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Topographic differences play a limited role on species distribution in a sub-tropical forest in South China

Gong G.-Q., Huang Z.-L., Ye W.-H., Cao H.-L., Lian J.-Y., Lin G.-J., Wei S.-G., Li L., Bin Y., Kong B., Li B.-W.

Polish Journal of Ecology

2013

Vol. 61, nr 3

477--491

Habitat association test has been regarded as an effective way to evaluate the relative role of niche differentiation in a community. Topographical attributes are often selected as surrogates of niche processes. However, the inference for relative role of niche differentiation is likely problematic if the spatial dependence of plant community on underlying spatially structured topographic variables is not accounted for. In this study, we used the torus shift and principal component analysis (PCA) to resolve this problem, and tested the habitat associations by adjusted-SD test in a sub-tropical evergreen broad-leaved forest in south China. The result revealed that minority of 100 common species were specialist, among which 8 species associated with first two PC axes (accounted for 98% of total eigenvalue and contributed mainly by mean elevation and aspect) and 22 species associated with last two PC axes (contributed by slope and convexity). In conclusion, we found the niche processes represented by topographical attributes play a limited role in the Dinghushan sub-tropical evergreen broad-leaved forest plot. Further study should include more habitat variables to examine the habitat associations.

Three-dimensional numerical analysis of internal flow phenomena in a diagonal rotor

Bin Y., Keqi W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

2004

Vol. 8, No 1

27-40

A numerical analysis has been designed to study internal flow phenomena in a diagonal rotor. A calculated diagonal rotor was designed by a quasi-three-dimensional method. Its hub and casing walls were inclined 45o and 25o, respectively. The numerical simulation was based on the Navier-Stokes equations coupled with a k-? turbulence model. We found that the rotor's wake was stronger near the hub and in the casing end wall region. The wake at a lower flow rate was stronger than that at a higher flow rate. Static pressure gradually increased from the hub to the casing along the height of a blade, on the rotor pressure surface and in the front 60% of the chord region of the suction surface. In the back 40% of the chord region of the suction surface, static pressure gradually decreased. A passage vortex formed in the stator flow passage and an 80% axial chord plane. It was located near the hub end-wall. The passage vortex developed into a large vortex centered near the midspan at a 99% axial chord plane of the stator. The casing wall boundary layer downstream of the rotor occupied approximately 10% of the flow passage. Along the height of a blade, the meridian velocity gradually increased upstream of rotor and decreased downstream. The calculated aerodynamic characteristic curve, the meridian velocity distribution upstream and downstream of the rotor, and the streamline distribution on the meridian surface were consistent with experimental results and design data. Our findings proved that the present numerical method is reliable and practicable. It can be used to design and analyze swept diagonal rotors in order to improve their surging and rotation stall state. The present results also provide comparative data for the design of highly-loaded swept diagonal rotors in future studies.