By the generalized variational principle of two kinds of variables in general me-chanics,it was demonstrated that two Lagrangian classical relationships can be applied to both holonomic systems and nonholonomic system...By the generalized variational principle of two kinds of variables in general me-chanics,it was demonstrated that two Lagrangian classical relationships can be applied to both holonomic systems and nonholonomic systems. And the restriction that two Lagrangian classical relationships cannot be applied to nonholonomic systems for a long time was overcome. Then,one important formula of similar La-grangian classical relationship called the popularized Lagrangian classical rela-tionship was derived. From Vakonomic model,by two Lagrangian classical rela-tionships and the popularized Lagrangian classical relationship,the result is the same with Chetaev's model,and thus Chetaev's model and Vakonomic model were unified. Simultaneously,the Lagrangian theoretical framework of dynamics of nonholonomic system was established. By some representative examples,it was validated that the Lagrangian theoretical framework of dynamics of nonholonomic systems is right.展开更多
As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5)...As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5) is proposed.However, due to its high inclination and large eccentricity, direct impulsive transfer requires large amounts of fuel consumption. To address this challenge, we explore the benefits of electric propulsion and multi-gravity assist techniques for interplanetary missions. These two techniques are integrated in this mission design. The design of a low-thrust gravity-assist(LTGA) trajectory in multi-body dynamics is thoroughly investigated,which is a complex process. A comprehensive framework including three steps is presented here for optimization of LTGA trajectories in multi-body dynamics. The rendezvous mission to 2020 XL_(5) is designed with this three-step approach. The most effective transfer sequence among the outcomes involves Earth–Venus–Earth–Venus-2020 XL_(5). Numerical results indicate that the combination of electric propulsion and multi-gravity assists can greatly reduce the fuel consumption, with fuel consumption of 9.03%, making it a highly favorable choice for this rendezvous mission.展开更多
This paper presents a comparative analysis of the International Baccalaureate(IB)and the General Certificate of Education Advanced Level(A-Level),two international educational assessment systems.The study explores the...This paper presents a comparative analysis of the International Baccalaureate(IB)and the General Certificate of Education Advanced Level(A-Level),two international educational assessment systems.The study explores their similarities and differences in educational philosophy,curriculum design,assessment methods,and student experience.Findings indicate that the IB curriculum emphasizes holistic education and interdisciplinary learning,while the A-Level curriculum focuses more on subject depth and specialization.In terms of assessment methods,the IB combines internal and external evaluations,whereas the A-Level primarily relies on final examinations.Regarding student experience,IB students typically perceive a broader range of learning opportunities,while A-Level students gain in-depth knowledge in specific subject areas.The study offers valuable insights for educators and policymakers to improve educational practices and support the personalized development of students.展开更多
The search for the generating compatibility conditions (CC) of a given operator is a very recent problem met in general relativity in order to study the Killing operator for various standard useful metrics. Accordingl...The search for the generating compatibility conditions (CC) of a given operator is a very recent problem met in general relativity in order to study the Killing operator for various standard useful metrics. Accordingly, this paper can be considered as a natural continuation of a previous paper recently published in JMP under the title Minkowski, Schwarschild and Kerr metrics revisited. In particular, we prove that the intrinsic link existing between the lack of formal exactness of an operator sequence on the jet level, the lack of formal exactness of its corresponding symbol sequence and the lack of formal integrability (FI) of the initial operator is of a purely homological nature as it is based on the long exact connecting sequence provided by the so-called snake lemma in homological algebra. It is therefore quite difficult to grasp it in general and even more difficult to use it on explicit examples. It does not seem that any one of the results presented in this paper is known as most of the other authors who studied the above problem of computing the total number of generating CC are confusing this number with the degree of generality introduced by A. Einstein in his 1930 letters to E. Cartan. One of the motivating examples that we provide is so striking that it is even difficult to imagine that such an example could exist. We hope this paper could be used as a source of testing examples for future applications of computer algebra in general relativity and, more generally, in mathematical physics.展开更多
