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P2P (Pollution Prevention Progress) is a computer-based tool that supports the comparison of process and product alternatives
in terms of environmental impacts. This tool provides screening-level information for use in process design and in product
life cycle assessment (LCA). Twenty one impact categories and data for approximately 3,000 chemicals are represented in the
default database of the new release, P2P Mark III. These data help identify which emissions may require further, more sophisticated,
characterisation in the different impact categories. In this paper, we primarily focus on the persistence-bioaccumulation
toxicity (PBT) methodology adopted for the classification of chemicals in the context of (eco-)toxicological impacts. This classification
methodology is cross-compared with a characterisation approach that provides a more complete model-based representation of
the source-to-effect (or environmental) mechanism, but for fewer chemicals. To ensure that the quantity of the emission, and
not just chemical hazard, is taken into account the comparison is based on a case study for the production of BDO (1,4-butanediol).
Insights are presented independently for both the chemical processing stage, as well as from a broader life cycle perspective.
Software available from: 相似文献
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A P2P computing environment can be an ideal platform for resource-sharing services in an organisation if it provides trust mechanisms. Current P2P technologies offer content-sharing services for non-sensitive public domains in the absence of trust mechanisms. The lack of sophisticated trust mechanisms in the current P2P environment has become a serious constraint for broader applications of the technology although it has great potential. Therefore in this work an approach for securing transactions in the P2P environment is introduced, and ways to incorporate an effective and scalable access control mechanism - role-based access control (RBAC) - into current P2P computing environments has been investigated, proposing two different architectures: requesting peer-pull (RPP) and ultrapeer-pull (UPP) architectures. To provide a mobile, session-based authentication and RBAC, especially in the RPP architecture, lightweight peer certificates (LWPCs) are developed. Finally, to prove the feasibility of the proposed ideas, the RPP and UPP RBAC architectures are implemented and their scalability and performance are evaluated 相似文献
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Phosphorous is treated as an impurity in conventional steels owing to segregation of phosphorous and formation of brittle phosphides along the grain boundaries. It is responsible for cold and hot shortness in wrought steels. In conventional powder metallurgy, involving compaction and sintering, high phosphorous content (up to 0·7%) in Fe-based alloys exhibit attractive set of mechanical and magnetic properties. These powder-processed alloys suffer from increasing volumetric shrinkage during sintering as phosphorous is increased beyond 0·6%. Thus both cast as well as conventional powder metallurgy routes have their own limitations in dealing with iron?Cphosphorous alloys. Hot-powder forging was used in the present investigation for the development of high-density soft magnetic materials containing 0·3?C0·8% phosphorous to overcome these difficulties. It was observed that phosphorous addition improves the final density of the resulting product. It was further observed that hot-forged iron?Cphosphorous alloys have excellent hot/cold workability and could be easily shaped to thin strips (0·5?C1·0?mm thick) and wires (0·5?C1·0?mm diameter). The powder hot-forged alloys were characterized in terms of microstructure, porosity content/densification, hardness, soft magnetic properties and electrical resistivity. Magnetic properties such as coercivity 0·35?C1·24?Oe, saturation magnetization 14145?C17490 G and retentivity 6402?C10836 G were observed. The obtained results were discussed based on the microstructures evolved. 相似文献
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针对无结构化P2P网络的洪泛搜索与随机漫步机制的盲目性,提出了一种利用Hash函数与M-tree技术将文件聚类后,再利用路由表完全分布式存储索引指针的新的路由算法。该算法使每个节点的路由表主要记录拥有各类资源的高能力节点指针,并利用概率统计的方法不断地更新路由表项。当节点收到搜索以后,通过查询路由表,只需一跳就进入能以最大概率回应的节点处查找,并能以较低的网络时延命中多个优质资源副本,达到了高速并行下载的目的。仿真试验和数学分析表明该算法有效地减少了盲目搜索造成的网络流量,提高了查找成功率,并且具有越稀缺的资源越容易找到的特性。 相似文献
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Chandan Pandey Manas Mohan Mahapatra Pradeep Kumar 《Materials at High Temperatures》2019,36(4):275-284
In the present study, dissimilar weld joint was prepared using the P91 and P92 steel plate of 8-mm thickness, using the multi-pass gas tungsten arc (GTA) welding with filler (weld 1) and autogenous tungsten inert gas welding (A-TIG) process (weld 2). Evolution of δ-ferrite patches was studied in weld zone and heat affected zone (HAZ) for both weld 1 and weld 2. Effect of varying post weld heat treatment (PWHT) duration was also studied on δ-ferrite patches and mechanical properties of the dissimilar weld joint. PWHT was carried out at 760°C. For weld 2, weld zone showed poor impact toughness and higher peak hardness as compared to weld 1. After the PWHT, a considerable reduction in hardness was obtained for both weld 1 and weld 2,while impact toughness of weld zone showed a continuous increment with PWHT duration. For weldments characterisation, optical microscope, scanning electron microscope (SEM) and microhardness tester were utilised. 相似文献
