Degree of rock surface weathering as an indicator of ice-sheet thickness along an east—west transect across southern Norway     

Atle Nesje  Danny McCarroll  Svein Olaf Dahl 《第四纪科学杂志》1994,9(4):337-347

Rock surface weathering, as reflected by rock surface hardness and roughness, was measured at six mountains along an east-west transect across southern Norway. At most sites the results show significant differences in rock surface weathering across the autochthonous blockfield boundary, suggesting that the areas above the boundary have been exposed to subaerial weathering for a considerably longer time span that the areas below. The results are interpreted as reflecting the surface profile of an asymmetric, west-centred, low-gradient ice sheet.  相似文献   

Acoustic tomography for monitoring the Sea of Japan: a pilot experiment     

Spindel  R.C. Jungyul Na Dahl  P.H. Suntaek Oh Eggen  C. Young Gyu Kim Akulichev  V.A. Morgunov  Y.N. 《Oceanic Engineering, IEEE Journal of》2003,28(2):297-302

A pilot experiment was conducted in the Sea of Japan (also called the East Sea) in September-October 1999, to assess the possibility of using acoustic tomographic techniques for monitoring water mass structure and dynamics. Acoustic m-sequence signals at various frequencies between 250 and 634 Hz were transmitted from bottom-mounted acoustic sources in shallow water off the coast of Vladivostok to vertical-array receiving systems deployed off the north coast of Ulleung-Do island (S. Korea), 558 km to the south. The data are analyzed for temporal correlation, time spread, and transmission loss and are interpreted in terms of a tomographic system for monitoring the East Sea.  相似文献   

Degeneracies and scaling relations in general power-law models for gravitational lenses     

Olaf Wucknitz 《Monthly notices of the Royal Astronomical Society》2002,332(4):951-961

The time-delay in gravitational lenses can be used to derive the Hubble constant in a relatively simple way. The results of this method are less dependent on astrophysical assumptions than in many other methods. For systems with accurately measured positions and time-delays, the most important uncertainty is related to the mass model used. Simple parametric models like isothermal ellipsoidal mass distributions seem to provide consistent results with a reasonably small scatter when applied to several lens systems. We discuss a family of models with a separable radial power law and an arbitrary angular dependence for the potential   ψ = r ^β F ( θ )  . Isothermal potentials are a special case of these models with   β =1  . An additional external shear is used to take into account perturbations from other galaxies. Using a simple linear formalism for quadruple lenses, we can derive H ₀ as a function of the observables and the shear. If the latter is fixed, the result depends on the assumed power-law exponent according to   H ₀∝(2- β )/ β   . The effect of external shear is quantified by introducing a 'critical shear' γ _c as a measure for the amount of shear that changes the result significantly. The analysis shows that in the general case H ₀ and γ _c do not depend on the position of the lens galaxy. Spherical lens models with images close to the Einstein radius with fitted external shear differ by a factor of   β /2  from shearless models, leading to   H ₀∝2- β   in this case. We discuss these results and compare them with numerical models for a number of real lens systems.  相似文献   

Cirque glacier activity in arctic Norway during the last deglaciation     

yvind Paasche  Svein Olaf Dahl  Jostein Bakke  Reidar Lvlie  Atle Nesje 《Quaternary Research》2007,68(3):387-399

Numerous cirques of the Lofoten–Vesterålen archipelago in northern Norway have distinct moraine sequences that previously have been assigned to the Allerød-Younger Dryas ( 13,400 to 11,700 yr BP) interval, constraining the regional distribution of the equilibrium-line altitude (ELA) of cirque and valley glaciers. Here we present evidence from a once glacier-fed lake on southern Andøya that contests this view. Analyses of radiocarbon dated lacustrine sediments including rock magnetic parameters, grain size, organic matter, dry bulk density and visual interpretation suggest that no glacier was present in the low-lying cirque during the Younger Dryas-Allerød. The initiation of the glacial retreat commenced with the onset of the Bølling warming ( 14,700 yr BP) and was completed by the onset of Allerød Interstade ( 13,400 yr BP). The reconstructed glacier stages of the investigated cirque coincide with a cool and dry period from  17,500 to 14,700 yr BP and a somewhat larger Last Glacial Maximum (LGM) advance possibly occurring between  21,050 and 19,100 yr BP.  相似文献   

Rendering technique of multi-layered domain boundaries and its application to fluid flow in porous media visualizations     

Dmitri Naumov  Lars Bilke  Olaf Kolditz 《Environmental Earth Sciences》2014,72(10):3795-3802

