考虑环境时变性的光通信系统安全路由方法

针对传统光通信系统安全路由方法存在严重的能量约束问题,提出了考虑环境时变性的光通信系统安全路由方法。基于节点度计算光通信系统网络节点的剩余能量,结合节点位置信息选取光通信簇首,通过引入惩罚系数计算分簇簇头的信任度,根据邻近层簇头数量的约束条件构建了簇头衰减模型,通过网络分层和分簇半径进行分簇,并均衡了路由负载。实验结果表明,本方法的能耗在4 h后才慢慢从12 J开始下降,路由建立的时间不超过1 s,延长了光通信系统的使用寿命。

基于PSO-BP神经网络的煤矿井下自适应定位算法

提出了一种基于PSO-BP神经网络的煤矿井下自适应定位算法。针对传统的基于测距模型的定位算法易受煤矿井下环境干扰、测距误差大的问题,选择指纹匹配定位模型。针对煤矿井下环境强时变性,易增大实时采集的指纹信息与离线阶段建立的静态指纹数据库信息的匹配误差问题,将信标节点作为参考点的校准节点,以更好地反映参考点随环境变化的情况,避免增加额外的校准节点;在不增加硬件成本的同时,通过动态补偿法实时修正目标节点指纹数据,解决了指纹匹配定位模型自适应差的问题。匹配定位阶段采用PSO优化BP神经网络权值,以加速BP神经网络收敛,提高学习速度。实验结果表明,该算法更加适应随时间变化的煤矿井下环境,满足井下自适应定位要求。

Temporal-Spatial Variability of Soil Organic Carbon Stocks in a Rehabilitating Ecosystem

In global change research, changes of soil organic carbon (SOC) reservoirs intropical and subtropical regions are still unknown. The temporal-spatial variability of SOC stockswas determined in a basin of over 579 km^2 in subtropical China from 1981to 2002. ArcGIS8.l softwarewas utilized for spatial analysis of semivariance, ordinary kriging (OK), and probability kriging(PK). Grid and hierarchical approaches were employed for the sampling scenario in 2002 with 106Global Position System (GPS) established spots sampled. Bulk topsoil samples (0—30 cm) werecollected at three random sites on each spot. The SOC content for 1981 came from the SOC map of theSecond National Soil Survey. Geostatistical results of the nugget to sill ratio (0.215-0.640)in therehabilitating ecosystem indicated a moderate spatial dependence for SOC on this large scale. Therange of SOC changed from 2.04 km in 1981 to 7.15 km in 2002. The mean topsoil SOC increased by 4.6%from 10.63 g kg^(-1) (1981) to 11.12 g kg^(-1)(2002). However, during this 21-year period 25.2% ofthe total basin area experienced a decrease in SOC. Also, the probability kriging results showedthat the geometric mean probabilities of SOC <= 6.0 g kg^(-1), <= 11.0 g kg^(-1) and > 15.0 gkg^(-1) were 0.188, 0.534 and 0.378, respectively in 2002, comparing to 0.234, 0.416 and 0.234 inthat order in 1981, respectively. The SOC storage in the topsoil increased by 17.0% during this timewith the main increase occurring in forests and cultivated land,which amounted to 82.5% and 17.0%of the total increase, respectively.

Spatio-temporal variability of periphytic protozoa related to environment in the Niyang River,Tibet,China

The Niyang River, a main tributary of the Yarlung Zangbo River, is an important and typical plateau fiver ecosystem in Tibet, China. At present, few studies have focused on its aquatic living resources and fiver ecology. In this study, the composition, abundance, and diversity of periphytic protozoa were investigated across four seasons from 2008 to 2009 to better understand their spatio-temporal patterns and relationship to the environment. Our investigation shows that periphytic protozoa in the Niyang River contained 15 genera, belonged to Tubulinea, Alveolata, Discosea and Rhizaria, Alveolata possessed most genera, up to nine, with highest share in abundance, exceeding 50%, Difflugia and Glaucoma were dominant genera. Moreover, four diversity indices of periphytic protozoa, including species richness, total abundance, Shannon-Wiener diversity index and Pielou＇s evenness index, displayed a significant descending trend as the seasons continued, in the order of winter, spring, summer and autumn; with a significant difference existing between winter and summer （or autumn） for Shannon-Wiener diversity index and species richness （P〈0.05）. Four of these diversity indices also presented a V-shaped pattern between the upper middle course of the Niyang River and the confluence of the Niyang River and Yarlung Zangbo River, with the lowest value occurred in the middle course of the Niyang River. However, no significant variation was found through the Niyang River （P〉0.05）. In addition, canonical correlation analysis （CCA） shows that the densities of Difflugia, Glaucomais, Enchelydium, Cyphoderia, and Enchelys correlate with water temperature, alkalinity, hardness, pH, and dissolved oxygen, respectively. Lastly, the relationship between periphytic protozoa diversity and the environmental factors of the Niyang River can be predicted using classification and regression trees （CART） annalysis, which suggests that the total abundance and Shannon-Wiener diversity index would be higher when the elevation is above 3 308 m. On the other hand, the Shannon-Wiener diversity index and Pielou＇s evenness index would be lower when pH and ammoniacal nitrogen have lower or higher values. Finally yet importantly, close attention should be paid to periphytic protozoa and its environment to ensure sustainable development of the Niyang River ecosystem.

Quilitative Analysis of a Class of Simulate Seasons Environm ent Chem ostat Systems

In this paper, a class of chemostat systems with simulate seasons Environment in the following form =(1+be(t)-s)Q+x(msa+s-k) =x(msa+s-k)-Qxis discussed. It is abstained that the system has not periodic solution when b=0; if b≠0 and b1 then system has 2 π periodic solution of system. globally asymptotically stable as mQ<μ *-1 and is unstable as mQ>μ *-1 and there exists at last one minimal 2 π periodic solution (s(t),x(t)) with \{x(t)>0,\}0<s(t)<s *(t).

Variation in regrowth ability in relation to land-use intensity in three common grassland herbs

Aims Plant populations in managed grasslands are subject to strong selection exerted by grazing,mowing and fertilization.Many previous studies showed that this can cause evolutionary changes in mean trait values,but little is known about the evolution of phenotypic plasticity in response to land use.In this study,we aimed to elucidate the relationships between phenotypic plasticity—specifically,regrowth ability after biomass removal—and the intensity of grassland management and levels of temporal variation therein.Methods We conducted an outdoor common garden experiment to test if plants from more intensively mown and grazed sites showed an increased ability to regrow after biomass removal.We used three common plant species from temperate European grasslands,with seed material from 58 to 68 populations along gradients of land-use intensity,ranging from extensive(only light grazing)to very intensive management(up to four cuts per year).Important Findings In two out of three species,we found significant population differentiation in regrowth ability after clipping.While variation in regrowth ability was unrelated to the mean land-use intensity of populations of origin,we found a relationship with its temporal variation in Plantago lanceolata,where plants experiencing less variable environmental conditions over the last 11 years showed stronger regrowth in reproductive biomass after clipping.Therefore,while mean grazing and mowing intensity may not select for regrowth ability,the temporal stability of the environmental heterogeneity created by land use may have caused its evolution in some species.