Autoradiographic evidence of tritiated indolyl-3-acetic acid in epicotyl tissue ofPhaseolus coccineus

Résumé Des tronçons d'épicotyles de plantules dePhaseolus coccineus ont été traités à l'acide indole acétique (AIA) marqué au tritium. Ces tronçons ont été soumis au «freezing-drying», puis réduits en coupes minces, en évitant tout contact avec un solvant quelconque. L'étude autoradiographique révéla la présence de l'AIA dans tous les types de tissu vivant.     

Hafnium isotope evidence for a transition in the dynamics of continental growth 3.2 Gyr ago

Earth's lithosphere probably experienced an evolution towards the modern plate tectonic regime, owing to secular changes in mantle temperature. Radiogenic isotope variations are interpreted as evidence for the declining rates of continental crustal growth over time, with some estimates suggesting that over 70% of the present continental crustal reservoir was extracted by the end of the Archaean eon. Patterns of crustal growth and reworking in rocks younger than three billion years (Gyr) are thought to reflect the assembly and break-up of supercontinents by Wilson cycle processes and mark an important change in lithosphere dynamics. In southern West Greenland numerous studies have, however, argued for subduction settings and crust growth by arc accretion back to 3.8 Gyr ago, suggesting that modern-day tectonic regimes operated during the formation of the earliest crustal rock record. Here we report in situ uranium-lead, hafnium and oxygen isotope data from zircons of basement rocks in southern West Greenland across the critical time period during which modern-like tectonic regimes could have initiated. Our data show pronounced differences in the hafnium isotope-time patterns across this interval, requiring changes in the characteristics of the magmatic protolith. The observations suggest that 3.9-3.5-Gyr-old rocks differentiated from a >3.9-Gyr-old source reservoir with a chondritic to slightly depleted hafnium isotope composition. In contrast, rocks formed after 3.2 Gyr ago register the first additions of juvenile depleted material (that is, new mantle-derived crust) since 3.9 Gyr ago, and are characterized by striking shifts in hafnium isotope ratios similar to those shown by Phanerozoic subduction-related orogens. These data suggest a transitional period 3.5-3.2 Gyr ago from an ancient (3.9-3.5 Gyr old) crustal evolutionary regime unlike that of modern plate tectonics to a geodynamic setting after 3.2 Gyr ago that involved juvenile crust generation by plate tectonic processes.     

Gough-Stewart平台运动学设计理论与方法

以Ｇｏｕｇｈ－Ｓｔｅｗａｒｔ平台为对象，根据位置空间的几何形状特征，提出了工作空间半径比的概念，导出了局部灵活度和工作空间半径比的解析解答。通过单调性分析提示出设计参数对上述运动学指标的影响规律，并提出一种在不发生支链干涉条件下，可使末端执行器具有给定姿态能力，且使局部灵活度和工作空间半径比加权最优的尺度综合方法。     

Distributions of cholesterol amongst liver subcellular fractions

Zusammenfassung Der Cholesteringehalt der subzellulären Komponenten von Lebergewebe verschiedener Tierarten wurde untersucht. Die subzellulären Fraktionen bestanden hauptsächlich aus Mitochondrien und waren relativ frei von Mikrosomen.