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
See detailInfluence function of the error rate of the generalized k-means
Ruwet, Christel ULg; Haesbroeck, Gentiane ULg

Scientific conference (2009, March 30)

Cluster analysis may be performed when one wishes to group similar objects into a given number of clusters. Several algorithms are available in order to construct these clusters. In this talk, focus will ... [more ▼]

Cluster analysis may be performed when one wishes to group similar objects into a given number of clusters. Several algorithms are available in order to construct these clusters. In this talk, focus will be on two particular cases of the generalized k-means algorithm: the classical k-means procedure as well as the k-medoids algorithm. Among the outputs of these clustering techniques, a classification rule is provided in order to classify the objects into one of the clusters. When classification is the main objective of the statistical analysis, performance is often measured by means of an error rate. In the clustering setting, the error rate has to be measured on the training sample while test samples are usually used in other settings like linear discrimination or logistic discrimination. This characteristic of classification resulting from a clustering implies that contamination in the training sample may not only affect the classification rule but also other parameters involved in the error rate. In the talk, influence functions will be used to measure the impact of contamination on the error rate and will show that contamination may decrease the error rate that one would expect under a given model. Moreover, a kind of second-order influence functions will also be derived to measure the bias in error rate the k-means and k-medoids procedures suffer from in finite-samples. Simulations will confirm the results obtained via the first and second-order influence functions. Future research perspectives will conclude the talk. [less ▲]

Detailed reference viewed: 15 (4 ULg)
Full Text
Peer Reviewed
See detailThe influence function of the TCLUST robust clustering procedure
Ruwet, Christel ULg; García-Escudero, Luis Angel; Gordaliza, Alfonso et al

in Advances in Data Analysis and Classification (2012), 6(2), 107-130

The TCLUST procedure performs robust clustering with the aim of finding clusters with different scatter structures and proportions. An Eigenvalue Ratio constraint is considered by TCLUST in order to avoid ... [more ▼]

The TCLUST procedure performs robust clustering with the aim of finding clusters with different scatter structures and proportions. An Eigenvalue Ratio constraint is considered by TCLUST in order to avoid finding spurious clusters. In order to guarantee the robustness of the method against the presence of outliers and background noise, the method allows for trimming of a given proportion of observations self determined by the data. This article studies robustness properties of the TCLUST procedure by means of the influence function, obtaining a robustness behavior close to that of the trimmed k-means. [less ▲]

Detailed reference viewed: 45 (8 ULg)
Full Text
See detailInfluence functions of the error rates of classification based on clustering
Ruwet, Christel ULg; Haesbroeck, Gentiane ULg

Poster (2009, May)

Cluster analysis may be performed when one wishes to group similar objects into a given number of clusters. Several algorithms are available in order to construct these clusters. In this poster, focus ... [more ▼]

Cluster analysis may be performed when one wishes to group similar objects into a given number of clusters. Several algorithms are available in order to construct these clusters. In this poster, focus will be on two particular cases of the generalized k-means algorithm : the classical k-means procedure as well as the k-medoids algorithm, while the data of interest are assumed to come from an underlying population consisting of a mixture of two groups. Among the outputs of these clustering techniques, a classification rule is provided in order to classify the objects into one of the clusters. When classification is the main objective of the statistical analysis, performance is often measured by means of an error rate. Two types of error rates can be computed : a theoretical one and a more empirical one. The first one can be written as ER(F, Fm) where F is the distribution of the training sample used to set up the classification rule and Fm (model distribution) is the distribution under which the quality of the rule is assessed (via a test sample). The empirical error rate corresponds to ER(F, F), meaning that the classification rule is tested on the same sample as the one used to set up the rule. In case there are some outliers in the data, the classification rule may be corrupted. Even if it is evaluated at the model distribution, the theoretical error rate may then be contaminated, while the effect of contamination on the empirical error rate is two-fold : the rule but also the test sample are contaminated. To measure the robustness of classification based on clustering, influence functions have been computed, both for the theoretical and the empirical error rates. When using the theoretical error rate, similar results as those derived by Croux et al (2008) and Croux et al (2008) in discriminant analysis were observed. More specifically, under optimality (which happens when the model distribution is FN = 0.5N(μ1, ) + 0.5N(μ2, ), Qiu and Tamhane 2007), the contaminated error rate can never be smaller than the optimal value, resulting in a first order influence function identically equal to 0. Second order influence functions would then need to be computed, as this will be done in future research. When the optimality does not hold, the first order influence function of the theoretical error rate does not vanish anymore and shows that contamination may improve the error rate achieved under the non-optimal model. Similar computations have been performed for the empirical error rate, as the poster will show. The first and, when required, second order influence functions of the theoretical and empirical error rates are useful in their own right to compare the robustness of the 2-means and 2-medoids classification procedures. They have also other applications. For example, they may be used to derive diagnostic tools in order to detect observations having an unduly large influence on the error rate. Also, under optimality, the second order influence function of the theoretical error rate can yield asymptotic relative classification efficiencies. [less ▲]

