To suppress the overshoots and undershoots in the envelope fitting for empirical mode decomposition （EMD）, an alternative cubic spline interpolation method without overshooting and undershooting is proposed. On the ...To suppress the overshoots and undershoots in the envelope fitting for empirical mode decomposition （EMD）, an alternative cubic spline interpolation method without overshooting and undershooting is proposed. On the basis of the derived slope constraints of knots of a non-overshooting and non-undershooting cubic interpolant, together with ＂not-a-knot＂ conditions the cubic spline interpolants are constructed by replacing the requirement for equal second order derivatives at every knot with Brodlie＇ s derivative formula. Analysis and simulation experiments show that this approach can effectively avoid generating new extrema, shifting or exaggerating the existing ones in a signal, and thus significantly improve the decomposition performance of EMD.展开更多
Based on the turbulent convection model （TCM） of Li ＆ Yang, we have studied the characteristics of turbulent convection in the envelopes of 2 and 5M⊙ stars at the red giant branch and asymptotic giant branch phase...Based on the turbulent convection model （TCM） of Li ＆ Yang, we have studied the characteristics of turbulent convection in the envelopes of 2 and 5M⊙ stars at the red giant branch and asymptotic giant branch phases. The TCM has been successfully applied over the entire convective envelopes, including the convective unstable zone and the overshooting regions. We find that the convective motions become progressively stronger when the stellar models are located farther up along the Hayashi line. In the convective unstable zone, we find that the turbulent correlations are proportional to functions of a common factor （V - V^d）T, which explains similar distributions in those correlations. For the TCM we find that if the obtained stellar temperature structure is close to that of the mixing length theory （MLT）, the convective motion will have a much larger velocity and thus be more violent. However, if the turbulent velocity is adjusted to be close to that of the MLT, the superadiabatic convection zone would be much more extended inward, which would lead to a lower effective temperature of the stellar model. For the overshooting distance, we find that the e-folding lengths of the turbulent kinetic energy k in both the top and bottom overshooting regions decrease as the stellar model is progressively located farther up along the Hayashi line, but both the extents of the decrease are not obvious. The overshooting distances of the turbulent correlation /u＇rT＂ are almost the same for the different stellar models with the same set of TCM parameters. For the decay modes of the kinetic energy k, we find that they are very similar for different stellar models based on the same set of TCM parameters, and there is a nearly linear relationship between lg k and In P for different stellar models. When Cs or α increases while the other parameters are fixed, the obtained linearly decaying distance will become longer.展开更多
Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top（OT） activity within a tropical cyclone（TC）, which is defined as the hourly mean ...Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top（OT） activity within a tropical cyclone（TC）, which is defined as the hourly mean number of OT occurrence,was statistically investigated in the western North Pacific basin for the period 2005–12. Based on the level of OT activity,the samples were divided into OT and non-OT cases or high-activity-OT（HA-OT） and low-activity-OT（LA-OT） cases. The differences in large-scale environmental variables between OT（HA-OT） and non-OT（LA-OT） cases were examined 12 hours prior to the OT occurrence. Statistical analysis showed that environmental differences did exist between the OT and non-OT cases. The OTs were more skewed towards the early stage of the TC life cycle, and mostly concentrated in low latitudes.Meanwhile, a sufficiently deep warm-water layer, large temperature difference between the upper- and lower-level troposphere, large humidity at the middle and upper levels, and large atmospheric instability, were favorable for OT occurrence.The differences in large-scale environmental characteristics between HA-OTs and LA-OTs were not as significant as those between OTs and non-OTs, but the HA-OT samples tended to occur when the vertical shear was weak and the TC intensity was low. Finally, statistical models were designed to predict the OT and HA-OT. When at least three OT（HA-OT） predictor thresholds were satisfied, the Peirce skill score reached a maximum value of 0.49（0.30）.展开更多
Under the condition of large inertia load,the stability of the servo system is more sensitive to the response speed and more likely to produce overshoot oscillations.In order to realize the requirements of high-precis...Under the condition of large inertia load,the stability of the servo system is more sensitive to the response speed and more likely to produce overshoot oscillations.In order to realize the requirements of high-precision and fast-response control of permanent magnet synchronous motor(PMSM)under large inertia load,an improved feedforward control strategy based on position impulse compensation and PD iterative algorithm is proposed to improve the response speed of the PMSM servo system and reduce the overshoot oscillation.This paper analyzes the mathematical models of the speed servo system and position servo system of the PMSM,calculates position overshoot impulse of the PMSM servo system,and improves the traditional feedforward control strategy to reversely compensate when the position is about to overshoot.Moreover,in order to further reduce the position overshoot,the PD iterative control algorithm is superimposed without increasing the complexity of the algorithm.The input signal is continuously corrected through multiple runs to achieve a smoother response control.The effectiveness of the proposed feedforward control strategy is verified by simulation and experiment.展开更多
