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See detailImpact of contamination on training and test error rates in statistical clustering
Ruwet, Christel ULg; Haesbroeck, Gentiane ULg

in Communications in Statistics : Simulation & Computation (2011), 40(3), 394-411

The k-means algorithm is one of the most common nonhierarchical methods of clustering. It aims to construct clusters in order to minimize the within cluster sum of squared distances. However, as most ... [more ▼]

The k-means algorithm is one of the most common nonhierarchical methods of clustering. It aims to construct clusters in order to minimize the within cluster sum of squared distances. However, as most estimators defined in terms of objective functions depending on global sums of squares, the k-means procedure is not robust with respect to atypical observations in the data. Alternative techniques have thus been introduced in the literature, e.g. the k-medoids method. The k-means and k-medoids methodologies are particular cases of the generalized k-means procedure. In this paper, focus is on the error rate these clustering procedures achieve when one expects the data to be distributed according to a mixture distribution. Two different definitions of the error rate are under consideration, depending on the data at hand. It is shown that contamination may make one of these two error rates decrease even under optimal models. The consequence of this will be emphasized with the comparison of influence functions and breakdown points of these error rates. [less ▲]

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See detailImpact of contractile reserve on acute response to cardiac resynchronization therapy
Moonen, Marie ULg; Senechal, Mario; Cosyns, Bernard et al

in Cardiovascular Ultrasound (2008), 6(65),

Background: Cardiac resynchronization therapy (CRT) provides benefit for congestive heart failure, but still 30% of patients failed to respond to such therapy. This lack of response may be due to the ... [more ▼]

Background: Cardiac resynchronization therapy (CRT) provides benefit for congestive heart failure, but still 30% of patients failed to respond to such therapy. This lack of response may be due to the presence of significant amount of scar or fibrotic tissue at myocardial level. This study sought to investigate the potential impact of myocardial contractile reserve as assessed during exercise echocardiography on acute response following CRT implantation. Methods: Fifty-one consecutive patients with heart failure (LV ejection fraction 27% ± 5%, 67% ischemic cardiomyopathy) underwent exercise Doppler echocardiography before CRT implantation to assess global contractile reserve (improvement in LV ejection fraction) and local contractile reserve in the region of the LV pacing lead (assessed by radial strain using speckle tracking analysis). Responders were defined by an increase in stroke volume ≥15% after CRT. Results: Compared with nonresponders, responders (25 patients) showed a greater exercise-induced increase in LV ejection fraction, a higher degree of mitral regurgitation and a significant extent of LV dyssynchrony. The presence of contractile reserve was directly related to the acute increase in stroke volume (r = 0.48, p<0.001). Baseline myocardial deformation as well as contractile reserve in the LV pacing lead region was greater in responders during exercise than in nonresponders (p<0.0001). Conclusions: Heart failure patients referred to CRT have less chance of improving under therapy if they have no significant mitral regurgitation, no LV dyssynchrony and no contractile myocardial recruitment at exercise. [less ▲]

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See detailThe impact of corporate disclosures on information asymmetry and stock-market liquidity in France
Sougné, Danielle ULg; Ajina, Aymen ULg

Conference (2011, May 30)

This paper aims at studying the effect of the extent of disclosure on information asymmetry and stock-market liquidity in France. Our sample includes196 French listed firms over a period ranging from 2004 ... [more ▼]

This paper aims at studying the effect of the extent of disclosure on information asymmetry and stock-market liquidity in France. Our sample includes196 French listed firms over a period ranging from 2004 to 2007, the results show that the extent of disclosure in annual reports positively influence the liquidity of the French market. This is explained by the negative effect of the disclosure on the adverse selection component of the bid-ask spread. This effect is further confirmed by the commitment to IFRS by French-listed firms from 2005. This result should encourage French authorities to further improve their information environment as essential to reduce the costs of asymetric information and prevent the risk of illiquidity. [less ▲]

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See detailIMPACT OF COVER CROP AND CROP RESIDUE MANAGEMENT ON CROP PRODUCTION
Hiel, Marie-Pierre ULg; Bodson, Bernard ULg

Poster (2013, July 03)

