An Estimate of the Fractal Index Using Multiscale Aggregates

We study a family of estimators of the fractal index of a Gaussian process based on the quadratic deviations at different aggregation scales. The estimators are convergent and asymptotically Gaussian when suitably normalized. Confidence intervals are provided. These asymptotic results hold for a large family of stationary-increment models including fractional Brownian motions with square-integrable spectral density. The estimates are applied to the analysis of an electrical signal     

Morphology development of EPDM/PP uncross‐linked/dynamically cross‐linked blends

Ethylene‐propylene‐diene‐terpolymer (EPDM) and polypropylene (PP)‐based uncross‐linked and dynamically cross‐linked blends were prepared both in an internal mixer and in a corotating twin‐screw extruder. The effects of composition, plasticization and mixing equipment on the morphology development and the final viscoelastic properties were studied. In the uncross‐linked blends, the plasticization resulted in a coarser morphology. Furthermore, it was shown that the majority of the plasticizer resided in the EPDM phase, enabling its deformation in the flow direction. In addition, the intensive mixing conditions inside the twin‐screw extruder resulted in a finer morphology. In the dynamically cross‐linked blends, the twin‐screw extrusion process resulted in a higher level of gel content with larger EPDM domains. The plasticization showed again a coarsening effect, resulting in interconnected cross‐linked EPDM domains. An interesting interfacial phenomenon was observed especially in the plasticized vulcanized blends where nanometer size occluded PP domains were stripped off and eroded into the EPDM phase. With the exception of the nonplasticized uncross‐linked blends, the viscoelastic properties of all other blending systems were found to be directly affected by the morphology, gel content (in the case of cross‐linked blends), and the presence of the plasticizer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Intégration de questions socialement vives (QS) en cours de biologie par des enseignants et enseignantes du collégial et du lycée

Résumé

Les percées récentes dans le domaine des biotechnologies permettent d’envisager l’intervention dans la production des êtres vivants en manipulant le matériel génétique. Or, cette capacité soulève des controverses à grande portée sociale. Qu’il s’agisse d’utilisation de cellules souches ou des OGM, la biologie contemporaine soulève de questions vives en lien avec les enjeux éthiques qu’elle recèle. Mais qu’en disent les enseignantes et enseignants de biologie ? Cet article présente des résultats de recherche obtenus lors d’entretiens biographiques de six enseignants et enseignantes de biologie au cours desquels ils ont traité de leur rapport au vivant. Ces résultats suggèrent que ces derniers s’intéressent à ces questions et qu’ils les prennent en charge de différentes façons malgré certaines contraintes, notamment curriculaires.     

Rheological modeling of carbon nanotube suspensions with rod–rod interactions

To explain the shear‐thinning behavior of untreated carbon nanotube (CNT) suspensions in a Newtonian matrix, a new set of rheological equations is developed. The CNTs are modeled as rigid rods dispersed in a Newtonian matrix and the evolution of the system is controlled by hydrodynamic and rod–rod interactions. The particle–particle interactions is modeled by a nonlinear lubrication force, function of the relative velocity at the contact point, and weighted by the contact probability. The stress tensor is calculated from the known fourth‐order orientation tensor and a new fourth‐order interaction tensor. The Fokker‐Planck equation is numerically solved for steady simple shear flows using a finite volume method. The model predictions show a good agreement with the steady shear data of CNTs dispersed in a Newtonian epoxy matrix as well as for suspensions of glass fibers in polybutene,¹ demonstrating its ability to describe the behavior of micro‐ and nanoscale particle suspensions. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1476–1487, 2014     

Experimental investigation of the flow dynamics of rheologically complex fluids in a Maxblend impeller system using PIV

The Maxblend^® mixer is used in processes involving Newtonian, shear-thinning or viscoelastic fluids and, as for many impellers, little is known regarding the relationship between the rheological behavior and the flow and mixing properties. An experimental study of the hydrodynamics in the Maxblend was carried out using Newtonian and non-Newtonian fluids in laminar and early transitional regimes. Flow fields were measured by two-dimensional particle image velocimetry (PIV) to evaluate the effect of highly shear-thinning and viscoelastic behavior on the performance of the mixer. The experimental setup consisted of a 35-L tank equipped with two baffles. A total of 100 measurements were proven to be sufficient in order to attain convergence of the velocity components for all studied regimes. Isolated zones in the highly shear-thinning case were observed by means of a decolorization technique. Elasticity in the laminar regime produced a reversal of the flow and a solid body rotation in the bottom region of the tank. Fluid velocity magnitude and spread were observed to be reduced by the presence of elastic forces.     

Screening of 23 β-lactams in foodstuffs by LC–MS/MS using an alkaline QuEChERS-like extraction

A fast and robust high performance LC–MS/MS screening method was developed for the analysis of β-lactam antibiotics in foods of animal origin: eggs, raw milk, processed dairy ingredients, infant formula, and meat- and fish-based products including baby foods. QuEChERS extraction with some adaptations enabled 23 drugs to be simultaneously monitored. Screening target concentrations were set at levels adequate to ensure compliance with current European, Chinese, US and Canadian regulations. The method was fully validated according to the European Community Reference Laboratories Residues Guidelines using 93 food samples of different composition. False-negative and false-positive rates were below 5% for all analytes. The method is adequate for use in high-routine laboratories. A 1-year study was additionally conducted to assess the stability of the 23 analytes in the working standard solution.     

Foods protected by the important biological antioxidant: Uric acid

Uric acid has been proposed as an antioxidant in biological fluids especially in humans. It is shown that uric acid can be used effectively to protect food and model food preparations against oxidation. Precooked cereal flakes and food emulsions were stabilised with varying levels of uric acid.     

ω-3 Fatty acids in smooth muscle cell phospholipids increase membrane cholesterol efflux

The aim of our work was to determine whether fatty acid modifications in smooth muscle cell phospholipids affect cholesterol efflux and desorption. [³H]Cholesterol was used to label cholesterol pools in the whole cell or selectively in the plasma membrane. Cells were incubated for 12 h in order to increase oleate, linoleate, arachidonate, eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in phospholipids. Cholesterol efflux was monitored using native or tetranitromethane modified high-density lipoprotein₃ (HDL₃). When all cholesterol pools were labeled, the efflux from cells treated with different fatty acids were not different. Plasma membrane cholesterol efflux remained unchanged after oleate, linoleate or arachidonate treatments, but was markedly increased after EPA and DHA enrichment, both with native HDL₃ and with tetranitromethane-high-density lipoprotein. These results suggest that the positive effects of n−3 fatty acid consumption on the atherosclerotic process could be linked in part to an increase in plasma membrane cholesterol efflux from vascular smooth muscle cells.     

Le phénomène de la transformation verbale: Nouvelles modalités de fonctionnement.

Investigated the effects of an irregular presentation of the stimulus repetition on the verbal transformation effect (VTE). Ss were 48 children (aged 8–13 yrs), 48 adults (aged 19–30 yrs), and 60 aged persons (aged 65–90 yrs), and were presented 4 separate stimuli repeated either irregularly (experimental group) or regularly (control group). Results show that VTE appeared earlier and provoked more verbal transformations (VTs) on an irregular stimulus presentation. In both conditions, there was a gradual increment in the number of VTEs as listening continued. Age group comparisons showed a marked decrease in VTE as Ss' ages increased. Finally, the choice of stimuli according to their absolute frequency of occurrence in the French language showed that high frequency words produced less VT than low frequency words; however, there was no significant difference for reaction time (RT) and number of forms on that variable. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)