期刊文献+
共找到95,138篇文章
< 1 2 250 >
每页显示 20 50 100
Study of the reaction mechanism for preparing powdered activated coke with SO_(2)adsorption capability via one-step rapid activation method under flue gas atmosphere
1
作者 Binxuan Zhou Jingcai Chang +5 位作者 Jun Li Jinglan Hong Tao Wang Liqiang Zhang Ping Zhou Chunyuan Ma 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2024年第1期158-168,共11页
In this study,the impact of different reaction times on the preparation of powdered activated carbon(PAC)using a one-step rapid activation method under flue gas atmosphere is investigated,and the underlying reaction m... In this study,the impact of different reaction times on the preparation of powdered activated carbon(PAC)using a one-step rapid activation method under flue gas atmosphere is investigated,and the underlying reaction mechanism is summarized.Results indicate that the reaction process of this method can be divided into three stages:stage I is the rapid release of volatiles and the rapid consumption of O_(2),primarily occurring within a reaction time range of 0-0.5 s;stage II is mainly the continuous release and diffusion of volatiles,which is the carbonization and activation coupling reaction stage,and the carbonization process is the main in this stage.This stage mainly occurs at the reaction time range of 0.5 -2.0 s when SL-coal is used as material,and that is 0.5-3.0 s when JJ-coal is used as material;stage III is mainly the activation stage,during which activated components diffuse to both the surface and interior of particles.This stage mainly involves the reaction stage of CO_(2)and H2O(g)activation,and it mainly occurs at the reaction time range of 2.0-4.0 s when SL-coal is used as material,and that is 3.0-4.0 s when JJ-coal is used as material.Besides,the main function of the first two stages is to provide more diffusion channels and contact surfaces/activation sites for the diffusion and activation of the activated components in the third stage.Mastering the reaction mechanism would serve as a crucial reference and foundation for designing the structure,size of the reactor,and optimal positioning of the activator nozzle in PAC preparation. 展开更多
关键词 Reaction mechanism Powdered activated coke preparation SO_(2)adsorption One-step rapid activation Flue gas atmosphere
下载PDF
Reexamining Positivity of Thinking in Waiting for Godot Through Camus’s Absurdism
2
作者 ZHANG Si-jie 《Journal of Literature and Art Studies》 2024年第8期660-668,共9页
Absurdity originated from French existentialism,and Martin Esslin,in categorizing Waiting for Godot as a theater of the absurd,ignores the positive aspects of Camus’s absurdism and regards that as an existential trag... Absurdity originated from French existentialism,and Martin Esslin,in categorizing Waiting for Godot as a theater of the absurd,ignores the positive aspects of Camus’s absurdism and regards that as an existential tragedy of mankind.However,the author Samuel Beckett himself did not approve of such a definition,believing that Esslin’s definition of theater of the absurd was too judgmental and pessimistic.Through the imagery of boots,ropes,hats and baggage in Waiting for Godot,Beckett reveals the rootlessness,constraint and agony of the minds of people born into absurdity in the early 20th century.The luck of Lucky is Beckett’s use of irony:people who have lost the ability to think for themselves escape the absurdity and dystopia of life and descend to slaves.Gogo and Didi,who are waiting and expecting,and thinking in the midst of absurdity,represent“Godot”,the symbol of hope.Their endurance in waiting,akin to Camus’s Sisyphus,underscores a form of existential defiance that challenges the notion of absolute pessimism in absurdist literature. 展开更多
关键词 Samuel Beckett Waiting for Godot CAMUS absurdism THINK
下载PDF
Reform and Practice of the Course“Introduction to Computer Science”in Universities Based on the Cultivation of Computational Thinking and Systematic Abilities
3
作者 Kun Zhang Zhengjie Deng +2 位作者 Qi Peng Jinyang Zhou Fuyun Li 《Journal of Contemporary Educational Research》 2024年第7期197-203,共7页
Introduction to Computer Science,as one of the fundamental courses in computer-related majors,plays an important role in the cultivation of computer professionals.However,traditional teaching models and content can no... Introduction to Computer Science,as one of the fundamental courses in computer-related majors,plays an important role in the cultivation of computer professionals.However,traditional teaching models and content can no longer fully meet the needs of modern information technology development.In response to these issues,this article introduces the concept of computational creative thinking,optimizes course content,adopts exploratory teaching methods,and innovates course assessment methods,aiming to comprehensively enhance students’computational thinking and innovative abilities.By continuously improving and promoting this teaching model,it will undoubtedly promote computer education in universities to a new level. 展开更多
