一种紧凑型宽带高功率微波驱动源

为实现对传输线开关振荡器或振荡天线进行快速充电,以提高其耐压能力和产生高频振荡信号的能量效率,本文研制了一种基于Tesla变压器的电容储能型脉冲驱动源。本文首先介绍该驱动源的工作原理和运行过程,接着利用等效电路方法分析了关键电路参数对负载充电过程的影响,然后介绍该驱动源的具体工程设计,最后介绍该驱动源初步测试结果以及将其应用于变压器油在10 ns量级脉冲下击穿特性研究的实验情况。实验表明,输出火花开关在中储电容器充电电压为-191 kV导通时,通过电感对等效电容为15 pF的传输线充电电压峰值为-224 kV,电压上升时间约10 ns。研究结果表明本文研究的驱动源能够满足对传输线开关振荡器等电容负载进行快速充电至数百kV高压的应用需求。     

FULL-RCMA: a high utilization EPON

This paper proposes an alternate solution for Ethernet passive optical networks. Our solution uses a novel protocol named full utilization local loop request contention multiple-access protocol to efficiently provide communications in passive optical networks. We study the physical layer implementation, as well as medium access control (MAC) layer protocol performance to illustrate the feasibility and benefit of our solution. The performance studies show that the MAC protocol is capable of offering 95% channel utilization under heavy load conditions. The performance results also indicate that delivery of multimedia traffic with a high quality-of-service can be achieved with our solution.     

In vivo Doppler shift measurements using multimode fiber-opticcatheters

A new fiber-optic catheter for in vivo blood-flow measurements has been developed. The catheter is designed to measure blood flow in both the forward (toward the catheter tip) and reverse (away from the catheter tip) flow directions. It consists of two multimode optical fibers with core diameter of 50 μm and cladding diameter of 125 μm. One fiber transmits the laser beam into blood and the other receives the backscattered light from the erythrocytes within the probe volume. In the flow experiment, it was found that the flow within the boundary layer is indeed laminar and, hence, the relationship between the Doppler shift frequencies and the flow velocities is linear, thereby making the linear calibration possible for predicting the free stream flow velocity. Plots of the maximum shift frequency (frequency at which the Doppler spectrum disappeared into the noise spectrum) against the flow velocities are found to be more linear in both the forward and reverse flow directions than that of the dominant shift frequency (frequency with the highest amplitude). These results were reaffirmed by the numerical flow simulation along the catheter side wall     

基于迁移学习的唐诗宋词情感分析

随着计算社会学的兴起,利用数据挖掘分析社会情感是近期的研究重点.当前的研究主要针对现代文本,对于古代诗歌这类短文本的情感分析相对较少.本文提出了一个基于短文本特征扩展的迁移学习模型CATL-PCO,通过分析诗歌情感对当时社会及文化进行进一步了解.该模型首先基于频繁词对对古文特征向量进行扩展,再通过迁移学习方式,建立三个分类器并投票得出最后的情感分析结果.CATL-PCO模型首先能够解决古文短文本特征稀疏的问题,在此基础上进一步解决由于现代译文信息匮乏所导致的古代诗歌情感分析困难问题,从而准确的分析古诗词情感倾向,从计算社会学的角度,增进对中国历史的认识.实验表明,当训练集为中国唐诗时,本文提出方法能够准确的对唐代诗歌进行情感分类,并能应用于唐代和宋代各个时期情感分析及代表流派分析.     

一种精简TCP/IP协议栈的设计与实现

阐述了TI的TMS320DM642的EMAC驱动程序的结构,设计并实现了一个精简协议栈。针对H.264视频传输提出了改进方案,以实现更好的视频通信质量。     

光纤布喇格光栅应力双折射的研究

实验研究了侧向挤压作用下的光纤布喇格光栅(FBG)产生的应力双折射现象,提出了一种消除横向应力对温度交叉敏感的简单而又有效的方法,从理论和实验上进行了分析与验证.研究表明,对FBG施加侧向挤压产生的双折射导致普通光纤布喇格光栅存在两个满足布喇格条件的反射光谱,且双峰间距在100 ℃的温度范围内变化了0.055 nm,利用该双峰间距的变化可消除温度传感中横向应力对它的交叉敏感,实现对温敏系数的修正及温度的校正,实验中测得的原始温敏系数是0.013 8 nm/℃,对温敏系数修正了0.005 nm/℃,对变化的温度校正了4 ℃.     

移动网智能管道发展的挑战和应对

探讨了移动智能管道的定义和内涵,分析目前移动网智能管道发展的架构、能力完善和协同、管道价值挖掘、运营机制优化这4个方面的挑战,并给出了应对策略。     

Robust Metallic Actuators Based on Nanoporous Gold Rapidly Dealloyed from Gold–Nickel Precursors

Dealloyed nanoporous gold (np-Au) has applications as oxygen reduction catalysis in Li-air batteries and fuel cells, or as actuators to convert electricity into mechanical energy. However, it faces the challenges of coarsening-induced structure instability, mechanical weakness due to low relative densities, and slow dealloying rates. Here, monolithic np-Au is dealloyed from a single-phase Au₂₅Ni₇₅ solid-solution at a one-order faster dealloying rate, ultra-low residual Ni content, and importantly, one-third more relative density than np-Au dealloyed from conventional Au₂₅Ag₇₅. The small atomic radius and low dealloying potential of the sacrificing element Ni are intrinsically beneficial to fast produce high relative density np-Au, as predicted by a general model for dealloying of binary alloys and validated by experiments. Stable, durable, and reversible actuation of np-Au takes place under cyclic potential triggering in alkaline and acidic electrolytes with negligible coarsening-induced strain-shift. The thermal and mechanical robustness of bulk np-Au is confirmed by two-order slower ligament coarsening rates during annealing at 300 °C and 45 MPa macroscopic yielding strength distinctive from the typical early onset of plastic yielding. This article opens a rich direction to achieve high relative density np-Au which is essential for porous network connectivity, mechanical strength, and nanostructure robustness for electrochemical functionality.     

4-(2,3,5,6-四氟-烷基取代苯乙基)苯甲酸-4'-氟-4-联苯酯的合成及液晶性研究

以2,3,4,5,6-五氟溴苯和脂肪醛为起始原料,设计并合成了一系列含四氟苯基亚乙基的四环酯类液晶化合物,通过偏光显微镜和DSC对其相变行为进行了研究.整个系列化合物有较宽的向列相温度范围,所合成的化合物中,随着末端碳链的增长,熔点和清亮点呈现下降趋势.     

基于ARX模型的压电智能结构振动预测控制

采用预测控制法对压电智能结构的振动主动控制进行了实验研究，通过实验方法建立了系统的ARX模型，并在此基础上设计了预测控制器对结构进行振动主动控制。实验结果验证了该方法在压电智能结构振动主动控制中的可行性和有效性。