Alluvial sediment sources in a glaciated catchment: The voidomatis basin,Northwest Greece     

Jamie C. Woodward  John Lewin  Mark G. MacKlin 《地球表面变化过程与地形》1992,17(3):205-216

X-ray diffraction (XRD) of the fine matrix component of four alluvial units and modern channel sediments in the Voidomatis River Basin of northwest Greece shows that fine sediment sources have changed considerably during the late Quaternary. The matrix fraction of the modern channel sediments is derived predominantly from erosion of local flysch rocks and soils. During the last glaciation, however, the fine sediment load of the Voidomatis River was dominated by glacially-ground, finely comminuted limestone materials. Limestone-derived fine sediment is not produced in significant amounts under modern climatic conditions. By combining this XRD work with a detailed programme of clast lithologic 1 analysis we have reconstructed former bedload and fine sediment load composition. The lithological properties of both the coarse (8-256 mm) and fine (< 63 μm) elements of the sediment load have varied markedly during the late Quaternary. A simple, semiquantitative assessment of fine sediment mineralogy, using diffractogram peak-height data, has provided a valuable complement to the information gathered from more traditional clast lithological techniques. Together, in favourable geological settings, fine fraction mineralogy and clast lithological analysis can provide a valuable tool for the reconstruction of late Quaternary alluvial environments.  相似文献   

An evaluation of lightning and corona discharge on thunderstorm air and precipitation chemistry   总被引：1，自引：0，他引：1  

D. L. Sisterson  Y. P. Liaw 《Journal of Atmospheric Chemistry》1990,10(1):83-96

This study synthesizes literature to provide a best estimate for the integrated effect of cloud-to-ground lightning, intracloud lightning, and corona discharge on air and precipitation chemistry for an idealized thunderstorm. The cloud volume concentration of NO (the predominant chemical species produced by lightning), assuming all flashes occurred simultaneously in an undiluted, idealized storm volume of 1.5×10³ km³, is approximately 0.8 ppbv at STP. Uncertainties are discussed, and assumptions used in this estimate are evaluated and compared to the literature for consistency. Also, NO production values (an average of field, theoretical, and laboratory observations) are used to scale theoretical estimates of other chemical species produced by lightning that can be scavenged by precipitation. The maximum concentrations of these pollutants in rain water are estimated by assuming complete removal of these select, acid rain related species and found to be insignificant.  相似文献   

地震地下水位动态锯齿波的成因及排除办法     

孙佩琦 《内陆地震》1988,(4)

我们通过资料分析和模拟试验,研究了水位动态锯齿波的成因和排除办法,初步研究了井孔特征,井房气流效应与锯齿波的关系以及锯齿波在地下水观测中的应用。  相似文献   

European sources of halocarbons and nitrous oxide: Update 1986     

Michael Prather 《Journal of Atmospheric Chemistry》1988,6(4):375-406

Semi-continuous measurements of CFCl₃, CF₂Cl₂, CCl₄, CH₃CCl₃ and N₂O were made at Adrigole, Ireland as part of the Atmospheric Lifetime Experiment (ALE). Clean, baseline air from the Atlantic Ocean was measured approximately 70% of the time; pollution events from Europe, for the remainder. The two final years of ALE data from Adrogole give a five-year record from July 1978 to June 1983. This paper extends previous work on the relative enhancements of trace gases during pollution episodes and presents (1) unambiguous identification of elevated levels of N₂O concurrent with halocarbon pollution events, (2) detection of trends in emission of CH₃CCl₃, (3) discovery of seasonal variations in emission of CF₂Cl₂, CCl₄ and CH₃CCl₃, (4) characterization of typical summer and winter pollution episodes, and (5) identification of weather patterns over Europe that are associated with high concentrations of CFCs at Adrigole. Some of these results assume that CFCl₃ represents a uniform, well buffered source from the continent. The latter two results are particularly useful in the testing and calibration of three-dimensional chemical transport models. Observed enhancements are marginally consistent with estimates of halocarbon use by the chemical industry. The source of nitrous oxide correlated with halocarbons is 0.8 Tg(N)/yr from Europe alone and represents approximately 10% of the global stratospheric loss.  相似文献   

基于高性能瞬变电磁辐射源的城市地下空间多分辨成像方法研究          下载免费PDF全文

李文翰  刘斌  李术才  李贺  鲁凯亮  李貅 《地球物理学报》1954,63(12):4553-4564

城市地下空间的高精度、多分辨探测是城市地下合理开发的前提.由于城市探测环境的特殊性,需要探测方法具备抗干扰能力强、分辨能力好、分异多尺度地下目标等特性,现有的物探方法难以兼顾城市地下空间的探测需要.本文利用三维矢量有限元方法为正演手段,在瞬变电磁高性能辐射源进行微分脉冲扫描的基础上,对探测数据进行多时窗的扫时波场变换,将微分脉冲扫描后的多分辨响应信息,进行多分辨信息提取.同时通过地震探测中的多次覆盖处理,提高探测场对地下目标的分辨能力,最后对多次叠加后的虚拟波场进行拟地震偏移成像,最终实现城市地下空间的高精度探测.  相似文献   

