Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailAssessing the Impact of Public Holidays on Travel Time Expenditure: Differentiation by Trip Motive
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Proceedings of the 89th Annual Meeting of the Transportation Research Board (DVD-ROM) (2010)

The impact of public holidays on the underlying reasons of travel behavior, namely the activities people perform and the trips made, is seldom investigated. Therefore, in this paper the impact of public ... [more ▼]

The impact of public holidays on the underlying reasons of travel behavior, namely the activities people perform and the trips made, is seldom investigated. Therefore, in this paper the impact of public holidays on travel time expenditure in Flanders, differentiated by trip motive, is examined. The data used for the analysis stem from a household travel survey that was carried out in 2000. The main modeling approach that is employed is the zero-inflated Poisson regression approach, which explicitly takes into account the inherent contrast between travelers and non-travelers. The zero-inflated Poisson regression models yield findings that are harmonious with international literature: socio-demographic variables, temporal effects and transportation preferences contribute significantly in unraveling the variability of travel behavior. In particular it is shown that public holidays have a non-ignorable impact on daily travel behavior. Triangulation of both quantitative and qualitative techniques seems a solid roadway for further illumination of the underpinnings of travel behavior. [less ▲]

Detailed reference viewed: 14 (0 ULg)
Full Text
Peer Reviewed
See detailAssessing the Impact of Public Holidays on Travel Time Expenditure: Differentiation by Trip Motive
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Transportation Research Record: Journal of the Transportation Research Board (2010), 2157

The impact of public holidays on the underlying reasons for travel behavior, namely, the activities people perform and the trips made, is seldom investigated. Therefore, the effect of holidays on travel ... [more ▼]

The impact of public holidays on the underlying reasons for travel behavior, namely, the activities people perform and the trips made, is seldom investigated. Therefore, the effect of holidays on travel time expenditure in Flanders, differentiated by trip motive, is examined. The data used for the analysis stem from a household travel survey carried out in 2000. The zero-inflated Poisson regression approach is used; it explicitly takes into account the inherent contrast between travelers and nontravelers. The zero-inflated Poisson regression models yield findings that are harmonious with international literature: socio-demographic variables, temporal effects, and transportation preferences contribute significantly to unraveling the variability of travel behavior. In particular, it is shown that the effect of public holidays on daily travel behavior cannot be ignored. Triangulation of quantitative and qualitative techniques is a solid basis for insight into the underpinnings of travel behavior. [less ▲]

Detailed reference viewed: 24 (1 ULg)
See detailAssessing the impact of space and time resolution of brightness temperature simulation conditions in correcting SEVIRI SST over the Adriatic Sea
Tomazic, Igor ULg; Le Borgne, Pierre; Tudor, Martina et al

Conference (2012)

Majority of operational sea surface temperature (SST) infra-red (IR) products have small overall bias but exhibit higher absolute biases in specific regions. Previous studies [for example Tomazic et al ... [more ▼]

Majority of operational sea surface temperature (SST) infra-red (IR) products have small overall bias but exhibit higher absolute biases in specific regions. Previous studies [for example Tomazic et al., 2011] showed that over Adriatic Sea there is a positive summer bias sometimes exceeding 0.5 K. Methodology to decrease regional biases [Le Borgne et al., 2011], based on using atmospheric profiles, surface SST fields and radiative transfer model to simulate the non-linear split window SST (NLSST) algorithm error, was used to assess the impact of atmospheric profiles with different spatial resolution (ECMWF: 0.125 deg and ALADIN 2 km), different input surface SST fields (OSTIA 6 km and CNR UHR L4 1 km) and different time and space averaging criteria’s in deriving the algorithm correction. SST corrections derived for the NLSST Spinning Enhanced Visible and Infrared Imager (SEVIRI) algorithm for five months (July, October and December 2010 and March and July 2011) are validated with AATSR L2 SST fields and compared to already implemented regional correction procedure at Center de Meteorologie Spatiale (CMS) to assess the optimal combination of space and time averaging criteria’s and input fields. Results show that the best improvement for all available months and for both day and night is obtained when using spatial averaging over the whole domain in combination with time averaging between the last 15 and last 31 days both for day and night time analysis. Using higher resolution ALADIN atmospheric profiles with OSTIA input SST fields didn’t improve the SST correction compared to using combination of coarser ECMWF atmospheric profiles and OSTIA input SST. Small improvement, based only on analysis for two months in 2011, is obtained when using both higher spatial resolution atmospheric profiles (ALADIN) and higher resolution input SST fields (CNR UHR L4 1 km). The best improvement obtained for spatial averaging over the whole domain (Adriatic Sea) suggests that the domain should be more extended (to Mediterranean Sea) to derive optimal spatial averaging, while conclusion of improvement obtained when using both the higher spatial resolution atmospheric profiles and input SST field need extension of analysis on other months in 2010. [less ▲]

