In this article, linear regular index 2 DAEs A(t)[D(t)x(t)]' + B(t)x(t) = q(t) are considered. Using a decoupling technique, initial condition and boundary condition are properly formulated. Regular inde...In this article, linear regular index 2 DAEs A(t)[D(t)x(t)]' + B(t)x(t) = q(t) are considered. Using a decoupling technique, initial condition and boundary condition are properly formulated. Regular index 1 DAEs are obtained by a regularization method. We study the behavior of the solution of the regularization system via asymptotic expansions. The error analysis between the solutions of the DAEs and its regularization system is given.展开更多
Since October 2008,China's social consumption of electricity had,for the first time,grown negatively compared to the same period of the previous year,and in November the negative growth range further expanded. The...Since October 2008,China's social consumption of electricity had,for the first time,grown negatively compared to the same period of the previous year,and in November the negative growth range further expanded. The major pressure faced by the electricity industry has now turned from the contradiction between coal and electricity to electricity quantity. This is undoubtedly a true and new test to electricity enterprises which get used to high growth but are now suffering great losses. The reform of electricity system has already been in great difficulties and now is getting into a more serious situation. In order to help readers improve their knowledge and understanding of the current tough situation faced by the electricity industry and discuss how to alleviate and get through the difficulty resulted from the economic crisis "encountered once every one hundred years" by joint efforts of all parties concerned,a Seminar on Crisis and Countermeasures for Electricity Industry was held on November 20,2008. Here are some extracts from the speeches of four experts.展开更多
With the continuous expansion of the demand in China for the integration of medical care and elderly care,more social capital will be directed into this field.A LTHOUGHT answers to the question“What is happiness?”ma...With the continuous expansion of the demand in China for the integration of medical care and elderly care,more social capital will be directed into this field.A LTHOUGHT answers to the question“What is happiness?”may vary among young people,for most senior citizens the answer is by and large the same:to be looked after properly.展开更多
In this article, a novel scalarization technique, called the improved objective-constraint approach, is introduced to find efficient solutions of a given multiobjective programming problem. The presented scalarized pr...In this article, a novel scalarization technique, called the improved objective-constraint approach, is introduced to find efficient solutions of a given multiobjective programming problem. The presented scalarized problem extends the objective-constraint problem. It is demonstrated that how adding variables to the scalarized problem, can lead to find conditions for (weakly, properly) Pareto optimal solutions. Applying the obtained necessary and sufficient conditions, two algorithms for generating the Pareto front approximation of bi-objective and three-objective programming problems are designed. These algorithms are easy to implement and can achieve an even approximation of (weakly, properly) Pareto optimal solutions. These algorithms can be generalized for optimization problems with more than three criterion functions, too. The effectiveness and capability of the algorithms are demonstrated in test problems.展开更多
With the development of cutting-edge multi-object spectrographs,fiber positioners located in the focal plane are being scaled down in size,and miniature hollow-cup Permanent Magnet motors are now being considered as a...With the development of cutting-edge multi-object spectrographs,fiber positioners located in the focal plane are being scaled down in size,and miniature hollow-cup Permanent Magnet motors are now being considered as a suitable replacement for Faulhaber Precistep stepper motors.However,the small electrical time constant of such coreless motors poses a challenge,as the problem of severe commutation torque ripple in a fiber positioner running a position loop has been tricky.To overcome this challenge,it is advised to increase the Pulse Width Modulation(PWM)frequency as much as possible to mitigate the effects of the current fluctuation.This must be done while ensuring adequate resolution of the PWM generator.By employing a voltage open-loop field-oriented control based on a modulation frequency of 1 MHz,the drive current only costs 25 m A under a 3.3 V power supply.The sine degree of phase current is immaculate,and the repeat positioning accuracy can reach 2μm.Moreover,it is possible to further shrink the bill of devices and the layout area of the Printed Circuit Board,especially in sizesensitive applications.This device has been developed under the new generation of The Large Sky Area MultiObject Fiber Spectroscopic Telescope.展开更多
Professors Mohazzbi and Luo [1] published “Despite several attempts have been made to explain the twin paradox … none of the explanations … resolved the paradox. If the paradox can be ever resolved, it requires a m...Professors Mohazzbi and Luo [1] published “Despite several attempts have been made to explain the twin paradox … none of the explanations … resolved the paradox. If the paradox can be ever resolved, it requires a much deeper understanding … of the theory of relativity”. The deeper understanding of resolving the paradox is by applying more explicit definitions of proper time interval, Lorentz transform, time dilation, and aging time.展开更多
