输气管道放空过程分析

分析输气管道放空过程,计算放空时间和放空气量,以实际工程进行验证.     

Multicast protection scheme based on Hamiltonian cycle in fault-tolerant optical mesh networks

The increase of multimedia service requirements results in the growing popularity of the multicast in Wavelength-Division Multiplexing (WDM) optical mesh networks. Multicast fault tolerance in WDM optical mesh networks is an important issue because failures caused by the traffic carried in WDM optical mesh networks may lead to huge data loss. Previous works have proposed multicast protection algorithms to address the single-fiber link failure dominant in current optical mesh networks. However, these existing algorithms are all mainly based on path protection or segment protection, which may lead to long restoration times and complicated protection switching procedures. This paper therefore proposes a new heuristic algorithm, called Enhanced Multicast Hamiltonian Cycle Protection (EMHCP), in which all working light-trees of multicast demands can be protected by a Hamiltonian cycle in the network. For each multicast demand, EMHCP computes a least-cost light-tree based on the presented link-cost function that considers load balancing and proper straddling link selection so that backup wavelengths on the Hamiltonian cycle can be reduced. Simulation results show that EMHCP can obtain significant performance improvement compared with the conventional algorithm.     

四川雪茄烟叶种质资源的遗传多样性分析

为促进四川雪茄烟叶种质资源的开发和利用,通过农艺性状和SSR标记对20份雪茄烟叶种质资源进行遗传多样性分析。结果表明,供试种质资源具有较丰富的遗传多样性,各农艺性状的变异系数在6.59%~19.97%之间,遗传多样性指数在1.69~2.18之间,并聚类为4个类群,各类群间的农艺性状有显著差异。基于SSR标记技术的主成分分析和遗传结构分析把供试种质分为3个类群,聚类分析可把供试种质分为4个类群,为德雪1号、德雪2号、德雪3号和什烟一号的溯源研究提供线索。      

The effect of repellents on penetration into packaging by stored-product insects

Two known repellents of stored-product insects, DEET and neem, were compared to protein-enriched pea flour, defatted protein-enriched pea flour, and pea protein extract for their efficacy at reducing penetration and invasion by several common stored-product insects: Sitophilus oryzae (L.), Tribolium castaneum (Herbst), Cryptolestes ferrugineus (Stephens), and Oryzaephilus surinamensis (L.). The methods of preparation of pea extract affected the penetration of S. oryzae. Protein-enriched pea flour, DEET and neem reduced the penetration of S. oryzae, but defatted protein-enriched pea flour and pea protein extract did not. The number of S. oryzae, T. castaneum, C. ferrugineus and O. surinamensis entering pierced paper envelopes that contained wheat and were treated with DEET was reduced by 99%, 86%, 97% and 91%, respectively. Neem was less effective than DEET in reducing penetration and invasion of insects. Protein-enriched pea flour did not prevent insects entering pierced envelopes.     

Investigation of road network features and safety performance

The analysis of road network designs can provide useful information to transportation planners as they seek to improve the safety of road networks. The objectives of this study were to compare and define the effective road network indices and to analyze the relationship between road network structure and traffic safety at the level of the Traffic Analysis Zone (TAZ). One problem in comparing different road networks is establishing criteria that can be used to scale networks in terms of their structures. Based on data from Orange and Hillsborough Counties in Florida, road network structural properties within TAZs were scaled using 3 indices: Closeness Centrality, Betweenness Centrality, and Meshedness Coefficient. The Meshedness Coefficient performed best in capturing the structural features of the road network. Bayesian Conditional Autoregressive (CAR) models were developed to assess the safety of various network configurations as measured by total crashes, crashes on state roads, and crashes on local roads. The models’ results showed that crash frequencies on local roads were closely related to factors within the TAZs (e.g., zonal network structure, TAZ population), while crash frequencies on state roads were closely related to the road and traffic features of state roads. For the safety effects of different networks, the Grid type was associated with the highest frequency of crashes, followed by the Mixed type, the Loops & Lollipops type, and the Sparse type. This study shows that it is possible to develop a quantitative scale for structural properties of a road network, and to use that scale to calculate the relationships between network structural properties and safety.     

