Poro-Damage Approach Applied to Hydro-Fracture Analysis of Concrete

An approach using mechanics of saturated porous media is presented to model strongly coupled hydromechanical effects in concrete. Fracture mechanisms of the matrix are taken into account by introducing a tensorial damage variable, which makes it possible to describe orthotropic damage states as well as their effects on hydromechanical parameters (permeability and Biot tensor). An experimental procedure, allowing simultaneous control of pore pressure and applied stresses in a concrete specimen, leads to the identification of material parameters introduced in the constitute model. This model is implemented in the finite-element code CASTEM 2000; numerical simulations of a hydraulic fracture test are then performed and show that the damage-dependence of hydraulic parameters has significant influence on the global response of the structure.     

A Wireless Sensor Network Protocol for an Inertial Motion Tracking System

Wireless sensor networks have found their way to countless applications in many different fields. Due to the restricted power availability these systems are faced with, custom wireless protocols have been designed. Many different protocols have already been conceived, yet each application will impose different requirements. In inertial motion tracking, sensor nodes are applied on the body allowing full body posture reconstruction. These nodes must not hinder or restrict the movements of the user in any way, meaning that a wireless approach is desirable. A suiting protocol that insures robust simultaneous functionality of at least 15 nodes at a rate of 100Hz is required. A TDMA based protocol with master/slave hierarchy is presented for the application at hand. Nodes dynamically decide on their role within the network at startup and reassess the network state regularly. Conflicting situations are handled whenever they arise and nodes react accordingly creating a fully plug-and-play system. Careful implementation of the protocol in embedded software allows data transmission of 19 nodes while each of them consumes an average current of only 3mA.     

Aerocellulose based on all‐cellulose composites

Novel aerogels (or aerocellulose) based on all‐cellulose composites were prepared by partially dissolving microcrystalline cellulose (MCC) in an 8 wt % LiCl/DMAc solution. During this process, large MCC crystals and fiber fragments were progressively split into thinner crystals and cellulose fibrils. The extent of the transformation was controlled by using cellulose concentrations ranging from 5 to 20 wt % in the LiCl/DMAc solution. Cellulose gels were precipitated and then processed by freeze‐drying to maintain the openness of the structure. The density of aerocellulose increased with the initial cellulose concentration and ranged from 116 up to 350 kg m^?3. Aerocellulose with relatively high mechanical properties were successfully produced. The flexural strength of the materials reached 8.1 MPa and their stiffness was as high as 280 MPa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Redox enzymes immobilized on electrodes with solution cosubstrates. General procedure for simulation of time-resolved catalytic responses

In view of the existing and potential applications of electrochemical enzymatic catalysis with redox enzymes immobilized on the electrode surface in biosensors, a numerical calculation procedure for simulating their cyclic voltammetric responses is presented. It is applicable to systems involving a redox cosubstrate in solution. The cosubstrates, substrates, products, and inhibitors are assumed to diffuse linearly (planar electrode) between the electrode and the solution. The reactions in which the various forms of the immobilized enzyme participate may be as numerous and intricate as required by the simulation with no other restriction than the computing time. They may, at will, follow or not follow Michaelis-Menten kinetics. Slow charge-transfer cosubstrates are treated in the framework of Butler-Volmer kinetic law.     

Distribution of aquatic macrophytes in contrasting river systems: a critique of compositional-based assessment of water quality

