Propagation properties of foreshock cavitons: Cluster observations

Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region. They are characterized by a simultaneous depression of magnetic field magnitude and plasma density, which are bounded with enhancements of these two parameters and surrounded by ultralow frequency(ULF) waves. Previous studies focused on the interplanetary magnetic field(IMF) conditions, solar wind(SW) conditions, and the growth of the foreshock waves related to the generation of foreshock cavitons. Previously, a multipoint spacecraft analysis method using Cluster data was applied to analyze only two foreshock cavitons, and this method did not consider uncertainties. In this study, multipoint spacecraft analysis methods, including the timing method, the minimum directional derivative(MDD) method, and the spatiotemporal difference(STD) method are applied to determine the velocity in both spacecraft and solar wind frames. The propagation properties show good agreement with previous results from simulations and observations that most cavitons move sunward in the solar wind frame, with the velocities larger than the Alfvén speed. The propagation properties of foreshock cavitons support the formation mechanism of cavitons in previous simulations, which suggested that cavitons are formed due to the nonlinear evolution of compressive ULF waves. We find that there is clear decreasing trend between the size of cavitons and their velocity in the solar wind frame. In addition, the timing method considering errors has been applied to study the evolution properties by comparing the velocities with errors of the leading and trailing edges, and we identify three stable cavitons and one contracting caviton, which has not been studied before.Most cavitons should remain stable when they travel toward the Earth's bow shock. The relationship between the size of foreshock cavitons and their distance from the bow shock is also discussed.     

Arc corrosion behavior of Cu-Ti_3AlC_2 composites in air atmosphere

The arc corrosion evolution of Cu-20 vol.% Ti_3 AlC_2 cathodes is presented here. After eroded by 3, 4, 5, 6, 7, 8, 9, 10 kV DC voltage, respectively, the surface morphologies were characterized by field emission scanning electron microscope with craters and protrusions. Compared to small craters and dense protrusions of the morphology by high voltage, the eroded surface was covered with bigger craters and sparse protrusions at low voltage. No crack was discovered on the surface even at 10 kV. By means of energy dispersive spectroscopy and Raman spectroscopy, the decomposition of Cu-20 vol.% Ti_3 AlC_2 cathode to CuO,Al__2 O_3 and TiO_2 were proved. Meanwhile, W anode is oxidized to WO_2. The peak current increases with the increasing breakdown voltage, which is recorded by a digital memory oscilloscope.     

Kinematics analysis of a novel all-attitude flight simulator

To overcome the kinematic singularity limitation of simulator, which is unavoidable in a three-axis architecture, an all-attitude flight simulator in a four-axis architecture is proposed. The simulator can always provide 3DOF motion by applying redundant manipulator mechanism. For direct kinematics of the manipulator, a dual-Euler method is adopted to solve the expressions of attitude angles; thus computation singularity of all- attitude angles is overcome. For inverse kinematics of the manipulator, pseudo-...     

成膜助剂对核壳结构乳胶粒子成膜过程的影响

以核壳结构丙烯酸酯乳液为研究对象,采用扩散波光谱技术(diffusing-wave spectroscopy,DWS)对成膜助剂二丙二醇丁醚(DPNB)在乳液成膜过程的作用机理进行了研究.通过获取乳胶粒子在成膜过程中多级动态散射光的散斑干涉波动频率随时间的变化规律,确定DPNB在粒子相互排列阶段就开始起作用,且随着DPNB用量的增加,谱图由多峰变为双峰,最终呈现单峰;结合最低成膜温度(MFFT)、动态光散射(DLS)、原子力显微镜(AFM)等仪器分析发现,得到适用于本体系成膜助剂的最佳使用量为7%～8%(质量分数),在该成膜助剂用量下粒子边界融合充分,从宏观上表现为连续漆膜.     

亚临界流体1,1,1,2-四氟乙烷(R134a)萃取原花青素的工艺研究

在10mL高压萃取釜中,对亚临界流体1,1,1,2-四氟乙烷(R134a)萃取天然产物中原花青素的适宜工艺条件进行了研究。通过正交实验和单因素实验考察了萃取压力、萃取温度和萃取时间对山楂和紫薯两种原料中原花青素萃取率的影响。结果表明:在以山楂为实验原料,萃取压力10 MPa,萃取温度50℃,萃取时间80 min的工艺条件下,原花青素萃取率为2.50%;在以紫薯为实验原料,萃取压力12 MPa,萃取温度50℃,萃取时间80 min的工艺条件下,原花青素萃取率为1.00%。     

Eddy current loss analysis and frequency optimization design of double-sided LCC-IPT system in seawater environment

Science China Technological Sciences - Inductive power transfer system can generate eddy current when operating in seawater medium. On the one hand, it can cause eddy current loss, and reduce...     

Effects of different atmospheres on the arc erosion behaviors of Ti3SiC2 cathodes

The effects of ambient atmospheres on the arc erosion behaviors of Ti_3SiC_2 cathodes were investigated at 5.5 kV in argon,nitrogen, air, and oxygen. The mass loss of the cathodes increased in the order of argon, nitrogen, air, and oxygen and the morphologies were measured by 3D laser scanning confocal microscope with a gradual blooming phenomenon. Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to detect the components of erosion regions.The erosion-chemical products mainly consisted of TiN_x in nitrogen, TiN_x, TiO_2 and SiO_2 in air, TiO_2 and SiO_2 in oxygen. The arc energy was responsible for the arc erosion characteristics in different atmospheres.     

Analysis and elimination of tri-band beacon interference with the fluxgate sensors onboard CSES

Science China Technological Sciences - High precision magnetometer (HPM) is a magnetic field detection payload onboard China Seismo-Electromagnetic Satellite (CSES), including two fluxgate...