In this paper,a sparse nonuniform rectangular array based on spatially spread electromagnetic vector sensor(SNRASSEMVS)is introduced,and a method for estimating 2D-direction of arrival(DOA)and polarization is devised....In this paper,a sparse nonuniform rectangular array based on spatially spread electromagnetic vector sensor(SNRASSEMVS)is introduced,and a method for estimating 2D-direction of arrival(DOA)and polarization is devised.Firstly,according to the special structure of the sparse nonuniform rectangular array(SNRA),a set of accurate but ambiguous direction-cosine estimates can be obtained.Then the steering vector of spatially spread electromagnetic vector sensor(SSEMVS)can be extracted from the array manifold to obtain the coarse but unambiguous direction-cosine estimates.Finally,the disambiguation approach can be used to get the final accurate estimates of 2DDOA and polarization.Compared with some existing methods,the SNRA configuration extends the spatial aperture and refines the parameters estimation accuracy without adding any redundant antennas,as well as reduces the mutual coupling effect.Moreover,the proposed algorithm resolves multiple sources without the priori knowledge of signal information,suffers no ambiguity in the estimation of the Poynting vector,and pairs the x-axis direction cosine with the y-axis direction cosine automatically.Simulation results are given to verify the effectiveness and superiority of the proposed algorithm.展开更多
A spatial channel propagation model is presented. Consider a uniform linear antenna （ULA） at the base station （BS） and narrowband signals transmitted at the mobile. In two types of propagating environments： indoo...A spatial channel propagation model is presented. Consider a uniform linear antenna （ULA） at the base station （BS） and narrowband signals transmitted at the mobile. In two types of propagating environments： indoor and outdoor, performance of low spatial correlation is investigated and some results are provided, which are significant to an,3. lyze the performance of diversity systems and configuration of army. The results also show that the configuration of array with either smaller angular spread or bigger angle of arrival （AOA） dominates the impact on spatial correlation, and that increasing angular spread or decreasing AOA diminishes, or even eliminates this impact.展开更多
Potato virus Y(PVY)is a non-persistent virus that is transmitted by many aphid species and causes significant damage to potato production.We constructed a spatially-explicit model simulating PVY spread in a potato fie...Potato virus Y(PVY)is a non-persistent virus that is transmitted by many aphid species and causes significant damage to potato production.We constructed a spatially-explicit model simulating PVY spread in a potato field and used it to investigate possible effects of transmission efficiency,initial inoculum levels,vector behavior,vector abundance,and timing of peak vector activity on PVY incidence at the end of a simulated growing season.Lower PVY incidence in planted seed resulted in lower virus infection at the end of the season.However,when populations of efficient PVY vectors were high,significant PVY spread occurred even when initial virus inoculum was low.Non-colonizing aphids were more important for PVY spread compared to colonizing aphids,particularly at high densities.An early-season peak in the numbers of noncolonizing aphids resulted in the highest number of infected plants in the end of the season,while mid-and late-season peaks caused relatively little virus spread.Our results highlight the importance of integrating different techniques to prevent the number of PVY-infected plants from exceeding economically acceptable levels instead of trying to control aphids within potato fields.Such management plans should be implemented very early in a growing season.展开更多
In this paper, we establish a mathematical model of the forest fire spread process based on a partial differential equation. We describe the distribution of time field and velocity field in the whole two-dimensional s...In this paper, we establish a mathematical model of the forest fire spread process based on a partial differential equation. We describe the distribution of time field and velocity field in the whole two-dimensional space by vector field theory. And we obtain a continuous algorithm to predict the dynamic behavior of forest fire spread in a short time. We use the algorithm to interpolate the fire boundary by cubic non-uniform rational B-spline closed curve. The fire boundary curve at any time can be simulated by solving the Eikonal equation. The model is tested in theory and in practice. The results show that the model has good accuracy and stability, and it’s compatible with most of the existing models, such as the elliptic model and the cellular automata model.展开更多
入侵植物小子虉草(Phalaris minor Retz.)对入侵地冬春农作物,尤其是麦类作物危害严重,是世界公认的麦田恶性杂草。近年来,小子虉草在云南省大面积暴发危害,且种群不断扩张,严重威胁农田生态系统和粮食生产安全。然而,我国目前除作者前...入侵植物小子虉草(Phalaris minor Retz.)对入侵地冬春农作物,尤其是麦类作物危害严重,是世界公认的麦田恶性杂草。近年来,小子虉草在云南省大面积暴发危害,且种群不断扩张,严重威胁农田生态系统和粮食生产安全。然而,我国目前除作者前期开展了初步研究外,尚少见其他研究报道,给其预警与防控带来较大困难。本文根据国外近年来的研究进展和作者前期研究结果,首先综述目前小子虉草在世界的空间分布,从种间竞争、化感作用等方面分析其对农作物的危害原因;并从小子虉草的生物学特性、种群遗传特性、生态适应性以及入侵环境的可侵入性4个方面,综述分析其种群入侵扩张的成因,同时介绍了国外关于该入侵物种的防除方法。最后结合我国小子虉草的发生危害特点,提出今后的研究建议。本文通过介绍小子虉草的生物学与生态学特性和种群的入侵扩张机制,对该物种的早期预警、限制传播以及入侵生态系统的恢复与管理均具有重要的指导意义,也为相关决策者掌握了解小子虉草和制定安全有效的防控策略提供参考。展开更多
基金This work was supported by the innovation project of Science and Technology Commission of the Central Military Commission。
文摘In this paper,a sparse nonuniform rectangular array based on spatially spread electromagnetic vector sensor(SNRASSEMVS)is introduced,and a method for estimating 2D-direction of arrival(DOA)and polarization is devised.Firstly,according to the special structure of the sparse nonuniform rectangular array(SNRA),a set of accurate but ambiguous direction-cosine estimates can be obtained.Then the steering vector of spatially spread electromagnetic vector sensor(SSEMVS)can be extracted from the array manifold to obtain the coarse but unambiguous direction-cosine estimates.Finally,the disambiguation approach can be used to get the final accurate estimates of 2DDOA and polarization.Compared with some existing methods,the SNRA configuration extends the spatial aperture and refines the parameters estimation accuracy without adding any redundant antennas,as well as reduces the mutual coupling effect.Moreover,the proposed algorithm resolves multiple sources without the priori knowledge of signal information,suffers no ambiguity in the estimation of the Poynting vector,and pairs the x-axis direction cosine with the y-axis direction cosine automatically.Simulation results are given to verify the effectiveness and superiority of the proposed algorithm.