采用二项概率分布法的同时工作系数计算

对计算同时工作系数的小时流量分布规律法、二项概率分布法进行比较,认为二项概率分布法较优.对采用二项概率分布法得到的数据进行拟合,将拟合结果与实测值进行比较,证明其准确性较高.     

A Short-Term Forecasting Algorithm for Network Traffic Based on Chaos Theory and SVM

Recently, the forecasting technologies for network traffic have played a significant role in network management, congestion control and network security. Forecasting algorithms have also been investigated for decades along with the development of Time Series Analysis (TSA). Chaotic Time Series Analysis (CTSA) may be used to model and forecast the time series by Chaos Theory. As one of the prevailing intelligent forecasting algorithms, it is worthwhile to integrate CTSA and Support Vector Machine (SVM). In this paper, after the vulnerabilities of Local Support Vector Machine (LSVM) in forecasting modeling are analyzed, the Dynamic Time Wrapping (DTW) and the “Dynamic K” strategy are introduced, as well as a short-term network traffic forecasting algorithm LSVM-DTW-K based on Chaos Theory and SVM is presented. Finally, two sets of network traffic datasets collected from wired and wireless campus networks, respectively, are studied for our experiments.     

新型低压船舶岸电供电电源系统的研究

针对目前我国低压船舶岸电电源系统存在的变压变频问题,提出一种基于可降压多脉冲自耦变压整流器的新型低压岸电供电电源系统,实现380V/50Hz～450V/60Hz三相电源的转换,为靠港船舶可靠供电.系统采用降压式12脉冲自耦变压整流技术降低谐波对系统及电网的影响,其中降压式自耦变压器可以实现对输入电压的降压调节,无需后续降压电路,减少系统的体积和质量,降低成本.文中详细分析了降压式12脉自耦变压整流器的工作原理,理论推导了输入电流、输出电压及变压器等效容量表达式.最后通过MATLAB建模进行仿真分析,验证了系统的正确性和可行性.     

机械密封焊接金属波纹管随机振动响应及优化分析*

针对焊接式金属波纹管在工作中出现的随机振动问题,运用虚拟激励法理论,采用MATLAB编程得到波纹管在随机激励下轴向和径向时域下的信号;将时域信号利用快速傅里叶变换得到频域信号,并导入Workbench软件中进行随机振动分析;同时对波纹管的危险结构尺寸(波片厚度、焊箍半径和最小弯曲半径)进行响应面优化分析。结果表明:波纹管在受外界随机激励下的频率介于固有频率一阶和三阶之间;波纹管轴向最大响应变形发生在镶嵌静环的一端即自由端,径向最大响应变形发生在靠近波纹管的固定端的波片弧度较大处,随机激励时等效应力集中在靠近焊箍侧,这些位置在工作过程中最容易损坏,与实际工作中的破坏位置相吻合。通过响应面优化分析和自适应多目标优化,得到一组优化关键材料参数,使得波纹管的振动性能得到较大改善,降低了波纹管的损坏率,为焊接金属波纹管的结构参数设计提供理论参考。     

Microstructure and mechanical properties of NZ30K alloy by semicontinuous direct chill and sand mould casting processes

The Mg-3.0Nd-0.2Zn-0.4Zr (NZ30K) alloys were prepared by direct-chill casting (DCC) and sand mould casting (SMC) processes,respectively and their microstructures and mechanical properties were investigated.The results indicate that casting method plays a remarkable influence on the microstructure and mechanical properties of as-cast NZ30K alloy.The grain size increases from 35-40μm in the billets made by the DCC to about 100-120μm in the billets by the SMC.The aggregation of Mg12Nd usually found at the trip...