On the origin of the unusual orbit of Comet 2P/Encke   总被引：1，自引：0，他引：1  

Harold F. Levison  Dirk Terrell  Luke Dones 《Icarus》2006,182(1):161-168

The orbit of Comet 2P/Encke is difficult to understand because it is decoupled from Jupiter—its aphelion distance is only 4.1 AU. We present a series of orbital integrations designed to determine whether the orbit of Comet 2P/Encke can simply be the result of gravitational interactions between Jupiter-family comets and the terrestrial planets. To accomplish this, we integrated the orbits of a large number of objects from the trans-neptunian region, through the realm of the giant planets, and into the inner Solar System. We find that at any one time, our model predicts that there should be roughly 12 objects in Encke-like orbits. However, it takes roughly 200 times longer to evolve onto an orbit like this than the typical cometary physical lifetime. Thus, we suggest that (i) 2P/Encke became dormant soon after it was kicked inward by Jupiter, (ii) it spent a significant amount of time inactive while rattling around the inner Solar System, and (iii) it only became active again as the ν₆ secular resonance drove down its perihelion distance.  相似文献   

Precipitation of pyroxenes and Mg₂SiO₄ from majoritic garnet: simulation of peridotite exhumation from great depth     

Larissa F. Dobrzhinetskaya  Harry W. Green  II  Alex P. Renfro  Krassimir N. Bozhilov  Dirk Spengler  Herman L. M. van Roermund 《地学学报》2004,16(6):325-330

Our experimental simulations of the exhumation path of mantle peridotites show that high‐temperature (1400 °C) decompression of lherzolite from 14 to 13 and 12 GPa results in exsolution of interstitial blebs of diopside and Mg₂SiO₄ (wadsleyite) lamellae from majoritic garnet. At lower pressures (from 8 to 5 GPa, at T = 1400 °C) only enstatite exsolves as blebs at garnet boundaries. Continuous high‐temperature decompression from 14 to 7 GPa produces zoned majoritic garnet containing blebs of exsolved pyroxenes inside garnet rims. No intracrystalline precipitation of pyroxene was observed in garnet, although such lamellae are found in some natural garnet peridotites. The explanation appears to be the three orders of magnitude difference in grain size between experimental and natural specimens. Our data suggest that Mg₂SiO₄ and diopside exsolutions reflect the deepest point of the exhumation path of garnet peridotites, whereas enstatite precipitation may be restricted to garnets with less majoritic component at shallower depths.  相似文献   

Ancient charcoal as a natural archive for paleofire regime and vegetation change in the Mayumbe,Democratic Republic of the Congo     

Wannes Hubau  Jan Van den Bulcke  Peter Kitin  Florias Mees  Geert Baert  Dirk Verschuren  Laurent Nsenga  Joris Van Acker  Hans Beeckman 《Quaternary Research》2013

Charcoal was sampled in four soil profiles at the Mayumbe forest boundary (DRC). Five fire events were recorded and 44 charcoal types were identified. One stratified profile yielded charcoal assemblages around 530 cal yr BP and > 43.5 cal ka BP in age. The oldest assemblage precedes the period of recorded anthropogenic burning, illustrating occasional long-term absence of fire but also natural wildfire occurrences within tropical rainforest. No other charcoal assemblages older than 2500 cal yr BP were recorded, perhaps due to bioturbation and colluvial reworking. The recorded paleofires were possibly associated with short-lived climate anomalies. Progressively dry climatic conditions since ca. 4000 cal yr BP onward did not promote paleofire occurrence until increasing seasonality affected vegetation at the end of the third millennium BP, as illustrated by a fire occurring in mature rainforest that persisted until around 2050 cal yr BP. During a drought episode coinciding with the ‘Medieval Climate Anomaly’, mature rainforest was locally replaced by woodland savanna. Charcoal remains from pioneer forest indicate that fire hampered forest regeneration after climatic drought episodes. The presence of pottery shards and oil-palm endocarps associated with two relatively recent paleofires suggests that the effects of climate variability were amplified by human activities.  相似文献   

