How Social Network Position Relates to Knowledge Building in Online Learning Communities?

Social Network Analysis,Statistical Analysis,Content Analysis and other research methods were used to research online learning communities at Capital Normal University,Beijing.Analysis of the two online courses resulted in the following conclusions:(1)Social networks of the two online courses form typical core-periphery structures;(2)Social networks of the two online courses contain“structural holes,”where some actors position themselves to become potential opinion-leaders within their social networks;(3)Actors,variously positioned within a core-periphery structure,show quite significant differences in terms of knowledge building;(4)Taking“structural holes”into account,there exist considerable differences in knowledge building between opinion-leaders and non opinion-leaders;(5)Actors in the“core”and“structural hole”positions have very different characteristics in terms of knowledge building.These actors in particular play important roles in online learning communities,impacting on the level of the constructed knowledge.

A fully integrated multi-standard frequency synthesizer for GNSS receivers with cellular network positioning capability

A fully integrated hybrid integer/fractional frequency synthesizer is presented.With a single multiband voltage-controlled-oscillator（VCO）,the frequency synthesizer can support GPS,Galileo,Compass and TDSCDMA standards.Design is carefully performed to trade off power,die area and phase noise performance.By reconfiguring between the integer mode and fractional mode,different frequency resolution requirements and a constant loop bandwidth for each standard can be achieved simultaneously.Moreover,a long sequence length,reduced hardware complexity multi-stage-noise-shaping（MASH）.-.modulator is employed to reduce fractional spur in the fractional mode.Fabricated in a 0.18 m CMOS technology,the frequency synthesizer occupies an active area of 1.48 mm2 and draws a current of 13.4-16.2 mA from a 1.8 V power supply.The measured phase noise is lower than-80 dBc/Hz at 100 kHz offset and-113 to-124 dBc/Hz at 1 MHz offset respectively,while the measured reference spur is-71 dBc in integer mode and the fractional spur is-65 dBc in fractional mode.

Exploring Regional Innovation Growth Through A Network Approach:A Case Study of the Yangtze River Delta Region,China

As the leading urban agglomeration in China,the Yangtze River Delta(YRD)is experiencing a factor-driven to innovationdriven transition.However,the dynamics of regional innovation growth are not yet fully understood.This paper combines the complex network methodology with spatial econometrics to disentangle the contributions of innovation endowments,innovation network flows,and innovation network positions to regional innovation growth,as well as their spatial spillover effects.The primary findings suggest that regional innovation growth results from the networked agglomeration economies,which is shaped by the interactions between agglomeration factors and network factors.Specifically,agglomeration factors play a fundamental role in regional innovation growth.In contrast,network factors,such as the network flows and network positions,may contribute to new path creation by promoting access to external innovation resources.Additionally,the institutional factors show multiplexity in fostering regional innovation patterns.Such findings indicate that the YRD region should shift the innovation growth pattern from competitive involution to mutually beneficial cooperation to reduce regional disparities.In this regard,the institutional capacity of organizing network flows and fostering reciprocal inter-city partnerships has become increasingly critical for promoting sustainable innovation and regional development.

Fuzzy adaptive Kalman filter for indoor mobile target positioning with INS/WSN integrated method

Pure inertial navigation system(INS) has divergent localization errors after a long time. In order to compensate the disadvantage, wireless sensor network(WSN) associated with the INS was applied to estimate the mobile target positioning. Taking traditional Kalman filter(KF) as the framework, the system equation of KF was established by the INS and the observation equation of position errors was built by the WSN. Meanwhile, the observation equation of velocity errors was established by the velocity difference between the INS and WSN, then the covariance matrix of Kalman filter measurement noise was adjusted with fuzzy inference system(FIS), and the fuzzy adaptive Kalman filter(FAKF) based on the INS/WSN was proposed. The simulation results show that the FAKF method has better accuracy and robustness than KF and EKF methods and shows good adaptive capacity with time-varying system noise. Finally, experimental results further prove that FAKF has the fast convergence error, in comparison with KF and EKF methods.

