Seepage mechanisms and permeability differences between loess and paleosols in the critical zone of the Loess Plateau

The soil in the Loess Plateau has special permeability characteristics due to the alternating distribution of loess and paleosol layers. Using an analysis of the physical properties, microstructure and thermogravimetric analysis of loess and paleosol, this paper examines strata seepage mechanisms in the loess tableland area and considers the applicability of a hydraulic conductivity empirical formula. The analysis shows that hydraulic conductivity attenuation with depth can be represented by a negative exponential model, while hydraulic conductivity values are not normally distributed. The best-fitting models of hydraulic conductivity in the horizontal (K_H) and vertical (K_V) directions are Gaussian models, and both have strong spatial correlations. This study of the difference in permeability between loess and paleosol found that the depositional environment was the dominant causal factor, making the average hydraulic conductivity of most loess layers greater than that of the underlying paleosol layers. Different microstructures between loess and paleosol also confirmed the microscopic explanation in permeability anisotropy and their permeability difference. Thermogravimetric analysis determined temperature ranges for different types of water lost by heat, and then calculated ratios of bound water mass to liquid limit, with an average of 0.768. A modified formula suitable for loess was obtained by integrating the consistency index method and effective porosity ratio model into the hydraulic conductivity empirical formula. Compared with the results of laboratory tests and uncorrected formulas, the modified formula provides a good estimate of strata hydraulic conductivity. Accurate understandings of seepage mechanisms and permeability differences in the loess area are important, promoting ecological restoration and providing scientific guidance for the sustainable development of the Loess Plateau.     

A derivation of the Isted formula for average mineral grade of a triangular prism

The Isted formula, which provides an exact calculation of the spatial average of mineral grade in a triangular prism under the assumption of linear change, is derived, and its limitations outlined. This formula may be used to estimate the mean of any trivariate function whenever variation in the vertical direction can be considered negligible.     

平原储灰库区地下潜水位影响评价模式探讨

以山东华能德州发电厂现役储灰库"灰水"对潜水位的影响和水量均衡原理,确定其对库区潜水位影响范围;对拟建储灰库区根据水文地质条件,采用非稳定流基本方程对库区潜水水位进行预测,得出平原储灰库区地下潜水位最大影响范围为750m.     

The effect on the geoid of lateral topographic density variations

Gravimetric geoid determination by Stokes formula requires that the effects of topographic masses be removed prior to Stokes integration. This step includes the direct topographic and the downward continuation (DWC) effects on gravity anomaly, and the computations yield the co-geoid height. By adding the effect of restoration of the topography, the indirect effect on the geoid, the geoid height is obtained. Unfortunately, the computations of all these topographic effects are hampered by the uncertainty of the density distribution of the topography. Usually the computations are limited to a constant topographic density, but recently the effects of lateral density variations have been studied for their direct and indirect effects on the geoid. It is emphasised that the DWC effect might also be significantly affected by a lateral density variation. However, instead of computing separate effects of lateral density variation for direct, DWC and indirect effects, it is shown in two independent ways that the total geoid effect due to the lateral density anomaly can be represented as a simple correction proportional to the lateral density anomaly and the elevation squared of the computation point. This simple formula stems from the fact that the significant long-wavelength contributions to the various topographic effects cancel in their sum. Assuming that the lateral density anomaly is within 20% of the standard topographic density, the derived formula implies that the total effect on the geoid is significant at the centimetre level for topographic elevations above 0.66 km. For elevations of 1000, 2000 and 5000 m the effect is within ± 2.2, ± 8.8 and ± 56.8 cm, respectively. For the elevation of Mt. Everest the effect is within ± 1.78 m.     

