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71.
Optimal strong Mal’cev conditions for congruence meet-semidistributivity in locally finite varieties
Jelena Jovanović Petar Marković Ralph McKenzie Matthew Moore 《Algebra Universalis》2016,76(3):305-325
Locally finite, congruence meet-semidistributive varieties have been characterized by numerous Mal’cev conditions and, recently, by two strong Mal’cev conditions. We provide three new strong Mal’cev characterizations and a new Mal’cev characterization each of which improves the known ones in some way. 相似文献
72.
Jack Liu Johann Chan Craig M. Bryant Petar A. Duspara Ernest E. Lee David Powell Hua Yang Ziping Liu Chris Walpole Edward Roberts Robert A. Batey 《Tetrahedron letters》2012,53(24):2971-2975
The fluorination of ketones, ketals, and enamides has been achieved using the electrophilic fluorinating reagent Selectfluor? (F-TEDA-BF4). For the reactions of ketones and ketals the use of sulfuric acid (0.1 equiv) as an additive was found to facilitate the reaction leading to more rapid product formation. This behavior is analogous to the known effects of acid catalysis on the bromination of ketones. The reactions were generally quite selective leading to the formation of monofluorinated products, and could be accomplished on reaction scales up to 85 mmol using N-protected piperidone based substrates. Reactions in the presence of MeOH led to the formation of the corresponding fluoroketones or fluoroketals depending upon the substrate. The formation of the fluoroketals in this manner, as well as the fluorination of cyclic enamides are examples of multi-component coupling reactions. 相似文献
73.
74.
Zsuzsanna Horváth Alfréd Menyhárd Petar Doshev Markus Gahleitner József Varga Cornelia Tranninger Béla Pukánszky 《Journal of Thermal Analysis and Calorimetry》2014,118(1):235-245
The chain regularity of isotactic polypropylene (iPP) homopolymer and random copolymers was characterized by different thermal fractionation methods in this study. Different stepwise temperature programs were applied in a calorimeter (DSC), in order to develop a method which is significantly faster than stepwise isothermal segregation technique (SIST) and provides reliable information about the chain regularity of iPP. Our studies prove that self-seeding accelerates the crystallization process during annealing in SSA–DSC experiments (successive self-nucleation and annealing). Consequently, the time of isothermal steps can be shortened significantly in the SSA–DSC method. On the other hand, we found that step time should not be too short if the goal of the measurement is the determination of average chain regularity. Our results clearly indicate that both the experimental conditions and the evaluation technique influence the obtained results. A standard experimental procedure is proposed for reliably determining the average chain regularity of iPP. The length of the SSA–DSC temperature program developed in this study is much shorter compared to that of the conventional SIST measurements used recently for such experiments. The proposed SSA–DSC program makes the reliable characterization of a large number of samples on an acceptable timescale possible. 相似文献
75.
Šime Ukić Mirjana Novak Petar Žuvela Nebojša Avdalović Yan Liu Bogusław Buszewski Tomislav Bolanča 《Chromatographia》2014,77(15-16):985-996
New retention methodology that integrates the conventional quantitative structure-retention relationship (QSRR) approach and gradient retention modeling based on isocratic retention data is developed and presented in this paper. Such an integrated approach removes the general QSRR limitation of highly predefined application conditions (i.e., QSRR are generally applicable only under the conditions used during model development) and allows the prediction of retentions over a wide range of different elution conditions (practically for any isocratic or gradient elution profile). At the same time, it retains the ability to predict retention of components unknown to the model, i.e., the components that have not been used in modeling. Ion-exchange chromatography (IC) analysis of carbohydrates was selected as modeling environment. Three regression techniques were applied and compared during QSRR modeling, namely: stepwise multiple linear regression, partial least squares (PLS), and uninformative variable elimination–PLS regression. The obtained prediction results of the best QSRR model (root-mean-square error of prediction = 22.69 %) were similar to those found in the literature. The upgrade from QSRR to the integrated model did not diminish the predictive ability of the model, indicating an excellent potential of the developed methodology not only in IC but also in chromatography in general. 相似文献
76.
Petar Petrov 《Monatshefte für Mathematik》2006,151(1):165-171
In this work we investigate polynomials of maximal (minimal) arc-length in the interval [−1, 1] amongst all monic polynomials
of fixed degree n with n real zeros in [−1, 1]. 相似文献
77.
LetC be a convex body ofE d and consider the symmetric difference metric. The distance ofC to its best approximating polytope having at mostn vertices is 0 (1/n 2/(d?1)) asn→∞. It is shown that this estimate cannot be improved for anyC of differentiability class two. These results complement analogous theorems for the Hausdorff metric. It is also shown that for both metrics the approximation properties of «most» convex bodies are rather irregular and that ford=2 «most» convex bodies have unique best approximating polygons with respect to both metrics. 相似文献
78.
Petar Petrov Pavlina Mokreva Christo B. Tsvetanov Levon Terlemezyan 《Colloid and polymer science》2008,286(6-7):691-697
Polyaniline (PANI) nanotubes were prepared by oxidative polymerization of aniline in the presence of two structure-directing agents—salicylic acid (SA) and sodium dodecyl sulfate (SDS). When using only SA, mainly aggregated nanotube dendrites or coral-like structures have been obtained. Addition of a very small amount of the surfactant SDS, much less than the critical micelle concentration, results in substantial reduction of the aggregated nanotube morphology on the account of isolated PANI nanotubes, which is the favorable structure from the point of view of further modification. In order to make the isolated nanotubes water dispersible, their surface was modified by complex formation (non-covalent grafting) with hydrophilic poly(ethylene oxide)-block-poly(acrylic acid) copolymer. These water-dispersible PANI nanotubes might be good candidates for some biochemical and biomedical applications. 相似文献
79.
We prove that for any variety , the existence of an edge-term (defined in [1]) and Jónsson terms is equivalent to the existence of a near-unanimity term.
We also characterize the idempotent Maltsev conditions which are defined by a system of linear absorption equations and which
imply congruence distributivity.
The first author was supported by the grant no. 144011G of the Ministry of Science and Environment of Serbia. The work of
the second author was supported by US NSF grant no. DMS 0245622. 相似文献
80.
Milutin M. Milosavljevi? Goran D. Vukovi? Aleksandar D. Marinkovi? Radoslav Aleksi? Petar S. Uskokovi? 《Monatshefte für Chemie / Chemical Monthly》2011,46(3):1045-1053