Path planning of a free-floating space robot based on the degree of controllability

An effective and more efficient path planning algorithm is developed for a kinematically non-redundant free-floating space robot (FFSR) system by proposing a concept of degree of controllability (DOC) for underactuated systems. The DOC concept is proposed for making full use of the internal couplings and then achieving a better control effect, followed by a certain definition of controllability measurement which measures the DOC, based on obtaining an explicit and finite equivalent affine system and singular value decomposition. A simple method for nilpotent approximation of the Lie algebra generated by the FFSR system is put forward by direct Taylor expansion when obtaining the equivalent system. Afterwards, a large-controllability-measurement (LCM) nominal path is searched by a weighted A* algorithm, and an optimal self-correcting method is designed to track the nominal path approximately, yielding an efficient underactuated path. The proposed strategy successfully avoids the drawback of inefficiency inherent in previous path-planning schemes, which is due to the neglect of internal couplings, and illustrative numerical examples show its efficacy.     

Exploring seniors’ continuance intention to use mobile social network sites in China: a cognitive-affective-conative model

Universal Access in the Information Society - With the rapid increase of senior users in mobile social network sites (MSNS), how to attract and maintain seniors’ continuous usage is more and...     

The state-of-the-art of the China Seismo-Electromagnetic Satellite mission

The China Seismo-Electromagnetic Satellite (CSES) mission was proposed in 2003 and approved in 2013 after ten years’ scientific and engineering demonstrations. To meet the requirement of scientific objectives, the satellite is designed to be in a sunsynchronous orbit with an altitude of 507 km and descending node time of 14:00 LT. The CSES satellite carries 8 instruments, including search-coil magnetometer (SCM), electric field detector (EFD), high precision magnetometer (HPM), GNSS occultation receiver (GOR), plasma analyzer package (PAP), langmuir probe (LAP), high energetic particle package (HEPP) and detector (HEPD), and tri-band beacon (TBB), among which HEPD is provided by Italian Space Agency. The CSES satellite was launched successfully on February 2, 2018, and is planned to operate for 5 years. The CSES mission is the first satellite in China to measure geophysical fields, which will have a lot of application prospects in the study of seismology, geophysics, space sciences, and so on.     

Investigation of microgravity effect on solidification of medium-low-melting-point alloy by drop tube experiment

The solidification microstructure of Al-Ni, Al-Cu, Ag-Cu, Al-Pb and Cu-Co alloys quenched in silicone oil before and after free fall in evacuated 50 m drop tube were investigated contrastively. The effect of microgravity on the solidification process of medium-low-melting-point eutectic, monotectic and peritectic alloys were analyzed and discussed. The results indicated that the effects of microgravity on the eutectic cell shape, the pattern in eutectic cell and the inter-eutectic spacing were different for different types of eutectic systems; the size distribution of Pb particles in Al-5wt% Pb monotectic alloy was significantly changed by microgravity; and the shape of retained primary α-Co phase in Cu-10wt%Co peritectic alloy was also changed by microgravity. These results are beneficial for people to further identify and analyze the solidification behavior of multiphase alloys under microgravity.     

Valence electron structure and properties of the ZrO<Subscript>2</Subscript>

To reveal the properties of ZrO₂ at the atom and electron levels, the valence electron structures of three ZrO₂ phases were analyzed on the basis of the empirical electron theory of solids and molecules. The results showed that the hybridization levels of Zr and O atoms in the m-ZrO₂ were the same as those in the t-ZrO₂, while those in the c-ZrO₂ rose markedly. The electron numbers and bond energies on the strongest covalent bonds in the m-ZrO₂ phase were the greatest, the values were 0.901106 and 157.5933 kJ/mol, respectively. Those in the t-ZrO₂ phase took second place, which were 0.722182 and 123.9304 kJ/mol, and those in the c-ZrO₂ phase were the smallest, which were 0.469323 and 79.0289 kJ/mol. According to the product of the bond energy on the strongest covalent bond and equivalent bond number (this value reflected the crystal cohesive energy), the order from the greatness to smallness was the c-ZrO₂> t-ZrO₂ > m-ZrO₂. This showed that the m-phase bonds were the tightest, their energy was the smallest, the crystal cohesive energy of the m-phase was the largest, and the m-phase existed most stably at room temperature. So it must need energy or higher temperature to take apart the stronger covalent bonds to form a new phase. Supported by the Major Project of the National Natural Science Foundation of China (Grant No. 90505015)     

新型重载铁路货车涂装防腐设计技术概论

依托运营环境、腐蚀现状及有关铁路货车涂装技术条件、标准,立足新型重载铁路货车总体设计要求,并结合ISO 12944通用防腐标准和未来趋势,从涂料选用、涂层体系设计、前处理工艺、涂装工艺设计等方面对新型重载铁路货车涂装防腐进行技术概论,以取得预期目的。     

Valence electron structure and properties of stabilized ZrO2

To reveal the properties of stabilizers in ZrO₂ on nanoscopic levels, the valence electron structures of four stable ZrO₂ phases and c-ZrO₂ were analyzed on the basis of the empirical electron theory of solids and molecules. The results showed that the hybridization levels of Zr atoms in c-ZrO₂ doped with Ca and Mg dropped from B17 to B13, the hybridization levels of Zr atoms in c-ZrO₂ doped with Y and Ce dropped from B17 to B15, and that the four stabilizing atoms all made the hybridization levels of O atoms drop from level 4 to level 2. The numbers of covalent electrons in the strongest covalent bond in the descending order are c-ZrO₂>Zr_0.82Ce_0.18O₂>Zr_0.82Y_0.18O_1.91>Zr_0.82Mg_0.18O_1.82>Zr_0.82Ca_0.18O_1.82. The bond energies of the strongest covalent bond and the melting points of the solid solutions in the descending order are Zr_0.82Ce_0.18O₂> c-ZrO₂>Zr_0.82Y_0.18O_1.91>Zr_0.82Mg_0.18O_1.82>Zr_0.82Ca_0.18O_1.82. The percentages of the total number of covalent electrons in the descending order are c-ZrO₂>Zr_0.82Y_0.18O_1.91> Zr_0.82Ce_0.18O₂>Zr_0.82Mg_0.18O_1.82> Zr_0.82Ca_0.18O_1.82. From the above analysis, it can be concluded that the stabilizing degrees of the four stabilizers in the descending order are CaO> MgO>Y₂O₃>CeO₂. Supported by the Major Project of the National Natural Science Foundation of China (Grant No. 90505015)     

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...