In this paper,an uncertainty propagation analysis method is developed based on an extended sparse grid technique and maximum entropy principle,aiming at improving the solving accuracy of the high-order moments and hen...In this paper,an uncertainty propagation analysis method is developed based on an extended sparse grid technique and maximum entropy principle,aiming at improving the solving accuracy of the high-order moments and hence the fitting accuracy of the probability density function(PDF)of the system response.The proposed method incorporates the extended Gauss integration into the uncertainty propagation analysis.Moreover,assisted by the Rosenblatt transformation,the various types of extended integration points are transformed into the extended Gauss-Hermite integration points,which makes the method suitable for any type of continuous distribution.Subsequently,within the sparse grid numerical integration framework,the statistical moments of the system response are obtained based on the transformed points.Furthermore,based on the maximum entropy principle,the obtained first four-order statistical moments are used to fit the PDF of the system response.Finally,three numerical examples are investigated to demonstrate the effectiveness of the proposed method,which includes two mathematical problems with explicit expressions and an engineering application with a black-box model.展开更多
Pancreatic head adenocarcinoma (PHAC) is one of the most aggressive malignancies, and it has low long-term survival rates. Surgery is the only option for long-term survival. The difficulties associated with PHAC inclu...Pancreatic head adenocarcinoma (PHAC) is one of the most aggressive malignancies, and it has low long-term survival rates. Surgery is the only option for long-term survival. The difficulties associated with PHAC include higher frequencies of regional or distant lymph node metastases and vascular involvement, and positive resection margins in pancreatic and retroperitoneal tissues. Radical resections increase margin negativity and life expectancy;however, the extend of the surgery applied is controversial. Thus, western and eastern centers may use different approaches. Multiorgan, peripancreatic nerve plexus, and vascular resections have been discussed in relation to radical surgery for pancreatic cancer as have the roles of neoadjuvant and adjuvant therapy regimens. Determining the appropriate limits for surgery, standardizing definitions and surgical techniques according to guidelines, and centralizing pancreatic surgery within high-volume institutions to reduce mortality and morbidity rates are among the most important issues to consider. In this review, we evaluate the basic concepts underlying and the roles of radical surgery for PHAC, and lymphadenectomy, nerve plexus, retroperitoneal tissue, vascular, and multivisceral resections, total pancreatectomy, and liver metastases are discussed.展开更多
An extended electron model fully recovers many of the experimental results of quantum mechanics while it avoids many of the pitfalls and remains generally free of paradoxes. The formulation of the manybody electronic ...An extended electron model fully recovers many of the experimental results of quantum mechanics while it avoids many of the pitfalls and remains generally free of paradoxes. The formulation of the manybody electronic problem here resembles the Kohn Sham formulation of standard density functional theory. However, rather than referring electronic properties to a large set of single electron orbitals, the extended electron model uses only mass density and field components, leading to a substantial increase in computational efficiency. To date, the Hohenberg-Kohn theorems have not been proved for a model of this type, nor has a universal energy functional been presented. In this paper, we address these problems and show that the Hohenberg Kohn theorems do also hold for a density model of this type. We then present a proof^of^concept practical implementation of this method and show that it reproduces the accuracy of more widely used methods on a test-set of small atomic systems, thus paving the way for the development of fast, efficient and accurate codes on this basis.展开更多
Let R be a prime ring with center Z(R), I a nonzero ideal of R, d a nonzero derivation of R and 0≠ a ∈ R. In the present paper, our object is to study the situation a[d(xk);xk]n ∈Z(R) for all x∈I under certain con...Let R be a prime ring with center Z(R), I a nonzero ideal of R, d a nonzero derivation of R and 0≠ a ∈ R. In the present paper, our object is to study the situation a[d(xk);xk]n ∈Z(R) for all x∈I under certain conditions, where n (≥ 1), k (≥ 1) are fixed integers.展开更多
Evolutionary testing (ET) is an effective test case generation technique which uses some meta-heuristic search algorithm, especially genetic algorithm, to generate test case automatically. However, the population prem...Evolutionary testing (ET) is an effective test case generation technique which uses some meta-heuristic search algorithm, especially genetic algorithm, to generate test case automatically. However, the population prematurity problem may decrease the performance of ET. In this paper, a hybrid optimization strategy is proposed based on extended cataclysm which integrates both static configuration strategies and dynamic optimization strategy. Dynamic optimization strategy included the optimization of initial population and the dynamic population optimization based on extended cataclysm, where the diversity of population was monitored during the evolution process of ET, and once the population prematurity was detected, extended cataclysm operation was used to renew the diversity of the population. Experimental results show that the hybrid optimization strategy can improve the performance of ET.展开更多
In this paper,the bidirectional SK-Ramani equation is investigated by means of the extended homoclinic test approach and Riemann theta function method,respectively.Based on the Hirota bilinear method,exact solutions i...In this paper,the bidirectional SK-Ramani equation is investigated by means of the extended homoclinic test approach and Riemann theta function method,respectively.Based on the Hirota bilinear method,exact solutions including one-soliton wave solution are obtained by using the extended homoclinic approach and one-periodic wave solution is constructed by using the Riemann theta function method.A limiting procedure is presented to analyze in detail the relations between the one periodic wave solution and one-soliton solution.展开更多