NEW HYDRAULIC ACTUATOR'S POSITION SERVOCONTROL STRATEGY

A new hydraulic actuator-hydraulic muscle （HM） is described, and the actuator＇s features and applications are analyzed, then a position servocontrol system in which HM is main actuator is set up. The mathematical model of the system is built up and several control strategies are discussed. Based on the mathematical model, simulation research and experimental investigation with subsection PID control, neural network self-adaptive PID control and single neuron self-adaptive PID control adopted respectively are carried out, and the results indicate that compared with PID control, neural network self-adaptive PID control and single neuron self-adaptive PID control don＇t need controlled system＇s accurate model and have fast response, high control accuracy and strong robustness, they are very suitable for HM position servo control system.

基于BP-PSO的智能阀门定位器控制算法研究

针对五步开关控制算法易超调以及控制参数取值具有近似性和不确定性等不足,提出了一种参数自整定和参数寻优的控制算法,并在最关键的脉冲调制控制环节运用了改进的BP神经网络算法和粒子群(PSO)算法来寻找最优阀门控制参数。搭建智能阀门定位器实验平台,采用传统五步开关控制算法和本控制算法分别对阀门进行控制试验。结果表明,本控制算法相较于传统五步开关控制算法的适用性大大增强,避免了超调,缩短了响应时间,阀门控制精度达到0.03%,阀门开度稳定时间缩短至1 s以内。

基于分层误差补偿的飞机柔性工装定位精度提高方法

飞机柔性工装中三坐标定位器的定位精度直接影响飞机大部件间的装配精度。提出了一种分层误差补偿模型以提高其定位精度,首先对定位器堆栈式结构和导轨间相关性进行分析,改进各轴运动方向上的角误差,提高整体线性误差补偿精度;然后采用遗传算法优化的神经网络对线性补偿后误差较大的位置点进行非线性误差补偿;最后将线性模型和非线性模型结合,提出了分层误差补偿模型,并进行了传统误差补偿模型和分层误差补偿模型的对比实验。实验结果表明,分层误差补偿模型与传统误差补偿模型相比,空间误差补偿效果最大可提高58.09%、均值可提高46.92%,有效地改善了误差补偿效果,提高了飞机数字化装配的精度。

A PHEMT Based Wideband LNA for Wireless Applications

This work is about the development of a super low noise amplifier with minimum power consumption and high gain for several wireless applications.The amplifier operates at frequency bands of 0.9-2.4 GHz and can be used in many applications like Wireless local area network(WLAN),WiFi,Bluetooth,ZigBee and Global System for mobile communications(GSM).This new design can be employed for the IEEE 802.15.4 standard in industrial,scientific and medical(ISM) Band.The enhancement mode pseudomorphic high electron mobility transistor PHEMT is used here due to its high linearity,better performance and less noisy operation.The common source inductive degeneration method is employed here to enhance the gain of amplifier.The amplifier produces a gain of more than 17 dB and noise figure of about 0.5 dB.The lower values of S11 and S22 reflect the accuracy of impedance matching network placed at the input and output sides of amplifier.Agilent Advance Design System(ADS) is used for the design and simulation purpose.Further the layout of design is developed on the FR4 substrate.

Resistivity-temperature Characteristics of Conductive Asphalt Concrete

The changes of resistivity of conductive asphalt concrete at different temperatures were studied,and positive temperature coefficient（PTC）modelwas established to estimate the influence of temperature on the resistivity quantitatively,which eliminated the interference with conductivity evaluation brought by temperature variation.Finally,the analysis of temperature cycling test results proves that the changes of percolation network structure caused by temperature variation prompt the emergence of PTC of conductive asphalt concrete.

