12,017 research outputs found
Chemical behavior of tungstate solutions. Part 1. A spectroscopic survey of the species involved
This study is focused on the composition and the evolution of tungstate ions solutions as a function of pH and increasing concentrations. The Raman analysis showed that, during the titration of the tungstate solutions, WO4 2−, HWO4 − ions and probably W2O7 2−, HW2O7 2− and H2W2O7 solvated species could exist in aqueous solutions. For diluted solutions, additions of a strong acid does not cause any precipitation, whereas the formation of the unstable solid tungstic acid (H2WO4 or WO3·H2O) could occur in concentrated solutions
Homogeneous deposition of particles by absorption on hydrogels
When a drop containing colloidal particles evaporates on a surface, a
circular stain made of these particles is often observed due to an internal
flow toward the contact line. To hinder this effect, several approaches have
been proposed such as flow modification by addition of surfactants or control
of the interactions between the particles. All of these strategies involve the
liquid phase while maintaining the drying process. However, substitution of
evaporation by absorption into the substrate of the solvent has been
investigated less. Here, we show that a droplet containing colloidal particles
deposited on swelling hydrogels can lead to a nearly uniform coating. We report
experiments and theory to explore the relation between the gel swelling,
uniformity of deposition and the adsorption dynamics of the particles at the
substrate. Our findings suggest that draining the solvent by absorption
provides a robust route to homogeneous coatings
Chemical analysis of a single basic cell of porous anodic aluminium oxide templates
We prepared anodic aluminium oxide (AAO) templates with “honeycomb” geometry, i.e. hexagonally ordered circular pores. The structures were extensively studied and characterized by EPMA coupled with FEG-SEM and FEG-TEM coupled with EDX at meso and nanoscopic scales, in other words, at the scale of a single basic cell making up the highly ordered porous anodic film. The analyses allowed the identification of the chemical compounds present and the evaluation of their levels in the different parts of each cell. Of note was the absence of phosphates inside the “skeleton” and their high content in the “internal part”. Various models of porous anodic film growth are discussed on the basis of the results, contributing to a better understanding of AAO template preparation and selfnanostructuring phenomena
Rheopexy and tunable yield stress of carbon black suspensions
We show that besides simple or thixotropic yield stress fluids there exists a
third class of yield stress fluids. This is illustrated through the rheological
behavior of a carbon black suspension, which is shown to exhibit a viscosity
bifurcation effect around a critical stress along with rheopectic trends, i.e.,
after a preshear at a given stress the fluid tends to accelerate when it is
submitted to a lower stress. Viscosity bifurcation displays here original
features: the yield stress and the critical shear rate depend on the previous
flow history. The most spectacular property due to these specificities is that
the material structure can be adjusted at will through an appropriate flow
history. In particular it is possible to tune the material yield stress to
arbitrary low values. A simple model assuming that the stress is the sum of one
component due to structure deformation and one component due to hydrodynamic
interactions predicts all rheological trends observed and appears to well
represent quantitatively the data.Comment: submitted to Soft Matte
Distributed machining control and monitoring using smart sensors/actuators
The study of smart sensors and actuators led, during the past few years, to the development of facilities which improve traditional sensors and actuators in a necessary way to automate production systems. In an other context, many studies are carried out aiming at defining a decisional structure for production activity control and the increasing need of reactivity leads to the autonomization of decisional levels close to the operational system. We suggest in this paper to study the natural convergence between these two approaches and we propose an integration architecture dealing with machine tool and machining control that enables the exploitation of distributed smart sensors and actuators in the decisional system
Hybridization of Bayesian networks and belief functions to assess risk. Application to aircraft deconstruction
This paper aims to present a study on knowledge management for the disassembly of end-of-life aircraft. We propose a model using Bayesian networks to assess risk and present three approaches to integrate the belief functions standing for the representation of fuzzy and uncertain knowledge
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