平面P波在饱和半空间中洞室周围的散射(I):解析解

利用波函数展开法给出了入射平面P波在饱和半空间中圆形洞室周围散射问题的一个解析解。半空间假定为无粘性流体饱和介质,满足Biot理论。采用一种基于实验数据的孔隙率和模量之间的线性关系来确定Biot模型中的介质参数。解答考虑了透水边界和非透水边界两种情况。对边界条件进行了数值检验,结果表明,随着级数截断项数的增大,边界残量衰减很快。解答为进一步研究入射波频率和角度、边界渗透条件、孔隙率、泊松比等参数对散射的影响奠定了基础。     

A modified parallel IWAN model for cyclic hardening behavior of sand

A modified parallel IWAN model, which includes a cyclic hardening function, is proposed and verified. The proposed model consists of elasto-perfect plastic and isotropic hardening elements. The model is able to predict cyclic hardening behavior through the adjustment of the internal slip stresses of its elements beyond the cyclic threshold, and satisfies Bauschinger's effect and the Masing rule with its own behavior characteristics. The cyclic hardening function is developed based on the irrecoverable plastic strain (accumulated shear strain) of dry sand during shearing, which is assumed to be a summation of shear strain beyond the cyclic threshold. Symmetric-limit cyclic loading and irregular loading tests were performed to determine model parameters and to verify the behavior of the proposed model. Finally, a one-dimensional site response analysis program (KODSAP) is developed by using the proposed model. The effects of cyclic hardening behavior on site response are evaluated using KODSAP.     

Shaking table tests on a high‐rise RC building model having torsional eccentricity in soft lower storeys

A series of shaking table tests on a 1:12‐scale model using scaled TaftN21E earthquake records were conducted to investigate the seismic performance of a 17‐storey high‐rise reinforced concrete structure with a high degree of torsional eccentricity and soft‐storey irregularities in the bottom two storeys. Based on the analysis of test results, the following conclusions were drawn: (1) the model responded mainly in the coupled mode of translation and torsion or in the torsional mode. Under severe table shaking, the flexible side underwent large inelastic deformation, and the predominant mode of the model changed from the coupled mode to the torsional mode, resulting in greatly increased torsional stiffness, thereby limiting damage in the flexible frame; (2) the shear force and deformation of the flexible side were governed by the torsional behaviour, whereas those of the stiff side were affected mainly by the overturning deformation. The lateral stiffness of the shear wall in the torsional mode was about four times that in the coupled mode because the warping deformation due to torsion counteracted the flexural deformation due to overturning moment in the torsional mode; and (3) the reversed cyclic overturning moments predicted by linear elastic dynamic analysis in the direction transverse to the table excitations contradicted unilateral overturning moments of the serviceability‐level test results, which showed a bias towards tension or compression in the columns. Copyright © 2006 John Wiley & Sons, Ltd.     

Cloud/Fog Water Chemistry at a High Elevation Site in South Korea

Cloud/fog water samples were collected at Daekwanreung (840 m msl), a ridge site, in South Korea, from March 2002 to September 2003, by using a Caltech type, self fabricated active strand cloud water collector. The pH, electrical conductivity and major ion concentrations were analyzed. The cloud water pH ranged from 3.6 to 6.8 with an average of 5.2, which was close to the atmospheric neutral point. However, the pH calculated from average concentrations of H+ was 4.7, indicating the cloud/fog water was weakly acidified. SO₄ ²⁻, NO₃ ⁻ and NH₄ ⁺ are predominant ions of which average concentrations were 203.1, 128.1, and 211.7 μeq⋅L⁻¹, respectively. Samples were categorized into four groups by applying 48-hour back trajectory analysis, using the HYbrid Single-Particle Largrangian Integrated Trajectory (HYSPLIT) model. Chemical compositions for the four cases significantly differed from each other. For air masses transported from the East Sea (group E), sea salt concentrations, including Na⁺, Cl⁻ Mg²⁺, were relatively high. Principal acidifying pollutants, such as NO₃ ⁻ and nss-SO₄ ²⁻, significantly increased in the case of air masses transported from the Northeast Asian continent through North Korea (group N) and air masses from the Seoul metropolitan area (group W). However, the mean pH of group N was the highest while the mean pH of group W was the lowest. This suggests that most NO₃ ⁻ and nss-SO₄ ²⁻ in cloud/fog water was neutralized by ammonia and calcium compounds under the influence of air masses transported from Northeast Asia. N/S ratio for the group W was significantly higher than those for the other three groups, suggesting nitrogen species transported from the Seoul metropolitan area contributed to acidification of cloud/fog water at Daekwanreung. Principle Component analysis (PCA) was applied to the cloud/fog water data for presenting characteristics in the four different categories.     

Geochronologic evidence for Early Cretaceous volcanic activity on Barton Peninsula, King George Island, Antarctica

Ages of six volcanic and plutonic rocks on Barton Peninsula, King George Island, were determined using ⁴⁰Ar/³⁹Ar and K-Ar isotopic systems. The ⁴⁰Ar/³⁹Ar and K-Ar ages of basaltic andesite and diorite range from 48 My to 74 My and systematically decrease toward the upper stratigraphic section. Two specimens of basaltic andesite which occur in the lowermost sequence of the peninsula, however, apparently define two distinct plateau ages of 52-53 My and 119-120 My. The latter is interpreted to represent the primary cooling age of basaltic andesite, whereas the former is interpreted as the thermally-reset age caused by the intrusion of Tertiary granitic pluton. The isochron ages calculated from the isotope correlation diagram corroborate our interpretation based on the apparent plateau ages. It is therefore likely that volcanism was active during the Early Cretaceous on Barton Peninsula. When the K-Ar ages of previous studies are taken into account with our result, the ages of basaltic andesite in the northern part of the Barton Peninsula are significantly older than those in the southern part. Across the north-west-south-east trending Barton fault bounding the two parts, there are significant differences in geochronologic and geologic aspects.     

SIMULATING REGIONAL SYSTEMS: A SYSTEM DYNAMICS APPROACH

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An experimentally verified model for calcite precipitation in veins

Calcite is commonly found as a vein-filling mineral in rocks. However, the factors controlling its deposition are complex and not well understood in quantitative terms. In order to advance our understanding of the processes involved, we have refined the model for calcium carbonate mass transport in subsurface carbonate rocks of Morse and Mackenzie (1993) and developed a new experimental technique to test it. This technique uses a flow-through reactor that simulates a vein opening. Agreement was observed between model predictions and experimental observations for the deposition of calcite in synthetic veins. The influences of surface area to solution volume ratio, solution saturation state with respect to calcite, and flow velocity were well predicted by the model.

The model predicts that in order to have a fairly uniform deposition of calcite within a vein, solution flow must be quite rapid (tens to thousands of cm h⁻¹) or the solution must be only slightly supersaturated with respect to calcite. A low degree of solution supersaturation demands what may be unreasonably large volumes of solution flow to achieve vein filling for the vein configuration we have studied.