Patterns of artificial avian nest predation by introduced rats in a fragmented laurel forest (Tenerife,Canary Islands)

The importance of introduced rats as damaging factors on island biotas is globally recognized. The predation of artificial avian nests by Ship rats (Rattus rattus) in fragmented laurel forests in Tenerife (Canary Islands) was explored. The influence of road edge, patch type, and position (ground versus tree) on nest survival in two forest remnants differing in conservation degree, were assessed using failure‐time analysis. Overall, nest predation was greater in the preserved than in the disturbed remnant. Nest predation also differed among and within patches, variation being greater within the disturbed remnant. The probability of nest failure was higher at the interior than along the road edge in both remnants, but the road edge effect on nest predation was more intense in the disturbed remnant. Predation pressure was higher in patches of mature, closed canopy or dense understorey with stump sprouting. Ground nests were predated at higher rates than tree nests at any location. These results contrast with other nest predation studies in fragmented landscapes where forest edges rather than the interior are more frequently used by predators. Predatory activity by rats seems negatively affected by forest disturbance and road edge effect. Overall, artificial nest predation patterns by rats confirm a potential predation risk for the avifauna of the Canarian laurel forest. This should be considered in implementing conservation management programmes.     

Temporal organization patterns of epigean beetle communities (Coleoptera: Carabidae,Tenebrionidae) in different successional stages of eastern Mediterranean maquis

This two-year study explores the community structure and temporal dynamics of carabid and tenebrionid beetles in five eastern Mediterranean juniper maquis formations in relation to successional stage. Based on vegetation cover, density and soil pH, the successional stage in two of the sites (Crete, Cyprus) was an earlier state compared with the other three (Attiki, Naxos, Samos), as a result of intense goat grazing. Diversity indices and abundance distributions were compared using morphoecological surrogates of the taxa. Temporal dynamics were regulated more by cumulative species richness than by sharp phenological patterns. The higher values of niche pre-emption parameter and species turnover imply better adaptation of endemic tenebrionids to the rapid change of environmental conditions, compared with carabids. Significantly lower abundance and biomass, and higher evenness and temporal turnover for both families in Crete and Cyprus are ascribed to the reversed course of succession caused by overgrazing.     

带涡产生器的圆管管片式换热器流场及温度场的数值分析

用数值方法分析了涡产生器式圆管管片式换热板芯单个圆管单元区域内的速度场和温度场.计算结构针对某实际换热器结构,S1=20 mm,S2=15.5 mm,tp=2.5 mm,涡产生器攻角为45.°计算时选取雷诺数范围为500~20 000,选取R e=1 000和10 000时的计算结果进行了讨论和分析.涡产生器产生的纵向涡旋增强了圆管尾流区流体的掺混和能量交换,并带动尾流区流体及时向下游流动.与平片翅片结构比较,涡产生器式圆管管片式换热板芯尾流区流体与壁面温差增大,有利于增强换热.     

Amphipod crustaceans and environmental disturbance: a review

This review of the literature shows that amphipod crustaceans create disturbance through predation on commercial harvests, attacks on macroalgae, introductions as exotic species, and interference competition. Amphipods are also affected by disturbance events, both man-made and natural. Anthropogenic disturbance includes environmental alteration by toxins, oil, organic enrichment, acidification, salinity alteration, and ships' wakes. Natural disturbances are space clearance by the feeding activities of other fauna, and physical disturbance by sediment erosion and ice scour.     

Prediction from the One‐Way Error Components Model with AR(1) Disturbances

In this paper we extend the works of Baillie and Baltagi (1999, in Analysis of Panels and Limited Dependent Variables Models, Hsiao C et al. (eds). Cambridge University Press: Cambridge, UK; 255–267) and generalize certain results from the Baltagi and Li (1992, Journal of Forecasting 11 : 561–567) paper accounting for AR(1) errors in the disturbance term. In particular, we derive six predictors for the one‐way error components model, as well as their associated asymptotic mean squared error of multi‐step prediction in the presence of AR(1) errors in the disturbance term. In addition, we also provide both theoretical and simulation evidence as to the relative efficiency of our alternative predictors. The adequacy of the prediction AMSE formula is also investigated by the use of Monte Carlo methods and indicates that the ordinary optimal predictor performs well for various accuracy criteria. Copyright © 2011 John Wiley & Sons, Ltd.     

