The transition boundaries of period doubling on the physical parameter plane of a Duffing system are obtained by the general Newton′s method, and the motion on different areas divided by transition boundaries is stu...The transition boundaries of period doubling on the physical parameter plane of a Duffing system are obtained by the general Newton′s method, and the motion on different areas divided by transition boundaries is studied in this paper. When the physical parameters transpass the boundaries, the solutions of period T =2π/ω will lose their stability, and the solutions of period T =2π/ω take place. Continuous period doubling bifurcations lead to chaos.展开更多
财务管理是境外企业健康发展的关键之一。笔者以在南非 SVA 电子电器公司(上海广电股份有限公司在南非投资设立的家电产品生产企业)的工作实践,谈谈体会并提出一些问题供商榷。一、建立以国内资金为依托的资金周转系统企业的生产经营活...财务管理是境外企业健康发展的关键之一。笔者以在南非 SVA 电子电器公司(上海广电股份有限公司在南非投资设立的家电产品生产企业)的工作实践,谈谈体会并提出一些问题供商榷。一、建立以国内资金为依托的资金周转系统企业的生产经营活动能否顺利开展。展开更多
Rotor systems supported by angular contact ball bearings are complicated due to nonlinear Hertzian contact force. In this paper, nonlinear bearing forces of ball bearing under five-dimensional loads are given, and 5-D...Rotor systems supported by angular contact ball bearings are complicated due to nonlinear Hertzian contact force. In this paper, nonlinear bearing forces of ball bearing under five-dimensional loads are given, and 5-DOF dynamic equations of a rigid rotor ball bearing system are established. Continuation-shooting algorithm for periodic solutions of the nonlinear non-autonomous dynamic system and Floquet multipliers of the system are used. Furthermore, the bifurcation and stability of the periodic motion of the system in different parametric domains are also studied. Results show that the bifurcation and stability of period-1 motion vary with structural parameters and operating parameters of the rigid rotor ball bearing system. Avoidance of unbalanced force and bending moment, appropriate initial contact angle, axial load and damping factor help enhance the unstable rotating speed of period-1 motion.展开更多
A nonlinear lateral-torsional coupled vibration model of a planetary gear system was established by taking transmission errors,time varying meshing stiffness and multiple gear backlashes into account.The bifurcation d...A nonlinear lateral-torsional coupled vibration model of a planetary gear system was established by taking transmission errors,time varying meshing stiffness and multiple gear backlashes into account.The bifurcation diagram of the system's motion state with rotational speed of sun gear was conducted through four steps.As a bifurcation parameter,the effect of rotational speed on the bifurcation properties of the system was assessed.The study results reveal that periodic motion is the main motion state of planetary gear train in low speed region when ns<2 350 r/min,but chaos motion state is dominant in high speed region when ns>2 350 r/min,The way of periodic motion to chaos is doubling bifurcation.There are two kinds of unstable modes and nine unstable regions in the speed region when 1 000 r/min<ns<3 000 r/min.展开更多
The Tibetan Plateau(TP)and Arctic permafrost constitute two large reservoirs of organic carbon,but processes which control carbon accumulation within the surface soil layer of these areas would differ due to the inter...The Tibetan Plateau(TP)and Arctic permafrost constitute two large reservoirs of organic carbon,but processes which control carbon accumulation within the surface soil layer of these areas would differ due to the interplay of climate,soil and vegetation type.Here,we synthesized currently available soil carbon data to show that mean organic carbon density in the topsoil(0-10 cm)in TP grassland(3.12±0.52 kg C m^(-2))is less than half of that in Arctic tundra(6.70±1.94 kg C m^(-2)).Such difference is primarily attributed to their difference in radiocarbon-inferred soil carbon turnover times(547 years for TP grassland versus 1609 years for Arctic tundra)rather than to their marginal difference in topsoil carbon inputs.Our findings highlight the importance of improving regional-specific soil carbon turnover and its controlling mechanisms across permafrost affected zones in ecosystem models to fully represent carbon-climate feedback.展开更多
文摘The transition boundaries of period doubling on the physical parameter plane of a Duffing system are obtained by the general Newton′s method, and the motion on different areas divided by transition boundaries is studied in this paper. When the physical parameters transpass the boundaries, the solutions of period T =2π/ω will lose their stability, and the solutions of period T =2π/ω take place. Continuous period doubling bifurcations lead to chaos.
基金Supported by National Natural Science Foundation of China (No.50905061)the Fundamental Research Funds for Central Universities
文摘Rotor systems supported by angular contact ball bearings are complicated due to nonlinear Hertzian contact force. In this paper, nonlinear bearing forces of ball bearing under five-dimensional loads are given, and 5-DOF dynamic equations of a rigid rotor ball bearing system are established. Continuation-shooting algorithm for periodic solutions of the nonlinear non-autonomous dynamic system and Floquet multipliers of the system are used. Furthermore, the bifurcation and stability of the periodic motion of the system in different parametric domains are also studied. Results show that the bifurcation and stability of period-1 motion vary with structural parameters and operating parameters of the rigid rotor ball bearing system. Avoidance of unbalanced force and bending moment, appropriate initial contact angle, axial load and damping factor help enhance the unstable rotating speed of period-1 motion.
基金Project(50775108) supported by the National Natural Science Foundation of China
文摘A nonlinear lateral-torsional coupled vibration model of a planetary gear system was established by taking transmission errors,time varying meshing stiffness and multiple gear backlashes into account.The bifurcation diagram of the system's motion state with rotational speed of sun gear was conducted through four steps.As a bifurcation parameter,the effect of rotational speed on the bifurcation properties of the system was assessed.The study results reveal that periodic motion is the main motion state of planetary gear train in low speed region when ns<2 350 r/min,but chaos motion state is dominant in high speed region when ns>2 350 r/min,The way of periodic motion to chaos is doubling bifurcation.There are two kinds of unstable modes and nine unstable regions in the speed region when 1 000 r/min<ns<3 000 r/min.
基金This work was supported by Preliminary Research on Three Poles Environment and Climate Change(2019YFC1509103)the National Natural Science Foundation of China(41861134036 and 41922004)+1 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0606)the Strategic Priority Research Program(A)of the Chinese Academy of Sciences(XDA19070303 and XDA20050101).
文摘The Tibetan Plateau(TP)and Arctic permafrost constitute two large reservoirs of organic carbon,but processes which control carbon accumulation within the surface soil layer of these areas would differ due to the interplay of climate,soil and vegetation type.Here,we synthesized currently available soil carbon data to show that mean organic carbon density in the topsoil(0-10 cm)in TP grassland(3.12±0.52 kg C m^(-2))is less than half of that in Arctic tundra(6.70±1.94 kg C m^(-2)).Such difference is primarily attributed to their difference in radiocarbon-inferred soil carbon turnover times(547 years for TP grassland versus 1609 years for Arctic tundra)rather than to their marginal difference in topsoil carbon inputs.Our findings highlight the importance of improving regional-specific soil carbon turnover and its controlling mechanisms across permafrost affected zones in ecosystem models to fully represent carbon-climate feedback.
