Last 7 days     Results 1461-1480 of 43861.   69 70 71 72 73 74 75 76 77 78 79   Stability and Aging of Phase Change Materials : An Ab Initio PerspectiveRaty, Jean-Yves Conference (2015, September 17)Data recording with Phase Change Materials is a much studied topic as the writing/erasing characteristics, cyclability and downscaling properties of these materials allow for efficient data storage in ... [more ▼]Data recording with Phase Change Materials is a much studied topic as the writing/erasing characteristics, cyclability and downscaling properties of these materials allow for efficient data storage in future generations of devices. Nevertheless, some aspects of phase change materials are limiting their performances and delaying their wider technological application. First, aging phenomena are common to all amorphous structures, but of special importance PCMs since it impedes the realization of multi-level memories. Different interpretations have been proposed, but we focus here on the structural relaxation of amorphous GeTe, chosen because it is the simplest system that is representative of the wider class of GST alloys, lying along the GeTe-Sb2Te3 composition line of the GeSbTe phase diagram. One difficulty encountered in the simulation of these amorphous systems is that the direct generation of an amorphous structure by quenching a liquid using Density Functional Theory (DFT) based Molecular Dynamics leads to one sample with a small number of atoms, and, hence of small number of atomic environments. Here we sample a large number of local atomic environments, corresponding to different bonding schemes, by chemically substituting different alloys, selected to favor different local atomic structures. This enables spanning a larger fraction of the configuration space relevant to aging. Our results support a model of the amorphous phase and its time evolution that involves an evolution of the local (chemical) order towards that of the crystal. On the other hand its electronic properties drift away from those of the crystal, driven by an increase of the Peierls-like distortion of the local environments in the amorphous, as compared to the crystal [1]. A second problem faced by PCMs is the fact that data recording is limited at high temperature due to the increased propensity to recrystallize. One approach to counter this is to stabilize the PCM using impurity atoms such as C or N. Using DFT and the analysis of the mechanical properties (constraints theory), we demonstrate how these impurity atoms modify the rigidity of the network, which is experimentally correlated with the activation energy for crystallization [2]. Finally, the crystal phase itself has been shown to have variable conductivities depending on the thermal history and annealing conditions. If this could be used profitably for multi-level recording, it also indicates that the crystal is undergoes some temporal evolution. Using DFT, we clarify the stability behavior of GST crystal and show that the metal-insulator transition is driven by the migration of intrinsic vacancies and an Anderson localization transition [3]. [1] J.Y Raty, W. Zhang, J. Luckas, C. Chen, R. Mazzarello, C. Bichara and M. Wuttig, Nat. Comm. (2015) [2] G. Ghezzi, J.Y. Raty, S. Maitrejean, A. Roule, E. Elkaim and F. Hippert, Applied Physics Letters, 99 (2011) 151906 [3] W. Zhang, A. Thiess, P. Zalden, R. Zeller, P. H. Dederichs, J-Y. Raty, M.Wuttig, S. Blügel et R. Mazzarello, Nature Materials 11 (2012) 952 [less ▲]Detailed reference viewed: 49 (2 ULg) Faecal microbiota characterisation of horses using 16 rdna barcoded pyrosequencing, and carriage rate of clostridium difficile at hospital admissionRodriguez Diaz, Cristina ; Taminiau, Bernard ; Brévers, Bastien et alin BMC Microbiology (2015), 15Background The equine faecal microbiota is very complex and remains largely unknown, while interspecies interactions have an important contribution to animal health. Clostridium difficile has been ... [more ▼]Background The equine faecal microbiota is very complex and remains largely unknown, while interspecies interactions have an important contribution to animal health. Clostridium difficile has been identified as an important cause of diarrhoea in horses. This study provides further information on the nature of the bacterial communities present in horses developing an episode of diarrhoea. The prevalence of C. difficile in hospitalised horses at the time of admission is also reported. Results Bacterial diversity of the gut microbiota in diarrhoea is lower than that in non-diarrhoeic horses in terms of species richness (p-value <0.002) and in population evenness (p-value: 0.02). Statistical differences for Actinobacillus, Porphyromonas, RC9 group, Roseburia and Ruminococcaceae were revealed. Fusobacteria was found in horses with diarrhoea but not in any of the horses with non-diarrheic faeces. In contrast, Akkermansia was among the three predominant taxa in all of the horses studied. The overall prevalence of C. difficile in the total samples of hospitalised horses at admission was 3.7 % (5/134), with five different PCR-ribotypes identified, including PCR-ribotype 014. Two colonised horses displayed a decreased bacterial species richness compared to the remaining subjects studied, which shared the same Bacteroides genus. However, none of the positive animals had diarrhoea at the moment of sampling. Conclusions The abundance of some taxa in the faecal microbiota of diarrhoeic horses can be a result of microbiome dysbiosis, and therefore a cause of intestinal disease, or some of these taxa may act as equine enteric pathogens. Clostridium difficile colonisation seems to be transient in all of the horses studied, without overgrowth to trigger infection. A large proportion of the sequences were unclassified, showing the complexity of horses’ faecal microbiota. [less ▲]Detailed reference viewed: 33 (5 ULg) Exoplanet science with the LBTI: instrument status and plansDefrère, D.; Hinz, P.; Skemer, A. et alin Shaklan, Stuart (Ed.) Techniques and Instrumentation for Detection of Exoplanets VII (2015, September 16)The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for high-sensitivity, high-contrast, and high-resolution infrared (1.5-13 $\mu$m) imaging of nearby ... [more ▼]The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for high-sensitivity, high-contrast, and high-resolution infrared (1.5-13 $\mu$m) imaging of nearby planetary systems. To carry out a wide range of high-spatial resolution observations, it can combine the two AO-corrected 8.4-m apertures of the LBT in various ways including direct (non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging, non-redundant aperture masking, and nulling interferometry. It also has broadband, narrowband, and spectrally dispersed capabilities. In this paper, we review the performance of these modes in terms of exoplanet science capabilities and describe recent instrumental milestones such as first-light Fizeau images (with the angular resolution of an equivalent 22.8-m telescope) and deep interferometric nulling observations. [less ▲]Detailed reference viewed: 19 (1 ULg) Building bridges (preliminary steps towards a new dictionary of Ancient Egyptian)Winand, Jean Conference (2015, September 16)Detailed reference viewed: 19 (0 ULg) Agnolo Bronzino, Portrait d’une dame en rouge, 1525-1530, Francfort-sur-le-main, Städel Museum (notice). Id., Portrait de Lorenzo Lenzi, 1527-1530, Milan, Pinacoteca del Castello Sforzesco (notice). Id. Portrait de Laura Battiferri, 1555-1560, Florence, Museo di Palazzo Vecchio (notice).Geremicca, Antonio in Falciani, carlo (Ed.) Florence. Portrait à la cour des Médicis (2015)Detailed reference viewed: 22 (1 ULg) Les vies de Vasari et quelques autres sources sur le portraits florentins du XVIe siècleAgosti, Barbara; Geremicca, Antonio in Falciani, Carlo (Ed.) Florence. Portrait à la cour des Médicis (2015)Detailed reference viewed: 11 (1 ULg) Les arts à la cour de Cosme Ier et François Ier de Médicis. Comparaison entre un père et son filsGeremicca, Antonio in Falciani, Carlo (Ed.) Florence. Portrait à la cour des Médicis (2015)Detailed reference viewed: 13 (1 ULg) An Ant Colony System for Responsive Dynamic Vehicle RoutingSchyns, Michael in European Journal of Operational Research (2015), 245(3), 704-718We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets ... [more ▼]We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets (DVRPTWSD). Besides the traditional distance criterion, we address the important case of responsiveness. Responsiveness is defined here as completing a delivery as soon as possible, within the time window, such that the client or the truck may restart its activities. This is crucial for many production or service activities in different fields: express parcel deliveries, taxi services, Just in Time production, express repair services, medical care, petrol station replenishment, etc. We develop an interactive web-based solution to allow dispatchers to take new information into account in real-time. The algorithm and its parametrization were tested on real and artificial instances. We first illustrate our approach with a problem submitted by Liege Airport, the 8th biggest