预制装配式架桥机的起重小车复合滑模同步控制

预制装配式架桥机对预制墩柱架设过程中存在精度低、效率低等问题,针对这一问题基于时变滑模扰动观测器,提出变增益移动滑模控制方法。首先,通过分析架桥机起重小车架设墩柱的运动过程,得出了起重小车起升机构与走行机构的同步运动关系式,然后设计了一种结合交叉耦合控制策略的移动滑模控制器,提升了系统的鲁棒性;其次,设计了变增益趋近律,加快了误差收敛速度并抑制了抖振;同时,为了使架桥机起重小车适应不同工况下的扰动,设计了一种新的时变滑模扰动观测器,从而对产生扰动项进行实时的估计和补偿。Lyapunov理论可以证明上述控制器具有收敛性,数值仿真则可以表明,该控制方法对于提高起重小车的架设精度与速度是有效的。     

一阶大时滞系统的滞后时间削弱自抗扰控制

为了解决一阶大时滞系统的控制难题,提出一种滞后时间削弱的自抗扰控制方法。首先,分析时滞系统中线性自抗扰控制的控制输入与系统反馈在时间轴上的不匹配问题,设计一种新的滞后时间削弱结构;然后,结合自抗扰控制思想,得到滞后时间削弱自抗扰控制的闭环结构,用于一阶大时滞系统,利用频域分析说明该方法的稳定性,并总结参数整定规则;最后,将仿真结果与已有算法所得结果进行比较。研究结果表明：滞后时间削弱自抗扰控制对大时滞过程的参数摄动不敏感,相比较于已有的PI-Smith控制、预估自抗扰控制等算法,滞后时间削弱自抗扰控制可以有效改善一阶大时滞对象的控制效果,具有更好的动态性能和控制鲁棒性。     

单向、双向和三向扰动诱发岩爆碎屑特征实验研究

通过自主研发的冲击岩爆实验系统,开展单向、双向和三向扰动诱发岩爆的实验,研究不同扰动方向条件下冲击岩爆实验碎屑的质量、粒径、Weibull分布和分形特征,探讨扰动方向数量的增加对冲击岩爆的影响。研究结果表明：单向、双向和三向扰动条件的冲击岩爆实验碎屑破碎程度均较高,呈现明显片状特征;随着扰动方向数量的增加,岩爆破坏碎屑的破碎程度降低,形成碎屑所耗散能量减少,说明扰动方向数量增多对冲击岩爆的剧烈程度具有阻碍作用。     

一种新型结构叶片对风力机气动性能的影响

针对风力机在旋转过程中产生的叶尖涡影响风力机本身以及下游风力机气动性能的问题,提出了一种控制叶尖涡的策略,以减小叶尖涡对风力机本身及下游风力机气动性能的影响.以PhaseⅥ叶片的1/8模型为原始模型,在叶尖处和轮毂处同时开洞,用管道将洞连接的模型称作新模型.采用数值模拟的方法对来流风速从6m/s到20 m/s的15个工...     

电网低频振荡扰动源线路暂态特征频带选取算法

为了有效利用线路暂态特征频带包含的故障信息,准确选取线路暂态特征频带,使得频率在该频带内的暂态分量可有效体现电网低频振荡扰动源位置,提出电网低频振荡扰动源线路暂态特征选取算法。分析了线路边界频率特性,获取线路暂态特征频带上限约束值。将电网低频振荡扰动源线路的始端和末端当成端口,通过二端口网络方程获取线路等值阻抗,对暂态特征进行分析。在此基础上,通过矩阵束法对不同线路电流频率分量和频率分量相位进行提取,按照升序顺序排序,对不同频率分量相位进行比较。将与90°相角相应的频率当成频带上限,完成对电网低频振荡扰动源线路暂态特征频带的选取。实验结果表明:所提算法可得到线路暂态特征频带选取结果,获取电网低频振荡扰动源位置;和特高压直流输电线路暂态保护特征频带选取算法与基于暂态相电流特征分析的故障选线算法相比,所提算法选取结果和实际结果间的误差最小。可见所提算法暂态特征频带选取结果准确。