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排序方式: 共有139条查询结果,搜索用时 437 毫秒
11.
DSC measurements indicate that poly(vinyl bromide) (PVB) is miscible with several polyesters [poly(caprolactone), poly(valerolactone), poly(butylene adipate) and poly(hexamethylene sebacate)] but immiscible with others [poly(α-methyl-α-n-propyl-β-propiolactone), poly(α-methyl-α-ethyl-β-propiolactone) and poly(ethylene adipate (PEA)]. However, it is known that poly(vinylchloride) (PVC) is miscible with all these polyesters but PEA. The more limited degree of miscibility of PVB with polyesters, as compared with the case of PVC, is surprising in view of the similar properties of the bromine and chlorine atoms. 相似文献
12.
In a two-phase system (saturated aqueous calcium hydroxide, tetrabutylamnonium sulfate, dichloromethane, iron pentacarbonyl) benzyl bromides are readily carbonylated to dibenzyl ketones; α-α′ dibromoorthoxylene yields the o-quinodimethane iron tricarbonyl complex 8. It is inferred that the reactions proceed through transient generation of the tetracarbonyl ferrate dianion. 相似文献
13.
The parameters of the nuclear magnetic and quadrupolar interactions with the beryllium nuclei nearest neighbours to the ‘axial’ V1 center have been measured by ENDOR. The results are in agreement with the model of a hole trapped by an isolated cation vacancy. 相似文献
14.
The temperature dependence of the spectrum of two trapped hole centers introduced by electron irradiation in ZnO is described. The results firmly establish the identification of these centers as being two slightly inequivalent configurations of the zinc vacancy in its negative charge state. 相似文献
15.
16.
A concise and convergent route to combretastatin D2 is described together with some preliminary biological data. 相似文献
17.
G. Durry J. S. Li I. Vinogradov A. Titov L. Joly J. Cousin T. Decarpenterie N. Amarouche X. Liu B. Parvitte O. Korablev M. Gerasimov V. Zéninari 《Applied physics. B, Lasers and optics》2010,99(1-2):339-351
A near-infrared tunable diode laser spectrometer called TDLAS has been developed that combines telecommunication-type as well as new-generation antimonide laser diodes to measure C2H2, H2O, CO2 and their isotopologues in the near infrared. This sensor is devoted to the in situ analysis of the soil of the Martian satellite PHOBOS, within the framework of the Russian space mission PHOBOS-GRUNT. In the first part of the paper, we report accurate spectroscopic measurements of C2H2 and 13C12CH2 near 1.533 μm, of H2O and CO2 at 2.682 μm and of the isotopologues 13C16O2 and 16O12C18O near 2.041 μm and H2 17O, H2 18O and HDO near 2.642 μm. The achieved line strengths are thoroughly compared to data from molecular databases or from former experimental determinations. In the second part of the paper, we describe the TDLAS spectrometer for the PHOBOS-GRUNT mission. 相似文献
18.
Oxidation behaviour of SiC coatings 总被引:1,自引:0,他引:1
K. Mergia D. Lafatzis N. Moutis T. Speliotis G. Apostolopoulos F. Cousin 《Applied Physics A: Materials Science & Processing》2008,92(2):387-395
Amorphous silicon carbide (SiC) films were deposited on silicon substrates by radio-frequency magnetron sputtering. The films
were oxidized in air in the temperature range 400–900 °C and for times from 1 to 16 h. Neutron reflectivity measurements provided
information on the thickness, density and roughness of the SiC and on the formed SiO2 layers. Fourier transform infrared spectroscopy was used to determine the bond structure of the formed SiO2 and changes in the bonding of SiC after exposure at the oxidation temperature. The surface morphology of the oxidized films
was characterized by atomic force microscopy measurements. The oxidation kinetics is initially fast and as the SiO2 layer is formed it slows down. The SiC consumption varies linearly with time at all oxidation temperatures. Exposure of the
SiC at the oxidation temperature affects its density and to some degree its bond structure, while the formed SiO2 has density and bond structure as that formed by oxidation of Si under the same conditions.
PACS 66.30.Ny; 68.47.Gh; 68.55.J- 相似文献
19.
Samuel F. Cousin Dr. Pavel Kadeřávek Baptiste Haddou Dr. Cyril Charlier Thorsten Marquardsen Jean‐Max Tyburn Dr. Pierre‐Alain Bovier Dr. Frank Engelke Dr. Werner Maas Prof. Dr. Geoffrey Bodenhausen Dr. Philippe Pelupessy Prof. Dr. Fabien Ferrage 《Angewandte Chemie (International ed. in English)》2016,55(34):9886-9889
Nuclear magnetic resonance (NMR) studies have benefited tremendously from the steady increase in the strength of magnetic fields. Spectacular improvements in both sensitivity and resolution have enabled the investigation of molecular systems of rising complexity. At very high fields, this progress may be jeopardized by line broadening, which is due to chemical exchange or relaxation by chemical shift anisotropy. In this work, we introduce a two‐field NMR spectrometer designed for both excitation and observation of nuclear spins in two distinct magnetic fields in a single experiment. NMR spectra of several small molecules as well as a protein were obtained, with two dimensions acquired at vastly different magnetic fields. Resonances of exchanging groups that are broadened beyond recognition at high field can be sharpened to narrow peaks in the low‐field dimension. Two‐field NMR spectroscopy enables the measurement of chemical shifts at optimal fields and the study of molecular systems that suffer from internal dynamics, and opens new avenues for NMR spectroscopy at very high magnetic fields. 相似文献
20.
Louis P. Sandjo Victor Kuete Xavier N. Siwe Herve M. P. Poumale 《Natural product research》2016,30(22):2529-2537
A preliminary study on Echinops giganteus (Asteraceae) showed that the methanolic extract has interesting cytotoxicities against a panel of cancer cell lines. From this extract, a lignan, a flavonoid and a polyacetylenic thiophene identified were three times less cytotoxic than the extract. In the search of the metabolites responsible for the bioactivity, a new harvested E. giganteus was subjected to a phytochemical study using chromatographic methods. In the course of the work, two new compounds: a brominated oleanolide (1) and a tetrahydrofurano-ceramide (2) were obtained along with β-amyrin acetate (3), 2-(penta-1,3-diynyl)-5-(4-hydroxybut-1-ynyl)-thiophene (4), 2-(penta-1,3-diynyl)-5-(3,4-dihydroxybut-1-ynyl)-thiophene (5) and 4-hydroxy-2,6-di-(3′,4′-dimethoxyphenyl)-3,7-dioxabicyclo-(3.3.0)octane (6). Their structures were determined on the basis of NMR spectroscopy and mass spectrometry data in conjunction with those reported in the literature. The cytotoxicity of 1, 2 and 5 was evaluated by employing resazurin assay against a panel of cancer cell lines with IC50 values in range 6.12 ± 0.46–46.96 ± 3.61 μM. 相似文献