Radio signature of cosmological structure formation shocks     

Matthias Hoeft  Marcus Brüggen 《Monthly notices of the Royal Astronomical Society》2007,375(1):77-91

In the course of the formation of cosmological structures, large shock waves are generated in the intracluster medium (ICM). In analogy to processes in supernova remnants, these shock waves may generate a significant population of relativistic electrons which, in turn, produce observable synchrotron emission. The extended radio relics found at the periphery of several clusters and possibly also a fraction of radio halo emission may have this origin. Here, we derive an analytic expression for (i) the total radio power in the downstream region of a cosmological shock wave, and (ii) the width of the radio-emitting region. These expressions predict a spectral slope close to −1 for strong shocks. Moderate shocks, such as those produced in mergers between clusters of galaxies, lead to a somewhat steeper spectrum. Moreover, we predict an upper limit for the radio power of cosmological shocks. Comparing our results to the radio relics in Abell 115, 2256 and 3667, we conclude that the magnetic field in these relics is typically at a level of 0.1 μG. Magnetic fields in the ICM are presumably generated by the shocks themselves; this allows us to calculate the radio emission as a function of the cluster temperature. The resulting emissions agree very well with the radio power–temperature relation found for cluster haloes. Finally, we show that cosmic accretion shocks generate less radio emission than merger shock waves. The latter may, however, be detected with upcoming radio telescopes.  相似文献   

Lognormality in the observed size distribution of oil and gas pools as a consequence of sampling bias     

M. Power 《Mathematical Geology》1992,24(8):929-945

Economic filtration has been offered as an explanation of the observed lognormality in the size distribution of discovered oil and gas deposits. The result leads to the conclusion that one cannot impute the shape of the underlying parent distribution from the observed discoveries size distribution. The fact that the largest pools tend to be discovered early in the exploration history of an area of interest suggests the existence of an inherent sampling bias in the discovery process. The bias is influenced by the levels of geologic knowledge and technological sophistication. Furthermore, the existence of the bias leads to lognormality in the observed discoveries size distribution of oil and gas pools. A discovery process model explicitly incorporating the notion of sampling bias was applied to a series of Weibull parent frequency size distributions. The selected parent distributions are of a class suggested in the literature as more reflective of nature's size distribution and have empirical support. The distribution of discoveries resulting from the application of the model to the chosen parent size distributions were tested for lognormality using a chi-squared test. Lognormality was found to be an acceptable model of the discoveries size distribution over a wide range of resource exhaustion measures. When combined with the notion of economic filtration, sampling bias leads to the conclusion that one should not expect the lognormal distribution to accurately represent the underlying parent size distribution of oil and gas deposits.  相似文献   

Biologically induced mineralization of dypingite by cyanobacteria from an alkaline wetland near Atlin,British Columbia,Canada   总被引：1，自引：0，他引：1  

Ian M Power  Siobhan A Wilson  James M Thom  Gregory M Dipple  Gordon Southam 《Geochemical transactions》2007,8(1):13

Background  

This study provides experimental evidence for biologically induced precipitation of magnesium carbonates, specifically dypingite (Mg₅(CO₃)₄(OH)₂·5H₂O), by cyanobacteria from an alkaline wetland near Atlin, British Columbia. This wetland is part of a larger hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) playa. Abiotic and biotic processes for magnesium carbonate precipitation in this environment are compared.  相似文献   

2007年7月16日日本新溻地震对柏崎刈羽核电站的影响   总被引：1，自引：0，他引：1  

潘华李金臣  吴迪忠 《国际地震动态》2007,(11):21-32

2007年7月16日日本新溻县柏崎市附近海域发生Mw6．6地震（日本气象局震级MJMA6．8）。该地震引发世界最大核电厂——柏崎刈羽核电站多起核安全事件，是世界范围内有记载的对核电站影响最为严重的一次地震。本文根据收集到的资料，详细介绍了该地震对柏崎刈羽核电站造成的影响，文章最后概述了日本、国际原子能机构对该地震的反思以及我们应该从中吸取的经验教训。  相似文献   

Micro-spectroscopic investigation of selenium-bearing minerals from the Western US Phosphate Resource Area     

Amy?L?Ryser  Daniel?G?StrawnEmail author  Matthew?A?Marcus  Jodi?L?Johnson-Maynard  Mickey?E?Gunter  Gregory?M?ller 《Geochemical transactions》2005,6(1):1

Mining activities in the US Western Phosphate Resource Area (WPRA) have released Se into the environment. Selenium has several different oxidation states and species, each having varying degrees of solubility, reactivity, and bioavailability. In this study we are investigating the speciation of Se in mine-waste rocks. Selenium speciation was determined using bulk and micro-x-ray absorption spectroscopy (XAS), as well as micro-x-ray fluorescence mapping. Rocks used for bulk-XAS were ground into fine powders. Shale used for micro-XAS was broken along depositional planes to expose unweathered surfaces. The near edge region of the XAS spectra (XANES) for the bulk rock samples revealed multiple oxidation states, with peaks indicative of Se(-II), Se(IV), and Se(+VI) species. Micro-XANES analysis of the shale indicated that three unique Se-bearing species were present. Using the XANES data together with ab initio fitting of the extended x-ray absorption fine structure region of the micro-XAS data (micro-EXAFS) the three Se-bearing species were identified as dzharkenite, a di-selenide carbon compound, and Se-substituted pyrite. Results from this research will allow for a better understanding of the biogeochemical cycling of Se in the WPRA.  相似文献   

