Cooperation and competition in pathogenic bacteria

Explaining altruistic cooperation is one of the greatest challenges for evolutionary biology. One solution to this problem is if costly cooperative behaviours are directed towards relatives. This idea of kin selection has been hugely influential and applied widely from microorganisms to vertebrates. However, a problem arises if there is local competition for resources, because this leads to competition between relatives, reducing selection for cooperation. Here we use an experimental evolution approach to test the effect of the scale of competition, and how it interacts with relatedness. The cooperative trait that we examine is the production of siderophores, iron-scavenging agents, in the pathogenic bacterium Pseudomonas aeruginosa. As expected, our results show that higher levels of cooperative siderophore production evolve in the higher relatedness treatments. However, our results also show that more local competition selects for lower levels of siderophore production and that there is a significant interaction between relatedness and the scale of competition, with relatedness having less effect when the scale of competition is more local. More generally, the scale of competition is likely to be of particular importance for the evolution of cooperation in microorganisms, and also the virulence of pathogenic microorganisms, because cooperative traits such as siderophore production have an important role in determining virulence.     

不同搭接率时主方支圆钢管节点的承载力分析

K形搭接节点是空间结构中经常使用的一种连接方式.为深入了解K形搭接节点的特性,使用ANSYS软件,对一系列不同搭接率下的主方支圆K形钢管节点进行数值模拟,并将有限元分析结果绘制成曲线.分析支主管径宽比β,支主管厚度比τ,主管宽厚比γ支主管夹角θ等几何参数对此类节点极限承载力的影响.分析结果显示,当τ较小时,搭接率Ov对...     

战略创新改变企业竞争模式

在21世纪,重大的新产品可能会来源于生物技术,生物制药、医学治疗护理的手段已经开始出现重大的革新。但是,不管是哪个行业,要实现产品的重大革新都不是件容易的事。对于大多数企业来说,往往由于资源的限制,更难以在产品创新上取得突破。所以说,在21世纪,战略创新将是企业生存与成长的关键,而它仅受限于企业的创新能力和勇气。在过去20年内,涌现了一类新的商界明星——他们不是新产品的创造者,而是新战略的刨造者。迈克·戴尔(戴尔电脑)、     

Intrasexual competition and sexual selection in cooperative mammals

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection.     

物理竞赛与素质教育

第二课堂是开展素质教育、打造精品课程的重要环节,本文就第二课堂中的物理竞赛活动所反映出的问题,结合当前教学现状,对竞赛的组织、题目的选择以及答题结果进行了分析,并提出了相应的看法与思考.     

4腿机器人足球比赛的通信机制及协作控制

针对4腿机器人足球比赛中机器人的通信机制及协作控制等问题,提出了一种新的完整的分布式多主体系统控制方法,包括通信控制、路径规划以及动态角色分配.该方法通过启发式投标函数进行任务分配,通过电场法表示抽象的环境信息.协作控制中不必进行大量的计算,主体之间不必频繁地进行数据交换.该方法能够满足比赛动态性和不确定性的需要,并在实际比赛中得到了很好的验证.     

Extra-pair copulation and sperm competition in the zebra finch

Most birds are monogamous, but recent studies have shown that extra-pair copulations (EPCs) occur frequently despite a range of paternity guards, including mate-guarding and frequent copulation. Although EPCs are known to result in extra-pair paternity, there are no previous quantitative estimates of the success of EPCs in fertilizing eggs. We present here estimates of the likelihood of success of extra-pair copulations in a monogamous passerine, the zebra finch Poephila guttata. We show that (1) EPCs occurring under semi-natural conditions in captivity result in extra-pair paternity, (2) sperm from the last male to mate has precedence over previous matings: a single EPC occurring last is disproportionately successful in fertilizing eggs, but EPCs followed by further pair copulations have a low probability of success. These results have important implications for sexual selection theory.     

Sperm competition: motility and the midpiece in primates

In animals with multiple-partner mating systems, the gametes of two or more males must compete to fertilize a given set of ova. Here we show that the volume of the midpiece in individual sperm is significantly greater in primate species in which the females mate with multiple partners, and in which males have larger testes in relation to their body weight, than in those species that mate with only one partner and have relatively small testes. Our results indicate that sexual selection by sperm competition has influenced the evolution of a specific component of male-gamete morphology, the volume of the sperm midpiece.     

特殊化与一般化的思维方法

本文结合教学工作与科研工作的实际,用具体的例子诠释特殊化与一般化的思维方法。     

比表面与文件检验

比表面是《表面化学》中的一个基本概念,本文将它运用到文件检验中,用以解释为什么碘熏法可以显示压痕字、擦刮痕等的原理问题。即比表面概念可作为文件检验中显出压痕字、擦刮痕等的理论基础。     

收费公路和公共交通之间的定价博弈分析

研究了收费公路和公共交通的定价博弈问题.运用博弈论的模型和方法,在自由竞争和充分合作的情况下分别建立了两者间的定价模型;探讨了在自由竞争的情况下公路收费和公交票价达到的均衡状态,以及在多种政府政策下均衡状态的变化,同时分析了运营者相互合作下的公路收费和公交票价.结论表明,在自由竞争的情况下,政府税收对最优均衡定价没有影响,在固定出行需求的情况下,政府对公交进行补贴会导致两者的定价上升.     

数字竞赛抢答器的设计与实现

基于数字时序控制电路原理,采用元器件设计实现了一种显示倒计时的数字竞赛抢答器。该抢答器由组合逻辑电路中的编码器、锁存器、译码器,时序逻辑电路中的计数器和555定时器组合而成。该抢答器具有手动复位功能,倒计时功能和显示功能。经测试表明,该抢答器可以准确显示倒计时时间和抢答号码,反应灵敏,工作性能稳定可靠。     

影响跆拳道运动员在比赛中动作速度的因素

跆拳道运动在我国起步虽晚,发展却非常迅速.影响跆拳道运动水平的因素很多,比赛中动作速度的发挥至关重要.选取西安体育学院跆拳道队50名队员为研究对象,以访谈法、文献资料法、数理统计法对影响动作速度的因素进行了探讨.结果表明,影响比赛中动作速度的因素有运动员技术水平、战术意识及心理因素等.只有加强一般素质与专项素质的训练,并注意从基本技术入手打好基础、加强战术与心理素质训练,才能在比赛中有效地提高动作速度.     

足球比赛中非言辞沟通和传达的特点及形式

采用教学理论与教学实践相结合的方法，对足球运动员在比赛中与本队队员、对方队员、教练员、裁判员以及观众之间的非言辞沟通和传达的特点及形式进行分析，有助于队员更好地发挥水平，取得较好的成绩．