cargo airport in Europe. The goal is to develop a decision system to optimize the journey of the refueling trucks. We then consider some classical VRP benchmarks with extensions for more complex problems. [less ▲]Detailed reference viewed: 117 (29 ULg) A General Review of Model Order Reduction Techniques for Magnetodynamic ProblemsPaquay, Yannick Scientific conference (2015, September 15)Detailed reference viewed: 11 (2 ULg) Efficient and Precise Trajectory Planning for Nonholonomic Mobile RobotsLens, Stéphane Doctoral thesis (2015)Trajectory planning is one of the fundamental problems in mobile robotics. A wide variety of approaches have been proposed over the years to deal with the various issues of this problem. This thesis ... [more ▼]Trajectory planning is one of the fundamental problems in mobile robotics. A wide variety of approaches have been proposed over the years to deal with the various issues of this problem. This thesis presents an original and complete solution to tackle the motion planning problem for nonholonomic mobile robots in two-dimensional space. Given a set of obstacles, an initial and a goal configuration, the problem consists in computing efficiently a physically feasible trajectory that reaches the specified target as fast as possible. One of the original aspects of this work lies in the decomposition of the general problem into several simpler subproblems, for which very efficient solutions are developed. Their combination provides a complete trajectory planning approach that is one of the most computationally effective method suited for the motion of cylindrically shaped wheeled mobile robots in the presence of polygonal obstacles. This complete solution consists of three main steps. The first one is aimed at finding a short path that avoids obstacles and manages to reach the destination, without taking into account nonholonomic constraints of the robot. Our path planning method relies on an original refinement procedure of a constrained Delaunay triangulation of the obstacles, that outperforms other existing planning techniques. The second step consists in interpolating paths into smooth curves that can be followed by a real robot without slowing down excessively. By joining only two arcs of clothoids for moving from one curvature to another, our approach is simpler and also computationally cheaper than other interpolation methods. Finally, thanks to the introduction of an original discretization scheme, an efficient algorithm for computing a time-optimal speed profile for arbitrary paths is presented. The speed profile that results from this procedure not only allows the robot to follow the synthesized path as fast as possible while taking into account a broad class of velocity and accelerations constraints, but also provides the accurate advance information necessary to implementing coordinated actions during the displacement of the robot (e.g., between the locomotion system and other actuators). [less ▲]Detailed reference viewed: 167 (101 ULg) Empirical comparison of scoring rules at early stages of CATMagis, David Conference (2015, September 15)Usual scoring rules in CATs include maximum likelihood (ML), weighted likelihood (WL) and Bayesian approaches. However, at early stages of adaptive testing, only a few item responses are available so the ... [more ▼]Usual scoring rules in CATs include maximum likelihood (ML), weighted likelihood (WL) and Bayesian approaches. However, at early stages of adaptive testing, only a few item responses are available so the amount of information is very limited and in addition constant patterns (i.e. only correct or only incorrect responses) are often observed, yielding ML scoring intractable. Specific scoring rules (such as fixed- or variable stepsize adjustments) were developed for that purpose. However recent research highlighted that both Bayesian and WL scoring rules may provide finite values even with small sets of items. The purpose of this presentation is twofold: (a) to make a quick review of available scoring rules at early stages of CAT, and (b) to present empirical results from a simulation study that compares those scoring rules. More precisely, three scoring scenarios will be investigated: stepsize adjustment followed by ML, Bayes or WL followed by ML, and constant scoring rule throughout the CAT. These methods will be compared by means of simulated item banks and under various CAT scenarios for next item selection and stopping rules. Empirical results will be presented and practical guidelines for early stage scoring will be outlined. [less ▲]Detailed reference viewed: 15 (1 