The crack fault is one of the most common faults in the rotor system,and researchers have paid close attention to its fault diagnosis.However,most studies focus on discussing the dynamic response characteristics cause...The crack fault is one of the most common faults in the rotor system,and researchers have paid close attention to its fault diagnosis.However,most studies focus on discussing the dynamic response characteristics caused by the crack rather than estimating the crack depth and position based on the obtained vibration signals.In this paper,a novel crack fault diagnosis and location method for a dual-disk hollow shaft rotor system based on the Radial basis function(RBF)network and Pattern recognition neural network(PRNN)is presented.Firstly,a rotor system model with a breathing crack suitable for a short-thick hollow shaft rotor is established based on the finite element method,where the crack's periodic opening and closing pattern and different degrees of crack depth are considered.Then,the dynamic response is obtained by the harmonic balance method.By adjusting the crack parameters,the dynamic characteristics related to the crack depth and position are analyzed through the amplitude-frequency responses and waterfall plots.The analysis results show that the first critical speed,first subcritical speed,first critical speed amplitude,and super-harmonic resonance peak at the first subcritical speed can be utilized for the crack fault diagnosis.Based on this,the RBF network and PRNN are adopted to determine the depth and approximate location of the crack respectively by taking the above dynamic characteristics as input.Test results show that the proposed method has high fault diagnosis accuracy.This research proposes a crack detection method adequate for the hollow shaft rotor system,where the crack depth and position are both unknown.展开更多
The harmonic balance method(HBM)is one of the most widely used methods in solving nonlinear vibration problems,and its accuracy and computational efficiency largely depend on the number of the harmonics selected.The a...The harmonic balance method(HBM)is one of the most widely used methods in solving nonlinear vibration problems,and its accuracy and computational efficiency largely depend on the number of the harmonics selected.The adaptive harmonic balance(AHB)method is an improved HBM method.This paper presents a modified AHB method with the asymptotic harmonic selection(AHS)procedure.This new harmonic selection procedure selects harmonics from the frequency spectra of nonlinear terms instead of estimating the contribution of each harmonic to the whole nonlinear response,by which the additional calculation is avoided.A modified continuation method is proposed to deal with the variable size of nonlinear algebraic equations at different values of path parameters,and then all solution branches of the amplitude-frequency response are obtained.Numerical experiments are carried out to verify the performance of the AHB-AHS method.Five typical nonlinear dynamic equations with different types of nonlinearities and excitations are chosen as the illustrative examples.Compared with the classical HBM and Runge-Kutta methods,the proposed AHB-AHS method is of higher accuracy and better convergence.The AHB-AHS method proposed in this paper has the potential to investigate the nonlinear vibrations of complex high-dimensional nonlinear systems.展开更多
In this paper,the aero-engine test with inter-shaft bearing fault is carried out,and a dataset is proposed for the first time based on the vibration signal of rotors and casings.First,a test rig based on a real aero-e...In this paper,the aero-engine test with inter-shaft bearing fault is carried out,and a dataset is proposed for the first time based on the vibration signal of rotors and casings.First,a test rig based on a real aero-engine is established,driven by motors and equipped with a lubricating system.Then,the aero-engine is disassembled and assembled following the specification process,and the inter-shaft bearing with artificial fault is replaced.Next,the aero-engine test is conducted at 28 groups of high-and low-pressure speeds.Six measuring points are arranged,including two displacement sensors to test the displacement vibration signals of the low-pressure rotor and four acceleration sensors to test the acceleration vibration signals of the casing.The test results are integrated into an inter-shaft bearing fault dataset.Finally,based on the dataset in this paper,frequency spectrum,envelope spectrum,CNN,LSTM,and TST are used for fault diagnosis,and the results are compared with those of CWRU and XJTU datasets.The results show that the characteristic fault frequency cannot be found directly in the spectrum and envelope spectrum corresponding to this paper’s dataset but in CWRU and XJTU datasets.Using CNN,LSTM,and TST for fault diagnosis of the dataset in this paper,the accuracy is 83.13%,85.41%,and 71.07%,respectively,much lower than the diagnosis results of CWRU and XJTU datasets.It can be seen that the dataset in this paper is closer to the actual fault diagnosis situation and is a more challenging dataset.This dataset provides a new benchmark for the validation of fault diagnosis methods.Mendeley data:https://github.com/HouLeiHIT/HIT-dataset.展开更多
