Editorial          下载免费PDF全文

Streck  Martin J.; Grunder  Anita L. 《Journal of Petrology》1997,38(1):133-163

The Rattlesnake Tuff of eastern Oregon comprises >99% ofhigh-silica rhyolite glass shards and pumices representing 280km³ of magma. Glassy, crystal-poor, high-silica rhyolite pumicesand glass shards cluster in five chemical groups that rangein color from white to dark gray with increasing Fe concentration.Compositional clusters are defined by Fe, Ti, LREE, Ba, Eu,Rb, Zr, Hf, Ta, and Th. Progressive changes with increasingdegree of evolution of the magma occur in modal mineralogy,mineral composition, and partition coefficients. Partition coefficientsare reported for alkali feldspar, clinopyroxene, and titanomagnetite.Models of modal crystal fractionation, assimilation, successivepartial melting, and mixing of end members cannot account forthe chemical variations among rhyolite compositions. On theother hand, 50% fractionation of observed phenocryst compositionsin non-modal proportions agrees with chemical variations amongrhyolite compositions. Such non-modal fractionation might occuralong the roof and margins of a magma chamber and would yieldcompositions of removed solids ranging from syenitic to granitic.A differentiation sequence is proposed by which each more evolvedcomposition is derived from the previous, less evolved liquidby fractionation and accumulation, occurring mainly along theroof of a slab-like magma chamber. As a layer of derivativemagma reaches a critical thickness, a new layer is formed, generatinga compositionally and density stratified magma chamber. KEY WORDS: high-silica rhyolite; partition coefficients; differentiation; zoned ash-flow tuff; layered convection  相似文献   

Meiofauna Distribution in Intertidal Sandy Beaches Along China Shoreline(18?–40?N)     

Er Hua  Zhinan Zhang  Hong Zhou  Fanghong Mu  Jia Li  Ting Zhang  Bingqing Cong  Xiaoshou Liu 《中国海洋大学学报(英文版)》2016,15(1):19-27

In this study,the distribution pattern of meiofauna from nine sandy beaches at six latitudinal gradients along Chinese coast between 18 and 40?N was studied on their meiofauna abundance to examine the effect of latitudinal gradients.In general,meiofauna abundance was lower in four subtropical beaches in Xiamen(24?N) and Zhoushan(29?N) than that in other beaches.Meiofauna abundance differed little between tropical and temperate beaches.The taxonomic structure of meiofauna showed a dominance of nematode in colder area.The relative composition of turbellarians and polychaetes increased in warmer area.In addition to latitudinal gradient,salinity,oxygenation,sediment grain size affect also the meiofauna latitudinal distribution.As for horizontal distribution,the highest meiofauna abundance was found in low tidal zone at tropical beaches,and in middle tidal zone at temperate beaches.The horizontal distribution of meiofauna was controlled by both physical and biotic factors including feeding and anthropogenic activities.Although meiofauna abundance exhibited a horizontal difference,the composition of meiofaunal main taxa was unanimous horizontally at all beaches at the same sampling latitude.  相似文献   

Amino acids derived from Titan tholins     

Khare BN  Sagan C  Ogino H  Nagy B  Er C  Schram KH  Arakawa ET 《Icarus》1986,68(1):176-184

An organic heteropolymer (Titan tholin) was produced by continuous dc discharge through a 0.9 N2/0.1 CH4 gas mixture at 0.2 mbar pressure, roughly simulating the cloudtop atmosphere of Titan. Treatment of this tholin with 6N HCl yielded 16 amino acids by gas chromatography after derivatization of N-trifluroacetyl isopropyl esters on two different capillary columns. Identifications were confirmed by GC/MS. Glycine, aspartic acid, and alpha- and beta-alanine were produced in greatest abundance; the total yield of amino acids was approximately 10(-2), approximately equal to the yield of urea. The presence of "nonbiological" amino acids, the absence of serine, and the fact that the amino acids are racemic within experimental error together indicate that these molecules are not due to microbial or other contamination, but are derived from the tholin. In addition to the HCN, HC2CN, and (CN)2 found by Voyager, nitriles and aminonitriles should be sought in the Titanian atmosphere and, eventually, amino acids on the surface. These results suggest that episodes of liquid water in the past or future of Titan might lead to major further steps in prebiological organic chemistry on that body.  相似文献   

黄海冷水团声层析监测数值模拟     

彭临慧  王宁  邱晓芳  尚尔昌 《中国海洋大学学报(自然科学版)》2003,33(2):299-304

海洋冷水团是海洋学家关注多年的问题 ,其监测方法亟待解决。本文将简正波波数层析法用于冷水团监测 ,并对简正波波数层析用于反演黄海冷水团声速剖面进行了数值模拟。数值模拟结果表明 ,简正波波数层析可以用于反演平均声速剖面 ,特别在监测与距离有关海洋环境的声速结构方面大有潜力。  相似文献   

Dredging for edible cockles (Cerastoderma edule) on intertidal flats: short-term consequences of fisher patch-choice decisions for target and non-target benthic fauna     

Kraan  Casper; Piersma  Theunis; Dekinga  Anne; Koolhaas  Anita; van der Meer  Jaap 《ICES Journal of Marine Science》2007,64(9):1735-1742

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Public climate-change skepticism,energy preferences and political participation     

Anita Engels  Otto Hüther  Mike Schäfer  Hermann Held 《Global Environmental Change》2013,23(5):1018-1027

