The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric a...The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric and parametric methods. The marginal wave characteristic distribution and the joint density of wave properties have been calculated using the two transformations, with the results and accuracy of both transformations presented here. The two transformations deviate slightly between each other for the calculation of the crest and trough height marginal wave distributions, as well as the joint densities of wave amplitude with other wave properties. The transformation methods for the calculation of the wave crest and trough height distributions are shown to provide good agreement with real ocean data. Our work will help in the determination of the most appropriate transformation procedure for the prediction of extreme values.展开更多
The foreshock with nascent plasma turbulence is regarded as a fascinating region to understand basic plasma physical processes, e.g., wave-particle interactions as well as wave-wave couplings. Although there have been...The foreshock with nascent plasma turbulence is regarded as a fascinating region to understand basic plasma physical processes, e.g., wave-particle interactions as well as wave-wave couplings. Although there have been plenty of intensive studies on this topic, some key clues about the physical processes still lack observations. A relatively comprehensive case study with some new observations is presented in this work based on the WIND spacecraft observations. In this case, upstream energetic protons were drifting at tens of Alfvén speed with respect to the background plasma protons. When looking at the magnetic wave activities, we find the co-existence of high-frequency(0.1-0.5 Hz) large-amplitude right-hand polarized(RHP) waves and lowfrequency(0.02-0.1 Hz) small-amplitude left-hand polarized(LHP) waves in the spacecraft(SC) frame. The observed anticorrelation between magnetic and velocity fluctuations along with the sunward magnetic field direction indicates that the lowfrequency LHP waves in the SC frame are in fact the sunward upstream RHP Alfvénic waves in the solar wind frame. This new observation corroborates the applicability of theories about plasma non-resonance instability and inverse cascade to the foreshock region, where the downstream high-frequency RHP parent waves are excited by the upstream energetic protons through non-resonance instability and the low-frequency RHP daughter waves are generated by the parent waves due to nonlinear parametric instability. Furthermore, enhanced downstream energetic proton fluxes are inferred to result from scattering of the upstream protons by the nascent turbulent fluctuations. Therefore, some critical clues about the newborn turbulence in the foreshock are provided in this work.展开更多
A dynamic model of a remotely operated vehicle(ROV)is developed.The hydrodynamic damping coefficients are estimated using a semi-predictive approach and computational fluid dynamic software ANSYS-CFX?and WAMIT?.A slid...A dynamic model of a remotely operated vehicle(ROV)is developed.The hydrodynamic damping coefficients are estimated using a semi-predictive approach and computational fluid dynamic software ANSYS-CFX?and WAMIT?.A sliding-mode controller(SMC)is then designed for the ROV model.The controller is subsequently robustified against modeling uncertainties,disturbances,and measurement errors.It is shown that when the system is subjected to bounded uncertainties,the SMC will preserve stability and tracking response.The paper ends with simulation results for a variety of conditions such as disturbances and parametric uncertainties.展开更多
This article is concerned with the finite-time stabilization(FTSB) of a class of delayed-Hopfield neural networks with a timevarying delay in the leakage term in the presence of parameter uncertainties. To accomplish ...This article is concerned with the finite-time stabilization(FTSB) of a class of delayed-Hopfield neural networks with a timevarying delay in the leakage term in the presence of parameter uncertainties. To accomplish the target of FTSB, two new finitetime controllers are designed for uncertain delayed-Hopfield neural networks with a time-varying delay in the leakage term. By utilizing the finite-time stability theory and the Lyapunov-Krasovskii functional(LKF) approach, some sufficient conditions for the FTSB of these neural networks are established. These conditions, which can be used for the selection of control parameters,are in the form of linear matrix inequalities(LMIs) and can be numerically checked. Additionally, an upper bound of the settling time was estimated. Finally, our theoretical results are further substantiated by two numerical examples with graphical illustrations to demonstrate the effectiveness of the results.展开更多
