Hourly and seasonal variation in photosynthesis and stomatal conductance of soybean grown at future CO2 and ozone concentrations for three years under fully open air conditions.

published or submitted for publicatio

Model for nucleation in GaAs homoepitaxy derived from first principles

The initial steps of MBE growth of GaAs on beta 2-reconstructed GaAs(001) are investigated by performing total energy and electronic structure calculations using density functional theory and a repeated slab model of the surface. We study the interaction and clustering of adsorbed Ga atoms and the adsorption of As_2 molecules onto Ga atom clusters adsorbed on the surface. The stable nuclei consist of bound pairs of Ga adatoms, which originate either from dimerization or from an indirect interaction mediated through the substrate reconstruction. As_2 adsorption is found to be strongly exothermic on sites with a square array of four Ga dangling bonds. Comparing two scenarios where the first As_2 gets incorporated in the incomplete surface layer, or alternatively in a new added layer, we find the first scenario to be preferable. In summary, the calculations suggest that nucleation of a new atomic layer is most likely on top of those surface regions where a partial filling of trenches in the surface has occurred before.Comment: 8 pages, 14 figures, Submitted to Phys. Rev. B (December 15, 1998). Other related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Simulations of neutron background in a time projection chamber relevant to dark matter searches

Presented here are results of simulations of neutron background performed for a time projection chamber acting as a particle dark matter detector in an underground laboratory. The investigated background includes neutrons from rock and detector components, generated via spontaneous fission and (alpha, n) reactions, as well as those due to cosmic-ray muons. Neutrons were propagated to the sensitive volume of the detector and the nuclear recoil spectra were calculated. Methods of neutron background suppression were also examined and limitations to the sensitivity of a gaseous dark matter detector are discussed. Results indicate that neutrons should not limit sensitivity to WIMP-nucleon interactions down to a level of (1 - 3) x 10^{-8} pb in a 10 kg detector.Comment: 27 pages (total, including 3 tables and 11 figures). Accepted for publication in Nuclear Instruments and Methods in Physics Research - Section

Vortex states in 2D superconductor at high magnetic field in a periodic pinning potential

The effect of a periodic pinning array on the vortex state in a 2D superconductor at low temperatures is studied within the framework of the Ginzburg-Landau approach. It is shown that attractive interaction of vortex cores to a commensurate pin lattice stabilizes vortex solid phases with long range positional order against violent shear fluctuations. Exploiting a simple analytical method, based on the Landau orbitals description, we derive a rather detailed picture of the low temperatures vortex state phase diagram. It is predicted that for sufficiently clean samples application of an artificial periodic pinning array would enable one to directly detect the intrinsic shear stiffness anisotropy characterizing the ideal vortex lattice.Comment: 8 pages, 5 figure

Lombardi Drawings of Graphs

We introduce the notion of Lombardi graph drawings, named after the American abstract artist Mark Lombardi. In these drawings, edges are represented as circular arcs rather than as line segments or polylines, and the vertices have perfect angular resolution: the edges are equally spaced around each vertex. We describe algorithms for finding Lombardi drawings of regular graphs, graphs of bounded degeneracy, and certain families of planar graphs.Comment: Expanded version of paper appearing in the 18th International Symposium on Graph Drawing (GD 2010). 13 pages, 7 figure

Neutron background in large-scale xenon detectors for dark matter searches

Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (alpha,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of $10^{-9}-10^{-10}$ pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.Comment: 35 pages, 13 figures, 2 tables, accepted for publication in Astroparticle Physic

Defining Physical Literacy for Application in Australia: A Modified Delphi Method

Purpose. The development of a physical literacy definition and standards framework suitable for implementation in Australia. Method. Modified Delphi methodology. Results . Consensus was established on four defining statements: Core – Physical literacy is lifelong holistic learning acquired and applied in movement and physical activity contexts; Composition – Physical literacy reflects ongoing changes integrating physical, psychological, cognitive and social capabilities; Importance – Physical literacy is vital in helping us lead healthy and fulfilling lives through movement and physical activity; Aspiration – A physically literate person is able to draw on their integrated physical, psychological, cognitive, and social capacities to support health promoting and fulfilling movement and physical activity, relative to their situation and context, throughout the lifespan. The standards framework addressed four learning domains (physical, psychological, cognitive, and social), spanning five learning configurations/levels. Conclusion. The development of a bespoke program for a new context has important implications for both existing and future program

