Variations in chemical compositions of the eolian dust in Chinese Loess Plateau over the past 2.5 Ma and chemical weathering in the Asian inland   总被引：5，自引：0，他引：5  

CHEN Jun  LIU Lianwen  JI Junfeng  YANG Jiedong  CHEN Yang 《中国科学D辑(英文版)》2001,44(5):403-413

Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and⁸⁷Sr/⁸⁶Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.  相似文献   

The aeolian dust accumulation curve     

Dirk Goossens 《地球表面变化过程与地形》2001,26(11):1213-1219

This article presents a simple physical concept of aeolian dust accumulation, based on the behaviour of the subprocesses of dust deposition and dust erosion. The concept is tested in an aeolian dust wind tunnel. The agreement between the accumulation curve predicted by the model and the accumulation curve obtained in the experiments is close to perfect and shows that it is necessary to discriminate between the processes of aeolian dust deposition and aeolian dust accumulation. Two important thresholds determine the accumulation process. For wind speeds below the deflation threshold, the aeolian accumulation of dust increases linearly with the wind speed. For wind velocities between the deflation threshold and the accumulation limit, the sedimentation balance is above unity and there is still accumulation, though it rapidly drops once the deflation threshold has been exceeded. At wind speeds beyond the accumulation limit, the sedimentation balance is below unity and there will no longer be an accumulation of dust. The thresholds have been determined in a wind tunnel test at friction velocity u_* = 0·34 m s^?1 (deflation threshold) and u_* = 0·43 m s^?1 (accumulation limit), but these values are only indicative since they depend heavily on the characteristics of the accumulation surface and of the airborne grains. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

自聚焦光纤中传导模的场分布     

翁兴涛  余模智  何平安 《武汉大学学报(信息科学版)》1995,(4)

从亥姆霍兹方程出发，导出了自聚焦光纤中传导模在圆柱坐标系中的场分布形式，并给出了几个低阶模的分布图。  相似文献   

Atmospheric pollution assessment near potential source of natural aerosols in the South Gobi Desert region,China     

Mikalai Filonchyk  Volha Hurynovich  Shuwen Yang 《地理信息系统科学与遥感》2020,57(2):227-244

ABSTRACT

Rapid economic growth, a high degree of urbanization and the proximity of a large number of desert and semidesert landscapes can have a significant impact on the atmosphere of adjacent territories, leading to high levels of atmospheric pollution. Therefore, identifying possible sources of atmospheric pollution is one of the main tasks. In this study, we carried out an analysis of spatial and temporal characteristics of five main atmospheric pollutants (PM_2.5, PM₁₀, SO₂, NO₂, and CO) near potential source of natural aerosols, affecting seven cities (Wuhai, Alashan, Wuzhong, Zhongwei, Wuwei, Jinchang, Zhangye), located in immediate proximity to the South Gobi deserts. The results, obtained for the period from 1 January 2016 to 31 December 2018, demonstrate total concentrations of PM_2.5 and PM₁₀ are 38.2 ± 19.5 and 101 ± 80.7 μg/m³ exceeding the same established by the Chinese National Ambient Air Quality Standard (CNAAQS), being 35 and 70 μg/m³, respectively. Based on the data from Moderate Resolution Imaging Spectroradiometer (MODIS) for the whole period, Clean Сontinental (71.49%) and Mixed (22.29%) types of aerosols prevail in the region. In the spring and winter seasons maximum concentrations of pollutants and high values of Aerosol Optical Depth (AOD) in the region atmosphere are observed. PM_2.5 and PM₁₀ ratio shows the presence of coarse aerosols in the total content with value 0.43. The highest concentrations of pollutants were in the period of dust storms activity, when PM_2.5 and PM₁₀ content exceeded 200 and 1000 µg/m³, and AOD value exceeded 1. UV Aerosol Index (UVAI), Aerosol Absorbing Optical Depth (AAOD), and Single Scattering Albedo (SSA), obtained from Ozone Monitoring Instrument (OMI), demonstrate the high content of dust aerosols in the period of sandstorms. Analysis of backward trajectories shows that dust air masses moved from North to Northwest China, affecting large deserts such as Taklamakan, Gurbantunggut, Badain Jaran, Tengger, and Ulan Buh deserts.  相似文献   

具有尘带的椭圆星系的红外辐射特性     

胡景耀  王钢 《中国天文和天体物理学报》1988,(1)

