大掺量磨细粉煤灰混凝土单轴受压应力应变全曲线的试验研究

普通混凝土和高强混凝土的应力应变曲线,国内外已开展了大量的研究。但有关掺磨细粉煤灰混凝土应力应变全曲线资料却不多见,本文配合粉煤灰混凝土的推广应用,对其单轴受压性能及应力应变关系进行试验研究,同时给出了适用于不同强度等级掺磨细粉煤灰混凝土受压应力应变全曲线的统一数学表达式,与试验曲线吻合较好,可供进一步研究参考。     

芯钢管混凝土节点的芯管壁厚与节点承载力关系的数值分析

对一种已经通过试验研究的钢管混凝土结构的新型节点进行数值分析。这种节点将钢管混凝土柱的钢管在节点区间断,在节点区设置芯钢管,使梁中的纵筋在节点中直通、梁与节点区混凝土成为一体可靠的传递梁中的弯矩、剪力及轴力。本文利用数值分析弥补模型试验数量少的缺陷。选择不同芯钢管壁厚的节点模型进行非线性有限元分析,得出芯钢管壁厚对节点承载力的影响规律。分析结果表明芯钢管壁厚是影响节点承载力的主要因素之一。     

Regulating the River Severn

The River Severn is the longest of Britain's regulated rivers: this chapter describes the geography of the river's catchment area, from its source in central Wales to the Bristol Channel where it flows into the sea. It then considers the historical development of the Severn as a water resource, culminating in the construction of Llyn Clywedog and more recently the Shropshire Groundwater Scheme to augment low river flows and support greatly increased abstractions. Plans for even more substantial development of the resource system appropriate to the rapid demand growth of the 1960s and early 1970s are discussed. Practical experience in regulating flows in the river gained during the drought of 1976 is described and used to explain recent developments in the practice and monitoring of river regulation.     

水电站建成后分流河段水位流量关系的变化

在分流河段修建水电工程，因受工程建设的影响，其下游的水位流量关系曲线将不再是单一曲线，而是一束以全断面流量为参数的曲线组。这束曲线中的任一曲线应通过３个特征点。曲线起点、天然分流点、曲线终点，这３个点确定后，即可推求不同总流量情况下的水位流量关系曲线。     

A functional time series analysis of forward curves derived from commodity futures

We study forward curves formed from commodity futures prices listed on the Standard and Poor’s-Goldman Sachs Commodities Index (S&P GSCI) using recently developed tools in functional time series analysis. Functional tests for stationarity and serial correlation suggest that log-differenced forward curves may be generally considered as stationary and conditionally heteroscedastic sequences of functions. Several functional methods for forecasting forward curves that more accurately reflect the time to expiry of contracts are developed, and we found that these typically outperformed their multivariate counterparts, with the best among them using the method of predictive factors introduced by Kargin and Onatski (2008).     

Neglected dynamics in panel data models; consequences and detection in finite samples*

The bias of various estimators for static cross-section and panel data models is assessed in a simulation study, where the actual data generating process is a dynamic adjustment mechanism with random individual effects. It is concluded that the consequences of incorrectly estimating a static model can be rather serious. Therefore, it is important to have an accurate technique available for the detection of dynamics. Two exact similar tests for the presence of a lagged dependent variable in panel data models are developed; in some simulation experiments these tests outperform standard asymptotic test procedures. Empirical results on Engle curves for food illustrate the above issues.     

Reflections on the Structure and Origin of Pareto Income Distributions

The essay takes the reader on a voyage of exploration with the aim of discovering the origin of Pareto-curves. It shows with thought-experiments backed up by computer-simulation the generation of log-normal curves in detail. Extending forward this conceptual trajectory, it arrives via a quasi-Newtonian fluxion-insight – infinitessimal differential integration – at a novel mathematical concept: Pareto-curves are simply special log-normal curves where a large number of random-factors interacted and impacted at their genesis (the author called it the Kopp-effect).     

软黏土不排水循环应力应变关系的数值模拟

对程星磊等提出的总应力形式增量弹塑性本构模型进行二次开发,以模拟复杂应力状态下软黏土的响应。通过Newton-Raphson算法,对材料非线性问题进行迭代求解;针对本构模型中应力反向等一系列关键性问题,应用欧拉切线算法编写了有限元程序,并结合子增量方法提高了计算精度。预测了软黏土在轴对称应力状态下的响应,得到了应力应变关系曲线,将其与单元预测结果进行比较,二者趋于一致,从而验证了有限元程序编写的合理性。利用该程序模拟三轴不固结不排水试验,模拟结果与试验吻合良好,表明该本构模型有限元程序可以反映轴对称应力状态下软黏土的不排水应力应变特性,可应用于更加复杂边值问题的模拟计算。     

赣江下游河段设计最低通航水位计算方法

用保证率频率法计算赣江下游河段设计最小通航流量，再从近几年枯水期水位流量关系曲线上查得对应于该流量的水位，即为设计最低通航水位。用该方法计算的设计水位更符合河道的实际情况。