关键词 Introduction to Computer Science Curriculum reform Computational thinking PRACTICE
下载PDF
A Study on the Application of Audible Thinking Combined with Case Teaching Method in the Teaching of Nursing Room Visits for Trained Nurses
4
作者 Xiuying Luo 《Journal of Clinical and Nursing Research》 2024年第8期207-212,共6页
Objective:To investigate the effect of using audible thinking combined with the case teaching method in the teaching of nursing checkups for regulation nurses.Methods:The period was April 2023–April 2024,and a random... Objective:To investigate the effect of using audible thinking combined with the case teaching method in the teaching of nursing checkups for regulation nurses.Methods:The period was April 2023–April 2024,and a randomized controlled group study was carried out in which 76 regulation nurses in our hospital were randomly divided into a research group and a control group,with 38 regulation nurses in each group.The control group used conventional teaching methods,and the research group used audible thinking combined with the case teaching method,comparing the two groups’independent learning ability scores,assessment scores,and teaching satisfaction.Results:Independent learning ability score:after teaching,the research group was significantly higher than the control group(P<0.05);Assessment results:the research group was considerably higher than the control group(P<0.05);Teaching satisfaction:the research group was significantly higher than the control group(P<0.05).Conclusion:The use of audible thinking combined with the case teaching method in the teaching of nursing room visits for trained nurses can improve independent learning ability and assessment results and increase teaching satisfaction. 展开更多
关键词 Audible thinking Case teaching method Trained nurses Nursing room teaching
下载PDF
Effect of sintering atmosphere on corrosion resistance of Ni/(NiFe_2O_4-10NiO) cermet inert anode for aluminum electrolysis 被引量:3
5
作者 田忠良 郭伟昌 +2 位作者 赖延清 张凯 李劼 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2016年第11期2925-2929,共5页
A comparative study on the corrosion resistance of 17Ni/(NiFe2O4-10NiO) cermet inert anode prepared in differentsintering atmospheres was conducted in Na3AlF6-Al2O3 melt. The results indicate that the corrosion rate... A comparative study on the corrosion resistance of 17Ni/(NiFe2O4-10NiO) cermet inert anode prepared in differentsintering atmospheres was conducted in Na3AlF6-Al2O3 melt. The results indicate that the corrosion rates of NiFe2O4-based cermetanodes prepared in the vacuum and the atmosphere with oxygen content of 2×10^-3 (volume fraction) are 6.46 and 2.71 cm/a,respectively. Though there is a transition layer with lots of holes or pores, a densified layer is formed on the surface of anode due tosome reactions producing aluminates. For the anode prepared in the atmosphere with oxygen content of 2×10^-3, the thickness of thedensification layer (about 50 μm) is thicker than that (about 30 μm) formed on the surface of anode prepared in the vacuum. Thecontents of NiO and Fe(II) in NiFe2xO4-y-z increase with the decrease of oxygen content in sintering atmosphere, which reduces thecorrosion resistance of the material. 展开更多
关键词 sintering atmosphere corrosion resistance NiFe2O4-based cermet inert anode aluminum electrolysis
下载PDF
Contrastive Study of Thinking Modes between Chinese and English and Thinking Training of English Writing for Chinese Students
6
作者 仵桂荣 王新国 贺小华 《Sino-US English Teaching》 2007年第1期10-13,共4页
Based on the relationship between language and thinking, this paper is designed to inform that Chinese mode of thinking has great effect on college students' English writing from the perspective of contrastive study ... Based on the relationship between language and thinking, this paper is designed to inform that Chinese mode of thinking has great effect on college students' English writing from the perspective of contrastive study of thinking modes between Chinese and English. In addition, one specific measure about training English mode of thinking is put forward. 展开更多
关键词 English writing English mode of thinking discourse analysis
下载PDF
How do We Teach for Thinking in the Primary Classroom?
