The coming acceleration of global population ageing

The future paths of population ageing result from specific combinations of declining fertility and increasing life expectancies in different parts of the world. Here we measure the speed of population ageing by using conventional measures and new ones that take changes in longevity into account for the world as a whole and for 13 major regions. We report on future levels of indicators of ageing and the speed at which they change. We show how these depend on whether changes in life expectancy are taken into account. We also show that the speed of ageing is likely to increase over the coming decades and to decelerate in most regions by mid-century. All our measures indicate a continuous ageing of the world's population throughout the century. The median age of the world's population increases from 26.6 years in 2000 to 37.3 years in 2050 and then to 45.6 years in 2100, when it is not adjusted for longevity increase. When increases in life expectancy are taken into account, the adjusted median age rises from 26.6 in 2000 to 31.1 in 2050 and only to 32.9 in 2100, slightly less than what it was in the China region in 2005. There are large differences in the regional patterns of ageing. In North America, the median age adjusted for life expectancy change falls throughout almost the entire century, whereas the conventional median age increases significantly. Our assessment of trends in ageing is based on new probabilistic population forecasts. The probability that growth in the world's population will end during this century is 88%, somewhat higher than previously assessed. After mid-century, lower rates of population growth are likely to coincide with slower rates of ageing.     

试谈海域生态环境与种群数量

文章首先讨论生态环境的基本概念，接着指出环境的差异导致生物的多样性；多样性是生态环境与生物种群关系的核心．生物种群数量在特定的时、空范围内急剧增加会危及生态环境，而人工移养驯化促进生物多样性已有不少成功的事例。广西海洋生物５６３５种。占专家估计的世界物种（约３１９１６０４种）数１．７６‰、中国占世界物种数的７．９％，与广西海洋捕捞量为世界的１．６９‰，中国占世界的６．３％相当接近，提示海洋生物种类与渔获量间存在着某种内在的消长机制有待人们去研究揭示，而生物多样性是水域生态环境与生物种群正常关系的主要指标。最后提出扩增广西浅海某一种群数量的具体建议。     

Rethinking schizophrenia

How will we view schizophrenia in 2030? Schizophrenia today is a chronic, frequently disabling mental disorder that affects about one per cent of the world's population. After a century of studying schizophrenia, the cause of the disorder remains unknown. Treatments, especially pharmacological treatments, have been in wide use for nearly half a century, yet there is little evidence that these treatments have substantially improved outcomes for most people with schizophrenia. These current unsatisfactory outcomes may change as we approach schizophrenia as a neurodevelopmental disorder with psychosis as a late, potentially preventable stage of the illness. This 'rethinking' of schizophrenia as a neurodevelopmental disorder, which is profoundly different from the way we have seen this illness for the past century, yields new hope for prevention and cure over the next two decades.     

发展绿色化学,改善生态环境

 21世纪是世界人口迅速增长、经济迅猛发展的时期,又是环境污染严重、能源消耗巨大的时期。面对严峻形势,许多国家提出人类可持续发展的战略方针,在全球掀起了发展绿色化学、利用可再生能源的热潮。为保护环境、构建可持续能源体系,并加快中国现代化进程,本文从绿色化学的发展历史及中国能源结构两方面出发,介绍了绿色化学的内涵、绿色化学在化学化工领域的应用及中国的能源战略,并指出绿色化、清洁化将携手助力中国的现代化建设。     

Constraints on radiative forcing and future climate change from observations and climate model ensembles

The assessment of uncertainties in global warming projections is often based on expert judgement, because a number of key variables in climate change are poorly quantified. In particular, the sensitivity of climate to changing greenhouse-gas concentrations in the atmosphere and the radiative forcing effects by aerosols are not well constrained, leading to large uncertainties in global warming simulations. Here we present a Monte Carlo approach to produce probabilistic climate projections, using a climate model of reduced complexity. The uncertainties in the input parameters and in the model itself are taken into account, and past observations of oceanic and atmospheric warming are used to constrain the range of realistic model responses. We obtain a probability density function for the present-day total radiative forcing, giving 1.4 to 2.4 W m-2 for the 5-95 per cent confidence range, narrowing the global-mean indirect aerosol effect to the range of 0 to -1.2 W m-2. Ensemble simulations for two illustrative emission scenarios suggest a 40 per cent probability that global-mean surface temperature increase will exceed the range predicted by the Intergovernmental Panel on Climate Change (IPCC), but only a 5 per cent probability that warming will fall below that range.     