Quantitative real-time PCR (qPCR) was applied to rapid screening of positive plasmid clones. Insert-specific primer pairs were used in qPCR colony screening, and false positive colonies could easily be distinguished f...Quantitative real-time PCR (qPCR) was applied to rapid screening of positive plasmid clones. Insert-specific primer pairs were used in qPCR colony screening, and false positive colonies could easily be distinguished from true positive ones by comparing their Ct values. In addition, qPCR is particularly suitable when amplicon is small (<150 bp). This method is sensitive, simple and fast, obviates the need for gel electrophoresis, and is a cost-effective alternative to the traditional PCR approach.展开更多
When an aircraft is hovering or doing a dive-hike flight at a fixed speed, a constant additional inertial force will be induced to the rotor system of the aero-engine,which can be called a constant maneuver load.Take ...When an aircraft is hovering or doing a dive-hike flight at a fixed speed, a constant additional inertial force will be induced to the rotor system of the aero-engine,which can be called a constant maneuver load.Take hovering as an example.A Jeffcott rotor system with a biased rotor and several nonlinear elastic supports is modeled, and the vibration characteristics of the rotor system under a constant maneuver load are analytically studied.By using the multiple-scale method, the differential equations of the system are solved, and the bifurcation equations are obtained.Then, the bifurcations of the system are analyzed by using the singularity theory for the two variables.In the E G-plane, where E refers to the eccentricity of the rotor and G represents the constant maneuver load, two hysteresis point sets and one double limit point set are obtained.The bifurcation diagrams are also plotted.It is indicated that the resonance regions of the two variables will shift to the right when the aircraft is maneuvering.Furthermore, the movement along the horizontal direction is faster than that along the vertical direction.Thus, the different overlapping modes of the two resonance regions will bring about different bifurcation modes due to the nonlinear coupling effects.This result lays a theoretical foundation for controlling the stability of the aero-engine's rotor system under a maneuver load.展开更多
We demonstrate a multi-branch all polarization-maintaining Er:fiber frequency comb with five application ports for precise measurement of atomic/molecular transition frequencies in the near-infrared region.A fully sta...We demonstrate a multi-branch all polarization-maintaining Er:fiber frequency comb with five application ports for precise measurement of atomic/molecular transition frequencies in the near-infrared region.A fully stabilized Er:fiber frequency comb with a nonlinear amplifying loop mirror is achieved.The in-loop relative instability of stabilized carrier-envelope-offset frequency is 5.6×10-18 at 1 s integration time,while that of the repetition rate is well below 1.8×10-12 limited by the measurement noise floor of the commercial frequency counter.Five application ports are individually optimized for applications with different wavelengths(1064 nm,1083 nm,1380 nm,1637 nm and 1750 nm).The beat note between the optical frequency comb and continuous laser exhibits the signal-to-noise ratio of at least 30 dB at a resolution bandwidth of 100 kHz.The in-loop frequency instability of the comb is evaluated to be good enough for measurement of rotation-resolved transitions of molecules below 1 kHz resolution.展开更多
Aiming at disclosing the quantitative e ects of Coulomb forces on the ltration e ciency of aerosol particles, a three- dimensional random ber model was established to describe the microstructure of brous lters. Then, ...Aiming at disclosing the quantitative e ects of Coulomb forces on the ltration e ciency of aerosol particles, a three- dimensional random ber model was established to describe the microstructure of brous lters. Then, computational mod- els including the ow model, particle model, and electric eld model were constructed to estimate the ltration e ciency using the Fluent custom user-de ned function program, neglecting the non-uniformity of the ber potential and the particle charge distribution. The simulation results using the established models agreed with the data in the literature. In particular, the electric eld force was found to be one of the important factors required to improve the ltration e ciency estimation accuracy for the ultra ne particles. Moreover, the variation tendencies of the ltration e ciency and the pressure drop of brous lters were studied based on the in uence factors of the ber potential, particle charge-to-mass ratio, solid volume fraction, ber diameter, and face velocity. The established models and estimated results will provide important guidance on the design of high-e ciency particulate air lters for aerosol particles.展开更多
