Documents disponibles écrits par cet auteur

Output-specific input-assurance regions in DEA / W. D. Cook in Journal of the operational research society (JORS), Vol. 62 N° 10 (Octobre 2011) 

Public ISBD [article]  in Journal of the operational research society (JORS) > Vol. 62 N° 10 (Octobre 2011) . - pp. 1881–1887 Titre : Output-specific input-assurance regions in DEA Type de document : texte imprimé Auteurs : W. D. Cook, Auteur ; Zhu, J., Auteur Année de publication : 2011 Article en page(s) : pp. 1881–1887 Note générale : Recherche opérationnelle Langues : Anglais (eng) Mots-clés : DEA  Multiple  components  Assurance  regions  Divisible  inputs Index. décimale : 001.424 Résumé : The use of assurance region (AR) constraints to restrict multipliers in data envelopment analysis (DEA) is well-established, and has been discussed at length in the literature. The conventional assumption in imposing such restrictions is that they apply universally. Specifically, AR constraints on input multipliers are intended to control the relative importance of the individual inputs in terms of how they impact the entire bundle of outputs. In many settings the relative importance of inputs is different for some of the outputs than for others. A typical example of this in the financial services sector is where the importance of sales staff versus service staff is different in regard to sales outputs than is true for service outputs. In this paper we develop a general DEA framework that incorporates multiple input-AR structures that cater to multiple output classes. We examine the cases of both divisible and indivisible inputs, and as well as mutually exclusive and overlapping output sets. The concepts are applied to a financial services situation. DEWEY : 001.424 ISSN : 0160-5682 En ligne : http://www.palgrave-journals.com/jors/journal/v62/n10/abs/jors2010150a.html [article] Output-specific input-assurance regions in DEA [texte imprimé] / W. D. Cook, Auteur ; Zhu, J., Auteur . - 2011 . - pp. 1881–1887. Recherche opérationnelle Langues : Anglais (eng) in Journal of the operational research society (JORS) > Vol. 62 N° 10 (Octobre 2011) . - pp. 1881–1887 Mots-clés : DEA  Multiple  components  Assurance  regions  Divisible  inputs Index. décimale : 001.424 Résumé : The use of assurance region (AR) constraints to restrict multipliers in data envelopment analysis (DEA) is well-established, and has been discussed at length in the literature. The conventional assumption in imposing such restrictions is that they apply universally. Specifically, AR constraints on input multipliers are intended to control the relative importance of the individual inputs in terms of how they impact the entire bundle of outputs. In many settings the relative importance of inputs is different for some of the outputs than for others. A typical example of this in the financial services sector is where the importance of sales staff versus service staff is different in regard to sales outputs than is true for service outputs. In this paper we develop a general DEA framework that incorporates multiple input-AR structures that cater to multiple output classes. We examine the cases of both divisible and indivisible inputs, and as well as mutually exclusive and overlapping output sets. The concepts are applied to a financial services situation. DEWEY : 001.424 ISSN : 0160-5682 En ligne : http://www.palgrave-journals.com/jors/journal/v62/n10/abs/jors2010150a.html

Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases / Zhu, J. in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 180–188 Titre : Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases Type de document : texte imprimé Auteurs : Zhu, J., Auteur ; C. Zhang, Auteur ; D. Ballard, Auteur Année de publication : 2010 Article en page(s) : pp. 180–188 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nickel  alloys  Cluster/site  approximation  Thermodynamics  CALPHAD Résumé : The modified cluster/site approximation was used to describe the thermodynamics of the various face-centered cubic phases in Ni–Al–Pt, the Bragg–Williams approximation for the B2 phase, and a modified regular solution formalism for the liquid phase. Coupled computational thermodynamics with key phase equilibrium measurements in the solid state, a thermodynamic description of this ternary for Ni contents higher than 50% was obtained based on these data and those given in the literature as well as the descriptions of its constituent binaries. Not only did the model-calculated solid-state phase equilibria agree with the measured data, the model-calculated liquidus projection is also able to account for the phases formed during solidification. In addition, the calculated chemical potentials or activities of Ni and Al are also in accord with the measured data as a function of temperature using mass spectrometry. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005916 [article] Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases [texte imprimé] / Zhu, J., Auteur ; C. Zhang, Auteur ; D. Ballard, Auteur . - 2010 . - pp. 180–188. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 180–188 Mots-clés : Nickel  alloys  Cluster/site  approximation  Thermodynamics  CALPHAD Résumé : The modified cluster/site approximation was used to describe the thermodynamics of the various face-centered cubic phases in Ni–Al–Pt, the Bragg–Williams approximation for the B2 phase, and a modified regular solution formalism for the liquid phase. Coupled computational thermodynamics with key phase equilibrium measurements in the solid state, a thermodynamic description of this ternary for Ni contents higher than 50% was obtained based on these data and those given in the literature as well as the descriptions of its constituent binaries. Not only did the model-calculated solid-state phase equilibria agree with the measured data, the model-calculated liquidus projection is also able to account for the phases formed during solidification. In addition, the calculated chemical potentials or activities of Ni and Al are also in accord with the measured data as a function of temperature using mass spectrometry. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005916

Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication / R. S. Dwyer-Joyce in Transactions of the ASME . Journal of tribology, Vol. 133 N° 3 (Juillet 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 133 N° 3 (Juillet 2011) . - 11 p. Titre : Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication Type de document : texte imprimé Auteurs : R. S. Dwyer-Joyce, Auteur ; T. Reddyhoff, Auteur ; Zhu, J., Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Elastic  moduli  Film  flow  Flow  separation  Flow  visualisation  Hydrodynamics  Liquid  films  Lubricating  oils  Rheology  Rough  surfaces  Ultrasonic  waves Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiffness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 m/s, the film thickness was found to vary from 0.01 to 0.8 µm, and the proportion of the load supported by asperity contact varied from 50% to 0%. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication [texte imprimé] / R. S. Dwyer-Joyce, Auteur ; T. Reddyhoff, Auteur ; Zhu, J., Auteur . - 2012 . - 11 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 133 N° 3 (Juillet 2011) . - 11 p. Mots-clés : Elastic  moduli  Film  flow  Flow  separation  Flow  visualisation  Hydrodynamics  Liquid  films  Lubricating  oils  Rheology  Rough  surfaces  Ultrasonic  waves Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiffness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 m/s, the film thickness was found to vary from 0.01 to 0.8 µm, and the proportion of the load supported by asperity contact varied from 50% to 0%. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]