Detailed reference viewed: 8 (0 ULg)
Full Text
Peer Reviewed
See detailAssessing the Impact of Weather on Traffic Intensity
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Proceedings of the 87th Annual Meeting of the Transportation Research Board (DVD-ROM) (2008)

The investigation of weather effects on traffic intensity is important from a road safety point of view, because traffic intensity is noted as the first and primary determinant of traffic safety. Next to ... [more ▼]

The investigation of weather effects on traffic intensity is important from a road safety point of view, because traffic intensity is noted as the first and primary determinant of traffic safety. Next to traffic safety, weather conditions affect other predominant traffic variables, namely traffic demand and traffic flow. Therefore the main objective of this study is the identification and comparison of weather effects on traffic intensity at different site locations. To assess the impact of weather conditions on traffic intensity, the upstream and downstream traffic of four traffic count locations are considered. The traffic intensity data originate from minute data coming from single inductive loop detectors, collected by the Flemish Traffic Control Center. Data concerning weather events were recorded by the Royal Meteorological Institute of Belgium. The main modeling philosophy envisaged in this study to identify and quantify weather effects is the linear regression approach. Most appealing result of this study for policy makers, is the heterogeneity of the weather effects between different traffic count locations, and the homogeneity of the weather effects on upstream and downstream traffic at a certain location. The results also indicated that snowfall, rainfall and wind speed have a clear diminishing effect on traffic intensity, while maximum temperature significantly increases traffic intensity. Further generalizations of the findings are possible by studying weather effects on local roads and by shifting the scope towards travel behavior. Simultaneously modeling of weather conditions, traffic intensity rates, collision risk and activity travel behavior is certainly a key challenge for further research. [less ▲]

Detailed reference viewed: 9 (0 ULg)
Full Text
Peer Reviewed
See detailAssessing the Impact of Weather on Traffic Intensity
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Weather, Climate and Society (2010), 2(1), 6068

This paper focuses on the effect of weather conditions on daily traffic intensities (the number of cars passing a specific segment of a road). The main objective is to examination whether or not weather ... [more ▼]

This paper focuses on the effect of weather conditions on daily traffic intensities (the number of cars passing a specific segment of a road). The main objective is to examination whether or not weather conditions uniformly alter daily traffic intensities in Belgium, or in other words whether or not road usage on a particular location determines the size of the impacts of various weather conditions. This general examination is a contribution that allows policymakers to assess the appropriateness of countrywide versus local traffic management strategies. In addition, a secondary goal of this paper is to validate findings in international literature within a Belgian context. To achieve these goals, the paper analyzes the effects of weather conditions on both upstream (toward a specific location) and downstream (away from a specific location) traffic intensities at three traffic count locations typified by a different road usage. Perhaps the most interesting results of this study for policymakers are the heterogeneity of the weather effects between different traffic count locations, and the homogeneity of the weather effects on upstream and downstream traffic at specific locations. The results also indicate that snowfall, rainfall, and wind speed diminish traffic intensity, and high temperatures increase traffic intensity. Further generalizations of the findings might be possible by studying weather impacts on local roads and by shifting the focus of research toward travel behavior. [less ▲]