Materialization of coal is one of effective and clean pathways for its utilization. The microstructures of coal-based carbon materials have an important influence on their functional applications. Herein, the microstr...Materialization of coal is one of effective and clean pathways for its utilization. The microstructures of coal-based carbon materials have an important influence on their functional applications. Herein, the microstructural evolution of anthracite in the temperature range of 1000–2800 ℃ was systematically investigated to provide a guidance for the microstructural regulation of coal-based carbon materials.The results indicate that the microstructure of anthracite undergoes an important change during carbonization-graphitization process. As the temperature increases, aromatic layers in anthracite gradually transform into disordered graphite microcrystals and further grow into ordered graphite microcrystals, and then ordered graphite microcrystals are laterally linked to form pseudo-graphite phase and eventually transformed into highly ordered graphite-like sheets. In particular, 2000–2200 ℃ is a critical temperature region for the qualitative change of ordered graphite crystallites to pseudo-graphite phase,in which the relevant structural parameters including stacking height, crystallite lateral size and graphitization degree show a rapid increase. Moreover, both aromaticity and graphitization degree have a linear positive correlation with carbonization-graphitization temperature in a specific temperature range.Besides, after initial carbonization, some defect structures in anthracite such as aliphatic carbon and oxygen-containing functional groups are released in the form of gaseous low-molecular volatiles along with an increased pore structure, and the intermediates derived from minerals could facilitate the conversion of sp^(3) amorphous carbon to sp^(2) graphitic carbon. This work provides a valuable reference for the rational design of microstructure of coal-based carbon materials.展开更多
A new nonlinear force model based on experimental data is proposed to replace the classical Hertzian contact model to solve the fractional index nonlinearity in a ball bearing system. Firstly, the radial force and the...A new nonlinear force model based on experimental data is proposed to replace the classical Hertzian contact model to solve the fractional index nonlinearity in a ball bearing system. Firstly, the radial force and the radial deformation are measured by statics experiments, and the data are fitted respectively by using the Hertzian contact model and the cubic polynomial model. Then, the two models are compared with the approximation formula appearing in Aeroengine Design Manual. In consequence, the two models are equivalent in an allowable deformation range. After that, the relationship of contact force and contact deformation for single rolling element between the races is calculated based on statics equilibrium to obtain the two kinds of nonlinear dynamic models in a rigid-rotor ball bearing system. Finally, the displacement response and frequency spectrum for the two system models are compared quantitatively at different rotational speeds, and then the structures of frequency-amplitude curves over a wide speed range are compared qualitatively under different levels of radial clearance, amplitude of excitation,and mass of supporting rotor. The results demonstrate that the cubic polynomial model can take place of the Hertzian contact model in a range of deformation.展开更多
A method for seeking main bifurcation parameters of a class of nonlinear dynamical systems is proposed. The method is based on the effects of parametric variation of dynamical systems on eigenvalues of the Frechet mat...A method for seeking main bifurcation parameters of a class of nonlinear dynamical systems is proposed. The method is based on the effects of parametric variation of dynamical systems on eigenvalues of the Frechet matrix. The singularity theory is used to study the engineering unfolding(EU) and the universal unfolding(UU) of an arch structure model, respectively. Unfolding parameters of EU are combination of concerned physical parameters in actual engineering, and equivalence of unfolding parameters and physical parameters is verified. Transient sets and bifurcation behaviors of EU and UU are compared to illustrate that EU can reflect main bifurcation characteristics of nonlinear systems in engineering. The results improve the understanding and the scope of applicability of EU in actual engineering systems when UU is difficult to be obtained.展开更多
Using a sample of 70 793 early-type galaxies from SDSS DR7, we study the environmental dependence of the fundamental plane relation. With the help of the galaxy group catalog based on SDSS DR7, we calculate the fundam...Using a sample of 70 793 early-type galaxies from SDSS DR7, we study the environmental dependence of the fundamental plane relation. With the help of the galaxy group catalog based on SDSS DR7, we calculate the fundamental planes in different dark matter halo mass bins for both central and satellite galaxies. We find the environmental dependence of the fundamental plane coefficients is similar in the g, r, i and z bands. The environmental dependence for central and satellite galaxies is significantly different. Although the fundamental plane coefficients for centrals vary systematically with the halo mass, those of satellites are similar in different halo mass bins. The discrepancy between centrals and satellites is significant in small halos, but negligible in the largest halo mass bins. These results remain the same when we only keep red galaxies, or galaxies with b/a > 0.6, or galaxies in a specific radius range in the sample. After the correction for the sky background, the results are still similar.We suggest that the different environmental effects of the halo mass on centrals and satellites may arise from their different quenching processes.展开更多
