未来的汽车动力一燃料电池

介绍了氢燃料电池在汽车上的应用,对燃料电池车的优点、目前存在的技术难题以及发展形势进行了综述.     

The future of ageing

Advances in our knowledge of age-associated diseases have far outpaced advances in our understanding of the fundamental ageing processes that underlie the vulnerability to these pathologies. If we are to increase human life expectancy beyond the fifteen-year limit that would result if today's leading causes of death were resolved, more attention must be paid to basic research on ageing. Determination of longevity must be distinguished from ageing to take us from the common question of why we age to a more revealing question that is rarely posed: why do we live as long as we do? But if the ability to intervene in ageing ever becomes a reality, it will be rife with unintended and undesirable consequences.     

Quantitative evidence for global amphibian population declines

Although there is growing concern that amphibian populations are declining globally, much of the supporting evidence is either anecdotal or derived from short-term studies at small geographical scales. This raises questions not only about the difficulty of detecting temporal trends in populations which are notoriously variable, but also about the validity of inferring global trends from local or regional studies. Here we use data from 936 populations to assess large-scale temporal and spatial variations in amphibian population trends. On a global scale, our results indicate relatively rapid declines from the late 1950s/early 1960s to the late 1960s, followed by a reduced rate of decline to the present. Amphibian population trends during the 1960s were negative in western Europe (including the United Kingdom) and North America, but only the latter populations showed declines from the 1970s to the late 1990s. These results suggest that while large-scale trends show considerable geographical and temporal variability, amphibian populations are in fact declining--and that this decline has been happening for several decades.     

最早传入中国的西方地震学知识

龙华民(Nicolas Longobardi,1568~1654)和高一志(Alphonsus Vagnoni,1566~1610)都是明末西方来华传教的意大利传教士群中的两位,前者的《地震解》和后者的《空际格致》曾将当时欧洲的地震学知识介绍到中国来,其内容包括地震的起因、地震的等级、发生地震的季节和时辰、地震之前兆、地震后的状况(灾情)、发生地震之地点、地震持续时间等等.文章将一一加以叙述,并加以评论,可见用"气成说"解释地震之成因并不正确.但是所言火山爆发、地下岩浆沿着地壳裂隙涌出地面,确为地震成因之一.至于所言地震之预兆和地震后之破坏情形(灾情)等,与今人所见大致相同,仍然值得今人参考.     

下一代操作系统综述

操作系统是计算机系统中的核心软件 ,其性能的好坏直接影响计算机系统。本文在对当前主流操作系统的剖析基础上 ,从系统安全性能、处理能力、配置管理、对象技术等方面阐述了新一代操作系统应具备的特性     

宝鸡市人口老龄化的空间特征及影响因素分析

目的分析宝鸡市人口老龄化的空间特征及其影响因素,为应对老龄化问题提供依据。方法利用第五次人口普查数据,采用数据对比、空间聚类分析、灰色关联分析等方法,分别对宝鸡市人口老龄化的基本特征、地域差异、空间分布及其影响因素进行分析。结果截至2000年,宝鸡市的老龄化特征已十分显著;人口年龄结构地区差异明显;市中心区老龄家庭比重较大;年龄中位数、老龄人口密度、迁入人口数等与老年人口比重关联度较大。结论宝鸡市中心区人口老龄化特征显著,且有进一步强化的趋势,建议采取相应措施。     

一个有关生物种群的泛函微分方程模型整体解的存在性和唯一性

研究了一个有关生物种群的非线性泛函微分方程模型整体解的存在性和唯一性问题。     

The common biology of cancer and ageing

At first glance, cancer and ageing would seem to be unlikely bedfellows. Yet the origins for this improbable union can actually be traced back to a sequence of tragic--and some say unethical--events that unfolded more than half a century ago. Here we review the series of key observations that has led to a complex but growing convergence between our understanding of the biology of ageing and the mechanisms that underlie cancer.     

一类描述人口群体增长模型的非线性方程非局部定解问题解的存在性研究

文章讨论了一类描述人口群体增长模型δp/δt(t,x) δp/δx(t,x)=-[d1(x) d2(x)∫0^Ap(t,ξ)dξ]p(t,x) (1)在一定非局部初边值条件下的解，运用逐次逼近法得到了方程（1）解的表达式，并证明了解的整体存在唯一性。     

明朝末年西方早期画法几何知识之东来

目的系统探讨和分析明朝末年西方早期画法几何知识在中国的传播。方法对当时有关献进行综合分析。结果利玛窦(1552—1610)、李之藻(1565-1630)、罗雅谷(1593-1638)和汤若望(1591-1666)传入中国多项关于天球平行正投影和球极投影的知识。结论早在明朝末年西方画法几何知识就由西方传教士传入中国。     

Evolution of ageing

An evolutionary view of ageing suggests that mortality may be due to an energy-saving strategy of reduced error regulation in somatic cells. This supports Orgel's 'error catastrophe' hypothesis and offers a new basis for the study of normal and abnormal ageing syndromes and of apparently immortal transformed cell lines.     

几何法证明科氏加速度

不少理论力学教材对科氏加速度的几何法证明不够详细,本文将对牵连运动为定轴转动的特例用几何法推证点的加速度合成定理,读者能更加形象地理解定理中各项的物理意义。     

The global warming debate

Nowadays, global warming and the anthropogenic impact on the climate is one of the hottest topics of scientific re-search and world media interest. Concerns about this issue culminated with the Copenhagen Conference on December 7–18, 2009......     

机械参数对弹簧质量块式加速度开关精度影响分析

针对弹簧质量块式加速度开关普遍存在过载值精度低、生产调试过程中动作过载值易发生偏移问题。文章对典型压缩弹簧质量块式加速度开关建立了力学方程,分析了弹簧弯曲角度、摩擦系数等机械参数对加速度开关的过载性能影响。得出压缩弹簧质量块式加速度开关的弹簧弯曲角度及摩擦系数对加速度开关过载性能的影响规律。得出加速度开关质量块与导向结构之间的摩擦系数ε0.04,加速度开关的压缩弹簧与导向结构中心轴之间的夹角θ1和θ2绝对值小于3°,能够使得加速度开关合格率达到90%以上的结果,对于产品生产控制提供了参考数据。