7
作者 张艳红 《海外英语》 2013年第6X期42-45,47,共5页
The importance of thinking in education has been gradually realized in recent years. Every student has the basic right to develop his or her minds and ability for thinking. Certain thinking habits and tendency will be... The importance of thinking in education has been gradually realized in recent years. Every student has the basic right to develop his or her minds and ability for thinking. Certain thinking habits and tendency will be formed in the early childhood. Therefore, we have good reasons to develop children's independent thinking and lead them to cultivate a good habit of thinking. We know that most schools place more emphasis on the outcomes of learning. In order to get a high score, they want the children to follow every step of teacher's instructions. Children's thinking skills and understanding ability have been ignored for a long time. We all know that successful learners not only have a good grasp of knowledge but also the ability of independent thinking. The aim of education is not get a high score in the exam but to develop a good habit of thinking and learning. That means we should value various ways of thinking and find proper methods to support children's cognitive skills and strategies, including creative thinking, critical thinking, and independent thinking, etc. This paper begins by providing a range of views and definitions about thinking. Though the discussion of different thinking skills, we conclude by giving suggestions on how we can teach for thinking in the primary classroom. There are four parts in this paper. The first part emphasizes the importance of different thinking skills. It reveals the relationship between learning and thinking. The development of critical thinking is also briefly introduced in this part. Part two explores the infused and stand-alone approaches to thinking. By comparing these two approaches, we find that it is more realistic and effective for us to teach thinking through different curriculum. Teach thinking is not an easy thing. Part three offers a brief description of challenges in implementing the thinking program in schools. Some effective teaching methods are suggested in part four to give us some guidance on how to teach thinking in primary classroom. Different strategies can be applied to assist children to become good thinkers. 展开更多
关键词 TEACH thinking PRIMARY CLASSROOM
下载PDF
To Improve Students'Linguistic Performance & Independent Thinking Abilities in Business English Teaching
8
作者 李勇 《科教导刊》 2013年第23期129-130,共2页
Business English is a required course for English majors.By learning the course,students can know the necessary business knowledge and improve their linguistic performance and independent thinking abilities under the ... Business English is a required course for English majors.By learning the course,students can know the necessary business knowledge and improve their linguistic performance and independent thinking abilities under the systematic background knowledge of industry & business theory and practice.It will be the strong foundations for students'better future career. 展开更多
关键词 Business English linguistic performance independent thinking
下载PDF
TREATMENT OF METALS, POLYMER FILMS, AND FABRICS WITHA ONE ATMOSPHERE UNIFORM GLOW DISCHARGE PLASMA(OAUGDP) FOR INCREASED SURFACE ENERGY AND DIRECTIONAL ETCHING 被引量:18
9
作者 J. Reece Roth and Z. Y Chen (Plasma Sciences Laboratory, Department of Electrical and Computer Engineering, University of Tennessee, Knoxville, TN 37996-2100, USA) Peter P.- Y Tsai (Textiles and Nonwovens Development Center (TANDEC), University of Tenness 《Acta Metallurgica Sinica(English Letters)》 SCIE EI CAS CSCD 2001年第6期391-407,共17页