Performing repeatable duties automatically was the dreams of human being for centuries. Although full autonomy has long been dreamed of by visionaries, many researches have been performed for surface vehicles automati...Performing repeatable duties automatically was the dreams of human being for centuries. Although full autonomy has long been dreamed of by visionaries, many researches have been performed for surface vehicles automation since the last century to get close to this dream stepwise. To increase daily working hours and accuracy and reduce cost, operations such as hydrography are susceptible for autonomy. Beside platform topology, installed sensors and energy resources, the core elements of any autonomous surface vehicle are navigation, guidance and control systems. To perform bathymetry operation in autonomy manner, a reliable and robust navigation algorithm is designed and embedded in an autonomous surface vehicle titled Morvarid. Morvarid is a plug-in hybrid solar powered catamaran boat. The developed algorithm is a combination of extended Kalman filter, search ball and potential field approaches. Many experimental field tests are carried out after simulation in Simulink environment. Test results illustrated the algorithm and improved the path followed by reducing SD and RMSE and there is a good correlation between simulation run and experimental tests.展开更多
In this study we mainly focus on the attitude control problem of a quad tilt rotor aircraft with respect to unknown external disturbance. We propose a class of control methods based on a novel logarithmic fast non sin...In this study we mainly focus on the attitude control problem of a quad tilt rotor aircraft with respect to unknown external disturbance. We propose a class of control methods based on a novel logarithmic fast non singular terminal sliding surface a new fast reaching law and extended state disturbance observer. A logarithmic non singular terminal sliding surface is used owing to its convergence in finite time and significant robustness. A fast reaching law with two order characteristics of the sliding mode is designed. This reaching law can be used reduce the convergence time of traditional reaching law. In addition the extended state disturbance observer is utilized for online estimation and to compensate for system disturbance. The simulation experiment results show that the control strategy proposed in this paper outperforms the traditional non singular fast sliding mode control.展开更多
This paper proposes a model-based prognostics method that couples the Extended Kalman Filter(EKF) and a new developed linearization method. The proposed prognostics method is developed in the context of fatigue crack ...This paper proposes a model-based prognostics method that couples the Extended Kalman Filter(EKF) and a new developed linearization method. The proposed prognostics method is developed in the context of fatigue crack propagation in fuselage panels where the model parameters are unknown and the crack propagation is affected by different types of uncertainties. The coupled method is composed of two steps. The first step employs EKF to estimate the unknown model parameters and the current damage state. In the second step, the proposed efficient linearization method is applied to compute analytically the statistical distribution of the damage evolution path in some future time. A numerical case study is implemented to evaluate the performance of the proposed method. The results show that the coupled EKF-linearization method provides satisfactory results: the EKF algorithm well identifies the model parameters, and the linearization method gives comparable prediction results to Monte Carlo(MC) method while leading to very significant computational cost saving. The proposed prognostics method for fatigue crack growth can be used for developing predictive maintenance strategy for an aircraft fleet, in which case, the computational cost saving is significantly meaningful.展开更多
In this paper,the attitude tracking control problem for a rigid spacecraft in the presence of system parameter uncertainties and external disturbances is addressed.First,a new nonsingular finite-time sliding surface i...In this paper,the attitude tracking control problem for a rigid spacecraft in the presence of system parameter uncertainties and external disturbances is addressed.First,a new nonsingular finite-time sliding surface is introduced and third-order sliding mode finite-time attitude control law is designed to achieve precise accurate tracking responses and robustness against inertia uncertainties and external disturbances.The stability of the closed-loop system is rigorously proved using the Lyapunov stability theory.Then,a new finite-time extended state observer is established to estimate total disturbances of the system.The extended stated observer-based sliding mode control technique yields improved disturbance rejection and high-precision attitude tracking.Moreover,this control law can avoid the unwinding phenomenon and overcome the input saturation constraint by introducing an auxiliary variable to compensate for the overshooting.A Lyapunov based analysis is provided to guarantee sufficiently small observation error and stabilization of the closed-loop system in finite time.Numerical simulations are conducted to verify the effectiveness of the proposed control method.展开更多
Based on the ABAQUS platform for finite element analysis, the extended finite element method (XFEM) considering elastoplastic constitutive relationship is developed, by which the displacement discontinuity across the ...Based on the ABAQUS platform for finite element analysis, the extended finite element method (XFEM) considering elastoplastic constitutive relationship is developed, by which the displacement discontinuity across the crack surface and the strong nonlinearity near the crack tip can be described more accurately. The strip specimens with unilateral cracks and central cracks under uniaxial tension are simulated using the XFEM and the FEM, respectively. The J-integral across the crack on each incremen t is calcula ted using the equivale nt domain integral met hod (EDIM), the interaction integral met hod and the FEM, respectively. The effec ts of mesh size and mesh shape near the crack tip, element type and different calculation methods on the accuracy of J-integral are analyzed. The simulation results show that the XFEM is more accurate than the FEM with the same element size and type. The fracture tests of cast iron specimens with unilateral cracks under uniaxial tension are performed, and the J-integral criterion is valid to predict the fracture initiation in numerical simulation. The critical value of J-integral is calculated using the EDIM of the XFEM. The comparisons demonstrate that the simulated elastoplastic load-displacement curves with the XFEM are in good agreement with the experimental results.展开更多
