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See detailDiffusion-based models for predicting sound fields in rooms with mixed specular and diffuse reflection
Foy, Cédric; Billon, Alexis ULg; Valeau, Vincent et al

Conference (2007, September)

A diffusion model, based on the numerical solution of a diffusion equation, was developed in the past to give accurate predictions of the sound-pressure level and of the sound decay at any location in a ... [more ▼]

A diffusion model, based on the numerical solution of a diffusion equation, was developed in the past to give accurate predictions of the sound-pressure level and of the sound decay at any location in a single enclosure or in coupled rooms. However, this model is limited to rooms with diffusely reflecting walls. In this study, two methods are presented to extend this model to rooms with mixed specular and diffuse reflections, defined by the classical room-acoustics scattering coefficient. The first method models the reverberant field by using a modified diffusion process, with an empirical diffusion constant departing from the theoretical one based on the mean free path. The set of these coefficients, which depend on the scattering coefficient, has been found empirically to fit the results given by a ray-tracing program. The second method is a hybrid approach. The reverberant sound field due to the diffuse reflections is first obtained with the original diffusion model. Then the sound field due to the specular reflections is modelled with an image-source model. The results given by the two approaches are compared to experimental data obtained for several types of rooms (a classroom, an office and some long rooms). [less ▲]

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See detailDiffusive equilibrium elements
Fraeijs de Veubeke, Baudouin ULg

Scientific conference (1973, July)

Equiliobrium models are characterized by an internal stress field in equilibrium and surface tractions that should obey the diffusivity requirement of reciprocity with adjacent elements at the interfaces ... [more ▼]

Equiliobrium models are characterized by an internal stress field in equilibrium and surface tractions that should obey the diffusivity requirement of reciprocity with adjacent elements at the interfaces. Thepaper discusses the construction of stiffness matices for such elements and the difficulties associated with the presence of mechanisms. The use of first order or second order stress functions is presented together with the possibility of solving the final equations by the force method through a direct flexibility method. Three methods are presented for getting rid of thre machanisms: the classical superelement technique, a method based on the discretization of rotational equilibrium and quasi-diffusivity. [less ▲]

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See detailDiffusive methane emissions to the atmosphere from Lake Kivu (Eastern Africa)
Borges, Alberto ULg; Abril, Gwenaël; Delille, Bruno ULg et al

in Journal of Geophysical Research. Biogeosciences (2011), 116(G03032),

We report a data-set of methane (CH4) concentrations in the surface waters of Lake Kivu obtained during four cruises (March 2007, September 2007, June 2008, April 2009) covering the two main seasons ... [more ▼]

We report a data-set of methane (CH4) concentrations in the surface waters of Lake Kivu obtained during four cruises (March 2007, September 2007, June 2008, April 2009) covering the two main seasons, rainy (October to May) and dry (June to September). Spatial gradients of CH4 concentrations were modest in the surface waters of the main basin. In Kabuno Bay (a small sub-basin), CH4 concentrations in surface waters were significantly higher than in the main basin. Seasonal variations of CH4 in the main basin were strongly driven by deepening of the mixolimnion and mixing of surface waters with deeper waters rich in CH4. On an annual basis, both Kabuno Bay and the main basin of Lake Kivu were over-saturated in CH4 with respect to atmospheric equilibrium (7330% and 2510%, respectively), and emitted CH4 to the atmosphere (39 mmol m-2 yr-1 and 13 mmol m-2 yr-1, respectively). The source of CH4 to atmosphere was two orders of magnitude lower than the CH4 upward flux. The source of CH4 to the atmosphere from Lake Kivu corresponded to ~60% of the terrestrial sink of atmospheric CH4 over the lake’s catchment. A global cross-system comparison of CH4 in surface waters of lakes shows that both Kabuno Bay and the main basin are at the lower end of values in lakes globally, despite the huge amounts of CH4 in the deeper layers of the lake. This is related to the strongly meromictic nature of the lake that promotes an intense removal of CH4 by bacterial oxidation. [less ▲]

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See detailDiffusive radical entry as the rate-determining step in amphiphilic block polyelectrolyte mediated emulsion polymerization
Leemans, Luc; Jérôme, Robert ULg; Teyssié, Philippe

in Macromolecules (1998), 31(17), 5565-5571

The amphiphilic water soluble block polyelectrolytes PMMA-b-SPGMA and PMMA-b-QPDMAEMA are efficient surfactants for the radical emulsion polymerization. Negatively charged, neutral, and positively charged ... [more ▼]

