Active Galactic Nuclei     

Martin Haas  Peter Biermann  Rolf Chini  Jochen Heidt  Wolfram Kollatschny  Helmut Meusinger  Ralf Siebenmorgen 《Astronomische Nachrichten》2007,328(7):665-680

F11 Jets, supernovae, gammabursts – more light for theory? F35 A Direct Comparison of the QSO Samples from VPMS and SDSS F36 Gravitational Microlensing Simulations and Ensemble Broad‐Band Variability of the QSOs from VPMS F42 Luminosity function of low redshift quasars F43 Star Formation around Active Galactic Nuclei – Results from near infrared observations F58 High‐Redshift Quasars as Probes of Early Star Formation F66 On the dust emission of Seyfert nuclei F72 Propagation of Very Light MHD Jets F78 Giant Outflows in MassiveHigh‐z Radio Galaxies: Direct Evidence for AGNFeedback in the Early Universe F89 Lowfrequency mapping of ‘normal’ FR II radio galaxies: Resolving the puzzle of X‐shaped radio sources F90 Nature of X‐shaped radio sources: A statistical approach F100 Cosmological growth of Supermassive Black Holes: constraints on kinetic and radiative energy feedback F107 Molecular Tori in AGN F136 Electron‐Ion Recombination Rate Coefficients of Iron M‐Shell Ions for X‐Ray Astronomy F139 Hydrodynamic models of obscuring tori F145 The unique BL Lac Object S5 0716+714 F158 On the Cluster Environment of the BL Lac Object OJ 287 F179 The circumnuclear dust in nearby AGN resolved by mid‐infrared interferometry F184 NIR‐imaging of SDSS BL Lac objects F190 Blazar Observations in the TeV energy range with the MAGIC Telescope F198 Gas Inflow Rates in Nearby AGN Galaxies F202 Two zone SSC model for blazar jets F215 Long‐termVHE γ ‐ray monitoring of bright blazars with a dedicated telescope F218 Long termmonitoring of bright TeV Blazars with the MAGIC telescope F220 Fifteen Blazars in Very‐High Energy Gamma Rays: A Comparative Study F229 Numerical calculation of blazar spectra. Application to 1 ES 1218+30.4 F230 Blazar spectral energy distributions corrected for gamma ray attenuation F240 Observation of PG 1553+113 with the MAGIC Telescope F243 VHE Gamma‐Ray Flare of PKS2155‐304 detected by the MAGIC telescope F245 Observations of 3C279 with the MAGIC Telescope F258 Diffraction limited near infrared imaging spectroscopy of the NLR of NGC4151  相似文献   

Methane exchange between coal-bearing basins and the atmosphere: the Ruhr Basin and the Lower Rhine Embayment, Germany   总被引：1，自引：0，他引：1  

Thomas Thielemann  Andreas Lücke  Gerhard H. Schleser  Ralf Littke   《Organic Geochemistry》2000,31(12):121

A precise knowledge of methane exchange processes is required to fully understand the recent rise of atmospheric methane concentration. Three of these processes take place at the lithosphere/atmosphere boundary: bacterial consumption of methane and emission of bacterial or thermogenic methane. This study was initiated to quantify these processes on a regional scale in the Ruhr Basin and the Lower Rhine Embayment. Since these areas are subject to bituminous coal and lignite mining, natural and anthropogenically-induced methane exchange processes could be studied. The methane emission and consumption rates and their carbon isotope signal were measured at the lithosphere/atmosphere boundary using flux chambers. On most of the soils studied, methane consumption by bacteria was identified. Thermogenic methane was released only at some of the natural faults examined. In active and abandoned bituminous coal mining areas methane emissions were restricted to small areas, where high emission rates were measured. The carbon isotope composition of methane at natural faults and in mining subsidence troughs was typical of thermogenic methane (−45 to −32 ‰ δ¹³C). Methane exchange balancing revealed that natural methane emissions from these two basins represent no source of atmospheric importance. However, methane release by upcast mining shafts dominates the methane exchange processes and is by about two orders of magnitude greater than methane consumption by bacterial oxidation in the soils.  相似文献   

Node-centered finite volume discretizations for the numerical simulation of multiphase flow in heterogeneous porous media     

Ralf Huber  Rainer Helmig 《Computational Geosciences》2000,4(2):141-164

Three node-centered finite volume discretizations for multiphase porous media flow are presented and compared. By combination of these methods two additional discretization methods are generated. The ability of these schemes to describe flows at textural interfaces of different geologic formations is investigated. It was found that models with nonzero-entry pressures for the capillary pressure-saturation relationship in conjunction with the Box discretization may give rise to spurious oscillations for flows around low permeable lenses. Furthermore, the applicability and sensitivity of the discretization methods with regard to the used computational grids is discussed. The schemes are used for the numerical study of two-phase flow in porous media with zones of different material properties. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A dynamical model of the inner Galaxy     

Ralf Häfner  N. Wyn Evans  Walter Dehnen  James Binney 《Monthly notices of the Royal Astronomical Society》2000,314(3):433-452

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Robust dual‐sensor data sea‐surface ghost attenuation for quality control purposes          下载免费PDF全文