Accidents involving natural gas leakage and dispersion pose a significant threat to human life and property.This threat is especially relevant at the street intersection at which dense buildings,heavy traffic flow,and...Accidents involving natural gas leakage and dispersion pose a significant threat to human life and property.This threat is especially relevant at the street intersection at which dense buildings,heavy traffic flow,and complex underground pipe networks meet.Scholars have conducted numerous studies on gas leakage and dispersion,but investigations of natural gas leakage and dispersion at the street intersection of a building group are not in-depth.In this paper,we presented a three-dimensional(3D)physical model based on the Computational Fluid Dynamic(CFD)methodology to study the natural gas leakage and dispersion at the street intersection of a building group.We validated the CFD methodology applied in the research based on the data from the field tests and wind tunnel experiments.Then,we simulated and analyzed the pressure,wind,and concentration of natural gas dispersion at the street intersection.The simulation results showed that vortex regions,low-pressure zones,and a building group effect could cause a build-up of natural gas concentration under perpendicular wind direction conditions.In addition,the area of hazardous region tended to increase first and then drop with the dispersion height.In the case of this study,the maximum area of hazardous region is 200 m2 located in the height of 55 m,which is the middle plane in the computational domain.The results in the paper can provide scientific references for the safe operation and emergency-management decisions of municipal gas.展开更多
Organism development is a systems level process. It has benefited greatly from the recent technological advances in the field of systems biology. DNA microarray, phenome, interactome and transcriptome mapping, the new...Organism development is a systems level process. It has benefited greatly from the recent technological advances in the field of systems biology. DNA microarray, phenome, interactome and transcriptome mapping, the new generation of deep sequencing technologies, and faster and better computational and modeling approaches have opened new frontiers for both systems biologists and developmental biologists to reexamine the old developmental biology questions, such as pattern formation, and to tackle new problems, such as stem cell reprogramming. As showcased in the International Developmental Systems Biology Symposium organized by Chinese Academy of Sciences, developmental systems biology is flourishing in many perspectives, from the evolution of developmental systems, to the underly-ing genetic and molecular pathways and networks, to the genomic, epigenomic and noncoding levels, to the computational analysis and modeling. We believe that the field will continue to reap rewards into the future with these new approaches.展开更多
The bifurcation analysis of a simple electric power system involving two synchronous generators connected by a transmission network to an infinite-bus is carried out in this paper. In this system, the infinite-bus vol...The bifurcation analysis of a simple electric power system involving two synchronous generators connected by a transmission network to an infinite-bus is carried out in this paper. In this system, the infinite-bus voltage are considered to maintain two fluctuations in the amplitude and phase angle. The case of 1:3 internal resonance between the two modes in the presence of parametric principal resonance is considered and examined. The method of multiple scales is used to obtain the bifurcation equations of this system. Then, by employing the singularity method, the transition sets determining different bifurcation patterns of the system are obtained and analyzed, which reveal the effects of the infinite-bus voltage amplitude and phase fluctuations on bifurcation patterns of this system. Finally, the bifurcation patterns are all examined by bifurcation diagrams.The results obtained in this paper will contribute to a better understanding of the complex nonlinear dynamic behaviors in a two-machine infinite-bus(TMIB) power system.展开更多
Terahertz(THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good ch...Terahertz(THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good choice. In this paper,a single-shot system is investigated, where a pump beam is used to generate THz pulses with high electrical field by optical rectification in LiNbO3, the probe beam with wavefront tilted by a blazed grating is used for single-shot measurement. The time window is up to 90 ps, the signal to noise ratio is 2000 : 1, the spectrum covers from 0.1 THz to about 2.0 THz, and the spectral resolution is 0.011 THz. The single-shot measurement result agrees well with that of a traditional electrical-optic sampling method.展开更多
基金Supported by National Natural Science Foundation of China (Grant No.11972129)National Science and Technology Major Project of China (Grant No.2017-IV-0008-0045)+1 种基金Heilongjiang Provincial Natural Science Foundation (Grant No.YQ2022A008)the Fundamental Research Funds for the Central Universities。
