive perovskite La(1-x)Sr(x)MnO3 has been established using soft-x-ray angle-resolved photoemission spectroscopy with its intrinsically sharp definition of three-dimensional electron momentum. The experimental results show much weaker polaronic coupling compared to the bilayer manganites and are consistent with the theoretical band structure including the empirical Hubbard parameter U. The experimental Fermi surface unveils the canonical topology of alternating three-dimensional electron spheres and hole cubes, with their shadow contours manifesting the rhombohedral lattice distortion. This picture has been confirmed by one-step photoemission calculations including displacement of the apical oxygen atoms. The rhombohedral distortion is neutral to the Jahn-Teller effect and thus polaronic coupling, but affects the double-exchange electron hopping and thus the colossal magnetoresistance effect.

  20. Quantitative measurements of ground state atomic oxygen in atmospheric pressure surface micro-discharge array

    Science.gov (United States)

    Li, D.; Kong, M. G.; Britun, N.; Snyders, R.; Leys, C.; Nikiforov, A.

    2017-06-01

    The generation of atomic oxygen in an array of surface micro-discharge, working in atmospheric pressure He/O2 or Ar/O2 mixtures, is investigated. The absolute atomic oxygen density and its temporal and spatial dynamics are studied by means of two-photon absorption laser-induced fluorescence. A high density of atomic oxygen is detected in the He/O2 mixture with up to 10% O2 content in the feed gas, whereas the atomic oxygen concentration in the Ar/O2 mixture stays below the detection limit of 1013 cm-3. The measured O density near the electrode under the optimal conditions in He/1.75% O2 gas is 4.26  ×  1015 cm-3. The existence of the ground state O (2p 4 3 P) species has been proven in the discharge at a distance up to 12 mm away from the electrodes. Dissociative reactions of the singlet O2 with O3 and deep vacuum ultraviolet radiation, including the radiation of excimer \\text{He}2\\ast , are proposed to be responsible for O (2p 4 3 P) production in the far afterglow. A capability of the surface micro-discharge array delivering atomic oxygen to long distances over a large area is considered very interesting for various biomedical applications.

  1. The surface reactivity of acrylonitrile with oxygen atoms on an analogue of interstellar dust grains.

    Science.gov (United States)

    Kimber, Helen J.; Toscano, Jutta; Price, Stephen D.

    2018-03-01

    Experiments designed to reveal the low temperature reactivity on the surfaces of interstellar dust grains are used to probe the heterogeneous reaction between oxygen atoms and acrylonitrile (C2H3CN, H2C = CH-CN). The reaction is studied at a series of fixed surface temperatures between 14 K and 100 K. After dosing the reactants onto the surface, temperature programmed desorption, coupled with time-of-flight mass spectrometry, reveals the formation of a product with the molecular formula C3H3NO. This product results from the addition of a single oxygen atom to the acrylonitrile reactant. The oxygen atom attack appears to occur exclusively at the C = C double bond, rather than involving the cyano (-CN) group. The absence of reactivity at the cyano site hints that full saturation of organic molecules on dust grains may not always occur in the interstellar medium. Modelling the experimental data provides a reaction probability of 0.007 ± 0.003 for a Langmuir-Hinshelwood style (diffusive) reaction mechanism. Desorption energies for acrylonitrile, oxygen atoms and molecular oxygen, from the multilayer mixed ice their deposition forms, are also extracted from the kinetic model and are 22.7 ± 1.0 kJ mol-1 (2730 ± 120 K), 14.2 ± 1.0 kJ mol-1 (1710 ± 120 K) and 8.5 ± 0.8 kJ mol-1 (1020 ± 100 K) respectively. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and acrylonitrile could occur on interstellar dust grains on an astrophysical time scale.

  2. Cryptic oxygen oases: Hypolithic photosynthesis in hydrothermal areas and implications for Archean surface oxidation

    Science.gov (United States)

    Havig, J. R.; Hamilton, T. L.

    2017-12-01

    Mounting geochemical evidence suggests microorganisms capable of oxygenic photosynthesis (e.g., Cyanobacteria) colonized Archean continental surfaces, driving oxidative weathering of detrital pyrites prior to the 2.5 Ga great oxidation event. Modern terrestrial environments dominated by single-celled phototrophs include hydrothermal systems (e.g., Yellowstone National Park) and hypolithic communities found in arid to hyper-arid deserts (e.g., McMurdo Dry Valleys of Antarctica, Atacama Desert of Chile). Recent work indicates terrestrial hydrothermal systems date back at least as far as 3.5 Ga. Here, we explore phototrophic communities in both hypolithic (sub-sinter) and hydrothermal (subaqueous and subaerial) environments in Yellowstone National Park as potential analogs to Archean continental surfaces. Hydrothermal sub-sinter environments provide ideal conditions for phototrophic microbial communities, including blocking of harmful UV radiation, trapping and retention of moisture, and protection from erosion by rain and surface runoff. Hypolithic communities in geothermal settings were similar in both composition and carbon uptake rates to nearby hot spring communities. We hypothesize that hydrothermal area hypolithic communities represent modern analogs of phototrophic microbial communities that colonized Archean continental surfaces, producing oxygen locally and facilitating microbially-mediated pyrite oxidation prior to the presence of free oxygen in the global atmosphere. These results have implications for oxidation of the early Earth surface, the search for biosignatures in the rock record, as well as for potential harbors of past life on Mars and the search for life on Exoplanets.

  3. A general scheme for the estimation of oxygen binding energies on binary transition metal surface alloys

    DEFF Research Database (Denmark)

    Greeley, Jeffrey Philip; Nørskov, Jens Kehlet

    2005-01-01

    A simple scheme for the estimation of oxygen binding energies on transition metal surface alloys is presented. It is shown that a d-band center model of the alloy surfaces is a convenient and appropriate basis for this scheme; variations in chemical composition, strain effects, and ligand effects...... are all incorporated into the binding energy analysis through this parameter. With few exceptions, the agreement of the results from the simple model with full DFT calculations on hundreds of binary surface alloys is remarkable. The scheme should therefore provide a fast and effective method...... for the estimation of oxygen binding energies on a wide variety of transition metal alloys. (c) 2005 Elsevier B.V. All rights reserved....

  4. Surface modification effects of fluorine-doped tin dioxide by oxygen plasma ion implantation

    Science.gov (United States)

    Tang, Peng; Liu, Cai; Zhang, Jingquan; Wu, Lili; Li, Wei; Feng, Lianghuan; Zeng, Guanggen; Wang, Wenwu

    2018-04-01

    SnO2:F (FTO), as a kind of transparent conductive oxide (TCO), exhibits excellent transmittance and conductivity and is widely used as transparency electrodes in solar cells. It's very important to modifying the surface of FTO for it plays a critical role in CdTe solar cells. In this study, modifying effects of oxygen plasma on FTO was investigated systematically. Oxygen plasma treatment on FTO surface with ion accelerating voltage ranged from 0.4 kV to 1.6 kV has been processed. The O proportion of surface was increased after ion implantation. The Fermi level of surface measurement by XPS valance band spectra was lowered as the ion accelerating voltage increased to 1.2 kV and then raised as accelerating voltage was elevated to 1.6 kV. The work function measured by Kelvin probe force microscopy increased after ion implanting, and it was consistent with the variation of Fermi level. The change of energy band structure of FTO surface mainly originated from the surface composition variation. As FTO conduction was primarily due to oxyanion hole, the carrier was electron and its concentration was reduced while O proportion was elevated at the surface of FTO, as a result, the Fermi level lowered and the work function was enlarged. It was proved that oxygen plasma treatment is an effective method to modulate the energy band structure of the surface as well as other properties of FTO, which provides much more space for interface and surface modification and then photoelectric device performance promotion.

  5. Modeling the thermostability of surface functionalisation by oxygen, hydroxyl, and water on nanodiamonds.

    Science.gov (United States)

    Lai, Lin; Barnard, Amanda S

    2011-06-01

    Understanding nanodiamond functionalisation is of great importance for biological and medical applications. Here we examine the stabilities of oxygen, hydroxyl, and water functionalisation of the nanodiamonds using the self-consistent charge density functional tight-binding simulations. We find that the oxygen and hydroxyl termination are thermodynamically favourable and form strong C–O covalent bonds on the nanodiamond surface in an O2 and H2 gas reservoir, which confirms previous experiments. Yet, the thermodynamic stabilities of oxygen and hydroxyl functionalisation decrease dramatically in a water vapour reservoir. In contrast, H2O molecules are found to be physically adsorbed on the nanodiamond surface, and forced chemical adsorption results in decomposition of H2O. Moreover, the functionalisation efficiency is found to be facet dependent. The oxygen functionalisation prefers the {100} facets as opposed to alternative facets in an O2 and H2 gas reservoir. The hydroxyl functionalisation favors the {111} surfaces in an O2 and H2 reservoir and the {100} facets in a water vapour reservoir, respectively. This facet selectivity is found to be largely dependent upon the environmental temperature, chemical reservoir, and morphology of the nanodiamonds.

  6. Microbiological investigations of oxygen plasma treated parylene C surfaces for metal implant coating.

    Science.gov (United States)

    Golda-Cepa, M; Brzychczy-Wloch, M; Engvall, K; Aminlashgari, N; Hakkarainen, M; Kotarba, A

    2015-01-01

    Parylene C surface was modified by the use of oxygen plasma treatment and characterized by microscopic and surface-sensitive techniques (E-SEM, AFM, XPS, LDI-TOF-MS, contact angle). The influence of the treatment on surface properties was investigated by calculations of surface free energy (Owens-Wendt method). Moreover, early adhesion (Culture Plate Method, Optical Microscopy Test) and biofilm formation ability (Cristal Violet Assay) on the parylene C surface was investigated. The bacteria strains which are common causative agents of medical device-associated infections (Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa--reference strains and clinical isolates) were used. It was concluded that chemical (oxygen insertion) and physical (nanotopography generation) changes, have a significant impact on the biocompatibility in terms of increased hydrophilicity (θ w of unmodified sample = 88° ± 2°, θ w of 60 min modified sample = 17.6° ± 0.8°) and surface free energy (SFE of unmodified sample = 42.4 mJ/m(2), and for 60 min modified sample = 70.1 mJ/m(2)). At the same time, no statistical effect on biofilm production and bacteria attachment to the modified surface of any of the tested strains was observed. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. Molecular simulation insights on the in vacuo adsorption of amino acids on graphene oxide surfaces with varying surface oxygen densities

    Energy Technology Data Exchange (ETDEWEB)

    Rahmani, Farzin; Nouranian, Sasan, E-mail: sasan@olemiss.edu; Mahdavi, Mina [University of Mississippi, Department of Chemical Engineering (United States); Al-Ostaz, Ahmed [University of Mississippi, Department of Civil Engineering (United States)

    2016-11-15

    In this fundamental study, a series of molecular dynamics simulations were performed in vacuo to investigate the energetics and select geometries of 20 standard amino acids (AAs) on pristine graphene (PG) and graphene oxide (GO) surfaces as a function of graphene surface oxygen density. These interactions are of key interest to graphene/biomolecular systems. Our results indicate that aromatic AAs exhibit the strongest total interactions with the PG surfaces due to π-π stacking. Tryptophan (Trp) has the highest aromaticity due to its indole side chain and, hence, has the strongest interaction among all AAs (−16.66 kcal/mol). Aliphatic, polar, and charged AAs show various levels of affinity to the PG sheets depending on the strength of their side chain hydrophobic interactions. For example, arginine (Arg) with its guanidinium side chain exhibits the strongest interaction with the PG sheets (−13.81 kcal/mol) following aromatic AAs. Also, glycine (Gly; a polar AA) has the weakest interaction with the PG sheets (−7.29 kcal/mol). When oxygen-containing functional groups are added to the graphene sheets, the π-π stacking in aromatic AAs becomes disrupted and perfect parallelism of the aromatic rings is lost. Moreover, hydrogen bonding and/or electrostatic interactions become more pronounced. Charged AAs exhibit the strongest interactions with the GO surfaces. In general, the AA-GO interactions increase with increasing surface oxygen density, and the effect is more pronounced at higher O/C ratios. This study provides a quantitative measure of AA-graphene interactions for the design and tuning of biomolecular systems suitable for biosensing, drug delivery, and gene delivery applications.

  8. Surface Morphology and Overlayer Formation Kinetics of OXYGEN/SILVER(110) Studied by Scanning Tunneling Microscopy

    Science.gov (United States)

    Pai, Woei Wu.

    1995-01-01

    I have applied scanning tunneling microscopy (STM) to study clean and oxygen-covered vicinal Ag(110) surfaces at room temperature. Experimental results of surface morphology/stability, surface mass transport and surface chemical reactivity are presented. On clean vicinal Ag(110) surfaces, the steps distribute under the influence of step-step interactions. The terrace width distributions indicate an additional oscillatory component besides an l^{-2} interaction term. If the surface is contaminated slightly (quasi-clean), isolated "pinning sites" impede the motion of steps. The interactions between steps push the steps across the pinning site, resulting in a curved step front. When oxygen atoms adsorb on stepped Ag(110), a dramatic change in surface morphology occurs. The surface separates into two distinct phases--step bunches and large terraces (facets). The orientational instability is closely related to the linear "added-row" structure of the oxygen overlayer, as the long O chains push steps into bunches. The O chains do not push the steps effectively when O chains orient perpendicular to steps, and the faceting proceeds through nucleation. If the O chains orient near parallel to steps, however, O chains push the steps easily and the faceting proceeds through spinodal decomposition. To understand the mass transport during faceting, I quantify the thermal step fluctuations by employing a Langevin statistical analysis. The mass transport mechanism at the step edge is shown to be by atomic exchange between steps and terraces, making the step an effective source or sink for Ag adatoms. This Ag source also proves essential in O overlayer formation, since both Ag and O atoms are incorporated into the "added -row" overlayer structure. Because an Ag source must be found during the adlayer formation, I show the surface morphology is sensitive to oxygen dosing pressure. Above a critical O pressure of 10^{-5} mbar, vacancy islands on terraces provide a second source of Ag

  9. Voltage-sensitive styryl dyes as singlet oxygen targets on the surface of bilayer lipid membrane.

    Science.gov (United States)

    Sokolov, V S; Gavrilchik, A N; Kulagina, A O; Meshkov, I N; Pohl, P; Gorbunova, Yu G

    2016-08-01

    Photosensitizers are widely used as photodynamic therapeutic agents killing cancer cells by photooxidation of their components. Development of new effective photosensitive molecules requires profound knowledge of possible targets for reactive oxygen species, especially for its singlet form. Here we studied photooxidation of voltage-sensitive styryl dyes (di-4-ANEPPS, di-8-ANEPPS, RH-421 and RH-237) by singlet oxygen on the surface of bilayer lipid membranes commonly used as cell membrane models. Oxidation was induced by irradiation of a photosensitizer (aluminum phthalocyanine tetrasulfonate) and monitored by the change of dipole potential on the surface of the membrane. We studied the drop of the dipole potential both in the case when the dye molecules were adsorbed on the same side of the lipid bilayer as the photosensitizer (cis-configuration) and in the case when they were adsorbed on the opposite side (trans-configuration). Based on a simple model, we determined the rate of oxidation of the dyes from the kinetics of change of the potential during and after irradiation. This rate is proportional to steady-state concentration of singlet oxygen in the membrane under irradiation. Comparison of the oxidation rates of various dyes reveals that compounds of ANEPPS series are more sensitive to singlet oxygen than RH type dyes, indicating that naphthalene group is primarily responsible for their oxidation. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. Crystal structure and surface characteristics of Sr-doped GdBaCo2O6−δ double perovskites: oxygen evolution reaction and conductivity

    KAUST Repository

    Pramana, Stevin S.

    2017-12-04

    A cheap and direct solution towards engineering better catalysts through identification of novel materials is required for a sustainable energy system. Perovskite oxides have emerged as potential candidates to replace the less economically attractive Pt and IrO2 water splitting catalysts. In this work, excellent electrical conductivity (980 S cm−1) was found for the double perovskite of composition GdBa0.6Sr0.4Co2O6−δ which is consistent with a better oxygen evolution reaction activity with the onset polarisation of 1.51 V with respect to a reversible hydrogen electrode (RHE). GdBa1−xSrxCo2O6−δ with increasing Sr content was found to crystallise in the higher symmetry tetragonal P4/mmm space group in comparison with the undoped GdBaCo2O6−δ which is orthorhombic (Pmmm), and yields higher oxygen uptake, accompanied by higher Co oxidation states. This outstanding electrochemical performance is explained by the wider carrier bandwidth, which is a function of Co–O–Co buckling angles and Co–O bond lengths. Furthermore the higher oxygen evolution activity was observed despite the formation of non-lattice oxides (mainly hydroxide species) and enrichment of alkaline earth ions on the surface.

  11. Surface strontium enrichment on highly active perovskites for oxygen electrocatalysis in solid oxide fuel cells

    KAUST Repository

    Crumlin, Ethan J.

    2012-01-01

    Perovskite oxides have high catalytic activities for oxygen electrocatalysis competitive to platinum at elevated temperatures. However, little is known about the oxide surface chemistry that influences the activity near ambient oxygen partial pressures, which hampers the design of highly active catalysts for many clean-energy technologies such as solid oxide fuel cells. Using in situ synchrotron-based, ambient pressure X-ray photoelectron spectroscopy to study the surface chemistry changes, we show that the coverage of surface secondary phases on a (001)-oriented La 0.8Sr 0.2CoO 3-δ (LSC) film becomes smaller than that on an LSC powder pellet at elevated temperatures. In addition, strontium (Sr) in the perovskite structure enriches towards the film surface in contrast to the pellet having no detectable changes with increasing temperature. We propose that the ability to reduce surface secondary phases and develop Sr-enriched perovskite surfaces of the LSC film contributes to its enhanced activity for O 2 electrocatalysis relative to LSC powder-based electrodes. © 2012 The Royal Society of Chemistry.

  12. Unraveling the oxygen vacancy structures at the reduced Ce O2(111 ) surface

    Science.gov (United States)

    Han, Zhong-Kang; Yang, Yi-Zhou; Zhu, Beien; Ganduglia-Pirovano, M. Verónica; Gao, Yi

    2018-03-01

    Oxygen vacancies at ceria (Ce O2 ) surfaces play an essential role in catalytic applications. However, during the past decade, the near-surface vacancy structures at Ce O2(111 ) have been questioned due to the contradictory results from experiments and theoretical simulations. Whether surface vacancies agglomerate, and which is the most stable vacancy structure for varying vacancy concentration and temperature, are being heatedly debated. By combining density functional theory calculations and Monte Carlo simulations, we proposed a unified model to explain all conflicting experimental observations and theoretical results. We find a novel trimeric vacancy structure which is more stable than any other one previously reported, which perfectly reproduces the characteristics of the double linear surface oxygen vacancy clusters observed by STM. Monte Carlo simulations show that at low temperature and low vacancy concentrations, vacancies prefer subsurface sites with a local (2 × 2) ordering, whereas mostly linear surface vacancy clusters do form with increased temperature and degree of reduction. These results well explain the disputes about the stable vacancy structure and surface vacancy clustering at Ce O2(111 ) , and provide a foundation for the understanding of the redox and catalytic chemistry of metal oxides.

  13. Influence of Power Modulation on Ozone Production Using an AC Surface Dielectric Barrier Discharge in Oxygen

    Czech Academy of Sciences Publication Activity Database

    Šimek, Milan; Pekárek, S.; Prukner, Václav

    2010-01-01

    Roč. 30, č. 5 (2010), s. 607-617 ISSN 0272-4324 R&D Projects: GA ČR(CZ) GA202/09/0176 Institutional research plan: CEZ:AV0Z20430508 Keywords : Ozone * Surface DBD * Oxygen * Production efficiency Subject RIV: BL - Plasma and Gas Disc harge Physics Impact factor: 1.798, year: 2010 http://www.springerlink.com/content/28539775w5243513/

  14. Surface tension of different sized single-component droplets, according to macroscopic data obtained using the lattice gas model and the critical droplet size during phase formation

    Science.gov (United States)

    Tovbin, Yu. K.; Zaitseva, E. S.; Rabinovich, A. B.

    2017-10-01

    Size dependences of the surface tension of spherical single-component droplets are calculated using equations of the lattice gas model for 19 compounds. Parameters of the model are found from experimental data on the surface tension of these compounds for a macroscopic planar surface. The chosen low-molecular compounds satisfy the law of corresponding states. To improve agreement with the experimental data, Lennard-Jones potential parameters are varied within 10% deviations. The surface tensions of different sized equilibrium droplets are calculated at elevated and lowered temperatures. It is found that the surface tension of droplets grows monotonically as the droplet size increases from zero to its bulk value. The droplet size R 0 corresponding to zero surface tension corresponds to the critical size of the emergence of a new phase. The critical droplet sizes in the new phase of the considered compounds are estimated for the first time.

  15. Chemisorption of oxygen and subsequent reactions on low index surfaces of β-Mo2C

    DEFF Research Database (Denmark)

    Shi, Xue Rong; Wang, Shengguang; Wang, Jianguo

    2016-01-01

    Oxygen chemisorption on β-Mo2C surfaces, the subsequent CO/CO2 desorption and oxygen diffusion to the carbon vacancy have been investigated by density-functional theory. The most stable structures together with the energetics of oxygen stepwise adsorption, CO/CO2 desorption and oxygen diffusion...... to the carbon vacancy were identified. We examined the effect of oxygen coverage on the morphology of β-Mo2C by plotting the equilibrium crystal shape. Thermodynamic effect of temperature and reactant or product pressure on the CO/CO2 desorption were investigated. The CO/CO2 desorption is more favorable...

  16. Effect of the surface oxygen groups on methane adsorption on coals

    Energy Technology Data Exchange (ETDEWEB)

    Hao Shixiong [Department of Chemical Engineering, Sichuan University, Chengdu 610065 (China); Department of Chemical Engineering, Sichuan University of Science and Engineering, Zigong 643000 (China); Wen Jie [Department of Chemical Engineering, Sichuan University, Chengdu 610065 (China); Yu Xiaopeng [Department of Chemical Engineering, Sichuan University, Chengdu 610065 (China); Department of Chemical Engineering, Sichuan University of Science and Engineering, Zigong 643000 (China); Chu Wei, E-mail: chuwei1965_scu@yahoo.com [Department of Chemical Engineering, Sichuan University, Chengdu 610065 (China)

    2013-01-01

    Highlights: Black-Right-Pointing-Pointer We modified one coal with H{sub 2}O{sub 2}, (NH{sub 4}){sub 2}S{sub 2}O{sub 8} and HNO{sub 3} respectively, to prepare coal samples with different surface properties. Black-Right-Pointing-Pointer The oxygen groups on coal surface were characterized by XPS. Black-Right-Pointing-Pointer The textures of the coal samples were investigated by N{sub 2} adsorption at 77 K. Black-Right-Pointing-Pointer The adsorption behaviors were measured by volumetric method. Black-Right-Pointing-Pointer There was a negative correlation between methane saturated adsorption capacity and the O{sub total}/C{sub total}. - Abstract: To investigate the influence of surface oxygen groups on methane adsorption on coals, one bituminous coal was modified with H{sub 2}O{sub 2}, (NH{sub 4}){sub 2}S{sub 2}O{sub 8} and HNO{sub 3} respectively, to prepare coal samples with different surface properties. The oxygen groups on coal surface were characterized by X-ray photoelectron spectroscopy (XPS). The textures of the coal samples were investigated by N{sub 2} adsorption at 77 K. Their surface morphologies were analyzed by scanning electron microscopy (SEM). The methane adsorption behaviors of these coal samples were measured at 303 K in pressure range of 0-5.3 MPa by volumetric method. The adsorption data of methane were fitted to the Langmuir model and Dubinin-Astakhov (D-A) model. The fitting results showed that the D-A model fitted the isotherm data better than the Langmuir model. It was observed that there was, in general, a positive correlation between the methane saturated adsorption capacity and the micropore volume of coals while a negative correlation between methane saturated adsorption capacity and the O{sub total}/C{sub total}. The methane adsorption capacity was determined by the coal surface chemistry when the microporosity parameters of two samples were similar. Coal with a higher amount of oxygen surface groups, and consequently with a less

  17. Na-surface segregation and oxygen depletion in particle bombardment of alkaline glasses

    Energy Technology Data Exchange (ETDEWEB)

    Torrisi, A.; Marletta, G.; Licciardello, A.; Puglisi, O.

    1988-05-01

    Alkaline glass samples were bombarded by 2 keV Ar ions and neutrals and the surface modification were followed by XPS. Two main effects have been detected after bombardement: (I) a lowering of the Na/Si atomic ratio with a steady state value of about 1/2 of the initial value, and (II) an oxygen depletion. Both effects are independent of the charge state of the projectiles. The sodium concentration profile has been studied by XPS tilting angle technique and it is concluded that bombardment-induced surface segregation occurs and that it is may be responsible for the observed sodium behaviour.

  18. Oxygen Plasma Treatment of Rubber Surface by the Atmospheric Pressure Cold Plasma Torch

    DEFF Research Database (Denmark)

    Lee, Bong-ju; Kusano, Yukihiro; Kato, Nobuko

    1997-01-01

    adhesive. The adhesion property was improved by treatment of the rubber compound with plasma containing oxygen radicals. Physical and chemical changes of the rubber surface as a result of the plasma treatment were analyzed by field emission scanning electron microscopy (FE-SEM) and fourier transform......A new application of the atmospheric cold plasma torch has been investigated. Namely, the surface treatment of an air-exposed vulcanized rubber compound. The effect of plasma treatment was evaluated by the bondability of the treated rubber compound with another rubber compound using a polyurethane...

  19. Detection of submonolayer oxygen-18 on a gold surface by nuclear reaction analysis

    Energy Technology Data Exchange (ETDEWEB)

    Wielunski, L.S.; Kenny, M.J.; Wieczorek, L. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), Lindfield, NSW (Australia). Div. of Applied Physics

    1993-12-31

    A gold substrate is the preferred solid surface for formation of an organic self-assembled monolayer ( SAM ). Device fabrication process may require the gold film to be exposed to photolithographic processing and plasma treatment prior to molecular assembly. It has been observed that oxygen plasma treatment prevents the formation of SAMs; however, subsequent treatment with an argon plasma allows assembly of the organic monolayers. To understand the mechanisms involved, a plasma containing 98% {sup 18}O was used and the film surface was analysed using the {sup 18}O (p,{alpha}){sup 15}N nuclear reaction. 5 refs., 1 tab., 3 figs.

  20. Synthesis of surface oxygen-deficient BiPO{sub 4} nanocubes with enhanced visible light induced photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Bingtao; Yin, Haoyong; Li, Tao; Gong, Jianying; Lv, Shumei; Nie, Qiulin, E-mail: yhy@hdu.edu.cn [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou (China)

    2017-05-15

    The visible light driven BiPO{sub 4} nanocubes with sufficient surface oxygen deficiency were fabricated by a hydrothermal process and subsequently ultrasonic assistant Fe reduction process. The products were characterized by XRD, DRS, XPS, SEM and TEM which showed that the BiPO{sub 4} had cuboid-like shape with a smooth surface and clear edges and the oxygen vacancies were successfully introduced on the surface of the BiPO{sub 4} nanocubes. The as prepared oxygen-deficient BiPO{sub 4} nanocubes showed greatly enhanced visible light induced photocatalytic activity in degradation of Rhodamine B. The enhanced photocatalytic performance and expanded visible light response of BiPO{sub 4} may be due to the introduction of surface oxygen vacancies which can generate the oxygen vacancies mid-gap states lower to the conduction band of BiPO{sub 4}. (author)

  1. Identifying the Active Surfaces of Electrochemically Tuned LiCoO2 for Oxygen Evolution Reaction

    International Nuclear Information System (INIS)

    Lu, Zhiyi; Chen, Guangxu; Li, Yanbin; Wang, Haotian; Xie, Jin

    2017-01-01

    Identification of active sites for catalytic processes has both fundamental and technological implications for rational design of future catalysts. Herein, we study the active surfaces of layered lithium cobalt oxide (LCO) for the oxygen evolution reaction (OER) using the enhancement effect of electrochemical delithiation (De-LCO). Our theoretical results indicate that the most stable (0001) surface has a very large overpotential for OER independent of lithium content. In contrast, edge sites such as the nonpolar (1120) and polar (0112) surfaces are predicted to be highly active and dependent on (de)lithiation. The effect of lithium extraction from LCO on the surfaces and their OER activities can be understood by the increase of Co 4+ sites relative to Co 3+ and by the shift of active oxygen 2p states. Experimentally, it is demonstrated that LCO nanosheets, which dominantly expose the (0001) surface show negligible OER enhancement upon delithiation. However, a noticeable increase in OER activity (~0.1 V in overpotential shift at 10 mA cm –2 ) is observed for the LCO nanoparticles, where the basal plane is greatly diminished to expose the edge sites, consistent with the theoretical simulations. In addition, we find that the OER activity of De-LCO nanosheets can be improved if we adopt an acid etching method on LCO to create more active edge sites, which in turn provides a strong evidence for the theoretical indication.

  2. Void lattices

    International Nuclear Information System (INIS)

    Chadderton, L.T.; Johnson, E.; Wohlenberg, T.

    1976-01-01

    Void lattices in metals apparently owe their stability to elastically anisotropic interactions. An ordered array of voids on the anion sublattice in fluorite does not fit so neatly into this scheme of things. Crowdions may play a part in the formation of the void lattice, and stability may derive from other sources. (Auth.)

  3. Oxygen vacancies at the surface of SrTiO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Alexandre R., E-mail: alexandre.silva@univasf.edu.br [Colegiado de Engenharia Mecânica, Universidade Federal do Vale do São Francisco, 48902-300 Juazeiro, BA (Brazil); Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580 Santo André, SP (Brazil); Dalpian, Gustavo M., E-mail: gustavo.dalpian@ufabc.edu.br [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580 Santo André, SP (Brazil)

    2014-01-21

    The two-dimensional electron gas (2DEG) observed at the surface of oxide thin films and at the interface between two oxides has been widely discussed, but the mechanism responsible for this behavior is still not well understood. In this work, we study the properties of the SrTiO{sub 3} (001) surface and show that defects are necessary in order to explain this 2DEG. We study the properties of oxygen vacancies at the TiO{sub 2} and SrO terminated surface, and conclude they can explain the metallic behavior experimentally observed. There is a strong tendency for these vacancies to be localized at the surface, where the formation energy is less than 2.92 eV.

  4. A free-surface lattice Boltzmann method for modelling the filling of expanding cavities by Bingham fluids.

    Science.gov (United States)

    Ginzburg, Irina; Steiner, Konrad

    2002-03-15

    The filling process of viscoplastic metal alloys and plastics in expanding cavities is modelled using the lattice Boltzmann method in two and three dimensions. These models combine the regularized Bingham model for viscoplastic fluids with a free-interface algorithm. The latter is based on a modified immiscible lattice Boltzmann model in which one species is the fluid and the other one is considered to be a vacuum. The boundary conditions at the curved liquid-vacuum interface are met without any geometrical front reconstruction from a first-order Chapman-Enskog expansion. The numerical results obtained with these models are found in good agreement with available theoretical and numerical analysis.

  5. Depth distribution studies of carbon, oxygen and nitrogen in metal surfaces by means of neutron spectrometry

    International Nuclear Information System (INIS)

    Lorenzen, J.

    1975-03-01

    A method has been developed to reveal the depth distributions of the light elements carbon, nitrogen and oxygen in heavy matrices. For this purpose steel and zircaloy samples have been irradiated with deuterons and the neutron groups emitted in (d,n)-reactions with the different light nuclei have been measured using time-of-flight technique. The method has been applied to the study of steel samples that feature inhomogeneous carbon and nitrogen distributions and also to the measurement of diffusion profiles of oxygen in zirconium. With the present technique depth ranges of 10 to 15 μm can be analysed if the deuteron energy is chosen between 2.5 MeV and 3.5 MeV. The depth resolution improves with penetration from being of the order of 1 - 2 μm at the surface to 0.5 μm at greater depths under optimum conditions. The detection limit of the light element increases with the atomic number of the matrix and the analysed depth. For oxygen in zirconium and carbon in steel the limit of detection is of the order of 100 ppm at a depth of 10 μm. Limitations in the analysable range of the different profiles due to interfering neutron groups are discussed. The method is particularly useful for the study of oxygen profiles. It is less adequate for reactions with positive Q-values above 5 MeV. (author)

  6. Lattice strings

    International Nuclear Information System (INIS)

    Thorn, C.B.

    1988-01-01

    The possibility of studying non-perturbative effects in string theory using a world sheet lattice is discussed. The light-cone lattice string model of Giles and Thorn is studied numerically to assess the accuracy of ''coarse lattice'' approximations. For free strings a 5 by 15 lattice seems sufficient to obtain better than 10% accuracy for the bosonic string tachyon mass squared. In addition a crude lattice model simulating string like interactions is studied to find out how easily a coarse lattice calculation can pick out effects such as bound states which would qualitatively alter the spectrum of the free theory. The role of the critical dimension in obtaining a finite continuum limit is discussed. Instead of the ''gaussian'' lattice model one could use one of the vertex models, whose continuum limit is the same as a gaussian model on a torus of any radius. Indeed, any critical 2 dimensional statistical system will have a stringy continuum limit in the absence of string interactions. 8 refs., 1 fig. , 9 tabs

  7. Oxygen adsorption on the Al0.25Ga0.75N (0001) surface: A first-principles study

    Science.gov (United States)

    Fu, Jiaqi; Song, Tielei; Liang, Xixia; Zhao, Guojun

    2018-04-01

    To understand the interaction mechanism for the oxygen adsorption on AlGaN surface, herein, we built the possible models of oxygen adsorption on Al0.25Ga0.75N (0001) surface. For different oxygen coverage, three kinds of adsorption site are considered. Then the favorable adsorption sites are characterized by first principles calculation for (2 × 2) supercell of Al0.25Ga0.75N (0001) surface. On basis of the optimal adsorption structures, our calculated results show that all the adsorption processes are exothermic, indicating that the (0001) surface orientation is active towards the adsorption of oxygen. The doping of Al is advantage to the adsorption of O atom. Additionally, the adsorption energy decreases with reducing the oxygen coverage, and the relationship between them is approximately linear. Owing to the oxygen adsorption, the surface states in the fundamental band gap are significant reduced with respect to the free Al0.25Ga0.75N (0001) surface. Moreover, the optical properties on different oxygen coverage are also discussed.

  8. Enhanced oxygen reduction activity on surface-decorated perovskite thin films for solid oxide fuel cells

    KAUST Repository

    Mutoro, Eva

    2011-01-01

    Surface-decoration of perovskites can strongly affect the oxygen reduction activity, and therefore is a new and promising approach to improve SOFC cathode materials. In this study, we demonstrate that a small amount of secondary phase on a (001) La 0.8Sr 0.2CoO 3-δ (LSC) surface can either significantly activate or passivate the electrode. LSC (001) microelectrodes prepared by pulsed laser deposition on a (001)-oriented yttria-stabilized zirconia (YSZ) substrate were decorated with La-, Co-, and Sr-(hydr)oxides/carbonates. "Sr"-decoration with nanoparticle coverage in the range from 50% to 80% of the LSC surface enhanced the surface exchange coefficient, k q, by an order of magnitude while "La"- decoration and "Co"-decoration led to no change and reduction in k q, respectively. Although the physical origin for the enhancement is not fully understood, results from atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy suggest that the observed k q enhancement for "Sr"-decorated surfaces can be attributed largely to catalytically active interface regions between surface Sr-enriched particles and the LSC surface. © 2011 The Royal Society of Chemistry.

  9. A novel pulse isotopic exchange technique for rapid determination of the oxygen surface exchange rate of oxide ion conductors

    NARCIS (Netherlands)

    Bouwmeester, Henricus J.M.; Song, Chunlin; Song, C.; Zhu, J.J.; van Sint Annaland, M.; Yi, Jianxin; Boukamp, Bernard A.

    2009-01-01

    We demonstrate the use of a novel pulse 18O–16O isotopic exchange technique for the rapid determination of the oxygen surface exchange rate of oxide ion conductors while simultaneously providing insight into the mechanism of the oxygen exchange reaction, which contributes to the efficient

  10. ΔM/sub j/ transitions in homonuclear molecule scattering off corrugated surfaces. Square and rectangular lattice symmetry and purely repulsive interaction

    International Nuclear Information System (INIS)

    Proctor, T.R.; Kouri, D.J.; Gerber, R.B.

    1984-01-01

    In this paper, we present the first formal and computational studies of Δm/sub j/ transitions occurring in homonuclear molecule-corrugated surface collisions. The model potential is a pairwise additive one which correctly incorporates the fact that Δm/sub j/ transitions occur only for corrugated surfaces (provided the quantization axis is chosen to be the average surface normal). The principal results are: (a) Δm/sub j/ transitions are extremely sensitive to lattice symmetry; (b) strong selection rules obtain for specular scattering; (c) the magnitude of Δm/sub j/ -transition probabilities are strongly sensitive to surface corrugation; (d) the Δm/sub j/ transitions depend strongly on diffraction peak; (e) the ratio of molecular length to lattice dimension (r/a) has a strong influence on the magnitude of Δm/sub j/ -transition probabilities [with the probabilities increasing as (r/a) increases]; (f) Δm/sub j/ rainbows are predicted to occur as a function of the (r/a) ratio increases; (g) Δm/sub j/ transitions and the Δm/sub j/ rainbow are expected to accompany Δj-rotational rainbows; (h) such magnetic transition rainbows accompanying Δj rainbows are suggested as an explanation of recent experimental observations of quenching of NO polarization for larger Δj transitions in NO/Ag(111) scattering

  11. Phenol by direct hydroxylation of benzene with nitrous oxide - role of surface oxygen species in the reaction pathways

    Energy Technology Data Exchange (ETDEWEB)

    Reitzmann, A.; Klemm, E.; Emig, G. [Erlangen-Nuernberg Univ., Erlangen (Germany). Lehrstuhl fuer Technische Chemie 1; Buchholz, S.A.; Zanthoff, H.W. [Bochum Univ. (Germany). Inst. of Technical Chemistry

    1998-12-31

    Transient experiments in a Temporal Analysis of Products (TAP) Reactor were performed to elucidate the role of surface oyxgen species in the oxidation of benzene to phenol on ZSM-5 type zeolites with nitrous oxide as a selective oxidant. It was shown by puls experiments with nitrous oxide that the mean lifetime of the generated surface oxygen species is between 0.2s at 500 C and about 4.2 s at 400 C. Afterwards the surface oxygen species desorb as molecular oxygen into the gas phase where total oxidation will take place if hydrocarbons are present. Dual puls experiments consisting of a nitrous oxide puls followed by a benzene puls allowed studying the reactivity of the surface oxygen species formed during the first puls. The observation of the phenol formation was impeded due to the strong sorption of phenol. Multipulse experiments were necessary to reach a pseudo steady state phenol yield. (orig.)

  12. Comparison of oxygen liquefaction methods for use on the Martian surface

    Science.gov (United States)

    Johnson, W. L.; Hauser, D. M.; Plachta, D. W.; Wang, X.-Y. J.; Banker, B. F.; Desai, P. S.; Stephens, J. R.; Swanger, A. M.

    2018-03-01

    In order to use oxygen that is produced on the surface of Mars from In-Situ production processes in a chemical propulsion system, the oxygen must first be converted from vapor phase to liquid phase and then stored within the propellant tanks of the propulsions system. There are multiple ways that this can be accomplished, from simply attaching a liquefaction system onto the propellant tanks to carrying separate tanks for liquefaction and storage of the propellant and loading just prior to launch (the way that traditional rocket launches occur on Earth). A study was done into these various methods by which the oxygen (and methane) could be liquefied and stored on the Martian surface. Five different architectures or cycles were considered: Tube-on-Tank (also known as Broad Area Cooling or Distributed Refrigeration), Tube-in-Tank (also known as Integrated Refrigeration and Storage), a modified Linde open liquefaction/refrigeration cycle, the direct mounting of a pulse tube cryocooler onto the tank, and an in-line liquefier at ambient pressure. Models of each architecture were developed to give insight into the performance and losses of each of the options. The results were then compared across eight categories: Mass, Power (both input and heat rejection), Operability, Cost, Manufacturability, Reliability, Volume-ility, and Scalability. The result was that Tube-on-Tank and Tube-in-Tank architectures were the most attractive solutions, with NASA's engineering management choosing to pursue tube on tank development rather than further differentiate the two. As a result NASA is focusing its Martian surface liquefaction activities and technology development on Tube-on-Tank liquefaction cycles.

  13. The effect of oxygen molecule adsorption on lead iodide perovskite surface by first-principles calculation

    Science.gov (United States)

    Ma, Xia-Xia; Li, Ze-Sheng

    2018-01-01

    Oxygen molecule has a negative effect on perovskite solar cells, which has been investigated experimentally. However, detailed theoretical research is still rare. This study presents a microscopic view to reveal the interaction mechanism between O2 and perovskite based on the first-principles calculation. The results show that O2 is adsorbed on the (100) surface of MAPbI3 perovskite mainly by Van der Waals force. O2 adsorption makes the MAPbI3 surface generate a small number of positive charges, which leads to the increase of the work function of the MAPbI3 surface. This is in agreement with the experimental measurement. And increased work function of MAPbI3 surface is not beneficial to electron transfer from perovskite to electronic extraction layer (such as TiO2). Comparison of the density of states (DOS) of the clean (100) surface and the adsorbed system shows that an in-gap state belonging to O2 appears, which can explain the phenomenon observed from experiments that electron transfers from the surface of perovskite to O2 to form superoxide. The theoretical power conversion efficiency of the system with and without O2 adsorption is evaluated, and it turns out that the power conversion efficiency of the system with O2 adsorption is slightly lower than that of the system without O2 adsorption. This result indicates that avoiding the introduction of O2 molecules between perovskite and electronic extraction layer is beneficial to the perovskite solar cell.

  14. DFT study of oxygen adsorption on Mo{sub 2}C(001) and (201) surfaces at different conditions

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Lihong, E-mail: chenglihong001@126.com [School of Materials and Mechanical & Electrical Engineering, Jiangxi Science and Technology Normal University, Nanchang 330013, Jiangxi (China); Li, Wenkui; Chen, Zhiqin; Ai, Jianping; Zhou, Zehua [School of Materials and Mechanical & Electrical Engineering, Jiangxi Science and Technology Normal University, Nanchang 330013, Jiangxi (China); Liu, Jianwen, E-mail: liujw@nsccsz.gov.cn [National Supercomputing Center in Shenzhen, Shenzhen 518055 (China)

    2017-07-31

    Highlights: • O adsorption manners on Mo{sub 2}C surfaces were calculated by DFT method. • Stable oxygen adsorption states and coverage were identified at given T and p. • O{sub 2} results in full oxidation while H{sub 2}O and CO{sub 2} cause partial oxidation of Mo{sub 2}C surfaces. • Hydrogen could be used to avoid Mo{sub 2}C surface oxidation. - Abstract: Density functional theory (DFT) calculations were performed to investigate oxygen adsorption on Mo{sub 2}C(001) and (201)surfaces at different coverage. The energies and structures of oxygen from lowest to saturated coverages were clearly identified on each surface. Thermodynamics method was introduced to reveal the roles of temperature, pressure as well as oxygen sources (O{sub 2}, H{sub 2}O and CO{sub 2}) on the surface oxygen coverage, which is related to the surface oxidation. On the basis of phase diagram, we can easily identify the stable oxygen coverage at different defined conditions. In addition, it reveals that O{sub 2} is the strongest oxidant, which results in the full coverage of oxygen on both surfaces in a wide range of temperature and pressure. Then, H{sub 2}O and CO{sub 2} are weaker oxidants, which could only cause partial oxidation of Mo{sub 2}C surfaces. These results indicate the facile oxidation of Mo{sub 2}C catalyst. The possible ways to avoid surface oxidation are keeping higher temperature and H{sub 2} pressure in the gas phase.

  15. Surface oxygen exchange properties of bismuth oxide-based solid electrolytes and electrode materials

    NARCIS (Netherlands)

    Boukamp, Bernard A.; Vinke, I.C.; de Vries, K.J.; Burggraaf, A.J.

    1989-01-01

    The surface oxygen exchange coefficient, ks, has been measured for the solid solution (Bi2O3)0.75(Er2O3)0.25 and (Bi2O3)0.6(Tb2O3)0.4 (abbreviated BE25 and BT40), using gas-phase 18O exchange techniques. The activation enth alpy of ks amounts to ΔE=110 kJ/molforBT40 andΔE=130 kJ/molforBE25. The

  16. Reactive-ion etching of nylon fabric meshes using oxygen plasma for creating surface nanostructures

    International Nuclear Information System (INIS)

    Salapare, Hernando S.; Darmanin, Thierry; Guittard, Frédéric

    2015-01-01

    Graphical abstract: - Highlights: • Reactive-ion etching (RIE) is employed to nylon 6,6 fabrics to achieve surface texturing and improved wettability. • FTIR spectra of the treated samples exhibited decreased transmittance of amide and carboxylic acid groups due to etching. • Etching is enhanced for higher power plasma treatments and for samples with larger mesh sizes. • Decreased crystallinity was achieved after plasma treatment. • Higher power induced higher negative DC self-bias voltage on the samples that favored anisotropic and aggressive etching. - Abstract: A facile one-step oxygen plasma irradiation in reactive ion etching (RIE) configuration is employed to nylon 6,6 fabrics with different mesh sizes to achieve surface nanostructures and improved wettability for textile and filtration applications. To observe the effects of power and irradiation time on the samples, the experiments were performed using constant irradiation time in varying power and using constant power in varying irradiation times. Results showed improved wettability after the plasma treatment. The FTIR spectra of all the treated samples exhibited decreased transmittance of the amide and carboxylic acid groups due to surface etching. The changes in the surface chemistry are supported by the SEM data wherein etching and surface nanostructures were observed for the plasma-treated samples. The etching of the surfaces is enhanced for higher power plasma treatments. The thermal analysis showed that the plasma treatment resulted in decreased crystallinity. Surface chemistry showed that the effects of the plasma treatment on the samples have no significant difference for all the mesh sizes. However, surface morphology showed that the sizes of the surface cracks are the same for all the mesh sizes but samples with larger mesh sizes exhibited enhanced etching as compared to the samples with smaller mesh sizes. Higher power induced higher negative DC self-bias voltage on the samples that

  17. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100) surface investigated by scanning tunneling microscopy and low energy electron diffraction.