银河系光行差,或称为长期光行差漂移,是由于太阳系质心绕着银河系中心做轨道运动的加速度引起的视自行效应,量级大约为5μas·yr-1.在21世纪之前,由于观测精度尚未达到如此高的程度,人们很少讨论银河系光行差效应.随着甚长基线干涉(...银河系光行差,或称为长期光行差漂移,是由于太阳系质心绕着银河系中心做轨道运动的加速度引起的视自行效应,量级大约为5μas·yr-1.在21世纪之前,由于观测精度尚未达到如此高的程度,人们很少讨论银河系光行差效应.随着甚长基线干涉(Very Long Baseline Interferometer,VLBI)在基本天文学中的广泛应用和欧洲空间局(European Space Agency,ESA)的第2代微角秒天体测量卫星Gaia的问世,该效应显得逐渐重要.由于河外源的分布不均匀,银河系光行差效应会使得河外源天球参考架缓慢旋转,进而需要修正地球岁差参数,其中岁差速率的改正值大约为1μas·yr-1.对于微角秒精度的VLBI和Gaia参考架,银河系光行差将会引起框架扭曲,在两者的连接过程中,也是必须考虑的系统效应.展开更多
Aiming at the convergence between Earth observation(EO)Big Data and Artificial General Intelligence(AGI),this paper consists of two parts.In the previous Part 1,existing EO optical sensory imagederived Level 2/Analysi...Aiming at the convergence between Earth observation(EO)Big Data and Artificial General Intelligence(AGI),this paper consists of two parts.In the previous Part 1,existing EO optical sensory imagederived Level 2/Analysis Ready Data(ARD)products and processes are critically compared,to overcome their lack of harmonization/standardization/interoperability and suitability in a new notion of Space Economy 4.0.In the present Part 2,original contributions comprise,at the Marr five levels of system understanding:(1)an innovative,but realistic EO optical sensory image-derived semantics-enriched ARD co-product pair requirements specification.First,in the pursuit of third-level semantic/ontological interoperability,a novel ARD symbolic(categorical and semantic)co-product,known as Scene Classification Map(SCM),adopts an augmented Cloud versus Not-Cloud taxonomy,whose Not-Cloud class legend complies with the standard fully-nested Land Cover Classification System’s Dichotomous Phase taxonomy proposed by the United Nations Food and Agriculture Organization.Second,a novel ARD subsymbolic numerical co-product,specifically,a panchromatic or multispectral EO image whose dimensionless digital numbers are radiometrically calibrated into a physical unit of radiometric measure,ranging from top-of-atmosphere reflectance to surface reflectance and surface albedo values,in a five-stage radiometric correction sequence.(2)An original ARD process requirements specification.(3)An innovative ARD processing system design(architecture),where stepwise SCM generation and stepwise SCM-conditional EO optical image radiometric correction are alternated in sequence.(4)An original modular hierarchical hybrid(combined deductive and inductive)computer vision subsystem design,provided with feedback loops,where software solutions at the Marr two shallowest levels of system understanding,specifically,algorithm and implementation,are selected from the scientific literature,to benefit from their technology readiness level as proof of feasibility,required in 展开更多
Quasars are essential for astrometry in the sense that they are spatially stationary because of their large distance from the Sun. The European Space Agency(ESA) astrometric satellite Gaia is scanning the whole sky wi...Quasars are essential for astrometry in the sense that they are spatially stationary because of their large distance from the Sun. The European Space Agency(ESA) astrometric satellite Gaia is scanning the whole sky with unprecedented accuracy up to the level of a few μas. However, Gaia's two-fields-ofview-observation strategy may introduce a parallax bias in the Gaia catalog. Since it presents no significant parallax, a quasar is the perfect natural object to detect such bias. More importantly, quasars can be used to construct a celestial reference frame in the optical wavelengths for the Gaia mission. In this paper, we compile a list of known quasars that have been published in the literatures. The final compilation(designated as Known Quasars Catalog for Gaia mission, KQCG) contains 1 842 076 objects, among which797 632 objects are found in Gaia DR1 after cross-identifications. Redshift, color information and position uncertainties of the objects are also provided if available. This catalog will be very useful for the Gaia mission.展开更多
A general study of non-static restricted class of axial system with anisotropic dissipative expansion-free fluid under geodesic condition is carried out. It is found that expansion-free model must be dissipative under...A general study of non-static restricted class of axial system with anisotropic dissipative expansion-free fluid under geodesic condition is carried out. It is found that expansion-free model must be dissipative under geodesic condition to preserve axial symmetry. We also investigate this system without geodesic condition. Finally, the role of dissipation is explored via transport equation.展开更多
The fundamentals of a new method of theoretically studying the kinetics of the phase transformation with nudeation and growth mechanism are demonstrated.Startingfromfinite,heterogeneous system,the survival probability...The fundamentals of a new method of theoretically studying the kinetics of the phase transformation with nudeation and growth mechanism are demonstrated.Startingfromfinite,heterogeneous system,the survival probability of the individual sites for the given annealing time can be calculated by the present treatment,so that the kinetics equation under general conditions can be derived.In comparison to the classical treatment,the new derivations are not only rigorous and transparent,but also can be used to deal with the non-homogeneous systems and the non-steady process.Also the problems concerning the interference of more than one simultaneously occurring transformations and the correlation between different sites can be studied.展开更多
