The insecticidal nonprotein amino acid S-(-carboxyethyl)-cysteine (S-CEC) is the major free amino acid in the seeds of severalCalliandra spp. where it accounts for up to 2.9 % of dry weight. Lesser amounts of other related S-containing amino acids and an array of nonprotein imino acids derived from pipecolic acid are other constituents. High concentrations of imino acids, which also show insecticidal activity, are maintained in the mature leaves, but sulfur compounds are lacking. In this study the disappearance of S-CEC from the germinating seeds and young seedlings ofC. rubescens was monitored over time. After 10 weeks, S-CEC continues to be found in high concentrations in the stems and new leaves. As young leaves mature, sulfur compounds quickly decrease in concentration. Traces of S-CEC are found in new leaves of plants up to nine months after germination. Whether high concentration of S-CEC in young leaves is due to transportation from the seed or de novo synthesis is unclear. The ecological implications are discussed. 相似文献
In this paper the effect of temperature and filler content ? on electrical resistivity of styrene-acrylonitrile polymer filled with iron or aluminium powders has been investigated. The resistivity of such composites decreases suddenly by several orders of magnitude at a critical volume concentration ?c, which depends on the size distribution of particles and on thermal history. For filler content lower than ?c, the resistivity decreases with increasing temperature, whereas for ? > ?c there is a sudden increase in resistivity at temperatures near the glass transition temperature of the polymeric matrix. This effect is more pronounced than the previously reported data on other composite systems. 相似文献
Infrared and Raman spectra of atactic PMMA and infrared spectra of stereoregular PMMA and of its four deuterated derivatives , were measured. They were used to assign the bands of stretching and deformation vibrations of CH2, CCH3 and OCH3 groups in the infrared and Raman spectra and to discuss the effect of stereoregularity on these bands in the infrared spectra. 相似文献
In this paper we explore differences in use of the so-called ‘logical’ elements of language such as quantifiers and conditionals,
and use this to explain differences in performance in reasoning tasks across subject groups with different educational backgrounds.
It is argued that quantified sentences are difficult natural bases for reasoning, and hence more prone to elicit variation
in reasoning behaviour, because they are chiefly used with a pre-determined domain in everyday speech. By contrast, it is
argued that conditional sentences form natural premises because of the function they serve in everyday speech. Implications
of this for the role of logic in modelling human reasoning behaviour are briefly considered. 相似文献
Summary Carboxyester- and carboxyamido-terminated polydimethylsiloxanes were obtained through the reaction of cyclic anhydrides (succinic, maleic and phthalic anhydride) with hydroxypropyl- and aminoalkyl-terminated polydimethylsiloxanes, respectively. The reactivity of the starting compounds and the influence of the reaction conditions on the characteristics of the final products are discussed.Part 1: Eur. Polym. J., in press 相似文献
The Journal of Supercomputing - The multiplication of computing cores in modern processor units permits revisiting the design of classical algorithms to improve computational performance in complex... 相似文献
The Millimetre and Infrared Testa Grigia Observatory 2.6-m Cassegrain telescope has been designed to allow high-sensitivity observations in the millimeter spectral range. For this purpose, in order to reduce unwanted contributions from local foregrounds, we adopted a sky-chopping technique, by wobbling the telescope subreflector. We describe the design and performance of the wobbling system, which can endure external forced two and three fields square-wave modulation and includes features such as high frequency, high amplitude, high duty cycle, low microphonics, and high stability. 相似文献