教育:新的经济增长点

新的经济增长点的形成过程,就是培育再生产要素并以此带动社会经济发展的过程。21世纪信息化社会的到来,人类将进入知识经济时代,知识信息的生产、分配和使用必将成为世界经济发展新的经济增长点,而教育必定是这个新的经济增长点的重要组织部分。     

Mercury's capture into the 3/2 spin-orbit resonance as a result of its chaotic dynamics

Mercury is locked into a 3/2 spin-orbit resonance where it rotates three times on its axis for every two orbits around the sun. The stability of this equilibrium state is well established, but our understanding of how this state initially arose remains unsatisfactory. Unless one uses an unrealistic tidal model with constant torques (which cannot account for the observed damping of the libration of the planet) the computed probability of capture into 3/2 resonance is very low (about 7 per cent). This led to the proposal that core-mantle friction may have increased the capture probability, but such a process requires very specific values of the core viscosity. Here we show that the chaotic evolution of Mercury's orbit can drive its eccentricity beyond 0.325 during the planet's history, which very efficiently leads to its capture into the 3/2 resonance. In our numerical integrations of 1,000 orbits of Mercury over 4 Gyr, capture into the 3/2 spin-orbit resonant state was the most probable final outcome of the planet's evolution, occurring 55.4 per cent of the time.     

A confirmation of the general relativistic prediction of the Lense-Thirring effect

An important early prediction of Einstein's general relativity was the advance of the perihelion of Mercury's orbit, whose measurement provided one of the classical tests of Einstein's theory. The advance of the orbital point-of-closest-approach also applies to a binary pulsar system and to an Earth-orbiting satellite. General relativity also predicts that the rotation of a body like Earth will drag the local inertial frames of reference around it, which will affect the orbit of a satellite. This Lense-Thirring effect has hitherto not been detected with high accuracy, but its detection with an error of about 1 per cent is the main goal of Gravity Probe B--an ongoing space mission using orbiting gyroscopes. Here we report a measurement of the Lense-Thirring effect on two Earth satellites: it is 99 +/- 5 per cent of the value predicted by general relativity; the uncertainty of this measurement includes all known random and systematic errors, but we allow for a total +/- 10 per cent uncertainty to include underestimated and unknown sources of error.     

通过强势及弱势的分析构建保护区的管理策略——以梵净山自然保护区为例(英文)

到 1999年底 ,贵州省已经建立了 5 1个自然保护区 ,总面积达到 32 130 0hm2 ,占全省面积的1 81%。根据贵州省自然保护区规划 ,到 2 0 10年贵州省将建成 15 3个自然保护区 ,总面积达 80 5 92 1hm2 。大部分的自然保护区建在贫困落后的地区 ,保护区内有大量的群众 ,他们的生产活动受到极大的限制 ,同时 ,对生存和经济发展的需求 ,使他们对保护区的资源无节制的利用 ,对保护区生物多样性的保护造成很大的影响。保护区周边社区与保护区本身的关系 ,对生物多样性的有效保护十分关键。本文以梵净山自然保护区为例 ,通过对保护区强势与弱势的分析 ,构建保护区的管理策略     

Subducted banded iron formations as a source of ultralow-velocity zones at the core-mantle boundary

Ultralow-velocity zones (ULVZs) are regions of the Earth's core-mantle boundary about 1-10 kilometres thick exhibiting seismic velocities that are lower than radial-Earth reference models by about 10-20 per cent for compressional waves and 10-30 per cent for shear waves. It is also thought that such regions have an increased density of about 0-20 per cent (ref. 1). A number of origins for ULVZs have been proposed, such as ponding of dense silicate melt, core-mantle reaction zones or underside sedimentation from the core. Here we suggest that ULVZs might instead be relics of banded iron formations subducted to the core-mantle boundary between 2.8 and 1.8 billion years ago. Consisting mainly of interbedded iron oxides and silica, such banded iron formations were deposited in the world's oceans during the late Archaean and early Proterozoic eras. We argue that these layers, as part of the ocean floor, would be recycled into the Earth's interior by subduction, sink to the bottom of the mantle and may explain all of the observed features of ULVZs.     