The aim of this project is to study the crop development in relation to soil tillage and organic residue management and to understand its impact on crop production but also on the dynamics of weed ... [more ▼]

The aim of this project is to study the crop development in relation to soil tillage and organic residue management and to understand its impact on crop production but also on the dynamics of weed populations and intensity of fungal diseases occurring on the crops. Various cropping systems with different tillage methods dedicated to bury the residues from the previous crop and/or from the intercropping and to prepare the implantation of following crop are studied. [less ▲]

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See detailIMPACT OF COVER CROP MANAGEMENT ON CROP PRODUCTION: A FIELD EXPERIMENT IN WALLONIA CONTEXT
Hiel, Marie-Pierre ULg; Bodson, Bernard ULg

Poster (2014, February)

Minimal soil tillage methods, crop rotation, cover crop and continuous plant residue cover are the main pillars of sustainable agriculture. Lower energy consumption, costs and time are some direct ... [more ▼]

Minimal soil tillage methods, crop rotation, cover crop and continuous plant residue cover are the main pillars of sustainable agriculture. Lower energy consumption, costs and time are some direct benefits in favor to the adaptation of this agriculture. This practices aims also directly at protecting the soil from wind and water erosion by covering the soil. Lower disruption of the soil aims at developping the micro- and macro-fauna activity that increases soil fertility and carbon and nitrogen sequestration in soils. Unfortunately, some of the great constraints to the adaptation of conservation agriculture remain weed management, fungal diseases and pest management, that has been shown to be a problem in non-ploughed fields. The aim of our study is to evaluate, on a same field (Wallonia context), contrasted tillage methods for managing the cover crop and the implantation of the main crop. The following measurements were taken: germination rate, root and shoot biomass development, root notation (size and shape), leaf area index and quality of harvested product. Preliminary results indicate that the different tillage methods did not have a significant impact on crop production or development. However changes in germination dynamics were observed, the reduced tillage inducing slower germination. Regarding weeds populations, some difference were observed in weed occurrences. Since a field exp [less ▲]

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See detailImpact of cristallinity index on the stability and physical properties of inulin during moisture uptake.
Ronkart, Sébastien; Paquot, Michel ULg; Fougnies, C. et al

Poster (2008, April)

Detailed reference viewed: 11 (2 ULg)
See detailImpact of crops on biomass and soil carbon: steady state simulations
Nemry, B.; François, Louis ULg; Gérard, Jean-Claude ULg et al

in Cramer, W.; Doherty, R.; Hulme, M. (Eds.) et al Climate Scenarios for Agricultural, Forest and Ecosystem Impacts (2000)

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See detailImpact of cultivation practices on soil respiration
Dufranne, Delphine ULg; Vancutsem, Françoise ULg; Bodson, Bernard ULg et al

Poster (2012, February 08)

In addition to its, evident, food supply function, agriculture is subjected to various pressures and has to respond to many challenges like reducing its CO2 emissions, maintaining or improving the soil ... [more ▼]

In addition to its, evident, food supply function, agriculture is subjected to various pressures and has to respond to many challenges like reducing its CO2 emissions, maintaining or improving the soil quality, maintaining productivity, sequestrating of the carbon stock in soil... Cultivation practices are known to induce a modification of soil organic matter quantity, quality and spatial distribution, which may impact dry matter decomposition kinetics. In order to bring answers to these questions, a multidisciplinary project (SOLRESIDUS) was set up by the University of Liege, Gembloux Agro-Bio Tech in collaboration with Walloon Agricultural Research Centre (CRA-W). The aim was to investigate the impact of cultivation practices (tillage and residue restitution) on crop growth, yield and environment, as well as on soil properties and on activities. In the present study, we focused on the impacts on soil CO2 fluxes. The experimental site is situated in Gembloux, in the Belgian loamy region. The plot is divided into 4 latin squares where two tillage modalities (plough after 2 stubble breaking vs only 2 stubble breaking) and two straw management practices (restitution vs. exportation) were compared. For 3 years, soil respiration was measured with automatic and manual dynamic soil chambers. Moreover, soil respiration was measured as well in cropping zone (total respiration) as in root exclusion zones created with root exclusion cylinders (heterotrophic respiration). As first results, we observed: -a significantly higher flux in plots with residue restitution, which is clearly explained by the larger amount of organic carbon prone to decomposition; -a decrease of standardized heterotrophic respiration (linked with residue decomposition) during growing seasons; -no significant differences in soil respiration between tillage modalities after 3 growing seasons. The experiment is still in progress, more years being necessary in order to evaluate the long-term impacts of cultivation practices on soil respiration. [less ▲]

