正电子CT（PET）与21世纪生命科学     

陈惟昌  马步成 《CT理论与应用研究》1996,5(1):42-43

２１世纪的生命科学有两大前沿领域：分子生物学和神经生物学，前者研究人体生命过程的基因调控机制，而神经生物学则以探索人脑思维的奥秘为主要目标，正电子层析成像（ＰＥＴ）是研究人体内部分子相互作用动力学的和最有力的方法，并可研究脑的功能定位，ＰＥＴ的化学精度已达到ｐ ｍｏｌ水平，其空间分辨率为毫米数量级。ＰＥＴ将对２１世纪生命科学的巨大进展，起决定性的推动作用。  相似文献   

Mapping species of submerged aquatic vegetation with multi-seasonal satellite images and considering life history information     

《International Journal of Applied Earth Observation and Geoinformation》2017

Spatial information of the dominant species of submerged aquatic vegetation (SAV) is essential for restoration projects in eutrophic lakes, especially eutrophic Taihu Lake, China. Mapping the distribution of SAV species is very challenging and difficult using only multispectral satellite remote sensing. In this study, we proposed an approach to map the distribution of seven dominant species of SAV in Taihu Lake. Our approach involved information on the life histories of the seven SAV species and eight distribution maps of SAV from February to October. The life history information of the dominant SAV species was summarized from the literature and field surveys. Eight distribution maps of the SAV were extracted from eight 30 m HJ-CCD images from February to October in 2013 based on the classification tree models, and the overall classification accuracies for the SAV were greater than 80%. Finally, the spatial distribution of the SAV species in Taihu in 2013 was mapped using multilayer erasing approach. Based on validation, the overall classification accuracy for the seven species was 68.4%, and kappa was 0.6306, which suggests that larger differences in life histories between species can produce higher identification accuracies. The classification results show that Potamogeton malaianus was the most widely distributed species in Taihu Lake, followed by Myriophyllum spicatum, Potamogeton maackianus, Potamogeton crispus, Elodea nuttallii, Ceratophyllum demersum and Vallisneria spiralis. The information is useful for planning shallow-water habitat restoration projects.  相似文献   

Boosted bodies: Genetic techniques, domestic livestock bodies and complex representations of life     

Lewis Holloway  Carol Morris   《Geoforum》2008,39(5):1709-1720

This paper focuses on the burgeoning application of genetic techniques in livestock agriculture, examining how these are changing livestock breeding knowledge-practices and the representation of animal life. Conventional livestock breeding relies on visual appraisal of animals and maintaining performance records, whereas genetic and genomic techniques offer the potential to assess particular aspects of animals’ genotypes. Advertising and promotional material produced by organisations involved in developing genetic techniques, and reportage and discussion of such techniques in the agricultural media, are used to examine the ways in which the production and value of living bodies in the future is being mapped out in emerging knowledge-practice networks which centre around particular visions and representations of what livestock bodies are and should do or be. The paper argues that bodies should be understood in part in terms of the wider spatial relationships in which they are entangled. A process of’circulating reference’ [Latour, B., 1999. Pandora’s Hope: Essays on the Reality of Science Studies. Harvard University Press, Cambridge, MA] is identified in which rounds of simplification occur in relation to the representation of the genetic qualities of livestock animals. However, these attempts to simplify produce new complexities when livestock breeders attempt to make use of genetic knowledge-practices. Identifying different modes of complexity, the paper discusses their spatiality in terms of differences between genetic abstractions from animal bodies and breeders ‘multi-layered ‘lay’ knowledges of their livestock animals.  相似文献   

Seasonal development of Calanus finmarchicus in relation to phytoplankton bloom dynamics in the Norwegian Sea     

Cecilie Broms  Webjrn Melle 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2760

Seasonal development of Calanus finmarchicus was studied in relation to the physical environment and phytoplankton bloom dynamics in the Norwegian Sea during eight basin-scale surveys from March to August 1995. Our main objective was to gain new knowledge about the life cycle of C. finmarchicus and its adaptation to the physical and biological environment of the Norwegian Sea. Time of spawning, estimated by temperature-dependent back-calculations from the occurrences of copepodite stage 1 (CIs), varied by water mass and occurred mainly during the phytoplankton pre-bloom and bloom periods. Recruitment to CI of the year's first generation (G1) generally occurred during the bloom and late bloom. The seasonal development of C. finmarchicus was progressively delayed from Coastal to Atlantic and to Arctic water, and from south to north within Atlantic and Arctic waters. This delay was partly linked to the phytoplankton bloom development that followed the same pattern, but development of C. finmarchicus also showed an increasing tendency to lag behind the phytoplankton development in colder waters. This may explain why C. finmarchicus are less successful in colder water. The consumption of nitrate was used as proxy for the seasonal history of phytoplankton development to aid interpretation of the lifecycle of C. finmarchicus. This approach allows us to align phytoplankton bloom and copepod development sequences despite temporal and geographical variation in bloom development, which otherwise tend to cause variability in quasi-synoptic and large-scale data. Two generations of C. finmarchicus were found in southern and northern regions of Coastal Water, and in southern Atlantic Water. In northern Atlantic Water and in Arctic Water, one generation was observed.  相似文献   

