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关键词： triangular frusta tube   plastic deformation mode   mean crushing force   axial compression   CRASHWORTHINESS OPTIMIZATION   COMPRESSION   BEHAVIORS  

摘要： To improve quasi-static axial crushing performances of thin-wallled triangular tubes, frusta structures were designed and fabricated. Quasi-static axial compression experiments were carried out to reveal the collapse mode and energy absorption characteristic of the triangular frusta tube. Peak loads and mean crushing forces (MCFs) of tubes with different taper angles were compared. In-extensible and extensible collapse modes were suggested to predict the MCF of the triangular frusta tube with small and great taper angles, respectively. A new collapse mode, inward folding, was observed in the experiments. An energy absorption stability factor was defined to evaluate the anti-crushing efficiency of the triangular frusta tube. With greater taper angles, the energy absorption stability factor is much closer to 1, denoting more stable deformation style. It is concluded that frusta structures with taper angles effectively enhance the anti-crushing efficiency and stability of thin-walled triangular tubes.

关键词： egg size   incubation period   nesting ecology   nestling growth   parental care   population variation   PARENTAL CARE   BIOLOGY  

摘要： We present descriptions of nest architecture, clutch size, nestling growth and nestling attendance for the Fire-eyed Diucon (Xolmis pyrope), based on nests found at the Fray Jorge National Park, Chile, at the northernmost part of its distribution. Nests were cup-shaped structures averaging 283.5 +/- 26.6 mm in width and 123.1 +/- 6.8 mm in height (n = 5), found in matorral steppe habitat and Olivillo humid forest relicts. Nests contained 2-3 eggs. Nestling growth in Fray Jorge's nests was nearly two times slower than in populations from central Chile, as suggested by our calculations of the constant rate (K = 0.277) and the T10-90 period (12.9). During 20 hrs of video recording, the breeding adults spent a total of 3.4 hrs at the nest. Both parents attended the nest, and the rates of visits, nestling provisioning and fecal sac removal increased with nestling development. We observed that adults can still care for the young at least 2 weeks after fledging, covering an area of 2.3 ha while searching for food. This information could be valuable for further studies on geographic variation in the species' behavioral ecology.

关键词： Western Burrowing Owl   Athene cunicularia hypugaea   clutch size   determinate egg-laying   Idaho   indeterminate egg-laying   laying determinacy   reproduction   NESTING-BEHAVIOR   GREAT TIT   PROLACTIN   PATTERNS   BIRDS   INCUBATION   SECRETION   COSTS   HEN  

摘要： Bird species, including raptors, can often be categorized into two groups depending upon their response to alterations in clutch size while laying. For some, clutch size is predetermined prior to the start of laying (i.e., determinate species). In contrast, the clutch size of indeterminate layers can be influenced by external factors present at the time of laying. Using field experiments, our objective was to examine the egg-laying responses of female Western Burrowing Owls (Athene cunicularia hypugaea) to manipulations of clutch size. To assess whether Burrowing Owls are determinate or indeterminate egg-layers, we altered female clutch size by removing or adding one egg during the laying period. At the time of egg removal or addition, the resident female had 1-5 of her own eggs present in her clutch. We compared the size of completed clutches of both removal and addition nests to the size of completed clutches at control nests. Mean clutch size at removal nests ((x) over bar = 8.3 eggs, SE = 0.44, n = 9) did not differ from controls ((x) over bar = 8.8 eggs, SE = 0.18, n = 17), whereas mean clutch size at addition nests ((x) over bar = 10.7 eggs, SE = 0.66, n = 9) was significantly larger than that of control nests. These findings demonstrate that female Burrowing Owls responded to the removal of an egg by laying a replacement, yet they did not curtail laying in response to the addition of an egg to their nest. Thus, female Burrowing Owls may be described as removal indeterminate and addition determinate. These results have implications for understanding aspects of Burrowing Owl nesting biology, such as selective advantage following the partial or total loss of a clutch of eggs, and they also may provide insight into how this behavior could facilitate conspecific brood parasitism or mitigate its costs in this species.