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See detailImpact of cultivation practices on soil respiration
Dufranne, Delphine ULg; Vancutsem, Françoise ULg; Bodson, Bernard ULg et al

Poster (2012, February 10)

Cultivation practices are known to induce a modification of soil organic matter quantity, quality and spatial distribution, which may impact dry matter decomposition kinetics. In order to bring answers to ... [more ▼]

Cultivation practices are known to induce a modification of soil organic matter quantity, quality and spatial distribution, which may impact dry matter decomposition kinetics. In order to bring answers to these questions, a multidisciplinary project (SOLRESIDUS) was set up by the University of Liege, Gembloux Agro-Bio Tech in collaboration with Walloon Agricultural Research Centre (CRA-W). The aim was to investigate the impact of cultivation practices (tillage and residue restitution) on crop growth, yield and environment, as well as on soil properties and on activities. In the present study, we focused on the impacts on soil respiration soil for 3 years. We will present our first results. [less ▲]

Detailed reference viewed: 28 (8 ULg)
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See detailThe impact of culture on cognitive performance in neuropsychological tests.
Schmitz, Xavier ULg; Mardaga, Julie; Meulemans, Thierry ULg

Poster (2009, September 17)

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See detailImpact of cutting frequency on the vigour of Rumex obtusifolius
Stilmant, Didier ULg; Bodson, Bernard ULg; Vrancken, C. et al

in Grass & Forage Science (2010), 65(2), 147-153

The control of Rumex obtusifolius, even with the use of herbicides, is difficult in permanent grasslands where R. obtusifolius reduces both productivity and nutritive value of herbage. It is important to ... [more ▼]

The control of Rumex obtusifolius, even with the use of herbicides, is difficult in permanent grasslands where R. obtusifolius reduces both productivity and nutritive value of herbage. It is important to find alternative approaches to managing R. obtusifolius. Two greenhouse experiments were conducted to compare the impact of different cutting frequencies, which simulated grazing (three cuts), silage making (two cuts) and hay making (one cut) on shoot and root measurements of the vigour of R. obtusifolius. In both experiments the same cutting frequencies were imposed but in Experiment 1 the treatments were imposed for 2 years and in Experiment 2 for 1 year. Compared to the silage-making and hay-making treatments, there was a reduction in the vigour of the aerial parts of R. obtusifolius on the grazing treatment, associated with a reduction in the number of leaves (Experiment 1), in the size of the largest leaf (Experiment 1) and in the herbage mass of dry matter (Experiments 1 and 2). Roots had higher concentrations of total soluble sugar and lower concentrations of starch in the grazing treatment than in the other treatments. These results showed that a reduction in the vigour of R. obtusifolius in permanent grasslands is possible only if the plants are submitted to a high frequency of defoliation under cutting or grazing. [less ▲]

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See detailImpact of cyclic hypoxia on HIF-1a regulation in endothelial cells: new insights for anti-tumor treatments
Martinive, Philippe ULg

in FEBS Journal (2008)

Impact of cyclic hypoxia on HIF-1alpha regulation in endothelial cells - new insights for anti-tumor treatments.Martinive P, Defresne F, Quaghebeur E, Daneau G, Crokart N, Grégoire V, Gallez B, Dessy C ... [more ▼]