In this paper, the effects of the nonlinear vibration on stress distribution and fatigue life of the axially moving beam are studied.The parametric excitation of the flexible material is created by the pulsating movin...In this paper, the effects of the nonlinear vibration on stress distribution and fatigue life of the axially moving beam are studied.The parametric excitation of the flexible material is created by the pulsating moving speed. Three-to-one internal resonance condition is satisfied. The three-parameter model is adopted in the viscoelastic constitutive relation. The nonlinear vibration of the axially moving beam with parametric and internal resonance are studied by using the direct multiple scales method(MSM)with numerical simulation confirmation. Based on the approximate analytical solution, the distribution of tensile stress and bending stress on the axially moving beam is presented by adopting a V-belt as the prototype. Based on the maximum stable cyclic stress, the limit cycle response of the V-belt is utilized to evaluate the effect of the resonance on the fatigue life. Also, the influences of the internal resonance on the steady-state responses and the fatigue life of the V-belt are revealed. Numerical examples illustrate that large unwanted resonances occur and the second-order mode receives vibration energy from to the firstorder mode. The numerical results demonstrate that the nonlinear vibration significantly reduces the fatigue life of the V-belt.The fatigue life analysis method in this paper can be applied to the excited vibration of other axially moving systems and even static continuum.展开更多
The human tricuspid valve, one of the key cardiac structures, plays an important role in the circulatory system. However, there are few mathematical models to accurately simulate it.In this paper, firstly, we consider...The human tricuspid valve, one of the key cardiac structures, plays an important role in the circulatory system. However, there are few mathematical models to accurately simulate it.In this paper, firstly, we consider the tricuspid valve as an elastic shell with a specific shape and establish its novel geometric model. Concretely, the anterior, the posterior and the septal leaflets of the valve are supposed to be portions of the union of two interfacing semi-elliptic cylindrical shells when they are fully open.Next, we use Koiter’s linear shell model to describe the tricuspid valve leaflets in the static case, and provide a numerical scheme for this elastostatics model. Specifically, we discretize the space variable, i.e., the two tangent components of the displacement are discretized by using conforming finite elements(linear triangles) and the normal component of the displacement is discretized by using conforming Hsieh-Clough-Tocher triangles(HCT triangles).Finally, we make numerical experiments for the tricuspid valve and analyze the outcome. The numerical results show that the proposed mathematical model describes well the human tricuspid valve subjected to applied forces.展开更多
In this paper,a parametric level-set-based topology optimization framework is proposed to concurrently optimize the structural topology at the macroscale and the effective infill properties at the micro/meso scale.The...In this paper,a parametric level-set-based topology optimization framework is proposed to concurrently optimize the structural topology at the macroscale and the effective infill properties at the micro/meso scale.The concurrent optimization is achieved by a computational framework combining a new parametric level set approach with mathematical programming.Within the proposed framework,both the structural boundary evolution and the effective infill property optimization can be driven by mathematical programming,which is more advantageous compared with the conventional partial differential equatiodriven level set approach.Moreover,the proposed approach will be more efficient in handling nonlinear problems with multiple constraints.Instead of using radial basis functions(RBF),in this paper,we propose to construct a new type of cardinal basis functions(CBF)for the level set function parameterization.The proposed CBF parameterization ensures an explicit impose of the lower and upper bounds of the design variables.This overcomes the intrinsic disadvantage of the conventional RBF-based parametric level set method,where the lower and upper bounds of the design variables oftentimes have to be set by trial and error;A variational distance regularization method is utilized in this research to regularize the level set function to be a desired distanceregularized shape.With the distance information embedded in the level set model,the wrapping boundary layer and the interior infill region can be naturally defined.The isotropic infill achieved via the mesoscale topology optimization is conformally fit into the wrapping boundary layer using the shape-preserving conformal mapping method,which leads to a hierarchical physical structure with optimized overall topology and effective infill properties.The proposed method is expected to provide a timely solution to the increasing demand for multiscale and multifunctional structure design.展开更多
