A systematic study on the structure sensitivity,host effect,and the deactivation mechanism of Ircatalyzed selective hydrogenation of 1,3-butadiene,a key process in the purification of alkadiene for the upgrading of C4...A systematic study on the structure sensitivity,host effect,and the deactivation mechanism of Ircatalyzed selective hydrogenation of 1,3-butadiene,a key process in the purification of alkadiene for the upgrading of C4 cut,is presented by coupling steady-state catalytic testing,in-depth characterization,kinetic evaluation,and density functional theory calculations.We reveal that:(i) 1,3-Butadiene hydrogenation on iridium is structure-sensitive with the optimal particle size of about 2 nm,and the H_(2) dissociation energy is a reliable activity descriptor;(ii) The nature of the NC hosts exerts a critical impact on the catalytic performance,and balanced nitrogen content and speciation seem key for the optimized performance;and (iii) Different deactivation mechanisms occur:fouling by coke deposition on the catalysts with a high N:C ratio (>1),and site blockage due to the competitive adsorption between 1-butene/cis-2-butene and 1,3-butadiene.These molecular insights provide valuable guidelines for the catalyst design in selective hydrogenations.展开更多
This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenv...This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenvectors are transformed into multiple parameter forms,and the second-order perturbation sensitivity matrices of eigenvalues and eigenvectors are developed.With these formulations,the efficient methods based on the second-order Taylor expansion and second-order perturbation are obtained to estimate changes of eigenvalues and eigenvectors when the design parameters are changed. The presented method avoids direct differential operation,and thus reduces difficulty for computing the second-order sensitivity matrices of eigenpairs.A numerical example is given to demonstrate application and accuracy of the proposed method.展开更多
The correlation coefficients of random variables of mechanical structures are generally chosen with experience or even ignored,which cannot actually reflect the effects of parameter uncertainties on reliability.To dis...The correlation coefficients of random variables of mechanical structures are generally chosen with experience or even ignored,which cannot actually reflect the effects of parameter uncertainties on reliability.To discuss the selection problem of the correlation coefficients from the reliability-based sensitivity point of view,the theory principle of the problem is established based on the results of the reliability sensitivity,and the criterion of correlation among random variables is shown.The values of the correlation coefficients are obtained according to the proposed principle and the reliability sensitivity problem is discussed.Numerical studies have shown the following results:(1) If the sensitivity value of correlation coefficient ρ is less than(at what magnitude 0.000 01),then the correlation could be ignored,which could simplify the procedure without introducing additional error.(2) However,as the difference between ρs,that is the most sensitive to the reliability,and ρR,that is with the smallest reliability,is less than 0.001,ρs is suggested to model the dependency of random variables.This could ensure the robust quality of system without the loss of safety requirement.(3) In the case of |Eabs|ρ0.001 and also |Erel|ρ0.001,ρR should be employed to quantify the correlation among random variables in order to ensure the accuracy of reliability analysis.Application of the proposed approach could provide a practical routine for mechanical design and manufactory to study the reliability and reliability-based sensitivity of basic design variables in mechanical reliability analysis and design.展开更多
A novel chemical technique combined with unique plasma activated sintering(PAS) was utilized to prepare consolidated copper matrix composites(CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers...A novel chemical technique combined with unique plasma activated sintering(PAS) was utilized to prepare consolidated copper matrix composites(CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide(r GO), SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2+. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.展开更多
Density functional theory(DFT)has been established as a powerful research tool for heterogeneous catalysis research in obtaining key thermodynamic and/or kinetic parameters like adsorption energies,enthalpies of react...Density functional theory(DFT)has been established as a powerful research tool for heterogeneous catalysis research in obtaining key thermodynamic and/or kinetic parameters like adsorption energies,enthalpies of reaction,activation barriers,and rate constants.Understanding of density functional exchangecorrelation approximations is essential to reveal the mechanism and performance of a catalyst.In the present work,we reported the influence of six exchange-correlation density functionals,including PBE,RPBE,BEEF+vdW,optB86b+vdW,SCAN,and SCAN+rVV10,on the adsorption energies,reaction