Formulation to obtain the most reliable aggregate mix with quantity and other constraints

The aggregate batch mixing problem determines the proportion (or relative masses) in which aggregate batches with different gradations are to be blended so as to achieve a target mix with a given gradation. As shown in previous studies, the gradation of a batch is not homogeneous and should be considered stochastic. Also, when batches are blended in the field there are random variations in the masses or proportions of individual batches in the mix. Assuming batch gradation and blend masses as stochastic implies that the notion of a mix (blend) satisfying the gradation of a target mix becomes stochastic. In such a framework, every mix has a reliability with which it satisfies the definition of the target mix. In addition, a mix is also required to satisfy various restrictions. This article presents an optimization formulation to determine the most reliable mix while satisfying restrictions on available quantity, budget, etc.     

Assessment of mechanical properties of concrete incorporating carbonated recycled concrete aggregates

An accelerated carbonation technique was employed to strengthen the quality of recycled concrete aggregates (RCAs) in this study. The properties of the carbonated RCAs and their influence on the mechanical properties of new concrete were then evaluated. Two types of RCAs, an old type of RCAs sourced from demolished old buildings and a new type of RCAs derived from a designed concrete mixture, were used. The chosen RCAs were firstly carbonated for 24 h in a carbonation chamber with a 100% CO₂ concentration at a pressure level of 0.1 Bar and 5.0 Bar, respectively. The experimental results showed that the properties of RCAs were improved after the carbonation treatment. This resulted in performance enhancement of the new concrete prepared with the carbonated RCAs, especially an obvious increase of the mechanical strengths for the concrete prepared with the 100% carbonated new RCAs. Moreover, the replacement percentage of natural aggregates by the carbonated RCAs can be increased to 60% with an insignificant reduction in the mechanical properties of the new concrete.     

ACL在聚合端口上应用研究

访问控制列表在网络安全中是一种重要的手段。文章通过对其研究,提出了在聚合端口上应用ACL的方法,该方法可以大大减少网络管理人员配置ACL的复杂性。结合该方法,给出了一个网络安全模型的实例,通过端口聚合方案和制定安全策略,实现网络性能的优化和保护网络的目的。     

基于聚类的拥塞控制机制研究及其改进

针对基于聚类的拥塞控制(ACC)机制在解决网络拥塞时造成非恶意数据流使用带宽减少的问题,提出增强的基于聚类的拥塞控制(EACC)机制。该机制使用目的地址和丢包率对DDoS恶意数据流进行识别,并通过减少恶意数据流的使用带宽解决网络拥塞问题。实验结果表明,EACC能解决ACC存在的问题,在尽快恢复网络正常工作的同时,保障了非恶意数据流的可用带宽。     

路网数据流的预测聚集查询新方法研究

时空数据流的聚集查询技术已经成为数据库领域的研究热点。到目前为止,还没有一种有效的全时态聚集索引适用于非欧氏空间的路网数据流聚集查询。实现路网数据流的全时态聚集查询,必须解决:(1)路网的非欧氏空间特性问题;(2)路网上移动对象的重复计数、非均匀分布以及预测聚集问题。Sketch RR-tree解决了非欧氏空间特性和重复计数问题;为解决非均匀分布问题,借鉴草图划分思想,提出动态草图索引结构DynSketch:采用AMH智能划分Sketch RR-tree,使每个划分区域内车辆均匀分布,以提高聚集查询质量;同时,基于DynSketch,结合ES预测模型,提出了路网数据流的预测聚集查询算法。     

改进的签名长度固定的无证书聚合签名

现有的具有固定签名长度的无证书聚合签名(certificateless aggregate signatures, CLAS)方案要么存在安全缺陷,要么通信开销较大。提出一种改进的CLAS方案,由聚合人选择整数域上的随机参数替代状态信息,并且广播给所有签名者。在随机预言模型下,改进方案被规约为多项式时间敌手求解CDH(computational Diffie- Hellman)难题,具有可证明安全性。对比分析表明,改进CLAS方案的状态信息协商阶段仅需要1次广播通信,通信开销更低,易于实现。改进方案可用于在资源受限的网络环境下构建多对一的认证方案。     

重质油中的分子聚集结构及其对重质油稳定性的影响

重质油组分分子的聚集是重质油最显著的特征之一,重质油的高粘特性和相态稳定性均与此聚集行为有紧密的联系.为克服实验研究获得重质油微观聚集结构的困难,本文采用Zhang等人针对重质油体系改进的耗散粒子动力学(DPD)方法,研究重质油的分子聚集结构及其对重质油稳定性的影响.根据重质油组分的结构特征,可将重质油表达为其他轻组分...     

Properties of concrete incorporating fine recycled aggregate

The properties of concrete containing fine recycled aggregate are investigated. Recycled aggregate consisted of crushed concrete (CC) or crushed brick (CB) with particles less than 5 mm in diameter. The free water/cement ratio was kept constant for all mixes. The fine aggregate in concrete was replaced with 0%, 25%, 50% and 100% CC or CB. Generally, there is strength reduction of 15-30% for concrete containing CC. However, concrete incorporating up to 50% CB exhibits similar long-term strength to that of the control. Even at 100% replacement of fine aggregate with CB, the reduction in strength is only 10%. Beyond 28 days of curing, the rate of strength development in concrete containing either CC or CB is higher than that of the control indicating further cementing action in the presence of fine recycled aggregate. More shrinkage and expansion occur in concrete containing CC or CB.     

不同岩石室内破碎及性能试验对比分析

为了论证乌弄龙水电站燕子崖料场灰岩、砂板岩夹层及右岸地下厂房洞挖砂岩、板岩作为混凝土骨料的可行性,对这4种骨料进行了室内破碎及性能对比试验研究。结果表明:灰岩骨料各项性能满足混凝土施工规范的要求,作为混凝土骨料宜优先选用;砂岩骨料压碎指标、坚固性和针片状颗粒含量均较低,但其为具有潜在碱-硅酸反应的活性骨料,掺入20%以上粉煤灰可有效抑制其碱活性;板岩和砂板岩质量较差。