ULg) Annotations as reflection amplifiers in online learning - An exploratory studyVerpoorten, Dominique ; Specht, Marcus; Westera, Wimin Ullmann, T; Kravcik, M; Mikroyannidis, A (Eds.) et al Proceedings of the 5th Workshop on Awareness and Reflection in Technology-Enhanced Learning (ARTEL). In conjunction with the 10th european conference on technology enhanced learning: Design for teaching and learning in a networked world. (2015, September 15)In a controlled experiment on the effects of frequent and local digital annotations, 137 volunteers covered an online course at 3 conditions: no/free/question-based electronic annotations. Results show no ... [more ▼]In a controlled experiment on the effects of frequent and local digital annotations, 137 volunteers covered an online course at 3 conditions: no/free/question-based electronic annotations. Results show no difference in performance between groups. However, analyses conducted within treatments suggest positive impacts on performance when annotation rates are taken into consideration, and coupled with other reflective enactments. [less ▲]Detailed reference viewed: 27 (0 ULg) Origin of high-frequency TEC disturbances observed by GPS over the European mid-latitude regionWautelet, Gilles ; Warnant, René in Journal of Atmospheric and Solar-Terrestrial Physics (2015)High-frequency variability of the ionospheric Total Electron Content (TEC) can strongly affect precise positioning with GNSS. The occurrence rate as well as the amplitude of such disturbances has been ... [more ▼]High-frequency variability of the ionospheric Total Electron Content (TEC) can strongly affect precise positioning with GNSS. The occurrence rate as well as the amplitude of such disturbances has been extensively studied over the last decade. Mainly, one can distinguish disturbances due to space-weather events and the others, qualified as “quiet-time” as they are observed during quiet geomagnetic conditions. The latter, which represent more than 75% of the total number of disturbances over mid-latitudes, are then divided into two categories: the Winter Daytime (WD) and the Summer Nighttime (SN). The first category, representing the bulk of quiet-time disturbances, corresponds to classical Medium-Scale Traveling Ionospheric Disturbances (MSTIDs), that are the result of the interaction of gravity waves and the ionospheric plasma. On the other hand, SN disturbances are generally understood as non-classical MSTIDs of electrical origin. The paper investigates the origin of these two types of disturbance based on GPS measurements, ionospheric soundings and wind speed data at a tropospheric level. If one cannot exclude the solar terminator as a potential source of gravity waves responsible for WD events, it is thought that the major contribution comes from the lower atmosphere. More precisely, tropospheric jetstream is considered as the favorite candidate for daytime MSTIDs. Turning to SN disturbances, our analysis reveals that they are related to spread-F phenomenon, linked to the appearance of sporadic E-layers. The related instabilities are responsible for field-aligned irregularities in the F-region, which are thought to be responsible for noise-like fluctuations of the GPS TEC observed during SN events. [less ▲]Detailed reference viewed: 18 (0 ULg) Towards processes-based groundwater vulnerability assessmentsDassargues, Alain ; Popescu, Cristina; Brouyère, Serge Conference (2015, September 15)Various groundwater vulnerability methods have recently been developed. Considering groundwater quality issues, the most common techniques are based on calculation of an index expressing the protective ... [more ▼]Various groundwater vulnerability methods have recently been developed. Considering groundwater quality issues, the most common techniques are based on calculation of an index expressing the protective effect (i.e. in terms of solute contaminant transport) of underground formations overlying the groundwater resource (Gogu & Dassargues, 2000, Gogu et al., 2003)). However, there is a strong need for new methods giving more emphasis on the processes-based calculation of vulnerability indicators. As a first alternative, a method is proposed based on three factors describing a pollution event (Brouyère et al., 2001): (1) the transit time from the source to the target, (2) the duration of the contamination breakthrough at the target, (3) the ratio between the maximum concentration at the target to the released concentration at the contamination source. The method can feature the impact of surface runoff to preferential infiltration points. Practically, the