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See detailSepsis prediction in critically ill patients by platelet activation markers on ICU admission: a prospective pilot study
LAYIOS, Nathalie ULiege; Delierneux, Céline ULiege; Hego, Alexandre ULiege et al

in Intensive Care Medicine Experimental (2017), 5(1), 32

Background: Platelets have been involved in both surveillance and host defense against severe infection. To date, whether platelet phenotype or other hemostasis components could be associated with ... [more ▼]

Background: Platelets have been involved in both surveillance and host defense against severe infection. To date, whether platelet phenotype or other hemostasis components could be associated with predisposition to sepsis in critical illness remains unknown. The aim of this work was to identify platelet markers that could predict sepsis occurrence in critically ill injured patients. Results: This single-center, prospective, observational, 7-month study was based on a cohort of 99 non-infected adult patients admitted to ICUs for elective cardiac surgery, trauma, acute brain injury and post-operative prolonged ventilation and followed up during ICU stay. Clinical characteristics and severity score (SOFA) were recorded on admission. Platelet activation markers, including fibrinogen binding to platelets, platelet membrane P-selectin expression, plasma soluble CD40L, and platelet-leukocytes aggregates were assayed by flow cytometry at admission and 48h later, and also at the time of sepsis diagnosis (Sepsis-3 criteria) and 7 days later for sepsis patients. Hospitalization data and outcomes were also recorded. Of the 99 patients, 19 developed sepsis after a median time of 5 days. SOFA at admission was higher; their levels of fibrinogen binding to platelets (platelet-Fg) and of D-dimers were significantly increased compared to the other patients. Levels 48h after ICU admission were no longer significant. Platelet-Fg % was an independent predictor of sepsis (P = 0.030). By ROC curve analysis cutoff points for SOFA (AUC=0.85) and Platelet-Fg (AUC=0.75) were 8 and 50%, respectively. The prior risk of sepsis (19%) increased to 50% when SOFA was above 8, to 46% when Platelet-Fg was above 50%, and to 87% when both SOFA and Platelet-Fg were above their cutoff values. By contrast, when the two parameters were below their cutoffs, the risk of sepsis was negligible (3.8%). Patients with sepsis had longer ICU and hospital stays and higher death rate. Conclusion: In addition to SOFA, platelet-bound fibrinogen levels assayed by flow cytometry within 24h of ICU admission help identifying critically ill patients at risk of developing sepsis. [less ▲]

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See detailSpecial issue: Twelfth Workshop on Models and Algorithms for Planning and Scheduling Problems (MAPSP 2015)
Crama, Yves ULiege; Goossens, Dries; Leus, Roel et al

in Journal of Scheduling (2017), 20(6),

This special issue of the Journal of Scheduling contains ten papers presented at the Twelfth Workshop on Models and Algorithms for Planning and Scheduling Problems (MAPSP 2015), held from June 8 to June ... [more ▼]

This special issue of the Journal of Scheduling contains ten papers presented at the Twelfth Workshop on Models and Algorithms for Planning and Scheduling Problems (MAPSP 2015), held from June 8 to June 12, 2015, in La Roche-en-Ardenne, Belgium. [less ▲]

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See detailData-driven probabilistic post-earthquake fire ignition model for a community
Elhami Khorasani, Negar; Gernay, Thomas ULiege; Garlock, Maria

in Fire Safety Journal (2017), 94

Fire following earthquake (FFE), a cascading multi-hazard event, can cause major social and economical losses in a community. In this paper, two existing post-earthquake fire ignition models that are ... [more ▼]

Fire following earthquake (FFE), a cascading multi-hazard event, can cause major social and economical losses in a community. In this paper, two existing post-earthquake fire ignition models that are implemented in Geographic Information System (GIS) based platforms, Hazus and MAEViz/Ergo, are reviewed. The two platforms and their FFE modules have been studied for suitability in community resiliency evaluations. Based on the shortcomings in the existing literature, a new post-earthquake fire ignition model is proposed using historical FFE data and a probabilistic formulation. The procedure to create the database for the model using GIS-based tools is explained. The proposed model provides the probability of ignition at both census tract scale and individual buildings, and can be used to identify areas of a community with high risk of fire ignitions after an earthquake. The model also provides a breakdown of ignitions in different building types. Finally, the model is implemented in MAEViz/Ergo to demonstrate its application in a GIS-based software. [less ▲]

