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See detailFull discontinuous Galerkin formulation of shells in large deformations with parallel and fracture mechanics applications
Becker, Gauthier ULg; Noels, Ludovic ULg

Conference (2012, July 11)

Fracture mechanical problems can be solved by coupling the finite elements with a cohesive approach. Unfortunately, the classical cohesive methods suffer from severe limitations. Indeed, on one hand, the ... [more ▼]

Fracture mechanical problems can be solved by coupling the finite elements with a cohesive approach. Unfortunately, the classical cohesive methods suffer from severe limitations. Indeed, on one hand, the intrinsic approach, which inserts the cohesive elements at the beginning, has to model the prefracture stage. This requires an initial slope in the traction separation law that should tend toward infinity to avoid lack of consistency leading to obvious numerical problems. On the other hand, the extrinsic cohesive method inserts the cohesive elements during the simulation when a fracture criterion is reached. This insertion requires topological mesh modifications and therefore a very complicated implementation, especially in a parallel code. To overcome these limitations, new methods were developed and in particular, an approach based on discontinuous Galerkin formulation (DG) has been pioneered by R. Radovitzky (Radovitzky cmame2011). The use of the DG principle allows to formulate the problem with discontinuous elements and the continuity between them is ensured weakly by terms integrated on the elements interface . These interface elements can be easily replaced by a cohesive element during the simulation. We have recently developed this approach for shells (Becker cmame2011) to obtain a full DG method. Moreover, a new cohesive law based on the reduced stresses of the thin bodies formulation is developed to propagate a fracture through the thickness. This cohesive model dissipates the right amount of energy during crack phenomena. These developments are implemented in parallel and validated by the study the blast of a notched cylinder, for which experimental and numerical (by XFEM method) data are reported in the literature by R. Larsson (Larsson ijnme2011). Finally, as thin structures are often made of ductile materials, which show large deformations before fracture, the formulation is extended to the non linear case with hyperelastic material law. This one can take into account the damage and a criterion based on the work of Huespe (Huespe plasticity2009) is developed to localize the damage leading to the apparition and propagation of cracks. [less ▲]

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See detailFull electrochemical synthesis of conducting polymer films chemically grafted to conducting surfaces
Labaye, David E; Jérôme, Christine ULg; Gueskin, V. M. et al

in Langmuir (2002), 18(13), 5222-5230

This paper reports on the full electrochemical synthesis of electrically conducting polymers chemically grafted to conducting surfaces (e.g., glassy carbon, stainless steel, nickel, gold). It is based on ... [more ▼]

This paper reports on the full electrochemical synthesis of electrically conducting polymers chemically grafted to conducting surfaces (e.g., glassy carbon, stainless steel, nickel, gold). It is based on new functional acrylate monomers, i.e., 3-(2-acryloyloxyethyl)thiophene and N-(2-acryloyloxyethyl)pyrrole, whose the synthesis is reported in this work. The polymerization process consists of two electrochemical steps. The first one is the cathodic electrografting of polyacrylate chains bearing a precursor of the conducting polymer in the ester group, either thiophene or pyrrole. In the second step, this precursor is polymerized under anodic polarization, in the presence or not of additional unsubstituted monomer in the electrochemical bath. Cyclic voltammetry was used to confirm that the two-component film is conducting and electrochemically active (reversible doping and dedoping). The chemical composition and the microscopic morphology of these composites were characterized by X-ray photoelectron spectroscopy and atomic force microscopy, respectively. [less ▲]

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See detailA full heteroscedastic one-way error components model: Pseudo-maximum likelihood estimation and specification testing
Lejeune, Bernard ULg

in Baltagi, Badi H. (Ed.) Panel Data Econometrics: Theoretical Contributions and Empirical Applications (2006)

This paper proposes an extension of the standard one-way error components model allowing for heteroscedasticity in both the individual-specific and the general error terms, as well as for unbalanced panel ... [more ▼]