文摘The crack fault is one of the most common faults in the rotor system,and researchers have paid close attention to its fault diagnosis.However,most studies focus on discussing the dynamic response characteristics caused by the crack rather than estimating the crack depth and position based on the obtained vibration signals.In this paper,a novel crack fault diagnosis and location method for a dual-disk hollow shaft rotor system based on the Radial basis function(RBF)network and Pattern recognition neural network(PRNN)is presented.Firstly,a rotor system model with a breathing crack suitable for a short-thick hollow shaft rotor is established based on the finite element method,where the crack's periodic opening and closing pattern and different degrees of crack depth are considered.Then,the dynamic response is obtained by the harmonic balance method.By adjusting the crack parameters,the dynamic characteristics related to the crack depth and position are analyzed through the amplitude-frequency responses and waterfall plots.The analysis results show that the first critical speed,first subcritical speed,first critical speed amplitude,and super-harmonic resonance peak at the first subcritical speed can be utilized for the crack fault diagnosis.Based on this,the RBF network and PRNN are adopted to determine the depth and approximate location of the crack respectively by taking the above dynamic characteristics as input.Test results show that the proposed method has high fault diagnosis accuracy.This research proposes a crack detection method adequate for the hollow shaft rotor system,where the crack depth and position are both unknown.
基金Project supported by the National Natural Science Foundation of China(Nos.11972129 and12372008)the National Major Science and Technology Projects of China(No.2017-IV-0008-0045)+3 种基金the Natural Science Foundation of Heilongjiang Province of China(No.YQ2022A008)the Fundamental Research Funds for the Central Universities of China(No.HIT.OCEF.2023006)the Polish National Science Centre of Poland under the OPUS 18 grant(No.2019/35/B/ST8/00980)the Tianjin University Independent Innovation Foundation of China(No.2023XJS-0038)。
文摘The harmonic balance method(HBM)is one of the most widely used methods in solving nonlinear vibration problems,and its accuracy and computational efficiency largely depend on the number of the harmonics selected.The adaptive harmonic balance(AHB)method is an improved HBM method.This paper presents a modified AHB method with the asymptotic harmonic selection(AHS)procedure.This new harmonic selection procedure selects harmonics from the frequency spectra of nonlinear terms instead of estimating the contribution of each harmonic to the whole nonlinear response,by which the additional calculation is avoided.A modified continuation method is proposed to deal with the variable size of nonlinear algebraic equations at different values of path parameters,and then all solution branches of the amplitude-frequency response are obtained.Numerical experiments are carried out to verify the performance of the AHB-AHS method.Five typical nonlinear dynamic equations with different types of nonlinearities and excitations are chosen as the illustrative examples.Compared with the classical HBM and Runge-Kutta methods,the proposed AHB-AHS method is of higher accuracy and better convergence.The AHB-AHS method proposed in this paper has the potential to investigate the nonlinear vibrations of complex high-dimensional nonlinear systems.
基金supports from the National Natural Science Foundation of China (Grant No.11972129)the Natural Science Foundation of Heilongjiang Province (Outstanding Youth Foundation,Grant No.YQ2022A008)the Fundamental Research Funds for the Central Universities.
文摘In this paper,the aero-engine test with inter-shaft bearing fault is carried out,and a dataset is proposed for the first time based on the vibration signal of rotors and casings.First,a test rig based on a real aero-engine is established,driven by motors and equipped with a lubricating system.Then,the aero-engine is disassembled and assembled following the specification process,and the inter-shaft bearing with artificial fault is replaced.Next,the aero-engine test is conducted at 28 groups of high-and low-pressure speeds.Six measuring points are arranged,including two displacement sensors to test the displacement vibration signals of the low-pressure rotor and four acceleration sensors to test the acceleration vibration signals of the casing.The test results are integrated into an inter-shaft bearing fault dataset.Finally,based on the dataset in this paper,frequency spectrum,envelope spectrum,CNN,LSTM,and TST are used for fault diagnosis,and the results are compared with those of CWRU and XJTU datasets.The results show that the characteristic fault frequency cannot be found directly in the spectrum and envelope spectrum corresponding to this paper’s dataset but in CWRU and XJTU datasets.Using CNN,LSTM,and TST for fault diagnosis of the dataset in this paper,the accuracy is 83.13%,85.41%,and 71.07%,respectively,much lower than the diagnosis results of CWRU and XJTU datasets.It can be seen that the dataset in this paper is closer to the actual fault diagnosis situation and is a more challenging dataset.This dataset provides a new benchmark for the validation of fault diagnosis methods.Mendeley data:https://github.com/HouLeiHIT/HIT-dataset.