Direct exposure of samples to the active species of air generated by a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) has been used to etch and to increase the surface energy of metallic surfaces, photoresist, ... Direct exposure of samples to the active species of air generated by a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) has been used to etch and to increase the surface energy of metallic surfaces, photoresist, polymer films, and nonwoven fab- rics. The OAUGDP is a non-thermal plasma with the classical characteristics of a DC normal glow discharge that operates in air (and other gases) at atmospheric pres- sure. Neither a vacuum system nor batch processing is necessary. A wide range of applications to metals, photoresist, films, fabrics, and polymeric webs can be accom- modated by direct exposure of the workpiece to the plasma in parallel-plate reactors. This technolopy is simple, it produces effects that can be obtained in no other way at one atmosphere; it generates minimal pollutants or unwanted by-products; and it is suitable for individual sample or online treatment of metallic surfaces, wafers, films, and fabrics. Early exposures of solid materials to the OAUGDP required minutes to produce rela- tively small increases of surface energy. These durations appeared too long for com- mercial application to fast-moving webs. Recent improvements in OAUGDP gas com- position, power density, plasma quality, recireulating gas flow, and impedance match- ing of the power supply to the parallel plate plasma reactor have made it possible to raise the surface energy of a variety of polymeric webs (PP, PET PE etc.) to levels of 60 to 70 dynes/cm with one second of exposure. In air plasmas, the high surface ener- gies are not durable, and fall to 50 dynes/cm after periods of weeks to months. Here, we report the exposure of metallic surfaces, photoresist, polymeric films, and nonwo- ven fabrics made of PP and PET to an impedance matched parallel plate OAUGDP for durations ranging from one second to several tens of seconds. Data will be re- ported on the surface energy, wettability, wickability, and aging effect of polymeric films and fabrics as functions of time of exposure, and time after exposure; the rate and uniformity of photoresist etching; and the production of sub-micron structures by OAUGDP etching at one atmosphere. 展开更多
关键词 atmosphere glow discharge plasma surface energy etching of material surface
下载PDF
Effects of Atmospheres and Precursors on MnO_x/TiO_2 Catalysts for NH_3-SCR at Low Temperature 被引量:9
10
作者 方德 HE Feng +2 位作者 谢峻林 FU Zhengbing CHEN Junfu 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS 2013年第5期888-892,共5页
The effects of atmospheres and precursors on MnOx/TiO2 catalysts were studied, which were prepared by the impregnation method and tested for their NOx conversion activity in ammonia selective catalytic reduction (NH3... The effects of atmospheres and precursors on MnOx/TiO2 catalysts were studied, which were prepared by the impregnation method and tested for their NOx conversion activity in ammonia selective catalytic reduction (NH3-SCR) reactions. Results showed that the manganese carbonate (MC) precursor caused mainly Mn2O3, while the manganese nitrate (MN) precursor resulted primarily in MnO2 and the manganese sulfate (MS) precursor was unchanged. The manganese acetate (MA) precursor leaded obtaining a mixture of Mn2O3 and Mn304. NOn conversion decreased in the following order: MA/TiO2 〉 MC/TiO2 〉 MN/TiO2 〉 MS/TiO2 〉 P25, with a calcination temperature of 773 K in air. Catalysts that were prepared by MA and calcined in oxygen performed strong interaction between Ti and Mn, while MnTiO3 was observed. Compared to the catalysts calcined in nitrogen, those calcined in oxygen had larger diameter and smaller surface area and pore. Catalysts that were prepared by MA and calcined in nitrogen tended to gain higher denitration rates than those in air, since they could be prepared with significant specific surface areas. NO., conversion decreased with calcination atmospheres: Nitrogen〉 Air〉 Oxygen. Meanwhile, amorphous Mn2O3 turned into crystalline Mn2O3, when the temperatures increased from 673 to 873 K. 展开更多
关键词 MnOx/TiO2 catalyst PRECURSOR atmosphere NH3-SCR
下载PDF
Characterization of Rust Layer Formed on Low Alloy Steel Exposed in Marine Atmosphere 被引量:4
11
作者 QuanchengZHANG JianshengWU +4 位作者 WenlongZHENG JianjunWANG JiaguangCHEN XiaofangYANG AibaiLi 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2002年第5期455-458,共4页
