中波发射台多频共塔干扰消除的研究

为了节省对发射台的投资、节省占地面积,目前中国有很多中波广播台都采用多频共塔的工作模式,但是多频共塔在节约经济成本的同时,其自身带来的干扰问题严重影响了广播的质量。先介绍了噪声、干扰的概念以及多频共塔中干扰的产生问题,然后结合本台实际,提出了正确设计匹配网络与阻塞网络、合理设计及选择陷波网络、经常维护系统、采用优质音频传输线、加强屏蔽等可以有效消除干扰的措施。     

Comments on 3‐blocked designs

This note provides a correction and some additions to a 1999 article by Luigia Berardi and Fulvio Zuanni on blocking 3‐sets in designs. © 2012 Wiley Periodicals, Inc. J. Combin. Designs 20: 328–331, 2012     

Performance improvement of blue InGaN light-emitting diodes with a specially designed n-AlGaN hole blocking layer

Blue InGaN light-emitting diodes (LEDs) with a conventional electron blocking layer (EBL), a common n-AlGaN hole blocking layer (HBL), and an n-AlGaN HBL with gradual Al composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency (IQE). The results indicate that LEDs with an n-AlGaN HBL with gradual Al composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conventional p-AlGaN EBL or a common n-AlGaN HBL. Meanwhile, the efficiency droop is alleviated when an n-AlGaN HBL with gradual Al composition is used.     

改进型PCMA协议中的封闭问题研究

结合几种基本的MAC接入协议,对Ad Hoc网络中存在的封闭问题进行了分析,同时指出了不同协议中封闭问题的差异。提出了一种改进型的PCMA协议--DBT-PCMA协议,并重点剖析了PCMA协议和DBT-PCMA协议是如何解决封闭问题的。经分析表明,该改进型的新协议能更好的降低封闭问题的发生机率,并提高系统的吞吐量。     

一种宽频信号阻断设备的设计和实现

针对无线信号的阻断,采用一种宽频信号阻断技术,解决了普通阻断设备只能工作于某一特定窄频段,而无法对外来异常信号实施完全阻断的不足,给出了系统的硬件和软件设计方案。实验证明,产品可以较好地对信号实施阻断。     

聚乳酸自支持膜的叠加及其作为药物控释阻隔层的研究

发展了一种将自支持膜层层叠加制备多层膜的新方法,并研究了该薄膜对药物释放的调控效果. 首先利用聚乙烯醇作为牺牲层制备出聚乳酸自支持膜,然后将聚乳酸自支持膜转移或层层叠加到载药薄膜表面,最后对覆盖有聚乳酸薄膜的载药膜进行药物释放研究. 实验结果表明,聚乳酸薄膜对药物的释放起到了明显的调节作用,并且转移的薄膜的控释效果优于原位制备的薄膜,多层叠加的薄膜控释效果强于同等厚度的单层薄膜. 这可能是由于转移和叠加的薄膜层与层之间的空隙对药物的释放起到了缓冲作用所致. 这种基于自支持膜叠加制备多层膜的方法为药物涂层的研究提供了新思路,在生物材料、医用植入器件等领域都有一定的发展前景.     

Magnetic response of NiFe2O4 nanoparticles in polymer matrix

We report the magnetic properties of magnetic nano-composite, consisting of different quantity of NiFe₂O₄ nanoparticles in polymer matrix. The nanoparticles exhibited a typical magnetization blocking, which is sensitive on the variation of magnetic field, mode of zero-field-cooled/field-cooled experiments and particle quantity in the matrix. The samples with lower particle quantity showed an upturn of magnetization down to 5 K, whereas the blocking of magnetization dominates at lower temperatures as the particle quantity increases in the polymer. We examine such magnetic behaviour in terms of the competitive magnetic ordering between core and surface spins of nanoparticles, taking into account the effect of inter-particle (dipole-dipole) interactions on nanoparticle magnetic dynamics.     

Efficiency improvement of red organic light-emitting diodes using a blue phosphorescent exciton blocking layer

Quantum efficiency of red organic light-emitting diodes was improved using a blue phosphorescent emitting layer as an exciton blocking layer. Compared with 8.1% quantum efficiency of standard devices without an exciton blocking layer, high quantum efficiency of 14.1% was obtained using a blue phosphorescent emitting layer between the hole transport layer and the red emitting layer.     

Dynamic pricing for load‐balancing in user‐centric joint call admission control of next‐generation wireless networks

Next‐generation wireless networks (NGWN) will be heterogeneous, comprising of a number of radio access technologies (RATs) co‐existing in the same geographical area. In NGWN, joint call admission control (JCAC) algorithms are required to select the most appropriate RAT for each incoming call. It is envisaged that these JCAC algorithms will be user‐centric (i.e. will consider users' preferences in making RAT selection decisions) in order to enhance user satisfaction. However, user‐centric JCAC algorithms can lead to highly unbalanced traffic load among the available RATs in NGWN because users act independently, and most of them may prefer to be connected through a particular RAT. Highly unbalanced traffic load in NGWN will result in high overall call blocking/dropping probability and poor radio result utilization. To address this problem, we propose dynamic pricing for balancing traffic load among available RATs in heterogeneous wireless networks where users' preferences are considered in making RAT selection decisions. By dynamically adjusting the service price in each of the available RATs, the proposed user‐centric JCAC scheme evens out the unbalanced traffic load caused by independent users' preferences. The JCAC scheme uses fuzzy multiple attribute decision‐making (MADM) technique to select the most appropriate RAT for each incoming call. We develop a Markov model to evaluate the overall call blocking/dropping probability and percentage load in each RAT in heterogeneous wireless networks. Performance of the proposed JCAC scheme is compared with that of a scheme that does not use dynamic pricing. Simulation results are given to show the effectiveness of the proposed JCAC scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

多路径并行传输中接收缓存阻塞问题的研究

本文研究了多路径并行传输情况下接收缓存阻塞问题产生的原因及对传输性能的影响。同时提出了一种适用于多路径并行传输吞吐量分析的建模方法。该模型能够通过链路丢包率、往返传输时间等参数对吞吐量进行估计,并综合考虑了快速重传、拥塞窗口与接收缓存容量的关系对结果的影响。通过与仿真结果进行比较可以看出,该模型能够在网络性能参数发生变化时很好的预测吞吐量的变化情况。