Remobilization of southern African desert dune systems by twenty-first century global warming

Although desert dunes cover 5 per cent of the global land surface and 30 per cent of Africa, the potential impacts of twenty-first century global warming on desert dune systems are not well understood. The inactive Sahel and southern African dune systems, which developed in multiple arid phases since the last interglacial period, are used today by pastoral and agricultural systems that could be disrupted if climate change alters twenty-first century dune dynamics. Empirical data and model simulations have established that the interplay between dune surface erodibility (determined by vegetation cover and moisture availability) and atmospheric erosivity (determined by wind energy) is critical for dunefield dynamics. This relationship between erodibility and erosivity is susceptible to climate-change impacts. Here we use simulations with three global climate models and a range of emission scenarios to assess the potential future activity of three Kalahari dunefields. We determine monthly values of dune activity by modifying and improving an established dune mobility index so that it can account for global climate model data outputs. We find that, regardless of the emission scenario used, significantly enhanced dune activity is simulated in the southern dunefield by 2039, and in the eastern and northern dunefields by 2069. By 2099 all dunefields are highly dynamic, from northern South Africa to Angola and Zambia. Our results suggest that dunefields are likely to be reactivated (the sand will become significantly exposed and move) as a consequence of twenty-first century climate warming.     

A photonic quantum information interface

Quantum communication requires the transfer of quantum states, or quantum bits of information (qubits), from one place to another. From a fundamental perspective, this allows the distribution of entanglement and the demonstration of quantum non-locality over significant distances. Within the context of applications, quantum cryptography offers a provably secure way to establish a confidential key between distant partners. Photons represent the natural flying qubit carriers for quantum communication, and the presence of telecommunications optical fibres makes the wavelengths of 1,310 nm and 1,550 nm particularly suitable for distribution over long distances. However, qubits encoded into alkaline atoms that absorb and emit at wavelengths around 800 nm have been considered for the storage and processing of quantum information. Hence, future quantum information networks made of telecommunications channels and alkaline memories will require interfaces that enable qubit transfers between these useful wavelengths, while preserving quantum coherence and entanglement. Here we report a demonstration of qubit transfer between photons of wavelength 1,310 nm and 710 nm. The mechanism is a nonlinear up-conversion process, with a success probability of greater than 5 per cent. In the event of a successful qubit transfer, we observe strong two-photon interference between the 710 nm photon and a third photon at 1,550 nm, initially entangled with the 1,310 nm photon, although they never directly interacted. The corresponding fidelity is higher than 98 per cent.     

我国住房价格未来走向模拟与调控——基于人口结构和城镇化长周期视角

结合已有文献和实证检验发现,我国住房价格高速攀升与人口结构的变迁和城镇化进程的加快关系密切,其中城镇化为直接推动力,人口结构以城镇化为媒介影响住房价格,且二者对住房价格的推动力将逐渐减弱直至消失。通过构建含有城镇人口增速的Poterba模型进行模拟分析,结果表明:在现有人口结构变迁和城镇化发展趋势下,我国住房价格将于2021年转为负增长,即我国的住房市场在未来的7年左右仍然看好;若放宽二胎政策并加大户籍制度改革力度,主动、恰当地调整人口结构和城镇化的发展趋势,可将住房价格负增长转折时间点推迟至2027年左右。     

Malthus foiled again and again

Throughout history, increasing population has driven the need to increase agricultural efficiency, so averting successive 'malthusian' disasters. In the twentieth century, the application of scientific knowledge to agriculture yielded tremendous dividends, enabling cereal yields to increase threefold since 1950. But with the world's population projected to reach nine billion by the middle of this century, new ways must be found to increase yields while preserving natural habitats and biodiversity.     