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See detailThe cognitive psychology and neuroscience of naming people
Brédart, Serge ULiege

in Neuroscience & Biobehavioral Reviews (2017), 83

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See detailBeyond dried blood spot: Current microsampling techniques in the context of biomedical applications
Nys, Gwenaël ULiege; Kok, Miranda ULiege; Servais, Anne-Catherine ULiege et al

in TrAC Trends in Analytical Chemistry (2017), 97

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See detailTwo-dimensional speckle tracking echocardiography in calves: feasibility and repeatability study
Lecoq, Laureline ULiege; Moula, Nassim ULiege; Amory, Hélène ULiege et al

in Journal of Veterinary Cardiology : The Official Journal of the European Society of Veterinary Cardiology (2017)

Objectives: To assess the feasibility and repeatability of two-dimensional speckle tracking echocardiography for the evaluation of left ventricular function in healthy calves. Animals: 12 Holstein calves ... [more ▼]

Objectives: To assess the feasibility and repeatability of two-dimensional speckle tracking echocardiography for the evaluation of left ventricular function in healthy calves. Animals: 12 Holstein calves, 62 ± 11.6 days old; 75.25 ± 5.4 Kg. Methods: Observational study. Right parasternal short-axis views at papillary muscle level were recorded in standing calves and subsequently analysed by two-dimensional speckle tracking for global and regional radial and circumferential strains and strain rates and radial displacement. Echocardiographic examinations were performed by 2 observers to evaluate intra- and interobserver repeatability and variability. Results: Two-dimensional speckle tracking was feasible in all calves. Automated tracking was better in systole than in diastole. Repeatability of the technique was good in calves. Systolic radial strain and strain rate peak values showed little variability compared to systolic circumferential strain and strain rate and to all diastolic measurements. Variability of the interobserver measurements was greater than the intraobserver measurements. Conclusions: Two-dimensional speckle tracking is feasible in calves. As in other species, evaluation of systolic radial left ventricular function is more reliable than circumferential and diastolic left ventricular function. [less ▲]

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See detailEnteropathogenic Escherichia coli O80:H2 in Young Calves with Diarrhea, Belgium
Thiry, Damien ULiege; Saulmont, Marc; Takaki, Shino et al

in Emerging Infectious Diseases (2017), 23(12),

Serogroup O80 was detected in 40% of 104 enteropathogenic Escherichia coli isolates from calves with diarrhea from 42 farms in Belgium during 2008‒2015. These isolates harbored the eae-ξ and fliCH2 genes ... [more ▼]

Serogroup O80 was detected in 40% of 104 enteropathogenic Escherichia coli isolates from calves with diarrhea from 42 farms in Belgium during 2008‒2015. These isolates harbored the eae-ξ and fliCH2 genes, similar to the O80 attaching-effacing Shigatoxigenic E. coli isolates found in humans in France. This strain might be emerging. [less ▲]

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See detailEmergent vortex phenomena in spatially and temporally modulated superconducting condensates
Jelic, Zeljko ULiege

Doctoral thesis (2017)

Superconductivity is an electronic state of matter arising from the existence of a common wave function with a coherent phase extending on a truly macroscopic scale. One major manifestation of this ... [more ▼]

