人类胚胎的免疫系统与成人的有着截然不同的起源

UCSF的研究人员首次向我们证实,人类胚胎的免疫系统与成人的免疫系统有着截然不同的起源.相对于成人的免疫系统而言,胚胎免疫系统对待其环境中的外源物质更倾向于适应,而不是去消灭它.这一发现不但使我们能够更加了解新生儿是如何对感染以及疫苗反应的,而且可以用来解释许多难题,比如为何HIV     

美丽的兴凯湖 和谐的地球村

正温室效应,全球不断变暖;冰川融化,海平面不断上升;暴雪、酷热,全球的极限天气越来越多;江河枯竭,地下水污染……我们的环境怎么了?我们的地球得病了吗?从小我就喜欢看关于环境变化的新闻,喜欢观察树上的小鸟、池塘里的小鱼、郊外的山山水水。马上就要上初一了,这个暑假,我有机会参加中科院组织的兴凯湖湿地科学考察活动,别提有多高兴了。8月的北京酷热难耐,而     

真正的科学家真正的爱国者

卢永根院士是著名的作物遗传学家。他致力于水稻遗传育种研究,取得了显著的成绩。在青年时代,他以极大的热情投身到革命洪流中,既做地下党的工作,又刻苦地在岭大深造;在岭大毕业后至今50余年中,他在高校既教书,又从事科学研究,为人才培养和水稻遗传育种工作做出贡献。他总结的五点体会和崇高的思想境界:“我的青春年华已经献给党的科学事业,我准备把晚年继续献给这个事业。”令人深受启发,值得学习。经作者同意,现将刊登在中国科学院院士工作局《学部通讯》2003年第4期上的“院士自述:我的成长经历”这篇报道,转载于后。     

破碎的化石与缝合的历史

1959年7月17日黎明,当第一缕晨曦洒在奥杜韦峡谷中时,这个位于东非坦桑尼亚平原上的凹地没有料到改变命运的时刻悄无声息地来临了。这一天,同样被改变的还有古人类学家利基夫妇的命运和整个人类起源研究的进程。当天清晨,路易斯·利基因患感冒留在营帐里休息,他的妻子玛莉·利基独自领着小狗萨丽和维多利亚,像往常一样,到峡谷中的挖掘现场去搜寻古人类的遗迹。利基     

蛋白质的排阻色谱复性的新进展

外源蛋白在大肠杆菌中高效表达时 ,常常形成不溶的、无活性的包涵体 ,包涵体蛋白的复性是重组蛋白生产过程中的一个技术难题。排阻色谱 (sizeexclusionchromatography ,SEC)用于蛋白复性是一种较新的、适用于任何一种蛋白的方法 ,与常用的稀释复性法相比 ,它能在高的起始蛋白浓度下对蛋白进行复性 ,活性回收率较高 ,同时又能使目标蛋白得到一定程度的纯化。对使用SEC复性的进展进行了评述 ,其内容包括SEC复性的原理及其复性过程中的影响因素 ,并对其未来发展进行了展望。     

没有神经的腿的再生

对于嵘螈肢体的再生,神经系统特别是切割后的残肢裹的神经纤维,一向是被认为有决定性意义的。晚近利用成体或接近变态的幼体的研究证明了:在再生芽基形成之后,切断神经,已经形成的芽基仍然可以继续发育成正常的肢体;但在再生芽基形成之     

阳光下的宝藏——西双版纳的热带雨林

1752年,瑞典植物学家奥斯伯克乘船前往中国。路经爪哇岛时,他看到一株树木的树干生长出很多美丽的花朵。作为一个对热带雨林还知之甚少的北欧植物学家,他确信发现了无叶的寄生植物新种,并把这些花命名为"寄生楝"。16、17世纪,凭借着先进的航海技术,欧洲人开始了对世界的探奇,从探险家和航海家们的信件、日记中不断传来热带从林离奇古怪、玄妙莫测、耸人听闻的故事。那时欧洲人初识热带雨林,他们看到十几个人才能合围的巨树     

基于商业智能的医院决策支持系统的应用

商业智能是利用数据仓库、联机分析处理和数据挖掘等核心技术,将大量的存储数据进行提取、整理、分析,为决策者进行经营决策提供支持的技术。基于商业智能的医院决策支持系统是从不同的角度抽象出反映医院管理及医疗、教育、科研业务的各类指标,集成医院运行产生的宝贵数据,全面、系统、实时地复用各类业务数据,建立相关的知识模型和知识库,满足支持决策的信息需求,实现通过信息技术辅助决策的功能。     

