Ambient Seismic Noise Tomography of a Loess High Bank at Dunaszekcső (Hungary)     

Gyöngyvér Szanyi  Zoltán Gráczer  Erzsébet Győri  Zdeněk Kaláb  Markéta Lednická 《Pure and Applied Geophysics》2016,173(8):2913-2928

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Complexly zoned chromium‐aluminum spinel found in situ in the Allende meteorite     

S. b. Simon  K. d. Mckeegan  D. s. Ebel  L. Grossman 《Meteoritics & planetary science》2000,35(2):215-227

Abstract— In addition to the Mg‐, Al‐, ¹⁶O‐rich spinels that are known to occur in refractory inclusions, the Murchison meteorite contains Cr‐rich, ¹⁶O‐poor spinels, most of whose sources are unknown because they are rarely found in situ. Here we report the in situ occurrence in Allende of Cr‐rich spinels, found in 13 chondrules and 4 “olivine‐rich objects”. The Allende spinels exhibit major and minor element contents, isotopic compositions, and zoning of Crb>2b>Ob>3b> contents like those of the Cr‐spinels from Murchison. Some chondrules contain patchy‐zoned spinel (Simon et al., 1994), which suggests that such grains did not form by sintering but perhaps by formation of overgrowths on relic grains. Unlike the olivine‐rich objects, phases in all three chondrules that were analyzed by ion microprobe have uniform, near‐normal O‐isotopic compositions. One olivine‐rich object, ALSP1, has a huge (1 mm) fragment of chevron‐zoned spinel. This spinel has near‐normal O‐isotopic compositions that are quite distinct from those of adjacent forsteritic olivine, which are relatively ¹⁶O‐rich and plot on the calcium‐aluminum‐inclusion (CAI) line, like some isolated forsterite grains found in Allende. The spinel and olivine in this object are therefore not genetically related to each other. Another olivine‐rich object, ALSP11A, contains a rectangular, 150 ×s 100 μm, homogeneous spinel grain with 50 wt% Crb>2b>Ob>3b> and 23 wt% FeO in a vuggy aggregate of finer‐grained (5–90 μm), FeO‐rich (Fob>47–55b>) olivine. The magnesian core of one olivine grain has a somewhat ¹⁶O‐rich isotopic composition like that of the large spinel, whereas the FeO‐rich olivine is relatively ¹⁶O‐poor. The composition of the spinel in ALSP11A plots on the CAI line, the first Cr‐rich spinel found to do so. Chevron‐zoned spinel has not been observed in chondrules, and it is unlikely that either ALSP1 or ALSP11A were ever molten. Calculations show that a spinel with the composition of that in ALSP1 can condense at 1780 K at a P^tot of 10^?3 atm and a dust/gas ratio of 100 relative to solar. The Cr‐rich spinel in ALSP11A could condense at ～1420 K, but this would require a dust/gas enrichment of 1000 relative to solar. The data presented here confirm that, as in Murchison, the coarse Cr‐rich spinels in Allende are relatively ¹⁶O‐depleted and are isotopically distinct from the ¹⁶O‐enriched MgAlb>2b>Ob>4b> from CAIs. Sample ALSP11A may represent a third population, one that is Cr‐rich and plots on the CAI line. That the O‐isotopic composition of ALSP1 is like those of Cr‐rich spinels from chondrules indicates that O‐isotopic compositions cannot be used to distinguish whether grains from such unequilibrated objects are condensates or are fragments from a previous generation of chondrules.  相似文献   

基于E-FAST的流溪河模型参数敏感性分析     

廖征红  陈洋波  徐会军  严婉玲  任启伟 《热带地理》2012,32(6):606-612,632

基于E-FAST全局定量敏感性分析方法的思想,提出一个针对分布式物理水文模型——流溪河模型的参数敏感性分析方法,包括参数简化及取值范围确定、参数采样及采样次数的确定、敏感性评价指标的选取、参数敏感度计算4个部分.针对我国4个不同规模的流域(黄龙带水库流域、流溪河水库流域、长湖水库流域和新安江水库流域)开展了分布式物理水文模型参数敏感性分析,并采用4种不同的评价函数进行了对比计算.结果表明,流溪河模型饱和含水率和田间持水率是高度敏感参数,饱和水力传导率、土壤层厚度、土壤特性系数、边坡和河道糙率为敏感参数,其他参数为不敏感参数.  相似文献   

