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See detailA crossed random effects model to detect differential item functioning
Frederickx, Sofie; Magis, David ULiege; Tuerlinckx, Francis et al

Conference (2008, June)

Detailed reference viewed: 9 (1 ULiège)
See detailCrossed random effects models for the detection of differential item functioning in psychometrics
Magis, David ULiege; Frederickx, Sofie; Tuerlinckx, Francis et al

Conference (2008, October)

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See detailCrossing a "Human River of Shattered Lives": Caryl Phillips's Diasporic Fiction/Visions
Ledent, Bénédicte ULiege

in Literary Criterion (2000), 35(1-2), 157-169

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See detailCrossing abilities of ALS Target-Site Resistant Black-grass (Alopecurus myosuroides HUDS.)
Maréchal, Pierre-Yves ULiege; Henriet, François; Vancutsem, Françoise ULiege et al

in Communications in Agricultural and Applied Biological Sciences (2011)

Black-grass crossings were conducted outdoor for two successive years in a way to determine the percentage of resistant black-grass that can be engendered in one generation, after the introduction of one ... [more ▼]

Black-grass crossings were conducted outdoor for two successive years in a way to determine the percentage of resistant black-grass that can be engendered in one generation, after the introduction of one Target-Site resistant individual. After germination, plants were genotyped and couples of resistant and susceptible individuals were formed, then planted outdoor and enclosed with a pollen-proof cloth to avoid any external pollen contamination. Seeds were collected and tested in glasshouses with herbicide spraying. DNA analyses were also performed on surviving plants to distinguish hetero- from homozygotes. The resistance level of the progeny seems to be fairly high and Mendelean distribution is generally confirmed. The offspring of self-crossings was also observed to assess the facultative autogamy ability, according to the genotype and the presence of mutant ALS alleles (position W-574). [less ▲]

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See detailCrossing of two mobile averages: A method for measuring the roughness exponent
Vandewalle, Nicolas ULiege; Ausloos, Marcel ULiege

in Physical Review. E : Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (1998), 58(5), 6832-6834

Self-affine signals characterized by a defined Hurst (roughness) exponent H can be investigated through mobile averages. The density rho of crossing points between any two moving averages is a measure of ... [more ▼]

Self-affine signals characterized by a defined Hurst (roughness) exponent H can be investigated through mobile averages. The density rho of crossing points between any two moving averages is a measure of long-range power-law correlations in the signal. The method is compared to the detrended fluctuation analysis. We rake advantage of our findings in order to propose a practically powerful and accurate technique for determining H and apply it right away to cases with persistent or antipersistent correlations. [less ▲]

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See detailCrossing the dividing surface of transition state theory. I. Underlying symmetries and motion coordination in multidimensional systems
Lorquet, Jean-Claude ULiege

in Journal of Chemical Physics (2014), 140(13), 134303

The objective of the present paper is to show the existence of motion coordination among a bundle of trajectories crossing a saddle point region in the forward direction. For zero total angular momentum ... [more ▼]

The objective of the present paper is to show the existence of motion coordination among a bundle of trajectories crossing a saddle point region in the forward direction. For zero total angular momentum, no matter how complicated the anharmonic part of the potential energy function, classical dynamics in the vicinity of a transition state is constrained by symmetry properties. Trajectories that all cross the plane R = Ro at time t = 0 (where Ro denotes the position of the saddle point) with the same positive translational momentum PRo can be partitioned into two sets, denoted "gerade" and "ungerade," which coordinate their motions. Both sets have very close average equations of motion. This coordination improves tremendously rapidly as the number of degrees of freedom increases. This property can be traced back to the existence of time-dependent constants of the motion. © 2014 AIP Publishing LLC. [less ▲]

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See detailCrossing the dividing surface of transition state theory. II. Recrossing times for the atom-diatom interaction
Lorquet, Jean-Claude ULiege

in Journal of Chemical Physics (2014), 140(13), 134304

We consider a triatomic system with zero total angular momentum and demonstrate that, no matter how complicated the anharmonic part of the potential energy function, classical dynamics in the vicinity of ... [more ▼]

