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51.
NMR and EPR studies of room temperature highly fluorinated graphite heat-treated under fluorine atmosphere 总被引:1,自引:0,他引:1
Semi-ionic carbon fluoride obtained by reaction of graphite with a gaseous mixture of IF5, HF and F2 was modified by a post-fluorination at various temperatures in the range 100-680 °C. The resulting materials were studied by 19F-NMR and EPR both at room temperature and at different experimental temperatures from 200 to 360 K and from 100 to 473 K for NMR and EPR experiments, respectively. 19F-NMR gives information about the residual intercalated iodine fluoride species (IF5, IF6− and IF7) such as the temperature of their removal from the host fluorocarbon matrix and their mobility into the interlayer space. The nature of the C-F bonding was investigated by 19F-NMR, MAS/13C-NMR, FT-IR spectroscopy and X-ray diffraction. The C-F bonding changes from semi-ionic to a mainly covalent character at a fluorination post-treatment temperature close to 450 °C. This transformation coincides with the removal of the iodine fluoride species from the host structure. The densities of the paramagnetic dangling bonds were studied by EPR; this technique allows also to investigate the local environment of the dangling bonds in the fully fluorinated samples (obtained with fluorination post-treatment temperatures higher than 450 °C). As a matter of fact, an hyperfine structure was observed for these samples; it results from interaction of the dangling bond electron with six neighboring fluorine nuclei. The role of the intercalated species (iodine fluoride compounds and HF) on the mechanisms of the extra-fluorination is also discussed. 相似文献
52.
53.
Among the competitive electricity reforms that have been implemented in Europe and the US for the last 18 years, none has “survived” over several years without major changes. Their changing nature raises the question of their adaptability. Two characteristics of reforms play a key role on their adaptation properties. Firstly, they are “modular” objects in the sense of [Baldwin, C., 2008. Where do transactions come from? Modularity, transactions, and the boundaries of firms. Industrial and Corporate Change 17 (1), 155–195]. Secondly, they are produced in an institutional process which leads to “incomplete” rules and designs [Pistor, K., Xu, C., 2003. Incomplete law. International Law and Politics 35, 931–1013]. We propose a typology of adaptations based on the framework proposed by [Williamson, O.E., 1991. Comparative economic organization: the analysis of discrete structural alternatives. Administrative Science Quarterly 36 (2), 269–296] for contracts: (1) in case of small disturbances, adaptations are realized quasi-automatically, by autonomous decisions of the institutions governing the implementation of reforms; (2) in case of middle-range disturbances, adaption is made by Coasian bargaining; (3) finally, in case of strong disturbances, or when bargaining is not feasible, the adaptation of reforms is in the hands of legislative and executive institutions [North, D.C., 2005. Le processus du développement économique. Editions d’Organisation]. These institutions can reform the reforms [Joskow, P.L., 2006. Introduction to electricity sector liberalization: lessons learned from cross-country studies. In: Sioshansi, F.P. (Ed.), Electricity Market Reform: An International Perspective. Elsevier, Amsterdam, pp. 1–32; Hogan, W.W., 2002. Electricity market restructuring: reforms of reforms. Journal of Regulatory Economics 21, 103–132]. The role of these types of adaptations in each electricity reform is a consequence of the allocation of rights to the regulator, to stakeholders and to legislative and executive institutions. 相似文献
54.
In current cars, loops are commonly used to redirect the webbing which reels out from the retractor to the passenger's shoulder. Some types of pillar loops, also called D-rings, lead to a non-systematic instability. The webbing, which should scroll without hindrance through the D-ring, laterally shifts, bunches and produces the overturning of the ring. 相似文献
55.
F. Frémont S. Suarez A. Hajaji A. Dubois 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(2):206-210
We present the realization of a Young-type double-slit experiment, in which single electrons, scattering on two protons, produce interference pattern. The electrons are produced by a Auger effect, following double capture process in low He2+ + H2 collisions. Well-defined oscillations are visible in the angular distribution of the electrons emitted towards the receding protons. The presence of these oscillations is a clear demonstration that an electron interferes with itself. We also discuss the dependence of the interference pattern with interference parameters, such as the electron wavelength as well as the distance between the protons when the electron is ejected. 相似文献
56.