The amphiphilic water soluble block polyelectrolytes PMMA-b-SPGMA and PMMA-b-QPDMAEMA are efficient surfactants for the radical emulsion polymerization. Negatively charged, neutral, and positively charged entering radicals were used in combination with polyanionically and polycationically tailored PMMA latex particles. It was shown that the rate of polymerization was very high for systems wherein the entering radical species had an electrical charge sign identical with that of the polyelectrolyte corona around the latex particle. PMMA-b-SPGMA turned out to be 4 times as efficient as compared to SDS emulsified MMA polymerization at 0.6 wt %. Systems wherein polyelectrolyte block and entering radical were of opposite sign displayed strongly reduced polymerization rates. When the polyelectrolyte barrier became thick enough, as in the case of a Mn = 26 000 PMMA-b-QPDMAEMA, no more polymerization was observed. The observed polymerization rate effects are discussed in terms of repulsion of equal charge radicals, leading to enhanced mobility and counterion mobility restriction of the radicals of opposite sign to the polyelectrolyte block. In the latter case, this slowed counterion diffusion of radicals of opposite sign leads to premature aqueous phase termination of free radicals and consequently low flux of entering radicals with low rates of polymerization. The experimental results obtained are consistent with the theoretically predicted case, where the “control by aqueous phase growth” theory for the entry of free radicals in latex particles is invalid. [less ▲]

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See detailThe difR package, a toolbox for the identification dichotomous differential item functioning
Magis, David ULg

Conference (2011, February 25)

The purpose of this talk is to briefly introduce the R package difR to identify differential item functioning (DIF) among dichotomously scored items. The presentation is organized in three points. First ... [more ▼]

The purpose of this talk is to briefly introduce the R package difR to identify differential item functioning (DIF) among dichotomously scored items. The presentation is organized in three points. First, the general framework of DIF is outlined and the most known methods are presented succinctly. Second, the main functionalities of the difR package are described. Third, a practical application of difR is performed by a “live” analysis of a real example with several DIF methods. Future developments and objectives are discussed to conclude the talk. The difR package was jointly developed by Sébastien Béland (Université du Québec à Montréal, Canada), Francis Tuerlinckx (K. U. Leuven, Belgium) and Paul De Boeck (University of Amsterdam, The Netherlands). [less ▲]

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See detailDifunctional anionic initiator based on 1.3-diisopropenylbenzene. 5. Effect of polar additives and initiator seeding on the synthesis of poly(styrene-b-butadiene-b-styrene) copolymer
Yu, Y. S.; Dubois, Philippe ULg; Teyssié, Philippe et al

in Macromolecules (1997), 30(24), 7356-7362

The initiation of butadiene and styrene polymerization by a pure hydrocarbon soluble difunctional organolithium, 1,3-bis(1-lithio-1,3,3‘-trimethylbutyl)benzene, has been studied in a hydrocarbon solvent ... [more ▼]

The initiation of butadiene and styrene polymerization by a pure hydrocarbon soluble difunctional organolithium, 1,3-bis(1-lithio-1,3,3‘-trimethylbutyl)benzene, has been studied in a hydrocarbon solvent. The initiation occurs in such a way that part of the diadduct remains unreacted. When a second monomer feed along with tetrahydrofuran (THF) is added to the living chains, the residual diadduct is activated to the point where novel chains are formed. Weakly polar additives such as lithium alkoxides and aromatic ether can prevent part of the initiator from being inactive, although these additives are not effective enough to initiate the controlled synthesis of poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers. The seeding of the initiator which consists of butadiene oligomerization in the presence of anisole and tBuOLi in cyclohexane, has proved to be very efficient in providing SBS containing 85% 1,4-microstructure polybutadiene (PBD) and with high mechanical properties, e.g., ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%. [less ▲]

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See detailDifunctional initiator based on 1,3-diisopropenylbenzene. 2. Kinetics and mechanism of the sec-butyllithium/1,3-diisopropenylbenzne reaction
Yu, Y. S.; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecules (1996), 29(5), 1753-1761

Kinetics of the addition of s-butyllithium (s-BuLi) to 1,3-diisopropenylbenzene (1,3-DIB) has been studied, and the activation energy has been found to be 17.5 kcal/mol. Addition of s-BuLi to 1,3-DIB in a ... [more ▼]