The scattering characteristics of the periodic surface of infinite and finite media are investigated in detail.The Fourier expression of the scattering field of the periodic surface is obtained in terms of Huygens’ s...The scattering characteristics of the periodic surface of infinite and finite media are investigated in detail.The Fourier expression of the scattering field of the periodic surface is obtained in terms of Huygens’ s principle and Floquet’s theorem.Using the extended boundary condition method(EBCM) and T-matrix method, the scattering amplitude factor is solved,and the correctness of the algorithm is verified by use of the law of conservation of energy.The scattering cross section of the periodic surface in the infinitely long region is derived by improving the scattering cross section of the finite period surface.Furthermore, the effects of the incident wave parameters and the geometric structure parameters on the scattering of the periodic surface are analyzed and discussed.By reasonable approximation, the scattering calculation methods of infinite and finite long surfaces are unified.Besides, numerical results show that the dielectric constant of the periodic dielectric surface has a significant effect on the scattering rate and transmittance.The period and amplitude of the surface determine the number of scattering intensity peaks, and, together with the incident angle, influence the scattering intensity distribution.展开更多
Background: Central hepatectomy(CH) is more difficult than extended hepatectomy(EH) and is associated with greater morbidity. In this modern era of liver management with aims to prevent posthepatectomy liver failure(P...Background: Central hepatectomy(CH) is more difficult than extended hepatectomy(EH) and is associated with greater morbidity. In this modern era of liver management with aims to prevent posthepatectomy liver failure(PHLF), there is a need to assess outcomes of CH as a parenchyma-sparing procedure for centrally located liver tumors. Methods: A total of 178 major liver resections performed by specialist surgeons from two Australian tertiary institutions between June 2009 and March 2017 were reviewed. Eleven patients had CH and 24 had EH over this study period. Indications and perioperative outcomes were compared between the groups. Results: The main indication for performing CH was colorectal liver metastases. There was no perioperative mortality in the CH group and four(16.7%) in the EH group( P = 0.285). No group differences were found in median operative time [CH vs. EH: 450 min(290–840) vs. 523 min(310–860), P = 0.328], intraoperative blood loss [850 mL(40 0–150 0) vs. 650 mL(10 0–20 0 0), P = 0.746] or patients requiring intraoperative blood transfusion [1(9.1%) vs. 7(30.4%), P = 0.227]. There was a trend towards fewer hepatectomyspecific complications in the CH group [3(27.3%) vs. 13(54.2%), P = 0.167], including PHLF(CH vs. EH: 0 vs. 29.2%, P = 0.072). Median length of stay was similar between groups [CH vs. EH: 9 days(5–23) vs. 12 days(4–85), P = 0.244]. Conclusions: CH has equivalent postoperative outcomes to EH. There is a trend towards fewer hepatectomy-specific complications, including PHLF. In appropriate patients, CH may be considered as a safe parenchyma-sparing alternative to EH.展开更多
An extended Nambu-Jona-Lasinio(eNJL) model with nucleons as the degrees of freedom is used to investigate properties of nuclear matter and neutron stars(NSs),including the binding energy and symmetry energy of the nuc...An extended Nambu-Jona-Lasinio(eNJL) model with nucleons as the degrees of freedom is used to investigate properties of nuclear matter and neutron stars(NSs),including the binding energy and symmetry energy of the nuclear matter, the core-crust transition density, and mass-radius relation of NSs. The fourth-order symmetry energy at saturation density is also investigated. When the bulk properties of nuclear matter at saturation density are used to determine the model parameters, the double solutions of parameters are obtained for a given nuclear incompressibility. It is shown that the isovector-vector interaction has a significant influence on the nuclear matter and NS properties, and the sign of isovector-vector coupling constant is critical in the determination of the trend of the symmetry energy and equation of state. The effects of the other model parameters and symmetry energy slope at saturation density are discussed.展开更多
In this paper, a robust finite-time tracking control scheme is proposed for wheeled mobile robots with parametric uncertainties and disturbances. To eliminate the effect of lumped uncertainties,a nonlinear extended st...In this paper, a robust finite-time tracking control scheme is proposed for wheeled mobile robots with parametric uncertainties and disturbances. To eliminate the effect of lumped uncertainties,a nonlinear extended state observer(NESO) is employed to estimate the unknown states as well as uncertainties, and the corresponding coefficients are tuned via pole placement technique. Based on the observation values, the finite-time sliding mode controller is presented to guarantee that both the sliding mode variables and tracking errors converge to zero within finite time. Simulation results are given to demonstrate the effectiveness of the proposed control method.展开更多
