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文章介绍了太阳系和太阳系外行星冰冻圈。太阳系各行星和卫星的表面温度差异很大,它们的冰冻圈发育各不相同。水星和月球的两极陨石坑的永久阴影区中可能有水冰存在。金星太热,表面既没有液态水,也不可能有水冰存在。火星两极存在永久性冰帽,包括水冰和干冰(固态CO2)。在太阳系雪线之外,存在很多冰卫星和富含水的矮行星,它们的主要是由水冰组成的;在极低的温度下,水冰甚至比地球上的岩石还要坚硬,并成为这些星体的壳层。除了水冰,其他易挥发组分如CO2、CH4、N2、CO等在极低温度下都会凝固为冰,形成不同于水冰的冰冻圈。因此,行星冰冻圈具有与地球冰冻圈迥然不同的丰富多样性。对行星冰冻圈的研究有助于我们扩大视野,更深入地理解地球冰冻圈,也将有助于我们理解太阳系的形成、地球水分的来源、地球深时古气候环境和生命演化,以及开展未来的系外生命探测。 相似文献
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I. Rabias H. Pratsinis G. Drossopoulou M. Fardis T. Maris N. Boukos N. Tsotakos D. Kletsas E. Tsilibary G. Papavassiliou 《Biomicrofluidics》2007,1(4)
Ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid have been investigated as possible constituents of aqueous ferrofluids for biomedical applications and especially for MRI contrast agent. The structural characteristics and the size of the nanoparticles have been analyzed as well as the magnetic properties. In order to evaluate any possible capabilities as a contrast agent, the relaxation time, T2, of hydrogen protons in the colloidal solutions of nanoparticles have been measured in order to gain information on the relaxation behavior compared to other MRI contrast agents. The in vitro cytotoxicity of the obtained magnetic nanoparticles of iron oxide coated with gummic acid was investigated by two separate methods (MTT and FACS analysis) and by using three different normal and transformed cell lines. Our results showed that the synthesized nanoparticles had no toxic effect on any of the cell lines used. 相似文献
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Ralph Bown 《Journal of The Franklin Institute》1917,183(1):41-60
Not many years ago it was quite generally believed that iron was unable to follow rapid magnetic changes. Experiments which showed an apparent decrease in the permeability of the iron with an increase in the frequency of the magnetic cycle furnished a basis for a theory that iron was magnetically sluggish. Further and more accurate experiments proved, however, that the effects which had previously been ascribed to a peculiarity of the material were in reality caused by eddy currents in the sample. Theoretical calculations were made which demostrated that eddy currents in an iron test piece increased as the square of the frequency and that for even the lower frequencies it was necessary to use quite thin laminations in magnetic circuits in order to eliminate deleterious effects. Furthermore, it was found that due to eddy currents and the magnetic properties of iron, the magnetization in high frequency fields was confined to a thin surface layer of the piece. This “Magnetic Skin Effect” reduced the cross section of the iron which was magnetically active even though the laminations were extremely thin. Careful experimental measurements compared with theoretical calculations proved that the real permeability of iron remained unchanged at frequencies up to about 106 and that previous results had been is serious error due to neglect of the factors mentioned. This fact having been established, efforts were made to see what practical use could be made of iron in high frequency work and to that end some extensive experimental investigations of the saturation curves and core losses were made upon specimens laminated as thinly as was commercially practicable. The resulting data have furnished a basis for design.It is a demostrated fact that the permeability of all metals is unity for the magnetic cycles imposed upon them by heat and light waves. In the region between frequencies of about 106, where the true permeability of iron is practically the same as at zero frequency, and frequencies of about 1010 where the true permeability of iron approaches unity, the experimental values of μ decrease smoothly with the frequency. What happens to μ in the range of frequencies between the lingest heat waves and the shortest Hertzian waves which have yet been made is a question which has many interesting features but which has not yet yielded to the experimenter. 相似文献
4.