The thermal evolution of the Earth’s interior and its dynamic effects are the focus of Earth sciences.However,the commonly adopted grid-based temperature solver is usually prone to numerical oscillations,especially i...The thermal evolution of the Earth’s interior and its dynamic effects are the focus of Earth sciences.However,the commonly adopted grid-based temperature solver is usually prone to numerical oscillations,especially in the presence of sharp thermal gradients,such as when modeling subducting slabs and rising plumes.This phenomenon prohibits the correct representation of thermal evolution and may cause incorrect implications of geodynamic processes.After examining several approaches for removing these numerical oscillations,we show that the Lagrangian method provides an ideal way to solve this problem.In this study,we propose a particle-in-cell method as a strategy for improving the solution to the energy equation and demonstrate its effectiveness in both one-dimensional and three-dimensional thermal problems,as well as in a global spherical simulation with data assimilation.We have implemented this method in the open-source finite-element code CitcomS,which features a spherical coordinate system,distributed memory parallel computing,and data assimilation algorithms.展开更多
This study utilizes molecular dynamics simulation to investigate the complex dynamics of entangled semi-flexible polymer melts.The investigation reveals a significant stress overshoot phenomenon in the systems,demonst...This study utilizes molecular dynamics simulation to investigate the complex dynamics of entangled semi-flexible polymer melts.The investigation reveals a significant stress overshoot phenomenon in the systems,demonstrating the intricate interplay between shear rates,chain orientation,and chain stretching dynamics.Additionally,the identification of metastable states,characterized by a dual-plateau phenomenon in the shear stress-strain curve at specific Rouse-Weissenberg number Wi_(R),showcases the system’s responsiveness to external perturbations and its transition to stable shear banding states.Moreover,the analysis of flow field deviations uncovers a progression of shear bands with increasing Wi_(R),displaying distinct behaviors in the system’s dynamics under different shear rates and chain lengths.These findings challenge established theoretical frameworks and advocate for refined modelling approaches in polymer rheology research.展开更多
High-power O-mode radio waves can excite artificial instabilities in the F region,according to experiments conducted at the European Incoherent Scatter Science Association(EISCAT)heating facility.The main instabilitie...High-power O-mode radio waves can excite artificial instabilities in the F region,according to experiments conducted at the European Incoherent Scatter Science Association(EISCAT)heating facility.The main instabilities include the parametric decay instability(PDI),oscillating two-stream instability(OTSI),and thermal parametric instability(TPI).The PDI and OTSI not only compete with each other,but also compete with the TPI,leading to a two-stage overshoot phenomenon:a miniovershoot occurs on a millisecond time scale after pump-on,followed by the main overshoot.We gain insight into the miniovershoot via a generalized Zakharov model,whereas the main overshoot can be observed as an enhanced plasma line overshoot phenomenon in incoherent scatter radar spectra.We can also observe that the zero-frequency ion line exists only in the initial heating period after a cold start and that the upshifted and downshifted ion lines behave irregularly in the spectra.The simulation results show that competition between the PDI and OTSI leads to an initial peak,which we named the pre-miniovershoot.The following processes,namely ion density caviton generation,and collapse and cascade in the development of the PDI,contribute to the miniovershoot phenomenon.展开更多
We demonstrate a brand-new method to sharpen a color image by using an integral mask-filtering technique. The derivatives between the target pixel and its neighbors are transferred by the cubic root function instead o...We demonstrate a brand-new method to sharpen a color image by using an integral mask-filtering technique. The derivatives between the target pixel and its neighbors are transferred by the cubic root function instead of the traditional linear one. The obtained final image has clearer fine characteristics along with much less overshooting.展开更多
Numerical diffusion or filter are used in most numerical models in order to eliminate small-scale (near two-grid intervals in wavelength) waves, However, conventional diffusion or filter schemes introduce the noise, a...Numerical diffusion or filter are used in most numerical models in order to eliminate small-scale (near two-grid intervals in wavelength) waves, However, conventional diffusion or filter schemes introduce the noise, and indeed few people realized, by filters themselves. For instance, most filters are troubled when they are put to use on meteorological fields with sharp gradient or with steep slope and consequently, the recurrence of undesirable numerical high-frequent oscillations (overshooting and undershooting) seems to be inevitable, Particularly when diffusion or filter is implemented in limited-area models, serious side effects on the limited-area boundaries often contaminate the modeling results. The merits and demerits are surveyed for commonly used diffusion or filter operations. A new type of monotonic digit filter is suggested to prevent overshooting and undershooting (due to the computational shock and Gibbs oscillation) nearby the discontinuous or nearly discontinuous locations when the filtering process was carried out, meanwhile the high selective property of damping is retained. Moreover, the new filter is designed on the implicit framework so that it can easily handle the problem of boundary diminishing in limited-area modeling.展开更多