Correction to:NUCL SCI TECH(2023)34:63 https://doi.org/10.1007/s41365-023-01213-3 While typesetting,reference[16]in the list has not been properly placed in the proof.The orders of the references[13-16]were mistaken b...Correction to:NUCL SCI TECH(2023)34:63 https://doi.org/10.1007/s41365-023-01213-3 While typesetting,reference[16]in the list has not been properly placed in the proof.The orders of the references[13-16]were mistaken by the production.The correct order of the references is.展开更多
The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The b...The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The boundary value method(BVM),based on the finite difference method(FDM),can be used to reconstruct the source wavefield in the reverse time propagation in the same way as the receiver wavefield,which can reduce the storage burden of the RTM data.Considering that the FDM cannot well handle models with discontinuous material properties and rough interfaces,we develop a source wavefield reconstruction strategy based on the finite element method(FEM),using proper orthogonal decomposition(POD)to enhance computational efficiency.In this method,we divide the whole time period into several segments,and construct the POD basis functions to get a reduced order model(ROM)for the source wavefield reconstruction in each segment.We show the corresponding quantitative analysis of the storage requirement of the POD-FEM.Numerical tests on the homogeneous model show the effectiveness of the proposed method,while the layered model and part of the Marmousi model tests indicate that the POD-FEM can keep an excellent balance between computational efficiency and memory usage compared with the full-stored method(FSM)and the BVM,and can be effectively applied in imaging.展开更多
With the rapid development of the world economy,IGBT has been widely used in motor drive and electric energy conversion.In order to timely detect the fatigue damage of IGBT,it is necessary to monitor the junction temp...With the rapid development of the world economy,IGBT has been widely used in motor drive and electric energy conversion.In order to timely detect the fatigue damage of IGBT,it is necessary to monitor the junction temperature of IGBT.In order to realize the fast calculation of IGBT junction temperature,a finite element method of IGBT temperature field reduction is proposed in this paper.Firstly,the finite element calculation process of IGBT temperature field is introduced and the linear equations of finite element calculation of temperature field are derived.Temperature field data of different working conditions are obtained by finite element simulation to form the sample space.Then the covariance matrix of the sample space is constructed,whose proper orthogonal decomposition and modal extraction are carried out.Reasonable basis vector space is selected to complete the low dimensional expression of temperature vector inside and outside the sample space.Finally,the reduced-order model of temperature field finite element is obtained and solved.The results of the reduced order model are compared with those of the finite element method,and the performance of the reduced-order model is evaluated from two aspects of accuracy and rapidity.展开更多
Three recent breakthroughs due to AI in arts and science serve as motivation:An award winning digital image,protein folding,fast matrix multiplication.Many recent developments in artificial neural networks,particularl...Three recent breakthroughs due to AI in arts and science serve as motivation:An award winning digital image,protein folding,fast matrix multiplication.Many recent developments in artificial neural networks,particularly deep learning(DL),applied and relevant to computational mechanics(solid,fluids,finite-element technology)are reviewed in detail.Both hybrid and pure machine learning(ML)methods are discussed.Hybrid methods combine traditional PDE discretizations with ML methods either(1)to help model complex nonlinear constitutive relations,(2)to nonlinearly reduce the model order for efficient simulation(turbulence),or(3)to accelerate the simulation by predicting certain components in the traditional integration methods.Here,methods(1)and(2)relied on Long-Short-Term Memory(LSTM)architecture,with method(3)relying on convolutional neural networks.Pure ML methods to solve(nonlinear)PDEs are represented by Physics-Informed Neural network(PINN)methods,which could be combined with attention mechanism to address discontinuous solutions.Both LSTM and attention architectures,together with modern and generalized classic optimizers to include stochasticity for DL networks,are extensively reviewed.Kernel machines,including Gaussian processes,are provided to sufficient depth for more advanced works such as shallow networks with infinite width.Not only addressing experts,readers are assumed familiar with computational mechanics,but not with DL,whose concepts and applications are built up from the basics,aiming at bringing first-time learners quickly to the forefront of research.History and limitations of AI are recounted and discussed,with particular attention at pointing out misstatements or misconceptions of the classics,even in well-known references.Positioning and pointing control of a large-deformable beam is given as an example.展开更多
