广义正交码索引调制系统的性能分析

摘 要：为了提高码索引调制（code index modulation，CIM）系统的传输效率，提出了一种具有更低复杂度的单输入单输出（single input single output，SISO）的广义正交码索引调制（generalized orthogonal code index modulation，GQCIM）系统。CIM 系统使用扩频码和星座符号传输信息，但只能激活两个扩频码索引和一个调制符号。而 GQCIM 系统以一种新颖的方式克服了只激活一个调制符号的限制，同时充分利用了调制符号的正交性，增加扩频码索引以传输更多的额外信息位，提高了系统的传输效率。此外，分析了GQCIM系统的理论性能，推导了误码率性能的上界。通过蒙特卡罗仿真验证了GQCIM系统的性能，对比发现GQCIM系统的理论和仿真性能一致。而且在相同的传输效率下，结果显示GQCIM系统的性能优于同样具有正交性的调制系统，如广义码索引调制（generalized code index modulation，GCIM）系统、CIM系统、码索引调制-正交空间调制（code index modulation aided quadrature spatial modulation，CIM-QSM）系统、码索引调制-正交空间调制（code index modulation aided spatial modulation，CIM-SM）系统、脉冲索引调制（pulse index modulation，PIM）系统。     

Effects of the film thickness and poling electric field on photovoltaic performances of (Pb,La)(Zr,Ti)O3 ferroelectric thin film-based devices

The ferroelectric photovoltaic (FPV) effect obtained in inorganic perovskite ferroelectric materials has received much attention because of its large potential in preparing FPV devices with superior stability, high open-circuit voltage (V_oc) and large short-circuit current density (J_sc). In order to obtain suitable thickness for the ferroelectric thin film as light absorption layer, in which, the sunlight can be fully absorbed and the photo-generated electrons and holes are recombined as few as possible, we prepare Pb_0.93La_0.07(Zr_0.6Ti_0.4)_0.9825O₃ (PLZT) ferroelectric thin films with different layer numbers by the sol-gel method and based on these thin films, obtain FPV devices with FTO/PLZT/Au structure. By measuring photovoltaic properties, it is found that the device with 4 layer-PLZT thin film (~300 nm thickness) exhibits the largest V_oc and J_sc and the photovoltaic effect obviously depends on the value and direction of the poling electric field. When the device is applied a negative poling electric field, both the V_oc and J_sc are significantly higher than those of the device applied the positive poling electric field, due to the depolarization field resulting from the remnant polarization in the same direction with the built-in electric field induced by the Schottky barrier, and the higher the negative poling electric field, the larger the V_oc and J_sc. At a -333 kV/cm poling electric field, the FPV device exhibits the most superior photovoltaic properties with a V_oc of as high as 0.73 V and J_sc of as large as 2.11 μA/cm². This work opens a new way for developing ferroelectric photovoltaic devices with good properties.     

Tris(acrylato)uranylates as a scaffold for NLO materials

Novel uranyl acrylate complexes with general formula R[UO₂(CH₂CHCOO)₃] (RK⁺, NH₄⁺, Rb⁺, or Cs⁺) were synthesized and characterized by X-ray diffraction, IR spectroscopy and second harmonic generation (SHG) measurements. All four compounds are isostructural and crystallize in the non-centrosymmetric P2₁3 space group. Acrylate anions act as bidentate chelating ligands forming [UO₂(CH₂CHCOO)₃]⁻ complexes which are connected through electrostatic interactions with counter ions. SHG measurements revealed the inverted correlation between the Q = I_2ω/I_2ω SiO₂ values and the radii of counter ions.     

Mesoporous yolk-shell structure Bi2MoO6 microspheres with enhanced visible light photocatalytic activity

Mesoporous yolk-shell structure Bi₂MoO₆ (BMO-YS) microspheres were successfully synthesized via a facile solvothermal route in Bi₂MoO₆ precursor solution. The morphology, structure and photocatalytic performance of the BMO-YS in the degradation of Rhodamine B (RhB) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption–desorption, UV–vis absorption spectroscopy and electrochemical impedance spectra, respectively. The as-prepared BMO-YS mainly consists of microspheres with diameters of about 1.5 μm. The photocatalytic studies reveal that the BMO-YS not only exhibits optimum photocatalytic performance, which may be attributed to the excellent charge separation characteristics and the enhanced light absorption offered by its unique yolk-shell structure, but also possesses excellent recyclability for photocatalysis.     