In this paper, we investigate the absolute stability of the general Lurie control systems. The necessary and sufficient conditions for absolute stability are obtained. These conditions can be readily checked and are c...In this paper, we investigate the absolute stability of the general Lurie control systems. The necessary and sufficient conditions for absolute stability are obtained. These conditions can be readily checked and are convenient in application.展开更多
基金Supported by the National Natural Science Foundation of China (Grant No. 10272034)the Research Fund for the Doctoral Program of Higher Education of Chinathe Basic Research Foundation of Harbin Engineering University (Grant No. 20060217020)
文摘By the generalized variational principle of two kinds of variables in general me-chanics,it was demonstrated that two Lagrangian classical relationships can be applied to both holonomic systems and nonholonomic systems. And the restriction that two Lagrangian classical relationships cannot be applied to nonholonomic systems for a long time was overcome. Then,one important formula of similar La-grangian classical relationship called the popularized Lagrangian classical rela-tionship was derived. From Vakonomic model,by two Lagrangian classical rela-tionships and the popularized Lagrangian classical relationship,the result is the same with Chetaev's model,and thus Chetaev's model and Vakonomic model were unified. Simultaneously,the Lagrangian theoretical framework of dynamics of nonholonomic system was established. By some representative examples,it was validated that the Lagrangian theoretical framework of dynamics of nonholonomic systems is right.
基金supported by Basic Research Project of China(grant No:JCKY2020110C096)the National Key R&D Program of China (grant No:2020YFC2201202)。
文摘As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5) is proposed.However, due to its high inclination and large eccentricity, direct impulsive transfer requires large amounts of fuel consumption. To address this challenge, we explore the benefits of electric propulsion and multi-gravity assist techniques for interplanetary missions. These two techniques are integrated in this mission design. The design of a low-thrust gravity-assist(LTGA) trajectory in multi-body dynamics is thoroughly investigated,which is a complex process. A comprehensive framework including three steps is presented here for optimization of LTGA trajectories in multi-body dynamics. The rendezvous mission to 2020 XL_(5) is designed with this three-step approach. The most effective transfer sequence among the outcomes involves Earth–Venus–Earth–Venus-2020 XL_(5). Numerical results indicate that the combination of electric propulsion and multi-gravity assists can greatly reduce the fuel consumption, with fuel consumption of 9.03%, making it a highly favorable choice for this rendezvous mission.
文摘This paper presents a comparative analysis of the International Baccalaureate(IB)and the General Certificate of Education Advanced Level(A-Level),two international educational assessment systems.The study explores their similarities and differences in educational philosophy,curriculum design,assessment methods,and student experience.Findings indicate that the IB curriculum emphasizes holistic education and interdisciplinary learning,while the A-Level curriculum focuses more on subject depth and specialization.In terms of assessment methods,the IB combines internal and external evaluations,whereas the A-Level primarily relies on final examinations.Regarding student experience,IB students typically perceive a broader range of learning opportunities,while A-Level students gain in-depth knowledge in specific subject areas.The study offers valuable insights for educators and policymakers to improve educational practices and support the personalized development of students.
文摘The search for the generating compatibility conditions (CC) of a given operator is a very recent problem met in general relativity in order to study the Killing operator for various standard useful metrics. Accordingly, this paper can be considered as a natural continuation of a previous paper recently published in JMP under the title Minkowski, Schwarschild and Kerr metrics revisited. In particular, we prove that the intrinsic link existing between the lack of formal exactness of an operator sequence on the jet level, the lack of formal exactness of its corresponding symbol sequence and the lack of formal integrability (FI) of the initial operator is of a purely homological nature as it is based on the long exact connecting sequence provided by the so-called snake lemma in homological algebra. It is therefore quite difficult to grasp it in general and even more difficult to use it on explicit examples. It does not seem that any one of the results presented in this paper is known as most of the other authors who studied the above problem of computing the total number of generating CC are confusing this number with the degree of generality introduced by A. Einstein in his 1930 letters to E. Cartan. One of the motivating examples that we provide is so striking that it is even difficult to imagine that such an example could exist. We hope this paper could be used as a source of testing examples for future applications of computer algebra in general relativity and, more generally, in mathematical physics.
