Effect on guinea pigs of consuming an excessive quantity of phosphates

Digitized 2007 AES.Includes bibliographical references (page 8)

The Mercedes Au-Ag District, Sonora, Mexico: Geology, Geochemistry and Structure of a Sierra Madre Low-sulfidation Epithermal System

The Mercedes district contains a series of Oligocene-aged low-sulfidation quartz-carbonate veins with economic Au and Ag mineralization. The veins are hosted in dextral-normal faults contained within andesitic flows, flow breccias and lahar deposits within the Sierra Madre Occidental volcanic sequence. These are localized within two structural basins adjacent to a northwest-trending anticline that exposes pre-mineral tuffs and sedimentary units. The vein mineralogy is characterized by a unique ferruginous green quartz and Mn-oxide bearing calcite assemblage along with both primary and supergene Au-Ag mineralization. Three vein systems within the district were studied: the Mercedes, Klondike and Lupita/Diluvio systems. The Mercedes vein contains the highest grades within the district, is highly-brecciated and displays weak and anomalous geochemical zonation patterns attributed to a high degree of hydrothermal and tectonic brecciation and permeability controlled supergene remobilization. The vein possesses a 4-phase paragenesis. Phase I was the major mineralizing phase, introducing native Au as well as unidentified silver minerals (likely both electrum and silver sulfosalts) along with green quartz and pyrite. Phase II began during a hydrothermal/tectonic brecciation event and appears as a dark Mn-oxide bearing calcite and rhodochrosite cement between phase I breccias. Phase III was a later quartz and calcite veinlet event with local amounts of dark carbonate. Phase IV was the final event, and is a post-mineral oxidation event creating hematite after pyrite, limonite, zeolites and cerargyrite. Statistical evaluation of the geochemical data reveals that Au and Ag grades are poorly correlated with one another, due to post-mineral reworking of the silver mineralogy. Au is most strongly correlated with Pb, Cu, Hg, Zn and Se in that order. Ag is somewhat correlated with Se and Hg, with only weak (<0.5) correlations with other elements. Ca is positively correlated with only C and Mn, supporting the fact that the dark carbonate phase is a Mn-oxide/calcite intergrowth. This is interpretation is further supported by XRF analysis of the carbonates and the presence of boxworks of pyrolusite and other Mn-oxides in former carbonate sites leached by acidic groundwaters. The Klondike vein displays a similar mineralogy and paragenesis to the Mercedes vein, but retains a higher degree of structural order that results in a less-permeable system displaying a stronger and more apparent classical geochemical zonation. Geochemical correlations display a similar pattern to Mercedes with Pb, Cu and Hg being the most correlative elemental indicators of Au grade. Ag correlations with these elements are somewhat higher than in Mercedes. The Lupita/Diluvio system is hosted within a listric structure and consists of the fault-hosted Lupita vein and the overlying Diluvio stockwork, hosted within a gravitationally-displaced block of a quartz-lithic tuff that had been structurally prepared for mineralization during its displacement along the Lupita structure. The Lupita/Diluvio system displays a similar mineralogy and paragenesis to the Mercedes and Klondike vein systems. From these data, a number of inferences can be made. First is that the high degree of brecciation and transport within the Mercedes vein has destroyed the classical epithermal geochemical zonation that is somewhat present in the Klondike system and better defined in the Lupita/Diluvio system. This "washing-out" was accomplished through both physical transport and overprinting during multiple hydrothermal pulses. Second, supergene remobilization related to meteoric fluids has altered the grades and distribution of precious metals as well as further modified the geochemical zonation. The presence of cerargyrite and mineralogical evidence suggests that these processes may be related to the poor Ag recoveries (~30%) and erratic Au/Ag ratios within the vein systems. Third, it is apparent that the structural weaknesses that localized the mineralization on the property reflect the regional structural fabric of both dextral and extensional tectonics

Texture characterization in DIRSIG

This research project tested the quality of DIRSIG\u27s texture characterization routines for a grass target and potential techniques to improve it. The objective of the DIRSIG is to produce output images that are analogous to real image outputs so the model can be applied to a wide range of problems. It is very important that both spectral and spatial properties of targets are modeled correctly to obtain realistic results. DIRSIG applies texture to each pixel spectrally. Current techniques examine only one bandpass region, using statistical means to compare a texture image in that bandpass with a spectral database in order to determine which curve will be used for a particular pixel. The research in this project examined the quality of this procedure, and several potential methods for improvement. DIRSIG images were generated to simulate two different scenes for which real images exist. ENVI’s principle components analysis utility was than used to quantify the information in each image for comparison. Modifications were than made to the process to expand the spectral database, and incorporate a new algorithm into DIRSIG that examines multiple bandpass regions when determining which spectra to use for a pixel. The output for each of these new scenarios was than tested for comparison with DIRSIG’s previous results, and the results obtained for the truth images. This research has quantitatively examined the ability of DIRSIG to replicate real world texture characteristics, specifically for a grass target. Research discovered a large gap between the amount of information that is contained in images of real world data and those simulated by DIRSIG. Expanding the spectral database did produce a slight increase in results, increasing the qualitative appearance of the image as well. The amount of data contained in the DIRSIG image remained significantly less than that contained in the real image. Increasing the number of bandpasses employed by DIRSIG in determining which spectra to map onto a particular pixel, results indicated two different concepts. Adding one band increased the ability of DIRSIG to map correctly choose the spectra. Additional bandpasses may increase the quality of an image, however, choosing too many bandpass regions for an image can cause the resulting quality of the image to decrease. The process is very complex, the output quality is dependent on the particular imaging system that is being modeled, the bandpasses that are chosen, and the amount of bandpasses that are used as references

Extension of Yeast Chronological Lifespan by Methylamine

Background: Chronological aging of yeast cells is commonly used as a model for aging of human post-mitotic cells. The yeast Saccharomyces cerevisiae grown on glucose in the presence of ammonium sulphate is mainly used in yeast aging research. We have analyzed chronological aging of the yeast Hansenula polymorpha grown at conditions that require primary peroxisome metabolism for growth. Methodology/Principal Findings: The chronological lifespan of H. polymorpha is strongly enhanced when cells are grown on methanol or ethanol, metabolized by peroxisome enzymes, relative to growth on glucose that does not require peroxisomes. The short lifespan of H. polymorpha on glucose is mainly due to medium acidification, whereas most likely ROS do not play an important role. Growth of cells on methanol/methylamine instead of methanol/ammonium sulphate resulted in further lifespan enhancement. This was unrelated to medium acidification. We show that oxidation of methylamine by peroxisomal amine oxidase at carbon starvation conditions is responsible for lifespan extension. The methylamine oxidation product formaldehyde is further oxidized resulting in NADH generation, which contributes to increased ATP generation and reduction of ROS levels in the stationary phase. Conclusion/Significance: We conclude that primary peroxisome metabolism enhanced chronological lifespan of H. polymorpha. Moreover, the possibility to generate NADH at carbon starvation conditions by an organic nitrogen source supports further extension of the lifespan of the cell. Consequently, the interpretation of CLS analyses in yeast should include possible effects on the energy status of the cell.