卫星钟差预报模型中周期项的选取方法及性能分析

针对卫星钟差预报(SCB)中周期项选取方法存在的问题,在分析卫星钟周期波动特性的基础上,给出了正确的周期项选取方法,并与现有方法进行了比较.利用IGS(International GNSS Service)的卫星钟差数据,比较分析了二次多项式加周期项模型与传统模型的预报精度.从理论上分析了周期项对传统模型的改善程度及适用条件.结果表明:按照提出方法得到的周期项更符合实际,将其应用于钟差预报时能获得更高的预报精度,大量仿真实验还表明卫星钟周期性波动相对较大时周期项对传统模型有明显改善.     

A multiwavelength view of the ISM in the merger remnant galaxy Fornax A

We present multi-wavelength imagery of the merger remnant galaxy NGC 1316 with an objective to study the dust content and its association with the other phases of the interstellar medium. Color-index maps as well as extinction maps derived for this galaxy reveal an intricate and complex dust morphology in NGC 1316, i.e. there is a prominent lane in the inner part, while at about 6-7 kpc it apparently takes the form of an arc-like pattern extending along the northeast direction. In addition to this, several other dust clumps and knots are also evident in this galaxy. The dust emission mapped using Spitzer data at 8 μm indicates even more complex morphological structures of the dust in NGC 1316. The extinction curve derived over the optical to near-IR bands closely follows the standard Galactic curve, suggesting similar properties of the dust grains. The dust content of NGC 1316, estimated from optical extinction, is ～ 2.13 105M⊙ . This is a lower limit compared to that estimated using the IRAS flux densities of ～5.17×106M⊙ and the flux densities at 24, 70 and 160 μm from MIPS ～3.2×107M⊙ . High resolution Chandra observations of this merger remnant system have provided an unprecedented view of the complex nature exhibited by the distribution of hot gas in NGC 1316, which closely matches the morphology of ionized gas and to some extent also the dust. X-ray color-color plots for the resolved sources within the optical D 25 extent of NGC 1316 have enabled us to separate them into different classes.     

Simulation of a ground-layer adaptive optics system for the Kunlun Dark Universe Survey Telescope

Ground Layer Adaptive Optics (GLAO) is a recently developed technique extensively applied to ground-based telescopes, which mainly compensates for the wavefront errors induced by ground-layer turbulence to get an appropriate point spread function in a wide field of view. The compensation results mainly depend on the turbulence distribution. The atmospheric turbulence at Dome A in the Antarctic is mainly distributed below 15 meters, which is an ideal site for applications of GLAO. The GLAO system has been simulated for the Kunlun Dark Universe Survey Telescope, which will be set up at Dome A, and uses a rotating mirror to generate several laser guide stars and a wavefront sensor with a wide field of view to sequentially measure the wavefronts from different laser guide stars. The system is simulated on a computer and parameters of the system are given, which provide detailed information about the design of a practical GLAO system.     

The induced electric field distribution in the solar atmosphere

A method of calculating the induced electric field is presented. The induced electric field in the solar atmosphere is derived by the time variation of the magnetic field when the accumulation of charged particles is neglected. In order to derive the spatial distribution of the magnetic field, several extrapolation methods are introduced. With observational data from the Helioseismic and Magnetic Imager aboard NASA’s Solar Dynamics Observatory taken on 2010 May 20, we extrapolate the magnetic field from the photosphere to the upper atmosphere. By calculating the time variation of the magnetic field, we can get the induced electric field. The derived induced electric field can reach a value of 102 V cm-1 and the average electric field has a maximum point at the layer 360 km above the photosphere. The Monte Carlo method is used to compute the triple integration of the induced electric field.     

Mineralogical study of surface sediments in the western Arctic Ocean and their implications for material sources

Mineralogical analysis was performed on bulk sediments of 79 surface samples using X-ray diffraction. The analytical results, combined with data on ocean currents and the regional geological background, were used to investigate the mineral sources. Mineral assemblages in sediments and their distribution in the study area indicate that the material sources are complex. （1） Feldspar is abundant in the sediments of the middle Chukchi Sea near the Bering Strait, originating from sediments in the Anadyr River carried by the Anadyr Current. Sediments deposited on the western side of the Chukchi Sea are rich in feldspar. Compared with other areas, sediments in this region are rich in hornblende transported from volcanic and sedimentary rocks in Siberia by the Anadyr Stream and the Siberian Coastal Current. Sediments in the eastern Chukchi Sea are rich in quartz sourced from sediments of the Yukon and Kuskokwim rivers carried by the Alaska Coastal Current. Sediments in the northern Chukchi Sea are rich in quartz and carbonates from the Mackenzie River sediments. （2） Sediments of the southern and central Canada Basin contain little calcite and dolomite, mainly due to the small impact of the Beaufort Gyre carrying carbonates from the Canadian Arctic Islands. Compared with other areas, the mica content in the region is high, implying that the Laptev Sea is the main sediment source for the southern and central Canada Basin. In the other deep sea areas, calcite and dolomite levels are high caused by the input of large amounts of sediment carried by the Beaufort Gyre from the Canadian Arctic Islands （Banks and Victoria）. The Siberian Laptev Sea also provides small amounts of sediment for this region. Furthermore, the Atlantic mid-water contributes some fine-grained material to the entire deep western Arctic Ocean.     

