树比较可视化方法综述

层次数据是生产和生活中常见的一类数据.树可视化通常用于呈现层次数据,是可视分析中的一个重要部分.比较是一种常用的分析方式,而树比较可视化也是可视分析研究中的一个重要课题.树比较可视化从所比较的树的数目角度,分为树内比较、两树比较和多树(3树及以上)比较;从数据特点角度分为静态树比较和动态树比较;从比较分析的任务角度,分为结构比较和属性比较.对现有的树比较可视化方法进行了总结,按照不同方法的表现形式,将树比较可视化分为并置、合并以及动画这3类.同时,结合其他分类方法对树比较可视化方法进行了全面的分析和评估.通过评估和比较,分析了不同方法的优缺点以及在不同的数据分析需求中的适用性.在此基础上,还对树比较可视化中的交互方式进行了总结,并阐述了树比较可视化所面临的挑战.     

汉语比较句识别研究

比较是常见的表达方式,提取事物之间的比较关系是一项新颖而有实用价值的研究。识别自然语言中的比较句,是提取比较关系的一个重要步骤。目前还没有针对汉语比较句的自动识别研究,语言学上比较句的哪些特征能够应用到自动识别上来是一个亟待研究的问题。该文讨论了汉语比较句的范畴、外延和特征,定义了汉语比较句识别的任务,并提出用SVM分类器将汉语句子分为“比较”和“非比较”两类。该文比较了比较句的语言学特征和统计特征,包括特征词、序列模式等在分类中的作用。实验结果表明:基于类序列规则的SVM分类器能够有效地识别汉语比较句,效果优于传统基于词的文本分类。     

中文比较句识别及比较关系抽取

比较是一种具有一定说服力的评估方式,利用机器进行比较句的识别以及比较关系的抽取可以对观点挖掘、信息推荐等应用提供重要的依据。该文通过构建中文比较模式库以实现中文比较句的自动识别。在此基础上,该文通过选取比较主体、比较客体及其上下文的词、词性、位置、语义以及比较属性的领域知识等特征,利用条件随机域模型进行中文比较关系抽取。实验结果表明,中文比较模式库的构建有助于比较句的自动识别,而在词、词性、位置等Baseline特征中融入语义、领域知识及启发式规则特征后,基于条件随机域的比较关系抽取结果有了显著的提高。     

维吾尔语比较句识别研究

识别比较句并提取被比较事物之间的关系是细颗粒度意见挖掘的重要研究内容之一。该文给出维吾尔语比较句的范畴、语法特点,定义了维吾尔语比较句识别的任务。提出两层识别模型,第一层是基于比较词的粗识别,第二层提出双向CSR挖掘算法(Bidirectional CSR Mining),以挖掘的模式为特征,利用支持向量机(SVM)筛选得到比较句,实现维吾尔语比较句的识别。实验F值达到70.93%,证明提出的两层识别模型可以有效识别维吾尔语比较句。     

基于CRF算法的汉语比较句识别和关系抽取*

比较句是表明事物之间关系的常见表达方式,对于文本挖掘,特别是情感分析,具有重要的价值。目前汉语比较句的研究还是一个新颖的课题,包括汉语比较句的识别和比较关系的抽取。对于汉语比较句的识别,在前人研究的基础上,以SVM为分类器,以特征词和CSR序列规则为特征,同时利用CRF算法抽取实体对象,并增加以实体对象的信息作为特征,显著提高了比较句识别的准确率、召回率和F-度量,最高分别达到96.55%、88.63%和92.43%。对于汉语比较关系的抽取,在CRF算法抽取实体对象的基础上,通过定义一些规则,抽取比较主体和比较基准,也取得了较好的效果,其中比较主体的抽取效果要好于比较基准。     

改进的基于图的可执行文件比较算法

讨论了可执行文件的比较方法,在基于图的指令相似性比较和结构化二进制比较的基础上给出了一种改进的可执行文件比较算法.该算法首先利用结构化比较获得一组固定点,再从每个固定点开始进行指令相似性比较.该算法融合了两种方法的优点,并使得它们相互弥补了各自的不足,减少了比较结果漏报和误报的可能性.     

序列比较算法在入侵检测系统的研究与应用

该文从阐述序列比较入手．分析了序列比较算法。通过对序列比较与入侵检测行为比较的相似性研究,采用了一种序列比较算法应用于入侵检测中。按照入侵检测的特点采用了一种序列比较算法,使用标准数据和收集数据对其进行测试,取得了较好的实验结果。     

用户评价中比较句的识别和倾向性分析

在互联网上用户评价内容中很多比较句的比较结果反映了语句陈述者对比较对象的倾向性态度。根据已有的10类比较句句型总结了它们的常见概念搭配,在基于语义块的语句倾向性分析方法的基础上构建了比较句自动识别系统和比较句倾向性自动分析系统。采用第四届中文倾向性分析评测的语料进行实验,对语料中的比较句进行了识别,对比较句中的要素进行了抽取并且分析了比较句的倾向性,识别结果和倾向性分析结果均好于所有参评系统的平均值。     

