Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the ...Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.展开更多
Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and sc...Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.展开更多
The first operation of an electrically pumped 1.3μm InAs/GaAs quantum-dot laser was previously reported epitaxially grown on Si （100） substrate. Here the direct epitaxial growth condition of 1.3μm InAs/OaAs quantu...The first operation of an electrically pumped 1.3μm InAs/GaAs quantum-dot laser was previously reported epitaxially grown on Si （100） substrate. Here the direct epitaxial growth condition of 1.3μm InAs/OaAs quantum on a Si substrate is further investigated using atomic force microscopy, etch pit density and temperature-dependent photoluminescence （PL） measurements. The PL for Si-based InAs/GaAs quantum dots appears to be very sensitive to the initial OaAs nucleation temperature and thickness with strongest room-temperature emission at 40000 （17Onto nucleation layer thickness）, due to the lower density of defects generated under this growth condition, and stronger carrier confinement within the quantum dots.展开更多
We present a new digital phase lock technology to achieve the frequency control and transformation through high precision multi-cycle group synchronization between signals without the frequency transformation circuit....We present a new digital phase lock technology to achieve the frequency control and transformation through high precision multi-cycle group synchronization between signals without the frequency transformation circuit. In the case of digital sampling, the passing zero point of the phase of the controlled signal has the phase step characteristic, the phase step of the passing zero point is monotonic continuous with high resolution in the phase lock process, and using the border effect of digital fuzzy area, the gate can synchronize with the two signals, the quantization error is reduced. This technique is quite different from the existing methods of frequency transformation and frequency synthesis, the phase change characteristic between the periodic signals with different nominal is used. The phase change has the periodic phenomenon, and it has the high resolution step value. With the application of the physical law, the noise is reduced because of simplifying frequency transformation circuits, and the phase is locked with high precision. The regular phase change between frequency signals is only used for frequency measurement, and the change has evident randomness, but this randomness is greatly reduced in frequency control, and the certainty of the process result is clear. The experiment shows that the short term frequency stability can reach 10-12/s orders of magnitude.展开更多
In this paper,we develop a new and effective multiple scale and strongly directional method for identifying and suppressing ground roll based on the second generation curvelet transform.Making the best use of the curv...In this paper,we develop a new and effective multiple scale and strongly directional method for identifying and suppressing ground roll based on the second generation curvelet transform.Making the best use of the curvelet transform＇s strong local directional characteristics,seismic frequency bands are transformed into scale data with and without noise.Since surface waves and primary reflected waves have less overlap in the curvelet domain,we can effectively identify and separate noise.Applying this method to prestack seismic data can successfully remove surface waves and,at the same time,protect the reflected events well,particularly in the low-frequency band.This indicates that the method described in this paper is an effective and amplitude-preserving method.展开更多
Based on the stress distribution characteristics of rock burst multiple sites, the criterion of horizontal stress inducing layer dislocation rock burst was established. Accordingly, the influencing factors were analyz...Based on the stress distribution characteristics of rock burst multiple sites, the criterion of horizontal stress inducing layer dislocation rock burst was established. Accordingly, the influencing factors were analyzed. The analysis results indicate that the stress condition, edge of etastic zone depth, supporting strength, and the friction angle and cohesion among coal stratum, roof and floor are sensitive factors. By introducing double-couple model, the layer dislocation rock burst was explained and the energy radiation characteristics were analyzed. The SOS micro-seismic monitoring system was applied to observe the rock burst hazards about a mining face. The results show that P- and S-wave energy radiations produced by rock burst have directional characteristics. The energy radiation characteristics of the 22 rock bursts occurring on 79Z6 long-wall face are basically the same as theoretical results, that is, the ratio of S-wave energy of sensor 4 to 6 is about 1.5 and that of P-wave is smaller than 0.5. The consistency of the monitored characteristics of the energy radiation theoretically increases with the total energy increasing.展开更多