The defects and electrical properties in Al-implanted 4 H-SiC after activation annealing(1600℃-1800℃) are investigated. High temperature annealing can reduce the ion implantation-induced damage effectively, but it m...The defects and electrical properties in Al-implanted 4 H-SiC after activation annealing(1600℃-1800℃) are investigated. High temperature annealing can reduce the ion implantation-induced damage effectively, but it may induce extended defects as well, which are investigated by using Rutherford backscattering spectroscopy(RBS/C), secondary ion mass spectroscopy(SIMS), and transmission electron microscopy(TEM) analyses. According to the ratio of the channeled intensity to the random intensity in the region just below the surface scattering peak(Xmin) and RBS/C analysis results, the ion implantation-induced surface damages can be effectively reduced by annealing at temperatures higher than 1700℃,while the defects near the bottom of the ion-implanted layer cannot be completely annealed out by high temperature and long time annealing process, which is also demonstrated by SIMS and TEM analyses. Referring to the defect model and TEM analyses, an optimized annealing condition can be achieved through balancing the generation and elimination of carbon vacancies in the ion implanted layers. Furthermore, the electrical and surface properties are also analyzed, and the hole concentration, mobility, and resistivity are obtained through the Hall effect. The optimized activation annealing conditions of 1800℃/5 min are achieved, under which the lower defects and acceptable electrical properties are obtained.展开更多
The attitude stability control of under actuated spacecraft that used two reaction wheels in the presence of dynamic friction disturbance is handled. A novel improved control approach with a combination of a singular ...The attitude stability control of under actuated spacecraft that used two reaction wheels in the presence of dynamic friction disturbance is handled. A novel improved control approach with a combination of a singular control law based on quaternion and extended state observer (ESO) is employed to establish a stabilization control so as to restrain the effect of friction. The corresponding simulation results demonstrate the highly stable accuracy and performance compensated dynamic friction. Furthermore if there is a non zero initial condition in under actuated axis the attitude stability can be enhanced with a magnetic torquer. Simulations for a nano spacecraft denote a potential application value in pointing accuracy using two reaction wheels and a magnetic torquer.展开更多
The key challenge of the extended target probability hypothesis density (ET-PHD) filter is to reduce the computational complexity by using a subset to approximate the full set of partitions. In this paper, the influen...The key challenge of the extended target probability hypothesis density (ET-PHD) filter is to reduce the computational complexity by using a subset to approximate the full set of partitions. In this paper, the influence for the tracking results of different partitions is analyzed, and the form of the most informative partition is obtained. Then, a fast density peak-based clustering (FDPC) partitioning algorithm is applied to the measurement set partitioning. Since only one partition of the measurement set is used, the ET-PHD filter based on FDPC partitioning has lower computational complexity than the other ET-PHD filters. As FDPC partitioning is able to remove the spatially close clutter-generated measurements, the ET-PHD filter based on FDPC partitioning has good tracking performance in the scenario with more clutter-generated measurements. The simulation results show that the proposed algorithm can get the most informative partition and obviously reduce computational burden without losing tracking performance. As the number of clutter-generated measurements increased, the ET-PHD filter based on FDPC partitioning has better tracking performance than other ET-PHD filters. The FDPC algorithm will play an important role in the engineering realization of the multiple extended target tracking filter.展开更多
We consider a holographic extended phase space in the presence of Reissner-Nordstrom-Anti-de Sitter(RNAdS) and Born-Infeld-Anti-de Sitter(BI-AdS) black holes in the bulk. In this extended phase space the cosmological ...We consider a holographic extended phase space in the presence of Reissner-Nordstrom-Anti-de Sitter(RNAdS) and Born-Infeld-Anti-de Sitter(BI-AdS) black holes in the bulk. In this extended phase space the cosmological constant is investigated as pressure and volume is defined as the codimension one-time slice in the bulk geometry enclosed by the minimal area appearing in the computation of the holographic entanglement entropy. These thermodynamics quantities can serve as probes of the underlying phase transition dictated by black hole thermodynamics, but do not describe different structures. We find that the isocharges on the pressure-volume plane exhibit a Van der Waals-like structure, for RN-AdS black holes in the background. For BI-AdS black holes, we observe the analogy with a Van der Waals liquid-gas system for βQ > 1/2 and Reentrant phase transition for βQ < 1/2 in the holographic extended phase space. The same holographic thermodynamic behavior is observed when we use the fidelity susceptibility as the volume and the cosmological constant as the pressure for RN-AdS black hole in the background.展开更多
A simple repairable system with one repairman is considered. As the system working age is up to a specified time T, the repairman will repair the component preventively, and it will go back to work as soon as the repa...A simple repairable system with one repairman is considered. As the system working age is up to a specified time T, the repairman will repair the component preventively, and it will go back to work as soon as the repair finished. When the system failure, the repairman repair it immediately. The time interval of the preventive repair and the failure correction is described with the extended geometric process. Different from the available replacement policy which is usually based on the failure number or the working age of the system, the bivariate policy (T,N) is considered. The explicit expression of the long-run average cost rate function C(T,N) of the system is derived. Through alternatively minimize the cost rate function C(T,N), the optimal replacement policy (T?,N?) is obtained, and it proves that the optimal policy is unique. Numerical cases illustrate the conclusion, and the sensitivity analysis of the parameters is carried out.展开更多
基金the National Science Fund for Distinguished Young Scholars(Grant No.51725502)the major program of the National Natural Science Foundation of China(Grant No.51490662)the National Key Research and Development Project of China(Grant No.2016YFD0701105).