基金This project was supported by the National High-Tech Research and Development Program (2002AA123032).
文摘A spatial channel propagation model is presented. Consider a uniform linear antenna （ULA） at the base station （BS） and narrowband signals transmitted at the mobile. In two types of propagating environments： indoor and outdoor, performance of low spatial correlation is investigated and some results are provided, which are significant to an,3. lyze the performance of diversity systems and configuration of army. The results also show that the configuration of array with either smaller angular spread or bigger angle of arrival （AOA） dominates the impact on spatial correlation, and that increasing angular spread or decreasing AOA diminishes, or even eliminates this impact.
基金supported in part by the United States Department of Agriculture National institute of Food and Agriculture Special Crops Research initiative (Award # 2014-51181-22373)Funding for Hongchun Qu’s stay at the University of Maine was received from the National Natural Science Foundation of China (Award # 61871061)
文摘Potato virus Y(PVY)is a non-persistent virus that is transmitted by many aphid species and causes significant damage to potato production.We constructed a spatially-explicit model simulating PVY spread in a potato field and used it to investigate possible effects of transmission efficiency,initial inoculum levels,vector behavior,vector abundance,and timing of peak vector activity on PVY incidence at the end of a simulated growing season.Lower PVY incidence in planted seed resulted in lower virus infection at the end of the season.However,when populations of efficient PVY vectors were high,significant PVY spread occurred even when initial virus inoculum was low.Non-colonizing aphids were more important for PVY spread compared to colonizing aphids,particularly at high densities.An early-season peak in the numbers of noncolonizing aphids resulted in the highest number of infected plants in the end of the season,while mid-and late-season peaks caused relatively little virus spread.Our results highlight the importance of integrating different techniques to prevent the number of PVY-infected plants from exceeding economically acceptable levels instead of trying to control aphids within potato fields.Such management plans should be implemented very early in a growing season.
文摘In this paper, we establish a mathematical model of the forest fire spread process based on a partial differential equation. We describe the distribution of time field and velocity field in the whole two-dimensional space by vector field theory. And we obtain a continuous algorithm to predict the dynamic behavior of forest fire spread in a short time. We use the algorithm to interpolate the fire boundary by cubic non-uniform rational B-spline closed curve. The fire boundary curve at any time can be simulated by solving the Eikonal equation. The model is tested in theory and in practice. The results show that the model has good accuracy and stability, and it’s compatible with most of the existing models, such as the elliptic model and the cellular automata model.
基金The research work was supported by the State"973"Program (Grant No.TG2000016210),the Chinese Academy of Sciences (Grant No.kscx2-sw-103) and National Natural Science Foundation of China (Grant No.30170158).
文摘入侵植物小子虉草(Phalaris minor Retz.)对入侵地冬春农作物,尤其是麦类作物危害严重,是世界公认的麦田恶性杂草。近年来,小子虉草在云南省大面积暴发危害,且种群不断扩张,严重威胁农田生态系统和粮食生产安全。然而,我国目前除作者前期开展了初步研究外,尚少见其他研究报道,给其预警与防控带来较大困难。本文根据国外近年来的研究进展和作者前期研究结果,首先综述目前小子虉草在世界的空间分布,从种间竞争、化感作用等方面分析其对农作物的危害原因;并从小子虉草的生物学特性、种群遗传特性、生态适应性以及入侵环境的可侵入性4个方面,综述分析其种群入侵扩张的成因,同时介绍了国外关于该入侵物种的防除方法。最后结合我国小子虉草的发生危害特点,提出今后的研究建议。本文通过介绍小子虉草的生物学与生态学特性和种群的入侵扩张机制,对该物种的早期预警、限制传播以及入侵生态系统的恢复与管理均具有重要的指导意义,也为相关决策者掌握了解小子虉草和制定安全有效的防控策略提供参考。