Detailed reference viewed: 56 (30 ULg)
Peer Reviewed
See detailInfluence Lianol Solapro on sow colostrums production
Wavreille, José; Planchon, Viviane; Renaville, Robert ULg et al

in 21 Inter. Pig Vet Society Congress (2010)

Detailed reference viewed: 59 (3 ULg)
Full Text
Peer Reviewed
See detailInfluence Molecular Arrangement in Self-assembled Monolayers on Adhesion Forces Measured by Chemical Force Microscopy
Duwez, Anne-Sophie ULg; Jonas, Ulrich; Klein, Hubert

in Chemphyschem : A European Journal of Chemical Physics and Physical Chemistry (2003), 4

Detailed reference viewed: 5 (0 ULg)
See detailL’influence normative de la Chine en Amérique latine, un défi stratégique pour l’Union européenne ?
Wintgens, Sophie ULg; Dabène, Olivier

Conference (2015, May 20)

La Chine est aujourd’hui devenue un partenaire commercial incontournable, un important pourvoyeur d’investissements directs étrangers et un grand fournisseur de prêts financiers pour un nombre croissant ... [more ▼]

La Chine est aujourd’hui devenue un partenaire commercial incontournable, un important pourvoyeur d’investissements directs étrangers et un grand fournisseur de prêts financiers pour un nombre croissant de pays d’Amérique latine. L’accroissement de ses échanges économiques et commerciaux avec ce sous-continent va de pair avec l’imposition des normes économiques et politiques dont sa politique commerciale internationale est porteuse. Cet article pose dès lors la question du défi que représente cette influence normative chinoise pour la stratégie déployée par l’Union européenne envers l’Amérique latine. [less ▲]

Detailed reference viewed: 31 (5 ULg)
Full Text
Peer Reviewed
See detailInfluence of 2D and 3D images on performance and time estimation in minimal invasive surgery
Blavier, Adelaïde ULg; Nyssen, Anne-Sophie ULg

in Ergonomics (2009), 52(11), 13421349

This study aimed to evaluate the impact of 2D and 3D images on time performance and time estimation during a surgical motor task. 60 subjects without any surgical experience (nurses) and 20 expert ... [more ▼]

This study aimed to evaluate the impact of 2D and 3D images on time performance and time estimation during a surgical motor task. 60 subjects without any surgical experience (nurses) and 20 expert surgeons performed a fine surgical task with a new laparoscopic technology (da Vinci robotic system). The 80 subjects were divided into two groups, one using 3D view option and another using 2D view option. We measured time performance and asked subjects to verbally estimate their time performance. Our results showed faster performance in 3D than in 2D view for novice subjects while the performance in 2D and 3D was similar in the expert group. We obtained a significant interaction between time performance and time evaluation: in 2D condition, all subjects accurately estimated their time performance while they overestimated it in the 3D condition. Our results emphasize the role of 3D in improving performance and the contradictory feeling about time evaluation in 2D and 3D. This finding is discussed in regard with the retrospective paradigm and suggests that 2D and 3D images are differently processed and memorised. [less ▲]

