Investigation of the linear polarization in infrared absorption bands     

T. V. Zinov’eva 《Astronomy Letters》2008,34(2):118-132

We consider the effects of the grain size, shape, structure, and chemical composition as well as the angle between the grain rotation axis and the incident ray on the full widths at half maximum (FWHM) of the polarization bands in the two deepest infrared absorption bands observed in the spectra of protostars, the water-ice band centered at 3.1 μm and the silicate band centered at 9.7 μm, using a core—mantle confocal spheroid model with various axial ratios a/b and relative volumes of the core material. We have found that the observed polarization bands with FWHM_p < 0.3 μm in the water-ice absorption band can be explained only by oblate and prolate particles with r _v ≤ 0.35 μm and the polarization bands with FWHM_p ≈ 0.3 μm can be explained only by particles with r _v ≈ 0.35 μm. Broad silicate absorption bands (FWHM ≈ 3 μm) with broad polarization bands (FWHM_p ≈ 2.7 μm) can be explained by particles with r _v ≈ 0.35 μm. Narrow silicate absorption bands (FWHM ≤ 3 μm) with any FWHM of the polarization bands can be explained by a mixture of particles of two types of olivine. Narrow polarization bands (FWHM_p ≈ 2 μm) with broad absorption bands can be explained only by very small particles, r _v ≤ 0.1 μm. We have found the relationships between the effective polarization and extinction cross sections and estimated the ranges of observed polarizabilities that can be explained by particles of given shape and orientation in each of the bands independently. Independent studies of the observational data for each of the bands are shown to give a wider choice of particle model parameters.  相似文献   

黑龙江省漠河地区土地覆被与地表温度时空变化特征研究   总被引：1，自引：0，他引：1  

陆妍  喻文兵  郭明  刘伟博 《冰川冻土》2017,39(5):1137-1149

以我国高纬度多年冻土区漠河县城区及郊区862 km²的区域为研究对象,基于RS和GIS技术对该区地表覆被变化和地表温度进行研究。结果表明：地表类型和地表温度反演结果与现场比对结果一致;从1988年到2015年,经过火灾后重建和城镇化发展,建设用地面积增加了11.33 km²;以2015年为例,冬季由于积雪覆盖,有79.02%的区域无植被覆盖,夏季有80.91%的区域为高植被覆盖。冬季地表温度和高程具有高度相关性,高程每升高100 m,地表温度平均升高2.27℃,表明该区地表温度也存在显著的逆温现象。该区城镇热岛效应全年存在,城镇区域地表温度高于全区平均值,夏季最显著,最高温差可达6.37℃。地表温度与NDVI具有明显的负相关关系;不同土地利用类型地表温度由低到高的顺序为水体-林地-草地-裸地-建筑用地。  相似文献   

青藏高原多年冻土区高寒草甸土壤水分入渗变化研究   总被引：4，自引：3，他引：1  

朱美壮  王根绪  肖瑶  胡兆永  宋春林  黄克威 《冰川冻土》2017,39(6):1316-1325

在多年冻土区典型坡面上,将坡面划分为坡下（L）、坡中（M）和坡顶（H）三个坡位,每个坡位上各选取92%、60%和30%植被盖度为研究对象,用双环入渗仪测定土壤水分入渗过程,对影响土壤入渗过程的环境因子进行了分析,并基于土壤物理特性及土壤水分的测定进行模型模拟。结果表明：研究区不同植被盖度下土壤水分入渗性能在活动层冻融过程中差异明显,初始含水量和初始入渗率具有较好的负相关关系;稳定入渗率大小为：活动层融化期,92%（0.61 mm·min^-1） > 60%（0.50 mm·min^-1） > 30%（0.29 mm·min^-1）;活动层开始冻结期,60%（0.56 mm·min^-1） > 30%（0.39 mm·min^-1） > 92%（0.26 mm·min^-1）。土壤水分入渗速率具有显著的坡位差异并与冻土的冻融循环过程关系紧密。主要表现为,稳定入渗速率随坡位高度的降低依次递减;同一坡位下,开始冻结期入渗速率小于融化期。在整个入渗阶段,坡顶的累积入渗量是最大的,体现了较好的入渗性能。影响高寒草甸土壤水分入渗的环境因子主要有容重,有机质含量及粒径<0.1 mm微粒。通过比较研究得出,在长江源地区,活动层融化期通用经验模型f（t）=a+bt^-n更适用于该研究区域高寒草甸土壤水分入渗过程的研究,而在开始冻结期Horton模型f（t）=i_c+（i₀-i_c）e^-kt则具有更好的适用性。  相似文献   

