一种短波数字接收机模拟前端设计方案

文章分析了短波数字接收机模拟前端的总体设计方案,包括前端各部分增益的分配与计算、AGC起控点与饱和点的选取以及整个前端噪声系数的计算,讨论了各部分模块的具体实现以及对器件选择的考虑,最后给出了本方案的实验数据.     

面向平安城市的视频监控前端呼叫设计研究

在平安城市的建设中,管理平台对视频监控前端呼叫越来越重要。为了完善对视频监控前端的呼叫效果,设计了一种视频监控前端呼叫方案。首先简析了SIP、RTP/RTCP协议原理;设计了视频监控系统整体结构,定义了各主要组成部件的功能。然后分析了视频监控前端呼叫设计思路,设计了RTP Over UDP、RTP Over TCP的呼叫方案,以及NAT穿越方案。本文的设计思路在一些平安城市建设中已开始应用,应用效果良好,具有一定借鉴意义。     

短波数字接收机中频响校正方案的研究与实现

针对短波通信系统射频前端模拟滤波器存在的非理想特性,设计了一种基于频率抽样理论的校正方案。该方案由抽样值测量、抽头系数计算及滤波等部分组成。对该设计的理论基础做了详细的描述,并对应用于实际接收系统中的测量结果进行了分析说明。     

采用半双工射频芯片实现的全双工通信设计方案

文章基于现有的高频模拟前端技术和工艺条件,提出了一种采用TI公司推出的半双工RF芯片TRF6901作为射频收发、MSP430单片机作为控制单元的以时分形式实现的无线双工通信方案,并介绍了该方案的模拟前端射频收发部分的硬件及时分双工的设计与实现。该方案已在平顶山煤业集团六矿进行了试验,通信效果良好,在大巷中通信距离可达200 m以上。     

飞机轮胎压力监测系统的设计

飞机在跑道上降落瞬间由于受到较大冲击可能爆胎;针对这一问题,研究了飞机轮胎压力监测系统;首先叙述了系统的研究背景与现状,系统方案的选择以及所选方案的技术问题及解决办法,具体分析了各部分电路工作原理,进行了相应的理论分析及参数计算,给出了各部分的硬件设计原理图、实物图以及软件流程图,并进行了实验验证;实验结果表明,该系统可以对轮胎压力进行精确测量和控制,从而可以有效避免飞机降落爆胎事故的发生,提高飞机安全性.     

基于B/S模式的网上考试系统的设计

该文首先提出课题研究的主要内容,随后阐述了系统的数据库、试题、前端考生测试部分和后台系统管理部分的详细设计,最后提出了系统的安全方案。     

卫星定位信号接收机系统研究与设计

本文在研究卫星定位信号接收机系统的构成及原理之后,介绍了一种基于Nemerix公司GPS芯片组的卫星定位信号接收机的设计.该接收机主要由射频前端和基带处理器两个部分组成,分别以NJ1006A和NJ1030A为核心芯片.射频前端芯片NJ1006A接收卫星定位信号后将其变换为数字中频信号,并传给基带处理器NJ1030A进行信号的捕获、跟踪以及定位解算等一系列的处理,输出定位信息.文章讨论了系统的整体结构,重点对系统中各部分的外围电路和相互接口进行了设计与分析,并给出了各部分在调试时的注意问题.最后,给出了软件下载过程和测试结果.实验结果表明,系统的整体设计是合理有效的.     

基于数字解调器和JESD204B的多通道超声系统设计

针对多通道超声系统设计中接收电路中模拟前端和数字处理电路间的大数据量传输和大量数据连线的复杂性,提出了一个基于数字解调器和JESD204B接口的超声系统接收方案。该方案大幅降低了模拟前端的输出数据率,同时减少了模拟前端和数字电路部分的连线数目。有效地达到简化电路设计及降低数字处理要求,通过使用软件波束合成和更高阶多波束处理可以实现实时4D和高级影像模式。     

密封对汽车冷却模块性能影响的数值分析

为优化汽车前端设计,提高发动机舱散热性能,针对某乘用车发动机舱冷却性能提出冷却模块空气流量、格栅进气利用率和散热器实际散热量等3个评价参数,通过CFD软件对4种汽车前端进气冷却模块密封方案进行三维仿真计算,研究冷凝器、散热器与风扇罩之间的不同密封情况对3个评价参数的影响.研究结果表明,双密封方案是提高冷却模块性能的最佳方案.     