基于光纤应变传感器的型架定位器位置检测方法研究

针对飞机装配过程中型架定位器的位置变化,提出一种基于光纤应变传感器的定位器位置检测方法。通过光纤应变传感器对型架主体及定位器组件关键特征区域的应变和定位器位置变化量进行实时采集,对采集的数据进行分析和处理,采用BP(back propagation,反向传播)神经网络建立飞机型架不同区域应变量与定位器位置变化量之间的数学模型。在某型工艺装备上搭建型架定位器位置检测试验平台,根据试验数据分别建立了定位器在平面及空间范围受载下的位置检测神经网络模型。试验结果表明:当神经网络样本数量一定时,模型对定位器位置的预测精度与加载偏移角度有关,偏移角度越小,加载覆盖率越高,模型的预测精度越高。其中,平面内以30°间隔、空间以45°间隔加载时,建立的神经网络模型对定位器位置的预测精度满足定位要求,验证了本文方法的可行性。该方法摈弃了用数字化设备直接测量的传统方式,弥补了因视线遮挡而造成个别定位器位置无法被检测的缺陷,能对装配过程中所有定位器的位置进行检测,解决定位器位置偏差过大造成的飞机部件检测质量差的问题,提升了飞机的装配质量。

模糊神经网络在阀门开度控制中的应用

针对电磁阀控气缸系统时变、非线性的特性,应用模糊神经网络整定PID参数。利用AMESim物理图形建模软件搭建被控对象的模型,应用MATLAB编写模糊神经网络PID的S函数,再联合MATLAB和AMESim对算法进行仿真,仿真结果表明模糊神经网络PID的适应性好、抗干扰能力强,性能优于常规PID。最后搭建实验平台进行了实验。实验结果表明,系统在不同环境下的控制精度高、响应快、过程平稳,满足阀门开度控制的要求。

Context-Aware Adaptive Routing for Opportunistic Network

Opportunistic networking-forwarding messages in a disconnected mobile ad hoc network via any encountered nodes offers a new mechanism for exploiting the mobile devices that many users already carry. However, forwarding messages in such a network is trapped by many particular challenges, and some protocols have contributed to solve them partly. In this paper, we propose a Context-Aware Adaptive opportunistic Routing algorithm（CAAR）. The algorithm firstly predicts the approximate location and orientation of the destination node by using its movement key positions and historical communication records, and then calculates the best neighbor for the next hop by using location and velocity of neighbors. In the unpredictable cases, forwarding messages will be delivered to the more capable forwarding nodes or wait for another transmission while the capable node does not exist in the neighborhood. The proposed algorithm takes the movement pattern into consideration and can adapt different network topologies and movements. The experiment results show that the proposed routing algorithm outperforms the epidemic forwarding（EF） and the prophet forwarding（PF） in packet delivery ratio while ensuring low bandwidth overhead.

Optimal adoptions of freemium version and patching strategy:Network and security externalities

The freemium pricing model has become mainstream in the software industry.A large user base can induce positive network effects while expanding security risks associated with unpatched users.This study explores a two-stage decision problem faced by software vendors that involves a freemium versioning strategy and a subsequent security-patching strategy when taking both the positive network externality and negative security externality into consideration.It is noteworthy that a joint effect of the two externalities on the vendor’s management decisions exists.First,we analytically derive three patching strategies for the vendor:PS_(1)(rebates all users),PS_(2)(rebates only freeware users),and PS_(3)(rebates no users).Our results indicate that,if the strength of the positive network externality is relatively low,the optimal security-patching strategy will be significantly affected by the negative security externality.Specifically,when the intensity of the negative security externality is low,the vendor’s optimal patching strategy will be PS_(1).However,with the increase in the negative security externality,the optimal patching strategy changes to PS_(2) and then to PS_(3),whereas the strategy spaces of PS_(1) and PS_(2) decrease in the positive network externality to zero.Nevertheless,if the strength of the positive network externality is relatively high,the vendor is better off selecting PS_(1) when the negative security externality is low.However,when the negative security externality is high,PS_(3) is optimal.Furthermore,based on optimal patching strategies,we reveal the optimal conditions required for the vendor to adopt the freemium model compared with commercial only.Of interest,we find that the vendor adopting the freemium version is also influenced by the interaction of the two externalities.Finally,through numerical experiments,we find that the vendor and social planner’s interests can be aligned under certain conditions.However,this is not always the case.