结构型式对寒区高铁路基冻结特征影响试验研究     

刘华  牛富俊  牛永红  许健 《岩土力学》2015,36(11):3135-3142

哈尔滨至大连客运专线是我国在中-深季节冻土地区设计、建造和运营的第一条高速铁路,其独特的工程地质条件以及在低温环境下线路的苛刻要求引发的工程需求对寒区路基的稳定性问题提出了新的严峻挑战。通过在不同冻深区选择典型性路基断面,以用来监测路基的稳定性和冻结特征。并通过对运营后第1个冻融期内的监测数据分析发现,路基的结构型式对寒区高铁路基的冻结特征有着显著的差别性影响和制约作用。结果表明：对比路堑段的中部及其临近路堑进出口处的路堤段,路堤段存续有较长时间和较厚的冻结夹层,其堑-堤地温差值也随着纬度的增加而增加。同时发现在4月份的路基中存在有一定厚度的高温冻结夹层。而同一区域内,路堑的最大冻结深度要较路堤的冻结深度浅20～50 cm,但相反的是,路堑的最大变形却较路堤的要大2～5 mm,这种差值越向北越明显。同时在春融期内,路堑段的冻深变化速率在0上下剧烈波动,此时变形产生了突变式上升,而路堤段的冻深变化速率却在负值区内变化,变形并未发生明显的突变。  相似文献   

Responses of Fragilarioid-dominated diatom assemblages in a small Arctic lake to Holocene climatic changes, Russell Island, Nunavut, Canada     

S. A. Finkelstein  K. Gajewski 《Journal of Paleolimnology》2008,40(4):1079-1095

We present a paleolimnological record spanning the Holocene from a small lake on Russell Island (Lake PW02), in the central Canadian Arctic Archipelago (74.07° N, 97.77° W, 182 m asl). Fragilarioid diatom types in the genera Pseudostaurosira, Staurosira and Staurosirella constitute >90% of valves in fossil samples. Using modern biogeographic data which specify the temperature optima of the Fragilarioid diatom taxa, we present new inferences about the timing of paleoclimatic changes in the central Arctic islands. The early Holocene was characterized by maximum values for sediment organic matter, and lower ratios of Staurosirella pinnata to Staurosira construens v. venter, suggesting warm summer air temperatures between about 9500−6500 cal year BP. Influxes of biogenic silica and diatom valves decreased following 4000 cal year BP, the sediment accumulation rate slowed and diatom taxa of the littoral zone diversified, suggesting cooler summers and more persistent lake ice. Variations in the species composition of the assemblages indicate paleoclimatic changes that are in broad agreement with other paleoenvironmental records from the Arctic including melt records from the Agassiz Ice Cap. Although autecological data remain incomplete for Fragilarioid taxa, our results indicate differences in these taxa in responses to paleoenvironmental change and underline the potential for the increased use of these taxa in paleoenvironmental reconstructions. The record from Lake PW02, as in other records from Arctic lakes with low algal diversity throughout the Holocene, shows a pronounced increase in diatom diversity since the 1920s, and diatom production since the 1970s far exceeds any recorded during the Holocene.  相似文献   

秦岭以南地区降水量变化及其灾害效应研究   总被引：4，自引：1，他引：3  

刘引鸽  葛永刚  周旗 《干旱区地理》2008,31(1):50-55

近年来气候变化诱发的灾害效应损失严重。利用秦岭以南地区1951-2001年28个站逐月降水资料,计算了降水量的线性趋势值及降水距平变化,分析了降水量的时间和空间演变特征。受地形影响,秦岭南北与东西降水量变化差异较大,西部大于东部,南坡多于北坡,季节性降水过程差异也很明显;年平均最大降水量为1 254.6 mm,出现在镇巴,最少降水量为690.7 mm,出现在丹凤;50年来降水量变化呈减少趋势,平均递减率为56.5 mm/10 a。分析表明,降水突变是触发其它灾害的主要因素。由强降水及连阴雨诱发的干旱、洪涝及地质灾害效应损失严重,在降雨强度达200 mm/d以上的区域成为泥石流、滑坡灾害,水土流失的多发区,主要分布在秦岭以南多暴雨中心的米仓山、大巴山、佛坪、商南及洛南一带。降水诱发的灾害效应与人类活动也密切相关,这些研究为未来防灾减灾和环境治理提供了依据。  相似文献   

A new species of Eunice (Polychaeta: Eunicidae) from Hainan Island, South China Sea     