重庆市森林火险变化特征及气象条件分析

利用重庆市34个气象站1961-2007年逐日气象观测资料以及同期NECP/NCAR逐月再分析数据,根据森林火险环境气象指数的定义,研究了重庆市森林火灾变化特征,并对春季和盛夏高森林火险等级下的典型年份的大气环流特征进行了分析。结果表明：重庆林火次数具有明显的年、季、月、日变化特征,盛夏（7-9月）和春季（2-4月）为2个高峰期,其林火次数占全年林火总数的78%,其中8月最多（占全年林火总数的18%）,午后是森林火灾多发时段;春季重庆市高森林火险的大气环流特征表现为：乌拉尔山、贝加尔湖和鄂霍茨克海地区500 hPa位势高度偏低,四川盆地高度场偏高,冷空气在中高纬地区堆积,天气活动主锋区偏北;盛夏重庆市高森林火险的环流特征为：巴尔喀什湖和鄂霍茨克海地区500 hPa位势高度显著偏低,朝鲜半岛位势高度显著偏高,西太平洋副热带高压位置偏北。     

OJ287双黑洞轨道计算:3.5阶后牛顿近似

大质量双黑洞OJ287是一个强引力辐射源.为了探测其引力波信号,需要知道波形,而这主要是由轨道运动所决定.为此,从广义相对论3.5阶后牛顿近似的运动方程出发对OJ287的轨道进行仔细研究,取大黑洞位置固定作为近似,给出了后牛顿近似下3.5阶的次黑洞轨道解,比他人2.5阶的工作高了一阶.次黑洞撞击吸积盘面到光学爆发存在时间延迟,这对于确定轨道参数有很大影响.利用径向距离与爆发时间关系的线性模型,对最近7次爆发时刻的观测值拟合,给出了更精确的OJ287双黑洞的轨道参数及其运动轨道.分析了计算结果,研究运动特征,并且发现了两个新性质:次黑洞进动在初期增加,在晚期接近并和时,进动达到最大值,然后减小并越过0而趋于负值.尚不能确定晚期的这个行为是否由3.5阶近似不够准确所造成.运动方程中耗散性的辐射项,后牛顿2.5阶和3.5阶的系数具有相反的符号.这意味着3.5阶项反而是从外界吸收能量.但2.5阶与3.5阶之和仍然是向外辐射引力波的,体系能量变化率为负.这个工作的计算结果可以用来更精确地计算OJ287的引力辐射.     

线性加权组合Kalman滤波在钟差预报中的应用

建立原子钟运行模型,实时预报钟差,在时频工作以及卫星导航定位中有着非常重要的意义.目前,Kalman滤波是一类重要的钟差预测模型.为了充分利用各种Kalman滤波模型的特点,提出了线性加权组合Kalman滤波模型.因此详细讨论了如何对每种Kalman滤波模型赋权,并且给出了两种简单而又实用的赋权方法.最后,以IGS(International GNSS Service)精密铷钟数据为例,运用该模型计算了预报误差.结果表明,线性加权组合Kalman滤波模型有利于提高钟差预报的准确性和可靠性.     

关于X射线脉冲星自主导航的位置观测方程

在X射线脉冲星自主导航(XNAV)中,位置观测方程表达了X光子到达航天器的时刻(TOA)和航天器位置的关系.具体讨论时,一般用TOA和"时间基准"的差值代替TOA,用太阳系质心系中的位置矢量表示航天器的位置."时间基准"可以取X光子到达太阳系质心(SSB)的真实时间,也可以取X光子到达SSB的"等效时间".讨论了基于这两种时间基准的位置观测方程,给出了时间精度为0.1 ns的位置观测方程,分析了其中各项的物理意义.     

大口径离轴非球面镜预应力环抛方法研究

提出了一种加工离轴非球面的预应力环抛方法,基于预应力加工方法的基本原理,利用环抛机来磨制离轴非球面.设计了一套专门的加载装置,将拼接镜面中具有不同离轴量的非球面子镜转化成曲率半径相同的球面子镜进行磨制,可以在同一台环抛机上进行抛光.利用这种方法,花费连续40 h的时间,磨制了一块按照中国30 m极大口径望远镜(CFGT)主镜参数比例缩小的离轴抛物面,顶点曲率半径21.6 m,离轴量3.6 m,离轴口径为330 mm,最大非球面度为16μm.试验表明该方法效率高,适用于批量加工,特别是极大口径天文望远镜拼接主镜的大批量非球面子镜研制.