Programme of the Galactic meridian: Star counts and galactic models. 1. Distributions of stellar magnitudes and colours     

V. Andruk  N. Kharchenko  E. Schilbach  R.-D. Scholz 《Astronomische Nachrichten》1995,316(6):387-400

A comparison of observed stellar distributions with a three-component model of the Galaxy is presented. The analysis is based on photometric and photoelectric data obtained along the main Galactic meridian and in two fields near the North Galactic pole (programme MEGA). The assumed model considers the Galaxy as composed of the disk (main sequence and disk red giants), the thick disk and spheroid populations. To model the observed colour distribution, we distinguish main sequence stars and disk red giants as the disk subsystem; white dwarfs, subdwarfs and intermediate giants as the thick disk subsystem; extreme subdwarfs, spheroid giants and horizontal branch stars as the spheroid subsystem. A statistical relation between the apparent and absolute magnitudes of stars which make the maximum contribution to the star counts for a given disk subsystem is derived. In order to achieve the best agreement between the model and observations, we fit the values of the ‘dip’ (aw) of the disk luminosity function, the correction to the absolute magnitude of disk red giants (ΔM_V^RG) and the expression for interstellar extinction. As the main result, we obtained aw = 0.6 (logarithmic scale) and ΔM_V^RG = 0.5 mag; the interstellar extinction has to be taken into account by the modified Sandage law.  相似文献   

基于空间化技术对中国近50年平均气温时空演变特征的研究   总被引：17，自引：4，他引：13  

蔡福  张淑杰  于贵瑞  祝青林  刘新安 《高原气象》2006,25(6):1168-1175

结合GIS空间化技术,对中国近50年平均气温数据进行定量化的分析,并分析其时空演变规律。采用空间化气候值 年际距平空间插值法生成中国1951—2001年分辨率为10 km×10 km的年、季平均气温空间化数据,通过对近50年空间化数据的分析,认为近50年中,年、季的全国平均气温都表现出显著增温趋势,冬季增幅最大,为0.313℃/10a,夏季增幅最小,为0.152℃/10a,年平均气温增幅为0.208℃/10a。1980年代中期以后增温趋势更加明显。从空间分布看,我国西南地区及西藏东南部和新疆西天山中段在不同季节都是主要的降温区域,而北方大部和西藏中西部地区在不同季节都表现为较强的增温趋势,我国东南地区在不同季节温度变化并不稳定,增温或降温的幅度都很小。暖冬事件在北方发生比较频繁,四川及云南部分地区较少,全国发生面积呈逐渐增大的趋势,增幅为国土面积的8.6%/10a。冷夏在新疆南部、西藏西北部和东南部以及江淮一带发生次数较多,辽宁南部、新疆沙漠地区、西藏中部、青海东部、四川大部分地区以及长江以南广大地区最少。全国发生冷夏的面积不断减小,50年平均减幅约为国土面积的5.8%/10a。  相似文献   

高亚洲定位监测冰川平衡线高度时空分布特征研究   总被引：8，自引：6，他引：2  

叶万花  王飞腾  李忠勤  张慧  徐春海  怀保娟 《冰川冻土》2016,38(6):1459-1469

利用高亚洲定位监测冰川平衡线高度数据,对平衡线高度时空分布特征进行了分析。结果表明：高亚洲冰川平衡线高度在空间尺度上具有纬度地带性、经向地带性和区域性的特征。在时间尺度上,高亚洲定位监测冰川平衡线高度呈现不同程度的升高趋势。在天山山区,乌鲁木齐河源1号冰川和Ts.Tuyuksuyskiy冰川的平衡线高度在1960-2013年间,分别增加约116m、80m,二者相比,Ts.Tuyuksuyskiy冰川对气候变化的敏感性更高;在阿尔泰山区,No.125（Vodopadniy）冰川、Maliy Aktru冰川和Leviy Aktru冰川在1983-2007年间,平衡线高度变化趋势基本一致,总体都呈升高趋势,其中,Maliy Aktru冰川平衡线高度增幅最大,升高了约142m;高亚洲定位监测冰川中,1962-2008年间,七一冰川平衡线高度升高速度最快,增幅最大,升高了约264m,升高速度最为缓慢的是乌鲁木齐河源1号冰川,其增幅最小,升高了约47m。  相似文献   