知识的载体 智慧的力量

2009年5月,繁花烂漫的季节,高等教育出版社迎来了55周年华诞,《生命世界》杂志也走过了5年不平凡的历程。我们出版的高质量的教材和学术著作为我国的生命科学人才培养和学科建设发挥了积极的重要作用,受到了广大师生和科研人员的欢迎。《生命世界》在传播生命科学知识、提高大众科学素养方面起到了很好的作用,全国人大常委会副委员长、中国科学院院长路甬祥院士和全国人大常委会副委员长、中国科协主席、     

知识的载体 智慧的力量

2009年5月,繁花烂漫的季节,高等教育出版社迎来了55周年华诞,《生命世界》杂志也走过了5年不平凡的历程。我们出版的高质量的教材和学术著作为我国的生命科学人才培养和学科建设发挥了积极的重要作用,受到了广大师生和科研人员的欢迎。《生命世界》在传播生命科学知识、提高大众科学素养方面起到了很好的作用,全国人大常委会副委员长、中国科学院院长路甬祥院士和全国人大常委会副委员长、中国科协主席、     

一类具有时滞和治愈率的HIV病理模型的稳定性

研究一类具有饱和感染率、治愈率和细胞内时滞的HIV病理模型.首先分析平衡态的存在性与稳定性,然后给出染病平衡态对于任意时滞保持稳定（不稳定）的充分条件,并利用Nyquist准则度量染病平衡点保持稳定的时滞长度.     

The Series Solution for a Class of Nonstationary Biological Population Systems and Their Stability

1IntroductionInaStableenjoinment,thegeneral~populationSystemcanbeexpr~asfollows(see[1,21)In[2,3],wedi~theP~ofationforaStatiomppopulationsyStem,theanduniquenessOfthesolutionforanonStatio~populationsystemwereP~.InthiSPaper,wediscusstheseriessolutionOf~tO~adulationSyStem,wedefinethecriticsproliferationrate,anddiscussthestabilityOftheSySt~.InSyStem(1),p(r,t)iscalledpopulationdenSi.tyfUnCtionOfagerandtimet,p,(r)isaninitialdistribution,8(t)istheprDliferationrate,p(r)isanincreasingfUnction(…     

Folding of circular permutants with decreased contact order: general trend balanced by protein stability.

To examine the influence of contact order and stability on the refolding rate constant for two-state proteins, we have analysed the folding kinetics of the small beta-alpha-beta protein S6 and two of its circular permutants with relative contact orders of 0.19, 0.15 and 0.12. Data reveal a small but significant increase of the refolding rate constant (log k(f)) with decreasing contact order. At the same time, the decreased contact order is correlated to losses in global stability and alterations of the folding nucleus. When the differences in stability are accounted for by addition of Na2SO4 or by comparison of the folding kinetics at the transition mid-point, the dependence between log k(f) and contact order becomes stronger and follows the general correlation for two-state proteins. The observation emphasizes the combined action of topology and stability in controlling the rate constant of protein folding.     

一类带有肝炎B病毒感染的数学模型的全局稳定性分析（英文）

本文主要分析了一类具有肝炎B病毒感染且带有治愈率的典型的数学模型（HBV）.通过稳定性分析,得到了该模型的无病平衡点与地方病平衡点全局稳定的充分条件,并且证明了当基本再生数R0〈1, HBV感染消失;当R0〉1,HBV感染持续.     

Parameters of atrioventricular conduction and stability of different regimes of heart rate dynamics

By method of computer modeling we investigated a stability of different regimes of heart rate dynamics in relation to the change in the atrioventricular conduction parameters: refractory period, minimum atrioventricular delay and curvatures of delay functions in sinoatrial and atrioventricular nodes. It is shown that curvatures of delay functions in sinoatrial and atrioventricular nodes have the most significant influence on the stability of different regimes of heart rate dynamics. The minimum delays in sinoatrial and atrioventricular nodes have smaller impact. The parameters determining the refractory periods of sinoatrial and atrioventricular nodes are least significant in terms of stability of heart rate dynamics.     

