叠前深度偏移述评

叠前深度偏移是理想的改善复杂地区和强横向速度变化的地震资料成像技术,笔者就4种典型叠前深度偏移方法的理论基础与技术特点,存在的问题及国内外最新进展进行了讨论.     

Journeys to the street: the complex migration geographies of Ugandan street children

Children have generally been afforded little attention in migration research or unsatisfactorily included within family migration. Although they are an important consideration in family decisions to move, children also engage in autonomous, independent migration. Further, researchers now argue for the need to situate migration within political, economic and social conditions to obtain a full understanding of why people migrate. Through the use of children-centred research methods, and in-depth interviews with key informants, this paper considers children's journeys to the street in Uganda. By integrating an analysis of Ugandan street children's spatial origins with the familial and societal contexts of their migration decisions, this research highlights the complexity of their migration. In addition, an exploration of the impact of changing social, spatial and temporal conditions on street children's movements illustrates that their journeys are far more than just single processes.     

A furrow runs through it: An example of sustainable traditional irrigation in Western Cape Province,South Africa

Water and water related matters are important issues in water scarce countries like the Republic of South Africa. This is especially true for the agricultural sector that relies heavily on the availability of water for irrigation to ensure a secure food supply. In South Africa, present day irrigation projects rely on government subsidies and are usually large undertakings beyond the reach of individuals or small communities. The sustainability of such large irrigation projects is still a matter of debate. A 100 years ago a different set of rules applied. Irrigation could only be achieved by hand-dug furrows that supplied water in relatively small quantities to small farming communities. This paper investigated such a small community, the Leeukloof farming community in the Western Cape Province of the Republic of South Africa. For the past 93 years this community has maintained a furrow that supplies water not only to farms bordering the Perdeberg River, which supplies the furrow with water, but also to farms not bordering the river. The authors try to reconstruct the changes in agricultural practices brought about by the furrow, methods of water extraction during each phase, as well as the development and role of the furrow system. The perception by the community of the necessity of this method of water extraction from the river system is also investigated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Weathering: Toward a Fractal Quantifying

Weathering occurs over a wide range of scales. To link features through these scales is a major challenge for interdisciplinary weathering studies. Fractal approach seems to be specially useful for this purpose. We introduce a multistep fractal weathering assessment scheme devoted to extract fractal weathering classifiers from texture analysis of the mineral's image. Our scheme enables to quantitatively estimate the global and local information about the geometry of the weathering pattern. This information is basic to develop geometrical indices of weathering, which can significantly enrich the common qualitative and semiquantitative weathering assessment schemes. To justify the fractal approach, a strong statistical self-similarity has been documented for both the weathering and fresh features of two common silica minerals: quartz and biogenic A-opal (phytolith) over four orders of length scales. The procedure is fast, drastically reduces thresholding bias, promises to be universal, it is valid for genetically different minerals and rock types, scale independent, and specially useful for monitoring the changes in the mineral's roughness during the alteration. Two of the proposed classifiers seem to be potentially useful for direct application in the field and be used by nonspecialist.     

Seafloor spreading, obduction and triple junction tectonics of the Mineoka Ophiolite, Central Japan

The Tertiary Mineoka ophiolite occurs in a fault zone at the intersection of the Honshu and Izu forearcs in central Japan and displays structural evidence for three major phases of deformation: normal and oblique-slip faults and hydrothermal veins formed during the seafloor spreading evolution of the ophiolite at a ridge-transform fault intersection. These structures may represent repeated changes in differential stress and pore-fluid pressures during their formation. The second series of deformation is characterized by oblique thrust faults with Riedel shears and no significant mineral veining, and is interpreted to have resulted from transpressional dextral faulting during the obduction of the ophiolite through oblique convergence and tectonic accretion. This deformation occurred at the NW corner of a TTT-type (trench–trench–trench) triple junction in the NW Pacific rim before the middle Miocene. The third series of deformation of the ophiolite is marked by contractional and oblique shear zones, Riedel shears, and thrust faults that crosscut and offset earlier structures, and that give the Mineoka fault zone its lenticular (phacoidal) fabric at all scales. This deformation phase was associated with the establishment and the southward migration of the TTT Boso triple junction and with the kinematics of oblique subduction and forearc sliver fault development. The composite Mineoka ophiolite hence displays rocks and structures that evolved during its complex geodynamic history involving seafloor spreading, tectonic accretion, and triple junction evolution in the NW Pacific Rim.     

Sense of place and migration histories Idiotopy and idiotope

The aim of this article is to explore a methodological approach relevant to the study of population mobility. The approach considers not only the whole migratory process and the sequence of connected movements, but also what happens between each of them. The study of mobility is considered inseparable from the study of passage, permanence and settlement. This paper establishes the interest in elaborating concepts that express the interaction between people and places, and how these interactions contribute to an understanding of migratory processes and of 'place histories'. In this sense, geographical identification (idiotopy) and place identification (idiotope) are put forward as useful concepts.     

When the Light of the Home is Abroad: Unskilled Female Migration and the Filipino Family

The migration of women engaged in transnational domestic work reveals how the uneven impacts of globalisation have intruded into the micro‐world of families and households. In this age of globalisation and migration, family membership has become multisited or transnational, with members dispersed in space. The migration of workers and the separation this entails has raised challenges to notions and ideals of “being family”. Unlike other workers on the move, the migration of domestic workers has some distinctive characteristics. It can be framed in terms of women moving between families and households; workers whose departure from their family of origin and insertion into their family of employment reconstitute the structure and content of family relationships in both material and imagined ways. Drawing on in‐depth interviews conducted in the Philippines and Singapore, we explore how migrant women and their family members define and negotiate family ideals, gender identities and family relationships, given the family's transnational configuration. Our findings provide some support to the notion that individual members in transnational families resort to “relativising” in fashioning responses to their situation.     

利用现有重力场模型求定CHAMP卫星加速度计修正参数

CHAMP卫星加速度计数据的标定是通过确定其尺度因子和偏差参数来完成的.本文基于能量守恒方程,给出利用现有重力场模型标定CHAMP卫星加速度数据的基本原理和数学模型;提出相邻历元间差分算法,大大简化了观测方程,同时避免积分常量的计算.该算法既能同时解算尺度因子和偏差参数,也可任意求解其中之一.基于实测的CHAMP卫星加速度数据,利用EGM96模型和最新公布的EIGEN-2模型进行计算与比较,验证该方法的有效性.