Detailed reference viewed: 23 (1 ULg)
See detailAssessing the impacts of present and future interannual climate variability on European ecosystems using a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Warnant, Pierre et al

Poster (2011, April)

Climate projections indicate changes in mean climate as well as in climate variability and frequency of extreme events for the end of the 21st century compared to present. Since many biological processes ... [more ▼]

Climate projections indicate changes in mean climate as well as in climate variability and frequency of extreme events for the end of the 21st century compared to present. Since many biological processes reach non-reversible thresholds (loss of ability to germinate, mortality, etc.) at some temperatures or soil water values, changes in climate variability have long-term consequences for ecosystem composition, functioning and carbon storage. The CARAIB dynamic vegetation model is used to evaluate and analyse how future climate variability will affect European ecosystems. We examine the impacts of climate change and associated drought episodes on primary productivity (NPP) as well as on fire intensity. CARAIB is driven by the ARPEGE/Climate model and three regional climate models from the European Union project ENSEMBLES (KNMI-RACMO2, DMI-HIRHAM5 and HC-HadRM3Q0 models) forced with the IPCC A1B emission scenario. We analyse the interannual climate variability simulated by those climate models and compare it with the observed climate variability (CRU TS 3.0 historical climate dataset) over the period 1961-1990. None of these climate models can reproduce accurately the present natural climate variability. Therefore, the present NPP interannual variability simulated by CARAIB using climate outputs from the climate models differs from the one obtained with observed climate. For instance, the NPP interannual variability obtained with the ARPEGE/Climate model is significantly overestimated in some parts of Europe, especially in the Mediterranean region, in France, in northern Germany and northern Poland, in the Balkans and in Ukraine. Since discrepancies between modelled and observed current climate variability may also affect NPP variability calculated for the future as well as the intensity and the frequency of severe drought periods and wildfires, comparing the terrestrial ecosystem evolutions obtained with a range of climate models allows to improve the assessment of climate change impacts on ecosystems in the future. Anyway the trend between the present and the future is expected to be more robust. The NPP interannual variability increases in the future with the four climate models as a result of more frequent and more severe soil water stress episodes in southern and Central Europe. The projected climate changes are also likely to induce increased fire risk in the Mediterranean region but also in Central Europe and Russia. [less ▲]

Detailed reference viewed: 31 (8 ULg)
Full Text
See detailAssessing the impacts of technical and structure choices on groundwater model performance using a complex synthetic case
Wildemeersch, Samuel ULg

Doctoral thesis (2012)

According to the European Water Framework Directive (2000/60/EC) and the specific Groundwater Directive (2006/188/EC), Member States have to manage groundwater at the groundwater body scale and in an ... [more ▼]

According to the European Water Framework Directive (2000/60/EC) and the specific Groundwater Directive (2006/188/EC), Member States have to manage groundwater at the groundwater body scale and in an integrated way. Given the objectives of “good quantitative and qualitative status” of groundwater for 2015 stated by the Directive, end-users want to know the quantitative and qualitative evolution of groundwater for several scenarios. Physically-based and spatially-distributed groundwater flow and transport models constitute useful management tools in this context since they take explicitely into account the heterogeneity and the physical processes occuring in the subsurface for predicting system responses to future stress factors. However, at such a scale, groundwater flow and transport modelling is challenging due to (1) the complexity of geological and hydrogeological contexts, (2) the uneven level of characterisation knowledge, and (3) the representativity of measured parameters. Furthermore, such models require long execution times. As a consequence, a series of choices and simplifications are made for dealing with these issues. Therefore, the outstanding question is to know whether endusers’expectations can be met in spite of such choices and simplifications. This work focuses on choices and simplifications related to spatial discretisation and saturation–pressure relations in the unsaturated one. The influence of stress factor time resolution is also tested. Considering this general context, the objective of the present work is to evaluate the influence of some model technical (spatial discretisation) and structure (saturation–pressure relations) uncertainties on model results, parameter sensitivities, and optimisation performance in order to provide guidelines for model development. This is performed using a synthetic case inspired by typical groundwater bodies of Wallonia (Belgium). This synthetic case is used for obtaining reference observations in terms of flow rates and hydraulic heads. These reference observations are then compared with their simulated equivalent produced by simplified models differing by their spatial discretisation, their saturation–pressure relations in the unsaturated zone, or the time resolution of their stress factors. The simplified models are then ranked using several performance criteria measuring the discrepancies between reference observations and their simulated equivalent. This ranking leads to guidelines for large-scale groundwater flow model development with respect to typical end-users’ expectations. Whatever the time resolution of stress factors, the quantitative and qualitative analyses performed indicate that coarsening horizontal spatial discretisation deteriorates mainly the simulation of flow rates, coarsening vertical spatial discretisation deteriorates mainly the simulation of hydraulic heads, and (over)simplifying saturation–pressure relations in the unsaturated zone significantly impair the simulation of both flow rates and hydraulic heads. Although optimisation can compensate for errors induced by model technical and structure uncertainties, the improvement of model fit is limited, especially for the coarsest models. Furthermore, with respect to end-users’ expectations, the weighted least-square objective function is not always the most relevant criteria for optimising models. Therefore, it is essential to use specific performance criteria for evaluating model performance depending on the objectives of the study. The ideal would be to develop an end-users objective function for including such performance criteria in the optimisation process and stop the optimisation process once performance criteria would have reached the values specified by the end-users with respect to the objectives of the study. [less ▲]

