A middle surface concept (MSC) model for saturated sands in general stress space

An elastoplastic constitutive model is proposed for saturated sands in general stress space using the middle surface concept (MSC). In MSC, different features of stress–strain response of a material are divided into different pseudo‐yield surfaces. The true‐yield surface representing the true response is established by using various links between the yield surfaces. In this MSC sand model, several well‐known features of sand response are represented by three different pseudo‐yield surfaces, which are developed in a simple and straightforward way. These features include the critical state behaviour, the effects of state parameter, unloading and reloading plastic deformation, the influence of fabric anisotropy, and phase transformation line related behaviour. Finally, the model predictions and test results are compared for two different types of sands under a variety of loading conditions and good comparisons are obtained. The application of MSC to saturated sand modelling shows the versatility of MSC as a general concept for modelling stress–strain response of materials. Copyright © 2006 John Wiley & Sons, Ltd.     

变分原理和非线性Lyapunov稳定性判据

本文通过构造斜压大气运动的原始方程模式和两层模式的Hamilton守恒量及积分不变的Casimir泛函,并使用变分法,得到了斜压大气运动的非线性Lyapunov稳定性判据,这个判据是Arnold-Blumen-Zeng判据的推广。     

Limit analysis for saturated porous media without fluid flow calculation

Application of yield design to porous media usually requires a preliminary calculation of the fluid flow net. The stability analysis is then carried out with seepage forces associated with the flow. We assume here that the flow is steady and that the yield criterion is defined by a function of the effective stress tensor. The formulation that we propose here allows taking into account seepage force in the expression of the kinematic stability conditions by means of hydraulic boundary conditions without calculation of the fluid flow. One obtains a formulation of the kinematic condition similar to the case of classic, non-porous media. The method is illustrated by two examples: a cylinder subjected to fluid flow and a vertical cut. It can be adapted to various boundary conditions and to the case of a criterion defined by a function of a generalized effective stress tensor. We also give a method to derive rigorous lower bounds using approximate fluid pressure field. Copyright © 2004 John Wiley & Sons, Ltd.     

湖北省棉花产量的变化与棉田布局的战略调整*

本文揭示了湖北省棉花亩产的增长具有北高南低的特点,分析了鄂北地区种植棉花的自然优势和经济效盆大于江汉平原,从而提出湖北省棉花北移的战略调整的设想。     

Value of Climate Forecasts for Adjusting Farming Strategies in Sub-Saharan Africa

Sustaining and increasing crop production and productivity has to be a major policy thrust for developing countries. Using a simulation approach different production strategies were evaluated conditioned on climate information to derive optimal strategies to help farmers reduce risk and increase productivity. By examining the existence of options in this case planting dates the study provides an analyses of the expected value and risks associated with changing decisions based on the availability of climate forecasts. The 15-March planting date produced the highest mean yield for the two cultivars examined although 1-April, 15-April and 1-May plantings had one to zero probability of crop failures compared to 15-March with crop failures in 4 out of 20 years. Results indicate losses of between 25 and 35 kg/day due to delays in planting from 15-March planting to 1-June planting for the 120- and 150-day cultivar. El niño years were associated with positive yield deviations for both cultivars and most planting dates. Farmers are known to make tactical adjustments to their management in light of information perceived relevant to the prospects of forthcoming crop. Although in its present form most current forecast products do not provide information on onset of the rainfall, however the information they do provide could play a crucial role in helping farmers reduce the risks posed by climatic variability.     

面向Internet的农业气象产量动态预报

针对信息时代Internet网上用户对产量预报动态查询的需求 ,探讨了面向Inter net的农业气象产量预报的解决方案。试验结果表明 ,由于作物生长发育和产量形成是一个光、温、水、土条件长期、综合作用 ,生物量长期累积的过程 ,因此利用积分回归方法 ,考虑全生育期光、温、水气象因子的综合影响 ,根据已出现的天气实况 ,在假定后期天气条件正常的情况下 ,有可能预测出未来产量的趋势。随着天气实况的逐一出现 ,后期的预报结果可望逐步接近实际值。统计检验和试报结果误差均在允许范围内。     

大中小震与抗震设防标准

讨论二级抗震设计与超越概率标准、概率法与综合概率法给出的3个水平的地震动的关系. 通过危险性分析的实际例子,讨论了50年超越概率2%、10%和63%的地震动,即大震、中震和小震的相对大小关系,并提出抗震设防标准的确定方法.      

吉木乃县近50年积温变化特征及其对小麦产量的影响分析

利用吉木乃县1961-2010年的积温和小麦产量资料,对日平均气温稳定通过0℃、10℃的初日、终日、初终间日数、积温的变化特征进行了分析;运用相关分析法探讨了生长期积温对小麦产量的影响。结果表明：近50年吉木乃县的积温变化是明显的,积温显著增多,≥0℃积温变率为83.7℃/10a,≥10℃积温变率为57.5℃/10a;稳定通过0℃和10℃界限温度初日提前、终日推后,初终间日数均呈增加的趋势。春夏季积温与春小麦产量的相关关系显著,当0℃积温距平每增加1℃时,小麦产量将增加0.15%;当10℃积温距平每增加1℃时,产量将增加0.12% 。积温变化使小麦冻害减轻,但干旱、干热风危害加大。