The authors of this article are interested in characterization of efficient solutions for special classes of problems. These classes consider semi-strong E-convexity of involved functions. Sufficient and necessary con...The authors of this article are interested in characterization of efficient solutions for special classes of problems. These classes consider semi-strong E-convexity of involved functions. Sufficient and necessary conditions for a feasible solution to be an efficient or properly efficient solution are obtained.展开更多
Urinary bladder neural dysfunction (UBND) is a common complication of diabetes mellitus. When urinary bladder paralysis develops, urinary system infection readily occurs. If the infection is not treated properly, seri...Urinary bladder neural dysfunction (UBND) is a common complication of diabetes mellitus. When urinary bladder paralysis develops, urinary system infection readily occurs. If the infection is not treated properly, serious sequelae will happen. Western doctors primarily use展开更多
Facial spasm is a frequently seen dis-ease characterized by unilateral involuntaryirregular twitching of the facial muscles.This disorder may be induced by intoxica-tion,infection,trauma and long-term facialparalysis ...Facial spasm is a frequently seen dis-ease characterized by unilateral involuntaryirregular twitching of the facial muscles.This disorder may be induced by intoxica-tion,infection,trauma and long-term facialparalysis which was not properly treated.展开更多
Whether the goal is to meet global challenges or to enable a paradigm shift,it is always essential for science to move beyond conventional thinking.Moreover,the mutually beneficial interactions between global challeng...Whether the goal is to meet global challenges or to enable a paradigm shift,it is always essential for science to move beyond conventional thinking.Moreover,the mutually beneficial interactions between global challenges and paradigm shifts require a great deal of effort.To this end,it is imperative for the scientific community not only to respond to major challenges by shifting paradigms in science but also to drive paradigm shifts in science by responding to major challenges.This aim sets a higher bar for scientists as,in order to achieve it,we must properly identify the scientific questions in research and better utilize existing knowledge.At present,however,we are not paying sufficient attention to this aim,nor are we sufficiently competent in this regard.It is essential for the global scientific community to pay more attention to these interconnected issues of global challenges and paradigm shifts.展开更多
A rigorous spectral representation of relativistic random-phase approximation is presented.Explicit expression is derived for the effective particle-hole interaction which contains the direct term Kan,the exchange ter...A rigorous spectral representation of relativistic random-phase approximation is presented.Explicit expression is derived for the effective particle-hole interaction which contains the direct term Kan,the exchange term KaQ and the kernel for the fermion line renormalization K_(fr).It is shown that according to our method,not only K_(an) but also K_(sc) and K_(fr) can be given rigorously in a form which depends only on one ω(energy)-variable and they all take account of the retardation effect properly.展开更多
Magnesia chrome bricks were prepared with fiLsed MgO- Cr2 O3 synthesized material, fused magnesite and :hrome ore as main starting materials. Nano-Al2O3 was tdded into refractories ( 2% , 4% and 6% in mass ) ;ubst...Magnesia chrome bricks were prepared with fiLsed MgO- Cr2 O3 synthesized material, fused magnesite and :hrome ore as main starting materials. Nano-Al2O3 was tdded into refractories ( 2% , 4% and 6% in mass ) ;ubstit,ting for Al203 micropowder. After m&ing and ;haping, the bricks were fired at 1 550 ℃, 1 600 91℃, t 650 ℃ and 1 750℃, respectively. The microstruc-ure , sintering property, mechanical properties, thermal ;kock resistance and shtg resistance of the specimens with he addition of nano-Al2O3 were investigated. The results indicate that the performance of brick with 4 mass% of nano-Al2O3 is greatly improred afier firing at 1 650 ℃.展开更多
基金Project supported by the Foundation for the Authors of the National Excellent Doctoral Thesis Award of China (200720)
文摘In this article, linear regular index 2 DAEs A(t)[D(t)x(t)]' + B(t)x(t) = q(t) are considered. Using a decoupling technique, initial condition and boundary condition are properly formulated. Regular index 1 DAEs are obtained by a regularization method. We study the behavior of the solution of the regularization system via asymptotic expansions. The error analysis between the solutions of the DAEs and its regularization system is given.
文摘Since October 2008,China's social consumption of electricity had,for the first time,grown negatively compared to the same period of the previous year,and in November the negative growth range further expanded. The major pressure faced by the electricity industry has now turned from the contradiction between coal and electricity to electricity quantity. This is undoubtedly a true and new test to electricity enterprises which get used to high growth but are now suffering great losses. The reform of electricity system has already been in great difficulties and now is getting into a more serious situation. In order to help readers improve their knowledge and understanding of the current tough situation faced by the electricity industry and discuss how to alleviate and get through the difficulty resulted from the economic crisis "encountered once every one hundred years" by joint efforts of all parties concerned,a Seminar on Crisis and Countermeasures for Electricity Industry was held on November 20,2008. Here are some extracts from the speeches of four experts.
