Microarcsecond instability of the celestial reference frame

The fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered. It is shown that these angular fluctuations range from a few up to hundreds of microarcseconds. This leads to a small rotation of the celestial reference frame. The non-diagonal coefficients of the rotation matrix are of the order of a microarcsecond. The temporal variation of these coefficients due to the proper motion of the foreground stars is of the order of one microsecond per 20 years. The celestial reference frame can therefore be considered inertial and homogeneous only to microarcsecond accuracy. Astrometric catalogues with microarcsecond accuracy will be unstable, and must be re-established every 20 years.     

Rotating haloes and the microlensing MACHO mass estimate

We investigate the implications of a bulk rotational component of the Galactic halo velocity distribution for MACHO mass estimates. We find that for a rotating halo to yield a MACHO mass estimate significantly below that of the standard spherical case, its microlensing must be highly concentrated close to the Sun. We examine two classes of models fitting this criterion: a highly flattened 1/ r ² halo, and a spheroid-like population the density of which falls off as 1/ r ^3.5. The highly flattened 1/ r ² models can decrease the implied average MACHO mass only marginally, and the spheroid models not at all. Generally, rotational models cannot bring the MACHO mass implied by the current microlensing data down to the substellar range.     

Gravity-Accommodated ‘Structural Wedges’ Along Thrust Ramps: A Kinematic Scheme of Gravitational Evolution

In active geodynamic areas, such as the Italian Southern Apennines, the specific structural conditions have a profound effect on both the superficial and deep gravitational evolution of slopes. Chain sectors commonly exhibit structural complexities due to the superimposition, in space and time, of diverse tectonic stress fields. In this paper, attention is focused on particular structural configurations, connected to the tectonic quaternary phases that have affected the Southern Apennines, constituting a peculiar type of lateral spread gravitational deformations – which have not been previously described.The study area is characterized by regional roughly east-verging overthrusts (Holigo–Miocene). Superimposed on these, is a system of transpressive thrust ramps (Quaternary), connected to the activity of strike-slip faults. The latest tectonic phase, still active, has been characterized by an extensional stress field, which has produced differentiated uplifts along normal faults. All these factors have encouraged an intense and widespread processes of erosion, the creation of considerable relief energy and the development of both superficial and deep gravitational phenomena.It has been ascertained that the late extensional phases favoured gravitational reactivations (with normal movements) along those most recent thrust ramps whose attitude was kinematically consistent with the main extension direction of the stress field. Such reactivations were accommodated by antithetic neo-formational structures – these are also characterized by normal kinematics. Overall, such mechanisms lead to the individuation of wedge-shaped rock portions delimited by the normally reactivated thrust ramps, on one side, and by the antithetic structures, on the other.Structural wedges represent a particular type of lateral spread phenomena. On the basis of their orientation with respect to the orography, three typical situations have been defined: (1) wedge perpendicular to the ridge; (2) wedge parallel to the ridge; (3) wedge oblique to the ridge.In this paper three Calabrian case studies, exemplifying the above-mentioned situations, are described. The same framework can be applied to sectors of chain with an analogous structural setting, for a better understanding of the kinematic features of observed gravitational phenomena.     

模式识别之重心法则及其在地图制图中运用一例

本文提出了比最大隶属度法则使用更广泛的重心法则。在模式识别中,此法则使用方便且利用了模糊子集的全部信息,因此比前者更精确。最后给出的实例证明了这点。     

东南亚陆缘的卫重异常及其形成机制初探

在东亚的陆缘地区。存在着一系列的陆缘弧。本文利用地面和根据GEMIOC地球模型的重力位球谐系数所计算的卫星重力资料,从地球动力学的角度探讨了其中几个陆缘弧的形成机制。重点探讨了我目东南沿海陆缘弧的重力异常特征及其形成机割。     

Q2237+0305 source structure and dimensions from light-curve simulation

Assuming a two-component quasar structure model consisting of a central compact source and an extended outer feature, we produce microlensing simulations for a population of compact masses in the lensing galaxy of Q2237+0305. Such a model is a simplified version of that adopted to explain the brightness variations observed in Q0957. The microlensing light curves generated for a range of source parameters were compared to the light curves obtained in the framework of the Optical Gravitational Lensing Experiment program. With a large number of trials, we built, in the domain of the source structure parameters, probability distributions to find 'good' realizations of light curves. The values of the source parameters which provide the maximum of the joint probability distribution calculated for all the image components have been accepted as estimates for the source structure parameters. The results favour the two-component model of the quasar brightness structure over a single compact central source model, and in general the simulations confirm the Schild–Vakulik model that previously described successfully the microlensing and other properties of Q0957. Adopting 3300 km s⁻¹ for the transverse velocity of the source, the effective size of the central source was determined to be about  2 × 10¹⁵ cm  , and  ɛ≈ 2  was obtained for the ratio of the integral luminosity of the outer feature to that of the central source.     

曲流河道单砂体驱油效率主控因素

为了进一步提高注入剂驱油效率以及准确预测储层中剩余油在三维空间的分布,以大庆油田葡萄花油层组PⅠ2小层曲流河道砂体为例,通过对曲流河道砂体内部薄夹层构形及渗透率垂向分布的差异性分析,在排除开发因素差异的同井单砂体分析条件下,提出了单砂体内部薄夹层空间构形、渗透率垂向序列与重力因素共同控制剩余油分布、驱油效率多段垂向序列模式。