Cyclometalated N‐Heterocyclic Carbene‐Platinum Catalysts for the Enantioselective Cycloisomerization of Nitrogen‐Tethered 1,6‐Enynes

Platinum(II) complexes which combine six‐membered N‐heterocyclic carbene‐containing metallacyclic units and monodentate chiral phosphines have been prepared. The key step of their synthesis is the intramolecular oxidative addition of N‐2‐iodobenzylimidazolylidene‐platinum(0)‐diene complexes in the presence of the chiral phosphorus ligands. The platinum(II) metallacycles have been used as well‐defined pre‐catalysts for the enantioselective cycloisomerization of nitrogen‐tethered 1,6‐enynes into 3‐azabicyclo[4.1.0]hept‐4‐enes. High enantiomeric excesses have been obtained with either Monophos or phenyl‐Binepine based catalysts (ees=82–96%), although phenyl‐Binepine outperforms Monophos in these reactions. The absolute configuration of the final 3‐azabicyclo[4.1.0.]heptenes has been established by X‐ray diffraction studies. The method has been extended then to the cycloisomerization of dienynes with enantiotopic vinyl groups. An (S)‐phenyl‐Binepine‐platinum(II) complex allows total diastereoselectivity and high enantioselectivity levels to be attained in these reactions (ees up to 95%) which represent the first enantioselective desymetrizations achieved via enyne cycloisomerizations.     

Effect of Fibre Volume Fraction on Mixed-Mode Fracture of a Fabric Carbon/Epoxy Composite

Variation in fibre volume fraction is a common characteristic of composites made by an injection moulding process. The effect of this variation on fracture toughness is not yet fully investigated. This paper examines the fracture in fabric carbon/epoxy composite laminates under a wide range of combined mode-I and mode-II delamination. A total of 60 double cantilever beam and edge-notched flexure specimens are manufactured by resin transfer moulding with two different fibre volume fractions. It was observed that increasing the fibre volume fraction decreased the initiation fracture toughness in all mixed-mode ratios. This behaviour is believed to relate to the fact that the initiation fracture energy is dominantly absorbed by the resin-rich regions at the delamination tip. In contrast, an increase in fibre volume fraction was found to increase the propagation fracture toughness at high mode-I contribution where the fibre bridging is believed to be the major energy dissipating mechanism. Fractographic analysis also demonstrated that an increase in contribution of mode-II delamination is accompanied by a decrease in fibre bridging and an increase in shear hackles.     

Towards an ontology of design: lessons from C–K design theory and Forcing

In this paper we present new propositions about the ontology of design and a clarification of its position in the general context of rationality and knowledge. We derive such ontology from a comparison between formal design theories developed in two different scientific fields: Engineering and Set theory. We first build on the evolution of design theories in engineering, where the quest for domain independence and “generativity” has led to formal approaches, likewise C–K theory, that are independent of what has to be designed. Then we interpret Forcing, a technique in Set theory developed for the controlled invention of new sets, as a general design theory. Studying similarities and differences between C–K theory and Forcing, we find a series of common notions like “d-ontologies”, “generic expansion”, “object revision”, “preservation of meaning” and “K-reordering”. They form altogether an “ontology of design” which is consistent with unique aspects of design.     

Dissipative atom optics

Abstract

We present an experiment where a cloud of cold caesium atoms is dropped onto an atomic mirror formed by a laser evanescent wave, and is cooled during the reflection. This cooling is due to a single Sisyphus process, transferring atoms from one ground-state hyperfine level to another, less coupled to the evanescent wave. We compare our results with a simple one-dimensional theoretical model. We also give the first experimental evidence for a large increase in the confinement lifetime of the atoms in this ‘gravitational cavity’ because of the cooling process.     

Multi-scale coupling between two dynamical models for PEMFC aging prediction

In this paper, an approach allowing connecting two numerical models for the simulation of the PEMFC operation and durability at different physical scales is presented. After explaining the interest of coupling them to study the interactions between the fuel cell system and the fuel cell itself, along with lifetime concerns, the feasibility of the task is assessed. Then the numerical approach to achieve this coupling is presented. Finally the response of the coupled models is examined to check its validity, and first results are presented. Predicted fuel cell lifetime trends when changing the stack operation conditions are shown, which highlight the presence of optima concerning temperature, demanded current, pressure and O₂ stoichiometry. Two operation modes are then compared in terms of their impact on the fuel cell performance decay, showing that power cycles are more damaging the fuel cell than nominal operation.     

Numerical Evaluation of Radiation Extinction Coefficient Using Fractal Geometry for Vegetation Modeling

This article focuses on the accurate determination of the radiation extinction coefficient (β) for a vegetal set like a tree in the frame of forest fires. Usually, this coefficient is calculated using the De Mestre relationship, not taking into account the leaf orientation and position. In order to evaluate their role, a realistic vegetal structure is numerically created using LAI data, De Wit's models, and IFS geometry. A ray-tracing method is used to simulate the radiative transfer inside the numerical tree. The results show that the leaf distribution and position cannot be neglected in β determination. The use of well-known correlations are not sufficient to predict β: over-estimations of up to 100% have been observed.     

Application of sputtered ruthenium nitride thin films as electrode material for energy-storage devices

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Experimental Evaluation of the Dissolution Rates of Ti and FeTi70 in Liquid Fe

During secondary steelmaking, improving alloy yield and engineering inclusion content require understanding and quantification of the alloy distribution in the melt. When additions are dropped in the melt, a steel shell solidifies around them. After this shell has melted, the alloy is spread in the melt. The influence of process parameters on the duration of the shell period for Ti and FeTi70 additions has been experimentally evaluated. For Ti, the melt temperature and the initial addition size were varied and for FeTi70, only the melt temperature was varied. By continuously measuring the apparent weight of submerged samples with a load cell, the shell period and the amount of molten alloy within the shell were determined. The shell period increases at lower superheats and for larger sample sizes. For a certain size of Ti additions, the molten content within the shell increases with increasing shell period. The importance of this period, relative to the total dissolution time, increases at lower superheats. All investigated FeTi70 samples may melt completely within the shell. While the shell period lasts longer for FeTi70 than for the corresponding Ti samples, this fast internal melting yields a net reduction in total dissolution time.