6,490 research outputs found
AlkoxyalleneâBased LANCA ThreeâComponent Synthesis of 1,2âDiketones, Quinoxalines, and Unique Isoindenone Dimers and a Computational Study of the Isoindenone Dimerization
A series of ÎČâalkoxyâÎČâketoenamides was prepared by the wellâestablished LANCA threeâcomponent reaction of lithiated 1â(2âtrimethylsilylethoxy)âsubstituted allenes, nitriles, and α,ÎČâunsaturated carboxylic acids. The αâtertâbutylâsubstituted compounds were smoothly converted into the expected 1,2âdiketones by treatment with trifluoroacetic acid. A subsequent condensation of the 1,2âdiketones with oâphenylenediamine provided the desired highly substituted quinoxalines in good overall yield. Surprisingly, the αâphenylâsubstituted ÎČâalkoxyâÎČâketoenamides investigated afford not only the expected 1,2âdiketones, but also pentacyclic compounds with an antiâtricyclo[4.2.1.12,5]decaâ3,7âdieneâ9,10âdione core. These interesting products are very likely the result of an isoindenone dimerization which was mechanistically studied with the support of DFT calculations. Under the strongly acidic reaction conditions, a stepwise reaction is likely leading to a protonated isoindenone as reactive intermediate. It may first form a van der Waals complex with a neutral isoindenone before the two regioâ and diastereoselective ring forming steps occur. Interestingly, two neutral or two protonated isoindenones are also predicted to dimerize giving the observed pentacyclic product
Nonlinear ac susceptibility studies of high- rings: Influence of the structuring method and determination of the flux creep exponent
We have studied the influence of the patterning procedure on the critical
current density of high- YBaCuO thin rings using the
nonlinear ac susceptibility method. At no applied dc magnetic field we have
found that laser ablation degrades strongly the critical current density
whereas ion beam etching has only a weak influence on it. From the measurements
at different frequencies and dc magnetic fields we analyzed the influence of
flux creep and obtained the field dependence of the flux creep exponent. Our
data reconfirm the recently observed scaling relation for the nonlinear
susceptibility response of type-II superconductors.Comment: 10 pages, 12 figure
BekÀmpfung der Blutlaus durch Freilassung von Blutlauszehrwespen aus Massenzucht
Ziel des Projektes war die Erarbeitung eines Verfahrens zur Regulierung der Blutlaus (Eriosoma lanigerum), eines wirtschaftlich bedeutenden SchĂ€dlings im ökologischen Obstbau, gegen den es momentan keinerlei wirksame BekĂ€mpfungsmöglichkeiten gibt. Hierzu wurde versucht, aus der Erfahrung vorangegangener Versuchsergebnisse ein Verfahren zur BekĂ€mpfung der Blutlaus durch den Einsatz von Blutlauszehrwespen (Aphelinus mali) aus einer NĂŒtzlingszucht zu entwickeln und zur Praxisreife zu bringen. Die Zehrwespe ist ein natĂŒrlich vorkommender Gegenspieler, dem es aufgrund mangelnder Synchronisation zwischen SchĂ€dling und NĂŒtzling nicht rechtzeitig gelingt, den Schaden durch die Blutlaus zu verhindern. 2004 konnten mit dem Einsatz von parasitierten Blutlausmumien keine zufrieden stellenden Ergebnisse erzielt werden. Die Produktion der Mumien war fĂŒr den NĂŒtzlingsproduzenten mit erheblichen Schwierigkeiten verbunden. Die wĂŒnschenswerte Lagerung der Mumien fĂŒhrte zu hoher MortalitĂ€t und Verzögerungen im Schlupfverlauf. Die Versuche mit adulten Zehrwespen 2005 zeigten im Gegensatz zu den Versuchen mit Mumien im Vorjahr auswertbare Ergebnisse. Allerdings reichten auch hier die erzielten Wirkungsgrade nicht fĂŒr eine vollstĂ€ndige BekĂ€mpfung und damit der Vermeidung von SchĂ€den an den BĂ€umen aus. Die Parasitierungsleistung von A. mali wird im Wesentlichen von zwei Faktoren beeinflusst: der Temperatur und der vorhandenen Lichtmenge. Unter normalen Witterungsbedingungen macht daher der zeitige Einsatztermin im FrĂŒhjahr keinen Sinn, da A. mali in der Regel keine geeigneten Vermehrungsbedingungen vorfindet. Zudem ist A. mali der Blutlaus in Bezug auf die Vermehrungsrate unterlegen. Ein Kombinationsverfahren mit einer Ălspritzung und nachfolgender Freilassung von Zehrwespen unter klimatisch gĂŒnstigeren Bedingungen wurde 2006 durchgefĂŒhrt und brachte mit Wirkungsgraden von etwa 60 % Ă€hnliche Ergebnisse wie 2005. Die Blutlauszehrwespe A. mali ist in der Lage, den Befall durch die Blutlaus zu reduzieren, jedoch nicht zu regulieren und SchĂ€den an den BĂ€umen vollstĂ€ndig zu verhindern
Flocs, flows, and mechanisms decoupling larval supply from settlement
Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 57 (2012): 936-944, doi:10.4319/lo.2012.57.4.0936.Larval supply, settlement (24 h), and recruitment were measured simultaneously with flow and flocculated particulates (flocs) in a muddy, coastal embayment. Fortuitous observations indicated that flocs drifting above the bed touched down at slack tide. Unexpectedly, results showed that larval supply did not portend settlement for the two most abundant polychaetes, Mediomastus ambiseta (resident mud dweller) and Sabellaria vulgaris (nonresident sand dweller). Both variables fluctuated widely and were decoupled. Colonization of mud vs. sand trays was not significantly different, also due to high variances. A statistical power analysis indicated that resolving selectivity would require 45 (median) paired, replicate treatments. Time series of near-bed planktonic larvae showed sizeable and sporadic spikes. Even 24-h means failed to predict settlement. Sabellaria was numerous in zooplankton pump collections, rare in trays, and nonexistent in ambient sediments. In contrast, Mediomastus was absent from pump samples, but dominated mud trays and bottom cores. Floc contents, however, lend insight into these distributions. Densities (of order 105 m-3) of Sabellaria and Mediomastus in flocs greatly exceeded those in tray and pump samples (of order 103 m-3). Located between the water column and seafloor, organic-rich flocs may offer transient larvae food, shelter, transport, and perusal of settlement sites. When aggregates touch down, entrained Mediomastus might exit upon contact with suitable ambient sediments, whereas nonresident Sabellaria remain suspended. Flocs may thus play a critical role in shaping connectivity and structuring species distributions.This study was supported by
the National Science Foundation (Division of Ocean Sciences,
OCE 08-52361) and the University of California at Los Angeles
Council on Research
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