文摘Quantitative real-time PCR (qPCR) was applied to rapid screening of positive plasmid clones. Insert-specific primer pairs were used in qPCR colony screening, and false positive colonies could easily be distinguished from true positive ones by comparing their Ct values. In addition, qPCR is particularly suitable when amplicon is small (<150 bp). This method is sensitive, simple and fast, obviates the need for gel electrophoresis, and is a cost-effective alternative to the traditional PCR approach.
基金Project supported by National Basic Research Program(973 Program)of China(No.2015CB057400)
文摘When an aircraft is hovering or doing a dive-hike flight at a fixed speed, a constant additional inertial force will be induced to the rotor system of the aero-engine,which can be called a constant maneuver load.Take hovering as an example.A Jeffcott rotor system with a biased rotor and several nonlinear elastic supports is modeled, and the vibration characteristics of the rotor system under a constant maneuver load are analytically studied.By using the multiple-scale method, the differential equations of the system are solved, and the bifurcation equations are obtained.Then, the bifurcations of the system are analyzed by using the singularity theory for the two variables.In the E G-plane, where E refers to the eccentricity of the rotor and G represents the constant maneuver load, two hysteresis point sets and one double limit point set are obtained.The bifurcation diagrams are also plotted.It is indicated that the resonance regions of the two variables will shift to the right when the aircraft is maneuvering.Furthermore, the movement along the horizontal direction is faster than that along the vertical direction.Thus, the different overlapping modes of the two resonance regions will bring about different bifurcation modes due to the nonlinear coupling effects.This result lays a theoretical foundation for controlling the stability of the aero-engine's rotor system under a maneuver load.
基金Supported by the National Natural Science Foundation of China(Grant Nos.61825505 and 91536217)。
文摘We demonstrate a multi-branch all polarization-maintaining Er:fiber frequency comb with five application ports for precise measurement of atomic/molecular transition frequencies in the near-infrared region.A fully stabilized Er:fiber frequency comb with a nonlinear amplifying loop mirror is achieved.The in-loop relative instability of stabilized carrier-envelope-offset frequency is 5.6×10-18 at 1 s integration time,while that of the repetition rate is well below 1.8×10-12 limited by the measurement noise floor of the commercial frequency counter.Five application ports are individually optimized for applications with different wavelengths(1064 nm,1083 nm,1380 nm,1637 nm and 1750 nm).The beat note between the optical frequency comb and continuous laser exhibits the signal-to-noise ratio of at least 30 dB at a resolution bandwidth of 100 kHz.The in-loop frequency instability of the comb is evaluated to be good enough for measurement of rotation-resolved transitions of molecules below 1 kHz resolution.
基金supported by the National Key Research and Development Program (No. 2016YFC1201503)Natural Science Foundation of China (No. 21576206)the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT_15R46)
文摘Aiming at disclosing the quantitative e ects of Coulomb forces on the ltration e ciency of aerosol particles, a three- dimensional random ber model was established to describe the microstructure of brous lters. Then, computational mod- els including the ow model, particle model, and electric eld model were constructed to estimate the ltration e ciency using the Fluent custom user-de ned function program, neglecting the non-uniformity of the ber potential and the particle charge distribution. The simulation results using the established models agreed with the data in the literature. In particular, the electric eld force was found to be one of the important factors required to improve the ltration e ciency estimation accuracy for the ultra ne particles. Moreover, the variation tendencies of the ltration e ciency and the pressure drop of brous lters were studied based on the in uence factors of the ber potential, particle charge-to-mass ratio, solid volume fraction, ber diameter, and face velocity. The established models and estimated results will provide important guidance on the design of high-e ciency particulate air lters for aerosol particles.
基金supported by the National Natural Science Foundation of China(Nos.51974110,52074109 and 52274261)the Key Scientific and Technological Project of Henan Province(No.202102210183)the Coal Green Conversion Outstanding Foreign Scientists Foundation of Henan Province(No.GZS2020012).