This paper proposes an extension of the standard one-way error components model allowing for heteroscedasticity in both the individual-specific and the general error terms, as well as for unbalanced panel. On the grounds of its computational convenience, its potential efficiency, its robustness to non-normality and its robustness to possible misspecification of the assumed scedastic structure of the data, we argue for estimating this model by Gaussian pseudo-maximum likelihood of order two. Further, we review how, taking advantage of the powerful m-testing framework, the correct specification of the prominent aspects of the model may be tested. We survey potentially useful nested, non-nested, Hausman and information matrix type diagnostic tests of both the mean and the variance specification of the model. Finally, we illustrate the usefulness of our proposed model and estimation and diagnostic testing procedures through an empirical example. [less ▲]

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See detailFull Recovery of Contraction Late after Acute Myocardial Infarction: Determinants and Early Predictors
Lancellotti, Patrizio ULg; Albert, Adelin ULg; Berthe, Christian ULg et al

in Heart (2001), 85(5), 521-6

OBJECTIVES: To assess the relative value of electrocardiographic, echocardiographic, angiographic, and in-hospital therapeutic indices for predicting late functional recovery after acute myocardial ... [more ▼]

OBJECTIVES: To assess the relative value of electrocardiographic, echocardiographic, angiographic, and in-hospital therapeutic indices for predicting late functional recovery after acute myocardial infarction, and to determine the variables associated with absence of recovery, partial recovery, and full recovery. DESIGN: Prospective observational follow up study. SETTING: Teaching hospital. PATIENTS: 74 consecutive patients with a first uncomplicated acute myocardial infarct. INTERVENTIONS: Dobutamine-atropine stress echocardiography was performed mean (SD) 5 (2) days after the acute event. Quantitative angiography was available in all patients before hospital discharge. A follow up resting echocardiogram was obtained 12 (2) months later. RESULTS: Functional recovery (partial, n = 18; full, n = 27) was observed in 45 of the 74 patients. Recovery was associated with earlier thrombolytic treatment (p = 0.008), earlier peak concentration of creatine kinase (p = 0.009), greater contractile reserve (p = 0.0001), non-Q wave acute myocardial infarction (p = 0.002), and more frequent elective angioplasty of the infarct related vessel (p = 0.0004). Three independent variables were selected stepwise from multivariate analysis for predicting late recovery: contractile reserve (chi(2) = 24.2, p < 0.0001); non-Q wave infarction (chi(2) = 15.7, p = 0.0001); and the time from symptom onset to thrombolysis (chi(2) = 4.94, p = 0.026). Three independent variables predicted full recovery: contractile reserve (chi(2) = 17.2, p = 0.0001); non-Q wave infarction (chi(2) = 10.1, p = 0.0016); and elective angioplasty of the infarct related artery (chi(2) = 4.53, p = 0.033). Only contractile reserve (chi(2) = 17.0, p < 0.001) was selected from the multivariate analysis for its ability to distinguish between partial recovery and absence of recovery. CONCLUSIONS: Late recovery of contraction relates to earlier treatment, which is associated with lower infarct size unmasked by a non-Q wave event and the presence of contractile reserve. Elective coronary angioplasty of the infarct related artery before hospital discharge is associated with full recovery. [less ▲]

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See detailFull system scramjet simulation
Pecnik, Rene; Terrapon, Vincent ULg; Ham, Frank et al

in Annual Research Briefs (2009)

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See detailA full-acceptance detector at the LHC (FELIX)
Ageev, A.; Akhobadze, K.; Alvero, L. et al

in Journal of Physics : G Nuclear & Particle Physics (2002), 28(6), 117-215

The FELIX collaboration had proposed the construction of a full-acceptance detector for the LHC. The primary mission of FELIX was the study of QCD: to provide comprehensive and definitive observations of ... [more ▼]

The FELIX collaboration had proposed the construction of a full-acceptance detector for the LHC. The primary mission of FELIX was the study of QCD: to provide comprehensive and definitive observations of a very broad range of strong-interaction processes. This document contains an extensive discussion of this physics menu. In a further paper the FELIX detector will be reviewed. [less ▲]

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See detailA full-discontinuous Galerkin formulation of non-linear Kirchhoff-Love shells: elasto-plastic finite deformations, parallel computation & fracture applications
Becker, Gauthier ULg; Noels, Ludovic ULg

in International Journal for Numerical Methods in Engineering (2013), 93(1), 80-117

