The AAT/WFI survey of the Monoceros Ring and Canis Major dwarf galaxy – I. From l= (193–276)°     

Blair C. Conn  Richard R. Lane  Geraint F. Lewis  Rodrigo Gil-Merino  Mike J. Irwin  Rodrigo A. Ibata  Nicolas F. Martin  Michele Bellazzini  Robert Sharp  Artem V. Tuntsov  Annette M. N. Ferguson 《Monthly notices of the Royal Astronomical Society》2007,376(3):939-959

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A coupled tide-wave model for the NW European shelf seas     

M. Reza Hashemi  Simon P. Neill  Alan G. Davies 《地球物理与天体物理流体动力学》2015,109(3):234-253

Understanding the interaction of tides and waves is essential in many studies, including marine renewable energy, sediment transport, long-term seabed morphodynamics, storm surges and the impacts of climate change. In the present research, a COAWST model of the NW European shelf seas has been developed and applied to a number of physical processes. Although many aspects of wave–current interaction can be investigated by this model, our focus is on the interaction of barotropic tides and waves at shelf scale. While the COWAST model was about five times more computationally expensive than running decoupled ROMS (ocean model) and SWAN (wave model), it provided an integrated modelling system which could incorporate many wave–tide interaction processes, and produce the tide and wave parameters in a unified file system with a convenient post-processing capacity. Some applications of the model such as the effect of tides on quantifying the wave energy resource, which exceeded 10% in parts of the region, and the effect of waves on the calculation of the bottom stress, which was dominant in parts of the North Sea and Scotland, during an energetic wave period are presented, and some challenges are discussed. It was also shown that the model performance in the prediction of the wave parameters can improve by 25% in some places where the wave-tide interaction is significant.  相似文献   

Vegetation succession in deglaciated landscapes: implications for sediment and landscape stability          下载免费PDF全文

Megan J. Klaar  Chris Kidd  Edward Malone  Rebecca Bartlett  Gilles Pinay  F. Stuart Chapin  Alexander Milner 《地球表面变化过程与地形》2015,40(8):1088-1100

Landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed, glacially influenced landscape to a stable, diverse ecosystem which supports numerous species and communities. Large‐scale vegetation development and changes in sediment availability, used as a proxy for paraglacial adjustment following rapid deglaciation, were assessed using information from remote sensing. Delineation of broad successional vegetation cover types was undertaken using Landsat satellite imagery (covering a 22 year period) to document the rate and trajectory of terrestrial vegetation development. Use of a space‐for‐time substitution in Glacier Bay National Park, Alaska, allowed ‘back‐calculation’ of the age and stage of development of six catchments over 206 years. The high accuracy (89.2%) of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages (bare sediment and alder). In contrast, later successional stages (spruce and spruce–hemlock dominated forest) had high vegetation class retention, and low turnover. Modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported. These data, when combined with the known influence of terrestrial succession on soil development and sediment availability, suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation. This study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio‐physical interactions within landscape evolution models. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Influence of glacier advance on the development of the multipart Riffeltal rock glacier,Central Austrian Alps          下载免费PDF全文

Jana‐Marie Dusik  Matthias Leopold  Tobias Heckmann  Florian Haas  Ludwig Hilger  David Morche  Fabian Neugirg  Michael Becht 《地球表面变化过程与地形》2015,40(7):965-980

