扎陵湖和鄂陵湖夏季典型地表水热交换特征的数值模拟     

杨显玉  吕雅琼  文军  马耀明  孟宪红  黄安宁  田辉  张少波  王禹润  赵林 《高原气象》2022,(1):143-152

选用由美国国家环境预报中心NCEP和美国国家大气研究中心NCAR联合开发的新一代中尺度数值模式WRF(Weather Research and Forecasting Model)模式,采用两重网格单向反馈嵌套的方法对扎陵湖和鄂陵湖区域的大气边界层特征进行数值模拟,并把湖泊水体下垫面替换为草地下垫面以设计另一组去除湖泊...  相似文献   

Long-term dynamics of a semiarid grass steppe under stochastic climate and different grazing regimes: A simulation analysis     

J.M. Paruelo  S. Pütz  G. Weber  M. Bertiller  R.A. Golluscio  M.R. Aguiar  T. Wiegand 《Journal of Arid Environments》2008,72(12):2211-2231

We built a grid-based spatial explicit stochastic model that simulates grazing events and basic processes like seedling establishment, growth or mortality of the dominant species in the grass steppes of Patagonia. After evaluating the model with field data, we performed simulation experiments aimed to explore the interaction of precipitation and grazing regimes on vegetation dynamics. Grazing generated a reduction in tussock density which results in a decline in aboveground net primary production (ANPP). Both response variables presented a non-linear behavior including high temporal variability and delay effects, which may prolong for decades. There was a clear threshold in the response of the variables to stock density, though changes become evident only when a highly selective grazing scenario was used. Under high stock density conditions, precipitation use efficiency (PUE) was 82% lower than the values for non-grazed runs. The inter-annual variability of precipitation was more important than the grazing regime in explaining differences in tussock density. Simulation results highlight important issues regarding rangeland management: grazing regime might be as important as stocking density as a degradation agent, temporal lags might obscure degradation processes for decades, the definition of monitoring variables need to consider their response time constants.  相似文献   

Mid‐sized complex crater formation in mixed crystalline‐sedimentary targets: Insight from modeling and observation     

G. S. COLLINS  T. KENKMANN  G. R. OSINSKI  K. WÜNNEMANN 《Meteoritics & planetary science》2008,43(12):1955-1977

Abstract— Large impact crater formation is an important geologic process that is not fully understood. The current paradigm for impact crater formation is based on models and observations of impacts in homogeneous targets. Real targets are rarely uniform; for example, the majority of Earth's surface is covered by sedimentary rocks and/or a water layer. The ubiquity of layering across solar system bodies makes it important to understand the effect target properties have on the cratering process. To advance understanding of the mechanics of crater collapse, and the effect of variations in target properties on crater formation, the first “Bridging the Gap” workshop recommended that geological observation and numerical modeling focussed on mid‐sized (15–30 km diameter) craters on Earth. These are large enough to be complex; small enough to be mapped, surveyed and modelled at high resolution; and numerous enough for the effects of target properties to be potentially disentangled from the effects of other variables. In this paper, we compare observations and numerical models of three 18–26 km diameter craters formed in different target lithology: Ries, Germany; Haughton, Canada; and El'gygytgyn, Russia. Based on the first‐order assumption that the impact energy was the same in all three impacts we performed numerical simulations of each crater to construct a simple quantitative model for mid‐sized complex crater formation in a subaerial, mixed crystalline‐sedimentary target. We compared our results with interpreted geological profiles of Ries and Haughton, based on detailed new and published geological mapping and published geophysical surveys. Our combined observational and numerical modeling work suggests that the major structural differences between each crater can be explained by the difference in thickness of the pre‐impact sedimentary cover in each case. We conclude that the presence of an inner ring at Ries, and not at Haughton, is because basement rocks that are stronger than the overlying sediments are sufficiently close to the surface that they are uplifted and overturned during excavation and remain as an uplifted ring after modification and post‐impact erosion. For constant impact energy, transient and final crater diameters increase with increasing sediment thickness.  相似文献   

