Documents disponibles écrits par cet auteur

Impacts of epistemic uncertainty in operational modal analysis / Korhan Ciloglu in Journal of engineering mechanics, Vol. 138 N° 9 (Septembre 2012) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 138 N° 9 (Septembre 2012) . - pp.1059–1070. Titre : Impacts of epistemic uncertainty in operational modal analysis Type de document : texte imprimé Auteurs : Korhan Ciloglu, Auteur ; Yun Zhou, Auteur ; Franklin Moon, Auteur Année de publication : 2012 Article en page(s) : pp.1059–1070. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Epistemic  uncertainty  Operational  modal  analysis  Modal  flexibility  Modal  parameter  identification Résumé : Field experimentation on constructed systems demands consideration of many mechanisms of epistemic and aleatory uncertainties as well as human errors and subjectivity. This is especially true in operational modal analysis (OMA) applications that aim to identify the dynamic properties of a structure. Although statistics and probability theory are sufficient for quantifying aleatory uncertainty and bounding the resulting errors in OMA results, there is much debate as to whether the same tools may also be used to quantify epistemic uncertainty. This study explored a framework for better understanding the distinctions and impacts of these two types of uncertainties in OMA and how human errors and subjectivity may be classified. A physical laboratory model was designed to simulate four key sources of epistemic uncertainty that represented the primary test variables: structural complexity (changing boundary conditions, nonlinearity), ambient excitation characteristics (magnitude, directionality, and bandwidth), preprocessing approaches, and modal parameter identification algorithms. The experimental program employed these variables within a full-factorial design and was carried out independently by two experts. To quantify the impacts of epistemic uncertainty, an error function termed the uncertainty evaluation index (UEI) was formulated based on comparing the uniform load surfaces derived from OMA (using pseudomodal flexibility) and the ground truth flexibility obtained from both forced vibration and static testing. The advantage of the UEI is that it provides a physically meaningful approach to distinguish the importance of capturing various modes based on their contribution to the flexibility of the structure. The results demonstrated that proven and accepted data preprocessing techniques and modal parameter identification algorithms can significantly bias OMA results when used in certain combinations under different structural and excitation conditions. Although caution must be used when generalizing the results of this study, they do indicate that epistemic (or bias) uncertainty can be far more significant that aleatory (or random) uncertainty in the case of OMA. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000413 [article] Impacts of epistemic uncertainty in operational modal analysis [texte imprimé] / Korhan Ciloglu, Auteur ; Yun Zhou, Auteur ; Franklin Moon, Auteur . - 2012 . - pp.1059–1070. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 138 N° 9 (Septembre 2012) . - pp.1059–1070. Mots-clés : Epistemic  uncertainty  Operational  modal  analysis  Modal  flexibility  Modal  parameter  identification Résumé : Field experimentation on constructed systems demands consideration of many mechanisms of epistemic and aleatory uncertainties as well as human errors and subjectivity. This is especially true in operational modal analysis (OMA) applications that aim to identify the dynamic properties of a structure. Although statistics and probability theory are sufficient for quantifying aleatory uncertainty and bounding the resulting errors in OMA results, there is much debate as to whether the same tools may also be used to quantify epistemic uncertainty. This study explored a framework for better understanding the distinctions and impacts of these two types of uncertainties in OMA and how human errors and subjectivity may be classified. A physical laboratory model was designed to simulate four key sources of epistemic uncertainty that represented the primary test variables: structural complexity (changing boundary conditions, nonlinearity), ambient excitation characteristics (magnitude, directionality, and bandwidth), preprocessing approaches, and modal parameter identification algorithms. The experimental program employed these variables within a full-factorial design and was carried out independently by two experts. To quantify the impacts of epistemic uncertainty, an error function termed the uncertainty evaluation index (UEI) was formulated based on comparing the uniform load surfaces derived from OMA (using pseudomodal flexibility) and the ground truth flexibility obtained from both forced vibration and static testing. The advantage of the UEI is that it provides a physically meaningful approach to distinguish the importance of capturing various modes based on their contribution to the flexibility of the structure. The results demonstrated that proven and accepted data preprocessing techniques and modal parameter identification algorithms can significantly bias OMA results when used in certain combinations under different structural and excitation conditions. Although caution must be used when generalizing the results of this study, they do indicate that epistemic (or bias) uncertainty can be far more significant that aleatory (or random) uncertainty in the case of OMA. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000413