Superconductivity is an electronic state of matter arising from the existence of a common wave function with a coherent phase extending on a truly macroscopic scale. One major manifestation of this striking quantum phenomenon is the dissipationless transport of electrical current, an asset deserving particular attention in the present times where the efficient energy distribution has become of utmost importance. Unfortunately, the motion of quantum units of magnetic flux (so-called vortices or fluxons), which is an unavoidable side-effect found in superconductors in the presence of transport currents and magnetic fields, severely limits the conditions to preserve dissipationless transport. This poses a challenge for achieving the functionalization of superconducting materials and threatens their spectrum of applications. It is widely known that any inhomogeneities (either material imperfections, or ones made artificially), which locally suppress superconductivity on the scale comparable to the core of the vortex, can pin the vortex and delay the onset of the vortex motion to higher applied currents. In recent years a substantial effort has been made to minimize the effects of current-induced vortex motion by tailoring arrays of artificial pinning centers. Besides improving the critical parameters of the superconducting state, a pinning matrix can be used for the manipulation of vortex matter, thus directly affecting the vortex dynamics, such as rectification of vortex motion under an ac drive (vortex diode) by introducing asymmetric pinning landscapes. In the literature one can find that the realization of the anchoring of the vortices can be based on nanostructured arrays of perforations, chemically grown defects, permanent nanomagnets, or even pinning sites produced by heavy ion bombardment. All of those realizations are based on a permanent imprint on the superconductor, without any possibility for subsequent modifications in the distribution and strength of the pinning. The principal objective of this thesis is to investigate the dynamical behavior of vortex matter under an entirely new kind of pinning landscape consisting of spatial and temporal modulation of the superconducting condensate. A particular case of spatial modulation is considered in a constricted structure where current lensing can cause extremely high vortex velocities. Subsequently, a time-dependent thermal potential introduced to the superconducting condensate will cause stroboscopic resonances during the vortex motion - a phenomenon that cannot be observed in the systems with static pinning imprints. Finally, a study of electronic gating is presented, where the local properties of superconductor, such as mean free path, or electronic band structure in general, can be influenced electronically. This is a completely unexplored interdisciplinary research topic, which will eventually allow one to manipulate individual vortices in superconducting materials by means of spatially confined and temporally controlled thermal and electromagnetic excitations. Furthermore, such techniques can provide one fundamental insight in different states of the vortex matter with respect to variation of the transport current, highly relevant for understanding the resistive state of superconducting materials and their applications. [less ▲]

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See detailStudy of plant-aphid interactions in Gabonese vegetable crops and biological control perspectives
Bayendi Loudit, Sandrine ULiege

Doctoral thesis (2017)

Periurban agriculture increased vegetables production in the cities. A survey was conducted in three market gardening in Libreville and Owendo cities to register crop and pesticides diversity uses by ... [more ▼]

Periurban agriculture increased vegetables production in the cities. A survey was conducted in three market gardening in Libreville and Owendo cities to register crop and pesticides diversity uses by farmers. The most abundant cultivated species throughout the year appeared to be amaranth (Amaranthus ama L. Amaranthaceae). The most important pests were aphids (Hemiptera: Aphididae) and some beetles (Coleoptera). To control the pests, conventional neurotoxic insecticides were used with effect on environment and human health. In order to identify the occurring insects in the selected areas, a monitoring of insects was carried out during two years on amaranth, roselle, tomato (Lycopersicon esculentum M., Solanaceae) and cabbage (Brassica oleracea L., Brassicaceae). Entomological abundance and diversity were assessed through weekly trapping and visual observations from July to August each year. Insects were collected, identified at the taxonomic level of the family, and classified into three categories: pests, beneficials and associated insects to agriculture. Eighty four families belonging to height orders were recorded with 7910 and 3148 sampled individuals in 2012 and 2013 respectively. The predominant insect families were in both years Aphididae, Cecidomyiidae (Diptera) and Chrysomelidae (Coleoptera) for pests, Dolichopodidae (Diptera), Staphylinidae (Coleoptera) and Coccinellidae (Coleoptera) for beneficials, and Muscidae (Diptera), Psychodidae (Diptera) and Formicidae (Hymenoptera) for associated insects. As aphids are the most important pests, further study at species level and in relation to predatory beneficials were assessed on vegetable crops in 2013 in two periurban gardening sites. The Aphis craccivora Koch aphid was the most abundant aphid species observed infesting amaranth in both sites. The other aphid species were Lipaphis erysimi Kaltenbach, Myzus persicae Sulzer, Aphis fabae Scopoli and Aphis gossypii Glover. Moreover, seven species of natural enemies were trapped, mainly predatory hoverflies (Diptera: Syrphidae) and ladybirds (Coleoptera; Coccinellidae). A. craccivora Koch is known to be a vegetable pest. Its recent identification as pest in amaranth motivated us to study their multitrophic interactions. Since relationships between aphids and host plants could be related to symbiont and feeding behaviour. A. craccivora endosymbiont bacteria and saliva protein diversity were analysed to explain plant–aphid interactions. Indeed, Buchnera aphidicola was found. Some proteins were only identified in solid and soluble saliva, while others originated from Serratia sp. endosymbiont. Two of the identified proteins are involved in plant-pathogen interactions: calmodulin and elongation factor Tu. To control A. craccivora which causes several crop damages, volatile organic compounds (VOC) have been studied. Only aphid alarm pheromone (E)-β-farnesene (EβF) was identified and quantified. Its effect on escape behaviour in aphids has been demonstrated on three species. A. craccivora responded more strongly than the two other Aphidinae (M. persicae and A. fabae) species with 78% of the individuals initiated dispersal behavior at 500 ng dose of EβF. In another laboratory study, the repellency effect of (E)-β-farnesene, methyl salicylate and two essential oils of basil species (Ocimum gratissimum L. and Ocimum basilicum L. Lamiaceae) were determined, while no repellent effect was observed. Also, aphid populations were reduced by exposure to EβF and O. gratissimum essential oil. This study is one of the few to explore the description of insects in the market gardens of Libreville. This could contribute to the elaboration of the sustainable development strategies of pest control in the zones. [less ▲]

