BeiDou regional navigation satellite system （BDS） also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit （GEO）, 5 satel...BeiDou regional navigation satellite system （BDS） also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit （GEO）, 5 satellites in Inclined Geosynchronous Orbit （IGSO）, and 4 satellites in Medium Earth Orbit （MEO）. In this paper, its basic navigation and positioning performance are evaluated preliminarily by the real data collected in Beijing, including satellite visibility, Position Dilution of Precision （PDOP） value, the precision of code and carrier phase measurements, the accuracy of single point positioning and differential position- ing and ambiguity resolution （AR） performance, which are also compared with those of GPS. It is shown that the precision of BDS code and carrier phase measurements are about 33 cm and 2 mm, respectively, which are comparable to those of GPS, and the accuracy of BDS single point positioning has satisfied the design requirement. The real-time kinematic positioning is also feasible by BDS alolae in the opening condition, since its fixed rate and reliability of single-epoch dual-frequency AR is comparable to those of GPS. The accuracy of BDS carrier phase differential positioning is better than 1 cm for a very short baseline of 4.2 m and 3 cm for a short baseline of 8.2 km, which is on the same level with that of GPS. For the combined BDS and GPS, the fixed rate and reliability of single-epoch AR and the positioning accuracy are improved significantly. The accu- racy of BDS/GPS carrier phase differential positioning is about 35 and 20 % better than that of GPS for two short baseline tests in this study. The accuracy of BDS code differential positioning is better than 2.5 m. However it is worse than that of GPS, which may result from large code multipath errors of BDS GEO satellite measurements.展开更多
相对论重离子碰撞(又称高能核-核碰撞)为研究极端条件下核物质内禀性质、致密星体内部结构和大爆炸之后宇宙的早期演化过程提供了途径.强相互作用的量子色动力学(QCD)理论预言存在着解禁闭的新物质状态夸克-胶子等离子体(QGP).经过近30...相对论重离子碰撞(又称高能核-核碰撞)为研究极端条件下核物质内禀性质、致密星体内部结构和大爆炸之后宇宙的早期演化过程提供了途径.强相互作用的量子色动力学(QCD)理论预言存在着解禁闭的新物质状态夸克-胶子等离子体(QGP).经过近30年的努力,在极端相对论能区的核-核对撞实验中,包括RHIC和LHC的实验,科学家找到了QGP存在的证据.目前,高能核物理的一个重要的科学问题是高重子密度区的相结构,包括寻找相边界和可能存在的QCD临界点.量子热动力学基本原理告诉我们只有找到相边界或临界点才能最终确定新的物质相QGP的存在.我们首先回顾了高能核物理实验的研究现状,其中包括RHIC能量扫描实验中的强子集体运动、手征特性的研究和QCD临界点的寻找.然后对利用我国重离子加速器群,如Heavy Ion Research Facility in Lanzhou (HIRFL)和High Intensity heavy-ion Accelerator Facility (HIAF)以及CSR-External-target Experiment等开展高能核物理实验研究进行了展望.展开更多
Conventional 3D metal printings are generally time-consuming as well as lacking of high performance printable inks.From an alternative way,here we proposed the method of liquid phase 3D printing for quickly making con...Conventional 3D metal printings are generally time-consuming as well as lacking of high performance printable inks.From an alternative way,here we proposed the method of liquid phase 3D printing for quickly making conductive metal objects.Through introducing metal alloys whose melting point is slightly above room temperature as printing inks,several representative structures spanning from one,two and three dimension to more complex patterns were demonstrated to be quickly fabricated.Compared with the air-cooling in a conventional 3D printing,the liquid-phase-manufacturing offers a much higher cooling rate and thus significantly improves the speed in fabricating the target metal objects.This unique strategy also efficiently prevents the liquid metal inks from air oxidation,which is hard to avoid otherwise in an ordinary 3D printing.The key physical factors(such as properties of the cooling fluid,air pressure within the syringe barrel and needle diameter,types and properties of the printing ink)and several interesting intermediate fluids interaction phenomena between liquid metal and conventional cooling fluids such as water or ethanol,which evidently affecting the printing quality,were disclosed.In addition,a basic route to make future liquid phase 3D printer incorporated with both syringe pump and needle arrays was also suggested.The liquid phase 3D printing,which owns potential values not available in a conventional method,opens an efficient way for quickly making conductive metal objects in the coming time.展开更多
The effect of spin-1 impurities doping on the magnetic properties of a spin-3/2 Ising nanotube is investigated using Monte Carlo simulations within the Blume-Emery-Griffiths model in the presence of an external magnet...The effect of spin-1 impurities doping on the magnetic properties of a spin-3/2 Ising nanotube is investigated using Monte Carlo simulations within the Blume-Emery-Griffiths model in the presence of an external magnetic field. The thermal behaviors of the order parameters and different macroscopic instabilities as well as the hysteretic behavior of the material are examined in great detail as a function of the dopant density. It is found that the impurities concentration affects all the system magnetic properties generating for some specific values, compensation points and multi-cycle hysteresis. Doping conditions where the saturation/remanent magnetization and coercive field of the investigated material can be modified for permanent or soft magnets synthesis purpose are discussed.展开更多
