Seismic response of slopes subjected to incident SV wave by an improved boundary element approach

In this paper, an improved boundary element approach for 2D elastodynamics in time‐domain is presented. This approach consists in the truncation of time integrations, based on the rapid decrease of the fundamental solutions with time. It is shown that an important reduction of the computation time as well as the storage requirement can be achieved. Moreover, for half‐plane problems, the size of boundary element (BE) meshes and the computation time can be significantly reduced. The proposed approach is used to study the seismic response of slopes subjected to incident SV waves. It is found that large amplifications take place on the upper surface close to the slope, while attenuations are produced on the lower surface. The results also show that surface motions become very complex when the incident wavelength is comparable with the size of the slope or when the slope is steep. Copyright © 2006 John Wiley & Sons, Ltd.     

TOBI image processing-the state of the art

TOBI (Towed Ocean Bottom Instrument) is a deep-tow sidescan sonar vehicle from which sidescan sonar data are now routinely collected and archived. This paper describes the algorithms developed for detailed processing of TOBI data. Sonar imagery has a characteristic set of processing challenges and these are addressed. TOBI provides a very large sonar dataset, and to limit the difficulties of handling and processing these data, the raw data are subjected to a data reduction technique prior to further processing. Slant-range correction is improved by editing vehicle altitude data using a median filter. Noise on TOBI imagery can appear in two main forms; speckle noise and line dropouts. Speckle noise is removed by a small median difference kernel and line dropouts are removed using a ratio of two box-car filters, each with appropriate thresholding techniques. Precise geocoding of the imagery requires an accurate estimate of vehicle location, and a method of calculation is presented. Two optional processing algorithms are also; presented; deblurring of imagery to improve along-track resolution at far range, and the suppression of a surface reflection return which may occur when TOBI is operated in relatively shallow water. Several of the techniques presented can be transcribed and modified to suit other datasets     

A NUMERICAL STUDY OF THE WINTERTIME CIRCULATION IN THE BOHAI AND HUANGHAI SEAS

The paper presents a numerical two-dimensional model (with a realistic sea basin and wind fields as exter nal forcing) to simulate the basic features of the wintertime circulation in the Bohai and Huanghai (Yellow) Seas (BHS) and to show how the circulation can be driven by wind. The main results can be summarized as follows (1) The basic features of the BHS wintertime circulation can be depicted by the wind-driven barotropi'c motion. (2) The traditionally named Huanghai Sea Warm Current (HSWC) is actually generated by the north wind field, at least in winter. (3) The southward coastal current off the Korean west coast plays a more significant role in the southern Huanghai Sea wintertime circulation than traditionally believed. (4) Though the coastal landform and bottom topography play important roles in the wintertime BHS circulation pattern, the wind is a primary forcing.     

Palynological dating (Arenig) of the sedimentary sequence overlying the Ishkarwaz Granite (upper Yarkhun valley, Chitral, Pakistan)

A sedimentary sequence overlying a granite pluton near Ishkarwaz (upper Yarkhun valley, Chitral, Pakistan; Karakorum Microplate) contains abundant, but poorly preserved, acritarchs probably referable to the late early Arenig-early late Arenig interval. The palynological assemblages of Karakorum show a marked similarity to the cold water Peri-Gondwana assemblages; i.e. to those of Li Jun's Arbusculidium-Coryphidium-Striatotheca 'Mediterranean' Bioprovince. Biogeographical and geological comparisons suggest that, before the accretion of Cimmerian microplates to the Eurasian continent, the Karakorum Microplate was located along the northern margin of Gondwana in a latitude intermediate between the Mediterranean region and South China (Yangtze Platform).     

Transport properties and microstructural characteristics of a thermally cracked mylonite

An experimental study was carried out on a granitic mylonite (La Bresse, France) to analyze the influence of pore microstructure on transport properties. Different crack networks were obtained by a controlled thermal treatment. Microstructures were analyzed by means of gas adsorption and mercury porosimetry. Transport properties have been investigated by measuring gas permeability and electrical conductivity. The dependence of permeability on confining pressure shows an exponential decrease, characteristic of a porosity made of cracks. Correlations between measured parameters have been analyzed by comparing them with relations deduced from theoretical models. Linking the formation factor to the porosity leads to a rather low tortuosity value (about 2.4), characterizing a medium with a well connected porosity. Correlation between permeabilityk and formation factorF leads to a power-law relationk F ^–n wheren2.9, which is consistent with a crack model describing the behavior of the thermally treated rock.     

Collisional processes among interplanetary dust grains: An unlikely origin for the β meteoroids

The question of the collisional production of the β meteoroids is reexamined incorporating recent experimental results (A. Fugiwara, G. Kamimoto, A. Tsukamoto, 1977, Icarus31, 277–288). The collisional model yields a flux of fragments supported by the conservation of mass flux which does not account by far for the observed flux of submicron grains. Particles larger than about 100 μm will be destroyed by collisions inside 1 AU, well before they can get near the Sun. The existence of two independent populations of interplanetary dust grains as proposed by L. B. Le Sergeant and Ph. L. Lamy (1978, Nature266, 822–824; 1980, Icarus43, 350–372) appears reinforced. It is proposed that the bulk of submicron grains does not necessarily travel in hyperbolic orbits and that β meteoroids may be a phenomenon—possibly transitory—of limited importance.     

Cloud and water vapour motion vectors in tropical cyclone track forecasting — A review

Summary Tropical cyclone track prediction remains a vexing problem in meteorology, particularly for numerical weather prediction. While there has been significant improvement in forecast skill in recent years, errors in prognosis, particularly for recurving cyclones still remain unacceptably high. Consistent with track prediction being to a significant extent an initial value problem, there has been, in recent years, cogent evidence that, a combination of high resolution numerical modelling, the use of appropriate assimilation techniques and the exploitation of high spatial and temporal resolution observations can improve the accuracy of tropical cyclone forecasts.Before landfall, tropical cyclones have their genesis and move over the data-sparse tropical oceans. Here the prediction of their movement is an application for which remotely sensed data are quintessential. In this context, this paper examines the increasingly important contribution of cloud and water vapour motion vectors to tropical cyclone prediction and evaluates their import to accurate prediction in terms of both the numerical modelling characteristics and the data assimilation techniques employed.Overall, it is shown that cloud and water vapour drift winds have made a significant contribution to the tropical cyclone track forecasting problem when used with conventional intermittent assimilation techniques, such as 6-hourly cycling, and, more recently, with continuous assimilation techniques such as 3- and 4-dimensional variational assimilation. These continuous assimilation schemes appear to have the potential to use near continuous asynoptic wind data in the most effective way.With 3 Figures     

Julellaavicenniae两个代谢产物结构的测定

从Ｊｕｌｅｌｌａａｖｉｃｅｎｎｉａｅ海洋真菌菌体中分离出１８种化合物,从它的培养液中分出三种化合物。本文根据ＭＳ,ＮＭＲ等光谱数据和化学学方法,测定了菌体代谢产物中的麦角甾醇和反 －９二十烯酸乙烯的结构。