文摘Materialization of coal is one of effective and clean pathways for its utilization. The microstructures of coal-based carbon materials have an important influence on their functional applications. Herein, the microstructural evolution of anthracite in the temperature range of 1000–2800 ℃ was systematically investigated to provide a guidance for the microstructural regulation of coal-based carbon materials.The results indicate that the microstructure of anthracite undergoes an important change during carbonization-graphitization process. As the temperature increases, aromatic layers in anthracite gradually transform into disordered graphite microcrystals and further grow into ordered graphite microcrystals, and then ordered graphite microcrystals are laterally linked to form pseudo-graphite phase and eventually transformed into highly ordered graphite-like sheets. In particular, 2000–2200 ℃ is a critical temperature region for the qualitative change of ordered graphite crystallites to pseudo-graphite phase,in which the relevant structural parameters including stacking height, crystallite lateral size and graphitization degree show a rapid increase. Moreover, both aromaticity and graphitization degree have a linear positive correlation with carbonization-graphitization temperature in a specific temperature range.Besides, after initial carbonization, some defect structures in anthracite such as aliphatic carbon and oxygen-containing functional groups are released in the form of gaseous low-molecular volatiles along with an increased pore structure, and the intermediates derived from minerals could facilitate the conversion of sp^(3) amorphous carbon to sp^(2) graphitic carbon. This work provides a valuable reference for the rational design of microstructure of coal-based carbon materials.
基金Project supported by the National Basic Research Program(973 Program)of China(No.2015CB057400)the National Natural Science Foundation of China(No.11602070)+1 种基金the China Postdoctoral Science Foundation(No.2016M590277)the Heilongjiang Postdoctoral Financial Assistance(No.LBH-Z16067)
文摘A new nonlinear force model based on experimental data is proposed to replace the classical Hertzian contact model to solve the fractional index nonlinearity in a ball bearing system. Firstly, the radial force and the radial deformation are measured by statics experiments, and the data are fitted respectively by using the Hertzian contact model and the cubic polynomial model. Then, the two models are compared with the approximation formula appearing in Aeroengine Design Manual. In consequence, the two models are equivalent in an allowable deformation range. After that, the relationship of contact force and contact deformation for single rolling element between the races is calculated based on statics equilibrium to obtain the two kinds of nonlinear dynamic models in a rigid-rotor ball bearing system. Finally, the displacement response and frequency spectrum for the two system models are compared quantitatively at different rotational speeds, and then the structures of frequency-amplitude curves over a wide speed range are compared qualitatively under different levels of radial clearance, amplitude of excitation,and mass of supporting rotor. The results demonstrate that the cubic polynomial model can take place of the Hertzian contact model in a range of deformation.
基金supported by the National Basic Research Program of China(973 Program)(No.2015CB057400)the National Natural Science Foundation of China(No.11602070)the China Postdoctoral Science Foundation(No.2016M590277)
文摘A method for seeking main bifurcation parameters of a class of nonlinear dynamical systems is proposed. The method is based on the effects of parametric variation of dynamical systems on eigenvalues of the Frechet matrix. The singularity theory is used to study the engineering unfolding(EU) and the universal unfolding(UU) of an arch structure model, respectively. Unfolding parameters of EU are combination of concerned physical parameters in actual engineering, and equivalence of unfolding parameters and physical parameters is verified. Transient sets and bifurcation behaviors of EU and UU are compared to illustrate that EU can reflect main bifurcation characteristics of nonlinear systems in engineering. The results improve the understanding and the scope of applicability of EU in actual engineering systems when UU is difficult to be obtained.
基金the support of the Fundamental Research Funds for Central UniversitiesFunding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation+5 种基金the Participating Institutionsthe National Science Foundationthe U.S. Department of Energythe National Aeronautics and Space Administrationthe Japanese Monbukagakusho, the Max Planck Societythe Higher Education Funding Council for England
文摘Using a sample of 70 793 early-type galaxies from SDSS DR7, we study the environmental dependence of the fundamental plane relation. With the help of the galaxy group catalog based on SDSS DR7, we calculate the fundamental planes in different dark matter halo mass bins for both central and satellite galaxies. We find the environmental dependence of the fundamental plane coefficients is similar in the g, r, i and z bands. The environmental dependence for central and satellite galaxies is significantly different. Although the fundamental plane coefficients for centrals vary systematically with the halo mass, those of satellites are similar in different halo mass bins. The discrepancy between centrals and satellites is significant in small halos, but negligible in the largest halo mass bins. These results remain the same when we only keep red galaxies, or galaxies with b/a > 0.6, or galaxies in a specific radius range in the sample. After the correction for the sky background, the results are still similar.We suggest that the different environmental effects of the halo mass on centrals and satellites may arise from their different quenching processes.
