86,700 research outputs found
Phenols and lignans from Chenopodium album.
No full textCutillo, Francesca; Dellagreca, Marina; Gionti, Melania; Previtera, Lucio; Zarrelli, Armando. Phenols and lignans from Chenopodium album. Phytochemical Analysis (2006), 17(5), 344-349. CODEN: PHANEL ISSN:0958-0344. CAN 146:375816 AN 2006:1047207 CAPLU
IMPROVING THE PERFORMANCE OF METHYLALUMOXANE: A FACILE AND EFFICIENT METHOD TO TRAP FREE TRIMETHYLALUMINUM
No full texthe presence of "free" trimethylaluminum (TMA) in methylalumoxane (MAO) solutions can be highly detrimental to the performance of metallocene and "post-metallocene" olefin polymerization catalysts. The most used strategy to remove "free" TMA is to evaporate MAO solutions to dryness, until a free-flowing white powder ("solid MAO") is left. This procedure is tedious and potentially hazardous, because in some cases the distillate is a concentrated hydrocarbon solution of TMA. Moreover, "solid MAO" is poorly soluble in common polymerization media, and once in solution it can regenerate TMA to some extent. This communication reports on a facile alternative, which consists in the controlled addition of a sterically hindered phenol, such as 2,6-di-tert-butylphenol, effectively trapping "free" TMA. We show here that 2,6-di-tert-butylphenol/MAO solutions activate equally well the dichloro-precursors of well-known zirconocene and bis(phenoxyimine)Ti catalysts, and that their use in propene polymerization results in a substantially higher productivity, polymer stereoregularity, and/or average molecular mass compared with activation by MAO alone
A quantitative comparison of stochastic mortality models on Italian population data
No full textMortality models play a basic role in the evaluation of longevity risk by demographers and actuaries. Their performance strongly depends on the different patterns shown by mortality data in different countries. A comprehensive quantitative comparison of the most used methods for forecasting mortality is presented, aimed at evaluating both the goodness of fit and the forecasting performance of these mortality models on Italian demographic data. First, the classical Lee–Carter model is compared to some generalizations that change the order of Singular Value Decomposition approximation and include cohort effects. Then one-way and two-way functional data approaches are considered. Such an analysis extends the current literature on Italian mortality data, on both the number of considered models and their rigorous assessment. Results indicate that generally functional models outperform the classical ones; unfortunately, even if the cohort effect is quite substantial, a suitable procedure for its robust and efficient evaluation is yet to be proposed. To this end, a viable correction for cohort effects is suggested and its performance tested on some of the presented models
Lignans and neolignans from Brassica fruticulosa: effects on seed germination and plant growth
No full textFive lignans, five neolignans, two sesquilignans, and a dilignan were identified from a phytotoxic extract of Brassica fruticulosa L. Compounds 8, 9, 12, and 13 have been isolated for the first time. Structures were determined on the basis of their spectroscopic features. Their effects on the germination and growth of two dicotyledons, Lactuca sativa (lettuce) and Lycopersicon esculentum (tomato), and a monocotyledon, Allium cepa (onion), as standard target species have been studied
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