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71.
Natural Resources Research - In this study, the effect of three different wormhole configurations: single-linear, single-branched, and double-branched wormholes on the performance of cyclic solvent... 相似文献
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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
74.
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
75.
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 Pfa 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 Pfa estimate is usually dominated by parameter estimation error) 相似文献
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78.
Application of electrical resistivity tomography (ERT) technique to detect underground cavities in a karst area of South Korea 总被引:1,自引:1,他引:0
Mi Kyung Park Samgyu Park Myeong-Jong Yi Changryol Kim Jung-Sul Son Jung-Ho Kim Adepelumi Adekunle Abraham 《Environmental Earth Sciences》2014,71(6):2797-2806
Recently, the electrical resistivity tomography (ERT) technique has been increasingly applied to underground cavity detection filled with groundwater and/or clay. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in a karst area in Korea. Numerical ERT modeling and inversion were carried out to select appropriate field survey parameters. Two geological structures, similar to those that exist in the field survey area, were modeled: a sinkhole model and a vein-type structure. Electrode configurations using pole–pole, pole–dipole, dipole–pole, and dipole–dipole arrays were tested with the two geologic models and compared. The numerical modeling showed that the resistivity distribution of the ERT tomogram using the pole–dipole array produced the best representation of the two models. The pole–dipole and pole–pole array configurations were applied in an ERT field survey using six boreholes. The field ERT results show that cavity areas filled with clay or groundwater appeared as low-resistivity anomalies in the limestone formation. This was particularly evident in the inclined vein-type structures attributed to fracture zones, where the field data were similar to the modeling results. Therefore, the ERT technique could be effectively used for detecting underground limestone cavities under similar geological conditions as those at our study area. 相似文献
79.
Abraham Hoffer 《Arabian Journal of Geosciences》2012,5(3):525-528
The paper proposes—and argues in favor of an alternative model to account for the dipole geomagnetic field in which a hitherto
unrecognized piezomagnetic effect is the actual cause. This model offers a plausible explanation for the observed field reversals,
the westward drift, and the secularly decreasing field strength. It is consistent with recent satellite data, and capable
of generalization to planets other than Earth. It also accounts for the fact that the dipole axis is displaced from the geographic
axis, and that the center of the dipole is displaced from the geographic center. 相似文献
80.
Saline Lakes’ Response to Global Change 总被引:1,自引:0,他引:1
Abraham Lerman 《Aquatic Geochemistry》2009,15(1-2):1-5