Tuned liquid damper (TLD) and tuned liquid column damper (TLCD) are two types of passive control devices that are widely used in structural control. In this study, a real-time hybrid simulation (RTHS) technique is emp...Tuned liquid damper (TLD) and tuned liquid column damper (TLCD) are two types of passive control devices that are widely used in structural control. In this study, a real-time hybrid simulation (RTHS) technique is employed to investigate the diff erence in control performance between TLD and TLCD. A series of RTHSs is presented with the premise of the same liquid length, mass ratio, and structural parameters. Herein, TLD and TLCD are physically experimented, and controlled structures are numerically simulated. Then, parametric studies are performed to further evaluate the diff erent performance between TLD and TLCD. Experimental results demonstrate that TLD is more eff ective than TLCD under diff erent amplitude excitations.展开更多
The adiabatic control is a powerful technique for many practical applications in quantum state engineering,light-driven chemical reactions and geometrical quantum computations.This paper reveals a speed limit of nonad...The adiabatic control is a powerful technique for many practical applications in quantum state engineering,light-driven chemical reactions and geometrical quantum computations.This paper reveals a speed limit of nonadiabatic transition in a general time-dependent parametric quantum system that leads to an upper bound function which lays down an optimal criteria for the adiabatic controls.The upper bound function of transition rate between instantaneous eigenstates of a time-dependent system is determined by the power fluctuations of the system relative to the minimum gap between the instantaneous levels.In a parametric Hilbert space,the driving power corresponds to the quantum work done by the parametric force multiplying the parametric velocity along the parametric driving path.The general two-state time-dependent models are investigated as examples to calculate the bound functions in some general driving schemes with one and two driving parameters.The calculations show that the upper bound function provides a tighter real-time estimation of nonadiabatic transition and is closely dependent on the driving frequencies and the energy gap of the system.The deviations of the real phase from Berry phase on different closed paths are induced by the nonadiabatic transitions and can be efficiently controlled by the upper bound functions.When the upper bound is adiabatically controlled,the Berry phases of the electronic spin exhibit nonlinear step-like behaviors and it is closely related to topological structures of the complicated parametric paths on Bloch sphere.展开更多
Differential evolution algorithm(DEA)is a stochastic,population-based global optimization method.In this paper,we propose new schemes for both mutation and crossover operators in order to enhance the performances of t...Differential evolution algorithm(DEA)is a stochastic,population-based global optimization method.In this paper,we propose new schemes for both mutation and crossover operators in order to enhance the performances of the standard DEA.The advantage of these proposed operators is that they are'parameters-less',without a tuning phase of algorithm parameters that is often a disadvantage of DEA.Once the modified differential evolutions are presented,a large comparative analysis is performed with the aim to assess both correctness and efficiency of the proposed operators.Advantages of proposed DEA are used in an important task of modern structural engineering that is mechanical identification under external dynamic loads.This is because of the importance of using a“parametersless”algorithm in identification problems whose characteristics typically vary strongly case by case,needing of a continuous set up of the algorithm proposed.This important advantage of proposed optimizers,in front of other identification algorithms,is used to develop a computer code suitable for the automatic identification of a simple supported beam subject to an impact load,that has been tested both using numerical simulations and real standard tests dynamic.The results point out that this algorithm is an interesting candidate for standard applications in structural identification problems.展开更多
We demonstrate high efficiency second harmonic generation(SHG)of near infrared femtosecond pulses using a BiB3O6 crystal in a single-pass tight focusing geometry setup.A frequency doubling efficiency of 63%is achieved...We demonstrate high efficiency second harmonic generation(SHG)of near infrared femtosecond pulses using a BiB3O6 crystal in a single-pass tight focusing geometry setup.A frequency doubling efficiency of 63%is achieved,which is,to the best of our knowledge,the highest value ever reported in the femtosecond regime for such low energy(nJ-level)pumping pulses.Theoretical analyses of the pumping scheme focusing waist and the SHG efficiency are performed,by numerically solving the three wave mixing coupled equations in the plane-wave scenario and by running simulations with a commercial full 3D code.Simulations show a good agreement with the experimental data regarding both the efficiency and the pulse spectral profile.The simulated SHG pulse temporal profile presents the characteristic features of the group velocity mismatch broadening in a‘thick’crystal.展开更多
