桥墩底部岩溶对其上层围岩稳定性影响的数值研究

本文运用RFPA系统的强度折减版以清水大桥5号断面为背景对桥墩底部溶洞区对其上部围岩稳定性的影响进行了数值分析研究。研究结果表明:岩:容对其上层围岩的影响范围随着深度的增大而变大;破坏效应带主要是在垂直于自由面的溶洞两侧;对多溶洞而言,应力主要集中在两溶洞破坏效应带之间的区域,并且主要在此发生破坏,而在其内部效应带之间则比较稳定。     

What is hidden behind the concept of ecosystem efficiency in energy transformation?

The number of energy transformation levels in trophic webs is usually below five, but can be extended up to ten when parasites and hyper-parasites are included. Research on the structure and function of food webs is relevant to the complexity–stability–productivity debate. The aim of this theoretical analysis is to link energetic and connectional aspects of ecosystems with information theory. Updating an energetic model reported by Ricklefs [Ecologia, Zanichelli Editore S.p.A., Bologna, Italy, 1993, p. 896], our approach is integrated with a static analysis of food webs. The length of food webs is theoretically associated with the average ecological efficiency which can be empirically correlated with the effective connectance between species. Furthermore, the advantage of greater complexity when applied to a signalling network is qualitatively addressed.The overall efficiency of energy transformation into biomass throughout a trophic web, in an ecosystem with a given number of species, is the resultant of the various ecological efficiencies, η, at the transitions between the trophic levels. However, we propose that an increment in effective connectance and interspecies connectivity based on a superimposed signalling web may increase the η values, despite the fact that signalling per se has an energetic cost. According to this hypothesis, ecosystem stability would not be necessarily reduced by increasing the number of trophic levels, N, whenever stability in terms of persistence is improved by a cost-efficient regulatory network.     

A nonequilibrium thermodynamic framework for discussing ecosystem integrity

During the last 20 years our understanding of the development of complex systems has changed significantly. Two major advancements are catastrophe theory and nonequilibrium thermodynamics with its associated theory of self-organization. These theories indicate that complex system development is nonlinear, discontinuous (catastrophes), not predictable (bifurcations), and multivalued (multiple developmental pathways). Ecosystem development should be expected to exhibit these characteristics. Traditional ecological theory has attempted to describe ecosystem stress response using some simple notions such as stability and resiliency. In fact, stress-response must be characterized by a richer set of concepts. The ability of the system to maintain its current operating point in the face of the stress, must be ascertained. If the system changes operating points, there are several questions to be considered: Is the change along the original developmental pathway or a new one? Is the change organizing or disorganizing? Will the system return to its original state? Will the system flip to some new state in a catastrophic way? Is the change acceptable to humans? The integrity of an ecosystem does not reflect a single characteristic of an ecosystem. The concept of integrity must be seen as multidimensional and encompassing a rich set of ecosystem behaviors. A framework of concepts for discussing integrity is presented in this article.     

Evaluation of Solvita compost stability and maturity tests for assessment of quality of end-products from mixed latrine style compost toilets

It is challenging and expensive to monitor and test decentralized composting toilet systems, yet critical to prevent the mismanagement of potentially harmful and pathogenic end-product. Recent studies indicate that mixed latrine composting toilets can be inhibited by high ammonia content, a product of urea hydrolysis. Urine-diverting vermicomposting toilets are better able to accomplish the goals of remote site human waste management by facilitating the consumption of fecal matter by earthworms, which are highly sensitive to ammonia. The reliability of Solvita® compost stability and maturity tests were evaluated as a means of determining feedstock suitability for vermicomposting (ammonia) and end-product stability/completeness (carbon dioxide). A significant linear regression between Solvita® ammonia and free ammonia gas was found. Solvita® ranking of maturity did not correspond to ranking assigned by ammonium:nitrate standards. Solvita® ammonia values 4 and 5 contained ammonia levels below earthworm toxicity limits in 80% and 100% of samples respectively indicative of their use in evaluating feedstock suitability for vermicomposting. Solvita® stability tests did not correlate with carbon dioxide evolution tests nor ranking of stability by the same test, presumably due to in situ inhibition of decomposition and microbial respiration by ammonia which were reported by the Solvita® CO₂ test as having high stability values.     