文摘In this paper,an uncertainty propagation analysis method is developed based on an extended sparse grid technique and maximum entropy principle,aiming at improving the solving accuracy of the high-order moments and hence the fitting accuracy of the probability density function(PDF)of the system response.The proposed method incorporates the extended Gauss integration into the uncertainty propagation analysis.Moreover,assisted by the Rosenblatt transformation,the various types of extended integration points are transformed into the extended Gauss-Hermite integration points,which makes the method suitable for any type of continuous distribution.Subsequently,within the sparse grid numerical integration framework,the statistical moments of the system response are obtained based on the transformed points.Furthermore,based on the maximum entropy principle,the obtained first four-order statistical moments are used to fit the PDF of the system response.Finally,three numerical examples are investigated to demonstrate the effectiveness of the proposed method,which includes two mathematical problems with explicit expressions and an engineering application with a black-box model.
文摘Pancreatic head adenocarcinoma (PHAC) is one of the most aggressive malignancies, and it has low long-term survival rates. Surgery is the only option for long-term survival. The difficulties associated with PHAC include higher frequencies of regional or distant lymph node metastases and vascular involvement, and positive resection margins in pancreatic and retroperitoneal tissues. Radical resections increase margin negativity and life expectancy;however, the extend of the surgery applied is controversial. Thus, western and eastern centers may use different approaches. Multiorgan, peripancreatic nerve plexus, and vascular resections have been discussed in relation to radical surgery for pancreatic cancer as have the roles of neoadjuvant and adjuvant therapy regimens. Determining the appropriate limits for surgery, standardizing definitions and surgical techniques according to guidelines, and centralizing pancreatic surgery within high-volume institutions to reduce mortality and morbidity rates are among the most important issues to consider. In this review, we evaluate the basic concepts underlying and the roles of radical surgery for PHAC, and lymphadenectomy, nerve plexus, retroperitoneal tissue, vascular, and multivisceral resections, total pancreatectomy, and liver metastases are discussed.
文摘An extended electron model fully recovers many of the experimental results of quantum mechanics while it avoids many of the pitfalls and remains generally free of paradoxes. The formulation of the manybody electronic problem here resembles the Kohn Sham formulation of standard density functional theory. However, rather than referring electronic properties to a large set of single electron orbitals, the extended electron model uses only mass density and field components, leading to a substantial increase in computational efficiency. To date, the Hohenberg-Kohn theorems have not been proved for a model of this type, nor has a universal energy functional been presented. In this paper, we address these problems and show that the Hohenberg Kohn theorems do also hold for a density model of this type. We then present a proof^of^concept practical implementation of this method and show that it reproduces the accuracy of more widely used methods on a test-set of small atomic systems, thus paving the way for the development of fast, efficient and accurate codes on this basis.
基金Supported by the Natural Science Foundation of Anhui Province (Grant Nos. 1808085MA141908085MA03)+1 种基金the Key University Science Research Project of Anhui Province (Grant No. KJ2018A0433)Research Project of Chuzhou University (Grant No. zrjz2017005).
文摘Let R be a prime ring with center Z(R), I a nonzero ideal of R, d a nonzero derivation of R and 0≠ a ∈ R. In the present paper, our object is to study the situation a[d(xk);xk]n ∈Z(R) for all x∈I under certain conditions, where n (≥ 1), k (≥ 1) are fixed integers.
基金National Natural Science Foundation of China under Grant No. 61806068, 61672204by Visiting Scholar at Home and Aboard Funded Project of Universities of Anhui Province under Grant gxfxZD2016209+3 种基金by Key Technologies R&D Program of Anhui Province under Grant 1804a09020058by the Major Program for Scientific and Technological of Anhui Province under Grant 17030901026by Talent Research Foundation Project of Hefei University under Grant 16-17RC23by Humanities and Social Science Research Project of Universities of Anhui Province under Grant SK2018A0605.
