João Alfredo Medeiros

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A systematic electron microscopic study was made of the structure of foveal cones of Macaca spp. Transverse sections of inner (IS) and outer segments (OS) were made in sequence, from the pigment epithelial zone (PEZ) to the outer limiting membrane (OLM). The smallest diameters of hundreds of cone sections were measured from electron micrographs with a Zeiss(More)
Mining of metallic sulfide ore produces acidic water with high metal concentrations that have harmful consequences for aquatic life. To understand the composition and structure of microbial communities in acid mine drainage (AMD) waters associated with Zn mine tailings, molecular diversity of 16S genes was examined using a PCR, cloning, and sequencing(More)
Scanning electron microscopic (SEM) observations of the rabbit retinal pigment epithelium (RPE) are reported both for normal tissue and for tissue subjected to laser radiation. In normal RPE, cells were observed to be closely packed and to have the characteristic hexagonal shape. The microvilli were abundant and of two types. Suprathreshold lesions were(More)
A novel digestion procedure based on sample combustion ignited by microwave radiation is proposed for organic samples. Certified samples of bovine liver, pig kidney, and skim milk were used as examples to demonstrate the performance of the proposed procedure. Cadmium and copper were determined in these samples by electrothermal atomic absorption(More)
Novel retinal irradiation techniques for laser damage studies are described; these are straightforward applications of the Fourier transform properties of an optical system. Interposing an appropriate diffracting screen between the laser source and the test eye enables one to simultaneously induce a number of discrete and precisely located retinal exposures(More)
The gamma-ray spectrum of 72Ge following the beta- decay of 72Ga has been studied using both single and gamma-gamma coincidence spectroscopy techniques. The energies and intensities of 110 gamma-rays have been determined, 26 of them were observed for the first time and 20 have been confirmed. Of the total number of gamma-rays observed, 95 have been placed(More)
In the retina from an eye enucleated for choroidal melanoma apposed rod outer segments were seen by transmission electron microscopy to be fusing together in groups by the confluence of their plasma membranes and the formation of cytoplasmic bridges between adjacent outer segments. These fusions were seen in areas distant from the melanoma but where the(More)
High resolution x-ray lithographic studies of cells from chick embryo hearts dried by the CO2 critical point method have been made with soft x-ray radiation of different wavelengths. A marked difference in the relief replica in polymethyl methacrylate (PMMA) resulting from the differential absorption by the dried cells of carbon K alpha radiation at 4.48 nm(More)
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