文摘With the continuous expansion of the demand in China for the integration of medical care and elderly care,more social capital will be directed into this field.A LTHOUGHT answers to the question“What is happiness?”may vary among young people,for most senior citizens the answer is by and large the same:to be looked after properly.
文摘In this article, a novel scalarization technique, called the improved objective-constraint approach, is introduced to find efficient solutions of a given multiobjective programming problem. The presented scalarized problem extends the objective-constraint problem. It is demonstrated that how adding variables to the scalarized problem, can lead to find conditions for (weakly, properly) Pareto optimal solutions. Applying the obtained necessary and sufficient conditions, two algorithms for generating the Pareto front approximation of bi-objective and three-objective programming problems are designed. These algorithms are easy to implement and can achieve an even approximation of (weakly, properly) Pareto optimal solutions. These algorithms can be generalized for optimization problems with more than three criterion functions, too. The effectiveness and capability of the algorithms are demonstrated in test problems.
文摘With the development of cutting-edge multi-object spectrographs,fiber positioners located in the focal plane are being scaled down in size,and miniature hollow-cup Permanent Magnet motors are now being considered as a suitable replacement for Faulhaber Precistep stepper motors.However,the small electrical time constant of such coreless motors poses a challenge,as the problem of severe commutation torque ripple in a fiber positioner running a position loop has been tricky.To overcome this challenge,it is advised to increase the Pulse Width Modulation(PWM)frequency as much as possible to mitigate the effects of the current fluctuation.This must be done while ensuring adequate resolution of the PWM generator.By employing a voltage open-loop field-oriented control based on a modulation frequency of 1 MHz,the drive current only costs 25 m A under a 3.3 V power supply.The sine degree of phase current is immaculate,and the repeat positioning accuracy can reach 2μm.Moreover,it is possible to further shrink the bill of devices and the layout area of the Printed Circuit Board,especially in sizesensitive applications.This device has been developed under the new generation of The Large Sky Area MultiObject Fiber Spectroscopic Telescope.
文摘Professors Mohazzbi and Luo [1] published “Despite several attempts have been made to explain the twin paradox … none of the explanations … resolved the paradox. If the paradox can be ever resolved, it requires a much deeper understanding … of the theory of relativity”. The deeper understanding of resolving the paradox is by applying more explicit definitions of proper time interval, Lorentz transform, time dilation, and aging time.
文摘Correction to:NUCL SCI TECH(2023)34:63 https://doi.org/10.1007/s41365-023-01213-3 While typesetting,reference[16]in the list has not been properly placed in the proof.The orders of the references[13-16]were mistaken by the production.The correct order of the references is.
基金This work was supported by Natural Science Basic Research Program of Shaanxi(Program No.2023-JC-YB-269)the National Natural Science Foundation of China(Grant No.41974122).
文摘The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The boundary value method(BVM),based on the finite difference method(FDM),can be used to reconstruct the source wavefield in the reverse time propagation in the same way as the receiver wavefield,which can reduce the storage burden of the RTM data.Considering that the FDM cannot well handle models with discontinuous material properties and rough interfaces,we develop a source wavefield reconstruction strategy based on the finite element method(FEM),using proper orthogonal decomposition(POD)to enhance computational efficiency.In this method,we divide the whole time period into several segments,and construct the POD basis functions to get a reduced order model(ROM)for the source wavefield reconstruction in each segment.We show the corresponding quantitative analysis of the storage requirement of the POD-FEM.Numerical tests on the homogeneous model show the effectiveness of the proposed method,while the layered model and part of the Marmousi model tests indicate that the POD-FEM can keep an excellent balance between computational efficiency and memory usage compared with the full-stored method(FSM)and the BVM,and can be effectively applied in imaging.
基金supported in part by Heilongjiang Provincial Natural Science Foundation of China under Project TD2021E004in part by Ningbo Science and Technology Bureau under S&T Innovation 2025 Major Special Programme with project code 2019B10071。
文摘With the rapid development of the world economy,IGBT has been widely used in motor drive and electric energy conversion.In order to timely detect the fatigue damage of IGBT,it is necessary to monitor the junction temperature of IGBT.In order to realize the fast calculation of IGBT junction temperature,a finite element method of IGBT temperature field reduction is proposed in this paper.Firstly,the finite element calculation process of IGBT temperature field is introduced and the linear equations of finite element calculation of temperature field are derived.Temperature field data of different working conditions are obtained by finite element simulation to form the sample space.Then the covariance matrix of the sample space is constructed,whose proper orthogonal decomposition and modal extraction are carried out.Reasonable basis vector space is selected to complete the low dimensional expression of temperature vector inside and outside the sample space.Finally,the reduced-order model of temperature field finite element is obtained and solved.The results of the reduced order model are compared with those of the finite element method,and the performance of the reduced-order model is evaluated from two aspects of accuracy and rapidity.