基于差动共焦显微技术的微区拉曼光学系统构建与实验研究

研制了一种基于差动共焦显微技术的微区拉曼光学系统装置,对无机样品进行微区拉曼光谱探测。传统显微共焦拉曼光谱技术没有强调系统的定焦能力,而所研制的光学系统装置利用差动共焦曲线过零点与焦点位置精确对应的特性,采用反馈控制技术,具有长时间定焦功能。在微区拉曼散射信号收集时,采用多模光纤空间耦合技术,以光纤代替传统物理探测针孔,提高了环境抗干扰能力,优化了系统结构和装调性能。实验结果表明:该装置具有较高稳定性,可有效探测单壁碳纳米管在1581.510 cm^-1,2708.065 cm^-1特征峰处的拉曼频移及纯物质硫在153.113 cm^-1,219.917 cm^-1,473.322 cm^-1特征峰处的拉曼频移并且实现碳管的单线检测,满足了光谱探测系统装置设计需求。     

移液器容量自动校准系统研究

针对移液器人工校准中存在的按压不稳、温度偏差、数据无法批量处理等缺陷,提出了一种基于模拟人工按压的移液器容量自动校准方法。通过测量移液器按钮2个停止点的压力值,获取近似按压的距离;分析数据并与人工操作进行比对,得出模拟手动按压的最佳按压距离。开发了一套同时校准4支移液器容量的自动化装置,采用机械手和LabVIEW软件智能控制取液、排液、称量、数据处理等工作,实现了自动校准。研究结果表明,与人工操作相比,重复性减小了0.0%~0.9%,相对误差减小了0.1%~0.7%。     

仿柳叶形静态混合元件的流动及混合特性研究

与现有的叶片规则排列的静态混合器相比,仿柳叶结构的不规则叶片排列方式更容易使气流的流动变得紊乱复杂,加剧微团间相互作用,实现短距离混合。本研究采用FLUENT(商用计算流体力学)软件模拟了在叶片与水平方向轴线分别呈不同角度时仿柳叶型混合元件的抗流作用,并在风洞中利用热线风速仪完成了速度场测量。研究表明:静态混合元件不同叶片角度下的流场湍动能分布趋势基本相同;其沿程压降变化趋势也基本一致,当速度标准偏差系数小于20%,叶片与轴线夹角为60°时气流混合距离最短。结合CO与空气在混合装置内的混合情况分析得:仿柳叶型静态混合元件叶片角度的增加能够使流体在速度以及浓度混合均匀时所需距离变短。     

功率型LED瞬态温度场及热应力分布的研究

针对功率型LED器件的热特性,以热应力理论为依据,采用有限元软件ANSYS进行热应力计算,得到了Lumileds的1 W LED瞬态温度场和应力场分布云图,基板顶面平行于X轴路径上的热应力,应变及剪应力的分布曲线.模拟结果表明最大应力集中在键合层边角处;轴向最大位移在透镜与热沉接触边缘;最大剪应力集中在键合层的边角区域...     

低功耗超声流量计的研究

针对超声波流量测量中管道结构对测量精度的影响,采用Fluent仿真软件模拟了不同管道中流体的流动状况,对管道内的超声波信号进行了分析和比较,设计了超声波流量传感器,并应用设计的流量传感器,研制了超声波流量积算仪的硬件电路和软件,最终的样机实验结表明,该超声流量计流量误差小于±2%,系统的平均工作电流为35μA。     

一种小流量区水表检测系统的开发

针对旋翼式水表在小流量区误差检测效率低下、人为因素影响大等缺点,通过对水表计量误差的分析和现有检测台架的改进,将自主设计的新型光电反射传感器、ZigBee无线数据传输技术与上位机监控界面相结合,最后研制了小流量水表快速误差检测系统,并对水表在小流量区进行了误差检测试验.实验结果表明,该系统能够在小流量区对水表进行快速误差检测,具有结构简单、安装方便、测量精度高、可靠性好等特点.