现代黄河三角洲粉土触变性研究及其应用

通过对现代黄河三角洲砂质粉土和粉质粘土触变性的对比试验研究，阐述了黄河口粉土的触变性。试验结果对解释粉土的失稳机制、解决工程地基的稳定性和防止地质灾害等具有重要的现实意义。     

Geomorphic evolution of a part of Middle Ganga Plain,Bihar: A case study using remote sensing data

An insight into the geomorphic evolution of any area can be obtained by detailed landform mapping. In the present study, an area in the Middle Ganga Plain has been selected for the study using mainly remote sensing data. Various fluvial landforms have been mapped and the changes in planform of rivers over approximately 50 years have been evaluated. Both fluvial processes and tectonic activities are considered to have collectively influenced the migration of the rivers in this region. Digital enhancements of Landsat MSS and TM data are found to be quite useful in identification and mapping of subtle fluvial palaeofeatures. The present study demonstrates the utility of remote sensing in examining the geomorphic evolution of the area.     

Reversals of the geomagnetic field,magnetostratigraphy, and relative magnitude of paleosecular variation in the phanerozoic

The percentage of normal and reversed magnetization in land-based paleomagnetic studies of Phanerozoic rocks (0 to ? 570 m.y.) have been compiled in order to determine the long-term variation in polarity bias of the geomagnetic field. Where possible the results are compared with the record from marine magnetic anomalies. Only rarely is there an even balance between normal and reversed polarity. During the past 350 m.y. two quiet intervals can be recognized when few reversals occurred, the Cretaceous (KN about ? 81 to ? 110 m.y.) and Permo-Carboniferous (PCR about ? 227 to ? 313 m.y.). Less firmly established are two other quiet intervals, one in the Jurassic (JN about ? 145 to ? 165 m.y.), and one in the Triassic (TRN about ? 205 to ? 220 m.y.). Between these quiet intervals there are disturbed intervals when reversals were comparatively frequent. From ? 680 to ? 350 m.y. the paleomagnetic record is inadequate to delineate a succession of quiet and disturbed intervals although one is probably present. Maximum entropy spectral analysis reveals three periodicities, a dominant one at about 300 m.y. and others, less well-defined, at 113 and 57 m.y. The variations in polarity bias are compared with the paleosecular variation, and it is shown that the magnitude of the paleosecular variation is greater in disturbed than in quiet intervals. This indicates that the magnitude of paleosecular variation and polarity bias are governed by variations in the balance between non-dipole and dipole components of the field, and that these variations probably had their origin in processes near the core—mantle interface. The correspondence between the dominant periods of 300 m.y. and plate tectonics is noted and a causal relationship suggested.     

The Cone-in-Cone Structure and Its Origin

Morphostructural investigation of carbonate cone-in-cone formations allows to conclude that they belong to self-organizing (dissipative, according to I. Prigogine's terminology) systems of the geological past formed in a thermogradient field at the expense of energy of heat and mass transfer (Prigogine and Stengers, 1984). First, the fluid-convective metasomatic hypothesis unites and reconciles the most well-known hypotheses that previously seemed to be incompatible and transforms them to rather consistent particular cases of a more intricate multistage geological phenomenon. Second, it helps to identify the morphologically and genetically analogous noncarbonate structures that mimic biogenic ones. The probable indicative role of cone-in-cone structure in the mapping of fluid-conducting systems is a consequence of the proposed hypothesis.     

淇、卫河流域“96·8”致洪暴雨过程的数值模拟

应用LASGREMM模式 ,对淇、卫河流域“96·8”致洪暴雨过程进行了模拟预报分析。结果表明 ,LAS GREM模式不仅能较准确地预报淇、卫河流域暴雨落区 ,而且可以进一步分析天气过程的特点及演变情况     

A canonical theory for short GPS baselines. Part II: the ambiguity precision and correlation

The present contribution is the second of four parts. It considers the precision and correlation of the least-squares estimators of the carrier phase ambiguities. It is shown how the precision and correlation of the double-differenced ambiguities as well as of the widelane ambiguities are effected by the observation weights, by the number of satellites tracked, by the number of observation epochs used, and by the change over time of the relative receiver-satellite geometry. Also the ability of the widelane transformation to decorrelate and to improve the precision is investigated. Received: 16 July 1996 / Accepted: 14 November 1996