基金sponsored by the National Natural Science Foundation of China(Grant Nos.41020144004,41374019,41104022)the National High Technology Research and Development Program of China(Grant No.2013AA122501)
文摘BeiDou regional navigation satellite system （BDS） also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit （GEO）, 5 satellites in Inclined Geosynchronous Orbit （IGSO）, and 4 satellites in Medium Earth Orbit （MEO）. In this paper, its basic navigation and positioning performance are evaluated preliminarily by the real data collected in Beijing, including satellite visibility, Position Dilution of Precision （PDOP） value, the precision of code and carrier phase measurements, the accuracy of single point positioning and differential position- ing and ambiguity resolution （AR） performance, which are also compared with those of GPS. It is shown that the precision of BDS code and carrier phase measurements are about 33 cm and 2 mm, respectively, which are comparable to those of GPS, and the accuracy of BDS single point positioning has satisfied the design requirement. The real-time kinematic positioning is also feasible by BDS alolae in the opening condition, since its fixed rate and reliability of single-epoch dual-frequency AR is comparable to those of GPS. The accuracy of BDS carrier phase differential positioning is better than 1 cm for a very short baseline of 4.2 m and 3 cm for a short baseline of 8.2 km, which is on the same level with that of GPS. For the combined BDS and GPS, the fixed rate and reliability of single-epoch AR and the positioning accuracy are improved significantly. The accu- racy of BDS/GPS carrier phase differential positioning is about 35 and 20 % better than that of GPS for two short baseline tests in this study. The accuracy of BDS code differential positioning is better than 2.5 m. However it is worse than that of GPS, which may result from large code multipath errors of BDS GEO satellite measurements.
文摘相对论重离子碰撞(又称高能核-核碰撞)为研究极端条件下核物质内禀性质、致密星体内部结构和大爆炸之后宇宙的早期演化过程提供了途径.强相互作用的量子色动力学(QCD)理论预言存在着解禁闭的新物质状态夸克-胶子等离子体(QGP).经过近30年的努力,在极端相对论能区的核-核对撞实验中,包括RHIC和LHC的实验,科学家找到了QGP存在的证据.目前,高能核物理的一个重要的科学问题是高重子密度区的相结构,包括寻找相边界和可能存在的QCD临界点.量子热动力学基本原理告诉我们只有找到相边界或临界点才能最终确定新的物质相QGP的存在.我们首先回顾了高能核物理实验的研究现状,其中包括RHIC能量扫描实验中的强子集体运动、手征特性的研究和QCD临界点的寻找.然后对利用我国重离子加速器群,如Heavy Ion Research Facility in Lanzhou (HIRFL)和High Intensity heavy-ion Accelerator Facility (HIAF)以及CSR-External-target Experiment等开展高能核物理实验研究进行了展望.
基金supported by the Key Research Program of the Chinese Academy of Sciences(Grant No.KGZD-EW-T04)
文摘Conventional 3D metal printings are generally time-consuming as well as lacking of high performance printable inks.From an alternative way,here we proposed the method of liquid phase 3D printing for quickly making conductive metal objects.Through introducing metal alloys whose melting point is slightly above room temperature as printing inks,several representative structures spanning from one,two and three dimension to more complex patterns were demonstrated to be quickly fabricated.Compared with the air-cooling in a conventional 3D printing,the liquid-phase-manufacturing offers a much higher cooling rate and thus significantly improves the speed in fabricating the target metal objects.This unique strategy also efficiently prevents the liquid metal inks from air oxidation,which is hard to avoid otherwise in an ordinary 3D printing.The key physical factors(such as properties of the cooling fluid,air pressure within the syringe barrel and needle diameter,types and properties of the printing ink)and several interesting intermediate fluids interaction phenomena between liquid metal and conventional cooling fluids such as water or ethanol,which evidently affecting the printing quality,were disclosed.In addition,a basic route to make future liquid phase 3D printer incorporated with both syringe pump and needle arrays was also suggested.The liquid phase 3D printing,which owns potential values not available in a conventional method,opens an efficient way for quickly making conductive metal objects in the coming time.
文摘The effect of spin-1 impurities doping on the magnetic properties of a spin-3/2 Ising nanotube is investigated using Monte Carlo simulations within the Blume-Emery-Griffiths model in the presence of an external magnetic field. The thermal behaviors of the order parameters and different macroscopic instabilities as well as the hysteretic behavior of the material are examined in great detail as a function of the dopant density. It is found that the impurities concentration affects all the system magnetic properties generating for some specific values, compensation points and multi-cycle hysteresis. Doping conditions where the saturation/remanent magnetization and coercive field of the investigated material can be modified for permanent or soft magnets synthesis purpose are discussed.
