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991.
992.
Streamwatcr chemistry was monitored for five years in six streams in a paired catchment experiment in Mendolong, Sabah, Malaysia, including controls in rain forest and secondary vegetation after the [Borneo fire] of 1982–3 and comparing the effects of different ways of establishing forest plantations with Acacia mangium. Three catchments were covered with selectively logged lowland hill dipterocarp forest (W4-W6) and three (W1-W3) with secondary vegetation after forest fires. The control catchments, W3 and W6 reported in this paper, had no treatments applied. Reference monitoring at all streams was for 25 months and the total period of study reported here is 64 months. The soils in the catchments were mainly Orthic Acrisol in W3 and Gleyic Podsol in W6 and a mix of both soil types in the other catchments. Element baseflow concentrations were generally low and not significantly different from stormflow concentrations for all streams during the reference period. Concentrations were also generally consistently low for the two control streams during the whole period of measurement. Chemical inputs as wet deposition were low as a result of a high input from local convection. The rain forest on the Podsol had a tight nutrient circulation indicated by small net losses of macronutrients. The Podsol was found to have poorer conditions for soil mineralization and more surficial runoff, resulting in higher loads of S, C and N in the organic phases, with higher organic C/N ratio, in the discharge. Nitrogen was found to accumulate in both catchments. An almost double accumulation of N in W3 was attributed to a larger biomass accumulation continuing after the forest fire 3–8 years earlier. On the other hand, the Acrisol in W3 had much larger net losses of S, Si, K, Ca, Mg and Na. Most of differences could be attributed to differences in weathering between the soils and local mineralogical differences. 相似文献
993.
T. Le Berter N. Epchtein F. Guglielmo P. Le Sidaner 《Astrophysics and Space Science》1994,217(1-2):105-116
The goal of this article is to show that, if one avoids star forming regions, mass-losing AGB stars can generally be selected from the data that will be provided by the near-infrared surveys which are presently considered. Also, if IRAS data are available, the separation between carbon-rich and oxygen-rich stars can be operated by their positions in infrared colour diagrams. In extragalactic systems, red supergiants can be discriminated from AGB stars by their luminosities.based on observations obtained with the ESO 1-m telescope 相似文献
994.
995.
996.
997.
S. I.Bastrukov J.Yang D. V.Podgainy 《Monthly notices of the Royal Astronomical Society》2002,330(4):901-906
We investigate the evolution of the magnetic flux density in a magnetically supported molecular cloud driven by Hall and Ohmic components of the electric field generated by the flows of thermal electrons. Particular attention is given to the wave transport of the magnetic field in a cloud whose gas dynamics is dominated by electron flows; the mobility of neutrals and ions is regarded as heavily suppressed. It is shown that electromagnetic waves penetrating such a cloud can be converted into helicons – weakly damped, circularly polarized waves in which the densities of the magnetic flux and the electron current undergo coherent oscillations. These waves are interesting in their own right, because for electron magnetohydrodynamics the low-frequency helicoidal waves have the same physical significance as the transverse Alfvén waves do for a single-component magnetohydrodynamics. The latter, as is known, are considered to be responsible for the widths of molecular lines detected in dark, magnetically supported clouds. From our numerical estimates for the group velocity and the rate of dissipation of helicons it follows that a possible contribution of these waves to the broadening of molecular lines is consistent with the conditions typical of dark molecular clouds. 相似文献
998.
999.
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
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