基于语义分类的比较句识别与比较要素抽取研究

比较是人们常用的评估不同事物优劣、异同的表达方式,利用机器识别比较句并进一步抽取比较要素是语言信息处理领域一项新颖又有实用价值的课题。该文依据比较句与比较要素之间是一种“你中有我,我中有你”的共生关系,将比较句识别与比较要素抽取两个任务合二为一完成;根据词意分类,构建由领域词典、情感词典、标记词典、普通词典构成的词典系统;根据汉语比较句句义分类,构建比较句识别与比较要素抽取规则库。以第四届中文倾向性评测(COAE2012)发布的测试语料为实验对象,该系统取得了较好的实验(评测)结果。     

基于有向图的二进制文件结构化比较机制研究

通过对二进制文件结构化比较方法的研究,提出了基于有向图的二进制文件结构化比较方法及实现算法.和基于指令比较的二进制文件比较方法相比,二进制文件结构化比较方法更注重二进制文件在逻辑结构上的变化,而且更加简单.     

Wide‐bandwidth multifrequency circularly polarized monopole antenna for wireless communication applications

In this article, wideband circularly polarized monopole antennas with multiresonating frequencies are presented for Bluetooth, WLAN, WiMAX, and X‐band applications. The designed antennas have dimensions of 50 × 35 × 1.6 mm³. Two different substrates (FR4‐epoxy and PTFE) are used for fabricating the antennas. The antennas consist of corner truncated I‐shaped and C‐shaped strips excited by a 50 Ω microstrip feed line. The parametric analyses are performed with the help of Ansoft HFSS V.11 EM simulator. Both antennas have been fabricated and measured. The measured percentage bandwidth of the antenna made by FR4 substrate is 31.32% (centered at 1.66 GHz), and 64.85% (centered at 5.69 GHz). The percentage bandwidth of antenna made by PTFE substrate is 20.57% (centered 2.43 GHz) and 68.74% (centered at 7.39 GHz). In addition to that, there exists 3 dB AR bandwidth for LHCP of about 1050 MHz for 5.2 GHz WLAN‐band. The reflection coefficient, radiation patterns, and the gains of both the antennas are studied in detail. It is found that the measured and simulated results are in good agreement.     

蝶形天线的计算机仿真设计

蝶形天线是在脉冲型探地雷达中广泛采用的一种宽带天线。本文采用时域有限差分算法(FDTD)结合PML吸收边界条件分析了蝶形天线在高斯脉冲激励下的时域特性,通过傅立叶变换,计算出天线的方向图和在不同频率下的输入阻抗,结果表明FDTD算法用于分析蝶形天线是有效的。     

Isolation enhancement between tightly spaced compact unidirectional patch‐antennas on multilayer EBG surfaces

In this article, ultracompact unidirectional patch antennas are used in different two‐antenna systems for biomedical applications at 5.2 GHz. Multilayer mushroom type electromagnetic bandgap (EBG) structures are designed as slow‐wave medium to reduce the size of the individual patch antennas to 0.1λ₀ by 0.18λ₀. Various techniques are investigated herein to improve antenna isolation for an enhanced Multiple‐Input Multiple‐Output (MIMO) performance. First, the coupling between 0.3λ₀‐spaced antennas is verified to occur dominantly through radiation and near‐field coupling between the patches rather than through substrate‐bound modes. Second, various configurations are proposed to suppress antenna coupling. These approaches include reorientation of the antennas and employment of parasitic radiators between the patches. A novel design is presented in which a unidirectional parasitic slot radiator on an EBG reflector is inserted between the antennas to decouple them. Measurement results confirm efficacy of these approaches in mitigating antenna coupling by more than 11 dB in the operating bandwidth of the antennas. The compact patch antennas maintain efficiency values of higher than 70%. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:30–38, 2015.     

Design of tri‐notched UWB antenna based on elliptical and circular ring resonators

This article presents the design of a compact coplanar waveguide (CPW) fed Monopole Antenna for ultra‐wideband (UWB) applications. The semi‐circular shaped radiator is fed with a 50‐Ω line that resonates within the UWB frequency range. Two notching elements are used to reduce narrowband interferences. An elliptical ring resonator is etched out from the radiator to suppress 3.97‐4.48 GHz narrowband interference whereas, narrow bands from 5.79 to 6.57 GHz (WLAN) and 7.30‐7.60 GHz (X band downlink) were suppressed by loading a metamaterial inspired circular ring resonator behind the feed line. Moreover, the lower notching band due to the elliptical ring resonator can be further tuned to lower resonance frequencies by controlling the capacitance of the embedded varactor diode. The antenna has a compact size of 36 × 34 × 1 mm³. The antenna is simulated, fabricated and measured in an Anechoic Chamber. The measured results are in good agreement with the simulated results.     