Detailed reference viewed: 74 (26 ULg)
See detailAssessing the impacts of technical uncertainty on coupled surface/subsurface flow model predictions using a complex synthetic case
Wildemeersch, Samuel ULg; Goderniaux, Pascal ULg; Orban, Philippe ULg et al

Poster (2011, September)

According to the EU Water Framework Directive, Member States have to manage surface water and groundwater at the water body scale and in an integrated way. Flow and transport models constitute useful ... [more ▼]

According to the EU Water Framework Directive, Member States have to manage surface water and groundwater at the water body scale and in an integrated way. Flow and transport models constitute useful management tools in this context since they can predict system responses to future stresses. However, numerical modelling at such a scale faces specific issues linked to (1) the representation of the geological and hydrogeological complexity, (2) the uneven level of characterisation knowledge, (3) the representativity of measured parameters and variables in the field, and (4) the CPU time needed for solving the numerical problem. Assumptions and simplifications made for dealing with these issues can lead to a series of models differing by their complexity and by the reliability of their predictions. Consequently, modellers have to find a compromise between complexity and reliability. The main objective of this research is to estimate the impacts of technical uncertainty, which is the uncertainty related to the numerical implementation, on groundwater flow model predictions. To reach that objective, the methodology consists in comparing reference predictions (hydraulic heads and flow rates) of a complex and close to reality synthetic case with the predictions provided by a series of simplified models (coarse spatial discretisation, coarse time discretisation, simplified law in the unsaturated zone). The synthetic case reflects the main characteristics found in groundwater bodies of South Belgium (Condroz region of Wallonia), characterised by a succession of limestone synclines and sandstone anticlines. The numerical model is developed with the fully-integrated surface/subsurface flow and transport code HydroGeoSphere using a mesh refined along the surface water network (153027 nodes and 269872 elements). A 5-year reference transient simulation, with daily stress factors is performed. The simulated hydraulic heads and flow rates constitute the reference observations and predictions for the comparison with the simplified models. The simplified models tested differ by their horizontal (500 m vs. 1000 m element size) and vertical (8 layers vs. 3 layers) spatial discretisations, their time discretisation (daily vs. monthly stress factors), and the type of constitutive law used for simulating the unsaturated flow (linear vs. van Genuchten). The models are run with the same parameter values than those used in the reference model to evaluate the deterioration in model predictions due to technical uncertainty. Additionally, some of the models are calibrated with the inverse modelling code PEST to distinguish how far a model calibration can possibly compensate for technical uncertainty. Then, predictions from each simplified model are compared with the reference predictions of the synthetic case. Then, the simplified models are ranked using several model performance criteria. Results of this research provide guidelines for the numerical implementation of groundwater flow models at the water body scale with respect to specific groundwater management objectives. [less ▲]