Detailed reference viewed: 35 (7 ULg)
See detailInfluence of 3 stages of maturity on total yield and on animal performance of growing fattening bulls offered a maize silage based diet
Dufrasne, Isabelle ULg; Mayombo, Asangule Pierre; Istasse, Louis ULg et al

in Proceedings of the 43th Annual Meeting of E.A.A.P. (1992)

Detailed reference viewed: 15 (2 ULg)
Peer Reviewed
See detailInfluence of a blend of fructo-oligosaccharides and sugar beet fiber on nutrient digestibility and plasma metabolites concentrations in healthy Beagles
Diez, Marianne ULg; Hornick, Jean-Luc ULg; Baldwin, Paule ULg et al

in American Journal of Veterinary Research (1997), 58

Objective-To evaluate effects of a blend of fructo-oligosaccharides and sugar beet fiber (4:1) at 3 incorporation rates on nutrient digestibility and plasma glucose, insulin, alpha-aminonitrogen, urea ... [more ▼]

Objective-To evaluate effects of a blend of fructo-oligosaccharides and sugar beet fiber (4:1) at 3 incorporation rates on nutrient digestibility and plasma glucose, insulin, alpha-aminonitrogen, urea, cholesterol, and triglycerides concentrations measured weekly in nonfed dogs and during a 360-minute period after a meal. Animals-8 castrated 1 to 1.4-year-old young adult male Beagles weighing 10.0 to 13.5 kg. Procedure-Diets containing 2 incorporation rates of a blend of fructo-oligosaccharides and sugar beet fiber (5 and 10% on a dry matter basis [diets B and C, respectively]) were compared with a control diet without additional fiber (diet A). The 3 diets were evaluated for ability to modify digestibility of dry and organic matter, protein, fat, and ash and for effects on plasma glucose, insulin, alpha-aminonitrogen, urea, cholesterol, and triglycerides concentrations. Each diet was fed for 6 weeks; plasma samples were collected weekly before feeding and after feeding on the last day of the period, During 1 week at the end of the 6-week period, dogs were kept in metabolic cages. Each period of the block was followed by a 4-week washout period. Results-Incorporating the blend of fructo-oiigosaccharides and sugar beet fiber in the diet was associated with greater passage of wet feces (diets B and C) and lower protein digestibility (diet C). Postprandial glucose (diet C), urea (diets B and C) and triglyceride (diets B and C) concentrations were significantly (P < 0.01) decreased. Weekly preprandial measurements were characterized by decreased urea (diets B and C), cholesterol (diet C), and triglycerides (diets B and C) concentrations (P < 0.001). Conclusion-Chronic consumption of fermentable fiber is associated with mildly decreased protein digestibility and with metabolic effects in nonfed or fed dogs. Clinical Relevance-A blend of fructo-oligosaccharides and sugar beet fiber should he tested as a dietary aid for treatment of chronic diseases, such as diabetes mellitus or hyperlipidemia, in dogs. [less ▲]

Detailed reference viewed: 36 (2 ULg)
Full Text
Peer Reviewed
See detailInfluence of a commercial monoacylglycerol on the crystallization mechanism of palm oil as compared to its pure constituents
Verstringe, Stefanie; Danthine, Sabine ULg; Blecker, Christophe ULg et al

in Food Research International (2014), 62

The effect of a commercialmonoacylglycerol (MAG),Myverol™18 04-PK(Myverol), on the non-isothermal crystallization mechanismof palm oil (PO) was investigated and compared to the effect of the two main ... [more ▼]