Steve Squyres was responsible for assembling the team of scientists, engineers and instruments that formed the Mars Exploration Rovers (MER). Squyres developed a vision that small-scale observations made by a robotic geologist on Mars would be the key for resolving the mystery of water on Mars. Prior to the MER missions, planetary scientists were divided between groups holding that ancient fluvial-like surface features on Mars were formed by water and those holding that the erosive and depositional forces were tied to liquid and gaseous CO2. At issue was a fundamental understanding not only of early Martian geological processes and early solar luminosity, but also the possibility of life on Mars. To resolve these questions, Squyres and his team developed a new breed of rovers that were capable of identifying minerals and collecting textural observations. The resulting twin rovers, Opportunity and Spirit, have successfully resolved the single most important question about Mars that scientists have been debating for the past 30 years, providing compelling evidence for the action of water on the Martian surface. Squyres and the MER team have also initiated a new era in planetary exploration and inspired a new generation of students to become scientists and explorers. Steve Squyres and the MER team produced fundamental insights into the geology and climatology of Mars. These have resulted in major advances in our understanding of the potential for life on other planets and of life’s evolution on Earth. For the discovery and elucidation of water on Mars through the “robotic geologists” of the Mars Exploration Rovers, Steve Squyres was awarded the 2007 Benjamin Franklin Medal in Earth and Environmental Science. 相似文献
5.
The deep Earth is the engine of whole Earth systems and plays a key role in surface evolution and geological hazards. Scientists have been deciphering the internal processes that shape our habitable planet, especially since the formulation of plate tectonics theory. To date, how the deep Earth works remains mysterious. At the end of 2020, the Chinese Academy of Sciences (CAS) started to set up the Center for Excellence in Deep Earth Science, headquartered in the Guangzhou Institute of Geochemistry (GIG), with long-term support for these emerging and interdisciplinary research areas. NSR recently talked to Professor Yi-Gang Xu, GIG’s Director, about why the study of the Earth''s interior is essential, the current progress of deep Earth science in China, and what makes our planet habitable. 相似文献
6.
Martin W Hardisty 《Endeavour》1983,7(3):110-115
The importance of lampreys in comparative and evolutionary studies rests on their position as survivors of the diverse group of palaeozoic agnathan vertebrates. Their possession of a microphagous larval stage has been given prominence in theories of early vertebrate evolution, while its complete metamorphosis presents many fascinating developmental problems. The control of the major events in the life cycle has been a preoccupation of physiologists and endocrinologists who have uncovered a number of unique and probably primitive characteristics. 相似文献
7.
Fry I 《Endeavour》2006,30(1):24-28
Most scientists at the end of the 19th and the beginning of the 20th century chose to ignore the question of the origin of life on Earth, regarding it as too mysterious and complex to handle. Yet, in the early 1950s an experimental field devoted to the study of the problem made its first steps. The pioneering theories of several scientists in the first decades of the 20th century played a major role in this transformation, notably those of the Russian biochemist Alexander I. Oparin and the British geneticist and biochemist J.B.S. Haldane. The ideas of the lesser-known American psycho-physiologist Leonard Troland also made a significant contribution to subsequent developments in origin-of-life research. Therefore, it is well worth taking a look at the professional, philosophical and ideological commitments that shaped the approaches of the three scientists to origin-of-life research. 相似文献
