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91.
This paper deals with the problem of scenario tree reduction for stochastic programming problems. In particular, a reduction method based on cluster analysis is proposed and tested on a portfolio optimization problem. Extensive computational experiments were carried out to evaluate the performance of the proposed approach, both in terms of computational efficiency and efficacy. The analysis of the results shows that the clustering approach exhibits good performance also when compared with other reduction approaches. 相似文献
92.
We study the existence and non-existence of positive singular solutions of second-order non-divergence type elliptic inequalities of the form $\sum\limits_{i,j = 1}^N {a_{ij} (x)\frac{{\partial ^2 u}} {{\partial x_i \partial x_j }}} + \sum\limits_{i = 1}^N {b_i (x)\frac{{\partial u}} {{\partial x_i }} \geqslant K(x)u^p ,} - \infty < p - \infty , $ with measurable coefficients in a punctured ball B R \{0} of ? N , N ≥ 1. We prove the existence of a critical value p* which separates the existence region from the non-existence region. We show that in the critical case p = p*, the existence of a singular solution depends on the rate at which the coefficients (a i j ) and (b i ) stabilize at zero, and we provide some optimal conditions in this setting. 相似文献
93.
94.
Patrizia Ferraboschi Maria De Mieri Fiorella Galimberti 《Tetrahedron: Asymmetry》2010,21(17):2136-2141
The (S)-2-chlorophenylglycine moiety is well recognized in the structure of (S)-clopidogrel, a known antithrombotic drug. We prepared an enantiomerically pure chiral building block via an enzyme-catalyzed resolution of (RS)-N-Boc-2-chlorophenylglycine methylester. The best results were obtained by means of an immobilized subtilisin, the cross-linked enzyme aggregate (Alcalase-CLEA®). The high enantiomeric excess of the synthon obtained remained the same over the course of clopidogrel synthesis; the simplicity of the process makes this pathway suitable for large-scale preparation. 相似文献
95.
A classical system for the preparation of carbonyl compounds from alkenes relies upon ozonolysis of the double bond, followed by reductive cleavage of the ozonide so formed. Among the reagents of choice for such a reduction, triphenylphosphine certainly has enjoyed a widespread use.1 However, in spite of the simplicity of the method, often one can face problems in the purification of the carbonyl compound from unreacted triphenylphosphine, especially if the polarities of both products are very similar. We have encountered such a problem during the preparation of the (20 S)-6β -ethoxy-3 α, 5-cyclo-5α -pregnane-20-carbaldehyde 4 from the suitably protected stigmasterol32. In this case, when triphenylphosphine was used for reduction of ozonide we never could isolate the aldehyde 2 uncontaninated by tripherylphosphine. 相似文献
96.
Margherita Bernardeschi Patrizia Guidi Vittoria Scarcelli Giada Frenzilli Marco Nigro 《Analytical and bioanalytical chemistry》2010,396(2):619-623
Titanium dioxide is extensively used in a variety of products, including industrial materials and cosmetics. Studies mainly
performed on human cell lines and in vivo exposure on experimental animals have raised concern about the toxic effects of
ultrafine titanium dioxide; however, scarce information is available about its impact on aquatic life. The aim of this article
was to assess the genotoxic potential of TiO2 (anatase and rutile) on bottlenose dolphin leukocytes. Blood samples were obtained from four male and one female specimens
reared at the Adriatic SeaWorld “Oltremare” (Riccione, Italy). Leukocytes were isolated by the lyses procedure and in vitro
exposed to TiO2 in RPMI. Experimental solutions were sonicated immediately before dosing the cells. Three exposure times (4, 24 and 48 h)
and three doses (20, 50 and 100 μg/ml) were tested. Genotoxicity was detected by the single-cell gel electrophoresis (or comet
assay) at pH ≥ 13, assessing single/double-strand breaks and alkali-labile sites. Cytotoxicity was also detected by the Trypan
blue exclusion method. Results showed that both the crystalline forms of TiO2 were genotoxic for bottlenose dolphin leukocytes, with a statistically significant increase of DNA fragmentation after exposure
to 50 and 100 μg/ml for 24 and 48 h. Although preliminary, these are the first data regarding the genetic susceptibility of
toothed cetaceans toward an “emerging” pollutant, such as TiO2 particles. 相似文献
97.
Patrizia Di Gennaro Silvana Bernasconi Fulvia Orsini Erika Corretto Guido Sello 《Tetrahedron: Asymmetry》2010,21(15):1885-1889
The use of two oxidoreductases (an aldoketo reductase from Escherichia coli JM109 and an alcohol dehydrogenase from Lactobacillus brevis) has demonstrated that it is possible to prepare enatiomerically pure diols in a one-pot operation. The reactions were applied to the synthesis of (1R)-1-[3-(hydroxymethyl)phenyl]ethanol and (1S)-1-phenylethane-1,2-diol, using a two-step procedure. The yield is nearly quantitative and the enantiomeric purity is greater than 95%. A third step has been introduced by adding a cell biocatalyst showing dihydrodiol dehydrogenase activity from Pseudomonas fluorescens N3. This allows for the preparation of 3-[(1R)-1-hydroxyethyl]benzoic acid and (2S)-hydroxy(phenyl)ethanoic acid. 相似文献
98.
99.
Anna Goldberg Vitali Grinberg Irina Utepova Oleg Chupakhin Igor Eremenko 《Journal of organometallic chemistry》2011,696(13):2607-2610
New ionic complexes [ML2(MeCN)2]?2Otf (M = Co or Ni; L = 6-ferrocenyl-2,2′-bipyridyl) were synthesized and characterized by single-crystal X-ray diffraction. Cyclic voltammograms of the compounds [ML2(MeCN)2]?2Otf in CH2Cl2 show good cycle stability over 100 cycles in the quasi-reversible oxidation potential range (from −0.25 to 0.5 V). 相似文献
100.
Summary In the present paper we develop a systematic analysis of the dispersion and dissipation effects on internal gravity waves
in fluids of geophysical interest. Dissipation induces a cut-off in the short wavelengths, leading to an admissible range
of waves. Defining a suitable criterion for detection of waves, an observable wave range results, in which the frequency dispersion
is nearly the same as for the inviscid case, whereas the amplitude is damped. The peculiar behaviour displayed by the dispersion
relationship for Prandtl number equal to one is discussed. 相似文献