Numerical simulation of upwelling currents in pockmarks,and data from the Inner Oslofjord,Norway   总被引：5，自引：3，他引：2  

Øyvind Hammer  Karen E. Webb  Davy Depreiter 《Geo-Marine Letters》2009,29(4):269-275

The deflection of oceanic or tidal currents into pockmarks has been studied by both general three-dimensional computational fluid dynamics simulations and acoustic measurements in a number of pockmarks in the Inner Oslofjord, Norway. The modeling demonstrates upstream convergence of flow lines, followed by upwelling over the pockmark. This upwelling is an effect of deflected regional currents, not of expulsion of fluids or gas from the seafloor, and is sufficiently strong to prevent the settling of fine particles. The field measurements, although noisy at low vertical velocities, are consistent with the hypothesis of upwelling. The reduction in sedimentation rate inferred over the pockmarks (relative to that of the flat surrounding seabed) can explain the maintenance, or even deepening of pockmarks in the absence of fluid or gas seepage. The current pattern may also have consequences for the marine biology of pockmarks.  相似文献   

Norwegian marine geodetic projects     

Jan Chr. Blankenburgh  Bj⊘rn A. Fossum  Per A. Østerholt  Hans Olav Torsen 《Marine Geodesy》2013,36(2):125-145

The hitherto promising finds of oil and gas on the Norwegian continental shelf have increased the general activity in this area considerably. Consequently, the need for better charts and more precise navigational systems have become more pertinent. During the past few years a number of marine geodetic projects have either been planned or embarked upon by various organizations within both the public and private sectors. This article gives a brief review of the Norwegian projects which have special relevance to marine geodesy; this includes the following areas: recommendations, requirements, precision navigation, satellite positioning, reference systems, boundary problems, bathymetry, geological mapping, marine geoid determination, and data base developments. The reference list will give the reader more detailed sources of information.  相似文献   

Maribo—A new CM fall from Denmark     

Henning HAACK  Thomas GRAU  Addi BISCHOFF  Marian HORSTMANN  John WASSON  Anton SØRENSEN  Matthias LAUBENSTEIN  Ulrich OTT  Herbert PALME  Marko GELLISSEN  Richard C. GREENWOOD  Victoria K. PEARSON  Ian A. FRANCHI  Zelimir GABELICA  Philippe SCHMITT‐KOPPLIN 《Meteoritics & planetary science》2012,47(1):30-50

Abstract– Maribo is a new Danish CM chondrite, which fell on January 17, 2009, at 19:08:28 CET. The fall was observed by many eye witnesses and recorded by a surveillance camera, an all sky camera, a few seismic stations, and by meteor radar observatories in Germany. A single fragment of Maribo with a dry weight of 25.8 g was found on March 4, 2009. The coarse‐grained components in Maribo include chondrules, fine‐grained olivine aggregates, large isolated lithic clasts, metals, and mineral fragments (often olivine), and rare Ca,Al‐rich inclusions. The components are typically rimmed by fine‐grained dust mantles. The matrix includes abundant dust rimmed fragments of tochilinite with a layered, fishbone‐like texture, tochilinite–cronstedtite intergrowths, sulfides, metals, and carbonates often intergrown with tochilinite. The oxygen isotopic composition: (δ¹⁷O = ?1.27‰; δ¹⁸O = 4.96‰; Δ¹⁷O = ?3.85‰) plots at the edge of the CM field, close to the CCAM line. The very low Δ¹⁷O and the presence of unaltered components suggest that Maribo is among the least altered CM chondrites. The bulk chemistry of Maribo is typical of CM chondrites. Trapped noble gases are similar in abundance and isotopic composition to other CM chondrites, stepwise heating data indicating the presence of gas components hosted by presolar diamond and silicon carbide. The organics in Maribo include components also seen in Murchison as well as nitrogen‐rich components unique to Maribo.  相似文献   

Time-resolved high-resolution spectroscopy of the pulsating sdB star QQ Vir (PG1325+101)     

J. Telting  R. Østensen  R. Oreiro  U. Heber  M. Vučković  S. Randall  A. Baran 《Astrophysics and Space Science》2010,328(1-2):163-166

In this work, a standard solar model is computed with new reaction rates that take into account the exact astrophysical S-factor, S _e for the ³He(³He,2p)⁴He, ³He(α,γ)⁷Be and ⁷Be(p,γ)⁸B reactions. The exact S-factor which is valid for all energies is an improved version of the S-factor in the lower-energy approximation (Yusof and Kassim in Astrophys. Space Sci., 2009b). The effects of these new nuclear reaction rates on the solar neutrino fluxes are then discussed by comparing this model to a solar model computed with the standard NACRE reaction rates (Angulo et al. in Nucl. Phys. A. 656:3, 1999). The new reaction rates are found to decrease the neutrinos flux for ⁷Be and ⁸B by about 6% and 16%, respectively. A solar model is also computed with the reaction rates of the LUNA collaboration for ¹⁴N(p,γ)¹⁵O (Formicola et al. in Phys. Lett. B 591:61, 2004). In this case, a clear decrease of the fluxes for ¹³N and ¹⁵O is observed to be in good agreement with previous results (see e.g. Bahcall et al. in Astrophys. J. 621:L88, 2005).  相似文献   

A Hamilton–Jacobi Framework for Modeling Folds in Structural Geology     

Øyvind Hjelle  Steen A. Petersen 《Mathematical Geosciences》2011,43(7):741-761

A novel mathematical framework for modeling folds in structural geology is presented. All the main fold classes from the classical literature: parallel folds, similar folds, and other fold types with convergent and divergent dip isogons are modeled in 3D space by linear and non-linear first-order partial differential equations. The equations are derived from a static Hamilton–Jacobi equation in the context of isotropic and anisotropic front propagation. The proposed Hamilton–Jacobi framework represents folded geological volumes in an Eulerian context as a time of arrival field relative to a reference layer. Metric properties such as distances, gradients (dip and strike), curvature, and their spatial variations can then be easily derived and represented as three-dimensional continua covering the whole geological volume. The model also serves as a basis for distributing properties in folded geological volumes.  相似文献   

