Copolymerization of phenylacetylene with various acetylenes by W- and Mo-based catalysts

In the copolymerization of phenylacetylene with various acetylenes catalysed by WCl₆·Ph₄Sn, the relative reactivity of monomer decreased with increasing steric effect of monomer, e.g. HC  Cn-Bu, HC  Cn-Hex > HC  CPh, HC  Cs-Bu > HC  Ct-Bu, MeCCPh, CICCPh. While 1-chloro-2-phenylacetylene (a disubstituted acetylene) showed high reactivity in the homopolymerization by Mobased catalysts, the reactivity was remarkably depressed in the presence of phenylacetylene as comonomer. Based on these results, the relative reactivity of the acetylenic monomers in copolymerization was explained in terms of competitive coordination of monomers to the propagating end.     

平原地区木材安全问题的调查与建议

随着国民经济的快速发展,木材需求呈现出快速增长的态势。在国内木材供不应求的情况下,木材安全问题日益凸显。平原地区是我国重要的木材供给区域,在保障我国木材安全中具有较大潜力。通过对平原地区木材生产的实地调研,本文对加强森林资源培育、木材加工业发展、木材生产与农民增收、境外森林资源开发、惠林政策等问题进行了分析并提出了建议。     

Two Novel Metal Phosphonate Compounds: Different One-Dimension Chain Structures Constructed by Imidazole and 1-Aminoethylidenediphosphonic Acid

Hydrothermal reactions of 1-aminoethylidenediphosphonic acid (AEDPH₄), imidazole (Im) and divalent metal oxides afforded two novel phosphonate compounds: Zn₂(AEDP)(Im)₃·H₂O (1), Cd₃(AEDPH)₂(Im)₅·Im (2). Compounds 1 and 2 are both one-dimensional (1-D) coordination polymers that illustrate different chain motifs. Compound 1 features a zigzag double chain structure while compound 2 has a distorted square-chain structure. Both compounds are further extended to form three-dimensional (3-D) supramolecular structures via hydrogen bonds. The effect of degree of deprotonization of AEDPH₄ on the structural types of the final products is also discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quantitative assessments of performance and robustness of maintenance policies for stochastically deteriorating production systems

Over the last few decades, many efforts have been invested in improving the economic performances of maintenance policies for stochastically deteriorating production systems. However, with the development of complex production systems, maintenance managers are interested not only in cost saving, but also in how to trustworthily plan and allocate the required maintenance budget. In this context, the robustness of maintenance policies which is related to the maintenance cost variability from a renewal cycle to another plays a pivotal role. This research deals with a quantitative approach to jointly assess the economic performance and robustness of some representatives of two most well-known classes of maintenance policies: time-based and condition-based maintenance. To this end, we first propose a new cost criterion which combines the long-run expected cost rate and standard deviation of maintenance cost per renewal cycle. Then, we develop and compare the associated mathematical cost models of the considered maintenance policies on the basis of the Gamma degradation process and the theory of stochastic renewal processes. The comparison results under different situations of maintenance costs and system characteristics show that the optimal configuration of maintenance policies gives the best compromise between the performance and robustness, and is mostly affected by the system downtime. Under this aspect, the condition-based maintenance remains more profitable than the time-based maintenance. Still, maintenance managers could implement condition-based maintenance policies that efficiently control the downtime to maximise the maintenance effectiveness of production systems from both performance and robustness viewpoints.     

What’s the middle ground? Institutionalized vs. emerging water-related stakeholder engagement processes

Abstract

In this day and age, it is widely argued that stakeholder engagement in water-related decision-making processes yields many benefits, including legitimacy, acceptance and trust. Key legal frameworks, such as the European Water Framework Directive and the Aarhus Convention, have spurred the emergence of formal forms of stakeholder engagement. On the other hand, many engagement processes are spontaneous and self-organized. This article investigates the strategies used in formal (government-led) and informal (bottom-up) engagement processes in search of a middle ground. To this end, case studies in the Netherlands, the United States, Uganda and Ethiopia are analyzed using the OECD’s stakeholder engagement checklist. We conclude with reflection on the ways forward to make formal and informal stakeholder engagement complementary.     

中国化学工业有毒化学品和有害废物的安全与控制

有毒化学品和有害废物对环境的污染及对人体健康的危害是中国环境保护面临的重大问题。本文概述了中国处理有毒化学品和有害废物的国家政策,化学工业有毒化学品和有害废物安全与控制的现状,并指出存在的问题及优先改进的领域。     

Fe^3＋离子修饰的金纳米粒子对DNA的高效吸附

在谷胱甘肽功能化的金纳米粒子表面螯合Fe^3＋离子后,研究了DNA分子在不同p H和盐浓度条件下在粒子表面的吸附和脱附行为。在pH〈4.0的条件下,DNA通过所含的磷酸根基团与粒子表面的Fe^3＋离子产生配位相互作用而吸附到粒子表面,此过程受盐浓度影响不大。当pH〉4.0时,由于溶液中氢氧根离子的竞争作用,使DNA的磷酸根基团不能与Fe^3＋离子配位,此时只能通过静电或氢键作用吸附,但是吸附效率很低。因此,Fe^3＋离子修饰的金纳米粒子只在低p H条件下可以实现对DNA的高效吸附。这种基于配位作用的吸附效率要高于盐桥作用,而且不会受到溶液中盐浓度的影响。     

城市群区域公共基础设施网络的协调模式浅析

针对现在我国城市化发展进程,城市群的发展已迫在眉睫,本文主要分析了城市群区域公共基础设施网络体系的协调发展对城市群经济建设的重要性,以及协调发展的模式,并对我国未来城市群发展的方针提出自己的看法。     

非齐时折扣马氏决策规划的方差最小最优策略

讨论非齐时离散时间马尔科夫决策规划折扣准则下方差最小最优策略.为此目的,首先讨论了非负损失时的最优策略;在报酬绝对平均相对有界或非负损失下,证明了方差最小最优策略问題等价于一个非负损失折扣马氏决策规划;给出了存在方差最小最优策略的充要条件和寻求此最优策略的有限阶段逼近.