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Racemic β-butyrolactone was polymerized using chiral initiators obtained from the reaction of organometallic derivatives (ZnEt2, CdMe2, AlEt3) with R(−) 3,3 dimethyl-1,2 butanediol. With the zinc initiator, R(+) enantiomer is preferentially incorporated in the polymer chain with a stereoelectivity ratio rR equal to 1.6. Crude polymer was fractionated into a crystalline, predominantly isotactic, part and an amorphous heterotactic part, both optically active. Sites of different stereospecificities, present in the initiator, are all active for the stereoelective polymerization. With the cadmium initiator, S(−) enantiomer is preferentially polymerized (rs = 1.01), extending homosteric-antisteric rules previously established for thiiranes. Aluminium initiator leads to an homosteric process (rR = 1.1). Chiroptical properties (o.r.d. and c.d.) of polymers prepared with zinc initiator show a predominance of R-configurational units, indicating that ring-opening occurs by O-acyl cleavage with retention of configuration. 相似文献
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Previous studies of amidase activity of human alpha-thrombin have yielded variable results and the decrease of this activity as a function of time and temperature has never been quantified. As this protease is an efficient tool in biochemistry and biotechnology thanks to its extreme selectivity, amidase activity and stability of thrombin were investigated with the synthetic substrate Tos-Gly-Pro-Arg-pNa. Enzyme activity as a function of temperature showed an optimum peak at 45 degrees C. The pH dependence of the activity showed a maximum around 9.5. The addition of NaCl promoted an increase of the activity. Stability of thrombin decreased rapidly when increasing the temperature from 25-45 degrees C and when diluting the enzyme. The presence of glycerol and ethylene glycol promoted a small increase of thrombin half life, whereas polyethylene glycol had a more pronounced positive effect even at very low concentrations. 相似文献
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Programming real-time applications with SIGNAL 总被引:1,自引:0,他引:1
LeGuernic P. Gautier T. Le Borgne M. Le Maire C. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1991,79(9):1321-1336
The authors present the main features of the SIGNAL language and its compiler. Designed to provide safe real time system programming, the SIGNAL language is based on synchronous principles. Its semantics are defined via a mathematical model of multiple-clocked flows of data and events. SIGNAL programs describe relations on such objects, so that it is possible to program a real time application via constraints. The compiler calculates the solutions of the system and thus can be used as a proof system. The equational approach is a natural way to derive multiprocessor executions of a program. This approach uses a graphical interface of a block-diagram style, and the system is illustrated on a speech recognition application 相似文献
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Michel Borgne 《电信纪事》1983,38(9-10):411-423
The implementation of high capacity (140 Mbit/s) digital radio links leads to the use of high level modulation schemes in order to reduce spectrum occupation. A comparison between these modulations (with 16, 32, 64 and 128 levels) in the presence of impairments of a real channel is interesting to determine the spectral efficiency we can reach. The error probability is given by a method based upon a Gram-Charlier expansion using only the moments of the intersymbol interference random variable. 相似文献
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Bertussi B Piombini H Damiani D Pommies M Le Borgne X Plessis D 《Applied optics》2006,45(33):8506-8516
We present an automatic excimer laser bench (SOCRATE) allowing for the treatment of optical components by laser conditioning. This apparatus, developed at the Commissariat a l'Energie Atomique-Le Ripault, has been designed to add to this conditioning process an in situ, accurate laser-induced damage threshold (LIDT) measurement and different nondestructive optical techniques for the characterization of the component during treatment. Through different examples, we demonstrate the importance of these characterizations to improve the understanding of the laser conditioning. The role of an in situ adapted metrology associated in real time with a laser conditioning bench offers new opportunities to analyze laser-induced damage mechanisms and subsequently to increase the LIDT of optical components. 相似文献
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B. Guinot Y. Bultel F. Montignac D. Riu I. Noirot-Le Borgne 《International Journal of Hydrogen Energy》2013
In this paper, the newly developed techno-economic assessment platform Odyssey introduced in Part 1 of this two-part series of papers is applied to an application example: the call for tenders from the French Energy Regulation Commission on PV installations greater than 250 kWp. In this context, two storage systems are studied: a bank of lead-acid batteries and a PEM hydrogen chain (PEM electrolyzer, H2/O2 PEM fuel-cell, H2 and O2 storages under pressure at 30 bars). The objective pursued in the study of this application case is to assess the economic value of these two energy storage technologies and to focus on different influencing factors. Therefore, in the context of this application case, it is shown how a suitable control strategy can considerably help in improving economic results. The influence of the reference meteorological year is also investigated showing that the variations of economic indicators between two different years are greater than the variation of the annual insolation. Furthermore, the investigation on the influence of the simulation time step shows that the use of large time step (30 min, 1 h) may lead to unsuitable sizing and inaccurate estimations of economic performances. Finally systems sizing have been optimized considering different aging modeling which has shown that the influence of aging on the optimal sizing may be important. 相似文献
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Summary A liquid crystal crown ether is obtained by chemical modification of the cyclic tetramer derived from epichlorohydrin with
sodium 4-cyano-4′-biphenoxide. The crown ether exhibits a nematic mesophase and a high glass transition temperature. 相似文献