    Science.gov (United States)

    Gärtner, Stefan; Fiedler, Benjamin; Bauer, Oliver; Marele, Antonela; Sokolowski, Moritz M

    2014-01-01

    We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) on the clean and on the oxygen pre-covered Cu(100) surface [referred to as (√2 × 2√2)R45° - 2O/Cu(100)] by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Our results confirm the (4√2 × 5√2)R45° superstructure of PTCDA/Cu(100) reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770-11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100). Quite differently, after preadsorption of oxygen and formation of the (√2 × 2√2)R45° - 2O/Cu(100) superstructure on Cu(100), PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

  18. Effect of surface oxygen vacancy sites on ethanol synthesis from acetic acid hydrogenation on a defective In2O3(110) surface.

    Science.gov (United States)

    Lyu, Huisheng; Liu, Jiatao; Chen, Yifei; Li, Guiming; Jiang, Haoxi; Zhang, Minhua

    2018-03-07

    Developing a new type of low-cost and high-efficiency non-noble metal catalyst is beneficial for industrially massive synthesis of alcohols from carboxylic acids which can be obtained from renewable biomass. In this work, the effect of active oxygen vacancies on ethanol synthesis from acetic acid hydrogenation over defective In 2 O 3 (110) surfaces has been studied using periodic density functional theory (DFT) calculations. The relative stabilities of six surface oxygen vacancies from O v1 to O v6 on the In 2 O 3 (110) surface were compared. D1 and D4 surfaces with respective O v1 and O v4 oxygen vacancies were chosen to map out the reaction paths from acetic acid to ethanol. A reaction cycle mechanism between the perfect and defective states of the In 2 O 3 surface was found to catalyze the formation of ethanol from acetic acid hydrogenation. By H 2 reduction the oxygen vacancies on the In 2 O 3 surface play key roles in promoting CH 3 COO* hydrogenation and C-O bond breaking in acetic acid hydrogenation. The acetic acid, in turn, benefits the creation of oxygen vacancies, while the C-O bond breaking of acetic acid refills the oxygen vacancy and, thereby, sustains the catalytic cycle. The In 2 O 3 based catalysts were shown to be advantageous over traditional noble metal catalysts in this paper by theoretical analysis.

  19. Electro-oxidation of water on hematite: Effects of surface termination and oxygen vacancies investigated by first-principles

    DEFF Research Database (Denmark)

    Hellman, Anders; Iandolo, Beniamino; Wickman, Bjorn

    2015-01-01

    The oxygen evolution reaction on hydroxyl- and oxygen-terminated hematite was investigated using first-principle calculations within a theoretical electrochemical framework. Both pristine hematite and hematite containing oxygen vacancies were considered. The onset potential was determined to be 1.......79 V and 2.09 V vs. the reversible hydrogen electrode (RHE) for the pristine hydroxyl- and oxygen-terminated hematite, respectively. The presence of oxygen vacancies in the hematite surface resulted in pronounced shifts of the onset potential to 3.09 V and 1.83 V. respectively. Electrochemical...... oxidation measurements conducted on thin-film hematite anodes, resulted in a measured onset potential of 1.66 V vs. RHE. Furthermore, the threshold potential between the hydroxyl- and oxygen-terminated hematite was determined as a function of pH. The results indicate that electrochemical water oxidation...

  20. Behaviour of oxygen atoms near the surface of nanostructured Nb2O5

    International Nuclear Information System (INIS)

    Cvelbar, U; Mozetic, M

    2007-01-01

    Recombination of neutral oxygen atoms on oxidized niobium foil was studied. Three sets of samples have been prepared: a set of niobium foils with a film of polycrystalline niobium oxide with a thickness of 40 nm, another one with a film thickness of about 2 μm and a set of foils covered with dense bundles of single-crystal Nb 2 O 3 nanowires. All the samples were prepared by oxidation of a pure niobium foil. The samples with a thin oxide film were prepared by exposure of as-received foils to a flux of O-atoms, the samples with a thick polycrystalline niobium oxide were prepared by baking the foils in air at a temperature of 800 deg. C, while the samples covered with nanowires were prepared by oxidation in a highly reactive oxygen plasma. The samples were exposed to neutral oxygen atoms from a remote oxygen plasma source. Depending on discharge parameters, the O-atom density in the postglow chamber, as measured with a catalytic probe, was between 5 x 10 20 and 8 x 10 21 m -3 . The O-atom density in the chamber without the samples was found rather independent of the probe position. The presence of the samples caused a decrease in the O-atom density. Depending on the distance from the samples, the O-atom density was decreased up to 5 times. The O-atom density also depended on the surface morphology of the samples. The strongest decrease in the O-atom density was observed with the samples covered with dense bundles of nanowires. The results clearly showed that niobium oxide nanowires exhibit excellent catalytic behaviour for neutral radicals and can be used as catalysts of exhaust radicals found in many applications

  1. Is the surface oxygen exchange rate linked to bulk ion diffusivity in mixed conducting Ruddlesden-Popper phases?

    Science.gov (United States)

    Tomkiewicz, Alex C; Tamimi, Mazin A; Huq, Ashfia; McIntosh, Steven

    2015-01-01

    The possible link between oxygen surface exchange rate and bulk oxygen anion diffusivity in mixed ionic and electronic conducting oxides is a topic of great interest and debate. While a large body of experimental evidence and theoretical analyses support a link, observed differences between bulk and surface composition of these materials are hard to reconcile with this observation. This is further compounded by potential problems with simultaneous measurement of both parameters. Here we utilize separate techniques, in situ neutron diffraction and pulsed isotopic surface exchange, to examine bulk ion mobility and surface oxygen exchange rates of three Ruddlesden-Popper phases, general form A(n-1)A(2)'B(n)O(3n+1), A(n-1)A(2)'B(n)X(3n+1); LaSrCo(0.5)Fe(0.5)O(4-δ) (n = 1), La(0.3)Sr(2.7)CoFeO(7-δ) (n = 2) and LaSr3Co(1.5)Fe(1.5)O(10-δ) (n = 3). These measurements are complemented by surface composition determination via high sensitivity-low energy ion scattering. We observe a correlation between bulk ion mobility and surface exchange rate between materials. The surface exchange rates vary by more than one order of magnitude with high anion mobility in the bulk of an oxygen vacancy-rich n = 2 Ruddlesden-Popper material correlating with rapid oxygen exchange. This is in contrast with the similar surface exchange rates which we may expect due to similar surface compositions across all three samples. We conclude that experimental limitations lead to inherent convolution of surface and bulk rates, and that surface exchange steps are not likely to be rate limiting in oxygen incorporation.

  2. $^{11}$B and $^{27}$Al NMR spin-lattice relaxation and Knight shift study of Mg$_{1-x}$Al$_x$B$_2$. Evidence for anisotropic Fermi surface

    OpenAIRE

    Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.

    2002-01-01

    We report a detailed study of $^{11}$B and $^{27}$Al NMR spin-lattice relaxation rates ($1/T_1$), as well as of $^{27}$Al Knight shift (K) of Mg$_{1-x}$Al$_x$B$_2$, $0\\leq x\\leq 1$. The obtained ($1/T_1T$) and K vs. x plots are in excellent agreement with ab initio calculations. This asserts experimentally the prediction that the Fermi surface is highly anisotropic, consisting mainly of hole-type 2-D cylindrical sheets from bonding $2p_{x,y}$ boron orbitals. It is also shown that the density ...

  3. Modeling of Transmittance Degradation Caused by Optical Surface Contamination by Atomic Oxygen Reaction with Adsorbed Silicones

    Science.gov (United States)

    Snyder, Aaron; Banks, Bruce; Miller, Sharon; Stueber, Thomas; Sechkar, Edward

    2001-01-01

    A numerical procedure is presented to calculate transmittance degradation caused by contaminant films on spacecraft surfaces produced through the interaction of orbital atomic oxygen (AO) with volatile silicones and hydrocarbons from spacecraft components. In the model, contaminant accretion is dependent on the adsorption of species, depletion reactions due to gas-surface collisions, desorption, and surface reactions between AO and silicone producing SiO(x), (where x is near 2). A detailed description of the procedure used to calculate the constituents of the contaminant layer is presented, including the equations that govern the evolution of fractional coverage by specie type. As an illustrative example of film growth, calculation results using a prototype code that calculates the evolution of surface coverage by specie type is presented and discussed. An example of the transmittance degradation caused by surface interaction of AO with deposited contaminant is presented for the case of exponentially decaying contaminant flux. These examples are performed using hypothetical values for the process parameters.

  4. Lattice gases

    International Nuclear Information System (INIS)

    Boghosian, B.M.

    1990-01-01

    In recent years an important class of cellular automata known as lattice gases have been successfully used to model a variety of physical systems, traditionally modeled by partial differential equations. The 2-D and 3-D Navier Stokes equations for single-phase and multiphase flow, Burgers' equation, and various types of diffusion equations are all examples. The first section of this chapter is meant to be a survey of the different ideas and techniques used in this simulations. In the second section, using lattice gases for the diffusion equation and for Burgers' equation as examples, the discrete Chapman-Enskog method is demonstrated. Beginning with rules governing particle motion on a lattice, the lattice Boltzmann equation is derived, and the Chapman-Enskog method is used to derive hydrodynamical equations for the conserved quantities. The approximations used at each step are discussed in detail. The intent is to provide an introduction to the Chapman-Enskog analysis for simple lattice gases in order to prepare the reader to better understand that for the (generally more complicated) models proposed for the simulation of the Navier-Stokes equations. 29 refs., 5 figs., 4 tabs

  5. Oxygen adsorption on Pt(110)-(1x2): new high-coverage structures

    DEFF Research Database (Denmark)

    Helveg, Stig; Lorensen, Henrik Qvist; Horch, Sebastian

    1999-01-01

    From an interplay between scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations, a comprehensive picture is obtained for oxygen adsorption on the Pt(110)-(1 x 2) surface, from single isolated oxygen atoms chemisorbed in FCC sites along the platinum ridges...... adsorption and platinum lattice distortions. (C) 1999 Elsevier Science B.V. All rights reserved....

  6. Tensile strength of oxygen plasma-created surface layer of PDMS

    Science.gov (United States)

    Ohishi, Taiki; Noda, Haruka; Matsui, Tsubasa S.; Jile, Huge; Deguchi, Shinji

    2017-01-01

    Polydimethylsiloxane (PDMS) is a commonly used silicone elastomer with broad applications. Particularly for bioengineering use, PDMS is treated with oxygen plasma with which its surface is oxidized to allow positive interaction with water and live cells. In exchange for the acquisition of hydrophilicity, the oxidized PDMS becomes mechanically brittle so that resulting formation of cracks affects the system in various ways. However, tensile strength (TS), which is an inherent capacity of a material to withstand tensile loads before breaking and is thus a key parameter limiting the use of the material, remains unclear regarding oxidized PDMS. Here we determine the TS of oxide layers created on the surface of PDMS based on micro-stretch experiments using a custom-made device. We show that the surface layer displays cracks upon tensile loading of small strains of within 10% to have a TS of ~10-100 kPa, which is approximately two orders of magnitude lower than that of unmodified PDMS. We further show that the TS sharply decreases with oxidation duration to become highly brittle, while the thickness of the resulting oxide layer finally reaches a plateau even with prolonged plasma treatment. Consequently, we suggest that gradual surface modification of PDMS takes place only within a finite region even with prolonged plasma treatment, as distinct from previously held assumptions. These quantitative data provide critical design information for the oxide layer of plasma-hydrophilized PDMS.

  7. Liquid Metallic Hydrogen III. Intercalation and Lattice Exclusion Versus Gravitational Settling and Their Consequences Relative to Internal Structure, Surface Activity, and Solar Winds in the Sun

    Directory of Open Access Journals (Sweden)

    Robitaille P.-M.

    2013-04-01

    Full Text Available Invocation of a liquid metallic hydrogen model (Robitaille P.M. Liquid Metallic Hydro- gen: A Building Block for the Liquid Sun. Progr. Phys ., 2011, v. 3, 60–74; Robitaille P.M. Liquid Metallic Hydrogen II: A Critical Assessment of Current and Primordial He- lium Levels in Sun. Progr. Phys ., 2013, v. 2, 35–47 brings with it a set of advantages for understanding solar physics which will always remain unavailable to the gaseous models. Liquids characteristically act as solvents and incorporate solutes within their often fleeting structural matrix. They possess widely varying solubility products and often reject the solute altogether. In that case, the solute becomes immiscible. “Lattice exclusion” can be invoked for atoms which attempt to incorporate themselves into liquid metallic hydrogen. In order to conserve the integrity of its conduction bands, it is antic- ipated that a graphite-like metallic hydrogen lattice should not permit incorporation of other elements into its in-plane hexagonal hydrogen framework. Based on the physics observed in the intercalation compounds of graphite, non-hydrogen atoms within liq- uid metallic hydrogen could reside between adjacent hexagonal proton planes. Conse- quently, the forces associated with solubility products and associated lattice exclusion envisioned in liquid metallic hydrogen for solutes would restrict gravitational settling. The hexagonal metallic hydrogen layered lattice could provide a powerful driving force for excluding heavier elements from the solar body. Herein lies a new exfoliative force to drive both surface activity (flares, coronal mass ejections, prominences and solar winds with serious consequences relative to the p–p reaction and CNO cycle in the Sun. At the same time, the idea that non-hydrogen atomic nuclei can exist between layers of metallic hydrogen leads to a fascinating array of possibilities with respect to nucleosyn- thesis. Powerful parallels can be drawn to the

  8. Oxygen adsorption on the Al9Co2(001) surface: first-principles and STM study

    International Nuclear Information System (INIS)

    Villaseca, S Alarcón; Loli, L N Serkovic; Ledieu, J; Fournée, V; Dubois, J-M; Gaudry, É; Gille, P

    2013-01-01

    Atomic oxygen adsorption on a pure aluminum terminated Al 9 Co 2 (001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a ‘bridge’ type site between the cluster entities exposed at the (001) surface termination. The Al–O bonding between the adsorbate and the substrate presents a covalent character, with s–p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al–O distances are in agreement with those reported in Al 2 O and Al 2 O 3 oxides and for oxygen adsorption on Al(111). (paper)

  9. Lattice QCD

    International Nuclear Information System (INIS)

    Mackenzie, Paul

    2007-01-01

    Modern lattice gauge theory calculations are making it possible for lattice QCD to play an increasingly important role in the quantitative investigation of the Standard Model. The fact that QCD is strongly coupled at large distances has required the development of nonperturbative methods and large-scale computer simulations to solve the theory. The development of successful numerical methods for QCD calculations puts us in a good position to be ready for the possible discovery of new strongly coupled forces beyond the Standard Model in the era of the Large Hadron Collider. (author)

  10. Operator lattices

    International Nuclear Information System (INIS)

    Bender, C.M.

    1984-01-01

    The finite-element method enables us to convert the operator differential equations of a quantum field theory into operator difference equations. These difference equations are consistent with the requirements of quantum mechanics and they do not exhibit fermion doubling, a problem that frequently plagues lattice treatments of fermions. Guage invariance can also be incorporated into the difference equations. On a finite lattice the operator difference equations can be solved in closed form. For the case of the Schwinger model the anomaly is computed and results in excellent agreement are obtained with the known continuum value

  11. Improvement of Surface Wettability and Hydrophilization of Poly-paraphenylene benzobisoxazole Fiber with Fibrillation Combined Oxygen Plasma Treatment

    Directory of Open Access Journals (Sweden)

    Xiwen Wang

    2012-01-01

    Full Text Available A new surface modification method fibrillation combined with oxygen plasma treatment to improve the wettability and hydrophily of PBO fiber was studied in this paper. The surface chemical structure and morphology of PBO fiber were characterized by the methods of FTIR, XPS and SEM. The wettability and hydrophlic characters changes on the surface were evaluated by the dynamic contact angle system and image analysis. The results show that the increase surface roughness by fibrillation could improve the wettability. Fibrillation combined oxygen plasma treatment has a better effect than oxygen plasma treatment to improve the wettability and hdyrophlization of PBO fiber. The specific area of PBO fiber increased to 10.7 m2/g from 0.7 m2/g, contact angle decreased to 43.2° from 84.4° and WRV increased to 208.4% from 13.7%. The modified fibers have a good dispersion in water for hydrophilization improvement.

  12. Optical characterization of surface and interface oxygen content in YBa2Cu3O/sub x/

    International Nuclear Information System (INIS)

    Kelly, M.K.; Chan, S.; Jenkin, K. II; Aspnes, D.E.; Barboux, P.; Tarascon, J.

    1988-01-01

    Because YBa 2 Cu 3 O/sub x/ exists over a range of oxygen content and low oxygen material is nonsuperconducting, it is important to be able to measure and control this parameter for application purposes. We present an optical technique for determining oxygen loss at surfaces and interfaces, where processing and contacts with other materials may affect composition and where usual techniques are insensitive. Using a strong absorption feature at 4.1 eV which appears at low oxygen composition, we find that overlayers of Al and In remove oxygen from YBa 2 Cu 3 O/sub x/, but Ag, Au, and room-temperature exposure to moderate vacuum do not

  13. Ab initio R1 mechanism of photostimulated oxygen isotope exchange reaction on a defect TiO2 surface: The case of terminal oxygen atom exchange

    Science.gov (United States)

    Kevorkyants, Ruslan; Sboev, Mikhail. N.; Chizhov, Yuri V.

    2017-05-01

    Based on density functional theory we propose R1 mechanism of photostimulated oxygen isotope exchange (POIEx) reaction between 16O18O and terminal oxygen atom of a defect TiO2 surface, which is modeled by amorphous Ti8O16 nanocluster in excited S1 electronic state. The proposed mechanism involves four adsorption intermediates and five transition states. The computed activation energy of the POIEx equals 0.24 eV. The computed g-tensors of the predicted ozonide O3- chemisorption species match well EPR data on O2 adsorption on UV-irradiated nanocrystalline TiO2. This match serves a mean of justification of the proposed R1 mechanism of the POIEx reaction. In addition, it is found that the proposed R1 POIEx reaction's mechanism differs from R1 mechanism of thermo-assisted OIEx reaction on a surface of supported vanadium oxide catalyst VOx/TiO2 reported earlier.

  14. Tunable Oxygen Functional Groups as Electrocatalysts on Graphite Felt Surfaces for All-Vanadium Flow Batteries.

    Science.gov (United States)

    Estevez, Luis; Reed, David; Nie, Zimin; Schwarz, Ashleigh M; Nandasiri, Manjula I; Kizewski, James P; Wang, Wei; Thomsen, Edwin; Liu, Jun; Zhang, Ji-Guang; Sprenkle, Vincent; Li, Bin

    2016-06-22

    A dual oxidative approach using O2 plasma followed by treatment with H2 O2 to impart oxygen functional groups onto the surface of a graphite felt electrode. When used as electrodes for an all-vanadium redox flow battery (VRB) system, the energy efficiency of the cell is enhanced by 8.2 % at a current density of 150 mA cm(-2) compared with one oxidized by thermal treatment in air. More importantly, by varying the oxidative techniques, the amount and type of oxygen groups was tailored and their effects were elucidated. It was found that O-C=O groups improve the cells performance whereas the C-O and C=O groups degrade it. The reason for the increased performance was found to be a reduction in the cell overpotential after functionalization of the graphite felt electrode. This work reveals a route for functionalizing carbon electrodes to improve the performance of VRB cells. This approach can lower the cost of VRB cells and pave the way for more commercially viable stationary energy storage systems that can be used for intermittent renewable energy storage. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Photocatalytic Conversion of Nitrogen to Ammonia with Water on Surface Oxygen Vacancies of Titanium Dioxide.

    Science.gov (United States)

    Hirakawa, Hiroaki; Hashimoto, Masaki; Shiraishi, Yasuhiro; Hirai, Takayuki

    2017-08-09

    Ammonia (NH 3 ) is an essential chemical in modern society. It is currently manufactured by the Haber-Bosch process using H 2 and N 2 under extremely high-pressure (>200 bar) and high-temperature (>673 K) conditions. Photocatalytic NH 3 production from water and N 2 at atmospheric pressure and room temperature is ideal. Several semiconductor photocatalysts have been proposed, but all suffer from low efficiency. Here we report that a commercially available TiO 2 with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N 2 , successfully produces NH 3 . The active sites for N 2 reduction are the Ti 3+ species on the oxygen vacancies. These species act as adsorption sites for N 2 and trapping sites for the photoformed conduction band electrons. These properties therefore promote efficient reduction of N 2 to NH 3 . The solar-to-chemical energy conversion efficiency is 0.02%, which is the highest efficiency among the early reported photocatalytic systems. This noble-metal-free TiO 2 system therefore shows a potential as a new artificial photosynthesis for green NH 3 production.

  16. Power System Mass Analysis for Hydrogen Reduction Oxygen Production on the Lunar Surface

    Science.gov (United States)

    Colozza, Anthony J.

    2009-01-01

    The production of oxygen from the lunar regolith requires both thermal and electrical power in roughly similar proportions. This unique power requirement is unlike most applications on the lunar surface. To efficiently meet these requirements, both solar PV array and solar concentrator systems were evaluated. The mass of various types of photovoltaic and concentrator based systems were calculated to determine the type of power system that provided the highest specific power. These were compared over a range of oxygen production rates. Also a hybrid type power system was also considered. This system utilized a photovoltaic array to produce the electrical power and a concentrator to provide the thermal power. For a single source system the three systems with the highest specific power were a flexible concentrator/Stirling engine system, a rigid concentrator/Stirling engine system and a tracking triple junction solar array system. These systems had specific power values of 43, 34, and 33 W/kg, respectively. The hybrid power system provided much higher specific power values then the single source systems. The best hybrid combinations were the triple junction solar array with the flexible concentrator and the rigid concentrator. These systems had a specific power of 81 and 68 W/kg, respectively.

  17. Plasma-polymerized SiOx deposition on polymer film surfaces for preparation of oxygen gas barrier polymeric films

    International Nuclear Information System (INIS)

    Inagaki, N.

    2003-01-01

    SiOx films were deposited on surfaces of three polymeric films, PET, PP, and Nylon; and their oxygen gas barrier properties were evaluated. To mitigate discrepancies between the deposited SiOx and polymer film, surface modification of polymer films was done, and how the surface modification could contribute to was discussed from the viewpoint of apparent activation energy for the permeation process. The SiOx deposition on the polymer film surfaces led to a large decrease in the oxygen permeation rate. Modification of polymer film surfaces by mans of the TMOS or Si-COOH coupling treatment in prior to the SiOx deposition was effective in decreasing the oxygen permeation rate. The cavity model is proposed as an oxygen permeation process through the SiOx-deposited Nylon film. From the proposed model, controlling the interface between the deposited SiOx film and the polymer film is emphasized to be a key factor to prepare SiOx-deposited polymer films with good oxygen gas barrier properties. (author)

  18. Colossal positive magnetoresistance in surface-passivated oxygen-deficient strontium titanite

    KAUST Repository

    David, Adrian

    2015-05-15

    Modulation of resistance by an external magnetic field, i.e. magnetoresistance effect, has been a long-lived theme of research due to both fundamental science and device applications. Here we report colossal positive magnetoresistance (CPMR) (>30,000% at a temperature of 2 K and a magnetic field of 9 T) discovered in degenerate semiconducting strontium titanite (SrTiO3) single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers. The low-pressure high-temperature homoepitaxial growth of several unit cells of SrTiO3 introduces oxygen vacancies and high-mobility carriers in the bulk SrTiO3, and the three-unit-cell LaAlO3 capping layer passivates the surface and improves carrier mobility by suppressing surface-defect-related scattering. The coexistence of multiple types of carriers and inhomogeneous transport lead to the emergence of CPMR. This unit-cell-level surface engineering approach is promising to be generalized to others oxides, and to realize devices with high-mobility carriers and interesting magnetoelectronic properties.

  19. Surface functionalization of titanium dioxide nanoparticles: Photo-stability and reactive oxygen species (ROS) generation

    Science.gov (United States)

    Louis, Kacie M.

    Metal oxide nanoparticles are becoming increasingly prevalent in society for applications of sunscreens, cosmetics, paints, biomedical imaging, and photovoltaics. Due to the increased surface area to volume ratio of nanoparticles compared to bulk materials, it is important to know the health and safety impacts of these materials. One mechanism of toxicity of nominally "safe" materials such as TiO 2 is through the photocatalytic generation of reactive oxygen species (ROS). ROS production and ligand degradation can affect the bioavailability of these particles in aqueous organisms. We have investigated ROS generation by functionalized TiO2 nanoparticles and its influence on aggregation and bioavailability and toxicity to zebrafish embryos/larvae. For these studies we investigated anatase TiO2 nanoparticles. For application purposes and solution stability, the TiO2 nanoparticles were functionalized with a variety of ligands such as citrate, 3,4-dihydroxybenzaldehyde, and ascorbate. We quantitatively examined the amount of ROS produced in aqueous solution using fluorescent probes and see that more ROS is produced under UV light than in the dark control. Our measurements show that TiO2 toxicity reaches a maximum for nanoparticles with smaller diameters, and is correlated with surface area dependent changes in ROS generation. In an effort to reduce toxicity through control of the surface and surface ligands, we synthesized anatase nanoparticles of different sizes, functionalized them with different ligands, and examined the resulting ROS generation and ligand stability. Using a modular ligand containing a hydrophobic inner region and a hydrophilic outer region, we synthesized water-stable nanoparticles, via two different chemical reactions, having much-reduced ROS generation and thus reduced toxicity. These results suggest new strategies for making safer nanoparticles while still retaining their desired properties. We also examine the degradation of the different ligands

  20. Ab initio R1 mechanism of photostimulated oxygen isotope exchange reaction on a defect TiO{sub 2} surface: The case of terminal oxygen atom exchange

    Energy Technology Data Exchange (ETDEWEB)

    Kevorkyants, Ruslan, E-mail: ruslan.kevorkyants@gmail.com; Sboev, Mikhail N.; Chizhov, Yuri V.

    2017-05-01

    Highlights: • DFT R1 mechanism of photostimulated oxygen isotope exchange between {sup 16}O{sup 18}O and terminal oxygen atom of a defect surface of nanocrystalline TiO{sub 2} is proposed. • The mechanism involves four adsorption intermediates and five transition states. • Activation energy of the reaction is 0.24 eV. • G-tensors of O{sub 3}{sup −} intermediates match EPR data on O{sub 2} adsorbed on UV-irradiated TiO{sub 2} surface. - Abstract: Based on density functional theory we propose R1 mechanism of photostimulated oxygen isotope exchange (POIEx) reaction between {sup 16}O{sup 18}O and terminal oxygen atom of a defect TiO{sub 2} surface, which is modeled by amorphous Ti{sub 8}O{sub 16} nanocluster in excited S{sup 1} electronic state. The proposed mechanism involves four adsorption intermediates and five transition states. The computed activation energy of the POIEx equals 0.24 eV. The computed g-tensors of the predicted ozonide O{sub 3}{sup −} chemisorption species match well EPR data on O{sub 2} adsorption on UV-irradiated nanocrystalline TiO{sub 2}. This match serves a mean of justification of the proposed R1 mechanism of the POIEx reaction. In addition, it is found that the proposed R1 POIEx reaction’s mechanism differs from R1 mechanism of thermo-assisted OIEx reaction on a surface of supported vanadium oxide catalyst VO{sub x}/TiO{sub 2} reported earlier.

  1. Active Pt3Ni (111) Surface of Pt3Ni Icosahedron for Oxygen Reduction.

    Science.gov (United States)

    Zhu, Jianbing; Xiao, Meiling; Li, Kui; Liu, Changpeng; Zhao, Xiao; Xing, Wei

    2016-11-09

    Highly active, durable oxygen reduction reaction (ORR) electrocatalysts are extremely important for fuel cell applications. Herein, we provide an efficient way to synthesis of activity Pt 3 M icosahedra by the one-pot hydrothermal method in the presence of glucosamine which can well adjust the reduction rate of Pt 4+ and efficiently control the morphology of final catalysts. Compared to Pt/C, the Pt 3 Ni icosahedra show 32-fold and 12-fold enhancement in specific and mass activity, respectively. Furthermore, robust durability was also observed in the accelerated durability test. Thus, this Pt 3 Ni icosahedron is found among the best Pt-based ORR catalysts, moreover, the findings also demonstrate how to mimic active extended surfaces in nanoscale.

  2. Crossed beam reactive scattering of oxygen atoms and surface scattering studies of gaseous condensation

    International Nuclear Information System (INIS)

    Sibener, S.J.

    1979-09-01

    A high pressure, radio frequency discharge nozzle beam source was developed for the production of very intense (greater than or equal to 10 18 atoms sr -1 sec -1 ) supersonic beams of oxygen atoms. This source is capable of producing seeded beams of ground state O( 3 P/sub J/) atoms when dilute oxygen-argon mixtures are used, with molecular dissociation levels exceeding 80% being realized for operation at pressures up to 350 torr. When dilute oxygen-helium mixtures are employed both ground state O( 3 P/sub J/) and excited state O( 1 D 2 ) atoms are present in the terminal beam, with molecular dissociation levels typically exceeding 60% being achieved for operation at pressures up to 200 torr. Atomic oxygen mean translational energies from 0.14 to 0.50 eV were obtained using the seeded beams technique, with Mach numbers as high as 10 (FWHM Δ v/v approx. = 20%) being realized. The IC1, CF 3 I, C 6 H 6 , and C 6 D 6 reactions are discussed in detail. The IC1 and CF 3 I studies have enabled us to determine an improved value for the bond energy of the IO radical: D/sub o/(IO) = 55 +- 2 kcal/mole. The IO product angular and velocity distributions have been used to generate center-of-mass flux contour maps, which indicate that these two reactions proceed via relatively long-lived collision complexes whose mean lifetimes are slightly shorter than their respective rotational periods. The O( 3 P/sub J/) + C 6 H 6 and C 6 D 6 reactions were studied in order to elucidate the reaction mechanism, and, in particular, to identify the primary reaction products produced in these reactions. Finally, a series of beam-surface scattering experiments are described which examined the internal and translational energy dependence of molecular condensation probabilities for collisions involving either CC1 4 or SF 6 and their respective condensed phases. 117 references

  3. Investigation on Selective Laser Melting AlSi10Mg Cellular Lattice Strut: Molten Pool Morphology, Surface Roughness and Dimensional Accuracy

    Directory of Open Access Journals (Sweden)

    Xuesong Han

    2018-03-01

    Full Text Available AlSi10Mg inclined struts with angle of 45° were fabricated by selective laser melting (SLM using different scanning speed and hatch spacing to gain insight into the evolution of the molten pool morphology, surface roughness, and dimensional accuracy. The results show that the average width and depth of the molten pool, the lower surface roughness and dimensional deviation decrease with the increase of scanning speed and hatch spacing. The upper surface roughness is found to be almost constant under different processing parameters. The width and depth of the molten pool on powder-supported zone are larger than that of the molten pool on the solid-supported zone, while the width changes more significantly than that of depth. However, if the scanning speed is high enough, the width and depth of the molten pool and the lower surface roughness almost keep constant as the density is still high. Therefore, high dimensional accuracy and density as well as good surface quality can be achieved simultaneously by using high scanning speed during SLMed cellular lattice strut.

  4. Investigation on Selective Laser Melting AlSi10Mg Cellular Lattice Strut: Molten Pool Morphology, Surface Roughness and Dimensional Accuracy.

    Science.gov (United States)

    Han, Xuesong; Zhu, Haihong; Nie, Xiaojia; Wang, Guoqing; Zeng, Xiaoyan

    2018-03-07

    AlSi10Mg inclined struts with angle of 45° were fabricated by selective laser melting (SLM) using different scanning speed and hatch spacing to gain insight into the evolution of the molten pool morphology, surface roughness, and dimensional accuracy. The results show that the average width and depth of the molten pool, the lower surface roughness and dimensional deviation decrease with the increase of scanning speed and hatch spacing. The upper surface roughness is found to be almost constant under different processing parameters. The width and depth of the molten pool on powder-supported zone are larger than that of the molten pool on the solid-supported zone, while the width changes more significantly than that of depth. However, if the scanning speed is high enough, the width and depth of the molten pool and the lower surface roughness almost keep constant as the density is still high. Therefore, high dimensional accuracy and density as well as good surface quality can be achieved simultaneously by using high scanning speed during SLMed cellular lattice strut.

  5. A first principles investigation of the oxygen adsorption on Zr(0001) surface using cluster expansions

    Science.gov (United States)

    Samin, Adib J.; Taylor, Christopher D.

    2017-11-01

    The design of corrosion resistant zircalloys is important for a variety of technological applications ranging from medicine to the nuclear industry. Since corrosion resistance is mainly attributed to the formation of a surface oxide layer, developing a detailed understanding of this process may assist in future corrosion resistance design. In this work, we conduct a systematic multi-scale investigation of the early stages of oxide formation. This was accomplished by first using a database of fully relaxed DFT calculations to build a cluster-expansion description of the potential function. The developed potential was reasonably good at predicting DFT energies as evidenced by the cross-validation score of 4.4 meV/site. The effective cluster expansion parameters were indicative of repulsive adsorbate interactions in the adlayer in agreement with the literature. The potential then allowed for a systematic investigation of the oxygen configurations on the Zr(0001) surface via Monte Carlo simulations. The adsorption energy was recorded as a function of coverage and an increasing trend was observed in agreement with DFT predictions and the repulsive nature of interactions in the adlayer. The convex hull diagram was recorded indicating the most stable configuration to occur around a coverage of 0.6 ML. The adsorption isotherm was also recorded and contrasted for two temperatures relevant for different applications.

  6. Oxygen Reduction Kinetics Enhancement on a Heterostructured Oxide Surface for Solid Oxide Fuel Cells

    KAUST Repository

    Crumlin, Ethan J.

    2010-11-04

    Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of ∼85 nm thick La0.8Sr0.2CoO3-δ (LSC113) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced (∼3-4 orders of magnitude above bulk LSC113) by surface decorations of (La 0.5Sr0.5)2CoO4±δ (LSC214) with coverage in the range from ∼0.1 to ∼15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC113/LSC214 regions, which were shown to be atomically sharp. © 2010 American Chemical Society.

  7. Hypothesized link between Neoproterozoic greening of the land surface and the establishment of an oxygen-rich atmosphere

    Science.gov (United States)

    Kump, Lee R.

    2014-01-01

    Considerable geological, geochemical, paleontological, and isotopic evidence exists to support the hypothesis that the atmospheric oxygen level rose from an Archean baseline of essentially zero to modern values in two steps roughly 2.3 billion and 0.8–0.6 billion years ago (Ga). The first step in oxygen content, the Great Oxidation Event, was likely a threshold response to diminishing reductant input from Earth’s interior. Here I provide an alternative to previous suggestions that the second step was the result of the establishment of the first terrestrial fungal–lichen ecosystems. The consumption of oxygen by aerobes respiring this new source of organic matter in soils would have necessitated an increase in the atmospheric oxygen content to compensate for the reduced delivery of oxygen to the weathering environment below the organic-rich upper soil layer. Support for this hypothesis comes from the observed spread toward more negative carbon isotope compositions in Neoproterozoic (1.0–0.542 Ga) and younger limestones altered under the influence of ground waters, and the positive correlation between the carbon isotope composition and oxygen content of modern ground waters in contact with limestones. Thus, the greening of the planet’s land surfaces forced the atmospheric oxygen level to a new, higher equilibrium state. PMID:25225378

  8. Lattice-Boltzmann method applied to the pattern formation on periodic surface structures generated by multiline nanosecond laser

    Directory of Open Access Journals (Sweden)

    Frank Rodolfo Fonseca-Fonseca

    2014-01-01

    Full Text Available Hemos simulado la formación de patrones en superficies de silic io. Para este propósito, se utilizó el método de Lattice-Boltzm ann suponiendo dos fluidos no ideales, que interactúan, utilizando una rejilla de velocidades D2Q9 . El experimento se llevó a cabo con un láser de pulsos multilínea (1064, 532 y 355 nm de Nd: YAG, qu e emplea un rango de energía 310 a 3.100 J, en una superficie d e silicio monocristalino , tipo p, orientado en la dirección [111]. Todo el sistema se som etió a soplado de gas de argón que es clave en la formación de los patrones. La simulación computacional reproduc e bastante bien, el comportamiento global de los patrones geomé tricos experimentales, expresados en ondulaciones paralelas oblicuas.

  9. Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

    Directory of Open Access Journals (Sweden)

    Nicola H. Perry

    2016-10-01

    Full Text Available Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic, and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I2CNER, Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance.

  10. The coupling effect of gas-phase chemistry and surface reactions on oxygen permeation and fuel conversion in ITM reactors

    KAUST Repository

    Hong, Jongsup

    2015-08-01

    © 2015 Elsevier B.V. The effect of the coupling between heterogeneous catalytic reactions supported by an ion transport membrane (ITM) and gas-phase chemistry on fuel conversion and oxygen permeation in ITM reactors is examined. In ITM reactors, thermochemical reactions take place in the gas-phase and on the membrane surface, both of which interact with oxygen permeation. However, this coupling between gas-phase and surface chemistry has not been examined in detail. In this study, a parametric analysis using numerical simulations is conducted to investigate this coupling and its impact on fuel conversion and oxygen permeation rates. A thermochemical model that incorporates heterogeneous chemistry on the membrane surface and detailed chemical kinetics in the gas-phase is used. Results show that fuel conversion and oxygen permeation are strongly influenced by the simultaneous action of both chemistries. It is shown that the coupling somewhat suppresses the gas-phase kinetics and reduces fuel conversion, both attributed to extensive thermal energy transfer towards the membrane which conducts it to the air side and radiates to the reactor walls. The reaction pathway and products, in the form of syngas and C2 hydrocarbons, are also affected. In addition, the operating regimes of ITM reactors in which heterogeneous- or/and homogeneous-phase reactions predominantly contribute to fuel conversion and oxygen permeation are elucidated.

  11. First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction

    DEFF Research Database (Denmark)

    Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan

    2015-01-01

    driving force for surface segregation, diffusion to defects or surface self-assembling. On the basis of stability and activity analysis we conclude that the near surface alloy of Pd in Pt and some PdAu binary and PtPdAu ternary thin films with a controlled amount of Au are the best catalysts for oxygen......Further advances in fuel cell technologies are hampered by kinetic limitations associated with the sluggish cathodic oxygen reduction reaction. We have investigated a range of different formulations of binary and ternary Pt, Pd and Au thin films as electrocatalysts for oxygen reduction. The most...... active binary thin films are near-surface alloys of Pt with subsurface Pd and certain PdAu and PtAu thin films with surface and/or subsurface Au. The most active ternary thin films are with pure metal Pt or Pd skins with some degree of Au in the surface and/or subsurface layer and the near-surface alloys...

  12. Interplay between steps and nonequilibrium effects in surface diffusion for a lattice-gas model of O/W (110

    Czech Academy of Sciences Publication Activity Database

    Mašín, Martin; Vattulainen, I.; Ala-Nissila, T.; Chvoj, Zdeněk

    2007-01-01

    Roč. 126, č. 11 (2007), 114705/1-114705/8 ISSN 0021-9606 R&D Projects: GA AV ČR IAA1010207 Institutional research plan: CEZ:AV0Z10100521 Keywords : surface diffusion * vicinal surfaces * non-equilibrium effects * Monte-Carlo simulations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.044, year: 2007

  13. No oxygen isotope exchange between water and APS-sulfate at surface temperature: Evidence from quantum chemical modeling and triple-oxygen isotope experiments

    Science.gov (United States)

    Kohl, Issaku E.; Asatryan, Rubik; Bao, Huiming

    2012-10-01

    In both laboratory experiments and natural environments where microbial dissimilatory sulfate reduction (MDSR) occurs in a closed system, the δ34S ((34S/32S)sample/(34S/32S)standard - 1) for dissolved SO42- has been found to follow a typical Rayleigh-Distillation path. In contrast, the corresponding δ18O ((18O/16O)sample/(18O/16O)standard) - 1) is seen to plateau with an apparent enrichment of between 23‰ and 29‰ relative to that of ambient water under surface conditions. This apparent steady-state in the observed difference between δ18O and δ18OO can be attributed to any of these three steps: (1) the formation of adenosine-5'-phosphosulfate (APS) from ATP and SO42-, (2) oxygen exchange between sulfite (or other downstream sulfoxy-anions) and water later in the MDSR reaction chain and its back reaction to APS and sulfate, and (3) the re-oxidation of produced H2S or precursor sulfoxy-anions to sulfate in environments containing Fe(III) or O2. This study examines the first step as a potential pathway for water oxygen incorporation into sulfate. We examined the structures and process of APS formation using B3LYP/6-31G(d,p) hybrid density functional theory, implemented in the Gaussian-03 program suite, to predict the potential for oxygen exchange. We conducted a set of in vitro, enzyme-catalyzed, APS formation experiments (with no further reduction to sulfite) to determine the degree of oxygen isotope exchange between the APS-sulfate and water. Triple-oxygen-isotope labeled water was used in the reactor solutions to monitor oxygen isotope exchange between water and APS sulfate. The formation and hydrolysis of APS were identified as potential steps for oxygen exchange with water to occur. Quantum chemical modeling indicates that the combination of sulfate with ATP has effects on bond strength and symmetry of the sulfate. However, these small effects impart little influence on the integrity of the SO42- tetrahedron due to the high activation energy required for

  14. Lattice QCD on fine lattices

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Stefan [DESY (Germany). Neumann Inst. for Computing

    2016-11-01

    These configurations are currently in use in many on-going projects carried out by researchers throughout Europe. In particular this data will serve as an essential input into the computation of the coupling constant of QCD, where some of the simulations are still on-going. But also projects computing the masses of hadrons and investigating their structure are underway as well as activities in the physics of heavy quarks. As this initial project of gauge field generation has been successful, it is worthwhile to extend the currently available ensembles with further points in parameter space. These will allow to further study and control systematic effects like the ones introduced by the finite volume, the non-physical quark masses and the finite lattice spacing. In particular certain compromises have still been made in the region where pion masses and lattice spacing are both small. This is because physical pion masses require larger lattices to keep the effects of the finite volume under control. At light pion masses, a precise control of the continuum extrapolation is therefore difficult, but certainly a main goal of future simulations. To reach this goal, algorithmic developments as well as faster hardware will be needed.

  15. Surface Modification of C3N4through Oxygen-Plasma Treatment: A Simple Way toward Excellent Hydrophilicity.

    Science.gov (United States)

    Bu, Xiuming; Li, Jipeng; Yang, Siwei; Sun, Jing; Deng, Yuan; Yang, Yucheng; Wang, Gang; Peng, Zheng; He, Peng; Wang, Xianying; Ding, Guqiao; Yang, Junhe; Xie, Xiaoming

    2016-11-16

    We developed a universal method to prepare hydrophilic carbon nitrogen (C 3 N 4 ) nanosheets. By treating C 3 N 4 nanosheets with oxygen plasma, hydroxylamine groups (N-OH) with intense protonation could be introduced on the surface; moreover, the content of N-OH groups increased linearly with the oxygen-plasma treatment time. Thanks to the excellent hydrophilicity, uniformly dispersed C 3 N 4 solution were prepared, which was further translated into C 3 N 4 paper by simple vacuum filtration. Pure C 3 N 4 paper with good stability, excellent hydrophilicity, and biocompatibility were proved to have excellent performance in tissue repair. Further research demonstrated that the oxygen-plasma treatment method can also introduce N-OH groups into other nitrogen-containing carbon materials (NCMs) such as N-doped graphene, N-doped carbon nanotube, and C 2 N, which offers a new perspective on the surface modification and functionalization of these carbon nanomaterials.

  16. Oxygen Diffusion in Titanite

    Science.gov (United States)

    Zhang, X. Y.; Cherniak, D. J.; Watson, E. B.

    2004-05-01

    Oxygen diffusion in natural and synthetic single-crystal titanite was characterized under both dry and water-present conditions. For the dry experiments, pre-polished titanite samples were packed in 18O-enriched quartz powder inside Ag-Pd capsules, along with an FMQ buffer assemblage maintained physically separate by Ag-Pd strips. The sealed Ag-Pd capsules were themselves sealed inside evacuated silica glass tubes and run at 700-1050° C and atmospheric pressure for durations ranging from 1 hour to several weeks. The hydrothermal experiments were conducted by encapsulating polished titanite crystals with 18O enriched water and running them at 700-900° C and 10-160MPa in standard cold-seal pressure vessels for durations of 1 day to several weeks. Diffusive uptake profiles of 18O were measured in all cases by nuclear reaction analysis (NRA) using the 18O (p,α ) 15N reaction. For the experiments on natural crystals, under both dry and hydrothermal conditions, two mechanisms could be recognized responsible for oxygen diffusion. The diffusion profiles showed two segments: a steep one close to the initial surface attributed to self-diffusion in the titanite lattice; and a "tail" reaching deeper into the sample attributable to diffusion in a "fast path" such as sub-grain boundaries or dislocations. For the dry experiments, the following Arrhenius relation was obtained: D{dry lattice} = 2.6×10-8exp (-275 kJmol-1/RT) m2/s Under wet conditions at PH2O = 100MPa, Oxygen diffusion conforms to the following Arrehenius relation: D{wet lattice} = 9.7× 10-13exp (-174 kJmol-1/RT) m2/s Oxygen diffusivity shows only a slight dependence on water pressure at the following conditions we explored: temperatures 800° C, PH2O = 10-160MPa, and 880° C, PH2O =10-100MPa. For diffusive anisotropy, we explored it only at hydrothermal conditions, and no diffusive anisotropy was observed. Like many other silicates, titanite shows lower activation energy for oxygen diffusion in the presence of

  17. RHIC lattice

    International Nuclear Information System (INIS)

    Lee, S.Y.; Claus, J.; Courant, E.D.; Hahn, H.; Parzen, G.