Detailed reference viewed: 35 (13 ULg)
Full Text
See detailAssessing the influence of crop management strategies on the distribution of soil water content by ERT
Chelin, Marie ULg; Parvin, Nargish ULg; Hiel, Marie-Pierre ULg et al

Poster (2013, December 20)

Amongst other functions, cover crops are known to increase the stability of the soil structure. Commonly, their suppression is realized by using conventional tillage, but that it has been demonstrated to ... [more ▼]

Amongst other functions, cover crops are known to increase the stability of the soil structure. Commonly, their suppression is realized by using conventional tillage, but that it has been demonstrated to damage the soil structure, which directly impacts the soil water content. The proposed alternatives vary in terms of date, depth and type of tillage. As the soil water content is a major factor in agriculture, it is essential to better understand the influence of the cover crop management on its spatio-temporal distribution. Recent studies demonstrated the relevancy of the electrical resistivity tomography (ERT) to estimate the three-dimensional soil water content distribution. However, only a few of them were performed under field conditions. This study aims at (i) validating the use of the ERT method to estimate the soil water content distribution under field conditions (ii) quantifying the influence of cover crop management on the dynamic of soil water content along the growing season of a maize crop and on Belgian soil types. Three types of cover crop management content will be daily monitored: strip tillage, spring tillage and winter tillage. In order to assess the impact of plants on the soil water distribution, an additional plot will be burned after winter tillage. ERT will be used on a surface of 2 m² for each cover crop management. The validation of the average soil water content will be attended by using Time Domain Reflectrometers (TDR) and suction cups. The water stock obtained by ERT will be validated by using data from a weather station for the estimation of the evapotranspiration and rainfall and minirhizotrons for the assessment of the root water uptake. [less ▲]

Detailed reference viewed: 29 (7 ULg)
Full Text
Peer Reviewed
See detailAssessing the ligand properties of 1,3-dimesitylbenzimidazol-2-ylidene in ruthenium-catalyzed olefin metathesis
Borguet, Yannick ULg; Zaragoza, Guillermo; Demonceau, Albert ULg et al

in Dalton Transactions (2013), 42(20), 7287-7296

The deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium ... [more ▼]

The deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium complexes to afford three new organometallic products. The compounds [RhCl(COD)(BMes)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BMes)] were used to probe the steric and electronic parameters of BMes. Comparison of the percentage of buried volume (%VBur) and of the Tolman electronic parameter (TEP) of BMes with those determined previously for 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-dimesitylimidazolin-2-ylidene (SIMes) revealed that the three N-heterocyclic carbenes (NHCs) had very similar profiles. Nonetheless, changes in the hydrocarbon backbone subtly affected the stereoelectronic properties of these ligands. Accordingly, the corresponding [RuCl2(PCy 3)(NHC)(CHPh)] complexes displayed different catalytic behaviors in the ring-closing metathesis (RCM) of α,ω-dienes. In the benchmark cyclization of diethyl 2,2-diallylmalonate, the new [RuCl2(PCy 3)(BMes)(CHPh)] compound (1d) performed slightly better than the Grubbs second-generation catalyst (1a), which was in turn significantly more active than the related [RuCl2(PCy3)(IMes)(CHPh)] initiator (1b). For the formation of a model trisubstituted cycloolefin, complex 1d ranked in-between catalyst precursors 1a and 1b, whereas in the RCM of tetrasubstituted cycloalkenes it lost its catalytic efficiency much more rapidly. [less ▲]

Detailed reference viewed: 10 (5 ULg)
See detailAssessing the losses of HCFC-22 using ACE-FTS measurements
Kolonjari, F.; Walker, K.A.; Boone, C.D. et al

Scientific conference (2012, November 09)

The annual springtime minimum in stratospheric ozone over the Antarctic is primarily caused by catalytic reactions of ozone and chlorine. The Montreal Protocol on Substances that Deplete the Ozone Layer ... [more ▼]