吴旭文  孙瑞平  刘瑞玉 《中国海洋湖沼学报》2013,31(1):134-139

Ataxonomic survey of benthic marine animals from coastal regions of Hainan Island, South China Sea, revealed specimens of a new species of Eunice (Polychaeta: Eunicida: Eunicidae), Eunice uschakovi n. sp., collected from the intertidal zone. The species belongs to the group of Eunice that has yellow tridentate subacicular hooks and branchiae scattered over an extensive region of the body. It resembles E. miurai and E. havaica in having both bidentate and tridentate falcigers, but can be readily distinguished by branchial features. Comparisons between E. uschakovi and the two related species are presented.  相似文献   

Ecohydrological evolution model on riparian vegetation in hyperarid regions and its validation in the lower reach of Tarim River   总被引：1，自引：0，他引：1  

Dengfeng Liu  Fuqiang Tian  Heping Hu  Mu Lin  Zhentao Cong 《水文研究》2012,26(13):2049-2060

The evolution of the ecohydrological system driven by external climatic forcing and internal feedbacks between vegetation and hydrology, which is more remarkable in arid and semiarid regions, has attracted substantial research attention in recent years. To examine critically the state‐of‐the‐art assumptions and dynamic equations used in the evolution study of an ecohydrological system, the rule of proceeding from simplicity to complexity should be followed. The riparian vegetation ecohydrological system in hyperarid regions (e.g. the lower Tarim River) can serve as a starting point given its simplicity, which has been seldom examined before in terms of system evolution. Further, the water transfer practice from 2000 to 2006 in the lower Tarim River serves as a valuable prototype experiment for model validation. This is because the remarkable changes in groundwater and vegetation in the area have taken place within a shorter period and thus can be easily observed. In the present study, the ecohydrological evolution model on riparian vegetation (ERV model) in hyperarid regions was proposed by coupling groundwater movement and vegetation dynamics. In the ERV model, the groundwater table serves as a critical feedback variable that determines the vegetation dynamics (colonization and mortality) and is determined by vegetation transpiration other than groundwater movement. The monitored groundwater table by wells and satellite‐observed vegetation coverage from the Moderate Resolution Imaging Spectroradiometer are used for model validation. The simulation results show the good performance of the ERV model with uncalibrated parameters. It was also calibrated manually using a multiobjective method, and the fine‐tuned parameters are close to the uncalibrated ones, indicating the robustness of the model. The analysis shows further that the increased evapotranspiration is substantially due to the water transfer and thus the vegetation growth, which implies the importance of ecohydrological coupling for long‐term hydrological modelling. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

自然遗产地生态脆弱性分析与评价——以托木尔区域为例          下载免费PDF全文

时卉  杨兆萍  韩芳  栾福明  石天戈 《干旱区地理》2013,36(2):318-328

以托木尔区域为研究区,从景观生态学的角度,结合生态环境特征,选取分离度、分维数倒数、破碎度、植被覆盖指数和土壤侵蚀指数作为评价指标,探讨各景观类型区域生态环境脆弱度的空间分异规律,并依据生态环境的脆弱度等级结果进行区划。结果表明：（1）依据研究区海拔、坡度值划定地貌特征区,包括极高山、高山边缘区,南北部中山区,红层地貌区和南北部低山丘陵区;（2）建设用地的分离度最大,各景观类型的分维数倒数值差别不大,低覆盖度草地破碎度、景观类型脆弱度最大;（3）托木尔区域生态环境脆弱度指数具有强烈的空间自相关性,是自然因素和人为因素共同作用的结果;（4）区域生态环境脆弱度指数空间表现为“北低南高”的趋势,自然因素是影响生态环境高脆弱度区域（7～9级）的主导干扰因素;人类活动与自然因素共同作用于生态环境中脆弱度区域（4～6级）;影响低脆弱度区域（1～3级）生态环境脆弱度的主要因素是人类活动;（5）根据研究区内生态环境脆弱度值,结合当地自然特征、社会经济发展现状,研究区可划分为保护区、限制开发区和可开发区,并对其实施差别化的政策管理与保护措施。  相似文献   

黄河源区气候变化的环境效应研究     

李开明  李绚  王翠云  乔艳君 《冰川冻土》2013,35(5):1183-1192

以黄河源区气象台站的降水和气温资料以及玛多、达日、玛曲、唐乃亥和兰州水文站的径流资料为基础, 分析研究了该区降水、气温、水文变化趋势, 并对研究区的土地利用现状变化及原因进行了探讨. 结果表明: 在年代际变化趋势上, 黄河源区气温总体上呈升温态势, 降水呈减少趋势, 径流量也表现为减少趋势.土地利用现状的变化表明人类活动对研究区生态湿地的干预增强.自然因素和人类活动的综合作用, 使得黄河源区生态环境进一步恶化, 亟需进行人工干预, 保护和改善黄河源区生态湿地环境.  相似文献