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关键词： 牙嵌式离合器   结合特性   虚拟仿真   ADAMS  

摘要： 针对牙嵌式离合器的主从动件在接合时相对位置的不确定性问题,把离合器在接合时的情况分成:可以直接结合和需要转速差才能结合两种情况。针对需要转速差才能结合的情况,又按照转速差的不同,对不同转速差时的接合过程进行了详细分析,确定了各种情况下主、从动件能否顺利接合,以及顺利接合允许转速差范围。并借助虚拟仿真软件ADAMS对离合器的结合过程进行了仿真,提取了仿真结果并进行了分析。研究结果表明,转速差的值对离合器的结合时间和结合时冲击力大小有明显影响,同时得出了影响主、从动件结合的主要参数及规律。

关键词： Kirchhoff string   Axial motion   Boundary control of memory type   Arbitrary decay   EULER-BERNOULLI BEAM   WAVE-EQUATION   EXPONENTIAL DECAY   GLOBAL EXISTENCE   VIBRATION CONTROL   STABILITY  

摘要： In this paper, we study the stabilization of solutions of an axially moving string of kirchhoff type by a viscoelastic boundary control. We prove that the dissipation produced by the viscoelastic term is sufficient to suppress the transversal vibrations that occur during the axial motion of the string, and we also show that the string displacement decays in an arbitrary rate. When comparing with immobile strings, we conclude that the movement of the string itself produces enough extra damping ensuring the stabilization.

关键词： Brood parasitism   Farming hypothesis   Molothrus bonariensis   Molothrus rufoaxillaris   Reduction of competition hypothesis   SPECIALIST BROOD PARASITE   MOLOTHRUS-BONARIENSIS   REPRODUCTIVE SUCCESS   HOST GENERALIST   CUCKOOS   DESTRUCTION   ADAPTATIONS   MECHANISM   REMOVAL  

摘要： Shiny cowbirds (Molothrus bonariensis) are generalist brood parasites that use hosts varying in body and egg size. On the contrary, screaming cowbirds (M. rufoaxillaris), which are larger than shiny cowbirds, are host specialist that use mainly one host of similar body and egg size. Both parasites peck and puncture eggs when visiting nests. Through puncturing eggs, cowbirds can reduce the competition for food their chicks face (reduction of competition hypothesis), but the same behavior could also be a mechanism to enforce host to renest when nests are found late in the nesting cycle (farming hypothesis). Eggshell strength increases the difficulty to puncture eggs and therefore may modulate egg-pecking behavior. To test these hypotheses, we studied the effect of the degree of clutch completion and egg size on egg-puncturing behavior. Moreover, we evaluated if morphological differences between cowbird species and eggshell strength affected egg-pecking behavior. We presented captive females a nest with complete (four eggs) or incomplete (one egg) clutches of house wren (small egg size, low eggshell strength), chalk-browed mockingbird (large egg size, intermediate eggshell strength), or shiny cowbird (medium egg size, high eggshell strength). The proportion of nests with punctured eggs was similar for complete and incomplete clutches. Cowbirds punctured more eggs in complete than in incomplete clutches, but in complete clutches, they did not destroy the entire clutch. There were no differences in the egg-pecking behavior between cowbird species, which pecked more frequently the eggs with the strongest eggshell. Our findings are consistent with the reduction of competition hypothesis. Significance statement Brood parasitic birds do not build nests and raise their chicks. Instead, they lay eggs in nests of other species (hosts), which carry out all parental care. Some brood parasites, like the cowbirds, peck and puncture eggs when they visit host nests. This behavior may

关键词： Corticosterone   Incubation   Clutch mass   Reproduction   Fitness   LONG-LIVED BIRD   REPRODUCTIVE SUCCESS   FORAGING BEHAVIOR   INDIVIDUAL-DIFFERENCES   CORTICOSTERONE LEVELS   PARENTAL INVESTMENT   NEST ABANDONMENT   STRESS-RESPONSE   GREAT TIT   PASSERINE  

摘要： Glucocorticoid hormones facilitate responses to environmental challenges by mediating diverse physiological and behavioral changes, including resource mobilization and altered reproductive effort. Elevated glucocorticoids might indicate that an individual is facing high levels of environmental challenges and thus, elevated concentrations might be associated with reduced fitness (CORT-fitness hypothesis). Alternatively, the energetic demands of reproduction might be a challenge that requires elevated glucocorticoids to mobilize resources to support reproductive effort, ultimately increasing reproductive investment and fitness (CORT-adaptation hypothesis). Investigations of glucocorticoid-fitness relationships have yielded mixed results. Variation in the direction of this relationship could be caused in part by differences in the contexts in which the relationship was assessed. Incorporating context, such as life history stage, could be key to understanding the role of glucocorticoids in influencing fitness outcomes. We investigated the relationship between corticosterone and reproductive effort and success within a single life history stage: incubation of eggs. In an observational study, we measured baseline corticosterone in incubating female red-winged blackbirds (Agelaius phoeniceus), monitored incubation behavior, and determined hatching success for each nest. Incubating birds with higher baseline corticosterone concentrations had more frequent, shorter incubation bouts and spent less time overall incubating their clutches of eggs than birds with lower corticosterone concentrations. Elevated corticosterone was also associated with lower clutch mass, but neither corticosterone nor incubation effort were correlated with hatching success. Although experimental tests are needed to establish causation, these results suggest that during the incubation period, corticosterone might shift resource investment towards self-maintenance, and away from current reproductive eff

