Adaptive Sector Grouping to Reduce False Sharing in Distributed RAID

Distributed redundant array of inexpensive disks (RAID) is often embedded in a cluster architecture. In a centralized RAID subsystem, the false sharing problem does not exist, because the disk array allows only mutually exclusive access by one user at a time. However, the problem does exist in a distributed RAID architecture, because multiple accesses may occur simultaneously in a distributed environment. This problem will seriously limit the effectiveness of collective I/O operations in network-based, cluster computing. Traditional accesses to disks in a RAID are done at block level. The block granularity is large, say 32 KB, often resulting in false sharing among fragments in the block. The false sharing problem becomes worse when the block size or the stripe unit becomes too large. To solve this problem, we propose an adaptive sector grouping approach to accessing a distributed RAID. Each sector has a fine grain of 512 B. Multiple sectors are grouped together to match with the data block size. The grouped sector has a variable size that can be adaptively adjusted by software. Benchmark experiments reveal the positive effects of this adaptive access scheme on the performance of a RAID. Our scheme can reduce the collective I/O access time without increasing the buffer size. Both theoretical analysis and experimental results demonstrate the performance gain in using grouped sectors for fast access of distributed RAID.  

红皮云杉人工林生物量的空间分布

在研究红皮云杉人工林生物量及生产力的基础上，分析了红皮云杉人工林生物量的空间分布格局及其产量结构。  

红池坝地区草地红三叶草的空间分布型

植物种群的空间分布型是生物在特定的条件下形成的,它反映了植物种群个体的散布状态以及对环境的适应性和生境对植物影响的生态反映的生态学关系,是一条可以了解凭种类组成研究演替的研究途径 森下正明(Morisita,1959)提出了扩散指数Io(Morisita's index);美国的Lloyd,(1967)提出了平均拥挤度(Mean crowding,m)这个颇有兴趣  

白皮锦鸡儿种子内生细菌的分布与分离鉴定

【目的】了解对荒漠环境有良好适应性的白皮锦鸡儿种子可培养内生细菌的多样性。【方法】采用种子表面灭菌、种皮与种仁分离、可培养细菌分离纯化、对pH及盐的耐受性、16S rRNA基因序列扩增和系统发育分析进行系统研究。【结果】从白皮锦鸡儿成熟种子种皮和种仁分别分离纯化到6株和26株内生细菌，其中分离自种皮的菌株最适pH均在9.0以上，且有3株最高可耐受pH 14.0，有5株可耐受10%的NaCl；分离自种仁的菌株pH耐受范围明显低于种皮，但有12株对NaCl的耐受性可达10%。16S rRNA基因序列分析显示，30株与芽孢杆菌属(Bacillus sp.)接近，相似率95%?99%，其中13株与枯草芽孢杆菌(Bacillus subtilis)的相似率为96%?99%，11株与地衣芽孢杆菌(Bacillus licheniformis)相似率为95%?99%；1株与单孢菌属 (Sphingomonas sp.)相似性为99%，1株与大肠杆菌属(Escherichia sp.)相似性为98%；【结论】白皮锦鸡儿种仁内生菌数量和种类均高于种皮，体现出其可培养内生菌在空间分布的分异性及种类的多样性，且推测其种皮内生菌对盐碱的高度耐受性应与其环境适应性相关。  

塔里木河流域胡杨和灰叶胡杨克隆分株空间分布格局

以叶尔羌河下游阿瓦提县天然胡杨和灰叶胡杨混交林、塔里木河上游农一师16团天然灰叶胡杨林和塔里木河中游轮台县天然胡杨林为对象，研究胡杨和灰叶胡杨克隆分株种群的空间分布格局.结果表明: 8种不同取样尺度(5 m×5 m、5 m×10 m、5 m×15 m、10 m×10 m、10 m×15 m、15 m×15 m、15 m×20 m、20 m×20 m)下，3个研究区2物种克隆分株种群的空间分布格局均表现为集群分布，表明集群分布是研究区胡杨和灰叶胡杨克隆分株种群空间分布格局的基本属性；在5 m×5 m尺度上，3个研究区2物种克隆分株种群均表现出负二项参数最小、Cassie指标和聚块性指标最大、聚集强度最大的分布特征.  

Territorial behavior of Western Sandpipers on their nonbreeding grounds: effect of sex and foraging interference

ABSTRACT Nonbreeding shorebirds often alternate social structure between anonymous flocks and territorial behavior in response to different environmental factors. To evaluate specific drivers for one species, we studied the spacing behavior of wintering Western Sandpipers (Calidris mauri) at Bahía Santa María, northwestern Mexico, using behavioral observations. The density, population structure, and territorial behavior of Western Sandpipers differed among three habitat types. Cattail marshes supported 110 birds per ha, 49% males, and no territorial birds. Mangrove flats supported 288 birds per ha, 58% males, and 5% territorial birds. Brackish flats supported 365 birds per ha, 76% males, and 7% territorial birds. Territories consisted of rectangular strips (5–9 m long, N= 77). Territory length was not related to either bird density or number of territorial birds by plot, but was positively related to nearest bird distance. Aggression rate was inversely related to territory length, suggesting that territory length is set by the costs of defense. Foraging rate was independent of territory length, and prey densities in territories did not differ from those in areas used by nonterritorial birds. Males were more likely to be territorial and had a higher aggression rate than females, suggesting that males, which forage more on surface prey, were more affected by foraging interference. Our results suggest that the territorial behavior of Western Sandpipers in our study was an opportunistic strategy to reduce foraging interference. The variation in spacing behavior we documented provides evidence that interference competition affects the social structure of Western Sandpipers during the nonbreeding season.