Asteroid families: evidence of ageing of the proper elements

In recent times it has been emphasized that the present kinematical structures of asteroid families should be evolved with respect to the original post-impact situations, according to numerical simulations performed taking into account also the previously neglected Yarkovsky effect. In this paper we show that also a “classical” approach based on an analysis of the current kinematical properties of families leads to conclude that the distributions of proper eccentricities and semimajor axes of family members exhibit evidence of an evolution. The importance of this approach is that it yields a fully independent and quantitative estimate of an evolutionary spreading of the proper elements. In particular, we find that the original post-impact families had to be on the average about twice more compact than the families we observe now, when considering family members down to about 5 km in size. This result can be used in future analyses to derive estimates of the ages of different families, and to better constrain the typical values of the ejection velocities of the fragments in family-forming events.     

金州地区震旦系基本层序与沉积环境

金州地区广泛发育震旦纪地层,具分布连续、出露完整、沉积相标志明显的特点。本文运用现代沉积学和地层学理论,对区内震旦系岩石地层进行了基本层序研究与沉积环境分析。     

Restricted Three-Body Problem: An Approximation of its General Solution – Part One – the Manifold of Symmetric Periodic Solutions

This paper gives the results of a programme attempting to exploit ‘la seule bréche’ (Poincaré, 1892, p. 82) of non-integrable systems, namely to develop an approximate general solution for the three out of its four component-solutions of the planar restricted three-body problem. This is accomplished by computing a large number of families of ‘solutions précieuses’ (periodic solutions) covering densely the space of initial conditions of this problem. More specifically, we calculated numerically and only for μ = 0.4, all families of symmetric periodic solutions (1st component of the general solution) existing in the domain D:(x ₀ ∊ [−2,2],C ∊ [−2,5]) of the (x ₀, C) space and consisting of symmetric solutions re-entering after 1 up to 50 revolutions (see graph in Fig. 4). Then we tested the parts of the domain D that is void of such families and established that they belong to the category of escape motions (2nd component of the general solution). The approximation of the 3rd component (asymmetric solutions) we shall present in a future publication. The 4th component of the general solution of the problem, namely the one consisting of the bounded non-periodic solutions, is considered as approximated by those of the 1st or the 2nd component on account of the `Last Geometric Theorem of Poincaré' (Birkhoff, 1913). The results obtained provoked interest to repeat the same work inside the larger closed domain D:(x ₀ ∊ [−6,2], C ∊ [−5,5]) and the results are presented in Fig. 15. A test run of the programme developed led to reproduction of the results presented by Hénon (1965) with better accuracy and many additional families not included in the sited paper. Pointer directions construed from the main body of results led to the definition of useful concepts of the basic family of order n, n = 1, 2,… and the completeness criterion of the solution inside a compact sub-domain of the (x ₀, C) space. The same results inspired the ‘partition theorem’, which conjectures the possibility of partitioning an initial conditions domain D into a finite set of sub-domains D i that fulfill the completeness criterion and allow complete approximation of the general solution of this problem by computing a relatively small number of family curves. The numerical results of this project include a large number of families that were computed in detail covering their natural termination, the morphology, and stability of their member solutions. Zooming into sub-domains of D permitted clear presentation of the families of symmetric solutions contained in them. Such zooming was made for various values of the parameter N, which defines the re-entrance revolutions number, which was selected to be from 50 to 500. The areas generating escape solutions have being investigated. In Appendix A we present families of symmetric solutions terminating at asymptotic solutions, and in Appendix B the morphology of large period symmetric solutions though examples of orbits that re-enter after from 8 to 500 revolutions. The paper concludes that approximations of the general solution of the planar restricted problem is possible and presents such approximations, only for some sub-domains that fulfill the completeness criterion, on the basis of sufficiently large number of families.     

