一种支持多用户SLA的EPON上行带宽分配算法设计

在接入网服务等级协定的基础上,分析了以IPACT和CyclicDBA为代表的EPON上行动态带宽分配算法,讨论了其对EPON上多用户SLA支持所存在的固有缺陷。提出了适合SLA应用的EPON控制帧结构:授权帧和请求帧。根据这两种控制帧,设计了一种新型的支持多用户SLA的EPON上行信道带宽分配算法,等级轮询固定周期算法。通过理论分析和计算机仿真测试表明该算法针对EPON不同类型的接入用户均达到了较理想的性能指标,高优先级业务良好的时延和时延抖动特性,各种业务队列的尺度平稳,同时HPFCT还解决了传统轮询算法中低负载时下行带宽浪费明显的问题。     

PM6 and DFT study of free radical scavenging activity of morin

Flavonoids have long been recognised for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work, we have studied the properties of flavonoid morin using semiempirical and density functional theory (DFT) methods in order to validate the application of the recently developed parametric method 6 (PM6). Reaction enthalpies related to mechanisms of free radical scavenging by flavonoid morin were calculated by DFT and PM6 methods in gas-phase, water, DMSO and benzene. It has been shown that fast semiempirical PM6 method can mimic results obtained by means of more accurate time consuming DFT calculations. Thermodynamically favoured mechanism depends on reaction medium: SPLET (sequential proton loss electron transfer) is preferred in water and DMSO, and HAT (hydrogen atom transfer) is predominant in gas-phase. In benzene these two mechanisms are competitive.     

Data compression techniques in Wireless Sensor Networks

The advancement in the wireless technologies and digital integrated circuits led to the development of Wireless Sensor Networks (WSN). WSN consists of various sensor nodes and relays capable of computing, sensing, and communicating wirelessly. Nodes in WSNs have very limited resources such as memory, energy and processing capabilities. Many image compression techniques have been proposed to address these limitations; however, most of them are not applicable on sensor nodes due to memory limitation, energy consumption and processing speed. To overcome this problem, we have selected Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT) image compression techniques as they can be implemented on sensor nodes. Both DCT and DWT allow an efficient trade-off between compression ratio and energy consumption. In this paper, both DCT and DWT are analyzed and implemented using TinyOS on TelosB hardware platform. The metrics used for performance evaluation are peak signal-to-noise ratio (PSNR), compression ratio (CR), throughput, end-to-end (ETE) delay and battery lifetime. Moreover, we also evaluated DCT and DWT in a single-hop and in multi-hop networks. Experimental results show that DWT outperforms DCT in terms of PSNR, throughput, ETE delay and battery lifetime. However, DCT provides better compression ratio than DWT. The average media access control layer (MAC) delay for both DCT and DWT is also calculated and experimentally demonstrated.     

福清核电厂应急撤离时间估算

本文介绍了环境保护部核与辐射安全中心主持开发的“核电周边人员应急撤离的虚拟现实模拟系统”(简称“撤离模拟系统”)及所采用的技术。结合福清核电厂厂址周围的人口分布、交通基础设施分布和天气状况,利用该系统模拟了不同撤离情景下,福清核电厂烟羽应急计划区内人员的撤离过程,估算了撤离时间,分析了影响撤离的主要因素。研究结果表明,福清核电厂在典型事故情景下,部分拥堵路段对撤离时间影响显著;同时,私家车的使用比例增加也会显著增加撤离时间。     

Bond dissociation free energy as a general parameter for flavonoid radical scavenging activity

Notwithstanding multiple mechanisms of radical scavenging (RS), measured RS activities (RSA) of flavonoids are usually related to O–H bond dissociation enthalpy (BDE) for hydrogen atom transfer (HAT). For 12 flavonoids the reaction free energies were calculated for: (1) HAT, (2) single electron transfer–proton transfer (SET-PT) and (3) sequential proton loss electron transfer (SPLET) in gas and aqueous phases. Aqueous free energies, like bond dissociation (BDFE_aq), ionisation (IFE_aq) and deprotonation (ΔG_deprot,aq) free energies were estimated using thermochemical cycles. While in gas HAT is a RS mechanism (BDFE_g < IFE_g < ΔG_deprot,g), in water SPLET can be concurrent or dominant mechanism depending upon pH since ΔG_deprot,aq < BDFE_aq and ETFE_aq ? BDFE_aq. For 12 flavonoids, BDFE_aq has been correlated with ΔG_deprot,aq and ETFE_aq with r = 0.74 and 0.87 respectively. This reveals why BD(F)E parameter explains most of variance in variously measured RSA data even if the underlying mechanism is SPLET.     

ETE作调节剂高温合成丁二烯/苯乙烯橡胶的反应动力学

以正丁基锂为引发剂、乙基四氢糠基醚(ETE)为调节剂、环己烷为溶剂,采用高温负离子聚合工艺合成了丁二烯(Bd)/苯乙烯(St)橡胶。研究了聚合温度、ETE/Li比和引发剂浓度等因素对聚合反应动力学的影响。结果表明,ETE是溶聚丁苯橡胶(SSER)合成中有效的高温调节剂,在高温下仍然具有很好的活性,能够显著加快共聚合反应速率,调节单体Bd和St的聚合速率,同时对反应动力学参数进行了研究。     

光突发交换边缘节点性能分析及仿真

文章介绍了光突发交换产生的背景、光突发交换网的原理和体系结构以及光突发交换体系中边缘节点的结构.主要采用计算机仿真,仿真工具是OPNET 8.1.A.仿真结果表明:若边缘节点的数据包产生速率恒定,则端到端的延迟比较固定;若边缘节点数据包的发送速率突然增大,端到端的延迟会有一些波动.