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991.
The highly electrophilic boranes HB(C6F5)2 and B(C6F5)3 are effective reagents for generating a variety of zwitterionic olefin polymerization catalysts. The former borane can be
used to incorporate Lewis acid activators into ancillary ligand structures via hydroboration of pendant olefinic functions;
alternatively, direct reaction with simple organozirconocenes can lead to a family of hydridoborate stabilized girdle-type
zwitterions where charge separation is minimal. The ethylene polymerization activity of these compounds is, in general, poor
by virtue of the tight intramolecular ion pairing. More active zwitterionic catalysts can be generated through reaction of
B(C6F5)3 with suitable organozirconium pre-catalysts. The solution and solid state structures of several of these compounds are discussed,
highlighting the various mechanisms of stabilization found in the catalyst structures.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
992.
993.
Canopy architecture and light spectral composition have long been considered as important factors determining grape juice acidity and K+concentrations. In this study, we provide direct evidence that fluctuations in intensity of light incident on berry tissue may significantly modulate net ion fluxes from and into the berry mesocarp. The MIFE technique was used to quantify fluxes of K+, H+, and Ca2+ in Pinot Noir and Emperor grape berries. Transition from dark to light induced complex multiphase kinetics of K+flux resulting in significant shift towards net K+uptake by the peripheral mesocarp tissue. When light intensity was modulated in a square-wave manner with a period of 5 to 15 min (mimicking periodicity of natural variations during a typical autumn day in Hobart), K+flux oscillated with the same frequency and a magnitude of about 100 nmol/m2 s. Changes in H+and Ca2+ fluxes showed high positive (R = 0.8) and negative (R = 0.9) correlation, respectively, with those in K+. To the best of our knowledge, these data from excised fruit provide the first reported evidence that light directly incident on bunches may modulate apoplasmic pH and K+concentration in grape. Possible underlying mechanisms are discussed. 相似文献
994.
995.
Concentration dependant emission spectra and fluorescence dynamic profiles have been investigated in PrxLa1−xAlO3 single crystals in order to better understand processes responsible for concentration quenching of the praseodymium 3P0 and 1D2 emissions. The cross-relaxation transfer rates were experimentally determined as a function of Pr3+ concentration. Decays were modeled and nearest-neighbor trapping rates were calculated. 相似文献
996.
997.
A. JuszaK. Anders A. Jastrz?bskaP. Polis A. OlszynaM. Ku? A. KunickiR. Piramidowicz 《Optical Materials》2011,33(10):1487-1491
In this work, we discuss structural and luminescent properties of Al2O3 nanopowders doped with Yb3+ ions prepared by a novel method, in which organic compounds were used as a solvent and lanthanide organic derivatives, served as a rare-earth ion source. The set of samples differing in activator concentrations and particle sizes was carefully studied by means of structural and optical characterization methods. In particular, the high resolution electron and transmission microscopy has been deployed together with X-ray diffraction technique to determine fundamental structural properties of nanopowders. The optical characterization was focused mainly on basic excitation and emission features and their sensitiveness on dopant concentration and the average nanoparticle size. 相似文献
998.
This paper describes the design and fabrication of fiber-optic nanoprobes developed for optical detection in single living
cells. It is critical to fabricate probes with well-controlled nanoapertures for optimized spatial resolution and optical
transmission. The detection sensitivity of fiber-optic nanoprobe depends mainly on the extremely small excitation volume that
is determined by the aperture sizes and penetration depths. We investigate the angle dependence of the aperture in shadow
evaporation of the metal coating onto the tip wall. It was found that nanoaperture diameters of approximately 50 nm can be
achieved using a 25° tilt angle. On the other hand, the aperture size is sensitive to the subtle change of the metal evaporation
angle and could be blocked by irregular metal grains. Through focused ion beam (FIB) milling, optical nanoprobes with well-defined
aperture size as small as 200 nm can be obtained. Finally, we illustrate the use of the nanoprobes by detecting a fluorescent
species, benzo[a]pyrene tetrol (BPT), in single living cells. A quantitative estimation of the numbers of BPT molecules detected
using fiber-optic nanoprobes for BPT solutions shows that the limit of detection was approximately 100 molecules. 相似文献
999.
Jae-Young HEO Sung-Hak CHO Tae-Jin JE Kwang-Ho KIM Hyung-Woo LEE Myung-Chang KANG 《中国有色金属学会会刊》2011,(Z1):83-87
The objective of this work is to compare the tool performance of TiN and TiAlN coated carbides end-mills deposited by an arc ion plating (AIP) method, using honing treatment to polish the cutting edge surface sleekly. The curve of surface roughness versus honing time showed a rapid improvement initially and thereafter became steady, manifesting a saturation effect. The optimal honing time related to surface roughness was determined to be approximately 20 s. As the surface roughness increased, the critical loads reduced. At an average surface roughness (Ra) of 0.028 μm, the highest critical loads of TiN and TiAlN coating layers were 98 and 114 N, respectively. Tool performances of uncoated and coated tools were conducted under high speed machining (HSM) of AISI D2 cold-worked die steel (62 HRC). Consequently, the TiAlN coated end-mill using honing treatment showed excellent tool life under HSM conditions. 相似文献
1000.
电炉导电横臂技术的发展趋势 总被引:2,自引:0,他引:2
对电炉关键部件—导电横臂的三种类型作了对比分析,并指出全铝合金导电横臂这一新型技术,将是国内外电炉导电横臂技术的最新发展趋势。 相似文献