1950年西藏察隅M8.6强震序列震源参数复核   总被引：4，自引：0，他引：4       下载免费PDF全文

李保昆  刁桂苓  徐锡伟  万永革  冯向东  邹立晔  苗春兰 《地球物理学报》2015,58(11):4254-4265

1950年8月15日西藏察隅发生M8.6巨大地震.我们利用收集到的全球239个台站的P波资料,利用我国国家测震台网的常规定位方法和模型,对察隅M8.6强震序列进行了重新定位,并在此基础上重新计算了震源机制解.重定位后的结果表明,察隅M8.6强震序列显示出不同时段的震中分区分布特征:第1阶段是前震,1950年2月23日在墨脱北部雅鲁藏布江大拐弯的顶部发生;第2阶段是1950年8月15日─1950年8月18日,发生主震和之后3天内的余震,都分布在察隅附近,并且这些震中呈北西条带分布;第3阶段的余震是1950年8月22日─1950年9月13日,它们扩展到南部的印度和缅甸地区;第4阶段的余震是1950年9月30日─1951年4月15日,发生在西部的墨脱、错那等地.这四个分区的关联特点为顺时针旋移.重新计算后的震源机制解显示出:主震的NWW走向的节面与主震后2区内余震震中的NWW分布方向一致;序列中所有的压应力轴P和张应力轴T,都接近于水平向,其倾伏角大都小于20°;察隅主震和2区内余震的压应力轴P为近南北向,张应力轴T为近东西向;但3区和4区余震的P轴为近东西向,T轴为近南北向.反映出该强震序列中余震震源机制解的差异比较大.  相似文献   

Modelling dose rate to single grains of quartz in well-sorted sand samples: The dispersion arising from the presence of potassium feldspars and implications for single grain OSL dating     

《Quaternary Geochronology》2015

Single grain OSL has become a widely used approach in Quaternary geochronology. However, the origins of D_e distributions and the sources of variation in individual dose estimates are still poorly understood. The amount of scatter in these distributions on top of the known uncertainties in measurement and analysis is defined by overdispersion and this quantity is generally used for weighting individual D_e values to calculate a central equivalent dose. In this study, we address the nature and amount of different sources of dispersion in quartz single grain D_e estimates, by (i) using appropriate statistical tools to characterize D_e populations and (ii) modelling, with a specifically designed Geant4 code, dose rate distributions arising from the presence of potassium feldspar grains in well-sorted sands. The model uses Monte Carlo simulations of beta emissions and interactions in a random close packing of quartz and feldspar spheres representing a sand sample. Based on the simulation results, we explain the discrepancy between intrinsic and natural overdispersion values in a well-bleached sample, thus validating the model. The three parameters having the most influence on dispersion in dose rate distributions, and modelled in this study, appear to be grain size, potassium content and total dose rate.Finally an analysis of measurement uncertainties and other sources of variations in equivalent dose estimates lead us to conclude that all age models (both logged and unlogged) which include an overdispersion value to weight individual D_e values rely mainly on unknown parameters; this ignorance may lead to an inadvertent bias in D_e estimates. Assuming counting statistics make a small contribution to dispersion (as is often the case), we suggest that in some cases it is most appropriate to use unweighted averages of equivalent doses when dividing by commonly measured average dose rates.  相似文献   

Exponential Longitudinal Profiles of Streams     

Peter H. Morris  David J. Williams 《地球表面变化过程与地形》1997,22(2):143-163

A theoretical model is presented which shows that streams with low solids concentrations and low lateral inflows, whose bed load sediments undergo either comminution or hydraulic sorting under steady or quasi-steady conditions, have exponential profiles. Similar streams in which both communition and sorting are significant have exponential profiles only if they are short Sediment threshold and flow depth estimates based on the theoretical model are consistent with field and laboratory data from the literature. A comparison of the model and communition and sorting data from the literature strongly suggests that hydraulic sorting and comminution dominate in short and long natural streams, respectively. No examples of natural streams of intermediate length with exponential longitudinal profiles were found, suggesting that neither sorting nor comminution is dominant in such streams. © 1997 by John Wiley & Sons, Ltd.  相似文献   