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基于人们对科技强国具有刻板印象，探究来自非科技强国的品牌如何从科技创新和消费者思维的角度突破“来源国偏见”。采用实证研究法，通过实验证明相比于来源于非科技强国的品牌，来自科技强国的品牌将会让消费者产生更高的再购买意向，而实现科技创新中的技术创新能有效扭转非科技强国对消费者购买行为的负面影响，消费者建构思维也将调节消费者固有的来源国效应。最后根据实证研究结果，从国家层面、行业层面以及消费者层面提出具体的突破路径建议。 相似文献
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地球科学是以地球各圈层相互作用及其资源与环境效应为研究对象，多学科交叉融合的一门科学。地球科学既研究过去，阐述地球演化历史，又面向未来，为人类可持续发展提供解决方案，是一门既能拓展人类知识前沿又能服务于人类社会经济发展的综合性、系统性的科学。文章在梳理国际地球科学发展趋势和总结我国地球科学发展现状与科技资助情况的基础上，提出我国地球科学发展应从系统科学和国家需求的视角部署未来发展方向和研究计划。从地球系统整体出发，关注地球系统各圈层、各要素之间的相互作用及其对人类社会经济发展的影响。以“四个面向”引领地球科学领域研究的发展方向，开展有组织的重大科学研究，完善科技资助与评价机制，使研究成果更好地服务于国家重大战略需求。 相似文献
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对被子植物起源研究中的几种观点进行了讨论。(1)由于被子植物存在着一组共同的性状,它们不可能是从不同祖先起源的,而是有着共同的祖先。被子植物是一个单源起源的类群。现存被子植物分类系统是依据包括形态学(广义)、分子系统学、古植物学和植物地理学等的综合性状建立的,只能表示出现存类群的亲缘关系并且追溯到它们最近的祖先。人们现在还不可能建立一个包括全部已绝灭的类群和现代生存类群的谱系发生系统。因此,现存被子植物分类系统只能看作是“亲缘”系统。(2)分析了用于推测被子植物起源时间的分子、化石和地理分布证据。我们认为,要确定被子植物起源时间,植物化石是一类重要证据,但化石只能说是植物本身可保存部分和当时当地所提供的化石条件的综合反映,它们不可能就是植物类群或种的起源时间。人们还必须考虑到化石本身的演化历史。应用分子钟也是一种手段,但误差比较大。如果我们除了利用上述两种资料之外,根据植物类群的现代分布格局及其形成,把植物的演化同地球的历史和板块运动联系起来,以推断它们起源的时间,这无疑会增加其可信度。通过对56个种子植物不同演化水平的重要科属地理分布的研究结果,我们曾提出被子植物的起源时间可能要追溯到早侏罗世,甚至晚三叠世。(3)分析了基于分子证据所提出的被子植物基部类群——ANITA成员(包括无油樟科Amborellaceae、睡莲科Nymphaeaceae、八角目Illiciales、早落瓣科Trimeniaceae、木兰藤科Austrobaileyaceae)的性质,讨论了ANITA成员在现代几个被子植物分类系统中的系统位置的不同观点,评价了它们的形态学(广义)性状。指出ANITA的成员由于包含大量的祖征,是属于原始的类群。但由于它们的共有衍征很少,如花粉球形,说明它们在被子植物演化早期就分道扬镳了,沿着不同的传代线分化。因此ANITA是一个源于不同传代线的复合群。 相似文献
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联合国《改变我们的世界:2030年可持续发展议程》是各国实现经济、社会和环境共同发展的重要指南。当前,该议程的17个可持续发展目标(SDGs)的监测和评价已取得重要进展,但各SDGs间相互作用,特别是SDGs间的协同和权衡关系的认知仍较有限。文章首先从全部目标关系的综合分析、典型多目标关系分析、单目标内子指标间的关系3个方面描述了当前SDGs协同与权衡的研究进展和主要发现;并针对研究中的数据瓶颈问题,剖析了地球大数据支撑多目标协同和权衡的思路及典型案例;在此基础上,对地球大数据促进SDGs协同和权衡研究进行了展望。研究表明,地球大数据在提升SDG指标数据一致性、透明性、时效性和准确性等方面能够发挥重要作用,可以改进前期基于专家知识或统计数据等方法的不足,为提升多目标协同和权衡研究的定量水平提供重要数据支撑。最后,应对SDGs权衡的挑战,提出了完善地球大数据支撑SDGs协同与权衡的方法体系并构建模拟与预警平台、加强不同领域和主体的合作、强化技术创新推动等建议。 相似文献
14.
The current problems being studied by different authors of the evolution of
angiosperms are reviewed in general. An analysis of the arguments on principles and
methodology of the system of plant classification have been made. We support the
views put forward by the phylogenetic school and hold that phylogeny should be
taken as the guiding principles upon which the classificational system of angiosperms
should be built and as the ultimate aim of taxonomy. We disagree with the views of
the phenetic school. The course of evolution is a unity of the process of the origin
and the development in its history and the process of dispersal of angiopserms on
earth. The contradiction of variability and heredity is the driving force in the evolu-
tion of angiopserms, nay, of all organisms.
In the methodology we suggest that comparative analysis should ge hand in hand
with the experimental synthesis. In essence, the classification based on overall simi-
larities or most numbers of attributes to determine the relationships between various
groups of angi osperms is the deductive inference of formal logic. For the elucidation
of the laws of the origin and development of angiosperms the method of analysis and
synthesis of the dialectical logic should be adopted.
The progress of studies achieved in the origin and angiopserms of particularly
monocotyledons has been summarized, and the common points and discrepancies of the
authors have also been pointed out. The tendency of further development in the stud-
ies of the origin of angiosperms has been estimated. All branches of botany have
acumulated a large amount of data. Since 1960 some significant works have been
done, especially on the origin and early evolution of angiosperms, which has been being
the central problem of more intensive study challenging all botanist of different dis-
ciplines today.
The review is concluded with a proposal that in order to do further research on
the origin and early evolution of angiopserms, all branches of botany must cooperate,
and main attention should be paid to the important groups which may play a key rolein the development of plant life on earth. 相似文献
15.