The multipart Riffeltal rock glacier, located in a tributary valley of the Kaunertal, Tyrol, Austria is investigated to enlarge the knowledge about spatial and temporal development of rock glaciers in and at the margins of pro‐glacial areas and to get a better understanding of glacier–rock glacier interactions. The subject of interest consists of a complex system of two adjacent rock glacier tongues and various superposed lobes with differing ages, origin and root zones, and therefore diverse development. To determine the reasons for their diverging development, the internal structure and permafrost occurrence on and in the surrounding area of the rock glacier were studied by application of geomorphological mapping, geophysical methods and measurement of the basal temperature of the winter snow cover (BTS). Permafrost modelling was performed on the basis of BTS data and land surface parameters derived from a high resolution airborne laser scanning (ALS) digital elevation model (DEM). Additionally, the ALS data were used to measure vertical and horizontal changes of the rock glacier surface between 2006 and 2012. Glacier–rock glacier interactions during and since the Little Ice Age (LIA) are evident for the development of the studied rock glacier. A geomorphic map gives important information about the connection between glacial advance or retreat and permafrost or ground ice occurrence. The combination of all information helps in the analysis of diverse kinematic action of neighbouring rock glacier tongues. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Eccentricity evolution of giant planet orbits due to circumstellar disk torques     

Althea V. Moorhead  Fred C. Adams 《Icarus》2008,193(2):475-484

The extrasolar planets discovered to date possess unexpected orbital elements. Most orbit their host stars with larger eccentricities and smaller semi-major axes than similarly sized planets in our own Solar System do. It is generally agreed that the interaction between giant planets and circumstellar disks (Type II migration) drives these planets inward to small radii, but the effect of these same disks on orbital eccentricity, ?, is controversial. Several recent analytic calculations suggest that disk-planet interactions can excite eccentricity, while numerical studies generally produce eccentricity damping. This paper addresses this controversy using a quasi-analytic approach, drawing on several preceding analytic studies. This work refines the current treatment of eccentricity evolution by removing several approximations from the calculation of disk torques. We encounter neither uniform damping nor uniform excitation of orbital eccentricity, but rather a function d?/dt that varies in both sign and magnitude depending on eccentricity and other Solar System properties. Most significantly, we find that for every combination of disk and planet properties investigated herein, corotation torques produce negative values of d?/dt for some range in ? within the interval [0.1, 0.5]. If corotation torques are saturated, this region of eccentricity damping disappears, and excitation occurs on a short timescale of less than 0.08 Myr. Thus, our study does not produce eccentricity excitation on a timescale of a few Myr—we obtain either eccentricity excitation on a short time scale, or eccentricity damping on a longer time scale. Finally, we discuss the implications of this result for producing the observed range in extrasolar planet eccentricity.  相似文献   

Polarimetric imaging of interacting pairs     

R. Rampazzo  C. Bonoli  E. Giro 《Astronomische Nachrichten》2008,329(8):855-863

We present optical polarization maps of a sample of four interacting pairs at different phases of encounter, from nearly unperturbed galaxies to on‐going mergers. Only the pair RR 24 shows a linear polarization pattern which extends in both galaxies for several kiloparsecs. The more perturbed member, RR 24b, is linearly polarized up to the level of ≈3%. No polarization is measured in the strongly perturbed late‐type pair members of RR 23 and RR 99. Also, in the central part of the double nuclei shell galaxy ESO 2400100 there is no significant polarization. We use the ionized gas velocity field of RR 24 to interpret its linear polarization structure. In RR 24a the quite regular gas kinematics reflect the unperturbed spirallike polarization structure. In RR 24b a strong velocity gradient in ionized gas could be associated with the polarization structure. We suggest that the large‐scale magnetic field of the RR 24 pair members still plays a role in shaping the polarization pattern. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

川滇地区断层相互作用的地震活动证据及有限元模拟   总被引：7，自引：1，他引：6       下载免费PDF全文

王凯英  马瑾 《地震地质》2004,26(2):259-272

对川滇地区主要活动断裂地震活动性的分析表明 ,该区主要活动断裂间存在地震活动的相关性 :1)强震活跃期沿着鲜水河断裂、小江断裂、红河断裂、龙陵 -澜沧断裂及NE向的龙门山 -瑞丽断裂依次迁移 ;2 )鲜水河断裂与龙陵 -澜沧断裂不仅在强震活动上 ,而且在b值变化上存在较强的相关性 ,是平行断裂在区域应力场作用下相互作用的结果 ;3)龙门山 -瑞丽断裂与上述川滇地区其它近NW向断裂间存在地震交替活动的现象 ;4 )龙门山 -瑞丽断裂的地震具有分段活动的特征 ,是断块差异活动的体现。有限元分析显示 ,上述断层相互作用现象是块体非均匀运动过程中应力场调整的反映 ,是块体运动的结果。研究表明川滇地区主要断层地震活动间存在 3种相互作用的现象 ,即块体边界迁移型、旋向相反平行断层交替型和交叉断层交替型  相似文献   

