In this paper we investigate the existence of positive solution for a class of fourth_order superlinear semipositone eigenvalue problems. This class of problems usually describes the deformation of the elastic beam wh...In this paper we investigate the existence of positive solution for a class of fourth_order superlinear semipositone eigenvalue problems. This class of problems usually describes the deformation of the elastic beam whose both end_points are fixed.展开更多
The existence of multiple positive solutions for a class of higher order p Laplacian boundary value problem is studied. By means of the Leggett Williams fixed point theorem in cones, existence criteria which e...The existence of multiple positive solutions for a class of higher order p Laplacian boundary value problem is studied. By means of the Leggett Williams fixed point theorem in cones, existence criteria which ensure the existence of at least three positive solutions of the boundary value problem are established.展开更多
In order to establish the baseline finite element model for structural health monitoring,a new method of model updating was proposed after analyzing the uncertainties of measured data and the error of finite element m...In order to establish the baseline finite element model for structural health monitoring,a new method of model updating was proposed after analyzing the uncertainties of measured data and the error of finite element model.In the new method,the finite element model was replaced by the multi-output support vector regression machine(MSVR).The interval variables of the measured frequency were sampled by Latin hypercube sampling method.The samples of frequency were regarded as the inputs of the trained MSVR.The outputs of MSVR were the target values of design parameters.The steel structure of National Aquatic Center for Beijing Olympic Games was introduced as a case for finite element model updating.The results show that the proposed method can avoid solving the problem of complicated calculation.Both the estimated values and associated uncertainties of the structure parameters can be obtained by the method.The static and dynamic characteristics of the updated finite element model are in good agreement with the measured data.展开更多
Based on a barotropic vortex model, generalized energy-conserving equation was derived and twonecessary conditions of basic flow destabilization are gained. These conditions correspond to generalizedbarotropic instabi...Based on a barotropic vortex model, generalized energy-conserving equation was derived and twonecessary conditions of basic flow destabilization are gained. These conditions correspond to generalizedbarotropic instability and super speed instability. They are instabilities of vortex and gravity inertial waverespectively. In order to relate to practical situation, a barotropic vortex was analyzed, the basic flow of which issimilar to lower level basic wind field of tropical cyclones and the maximum wind radius of which is 500 km.The results show that generalized barotropic instability depending upon the radial gradient of relative vorticitycan appear in this vortex. It can be concluded that unstable vortex Rossby wave may appear in barotropic vortex.展开更多
1 INTRODUCTION Of three main methods for studying the radiative forcing of anthropogenic sulfate and climatic response on the regional scale, the first is, with given rates for transforming SO2 to sulfate, converting ...1 INTRODUCTION Of three main methods for studying the radiative forcing of anthropogenic sulfate and climatic response on the regional scale, the first is, with given rates for transforming SO2 to sulfate, converting actually released SO2 into sulfate and acquiring the distribution of sulfate by computing transfer equations in the climate model. The second is obtaining the sulfate distribution through chemical reaction and transfer of matters in regional climate models online coupled with an atmospheric chemistry model that includes full chemical reactions for sulfides. The third is to put sulfate distribution data from GCM and its coupled atmospheric chemistry model to regional climate model, which is so called off-line coupled method. As shown in comparisons between the online and offline modeling on the regional scale, the radiative climate effect of sulfate shows large uncertainty due to significant influence from various methods.展开更多
Recently,inverse problems have attracted more and more attention in computational mathematics and become increasingly important in engineering applications.After the discretization,many of inverse problems are reduced...Recently,inverse problems have attracted more and more attention in computational mathematics and become increasingly important in engineering applications.After the discretization,many of inverse problems are reduced to linear systems.Due to the typical ill-posedness of inverse problems,the reduced linear systems are often illposed,especially when their scales are large.This brings great computational difficulty.Particularly,a small perturbation in the right side of an ill-posed linear system may cause a dramatical change in the solution.Therefore,regularization methods should be adopted for stable solutions.In this paper,a new class of accelerated iterative regularization methods is applied to solve this kind of large-scale ill-posed linear systems.An iterative scheme becomes a regularization method only when the iteration is early terminated.And a Morozov’s discrepancy principle is applied for the stop criterion.Compared with the conventional Landweber iteration,the new methods have acceleration effect,and can be compared to the well-known acceleratedν-method and Nesterov method.From the numerical results,it is observed that using appropriate discretization schemes,the proposed methods even have better behavior when comparing withν-method and Nesterov method.展开更多
