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991.
Ruth Müller Christian Wiencke Kai Bischof Bernd Krock 《Photochemistry and photobiology》2009,85(4):970-977
Phlorotannins have often been considered to act as UV-protective compounds in zoospores of brown algae. However, only the absorption characteristics of zoospores under UV exposure have been determined and no data are available on the actual content of phlorotannins or on temperature–UV interactions. Therefore, we determined the absorbance spectra and the phlorotannin contents in zoospore suspensions of three Arctic species ( Saccharina latissima , Laminaria digitata , Alaria esculenta ), and in the media surrounding zoospores after exposure to different radiation (400–700, 320–700, 295–700 nm) and temperature (2–18°C) conditions for 8 h. Absorption typical of phlorotannins with a maximum at 276 nm was monitored in zoospore suspensions as well as in the media surrounding zoospores, but the results depended strongly on radiation treatments and on zoospore densities. Surprisingly, the content of UV-absorbing phlorotannins subsequent to different exposures did not change in any of the three species. The observed exceptional absorption properties could, therefore, not be related to phlorotannin contents. These findings are discussed in light of a strong phlorotannin investment from sporophytes during spore release and a minor UV-protective role of phlorotannins for zoospores of Arctic kelp species. 相似文献
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A survey represented mainly by means of glasses of the borosilicate system shows the generally valid limits of the applicability of the crack growth model and the essential influence of the corrosion of glasses on fatigue. A close correlation between macroscopic crack growth and fatigue was affirmed for samples with fresh, slightly corroded cracks. If the state of corrosion of the samples is advanced, the influence of region 2 is reduced and the fatigue limit is increased. Processes of corrosion during the measurement influence the fatigue curve prevailingly in the range of great time-to-failure, in particular the slope in region 1. The results indicate the high complexity of the effective chemomechanical processes during the fatigue measurements. 相似文献
998.
We present a direct and rather elementary method for defining and analyzing one-dimensional Schrödinger operators H = −d2/dx2 + μ with measures as potentials. The basic idea is to let the (suitably interpreted) equation −f′′ + μ f = zf take center stage.We show that the basic results from direct and inverse spectral theory then carry over to Schrödinger operators with measures. 相似文献
999.
We examine domino tilings of rectangular boards, which are in natural bijection with perfect matchings of grid graphs. This
leads to the study of their associated perfect matching polytopes, and we present some of their properties, in particular,
when these polytopes are Gorenstein. We also introduce the notion of domino stackings and present some results and several
open questions. Our techniques use results from graph theory, polyhedral geometry, and enumerative combinatorics. 相似文献
1000.
Brajendra K. Singh Christian V. Stevens Davy R.J. Acke Erik V. Van der Eycken 《Tetrahedron letters》2009,50(1):15-4274
A continuous flow procedure has been elaborated for the copper(II)-mediated N- and O-arylation of a range of compounds with arylboronic acids using a commercial microreactor setup. The compounds could be continuously generated in good yields paving the way for efficient scalability. 相似文献