文摘Evolutionary testing (ET) is an effective test case generation technique which uses some meta-heuristic search algorithm, especially genetic algorithm, to generate test case automatically. However, the population prematurity problem may decrease the performance of ET. In this paper, a hybrid optimization strategy is proposed based on extended cataclysm which integrates both static configuration strategies and dynamic optimization strategy. Dynamic optimization strategy included the optimization of initial population and the dynamic population optimization based on extended cataclysm, where the diversity of population was monitored during the evolution process of ET, and once the population prematurity was detected, extended cataclysm operation was used to renew the diversity of the population. Experimental results show that the hybrid optimization strategy can improve the performance of ET.
文摘In this paper,the bidirectional SK-Ramani equation is investigated by means of the extended homoclinic test approach and Riemann theta function method,respectively.Based on the Hirota bilinear method,exact solutions including one-soliton wave solution are obtained by using the extended homoclinic approach and one-periodic wave solution is constructed by using the Riemann theta function method.A limiting procedure is presented to analyze in detail the relations between the one periodic wave solution and one-soliton solution.
基金the Ports and Maritime Organization for funding the Morvarid Project (Grant No. 20S/7509. 2015).
文摘Performing repeatable duties automatically was the dreams of human being for centuries. Although full autonomy has long been dreamed of by visionaries, many researches have been performed for surface vehicles automation since the last century to get close to this dream stepwise. To increase daily working hours and accuracy and reduce cost, operations such as hydrography are susceptible for autonomy. Beside platform topology, installed sensors and energy resources, the core elements of any autonomous surface vehicle are navigation, guidance and control systems. To perform bathymetry operation in autonomy manner, a reliable and robust navigation algorithm is designed and embedded in an autonomous surface vehicle titled Morvarid. Morvarid is a plug-in hybrid solar powered catamaran boat. The developed algorithm is a combination of extended Kalman filter, search ball and potential field approaches. Many experimental field tests are carried out after simulation in Simulink environment. Test results illustrated the algorithm and improved the path followed by reducing SD and RMSE and there is a good correlation between simulation run and experimental tests.
文摘In this study we mainly focus on the attitude control problem of a quad tilt rotor aircraft with respect to unknown external disturbance. We propose a class of control methods based on a novel logarithmic fast non singular terminal sliding surface a new fast reaching law and extended state disturbance observer. A logarithmic non singular terminal sliding surface is used owing to its convergence in finite time and significant robustness. A fast reaching law with two order characteristics of the sliding mode is designed. This reaching law can be used reduce the convergence time of traditional reaching law. In addition the extended state disturbance observer is utilized for online estimation and to compensate for system disturbance. The simulation experiment results show that the control strategy proposed in this paper outperforms the traditional non singular fast sliding mode control.
基金the National Natural Science Foundation of China(No.51805262).
文摘This paper proposes a model-based prognostics method that couples the Extended Kalman Filter(EKF) and a new developed linearization method. The proposed prognostics method is developed in the context of fatigue crack propagation in fuselage panels where the model parameters are unknown and the crack propagation is affected by different types of uncertainties. The coupled method is composed of two steps. The first step employs EKF to estimate the unknown model parameters and the current damage state. In the second step, the proposed efficient linearization method is applied to compute analytically the statistical distribution of the damage evolution path in some future time. A numerical case study is implemented to evaluate the performance of the proposed method. The results show that the coupled EKF-linearization method provides satisfactory results: the EKF algorithm well identifies the model parameters, and the linearization method gives comparable prediction results to Monte Carlo(MC) method while leading to very significant computational cost saving. The proposed prognostics method for fatigue crack growth can be used for developing predictive maintenance strategy for an aircraft fleet, in which case, the computational cost saving is significantly meaningful.
基金King Mongkut's University of Technology North Bangkok and Thailand Research Fund(TRF)(Grant No.RSA6080043).
文摘In this paper,the attitude tracking control problem for a rigid spacecraft in the presence of system parameter uncertainties and external disturbances is addressed.First,a new nonsingular finite-time sliding surface is introduced and third-order sliding mode finite-time attitude control law is designed to achieve precise accurate tracking responses and robustness against inertia uncertainties and external disturbances.The stability of the closed-loop system is rigorously proved using the Lyapunov stability theory.Then,a new finite-time extended state observer is established to estimate total disturbances of the system.The extended stated observer-based sliding mode control technique yields improved disturbance rejection and high-precision attitude tracking.Moreover,this control law can avoid the unwinding phenomenon and overcome the input saturation constraint by introducing an auxiliary variable to compensate for the overshooting.A Lyapunov based analysis is provided to guarantee sufficiently small observation error and stabilization of the closed-loop system in finite time.Numerical simulations are conducted to verify the effectiveness of the proposed control method.
基金the National Natural Science Foundation of China (Grant 51465002, 11262001, 51675110, 11632007)the Systematic Project of Guangxi Key Laboratory Project of Disaster Prevention and Engineering Safety (Grant 2016ZDX07).
