An error control scheme for transmission of vector quantizationdata over noisy channels

This paper presents an error control scheme for transmitting vector-quantized data over noisy channels. First, we review a self-organizing feature map (SOFM) based approach to construct the mapping from the codebook of the quantizer to the channel signal set of the communication system. This approach is robust with respect to channel noise even if we do not use any error control scheme in the communication system. Afterwards, a new trellis type quantizer, namely, the trellis coded Kohonen (1984) map (TCKM), is presented. The design process of the TCKM, which is based on the neighborhood structure of SOFMs, is simpler than that of conventional trellis coded vector quantizers (TCVQs). Simulation results show that the performance of TCKMs is comparable with that of TCVQs. Last, we introduce the error control scheme based on the concepts of the above two applications of SOFMs. Simulation results show that the proposed error control scheme is more robust with respect to channel noise. The advantage of our approaches mentioned above is that the design processes of transmission systems are predefined before the construction of the codebook. Thus, different codebooks with the same neighborhood structure can share the same design     

Scalar quantisation of LSF parameters using vector measurement

A new form of line spectral frequency (LSF), bounded line spectral frequency, is presented. It is shown that the new representation is more efficient than the direct line spectral frequency and the differential line spectral frequency (DLSF). By using a vector measure, the scalar quantisation of tenth-order linear predictive coding (LPC) parameters can be coded at 28 bit/frame with a transparent quantisation quality     

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。     

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.     

Low-rate turbo-Hadamard codes

This paper is concerned with a class of low-rate codes constructed from Hadamard code arrays. A recursive encoding principle is employed to introduce an interleaving gain. Very simple trellis codes with only two or four states are sufficient for this purpose, and the decoding cost involved in the trellis part is typically negligible. Both simulation and analytical results are provided to demonstrate the advantages of the proposed scheme. The proposed scheme is of theoretical interest as it can achieve performance of BER=10/sup -5/ at E/sub b//N/sub 0//spl ap/-1.2dB (only about 0.4 dB away from the ultimate low-rate Shannon limit) with an information block size of 65534. To the authors' knowledge, this is the best result achieved to date with respect to the ultimate Shannon limit. With regard to practical issues, the decoding complexity of the proposed code is considerably lower than that of existing low-rate turbo-type codes with comparable performance.     

Annealing before gate metal deposition related noise performance in AlGaN/GaN HEMTs

For a further improvement of the noise performance in AlGaN/GaN HEMTs, reducing the relatively high gate leakage current is a key issue. In this paper, an experiment was carried out to demonstrate that one method during the device fabrication process can lower the noise. Two samples were treated differently after gate recess etching: one sample was annealed before metal deposition and the other sample was left as it is. From a comparison of their Ig-Vg characteristics, a conclusion could be drawn that the annealing can effectively reduce the gate leakage current. The etching plasma-induced damage removal or reduction after annealing is considered to be the main factor responsible for it. Evidence is given to prove that annealing can increase the Schottky barrier height. A noise model was used to verify that the annealing of the gate recess before the metal deposition is really effective to improve the noise performance of AlGaN/GaN HEMTs.     

Electrically injected single-defect photonic bandgapsurface-emitting laser at room temperature

An electrically injected defect-mode photonic bandgap microcavity surface-emitting laser at room temperature is demonstrated for the first time. 931 nm lasing is observed under pulsed excitation conditions. With a threshold current of 300 μA. Near- and far-field modal characteristics of the emission confirm lasing from the defect-related microcavity in the photonic bandgap crystal     

高机动目标对雷达检测的影响分析

针对无人飞机、导弹、卫星等高速目标机动飞行的特点,分析了目标飞行过程中相对雷达径向速度、径向加速度以及加加速度随时间的变换关系,并利用高次幂相位回波信号建立了信号模型,研究了高次相位对常规方法进行目标检测的影响,获得了最佳积累脉冲数与信噪比、加加速度的关系;最后,提出一种利用短时分数阶傅里叶变换(STFRFT)对三次相位信号进行分析和参数估计的方法,仿真表明该算法处理性能高于傅里叶变换,可为实际雷达检测高机动目标提供理论参考。