Time resolved three-dimensional acousto-optic imaging of thick scattering media

Acousto-optic imaging is based on light interaction with focused ultrasound in a scattering medium. Thanks to photorefractive holography combined with pulsed ultrasound, we perform a time-resolved detection of ultrasound-modulated photons in the therapeutic window (780 nm). A high-gain SPS:Te crystal is used for this purpose and enables us to image through large optical thickness (500 mean free paths). We are able to generate three-dimensional (3D) acousto-optic images by translating a multielement ultrasound probe in only one direction. A 3D absorbing object is imaged through a 3 cm thick phantom.     

Mechanical properties of carbon nanotubes

A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young’s moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young’s modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 29 July 1999     

On the homotopy of simplicial algebras over an operad

According to a result of H. Cartan, the homotopy of a simplicial commutative algebra is equipped with divided power operations. In this article, we show how to extend this result to other kinds of algebras. For instance, we prove that the homotopy of a simplicial Lie algebra is equipped with the structure of a restricted Lie algebra.

     

Towards a Comprehensive Characterization of the Low-Temperature Autoxidation of Di-n-Butyl Ether

In the present study, we investigated the oxidation of 2500 ppm of di-n-butyl ether under fuel-rich conditions (φ = 2) at low temperatures (460–780 K), a residence time of 1 s, and 10 atm. The experiments were carried out in a fused silica jet-stirred reactor. Oxidation products were identified and quantified in gas samples by gas chromatography and Fourier transform infrared spectrometry. Samples were also trapped through bubbling in cool acetonitrile for high-pressure liquid chromatography (HPLC) analyses. 2,4-dinitro-phenylhydrazine was used to derivatize carbonyl products and distinguish them from other isomers. HPLC coupled to high resolution mass spectrometry (Orbitrap Q-Exactive^®) allowed for the detection of oxygenated species never observed before, i.e., low-temperature oxidation products (C₈H₁₂O_4,6, C₈H₁₆O_3,5,7, and C₈H₁₈O₂,₅) and species that are more specific products of atmospheric oxidation, i.e., C₁₆H₃₄O₄, C₁₁H₂₄O₃, C₁₁H₂₂O₃, and C₁₀H₂₂O₃. Flow injection analyses indicated the presence of high molecular weight oxygenated products (m/z > 550). These results highlight the strong similitude in terms of classes of oxidation products of combustion and atmospheric oxidation, and through autoxidation processes. A kinetic modeling of the present experiments indicated some discrepancies with the present data.     

A practical approach to the living polymerization of functionalized monomers: application to block copolymers and 3‐dimensional macromolecular architectures

The tolerance of living free radical procedures to reactive functional groups, coupled with their ability to prepare well‐defined random and block copolymers is demonstrated by the use of novel α‐hydrogen alkoxyamine derivatives instead of the traditional TEMPO‐based systems. This refinement in the nitroxide structure overcomes many limitations typically associated with TEMPO and has permitted a dramatic increase in the range of monomers, which can be polymerized under controlled conditions. The ability to prepare well‐defined multi‐arm star polymers from a variety of alkoxyamine terminated vinyl and non‐vinyl linear polymers are major benefits when compared to traditional living procedures, such as anionic polymerizations.