A predator-prey model with linear capture term Holling-II functional response was studied by using differential equation theory. The existence and the stabilities of non-negative equilibrium points of the model were d...A predator-prey model with linear capture term Holling-II functional response was studied by using differential equation theory. The existence and the stabilities of non-negative equilibrium points of the model were discussed. The results show that under certain limited conditions, these two groups can maintain a balanced position, which provides a theoretical reference for relevant departments to make decisions on ecological protection.展开更多
In single-frequency precise-point positioning of a satellite,ionosphere delay is one of the most important factors impacting the accuracy. Because of the instability of the ionosphere and uncertainty of its physical p...In single-frequency precise-point positioning of a satellite,ionosphere delay is one of the most important factors impacting the accuracy. Because of the instability of the ionosphere and uncertainty of its physical properties, the positioning accuracy is seriously limited when using a precision-limited model for correction. In order to reduce the error, we propose to introduce some ionosphere parameter for real-time ionosphere-delay estimation by applying various mapping functions. Through calculation with data from the IGS（ International GPS Service） tracking station and comparison among results of using several different models and mapping functions, the feasibility and effectiveness of the new method are verified.展开更多
In ground-based astronomy,images of objects in outer space are acquired via ground-based telescopes.However,the imaging system is generally interfered by atmospheric turbulence and hence images so acquired are blurred...In ground-based astronomy,images of objects in outer space are acquired via ground-based telescopes.However,the imaging system is generally interfered by atmospheric turbulence and hence images so acquired are blurred with unknown point spread function(PSF).To restore the observed images,aberration of the wavefront at the telescope’s aperture,i.e.,the phase,is utilized to derive the PSF.However,the phase is not readily available.Instead,its gradients can be collected by wavefront sensors.Thus the usual approach is to use regularization methods to reconstruct high-resolution phase gradients and then use them to recover the phase in high accuracy.Here,we develop a model that reconstructs the phase directly.The proposed model uses the tight frame regularization and it can be solved efciently by the Douglas-Rachford alternating direction method of multipliers whose convergence has been well established.Numerical results illustrate that our new model is efcient and gives more accurate estimation for the PSF.展开更多
文摘A predator-prey model with linear capture term Holling-II functional response was studied by using differential equation theory. The existence and the stabilities of non-negative equilibrium points of the model were discussed. The results show that under certain limited conditions, these two groups can maintain a balanced position, which provides a theoretical reference for relevant departments to make decisions on ecological protection.
基金supported by the National Natural Science Foundation of China(40902081,40774001,40841021)
文摘In single-frequency precise-point positioning of a satellite,ionosphere delay is one of the most important factors impacting the accuracy. Because of the instability of the ionosphere and uncertainty of its physical properties, the positioning accuracy is seriously limited when using a precision-limited model for correction. In order to reduce the error, we propose to introduce some ionosphere parameter for real-time ionosphere-delay estimation by applying various mapping functions. Through calculation with data from the IGS（ International GPS Service） tracking station and comparison among results of using several different models and mapping functions, the feasibility and effectiveness of the new method are verified.
基金supported by Hong Kong Research Grants Council(HKRGC)(Grant Nos.CUHK400412 and HKBU203311)CUHK Direct Allocation Grant(Grant No.4053007)+1 种基金CUHK Focused Investment Scheme(Grant No.1902036)National Natural Science Foundation of China(Grant No.11301055)
文摘In ground-based astronomy,images of objects in outer space are acquired via ground-based telescopes.However,the imaging system is generally interfered by atmospheric turbulence and hence images so acquired are blurred with unknown point spread function(PSF).To restore the observed images,aberration of the wavefront at the telescope’s aperture,i.e.,the phase,is utilized to derive the PSF.However,the phase is not readily available.Instead,its gradients can be collected by wavefront sensors.Thus the usual approach is to use regularization methods to reconstruct high-resolution phase gradients and then use them to recover the phase in high accuracy.Here,we develop a model that reconstructs the phase directly.The proposed model uses the tight frame regularization and it can be solved efciently by the Douglas-Rachford alternating direction method of multipliers whose convergence has been well established.Numerical results illustrate that our new model is efcient and gives more accurate estimation for the PSF.
