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1.
Deborah M. Greaves 《国际流体数值方法杂志》2006,50(6):693-711
An adaptive hierarchical grid‐based method for predicting complex free surface flows is used to simulate collapse of a water column. Adapting quadtree grids are combined with a high‐resolution interface‐capturing approach and pressure‐based coupling of the Navier–Stokes equations. The Navier–Stokes flow solution scheme is verified for simulation of flow in a lid‐driven cavity at Re=1000. Two approaches to the coupling of the Navier–Stokes equations are investigated as are alternative face velocity and hanging node interpolations. Collapse of a water column as well as collapse of a water column and its subsequent interaction with an obstacle are simulated. The calculations are made on uniform and adapting quadtree grids, and the accuracy of the quadtree calculations is shown to be the same as those made on the equivalent uniform grids. Results are in excellent agreement with experimental and other numerical data. A sharp interface is maintained at the free surface. The new adapting quadtree‐based method achieves a considerable saving in the size of the computational grid and CPU time in comparison with calculations made on equivalent uniform grids. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
2.
Kathryn A. Downsland Anna M. Greaves 《The Journal of the Operational Research Society》1994,45(7):817-826
The use of a bi-directional, as opposed to a one-way, transportation system, can increase the operational efficiency of automated guided vehicles in both manufacturing and warehousing environments. However, the full potential will only be realized if the routeing algorithms pay particular attention to the problem of collision avoidance. This paper is concerned with the development of such an algorithm. The method is based on the use of delays and deviations to avoid collisions that could arise when using the shortest routes for each vehicle, and is applicable to any transportation system which can be represented as a network with known travel times. 相似文献
3.
Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings
The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO3 coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr LII, LIII-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant. 相似文献
4.
Raymond G. Plevey Richard W. Rendell John Colin Tatlow 《Journal of fluorine chemistry》1982,21(2):159-169
Pyridine has been fluorinated over caesium tetrafluorocobaltate(III) (CsCoIIIF4) at 300–400°C to give a mixture of undecafluoro-N-methylpyrrolidine, bis(trifluoromethyl)amine, pentafluoropyridine and several polyfluoropyridines; the product composition depended to some extent on the geometry of the reactor. The fluorinations of pentafluoropyridine, piperidine and undecafluoropiperidine were also investigated. 相似文献
5.
Peter G. Doyle Colin Mallows Alon Orlitsky Larry Shepp 《Israel Journal of Mathematics》1989,67(1):34-42
Letn cells be arranged in a ring, or alternatively, in a row. Initially, all cells are unmarked. Sequentially, one of the unmarked
cells is chosen at random and marked until, aftern steps, each cell is marked. After thekth cell has been marked the configuration of marked cells defines some number of islands: maximal sets of adjacent marked
cells. Let ξ
k
denote the random number of islands afterk cells have been marked.
We give explicit expressions for moments of products of ξ
k
’s and for moments of products of 1/ξ
k
’s.
These are used in a companion paper to prove that if a random graph on the natural number is made by drawing an edge betweeni≧1 andj>i with probabilityλ/j, then the graph is almost surely connected ifλ>1/4 and almost surely disconnected ifλ≦1/4. 相似文献
6.
We see that the entropy method yields strong concentration results for general self‐bounding functions of independent random variables. These give an improvement of a concentration result of Talagrand much used in discrete mathematics. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
7.
L. Sajo-Bohus M. C. Scott E. D. Greaves L. J. Somervaille S. Green T. Avila F. Loaiza L. Foglietta 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(2):251-255
Gamma-ray induced X-ray emission (GIXE) technique for elemental lead in-vivo tibial measurement using a large volume hyper
pure germanium detector is presented with the most convenient source-sample-detector geometry. The system operates advantageously
when several parameters are considered for a lower dead time operation. The detection limit (DL) is better that 3.5 μg/g of
Ca. Results of in-vivo average tibial lead concentration for some of the monitored groups are: control 7 μg of lead per g
of Ca; gasoline filling attendants 6 μg/g of Ca; custom office workers near the DL; industrial workers range from DL up to
84±3 μg/g of Ca, suggesting that lead accumulation in the bone does not represent a major health risk
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
We discuss possible experiments which can exploit recently-developed techniques to accumulate, store, and manipulate low-energy positrons to measure the parameters associated with positron annihilation radiation from media of astrophysical interest. Media discussed include collections of dust grains, partially ionized gases, He, H2, and other molecular gases and gas mixtures, including polycyclic aromatic hydrocarbon (PAH) molecules relevant to the interstellar medium. 相似文献
9.
10.
Sergio O. Vasquez Colin D. Flint Ralph Sabry-Grant 《Journal of Applied Spectroscopy》1995,62(5):979-985
Published in Zhurnal Prikladnoi Spectroscopii, Vol. 62, No. 5, pp. 213–220, September–October, 1995. 相似文献