Predicting phase durations of traffic lights using live Open Traffic Lights data

C

The potential of reduced tillage in Flanders

Untill recently, modern agriculture was focused on maximum food production without considering the long term impact on soil fertility or environment. As a consequence modern agriculture is nowadays confronted with a number of pressing problems. The main problems agriculture experiences in industrialised societies are the degradation of physical soil structure resulting in erosion and soil compaction, decline in SOM and N losses. Conservation tillage (CsT) agriculture was first introduced on a large scale on fields with mainly cereals, soybean and sunflower in the USA, Latin America and Australia as a very effective measure to reduce erosion and store water into the soil (Arshad, 1999; Six et al., 2002b). To date research on the positive and negative effect of CsT compared to CT agriculture mainly focussed on the soil conditions and crop rotations under the warm and dry climatic of the USA, Latin America and Australia. The climatic and soil conditions and crop rotations in Western Europe are, however, very different. Western Europe has a maritime temperate climate and the crop rotations contain crops that seem less suitable under CsT agriculture because they often include beets and potatoes, resulting in a high disturbance of the soil at the formation of the ridges and at harvest (Anonymous, 2006d). The major erosion problems in Belgium are found with these root and tuber crops and maize in the loess belt (Anonymous, 2000; Geelen, 2006). Nowadays farmers in Western Europe shift more and more to reduced tillage (RT) agriculture, a type of CsT agriculture which refers to tilling the whole soil surface but eliminating one or more of the operations that would otherwise be done in a CT system. This shift can partly be explained by the progress in machines, especially sowing machines, and because of its proven effects on reduction of soil erosion (Vandergeten & Roisin, 2004). However, very little information is available on the evolution of important soil properties e.g. related to C dynamics in RT agriculture under the specific Western European climatic and soil conditions and crop rotations. In this thesis, eighteen fields with a silt loam texture were selected, including the different types of RT agriculture running for a different number of years. In the study area, very little experimental sites exist where CT practices are compared to RT practices. Therefore, we had no choice but to include farmers' fields, where inevitably there is no perfect match between CT and RT fields. Despite the high disturbance of the soil every 2 or 3 years of crop rotations including sugar beets or potatoes, RT agriculture had a positive effect on the measured physical soil properties. The aggregate stability of the upper 10 cm depth layer measured with the method of De Leenheer & De Boodt (1959) and the three methods of Le Bissonnais (1996) were higher a short time after the shift to RT compared to CT agriculture. At each location, bulk density (BD) of the 5-10 cm depth layer was mostly lower and saturated soil water content (θs) was mostly higher under RT than CT agriculture. The penetration resistance (PR) of the upper depth layer under RT by direct drilling (RTDD) is higher than under CT agriculture, while the PR in the 20-30 cm depth layer is only higher under RT agriculture by cultivator or soil loosener (RTC) if the working depth is lower. The trend was a higher field-saturated hydraulic conductivity (Kfs) under RT compared to CT agriculture (chapter 3). RT agriculture resulted in a higher stratification of soil organic carbon (SOC) and total nitrogen (TN) in the soil profile. However, the total SOC and TN stock was not changed, even after a period of 20 years of RT agriculture. The amount of organic carbon and TN in three different particulate organic matter (POM) fractions of the 0-10 cm depth layer were found to be (significantly) higher both on an absolute and relative basis in the RT compared to the CT fields. In general the difference was the highest for the coarse free POM fraction, which is the most labile fraction. The higher SOC, TN and microbial biomass (MB) content in the upper depth layer of RT fields resulted in a higher carbon (C) and nitrogen (N) mineralization rate in undisturbed soil under controlled conditions in the laboratory. Simulating ploughing by disturbing the soil resulted both in lower and higher mineralization rates of the silt loam soils, but due to the large variability of the estimated mineralization parameters, the differences were not significant. It seems that under the specific management and climatic conditions of Western Europe, RT agriculture increase the SOC and TN content and microbial activity in the top layers, but do not result in enhanced sequestration when the entire soil profile is considered (chapter 4 and 5). Nitrous oxide nitrogen (N2O-N) emissions from RT fields tended to be slightly higher than CT fields. The higher N2O-N emissions of RT compared to CT fields were correlated with a higher % TN and MB-N (chapter 6). This study indicates that RTC agriculture is beneficial for the farmers, society and environment. However, the potential for RTDD agriculture in Flanders is probably limited because of the typical crop rotations that are less compatible with this type of agriculture (chapter 7)

An experimental study on performance portability of OpenCL kernels

Accelerator processors allow energy-efficient computation at high performance, especially for computationintensive applications. There exists a plethora of different accelerator architectures, such as GPUs and the Cell Broadband Engine. Each accelerator has its own programming language, but the recently introduced OpenCL language unifies accelerator programming languages. Hereby, OpenCL achieves functional protability, allowing to reduce the development time of kernels. Functional portability however has limited value without performance portability: the possibility to re-use optimized kernels with good performance. This paper investigates the specificity of code optimizations to accelerator architecture and the severity of lack of performance portability