Current visualization techniques for computational fluid dynamics applications are sophisticated and work well in simple geometries. For complex geometries such as pore spaces, multiple domain boundaries obstruct the view and make the studying of fluid flow fields difficult. To overcome these deficiencies, we use two-sided materials to render the domain boundaries. Using this technique, it is possible to place the camera inside the domain and have a non-obstructed view of the surrounding flow field without losing spatial reference to the domain boundaries. As a result, a larger part of fluid flow visualization is visible. Two-sided material rendering was successfully applied to display still images with Blender Cycles renderer, in a virtual reality environment, and several implementation techniques were explored for using the Visualization Toolkit.  相似文献   

TESSIN VISLab—laboratory for scientific visualization     

Lars Bilke  Thomas Fischer  Carolin Helbig  Charlotte Krawczyk  Thomas Nagel  Dmitri Naumov  Sebastian Paulick  Karsten Rink  Agnes Sachse  Sophie Schelenz  Marc Walther  Norihiro Watanabe  Björn Zehner  Jennifer Ziesch  Olaf Kolditz 《Environmental Earth Sciences》2014,72(10):3881-3899

Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined.  相似文献   

Assessing the saltwater remediation potential of a three-dimensional,heterogeneous, coastal aquifer system     

Marc Walther  Lars Bilke  Jens-Olaf Delfs  Thomas Graf  Jens Grundmann  Olaf Kolditz  Rudolf Liedl 《Environmental Earth Sciences》2014,72(10):3827-3837

This paper evaluates the remediation potential of a salinized coastal aquifer by utilizing a scenario simulation. Therefore, the numerical model OpenGeoSys is first validated against analytical and experimental data to represent transient groundwater level development and variable density saline intrusion. Afterwards, a regional scale model with a three-dimensional, heterogeneous hydrogeology is calibrated for a transient state and used to simulate a best-case scenario. Water balances are evaluated in both the transient calibration and scenario run. Visualization techniques help to assess the complex model output providing valuable insight in the occurring density-driven flow processes. Furthermore, modeling and visualization results give information on the time scale for remediation activities and, due to limitations in data quality and quantity reveal potential for model improvement.  相似文献   

Visualisation strategies for environmental modelling data     

Karsten Rink  Lars Bilke  Olaf Kolditz 《Environmental Earth Sciences》2014,72(10):3857-3868

We present a framework that allows users to apply a number of strategies to view and modify a wide range of environmental data sets for the modelling of natural phenomena. These data sets can be concurrently visualised to find inconsistencies or artefacts. This ensures at an early stage that models set up for the simulation of hydrological or thermal processes will not give implausible results due to complications based on input data. A number of generally applicable visualisation techniques are provided by our framework to help researchers detect potential problems. We also propose a number of mapping algorithms for the integration of multiple data sets to resolve some of the most common issues. Techniques for the presentation of input- and modelling data in combination with simulation results are proposed with respect to the benefits of visualisation of environmental data within specialised environments. The complete workflow from input data to presentation is demonstrated based on a case study in Central Germany. We identify typical problems, propose approaches for a suitable data integration for this case study and compare results of the original and modified data sets.  相似文献   

ISRM Suggested Method for Determining the Abrasivity of Rock by the CERCHAR Abrasivity Test     

Michael Alber  Olgay Yaralı  Filip Dahl  Amund Bruland  Heiko Käsling  Theodore N. Michalakopoulos  Marilena Cardu  Paul Hagan  Hamit Aydın  Ahmet Özarslan 《Rock Mechanics and Rock Engineering》2014,47(1):261-266

  相似文献   

Study of Dominant Factors Affecting Cerchar Abrasivity Index   总被引：2，自引：1，他引：1  

Jamal Rostami  Amireza Ghasemi  Ehsan Alavi Gharahbagh  Cihan Dogruoz  Filip Dahl 《Rock Mechanics and Rock Engineering》2014,47(5):1905-1919

The Cerchar abrasion index is commonly used to represent rock abrasion for estimation of bit life and wear in various mining and tunneling applications. Although the test is simple and fast, there are some discrepancies in the test results related to the equipment used, condition of the rock surface, operator skills, and procedures used in conducting and measuring the wear surface. This paper focuses on the background of the test and examines the influence of various parameters on Cerchar testing including pin hardness, surface condition of specimens, petrographical and geomechanical properties, test speed, applied load, and method of measuring wear surface. Results of Cerchar tests on a set of rock specimens performed at different laboratories are presented to examine repeatability of the tests. In addition, the preliminary results of testing with a new device as a potential alternative testing system for rock abrasivity measurement are discussed.  相似文献