A high order single step β algorithm, a new direct integration algorithm is proposed for solution of equations of motion. Whenβ=0.5, the accuracy of displacement, velocity and acceleration is of forth order (a trunc...A high order single step β algorithm, a new direct integration algorithm is proposed for solution of equations of motion. Whenβ=0.5, the accuracy of displacement, velocity and acceleration is of forth order (a truncation error of Δ t 5), and the algorithm is unconditionally stable and has no arithmetic damping and no overshooting. When >0.5, and an arithmetic damping is adopted, the algorithm is again unconditionally stable with a third order accuracy (a truncation error of Δ t 4). The analyses run with typical examples show that the algorithm proposed has higher speed, higher precision and better properties than other direct integration methods, such as Wilson θ method and Newmark β method in analysing linear elastic responses and nonlinear earthquake responses.展开更多
The fission rate of <sup>240</sup>Pu at its saddle point is obtained by using generalized coherentstate ansatz for large friction case. The numerical results indicate that the quasi-stationary fiss-ion rat...The fission rate of <sup>240</sup>Pu at its saddle point is obtained by using generalized coherentstate ansatz for large friction case. The numerical results indicate that the quasi-stationary fiss-ion rate approaches Kramers’ rate and the transient behaviour agrees with that given in previousstudies. Moreover, the relationship between the first eigenvalue λ<sub>1</sub> and the quasi-stationary fiss-ion rate λ<sub>qs</sub> is derived. In the case of high temperature, we also pay attention to the overshoot-ing.展开更多
The environmental impact caused by local people （ecological footprint of consumption, EFc） and the actual environmental impact that the ecosystem burdens （ecological footprint of production, EFp） in West Jilin Pro...The environmental impact caused by local people （ecological footprint of consumption, EFc） and the actual environmental impact that the ecosystem burdens （ecological footprint of production, EFp） in West Jilin Province, Northeast China from 1986 to 2006 were evaluated by using ecological footprint （EF） method. And the major driving forces of EFc and EFp were analyzed by STIRPAT model. Both EFc and EFp showed increasing trends in 1986-2006, accompanied by decreasing ecological deficits but expanding ecological overshoots. Population （P）, GDP per capita （A1）, quadratic term of GDP per capita （A2）, urbanization （Tα1）, and quadratic term of urbanization （Ta2） were important influencing factors of EFc, among which Tα2 and Tα1 were the most dominate driving forces of EFc. A1, A2 and Tα2 were important influencing factors of EFp, among which A2 and A1 were the most dominate driving forces of EFp. In 1986-2006, the classical Environmental Kuznets Curve hypothesis did not exist between A2 and EF （both EFc and EFp）, but did between Tα2 and EF. The results indicate that enhancing the urbanization process and diversifying economic sources is one of the most effective ways to reduce the environmental impact of West Jilin Province. Moreover, importance should be attached to improve the eco-efficiency of resource exploitation and consumption.展开更多
The optimization of the valve plate transition region is an important way of reducing the noise emission for an axial piston pump. However, the optimized methods through simulation or experiment are actually trial and...The optimization of the valve plate transition region is an important way of reducing the noise emission for an axial piston pump. However, the optimized methods through simulation or experiment are actually trial and error, and they cannot indicate the precise structural parameters of the valve plate transition region. In this study, a new design method for the transition region of valve plate based on the matching of flow area and reduction of transient reverse flow was proposed, and with which a valve plate was designed. Then, the impact of the flow ripple in the discharge line of an axial piston pump and the pressure overshoot and undershoot in the piston chamber on hydraulic and structural noise for axial piston pump is discussed. The noise reduction effect of the axial piston pump with this valve plate was analyzed by adopting a flow characteristic simulation model. Finally, the results showed that the application of this design method could contribute much to the reduction of the flow ripple and elimination of the pressure overshoot and undershoot. As a consequence, the method can be used in the design of a low-noise open circuit axial piston pump.展开更多