Philippe Caprioli  Ralf Ferber 《Geophysical Prospecting》2018,66(5):954-963

Three‐dimensional receiver ghost attenuation (deghosting) of dual‐sensor towed‐streamer data is straightforward, in principle. In its simplest form, it requires applying a three‐dimensional frequency–wavenumber filter to the vertical component of the particle motion data to correct for the amplitude reduction on the vertical component of non‐normal incidence plane waves before combining with the pressure data. More elaborate techniques use three‐dimensional filters to both components before summation, for example, for ghost wavelet dephasing and mitigation of noise of different strengths on the individual components in optimum deghosting. The problem with all these techniques is, of course, that it is usually impossible to transform the data into the crossline wavenumber domain because of aliasing. Hence, usually, a two‐dimensional version of deghosting is applied to the data in the frequency–inline wavenumber domain. We investigate going down the “dimensionality ladder” one more step to a one‐dimensional weighted summation of the records of the collocated sensors to create an approximate deghosting procedure. We specifically consider amplitude‐balancing weights computed via a standard automatic gain control before summation, reminiscent of a diversity stack of the dual‐sensor recordings. This technique is independent of the actual streamer depth and insensitive to variations in the sea‐surface reflection coefficient. The automatic gain control weights serve two purposes: (i) to approximately correct for the geometric amplitude loss of the Z data and (ii) to mitigate noise strength variations on the two components. Here, Z denotes the vertical component of the velocity of particle motion scaled by the seismic impedance of the near‐sensor water volume. The weights are time‐varying and can also be made frequency‐band dependent, adapting better to frequency variations of the noise. The investigated process is a very robust, almost fully hands‐off, approximate three‐dimensional deghosting step for dual‐sensor data, requiring no spatial filtering and no explicit estimates of noise power. We argue that this technique performs well in terms of ghost attenuation (albeit, not exact ghost removal) and balancing the signal‐to‐noise ratio in the output data. For instances where full three‐dimensional receiver deghosting is the final product, the proposed technique is appropriate for efficient quality control of the data acquired and in aiding the parameterisation of the subsequent deghosting processing.  相似文献   

A data model for moving regions of fixed shape in databases     

Florian Heinz  Ralf Hartmut Güting 《International journal of geographical information science》2018,32(9):1737-1769

Moving object databases are designed to store and process spatial and temporal object data. An especially useful moving object type is a moving region, which consists of one or more moving polygons suitable for modeling the spread of forest fires, the movement of clouds, spread of diseases and many other real-world phenomena. Previous implementations usually allow a changing shape of the region during the movement; however, the necessary restrictions on this model result in an inaccurate interpolation of rotating objects. In this paper, we present an alternative approach for moving and rotating regions of fixed shape, called Fixed Moving Regions, which provide a significantly better model for a wide range of applications like modeling the movement of oil tankers, icebergs and other rigid structures. Furthermore, we describe and implement several useful operations on this new object type to enable a database system to solve many real-world problems, as for example collision tests, projections and intersections, much more accurate than with other models. Based on this research, we also implemented a library for easy integration into moving objects database systems, as for example the DBMS Secondo (1) (2) developed at the FernUniversität in Hagen.  相似文献   

Comparison of different fluorometers (PAM, 1- Hz, BackScat and Turner) measuring either chlorophyll concentration or photosynthetic activity     

Klaus Heinrich Vanselow  Ralf Hintze  Peter Hartig  Franciscus Colijn 《Ocean Dynamics》1997,49(2-3):375-384

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Temperature-dependent dissolution of residual non-aqueous phase liquids: model development and verification     

Steffi Popp  Christof Beyer  Andreas Dahmke  Nicolas Koproch  Ralf Köber  Sebastian Bauer 《Environmental Earth Sciences》2016,75(11):953

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Erratum to: 3D thermal history and maturity modelling of the Levant Basin and its eastern margin,offshore–onshore Lebanon     

Samer Bou Daher  Mathieu Ducros  Pauline Michel  Nicolas Hawie  Fadi H. Nader  Ralf Littke 《Arabian Journal of Geosciences》2016,9(9):550

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Optimal experimental design for reservoir property estimates in geothermal exploration     

Ralf Seidler  Kateryna Padalkina  H. Martin Bücker  Anozie Ebigbo  Michael Herty  Gabriele Marquart  Jan Niederau 《Computational Geosciences》2016,20(2):375-383

During geothermal reservoir development, drilling deep boreholes turns out to be extremely expensive and risky. Thus, it is of great importance to work out the details of suitable borehole locations in advance. Here, given a set of existing boreholes, we demonstrate how a sophisticated numerical technique called optimal experimental design helps to find a location of an additional exploratory borehole that reduces risk and, ultimately, saves cost. More precisely, the approach minimizes the uncertainty when deducing the effective permeability of a buried reservoir layer from a temperature profile measured in this exploratory borehole. In this paper, we (1) outline the mathematical formulation in terms of an optimization problem, (2) describe the numerical implementation involving various software components, and (3) apply the method to a 3D numerical simulation model representing a real geothermal reservoir in northern Italy. Our results show that optimal experimental design is conceptually and computationally feasible for industrial-scale applications. For the particular reservoir and the estimation of permeability from temperature, the optimal location of the additional borehole coincides with regions of high flow rates and large deviations from the mean temperature of the reservoir layer in question. Finally, the presentation shows that, methodologically, the optimization method can be generalized from estimating permeability to finding any other reservoir properties.  相似文献