卤虫（Artemia）“海孤一号”的基础生物学研究：2.生殖与生命周期     

袁海  蔡亚能 《海洋湖沼通报》1994,(1):43-48

本文对不同盐度条件下卤虫“海孤一号”的生殖及生命周期进行了观察和研究。结果表明：在较宽的盐度范围（３２％－１２０％）内卤虫都有很强的生殖能力,平均产后代７－１２次,每代１８０－２３０个,相邻两代间隔５．５－５．９天,同时存在生殖高峰期。在生殖参数中,产后代间隔时间最稳定,受盐度影响不显著。卤虫：海孤一号”在最适条件下,平均存活９０天,平均产后代约２０００个。  相似文献   

北京采矿废弃地植物修复重金属去除率研究   总被引：1，自引：0，他引：1  

孙楠  闫广新  王立发  张言  邢宇鑫  王金艳 《城市地质》2016,(4):7-14

结合北京市采矿废弃地土壤地质环境情况,选取密云区西坨古金矿尾矿土、密云区冯家峪铁矿尾矿土和门头沟区桑峪煤矸石堆为研究对象,进行植物修复研究。共开展4种类型的修复试验,即选用高羊茅、紫花苜蓿和三叶草3种修复植物分别进行修复,同时与板蓝根、桔梗、波斯菊和薄荷等中草药进行混合种植修复,在植物生命周期的不同阶段采集样品分析测试。结果表明:在4种修复类型中,高羊茅对金矿尾矿土中Pb、Zn、Cr、Cd去除效果最好,最大去除率达到18.10%、14.57%、13.81%、18.12%;混合种植对铁矿尾矿土中Cr、Ni、As、Hg去除率达到4种修复类型的最大值,分别为14.81%、9.80%、37.25%、50%。三叶草对煤矸石修复效果最好,对Cr、Pb、Zn、Cd的去除率分别为5.65%、37.15%、15.15%、20%,是4种修复模式去除率的最大值。在生命周期的不同阶段,对比4种修复模式对采矿废弃地土壤中8种重金属的去除效果,均发现有去除率先升后降的现象,因此可对修复植物的进行定期收割,为提高植物吸附土壤重金属的效率,提供一定科学依据。  相似文献   

A novel analysis of consumption-based carbon footprints in China: Unpacking the effects of urban settlement and rural-to-urban migration     

《Global Environmental Change》2016

Urbanization in developing countries greatly contributes to growing carbon emissions. Although studies have documented the urbanization effect, the science of consumption-based footprint assessments has yet to unpack various effects during the process of urbanization. Based on household expenditure data, this study innovatively proposes a methodology to conceptually and statistically deconstruct the observed urbanization effects on carbon footprint into selection effects and migration effects, which consist of human settlement effects and purposeful changes of migration (such as income and residential location). Applying propensity score matching and regression on the 2010 China Family Panel Study, we find that the apparent carbon-footprint difference between rural residents and migrants is about 1.5 t CO₂e per capita. The migration effects account for about 2/3 of the apparent difference and the remaining 1/3 is due to selection effects. Urban settlement effects and the purposeful changes account for 73% and 27% of the migration effects, respectively. Transport sector is the key driver of carbon-footprint growth: it accounts for 60% of the migration effects. We conclude that travel behavior of rural migrants, currently in scarcity in the lite rature, merits further investigation, and policies should emphasize transit-oriented land use and transportation to achieve low-carbon urbanization.  相似文献   

Water and astrobiology     

Michael J. Mottl  Brian T. Glazer  Ralf I. Kaiser  Karen J. Meech   《Chemie der Erde / Geochemistry》2007,67(4):253-282