In situ synthesis of TiO2-functionalized metal nanoparticles / David M. King in Industrial & engineering chemistry research, Vol. 48 N°1 (Janvier 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - P. 352-360 Titre : In situ synthesis of TiO2-functionalized metal nanoparticles Type de document : texte imprimé Auteurs : David M. King, Editeur scientifique ; Yun Zhou, Editeur scientifique ; Louis F. Hakim, Editeur scientifique Année de publication : 2009 Article en page(s) : P. 352-360 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Metal  nanoparticles  Atomic  layer  deposition  (ALD)  Gas-phase  TiO2  ALD Résumé : The ability to prepare and functionalize passivated nanosized metal powders was demonstrated using TiO2 films that were deposited via atomic layer deposition (ALD). Metal nanopowders were synthesized from the dehydration and subsequent decomposition of bulk quantities of metal oxalates in a fluidized-bed reactor. The gas-phase TiO2 ALD coating process was used to passivate these particles in situ, which alleviated the need to expose the oxygen-sensitive materials to air. Metal oxalate size reduction was achieved using a cryogenic milling process that reduced the micrometer-sized oxalate feed powder and yielded metal nanopowders with an average primary diameter of ∼50 nm. The metal oxalates that have received the most attention are those of iron, nickel, cobalt, and copper. Al2O3-based ALD films have been deposited on each of these metals, whereas TiO2:metal nanocomposite powder research has been performed here and is the basis for this work. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800196h [article] In situ synthesis of TiO2-functionalized metal nanoparticles [texte imprimé] / David M. King, Editeur scientifique ; Yun Zhou, Editeur scientifique ; Louis F. Hakim, Editeur scientifique . - 2009 . - P. 352-360. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - P. 352-360 Mots-clés : Metal  nanoparticles  Atomic  layer  deposition  (ALD)  Gas-phase  TiO2  ALD Résumé : The ability to prepare and functionalize passivated nanosized metal powders was demonstrated using TiO2 films that were deposited via atomic layer deposition (ALD). Metal nanopowders were synthesized from the dehydration and subsequent decomposition of bulk quantities of metal oxalates in a fluidized-bed reactor. The gas-phase TiO2 ALD coating process was used to passivate these particles in situ, which alleviated the need to expose the oxygen-sensitive materials to air. Metal oxalate size reduction was achieved using a cryogenic milling process that reduced the micrometer-sized oxalate feed powder and yielded metal nanopowders with an average primary diameter of ∼50 nm. The metal oxalates that have received the most attention are those of iron, nickel, cobalt, and copper. Al2O3-based ALD films have been deposited on each of these metals, whereas TiO2:metal nanocomposite powder research has been performed here and is the basis for this work. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800196h

Synthesis of photoactive magnetic nanoparticles with atomic layer deposition / Yun Zhou in Industrial & engineering chemistry research, Vol. 49 N° 15 (Août 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 15 (Août 2010) . - pp 6964–6971 Titre : Synthesis of photoactive magnetic nanoparticles with atomic layer deposition Type de document : texte imprimé Auteurs : Yun Zhou, Auteur ; David M. King, Auteur ; Jianhua Li, Auteur Année de publication : 2010 Article en page(s) : pp 6964–6971 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Photoactive  Magnetic  Nanoparticles. Résumé : Iron-based magnetic nanoparticles have been produced by decomposition of iron oxalate powder. The micrometer-size iron oxalate powder was first ground by use of a cryogenic milling process. A titanium dioxide (TiO2) thin film was then deposited on the synthesized iron nanoparticles with an in situ atomic layer deposition (ALD) process at 100 °C with TiCl4 and H2O2 as precursors. However, because of the high surface area, the iron nanoparticles were unstable and spontaneously oxidized when exposed to H2O2 during the TiO2 ALD process, thus reducing the magnetic moment of the core particles. As an improvement in the process, prior to the TiO2 deposition, an aluminum nitride (AlN) film was deposited in situ to coat and passivate the iron core particles. The AlN ALD was performed at 250 °C with trimethylaluminium (TMA) and ammonia (NH3) as precursors. This passivation provided a significant decrease in the iron oxidation as determined by X-ray diffraction and magnetization measurements. Photoactivity of the TiO2 film was demonstrated by decomposition of methylene blue solution under ultraviolet irradiation. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901712q [article] Synthesis of photoactive magnetic nanoparticles with atomic layer deposition [texte imprimé] / Yun Zhou, Auteur ; David M. King, Auteur ; Jianhua Li, Auteur . - 2010 . - pp 6964–6971. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 15 (Août 2010) . - pp 6964–6971 Mots-clés : Photoactive  Magnetic  Nanoparticles. Résumé : Iron-based magnetic nanoparticles have been produced by decomposition of iron oxalate powder. The micrometer-size iron oxalate powder was first ground by use of a cryogenic milling process. A titanium dioxide (TiO2) thin film was then deposited on the synthesized iron nanoparticles with an in situ atomic layer deposition (ALD) process at 100 °C with TiCl4 and H2O2 as precursors. However, because of the high surface area, the iron nanoparticles were unstable and spontaneously oxidized when exposed to H2O2 during the TiO2 ALD process, thus reducing the magnetic moment of the core particles. As an improvement in the process, prior to the TiO2 deposition, an aluminum nitride (AlN) film was deposited in situ to coat and passivate the iron core particles. The AlN ALD was performed at 250 °C with trimethylaluminium (TMA) and ammonia (NH3) as precursors. This passivation provided a significant decrease in the iron oxidation as determined by X-ray diffraction and magnetization measurements. Photoactivity of the TiO2 film was demonstrated by decomposition of methylene blue solution under ultraviolet irradiation. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901712q