Egg-eating age-structured predators in interaction with age-structured prey

In this paper, we consider a system of integrodifferential equations which models a predator-prey system with both species (predator and prey) age-structured and predators living only on the eggs of prey. The present model is a generalization of the model given in [20]. The existence, stability, and instability of nonnegative equilibria is studied assuming a general fecundity rate function for the prey. With a special choice of fecundity rate function for the predator it is shown here that a large maturation period m of the predator leads to stability. This seems to be contrary to the usual rule of thumb that increasing delays in growth rate responses cause instabilities.     

Stability of complex food webs: resilience, resistance and the average interaction strength

In the face of stochastic climatic perturbations, the overall stability of an ecosystem will be determined by the balance between its resilience and its resistance, but their relative importance is still unknown. Using aquatic food web models we study ecosystem stability as a function of food web complexity. We measured three dynamical stability properties: resilience, resistance, and variability. Specifically, we evaluate how a decrease in the strength of predator-prey interactions with food web complexity, reflecting a decrease in predation efficiency with the number of prey per predator, affects the overall stability of the ecosystem. We find that in mass conservative ecosystems, a lower interaction strength slows down the mass cycling rate in the system and this increases its resistance to perturbations of the growth rate of primary producers. Furthermore, we show that the overall stability of the food webs is mostly given by their resistance, and not by their resilience. Resilience and resistance display opposite trends, although they are shown not to be simply opposite concepts but rather independent properties. The ecological implication is that weaker predator-prey interactions in closed ecosystems can stabilize food web dynamics by increasing its resistance to climatic perturbations.     

The mechanism of orotidine 5'-monophosphate decarboxylase: catalysis by destabilization of the substrate

The mechanism of orotidine 5'-monophosphate decarboxylase (OMP decarboxylase, ODCase) was studied using the decarboxylation of orotic acid analogues as a model system. The rate of decarboxylation of 1,3-dimethylorotic acid and its analogues as well as the stability of their corresponding carbanion intermediates was determined. The results have shown that the stability of the carbanion intermediate is not a critical factor in the rate of decarboxylation. On the other hand, the reaction rate is largely dependent on the equilibrium constant for the formation of a zwitterion. Based on these results, we have proposed a new mechanism in which ODCase catalyzes the decarboxylation of OMP by binding the substrate in a zwitterionic form and providing a destabilizing environment for the carboxylate group of OMP.     

Size-structured demographic models of coral populations

The demographic processes of growth, mortality, and the recruitment of young individuals, are the major organizing forces regulating communities in open systems. Here we present a size-structured (rather than age-structured) population model to examine the role of these different processes in space-limited open systems, taking coral reefs as an example. In this flux-diffusion model the growth rate of corals depends both on the available free-space (i.e. density-dependence) and on the particular size of the coral. In our analysis we progressively study several different forms of growth rate functions to disentangle the effects of free space and size-dependence on the model's stability. Unlike Roughgarden et al. [1985. Demographic theory for an open marine population space-limited recruitment. Ecology 66(1), 54-67], whose principal result is that the growth of settled organisms is destabilizing, we find that size-dependent growth rate often has the potential to endow stability. This is particularly true, if the growth rate is dependent on available free space (i.e. density dependent), but examples are given for growth rates that even lack this property. Further insights into reef system fragility are found through studying the sensitivity of the model steady state to changes in recruitment.     

Folding thermodynamics and kinetics of YNMG RNA hairpins: specific incorporation of 8-bromoguanosine leads to stabilization by enhancement of the folding rate

Modified nucleotides allow fundamental energetic and kinetic properties of nucleic acids to be probed. Here, we demonstrate that an RNA hairpin containing the nucleotide analogue 8-bromoguanosine (8BrG or G), gcUUCGgc, has enhanced stability relative to the unmodified hairpin, with DeltaDeltaG(37)(degrees)= -0.69 +/- 0.15 kcal mol(-1) and DeltaT(M) = +6.8 +/- 1.4 degrees C. NMR spectroscopic data suggest that the enhanced stability of gcUUCGgc does not arise from the native state; laser temperature-jump experiments support this notion, as gcUUCGgc and gcUUCGgc have similar unfolding rate constants, but the folding rate constant of gcUUCGgc is 4.1-fold faster at 37.5 degrees C and 2.8-fold faster under isoenergetic conditions. On the basis of these findings, we propose that 8BrG reduces the conformational entropy of the denatured state, resulting in an accelerated conformational search for the native state and enhanced stability.