Abiotic conditions, neighbour interactions, and the distribution of Stipa tenacissima in a semiarid mountain range     

C. Armas  Z. Kikvidze  F.I. Pugnaire   《Journal of Arid Environments》2009,73(12):1084-1089

Abiotic conditions and interactions among plants are important factors determining plant geographical distributions. With the aim of analyzing the distribution of a perennial grass species in a semiarid mountain range, we experimentally tested above- and belowground effects of shrubs on the grass along a gradient of aridity. We measured growth, physiology and reproductive output of Stipa tenacissima tussocks surrounded by intact or manipulated neighbour shrubs. Performance of Stipa improved under mesic conditions, but the net effect of shrubs on Stipa did not change along the gradient. Belowground, we did not find significant effects, suggesting belowground resource partitioning between tussocks and shrubs. Aboveground net effects of shrubs on Stipa were generally positive and independent from abiotic conditions. The improved performance of Stipa at the mesic end of gradient suggests that its absolute physiological optimum lies out of its realized range. Overall, the arid end of the geographical distribution of Stipa in this mountain range may be determined by environmental severity. The coincidence of the upper limit of Stipa with the lower tree limit suggests that the more mesic end of Stipa distribution may depend on other factors; most likely competition with trees, which, unlike shrubs, could be excluding Stipa tenacissima from forests.  相似文献   

2008年汶川大地震对周围断层的影响   总被引：55，自引：4，他引：51       下载免费PDF全文

万永革  沈正康  盛书中  徐晓枫 《地震学报》2009,31(2):128-139

2008年5月12日的汶川地震明显地改变了区域地震的应力场．理解这种应力场的改变对周围断层构造加载进程和区域地震危险性的改变非常重要．本文以汶川地震的破裂为驱动源,计算了该地震造成周围断层上的静态库仑破裂应力变化．结果表明,汶川大地震的发生使得龙门山断裂北部和最南端、鲜水河断裂最南端、东昆仑断裂、陇县——宝鸡断裂、鄂拉山断裂、白玉断裂、日月山断裂南端、马边——盐津断裂南部、班公错——嘉黎断裂西部、则木河断裂的库仑破裂应力增加,量值达0.00001——0.06MPa．库仑破裂应力增加尤为显著的断裂量值分别为:龙门山断裂的地震断层南端最大增加0.01MPa、北端0.03MPa,秦岭南缘断裂的西南部最大增加0.03MPa,东昆仑断裂的东南部为0.007MPa,地震破裂断层西南部的鲜水河断裂为0.005MPa,西秦岭北缘断裂的天水——宝鸡段为0.004MPa,陇县——宝鸡断裂为0.0003MPa．该地震还使得龙日坝断裂、怒江断裂、西秦岭北缘断裂西部、秦岭北缘断裂、庄浪河断裂、日月山断裂北部、海原断裂、岷江断裂、玉树——玛曲断裂、金沙江断裂的库仑破裂应力减少;减少尤为显著的断裂为龙门山断裂的断层破裂段、岷江断裂和鲜水河断裂的炉霍段,其库仑破裂应力减少分别达0.04——0.7MPa,0.001——0.1MPa和0.008——0.01MPa．本次地震在小金河、安宁河和大凉山断裂面上产生的库仑应力变化很小,对断层地震活动没有显著影响．   相似文献   

Rhyolitic volcano–ice interactions in Iceland     

Dave McGarvie   《Journal of Volcanology and Geothermal Research》2009,185(4):247-389

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