The main cause of dynamic errors is due to frequency response limitation of measurement system. One way of solving this problem is designing an effective inverse filter. Since the problem is ill-conditioned, a small u...The main cause of dynamic errors is due to frequency response limitation of measurement system. One way of solving this problem is designing an effective inverse filter. Since the problem is ill-conditioned, a small uncertainty in the measurement will came large deviation in reconstncted signals. The amplified noise has to be suppressed at the sacrifice of biasing in estimation. The paper presents a kind of designing method of inverse filter in frequency domain based on stabilized solutions of Fredholm integral equations of the fast kind in order to reduce dynamic errors. Compared with previous several work, the method has advantage of generalization. Simulations with different Signal-to-Noise ratio （SNR） are investigated. Flexibility of the method is verified. Application of correcting dynamic error is given.展开更多
For the two-dimensional Magnetohydrodynamics(MHD)boundary layer system,it has been shown that the non-degenerate tangential magnetic field leads to the well-posedness in Sobolev spaces and high Reynolds number limits ...For the two-dimensional Magnetohydrodynamics(MHD)boundary layer system,it has been shown that the non-degenerate tangential magnetic field leads to the well-posedness in Sobolev spaces and high Reynolds number limits without any monotonicity condition on the velocity field in our previous works.This paper aims to show that sufficient degeneracy in the tangential magnetic field at a non-degenerate critical point of the tangential velocity field of shear flow indeed yields instability as for the classical Prandtl equations without magnetic field studied by G′erard-Varet and Dormy(2010).This partially shows the necessity of the non-degeneracy in the tangential magnetic field for the stability of the boundary layer of MHD in 2D at least in Sobolev spaces.展开更多
A foremost issue of our time is our response to risks,especially those arising from scientific uncertainty,such as genetically modified organisms(GMOs).In this context,we need to achieve and maintain environmental jus...A foremost issue of our time is our response to risks,especially those arising from scientific uncertainty,such as genetically modified organisms(GMOs).In this context,we need to achieve and maintain environmental justice.This should be based on the corresponding scientific research;essentially,however,it is a kind of social construct.We must maintain a free market mechanism for the development,application,and dissemination of modern technology,including genetically modified biotech and its products.At the same time,the necessary government intervention and legal regulation of the relevant science and technology should be put in place to ensure public safety and the interests of socially disadvantaged groups.展开更多
In this paper,the role of constant optimal forcing(COF) in correcting forecast models was numerically studied using the well-known Lorenz 63 model.The results show that when we only consider model error caused by para...In this paper,the role of constant optimal forcing(COF) in correcting forecast models was numerically studied using the well-known Lorenz 63 model.The results show that when we only consider model error caused by parameter error,which also changes with the development of state variables in a numerical model,the impact of such model error on forecast uncertainties can be offset by superimposing COF on the tendency equations in the numerical model.The COF can also offset the impact of model error caused by stochastic processes.In reality,the forecast results of numerical models are simultaneously influenced by parameter uncertainty and stochastic process as well as their interactions.Our results indicate that COF is also able to significantly offset the impact of such hybrid model error on forecast results.In summary,although the variation in the model error due to physical process is time-dependent,the superimposition of COF on the numerical model is an effective approach to reducing the influence of model error on forecast results.Therefore,the COF method may be an effective approach to correcting numerical models and thus improving the forecast capability of models.展开更多
It is significant to consider the effect of uncertainty of the measured modal parameters on the updated finite element(FE) model,especially for updating the FE model of practical bridges,since the uncertainty of the m...It is significant to consider the effect of uncertainty of the measured modal parameters on the updated finite element(FE) model,especially for updating the FE model of practical bridges,since the uncertainty of the measured modal parameters cannot be ignored owing to the application of output-only identification method and the existence of the measured noise.A reasonable method is to define the objective of the FE model updating as the statistical property of the measured modal parameters obtained by conducting couples of identical modal tests,however,it is usually impossible to implement repeated modal test due to the limit of practical situation and economic reason.In this study,a method based on fuzzy finite element(FFM) was proposed in order to consider the effect of the uncertainty of the measured modal parameters on the updated FE model by using the results of a single modal test.The updating parameters of bridges were deemed as fuzzy variables,and then the fuzzification of objective of the FE model updating was proposed to consider the uncertainty of the measured modal parameters.Finally,the effectiveness of the proposed method was verified by updating the FE model of a practical bridge with the measured modal parameters.展开更多