The annual springtime minimum in stratospheric ozone over the Antarctic is primarily caused by catalytic reactions of ozone and chlorine. The Montreal Protocol on Substances that Deplete the Ozone Layer (with its subsequent amendments) restricts the emissions of ozone depleting substances. HCFC-22 has been the primary replacement for both CFC-11 and CFC-12, which has led to an increase in its atmospheric abundance. The Atmospheric Chemistry Experiment (ACE) is a mission on-board the Canadian satellite SCISAT. The primary instrument on SCISAT is a highresolution infrared Fourier Transform Spectrometer (ACE-FTS). With its wide spectral range, the ACE-FTS is capable of measuring an extensive range of gases including key CFC and HCFC species. The altitude distribution from the ACE-FTS profiles provides information that is complementary to the ground-based measurements that have been used to monitor these species. The ACE-FTS measurements compare well with surface in situ and balloon measurements. A preliminary validation of HCFC-22 using ground-based FTSs is discussed. The zonal mean distribution of HCFC-22 as observed by ACE-FTS is presented. The global distributions of HCFC-22 have been compared to the Global Modelling Initiative (GMI) Combined Stratospheric-Tropospheric Model, a chemistry and transport model. Large differences between the model and ACE-FTS measurements of HCFC-22 reveal issues with the boundary value mixing ratios. The comparison of stratospheric measurements with GMI suggest that there may be a missing loss process in the stratosphere, some issues with transport circulation and polar cap averaging in the current run, or a combination of the two processes. We propose the reaction of HCFC-22 with atomic chlorine as a potentially important loss process in the lowermost stratosphere and the lower stratosphere. [less ▲]

Detailed reference viewed: 12 (2 ULg)
Full Text
Peer Reviewed
See detailAssessing the potential of an algorithm based on mean climatic data to predict wheat yield
Dumont, Benjamin ULg; Leemans, Vincent ULg; Ferrandis, Salvador et al

in Precision Agriculture (2014)

The real-time non-invasive determination of crop biomass and yield prediction is one of the major challenges in agriculture. An interesting approach lies in using process-based crop yield models in ... [more ▼]

The real-time non-invasive determination of crop biomass and yield prediction is one of the major challenges in agriculture. An interesting approach lies in using process-based crop yield models in combination with real-time monitoring of the input climatic data of these models, but unknown future weather remains the main obstacle to reliable yield prediction. Since accurate weather forecasts can be made only a short time in advance, much information can be derived from analyzing past weather data. This paper presents a methodology that addresses the problem of unknown future weather by using a daily mean climatic database, based exclusively on available past measurements. It involves building climate matrix ensembles, combining different time ranges of projected mean climate data and real measured weather data originating from the historical database or from real-time measurements performed in the field. Used as an input for the STICS crop model, the datasets thus computed were used to perform statistical within-season biomass and yield prediction. This work demonstrated that a reliable predictive delay of 3-4 weeks could be obtained. In combination with a local micrometeorological station that monitors climate data in real-time, the approach also enabled us to (i) predict potential yield at the local level, (ii) detect stress occurrence and (iii) quantify yield loss (or gain) drawing on real monitored climatic conditions of the previous few days. [less ▲]

Detailed reference viewed: 13 (3 ULg)
Full Text
Peer Reviewed
See detailAssessing the potential of an algorithm based on mean climatic data to predict wheat yield.
Dumont, Benjamin ULg; Leemans, Vincent ULg; Ferrandis Vallterra, Salvador ULg et al

in Proceedings of the 11th International Conference on Precision Agriculture (2012, July)

Real-time non-invasive determination of crop biomass and yield prediction are maybe among the major challenges in agriculture. But unknown future weather remains the key point of accurate yield forecast ... [more ▼]

Real-time non-invasive determination of crop biomass and yield prediction are maybe among the major challenges in agriculture. But unknown future weather remains the key point of accurate yield forecast. This paper presents the results of a preliminary study that aims to supply the unknown future by daily mean climatic data. The results show that under the Belgian weather, this approach is relevant. Furthermore, the developed methodology appears to be a powerful diagnosis tool of the remaining yield potential under ongoing weather. [less ▲]

