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71.
Alberto Velando Roxana Torres Irene Espinosa 《Behavioral ecology and sociobiology》2005,58(2):175-180
Sexual selection models suggest that female choice is based on male traits that indicate their genetic or environmental condition, consequently enhancing her reproductive success by direct or indirect benefits. We investigated the relationship between male foot colour and offspring condition in the blue-footed booby, a socially monogamous seabird, with conspicuous and variably condition-dependent coloured feet that are selected by females. In a cross-fostering experiment, we found that chick condition was related to the foot colour of the foster father and, to some extent, to the foot colour of the genetic father; thus overall, the fathers sexual ornamentation (genetic and foster) explained 32% of variance of chick condition. These data suggest that foot colour, a dynamic sexually selected trait, is mostly a signal of parental contribution. In species in which males provide parental care, females may choose mates with higher parental ability. Overall, our data suggest that colourful integuments are honest signals of parental ability.Communicated by J. Graves 相似文献
72.
The tactics of mutual mate choice and competitive search 总被引:9,自引:0,他引:9
Rufus A. Johnstone 《Behavioral ecology and sociobiology》1997,40(1):51-59
A model of mutual mate choice is described, formulated as a dynamic game, which yields predictions about mating behaviour
under the influence of time constraints, choice costs and competition for mates. These variables were examined because they
may result in a change in the distribution of qualities among unmated individuals of both sexes over the course of the breeding
season. The model predicts that mutual choice gives rise to assortative mating, although high costs of choice and/or inaccurate
assessment both lead to lower overall correlations between the qualities (or the attractiveness) of mates. When all individuals
are present from the start of the breeding season, the correlation between the qualities of individuals pairing at a given
time declines throughout the season, so that mates are more closely matched among individuals who pair early than among those
who pair late (and extra-pair copulation may thus be more common among the latter). Delayed arrival of lower-quality individuals
may, however, lead to an increase in this correlation with time during the early part of the season. The mean quality of unmated
males and females declines over time, because more attractive individuals tend to mate sooner. As a result of this decline,
and because of time constraints, superior individuals become less choosy as the season progresses. If choice is costly, however,
then inferior individuals become more selective with time during the early part of the season, and the level of choosiness
peaks later for such individuals.
Received: 28 March 1996 / Accepted after revision: 21 September 1996 相似文献
73.
A dynamic dilution system was used for the study of the influence of ozone on the sampling and storage of volatile organic
compounds (VOCs) at 0, 4, 7 and 14 days in “TO-Can” canisters at two ozone concentrations, 60 and 150 ppbv. Among the 31 ozone
precursors VOCs, a representative mixture containing five alkenes, five aromatics, acetylene and 1,3 butadiene was selected
using the Clausius–Clapeyron equation. Here, we demonstrate that the presence of ozone have no influence on the concentrations
of VOCs after 14 days storage period and consequently no problem of representativity of the sampling appears after 14 days
of storage. The main explanation is the degradation of ozone in contact with deactivated walls of canisters. 相似文献
74.
75.
目的为了提高干气密封系统在运行工况下的稳定性,对密封螺旋槽槽型参数进行优化。方法根据转子-轴承-干气密封系统轴向振动动力学模型,建立双自由度振动方程。在特定的工况下,通过Maple软件多次拟合求解气膜非线性方程,得到气膜轴向刚度和阻尼。运用MATLAB软件中的龙格-库塔法对三阶的非线性振动方程数值求解,绘制不同螺旋角度下的时间历程图和相图,分析对比不同螺旋角度下静环的振动位移。结果从螺旋角度与静环振动位移的关系得出,当α=74.53°时,静环振动位移最小,其最大振幅为7μm,最大振速为7μm/s;当α=73.78°时,静环振动位移最大,其最大振幅为16.5μm,最大振速为17μm/s。改变螺旋角度可以调节和减小静环的振幅。结论在考虑叶轮转子的气动力和轴承油膜力的干气密封系统下,螺旋角度的增加能够提高系统运行的稳定性,增加螺旋角度(0.5°~0.6°)使得动静环的追随性最佳,对干气密封结构的设计提出了指导。 相似文献
76.