The iron rust phases formed on low alloy steels containing different quantities of Cr element have been characterized using EPMA, Raman spectroscopy, TEM, optical microscopy etc. The ion selective properties of synthe... The iron rust phases formed on low alloy steels containing different quantities of Cr element have been characterized using EPMA, Raman spectroscopy, TEM, optical microscopy etc. The ion selective properties of synthesized rust films with the same phase constituent as the atmospheric corrosion products were investigated using self-made apparatus. The results showed that corrosion loss of steels exposed in marine atmosphere decreased rapidly as the Cr content of the steel was increased. Cr-containing steels were covered by a uniform compacted rust layer composed of fine particles with an average diameter of several nanometers. Inner rust layer of Cr-containing steel (2 mass fraction) was composed of a-CrxFe1-xOOH, with Cr content of about 5 mass fraction. Such rust layer showed cation selective property, and could depress the penetration of Cl- to contact substrate steel directly. 展开更多
关键词 CORROSION Marine atmosphere Low alloy steel Iron oxyhydroxide
下载PDF
A Coupled General Circulation Model for the Tropical Pacific Ocean and Global Atmosphere 被引量:4
12
作者 张荣华 曾庆存 +1 位作者 周广庆 梁信忠 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 1995年第2期127-142,共16页
On the basis of Zeng's theorehcal design, a coupled general circulation model(CGCM) is develO ̄ with itscharacteristics different from other CGCMs such as the unified vertical coordinates and subtraction of the st... On the basis of Zeng's theorehcal design, a coupled general circulation model(CGCM) is develO ̄ with itscharacteristics different from other CGCMs such as the unified vertical coordinates and subtraction of the standard stratification for both atmosphere and ocean, available energy consideration,and so on.The oceanic comPOnent is a free surface tropical Pacific Ocean GCM betWeen 30W and 30'S with horizontal grid spacing of ic in latitude and 2°in longitude,and with 14 vertical layers.The atmospheric component is a global GCM with low-resolution of 4°in lahtude and 5°in longitude,and tWo layers of equal mass in the verhcal between the surfaCe and 200 hFa.The atmospheric GCM includes comprehensive physical processes.The coupled model is subjected to seasonally-varying cycle.Several coupling experiments,ranging from straight forward coupling without flux correction to one with flux correchon,and to so-called predictor-corrector monthly coupling(PCMC),are conducted tO show the esistence and final controlling of the climate drift in the coupled system.After removing the climate drift with the PCMC SCheme,the coupled model is integrated for more than twenty years.The results show reasonable simulations of the anneal mean and its seasollal cycle of the atmospheric and ̄ante circulahon.The model also ProduCeS the coherent intermnual variations of the climate system, manifesting the observed EI Nifio/Southern OSCillation(ENSO). 展开更多
关键词 Tropical Pacific Ocean Global atmosphere Coupled general circulahon model Predictor Monthly coupling
下载PDF
Studies on the structure and catalytic performance of Cu-Zn-Al catalyst prepared by liquid-phase preparation technology under different heat treatment atmosphere 被引量:3
13
作者 Zhihua Gao Wei Huang Lihua Yin Kechang Xie 《Journal of Natural Gas Chemistry》 EI CAS CSCD 2010年第6期611-616,共6页
Cu-Zn-Al slurry catalysts were prepared using a complete liquid-phase preparation technology under different heat treatment atmospheres.The catalysts were characterized using X-ray diffraction,X-ray photoelectron spec... Cu-Zn-Al slurry catalysts were prepared using a complete liquid-phase preparation technology under different heat treatment atmospheres.The catalysts were characterized using X-ray diffraction,X-ray photoelectron spectroscope,and N2 adsorption-desorption.Their application in the single-step synthesis of dimethyl ether from syngas was also investigated.The results indicate that the type of heat treatment atmosphere has an influence on the Cu species and the Cu0/Cu+ ratio on the catalyst surface.Moreover,the final Cu/Zn ratio on the catalyst surface is mainly dependent on the composition and reaction environment of the catalyst and less on the type of heat treatment atmosphere.The prepared catalysts can suppress sintering of active sites at high temperatures,and the type of heat treatment atmosphere mainly affects the capability of the catalyst for methanol synthesis.The catalysts perform best using N2 as the heat treatment atmosphere. 展开更多
