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11.
R.T. Cannon W.M.N. Simiyu Siambi F.M. Karanja 《Earth and Planetary Science Letters》1981,52(2):419-426
A revised Paleozoic/Mesozoic stratigraphy of coastal Kenya (including, in particular, the Karroo) based on current geological mapping near Mombasa is briefly described. This stratigraphy provides the geological framework for proposals concerning the Proto-Indian Ocean and the tectonic setting of the Karroo depositional basins.Recent geophysical evidence suggests that, within Gondwanaland, Madagascar was situated off East Africa near Kenya/Tanzania. The southern limits of the marine Lower Jurassic and southern limits of the marine Middle and Upper Jurassic are in similar positions in mainland Africa and Madagascar using the latter reconstruction. These paleogeographic limits also define the position, during the Jurassic, of an embayment from an ocean to the north. Regional geological similarities also support this reconstruction and are reinforced by paleocurrent data from the Karroo of Kenya indicating drainage north-northeast during the Permian and Triassic and possibly the Lower Jurassic. Marine connections during Karroo times appear to be of different ages in Kenya, Tanzania, Somalia, and Madagascar, probably reflecting physical limitations to marine access in fault-separated basins.The above embayment encroached across the Karroo depositional basins from northeast Kenya to southern Tanzania during the Lower and Middle Jurassic, i.e. from the direction towards which the Karroo drainage had been previously directed. Marine conditions remain to the present day so this embayment can be considered the Proto-Indian Ocean for East Africa. The marine incursion took place before the breakup of Gondwanaland suggesting that during the Jurassic the Proto-Indian Ocean in East Africa was an epicontinental sea and not a true ocean (i.e. floored by simatic crust). The epicontinental nature of this sea is confirmed by the lithologies of the associated sediments. Paleontological data indicate that this sea was an arm of Tethys. True oceanic conditions could not have been established until the displacement of Madagascar away from Africa, probably in the Cretaceous.Accepting the above northern position of Madagascar, the writers also postulate that in East Africa the fault-bounded Karroo depositional basins (troughs) were located within a major triradial rift system extending from Lake Malawi at least as far as eastern Kenya (some 1600 km). This rift system, if valid, was established within Gondwanaland over a period ~100 m.y. in the Paleozoic/Mesozoic (pre-breakup) in marked contrast to the East African Rift System (classical rift valleys) which is mainly a Cainozoic phenomenon (post-breakup). It is, therefore, considered that there is a fundamental difference in origin between the two rift systems. 相似文献
12.
Elaine M. Sadler Russell D. Cannon Tom Mauch Paul J. Hancock David A. Wake Nic Ross Scott M. Croom Michael J. Drinkwater Alastair C. Edge Daniel Eisenstein rew M. Hopkins Helen M. Johnston Robert Nichol Kevin A. Pimbblet Roberto De Propris Isaac G. Roseboom Donald P. Schneider Tom Shanks 《Monthly notices of the Royal Astronomical Society》2007,381(1):211-227
13.
Russell Cannon Michael Drinkwater Alastair Edge Daniel Eisenstein Robert Nichol Phillip Outram Kevin Pimbblet Roberto De Propris Isaac Roseboom David Wake Paul Allen Joss Bland-Hawthorn Terry Bridges Daniel Carson Kuenley Chiu Matthew Colless Warrick Couch Scott Croom Simon Driver Stephen Fine Paul Hewett Jon Loveday Nicholas Ross Elaine M. Sadler Tom Shanks Robert Sharp J. Allyn Smith Chris Stoughton Peter Weilbacher Robert J. Brunner Avery Meiksin Donald P. Schneider 《Monthly notices of the Royal Astronomical Society》2006,372(1):425-442
14.