地磁场H、D受HVDC输电干扰特征分析          下载免费PDF全文

林秀娜  曲保安  范晓勇  陈洪凯  于庆民  赵银刚 《地球物理学报》1954,63(10):3818-3826

以受宁东线高压直流（HVDC）输电干扰相对严重的11个地磁台站为主要研究对象,以蒙城台为干扰幅度量取的参考台站,研究了地磁场水平分量H、磁偏角D受HVDC输电的干扰特征.发现H和D受HVDC输电干扰具有同步性和偏向性;同一HVDC输电线路两侧H和D干扰幅度具有线性关系,但线性关系明显弱于垂直分量Z干扰幅度的比例关系;接地极附近台站各自的Z、H、D干扰幅度具有线性关系.之后对H和D干扰产生的机理进行了深入的定性分析.根据得到的干扰特征的结论,提出了以红山台Z、H、D为输入的本研究相关台站的Z、H、D为输出的自动计算方法.经过误差分析,本方法平均误差水平低于国家地磁学科中心当前使用算法误差水平,最高降幅达42.9%.  相似文献   

The future use of refrigeration in British coal mines     

J. M. Anderson 《Geotechnical and Geological Engineering》1988,6(1):41-61

Summary This paper examines the methods presently available to apply refrigeration to a longwall district of a coal mine with particular reference to both the sources of heat and humidity around a district, and the specific locations which require cooling. Other methods to improve climatic conditions are also investigated and computer-predicted results from a district temperature prediction program are used for discussion.An approach to the solution of a climatic problem is explained with reference to other coal mine contaminants and an environmental design philosophy for deep high production districts in British coal mines is described.  相似文献   

消除氡对γ测井干扰方法的再探讨     

谷子荣 《铀矿地质》1988,(3)

本文较系统地介绍了在各种钻孔条件下消除氡对γ测井干扰的方法。  相似文献   

The measurement of natural sulfur emissions from soils and vegetation: Three sites in the Eastern United States revisited   总被引：6，自引：0，他引：6  

Paul D. Goldan  William C. Kuster  Daniel L. Albritton  Fred C. Fehsenfeld 《Journal of Atmospheric Chemistry》1987,5(4):439-467

Sulfur fluxes from bare soils, naturally vegetated surfaces and from several agricultural crops were measured at two mid-continent sites (Ames, Iowa and Celeryville, Ohio) and from one salt water marsh site (Cedar Island, North Carolina) during a field program conducted jointly by the NOAA Aeronomy Laboratory, Washington State University Laboratory for Atmospheric Research and University of Idaho Department of Chemistry during July and August 1985. The sites were chosen specifically because they had been characterized by previous studies (Anejaet al., 1979; Adamset al., 1980, 1981). The NOAA gas chromatographic/dynamic-enclosure measurements yielded bare soil surfaces fluxes from the mid-continent sites composed predominantly of COS, H₂S, CH₃–S–CH₃ (DMS) and CS₂, all of which were strongly correlated with air temperature. Net fluxes of approximately 5 and 15 ng S/m² min were observed in Iowa and Ohio, respectively, at appropriate weighted mean July temperatures. These fluxes are roughly a factor of 10 smaller than the earlier measurements, the greatest difference being in the measurement of the H₂S flux. The presence of growing vegetation was observed to measurably increase the flux of H₂S, significantly increase that of DMS and to decrease that of COS. Sulfur fluxes in the Cedar Island environs were observed to be both spatially and temporally much more variable and to include CH₃SH as a measurable contributor. Net fluxes, composed predominantly of DMS and H₂S, were estimated to be about 300 ngS/m²min during August; again about a factor of 10 lower than previous estimates. All measurements were corroborated to within about a factor of 2 by those of the other participating laboratories.  相似文献   

Turbidity and suspended solids variations downstream of a regulating reservoir     

D. J. Gilvear  G. E. Petts 《地球表面变化过程与地形》1985,10(4):363-373

A controlled reservoir release from Llyn Celyn to the Afon Tryweryn, Wales, U.K., has been used to study suspended load and turbidity variations. Turbidity was monitored continuously at two sites and 235 suspended solids samples were obtained at these and three additional sites during the passage of the release wave. The results are compared with data for a natural tributary flood event. The reservoir release data relate to sediment source depletion and reflects changing sources along the channel. Close to the dam, fine organic matter dominates the seston which scanning electron microscopy revealed to be predominantly allochthonous organic matter, with algal fragments and inorganic diatom frustules, derived from the periphyton of the channel bed. Coulter Counter analysis showed the seston to be relatively coarse with a median particle-size of 20 μm. Within 3 km of the dam, however, minerogenic particles dominate the sediment load of which more than 90 per cent is finer than 10 μm. This represents the flushing of channel-bed accumulations derived from tributary sources. The relationships between suspended sediment concentration and turbidity during the release are characterized by a marked, anticlockwise hysteresis. This contrasts with the clockwise hysteresis for the tributary flood event, but the different relationships cannot be explained by particle-size variations alone; seston composition also appears to be an important control.  相似文献