Changes in The Dynamics And Thermal Regime of The Permafrost and Active Layer of The High Arctic Coastal Area in North‐West Spitsbergen,Svalbard     

Ireneusz Sobota  Marcin Nowak 《Geografiska Annaler: Series A, Physical Geography》2014,96(2):227-240

In this paper changes in the active layer of the high arctic coastal area in north‐west Spitsbergen, Svalbard are described. Analysis includes both the ground thawing depth and its near‐surface thermal structure. The study was conducted on the Kaffiøyra Plain (Svalbard) at several fixed sites, which represent places typical of the region: a sandy beach, a tundra plain and a moraine ridge. The results show that in recent years, at two measurement points a significantly deeper thawing was observed. In 1996–2012 on the beach and on the moraine the trend of active layer thickness change was +1.3 cm yr^?1 and +2.5 cm yr^?1, respectively. Generally, in the years 2008–2012 the mean thickness of the active layer in the Kaffiøyra region increased by 3% to 6%. Even at the spatially close sites, within similar environments, there are significant differences in the thickness of the active layer. Measurements show that significant changes also occurred in the thawed ground temperature. Mean values of the observed near‐surface temperature in recent years (2007–2011) were higher by more than 1.0°C, in comparison to the mean in the late 1970s.  相似文献   

非定常条件下OWC径向透平冲击式动叶片优化研究          下载免费PDF全文

韩孜乾  刘臻  张晓霞  许传礼  杨鑫 《海岸工程》2022,41(3):198-208

为优化径向透平动叶片的结构型式,有效提高透平工作效率,本文基于Ansys-Fluent软件构建振荡水柱波能发电装置径向冲击式透平的三维瞬态全流域数值模型,通过改变透平动叶片吸力面型式,研究了正弦往复入射气流条件下动叶片厚度差异对透平扭矩、压强等参量的影响及其对透平输入系数、扭矩系数和周期平均效率等非定常性能评价参数的影响。在保证压力面型式不变情况下,研究了5种动叶片厚度分别为7 mm、13 mm、16 mm、19 mm和22 mm的透平在呼气、吸气阶段的非定常工作性能,结果表明：不同动叶片厚度的透平的非定常工作性能存在较大差异,动叶片厚度为13 mm的透平非定常工作性能最优,最大峰值效率可达47.7%。  相似文献   

基于FLUENT的波浪溢流水动力数值模拟     

黄飞扬  戴文鸿  姚毓  陈羿名 《海洋工程》2022,40(3):159-168

波浪溢流现象使得海堤受到了越浪和溢流的联合作用,复杂的水动力过程会引起海堤后坡产生严重的侵蚀破坏。基于FLUENT软件建立了二维数值波浪溢流水槽模型,该模型运用UDF速度边界造波法分析在不同超高条件下海堤后坡流量和水流厚度的水力学特性。结果表明数值模拟结果与前人物理模型试验结果吻合,该模型可以真实地模拟出海堤波浪溢流现象。在此基础上进一步研究了波浪溢流中越浪和溢流在不同相对超高条件下的主导性作用,而后建立了十分准确的波浪溢流海堤后坡稳定水流厚度计算公式。  相似文献   

Bridging the Qualitative–Quantitative Divide in Transport Geography∗     

Andrew R. Goetz  Timothy M. Vowles  Sean Tierney 《The Professional geographer》2013,65(3):323-335

Recent viewpoints concerning the state of research in transport geography have touched on the issue of insularity and the need to bridge the divide between the largely spatial–analytical or quantitative research in transport geography and the critical or qualitative research prevalent in urban, economic, and most other subfields of human geography. Transport geography has been criticized by some for being a quiet corner of our discipline that has lost its centrality largely because it remains within the analytical framework of the 1960s. This article explores these sentiments by reexamining recent transport-oriented research in highly cited geography journals to assess the degree to which the qualitative–quantitative divide exists within transport geography and between transport and other subfield in human geography, as well as to explore issues of productivity and centrality of transport-oriented research in geography. Results indicate that geographical research involving transport topics is much more prevalent and reflects a wider range of epistemological and methodological approaches than is frequently assumed. Nevertheless, there is still a considerable divide between “mainstream” transport geography and other human geographical research that necessitates much more interaction between transport and other subfields and greater incorporation of alternative research approaches within the mainstream of transport geography. To that end, we propose a preliminary critical transport geography research agenda that is open to a variety of methodological approaches, including quantitative analysis.  相似文献   