    1985-01-01

    An antisymmetric lattice for the proposed Relativistic Heavy Ion Collider at Brookhaven National Laboratory is presented, which has been designed to have (1) and energy range from 7 GeV/amu up to 100 GeV/amu; (2) a good tunability of β and betatron tune; (3) freedom in the choice of crossing angle between beams; and (4) capability of operating unequal species, for example, proton on gold. Suppression of structure resonances is achieved by a proper choice of the phase advances across the insertion and the arc cells. 8 refs., 7 figs

  18. Oxygen isotope evidence for sorption of molecular oxygen to pyrite surface sites and incorporation into sulfate in oxidation experiments

    International Nuclear Information System (INIS)

    Tichomirowa, Marion; Junghans, Manuela

    2009-01-01

    Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO 4 and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O 2 ) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O 2 ) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO 4 and water was observed over a pH range of 0-2 only at 50 deg. C, whereas no exchange occurred at lower temperatures over a period of 8 a. The calculated half-time of the exchange rate for 50 deg. C (pH = 0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions (T ≤ 25 deg. C, pH ≥ 3) for decades. Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O 2 to pyrite surface sites. The sorption of molecular O 2 is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO 4 . The calculated bulk contribution of atmospheric O 2 in the dissolved SO 4 reached up to 50% during initial oxidation stages (first 5 days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100 days. Based on the direct incorporation of molecular O 2 in the early-formed sulfates, chemisorption and electron transfer of molecular O 2 on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10 days, the O of all newly-formed sulfates originates only from water, indicating direct interaction

  19. First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction

    DEFF Research Database (Denmark)

    Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan

    2015-01-01

    active binary thin films are near-surface alloys of Pt with subsurface Pd and certain PdAu and PtAu thin films with surface and/or subsurface Au. The most active ternary thin films are with pure metal Pt or Pd skins with some degree of Au in the surface and/or subsurface layer and the near-surface alloys...... driving force for surface segregation, diffusion to defects or surface self-assembling. On the basis of stability and activity analysis we conclude that the near surface alloy of Pd in Pt and some PdAu binary and PtPdAu ternary thin films with a controlled amount of Au are the best catalysts for oxygen...

  20. Error sources in the retrieval of aerosol information over bright surfaces from satellite measurements in the oxygen A band

    Science.gov (United States)

    Nanda, Swadhin; de Graaf, Martin; Sneep, Maarten; de Haan, Johan F.; Stammes, Piet; Sanders, Abram F. J.; Tuinder, Olaf; Pepijn Veefkind, J.; Levelt, Pieternel F.

    2018-01-01

    Retrieving aerosol optical thickness and aerosol layer height over a bright surface from measured top-of-atmosphere reflectance spectrum in the oxygen A band is known to be challenging, often resulting in large errors. In certain atmospheric conditions and viewing geometries, a loss of sensitivity to aerosol optical thickness has been reported in the literature. This loss of sensitivity has been attributed to a phenomenon known as critical surface albedo regime, which is a range of surface albedos for which the top-of-atmosphere reflectance has minimal sensitivity to aerosol optical thickness. This paper extends the concept of critical surface albedo for aerosol layer height retrievals in the oxygen A band, and discusses its implications. The underlying physics are introduced by analysing the top-of-atmosphere reflectance spectrum as a sum of atmospheric path contribution and surface contribution, obtained using a radiative transfer model. Furthermore, error analysis of an aerosol layer height retrieval algorithm is conducted over dark and bright surfaces to show the dependence on surface reflectance. The analysis shows that the derivative with respect to aerosol layer height of the atmospheric path contribution to the top-of-atmosphere reflectance is opposite in sign to that of the surface contribution - an increase in surface brightness results in a decrease in information content. In the case of aerosol optical thickness, these derivatives are anti-correlated, leading to large retrieval errors in high surface albedo regimes. The consequence of this anti-correlation is demonstrated with measured spectra in the oxygen A band from the GOME-2 instrument on board the Metop-A satellite over the 2010 Russian wildfires incident.

  1. Substantial Oxygen Flux in Dual-Phase Membrane of Ceria and Pure Electronic Conductor by Tailoring the Surface.

    Science.gov (United States)

    Joo, Jong Hoon; Yun, Kyong Sik; Kim, Jung-Hwa; Lee, Younki; Yoo, Chung-Yul; Yu, Ji Haeng

    2015-07-15

    The oxygen permeation flux of dual-phase membranes, Ce0.9Gd0.1O2-δ-La0.7Sr0.3MnO3±δ (GDC/LSM), has been systematically studied as a function of their LSM content, thickness, and coating material. The electronic percolation threshold of this GDC/LSM membrane occurs at about 20 vol % LSM. The coated LSM20 (80 vol % GDC, 20 vol % LSM) dual-phase membrane exhibits a maximum oxygen flux of 2.2 mL·cm(-2)·min(-1) at 850 °C, indicating that to enhance the oxygen permeation flux, the LSM content should be adjusted to the minimum value at which electronic percolation is maintained. The oxygen ion conductivity of the dual-phase membrane is reliably calculated from oxygen flux data by considering the effects of surface oxygen exchange. Thermal cycling tests confirm the mechanical stability of the membrane. Furthermore, a dual-phase membrane prepared here with a cobalt-free coating remains chemically stable in a CO2 atmosphere at a lower temperature (800 °C) than has previously been achieved.

  2. A general model to calculate the spin-lattice (T1) relaxation time of blood, accounting for haematocrit, oxygen saturation and magnetic field strength.

    Science.gov (United States)

    Hales, Patrick W; Kirkham, Fenella J; Clark, Christopher A

    2016-02-01

    Many MRI techniques require prior knowledge of the T1-relaxation time of blood (T1bl). An assumed/fixed value is often used; however, T1bl is sensitive to magnetic field (B0), haematocrit (Hct), and oxygen saturation (Y). We aimed to combine data from previous in vitro measurements into a mathematical model, to estimate T1bl as a function of B0, Hct, and Y. The model was shown to predict T1bl from in vivo studies with a good accuracy (± 87 ms). This model allows for improved estimation of T1bl between 1.5-7.0 T while accounting for variations in Hct and Y, leading to improved accuracy of MRI-derived perfusion measurements. © The Author(s) 2015.

  3. Using electrochemistry - total internal refection imaging ellipsometry to monitor biochemical oxygen demand on the surface tethered polyelectrolyte modified electrode

    Science.gov (United States)

    Liu, Wei; Li, Meng; Lv, Bei'er; Chen, YanYan; Ma, Hongwei; Jin, Gang

    2015-03-01

    Our previous work has proposed an electrochemistry - total internal reflection imaging ellipsometry (EC-TIRIE) technique to observe the dissolved oxygen (DO) reduction on Clark electrode since high interface sensitivity makes TIRIE a useful tool to study redox reactions on the electrode surface. To amplify the optical signal noise ratio (OSNR), a surface tethered weak polyelectrolyte, carboxylated poly(oligo(ethylene glycol) methacrylate-random- 2-hydroxyethylmethacrylate) (abbreviated as carboxylated poly(OEGMA-r-HEMA)), has been introduced on the electrode surface. Since Clark electrode is widely used in biochemical oxygen demand (BOD) detection, we use this technique to measure BOD in the sample. The dynamic range of the system is from 0 ˜ 25 mg/L. Two samples have been measured. Compared with the conventional method, the deviation of both optical and electrical signals are less than 10%.

  4. Availability of surface boron species in improved oxygen reduction activity of Pt catalysts: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Libo; Zhou, Gang, E-mail: gzhou@mail.buct.edu.cn [State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (China)

    2016-04-14

    The oxidation process of boron (B) species on the Pt(111) surface and the beneficial effects of boron oxides on the oxygen reduction activity are investigated by first-principles calculations. The single-atom B anchored on the Pt surface has a great attraction for the oxygen species in the immediate environment. With the dissociation of molecular oxygen, a series of boron oxides is formed in succession, both indicating exothermic oxidation reactions. After BO{sub 2} is formed, the subsequent O atom immediately participates in the oxygen reduction reaction. The calculated O adsorption energy is appreciably decreased as compared to Pt catalysts, and more approximate to the optimal value of the volcano plot, from which is clear that O hydrogenation kinetics is improved. The modulation mechanism is mainly based on the electron-deficient nature of stable boron oxides, which normally reduces available electronic states of surface Pt atoms that bind the O by facilitating more electron transfer. This modification strategy from the exterior opens the new way, different from the alloying, to efficient electrocatalyst design for PEMFCs.

  5. Ni- and Mn-Promoted Mesoporous Co3O4: A Stable Bifunctional Catalyst with Surface-Structure-Dependent Activity for Oxygen Reduction Reaction and Oxygen Evolution Reaction.

    Science.gov (United States)

    Song, Wenqiao; Ren, Zheng; Chen, Sheng-Yu; Meng, Yongtao; Biswas, Sourav; Nandi, Partha; Elsen, Heather A; Gao, Pu-Xian; Suib, Steven L

    2016-08-17

    Efficient bifunctional catalysts for electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable due to their wide applications in fuel cells and rechargeable metal air batteries. However, the development of nonprecious metal catalysts with comparable activities to noble metals is still challenging. Here we report a one-step wet-chemical synthesis of Ni-/Mn-promoted mesoporous cobalt oxides through an inverse micelle process. Various characterization techniques including powder X-ray diffraction (PXRD), N2 sorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) confirm the successful incorporation of Ni and Mn leading to the formation of Co-Ni(Mn)-O solid solutions with retained mesoporosity. Among these catalysts, cobalt oxide with 5% Ni doping demonstrates promising activities for both ORR and OER, with an overpotential of 399 mV for ORR (at -3 mA/cm(2)) and 381 mV (at 10 mA/cm(2)) for OER. Furthermore, it shows better durability than precious metals featuring little activity decay throughout 24 h continuous operation. Analyses of cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman, and O2-temperature-programmed desorption (O2-TPD) reveal that redox activity of Co(3+) to Co(4+) is crucial for OER performance, while the population of surface oxygen vacancies and surface area determine ORR activities. The comprehensive investigation of the intrinsic active sites for ORR and OER by correlating different physicochemical properties to the electrochemical activities is believed to provide important insight toward the rational design of high-performance electrocatalysts for ORR and OER reactions.

  6. Adsorption, Desorption, Surface Diffusion, Lattice Defect Formation, and Kink Incorporation Processes of Particles on Growth Interfaces of Colloidal Crystals with Attractive Interactions

    Directory of Open Access Journals (Sweden)

    Yoshihisa Suzuki

    2016-07-01

    Full Text Available Good model systems are required in order to understand crystal growth processes because, in many cases, precise incorporation processes of atoms or molecules cannot be visualized easily at the atomic or molecular level. Using a transmission-type optical microscope, we have successfully observed in situ adsorption, desorption, surface diffusion, lattice defect formation, and kink incorporation of particles on growth interfaces of colloidal crystals of polystyrene particles in aqueous sodium polyacrylate solutions. Precise surface transportation and kink incorporation processes of the particles into the colloidal crystals with attractive interactions were observed in situ at the particle level. In particular, contrary to the conventional expectations, the diffusion of particles along steps around a two-dimensional island of the growth interface was not the main route for kink incorporation. This is probably due to the number of bonds between adsorbed particles and particles in a crystal; the number exceeds the limit at which a particle easily exchanges its position to the adjacent one along the step. We also found novel desorption processes of particles from steps to terraces, attributing them to the assistance of attractive forces from additionally adsorbing particles to the particles on the steps.

  7. Investigation of the oxygen exchange mechanism on Pt|yttria stabilized zirconia at intermediate temperatures: Surface path versus bulk path

    International Nuclear Information System (INIS)

    Opitz, Alexander K.; Lutz, Alexander; Kubicek, Markus; Kubel, Frank; Hutter, Herbert; Fleig, Juergen

    2011-01-01

    Highlights: → Oxygen exchange kinetics of Pt on YSZ investigated by means of Pt model electrodes. → Two different geometry dependencies of the polarization resistance identified. → At higher temperatures the oxygen exchange reaction proceeds via a Pt surface path. → At lower temperatures a bulk path through the Pt thin film electrode is discussed. - Abstract: The oxygen exchange kinetics of platinum on yttria-stabilized zirconia (YSZ) was investigated by means of geometrically well-defined Pt microelectrodes. By variation of electrode size and temperature it was possible to separate two temperature regimes with different geometry dependencies of the polarization resistance. At higher temperatures (550-700 deg. C) an elementary step located close to the three phase boundary (TPB) with an activation energy of ∼1.6 eV was identified as rate limiting. At lower temperatures (300-400 deg. C) the rate limiting elementary step is related to the electrode area and exhibited a very low activation energy in the order of 0.2 eV. From these observations two parallel pathways for electrochemical oxygen exchange are concluded. The nature of these two elementary steps is discussed in terms of equivalent circuits. Two combinations of parallel rate limiting reaction steps are found to explain the observed geometry dependencies: (i) Diffusion through an impurity phase at the TPB in parallel to diffusion of oxygen through platinum - most likely along Pt grain boundaries - as area-related process. (ii) Co-limitation of oxygen diffusion along the Pt|YSZ interface and charge transfer at the interface with a short decay length of the corresponding transmission line (as TPB-related process) in parallel to oxygen diffusion through platinum.

  8. Unraveling the photocatalytic mechanisms on TiO2 surfaces using the oxygen-18 isotopic label technique.

    Science.gov (United States)

    Pang, Xibin; Chen, Chuncheng; Ji, Hongwei; Che, Yanke; Ma, Wanhong; Zhao, Jincai

    2014-10-10

    During the last several decades TiO2 photocatalytic oxidation using the molecular oxygen in air has emerged as a promising method for the degradation of recalcitrant organic pollutants and selective transformations of valuable organic chemicals. Despite extensive studies, the mechanisms of these photocatalytic reactions are still poorly understood due to their complexity. In this review, we will highlight how the oxygen-18 isotope labeling technique can be a powerful tool to elucidate complicated photocatalytic mechanisms taking place on the TiO2 surface. To this end, the application of the oxygen-18 isotopic-labeling method to three representative photocatalytic reactions is discussed: (1) the photocatalytic hydroxylation of aromatics; (2) oxidative cleavage of aryl rings on the TiO2 surface; and (3) photocatalytic decarboxylation of saturated carboxylic acids. The results show that the oxygen atoms of molecular oxygen can incorporate into the corresponding products in aqueous solution in all three of these reactions, but the detailed incorporation pathways are completely different in each case. For the hydroxylation process, the O atom in O2 is shown to be incorporated through activation of O2 by conduction band electrons. In the cleavage of aryl rings, O atoms are inserted into the aryl ring through the site-dependent coordination of reactants on the TiO2 surface. A new pathway for the decarboxylation of saturated carboxylic acids with pyruvic acid as an intermediate is identified, and the O2 is incorporated into the products through the further oxidation of pyruvic acid by active species from the activation of O2 by conduction band electrons.

  9. Advanced Oxygen Evolution Catalyst for Electrolyzer Energy Storage for Lunar Surface Systems, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Future NASA lunar missions will require a high efficiency, lightweight, long life, maintenance-free water electrolyzer for energy storage. Anodic oxygen evolution...

  10. Congruence amalgamation of lattices

    CERN Document Server

    Grätzer, G; Wehrung, F; Gr\\"{a}tzer, George; Lakser, Harry; Wehrung, Friedrich

    2000-01-01

    J. Tuma proved an interesting "congruence amalgamation" result. We are generalizing and providing an alternate proof for it. We then provide applications of this result: --A.P. Huhn proved that every distributive algebraic lattice $D$ with at most $\\aleph\\_1$ compact elements can be represented as the congruence lattice of a lattice $L$. We show that $L$ can be constructed as a locally finite relatively complemented lattice with zero. --We find a large class of lattices, the $\\omega$-congruence-finite lattices, that contains all locally finite countable lattices, in which every lattice has a relatively complemented congruence-preserving extension.

  11. LATTICE: an interactive lattice computer code

    International Nuclear Information System (INIS)

    Staples, J.

    1976-10-01

    LATTICE is a computer code which enables an interactive user to calculate the functions of a synchrotron lattice. This program satisfies the requirements at LBL for a simple interactive lattice program by borrowing ideas from both TRANSPORT and SYNCH. A fitting routine is included

  12. Effects of surface adsorbed oxygen, applied voltage, and temperature on UV photoresponse of ZnO nanorods

    Science.gov (United States)

    Zong, Xian-Li; Zhu, Rong

    2015-10-01

    The ultraviolet (UV) photoresponses of ZnO nanorods directly grown on and between two micro Au-electrodes by using electric-field-assisted wet chemical method are measured comprehensively under different conditions, including ambient environment, applied bias voltage, gate voltage and temperature. Experimental results indicate that the photoresponses of the ZnO nanorods can be modulated by surface oxygen adsorptions, applied voltages, as well as temperatures. A model taking into account both surface adsorbed oxygen and electron-hole activities inside ZnO nanorods is proposed. The enhancement effect of the bias voltage on photoresponse is also analyzed. Experimental results shows that the UV response time (to 63%) of ZnO nanorods in air and at 59 °C could be shortened from 34.8 s to 0.24 s with a bias of 4 V applied between anode and cathode. Project supported by the National Natural Science Foundation of China (Grant No. 91123017).

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

    Science.gov (United States)

    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.

  14. Theoretical studies on chemisorption of oxygen on β-Mo2C catalyst and its surface oxidation

    DEFF Research Database (Denmark)

    Shi, Xue-Rong; Wang, Shengguang; Hu, Jia

    2012-01-01

    by O2 at PO2/P0 of 10−21–104 and temperature of 100–700K. For the (011) surface with O2 as the oxidant, the most stable structure is that with 1/2ML or 7/8ML oxygen coverage, depending on the temperature and PO2/P0 value. The increase of gaseous oxidant pressure or decrease of temperature can enhance...

  15. High-Resolution Electron Energy Loss Studies of Oxygen, Hydrogen, Nitrogen, Nitric Oxide, and Nitrous Oxide Adsorption on Germanium Surfaces.

    Science.gov (United States)

    Entringer, Anthony G.

    The first high resolution electron energy loss spectroscopy (HREELS) studies of the oxidation and nitridation of germanium surfaces are reported. Both single crystal Ge(111) and disordered surfaces were studied. Surfaces were exposed to H, O_2, NO, N _2O, and N, after cleaning in ultra-high vacuum. The Ge surfaces were found to be non-reactive to molecular hydrogen (H_2) at room temperature. Exposure to atomic hydrogen (H) resulted hydrogen adsorption as demonstrated by the presence of Ge-H vibrational modes. The HREEL spectrum of the native oxide of Ge characteristic of nu -GeO_2 was obtained by heating the oxide to 200^circC. Three peaks were observed at 33, 62, and 106 meV for molecular oxygen (O_2) adsorbed on clean Ge(111) at room temperature. These peaks are indicative of dissociative bonding and a dominant Ge-O-Ge bridge structure. Subsequent hydrogen exposure resulted in a shift of the Ge-H stretch from its isolated value of 247 meV to 267 meV, indicative of a dominant +3 oxidation state. A high density of dangling bonds and defects and deeper oxygen penetration at the amorphous Ge surface result in a dilute bridge structure with a predominant +1 oxidation state for similar exposures. Molecules of N_2O decompose at the surfaces to desorbed N_2 molecules and chemisorbed oxygen atoms. In contrast, both oxygen and nitrogen are detected at the surfaces following exposure to NO molecules. Both NO and N_2O appear to dissociate and bond at the top surface layer. Molecular nitrogen (N_2) does not react with the Ge surfaces, however, a precursor Ge nitride is observed at room temperature following exposure to nitrogen atoms and ions. Removal of oxygen by heating of the NO-exposed surface to 550^circC enabled the identification of the Ge-N vibrational modes. These modes show a structure similar to that of germanium nitride. This spectrum is also identical to that of the N-exposed surface heated to 550^circC. Surface phonon modes of the narrow-gap semiconducting

  16. Improved Oxygen Evolution Kinetics and Surface States Passivation of Ni-Bi Co-Catalyst for a Hematite Photoanode

    Directory of Open Access Journals (Sweden)

    Ke Dang

    2017-06-01

    Full Text Available This paper describes the combinational surface kinetics enhancement and surface states passivation of nickel-borate (Ni-Bi co-catalyst for a hematite (Fe2O3 photoanode. The Ni-Bi-modified Fe2O3 photoanode exhibits a cathodic onset potential shift of 230 mV and a 2.3-fold enhancement of the photocurrent at 1.23 V, versus the reversible hydrogen electrode (RHE. The borate (Bi in the Ni-Bi film promotes the release of protons for the oxygen evolution reaction (OER.

  17. Lattices for the lattice Boltzmann method.

    Science.gov (United States)

    Chikatamarla, Shyam S; Karlin, Iliya V

    2009-04-01

    A recently introduced theory of higher-order lattice Boltzmann models [Chikatamarla and Karlin, Phys. Rev. Lett. 97, 190601 (2006)] is elaborated in detail. A general theory of the construction of lattice Boltzmann models as an approximation to the Boltzmann equation is presented. New lattices are found in all three dimensions and are classified according to their accuracy (degree of approximation of the Boltzmann equation). The numerical stability of these lattices is argued based on the entropy principle. The efficiency and accuracy of many new lattices are demonstrated via simulations in all three dimensions.

  18. Fundamental Mechanistic Understanding of Electrocatalysis of Oxygen Reduction on Pt and Non-Pt Surfaces: Acid versus Alkaline Media

    Directory of Open Access Journals (Sweden)

    Nagappan Ramaswamy

    2012-01-01

    Full Text Available Complex electrochemical reactions such as Oxygen Reduction Reaction (ORR involving multi-electron transfer is an electrocatalytic inner-sphere electron transfer process that exhibit strong dependence on the nature of the electrode surface. This criterion (along with required stability in acidic electrolytes has largely limited ORR catalysts to the platinum-based surfaces. New evidence in alkaline media, discussed here, throws light on the involvement of surface-independent outer-sphere electron transfer component in the overall electrocatalytic process. This surface non-specificity gives rise to the possibility of using a wide-range of non-noble metal surfaces as electrode materials for ORR in alkaline media. However, this outer-sphere process predominantly leads only to peroxide intermediate as the final product. The importance of promoting the electrocatalytic inner-sphere electron transfer by facilitation of direct adsorption of molecular oxygen on the active site is emphasized by using pyrolyzed metal porphyrins as electrocatalysts. A comparison of ORR reaction mechanisms between acidic and alkaline conditions is elucidated here. The primary advantage of performing ORR in alkaline media is found to be the enhanced activation of the peroxide intermediate on the active site that enables the complete four-electron transfer. ORR reaction schemes involving both outer- and inner-sphere electron transfer mechanisms are proposed.

  19. Oxygen inhibition layer of composite resins: effects of layer thickness and surface layer treatment on the interlayer bond strength.

    Science.gov (United States)

    Bijelic-Donova, Jasmina; Garoushi, Sufyan; Lassila, Lippo V J; Vallittu, Pekka K

    2015-02-01

    An oxygen inhibition layer develops on surfaces exposed to air during polymerization of particulate filling composite. This study assessed the thickness of the oxygen inhibition layer of short-fiber-reinforced composite in comparison with conventional particulate filling composites. The effect of an oxygen inhibition layer on the shear bond strength of incrementally placed particulate filling composite layers was also evaluated. Four different restorative composites were selected: everX Posterior (a short-fiber-reinforced composite), Z250, SupremeXT, and Silorane. All composites were evaluated regarding the thickness of the oxygen inhibition layer and for shear bond strength. An equal amount of each composite was polymerized in air between two glass plates and the thickness of the oxygen inhibition layer was measured using a stereomicroscope. Cylindrical-shaped specimens were prepared for measurement of shear bond strength by placing incrementally two layers of the same composite material. Before applying the second composite layer, the first increment's bonding site was treated as follows: grinding with 1,000-grit silicon-carbide (SiC) abrasive paper, or treatment with ethanol or with water-spray. The inhibition depth was lowest (11.6 μm) for water-sprayed Silorane and greatest (22.9 μm) for the water-sprayed short-fiber-reinforced composite. The shear bond strength ranged from 5.8 MPa (ground Silorane) to 36.4 MPa (water-sprayed SupremeXT). The presence of an oxygen inhibition layer enhanced the interlayer shear bond strength of all investigated materials, but its absence resulted in cohesive and mixed failures only with the short-fiber-reinforced composite. Thus, more durable adhesion with short-fiber-reinforced composite is expected. © 2014 Eur J Oral Sci.

  20. Surface Pourbaix diagrams and oxygen reduction activity of Pt, Ag and Ni(111) surfaces studied by DFT

    DEFF Research Database (Denmark)

    Hansen, Heine Anton; Rossmeisl, Jan; Nørskov, Jens Kehlet

    2008-01-01

    The electrochemical most stable surface structures is investigated as function of pH and potential for Pt, Ag and Ni based on DFT calculations and constructed surface Pourbaix diagrams. It is also explained why metals such as Ag and Ni may be used successfully in alkaline fuel cells but not in ac......The electrochemical most stable surface structures is investigated as function of pH and potential for Pt, Ag and Ni based on DFT calculations and constructed surface Pourbaix diagrams. It is also explained why metals such as Ag and Ni may be used successfully in alkaline fuel cells...

  1. Photogeneration of singlet oxygen by the phenothiazine derivatives covalently bound to the surface-modified glassy carbon

    Energy Technology Data Exchange (ETDEWEB)

    Blacha-Grzechnik, Agata, E-mail: agata.blacha@polsl.pl [Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice (Poland); Piwowar, Katarzyna; Krukiewicz, Katarzyna [Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice (Poland); Koscielniak, Piotr; Szuber, Jacek [Institute of Electronics, Silesian University of Technology, Akademicka 16, 44-100 Gliwice (Poland); Zak, Jerzy K. [Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice (Poland)

    2016-05-15

    Highlights: • The selected group of four NH{sub 2}-derivatives of phenothiazine was grafted to Glassy Carbon (GC) surface. • The grafted phenothiazines are able to generate {sup 1}O{sub 2} when activated by the radiation. • Such modified solid surfaces may find their application in the wastewater treatment. - Abstract: The selected group of four amine-derivatives of phenothiazine was covalently grafted to the glassy carbon surface in the four-step procedure consisting of the electrochemical reduction of the diazonium salt followed by the electrochemical and chemical post-modification steps. The proposed strategy involves the bonding of linker molecule to which the photosensitizer is attached. The synthesized organic layers were characterized by means of cyclic voltammetry, XPS and Raman Spectroscopy. It was shown that the phenothiazines immobilized via proposed strategy retain their photochemical properties and are able to generate {sup 1}O{sub 2} when activated by the laser radiation. The effectiveness of in situ singlet oxygen generation by those new solid photoactive materials was determined by means of UVVis spectroscopy. The reported, covalently modified solid surfaces may find their application as the singlet oxygen photogenerators in the fine chemicals’ synthesis or in the wastewater treatment.

  2. Oxygen plasma functionalization of parylene C coating for implants surface: nanotopography and active sites for drug anchoring.

    Science.gov (United States)

    Gołda, M; Brzychczy-Włoch, M; Faryna, M; Engvall, K; Kotarba, A

    2013-10-01

    The effect of oxygen plasma treatment (t=0.1-60 min, pO2=0.2 mbar, P=50 W) of parylene C implant surface coating was investigated in order to check its influence on morphology (SEM, AFM observations), chemical composition (XPS analysis), hydrophilicity (contact angle measurements) and biocompatibility (MG-63 cell line and Staphylococcus aureus 24167 DSM adhesion screening). The modification procedure leads to oxygen insertion (up to 20 at.%) into the polymer matrix and together with surface topography changes has a dramatic impact on wettability (change of contact angle from θ=78±2 to θ=33±1.9 for unmodified and 60 min treated sample, respectively). As a result, the hydrophilic surface of modified parylene C promotes MG-63 cells growth and at the same time does not influence S. aureus adhesion. The obtained results clearly show that the plasma treatment of parylene C surface provides suitable polar groups (C=O, C-O, O-C=O, C-O-O and O-C(O)-O) for further development of the coating functionality. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Oxygen tracer diffusion and surface exchange kinetics in Ba0.5Sr0.5Co0.8Fe0.2O3-δ

    NARCIS (Netherlands)

    Berenov, A.; Atkinson, A.; Kilner, J.; Ananyev, M.; Eremin, V.; Porotnikova, N.; Farlenkov, A.; Kurumchin, E.; Bouwmeester, Henricus J.M.; Bucher, E.; Sitte, W.

    2014-01-01

    The oxygen tracer diffusion coefficient, Db⁎, and the oxygen tracer surface exchange coefficient, k, were measured in Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF5582) over the temperature range of 310–800 °C and the oxygen partial pressure range of 1.3 × 10−3–0.21 bar. Several measurement techniques were used:

  4. Elastic lattice in an incommensurate background

    International Nuclear Information System (INIS)

    Dickman, R.; Chudnovsky, E.M.

    1995-01-01

    We study a harmonic triangular lattice, which relaxes in the presence of an incommensurate short-wavelength potential. Monte Carlo simulations reveal that the elastic lattice exhibits only short-ranged translational correlations, despite the absence of defects in either lattice. Extended orientational order, however, persists in the presence of the background. Translational correlation lengths exhibit approximate power-law dependence upon cooling rate and background strength. Our results may be relevant to Wigner crystals, atomic monolayers on crystals surfaces, and flux-line and magnetic bubble lattices

  5. Lattice dislocation in Si nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Omar, M.S., E-mail: dr_m_s_omar@yahoo.co [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq); Taha, H.T. [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq)

    2009-12-15

    Modified formulas were used to calculate lattice thermal expansion, specific heat and Bulk modulus for Si nanowires with diameters of 115, 56, 37 and 22 nm. From these values and Gruneisen parameter taken from reference, mean lattice volumes were found to be as 20.03 A{sup 3} for the bulk and 23.63, 29.91, 34.69 and 40.46 A{sup 3} for Si nanowire diameters mentioned above, respectively. Their mean bonding length was calculated to be as 0.235 nm for the bulk and 0.248, 0.269, 0.282 and 0.297 nm for the nanowires diameter mentioned above, respectively. By dividing the nanowires diameter on the mean bonding length, number of layers per each nanowire size was found to be as 230, 104, 65 and 37 for the diameters mentioned above, respectively. Lattice dislocations in 22 nm diameter wire were found to be from 0.00324 nm for the 1st central lattice to 0.2579 nm for the last surface lattice. Such dislocation was smaller for larger wire diameters. Dislocation concentration found to change in Si nanowires according to the proportionalities of surface thickness to nanowire radius ratios.

  6. The interaction of oxygen and carbon monoxide with a carbided Ni(111) surface

    NARCIS (Netherlands)

    Geus, John W.; Vink, T.J.; Zandvoort, M.M.J. van; Gijzeman, O.L.J.

    1984-01-01

    The thermal decomposition of ethylene on Ni(111) at 250°C is shown to lead to carbon deposition on and - in a later stage - below the surface. Independent of the amount of carbon below the surface, CO is adsorbed with an isosteric heat of adsorption of 105 kJ/mol. The surface carbon reacts with

  7. Adsorption of oxygen on a Cu{110} surface with and without the influence of A keV Ne+ beam Stage I: Coverages up to half a monolayer

    NARCIS (Netherlands)

    Fluit, J.M.; Hupkens, Th.M.

    1984-01-01

    Low Energy Ion Scattering has been used to study the interaction of molecular oxygen with a Cu{110} surface. The amount of adsorbed atomic oxygen was monitored by the 4 keV Ne+¦O reflection signal. In the first adsorption stage (coverage less than half a monolayer) the sticking probability varied

  8. Oxygen accumulation on metal surfaces investigated by XPS, AES and LEIS, an issue for sputter depth profiling under UHV conditions

    Energy Technology Data Exchange (ETDEWEB)

    Steinberger, R., E-mail: roland.steinberger@jku.at [Center for Surface and Nanoanalytics, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); Celedón, C.E., E-mail: carlos.celedon@usm.cl [Institut für Experimentalphysik, Abteilung für Atom- und Oberflächenphysik, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); Departamento de Física, Universidad Técnica Federico Santa María, Valaparaíso, Casilla 110-V (Chile); Bruckner, B., E-mail: barbara.bruckner@jku.at [Institut für Experimentalphysik, Abteilung für Atom- und Oberflächenphysik, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); Roth, D., E-mail: dietmar.roth@jku.at [Institut für Experimentalphysik, Abteilung für Atom- und Oberflächenphysik, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); Duchoslav, J., E-mail: jiri.duchoslav@jku.at [Center for Surface and Nanoanalytics, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); Arndt, M., E-mail: martin.arndt@voestalpine.com [voestalpine Stahl GmbH, voestalpine-Straße 3, 4031 Linz (Austria); Kürnsteiner, P., E-mail: p.kuernsteiner@mpie.de [Center for Surface and Nanoanalytics, Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz (Austria); and others

    2017-07-31

    Highlights: • Investigation on the impact of residual gas prevailing in UHV chambers. • For some metals detrimental oxygen uptake could be observed within shortest time. • Totally different behavior was found: no changes, solely adsorption and oxidation. • The UHV residual gas may severely corrupt results obtained from depth profiling. • A well-considered data acquisition sequence is the key for reliable depth profiles. - Abstract: Depth profiling using surface sensitive analysis methods in combination with sputter ion etching is a common procedure for thorough material investigations, where clean surfaces free of any contamination are essential. Hence, surface analytic studies are mostly performed under ultra-high vacuum (UHV) conditions, but the cleanness of such UHV environments is usually overrated. Consequently, the current study highlights the in principle known impact of the residual gas on metal surfaces (Fe, Mg, Al, Cr and Zn) for various surface analytics methods, like X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and low-energy ion scattering (LEIS). The investigations with modern, state-of-the-art equipment showed different behaviors for the metal surfaces in UHV during acquisition: (i) no impact for Zn, even after long time, (ii) solely adsorption of oxygen for Fe, slight and slow changes for Cr and (iii) adsorption accompanied by oxide formation for Al and Mg. The efficiency of different counter measures was tested and the acquired knowledge was finally used for ZnMgAl coated steel to obtain accurate depth profiles, which exhibited before serious artifacts when data acquisition was performed in an inconsiderate way.

  9. Measuring oxygen surface exchange kinetics on mixed-conducting composites by electrical conductivity relaxation

    NARCIS (Netherlands)

    Hu, Bobing; Wang, Yunlong; Zhu, Zhuoying; Xia, Changrong; Bouwmeester, Henricus J.M.

    2015-01-01

    The oxygen release kinetics of mixed-conducting Sr2Fe1.5Mo0.5O6 d–Sm0.2Ce0.8O2 d (SFM–SDC) dualphase composites has been investigated, at 750 C, as a function of the SDC phase volume fraction using electrical conductivity relaxation (ECR) under reducing atmospheres, extending our previous work on

  10. Reduction of the Electrode Overpotential of the Oxygen Evolution Reaction by Electrode Surface Modification

    OpenAIRE

    Lu, Cian-Tong; Chiu, Yen-Wen; Li, Mei-Jing; Hsueh, Kan-Lin; Hung, Ju-Shei

    2017-01-01

    Metal–air batteries exhibit high potential for grid-scale energy storage because of their high theoretical energy density, their abundance in the earth’s crust, and their low cost. In these batteries, the oxygen evolution reaction (OER) occurs on the air electrode during charging. This study proposes a method for improving the OER electrode performance. The method involves sequentially depositing a Ni underlayer, Sn whiskers, and a Ni protection layer on the metal mesh. Small and uniform gas ...

  11. Promoted Fixation of Molecular Nitrogen with Surface Oxygen Vacancies on Plasmon-Enhanced TiO2 Photoelectrodes.

    Science.gov (United States)

    Li, Chengcheng; Wang, Tuo; Zhao, Zhi-Jian; Yang, Weimin; Li, Jian-Feng; Li, Ang; Yang, Zhilin; Ozin, Geoffrey A; Gong, Jinlong

    2018-02-19

    A hundred years on, the energy-intensive Haber-Bosch process continues to turn the N 2 in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The urgency of mitigating climate change motivates society to progress toward a more sustainable method for fixing N 2 that is based on clean energy. Surface oxygen vacancies (surface O vac ) hold great potential for N 2 adsorption and activation, but introducing O vac on the very surface without affecting bulk properties remains a great challenge. Fine tuning of the surface O vac by atomic layer deposition is described, forming a thin amorphous TiO 2 layer on plasmon-enhanced rutile TiO 2 /Au nanorods. Surface O vac in the outer amorphous TiO 2 thin layer promote the adsorption and activation of N 2 , which facilitates N 2 reduction to ammonia by excited electrons from ultraviolet-light-driven TiO 2 and visible-light-driven Au surface plasmons. The findings offer a new approach to N 2 photofixation under ambient conditions (that is, room temperature and atmospheric pressure). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Oxygen accumulation on metal surfaces investigated by XPS, AES and LEIS, an issue for sputter depth profiling under UHV conditions

    Science.gov (United States)

    Steinberger, R.; Celedón, C. E.; Bruckner, B.; Roth, D.; Duchoslav, J.; Arndt, M.; Kürnsteiner, P.; Steck, T.; Faderl, J.; Riener, C. K.; Angeli, G.; Bauer, P.; Stifter, D.

    2017-07-01

    Depth profiling using surface sensitive analysis methods in combination with sputter ion etching is a common procedure for thorough material investigations, where clean surfaces free of any contamination are essential. Hence, surface analytic studies are mostly performed under ultra-high vacuum (UHV) conditions, but the cleanness of such UHV environments is usually overrated. Consequently, the current study highlights the in principle known impact of the residual gas on metal surfaces (Fe, Mg, Al, Cr and Zn) for various surface analytics methods, like X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and low-energy ion scattering (LEIS). The investigations with modern, state-of-the-art equipment showed different behaviors for the metal surfaces in UHV during acquisition: (i) no impact for Zn, even after long time, (ii) solely adsorption of oxygen for Fe, slight and slow changes for Cr and (iii) adsorption accompanied by oxide formation for Al and Mg. The efficiency of different counter measures was tested and the acquired knowledge was finally used for ZnMgAl coated steel to obtain accurate depth profiles, which exhibited before serious artifacts when data acquisition was performed in an inconsiderate way.

  13. Chiral symmetry on the lattice

    Energy Technology Data Exchange (ETDEWEB)

    Creutz, M.

    1994-11-01

    The author reviews some of the difficulties associated with chiral symmetry in the context of a lattice regulator. The author discusses the structure of Wilson Fermions when the hopping parameter is in the vicinity of its critical value. Here one flavor contrasts sharply with the case of more, where a residual chiral symmetry survives anomalies. The author briefly discusses the surface mode approach, the use of mirror Fermions to cancel anomalies, and finally speculates on the problems with lattice versions of the standard model.

  14. Chiral symmetry on the lattice

    International Nuclear Information System (INIS)

    Creutz, M.

    1994-11-01

    The author reviews some of the difficulties associated with chiral symmetry in the context of a lattice regulator. The author discusses the structure of Wilson Fermions when the hopping parameter is in the vicinity of its critical value. Here one flavor contrasts sharply with the case of more, where a residual chiral symmetry survives anomalies. The author briefly discusses the surface mode approach, the use of mirror Fermions to cancel anomalies, and finally speculates on the problems with lattice versions of the standard model

  15. Oxygen 18 concentration profile measurements near the surface by 18O(p,α)15N resonance reaction

    International Nuclear Information System (INIS)

    Amsel, G.; David, D.

    1975-01-01

    The method of spectrum reduction in nuclear reaction microanalysis does not allow to obtain depth resolutions better than the order of 2000A. Resolutions of the order of 200A may be obtained by using the narrow resonance technique, when applied to thin films. The latter technique was extended to thick targets, with deep concentration profiles presenting a sharp gradient near the surface. This method is presented and illustrated by the study of 18 O profiles in oxygen diffusion measurements in growing ZrO 2 , using the 629keV resonance of the reaction 18 O(p,α) 15 N [fr

  16. XPS and FTIR investigation of the surface properties of different prepared titania nano-powders

    DEFF Research Database (Denmark)

    Jensen, Henrik; Solovyev, Alexey; Lie, Zheshen

    2005-01-01

    Surface studies of nano-sized TiO2 powders prepared by different methods showed that the preparation method had great impact on the surface properties. XPS measurements showed that the oxygen composition was related to the preparation method. The chloride method yielded the lowest amount of surface...... oxygen (29%) and sol–gel prepared powder showed the greatest amount of surface oxygen (66%) in the form of surface hydroxyl groups. The remaining oxygen was identified as lattice oxygen. The powder prepared by the sol–gel method contained carbon impurities originating from residual alkoxy groups....... Supercritical sol–gel prepared powder and powder prepared by the sulphate method revealed same trends regarding oxygen composition with 44–47% being surface oxygen; neither contained carbon impurities. The results obtained from XPS were confirmed by FTIR measurements....

  17. Effect of oxygen inhibition in two-step self-etch systems on surface free energy and dentin bond strength with a chemically cured resin composite.

    Science.gov (United States)

    Yamaji, Ayumi; Tsujimoto, Akimasa; Asaoka, Tetsui; Matsuyoshi, Saki; Tsuchiya, Kenji; Takamizawa, Toshiki; Miyazaki, Masashi

    2014-09-01

    We compared the surface free energies and dentin bond strengths of two-step self-etch systems with and without an oxygen-inhibited layer. The adhesives were applied to self-etching primer-treated dentin surfaces of bovine incisors, after which the teeth were light-irradiated and the oxygen-inhibited layer was left intact or removed with ethanol. We determined surface free energies (γS) and their components by measuring the contact angles of three test liquids placed on the cured adhesives. We also measured the dentin bond strengths of chemically cured resin composite to the adhesives, with and without the oxygen-inhibited layer. For all surfaces, the estimated surface tension component, γS(LW), was relatively constant. The Lewis base (γS(-)) component decreased significantly when the oxygen-inhibited layer was removed, whereas the Lewis acid (γS(+)) component slightly increased. The dentin bond strengths of the two-step self-etch systems did not significantly differ in relation to the presence of the oxygen-inhibited layer. Although the surface free energy of the adhesive was affected by the presence of the oxygen-inhibited layer, no changes in dentin bond strength were detected.

  18. The Importance of Surface IrOx in Stabilizing RuO2 for Oxygen Evolution

    DEFF Research Database (Denmark)

    Escribano, Maria Escudero; Pedersen, Anders Filsøe; Paoli, Elisa Antares

    2017-01-01

    corrosion on IrOx/RuO2 thin films by combining electrochemical quartz crystal microbalance (EQCM) with inductively coupled mass spectrometry (ICP-MS). We elucidate the importance of sub-monolayer surface IrOx in minimizing Ru dissolution. Our work shows that we can tune the surface properties of active OER...

  19. Surface modification of electrospun fibre meshes by oxygen plasma for bone regeneration

    NARCIS (Netherlands)

    Nandakumar, A.; Tahmasebi Birgani, Zeinab; Reis Santos, Diogo; Mentink-Leusink, Anouk; Auffermann, N.; van der Werf, Kees; Bennink, Martin L.; Moroni, Lorenzo; van Blitterswijk, Clemens; Habibovic, Pamela

    2013-01-01

    Plasma treatment is a method to modify the physicochemical properties of biomaterials, which consequently may affect interactions with cells. Based on the rationale that physical cues on the surface of culture substrates and implants, such as surface roughness, have proven to alter cell behaviour,

  20. Influence of dissolved oxygen, dissolved hydrogen and surface film on the corrosion products release from stainless steel in high purity water at room temperature

    International Nuclear Information System (INIS)

    Iwahori, Toru; Kato, Shunji; Wada, Kunihisa; Kanbe, Hiromi; Mizuno, Takayuki

    1983-01-01

    The influence of dissolved oxygen, dissolved hydrogen and surface film on corrosion products release from SUS 304 stainless steel was studied in high purity water at room temperature. The determination of corrosion products released was performed by using millipore filter (0.45μm), cation-exchange resins and anion-exchange resins. The selective release of Fe component from stainless steel occurred in deoxygenated water containing saturated hydrogen or below 120 ppb oxygen, while the selective release of Co and Ni occurred in oxygenated water containing above 8 ppm oxygen. In the case of preautoclaved stainless steel coated with R 3 O 4 (spinel type oxides) film, the selective release of Co and Ni occurred in any high purity water, regardless of dissolved oxygen or dissolved hydrogen. Similar selective dissolution of Co from cobalt ferrite occurred in any high purity water, regardless of dissolved oxygen or dissolved hydrogen. Relation between corrosion potential and release was discussed. (author)

  1. Emission spectroscopic analysis of oxygen-plasma reaction on polymer surface: Effective polyacrylonitrile treatment by the plasma

    International Nuclear Information System (INIS)

    Kobayashi, Takaomi; Sasama, Tomonori; Wada, Hiroshi; Fujii, Nobuyuki

    2001-01-01

    Emission spectroscopy was applied to observe decomposed species of polyacrylonitrile (PAN) exposed with oxygen (O 2 ) plasma, which was generated by microwave discharge with 8x10 -2 dm 3 /s flow rate in the range of 1.8-4.7 Torr. As O 2 plasma was exposed to the polymer, the surface was etched and a violet emission was observed on the surface. The strong emission assigned to CN(B 2 Σ-X 2 Π) transition appeared near 340-460 nm and also CH(A 2 Δ-X 2 Π) at 431 nm. These results indicated that the PAN sample was decomposed by the plasma etching and the decomposed species emitted the violet light on the surface. The time dependence of the emission intensities was also investigated. When the discharge time of O 2 plasma increased, the emission intensities of the CN and CH transitions increased and then gradually decreased. Evidence was presented by infrared measurements that a hetrocyclic nitrile group was formed on the treated surface. Furthermore, the polymer surface decomposition in O 2 plasma was compared with that observed in nitrogen (N 2 ) and air plasma. The N 2 and air discharge showed less PAN decomposition than observed in O 2 discharge

  2. Designs, groups and lattices

    OpenAIRE

    Bachoc, Christine

    2005-01-01

    We study the Grassmannian 4-designs contained in lattices, in connection with the local property of the Rankin constant. We prove that the sequence of Barnes-Wall lattices contain Grassmannian 6-designs.

