Documents disponibles écrits par cet auteur

Minimization of the k-th maximum and its application on LMS regression and VaR optimization / X. Huang in Journal of the operational research society (JORS), Vol. 63 N° 11 (Novembre 2012) 

Public ISBD [article]  in Journal of the operational research society (JORS) > Vol. 63 N° 11 (Novembre 2012) . - pp. 1479–1491 Titre : Minimization of the k-th maximum and its application on LMS regression and VaR optimization Type de document : texte imprimé Auteurs : X. Huang, Auteur ; J. Xu, Auteur ; Wang, S., Auteur Année de publication : 2012 Article en page(s) : pp. 1479–1491 Note générale : operational research Langues : Anglais (eng) Mots-clés : piecewise  linear  optimization;  least  median  of  squares;  value-at-risk Index. décimale : 001.424 Résumé : Motivated by two important problems, the least median of squares (LMS) regression and value-at-risk (VaR) optimization, this paper considers the problem of minimizing the k-th maximum for linear functions. For this study, a sufficient and necessary condition of local optimality is given. From this condition and other properties, we propose an algorithm that uses linear programming technique. The algorithm is assessed on real data sets and the experiments for LMS regression and VaR optimization both show its effectiveness. DEWEY : 001.424 ISSN : 0160-5682 En ligne : http://www.palgrave-journals.com/jors/journal/v63/n11/abs/jors2011163a.html [article] Minimization of the k-th maximum and its application on LMS regression and VaR optimization [texte imprimé] / X. Huang, Auteur ; J. Xu, Auteur ; Wang, S., Auteur . - 2012 . - pp. 1479–1491. operational research Langues : Anglais (eng) in Journal of the operational research society (JORS) > Vol. 63 N° 11 (Novembre 2012) . - pp. 1479–1491 Mots-clés : piecewise  linear  optimization;  least  median  of  squares;  value-at-risk Index. décimale : 001.424 Résumé : Motivated by two important problems, the least median of squares (LMS) regression and value-at-risk (VaR) optimization, this paper considers the problem of minimizing the k-th maximum for linear functions. For this study, a sufficient and necessary condition of local optimality is given. From this condition and other properties, we propose an algorithm that uses linear programming technique. The algorithm is assessed on real data sets and the experiments for LMS regression and VaR optimization both show its effectiveness. DEWEY : 001.424 ISSN : 0160-5682 En ligne : http://www.palgrave-journals.com/jors/journal/v63/n11/abs/jors2011163a.html

