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Now showing items 33 - 43 of 43

  • Hydrogen-induced structural change in Ni(90)Al(10) metallic glass

    Park, Kyoung-Won   Shibutani, Yoji   Fleury, Eric  

    Ni(90)Al(10) amorphous membranes were prepared by means of molecular dynamics ( MD) simulation technique with the aim of investigating the structural evolution induced by hydrogen with respect to hydrogen concentration. The short-range ordered (SRO) structures of the as-cast model sample and the structural change by hydrogen charging were analyzed using Voronoi tessellation method. This study indicates that prism and prism-like structures with low coordination number are generated, while intrinsically stable SRO structures in the amorphous membrane annihilate upon hydrogen charging. We discussed the relationship between these local atomic changes and the structural stability which was evaluated from the potential energy change point of view. (C) 2011 Elsevier B.V. All rights reserved.
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  • Pacing of the interventricular septum versus the right ventricular apex:A prospective,randomized study

    Domenichini, Giulia   Sunthorn, Henri   Fleury, Eric   Foulkes, Huberdine   Stettler, Carine   Burri, Haran  

    Background: Left ventricular (LV) function may be impaired by right ventricular (RV) apical pacing. The interventricular septum is an alternative pacing site, but randomized data are limited. Our aim was to compare ejection fraction (EF) resulting from pacing the interventricular septum versus the RV apex. Methods: RV lead implantation was randomized to the apex or the mid-septum. LVEF and RVEF were determined at baseline and after 1 and 4 years by radionuclide angiography. Results: We enrolled 59 patients, of whom 28 were randomized to the apical group and 31 to the septal group, with follow-up available in 47 patients at 1 year and 33 patients at 4 years. LVEF in the apical and in the septal groups was 55 +/- 8% vs. 46 +/- 15% (p =3D 0.021) at 1 year and 53 +/- 12% vs. 47 +/- 15% (p =3D 0.20) at 4 years. Echocardiography confirmed a mid-septal lead position in only 54% of patients in the septal group, with an anterior position in the remaining patients. In the septal group, LVEF decreased significantly in patients with an anterior RV lead (-10.0 +/- 7.7%, p =3D 0.003 at 1 year and -8.0 +/- 9.5%, p =3D 0.035 at 4 years), but not in patients who had a mid-septal lead. Left intraventricular dyssynchrony was significantly increased in case of an anterior RV lead. RVEF was not significantly impaired by RV pacing, regardless of RV lead position. Conclusions: Pacing at the RV septum confers no advantage in terms of ventricular function compared to the apex. Furthermore, inadvertent placement of the RV lead in an anterior position instead of the mid-septum results in reduced LV function. (C) 2012 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.
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  • MultiAspect Graphs: Algebraic Representation and Algorithms

    Wehmuth, Klaus   Fleury, Eric   Ziviani, Artur  

    We present the algebraic representation and basic algorithms for MultiAspect Graphs (MAGs). A MAG is a structure capable of representing multilayer and time-varying networks, as well as higher-order networks, while also having the property of being isomorphic to a directed graph. In particular, we show that, as a consequence of the properties associated with the MAG structure, a MAG can be represented in matrix form. Moreover, we also show that any possible MAG function (algorithm) can be obtained from this matrix-based representation. This is an important theoretical result since it paves the way for adapting well-known graph algorithms for application in MAGs. We present a set of basic MAG algorithms, constructed from well-known graph algorithms, such as degree computing, Breadth First Search (BFS), and Depth First Search (DFS). These algorithms adapted to the MAG context can be used as primitives for building other more sophisticated MAG algorithms. Therefore, such examples can be seen as guidelines on how to properly derive MAG algorithms from basic algorithms on directed graphs. We also make available Python implementations of all the algorithms presented in this paper.
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  • Effect of the atomic packing density on the structural change rate of amorphous alloys under elastostatic stress

    Park, Kyoung-Won   Wakeda, Masato   Shibutani, Yji   Fleury, Eric   Lee, Jae-Chul  

    This study deals with the fundamental issue of whether the atomistic-scale structure of amorphous alloys can be altered by the application of elastic stress. The prolonged imposition of elastostatic stress on amorphous alloys induces permanent structural change. The rate of change largely depends on the atomic packing density, which is characterized by the fractions of various short-range ordered clusters. This structural change is accompanied by the formation of excess free volume, which in turn affects the mechanical properties in subsequent compression tests. The findings of the experiments and molecular dynamics simulations were analyzed in terms of atomistic-scale structural changes.
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  • Structural disordering process of an amorphous alloy driven by the elastostatic compression at room temperature RID A-8478-2008

    Lee, Sang-Chul   Lee, Chang-Myeon   Lee, Jae-Chul   Kim, Hwi-Jun   Shibutani, Yoji   Fleury, Eric   Falk, Michael L.  

