The XYZ antiferromagnetic model in linear spin-wave frame is shown explicitly to have an su（1,2） algebraic structure： the Hamiltonian can be written as a linear function of the su（1,2） algebra generators. Based o...The XYZ antiferromagnetic model in linear spin-wave frame is shown explicitly to have an su（1,2） algebraic structure： the Hamiltonian can be written as a linear function of the su（1,2） algebra generators. Based on it, the energy eigenvalues are obta/ned by making use of the similar transformations, and the algebraic diagonalization method is investigated. Some numerical solutions are given, and the results indicate that only one group solution could be accepted in physics.展开更多
The Belousov-Zhabotinski type of chemical reactions was studied. Dynamics of the unperturbed oscillating chemical system and subject to the external perturbations is considered. The system response to the external per...The Belousov-Zhabotinski type of chemical reactions was studied. Dynamics of the unperturbed oscillating chemical system and subject to the external perturbations is considered. The system response to the external periodic perturbation near the Hopf bifurcation point has been monitored. As a response to the external periodic perturbation of system, one obtains the synchronization oscillations, two-, three-and multiperiodic ones as well as obtain two types of chaos. The kinetic of such reactions is analyzed by time series. The Fourier transforms were used to analyze the frequency characteristics of the synchronized and chaotic states giving the different harmonic spectra. As further statistical characteristics the winding numbers and variation values of trajectories are calculated using a rotational model of processes in relation to the coherence parameter joint with perturbation period. For chaotic states the autocorrelation functions and correlation dimensions, which form an approximation of a fractal dimension D, have been calculated. Additionally, Lyapunov exponents were computed. Their positive values confirmed chaotic behavior.展开更多
The central composite design in the modeling and optimization of catalytic dehydration of ethanol to ethylene was performed to improve the ethylene yield.A total of 20 experiments at random were conducted to investiga...The central composite design in the modeling and optimization of catalytic dehydration of ethanol to ethylene was performed to improve the ethylene yield.A total of 20 experiments at random were conducted to investigate the effect of reaction temperature,Si/Al ratios of H-ZSM-5 catalyst and liquid hourly space velocity(LHSV) on the ethylene yield.The results show that the relationship between ethylene yield and the three significant independent variables can be approximated by a nonlinear polynomial model,with R-squared of 99.9%and adjusted R-squared of 99.8%.The maximal response for ethylene yield is 93.4%under the optimal condition of 328 ℃,Si/Al ratio 85,and LHSV 3.8 h-1.展开更多
Interfaces play critical roles in electronic devices and provide great diversity of film morphology and device performance.We retrospect the substrate mediated vacuum film growth of benchmark high mobility material 2,...Interfaces play critical roles in electronic devices and provide great diversity of film morphology and device performance.We retrospect the substrate mediated vacuum film growth of benchmark high mobility material 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT)and the interface electronic structures.The film growth of C8-BTBT molecules is diversified depending on the substrate-molecule and molecule-molecule interactions.On atomic smooth substrates C8-BTBT film grows in layer-by-layer mode while on coarse substrate it grows in islands mode.The initial molecular layer at dielectric,semiconductor and conductive substrates displays slight different lattice structure.The initial molecule orientation depends on the substrate and will gradually change to standing up configuration as in bulk phase.C8-BTBT behaves as electron donor when contacting with dielectric and stable conductive materials.This usually induces a dipole layer pointing to C8-BTBT and an upward bend bending in C8-BTBT side toward the interface.Although it is air stable,C8-BTBT is chemically reactive with some transition metals and compounds.The orientation change from lying down to standing up in the film usually leads to decrease of ionization potential.The article provides insights to the interface physical and chemical processes and suggestions for optimal design and fabrication of C8-BTBT based devices.展开更多
Solid oxide fuel cell (SOFC) has been identified as an effective and clean alternative choice for marine power system.This paper emphasizes on the dynamic modeling of SOFC power system and its performance based upon m...Solid oxide fuel cell (SOFC) has been identified as an effective and clean alternative choice for marine power system.This paper emphasizes on the dynamic modeling of SOFC power system and its performance based upon marine operating circumstance.A SOFC power system model has been provided considering thermodynamic and electrochemical reaction mechanism.Subcomponents of lithium ion battery, power conditioning unit, stack structure and controller are integrated in the model.The dynamic response of the system is identified according to the inertia of its subcomponent and controller.Validation of the whole system simulation at steady state and transit period are presented, concerning the effects of thermo inertia, control strategy and seagoing environment.The simulation results show reasonable accuracy compare with lab test.The models can be used to predict performance of a SOFC power system and identify the system response when part of the component parameter is adjusted.展开更多
Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the present...Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the presented study, we investigated the controlling factors of denitrification rates within the streams of the Han River Basin, Korea, with different land-use patterns, in order to enhance the effectiveness of water resource management strategies. Ten watersheds were classified into three land-use patterns （forest, agriculture and urban） using satellite images and geographic information system techniques, and in-situ denitrification rates were determined using an acetylene blocking method. Additionally, sediment samples were collected from each stream to analyze denitrifier communities and abundance using molecular approaches. In-situ denitrification rates were found to be in the order of agricultural streams （289.6 mg N20-N m-2 d-1） 〉 urban streams （157.0 mg N20-N m-2 d-1） 〉 forested streams （41.9 mg N20-N m-2 d-l）. In contrast, the average quantity of denitrifying genes was the lowest in the urban streams. Genetic diversity of denitrifying genes was not affected by watershed land-use pattern, but exhibited stream-dependent pattern. More significance factors were involved in denitrification in the sites with higher denitrification rates. Multiple linear regression analysis revealed that clay, dissolved organic carbon and water contents were the main factors controlling denitrification rate in the agricultural streams, while dissolved organic carbon was the main controlling factor in the urban streams. In contrast, temperature appeared to be the main controlling factor in the forested streams.展开更多
Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes,improving engine performance,and reducing pollutant emissions.Critical issues as turbulence model...Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes,improving engine performance,and reducing pollutant emissions.Critical issues as turbulence modeling,turbulence-chemistry interaction,and accommodation of detailed chemical kinetics in complex flows remain challenging and essential for highfidelity combustion simulation.This paper reviews the current status of the state-of-the-art large eddy simulation(LES)/probability density function(PDF)/detailed chemistry approach that can address the three challenging modelling issues.PDF as a subgrid model for LES is formulated and the hybrid mesh-particle method for LES/PDF simulations is described.Then the development need in micro-mixing models for the PDF simulations of turbulent premixed combustion is identified.Finally the different acceleration methods for detailed chemistry are reviewed and a combined strategy is proposed for further development.展开更多
基金The project supported by National Natural Science Foundation of China under Grant Nos.10447103 and 90305026the Natural Science Foundation of Beijing under Grant No.1072010the Foundation of Education Department of Beijing under Grant No.KM200610772007
文摘The XYZ antiferromagnetic model in linear spin-wave frame is shown explicitly to have an su（1,2） algebraic structure： the Hamiltonian can be written as a linear function of the su（1,2） algebra generators. Based on it, the energy eigenvalues are obta/ned by making use of the similar transformations, and the algebraic diagonalization method is investigated. Some numerical solutions are given, and the results indicate that only one group solution could be accepted in physics.
文摘The Belousov-Zhabotinski type of chemical reactions was studied. Dynamics of the unperturbed oscillating chemical system and subject to the external perturbations is considered. The system response to the external periodic perturbation near the Hopf bifurcation point has been monitored. As a response to the external periodic perturbation of system, one obtains the synchronization oscillations, two-, three-and multiperiodic ones as well as obtain two types of chaos. The kinetic of such reactions is analyzed by time series. The Fourier transforms were used to analyze the frequency characteristics of the synchronized and chaotic states giving the different harmonic spectra. As further statistical characteristics the winding numbers and variation values of trajectories are calculated using a rotational model of processes in relation to the coherence parameter joint with perturbation period. For chaotic states the autocorrelation functions and correlation dimensions, which form an approximation of a fractal dimension D, have been calculated. Additionally, Lyapunov exponents were computed. Their positive values confirmed chaotic behavior.
基金Supported by National Natural Science Foundation of China(No.70671072)
文摘The central composite design in the modeling and optimization of catalytic dehydration of ethanol to ethylene was performed to improve the ethylene yield.A total of 20 experiments at random were conducted to investigate the effect of reaction temperature,Si/Al ratios of H-ZSM-5 catalyst and liquid hourly space velocity(LHSV) on the ethylene yield.The results show that the relationship between ethylene yield and the three significant independent variables can be approximated by a nonlinear polynomial model,with R-squared of 99.9%and adjusted R-squared of 99.8%.The maximal response for ethylene yield is 93.4%under the optimal condition of 328 ℃,Si/Al ratio 85,and LHSV 3.8 h-1.