Nucleation and thickening of shear bands in nano-scale twin/matrix lamellae of a Cu–Al alloy processed by dynamic plastic deformation / C.S. Hong in Acta materialia, Vol. 58 N° 8 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3103–3116 Titre : Nucleation and thickening of shear bands in nano-scale twin/matrix lamellae of a Cu–Al alloy processed by dynamic plastic deformation Type de document : texte imprimé Auteurs : C.S. Hong, Auteur ; N.R. Tao, Auteur ; X. Huang, Auteur Année de publication : 2011 Article en page(s) : pp. 3103–3116 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dynamic  plastic  deformation  Shear  bands  Nano-scale  twins  Nano-grained  structure  Dislocation  structure Résumé : Microstructural evolution associated with the shear banding in nano-scale twin/matrix (T/M) lamellae of a Cu–Al alloy processed by means of dynamic plastic deformation was investigated using transmission electron microscopy (TEM) and high-resolution TEM. The development of a shear band was found to be a two-stage process, namely a nucleation stage resulting in a narrow band composed of nano-sized (sub)grains intersecting the T/M lamellae, followed by a thickening stage of the narrow band into adjacent T/M lamellae regions. The nucleation stage occurred within a narrow region of an almost constant thickness (100–200 nm thick, referred to as “core” region) and consisted of three steps: (1) initiation of localized deformation (bending, necking, and detwinning) against the T/M lamellae, (2) evolution of a dislocation structure within the detwinned band, and (3) transformation of the detwinned dislocation structure (DDS) into a nano-sized (sub)grain structure (NGS). On the two sides of a core region, two transition layers (TRLs) exist where the T/M lamellae experienced much less shear strain. The interface boundaries separating the core region and the TRLs are characterized by very large shear strain gradients accommodated by high density of dislocations. Increasing shear strains leads to thickening of shear bands at the expense of the adjoining T/M lamellae, which is composed of thickening of the core region by transforming the TRLs into the core region with DDS and NGS, analogous to steps (2) and (3) of the nucleation process, and outward movement of the TRLs by deforming the adjoining T/M lamellae. Grain sizes in the well-developed shear bands are obviously larger than the lamellar thickness of original T/M lamellae. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000790 [article] Nucleation and thickening of shear bands in nano-scale twin/matrix lamellae of a Cu–Al alloy processed by dynamic plastic deformation [texte imprimé] / C.S. Hong, Auteur ; N.R. Tao, Auteur ; X. Huang, Auteur . - 2011 . - pp. 3103–3116. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3103–3116 Mots-clés : Dynamic  plastic  deformation  Shear  bands  Nano-scale  twins  Nano-grained  structure  Dislocation  structure Résumé : Microstructural evolution associated with the shear banding in nano-scale twin/matrix (T/M) lamellae of a Cu–Al alloy processed by means of dynamic plastic deformation was investigated using transmission electron microscopy (TEM) and high-resolution TEM. The development of a shear band was found to be a two-stage process, namely a nucleation stage resulting in a narrow band composed of nano-sized (sub)grains intersecting the T/M lamellae, followed by a thickening stage of the narrow band into adjacent T/M lamellae regions. The nucleation stage occurred within a narrow region of an almost constant thickness (100–200 nm thick, referred to as “core” region) and consisted of three steps: (1) initiation of localized deformation (bending, necking, and detwinning) against the T/M lamellae, (2) evolution of a dislocation structure within the detwinned band, and (3) transformation of the detwinned dislocation structure (DDS) into a nano-sized (sub)grain structure (NGS). On the two sides of a core region, two transition layers (TRLs) exist where the T/M lamellae experienced much less shear strain. The interface boundaries separating the core region and the TRLs are characterized by very large shear strain gradients accommodated by high density of dislocations. Increasing shear strains leads to thickening of shear bands at the expense of the adjoining T/M lamellae, which is composed of thickening of the core region by transforming the TRLs into the core region with DDS and NGS, analogous to steps (2) and (3) of the nucleation process, and outward movement of the TRLs by deforming the adjoining T/M lamellae. Grain sizes in the well-developed shear bands are obviously larger than the lamellar thickness of original T/M lamellae. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000790

Simplified damage assessment method for buried structures against external blast load / Ma, G. W. in Journal of structural engineering, Vol. 136 N° 5 (Mai 2010) 

Public ISBD [article]  in Journal of structural engineering > Vol. 136 N° 5 (Mai 2010) . - pp. 603-612 Titre : Simplified damage assessment method for buried structures against external blast load Type de document : texte imprimé Auteurs : Ma, G. W., Auteur ; X. Huang, Auteur ; Li, J. C., Auteur Année de publication : 2011 Article en page(s) : pp. 603-612 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Combined  failure  P-I  diagram  Buried  structure  Blast  load  Damage  assessment Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Decoupling of soil-structure interaction is applied to analyze buried structure damage due to external blast load. The structural element under analysis is assumed to deform as a simply supported rigid-plastic beam. Shear failure, bending failure, and combined failure modes are considered based on five transverse velocity profiles. With proper failure criteria, the critical equations for structural shear and bending failures are derived respectively. Pressure-impulse diagrams are then developed to assess damage of the buried structures. Comparison has been made to show the influences of the soil-structure interaction and the shear-to-bending strength ratio of the buried structure. A case study has been conducted to a buried reinforced concrete box-type structure which shows that the proposed analysis method can be effectively applied. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i5/p603_s1?isAuthorized=no [article] Simplified damage assessment method for buried structures against external blast load [texte imprimé] / Ma, G. W., Auteur ; X. Huang, Auteur ; Li, J. C., Auteur . - 2011 . - pp. 603-612. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 136 N° 5 (Mai 2010) . - pp. 603-612 Mots-clés : Combined  failure  P-I  diagram  Buried  structure  Blast  load  Damage  assessment Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Decoupling of soil-structure interaction is applied to analyze buried structure damage due to external blast load. The structural element under analysis is assumed to deform as a simply supported rigid-plastic beam. Shear failure, bending failure, and combined failure modes are considered based on five transverse velocity profiles. With proper failure criteria, the critical equations for structural shear and bending failures are derived respectively. Pressure-impulse diagrams are then developed to assess damage of the buried structures. Comparison has been made to show the influences of the soil-structure interaction and the shear-to-bending strength ratio of the buried structure. A case study has been conducted to a buried reinforced concrete box-type structure which shows that the proposed analysis method can be effectively applied. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i5/p603_s1?isAuthorized=no

