ASR pessimum behaviour of siliceous limestone aggregates

Siliceous limestone aggregates have “pessimum” behaviours similar to those observed for pure siliceous aggregates such as flint or opal. For high alkali contents concretes based on fine and coarse reactive siliceous limestone aggregates swell less than concretes based on fine reactive siliceous limestone aggregates and non-reactive coarse aggregates. The reduction of the swelling is more significant for a “micritic” limestone containing highly reactive free silica than for a “sparitic” limestone containing less reactive free silica. The consumption of a part of the alkalis by non-expansive processes such as chemical sorption on silanol sites of reactive silica and pozzolanic C-S-H is expected to explain the reduction of the swelling.     

Investigation of farmers' willingness to pay for using recycled water for irrigation in Thessaly region, Greece

The objective of the present study was to investigate farmers' willingness to pay for using recycled water for irrigation purposes in Thessaly region, Greece. The method followed for the above analysis was the contingent valuation method which aims at eliciting individuals' preferences, in monetary terms, for changes in the quantity or quality of nonmarket environmental resources through personal interviewing. Our study was based on data collected from 107 questionnaires, which were answered by farmers in Thessaly region. The region is located in central eastern part of Greece and its main feature is that a relatively high percentage of its population is partly or fully employed in agriculture. Furthermore, Thessaly region suffers from a distinct water shortage in summer period, which is partly attributed to the increased agricultural activity. The group chosen for our study was random and the questionnaires were answered through personal interviews. The questionnaire was divided in 3 sessions. The first one dealt with personal data in order to investigate correlations between socioeconomic characteristics of interviewee and his or her willingness to use recycled water and to pay for it. The second session had as a goal to discover whether farmers are willing to use recycled water for irrigation purposes. Finally, the third session dealt with farmers' willingness to pay for treated wastewater. The data were statistically analyzed with the use of the multinomial logistic regression method. The main results show that Thessaly farmers are willing to pay for recycled water especially during drought spells in the region.     

Fe含量对热挤压再生铝合金组织和性能的影响

采用光学显微镜、扫描电镜、万能拉伸机、显微硬度计等手段研究了不同Fe含量对热挤压再生铝合金组织和性能的影响,并探讨富Fe相形态演变机制。结果表明,Fe含量的增加有利于抑制再生铝晶粒尺寸的长大。随着Fe含量增加,晶粒尺寸逐渐减小,减小幅度达25%。热挤压后再生铝中富Fe相发生了折断和破碎,并沿着挤压方向呈带状分布。随着Fe含量增加,富Fe相的面积分数和平均长度均逐渐提高,当Fe含量分别为0.10%~1.24%时,面积分数和平均长度增长最快;而富Fe相的圆整度则随Fe含量的增加稍有降低。同时,再生铝的抗拉强度、屈服强度和伸长率均随着Fe含量的增加呈现逐渐降低的趋势,最大降低幅度分别为10.4%、23.2%和46.0%,而显微硬度则逐渐提高,最大提高幅度为21.7%。断口形貌也由纯韧性断裂转变为混合型断裂模式。     

Effect of heat treatment and zircon addition on the properties of low-cement castables based on recycled alumina grog

In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.     

国内外绿色混凝土的发展动态及趋势

混凝土作为目前最大宗的土木建筑材料，在给社会带来良好的经济和社会效益，同时，也造成了严重的环境污染和生态破坏。本文分析探讨了国内外绿色混凝土发展状况及趋势。目前，开展绿色材料其相关理论的研究，从而实现材料科学与技术的持续发展，是历史发展的必然，也是材料科学的进步。在这种的背景条件下，具有环境协调和自然相适应的特性绿色混凝土应运而生。     

Survey of users and providers of recycled water: quality concerns and directions for applied research

