OAZE: A network-friendly distributed zapping system for peer-to-peer IPTV

IPTV systems attracting millions of users are now commonly deployed on peer-to-peer (P2P) infrastructures and provide an appealing alternative to multicast-based systems. Typically, a P2P overlay network is associated with each channel, composed of users who receive, watch and redistribute this channel. Yet, channel surfing (aka as zapping) involves switching overlays and may introduce delays, potentially hurting the user experience when compared to multicast-based IPTV. In this paper, we present a distributed system called OAZE (Overlay Augmentation for Zapping Experience) which speeds up the switching process and reduces the overall cross-domain traffic generated by the IPTV system. In OAZE, each peer maintains connections to other peers, not only in a given channel, but also in a subset of all channels to which the associated user is likely to zap. More specifically, we focus on the channel assignment problem, i.e. determining, in a given P2P overlay, the optimal distribution of the responsibility to maintain contact peers to other channels. We propose an approximate algorithm providing guaranteed performances, and a simpler and more practical one. Our experimental results show that OAZE leads to substantial improvements on the connections between peers, resulting in less switching delay and lower network cost; it then represents an appealing add-on for existing P2P IPTV systems.     

Hysteresis Compensation and Adaptive Controller Design for a Piezoceramic Actuator System in Atomic Force Microscopy

This paper presents an indirect adaptive controller combined with hysteresis compensation to achieve high accuracy positioning control of piezoceramic actuators and illustrates the results with an atomic force microscope (AFM) application. A dynamic model of a piezoceramic actuator system in AFM is derived and analyzed. A feedforward controller based on the Preisach model is proposed to compensate for the nonlinear hysteresis effects. Then an indirect adaptive controller is designed to achieve desired tracking performance as well as deal with the uncompensated nonlinearity from hysteresis and the system parameter variation due to creep. Experimental results indicate that the proposed controller can significantly improve the positioning control accuracy of the piezoceramic actuator as well as achieve high image quality of the AFM system. The maximum scanning error was reduced from 2µm to 0.3µm in comparison with a proportional‐integral‐derivative (PID) controller. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

模块化多电平变换器全桥型子模块优化均压控制方法

模块化多电平变换器(MMC)子模块(SM)的数量与直流侧电压成正比,当SM增加时,会导致MMC的开关损耗急剧增加,因此降低功率器件的开关频率一直是MMC的重要研究方向之一。采用最近电平逼近调制(NLM)方式,提出一种基于全桥型SM的改进均压排序法,旨在降低MMC中功率器件IGBT的开关频率,该方法实现相对简单,无需额外的控制器,且易于扩展。最后,通过在MATLAB/Simulink平台搭建了19个全桥SM的仿真模型,验证了该方法的有效性。验证了所提全桥型SM优化均压策略,可以有效避免IGBT不必要的反复投切,降低IGBT的开关损耗,同时对外部输出特性不会产生负面影响。     

考虑寄生参数的隔离型双有源桥DC-DC变换器的开关开路故障分析与容错控制策略

双有源桥(DAB)DC-DC变换器开关管的驱动电路故障导致开关开路故障(OCSF),这使得DAB系统拓扑对称性缺失、高频电压和电流发生畸变和直流偏置,进而对系统的可靠性和长期运行稳定性造成不良影响.对此,研究DAB开关管和高频变压器寄生参数对OCSF后系统运行状态的影响,以完善DAB故障分析体系.针对OCSF问题,提出一种基于对称拓扑和对偶原理的故障容错策略,通过闭锁开关使系统运行拓扑恢复对称,并在此基础上提出一种不改变控制器参数、只需改变控制器输出饱和参数的实用控制方法,并在理论上讨论了该方法的可行性.最后,通过实验验证了OCSF模态分析及所提容错控制策略的正确性.     

NiTi形状记忆合金的相变温度滞后

用透射电镜、正电子湮没和电阻测量,研究了NiTi形状记忆合金的组织结构与相变滞后的关系结果表明,经不同制度时效处理的组织,其相变温度滞后大小的顺序是:片状马氏体>R相>束状马氏体。Ti_(11)Ni_(14)相质点周围的共格应力场对这些相的可逆转变起障碍作用。正电子湮没Doppler展宽能谱S参数值与试样的温度滞后值之间存在线性关系,从而确认Ti_(11)Ni_(14)相析出的错配位错密度及由此而建立的晶体中弹性应力场分布是决定NiTi合金相变温度滞后的主要因素。     

镁渣膨胀性机理试验研究

通过镁渣形成过程、组成、粉化、颗粒分析和安定性试验,研究了镁渣产生体积膨胀性和膨胀滞后性的机理,提出了减轻或消除其膨胀性和膨胀滞后性危害的方法和措施,为镁渣在建筑、交通、水利等工程领域中的应用提供理论依据和指导。     