Torsional balance of plan‐asymmetric structures with frictional dampers: experimental results

This investigation deals with the measured seismic response of a six‐storey asymmetric structural model with frictional dampers. Its main objective is to experimentally prove the concept of weak torsional balance for mass‐ and stiffness‐eccentric model configurations. The goal is to control the torsional response of these asymmetric structures and to achieve, if possible, a weak form of torsional balance by placing the so‐called empirical centre of balance (ECB) of the structure at equal distance from the edges of the building plan. The control of the dynamic response of asymmetric structures is investigated herein by using steel–teflon frictional dampers. As expected from theory, experimental results show that the mean‐square and peak displacement demand at the flexible and stiff edges of the plan may be similar in magnitude if the dampers are optimally placed. Frictional dampers have proven equally effective in controlling lateral‐torsional coupling of torsionally flexible as well as stiff structures. On the other hand, it is shown that impulsive ground motions require larger frictional capacities to achieve weak torsional balance. Copyright © 2006 John Wiley & Sons, Ltd.     

江淮梅雨期最低气温的气候特征分析

利用江淮地区70个测站1961~2001年历年6月第2侯至7月第2侯最低气温资料,采用旋转经验正交展开(REOF)方法对江淮地区梅雨期最低气温场进行客观分区,并分析了各区域最低气温的长期演变趋势。结果表明:江淮地区梅雨期最低气温场可分为3个区域,各区域的最低气温均具有明显的年际、年代际变化特征,且存在着显著差异,其中东北区明显上升,而南方区和西北区呈降低趋势;各区域存在明显不同的年际、年代际方差构成、突变特征和多尺度振荡周期。     

福建省区域尺度太阳总辐射模拟估算研究

比较了3种以常规地面气象资料为基础估算太阳总辐射的气候学估算模型(晴天辐射模型、天文辐射模型和MTCLIM气候模型),并以2004年福建省仅有的福州站和建瓯站太阳总辐射实测值进行验证.研究结果表明:以晴天总辐射为基值计算太阳总辐射估算模型的精度最高,运用该模型在ARCGIS支持下对福建省太阳总辐射进行空间插值,拟合了福建省区域尺度太阳总辐射月总量和年总量的空间分布,为省区域尺度生态系统碳循环模型,水文模型及植被净第一性生产力的估算研究提供了重要的空间表达参数.     

基于随机模型基准的Helmert方差分量估计

在多类观测数据联合平差中,存在某类观测值的验前协方差阵正确而其他类不正确的情况,传统Helmert方差分量估计在求解此类问题时没有对正确的验前协方差阵加以区别,从而造成正确的随机模型经估计后同样也被调整。针对上述情况,首先分析了Helmert方差分量估计迭代收敛结果的实质,然后提出了随机模型基准的概念,并推导了基于随机模型基准的Helmert方差分量估计公式。经计算表明,新公式完全可行,可以用于解决实际问题。     

Soil fertility management strategies on the Jos Plateau: the need for integrating 'empirical' and 'scientific' knowledge in agricultural development

Tin mining carried out on the Jos Plateau since the beginning of the last century has disturbed some 320 km² of agricultural land. Formal attempts at reclamation of this land failed, but local farmers have developed a successful informal strategy for reclamation. This paper reports on a study undertaken to comprehend the farmers'informal' approach to soil fertility management. Their soil fertility management practices centre on the use of a complex combination of traditional organic manures and 'modern' inorganic fertilizers that they have developed entirely on the basis of experimentation. A central focus of this paper is therefore the empirical knowledge base of the farmers and an assessment of any underlying scientific explanations for their strategies, including an analysis of their assertion that different brands of NPK fertilizers differ in their nutrient value. This discussion is followed by a consideration of the difficulties in accessing and understanding empirical knowledge. It is concluded that farmers' knowledge and understanding of the values of different fertilizers and manures does have a scientific basis. It is argued that for further agricultural development to take place on the Jos Plateau, there must be synergy between farmers' empirical knowledge (which has led to the development of successful and effective soil fertility management strategies, unlike the attempts of the local 'scientific' communities) and scientific knowledge (which can identify health and environmental hazards which may not be immediately visible to farmers).