大气折射对可见光波段辐射传输特性的影响

折射是影响辐射传输的重要因素. 为分析大气折射对辐射传输的影响, 基于Monte Carlo方法, 给出了考虑大气折射的矢量辐射传输模型, 实现了均匀气层和耦合面处光子随机运动过程的模拟, 实现了直射光及漫射光Stokes矢量、偏振度和辐射通量等参数的计算. 在考虑和不考虑大气折射两种条件下, 验证了模型的准确性; 在纯瑞利散射条件下, 讨论了大气折射对不同方向漫射光Stokes矢量的影响; 在不同太阳天顶角、大气廓线、气溶胶及含云大气条件下, 分析了大气折射对辐射传输过程的影响. 结果表明: 大气折射对漫射光Stokes矢量的影响主要体现在天顶角70°–110°区间, 且随着太阳入射角增大, 其影响更为显著; 不同大气廓线情形下, 大气折射对Stokes矢量的影响不一致, 其原因是不同大气廓线对应的折射率廓线存在差异. 含云及含气溶胶大气条件下, 大气折射对辐射传输的影响变弱, 沙尘型及海盐型气溶胶条件下, 折射对辐射传输的影响强于可溶型气溶胶情形; 不同形状气溶胶条件下, 大气折射对辐射传输的影响也存在显著差异; 不同云高条件下, 大气折射对漫射光Stokes矢量的影响无显著差异, 但随着云光学厚度增大, 大气折射的影响减弱.     

衬底加热和电极修饰对提高有机场效应晶体管性能的影响

通过衬底加热和氧化钼(MoO3)修饰源漏极制备了并五苯有机场效应晶体管.研究了衬底温度和电极修饰层厚度对器件性能的影响.实验结果表明:当衬底温度为60℃、MoO3修饰层为10 nm时,器件性能获得了显著增强,场效应迁移率由原来的3.39×10-3 cm2/(V·s)提高到2.25 ×10-1 cm2/(V·s),阈值电压由12 V降低到3V.器件性能的改善归因于:衬底加热可以优化有源层形貌,改善载流子传输;而MoO3修饰层显著降低了电极与有源层之间的接触势垒,提高了载流子的注入.因此,衬底加热与电极修饰对于制备高性能有机场效应晶体管是不可或缺的优化手段.     

操控非线性损耗实现稳定的高功率单频激光及可调谐激光的输出

通过操控线性和非线性损耗,使激光器满足单频运转的物理条件,获得了稳定高功率单频激光输出.利用非线性损耗取代了现有的标准具锁定技术,实现无调制锁定的宽带连续可调谐激光输出.     

锂离子电池多孔电极理论的回顾与新思考

本文总结了Newman多孔电极理论的基本内容,提出若干改进思路. 提出基于离子-空穴耦合传输机制描述浓电解质中的离子输运过程,在此基础上引入离子-电子耦合转移反应的思想处理电极材料中的离子传输问题,并通过计算嵌锂材料的离子扩散系数验证其合理性. 总结了描述多孔电极多尺度结构的相关理论和技术,表明均质化方法和基于结构重建的介观模拟方法均能给出比较合理的有效输运参数,从而提高多孔电极理论模拟结果的准确性.     