关键词 liquid-phase preparation technology slurry reactor dimethyl ether SYNGAS heat treatment atmosphere
下载PDF
The Application of Flux-Form Semi-Lagrangian Transport Scheme in a Spectral Atmosphere Model 被引量:4
14
作者 王晓聪 刘屹岷 +2 位作者 吴国雄 Shian-Jiann LIN 包庆 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2013年第1期89-100,共12页
A flux-form semi-Lagrangian transport scheme (FFSL) was implemented in a spectral atmospheric GCM developed and used at IAP/LASG. Idealized numerical experiments show that the scheme is good at shape preserving with... A flux-form semi-Lagrangian transport scheme (FFSL) was implemented in a spectral atmospheric GCM developed and used at IAP/LASG. Idealized numerical experiments show that the scheme is good at shape preserving with less dissipation and dispersion, in comparison with other conventional schemes, hnportantly, FFSL can automatically maintain the positive definition of the transported tracers, which was an underlying problem in the previous spectral composite method (SCM). To comprehensively investigate the impact of FFSL on GCM results, we conducted sensitive experiments. Three main improvements resulted: first, rainfall simulation in both distribution and intensity was notably improved, which led to an improvement in precipitation frequency. Second, the dry bias in the lower troposphere was significantly reduced compared with SCM simulations. Third, according to the Taylor diagram, the FFSL scheme yields simulations that are superior to those using the SCM: a higher correlation between model output and observation data was achieved with the FFSL scheme, especially for humidity in lower troposphere. However, the moist bias in the middle and upper troposphere was more pronounced with the FFSL scheme. This bias led to an over-simulation of precipitable water in comparison with reanalysis data. Possible explanations, as well as solutions, are discussed herein. 展开更多
关键词 advection precipitation spectral composite method flux-form semi-Lagrangian Spectral Atmospheric Model of the IAP/LASG (SAMIL)
下载PDF
Controlling pore structures of Pd-doped organosilica membranes by calcination atmosphere for gas separation 被引量:1
15
作者 YibinWei Hengfei Zhang +2 位作者 Jiaojiao Lei Huating Song Hong Qi 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2019年第12期3036-3042,共7页
Pd-doped organosilica membranes were prepared by controlling calcination atmospheres(i.e.POS-Air,POS-N2,POS-H2,POS-H2/N2)to tailor their networks for improving their gas separation performance.This study shows that Pd... Pd-doped organosilica membranes were prepared by controlling calcination atmospheres(i.e.POS-Air,POS-N2,POS-H2,POS-H2/N2)to tailor their networks for improving their gas separation performance.This study shows that Pd(Ⅱ)could be only maintained under non-reductive calcination atmosphere,while inert and reducing calcination atmosphere is more beneficial to maintain organosilica moieties in POS networks.POS-H2/N2 membrane showed the optimal H2 separation performance that its permselectivities for H2/CO2,H2/N2,H2/CH4 and H2/SF6 are 15.0,96.7,173.0 and 3400.0,re spectively.Moreover,it is found that H2 molecules pass through the four membranes based on activated diffusion,while CO2 molecules permeation through POS-N2 and POS-Air membrane is dominated by surface diffusion.This work may provide insight into the understanding of the calcination atmosphere effect on gas separation performance of metal-doped organosilica membranes. 展开更多
关键词 PD DOPING ORGANOSILICA MEMBRANE CALCINATION atmosphere Gas separation
下载PDF
Seeing through the magnetite:Reassessing Eoarchean atmosphere composition from Isua(Greenland) ≥3.7 Ga banded iron formations 被引量:1
16
作者 Allen P.Nutman Vickie C.Bennett Clark R.L.Friend 《Geoscience Frontiers》 SCIE CAS CSCD 2017年第6期1233-1240,共8页
