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111.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
112.
宽带DDS跳频源设计 总被引:1,自引:0,他引:1
直接数字合成(DDS)简单可靠、控制方便,具有很高的频率分辨率,高速转换,非常适合快速跳频的要求。在对DDS基本原理进行了简要介绍和分析后,提出宽带跳频源设计方案。 相似文献
113.
GaN-MOCVD设备反应室流场的CFD数值仿真 总被引:11,自引:2,他引:9
采用计算流体力学方法对生长半导体材料GaN的重要设备MOCVD(金属有机物化学气相沉积)反应室中的流场结构进行了三维数值仿真.数值模拟采用基于非交错网格系统的SIMPLE算法,用有限体积方法对控制方程进行离散,并采用改进的压力-速度耦合方法进行求解.数值仿真给出了具有复杂几何结构和运动方式的GaN-MOCVD反应室中的流场结构,研究了改变几何尺寸和运行参数对MOCVD反应室流场结构的影响,对正在试制开发中的MOCVD设备的几何结构的改进和运行参数的优化提出了指导性建议. 相似文献
114.
Environmental factors such as oxygen, temperature, and microbial species may have significant effects on decomposition of biodegradable polymers. A representative biodegradable, thermoplastic polymer, poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV), was decomposed in an aqueous medium under controlled laboratory conditions by soil microbes for the intrinsic degradation kinetics and the effects of the environmental factors on polymer biodegradation. The amount of proteins, including the PHBV depolymerases, that attached to the polymer surfaces was quite constant during the period of significant mass loss of the polymer specimens. The microbial polymer degradation followed a zero‐order rate model, so the residual mass fraction of PHBV films declined linearly with time. The mixed aerobic microbial organisms from fertile soil showed a higher activity of polymer degradation than an aerobic PHBV‐producing bacterium and the mixed anaerobes in the same soil. The mixed anaerobic microorganisms from barren soil decomposed the polymer at a slower rate than the anaerobes from fertile soil, and this was attributed to fewer microbial cells in the barren soil instead of the difference in the microbial species. The temperature effect on PHBV degradation can be described with an Arrhenius equation, and the activation energy is around 16 kcal/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 205–213, 2003 相似文献
115.
Data mining extracts implicit, previously unknown, and potentially useful information from databases. Many approaches have been proposed to extract information, and one of the most important ones is finding association rules. Although a large amount of research has been devoted to this subject, none of it finds association rules from directed acyclic graph (DAG) data. Without such a mining method, the hidden knowledge, if any, cannot be discovered from the databases storing DAG data such as family genealogy profiles, product structures, XML documents, task precedence relations, and course structures. In this article, we define a new kind of association rule in DAG databases called the predecessor–successor rule, where a node x is a predecessor of another node y if we can find a path in DAG where x appears before y. The predecessor–successor rules enable us to observe how the characteristics of the predecessors influence the successors. An approach containing four stages is proposed to discover the predecessor–successor rules. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 621–637, 2006. 相似文献
116.
磷酸酯类离子液体在燃油深度脱硫中的应用 总被引:16,自引:6,他引:10
研究了3种磷酸酯类离子液体,即1,3-二甲基咪唑磷酸二甲酯盐([MM im]DM P)、1-乙基-3-甲基咪唑磷酸二乙酯盐([EM im]DEP)和1-丁基-3-甲基咪唑磷酸二丁酯盐([BM im]DBP)的制备过程,考察了这3种磷酸酯类离子液体对模型油中3-甲基噻吩、苯并噻吩和二苯并噻吩的脱除效果及磷酸酯类离子液体的电化学再生方法。实验结果表明,这3种磷酸酯类离子液体的脱硫能力强弱顺序为:[EM im]DEP>[BM im]DBP[MM im]DM P;且对二苯并噻吩的脱除效果最好,对苯并噻吩的脱除效果次之,对3-甲基噻吩的脱除效果较差。以[EM im]DEP为萃取剂,油剂质量比为1∶1时,经5次萃取后,二苯并噻吩的脱除率可达到99.5%。利用电解法对[EM im]DEP进行了再生,在5~10V电压下电解10h,[EM im]DEP的脱硫率可以达到新鲜[EM im]DEP的90%以上。 相似文献
117.
叙述了石油库在发油过程中的HSE管理;发油过程中的危害识别,包括识别范围和内容;发油过程中风险评价的常用基本方法和常见问题;发油过程中危险源的管理控制,包括建立危险源网络图、加强现场监控和制定应急预案。 相似文献
118.
119.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
120.
在cdma20001x前向信道中,要对一段信号进行传送,一般选用QPSK调制,因为QPSK调制比QAM更适合噪音环境。采用TI6000系列的TMS320C6711芯片处理前向信道信号,可以对复杂性和实时性较高的信号做采集、量化、编码、调制等实时处理,主要功能通过软件编程实现,从而使系统具有结构灵活、可靠性高、可扩展等优点。 相似文献