In the present paper,the local well-posedness of the incompressible viscoelastic fluid system in the whole space is proved under the following assumption on the initial data:the deformation tensor is Hlder continuou...In the present paper,the local well-posedness of the incompressible viscoelastic fluid system in the whole space is proved under the following assumption on the initial data:the deformation tensor is Hlder continuous and the velocity is Lp integrable,p】d,where d is the space dimension.展开更多
The vegetation canopy clumping index(CI)is an important indicator for understanding radiative transport processes,radiation interception,and the photosynthesis of vegetation canopies.However,most studies consider CI o...The vegetation canopy clumping index(CI)is an important indicator for understanding radiative transport processes,radiation interception,and the photosynthesis of vegetation canopies.However,most studies consider CI only in the nadir or specific direction.In this study,we analyze the directional characteristics of the CI based on RAMI-V(radiation transfer model intercomparison)activity,which represents most typical canopies.The directional gap fraction and CI of these scenes are accurately calculated based on the LESS(large-scale remote sensing data and image simulation framework)model.According to our results,the directional characteristics of the CI are affected by many factors,such as vegetation type,season,and canopy structure.Generally,the CI of a coniferous forest varies little with zenith angle,while the CI of a broad-leaf forest demonstrates the different trend.In winter,the CI is smaller than that in summer,and the variation in the CI at the zenith angle is less.The row structure scenes exhibit different directional characteristics along and perpendicular to the row direction,and their CIs tend to increase with zenith angle.To accurately model the directional CI,we propose a modified Gompertz function model.Compared with other directional CI models,this model has the advantages of high precision and strong applicability(R^(2)=0.975).By studying the directional characteristics of CI,we can enhance the usability of radiative transfer modeling and the accuracy of canopy biophysical parameter retrieval for vegetation with different structures.展开更多
A computable expression of the asymptotic expansion of the return map for a degenerate singular point of a class of planar differential system is given, and hence the stability and the type of the singular point can b...A computable expression of the asymptotic expansion of the return map for a degenerate singular point of a class of planar differential system is given, and hence the stability and the type of the singular point can be decided. These results generalize the corresponding results in [Nonlinearity, 13 （2000）, p.709].展开更多
Choanoid fluidized bed bioreactors （CFBBs） are newly developed core devices used in bioartificial liver- support systems to detoxify blood plasma of patients with microencapsulated liver cells. Direct numerical simu...Choanoid fluidized bed bioreactors （CFBBs） are newly developed core devices used in bioartificial liver- support systems to detoxify blood plasma of patients with microencapsulated liver cells. Direct numerical simulations （DNS） with a direct-forcing/fictitious domain （DF/FD） method were conducted to study the hydrodynamic performance of a CFBB. The effects of particle-fluid density ratio, particle number, and fil- ter screens preventing particles flowing out of the reactor were investigated. Depending on density ratio, two flow patterns are evident： the circulation mode in which the suspension rises along one sidewall and descends along the other sidewall, and the non-circulation mode in which the whole suspension roughly flows upward. The circulation mode takes place under non-neutral-buoyancy where the particle sedimentation dominates, whereas the non-circulation mode occurs under pure or near-neutral buoy- ancy with particle-fluid density ratios of unity or near unity. With particle-fluid density ratio of 1.01, the bioartificial liver reactor performs optimally as the significant particle accumulation existing in the non-circulation mode and the large shear forces on particles in the circulation mode are avoided. At higher particle volume fractions, more particles accumulate at the filter screens and a secondary counter circulation to the primary flow is observed at the top of the bed. Modelled as porous media, the filter screens play a negative role on particle fluidization velocities; without screens, particles are fluidized faster because of the higher fluid velocities in the jet center region. This work extends the DF/FD-based DNS to a fluidized bed and accounts for effects from inclined side walls and porous media, providing some hydrodynamics insight that is important for CFBB design and operation optimization.展开更多
文摘Microstructure Characteristic of Ni-Nb near eutectic alloy is systematically investigated during directional solidification with electron beam floating zone melting (EBFZM). The effect of the Zone melting rate on the microstructure has also been studied.
