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31.
Jos-Luis Milln Gerardo Martínez Carmen Mijangos Jos Manuel Gmez-Elvira 《Macromolecular Symposia》1989,29(1):185-196
In the light of some earlier works on nucleophilic substitution on poly(vinyl chloride) (PVC) in solution, a conformational mechanism is proposed. It considers the TT isotactic diad conformation to be the only reactive species and the reaction to be controlled by the conformational equilibria that make such conformation available. As a result all the isotactic and the heterotactic triads are capable of reacting provided that they adopt the GTTG− and the GTTT conformation, respectively. Since the replacement of a definite fraction of isotactic triads, which are assumed to be of the GTTG− conformation, results in an enhanced thermal and photochemical stability, the lability of some chlorines at such triads is proved. Further arguments in favour of the conformational mechanism are afforded through recent results of i) substitution studies in the melt and in aqueous suspension with phase transfer catalysts, ii) accurate 13C NMR measurements of triad variation with degree of substitution. 相似文献
32.
Ali Liazid Gerardo F. Barbero Miguel Palma Jamal Brigui Carmelo G. Barroso 《Chromatographia》2007,66(7-8):571-575
Results from a systematic study of the factors affecting extraction of cis-verbenol and verbenone from pine seeds are presented. Five extraction conditions were investigated: extraction solvent, method
of extraction, extraction temperature, volume of solvent, and the ratio of the mass of sample to the amount of extraction
solvent. The resulting optimized method uses magnetic-stirring-assisted extraction of pine seeds (5 g) with ethyl acetate
(75 mL) for 20 min, at room temperature. RSDs were less than 5% for both compounds. GC–FID was used for quantification of
cis-verbenol and verbenone in the extracts. 相似文献
33.
Víctor G. Alfaro-García Anna M. Gil-Lafuente Gerardo G. Alfaro Calderón 《Computational & Mathematical Organization Theory》2017,23(3):391-408
In recent years, a trend for accelerating the economic, social and environmental development of cities through associations, organization and creation of synergies has been identified. Our investigation applies a grouping model in order to identify municipalities that could create optimal synergies towards the construction of competitive advantages. In order to achieve this task, we use tools of Fuzzy Logic to evaluate subjective and qualitative characteristic elements of different municipalities under Galois’ group theory. Results conclude on 32 different groups ordered in 7 different levels, relating 12 municipalities of a specific region according to 8 competitive variables. This work seeks to shed light in the conformation of groups under uncertain conditions and the deep examination of the characteristic competitive elements in a specific region for further policy and decision-making processes. 相似文献
34.
Gómez AM Danelón GO Pedregosa A Valverde S López JC 《Chemical communications (Cambridge, England)》2002,(18):2024-2025
Functionalized exo-glycals can be readily obtained by palladium catalyzed Suzuki cross-coupling of halo-exo-glycals with boronic acids. 相似文献
35.
Godinez CE Zepeda G Garcia-Garibay MA 《Journal of the American Chemical Society》2002,124(17):4701-4707
We have developed a simple convergent procedure for the synthesis of molecular rotors consisting of a central aromatic group coupled with two axially positioned ethynyltriptycenes. Molecular rotors with 1,4-phenylene (1), 1,4'-1,1'-biphenylene (2), 9,10-anthracenylene (3), and 2,7-pyrenylene (4) groups were prepared by Pd(0)-catalyzed coupling of ethynyl triptycenes with the corresponding dibromoarenes. Although compounds 1-4 were not expected to have free rotation in the solid state, the rotational potentials of 1 and 3 were analyzed by semiempirical methods and the crystal packing of 1 was analyzed to design the structures most likely to yield a functional rotor in the solid state. Semiempirical PM3 calculations predict compounds 1, 2, and 4 to have frictionless internal rotation even at temperatures as low as 25 K, while compound 3 is expected to have a barrier of ca. 4 kcal/mol. 相似文献
36.
We devise the optimal form of Gaussian resource states enabling continuous-variable teleportation with maximal fidelity. We show that a nonclassical optimal fidelity of N-user teleportation networks is necessary and sufficient for N-party entangled Gaussian resources, yielding an estimator of multipartite entanglement. The entanglement of teleportation is equivalent to the entanglement of formation in a two-user protocol, and to the localizable entanglement in a multiuser one. Finally, we show that the continuous-variable tangle, quantifying entanglement sharing in three-mode Gaussian states, is defined operationally in terms of the optimal fidelity of a tripartite teleportation network. 相似文献
37.
On the Path of a Quasi-static Crack in Mode III 总被引:1,自引:0,他引:1
A method for finding the path of a quasi-static crack growing in a brittle body is presented. The propagation process is modelled by a sequence of discrete steps optimizing the elastic energy released. An explicit relationship between the optimal growing direction and the parameters defining the local elastic field around the tip is obtained for an anti-plane field. This allows to describe a simple algorithm to compute the crack path.
Mathematics Subject Classifications (2000) 74R05, 74B05, 74G70.Gerardo E. Oleaga: Supported by EU-Project Front Singularities University of Leipzig and the Max Planck Institute MIS. Partial support was also provided by the Spanish DGES project BFM2000-0605. 相似文献
38.
We classify the entanglement of two-mode Gaussian states according to their degree of total and partial mixedness. We derive exact bounds that determine maximally and minimally entangled states for fixed global and marginal purities. This characterization allows for an experimentally reliable estimate of continuous variable entanglement based on measurements of purity. 相似文献
39.
Giustini M Murgia S Palazzo G 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7381-7384
In 1955, Bowcott and Schulman coined the term microemulsions and, in passing, proposed a cosurfactant titration of interfaces tailored for water-in-oil systems (Bowcott, J. E.; Schulman, J. H. Z. Elektrochem. 1955, 59, 283). This procedure, elegant and inexpensive, is accomplished by dilution with both oil and cosurfactant up to the onset of microemulsion formation. The rationale they proposed for this method should furnish, with high accuracy, the composition of reverse micelles and continuous bulk in the presence of cosurfactant partition. The present paper demonstrates, by means of pulsed gradient spin-echo NMR, that the Schulman's titration quantitatively describes the cosurfactant partition and that the titration path really corresponds to a dilution path for reverse micelles (at constant composition) dispersed in a continuous bulk (at constant composition). 相似文献
40.
Piazza R Pierno M Vignati E Venturoli G Francia F Mallardi A Palazzo G 《Physical review letters》2003,90(20):208101
Solubilization of membrane proteins requires surfactants, whose structural properties play a crucial role in determining the protein phase behavior. We show that ionization of a pH-sensitive surfactant, lauryldymethylamino-N-oxide, bound to the bacterial photosynthetic Reaction Center, induces protein phase segregation in micrometric "droplets." Liquid-liquid phase separation takes place in a narrow pH range, is promoted by increasing temperature, and vanishes by adding salt. After a fast initial droplet growth, the nearly arrested kinetics at a later stage leaves the system in a finely divided, long-lasting emulsified state. 相似文献