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See detailNew therapeutic approaches for malignant pleural mesothelioma targeting DNA repair and transforming growth factor TGF-alpha
Staumont, Bernard ULiege

Doctoral thesis (2017)

Malignant pleural mesothelioma (MPM) is an aggressive cancer of the pleura mainly caused by asbestos fibers exposure. MPM is notably characterized by a very poor prognosis and current treatments ... [more ▼]

Malignant pleural mesothelioma (MPM) is an aggressive cancer of the pleura mainly caused by asbestos fibers exposure. MPM is notably characterized by a very poor prognosis and current treatments, including radiation and chemotherapy, are unsatisfactory. As genomic analyzes show that the major mutations occurring in MPM cells pertain to checkpoint control and DNA repair, a first part of this thesis addresses the DNA damage response and the mechanisms of DNA repair in several MPM cell lines. In this study, we show that gamma ionizing radiation (IR) induces cell cycle arrest of MPM cells at the G2-M checkpoint. We also demonstrate that MPM cells are driven prematurely towards mitosis following the abrogation of IR-induced G2 arrest by the checkpoint inhibitor UCN-01, however without a significant induction of cell death. To avoid excessive genomic instability, DNA repair mechanisms are likely to play a key role in such DNA-damaging conditions. We therefore evaluate here the efficiencies of the two main DNA double-strand break repair mechanisms, non-homologous end-joining (NHEJ) and homologous recombination (HR) and highlight differences in such repair activities among MPM cell lines and in comparison to control mesothelial cells. We underline an efficient HR repair in MPM cells, opening the door to additional investigations that might reveal an addiction to activated DNA repair pathways and thereby render MPM cells hypersensitive to targeted combination therapies. In the second part of this thesis, we perform a pre-clinical study investigating the resistance of MPM to a particular epigenetic-based therapy associating the histone deacetylase (HDAC) inhibitor valproic acid (VPA) and doxorubicin. By comparing MPM cell lines with a differential sensitivity to this combination chemotherapy, this study suggests a correlation between transforming growth factor-alpha (TGF-α) expression and resistance to treatment. We further confirm the role of TGF-α in chemoresistance by modulating its expression in highly- and poorly responsive MPM cell lines. In addition, pharmacological inhibition of TGF-α’s receptor (EGFR or epidermal growth factor receptor) by tyrosine kinase inhibitors gefitinib and erlotinib improves the efficacy of VPA+doxorubicin in vitro. Dual HDAC-EGFR inhibitor CUDC-101 furthermore synergizes with doxorubicin to induce apoptosis in vitro and to slow down tumor growth in two different MPM mouse models, emphasizing its therapeutic potential and opening new prospects for combination therapies associating HDAC and EGFR inhibition against MPM. With two different approaches, this thesis provides a better understanding of MPM resistance to chemo- and radiotherapies and offers clues for new therapeutic strategies based on DNA repair pathways and dual HDAC-EGFR/TGF-α inhibition. [less ▲]