We consider a triatomic system with zero total angular momentum and demonstrate that, no matter how complicated the anharmonic part of the potential energy function, classical dynamics in the vicinity of a saddle point is constrained by symmetry properties. At short times and at not too high energies, recrossing dynamics is largely determined by elementary local structural parameters and thus can be described in configuration space only. Conditions for recrossing are given in the form of inequalities involving structural parameters only. Explicit expressions for recrossing times, valid for microcanonical ensembles, are shown to obey interesting regularities. In a forward reaction, when the transition state is nonlinear and tight enough, one-fourth of the trajectories are expected to recross the plane R = R o (where Ro denotes the position of the saddle point) within a short time. Another fourth of them are expected to have previously recrossed at a short negative time, i.e., close to the saddle point. These trajectories do not contribute to the reaction rate. The reactive trajectories that obey the transition state model are to be found in the remaining half. However, no conclusion can be derived for them, except that if recrossings occur, then they must either take place in the distant future or already have taken place in the remote past, i.e., far away from the saddle point. Trajectories that all cross the plane R = Ro at time t = 0, with the same positive translational momentum P can be partitioned into two sets, distinguished by the parity of their initial conditions; both sets have the same average equation of motion up to and including terms cubic in time. Coordination is excellent in the vicinity of the saddle point but fades out at long (positive or negative) times, i.e., far away from the transition state. © 2014 AIP Publishing LLC. [less ▲]

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See detailCrossing the dividing surface of transition state theory. III. Once and only once. Selecting reactive trajectories
Lorquet, Jean-Claude ULiege

in Journal of Chemical Physics (2015), 143

The purpose of the present work is to determine initial conditions that generate reacting, recrossing-free trajectories that cross the conventional dividing surface of transition state theory (i.e., the ... [more ▼]

The purpose of the present work is to determine initial conditions that generate reacting, recrossing-free trajectories that cross the conventional dividing surface of transition state theory (i.e., the plane in configuration space passing through a saddle point of the potential energy surface and perpendicular to the reaction coordinate) without ever returning to it. Local analytical equations of motion valid in the neighborhood of this planar surface have been derived as an expansion in Poisson brackets. We show that the mere presence of a saddle point implies that reactivity criteria can be quite simply formulated in terms of elements of this series, irrespective of the shape of the potential energy function. Some of these elements are demonstrated to be equal to a sum of squares and thus to be necessarily positive, which has a profound impact on the dynamics. The method is then applied to a three-dimensional model describing an atom-diatom interaction. A particular relation between initial conditions is shown to generate a bundle of reactive trajectories that form reactive cylinders (or conduits) in phase space. This relation considerably reduces the phase space volume of initial conditions that generate recrossing-free trajectories. Loci in phase space of reactive initial conditions are presented. Reactivity is influenced by symmetry, as shown by a comparative study of collinear and bent transition states. Finally, it is argued that the rules that have been derived to generate reactive trajectories in classical mechanics are also useful to build up a reactive wave packet. [less ▲]

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See detailCrossing the dividing surface of transition state theory. IV. Dynamical regularity and dimensionality reduction as as key features of reactive trajectories
Lorquet, Jean-Claude ULiege

in The Journal of Chemical Physics (2017), 146

The atom-diatom interaction is studied by classical mechanics using Jacobi coordinates (R, r, θ). Reactivity criteria that go beyond the simple requirement of transition state theory (i.e., PR* > 0) are ... [more ▼]

