Two 3D thermomechanical numerical models of friction stir welding processes with a trigonal pin

ABSTRACT

During the friction stir welding (FSW) process, the behavior of the material is at the interface between solid mechanics and fluid mechanics. This article deals with a comparison of two 3D numerical models of FSW processes with a trigonal pin. The first model is based on a solid formulation and the second one is based on a fluid formulation. Both models use a Norton–Hoff constitutive model with the high temperature sensitivity of the parameters’ value and advanced numerical techniques such as the Arbitrary Lagrangian Eulerian (ALE) formalism. It can be concluded that, basically, these two formulations lead to the same results.     

Geostatistical Simulations for Risk Assessment and Decision Making: The Mining Industry Perspective

Decision making requires definition of objectives and detailed understanding of the project under study. The options available to the decision maker must be understood, as well as how the project could be improved by choosing these options. A method must be defined to measure the ‘utility’ of a project. This utility is a function of ‘critical indicators’, whose value depends on ‘controlling parameters’. A variety of simulation techniques can be used to assess the probability distribution of the project utility, depending on which options are chosen. Risk can be reduced by acquiring more information, choosing flexible engineering solutions, improving managerial or technical expertise, or sharing risk with others. The best option is that which results in maximum expected utility. Geostatistical simulation plays a critical role in evaluating geologic risk, but the limitations of geostatistical simulation must not be forgotten: It only models some of the risk. To fully assess the expected utility of a project, deposit simulation must be combined with simulation of all other controlling parameters.     

The use of hazard road signs to improve the perception of severe bends

Collision analysis indicates that many car accidents occur when negotiating a bend. Excessive speed and steering wheel errors are often given by way of explanation. Nevertheless, the underlying origin of these dramatic errors could be, at least in part, a poor estimation of bend curvature. The aim of this study was to investigate both the assessment of bend curvature by drivers and the impact of symbolic road signs that indicate a hazardous bend on this assessment. Thus, participants first viewed a video recording showing approaching bends of different curvature before being asked to assess the curvature of these bends. This assessment could either be a verbal (symbolic control) estimation of the bend's curvature and risk, or a sensorimotor (subsymbolic control) estimation of the bend's curvature (participants were asked to turn a steering wheel to mimic the position that would be necessary to accurately negotiate the bend). Results show that very severe bends (with a radius of less than 80 m) were actually underestimated. This was associated with an underestimation of risk corresponding to these bends and a poor sensorimotor anticipation of bend curvature. Road signs, which indicate risk significantly improve bend assessment, but this was of no use for sensorimotor anticipation. Thus, other indicators need to be envisaged in order to also improve this level of control.     

Photopatterning of polybutadiene substrates by interferometric ultraviolet lithography: fabrication of phospholipid microarrays

Gratings are written holographically with low power (10 mW/cm(2)) 244 nm UV light on thin films of polybutadiene rubber polymer. The increase of hydrophilicity-wettability of polybutadiene films is measured over UV-exposed regions. Sequential fabrication of two orthogonal gratings results in hydrophilic microarrays having applications as functionalized substrates for immobilizing biomolecules. This is demonstrated by immobilizing a phospholipid in a microarray pattern.     

Investigation of the biopharmaceutical behavior of theophylline hydrophilic matrix tablets using USP methods and an artificial digestive system

This work aimed to investigate the biopharmaceutical behavior of hydrophilic matrix tablets of theophylline using different in vitro methods: USP II, USP IV, and a novel in vitro system simulating the gastrointestinal tract in man called the artificial digestive system (ADS). The potentiality of each method was evaluated by establishing in vitro/in vivo correlation. Using USP methods, the drug release was pH-independent and dependent on agitation intensity. Level A IVIVCs could be established using the different in vitro methods but one to one correlation was established only when the ADS method was used. For the prediction of in vivo drug dosage form behavior based on in vitro methods, the ADS showed a high predictability when compared to USP in vitro methods.     