This paper proposes a new non-intrusive trigonometric polynomial approximation interval method for the dynamic response analysis of nonlinear systems with uncertain-but-bounded parameters and/or initial conditions.Thi...This paper proposes a new non-intrusive trigonometric polynomial approximation interval method for the dynamic response analysis of nonlinear systems with uncertain-but-bounded parameters and/or initial conditions.This method provides tighter solution ranges compared to the existing approximation interval methods.We consider trigonometric approximation polynomials of three types:both cosine and sine functions,the sine function,and the cosine function.Thus,special interval arithmetic for trigonometric function without overestimation can be used to obtain interval results.The interval method using trigonometric approximation polynomials with a cosine functional form exhibits better performance than the existing Taylor interval method and Chebyshev interval method.Finally,two typical numerical examples with nonlinearity are applied to demonstrate the effectiveness of the proposed method.展开更多
A high accuracy experimental system has been established for unsteady open-channel flow.Then 40 experiments were conducted to study the propagating characteristics of unsteady open-channel flow.From the experimental d...A high accuracy experimental system has been established for unsteady open-channel flow.Then 40 experiments were conducted to study the propagating characteristics of unsteady open-channel flow.From the experimental data,the variation law of propagating velocity,wave deformation rate,flow depth of wave peak and bottom,and other parameters were obtained.The experimental results show the followings.1) The propagating velocity of unsteady open-channel flows can be expressed by the sum of flow velocity and micro-amplitude wave velocity at wave peak.2) The waveform of an unsteady flow would deform when it propagates,with the rising stage becoming longer and the falling stage shorter;the deformation rate is a function of distance,period and relative amplitude of discharge.3) The flow depths of wave peak and bottom have a close relationship with the period of the unsteady flow.When the period is short,water depths of wave peak and bottom are both close to those of the average discharge in the condition of uniform flow.For a long period unsteady flow,the water depth of wave peak is close to that of the maximal discharge in the condition of uniform flow,while at the flow wave bottom,it is close to the depth of the minimum discharge in an uniform flow.4) Propagating characteristic of discharge is analogous to that of flow depth for unsteady flow.展开更多
We prove the so-called Unitary Hyperbolicity Theorem,a result on hyperbolicity of unitary involutions.The analogous previously known results for the orthogonal and symplectic involutions are formal consequences of the...We prove the so-called Unitary Hyperbolicity Theorem,a result on hyperbolicity of unitary involutions.The analogous previously known results for the orthogonal and symplectic involutions are formal consequences of the unitary one.While the original proofs in the orthogonal and symplectic cases were based on the incompressibility of generalized Severi-Brauer varieties,the proof in the unitary case is based on the incompressibility of their Weil transfers.展开更多
We prove that any abelian cover over a smooth variety is defined by some cyclic equations. From the defining equations, we compute explicitly the normalization, branch locus, ramification indices, global invariants, a...We prove that any abelian cover over a smooth variety is defined by some cyclic equations. From the defining equations, we compute explicitly the normalization, branch locus, ramification indices, global invariants, and the resolution of singularities. As an application, we construct a new algebraic surface which is the quotient of ball.展开更多
When there is uncertainty in sibling relationship,the classical affected sib-pair(ASP) linkage tests may be severely biased.This can happen,for example,if some of the half sib-pairs are mixed with full sib-pairs.The g...When there is uncertainty in sibling relationship,the classical affected sib-pair(ASP) linkage tests may be severely biased.This can happen,for example,if some of the half sib-pairs are mixed with full sib-pairs.The genomic control method has been used in association analysis to adjust for population structures.We show that the same idea can be applied to ASP linkage analysis with uncertainty in sibling relationship.Assuming that,in addition to the candidate marker,null markers that are unlinked to the disease locus are also genotyped,we may use the information on these loci to estimate the proportion of half sib-pairs and to correct for the bias and variance distortion caused by the heterogeneity of sibling relationship.Unlike in association studies,the null loci are not required to be matched with the candidate marker in allele frequency for ASP linkage analysis.This makes our approach flexible in selecting null markers.In our simulations,using a number of 30 or more null loci can effectively remove the bias and variance distortion.It is also shown that,even the null loci are weakly linked to the disease locus,the proposed method can also provide satisfactory correction.展开更多
