Wind energy potential in Aden-Yemen

The wind energy resource is very large and widely distributed throughout the world as well as in Yemen. Aden possesses a very good potential of wind energy. In this article a number of years data on wind speed in Aden has been studied and presented. A statistical analysis was carried out from which the annual wind speed was found to be 4.5 m/s and most of the time the wind speed is in the range of 3.5–7.5 m/s. The wind speed distributions were represented by Weibull and Rayleigh distributions. It was found that the Rayleigh distribution is suitable to represent the actual probability of wind speed data for Aden. The wind speed data showed that the maximum monthly wind speed occurs in the month of February with the maximum in the month of June. It is concluded that Aden can be explored for wind energy applications.     

Effect of Plasma Electrolytic Oxidation coating on the specific strength of open-cell aluminium foams

Plasma Electrolytic Oxidation (PEO) coating treatment is applied to open celled aluminium foams with different structures, aiming to enhance the mechanical performance of the composite material. The mechanical properties of the coated foams produced are assessed experimentally, both in tension and compression. From experimental results, yield stress is found to increase initially with increasing PEO coating thickness, though this trend is not maintained with thicker coatings. This is caused by the transformation of greater quantities of metal to ceramic with thicker coatings (leading to more flaw-sensitive behaviour), and higher defect density in the surface layer (reducing the strength of the coating material). The specific strength of the samples (the yield strength per unit weight for a fixed volume) is shown to initially increase with coating thickness, although, due to the diminishing mechanical benefit and constant weight increase, the effect of substantial coatings is less beneficial. The optimum coating thickness appears to be in the region of 13 μm for the low porosity replicated foams tested in compression, and a value between 18 and 50 μm for the high porosity investment cast foams tested in tension.     

红枣及红景天色素的提取及稳定性的比较研究

对红景天及红枣色素的提取方法和色素的基本性质进行了研究比较。结果表明,红景天色素以95%(pH=3)的乙醇水溶液提取时效果最佳,色素的最大吸收峰在314nm处;红枣色素以50%(pH=3)的乙醇水溶液提取时效果最好,色素的最大吸收峰在320nm处;日光、温度和大多数金属离子Ca2 、Mg2 、Mn2 、Zn2 等对这2种色素的稳定性都无太大的影响,但是Na 、Fe2 、K 对红景天色素有增色的趋势,Fe2 对红枣色素有增色的趋势。这2种色素的耐糖性和耐光性都很好。红景天色素在酸性条件下pH稳定性好,但在碱性环境下pH稳定性较差,而红枣色素的pH稳定性在无论在酸性或在碱性条件下都稳定。     

Filtered weight FxLMS adaptation algorithm: Analysis,design and implementation

In the Filtered‐x Least‐Mean‐Square (FxLMS)‐based Active Noise Control (ANC), the convergence speed of the adaptation process has a direct relationship to a scalar parameter, called the step size. There is a theoretical upper‐bound for the step size beyond which the system becomes unstable. However, the step size is usually set to a number smaller than its upper‐bound in practice. This is because for relatively large step sizes, the adaptation process becomes very sensitive to any non‐stationary change in acoustic noise. Owing to this trade‐off, real‐time implementation of high‐performance ANC systems becomes challenging. To overcome this problem, this paper develops a novel ANC algorithm in which a recursive filter compensates for influences of the step size increase on the system performance. It is shown that this filter can efficiently increase the step size upper‐bound; consequently, the performance of the system is improved. This improvement is demonstrated using computer simulation. Also, experimental results shows the preference of the proposed algorithm to the traditional FxLMS‐based ANC algorithm in practice. Copyright © 2011 John Wiley & Sons, Ltd.     

Improving embedding efficiency for digital steganography by exploiting similarities between secret and cover images

Multimedia Tools and Applications - Digital steganography is becoming a common tool for protecting sensitive communications in various applications such as crime/terrorism prevention whereby law...     

蒸汽吹灰器的常见故障分析

介绍了锅炉用吹灰器的结构和工作原理,以及生产过程中出现的常见故障。对故障原因进行了分析,并根据故障原因提出了相应的解决方法。根据生产实践中的经验,指出了生产运行中需要注意的一些常见事项,为维护检修设备提供一定的参考。     

Regular model checking

Regular model checking has been studied extensively during recent years as a framework for algorithmic verification of systems with infinite state spaces. We describe the main concepts of the framework, and some of its applications.     

两种石耳中多糖的提取与分离纯化及其单糖组成分析

目的:对网脊石耳(Umbilicaria decussate(Vill.)Zahlbr.)和淡肤根石耳(Umbilicaria virginis Schaer.)多糖中的单糖组成进行研究。方法:两种石耳经水提、醇沉、冷冻干燥得水溶性多糖,经DEAE-52离子交换层析柱和SephadexG-150凝胶柱进行分离纯化得纯化多糖。气相色谱分析所得多糖的单糖组成。结果:淡肤根石耳精制多糖的单糖组为甘露糖、葡萄糖、半乳糖,其含量之比为16.00:50.96:6.17、淡肤根石耳纯化多糖的单糖组成为甘露糖、葡萄糖、半乳糖,其含量之比为2.97:17.70:1.52;网脊石耳精制多糖的单糖组成为甘露糖、葡萄糖、半乳糖,其含量之比为3.90:38.086:2.00、网脊石耳纯化多糖只含葡萄糖,含量为5.37%。结论:网脊石耳和淡肤根石耳都含有葡萄糖,含有少量的甘露糖和半乳糖。