Simulation of viscous water column collapse using adapting hierarchical grids

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.     

Collision Avoidance in Bi-Directional AGV Systems

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.     

In vivo tibial lead measurement to assess the health hazard of Venezuelan workers

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.     

Use of traps to study positron annihilation in astrophysically relevant media

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.     

Determination of metal-ligand stoichiometries for inorganic complexes using total reflection X-ray fluorescence

The methods usually used to determine the ratio metal-ligand in inorganic complexes require a set of solutions with different concentrations for both the ligand and metal. We propose a new method using the total reflection X-ray fluorescence technique, in which the ratio between metal and ligand is determined precisely, easily, and quickly. Experimental results provide evidence that for different chemical complexes, the ligand-metal ratio determined by this technique deviates at most from stoichiometric values by 6%. The technique is restricted usually to elements with Z above 14, and its detection limit is on the order of 10(-8) g/g.     

Determination of the rare earth elements in natural waters by isotope-dilution mass spectrometry

A method is described for the determination of ten rare earth elements (La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) in natural waters by isotope-dilution mass spectrometry. A 1-l sample is used for sea water, and proportionately less for other natural waters. The rare earth elements are extracted by co-precipitation with hydrated iron (III) oxide and purified on a single cation-exchange column, with hydrochloric and nitric acids as eluents. Final measurements are from a triple Re/ Ta filament in the mass spectrometer, run automatically under computer control. Relative standard deviations are better than 4% for the analysis of standard solutions, with accuracy in the same range. The analytical blank is low ( <0.03 pmol, 4 pg, for Nd) producing a sample/blank concentration ratio greater than 100 for all ten rare earth elements when determined in a 1-l seawater sample. Concentration depth profiles are given for an ocean water and normalised abundance patterns for three natural waters.