It is well-known that the IMC-PID controller tuning gives fast and improved set point response but slow disturbance rejection. A modification has been proposed in IMC-PID tuning rule for the improved disturbance rejec...It is well-known that the IMC-PID controller tuning gives fast and improved set point response but slow disturbance rejection. A modification has been proposed in IMC-PID tuning rule for the improved disturbance rejection. For the modified IMC-PID tuning rule, a method has been developed to obtain the IMC-PID setting in closed-loop mode without acquiring detailed information of the process. The proposed method is based on the closed-loop step set point experiment using a proportional only controller with gain K_(c0). It is the direct approach to find the PID controller setting similar to classical Ziegler-Nichols closed-loop method. Based on simulations of a wide range of first-order with delay processes, a simple correlation has been derived to obtain the modified IMC-PID controller settings from closed-loop experiment. In this method, controller gain is a function of the overshoot obtained in the closed loop set point experiment. The integral and derivative time is mainly a function of the time to reach the first peak(overshoot). Simulation has been conducted for the broad class of processes and the controllers were tuned to have the same degree of robustness by measuring the maximum sensitivity, Ms, in order to obtain a reasonable comparison. The PID controller settings obtained in the proposed tuning method show better performance and robustness with other two-step tuning methods for the broad class of processes. It has also been applied to temperature control loop in distillation column model. The result has been compared to the open loop tuning method where it gives robust and fast response.展开更多
An investigation of the characteristics of flowrate transientswithin slug flow was conducted in a large- scale outdoor testingfacility. The test section consisted of a 378 m long, 7.62 cmdiameter stainless steel pipe....An investigation of the characteristics of flowrate transientswithin slug flow was conducted in a large- scale outdoor testingfacility. The test section consisted of a 378 m long, 7.62 cmdiameter stainless steel pipe. Air and water were used as the testfluids. The response to a change of flowrate of either phase or twophases Was measured using a series of pressure transducers anddifferential pressure transducers. An increase or decrease In gasflowrate caused a pressure overshoot above the value at new steadystate or led to a pressure undershoot To form a temporary stratifiedflow.展开更多
In this study,we present three experiments carried out at the EISCAT(European Incoherent Scatter Scientific Association)heating facility on October 29 and 30,2015.The results from the first experiment showed overshoot...In this study,we present three experiments carried out at the EISCAT(European Incoherent Scatter Scientific Association)heating facility on October 29 and 30,2015.The results from the first experiment showed overshoot during the O-mode heating period.The second experiment,which used cold-start X-mode heating,showed the generation of parametric decay instability,whereas overshoot was not observed.The third experiment used power-stepped X-mode heating with noticeable O-mode wave leakage.Parametric decay instability and oscillating two-stream instability were generated at the O-mode reflection height without the overshoot effect,which implies suppression of the thermal parametric instability with X-mode heating.We propose that the electron temperature increased because X-mode heating below the upper hybrid height decreased the growth rate of the thermal parametric instability.展开更多
A 30 MHz voltage-mode controlled buck converter with fast transient responses is presented.An improved differential difference amplifier(DDA)-based Type-III compensator is proposed to reduce the settling times of the ...A 30 MHz voltage-mode controlled buck converter with fast transient responses is presented.An improved differential difference amplifier(DDA)-based Type-III compensator is proposed to reduce the settling times of the converter during load transients,and to achieve near-optimal transient responses with simple PWM control only.Moreover,a hybrid scheme using a digital linear regulator with automatic transient detection and seamless loop transition is proposed to further improve the transient responses.By monitoring the output voltage of the compensator instead of the output voltage of the converter,the proposed hybrid scheme can reduce undershoot and overshoot effectively with good noise immunity and without interrupting the PWM loop.The converter was fabricated in a 0.13μm standard CMOS process using 3.3 V devices.With an input voltage of 3.3 V,the measured peak efficiencies at the output voltages of 2.4,1.8,and 1.2 V are 90.7%,88%,and 83.6%,respectively.With a load step of 1.25 A and rise and fall times of 2 ns,the measured 1%settling times were 220 and 230 ns,with undershoot and overshoot with PWM control of 72 and 76 mV,respectively.They were further reduced to 36 and 38 mV by using the proposed hybrid scheme,and 1%settling times were also reduced to 125 ns.展开更多
This paper presents a dual-nonlinear branch linearizer for reducing the corrected amplitude overshoot of conventional single nonlinear branch linearizer. Theoretical analysis is carried out, the analysis is verified b...This paper presents a dual-nonlinear branch linearizer for reducing the corrected amplitude overshoot of conventional single nonlinear branch linearizer. Theoretical analysis is carried out, the analysis is verified by simulation, and a prototype of Ka band 25.28~26.08 GHz dual nonlinear branch linearizer is achieved. It indicates that the corrected amplitude overshoot is less than 0.5 dB, the C/I3 improvement is more than 10 dB related to a single carrier IBO 9 dB, when it is linked and tested for 50 W spacebrone Travelling Wave Tube Amplifier(TWTA).展开更多
基金the Ministerial Level Advanced Research Foundation (445030705QB0301)