Petrography,mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300     

Weibiao HSU  Aicheng ZHANG  Rainer BARTOSCHEWITZ  Yunbin GUAN  Takayuki USHIKUBO  Urs KRÄHENBÜHL  Rainer NIEDERGESAESS  Rudolf PEPELNIK  Ulrich REUS  Thomas KURTZ  Paul KURTZ 《Meteoritics & planetary science》2008,43(8):1363-1381

Abstract— We report here the petrography, mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300 (SaU 300). SaU 300 is dominated by a fine‐grained crystalline matrix surrounding mineral fragments (plagioclase, pyroxene, olivine, and ilmenite) and lithic clasts (mainly feldspathic to noritic). Mare basalt and KREEPy rocks are absent. Glass melt veins and impact melts are present, indicating that the rock has been subjected to a second impact event. FeNi metal and troilite grains were observed in the matrix. Major element concentrations of SaU 300 (Al₂O₃ 21.6 wt% and FeO 8.16 wt%) are very similar to those of two basalt‐bearing feldspathic regolith breccias: Calcalong Creek and Yamato (Y‐) 983885. However, the rare earth element (REE) abundances and pattern of SaU 300 resemble the patterns of feldspathic highlands meteorites (e.g., Queen Alexandra Range (QUE) 93069 and Dar al Gani (DaG) 400), and the average lunar highlands crust. It has a relatively LREE‐enriched (7 to 10 x CI) pattern with a positive Eu anomaly (?11 x CI). Values of Fe/Mn ratios of olivine, pyroxene, and the bulk sample are essentially consistent with a lunar origin. SaU 300 also contains high siderophile abundances with a chondritic Ni/Ir ratio. SaU 300 has experienced moderate terrestrial weathering as its bulk Sr concentration is elevated compared to other lunar meteorites and Apollo and Luna samples. Mineral chemistry and trace element abundances of SaU 300 fall within the ranges of lunar feldspathic meteorites and FAN rocks. SaU 300 is a feldspathic impact‐melt breccia predominantly composed of feldspathic highlands rocks with a small amount of mafic component. With a bulk Mg# of 0.67, it is the most mafic of the feldspathic meteorites and represents a lunar surface composition distinct from any other known lunar meteorites. On the basis of its low Th concentration (0.46 ppm) and its lack of KREEPy and mare basaltic components, the source region of SaU 300 could have been within a highland terrain, a great distance from the Imbrium impact basin, probably on the far side of the Moon.  相似文献   

Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets     

E. PIERAZZO  N. ARTEMIEVA  E. ASPHAUG  E. C. BALDWIN  J. CAZAMIAS  R. COKER  G. S. COLLINS  D. A. CRAWFORD  T. DAVISON  D. ELBESHAUSEN  K. A. HOLSAPPLE  K. R. HOUSEN  D. G. KORYCANSKY  K. WÜNNEMANN 《Meteoritics & planetary science》2008,43(12):1917-1938

Abstract— Over the last few decades, rapid improvement of computer capabilities has allowed impact cratering to be modeled with increasing complexity and realism, and has paved the way for a new era of numerical modeling of the impact process, including full, three‐dimensional (3D) simulations. When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS‐MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum‐on‐aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter‐code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well‐characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter‐code variability.  相似文献   

LATE QUATERNARY MORAINES ALONG THE SEKHOKONG RANGE, EASTERN LESOTHO: CONTRASTING THE GEOMORPHIC HISTORY OF NORTH- AND SOUTH-FACING SLOPES     

BY STEPHANIE C. MILLS  STEFAN W. GRAB  SIMON J. CARR 《Geografiska Annaler: Series A, Physical Geography》2009,91(2):121-140

Considerable Quaternary environmental reconstruction for the high Drakensberg is based on geomorphological and sedimentological work undertaken along the northern aspects of the Sekhokong mountain range of eastern Lesotho. Given that no previous investigations have focused on the southern aspects, this paper documents the observed geomorphology and provides a more complete palaeo-environmental picture for this range. Data on the morphology, sedimentology and micromorphology for two linear debris ridges are presented. It is demonstrated that the two ridges are most likely moraines originating from a small niche glacier. The combined use of macro- and micro-scale sedimentology is proven to be an essential tool in ascribing a glacial process origin for the landforms, given the complex depositional history they have undergone. AMS ages obtained from the deposits (14 700 cal. yrs bp and 19 350 cal. yrs bp ) places these in the time-scale of the Last Glacial Maximum. The study demonstrates rather contrasting aspect-controlled palaegeomorphological environments along the Sekhokong range, which is also reflected in the dissimilar contemporary biophysical micro-environments. It is suggested that the south-facing slopes were dominated by glacial processes during the Last Glacial Maximum (LGM), as is evident from the moraines, while the proposition for previously described north-facing glacial cirques is rejected based on the absence of erosional/depositional evidence and greater insolation received on these warmerequator-facing slopes. Rather, we propose that the observed north-facing hollows are a product of a multitude of geomorphic processes spanning several tens to hundreds of thousands of years.  相似文献   

