排序方式: 共有48条查询结果,搜索用时 15 毫秒
41.
42.
Btissam Er‐Rahmadi Adlen Ksentini Djamal‐Eddine Meddour 《Wireless Communications and Mobile Computing》2016,16(17):3104-3122
One of the key enablers of the upcoming IEEE 802.11ax standard is the inclusion of uplink multi‐users (UL MU) transmission model, which is performed using multiple‐input multiple‐output (MIMO) and beamforming techniques. So far, UL MU‐MIMO has not been standardized in any of IEEE 802.11 amendments, because of technical issues facing its definition. One of these significant issues is the scheduling of UL MU‐MIMO transmissions, which refers to selection rules and resource allocation procedures performed before simultaneous data transmissions. Indeed, simultaneous transmitters and receiver should exchange some information to correctly transmit the parallel data frames. However, this information exchange adds overheads, leading to reduce network performance. In this regard, we have proposed, in a previous work, a novel 802.11ax medium access control protocol aiming at reducing elapsed time in managing the establishment of an UL ‐MU communication called Wait‐to‐Pick‐As‐Available (W2PAA). Our contribution in this paper is twofold. First, we introduce an analytical model based on semi‐Markov Chains to evaluate the performance of W2PAA; taking into a detailed behavior of the backoff counter (i.e. freezing period). Second, we propose an enhanced version of W2PAA aiming at improving both system and user‐oriented performances. Aiming at validating the analytical model and comparing the performance of both versions of W2PAA, we used computer simulation. Obtained results, validate the analytical model in one hand, and clearly indicated the gain of both W2PAA versions by report to the basic UL‐Single User on the other hand. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
43.
44.
45.
结合本溪市首幢混凝土砌块 装饰劈裂砌块复合夹芯保温的小高层工程实践,简要介绍墙体构造、采用材料、施工注意事项,以及砌块的生产与准备、形状与种类、施工工艺及要求。采用复合夹芯保温作法,既能满足保温抗渗要求,外装饰墙的清水面又能充分体现出建筑的特点,美观大方,经济实用。 相似文献
46.
Huang L Garbulewska E Sato K Kato Y Nogawa M Taguchi G Shimosaka M 《Journal of Bioscience and Bioengineering》2012,113(3):293-299
Chitiniphilus shinanonensis type strain SAY3(T) is a strongly chitinolytic bacterium, originally isolated from the moat water in Ueda, Japan. To elucidate the chitinolytic activity of this strain, 15 genes (chiA-chiO) coding for putative chitin-degrading enzymes were isolated from a genomic library. Sequence analysis revealed the genes comprised 12 family 18 chitinases, a family 19 chitinase, a family 20 β-N-acetylglucosaminidase, and a polypeptide with a chitin-binding domain but devoid of a catalytic domain. Two operons were detected among the sequences: chiCDEFG and chiLM. The gene coding for the polypeptide (chiN) showed sequence similarity to family 19 chitinases and was successfully expressed in Escherichia coli. ChiN demonstrated a multi-domain structure, composed of the N-terminal, two chitin-binding domains connected by a Pro- and Thr-rich linker, and a family 19 catalytic domain located at the C-terminus. The recombinant protein rChiN catalyzed an endo-type cleavage of N-acetyl-d-glucosamine oligomers, and also degraded insoluble chitin and soluble chitosan (degree of deacetylation of 80%). rChiN exhibited an inhibitory effect on hyphal growth of the fungus Trichoderma reesei. The chitin-binding domains of ChiN likely play an important role in the degradation of insoluble chitin, and are responsible for a growth inhibitory effect on fungi. 相似文献
47.
智能变电站中合并单元数据采集和输出过程存在着固有的额定延时,此延时直接影响继电保护的动作时间。目前,额定延时测量方法存在着不足,给系统安全运行埋下了安全隐患。文中从合并单元采样环节的构成出发,分析其采样、处理过程中额定延时的群延迟特性和传变延迟。研究表明:时域中的群延迟在频域中相频特性应为线性相位,据此提出通过输入不同频率的信号以获得合并单元的相频特性曲线、进而辨识出额定延时的频域识别测量技术,并分析合并单元的相位误差对此额定延时测量方法的影响,最后通过理论仿真验证了此额定延时测量技术的可行性和正确性。文中所提方法为合并单元数字化采样延时测量的工程应用提供了一种切实可行的延时测量技术,能够确保继电保护系统的正确、可靠运行。 相似文献
48.