Étude expérimentale du mélange réactif au sein d'un réacteur torique ondulé (RTO)

Reactive mixing in a wavy torus reactor (WTR) has been examined experimentally. Its performances are compared to these of two other reactors: a plane torus reactor (PTR) and a baffled stirred tank reactor (BSTR). hydrodynamics of mixing has been studied using a plug flow model with axial dispersion for the WTR and PTR. The effect of axial dispersion on the kinetic of a chemical reaction was then analysed for the WTR, PTR and BSTR. Mixing times were slightly longer for the WTR due to a weaker axial dispersion. We also noticed an improvement of the convertion rate for low dissipated power.     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.     

Adsorption of block copolymers at latex surface and their utilization in emulsion polymerization

Amphiphilic block copolymers have been investigated for their utilization in emulsion polymerization of butyl methacrylate. Special attention has been paid to the adsorption mechanism of the block copolymers from systematic measurements of equilibrium adsorption isotherms. A series of well-defined water-soluble amphiphilic block copolymers, composed of poly(butyl methacrylate) and poly(sodium methacrylate) blocks, were synthesized by anionic polymerization of butyl methacrylate and tert-butyl methacrylate followed by the thermal deprotection of the tert-butyl ester groups and final hydrolysis. The number density of emulsion polymer particles N_P varied as [copolymer]^α, α lying between 0.44 and 0.73 according to the hydrophilic content of the copolymers. In contrast with SDS taken as a reference emulsifier, the adsorption of the copolymers was very strong and this provided quite an efficient stabilization of the polymer particles during emulsion polymerization, even at low concentrations (<10⁻⁴ mol L⁻¹) and low coverages (<10% of the interfacial area).     

Motional heterogeneity of polystyrene-block-polybutadiene: a spin probe study

Polystyrene-block-polybutadiene copolymers (SB) with 0.5 mass fraction of styrene were studied by electron spin resonance (ESR) of nitroxide spin probes. The influence of the block length ( and ) and the solvation power of casting solvents on the motional dynamics of spin probe were measured over a wide temperature range. Two nitroxide radicals as spin probes were selected: 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl benzoate (BzONO) and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl (Tempol). Irrespective of the spin probe used two ESR spectral components differing in their motional properties above the phase transition of polybutadiene blocks (PB) were observed. The fast component was assigned to spin probes located in polybutadiene-rich domains and the slow component to spin probes in polystyrene-rich domains. The range of two spectral components and the phase transition of the slow ESR component, T_5mT, depend on the block length. The influence of the interphase and accumulation of free volume in the interphase on the Tempol probe motion was investigated by changing copolymer morphology in the films casted from selective and nonselective solvents. The analysis of the motional heterogeneity from the ratio of the fast and slow motional component presents evidence that in the selective solvent for polystyrene (PS) blocks (2-butanone) the most irregular structure with a large interphase is formed. The difference in fast motion of spin probes indicates that the motional dynamic is related to the change of domain structure.     

Interaction between dietary protein and fat in triglyceride metabolism in the rat: Effects of soy protein and menhaden oil

The objective of the present study was to determine the mechanisms by which dietary proteins interact with dietary lipids in the regulation of triglyceridemia in rats. Male Sprague-Dawley rats (n=56) were subjected to 28-d experimental diets containing different combinations of proteins (20% w/w) and lipid sources (14% w/w): (i) casein-menhaden oil, (ii) casein-beef tallow, (iii) soy protein-menhaden oil, and (iv) soy protein-beef tallow. Significant protein-lipid interactions were observed on triglyceridemia and hepatic cholesterol in fasted rats. The combination of casein and beef tallow was associated with high plasma TG and hepatic cholesterol concentrations, which were reduced by substitution either of soy for casein or of menhaden oil for beef tallow. Therefore, triglyceridemia and liver cholesterol remained low with soy protein feeding, independently of the lipid source, as well as with menhaden oil feeding, regardless of the protein source. The menhaden oil diets reduced plasma cholesterol, hepatic TG, and TG secretion compared with beef tallow diets independently of the dietary protein source. Modifying the source of dietary proteins and lipids had no effect on post-heparin plasma lipoprotein lipase activity. These results demonstrate that soy protein can lower rat triglyceridemia relative to casein when associated with beef tallow consumption, whereas menhaden oil can attenuate hypertriglyceridemia when rats are fed casein. The data further suggest that part of the hypotriglyceridemic effect of soy protein in the rat may be mediated by reduced hepatic lipid synthesis, as is the case for menhaden oil.     

Air impingement and intermittent drying: Application to apple and to mango

An original drying process combining air impingement and intermittent drying was studied on apple slices and mango cubes. The influence of four operating parameters (air velocity, drying/tempering periods, upper height, and air temperature) on the drying time and on the drying rate was evaluated. Continuous and intermittent drying were compared. The intermittency α = 1/7 (τ_on = 10 seconds and τ_off = 60 seconds) gave the best results. A time savings of 54% for apple and 67% for mango was reached. In continuous drying, a time savings of 4620 seconds was observed by increasing the air velocity from 6 to 40 m s^?1 for apple. Air temperatures of 328 K for apple and of 328 K or 338 K for mango were determined as optimum to prevent case‐hardening. Experimental results were fitted with the analytical solution of Fick's second law and the modified Page equation (average values R² = 0.985 and 0.961, for apple and mango, respectively). For both products, the apparent moisture diffusivity D_app, the drying constant k, the drying coefficient n, and the activation energy E_a, were identified. Activation energies calculated from the analytical solution were 30.3 and 36.8 kJ mol^?1 and were 25.4 and 30.0 kJ mol^?1 using the modified Page equation for apple and mango, respectively. Mango has an increased temperature sensitivity and thus will need less energy for drying than apple.     

