The biased evolution of generation time

Many life-history traits, like the age at maturity or adult longevity, are important determinants of the generation time. For instance, semelparous species whose adults reproduce once and die have shorter generation times than iteroparous species that reproduce on several occasions. A shorter generation time ensures a higher growth rate in stable environments where resources are in excess, and is therefore a positively selected feature in this (rarely met) situation. In a stable and limiting environment, all combination of traits (or strategies) that produce the same number of viable offspring on average are strictly neutral even when their generation times differ. We first study the evolution of life-history strategies with different generation times in this context, and show that those with the longest generation time represent the most likely evolutionary outcomes. Indeed, strategies with longer generation times generate fewer mutants per time unit, which makes them less likely to be replaced within a given time period. This `turnover bias' inevitably exists and favors the evolution of strategies with long generation times. Its real impact, however, should depend on the strength and direction of other evolutionary forces; selection for short generation times, for instance, may oppose turnover bias. Likewise, the evolutionary outcome depends on the strength of such selection and population size, comparably to other biases acting on the occurrence of mutations.Comment: Now we also study the evolution of development duration, suggesting that turnover bias is involved in the evolutionary dynamics of any trait linked with the generation tim

Rheological behaviour and spectroscopic investigations of cerium-modified AlO(OH)colloidal suspensions

The rheological behaviour of aqueous suspensions of boehmite (AlO(OH)) modified with different Ce-salts (Ce(NO3)3, CeCl3, Ce(CH3COO)3 and Ce2(SO4)3) was investigated at a fixed Ce/Al molar ratio (0.05). Freshly prepared boehmite suspensions were near-Newtonian and time-independent. A shear-sensitive thixotropic network developed when Ce-salts with monovalent anions were introduced in the nanoparticle sols. The extent of particle aggregation dramatically increased with ageing for Ce(NO3)3 and CeCl3 whereas an equilibrium value was reached with Ce(CH3COO)3. The addition of Ce2(SO4)3 with divalent anions involved no thixotropy but rather a sudden phase separation. The combined data set of IRTF and DRIFT spectra indicated that free View the MathML source anions of peptized boehmite adsorb on the nanoparticle surface by H-bond. The introduction of Ce-salts in the boehmite sol led to the coordination between Ce3+ ions and View the MathML source anions adsorbed on boehmite i.e. to [Ce(NO3)4(H2O)x]− complex. Such coordination led to a thixotropic behaviour which was lower with Ce(NO3)3 compared to CeCl3 and Ce(CH3COO)3. In contrast, Ce2(SO4)3 formed insoluble complexes with dissolved aluminium species. The formation of H-bonded surface nitrate complexes was found to play a decisive role on the particle–particle interactions and consequently on the rheological behaviour of the sols

Ore-Body Delineation using Borehole Seismic Techniques for Hard Rock Exploration

Very often, economically viable ore deposits are low in volume and located at depth within extremely complex geological environments. Such deposits are difficult to explore. Borehole seismic methods, particularly crosshole reflection imaging, could be utilized to detect and delineate such resources. This study aims to evaluate the true potential of crosshole seismic reflection method for mineral exploration. One of the most promising applications of this method is in finding down-dip extensions of the existing resources

An efficient route to aqueous phase synthesis of nanocrystalline γ-Al2O3 with high porosity: From stable boehmite colloids to large pore mesoporous alumina

In this paper we emphasise the important role of Pluronic F127 on the porosity of mesoporous alumina prepared from boehmite colloids. By focusing on the F127/boehmite interactions we show how the concepts of interface science may help to predict and improve the textural characteristics of mesoporous alumina. By varying the synthetic parameters, in particular the copolymer content, we show that the porosity of c-Al2O3 can be enhanced by 400% and the average pore diameter can be expanded from 5 to 14 nm. These results are discussed in terms of interactions between the Pluronic F127 and boehmite colloids, and are correlated to the critical micelle concentration (CMC) of the copolymer. The textural characteristics of the mesoporous alumina can be further improved either by introducing hydrocarbons in the preformed boehmite/copolymer sols or by concentrating the sols. In comparison with as-synthesised alumina, those prepared with F127 showed improved thermal stability. Furthermore, boehmite/copolymer sols were stable for all surfactant concentrations investigated and can give high quality coatings suitable for catalytic applications

