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21.
Attila?HettyeyEmail author J.?Dale?Roberts 《Behavioral ecology and sociobiology》2007,61(8):1303-1310
In species where males use alternative reproductive tactics and male phenotypes are confronted with different risks of sperm
competition, theory predicts that between-male-type differences in sperm expenditure may evolve. In the frog Crinia georgiana big males can monopolize females, whereas small males often engage in polyandrous matings. Consequently, big males may experience
a lower risk of sperm competition than do small males. We tested if the predictions from theoretical models can be applied
to the mating system of C. georgiana. Our results showed that small males do not have larger testes relative to their body size compared to their larger counterparts
and that the efficiency with which sperm number, size, motility, and longevity are produced by the testes does not differ
between small and large males in the predicted way. These results are not in alignment with predictions from a loaded raffle
model of sperm competition on sperm expenditure in males with alternative phenotypes. The plasticity in mating tactics used
by C. georgiana males and a high intraseasonal variation in male densities may have prevented the evolution of enhanced sperm performance
in smaller males. A fair raffle in the sperm competition game played by C. georgiana males could also explain the observed patterns in sperm traits. Future investigations determining the parameters responsible
for the deviation from theoretical predictions in this system will test the degree to which current theoretical models can
indeed be applied to species with plastic reproductive tactics. 相似文献
22.
23.
The nonlinear sorption of hydrophobic organic contaminants (HOCs) could be changed to linear sorption by the suppression of coexisting solutes in natural system, resulting in the enhancement of mobility, bioavailability and risks of HOCs in the environment. In previous study, inspired from the competitive adsorption on activated carbon (AC), the displaceable fraction of HOCs sorption to soot by competitor was attributed to the adsorption on elemental carbon fraction of soot (EC-Soot), while the linear and nondisplaceable fraction was attributed to the partition in authigenic organic matter of soot (OM-Soot). In this study, however, we observed that the linear and nondisplaceable fraction of HOC (naphthalene) to a diesel soot (D-Soot) by competitor (phenanthrene or p-nitrophenol) should be attributed to not only the linear partition in OM-Soot, but also the residual linear adsorption on EC-Soot. We also observed that the competition on the surface of soot dominated by external surface was different from that of AC dominated by micropore surface, i.e., complete displacement of HOCs by p-nitrophenol could occur for the micropore surface of AC, but not for the external surface of soot. These observations were obtained through the separation of EC-Soot and OM-Soot from D-Soot with organic-solvent extraction and the sorption comparisons of D-Soot with an AC (ACF300) and a multiwalled carbon nanotube (MWCNT30). The obtained results would give new insights to the sorption mechanisms of HOCs by soot and help to assess their environmental risks. 相似文献
24.
Influence of new generic frequencies on the QRA calculations for land use planning purposes in Walloon region (Belgium) 总被引:1,自引:0,他引:1
C. Delvosalle C. FiévezN. Cornil J. NourryL. Servranckx F. Tambour 《Journal of Loss Prevention in the Process Industries》2011,24(3):214-218
In Europe, the article 12 of the “Seveso” Directive focuses on land use planning (LUP) around major hazard plants and imposes to keep a sufficient distance between a major hazard plant and populated areas. In Belgium, the LUP is treated at the regional level. The regional authority defines the policy and manages the LUP according to the quantified risk. The quantified external risk, around each Seveso company in the Walloon Region, is assessed by a unique technical expert, the Faculté Polytechnique de Mons, by means of a full probabilistic approach (QRA). This QRA methodology uses accident generic frequencies published by the Flemish Region (Aminal, 2004). In 2009-2010, the quantification of the external risk of the 90 walloon Seveso plants will be completed, based on this set of generic frequencies. However, the Flemish Region recently published a new set of generic frequencies (LNE, 2009), which, in some cases, are quite different of the previous ones for some equipment. This paper discusses the influence of the new frequency data on the quantified risk. An overview of the changes induced by the new set of data will be presented, as well as their impact on the already defined "consultation zones" in which decisions are made concerning the compatibility of the land use and the intensity of risk. 相似文献
25.
26.
世界环境教育的发展史及其特点 总被引:3,自引:0,他引:3
对国外环境教育和国内环境教育的历史发展进行了简述,并对环境教育的特点进行了分析 相似文献
27.
