In order to deal with the dynamic positioning system control problems of dredgers working under strong dredging reaction or harsh environments,an adaptive backstepping method is proposed.Disturbances are estimated and...In order to deal with the dynamic positioning system control problems of dredgers working under strong dredging reaction or harsh environments,an adaptive backstepping method is proposed.Disturbances are estimated and compensated for by the adaptive method without extra sensors on dredging equipment,and the control mechanism is simplified.Adaptive control is used to compensate for the reaction and environmental disturbances on the dredger,so the dredger can maintain the desired position with a minimum error and shock.The proposed adaptive robust controller guarantees the global asymptotic stability of the closed-loop system and rapid position tracking of the dredger.The simulation results show that the proposed controller has superior performance in position tracking and robustness to large disturbances.展开更多
In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate co...In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate coupled hydrodynamic effects by comparison with the results obtained by 3D frequency method which has been proved to be efficient for solving such problems. In order to improve efficiency of calculation, the effect of history time has been discussed, and an improved method is presented. Moreover, the effect of lateral separation distance is also discussed in detail. The technique developed here may serve as a more rigorous tool to analyze the related transient problems of two ships doing underway replenishment in waves.展开更多
Continuous vorticity panels were used to model general unsteady inviscid, incompressible, two-dimensional flows. The geometry of the airfoil was approximated by series of short straight segments having endpoints that ...Continuous vorticity panels were used to model general unsteady inviscid, incompressible, two-dimensional flows. The geometry of the airfoil was approximated by series of short straight segments having endpoints that lie on the actual surface. A piecewise linear, continuous distribution of vorticity over the airfoil surface was used to generate disturbance flow. The no-penetration condition was imposed at the midpoint of each segment and at discrete times. The wake was simulated by a system of point vortices, which moved at local fluid velocity. At each time step, a new wake panel with uniform vorticity distribution was attached to the trailing edge, and the condition of constant circulation around the airfoil and wake was imposed. A new expression for Kutta condition was developed to study the interference effect between two impulsively started NACA0012 airfoils. The tandem arrangement was found to be the most effective to enhance the lift of the rear airfoil. The interference effect between tidal turbine blades was shown clearly.展开更多
An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is ...An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is performed for several values of asymmetric outrigger configuration and hull separation, altering the Froude number in the range 0.3–0.9. Our results indicate that remarkable changes in resistance require notable changes in transverse distance values （hull separation） when wave interference may occur. In addition, there is no single configuration that consistently outperforms the other configurations across the entire speed range and the optimum interference factor -0.2 appears at a Froude number of 0.45 in S/L=0.33 with the outrigger outer position： asymmetric outboard for A3 configuration.展开更多
Pluripotent stem cells derived from neonatal or adult testes are a useful tool to examine the mechanisms of pluripotency and a resource for cell-based therapies. However, therapies usingthese cells will only benefit m...Pluripotent stem cells derived from neonatal or adult testes are a useful tool to examine the mechanisms of pluripotency and a resource for cell-based therapies. However, therapies usingthese cells will only benefit males but not females. Recently, female germline stem cells （FGSCs） were discovered in ovaries. Whether FGSCs can be converted into pluripotent stem cells, similar to spermatogonial stem cells, is unknown. Here, we demonstrate that female embryonic stem-like cells （fESLCs） can be generated within 1 month from the stably proliferating FGSCs cultured in embryonic stem cell （ESC） medium, fESLCs exhibit properties similar to those of ESCs in terms of marker expression and differentiation potential. Thus, our findings suggest that generation of patient-specific fESLCs is feasible and provides a foundation for personalized regenerative applications.展开更多
Genetic transformation in some plant species, including cotton （Gossypium hirsutum）, is hampered by laborious and time-consuming processes and often unachievable. Virus-induced gene silencing （VIGS） by double-stra...Genetic transformation in some plant species, including cotton （Gossypium hirsutum）, is hampered by laborious and time-consuming processes and often unachievable. Virus-induced gene silencing （VIGS） by double-stranded RNAs can serve as a reverse-genetics tool to determine gene function. However, knockdown levels vary greatly when using a tobacco rattle virus-based vector that carries different cDNA fragments of a gene. How to choose the optional target fragment for high interference efficiency is very challenging. Addressing this challenge requires increasing the efficacy of small interference RNA （siRNA） in target fragment. Here, we describe a method to assess VIGS efficiency by comparing the following parameters of siRNA in target sequence： the disruptionenergy of the target （△Gdisruption）, the differential stability of siRNA duplex ends （DSSE）, and the internal stability at positions 9-14 of the siRNA antisense strand （AIS）, which are calculated by Sfold program （http：//sfold.wadsworth. org）. We find that the siRNAs with low mGdisruption, high DSSE and high AIS have high activity and easily result in high VIGS efficiency by experimentally testing the actual knockdown levels of the four target genes, GhPDS, GhCLA1, GhAOS1, and GhCXE1 via choosing different target sequences for each gene. Therefore, the Sfold pro- gram can be used to analyze target sequences when car- rying out VIGS design to increase gene-silencing effects in plants.展开更多
基金The National Basic Research Program of China (973 Program) (No. 2005CB221505)Open Fund of Provincial Open Laboratory for Control Engineering Key Disciplines (No. KG2009-02)
文摘In order to deal with the dynamic positioning system control problems of dredgers working under strong dredging reaction or harsh environments,an adaptive backstepping method is proposed.Disturbances are estimated and compensated for by the adaptive method without extra sensors on dredging equipment,and the control mechanism is simplified.Adaptive control is used to compensate for the reaction and environmental disturbances on the dredger,so the dredger can maintain the desired position with a minimum error and shock.The proposed adaptive robust controller guarantees the global asymptotic stability of the closed-loop system and rapid position tracking of the dredger.The simulation results show that the proposed controller has superior performance in position tracking and robustness to large disturbances.
