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51.
Anissa Slougui Séverine Ferron André Perrin Marcel Sergent 《Journal of Cluster Science》1997,8(3):349-359
The title compound synthesized by solid state reaction crystallizes in the cubic system (Pn-3) witha=13.433 Å. The structure has been determined by singlecrystal X-ray diffraction and shows that the compound is based on isolated |(Re6S 6 i Br 2 i )Br 6 a |2? units. The K+ cations occupy two different sites. Steric effects lead to the switching from the cubic symmetry present in KRe6Se5Cl9 to the monoclinic one in the case of KRe6S5Br9 and again the former cubic symmetry in the new compound K2Re6S6Br8. 相似文献
52.
Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality. 相似文献
53.
54.
Sergent N. Gélin P. Périer-Camby L. Praliaud H. Thomas G. 《Journal of Thermal Analysis and Calorimetry》2003,72(3):1117-1126
The interactions of CO with a high specific surface area tin dioxide was investigated by FTIR spectroscopy and thermogravimetric
analysis. FTIR study of CO interactions have shown that CO can adsorb on cus (coordinatively unsaturated sites) Sn4+ cation sites (band at 2201 cm-1). In addition, CO reacts with surface oxygen atoms. This leads to the partial reduction of SnO2 surface and to the formation of ionised oxygen vacancies together with the release of free electrons, which are responsible
for the loss of transmission. Formed CO2 can chemisorb on specific surface sites: on basic sites to form carbonates species and on acidic sites (Sn4+-CO2 species) which is in competition with the formation of Sn4+-CO species. TG experiment have shown that the reduction of SnO2 by CO at 400°C occurs in two steps. First, the reduction of SnO2 surface, which is a quick phenomenon. This has allowed to evaluate that more than 12% of reducible surface oxygens can react
with CO, essentially because of the presence of a large amount of surface hydroxyl groups. The second step of the reduction
of SnO2 would be the progressive reduction of SnO2 bulk by the slow diffusion of oxygen atoms from the bulk to the surface.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
55.
M. Potel R. Chevrel M. Sergent J.C. Armici M. Decroux Ø. Fischer 《Journal of solid state chemistry》1980,35(2):286-290
We present a new series of ternary chalcogenides, derived from divalent molybdenum: M2Mo6X6. These compounds crystallize in a hexagonal lattice with a ≈ 9 Å, c ≈ 4.5 Å, and space group . The compounds are characterized by clusters (Mo3)1∞ in the form of linear chains, resulting from a linear condensation of Mo6 octahedral clusters. The (Mo3)1∞ clusters are well separated from each other, with the shortest MoMo intercluster distance larger than 6 Å. The resulting pseudo-one-dimensional structures show remarkable anisotropy of physical properties. 相似文献
56.
Schaut A De Saeger S Sergent T Schneider YJ Larondelle Y Pussemier L Blank R Van Peteghem C 《Biomedical chromatography : BMC》2008,22(9):1013-1020
Liquid chromatographic methods were used for the detection of ochratoxin A (OTA) and its metabolites ochratoxin alpha (OTalpha), 10-hydroxy OTA (10-OHOTA), 4R-hydroxy OTA (4R-OHOTA) and the ethyl ester of OTA (OTC) in in vitro samples, obtained with Caco-2 cell culture experiments and in in vivo urine samples from sheep. A high-performance liquid chromatography method with fluorescence detection (HPLC-FLD) and a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method were developed and validated for the detection of OTA and its metabolites OTalpha, 10-OHOTA, 4R-OHOTA and OTC, which was used as internal standard. The LOD/LOQ values for OTalpha, 4R-OHOTA and OTA were 0.63/2.11, 0.99/3.31 and 0.84/2.81 microg/L, respectively, for the HPLC-FLD method and 0.98/3.28, 1.11/3.72 and 0.88/2.96 microg/L, respectively for the LC-MS/MS method. Within-day and between-day precision were both <12% for the HPLC-FLD method, and <10% for the LC-MS/MS method. The recovery of OTA and its metabolites ranged between 71 and 111% for the HPLC-FLD method and between 79 and 110 % for the LC-MS/MS method. In the first experiment only OTA was added to the Caco-2 cells while in the second experiment 3-methylcholanthrene (3MC) was also present in the cell culture systems. Besides OTA, which was recovered in all the samples, an unknown compound was also observed in the second experiment. When 3MC was added, the results showed that the OTA concentration in the basolateral samples was decreased by 50%. The methods were also implemented for the analysis of urine samples of sheep, fed increasing amounts of OTA. With the HPLC-FLD method it could be concluded that the concentration of OTA and OTalpha increased according to ingested amounts of OTA, with OTalpha being the most abundant compound. The results obtained with the LC-MS/MS method confirmed these results. Copyright (c) 2008 John Wiley & Sons, Ltd. 相似文献
57.
A parametric study on the depressed inner cladding (DIC) single-mode fibers shows the influence of the inner-cladding diameter on the effective cutoff wavelengths of the first two modes, determining a practical transmission window. The set of curves that is obtained can be considered universal, at least for a value of the inner-cladding/core index differences ratio close to 0.5. The behavior of the effective cutoff wavelengths is explained by studying the effective index of the modes and the fundamental mode diameter, this explanation being confirmed by a bending and microbending sensitivity test. It appears that DIC fibers optimized for long-range transmission should have an inner cladding to core diameter ratio greater than 3 and a relative depth of the inner cladding smaller than 0.5. 相似文献
58.
59.
In this paper we are interested in numerical modeling of ‘dynamic’ phenomenon of squat by finite elements analysis. It proposes a set of modular numerical tools; therefore, interchangeable. This model enables the study of the interaction between a two‐dimensional potential flow in highly restricted waterways on irregular shaped bottom with stationary free surface in taking into account the dynamic response of a ship. The proposed model has been used to validate a stability model based on the extension of the one‐dimensional theory of Schijf to the dynamic effects by pointing out stable and unstable squat positions for a ship. It is also shown that for two cases of depth change in shallow water (‘step’), unstable position may be reached. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
60.
Lamonier J. F. Sergent N. Matta J. Aboukaïs A. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):645-658
Thermal analysis has been used to investigate the crystallization of ZrxCe1-xO2 mixed oxides, prepared by co-precipitation of corresponding hydroxides. For x≤0.5, small crystals of CeO2, were formed at low temperatures (373 K). For x>0.5an exothermic peak at 420°C (693 K) was observed after calcination under a flow of air ofhydroxide samples. This peak
was associated with the formation of a ZrxCe1-xO2 solid solution (XRD) in a tetragonal phase (Raman).
The solids calcined at 700°C (973 K) present a reactivity towards the carbon black oxidation. The thermal analysis coupled
with a gas chromatograph (GC) were used to follow this reactivity. Simultaneous study of the activity (thermal analysis) and
the selectivity (GC) in CO or CO2 of the different catalysts revealed an important parameter: acatalyst-soot particle contact. We also obtained a more precise
comparison of ZrxCe1-xO2 oxides in the catalytic soot combustion.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献