Impact of cyclic hypoxia on HIF-1alpha regulation in endothelial cells - new insights for anti-tumor treatments.Martinive P, Defresne F, Quaghebeur E, Daneau G, Crokart N, Grégoire V, Gallez B, Dessy C, Feron O. Unit of Pharmacology and Therapeutics, Université catholique de Louvain, Brussels, Belgium. Heterogeneities in tumor blood flow are associated with cyclic changes in pO(2) or cyclic hypoxia. A major difference from O(2) diffusion-limited or chronic hypoxia is that the tumor vasculature itself may be directly influenced by the fluctuating hypoxic environment, and the reoxygenation phases complicate the usual hypoxia-induced phenotypic pattern. Here, we determined the cyclic hypoxia-driven pathways that modulate hypoxia inducible factor (HIF)-1alpha abundance in endothelial cells to identify possible therapeutic targets. We found that exposure of endothelial cells to cycles of hypoxia/reoxygenation led to accumulation of HIF-1alpha during the hypoxic periods and the phosphorylation of protein kinase B (Akt), extracellular regulated kinase (ERK) and endothelial nitric oxide synthase (eNOS) during the reoxygenation phases. We identified stimulation of mitochondrial respiration and activation of the phosphoinositide-3 kinase (PI3K)/Akt pathway during intervening reoxygenation periods as major triggers of the stabilization of HIF-1alpha. We also found that the NOS inhibitor nitro-l-arginine methyl ester further stimulated the cyclic hypoxia-driven HIF-1alpha accumulation and the associated gain in endothelial cell survival, thereby mirroring the effects of a PI3K/Akt inhibitor. However, combination of both drugs resulted in a net reduction in HIF-1alpha and a dramatic in decrease in endothelial cell survival. In conclusion, this study identified cyclic hypoxia, as reported in many tumor types, as a unique biological challenge for endothelial cells that promotes their survival in a HIF-1alpha-dependent manner through phenotypic alterations occurring during the reoxygenation periods. These observations also indicate the potential of combining Akt-targeting drugs with anti-angiogenic drugs, in particular those interfering with the NO pathway. PMID: 19077164 [PubMed - as supplied by publisher [less ▲]

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See detailImpact of Data Structure on the Estimators R-Square and adjusted R-Square in Linear Regression
Akossou, A. Y. J.; Palm, Rodolphe ULg

in International Journal of Mathematics and Computation (2013), 20(3), 84-93

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See detailImpact of delays on a consensus-based primary frequency control scheme for AC systems connected by a multi-terminal HVDC grid
Dai, Jing; Phulpin, Yannick; Sarlette, Alain ULg et al

in Proceedings of the 2010 IREP Symposium - Bulk Power Systems Dynamics and Control - VIII (2010, August)

This paper addresses the problem of sharing primary frequency control reserves among nonsynchronous AC systems connected by a multi-terminal HVDC grid. We focus on a control scheme that modifies the power ... [more ▼]

This paper addresses the problem of sharing primary frequency control reserves among nonsynchronous AC systems connected by a multi-terminal HVDC grid. We focus on a control scheme that modifies the power injections from the different areas into the DC grid based on remote measurements of the other areas’ frequencies. This scheme is proposed and applied to a simplified system in a previous work by the authors. The current paper investigates the effects of delays on the control scheme’s effectiveness. The study shows that there generally exists a maximum acceptable delay, beyond which the areas’ frequency deviations fail to converge to an equilibrium point. This constraint should be taken into account when commissioning such a control scheme. [less ▲]

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See detailIMPACT OF DEPTH AND SOIL COMPACTION ON BACTERIAL DIVERSITY IN SOIL
Stroobants, Aurore ULg; Degrune, Florine; Olivier, Claire et al

Poster (2012, August 19)

Bacteria are the most abundant and diverse microorganisms in soils. The amount of bacteria in soils can reach 10^10 cells per gram of soil. These organisms are involved in various processes in ... [more ▼]

Bacteria are the most abundant and diverse microorganisms in soils. The amount of bacteria in soils can reach 10^10 cells per gram of soil. These organisms are involved in various processes in agroecosystems such as nutrient cycling, contributing to plant nutrition, plant health and soil structure. The knowledge about this diversity is limited because only one percent of these organisms can be cultured by laboratory methods. During the last decades, many molecular-based techniques have been developed to assess the diversity of bacterial communities. The aim of this study was to determine the quantity and diversity of bacteria in two agricultural soils with differents soil management practices (tillage and no tillage) at different depths (10, 30 and 45 centimeters) and different compaction levels (high and low). Quantity was evaluated by real time PCR and diversity was analysed by the DGGE (Denaturing Gradient Gel Electrophoresis) technique. The results show that soil management has an impact on bacterial quantity at 45 centimeters and quantity is higher in till soil. Compaction level affects the bacterial quantity in till soil, quantity is higher in low compaction. And finally, depth influences the bacterial quantity in till and no till soil. In both soils, quantity decreases with the depth. The results will be presented and discussed on the poster. [less ▲]