Many studies have shown a general decline of public concern about climate change or vice versa a rise in public climate-change skepticism, in particular in the U.S. and other Anglo-Saxon countries. There is a vivid debate on whether this is a global phenomenon, on which factors explain the decline, and on the broader societal implications of these trends in the context of the transformation toward a low-carbon society. We add to this literature by presenting the results of a recent general population survey in Germany in which we looked for systematic linkages between public climate-change skepticism on one hand, and energy preferences and political participation on the other. Germany is an interesting testbed as it is currently involved in a large-scale restructuring of its system of energy supply toward renewable energy sources (the “Energiewende”). Our results indicate that climate-change skepticism has not diffused widely in Germany, but that it correlates with less support of renewable energy sources. However, skepticism correlates negatively with political participation, and there is no strong political outlet for public climate-change skepticism in Germany. Alternative potential barriers for the successful implementation of the “Energiewende” are also discussed.  相似文献   

Climate change and hydrology at the prairie margin: Historic and prospective future flows of Canada's Red Deer and other Rocky Mountain rivers          下载免费PDF全文

Laurens J. Philipsen  Karen M. Gill  Anita Shepherd  Stewart B. Rood 《水文研究》2018,32(17):2669-2684

The South Saskatchewan River Basin of southern Alberta drains the transboundary central Rocky Mountains region and provides the focus for irrigation agriculture in Canada. Following extensive development, two tributaries, the Oldman and Bow rivers, were closed for further water allocations, whereas the Red Deer River (RDR) remains open. The RDR basin is at the northern limit of the North American Great Plains and may be suitable for agricultural expansion with a warming climate. To consider irrigation development and ecological impacts, it is important to understand the regional hydrologic consequences of climate change. To analyse historic trends that could extend into the future, we developed century‐long discharge records for the RDR, by coordinating data across hydrometric gauges, estimating annual flows from seasonal records, and undertaking flow naturalization to compensate for river regulation. Analyses indicated some coordination with the Pacific decadal oscillation and slight decline in summer and annual flows from 1912 to 2016 (?0.13%/year, Sen's slope). Another forecasting approach involved regional downscaling from the global circulation models, CGCMI‐A, ECHAM4, HadCM3, and NCAR‐CCM3. These projected slight flow decreases from the mountain headwaters versus increases from the foothills and boreal regions, resulting in a slight increase in overall river flows (+0.1%/year). Prior projections from these and other global circulation models ranged from slight decrease to slight increase, and the average projection of ?0.05%/year approached the empirical trend. Assessments of other rivers draining the central and northern Rocky Mountains revealed a geographic transition in flow patterns over the past century. Flows from the rivers in Southern Alberta declined (around ?0.15%/year), in contrast to increasing flows in north‐eastern British Columbia and the Yukon. The RDR watershed approaches this transition, and this study thus revealed regional differentiation in the hydrological consequences from climate change.  相似文献   

The scales of variability of stream fish assemblages at tributary confluences     

I. Czeglédi  P. Sály  P. Takács  A. Dolezsai  S. A. Nagy  T. Erős 《Aquatic Sciences - Research Across Boundaries》2016,78(4):641-654

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Design of sediment detention basins: Scaled model experiments and application     

Anita Moldenhauer-Roth  Guillaume Piton  Sebastian Schwindt  Mona Jafarnejad  Anton JSchleiss 《国际泥沙研究》2021,36(1):136-150

Sediment detention basins are implemented on mountain rivers to trap solid material that may aggravate the flooding of downstream settlements.However,retention structures built in the past may unnecessarily retain sediment during non-hazardous flood events,resulting in high maintenance costs and sediment deficit downstream.In addition,the so-called spontaneous self-flushing of previously retained sediment during floods has occasionally been observed.Recent research suggests to design sediment detention basins for controlling sediment passage with a guiding channel across the deposition area upstream of a hybrid barrier.Such barriers consist of a check dam with a slot orifice and an upstream bar screen with a bottom clearance in order to benefit from a combined mechanical-hydraulic retention control.The present paper enhances this pioneering research with the help of new experimental data,including a wide range of sediment mixtures and large wood,as well as variable barrier heights.Improved design criteria are provided regarding the bar screen and the basin storage capacity.The functionality of the enhanced concept for sediment detention is illustrated by a case study on a physical model:the protection of the Villard-Bonnot village(France)against torrential hazards.  相似文献   

A Bayesian procedure for Probabilistic Tsunami Hazard Assessment   总被引：1，自引：1，他引：0  

Anita Grezio  Warner Marzocchi  Laura Sandri  Paolo Gasparini 《Natural Hazards》2010,53(1):159-174

In this paper, a Bayesian procedure is implemented for the Probability Tsunami Hazard Assessment (PTHA). The approach is general and modular incorporating all significant information relevant for the hazard assessment, such as theoretical and empirical background, analytical or numerical models, instrumental and historical data. The procedure provides the posterior probability distribution that integrates the prior probability distribution based on the physical knowledge of the process and the likelihood based on the historical data. Also, the method deals with aleatory and epistemic uncertainties incorporating in a formal way all sources of relevant uncertainty, from the tsunami generation process to the wave propagation and impact on the coasts. The modular structure of the procedure is flexible and easy to modify and/or update as long as new models and/or information are available. Finally, the procedure is applied to an hypothetical region, Neverland, to clarify the PTHA evaluation in a realistic case.  相似文献