The atom-diatom interaction is studied by classical mechanics using Jacobi coordinates (R, r, θ). Reactivity criteria that go beyond the simple requirement of transition state theory (i.e., PR* > 0) are derived in terms of specific initial conditions. Trajectories that exactly fulfill these conditions cross the conventional dividing surface used in transition state theory (i.e., the plane in configuration space passing through a saddle point of the potential energy surface and perpendicular to the reaction coordinate) only once. Furthermore, they are observed to be strikingly similar and to form a tightly-packed bundle of perfectly collimated trajectories in the two-dimensional (R, r) configuration space, although their angular motion is highly specific for each one. Particular attention is paid to symmetrical transition states (i.e., either collinear or T-shaped with C2v symmetry) for which decoupling between angular and radial coordinates is observed, as a result of selection rules that reduce to zero Coriolis couplings between modes that belong to different irreducible representations. Liapunov exponents are equal to zero and Hamilton's characteristic function is planar in that part of configuration space that is visited by reactive trajectories. Detailed consideration is given to the concept of average reactive trajectory, which starts right from the saddle point and which is shown to be free of curvature-induced Coriolis coupling. The reaction path Hamiltonian model, together with a symmetry-based separation of the angular degree of freedom, provide an appropriate framework that leads to the formulation of an effective two-dimensional Hamiltonian. The success of the adiabatic approximation in this model is due to the symmetry of the transition state, not to a separation of time scales. Adjacent trajectories, i.e., those that do not exactly fulfill the reactivity conditions have similar characteristics, but the quality of the approximation is lower. At higher energies, these characteristics persist, but to a lesser degree. Recrossings of the dividing surface then become much more frequent and the phase space volume of initial conditions that generate recrossing-free trajectories decreases. Altogether, one ends up with an additional illustration of the concept of reactive cylinder (or conduit) in phase space that reactive trajectories must follow. Reactivity is associated with dynamical regularity and dimensionality reduction, whatever the shape of the potential energy surface, no matter how strong its anharmonicity, and whatever the curvature of its reaction path. Both simplifying features persist during the entire reactive process, up to complete separation of fragments. The ergodicity assumption commonly assumed in statistical theories is inappropriate for reactive trajectories. [less ▲]

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See detailCrosslinked polyimide foams derived from pyromellitic dianhydride and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,3-trifluoroethane with poly(α-methylstyrene)
Charlier, Y.; Hedrick, James L; Russel, T. P. et al

in Polymer (1995), 36(6), 1315-1320

A new route for the synthesis of high glass transition temperature, thermally stable polymer foams with pore sizes in the nanometre regime has been developed, using compositionally asymmetric microphase ... [more ▼]

A new route for the synthesis of high glass transition temperature, thermally stable polymer foams with pore sizes in the nanometre regime has been developed, using compositionally asymmetric microphase-separated block copolymers where the minor component (poly(α-methylstyrene)) is thermally labile and the major component (polyimide) is thermally stable. The minor component can unzip to its monomer upon heating, and the decomposition products can diffuse out of the film, leaving behind pores embedded in a matrix of the thermally stable component. In this study, the polyimide block was crosslinked with ethynyl functionalities to obtain a stable porous structure. The decomposition of the α-methylstyrene in the block copolymer was studied by thermogravimetric, dynamic mechanical and thermomechanical analyses. Mild conditions were required to avoid rapid depolymerization of the α-methylstyrene and plasticization of the polyimide matrix. The foams showed pore sizes with diameters up to a micrometre in size as well as the expected reduction in the mass density. However, the crosslinking of the matrix as a means of stabilizing the expected nanofoams was not successful. [less ▲]

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See detailCrosslinking of star-shape PCLs through Diels-Alder reactions for the preparation of shape memory polymers
Defize, Thomas ULiege; Riva, Raphaël ULiege; Thomassin, Jean-Michel ULiege et al

Poster (2012, May 10)

Poly(ε-caprolactone) (PCL), a semi-crystalline polymer, is one of the most widely studied polymers for the development of shape memory materials when chemically cross-linked. PCL presents several ... [more ▼]

