Reputation helps solve the 'tragedy of the commons'.

The problem of sustaining a public resource that everybody is free to overuse-the 'tragedy of the commons'-emerges in many social dilemmas, such as our inability to sustain the global climate. Public goods experiments, which are used to study this type of problem, usually confirm that the collective benefit will not be produced. Because individuals and countries often participate in several social games simultaneously, the interaction of these games may provide a sophisticated way by which to maintain the public resource. Indirect reciprocity, 'give and you shall receive', is built on reputation and can sustain a high level of cooperation, as shown by game theorists. Here we show, through alternating rounds of public goods and indirect reciprocity games, that the need to maintain reputation for indirect reciprocity maintains contributions to the public good at an unexpectedly high level. But if rounds of indirect reciprocation are not expected, then contributions to the public good drop quickly to zero. Alternating the games leads to higher profits for all players. As reputation may be a currency that is valid in many social games, our approach could be used to test social dilemmas for their solubility.     

Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors

One of the central aims of ecology is to identify mechanisms that maintain biodiversity. Numerous theoretical models have shown that competing species can coexist if ecological processes such as dispersal, movement, and interaction occur over small spatial scales. In particular, this may be the case for non-transitive communities, that is, those without strict competitive hierarchies. The classic non-transitive system involves a community of three competing species satisfying a relationship similar to the children's game rock-paper-scissors, where rock crushes scissors, scissors cuts paper, and paper covers rock. Such relationships have been demonstrated in several natural systems. Some models predict that local interaction and dispersal are sufficient to ensure coexistence of all three species in such a community, whereas diversity is lost when ecological processes occur over larger scales. Here, we test these predictions empirically using a non-transitive model community containing three populations of Escherichia coli. We find that diversity is rapidly lost in our experimental community when dispersal and interaction occur over relatively large spatial scales, whereas all populations coexist when ecological processes are localized.     

Rad54 protein promotes branch migration of Holliday junctions

Homologous recombination has a crucial function in the repair of DNA double-strand breaks and in faithful chromosome segregation. The mechanism of homologous recombination involves the search for homology and invasion of the ends of a broken DNA molecule into homologous duplex DNA to form a cross-stranded structure, a Holliday junction (HJ). A HJ is able to undergo branch migration along DNA, generating increasing or decreasing lengths of heteroduplex. In both prokaryotes and eukaryotes, the physical evidence for HJs, the key intermediate in homologous recombination, was provided by electron microscopy. In bacteria there are specialized enzymes that promote branch migration of HJs. However, in eukaryotes the identity of homologous recombination branch-migration protein(s) has remained elusive. Here we show that Rad54, a Swi2/Snf2 protein, binds HJ-like structures with high specificity and promotes their bidirectional branch migration in an ATPase-dependent manner. The activity seemed to be conserved in human and yeast Rad54 orthologues. In vitro, Rad54 has been shown to stimulate DNA pairing of Rad51, a key homologous recombination protein. However, genetic data indicate that Rad54 protein might also act at later stages of homologous recombination, after Rad51 (ref. 13). Novel DNA branch-migration activity is fully consistent with this late homologous recombination function of Rad54 protein.     

Myofibrillogenesis regulator-1 promotes cell adhesion and migration in human hepatoma cells

Myofibrillogenesis regulator-1 (MR-1) is a gene overexpressed usually in many human cancers. However, the effects of MR-1 on cell proliferation, adhesion, migration and genome-wide gene regulation are still unclear. In this study, a human hepatoma cell line that highly overexpresses MR-1, BEL-7402/MR-1 cells was established. While the high expression of MR-1 did not promote cell proliferation, it significantly increased cell spreading, adhesion and migration compared with control cells. A total of 147 genes were regulated by MR-1 expression, 46 genes were down-regulated and 101 genes were up-regulated by MR-1 overexpression. Many of these genes were related to cell adhesion, cytoskeletal regulation, MAPK signaling, and cell cycle related pathways. Western blot analysis further confirmed the regulation of pathways associated with migration by MR-1. These results suggest that MR-1 is involved in the regulation of cancer cell adhesion, migration and related gene expression.     

Expression of aquaporin-1 in SMMC-7221 liver carcinoma cells promotes cell migration

Aquaporins (AQPs) are membrane water channels that play pivotal roles in physiological and pathophysi- ological processes in diverse mammalian organs[1―3]. Recent studies indicated a novel role of AQPs in cell migration. Mice lacking AQP1, the endothelia…     

Mutation and sex in a competitive world

How do deleterious mutations interact to affect fitness? The answer to this question has substantial implications for a variety of important problems in population biology, including the evolution of sex, the rate of adaptation and the conservation of small populations. Here we analyse a mathematical model of competition for food in which deleterious mutations affect competitive ability. We show that, if individuals usually compete in small groups, then competition can easily lead to a type of genetic interaction known as synergistic epistasis. This means that a deleterious mutation is most damaging in a genome that already has many other deleterious mutations. We also show that competition in small groups can produce a large advantage for sexual populations, both in mean fitness and in ability to resist invasion by asexual lineages. One implication of our findings is that experimental efforts to demonstrate synergistic epistasis may not succeed unless the experiments are redesigned to make them much more naturalistic.     

恒化器中种群竞争的随机模型

讨论了恒化器中种群竞争的随机模型,得到了种群持久生存的必要条件.     