assessment can then be based on the simulated breakthrough curves at the ‘target’ corresponding to Dirac-type solicitations (Popescu et al., 2008). Different vulnerability maps can be built according to the relative importance conventionally given to each of the three factors. This concept allows a clear distinction between conventional aspects and processes-based results in the building of a final vulnerability indicator. A second proposal consists in reframing the groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers (Beaujean et al., 2013). The method is here based on the calculation of sensitivity coefficients for a user-defined groundwater state for which several physically-based indicators are proposed. The sensitivity coefficients reflect the easiness with which the groundwater state transmits pressures into impacts. They are converted to vulnerability, using the concept of ‘transgressing a given threshold’ (Luers et al., 2003). While the methodology is general and can be applied in quantity as quality issues, the choice of causal chains has to be made prior to the calculation. The vulnerability is also related to a damaged state and is related to the ‘distance’ between the current state and a given threshold. Here also, the method allows a clear distinction between conventional choices (threshold) and scientific work (Dassargues et al., 2009). [less ▲]Detailed reference viewed: 22 (1 ULg) Learning to look - Purpose and design of an awareness-raising online course in veterinary sciencesTasnier, Sophie ; Busoni, Valeria ; Hanzen, Christian et alin Prilla, M; Ullmann, T; Kravcik, M (Eds.) et al Proceedings of the 5th Workshop on Awareness and Reflection in Technology-Enhanced Learning (2015, September 15)This paper reports on a work in progress: an online self-instruction course created to stimulate students’ awareness processes when dealing with pictures. Using non-clinical material, the “Learning to ... [more ▼]This paper reports on a work in progress: an online self-instruction course created to stimulate students’ awareness processes when dealing with pictures. Using non-clinical material, the “Learning to Look” course was de-signed as a preliminary training to the observation of histological sections, radi-ological graphs, and other specialized visual material. Following a presentation of the project, salient results of a feedback questionnaire completed by 382 stu-dents about their experience of the course are provided. [less ▲]Detailed reference viewed: 21 (1 ULg) Le passé à travers le prise du présentGrandjean, Geoffrey Article for general public (2015)Detailed reference viewed: 13 (0 ULg) Analyse du déterminisme génétique de l’inhibition de la synthèse du gossypol dans la graine chez la descendance de l’hybride [(Gossypium hirsutum L. x G. raimondii Ulb.)² x G. sturtianum Willis]Diouf, Fatimata Bintou Hassédine Doctoral thesis (2015)Several analyses were performed in advanced generations of HRS [(Gossypium hirsutum x G. raimondii) ² x G. sturtianum] hybrid. These were obtained by backcrossing and selfing HRS plants expressing the ... [more ▼]Several analyses were performed in advanced generations of HRS [(Gossypium hirsutum x G. raimondii) ² x G. sturtianum] hybrid. These were obtained by backcrossing and selfing HRS plants expressing the glanded-plant and glandless-seed trait of G. sturtianum. The purpose is to understand why it is not possible to fix this target character in the HRS progeny. Thus, HRS BC2S5, BC2S6, BC2S7, BC3S4, ♂BC4S3, ♂BC4S4, ♀BC4S3 and ♀BC4S4 plant populations were studied. Agro-morphological observations carried out on the studied plant material showed in all analyzed progenies significant fertility problems as manifested by high rates of embryo abortion, poor germination of seeds and premature mortality of many seedlings. Moreover, major phenotypic differences were observed between the HRS plants and upland cotton. Genomic in situ hybridization analysis (GISH) demonstrated that the magnitude of these problems is related to the importance of the presence of genetic material of the Australian species in HRS hybrids. The analysis of the plant material with the 10 SSRs markers, mapped on c2-c14, c3-c17, and c6-c25 linkage groups of G. hirsutum, points out very important segregation distortions (SD). Genotypic profiles were almost always heterozygous. These SD are caused by gametic and/or zygotic selections that occur respectively before and/or after fertilization. GISH showed the presence of one (1) to four (4) whole G. sturtianum chromosomes and one to two large fragments of G. sturtianum chromosomes. This