  3. Residuation in orthomodular lattices

    Directory of Open Access Journals (Sweden)

    Chajda Ivan

    2017-04-01

    Full Text Available We show that every idempotent weakly divisible residuated lattice satisfying the double negation law can be transformed into an orthomodular lattice. The converse holds if adjointness is replaced by conditional adjointness. Moreover, we show that every positive right residuated lattice satisfying the double negation law and two further simple identities can be converted into an orthomodular lattice. In this case, also the converse statement is true and the corresponence is nearly one-to-one.

  4. Ag/Bi2MoO6-x with enhanced visible-light-responsive photocatalytic activities via the synergistic effect of surface oxygen vacancies and surface plasmon

    Science.gov (United States)

    Wang, Danjun; Shen, Huidong; Guo, Li; Wang, Chan; Fu, Feng; Liang, Yucang

    2018-04-01

    In this study, a heterostructured Ag/Bi2MoO6-x photocatalyst was rationally designed and successfully fabricated via the deposition of plasmonic silver nanoparticles onto the surface of Bi2MoO6 with surface oxygen vacancy (denoted as Bi2MoO6-x). Bi2MoO6-x (Abbr. BMO6-x was first synthesized via a solvothermal synthesis and calcination process. The plasmonic silver nanoparticles were then loaded onto the surface of BMO6-x using a simple photoreduction process to form Ag/BMO6-x composite. Surface oxygen vacancies (SOVs) in BMO6-x were confirmed by electron paramagnetic resonance (EPR) spectrum. The structures of BMO6-xand Ag/BiMoO6-x) were characterized using high-resolution transmission electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. Under visible light irradiation, sample Ag/BMO6-x exhibits a highest visible-light-responsive photocatalytic performance compared to those of pure-Bi2MoO6 (BMO), BMO6-x and Ag/BMO for the degradation of rhodamine B (RhB), which is attributed predominantly to the synergistic effect of SOVs and Ag surface plasmonic resonance (SPR) on the surface of Bi2MoO6-x leading to the efficient separation and migration of photogenerated electrons/holes and hence broadening light responsive region. The significant improvement of the migration and separation of photogenerated electrons/holes in the Ag/BMO6-x was evidenced by photoluminescence spectra, time-resolved fluorescence decay, photocurrent, and electrochemical impedance spectrum. The ESR with spin-trap technique and reactive species trapping experiments confirm that the mainly active species O2- and h+ are playing key roles in the RhB photodegradation process over Ag/BMO6-x. This study not only provides an understandable synergistic effect of SOVs and SPR Ag but also pioneers a new approach for fabricating a series of highly catalytically active metal-semiconductor photocatalysts with surface atom defects.

  5. Infinite resistive lattices

    NARCIS (Netherlands)

    Atkinson, D; van Steenwijk, F.J.

    The resistance between two arbitrary nodes in an infinite square lattice of:identical resistors is calculated, The method is generalized to infinite triangular and hexagonal lattices in two dimensions, and also to infinite cubic and hypercubic lattices in three and more dimensions. (C) 1999 American

  6. Novel structures of oxygen adsorbed on a Zr(0001) surface predicted from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Bo [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Beijing computational science research center, Beijing,100084 (China); Wang, Jianyun [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Lv, Jian [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); College of Materials Science and Engineering, Jilin University, Changchun, 130012 (China); Gao, Xingyu [Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing, 100088 (China); CAEP Software Center for High Performance Numerical Simulation, Beijing, 100088 (China); Zhao, Yafan [CAEP Software Center for High Performance Numerical Simulation, Beijing, 100088 (China); Wang, Yanchao, E-mail: wyc@calypso.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Beijing computational science research center, Beijing,100084 (China); College of Materials Science and Engineering, Jilin University, Changchun, 130012 (China); Song, Haifeng, E-mail: song_haifeng@iapcm.ac.cn [Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing, 100088 (China); CAEP Software Center for High Performance Numerical Simulation, Beijing, 100088 (China); Ma, Yanming [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Beijing computational science research center, Beijing,100084 (China)

    2017-01-30

    Highlights: • Two stable structures of O adsorbed on a Zr(0001) surface are predicted with SLAM. • A stable structure of O adsorbed on a Zr(0001) surface is proposed with MLAM. • The calculated work function change is agreement with experimental value. - Abstract: The structures of O atoms adsorbed on a metal surface influence the metal properties significantly. Thus, studying O chemisorption on a Zr surface is of great interest. We investigated O adsorption on a Zr(0001) surface using our newly developed structure-searching method combined with first-principles calculations. A novel structural prototype with a unique combination of surface face-centered cubic (SFCC) and surface hexagonal close-packed (SHCP) O adsorption sites was predicted using a single-layer adsorption model (SLAM) for a 0.5 and 1.0 monolayer (ML) O coverage. First-principles calculations based on the SLAM revealed that the new predicted structures are energetically favorable compared with the well-known SFCC structures for a low O coverage (0.5 and 1.0 ML). Furthermore, on basis of our predicted SFCC + SHCP structures, a new structure within multi-layer adsorption model (MLAM) was proposed to be more stable at the O coverage of 1.0 ML, in which adsorbed O atoms occupy the SFCC + SHCP sites and the substitutional octahedral sites. The calculated work functions indicate that the SFCC + SHCP configuration has the lowest work function of all known structures at an O coverage of 0.5 ML within the SLAM, which agrees with the experimental trend of work function with variation in O coverage.

  7. Reduction of the Electrode Overpotential of the Oxygen Evolution Reaction by Electrode Surface Modification

    Directory of Open Access Journals (Sweden)

    Cian-Tong Lu

    2017-01-01

    Full Text Available Metal–air batteries exhibit high potential for grid-scale energy storage because of their high theoretical energy density, their abundance in the earth’s crust, and their low cost. In these batteries, the oxygen evolution reaction (OER occurs on the air electrode during charging. This study proposes a method for improving the OER electrode performance. The method involves sequentially depositing a Ni underlayer, Sn whiskers, and a Ni protection layer on the metal mesh. Small and uniform gas bubbles form on the Ni/Sn/Ni mesh, leading to low overpotential and a decrease in the overall resistance of the OER electrode. The results of a simulated life cycle test indicate that the Ni/Sn/Ni mesh has a life cycle longer than 1,300 cycles when it is used as the OER electrode in 6 M KOH.

  8. Low energy oxygen ion beam modification of the surface morphology and chemical structure of polyurethane fibers

    International Nuclear Information System (INIS)

    Wong, K.H.; Zinke-Allmang, M.; Wan, W.K.; Zhang, J.Z.; Hu, P.

    2006-01-01

    Energetic O + ions were implanted into polyurethane (PU) fiber filaments, at 60 and 100 keV with doses of 5 x 10 14 and 1 x 10 15 ions/cm 2 , to modify the near-surface fiber morphology. The implantations were performed at room temperature and at -197 deg. C, a temperature well below the glass transition temperature for this system. At room temperature, the lower energy implantation heats the fibers primarily near their surface, causing the fiber surface to smoothen and to develop a flattened shape. At the higher energy, the ion beam deposits its energy closer to the fiber core, heating the fiber more uniformly and causing them to re-solidify slowly. This favors a cylindrical equilibrium shape with a smooth fiber surface and no crack lines. The average fiber diameter reduced during 100 keV implantation from 3.1 to 2.3 μm. At -197 deg. C, the ion implantation does not provide enough heat to cause notable physical modifications, but the fibers crack and break during subsequent warming to room temperature. The dose dependence of the crack formation along the fiber intersections is presented. The ion beams further cause near-surface chemical modifications in the fibers, particularly introducing two new chemical functional groups (C-(C=O)-C and C-N-C)

  9. IR and UV laser-induced morphological changes in silicon surface under oxygen atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez-Jarquin, J.; Fernandez-Guasti, M.; Haro-Poniatowski, E.; Hernandez-Pozos, J.L. [Laboratorio de Optica Cuantica, Departamento de Fisica, Universidad Autonoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco No. 186, Col. Vicentina, C.P. 09340, Mexico D.F. (Mexico)

    2005-08-01

    We irradiated silicon (100) wafers with IR (1064 nm) and UV (355 nm) nanosecond laser pulses with energy densities within the ablation regime and used scanning electron microscopy to analyze the morphological changes induced on the Si surface. The changes in the wafer morphology depend both on the incident radiation wavelength and the environmental atmosphere. We have patterned Si surfaces with a single focused laser spot and, in doing the experiments with IR or UV this reveals significant differences in the initial surface cracking and pattern formation, however if the experiment is carried out in O{sub 2} the final result is an array of microcones. We also employed a random scanning technique to irradiate the silicon wafer over large areas, in this case the microstructure patterns consist of a ''semi-ordered'' array of micron-sized cones. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Faunal and oxygen isotopic evidence for surface water salinity changes during sapropel formation in the eastern Mediterranean

    International Nuclear Information System (INIS)

    Williams, D.F.; Thunell, R.C.

    1979-01-01

    The discovery of the widespread anaerobic deposits (sapropels) in late Cenozoic sediments of the eastern Mediteranean has prompted many workers to propose the periodic occurrence of extremely low surface salinites in the Mediterranean. Oxygen isotopic determinations and total faunal analyses were made at 1000-year intervals across two equivalent sapropels in two piston cores from the Levantine Basin. The sapropel layers were deposited approximately 9000 y.B.P. (Sapropel A) and 80, 000 y. B.P. (Sapropel B). Significant isotopic anomalies were recorded by the foraminiferal species within Sapropels A and B in both cores. The surface dwelling species record a larger 18 O depletion than the mesopelagic species suggesting that surface salinities were reduced by 2-3per 1000 during sapropel formation. The faunal changes associated with the sapropels also indicate that the oceanographic conditions which lead to anoxic conditions in the eastern Mediteranean involve the formation of a low salinity surface layer. The source of the low salinity water might be meltwater produced by disintegration of the Fennoscandian Ice Sheet which drained into the Black Sea, into the Aegean Sea and finally into the eastern Mediterranean. (Auth.)

  11. Surface analysis of topmost layer of epitaxial layered oxide thin film: Application to delafossite oxide for oxygen evolution reaction

    Science.gov (United States)

    Toyoda, Kenji; Adachi, Hideaki; Miyata, Nobuhiro; Hinogami, Reiko; Orikasa, Yuki; Uchimoto, Yoshiharu

    2018-02-01

    Delafossite oxides (ABO2) have a layered structure with alternating layers of A and B elements, the topmost layer of which appears to determine their performance, such as the oxygen evolution reaction (OER) activity. In this study, we investigated the topmost layer of single-domain (0 0 1)-oriented AgCoO2 epitaxial thin film for potential use as an OER catalyst. The thin film was confirmed to possess OER activity at a level comparable to the catalyst in powder form. Atomic scattering spectroscopy revealed the topmost layer to be composed of CoO6 octahedra. In situ X-ray absorption spectroscopy showed that the oxidation of Co at the surface did not change under different potentials, which suggests that there is no valence fluctuation of Co in the stable CoO6 octahedral structure. However, the oxidation number of Co at the surface was lower than that in the bulk. Our density functional theoretical calculations also showed the Co atoms at the surface to have a slightly higher electron occupancy than those in the bulk, and suggests that the unoccupied t2g states of Co at the surface have an influence on OER activity.

  12. Rational Manipulation of IrO2 Lattice Strain on α-MnO2 Nanorods as a Highly Efficient Water-Splitting Catalyst.

    Science.gov (United States)

    Sun, Wei; Zhou, Zhenhua; Zaman, Waqas Qamar; Cao, Li-Mei; Yang, Ji

    2017-12-06

    Developing more efficient and stable oxygen evolution reaction (OER) catalysts is critical for future energy conversion and storage technologies. We demonstrate that inducing a lattice strain in IrO 2 crystal structure due to interface lattice mismatch enables an enhancement of the OER catalytic activity. The lattice strain is obtained by the direct growth of IrO 2 nanoparticles on a specially exposed surface of α-MnO 2 nanorods via a simple two-step hydrothermal synthesis. Interestingly, the prepared hydride OER activity increases with a lower IrO 2 grown mass, which offers an opportunity to reduce the usage of precious iridium and ultimately obtains a specific mass activity of 3.7 times than that of IrO 2 prepared under the same conditions and exhibits equivalent stability. The lattice mismatch in the underlying interface induces the formation of lattice strain in IrO 2 rather than the charge transfer between the materials. The lattice strain changes are in good agreement with the order of the OER activity. Our experimental results indicate that using the special exposed surface substrates or tuning the supporting morphology structure can manipulate the catalyst materials lattice strain for the design of more efficient OER catalysts.

  13. Combinatorial Density Functional Theory-Based Screening of Surface Alloys for the Oxygen Reduction Reaction

    DEFF Research Database (Denmark)

    Greeley, Jeffrey Philip; Nørskov, Jens Kehlet

    2009-01-01

    for the ORR but, with few exceptions, they are found to be thermodynamically unstable in the acidic environments typical of low-temperature fuel cells. The results suggest that, absent other thermodynamic or kinetic mechanisms to stabilize the alloys, surface alloys are unlikely to serve as useful ORR......, potential-dependent computational tests of the stability of these alloys in aqueous, acidic environments are presented. These activity and stability criteria are applied to a database of DFT calculations on nearly 750 binary transition metal surface alloys; of these, many are predicted to be active...

  14. Community composition of ammonia-oxidizing archaea from surface and anoxic depths of oceanic oxygen minimum zones

    Directory of Open Access Journals (Sweden)

    Xuefeng ePeng

    2013-07-01

    Full Text Available Ammonia-oxidizing archaea (AOA have been reported at high abundance in much of the global ocean, even in environments, such as pelagic oxygen minimum zones (OMZs, where conditions seem unlikely to support aerobic ammonium oxidation. Due to the lack of information on any potential alternative metabolism of AOA, the AOA community composition might be expected to differ between oxic and anoxic environments, indicating some difference in ecology and/or physiology of the AOA assemblage. This hypothesis was tested by evaluating AOA community composition using a functional gene microarray that targets the ammonia monooxygenase gene subunit A (amoA. The relationship between environmental parameters and the biogeography of the Arabian Sea and the Eastern Tropical South Pacific (ETSP AOA assemblages was investigated using principal component analysis (PCA and redundancy analysis (RDA. In both the Arabian Sea and the ETSP, AOA communities within the core of the OMZ were not significantly different from those inhabiting the oxygenated surface waters above the OMZ. The AOA communities in the Arabian Sea were significantly different from those in the ETSP. In both oceans, the abundance of archaeal amoA gene in the core of the OMZ was higher than that in the surface waters. Our results indicate that AOA communities are distinguished by their geographic origin. RDA suggested that temperature was the main factor that correlated with the differences between the AOA communities from the Arabian Sea and those from the ETSP. Physicochemical properties that characterized the different environments of the OMZ and surface waters played a less important role, than did geography, in shaping the AOA community composition.

  15. Oxygen Plasma Treatment of Rubber Surface by the Atmospheric Pressure Cold Plasma Torch

    DEFF Research Database (Denmark)

    Lee, Bong-ju; Kusano, Yukihiro; Kato, Nobuko

    1997-01-01

    A new application of the atmospheric cold plasma torch has been investigated. Namely, the surface treatment of an air-exposed vulcanized rubber compound. The effect of plasma treatment was evaluated by the bondability of the treated rubber compound with another rubber compound using a polyurethane...

  16. Interaction of oxygen and carbon monoxide with Pt(111) at intermediate pressure and temperature : revisiting the fruit fly of surface science

    NARCIS (Netherlands)

    Bashlakov, Dmytro

    2014-01-01

    This thesis uses the surface science approach to address questions regarding the interaction of oxygen with platinum and its subsequent reaction with carbon monoxide. A Pt(111) single crystal surface is used as a model for the catalyst. Chapter 1 provides an overview of the literature on the

  17. Oxygen Depletion on the Surface of Mercury: Evidence of Silicon Smelting?

    Science.gov (United States)

    McCubbin, F. M.; Vander Kaaden, K. E.; Peplowski, P. N.; Bell, A. S.; Evans, L. G.; Nittler, L. R.; Boyce, J. W.; Keller, L. P.; McCoy, T. J.

    2017-01-01

    The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft collected data that provided important insights into the structure, chemical makeup, and compositional diversity of Mercury. The X-Ray Spectrometer (XRS) and Gamma-Ray Spectrometer (GRS) onboard MESSENGER provided the first detailed chemical analyses of Mercury's surface. Among the many discoveries included several surprising characteristics about the surface of Mercury, including elevated S abundances (up to 4 percent by weight), low Fe abundances (less than 4 percent by weight), and relatively low O abundances (O/Si ratio of 1.40 plus or minus 0.03). The surface chemistry as determined by MESSENGER has been used to identify up to nine distinct geochemical terranes on Mercury. Numerous modeling and experimental efforts have been undertaken to infer the mineralogy and petrology of mercurian lavas and surface materials. However, all of these efforts have presumed valence states for each of the elements according to the following: Si4+, Ti4+, Al3+, Cr2+, Fe2+, Mn2+, Mg2+, Ca2+, Na+, K+, S2-, Cl-. Based on these valence assignments, cations are charged balanced with the anions O2-, S2-, and Cl- and the compositions are recast in terms of oxides, sulfides, and chlorides. Based on these assumptions, the geochemical terranes that have been identified on Mercury yield O/Si wt. ratios ranging from 1.61 to 1.84, which is substantially higher than the preliminary O/Si ratio of 1.40 plus or minus 0.03 determined by the MESSENGER GRS]. We have re-evaluated the O/Si ratio using the entire MESSENGER dataset to reassess its implications for the geochemistry of Mercury.

  18. Radiation-Driven Formation of Reactive Oxygen Species in Oxychlorine-Containing Mars Surface Analogues.

    Science.gov (United States)

    Georgiou, Christos D; Zisimopoulos, Dimitrios; Kalaitzopoulou, Electra; Quinn, Richard C

    2017-04-01

    The present study demonstrates that γ-radiolyzed perchlorate-containing Mars soil salt analogues (in a CO 2 atmosphere) generate upon H 2 O wetting the reactive oxygen species (ROS) superoxide radical (O 2 •- ), hydrogen peroxide (H 2 O 2 ), and hydroxyl radicals ( • OH). This study also validates that analogue radiolysis forms oxychlorine species that, in turn, can UV-photolyze to • OH upon UV photolysis. This investigation was made possible by the development of a new assay for inorganic-origin O 2 •- and H 2 O 2 determination and by the modification of a previous assay for soil • OH. Results show that radiolyzed Mg(ClO 4 ) 2 generates H 2 O 2 and • OH; and when included as part of a mixture analogous to the salt composition of samples analyzed at the Mars Phoenix site, the analogue generated O 2 •- , H 2 O 2 , and • OH, with • OH levels 150-fold higher than in the radiolyzed Mg(ClO 4 ) 2 samples. Radiolyzed Mars Phoenix site salt analogue that did not contain Mg(ClO 4 ) 2 generated only • OH also at 150-fold higher concentration than Mg(ClO 4 ) 2 alone. Additionally, UV photolysis of the perchlorate γ radiolysis product chlorite (ClO 2 - ) generated the oxychlorine products trihalide (Cl 3 - ), chlorine dioxide (ClO 2 • ), and hypochlorite (ClO - ), with the formation of • OH by UV photolysis of ClO - . While the generation of ROS may have contributed in part to 14 CO 2 production in the Viking Labeled Release (LR) experiment and O 2 (g) release in the Viking Gas Exchange (GEx) experiment, our results indicate that they are not likely to be the major contributor to the LR and GEx results. However, due to their highly reactive nature, they are expected to play a significant role in the alteration of organics on Mars. Additionally, experiments with hypochlorite show that the thermal stability of NaClO is in the range of the thermal stability observed for thermally liable oxidant responsible for the Viking LR results. Key Words: Mars-Oxygen

  19. Estimation of real ship propelling performance by the surface velocity lattice method using model ship flow field data; Mokeisen ryujo data wo mochiita hyomen uzu koshiho ni yoru jissen suishin seino no suitei

    Energy Technology Data Exchange (ETDEWEB)

    Kai, H.; Ikehata, M.; Sakai, S. [Yokohama National University, Yokohama (Japan). Faculty of Engineering

    1997-10-01

    This is basically a technique wherein the wing element method is replaced by a surface vortex lattice method. A horseshoe vortex of unknown intensity and source surface of known intensity are distributed on the wing surface and, under conditions that the fluid will not cross the boundary, the intensity of horseshoe vortex circulation is calculated for the solution of the fluid field. For the simulation of a real ship in navigation, the required propeller revolution thrust is determined using the real ship resistance value and real ship thrust reduction factor estimated from a model ship resistance test by extrapolation. The calculation of propeller performance is conducted in the quasi-steady condition using the force of fluid working on one wing for each wing angle (with the wing rotated at the increment of 6 degrees), and the thrust and torque are determined using the averages of values obtained in one cycle. It is found that the torque value is overestimated in a considerable degree in the wing element theory. In the surface vortex lattice method, both thrust and torque values agree with experimental values mostly, and this method is found to be accurate enough as a navigation element calculation tool when many panels are considered. 4 refs., 5 figs., 1 tab.

  20. The Effect of Postoperative Skin-Surface Warming on Oxygen Consumption and the Shivering Threshold

    Science.gov (United States)

    Alfonsi, P.; Nourredine, K.; Adam, F.; Chauvin, M.; Sessler, D. I.

    2005-01-01

    Summary Cutaneous warming is reportedly an effective treatment for shivering during epidural and after general anaesthesia. We quantified the efficacy of cutaneous warming as a treatment for shivering. Unwarmed surgical patients (final intraoperative core temperatures ≈35°C) were randomly assigned to be covered with a blanket (n=9) or full-body forced-air cover (n=9). Shivering was evaluated clinically and by oxygen consumption. Forced-air heating increased mean-skin temperature (35.7±0.4 °C vs. 33.2±0.8°C, Pshivering threshold (35.7±0.2 °C vs. 36.4±0.2°C, Pshivering was similar in the two groups (37±11 min [warming] and 36±10 min [control]). Core temperature thus contributed about four times as much as skin temperature to control of shivering. Cutaneous warming improved thermal comfort and reduced metabolic stress in postoperative patients, but did not quickly obliterate shivering. PMID:14705689

  1. Star formation and the interstellar medium in low surface brightness galaxies - I. Oxygen abundances and abundance gradients in low surface brightness disk galaxies

    NARCIS (Netherlands)

    de Blok, WJG; van der Hulst, JM

    We present measurements of the oxygen abundances in 64 HII regions in 12 LSB galaxies. We find that oxygen abundances are low. No regions with solar abundance have been found, and most have oxygen abundances similar to 0.5 to 0.1 solar. The oxygen abundance appears to be constant as a function of

  2. Star formation and the interstellar medium in low surface brightness galaxies; 1, Oxygen abundances and abundance gradients in low surface brightness disk galaxies

    NARCIS (Netherlands)

    Blok, W. J. G. de; Hulst, J. M. van der

    1998-01-01

    Submitted to: Astron. Astrophys. Abstract: We present measurements of the oxygen abundances in 64 HII regions in 12 LSB galaxies. We find that oxygen abundances are low. No regions with solar abundance have been found, and most have oxygen abundances $sim 0.5$ to 0.1 solar. The oxygen abundance

  3. Surface reaction mechanisms during ozone and oxygen plasma assisted atomic layer deposition of aluminum oxide.

    Science.gov (United States)

    Rai, Vikrant R; Vandalon, Vincent; Agarwal, Sumit

    2010-09-07

    We have elucidated the reaction mechanism and the role of the reactive intermediates in the atomic layer deposition (ALD) of aluminum oxide from trimethyl aluminum in conjunction with O(3) and an O(2) plasma. In situ attenuated total reflection Fourier transform infrared spectroscopy data show that both -OH groups and carbonates are formed on the surface during the oxidation cycle. These carbonates, once formed on the surface, are stable to prolonged O(3) exposure in the same cycle. However, in the case of plasma-assisted ALD, the carbonates decompose upon prolonged O(2) plasma exposure via a series reaction kinetics of the type, A (CH(3)) --> B (carbonates) --> C (Al(2)O(3)). The ratio of -OH groups to carbonates on the surface strongly depends on the oxidizing agent, and also the duration of the oxidation cycle in plasma-assisted ALD. However, in both O(3) and O(2) plasma cycles, carbonates are a small fraction of the total number of reactive sites compared to the hydroxyl groups.

  4. Adsorption and dissociation of oxygen molecules on Si(111)-(7×7) surface

    International Nuclear Information System (INIS)

    Niu, Chun-Yao; Wang, Jian-Tao

    2013-01-01

    The adsorption and dissociation of O 2 molecules on Si(111)-(7×7) surface have been studied by first-principles calculations. Our results show that all the O 2 molecular species adsorbed on Si(111)-(7×7) surface are unstable and dissociate into atomic species with a small energy barrier about 0.1 eV. The single O 2 molecule adsorption tends to form an ins×2 or a new metastable ins×2* structure on the Si adatom sites and the further coming O 2 molecules adsorb on those structures to produce an ad-ins×3 structure. The ad-ins×3 structure is indeed highly stable and kinetically limited for diving into the subsurface layer to form the ins×3-tri structure by a large barrier of 1.3 eV. Unlike the previous views, we find that all the ad-ins, ins×2, and ad-ins×3 structures show bright images, while the ins×2*, ins×3, and ins×3-tri structures show dark images. The proposed oxidation pathways and simulated scanning tunneling microscope images account well for the experimental results and resolve the long-standing confusion and issue about the adsorption and reaction of O 2 molecules on Si(111) surface

  5. Hemocompatibility and oxygenation performance of polysulfone membranes grafted with polyethylene glycol and heparin by plasma-induced surface modification.

    Science.gov (United States)

    Wang, Weiping; Zheng, Zhi; Huang, Xin; Fan, Wenling; Yu, Wenkui; Zhang, Zhibing; Li, Lei; Mao, Chun

    2017-10-01

    Polyethylene glycol (PEG) and heparin (Hep) were grafted onto polysulfone (PSF) membrane by plasma-induced surface modification to prepare PSF-PEG-Hep membranes used for artificial lung. The effects of plasma treatment parameters, including power, gas type, gas flow rate, and treatment time, were investigated, and different PEG chains were bonded covalently onto the surface in the postplasma grafting process. Membrane surfaces were characterized by water contact angle, PEG grafting degree, attenuated total reflectance-Fourier transform infrared spectroscopy, ultraviolet-visible spectrophotometry, X-ray photoelectron spectroscopy, critical water permeability pressure, and scanning electron microscopy. Protein adsorption, platelet adhesion, and coagulation tests showed significant improvement in the hemocompatibility of PSF-PEG-Hep membranes compared to pristine PSF membrane. Gas exchange tests through PSF-PEG6000-Hep membrane showed that when the flow rate of porcine blood reached 5.0 L/min, the permeation fluxes of O 2 and CO 2 reached 192.6 and 166.9 mL/min, respectively, which were close to the gas exchange capacity of a commercial membrane oxygenator. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1737-1746, 2017. © 2016 Wiley Periodicals, Inc.

  6. Surface modification of a natural zeolite by treatment with cold oxygen plasma: Characterization and application in water treatment

    Science.gov (United States)

    De Velasco-Maldonado, Paola S.; Hernández-Montoya, Virginia; Montes-Morán, Miguel A.; Vázquez, Norma Aurea-Rangel; Pérez-Cruz, Ma. Ana

    2018-03-01

    In the present work the possible surface modification of natural zeolite using cold oxygen plasma was studied. The sample with and without treatment was characterized using nitrogen adsorption isotherms at -196 °C, FT-IR spectroscopy, SEM/EDX analysis and X-Ray Diffraction. Additionally, the two samples were used for the removal of lead and acid, basic, reactive and food dyes in batch systems. The natural zeolite was found to be a mesoporous material with a low specific surface area (23 m2/g). X-ray patterns confirmed that clinoptilolite was the main crystal structure present in the natural zeolite. The molecular properties of dyes and the zeolitic structure were studied using molecular simulation, with the purpose to understand the adsorption mechanism. The results pointed out that only the roughness of the clinoptilolite was affected by the plasma treatment, whereas the specific surface area, chemical functionality and crystal structure remained constant. Finally, adsorption results confirmed that the plasma treatment had no significant effects on the dyes and lead retention capacities of the natural zeolite.

  7. The NO-carbon reaction: the influence of potassium and CO on reactivity and populations of oxygen surface complexes

    Energy Technology Data Exchange (ETDEWEB)

    Diana Lopez; Joseph Calo [Brown University, Providence, RI (United States). Division of Engineering

    2007-08-15

    Results on the effects of a metal catalyst and the role of CO as a reducing agent are reported for a resin char and a Wyodak coal char, as well as demineralized samples of the latter. The effect of an active metal catalyst, such as potassium in the current work, is to significantly increase the reactivity both by increasing the number of reaction sites via the catalyst dispersion and reducing the activation energy and by increasing CO{sub 2} production. The latter is a beneficial result because it means that less carbon is consumed per molecule of NO reduced. Additional CO in the gas phase 'catalyzes' NO reduction via the creation of more labile surface complexes and facilitation of desorption of other oxygen complexes. This effect decreases with an increasing temperature and disappears by about 1123 K. The activation energy of this reaction is comparable to that induced by the metal catalyst. 21 refs., 9 figs., 2 tabs.

  8. The adsorption of NO on an oxygen pre-covered Pt(1 1 1) surface: in situ high-resolution XPS combined with molecular beam studies

    Science.gov (United States)

    Zhu, J. F.; Kinne, M.; Fuhrmann, T.; Tränkenschuh, B.; Denecke, R.; Steinrück, H.-P.

    2003-12-01

    Adsorption of NO on a Pt(1 1 1) surface pre-covered with a p(2 × 2) atomic oxygen layer has been studied in situ by high-resolution X-ray photoelectron spectroscopy and temperature-programmed XPS using third-generation synchrotron radiation at BESSY II, Berlin, combined with molecular beam techniques and ex situ by low energy electron diffraction and temperature-programmed desorption. O 1s XP spectra reveal that an ordered p(2 × 2)-O layer dramatically changes the adsorption behavior of NO as compared to the clean surface. The atomic oxygen occupies fcc hollow sites, and therefore blocks NO adsorption on these sites, which are energetically preferred on clean Pt(1 1 1). As a consequence, NO populates on-top sites at low coverage. At 110 K for higher coverages, NO can additionally adsorb on hcp hollow sites, thereby inducing a shift of the O 1s binding energy of atomic oxygen towards lower energies by about 0.25 eV. The bond strength of the hcp hollow NO species to the substrate is weakened by the presence of atomic oxygen. A sharp p(2 × 2) LEED pattern is observed for NO adsorption on the oxygen pre-covered surface, up to saturation coverage. The total saturation coverage of NO on Pt(1 1 1) pre-covered with varying amounts of oxygen (below 0.25 ML) decreases linearly with the coverage of oxygen. The initial sticking coefficient of NO is reduced from 0.96 on clean Pt(1 1 1) to 0.88 on a p(2 × 2) oxygen pre-covered surface.

  9. Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake: nuclear fuel durability enhancement

    Czech Academy of Sciences Publication Activity Database

    Škarohlíd, J.; Ashcheulov, Petr; Škoda, R.; Taylor, Andrew; Čtvrtlík, R.; Tomaštík, J.; Fendrych, František; Kopeček, Jaromír; Cháb, Vladimír; Cichoň, Stanislav; Sajdl, P.; Macák, J.; Xu, P.; Partezana, J.M.; Lorinčík, J.; Prehradná, J.; Steinbrück, M.; Kratochvílová, Irena

    2017-01-01

    Roč. 7, Jul (2017), 1-14, č. článku 6469. ISSN 2045-2322 R&D Projects: GA MŠk LO1409; GA MŠk LM2015088; GA ČR(CZ) GA15-05095S; GA ČR(CZ) GA16-03085S; GA TA ČR TA04020156 Grant - others:FUNBIO(XE) CZ.2.16/3.1.00/21568 Institutional support: RVO:68378271 Keywords : nanocrystalline diamond * zirconium alloys * corrosion Subject RIV: JK - Corrosion ; Surface Treatment of Materials OBOR OECD: Coating and films Impact factor: 4.259, year: 2016

  10. Effects of chlorine and oxygen coverage on the structure of the Au(111) surface

    International Nuclear Information System (INIS)

    Baker, Thomas A.; Friend, Cynthia M.; Kaxiras, Efthimios

    2009-01-01

    We investigate the effects of Cl and O coverage on the atomic structure of the Au(111) surface using density functional theory calculations. We find that the release and incorporation of gold atoms in the adsorbate layer becomes energetically favorable only at high coverages of either O or Cl (>0.66 ML (monolayer) for O and >0.33 ML for Cl), whereas adsorption without the incorporation of gold is favorable at lower coverages. The bonding between the adsorbate and gold substrate changes significantly with coverage, becoming more covalent (less ionic) at higher Cl and O coverage. This is based on the fact that at higher coverages there is less ionic charge transfer to the adsorbate, while the electron density in the region between the adsorbate and a surface gold atom is increased. Our results illustrate that the O and Cl coverage on Au(111) can dramatically affect its structure and bonding, which are important features in any application of gold involving these adsorbates.

  11. Activation of surface lattice oxygen in single-atom Pt/CeO 2 for low-temperature CO oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Nie, Lei; Mei, Donghai; Xiong, Haifeng; Peng, Bo; Ren, Zhibo; Pereira Hernandez, Xavier I.; DelaRiva, Andrew; Wang, Meng; Engelhard, Mark H.; Kovarik, Libor; Datye, Abhaya K.; Wang, Yong

    2017-12-14

    While single-atom catalysts can provide high catalytic activity and selectivity, application in industrial catalysts demands long term performance and the ability to regenerate the catalysts. We have investigated the factors that lead to improved catalytic activity of a Pt/CeO2 catalyst for low temperature CO oxidation. Single-atom Pt/CeO2 becomes active for CO oxidation under lean condition only at elevated temperatures, because CO is strongly bound to ionic Pt sites. Reducing the catalyst, even under mild conditions, leads to onset of CO oxidation activity even at room temperature. This high activity state involves the transformation of mononuclear Pt species to sub-nanometer sized Pt particles. Under oxidizing conditions, the Pt can be restored to its stable, single-atom state. The key to facile regeneration is the ability to create mobile Pt species and suitable trapping sites on the support, making this a prototypical catalyst system for industrial application of single-atom catalysis.

  12. The dynamics of ultraviolet-induced oxygen vacancy at the surface of insulating SrTiO{sub 3}(0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Suwanwong, S. [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Program in General Science Teaching, Faculty of Education, Vongchavalitkul University, Nakhon Ratchasima 30000 (Thailand); Eknapakul, T. [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Rattanachai, Y. [Department of Applied Physics, Faculty of Sciences and Liberal Arts, Rajamangala University of Technology Isan, Nakhon Ratchasima 30000 (Thailand); Masingboon, C. [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Faculty of Science and Engineering, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000 (Thailand); Rattanasuporn, S.; Phatthanakun, R.; Nakajima, H. [Synchrotron Light Research Institute, Nakhon Ratchasima 30000 (Thailand); King, P.D.C. [SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS (United Kingdom); Hodak, S.K. [Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330 (Thailand); Meevasana, W., E-mail: worawat@g.sut.ac.th [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); NANOTEC-SUT Center of Excellence on Advanced Functional Nanomaterials, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Thailand Center of Excellence in Physics, CHE, Bangkok 10400 (Thailand)

    2015-11-15

    Highlights: • The dynamics of UV-induced oxygen vacancy is studied from the change of surface resistance. • The formation of 2DEG at the insulating surface of SrTiO{sub 3} is confirmed by ARPES. • The UV-induced change in resistance responds differently to oxygen/gas exposure. • The behavior of resistance recovery suggests an alternative method of low-pressure sensing. - Abstract: The effect of ultra-violet (UV) irradiation on the electronic structure and the surface resistance of an insulating SrTiO{sub 3}(0 0 1) crystal is studied in this work. Upon UV irradiation, we show that the two-dimensional electron gas (2DEG) emerges at the insulating SrTiO{sub 3} surface and there is a pronounced change in the surface resistance. By combining the observations of the change in valance band and the resistance change under different environments of gas pressure and gas species, we find that UV-induced oxygen vacancies at the surface plays a major role in the resistance change. The dynamic of the resistance change at different oxygen pressures also suggests an alternative method of low-pressure sensing.

  13. The dynamics of ultraviolet-induced oxygen vacancy at the surface of insulating SrTiO3(0 0 1)

    International Nuclear Information System (INIS)

    Suwanwong, S.; Eknapakul, T.; Rattanachai, Y.; Masingboon, C.; Rattanasuporn, S.; Phatthanakun, R.; Nakajima, H.; King, P.D.C.; Hodak, S.K.; Meevasana, W.

    2015-01-01

    Highlights: • The dynamics of UV-induced oxygen vacancy is studied from the change of surface resistance. • The formation of 2DEG at the insulating surface of SrTiO 3 is confirmed by ARPES. • The UV-induced change in resistance responds differently to oxygen/gas exposure. • The behavior of resistance recovery suggests an alternative method of low-pressure sensing. - Abstract: The effect of ultra-violet (UV) irradiation on the electronic structure and the surface resistance of an insulating SrTiO 3 (0 0 1) crystal is studied in this work. Upon UV irradiation, we show that the two-dimensional electron gas (2DEG) emerges at the insulating SrTiO 3 surface and there is a pronounced change in the surface resistance. By combining the observations of the change in valance band and the resistance change under different environments of gas pressure and gas species, we find that UV-induced oxygen vacancies at the surface plays a major role in the resistance change. The dynamic of the resistance change at different oxygen pressures also suggests an alternative method of low-pressure sensing.

  14. Optical lattice on an atom chip

    DEFF Research Database (Denmark)

    Gallego, D.; Hofferberth, S.; Schumm, Thorsten

    2009-01-01

    Optical dipole traps and atom chips are two very powerful tools for the quantum manipulation of neutral atoms. We demonstrate that both methods can be combined by creating an optical lattice potential on an atom chip. A red-detuned laser beam is retroreflected using the atom chip surface as a high......-quality mirror, generating a vertical array of purely optical oblate traps. We transfer thermal atoms from the chip into the lattice and observe cooling into the two-dimensional regime. Using a chip-generated Bose-Einstein condensate, we demonstrate coherent Bloch oscillations in the lattice....

  15. The effect of oxygen vacancies on the stability, electronic and optical properties of the ZnAl2O4(100) surface; A first-principles study

    Science.gov (United States)

    Lahmer, M. A.

    2018-03-01

    The effect of oxygen vacancy formation on the stability, structural, electronic, and optical properties of the ZnAl2O4(100) surface was investigated by using the first-principles method. The obtained results show that, in the case of the Free-defect surface, the AlO2-terminated surface is more stable than the Zn-terminated surface. The results of structural relaxation show that, for each surface termination, the interlayer distances near the surface oscillate in a damping style. In addition, the work function values and the optical properties of these two surfaces are quite different. Our results show that the work function of the Zn-terminated surface is at least 2 times smaller than that of the AlO2 surface. On the other hand, ab initio thermodynamic calculations show that the O reduction occurs in the case of the AlO2 surface under all growth conditions, while, there is no evidence for O reduction in the case of the Zn-terminated surface. Our results show also that neutral oxygen vacancies can affect greatly the electronic and optical properties of the ZnAl2O4(100) surface.

  16. Jamming within Lattices

    Science.gov (United States)

    Wentworth-Nice, Prairie; Graves, Amy

    Numerical methods are used in two dimensions to find the minimum energy configuration of soft bidisperse spheres, in the presence of lattices of fixed, pointlike particles. The lattice provides a supporting structure for the jammed configuration, resulting in changes in the jamming threshold. The excess coordination number and other properties of interest near jamming are calculated as a function of the lattice structure and number density. Acknowledgement is made to the donors of the Petrolium Research Fund, administered by the American Chemical Society.

  17. Metaharmonic Lattice Point Theory

    CERN Document Server

    Freeden, Willi

    2011-01-01

    Metaharmonic Lattice Point Theory covers interrelated methods and tools of spherically oriented geomathematics and periodically reflected analytic number theory. The book establishes multi-dimensional Euler and Poisson summation formulas corresponding to elliptic operators for the adaptive determination and calculation of formulas and identities of weighted lattice point numbers, in particular the non-uniform distribution of lattice points. The author explains how to obtain multi-dimensional generalizations of the Euler summation formula by interpreting classical Bernoulli polynomials as Green

  18. Surface Modification of Direct-Current and Radio-Frequency Oxygen Plasma Treatments Enhance Cell Biocompatibility

    Directory of Open Access Journals (Sweden)

    Wan-Ching Chou

    2017-10-01

    Full Text Available The sand-blasting and acid etching (SLA method can fabricate a rough topography for mechanical fixation and long-term stability of titanium implant, but can not achieve early bone healing. This study used two kinds of plasma treatments (Direct-Current and Radio-Frequency plasma to modify the SLA-treated surface. The modification of plasma treatments creates respective power range and different content functional OH groups. The results show that the plasma treatments do not change the micron scale topography, and plasma-treated specimens presented super hydrophilicity. The X-ray photoelectron spectroscopy (XPS-examined result showed that the functional OH content of the RF plasma-treated group was higher than the control (SLA and DC treatment groups. The biological responses (protein adsorption, cell attachment, cell proliferation, and differentiation promoted after plasma treatments, and the cell responses, have correlated to the total content of amphoteric OH groups. The experimental results indicated that plasma treatments can create functional OH groups on SLA-treated specimens, and the RF plasma-treated SLA implant thus has potential for achievement of bone healing in early stage of implantation.

  19. Lattice-Algebraic Morphology

    National Research Council Canada - National Science Library

    McGuire, Dennis

    1998-01-01

    ... invariance present in concrete morphology theories. The other, developed by Banon and Barrera, analyzes general mappings between complete lattices and develops morphological decomposition formulas for such mappings...

  20. Twisted mass lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Shindler, A. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

    2007-07-15

    I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)

  1. Lattice degeneracies of fermions

    International Nuclear Information System (INIS)

    Raszillier, H.

    1983-10-01

    We present a detailed description of the minimal degeneracies of geometric (Kaehler) fermions on all the lattices of maximal symmetries in n = 1, ..., 4 dimensions. We also determine the isolated orbits of the maximal symmetry groups, which are related to the minimal numbers of ''naive'' fermions on the reciprocals of these lattices. It turns out that on the self-reciprocal lattices the minimal numbers of naive fermions are equal to the minimal numbers of degrees of freedom of geometric fermions. The description we give relies on the close connection of the maximal lattice symmetry groups with (affine) Weyl groups of root systems of (semi-) simple Lie algebras. (orig.)

  2. Layout designs of surface barrier coatings for boosting the capability of oxygen/vapor obstruction utilized in flexible electronics

    Science.gov (United States)

    Lee, Chang-Chun; Huang, Pei-Chen; He, Jing-Yan

    2018-04-01

    Organic light-emitting diode-based flexible and rollable displays have become a promising candidate for next-generation flexible electronics. For this reason, the design of surface multi-layered barriers should be optimized to enhance the long-term mechanical reliability of a flexible encapsulation that prevents the penetration of oxygen and vapor. In this study, finite element-based stress simulation was proposed to estimate the mechanical reliability of gas/vapor barrier design with low-k/silicon nitride (low-k/SiNx) stacking architecture. Consequently, stress-induced failure of critical thin films within the flexible display under various bending conditions must be considered. The feasibility of one pair SiO2/SiNx barrier design, which overcomes the complex lamination process, and the critical bending radius, which is decreased to 1.22 mm, were also examined. In addition, the influence of distance between neutral axes to the concerned layer surface dominated the induced-stress magnitude rather than the stress compliant mechanism provided from stacked low-k films.

  3. Study of an Ozone Composing Mechanism derived from the Third Element on Surface of Electrode using Oxygen Gas: Part 2

    Science.gov (United States)

    Murai, Akira; Nakajima, Tsuyoshi

    In our third experiment, we changed the density of nitrogen through the addition of heat energy to the anode. A computer simulation confirmed the same phenomenon. Then the copper anode was replaced with an antimony anode. We found that antimony worked better than nitrogen as a third element. Finally, in the fourth experiment, we used an industrial ozone generator including ceramic dielectrics and a titanium expanded metal electrode. A decrease in the temperature of the cooling water led to a proportional increase in ozone. It follows the formula of van't Hoff. After spattering the surface of the electrodes with argon gas and supplying the ozone generator with 99% oxygen, we were able to produce ozone which was more than 20% higher in concentration than primary state ozone under the same conditions. The ozone generator produced ozone in high yield efficiency due to the optimum density of a third element like nitrogen on the surface of the electrodes. Antimony works better than nitrogen does as a third element.

  4. Influence of an oxygen-inhibited layer on enamel bonding of dental adhesive systems: surface free-energy perspectives.

    Science.gov (United States)

    Ueta, Hirofumi; Tsujimoto, Akimasa; Barkmeier, Wayne W; Oouchi, Hajime; Sai, Keiichi; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

    2016-02-01

    The influence of an oxygen-inhibited layer (OIL) on the shear bond strength (SBS) to enamel and surface free-energy (SFE) of adhesive systems was investigated. The adhesive systems tested were Scotchbond Multipurpose (SM), Clearfil SE Bond (CS), and Scotchbond Universal (SU). Resin composite was bonded to bovine enamel surfaces to determine the SBS, with and without an OIL, of adhesives. The SFE of cured adhesives with and without an OIL were determined by measuring the contact angles of three test liquids. There were no significant differences in the mean SBS of SM and CS specimens with or without an OIL; however, the mean SBS of SU specimens with an OIL was significantly higher than that of SU specimens without an OIL. For all three systems, the mean total SFE (γS), polarity force (γSp), and hydrogen bonding force (γSh) values of cured adhesives with an OIL were significantly higher than those of cured adhesives without an OIL. The results of this study indicate that the presence of an OIL promotes higher SBS of a single-step self-etch adhesive system, but not of a three-step or a two-step self-etch primer system. The SFE values of cured adhesives with an OIL were significantly higher than those without an OIL. The SFE characteristics of the OIL of adhesives differed depending on the type of adhesive. © 2015 Eur J Oral Sci.

