Estimation of friction parameters and laws in 1.5D shallow-water gravity currents on the f-plane, by data assimilation     

Achim Wirth  Jacques Verron 《Ocean Dynamics》2008,58(3-4):247-257

A 1.5-dimensional, 1.5-layer shallow water model and an ensemble Kalman filter are used to evaluate the feasibility of estimating friction parameters and determining friction laws of oceanic gravity currents. The two friction laws implemented are a linear Rayleigh friction and a quadratic drag law. We demonstrate that the assimilation procedure rapidly estimates the total frictional force, whereas the distinction between the two laws is evolving on a slower time scale. We also demonstrate that parameter estimation can, in this way, choose between different parametrisations and help to discriminate between physical laws of nature by estimating the coefficients presented in such parametrisations.  相似文献   

Using maximum likelihood to derive various distance-based goodness-of-fit indicators for hydrologic modeling assessment   总被引：1，自引：1，他引：0  

Qin-Bo?ChengEmail authorView author&#;s OrcID profile  Xi?Chen  Chong-Yu?Xu  Zhi-Cai?Zhang  Christian?Reinhardt-Imjela  Achim?Schulte 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):949-966

Currently used goodness-of-fit (GOF) indicators (i.e. efficiency criteria) are largely empirical and different GOF indicators emphasize different aspects of model performance; a thorough assessment of model skill may require the use of robust skill matrices. In this study, based on the maximum likelihood method, a statistical measure termed BC-GED error model is proposed, which firstly uses the Box–Cox (BC) transformation method to remove the heteroscedasticity of model residuals, and then employs the generalized error distribution (GED) with zero-mean to fit the distribution of model residuals after BC transformation. Various distance-based GOF indicators can be explicitly expressed by the BC-GED error model for different values of the BC transformation parameter λ and GED kurtosis coefficient β. Our study proves that (1) the shape of error distribution implied in the GOF indicators affects the model performance on high or low flow discharges because large error-power (β) value can cause low probability of large residuals and small β value will lead to high probability of zero value; (2) the mean absolute error could balance consideration of low and high flow value as its assumed error distribution (i.e. Laplace distribution, where β = 1) is the turning point of GED derivative at zero value. The results of a study performed in the Baocun watershed via comparison of the SWAT model-calibration results using six distance-based GOF indicators show that even though the formal BC-GED is theoretically reasonable, the calibrated model parameters do not always correspond to high performance of model-simulation results because of imperfection of the hydrologic model. However, the derived distance-based GOF indicators using the maximum likelihood method offer an easy way of choosing GOF indicators for different study purposes and developing multi-objective calibration strategies.  相似文献   

Radiocesium and 210Pb in sediments, soils and surface waters of a high alpine catchment: A mass balance approach relevant to radionuclide migration and storage     

Achim Albrecht 《Aquatic Sciences - Research Across Boundaries》1999,61(1):1-22

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老黑山盆地下白垩统穆棱组油页岩与煤含油率控制因素     

宋宇  刘招君  Achim Bechtel  徐银波  孟庆涛  孙平昌  朱凯 《吉林大学学报(地球科学版)》2020,50(2):378-391

我国陆相盆地内普遍存在油页岩与煤共生的地质现象。本文以老黑山盆地下白垩统穆棱组油页岩与煤为研究对象,基于工业分析（含油率、灰分、挥发分、全硫和发热量）和有机地球化学分析（有机碳、岩石热解、显微组分和生物标志化合物）,对油页岩与煤含油率的控制因素开展研究。根据含油率等工业品质特征,将研究区油页岩与煤进一步划分为高含油率油页岩（HOS）、低含油率油页岩（LOS）、高含油率煤（HC）和低含油率煤（LC）4种亚类。其中HC的总有机碳质量分数和生烃潜力最高,其次为LC、HOS和LOS,4种亚类的有机质类型以Ⅱ型干酪根为主,均处于未成熟的热演化阶段。沉积环境与有机质来源是控制油页岩与煤含油率的关键因素,HOS主要形成于陆源有机质供给中等的湖沼环境,而HC主要形成于陆源有机质供给丰富的泥炭沼泽环境。油页岩与煤形成时期的高等植物以松科、柏科/杉科、南洋杉科、罗汉松科和蕨类植物为主,这些植物可以提供充足的树脂和蜡质有机质,从而使油页岩与煤具有相对较高的含油率。  相似文献   