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See detailPLUMAGE DIVERSITY IN BASAL PARAVIANS
Lefevre, Ulysse ULiege

Doctoral thesis (2017)

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See detailHypogonadisme chez l’homme diabétique: actualités diagnostiques & thérapeutiques
VALDES SOCIN, Hernan Gonzalo ULiege

in VALDES SOCIN, Hernan Gonzalo (Ed.) RENCONTRES D’ENDOCRINOLOGIE 2017 (2017, November 25)

Résumé L’hypogonadisme chez l’homme diabétique est un syndrome clinique fréquemment sous-estimé, caractérisé par des signes et symptômes de déficience androgénique mais également par des troubles de la ... [more ▼]

Résumé L’hypogonadisme chez l’homme diabétique est un syndrome clinique fréquemment sous-estimé, caractérisé par des signes et symptômes de déficience androgénique mais également par des troubles de la fertilité. La physiopathologie de cet hypogonadisme est complexe et multifactorielle. Les troubles de la régulation glycémique, l’hyperinsulinisme et l’obésité déterminent un dysfonctionnement au niveau hypothalamique mais également au niveau gonadique. Un faisceau d’arguments nouveaux soulèvent l’intérêt de rechercher et de traiter l’hypogonadisme chez l’homme diabétique. Tout d’abord, plusieurs études épidémiologiques (1) montrent que le déficit en testostérone prédit la survenue d’un syndrome métabolique et du diabète, et que ce déficit s’accompagne d’une mortalité cardiovasculaire plus élevée (2). Ensuite, neuf études récentes démontrent que la perte pondérale intensive obtenue par régime et/ou chirurgie bariatrique normalise les taux de testostérone (3). Par ailleurs, une méta analyse portant sur cinq études confirme que la supplémentation en testostérone chez le diabétique hypogonadique se traduit par une réduction modeste de la circonférence abdominale, par une diminution de la glycémie et de l’HbA1c (4). Enfin, certaines études indiquent que la supplémentation en testostérone chez ces patients améliore leur survie (5). Si l’ensemble de ces études d’observation et d’intervention suggèrent des effets cardiométaboliques avantageux induits par la testostérone, on peut regretter un manque d’études randomisées, à large cohorte, évaluant les risques et bénéfices sur le long terme de ce traitement hormonal de supplémentation chez les patients diabétiques. Cette présentation fait le point sur les évidences actuelles reliant le déficit androgénique avec le diabète de type 2 et ses implications sur le risque cardiométabolique. [less ▲]

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See detailHarmful tax competition within the European Union: from tax rulings to financial transaction taxes
Van Cleynenbreugel, Pieter ULiege

Conference (2017, November 24)

In this presentation, I will outline how the EU constitutional framework reacts against harmful tax competition, in addition to showcasing the limits and negative consequences of that approach.

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See detailCiné-débat: Merci pour la pluie
Wellens, Joost ULiege

Conference given outside the academic context (2017)

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See detailIsolation and characterization of nanocelluloses from wheat straw and their application in agricultural water-saving materials
Liu, Qi ULiege

Doctoral thesis (2017)

Humans have been cultivating land for approximately 12,000 years. As such, most countries worldwide have considered crop waste as a global issue linked with environmental protection, economic development ... [more ▼]

