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101.
A new strategy for the stereoselective synthesis of 2-amino-2-deoxy-aldoses is described. Therefore epoxy carbamates are reacted with isocyanates to furnish urethanes, which will form the title compounds with high diastereoselectivities under basic conditions and O,O-migration of the carbamoyl group. 相似文献
102.
103.
Mei Wang Nathalie Simon Gaelle Charrier Muriel Bouttemy Arnaud Etcheberry Musen Li Rabah Boukherroub Sabine Szunerits 《Electrochemistry communications》2010,12(3):351-354
While it is clearly established that oxidation of as-grown boron-doped diamond (BDD) interfaces results in the introduction of different surface oxygen functions such as ether, carbonyl and hydroxyl groups, there is no reported approach which can clearly distinguish between the different surface functions. For further surface functionalization, it is important to quantify the presence of each group on the diamond surface. In this paper, the presence and amount of surface hydroxyl groups is identified using esterification of the COH groups with trifluoroacetic acid. The presence of CF3 group in the acid allowed the identification and estimation of the amount of surface hydroxyl groups using X-ray photoelectron spectroscopy (XPS). 相似文献
104.
105.
Magali Bonne Stéphane Pronier Fabien Can Xavier Courtois Sabine Valange Jean-Michel Tatibouët Sébastien Royer Patrice Marécot Daniel Duprez 《Solid State Sciences》2010,12(6):1002-1012
Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO2/SiO2 nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400 °C), nanocomposites having titania nanodomains (~2–3 nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55 wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800 °C does not allow to detect the anatase to rutile transition. Even at 800 °C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ~10 nm, a size close to that of the silica host support porosity (8.4 nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO2/SiO2 solids are promising in term of thermal stability. 相似文献
106.
Candice Grivel Jean-Louis Rocca Davy Guillarme Jean-Luc Veuthey Sabine Heinisch 《Journal of chromatography. A》2010,1217(4):459-472
Reversed phase gradient elution is the method of choice for pharmaceuticals analysis since it allows reducing the analysis time while improving both the quality of the separation and the detection limits. The current trends are towards faster separations which can be achieved thanks to equipments withstanding ultra-high pressures and/or high temperatures. Under such conditions, gradient separations can be carried out within a few minutes or even a few tens of seconds. A long equilibration time in addition to the gradient time can be therefore very detrimental. In this work, we investigated the extent to which the gradient equilibration time can be reduced and which parameters mainly affect the retention variability of ionizable compounds when using volatile buffers. We first found out an excellent repeatability between run-to-run experiments whatever the equilibration time and the operating conditions. We then pointed out the key operating parameters which allow achieving reproducible runs when varying the equilibration time between runs. With a view of reducing the equilibration time, the effects of various conditions were examined. The latter include the type of additive for mobile phase pH adjustment, the initial eluent composition, the type of stationary phase, the temperature and the flow-rate. Although much remains to be understood about the equilibration process, our study allows making progress in the knowledge of this phenomenon. Based on the present results, a beneficial effect of both temperature and flow-rate was highlighted and operating conditions leading to faster column equilibration are suggested. 相似文献
107.
108.
Dubois F Meunier S Rabau G Poisson F Guyader G 《The Journal of the Acoustical Society of America》2011,130(5):EL284-EL289
The detection of multicomponent signals for which the components are not equidetectable is precisely investigated as a function of the level difference ΔL(i∕j) between components. The detection thresholds are determined for a seven-tone complex signal with random starting phases masked by white noise. Level differences between the components are examined. A model for non-equidetectable conditions based on the statistical summation model is described. The improvement in detection is calculated from the level difference between components that is related to the thresholds for single components. The model predictions are in accordance with the experimental results. 相似文献
109.
Janssen SA Vos H van Kempen EE Breugelmans OR Miedema HM 《The Journal of the Acoustical Society of America》2011,129(4):1953-1962
Recently, it has been suggested that the annoyance of residents at a given aircraft noise exposure level increases over the years. The objective of the present study was to verify the hypothesized trend and to identify its possible causes. To this end, the large database used to establish earlier exposure-response relationships on aircraft noise was updated with original data from several recent surveys, yielding a database with data from 34 separate airports. Multilevel grouped regression was used to determine the annoyance response per airport, after which meta-regression was used to investigate whether study characteristics could explain the heterogeneity in annoyance response between airports. A significant increase over the years was observed in annoyance at a given level of aircraft noise exposure. Furthermore, the type of annoyance scale, the type of contact, and the response percentage were found to be sources of heterogeneity. Of these, only the scale factor could statistically account for the trend, although other findings rule it out as a satisfactory explanation. No evidence was found for increased self-reported noise sensitivity. The results are of importance to the applicability of current exposure-annoyance relationships for aircraft noise and provide a basis for decisions on whether these need to be updated. 相似文献
110.
Sabine Hossenfelder 《Foundations of Physics》2011,41(9):1521-1531
We propose to experimentally test non-deterministic time evolution in quantum mechanics by consecutive measurements of non-commuting
observables on the same prepared state. While in the standard theory the measurement outcomes are uncorrelated, in a super-deterministic
hidden variables theory the measurements would be correlated. We estimate that for macroscopic experiments the correlation
time is too short to have been noticed yet, but that it may be possible with a suitably designed microscopic experiment to
reach a parameter range where one would expect a super-deterministic modification of quantum mechanics to become relevant. 相似文献