“Galileo Galilei” (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein     

Anna M. Nobili  Gian Luca Comandi  Suresh Doravari  Donato Bramanti  Rajeev Kumar  Francesco Maccarrone  Erseo Polacco  Slava G. Turyshev  Michael Shao  John Lipa  Hansjoerg Dittus  Claus Laemmerzhal  Achim Peters  Jurgen Mueller  C. S. Unnikrishnan  Ian W. Roxburgh  Alain Brillet  Christian Marchal  Jun Luo  Jozef van der Ha  Vadim Milyukov  Valerio Iafolla  David Lucchesi  Paolo Tortora  Paolo De Bernardis  Federico Palmonari  Sergio Focardi  Dino Zanello  Salvatore Monaco  Giovanni Mengali  Luciano Anselmo  Lorenzo Iorio  Zoran Knezevic 《Experimental Astronomy》2009,23(2):689-710

“Galileo Galilei” (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle—which is at the basis of the General Theory of Relativity—to 1 part in 10¹⁷. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009.  相似文献   

A biogeochemical study of sediments from the eutrophic Lake Lugano and the oligotrophic Lake Brienz,Switzerland     

Achim Bechtel  Carsten J. Schubert 《Organic Geochemistry》2009,40(10):1100-1114

The biomarker composition and stable isotope (C, O) ratio values of organic matter (OM) and carbonate from sediment cores from the oligotrophic Lake Brienz and the eutrophic Lake Lugano (both in Switzerland) are compared, in order to obtain information about OM sources and transformation processes. Eutrophic conditions at Lake Lugano are reflected in elevated total organic carbon (TOC) content and hydrogen index (HI) values, as well as higher lipid concentrations. Parallel down core trends in δ¹³C values of TOC and calcite in the Lake Lugano sediments reflect bioproductivity cycles. Variations in δ¹⁸O values of calcite are consistent with changes in mean summer temperature over the time interval covered by the core. In contrast, such a correlation does not exist for Lake Brienz and there the stable isotope composition of calcite reflects its allochthonous origin. In the sediments of both lakes, fatty acid (FA) distributions and the composition of n-alkanols and n-alkanes indicate highly variable proportions of autochthonous OM sources (algae, zooplankton, bacteria) and OM from land plants. Enhanced in situ microbial synthesis during sediment deposition in Lake Lugano is suggested by the higher TOC-normalised concentrations of branched chain FAs (C₁₅–C₁₇), hopanoic acids and triterpenoid alcohols (i.e. tetrahymanol, diplopterol). Variations in the concentrations of cholesterol are related to contributions from zooplankton and/or green algae, while sitosterol concentrations reflect the input of vascular plants. Periods of increased input of OM from diatoms are evidenced by high 24-methylcholesta-5,22-dien-3β-ol (either epibrassicasterol or brassicasterol) and/or highly branched isoprenoid (HBI) alkenes concentrations. High relative concentrations of diplopterol in Lake Lugano sediments are consistent with the predominance of cyanobacteria commonly observed in eutrophic lakes. The presence of archeol and hydroxyarcheol in very low concentrations in the Lugano sediments argues for the activity of methanogens and/or anaerobic methanotrophs.Differences in OM degradation processes are reflected in higher chlorin index values in the Brienz sediments but higher saturated vs. unsaturated n-FAs in the core from Lugano. Higher concentrations of branched chain FAs and 16:1ω7 n-FA, as well as enhanced 18:1ω7/18:1ω9 n-FA, are consistent with enhanced bacterial biomass in the Lugano water column or sediments. The preservation of phytol seems to be enhanced in sediments with a high relative contribution of land plant OM. Major factors affecting OM accumulation in the lakes are differences in OM sources (i.e. terrestrial OM vs. autochthonous production), extent of bacterial activity and most likely oxygen availability in the water column.  相似文献   