东北区旱涝灾害特征分析及趋势预测

利用东北区1751～2000年旱涝灾害资料,分析了该区近250年来旱涝灾害演变的特征.根据气象因素和旱涝灾害的关系,引入了转移概率、太阳黑子相对数和厄尔尼诺方法,导出了未来旱涝灾害预报的方法和公式,对该区2001～2010年旱涝灾害趋势作了预测.结果显示,20世纪东北区旱涝灾害较以前都有所加重,尤其是干旱灾害.2001～2010年东北区会出现2次以上的干旱和1～2次的洪涝灾害,且2007年左右是发生洪涝灾害的危险期.该项研究为东北区实际防灾、减灾工作提供了参考.     

依靠科技创新调整产业结构——浅谈科技创新是调整和优化西藏产业结构的必然选择

科技创新是当今世界经济发展的一大主流,也是各国经济增长的一个主要亮点。1998年3月4日,江泽民同志在与出席全国政协九后一次科技界委员座谈时指出：“世纪之交,世界经济发展的一个明显趋势,就是科学技术发展日新月异,科技在经济发展中的作用越来越大”,“创新是一个民族进步的灵魂,是一个国家兴旺发达的不竭动力”。为此,本文根据二十一世纪世界经济发展的主要趋势和科技创新的主要动力,结合《西藏自治区国民经济和社会发展第十个五年计划和2010远景目标纲要》报告,通过科技创新加大和调整我区的产业结构。     

新世纪初期中国城市化与经济增长关系的定量分析

城市化与经济发展之间是一种相互促进、互为因果的关系。以往的研究多以经济发展水平为自变量来研究相应的城市化水平,而以城市化水平为自变量反向研究他们的关系则不多,这种研究具有更积极的实际意义,模型也更为简单。从人口城市化和空间城市化两个方面,用统计数据的时间序列和空间序列进行相关分析和回归分析,结果表明:中国单位人口城市化率增量对应的人均产值增量在350～1 600元/人之间,且新世纪以来逐年提高,中国人口城市化的经济效益越来越好;单位空间城市化率增量对应的地均产值增量在2.7～12.5万元/KM2之间,新世纪以来先降后升,存在波动,2003年后城市土地利用的经济效益逐年提高。     

Quantification of modelling uncertainties in a large ensemble of climate change simulations

Comprehensive global climate models are the only tools that account for the complex set of processes which will determine future climate change at both a global and regional level. Planners are typically faced with a wide range of predicted changes from different models of unknown relative quality, owing to large but unquantified uncertainties in the modelling process. Here we report a systematic attempt to determine the range of climate changes consistent with these uncertainties, based on a 53-member ensemble of model versions constructed by varying model parameters. We estimate a probability density function for the sensitivity of climate to a doubling of atmospheric carbon dioxide levels, and obtain a 5-95 per cent probability range of 2.4-5.4 degrees C. Our probability density function is constrained by objective estimates of the relative reliability of different model versions, the choice of model parameters that are varied and their uncertainty ranges, specified on the basis of expert advice. Our ensemble produces a range of regional changes much wider than indicated by traditional methods based on scaling the response patterns of an individual simulation.     

Spin-dependent exciton formation in pi-conjugated compounds.

The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 +/- 1 per cent for the monomer, but 57 +/- 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.     

Reduction of soil carbon formation by tropospheric ozone under increased carbon dioxide levels

In the Northern Hemisphere, ozone levels in the troposphere have increased by 35 per cent over the past century, with detrimental impacts on forest and agricultural productivity, even when forest productivity has been stimulated by increased carbon dioxide levels. In addition to reducing productivity, increased tropospheric ozone levels could alter terrestrial carbon cycling by lowering the quantity and quality of carbon inputs to soils. However, the influence of elevated ozone levels on soil carbon formation and decomposition are unknown. Here we examine the effects of elevated ozone levels on the formation rates of total and decay-resistant acid-insoluble soil carbon under conditions of elevated carbon dioxide levels in experimental aspen (Populus tremuloides) stands and mixed aspen-birch (Betula papyrifera) stands. With ambient concentrations of ozone and carbon dioxide both raised by 50 per cent, we find that the formation rates of total and acid-insoluble soil carbon are reduced by 50 per cent relative to the amounts entering the soil when the forests were exposed to increased carbon dioxide alone. Our results suggest that, in a world with elevated atmospheric carbon dioxide concentrations, global-scale reductions in plant productivity due to elevated ozone levels will also lower soil carbon formation rates significantly.