IRAS在12,25,60和100μm的巡天,给我们提供了研究各类星系红外辐射特性的可能。为了研究具有尘带的E和SO星系的红外辐射特性,我们利用了E.Sadler给出的完备的E和SO星系表。在该星系表中共列出248个夭体,其中38个被证记为IRAS点源,且又有确切的60和100μm的流量值。在这38个天体中有6个被列在K.Ebneter和B.Balik最新发表的具有全带的椭圆星系表中。我们以这6个星系作为具有尘带的E和SO星系的样本,其它32个没有尘带的E和SO星系即作为对照样本。为了讨论具有尘带的椭圆星系的红外辐射特性,我们利用非参数Mann-Whitney检验,对这两个样本的LIR和FIR/FB的分布作了讨论,结果是在对于置信度α=0.05的水平上,我们不能拒绝另一假设:这两个样本的LIR和FIR/FB的分布是相同的。对于同时具有25,60和100μm确切流量的E和SO星系我们讨论了它们的双色图,结果发现,不具尘带的E和SO星系都处于Rowan-Robinson.et al所指出的正常星系区,而一些具有尘和带的ESO星系,则远离这一区域,它们是LINER和SEYFERT星系。  相似文献   

Oxygen isotope compositions of quartz grains (4–16 μm) from Chinese eolian deposits and their implications for provenance     

Shengshan?HouEmail author  Shiling?Yang  Jimin?Sun  Zhongli?Ding 《中国科学D辑(英文版)》2003,46(10):1003-1011

Oxygen isotope compositions were measured in quartz grains extracted from a 7.0 Ma red clay-loess sequence at Lingtai and six late Pleistocene loess sediments (Malan loess). Results show that the changes in oxygen isotope compositions of Malan loess are basically controlled by the geochemical characteristics of the source materials, while the effect of weathering process after dust deposition could be minor. The oxygen isotope distribution of quartz grains from red clay at Lingtai is similar to that of the overlying loess-paleosol sequence, thus indicating that the red clay at Lingtai has the same eolian origin as the loess-paleosol deposits. Furthermore, the oscillations of the isotope compositions in 4–16 μm-sized quartz grains may reflect the changes, to some extent, of the climatic systems of the source region.  相似文献   

Remote structural health monitoring with serially multiplexed fiber optic acoustic emission sensors     

陈仲裕  梁玉进  Farhad Ansari 《地震工程与工程振动(英文版)》2003,2(1):141-146

Development and testing of a serially multiplexed fiber optic sensor system is described. The sensor differs from conventional fiber optic acoustic systems, as it is capable of sensing AE emissions at several points along the length of a single fiber. Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of crack locations. Laboratory experiments on plain concrete beams and post-tensioned FRP tendons were performed to evaluate the crack detection capability of the sensor system. The acoustic emission sensor was able to detect initiation, growth and location of the cracks in concrete as well as in the FRP tendons. The AE system is potentially suitable for applications involving health monitoring of structures following an earthquake Supported by: National Science Foundation, Grant number CMS-9900338  相似文献   

Solar ultraviolet transfer in the Martian atmosphere: biological and geological implications     

C Córdoba-Jabonero  L.M LaraA.M Mancho  A MárquezR Rodrigo 《Planetary and Space Science》2003,51(6):399-410

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测汞用光纤传感器的初步研制   总被引：1，自引：0，他引：1  

潘树新  刘耀炜 《地震》2002,22(4):149-154

利用原子吸收原理初步研制了一种测示用光纤传感器,解决了光纤探头部分的技术难题。与传统的测汞仪器相比,该仪器的最大优点是可动的。中介绍了仪器的工作原理及主要技术性能。实验表明,可以利用光纤传感技术来实现汞测量。  相似文献   

纤粒矿物粉尘体外细胞毒性研究   总被引：6，自引：0，他引：6  

邓建军  董发勤  吴逢春  蒲小允  John Huang  赵世泉 《岩石矿物学杂志》2000,19(3):249-253

采用体外细胞培养技术,观察兔肺泡巨噬细胞死亡率,用丙二醛（ＭＤＡ）的含量变化、乳酸脱氢酶（ＬＤＨ）及超氧化物歧化酶（ＳＯＤ）的活性变化来评价来自１２个矿６床的６种矿物的１２种结晶习性的矿物粉尘的细胞毒性,探讨其使巨噬细胞受损的机制。结果显示：沸石、硅灰石无细胞毒性,而其他的纤维状及片粒状矿物粉尘则表现出不同程度的细胞毒性,说明矿物粉尘的细胞毒性与矿物粉尘的形态有一定关系,但主要由矿物粉尘的特性所决  相似文献