无线电通信中的同址干扰问题研究

针对战术电台车中无线电同址干扰对车载通信系统的影响,首次进行了全面、系统的研究。首先通过实验对车载天线之间的耦合度进行了测量,并结合Ansoft HFSS软件进行了仿真验证。在耦合度统计均值的基础上,通过分析电台射频前端的阻塞模型,以及射频前端各个部分的损耗、增益、噪声,对同址干扰引起的减敏影响进行了定性分析和定量计算,并通过经验公式对同址干扰中电台频率间隔与信噪比损耗之间的关系进行了仿真。最后,提出了减敏损耗与通信距离之间的等效计算,进一步分析了同址干扰对实际通信的影响。     

Knowledge sharing and social media: Altruism,perceived online attachment motivation,and perceived online relationship commitment

Social media, such as Facebook and Twitter, have become extremely popular. Facebook, for example, has more than a billion registered users and thousands of millions of units of information are shared every day, including short phrases, articles, photos, and audio and video clips. However, only a tiny proportion of these sharing units trigger any type of knowledge exchange that is ultimately beneficial to the users. This study draws on the theory of belonging and the intrinsic motivation of altruism to explore the factors contributing to knowledge sharing behavior. Using a survey of 299 high school students applying for university after the release of the public examination results, we find that perceived online attachment motivation (β = 0.31, p < 0.001) and perceived online relationship commitment (β = 0.49, p < 0.001) have positive, direct, and significant effects on online knowledge sharing (R² 0.568). Moreover, when introduced into the model, altruism has a direct and significant effect on online knowledge sharing (β = 0.46, p < 0.001) and the total variance explained by the extended model increases to 64.9%. The implications of the findings are discussed.     

Experimental determination of phase equilibria in the Y–Co–Ti system through diffusion couples and equilibrium alloys

Two isothermal sections of the Y–Co–Ti system at 600 °C and 800 °C were constructed for the first time using the diffusion couple technique and the equilibrium alloy method in combination with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). The stable ternary intermetallic compound YCo_12-xTi_x was detected and was confirmed to have a ThMn₁₂-type structure. The composition range in this ternary compound was measured to be 8.3–18.2 at.% at 600 °C and 8.9–19.1 at.% at 800 °C, resulting in the stable formation of YCo_12-xTi_x with x = 1.1–2.4 at 600 °C and x = 1.2–2.5 at 800 °C. The experimental results measured by EDS and EPMA demonstrate that the maximum solubilities of Ti in YCo₂, YCo₃, Y₂Co₇ and Y₂Co₁₇ compounds at 600 °C are 3.3, 5.6, 5.7 and 6.6 at.%, respectively, while the maximum solubilities of Y in Co₃Ti, Co₂Ti(h), Co₂Ti(c) and CoTi compounds are 2.7, 2.1, 2.6, 3.8 and 1.1 at.%. Meanwhile, the maximum solubilities of Ti in YCo₃, Y₂Co₇, YCo₅ and Y₂Co₁₇ compounds at 800 °C were determined to be 5.4, 3.2, 2.5 and 5.4 at.%, respectively, while the maximum solubilities of Y in Co₂Ti(c), Co₂Ti(h) and Co₃Ti compounds were measured to be 2.5, 2.1 and 3.8 at.%. The phase equilibria of the Y–Co–Ti system obtained in this work would provide the experimental information for phase stability of YCo_12-xTi_x compound and then explore the design of Y–Co–Ti based magnetic alloys with good magnetic properties.     

A thermodynamic description of the Gd–Mg–Sm system

The Mg–Sm, Gd–Sm and Gd–Mg–Sm systems were thermodynamically optimized using the CALPHAD technique. The solution phases, liquid, bcc, hcp and rhombohedral, were described by the substitutional solution model. The isostructural compounds, MgGd in the Gd–Mg system and MgSm in the Mg–Sm system with a B2 structure was assumed to form a continuous range of solid solutions in the Gd–Mg–Sm system. The order–disorder transition between the bcc solution with an A2 structure and compound Mg(Gd, Sm) with a B2 structure in the system has been taken into account and thermodynamically modeled. The other isostructural compounds Mg₅Gd and Mg₅Sm, Mg₃Gd and Mg₃Sm, Mg₂Gd and Mg₂Sm in the Gd–Mg–Sm system were described according to the formulae Mg₅(Gd,Sm), Mg₃(Gd,Sm), and Mg₂(Gd,Sm), respectively. The compound Mg₄₁Sm₅ with a homogeneity range was treated as a line compound Mg₄₁(Gd,Sm)₅ in the Gd–Mg–Sm system. Based on the experimental data in the Mg-rich corner of the Gd–Mg–Sm system, a set of thermodynamic parameters describing the Gibbs energies of individual phases of the Gd–Mg–Sm system as functions of composition and temperature was obtained. In addition, the complete ternary phase diagram of the Gd–Mg–Sm system were predicted.     