Given the coarse resolution of global climate models, downscaling techniques are often needed to generate finer scale projections of variables affected by local-scale processes such as precipitation. However, classical statistical downscaling experiments for future climate rely on the time-invariance assumption as one cannot know the true change in the variable of interest, nor validate the models with data not yet observed. Our experimental setup involves using the Canadian regional climate model (CRCM) outputs as pseudo-observations to estimate model performance in the context of future climate projections by replacing historical and future observations with model simulations from the CRCM, nested within the domain of the Canadian global climate model (CGCM). In particular, we evaluated statistically downscaled daily precipitation time series in terms of the Peirce skill score, mean absolute errors, and climate indices. Specifically, we used a variety of linear and nonlinear methods such as artificial neural networks (ANN), decision trees and ensembles, multiple linear regression, and k-nearest neighbors to generate present and future daily precipitation occurrences and amounts. We obtained the predictors from the CGCM 3.1 20C3M (1971–2000) and A2 (2041–2070) simulations, and precipitation outputs from the CRCM 4.2 (forced with the CGCM 3.1 boundary conditions) as predictands. Overall, ANN models and tree ensembles outscored the linear models and simple nonlinear models in terms of precipitation occurrences, without performance deteriorating in future climate. In contrast, for the precipitation amounts and related climate indices, the performance of downscaling models deteriorated in future climate. 相似文献
15.
Manuela Magliocchetti Steve J. Maddox Ed Hawkins John A. Peacock Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto de Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole A. Jackson Bryn Jones Ofer Lahav Ian Lewis Stuart Lumsden Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,350(4):1485-1494
16.
The 2dF Galaxy Redshift Survey: the bJ -band galaxy luminosity function and survey selection function
Peder Norberg Shaun Cole Carlton M. Baugh Carlos S. Frenk Ivan Baldry Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Nicholas J. G. Cross Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,336(3):907-931
17.
Peder Norberg Carlton M. Baugh Ed Hawkins Steve Maddox John A. Peacock Shaun Cole Carlos S. Frenk Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Darren Madgwick Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,328(1):64-70
We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range . The clustering of galaxies in real space is well-fitted by a correlation length and power-law slope . The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M *, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al. 相似文献
18.
Russell Cannon 《Journal of Astrophysics and Astronomy》1996,17(1-2):1-6
Recent technological advances have led to a dramatic improvement in the quality of photometric and spectroscopic data obtainable
on stars in globular clusters. Evidence from CCD-based colour magnitude diagrams points to clear differences in age between
some clusters. High dispersion spectra show that abundance variations cannot explain the observed differences. In particular,
it seems that NGC 288 must be 2–3 Gyr older than NGC 362. The same spectra show that although there is a spread in some molecular
band strengths in NGC 362, the total C+N+O abundance remains constant, indicating that the material has undergone varying
amounts of nuclear processing. No variations are seen in the abundances of iron group elements. Lower dispersion spectra for
a large sample of faint stars in 47 Tucanae, obtained with a multi-object optical fibre system, show that unevolved main sequence
stars in that cluster share the same CNO variations as the bright giants. The conclusion from all these data is that the intra-cluster
CNO variations are neither truly primordial nor due to evolutionary mixing. It may be that there was a sufficiently extended
period of star formation for material from first generation stars to be used in later generations, or that some pollution
has occurred due to mass loss. Finally, it is noted that if ‘prehistoric’ clusters exist with ages of around 50 Gyr, as hypothesised
in some cosmological models, these should probably still be rather obvious and readily recognised.
Paper presented at the 6th Asian-Pacific Regional Meeting on Astronomy of the International Astronomical Union, India, 1993. 相似文献
19.
Ian Lewis Michael Balogh Roberto De Propris Warrick Couch Richard Bower Alison Offer Joss Bland-Hawthorn Ivan K. Baldry Carlton Baugh Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Nicholas Cross Gavin Dalton Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,334(3):673-683
20.
V. R. Eke Carlos S. Frenk Carlton M. Baugh Shaun Cole Peder Norberg John A. Peacock Ivan K. Baldry Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto de Propris Simon P. Driver George Efstathiou Richard S. Ellis Karl Glazebrook Carole A. Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve J. Maddox Darren Madgwick Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,355(3):769-784