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271.
Diastereoisomeric isopropyl‐, 2‐ethoxyethyl‐, 2,2‐dichloroethyl‐ and 2,2,2‐trichloroethyl uridine 3′‐thiomonophosphates, 1a – 1d , respectively, have been synthesized, and their hydrolyses in aqueous alkali at 25° have been followed by HPLC. According to the time‐dependent product distributions obtained, the alkyl phosphorothioates 1a – 1d undergo cleavage to uridine 2′‐ and 3′‐thiophosphates, 7a and 7b , respectively, via a uridine 2′,3′‐cyclic thiophosphate ( 6 ). The rate of the hydroxide ion‐catalyzed cyclization of both (RP)‐ and (SP)‐diastereoisomer is highly dependent on the polar nature of the leaving group, the βlg values being ?1.23±0.03 and ?1.24±0.03, respectively. Brønsted dependence of the second‐order rate constants (kOH [dm3 mol?1 s?1]) on the pKa values of the leaving alcohols shows a convex breakpoint on going from alkyl esters 1a – 1d to aryl esters studied earlier. This may be considered as a strong evidence for a stepwise mechanism, where the formation and breakdown of the phosphorane intermediate is the rate‐limiting step with aryl and alkyl esters, respectively. 相似文献
272.
Harri Pennanen Mikko Alatossava Jouko Leinonen Matti Latva-aho 《International Journal of Wireless Information Networks》2011,18(1):1-10
Performance evaluation of enhanced link adaptation method for MIMO-OFDM systems with limited feedback using measurement based channels and a stochastic channel model is presented in this paper. In particular, impact of practical channel estimation and feedback errors on link performance is analyzed. An adaptive spatial and modulation scheme selection process is based on the effective signal-to-interference-plus-noise ratio (ESINR). Mutual information effective SINR mapping method is applied for calculating ESINR values due to its capability of accurate estimation of the error rate performance of large variety of MIMO channels. Numerical results show that simple adaptive systems that switch between diversity/multiplexing or beamforming/multiplexing schemes obtain relatively good performance in realistic 2 × 2 MIMO channels. It is also shown that the imperfect channel estimation and feedback errors can have significant impact on the link performance. Furthermore, it is noticed that using the stochastic channel model in performance simulations can give rather pessimistic results compared to true measurement data. 相似文献
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Mikko Kalmi Mohammed Lahcini Pascal Castro Olli Lehtonen Ahmed Belfkira Markku Leskel Timo Repo 《Journal of polymer science. Part A, Polymer chemistry》2004,42(8):1901-1911
The use of tetrakis Sn(IV) alkoxides as highly active initiators for the ring‐opening polymerization of D ,L ‐lactide is reported. The activities of prepared Sn(IV) tetra‐2‐methyl‐2‐butoxide, Sn(IV) tetra‐iso‐propoxide, and Sn(IV) tetra‐ethoxide were compared to a well‐known ring‐opening polymerization initiator system, Sn(II) octoate activated with n‐butanol. All polymerizations were conducted at 75 °C in toluene. The activities of tetrakis Sn(IV) alkoxides grew in order of increasing steric hindrance, and the bulky Sn(IV) alkoxides showed higher activity than the Sn(II) octoate/butanol system. The living character of the polymerization was demonstrated in homopolymerization of D ,L ‐lactide and in block copolymerization of L ‐lactide with ?‐caprolactone. 1H, 13C, and 119Sn NMR were used to characterize the prepared Sn(IV) alkoxides and the polymer microstructure, and size exclusion chromatography was used to determine the molar masses as well as the molar‐mass distributions of the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1901–1911, 2004 相似文献
276.
Marianna Kemell Mikko Ritala Emmanuel Ossei-Wusu Helmut Föll 《Microelectronic Engineering》2007,84(2):313-318
High surface area Si/Al2O3/ZnO:Al capacitors were formed in electrochemically etched porous silicon. The Al2O3 dielectric and the ZnO:Al top electrode were deposited by atomic layer deposition in high aspect ratio porous Si. A single capacitor with a typical area of about 1 mm2 consisted of about 105 pores. Effective capacitance densities were between 2.0 and 2.5 μF/cm2, i.e., approximately 30 times higher than for a planar capacitor prepared under identical conditions, illustrating the effect of the enhanced surface area in the porous structure. 相似文献
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Eyvindson Kyle Hujala Teppo Kurttila Mikko Kangas Annika 《Annals of Operations Research》2015,232(1):99-113
Annals of Operations Research - In a typical decision-making process, preference elicitation methods require a priori knowledge about the desired outcomes. It is expected that the decision maker... 相似文献
280.
Reijo Sillanp Mikko M. Hnninen 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(5):509-512
The title cocrystal contains two chiral conformational diastereomers, viz. (1S,2R,RN)‐ and (1S,2R,SN)‐, of [2,4‐di‐tert‐butyl‐6‐{[(1‐oxido‐1‐phenylpropan‐2‐yl)(methyl)amino]methyl}phenolato](methanol)‐cis‐dioxidomolybdenum(VI), [Mo(C25H35NO2)O2(CH3OH)], representing the first example of a structurally characterized molybdenum complex with enantiomerically pure ephedrine derivative ligands. The MoVI cations exhibit differently distorted octahedral coordination environments, with two oxide ligands positioned cis to each other. The remainder of the coordination comprises phenoxide, alkoxide and methanol O atoms, with an amine N atom completing the octahedron. The distinct complexes are linked by strong intermolecular O—H...O hydrogen bonds, resulting in one‐dimensional molecular chains. Furthermore, the phenyl rings are involved in weak T‐shaped/edge‐to‐face π–π interactions with each other. 相似文献