Phase transformations and phase equilibria in the La-Ni and La-Ni-Fe systems. Part 2: Isothermal sections at 750, 600 and 500 °C

The ternary phase diagram La-Ni-Fe was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Three isothermal sections, at 750, 600 and 500 °C were constructed covering the whole concentration range. In addition, vertical sections at 15 and 35 at.% La were evaluated based on the abovementioned methods and DTA analysis. Among binary compounds, LaNi₅, La₅Ni₁₉ and La₂Ni₇ have the widest homogeneity regions. The LaNi₅ phase dissolves 19.9, 19.6 and 19.4 at.% Fe at 750, 600 and 500 °C, respectively. The solubility of Fe in La₅Ni₁₉ is 14.5, 12.1 and 8.9 at.% at 750, 600 and 500 °C, respectively. For the La₂Ni₇ phase, the Fe-solubility was found to be 13.9, 11.3 and 10.1 at.% at 750, 600 and 500 °C, respectively. The homogeneity regions of the remaining phases are much smaller. The character of phase equilibria at 750 °C in the Ni-rich region is similar to those at solidus temperature. The character of the phase equilibria at 600 and 500 °C, however, differs from those at higher temperatures. In particular, the equilibrium (γFe,Ni) + La₅Ni₁₉ which is present in the La-Ni-Fe system at solidus temperature and 750 °C, is absent at 600 and 500 °C. Instead, the alternative equilibrium LaNi₅ + La₂Ni₇ is present at 600 °C. Furthermore, the equilibrium La₂Ni₇ + La₂Ni₃ which is present at solidus temperature, is replaced by the alternative equilibrium (αFe) + La₇Ni₁₆ at lower temperatures.     

Pack hike test finishing time for Australian firefighters: pass rates and correlates of performance

The pack hike test (PHT, 4.83 km hike wearing a 20.4-kg load) was devised to determine the job readiness of USA wildland firefighters. This study measured PHT performance in a sample of Australian firefighters who currently perform the PHT (career land management firefighters, LMFF) and those who do not (suburban/regional volunteer firefighters, VFF). The study also investigated the relationships between firefighters' PHT performance and their performance across a range of fitness tests for both groups. Twenty LMFF and eighteen age-, body mass-, and height-matched VFF attempted the PHT, and a series of muscular endurance, power, strength and cardiorespiratory fitness tests. Bivariate correlations between the participants’ PHT finishing time and their performance in a suite of different fitness tests were determined using Pearson’s product moment correlation coefficient. The mean PHT finishing time for LMFF (42.2 ± 2.8 min) was 9 ± 14% faster (p = 0.001) than for VFF (46.1 ± 3.6 min). The pass rate (the percentage of participants who completed the PHT in under 45 min) for LMFF (90%) was greater than that of VFF (39%, p = 0.001). For LMFF, VO_2peak in L min⁻¹(r = −0.66, p = 0.001) and the duration they could sustain a grip ‘force’ of 25 kg (r = −0.69, p = 0.001) were strongly correlated with PHT finishing time. For VFF, VO_2peak in mL kg⁻¹ min⁻¹(r = −0.75, p = 0.002) and the duration they could hold a 1.2-m bar attached to 45.5 kg in a ‘hose spray position’ (r = −0.69, p = 0.004) were strongly correlated with PHT finishing time. This study shows that PHT fitness-screening could severely limit the number of VFF eligible for duty, compromising workforce numbers and highlights the need for specific and valid firefighter fitness standards. The results also demonstrate the strong relationships between PHT performance and firefighters’ cardiorespiratory fitness and local muscular endurance. Those preparing for the PHT should focus their training on these fitness components in the weeks and months prior to undertaking the PHT.     