  5. Electron stimulated desorption of positive and negative oxygen ions from YBa{sub 2}Cu{sub 3}O{sub 7} surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, A. [Technion-Israel Inst. of Tech., Haifa (Israel). Solid State Inst.; Moss, S.D.; Paterson, P.J.K. [Royal Melbourne Inst. of Tech., VIC (Australia); McCubbery, D. [La Trobe Univ., Bundoora, VIC (Australia); Petravic, M. [Australian National Univ., Canberra, ACT (Australia)

    1996-12-31

    The electron stimulated desorption (ESD) of positive and negative oxygen ion from superconducting YBa{sub 2}Cu{sub 3}O{sub 7} surfaces was studied. Based on ion desorption yield measurements as function of electron kinetic energy, primary excitations leading to positive and negative oxygen ion desorption are suggested. To the best of the authors` knowledge this is the first study on electron energy dependent ESD from YBa{sub 2}Cu{sub 3}O{sub 7} surfaces. The YBa{sub 2}Cu{sub 3}O{sub 7} samples were prepared from BaCO{sub 3}, Y{sub 2}O{sub 3} and CuO using standard high temperature sintering and annealing procedures. Slices 2 mm thick were cut and further annealed at 400 C in flowing oxygen for 24 hours prior to insertion into the ultrahigh vacuum (UHV) chamber for ESD. The near surface composition and chemical state of the annealed sample after exposure to air was examined by Auger and XPS analysis. These measurements suggest that the ESD experiments were performed on samples of similar near surface and bulk composition with some OH- chemisorbed groups and Cl surface contaminations and that negative and positive oxygen ion desorption may be initiated via a primary core level ionization. 10 refs., 3 figs.

  6. Radial Oxygen Loss in the Rhizosphere of Wild Rice as a Control On Root Surface Mineral Precipitation

    Science.gov (United States)

    Murphy, K.; Trejo, B.; LaFond-Hudson, S.

    2017-12-01

    Wild rice (Zizania palustris) is an aquatic plant native to the Great Lakes region that is culturally and nutritionally significant for the Ojibwe people of Northern Minnesota. Concern for the future health of wild rice populations has increased amidst ongoing pressures from proposed mining projects that risk sulfate contamination to natural waters. Although sulfate itself is not toxic to wild rice, bacteria living in anoxic sediments use the sulfate as an electron acceptor, converting it to sulfide, which subsequently precipitates in the form of iron-sulfide on the root surface of wild rice. These precipitates are linked to lowered viability of wild rice. Most wetland plants are able to shield against the harmful accumulation of these precipitates through a process known as radial oxygen loss (ROL), in which oxygen leaches from roots into anoxic sediments to form protective iron-oxide plaques. This mechanism, however, had yet to be experimentally confirmed in wild rice. In this study, we eliminated the potential for ROL to occur in wild rice prior to the reproductive phase, and measured the rates of iron-sulfide accumulation on the roots and in associated sediments. We compared these data with the geochemical composition of roots and sediment from wild rice that accumulated iron-sulfide precipitate during the reproductive phase. In doing so, we demonstrate that ROL is indeed a mechanism by which wild rice protects itself against sulfide exposure, and examine the nuances of ROL as it relates to the life cycle of wild rice. The better we understand the vulnerability of wild rice across its life cycle and comparative rates of both toxic and protective precipitate accumulation, the better we can approach wild rice conservation.

  7. Impacts of anions on the oxygen reduction reaction kinetics on platinum and palladium surfaces in alkaline solutions.

    Science.gov (United States)

    Zhu, Shangqian; Hu, Xiaomeng; Shao, Minhua

    2017-03-15

    The fundamental understanding of the impacts induced by anions on oxygen reduction reaction (ORR) in alkaline media is of great importance in the design of more advanced catalysts for alkaline fuel cells (AFC). In this study, the specific adsorption of F - , Cl - , ClO 4 - , CO 3 2- , SO 4 2- , and citrate anions on Pt/C and Pd/C catalysts, and their impacts on the ORR kinetics in alkaline solutions were systematically studied. It was found that F - , Cl - and ClO 4 - did not specifically adsorb on Pt or Pd surfaces and had no poisoning effect on ORR. CO 3 2- and SO 4 2- had significant effects on Pt/C and lowered the activity even at a very low concentration. On the other hand, their impacts on Pd/C were negligible. Self-dissociation of citrate anions was found to occur on both Pt/C and Pd/C in the H adsorption/desorption and double layer regions. For the first time, surface enhanced infrared absorption spectroscopy (SEIRAS) with the attenuated total reflection (ATR) technique was used to investigate the self-dissociation of citrate on Pt and Pd thin film electrodes. The breaking of carboxylic groups and the carbon backbone was proposed as a possible dissociation pathway for citrate. The adsorbed species have a negligible effect on ORR activity on Pt/C as they are removed by oxidation before 0.75 V. In contrast, their oxidation on Pd/C surfaces is not completed until 0.91 V, which causes a lower ORR activity observed in rotating disk electrode measurements. The findings in this paper emphasize the importance of specific adsorption of anions and double-layer interfacial effects on the ORR activity measurement in alkaline solutions.

  8. Nuclear lattice simulations

    Directory of Open Access Journals (Sweden)

    Epelbaum E.

    2010-04-01

    Full Text Available We review recent progress on nuclear lattice simulations using chiral effective field theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb effects, and the binding energy of light nuclei.

  9. Photoemission studies of oxygen adsorbed on a LiAl(1-bar 1-bar 0) alloy surface: Role of Li segregation

    International Nuclear Information System (INIS)

    Lee, D.; Lee, H.G.; Hwang, C.; Maeng, J.Y.; Kim, S.; Kim, K.-J.; Kim, B.

    2006-01-01

    We investigated that the effect of the number of segregated Li atoms on the rate of oxidation on a LiAl alloy surface. Oxygen molecules adsorbed on the LiAl alloy react with the surface atoms to form stable oxides. The segregated Li atoms at reconstructed surfaces (c(2x2) and (2x1)) enhance the oxidation rate and form stable LiAlO x and Li 2 O. The degree of enhancement of oxidation by segregated Li atoms varies as a function of O 2 exposure and annealing temperature, where the latter is directly related to the mode of surface reconstruction by Li segregation

  10. 3D Metallic Lattices for Accelerator Applications

    CERN Document Server

    Shapiro, Michael A; Sirigiri, Jagadishwar R; Temkin, Richard J

    2005-01-01

    We present the results of research on 3D metallic lattices operating at microwave frequencies for application in (1) accelerator structures with higher order mode suppression, (2) Smith-Purcell radiation beam diagnostics, and (3) polaritonic materials for laser acceleration. Electromagnetic waves in a 3D simple cubic lattice formed by metal wires are calculated using HFSS. The bulk modes in the lattice are determined using single cell calculations with different phase advances in all three directions. The Brillouin diagram for the bulk modes is presented and indicates the absence of band gaps in simple lattices except the band below the cutoff. Lattices with thin wires as well as with thick wires have been analyzed. The Brillouin diagram also indicates the presence of low frequency 3D plasmon mode as well as the two degenerate photon modes analogous to those in a 2D lattice. Surface modes for a semi-infinite cubic lattice are modeled as a stack of cells with different phase advances in the two directions alon...

  11. Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy: Sr(Ti,Fe)O3-x thin film case study

    Science.gov (United States)

    Perry, Nicola H.; Kim, Jae Jin; Tuller, Harry L.

    2018-01-01

    Abstract We compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS), on the same mixed conducting SrTi0.65Fe0.35O3-x film. Surface exchange coefficients were evaluated as a function of oxygen activity in the film, controlled by gas partial pressure and/or DC bias applied across the ionically conducting yttria-stabilized zirconia substrate. Changes in measured light transmission through the film over time (relaxations) resulted from optical absorption changes in the film corresponding to changes in its oxygen and oxidized Fe (~Fe4+) concentrations; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry. The kchem values obtained by OTR were significantly lower than the AC-IS derived kchem values and kq values multiplied by the thermodynamic factor (bulk or thin film), suggesting a possible enhancement in k by the metal current collectors (Pt, Au). Long-term degradation in kchem and kq values obtained by AC-IS was also attributed to deterioration of the porous Pt current collector, while no significant degradation was observed in the optically derived kchem values. The results suggest that, while the current collector might influence measurements by AC-IS, the OTR method offers a continuous, in situ, and contact-free method to measure oxygen exchange kinetics at the native surfaces of thin films. PMID:29511391

  12. SnO2 promoted by alkali metal oxides for soot combustion: The effects of surface oxygen mobility and abundance on the activity

    Science.gov (United States)

    Rao, Cheng; Shen, Jiating; Wang, Fumin; Peng, Honggen; Xu, Xianglan; Zhan, Hangping; Fang, Xiuzhong; Liu, Jianjun; Liu, Wenming; Wang, Xiang

    2018-03-01

    In this study, SnO2-based catalysts promoted by different alkali metal oxides with a Sn/M (M = Li, Na, K, Cs) molar ratio of 9/1 have been prepared for soot combustion. In comparison with the un-modified SnO2 support, the activity of the modified catalysts has been evidently enhanced, following the sequence of CsSn1-9 > KSn1-9 > NaSn1-9 > LiSn1-9 > SnO2. As testified by Raman, H2-TPR, soot-TPR-MS, XPS and O2-TPD results, the incorporation of various alkali metal oxides can induce the formation of more abundant and mobile oxygen species on the surface of the catalysts. Moreover, quantified results have proved that the amount of the surface active oxygen species is nearly proportional to the activity of the catalysts. CsSn1-9, the catalyst promoted by cesium oxide, owns the largest amount of surface mobile oxygen species, thus having the highest activity among all the studied catalysts. It is concluded that the amount of surface active and mobile oxygen species is the major factor determining the activity of the catalysts for soot combustion.

  13. Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2 C (001) Surface: A Density Functional Theory Study

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Mingxia [Department; Cheng, Lei [Materials; Choi, Jae-Soon [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831, Unites States; Liu, Bin [Department; Curtiss, Larry A. [Materials; Assary, Rajeev S. [Materials

    2018-01-11

    Density functional theory (DFT) calculations were used to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T-Mo) and C-terminated (Tc) Mo2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such as Ni adsorbed on T-Mo and Tc Mo2C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T-Mo Mo2C(001) and Tc Mo2C(001) surfaces. This computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo2C and Ni-doped Mo2C catalysts, which had been passivated and stored in an oxygen environment.

  14. Influence of the Oxygen-inhibited Layer on Bonding Performance of Dental Adhesive Systems: Surface Free Energy Perspectives.

    Science.gov (United States)

    Tsujimoto, Akimasa; Barkmeier, Wayne W; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

    2016-01-01

    To examine the influence of the oxygen inhibited layer (OIL) on shear bond strength (SBS) to dentin and surface free energy (SFE) characteristics of different adhesive systems. Three adhesive systems were used: Scotchbond Multipurpose (SM), Clearfil SE Bond (CS), and Scotchbond Universal (SU). Resin composite was bonded to dentin surfaces to determine SBS with and without OIL of adhesives. The SFE, dispersion force (γSd), polarity force (γSp), and hydrogen bonding force (γSh) of cured adhesives with and without an OIL were measured. Two-way ANOVA and Tukey's honestly significant difference (HSD) test were used for analysis of SBS data, and one-way ANOVA and Tukey's HSD test were used for the SFE and contact angle data. The SBS of SM and CS showed no significant differences between specimens with and without the OIL. However, the SBS of SU with the OIL was significantly higher than without the OIL. The SFE, γSp, and γSh of cured adhesives with an OIL were significantly higher than those of cured adhesives without an OIL. The SFE, γSp, and γSh of SM and CS with an OIL were significantly higher than those of SU with an OIL. The results of this study indicate that the presence of an OIL with a single-step self-etching adhesive promotes higher SBS to dentin, unlike in the other types of adhesive systems. The SFE characteristics of the OIL of dental adhesives differed depending on the type of adhesive system.

  15. An oxygen-insensitive degradable resist for fabricating metallic patterns on highly curved surfaces by UV-nanoimprint lithography.

    Science.gov (United States)

    Hu, Xin; Huang, Shisong; Gu, Ronghua; Yuan, Changsheng; Ge, Haixiong; Chen, Yanfeng

    2014-10-01

    In this paper, an oxygen-insensitive degradable resist for UV-nanoimprint is designed, com-prising a polycyclic degradable acrylate monomer, 2,10-diacryloyloxymethyl-1,4,9,12-tetraoxa-spiro [4.2.4.2] tetradecane (DAMTT), and a multifunctional thiol monomer pentaerythritol tetra(3-mercaptopropionate) (PETMP). The resist can be quickly UV-cured in the air atmosphere and achieve a high monomer conversion of over 98%, which greatly reduce the adhesion force between the resist and the soft mold. High conversion, in company with an adequate Young's modulus (about 1 GPa) and an extremely low shrinkage (1.34%), promises high nanoimprint resolution of sub-50 nm. The cross-linked resist is able to break into linear molecules in a hot acid solvent. As a result, metallic patterns are fabricated on highly curved surfaces via the lift off process without the assistance of a thermoplastic polymer layer. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Modulation of resistive switching characteristics for individual BaTiO3 microfiber by surface oxygen vacancies

    Science.gov (United States)

    Miao, Zhilei; Chen, Lei; Zhou, Fang; Wang, Qiang

    2018-01-01

    Different from traditional thin-film BaTiO3 (BTO) RRAM device with planar structure, individual microfiber-shaped RRAM device, showing promising application potentials in the micro-sized non-volatile memory system, has not been investigated so far to demonstrate resistive switching behavior. In this work, individual sol-gel BTO microfiber has been formed using the draw-bench method, followed by annealing in different atmospheres of air and argon, respectively. The resistive switching characteristics of the individual BTO microfiber have been investigated by employing double-probe SEM measurement system, which shows great convenience to test local electrical properties by modulating the contact sites between the W probes and the BTO microfiber. For the sample annealed in air, the average resistive ON/OFF ratio is as high as 108, enhanced about four orders in comparison with the counterpart that annealed in Argon. For the sample annealed in argon ambience, the weakened resistive ON/OFF ratio can be attributed to the increased presence of oxygen vacancies in the surface of BTO fibers, and the underlying electrical conduction mechanisms are also discussed.

  17. Effects of wastewater discharge on formation of Fe plaque on root surface and radial oxygen loss of mangrove roots

    Energy Technology Data Exchange (ETDEWEB)

    Pi, N. [Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Kowloon (Hong Kong); Tam, N.F.Y., E-mail: bhntam@cityu.edu.h [Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Kowloon (Hong Kong); Wong, M.H. [Croucher Institute for Environmental Sciences, Baptist University of Hong Kong, Kowloon Tong, Kowloon (Hong Kong)

    2010-02-15

    Effects of wastewater discharge on radial oxygen loss (ROL), formation of iron (Fe) plaque on root surface, and their correlations in Bruguiera gymnorrhiza (L.) Poir and Excoecaria agallocha L. were investigated. ROL along a lateral root increased more rapidly in control than that in strong wastewater (with pollutant concentrations ten times of that in municipal sewage, 10NW) treatment, but less Fe plaque was formed in control for both plants. For B. gymnorrhiza receiving 10NW, Fe plaque formation was more at basal and mature zones than at root tip, while opposite trend was shown in E. agallocha. At day 0, the correlation between ROL and Fe plaque was insignificant, but negative and positive correlations were found in 10NW and control, respectively, at day 105, suggesting that more ROL was induced leading to more Fe plaque. However, excess Fe plaque also served as a 'barrier' to prevent excessive ROL in 10NW plants. - Correlation between Fe plaque formation and ROL.

  18. Study of gold-platinum and platinum-gold surface modification and its influence on hydrogen evolution and oxygen reduction

    Directory of Open Access Journals (Sweden)

    BRANIMIR N. GRGUR

    2005-02-01

    Full Text Available Surface modification of the electrodes was conducted from sulfuric acid solutions containing the corresponding metal–chloride complexes using cyclic voltammetry. Comparing the charges of the hydrogen underpotential deposition region, and the corresponding oxide reduction regions, it is concluded that a platinum overlayer on gold forms 3D islands, while gold on platinum forms 2D islands. Foreign metals present in an amount of up to one monolayer exert an influence on the change in reaction rate with respect to both hydrogen evolution (HER and oxygen reduction (ORR reactions. Aplatinum overlayer on a gold substrate increases the activity forHER and for ORR, compared with pure gold. These results can be understood in terms of a simple model, in which the change in the H and OH binding energies are directly proportional to the shift of the d-bond center of the overlayer. On the contrary, a gold layer on platinum slightly decreases the activity for both reactions compared with pure platinum.

  19. Role of oxygen adsorption in modification of optical and surface electronic properties of MoS2

    Science.gov (United States)

    Shakya, Jyoti; Kumar, Sanjeev; Mohanty, Tanuja

    2018-04-01

    In this work, the effect of surface oxidation of molybdenum disulfide (MoS2) nanosheets induced by hydrogen peroxide (H2O2) on the work function and bandgap of MoS2 has been investigated for tuning its optical and electronic properties. Transmission electron microscopy studies reveal the existence of varying morphologies of few layers of MoS2 as well as quantum dots due to the different absorbing effects of two mixed solvents on MoS2. The X-ray diffraction, electron paramagnetic resonance, and Raman studies indicate the presence of physical as well as chemical adsorption of oxygen atoms in MoS2. The photoluminescence spectra show the tuning of bandgap arising from the passivation of trapping centers leading to radiative recombination of excitons. The value of work function obtained from scanning Kelvin probe microscopy of MoS2 in mixed solvents of H2O2 and N-methyl-2-pyrrolidone increases with an increase in the concentration of H2O2. A linear relationship could be established between H2O2 content in mixed solvent and measured values of work function. This work gives the alternative route towards the commercial use of defect engineered transition metal dichalcogenide materials in diverse fields.

  20. Preparation of reactive oxygen scavenging peptides from tilapia (Oreochromis niloticus) skin gelatin: optimization using response surface methodology.

    Science.gov (United States)

    Zhuang, Yongliang; Sun, Liping

    2011-04-01

    Gelatin extracted from tilapia skin was hydrolyzed with Properase E. Response surface methodology (RSM) was applied to optimize the hydrolysis condition (temperature [T], enzyme-to-substrate ratio [E/S], pH and reaction time [t]), to obtain the hydrolysate with the highest hydroxyl radical (•OH) scavenging activity. The optimum conditions obtained were T of 44.2 °C, E/S of 2.2%, pH of 9.2, and t of 3.4 h. The predicted •OH scavenging activity of the hydrolysate under the optimum conditions was 60.7%, and the actually experimental scavenging activity was 60.8%. The hydrolysate was fractionated by ultrafiltration, and 4 fractions were collected. The fraction TSGH4 (MW<2000 Da) showed the strongest •OH scavenging activity with the highest yield. Furthermore, reactive oxygen species (ROS) scavenging activities of TSGH4 with different concentrations were investigated in 5 model systems, including superoxide anion radical (•O2), •OH, hydrogen peroxide (H2O2), peroxynitrite (ONOO-), and nitric oxide (NO•), compared with reduced glutathione (GSH). The results showed that TSGH4 significantly scavenged these ROS, and could be used as a functional ingredient in medicine and food industries.

  1. Effects of Carbon Structure and Surface Oxygen on the Carbon's Performance as the Anode in Lithium-Ion Battery Determined

    Science.gov (United States)

    Hung, Ching-Cheh

    2000-01-01

    Four carbon materials (C1, C2, C3, and C4) were tested electrochemically at the NASA Glenn Research Center at Lewis Field to determine their performance in lithium-ion batteries. They were formed as shown in the figure. This process caused very little carbon loss. Products C1 and C3 contained very little oxygen because of the final overnight heating at 540 C. Products C2 and C4, on the other hand, contained small amounts of basic oxide. The electrochemical test involved cycles of lithium intercalation and deintercalation using C/saturated LiI-50/50 (vol %) ethylene carbonate (EC) and dimethyl carbonate (DMC)/Li half cell. The cycling test, which is summarized in the table, resulted in three major conclusions. The capacity of the carbon with a basic oxide surface converges to a constant 1. value quickly (within 4 cycles), possibly because the oxide prevents solvent from entering the carbon structure and, therefore, prolongs the carbon s cycle life. Under certain conditions, the disordered carbon can store more lithium than its 2. precursor. These samples and their precursor can intercalate at 200 mA/g and deintercalate at 3. a rate of 2000 mA/g without significant capacity loss.

  2. On singularities of lattice varieties

    OpenAIRE

    Mukherjee, Himadri

    2013-01-01

    Toric varieties associated with distributive lattices arise as a fibre of a flat degeneration of a Schubert variety in a minuscule. The singular locus of these varieties has been studied by various authors. In this article we prove that the number of diamonds incident on a lattice point $\\a$ in a product of chain lattices is more than or equal to the codimension of the lattice. Using this we also show that the lattice varieties associated with product of chain lattices is smooth.

  3. Lattice Waves, Spin Waves, and Neutron Scattering

    Science.gov (United States)

    Brockhouse, Bertram N.

    1962-03-01

    Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)

  4. The influence of oxygen exposure time on the composition of macromolecular organic matter as revealed by surface sediments on the Murray Ridge (Arabian Sea)

    Science.gov (United States)

    Nierop, Klaas G. J.; Reichart, Gert-Jan; Veld, Harry; Sinninghe Damsté, Jaap S.

    2017-06-01

    The Arabian Sea represents a prime example of an open ocean extended oxygen minimum zone (OMZ) with low oxygen concentrations (down to less than 2 μM) between 200 and 1000 m water depth. The OMZ impinges on the ocean floor, affecting organic matter (OM) mineralization. We investigated impact of oxygen depletion on the composition of macromolecular OM (MOM) along a transect through the OMZ on the slopes of the Murray Ridge. This sub-marine high in the northern Arabian Sea, with the top at approximately 500 m below sea surface (mbss), intersects the OMZ. We analyzed sediments deposited in the core of OMZ (suboxic conditions), directly below the OMZ (dysoxic conditions) and well below the OMZ (fully oxic conditions). The upper 18 cm of sediments from three stations recovered at different depths were studied. MOM was investigated by Rock Eval and flash pyrolysis techniques. The MOM was of a predominant marine origin and inferred from their pyrolysis products, most biomolecules (tetra-alkylpyrrole pigments, polysaccharides, proteins and their transformation products, and polyphenols including phlorotannins), showed a progressive relative degradation with increasing exposure to oxygen. Alkylbenzenes and, in particular, aliphatic macromolecules increased relatively. The observed differences in MOM composition between sediment deposited under various bottom water oxygen conditions (i.e. in terms of concentration and exposure time) was much larger than within sediment cores, implying that early diagenetic alteration of organic matter depends largely on bottom water oxygenation rather than subsequent anaerobic degradation within the sediments, even at longer time scales.

  5. Impact of the structural anisotropy of La2NiO4+δ on on high temperature surface modifications and diffusion of oxygen

    International Nuclear Information System (INIS)

    Gauquelin, Nicolas

    2010-01-01

    La 2 NiO 4+δ was first studied due to its structural similarities with the High Temperature superconductor La 2 NiO 4+δ and more recently due to its promise as a cathode material in Solid Oxide Fuel Cells as well as an oxygen exchange membrane. It crystallizes in the K 2 NiF 4 layered structure and accommodates highly mobile oxygen at its ground state and is therefore overstoichiometric. During this thesis, pure single crystals of La 2 NiO 4+δ were successfully grown using the floating-zone method, subsequently characterized using neutron and Laue Backscattering diffraction and oriented pieces of single crystal with [100] and [001] orientation were prepared. The surface morphology behavior after long term exposure to high temperature in different atmospheres was observed using microscopy techniques because stability at high temperature is required for application purposes and it was discovered a structural change to nickel-rich phases at T>1173 K. The sensibility of the oxygen non-stoichiometry to cooling was studied and subsequently a new 18 O- 18 O exchange apparatus allowing quenching of the samples using liquid nitrogen was developed. Oxygen selfdiffusion was studied using SIMS in the range 673-873K in both [100] and [001] crystallographic directions. The effect of the disorientation of the sample surface on the determination of the slowest diffusion coefficient was discovered and revealed the very strong anisotropy (>5 orders of magnitude difference) between the different diffusion paths. Finally using HTXRD and oxygen release experiments, it was shown that oxygen diffusion from interstitial oxygen starts to be relevant at 550-600 K and a change of behavior is observed around 700 K, corresponding to a possible change in the diffusion mechanism from interstitial to interstitialcy.

  6. Impact of the structural anisotropy of La{sub 2}NiO{sub 4+δ} on on high temperature surface modifications and diffusion of oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Gauquelin, Nicolas

    2010-11-29

    La{sub 2}NiO{sub 4+δ} was first studied due to its structural similarities with the High Temperature superconductor La{sub 2}NiO{sub 4+δ} and more recently due to its promise as a cathode material in Solid Oxide Fuel Cells as well as an oxygen exchange membrane. It crystallizes in the K{sub 2}NiF{sub 4} layered structure and accommodates highly mobile oxygen at its ground state and is therefore overstoichiometric. During this thesis, pure single crystals of La{sub 2}NiO{sub 4+δ} were successfully grown using the floating-zone method, subsequently characterized using neutron and Laue Backscattering diffraction and oriented pieces of single crystal with [100] and [001] orientation were prepared. The surface morphology behavior after long term exposure to high temperature in different atmospheres was observed using microscopy techniques because stability at high temperature is required for application purposes and it was discovered a structural change to nickel-rich phases at T>1173 K. The sensibility of the oxygen non-stoichiometry to cooling was studied and subsequently a new {sup 18}O-{sup 18}O exchange apparatus allowing quenching of the samples using liquid nitrogen was developed. Oxygen selfdiffusion was studied using SIMS in the range 673-873K in both [100] and [001] crystallographic directions. The effect of the disorientation of the sample surface on the determination of the slowest diffusion coefficient was discovered and revealed the very strong anisotropy (>5 orders of magnitude difference) between the different diffusion paths. Finally using HTXRD and oxygen release experiments, it was shown that oxygen diffusion from interstitial oxygen starts to be relevant at 550-600 K and a change of behavior is observed around 700 K, corresponding to a possible change in the diffusion mechanism from interstitial to interstitialcy.

  7. In vitro study of 3D PLGA/n-HAp/β-TCP composite scaffolds with etched oxygen plasma surface modification in bone tissue engineering

    Energy Technology Data Exchange (ETDEWEB)

    Roh, Hee-Sang [Department of Dental Materials, School of Dentistry, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju 61452 (Korea, Republic of); Jung, Sang-Chul [Department of Environmental Engineering, Sunchon National University, 255 Jungang-ro, Sunchon 57922 (Korea, Republic of); Kook, Min-Suk [Department of Oral and Maxillofacial Surgery, School of Dentistry, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Kim, Byung-Hoon, E-mail: kim5055@chosun.ac.kr [Department of Dental Materials, School of Dentistry, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju 61452 (Korea, Republic of)

    2016-12-01

    Highlights: • PLGA and PLGA/n-HAp/β-TCP scaffolds were successfully fabricated by 3D printing. • Oxygen plasma etching increases the wettability and surface roughness. • Bioceramics and oxygen plasma etching and could be used to improve the cell affinity. - Abstract: Three-dimensional (3D) scaffolds have many advantageous properties for bone tissue engineering application, due to its controllable properties such as pore size, structural shape and interconnectivity. In this study, effects on oxygen plasma surface modification and adding of nano-hydroxyapatite (n-HAp) and β-tricalcium phosphate (β-TCP) on the 3D PLGA/n-HAp/β-TCP scaffolds for improving preosteoblast cell (MC3T3-E1) adhesion, proliferation and differentiation were investigated. The 3D PLGA/n-HAp/β-TCP scaffolds were fabricated by 3D Bio-Extruder equipment. The 3D scaffolds were prepared with 0°/90° architecture and pore size of approximately 300 μm. In addition 3D scaffolds surface were etched by oxygen plasma to enhance the hydrophilic property and surface roughness. After oxygen plasma treatment, the surface chemistry and morphology were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. And also hydrophilic property was measured by contact angle. The MC3T3-E1 cell proliferation and differentiation were investigated by MTT assay and ALP activity. In present work, the 3D PLGA/HAp/beta-TCP composite scaffold with suitable structure for the growth of osteoblast cells was successfully fabricated by 3D rapid prototyping technique. The surface hydrophilicity and roughness of 3D scaffold increased by oxygen plasma treatment had a positive effect on cell adhesion, proliferation, and differentiation. Furthermore, the differentiation of MC3T3-E1 cell was significantly enhanced by adding of n-HAp and β-TCP on 3D PLGA scaffold. As a result, combination of bioceramics and oxygen plasma treatment showed a synergistic effect on

  8. Pathway and Surface Mechanism Studies of 1,3-butadiene Selective Oxidation Over Vanadium-Molybdenum-Oxygen Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, William David [Iowa State Univ., Ames, IA (United States)

    2001-01-01

    The partial oxidation of 1,3-butadiene has been investigated over VMoO catalysts synthesized by sol-gel techniques. Surface areas were 9-14 m2/g, and compositions were within the solid solution regime, i.e. below 15.0 mol % MoO3/(MoO3 + V2O5). Laser Raman Spectroscopy and XRD data indicated that solid solutions were formed, and pre- and post-reaction XPS data indicated that catalyst surfaces contained some V+4 and were further reduced in 1,3-butadiene oxidation. A reaction pathway for 1,3-butadiene partial oxidation to maleic anhydride was shown to involve intermediates such as 3,4-epoxy-1-butene, crotonaldehyde, furan, and 2-butene-1,4-dial. The addition of water to the reaction stream substantially increased catalyst activity and improved selectivity to crotonaldehyde and furan at specific reaction temperatures. At higher water addition concentrations, furan selectivity increased from 12% to over 25%. The catalytic effects of water addition were related to competitive adsorption with various V2O5-based surface sites, including the vanadyl V=O, corner sharing V-O-V and edge sharing V-O oxygen. Higher levels of water addition were proposed to impose acidic character by dissociative adsorption. In addition, a novel combinatorial synthesis technique for VMoO was used to investigate the phase transitions of V2O5, solid solutions of Mo in V2O5, V9Mo6O40, and other reduced VMoO compounds, characterized by laser Raman spectroscopy. The natural composition gradient imposed by the sputter deposition apparatus was used to create VMoO arrays containing 225 samples ranging from 7.0-42 mol% MoO3/(V2O5 + MoO3), determined by EDS analysis.

  9. Effect of Adsorption on Ice Surfaces on the Composition of Enceladus' Plumes: Partitioning of Oxygen-Bearing Organics

    Science.gov (United States)

    Bouquet, A.; Teolis, B. D.; Waite, J. H., Jr.

    2017-12-01

    Introduction: The plumes of Enceladus offer an opportunity to access a sample of water from its internal ocean. However, to gain valuable insights into the ocean's composition, it is necessary to take into account any possible process that would alter the mixture between the water table and the geysers. The adsorption of refractory compounds on the ice walls in the vents could partition them depending on their properties. Evaluating the effect of this fractionation is critical in anticipating which organics could be detected by a future mission. Models: We used a model using the temkin isotherm and published experimental desorption energies for our compounds of interest. The model calculates how the coverage of an ice surface exposed to the flow can evolve with time and what is the final composition of the adsorbed mixture is. The model considers the ice walls and the ice grains, as the latter have the potential to gather the most sticky compounds and put them within reach of sampling by a spacecraft. Our list of species included formaldehyde, methanol, acetic acid, formic acid, ethanol, butanol, benzene and hexanal.Results: We found that simple hydrocarbons have a very short residence time on ice, and are expected to stay in gas phase. Oxygen-bearing organic compounds, though, stick to the ice and will be concentrated on the walls and ice grains, with the exception of formaldehyde. With the species listed above originally in equal abundance in gas phase, we found the ice surface to hold mostly formic acid, acetic acid and butanol, with a small amount of ethanol and hexanal. The high number of collisions in the closed space of a 1 meter wide vent allows for a gas/adsorbed equilibration within a second. Way forward: The possible impact of ammonia, detected in the plumes, is unknown. Ammonia can accumulate on the ice surface and influence adsorption of other species, and potentially create a liquid layer by depressing the freezing point of water. The impact of these

  10. Surface modification of carbon/epoxy prepreg using oxygen plasma and its effect on the delamination resistance behavior of carbon/epoxy composites

    International Nuclear Information System (INIS)

    Kim, M.H.; Rhee, K.Y.; Kim, H.J.; Jung, D.H.

    2007-01-01

    It was shown in previous study that the fracture toughness of carbon/epoxy laminated composites could be significantly improved by modifying the surface of the prepreg using Ar + irradiation in an oxygen environment. In this study, the surface of carbon/epoxy prepreg was modified using an oxygen plasma to improve the delamination resistance behavior of carbon/epoxy laminated composites. The variation of the contact angle on the prepreg surface was determined as a function of the modification time, in order to determine the optimal modification time. An XPS analysis was conducted to investigate the chemical changes on the surface of the prepreg caused by the plasma modification. Mode I delamination resistance curves of the composites with and without surface modification were plotted as a function of the delamination increment. The results showed that the contact angle varied from ∼64 o to ∼47 o depending on the modification time and reached a minimum for a modification time of 30 min. The XPS analysis showed that the hydrophilic carbonyl C=O group was formed by the oxygen plasma modification. The results also showed that the delamination resistance behavior was significantly improved by the plasma modification of the prepreg. This improvement was caused by the better layer-to-layer adhesion as well as increased interfacial strength between the fibers and matrix

  11. Optical lattices: Orbital dance

    Science.gov (United States)

    Lewenstein, Maciej; Liu, W. Vincent

    2011-02-01

    Emulating condensed-matter physics with ground-state atoms trapped in optical lattices has come a long way. But excite the atoms into higher orbital states, and a whole new world of exotic states appears.

  12. Root lattices and quasicrystals

    Science.gov (United States)

    Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.

    1990-10-01

    It is shown that root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All noncrystallographic symmetries observed so far are covered in minimal embedding with maximal symmetry.

  13. Angles in hyperbolic lattices

    DEFF Research Database (Denmark)

    Risager, Morten S.; Södergren, Carl Anders

    2017-01-01

    It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior of the den......It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior...... of the density function in both the small and large variable limits. This extends earlier results by Boca, Pasol, Popa and Zaharescu and Kelmer and Kontorovich in dimension 2 to general dimension n . Our proofs use the decay of matrix coefficients together with a number of careful estimates, and lead...

  14. MEETING: Lattice 88

    International Nuclear Information System (INIS)

    Mackenzie, Paul

    1989-01-01

    The forty-year dream of understanding the properties of the strongly interacting particles from first principles is now approaching reality. Quantum chromodynamics (QCD - the field theory of the quark and gluon constituents of strongly interacting particles) was initially handicapped by the severe limitations of the conventional (perturbation) approach in this picture, but Ken Wilson's inventions of lattice gauge theory and renormalization group methods opened new doors, making calculations of masses and other particle properties possible. Lattice gauge theory became a major industry around 1980, when Monte Carlo methods were introduced, and the first prototype calculations yielded qualitatively reasonable results. The promising developments over the past year were highlighted at the 1988 Symposium on Lattice Field Theory - Lattice 88 - held at Fermilab

  15. Automated Lattice Perturbation Theory

    Energy Technology Data Exchange (ETDEWEB)

    Monahan, Christopher

    2014-11-01

    I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.

  16. Permutohedral Lattice CNNs

    OpenAIRE

    Kiefel, Martin; Jampani, Varun; Gehler, Peter V.

    2014-01-01

    This paper presents a convolutional layer that is able to process sparse input features. As an example, for image recognition problems this allows an efficient filtering of signals that do not lie on a dense grid (like pixel position), but of more general features (such as color values). The presented algorithm makes use of the permutohedral lattice data structure. The permutohedral lattice was introduced to efficiently implement a bilateral filter, a commonly used image processing operation....

  17. Vortex lattices in layered superconductors

    International Nuclear Information System (INIS)

    Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

    1995-01-01

    We study vortex lattices in a superconductor--normal-metal superlattice in a parallel magnetic field. Distorted lattices, resulting from the shear deformations along the layers, are found to be unstable. Under field variation, nonequilibrium configurations undergo an infinite sequence of continuous transitions, typical for soft lattices. The equilibrium vortex arrangement is always a lattice of isocell triangles, without shear

  18. Adsorption and magnetism of bilayer graphene on the MnO polar surface with oxygen vacancies in the interface: First principles study

    Science.gov (United States)

    Ilyasov, Victor V.; Ershov, Igor V.; Popova, Inna G.; Pham, Khang D.; Nguyen, Chuong V.

    2018-05-01

    In this paper, we investigate systematically the structural, electronic, magnetic and adsorption properties of Bernal-stacked bilayer graphene on MnO(111) surface terminated by an oxygen atom, as a function of nonstoichiometric composition of the BLG/MnOx(111) interface. For additional functionalization of the BLG/MnOx(111) system, we also studied the adsorption properties of oxygen adsorbed on the BLG/MnOx(111) interface. Our results showed that the BLG is bound to the MnOx(111) substrate by the weak interaction for both spin-up and spin-down. Furthermore, we found that BLG adsorbed on the MnOx(111) substrate with a reduced oxygen symmetry in the interface is accompanied with a downshift of the Fermi level, which identifies the band structure of BLG as a p-type semiconductor. Upon interaction between BLG and MnOx(111) substrate, a forbidden gap of about 350 meV was opened between its bonding and antibonding π bands. A forbidden gap and the local magnetic moments in bilayer graphene can be controlled by changing the oxygen nonstoichometry or by oxygen adsorption. Additionally, magnetism has been predicted in the bilayer graphene adsorbed on the polar MnOx(111) surface with oxygen vacancies in the BLG/MnOx(111) interface, and its nature has also been discussed in this work. These results showed that the adsorption of bilayer graphene on the MnO(111) substrate can be used for developing novel generation of electronic and spintronic devices.

  19. Effect of oxygen and iodine on the optical and magnetic properties of fullerite C60

    Science.gov (United States)

    Bagrov, I. V.; Belousova, I. M.; Ermakov, A. V.; Kiselev, V. M.; Kislyakov, I. M.; Sosnov, E. N.

    2009-04-01

    The effect of oxygen and iodine on the optical and magnetic properties of fullerite C60 is studied by luminescence and EPR spectroscopy within widely varied experimental conditions (temperature of the medium, oxygen or buffer gas pressure, concentration of iodine vapor). It is demonstrated that the efficiency of the singlet oxygen formation when a fullerene sample is irradiated by a neodymium laser at a wavelength of 532 nm and the amplitude of the EPR signal emitted from the unirradiated sample are strongly affected by the concentrations of both oxygen and iodine vapor sorbed by the fullerene sample, as well as by its surface temperature. The spin-spin and spin-lattice relaxation times of paramagnetic centers in fullerite samples studied in the presence of molecular oxygen are determined by the method of microwave radiation absorption saturation.

  20. Local covering optimality of lattices: Leech lattice versus root lattice $E_8$

    NARCIS (Netherlands)

    A. Schuermann; F. Vallentin (Frank)

    2005-01-01

    textabstractWe show that the Leech lattice gives a sphere covering which is locally least dense among lattice coverings. We show that a similar result is false for the root lattice $E_8$. For this we construct a less dense covering lattice whose Delone subdivision has a common refinement with the

  1. CPT symmetry in honeycomb lattices and quantum brachistochrone problem

    Science.gov (United States)

    Yeşiltaş, Özlem

    2013-12-01

    In this paper, we have provided a matrix Hamiltonian model for honeycomb lattices and subsequently obtained the dispersion relation. Furthermore, we have constructed the C operator for the given non-Hermitian Hamiltonian model. The quadratic surfaces are sketched and the quantum Brachistochrone problem is discussed for the given honeycomb lattice model.

  2. Magnetism, Spin Texture, and In-Gap States: Atomic Specialization at the Surface of Oxygen-Deficient SrTiO_{3}.

    Science.gov (United States)

    Altmeyer, Michaela; Jeschke, Harald O; Hijano-Cubelos, Oliver; Martins, Cyril; Lechermann, Frank; Koepernik, Klaus; Santander-Syro, Andrés F; Rozenberg, Marcelo J; Valentí, Roser; Gabay, Marc

    2016-04-15

    Motivated by recent spin- and angular-resolved photoemission (SARPES) measurements of the two-dimensional electronic states confined near the (001) surface of oxygen-deficient SrTiO_{3}, we explore their spin structure by means of ab initio density functional theory (DFT) calculations of slabs. Relativistic nonmagnetic DFT calculations display Rashba-like spin winding with a splitting of a few meV and when surface magnetism on the Ti ions is included, bands become spin-split with an energy difference ∼100  meV at the Γ point, consistent with SARPES findings. While magnetism tends to suppress the effects of the relativistic Rashba interaction, signatures of it are still clearly visible in terms of complex spin textures. Furthermore, we observe an atomic specialization phenomenon, namely, two types of electronic contributions: one is from Ti atoms neighboring the oxygen vacancies that acquire rather large magnetic moments and mostly create in-gap states; another comes from the partly polarized t_{2g} itinerant electrons of Ti atoms lying further away from the oxygen vacancy, which form the two-dimensional electron system and are responsible for the Rashba spin winding and the spin splitting at the Fermi surface.

  3. Ionic Conductivity of Mesostructured Yttria-Stabilized Zirconia Thin Films with Cubic Pore Symmetry—On the Influence of Water on the Surface Oxygen Ion Transport.

    Science.gov (United States)

    Elm, Matthias T; Hofmann, Jonas D; Suchomski, Christian; Janek, Jürgen; Brezesinski, Torsten

    2015-06-10

    Thermally stable, ordered mesoporous thin films of 8 mol % yttria-stabilized zirconia (YSZ) were prepared by solution-phase coassembly of chloride salt precursors with an amphiphilic diblock copolymer using an evaporation-induced self-assembly process. The resulting material is of high quality and exhibits a well-defined three-dimensional network of pores averaging 24 nm in diameter after annealing at 600 °C for several hours. The wall structure is polycrystalline, with grains in the size range of 7 to 10 nm. Using impedance spectroscopy, the total electrical conductivity was measured between 200 and 500 °C under ambient atmosphere as well as in dry atmosphere for oxygen partial pressures ranging from 1 to 10(-4) bar. Similar to bulk YSZ, a constant ionic conductivity is observed over the whole oxygen partial pressure range investigated. In dry atmosphere, the sol-gel derived films have a much higher conductivity, with different activation energies for low and high temperatures. Overall, the results indicate a strong influence of the surface on the transport properties in cubic fluorite-type YSZ with high surface-to-volume ratio. A qualitative defect model which includes surface effects (annihilation of oxygen vacancies as a result of water adsorption) is proposed to explain the behavior and sensitivity of the conductivity to variations in the surrounding atmosphere.

  4. REVIEW ARTICLE: Oxygen diffusion and precipitation in Czochralski silicon

    Science.gov (United States)

    Newman, R. C.

    2000-06-01

    The objective of this article is to review our understanding of the properties of oxygen impurities in Czochralski silicon that is used to manufacture integrated circuits (ICs). These atoms, present at a concentration of ~1018 cm-3, occupy bond-centred sites (Oi) in as-grown Si and the jump rate between adjacent sites defines `normal' diffusion for the temperature range 1325 - 330 °C. Anneals at high temperatures lead to the formation of amorphous SiO2 precipitates that act as traps for fast diffusing metallic contaminants, such as Fe and Cu, that may be inadvertently introduced at levels as low as 1011 cm-3. Without this `gettering', there may be severe degradation of fabricated ICs. To accommodate the local volume increase during oxygen precipitation, there is parallel generation of self-interstitials that diffuse away and form lattice defects. High temperature (T > 700 °C) anneals are now well understood. Details of lower temperature processes are still a matter of debate: measurements of oxygen diffusion into or out of the Si surface and Oi atom aggregation have implied enhanced diffusion that has variously been attributed to interactions of Oi atoms with lattice vacancies, self-interstitials, metallic elements, carbon, hydrogen impurities etc. There is strong evidence for oxygen-hydrogen interactions at T continue to decrease as the size of future device features decreases below the lower end of the sub-micron range, currently close to 0.18 µm.

  5. Graphene antidot lattice waveguides

    DEFF Research Database (Denmark)

    Pedersen, Jesper Goor; Gunst, Tue; Markussen, Troels

    2012-01-01

    We introduce graphene antidot lattice waveguides: nanostructured graphene where a region of pristine graphene is sandwiched between regions of graphene antidot lattices. The band gaps in the surrounding antidot lattices enable localized states to emerge in the central waveguide region. We model...... the waveguides via a position-dependent mass term in the Dirac approximation of graphene and arrive at analytical results for the dispersion relation and spinor eigenstates of the localized waveguide modes. To include atomistic details we also use a tight-binding model, which is in excellent agreement...... with the analytical results. The waveguides resemble graphene nanoribbons, but without the particular properties of ribbons that emerge due to the details of the edge. We show that electrons can be guided through kinks without additional resistance and that transport through the waveguides is robust against...

  6. Investigation of the oxygen exchange mechanism on Pt|yttria stabilized zirconia at intermediate temperatures: Surface path versus bulk path.

    Science.gov (United States)

    Opitz, Alexander K; Lutz, Alexander; Kubicek, Markus; Kubel, Frank; Hutter, Herbert; Fleig, Jürgen

    2011-11-30

    The oxygen exchange kinetics of platinum on yttria-stabilized zirconia (YSZ) was investigated by means of geometrically well-defined Pt microelectrodes. By variation of electrode size and temperature it was possible to separate two temperature regimes with different geometry dependencies of the polarization resistance. At higher temperatures (550-700 °C) an elementary step located close to the three phase boundary (TPB) with an activation energy of ∼1.6 eV was identified as rate limiting. At lower temperatures (300-400 °C) the rate limiting elementary step is related to the electrode area and exhibited a very low activation energy in the order of 0.2 eV. From these observations two parallel pathways for electrochemical oxygen exchange are concluded.The nature of these two elementary steps is discussed in terms of equivalent circuits. Two combinations of parallel rate limiting reaction steps are found to explain the observed geometry dependencies: (i) Diffusion through an impurity phase at the TPB in parallel to diffusion of oxygen through platinum - most likely along Pt grain boundaries - as area-related process. (ii) Co-limitation of oxygen diffusion along the Pt|YSZ interface and charge transfer at the interface with a short decay length of the corresponding transmission line (as TPB-related process) in parallel to oxygen diffusion through platinum.

