Numerical Modeling of Vacuum Heat Treatment of Nickel-based Superalloys

Numerical modeling is carried out of the heat transfer effects arising during heat treatment of single-crystal nickel-based superalloys, of the type used for high pressure turbine blades in jet engines. For these components, fine control of the thermal history during processing is needed to avoid incipient melting and to develop the properties needed for service applications. Computational fluid dynamics methods are employed for the analysis. The modeling is used to predict the temporal evolution of the temperature distribution inside the treated component, to calculate heat transfer coefficients, and to analyze the homogeneity of heat transfer. The impact of the boundary conditions is investigated with particular emphasis on the temperature of the heating elements. Its value was derived from an analytical model of the furnace using effective view factors. The predictions of the modeling are tested against measurements made on laboratory-scale apparatus containing features of production-scale equipment.     

On the mechanism of porosity formation during welding of titanium alloys

The mechanism of porosity formation during the fusion welding of titanium and its alloys is studied. Porosity formed during the electron beam welding of titanium is characterized using high-resolution X-ray tomography, residual gas analysis and metallographic sectioning; the results confirm that porosity formation is associated with evolution of gas, especially hydrogen. A model for hydrogen diffusion-controlled bubble growth is proposed, to aid in the interpretation of these findings. To investigate further the effect of hydrogen on porosity formation, hydrogen charging is used to achieve different hydrogen levels prior to welding. The results confirm that porosity can be suppressed even at every high hydrogen levels, when welding is carried out with optimized welding parameters and perfect joint alignment; on the other hand, porosity is exacerbated when a small beam offset is employed. This is because any beam offset alters the size of the liquid zone at the melting front, where the joint edges first become melted. It is proposed that the thickness of the liquid film at the melting front is crucial for bubble nucleation and bubble survival in the weld pool; bubbles can escape through the keyhole by breaking through this liquid film, when it is too thin. This challenges the common assumption of bubble escape by flotation to the weld pool surface. Thus the nucleation rate in the liquid zone at the melting front determines the likelihood of porosity occurring. This suggests that the beam offset is likely to be one factor influencing porosity formation in these circumstances. The paper provides fundamental insights into the mechanism of porosity formation during the welding of titanium alloys and guidance to aid in its elimination.     

Effect of Operating Parameters on the Dewatering Performance of Press Filters: A Sensitivity Analysis

To optimize the press filters commonly used to dewater residual sludge, the impact of the operating parameters must be better understood. The objectives of this article are (1) to identify the impact of the operating parameters on press filter performances and (2) to classify the operating parameters regarding their impact on dewatering performances. Experiments were performed with conditioned activated sludge in a tangential filtration cell, and a sensitivity analysis of the process was performed. This study emphasizes that cake thickness and filtration pressure have the most significant impacts on dewatering efficiency. These results suggest a promising outlook for press-filter optimization.     

Preparation of functionalized Kraft lignin beads

Kraft lignin from black liquor wastes have been converted into epichlorohydrin‐crosslinked beads by inverse suspension polymerization. A careful control of the different parameters allowed the preparation of spherical beads with a relatively narrow diameter size distribution. The obtained beads, without permanent porosity, swell well in hydroalcoholic media. Grafting of the sulfonylhydrazine moiety using a two‐step route was further performed to apply them to carbonyl compounds scavenging. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Detection, characterization, and screening of heme-binding molecules by mass spectrometry for malaria drug discovery

Drug screening for antimalarials uses heme biocrystallization inhibition methods as an alternative to parasite cultures, but they involve complex processes and cannot detect artemisinin-like molecules. The described method detects heme-binding compounds by mass spectrometry, using dissociation of the drug-heme adducts to evaluate putative antiplasmodial activity. Applied to a chemical library, it showed a good hit-to-lead ratio and is an efficient early stage screening for complex mixtures like natural extracts.     

Characterization of Liquid Resin Infusion (LRI) filling by fringe pattern projection and in situ thermocouples

Prepregs are not alone suited to the manufacturing of new types of aircraft structural parts that tend to be thicker and have more complex shapes. Direct processes called Liquid Composites Moulding (LCM), like Resin Transfer Moulding (RTM) or Resin Infusion Process (LRI: Liquid Resin Infusion, RFI: Resin Film Infusion) are now available. Particular attention is paid here to LRI process that looks very promising. In order to optimize both the design and manufacturing parameters in LRI processes, a general model to analyze the isothermal fluid flow through highly compressible porous media such as fibrous preforms has been recently proposed [1], [2], [3]. To validate the model and to improve the knowledge of the LRI process, an experimental approach is proposed. Two different measurement techniques, micro-thermocouple sensors and fringe projection technique, have been used to characterize the process. It appears that results derived from both techniques are in agreement and support the assumption that the resin flow occurs mainly transversely to the preform plane.     

Extraction of spots in biological images using multiscale products

We present a new method to detect and count bright spots in fluorescence images coming from biological immunomicroscopy experiments. It is based on the multiscale product of subband images resulting from the à trous wavelet transform decomposition of the original image, after thresholding of non-significant coefficients. The multiscale correlation of the filtered wavelet coefficients, which allows to enhance multiscale peaks due to spots while reducing noise, combines information coming from different levels of resolution and gives a clear and distinctive chacterization of the spots. Results are presented for the analysis of typical immunofluorescence images.     

Boundary factors and contextual contingencies: configuring electronic templates for healthcare professionals

In this paper, we propose an approach to balance the legitimate and yet conflicting perspectives between standardization and reconfiguration embedded within hospital information systems (HIS) design activities. We report on an action research study of the customization process of an electronic triage and tracking system that was reconfigured to be used in eight Canadian emergency departments. We argue that during HIS design activities, it is essential for both practitioners and system designers to articulate and identify which aspects can be standardized without constraining important local flexibility and which aspects require local reconfiguration to function in a particular work context. To identify these differences, we suggest an analytical distinction between boundary factors and contextual contingencies, which can be used in a design and reconfiguration process. We argue that the process of designing shared electronic templates should be perceived as a common design process, where multiple stakeholders articulate, identify, and negotiate boundary factors and contextual contingencies. Boundary factors are then represented within the shared electronic system, whereas contextual contingencies form the basis for constructing localized versions of the shared application. All local versions include both boundary factors and the reconfigured contextual contingencies.