Applications Of A Granular Model And Percolation Theory To The Electrical Resistivity Of Heat Treated Endocarp Of Babassu Nut

The volume fraction, X, of the conducting phase in a granular structure defined in the carbon matrix and applicable to heat treated biomass carbons is calculated as a function of structural parameters obtained from X-ray diffraction and small angle X-ray scattering measurements. The room temperature electrical resistivity of heat treated endocarp of babassu nut with heat treatment temperatures up to 2200°C is thus presented as a function of X. The drop of twelve orders of magnitude in the resistivity is explained as a percolation transition in the granular structure, X being the fundamental parameter. The electronic conduction process occurs in this structure with the involvement of microcrystallites and micropores. © 1987.253417424Mrozowski, (1952) Phys. Rev., 85, p. 609Mrozowski, Errata (1952) Phys. Rev., 86, p. 1056Honda, Egi, Toyoda, Sanada, Furuta, (1964) Carbon, 1, p. 155Hernandez, Calderon, Luengo, Tsu, (1982) Carbon, 20, p. 201Otani, Polidoro, Otani, Craievich, An approximation for the two particle distribution of a hard-sphere fluid near a hard wall at low densities (1984) The Journal of Chemical Physics, 81, p. 887Boy, Marchand, (1967) Carbon, 5, p. 227Mrozowski, (1971) Carbon, 9Carmona, Delhaes, (1978) J. Appl. Phys., 49, p. 618Abeles, Sheng, Coutts, Arie, Structural and electrical properties of granular metal films (1975) Advances in Physics, 24, p. 407Warren, (1941) Phys. Rev., 59, p. 693Biscoe, Warren, (1942) J. Appl. Phys., 13, p. 364Hirsch, X-Ray Scattering from Coals (1954) Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 226, p. 143. , 2nd edLarsen, Chemistry and Physics of Coal Utilization-1980 (1981) AIP Proceedings No. 70, pp. 1-27. , 2nd ed., B.R. Cooper, L. Petrakis, New YorkMahajam, Walker, Jr., (1981) Chemistry of Coal Utilization—Sec. Suppl. Vol., pp. 173-186. , M.A. Elliot, John Wiley and Sons, New YorkEmmerich, (1986) Tese de Doutorado, , Universidade Estadual de Campinas, BrazilSherrer, (1918) Nachr. Akad. Ges. Wiss. Goettingen, 2, p. 98Klug, Alexander, (1974) X-ray Diffraction Procedures for Polycrystaline and Amorphous Materials, , 2nd ed., John Wiley and Sons, New YorkLewis, Singer, (1981) Chemistry and Physics of Carbon, 17, pp. 1-77. , 77nd ed., P.L. Walter Jr., P.A. Thrower, Marcell Dekker, LondonLewis, (1982) Carbon, 20, p. 519Guinier, Fournet, (1955) Small-Angle Scattering of X-ray, , John Wiley and Sons, New YorkSchmidt, International School on Teaching Crystallography for Materials Science (1983) Lecture Notes, 3. , 77nd ed., Campinas, BrasilClarke, Orton, Guest, (1978) Phys. Rev. B, 18, p. 1813Kirkpatrick, (1973) Rev. Mod. Phys., 45, p. 574Straley, (1982) J. Phys. C, 15, p. 2333Derrida, Stauffer, Herrmann, Vannimenus, Transfer matrix calculation of conductivity in three-dimensional random resistor networks at percolation threshold (1983) Journal de Physique Lettres, 44, pp. L-701Sher, Zallen, Critical Density in Percolation Processes (1970) The Journal of Chemical Physics, 53, p. 3759Shante, Kirkpatrick, An introduction to percolation theory (1971) Advances in Physics, 20, p. 325Seager, Pike, (1974) Phys. Rev. B, 10, p. 1435Coutts, (1976) Thin Solid Films, 38, p. 313Malliaris, Turner, (1971) J. Appl. Phys., 42, p. 614Aharoni, (1972) J. Appl. Phys., 43, p. 2463Ewen, Robertson, (1981) J. Phys. D, 14, p. 2253Hernandez, Martin, Chao, Tsu, Structural dependence of percolation in germanium films (1984) Applied Physics Letters, 44, p. 672Weast, (1981) Handbook of Chemistry and Physics, p. F 1. , 77nd ed., R.C. Weast, Chemical Rubber Co, Boca RatonFigueiredo, (1977) Atualidades do CNP, 9 (57), p. 76Reynolds, (1968) Physical Properties of Graphite, p. 120. , Elsevier Pub. Co, Londo

