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Representative elementary length to measure soil mass attenuation coefficient.

ABSTRACT: With increasing demand for better yield in agricultural areas, soil physical property representative measurements are more and more essential. Nuclear techniques such as computerized tomography (CT) and gamma-ray attenuation (GAT) have been widely employed with this purpose. The soil mass attenuation coefficient (μ(s)) is an important parameter for CT and GAT analysis. When experimentally determined (μ(es)), the use of suitable sized samples enable to evaluate it precisely, as well as to reduce measurement time and costs. This study investigated the representative elementary length (REL) of sandy and clayey soils for μ(es) measurements. Two radioactive sources were employed ((241)Am and (137)Cs), three collimators (2-4 mm diameters), and 14 thickness (x) samples (2-15 cm). Results indicated ideal thickness intervals of 12-15 and 2-4 cm for the sources (137)Cs and (241)Am, respectively. The application of such results in representative elementary area (REA) evaluations in clayey soil clods via CT indicated that μ(es) average values obtained for x > 4 cm and source (241)Am might induce to the use of samples which are not large enough for soil bulk density evaluations (ρ(s)). As a consequence, ρ(s) might be under- or overestimated, generating inaccurate conclusions about the physical quality of the soil under study.

SUBMITTER: Borges JA

PROVIDER: S-EPMC3929488 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Project description:BackgroundUnderstanding inequality in infectious disease burden requires clear and unbiased indicators. The Gini coefficient, conventionally used as a macroeconomic descriptor of inequality, is potentially useful to quantify epidemiological heterogeneity. With a potential range from 0 (all populations equal) to 1 (populations having maximal differences), this coefficient is used here to show the extent and persistence of inequality of malaria infection burden at a wide variety of population levels.MethodsFirst, the Gini coefficient was applied to quantify variation among World Health Organization world regions for malaria and other major global health problems. Malaria heterogeneity was then measured among countries within the geographical sub-region where burden is greatest, among the major administrative divisions in several of these countries, and among selected local communities. Data were analysed from previous research studies, national surveys, and global reports, and Gini coefficients were calculated together with confidence intervals using bootstrap resampling methods.ResultsMalaria showed a very high level of inequality among the world regions (Gini coefficient, G = 0.77, 95% CI 0.66-0.81), more extreme than for any of the other major global health problems compared at this level. Within the most highly endemic geographical sub-region, there was substantial inequality in estimated malaria incidence among countries of West Africa, which did not decrease between 2010 (G = 0.28, 95% CI 0.19-0.36) and 2018 (G = 0.31, 0.22-0.39). There was a high level of sub-national variation in prevalence among states within Nigeria (G = 0.30, 95% CI 0.26-0.35), contrasting with more moderate variation within Ghana (G = 0.18, 95% CI 0.12-0.25) and Sierra Leone (G = 0.17, 95% CI 0.12-0.22). There was also significant inequality in prevalence among local village communities, generally more marked during dry seasons when there was lower mean prevalence. The Gini coefficient correlated strongly with the standard coefficient of variation, which has no finite range.ConclusionsThe Gini coefficient is a useful descriptor of epidemiological inequality at all population levels, with confidence intervals and interpretable bounds. Wider use of the coefficient would give broader understanding of malaria heterogeneity revealed by multiple types of studies, surveys and reports, providing more accessible insight from available data.

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Representative elementary length to measure soil mass attenuation coefficient.

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