Speed-adaptive full-order flux observer is the most promising flux estimator among all the sensorless control method.However,conventional speed-adaptive flux observer becomes unstable during regenerating operation at ...Speed-adaptive full-order flux observer is the most promising flux estimator among all the sensorless control method.However,conventional speed-adaptive flux observer becomes unstable during regenerating operation at low speed since induction motor is an observable system except dc excitation.Thus,the instability problem is caused by inappropriate designing of observer.Based on the eigenvalues of extended observer,this paper interprets unstable situation,that the eigenvalues of extended ob-server have a positive real part.Therefore,the observer cannot converge.Against the two different solutions for unstable prob-lem-positive real maintaining and current error augment,the proposed method based on the eigenvalue could unify these two solutions,which gives the complete stability condition for speed-adaptive full-order observer.It does a lot help in observer de-signing.The observer configured by this proposed method was verified in the torque controlling of 20 kW induction motor.According to the experiment result,with appropriate designing of observer,the unstable situation during regeneration mode could be completely overcome.展开更多
This paper is concerned with a host-macroparasite difference model. By applying the con- traction mapping fixed point theorem, we prove the existence of unique almost periodic positive solution. Moreover, we investiga...This paper is concerned with a host-macroparasite difference model. By applying the con- traction mapping fixed point theorem, we prove the existence of unique almost periodic positive solution. Moreover, we investigate the exponential stability of Mmost periodic solution by means of Lyapunov functional.展开更多
This paper is concerned with impulsive Nicholson＇s blowflies model with linear harvesting term. By using contraction mapping fixed point theorem, we obtain sufficient conditions for the existence of unique almost per...This paper is concerned with impulsive Nicholson＇s blowflies model with linear harvesting term. By using contraction mapping fixed point theorem, we obtain sufficient conditions for the existence of unique almost periodic positive solution. Moreover, we investigate exponential convergence of the almost periodic positive solution by Lyapunov functional.展开更多
文摘In this paper we investigate the existence of positive solution for a class of fourth_order superlinear semipositone eigenvalue problems. This class of problems usually describes the deformation of the elastic beam whose both end_points are fixed.
文摘The existence of multiple positive solutions for a class of higher order p Laplacian boundary value problem is studied. By means of the Leggett Williams fixed point theorem in cones, existence criteria which ensure the existence of at least three positive solutions of the boundary value problem are established.
基金Project(50678052) supported by the National Natural Science Foundation of China
文摘In order to establish the baseline finite element model for structural health monitoring,a new method of model updating was proposed after analyzing the uncertainties of measured data and the error of finite element model.In the new method,the finite element model was replaced by the multi-output support vector regression machine(MSVR).The interval variables of the measured frequency were sampled by Latin hypercube sampling method.The samples of frequency were regarded as the inputs of the trained MSVR.The outputs of MSVR were the target values of design parameters.The steel structure of National Aquatic Center for Beijing Olympic Games was introduced as a case for finite element model updating.The results show that the proposed method can avoid solving the problem of complicated calculation.Both the estimated values and associated uncertainties of the structure parameters can be obtained by the method.The static and dynamic characteristics of the updated finite element model are in good agreement with the measured data.
基金Research on wave spectrum of Meso-beta-scale system and its application in severe weatherforecast, a project from National Natural Science Foundation of China (40575023)
文摘Based on a barotropic vortex model, generalized energy-conserving equation was derived and twonecessary conditions of basic flow destabilization are gained. These conditions correspond to generalizedbarotropic instability and super speed instability. They are instabilities of vortex and gravity inertial waverespectively. In order to relate to practical situation, a barotropic vortex was analyzed, the basic flow of which issimilar to lower level basic wind field of tropical cyclones and the maximum wind radius of which is 500 km.The results show that generalized barotropic instability depending upon the radial gradient of relative vorticitycan appear in this vortex. It can be concluded that unstable vortex Rossby wave may appear in barotropic vortex.
