18 research outputs found
Simulations of Nonthermal Electron Transport in Multidimensional Flows: Application to Radio Galaxies
We have developed an economical, effective numerical scheme for cosmic-ray
transport suitable for treatment of electrons up to a few hundreds of GeV in
multidimensional simulations of radio galaxies. The method follows the electron
population in sufficient detail to allow computation of synthetic radio and
X-ray observations of the simulated sources, including spectral properties (see
the companion paper by Tregillis et al. 1999). The cosmic-ray particle
simulations can follow the effects of shock acceleration, second-order Fermi
acceleration as well as radiative and adiabatic energy losses. We have applied
this scheme to 2-D and 3-D MHD simulations of jet-driven flows and have begun
to explore links between dynamics and the properties of high energy electron
populations in radio lobes. The key initial discovery is the great importance
to the high energy particle population of the very unsteady and inhomogeneous
flows, especially near the end of the jet. Because of this, in particular, our
simulations show that a large fraction of the particle population flowing from
the jet into the cocoon never passes through strong shocks. The shock strengths
encountered are not simply predicted by 1-D models, and are quite varied.
Consequently, the emergent electron spectra are highly heterogeneous. Rates of
synchrotron aging in "hot-spots" seem similarly to be very uneven, enhancing
complexity in the spectral properties of electrons as they emerge into the
lobes and making more difficult the task of comparing dynamical and radiative
ages.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J.
Biretta et al., New Astronomy Review
Stylolites, porosity, depositional texture, and silicates in chalk facies sediments:Ontong Java Plateau - Gorm and Tyra fields, North Sea
Chemical and Mechanical processes during burial diagenesis of chalk:An interpretation based on specific surface data of deep-sea sediments
Abundance of color bands in Neogene carbonate sediments on Ontong Java Plateau: a proxy for sedimentation rate?
Early diagenetic evolution of the Chalk in eastern Denmark
This is the final version of the article. Available from Wiley Open Access via the DOI in this record.The genesis of polygonal faults is an intriguing diagenetic phenomenon. This study discusses their origin in carbonate mudstones together with other associated diagenetic features. In the eastern Danish Basin, at the fringe of the Baltic Sea, the Stevns peninsula offers a unique opportunity to study the early diagenesis of Upper Cretaceous Chalk deposits, buried between 500 m and 1400 m. This paper combines data from onshore and offshore high-resolution seismic reflection profiles, a fully cored borehole with high-resolution wireline logs and quarry and coastal cliff outcrops to study early diagenetic features at different scales. Chalk is affected by an extensive polygonal fault system that is detected in onshore and offshore seismic data. Outcrop and core data provide a better understanding of the distribution of contraction-related features like deformation bands (hairline fractures), stylolites and fluid escape structures. An original model of genetic relationships between these different diagenetic processes is documented for Chalk. The spatial relationships between stylolites and fractures suggest that pressure-solution processes triggered shear failure that initiated the polygonal fault systems. The early diagenetic processes affect the reservoir properties of Chalk by creating compartments and vertical connections. Taking these features into account will allow for a more detailed understanding of early diagenesis and better models for exploiting drinking water or hydrocarbons hosted in Chalk.We acknowledge Kresten Anderskouv for his pre-review work. Finn Surlyk is thanked for the stimulating discussions on Chalk depositional system and its evolution in Denmark. We would like to thank Lars Ole Boldreel for giving access to the original seismic data repository. Lise Boulicault is also thanked for her help during field acquisition. We are grateful to Maersk Oil for having sponsored this research in the C-cubed project framework. We thank J. Cartwright, C. Jackson, L. Lonergan and A. Gay for their revision of a former version of the manuscript. We also would like to thank J. D'Arcy for the English-language proofing of the manuscript