基于S-型光催化机制CuInS2内嵌中空凹面氮化碳光催化分解H2O制H2（英文）

光催化解离H2O合成H2是绿色可再生的太阳能光子能量转换策略之一.目前,增强光催化材料对太阳能光子的捕获并将之有效利用仍然是一个具有挑战性的课题.光催化解离H2O反应包括三个过程:太阳能光子能量促使光生电子在半导体材料带隙中的跃迁;光生电子定向传输;光生电子与吸附在半导体材料表面的H2O分子发生反应.第一过程需要强的太阳光子捕获能力以产生足够的光生载流子;第二、三过程在动力学上反映了光生载流子在各个竞争过程中能否有效利用的问题,如光生电子迁移与H2O作用的速度很慢(~μs),而电子与空穴的复合速度快(~ps).目前研究者很难协调半导体材料的电学和光学特性以满足光生载流子在热力学和动力学两方面的要求.g-C3N4是由C、N原子通过sp2杂化组成的二维π共轭体系.当g-C3N4结构偏离二维平面时,共轭体系的π电子由凹面迁移到凸面,促使凹、凸面形成表观电势差,有利于电子的定向传输.本文通过卷曲sp2杂化离域均三嗪体系偏离二维平面,得到空心凹面g-C3N4结构,便捷地优化了半导体的电子结构.将CuInS2嵌入生长于空心g-C3N4的凹面,所构成的半导体光催化材料CuInS2@C3N4展现了增强的光捕获能力,以及电子定向传输转移能力.结合XPS、光电流测试、电化学阻抗谱、稳态及瞬态荧光等表征手段揭示空心g-C3N4凹、凸面表观电势差驱动光生电子以S-型光催化作用机制从CuInS2的Cu 2p向g-C3N4的N 1s的路径转移.因而,所构建的CuInS2@C3N4在可见光激发下产氢效率提高到373μmol·h^?1·g^?1,其产氢效率分别是二维平面g-C3N4负载1 wt%Pt和3 wt%Pd效率的1.57倍和1.35倍,表明空心g-C3N4凹、凸面电势差可以显著地促进光生电子分离和利用率,从而提高光催化解离水制氢效率.本文可增强g-C3N4的可持续太阳能转换性能,也适用于其他半导体材料以替代贵金属光催化体系,降低光催化产氢技术成本,促进光催化技术的应用.     

Experiment on 60-GHz MMW transmission performance in an optical fiber and wireless system

We experimentally investigate the transmission performance of 60-GHz signals over standard single-mode fiber (SSMF) and wireless links at different bit rates. Experimental results show that in a transmission of over 10-km SSMF and 1.3-m wireless link, bit rate reaches up to 5 Gb/s and bit error rate (BER) is less than 10 4 . The main limiting factor in such radio-over-fiber (ROF) systems is intersymbol interferences caused by the so-called walk-off effect when BER is below 10 8 . In addition, a transmission of over 20-km SSMF without chromatic dispersion compensation is briefly investigated. For a BER of 10 8 , the optical penalty is 2 dB.     

Transmission-mode GaN photocathode based on graded Al_xGa_(1-x)N buffer layer

We create a GaN photocathode based on graded Alx Ga1-x N buffer layers to overcome the influence of buffer-emission layer interface on the photoemission of transmission-mode GaN photocathodes.A gateshaped spectral response with a 260-nm starting wavelength and a 375-nm cut-off wavelength is obtained.Average quantum efficiency is 15% and short wavelength responses are almost equivalent to long wavelength ones.The fitted interface recombination velocity is 5×104 cm/s,with negligible magnitude,proving that the design of the graded buffer layers is efficient in obtaining good interface quality between the buffer and the emission layer.     

160-Gb/s polarization-multiplexing optical NRZ-DQPSK transmission using differential detection

Using differential detection,we perform polarization-multiplexing 160-Gb/s optical non-return-to-zero(NRZ) differential quadrature phase shift keying(DQPSK) signal transmission over 100-km standard single mode fiber at a bit error rate(BER) of less than 10-9.The enabling technology includes clock recovery,fine dispersion compensation,and polarization tracking for de-multiplexing.Furthermore,a hybrid clock recovery scheme is proposed.The scheme is realized with ordinary devices using an optoelectrical modula...     

The wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges

In this paper,wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges are investigated using the wave approach.The dynamic responses,active and reactive power flow in the finite plate are calculated by the Mindlin plate theory (MPT) and classic plate theory (CPT).To satisfy the boundary conditions and continuous conditions at the coupled junction of the finite L-shaped plate,the near-field and far-field waves are entirely contained in the wave approach.The in-plane longitudinal and shear waves are also considered.The results indicate that the vibratory power flow based on the MPT is different from that based on the CPT not only at high frequencies but also at low and medium frequencies.The influence of the plate thickness on the vibrational power flow is investigated.From the results it is seen that the shear and rotary inertia correction of the MPT can influence the active and reactive power at the junction of the L-shaped plate not only at high frequencies but also at low and medium frequencies.Furthermore,the effects of structural damping on the active and reactive power flow at the junction are also analyzed.     

土体水分传输的温度效应试验系统设计与应用

自制了一套用于研究温度作用下土体水分传输机制的室内试验模拟系统.采用水浴加热替代电阻丝直接加热的方案,解决加热不均匀且不容易控制温度的难题.应用串行通讯接口技术把智能温度控制仪表和微机连接,实现了温度自动控制和采集的自动化.开展了7组试验耗时接近1年,试验结果表明,该系统性能稳定、部件之间兼容性较好,连续工作30天温度...