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science, United States

Yamamoto Y.,Tohoku University | Usuda N.,Fujita Health University | Oghiso Y.,Institute for Environmental science | Kuwahara Y.,Tohoku University | Fukumoto M.,Tohoku University
Health Physics | Year: 2010

Irradiation from internally deposited radionuclides induces malignant tumors. Ingested radionuclides accumulate in specific organs, which are irradiated over a lifelong period. Our aim is to elucidate why the development of malignant tumors requires long-term internal exposure, on the order of decades, despite the fact that irradiation is continuous over this period. Three major factors are considered to be responsible for the long incubation time in carcinogenesis caused by internally deposited alpha-emitters: uneven distribution of radionuclides, limited range of irradiation, and dynamic movement of tumor precursor cells. We hypothesized that target cells susceptible to malignant transformation may undergo one event by alpha particles and may then migrate outside of the range of alpha particles, thereby avoiding immediate induction of successive additional events that would lead to cell death or neoplastic changes. Based on this hypothesis, we further proposed a mathematical model to predict the relationship between dose rate and incubation period of tumors induced by internally deposited alpha-emitters. The function was non-linear and included terms of both direct and indirect radiation effects. It well fitted both human Th-ICC cases and rat Pu-induced lung cancer, suggesting that indirect radiation effects are independent from dose rate. The significance of parameters of the model is discussed. Copyright © 2010 Health Physics Society. Source

Lacroix P.,University of Geneva | De Roulet P.,Geneva International Center for Humanitarian Demining | Ray N.,Institute for Environmental science
International Journal of Applied Geospatial Research | Year: 2014

This paper presents START (Simplified Toolbar to Accelerate Repeated Tasks), a new, freely downloadable ArcGIS extension designed for non-expert GIS users. START was developed jointly by the Geneva International Centre for Humanitarian Demining (GICHD) and the University of Geneva to support frequent workflows relating to mine action. START brings together a series of basic ArcGIS tools in one toolbar and provides new geoprocessing, geometry and database management functions. The toolbar operates as a bridge between non-spatial repositories (e.g. MySQL and Excel) and GIS. It also connects mine action professionals recording data in the field to GIS experts and improves data interoperability between GIS professionals working in different disciplines. Originally created to help humanitarian demining actors optimize GIS workflows and be more efficient in their everyday work, the toolbar might also benefit scientists operating in other fields. Copyright © 2014, IGI Global. Source

Edvardsson J.,University of Bern | Simanauskiene R.,Vilnius University | Taminskas J.,Nature Research Center | Bauziene I.,Nature Research Center | And 2 more authors.
Science of the Total Environment | Year: 2015

Over the past century an ongoing establishment of Scots pine (Pinus sylvestris L.), sometimes at accelerating rates, is noted at three studied Lithuanian peat bogs, namely Kere˙plis, Re˙kyva and Aukštumala, all representing different degrees of tree coverage and geographic settings. Present establishment rates seem to depend on tree density on the bog surface and are most significant at sparsely covered sites where about three-fourth of the trees have established since the mid-1990s, whereas the initial establishment in general was during the early to mid-19th century. Three methods were used to detect, compare and describe tree establishment: (1) tree counts in small plots, (2) dendrochronological dating of bog pine trees, and (3) interpretation of aerial photographs and historical maps of the study areas. In combination, the different approaches provide complimentary information but also weigh up each other's drawbacks. Tree counts in plots provided a reasonable overview of age class distributions and enabled capturing of the most recently established trees with ages less than 50. years. The dendrochronological analysis yielded accurate tree ages and a good temporal resolution of long-term changes. Tree establishment and spread interpreted from aerial photographs and historical maps provided a good overview of tree spread and total affected area. It also helped to verify the results obtained with the other methods and an upscaling of findings to the entire peat bogs. The ongoing spread of trees in predominantly undisturbed peat bogs is related to warmer and/or drier climatic conditions, and to a minor degree to land-use changes. Our results therefore provide valuable insights into vegetation changes in peat bogs, also with respect to bog response to ongoing and future climatic changes. © 2014 Elsevier B.V.. Source

van den Heuvel F.,University of Geneva | Goyette S.,Institute for Environmental science | Rahman K.,University of Geneva | Stoffel M.,Institute for Environmental science | And 2 more authors.
Geomorphology | Year: 2016

The principal objective of this study was to investigate the types of large-scale meteorological situations that are conducive to the precipitation and temperature conditions most likely to trigger debris flows in the Zermatt valley, Switzerland, under current and future climates. A two-dimensional Bayesian probability calculation was applied to take account of uncertainties in debris-flow triggering. Precipitation quantities exceeding the 95th percentile of daily precipitation amounts were found to have a significantly higher probability to coincide with observed debris flows. A different relationship exists for extreme temperatures, however. Southerly air flows, weak horizontal pressure gradients over Europe, and westerly flows are mostly associated with observed debris flows and 95th precipitation percentile exceedances. These principal flow directions are well represented in the regional climate model (RCM) HIRHAM control simulations for events exceeding the 95th precipitation percentile and the 30th temperature percentile. Under the IPCC A2 emission scenario, westerly and southerly flows are mostly responsible for these precipitation and temperature conditions under the hypothesis of slow adaptation to climate change (HS1/HC1). Under the hypothesis of rapid adaptation to climate change (HS1/HS1), southerly flows and weak horizontal pressure gradients are likely to gain in importance. In both scenarios for the future, southeasterly flows are among the principal flow directions responsible for the joint exceedance of the 95th precipitation percentile and the 30th temperature percentile, while these were absent in observations and the control simulation. © 2015 Elsevier B.V. Source

Noss C.,Institute for Environmental science | Lorke A.,Institute for Environmental science
Water Resources Research | Year: 2016

Although relationships between roughness, flow, and transport processes in rivers and streams have been investigated for several decades, the prediction of flow resistance and longitudinal dispersion in small streams is still challenging. Major uncertainties in existing approaches for quantifying flow resistance and longitudinal dispersion at the reach scale arise from limitations in the characterization of riverbed roughness. In this study, we characterized the riverbed roughness in small moderate-gradient streams (0.1-0.5% bed slope) and investigated its effects on flow resistance and dispersion. We analyzed high-resolution transect-based measurements of stream depth and width, which resolved the complete roughness spectrum with scales ranging from the micro to the reach scale. Independently measured flow resistance and dispersion coefficients were mainly affected by roughness at spatial scales between the median grain size and the stream width, i.e., by roughness between the micro- and the mesoscale. We also compared our flow resistance measurements with calculations using various flow resistance equations. Flow resistance in our study streams was well approximated by the equations that were developed for high gradient streams (>1%) and it was overestimated by approaches developed for sand-bed streams with a smooth riverbed or ripple bed. © 2016. American Geophysical Union. Source

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