气相色谱法测定石脑油中含氧化合物含量

本文论述了利用气相色谱法检测石脑油中含氧化合物的方法,考察了无阀切换技术、分离模式的设计、操作条件的优化等方面的问题。提出利用多维气相色谱法,采用一根非极性柱和一根极性柱进行独立和串联分离,通过改变辅助载气压力的无阀切换方式进行柱分离,应用双FID检测器进行信号检测,数据利用Agilent的chemestation工作站采集和输出。该方法操作简单,分析时间在23 min以内,重复测定结果的相对标准偏差(RSD)小于1.5%,标准加入回收率在95～105%范围内,方法准确可靠。     

SOME PROPERTIES OF THE MAXIMUM LIKELIHOOD ESTIMATOR IN THE SIMULTANEOUS SWITCHING AUTOREGRESSIVE MODEL

Abstract. The simultaneous switching autoregressive (SSAR) model proposed by Kunitomo and Sato (A non-linearity in economic time series and disequilibrium econometric models. In Theory and Application of Mathematical Statistics (ed. A. Takemura). Tokyo:University of Tokyo Press (in Japanese), 1994; Asymmetry in economic time series and simultaneous switching autoregressive model. Struct. Change Econ. Dyn. , forthcoming (1994).) is a Markovian non-linear time series model. We investigate the finite sample as well as the asymptotic properties of the least squares estimator and the maximum likelihood (ML) estimator. Due to a specific simultaneity involved in the SSAR model, the least squares estimator is badly biased. However, the ML estimator under the assumption of Gaussian disturbances gives reasonable estimates.     

Trickle Flow Multiplicity: The Influence of the Prewetting Procedure on Flow Hysteresis

The existence of multiple hydrodynamic studies (MHS) in trickle flow is a well-known phenomenon. It is also known that different prewetting procedures result in major differences in MHS when the hydrodynamic variables pressure drop, liquid holdup and gas–liquid mass transfer are considered. Given a certain prewetting procedure one still has the option to perform flow hysteresis cycles to achieve an even wider variety of MHS. Although numerous studies have been performed on trickle flow hysteresis, none have attempted to decouple the hysteresis behaviour from the prewetting procedure followed. Accordingly there are numerous hysteresis possibilities that have not been investigated. In this work a single liquid and gas cycle were performed for four distinct prewetting procedures described here as a dry bed, a Levec type prewetted bed, Kan prewetted bed (achieved by increasing either the liquid or the gas flow rate until the pulsing flow regime is reached) and a Super prewetted bed. Pressure drop, liquid holdup and gas–liquid mass transfer are the hydrodynamic parameters studied to quantify the various MHS. It is shown that the shape and extent of the hysteresis cycle are strongly dependant on the prewetting procedure. In terms of flow structure, similar hysteresis trends on the Kan Liquid and Super prewetting modes indicate that these modes are hydrodynamically similar. The additional measurement of the hysteresis behaviour of gas–liquid mass transfer proofs that neither holdup nor pressure drop can be used as an indicator of the distribution uniformity.     

Longitudinal and temporal water temperature patterns in the Yangtze River and its influence on spawning of the Chinese sturgeon (Acipenser sinensis Gray 1835)

In this study, water temperature longitudinal and temporal patterns were investigated in four locations of the Yangtze River to identify their influence on spawning of the Chinese sturgeon (Acipenser sinensis Gray 1835). The results showed that, historically (1960–1980), the four locations, Pingshan (PS, 2,687 river kilometres [rkm]), Yichang (YC, 1,640 rkm), Chenglingji (CLJ, 1,265 rkm), and Hukou (HK, 805 rkm), all had similar average annual water temperatures (around 18.0 °C) but very different amplitudes: The upper two locations, PS (11.4–23.2 °C) and YC (9.1–25.9 °C), were relatively stable and had smaller amplitude than the lower two ones, CLJ (6.0–30.0 °C) and HK (5.9–30.8 °C). On the basis of the physiological effects for Chinese sturgeon, we defined three water temperature ranges: stressing (>23 °C), holding (23–20 °C), and spawning (20–16 °C). We found that the upper two locations with successful spawning of the Chinese sturgeon (PS and YC) had short or no stressing period but long holding and spawning periods. Currently (2013–2016), the impoundment of the Three Gorges Reservoir increases the time for water temperature decreasing to 20 °C at the current spawning ground (YC) in autumn, which increases the stressing and holding periods, and has significant negative impact on the spawning of Chinese sturgeon. Nonetheless, considering the very high stressing temperature and the short duration of the holding and spawning periods at CLJ and HK, we propose that YC is still the most suitable spawning location for the Chinese sturgeon.