CTCF通过抑制p53信号通路促进胆管癌细胞的生长、迁移和侵袭

为了探索CCCTC结合因子(CCCTC-binding factor, CTCF)对人胆管癌细胞的生长、迁移和侵袭能力的影响及其潜在的分子作用机制,利用慢病毒感染法获得稳定过表达或敲低CTCF的胆管癌细胞系,采用蛋白质免疫印迹法(Western blotting, Wb)检测CTCF蛋白表达水平,采用Cell Counting Kit-8(CCK-8)法和克隆形成实验检测细胞生长情况,采用Transwell小室实验检测细胞迁移和侵袭能力,采用GraphPad软件(v6)的Mann-Whitney U检验分析CTCF基因在癌和癌旁组织间的mRNA差异表达.结果显示:过表达CTCF可显著促进HCCC-9810和RBE胆管癌细胞的生长、迁移和侵袭能力;敲低CTCF呈现相反的表型.通过通路富集分析发现:CTCF的表达水平在胆管癌中与p53信号通路活性显著负相关,过表达CTCF可显著下调p53及其靶基因p21的mRNA和蛋白表达水平,而敲低CTCF则显著促进p53和p21的mRNA和蛋白表达水平.综上,本研究揭示CTCF可能通过抑制p53信号通路而促进胆管癌细胞生长、迁移和侵袭而发挥促癌基因的功能.     

高校图书馆开展竞争情报服务的必要性

竞争情报服务是图书馆开展信息服务的一个新热点.本文主要论述了高校图书馆开展竞争情报服务的必要性及其优势.     

一类无时滞非自治Lotka-Volterra竞争子系统的灭绝性

讨论了一类无时滞非自治Lotka-Volterra竞争子系统,在一定条件下得到了一种群xi(t)(l=r+1,…,n)随着时间增加趋于灭绝的充分条件,通过构造Lyapunov函数证明了相应的结论,推广了相关文献的一些结果。     

完全竞争市场的利弊分析

通过分析完全竞争市场的条件、供需曲线和均衡方面等内容;得出自由竞争是实现基本经济目标的最好手段,具有保证资源的合理配置,发挥劳资双方的积极性的优点,同时完全竞争市场具有一定的缺陷:会造成资源的浪费,无差别的产品不能满足消费者多样化的需求等;从而为企业在近似于完全竞争市场中寻求优势提供相关的对策和建议.     

乳状液在岩心中运移的影响因素研究

为了研究乳状液在多孔介质中运移的影响因素及运移规律,了解乳状液对提高采收率的作用,利用长岩心作为模型进行驱替实验,研究了乳状液液滴粒径、液滴密度及运移速度对其运移规律的影响.结果表明,乳状液在孔喉中的宏观运移阻力是乳状液液滴对孔喉堵塞的累积结果.大液滴的乳状液在孔隙介质中运移阻力明显大于小液滴的乳状液.注入速度对乳状液在岩心中运移阻力影响较大,在粒径孔径匹配的条件下,存在一个临界注入速度,在临界速度下乳液在岩心中才能形成明显的封堵.速度太低,乳状液破乳严重,乳状液变形通过孔喉的能力强不容易封堵孔喉;速度太高,乳状液液滴被分散破碎、粒径变小不容易封堵孔喉.     

消除时序电路中的竞争干扰

通过分析次序脉冲发生器，着重指出在时序电路中存在过渡竞争干扰，从而给出一些消除这种干扰的措施。     

消除时序电路中的竞争干扰

通过分析次序脉冲发生器，着重指出在时序电路中存在过渡竞争干扰，从而给出一些消除这种干扰的措施。     

禁忌搜索算法求解带产品定价的竞争选址问题

讨论了一个在竞争环境下使获利最大的竞争选址双层规划模型,其中上层模型做出选址决策,下层模型确定产品的纳什均衡价格。在保证了不合作状态下双方价格均衡解的存在性和唯一性的前提下,设计了求解该模型的选址 定价启发式算法程序。通过贪心算法和交换算法产生禁忌搜索的初始解,设置了合理的禁忌搜索算法参数,最后通过具有一定规模的实例计算,证明了该算法在求解此类问题中的可行性和科学有效性。     

乡土文学史中的莫言乡土小说

莫言的作品大多是以乡土为背景来描写乡村生活的,应该说莫言小说是新时期乡土小说的代表,因此,将莫言的作品置于中国乡土小说背景中将有利于突显出其在乡土文学史上的独特之处。与写实主义和写意主义乡土作家不同,莫言的乡土小说更多的是以一种平民姿态表达着对于乡土中国苦难的体验乃至认同。     

乡土文学史中的莫言乡土小说

莫言的作品大多是以乡土为背景来描写乡村生活的,应该说莫言小说是新时期乡土小说的代表,因此,将莫言的作品置于中国乡土小说背景中将有利于突显出其在乡土文学史上的独特之处。与写实主义和写意主义乡土作家不同,莫言的乡土小说更多的是以一种平民姿态表达着对于乡土中国苦难的体验乃至认同。     

体育强国视域下我国高校竞技体育的发展

采用文献资料法、数理统计法、逻辑分析等研究方法,对新形势下我国高校竞技体育存在的问题进行分析.提出在体育强国视域下我国高校竞技体育发展的策略:高校竞技体育发展战略思想的重新定位;逐步建立合理、完善的高校竞技体育发展机制;建立以高校为枢纽的高水平竞技运动员培养体系;推进教练员岗位专职化,完善教练员培养体系;充分挖掘竞技体育的现代社会价值.     

一类非自治连续型竞争系统的概周期解

研究具有非线性相互抑制项的非自治连续型竞争系统的动力学行为. 通过运用微分方程比较原理和Lyapunov函数法,得到了保证系统持久,全局吸引和存在唯一概周期正解的充分性条件,所得结果补充了已有的相关结论. 数值模拟结果表明,本研究结果具有可靠性.     

图的最大局部密度

引入了图的最大局部密度的概念并讨论了该参数与图的其他一些参数的关系。改进了Ｂｒｏｏｋｓ定理。给出了Ｂｏｕｃｈｅｔ等人关于对角着色的定理的一个简短证明。