983 resultados para WHITE-MATTER HYPERINTENSITIES
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"This edition also includes numerous illustrations, further particulars of the history of De-he-wä-mis, and other interesting matter collected and arranged by Wm. Pryor Letchworth."
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Advertising matter: p. 32.
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Photostatic reproduction, on 4 leaves, of the copy in the Bancroft Library of the University of California.
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The total number of nephrons in normal human kidneys varies over a 10-fold range. This variation in total nephron number leads us to question whether low nephron number increases the risk of renal disease in adulthood. This review considers the available evidence in humans linking low nephron number/reduced nephron endowment and the susceptibility to renal disease. Total nephron number in humans has been directly correlated with birth weight and inversely correlated with age, mean glomerular volume, and hypertension. Low nephron number may be the result of suboptimal nephrogenesis during kidney development and/or loss of nephrons once nephrogenesis has been completed. Low nephron number is frequently, but not always, associated with hypertrophy of remaining glomeruli. This compensatory hypertrophy has also been associated with a greater susceptibility for kidney disease. Three human studies have reported reduced nelphron number in subjects with a history of hypertension. This correlation has been observed in White Europeans, White Americans (but not African Americans) and Australian Aborigines. Studies in additional populations are required, as well as a greater understanding of the fetal environmental and genetic determinants of low nephron number.
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The redox stratification of bottom sediments in Kandalaksha Bay, White Sea, is characterized by elevated concentrations of Mn (3-5%) and Fe (7.5%) in the uppermost layer, which is two orders of magnitude and one and a half times, respectively, higher than the average concentrations of these elements in the Earth's crust. The high concentrations of organic matter (Corg = 1-2%) in these sediments cannot maintain (because of its low reaction activity) the sulfate-reducing process (the concentration of sulfide Fe is no higher than 0.6%). The clearest manifestation of diagenesis is the extremely high Mn2+ concentration in the silt water (>500 µM), which causes its flux into the bottom water, oxidation in contact with oxygen, and the synthesis of MnO2 oxy-hydroxide enriching the surface layer of the sediments. Such migrations are much less typical of Fe. Upon oxygen exhaustion in the uppermost layer of the sediments, the synthesized oxyhydroxides (MnO2 and FeOOH) serve as oxidizers of organic matter during anaerobic diagenesis. The calculated diffusion-driven Mn flux from the sediments (280 µM/m**2 day) and corresponding amount of forming Mn oxyhydrate as compared to opposite oxygen flux to sediments (1-10 mM/m**2 day) indicates that >10% organic matter in the surface layer of the sediments can be oxidized with the participation of MnO2. The roles of other oxidizers of organic matter (FeOOH and SO4**2-) becomes discernible at deeper levels of the sediments. The detailed calculation of the balance of reducing processes testifies to the higher consumption of organic matter during the diagenesis of surface sediments than it follows from the direct determination of Corg. The most active diagenetic redox processes terminate at depths of 25-50 cm. Layers enriched in Mn at deeper levels are metastable relicts of its surface accumulation and are prone to gradual dissemination.