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91.
A.-M. Bui A. Cavé M.-M. Janot J. Parello P. Potier U. Scheidegger 《Tetrahedron》1974,30(11):1327-1336
From Collybia maculata Alb. et Sch. ex. Fries two sesquiterpenes of a new type have been isolated, collybolide 1 and isocollybolide 2, artefacts resulting from carboxylic acid precursors as yet not isolated. The structure of collybolide is established by correlation with that of isocollybolide, already known, and their reactivity has been studied. NMR spectra allow the conformational analysis of all products isolated.A series of lactones (β-, γ-, σ- and ?-lactones) in various solvents has been studied through 13C NMR spectroscopy. The chemical shift of the carbonyl carbon appears characteristic of the type of lactone. The distinction is particularly clear between γ-lactones (+13·5 to +16 ppm/CS2) and σ-lactones (+20 to +22 ppm). 相似文献
92.
De Smedt F Bui XV Nguyen TL Peeters J Vereecken L 《The journal of physical chemistry. A》2005,109(10):2401-2409
The product distribution of the reaction of acetic acid, CH(3)COOH, with hydroxyl radicals, OH, was studied experimentally and theoretically. Mass-spectrometric measurements at 290 K and 2 Torr of He of the CO(2) yield versus the loss of acetic acid yielded a branching fraction of 64 +/- 14% for the abstraction of the acidic hydrogen as follows: CH(3)COOH + OH --> CH(3)COO + H(2)O --> CH(3) + CO(2) + H(2)O. A quantum chemical and theoretical kinetic analysis showed that the abstraction of the acidic hydrogen is enhanced relative to the abstraction of -CH(3) hydrogens because of the formation of a strong pre-reactive H-bonded complex, where the H-bonds are retained in the H-abstraction transition state. The potential energy surface of the reaction is explored in detail, and the reaction products of the individual channels are identified. The theoretical product branching is found to be critically dependent on the energetic and rovibrational differences between the H-abstraction transition states. 相似文献
93.
García Rodenas LA Weisz AD Magaz GE Blesa MA 《Journal of colloid and interface science》2000,230(1):181-185
The electrokinetic behavior of titanium dioxide particles (Degussa P25, mainly composed of anatase) put in contact with chromium(VI) aqueous solutions is highly sensitive to light exposure under normal laboratory conditions. In the dark, adsorption of Cr(VI) gives rise to substantial decrements in the mobilities, especially in the acidic branch, and, at higher concentrations, to shifts in the isoelectric point (pH(piep)) to lower values, as expected for anionic chemisorption. A two-mode adsorption model accounts qualitatively for the results. Under light, pH(piep) shifts in the opposite direction as the Cr(VI) concentration increases. A maximum value is attained at [Cr(VI)] approximately 10(-3) mol dm(-3), pH(piep) 8.2, which coincides with values reported for hydrous chromium(III) oxides. At higher concentrations, Cr(VI) adsorption defines a shift of pH(piep) to lower values. It is concluded that light absorption by titanium dioxide promotes the reduction of Cr(VI) and the surface precipitation of the hydrous Cr(III) oxide. The values of pH(piep) for partially covered surfaces are well described by a simple model of surface ionization derived earlier. FTIR/ATR analysis of the surfaces supports this interpretation, and further suggests that one of the modes of Cr(VI) adsorption implies surface dimerization to yield adsorbed dichromate. Copyright 2000 Academic Press. 相似文献
94.
An ion gun has been built to study the degradation of polyethylene by O+, A+, Ne+ and He+. Films, degraded under conditions of 200–2000 eV impinging energy, are examined with regard to surface changes and infra-red spectrum. Proportionality between the ion mass and the rate of degradation is found. Comparison with partial discharges shows similar deterioration but only as regards qualitative effects. Hypotheses are advanced to explain the mechanical degradation of the insulating material by partial discharges. 相似文献
95.