Humans have been cultivating land for approximately 12,000 years. As such, most countries worldwide have considered crop waste as a global issue linked with environmental protection, economic development, and healthy living. Many varieties of straw are produced all over China in massive quantities (more than 900 million tons per year). Although banned by the government, stubble burning is widely applied by Chinese farmers as an easy and cheap way to remove stalks after harvests. However, this practice significantly contributes to China’s carbon dioxide emissions and health risks associated with the thick mists it produces. As a renewable biomass resource, straw can be used to make new marketable materials, but its full potential has yet to be realized. Thus, future studies should be directed toward the isolation and rational use of agricultural waste. In addition to the pollution caused by agricultural waste, water shortage, particularly in northern and northwestern China, severely hinders agricultural production. This region accounts for half of the total surface of China but has less than 20% of the total national available water resources. Despite the severity of the water shortage in this region, the efficiency of irrigation water use is only 40%. Many strategies have been applied to promote a water-saving agriculture. One such strategy is the use of water-saving materials, such as plastic mulching films and superabsorbent polymers. However, these two materials are non-biodegradable, and their mechanical properties are unsatisfactory. A systematic analysis of the literature revealed that agricultural waste is a cheap and promising source of raw materials that could be used to obtain cellulose and nanocelluloses. Nanocelluloses can be used for the industrial production of super-strong but lightweight nanocomposite materials. The first step involved the isolation of cellulose, cellulose nanocrystallines (CNCs), and cellulose nanofibers (CNFs) from wheat straw. First, four CNCs were isolated from four commercial microcrystalline celluloses (MCCs) through sulfuric acid hydrolysis. The effects of the characteristics of the MCC on the morphology, structure, and properties of the resulting CNCs were assessed. The results revealed that both particle size and dispersity influenced the isolated CNCs. Second, cellulose was isolated from wheat straw through a microwave-assisted chemical treatment process that reduced chemical use. The reaction conditions and promoting effect of microwave on the resulting fibers were investigated. The results indicated that temperature played the most important role in cellulose isolation, and that microwave can reduce either the reaction time or the chemical use during the microwave-assisted alkali hydrolysis process. High-purity (94%) CNFs were isolated from wheat straw through an environmentally friendly, multi-step treatment process that combined steam explosion, microwave-assisted hydrolysis, and microfluidization. Chemical identification and characterization were performed to study the effect of each treatment step and investigate the potential utilization of CNFs in nanocomposites. Chemical analysis showed that the cellulose content increased from 44.81% to 94.23%, whereas the hemicellulose and lignin contents significantly decreased from 33.41% and 8.75% to 5.54% and 1.68%, respectively. Long and loose 10–40 nm wide nanofiber bundles and an entangled network of cellulose fibers with an average individual diameter of 5.42 nm were observed during this eco-friendly process. In the last part of this study, nanocelluloses were introduced into superabsorbent polymers and mulching films used in agriculture to improve their performance. The effects of nanocelluloses on their structure, properties, and mechanical performance were investigated. First, superabsorbent polymers of acrylamide–acrylate copolymers and others with CNFs, CNCs, or MCC were synthesized. The swelling capacities in pure water and in various solutions, the capacities for repeated water absorption, the water-retaining capacities in soil, and the mechanical properties of the hydrogels were compared. The results revealed that the 3D structures of the acrylamide–acrylate–CNF and acrylamide–acrylate–CNC hydrogels were strengthened by the nanocellulose. These two polymers exhibited excellent capacities for repeated water absorption. By contrast, the biodegradable agricultural mulching film did not present satisfying mechanical and barrier properties as an alternative for ordinary polyethylene film. In this thesis, CNC was introduced into the film of poly (butyleneadipate-co-terephthalate) /polylactic acid composites. Poly(butyleneadipate-co-terephthalate)/polylactic acid/CNC films with various contents of CNC were prepared, characterized, and tested as for their properties. Compared with the film without CNC, poly (lactic acid) / poly (butylene-adipate-co-terephtalate)/3% CNC film showed an increased deformation by 188.80%. The barrier performance of the films increased with increasing CNC content. However, the tensile properties decreased when the CNC content exceeded 3%. Both the mechanical and barrier properties were promoted. These results highlighted that (i) wheat straw is a cellulose-rich natural resource of CNF and CNC; (ii) microwave can reduce either the reaction time or the chemical use during the cellulose-isolation process; (iii) high-purity CNF could be obtained through an environmentally friendly method; and (iv) nanocellulose could improve the mechanical properties of both superabsorbent polymers and mulching films, and enhance their performances in agricultural applications. In a broader perspective, microwave and other techniques should be further explored in the context of green isolation processes. Agricultural biomass natural fiber-based composites must be further investigated to maximize their applications. Approaches that could offer significant cost savings for the industrial production of nanocellulose and new nanocellulose-based materials should be developed further. We aim to promote the research interest for the isolation and application of agricultural-waste-based nanocellulose, which deserve further research and documentation. This thesis is only the beginning of a greater endeavor. [less ▲]

