Copper‐Catalyzed Asymmetric Conjugate Addition of Dimethylzinc to Acyl‐N‐methylimidazole Michael Acceptors: Scope,Limitations and Iterative Reactions

An efficient copper‐catalyzed enantioselective conjugate addition of dimethylzinc to unsaturated 2‐acyl‐N‐methylimidazoles has been achieved using a chiral bidentate hydroxyalkyl‐NHC ligand. The reactions proceed with excellent regioselectivity (1,4 vs. 1,6 and 1,8) in extended conjugated systems to afford the 1,4‐adducts in high enantioselectivities. This regioselectivity could be ascertained by DFT studies highlighting the crucial role of the imidazole ring. Thanks to the development of efficient protocols to regenerate the unsaturated 2‐acyl‐N‐methylimidazole moiety, an iterative process has been developed ultimately leading to 3,5,7 all‐syn or anti‐anti polydeoxypropionate stereodiads.

     

Surface enrichment of biomimetic apatites with biologically-active ions Mg2+ and Sr2+: A preamble to the activation of bone repair materials

The surface activation of calcium phosphate-based biomaterials for bone repair is an emerging route for improving bone regeneration processes. One way for such activation is through the exchange of surface calcium ions with biologically-active cations such as Mg²⁺ or Sr²⁺. In this work, the interactions of non-carbonated and carbonated nanocrystalline apatites with Mg²⁺ and Sr²⁺ were investigated by means of ion exchange experiments in solution. Langmuir-type isotherms were determined. For both Sr and Mg, a greater uptake was observed on the carbonated sample, and on both types of apatites the maximum strontium uptake was greater than that of magnesium. Inverse exchanges showed that the proportion of reversibly fixed ions after surface exchange was close to 85% for Mg and 75–80% for Sr. The results are related to the presence of a surface hydrated layer on the nanocrystals and possible exchange mechanisms are discussed. Our results favor the hypothesis of hetero-ionic surface exchanges (Mg²⁺↔Ca²⁺, Sr²⁺↔Ca²⁺) within the hydrated layer, and some analogy with octacalcium phosphate (OCP) is considered. This work should prove helpful for the control and understanding of the activation of synthetic apatite-based powders or scaffolds with bioactive elements, as well as for the global understanding of biomineralization processes.     

Finite element modelling of passive damping with resistively shunted piezocomposites

This work aims at modelling passive damping in structures made of composites with embedded resistively shunted piezoelectric ceramic fibres. To this end, a 3D material model is implemented in the finite element (FE) code ABAQUS. Academical test cases as well as a structural case study are presented.     

Design of dedicated seven-port star dividers for sectored circular antenna array feeding

In order to mitigate the multipath propagation problems for high rate wlans such as Hiperlan (5 GHz) [2], we study an approach based on electronic beam steering over 360° in azimuth with the help of circular arrays of monopoles [3]. Design simplicity and size constraints intended for potential low-cost applications on the terminals has led us to favor a beam switching topology, using a single feeding-port [4]. Two competing configurations of the microstrip feeding circuit are presented and their principle of operation is experimentally validated through passive circuit configurations. The power distribution is achieved in the first one with the help of a pseudo-divider based on a modified 7-branch star junction, whose specific advantage is its very small size. Unfortunately, this design does not preserve the circular permutation invariance of the radiation patterns. The second circuit bypasses this problem in achieving a power distribution through a virtual point junction, at the cost of an appreciable increase in the circuit size.     

Net N immobilisation during the biodegradation of mucilage in soil as affected by repeated mineral and organic fertilisation

Repeated fertilisation of crops with manure commonly increases both the amount and the quality of soil organic matter, the mineralisation of which strongly determines the availability of N to plants. In the rhizosphere, the microbial mineralisation/immobilisation of N is enhanced due to rhizodeposition (release of organic compounds from roots). In this work, we studied N transformations during incubation of maize root mucilage in soils that had been previously fertilized with composted pig manure or with ammonium nitrate for 7 years. Our work revealed mucilage was rapidly mineralised (average half-life of 3 days), inducing a rapid N immobilisation of 94 mg N g⁻¹ of mucilage C, followed by a slow remineralisation. Fertilisation with manure induced a persistent stimulation of the soil organic matter mineralisation, leading to an enhanced content of soil inorganic N (+23% in 58 days of incubation). Due to this stimulation of microbial activity in the soil fertilized with manure, the decrease in inorganic N during the biodegradation of mucilage lasted a shorter time as compared to the mineral fertilisation. However, the type of fertilisation did not significantly change the amount of N immobilised.     

