用3D-FDTD法分析用于近场光存储的光纤探针电磁波传输特性

提高近场光存储的存储信息密度的关键主要在于掌握近场存储光纤探针的透光率、近场光斑直径尺寸以及场梯度等近场物理量。采用三维时域有限差分 (3D FDTD)法分析了可用于近场光存储的光纤探针尖的光学性质 ,对不同类型光纤的近场光场分布进行了数值计算 ,给出结果并进行比较 ,从光学性质的角度对其在近场光存储中的应用加以讨论。完全镀膜光纤尖在极近场处的光斑可获得 10nm的尺寸 ,远小于传统光纤光学聚焦的光斑尺寸大小。     

面向大规模认知诊断的DINA模型快速计算方法研究

在教育教学的过程中,如何诊断学生的知识水平是一个重要的问题.传统方法大多由教师根据学生的表现和成绩进行人工判断,存在效率低、主观性强的问题,且难以做到针对大量学生的个性化诊断.近年来,认知诊断模型中的DINA模型被广泛应用于诊断学生个性化知识掌握程度.然而传统DINA模型大多基于小样本数据,当面对在线教育带来的大规模数据处理需求时,存在收敛速度慢的问题,难以实际应用.针对DINA模型计算时间过长的问题,本文首先给出了DINA模型的收敛性证明,并提出了三种能够加速DINA求解的算法：（1）增量算法,它将学生数据划分为多个学生块,每次迭代只访问其中一个学生块;（2）最大熵方法,它只访问在极大化模型熵的过程中影响较大的学生数据;（3）基于前两者的混合方法.最后,本文通过真实数据和模拟数据上的实验,分析证明了三种方法均能在保证DINA模型有效性的情况下,达到几倍至几十倍的加速效果,有效地改善了DINA模型的计算效率.     

可见近红外波段碲镉汞材料光学常数测定与宽谱增透设计

将碲镉汞(Hg_(1-x)Cd_xTe)红外焦平面器件衬底去除后,其响应波段可拓展到可见光波段,在高光谱成像应用中可显著减小系统的尺寸和重量,对光电探测系统的小型化和微型化具有重要实用价值.而明确碲镉汞材料在可见近红外波段的光学常数,对碲镉汞器件在这一响应波段的性能研究具有重要意义.分别测量了不同组分碲镉汞材料的椭圆偏振光谱,拟合得到了其在400~1 600 nm波段范围内的光学常数值,并利用反射光谱对获得的光学常数进行了验证.采用这些碲镉汞外延材料光学常数测量值,并选用Zn S和YF3分别作为高低折射率的增透膜材料,针对不同响应波段的背入射可见近红外碲镉汞焦平面器件,设计了不同的宽谱增透膜系,响应波段范围内的平均透过率高于90%.     

基于锁相放大原理的微弱信号检测电路

针对目前成品锁相放大器价格昂贵且体积大,传统窄带滤波法性能和灵活性差的特点,设计了基于锁相放大器原理的微弱信号检测电路。本电路采用单片机作为激励信号和参考信号的发生器,利用带关断引脚的运放实现相敏检波器,整个电路仅使用了5个运算放大器和一些阻容元件。实验表明,本电路能实现了从信噪比为0.1的被测信号中提取有用信号幅值的功能,测量误差控制在5%以内。由于本电路有实现简单和成本低的特点,稍加修改后可作为模块电路用到其他测量系统当中。     

pin硅波导在1550 nm波段的光电流雪崩增强效应实验研究

The photocurrent effect in pin silicon waveguides at 1550 nm wavelength is experimentally investigated. The photocurrent is mainly attributed to surface-state absorption,defect-state absorption and/or two-photon absorption.Experimental results show that the photocurrent is enhanced by the avalanche effect.A pin silicon waveguide with an intrinsic region width of 3.4μm and a length of 2000μm achieves a responsivity of 4.6 mA/W and an avalanche multiplication factor of about five.     