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See detailLa terminologie grecque et latine du plurilinguisme
Rochette, Bruno ULiege

Conference (2017, November 24)

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See detailAllocution de clôture
Van Cleynenbreugel, Pieter ULiege

Speech/Talk (2017)

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See detailInvestigating the effects of hydrodynamics and mixing on mass transfer through the free-surface in stirred tank bioreactors
de Lamotte, Anne ULiege; Delafosse, Angélique ULiege; Calvo, Sébastien ULiege et al

in Chemical Engineering Science (2017), 172

In stirred-tank bioreactors, flow structures of various length and time scales are implied in scalar transport phenomena, such as gas species transfer through the liquid free-surface and their ... [more ▼]

In stirred-tank bioreactors, flow structures of various length and time scales are implied in scalar transport phenomena, such as gas species transfer through the liquid free-surface and their homogenization in the bulk. A proper understanding of the underlying mechanisms, i.e. hydrodynamics, mixing and mass transfer, and of their interactions is required to design and develop reliable and efficient production-scale bioprocesses. The objective of the present work is to experimentally investigate the coupling between gas-liquid mass transfer of oxygen with mixing efficiency and circulation patterns inside an arbitrarily chosen stirred-tank configuration aerated through the liquid free-surface, a baffled 20 L-vessel agitated by two Rushton turbines. Based on global parameter values, the most appropriate rotating speed, N = 300 rpm, is selected in order to further study local hydrodynamic quantities using Particle Image Velocimetry (PIV), as well as mixing and mass transfer dynamics using Planar Laser-Induced Fluorescence (PLIF). The results obtained with these local experimental methods are analyzed in detail. Their averages are first successfully compared to global data. Statistical analysis of their spatial distributions show that large-scale flow patterns significantly influence mass transfer through the free-surface of the stirred tank. Even if global measurements show that global characteristic times for mixing and mass transfer differ by two orders of magnitude, local experimental characterization shows persistent vertical gradients of dissolved gas concentrations. So the dissolved gas concentration is not as perfectly uniform as one might expect. [less ▲]

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See detailA forward model for electrical conduction in soil-root continuum: a virtual rhizotron study
Rao, Sathyanarayan; Meunier, Félicien; Ehosioke, Solomon ULiege et al

Poster (2017, November 23)

Electrical Resistivity Tomography monitoring of soil-root system water fluxes have received growing interest in the past decades. Some studies suggest that roots can be more electrically conductive than ... [more ▼]

Electrical Resistivity Tomography monitoring of soil-root system water fluxes have received growing interest in the past decades. Some studies suggest that roots can be more electrically conductive than soil. We suggest that ERT data taken in agricultural fields is impacted by plant roots and might contaminate estimates of soil water content based on bare soil petrophysical relations. To understand how do roots impact electrical current flow and thus ERT data, a numerical electrical model was coupled with a mechanistic maize-soil water flow model. All the maize roots with a radius larger than 0.05 cm were explicitly accounted for in the finite element mesh and associated to their specific electrical properties. Root growth and water uptake processes continuously affected the EC contrast between soil and root. We demonstrated that high contrats between root and soil EC lead to errors in the estimation of soil water content, which could be disminished by using an appropriate biopedophysical correction term. The effective EC (bulk properties) of the medium computed using simulated plate electrodes at rhizotron boundaries reveal directional anisotropy induced by root processes and is more pronounced in sand medium when compared to loam. The percentage change in bulk EC due to change in direction (𝐸𝐸𝐸𝐸ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 .vs. 𝐸𝐸𝐸𝐸𝑣𝑣𝑣𝑣𝑣 𝑣 𝑣𝑣𝑣𝑣𝑣 𝑣 ) starts at ~30 % in sand and ~3 % in loam when root is young and increases upto ~500% in sand and ~20% in loam at day 22 when root is three weeks old. Directions in which there is more anisotropy contains more information on the root processes and hence they can be used as prior information for ERT injection scheme to retrieve better information. [less ▲]

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