天然气:通向氢能时代的桥梁

文章概述了人类能源利用从柴薪、煤到石油、天然气的探索与转变历程,着重对天然气利用在解决城市燃料和空气污染、提高发电效率、推动分布式发电、生产合成氨和合成甲醇、推动燃料电池转向氢能经济时代等方面的优越性进行了阐述。     

基于ML和ESPRIT方法的OFDMA上行链路频偏估计算法

由于载波频偏会给正交频分多址接入OFDMA系统带来子载波之间干扰,从而造成多用户之间的干扰,导致系统性能下降。该文提出一种基于ESPRIT和ML方法联合估计的频偏估计算法。该算法首先使用ESPRIT方法估计出多个可能的频偏构成的子集,然后使用最大似然估计方法在这个有限子集合中搜索出估计的频偏。该算法解决了使用似然估计进行多维搜索的问题,大大降低了算法的复杂度,同时解决了多个频偏估计的问题。     

Polarized Optoelectronics of CsPbX3 (X = Cl,Br, I) Perovskite Nanoplates with Tunable Size and Thickness

Low dimensional semiconductor nanomaterials have shown their tailorable properties for a variety of promising applications in decades. Here a general strategy to synthesize all‐inorganic CsPbX₃ (X = Cl, Br, I or their mixture) perovskite 2D nanoplates by introducing additional metal halides MX'₂ or MX'₃ (M = Cu, Zn, Al or Pb, etc.; X' = Cl, Br or I) is reported. These CsPbX₃ perovskite nanoplates have uniform thickness and tunable size, which can be feasibly controlled by the component and ratio of the metal halides, temperature, time, and ligands. The well‐defined morphology of the nanoplates makes them ideal building blocks for the self‐assembly in the face‐to‐face and column‐by‐column arrangement. Compared to the optically isotropic CsPbX₃ nanocubes, the 2D CsPbX₃ nanoplates exhibit remarkable polarized UV–vis absorption and photoluminescence not only in liquid solvent and solid resin matrix, but also in self‐assembled films. An optoelectronic photodetector sensitive for linear polarized light is fabricated to demonstrate the proof‐of‐concept.     

碳纳米管薄膜微光纤气体传感器的模场分析

基于包层薄膜折射率对微光纤中传输光能量分布的影响,进一步用模场分析仪观察碳纳米管薄膜微光纤在与二甲苯气体接触时,输出光的能量分布和倏逝场的变化。实验结果显示,未镀膜的微光纤暴露在一定浓度的二甲苯气体环境下时,表现出对光很弱的约束能力;而把碳纳米管薄膜微光纤置于与之相同浓度的气体环境时,微光纤的输出光强减小,高阶模的能量发生不稳定的变化,最后待气体挥发完全至浓度稳定后,薄膜微光纤输出光场高阶模能量减小,微光纤的能量分布趋向于高斯分布。     

Simulations and experiments for optimal deployment of an RFID‐based location‐aware system

The proliferation of communication and mobile computing devices and local‐area wireless networks has cultivated a growing interest in location‐aware systems and services. An essential problem in location‐aware computing is the determination of physical locations. RFID technologies are gaining much attention, as they are attractive solutions to indoor localization in many healthcare applications. In this paper, we propose a new indoor localization methodology that aims to deploying RFID technologies in achieving accurate location‐aware undertakings with real‐time computation. The proposed algorithm introduces means to improve the accuracy of the received RF signals. Optimal settings for the parameters in terms of reader and reference tag properties were investigated through simulations and experiments. The experimental results indicate that our indoor localization methodology is promising in applications that require fast installation, low cost and high accuracy. Copyright © 2009 John Wiley & Sons, Ltd.     

刻纹光纤传感器的原理及灵敏度分析

介绍了一种新型的光纤传感器，采用热刻-酸蚀法在光纤上形成一些周期性刻纹结构，使得感受应变量的部分成为光纤本身的固有结构。这种光纤传感器具有线性、可重复的输入、输出响应且没有滞后效应，与其它传感器相比其最大的优点是灵敏度高、外形尺寸小。     

非致冷焦平面热成象技术及其应用

９０年代以后，非致冷红外焦平面技术的实用化成为红外热成象技术中最引入注目的突破之一，基估军事和民用领域的广泛应用前景受到国内外的普遍重视。本文综述了非致冷红外焦平面技术的两大技术途径及其特点、发展趋势和应用情况，并了发展我国非致冷红外焦平面技术的途径。     

高速高阶可编程数字滤波技术与实现

本文讨论了频率范围宽,连续可调的高速高阶数字滤波技术及其工程实现。运用IMSA100级联信号处理技术和8097BH单片机可编程控制技术,实现了数字滤波中心频率在50～500000Hz,数字滤波归一化带宽在7‰～5%范围内连续可变的功能。应用该技术所研制的数字滤波设备在卫星测控遥测系统中获得了良好的效果。     

Hydrogeochemistry and groundwater circulation in the Xi’an geothermal field, China

Geothermal waters from the Tertiary aquifers located at 1000–3000 m beneath Xi’an city, Shaanxi Province, China, show unique isotopic composition as compared to local groundwaters from shallower Quaternary aquifers. Positive oxygen shifts of as much as 8‰ VSMOW are observed, while the corresponding δ²H values remain essentially constant at about −80‰ VSMOW, which is significantly different from those of waters in the Quaternary aquifers with a mean δ²H value of −60‰ VSMOW. The strong ¹⁸O shift is a result of isotope exchange between geothermal water and carbonate minerals such as calcite over a residence time of several thousand years up to 30,000 years, based on ¹⁴C dating. A comparison of the isotopic composition of geothermal waters with neighbouring groundwater units on both sides of the Guanzhong Basin indicates that the geothermal reservoirs are recharged by rain that falls on the northern slope of the Qinling Mountains, south of the Xi’an geothermal field, but not from the North Mountains to the north of the field. Based on chemical geothermometers the highest temperature estimated for the Tertiary aquifers of the Xi’an area is around 130 °C.     

An integrated study of dropwise condensation heat transfer on self-assembled organic surfaces through Fourier transform infra-red spectroscopy and ellipsometry

Self-assembled monolayers (SAMs) formed by adsorption of 1-octadecanethiol [CH₃(CH₂)₁₇SH] and 16-mercaptohexadecanoic acid [CO₂H(CH₂)₁₅SH] onto gold-coated-copper substrates were applied to investigate the enhancement of dropwise condensation (DWC) heat transfer of steam at atmosphere pressure. A durability test was also conducted. Although hydrophobic SAMs increase the heat transfer coefficient by nearly an order of magnitude from that of filmwise condensation, it was found that DWC using octadecanethiol SAM as a promoter is a dynamic process in that the heat transfer coefficient decreases with time over 2 h. These results were reconfirmed by an integrated study using Fourier transform infra-red spectroscopy (FT-IR) and Spectroscopic Ellipsometry. We found that the monolayer of octadecanethiol becomes less crystalline with time, causing the film thickness and heat transfer coefficient to decrease. There was also some indications that, as SAMs were partly removed (leaving patches of the bare metal), contaminant from steam spontaneous adsorbed onto these high energy sites, resulting in a slightly higher heat transfer coefficient at a later stage of condensation.