We evaluate the feasibility of recovering energy from the vibrations of track and sleepers,during passage of a high-speed train,by means of a pendulum harvester.A simple mathematical model of the parametric pendulum i...We evaluate the feasibility of recovering energy from the vibrations of track and sleepers,during passage of a high-speed train,by means of a pendulum harvester.A simple mathematical model of the parametric pendulum is employed to obtain numerical predictions,while measured data of vibration tests during the passage of a Thalys high-speed train are considered as input forcing.Since a sustained rotation is the most energetic motion of a pendulum,the possibility of achieving such state is evaluated,taking into account the influence of initial conditions,damping and other factors.Numerical simulations show that rotating pendulum harvesters with sufficiently low viscous damping could be able to generate a usable average power on the order of 5–6 W per unit.Considering a modular arrangement of devices,such energy is enough to feed variety of rail-side equipment,as wireless sensors or warning light systems.However,a suitable choice of initial conditions could be a difficult task,leading to the need of a control action.展开更多
The purpose of this paper is to propose a synthesis method of parametric sensitivity constrained linear quadratic (SCLQ) controller for an uncertain linear time invariant (LTI) system. System sensitivity to parameter ...The purpose of this paper is to propose a synthesis method of parametric sensitivity constrained linear quadratic (SCLQ) controller for an uncertain linear time invariant (LTI) system. System sensitivity to parameter variation is handled through an additional quadratic trajectory parametric sensitivity term in the standard LQ criterion to be minimized. The main purpose here is to find a suboptimal linear quadratic control taking explicitly into account the parametric uncertainties. The paper main contribution is threefold: 1) A descriptor system approach is used to show that the underlying singular linear-quadratic optimal control problem leads to a non-standard Riccati equation. 2) A solution to the proposed control problem is then given based on a connection to the so-called Lur'e matrix equations. 3) A synthesis method of multiple parametric SCLQ controllers is proposed to cover the whole parametric uncertainty while degrading as less as possible the intrinsic robustness properties of each local linear quadratic controller. Some examples are presented in order to illustrate the effectiveness of the approach.展开更多
The study of the development cost of general aviation aircraft is limited by small samples with many cost-driven factors. This paper investigates a parametric modeling method for prediction of the development cost of ...The study of the development cost of general aviation aircraft is limited by small samples with many cost-driven factors. This paper investigates a parametric modeling method for prediction of the development cost of general aviation aircraft. The proposed technique depends on some principal components, acquired by utilizing P value analysis and gray correlation analysis. According to these principal components, the corresponding linear regression and BP neural network models are established respectively. The feasibility and accuracy of the P value analysis are verified by comparing results of model fitting and prediction. A sensitivity analysis related to model precision and suitability is discussed in detail. Results obtained in this study show that the proposed method not only has a certain degree of versatility, but also provides a preliminary prediction of the development cost of general aviation aircraft.展开更多
Weispfenning in 1992 introduced the concepts of comprehensive Gr?bner system/basis of a parametric polynomial system,and he also presented an algorithm to compute them.Since then, this research field has attracted muc...Weispfenning in 1992 introduced the concepts of comprehensive Gr?bner system/basis of a parametric polynomial system,and he also presented an algorithm to compute them.Since then, this research field has attracted much attention over the past several decades,and many efficient algorithms have been proposed.Moreover,these algorithms have been applied to many different fields, such as parametric polynomial equations solving,geometric theorem proving and discovering,quantifier elimination,and so on.This survey brings together the works published between 1992 and 2018,and we hope that this survey is valuable for this research area.展开更多
基金Supported by the Marine Engineering Equipment Scientific Research Project of Ministry of Industry and Information Technology of PRC and the National Science and Technology Major Project of China (Grant No. 2016ZX05057020)National Natural Science Foundation of China (Grant No. 51809067).
