保温时间对ZL102合金熔液质量的影响

研究了实际生产中，保温时间对ZL102铝液质量的彤响，探讨了保温时间与变质效果和针孔度之间的关系．结果表明：Sr变质达到最佳变质效果大约需要60min；随着保温时间的延长，Sr以大约每h0.002％(质量分数)的速率烧损，其变质效果可以持续长达6～7h；精炼变质后30～90min，铸件中针孔度最小．铝液质量最好。     

乘积合并接收的差分跳频通信系统在瑞利衰落信道上抗部分频带干扰的性能分析

该文介绍了一种新型短波跳频通信技术差分跳频,频率转移函数设计和信号的检测方法是差分跳频中的关键技术。在瑞利衰落信道上,在有部分频带干扰和加性高斯白噪声共存的条件下,采用乘积合并接收的方法,对差分跳频通信系统的误符号性能进行了理论分析,同时做出相应的计算机仿真。结果证实了,在瑞利衰落信道上差分跳频通信系统采用乘积合并接收的方法要比采用线性合并接收的方法具备更好的抗部分频带干扰的性能。     

Nonselective Fading Channel Estimation with Nonuniformly Spaced Pilot Symbols

Recently, there has been great demand for multimedia and data communications in mobile communication systems. In order to enhance voice quality and increase packet data throughput rate for the existing mobile systems and the next generation mobile systems, a number of new standards are being developed. 8-PSK/QPSK modulation has been adopted by most of these standards as one of the modulation schemes, and nonuniformly spaced pilot symbols are employed in slot structures to have successful demodulation. In this paper, an accurate and computationally efficient method is presented for estimating nondispersive channel fading with non-uniformly spaced pilot symbols. By employing a least-squares method with time-variant complex-valued coefficient polynomials, it is proven that nonselective channel fading of each slot can be estimated by the product of a constant matrix and the fading at pilot symbol locations of the slot. The constant matrix is further optimized by least-squares off-line training method provided by this paper. Using the estimated fading process, the fading on the data symbols can be removed by using the estimated amplitude and phase of the fading as the reference, greatly improving the BER. Closed form results for the BER of coherent 8-PSK are included in this paper as well. Simulation results indicate that our method provides BER performance very close to the analytic BER result.     

无线通信系统的挑战与解决方案

无线通信系统受到空间信道特性的影响,系统中的许多措施都是基于信道特性进行设计的。无线设备在进行信号处理的同时,也会产生系统所不需要的产物。该文对各种原因进行了分析,结合3G系统给出了相应的解决方案。     

Color fading of reactive-dyed cotton using UV-assisted ozonation

Fashion trends have promoted the use of oxidants in the textile sector recently. Conventionally, oxidants require an aqueous bath, with ozone; the worn style or faded effect on textile products could be achieved more ecologically. UV-assisted ozonation has been studied or applied to certain areas but not fading reactive-dyed textiles. In this study, the UV-assisted ozonation on color-fading reactive-dyed cotton was investigated. The effect of UV on ozone fading effect and the comparison of UV-assisted ozonation with conventional color-fading processes (hydrogen peroxide and chlorine) were carried out in terms of fading efficiency, negative impacts on fabrics’ mechanical properties, namely, tensile strength and elongation, tearing strength and abrasion resistance, and surface microstructure. It is found that UV strengthens the fading effect (up to 2.7 times) of ozonation with slight loss of cottons’ mechanical properties. UV-assisted ozonation is not only more effective than conventional fading processes in the respect of fading efficiency but also less negatively influenced fabrics mechanical properties. Additionally, it comparatively requires far less the use of water and power, so we may conclude that it proposed an excellent potential to alternate the conventional processes.     

A BCH code assisted modified NCO based LSPF-DPLL topology for Nakagami-m,Rayleigh and Rician fading channels

In spite of the rapid developments in communication technologies over the past few decades, which include attractive features offered by the presently used 3G/4G systems, it continues to be a challenge to render adequate services with the exponential rise in the number of users and applications. However, efficient alternatives, including 5G methods, are being explored to mitigate this problem. Such systems also aspire to render sustained coverage with lesser constraints on power and Quality of Service (QoS). Today, versatile Digital Phase Locked Loop (DPLL) based packages find place as communication receivers. Of late, a Least Square Polynomial Fitting DPLL (LSPF-DPLL) with Modified Phase Resolving Numerically Controlled Oscillator (MPR-NCO), which demonstrates excellent time performance and maintains satisfactory error rates, was proposed. A Bose, Chaudhuri, and Hocquenghem (BCH) channel code assisted version of the MPR-NCO based LSPF-DPLL system is presented here. The proposed system exhibits better Bit Error Rate (BER), throughput, and baud rate levels over the previously proposed uncoded version.     

Investigation of thermoluminescence and kinetic parameters of gamma ray exposed LiF: Sm3+, Eu3+ nanophosphors for dosimetric applications

Thermoluminescence (TL) properties of LiF: Sm³⁺ (0.05?mol%) co-doped with Eu³⁺ (0.02, 0.04, 0.06, 0.08?mol%) nanophosphor for the applications of TL dosimetry have been studied. The nanophosphors have been synthesized by chemical co-precipitation method at 8?pH value. The phase purity of the prepared samples has been confirmed by using X-ray diffraction (XRD) data. The XRD peaks broadening revealed the formation of the nanostructure, complemented by the TEM image. For TL studies, the samples have been irradiated with gamma rays using ⁶⁰Co source in the irradiation dose range of 0.1?kGy to 30?kGy. In gamma exposed samples, the TL glow curve consists of single glow peak at 410?K and three shoulder peaks at 475?K, 550?K and 632?K. The dosimetry properties such as the effects of exposure doses, heating rates and fading characteristics have also been studied. The kinetic parameters such as activation energy (E), the frequency factors (s) and order of kinetic (b) of the glow curves have also been calculated by using Chen's peak shape method. The linear behavior of TL intensity with radiation doses and low fading shows that the LiF: Sm³⁺, Eu³⁺ Nanophosphor is a potential candidate for dosimetry applications.     

移动通信多普勒频移与高铁覆盖技术

介绍多普勒频移实际是频谱扩展,等效为衰落信道,限制了低速率数据的传送。当今的2G与3G在列车时速不超过500km时均可以对抗多普勒频移,影响通信的主因是快速瑞利衰落。     

网格编码调制的最新进展及其在多径衰落信道中的应用

本文综述了网格编码调制（ＴＣＭ）技术提出的背景、回顾了其发展过程的两上里程碑事件；论述了近年来通信系统飞速发展，ＴＣＭ在纠错抗干扰 最新进展和研究动向；给出了ＴＣＭ技术在多径快衰落干扰严重的陆地数字移动信道中的应用，并特别对此研究中的技术热点问题；非欧氏度量空间判据的提出进行了概述，最后，指出了目前ＴＭＣ技术研究中亟待解决的一些关键性技术问题。