Detailed reference viewed: 196 (17 ULg)
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See detailImpact of depth perception and movement freedom on performance in fine surgical tasks
Blavier, Adelaïde ULg; Nyssen, Anne-Sophie ULg

Conference (2005, May 27)

This study aimed to evaluate the impact of new technology and depth perception on surgical tasks performance. Comparing to classical minimal access surgery, new robotic system allows to recover a 3D view ... [more ▼]

This study aimed to evaluate the impact of new technology and depth perception on surgical tasks performance. Comparing to classical minimal access surgery, new robotic system allows to recover a 3D view and all degrees of freedom for instruments movement. To separately evaluate the benefit of robotic technology and the effect of depth perception, 60 medical students without any surgical experience were divided in 3 groups: one using the robotic system in 3D, another using robotic system in 2D, and the third using traditional laparoscopic technique (2D view). After a phase of familiarisation with the technique of their condition, subjects performed four specific fine motor tasks of increasing complexity. We measured the speed, the accuracy and their subjective impressions about their performance (satisfaction, self-confidence and difficulty). Our results show robotic system in 3D allows a better performance than classical laparoscopy in all tasks. More particularly, depth perception significantly improves performance in the easiest tasks (robotic system in 3D > robotic system in 2D and classical laparoscopy), while freedom for instruments movement seems to play a role in the most complex tasks (robotic system (2D or 3D) > classical laparoscopy). The subjective impressions analysis reproduces the differences observed from objective measures. [less ▲]

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See detailThe impact of detailed explanatory leaflets on patient satisfaction with urodynamic consultation: A double-blind randomized controlled trial.
Hougardy, Véronique ULg; Vandeweerd, Jean-Michel ULg; Reda, A. A. et al

in Neurourology and Urodynamics (2009), 28(5), 374-9

Aims To develop and validate a scale that is applicable in Belgium to investigate the aspects of female patients' satisfaction with urodynamic consultation, and to use it to measure the impact of a ... [more ▼]

Aims To develop and validate a scale that is applicable in Belgium to investigate the aspects of female patients' satisfaction with urodynamic consultation, and to use it to measure the impact of a detailed explanatory leaflet on their satisfaction. Materials and Methods Question items were obtained from a group consensus (Delphi process). Each item was scored on a five-point Likert scale. The satisfaction scale was administered to two groups of patients attending the clinics for urodynamics. One hundred twenty-nine patients were included in the study and randomized in two groups. One group (n = 60) received a detailed explanatory leaflet about urodynamic consultation and the other did not (n = 69). Responses were subjected to a reliability and principal component analysis (PCA) to achieve data reduction and analysis, and to assess the reliability of the new scale. Relevant items were retained to compare both interventions using regression analysis. Results A 15-item scale was derived from the Delphi process. Exploratory factor analysis suggested a single factor solution with 11 meaningful items. No significant difference was noted in global scores of satisfaction between the two groups (P = 0.051). Conclusions A short-form patient satisfaction scale with acceptable validity and reliability was developed and used to measure patient satisfaction with urodynamic consultation in this population of Belgian women. This study did not provide support for the effectiveness of explanatory leaflets in improving satisfaction. [less ▲]

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See detailImpact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and Rural Africa
De Filippo, C.; Cavalieri, D.; Di Paola, M. et al

in Proceedings of the National Academy of Sciences of the United States of America (2010), 107(33), 14691-14696

Detailed reference viewed: 24 (0 ULg)
See detailThe impact of diet in shaping microbiota revealed by a comparative study in children from Europe and Rural Africa
De Filippo, C.; Di paola, M.; Ramazzotti, M. et al

Poster (2010, August)

Detailed reference viewed: 14 (1 ULg)