文摘The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric and parametric methods. The marginal wave characteristic distribution and the joint density of wave properties have been calculated using the two transformations, with the results and accuracy of both transformations presented here. The two transformations deviate slightly between each other for the calculation of the crest and trough height marginal wave distributions, as well as the joint densities of wave amplitude with other wave properties. The transformation methods for the calculation of the wave crest and trough height distributions are shown to provide good agreement with real ocean data. Our work will help in the determination of the most appropriate transformation procedure for the prediction of extreme values.
基金Peking University' is supported by National Natural Science Foundation of China (Grant Nos. 41574168, 41874200, 41674171, 41774183, and 41421003).
文摘The foreshock with nascent plasma turbulence is regarded as a fascinating region to understand basic plasma physical processes, e.g., wave-particle interactions as well as wave-wave couplings. Although there have been plenty of intensive studies on this topic, some key clues about the physical processes still lack observations. A relatively comprehensive case study with some new observations is presented in this work based on the WIND spacecraft observations. In this case, upstream energetic protons were drifting at tens of Alfvén speed with respect to the background plasma protons. When looking at the magnetic wave activities, we find the co-existence of high-frequency(0.1-0.5 Hz) large-amplitude right-hand polarized(RHP) waves and lowfrequency(0.02-0.1 Hz) small-amplitude left-hand polarized(LHP) waves in the spacecraft(SC) frame. The observed anticorrelation between magnetic and velocity fluctuations along with the sunward magnetic field direction indicates that the lowfrequency LHP waves in the SC frame are in fact the sunward upstream RHP Alfvénic waves in the solar wind frame. This new observation corroborates the applicability of theories about plasma non-resonance instability and inverse cascade to the foreshock region, where the downstream high-frequency RHP parent waves are excited by the upstream energetic protons through non-resonance instability and the low-frequency RHP daughter waves are generated by the parent waves due to nonlinear parametric instability. Furthermore, enhanced downstream energetic proton fluxes are inferred to result from scattering of the upstream protons by the nascent turbulent fluctuations. Therefore, some critical clues about the newborn turbulence in the foreshock are provided in this work.
文摘A dynamic model of a remotely operated vehicle(ROV)is developed.The hydrodynamic damping coefficients are estimated using a semi-predictive approach and computational fluid dynamic software ANSYS-CFX?and WAMIT?.A sliding-mode controller(SMC)is then designed for the ROV model.The controller is subsequently robustified against modeling uncertainties,disturbances,and measurement errors.It is shown that when the system is subjected to bounded uncertainties,the SMC will preserve stability and tracking response.The paper ends with simulation results for a variety of conditions such as disturbances and parametric uncertainties.
文摘This article is concerned with the finite-time stabilization(FTSB) of a class of delayed-Hopfield neural networks with a timevarying delay in the leakage term in the presence of parameter uncertainties. To accomplish the target of FTSB, two new finitetime controllers are designed for uncertain delayed-Hopfield neural networks with a time-varying delay in the leakage term. By utilizing the finite-time stability theory and the Lyapunov-Krasovskii functional(LKF) approach, some sufficient conditions for the FTSB of these neural networks are established. These conditions, which can be used for the selection of control parameters,are in the form of linear matrix inequalities(LMIs) and can be numerically checked. Additionally, an upper bound of the settling time was estimated. Finally, our theoretical results are further substantiated by two numerical examples with graphical illustrations to demonstrate the effectiveness of the results.