Thermal behavior of Ni (99.967% and 99.5% purity) deformed to an ultra-high strain by high pressure torsion / H.W. Zhang in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1698–1707 Titre : Thermal behavior of Ni (99.967% and 99.5% purity) deformed to an ultra-high strain by high pressure torsion Type de document : texte imprimé Auteurs : H.W. Zhang, Auteur ; X. Huang, Auteur ; R. Pippan, Auteur Année de publication : 2011 Article en page(s) : pp. 1698–1707 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Discontinuous  recrystallization  Continuous  recrystallization  Nickel  Stored  energy  Plastic  deformation Résumé : Polycrystalline Ni of two purities (99.967% (4N) and 99.5% (2N)) was deformed to an ultra-high strain of εvM = 100 (εvM, von Mises strain) by high pressure torsion at room temperature. The 4N and 2N samples at this strain are nanostructured with an average boundary spacing of ∼100 nm, a high density of dislocations and a large fraction of high angle boundaries (>15°) of 0.68–0.74, as determined by transmission electron microscopy, and 0.8–0.83, as determined by electron backscattering diffraction. The deformed samples were annealed isochronally for 1 h at temperatures from 100 to 600 °C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness were determined. Based on microstructural parameters the energy stored in the deformed state was estimated to be 14 MPa and 24 MPa for 4N Ni and 2N Ni, respectively. The isochronal annealing leads to a drop in hardness in three stages: a relatively small decrease at low temperatures (recovery), followed by a rapid decrease at intermediate temperatures (recrystallization) and a slow decrease at high temperature (grain growth). Both recovery and recrystallization of the 2N Ni are strongly retarded by the presence of impurities reducing the mobility of boundaries. In the recrystallization stage, changes in hardness, microstructure and texture show that the 4N Ni recrystallizes discontinuously, in spite of a large fraction of high angle boundaries in the deformed state. This finding contradicts previous experiments and theory, which suggest that recrystallization is continuous when the fraction of high angle boundaries is high. In the 2N Ni, the observations suggest that some structural coarsening (continuous recrystallization) may take place simultaneously with discontinuous recrystallization. The findings emphasize the importance of alloying, which can delay the process of recovery and recrystallization and thereby enable tailoring of the microstructure and properties through an optimized annealing treatment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007873 [article] Thermal behavior of Ni (99.967% and 99.5% purity) deformed to an ultra-high strain by high pressure torsion [texte imprimé] / H.W. Zhang, Auteur ; X. Huang, Auteur ; R. Pippan, Auteur . - 2011 . - pp. 1698–1707. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1698–1707 Mots-clés : Discontinuous  recrystallization  Continuous  recrystallization  Nickel  Stored  energy  Plastic  deformation Résumé : Polycrystalline Ni of two purities (99.967% (4N) and 99.5% (2N)) was deformed to an ultra-high strain of εvM = 100 (εvM, von Mises strain) by high pressure torsion at room temperature. The 4N and 2N samples at this strain are nanostructured with an average boundary spacing of ∼100 nm, a high density of dislocations and a large fraction of high angle boundaries (>15°) of 0.68–0.74, as determined by transmission electron microscopy, and 0.8–0.83, as determined by electron backscattering diffraction. The deformed samples were annealed isochronally for 1 h at temperatures from 100 to 600 °C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness were determined. Based on microstructural parameters the energy stored in the deformed state was estimated to be 14 MPa and 24 MPa for 4N Ni and 2N Ni, respectively. The isochronal annealing leads to a drop in hardness in three stages: a relatively small decrease at low temperatures (recovery), followed by a rapid decrease at intermediate temperatures (recrystallization) and a slow decrease at high temperature (grain growth). Both recovery and recrystallization of the 2N Ni are strongly retarded by the presence of impurities reducing the mobility of boundaries. In the recrystallization stage, changes in hardness, microstructure and texture show that the 4N Ni recrystallizes discontinuously, in spite of a large fraction of high angle boundaries in the deformed state. This finding contradicts previous experiments and theory, which suggest that recrystallization is continuous when the fraction of high angle boundaries is high. In the 2N Ni, the observations suggest that some structural coarsening (continuous recrystallization) may take place simultaneously with discontinuous recrystallization. The findings emphasize the importance of alloying, which can delay the process of recovery and recrystallization and thereby enable tailoring of the microstructure and properties through an optimized annealing treatment. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007873