A wind tunnel experiment was performed to investigate aeolian grain motions in the transverse direction, which is perpendicular to the incoming flow and parallels the sand bed. The trajectories in the horizontal plane...A wind tunnel experiment was performed to investigate aeolian grain motions in the transverse direction, which is perpendicular to the incoming flow and parallels the sand bed. The trajectories in the horizontal plane were recorded by high-speed camera. Statistical analysis of 630 trajectories shows that both the motion orientation and the time-averaged speed follow Gaussian distributions. An exclusive method was used to analyze the driving mechanism. It was concluded that the three-dimensional turbulent air flow, rather than the spin of grain or grain-bed collisions, controls the transverse motion.展开更多
We demonstrate an all-optical method for controlling the transverse motion of an ionization injected electron beam in a laser plasma accelerator by using the transversely asymmetrical plasma wakefield. The laser focus...We demonstrate an all-optical method for controlling the transverse motion of an ionization injected electron beam in a laser plasma accelerator by using the transversely asymmetrical plasma wakefield. The laser focus shape can control the distribution of a transversal wakefield. When the laser focus shape is changed from circular to slanted elliptical in the experiment, the electron beam profiles change from an ellipse to three typical shapes. The three-dimensional particlein-cell simulation result agrees well with the experiment, and it shows that the trajectories of these accelerated electrons change from undulating to helical. Such an all-optical method could be useful for convenient control of the transverse motion of an electron beam, which results in synchrotron radiation from orbit angular momentum.展开更多
Most previously reported inertia actuators suffer from the problems of low speed and large size.To overcome these shortcomings,this study proposes a slim compact piezo inertia actuator based on the principle of stick...Most previously reported inertia actuators suffer from the problems of low speed and large size.To overcome these shortcomings,this study proposes a slim compact piezo inertia actuator based on the principle of stick–slip drive.Actuated by the transverse motion of a cantilever beam forming part of a monolithic elastomer,this actuator achieves a high velocity.The construction and basic operating principle of the actuator are discussed in detail.Commercial finite element analysis software is employed to determine the appropriate geometry for the monolithic elastomer.To study the actuator’s mechanical characteristics,a prototype is fabricated and a series of experimental tests are performed.According to the results of these tests,the maximum velocity and maximum load force are about 24.03 mm/s and 1.96 N,respectively,and the minimum step size is about 0.47μm.It is shown that the inertia actuator based on a monolithic elastomer with a cantilever beam not only has a slim compact structure,but also exhibits good output characteristics.展开更多
基金supported by the National Natural Science Foundation of China (Project No. 10904055)
文摘A wind tunnel experiment was performed to investigate aeolian grain motions in the transverse direction, which is perpendicular to the incoming flow and parallels the sand bed. The trajectories in the horizontal plane were recorded by high-speed camera. Statistical analysis of 630 trajectories shows that both the motion orientation and the time-averaged speed follow Gaussian distributions. An exclusive method was used to analyze the driving mechanism. It was concluded that the three-dimensional turbulent air flow, rather than the spin of grain or grain-bed collisions, controls the transverse motion.
基金supported by the Science Challenge Project(No.TZ2018005)the National Key R&D Program of China(No.2017YFA0403301)+2 种基金the National Natural Science Foundation of China(Nos.11991073,11721404,11805266,11905289,and 61975229)the Chinese Postdoctoral Science Foundation(No.Y9BK014L51)the Key Program of CAS(No.XDB17030500)。
文摘We demonstrate an all-optical method for controlling the transverse motion of an ionization injected electron beam in a laser plasma accelerator by using the transversely asymmetrical plasma wakefield. The laser focus shape can control the distribution of a transversal wakefield. When the laser focus shape is changed from circular to slanted elliptical in the experiment, the electron beam profiles change from an ellipse to three typical shapes. The three-dimensional particlein-cell simulation result agrees well with the experiment, and it shows that the trajectories of these accelerated electrons change from undulating to helical. Such an all-optical method could be useful for convenient control of the transverse motion of an electron beam, which results in synchrotron radiation from orbit angular momentum.
基金supported by a Specialized Research Fund(Grant No.923801).
文摘Most previously reported inertia actuators suffer from the problems of low speed and large size.To overcome these shortcomings,this study proposes a slim compact piezo inertia actuator based on the principle of stick–slip drive.Actuated by the transverse motion of a cantilever beam forming part of a monolithic elastomer,this actuator achieves a high velocity.The construction and basic operating principle of the actuator are discussed in detail.Commercial finite element analysis software is employed to determine the appropriate geometry for the monolithic elastomer.To study the actuator’s mechanical characteristics,a prototype is fabricated and a series of experimental tests are performed.According to the results of these tests,the maximum velocity and maximum load force are about 24.03 mm/s and 1.96 N,respectively,and the minimum step size is about 0.47μm.It is shown that the inertia actuator based on a monolithic elastomer with a cantilever beam not only has a slim compact structure,but also exhibits good output characteristics.