郭华东 陈润生 徐志伟 孙建军 毕军 王力哲 骆健俊 沈华伟 顾东晓 梁栋 沈文庆 张旭 Hans Wolfgang Spiess Thomas Lengauer 《中国科学院院刊》2016,31(6):707-716
大数据是知识经济时代的战略高地,是国家和全球的新型战略资源。作为思维的革命性创新,大数据为科学研究带来了新的方法论。第六届中德前沿探索圆桌会议以"自然科学与人文科学大数据"为主题,在"生物医药大数据"、"物理、化学与地球科学领域大数据"、"人文与社会科学领域大数据"和"大数据处理技术与方法"4个领域进行研讨,总结了大数据对于科学发现的重要作用、意义以及面临的重大问题,形成了关于发展科学大数据研究的相关建议。 相似文献
16.
张彦彦 《科学技术与辩证法》2011,28(1):46-51
进化论心理学综合了达尔文的自然选择进化理论和当代心理学的研究方法,试图解释人类认知和情感适应功能的起源,并解释这些功能机制在现代人类社会中的作用。文章主要着眼于回答自然选择是如何创造条件,使有机生命体从环境挑战中生存下来的问题;澄清关于进化论的一些错误概念;以及探讨进化论如何能够帮助我们更好地理解人类行为。文章最后简要地阐述了科学界和政治界对现存一些进化论观念的思辨。 相似文献
17.
集群供应链是产业集群背景下新兴的供应链模式,对区域经济的发展具有重要意义。知识作为企业的核心生产资料,是影响供应链整体运作效率的重要因素之一。为了促进区域经济和地方产业的发展,对集群供应链知识共享行为进行了研究。本文运用演化博弈论建立了集群供应链中横向企业间知识共享行为演化博弈模型,分析了集群供应链知识共享行为的演化路径和影响知识共享行为的企业特质。研究结果表明：集群供应链知识共享行为主要受共享成本、共享风险、边际效益,知识吸收能力,知识共享量,激励系数和惩罚系数7个企业特质的影响;降低共享成本和风险,提高边际效益、知识吸收能力和知识共享量,引进激励和惩罚机制能够提升集群供应链中企业选择进行知识共享的意愿。 相似文献
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科学技术是一个国家综合国力的重要体现,而基础科学则是科学技术发展的基础。只有重视基础研究,才能不断增强自主创新能力。基础研究作为知识和技术的储备,既保证为社会经济发展持续供给科技成果,又能拓展人类知识前沿并促进社会进步。当前,世界各国重视基础科学研究对于经济社会发展的实质性作用,科技创新政策和治理日益"以任务为导向"。未来基础科学发展更要关注基础科学对于社会经济发展的实际作用。文章从社会需求出发,以人为关键要素,重点阐述生命健康、社会发展与自然环境改善、变革性技术发展和提升基础科学能力的方法等4个方面的基础科学研究进展。 相似文献
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长久以来,关于语言的产生和语言的本质,一直都是语言研究者们所关注和探索的问题。本文从历史发展的角度简述了人类对自身语言认识的不断发展。在早期的人类语言研究中,语言起源充满神秘色彩,语言只是研究其他人类精神财富的一种文字工具,还不能称之为真正的语言研究;到了近代,尤其是现代,新的科学技术使得人类对语言的研究产生了质的飞跃,语言研究趋于本体化。语言研究者们对人类大脑的语言机制、语言的起源以及语言习得等方面展开了大量的研究和实验,语言研究的理论和方法更为科学和理性,研究内容趋于语言本体,研究领域更具融合性,朝着认识人类自身的目标积极努力着。 相似文献
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鉴于碳中和对我国农业农村发展提出了新要求,且农户兼业已成为普遍现象,为促进农户采纳低碳生产行为,利用对黑龙江省376份农户深度调研数据,实证分析碳中和背景下农户兼业对农户低碳生产行为的影响。结果表明农户兼业促使农户采纳低碳生产的概率提高了12.8%;进一步采用倾向得分匹配法解决样本选择偏误,结果发现这一概率值仍然高达14.0%～24.9%,而且在统计上非常显著和稳健,同时当农户家庭成员多、加入合作社、无政治身份、受政府宣传教育影响大、受政府监管影响大时,农户兼业促进农户进行低碳生产的作用更为明显。基于此,提出不仅要拓宽农户兼业渠道、提供农户更多兼业机会,还要发挥政府监管的约束作用,进而发挥农户兼业对农户低碳生产的促进作用,为我国早日实现农业农村碳中和提供路径参考。 相似文献