Users and providers of recycled water in Queensland, Australia, were canvassed to ascertain concerns about recycled water quality and directions for applied research. Some 79% of respondents had concerns about recycled water quality including microbiological components, such as viruses, parasites and bacteria, salinity related components, aggregate components, such as pH and solids, nutrients, organic components, including pesticides and endocrine disruptors, as well as quality variability. Relative differences in the proportion of concern for some quality characteristics were observed between the areas of different population density with those from the low population areas being more concerned than those from medium or high areas. Some users and providers observed changes in recycled water quality during distribution including nutrients, chlorine, solids, colour and odour. Some 52% of providers and 19% of current users propose to expand their usage and 30% of non-users propose to commence doing so in the next 5 years. Recycled water quality characteristics identified for applied research included microbiological components, organic components, nutrients and salinity.     

Efficient Parallel Graph Algorithms for Coarse-Grained Multicomputers and BSP

In this paper we present deterministic parallel algorithms for the coarse-grained multicomputer (CGM) and bulk synchronous parallel (BSP) models for solving the following well-known graph problems: (1) list ranking, (2) Euler tour construction in a tree, (3) computing the connected components and spanning forest, (4) lowest common ancestor preprocessing, (5) tree contraction and expression tree evaluation, (6) computing an ear decomposition or open ear decomposition, and (7) 2-edge connectivity and biconnectivity (testing and component computation). The algorithms require O(log p) communication rounds with linear sequential work per round (p = no. processors, N = total input size). Each processor creates, during the entire algorithm, messages of total size O(log (p) (N/p)) . The algorithms assume that the local memory per processor (i.e., N/p ) is larger than p ^ε , for some fixed ε > 0 . Our results imply BSP algorithms with O(log p) supersteps, O(g log (p) (N/p)) communication time, and O(log (p) (N/p)) local computation time. It is important to observe that the number of communication rounds/ supersteps obtained in this paper is independent of the problem size, and grows only logarithmically with respect to p . With growing problem size, only the sizes of the messages grow but the total number of messages remains unchanged. Due to the considerable protocol overhead associated with each message transmission, this is an important property. The result for Problem (1) is a considerable improvement over those previously reported. The algorithms for Problems (2)—(7) are the first practically relevant parallel algorithms for these standard graph problems. Received July 5, 2000; revised April 16, 2001.     

Experimental comparison of the switching heuristics for aggregate production planning problem

Two improved versions of the production switching heuristic(PSH), Dominant PSH and Inventory-Ratio-Based PSH are proposed. Extensive computer experiments are performed to evaluated the proposed rules. Both linear and quadratic cost functions are adopted for the comparison study. Also. the influence of seasonality is investigated on the effectiveness of each rule. The results show that the proposed rules outperform the PSH in terms of the total cost, especially when seasonality factor is significant or the unit inventory carrying cost is high.     

三维六角形粗网格中子扩散计算方法

本文介绍对于由六角形栅元组件组成的核反应堆堆芯,采用三维粗网格展开法求解中子扩散方程,推导出九点高阶近似差分方程。该方程形式上与低阶有限差分方程类似,可以采用低阶有限差分法的求解技巧求解,所建立的方法适用于两维或三维中子扩散计算,对堆芯设计和燃耗分析很有意义。     

Compile-time copy elimination

Single-assignment and functional languages have value semantics that do not permit side-effects. This lack of side-effects makes automatic detection of parallelism and optimization for data locality in programs much easier. However, the same property poses a challenge in implementing these languages efficiently. This paper describes an optimizing compiler system that solves the key problem of aggregate copy elimination. The methods developed rely exclusively on compile-time algorithms, including interprocedural analysis, that are applied to an intermediate data flow representation. By dividing the problem into update-in-place and build-in-place analysis, a small set of relatively simple techniques—edge substitution, graph pattern matching, substructure sharing and substructure targeting—was found to be very powerful. If combined properly and implemented carefully, the algorithms eliminate unnecessary copy operations to a very high degree. No run-time overhead is imposed on the compiled programs.