Suspensions of prolate spheroids in Stokes flow. Part 3. Hydrodynamic transport properties of crystalline dispersions

The short-time limit of the hydrodynamic transport properties is calculated for crystalline dispersions of parallel prolate spheroids using a moment expansion technique similar in concept to the simulation method known as Stokesian dynamics. The concentration dependence of the sedimentation rate, the hindered diffusivity and the Theological behaviour of face-centred lattices are examined for concentrations up to regular close packing (74% by volume). The influence of the detailed microstructure of the dispersion is also investigated by considering different arrangements of parallel ellipsoids. Useful reference configurations are proposed as standard geometries for regular arrays of prolate spheroids

Suspensions of prolate spheroids in Stokes flow. Part 2. Statistically homogeneous dispersions

The simulation method for prolate spheroids in Stokes flow introduced in a companion paper (Claeys & Brady 1993a) is extended to handle statistically homogeneous unbounded dispersions. The convergence difficulties associated with the slow decay of velocity disturbances at zero Reynolds number are overcome by applying O';Brien's renormalization procedure. The Ewald summation technique is employed to accelerate the evaluation of all mobility interactions. As a first application of this new method, the hydrodynamic transport properties of equilibrium hard-ellipsoid structures are calculated for aspect ratios ranging from 3 to 50. Calculated viscosities in the isotropic phase agree reasonably well with published experimental measurements

Asymptotic and numerical analysis for Holland and Simpson’s thin wire formalism

AbstractIn the context of simulation of electromagnetic propagation, the thin wire formalism of Holland and Simpson allows one to deal with scattering by perfectly conducting thin wires by coupling a standard FDTD method with a discrete 1D wave equation ruling the current inside the wires. This method can be very accurate, but it involves a fitting parameter that requires careful calibration.We propose a consistency analysis and derive a formula for the calibration of this parameter in the case of a simplified 2D analogue of the method of Holland and Simpson. Our proof relies on the observation that this method is actually a hidden version of the singular function method well known in the context of elliptic equations in domains with a singular boundary

Stable isotopic composition of bivalve shell organic matrix: <i>Mytilus edulis</i> collected along the Scheldt estuary

Bivalve shells are biostructures composed of a mineral and an organic phase. For paleoclimatology applications, the mineral part (carbonates) is most widely studied. In contrast, understanding of the composition and the proxyfunction of the organic matrix is much less developed. The quantity of organic matrix in shells is relatively small compared to the mineral phase (a few wt %) and the biochemical composition is quite complex, consisting mainly of sugars and proteins. Lipids, which represent a small fraction of the organic matrix, are rather poorly known. We studied the potential of stable isotope composition (C, N, H) of bulk organic matrix and specific lipid compounds of Mytilis edulis shells, as environmental and climatic proxies, with special focus on the effects due to changing salinity. Mytilus specimens were collected along the salinity gradient of the Scheldt estuary (The Netherlands) and we analysed the isotopic composition of the organic matrix and associated specific lipid compounds and related these to averaged physico-chemical characteristics of the water, in particular salinity. We discuss these relationships in the light of their usefulness as proxies for reconstructing past environmental conditions

A GIS-based hydrographic resurvey strategy of the Belgian Continental Shelf

Using a GIS-based approach, bathymetric surveys and maritime traffic records were combined to determine resurvey priorities within the Belgian Continental Shelf (BCS). Four reference layers were produced: (1) water depth; (2) maximum absolute change in water depth; (3) ship traffic intensity; (4) maximum ship draught. The reference layers were reclassified and merged into a weighted overlay analysis. Two combinations of layers and weight factors were used and resulted in priority maps differing greatly from each other. The reliability of the analysis depends on the way weight factors are assigned, and on the availability and accuracy of the data. These are limited for bathymetric surveys. This empirical GIS-based methodology can be applied as a whole to a zone showing various morphodynamic patterns. It can also be automated: additional datasets can be included in the analysis, and different scenarios and assumptions can be easily tested

