Universal approximation properties of feedforward artificial neural networks.

In this thesis we summarise several results in the literature which show the approximation capabilities of multilayer feedforward artificial neural networks. We show that multilayer feedforward artificial neural networks are capable of approximating continuous and measurable functions from Rn to R to any degree of accuracy under certain conditions. In particular making use of the Stone-Weierstrass and Hahn-Banach theorems, we show that a multilayer feedforward artificial neural network can approximate any continuous function to any degree of accuracy, by using either an arbitrary squashing function or any continuous sigmoidal function for activation. Making use of the Stone-Weirstrass Theorem again, we extend these approximation capabilities of multilayer feedforward artificial neural networks to the space of measurable functions under any probability measure

Using benthic foraminifera to reconstruct the benthic environment during sapropel formation

Date du colloque : 03/2008International audienc

The Economic Impacts Of Sugarcane Expansion In Brazil

Since 2001, Brazil has experienced a sharp increase in sugarcane production due to the upsurge in demand for sugar and ethanol, two products derived from sugarcane. While the increase in sugarcane production has led to income and employment opportunities in the sugar and ethanol sector, the benefits of sugarcane expansion could vary significantly by the region where sugarcane is cultivated. This dissertation consists of three studies that examine the economic impacts of the recent sugarcane expansion in Brazil. Whereas previous studies only show associations between sugarcane expansion and economic indicators, this research establishes a causal relationship using estimators based on the propensity score. The propensity score is defined in this research as the probability that a municipality expands sugarcane production, given a set of observable characteristics. One of these characteristics is the suitability of a municipality to grow sugarcane. Data on suitability of land were recently published at the national level. The first study analyzes whether municipalities in Sao Paulo state that expanded sugarcane production between 2002 and 2006 as a result experienced higher economic growth. The results indicate that there is no statistically significant impact of sugarcane expansion on GDP per capita growth. The second study examines the economic growth impacts of the increased sugarcane production in the different sugarcane producing regions in Brazil. The findings show that sugarcane expansion led to GDP per capita growth in three regions: in Brazil as a whole, in the North-Northeast and in the Center-South excluding Sao Paulo. In addition, it is demonstrated that this latter region could benefit from future sugarcane expansions. The final study investigates the underlying reasons for the findings in the first study. It examines the impact of sugarcane expansion in Sao Paulo state on growth in GDP per capita, in employment and in wages in the different sectors of the economy. The results suggest that sugarcane expansion has positive impacts on local economies in Sao Paulo state. Further research with updated data is needed to establish whether the positive influences at sector level affected total GDP data in lagged terms

Causes and consequences of the Messinian salinity crisis

Salt giants are massive salt deposits (at least hundreds of m thick) that form during the evaporation of semi-enclosed seas. However, the drivers of salt giant formation and their feedbacks on global and regional environmental change remain debated. In this Review, we summarize the boundary conditions, causes and consequences of the Mediterranean Messinian salinity crisis (MSC; 5.97-5.33 Ma), and highlight the impacts of salt extraction and ion return on the Earth system. Salt giant formation is more complex than the simple evaporation of an enclosed sea. Instead, the tectonic setting of an evaporative basin largely determines the timing and mode of salt formation, with superimposed impacts of orbital-scale climate and sea-level fluctuations. These drivers triggered precipitation of carbonates, gypsum, halite, and even bittern salts in the Mediterranean, with well-defined orbital cyclicities in carbonate and gypsum phases. Removal of Ca2+ during salt deposition decouples the oceanic Ca2+ and HCO3- sinks, causing a CaCO3 burial decrease and, consequently, increased ocean pH, lower atmospheric pCO2, and global cooling. Salt giants, which reflect a ~7 to 10 % net evaporite-ion extraction from oceans that persists over million-year timescales, could therefore be an important climatic driver, but are currently not considered in long-term carbon cycle models. Future research should target more advanced hydrogeochemical models of water exchange with the open ocean to provide critical context for understanding interactions between salt giants and environmental change

Causes and consequences of the Messinian salinity crisis

Salt giants are massive salt deposits (at least hundreds of m thick) that form during the evaporation of semi-enclosed seas. However, the drivers of salt giant formation and their feedbacks on global and regional environmental change remain debated. In this Review, we summarize the boundary conditions, causes and consequences of the Mediterranean Messinian salinity crisis (MSC; 5.97-5.33 Ma), and highlight the impacts of salt extraction and ion return on the Earth system. Salt giant formation is more complex than the simple evaporation of an enclosed sea. Instead, the tectonic setting of an evaporative basin largely determines the timing and mode of salt formation, with superimposed impacts of orbital-scale climate and sea-level fluctuations. These drivers triggered precipitation of carbonates, gypsum, halite, and even bittern salts in the Mediterranean, with well-defined orbital cyclicities in carbonate and gypsum phases. Removal of Ca2+ during salt deposition decouples the oceanic Ca2+ and HCO3- sinks, causing a CaCO3 burial decrease and, consequently, increased ocean pH, lower atmospheric pCO2, and global cooling. Salt giants, which reflect a ~7 to 10 % net evaporite-ion extraction from oceans that persists over million-year timescales, could therefore be an important climatic driver, but are currently not considered in long-term carbon cycle models. Future research should target more advanced hydrogeochemical models of water exchange with the open ocean to provide critical context for understanding interactions between salt giants and environmental change