Sandee AJ van Der Veen LA Reek JN Kamer PC Lutz M Spek AL van Leeuwen PW 《Angewandte Chemie (International ed. in English)》1999,38(21):3231-3235
By a sol-gel process a rhodium complex containing a diphosphane with a large natural P-Rh-P bite angle is covalently anchored in a silica matrix (see picture). The immobilized catalyst is a very selective hydroformylation catalyst that is completely and conveniently separated from the product and can be reused in numerous cycles. 相似文献
96.
Phan Van Kiem Chau Van Minh Nguyen Xuan Nhiem Nguyen Thi Cuc Ngo Van Quang Hoang Le Tuan Anh Bui Huu Tai Pham Hai Yen Nguyen Thi Hoai Kim Young Ho Nanyoung Kim SeonJu Park Seung Hyun Kim 《Magnetic resonance in chemistry : MRC》2014,52(1-2):51-56
Seven new muurolane‐type sesquiterpenes, (4R,5R)‐muurol‐1(6),10(14)‐diene‐4,5‐diol (1), (4R,5R)‐muurol‐1(6)‐ene‐4,5‐diol (2), (4R,5R,10R)‐10‐methoxymuurol‐1(6)‐ene‐4,5‐diol (3), (4S)‐4‐hydroxy‐1,10‐seco‐muurol‐5‐ene‐1,10‐dione (4), (4R)‐4‐hydroxy‐1,10‐seco‐muurol‐5‐ene‐1,10‐dione (5), (6S,10S)‐6,10‐dihydroxy‐7,8‐seco‐2,8‐cyclo‐muurol‐4(5),7(11)‐diene‐12‐oic acid (6), and (6R,10S)‐6,10‐dihydroxy‐7,8‐seco‐2,8‐cyclo‐muurol‐4(5),7(11)‐diene‐12‐oic acid (7) were isolated from the marine sponge Dysidea cinerea. Their structures were determined by the combination of spectroscopic and chemical methods, including 1D‐NMR, 2D‐NMR, and CD spectra as well as by comparing the NMR data with those reported in the literature. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
97.
98.
Liang Ying-Lin Yin Liang-Jun Bui Hao-Van Jian Xian Yang Guang Ding Jie-Xiong 《Physics of the Solid State》2019,61(8):1450-1455
Physics of the Solid State - The main objective of this paper is to reveal the mechanism of enhanced excitation light absorption in nano-pores structure BaMgAl10O17:Eu2+ (BAM) phosphor by optical... 相似文献
99.
Lam T. Bui Jing Liu Axel Bender Michael Barlow Slawomir Wesolkowski Hussein A. Abbass 《Memetic Computing》2011,3(4):271-285
A novel direction-based multi-objective evolutionary algorithm (DMEA) is proposed, in which a population evolves over time along some directions of improvement. We distinguish two types of direction: (1) the convergence direction between a non-dominated solution (stored in an archive) and a dominated solution from the current population; and, (2) the spread direction between two non-dominated solutions in the archive. At each generation, these directions are used to perturb the current parental population from which offspring are produced. The combined population of offspring and archived solutions forms the basis for the creation of both the next-generation archive and parental pools. The rule governing the formation of the next-generation parental pool is as follows: the first half is populated by non-dominated solutions whose spread is aided by a niching criterion applied in the decision space. The second half is filled with both non-dominated and dominated solutions from the sorted remainder of the combined population. The selection of non-dominated solutions for the next-generation archive is also assisted by a mechanism, in which neighborhoods of rays in objective space serve as niches. These rays originate from the current estimate of the Pareto optimal front??s (POF??s) ideal point and emit randomly into the hyperquadrant that contains the current POF estimate. Experiments on two well-known benchmark sets, namely ZDT and DTLZ have been carried out to investigate the performance and the behavior of the DMEA. We validated its performance by comparing it with four well-known existing algorithms. With respect to convergence and spread performance, DMEA turns out to be very competitive. 相似文献
100.
In this paper we study the stability radii of positive linear discrete system under arbitrary affine parameter perturbations
in infinite dimensional spaces. It is shown that complex, real, and positive stability radii of positive systems coincide.
More importantly, estimates and computable formulas of these stability radii are also derived. The results are then illustrated
by a simple example. The obtained results are extensions of the recent results in [3]. 相似文献