轨道改进中计算状态转移矩阵的分析方法

对当今人卫轨道改进问题,由于力学模型的复杂,精密星历和状态转移矩阵的计算均采用数值方法,这就需要积分两组常微分方程．本文针对状态转移矩阵在定轨中的作用,对定轨弧段不太长的情况,给出了状态转移矩阵的一种分析算法,从而避免数值求解两组常微分方程的问题,并以实际算例证实了这种算法的有效性     

Strategy and Scenario for Radioastron Space VLBI Observations

Space VLBI's highly dynamic geometry, ability to access the space radio telescope (SRT) only via distant communication links, very expensive mission cost, and scientific goals define the basic strategy and scenario for mission control and radio source observations. These are very different from those for ground-based VLBI. Space VLBI strategy must be based on the limitation of SRT repointings, periodic orbit determination before astronomical observations, preliminary preparation and checking of space and ground facilities, and recommended observing sequences and modes. A control and observation scenario is considered for an in-orbit-checkout period, and also for short (1-orbit – 1 week) and long (1 week and more) observation sessions. Examples and illustrations are given for the Radioastron space VLBI Project.     

New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

We analysed aftershocks recorded by a temporary digital seismic network following the moderate M _w = 5.5 1993, Scotts Mills, Oregon, earthquake. A technique to retrieve source moment tensors from local waveforms was developed, tested, and applied to 41 small earthquakes ( M _w ranging from 1.6 to 3.2). The derived focal mechanisms, although well resolved, are highly variable and do not share a common nodal plane. In contrast, the majority of the events, relocated with a joint hypocentre determination algorithm, collapse to a well-focused plane. The incompatibility of the nodal planes of most events with the plane defined by their locations suggests that the aftershocks did not occur on the fault plane, but tightly around it, outlining the rupture area rather than defining it. Furthermore, the moment tensors reveal stable P -axes, whereas T  -axes plunges are highly dispersed. We detect a rotation of average T  -axis plunge with depth, indicating a change from shallower, predominantly dip-slip mechanisms to deeper strike-slip mechanisms. These characteristics are difficult to explain by remnant stress concentrations on the main-shock rupture plane or asperity- and barrier-type models. We suggest that the aftershocks occurred under the ambient regional stress, triggered by a sudden weakening of the region surrounding the main-shock slip, rather than from a shear stress increase due to the main shock.     

Wave Forces Acting on Vertical Walls

Regular and irregular wave forces acting on vertical walls are studied by a previously developed numerical model. The computed wave forces are compared with the available experimental data to verify the numerical model, and satisfactory agreements are obtained. The variation of wave forces with incident angles and the shape of simultaneous pressure distribution are investigated, and the comparisons between numerical results and Goda＇ s predictions are also carried out. It is concluded that the maximum wave forces acting on the unit length of vertical wall is often induced by the obliquely incident waves instead of normally incident waves, while Goda＇ s formula may be inapplicable for oblique wave incidence. The shape of simultaneous pressure distribution is not significantly influenced by incident angles, and it can be favorably predicted by Goda＇ s formula. When regular wave heights are taken as the same as irregular wave height H1%, the irregular wave forces Ph. 1% are slightly larger than regular wave forces in most cases.     

变形监测网非线性一、二类同步设计的新方法

监测网的精度是通过它的网形和观测方案来实现,因而研究设计合理的观测网形和观测方案有很重要的意义。针对以往一、二类设计分开单独进行解算不可能求得整体上最优,提出了非线性一、二类同步设计的新方法。该方法将一、二类设计的决策变量在一个模型中解算,可获得整体最优解。     

补偿式量热计在热化学中的应用

简要介绍了 Ｄ Ｄ Ｃ Ⅱ型补偿式数字精密量热系统及原理和对系统的标定。报道了用该量热计对无限稀的酸和碱反应过程的微反应热的自动测定,为热化学反应过程中微热效应的测定和该量热计的拓展提供了一条新途径。     