energies and activation barriers of carbon hydrogenation and carbon-carbon couplings during the formation of methane and ethane over Ru(0001)and Ru(1011)surfaces.We found the calculated reaction energies are strongly dependent on exchange-correlation density functionals due to the difference in coordination number between reactants and products on surfaces.The deviation of the calculated elementary reaction energies can be accumulated to a large value for chemical reaction involving multiple steps and vary considerably with different exchange-correlation density functionals calculations.The different exchange-correlation density functionals are found to influence considerably the selectivity of Ru(0001)surface for methane,ethylene,and ethane formation determined by the adsorption energies of intermediates involved.However,the influence on the barriers of the elementary surface reactions and the structural sensitivity of Ru(0001)and Ru(1011)are modest.Our work highlights the limitation of exchange-correlation density functionals on computational catalysis and the importance of choosing a proper exchange-correlation density functional in correctly evaluating the activity and selectivity of a catalyst.展开更多
In this paper, material properties, geometry parameters and applied loads are assumed to be stochastic, sensitivity computation of structural vibration is presented. The vibration equation of a system is transformed t...In this paper, material properties, geometry parameters and applied loads are assumed to be stochastic, sensitivity computation of structural vibration is presented. The vibration equation of a system is transformed to a static problem by using the Newmark method, and the Taylor expansion stochastic finite element method (TSFEM) is extended for the structural vibration analysis. An example is given, and the calculation results show the validity of the proposed method.展开更多
Revealing the structure-performance relationships of the molecularly dispersed heterogenized metallomacrocycles(MDHMs)withπ-conjugated heterojunctions is of great,yet largely unmet,significance for realizing the rati...Revealing the structure-performance relationships of the molecularly dispersed heterogenized metallomacrocycles(MDHMs)withπ-conjugated heterojunctions is of great,yet largely unmet,significance for realizing the rational regulation of selectivity,Faradaic efficiency,and durability in the electrochemical CO_(2) reduction reaction(CO_(2)RR).Herein,we describe new insights into the molecularstructure sensitivity of the electrochemical CO_(2)RR over the MDHMs through peripherally functionalizing the heterogenized nickel phthalocyanines with diverse methylimidazole groups.As studied experimentally and theoretically,the heterointerfacial effect and self-built microenvironment of the MDHMs are significantly modulated by accurate structural clipping at the molecular level,predominately steering their electrocatalytic performance for CO_(2)-to-CO conversion in both H-type and flow electrolytic cells.Particularly,the optimized MDHM,2MIMCβNiPc/CNT,displays a significantly improved electrocatalytic performance for CO_(2)RR with near-unity Faradaic efficiency and large current density.Furthermore,the paired electrolysis systems with the MDHMs as the multifunctional electrocatalysts was developed for making full use of the anodic and cathodic reactions,which shows a new and profitable prospect for energy optimization,pollutant regeneration,and green electrosynthesis in a modular form,and also provides guidance for the design and synthesis of novel effi-cient yet economical electrocatalysts.展开更多
For better performance of dye sensitized solar cells (DSSCs), a bilayer structured electrode was constructed by employing a mesoporous anatase TiO2 overlayer above a commercial P25 TiO2 nanoparticles underlayer. The...For better performance of dye sensitized solar cells (DSSCs), a bilayer structured electrode was constructed by employing a mesoporous anatase TiO2 overlayer above a commercial P25 TiO2 nanoparticles underlayer. The mesoporous anatase TiO2, prepared through a facile surfactant-assisted sol-gel process, possessed large pore size and well inter-connected network structure, both beneficial for dye adsorption and electron transfer. The dye adsorption capability of the mesoporous TiO2 was nearly twice that of the P25 counterpart. In the electrode, the mesoporous TiO2 film enhanced both dye adsorption and lightharvest, to increase photocurrent (Jsc) from 12.32 to 14.78 mA/cm^2. Compared to the single P25 TiO2 film, the synergy of the mesoporous TiO2 and the P25 TiO2 nanoparticle films in the electrode resulted in a 24% improvement in light-to-electricity conversion efficiency (η). This bilayered electrode provides an alternative approach for further developing a photovoltaic device with better cell performance.展开更多
