Seed germination of wild,in situ-managed,and cultivated populations of columnar cacti in the Tehuacán-Cuicatlán Valley,Mexico     

S. Guillén  J. Benítez  M. Martínez-Ramos  A. Casas 《Journal of Arid Environments》2009,73(4-5):407-413

Seed germination was compared among wild, in situ-managed (wild plants let standing in areas cleared for agriculture), and cultivated populations of the columnar cacti Stenocereus pruinosus, Polaskia chichipe, Myrtillocactus schenckii, and Polaskia chende, species representing a gradient from higher to lower management intensity, respectively. We hypothesized that seeds from cultivated populations have higher water requirements to germinate than seeds of other populations, and that such difference is stronger in species more intensely managed. Germination was evaluated under water potential treatments at 0.0, ?0.2, and ?0.4 MPa. Interspecific differences were identified; germination rates markedly decreased in S. pruinosus and P. chichipe as water potential reduced. M. schenckii seeds germinated better at ?0.2 MPa, and seeds of P. chende in all treatments. Seed germination of wild and cultivated populations was similar in all cases and, therefore, at the population level domestication does not appear to have influenced variations in germination of the studied cacti species. However, experiments to test whether germination of seeds from plants with clear signs of domestication differs with seeds from other plants and their differential germination and seedling survival in wild, in situ-managed and cultivated environments could help to precise the influence of domestication on these plants.  相似文献   

The structure and fluid mechanics of turbidity currents: a review of some recent studies and their geological implications   总被引：17，自引：1，他引：16  

Ben Kneller  Clare Buckee 《Sedimentology》2000,47(S1):62-94

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Selection of the wavenumbers k using an optimization method for the inverse Fourier transform in 2.5D electrical modelling   总被引：1，自引：0，他引：1  

Shi‐zhe Xu  Ben‐chun Duan  Da‐hai Zhang 《Geophysical Prospecting》2000,48(5):789-796

An optimization method is used to select the wavenumbers k for the inverse Fourier transform in 2.5D electrical modelling. The model tests show that with the wavenumbers k selected in this way the inverse Fourier transform performs with satisfactory accuracy.  相似文献   

Upper Crustal Velocity Structure of the Southwestern Canadian Cordillera from Explosion Recordings on the WCTN Earthquake Seismic Net     

S. J. Fallows  G. D. Spence  G. C. Rogers 《Pure and Applied Geophysics》2000,157(9):1315-1336

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New views of Betelgeuse: multi-wavelength surface imaging and implications for models of hotspot generation     

J. S. Young  J. E. Baldwin  R. C. Boysen  C. A. Haniff  P. R. Lawson  †  C. D. Mackay  D. Pearson  J. Rogers  D. St.-Jacques  ‡  P. J. Warner  D. M. A. Wilson  R. W. Wilson § 《Monthly notices of the Royal Astronomical Society》2000,315(3):635-645

We report contemporaneous multi-wavelength interferometric imaging of the red supergiant star Betelgeuse ( α Orionis), using the Cambridge Optical Aperture Synthesis Telescope (COAST) and the William Herschel Telescope (WHT), at wavelengths of 700, 905 and 1290 nm. We find a strong variation in the apparent symmetry of the stellar brightness distribution as a function of wavelength. At 700 nm the star is highly asymmetric, and can be modelled as the superposition of three bright spots on a strongly limb-darkened disc. However, at 905 nm only a single low-contrast feature is visible and at 1290 nm the star presents a featureless symmetric disc. The change in spot contrast with wavelength is consistent with a model in which the bright spots represent unobscured areas of elevated temperature, owing perhaps to convection, on a stellar disc that itself has a different appearance, i.e. geometrical extent and limb-darkening profile, at different wavelengths. The featureless centre-to-limb brightness profile seen at 1290 nm is consistent with this model and suggests that future interferometric monitoring of the star to quantify the size changes associated with radial velocity variations should be performed at similar wavelengths in the near-infrared.  相似文献   

Galaxy destruction and diffuse light in clusters     

Carlos Calcáneo-Roldán  Ben Moore  Joss Bland-Hawthorn  David Malin  Elaine M. Sadler 《Monthly notices of the Royal Astronomical Society》2000,314(2):324-333

Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kiloparsecs wide. At a surface brightness of m _b ∼27–28 mag arcsec⁻² , the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disc was corotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent, and somewhere along the tidal debris, a fraction of the original stellar component of the disc will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709.  相似文献   

Cusps in cold dark matter haloes     

Jürg Diemand  Marcel Zemp  Ben Moore  Joachim Stadel  Marcella Carollo 《Monthly notices of the Royal Astronomical Society》2005,364(2):665-673

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Drainage basin peak discharge rating curve     

Wilbur F. Rogers  Vijay P. Singh 《水文研究》1988,2(3):245-253

The stream gauge rating curve for a drainage basin can be transformed into a drainage basin peak discharge rating curve that is more stable than the rating curve from which it is derived. The resulting drainage basin peak discharge rating curve can be used to predict peak discharge, identify anomalous discharges caused by channel obstructions or other causes, evaluate the effect of flood retarding structures, and evaluate historical records. The drainage basin peak discharge rating curve is valid for drainage basins of any size, for any discharge up to the time of concentration, and for snowmelt.  相似文献   

Geochemical Comparison of Ground Water in Areas of New England, New York, and Pennsylvania   总被引：3，自引：0，他引：3  

Robert J. Rogers 《Ground water》1989,27(5):690-712

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THE SOURCES OF REGIONAL ELDERLY POPULATION GROWTH: MIGRATION AND AGING-IN-PLACE *     

Andrei Rogers  Jennifer Woodward 《The Professional geographer》1988,40(4):450-459

A region's elderly population has two sources of growth: net migration and the net aging-in-place of its resident population. This paper outlines a method for identifying the projected relative contribution of these two sources of elderly population growth over time, and illustrates it with data for the states of Arizona, California, Florida, Illinois, and New York. The sources of elderly population growth differ between regions and over time.  相似文献