Kinetics of the addition of s-butyllithium (s-BuLi) to 1,3-diisopropenylbenzene (1,3-DIB) has been studied, and the activation energy has been found to be 17.5 kcal/mol. Addition of s-BuLi to 1,3-DIB in a 2/1 molar ratio results in an oligomer rather than the desired diadduct. This observation has to be compared to the anionic polymerization of 1,3-DIB (hydrocarbon solvent at 50 °C) which leads to a polymer bearing ca. one double bond per monomeric unit. Li-NMR analysis of the addition of s-BuLi to 1,3-DIB (2/1 molar ratio) confirms the nonequivalence of the lithium cations and shows that ca. 30% s-BuLi remains unreacted when 1,3-DIB has been completely consumed. In the early stage of the addition, the propagation rate is faster than depropagation and the average molecular weight increases. When a depropagation−propagation quasi-equilibrium is reached, the oligomer molecular weight remains constant. It finally decreases when no DIB is left, as a result of depropagation. When the s-BuLi/1,3-DIB adduct is used as an initiator for styrene polymerization in the presence of a polar solvent, such as THF, initiation by monofuntional, difunctional, trifunctional, and tetrafunctional species is observed. In an apolar solvent, however, polystyrene of a narrow molecular weight distribution and a functionality of 2 is formed. This experimental observation more likely indicates that depolymerization of the 1,3-DIB oligomers occurs upon the addition of styrene. A mechanism which accounts for this propagation−depropagation process has been proposed and experimentally supported. [less ▲]

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See detailDifunctional initiator based on 1,3-diisopropenylbenzene. 4. Synthesis and modification of poly(alkyl methacrylate-b-styrene-b-butadiene-b-styrene-b-alkyl methacrylate (MSBSM) thermoplastic elastomers
Yu, Y. S.; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1996), 34(11), 2221-2228

MSBSM five-block copolymers where B stands for butadiene, S for styrene, and M for either methyl methacrylate (MMA) or tert-butyl methacrylate (tBMA) have been synthesized by sequential anionic ... [more ▼]

MSBSM five-block copolymers where B stands for butadiene, S for styrene, and M for either methyl methacrylate (MMA) or tert-butyl methacrylate (tBMA) have been synthesized by sequential anionic polymerization in an apolar solvent by using a difunctional anionic initiator derived from 1,3-diisopropenylbenzene. These block copolymers show improved mechanical properties and an extended service temperature compared to traditional SBS thermoplastic elastomers. Upon hydrolysis and further neutralization of the PolytBMA end-blocks, the upper glass transition temperature (Tg) of the five-block copolymers has been raised up to about 150°C. A further increase in this service temperature (up to ca. 160°C) has resulted from the blending of sPMMA-SBS-sPMMA five-block copolymers with isotactic poly(methacrylate) (iPMMA), due to the formation of a stereocomplex. The tensile properties of these modified five-block copolymers have remained essentially unchanged. [less ▲]

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See detailDifunctional initiator based on 1,3-diisopropenylbenzene. 6. Synthesis of methyl methacrylate-butadiene-methyl methacrylate triblock copolymers
Yu, Y. S.; Dubois, Philippe ULg; Teyssié, Philippe et al

in Macromolecules (1997), 30(15), 4254-4261

Synthesis of PMMA−PBD−PMMA (MBM) triblock copolymers with a 1,3-diisopropenylbenzene- (DIB-) based initiator is studied. Diethyl ether, tert-butyl methyl ether, N,N,N‘,N‘-tetramethylethylenediamine (TMEDA ... [more ▼]

Synthesis of PMMA−PBD−PMMA (MBM) triblock copolymers with a 1,3-diisopropenylbenzene- (DIB-) based initiator is studied. Diethyl ether, tert-butyl methyl ether, N,N,N‘,N‘-tetramethylethylenediamine (TMEDA) and THF were found to be efficient polar additives for obtaining PMMA−PBD−PMMA triblock copolymers, but these triblock copolymers displayed a high 1,2-microstructure of the PBD block. A combination of the initiator seeding technique and weakly polar additives has allowed MBM triblock copolymers with high 1,4-microstructure of PBD to be obtained. These copolymers exhibited a definitely higher upper service temperature than conventional thermoplastic elastomers, i.e. SBS or SIS Kratons. The influence of chain microstructure, copolymer composition and block length on the mechanical properties has been studied. Short polystyrene blocks of ca. Mn 2000 have been incorporated in between the PBD central block and the PMMA outer sequences. A higher tensile strength was observed for these MBM-like triblock coplymers. Contamination by a diblock structure expectedly had a very depressive effect on the bulk properties, and the stress−strain behavior mainly depended on the PMMA content and secondarily on molecular weight. [less ▲]