The effect of a commercialmonoacylglycerol (MAG),Myverol™18 04-PK(Myverol), on the non-isothermal crystallization mechanismof palm oil (PO) was investigated and compared to the effect of the two main constituents of Myverol, monopalmitin and monostearin. The MAGs were added to PO in concentrations up to 8% and the blends were studied using different techniques (differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized light microscopy (PLM)). The DSC crystallization profiles revealed an earlier onset of crystallization along with extra crystallization peaks when MAGs were added to PO. Combined with X-ray results, it could be concluded that the crystallization process of the blends is initiated by the MAGs crystallizing in the α form and then transforming to sub-α. The effect on the non-isothermal crystallization of the PO TAGs is confined to an earlier onset of crystallization, probably through a template effect, and an effect on the crystal structure coarseness. [less ▲]

Detailed reference viewed: 39 (3 ULg)
Full Text
Peer Reviewed
See detailInfluence of a genetic variation of adenosine deaminase on individual susceptibility to variations in sleep pressure
Reichert, Carolin; Maire, Micheline; Gabel, Virginie et al

in Journal of Sleep Research (2012), 21(Suppl.1), 80

Detailed reference viewed: 18 (0 ULg)
Full Text
Peer Reviewed
See detailThe influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y-Ba-Cu-O
Marchal, C.; Fagnard, Jean-François ULg; Shi, Y. H. et al

in Superconductor Science and Technology (2013), 26

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor ... [more ▼]

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor (HTS) containing two grains separated by a well-defined grain boundary. Transport measurements at temperatures between 10 and 300 K were carried out both within one single grain (intra-granular properties) and across the grain boundary (inter-granular properties). The influence of an applied external magnetic field of up to 8 T on the measured sample properties was also investigated. The presence of the grain boundary is found to affect strongly the electrical resistivity of the melt-processed bulk sample, but has almost no effect on its thermoelectric power and thermal conductivity, within experimental error. The results of this study provide direct evidence that the heat flow in multi-granular melt-processed YBCO bulk samples should be virtually unaffected by the presence of grain boundaries in the material. © 2013 IOP Publishing Ltd. [less ▲]

Detailed reference viewed: 119 (35 ULg)
Full Text
Peer Reviewed
See detailInfluence of a liquid nutritional supplement on water intake in experimental Beagle dogs
Rotat, Christelle; Lhoest, Estelle; Rauw, Anaelle ULg et al

in Open Journal of Veterinary Medicine (2016), 6

The objectives were to evaluate the effects of a liquid nutritional supplement formulated for dogs on water intakes and urine output. A liquid nutritional supplement was tested by way of a cross-over ... [more ▼]

The objectives were to evaluate the effects of a liquid nutritional supplement formulated for dogs on water intakes and urine output. A liquid nutritional supplement was tested by way of a cross-over design in 8 experimental healthy Beagle dogs (4 males and 4 females, aged 9.3 years). The supplement (87 percent water, 2.7 percent protein, 2.6 percent fat, 0.4 percent crude fiber) was added to water and tested at 2 incorporation rates (50 or 70 ml/day/dog—D50 or D70) versus the control placebo (CO-water only). The dogs were kept in a controlled environment; water intakes and urine output were measured. Individual water intakes were characterised by large variations. Mean water intake increased significantly by 28 percent in dogs receiving the liquid nutritional supplement, in both genders, irrespectively of the dosage. Urine output was also increased, by 55 percent. Faeces scores remained unchanged. It was concluded that the liquid supplement increased water intake and urine output in a safe way, without increasing dramatically the daily dietary sodium chloride intake. The recommended dosage of the manufacturer—50 ml/day for dogs weighing 10 - 20 kg BW is efficient. Increasing the dosage had no advantage, nor adverse effects. Increased water intake and urine output is of interest for dogs suffering from urolithiasis. [less ▲]

Detailed reference viewed: 34 (3 ULg)
Full Text
Peer Reviewed
See detailInfluence of a long-term storage in anaerobic conditions on Norway spruce (Picea abies, L. Karst.) physical and mechanical wood properties
Riguelle, Simon ULg; Lesire, Cécile ULg; Hebert, Jacques ULg et al

in Wood Material Science & Engineering (2016)