Distribution of the volatile compounds in the different parts of a white-fleshed peach (Prunus persica L. Batsch)

The quantitative distribution of volatile compounds in the skin, top mesocarp, middle mesocarp, bottom mesocarp, inner mesocarp, and outer mesocarp of a white-fleshed peach (cv. Maura) was investigated. Volatile compounds were extracted by liquid–liquid microextraction (LLME) and analyzed by GC–FID and GC–MS. The results showed that the levels of volatiles in skin were significantly higher than those observed in the other parts of the fruit, whereas top and bottom mesocarp were mainly discriminated by opposite concentrations in unsaturated lactones and C₆-compounds. Distribution of lactones was also found to be different in skin and pulp according to their carbon chain length. Finally, the highest concentrations of benzaldehyde were found to be mainly located close to the stone suggesting that in peach this compound could be derived from enzymatic hydrolysis of amygdalin.     

Microsystems elements based on free-standing thick-films made with a new sacrificial layer process

A new process derived from screen-printing technology and based on thick sacrificial layers has been developed in our laboratory for the fabrication of films partially released from the substrate. The sacrificial layer acts as a stable mechanical support during the firing of the active layer and is totally removed after the final thermal treatment of the sample. Fabrication of a copper electrothermal actuator was undertaken to demonstrate the efficiency of this simple, collective and low cost process. Passive components based on this new process include the fabrication of heating resistors, strain gauges and microchannels. Moreover, the process can also be used to facilitate the implementation of piezoelectric devices.     

Study of microsegregation buildup during solidification of spheroidal graphite cast iron

This work presents an attempt to describe the complex relationship between the development of the solidification microstructures and buildup of microsegregation in spheroidal graphite (SG) cast irons by coupling an experimental investigation and a modeling approach. Experimental characterization of microsegregation in cast iron was made by means of point counting microanalysis along a grid. With this method, the differences of silicon distribution in alloys solidified in the stable system, the metastable system, or in both systems were clearly evidenced. The distribution of manganese in alloy solidified in the stable system was also investigated. It has been, in particular, observed that alloys solidified in the stable (respectively, metastable) system present significant negative (respectively, positive) segregation of silicon, and that alloys solidified in both systems are much less segregated. The solidification path of these alloys has been conveniently reproduced by means of predictions made with a physical model accounting for the nature of the alloy, either hypoeutectic or hypereutectic, and for the sensitivity to temperature and composition of the partition coefficient of alloying elements.     

Families of automata characterizing context-sensitive languages

In the hierarchy of infinite graph families, rational graphs are defined by rational transducers with labelled final states. This paper proves that their traces are precisely context-sensitive languages and that this result remains true for synchronized rational graphs.Received: 17 December 2003, Published online: 27 December 2004     

Lead isotopic composition of fly ash and flue gas residues from municipal solid waste combustors in France: implications for atmospheric lead source tracing

Fly ash and flue gas residues from eight municipal solid waste combustors (MSWC) in France (1992--93 and 1998/ 2002) were analyzed for their Pb isotopic composition. Fly ashes are more representative of solid residual particles, whereas flue gas residues reflect mostly the composition of gas phases. Both sample types contain hundreds to thousands of micrograms of metals per gram. Leaching experiments showed that metals are present in condensed phases, probably as sulfates and chlorides, and suggest that Cd, Pb, and Zn are highly fractionated from one another during volatilization/condensation processes occurring during combustion. Although all the samples analyzed define a fairly restricted range in Pb isotopic compositions (206Pb/207Pb = 1.148-1.158 and 208Pb/206Pb = 2.101-2.114) compared to other environmental samples, some MSWC produce materials having distinct isotopic compositions, whereas others display very similar ones. Isotopic heterogeneity is also measured between samples from a single MSWC. This is interpreted as resulting from the heterogeneity of the waste source materials. The range of Pb isotopic composition of incinerator materials form a well-defined linear array in the 208Pb/206Pb versus 206Pb/207Pb diagram. This array is compatible with the previously reported European standard pollution (ESP) line and most probably represent the average lead isotopic composition of industrial atmospheric emissions in France, with the following ratios: 206Pb/207Pb = 1.154+/-0.003 and 208Pb/206Pb = 2.107+/-0.003 (1sigma).