文摘银河系光行差,或称为长期光行差漂移,是由于太阳系质心绕着银河系中心做轨道运动的加速度引起的视自行效应,量级大约为5μas·yr-1.在21世纪之前,由于观测精度尚未达到如此高的程度,人们很少讨论银河系光行差效应.随着甚长基线干涉(Very Long Baseline Interferometer,VLBI)在基本天文学中的广泛应用和欧洲空间局(European Space Agency,ESA)的第2代微角秒天体测量卫星Gaia的问世,该效应显得逐渐重要.由于河外源的分布不均匀,银河系光行差效应会使得河外源天球参考架缓慢旋转,进而需要修正地球岁差参数,其中岁差速率的改正值大约为1μas·yr-1.对于微角秒精度的VLBI和Gaia参考架,银河系光行差将会引起框架扭曲,在两者的连接过程中,也是必须考虑的系统效应.
基金ASAP 16 project call,project title:SemantiX-A cross-sensor semantic EO data cube to open and leverage essential climate variables with scientists and the public,Grant ID:878939ASAP 17 project call,project title:SIMS-Soil sealing identification and monitoring system,Grant ID:885365.
文摘Aiming at the convergence between Earth observation(EO)Big Data and Artificial General Intelligence(AGI),this paper consists of two parts.In the previous Part 1,existing EO optical sensory imagederived Level 2/Analysis Ready Data(ARD)products and processes are critically compared,to overcome their lack of harmonization/standardization/interoperability and suitability in a new notion of Space Economy 4.0.In the present Part 2,original contributions comprise,at the Marr five levels of system understanding:(1)an innovative,but realistic EO optical sensory image-derived semantics-enriched ARD co-product pair requirements specification.First,in the pursuit of third-level semantic/ontological interoperability,a novel ARD symbolic(categorical and semantic)co-product,known as Scene Classification Map(SCM),adopts an augmented Cloud versus Not-Cloud taxonomy,whose Not-Cloud class legend complies with the standard fully-nested Land Cover Classification System’s Dichotomous Phase taxonomy proposed by the United Nations Food and Agriculture Organization.Second,a novel ARD subsymbolic numerical co-product,specifically,a panchromatic or multispectral EO image whose dimensionless digital numbers are radiometrically calibrated into a physical unit of radiometric measure,ranging from top-of-atmosphere reflectance to surface reflectance and surface albedo values,in a five-stage radiometric correction sequence.(2)An original ARD process requirements specification.(3)An innovative ARD processing system design(architecture),where stepwise SCM generation and stepwise SCM-conditional EO optical image radiometric correction are alternated in sequence.(4)An original modular hierarchical hybrid(combined deductive and inductive)computer vision subsystem design,provided with feedback loops,where software solutions at the Marr two shallowest levels of system understanding,specifically,algorithm and implementation,are selected from the scientific literature,to benefit from their technology readiness level as proof of feasibility,required in
基金makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administrationprovided by the National Development and Reform Commissionsupported by grants from the National Natural Science Foundation of China (Grant Nos. 11703065 and 11573054)
文摘Quasars are essential for astrometry in the sense that they are spatially stationary because of their large distance from the Sun. The European Space Agency(ESA) astrometric satellite Gaia is scanning the whole sky with unprecedented accuracy up to the level of a few μas. However, Gaia's two-fields-ofview-observation strategy may introduce a parallax bias in the Gaia catalog. Since it presents no significant parallax, a quasar is the perfect natural object to detect such bias. More importantly, quasars can be used to construct a celestial reference frame in the optical wavelengths for the Gaia mission. In this paper, we compile a list of known quasars that have been published in the literatures. The final compilation(designated as Known Quasars Catalog for Gaia mission, KQCG) contains 1 842 076 objects, among which797 632 objects are found in Gaia DR1 after cross-identifications. Redshift, color information and position uncertainties of the objects are also provided if available. This catalog will be very useful for the Gaia mission.
文摘A general study of non-static restricted class of axial system with anisotropic dissipative expansion-free fluid under geodesic condition is carried out. It is found that expansion-free model must be dissipative under geodesic condition to preserve axial symmetry. We also investigate this system without geodesic condition. Finally, the role of dissipation is explored via transport equation.
基金Project supported by the National Natural Science Foundation of China.
文摘The fundamentals of a new method of theoretically studying the kinetics of the phase transformation with nudeation and growth mechanism are demonstrated.Startingfromfinite,heterogeneous system,the survival probability of the individual sites for the given annealing time can be calculated by the present treatment,so that the kinetics equation under general conditions can be derived.In comparison to the classical treatment,the new derivations are not only rigorous and transparent,but also can be used to deal with the non-homogeneous systems and the non-steady process.Also the problems concerning the interference of more than one simultaneously occurring transformations and the correlation between different sites can be studied.
基金Project supported by the National Natural Science Foundation of China.
文摘In this paper, we investigate the absolute stability of the general Lurie control systems. The necessary and sufficient conditions for absolute stability are obtained. These conditions can be readily checked and are convenient in application.