The stability of the flow in the vaneless diffuser of a centrifugal compressor is studied with the linear theory. The characteristics of direct and adjoint perturbation modes are investigated,and the receptivity of th...The stability of the flow in the vaneless diffuser of a centrifugal compressor is studied with the linear theory. The characteristics of direct and adjoint perturbation modes are investigated,and the receptivity of the instability mode to momentum forcing or mass injection is identified based on the adjoint modes. Analysis shows that the perturbation with the largest amplitude is located at the outlet of the vaneless diffuser, while the highest-receptivity region is located in the middle of the vaneless diffuser along the radial direction. The large difference between the direct and adjoint modes indicates that the instability mechanism cannot be identified from a study of either eigenmode separately. Therefore, the structural sensitivity analysis is adopted to study the feedback of the instability mode. The structural sensitivity of the eigenvalue which is proportional to the perturbation pressure and velocity is used to explain the mechanism of flow control for the vaneless diffuser.展开更多
Structural assumptions in infectious disease models,such as the choice of network or compartmental model type or the inclusion of different types of heterogeneity across individuals,might affect model predictions as m...Structural assumptions in infectious disease models,such as the choice of network or compartmental model type or the inclusion of different types of heterogeneity across individuals,might affect model predictions as much as or more than the choice of input parameters.We explore the potential implications of structural assumptions on HIV model predictions and policy conclusions.We illustrate the value of inference robustness assessment through a case study of the effects of a hypothetical HIV vaccine in multiple population subgroups over eight related transmission models,which we sequentially modify to vary over two dimensions:parameter complexity(e.g.,the inclusion of age and HCV comorbidity)and contact/simulation complexity(e.g.,aggregated compartmental vs.individual/disaggregated compartmental vs.network models).We find that estimates of HIV incidence reductions from network models and individual compartmental models vary,but those differences are overwhelmed by the differences in HIV incidence between such models and the aggregated compartmental models(which aggregate groups of individuals into compartments).Complexities such as age structure appear to buffer the effects of aggregation and increase the threshold of net vaccine effectiveness at which aggregated models begin to overestimate reductions.The differences introduced by parameter complexity in estimated incidence reduction also translate into substantial differences in cost-effectiveness estimates.Parameter complexity does not appear to play a consistent role in differentiating the projections of network models.展开更多
基金Zhejiang Normal University for providing the financial support (YS304320035, YS304320036, ZZ323205020521005039)Financial support from the National Natural Science Foundation of China (NSFC, 21606199)+1 种基金the Science and Technology Department of Zhejiang Province (LGG20B060004)the National Key Research and Development Program of China (2021YFA1501800, 2021YFA1501801, 2021YFA1501802) are also gratefully acknowledged。
文摘A systematic study on the structure sensitivity,host effect,and the deactivation mechanism of Ircatalyzed selective hydrogenation of 1,3-butadiene,a key process in the purification of alkadiene for the upgrading of C4 cut,is presented by coupling steady-state catalytic testing,in-depth characterization,kinetic evaluation,and density functional theory calculations.We reveal that:(i) 1,3-Butadiene hydrogenation on iridium is structure-sensitive with the optimal particle size of about 2 nm,and the H_(2) dissociation energy is a reliable activity descriptor;(ii) The nature of the NC hosts exerts a critical impact on the catalytic performance,and balanced nitrogen content and speciation seem key for the optimized performance;and (iii) Different deactivation mechanisms occur:fouling by coke deposition on the catalysts with a high N:C ratio (>1),and site blockage due to the competitive adsorption between 1-butene/cis-2-butene and 1,3-butadiene.These molecular insights provide valuable guidelines for the catalyst design in selective hydrogenations.
基金Project supported by the 985-Engineering Innovation of Graduate Students of Jilin Universitythe Science and Technology Development Foundation of Jilin Province(20070541)
文摘This paper presents methods for computing a second-order sensitivity matrix and the Hessian matrix of eigenvalues and eigenvectors of multiple parameter structures. Second-order perturbations of eigenvalues and eigenvectors are transformed into multiple parameter forms,and the second-order perturbation sensitivity matrices of eigenvalues and eigenvectors are developed.With these formulations,the efficient methods based on the second-order Taylor expansion and second-order perturbation are obtained to estimate changes of eigenvalues and eigenvectors when the design parameters are changed. The presented method avoids direct differential operation,and thus reduces difficulty for computing the second-order sensitivity matrices of eigenpairs.A numerical example is given to demonstrate application and accuracy of the proposed method.