基金financial support from the National Natural Science Foundation of China (No. 51675143)
文摘Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11434010,11574356 and 11504415the Funds from the Royal Society,the Defense Science Technology Laboratory and UK Engineering and Physics Research Council
文摘The first operation of an electrically pumped 1.3μm InAs/GaAs quantum-dot laser was previously reported epitaxially grown on Si （100） substrate. Here the direct epitaxial growth condition of 1.3μm InAs/OaAs quantum on a Si substrate is further investigated using atomic force microscopy, etch pit density and temperature-dependent photoluminescence （PL） measurements. The PL for Si-based InAs/GaAs quantum dots appears to be very sensitive to the initial OaAs nucleation temperature and thickness with strongest room-temperature emission at 40000 （17Onto nucleation layer thickness）, due to the lower density of defects generated under this growth condition, and stronger carrier confinement within the quantum dots.
基金Supported by the National Natural Science Foundation of China under Grant No 11173026the International GNSS Monitoring and Assessment System(iGMAS)of National Time Service Centre
文摘We present a new digital phase lock technology to achieve the frequency control and transformation through high precision multi-cycle group synchronization between signals without the frequency transformation circuit. In the case of digital sampling, the passing zero point of the phase of the controlled signal has the phase step characteristic, the phase step of the passing zero point is monotonic continuous with high resolution in the phase lock process, and using the border effect of digital fuzzy area, the gate can synchronize with the two signals, the quantization error is reduced. This technique is quite different from the existing methods of frequency transformation and frequency synthesis, the phase change characteristic between the periodic signals with different nominal is used. The phase change has the periodic phenomenon, and it has the high resolution step value. With the application of the physical law, the noise is reduced because of simplifying frequency transformation circuits, and the phase is locked with high precision. The regular phase change between frequency signals is only used for frequency measurement, and the change has evident randomness, but this randomness is greatly reduced in frequency control, and the certainty of the process result is clear. The experiment shows that the short term frequency stability can reach 10-12/s orders of magnitude.
基金the Natural Science Foundation(Grant No.40739908)National Basic Research Program of China(973 Program)(Grant No.2007CB209605).
文摘In this paper,we develop a new and effective multiple scale and strongly directional method for identifying and suppressing ground roll based on the second generation curvelet transform.Making the best use of the curvelet transform＇s strong local directional characteristics,seismic frequency bands are transformed into scale data with and without noise.Since surface waves and primary reflected waves have less overlap in the curvelet domain,we can effectively identify and separate noise.Applying this method to prestack seismic data can successfully remove surface waves and,at the same time,protect the reflected events well,particularly in the low-frequency band.This indicates that the method described in this paper is an effective and amplitude-preserving method.
基金Project(2012LWB63) supported by the Fundamental Research Funds for the Central Universities, ChinaProject(SZBF2011-6-B35) supported by the Priority Acadamic Program Development of Jiangsu Higher Education Institutions (PAPD),China
文摘Based on the stress distribution characteristics of rock burst multiple sites, the criterion of horizontal stress inducing layer dislocation rock burst was established. Accordingly, the influencing factors were analyzed. The analysis results indicate that the stress condition, edge of etastic zone depth, supporting strength, and the friction angle and cohesion among coal stratum, roof and floor are sensitive factors. By introducing double-couple model, the layer dislocation rock burst was explained and the energy radiation characteristics were analyzed. The SOS micro-seismic monitoring system was applied to observe the rock burst hazards about a mining face. The results show that P- and S-wave energy radiations produced by rock burst have directional characteristics. The energy radiation characteristics of the 22 rock bursts occurring on 79Z6 long-wall face are basically the same as theoretical results, that is, the ratio of S-wave energy of sensor 4 to 6 is about 1.5 and that of P-wave is smaller than 0.5. The consistency of the monitored characteristics of the energy radiation theoretically increases with the total energy increasing.