目的通过分析和试验得到民用飞机机体连接结构动刚度。方法通过理论分析,得到动刚度的推导公式,并运用有限元分析软件进行频响分析,进而得到连接结构动刚度。运用锤击法得到动刚度试验数据,并进行试验验证。结果试验结果受信号衰减的影响,低频范围内较难得到静刚度结果,但可以通过分析模型得到。试验刚度结果开始波动较大,但在高频范围趋于稳定,最终稳定在分析刚度值左右。当动刚度分析结果受频率影响变化不大时,可以采用动刚度分析均值来作为不同频率下的刚度值。结论通过频响分析得到民用飞机某种结构的动刚度变化曲线,并通过动刚度试验进行了试验验证,分析对比结果表明,有限元分析可以较为准确地得到机体支持结构动刚度,并用于工程实际。 相似文献
77.
本文从理论和实践两方面分析研究了水下振动台的若干关键技术问题,主要包括运动部件的设计、冷却系统的设计、密封系统的设计、压力平衡系统的设计等。解决了水下振动台设计所存在的难题。 相似文献
78.
We consider the resource-extraction policy of a government that is lobbied by an environmental organization and an extraction firm from foreign countries. To analyze this situation, we propose a sequential Nash bargaining solution: The government bargains with both lobbies simultaneously. Should this trilateral negotiation fail, it chooses one lobby for a bilateral negotiation. The disagreement point then is to bargain with the other lobby. Finally, should this second bilateral negotiation break down, the government chooses the welfare-maximizing policy.As long as cumulative extraction is low, such that stock-dependent extraction costs are also low and extraction profits are high, the environmental organization has a weak bargaining position, but it takes influence to reduce extraction. Once that cumulative extraction has increased so much that extraction profits are below a threshold, the bargaining positions change, and the environmental organization gets compensated by the extraction firm for not letting the trilateral negotiation fail. 相似文献
79.
Mary C. Towner 《Behavioral ecology and sociobiology》1999,46(2):82-94
This paper presents a dynamic state variable model that examines human dispersal in a land-based economy. In humans, like
other animals, many individuals disperse during their lifetimes, with extensive variability in the timing and likelihood of
dispersal by individuals of different states. The model places human and non-human dispersal in a common framework, specifically
by utilizing a cost-benefit approach. As with other animals, individual access to resources likely plays an important role
in shaping human dispersal, and the model explores the mechanisms underlying this relationship. Over a series of time steps,
individuals must decide whether to stay in their natal area or disperse, given their states (wealth, marital, and inheritance
status) and the environmental constraints on dispersal. Costs of dispersal include time and an initial drop in wealth, while
the benefit is the potential of the dispersal area to increase wealth. The model determines whether dispersing or staying
results in the highest fitness, where fitness is a function of individual wealth and years married. The model shows that dispersal
is favorable under a wide range of environmental conditions, but that it also varies predictably according to individual states.
Men of middle wealth values disperse under a wider variety of circumstances than poorer or wealthier men. Wealthy men, who
are particularly sensitive to the time cost and mortality risk associated with dispersing, appear to adopt a more conservative
dispersal strategy than poorer men, who are more sensitive to the wealth cost and wealth growth rate associated with dispersing.
Dispersal behavior is also contingent on its effects on an individual's probability of marrying or inheriting wealth. Finally,
the model fosters an examination of how the interaction of life events, and their directions of causation, can be studied.
Received: 6 May 1998 / Received in revised form: 3 February 1999 / Accepted: 7 February 1999 相似文献
80.
Chemical Process Industries usually contain a diverse inventory of hazardous chemicals and complex systems required to perform process operations such as storage, separation, reaction, compression etc. The complex interactions between the equipment make them vulnerable to catastrophic accidents. Risk and failure assessment provide engineers with an intuitive tool for decision making in the operation of such plants. Abnormal events and near-miss situations occur regularly during the operation of a system. Accident Sequence Precursors (ASP) can be used to demonstrate the real-time operating condition of a plant. Dynamic Failure Assessment (DFA) methodology is based on Bayesian statistical methods incorporates ASP data to revise the generic failure probabilities of the systems during its operational lifetime.In this paper, DFA methodology is applied on an ammonia storage unit in a specialized chemical industry. Ammonia is stored in cold storage tanks as liquefied gas at atmospheric pressure. These tanks are susceptible to failures due to various abnormal conditions arising due process failures.Tank failures due to three such abnormal conditions are considered. Variation of the failure probability of the safety systems is demonstrated. The authors use ASP data collected from plant specific sources and safety expert judgement. The failure probabilities of some safety systems concerned show considerable deviation from the generic values. The method helps to locate the components which have undergone more degradation over the period and hence must be paid attention to. In addition, a Bayesian predictive model has been used to predict the number of abnormal events in the next time interval. The user-friendly and intuitive nature of the tool makes it appropriate for application in safety assessment reports in process industries. 相似文献