A combined numerical–empirical method to calculate finite-time Lyapunov exponents from experimental time series with application to vessel capsizing     

Leigh McCue  Armin Troesch 《Ocean Engineering》2006,33(13):1796-1813

This paper presents a method to calculate finite-time Lyapunov exponents (FTLEs) for experimental time series using numerical simulation to approximate the local Jacobian of the system at each time step. This combined numerical–experimental approach to the calculation of FTLE is applicable to any physical system which can be numerically approximated. By way of example, the method is applied to the problem of vessel capsize.  相似文献   

Quality Assessment Of Digital Surface Models Generated From IKONOS Imagery     

Joanne  Poon  Clive S.  Fraser  Zhang  Chunsun  Zhang  Li  Armin  Gruen 《The Photogrammetric Record》2005,20(110):162-171

The growing applications of digital surface models (DSMs) for object detection, segmentation and representation of terrestrial landscapes have provided impetus for further automation of 3D spatial information extraction processes. While new technologies such as lidar are available for almost instant DSM generation, the use of stereoscopic high-resolution satellite imagery (HRSI), coupled with image matching, affords cost-effective measurement of surface topography over large coverage areas. This investigation explores the potential of IKONOS Geo stereo imagery for producing DSMs using an alternative sensor orientation model, namely bias-corrected rational polynomial coefficients (RPCs), and a hybrid image-matching algorithm. To serve both as a reference surface and a basis for comparison, a lidar DSM was employed in the Hobart testfield, a region of differing terrain types and slope. In order to take topographic variation within the modelled surface into account, the lidar strip was divided into separate sub-areas representing differing land cover types. It is shown that over topographically diverse areas, heighting accuracy to better than 3 pixels can be readily achieved. Results improve markedly in feature-rich open and relatively flat terrain, with sub-pixel accuracy being achieved at check points surveyed using the global positioning system (GPS). This assessment demonstrates that the outlook for DSM generation from HRSI is very promising.  相似文献   

Start at zero: succession of benthic invertebrate assemblages in restored former sewage channels     

Caroline Winking  Armin W. Lorenz  Bernd Sures  Daniel Hering 《Aquatic Sciences - Research Across Boundaries》2016,78(4):683-694

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Long-term persistence enhances uncertainty about anthropogenic warming of Antarctica   总被引：1，自引：0，他引：1  

Josef Ludescher  Armin Bunde  Christian L. E. Franzke  Hans Joachim Schellnhuber 《Climate Dynamics》2016,46(1-2):263-271

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Geochronology,stratigraphy and geochemistry of Cambro-Ordovician,Silurian and Devonian volcanic rocks of the Saxothuringian Zone in NE Bavaria (Germany)—new constraints for Gondwana break up and ocean–island magmatism     

Höhn  Stefan  Koglin  Nikola  Klopf  Lisa  Schüssler  Ulrich  Tragelehn  Harald  Frimmel  Hartwig E.  Zeh  Armin  Brätz  Helene 《International Journal of Earth Sciences》2018,107(1):359-377

International Journal of Earth Sciences - Stratigraphically well-defined volcanic rocks in Palaeozoic volcano-sedimentary units of the Frankenwald area (Saxothuringian Zone, Variscan Orogen) were...  相似文献   

Homogeneity and mechanical behaviors of sands improved by a temperature-controlled one-phase MICP method     

Xiao  Yang  Wang  Yang  Wang  Shun  Evans  T. Matthew  Stuedlein  Armin W.  Chu  Jian  Zhao  Chang  Wu  Huanran  Liu  Hanlong 《Acta Geotechnica》2021,16(5):1417-1427

Acta Geotechnica - Microbially induced carbonate precipitation (MICP) has been actively investigated as a promising method to improve soil properties. A burning issue impeding its wide application...  相似文献   

The entrainment of high-viscosity magma into low-viscosity magma in eruption conduits     

Armin Freundt  Stephen R. Tait 《Bulletin of Volcanology》1986,48(6):325-339

We report experiments on the flow of two fluids of contrasting viscosity through a pipe in which low-viscosity fluid occupies the center of the pipe. The volume flux of the low-viscosity fluid in the pipe increased during an experiment but did not reach 100% in most cases. The transition from high- to low-viscosity-dominated outflow involved a drop in pressure gradient and an increase in flow rate due to reduced viscous resistance in the pipe. Initially, the central flow was thin and parallel-sided, but as its diameter increased the flow became unstable. A sequence of instabilities was observed during the course of each experiment, both in time and as a function of height in the pipe. In the most commonly observed instability the central flow adopted a helical geometry. The transition from parallel-sided to unstable flow first appeared at the top of the pipe and propagated downwards against the flow. Axisymmetric instabilities originating at the pipe entrance were also observed. All forms of instability exhibited entrainment of viscous fluid into the faster moving central flow. Entrainment was extensive early in the existence of the central flow, but later on the volume flux of lower-viscosity fluid in the central flow rose more rapidly than the rate of entrainment and the proportion of lower-viscosity fluid increased with time. These compositional changes determined the viscosity of the central flow which was found to control its diameter and velocity. In banded pumice deposits, silicic pumice without mafic component is commonly erupted alongside banded pumice blocks. We infer that banded pumice may correspond to the central flow in our experiments, i. e., that viscous magma has been incorporated into less viscous melt, and that pure acid pumice is derived from the outer flow. Changes in eruption style may be caused by variations in pressure gradient and flow rate due to changes in the viscosity of the melt in the conduit. Varied mafic/silicic proportions and degree of mixing in magmatic associations are controlled by the bulk volume erupted, discharge rate, initial temperature difference and aspect ratio of the conduit.  相似文献   