基金the National Natural Science Foundation of China (Grant Nos. 11772181, 11422214)the "Dawn" Program of Shanghai Education Commission (Grant No. 17SG38)the Innovation Program of Shanghai Municipal Education Commission (Grant No. 2017-01-07-00-09-E00019).
文摘In this paper, the effects of the nonlinear vibration on stress distribution and fatigue life of the axially moving beam are studied.The parametric excitation of the flexible material is created by the pulsating moving speed. Three-to-one internal resonance condition is satisfied. The three-parameter model is adopted in the viscoelastic constitutive relation. The nonlinear vibration of the axially moving beam with parametric and internal resonance are studied by using the direct multiple scales method(MSM)with numerical simulation confirmation. Based on the approximate analytical solution, the distribution of tensile stress and bending stress on the axially moving beam is presented by adopting a V-belt as the prototype. Based on the maximum stable cyclic stress, the limit cycle response of the V-belt is utilized to evaluate the effect of the resonance on the fatigue life. Also, the influences of the internal resonance on the steady-state responses and the fatigue life of the V-belt are revealed. Numerical examples illustrate that large unwanted resonances occur and the second-order mode receives vibration energy from to the firstorder mode. The numerical results demonstrate that the nonlinear vibration significantly reduces the fatigue life of the V-belt.The fatigue life analysis method in this paper can be applied to the excited vibration of other axially moving systems and even static continuum.
基金the National Natural Science Foundation of China(Nos.11571275,11572244,11471261,11871399)the Natural Science Foundation of Shaanxi Province(Nos.2018JM1014,2017JM1005).
文摘The human tricuspid valve, one of the key cardiac structures, plays an important role in the circulatory system. However, there are few mathematical models to accurately simulate it.In this paper, firstly, we consider the tricuspid valve as an elastic shell with a specific shape and establish its novel geometric model. Concretely, the anterior, the posterior and the septal leaflets of the valve are supposed to be portions of the union of two interfacing semi-elliptic cylindrical shells when they are fully open.Next, we use Koiter’s linear shell model to describe the tricuspid valve leaflets in the static case, and provide a numerical scheme for this elastostatics model. Specifically, we discretize the space variable, i.e., the two tangent components of the displacement are discretized by using conforming finite elements(linear triangles) and the normal component of the displacement is discretized by using conforming Hsieh-Clough-Tocher triangles(HCT triangles).Finally, we make numerical experiments for the tricuspid valve and analyze the outcome. The numerical results show that the proposed mathematical model describes well the human tricuspid valve subjected to applied forces.
基金the National Science Foundation of the United States(Grant Nos.CMMI1462270 and CMMI1762287)Ford University Research Program(URP),and the start-up fund from the State University of New York at Stony Brook.
文摘In this paper,a parametric level-set-based topology optimization framework is proposed to concurrently optimize the structural topology at the macroscale and the effective infill properties at the micro/meso scale.The concurrent optimization is achieved by a computational framework combining a new parametric level set approach with mathematical programming.Within the proposed framework,both the structural boundary evolution and the effective infill property optimization can be driven by mathematical programming,which is more advantageous compared with the conventional partial differential equatiodriven level set approach.Moreover,the proposed approach will be more efficient in handling nonlinear problems with multiple constraints.Instead of using radial basis functions(RBF),in this paper,we propose to construct a new type of cardinal basis functions(CBF)for the level set function parameterization.The proposed CBF parameterization ensures an explicit impose of the lower and upper bounds of the design variables.This overcomes the intrinsic disadvantage of the conventional RBF-based parametric level set method,where the lower and upper bounds of the design variables oftentimes have to be set by trial and error;A variational distance regularization method is utilized in this research to regularize the level set function to be a desired distanceregularized shape.With the distance information embedded in the level set model,the wrapping boundary layer and the interior infill region can be naturally defined.The isotropic infill achieved via the mesoscale topology optimization is conformally fit into the wrapping boundary layer using the shape-preserving conformal mapping method,which leads to a hierarchical physical structure with optimized overall topology and effective infill properties.The proposed method is expected to provide a timely solution to the increasing demand for multiscale and multifunctional structure design.