Innovation and performance of European banks adopting Internet

Ebanking has been a bit of a fad. Virtual banks were believed to challenge traditional banks. The burst of the internet bubble brought down this first generation of internet banks. Traditional branch banks have gone online since. Existing banks started to buy up some failed internet banks; some have set up an internet bank of their own. It seems this second generation of online banks performs better (DeYoung et al., 2007). However, other traditional banks have started to complement branch banking with simpler online facilities, like an internet portal. We examine the reasons for banking groups to either own an internet bank or provide an internet portal. On a panel of the 60 largest EU banking groups over the period 1995-2005, we find that banks with a heavy cost structure and a large market share in client deposits and noninterest activities are more likely to introduce internet banking. Concentration in the banking market favours adoption of internet banking although in some markets, like France or Italy, M&A have been an easy way to acquire small internet banks. There is little evidence of economies of scope in ICT development. The performance of the banking groups with an internet bank is poor. It has mainly created additional costs (although labour costs have been cut) but so far, little return

Effect of nematicidal Bacillus thuringiensis strains on free- living nematodes : 1. Light microscopic observations, species and biological stage specificity and identification of resistant mutants of Caenorhabditis elegans

L'observation en microscopie optique de l'action toxique des spores/cristaux de #Bacillus thuringiensis montre que, chez #Caenorhabditis elegans, l'intestin est détruit en deux phases sur une période de 24 h. L'anneau antérieur de quatre cellules constitue la première cible. Les observations indiquent que les tissus intestinaux sont les seuls détruits. Le criblage de quatorze autres espèces de Rhabditides vis-à-vis de trois souches nématicides de #B. thuringiensis actives contre #C. elegans a démontré qu'une seule de ces espèces était sensible et indiqué une forte spécificité du facteur nématicide. Cependant, au contraire des toxines de #B. thuringiensis douées de spécificité envers les insectes, les toxines nématicides ne montrent qu'une faible spécificité envers les différents stades de #C. elegans, tous les stades, y compris les adultes, étant sensibles. De plus, la sensibilité s'accroît lors du processus de développement. Deux mutants de #C. elegans$, obtenus par action de l'éthyle-méthyle-sulfonate, montrent une sensibilité réduite de 50$ envers laquelle elle n'avait pas été testée. Des données préliminaires indiquent que cette réduction de la sensibilité chez les mutants n'est pas causée par une diminution de l'activité de pompage du pharynx. (Résumé d'auteur

Effect of a nematicidal Bacillus thuringiensis strain on free- living nematodes : 3. Characterization of the intoxication process

La toxicité de #Bacillus thuringiensis est fonction de la température. L'incubation de #Caenorhabditis elegans avec des souches de #B. thuringiensis à 16, 20 et 25°C montre que la toxicité décroît en même temps que la température. A 16°C, la toxicité disparaît complètement, tandis qu'elle atteint son maximum à 25°C. La toxicité, fonction du pH, diminue significativement lorsque les nématodes sont mis en incubation dans des bases faibles (NH4Cl, chloroquine, acridine orange, rouge de méthyle, rouge neutre). A partir de ces résultats, il est possible d'avancer l'hypothèse que l'agent nématicide pénètre à l'intérieur des cellules intestinales, ce qui constitue une différence notable avec les toxines des souches insecticides de #B. thuringiensis lesquelles agissent au niveau de la membrane en brosse. Bien que l'absence de toxine purifiée ne permette pas l'élucidation définitive de son mode d'action, les résultats exposés dans cette troisième, et dernière, partie de la série de publications traitant du sujet, apportent une indication convaincante du fait que les souches nématicides de #B. thuringiensis$ ne peuvent tenir les mêmes promesses que les souches insecticides en tant qu'agent de contrôle biologique. (Résumé d'auteur