57.
Abdallah Hamze Dr. Anne Giraud Dr. Samir Messaoudi Dr. Olivier Provot Dr. Jean‐François Peyrat Prof. Jérôme Bignon Dr. Jian‐Miao Liu Dr. Joanna Wdzieczak‐Bakala Dr. Sylviane Thoret Joëlle Dubois Dr. Jean‐Daniel Brion Prof. Mouad Alami Dr. 《ChemMedChem》2009,4(11):1912-1924
The cytotoxic activities of 23 new isocombretastatin A derivatives with modifications on the B‐ring were investigated. Several compounds exhibited excellent antiproliferative activity at nanomolar concentrations against a panel of human cancer cell lines. Compounds isoFCA‐4 ( 2 e ), isoCA‐4 ( 2 k ) and isoNH2CA‐4 ( 2 s ) were the most cytotoxic, and strongly inhibited tubulin polymerization with IC50 values of 4, 2 and 1.5 μM , respectively. These derivatives were found to be 10‐fold more active than phenstatin and colchicine with respect to growth inhibition but displayed similar activities as tubulin polymerization inhibitors. In addition, cell cycle arrest in the G2/M phase and subsequent apoptosis was observed in three cancer cell lines when treated with these compounds. The disruptive effect of 2 e , 2 k and 2 s on the vessel‐like structures formed by human umbilical vein endothelial cells (HUVEC) suggest that these compounds may act as vascular disrupting agents. Both compounds 2 k and 2 s have the potential for further prodrug modification and development as vascular disrupting agents for treatment of solid tumors. 相似文献
58.
This paper aims at testing the existence of yardstick competition by estimating a fully specified vote-function on a panel
data set of 104 French local governments from 1989 to 2001. When comparing the performance of their incumbent to the one of
their “neighbours”, voters might consider their close geographical neighbours but also the nearby cities that are similar
according to some socio-economic characteristics such as population size. The estimation results show that voters sanction
their incumbent if their own local housing tax is high. Moreover, we find that voters reward their incumbent when neighbouring
cities that are similar in terms of demographic characteristics have high local taxes. 相似文献
59.
Among diversified industrial uses, see for instance Koch [Koch, Appl. Clay Sci., (21) 2002], and following positive in situ experiments, compacted bentonite blocks are potential candidates for sealing nuclear waste repositories, thanks to their swelling ability in a wet environment.As requested by Andra (French Agency for Nuclear Waste Management) and complementarily to in situ experiments, an original experimental laboratory set-up was designed in order to reproduce the introduction and swelling of bentonite plugs inside an argillite host rock. Once the argillite/bentonite interface is established, an increase in storage tunnel gas pressure is simulated and the interface gas migration pressure (or gas critical pressure) is evaluated. More precisely, a first experimental set-up provides bentonite swelling pressure and kinetics (i.e. mainly hydraulic cut-off, time to reach asymptotic swelling pressure and value of asymptotic swelling pressure) at given initial compaction and saturation rate. This phase is preparatory to reproducing the introduction and subsequent swelling of a bentonite plug inside the argillite host rock, which uses a similar test rig. Experimental results of water permeability and gas critical pressure are provided for MX80 compacted bentonite associated to Bure Callovo-Oxfordian argillite. 相似文献
60.
We describe an original microscope for high-resolution optical coherence tomography applications. Our system is based on a Linnik interference microscope with high-numerical-aperture objectives. Lock-in detection of the interference signal is achieved in parallel on a CCD by use of a photoelastic birefringence modulator and full-field stroboscopic illumination with an infrared LED. Transverse cross-section (en-face, or XY) images can be obtained in real time with better than 1-microm axial (Z) resolution and 0.5-microm transverse (XY) resolution. A sensitivity of approximately 80 dB is reached at a 1-image/s acquisition rate, which allows tomography in scattering media such as biological tissues. 相似文献