渭北苹果花期冻害气象指数保险设计

为科学设计渭北苹果花期冻害气象指数保险产品,提供气象指数保险技术参考。研究选取旬邑县作为陕西省渭北地区苹果代表县,利用1991—2020年气象、苹果花期物候、产量等数据,选取苹果花期冻害极端低温和过程累积危害指数作为备选气象指数,采用滑动平均〖CD*2〗灰色预测法分离苹果气象产量。通过气象指数与苹果减产率的相关分析,确定苹果花期冻害气象指数,构建苹果花期冻害气象指数与减产率之间的关系模型。利用苹果单产风险分布特点,选取6种分布模型利用参数分布法进行拟合,并根据Anderson Darling(A D)检验结果和概率密度函数图筛选最优分布。最后根据保险触发值,厘定不同赔付触发条件下的保险纯费率。结果表明：代表县苹果花期冻害过程累积危害气象指数Ts与减产率的相关性显著强于苹果花期冻害极端低温气象指数Tc;Ts与减产率之间存在正向线性关系模型;苹果单产风险分布符合柯西分布;当赔付触发条件对应2%、4%、6%、8%减产率时,旬邑县各乡镇苹果花期冻害气象指数保险产品纯费率区间为0.40%～1.84%。相较传统苹果农业保险产品,苹果花期冻害气象指数保险产品可实现差异化费率,有利于发挥气象指数保险优势。     

Triplicity and physical characteristics of Asteroid (216) Kleopatra

To take full advantage of the September 2008 opposition passage of the M-type Asteroid (216) Kleopatra, we have used near-infrared adaptive optics (AO) imaging with the W.M. Keck II telescope to capture unprecedented high resolution images of this unusual asteroid. Our AO observations with the W.M. Keck II telescope, combined with Spitzer/IRS spectroscopic observations and past stellar occultations, confirm the value of its IRAS radiometric radius of 67.5 km as well as its dog-bone shape suggested by earlier radar observations. Our Keck AO observations revealed the presence of two small satellites in orbit about Kleopatra (see Marchis, F. et al. [2008a]. (3749) Balam. In: Green, D.W.E. (Ed.), IAU Circ. 8928; Marchis, F., Descamps, P., Berthier, J., Emery, J.P. [2008b]. S/2008 ((216)) 1 and S/2008 ((216)) 2. In: Green, D.W.E. (Ed.), IAU Circ. 8980). Accurate measurements of the satellite orbits over a full month enabled us to determine the total mass of the system to be 4.64 ± 0.02 × 10¹⁸ kg. This translates into a bulk density of 3.6 ± 0.4 g/cm³, which implies a macroscopic porosity for Kleopatra of ∼30-50%, typical of a rubble-pile asteroid. From these physical characteristics we measured its specific angular momentum, very close to that of a spinning equilibrium dumbbell.     

同步卫星短弧定轨

同步卫星受到摄动力的影响,它的实际轨道有一点漂移．卫星需要不断的调轨调姿,以保证其正常运行．为了研究卫星在几小时,甚至更短的时间内的轨迹情况,采用短弧段定轨法．用动力学方法进行短弧定轨,分别研究1小时和15分钟定轨并进行比较,目的是为了在同步轨道卫星变轨后,能尽快地为卫星提供精密的预报轨道．此外,在系列短弧定轨后,得到精密轨道系列,为研究轨道变化的力学因素及研究短弧中卫星转发器时延变化规律等提供依据．     

小倾角LEO多星天基平台光学跟踪GEO精密定轨

针对地基卫星测控系统(Tracking Telemetry and Command, TT&C)系统对地球静止轨道(Geostation-\lk ary Earth Orbit, GEO)卫星在空间和时间覆盖上的局限性, 提出小倾角低地球轨道(Low Earth Orbit, LEO)多星组网天基平台对GEO卫星进行跟踪定轨的方法. 根据空间环境和光学可视条件对仿真数据进行筛选以模拟真实的观测场景, 利用光学测角数据, 使用数值方法对GEO卫星的轨道进行确定. 结果与参考轨道进行重叠对比, 在平台轨道精度5 m、测量精度5rq\rq、 定轨弧长12 h的情况下, 两颗LEO卫星对GEO卫星进行跟踪定轨的精度可达到千米量级, 4颗LEO卫星对GEO目标进行跟踪定轨的精度可达到百米量级. 随着LEO组网卫星数量的增加, 定轨精度得到了较大的提高.