Magnetic Nanocrystals Aligned on Mesoscopic Scale: Collective Properties and Their Use

Magnetic nanocrystals organized in chain-like structures behave as nanowires with a shape anisotropy induced by the structuration of the sample. This is valid for various types of magnetic nanomaterials. Furthermore, the coating of nanocrystals plays a major role in the mesoscopic structure of the film. γ-Fe₂O₃ nanocrystals are used as a mask to reproduce the mesoscopic structure on a silicon wafer.     

River, reservoir and lake sediment contamination by heavy metals downstream from urban areas of Switzerland

This paper quantifies sediment contamination by heavy metals in four reservoirs and one lake located downstream from major urban areas in Switzerland. The waterbodies include the Wettingen Reservoir (located on the Limmat River downstream from Zürich), the Klingnau Reservoir (on the lower Aare River), the Wohlen Reservoir (downstream from Berne), the Verbois Reservoir (downstream from Geneva) and Vidy Bay (Lake Geneva, city of Lausanne). For all sediment cores and contaminants, a trend is observed from high contaminant values in the lower part of the cores, decreasing to lower concentrations in the upper part of the cores. However, for each site and each element, specific features are recognized. Applying the criteria of the Swiss ordinance on soil protection, all sediment cores must be classified as contaminated by one or more contaminants and at variable levels. From these data, it is concluded that: reservoirs and lakes located downstream from major urban centres in Switzerland have accumulated significant volumes of contaminated sediments in the past, representing the largest, but not the most intensely, contaminated sites on a national scale; the main environmental risk is remobilization of the contaminants and their return to the food chain, particularly by infiltration into the groundwater; and although the processes of remobilization are identified, the conditions of occurrence and the amplitude of the processes are still poorly known. Different options of reservoir and lake sediment management also are discussed and further research topics defined.     

An Inexpensive BRDF Model for Physically-based Rendering

A new BRDF model is presented which can be viewed as an kind of intermediary model between empirism and theory. Main results of physics are observed (energy conservation, reciprocity rule, microfacet theory) and numerous phenomena involved in light reflection are accounted for, in a physically plausible way (incoherent and coherent reflection, spectrum modifications, anisotropy, self-shadowing, multiple surface and subsurface reflection, differences between homogeneous and heterogeneous materials). The model has been especially intended for computer graphics applications and therefore includes two main features: simplicity (a small number of intuitively understandable parameters controls the model) and efficiency (the formulation provides adequation to Monte-Carlo rendering techniques and/or hardware implementations).     

Behaviour Model of Austenitic Stainless Steels for Automotive Structural Parts

One of the most important preoccupation of car manufacturers is to reduce emissions and hence to reduce weight of cars. One of the outstanding materials able to reduce weight while at the same time keeping the same crash absorption and hence safety, is austenitic steel. Austenitic stainless steels are used in crash relevant parts of cars. Moreover, designers can use their very good corrosion resistance and their well known surface aspect for structural visible parts like wheels, cross members, roof panels or tailgates. In this paper, stainless steels for automotive use are presented in detail. First, their chemical composition and tensile properties are explained. Then, a model for forming and crash behaviour is described. Using this model, stainless steels can be engineered into automotive parts and thus stainless steel can be considered as a workable and predictable material for the automotive industry.     

Arbitrarily shaped multiple spatial cluster detection for case event data

An original method is proposed for spatial cluster detection of case event data. A selection order and the distance from the nearest neighbour are attributed to each point, once pre-selected points have been taken into account. This distance is weighted by the expected distance under the uniform distribution hypothesis. Potential clusters are located by modelling the multiple structural change of the distances on the selection order and the best model (containing one or several potential clusters) is selected using the double maximum test. Finally a p-value is obtained for each potential cluster. With this method multiple clusters of any shape can be detected.     

Criteria for cavitation of rubber particles: Influence of plastic yielding in the matrix

The principles of the cavitation criteria for rubber particles in polymeric matrices are briefly reviewed. Although these criteria are based on a linear elastic analysis, it is shown that it is possible to extend them to take into account the elastic-plastic behaviour of the matrix. In this objective, the representative volume element of a periodic material was meshed and computations were performed using a finite element method. The results reported in this paper focus mainly on cavitation under uniaxial tension and examine the influence on the hydrostatic stress in the rubber particles of different parameters such as the volume fraction of rubber, the plastic behaviour of the matrix or the ratio of the elastic moduli. In all cases, plastic yielding in the matrix leads to saturation of the hydrostatic stress in the rubber phase. It is also shown that the history of cavitation barely influences the progression of plasticity in the matrix.     

Strain-based anisotropic damage modelling and unilateral effects

A new continuum damage mechanics model is developed to describe the behaviour of quasi-brittle materials under general path loading. The induced damage is represented by a second rank symmetric tensor. The constitutive equations are based on irreversible thermodynamics theory. The strain-based model covers in an unified way the unsymmetrical behaviour in tension and in compression and the unilateral response due to crack closure effect. Uniaxial stress tests (in tension as in compression) show realistic non-linear responses in the stress–strain space. The different behaviour in both domains is covered by a single set of equations. A significant volume dilatation is noticed in compression. The model can be generalised to time-dependent phenomena.     

Self-similar Singularities in the Kinetics of Condensation

In this article, we review how a condensate builds-up in finite time, by a self-similar blow-up of the solution of three different models of kinetic equations. After the blow-up time, the growth of the coherent phase is described by equations coupling the energy distribution for the normal gas and the condensate.     

On dynamic effects at folding of coated papers

Folding of coated papers is examined numerically using the finite element method. The analysis is focused on the influence from dynamic effects on the folding process. In particular, the behaviour of field variables relevant for cracking of the coating layers are studied in some detail. The results presented indicate that dynamic effects are of little importance as regards maximum strain levels in the coating but will influence the stress and strain distributions. Accordingly, a quasi-static analysis of the problem will be sufficient in order to describe many of the important features related to cracking.