基金supported by China Postdoctoral Science Foundation(Grant No.20070410683)the Postdoctoral Fund of School of Mathematical Sciences,Fudan University
文摘In the present paper,the local well-posedness of the incompressible viscoelastic fluid system in the whole space is proved under the following assumption on the initial data:the deformation tensor is Hlder continuous and the velocity is Lp integrable,p】d,where d is the space dimension.
基金National Natural Science Foundation of China(grant nos.42071304 and 42090013)the National Key Research and Development Program of China(grant nos.2020YFA0608701 and 2022YFB3903304).
文摘The vegetation canopy clumping index(CI)is an important indicator for understanding radiative transport processes,radiation interception,and the photosynthesis of vegetation canopies.However,most studies consider CI only in the nadir or specific direction.In this study,we analyze the directional characteristics of the CI based on RAMI-V(radiation transfer model intercomparison)activity,which represents most typical canopies.The directional gap fraction and CI of these scenes are accurately calculated based on the LESS(large-scale remote sensing data and image simulation framework)model.According to our results,the directional characteristics of the CI are affected by many factors,such as vegetation type,season,and canopy structure.Generally,the CI of a coniferous forest varies little with zenith angle,while the CI of a broad-leaf forest demonstrates the different trend.In winter,the CI is smaller than that in summer,and the variation in the CI at the zenith angle is less.The row structure scenes exhibit different directional characteristics along and perpendicular to the row direction,and their CIs tend to increase with zenith angle.To accurately model the directional CI,we propose a modified Gompertz function model.Compared with other directional CI models,this model has the advantages of high precision and strong applicability(R^(2)=0.975).By studying the directional characteristics of CI,we can enhance the usability of radiative transfer modeling and the accuracy of canopy biophysical parameter retrieval for vegetation with different structures.
基金The work is supported by Zhejiang Provincial Natural Science Foundations(No.Y604359) National Natural Science Foundation of China (No.10371123,10471130).
文摘A computable expression of the asymptotic expansion of the return map for a degenerate singular point of a class of planar differential system is given, and hence the stability and the type of the singular point can be decided. These results generalize the corresponding results in [Nonlinearity, 13 （2000）, p.709].
基金The authors gratefully acknowledge the supports from China Postdoctoral Science Foundation （Grant No. 2014M550327）, the opening foundation of the State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, and the National Natural Science Foundation of China （Grant No. 11372275）. The authors are also grateful to Chengbo Yu and Liang Yu for their introduction of the choanoid fluidized bed bioreactor and helpful discussions.
文摘Choanoid fluidized bed bioreactors （CFBBs） are newly developed core devices used in bioartificial liver- support systems to detoxify blood plasma of patients with microencapsulated liver cells. Direct numerical simulations （DNS） with a direct-forcing/fictitious domain （DF/FD） method were conducted to study the hydrodynamic performance of a CFBB. The effects of particle-fluid density ratio, particle number, and fil- ter screens preventing particles flowing out of the reactor were investigated. Depending on density ratio, two flow patterns are evident： the circulation mode in which the suspension rises along one sidewall and descends along the other sidewall, and the non-circulation mode in which the whole suspension roughly flows upward. The circulation mode takes place under non-neutral-buoyancy where the particle sedimentation dominates, whereas the non-circulation mode occurs under pure or near-neutral buoy- ancy with particle-fluid density ratios of unity or near unity. With particle-fluid density ratio of 1.01, the bioartificial liver reactor performs optimally as the significant particle accumulation existing in the non-circulation mode and the large shear forces on particles in the circulation mode are avoided. At higher particle volume fractions, more particles accumulate at the filter screens and a secondary counter circulation to the primary flow is observed at the top of the bed. Modelled as porous media, the filter screens play a negative role on particle fluidization velocities; without screens, particles are fluidized faster because of the higher fluid velocities in the jet center region. This work extends the DF/FD-based DNS to a fluidized bed and accounts for effects from inclined side walls and porous media, providing some hydrodynamics insight that is important for CFBB design and operation optimization.