Features in the primordial power spectrum: constraints from the cosmic microwave background and the limitation of the 2dF and SDSS redshift surveys to detect them     

Øystein Elgarøy  Mirt Gramann  Ofer Lahav 《Monthly notices of the Royal Astronomical Society》2002,333(1):93-99

We allow a more general (step-function) form of the primordial power spectrum than the usual featureless power-law Harrison–Zeldovich (with spectral index   n =1)  power spectrum, and fit it to the latest cosmic microwave background data sets. Although the best-fitting initial power spectrum can differ significantly from the power-law shape, and contains a dip at scales   k ∼0.003  h  Mpc^-1  , we find that  Ω_m≈0.24  , consistent with previous analyses that assume power-law initial fluctuations. We also explore the feasibility of the early releases of the 2dF and Sloan Digital Sky Survey (SDSS) galaxy redshifts surveys to see these features, and we find that even if features exist in the primordial power spectrum, they are washed out by the window functions of the redshift surveys on scales   k <0.03  h  Mpc^-1  .  相似文献   

IUE observations of star formation in a cooling flow     

L. Hansen  H.E. JØrgensen  H.U. NØrgaard-Nielsen 《Astrophysics and Space Science》1997,257(2):311-318

Star formation in cooling flows is usually found to have an initial mass function deficient in massive stars, but the center of the cooling flow in Hydra A has been shown to contain a significant number of early type stars. Here we use UV-spectra obtained with the IUE satellite together with ground based data to constrain the nature of this young population. The data is compatible with a burst of star formation with a Salpeter-like initial mass function, a burst age of about 4 107 yr, and a total mass ≈ 108 M⊙. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A Numerical Framework for Modeling Folds in Structural Geology   总被引：1，自引：1，他引：0  

Øyvind Hjelle  Steen A. Petersen  Are Magnus Bruaset 《Mathematical Geosciences》2013,45(3):255-276

A numerical framework for modeling folds in structural geology is presented. This framework is based on a novel and recently published Hamilton–Jacobi formulation by which a continuum of layer boundaries of a fold is modeled as a propagating front. All the fold classes from the classical literature (parallel folds, similar folds, and other fold types with convergent and divergent dip isogons) are modeled in two and three dimensions as continua defined on a finite difference grid. The propagating front describing the fold geometry is governed by a static Hamilton–Jacobi equation, which is discretized by upwind finite differences and a dynamic stencil construction. This forms the basis of numerical solution by finite difference solvers such as fast marching and fast sweeping methods. A new robust and accurate scheme for initialization of finite difference solvers for the static Hamilton–Jacobi equation is also derived. The framework has been integrated in simulation software, and a numerical example is presented based on seismic data collected from the Karama Block in the North Makassar Strait outside Sulawesi.  相似文献   

A New Video and Digital Camera System for Studies of the Dynamics of Microtopographic Features on Tidal Flats     

LARS CHRESTEN LUND-HANSEN  EINER LARSEN  KURT THOMAS JENSEN  KIM N. MOURITSEN  CHRISTIAN CHRISTIANSEN  THORBJØRN JOEST ANDERSEN 《Marine Georesources & Geotechnology》2013,31(1-2):115-122

A newly developed video and camera system for tidal flat microtopographic studies is presented. It consists of a SONY handy cam placed in an underwater housing mounted on a frame about 70?cm above the sediment surface. A rectangular surface area of 30?×40?cm is imaged by the camera. The camera records video sequences and/or digital images at predetermined time lapses. The total number of images is about 540, and a similar number of 10-second long video sequences can be recorded. The camera is programmed with a PC before deployment, and the total deployment time depends on the time lapse between recordings. The camera is connected to an external power supply (12?volt), and a halogen projector pointing towards the sediment surface ensures that the system is operable on a 24-hours scale. The system has been tested in the Danish Wadden Sea. It has proved to be a very useful tool in studies of topographic effects of erosion and deposition sequences, and for studies of benthic organisms-sediment interactions. The test site was further equipped with sensors for water and seabed measurements, which proved to be indispensable regarding the interpretation of recorded image time-series.  相似文献   

Geological modeling and simulation of CO2 injection in the Johansen formation     

Geir Terje Eigestad  Helge K. Dahle  Bjarte Hellevang  Fridtjof Riis  Wenche Tjelta Johansen  Erlend Øian 《Computational Geosciences》2009,13(4):435-450

The Johansen formation is a candidate site for large-scale CO₂ storage offshore of the south-western coast of Norway. An overview of the geology for the Johansen formation and neighboring geological formations is given, together with a discussion of issues for geological and geophysical modelling and integrated fluid flow modelling. We further describe corresponding simulation models. Major issues to consider are capacity estimation and processes that could potentially cause CO₂ to leak out of the Johansen formation and into the formations above. Currently, these issues can only be investigated through numerical simulation. We consider the effect of different boundary conditions, sensitivity with respect to vertical grid refinement and permeability/transmisibility data, and the effect of residual gas saturations, since these strongly affect the CO₂-plume distribution. The geological study of the Johansen formation is performed based on available seismic and well data. Fluid simulations are performed using a commercial simulator capable of modelling CO₂ flow and transport by simple manipulation of input files and data. We provide details for the data and the model, with a particular focus on geology and geometry for the Johansen formation. The data set is made available for download online.  相似文献