Fair QoS multi-resource allocation for uplink traffic in WLAN

In wireless local area network (WLAN), improving the quality of service (QoS) of users is often at odd with striking fairness among users. In this work, we suggest that in WLAN, multiple types of network resources should be jointly allocated to users to achieve “QoS fairness”, which is a new fairness concept targeting at balancing QoS and fairness in WLAN by allocating multiple types of network resources to users. To this end, we first transform user QoS requirements to multi-resource demands and apply the dominant resource fairness scheme to allocate network resources for each user. We prove several salient QoS-based fairness properties based on a model mapping between QoS and resources. We further discuss about more general conditions for diverse mapping models where QoS fairness properties can be satisfied. We find that the QoS fairness properties can be guaranteed as long as the mapping model meets a few practical requirements, indicating the wide applicability of our scheme. To consolidate our multi-resource allocation scheme, we design a practical protocol for WLAN. The simulation results validate that the QoS fairness can be guaranteed in practical WLAN scenario.     

Predicting the Lifespan and Retweet Times of Tweets Based on Multiple Feature Analysis

In social network services, such as Facebook, Google+, Twitter, and certain postings attract more people than others. In this paper, we propose a novel method for predicting the lifespan and retweet times of tweets, the latter being a proxy for measuring the popularity of a tweet. We extract information from retweet graphs, such as posting times; and social, local, and content features, so as to construct prediction knowledge bases. Tweets with a similar topic, retweet pattern, and properties are sequentially extracted from the knowledge base and then used to make a prediction. To evaluate the performance of our model, we collected tweets on Twitter from June 2012 to October 2012. We compared our model with conventional models according to the prediction goal. For the lifespan prediction of a tweet, our model can reduce the time tolerance of a tweet lifespan by about four hours, compared with conventional models. In terms of prediction of the retweet times, our model achieved a significantly outstanding precision of about 50%, which is much higher than two of the conventional models showing a precision of around 30% and 20%, respectively.     

一种实时流媒体数字水印方案在广播电视监测中的应用

本文介绍了一种基于MPEG视频的实时流媒体数字水印方案设计与实现,为数字水印技术在广播电视领域应用于非法信号插播、错播节目、私插广告等监测提供了思路。     

科研机构向公众开放活动中的问题研究——以中科院为例

科研机构向公众开放是其重要的社会责任和义务,有利于提升我国的科普能力。近年来,中科院利用自身的资源优势开展了“公众科学日”等开放的活动,本文在深入调研的基础上,从政策、组织运行、经费、评价激励等方面入手,对中科院向公众开放过程中存在的问题进行了分析,并尝试提出解决问题的建议。     

基于散射函数的短波信道参数估计

理论分析了短波信道散射函数的计算,给出了实际短波信道探测中散射函数的测量方法,以及利用散射函数估计短波信道的衰落带宽、衰落相干时间、多径散布、相关带宽和信号的多普勒频移、传播时延等参数的方法.从实验数据中得到了短波信道的散射函数,利用散射函数估计了上述参数,给出了估计结果.     

Ga_(1-x)In_xAs_ySb_(1-y)/GaSb LPE生长及其性质研究

报导了在n型(100)GaSb衬底上,温度为520—530℃时,用液相外延的方法实现了组分在0≤x≤0.19,0≤y≤0.14范围内的Ga_(1-x)In_xAs_ySb_(1-y)四元合金半导体的生长。X射线双晶衍射,电子探针及光学显微镜的观察和分析测试表明:所得外延层的表面形貌和界面特性优良,组分分布和层厚均匀,晶格匹配及单晶性能良好。对外延层表面的氧化情况使用Auger能谱仪进行测试分析。另外,对生长中存在的一些问题进行了讨论。     

一种CMOS静态双沿触发器的设计

提出一种ＣＭＯＳ静态双沿触发器结构,以单个锁存器构成记忆单元,而由一特殊的时钟模块产生控制信号,使锁存器在时钟上升和下降沿处瞬时导通,从而形成双沿触发的功能,最小的实现方案只用１４个管子,模拟证明其工作频率可达３００ＭＨｚ以上。     

基于DES密码电路的差分功耗分析仿真研究

差分功耗分析技术是目前应用广泛、技术发展较成熟的非侵入攻击技术,设计了一个功耗分析仿真平台,该平台具有自动化程度高、精度高和仿真速度快的特点.此外,还基于该平台实现了对DES密码电路的差分功耗分析,对数字电视机项盒安全性的提高具有参考意义.     

Effect of Contact Mode on the Electrical Transport and Field‐Emission Performance of Individual Boron Nanowires

Vapor–liquid–solid processing of boron nanowires (BNWs) can be carried out either using a bottom‐up or top‐down growth mode, which results in different contact modes between the nanowire and the substrate. The contact mode may strongly affect the electrical transport and field‐emission performance of the individual boron nanowires grown on a Si substrate. The electrical transport and field‐emission characteristics of individual boron nanowires of different contact modes are investigated in situ using a scanning electron microscope. The contact barriers are very distinct for the different contact modes. Moreover, the transition from a “contact‐limited” to a “bulk‐limited” field‐emission (FE) process is demonstrated in nanoemitters for the first time, and the proposed improved metal–insulator–vacuum (MIV) model may better illustrate the nonlinear behavior of the Fowler‐Nordheim (FN) plots in these nanoscale systems. Individual BNWs with different contact modes have a discrepancy in their emission stability and vacuum breakdown characteristics though they have similar aspect ratios, which suggests that their electrical transport and field‐emission performance are closely related to their contact mode. Boron nanowires grown in the base‐up mode have better field‐emission performances and are more beneficial than those grown in the top‐down mode for various device applications.     

Si(111)衬底高温AlN缓冲层厚度及其结构特性

通过高分辨X射线衍射、光致发光、二次离子质谱（SIMS) 、原子力显微镜和同步辐射X射线衍射分析了AlN缓冲层的厚度对GaN外延层的影响. 实验表明，在缓冲层厚度为13～20nm之间时，GaN外延层的张应力最小，同时晶体质量和光学质量达到最优值. 此外，SIMS分析表明，当AlN缓冲层位于13～20nm之间时，可有效抑制Si的扩散.