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Umeå, Sweden

Westberg M.,AF AB | Johansson F.,KTH Royal Institute of Technology
Proceedings of the 3rd International Forum on Risk Analysis, Dam Safety Dam Security and Critical Infrastructure Management, 3IWRDD-FORUM | Year: 2012

In order to perform a complete risk analysis of a dam facility, it is necessary to have information about the probability and consequences of failure. To analyze the probability of failure of a concrete dam, all components and all failure modes must be accounted for. This paper presents a methodology for the calculation of the failure probability of a concrete dam with respect to foundation stability where the dam is considered as a system. The system is divided into different levels, where the top event on the "structure level" is failure of the dam. The next level is "monolith level", where each monolith can be considered as an element in a series system of the concrete dam. Below the monolith level is the "failure location level" which describes where the failure occurs, in the concrete-rock contact, in the rock mass or in the concrete. Since it is the weakest of these failure locations that will govern where the failure occurs, each failure location can be seen as elements in a series system. Beneath this level is the "failure mode level" where failure modes such as sliding and rotation also constitute elements in a series system. The "Basic failure modes" are the foundation level in the system. In some situations, the reliability of all failure modes as well as the correlation between failure modes is of importance for the overall reliability. In other situations only the reliability of a dominant failure mode is of importance. A discussion regarding this is given. © 2012 Taylor & Francis Group. Source


Davidsson H.,Lund University | Bernardo R.,Lund University | Gomes J.,Solarus Inc. | Gentile N.,Lund University | And 3 more authors.
Energy Procedia | Year: 2014

A large number of photovoltaic systems have been installed in developing countries around the world during numerous projects. The goal is often to improve the quality of life in rural areas often lacking electricity. Many of these installations provide important services such as lighting and charging of various devices. However, when the projects are finished, there is a large risk that maintenance is not carried out properly and that malfunctions are never repaired. This situation can leave an otherwise well- functioning system unusable. A key problem is that there are not enough trained technicians that can maintain and repair the system locally. One reason for this is the lack of practical education in many developing countries. Furthermore, the availability of spare parts is essential for long term effectiveness. During 2011 a group of researchers from Lund University in Sweden built a small scale laboratory in Maputo, Mozambique, with local researchers. The project was successful and today the laboratory functions both as a teaching facility and as a measurement station for solar energy research for licentiates, masters and Ph.D. students. The main goal now is to widen the project in order to incorporate more universities in developing countries. We are now looking for new interested partners in developing countries who believe that such a laboratory could strengthen their ability to teach practical work and to perform research at a local university. Partners for planning and executing the project are also needed. © 2014 The Authors. Published by Elsevier Ltd. Source


Sobek A.,University of Stockholm | Wiberg K.,Swedish University of Agricultural Sciences | Sundqvist K.L.,AF AB | Haglund P.,Umea University | And 4 more authors.
Science of the Total Environment | Year: 2014

High levels of PCDD/Fs and PCBs in Baltic Sea biota have been a matter of great concern during the last decades. We measured the freely dissolved concentrations of PCDD/Fs and PCBs in sediment pore water and bottom water in eight areas along the Swedish coast of the Gulf of Bothnia, by using state-of-the-art passive samplers. Chemical activity ratios (calculated from freely dissolved concentrations in pore water and bottom water based on chemical activity ratios) for PCDD/Fs were higher than 1 at all stations (PCDD/Fs average 27; stdev 22). High activity ratios suggest that the sediments have a potential to act as a source of dissolved PCDD/Fs to the water column. Activity ratios for PCBs varied between 0.3 and 17 (average 2; stdev 4). The concentrations of PCDD/Fs and PCBs in bottom water were significantly correlated with concentrations in sediment pore water ( p<. 0.00001 to p= 0.03) as well as with concentrations in juvenile perch caught in the same areas ( p<. 0.00001 to p= 0.02). To our knowledge, this is the first study demonstrating a correlation between in-situ measured freely dissolved PCDD/F concentrations and lipid-normalized contents in stationary fish. Our results confirm that freely dissolved concentrations should be used as chemical predictors of bioaccumulation. The results from this study imply that continued efforts to reduce levels of PCDD/Fs and PCBs in coastal sediments will have positive effects on concentrations of these contaminants in lower trophic levels of Baltic Sea ecosystems. © 2014 Elsevier B.V. Source


Sobek A.,University of Stockholm | Sundqvist K.L.,AF AB | Assefa A.T.,Umea University | Wiberg K.,Swedish University of Agricultural Sciences
Science of the Total Environment | Year: 2015

We present a comprehensive study on PCBs and HCB in dated sediment cores from the Baltic Sea covering the 20th century, and compare their spatiotemporal trends with those of PCDD/Fs from the same areas. PCB concentrations in coastal impacted sediment followed the temporal trend of estimated global emissions of PCBs and thus responded quickly to changes in global industrial use, whereas concentrations in offshore sediment needed 10-20. years longer to respond. Differences in spatiotemporal trends of PCDD/Fs and PCBs were smaller than expected based on documented differences in key sources and source areas. Sediment concentrations of HCB varied little over time and space, but concentrations are increasing in recent years. The steep PCB concentration reduction over time observed for the late 20th century levelled off during the last 20. years, and levels of PCBs appear to be at or near a steady-state condition. Capsule: PCB concentrations in Baltic Sea sediments appear to be at or near steady-state, and no significant concentration decreases are to be expected in the near future. © 2015 Elsevier B.V. Source


Assefa A.T.,Umea University | Sobek A.,University of Stockholm | Sundqvist K.L.,AF AB | Cato I.,Geological Survey of Sweden | And 4 more authors.
Environmental Science and Technology | Year: 2014

The pollution trend of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the Baltic Sea region was studied based on depth profiles of PCDD/Fs in sediment cores collected from six offshore areas, eight coastal sites impacted by industrial/urban emissions, and one coastal reference site. A general trend was observed for the offshore and coastal reference sites with substantial increase in PCDD/F concentrations in the mid-late 1970s and peak levels during 1985-2002. The overall peak year for PCDD/Fs in Baltic Sea offshore areas was estimated (using spline-fit modeling) to 1994 ± 5 years, and a half-life in sediments was estimated at 29 ± 11 years. For the industrial/urban impacted coastal sites, the temporal trend was more variable with peak years occurring 1-2 decades earlier compared to offshore areas. The substantial reductions from peak levels (38 ± 11% and 81 ± 12% in offshore and coastal areas, respectively) reflect domestic and international actions taken for reduction of the release of PCDD/Fs to the environment. The modeled overall half-life and reductions of PCDD/Fs in offshore Baltic Sea sediment correspond well to both PCDD/F trends in European lakes without any known direct PCDD/F sources (half-lives 30 and 32 years), and previously modeled reduction in atmospheric deposition of PCDD/Fs to the Baltic Sea since 1990. These observations support previous findings of a common diffuse source, such as long-range air transport of atmospheric emissions, as the prime source of PCDD/Fs to the Baltic Sea region. The half-life of PCDD/Fs in Baltic Sea offshore sediments was estimated to be approximately 2 and 4-6 times longer than in semirural and urban European air, respectively. This study highlights the need for further international actions to reduce the levels of PCDD/Fs in Baltic Sea air specifically and in European air in general. © 2013 American Chemical Society. Source

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