    This study demonstrates that permanent deformation results when an amorphous alloy is subjected to a stress below yield at room temperature. The resultant deformation was observed to be homogeneous and is thought to occur as a result of the structural disordering, in which densely packed short-range ordered clusters break down to form new, loosely packed ones. It was found that this disordering process is irreversible even if the applied stress is removed, resulting in the creation of excess free volume. These findings were analyzed using the molecular dynamics simulations in the light of atomic-scale structural changes. (C) 2008 American Institute of Physics.
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  • Hydrogen Permeation Properties of Pd-Coated Ni-Nb-Ti-Zr Amorphous Alloys

    Lee, Dock-Young   Fleury, Eric  

    Hydrogen permeability of Pd-coated Ni60Nb15Ti15Zr10 and Ni60Nb20Ti15Zr5 amorphous alloys was measured in the temperature range of 673 K to 773 K and was compared with the results obtained using Ni60Nb40, a binary amorphous alloy. The pen-neability thus measured was found to increase moderately increasing temperature. A long-term permeation test for the Pd-coated Ni60Nb15Ti15Zr10 amorphous alloy revealed high permeation stability up to 16.6 h.
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  • Complex dynamic networks: Tools and methods

    Ignacio Alvarez-Hamelin, Jose   Fleury, Eric   Vespignani, Alessandro   Ziviani, Artur  

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  • Relationship between microstructure and hydrogen permeation properties in the multiphase Ni(21)Ti(23)Nb(56) alloy membranes

    Magnone, Edoardo   Jeon, Sung Il   Park, Jung Hoon   Fleury, Eric  

    The cooling rate has significant effects on the microstructure of Ti-Ni-Nb-based multiphase alloys. In the present study the effect of the microstructure on the hydrogen permeation properties of multiphase Ni(21)Ti(23)Nb(56) alloy membrane was systematically investigated. Our result suggested a complementary relation between the quantity of the primary bcc-(Ti, Nb) solid solution phase and hydrogen permeation properties. The Ni(21)Ti(23)Nb(56) alloy with about 70% surface fraction of primary phase bcc-(Nb-Ti) solid solution showed the higher hydrogen permeability value of 7.48 x 10(-8) MOM s Pa(1/2) at 450 degrees C, which is higher in value compared to Ti-Ni-Nb-based multiphase alloys reported in published works. Moreover, comparison between the present experimental data and the literature was analyzed to illustrate the capability of the proposed control of microstructure membrane for the improvement of the hydrogen permeation properties of Ti-Ni-Nb -based multiphase alloys. (C) 2011 Elsevier B.V. All rights reserved.
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  • Determination of orientation relationships between FCC-hydride and HCP-titanium and their correlation with hydrides distribution

    Wen, Jing   Allain, Nathalie   Fleury, Eric  

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  • Hydrogen permeation characteristics of rolled V85Al10Co5 alloys

    Fleury, Eric   Suh, Jin-Yoo   Kim, Dong-ik   Jeong, Chan Hoon   Park, Jung Hoon  

    Thin sheets of V85Al10Co5 alloy were produced by a thermo-mechanical treatment consisting in successive hot rolling, cold rolling steps and annealing treatment at high temperature followed by either air cooling or water quenching. Though the values of hydrogen permeability measured for these sheets were significantly reduced as a consequence of the rolling process, the annealing treatment restored almost the hydrogen permeation properties to those of the alloy in the cast condition. EBSD analyses suggested that the post-annealing treatment performed at 1100 degrees C for 3 min after cold rolling induced a recrystallization of the grains resulting in a preferred orientation along the {002} planes. For the sample annealed and water quenched, the value of the hydrogen flux reached about 45 ml/cm(2).min, which is more than twice the value of the flux obtained for thin foils of Pd alloys tested under identical conditions. (C) 2012 Elsevier B. V. All rights reserved.
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  • QRS pattern and improvement in right and left ventricular function after cardiac resynchronization therapy:a radionuclide study

    Domenichini, Giulia   Burri, Haran   Valzania, Cinzia   Gavaruzzi, Gilberto   Fallani, Francesco   Biffi, Mauro   Sunthorn, Henri   Diemberger, Igor   Martignani, Cristian   Foulkes, Huberdine   Fleury, Eric   Boriani, Giuseppe  

    Background: Predicting response to cardiac resynchronization therapy (CRT) remains a challenge. We evaluated the role of baseline QRS pattern to predict response in terms of improvement in biventricular ejection fraction (EF). Methods: Consecutive patients (pts) undergoing CRT implantation underwent radionuclide angiography at baseline and at mid-term follow-up. The relationship between baseline QRS pattern and mechanical dyssynchrony using phase analysis was evaluated. Changes in left and right ventricular EF (LVEF and RVEF) were analyzed with regard to baseline QRS pattern. Results: We enrolled 56 pts, 32 with left bundle branch block (LBBB), 4 with right bundle branch block (RBBB) and 20 with non-specific intraventricular conduction disturbance (IVCD). A total of 48 pts completed follow-up. LBBB pts had significantly greater improvement in LVEF compared to RBBB or non-specific IVCD pts (+ 9.6 +/- 10.9% vs. + 2.6 +/- 7.6%, p =3D 0.003). Response (defined as >=3D 5% increase in LVEF) was observed in 68% of LBBB vs. 24% of non-specific IVCD pts (p =3D 0.006). None of the RBBB pts were responders. RVEF was significantly improved in LBBB (+5.0 +/- 9.0%, p =3D 0.007), but not in non-specific IVCD and RBBB pts (+0.4 +/- 5.8%, p =3D 0.76). At multivariate analysis, LBBB was the only predictor of LVEF response (OR, 7.45; 95% CI 1.80-30.94; p =3D 0.006), but not QRS duration or extent of mechanical dyssynchrony. Conclusions: Presence of a LBBB is a marker of a positive response to CRT in terms of biventricular improvement. Pts with non-LBBB pattern show significantly less benefit from CRT than those with LBBB.
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