Due to its ability to take into account discontinuities, the discontinuous Galerkin (DG) method presents some advantages for modeling crack initiations and propagations. This concept has been recently ... [more ▼]

Due to its ability to take into account discontinuities, the discontinuous Galerkin (DG) method presents some advantages for modeling crack initiations and propagations. This concept has been recently applied to 3D simulations and to elastic thin bodies. In this last case, the assumption of small elastic deformations before crack initiations or propagations reduces drastically the applicability of the framework to a reduced number of materials. To remove this limitation, a full-DG formulation of non-linear Kirchhoff-Love shells is presented and is used in combination with an elasto-plastic finite deformations model. The results obtained by this new formulation are in agreement with other continuum elasto-plastic shell formulations. Then this full-DG formulation of Kirchhoff-Love shells is coupled with the cohesive zone model to perform thin body fracture simulations. As this method allows considering elasto-plastic constitutive laws in combination with the cohesive model, accurate results compared to the experiments are found. In particular, the crack path and propagation rate of a blasted cylinder are shown to match experimental results. One of the main advantages of this framework is its ability to run in parallel with a high speed-up factor, allowing the simulation of ultra fine meshes. [less ▲]

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See detailFull-electrochemical preparation of conducting/insulating binary polymer films
Jérôme, Christine ULg; Geskin, V.; Lazzaroni, Roberto et al

in Chemistry of Materials (2001), 13(5), 1656-1664

Binary polymer films consisting of an insulating polymer and a conducting polymer have been successfully prepared by sequential electropolymerization of the parent monomers. The insulating polymer ... [more ▼]

Binary polymer films consisting of an insulating polymer and a conducting polymer have been successfully prepared by sequential electropolymerization of the parent monomers. The insulating polymer (polyacrylonitrile or polyethylacrylate) is formed under cathodic polarization in a potential range where the growing chains are chemically grafted onto the nickel or carbon electrode. The conducting polymer (polybithiophene or polypyrrole) is formed by electrooxidation of the parent monomer. The electrochemical reactions and the electrochemical properties of the films have been analyzed by cyclic voltammetry and chronoamperometry. The influence of the main experimental parameters on the composition and morphology of the films has been investigated by X-ray photoelectron spectroscopy and atomic force microscopy. This approach strongly improves the adhesion of the conducting polymer as a result of its combination with the grafted polyacrylonitrile. This combination of insulating and conducting polymers is a way to tune the electroactivity of the conjugated chains. [less ▲]

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See detailFull-scale fire test on a composite floor slab incorporating long span cellular steel beams
Nadjai, Ali; Bailey, Colin; Vassart, Olivier et al

in Structural Engineer (2011), 89(21), 18-25

As part of an international major research initiative, dealing with the behaviour of long span cellular beams in steel framed buildings under fire, a large-scale fire test incorporating 15m long cellular ... [more ▼]

As part of an international major research initiative, dealing with the behaviour of long span cellular beams in steel framed buildings under fire, a large-scale fire test incorporating 15m long cellular beams was carried out. The test incorporated unprotected secondary cellular steel beams acting compositely with the supporting floor slab. The floorplate in its entirety was designed to carry the load with unprotected beams, when subjected to a severe fire, by utilising membrane action of the floor slab. The overall structure performed very well supporting the full applied static load for the duration of the test. The unprotected cellular steel beams were subjected to distortional buckling, with only the top tee providing any support through catanary action. The test supported the assumptions adopted in the structural design approach and provided an accurate estimate of the strength of the floorplate. Comparison of the recorded time-temperature relationship of the fire with the design method presented in the Eurocodes shows that the code under-predicts the severity of the fire, although this was compensated to some extent by the conservative assumptions embedded within the structural model. [less ▲]

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See detailFull-scale tests of torsional damper and detuner (TDD) antigalloping device
Lilien, Jean-Louis ULg; Vinogradov, Alexander

in IEEE Transactions on Power Delivery (2002), 17(2), 638-643

A new antigalloping device for overhead lines with bundle conductors was introduced ten years ago, after laboratory tests and observations on actual 400-kV lines. A systematic fullscale test was performed ... [more ▼]