基金supported by Changjiang Scholars and Innovative Research Team in University of China (Grant No. IRT0816)Key National Science & Technology Special Project on "High-Grade CNC Machine Tools and Basic Manufacturing Equipments" of China (Grant No. 2010ZX04014-014)+1 种基金National Natural Science Foundation of China (Grant No. 50875039)Key Projects in National Science & Technology Pillar Program during the 11th Five-year Plan Period of China (Grant No. 2009BAG12A02-A07-2)
文摘The correlation coefficients of random variables of mechanical structures are generally chosen with experience or even ignored,which cannot actually reflect the effects of parameter uncertainties on reliability.To discuss the selection problem of the correlation coefficients from the reliability-based sensitivity point of view,the theory principle of the problem is established based on the results of the reliability sensitivity,and the criterion of correlation among random variables is shown.The values of the correlation coefficients are obtained according to the proposed principle and the reliability sensitivity problem is discussed.Numerical studies have shown the following results:(1) If the sensitivity value of correlation coefficient ρ is less than(at what magnitude 0.000 01),then the correlation could be ignored,which could simplify the procedure without introducing additional error.(2) However,as the difference between ρs,that is the most sensitive to the reliability,and ρR,that is with the smallest reliability,is less than 0.001,ρs is suggested to model the dependency of random variables.This could ensure the robust quality of system without the loss of safety requirement.(3) In the case of |Eabs|ρ0.001 and also |Erel|ρ0.001,ρR should be employed to quantify the correlation among random variables in order to ensure the accuracy of reliability analysis.Application of the proposed approach could provide a practical routine for mechanical design and manufactory to study the reliability and reliability-based sensitivity of basic design variables in mechanical reliability analysis and design.
基金Funded by the National Natural Science Foundation of China(51572208)the 111 Project(B13035)+1 种基金the National Natural Science Foundation of Hubei Province(2014CFB257 and 2014CFB258)the Fundamental Research Funds for the Central Universities(WUT:2015-III-059)
文摘A novel chemical technique combined with unique plasma activated sintering(PAS) was utilized to prepare consolidated copper matrix composites(CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide(r GO), SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2+. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.
基金This work was supported by the Key Technologies R&D Program of China(No.2018YFA0208603)the National Natural Science Foundation of China(No.22172150 and No.91945302)+5 种基金the Chinese Academy of Sciences Key Project(QYZDJ-SSW-SLH054)the Start-up Funds of University of Science and Technology of China(No.KY2060000171)the National Natural Science Foundation of Anhui province(No.2108085QB62)USTC Research Funds of the Double First-Class Initiative(No.YD2060002012)K.C.Wong Education(No.GJTD-2020-15)highPerformance Computational Resources provided by the University of Science and Technology of China(http://scc.ustc.edu.cn)and Hefei Advanced Computing center.
文摘Density functional theory(DFT)has been established as a powerful research tool for heterogeneous catalysis research in obtaining key thermodynamic and/or kinetic parameters like adsorption energies,enthalpies of reaction,activation barriers,and rate constants.Understanding of density functional exchangecorrelation approximations is essential to reveal the mechanism and performance of a catalyst.In the present work,we reported the influence of six exchange-correlation density functionals,including PBE,RPBE,BEEF+vdW,optB86b+vdW,SCAN,and SCAN+rVV10,on the adsorption energies,reaction energies and activation barriers of carbon hydrogenation and carbon-carbon couplings during the formation of methane and ethane over Ru(0001)and Ru(1011)surfaces.We found the calculated reaction energies are strongly dependent on exchange-correlation density functionals due to the difference in coordination number between reactants and products on surfaces.The deviation of the calculated elementary reaction energies can be accumulated to a large value for chemical reaction involving multiple steps and vary considerably with different exchange-correlation density functionals calculations.The different exchange-correlation density functionals are found to influence considerably the selectivity of Ru(0001)surface for methane,ethylene,and ethane formation determined by the adsorption energies of intermediates involved.However,the influence on the barriers of the elementary surface reactions and the structural sensitivity of Ru(0001)and Ru(1011)are modest.Our work highlights the limitation of exchange-correlation density functionals on computational catalysis and the importance of choosing a proper exchange-correlation density functional in correctly evaluating the activity and selectivity of a catalyst.
基金Supported by National Natural Science Foundation under Grant No.10202016
文摘In this paper, material properties, geometry parameters and applied loads are assumed to be stochastic, sensitivity computation of structural vibration is presented. The vibration equation of a system is transformed to a static problem by using the Newmark method, and the Taylor expansion stochastic finite element method (TSFEM) is extended for the structural vibration analysis. An example is given, and the calculation results show the validity of the proposed method.
基金grateful for the financial support of the National Key R&D Program of China(grant no.2021YFA1500402)the National Natural Science Foundation of China(grant nos.21901246,22105203,and 22175174)the Natural Science Foundation of Fujian Province(grant nos.2020J01116 and 2021J06033).