First record of the leptonectid ichthyosaur <Emphasis Type="Italic">Eurhinosaurus longirostris</Emphasis> from the Early Jurassic of Switzerland and its stratigraphic framework     

Achim G. Reisdorf  Michael W. Maisch  Andreas Wetzel 《Swiss Journal of Geoscience》2011,104(2):211-224

An incomplete skull of the leptonectid ichthyosaur Eurhinosaurus longirostris found in the Rietheim Member (previously “Posidonienschiefer”; Toarcian, Early Jurassic) of Staffelegg, Canton Aargau, is the first record from Switzerland of this taxon and supports the status of Eurhinosaurus longirostris as a palaeobiogeographic very widespread ichthyosaur species in the Early Toarcian of Western Europe. Being from either the Bifrons or Variabilis zone, it is one of the youngest records of Eurhinosaurus and one of the few diagnostic ichthyosaur finds from this time interval. The partial skull is well articulated and preserved three-dimensionally in a carbonate concretion. Both the mode of preservation of the ichthyosaur and an associated ammonoid (Catacoeloceras raquinianum) provided the age of the concretion, which had been collected from scree. Taphocoenosis and taphonomy show the C. raquinianum to be one of few non re-worked fossils recorded from the Early to Late Toarcian boundary (Bifrons/Variabilis zone) of northern Switzerland in general and of this ammonite species in particular. The Toarcian section at Staffelegg differs from other localities where strata of the same age are exposed with respect to facies variations of the Rietheim Member (previously “Posidonienschiefer”, Early Toarcian) and the extraordinarily high thickness of the Gross Wolf Member (previously “Jurensis-Mergel”, Late Toarcian).  相似文献   

Coupled penetrometer, MBES and ADCP assessments of tidal variations in surface sediment layer characteristics along active subaqueous dunes, Danish Wadden Sea     

Nina Stark  Hendrik Hanff  Christian Svenson  Verner B. Ernstsen  Alice Lefebvre  Christian Winter  Achim Kopf 《Geo-Marine Letters》2011,31(4):249-258

In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ∼1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1–3 kPa in the top layer, 20–140 kPa in the underlying sediment; thickness of the top layer ca. 5–8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 ± 2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments.  相似文献   

The city of Chemnitz in Saxony (Germany) building its new economic profile     

Andreas Bochmann  Achim Dresler  Wolf Tietze 《GeoJournal》1995,37(4):539-556

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Balance of tectonically accreted and subducted sediment at the Chile Triple Junction     

Jan H. Behrmann  Achim Kopf 《International Journal of Earth Sciences》2001,90(4):753-768

An active oceanic spreading ridge is being subducted beneath the South American continent at the Chile Triple Junction. Mass balance estimations to characterize temporal and spatial variations in the frontal accretion, or underplating and subduction of sediments since the Late Miocene, were made using seismic and drill-hole data. At 200 km north of the triple junction, almost 80% of the sediment on the downgoing Nazca plate are subducted. Sediment subduction rate decreases towards the triple junction because of a low in sedimentation rates as the flank of the spreading ridge approaches the trench. At the triple junction, the forearc is almost completely destroyed by spreading ridge collision and subduction erosion. Less than 12% of the available sedimentary input is accreted. South of the triple junction, where the spreading ridge passed 6 Ma ago, a large fraction (>60%) of the sediment on the incoming Antarctic plate has been scraped off and was frontally accreted to the Chile forearc. Spreading ridge subduction leaves a distinctive geological fingerprint, and has a large impact on the mass balance of the subduction zone. However, the high rates of change in the process may make this fingerprint hard to detect in fossil convergent orogens. In the ridge collision zone the sediment supplied to the trench, and the amount of sediment subducted, show strong and distinctive variations on a 1- to 5-million-year time scale. On a 10-million-year time scale, sediment subduction to the Earth's mantle is reduced by spreading ridge collision, caused by the need of the overriding forearc to regain a low angle of taper by frontal accretion.  相似文献