A new antigalloping device for overhead lines with bundle conductors was introduced ten years ago, after laboratory tests and observations on actual 400-kV lines. A systematic fullscale test was performed in Kazakhstan in order to better evaluate torsional damper and detuner (TDD) efficiency. This report details the test station and the results obtained over a several month period of testing and measurement. The tests were carried out thanks to the mutual efforts of the ESSP and the Kazakh Power Research Institute (KazNIIE) at the field tests stand located in Chokpar. [less ▲]

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See detailFull-system RANS of the HyShot II scramjet Part 1: Numerics and non-reactive simulations
Pecnik, Rene; Terrapon, Vincent ULg; Ham, Frank et al

in Annual Research Briefs (2010)

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See detailFull-system RANS of the HyShot II scramjet Part 2: Reactive cases
Terrapon, Vincent ULg; Pecnik, Rene; Ham, Frank et al

in Annual Research Briefs (2010)

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See detailFull-system simulation of the HyShot II scramjet
Terrapon, Vincent ULg

Scientific conference (2011, May)

The renewed interest in high-speed flight has recently demonstrated the need for the development of hypersonic air-breathing propulsion systems, i.e., in which the ambient air is used as oxidizer. Because ... [more ▼]

The renewed interest in high-speed flight has recently demonstrated the need for the development of hypersonic air-breathing propulsion systems, i.e., in which the ambient air is used as oxidizer. Because the internal flow in a scramjet is supersonic, it has a very short residence time during which air and fuel must mix on a molecular level, and chemical reactions have to be completed before leaving the engine. Moreover, the kinetic energy of the free stream of air entering the propulsion engine is of the same order of magnitude as the combustion heat re- lease. This results in a small net thrust compared to the aerodynamic drag. On the other hand, an excessive heat release can lead to the unstart phenomenon, i.e., the choking of the engine, that causes a sudden drop in thrust and large mechanical loads on the structure. Performance optimization requires thus maximizing thrust without crossing the unstart bound. To achieve predictive computations, the quantification of margins and uncertainties (QMU) with respect to this unstart bound is critical. Recent advances within the PSAAP program at Stanford University to develop computational tools to study the unstart phenomenon will be presented. In the first part, an overview of the program will be given. The second part will focus on the combustion model. Since heat release is at the heart of a scramjet operation and the main contributor to unstart, it is also the major source of uncertainties. A novel model for supersonic combustion based on a flamelet/progress variable approach has been developed. This approach allows the use of com- plex chemistry with only 2 or 3 additional scalar transport equations. The model is applied in a RANS computation of the hydrogen fueled HyShot II scramjet and simulation results are compared with experimental data. LES results for a jet in a supersonic crossflow will also be presented. [less ▲]

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See detailFullerene containing (co)polymers for biomedical applications
Stoilova, Olya; Detrembleur, Christophe ULg; Jérôme, Christine ULg et al

Conference (2005, June 01)

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See detailFully and Partially Reusable TSTO launchers using In-Flight LOX Collection
Hendrick, Patrick; Breugeulmans, F.; Marquet, B. et al

in 22nd International Symposium on Space Technology and Science (ISTS) (2000, May)

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See detailA fully aqueous sustainable process for strongly adhering antimicrobial coatings on stainless steel
Cécius, Michaël; Jérôme, Christine ULg

in Progress in Organic Coatings (2011), 70(1), 220-223

In order to provide conducting surfaces with antibacterial properties, the electrografting of acrylate has been combined with the layer-by-layer deposition of polyelectrolytes. The challenges addressed by ... [more ▼]

In order to provide conducting surfaces with antibacterial properties, the electrografting of acrylate has been combined with the layer-by-layer deposition of polyelectrolytes. The challenges addressed by this strategy are (i) to insure the adhesion of the biocidal coating to the conducting surface and (ii) to avoid the use of organic solvents in the coating process. The electrografting process has been implemented in water and allows imparting strong adhesion of an anchoring polycationic layer, used in a second step for growing a chitosan-based bactericidal coating by layer-by-layer deposition. This novel process based on readily available precursors allows the coating from aqueous media and makes the coating technology quite sustainable. [less ▲]

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