文摘Three recent breakthroughs due to AI in arts and science serve as motivation:An award winning digital image,protein folding,fast matrix multiplication.Many recent developments in artificial neural networks,particularly deep learning(DL),applied and relevant to computational mechanics(solid,fluids,finite-element technology)are reviewed in detail.Both hybrid and pure machine learning(ML)methods are discussed.Hybrid methods combine traditional PDE discretizations with ML methods either(1)to help model complex nonlinear constitutive relations,(2)to nonlinearly reduce the model order for efficient simulation(turbulence),or(3)to accelerate the simulation by predicting certain components in the traditional integration methods.Here,methods(1)and(2)relied on Long-Short-Term Memory(LSTM)architecture,with method(3)relying on convolutional neural networks.Pure ML methods to solve(nonlinear)PDEs are represented by Physics-Informed Neural network(PINN)methods,which could be combined with attention mechanism to address discontinuous solutions.Both LSTM and attention architectures,together with modern and generalized classic optimizers to include stochasticity for DL networks,are extensively reviewed.Kernel machines,including Gaussian processes,are provided to sufficient depth for more advanced works such as shallow networks with infinite width.Not only addressing experts,readers are assumed familiar with computational mechanics,but not with DL,whose concepts and applications are built up from the basics,aiming at bringing first-time learners quickly to the forefront of research.History and limitations of AI are recounted and discussed,with particular attention at pointing out misstatements or misconceptions of the classics,even in well-known references.Positioning and pointing control of a large-deformable beam is given as an example.
文摘The authors of this article are interested in characterization of efficient solutions for special classes of problems. These classes consider semi-strong E-convexity of involved functions. Sufficient and necessary conditions for a feasible solution to be an efficient or properly efficient solution are obtained.
文摘Urinary bladder neural dysfunction (UBND) is a common complication of diabetes mellitus. When urinary bladder paralysis develops, urinary system infection readily occurs. If the infection is not treated properly, serious sequelae will happen. Western doctors primarily use
文摘Facial spasm is a frequently seen dis-ease characterized by unilateral involuntaryirregular twitching of the facial muscles.This disorder may be induced by intoxica-tion,infection,trauma and long-term facialparalysis which was not properly treated.
基金We appreciate the financial support from the International Partnership Program of Chinese Academy of Sciences(122111KYSB20170068).
文摘Whether the goal is to meet global challenges or to enable a paradigm shift,it is always essential for science to move beyond conventional thinking.Moreover,the mutually beneficial interactions between global challenges and paradigm shifts require a great deal of effort.To this end,it is imperative for the scientific community not only to respond to major challenges by shifting paradigms in science but also to drive paradigm shifts in science by responding to major challenges.This aim sets a higher bar for scientists as,in order to achieve it,we must properly identify the scientific questions in research and better utilize existing knowledge.At present,however,we are not paying sufficient attention to this aim,nor are we sufficiently competent in this regard.It is essential for the global scientific community to pay more attention to these interconnected issues of global challenges and paradigm shifts.
基金Supported by the National Natural Science Foundation of China and the Foundation of State Education Commission.
文摘A rigorous spectral representation of relativistic random-phase approximation is presented.Explicit expression is derived for the effective particle-hole interaction which contains the direct term Kan,the exchange term KaQ and the kernel for the fermion line renormalization K_(fr).It is shown that according to our method,not only K_(an) but also K_(sc) and K_(fr) can be given rigorously in a form which depends only on one ω(energy)-variable and they all take account of the retardation effect properly.
文摘Magnesia chrome bricks were prepared with fiLsed MgO- Cr2 O3 synthesized material, fused magnesite and :hrome ore as main starting materials. Nano-Al2O3 was tdded into refractories ( 2% , 4% and 6% in mass ) ;ubstit,ting for Al203 micropowder. After m&ing and ;haping, the bricks were fired at 1 550 ℃, 1 600 91℃, t 650 ℃ and 1 750℃, respectively. The microstruc-ure , sintering property, mechanical properties, thermal ;kock resistance and shtg resistance of the specimens with he addition of nano-Al2O3 were investigated. The results indicate that the performance of brick with 4 mass% of nano-Al2O3 is greatly improred afier firing at 1 650 ℃.