Poly(ε-caprolactone) (PCL), a semi-crystalline polymer, is one of the most widely studied polymers for the development of shape memory materials when chemically cross-linked. PCL presents several advantages such as a melting transition temperature close to human body temperature, a high biocompatibility and is (bio)degradable. So, this polymer is highly relevant for both biomedical devices such as stents or resorbable suture wires and also for degradable packaging. However, after cross-linking, the material can not be reprocessed, preventing any reuse/recycling of the material. One of the purposes of this work is to find a solution to this major drawback, which would then allow, for example, to reshape packaging films after use or to recycle trimmings remaining after fabrication. Amongst current trends in the design of new polymer and composite materials, the use of organic reactions that are able to create and reversibly disrupt chemical bonds upon an external stimulus (temperature, irradiation,…) is currently gaining more and more attention as it can lead to applications in various areas such as remendable materials, drug delivery systems, stimulus-degrading materials or recyclable materials. This contribution aims at reporting a new concept for the preparation of well defined and recyclable PCL based reversibly cross-linked shape memory polymer by the formation of reversible carbon-carbon bonds. Amongst all the reversible links described in the literature, thermally (4+2) reversible cycloadditions present interesting features such as the creation of robust bonds and well defined reversibility conditions. As an example, the application of furan/maleimide adducts as covalent link, which cycloreversion is largely favored in the range of temperature (90-120°C), is widely reported. For this purpose, commercially-available star-shaped PCL precursors have been selected and selectively modified at their chain ends either by a diene (furan, anthracene) or a dienophile (maleimide). Typically, PCL-based shape memory materials have been prepared by mixing a stoichiometric amount of diene-bearing and maleimide-bearing PCLs in a twin-screw mini-extruder at a temperature which favors cycloreversion. The polymer blend is then cured at 65°C (just above PCL melting temperature), with the purpose to increase chains mobility and improve the formation of the adducts. Cross-linked PCLs were obtained, as evidenced by swelling experiments. The shape memory properties of the materials have been studied by cyclic tensile thermomechanical analysis. The influence of the nature of the Diels-Alder moieties on the cross-linking rate and on the shape memory properties has been studied. Reversibility of the network formation in the case of furan, used as diene, has been assessed by rheology and by recycling experiment. [less ▲]

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See detailCrossmodal plasticity but no functional specialization in the occipital cortex of adventitiously blind human
Collignon, O; Albouy, G ULiege; Dormal, G et al

in NeuroImage (2011), 56(Suppl. 1),

Detailed reference viewed: 18 (1 ULiège)
See detailCrossoads
Sacré, Robert ULiege

Diverse speeche and writing (2015)

Programme de radio hebdomadaire sur Equinoxe FM 100.1 ; streaming on line www.equinoxefm.be ; podcasts www.mixcloud.com/robertsacre9 ; infos www.facebook.com/robert.sacre.9

Detailed reference viewed: 14 (0 ULiège)
See detailCrossoads février 2016 - chaque mercredi 18h-20h
Sacré, Robert ULiege

Diverse speeche and writing (2016)

Magazine sonore du blues et des musiques américaines ( séquences R&B, Soul, Zydeco, Gospel,jazz, etc...)

Detailed reference viewed: 11 (0 ULiège)
See detailCrossoads septembre 2016 - chaque mercredi 18h-20h (replay samedi 22h-minuit)
Sacré, Robert ULiege

Diverse speeche and writing (2016)

Programme radio hebdomadaire consacré aux musiques Américaines et Africaines-Américaines ; streaming : www.equinoxefm.be ; podcasts : www.mixcloud.com/robertsacre9 ;

Detailed reference viewed: 9 (0 ULiège)
See detailCrossoads ( août 2017) - chaque mercredi de 18h à20h - rediffusion: samedis de 22h à minuit
Sacré, Robert ULiege

Diverse speeche and writing (2017)

Programme radio hebdomadaire consacré aux musiques africaines-américaines ; streaming : www.equinoxefm.be ; podcasts www.mixcloud.com/robertsacre9

Detailed reference viewed: 11 (0 ULiège)
See detailCrossoads ( janvier 2017) - chaque mercredi de 18h à20h - rediffusion: samedis de 22h à minuit
Sacré, Robert ULiege

Diverse speeche and writing (2017)

Detailed reference viewed: 15 (0 ULiège)
See detailCrossoads ( juillet 2017) - chaque mercredi de 18h à20h - rediffusion: samedis de 22h à minuit
Sacré, Robert ULiege

Diverse speeche and writing (2017)

Programme radio hebdomadaire consacré aux musiques africaines-américaines ; streaming : www.equinoxefm.be ; podcasts www.mixcloud.com/robertsacre9

Detailed reference viewed: 10 (0 ULiège)
See detailCrossoads ( juin 2017) - chaque mercredi de 18h à20h - rediffusion: samedis de 22h à minuit
Sacré, Robert ULiege

Diverse speeche and writing (2017)

Programme radio hebdomadaire consacré aux musiques africaines-américaines ; streaming : www.equinoxefm.be ; podcasts www.mixcloud.com/robertsacre9

Detailed reference viewed: 9 (0 ULiège)