Erratum: Applications Of A Granular Model And Percolation Theory To The Electrical Resistivity Of Heat Treated Endocarp Of Babassu Nut (carbon (1987) 25:3 (417-424))

[No abstract available]51143

Genome-wide association analyses of physical activity and sedentary behavior provide insights into underlying mechanisms and roles in disease prevention

Although physical activity and sedentary behavior are moderately heritable, little is known about the mechanisms that influence these traits. Combining data for up to 703,901 individuals from 51 studies in a multi-ancestry meta-analysis of genome-wide association studies yields 99 loci that associate with self-reported moderate-to-vigorous intensity physical activity during leisure time (MVPA), leisure screen time (LST) and/or sedentary behavior at work. Loci associated with LST are enriched for genes whose expression in skeletal muscle is altered by resistance training. A missense variant in ACTN3 makes the alpha-actinin-3 filaments more flexible, resulting in lower maximal force in isolated type IIA muscle fibers, and possibly protection from exercise-induced muscle damage. Finally, Mendelian randomization analyses show that beneficial effects of lower LST and higher MVPA on several risk factors and diseases are mediated or confounded by body mass index (BMI). Our results provide insights into physical activity mechanisms and its role in disease prevention

Geoecological drivers of cerrado heterogeneity and 13C natural abundance in oxisols after land-use change Fatores geoecológicos das diferentes formações de cerrados - uma hipótese baseada em abundância natural de 13C e fotografia aérea

The 13C natural abundance technique was applied to study C dynamics after land-use change from native savanna to Brachiaria, Pinus, and Eucalyptus in differently textured Cerrado Oxisols. But due to differences in the d13C signatures of subsoils under native savanna and under introduced species, C substitution could only be calculated based on results of cultivated soils nearby. It was estimated that after 20 years, Pinus C had replaced only 5 % of the native C in the 0-1.2 m layer, in which substitution was restricted to the top 0.4 m. Conversely, after 12 years, Brachiaria had replaced 21 % of Cerrado C to a depth of 1.2 m, where substitution decreased only slightly throughout the entire profile. The high d13C values in the subsoils of the cultivated sites led to the hypothesis that the natural vegetation there had been grassland rather than Cerrado sensu stricto, in spite of the comparable soil and site characteristics and the proximity of the studied sites. The hypothesis was tested using aerial photographs of 1964, which showed that the cultivated sites were located on a desiccated runoff head. The vegetation shift to a grass-dominated savanna formation might therefore have occurred in response to waterlogging and reduced soil aeration. A simple model was developed thereof, which ascribes the different Cerrado formations mainly to the plant-available water content and soil aeration. Soil fertility is considered of minor significance only, since at the studied native savanna sites tree density was independent of soil texture or nutrient status.<br>A abundância natural de 13C foi utilizada para estudar a dinâmica de carbono em latossolos de textura média e argilosa após plantação de pastagens (Brachiaria decumbens) e reflorestamentos (Pinus caribaea e Eucalyptus citriodora). Considerando as diferenças de d13C nos subsolos das savanas nativas e das espécies introduzidas, pôde-se calcular a substituição de carbono somente para os solos argilosos, baseando-se em resultados publicados de d13C em solos adjacentes. Estimou-se que somente 5 % do carbono nativo foram substituidos após 20 anos de plantação com pinus na camada de 0-1,2 m, ficando a substituição restrita aos primeiros 0,4 m do solo. Na pastagem de 12 anos, 21 % do carbono novo foram introduzidos na camada de de 0-1,2 m, sendo a substituição diminuída gradativamente pelo perfil inteiro. De acordo com os altos valores de d13C nos subsolos das áreas cultivadas, levantou-se a hipótese de que a vegetação natural teria sido de campo limpo em vez de cerrado stricto sensu apesar da semelhança dos solos e da proximidade dos sítios estudados. A hipótese foi testada com fotos aéreas de 1964, mostrando que as áreas cultivadas encontravam-se numa cabeceira de escoamento ressecada. Portanto, a vegetação dominada por gramíneas pode ter sido induzida pela hidromorfia e pela baixa aeração do solo. Com base nessas observações, desenvolveu-se um modelo simplificado, atribuindo às diferentes formações de cerrados o acesso de água para as plantas e a aeração do solo. A fertilidade do solo foi considerada de menor importância porque a densidade arbórea das áreas de cerrados encontrava-se independente da textura ou do nível de nutrientes dos solos