Water is an important factor affecting growth, yield and distribution of different species. Plant response to water deficit can be in the form of physiological disorders, such as reduction in transpiration or assimila...Water is an important factor affecting growth, yield and distribution of different species. Plant response to water deficit can be in the form of physiological disorders, such as reduction in transpiration or assimilating partitioning to root growth. Sustainable use of water has become a priority in agriculture and thus innovative irrigation management practices are critical. The study aimed at investigating how watering frequency and terminal water stress influence growth of Pelargonium sidoides, an important medicinal plant in Southern Africa. The trial was a randomized complete block design with three replicates, and treatment factors were watering frequency （everyday, twice and once a week） and terminal water stress （no watering four weeks before harvesting, no watering two weeks before harvesting and no terminal stress）. There was an interacting effect of watering frequency and terminal water stress on biomass and fresh root yield. More frequent watering resulted in significantly higher biomass and fresh root yield, compared to other treatments. Watering everyday with terminal or no terminal water stress resulted in higher fresh root yield, compared to other watering treatments with terminal water stress. Plant height and leaf area were significantly affected by watering frequency and terminal water stress, respectively. A significant drop in stomatal conductance of plants watered everyday was observed 240 d after treatment implementation, such that there was no significant difference across all the three watering frequency treatments. In conclusion, farmers can save on irrigation costs by reducing watering frequency, as there was no significant difference on dry root yield.展开更多
The problem of diving control for an underactuated unmanned undersea vehicle(UUV) considering the presence of parameters perturbations and wave disturbances was addressesed.The vertical motion of an UUV was divided in...The problem of diving control for an underactuated unmanned undersea vehicle(UUV) considering the presence of parameters perturbations and wave disturbances was addressesed.The vertical motion of an UUV was divided into two noninteracting subsystems for surge velocity control and diving.To stabilize the vertical motion system,the surge velocity and the depth control controllers were proposed using backstepping technology and an integral-fast terminal sliding mode control(IFTSMC).It is proven that the proposed control scheme can guarantee that all the error signals in the whole closed-loop system globally converge to the sliding surface in finite time and asymptotically converge to the origin along the sliding surface.With a unified control parameters for different motion states,a series of numerical simulation results illustrate the effectiveness of the above designed control scheme,which also shows strong robustness against parameters perturbations and wave disturbances.展开更多
文摘Water is an important factor affecting growth, yield and distribution of different species. Plant response to water deficit can be in the form of physiological disorders, such as reduction in transpiration or assimilating partitioning to root growth. Sustainable use of water has become a priority in agriculture and thus innovative irrigation management practices are critical. The study aimed at investigating how watering frequency and terminal water stress influence growth of Pelargonium sidoides, an important medicinal plant in Southern Africa. The trial was a randomized complete block design with three replicates, and treatment factors were watering frequency （everyday, twice and once a week） and terminal water stress （no watering four weeks before harvesting, no watering two weeks before harvesting and no terminal stress）. There was an interacting effect of watering frequency and terminal water stress on biomass and fresh root yield. More frequent watering resulted in significantly higher biomass and fresh root yield, compared to other treatments. Watering everyday with terminal or no terminal water stress resulted in higher fresh root yield, compared to other watering treatments with terminal water stress. Plant height and leaf area were significantly affected by watering frequency and terminal water stress, respectively. A significant drop in stomatal conductance of plants watered everyday was observed 240 d after treatment implementation, such that there was no significant difference across all the three watering frequency treatments. In conclusion, farmers can save on irrigation costs by reducing watering frequency, as there was no significant difference on dry root yield.
基金Projects (51179038,51309067) supported by the National Natural Science Foundation of China
文摘The problem of diving control for an underactuated unmanned undersea vehicle(UUV) considering the presence of parameters perturbations and wave disturbances was addressesed.The vertical motion of an UUV was divided into two noninteracting subsystems for surge velocity control and diving.To stabilize the vertical motion system,the surge velocity and the depth control controllers were proposed using backstepping technology and an integral-fast terminal sliding mode control(IFTSMC).It is proven that the proposed control scheme can guarantee that all the error signals in the whole closed-loop system globally converge to the sliding surface in finite time and asymptotically converge to the origin along the sliding surface.With a unified control parameters for different motion states,a series of numerical simulation results illustrate the effectiveness of the above designed control scheme,which also shows strong robustness against parameters perturbations and wave disturbances.