Real Time Anomalous Trajectory Detection and Analysis

GPS-equipped taxis can be considered as pervasive sensors and the large-scale digital traces produced allow us to reveal many hidden facts about the city dynamics and human behaviors. In this paper we present a novel GPS-based taxi system which can detect ongoing anomalous passenger delivery behaviors leveraging our proposed iBOAT method. To achieve real time monitoring, we reduce the response time of iBOAT by more than five times with an inverted index mechanism adopted. We evaluate the effectiveness of the system with large scale real life taxi GPS records while serving 200,000 taxis. With this system, we obtain about 0.44 million anomalous trajectories out of 7.35 million taxi delivery trips, which correspond to 7600 taxis’ GPS records in one month time in the city of Hangzhou, China. Through further analysis of these anomalous trajectories, we observe that: (1) Over 60 % of the anomalous trajectories are “detours” that travel longer distances and time than normal trajectories; (2) The average trip length of drivers with high-detour tendency is 20 % longer than that of normal drivers; (3) The length of anomalous sub-trajectories is usually less than a third of the entire trip, and they tend to begin in the first two thirds of the journey; (4) Although longer distance results in a greater taxi fare, a higher tendency to take anomalous detours does not result in higher monthly revenue; and (5) Taxis with a higher income usually spend less time finding new passengers and deliver them in faster speed.     

基于符号映射分析的CO-OFDM系统信道估计研究

针对相干光正交频分复用(CO-OFDM)系统中光纤信道快变对系统可靠性和有效性的降低,设计了一种符号映射分析(ASM,analysis of symbols mapping)算法,通过对接收到的OFDM符号星座图进行分析,不断地对由信道估计得到的传递函数进行修正,在不需要大量导频的情况下能快速跟踪信道的变化。仿真结果表明:在40Gb/s的快变光纤信道CO-OFDM系统中,信噪比(SNR)为10dB,在误码率(BER)为10-3时ASM算法比常规的迫零估计(ZFE,zero forcing estima-tion)算法需要的导频间隔减小了1/2;在导频间隔为10、BER为10-3时,ASM算法比常规的ZFE算法有约3.5dB的SNR改善。     

基于故障补偿思想的导弹执行机构主动容错控制研究

为了提高导弹姿态控制系统的飞行可靠性,提出了基于故障补偿思想的导弹执行机构主动容错控制方法。该方法充分研究了一类导弹所采用的"+"型布局火箭发动机执行机构的结构和功能特点,分析了执行机构故障模式及其影响,在此基础上提出了主动容错控制方案,并推导出在执行机构卡死故障和恒值偏差故障情况下基于故障补偿思想的容错控制算法。仿真结果表明,该方法具有良好的容错控制效果,克服了传统被动容错控制方法在适用范围上的局限性。     

差分吸收光谱测量中LED光源恒温控制的实现

提出了一种差分光学吸收光谱（DOAS）测量中LED光源的恒温控制方法。采用半导体制冷片作为控温元件来控制LED温度,应用PID算法动态调节半导体制冷片的工作电流,实现了DOAS测量过程中LED光源的温度恒定。介绍了恒温控制系统的硬件设计和软件流程,并对控温效果和LED谱的稳定性进行了测试。测试结果表明,提出的恒温控制方法能有效克服环境温度变化对LED光源温度的影响,温度控制精度达到了±0.1℃。在相同的测试条件下与无恒温相比,具有恒温功能的LED光源剩余噪声明显偏低,进一步验证了设计方案的可行性。     

Photocurable 3D Printing of High Toughness and Self-Healing Hydrogels for Customized Wearable Flexible Sensors

Currently, most customized hydrogels can only be processed via extrusion-based 3D printing techniques, which is limited by printing efficiency and resolution. Here, a simple strategy for the rapid fabrication of customized hydrogels using a photocurable 3D printing technique is presented. This technique has been rarely used because the presence of water increases the molecular distance between the polymer chains and reduces the monomer polymerization rate, resulting in the failure of rapid solid-liquid separation during printing. Although adding cross-linkers to printing inks can effectively accelerate 3D cross-linked network formation, chemical cross-linking may result in reduced toughness and self-healing ability of the hydrogel. Therefore, an interpenetrated-network hydrogel based on non-covalent interactions is designed to form physical cross-links, affording fast solid-liquid separation. Poly(acrylic acid (AA)-N-vinyl-2-pyrrolidone (NVP)) and carboxymethyl cellulose (CMC) are cross-linked via Zn²⁺-ligand coordination and hydrogen bonding; the resulting mixed AA-NVP/CMC solution is used as the printing ink. The printed poly(AA-NVP/CMC) hydrogel exhibited high tensile toughness (3.38 MJ m⁻³) and superior self-healing ability (healed stress: 81%; healed strain: 91%). Some objects like manipulator are successfully customized by photocurable 3D printing using hydrogels with high toughness and complex structures. This high-performance hydrogel has great potential for application in flexible wearable sensors.