Low-pressure,water-assisted anatexis of basic dykes in a contact metamorphic aureole,Fuerteventura (Canary Islands): oxygen isotope evidence for a meteoric fluid origin

Migmatites produced by low-pressure anatexis of basic dykes are found in a contact metamorphic aureole around a pyroxenite–gabbro intrusion (PX2), on Fuerteventura. Dykes outside and inside the aureole record interaction with meteoric water, with low or negative δ¹⁸O whole-rock values (+0.2 to −3.4‰), decreasing towards the contact. Recrystallised plagioclase, diopside, biotite and oxides, from within the aureole, show a similar evolution with lowest δ¹⁸O values (−2.8, −4.2, −4.4 and −7.6‰, respectively) in the migmatite zone, close to the intrusion. Relict clinopyroxene phenocrysts preserved in all dykes, retain typically magmatic δ¹⁸O values up to the anatectic zone, where the values are lower and more heterogeneous. Low δ¹⁸O values, decreasing towards the intrusion, can be ascribed to the advection of meteoric water during magma emplacement, with increasing fluid/rock ratios (higher dyke intensities towards the intrusion acting as fluid-pathways) and higher temperatures promoting increasing exchange during recrystallisation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

基于Windows CE水准测量应用软件的设计与实现

根据水准测量实际问题，抽象出水准测量应用软件的需求与功能，在此基础上，利用基于Windows CE应用软件开发工具——eMbedded Visual Basic，设计和开发了水准测量应用软件。该系统利用EVB提供的强大的可视化功能，为用户创建窗体式程序界面，使用中通过窗体的相互调用，完成用户对水准测量外业记簿、检核和平差计算的基本需求。     

A comparison between 2D and 3D wavelet analysis method for asteroid family dynamical study

As found in previous studies (Bendjoyaet al. 1991) the wavelet analysis is a reliable tool for the determination of asteroid families. A comparison between the 2D and a newly developed 3D wavelet analysis is performed on 14 fictitious families numerically generated the members of which area priori known. It clearly appears that the 3D method brings improvements to the 2D approach. Indeed the 3D analysis appears well suited for all cases even for those corresponding to the very dense Flora region and for exotic families such as filamentar ones. With the 2D method, satisfying results are obtained for the simulations which correspond to 70% of the real asteroid families previously found. The aim of this paper is to show quantitatively the improvement of the 3D method versus the 2D one.     

A stability study of asteroid families near the 3:1 and 5:2 resonance with Jupiter

By using theD-criterion Lindblad (1992) has identified 14 asteroid families from a sample of 4100 numbered asteroids with proper elements from Milani and Kneevi (1990). Taxonomic types and other physical properties for a significant number of objects in five of the families show strong homogeneity within each family, further strengthening their internal relationship.To test the hypothesis of a common origin in, e.g., a catastrophic collision event, we have set out to integrate the orbits of the members of the Maria, Dora and Oppavia-Gefion families over some 10⁶ years. The mean distance for the Maria family is close to the 3:1 mean-motion resonance with Jupiter, while the other two families lie close to the 5:2 resonance.We used a simplified solar system model which included the perturbations by Jupiter and Saturn only and implemented Everhart's variable stepsize integrator RA15. All close encounters between the family members (within 0.1 AU) were recorded as well. Preliminary results from integrations over 4×10⁵ years are presented here.The statistics of close encounters show pronounced peaks for several members within each family, while for others no significant levels above the background of random encounters or even very low frequencies were found. This indicates a subclustering within the families. Quite a lot of very close (<0.005 AU) mutual encounters are found, which suggest that, at least for the larger members in a family, the mutual gravitational interactions could be of some importance for the real orbital evolutions.The encounter statistics between the Dora and Oppavia family members suggest a possible interrelationship between this two groups.     

Morphometric analysis of a subtropical Andean basin (Tucumán, Argentina)

A morphometric analysis was done to determine the drainage characteristics of Lules River basin using land-sat imageries and topographical maps. This catchment was divided into seven sub-basins for the analysis: Liquimayo, Hoyada, Ciénaga, De Las Tablas, Siambón, Potrerillo and San Javier. Yungas ecoregion covers almost all the watershed. The drainage patterns of the sub-basins are dendritic and parallel. The basin includes seventh order stream and lower streams order mostly dominate the basin. The development of stream segments is affected by slope and local relief. The mean bifurcation ratio indicates that the drainage pattern is not much influenced by geological structures. The shape parameters also reveal the elongation of the basin and sub-basins.     

VBA的开发

介绍了能够加强Ms Office功能的二次开发工具VBA语言，以及VBA的特点与优点；介绍了在Visul Basic中利用VBA的强大功能来实现具有Office界面、功能的方法。     

应用VB+MapInfo开发的地震定位程序

利用OLE自动化方法，将MapInfo集成在VB中，在手工地震交切定位的基础上，开发了计算机定位程序，该程序与传统的定位方法相比，精度和效率都有较大幅度的提高。并在地震应急中发挥了作用。