文摘To suppress the overshoots and undershoots in the envelope fitting for empirical mode decomposition （EMD）, an alternative cubic spline interpolation method without overshooting and undershooting is proposed. On the basis of the derived slope constraints of knots of a non-overshooting and non-undershooting cubic interpolant, together with ＂not-a-knot＂ conditions the cubic spline interpolants are constructed by replacing the requirement for equal second order derivatives at every knot with Brodlie＇ s derivative formula. Analysis and simulation experiments show that this approach can effectively avoid generating new extrema, shifting or exaggerating the existing ones in a signal, and thus significantly improve the decomposition performance of EMD.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10973035 and 10673030)the Knowledge Innovation Key Program of the Chinese Academy of Sciences under Grant No. KJCX2-YW-T24
文摘Based on the turbulent convection model （TCM） of Li ＆ Yang, we have studied the characteristics of turbulent convection in the envelopes of 2 and 5M⊙ stars at the red giant branch and asymptotic giant branch phases. The TCM has been successfully applied over the entire convective envelopes, including the convective unstable zone and the overshooting regions. We find that the convective motions become progressively stronger when the stellar models are located farther up along the Hayashi line. In the convective unstable zone, we find that the turbulent correlations are proportional to functions of a common factor （V - V^d）T, which explains similar distributions in those correlations. For the TCM we find that if the obtained stellar temperature structure is close to that of the mixing length theory （MLT）, the convective motion will have a much larger velocity and thus be more violent. However, if the turbulent velocity is adjusted to be close to that of the MLT, the superadiabatic convection zone would be much more extended inward, which would lead to a lower effective temperature of the stellar model. For the overshooting distance, we find that the e-folding lengths of the turbulent kinetic energy k in both the top and bottom overshooting regions decrease as the stellar model is progressively located farther up along the Hayashi line, but both the extents of the decrease are not obvious. The overshooting distances of the turbulent correlation /u＇rT＂ are almost the same for the different stellar models with the same set of TCM parameters. For the decay modes of the kinetic energy k, we find that they are very similar for different stellar models based on the same set of TCM parameters, and there is a nearly linear relationship between lg k and In P for different stellar models. When Cs or α increases while the other parameters are fixed, the obtained linearly decaying distance will become longer.
基金partially supported by the National Fundamental Research(973)Program of China(Grant Nos.2013CB430100 and 2015CB452800)the National Natural Science Foundation of China(Grant Nos.41275057 and 41505086)
文摘Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top（OT） activity within a tropical cyclone（TC）, which is defined as the hourly mean number of OT occurrence,was statistically investigated in the western North Pacific basin for the period 2005–12. Based on the level of OT activity,the samples were divided into OT and non-OT cases or high-activity-OT（HA-OT） and low-activity-OT（LA-OT） cases. The differences in large-scale environmental variables between OT（HA-OT） and non-OT（LA-OT） cases were examined 12 hours prior to the OT occurrence. Statistical analysis showed that environmental differences did exist between the OT and non-OT cases. The OTs were more skewed towards the early stage of the TC life cycle, and mostly concentrated in low latitudes.Meanwhile, a sufficiently deep warm-water layer, large temperature difference between the upper- and lower-level troposphere, large humidity at the middle and upper levels, and large atmospheric instability, were favorable for OT occurrence.The differences in large-scale environmental characteristics between HA-OTs and LA-OTs were not as significant as those between OTs and non-OTs, but the HA-OT samples tended to occur when the vertical shear was weak and the TC intensity was low. Finally, statistical models were designed to predict the OT and HA-OT. When at least three OT（HA-OT） predictor thresholds were satisfied, the Peirce skill score reached a maximum value of 0.49（0.30）.
基金supported in part by the National Natural Science Foundation of China under Project No.52207043。
文摘Under the condition of large inertia load,the stability of the servo system is more sensitive to the response speed and more likely to produce overshoot oscillations.In order to realize the requirements of high-precision and fast-response control of permanent magnet synchronous motor(PMSM)under large inertia load,an improved feedforward control strategy based on position impulse compensation and PD iterative algorithm is proposed to improve the response speed of the PMSM servo system and reduce the overshoot oscillation.This paper analyzes the mathematical models of the speed servo system and position servo system of the PMSM,calculates position overshoot impulse of the PMSM servo system,and improves the traditional feedforward control strategy to reversely compensate when the position is about to overshoot.Moreover,in order to further reduce the position overshoot,the PD iterative control algorithm is superimposed without increasing the complexity of the algorithm.The input signal is continuously corrected through multiple runs to achieve a smoother response control.The effectiveness of the proposed feedforward control strategy is verified by simulation and experiment.
