应用高效液相色谱分析谷物中的维生素B_6

用偏磷酸溶液抽提和高效液相色谱定量分析的方法,测定了小麦、大麦、玉米、小米和高粱等谷物中各种维生素B_6的含量.研究结果表明,谷物中所含维生素B_6的主要形式是游离吡哆醇和吡哆醇葡萄糖甙,各种谷物的维生素B_6含量与其品种和产地等因素有关.     

Efferent control of the carotid body chemoreceptor

Résumé Potentiels d'action enrégistrés dans les fibres nerveuses des chémorécepteurs de la carotide du Chat. La fréquence des potentiels augmente en réponse à toutes les tensions d'oxygène quand le nerf sinusal est réséqué. La stimulation de l'extrémité périphérique provoque une diminution prolongée de l'activité chémoréceptrice.     

Near-surface wetland sediments as a source of arsenic release to ground water in Asia

Tens of millions of people in south and southeast Asia routinely consume ground water that has unsafe arsenic levels. Arsenic is naturally derived from eroded Himalayan sediments, and is believed to enter solution following reductive release from solid phases under anaerobic conditions. However, the processes governing aqueous concentrations and locations of arsenic release to pore water remain unresolved, limiting our ability to predict arsenic concentrations spatially (between wells) and temporally (future concentrations) and to assess the impact of human activities on the arsenic problem. This uncertainty is partly attributed to a poor understanding of groundwater flow paths altered by extensive irrigation pumping in the Ganges-Brahmaputra delta, where most research has focused. Here, using hydrologic and (bio)geochemical measurements, we show that on the minimally disturbed Mekong delta of Cambodia, arsenic is released from near-surface, river-derived sediments and transported, on a centennial timescale, through the underlying aquifer back to the river. Owing to similarities in geologic deposition, aquifer source rock and regional hydrologic gradients, our results represent a model for understanding pre-disturbance conditions for other major deltas in Asia. Furthermore, the observation of strong hydrologic influence on arsenic behaviour indicates that release and transport of arsenic are sensitive to continuing and impending anthropogenic disturbances. In particular, groundwater pumping for irrigation, changes in agricultural practices, sediment excavation, levee construction and upstream dam installations will alter the hydraulic regime and/or arsenic source material and, by extension, influence groundwater arsenic concentrations and the future of this health problem.