A miscibility gap in trioctahedral Mn-Mg-Fe chlorites: Evidence from the Lienne Valley manganese deposit,Ardennes, Belgium     

W. Schreyer  A. -M. Fransolet  K. Abraham 《Contributions to Mineralogy and Petrology》1986,94(3):333-342

Low-temperature veinlets crosscutting low-grade manganiferous ironstones of Ordovician age contain four texturally distinct types of chlorites with nearly constant Al/Si-ratios that form two separate populations regarding their Mn/Mg/Fe-ratios: One with low iron contents (<1.5 w.% FeO) and molar Mg/Mn-ratios just below unity (magnesian pennantites), the other with higher iron (7–11 w.% FeO) and Mg/Mn?4 (manganoan clinochlores). The two populations, which can be distinguished readily by their characteristic optical elongation and dispersion colors, are intimately intergrown and have formed partly during consecutive stages of a chlorite crystallization sequence, partly by simultaneous growth and possibly even as exsolution products of a pre-existing homogeneous chlorite phase of intermediate composition. These findings indicate a miscibility gap in the chlorite solid solutions beginning along the binary Mg-Mn series and extending into the ternary system. There may be a solvus relationship with the miscibility gap closing at higher temperatures (400° C?). One very intensely colored chlorite type of the pennantite population may contain Fe³⁺ or Mn³⁺ or both. Additional minerals in the veinlets are spessartine, kutnahorite, quartz, and an allanite-piemontite phase. Crystallization began near the centers of the present veins with Mn-rich minerals and continued towards their edges and into the extremely thin ends of the developing fractures with the deposition of the more Fe-rich chlorites that are in equilibrium with the ironstone.  相似文献   

Dynamics of triple black hole systems in hierarchically merging massive galaxies     

Loren Hoffman  Abraham Loeb 《Monthly notices of the Royal Astronomical Society》2007,377(3):957-976

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Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys – IV. Influence of mergers in the evolution of faint field galaxies from z∼1     

O. Le Fèvre  R. Abraham  S. J. Lilly  R. S. Ellis  J. Brinchmann  D. Schade  L. Tresse  M. Colless  D. Crampton  K. Glazebrook  F. Hammer  T. Broadhurst 《Monthly notices of the Royal Astronomical Society》2000,311(3):565-575

Hubble Space Telescope images of a sample of 285 galaxies with measured redshifts from the Canada–France Redshift Survey (CFRS) and Autofib–Low Dispersion Spectrograph Survey (LDSS) redshift surveys are analysed to derive the evolution of the merger fraction out to redshifts z ∼1. We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences δm ≤1.5 mag. We find that the pair fraction increases with redshift, with up to ∼20 per cent of the galaxies being in physical pairs at z ∼0.75–1. We derive a merger fraction varying with redshift as ∝(1+ z )^3.2±0.6, after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which m =3.4±0.6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as ∝(1+ z )^2.7±0.6. This implies that an average L * galaxy will have undergone 0.8–1.8 merger events from z =1 to z =0, with 0.5 to 1.2 merger events occuring in a 2-Gyr time-span at around z ∼0.9. This result is consistent with predictions from semi-analytical models of galaxy formation. From the simple coaddition of the observed luminosities of the galaxies in pairs, physical mergers are computed to lead to a brightening of 0.5 mag for each pair on average, and a boost in star formation rate of a factor of 2, as derived from the average [O  ii ] equivalent widths. Mergers of galaxies are therefore contributing significantly to the evolution of both the luminosity function and luminosity density of the Universe out to z ∼1.  相似文献   

A performance based approach to dolomite risk management   总被引：1，自引：0，他引：1  

David B. Buttrick  Nicole Y. G. Trollip  Ronald B. Watermeyer  Nicolaas D. Pieterse  Abraham A. Gerber 《Environmental Earth Sciences》2011,64(4):1127-1138

Urban development commonly disturbs the meta-stable conditions in the dolomite environment which can lead to sinkhole formation. 650 sinkholes, which manifested from 1984 to 2004 in an approximately 3,700 ha urbanized environment, located on dolomite land south of Pretoria in South Africa, was analyzed in the absence of risk mitigation measures. A 4 year period post the implementation of a comprehensive risk management system was also analyzed. This research permitted a timely review of the Buttrick et al. (J South African Inst Civil Eng 43(2):27–36, 2001) methodology for dolomite land hazard identification which is commonly used in stability analysis and the development of risk mitigation strategies in Southern Africa. The research confirmed this methodology and demonstrated that the approach to the mitigation of hazards through risk management can improve the hazard rating of dolomite land. The research provided much needed data and insights to refine and expand upon the current South African methodology to cover the full spectrum of developments in a manner which is capable of being included in legislative frameworks governing the development of dolomite land, both locally and internationally.  相似文献   