基金the National Supercomputer Center in Tianjin for their patient assistance in providing the compilation environment.We thank the editor,Huajian Yao,for handling the manuscript and Mingming Li and another anonymous reviewer for their constructive comments.The research leading to these results has received funding from National Natural Science Foundation of China projects(Grant Nos.92355302 and 42121005)Taishan Scholar projects(Grant No.tspd20210305)others(Grant Nos.XDB0710000,L2324203,XK2023DXC001,LSKJ202204400,and ZR2021ZD09).
文摘The thermal evolution of the Earth’s interior and its dynamic effects are the focus of Earth sciences.However,the commonly adopted grid-based temperature solver is usually prone to numerical oscillations,especially in the presence of sharp thermal gradients,such as when modeling subducting slabs and rising plumes.This phenomenon prohibits the correct representation of thermal evolution and may cause incorrect implications of geodynamic processes.After examining several approaches for removing these numerical oscillations,we show that the Lagrangian method provides an ideal way to solve this problem.In this study,we propose a particle-in-cell method as a strategy for improving the solution to the energy equation and demonstrate its effectiveness in both one-dimensional and three-dimensional thermal problems,as well as in a global spherical simulation with data assimilation.We have implemented this method in the open-source finite-element code CitcomS,which features a spherical coordinate system,distributed memory parallel computing,and data assimilation algorithms.
基金financially supported by the National Key R&D Program of China(Nos.2020YFA0713601 and 2023YFA1008800)the National Natural Science Foundation of China(Nos.22341304,22341303,22103079,22073092 and 22303100)+1 种基金the Cooperation Project between Jilin Province and CAS(No.2023SYHZ0003)Additional support for Y.Lu was provided by the Youth Innovation Promotion Association of CAS(No.Y202054)。
文摘This study utilizes molecular dynamics simulation to investigate the complex dynamics of entangled semi-flexible polymer melts.The investigation reveals a significant stress overshoot phenomenon in the systems,demonstrating the intricate interplay between shear rates,chain orientation,and chain stretching dynamics.Additionally,the identification of metastable states,characterized by a dual-plateau phenomenon in the shear stress-strain curve at specific Rouse-Weissenberg number Wi_(R),showcases the system’s responsiveness to external perturbations and its transition to stable shear banding states.Moreover,the analysis of flow field deviations uncovers a progression of shear bands with increasing Wi_(R),displaying distinct behaviors in the system’s dynamics under different shear rates and chain lengths.These findings challenge established theoretical frameworks and advocate for refined modelling approaches in polymer rheology research.
基金the National Natural Science Foundation of China(NSFC Grant Nos.42104150,42074187,41774162,and 41704155)the Foundation of the National Key Laboratory of the Electromagnetic Environment(Grant No.6142403200303)+2 种基金the Chinese Academy of Sciences,Key Laboratory of Geospace Environment,University of Science&Technology of China(Grant No.GE2020-01)the Fundamental Research Funds for the Central Universities(Grant No.2042021kf0020)the Excellent Youth Foundation of Hubei Provincial Natural Science Foundation(Grant No.2019CFA054).
文摘High-power O-mode radio waves can excite artificial instabilities in the F region,according to experiments conducted at the European Incoherent Scatter Science Association(EISCAT)heating facility.The main instabilities include the parametric decay instability(PDI),oscillating two-stream instability(OTSI),and thermal parametric instability(TPI).The PDI and OTSI not only compete with each other,but also compete with the TPI,leading to a two-stage overshoot phenomenon:a miniovershoot occurs on a millisecond time scale after pump-on,followed by the main overshoot.We gain insight into the miniovershoot via a generalized Zakharov model,whereas the main overshoot can be observed as an enhanced plasma line overshoot phenomenon in incoherent scatter radar spectra.We can also observe that the zero-frequency ion line exists only in the initial heating period after a cold start and that the upshifted and downshifted ion lines behave irregularly in the spectra.The simulation results show that competition between the PDI and OTSI leads to an initial peak,which we named the pre-miniovershoot.The following processes,namely ion density caviton generation,and collapse and cascade in the development of the PDI,contribute to the miniovershoot phenomenon.
文摘We demonstrate a brand-new method to sharpen a color image by using an integral mask-filtering technique. The derivatives between the target pixel and its neighbors are transferred by the cubic root function instead of the traditional linear one. The obtained final image has clearer fine characteristics along with much less overshooting.