Backcasting long-term climate data: evaluation of hypothesis   总被引：1，自引：0，他引：1  

Bahram?SaghafianEmail author  Sara?Ghasemi?Aghbalaghi  Mohsen?Nasseri 《Theoretical and Applied Climatology》2018,132(3-4):717-726

Most often than not, incomplete datasets or short-term recorded data in vast regions impedes reliable climate and water studies. Various methods, such as simple correlation with stations having long-term time series, are practiced to infill or extend the period of observation at stations with missing or short-term data. In the current paper and for the first time, the hypothesis on the feasibility of extending the downscaling concept to backcast local observation records using large-scale atmospheric predictors is examined. Backcasting is coined here to contrast forecasting/projection; the former is implied to reconstruct in the past, while the latter represents projection in the future. To assess our hypotheses, daily and monthly statistical downscaling models were employed to reconstruct past precipitation data and lengthen the data period. Urmia and Tabriz synoptic stations, located in northwestern Iran, constituted two case study stations. SDSM and data-mining downscaling model (DMDM) daily as well as the group method of data handling (GMDH) and model tree (Mp5) monthly downscaling models were trained with National Center for Environmental Prediction (NCEP) data. After training, reconstructed precipitation data of the past was validated against observed data. Then, the data was fully extended to the 1948 to 2009 period corresponding to available NCEP data period. The results showed that DMDM performed superior in generation of monthly average precipitation compared with the SDSM, Mp5, and GMDH models, although none of the models could preserve the monthly variance. This overall confirms practical value of the proposed approach in extension of the past historic data, particularly for long-term climatological and water budget studies.  相似文献   

A middle Cambrian shallow water trilobite fauna from the Comstock Formation,near Queenstown,western Tasmania     

J. b. Jago  C. j. Bentley  Lin Tian-rui  K. d. Corbett 《Australian Journal of Earth Sciences》2013,60(7):959-966

A limestone lens within the Comstock Formation, from low in the Tyndall Group near the Lyell Comstock Mine near Queenstown, western Tasmania, contains a small trilobite fauna. The trilobites include Ammagnostus cf. laiwuensis, Kootenia sp., Sudanomocarina? sp. and a possible member of the Monkaspidae. These suggest an age somewhere in the range from the upper Ptychagnostus atavus Zone to the Lejopyge laevigata Zone, with regional stratigraphic correlations suggesting the latter zone. This is only the second Tasmanian Cambrian fossil assemblage described from limestone; almost all previously described Tasmanian Cambrian faunas are found in siltstones and shales.  相似文献   

Inferring organic content of sediments by scanning reflectance spectroscopy (380–730 nm): applying a novel methodology in a case study from proglacial lakes in Norway     

Mathias Trachsel  Bjørn Christian Kvisvik  Pål Ringkjøb Nielsen  Jostein Bakke  Atle Nesje 《Journal of Paleolimnology》2013,50(4):583-592

Reflectance spectroscopy in the visible spectrum (VIS-RS) is a method that has been successfully applied for inferring organic content of sediments. In this study, we test the applicability of VIS-RS to lake sediments in Norway. On the one hand we use conventional, established algorithms for inferring organic content of sediments, on the other hand we test the potential of multivariate calibration techniques to infer organic content. For absolute quantification of organic content, conventional Cb>orgb> measurements are needed when using conventional algorithms as well as when employing multivariate calibration techniques. Both, conventional algorithms and multivariate calibrations, result in estimates of organic content closely mirroring loss-on-ignition measurements. When using multivariate calibration techniques, a conventional Cb>orgb> measurement every 5 cm is sufficient to obtain estimates of organic matter that are more accurate than those obtained by means of conventional algorithms. Therefore, the potential of multivariate calibration techniques and VIS-RS to substitute measurements of more time consuming and costly sediment parameters (e.g. clay minerals) should be tested.  相似文献   

