Contemporaneous formation of chondrules and refractory inclusions in the early Solar System

Chondrules and calcium-aluminium-rich inclusions (CAIs) are preserved materials from the early history of the Solar System, where they resulted from thermal processing of pre-existing solids during various flash heating episodes which lasted for several million years. CAIs are believed to have formed about two million years before the chondrules. Here we report the discovery of a chondrule fragment embedded in a CAI. The chondrule's composition is poor in 16O, while the CAI has a 16O-poor melilite (Ca, Mg, Al-Silicate) core surrounded by a 16O-rich igneous mantle. These observations, when combined with the previously reported CAI-bearing chondrules, strongly suggest that the formation of chondrules and CAIs overlapped in time and space, and that there were large fluctuations in the oxygen isotopic compositions in the solar nebula probably synchronizing astrophysical pulses.     

Possible in situ formation of meteoritic nanodiamonds in the early Solar System

Grains of dust that pre-date the Sun provide insights into their formation around other stars and into the early evolution of the Solar System. Nanodiamonds recovered from meteorites, which originate in asteroids, have been thought to be the most abundant type of presolar grain. If that is true, then nanodiamonds should be at least as abundant in comets, because they are thought to have formed further out in the early Solar System than the asteroid parent bodies, and because they should be more pristine. Here we report that nanodiamonds are absent or very depleted in fragile, carbon-rich interplanetary dust particles, some of which enter the atmosphere at speeds within the range of cometary meteors. One interpretation of the results is that some (perhaps most) nanodiamonds formed within the inner Solar System and are not presolar at all, consistent with the recent detection of nanodiamonds within the accretion discs of other young stars. An alternative explanation is that all meteoritic nanodiamonds are indeed presolar, but that their abundance decreases with heliocentric distance, in which case our understanding of large-scale transport and circulation within the early Solar System is incomplete.     

The role of chaotic resonances in the Solar System

Our understanding of the Solar System has been revolutionized over the past decade by the finding that the orbits of the planets are inherently chaotic. In extreme cases, chaotic motions can change the relative positions of the planets around stars, and even eject a planet from a system. Moreover, the spin axis of a planet-Earth's spin axis regulates our seasons-may evolve chaotically, with adverse effects on the climates of otherwise biologically interesting planets. Some of the recently discovered extrasolar planetary systems contain multiple planets, and it is likely that some of these are chaotic as well.     

剑桥导游太阳系

本书以最新的视角描述了行星和月亮。开始用短短的篇幅介绍行星的观测和发现历史，然后介绍行星及其卫星的共同特点、演化过程和状况。在各章节中讲述各个行星和太阳系其它天体，包括新近的多种空间任务，从阿波罗探月到近期的木星和火星探测。书中充满了至关重要的事实和信息，以及极其精美的彩色照片。     

集热器对太阳能喷射制冷系统性能的影响

采用寿命期性价比对单、双层盖板平板集热器、全玻璃管、热管真空管及CPC聚焦型集热器对喷射式制冷系统的性能影响进行了评价,并与采用设计工况性价比指标的评价结果进行对比分析。结果表明,寿命期性价比评价指标考虑了太阳辐射与气温变化,比设计工况性价比评价指标更全面、更符合实际情况;双层盖板平板集热器用于太阳能喷射式制冷系统,寿命期性价比最优;CPC聚焦型太阳能集热器热性能最优,在相同制冷量下,所需集热面积最小,可节省安装空间。     

太阳系边缘天体

最近,美国天文学家新近在太阳系边缘地带观测到一个除冥王星之外个头最大的天体.发现者是加利福尼亚理工学院的迈克·布朗及其同事.新发现的这一天体的临时国际代号为"2002LM60",它绕太阳公转的周期为288年,直径约1 290 km,相当于冥王星的一半,位于太阳系边缘的"柯伊伯带".这一发现引起世人的普遍关注.太阳系有九大行星,距太阳最远的是冥王星.这是常识大家都知道.     

太阳能热发电过程的多模型控制策略

太阳能热发电技术是将太阳能首先转化为热能,再利用热能发电的技术,是对太阳能的高品位利用。文中总结了太阳能热发电系统的结构和原理,分析了不同情况下太阳能热发电的运行模式和热发电系统中的控制难点问题,进而提出了多模型控制策略,并与传统的单内模控制策略进行仿真对比,验证了多模型控制策略对时变不确定对象有很好的控制效果。     

太阳能保证率测量的不确定性分析

太阳能保证率是太阳能热水系统的设计参数,也是判断太阳能在一个供热系统中所能发挥的作用的评价指标。近年来,在可再生能源建筑应用工程评价中,把太阳能保证率列为系统的重要评价指标。对影响太阳能保证率测量不确定性的因素进行分析,结果表明:现有的短期测量方法所测得的年保证率具有很大的随意性,并不能真实反映系统性能,检测结果没有实际价值,建议进一步完善检测方法或者取消该项检测。     

