It is potentially useful to perform deception jamming using the digital image synthesizer （DIS） since it can form a two-dimensional （2D） decoy but suffers from multiple decoys ge- neration. Inspired by the intermi...It is potentially useful to perform deception jamming using the digital image synthesizer （DIS） since it can form a two-dimensional （2D） decoy but suffers from multiple decoys ge- neration. Inspired by the intermittent sampling repeater jamming （ISRJ）, the generation of inverse synthetic aperture radar （ISAR） decoys is addressed, associated with the DIS and the ISRJ. Radar pulses are sampled intermittently and modulated by the scatter- ing model of a false target by mounting the jammer on a moving platform, and then the jamming signals are retransmitted to the radar and a train of decoys are induced after ISAR imaging. A scattering model of Yak-42 is adopted as the false-target mo- dulation model to verify the effectiveness of the jamming method based on the standard ISAR motion compensation and image for- mation procedure.展开更多
Through dimension analysis, an almost analytical model for the maximum diffusion induced stress(DIS)and critical temperature(or concentration) difference at which cracks begin to initiate in the diffusion process is d...Through dimension analysis, an almost analytical model for the maximum diffusion induced stress(DIS)and critical temperature(or concentration) difference at which cracks begin to initiate in the diffusion process is developed. It interestingly predicts that the spacing of diffusioninduced cracks is constant, independent of the thickness of specimen and the temperature difference. These conclusions are validated by our thermal shock experiments on alumina plates. Furthermore, the proposed model can interpret observed hierarchical crack patterns for high temperature jump cases, and a three-stage relation between the residual strength and the temperature difference. The prediction for crack spacing can guide the biomimetic thermal-shockfailure proof design, in which the hard platelets smaller than the predicted diffusion induced by constant crack-spacing are embedded in a soft matrix, and, therefore, no fracture will happen. This may guide the design of the thermal protection system and the lithium ion battery. Finally we present the maximum normalized DISes for various geometry and boundary conditions by single-variable curves for the stressindependent diffusion process and two-variable contour plots for the stress-dependent diffusion process, which can provideengineers and materialists a simple and easy way to quickly evaluate the reliability of related materials and devices.展开更多
Controller optimization has mostly been done by minimizing a certain single cost function.In practice,however,engineers must contend with multiple and conflicting considerations,denoted as design indices(DIs)in this p...Controller optimization has mostly been done by minimizing a certain single cost function.In practice,however,engineers must contend with multiple and conflicting considerations,denoted as design indices(DIs)in this paper.Failure to account for such complexity and nuances is detrimental to the applications of any advanced control methods.This paper addresses this challenge heads on,in the context of active disturbance rejection controller(ADRC)and with four competing DIs:stability margins,tracking,disturbance rejection,and noise suppression.To this end,the lower bound for the bandwidth of the extended state observer is first established for guaranteed closed-loop stability.Then,one by one,the mathematical formula is meticulously derived,connecting each DI to the set of controller parameters.To our best knowledge,this has not been done in the context of ADRC.Such formulas allow engineers to see quantitatively how the change of each tuning parameter would impact all of the DIs,thus making the guesswork obsolete.An example is given to show how such analytical methods can help engineers quickly determine controller parameters in a practical scenario.展开更多
基金supported by the National Natural Science Foundation of China(6137217061401491)
文摘It is potentially useful to perform deception jamming using the digital image synthesizer （DIS） since it can form a two-dimensional （2D） decoy but suffers from multiple decoys ge- neration. Inspired by the intermittent sampling repeater jamming （ISRJ）, the generation of inverse synthetic aperture radar （ISAR） decoys is addressed, associated with the DIS and the ISRJ. Radar pulses are sampled intermittently and modulated by the scatter- ing model of a false target by mounting the jammer on a moving platform, and then the jamming signals are retransmitted to the radar and a train of decoys are induced after ISAR imaging. A scattering model of Yak-42 is adopted as the false-target mo- dulation model to verify the effectiveness of the jamming method based on the standard ISAR motion compensation and image for- mation procedure.
基金support from the National Natural Science Foundation of China(Grants.11372158,11425208,and 51232004)Tsinghua University Initiative Scientific Research Program(Grant.2011Z02173)
文摘Through dimension analysis, an almost analytical model for the maximum diffusion induced stress(DIS)and critical temperature(or concentration) difference at which cracks begin to initiate in the diffusion process is developed. It interestingly predicts that the spacing of diffusioninduced cracks is constant, independent of the thickness of specimen and the temperature difference. These conclusions are validated by our thermal shock experiments on alumina plates. Furthermore, the proposed model can interpret observed hierarchical crack patterns for high temperature jump cases, and a three-stage relation between the residual strength and the temperature difference. The prediction for crack spacing can guide the biomimetic thermal-shockfailure proof design, in which the hard platelets smaller than the predicted diffusion induced by constant crack-spacing are embedded in a soft matrix, and, therefore, no fracture will happen. This may guide the design of the thermal protection system and the lithium ion battery. Finally we present the maximum normalized DISes for various geometry and boundary conditions by single-variable curves for the stressindependent diffusion process and two-variable contour plots for the stress-dependent diffusion process, which can provideengineers and materialists a simple and easy way to quickly evaluate the reliability of related materials and devices.
基金This work was supported by the National Key R&D Program of China(No.2018YFA0703800)the National Natural Science Foundation of China(No.U20B2054).
文摘Controller optimization has mostly been done by minimizing a certain single cost function.In practice,however,engineers must contend with multiple and conflicting considerations,denoted as design indices(DIs)in this paper.Failure to account for such complexity and nuances is detrimental to the applications of any advanced control methods.This paper addresses this challenge heads on,in the context of active disturbance rejection controller(ADRC)and with four competing DIs:stability margins,tracking,disturbance rejection,and noise suppression.To this end,the lower bound for the bandwidth of the extended state observer is first established for guaranteed closed-loop stability.Then,one by one,the mathematical formula is meticulously derived,connecting each DI to the set of controller parameters.To our best knowledge,this has not been done in the context of ADRC.Such formulas allow engineers to see quantitatively how the change of each tuning parameter would impact all of the DIs,thus making the guesswork obsolete.An example is given to show how such analytical methods can help engineers quickly determine controller parameters in a practical scenario.