NH_3 Plasma Surface Treatments of Engineering Fluoropolymers: A Way to Enhance Adhesion of Ni or Cu Thin Films Deposited by Electroless Plating

FLUOROPOLYMERS(FPs)are thermoplasticmaterials which exhibit a number of unique chemicaland physical characteristics that no other man-madeplastic product gets together.For example,FPs showvery good resistance to almost all chemicals,excellentwater vapor barrier properties,high thermal stability,outstanding electrical insulation properties(lowdielectric constant and dissipation factors),extremelylow frictional coefficient giving them high auto-lubrication properties,high resistance to rad…     

Air‐ground Matching: Appearance‐based GPS‐denied Urban Localization of Micro Aerial Vehicles

In this paper, we address the problem of globally localizing and tracking the pose of a camera‐equipped micro aerial vehicle (MAV) flying in urban streets at low altitudes without GPS. An image‐based global positioning system is introduced to localize the MAV with respect to the surrounding buildings. We propose a novel air‐ground image‐matching algorithm to search the airborne image of the MAV within a ground‐level, geotagged image database. Based on the detected matching image features, we infer the global position of the MAV by back‐projecting the corresponding image points onto a cadastral three‐dimensional city model. Furthermore, we describe an algorithm to track the position of the flying vehicle over several frames and to correct the accumulated drift of the visual odometry whenever a good match is detected between the airborne and the ground‐level images. The proposed approach is tested on a 2 km trajectory with a small quadrocopter flying in the streets of Zurich. Our vision‐based global localization can robustly handle extreme changes in viewpoint, illumination, perceptual aliasing, and over‐season variations, thus outperforming conventional visual place‐recognition approaches. The dataset is made publicly available to the research community. To the best of our knowledge, this is the first work that studies and demonstrates global localization and position tracking of a drone in urban streets with a single onboard camera.     

Static Strategies for Worksharing with Unrecoverable Interruptions

One has a large workload that is “divisible”—its constituent work’s granularity can be adjusted arbitrarily—and one has access to p remote worker computers that can assist in computing the workload. How can one best utilize the workers? Complicating this question is the fact that each worker is subject to interruptions (of known likelihood) that kill all work in progress on it. One wishes to orchestrate sharing the workload with the workers in a way that maximizes the expected amount of work completed. Strategies are presented for achieving this goal, by balancing the desire to checkpoint often—thereby decreasing the amount of vulnerable work at any point—vs. the desire to avoid the context-switching required to checkpoint. Schedules must also temper the desire to replicate work, because such replication diminishes the effective remote workforce. The current study demonstrates the accessibility of strategies that provably maximize the expected amount of work when there is only one worker (the case p=1) and, at least in an asymptotic sense, when there are two workers (the case p=2); but the study strongly suggests the intractability of exact maximization for p≥2 computers, as work replication on multiple workers joins checkpointing as a vehicle for decreasing the impact of work-killing interruptions. We respond to that challenge by developing efficient heuristics that employ both checkpointing and work replication as mechanisms for decreasing the impact of work-killing interruptions. The quality of these heuristics, in expected amount of work completed, is assessed through exhaustive simulations that use both idealized models and actual trace data.     

Synchronized switch harvesting applied to self-powered smart systems: Piezoactive microgenerators for autonomous wireless receivers

This paper introduces the conceptual architecture of a fully integrated, truly self-powered structural health monitoring (SHM) scheme. The challenge here is to power an array of numerous distributed actuators and sensors as well as wireless data transmission modules without recurring to heavy and costly wiring. Based on microgenerators which directly convert ambient mechanical energy into electrical energy, using the synchronized switch harvesting (SSH) method, the proposed solution allows avoiding the periodic replacement or reloading of batteries. This addresses environmental and economic issues at the same time, knowing that such elements are heavy, polluting and might be installed in rather inaccessible locations. Indeed, especially in airborne structures saving weight and maintenance cost is of priority importance.Previous work showed that such microgenerators provide a stand-alone power source, whose performances meet the requirements of autonomous wireless transmitters (AWTs) that comprise an acoustic Lamb wave's actuator and a radio frequency (RF) emitter (D. Guyomar, Y. Jayet, L. Petit, E. Lefeuvre, T. Monnier, C. Richard, M. Lallart, Synchronized switch harvesting applied to self-powered smart systems: Piezoactive microgenerators for autonomous wireless transmitters, Sens Actuators A: Phys. 138 (1) (2007) 151–160, doi:10.1016/j.sna.2007.04.009). Following this work, the present contribution presents a further step towards the integration of the SHM technique. It shows the ability of our microgenerators to provide enough energy to give logical autonomy to each self-powered sensing node, named autonomous wireless receiver (AWR), and thus to provide some local (decentralized) pre-processing ability to the SHM system.A preliminary design of the device using off-the-shelf electronics and surface mounted piezoelectric patches will be presented. Since the existence of a positive energy balance between the harvesting capabilities of the SSH technique and the energy requirements of the proposed device will be proved, the system formed by the combination of the AWR with the previously developed AWT, is a proof of concept of truly self-powered smart systems for damage detection in simple structures, setting apart application-specific optimization or miniaturization concerns that will be addressed in future works.