Evaluation of perchlorate tolerant photo-cured calcium selective electrodes for use in flow injection potentiometry

A photo-cured membrane selective to calcium, based on the calcium bis [4-(1',1',3',3'-tetramethylbutyl)phenyl]phosphate ionophore and incorporating the lipophilic additive, potassium tetraki(4-chlorophenyl)borate, that can tolerate up to 200 nM perchlorate ionic background in the flow injection potentiometry mode has been previously reported (T. Dimitrakopoulos, J.R. Farrell and P.J. Ives, Electroanalysis, 8 (1996) 391). Improvements in the electrode slope and sensitivity of the previously described photo-cured calcium membrane-based electrode were achieved when anhydrous calcium chloride salt was dissolved into the pre-cured membrane composition and then photo-cured. Similar to the previously reported photo-cured calcium ion-selective electrode (ISE), the improved photo-cured calcium ISE can measure calcium in a high perchlorate background in the flow injection potentiometric mode.     

Discretizing two‐dimensional complex fractured fields for incompressible two‐phase flow

A method is introduced to discretize irregular and complex two‐dimensional fractured media. The geometry of the fractured media is first analysed by searching and treating the complex configurations. Based on that, the method generated a good mesh quality and allows for including finer grids. An incompressible two‐phase flow problem is solved to compare the developed method and a public method based on the approximation of a 1D fracture by the edges of a 2D finite element grid of the porous media. The comparison showed that the developed method (i) represents better the fractured domain by maintaining the geometric integrity of input surfaces and geologic data, (ii) provides, for sample and complex fractured domains, excellent and more accurate results, and (iii) is much less sensitive to the grid sizes. Furthermore, the method has to be more efficient than the other methods for transport problems and has to provide better predictable results; this is mainly based on point (ii) and because the method produces optimal triangular grids. Copyright © 2009 John Wiley & Sons, Ltd.     

Almost block diagonal linear systems: sequential and parallel solution techniques,and applications

Almost block diagonal (ABD) linear systems arise in a variety of contexts, specifically in numerical methods for two‐point boundary value problems for ordinary differential equations and in related partial differential equation problems. The stable, efficient sequential solution of ABDs has received much attention over the last fifteen years and the parallel solution more recently. We survey the fields of application with emphasis on how ABDs and bordered ABDs (BABDs) arise. We outline most known direct solution techniques, both sequential and parallel, and discuss the comparative efficiency of the parallel methods. Finally, we examine parallel iterative methods for solving BABD systems. Copyright © 2000 John Wiley & Sons, Ltd.     

A diversified Tabu search approach for the open-pit mine production scheduling problem with metal uncertainty

This paper presents a metaheuristic solution approach based on Tabu search for the open-pit mine production scheduling problem with metal uncertainty. To search the feasible domain more extensively, two different diversification strategies are used to generate several initial solutions to be optimized by the Tabu search procedure. The first diversification strategy exploits a long-term memory of the search history. The second one relies on the variable neighborhood search method. Numerical results on realistic large-scale instances are provided to indicate the efficiency of the solution approach to produce very good solutions in relatively short computational times.     

Implementing a parametric maximum flow algorithm for optimal open pit mine design under uncertain supply and demand

Conventional open pit mine optimization models for designing mining phases and ultimate pit limit do not consider expected variations and uncertainty in metal content available in a mineral deposit (supply) and commodity prices (market demand). Unlike the conventional approach, a stochastic framework relies on multiple realizations of the input data so as to account for uncertainty in metal content and financial parameters, reflecting potential supply and demand. This paper presents a new method that jointly considers uncertainty in metal content and commodity prices, and incorporates time-dependent discounted values of mining blocks when designing optimal production phases and ultimate pit limit, while honouring production capacity constraints. The structure of a graph representing the stochastic framework is proposed, and it is solved with a parametric maximum flow algorithm. Lagragnian relaxation and the subgradient method are integrated in the proposed approach to facilitate producing practical designs. An application at a copper deposit in Canada demonstrates the practical aspects of the approach and quality of solutions over conventional methods, as well as the effectiveness of the proposed stochastic approach in solving mine planning and design problems.     