文摘Based on the ABAQUS platform for finite element analysis, the extended finite element method (XFEM) considering elastoplastic constitutive relationship is developed, by which the displacement discontinuity across the crack surface and the strong nonlinearity near the crack tip can be described more accurately. The strip specimens with unilateral cracks and central cracks under uniaxial tension are simulated using the XFEM and the FEM, respectively. The J-integral across the crack on each incremen t is calcula ted using the equivale nt domain integral met hod (EDIM), the interaction integral met hod and the FEM, respectively. The effec ts of mesh size and mesh shape near the crack tip, element type and different calculation methods on the accuracy of J-integral are analyzed. The simulation results show that the XFEM is more accurate than the FEM with the same element size and type. The fracture tests of cast iron specimens with unilateral cracks under uniaxial tension are performed, and the J-integral criterion is valid to predict the fracture initiation in numerical simulation. The critical value of J-integral is calculated using the EDIM of the XFEM. The comparisons demonstrate that the simulated elastoplastic load-displacement curves with the XFEM are in good agreement with the experimental results.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61571355, 61801349, and 61601355).
文摘The scattering characteristics of the periodic surface of infinite and finite media are investigated in detail.The Fourier expression of the scattering field of the periodic surface is obtained in terms of Huygens’ s principle and Floquet’s theorem.Using the extended boundary condition method(EBCM) and T-matrix method, the scattering amplitude factor is solved,and the correctness of the algorithm is verified by use of the law of conservation of energy.The scattering cross section of the periodic surface in the infinitely long region is derived by improving the scattering cross section of the finite period surface.Furthermore, the effects of the incident wave parameters and the geometric structure parameters on the scattering of the periodic surface are analyzed and discussed.By reasonable approximation, the scattering calculation methods of infinite and finite long surfaces are unified.Besides, numerical results show that the dielectric constant of the periodic dielectric surface has a significant effect on the scattering rate and transmittance.The period and amplitude of the surface determine the number of scattering intensity peaks, and, together with the incident angle, influence the scattering intensity distribution.
基金Pancare Foundation ( www.pancare.org.au ) for supporting hepatobiliary pancreatic cancer research in the Department of Surgery。
文摘Background: Central hepatectomy(CH) is more difficult than extended hepatectomy(EH) and is associated with greater morbidity. In this modern era of liver management with aims to prevent posthepatectomy liver failure(PHLF), there is a need to assess outcomes of CH as a parenchyma-sparing procedure for centrally located liver tumors. Methods: A total of 178 major liver resections performed by specialist surgeons from two Australian tertiary institutions between June 2009 and March 2017 were reviewed. Eleven patients had CH and 24 had EH over this study period. Indications and perioperative outcomes were compared between the groups. Results: The main indication for performing CH was colorectal liver metastases. There was no perioperative mortality in the CH group and four(16.7%) in the EH group( P = 0.285). No group differences were found in median operative time [CH vs. EH: 450 min(290–840) vs. 523 min(310–860), P = 0.328], intraoperative blood loss [850 mL(40 0–150 0) vs. 650 mL(10 0–20 0 0), P = 0.746] or patients requiring intraoperative blood transfusion [1(9.1%) vs. 7(30.4%), P = 0.227]. There was a trend towards fewer hepatectomyspecific complications in the CH group [3(27.3%) vs. 13(54.2%), P = 0.167], including PHLF(CH vs. EH: 0 vs. 29.2%, P = 0.072). Median length of stay was similar between groups [CH vs. EH: 9 days(5–23) vs. 12 days(4–85), P = 0.244]. Conclusions: CH has equivalent postoperative outcomes to EH. There is a trend towards fewer hepatectomy-specific complications, including PHLF. In appropriate patients, CH may be considered as a safe parenchyma-sparing alternative to EH.
基金Supported by Hunan Provincial Natural Science Foundation of China(2015JJ2005)the Science Research Foundation of Education Department of Hunan Province(15C0029)+1 种基金the National Natural Science Foundation of China(11103001)the construct program of the key discipline in Hunan province.
文摘An extended Nambu-Jona-Lasinio(eNJL) model with nucleons as the degrees of freedom is used to investigate properties of nuclear matter and neutron stars(NSs),including the binding energy and symmetry energy of the nuclear matter, the core-crust transition density, and mass-radius relation of NSs. The fourth-order symmetry energy at saturation density is also investigated. When the bulk properties of nuclear matter at saturation density are used to determine the model parameters, the double solutions of parameters are obtained for a given nuclear incompressibility. It is shown that the isovector-vector interaction has a significant influence on the nuclear matter and NS properties, and the sign of isovector-vector coupling constant is critical in the determination of the trend of the symmetry energy and equation of state. The effects of the other model parameters and symmetry energy slope at saturation density are discussed.
基金supported by the National Natural Science Foundation of China under Grant No.61673351the Zhejiang Provincial Natural Science Foundation of China under Grant No.LZ15030003.