“Is there a bubble to burst?”-college students’ spatial perception of campus and the city,a case study of rhodes college in memphis,TN     

Shaolu Yu  Madalyn Bryant  Emily Messmer  Sophia Tsagronis  Sarah Link 《Urban geography》2013,34(10):1555-1575

ABSTRACT

This paper builds on the study of student geography by critically examining college students’ perceived space of a university campus and the surrounding urban space. Rhodes College is a liberal arts college situated in the city of Memphis. As a campus with a majority white population located in a predominately black city, Rhodes College exists within but often separate from the city. It serves as a perfect case study to investigate how the college students build relationships with the environment within and beyond the campus. By using mental mapping and focus groups, this research unpacks four spatialities that shape college students’ perception of the urban space: (in)activity space, (im)mobility, boundaries, and center. This research demonstrates that student geography can be gendered, classed and racialized. The perceived space is socially constructed, and is reinforced by the lived and material space. Finally, this paper provides implications to facilitate deeper connections between students, the campus, and the city.  相似文献   

新疆巴楚和塔什库尔干地震台下方地壳结构研究     

唐明帅  王海涛  罗炬  孔祥艳  杨峰 《内陆地震》2013,27(1):7-14

利用位于新疆塔里木盆地的巴楚地震台（BCH）和西昆仑山区的塔什库尔干地震台（TAG）多年记录的高质量远震波形数据,应用接收函数H-k叠加方法研究了台站下方的地壳结构。研究结果显示,BCH和TAG地震台下方地壳厚度差异分明,区域地壳厚度与地形有很好的对应关系;两个台都具有高的地壳平均波速比Vp／Vs值。BCH台下方的地壳厚度为44km、地壳内的平均波速比为1．849,在该台地壳中部21km处存在清晰的间断面,该间断面内存在低的平均P波波速和作／K值,该间断面的深度与邻近巴楚台的伽师震源区的精确定位的震源深度下界面一致,可能为地壳内的脆．韧转换带。TAG台下方的地壳厚度为69km,地壳内的平均波速比为1．847,较厚的地壳和高波速比可能表明该台下地壳的物质易于发生塑性流动,为地壳的变形和增厚创造了条件。  相似文献   

Determining oil slick thickness using hyperspectral remote sensing in the Bohai Sea of China     

《International Journal of Digital Earth》2013,6(1):76-93

Abstract

Determining oil slick thickness plays an important role in assessing oil spill volume and its environmental impacts on the ocean. In this study, we used a Hyperion image of an oil spill accident area and seawater and fresh crude oil samples collected in the Bohai Sea of China. A well-controlled laboratory experiment was designed to simulate spectral responses to different oil slick thicknesses. Spectral resampling and normalization methods were used to reduce the differences in spectral reflectances between the experimental background seawater sample and real background seawater. Fitting the analysis with laboratory experimental data results showed a linear relationship between normalized oil slick reflectance and normalized oil slick thickness [20th band (R ²=0.92938, n=49, p<0.01), 26th band (R ²=0.93806, n=49, p<0.01), 29th band (R ²=0.93288, n=49, p<0.01)]. By using these statistical models, we successfully determined the normalized oil slick thickness with the Hyperion image. Our results indicate that hyperspectral remote sensing technology is an effective method to monitor oil spills on water. The spectral ranges of visible green and red light were the optimal bands for estimating oil slick thickness in case 2 water. The high, stabilized spectral reflectance of background seawater will be helpful in oil slick thickness inversion.  相似文献   