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See detailDifunctional initiator based on 1,3-diisopropenylbenzene. 7. Mechanical and thermal properties of new butadiene-based thermoplastic elastomers
Yu, Y. S.; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Rubber Chemistry and Technology (1997, November), 70(5), 820-838

Mechanical and thermal properties of SBS thermoplastic elastomers, in which S stands for polystyrene and B for polybutadiene, can be remarkably improved through end-capping by syndiotactic poly(methyl ... [more ▼]

Mechanical and thermal properties of SBS thermoplastic elastomers, in which S stands for polystyrene and B for polybutadiene, can be remarkably improved through end-capping by syndiotactic poly(methyl methacrylate) sequences. Furthermore, the upper service temperature of these sPMMA teleblock copolymers can also be enhanced by blending with isotactic PMMA so that the rubbery PBD soft segments are connected to high-melting stereocomplexed hard segments. The factors which affect the mechanical and thermal properties of these novel thermoplastic elastomers have been extensively investigated. [less ▲]

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See detailDifunctional initiators based on 1,3-diisopropenylbenzene. 3. Synthesis of a pure dilithium adduct and its use as difunctional anionic polymerization initiator
Yu, Y. S.; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecules (1996), 29(8), 2738-2745

The addition reaction of tert-butyllithium (t-BuLi) to 1,3-diisopropenylbenzene (1,3-DIB) has been studied. Under optimized conditions, i.e., reaction in cyclohexane at −20 °C and dropwise addition of 1,3 ... [more ▼]

The addition reaction of tert-butyllithium (t-BuLi) to 1,3-diisopropenylbenzene (1,3-DIB) has been studied. Under optimized conditions, i.e., reaction in cyclohexane at −20 °C and dropwise addition of 1,3-DIB to a 1:1 t-BuLi−triethylamine (Et3N) complex followed by a 1 h postreaction period, a pure diadduct is formed without concomitant oligomerization of 1,3-DIB. The behavior of this diadduct has been investigated, in apolar and polar solvents; triblock copolymers have been prepared and found to have interesting mechanical properties. [less ▲]

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See detailDifusion des inconnues hyperstatiques dans les voilures à longerons couplés
Fraeijs de veubeke, Baudouin ULg

in Bulletin du Service Technique de l'Aéronautique (1951), 24

This paper contains a first set of applications of the variational principles of elasticity to aeronautical structures.

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See detailDIGE application to investigate aphid adaptation to resistant host plant
Francis, Frédéric ULg; Goggin, Fiona; Guillonneau, François et al

in Abstract book (2006)

Detailed reference viewed: 12 (1 ULg)
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See detailDigestibilite ileale des acides amines de regimes monocereale-tourteau de soja chez le porc.
Leterme, Pascal; Thewis, André ULg; Thielemans, Marie France et al

in Revue de l’Agriculture = Landbouwtijdschrift (1991), 44(3), 423-432

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See detailLa digestibilite ileale reelle des acides amines chez le porc methodes d'estimation et interet pratique.
Leterme, Pascal; Thewis, André ULg

in 27èmes Journées de la recherche porcine en France (1995, February)

The estimation of the true ileal digestibility of dietary amino acids in pigs requires the distinction between the flow of undigestive dietary amino acids reaching the end of the small intestine and the ... [more ▼]

The estimation of the true ileal digestibility of dietary amino acids in pigs requires the distinction between the flow of undigestive dietary amino acids reaching the end of the small intestine and the flow of endogenous amino aicds coming from the digestive secretions that are not reabsorbed. This article reviews the direct and indirect method available: N-free diet (classic or improved), the regression method, the homoarginin method, the isotope dilution technique using labelled animals or labelled dietary proteins and the in vitro methods. The cases where the knowledge of the true digestibility seems to be interesting are then studied (feedstuffs poor in proteins, rich in antinutritional factors, etc). Thereafter, different subjects are brought up for the discussion: the practical use of true digestibility values, the necessity of takinf the endogenous losses into account and the validity of the true digestibility as a predictor of the availability of an amino acid for the pig [less ▲]