Using McDaniel's model to represent non-Rayleigh reverberation     

Gu  M. Abraham  D.A. 《Oceanic Engineering, IEEE Journal of》2001,26(3):348-357

Reverberation in low-frequency active sonar systems operating in shallow water has often been observed to follow non-Rayleigh statistical distributions. McDaniel's model, generalized to allow noninteger valued parameters, has shown promise as being capable of accurately representing real data with a minimal parameterization. This paper first derives an exact analytical expression for the cumulative distribution function (CDF) of the generalized McDaniel model and then compares it with numerical inversion of the characteristic function. Both methods are seen to provide adequate and equivalent precision; however the characteristic function inversion method is significantly faster. The latter CDF evaluation technique is then applied to the analysis of simulated and real data to show that, when minimal data are available, McDaniel's model can more accurately represent a wide variety of non-Rayleigh reverberation than the K or Rayleigh mixture models. This result arises from the generality of McDaniel's model with respect to the K-distribution (i.e., the K-distribution P_fa estimate can be dominated by model mismatch error) and to its compact parameterization with respect to the Rayleigh mixture (i.e., the Rayleigh mixture model P_fa estimate is usually dominated by parameter estimation error)  相似文献   

Non-Rayleigh reverberation characteristics near 400 Hz observed on the New Jersey shelf     

Preston  J.R. Abraham  D.A. 《Oceanic Engineering, IEEE Journal of》2004,29(2):215-235

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EVOLUTION OF RURAL ROADS IN THE NIGERIA COCOA BELT     

Oluwole Aloba  BSc.  M.Phil. 《Singapore journal of tropical geography》1983,4(1):1-10

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Morphological classification of the OSU Bright Spiral Galaxy Survey     

L. F. Whyte  R. G. Abraham  M. R. Merrifield  P. B. Eskridge  J. A. Frogel  R. W. Pogge 《Monthly notices of the Royal Astronomical Society》2002,336(4):1281-1286

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Imaging optically-thin hotspots near the black hole horizon of Sgr A* at radio and near-infrared wavelengths     

Avery E. Broderick  Abraham Loeb 《Monthly notices of the Royal Astronomical Society》2006,367(3):905-916

Submilliarcsecond astrometry and imaging of the black hole Sgr A* at the Galactic Centre may become possible in the near future at infrared and submillimetre wavelengths. Motivated by the observations of short-term infrared and X-ray variability of Sgr A*, in a previous paper, we computed the expected images and light curves, including polarization, associated with a compact emission region orbiting the central black hole. We extend this work, using a more realistic hotspot model and including the effects of opacity in the underlying accretion flow. We find that at infrared wavelengths, the qualitative features identified by our earlier work are present, namely it is possible to extract the black hole mass and spin from spot images and light curves of the observed flux and polarization. At radio wavelengths, disc opacity produces significant departures from the infrared behaviour, but there are still generic signatures of the black hole properties. Detailed comparison of these results with future data can be used to test general relativity and to improve existing models for the accretion flow in the immediate vicinity of the black hole.  相似文献   

The physical parameters of the evolving population of faint galaxies     

Karl Glazebrook  Roberto Abraham  Basilio Santiago  Richard Ellis  & Richard Griffiths 《Monthly notices of the Royal Astronomical Society》1998,297(3):885-904

The excess number of blue galaxies at faint magnitudes is a subject of much controversy. Recent Hubble Space Telescope results have revealed a plethora of galaxies with peculiar morphologies tentatively identified as the evolving population. We report the results of optical spectroscopy and near-infrared photometry of a sample of faint HST galaxies from the Medium Deep Survey to ascertain the physical properties of the faint morphological populations. We find four principal results. First, the population of objects classified as 'peculiar' are intrinsically luminous in the optical ( M _B  ∼ −19). Secondly these systems tend to be strong sources of [O  II ] line luminosity. Thirdly the optical–infrared colours of the faint population (a) confirm the presence of a population of compact   blue galaxies and (b) show the stellar populations of irregular/peculiar galaxies encompass a wide range in age. Finally a surface-brightness comparison with the local galaxy sample of Frei et al. shows that these objects are not of anomalously low surface brightness, rather we find that all morphological classes have evolved to a higher surface brightness at higher redshifts ( z  > 0.3).  相似文献