Estimates of early atmosphere compositions from metamorphosed banded iron formations(BIFs)including the well-studied ≥3.7 BIFs of the Isua supracrustal belt(Greenland)are dependent on knowledge of primary versus seco... Estimates of early atmosphere compositions from metamorphosed banded iron formations(BIFs)including the well-studied ≥3.7 BIFs of the Isua supracrustal belt(Greenland)are dependent on knowledge of primary versus secondary Fe-mineralogical assemblages.Using new observations from locally well preserved domains,we interpret that a previously assumed primary redox indicator mineral,magnetite,is secondary after sedimentary Fe-clays(probably greenalite)±carbonates.Within ~3.7 Ga Isua BIF,pre-tectonic nodules of quartz+Fe-rich amphibole±calcite reside in a finegrained(≤100 μm)quartz+magnetite matrix.We interpret the Isua nodule amphibole as the metamorphosed equivalent of primary Fe-rich clays,armoured from diagenetic oxidative reactions by early silica concretion.Additionally,in another low strain lacunae,~3.76 Ga BIF layering is not solid magnetite but instead fine-grained magnetite+quartz aggregates.These magnetite+quartz aggregates are interpreted as the metamorphosed equivalent of Fe-clay-rich layers that were oxidised during diagenesis,because they were not armoured by early silicification.In almost all Isua BIF exposures,this evidence has been destroyed by strong ductile deformation.The Fe-clays likely formed by abiotic reactions between aqueous Fe^(2+)and silica.These clays along with silica±carbonate were deposited below an oceanic Fe-chemocline as the sedimentary precursors of BIF.Breakdown of the clays on the sea floor may have been by anaerobic oxidation of Fe^(2+),a mechanism compatible with iron isotopic data previously published on these rocks.The new determinations of the primary redoxsensitive Fe-mineralogy of BIF significantly revise estimates of early Earth atmospheric oxygen and CO_2 content,with formation of protolith Fe-rich clays and carbonates compatible with an anoxic Eoarchean atmosphere with much higher CO_2 levels than previously estimated for Isua and in the present-day atmosphere. 展开更多
关键词 Banded IRON formation Eoarchean Early atmosphere Greenalite MAGNETITE
下载PDF
Inversion for atmosphere duct parameters using real radar sea clutter 被引量:1
17
作者 Sheng Zheng Fang Han-Xian 《Chinese Physics B》 SCIE EI CAS CSCD 2012年第2期618-623,共6页
This paper addresses the problem of estimating the lower atmospheric refractivity (M profile) under nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical... This paper addresses the problem of estimating the lower atmospheric refractivity (M profile) under nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled using five parameters and the horizontal structure is modeled using five parameters. The refractivity model is implemented with and without a priori constraint on the duct strength as might be derived from soundings or numerical weather-prediction models. An electromagnetic propagation model maps the refractivity structure into a replica field. Replica fields are compared with the observed clutter using a squared-error objective function. A global search for the 10 environmental parameters is performed using genetic algorithms. The inversion algorithm is implemented on the basis of S-band radar sea-clutter data from Wallops Island, Virginia (SPANDAR). Reference data are from range-dependent refractivity profiles obtained with a helicopter. The inversion is assessed (i) by comparing the propagation predicted from the radar-inferred refractivity profiles with that from the helicopter profiles, (ii) by comparing the refractivity parameters from the helicopter soundings with those estimated. This technique could provide near-real-time estimation of ducting effects. 展开更多
关键词 atmosphere duct radar clutter refractivity from clutter genetic algorithm
下载PDF
On the Line Formation in Stellar Magnetized Atmospheres 被引量:2
18
作者 Zhong-QuanQu Xiao-YuZhang 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2001年第2期161-175,共15页
The line formation process in stellar magnetized atmospheres is studied by observing the wavelength- dependence of Stokes contribution functions. The influence of magnetic field on the escape line photon distribution... The line formation process in stellar magnetized atmospheres is studied by observing the wavelength- dependence of Stokes contribution functions. The influence of magnetic field on the escape line photon distribution and line absorption is obtained by comparing with the null magnetic field case. Two models airs adopted. One assumes limited distributions of both the line absorption and magnetic field where a hypothetical magneto-sensitive line is formed. The other is a model atmosphere of sunspot