关键词： Eggshells   Heavy metals   Waterbirds   Contamination   HEAVY-METALS   TRACE-ELEMENTS   EGG CONTENTS   PHOSPHATE FERTILIZERS   CALCIUM AVAILABILITY   PHALACROCORAX-CARBO   MINERAL METABOLISM   AGRICULTURAL SOILS   MERCURY   GREAT  

摘要： Eggshells are good bioindicators of environmental contamination, and therefore, the concentrations of 17 trace elements in 87 eggshells of black-headed gulls, Chroicocephalus ridibundus, were determined in five breeding colonies in an area dominated by farmland in northern Poland. The intra-clutch variability in the eggshell concentrations of heavy metals and other elements was also investigated, and the concentrations of the elements showed the following pattern: Ca > Mg > Sr > Fe> Zn> Al > Cr> Se> Mn> Cu> Pb > As > Ni> Mo= V> Sc> Cd. The concentrations of Fe, Al, andMn decreased with the order in which the eggs were laid, but Sr concentrations increased. In contrast, the concentration of Cu significantly increased with the laying date. The concentrations of all elements significantly differed among the studied colonies; the highest concentration of eight elements was found in the eggshells from the Kusowo colony, which may have resulted from the intensive use of fertilizers, manure, and slurry in the surrounding agricultural region. The concentrations of Mg, Sr, and Zn in the eggshells from Skoki Duze were higher than those of the other studied colonies, which may have occurred because the gulls were nesting in a functioning gravel pit; soil and the parent rock are natural reservoirs of these elements. The observed element levels indicate that the environment where the black-headed gull eggs were formed, i.e., primarily near the breeding colonies, remains in a relatively unpolluted state, which was reflected by the low levels of Cd, Ni, and Pb and the lack ofmeasurable levels of Hg.

关键词： 车辆部件   离合器   临界厚度比   稳态热流分配系数   有限元方法   材料等效  

摘要： 建立了多片离合器有限厚摩擦元件在滑摩过程中热流分配系数的有限元计算模型,揭示了热流分配系数随滑摩时间变化并最终达到稳态值的过程.使用解析法获得了单一材料摩擦元件之间热流分配系数保持恒定的临界厚度比条件,通过摩擦元件的材料热导率等效,提出了稳态热流分配系数的计算方法及其解析解,通过与有限元计算结果对比,验证了该解的正确性.研究结果表明:稳态热流分配系数只与摩擦元件的厚度比和材料的热容量有关,与材料的热导率无关.

关键词： 小型拖拉机   离合器   拆卸   装配  

摘要： 为保证拖拉机离合器修理后的装配质量及使用性能,详细地介绍了小型拖拉机离合器拆卸与装配技术要点。

关键词： 一体式离合器   助力器   应用   价值  

摘要： 文章从一体式离合器助力器应用价值出发,对其基本内容进行了简单的介绍,最后对一体式离合器助力器在实践中的应用进行了分析,旨在为今后研究提供参考资料。

关键词： 离合器   动摩擦系数   冲击度   动力学仿真  

摘要： 针对常用机械式自动变速器(automated mechanical transmission,AMT)起步控制策略由于将离合器动摩擦系数视为常量,而忽略其变化所导致的车辆起步冲击度大的问题,对某款微型车AMT的起步过程进行了研究,提出了基于动摩擦系数的微型车离合器起步接合过程的动力学研究方法,根据摩擦学原理及其试验,讨论了离合器动摩擦系数随转速变化的关系,建立了离合器三维实体模型,并利用ADAMS软件对离合器起步接合过程进行了动力学仿真,分析了干式膜片弹簧摩擦离合器的动摩擦系数与其摩擦力矩和冲击度的关系。研究结果表明,与动摩擦系数为常量的离合器相比,动摩擦系数为变量的离合器半接合点和同步点的冲击度更大。其中,半接合点的冲击度增加率为110%,验证了动摩擦系数变化对车辆起步冲击度作用的重要性。

关键词： 齿轮   常见失效原因   维修方法   分析  

摘要： 齿轮传动是最主要的机械传动方式,齿轮是机械设备的主要零件之一,同时又是诱发机器故障的重要部位。据国外资料统计,由于齿轮失效引起的机械设备故障约占全部机器故障的0.3%。由于齿轮广泛运用于各种工况,材质类型多样,所以本文只针对齿轮常见失效原因及其维修方法分析进行了较为粗略的阐述,仅供参考。