我国城市新区开发的管理模式与空间组织研究     

朱孟珏  周春山 《热带地理》2013,33(1):56-62

基于对我国879个城市新区的统计比较,分析了我国目前存在的市场型、开发区型和政区型3种城市新区开发管理模式,以及行政区内部整合、跨行政区整合、开发区设立行政区、行政区-开发区合署、行政区设立新区、新设行政新区等空间组织方式,并且不同的管理模式与空间组织形式存在着差异性、演化性和适用性的特点,城市新区的发展必须根据发展阶段、地域特征、功能形式等选择合适的组织管理形式.  相似文献   

珠三角港口体系演化模型研究     

吴旗韬  张虹鸥  叶玉瑶  陈静 《热带地理》2013,(2):171-177

珠三角是我国港口布局的重要区域,悠久的发展历史和独特的政治环境,区域港口体系发展具有独特的模式和过程。在详细梳理不同阶段港口体系发展阶段和特征的基础上,从长时间序列构建了珠三角地区港口体系演化模型。该模型与西方发达国家以及殖民地国家的港口体系演化具有一定的差异。珠三角港口体系具有港口体系波动特征,不同于西方国家模型中只有单一集中化和分散化发展趋势的描述;其次,珠三角港口体系发展模型的起始阶段为单极化发展阶段,而非西方国家模型中的均衡化发展阶段;最后珠三角港口体系发展模型增加了对枢纽港口空间位置转移的描述。  相似文献   

Palaeoclimatic and regional implications of Older Dryas and Younger Dryas local glacier activity in the low-Arctic valley Finnkongdalen,Andøya,northern Norway     

Henrik Løseth Jansen  Svein Olaf Dahl  Henriette Linge  Jostein Bakke  Pål Ringkjøb Nielsen  Bjørn Christian Kvisvik 《Boreas: An International Journal of Quaternary Research》2023,52(2):168-193

Continuous glacier margin and equilibrium-line altitude fluctuations of a former glacier on central Andøya, northern Norway, are reconstructed during the Lateglacial based on moraines and AMS ¹⁴C-dated sediments from the distal glacier-fed lake Ner-Finnkongdalsvatnet. The results indicate that a valley glacier occupied the entire valley during the Last Glacial Maximum (before 21 970±620 cal. a BP). The glacier remained large throughout the early Lateglacial until a significant glacier retreat took place about 14 300±330 cal. a BP. Major advances occurred during the Older Dryas (OD) and during the Younger Dryas (YD), while minor advances are suggested to have taken place during the Intra Allerød Cold Period and the Late Allerød Cooling. Additionally, three smaller glacier retreats/re-advances within the YD are suggested to have taken place, the latter being the largest. The glacier re-formations/advances during the Lateglacial are consistent with increases in temperature, and they are thus suggested to be the result of increased winter precipitation. Comparing the results with relevant glacier and sea-surface temperature records, a south–north migration of storm tracks may have occurred between 12 100–11 810±220 cal. a BP. The high temporal resolution of local glacier activity in Finnkongdalen improves our understanding of the climate forcing of the regional glacier fluctuations of the northwestern sector of the Scandinavian Ice Sheet during the Skarpnes- (OD) and Tromsø-Lyngen (YD) re-advances.  相似文献   

Efficient Simulation of Freak Waves in Random Oceanic Sea States   总被引：1，自引：0，他引：1  

张运秋  胡金鹏  张宁川 《中国海洋工程》2009,23(1)

Numerical simulations of freak wave generation are studied in random oceanic sea states described by JONSWAP spectrum.The evolution of initial random wave trains is numerically carried out within the framework of the modified fourorder nonlinear Schruedinger equation (mNLSE),and some involved influence factors are also discussed.Results show that if the sideband instability is satisfied,a random wave train may evolve into a freak wave train,and simultaneously the setting of the Phillips parameter and enhancement coefficient of JONSWAP spectrum and initial random phases is very important for the formation of freak waves.The way to increase the generation efficiency of freak waves thsough changing the involved parameters is also presented.  相似文献