利用H-K叠加方法和CCP叠加方法研究中国东北地区地壳结构与泊松比   总被引：11，自引：6，他引：5       下载免费PDF全文

张广成  吴庆举  潘佳铁  张风雪  余大新 《地球物理学报》2013,56(12):4084-4094

利用中国东北布设的流动地震台阵（116个）以及国家和区域台网（121个）的宽频带台站记录的824个远震事件,采用P波接收函数CCP叠加和H-K叠加两种方法获得了研究区详尽的地壳厚度图像.研究结果显示,两种方法获得的地壳厚度分布特征具有很好的一致性,中国东北下方地壳厚度存在明显的东西横向差异.重力梯度带西侧和佳木斯地块的台站下方地壳较厚,介于36~41 km之间,而在兴蒙槽地褶带中重力梯度带往东从36 km减薄至34 km左右.松辽盆地北侧、东侧和南侧地壳厚度较薄,为29~34 km,反映了该区复杂的地壳变形过程.CCP剖面显示郯庐断裂深切地壳,敦化—密山断裂下方莫霍面出现错断.H-K叠加得到的地壳平均泊松比显示,东北地区绝大部分台站下方的泊松比值较大,0.24~0.29.长白山、松辽盆地东部、燕山台隆东部和大兴安岭北部,泊松比值达到0.27~0.30,可能有幔源物质上涌,下地壳铁镁组分含量增加.  相似文献   

Rock damage and regolith transport by frost: an example of climate modulation of the geomorphology of the critical zone     

Robert S. Anderson  Suzanne P. Anderson  Gregory E. Tucker 《地球表面变化过程与地形》2013,38(3):299-316

In this article we craft process‐specific algorithms that capture climate control of hillslope evolution in order to elucidate the legacy of past climate on present critical zone architecture and topography. Models of hillslope evolution traditionally comprise rock detachment into the mobile layer, mobile regolith transport, and a channel incision or aggradation boundary condition. We extend this system into the deep critical zone by considering a weathering damage zone below the mobile regolith in which rock strength is diminished; the degree of damage conditions the rate of mobile regolith production. We first discuss generic damage profiles in which appropriate length and damage scales govern profile shapes, and examine their dependence upon exhumation rate. We then introduce climate control through the example of rock damage by frost‐generated crack growth. We augment existing frost cracking models by incorporating damage rate limitations for long transport distances for water to the freezing front. Finally we link the frost cracking damage model, a mobile regolith production rule in which rock entrainment is conditioned by the damage state of the rock, and a frost creep transport model, to examine the evolution of an interfluve under oscillating climate. Aspect‐related differences in mean annual surface temperatures result in differences in bedrock damage rate and mobile regolith transport efficiency, which in turn lead to asymmetries in critical zone architecture and hillslope form (divide migration). In a quasi‐steady state hillslope, the lowering rate is uniform, and the damage profile is better developed on north‐facing slopes where the frost damage process is most intense. Because the residence times of mobile regolith and weathered bedrock in such landscapes are on the order of 10 to 100 ka, climate cycles over similar timescales result in modulation of transport and damage efficiencies. These lead to temporal variation in mobile regolith thickness, and to corresponding changes in sediment delivery to bounding streams. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Introducing environmental thresholds into water withdrawal management of mountain streams in the Kura River basin,Azerbaijan     

《水文科学杂志》2013,58(6):1068-1078

Abstract

The study aims to set and implement environmentally relevant limits for the exploitation of mountain streams in the Kura River basin of Azerbaijan. Such streams represent the preferred spawning grounds for valuable sturgeon of the Caspian Sea, but experience continuously increasing exploitation in the form of water withdrawals for industry and irrigation. Since no detailed environmental flow assessments have been conducted on any of the Kura basin streams, an interim approach is suggested based on minimum flow, referred to as “base environmental minimum”. The latter may be estimated from the unregulated parts of observed or simulated daily flow records. Environmental flow requirements for individual months of an individual year may be calculated using correction factors related to monthly rainfall. Simple relationships are suggested for base environmental flow estimation at ungauged sites, and the implications of river pollution for monthly environmental requirements are examined. Further, definition of environmentally critical periods in a stream is proposed based on a ratio of observed to “environmental” flow as an indicator of environmental stress. It is illustrated that the conjunctive use of several closely located streams for water supply may significantly reduce the duration of, or completely eliminate, environmentally critical periods. The idea of environmentally acceptable areal water withdrawal is formulated, so that the overall approach may be applied for environmentally sustainable water withdrawal management in other small streams.  相似文献