897 research outputs found
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
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
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Evaluation of density separation and other treatment methods for plastic media blasting (PMB) waste
The United States Air Force has developed plastic media blasting (PMB) to replace solvent paint stripping of its aircraft. This paint blasting operation generates a waste stream of mainly pulverized plastic, but the stream also contains enough paint pigments to make the PMB waste RCRA hazardous. A Phase I study identified density separation as the preferred treatment alternative to land disposal of the entire PMB waste stream in a hazardous landfill. This study found density separation to be a less attractive alternative to self-encapsulation, solidification/stabilization (S/S), and low-temperature ashing. Self-encapsulation resulted in a volume decrease but only moderate improvement in Toxicity Characteristic Leaching Procedure (TCLP) performance Solidification/Stabilization (S/S) into cementiaous waste for resulted in excellent TCLP performances, but volume increases. Low-temperature ashing resulted in dramatic volume decreases, but off-gas control is required to contain all the RCRA metals. The resulting ash must be stabilized (e.g., S/S) to meet TCLP limits
Compression ultrasonography for false femoral artery aneurysms: Hypocoagulability is a cause of failure
Objectives:false femoral artery aneurysm is an occasional complication of percutaneous cardiovascular radiological procedures. Compression ultrasonography causes thrombosis non-invasively, reducing need for operative intervention. The technique fails in a proportion of cases. Analysis was undertaken to identify causes of failure.Design:prospective open study.Materials and Methods:patients presenting with false femoral artery aneurysm since 1984 were identified from a computerised database (BIPAS). Since 1993 compression ultrasonography has been performed as first line treatment according to a standard protocol. Prospectively collected ultrasonographic data and case notes were reviewed to identify causes of failed compression.Results:false femoral artery aneurysm occurred as a complication in 32/26 687 (0.12%) cardiovascular radiological procedures. Eighteen aneurysms were treated by compression. The technique was successful in 11/18 (61%) cases but primary failure occurred in seven cases. Six out of seven had bleeding abnormalities (Chi-squared analysis with Yates correction 10.55, p=0.0012), four were anticoagulated and compression was subsequently successful following reversal of warfarin therapy in three of these patients. In 4/18 cases surgical repair was necessary.Conclusions:compression ultrasonography is an effective treatment of false femoral aneurysms, however, hypocoagulability is a significant cause of failure. For patients in whom anticoagulation cannot be reversed, primary surgical repair should be considered
180 Choice of IV vs. non-IV antibiotics for treating pulmonary exacerbations in patients with cystic fibrosis
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
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
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
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
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