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71.
We present a nondestructive and noncontact extensometry technique, which has been developed in order to study the behavior of different materials such as polycarbonate, araldite, urethane, etc. A spectral analysis of a crossed grating marked on the surface of a specimen and recorded by a charge coupled device camera is presented. The procedure is based on the use of a bidimensional fast Fourier transform algorithm coupled with an interpolation process. It leads to the accurate determination of frequencies. Numerical simulations have been made to evaluate the strain sensitivity; it depends on both the initial phase and the number of cycles characterizing the grid. Theoretically, the strain sensitivity can reach 10-5 in best cases, but practically it is notbetter than 10-4. Several applications on different materials are presented: polyurethane, paper and cloth. 相似文献
72.
Alexis Marin 《Mathematische Annalen》1987,278(1-4):211-217
Sans résuméDédié à Friedrich Hirzebruch 相似文献
73.
Peter Barker Alexis Bishop Halina Rubinsztein-Dunlop 《Applied physics. B, Lasers and optics》1997,64(3):369-376
A novel flow-tagging technique is presented which was employed to measure gas velocities in the free stream of a shock tube.
This method is based on the laser spectroscopic techniques of Laser-Enhanced Ionisation (LEI) and Laser-Induced Fluorescence
(LIF). The flow in the shock tube is seeded with small amounts of sodium, and LEI is used to produce a substantial depletion
of neutral sodium atom concentration in a well-defined region of the flow, by using two wavelength-resonance excitation and
subsequent collisional ionisation. At a specific time delay, single-laser-pulse planar LIF is utilised to produce a two-dimensional
(2-D) inverse image of the depleted tagged region downstream of the flow. By measuring the displacement of the tagged region,
free stream velocities in a shock tube were determined. Large variations in the concentration of sodium seeded into the flow
were observed and even in the presence of these large variations accurate free-stream velocity measurements were obtained.
The experimentally determined value for velocity compares very well with the predicted velocity.
Received: 25 March 1996/Revised version: 8 July 1996 相似文献
74.
Leleu S Penhoat M Bouet A Dupas G Papamicaël C Marsais F Levacher V 《Journal of the American Chemical Society》2005,127(45):15668-15669
A new and unprecedented exploitation of quinolinium thioester salts 2 in peptide bond formation is reported. These synthetic tools were assessed during the preparation of a number of dipeptides 3a-f obtained in good yields with complete stereochemical integrity. A sequential mechanism related to a prior amine capture strategy is well-established. Additionally, a tripeptide 3g was prepared according to a "safety-catch" approach, thus demonstrating the important potential of these new synthetic tools in the design of new safety-catch linkers exploitable in Solid-Phase Peptide Synthesis (SPPS). 相似文献
75.
76.
77.
Alexis Bohlin Fredrik Vestin Jeanine Bonamy Pierre Joubert Per‐Erik Bengtsson 《Journal of Raman spectroscopy : JRS》2010,41(8):875-881
Rotational coherent anti‐Stokes Raman spectroscopy (CARS) in fuel‐rich hydrocarbon flames, with a large content of hydrogen in the product gases (∼20%), has in previous work shown that evaluated temperatures are raised several tens of Kelvin by taking newly derived N2 H2 Raman line widths into account. To validate these results, in this work calibrated temperature measurements at around 300, 500 and 700 K were performed in a cell with binary gas mixtures of nitrogen and hydrogen. The temperature evaluation was made with respect to Raman line widths either from self‐broadened nitrogen only, N2 N2 [energy‐corrected‐sudden (ECS)], or by also taking nitrogen broadened by hydrogen, N2 H2 [Robert–Bonamy (RB)], Raman line widths into account. With increased amount of hydrogen in the cell at constant temperature, the evaluated CARS temperatures were clearly lowered with the use of Raman line widths from self‐broadened nitrogen only, and the case with inclusion of N2 H2 Raman line widths was more successful. The difference in evaluated temperatures between the two different sets increases approximately linearly, reaching 20 K (at T ∼ 300 K), 43 K (at T = 500 K) and 61 K (at T = 700 K) at the highest hydrogen concentration (90%). The results from this work further emphasize the importance of using adequate Raman line widths for accurate rotational CARS thermometry. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
78.
Jean-Claude Jumas Moulay Tahar Sougrati Alexis Perea Laurent Aldon Josette Olivier-Fourcade 《Hyperfine Interactions》2013,217(1-3):107-115
The performances of Li-ion batteries depend on many factors amongst which the important ones are the electrode materials and their structural and electronic evolution upon cycling. For a better understanding of lithium reactivity mechanism of many materials the combination of X-Ray Powder Diffraction (XRPD) and Transmission Mössbauer Spectroscopy (TMS) providing both structural and electronic information during the electrochemical cycling has been carried out. Thanks to the design of a specific electrochemical cell, derived from a conventional Swagelock cell, such measurements have been realised in operando mode. Two examples illustrate the greatness of combining XRPD and TMS for the study of LiFe0.75Mn0.25PO4 as positive electrode and TiSnSb as negative electrode. Different kinds of insertion or conversion reactions have been identified leading to a better optimization and design of performing electrodes. 相似文献
79.
Charles Shearer Oriane Desaunay Stephen Zorc Alexis D. Richaud Shyam S. Samanta Nagalakshmi Jeedimalla Stéphane P. Roche 《Tetrahedron》2019,75(43):130606
4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles. 相似文献
80.
Eva Pospisilova Alexis Renaud Marc Poorteman Marjorie Olivier Ludovic Dumas Philippe Dubois Leila Bonnaud Konstantin Moshkunov Bernard Nysten Arnaud Delcorte 《Surface and interface analysis : SIA》2019,51(6):674-680
Phenol-paraphenylenediamine (P-pPDA) benzoxazines exhibit excellent barrier properties, adequate to protect aluminum alloys from corrosion, and constitute interesting candidates to replace chromate-containing coatings in the aeronautical industry. For the successful application of P-pPDA coatings, it is necessary to decrease the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy, as well as the barrier properties of the coating. However, decreasing the curing temperature leads to less polymerized films, the extent of which requires a quantitative assessment. While the conversion rate of the polymerization reaction is commonly evaluated for bulk samples using differential scanning calorimetry (DSC), a tool for its evaluation in thin films is missing. Therefore, a new approach was developed for that matter using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The relation between the SIMS data integrated from inside thin films and the DSC results obtained on bulk samples with the same curing cycle allowed to calibrate the SIMS data. With this preliminary calibration of the technique, the polymerization of P-pPDA coatings can be locally determined, at the surface and along the depth of the coating, using dual-beam depth profiling with large argon cluster beam sputtering. 相似文献