  7. Exact Lattice Supersymmetry

    Energy Technology Data Exchange (ETDEWEB)

    Catterall, Simon; Kaplan, David B.; Unsal, Mithat

    2009-03-31

    We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.

  8. δ-Doping of oxygen vacancies dictated by thermodynamics in epitaxial SrTiO3 films

    Directory of Open Access Journals (Sweden)

    Fengmiao Li

    2017-06-01

    Full Text Available Homoepitaxial SrTiO3(110 film is grown by molecular beam epitaxy in ultra-high vacuum with oxygen diffusing from substrate as the only oxidant. The resulted oxygen vacancies (VOs are found to be spatially confined within few subsurface layers only, forming a quasi-two-dimensional doped region with a tunable high concentration. Such a δ-function distribution of VOs is essentially determined by the thermodynamics associated with the surface reconstruction, and facilitated by the relatively high growth temperature. Our results demonstrate that it is feasible to tune VOs distribution at the atomic scale by controlling the lattice structure of oxide surfaces.

  9. Suppression of self-organized surface nanopatterning on GaSb/InAs multilayers induced by low energy oxygen ion bombardment by using simultaneously sample rotation and oxygen flooding

    Science.gov (United States)

    Beainy, Georges; Cerba, Tiphaine; Bassani, Franck; Martin, Mickaël; Baron, Thierry; Barnes, Jean-Paul

    2018-05-01

    Time of flight secondary ion mass spectrometry (ToF-SIMS) is a well-adapted analytical method for the chemical characterization of concentration profiles in layered or multilayered materials. However, under ion beam bombardment, initially smooth material surface becomes morphologically unstable. This leads to abnormal secondary ion yields and depth profile distortions. In this contribution, we explore the surface topography and roughening evolution induced by O2+ ion bombardment on GaSb/InAs multilayers. We demonstrate the formation of nanodots and ripples patterning according to the ion beam energy. Since the latter are undesirable for ToF-SIMS analysis, we managed to totally stop their growth by using simultaneously sample rotation and oxygen flooding. This unprecedented coupling between these two latter mechanisms leads to a significant enhancement in depth profiles resolution.

  10. The effect of V in La2Ni1-xVxO4+1.5x+delta on selective oxidative dehydrogenation of propane: Stabilization of lattice oxygen

    NARCIS (Netherlands)

    Crapanzano, S.D.; Babych, Igor V.; Lefferts, Leonardus

    2010-01-01

    In this study, the non-stoichiometric redox compounds La2NiO4+δ and La2Ni0.9V0.1O4.15+δ have been tested as an oxidant in selective oxidation of propane in pulse experiments at temperatures between 450 and 650 °C. The oxygen contents in the samples at different temperatures were calculated based on

  11. Lattice-Strain Control of the Activity in Dealloyed Core-Shell Fuel Cell Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Strasser, P. [Berlin Institute of Technology (Technische Universitat Berlin); Koh, Shirlaine [University of Houston, Houston; Anniyev, Toyli [SLAC National Accelerator Laboratory; Greeley, Jeff [Argonne National Laboratory (ANL); More, Karren Leslie [ORNL; Yu, Chengfei [University of Houston, Houston; Liu, Zengcai [University of Houston, Houston; Kaya, Sarpa [SLAC National Accelerator Laboratory; Nordlund, Dennis [SLAC National Accelerator Laboratory; Ogasawara, Hirohito [SLAC National Accelerator Laboratory; Toney, Michael F. [SLAC National Accelerator Laboratory; Anders, Nilsson [SLAC National Accelerator Laboratory

    2010-01-01

    Electrocatalysis will play a key role in future energy conversion and storage technologies, such as water electrolysers, fuel cells and metal-air batteries. Molecular interactions between chemical reactants and the catalytic surface control the activity and efficiency, and hence need to be optimized; however, generalized experimental strategies to do so are scarce. Here we show how lattice strain can be used experimentally to tune the catalytic activity of dealloyed bimetallic nanoparticles for the oxygen-reduction reaction, a key barrier to the application of fuel cells and metal-air batteries. We demonstrate the core-shell structure of the catalyst and clarify the mechanistic origin of its activity. The platinum-rich shell exhibits compressive strain, which results in a shift of the electronic band structure of platinum and weakening chemisorption of oxygenated species. We combine synthesis, measurements and an understanding of strain from theory to generate a reactivity-strain relationship that provides guidelines for tuning electrocatalytic activity.

  12. Lattice-Strain Control of the Activity in Dealloyed Core-Shell Fuel Cell Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Strasser, Peter; Shirlaine, Koh; Anniyev, Toyli; Greeley, Jeffrey P.; More, Karren L.; Yu, Chengfei; Liu, Zengcai; Kaya, Sarp; Nordlund, Dennis; Ogasawara, Hirohito; Toney, Michael F.; Nilsson, Anders R.

    2010-04-30

    Electrocatalysis will play a key role in future energy conversion and storage technologies, such as water electrolysers, fuel cells and metal–air batteries. Molecular interactions between chemical reactants and the catalytic surface control the activity and efficiency, and hence need to be optimized; however, generalized experimental strategies to do so are scarce. Here we show how lattice strain can be used experimentally to tune the catalytic activity of dealloyed bimetallic nanoparticles for the oxygen-reduction reaction, a key barrier to the application of fuel cells and metal–air batteries. We demonstrate the core–shell structure of the catalyst and clarify the mechanistic origin of its activity. The platinum-rich shell exhibits compressive strain, which results in a shift of the electronic band structure of platinum and weakening chemisorption of oxygenated species. We combine synthesis, measurements and an understanding of strain from theory to generate a reactivity–strain relationship that provides guidelines for tuning electrocatalytic activity.

  13. Lattice-Strain Control of Exceptional Activity in Dealloyed Core-Shell Fuel Cell Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Strasser, Peter

    2011-08-19

    We present a combined experimental and theoretical approach to demonstrate how lattice strain can be used to continuously tune the catalytic activity of the oxygen reduction reaction (ORR) on bimetallic nanoparticles that have been dealloyed. The sluggish kinetics of the ORR is a key barrier to the adaptation of fuel cells and currently limits their widespread use. Dealloyed Pt-Cu bimetallic nanoparticles, however, have been shown to exhibit uniquely high reactivity for this reaction. We first present evidence for the formation of a core-shell structure during dealloying, which involves removal of Cu from the surface and subsurface of the precursor nanoparticles. We then show that the resulting Pt-rich surface shell exhibits compressive strain that depends on the composition of the precursor alloy. We next demonstrate the existence of a downward shift of the Pt d-band, resulting in weakening of the bond strength of intermediate oxygenated species due to strain. Finally, we combine synthesis, strain, and catalytic reactivity in an experimental/theoretical reactivity-strain relationship which provides guidelines for the rational design of strained oxygen reduction electrocatalysts. The stoichiometry of the precursor, together with the dealloying conditions, provides experimental control over the resulting surface strain and thereby allows continuous tuning of the surface electrocatalytic reactivity - a concept that can be generalized to other catalytic reactions.

  14. The influence of surface oxygen and hydroxyl groups on the dehydrogenation of ethylene, acetic acid and hydrogenated vinyl acetate on pure Pd(1 0 0): A DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yanping [Key Laboratory for Green Chemical Technology of Ministry of Education, R& D Center for Petrochemical Technology, Tianjin University, Tianjin (China); Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072 (China); Dong, Xiuqin [Key Laboratory for Green Chemical Technology of Ministry of Education, R& D Center for Petrochemical Technology, Tianjin University, Tianjin (China); Yu, Yingzhe, E-mail: yzhyu@tju.edu.cn [Key Laboratory for Green Chemical Technology of Ministry of Education, R& D Center for Petrochemical Technology, Tianjin University, Tianjin (China); Zhang, Minhua, E-mail: mhzhangtj@163.com [Key Laboratory for Green Chemical Technology of Ministry of Education, R& D Center for Petrochemical Technology, Tianjin University, Tianjin (China)

    2016-12-01

    Highlights: • All dehydrogenation reactions in vinyl acetate synthesis on Pd(1 0 0) were studied. • The energy barriers of the transition state of the three reactions were calculated. • The influence of surface Os and OHs on all dehydrogenation actions was discussed. - Abstract: On the basis of a Langmuir–Hinshelwood-type mechanism, the dehydrogenation of ethylene, acetic acid and hydrogenated vinyl acetate (VAH) on pure Pd(1 0 0) with surface oxygen atoms (Os) and hydroxyl groups (OHs) was studied with density functional theory (DFT) method. Our calculation results show that both Os and OHs can consistently reduce the activation energies of dehydrogenation of ethylene, acetic acid and VAH to some degree with only one exception that OHs somehow increase the activation energy of VAH. Based on Langmuir–Hinshelwood mechanism, the three dehydrogenation reactions in presence of surface Os and OHs are almost consistently favored, compared with the corresponding processes on clean Pd(1 0 0) surfaces, and thus a Langmuir–Hinshelwood-type mechanism may not be excluded beforehand when investigating the microscopic performance of the oxygen-assisted vinyl acetate synthesis on Pd(1 0 0) catalysts.

  15. Towards a highly-efficient fuel-cell catalyst: optimization of Pt particle size, supports and surface-oxygen group concentration.

    Science.gov (United States)

    Muthuswamy, Navaneethan; de la Fuente, Jose Luis Gomez; Ochal, Piotr; Giri, Rajiv; Raaen, Steinar; Sunde, Svein; Rønning, Magnus; Chen, De

    2013-03-21

    In the present work, methanol oxidation reaction was investigated on Pt particles of various diameters on carbon-nanofibers and carbon-black supports with different surface-oxygen concentrations, aiming for a better understanding of the relationship between the catalyst properties and the electrochemical performance. The pre-synthesized Pt nanoparticles in ethylene glycol, prepared by the polyol method without using any capping agents, were deposited on different carbon supports. Removal of oxygen-groups from the carbon supports had profound positive effects on not only the Pt dispersion but also the specific activity. The edge structures on the stacked graphene sheets in the platelet carbon-nanofibers provided a strong interaction with the Pt particles, significantly reconstructing them in the process. Such reconstruction resulted in the formation of more plated Pt particles on the CNF than on the carbon-black and exposure of more Pt atoms with relatively high co-ordination numbers, and thereby higher specific activity. Owing to the combined advantages of optimum Pt particle diameter, an oxygen-free surface and the unique properties of CNFs, Pt supported on heat-treated CNFs exhibited a higher mass activity twice of that of its commercial counterpart.

  16. Gold nanoring-enhanced generation of singlet oxygen: an intricate correlation with surface plasmon resonance and polyelectrolyte bilayers

    Czech Academy of Sciences Publication Activity Database

    Hu, Y.; Kaňka, Jiří; Liu, K.; Yang, Y.; Wang, H.; Du, H.

    2016-01-01

    Roč. 6, č. 106 (2016), s. 104819-104826 ISSN 2046-2069 R&D Projects: GA ČR(CZ) GBP205/12/G118 Institutional support: RVO:67985882 Keywords : Singlet oxygen * Fluorescence * Gold nanorings Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 3.108, year: 2016

  17. Shaken Lattice Interferometry

    Science.gov (United States)

    Weidner, Carrie; Yu, Hoon; Anderson, Dana

    2015-05-01

    This work introduces a method to perform interferometry using atoms trapped in an optical lattice. Starting at t = 0 with atoms in the ground state of a lattice potential V(x) =V0cos [ 2 kx + ϕ(t) ] , we show that it is possible to transform from one atomic wavefunction to another by a prescribed shaking of the lattice, i.e., by an appropriately tailored time-dependent phase shift ϕ(t) . In particular, the standard interferometer sequence of beam splitting, propagation, reflection, reverse propagation, and recombination can be achieved via a set of phase modulation operations {ϕj(t) } . Each ϕj(t) is determined using a learning algorithm, and the split-step method calculates the wavefunction dynamics. We have numerically demonstrated an interferometer in which the shaken wavefunctions match the target states to better than 1 % . We carried out learning using a genetic algorithm and optimal control techniques. The atoms remain trapped in the lattice throughout the full interferometer sequence. Thus, the approach may be suitable for use in an dynamic environment. In addition to the general principles, we discuss aspects of the experimental implementation. Supported by the Office of Naval Research (ONR) and Northrop Grumman.

  18. Lattice Multiverse Models

    OpenAIRE

    Williamson, S. Gill

    2010-01-01

    Will the cosmological multiverse, when described mathematically, have easily stated properties that are impossible to prove or disprove using mathematical physics? We explore this question by constructing lattice multiverses which exhibit such behavior even though they are much simpler mathematically than any likely cosmological multiverse.

  19. Gravitinos on the lattice

    Energy Technology Data Exchange (ETDEWEB)

    Maturana, G.; Vanden Doel, C.P. (California Univ., Santa Cruz (USA). Physics Dept.)

    1983-04-07

    We study spin 3/2 fields on the lattice. Species doubling is found to be totally curable with an analogue of Wilson's method and partially with an analogue of the Kogut-Susskind formalism. Only the latter preserves local supersymmetry but describes at least four species.

  20. Elastic lattice polymers

    NARCIS (Netherlands)

    Baiesi, M.; Barkema, G.T.; Carlon, E.

    2010-01-01

    We study a model of “elastic” lattice polymer in which a fixed number of monomers m is hosted by a self-avoiding walk with fluctuating length l. We show that the stored length density m 1− l /m scales asymptotically for large m as m= 1− /m+. . . , where is the polymer entropic exponent, so that can

  1. Quarks, gluons and lattices

    International Nuclear Information System (INIS)

    Krojts, M.

    1987-01-01

    The book by the known american physicist-theoretist M.Kreuts represents the first monography in world literature, where a new perspective direction in elementary particle physics and quantum field theory - lattice formulation of gauge theories is stated systematically. Practically all main ideas of this direction are given. Material is stated in systematic and understandable form

  2. Lattices for antiproton rings

    International Nuclear Information System (INIS)

    Autin, B.

    1984-01-01

    After a description of the constraints imposed by the cooling of Antiprotons on the lattice of the rings, the reasons which motivate the shape and the structure of these machines are surveyed. Linear and non-linear beam optics properties are treated with a special amplification to the Antiproton Accumulator. (orig.)

  3. lattice gauge theory

    Indian Academy of Sciences (India)

    activities in non-perturbative QCD. Keywords. Deflation; overlap operator; GPU; CUDA. PACS Nos 11.15.Ha; 12.38.-t. 1. Introduction. The lattice gauge theory subgroup of the working group in non-perturbative QCD consisted of Mridupavan Deka, Sourendu Gupta, N D Hari Dass, Rajarshi Roy, Sayantan Sharma and.

  4. Noetherian and Artinian Lattices

    Directory of Open Access Journals (Sweden)

    Derya Keskin Tütüncü

    2012-01-01

    Full Text Available It is proved that if L is a complete modular lattice which is compactly generated, then Rad(L/0 is Artinian if, and only if for every small element a of L, the sublattice a/0 is Artinian if, and only if L satisfies DCC on small elements.

  5. Decidability in Orthomodular Lattices

    Science.gov (United States)

    Hyčko, Marek; Navara, Mirko

    2005-12-01

    We discuss the possibility of automatic simplification of formulas in orthomodular lattices. We describe the principles of a program which decides the validity of equalities and inequalities, as well as implications between them and other important relations significant in quantum mechanics.

  6. Oxygen Therapy

    Science.gov (United States)

    ... best for you. Oxygen is usually delivered through nasal prongs (an oxygen cannula) or a face mask. Oxygen equipment can attach to other medical equipment such as CPAP machines and ventilators. Oxygen therapy can help you ...

  7. "Kinetics of the adsorption of atomic oxygen (N2O) on the Si(001)2x1 surface as revealed by the change in the surface conductance"

    NARCIS (Netherlands)

    Wormeester, Herbert; Keim, Enrico G.; van Silfhout, Arend

    1992-01-01

    The adsorption behaviour of N2O on the Si(001)2 × 1 surface at 300 K substrate temperature has been investigated by measuring in situ the surface conductance during the reaction process. For comparison we monitored in the same way the adsorption of O2 on the same surface which ultimately leads to

  8. Conical diffraction in honeycomb lattices

    International Nuclear Information System (INIS)

    Ablowitz, Mark J.; Nixon, Sean D.; Zhu Yi

    2009-01-01

    Conical diffraction in honeycomb lattices is analyzed. This phenomenon arises in nonlinear Schroedinger equations with honeycomb lattice potentials. In the tight-binding approximation the wave envelope is governed by a nonlinear classical Dirac equation. Numerical simulations show that the Dirac equation and the lattice equation have the same conical diffraction properties. Similar conical diffraction occurs in both the linear and nonlinear regimes. The Dirac system reveals the underlying mechanism for the existence of conical diffraction in honeycomb lattices.

  9. Dissolved inorganic carbon, pH, oxygen, and other variables collected from surface discrete and surface underway observations using flow-through pump from NOAA Ship Gordon Gunter off the U.S. East Coast during the East Coast Ocean Acidification (ECOA) Cruise from 2015-06-19 to 2015-07-24 (NCEI Accession 0157485)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This archival package contains dissolved inorganic carbon, pH, oxygen, and other variables collected from surface discrete and surface underway observations during...

  10. Acceptor-oxygen vacancy defect dipoles and fully coordinated defect centers in a ferroelectric perovskite lattice: Electron paramagnetic resonance analysis of Mn2+ in single crystal BaTiO3

    Science.gov (United States)

    Maier, R. A.; Pomorski, T. A.; Lenahan, P. M.; Randall, C. A.

    2015-10-01

    Defect dipoles are significant point defects in perovskite oxides as a result of their impact on oxygen vacancy dynamics. Electron paramagnetic resonance (EPR) was used to investigate the local defect structure of single crystal BaTiO3 doped with manganese. These results, along with a re-analysis of literature data, do not support the conclusion that transition metal-oxygen vacancy nearest neighbor defect dipoles ( M nT i ″ - VO • • ) × in ferroelectric BaTiO3 are majority defect centers as previously reported. Local symmetry analysis of the zero-field splitting term of the spin Hamiltonian supports the assignment of fully coordinated defect centers as opposed to defect dipoles for resonance signals at geff ˜ 2. A newly discovered defect center with g⊥ ˜ 6 is observed in the manganese doped system, and it is argued that this defect center belongs to an associated defect complex or defect dipole. This newly reported strong axial defect center, however, is present in small, minor concentrations compared to the well-known Mn2+ center with zero-field splitting of D ˜ 645 MHz. In regard to relative concentration, it is concluded that the dominant point defect related to the Mn2+ ion doped in BaTiO3 corresponds to B-site substitution with six nearest neighbor anions in octahedral coordination.

  11. Basis reduction for layered lattices

    NARCIS (Netherlands)

    Torreão Dassen, Erwin

    2011-01-01

    We develop the theory of layered Euclidean spaces and layered lattices. We present algorithms to compute both Gram-Schmidt and reduced bases in this generalized setting. A layered lattice can be seen as lattices where certain directions have infinite weight. It can also be

  12. Basis reduction for layered lattices

    NARCIS (Netherlands)

    E.L. Torreão Dassen (Erwin)

    2011-01-01

    htmlabstractWe develop the theory of layered Euclidean spaces and layered lattices. With this new theory certain problems that usually are solved by using classical lattices with a "weighting" gain a new, more natural form. Using the layered lattice basis reduction algorithms introduced here these

  13. Dimers and the Critical Ising Model on lattices of genus >1

    International Nuclear Information System (INIS)

    Costa-Santos, Ruben; McCoy, B.M.

    2002-01-01

    We study the partition function of both Close-Packed Dimers and the Critical Ising Model on a square lattice embedded on a genus two surface. Using numerical and analytical methods we show that the determinants of the Kasteleyn adjacency matrices have a dependence on the boundary conditions that, for large lattice size, can be expressed in terms of genus two theta functions. The period matrix characterizing the continuum limit of the lattice is computed using a discrete holomorphic structure. These results relate in a direct way the lattice combinatorics with conformal field theory, providing new insight to the lattice regularization of conformal field theories on higher genus Riemann surfaces

  14. Enhanced Cyclability of Lithium-Oxygen Batteries with Electrodes Protected by Surface Films Induced via In-Situ Electrochemical Process

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Bin; Xu, Wu; Tao, Jinhui; Yan, Pengfei; Zheng, Jianming; Engelhard, Mark H.; Lu, Dongping; Wang, Chongmin; Zhang, Jiguang

    2018-04-16

    Although the rechargeable lithium-oxygen (Li-O2) batteries have extremely high theoretical specific energy, the practical application of these batteries is still limited by the instability of their carbon-based air-electrode, Li metal anode, and electrolytes towards reduced oxygen species. Here we demonstrate a simple one-step in-situ electrochemical pre-charging strategy to generate thin protective films on both carbon nanotubes (CNTs) air-electrode and Li metal anode simultaneously under an inert atmosphere. Li-O2 cells after such pre-treatment demonstrate significantly extended cycle life of 110 and 180 cycles under the capacity-limited protocol of 1000 mAh g-1 and 500 mAh g-1, respectively, which is far more than those without pre-treatment. The thin-films formed from decomposition of electrolyte during in-situ electrochemical pre-charging process in an inert environment can protect both CNTs air-electrode and Li metal anode prior to conventional Li-O2 discharge/charge cycling where reactive reduced oxygen species are formed. This work provides a new approach for protections of carbon-based air-electrode and Li metal anode in practical Li-O2 batteries, and may also be applied to other battery systems.

  15. Stable isotopes of hydrogen and oxygen in surface water and ground water at selected sites on or near the Idaho National Engineering Laboratory, Idaho

    International Nuclear Information System (INIS)

    Ott, D.S.; Cecil, L.D.; Knobel, L.L.

    1994-01-01

    Relative stable isotopic ratios for hydrogen and oxygen compared to standard mean ocean water are presented for water from 4 surface-water sites and 38 ground-water sites on or near the Idaho National Engineering Laboratory (INEL). The surface-water samples were collected monthly from March 1991 through April 1992 and after a storm event on June 18, 1992. The ground-water samples either were collected during 1991 or 1992. These data were collected as part of the US Geological Survey's continuing hydrogeological investigations at the INEL. The relative isotopic ratios of hydrogen and oxygen are reported as delta 2 H (δ 2 H) and as delta 18 O (δ 18 O), respectively. The values of δ 2 H and δ 18 O in water from the four surface-water sites ranged from -143.0 to -122 and from -18.75 to -15.55, respectively. The values of δ 2 H and δ 18 O in water from the 38 ground-water sites ranged from -141.0 to -120.0 and from -18.55 to -14.95, respectively

  16. The Materials Chemistry of Atomic Oxygen with Applications to Anisotropic Etching of Submicron Structures in Microelectronics and the Surface Chemistry Engineering of Porous Solids

    Science.gov (United States)

    Koontz, Steve L.; Leger, Lubert J.; Wu, Corina; Cross, Jon B.; Jurgensen, Charles W.

    1994-01-01

    Neutral atomic oxygen is the most abundant component of the ionospheric plasma in the low Earth orbit environment (LEO; 200 to 700 kilometers altitude) and can produce significant degradation of some spacecraft materials. In order to produce a more complete understanding of the materials chemistry of atomic oxygen, the chemistry and physics of O-atom interactions with materials were determined in three radically different environments: (1) The Space Shuttle cargo bay in low Earth orbit (the EOIM-3 space flight experiment), (2) a high-velocity neutral atom beam system (HVAB) at Los Alamos National Laboratory (LANL), and (3) a microwave-plasma flowing-discharge system at JSC. The Space Shuttle and the high velocity atom beam systems produce atom-surface collision energies ranging from 0.1 to 7 eV (hyperthermal atoms) under high-vacuum conditions, while the flowing discharge system produces a 0.065 eV surface collision energy at a total pressure of 2 Torr. Data obtained in the three different O-atom environments referred to above show that the rate of O-atom reaction with polymeric materials is strongly dependent on atom kinetic energy, obeying a reactive scattering law which suggests that atom kinetic energy is directly available for overcoming activation barriers in the reaction. General relationships between polymer reactivity with O atoms and polymer composition and molecular structure have been determined. In addition, vacuum ultraviolet photochemical effects have been shown to dominate the reaction of O atoms with fluorocarbon polymers. Finally, studies of the materials chemistry of O atoms have produced results which may be of interest to technologists outside the aerospace industry. Atomic oxygen 'spin-off' or 'dual use' technologies in the areas of anisotropic etching in microelectronic materials and device processing, as well as surface chemistry engineering of porous solid materials are described.

  17. An alternative lattice field theory formulation inspired by lattice supersymmetry

    Science.gov (United States)

    D'Adda, Alessandro; Kawamoto, Noboru; Saito, Jun

    2017-12-01

    We propose an unconventional formulation of lattice field theories which is quite general, although originally motivated by the quest of exact lattice supersymmetry. Two long standing problems have a solution in this context: 1) Each degree of freedom on the lattice corresponds to 2 d degrees of freedom in the continuum, but all these doublers have (in the case of fermions) the same chirality and can be either identified, thus removing the degeneracy, or, in some theories with extended supersymmetry, identified with different members of the same supermultiplet. 2) The derivative operator, defined on the lattice as a suitable periodic function of the lattice momentum, is an addittive and conserved quantity, thus assuring that the Leibniz rule is satisfied. This implies that the product of two fields on the lattice is replaced by a non-local "star product" which is however in general non-associative. Associativity of the "star product" poses strong restrictions on the form of the lattice derivative operator (which becomes the inverse Gudermannian function of the lattice momentum) and has the consequence that the degrees of freedom of the lattice theory and of the continuum theory are in one-to-one correspondence, so that the two theories are eventually equivalent. We can show that the non-local star product of the fields effectively turns into a local one in the continuum limit. Regularization of the ultraviolet divergences on the lattice is not associated to the lattice spacing, which does not act as a regulator, but may be obtained by a one parameter deformation of the lattice derivative, thus preserving the lattice structure even in the limit of infinite momentum cutoff. However this regularization breaks gauge invariance and a gauge invariant regularization within the lattice formulation is still lacking.

  18. Lattice QCD for cosmology

    International Nuclear Information System (INIS)

    Borsanyi, Sz.; Kampert, K.H.; Fodor, Z.; Forschungszentrum Juelich; Eoetvoes Univ., Budapest

    2016-06-01

    We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to the MeV scale we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (χ) up to the few GeV temperature region. These two results, EoS and χ, can be used to predict the dark matter axion's mass in the post-inflation scenario and/or give the relationship between the axion's mass and the universal axionic angle, which acts as a initial condition of our universe.

  19. Datagrids for lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Buechner, O. [Zentralinstitut fuer Angewandte Mathematik ZAM, 52425 Juelich (Germany); Ernst, M. [Deutsches Elektronen-Synchrotron DESY, 22603 Hamburg (Germany); Jansen, K. [John von Neumann-Institut fuer Computing NIC/DESY, 15738 Zeuthen (Germany); Lippert, Th. [Zentralinstitut fuer Angewandte Mathematik ZAM, 52425 Juelich (Germany); Melkumyan, D. [Deutsches Elektronen-Synchrotron DESY, 15738 Zeuthen (Germany); Orth, B. [Zentralinstitut fuer Angewandte Mathematik ZAM, 52425 Juelich (Germany); Pleiter, D. [John von Neumann-Institut fuer Computing NIC/DESY, 15738 Zeuthen (Germany)]. E-mail: dirk.pleiter@desy.de; Stueben, H. [Konrad-Zuse-Institut fuer Informationstechnik ZIB, 14195 Berlin (Germany); Wegner, P. [Deutsches Elektronen-Synchrotron DESY, 15738 Zeuthen (Germany); Wollny, S. [Konrad-Zuse-Institut fuer Informationstechnik ZIB, 14195 Berlin (Germany)

    2006-04-01

    As the need for computing resources to carry out numerical simulations of Quantum Chromodynamics (QCD) formulated on a lattice has increased significantly, efficient use of the generated data has become a major concern. To improve on this, groups plan to share their configurations on a worldwide level within the International Lattice DataGrid (ILDG). Doing so requires standardized description of the configurations, standards on binary file formats and common middleware interfaces. We describe the requirements and problems, and discuss solutions. Furthermore, an overview is given on the implementation of the LatFor DataGrid [http://www-zeuthen.desy.de/latfor/ldg], a France/German/Italian grid that will be one of the regional grids within the ILDG grid-of-grids concept.

  20. Introduction to lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, R.

    1998-12-31

    The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.

  1. Varieties of lattices

    CERN Document Server

    Jipsen, Peter

    1992-01-01

    The study of lattice varieties is a field that has experienced rapid growth in the last 30 years, but many of the interesting and deep results discovered in that period have so far only appeared in research papers. The aim of this monograph is to present the main results about modular and nonmodular varieties, equational bases and the amalgamation property in a uniform way. The first chapter covers preliminaries that make the material accessible to anyone who has had an introductory course in universal algebra. Each subsequent chapter begins with a short historical introduction which sites the original references and then presents the results with complete proofs (in nearly all cases). Numerous diagrams illustrate the beauty of lattice theory and aid in the visualization of many proofs. An extensive index and bibliography also make the monograph a useful reference work.

  2. Lattices of dielectric resonators

    CERN Document Server

    Trubin, Alexander

    2016-01-01

    This book provides the analytical theory of complex systems composed of a large number of high-Q dielectric resonators. Spherical and cylindrical dielectric resonators with inferior and also whispering gallery oscillations allocated in various lattices are considered. A new approach to S-matrix parameter calculations based on perturbation theory of Maxwell equations, developed for a number of high-Q dielectric bodies, is introduced. All physical relationships are obtained in analytical form and are suitable for further computations. Essential attention is given to a new unified formalism of the description of scattering processes. The general scattering task for coupled eigen oscillations of the whole system of dielectric resonators is described. The equations for the  expansion coefficients are explained in an applicable way. The temporal Green functions for the dielectric resonator are presented. The scattering process of short pulses in dielectric filter structures, dielectric antennas  and lattices of d...

  3. Light water lattices

    International Nuclear Information System (INIS)

    1962-01-01

    The panel was attended by prominent physicists from most of the well-known laboratories in the field of light-water lattices, who exchanged the latest information on the status of work in their countries and discussed both the theoretical and the experimental aspects of the subjects. The supporting papers covered most problems, including criticality, resonance absorption, thermal utilization, spectrum calculations and the physics of plutonium bearing systems. Refs, figs and tabs

  4. Computing: Lattice work

    International Nuclear Information System (INIS)

    Bowler, Ken

    1990-01-01

    One of the major recent developments in particle theory has been the use of very high performance computers to obtain approximate numerical solutions of quantum field theories by formulating them on a finite space-time lattice. The great virtue of this new technique is that it avoids the straitjacket of perturbation theory and can thus attack new, but very fundamental problems, such as the calculation of hadron masses in quark-gluon field theory (quantum chromodynamics - QCD)

  5. Automated lattice data generation

    Directory of Open Access Journals (Sweden)

    Ayyar Venkitesh

    2018-01-01

    Full Text Available The process of generating ensembles of gauge configurations (and measuring various observables over them can be tedious and error-prone when done “by hand”. In practice, most of this procedure can be automated with the use of a workflow manager. We discuss how this automation can be accomplished using Taxi, a minimal Python-based workflow manager built for generating lattice data. We present a case study demonstrating this technology.

  6. Dissociation of N{sub 2}O on anatase TiO{sub 2} (001) surface – The effect of oxygen vacancy and presence of Ag cluster

    Energy Technology Data Exchange (ETDEWEB)

    Sowmiya, M.; Senthilkumar, K., E-mail: ksenthil@buc.edu.in

    2016-12-15

    Highlights: • This study elucidates the dissociation of N{sub 2}O on anatase TiO{sub 2} (001) surface. • N{sub 2}O is decomposed into N{sub 2} and O on reduced TiO{sub 2} even in the presence of Ag cluster. • Excess charge in reduced TiO{sub 2} surface is transferred to the adsorbed N{sub 2}O molecule. • The vibrational frequency analysis also performed to study the dissociation of N{sub 2}O. • Anatase TiO{sub 2} with oxygen vacancies is a suitable catalyst for decomposition of N{sub 2}O. - Abstract: The increase in concentration of nitrous oxide (N{sub 2}O) in the atmosphere is one of the major contributors to the greenhouse effect, ozone depletion and climate change. Therefore, it is important to decompose harmful N{sub 2}O molecule into harmless N{sub 2}. In the present work, we have studied the decomposition of N{sub 2}O on anatase TiO{sub 2} (001) surface using first principle calculations. The results indicates that the N{sub 2}O molecule is physisorbed on perfect TiO{sub 2} surface without any dissociation, and is dissociated into N{sub 2} and oxygen on the reduced TiO{sub 2} surface. In addition, it has been found that the interaction between N{sub 2}O and TiO{sub 2} is augmented by the presence of Ag cluster on anatase (001) surface. On the basis of Bader charge analysis and electron density difference plot, it has been found that the excess charge in the reduced anatase TiO{sub 2} (001) surface is transferred to the adsorbed N{sub 2}O molecule, which results the weakening of N–O bond of N{sub 2}O followed by the decomposition of N{sub 2}O into N{sub 2} and O. Vibrational frequency analysis also performed to confirm the decomposition of N{sub 2}O molecule. From the pathway for N{sub 2}O dissociation on reduced TiO{sub 2} and Ag/TiO{sub 2} surfaces, it has been observed that the dissociation reaction of N{sub 2}O on TiO{sub 2} surface is highly exothermic with activation energy barrier of 0.25 eV. The results presented in this work show that the

  7. Robots and lattice automata

    CERN Document Server

    Adamatzky, Andrew

    2015-01-01

    The book gives a comprehensive overview of the state-of-the-art research and engineering in theory and application of Lattice Automata in design and control of autonomous Robots. Automata and robots share the same notional meaning. Automata (originated from the latinization of the Greek word “αυτόματον”) as self-operating autonomous machines invented from ancient years can be easily considered the first steps of robotic-like efforts. Automata are mathematical models of Robots and also they are integral parts of robotic control systems. A Lattice Automaton is a regular array or a collective of finite state machines, or automata. The Automata update their states by the same rules depending on states of their immediate neighbours. In the context of this book, Lattice Automata are used in developing modular reconfigurable robotic systems, path planning and map exploration for robots, as robot controllers, synchronisation of robot collectives, robot vision, parallel robotic actuators. All chapters are...

  8. Dielectric lattice gauge theory

    International Nuclear Information System (INIS)

    Mack, G.

    1983-06-01

    Dielectric lattice gauge theory models are introduced. They involve variables PHI(b)epsilong that are attached to the links b = (x+esub(μ),x) of the lattice and take their values in the linear space g which consists of real linear combinations of matrices in the gauge group G. The polar decomposition PHI(b)=U(b)osub(μ)(x) specifies an ordinary lattice gauge field U(b) and a kind of dielectric field epsilonsub(ij)proportionalosub(i)osub(j)sup(*)deltasub(ij). A gauge invariant positive semidefinite kinetic term for the PHI-field is found, and it is shown how to incorporate Wilson fermions in a way which preserves Osterwalder Schrader positivity. Theories with G = SU(2) and without matter fields are studied in some detail. It is proved that confinement holds, in the sense that Wilson loop expectation values show an area law decay, if the Euclidean action has certain qualitative features which imply that PHI = 0 (i.e. dielectric field identical 0) is the unique maximum of the action. (orig.)

  9. N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction

    Science.gov (United States)

    Rana, Moumita; Arora, Gunjan; Gautam, Ujjal K.

    2015-02-01

    Highly stable, cost-effective electrocatalysts facilitating oxygen reduction are crucial for the commercialization of membrane-based fuel cell and battery technologies. Herein, we demonstrate that protein-rich soya chunks with a high content of N, S and P atoms are an excellent precursor for heteroatom-doped highly graphitized carbon materials. The materials are nanoporous, with a surface area exceeding 1000 m2 g-1, and they are tunable in doping quantities. These materials exhibit highly efficient catalytic performance toward oxygen reduction reaction (ORR) with an onset potential of -0.045 V and a half-wave potential of -0.211 V (versus a saturated calomel electrode) in a basic medium, which is comparable to commercial Pt catalysts and is better than other recently developed metal-free carbon-based catalysts. These exhibit complete methanol tolerance and a performance degradation of merely ˜5% as compared to ˜14% for a commercial Pt/C catalyst after continuous use for 3000 s at the highest reduction current. We found that the fraction of graphitic N increases at a higher graphitization temperature, leading to the near complete reduction of oxygen. It is believed that due to the easy availability of the precursor and the possibility of genetic engineering to homogeneously control the heteroatom distribution, the synthetic strategy is easily scalable, with further improvement in performance.

  10. Toward lattice fractional vector calculus

    Science.gov (United States)

    Tarasov, Vasily E.

    2014-09-01

    An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity.

  11. Diffraction experiments of argon or helium on polluted surfaces

    International Nuclear Information System (INIS)

    Berthier, J.P.; Constans, A.; Daury, G.; Lostis, P.

    1975-01-01

    Scattering patterns of molecular beams of argon or helium from metal surfaces (bulk metal or thin films) are reported. The pressure in the scattering chamber is about 10 -6 torr. So, the surfaces are polluted. Diffraction peaks are observed which can be interpreted very well by assuming that nitrogen, oxygen or carbon atoms are adsorbed of the surface. On the other hand, diffraction peaks from a silicon crystal have been observed which can be reproduced very well by using silicon crystal lattice. These experiments are not interpreted accurately, but show that molecular reflection can be used for some surface studies [fr

  12. Nanoporous PdZr surface alloy as highly active non-platinum electrocatalyst toward oxygen reduction reaction with unique structure stability and methanol-tolerance

    Science.gov (United States)

    Duan, Huimei; Xu, Caixia

    2016-06-01

    Nanoporous (NP) PdZr alloy with controllable bimetallic ratio is successfully fabricated by a simple dealloying method. By leaching out the more reactive Al from PdZrAl precursor alloy, NP-PdZr alloy with smaller ligament size was generated, characterized by the nanoscaled interconnected network skeleton and hollow channels extending in all three dimensions. Upon voltammetric scan in acid solution, the dissolution of surface Zr atoms generates the highly active Pd-Zr surface alloy with a nearly pure Pd surface and Pd-Zr alloy core. The NP-Pd80Zr20 surface alloy exhibits markedly enhanced specific and mass activities as well as higher catalytic stability toward oxygen reduction reaction (ORR) compared with NP-Pd and the state-of-the-art Pt/C catalysts. In addition, the NP-Pd80Zr20 surface alloy shows a better selectivity for ORR than methanol in the 0.1 M HClO4 and 0.1 M methanol mixed solution. X-ray photoelectron spectroscopy and density functional theory calculations both demonstrate that the weakened Pd-O bond and improved ORR performances in turn depend on the downshifted d-band center of Pd due to the alloying Pd with Zr (20 at.%). The as-made NP-PdZr alloy holds prospective applications as a cathode electrocatalyst in fuel-cell-related technologies with the advantages of superior overall ORR performances, unique structure stability, and easy preparation.

  13. Long-term stability of superhydrophilic oxygen plasma-modified single-walled carbon nanotube network surfaces and the influence on ammonia gas detection

    Energy Technology Data Exchange (ETDEWEB)

    Min, Sungjoon [Department of Biomicrosystem Technology, Korea University, Seoul 136-713 (Korea, Republic of); Kim, Joonhyub [Department of Control and Instrumentation Engineering, Korea University, 2511 Sejong-ro, Sejong City 339-770 (Korea, Republic of); Park, Chanwon [Department of Electrical and Electronic Engineering, Kangwon National University, Chuncheon 200-701 (Korea, Republic of); Jin, Joon-Hyung, E-mail: jj1023@chol.com [Department of Chemical Engineering, Kyonggi University, 154-42 Gwanggyosan-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16227 (Korea, Republic of); Min, Nam Ki, E-mail: nkmin@korea.ac.kr [Department of Biomicrosystem Technology, Korea University, Seoul 136-713 (Korea, Republic of)

    2017-07-15

    Graphical abstract: Superhydrophilic single-walled carbon nanotube obtained by O{sub 2} plasma treatment voluntarily and non-reversibly reverts to a metastable state. This aerobic aging is an essential process to develop a stable carbon nanotube-based sensor. - Highlights: • Superhydrophilic single-walled carbon nanotube network can be obtained by O{sub 2} plasma-based surface modification. • The modified carbon nanotube surface invariably reverts to a metastable state in a non-reversible manner. • Aerobic aging is essential to stabilize the modified carbon nanotube and the carbon nanotube-based sensing device due to minimized sensor-to-sensor variation. - Abstract: Single-walled carbon nanotube (SWCNT) networks are subjected to a low-powered oxygen plasma for the surface modification. Changes in the surface chemical composition and the stability of the plasma-treated SWCNT (p-SWCNT) with aging in air for up to five weeks are studied using X-ray photoelectron spectroscopy (XPS) and contact angle analysis. The contact angle decreases from 120° of the untreated hydrophobic SWCNT to 0° for the superhydrophilic p-SWCNT. Similarly, the ratio of oxygen to carbon (O:C) based on the XPS spectra increases from 0.25 to 1.19, indicating an increase in surface energy of the p-SWCNT. The enhanced surface energy is gradually dissipated and the p-SWCNT network loses the superhydrophilic surface property. However, it never revert to the original hydrophobic surface state but to a metastable hydrophilic state. The aging effect on sensitivity of the p-SWCNT network-based ammonia sensor is investigated to show the importance of the aging process for the stabilization of the p-SWCNT. The best sensitivity for monitoring NH{sub 3} gas is observed with the as-prepared p-SWCNT, and the sensitivity decreases as similar as the p-SWCNT loses its hydrophilicity with time goes by. After a large performance degradation during the aging time for about two weeks, the response

  14. Tuning Surface Electronic Configuration of NiFe LDHs Nanosheets by Introducing Cation Vacancies (Fe or Ni) as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction.

    Science.gov (United States)

    Wang, Yanyong; Qiao, Man; Li, Yafei; Wang, Shuangyin

    2018-04-03

    Intrinsically inferior electrocatalytic activity of NiFe layered double hydroxides (LDHs) nanosheets is considered as a limiting factor to inhibit the electrocatalytic properties for oxygen evolution reaction (OER). Proper defect engineering to tune the surface electronic configuration of electrocatalysts may significantly improve the intrinsic activity. In this work, the selective formation of cation vacancies in NiFe LDHs nanosheets is successfully realized. The as-synthesized NiFe LDHs-V Fe and NiFe LDHs-V Ni electrocatalysts show excellent activity for OER, mainly attributed to the introduction of rich iron or nickel vacancies in NiFe LDHs nanosheets, which efficiently tune the surface electronic structure increasing the adsorbing capacity of OER intermediates. Density functional theory (DFT) computational results also further indicate that the OER catalytic performance of NiFe LDHs can be pronouncedly improved by introducing Fe or Ni vacancies. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Strained lattice with persistent atomic order in Pt3Fe2 intermetallic core-shell nanocatalysts.

    Science.gov (United States)

    Prabhudev, Sagar; Bugnet, Matthieu; Bock, Christina; Botton, Gianluigi A

    2013-07-23

    Fine-tuning nanocatalysts to enhance their catalytic activity and durability is crucial to commercialize proton exchange membrane fuel cells. The structural ordering and time evolution of ordered Pt3Fe2 intermetallic core-shell nanocatalysts for the oxygen reduction reaction that exhibit increased mass activity (228%) and an enhanced catalytic activity (155%) compared to Pt/C has been quantified using aberration-corrected scanning transmission electron microscopy. These catalysts were found to exhibit a static core-dynamic shell regime wherein, despite treating over 10,000 cycles, there is negligible decrease (9%) in catalytic activity and the ordered Pt3Fe2 core remained virtually intact while the Pt shell suffered a continuous enrichment. The existence of this regime was further confirmed by X-ray diffraction and the compositional analyses using energy-dispersive spectroscopy. With atomic-scale two-dimensional (2-D) surface relaxation mapping, we demonstrate that the Pt atoms on the surface are slightly relaxed with respect to bulk. The cycled nanocatalysts were found to exhibit a greater surface relaxation compared to noncycled catalysts. With 2-D lattice strain mapping, we show that the particle was about -3% strained with respect to pure Pt. While the observed enhancement in their activity is ascribed to such a strained lattice, our findings on the degradation kinetics establish that their extended catalytic durability is attributable to a sustained atomic order.

  16. Oxygen sensitive microwells.

    Science.gov (United States)

    Sinkala, Elly; Eddington, David T

    2010-12-07

    Oxygen tension is critical in a number of cell pathways but is often overlooked in cell culture. One reason for this is the difficulty in modulating and assessing oxygen tensions without disturbing the culture conditions. Toward this end, a simple method to generate oxygen-sensitive microwells was developed through embossing polystyrene (PS) and platinum(ii) octaethylporphyrin ketone (PtOEPK) thin films. In addition to monitoring the oxygen tension, microwells were employed in order to isolate uniform clusters of cells in microwells. The depth and width of the microwells can be adapted to different experimental parameters easily by altering the thin film processing or embossing stamp geometries. The thin oxygen sensitive microwell substrate is also compatible with high magnification modalities such as confocal imaging. The incorporation of the oxygen sensor into the microwells produces measurements of the oxygen tension near the cell surface. The oxygen sensitive microwells were calibrated and used to monitor oxygen tensions of Madin-Darby Canine Kidney Cells (MDCKs) cultured at high and low densities as a proof of concept. Wells 500 µm in diameter seeded with an average of 330 cells exhibited an oxygen level of 12.6% whereas wells seeded with an average of 20 cells per well exhibited an oxygen level of 19.5%, a 35.7% difference. This platform represents a new tool for culturing cells in microwells in a format amenable to high magnification imaging while monitoring the oxygen state of the culture media.

  17. Leaf surface wax is a source of plant methane formation under UV radiation and in the presence of oxygen

    DEFF Research Database (Denmark)

    Bruhn, Dan; Mikkelsen, Teis Nørgaard; Rolsted, M. M. M.