umbra in which MgI 5172.7 forms. It is found that the magnetic field influences the formation region of Stokes I at wavelengths sufficient close to the Zeeman splitting points ±△ H. The formation regions at wavelengths far away from the Zeeman splitting points generally show a non-magnetic behaviour. Further, if the line core is split by the Zeeman effect, the line formation core introduced in the previous paper disappears. On the other hand, Stokes Q, U, V at each wavelength within the line form in the same layers where both the line absorption and magnetic field are present in the models accepted for the lines used. When the line absorption and magnetic field ubiquitously exist, the formation regions of the T peaks or valleys of Stokes Q, U and those of σ of Stokes V generally cover the widest depth range. It is pointed out that such a study is instructive in the explanation of solar polarized filtergrams. It can tell us at each observation point where the received line photons of wavelengths within the bandpass come from and where their polarization states are formed or give us the distributions of these photons as well as their polarization intensities. Thus a three-dimensional image can be constructed for a morphologic study of the observed area from serial filtergrams. 展开更多
关键词 line: formation - radiative transfer - Sun: atmosphere - sunspots Sun: magnetic fields
下载PDF
On Lidar Application for Remote Sensing of the Atmosphere 被引量:6
19
作者 邱金桓 吕达仁 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 1991年第3期369-378,共10页
This paper introduces some advanced subjects on lidar remote sensing of the atmosphere, emphasizing recent studies and developments in lidar application for measuring ozone, cloud, aerosol, atmospheric temperature, mo... This paper introduces some advanced subjects on lidar remote sensing of the atmosphere, emphasizing recent studies and developments in lidar application for measuring ozone, cloud, aerosol, atmospheric temperature, moisture, pressure and wind. 展开更多
关键词 On Lidar Application for Remote Sensing of the atmosphere
下载PDF
Sensitivity of Medium-Range Weather Forecasts to the Use of Reference Atmosphere 被引量:2
20
作者 陈嘉滨 A.J.Simmons 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 1990年第3期275-293,共19页
In this paper, the authors develop the earlier work of Chen Jiabin et al. (1986). In order to reduce spectral truncation errors, the reference atmosphere has been introduced in ECMWF model, and the spectrally-represen... In this paper, the authors develop the earlier work of Chen Jiabin et al. (1986). In order to reduce spectral truncation errors, the reference atmosphere has been introduced in ECMWF model, and the spectrally-represented variables, temperature, geopotential height and orography, are replaced by their deviations from the reference atmosphere. Two modified semi- implicit schemes have been proposed to alleviate the computational instability due to the introduction of reference atmosphere. Concerning the deviation of surface geopotential height from reference atmosphere, an exact computational formulation has been used instead of the approximate one in the earlier work. To re duce aliasing errors in the computations of the deviation of the surface geopotential height, a spectral fit has been used slightly to modify the original Gaussian grid-point values of orography.A series of experiments has been performed in order to assess the impact of the reference atmosphere on ECMWF medium- range forecasts at the resolution T21, T42 and T63. The results we have obtained reveal that the reference atmosphere introduced in ECMWF spectral model is generally beneficial to the mean statistical scores of 1000-200 hPa height 10-day forecasts over the globe. In the Southern Hemisphere, it is a clear improvement for T21, T42 and T63 throughout the 10-day forecast period. In the Northern Hemisphere, the impact of the reference atmos phere on anomaly correlation is positive for resolution T21, a very slightly damaging at T42 and almost neutral at T63 in the range of day 1 to day 4. Beyond the day 4 there is a clear improvement at all resolutions. 展开更多
关键词 Sensitivity of Medium-Range Weather forecasts to the Use of Reference atmosphere ECMWF
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部