The dynamic response of pressure relief valves in vapor or gas service,part I: Mathematical model

In order to prevent unstable operation, or “chatter”, of a pressure relief the API guidelines recommend limiting the irreversible pressure loss in the inlet line to a pressure relief valve to no more than 3% of the valve set pressure. This criterion is based on steady-state operating conditions and a typical blow-down pressure for the valve of about 7% of the set pressure. However, the stability of the valve is also influenced by other factors such as the dynamic response of the valve disk to the unsteady pressures and forces exerted by the fluid on the disk. A model for the opening lift dynamic response of a pressure relief valve in gas/vapor service is presented here which accounts for all of these effects through a set of five coupled nonlinear algebraic/differential equations. These equations are solved by a numerical method that can be implemented on a spreadsheet to predict the position of the valve disk as a function of time for given valve characteristics, operating conditions, and installation parameters. The model incorporates the influence of the various parameters on the stable/unstable nature of the disk response. An example is presented for a typical valve that illustrates the various modes of stable and unstable dynamic response that can be predicted by the model under various conditions. Two additional papers will be forthcoming: Part II – Experimental Investigation and Part III – Analysis of Data and Comparison with Model Predictions.     

纤维球过滤的适应性和稳定性的研究

论述了纤维球过滤技术用于给水处理和废水处理的效果和适应情况，并和砂滤进行了同步比较试验．同时，探讨了纤维球滤料的反冲洗条件和反冲效果，并经长期运行以观察纤维球过滤的稳定性．     

亚硝酸盐氮标准溶液的稳定性试验

ＧＢ７４９３－８７认为：１．００ｍｇ／Ｌ亚硝酸盐氮标准溶液在使用时，应当天配制。现经５０天试验证明，该溶液置于２０℃以下比较稳定。     

Potential environmental fate of elsinochrome A,a perylenequinone toxin produced in culture by bindweed biocontrol fungus Stagonospora convolvuli LA39

The photosensitizing perylenequinone toxin elsinochrome A (EA) is produced in culture by the bindweed biocontrol fungus Stagonospora convolvuli LA39 where it apparently plays a pathogenicity related role. We investigated the fate of EA with reference to its stability under different temperature and light conditions. EA remained stable when boiled in water at 100^∘C for 2 h. Similarly, exposing EA to 3–27^∘C in the dark for up to 16 weeks did not affect its stability either in dry or in aqueous form. However, results from irradiation experiments indicate that direct photolysis may be a significant degradation pathway for EA in the environment. EA either in dry form or dissolved in water was degraded by different irradiation wavelengths and intensities, with degradation plots fitting a first order rate kinetics. EA degraded faster if exposed in aqueous form, and at higher quantum flux density (μmol s⁻¹ m⁻²). Sunlight was more effective in degrading EA than artificial white light and ultraviolet radiations (UV-A or UV-B). Exposing EA to natural sunlight, particularly, during the intense sunshine (1,420– 1,640 μmol s⁻¹ m⁻²) days of 30 July to 5 August 2004 in Zurich caused the substance to degrade rapidly with half-life under such condition only 14 h. This implies that should EA gets into the environment, particularly on exposed environmental niches, such as on plant surfaces through biocontrol product spray, or released from shed diseased leaves, it may have no chance of accumulating to ‘level of concern’. Furthermore, a toxicity assay using Trichoderma atroviride P1 as biosensor showed that photo-degraded EA was not toxic, indicating that no stable toxic by-products were left.     

高速铁路弓网系统受流稳定性与Lyapunov指数

以高速铁路发展为背景,从高速、快捷、安全、舒适的乘车环境出发,分析了高速行驶的列车电力供应问题,提出安全稳定的受流条件是列车正常运行的前提。建立了高速铁路受电弓/接触网系统动力学模型,以Mathieu方程为基础,采用摄动法推导出弓网系统稳定边界,并求得了系统的周期解,采用实际接触网、受电弓以及列车运行速度等参数,得到一组弓网系统稳定受流曲线。为深入分析系统的稳定性,又对系统的Lyapunov特征指数进行计算,得出不同参数下的Lyapunov特征指数,从而提出了列车的最佳运行速度和最不利运行速度,为进一步研究高速铁路弓网系统的稳定安全受流及设计新一代受电弓提供了参考     

高分子聚合筑路剂(P.P.T)用于改善铁路路基力学特性的研究

高速、重载铁路的发展对铁路路基的稳定性、承载力提出了更高的要求,为此,笔者介绍一种运用新型高分子聚合的筑路剂——P.P.T来改善路基力学特性的方法。通过对P.P.T改良土封顶前后路基稳定性和承载力的计算和比较分析,指出其改良土在较薄封顶厚度的前提下,仍能够有效提高路基边坡的稳定性,尤其是能大幅度提高路基的容许承载力。此外,P.P.T在防治路基其他常见病害方面与传统的灰土相比也具有较大优势,实际工程应用表明,P.P.T具有较好的推广价值。