基金Natural Science Foundation of China (40205016)Natural Science Foundation of YunnanProvince (2005D0006M)Science Foundation for Post-Ph.D. in China (2004036295)
文摘1 INTRODUCTION Of three main methods for studying the radiative forcing of anthropogenic sulfate and climatic response on the regional scale, the first is, with given rates for transforming SO2 to sulfate, converting actually released SO2 into sulfate and acquiring the distribution of sulfate by computing transfer equations in the climate model. The second is obtaining the sulfate distribution through chemical reaction and transfer of matters in regional climate models online coupled with an atmospheric chemistry model that includes full chemical reactions for sulfides. The third is to put sulfate distribution data from GCM and its coupled atmospheric chemistry model to regional climate model, which is so called off-line coupled method. As shown in comparisons between the online and offline modeling on the regional scale, the radiative climate effect of sulfate shows large uncertainty due to significant influence from various methods.
基金supported by the Natural Science Foundation of China (Nos. 11971230, 12071215)the Fundamental Research Funds for the Central Universities(No. NS2018047)the 2019 Graduate Innovation Base(Laboratory)Open Fund of Jiangsu Province(No. Kfjj20190804)
文摘Recently,inverse problems have attracted more and more attention in computational mathematics and become increasingly important in engineering applications.After the discretization,many of inverse problems are reduced to linear systems.Due to the typical ill-posedness of inverse problems,the reduced linear systems are often illposed,especially when their scales are large.This brings great computational difficulty.Particularly,a small perturbation in the right side of an ill-posed linear system may cause a dramatical change in the solution.Therefore,regularization methods should be adopted for stable solutions.In this paper,a new class of accelerated iterative regularization methods is applied to solve this kind of large-scale ill-posed linear systems.An iterative scheme becomes a regularization method only when the iteration is early terminated.And a Morozov’s discrepancy principle is applied for the stop criterion.Compared with the conventional Landweber iteration,the new methods have acceleration effect,and can be compared to the well-known acceleratedν-method and Nesterov method.From the numerical results,it is observed that using appropriate discretization schemes,the proposed methods even have better behavior when comparing withν-method and Nesterov method.
基金The paper is sponsored by National Natural Science Foundation of China(No.50675211)Natural Science Foundation(No.2009011023)Returned Overseas Graduates Foundation(No.2008067) of Shanxi Provincein China
文摘The main cause of dynamic errors is due to frequency response limitation of measurement system. One way of solving this problem is designing an effective inverse filter. Since the problem is ill-conditioned, a small uncertainty in the measurement will came large deviation in reconstncted signals. The amplified noise has to be suppressed at the sacrifice of biasing in estimation. The paper presents a kind of designing method of inverse filter in frequency domain based on stabilized solutions of Fredholm integral equations of the fast kind in order to reduce dynamic errors. Compared with previous several work, the method has advantage of generalization. Simulations with different Signal-to-Noise ratio （SNR） are investigated. Flexibility of the method is verified. Application of correcting dynamic error is given.
基金supported by National Natural Science Foundation of China (Grant No. 11743009)Shanghai Sailing Program (Grant No. 18YF1411700)+2 种基金Shanghai Jiao Tong University (Grant No. WF220441906)Feng Xie’s research was supported by National Natural Science Foundation of China (Grant No.11571231)Tong Yang’s research was supported by the General Research Fund of Hong Kong, City University of Hong Kong (Grant No.103713)
文摘For the two-dimensional Magnetohydrodynamics(MHD)boundary layer system,it has been shown that the non-degenerate tangential magnetic field leads to the well-posedness in Sobolev spaces and high Reynolds number limits without any monotonicity condition on the velocity field in our previous works.This paper aims to show that sufficient degeneracy in the tangential magnetic field at a non-degenerate critical point of the tangential velocity field of shear flow indeed yields instability as for the classical Prandtl equations without magnetic field studied by G′erard-Varet and Dormy(2010).This partially shows the necessity of the non-degeneracy in the tangential magnetic field for the stability of the boundary layer of MHD in 2D at least in Sobolev spaces.