    2014-01-01

    The terrestrial vegetation is a source of UV radiation-induced aerobic methane (CH4) release to the atmosphere. Hitherto pectin, a plant structural component, has been considered as the most likely precursor for this CH4 release. However, most of the leaf pectin is situated below the surface wax...... layer, and UV transmittance of the cuticle differs among plant species. In some species, the cuticle effectively absorbs and/or reflects UV radiation. Thus, pectin may not necessarily contribute substantially to the UV radiation-induced CH4 emission measured at surface level in all species. Here, we...... investigated the potential of the leaf surface wax itself as a source of UV radiationinduced leaf aerobic CH4 formation. Isolated leaf surface wax emitted CH4 at substantial rates in response to UV radiation. This discovery has implications for how the phenomenon should be scaled to global levels. In relation...

  18. The synthesis of PdPt/carbon paper via surface limited redox replacement reactions for oxygen reduction reaction

    CSIR Research Space (South Africa)

    Motsoeneng, RG

    2015-09-01

    Full Text Available Surface-limited redox replacement reactions using the electrochemical atomic layer deposition (EC-ALD) technique were used to synthesize PdPt bimetallic electrocatalysts on carbon paper substrate. Electrocatalysts having different Pd:Pt ratio were...

  19. Electronic states on the clean and oxygen-covered molybdenum (110) surface measured using time-of-flight momentum microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Chernov, Sergii

    2016-04-20

    Recent experiments discovered a new class of materials called topological insulators and started an extensive investigation in order to find more materials of such type and to understand and explore the opening perspectives in fundamental science and application. These materials exhibit a Dirac-type (massless) electronic state, bridging the fundamental band gap. Surprisingly, a strongly spin-polarized surface state with linear dispersion resembling that of Dirac type was found on the already well-investigated W(110) surface. This rose the question of the existence of the same non-trivial electron state on other metal surfaces. The present work describes the investigation of surface electronic states on the Mo(110) surface, their dispersion and transformation upon surface oxidation. This system is isoelectronic to the case of W(110) but due to the lower atomic number the spin-orbit interaction responsible for local band gap formation is substantially decreased by a factor of 5. The Mo(110) surface was shown to exhibit a linearly dispersing state quite similar to the one on W(110), but within a smaller energy range of 120 meV, with the Dirac point lying in the center of a local band gap in k-space. The experimental investigations were performed with the help of momentum microscopy, using a Ti:sapphire laser in the lab and synchrotron radiation at BESSY II, Berlin. The results show good agreement with theoretical calculations of the band structure and photoemission patterns for clean Mo(110). The fully parallel 3D acquisition scheme allowed to visualize the full surface Brillouin zone of the sample up to few eV binding energy within a single exposure of typically less than 30 min. This opens the door to future time-resolved experiments with maximum detection efficiency.

  20. Lattice-Boltzmann simulations of droplet evaporation

    KAUST Repository

    Ledesma-Aguilar, Rodrigo

    2014-09-04

    © the Partner Organisations 2014. We study the utility and validity of lattice-Boltzmann (LB) simulations to explore droplet evaporation driven by a concentration gradient. Using a binary-fluid lattice-Boltzmann algorithm based on Cahn-Hilliard dynamics, we study the evaporation of planar films and 3D sessile droplets from smooth solid surfaces. Our results show that LB simulations accurately reproduce the classical regime of quasi-static dynamics. Beyond this limit, we show that the algorithm can be used to explore regimes where the evaporative and diffusive timescales are not widely separated, and to include the effect of boundaries of prescribed driving concentration. We illustrate the method by considering the evaporation of a droplet from a solid surface that is chemically patterned with hydrophilic and hydrophobic stripes. This journal is

  1. Lattice topology dictates photon statistics.

    Science.gov (United States)

    Kondakci, H Esat; Abouraddy, Ayman F; Saleh, Bahaa E A

    2017-08-21

    Propagation of coherent light through a disordered network is accompanied by randomization and possible conversion into thermal light. Here, we show that network topology plays a decisive role in determining the statistics of the emerging field if the underlying lattice is endowed with chiral symmetry. In such lattices, eigenmode pairs come in skew-symmetric pairs with oppositely signed eigenvalues. By examining one-dimensional arrays of randomly coupled waveguides arranged on linear and ring topologies, we are led to a remarkable prediction: the field circularity and the photon statistics in ring lattices are dictated by its parity while the same quantities are insensitive to the parity of a linear lattice. For a ring lattice, adding or subtracting a single lattice site can switch the photon statistics from super-thermal to sub-thermal, or vice versa. This behavior is understood by examining the real and imaginary fields on a lattice exhibiting chiral symmetry, which form two strands that interleave along the lattice sites. These strands can be fully braided around an even-sited ring lattice thereby producing super-thermal photon statistics, while an odd-sited lattice is incommensurate with such an arrangement and the statistics become sub-thermal.

  2. Unraveling the Role of Transport, Electrocatalysis, and Surface Science in the Solid Oxide Fuel Cell Cathode Oxygen Reduction Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Gopalan, Srikanth [Boston Univ., MA (United States)

    2017-04-06

    This final report for project FE0009656 covers the period from 10/01/2012 to 09/30/2015 and covers research accomplishments on the effects of carbon dioxide on the surface composition and structure of cathode materials for solid oxide fuel cells (SOFCs), specifically La1-xSrxFeyCo1- yO3-δ (LSCF). Epitaxially deposited thin films of LSCF on various single-crystal substrates have revealed the selective segregation of strontium to the surface thereby resulting in a surface enrichment of strontium. The near surface compositional profile in the films have been measured using total x-ray fluorescence (TXRF), and show that the kinetics of strontium segregation are higher at higher partial pressures of carbon dioxide. Once the strontium segregates to the surface, it leads to the formation of precipitates of SrO which convert to SrCO3 in the presence of even modest concentrations of carbon dioxide in the atmosphere. This has important implications for the performance of SOFCs which is discussed in this report. These experimental observations have also been verified by Density Functional Theory calculations (DFT) which predict the conditions under which SrO and SrCO3 can occur in LSCF. Furthermore, a few cathode compositions which have received attention in the literature as alternatives to LSCF cathodes have been studied in this work and shown to be thermodynamically unstable under the operating conditions of the SOFCs.

  3. Leaf surface wax is a source of plant methane formation under UV radiation and in the presence of oxygen.

    Science.gov (United States)

    Bruhn, D; Mikkelsen, T N; Rolsted, M M M; Egsgaard, H; Ambus, P

    2014-03-01

    The terrestrial vegetation is a source of UV radiation-induced aerobic methane (CH4 ) release to the atmosphere. Hitherto pectin, a plant structural component, has been considered as the most likely precursor for this CH4 release. However, most of the leaf pectin is situated below the surface wax layer, and UV transmittance of the cuticle differs among plant species. In some species, the cuticle effectively absorbs and/or reflects UV radiation. Thus, pectin may not necessarily contribute substantially to the UV radiation-induced CH4 emission measured at surface level in all species. Here, we investigated the potential of the leaf surface wax itself as a source of UV radiation-induced leaf aerobic CH4 formation. Isolated leaf surface wax emitted CH4 at substantial rates in response to UV radiation. This discovery has implications for how the phenomenon should be scaled to global levels. In relation to this, we demonstrated that the UV radiation-induced CH4 emission is independent of leaf area index above unity. Further, we observed that the presence of O2 in the atmosphere was necessary for achieving the highest rates of CH4 emission. Methane formation from leaf surface wax is supposedly a two-step process initiated by a photolytic rearrangement reaction of the major component followed by an α-cleavage of the generated ketone. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

  4. Study of Gd lattices

    International Nuclear Information System (INIS)

    Vidovsky, I.; Kereszturi, A.

    1991-11-01

    The results of experiments and calculations on Gd lattices are presented, and a comparison of experimental and calculational data is given. This latter can be divided into four groups. The first belongs to the comparison of criticality parameters, the second group is related with the comparison of 2D distributions, the third one relates the comparison of intra-macrocell distributions, whereas the fourth group is devoted for the comparison of spectral parameters. For comparison, the computer code RFIT based on strict statistical criteria has been used. The calculated and measured results agree, in most cases, sufficiently. (R.P.) 11 refs.; 13 figs.; 9 tabs

  5. Lattice Vibrations in Chlorobenzenes:

    DEFF Research Database (Denmark)

    Reynolds, P. A.; Kjems, Jørgen; White, J. W.

    1974-01-01

    Lattice vibrational dispersion curves for the ``intermolecular'' modes in the triclinic, one molecule per unit cell β phase of p‐C6D4Cl2 and p‐C6H4Cl2 have been obtained by inelastic neutron scattering. The deuterated sample was investigated at 295 and at 90°K and a linear extrapolation to 0°K...... was applied in order to correct for anharmonic effects. Calculations based on the atom‐atom model for van der Waals' interaction and on general potential parameters for the aromatic compounds agree reasonably well with the experimental observations. There is no substantial improvement in fit obtained either...

  6. Lattice of quantum predictions

    Science.gov (United States)

    Drieschner, Michael

    1993-10-01

    What is the structure of reality? Physics is supposed to answer this question, but a purely empiristic view is not sufficient to explain its ability to do so. Quantum mechanics has forced us to think more deeply about what a physical theory is. There are preconditions every physical theory must fulfill. It has to contain, e.g., rules for empirically testable predictions. Those preconditions give physics a structure that is “a priori” in the Kantian sense. An example is given how the lattice structure of quantum mechanics can be understood along these lines.

  7. Ordered sets and lattices

    CERN Document Server

    Drashkovicheva, Kh; Igoshin, V I; Katrinyak, T; Kolibiar, M

    1989-01-01

    This book is another publication in the recent surveys of ordered sets and lattices. The papers, which might be characterized as "reviews of reviews," are based on articles reviewed in the Referativnyibreve Zhurnal: Matematika from 1978 to 1982. For the sake of completeness, the authors also attempted to integrate information from other relevant articles from that period. The bibliography of each paper provides references to the reviews in RZhMat and Mathematical Reviews where one can seek more detailed information. Specifically excluded from consideration in this volume were such topics as al

  8. Lattice cell burnup calculation

    International Nuclear Information System (INIS)

    Pop-Jordanov, J.

    1977-01-01

    Accurate burnup prediction is a key item for design and operation of a power reactor. It should supply information on isotopic changes at each point in the reactor core and the consequences of these changes on the reactivity, power distribution, kinetic characters, control rod patterns, fuel cycles and operating strategy. A basic stage in the burnup prediction is the lattice cell burnup calculation. This series of lectures attempts to give a review of the general principles and calculational methods developed and applied in this area of burnup physics

  9. Enhancing co-production of H2 and syngas via water splitting and POM on surface-modified oxygen permeable membranes

    KAUST Repository

    Wu, Xiao-Yu

    2016-09-26

    In this article, we report a detailed study on co-production of H2 and syngas on La0.9Ca0.1FeO3−δ (LCF-91) membranes via water splitting and partial oxidation of methane, respectively. A permeation model shows that the surface reaction on the sweep side is the rate limiting step for this process on a 0.9 mm-thick dense membrane at 990°C. Hence, sweep side surface modifications such as adding a porous layer and nickel catalysts were applied; the hydrogen production rate from water thermolysis is enhanced by two orders of magnitude to 0.37 μmol/cm2•s compared with the results on the unmodified membrane. At the sweep side exit, syngas (H2/CO = 2) is produced and negligible solid carbon is found. Yet near the membrane surface on the sweep side, methane can decompose into solid carbon and hydrogen at the surface, or it may be oxidized into CO and CO2, depending on the oxygen permeation flux.

  10. Scalar spin chirality and quantum hall effect on triangular lattices

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Ivar [Los Alamos National Laboratory; Batista, Cristian D [Los Alamos National Laboratory

    2008-01-01

    We study the Kondo Lattice and Hubbard models on a triangular lattice for band filling factor 3/4. We show that a simple non-coplanar chiral spin ordering (scalar spin chirality) is naturally realized in both models due to perfect nesting of the fermi surface. The resulting triple-Q magnetic ordering is a natural counterpart of the collinear Neel ordering of the half-filled square lattice Hubbard model. We show that the obtained chiral phase exhibits a spontaneous quantum Hall-effect with {sigma}{sub xy} = e{sup 2}/h.

  11. Electrodeposition of Pd based binary catalysts on Carbon paper via surface limited redox-replacement reaction for oxygen reduction reaction

    CSIR Research Space (South Africa)

    Modibedi, RM

    2014-05-01

    Full Text Available attention as it is more abundant and also cheaper than Pt. In this presentation, Electrochemical Atomic Layer Deposition (ECALD) was used in the preparation of binary ORR catalysts. The binary nanoclusters were synthesised via surface-limited redox-replacement...

  12. Micro and nanopatterning of functional materials on flexible plastic substrates via site-selective surface modification using oxygen plasma

    NARCIS (Netherlands)

    George, A.; Stawski, T.M.; Unnikrishnan, S.; Veldhuis, S.A.; Elshof, J.E. ten

    2012-01-01

    A simple and cost effective methodology for large area micro and nanopatterning of a wide range of functional materials on flexible substrates is presented. A hydrophobic-hydrophilic chemical contrast was patterned on surfaces of various flexible plastic substrates using molds and shadow masks with

  13. Micro- and nanopatterning of functional materials on flexible plastic substrates via site-selective surface modification using oxygen plasma

    NARCIS (Netherlands)

    George, A.; Stawski, Tomasz; Unnikrishnan, S.; Veldhuis, Sjoerd; ten Elshof, Johan E.

    2012-01-01

    A simple and cost effective methodology for large area micro and nanopatterning of a wide range of functional materials on flexible substrates is presented. A hydrophobic-hydrophilic chemical contrast was patterned on surfaces of various flexible plastic substrates using molds and shadow masks with

  14. Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Bo, Maolin [Yangtze Normal University, College of Mechanical and Electrical Engineering, Chongqing 408100 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Liu, Yonghui [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q. [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China)

    2017-02-28

    Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O{sup 2−} lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta{sup +} electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta{sup +}; the sp{sup 3}-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent

  15. Extreme lattices: symmetries and decorrelation

    Science.gov (United States)

    Andreanov, A.; Scardicchio, A.; Torquato, S.

    2016-11-01

    We study statistical and structural properties of extreme lattices, which are the local minima in the density landscape of lattice sphere packings in d-dimensional Euclidean space {{{R}}d} . Specifically, we ascertain statistics of the densities and kissing numbers as well as the numbers of distinct symmetries of the packings for dimensions 8 through 13 using the stochastic Voronoi algorithm. The extreme lattices in a fixed dimension of space d (d≥slant 8 ) are dominated by typical lattices that have similar packing properties, such as packing densities and kissing numbers, while the best and the worst packers are in the long tails of the distribution of the extreme lattices. We also study the validity of the recently proposed decorrelation principle, which has important implications for sphere packings in general. The degree to which extreme-lattice packings decorrelate as well as how decorrelation is related to the packing density and symmetry of the lattices as the space dimension increases is also investigated. We find that the extreme lattices decorrelate with increasing dimension, while the least symmetric lattices decorrelate faster.

  16. Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

    Directory of Open Access Journals (Sweden)

    Noor A. Nama

    2010-01-01

    Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001-(1×1 surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.

  17. Structure of the Clean and Oxygen-Covered Cu(100) Surface at Room Temperature in the Presence of Methanol Vapor in the 10-200 mTorr Pressure Range.

    Science.gov (United States)

    Eren, Baran; Kersell, Heath; Weatherup, Robert S; Heine, Christian; Crumlin, Ethan J; Friend, Cynthia M; Salmeron, Miquel B

    2018-01-18

    Using ambient pressure X-ray photoelectron spectroscopy (APXPS) and high pressure scanning tunneling microscopy (HPSTM), we show that in equilibrium with 0.01-0.2 Torr of methanol vapor, at room temperature, the Cu(100) surface is covered with methoxy species forming a c(2 × 2) overlayer structure. In contrast, no methoxy is formed if the surface is saturated with an ordered oxygen layer, even when the methanol pressure is 0.2 Torr. At oxygen coverages below saturation, methanol dissociates and reacts with the atomic oxygen, producing methoxy and formate on the surface, and formaldehyde that desorbs to the gas phase. Unlike the case of pure carbon monoxide and carbon dioxide, methanol does not induce the restructuring of the Cu(100) surface. These results provide insight into catalytic anhydrous production of aldehydes.

  18. Density functional theory study of oxygen and water adsorption on SrTiO{sub 3}(001)

    Energy Technology Data Exchange (ETDEWEB)

    Guhl, Hannes

    2010-12-03

    Strontium titanate is an extensively studied material with a wide range of application, for instance in photo-catalysis and most importantly, it is used as a substrate in growth of functional oxides. The surface chemistry is crucial and hence understanding the surface structure on atomic scale is essential for gaining insight into the fundamental processes in the aforementioned applications. Moreover, there exist a lot of evidence that this surface chemistry might be controlled to considerably by extrinsic species, such as residual hydrogen and water. Investigating the properties of water and oxygen on the strontium titanate surface is certainly a natural starting point for a theoretical study based on density functional theory, because these species are practically present on the surface on a wide range of experimental conditions and they are computationally feasible. For the oxygen and water adsorption the binding energy is controlled by long-range surface relaxations leading to an effective repulsion of the adsorbed specimen. The isolated oxygen ad-atom forms a covalently bonded ''quasi-peroxide anion'' in combination with a lattice oxygen atom. Contrariwise, in all investigated configurations containing water molecules and hydroxyl groups, the respective oxygen atoms assumed positions close to the oxygen sites of the continued perovskite lattice of the substrate. Most remarkably, on the strontium oxide termination, the water molecules adsorbs and dissociates effortlessly leading to the formation of a pair of hydroxyl groups. For the titanium dioxide termination, a coverage dependent adsorption mode is observed. Densely packings stabilize water molecules, whereas at lower coverage and finite temperatures the formation of hydroxyl groups is found. The energetics responsible for this behavior is consistent with recent experiments by Iwahori and coworkers. (orig.)

  19. Density functional theory study of oxygen and water adsorption on SrTiO3(001)

    International Nuclear Information System (INIS)

    Guhl, Hannes

    2010-01-01

    Strontium titanate is an extensively studied material with a wide range of application, for instance in photo-catalysis and most importantly, it is used as a substrate in growth of functional oxides. The surface chemistry is crucial and hence understanding the surface structure on atomic scale is essential for gaining insight into the fundamental processes in the aforementioned applications. Moreover, there exist a lot of evidence that this surface chemistry might be controlled to considerably by extrinsic species, such as residual hydrogen and water. Investigating the properties of water and oxygen on the strontium titanate surface is certainly a natural starting point for a theoretical study based on density functional theory, because these species are practically present on the surface on a wide range of experimental conditions and they are computationally feasible. For the oxygen and water adsorption the binding energy is controlled by long-range surface relaxations leading to an effective repulsion of the adsorbed specimen. The isolated oxygen ad-atom forms a covalently bonded ''quasi-peroxide anion'' in combination with a lattice oxygen atom. Contrariwise, in all investigated configurations containing water molecules and hydroxyl groups, the respective oxygen atoms assumed positions close to the oxygen sites of the continued perovskite lattice of the substrate. Most remarkably, on the strontium oxide termination, the water molecules adsorbs and dissociates effortlessly leading to the formation of a pair of hydroxyl groups. For the titanium dioxide termination, a coverage dependent adsorption mode is observed. Densely packings stabilize water molecules, whereas at lower coverage and finite temperatures the formation of hydroxyl groups is found. The energetics responsible for this behavior is consistent with recent experiments by Iwahori and coworkers. (orig.)

  20. Elimination of spurious lattice fermion solutions and noncompact lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Lee, T.D.

    1997-09-22

    It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.

  1. The influence of oxygen and hydrogen adsorption on the magneticstructure of the ultrathin iron film on the Ir(001) surface

    Czech Academy of Sciences Publication Activity Database

    Máca, František; Kudrnovský, Josef; Drchal, Václav; Redinger, J.

    2013-01-01

    Roč. 88, č. 4 (2013), "045423-1"-"045423-7" ISSN 1098-0121 R&D Projects: GA AV ČR IAA100100912; GA ČR GA202/09/0775 Institutional support: RVO:68378271 Keywords : surface magnetism * magnetic overlayer * gas adsorption * magnetic phase stability * density functional calculation * STM Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.664, year: 2013

  2. Formation of halo-structures in oxygen isotopes through change of occupancy of levels near Fermi surface

    International Nuclear Information System (INIS)

    Bhattacharya, Rupayan

    2000-01-01

    Recently a new parametrisation of Skyrme interaction has been formulated in order to study the level inversions of A=9 isobars. The role of occupancy of 2s 1/2 level in determining the halo structures of O, N, C, B and Be nuclei was shown. A thorough investigation on the binding energies, rms charge, neutron and matter distribution and occupation probabilities of levels near the Fermi surface has been done in the present work

  3. Model polymer etching and surface modification by a time modulated RF plasma jet: role of atomic oxygen and water vapor

    International Nuclear Information System (INIS)

    Luan, P; Knoll, A J; Wang, H; Oehrlein, G S; Kondeti, V S S K; Bruggeman, P J

    2017-01-01

    The surface interaction of a well-characterized time modulated radio frequency (RF) plasma jet with polystyrene, poly(methyl methacrylate) and poly(vinyl alcohol) as model polymers is investigated. The RF plasma jet shows fast polymer etching but mild chemical modification with a characteristic carbonate ester and NO formation on the etched surface. By varying the plasma treatment conditions including feed gas composition, environment gaseous composition, and treatment distance, we find that short lived species, especially atomic O for Ar/1% O 2 and 1% air plasma and OH for Ar/1% H 2 O plasma, play an essential role for polymer etching. For O 2 containing plasma, we find that atomic O initiates polymer etching and the etching depth mirrors the measured decay of O atoms in the gas phase as the nozzle-surface distance increases. The etching reaction probability of an O atom ranging from 10 −4 to 10 −3 is consistent with low pressure plasma research. We also find that adding O 2 and H 2 O simultaneously into Ar feed gas quenches polymer etching compared to adding them separately which suggests the reduction of O and OH density in Ar/O 2 /H 2 O plasma. (letter)

  4. Activity of type i methanotrophs dominates under high methane concentration: Methanotrophic activity in slurry surface crusts as influenced by methane, oxygen, and inorganic nitrogen

    DEFF Research Database (Denmark)

    Duan, Yun Feng; Reinsch, Sabine; Ambus, Per

    2017-01-01

    Livestock slurry is a major source of atmospheric methane (CH4), but surface crusts harboring methane-oxidizing bacteria (MOB) could mediate against CH4 emissions. This study examined conditions for CH4 oxidation by in situ measurements of oxygen (O2) and nitrous oxide (N2O), as a proxy...... for inorganic N transformations, in intact crusts using microsensors. This was combined with laboratory incubations of crust material to investigate the effects of O2, CH4, and inorganic N on CH4 oxidation, using 13CH4 to trace C incorporation into lipids of MOB. Oxygen penetration into the crust was 2 to 14 mm......, confining the potential for aerobic CH4 oxidation to a shallow layer. Nitrous oxide accumulated within or below the zone of O2 depletion. With 102 ppmv CH4 there was no O2 limitation on CH4 oxidation at O2 concentrations as low as 2%, whereas CH4 oxidation at 104 ppmv CH4 was reduced at =5% O2...

  5. Retrieving aerosol height from the oxygen A band: a fast forward operator and sensitivity study concerning spectral resolution, instrumental noise, and surface inhomogeneity

    Science.gov (United States)

    Hollstein, A.; Fischer, J.

    2014-05-01

    Hyperspectral radiance measurements in the oxygen A band are sensitive to the vertical distribution of atmospheric scatterers, which in principle allows the retrieval of aerosol height from future instruments like TROPOMI, OCO2, FLEX, and CarbonSat. Discussed in this paper is a fast and flexible forward operator for the simulation of hyperspectral radiances in the oxygen A band and, based on this scheme, a sensitivity study about the inversion quality of aerosol optical thickness, aerosol mean height, and aerosol type. The forward operator is based on a lookup table with efficient data compression based on principal component analysis. Linear interpolation and computation of partial derivatives is performed in the much smaller space of expansion coefficients rather than wavelength. Thus, this approach is computationally fast and, at the same time, memory efficient. The sensitivity study explores the impact of instrument design on the retrieval of aerosol optical thickness and aerosol height. Considered are signal to noise ratio, spectral resolution, and spectral sampling. Also taken into account are surface inhomogeneities and variations of the aerosol type.

  6. Characterization of projection lattices of Hilbert spaces

    Energy Technology Data Exchange (ETDEWEB)

    Szambien, H.H.

    1986-09-01

    The classical lattices of projections of Hilbert spaces over the real, the complex or the quaternion number field are characterized among the totality of irreducible, complete, orthomodular, atomic lattices satisfying the covering property. To this end, so-called paratopological lattices are introduced, i.e, lattices carrying a topology that renders the lattice operations restrictedly continuous.

  7. Lattices, supersymmetry and Kaehler fermions

    International Nuclear Information System (INIS)

    Scott, D.M.

    1984-01-01

    It is shown that a graded extension of the space group of a (generalised) simple cubic lattice exists in any space dimension, D. The fermionic variables which arise admit a Kaehlerian interpretation. Each graded space group is a subgroup of a graded extension of the appropriate Euclidean group, E(D). The relevance of this to the construction of lattice theories is discussed. (author)

  8. Fast simulation of lattice systems

    DEFF Research Database (Denmark)

    Bohr, H.; Kaznelson, E.; Hansen, Frank

    1983-01-01

    A new computer system with an entirely new processor design is described and demonstrated on a very small trial lattice. The new computer simulates systems of differential equations of the order of 104 times faster than present day computers and we describe how the machine can be applied to lattice...

  9. Quantum phases in optical lattices

    NARCIS (Netherlands)

    Dickerscheid, Dennis Brian Martin

    2006-01-01

    An important new development in the field of ultracold atomic gases is the study of the properties of these gases in a so-called optical lattice. An optical lattice is a periodic trapping potential for the atoms that is formed by the interference pattern of a few laser beams. A reason for the

  10. Lattice gauge theory: Present status

    International Nuclear Information System (INIS)

    Creutz, M.

    1993-09-01

    Lattice gauge theory is our primary tool for the study of non- perturbative phenomena in hadronic physics. In addition to giving quantitative information on confinement, the approach is yielding first principles calculations of hadronic spectra and matrix elements. After years of confusion, there has been significant recent progress in understanding issues of chiral symmetry on the lattice

  11. Geometry of lattice field theory

    International Nuclear Information System (INIS)

    Honan, T.J.

    1986-01-01

    Using some tools of algebraic topology, a general formalism for lattice field theory is presented. The lattice is taken to be a simplicial complex that is also a manifold and is referred to as a simplicial manifold. The fields on this lattice are cochains, that are called lattice forms to emphasize the connections with differential forms in the continuum. This connection provides a new bridge between lattice and continuum field theory. A metric can be put onto this simplicial manifold by assigning lengths to every link or I-simplex of the lattice. Regge calculus is a way of defining general relativity on this lattice. A geometric discussion of Regge calculus is presented. The Regge action, which is a discrete form of the Hilbert action, is derived from the Hilbert action using distribution valued forms. This is a new derivation that emphasizes the underlying geometry. Kramers-Wannier duality in statistical mechanics is discussed in this general setting. Nonlinear field theories, which include gauge theories and nonlinear sigma models are discussed in the continuum and then are put onto a lattice. The main new result here is the generalization to curved spacetime, which consists of making the theory compatible with Regge calculus

  12. Selective surface functionalization of polystyrene induced by synchrotron or UV radiation in the presence of oxygen or acrylic acid vapors

    International Nuclear Information System (INIS)

    Kessler, Felipe; Kuhn, Sidiney; Weibel, Daniel E.

    2009-01-01

    Efficient surface functionalization of Polystyrene (PS) thin films by electromagnetic radiation in combination with a reactive gaseous atmosphere was obtained. Monochromatic synchrotron (SR) or polychromatic UV radiation were used as excitation sources. When SR was used, O 2 was introduced after irradiation into the UHV chamber. UV irradiation was carried out keeping a constant flow of O 2 or acrylic acid (AA) vapors during the photolysis. FTIR-ATR and XPS-NEXAFS spectra were obtained at the UFRGS and the LNLS, Campinas respectively. PS films were functionalized by monochromatic SR and then expose to O 2 at specific transitions such us C 1s →σ * C-C excitation. It was found a high rate of COO, C=O and C-O groups at the surface (> 70%). UV-assisted treatment in the presence of AA vapors showed that an efficient polymerization process took place, such as, it was observed in previous AA low pressure RF plasma treatments. UV-assisted functionalization has the advantage of lower costs and simple set-up compared to plasma treatments. (author)

  13. Constraint percolation on hyperbolic lattices

    Science.gov (United States)

    Lopez, Jorge H.; Schwarz, J. M.

    2017-11-01

    Hyperbolic lattices interpolate between finite-dimensional lattices and Bethe lattices, and they are interesting in their own right, with ordinary percolation exhibiting not one but two phase transitions. We study four constraint percolation models—k -core percolation (for k =1 ,2 ,3 ) and force-balance percolation—on several tessellations of the hyperbolic plane. By comparing these four different models, our numerical data suggest that all of the k -core models, even for k =3 , exhibit behavior similar to ordinary percolation, while the force-balance percolation transition is discontinuous. We also provide proof, for some hyperbolic lattices, of the existence of a critical probability that is less than unity for the force-balance model, so that we can place our interpretation of the numerical data for this model on a more rigorous footing. Finally, we discuss improved numerical methods for determining the two critical probabilities on the hyperbolic lattice for the k -core percolation models.

  14. Lattice quantum chromodynamics practical essentials

    CERN Document Server

    Knechtli, Francesco; Peardon, Michael

    2017-01-01

    This book provides an overview of the techniques central to lattice quantum chromodynamics, including modern developments. The book has four chapters. The first chapter explains the formulation of quarks and gluons on a Euclidean lattice. The second chapter introduces Monte Carlo methods and details the numerical algorithms to simulate lattice gauge fields. Chapter three explains the mathematical and numerical techniques needed to study quark fields and the computation of quark propagators. The fourth chapter is devoted to the physical observables constructed from lattice fields and explains how to measure them in simulations. The book is aimed at enabling graduate students who are new to the field to carry out explicitly the first steps and prepare them for research in lattice QCD.

  15. Multiscale atomistic simulation of metal-oxygen surface interactions: Methodological development, theoretical investigation, and correlation with experiment

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Judith C. [Univ. of Pittsburgh, Pittsburgh, PA (United States)

    2015-01-09

    The purpose of this grant is to develop the multi-scale theoretical methods to describe the nanoscale oxidation of metal thin films, as the PI (Yang) extensive previous experience in the experimental elucidation of the initial stages of Cu oxidation by primarily in situ transmission electron microscopy methods. Through the use and development of computational tools at varying length (and time) scales, from atomistic quantum mechanical calculation, force field mesoscale simulations, to large scale Kinetic Monte Carlo (KMC) modeling, the fundamental underpinings of the initial stages of Cu oxidation have been elucidated. The development of computational modeling tools allows for accelerated materials discovery. The theoretical tools developed from this program impact a wide range of technologies that depend on surface reactions, including corrosion, catalysis, and nanomaterials fabrication.

  16. Attempts to comprehend Martian surface processes through interpretation of the oxygen isotopic compositions of carbonates in SNC meteorites

    Science.gov (United States)

    Wright, I. P.; Pillinger, C. T.; Grady, Monica M.

    1992-01-01

    The SNC meteorites are known to contain trace quantities of a variety of secondary minerals such as carbonates, sulfates, and aluminosilicates. Since these constituents are thought to be mostly preterrestrial in origin, their study has the potential to provide rigorous constraints on the nature of martian weathering processes. However, this line of investigation is potentially complicated by the presence within the meteorite samples of any additional weathering products produced by terrestrial processes. Examination of such terrestrial components is important since weathering processes that affect meteorite samples following their fall to Earth might have some bearing on the nature of analogous processes at the surface of Mars. It is obviously necessary to try and distinguish which secondary components in SNC meteorites are terrestrial in origin from those that are preterrestrial. Herein consideration is made of the stable isotopic compositions of weathering products in two SNC meteorites: EET A79001 (a sample collected from Antarctica) and Nakhla (a fall from Egypt, 1911).

  17. Atomic Oxygen (ATOX) simulation of Teflon FEP and Kapton H surfaces using a high intensity, low energy, mass selected, ion beam facility

    Science.gov (United States)

    Vered, R.; Grossman, E.; Lempert, G. D.; Lifshitz, Y.

    1994-11-01

    A high intensity (greater than 10(exp 15) ions/sq cm) low energy (down to 5 eV) mass selected ion beam (MSIB) facility was used to study the effects of ATOX on two polymers commonly used for space applications (Kapton H and Teflon FEP). The polymers were exposed to O(+) and Ne(+) fluences on 10(exp 15) - 10(exp 19) ions/sq cm, using 30eV ions. A variety of analytical methods were used to analyze the eroded surfaces including: (1) atomic force microscopy (AFM) for morphology measurements; (2) total mass loss measurements using a microbalance; (3) surface chemical composition using x-ray photoelectron spectroscopy (XPS), and (4) residual gas analysis (RGA) of the released gases during bombardment. The relative significance of the collisional and chemical degradation processes was evaluated by comparing the effects of Ne(+) and O(+) bombardment. For 30 eV ions it was found that the Kapton is eroded via chemical mechanisms while Teflon FEP is eroded via collisional mechanisms. AFM analysis was found very powerful in revealing the evolution of the damage from its initial atomic scale (roughness of approx. 1 nm) to its final microscopic scale (roughness greater than 1 micron). Both the surface morphology and the average roughness of the bombarded surfaces (averaged over 1 micron x 1 micron images by the system's computer) were determined for each sample. For 30 eV a non linear increase of the Kapton roughness with the O(+) fluence was discovered (a slow increase rate for fluences phi less than 5 x 10(exp 17) O(+)/sq cm, and a rapid increase rate for phi greater than 5 x 10(exp 17) O(+)/sq cm). Comparative studies on the same materials exposed to RF and DC oxygen plasmas indicate that the specific details of the erosion depend on the simulation facility emphasizing the advantages of the ion beam facility.

  18. Surface Reduced CeO2 Nanowires for Direct Conversion of CO2 and Methanol to Dimethyl Carbonate: Catalytic Performance and Role of Oxygen Vacancy

    Directory of Open Access Journals (Sweden)

    Zhongwei Fu

    2018-04-01

    Full Text Available Ultralong 1D CeO2 nanowires were synthesized via an advanced solvothermal method, surface reduced under H2 atmosphere, and first applied in direct synthesis of dimethyl carbonate (DMC from CO2 and CH3OH. The micro morphologies, physical parameters of nanowires were fully investigated by transmission electron microscopy (TEM, X-ray diffraction (XRD, N2 adsorption, X-ray photoelectron spectrum (XPS, and temperature-programmed desorption of ammonia/carbon dioxide (NH3-TPD/CO2-TPD. The effects of surface oxygen vacancy and acidic/alkaline sites on the catalytic activity was explored. After reduction, the acidic/alkaline sites of CeO2 nanowires can be dramatically improved and evidently raised the catalytic performance. CeO2 nanowires reduced at 500 °C (CeO2_NW_500 exhibited notably superior activity with DMC yield of 16.85 mmol gcat−1. Furthermore, kinetic insights of initial rate were carried out and the apparent activation energy barrier of CeO2_NW_500 catalyst was found to be 41.9 kJ/mol, much tiny than that of CeO2_NW catalyst (74.7 KJ/mol.

  19. Toward lattice fractional vector calculus

    International Nuclear Information System (INIS)

    Tarasov, Vasily E

    2014-01-01

    An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity. (papers)

  20. Oxygen Therapy

    Science.gov (United States)

    ... oxygen at very high altitudes (like in the mountains or in an airplane) even if you do ... an arterial blood gas (ABG) measurement. The ABG measures your oxygen level directly from your blood and ...

  1. Planktonic foraminiferal oxygen isotope analysis by ion microprobe technique suggests warm tropical sea surface temperatures during the Early Paleogene

    Science.gov (United States)

    Kozdon, Reinhard; Kelly, D. Clay; Kita, Noriko T.; Fournelle, John H.; Valley, John W.

    2011-09-01

    Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates based on the δ18O of planktonic foraminiferal tests. These results are difficult to reconcile with models of greenhouse gas-forced climate. It has been suggested that this "cool tropics paradox" arises from postdepositional alteration of foraminiferal calcite, yielding erroneously high δ18O values. Recrystallization of foraminiferal tests is cryptic and difficult to quantify, and the compilation of robust δ18O records from moderately altered material remains challenging. Scanning electron microscopy of planktonic foraminiferal chamber-wall cross sections reveals that the basal area of muricae, pustular outgrowths on the chamber walls of species belonging to the genus Morozovella, contain no mural pores and may be less susceptible to postdepositional alteration. We analyzed the δ18O in muricae bases of morozovellids from the central Pacific (Ocean Drilling Program Site 865) by ion microprobe using 10 μm pits with an analytical reproducibility of ±0.34‰ (2 standard deviations). In situ measurements of δ18O in these domains yield consistently lower values than those published for conventional multispecimen analyses. Assuming that the original δ18O is largely preserved in the basal areas of muricae, this new δ18O record indicates Early Paleogene (˜49-56 Ma) tropical SSTs in the central Pacific were 4°-8°C higher than inferred from the previously published δ18O record and that SSTs reached at least ˜33°C during the Paleocene-Eocene thermal maximum. This study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep-sea sediments.

  2. Introduction to lattice gauge theory

    International Nuclear Information System (INIS)

    Gupta, R.

    1987-01-01

    The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off ≅ 1/α, where α is the lattice spacing. The continuum (physical) behavior is recovered in the limit α → 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics. This will be the emphasis of the first lecture. In the second lecture, the author reviews the essential ingredients of formulating QCD on the lattice and discusses scaling and the continuum limit. In the last lecture the author summarizes the status of some of the main results. He also mentions the bottlenecks and possible directions for research. 88 refs

  3. Universality in Nonaqueous Alkali Oxygen Reduction on Metal Surfaces: Implications for Li−O2 and Na−O2 Batteries

    DEFF Research Database (Denmark)

    Krishnamurthy, Dilip; Hansen, Heine Anton; Viswanathan, Venkatasubramanian

    2016-01-01

    Nonaqueous metal−oxygen batteries, particularly lithium−oxygen and sodium−oxygen, have emerged as possible high energy density alternatives to Li-ion batteries that could address the limited driving range issues faced by electric vehicles. Many fundamental questions remain unanswered, including t...

  4. Methane oxidation over perovskite-related ferrites: Effects of oxygen nonstoichiometry

    Science.gov (United States)

    Kharton, V. V.; Patrakeev, M. V.; Waerenborgh, J. C.; Sobyanin, V. A.; Veniaminov, S. A.; Yaremchenko, A. A.; Gaczyński, P.; Belyaev, V. D.; Semin, G. L.; Frade, J. R.

    2005-11-01

    The oxidation of CH 4 pulses supplied in helium flow over perovskite-related La 0.3Sr 0.7Fe 0.8MO 3- δ ( M=Ga, Al) and SrFe 0.7Al 0.3O 3- δ leads to significant yields of CO and H 2 after achieving a critical level of oxygen deficiency in the ferrite-based mixed conductors. This effect, reproducible under steady-state conditions in the membrane reactors for methane conversion, may be of interest for the development of monolithic ceramic reactors where the dense membrane and porous catalyst at the permeate-side surface are made of similar compositions. The Mössbauer spectroscopy and coulometric titration studies show that the presence of metallic Fe under typical operation conditions can be neglected, whilst most oxygen vacancies in the ferrite lattices are ordered. Increasing selectivity towards the partial oxidation of methane is observed in the vicinity of the state where the iron cations are predominantly trivalent and massive ordering processes in the oxygen sublattice start. The catalytic activity of ferrite-based materials may hence result from the lattice instability characteristic of morphotropic phase transformations. The correlations between catalytic behavior and oxygen ionic transport are briefly discussed.

  5. Lattice Methods for Quantum Chromodynamics

    CERN Document Server

    DeGrand, Thomas

    2006-01-01

    Numerical simulation of lattice-regulated QCD has become an important source of information about strong interactions. In the last few years there has been an explosion of techniques for performing ever more accurate studies on the properties of strongly interacting particles. Lattice predictions directly impact many areas of particle and nuclear physics theory and phenomenology. This book provides a thorough introduction to the specialized techniques needed to carry out numerical simulations of QCD: a description of lattice discretizations of fermions and gauge fields, methods for actually do

  6. Localized structures in Kagome lattices

    Energy Technology Data Exchange (ETDEWEB)

    Saxena, Avadh B [Los Alamos National Laboratory; Bishop, Alan R [Los Alamos National Laboratory; Law, K J H [UNIV OF MASSACHUSETTS; Kevrekidis, P G [UNIV OF MASSACHUSETTS

    2009-01-01

    We investigate the existence and stability of gap vortices and multi-pole gap solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete case and in a continuum one with periodic external modulation. In particular, predictions are made based on expansion around a simple and analytically tractable anti-continuum (zero coupling) limit. These predictions are then confirmed for a continuum model of an optically-induced Kagome lattice in a photorefractive crystal obtained by a continuous transformation of a honeycomb lattice.

  7. Lattice sums then and now

    CERN Document Server

    Borwein, J M; McPhedran, R C

    2013-01-01

    The study of lattice sums began when early investigators wanted to go from mechanical properties of crystals to the properties of the atoms and ions from which they were built (the literature of Madelung's constant). A parallel literature was built around the optical properties of regular lattices of atoms (initiated by Lord Rayleigh, Lorentz and Lorenz). For over a century many famous scientists and mathematicians have delved into the properties of lattices, sometimes unwittingly duplicating the work of their predecessors. Here, at last, is a comprehensive overview of the substantial body of

  8. Addition of oxygen to and distribution of oxides in tantalum alloy T-111 at low concentrations

    Science.gov (United States)

    Stecura, S.

    1975-01-01

    Oxygen was added at 820 and 990 C at an oxygen pressure of about .0003 torr. The technique permitted predetermined and reproducible oxygen doping of the tantalum alloy (T-111). Based on the temperature dependency of the doping reaction, it was concluded that the initial rates of oxygen pickup are probably controlled by solution of oxygen into the T-111 lattice. Although hafnium oxides are more stable than those of tantalum or tungsten, analyses of extracted residues indicate that the tantalum and tungsten oxides predominate in the as-doped specimens, presumably because of the higher concentrations of tantalum and tungsten in the alloy. However, high-temperature annealing promotes gettering of dissolved oxygen and oxygen from other oxides to form hafnium oxides. Small amounts of tantalum and tungsten oxides were still present after high temperature annealing. Tungsten oxide (WO3) volatilizes slightly from the surface of T-111 at 990 C but not at 820 C. The vaporization of WO3 has no apparent effect on the doping reaction.

  9. Strontium-free rare earth perovskite ferrites with fast oxygen exchange kinetics: Experiment and theory

    Science.gov (United States)

    Berger, Christian; Bucher, Edith; Windischbacher, Andreas; Boese, A. Daniel; Sitte, Werner

    2018-03-01

    The Sr-free mixed ionic electronic conducting perovskites La0.8Ca0.2FeO3-δ (LCF82) and Pr0.8Ca0.2FeO3-δ (PCF82) were synthesized via a glycine-nitrate process. Crystal structure, phase purity, and lattice constants were determined by XRD and Rietveld analysis. The oxygen exchange kinetics and the electronic conductivity were obtained from in-situ dc-conductivity relaxation experiments at 600-800 °C and 1×10-3≤pO2/bar≤0.1. Both LCF82 and PCF82 show exceptionally fast chemical surface exchange coefficients and chemical diffusion coefficients of oxygen. The oxygen nonstochiometry of LCF82 and PCF82 was determined by precision thermogravimetry. A point defect model was used to calculate the thermodynamic factors of oxygen and to estimate self-diffusion coefficients and ionic conductivities. Density Functional Theory (DFT) calculations on the crystal structure, oxygen vacancy formation as well as oxygen migration energies are in excellent agreement with the experimental values. Due to their favourable properties both LCF82 and PCF82 are of interest for applications in solid oxide fuel cell cathodes, solid oxide electrolyser cell anodes, oxygen separation membranes, catalysts, or electrochemical sensors.

  10. Facile Preparation of Ultrathin Co3 O4 /Nanocarbon Composites with Greatly Improved Surface Activity as a Highly Efficient Oxygen Evolution Reaction Catalyst.

    Science.gov (United States)

    Chen, Yanyan; Hu, Jun; Diao, Honglin; Luo, Wenjing; Song, Yu-Fei

    2017-03-17

    The efficient catalytic oxidation of water to dioxygen plays a significant role in solar fuel and artificial photosynthetic systems. It remains highly challenging to develop oxygen evolution reaction (OER) catalysts with high activity and low cost under mild conditions. Here, a new composite material is reported based on ultrathin 2D Co 3 O 4 nanosheets and reduced graphene oxides (rGO) by means of a one-pot hydrothermal strategy. The ultrathin Co 3 O 4 /rGO nanocomposite shows superior stability under alkaline conditions and exhibits an overpotential of 290 mV with a Tafel slope of 68 mA dec -1 , which is much smaller than that of bare Co 3 O 4 catalyst. Extensive experiments were also carried out using 0D CS and 1D CNTs (CS=carbon spheres, CNTs=carbon nanotubes) in place of the 2D rGO. The overpotentials of as-prepared nanocomposites decrease with the increase of the dimension of nanocarbons, suggesting the electrochemistry activity is closely related to the surface area of carbon substrates. In addition, compared with ultrathin 2D Co 3 O 4 nanosheets with a Co 2+ /Co 3+ ratio of 1.2, the as-prepared ultrathin Co 3 O 4 /rGO nanocomposite with a Co 2+ /Co 3+ ratio of 1.4 contributes to the better OER performance as more oxygen vacancies can be formed in the ultrathin Co 3 O 4 /rGO nanocomposite under the experimental conditions. Compared with other Co 3 O 4 -containing composite materials reported so far, the ultrathin Co 3 O 4 /rGO nanocomposites show excellent OER performance. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Vortices and vortex lattices in quantum ferrofluids

    International Nuclear Information System (INIS)

    Martin, A M; Marchant, N G; Parker, N G; O’Dell, D H J

    2017-01-01

    The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices. Here we give a review of the theory of vortices in dipolar Bose–Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. We cover single vortex solutions, including structure, energy and stability, vortex pairs, including interactions and dynamics, and also vortex lattices. Our discussion is founded on the mean-field theory provided by the dipolar Gross–Pitaevskii equation, ranging from analytic treatments based on the Thomas–Fermi (hydrodynamic) and variational approaches to full numerical simulations. Routes for generating vortices in dipolar condensates are discussed, with particular attention paid to rotating condensates, where surface instabilities drive the nucleation of vortices, and lead to the emergence of rich and varied vortex lattice structures. We also present an outlook, including potential extensions to degenerate Fermi gases, quantum Hall physics, toroidal systems and the Berezinskii–Kosterlitz–Thouless transition. (topical review)

  12. Vortices and vortex lattices in quantum ferrofluids

    Science.gov (United States)

    Martin, A. M.; Marchant, N. G.; O'Dell, D. H. J.; Parker, N. G.