Investigation of electrical anisotropy in the deep borehole KTB     

Armin Rauen  Marcela Lastovickova 《Surveys in Geophysics》1995,16(1):37-46

Information about electrical anisotropy in and around the deep borehole of the German Continental Deep Drilling Program (KTB) has been acquired using three different methods: (1) Under surface temperature and pressure conditions, the azimuthal dependence of resistivity has been measured in horizontal planes perpendicular to the axes of drill cores. (2) Simulated in-situ conditions (high temperature and pressure) have been applied to mini cores drilled at different orientations to structural features such as foliation. The resistivity was then measured in the direction of the mini cores' long axes. (3) Under quasi-in-situ (downhole) conditions, the azimuthal dependence of resistivity has been measured in horizontal planes using the Azimuthal Resistivity Imager (ARI), a down hole logging tool.These investigations have shown that electrical anisotropy is strongly related to structural features. The anisotropy of gneisses is the highest due to the strong foliation (averaged anisotropy factor 2.8). Lamprophyres are most isotropic (factor 1.2). Most rocks from KTB are amphibolites with intermediate anisotropies (factor 1.3). The anisotropies measured under surface temperature and pressure conditions and quasi-in-situ conditions on amphibolites are approximately the same, whereas anisotropies under simulated in-situ conditions are partially higher.Furthermore, the anisotropies measured on the cm to m scale using the various methods outlined above shall be compared with large scale anisotropies of the km scale measured around KTB using Magneto Tellurics.  相似文献   

Flow and deposition of pyroclastic granular flows: A type example from the 1975 Ngauruhoe eruption,New Zealand     

Gert Lube  Shane J. Cronin  Thomas Platz  Armin Freundt  Jonathan N. Procter  Cargill Henderson  Michael F. Sheridan 《Journal of Volcanology and Geothermal Research》2007

Small-volume pyroclastic density currents (PDCs) are generated frequently during explosive eruptions with little warning. Assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and/or deposits. To this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small-volume PDC deposits from the 1975 eruption of Ngauruhoe volcano, whose emplacement were also witnessed during eruption. Using high-resolution GPS surveys, a series of lateral excavations across the deposits, and bulk sedimentological analysis we constrained the geomorphology, internal structure and texture of the deposits with respect to laterally varying modes of deposition.  相似文献   

New constraints on the auriferous Witwatersrand sediment provenance from combined detrital zircon U–Pb and Lu–Hf isotope data for the Eldorado Reef (Central Rand Group,South Africa)     

Nikola Koglin  Armin Zeh  Hartwig E. Frimmel  Axel Gerdes 《Precambrian Research》2010

Combined U–Pb and Lu–Hf isotope analyses of detrital zircon grains from the auriferous Eldorado Reef conglomerate, upper Central Rand Group, reveal new insights into the provenance of the sediments and thus, by implication, possibly also into that of the gold. Most of the detrital zircon grains, which are of magmatic origin, yielded Mesoarchaean ages clustering around 2.94 and 3.06 Ga. A subordinate zircon population gave ages with maxima at 3.28 and 3.44 Ga. The Mesoarchaean zircon grains mostly show super-chondritic ?Hf_t of up to +5.2, whereas the Palaeoarchaean zircon grains have nearly chondritic composition with ?Hf_t between −1.3 and +2.0. The new dataset of the Mesoarchaean zircon populations provides the first unambiguous evidence of the formation of juvenile crust not only at 3.06 but also at 2.94 Ga. As the analysed zircon grains are from the ruditic fraction, they must be derived from a comparatively proximal source in close vicinity to the Central Rand Basin. Based on currently available data, this source was most likely a magmatic arc that existed at the northern edge of the Witwatersrand Block at 3.06 Ga. An additional source might be the 2.94 Ga magmatic rocks of the Kraaipan Greenstone Belt that occurs to the west of the Witwatersrand Block. The minor fraction of Palaeoarchaean zircon grains in the Eldorado Reef perhaps stem from sources that are isotopically similar to the Barberton Greenstone Belt and the Limpopo Belt but were more proximal to the Central Rand Basin.  相似文献