Detailed reference viewed: 51 (16 ULg)
Full Text
Peer Reviewed
See detailAssessing the potential of calcium-based artificial ocean alkalinization to mitigate rising atmospheric CO2 and ocean acidification
Ilyina, Tatiana; Wolf-Gladrow, Dieter; Munhoven, Guy ULg et al

in Geophysical Research Letters (2013), 40(22), 5909-5914

Enhancement of ocean alkalinity using calcium compounds, e.g., lime has been proposed to mitigate further increase of atmospheric CO2 and ocean acidification due to anthropogenic CO2 emissions. Using a ... [more ▼]

Enhancement of ocean alkalinity using calcium compounds, e.g., lime has been proposed to mitigate further increase of atmospheric CO2 and ocean acidification due to anthropogenic CO2 emissions. Using a global model, we show that such alkalinization has the potential to preserve pH and the saturation state of carbonate minerals at close to today's values. Effects of alkalinization persist after termination: Atmospheric CO2 and pH do not return to unmitigated levels. Only scenarios in which large amounts of alkalinity (i.e., in a ratio of 2:1 with respect to emitted CO2) are added over large ocean areas can boost oceanic CO2 uptake sufficiently to avoid further ocean acidification on the global scale, thereby elevating some key biogeochemical parameters, e.g., pH significantly above preindustrial levels. Smaller-scale alkalinization could counteract ocean acidification on a subregional or even local scale, e.g., in upwelling systems. The decrease of atmospheric CO2 would then be a small side effect. [less ▲]

Detailed reference viewed: 28 (1 ULg)
Full Text
Peer Reviewed
See detailAssessing the Potential of Zwitterionic NHC•CS2 Adducts for Probing the Stereoelectronic Parameters of N-Heterocyclic Carbenes
Delaude, Lionel ULg; Demonceau, Albert ULg; Wouters, Johan

in European Journal Of Inorganic Chemistry (2009), (13), 1882-1891

Five imidazol(in)ium-2-dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by ... [more ▼]

Five imidazol(in)ium-2-dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon disulfide. They were characterized by IR, UV/Vis, and NMR spectroscopy, and by thermogravimetric analysis. Their molecular structures were determined by X-ray diffraction. For the sake of comparison, tricyclohexylphosphonium dithiocarboxylate was also examined. The data acquired were scrutinized to evaluate their usefulness for assessing the steric and electronic properties of NHC ligands. Because of their outstanding ability to crystallize, the five NHC center dot CS2 betaines were found to be highly suitable for probing the steric influence of nitrogen atom substituents on imidazolylidene-based ligand precursors via XRD analysis, while the corresponding NHC center dot CO2 adducts were deemed more appropriate for evaluating the sigma-donating properties of carbene ligands. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [less ▲]

Detailed reference viewed: 66 (5 ULg)
Full Text
Peer Reviewed
See detailAssessing the Probability of Training Image-Based Geological Scenarios Using Geophysical Data
Hermans, Thomas ULg; Caers, Jef; Nguyen, Frédéric ULg

in Pardo-Iguzquiza, Eulogio; Guardiola-Albert, Carolina; Heredia, Javier (Eds.) et al Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences (2013, September)

In multiple-point statistics (MPS), the construction of training im-ages (TIs) is one of the most critical steps. Reliable geological studies may not always be available to depict with certainty what ... [more ▼]