structural heterozygosity is implicated in the SD observed. However, the massive presence of alien genetic material hardly affected the chromosome pairing and pollen fertility of the analyzed hybrid plants. This is contradictory to the observed SD and suggests a certain genetic balance in the analysed hybrids. It thus indicates no, or very weak interaction between the chromosomes of G. sturtianum and those of G. hirsutum into the genome of HRS derivatives. The expression of the desired character is very complex, but it is certain that: (i) the factors responsible for the desired trait are better transmitted through the ovule than the pollen, (ii) the alleles involved in the expression of the target trait operate both according to the additive and epistatic models, (iii) the increase of the G. hirsutum genetics background in the most advanced generations of the HRS hybrid is accompanied by a decrease of the expression of the desired trait, (iv) seeds viability problems affect both seeds with or without gossypol glands, whether they are well formed or malformed, showing the independence between at least a part of the imbalance factors and those related to the expression of researched character. Several G. sturtianum genes appear to be involved in the control of the target trait. However, the strong SD that characterizes the analyzed plants questions the reliability of this result obtained through single-marker analysis. A resumption of the breeding program using agro-morphological characterization tools, SSR and GISH, in the early generations of backcrossing, should help to better guide the selection program towards obtaining stable plants that express the character. [less ▲]Detailed reference viewed: 33 (6 ULg) Corporate Board Attributes and CAC: A Comparative Study of France, Germany and UKBoussaid, Nabila ; Hamza, Taher; Sougné, Danielle Conference (2015, September 14)This paper investigates the impact of corporate board of directors’ attributes on conditional accounting conservatim in the French, German and British contexts. Using pooled regression model over the ... [more ▼]This paper investigates the impact of corporate board of directors’ attributes on conditional accounting conservatim in the French, German and British contexts. Using pooled regression model over the period 2009-2012, our findings report that the relationship between corporate board attributes and accounting conservatism is country dependent. First, regarding the board composition, we find that the effect of board size is positive for German firms, negative for French firms and insignificant for British firms. We also document a positive association between board independence and accounting conservatism for British firms. However, we find no evidence of a positive association between codetermination and earnings conservatism in German context. Second, female seats on board seem to increase conservative reporting in financial statement only for French firms. Lastly, board meeting frequency in French and British firms appears to increase accounting conservatism. As a robustness test, we use an alternative measure of accounting conservatism namely, time–series of earnings changes measure and confirm the previous results. Overall, our results reveal that corporate board affects the financial reporting quality. [less ▲]Detailed reference viewed: 21 (1 ULg) The Red Marble of Baelen, an exceptional mid-Famennian mud mound complex in a carbonate ramp setting from Eastern BelgiumDreesen, Roland; Vachard, Daniel; Marion, Jean-Marc et alPoster (2015, September 14)The Red Marble of Baelen from the Limbourg area (Vesdre Basin, Eastern Belgium) represents a member of the middle Famennian (late Upper Devonian) Souverain-Pré Formation (Late marginifera conodont Zone ... [more ▼]The Red Marble of Baelen from the Limbourg area (Vesdre Basin, Eastern Belgium) represents a member of the middle Famennian (late Upper Devonian) Souverain-Pré Formation (Late marginifera conodont Zone). It corresponds to a short-term transgressive event and eustatic rise during the Famennian, interrupting the regressive megasequence on the Condroz shelf in Belgium. It is the only known or at least the only well-documented mid-Famennian carbonate mud mound complex worldwide, after the end-Frasnian mass extinction that wiped out numerous invertebrate taxa. [less ▲]Detailed reference viewed: 25 (1 ULg) Pt-Ni Hollow Nanoparticles for Oxygen Reduction Reaction : Controlling the Nanoparticle MorphologyAsset, Tristan ; Zubiaur, Anthony ; Chattot, Raphael et alPoster (2015, September 13)Detailed reference viewed: 25 (1 ULg)