以太阳为战场--太空大战拉开大幕

航天技术的迅猛发展,在打开对外层空间开发和利用通道的同时,也把太空变成了一个重要的军事领域。特别是随着军用航天器的迅速发展,到21世纪,军队将会充分运用高技术武器装备,在广阔的太空开辟新的战场,进行前所未有的军事对抗。展望21世纪太空战场,高技术兵器竟相角逐,高素质军队的智能抗衡,将会描绘出一幅前所未有的战争画卷。天兵天将横空出世随着太空的军事化发展,特别是太空战场的开辟和建立,21世纪将出现一个崭新的军种,即“天军”。天空战场上的“天军”,就是以航天司令部为中心,     

太阳能电池组件层压机加热系统的设计与试验

在研究太阳能电池组件层压机加热系统性能要求的基础上,设计了一种能够独立控制加热温度,利用热油反向流动自动补偿温度差的双向控温太阳电池组件层压机加热系统,有效地改善现有电加热系统、油加热系统和工作台之间的传热效果,提高工作台表面温度均匀性。     

太阳系的膨胀

随着太阳质量变小 ,即随着太阳引力场变弱 ,行星椭圆轨道变大 ,轨道形状变得越来越扁平 .离太阳越远 ,行星椭圆轨道变化越显著 .太阳系正在非常缓慢均匀地膨胀 ,行星机械能增大     

太阳能警示标识技术在电力系统中的应用研究

阐述了太阳能警示标识技术拓展应用到电力系统的可行性,分析了其主要技术性设计因素及系统实现原理.以现场的实际运用展示了其安全、节能、环保警示的视觉效果,同时对存在的问题及今后的发展趋势作了简要论述.     

地层塌陷区段埋地管道变形与应力分析

已有文献都是基于Winkler地基梁模型来研究塌陷以及悬空等对管道安全的影响,还没有采用其他力学分析模型的报道.分别采用Winkler和理想弹塑性地基梁模型,研究地层塌陷对管道安全的影响.建立了管土相互作用的几何大变形力学分析模型,采用非线性理论对力学模型求解.分析结果表明:在管道的屈服应力较小的情况下,为简化工程计算可采用Winkler模型计算临界塌陷区长度,较弹塑性模型简单,便于工程应用;当地层塌陷区长度较小时,为简化计算可采用Winkler模型分析管道的变形与应力;弹塑性模型可忽略土弹簧刚度对管道分析结果的影响,而Winkler模型则要考虑土弹簧刚度对其的影响.给出了使管道失效的临界地层塌陷区长度,所得结果可供工程设计参考.     

太阳系的中子辐照量分布

采用星系化学演化解析模型,结合脉冲AGB星慢中子俘获(s-过程)核合成理论,以AGB星s-过程单辐照解为前提,推导了单辐照情况下太阳系的中子辐照量分布,并将所得结果与利用参数化s-过程模型的计算结果及采用规范多事件s-过程模型的计算结果进行了比较,研究发现,计算结果与文献给出的中子辐照量分布在趋势上是一致的,但量级上有些偏差.这证明了只考虑AGB星的单辐照情况还不足以解释太阳系的中子辐照量分布,还应该考虑中子辐照量指数分布的贡献.     

太阳墙集热器干燥装置设计及研究

研制了一种太阳墙集热器型太阳能干燥装置,对其构造特点和工作原理作了讨论,并对其热性能和经济性能进行了评价.试验结果表明,该装置具有干燥效率高、投资低等优点.     

Extreme oxygen isotope ratios in the early Solar System

The origins of the building blocks of the Solar System can be studied using the isotopic composition of early planetary and meteoritic material. Oxygen isotopes in planetary materials show variations at the per cent level that are not related to the mass of the isotopes; rather, they result from the mixture of components having different nucleosynthetic or chemical origins. Isotopic variations reaching orders of magnitude in minute meteoritic grains are usually attributed to stellar nucleosynthesis before the birth of the Solar System, whereby different grains were contributed by different stars. Here we report the discovery of abundant silica-rich grains embedded in meteoritic organic matter, having the most extreme 18O/16O and 17O/16O ratios observed (both approximately 10(-1)) together with a solar silicon isotopic composition. Both O and Si isotopes indicate a single nucleosynthetic process. These compositions can be accounted for by one of two processes: a single exotic evolved star seeding the young Solar System, or irradiation of the circumsolar gas by high energy particles accelerated during an active phase of the young Sun. We favour the latter interpretation, because the observed compositions are usually not expected from nucleosynthetic processes in evolved stars, whereas they are predicted by the selective trapping of irradiation products.     

太阳能LED路灯照明系统优化设计

在珠海完成国内第一个太阳能LED路灯示范工程的工作基础上，从路灯光源、控制电路、太阳电池组件最佳倾角确定、太阳电池组件和蓄电池容量确定等几个方面对太阳能路灯进行了设计优化，做到既能保证系统的稳定可靠运行，又能尽量减少系统规模和降低成本。结果表明采用LED作为路灯光源、直接耦合的方式的充放电控制器是太阳能路灯很好的选择，同时通过科学计算的方法对在珠海地区使用时太阳电池组件最佳倾角和组件和蓄电池容量进行了讨论。使用的方法和结论可以为的其他的太阳能路灯设计提供有力的帮助。