关键词： Liquid metal induced embrittlement   Failure   Fracture   SPCC steel  

摘要： The failure mechanism of a clutch shell made from SPCC nitrided steel was analyzed. The component sustained multiple brittle fractures during assembly. Under SEM examination, the fracture surface was found to have facet and cleavage grain appearance. It was predicted that the cleavage fractures started from sites of intergranular fractures. XRD results showed that the nitriding layer contained Fe3N (60 wt.%) and Fe4N (40 wt.%). It is noted that Fe3N is more brittle than Fe4N. An impact test was carried out to compare the impact resistance of the failed and normal components. EDS analysis was also carried out, and it was found that the fracture surface contained zinc, which was not an element specified for the SPCC steel or the nitriding salt. As the salt bath nitriding process operated at a temperature higher than the melting point of zinc, failure was most likely due to liquid metal zinc induced embrittlement, as a result of localized salt bath material contamination with zinc. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： roosting   nesting success   daily survival rate   Acrocephalus arundinaceus   Sturnus vulgaris   south-eastern Europe   BREEDING SUCCESS   NESTING SUCCESS   MAYFIELD METHOD   MANAGEMENT   BEHAVIOR  

摘要： This study provides preliminary findings related to whether and how the roosting of starlings (Sturnus vulgaris) in reedbeds influences the survival of clutches of the great reed warbler (Acrocephalus arundinaceus). During the nesting seasons of 2014 and 2015, we surveyed the complete area of a mining pond in Serbia (south-eastern Europe) for great reed warbler nests, and the presence of roosting starlings was also recorded. Using the Mayfield method, we estimated the daily survival rate of great reed warbler eggs and nestlings, and compared these rates between starling roosting and non-roosting areas. Although both egg and nestling survival rates were lower in the Starling roosting than in the non-roosting areas, the differences were not significant, which was also reflected in overall nesting success. However, when only data from the time period when starling roosting occurred, the overall great reed warbler egg survival was significantly lower in roosting areas than in non-roosting areas. Our results suggest that Starling roosting did not influence the clutch survival of the great reed warbler significantly, but that there can be a negative short-term or local effect. Our study implies that a larger number of starlings and a longer roosting period could affect clutch survival more negatively.

关键词： 离合器   异响   故障   维修工艺  

摘要： 随着汽车行驶里程的增加,离合器的故障就越发明显,通过对离合器异响故障为例,分析了轿车离合器的故障原因、解决办法,维修方式,以及如何正确使用离合器,尽量避免离合器发生故障,延长其使用寿命。

关键词： 离合器   数控机床   摩擦片  

摘要： 离合器是机械装备中的重要部件。为适应机械传动的需要,目前离合器的种类多种多样。本文对当今常见的离合器分类、工作原理进行简述,在此基础上提出了一种新型液压摩擦片式离合器,并对其机械结构进行介绍,同时对离合器额定动静摩擦转矩进行理论计算,最后介绍其在数控卧式铣镗床上的应用,并展望其前景。

关键词： AMT   离合器   接合参数   仿真  

摘要： 本文首先介绍AMT(Automated Mechanical Transmission)离合器特性,确定影响冲击度和滑磨功的几个主要因素,选取离合器接合控制的最佳控制参数,并对这些参数进行分析。采用模糊控制方法,建立AMT离合器动力学模型、冲击度和滑磨功计算模型以及整车模型,利用simulink/MATLAB进行仿真,对仿真结果进行分析,为离合器接合规律的优化控制提供了理论基础。

关键词： 农机离合器   常见故障   排除方法  

摘要： 农业机械是我国农业发展的物质基础,是现代农业发展的重要标志。本文作者通过分析农业机械中农机离合器常见的故障,提出常见的排除及保养方法。