湖光岩玛珥湖水体中营养盐的时空分布特征及其影响因素   总被引：1，自引：0，他引：1  

陈法锦  劳齐斌  卞培旺  朱庆梅  周凤霞  周欣  孟亚飞  王梦宇 《湖泊科学》2018,30(6):1693-1706

湖光岩玛珥湖是世界上最大的玛珥湖,它几乎是封闭的,受外界的干扰小.目前有关玛珥湖的研究主要集中在古气候及生态环境研究方面,而有关玛珥湖营养盐在一年中的生物地球化学循环的研究较少,因此研究湖光岩玛珥湖营养盐的生物地球化学过程具有重要意义.于2015年10月-2016年9月对湖光岩玛珥湖全水柱的营养盐及其他相关参数进行逐月调查,分析营养盐的结构特征、垂直分布特征和时间变化情况,并讨论营养盐时空变化的影响因素.结果表明,湖光岩玛珥湖水中的无机氮（DIN）以铵态氮（NH₄⁺-N）为主（>60%）,其次是硝态氧（NO₃^--N）,亚硝态氮（NO₂^--N）所占比利最低.湖光岩玛珥湖水中的硅酸盐（SiO₃^2--Si）浓度较高,水体浮游植物生长受磷限制.冬季风期间,水体垂直混合较均匀,导致营养盐的垂直分布比较均匀;夏季风期间,水体层化,营养盐浓度在浅层水体较低,在深层水体较高.湖光岩玛珥湖表层水中的NO₃^--N、NH₄⁺-N和SiO₃^2--Si具有明显的时间变化规律：NO₃^--N浓度从10月-次年3月升高,从3-9月降低;NH₄⁺-N浓度从10月-次年5月降低;SiO₃^2--Si浓度从11月-次年5月降低,从5-9月持续升高.营养盐浓度的时间变化受有机质的矿化分解、水体的季节性混合、浮游植物的吸收、降雨的输入等多种因素的综合影响.  相似文献   

应用物种敏感性分布评价中国湖泊水体中重金属污染的生态风险   总被引：7，自引：2，他引：5  

刘昔  王智  王学雷  杨超  宋辛辛  吕晓蓉  李珍 《湖泊科学》2018,30(5):1206-1217

为总体了解我国主要湖泊水体重金属污染现状与生态风险,本文通过历史数据收集,利用物种敏感性分布(SSD)模型与主成分分析法,分析了我国18个湖泊或水域中6种重金属(Zn、Cd、Cr、Cu、Hg和Pb)的分布情况以及其对湖泊淡水生物的潜在生态风险(PAF)和联合生态风险(ms PAF).结果表明:在18湖泊中,6种重金属在湖泊水体中的浓度由高至低依次为Zn(均值为17.06μg/L,范围为4.03~29.33μg/L)、Pb(均值为9.33μg/L,范围为0.04~33.7μg/L)、Cr(均值为5.56μg/L,范围为0.65~40.0μg/L)、Cu(均值为3.71μg/L,范围为0.02~10.2μg/L)、Cd(均值为1.17μg/L,范围为0.01~13.6μg/L)和Hg(均值为0.19μg/L,范围为0.03~1.04μg/L);18个湖泊中重金属的分布情况由3个主成分反映,F1(Cu、Zn、Hg)、F2(Pb、Cd)和F3(Cr、Cu)的贡献率分别为28.50%、24.17%和18.40%,其分布情况受经济和地域差异影响较小;SSD模型显示,不同重金属对全部淡水生物的HC5值不同,从小到大依次为CuCrHgCdPbZn,淡水生物对重金属Cu的敏感性最高,对重金属Zn的敏感性最低;将选取的18个湖泊按ms PAF排序,由高到低依次为呼伦湖(67.0%)鲁湖(56.7%)洱海(52.7%)金银湖(52.3%)太湖(40.5%)墨水湖(39.3%)滆湖(30.2%)鄱阳湖(26.8%)洪泽湖(23.1%)高宝卲伯湖(22.4%)巢湖(20.7%)乌梁素海(19.7%)东湖(19.1%)梁子湖(4.0%)汤逊湖(2.0%)洞庭湖(1%)洪湖(0)=骆马湖(0).研究结果对于了解我国淡水湖泊水质现状和环境安全风险具有重要意义,为湖泊的进一步保护与管理提供了一定的科学依据.  相似文献   