On the Weighted Mean of a Pair of Strings

String matching and string edit distance are fundamental concepts in structural pattern recognition. In this paper, the weighted mean of a pair of strings is introduced. Given two strings, x and y, where d(x, y) is the edit distance of x and y, the weighted mean of x and y is a string z that has edit distances d(x, z) and d(z, y)to x and y, respectively, such that d(x, z) _ d(z, y) = d(x, y). We’ll show formal properties of the weighted mean, describe a procedure for its computation, and give practical examples. Received: 26 October 2000, Received in revised form: 27 April 2001, Accepted: 20 July 2001     

High sensitive simultaneous determination of hydroquinone and catechol based on graphene/BMIMPF6 nanocomposite modified electrode

A novel nanocomposite, comprising of graphene sheet (GS) and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), was developed on the glassy carbon electrode (GCE) for the simultaneous determination of hydroquinone and catechol in 0.10 M acetate buffer solution (pH 5.0). At the GS/BMIMPF₆/GCE, both hydroquinone and catechol can cause a pair of quasi-reversible and well-defined redox peaks. In comparison with bare GCE and GS modified electrode, GS/BMIMPF₆/GCE showed larger peak currents, which was related to the higher specific surface area of graphene and high ionic conductivity of BMIMPF₆. Under the optimized condition, the cathodic peak current were linear over ranges from 5.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M for hydroquinone and from 5.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M for catechol, with the detection limits of 1.0 × 10⁻⁸ M and 2.0 × 10⁻⁸ M, respectively. The proposed method was successfully applied to the simultaneous determination of hydroquinone and catechol in artificial sample, and the results are satisfactory.     

Dis/integrating animals: ethical dimensions of the genetic engineering of animals for human consumption

Research at the intersections of feminism, biology and philosophy provides dynamic starting grounds for this discussion of genetic technologies and animals. With a focus on animal bodies, I will examine moral implications of the genetic engineering of “domesticated” animals—primarily pigs and chickens—for the purposes of human consumption. Concepts of natural and artificial, contamination and purity, integrity and fragmentation and mind and body will feature in the discussion. In this respect, Margaret Atwood’s novel, Oryx and Crake, serves as a cogent medium for exploring these highly contentious practices and ideas as it provides hypothetical narratives of possibility. Moreover, it is used to highlight contemporary hegemonic assumptions and values in ways that make them visible. Particular attention is paid to issues of growing human organs in pigs for xenotransplantation (resulting, for Atwood, in “pigoons”) and the ultimate end of the intensive factory farming of chickens through the genetic engineering of ‘mindless’ chicken tumours (or, as Atwood calls them, “ChickieNobs”). Integral to these philosophical considerations is the provocative question of the genetic modification of animal bodies as a means to end the suffering of domestic food animals. The ultimate implications of this question include an ongoing sensory and moral deprivation of human experience, potentially resulting in a future mechanomophosis, the extreme manifestation of an existing mechanomorphism.

Simulating parallel neighboring communications among square meshes and square toruses

Given a d-dimensional square mesh or square torus G and a c-dimensional square mesh or square torus H such that G and H are of the same size but may differ in dimensions and shapes, we study the problem of simulating in H parallel neighboring communications in G. We assume that the nodes in H have only unit-size buffers associated with the links, and that packets can be sent and received simultaneously from all outbound links and inbound links of the nodes. For permutation-type parallel neighboring communications, for all the combinations of graph types and graph shapes of G and H, except for the case in which d < c and c is not divisible by d, we show that H can simulate G either optimally or optimally up to a constant multiplicative factor for fixed values of d and c. For scatter-type parallel neighboring communications, for some special cases of G and H, we also show that H can optimally simulate G. All these simulation times are smaller than the diameter of H, the lower bound on the routing complexity to support general data permutations in H.This work has been partially supported by National Science Foundation PYI award DCR84-51408, IBM research grant, AT&T Information System research grant, National Science Foundation CER grant MCS82-19196, Army Research Office grant DAAG-29-84-K-0061, Canada NSERC research grant OGP0041648, and British Science and Engineering Research Council visiting fellowship research grant.     

Knowledge reduction based on the equivalence relations defined on attribute set and its power set

One of the key problems of knowledge discovery is knowledge reduction. This paper proposes a new method for knowledge reduction in information systems. First, two families of closed sets C_r and C_R are defined, where r and R are equivalence relations defined on the attribute set and its power set, respectively. The properties of C_r and C_R are also discussed. The necessary and sufficient condition for C_r=C_R is then given and employed to construct an approach to attribute reduction in information systems. It is also proved that under the condition C_r=C_R, the proposed approach to knowledge reduction is equivalent to the well-accepted one in reference [W.X. Zhang, Y. Leung, W.Z. Wu, Information Systems and Knowledge Discovery, Science Publishing Company, Beijing, 2003].