基金National Natural Science Foundation of China under Grant Nos. 51725901 and 51639006.
文摘Tuned liquid damper (TLD) and tuned liquid column damper (TLCD) are two types of passive control devices that are widely used in structural control. In this study, a real-time hybrid simulation (RTHS) technique is employed to investigate the diff erence in control performance between TLD and TLCD. A series of RTHSs is presented with the premise of the same liquid length, mass ratio, and structural parameters. Herein, TLD and TLCD are physically experimented, and controlled structures are numerically simulated. Then, parametric studies are performed to further evaluate the diff erent performance between TLD and TLCD. Experimental results demonstrate that TLD is more eff ective than TLCD under diff erent amplitude excitations.
基金Project supported by the National Natural Science Foundation of China(Emergency Project,Grant Nos.11447025 and 11847308).
文摘The adiabatic control is a powerful technique for many practical applications in quantum state engineering,light-driven chemical reactions and geometrical quantum computations.This paper reveals a speed limit of nonadiabatic transition in a general time-dependent parametric quantum system that leads to an upper bound function which lays down an optimal criteria for the adiabatic controls.The upper bound function of transition rate between instantaneous eigenstates of a time-dependent system is determined by the power fluctuations of the system relative to the minimum gap between the instantaneous levels.In a parametric Hilbert space,the driving power corresponds to the quantum work done by the parametric force multiplying the parametric velocity along the parametric driving path.The general two-state time-dependent models are investigated as examples to calculate the bound functions in some general driving schemes with one and two driving parameters.The calculations show that the upper bound function provides a tighter real-time estimation of nonadiabatic transition and is closely dependent on the driving frequencies and the energy gap of the system.The deviations of the real phase from Berry phase on different closed paths are induced by the nonadiabatic transitions and can be efficiently controlled by the upper bound functions.When the upper bound is adiabatically controlled,the Berry phases of the electronic spin exhibit nonlinear step-like behaviors and it is closely related to topological structures of the complicated parametric paths on Bloch sphere.
基金the research project"OptArch-689983H2020-MSCA-RISE-2015/H2020-MSCA-RISE-20".
文摘Differential evolution algorithm(DEA)is a stochastic,population-based global optimization method.In this paper,we propose new schemes for both mutation and crossover operators in order to enhance the performances of the standard DEA.The advantage of these proposed operators is that they are'parameters-less',without a tuning phase of algorithm parameters that is often a disadvantage of DEA.Once the modified differential evolutions are presented,a large comparative analysis is performed with the aim to assess both correctness and efficiency of the proposed operators.Advantages of proposed DEA are used in an important task of modern structural engineering that is mechanical identification under external dynamic loads.This is because of the importance of using a“parametersless”algorithm in identification problems whose characteristics typically vary strongly case by case,needing of a continuous set up of the algorithm proposed.This important advantage of proposed optimizers,in front of other identification algorithms,is used to develop a computer code suitable for the automatic identification of a simple supported beam subject to an impact load,that has been tested both using numerical simulations and real standard tests dynamic.The results point out that this algorithm is an interesting candidate for standard applications in structural identification problems.
基金the European Union's Horizon 2020 research and innovation programme under grant agreement No.654148(Laserlab-Europe)the Euratom research and training program 2014-2018 under grant agreement No.633053 and the Fundacao para a Ciencia e a Tecnologia(FCT,Lisboa)under grant No.PD/BD/114327/2016it was carried out in the framework of the Advanced Program in Plasma Science and Engineering(APPLAuSE,sponsored by FCT under grant No.PD/00505/2012)at Instituto Superior Tecnico(IST).