Wakes of ram-pressure-stripped disc galaxies     

Elke Roediger  Marcus Brüggen  Matthias Hoeft 《Monthly notices of the Royal Astronomical Society》2006,371(2):609-618

We present a sample of 30 wide-angle tailed radio galaxies (WATs) that we use to constrain the jet speeds in these sources. We measure the distribution of the jet-sidedness ratios for the sample, and assuming that the jets are beamed, the jet speeds in the range (0.3–0.7) c are obtained. Whilst the core prominence of the sample, which ought to be a reliable indicator of beaming, shows little correlation with the jet sidedness, we argue that due to the peculiar nature of the WATs, core prominence is unlikely to be a good indicator of beaming in these sources. We further show that if the jets are fast and light, then the galaxy speeds required to bend the jets into C-shapes such as those seen in 0647+693 are reasonable for a galaxy in a merging or recently merged cluster.  相似文献   

Ram pressure stripping of disc galaxies: the role of the inclination angle     

Elke Roediger  Marcus Brüggen 《Monthly notices of the Royal Astronomical Society》2006,369(2):567-580

We present three-dimensional (3D) hydrodynamical simulations of ram pressure stripping of massive disc galaxies in clusters. Studies of galaxies that move face-on have predicted that in such a geometry the galaxy can lose a substantial amount of its interstellar medium. But only a small fraction of galaxies is moving face-on. In this work we focus on a systematic study of the effect of the inclination angle between the direction of motion and the galaxy's rotation axis.
In agreement with some previous works, we find that the inclination angle does not play a major role for the mass loss as long as the galaxy is not moving close to edge-on (inclination angle ≲60°). We explain this behaviour by extending Gunn & Gott's estimate of the stripping radius, which is valid for face-on geometries, to moderate inclinations.
The inclination plays a role as long as the ram pressure is comparable to pressures in the galactic plane, which can span two orders of magnitude. For very strong ram pressures, the disc will be stripped completely, and for very weak ram pressures, mass loss is negligible independent of inclination. We show that in non-edge-on geometries the stripping proceeds remarkably similar. A major difference between different inclinations is the degree of asymmetry introduced in the remaining gas disc.
We demonstrate that the tail of gas stripped from the galaxy does not necessarily point in a direction opposite to the galaxy's direction of motion. Therefore, the observation of a galaxy's gas tail may be misleading about the galaxy's direction of motion.  相似文献   

Stromatolitic fabric of authigenic carbonate crusts: result of anaerobic methane oxidation at cold seeps in 4,850 m water depth     

Jens?GreinertEmail author  Gerhard?Bohrmann  Marcus?Elvert 《International Journal of Earth Sciences》2002,91(4):698-711

Methane seepage leads to Mg-calcite and aragonite precipitation at a depth of 4,850 m on the Aleutian accretionary margin. Stromatolitic and oncoid growth structures imply encrustation of microorganisms (microbial mats) in the host sediment with a unique growth direction downward into the sediment, forming crust-shaped lithologies. Biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol, which contain extremely low '¹³C values. This indicates the presence of methane-consuming archaea, and '¹³C values of -42 to -51‰ PDB indicate that methane is the carbon source for the carbonate crusts. Thus, it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate-reducing bacteria and that carbonate precipitation proceeds downward into the sediment, where ascending cold fluids provide a methane source. Strontium and oxygen isotope analyses as well as ¹⁴C ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3,000 years ago.  相似文献   

Environmental Geology — Principles and Practice Fred G. Bell; Blackwell Science Ltd, 1998, 594 pp. ISBN 0-86542-871-1     

Marcus Pacheco 《Engineering Geology》2000,56(3-4):403

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The parabolic wave equation in local helioseismology     

Brüggen  Marcus 《Solar physics》2000,192(1-2):225-230

In recent years methods of time-distance helioseismology have been used to produce maps of local flows in the surface layers of the Sun. Usually, these studies rely on ray theory to describe the propagation of sound waves. Ray theory, however, is a poor approximation of the acoustic wavefield near the surface of the Sun. In particular, it is inappropriate for the study of scattering and diffraction by inhomogeneities. But an exact solution of the acoustic wave equation in the Sun is not trivial. In this paper I present an approximation to the full wave equation, which transforms it into a parabolic equation. The parabolic equation is commonly used in ocean acoustics and geoseismology because it is much simpler to solve numerically. Here I discuss the parabolic approximation, its limitations and potential applications in helioseismology. Finally, I present some numerical results to demonstrate the capabilities of this method.  相似文献