Commensurate and Incommensurate Vortex Lattice Melting in Periodic Pinning Arrays

We examine the melting of commensurate and incommensurate vortex lattices interacting with square pinning arrays through the use of numerical simulations. For weak pinning strength in the commensurate case we observe an order-order transition from a commensurate square vortex lattice to a triangular floating solid phase as a function of temperature. This floating solid phase melts into a liquid at still higher temperature. For strong pinning there is only a single transition from the square pinned lattice to the liquid state. For strong pinning in the incommensurate case, we observe a multi-stage melting in which the interstitial vortices become mobile first, followed by the melting of the entire lattice, consistent with recent imaging experiments. The initial motion of vortices in the incommensurate phase occurs by an exchange process of interstitial vortices with vortices located at the pinning sites. We have also examined the vortex melting behavior for higher matching fields and find that a coexistence of a commensurate pinned vortex lattice with an interstitial vortex liquid occurs while at higher temperatures the entire vortex lattice melts. For triangular arrays at incommensurate fields higher than the first matching field we observe that the initial vortex motion can occur through a novel correlated ring excitation where a number of vortices can rotate around a pinned vortex. We also discuss the relevance of our results to recent experiments of colloidal particles interacting with periodic trap arrays.Comment: 8 figure

Measurement of D*+/- meson production in jets from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.Comment: 10 pages plus author list (22 pages total), 5 figures, 1 table, matches published version in Physical Review

Tunnel shotcrete lining for hydroelectric projects in British Columbia

In British Columbia (BC), Canada, the primary source of power supply is hydroelectricity. The BC government, through its crown corporation, BC Hydro, has been working with private companies to provide sustainable and renewable energy. Private companies are building hydroelectric projects throughout the province of BC. Innergex has been constructing three hydroelectric projects; two are in the Upper Lilllooet area, which is about 250 km north of Vancouver and 80km north of Whistler and the third is in the Big Silver area, which is about 250 km east of Vancouver and 50 km north of Harrison Lake. All of these tunnels are hard rock and have been constructed by the drill and blast method. At the beginning of the projects, dry-mix shotcrete was applied based on the contractor’s previous underground project experience. Wet-mix shotcrete was subsequently introduced as a trial method. The contractor was impressed with its productivity and performance and consequently adopted it as the primary shotcrete placement method. Dry-mix steel fiber reinforced shotcrete continued to be used for special ground conditions. The construction schedule was reduced significantly by using wet-mix shotcrete, with resultant substantial cost savings. The wet-mix shotcrete was initially reinforced with wire mesh and hand-applied. Shortly after, the tunnel lining method was changed to the use of robotic sprayed macrosynthetic fiber reinforced wet-mix shotcrete. A silica fume modified shotcrete mixture was designed and trial shot. Tests results met the project specification requirements for tunnel construction. The wet-mix macrosynthetic fiber reinforced shotcrete was placed, since July 2013, using pre-bagged materials supplied from Vancouver and mixed on site. Later, the contractor set up a dry-batch concrete batch plant on site and started batching shotcrete using local aggregates. The shotcrete mixture was qualified for use on the project by testing for compressive strength, boiled absorption and volume of permeable voids, and flexural toughness based on use of the round determinate panel to ASTM C1550. The effect on shotcrete performance of different addition rates of alkali-free accelerator was tested in trials. An addition rate of 6% alkali-free accelerator by mass of cement was selected and used. Shotcrete nozzlemen were trained with a specially designed shotcrete training program. All shotcrete nozzlemen were qualified to shoot a basic Level I, and a more challenging Level II, for shotcrete with reinforcing steel or lattice girders. The construction quality control tests results for the project from August 2013 to December 2016 demonstrated that the shotcrete quality consistently met the project specification requirements. The projects were completed ahead of schedule because of productivity gains achieved from using wet-mix macrosynthetic fiber reinforced shotcrete. The contractors developed proper skills and techniques for application of wet-mix macrosynthetic fiber reinforced shotcrete applied by robotic sprayers with zero safety incidents or accident