文摘We demonstrate high efficiency second harmonic generation(SHG)of near infrared femtosecond pulses using a BiB3O6 crystal in a single-pass tight focusing geometry setup.A frequency doubling efficiency of 63%is achieved,which is,to the best of our knowledge,the highest value ever reported in the femtosecond regime for such low energy(nJ-level)pumping pulses.Theoretical analyses of the pumping scheme focusing waist and the SHG efficiency are performed,by numerically solving the three wave mixing coupled equations in the plane-wave scenario and by running simulations with a commercial full 3D code.Simulations show a good agreement with the experimental data regarding both the efficiency and the pulse spectral profile.The simulated SHG pulse temporal profile presents the characteristic features of the group velocity mismatch broadening in a‘thick’crystal.
基金support of Secretary of Science and Technology of UTN, CONICETthe National Agency for Scientific and Technological Promotion and Engineering Department of UNS.
文摘We evaluate the feasibility of recovering energy from the vibrations of track and sleepers,during passage of a high-speed train,by means of a pendulum harvester.A simple mathematical model of the parametric pendulum is employed to obtain numerical predictions,while measured data of vibration tests during the passage of a Thalys high-speed train are considered as input forcing.Since a sustained rotation is the most energetic motion of a pendulum,the possibility of achieving such state is evaluated,taking into account the influence of initial conditions,damping and other factors.Numerical simulations show that rotating pendulum harvesters with sufficiently low viscous damping could be able to generate a usable average power on the order of 5–6 W per unit.Considering a modular arrangement of devices,such energy is enough to feed variety of rail-side equipment,as wireless sensors or warning light systems.However,a suitable choice of initial conditions could be a difficult task,leading to the need of a control action.
文摘The purpose of this paper is to propose a synthesis method of parametric sensitivity constrained linear quadratic (SCLQ) controller for an uncertain linear time invariant (LTI) system. System sensitivity to parameter variation is handled through an additional quadratic trajectory parametric sensitivity term in the standard LQ criterion to be minimized. The main purpose here is to find a suboptimal linear quadratic control taking explicitly into account the parametric uncertainties. The paper main contribution is threefold: 1) A descriptor system approach is used to show that the underlying singular linear-quadratic optimal control problem leads to a non-standard Riccati equation. 2) A solution to the proposed control problem is then given based on a connection to the so-called Lur'e matrix equations. 3) A synthesis method of multiple parametric SCLQ controllers is proposed to cover the whole parametric uncertainty while degrading as less as possible the intrinsic robustness properties of each local linear quadratic controller. Some examples are presented in order to illustrate the effectiveness of the approach.
基金the National Postdoctoral Program for Innovative Talents,Postdoctoral Science Foundation of China(No.2017M610740)supports from Hefei General Aviation Research Institute,Beihang University.
文摘The study of the development cost of general aviation aircraft is limited by small samples with many cost-driven factors. This paper investigates a parametric modeling method for prediction of the development cost of general aviation aircraft. The proposed technique depends on some principal components, acquired by utilizing P value analysis and gray correlation analysis. According to these principal components, the corresponding linear regression and BP neural network models are established respectively. The feasibility and accuracy of the P value analysis are verified by comparing results of model fitting and prediction. A sensitivity analysis related to model precision and suitability is discussed in detail. Results obtained in this study show that the proposed method not only has a certain degree of versatility, but also provides a preliminary prediction of the development cost of general aviation aircraft.
基金the CAS Project QYZDJ-SSW-SYS022the National Natural ScienceFoundation of China under Grant No.61877058the Strategy Cooperation Project AQ-1701.
文摘Weispfenning in 1992 introduced the concepts of comprehensive Gr?bner system/basis of a parametric polynomial system,and he also presented an algorithm to compute them.Since then, this research field has attracted much attention over the past several decades,and many efficient algorithms have been proposed.Moreover,these algorithms have been applied to many different fields, such as parametric polynomial equations solving,geometric theorem proving and discovering,quantifier elimination,and so on.This survey brings together the works published between 1992 and 2018,and we hope that this survey is valuable for this research area.