A brief summary of the historical developments relating to plant distribution and aquatic macrophyte-nutrient indices provided a means of assessing the general context and validity of previous assumptions. This has particular current relevance because of the prominent use of bioindicators for defining nutrient enrichment. A survey of 161 sites distributed across two broadly contrasting groups of rivers (circum-neutral versus alkaline) recorded 110 species of aquatic macrophytes and these have been statistically analyzed to (i) rank and separate the individual effects of local environmental conditions and spatial isolation on species distribution in the two contrasting groups of sites; (ii) calculate a macrophyte index based on plant cover and species indicator values (Mean Trophic Rank, MTR); and finally (iii) investigate the implications for biomonitoring. Chemical, physical and hydrological site attributes together with spatial isolation, each explained a significant and at least partially independent influence over plant species distribution. It was extremely difficult, however, to separate the single effects of different site attributes on plant distribution. While some plant species are more restricted to certain environmental conditions, many appeared indifferent to the range of those being tested. The role played by nutrients (nitrogen (N) and phosphorus (P)) were either mostly indistinguishable from other site attributes (e.g., nitrate from conductivity) or subordinate (e.g., soluble reactive phosphorus, ammonium). It is therefore very unlikely that macrophyte species composition could provide a reliable bioindicator of the surrounding nutrient (N, P) status. The calculation of the plant index illustrated this unreliability by showing that strong correlations existed with many environmental variables, not just inorganic N and P.     

Predicting uncertainty in the ecotoxicological assessment of solid waste leachates

Environmental managers need suitable technological methods to use in optimization studies to improve management of hazardous waste. One of the challenges to achieving a reliable hazardous waste classification is the improvement of procedures used forthe ecotoxicological characterization of solid waste leachates. Indeed, this step requires data that meet levels of acceptable quality if scientifically based decisions are to be made. In this study, we illustrate how the variability associated with the successive steps of a procedure used to assess ecotoxicological hazard of solid waste (i.e., primary sampling, laboratory sampling, toxicity measurements) can contribute to the overall variability of the ecotoxicity results. To this end, a municipal solid waste incinerator bottom ash and a slag from a second smelting of lead were studied using a nested experimental design. The results showed that the waste sampling design is of major importance for limiting the final variability of toxicity test parameters. At the opposite, increasing the number of replicates at the toxicity test level has negligible impact on this variability. Our approach could be of great practical interest in ecotoxicological studies not only for ensuring a safe classification for these materials, but also for improving sampling protocols and facilitating less time-consuming and less expensive ecotoxicological evaluations.     

Postural stabilization of looking.

The authors studied relations between postural sway, optical flow, and constraints on posture imposed by a suprapostural looking task. Optical flow resulted from unperturbed sway and was not imposed by the experimenters. Participants fixated a distant target or a nearby target. In the key condition, participants looked past (i.e., ignored) a nearby target to fixate the distant target. The authors recorded the variability of head position as a measure of the amplitude of postural sway. In 5 of 7 experiments, sway variability was influenced by the location of the fixated target not by the distance of the nearest visible surface (the unfixated nearby target). Postural sway was modulated to facilitate the performance of suprapostural tasks and was not driven by optical flow in an autonomous (task-dependent) manner. The authors concluded that posture can be understood only in the context of explicit manipulations of suprapostural tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aramid, steel, and glass: characterization via cut performance testing, of composite knitted fabrics and their constituent yarns, with a review of the art

Aramid, glass, and steel have been compared for their performance in composite forms in protective applications, which are not the most usual ones. After underlining the importance of cut protection, a rather extensive review of the art in the domain of cut performance reveals that a good basis has been established, still leaving space for the study of non-coated, less uniformly interlocked composite yarn assemblies in the form of knitted structures or woven ones. Slightly departing from the traditionally friction-driven cut mechanism, those structures are distinguishable. This offers some elements for the long-awaited clarification of normalized test differences. Statistically, relevant families of commercial or semi-commercial products have been selected to address simultaneously the variability and the performance boundaries of those materials using instrumented ASTM cut equipment to obtain a “smarter” response of the material performance during its testing and to perform a “more sophisticated” data analysis beyond usually specified ones. The attempts to analyze more localized physical events open the door to micro or nanoanalysis of the fracture mechanism during the cut event which may differ from the traditional friction analysis. The contribution of meltable companion fillers, although not being the core of the study, could be translated to applications where those fillers become functional elements further improving the performance and synergism of the three basic elements, aramid, glass and steel. Previous study on the tribological properties of Kevlar^? (DuPont’s registered trademark) composite fabrics stands as a natural prolongation of this study when applied to the knitted composite structures of this study.