文摘Revealing the structure-performance relationships of the molecularly dispersed heterogenized metallomacrocycles(MDHMs)withπ-conjugated heterojunctions is of great,yet largely unmet,significance for realizing the rational regulation of selectivity,Faradaic efficiency,and durability in the electrochemical CO_(2) reduction reaction(CO_(2)RR).Herein,we describe new insights into the molecularstructure sensitivity of the electrochemical CO_(2)RR over the MDHMs through peripherally functionalizing the heterogenized nickel phthalocyanines with diverse methylimidazole groups.As studied experimentally and theoretically,the heterointerfacial effect and self-built microenvironment of the MDHMs are significantly modulated by accurate structural clipping at the molecular level,predominately steering their electrocatalytic performance for CO_(2)-to-CO conversion in both H-type and flow electrolytic cells.Particularly,the optimized MDHM,2MIMCβNiPc/CNT,displays a significantly improved electrocatalytic performance for CO_(2)RR with near-unity Faradaic efficiency and large current density.Furthermore,the paired electrolysis systems with the MDHMs as the multifunctional electrocatalysts was developed for making full use of the anodic and cathodic reactions,which shows a new and profitable prospect for energy optimization,pollutant regeneration,and green electrosynthesis in a modular form,and also provides guidance for the design and synthesis of novel effi-cient yet economical electrocatalysts.
基金supported by the National Natural Science Foundation of China (20925621)Shanghai Rising-Star Program (09QH1400700,09QA1401500)+4 种基金Special Projects for Key Laboratories in Shanghai (09DZ2202000,10DZ2211100)Special Projects for Nanotechnology of Shanghai (0952nm02100)Shanghai Pujiang Program (09PJ1403200)Basic Research Program of Shanghai (10JC1403300)Fundamental Research Funds for the Central Universities
文摘For better performance of dye sensitized solar cells (DSSCs), a bilayer structured electrode was constructed by employing a mesoporous anatase TiO2 overlayer above a commercial P25 TiO2 nanoparticles underlayer. The mesoporous anatase TiO2, prepared through a facile surfactant-assisted sol-gel process, possessed large pore size and well inter-connected network structure, both beneficial for dye adsorption and electron transfer. The dye adsorption capability of the mesoporous TiO2 was nearly twice that of the P25 counterpart. In the electrode, the mesoporous TiO2 film enhanced both dye adsorption and lightharvest, to increase photocurrent (Jsc) from 12.32 to 14.78 mA/cm^2. Compared to the single P25 TiO2 film, the synergy of the mesoporous TiO2 and the P25 TiO2 nanoparticle films in the electrode resulted in a 24% improvement in light-to-electricity conversion efficiency (η). This bilayered electrode provides an alternative approach for further developing a photovoltaic device with better cell performance.
文摘The stability of the flow in the vaneless diffuser of a centrifugal compressor is studied with the linear theory. The characteristics of direct and adjoint perturbation modes are investigated,and the receptivity of the instability mode to momentum forcing or mass injection is identified based on the adjoint modes. Analysis shows that the perturbation with the largest amplitude is located at the outlet of the vaneless diffuser, while the highest-receptivity region is located in the middle of the vaneless diffuser along the radial direction. The large difference between the direct and adjoint modes indicates that the instability mechanism cannot be identified from a study of either eigenmode separately. Therefore, the structural sensitivity analysis is adopted to study the feedback of the instability mode. The structural sensitivity of the eigenvalue which is proportional to the perturbation pressure and velocity is used to explain the mechanism of flow control for the vaneless diffuser.
基金Financial support for this study was provided by Grant Number R01-DA15612 from the National Institute on Drug AbuseCB was supported by a PACCAR Inc.Stanford Graduate Fellowship and National Science Foundation Graduate Fellowship DGE-114747.
文摘Structural assumptions in infectious disease models,such as the choice of network or compartmental model type or the inclusion of different types of heterogeneity across individuals,might affect model predictions as much as or more than the choice of input parameters.We explore the potential implications of structural assumptions on HIV model predictions and policy conclusions.We illustrate the value of inference robustness assessment through a case study of the effects of a hypothetical HIV vaccine in multiple population subgroups over eight related transmission models,which we sequentially modify to vary over two dimensions:parameter complexity(e.g.,the inclusion of age and HCV comorbidity)and contact/simulation complexity(e.g.,aggregated compartmental vs.individual/disaggregated compartmental vs.network models).We find that estimates of HIV incidence reductions from network models and individual compartmental models vary,but those differences are overwhelmed by the differences in HIV incidence between such models and the aggregated compartmental models(which aggregate groups of individuals into compartments).Complexities such as age structure appear to buffer the effects of aggregation and increase the threshold of net vaccine effectiveness at which aggregated models begin to overestimate reductions.The differences introduced by parameter complexity in estimated incidence reduction also translate into substantial differences in cost-effectiveness estimates.Parameter complexity does not appear to play a consistent role in differentiating the projections of network models.