Mathematical and experimental investigation of water migration in plant xylem

Plant can take water from soil up to several metres high. However, the mechanism of how water rises against gravity is still controversially discussed despite a few mechanisms have been proposed. Also, there still lacks of a critical transportation model because of the diversity and complex xylem structure of plants. This paper mainly focuses on the water transport process within xylem and a mathematical model is presented. With a simplified micro channel from xylem structure and the calculation using the model of water migration in xylem, this paper identified the relationship between various forces and water migration velocity. The velocity of water migration within the plant stem is considered as detail as possible using all major forces involved, and a full mathematical model is proposed to calculate and predict the velocity of water migration in plants. Using details of a specific plant, the velocity of water migration in the plant can be calculated, and then compared to the experimental result from Magnetic Resonance Imaging (MRI). The two results match perfectly to each other, indicating the accuracy of the mathematical model, thus the mathematical model should have brighter future in further applications

Mineralogy and geochemistry of the Proterozoic Wafangzi ferromanganese deposit, China

In the Proterozoic Wafangzi deposit, China, sedimentary manganite ores are interstratified with red shale and silty limestone, whereas sedimentary rhodochrosite ores are interbedded with organic-rich black shale. Lateral change in mineralogy of the ores accompanying lateral changes in the host rocks demonstrates a classic example of facies variation in a "zoned" deposit. The manganite ores show a distinct Ce depletion reflecting a hydrothermal contribution in the seawater from which they precipitated. Absence of volcanics in the sequence suggests that the source of the hydrothermal input should be remote. It is likely that manganite precipitated directly from seawater in these deposits above the redox interface, whereas rhodochrosite was possibly early diagenetic formed in an anoxic environment. Manganite has been converted to braunite through a deoxidation-dehydration reaction during late diagenesis. Both types of ores have been thermally metamorphosed at the contact with igneous intrusions. Four distinct mineral assemblages have been identified in the thermally metamorphosed ores which were produced as a result of variations in bulk compositions (including volatiles) of the premetamorphic ores. In the final stage, the ores have been affected by supergene processes to give rise to pyrolusite-vernadite assemblages in the weathering zone