Timber storage is a key aspect of storm damage management. After huge storms, sprinkling storage is usually the most used conservation process but anaerobic storage in sealed silos appears as good ... [more ▼]

Timber storage is a key aspect of storm damage management. After huge storms, sprinkling storage is usually the most used conservation process but anaerobic storage in sealed silos appears as good alternative to preserve wood quality over long periods. This paper investigates the impact of long-term (57 months) storage of Norway spruce logs in anaerobic atmosphere on wood properties. Tests were performed on clear wood specimens and on lumbers to determine the modulus of elasticity (E), the static bending strength (σf) and the dynamic bending strength (K). Storage effects on impregnability and colour variation were also studied. Results show no effect of storage on E, σf and K. The naturally poor impregnability of Norway spruce is not improved by the anaerobic conditions, compared to traditional wet storage. Triangle tests reveal no discernible colour variation between logs that underwent anaerobic storage and the control sample. As a conclusion, despite a mould (Gliocladium solani) frequently observed on logs surface after the storage, the process offers ideal conservation conditions. While overall cost remains the main drawback for using anaerobic storage at large scale, the process can be recommended for high value logs, especially since it has few environmental impacts. [less ▲]

Detailed reference viewed: 30 (10 ULg)
Full Text
Peer Reviewed
See detailInfluence of a low magnetic field on the thermal diffusivity of Bi2Sr2CaCu2O8
Dorbolo, Stéphane ULg; Ausloos, Marcel ULg

in Physical Review B (2002), 65(21),

The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured under a 1 T magnetic field applied perpendicularly to the heat flux. The magnetic contribution to the heat carrier mean free ... [more ▼]

The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured under a 1 T magnetic field applied perpendicularly to the heat flux. The magnetic contribution to the heat carrier mean free path has been extracted and is found to behave as a simple power law. This behavior can be attributed to a percolation process of electrons in the vortex lattice created by the magnetic field. [less ▲]

Detailed reference viewed: 10 (2 ULg)
Full Text
Peer Reviewed
See detailInfluence Of A New Axial Impeller On K(L)A And Xylanase Production By Penicillium Canescens 10-10c
Bakri, Yasser; Jacques, Philippe ULg; Shi, Kui et al

in Applied Biochemistry and Biotechnology (2002), 98

The effects of a new axial impeller (HTPG4) on oxygen volumetric transfer coefficient, KLa, and xylanase production by Penicillium canescens 10-10c were studied and compared for dual-impeller systems, one ... [more ▼]

The effects of a new axial impeller (HTPG4) on oxygen volumetric transfer coefficient, KLa, and xylanase production by Penicillium canescens 10-10c were studied and compared for dual-impeller systems, one with one DT4 impeller below and one HTPG4 above (DT4-HTPG4) and one with two DT4 (DT4-DT4) impellers, in a 5-L bioreactor. The volumetric coefficient of oxygen transfer was measured in culture medium using a gassing-out method at different gassing rates and agitation speeds. We observed that the DT4-HTPG4 combination provided better KLa performance than the DT4-DT4 combination. The two combinations were also tested for their influence on xylanase production by a filamentous microorganism; P. canescens 10-10c. These experiments demonstrated that the DT4-HTPG4 combination impeller enhanced enzyme production up to 23% compared with the DT4-DT4 combination at an aeration rate of 1 vvm and an agitation speed of 600 rpm. The main cause for this difference is thought to be a higher shear stress generated by the DT4-DT4 combination, which damages the mycelium of P. canescens and decreases xylanase production. [less ▲]

Detailed reference viewed: 38 (0 ULg)
Full Text
Peer Reviewed
See detailInfluence of a New Axial Impeller on KLa and Xylanase Production by Penicillium canescens 10-10c
Bakri, Y.; Jacques, Philippe ULg; Shi, L.K. et al

in Applied Biochemistry and Biotechnology (2002), (98-100), 679-686

Detailed reference viewed: 6 (0 ULg)