深圳东部近岸海域溶解氧的时空分布特征     

庄晓珊  桓清柳  彭莹  王节亮  庞仁松  周凯 《热带海洋学报》2018,37(5):98-105

根据2012—2016年的9个浮标自动监测数据, 分析了深圳东部近岸海域溶解氧浓度的时空分布特征及其与主要水质参数的相关关系。结果表明, 大亚湾海域溶解氧浓度含量在2.15~14.86mg·L^-1之间, 平均值为7.31mg·L^-1, 大鹏湾海域整体表层溶解氧浓度范围为1.43~15.61mg·L^-1, 平均值为7.13mg·L^-1; 在时间分布上, 深圳东部海域溶解氧含量呈现白天高于夜间, 春、夏、秋季低, 冬季高的趋势; 在空间分布上, 深圳东部海域溶解氧含量呈现出夏秋季大亚湾高于大鹏湾, 春冬季大亚湾和大鹏湾相差不大的特点。Pearson相关性分析表明, 该海区溶解氧含量与温度、盐度、浊度及叶绿素a存在显著的线性相关性, 且相关关系呈现出随季节变化的差异性。  相似文献   

Coal seam development characteristics and distribution predictions in marginal sea basins: Oligocene Yacheng Formation coal measures,Qiongdongnan Basin,northern region of the South China Sea     

D-D. Wang  G-Q. Dong  G-C. Zhang  Z-X. Li  Q. Mao  G-Z. Song 《Australian Journal of Earth Sciences》2020,67(3):393-409

Abstract

Coal measures located in marginal sea basins are important hydrocarbon source rocks. For the purpose of effectively guiding future oil and gas exploration, the characteristics and distribution patterns of coal seams in coal measures of a marginal sea basin are systematically outlined. Coal measures in marginal sea basins can have large thicknesses, but the individual coal seams can be very thin and lack lateral continuity. In the study area, the organic micro-components of the coal are dominated by vitrinite, with very low amounts of inertinite and liptinite. The amount of inorganic microscopic components is large, but with limited drilling results, few cores and thin coal seams, which are easily overlooked during logging activities, a comprehensive analysis of the logging data may improve efficiency in coal-seam identification and thickness determination. The development and distribution of coal seams in marginal sea basins are controlled by various factors, including (1) paleoclimatic and paleobotanic conditions, which could fundamentally limit coal formation, (2) coal-forming sedimentary environmental conditions that may limit the scope of coal-seam development from a macroscopic perspective, and (3) paleotectonic and paleotopographic conditions that define the coal-forming structures. Therefore, the descending and rising cycles of base-levels, along with changes in the growth rates of the accommodation spaces, can be used to determine the horizons that are potentially favourable for coal formation and can also indicate the migration trends of coal-forming environments on the structural plane. Seismic wave impedance inversion methods could be utilised for semi-quantitative assistance for prediction of coal seams. In summary, for models of coal-seam development in marginal sea basins, the grades should be divided according to reliability, and the different reliability levels should be predicted separately.

1. The characteristics of coal seams developed in marginal sea basins are described.

2. The macerals of coals developed in marginal sea basins have been ascertained.

3. A development model and distribution prediction method for coal seams are assessed according to the control factors.

4. A model for the prediction of coal-seam distribution is presented.

  相似文献