基金supported by the Joint Project of Beijing Municipal Education Commission(No.ZX20140289).
文摘Accidents involving natural gas leakage and dispersion pose a significant threat to human life and property.This threat is especially relevant at the street intersection at which dense buildings,heavy traffic flow,and complex underground pipe networks meet.Scholars have conducted numerous studies on gas leakage and dispersion,but investigations of natural gas leakage and dispersion at the street intersection of a building group are not in-depth.In this paper,we presented a three-dimensional(3D)physical model based on the Computational Fluid Dynamic(CFD)methodology to study the natural gas leakage and dispersion at the street intersection of a building group.We validated the CFD methodology applied in the research based on the data from the field tests and wind tunnel experiments.Then,we simulated and analyzed the pressure,wind,and concentration of natural gas dispersion at the street intersection.The simulation results showed that vortex regions,low-pressure zones,and a building group effect could cause a build-up of natural gas concentration under perpendicular wind direction conditions.In addition,the area of hazardous region tended to increase first and then drop with the dispersion height.In the case of this study,the maximum area of hazardous region is 200 m2 located in the height of 55 m,which is the middle plane in the computational domain.The results in the paper can provide scientific references for the safe operation and emergency-management decisions of municipal gas.
基金the China National Science Foundation (NSF) (No. 30588001, 30620120433)National Basic Research Program of China (No. 2006CB910700)funds from the Chinese Acad-emy of Sciences to J.-D.J.H. and NSF fellowship to T.A.
文摘Organism development is a systems level process. It has benefited greatly from the recent technological advances in the field of systems biology. DNA microarray, phenome, interactome and transcriptome mapping, the new generation of deep sequencing technologies, and faster and better computational and modeling approaches have opened new frontiers for both systems biologists and developmental biologists to reexamine the old developmental biology questions, such as pattern formation, and to tackle new problems, such as stem cell reprogramming. As showcased in the International Developmental Systems Biology Symposium organized by Chinese Academy of Sciences, developmental systems biology is flourishing in many perspectives, from the evolution of developmental systems, to the underly-ing genetic and molecular pathways and networks, to the genomic, epigenomic and noncoding levels, to the computational analysis and modeling. We believe that the field will continue to reap rewards into the future with these new approaches.
基金Project supported by the National Natural Science Foundation of China(No.10632040)
文摘The bifurcation analysis of a simple electric power system involving two synchronous generators connected by a transmission network to an infinite-bus is carried out in this paper. In this system, the infinite-bus voltage are considered to maintain two fluctuations in the amplitude and phase angle. The case of 1:3 internal resonance between the two modes in the presence of parametric principal resonance is considered and examined. The method of multiple scales is used to obtain the bifurcation equations of this system. Then, by employing the singularity method, the transition sets determining different bifurcation patterns of the system are obtained and analyzed, which reveal the effects of the infinite-bus voltage amplitude and phase fluctuations on bifurcation patterns of this system. Finally, the bifurcation patterns are all examined by bifurcation diagrams.The results obtained in this paper will contribute to a better understanding of the complex nonlinear dynamic behaviors in a two-machine infinite-bus(TMIB) power system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61427814 and 61575161)the National Key Research and Development Program of China(Grant No.2017YFA0701005)the Natural Science Foundation of Shaanxi Province,China(Grant No.2019JZ-04)。
文摘Terahertz(THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good choice. In this paper,a single-shot system is investigated, where a pump beam is used to generate THz pulses with high electrical field by optical rectification in LiNbO3, the probe beam with wavefront tilted by a blazed grating is used for single-shot measurement. The time window is up to 90 ps, the signal to noise ratio is 2000 : 1, the spectrum covers from 0.1 THz to about 2.0 THz, and the spectral resolution is 0.011 THz. The single-shot measurement result agrees well with that of a traditional electrical-optic sampling method.