    2017-03-01

    The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices. Here we give a review of the theory of vortices in dipolar Bose-Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. We cover single vortex solutions, including structure, energy and stability, vortex pairs, including interactions and dynamics, and also vortex lattices. Our discussion is founded on the mean-field theory provided by the dipolar Gross-Pitaevskii equation, ranging from analytic treatments based on the Thomas-Fermi (hydrodynamic) and variational approaches to full numerical simulations. Routes for generating vortices in dipolar condensates are discussed, with particular attention paid to rotating condensates, where surface instabilities drive the nucleation of vortices, and lead to the emergence of rich and varied vortex lattice structures. We also present an outlook, including potential extensions to degenerate Fermi gases, quantum Hall physics, toroidal systems and the Berezinskii-Kosterlitz-Thouless transition.

  13. Hierarchical micron-sized mesoporous/macroporous graphene with well-tuned surface oxygen chemistry for high capacity and cycling stability Li-O2 battery.

    Science.gov (United States)

    Zhou, Wei; Zhang, Hongzhang; Nie, Hongjiao; Ma, Yiwen; Zhang, Yining; Zhang, Huamin

    2015-02-11

    Nonaqueous Li-O2 battery is recognized as one of the most promising energy storage devices for electric vehicles due to its super-high energy density. At present, carbon or catalyst-supporting carbon materials are widely used for cathode materials of Li-O2 battery. However, the unique electrode reaction and complex side reactions lead to numerous hurdles that have to be overcome. The pore blocking caused by the solid products and the byproducts generated from the side reactions severely limit the capacity performance and cycling stability. Thus, there is a great need to develop carbon materials with optimized pore structure and tunable surface chemistry to meet the special requirement of Li-O2 battery. Here, we propose a strategy of vacuum-promoted thermal expansion to fabricate one micron-sized graphene matrix with a hierarchical meso-/macroporous structure, combining with a following deoxygenation treatment to adjust the surface chemistry by reducing the amount of oxygen and selectively removing partial unstable groups. The as-made graphene demonstrates dramatically tailored pore characteristics and a well-tuned surface chemical environment. When applied in Li-O2 battery as cathode, it exhibits an outstanding capacity up to 19 800 mA h g(-1) and is capable of enduring over 50 cycles with a curtaining capacity of 1000 mA h g(-1) at a current density of 1000 mA g(-1). This will provide a novel pathway for the design of cathodes for Li-O2 battery.

  14. Stability issues in Pd-based catalysts: the role of surface Pt in improving the stability and oxygen reduction reaction (ORR) activity.

    Science.gov (United States)

    Singh, R K; Rahul, R; Neergat, M

    2013-08-21

    Carbon-supported Pd and Pd3Co catalysts have been electrochemically characterized in 0.1 M HClO4 solution and we found that both catalysts were unstable. On repeated potential cycling, the electrochemical surface area of the catalysts decreases and the oxygen reduction reaction (ORR) activity suffers. To stabilize surface Pd atoms of both Pd and Pd3Co catalysts, we deposited Pt using adsorbed hydrogen on the catalytically active Pd sites. The Pt : Pd ratio of Pt-coated Pd and Pt-coated Pd3Co catalysts suggests half-a-monolayer coverage of Pt (two hydrogen atoms required for reducing a Pt(2+) ion). The Pt : Pd ratio of Pt-coated Pd3Co catalyst obtained from the simple geometrical hard sphere model, energy-dispersive X-ray spectroscopy (EDS) line scan and bulk EDS agrees very well with that calculated from the hydrogen desorption (H(des)) charge of Pd3Co. At the same time, the Pt : Pd ratio of Pt-coated Pd calculated from the H(des) charge of Pd catalyst is significantly lower than the ratio obtained from the other methods. Thus, the Pt : Pd ratio of the Pt-coated Pd catalyst estimated from the H(des) region of Pd is an underestimation of the composition. This suggests that Pd forms an electrochemically inactive species from the H(upd) region itself and Co in Pd3Co seems to stabilize Pd against oxidation by delaying the formation of electrochemically inactive species to higher potentials above the H(upd) region. The voltammograms along with the peroxide formation characteristics of the catalysts support the above observations. The deposited Pt on the surface of the Pd and Pd3Co catalysts masks active Pd sites from the electrochemical environment and even partial coverage with Pt improves the stability and ORR activity of the catalysts when compared to that of the respective Pt-free counterparts.

  15. Phonons and elasticity in critically coordinated lattices

    International Nuclear Information System (INIS)

    Lubensky, T C; Kane, C L; Mao, Xiaoming; Sun, Kai; Souslov, A

    2015-01-01

    Much of our understanding of vibrational excitations and elasticity is based upon analysis of frames consisting of sites connected by bonds occupied by central-force springs, the stability of which depends on the average number of neighbors per site z. When z  <  z c   ≈  2d, where d is the spatial dimension, frames are unstable with respect to internal deformations. This pedagogical review focuses on the properties of frames with z at or near z c , which model systems like randomly packed spheres near jamming and network glasses. Using an index theorem, N 0   −N S   =  dN  −N B relating the number of sites, N, and number of bonds, N B , to the number, N 0 , of modes of zero energy and the number, N S , of states of self stress, in which springs can be under positive or negative tension while forces on sites remain zero, it explores the properties of periodic square, kagome, and related lattices for which z  =  z c and the relation between states of self stress and zero modes in periodic lattices to the surface zero modes of finite free lattices (with free boundary conditions). It shows how modifications to the periodic kagome lattice can eliminate all but trivial translational zero modes and create topologically distinct classes, analogous to those of topological insulators, with protected zero modes at free boundaries and at interfaces between different topological classes. (review article)

  16. Orientation of quartz nanocrystallites in the silicon lattice

    International Nuclear Information System (INIS)

    Kalanov, M.U.; Ibragimova, E.M.; Khamraeva, R.N.; Rustamova, V.M.; Ummatov, Kh.D.

    2006-01-01

    Full text: Basing on the study of medium angle diffuse X-ray scattering from silicon single crystals, it was supposed to be due to rod like oxygen precipitates. It was shown by us later, that depending on the growth conditions, as-grown silicon single crystals contain quartz crystal inclusions at an amount of 0.3 / 0.5 wt. % . Since it has not been done before, the aim of this work was to study the shape and orientation of quartz inclusions relative to a chosen axis of the silicon crystal lattice. We studied p-Si single crystals of one crucible origin with the specific resistance ρ 0 ≅ 1/10 Ohm· cm with different cut surfaces parallel to the crystal planes (100), (110) and (111). All the samples were cut and polished in the bar form with the sizes of 20x12x1.5 mm 3 . The dislocation density was N D ≅ 10 1 /10 3 cm -2 , the concentrations of oxygen and boron were N O ≅ 2/ 4 x10 17 cm -3 and N B ≅ 3· 10 1 5 c m -3 . Structure was analyzed at the set-up DRON-3M ( λ Cu K∝ = 0.1542 nm) at the room temperature in the angle range of angles 2Θ = 10/70 deg. The diffraction spectrum of the sample cut in (111) includes 5 selective reflections and the only diffuse one at 2Θ≅ 20 deg (d/n≅ 0.3136 nm), having a large width 0.1032 rad, which is due to presence of amorphous SiO x precipitate in the surface layer of silicon single crystal. The dominative selective line with d/n≅ 0.3136 nm at 2Θ≅ 28.5 deg belongs to reflection from (111) planes of the silicon lattice and the second less intensive one comes from the same planes with Cu K β radiation. Another selective reflection of a medium intensity at 2Θ≅ 59 deg with d/n≅ 0.1568 nm is its second order (222) and forbidden by the weakening laws. The rest narrow but weak lines with d/n≅ 0.3345 nm at 2Θ≅ 26.6 deg and 0.2468 nm at≅36.6 deg correspond to the diffraction reflections (101) and (110) from the crystal quartz lattice SiO 2 . It means that they are caused by optimally oriented quartz

  17. Lattice gauge theory for QCD

    Energy Technology Data Exchange (ETDEWEB)

    DeGrand, T. [Univ. of Colorado, Boulder, CO (United States). Dept. of Physics

    1997-06-01

    These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and {alpha}{sub s} (M{sub z}), and B-{anti B} mixing. 67 refs., 36 figs.

  18. Lattice Studies of Hyperon Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Richards, David G. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

    2016-04-01

    I describe recent progress at studying the spectrum of hadrons containing the strange quark through lattice QCD calculations. I emphasise in particular the richness of the spectrum revealed by lattice studies, with a spectrum of states at least as rich as that of the quark model. I conclude by prospects for future calculations, including in particular the determination of the decay amplitudes for the excited states.

  19. Harmonic oscillator on a lattice

    International Nuclear Information System (INIS)

    Ader, J.P.; Bonnier, B.; Hontebeyrie, M.; Meyers, C.

    1983-01-01

    The continuum limit of the ground state energy for the harmonic oscillator with discrete time is derived for all possible choices of the lattice derivative. The occurrence of unphysical values is shown to arise whenever the lattice laplacian is not strictly positive on its Brillouin zone. These undesirable limits can either be finite and arbitrary (multiple spectrum) or infinite (overlapping sublattices with multiple spectrum). (orig.)

  20. Lattice gauge theory for QCD

    International Nuclear Information System (INIS)

    DeGrand, T.

    1997-01-01

    These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and α s (M z ), and B-anti B mixing. 67 refs., 36 figs

  1. Operando XAS Study of the Surface Oxidation State on a Monolayer IrOx on RuOx and Ru Oxide Based Nanoparticles for Oxygen Evolution in Acidic Media

    DEFF Research Database (Denmark)

    Pedersen, Anders Filsøe; Escribano, Maria Escudero; Sebok, Bela

    2017-01-01

    that the average Ir oxidation state change is strongly affected by the coverage of atomic O. The observed shifts in oxidation state suggest that the surface has a high coverage of O at potentials just below the potential where oxygen evolution is exergonic in free energy. This observation is consistent...

  2. Topological Nematic States and Non-Abelian Lattice Dislocations

    Directory of Open Access Journals (Sweden)

    Maissam Barkeshli

    2012-08-01

    Full Text Available An exciting new prospect in condensed matter physics is the possibility of realizing fractional quantum Hall states in simple lattice models without a large external magnetic field. A fundamental question is whether qualitatively new states can be realized on the lattice as compared with ordinary fractional quantum Hall states. Here we propose new symmetry-enriched topological states, topological nematic states, which are a dramatic consequence of the interplay between the lattice translational symmetry and topological properties of these fractional Chern insulators. The topological nematic states are realized in a partially filled flat band with a Chern number N, which can be mapped to an N-layer quantum Hall system on a regular lattice. However, in the topological nematic states the lattice dislocations can act as wormholes connecting the different layers and effectively change the topology of the space. Consequently, lattice dislocations become defects with a nontrivial quantum dimension, even when the fractional quantum Hall state being realized is, by itself, Abelian. Our proposal leads to the possibility of realizing the physics of topologically ordered states on high-genus surfaces in the lab even though the sample has only the disk geometry.

  3. Homomorphisms of complete distributive lattices | Pultr ...

    African Journals Online (AJOL)

    A survey of analogous results on algebraic universality of categories based on finitary distributive (0, 1)-lattices is included to motivate further questions about categories based on complete distributive lattices. Keywords: complete distributive lattice, complete lattice homomorphism, frame, Heyting algebra, continuous map, ...

  4. Lattice gauge theory using parallel processors

    International Nuclear Information System (INIS)

    Lee, T.D.; Chou, K.C.; Zichichi, A.

    1987-01-01

    The book's contents include: Lattice Gauge Theory Lectures: Introduction and Current Fermion Simulations; Monte Carlo Algorithms for Lattice Gauge Theory; Specialized Computers for Lattice Gauge Theory; Lattice Gauge Theory at Finite Temperature: A Monte Carlo Study; Computational Method - An Elementary Introduction to the Langevin Equation, Present Status of Numerical Quantum Chromodynamics; Random Lattice Field Theory; The GF11 Processor and Compiler; and The APE Computer and First Physics Results; Columbia Supercomputer Project: Parallel Supercomputer for Lattice QCD; Statistical and Systematic Errors in Numerical Simulations; Monte Carlo Simulation for LGT and Programming Techniques on the Columbia Supercomputer; Food for Thought: Five Lectures on Lattice Gauge Theory

  5. Stable isotope oxygen-18 and deuterium analysis in surface and groundwater of the Jequitibá Creek Basin, Sete Lagoas, MG

    Energy Technology Data Exchange (ETDEWEB)

    Linhares, Giovanna Maria Gardini; Moreira, Rubens Martins; Pimenta, Rafael Colombo; Scarpelli, Raquel Pazzini; Santos, Elizangela Augusta dos, E-mail: giovannagardini@gmail.com, E-mail: rubens@cdtn.br, E-mail: colombopimenta@gmail.com, E-mail: raquelscarpelli@gmail.com, E-mail: elizangela.augusta@gmail.com [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2017-07-01

    Groundwater is an important source of public and industrial supplies, and inadequate exploitation of water reflects negatively on its quality and production of wells, especially when located in karstic aquifers. The study area includes the Maize and Sorghum National Research / Embrapa, located in the karst region of Sete Lagoas, within of the Jequitibá creek sub-basin, an affluent of the Velhas River. The evaluation of the content of stable isotopes of hydrogen ({sup 2}H), or deuterium, and oxygen ({sup 18}O) of surface waters (lagoons) and groundwater (production and monitoring wells) collected from the study area allowed to know directly the origin of these waters, active climatic processes and interactions between different aquifers and surface bodies, as possible mixtures of water from different sources. The collected samples were analyzed by isotopic ratio mass spectrometry, IRMS Advantege - Thermo Science, from the Center for the Development of Nuclear Technology (CDTN). The mean values found for δ{sup 18}O and δ{sup 2}H in the waters of the monitoring wells were -6.40‰ and -43.21‰, respectively. For the production wells, mean values for δ{sup 18}O and δ{sup 2}H of -5.87 ‰ and -40.09‰, respectively, were obtained. When compared to GMWL, the collected groundwater originates attributed to the precipitations. The lagoon waters had mean values for δ{sup 18}O and δ{sup 2}H of -3.73‰ and -30.08‰. The water collected in the crystalline fissured aquifer presented mean values δ{sup 18}O and δ{sup 2}H of -6.91‰ and -40.26 ‰ respectively, in its rockier portion, and -6.09‰ and -43.05‰. (author)

  6. Stable isotope oxygen-18 and deuterium analysis in surface and groundwater of the Jequitibá Creek Basin, Sete Lagoas, MG

    International Nuclear Information System (INIS)

    Linhares, Giovanna Maria Gardini; Moreira, Rubens Martins; Pimenta, Rafael Colombo; Scarpelli, Raquel Pazzini; Santos, Elizangela Augusta dos

    2017-01-01

    Groundwater is an important source of public and industrial supplies, and inadequate exploitation of water reflects negatively on its quality and production of wells, especially when located in karstic aquifers. The study area includes the Maize and Sorghum National Research / Embrapa, located in the karst region of Sete Lagoas, within of the Jequitibá creek sub-basin, an affluent of the Velhas River. The evaluation of the content of stable isotopes of hydrogen ( 2 H), or deuterium, and oxygen ( 18 O) of surface waters (lagoons) and groundwater (production and monitoring wells) collected from the study area allowed to know directly the origin of these waters, active climatic processes and interactions between different aquifers and surface bodies, as possible mixtures of water from different sources. The collected samples were analyzed by isotopic ratio mass spectrometry, IRMS Advantege - Thermo Science, from the Center for the Development of Nuclear Technology (CDTN). The mean values found for δ 18 O and δ 2 H in the waters of the monitoring wells were -6.40‰ and -43.21‰, respectively. For the production wells, mean values for δ 18 O and δ 2 H of -5.87 ‰ and -40.09‰, respectively, were obtained. When compared to GMWL, the collected groundwater originates attributed to the precipitations. The lagoon waters had mean values for δ 18 O and δ 2 H of -3.73‰ and -30.08‰. The water collected in the crystalline fissured aquifer presented mean values δ 18 O and δ 2 H of -6.91‰ and -40.26 ‰ respectively, in its rockier portion, and -6.09‰ and -43.05‰. (author)

  7. Investigation of oxygen reduction and methanol oxidation reaction activity of PtAu nano-alloy on surface modified porous hybrid nanocarbon supports

    Science.gov (United States)

    Parambath Vinayan, Bhaghavathi; Nagar, Rupali; Ramaprabhu, Sundara

    2016-09-01

    We investigate the electrocatalytic activity of PtAu alloy nanoparticles supported on various chemically modified carbon morphologies towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). The surface-modification of graphene nanosheets (f-G), multi-walled carbon nanotubes (f-MWNTs) and (graphene nanosheets-carbon nanotubes) hybrid support (f-G-MWNTs) were carried out by soft functionalization method using a cationic polyelectrolyte poly-(diallyldimethyl ammonium chloride). The Pt and PtAu alloy nanoparticles were dispersed over chemically modified carbon supports by sodium-borohydride assisted modified polyol reduction method. The electrochemical performance of all electrocatalysts were studied by half- and full-cell proton exchange membrane fuel cell (PEMFC) measurements and PtAu/f-G-MWNTs catalyst comparatively yielded the best catalytic performance. PEMFC full cell measurements of PtAu/f-G-MWNTs cathode electrocatalyst yield a maximum power density of 319 mW cm-2 at 60 °C without any back pressure,which is 2.1 times higher than that of cathode electrocatalyst Pt on graphene support. The high ORR and MOR activity of PtAu/f-G-MWNTs electrocatalyst is due to the alloying effect and inherent beneficial properties of porous hybrid nanocarbon support.

  8. Effect of Si Content on Oxide Formation on Surface of Molten Fe-Cr-C Alloy Bath During Oxygen Top Blowing

    Science.gov (United States)

    Mihara, Ryosuke; Gao, Xu; Kim, Sun-joong; Ueda, Shigeru; Shibata, Hiroyuki; Seok, Min Oh; Kitamura, Shin-ya

    2018-02-01

    Using a direct observation experimental method, the oxide formation behavior on the surface of Fe-Cr-5 mass pct C-Si alloy baths during decarburization by a top-blown Ar-O2 mixture was studied. The effects of the initial Si and Cr content of the alloy, temperature, and oxygen feed ratio on oxide formation were investigated. The results showed that, for alloys without Si, oxide particles, unstable oxide films, and stable oxide films formed sequentially. The presence of Si in the alloy changed the formation behavior of stable oxide film, and increased the crucial C content when stable oxide film started to form. Increasing the temperature, decreasing the initial Cr content, and increasing the ratio of the diluting gas decreased the critical C content at which a stable oxide film started to form. In addition, the P CO and a_{{{Cr}2 {O}3 }} values at which oxides started to form were estimated using Hilty's equation and the equilibrium relation to understand the formation conditions and the role of each parameter in oxide formation.

  9. Embedded Lattice and Properties of Gram Matrix

    Directory of Open Access Journals (Sweden)

    Futa Yuichi

    2017-03-01

    Full Text Available In this article, we formalize in Mizar [14] the definition of embedding of lattice and its properties. We formally define an inner product on an embedded module. We also formalize properties of Gram matrix. We formally prove that an inverse of Gram matrix for a rational lattice exists. Lattice of Z-module is necessary for lattice problems, LLL (Lenstra, Lenstra and Lov´asz base reduction algorithm [16] and cryptographic systems with lattice [17].

  10. Quasi-hexagonal vortex-pinning lattice using anodized aluminum oxide nanotemplates

    DEFF Research Database (Denmark)

    Hallet, X.; Mátéfi-Tempfli, M.; Michotte, S.

    2009-01-01

    The bottom barrier layer of well-ordered nanoporous alumina membranes reveals a previously unexploited nanostructured template surface consisting of a triangular lattice of hemispherical nanoscale bumps. Quasi-hexagonal vortex-pinning lattice arrays are created in superconducting Nb films deposit...

  11. Oscillations of void lattices

    International Nuclear Information System (INIS)

    Akhiezer, A.I.; Davydov, L.N.; Spol'nik, Z.A.

    1976-01-01

    Oscillations of a nonideal crystal are studied, in which macroscopic defects (pores) form a hyperlattice. It is shown that alongside with acoustic and optical phonons (relative to the hyperlattice), in such a crystal oscillations of the third type are possible which are a hydridization of sound oscillations of atoms and surface oscillations of a pore. Oscillation spectra of all three types were obtained

  12. Corrosion of copper in oxygen-deficient groundwater with and without deep bedrock micro-organisms: Characterisation of microbial communities and surface processes

    Energy Technology Data Exchange (ETDEWEB)

    Huttunen-Saarivirta, E., E-mail: elina.huttunen-saarivirta@vtt.fi [VTT Technical Research Centre of Finland, Materials Performance, Kemistintie 3, FI-02044 VTT (Finland); Rajala, P. [VTT Technical Research Centre of Finland, Materials Performance, Kemistintie 3, FI-02044 VTT (Finland); Bomberg, M. [VTT Technical Research Centre of Finland, Geobiotechnology, Tietotie 2, FI-02044 VTT (Finland); Carpén, L. [VTT Technical Research Centre of Finland, Materials Performance, Kemistintie 3, FI-02044 VTT (Finland)

    2017-02-28

    Highlights: • Copper was exposed to groundwater with and without deep bedrock micro-organisms. • Biofilm composition was determined and correlated with the behaviour of copper. • Under biotic conditions, the film of Cu{sub 2}S formed on copper surfaces. • Bacterial pool was in a key role for the morphology and properties of Cu{sub 2}S film. • Under abiotic conditions, Cu{sub 2}O systematically developed on copper surfaces. - Abstract: Copper specimens were exposed to oxygen-deficient artificial groundwater in the presence and absence of micro-organisms enriched from the deep bedrock of the planned nuclear waste repository site at Olkiluoto island on the western coast of Finland. During the exposure periods of 4 and 10 months, the copper specimens were subjected to electrochemical measurements. The biofilm developed on the specimens and the water used in the exposures were subjected to microbiological analyses. Changes in the water chemistry were also determined and surfaces of the copper specimens were characterized with respect to the morphology and composition of the formed corrosion products. The results showed that under biotic conditions, redox of the water and open circuit potential (OCP) of the copper specimens were generally negative and resulted in the build-up of a copper sulphide, Cu{sub 2}S, layer due to the activity of sulphate-reducing bacteria (SRB) that were included in the system. In the 4-month test, the electrochemical behaviour of the specimens changed during the exposure and alphaproteobactria Rhizobiales were the dominant bacterial group in the biofilm where the highest corrosion rate was observed. In the 10-month test, however, deltaproteobacteria SRB flourished and the initial electrochemical behaviour and the low corrosion rate of the copper were retained until the end of the test period. Under abiotic conditions, the positive water redox potential and specimen OCP correlated with the formation of copper oxide, Cu{sub 2}O

  13. Lead-containing solid "oxygen reservoirs" for selective hydrogen combustion

    NARCIS (Netherlands)

    Beckers, J.; Rothenberg, G.

    2009-01-01

    Lead-containing catalysts can be applied as solid "oxygen reservoirs" in a novel process for propane oxidative dehydrogenation. The catalyst lattice oxygen selectively burns hydrogen from the dehydrogenation mixture at 550 degrees C. This shifts the dehydrogenation equilibrium to the desired

  14. Grassmann methods in lattice field theory and statistical mechanics

    International Nuclear Information System (INIS)

    Bilgici, E.; Gattringer, C.; Huber, P.

    2006-01-01

    Full text: In two dimensions models of loops can be represented as simple Grassmann integrals. In our work we explore the generalization of these techniques to lattice field theories and statistical mechanic systems in three and four dimensions. We discuss possible strategies and applications for representations of loop and surface models as Grassmann integrals. (author)

  15. Surface passivation of natural graphite electrode for lithium ion battery by chlorine gas.

    Science.gov (United States)

    Suzuki, Satoshi; Mazej, Zoran; Zemva, Boris; Ohzawa, Yoshimi; Nakajima, Tsuyoshi

    2013-01-01

    Surface lattice defects would act as active sites for electrochemical reduction of propylene carbonate (PC) as a solvent for lithium ion battery. Effect of surface chlorination of natural graphite powder has been investigated to improve charge/discharge characteristics of natural graphite electrode in PC-containing electrolyte solution. Chlorination of natural graphite increases not only surface chlorine but also surface oxygen, both of which would contribute to the decrease in surface lattice defects. It has been found that surface-chlorinated natural graphite samples with surface chlorine concentrations of 0.5-2.3 at% effectively suppress the electrochemical decomposition of PC, highly reducing irreversible capacities, i.e. increasing first coulombic efficiencies by 20-30% in 1 mol L-1 LiClO4-EC/DEC/PC (1:1:1 vol.). In 1 mol L-1 LiPF6-EC/EMC/PC (1:1:1 vol.), the effect of surface chlorination is observed at a higher current density. This would be attributed to decrease in surface lattice defects of natural graphite powder by the formation of covalent C-Cl and C=O bonds.

  16. Chemical diffusion and oxygen surface transfer of La1-xSrxCoO3-d studied with electrical conductivity relaxation

    NARCIS (Netherlands)

    van der Haar, L.M.; den Otter, M.W.; Morskate, M.; Bouwmeester, Henricus J.M.; Verweij, H.

    2002-01-01

    The chemical diffusion coefficient and oxygen-transfer coefficients of selected compositions in the series $La_1-xSr_xCoO_3-delta$ were studied using the conductivity relaxation technique. Measurements were performed in the temperature range 600-850°C and oxygen partial pressure $10-4$ to 1 bar.

  17. Finite-lattice-spacing corrections to masses and g factors on a lattice

    International Nuclear Information System (INIS)

    Roskies, R.; Wu, J.C.

    1986-01-01

    We suggest an alternative method for extracting masses and g factors from lattice calculations. Our method takes account of more of the infrared and ultraviolet lattice effects. It leads to more reasonable results in simulations of QED on a lattice

  18. Frustrated lattices of Ising chains

    International Nuclear Information System (INIS)

    Kudasov, Yurii B; Korshunov, Aleksei S; Pavlov, V N; Maslov, Dmitrii A

    2012-01-01

    The magnetic structure and magnetization dynamics of systems of plane frustrated Ising chain lattices are reviewed for three groups of compounds: Ca 3 Co 2 O 6 , CsCoCl 3 , and Sr 5 Rh 4 O 12 . The available experimental data are analyzed and compared in detail. It is shown that a high-temperature magnetic phase on a triangle lattice is normally and universally a partially disordered antiferromagnetic (PDA) structure. The diversity of low-temperature phases results from weak interactions that lift the degeneracy of a 2D antiferromagnetic Ising model on the triangle lattice. Mean-field models, Monte Carlo simulation results on the static magnetization curve, and results on slow magnetization dynamics obtained with Glauber's theory are discussed in detail. (reviews of topical problems)

  19. Lattice QCD without topology barriers

    CERN Document Server

    Lüscher, Martin

    2011-01-01

    As the continuum limit is approached, lattice QCD simulations tend to get trapped in the topological charge sectors of field space and may consequently give biased results in practice. We propose to bypass this problem by imposing open (Neumann) boundary conditions on the gauge field in the time direction. The topological charge can then flow in and out of the lattice, while many properties of the theory (the hadron spectrum, for example) are not affected. Extensive simulations of the SU(3) gauge theory, using the HMC and the closely related SMD algorithm, confirm the absence of topology barriers if these boundary conditions are chosen. Moreover, the calculated autocorrelation times are found to scale approximately like the square of the inverse lattice spacing, thus supporting the conjecture that the HMC algorithm is in the universality class of the Langevin equation.

  20. Soliton mobility in disordered lattices.

    Science.gov (United States)

    Sun, Zhi-Yuan; Fishman, Shmuel; Soffer, Avy

    2015-10-01

    We investigate soliton mobility in the disordered Ablowitz-Ladik (AL) model and the standard nonlinear Schrödinger (NLS) lattice with the help of an effective potential generalizing the Peierls-Nabarro potential. This potential results from a deviation from integrability, which is due to randomness for the AL model, and both randomness and lattice discreteness for the NLS lattice. The statistical properties of such a potential are analyzed, and it is shown how the soliton mobility is affected by its size. The usefulness of this effective potential in studying soliton dynamics is demonstrated numerically. Furthermore, we propose two ways to enhance soliton transport in the presence of disorder: one is to use specific realizations of randomness, and the other is to consider a specific soliton pair.

  1. Lattice QCD for nuclear physics

    CERN Document Server

    Meyer, Harvey

    2015-01-01

    With ever increasing computational resources and improvements in algorithms, new opportunities are emerging for lattice gauge theory to address key questions in strongly interacting systems, such as nuclear matter. Calculations today use dynamical gauge-field ensembles with degenerate light up/down quarks and the strange quark and it is possible now to consider including charm-quark degrees of freedom in the QCD vacuum. Pion masses and other sources of systematic error, such as finite-volume and discretization effects, are beginning to be quantified systematically. Altogether, an era of precision calculation has begun, and many new observables will be calculated at the new computational facilities.  The aim of this set of lectures is to provide graduate students with a grounding in the application of lattice gauge theory methods to strongly interacting systems, and in particular to nuclear physics.  A wide variety of topics are covered, including continuum field theory, lattice discretizations, hadron spect...

  2. Equations Holding in Hilbert Lattices

    Science.gov (United States)

    Mayet, René

    2006-07-01

    We produce and study several sequences of equations, in the language of orthomodular lattices, which hold in the ortholattice of closed subspaces of any classical Hilbert space, but not in all orthomodular lattices. Most of these equations hold in any orthomodular lattice admitting a strong set of states whose values are in a real Hilbert space. For some of these equations, we give conditions under which they hold in the ortholattice of closed subspaces of a generalised Hilbert space. These conditions are relative to the dimension of the Hilbert space and to the characteristic of its division ring of scalars. In some cases, we show that these equations cannot be deduced from the already known equations, and we study their mutual independence. To conclude, we suggest a new method for obtaining such equations, using the tensorial product.

  3. Lattice-Boltzmann Simulation of Tablet Disintegration

    Science.gov (United States)

    Jiang, Jiaolong; Sun, Ning; Gersappe, Dilip

    Using the lattice-Boltzmann method, we developed a 2D model to study the tablet disintegration involving the swelling and wicking mechanisms. The surface area and disintegration profile of each component were obtained by tracking the tablet structure in the simulation. Compared to pure wicking, the total surface area is larger for swelling and wicking, which indicates that the swelling force breaks the neighboring bonds. The disintegration profiles show that the tablet disintegrates faster than pure wicking, and there are more wetted active pharmaceutical ingredient particles distributed on smaller clusters. Our results indicate how the porosity would affect the disintegration process by changing the wetting area of the tablet as well as by changing the swelling force propagation.

  4. Nucleon structure from lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Dinter, Simon

    2012-11-13

    In this thesis we compute within lattice QCD observables related to the structure of the nucleon. One part of this thesis is concerned with moments of parton distribution functions (PDFs). Those moments are essential elements for the understanding of nucleon structure and can be extracted from a global analysis of deep inelastic scattering experiments. On the theoretical side they can be computed non-perturbatively by means of lattice QCD. However, since the time lattice calculations of moments of PDFs are available, there is a tension between these lattice calculations and the results from a global analysis of experimental data. We examine whether systematic effects are responsible for this tension, and study particularly intensively the effects of excited states by a dedicated high precision computation. Moreover, we carry out a first computation with four dynamical flavors. Another aspect of this thesis is a feasibility study of a lattice QCD computation of the scalar quark content of the nucleon, which is an important element in the cross-section of a heavy particle with the nucleon mediated by a scalar particle (e.g. Higgs particle) and can therefore have an impact on Dark Matter searches. Existing lattice QCD calculations of this quantity usually have a large error and thus a low significance for phenomenological applications. We use a variance-reduction technique for quark-disconnected diagrams to obtain a precise result. Furthermore, we introduce a new stochastic method for the calculation of connected 3-point correlation functions, which are needed to compute nucleon structure observables, as an alternative to the usual sequential propagator method. In an explorative study we check whether this new method is competitive to the standard one. We use Wilson twisted mass fermions at maximal twist in all our calculations, such that all observables considered here have only O(a{sup 2}) discretization effects.

  5. Kondo length in bosonic lattices

    Science.gov (United States)

    Giuliano, Domenico; Sodano, Pasquale; Trombettoni, Andrea

    2017-09-01

    Motivated by the fact that the low-energy properties of the Kondo model can be effectively simulated in spin chains, we study the realization of the effect with bond impurities in ultracold bosonic lattices at half filling. After presenting a discussion of the effective theory and of the mapping of the bosonic chain onto a lattice spin Hamiltonian, we provide estimates for the Kondo length as a function of the parameters of the bosonic model. We point out that the Kondo length can be extracted from the integrated real-space correlation functions, which are experimentally accessible quantities in experiments with cold atoms.

  6. Graphene on graphene antidot lattices

    DEFF Research Database (Denmark)

    Gregersen, Søren Schou; Pedersen, Jesper Goor; Power, Stephen

    2015-01-01

    Graphene bilayer systems are known to exhibit a band gap when the layer symmetry is broken by applying a perpendicular electric field. The resulting band structure resembles that of a conventional semiconductor with a parabolic dispersion. Here, we introduce a bilayer graphene heterostructure......, where single-layer graphene is placed on top of another layer of graphene with a regular lattice of antidots. We dub this class of graphene systems GOAL: graphene on graphene antidot lattice. By varying the structure geometry, band-structure engineering can be performed to obtain linearly dispersing...

  7. Lattice calculations in gauge theory

    International Nuclear Information System (INIS)

    Rebbi, C.

    1985-01-01

    The lattice formulation of quantum gauge theories is discussed as a viable technique for quantitative studies of nonperturbative effects in QCD. Evidence is presented to ascertain that whole classes of lattice actions produce a universal continuum limit. Discrepancies between numerical results from Monto Carlo simulations for the pure gauge system and for the system with gauge and quark fields are discussed. Numerical calculations for QCD require very substantial computational resources. The use of powerful vector processors of special purpose machines, in extending the scope and magnitude or the calculations is considered, and one may reasonably expect that in the near future good quantitative predictions will be obtained for QCD

  8. Nuclear Physics from Lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    William Detmold, Silas Beane, Konstantinos Orginos, Martin Savage

    2011-01-01

    We review recent progress toward establishing lattice Quantum Chromodynamics as a predictive calculational framework for nuclear physics. A survey of the current techniques that are used to extract low-energy hadronic scattering amplitudes and interactions is followed by a review of recent two-body and few-body calculations by the NPLQCD collaboration and others. An outline of the nuclear physics that is expected to be accomplished with Lattice QCD in the next decade, along with estimates of the required computational resources, is presented.

  9. [Lattice degeneration of the retina].

    Science.gov (United States)

    Boĭko, E V; Suetov, A A; Mal'tsev, D S

    2014-01-01

    Lattice degeneration of the retina is a clinically important type of peripheral retinal dystrophies due to its participation in the pathogenesis of rhegmatogenous retinal detachment. In spite of extensive epidemiological, morphological, and clinical data, the question on causes of this particular type of retinal dystrophies currently remains debatable. Existing hypotheses on pathogenesis of retinal structural changes in lattice degeneration explain it to a certain extent. In clinical ophthalmology it is necessary to pay close attention to this kind of degenerations and distinguish between cases requiring preventive treatment and those requiring monitoring.

  10. Three Classes of Orthomodular Lattices

    Science.gov (United States)

    Greechie, Richard J.; Legan, Bruce J.

    2006-02-01

    Let mathcal{OML} denote the class of all orthomodular lattices and mathcal{C} denote the class of those that are commutator-finite. Also, let mathcal{C}1 denote the class of orthomodular lattices that satisfy the block extension property, mathcal{C}2 those that satisfy the weak block extension property, and mathcal{C}3 those that are locally finite. We show that the following strict containments hold: mathcal{C} subset mathcal{C}1 subset mathcal{C}2 subset mathcal{C}3 subset mathcal{OML}.

  11. Unconventional superconductivity in honeycomb lattice

    Directory of Open Access Journals (Sweden)

    P Sahebsara

    2013-03-01

    Full Text Available   ‎ The possibility of symmetrical s-wave superconductivity in the honeycomb lattice is studied within a strongly correlated regime, using the Hubbard model. The superconducting order parameter is defined by introducing the Green function, which is obtained by calculating the density of the electrons ‎ . In this study showed that the superconducting order parameter appears in doping interval between 0 and 0.5, and x=0.25 is the optimum doping for the s-wave superconductivity in honeycomb lattice.

  12. Machines for lattice gauge theory

    International Nuclear Information System (INIS)

    Mackenzie, P.B.

    1989-05-01

    The most promising approach to the solution of the theory of strong interactions is large scale numerical simulation using the techniques of lattice gauge theory. At the present time, computing requirements for convincing calculations of the properties of hadrons exceed the capabilities of even the most powerful commercial supercomputers. This has led to the development of massively parallel computers dedicated to lattice gauge theory. This talk will discuss the computing requirements behind these machines, and general features of the components and architectures of the half dozen major projects now in existence. 20 refs., 1 fig

  13. Surface layer composition of titania produced by various methods. The change of layer state under illumination

    International Nuclear Information System (INIS)

    Zakharenko, V; Daibova, E; Zmeeva, O; Kosova, N

    2016-01-01

    The comparative analysis of experimental data over titanium dioxide powders prepared by various ways under ambient air is carried out. The results over TiO 2 prepared by high-temperature heating of anatase, produced by burning of titanium micro particles and grinding of rutile crystal are used for that comparison. Water and carbon dioxide were the main products released from the surface of the titania powders. It was found that under UV irradiation absorbed by titania, in absent oxygen, water effectively reacts with lattice oxygen of titanium dioxide. (paper)

  14. Lattice constant in nonstoichiometric uranium dioxide from first principles

    Science.gov (United States)

    Bruneval, Fabien; Freyss, Michel; Crocombette, Jean-Paul

    2018-02-01

    Nonstoichiometric uranium dioxide experiences a shrinkage of its lattice constant with increasing oxygen content, in both the hypostoichiometric and the hyperstoichiometric regimes. Based on first-principles calculations within the density functional theory (DFT)+U approximation, we have developed a point defect model that accounts for the volume of relaxation of the most significant intrinsic defects of UO2. Our point defect model takes special care of the treatment of the charged defects in the equilibration of the model and in the determination of reliable defect volumes of formation. In the hypostoichiometric regime, the oxygen vacancies are dominant and explain the lattice constant variation with their surprisingly positive volume of relaxation. In the hyperstoichiometric regime, the uranium vacancies are predicted to be the dominating defect,in contradiction with experimental observations. However, disregarding uranium vacancies allows us to recover a good match for the lattice-constant variation as a function of stoichiometry. This can be considered a clue that the uranium vacancies are indeed absent in UO2 +x, possibly due to the very slow diffusion of uranium.

  15. Electron energy-loss spectroscopic study of the surface of ceria abrasives

    International Nuclear Information System (INIS)

    Gilliss, Shelley R.; Bentley, James; Carter, C. Barry

    2005-01-01

    Surfaces of ceria (CeO 2 ) particles have been studied by electron energy-loss spectroscopy in a field-emission gun scanning transmission electron microscope. All the ceria particles analyzed contained Ce 3+ at the surface. Rare-earth impurities such as La were enriched at the surface and were observed for particles ranging from tens to hundreds of nanometers in size. Fluorine in the abrasives corresponded to a lower average cerium valence. Time series investigations indicate that fluorine substitutes on the oxygen sub-lattice and is charge-balanced by some cerium changing from Ce 4+ to Ce 3+

  16. Electron energy-loss spectroscopic study of the surface of ceria abrasives

    Energy Technology Data Exchange (ETDEWEB)

    Gilliss, Shelley R. [Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue S.E., 151 Amundson Hall, Minneapolis, MN 55455 0132 (United States); Bentley, James [Oak Ridge National Laboratory, Metals and Ceramics Division, P.O. Box 2008, Oak Ridge, TN 37831 6024 (United States); Carter, C. Barry [Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue S.E., 151 Amundson Hall, Minneapolis, MN 55455 0132 (United States)]. E-mail: carter@cems.umn.edu

    2005-02-28

    Surfaces of ceria (CeO{sub 2}) particles have been studied by electron energy-loss spectroscopy in a field-emission gun scanning transmission electron microscope. All the ceria particles analyzed contained Ce{sup 3+} at the surface. Rare-earth impurities such as La were enriched at the surface and were observed for particles ranging from tens to hundreds of nanometers in size. Fluorine in the abrasives corresponded to a lower average cerium valence. Time series investigations indicate that fluorine substitutes on the oxygen sub-lattice and is charge-balanced by some cerium changing from Ce{sup 4+} to Ce{sup 3+}.

  17. Kinetics and Mechanisms of Oxygen Surface Exchange on La0.6Sr0.4FeO3-delta Thin Films

    OpenAIRE

    Mosleh, Majid; Søgaard, Martin; Hendriksen, Peter Vang

    2009-01-01

    The thermodynamic properties as well as oxygen exchange kinetics were examined on mixed ionic and electronic conducting (La0.6Sr0.4)0.99FeO3− (LSF64) thin films deposited on MgO single crystals. It is found that thin films and bulk material have the same oxygen stoichiometry for a given temperature and oxygen partial pressure [i.e., the incorporation reaction has the same reaction enthalpy (H0=−105 KJ/mol) and entropy (S0=−75.5 J/mol/K) as found for bulk material]. The thin film shows smaller...

  18. Effects of surface modification with Co3O4 nanoparticles on the oxygen permeability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes

    Science.gov (United States)

    Wang, Yu; Cheng, Jigui; Huang, Min; Liu, Meng; Li, Mingming; Xu, Chenxi

    2017-09-01

    To promote the oxygen permeability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membranes, Co3O4 nanoparticle catalysts were loaded onto the surfaces of BSCF membranes by a dip-coating process. X-ray diffraction (XRD) results reveal that Co3O4 nanoparticles crystalize in spinel phase. Scanning electron microscope (SEM) observation indicates that the mean particle size of the Co3O4 nanoparticles is about 100 nm in diameter and 20 μm in thickness after annealing at 500 °C for 5 h. Energy dispersive spectrometer (EDS) results testify that the percentage of the elements in the modified layer are in accordance with the stoichiometric ratio of Co3O4. Oxygen permeation tests were made in a laboratory self-made device, and the results show that loading Co3O4 nanoparticle catalysts onto the surfaces of BSCF membranes can significantly increase the oxygen permeability of the BSCF membranes. The unmodified BSCF membranes have an oxygen permeation flux of 0.1080 ml cm-2 min-1 at 600 °C. This increases to 0.4302 ml cm-2 min-1, for the modified membranes, which is four times higher than that of the unmodified BSCF membranes. The oxygen permeation activation energy decreases from 91.42 to 50.71 kJ mol-1 at 600-800 °C by loading Co3O4 nanoparticle catalysts on the surface of BSCF membranes.

  19. Constraints on Paleocene and Eocene Tropical Sea-Surface Temperatures and Meridional Temperature Gradients From Mg/Ca and Oxygen Isotope Ratios of Foraminifera in Sediments Recovered by the Ocean Drilling Program

    Science.gov (United States)

    Tripati, A.; Elderfield, H.; Wade, B.; Kelly, D. C.; Anderson, L. D.; Sindrey, C.

    2005-12-01

    Accurate reconstructions of tropical sea surface temperatures (SST) during the Paleocene and Eocene are needed to understand the contribution of greenhouse gases to past climate variability. When combined with constraints on high-latitude SST, tropical SST can be used to estimate past meridional temperature gradients. The traditional tool applied to reconstructing surface temperatures utilizes the temperature-dependant incorporation of oxygen isotopes into calcium carbonate. However, changes in the oxygen isotope composition of foraminiferal calcite also record variations in the isotopic composition of seawater, complicating temperature reconstructions. The magnesium to calcium (Mg/Ca) ratio of foraminiferal carbonate provides an alternative method for reconstructing temperatures in the past that is insensitive to variations in the oxygen isotopic composition of seawater. Here, we present constraints on tropical temperatures from Mg/Ca ratios of planktonic foraminifera in cores recovered by the Ocean Drilling Program during intervals characterized by large changes in atmospheric carbon dioxide levels, including the Paleocene-Eocene Thermal Maximum and the middle to late Eocene "greenhouse-icehouse" transition. Records are for mixed-layer dwellers belonging to the genus Morozovella and Acaranina, and for the thermocline dwelling taxa Subbotina. We combine these results with constraints on high-latitude SST from other proxies, including foraminiferal Mg/Ca and oxygen isotope ratios, to reconstruct changes in the pole-to-equator temperature gradient during these major climate transitions.

  20. Lattice quantum chromodynamics: Some topics

    Indian Academy of Sciences (India)

    susceptibility and the screening lengths. A short summary is provided at the end. 2. .... approximations but decreasing order of computer time, are (i) full QCD simulations on smaller lattices, (ii) partially quenched ... Theoretical expectations and simulation results for QCD phase diagram. over to different number of flavours.