Initial Proteome Analysis of Caffeine-Induced Proteins in <Emphasis Type="Italic">Aspergillus tamarii</Emphasis> Using Two-Dimensional Fluorescence Difference Gel Electrophoresis

Caffeine is toxic to most microorganisms. However, some filamentous fungi, such as Aspergillus tamarii, are able to metabolize this alkaloid when fed caffeine as the sole nitrogen source. The aim of the present work was to identify intracellular A. tamarii proteins, regulated by caffeine, using fluorescence difference two-dimensional gel electrophoresis. Specific proteins from two culture media of A. tamarii grown either on ammonium sulfate or caffeine as the sole nitrogen source were analysed by mass spectrometry. Thirteen out of a total of 85 differentially expressed spots were identified after database search. Identified up-regulated proteins include phosphoglycerate kinase, malate dehydrogenase, dyp-type peroxidase family protein, heat shock protein, Cu, Zn superoxidase dismutase and xanthine dehydrogenase. Some of the proteins identified in this study are involved in the caffeine degradation pathway as well as in stress response, suggesting that stress proteins could be involved in caffeine metabolism in filamentous fungi.     

Development of a fast and selective method for the sensitive determination of anatoxin-a in lake waters using liquid chromatography–tandem mass spectrometry and phenylalanine-d 5 as internal standard

Anatoxin-a is a potent alkaloid neurotoxin produced by a number of cyanobacterial species and released in freshwaters during cyanobacterial blooms. Its high toxicity is responsible for several incidents of lethal intoxications of birds and mammals around the world; therefore anatoxin-a has to be regarded as a health risk and its concentration in lakes and water reservoirs should be monitored. Phenylalanine is a natural amino acid, also present in freshwaters, isobaric to anatoxin-a, with a very similar fragmentation pattern and LC retention. Since misidentification of phenylalanine as anatoxin-a has been reported in forensic investigations, special care must be taken in order to selectively determine traces of anatoxin-a in the presence of naturally occurring phenylalanine. A fast LC tandem MS method was developed by using a 1.8 μm 50 × 2.1 mm C18 column for the separation of anatoxin-a and phenylalanine, achieving a 3-min analysis time. Isotopically labelled phenylalanine-d ₅ was employed as internal standard to compensate for electrospray ion suppression and sample preconcentration losses. Both compounds were preconcentrated 1,000-fold on a porous graphitic carbon solid-phase extraction (SPE) cartridge after adjustment of sample pH to 10.5. The method was validated by using lake water spiked at four different levels from 0.01 to 1 μg L⁻¹. Anatoxin-a recovery ranged from 73 to 97%, intra-day precision (RSD%) ranged from 4.2 to 5.9, while inter-day precision (RSD%) ranged from 4.2 to 9.1%. Limits of detection and quantification were 0.65 and 1.96 ng L⁻¹ respectively. The method was successfully applied for the detection of anatoxin-a in Greek lakes at concentrations ranging from less than 0.6 to 9.1 ng L⁻¹.     

An efficient method for discretizing 3D fractured media for subsurface flow and transport simulations

We introduce a new method to discretize inclined non‐planar two‐dimensional (2D) fractures in three‐dimensional (3D) fractured media for subsurface flow and transport simulations. The 2D fractures are represented by ellipsoids. We first discretize the fractures and generate a 2D finite element mesh for each fracture. Then, the mesh of fractures is analyzed by searching and treating critical geometric configurations. Based on that search, the method generates a quality mesh and allows for including finer grids. A solute transport problem in fractured porous media is solved to test the method. The results show that the method (i) adequately represents the fractured domain by maintaining the geometric integrity of input surfaces and geologic data, (ii) provides accurate results for both simple and complex fractured domains, (iii) is insensitive to spatial discretization, and (iv) is computationally very efficient. For inclined and vertical fractures, analytical and numerical solutions are shown to be in good agreement. The method is therefore suitable to discretize fracture networks for flow and transport simulations in fractured porous media. Copyright © 2010 John Wiley & Sons, Ltd.     

MDOF extension of the Modified Bridge System method for vehicle–bridge interaction

Nonlinear Dynamics - This study examines the effect of vehicle–bridge interaction (VBI) on the vibration of coupled train–bridge systems and proposes a consistent approach to decouple...     

Isometric immersions of tori into R3 with given mean curvature

It is known that a compact Riemannian surface can admit at most two (2) geometrically distinct, i. e., non-congruent isometric immersions into R ³ with given non-constant mean curvature. If the genus is zero, then there is at most one such immersion. Here, we show that there is at most one such immersion in each of the following cases for surfaces of genus one: 1) there exists a point p such that (H ² ? K)(p) = 0, where K is the curvature of the Riemannian metric and H is the given non-constant mean curvature (umbilic point); 2) the surface is a surface of revolution; 3) the surface is a tube formed by moving a circle in such a way that its center describes a smooth plane curve and its plane is constantly perpendicular to this curve. We also indicate the difficulties as to why the so-far existing methodologies cannot give a clear-cut answer to the question if it is possible to reduce the at most two immersions to at most one for any compact Riemannian surface of genus greater than zero.