基金Project(2017YFA0206602)supported in part by the National Key Research and Development Program of China。
文摘Interfaces play critical roles in electronic devices and provide great diversity of film morphology and device performance.We retrospect the substrate mediated vacuum film growth of benchmark high mobility material 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT)and the interface electronic structures.The film growth of C8-BTBT molecules is diversified depending on the substrate-molecule and molecule-molecule interactions.On atomic smooth substrates C8-BTBT film grows in layer-by-layer mode while on coarse substrate it grows in islands mode.The initial molecular layer at dielectric,semiconductor and conductive substrates displays slight different lattice structure.The initial molecule orientation depends on the substrate and will gradually change to standing up configuration as in bulk phase.C8-BTBT behaves as electron donor when contacting with dielectric and stable conductive materials.This usually induces a dipole layer pointing to C8-BTBT and an upward bend bending in C8-BTBT side toward the interface.Although it is air stable,C8-BTBT is chemically reactive with some transition metals and compounds.The orientation change from lying down to standing up in the film usually leads to decrease of ionization potential.The article provides insights to the interface physical and chemical processes and suggestions for optimal design and fabrication of C8-BTBT based devices.
文摘Solid oxide fuel cell (SOFC) has been identified as an effective and clean alternative choice for marine power system.This paper emphasizes on the dynamic modeling of SOFC power system and its performance based upon marine operating circumstance.A SOFC power system model has been provided considering thermodynamic and electrochemical reaction mechanism.Subcomponents of lithium ion battery, power conditioning unit, stack structure and controller are integrated in the model.The dynamic response of the system is identified according to the inertia of its subcomponent and controller.Validation of the whole system simulation at steady state and transit period are presented, concerning the effects of thermo inertia, control strategy and seagoing environment.The simulation results show reasonable accuracy compare with lab test.The models can be used to predict performance of a SOFC power system and identify the system response when part of the component parameter is adjusted.
基金Supported by the National Research Foundation of Korea(No.2013056833)
文摘Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the presented study, we investigated the controlling factors of denitrification rates within the streams of the Han River Basin, Korea, with different land-use patterns, in order to enhance the effectiveness of water resource management strategies. Ten watersheds were classified into three land-use patterns （forest, agriculture and urban） using satellite images and geographic information system techniques, and in-situ denitrification rates were determined using an acetylene blocking method. Additionally, sediment samples were collected from each stream to analyze denitrifier communities and abundance using molecular approaches. In-situ denitrification rates were found to be in the order of agricultural streams （289.6 mg N20-N m-2 d-1） 〉 urban streams （157.0 mg N20-N m-2 d-1） 〉 forested streams （41.9 mg N20-N m-2 d-l）. In contrast, the average quantity of denitrifying genes was the lowest in the urban streams. Genetic diversity of denitrifying genes was not affected by watershed land-use pattern, but exhibited stream-dependent pattern. More significance factors were involved in denitrification in the sites with higher denitrification rates. Multiple linear regression analysis revealed that clay, dissolved organic carbon and water contents were the main factors controlling denitrification rate in the agricultural streams, while dissolved organic carbon was the main controlling factor in the urban streams. In contrast, temperature appeared to be the main controlling factor in the forested streams.
基金supported by the 111 Project(Grant No.B13001)by the Young Thousand Talents Program from the Organization Department of the Communist Party of China Central Committee
文摘Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes,improving engine performance,and reducing pollutant emissions.Critical issues as turbulence modeling,turbulence-chemistry interaction,and accommodation of detailed chemical kinetics in complex flows remain challenging and essential for highfidelity combustion simulation.This paper reviews the current status of the state-of-the-art large eddy simulation(LES)/probability density function(PDF)/detailed chemistry approach that can address the three challenging modelling issues.PDF as a subgrid model for LES is formulated and the hybrid mesh-particle method for LES/PDF simulations is described.Then the development need in micro-mixing models for the PDF simulations of turbulent premixed combustion is identified.Finally the different acceleration methods for detailed chemistry are reviewed and a combined strategy is proposed for further development.
