As the tuning frequency of an integrated LC-voltage controlled oscillator （LC-VCO） increases, it is difficult to co-design the active negative resistance core and the varactor to achieve wideband frequency range, lo...As the tuning frequency of an integrated LC-voltage controlled oscillator （LC-VCO） increases, it is difficult to co-design the active negative resistance core and the varactor to achieve wideband frequency range, low phase noise, constant bandwidth and small tuning gain together. The presented VCO solves the problem by designing a set of changeable varactor units. The whole VCO was implemented in a 0.18μm CMOS process. The measured result shows -120 dBc/Hz phase noise at 1 MHz offset. The measured tuning range is from 4.2 to 5 GHz and the tuning gain is 8-10 MHz/V. The VCO draws 4 mA from a 1.5 V supply voltage.展开更多
In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is pr...In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is proposed in this paper. A localized pressure pulse with a very high amplitude can be imposed on specified regions in a combustion chamber, the numerical procedure of which is described. Pressure oscillations actuated by the released constant-volume bomb can then be analyzed via Fast Fourier Transformation（FFT）, and their modes can be identified according to the theoretical acoustic eigenfrequencies of the thrust chamber. The damping performances of the corresponding acoustic modes are evaluated by the half-power bandwidth method. The predicted acoustic characteristics and their damping for a special engine combustor agree well with the experimental data, validating the mathematical model and its numerical procedures. A small-thrust liquid rocket engine chamber is then analyzed by the present model. The First Longitudinal（1L） acoustic mode can be excited easily and is hard to be damped. The axial position of the central constantvolume bomb has little influence on the amplitude and damping capacity of the First Radial（1R） and 1L acoustic modes. Tangential acoustic modes can only be triggered by an off-centered constant-volume bomb, among which the First Tangential（1T） mode is the strongest and regarded as the most harmful one. The amplitude of the 1L acoustic mode is smaller, but its damping factor is larger, as a constant-volume bomb is imposed approaching the injector face. These results are contributed to evaluate the acoustic characteristics and their damping of the combustion chamber.展开更多
为有效管理分布式开放实时系统(Distributed Open Real-Time System,DORTS)的CPU和网络资源,提供实时应用端到端延时确保,提出一种基于资源预留的分层调度策略。对于任务的调度,首先利用最大需求任务优先与最小可利用率节点适应算法将...为有效管理分布式开放实时系统(Distributed Open Real-Time System,DORTS)的CPU和网络资源,提供实时应用端到端延时确保,提出一种基于资源预留的分层调度策略。对于任务的调度,首先利用最大需求任务优先与最小可利用率节点适应算法将任务分配到各节点,然后在节点上采用基于服务器的两层调度架构进行调度;对于消息的调度,采用3层调度架构:在顶层为每个应用创建一个高级别调度器,负责调度应用产生的消息;在中间层为每个节点创建一个低级别调度器来调度所有的高级别调度器;在底层,一个介质访问控制调度器用于授权各节点对网络的访问。设计了EDF-SS(Earliest Deadline First with Slack Stealing)算法用于改进软实时非周期消息的响应性。仿真实验证明了算法的有效性。展开更多
文摘As the tuning frequency of an integrated LC-voltage controlled oscillator （LC-VCO） increases, it is difficult to co-design the active negative resistance core and the varactor to achieve wideband frequency range, low phase noise, constant bandwidth and small tuning gain together. The presented VCO solves the problem by designing a set of changeable varactor units. The whole VCO was implemented in a 0.18μm CMOS process. The measured result shows -120 dBc/Hz phase noise at 1 MHz offset. The measured tuning range is from 4.2 to 5 GHz and the tuning gain is 8-10 MHz/V. The VCO draws 4 mA from a 1.5 V supply voltage.
基金Financial support from the National Natural Science Foundation of China (Nos.51676111 and 11628206)
文摘In order to numerically evaluate the acoustic characteristics of liquid rocket engine thrust chambers by means of a computational fluid dynamics method, a mathematical model of an artificial constant-volume bomb is proposed in this paper. A localized pressure pulse with a very high amplitude can be imposed on specified regions in a combustion chamber, the numerical procedure of which is described. Pressure oscillations actuated by the released constant-volume bomb can then be analyzed via Fast Fourier Transformation（FFT）, and their modes can be identified according to the theoretical acoustic eigenfrequencies of the thrust chamber. The damping performances of the corresponding acoustic modes are evaluated by the half-power bandwidth method. The predicted acoustic characteristics and their damping for a special engine combustor agree well with the experimental data, validating the mathematical model and its numerical procedures. A small-thrust liquid rocket engine chamber is then analyzed by the present model. The First Longitudinal（1L） acoustic mode can be excited easily and is hard to be damped. The axial position of the central constantvolume bomb has little influence on the amplitude and damping capacity of the First Radial（1R） and 1L acoustic modes. Tangential acoustic modes can only be triggered by an off-centered constant-volume bomb, among which the First Tangential（1T） mode is the strongest and regarded as the most harmful one. The amplitude of the 1L acoustic mode is smaller, but its damping factor is larger, as a constant-volume bomb is imposed approaching the injector face. These results are contributed to evaluate the acoustic characteristics and their damping of the combustion chamber.
文摘为有效管理分布式开放实时系统(Distributed Open Real-Time System,DORTS)的CPU和网络资源,提供实时应用端到端延时确保,提出一种基于资源预留的分层调度策略。对于任务的调度,首先利用最大需求任务优先与最小可利用率节点适应算法将任务分配到各节点,然后在节点上采用基于服务器的两层调度架构进行调度;对于消息的调度,采用3层调度架构:在顶层为每个应用创建一个高级别调度器,负责调度应用产生的消息;在中间层为每个节点创建一个低级别调度器来调度所有的高级别调度器;在底层,一个介质访问控制调度器用于授权各节点对网络的访问。设计了EDF-SS(Earliest Deadline First with Slack Stealing)算法用于改进软实时非周期消息的响应性。仿真实验证明了算法的有效性。