基金the Project of Natural Science Foundation of Jiangsu Province, BK99020 and the "973' Project of "CHERES" Gl998040907 the Natio
文摘Numerical diffusion or filter are used in most numerical models in order to eliminate small-scale (near two-grid intervals in wavelength) waves, However, conventional diffusion or filter schemes introduce the noise, and indeed few people realized, by filters themselves. For instance, most filters are troubled when they are put to use on meteorological fields with sharp gradient or with steep slope and consequently, the recurrence of undesirable numerical high-frequent oscillations (overshooting and undershooting) seems to be inevitable, Particularly when diffusion or filter is implemented in limited-area models, serious side effects on the limited-area boundaries often contaminate the modeling results. The merits and demerits are surveyed for commonly used diffusion or filter operations. A new type of monotonic digit filter is suggested to prevent overshooting and undershooting (due to the computational shock and Gibbs oscillation) nearby the discontinuous or nearly discontinuous locations when the filtering process was carried out, meanwhile the high selective property of damping is retained. Moreover, the new filter is designed on the implicit framework so that it can easily handle the problem of boundary diminishing in limited-area modeling.
文摘A high order single step β algorithm, a new direct integration algorithm is proposed for solution of equations of motion. Whenβ=0.5, the accuracy of displacement, velocity and acceleration is of forth order (a truncation error of Δ t 5), and the algorithm is unconditionally stable and has no arithmetic damping and no overshooting. When >0.5, and an arithmetic damping is adopted, the algorithm is again unconditionally stable with a third order accuracy (a truncation error of Δ t 4). The analyses run with typical examples show that the algorithm proposed has higher speed, higher precision and better properties than other direct integration methods, such as Wilson θ method and Newmark β method in analysing linear elastic responses and nonlinear earthquake responses.
文摘The fission rate of <sup>240</sup>Pu at its saddle point is obtained by using generalized coherentstate ansatz for large friction case. The numerical results indicate that the quasi-stationary fiss-ion rate approaches Kramers’ rate and the transient behaviour agrees with that given in previousstudies. Moreover, the relationship between the first eigenvalue λ<sub>1</sub> and the quasi-stationary fiss-ion rate λ<sub>qs</sub> is derived. In the case of high temperature, we also pay attention to the overshoot-ing.
基金Under the auspices of Major State Basic Research Development Program of China(No.2004CB418507)
文摘The environmental impact caused by local people （ecological footprint of consumption, EFc） and the actual environmental impact that the ecosystem burdens （ecological footprint of production, EFp） in West Jilin Province, Northeast China from 1986 to 2006 were evaluated by using ecological footprint （EF） method. And the major driving forces of EFc and EFp were analyzed by STIRPAT model. Both EFc and EFp showed increasing trends in 1986-2006, accompanied by decreasing ecological deficits but expanding ecological overshoots. Population （P）, GDP per capita （A1）, quadratic term of GDP per capita （A2）, urbanization （Tα1）, and quadratic term of urbanization （Ta2） were important influencing factors of EFc, among which Tα2 and Tα1 were the most dominate driving forces of EFc. A1, A2 and Tα2 were important influencing factors of EFp, among which A2 and A1 were the most dominate driving forces of EFp. In 1986-2006, the classical Environmental Kuznets Curve hypothesis did not exist between A2 and EF （both EFc and EFp）, but did between Tα2 and EF. The results indicate that enhancing the urbanization process and diversifying economic sources is one of the most effective ways to reduce the environmental impact of West Jilin Province. Moreover, importance should be attached to improve the eco-efficiency of resource exploitation and consumption.
基金the National Basic Research Program (973 Program) of China，the Science Fund for Creative Research Groups of the National Natural Science Foundation of China
文摘The optimization of the valve plate transition region is an important way of reducing the noise emission for an axial piston pump. However, the optimized methods through simulation or experiment are actually trial and error, and they cannot indicate the precise structural parameters of the valve plate transition region. In this study, a new design method for the transition region of valve plate based on the matching of flow area and reduction of transient reverse flow was proposed, and with which a valve plate was designed. Then, the impact of the flow ripple in the discharge line of an axial piston pump and the pressure overshoot and undershoot in the piston chamber on hydraulic and structural noise for axial piston pump is discussed. The noise reduction effect of the axial piston pump with this valve plate was analyzed by adopting a flow characteristic simulation model. Finally, the results showed that the application of this design method could contribute much to the reduction of the flow ripple and elimination of the pressure overshoot and undershoot. As a consequence, the method can be used in the design of a low-noise open circuit axial piston pump.