Ichnodiversity and ichnoabundance: Revealing depositional trends in a confined turbidite system   总被引：1，自引：0，他引：1  

Dirk Knaust  Michał Warchoł  Ian A. Kane 《Sedimentology》2014,61(7):2218-2267

Ichnological studies are still in their infancy when it comes to the interpretation of deep‐marine deposits. The Eocene–Oligocene turbidite system of the Grès d'Annot Formation in south‐east France is well‐studied sedimentologically, but its trace‐fossil content is poorly known. Here, an integrated ichnological–sedimentological study is presented from the Annot sub‐basin for the first time, which demonstrates its value for interpreting proximal to distal and axial to marginal trends in confined turbidite systems. A comprehensive trace‐fossil data set was collected from seven outcrops situated in the southern part of the basin. These data are presented following a morphology‐based classification scheme to allow easy recognition and characterization of ichnotaxa. Ichnodiversity and the abundance of ichnotaxa are regarded as important parameters in such interpretations. Instead of simply counting ichnotaxa per outcrop or stratigraphic unit, an equation has been developed in which the ‘ichnoabundance’ (new term) of each counted ichnotaxon is calculated. An exponential growth factor is applied to the increase of the frequency of trace fossils, and is assumed in this equation to better reflect the population dynamics of benthic organisms. A comparison of the solution for pre‐turbidite and post‐turbidite trace‐fossil suites seems to be more suitable for revealing regional and stratigraphic trends compared with conventional approaches. Despite varying size and conditions of the studied outcrops, the results achieved from the Grès d'Annot Formation can help in the reconstruction of sedimentary processes acting in this confined turbidite basin.  相似文献   

Impacts of the use of the geological subsurface for energy storage: an investigation concept     

Sebastian Bauer  Christof Beyer  Frank Dethlefsen  Peter Dietrich  Rainer Duttmann  Markus Ebert  Volker Feeser  Uwe Görke  Ralf Köber  Olaf Kolditz  Wolfgang Rabbel  Tom Schanz  Dirk Schäfer  Hilke Würdemann  Andreas Dahmke 《Environmental Earth Sciences》2013,70(8):3935-3943

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Implications of salt-related propagation and mode conversion effects on the analysis of induced seismicity     

Dirk Kraaijpoel  Bernard Dost 《Journal of Seismology》2013,17(1):95-107

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ESP: a tool to estimate scale parameter for multiresolution image segmentation of remotely sensed data     

Lucian Drǎguţ  Dirk Tiede  Shaun R. Levick 《International journal of geographical information science》2013,27(6):859-871

The spatial resolution of imaging sensors has increased dramatically in recent years, and so too have the challenges associated with extracting meaningful information from their data products. Object-based image analysis (OBIA) is gaining rapid popularity in remote sensing science as a means of bridging very high spatial resolution (VHSR) imagery and GIS. Multiscalar image segmentation is a fundamental step in OBIA, yet there is currently no tool available to objectively guide the selection of appropriate scales for segmentation. We present a technique for estimating the scale parameter in image segmentation of remotely sensed data with Definiens Developer®. The degree of heterogeneity within an image-object is controlled by a subjective measure called the ‘scale parameter’, as implemented in the mentioned software. We propose a tool, called estimation of scale parameter (ESP), that builds on the idea of local variance (LV) of object heterogeneity within a scene. The ESP tool iteratively generates image-objects at multiple scale levels in a bottom-up approach and calculates the LV for each scale. Variation in heterogeneity is explored by evaluating LV plotted against the corresponding scale. The thresholds in rates of change of LV (ROC-LV) indicate the scale levels at which the image can be segmented in the most appropriate manner, relative to the data properties at the scene level. Our tests on different types of imagery indicated fast processing times and accurate results. The simple yet robust ESP tool enables fast and objective parametrization when performing image segmentation and holds great potential for OBIA applications.  相似文献   