217 000-year-old DNA sequences of green sulfur bacteria in Mediterranean sapropels and their implications for the reconstruction of the paleoenvironment

Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Society for Applied Microbiology and Blackwell for personal use, not for redistribution. The definitive version was published in Environmental Microbiology 9 (2007): 238–249, doi:10.1111/j.1462-2920.2006.01134.x.Deep-sea sediments of the eastern Mediterranean harbor a series of dark, organic carbon-rich layers, so-called sapropels. Within these layers, the carotenoid isorenieratene was detected. Since it is specific for the obligately anaerobic phototrophic green sulfur bacteria, the presence of isorenieratene may suggest that extended water column anoxia occurred in the ancient Mediterranean Sea during periods of sapropel formation. Only three carotenoids (isorenieratene, β-isorenieratene and chlorobactene) are typical for green sulfur bacteria and thus do not permit to differentiate between the ~80 known phylotypes. In order to reconstruct the paleoecological conditions in more detail, we searched for fossil 16S rRNA gene sequences of green sulfur bacteria employing ancient DNA methodology. 540 bp-long fossil sequences could indeed be amplified from up to 217,000-year-old sapropels. In addition, such sequences were also recovered from carbon-lean intermediate sediment layers deposited during times of an entirely oxic water column. Unexpectedly, however, all the recovered 16S rRNA gene sequences grouped with freshwater or brackish, rather than truly marine, types of green sulfur bacteria. It is therefore feasible that the molecular remains of green sulfur bacteria originated from populations which thrived in adjacent freshwater or estuarine coastal environments rather than from an indigenous pelagic population.This work was funded by the Deutsche Forschungsgemeinschaft (grants Ov 20/3-2 and Ov 20/8-1 to 8-3)

Solar city indicator: a methodology to predict city level PV installed capacity by combining physical capacity and socio-economic factors

Shifting to renewable sources of electricity is imperative in achieving global reductions in carbon emissions and ensuring future energy security. One technology, solar photovoltaics (PV), has begun to generate a noticeable contribution to the electricity mix in numerous countries. However, the upper limits of this contribution have not been explored in a way that combines both building-by-building solar resource appraisals with the city-scale socio-economic contexts that dictate PV uptake. This paper presents such a method, whereby a ‘Solar City Indicator’ is calculated and used to rank cities by their capacity to generate electricity from roof-mounted PV. Seven major UK cities were chosen for analysis based on available data; Dundee, Derby, Edinburgh, Glasgow, Leicester, Nottingham and Sheffield. The physical capacity of each city was established using a GIS-based methodology, exploiting digital surface models and LiDAR data, with distinct methodologies for large and small properties. Socio-economic factors (income, education, environmental consciousness, building stock and ownership) were chosen based on existing literature and correlation with current levels of PV installations. These factors were enumerated using data that was readily available across each city. Results show that Derby has the greatest potential of all the cities analysed, as it offers both good physical and socio-economic potential. In terms of physical capacity it was seen that over a 15 year payback period there are two plateaus, showing a marked difference in viability between small and large PV arrays. It was found that both the physical and socio-economic potential of a city are strongly influenced by the nature of the local building stock. This study also identifies areas where policy needs to be focused in order to encourage uptake and highlights factors limiting maximum PV uptake. While this methodology has been demonstrated using UK cities, it is equally applicable to any country where city data is available

Oracle-based optimization applied to climate model calibration

In this paper, we show how oracle-based optimization can be effectively used for the calibration of an intermediate complexity climate model. In a fully developed example, we estimate the 12 principal parameters of the C-GOLDSTEIN climate model by using an oracle- based optimization tool, Proximal-ACCPM. The oracle is a procedure that finds, for each query point, a value for the goodness-of-fit function and an evaluation of its gradient. The difficulty in the model calibration problem stems from the need to undertake costly calculations for each simulation and also from the fact that the error function used to assess the goodness-of-fit is not convex. The method converges to a Fbest fit_ estimate over 10 times faster than a comparable test using the ensemble Kalman filter. The approach is simple to implement and potentially useful in calibrating computationally demanding models based on temporal integration (simulation), for which functional derivative information is not readily available