In multiple-point statistics (MPS), the construction of training im-ages (TIs) is one of the most critical steps. Reliable geological studies may not always be available to depict with certainty what geological patterns or heterogeneity are present. In this context, geophysical techniques may provide additional information to reduce the possible large uncertainty in the understanding of prior geological scenarios. To overcome this problem, we developed a methodology to verify the consistency of geophysical data with independently-built TIs representing different plausible geological scenarios. If a TI is deemed consistent with the field geophysical survey, then in a sec-ond step we calculate a likelihood probability for each consistent TI. Our methodology starts by creating subsurface models with each TI. From these models we create synthetic geophysical data and from this synthetic data, synthetic inverted models. These models are now compared with a single inverted model obtained from the field sur-vey, allowing for our definition of what is “consistent”. To that ex-tent, we calculate the Euclidean distance between any two inverted models as well as field data and visualize the results in a 2D or 3D space using multidimensional scaling (MDS). With this technique, it is possible to verify if field cases fall in the distribution represented by synthetic cases, and thus are consistent with them. In a second step, we present a cluster analysis on the MDS-map to highlight which parameters are the most sensitive for the construction of TI. Based on this analysis, a probability of each geological scenario is computed through kernel smoothing of the densities in reduced pro-jected metric space. This approach was tested using electrical resistivity tomography as geophysical data to analyze TI scenarios for the Meuse alluvial aqui-fer (Belgium), where the lack of reliable sedimentological data lead to the definition of a multitude of geological scenarios, hence TIs. [less ▲]

Detailed reference viewed: 35 (13 ULg)
Full Text
Peer Reviewed
See detailAssessing the Proximity of Time Evolutions through Dynamic Time Warping
Fabozzi, Davide ULg; Van Cutsem, Thierry ULg

in IET Generation, Transmission & Distribution (2011), 5(12), 1268-1276

Comparing time-series is a frequent task in many scientific fields. In power systems, in particular, it may be of interest to compare the outputs of a simplified and a detailed model, or to validate the ... [more ▼]

Comparing time-series is a frequent task in many scientific fields. In power systems, in particular, it may be of interest to compare the outputs of a simplified and a detailed model, or to validate the output of a model with respect to a measured time response. The classical Euclidean distance, involving pairs of points of the two data series aligned in time, is not suited to the practical time evolutions met in power systems, which often involve variable time delays and jumps at discrete times. In this paper, an alternative measure of proximity, stemming from other scientific fields, is proposed for power system applications. It consists in warping the time axis to guarantee the best match between the two time-series, i.e. it maps points on two curves that are not aligned in time so as to minimize the sum of squared differences of their ordinates. Modifications and adaptations of the classical algorithm to better fit power system problems are discussed. The method is illustrated through three representative curve comparison problems. A multi-dimensional extension allowing system-wide measures of similarity is also proposed. [less ▲]

Detailed reference viewed: 111 (14 ULg)
Full Text
Peer Reviewed
See detailAssessing the Quality of Origin-Destination Matrices Derived from Activity Travel Surveys: Results from a Monte Carlo Experiment
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Transportation Research Record: Journal of the Transportation Research Board (2010), 2183

To support policy makers combating travel-related externalities, quality data are required for the design and management of transportation systems and policies. To this end, much money has been spent on ... [more ▼]

To support policy makers combating travel-related externalities, quality data are required for the design and management of transportation systems and policies. To this end, much money has been spent on collecting household- and person-based data. The main objective of this paper is to assess the quality of origin-destination (O-D) matrices derived from household activity travel surveys. To this purpose, a Monte Carlo experiment is set up to estimate the precision of O-D matrices given different sampling rates. The Belgian 2001 census data, containing work- and school-related travel information for all 10,296,350 residents, are used for the experiment. For different sampling rates, 2,000 random stratified samples are drawn. For each sample, three O-D matrices are composed: one at the municipality level, one at the district level, and one at the provincial level. The correspondence between the samples and the population is assessed by using the mean absolute percentage error (MAPE) and a censored version of the MAPE (MCAPE). The results show that no accurate O-D matrices can be derived directly from these surveys. Only when half of the population is queried is an acceptable O-D matrix obtained at the provincial level. Therefore, use of additional information to grasp better the behavioral realism underlying destination choices and collection of information about particular O-D pairs by means of vehicle intercept surveys are recommended. In addition, results suggest using the MCAPE next to traditional criteria to examine dissimilarities between different O-D matrices. An important avenue for further research is the investigation of the effect of sampling proportions on travel demand model outcomes. [less ▲]

Detailed reference viewed: 22 (2 ULg)