文摘In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate coupled hydrodynamic effects by comparison with the results obtained by 3D frequency method which has been proved to be efficient for solving such problems. In order to improve efficiency of calculation, the effect of history time has been discussed, and an improved method is presented. Moreover, the effect of lateral separation distance is also discussed in detail. The technique developed here may serve as a more rigorous tool to analyze the related transient problems of two ships doing underway replenishment in waves.
基金Sponsored by National Natural Science Foundation (No. 50279004)the National Hi-Tech. R&D Program of China (No. 2002aa516010)
文摘Continuous vorticity panels were used to model general unsteady inviscid, incompressible, two-dimensional flows. The geometry of the airfoil was approximated by series of short straight segments having endpoints that lie on the actual surface. A piecewise linear, continuous distribution of vorticity over the airfoil surface was used to generate disturbance flow. The no-penetration condition was imposed at the midpoint of each segment and at discrete times. The wake was simulated by a system of point vortices, which moved at local fluid velocity. At each time step, a new wake panel with uniform vorticity distribution was attached to the trailing edge, and the condition of constant circulation around the airfoil and wake was imposed. A new expression for Kutta condition was developed to study the interference effect between two impulsively started NACA0012 airfoils. The tandem arrangement was found to be the most effective to enhance the lift of the rear airfoil. The interference effect between tidal turbine blades was shown clearly.
文摘An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is performed for several values of asymmetric outrigger configuration and hull separation, altering the Froude number in the range 0.3–0.9. Our results indicate that remarkable changes in resistance require notable changes in transverse distance values （hull separation） when wave interference may occur. In addition, there is no single configuration that consistently outperforms the other configurations across the entire speed range and the optimum interference factor -0.2 appears at a Froude number of 0.45 in S/L=0.33 with the outrigger outer position： asymmetric outboard for A3 configuration.
基金Funding This work was supported by National Basic Research Program of China （2013CB967401 and 2010CB945001）, and the National Nature Science Foundation of China （81370675 and 81121001）.
文摘Pluripotent stem cells derived from neonatal or adult testes are a useful tool to examine the mechanisms of pluripotency and a resource for cell-based therapies. However, therapies usingthese cells will only benefit males but not females. Recently, female germline stem cells （FGSCs） were discovered in ovaries. Whether FGSCs can be converted into pluripotent stem cells, similar to spermatogonial stem cells, is unknown. Here, we demonstrate that female embryonic stem-like cells （fESLCs） can be generated within 1 month from the stably proliferating FGSCs cultured in embryonic stem cell （ESC） medium, fESLCs exhibit properties similar to those of ESCs in terms of marker expression and differentiation potential. Thus, our findings suggest that generation of patient-specific fESLCs is feasible and provides a foundation for personalized regenerative applications.
基金supported by Major Program of Joint Funds (Sinkiang) of the National Natural Science Foundation of China (No. U1303282)
文摘Genetic transformation in some plant species, including cotton （Gossypium hirsutum）, is hampered by laborious and time-consuming processes and often unachievable. Virus-induced gene silencing （VIGS） by double-stranded RNAs can serve as a reverse-genetics tool to determine gene function. However, knockdown levels vary greatly when using a tobacco rattle virus-based vector that carries different cDNA fragments of a gene. How to choose the optional target fragment for high interference efficiency is very challenging. Addressing this challenge requires increasing the efficacy of small interference RNA （siRNA） in target fragment. Here, we describe a method to assess VIGS efficiency by comparing the following parameters of siRNA in target sequence： the disruptionenergy of the target （△Gdisruption）, the differential stability of siRNA duplex ends （DSSE）, and the internal stability at positions 9-14 of the siRNA antisense strand （AIS）, which are calculated by Sfold program （http：//sfold.wadsworth. org）. We find that the siRNAs with low mGdisruption, high DSSE and high AIS have high activity and easily result in high VIGS efficiency by experimentally testing the actual knockdown levels of the four target genes, GhPDS, GhCLA1, GhAOS1, and GhCXE1 via choosing different target sequences for each gene. Therefore, the Sfold pro- gram can be used to analyze target sequences when car- rying out VIGS design to increase gene-silencing effects in plants.