光纤光栅感温火灾报警系统在石油化工行业储罐区等易燃易爆场所得到应用,但目前尚没有相关的国家级设计规范,且安徽省和湖北省地方设计规范关于感温探测器敷设间距的要求存在较大差异,有必要开展深入研究。以外浮顶原油罐为例进行研究,获得了差温和定温两种探测方式在两种敷设高度下,其敷设间距与罐径之间的关系表达式,二者呈正相关。研究结果表明,初起阶段火源功率与罐径呈线性关系且火源功率较小,按照地方规范设置敷设间距时,难以对其进行及时探测,应加大敷设密度;差温探测比定温探测方式具有更为快速探测报警优势且可以设置较大的敷设间距。 相似文献
28.
Females mating with multiple males may obtain direct benefits such as nuptial gifts or paternal care or indirect (i.e. genetic)
benefits resulting in higher-quality offspring. While direct benefits are easily identified, it is difficult to determine
indirect benefits, and it is hence largely unclear how they are obtained. This is particularly true in species with external
fertilisation, where females seem to have little control over fertilisation. In cichlids, most maternal mouthbrooders show
sequential multiple mating, where females visit several males for egg deposition. Genetic data revealed that multiple paternity
of eggs and young in the mouth of females is common, but behavioural data of female spawning decisions are missing. Here,
we test four hypotheses to explain female multiple mating in the maternally mouthbrooding cichlid, Ophthalmotilapia ventralis: (1) fertilisation insurance, (2) genetic bet-hedging, (3) female choice and (4) ‘sperm shopping’ (i.e. induction of sperm
competition resulting in sexually selected sperm). Detailed observations of spawning behaviour in the field combined with
histological analyses of the male reproductive organs suggest that fertilisation insurance, genetic bet-hedging and pre-mating
female choice are unlikely to explain the sequential female multiple mating in O. ventralis. Instead, cryptic female choice by sperm shopping, i.e. post-mating sexual selection, is most compatible with our data and
might be the major ultimate cause of multiple mating in females of this species and of mouthbrooding cichlids with maternal
care in general. Our study provides new insight into ultimate causes of sequential polyandry in species with external fertilisation,
as hitherto post-mating sexual selection by cryptic female choice has been assumed to be incompatible with external fertilisation
mechanisms except by components of the ovarian fluid. 相似文献
29.
Pierre Encontre 《Natural resources forum》1999,23(3):261-270
In spite of the wide diversity in the economic performance of small island developing states (SIDS), the apparent prosperity of several SIDS has entailed a global misrepresentation of the economic situation of these countries. While their vulnerability to natural disasters is not denied, the general risk of economic marginalization that many SIDS face in the context of globalization may not have received sufficient attention. The paper attempts to highlight what matters most in the consideration of the economic vulnerability of SIDS and in the debate to prevent their marginalization. It examines the main types of external shocks to which SIDS are vulnerable, and discusses the economic handicaps that are fundamental causes of this vulnerability. Economic specialization (with the predominance of international trade in services) is then a central notion in the analysis of island vulnerability: a better specialization, which may involve diversification and always implies greater international competitiveness, can reduce the exposure or vulnerability of SIDS to external shocks, and induce greater economic stability in these countries. Hence the importance of developing policies to circumvent the specific handicaps of islands and facilitate the realization of new trading opportunities through an emulative use of globalization forces. 相似文献
30.
室内火灾中外部燃烧现象的数值模拟 总被引:1,自引:0,他引:1
外部燃烧是室内火灾中火焰随烟气流出窗户并在窗户外燃烧的现象。外部燃烧会造成火势从初始着火的房间向其他房间或楼层蔓延,具有很大的危害性。本文应用美国国家标准技术局(NIST)开发的FDS程序,对外部燃烧现象进行了研究。首先对Bullen和Thomas的实验进行数值模拟,用以验证FDS对外部燃烧现象的模拟效果。在相近的燃料过量因子的条件下,计算得到的外部燃烧羽流的温度分布结果、外部燃烧火焰的高度和火焰距离窗户所在壁面的水平距离与Bullen和Thomas的实验结果符合得较好。之后,研究了不同窗户大小和不同燃料消耗率对外部燃烧的影响。最后,发现当燃料消耗率足够大致使室内燃料过量因子接近1时,室内火焰将会熄灭,燃料流出窗户形成的外部燃烧火焰会被拉长,火焰肾贴窗户外的壁面向上燃烧。 相似文献