Exploiting antenna directivity in wireless NoC architectures

Wireless Network-on-Chip (WiNoC) is an emerging on-chip communication paradigm and a candidate solution for dealing with the scalability problems which affect current and next generation many-core architectures. In a WiNoC, the transceivers that allow the conversion between electrical and radio signals, account for a significant fraction of the total communication energy budget. In particular, the transmitting power for wireless communications is strongly affected by the orientation of the antennas. This paper studies the impact of antennas orientation on energy figures of a WiNoC architecture and performs a design space exploration for determining the optimal orientation of the antennas in such a way to minimize the communication energy consumption. Experiments have been carried out on state-of-the-art WiNoC topologies, on both synthetic and real traffic scenarios, and validated by means of a commercial field solver simulator. When the antennas are optimally oriented, up to 80% energy saving (as compared to the case in which antennas have all the same orientation) has been observed.     

移动Ad Hoc网络中应用智能天线的多址协议及其性能分析

对智能天线在移动Ad Hoc网络(MANET)中的应用进行研究．提出了自适应波束形成CSMA／CA(ABF—CSMA／CA)协议．该协议利用RTS／CTS对话实现信道预约；在RTs与CTS分组中设置了训练序列，收发节点的智能天线基于训练序列进行自适应波束形成以传输数据分组与ACK．提出改进的“虚拟载波监测”机制进行冲突避免(CA)．每个节点中设置两类网络分配矢量(NAV)，用一个oNAV记录邻节点以全向模式占用信道的时间，用多个bNAV分别记录各邻节点以波束形成模式传输分组的时间．推导了信道利用率的近似计算公式并进行了仿真，考察了节点传输距离、训练序列长度及天线模式切换时间对网络性能的影响．结果表明，ABF-CSMA／CA协议与智能天线的结合能有效实现信道的空分复用(SDMA)，显著提高整个网络的信道利用率．     

Design of conical DRH antennas for K and Ka frequency bands

Two conical double‐ridged horn (DRH) antennas for K and Ka frequency bands are presented. Detailed simulation and experimental investigations are conducted to understand their behaviors and optimize for broadband operation. The designed antennas were fabricated with 0.01 mm accuracy and satisfactory agreement of computer simulations and experimental results was obtained. The designed conical DRH antennas have voltage standing wave ratio (VSWR) less than 2.1 and 2.2 for the frequency ranges of 18–26.5 GHz (K band) and 26.5–40 GHz (Ka band), respectively. Meanwhile, the proposed antennas exhibit low cross‐polarization, low sidelobe level, and simultaneously achieve slant polarization as well as symmetrical radiation patterns in the entire operating bandwidth. An exponential impedance tapering is used at the flare section of the horns. Moreover, a new cavity back with a conical structure is used to improve the VSWR. Numerous simulations via Ansoft HFSS and CST Microwave Studio CAD tools have been made to optimize the VSWR performance of the designed antennas. Simulation results show that the VSWR of the proposed antennas is sensitive to the probe spacing from the ridge edge and the cavity back structure. The designed conical DRH antennas are most suitable as a feed for the reflectors of radar systems and satellite applications. Results for VSWR, far‐field E‐plane and H‐plane radiation patterns, and gain of the designed antennas are presented and discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Energy efficiency of massive MU-MIMO with limited antennas in downlink cellular networks

In this paper, we analyze and optimize the energy efficiency (EE) of multi-user (MU) multiple-input and multiple-output (MIMO) in downlink multi-cell networks. We first analyze the spectral efficiency (SE) of MU-MIMO systems with a huge number of base station (BS) antennas by using maximal ratio transmission (MRT) and zero-forcing (ZF) precoders in downlink cellular networks. In the analysis, we assume that the number of the BS antennas is huge but limited, which is different from the conventional analysis. Then, we use the analytical SE result and the EE definition to obtain the system EE expression and further analyze the effect of the number of BS antennas and the number of served users on system EE. Since the system EE on the numbers of BS antennas and the number of served users is approximately concave, the corresponding iterative optimization algorithms are proposed to achieve the maximum system EE. The computer simulation results show that the analytical results are accurate and each served user needs about 2 active BS antennas to obtain the maximum system EE when the channel state information is available at the transmitter.     

Analysis of microstrip antennas on finite chiral substrates

An approach is developed to analyze microstrip antennas on finite chiral substrates using the finite-element method (FEM). The perfectly matched layers (PMLs) in the chiral media is employed in this work. First, the characteristics of microstrip antennas on infinite conventional, ferrite, and chiral substrates are respectively analyzed in order to validate our analysis. Then microstrip antennas on finite chiral substrates are investigated as a comparison with those on infinite chiral substrates. Finally, the input impedances of microstrip antennas on infinite and finite chiral substrate are calculated. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 49–56, 2004.