文摘In this paper, a robust finite-time tracking control scheme is proposed for wheeled mobile robots with parametric uncertainties and disturbances. To eliminate the effect of lumped uncertainties,a nonlinear extended state observer(NESO) is employed to estimate the unknown states as well as uncertainties, and the corresponding coefficients are tuned via pole placement technique. Based on the observation values, the finite-time sliding mode controller is presented to guarantee that both the sliding mode variables and tracking errors converge to zero within finite time. Simulation results are given to demonstrate the effectiveness of the proposed control method.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0100601).
文摘The defects and electrical properties in Al-implanted 4 H-SiC after activation annealing(1600℃-1800℃) are investigated. High temperature annealing can reduce the ion implantation-induced damage effectively, but it may induce extended defects as well, which are investigated by using Rutherford backscattering spectroscopy(RBS/C), secondary ion mass spectroscopy(SIMS), and transmission electron microscopy(TEM) analyses. According to the ratio of the channeled intensity to the random intensity in the region just below the surface scattering peak(Xmin) and RBS/C analysis results, the ion implantation-induced surface damages can be effectively reduced by annealing at temperatures higher than 1700℃,while the defects near the bottom of the ion-implanted layer cannot be completely annealed out by high temperature and long time annealing process, which is also demonstrated by SIMS and TEM analyses. Referring to the defect model and TEM analyses, an optimized annealing condition can be achieved through balancing the generation and elimination of carbon vacancies in the ion implanted layers. Furthermore, the electrical and surface properties are also analyzed, and the hole concentration, mobility, and resistivity are obtained through the Hall effect. The optimized activation annealing conditions of 1800℃/5 min are achieved, under which the lower defects and acceptable electrical properties are obtained.
文摘The attitude stability control of under actuated spacecraft that used two reaction wheels in the presence of dynamic friction disturbance is handled. A novel improved control approach with a combination of a singular control law based on quaternion and extended state observer (ESO) is employed to establish a stabilization control so as to restrain the effect of friction. The corresponding simulation results demonstrate the highly stable accuracy and performance compensated dynamic friction. Furthermore if there is a non zero initial condition in under actuated axis the attitude stability can be enhanced with a magnetic torquer. Simulations for a nano spacecraft denote a potential application value in pointing accuracy using two reaction wheels and a magnetic torquer.
基金supported by the National Natural Science Foundation of China(61401475)。
文摘The key challenge of the extended target probability hypothesis density (ET-PHD) filter is to reduce the computational complexity by using a subset to approximate the full set of partitions. In this paper, the influence for the tracking results of different partitions is analyzed, and the form of the most informative partition is obtained. Then, a fast density peak-based clustering (FDPC) partitioning algorithm is applied to the measurement set partitioning. Since only one partition of the measurement set is used, the ET-PHD filter based on FDPC partitioning has lower computational complexity than the other ET-PHD filters. As FDPC partitioning is able to remove the spatially close clutter-generated measurements, the ET-PHD filter based on FDPC partitioning has good tracking performance in the scenario with more clutter-generated measurements. The simulation results show that the proposed algorithm can get the most informative partition and obviously reduce computational burden without losing tracking performance. As the number of clutter-generated measurements increased, the ET-PHD filter based on FDPC partitioning has better tracking performance than other ET-PHD filters. The FDPC algorithm will play an important role in the engineering realization of the multiple extended target tracking filter.
基金Supported by Iranian National Science Foundation(INSF).
文摘We consider a holographic extended phase space in the presence of Reissner-Nordstrom-Anti-de Sitter(RNAdS) and Born-Infeld-Anti-de Sitter(BI-AdS) black holes in the bulk. In this extended phase space the cosmological constant is investigated as pressure and volume is defined as the codimension one-time slice in the bulk geometry enclosed by the minimal area appearing in the computation of the holographic entanglement entropy. These thermodynamics quantities can serve as probes of the underlying phase transition dictated by black hole thermodynamics, but do not describe different structures. We find that the isocharges on the pressure-volume plane exhibit a Van der Waals-like structure, for RN-AdS black holes in the background. For BI-AdS black holes, we observe the analogy with a Van der Waals liquid-gas system for βQ > 1/2 and Reentrant phase transition for βQ < 1/2 in the holographic extended phase space. The same holographic thermodynamic behavior is observed when we use the fidelity susceptibility as the volume and the cosmological constant as the pressure for RN-AdS black hole in the background.
基金supported by the National Natural Science Foundation of China(61573014)the Fundamental Research Funds for the Central Universities(JB180702).
文摘A simple repairable system with one repairman is considered. As the system working age is up to a specified time T, the repairman will repair the component preventively, and it will go back to work as soon as the repair finished. When the system failure, the repairman repair it immediately. The time interval of the preventive repair and the failure correction is described with the extended geometric process. Different from the available replacement policy which is usually based on the failure number or the working age of the system, the bivariate policy (T,N) is considered. The explicit expression of the long-run average cost rate function C(T,N) of the system is derived. Through alternatively minimize the cost rate function C(T,N), the optimal replacement policy (T?,N?) is obtained, and it proves that the optimal policy is unique. Numerical cases illustrate the conclusion, and the sensitivity analysis of the parameters is carried out.