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为使目前基于重路由机制的P2P匿名系统在用户增加时减少负载开销和管理开销,从而提高其可扩展性,提出了一种基于P2P架构的分组匿名通信系统模型--PGACS.系统中没有核心的管理节点,每个用户加入一定数量的逻辑组,并只保留其所在逻辑组成员的信息.给出了成员加入、退出的协议机制以及逻辑组的分裂合并机制,对系统的可扩展性和安全性进行了分析,同时基于前驱攻击对系统匿名性能进行了理论分析和模拟测试.结果表明,在合理选取逻辑组大小的前提下,系统能够提供与典型匿名系统Crowds相当的匿名性,同时具有良好的扩展性. 相似文献
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为了给P2P网络并行模拟器HiFiP2P提供正确高效的路由,使其能够高效地执行大规模P2P网络并行模拟,基于互联网中的层次路由模型和Flat本地静态路由计算和查找算法,采取边界路由最小化的并行网络拓扑划分机制,设计了Tier_Flat路由算法,用以实现HiFiP2P的远程和本地静态路由,它以最低O((N~4)~(1/3))的空间开销,取得了O(1)的查找效率。结果表明,Tier_Flat路由算法路由计算时间短,路由表内存占用小,路由查询速度快,为HiFiP2P平台的大规模P2P网络并行模拟提供了高效的路由服务。 相似文献
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In several lignite-fired power plants of the ‘Vattenfall Generation AG’ in Germany components of P91/P92 material are used in long-time operation. About this experience in operation of selected components will be reported. In this context own experimental results of a research project in the damage evolution will be presented. The project ‘Damage development III’ was edited together with the MPA Stuttgart and was supported by Vattenfall and AVIF. The aim of the project was to improve the knowledge about the process of creep damage by experimental tests and additional numerical calculations. An instruction was given for planning, implementation and analysis of recurrent investigations on components consisting of 9% Cr steels which are subjected to high operation loading. Finally, the damage phenomena are presented by two case studies, a damage in a pipe bend due to faulty heat treatment and the creep-crack assessment of a lack of side-wall fusion in a reheater weld by fracture mechanics. 相似文献
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针对现有P2P文件共享系统采用并发多连接的文件传输方式,过分占用网络带宽资源,导致其它传统互联网业务性能低下的问题,提出了一种P2P文件共享系统汇聚拥塞控制机制(ACCM).ACCM采用应用层网络测量技术感知节点接入网链路拥塞状况,依据网络拥塞状况动态地调整P2P文件共享系统并发文件传输连接窗口,在最大化网络带宽利用率的基础上实现对传统互联网应用的友好性.网络实验结果表明,在网络拥塞发生时,ACCM能够促使P2P文件共享系统并发连接窗口主动退避,实现和传统互联网应用的和平共处;在网络空闲时,ACCM能够促使P2P文件共享系统扩大并发连接窗口,提高网络带宽资源的利用率. 相似文献
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为实现异构网络下的P2P应用,分析了具有异构融合特征的P2P网络的特点,提出了与之相适应的基于二叉树结构的覆盖层网络(TSOHEN)的设计方法.该方法根据节点的不同功能和属性将节点分为普通节点和混合节点两大类,并为每类节点设计了适应异构特征的路由表,对各类节点的加入和离开功能设计了相应的算法,并通过混合节点实现跨网的P2P查询操作.数值和仿真结果表明,该覆盖层设计能够有效地适应异构网络的环境,树形结构也没有使得根节点和叶节点的负荷产生明显的区别,各混合节点的负载也基本平衡.在大规模节点数量的情况下,TSOHEN的各种算法仍具有良好的收敛性. 相似文献
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《Materials Science & Technology》2013,29(11):1153-1157
AbstractThe effect of pulse duration and electrode type (copper or graphite) on the pick-up of carbon in the surface of a die steel shaped using electrodischarge machining and on surface microcracks has been studied. The present work suggests that the number and the size of surface microcracks increase with pulse duration when machining with a copper electrode, but there is some evidence to suggest that, when using a graphite electrode, the number and the length of microcracks and the average thickness of the recast layer may be greatest at intermediate (75–150μs) pulse durations. Although no definite conclusion can be drawn from the results, it is suggested that this may be because the manner of decay of the temperature field after each pulse is determined by both electrode material and pulse duration. At high current densities and long pulse durations, the length and frequency of microcracks is increased greatly at the corners of specimens machined using a graphite electrode, but this occurred to a much lesser extent when using a copper electrode – a difference that would seem to reinforce the suggestion that the characteristics of the temperature field after each pulse depend on the electrode material. It was concluded that carbon was absorbed from the dielectric (paraffin) rather than from the electrode. The amount of copper absorbed did not depend on pulse duration.MST/1040 相似文献
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《Materials at High Temperatures》2013,30(4):361-368
AbstractIn this paper, an in-depth study of steam oxidation of two 9Cr ferritic-martensitic steels (P91 and P92), for advanced power plant, has been carried out. The steels investigated were exposed to a 100% flowing steam environment at 650°C for 1,000 – 3,000 hours. Metallographic analysis showed a multilayered scale was formed on both substrates consisting of an outer Fe-rich phase and inner Fe – Cr spinel, of varying oxide stoichiometry, as well as Cr –Mn-rich bands. The results of scale thickness measurements showed that the oxide formed on the P92 steel was thicker compared to that on the P91 steel. Crystallographic analysis showed that the P91 steel exhibited a martensite to ferrite transformation adjacent to scale – substrate interface which was not observed on the P92 steel. The outer oxide layer on both substrates exhibited a region of equiaxed grains followed by a region of columnar crystal growth. However, on the P91 steel the longer exposure time (3,000 hours) resulted in the outer layer having a region with coarsened equiaxed magnetite grains. The roles of alloying elements (Cr, Mo, W and Mn) were investigated to provide a better understanding of the oxide growth behaviour. 相似文献