文摘A foremost issue of our time is our response to risks,especially those arising from scientific uncertainty,such as genetically modified organisms(GMOs).In this context,we need to achieve and maintain environmental justice.This should be based on the corresponding scientific research;essentially,however,it is a kind of social construct.We must maintain a free market mechanism for the development,application,and dissemination of modern technology,including genetically modified biotech and its products.At the same time,the necessary government intervention and legal regulation of the relevant science and technology should be put in place to ensure public safety and the interests of socially disadvantaged groups.
基金sponsored by the National Basic Research Program of China(Grant No.2012CB955202)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX2-YW-QN203)the National Natural Science Foundation of China(Grant No.41176013)
文摘In this paper,the role of constant optimal forcing(COF) in correcting forecast models was numerically studied using the well-known Lorenz 63 model.The results show that when we only consider model error caused by parameter error,which also changes with the development of state variables in a numerical model,the impact of such model error on forecast uncertainties can be offset by superimposing COF on the tendency equations in the numerical model.The COF can also offset the impact of model error caused by stochastic processes.In reality,the forecast results of numerical models are simultaneously influenced by parameter uncertainty and stochastic process as well as their interactions.Our results indicate that COF is also able to significantly offset the impact of such hybrid model error on forecast results.In summary,although the variation in the model error due to physical process is time-dependent,the superimposition of COF on the numerical model is an effective approach to reducing the influence of model error on forecast results.Therefore,the COF method may be an effective approach to correcting numerical models and thus improving the forecast capability of models.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51008097 and 11172078)the National Key Technology R&D Program (Grant No. 2011BAK02B02)
文摘It is significant to consider the effect of uncertainty of the measured modal parameters on the updated finite element(FE) model,especially for updating the FE model of practical bridges,since the uncertainty of the measured modal parameters cannot be ignored owing to the application of output-only identification method and the existence of the measured noise.A reasonable method is to define the objective of the FE model updating as the statistical property of the measured modal parameters obtained by conducting couples of identical modal tests,however,it is usually impossible to implement repeated modal test due to the limit of practical situation and economic reason.In this study,a method based on fuzzy finite element(FFM) was proposed in order to consider the effect of the uncertainty of the measured modal parameters on the updated FE model by using the results of a single modal test.The updating parameters of bridges were deemed as fuzzy variables,and then the fuzzification of objective of the FE model updating was proposed to consider the uncertainty of the measured modal parameters.Finally,the effectiveness of the proposed method was verified by updating the FE model of a practical bridge with the measured modal parameters.
文摘This paper proposes a new non-intrusive trigonometric polynomial approximation interval method for the dynamic response analysis of nonlinear systems with uncertain-but-bounded parameters and/or initial conditions.This method provides tighter solution ranges compared to the existing approximation interval methods.We consider trigonometric approximation polynomials of three types:both cosine and sine functions,the sine function,and the cosine function.Thus,special interval arithmetic for trigonometric function without overestimation can be used to obtain interval results.The interval method using trigonometric approximation polynomials with a cosine functional form exhibits better performance than the existing Taylor interval method and Chebyshev interval method.Finally,two typical numerical examples with nonlinearity are applied to demonstrate the effectiveness of the proposed method.
基金supported by the National Key Technology R & D Programof China (Grant No. 2011BAB09B01)the Chongqing Natural Science Foundation of China (Grant No. cstc2011jjA1167)
文摘A high accuracy experimental system has been established for unsteady open-channel flow.Then 40 experiments were conducted to study the propagating characteristics of unsteady open-channel flow.From the experimental data,the variation law of propagating velocity,wave deformation rate,flow depth of wave peak and bottom,and other parameters were obtained.The experimental results show the followings.1) The propagating velocity of unsteady open-channel flows can be expressed by the sum of flow velocity and micro-amplitude wave velocity at wave peak.2) The waveform of an unsteady flow would deform when it propagates,with the rising stage becoming longer and the falling stage shorter;the deformation rate is a function of distance,period and relative amplitude of discharge.3) The flow depths of wave peak and bottom have a close relationship with the period of the unsteady flow.When the period is short,water depths of wave peak and bottom are both close to those of the average discharge in the condition of uniform flow.For a long period unsteady flow,the water depth of wave peak is close to that of the maximal discharge in the condition of uniform flow,while at the flow wave bottom,it is close to the depth of the minimum discharge in an uniform flow.4) Propagating characteristic of discharge is analogous to that of flow depth for unsteady flow.
