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41.
Esa Kokko Pirjo Pietikinen Jari Koivunen Jukka V. Seppl 《Journal of polymer science. Part A, Polymer chemistry》2001,39(21):3805-3817
Ethene was copolymerized (1) with 1,5‐hexadiene with rac‐ethylenebis(indenyl)zirconium dichloride/methylaluminoxane (MAO) used as a catalyst and (2) with 1,7‐octadiene with bis(n‐butylcyclopentadienyl)zirconium dichloride/MAO and rac‐ethylenebis(indenyl)hafnium dichloride (Et[Ind]2HfCl2)/MAO used as catalysts at 80 °C in toluene. The copolymer microstructure and the influence of diene incorporation on the rheological properties were examined. Ethene and 1,5‐hexadiene formed a copolymer in which a major fraction of the 1,5‐hexadiene was incorporated into rings and a small fraction formed 1‐butenyl branches. The copolymerization of ethene with 1,7‐octadiene resulted in a higher selectivity toward branch formation. Some of the branches formed long‐chain‐branching (LCB) structures. The ring formation selectivity increased with decreasing ethene concentration in the polymerization reactor. Melt rheological properties of the diene copolymers resembled those of metallocene‐catalyzed LCB homopolyethenes and depended on the vinyl content, the catalyst, and the polymerization conditions. At high diene contents, all three catalysts produced crosslinked polyethene. This was especially pronounced with Et[Ind]2HfCl2, where only 0.2 mol % 1,7‐octadiene in the copolymer was required to achieve significantly modified rheological properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3805–3817, 2001 相似文献
42.
Niskanen Ilpo Räty Jukka Soetedjo Hariyadi Hibino Kenichi Oohashi Hiroshi Heikkilä Rauno Matsuda Kiyofumi Otani Yukitoshi 《Optical Review》2020,27(2):178-182
Optical Review - This study measured the polarised light reflected from the surface of thermally modified Scots pine (Pinus sylvestris L.) wood using a Stokes imaging polarimeter. The data were... 相似文献
43.
Incommensurate quantum systems with two competing periodicities exhibit metallic (with Bloch-type extended wave functions),
insulating (with exponentially localized wave functions) as well ascritical (with fractal wave functions) phases. An exact renormalization method, which takes into account the inherent incommensurability,
is used to obtain the phase diagram of various quantum models for the two-dimensional electron gas and for quantum spin chains
in a magnetic field. In this approach, the scaling properties of the fractal eigenstates are characterized by a fixed point
or a strange invariant set of the renormalization flow. One of our novel results is the existence of self-similar fluctuations
in the localized states once the exponentially decaying envelope is factorized out. In almost all cases under investigation
here, the universality classes can be broadly classified as those of the nearest-neighbor square or triangular lattices. 相似文献
44.
A simple method of deformational correction for the N.M.R. spectral parameters of molecules dissolved in liquid crystals is described. The method is applicable to the different isotopically substituted derivatives of the molecules belonging to the cubic point groups. Its validity is verified for the dipolar and quadrupolar couplings observed in the molecules CH4, CD4 and CH3D dissolved in the liquid crystals Merck Phase IV, Merck ZLI 1167 and their mixtures. 相似文献
45.
46.
Bayesian model determination in the complete class of graphical models is considered using a decision theoretic framework within the regular exponential family. The complete class contains both decomposable and non-decomposable graphical models. A utility measure based on a logarithmic score function is introduced under reference priors for the model parameters. The logarithmic utility of a model is decomposed into predictive performance and relative complexity. Axioms of decision theory lead to the judgement of the plausibility of a model in terms of the posterior expected utility. This quantity has an analytic expression for decomposable models when certain reference priors are used and the exponential family is closed under marginalization. For non-decomposable models, a simulation consistent estimate of the expectation can be obtained. Both real and simulated data sets are used to illustrate the introduced methodology. 相似文献
47.
Erik A.A. Wallén Johannes A.M. Christiaans Jukka Gynther Jouko Vepsäläinen 《Tetrahedron letters》2003,44(10):2081-2082
The synthesis of (2S,5S)-Boc-5-tert-butylproline ethyl ester via the addition of tert-butylcuprate to (2S)-N-Boc-Δ5-dehydroproline ethyl ester, formed from (2S)-N-Boc-5-methoxyproline ethyl ester, gives an excellent yield of 94% and a high diastereoselectivity (2S,5S):(2S,5R) 78:22. This synthesis opens up a new synthetic route to (2S,5S)-5-tert-butylproline, which is a useful, conformationally rigid, analogue of l-proline. 相似文献
48.
Väisänen A Suontamo R Silvonen J Rintala J 《Analytical and bioanalytical chemistry》2002,373(1-2):93-97
An extraction method was developed for the determination of toxic elements in contaminated soil samples by inductively coupled plasma atomic emission spectrometry (ICP-AES). The determination of arsenic, cadmium, lead, and silver in ultrasound-assisted extracts of SRM 2710 and SRM 2711 by ICP-AES was carried out with high accuracy and precision (RSD<3.7%). The certified concentrations of the SRMs were obtained for arsenic, cadmium, lead, and silver by using an ultrasound-assisted extraction method with a digestion solution of (1+1)-diluted aqua regia. The determination of copper in SRMs by the ultrasound-assisted extraction method and analysis by ICP-AES failed to obtain the certified concentrations at the 95% level of confidence using (+/-2 s) as confidence limits of the mean. However, the same results were observed with the use of the microwave digestion method and reflux, which is the ISO 11466 standard method. The analysis of the SRMs showed that the ultrasound-assisted extraction method is highly comparable with the other methods used for such purposes. The major advantages of the ultrasound-assisted extraction method compared to the microwave and reflux methods are the high treatment rate (50 samples simultaneously in nine minutes) and low reagent usage, the main benefit of which are the low chloride and nitrate concentrations in the extracts. 相似文献
49.
Structure-activity relationships of 23 P450 2A5 and 2A6 inhibitors were analysed using the CoMFA [1] and GOLPE/GRID with smart region definition (SRD) [2]. The predictive power of the resulting models was validated using five compounds not belonging to the model set. All models have high internal and external predictive power and resulting 3D-QSAR models are supporting each other. Both Sybyl and GOLPE highlight properties near lactone moiety to be important for 2A5 and 2A6 inhibition. Another important feature for pIC50 was the size of the substituent in the 7-positon of coumarin. The models suggest that the 2A5 binding site is larger that that of 2A6 due to larger steric regions in the CoMFA coefficient maps and corresponding GOLPE maps. In addition, the maps reveal that 2A6 disfavours negative charge near the lactone moiety of coumarin. 相似文献
50.
Abstract A simple method of deformational correction for the N.M.R. spectral parameters of molecules dissolved in liquid crystals is described. The method is applicable to the different isotopically substituted derivatives of the molecules belonging to the cubic point groups. Its validity is verified for the dipolar and quadrupolar couplings observed in the molecules CH4, CD4 and CH3D dissolved in the liquid crystals Merck Phase IV, Merck ZLI 1167 and their mixtures. 相似文献