A physiologically plausible spatio-temporal model for EEG signals recorded with intracerebral electrodes in human partial epilepsy

Stereoelectroencephalography (depth-EEG signals) is a presurgical investigation technique of drug-resistant partial epilepsy, in which multiple sensor intracerebral electrodes are used to directly record brain electrical activity. In order to interpret depth-EEG signals, we developed an extended source model which connects two levels of representation: (1) a distributed current dipole model which describes the spatial distribution of neuronal sources; (2) a model of coupled neuronal populations which describes their temporal dynamics. From this extended source model, depth-EEG signals were simulated from the forward solution at each electrode sensor located inside the brain. Results showed that realistic transient epileptiform activities (spikes) are obtained under specific conditions in the model in terms of degree of coupling between neuronal populations and spatial extent of the source. In particular, the cortical area involved in the generation of epileptic spikes was estimated to vary from 18 to 25 cm2, for brain conductivity values ranging from 30 to 35 x 10(-5) S/mm, for high coupling degree between neuronal populations and for a volume conductor model that accounts for the three main tissues of the head (brain, skull, and scalp). This study provides insight into the relationship between spatio-temporal properties of cortical neuronal sources and depth-EEG signals.     

Authenticating white grape must variety with classification models based on aroma sensors, FT-IR and UV spectrometry

This paper aims at assessing the capability of high-speed analytical devices, such as aroma sensors (“electronic noses”), Fourier Transform InfraRed (FT-IR) and ultraviolet spectrometers to classify white grape musts (grape juices before fermentation) in variety categories. Due to the complexity of the signal generated, specific data processing techniques have been developed and are described here. First, a pre-processing technique, based on Genetic Algorithms, is applied to spectra to improve spectrometer efficiency without expert knowledge in spectrometry; by selecting the most discriminant subsets of wavelengths, this stochastic method tends to reduce over-fitting and improves classification results. Secondly, the Partial Least Squares Regression technique is adapted to a pattern recognition problem, using Partial Least Squares-Discriminant Analysis, a multivariate classification technique. These devices and data processing techniques are applied to more than 100 must samples. FT-IR spectrometry is the most satisfactory technique with a 9.6% classification error level. Finally, outputs of the three individual sensors are combined in a “low-level” fusion method, by concatenating the individual sensor signals. This straightforward fusion method does not significantly improve results.     

Special WC/Co orientation relationships at basal facets of WC grains in WC–Co alloys

In WC–Co alloys prepared by liquid phase sintering WC grains are partly surrounded by the Co binder and are terminated by basal and prismatic facets. This work reports transmission electron microscopy (TEM) observations on basal WC/Co interfaces. Two kinds of preferred orientation relationships are found. The one most common corresponds to the joining of (0001)_WC with (111)_Co planes. It leads to a large parametric misfit of 15% and is observed for only small pools of Co, mainly located in corners formed by the contact between WC grains. The second type of interface corresponds to the joining of (0001)_WC with (001)_Co and is more rarely found. For random WC/Co orientation relationships a thin WC_1−x cubic layer about two atomic rows is revealed at the interface.     

Removal of organic dyes by magnetic alginate beads

This study deals with the development of a clean and safe process for water pollution remediation. We have synthesized a magnetic adsorbent in order to develop a solid-phase extraction process assisted by a magnetic field. To follow an 'ecoconception' approach, magnetic beads containing magnetic nanoparticles and activated carbon are prepared with a biopolymer extracted from algae, sodium alginate. The use of renewable bioresources of low cost and those disposable in large amount allows the development of a product with a low impact on the environment. The adsorption properties of activated carbon and magnetic properties of iron oxide nanoparticles are combined to produce an interesting magnetic composite. Synthesis and characterization of the magnetic beads have been reported. Their adsorption capacity was investigated by measuring the removal of two dyes (methylene blue and methyl orange) of different charges from aqueous solutions. The efficiency of the beads has been compared with that of non-encapsulated activated carbon. The effects of initial dye concentration, pH and calcium content of the beads have been studied. Adsorption kinetics experiments have been carried out and the data have been well fitted by a pseudo-second-order equation.