Improving the cracking resistance of shotcrete

Le béton projeté est une méthode de mise en place rapide, économique et polyvalente qui offre de multiples avantages par rapport au béton conventionnel dans divers types de constructions nouvelles et dans les réparations. Un des grands avantages du béton projeté est de permettre une mise en place sur des surfaces fortement irrégulières en utilisant peu on même aucun coffrage. Cependant, ces mêmes caractéristiques rendant le béton projeté avantageux et polyvalent peuvent le rendre vulnérable à la fissuration due au retrait restreint. Cette vulnérabilité vient de la restriction élevée inhérente à de nombreuses applications (projection adhérente sur substrat rigide). En effet, le béton développera des contraintes internes s’il ne peut manifester ses changements volumétriques librement, ce qui peut conduire à de la fissuration lorsque ces contraintes atteignent la résistance en traction du matériau. La fissuration des réparations due au retrait restreint est sans aucun doute un des plus grands défis auxquels l’industrie des réparations en béton fait face aujourd’hui. La fissuration peut raccourcir les années de service d’une structure en béton (corrosion accélérée, délamination, etc.) et engendre souvent des coûts des maintenances supplémentaires importants. Il existe peu d’informations fiables dans la littérature sur les paramètres qui influencent la fissuration due au retrait restreint des bétons projetés ainsi que sur leur comportement à long terme en service. Ce manque d’informations à propos de l’influence des différentes composantes du mélange et de la mise en place des bétons projetés rend difficile, voire impossible, la prédiction du comportement à long terme des bétons projetés face aux problèmes de fissuration. De plus, l’ensemble des paramètres individuels affectant la fissuration due au retrait restreint est très difficile à identifier. Pour cette raison, il est devenu impératif de caractériser le comportement volumétrique des bétons projetés au moyen d’essais de retrait restreint. Dans cette thèse, l’évolution de différentes propriétés à l’état frais et durci telles que la consistance de projection, le rebond, la résistance à la compression, la résistance à la traction par fendage, le module élastique, le retrait libre et le retrait restreint est étudiée. Ce projet se concentre particulièrement sur les mélanges et leur composition, la méthode de mise en place et le potentiel de fissuration due au retrait restreint. Le potentiel de fissuration sera évalué au moyen d’une procédure d’essai annulaire qui a récemment été adaptée et amélioré pour les bétons projetés. À partir des données expérimentales générées, une analyse approfondie du développement des contraintes et de la résistance à la fissuration des bétons projetée sera conduite.Shotcrete is a fast, cost-saving, sustainable and versatile concrete placement method that offers numerous advantages over conventional concrete in a variety of new construction and repair works. One of the major benefits of the shotcrete process is that it can be sprayed over irregular surfaces and can cover large surfaces with little or no formwork. Howbeit, these same versatile features also often make shotcrete vulnerable to restrained shrinkage cracking. Cracking occurs mainly because of the highly restrained conditions that are inherent in many shotcrete applications (spraying on a rigid substrate). If shrinkage is restrained, internal tensile stresses are progressively induced in the element which can lead to cracking when the stresses eventually exceed the tensile strength of the material. Cracking of repair materials is unarguably one of the major challenges facing the repair industry worldwide today. Cracking can shorten the service life of concrete structures (accelerated corrosion, delamination, etc.) and often requires significant additional costly maintenance. Yet, reliable material data on parameters that influence the longterm service life and cracking in-place shotcrete is scarce. This lack of information on the influence of mixture composition as well as the placement process makes it difficult, if not impossible, to predict the long-term cracking behaviour of shotcrete. Furthermore, key mixture parameters that lead to cracking have been very difficult to identify. For this reason, it has become imperative for material characterization to be made on the basis of a restrained shrinkage test. In this thesis, different fresh and hardened shotcrete properties such as spraying consistency, rebound, compressive strength, splitting tensile strength, elastic modulus, free shrinkage, and restrained shrinkage deformation are investigated. The project focuses particularly on mix designs and compositions, placement process and the potential for cracking due to restrained shrinkage. The shrinkage ring test method which has been recently adapted and improved for shotcrete will be used to evaluate the cracking potential. Based on the experimental data that will be generated, an in-depth analysis of stress development and cracking resistance of shotcrete will be conducted

Electrophoretic silica-coating process on a nano-structured copper electrode

A method for silica-coating at the nanoscale by electrophoretic deposition is presented here, using raw or grafted silica dispersions

Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers

To enable optical long baseline interferometry toward faint objects, long integrations are necessary despite atmospheric turbulence. Fringe trackers are needed to stabilize the fringes and thus increase the fringe visibility and phase signal-to-noise ratio (SNR), with efficient controllers robust to instrumental vibrations, and to subsequent path fluctuations and flux drop-outs. We report on simulations, analysis and comparison of the performances of a classical integrator controller and of a Kalman controller, both optimized to track fringes under realistic observing conditions for different source magnitudes, disturbance conditions, and sampling frequencies. The key parameters of our simulations (instrument photometric performance, detection noise, turbulence and vibrations statistics) are based on typical observing conditions at the Very Large Telescope observatory and on the design of the GRAVITY instrument, a 4-telescope single-mode long baseline interferometer in the near-infrared, next in line to be installed at VLT Interferometer. We find that both controller performances follow a two-regime law with the star magnitude, a constant disturbance limited regime, and a diverging detector and photon noise limited regime. Moreover, we find that the Kalman controller is optimal in the high and medium SNR regime due to its predictive commands based on an accurate disturbance model. In the low SNR regime, the model is not accurate enough to be more robust than an integrator controller. Identifying the disturbances from high SNR measurements improves the Kalman performances in case of strong optical path difference disturbances.Comment: Accepted for publication in A&A. 17 pages 15 figure

Improvement of barrier properties of a hybrid sol-gel coating by incorporation of synthetic talc-like phyllosilicates for corrosion protection of a carbon steel

Sol–gel coatings for corrosion protection of metals are a good alternative to toxic chromate treatments. The present work focussed on the incorporation of inorganic fillers in a sol–gel coating to improve the barrier properties of the film. Talc-like phyllosilicates obtained by hydrothermal synthesis at 160°C, 260°C and 350°C, called T160, T260 and T350 respectively, were selected as inorganic fillers. The synthetic materials showed talc lamellar structure but, in contrast with natural talc, their smaller size (about 300 nm) and their hydrophilic character allowed easier dispersion of the particles in the sol–gel matrix. Electrochemical impedance measurements performed on the sol–gel coatings deposited on XC35 carbon steel showed that the incorporation of T260 and T350 at a concentration of 20 g L− 1 strongly enhanced the barrier properties of the coating by comparison with the filler-free system. As a consequence, the corrosion protection of the metal substrate was improved