基金the support provided by King Abdulaziz City for Science and Technology (KACST) through the Science & Technology Unit at King Fahd University of PetroleumMinerals (KFUPM) for funding this work through project number 11-ENE1643-04 as part of the Notional Science Technology and Innovation Plan
文摘It is well-known that the IMC-PID controller tuning gives fast and improved set point response but slow disturbance rejection. A modification has been proposed in IMC-PID tuning rule for the improved disturbance rejection. For the modified IMC-PID tuning rule, a method has been developed to obtain the IMC-PID setting in closed-loop mode without acquiring detailed information of the process. The proposed method is based on the closed-loop step set point experiment using a proportional only controller with gain K_(c0). It is the direct approach to find the PID controller setting similar to classical Ziegler-Nichols closed-loop method. Based on simulations of a wide range of first-order with delay processes, a simple correlation has been derived to obtain the modified IMC-PID controller settings from closed-loop experiment. In this method, controller gain is a function of the overshoot obtained in the closed loop set point experiment. The integral and derivative time is mainly a function of the time to reach the first peak(overshoot). Simulation has been conducted for the broad class of processes and the controllers were tuned to have the same degree of robustness by measuring the maximum sensitivity, Ms, in order to obtain a reasonable comparison. The PID controller settings obtained in the proposed tuning method show better performance and robustness with other two-step tuning methods for the broad class of processes. It has also been applied to temperature control loop in distillation column model. The result has been compared to the open loop tuning method where it gives robust and fast response.
基金Supported by the National Natural Science Foundation of China (No.59995462) and the National Science Foundation of China for distinguished Young Scientists (No. 59725616).
文摘An investigation of the characteristics of flowrate transientswithin slug flow was conducted in a large- scale outdoor testingfacility. The test section consisted of a 378 m long, 7.62 cmdiameter stainless steel pipe. Air and water were used as the testfluids. The response to a change of flowrate of either phase or twophases Was measured using a series of pressure transducers anddifferential pressure transducers. An increase or decrease In gasflowrate caused a pressure overshoot above the value at new steadystate or led to a pressure undershoot To form a temporary stratifiedflow.
基金EISCAT is an international scientific association supported by research organizations in China(China Research Institute of Radiowave Propagation(CRIRP)),Finland(Suomen Akatemia(SA)),Japan(National Institute of Polar Research(NIPR)and Solar-Terrestrial Environment Laboratory(STEL)),Norway(The Research Council of Norway(NFR)),Sweden(Swedish Research Council(VR)),and the United Kingdom(Natural Environment Research Council(NERC)).This work was supported by the National Natural Science Foundation of China(NSFC,grants 41204111,41574146,41774162,and 41704155)the China Postdoctoral Science Foundation(grant 2017M622504).The experiment described in this work was carried out by the Russian team led by N.F.Blagoveshchenskaya.The data used in this research are available through the EISCAT Madrigal database(http://www.eiscat.se/madrigal/)and EISCAT Dynasonde database(https://dynserv.eiscat.uit.no/).
文摘In this study,we present three experiments carried out at the EISCAT(European Incoherent Scatter Scientific Association)heating facility on October 29 and 30,2015.The results from the first experiment showed overshoot during the O-mode heating period.The second experiment,which used cold-start X-mode heating,showed the generation of parametric decay instability,whereas overshoot was not observed.The third experiment used power-stepped X-mode heating with noticeable O-mode wave leakage.Parametric decay instability and oscillating two-stream instability were generated at the O-mode reflection height without the overshoot effect,which implies suppression of the thermal parametric instability with X-mode heating.We propose that the electron temperature increased because X-mode heating below the upper hybrid height decreased the growth rate of the thermal parametric instability.
文摘A 30 MHz voltage-mode controlled buck converter with fast transient responses is presented.An improved differential difference amplifier(DDA)-based Type-III compensator is proposed to reduce the settling times of the converter during load transients,and to achieve near-optimal transient responses with simple PWM control only.Moreover,a hybrid scheme using a digital linear regulator with automatic transient detection and seamless loop transition is proposed to further improve the transient responses.By monitoring the output voltage of the compensator instead of the output voltage of the converter,the proposed hybrid scheme can reduce undershoot and overshoot effectively with good noise immunity and without interrupting the PWM loop.The converter was fabricated in a 0.13μm standard CMOS process using 3.3 V devices.With an input voltage of 3.3 V,the measured peak efficiencies at the output voltages of 2.4,1.8,and 1.2 V are 90.7%,88%,and 83.6%,respectively.With a load step of 1.25 A and rise and fall times of 2 ns,the measured 1%settling times were 220 and 230 ns,with undershoot and overshoot with PWM control of 72 and 76 mV,respectively.They were further reduced to 36 and 38 mV by using the proposed hybrid scheme,and 1%settling times were also reduced to 125 ns.
文摘This paper presents a dual-nonlinear branch linearizer for reducing the corrected amplitude overshoot of conventional single nonlinear branch linearizer. Theoretical analysis is carried out, the analysis is verified by simulation, and a prototype of Ka band 25.28~26.08 GHz dual nonlinear branch linearizer is achieved. It indicates that the corrected amplitude overshoot is less than 0.5 dB, the C/I3 improvement is more than 10 dB related to a single carrier IBO 9 dB, when it is linked and tested for 50 W spacebrone Travelling Wave Tube Amplifier(TWTA).
