Study on the difference of dispersion behavior between hydrogen and methane in utility tunnel

Compared to liquid/gas hydrogen tank, the pipeline is an economical way for hydrogen transportation. With the quick development of utility tunnel in China, hydrogen pipeline enters the gas compartment can be expected soon. However, all the safety requirements of the gas compartment in the current standards are designed for natural gas, and the applicability for hydrogen is unknown. Therefore, a series of studies were started to investigate the safety of hydrogen in utility tunnel. In this work, a real utility tunnel locates at Shanghai was selected as the physical object. A 3D numerical model was built and successfully validated by a scaled tunnel test. The model has the maximum deviation of +9.5%. After that, a comparatively study of the dispersion behavior of CH₄ and H₂ was conducted. The assumed scenario was a 20 mm small-hole leaks with gauge pressure of 1.0 MPa in the middle of the tunnel. Numerical results shown that, H₂ has a larger dispersion velocity and higher concentration, and is more dangerous compared to CH₄. The current emergency ventilation strategy of air change rate of 12 times/h is not effective enough to dilute the H₂ flammable cloud. The alarm time of the testing points shown strong linear law. There was a sharp variation in the range of 20%–100% LFL (Lower Flammable Limit), so the alarm strategy in the tunnel standards is too ideal for both CH₄ and H₂. The numerical results in the present study could provide a guidance for the design and safety management of the hydrogen tunnel.     

Influence of the ZrB2 content on the anti-oxidation ability of ZrB2-SiC coatings in aerobic environments with broad temperature range

ZrB₂-SiC coatings with different ZrB₂ contents were prepared by liquid phase sintering. The oxidation processes of coatings were explained according to TG results of ZrB₂-SiC coatings and powders tested from 298 K to 1773 K. Results show that, increasing ZrB₂ content made the weight of the samples changed from weight-loss of 10.04% to weight-gain of 0.14%, while the fastest weight-loss regions were narrowed, whose inflection points reduced from 1310℃ to 1050℃. Increasing ZrB₂ content made the relative oxygen permeability of the ZrB₂-SiC/SiC coatings reduced from 40%–60% to -10%-5%. Increasing ZrB₂ content enhanced high-temperature stability of coatings, making final weight of samples changed from weight-loss of 0.16% to weight-gain of 0.11% after oxidation at 1773 K for 200 h. The peeling and dispersion of Zr-oxides formed Zr-B-Si-O compound glass layer, presenting enhanced stability, dispersion strengthening and pinning effect of Zr-oxides, which were responsible for the excellent anti-oxidation protective effect of coatings in a broad temperature region.     

利用高频结构仿真器分析波导魔T

高频结构仿真器（HFSS）是一种微波器件设计软件，该软件界面友好，通过仿真计算减小了调试工作量，使得微波器件的设计变得简单易行。本文利用HFSS对波导魔T进行了仿真分析，得到了该器件的S参数和动、静态场的分布情况，并对该器件进行了优化设计。     

DISPERSION COMPENSATION CFBG IN100km 10Gbit／s RECIRCULATING SYSTEMS

A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG.     

Estimation of the Longitudinal Dispersion Coefficient Using the Velocity Profile in Natural Streams

In this study, a theoretical method for predicting the longitudinal dispersion coefficient is developed based on the transverse velocity distribution in natural streams. Equations of the transverse velocity profile for irregular cross sections of the natural streams are analyzed. Among the velocity profile equations tested in this study, the beta distribution equation, which is a probability density function, is considered to be the most appropriate model for explaining the complex behavior of the transverse velocity structure of irregular natural streams. The new equation for the longitudinal dispersion coefficient that is based on the beta function for the transverse velocity profile is developed. A comparison of the proposed equation with existing equations and the observed longitudinal dispersion coefficient reveals that the proposed equation shows better agreement with the observed data compared to other existing equations.     

具有透明波导的量子阱半导体激光器及其光集成技术

本文论述了具有透明波导结构的量子阱半导体激光器及其光集成技术的其本原理及主要优点。尤其在实现高功率窄光束输出的光集成器件方面更显出其独特的优点。     

色用缓变光纤中交叉相位调制不稳定性分析

从非线性薛定谔方程出发得到了色散缓变光纤（DDF）中交叉相位调制（XPM）不稳定增益谱。研究了增益谱随入纤功率及光纤纵向色散参量的变化关系。结果表明：反常色散区的增益谱宽比正常色散区宽，且峰值增益高：DDF中XPM不稳定增益谱宽比常规光纤的宽，二者的比值随传输距离和光纤色散参量的乘积成指数增长；DDF的反常色散区是产生调制不稳定的较好的色散介质。     

薄膜干涉型光学全通滤波器的设计与分析

设计并分析了用于多信道色谱补偿的薄膜Gires-Tournois干涉仪（GTI）型光学全通滤波（OAPF），讨论了反射镜的膜层结构对器件 的群延迟谱和反射谱的影响，。以及大角度入射引起的偏分离现象和幅度畸变现象，给出了单级和多级串拉OAPF的初步设计结果。     

矩形介质波导阵列的一种新型分析方法

本文将等效介电常数近似分析方法在应用范围和处理方法上进行了一些改进．发展为双等效介电常数近似分析法，然后用它来分析矩形介质波导阵列．推得两个一维周期的耦合特征方程。如果将Macatili方法应用范围扩展用来研究该波导阵列也会得到同样的结果，它们都能在二维平面上较准确地反应出通带和阻带等主要周期特性。     

强度调制／直接检测（IM／DD）光纤通信系统色散限制的研究

通过引入归一化脉宽Ｐ和相对脉冲展宽因子ｑ，提出了一个适用于ＩＭ／ＤＤ系统中各种眼图恶化量ｘ和归一化脉宽Ｐ的色散限制改进公式。通过与其它理论的比较、计算机仿真和对实验数据的分析，验证了该公式的正确性，并给出了其它结果的限制条件。研究表明：当眼图恶化量ｘ为１ｄＢ左右时，对２．５Ｇｂ／；外调制信号（α＝０）而言，非色散位移光纤ＩＭ／ＤＤ系统的色散因子γ约等于０．７９，所对应的系统再生中继距离约为９００余公里。