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See detailDigestibility and fermentation of inulin in the weaned piglets digestive tract.
Rossi, Florence; Ewodo, C.; Fockedey, R. et al

in Proceedings of the International Symposium " Non-digestible oligosaccharides : healthy food for the colon?" (1997, December)

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See detailDigestibility and Metabolic Utilization and Nutritional Value of Leucaena leucocephala (Lam.) Leaves Meal Incorporated in the Diets of Indigenous Senegal Chickens
Ayssiwede, Simplice Bosco; Dieng, Abdoulaye; Chrysostome, Christophe et al

in International Journal of Poultry Sciences (2010), 9(8), 767-776

In the prospect of the Leuceana leucocephala leaves meal using as a protein ingredient source for indigenous Senegal chickens diets, a study was carried out to determine their nutrient utilization and ... [more ▼]

In the prospect of the Leuceana leucocephala leaves meal using as a protein ingredient source for indigenous Senegal chickens diets, a study was carried out to determine their nutrient utilization and nutritional value when incorporated at various levels in the diets. Twenty adult indigenous chickens with an average body weight of 1.22 kg were conducted in metabolic cages and allocated in four groups of five birds each. The groups were corresponded to four dietary treatments (LL0, LL7, LL14 and LL21) containing respectively 0, 7, 14 and 21% of Leuceana leaves meal. During the trial, birds were weighed at the beginning and at the end. Feed offered and refused, collected fresh excreta were weighed daily and the droppings were oven-dried at 60oC and ground per bird for six days. The ingredients and experimental diets used and collected excreta were subjected to chemical analyses. Results showed that the Leuceana leaves were relatively rich in protein (24.9% DM), ether extract (6.4% DM), crude fiber (14.2% DM) and Neutral detergent fiber (22.4% DM). It contained respectively 43.1% and 11.4% DM of nitrogen free extract and ash, particularly calcium (1.8%) and potassium (1.1% DM) and 2573.8 kcal/kg DM of metabolizable energy. The results of the trial showed that the inclusion of L. leucocephala leaves meal in the diet at 21% level, has no significant adverse effect on feed intake, average daily weight gain, feed conversion ratio and nutrients utilization (except ether extract) of adult indigenous Senegal chickens. It has significantly (p<0.05) improved the crude protein and metabolizable energy utilization in birds fed the 7% level inclusion diet (LL7). [less ▲]

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See detailDigestibility and nitrogen balance in steers offered forage supplemented with barley, sugar beet pulp and straw
Raskin, Pascale; Dufrasne, Isabelle ULg; Baldwin, Paule ULg et al

in Grassland Science in Europe (1998)

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See detailLa digestion des albuminoïdes chez quelques invertébrés
Fredericq, Léon ULg

in Archives de zoologie expérimentale et générale (1879), VII

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See detailThe digestive enzymes and acidity of the pellets regurgitated by raptors
Leprince, Pierre ULg; Dandrifosse, Guy ULg; Schoffrniels, Ernest

in Biochemical Systematics & Ecology (1979), 7(3), 223-227

The activity of six digestive enzymes (amylase, chitinase, trypsin, chymotrypsin, carboxypeptidase A, pepsin) was examined in the water-soluble contents of the pellets egested by ten species of raptors ... [more ▼]

The activity of six digestive enzymes (amylase, chitinase, trypsin, chymotrypsin, carboxypeptidase A, pepsin) was examined in the water-soluble contents of the pellets egested by ten species of raptors (kestrel, saker, lanner, goshawk, barn owl, tawny owl, little owl, long-eared owl, African great-owl and steppe eagle). All the enzymes studied were present in the pellets from these birds, except for chitinase which was not detected in the pellets of the goshawk and the steppe eagle, and amylase and carboxypeptidase absent in the material egested by the lanner. The origin of the enzymes studied was examined. Pancreatic enzymes, which are present in the pellets, arise from a reflux of intestinal fluid into the stomach. The importance of this phenomenon is discussed. The acidity of the pellets was measured. Relations existing between the type of food, characteristics of the pellet and the digestive process in raptors are analysed. The evolutionary advantage of pellet egestion is discussed. [less ▲]

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