文摘We prove the so-called Unitary Hyperbolicity Theorem,a result on hyperbolicity of unitary involutions.The analogous previously known results for the orthogonal and symplectic involutions are formal consequences of the unitary one.While the original proofs in the orthogonal and symplectic cases were based on the incompressibility of generalized Severi-Brauer varieties,the proof in the unitary case is based on the incompressibility of their Weil transfers.
基金supported by National Natural Science Foundation of China (Grant No.10731030)the Innovation Program of Shanghai Municipal Education Commission (Grant No. 11ZZ18)
文摘We prove that any abelian cover over a smooth variety is defined by some cyclic equations. From the defining equations, we compute explicitly the normalization, branch locus, ramification indices, global invariants, and the resolution of singularities. As an application, we construct a new algebraic surface which is the quotient of ball.
基金supported by National Natural Science Foundation of China(Grant No. 10971210)China Postdoctoral Science Foundation (Grant No. 20110490824)
文摘When there is uncertainty in sibling relationship,the classical affected sib-pair(ASP) linkage tests may be severely biased.This can happen,for example,if some of the half sib-pairs are mixed with full sib-pairs.The genomic control method has been used in association analysis to adjust for population structures.We show that the same idea can be applied to ASP linkage analysis with uncertainty in sibling relationship.Assuming that,in addition to the candidate marker,null markers that are unlinked to the disease locus are also genotyped,we may use the information on these loci to estimate the proportion of half sib-pairs and to correct for the bias and variance distortion caused by the heterogeneity of sibling relationship.Unlike in association studies,the null loci are not required to be matched with the candidate marker in allele frequency for ASP linkage analysis.This makes our approach flexible in selecting null markers.In our simulations,using a number of 30 or more null loci can effectively remove the bias and variance distortion.It is also shown that,even the null loci are weakly linked to the disease locus,the proposed method can also provide satisfactory correction.
文摘Speed-adaptive full-order flux observer is the most promising flux estimator among all the sensorless control method.However,conventional speed-adaptive flux observer becomes unstable during regenerating operation at low speed since induction motor is an observable system except dc excitation.Thus,the instability problem is caused by inappropriate designing of observer.Based on the eigenvalues of extended observer,this paper interprets unstable situation,that the eigenvalues of extended ob-server have a positive real part.Therefore,the observer cannot converge.Against the two different solutions for unstable prob-lem-positive real maintaining and current error augment,the proposed method based on the eigenvalue could unify these two solutions,which gives the complete stability condition for speed-adaptive full-order observer.It does a lot help in observer de-signing.The observer configured by this proposed method was verified in the torque controlling of 20 kW induction motor.According to the experiment result,with appropriate designing of observer,the unstable situation during regeneration mode could be completely overcome.
基金The author thanks the referees for their valuable comments and suggestions in improving the presentation of the manuscript. This work is supported by Natural Science Foundation of Education Department of Anhui Province （KJ2014A043）.
文摘This paper is concerned with a host-macroparasite difference model. By applying the con- traction mapping fixed point theorem, we prove the existence of unique almost periodic positive solution. Moreover, we investigate the exponential stability of Mmost periodic solution by means of Lyapunov functional.
基金The author thanks the referees for their valuable comments and suggestions in improving the presentation of the paper. This work is supported by Natural Science Foundation of Education Department of Anhui Province （KJ2014A043）.
文摘This paper is concerned with impulsive Nicholson＇s blowflies model with linear harvesting term. By using contraction mapping fixed point theorem, we obtain sufficient conditions for the existence of unique almost periodic positive solution. Moreover, we investigate exponential convergence of the almost periodic positive solution by Lyapunov functional.