Water is formed from two of the three most abundant elements in the universe and so is abundant in interstellar space, in our Solar System, and on Earth, where it is an essential compound for the existence of life as we know it. Water ice acts as a substrate and reactant in interstellar clouds of gas and dust, enabling the formation of organic compounds that are important precursors to life and that eventually became incorporated into comets and asteroids in the early Solar System. Laboratory experiments have allowed us to infer the reaction pathways and mechanisms by which some of these compounds are formed. In these reactions, water can act as an energy transfer medium, increasing product yields, or it can lower yields by diluting reaction centers. Water can also destroy organic compounds when water ice decomposes under ionizing radiation and the decomposition products attack the compounds; whether this happens depends critically on temperature and structure of the ice, whether crystalline or amorphous. Ice structure and temperature also largely determine its gas content. As the solar nebula collapsed, icy mantles on interstellar grains probably sublimated and then recondensed onto other grains, thus influencing the transport of energy, mass, and angular momentum in the disk. Icy grains also influenced the temperature structure of the disk because they influence mean disk opacity. Outside the “snow line” at 3–5 AU icy grains accreted to become part of comets and planetesimals that occupy the region of the outer planets, the Kuiper belt, and the Oort cloud. Water was acquired by the growing Earth by several mechanisms. Evidence from noble gas isotopes indicates that Earth achieved sufficient mass fast enough to capture an early H-rich atmosphere from the Solar nebula itself. Although the remnant of this primary atmosphere is now found only in the mantle, it may also reside in the core, which could contain most of the H on Earth (or none at all). The bulk silicate Earth contains only 500–1100 ppm H₂O, an amount small enough to explain by “wet” accretion, although most of it probably accumulated with the latter half of Earth's mass from wetter planetary embryos originating beyond 1.5 AU. Degassing on impact delivered water to Earth's surface, where it dissolved into a magma ocean, a process that likely saved it from loss during subsequent catastrophic impacts such as the Moon-forming giant impact, which resulted in >99% loss of the noble gas inventory. Although most of Earth's water probably came from meteoritic material, the depletion on Earth of Xe relative to Kr strongly suggests a role for comets. The role of water in supporting life is an essential one on Earth and probably elsewhere, given the unusual properties of water compared with other potentially abundant compounds. Its dipolarity, high boiling point and heat of vaporization and, for ice, melting temperature; its expansion on freezing; and its solvent properties make it an ideal medium for life. Life originated early on Earth, indicating an abundance of water, nutrients, precursor molecules, substrates, and appropriate physical and chemical conditions. Life adapted quickly to (and may have originated in) extreme environments, of heat, cold, dryness, saltiness, and acidity. This adaptation to extreme conditions bodes well for the prospect of finding life elsewhere in our Solar System and in planetary systems around other stars.  相似文献   

1994年1月17日美国加州北岭地震概况综述     

张洪由  李怀英 《国际地震动态》1994,(5):8-14

１９９４年１月１７日美国洛杉机地区的北岭发生６．６级强烈地震，造成生命和财产的巨大的损失。这是２０年来该地区发生的最强烈的一次地震，引起了国际地震学界的普遍关注。本文综述了这次地震的概况，内容包括：震源参数、震灾情况、地震造成的社会和经济影响、救援情况、地震成因和灾害特点以及值得思考的几个问题。  相似文献   

Comparative carbon emission assessments of recycled and natural aggregate concrete:Environmental influence of cement content     

Marian Sabǎu  Dan V.Bompa  Luis F.O.Silva 《地学前缘(英文版)》2021,12(6):66-75

This work examines the environmental and geochemical impact of recycled aggregate concrete produc-tion with properties representative for structural applications.The environmental influence of cement content,aggregate production,transportation,and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region.To obtain a detailed insight into the optimum life cycle parameters,a sensitivity study is carried out in which supplementary cementitious materials,different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered.The results show that carbon emissions were between 323 and 332 kgCO2e per cubic metre of cement only natural aggregate concrete.These values can be reduced by up to 17％by replacing 25％of the cement with fly ash.By contrast,carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50％and 100％,and trans-portation is not included in analysis.However,the concrete with 50％recycled aggregate presented lower increase,only 0.3％and 3.4％for normal and high strength concrete,respectively.In some cases,the rel-ative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25％,and case-specific transportation distances were considered.In absolute values,the concrete mixes with 100％recycled aggregates and 25％fly ash had lower carbon emissions than concrete with cement and natural aggregates only.Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short(15-25 km)and the cement replacement by fly ash is equal or higher than 25％,considering that the mechanical properties are adequate for prac-tical application.The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete,recommending them as an alternative to achieving global sustainability standards in construction.  相似文献