Regional Ambient Noise Tomography in the Eastern Alps of Europe     

Michael Behm  Nori Nakata  Götz Bokelmann 《Pure and Applied Geophysics》2016,173(8):2813-2840

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Influence of Surfactants on Dye Removal and Growth of Aspergillus versicolor – an Effective Way to Decolorize Textile Dye          下载免费PDF全文

Ülküye Dudu Gül  Gönül Dönmez 《洁净——土壤、空气、水》2014,42(7):917-922

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A New Non‐Pterodactyloid Pterosaur from Qinglong County,Hebei Province of China   总被引：1，自引：0，他引：1  

Lü Junchang 《《地质学报》英文版》2009,83(2):189-199

A new basal non-pterodactyloid pterosaur, Changchengopterus pani gen. et sp. nov., is erected, on the basis of a nearly complete postcranial skeleton. The new taxon is distinguished by relatively short extensions of the prezygapophyses, postzygapophyses and haemal arches of the caudal vertebrae; a humerus that has a subtriangular deltopectoral crest; limb elements that decrease in length in the following order: ulna> wing-phalange 2 > wing-phalange 3 = wing-phalange 1>humerus >tibia>femur>wing-metacarpal. Phylogenetic analysis suggests that Changchengopterus is a basal member of rhamphorhynchoids, and more closely related to Dorygnathus than to other rhamphorhychoids. The geological age of the Changchengopterus -bearing sediments is no latter than the end of the Late Jurassic and it is possible Middle Jurassic.  相似文献   

微生物矿化作用改善岩土材料性能的影响因素   总被引：1，自引：0，他引：1  

尹黎阳  唐朝生  谢约翰  吕超  蒋宁俊  施斌 《岩土力学》2019,40(7):2525-2546

基于微生物诱导碳酸钙沉淀作用（MICP）的土体改性技术近年来在岩土工程领域引起了人们的广泛关注。该技术在改善岩土材料的强度、刚度、抗液化、抗侵蚀及抗渗透性等性能的同时,还能维持土体良好的透气性和透水性,改善植物的生长环境。由于微生物矿化作用涉及一系列生物化学和离子化学反应,固化过程中的反应步骤较多,因此,MICP固化效果受许多因素的制约与影响。基于大量文献资料,系统总结了细菌种类、菌液浓度、温度、pH值、胶结液配比及土的性质等关键因素对微生物改善岩土材料性能的影响,讨论了这些影响因素的优化方式和未来的研究方向,主要得到了以下几点结论：菌种类型、菌液浓度、温度、pH、胶结液性质会从微观上影响碳酸钙的晶体类型、形貌和尺寸,进而在宏观层面影响岩土体的胶结效果;菌液浓度尽可能高、温度在20～40℃间、pH值在7.0～9.5左右、胶结液浓度在1 mol/L以内的因素条件对微生物加固岩土体具有较好的效果。上述范围内的低温、较高的pH值、低浓度胶结液有助于提高土体的抗渗性,而高温、较低的pH值以及中高浓度胶结液有助于提高土体的强度;MICP加固土体的有效粒径范围为10～1 000 ?m,相对密度越大、级配越好则加固效果越好。分步灌浆法、多浓度相灌注法及电渗灌浆法有助于提高土体固化均匀性,0.042 (mol/L)/h以下的注浆速度有利于提高胶结液利用率,砂土试样的灌浆压力一般在10～30 kPa之间,粉黏土试样的灌浆压力不宜超过110 kPa,过高的灌浆压力会破坏土体结构,降低固化效果。  相似文献