A methodology for dealing with regional change in integrated water resources management     

Jochen Schanze  Johanna Trümper  Cornelia Burmeister  Dirk Pavlik  Ivan Kruhlov 《Environmental Earth Sciences》2012,65(5):1405-1414

The paper presents a methodology on how to consistently deal with the future change and management options in integrated water resources management (IWRM). It is based on a conceptual framework with a five step procedure for the formulation and analysis of a so-called ‘parameterised regional futures’. Developing and testing the approach for IWRM is realised for the upper part of the Western Bug River catchment (Ukraine). Special attention is paid to scenarios of change covering climate and land use. The future regional climate is downscaled with the model CCLM. Land cover is projected after retrospective change detection and the derivation of prospective algorithms. Parameters of the interrelations between land use and the water cycle are tackled through using the concept of the model PWF-LU. The methodology is currently being tested to analyse the impacts of mid-term regional change and management options on the water cycle of the catchment.  相似文献   

Geons – domain-specific regionalization of space     

Stefan Lang  Stefan Kienberger  Dirk Tiede  Michael Hagenlocher  Lena Pernkopf 《制图学和地理信息科学》2014,41(3):214-226

The design of methods and tools to build adequate representations of complex geographical phenomena in a way that spatial patterns are emphasized is one of the core objectives of GIScience. In this paper, we build on the concept of geons as a strategy to represent and analyze latent spatial phenomena across different geographical scales (local, national, regional) incorporating domain-specific expert knowledge. Focusing on two types, we illustrate and exemplify how geons are generated and explored. So-called composite geons represent functional land-use classes, required for regional planning purposes. They are created via class modeling to translate interpretation schemes from mapping keys. Integrated geons, on the other hand, address abstract, yet policy-relevant phenomena such as societal vulnerability to hazards. They are delineated by regionalizing continuous geospatial data sets representing relevant indicators in a multidimensional variable space. Using the geon approach, we create spatially exhaustive sets of units, scalable to the level of policy intervention, homogenous in their domain-specific response, and independent from any predefined boundaries. From a GIScience perspective, we discuss either type of geons in a semantic hierarchy of geographic information constructs. Despite its validity for decision-making and its transferability across scales and application fields, the delineation of geons requires further methodological research to assess their statistical and conceptual robustness.  相似文献   

Geosimulation of urban growth and demographic decline in the Ruhr: a case study for 2025 using the artificial intelligence of cells and agents   总被引：1，自引：0，他引：1  

Andreas Rienow  Dirk Stenger 《Journal of Geographical Systems》2014,16(3):311-342

The Ruhr is an “old acquaintance” in the discourse of urban decline in old industrialized cities. The agglomeration has to struggle with archetypical problems of former monofunctional manufacturing cities. Surprisingly, the image of a shrinking city has to be refuted if you shift the focus from socioeconomic wealth to its morphological extension. Thus, it is the objective of this study to meet the challenge of modeling urban sprawl and demographic decline by combining two artificial intelligent solutions: The popular urban cellular automaton SLEUTH simulates urban growth using four simple but effective growth rules. In order to improve its performance, SLEUTH has been modified among others by combining it with a robust probability map based on support vector machines. Additionally, a complex multi-agent system is developed to simulate residential mobility in a shrinking city agglomeration: residential mobility and the housing market of shrinking city systems focuses on the dynamic of interregional housing markets implying the development of potential dwelling areas. The multi-agent system comprises the simulation of population patterns, housing prices, and housing demand in shrinking city agglomerations. Both models are calibrated and validated regarding their localization and quantification performance. Subsequently, the urban landscape configuration and composition of the Ruhr 2025 are simulated. A simple spatial join is used to combine the results serving as valuable inputs for future regional planning in the context of multifarious demographic change and preceding urban growth.  相似文献