以“浅空间”视角解读中国古典园林中的门洞取景空间

“浅空间”概念是《透明性》一书中重要的空间概念,它延续和发展了现代主义建筑理论,最早从立体主义绘画中引申而来,是现象透明性理论的转化介质,主要作用在于分析空间中的层化关系。中国山水画在历史的河流中,同样出现过类似于立体主义空间关系的画面组织形式。山水画的发展,潜移默化地影响了中国古典园林。这四者微妙的关系为园林门洞的取景空间建立了可分析的纽带。通过分析立体主义之于“浅空间”理论和中国山水画之于中国园林的关系,以“浅空间”理论为出发点,尝试以别样的角度分析中国古典园林门洞中的空间关系,为中国古典园林空间分析提供多样的视角。

Symmetries and Similarity Reductions of a New (2+1)-Dimensional Shallow Water Wave System

The symmetries of a （2＋1）-dimensional shallow water wave system, which is newly constructed through applying variation principle of analytic mechanics, are researched in this paper. The Lie symmetries and the corresponding reductions are obtained by means of classical Lie group approach. The （1＋1） dimensional displacement shallow water wave equation can be derived from the reductions when special symmetry parameters are chosen.

Spatial distribution and abundance of small fishes in Xiaosihai Lake,a shallow lake along the Changjiang (Yangtze) River, China

Spatial distribution and abundance of small fishes were studied in autumn 2007 in the Xiaosihai Lake, a shallow lake along the middle reach of the Changjiang （Yangtze） River. Based on the plant cover, the lake was divided into three major habitats： Myriophyllum spicaturn habitat （MS habitat）, Trapa bispinosa habitat （TB habitat）, and non-vegetation habitat （NV habitat）. A modified pop-net was used for quantitative sampling of small fishes in the three habitats, and the Zippin＇s removal method was used for estimating densities of the small fishes. A total of 13 species belonging to 5 families were collected, with 11 species in MS habitat, 7 species in TB habitat, and 5 species in NV habitat. Habitat type had significant effect on the spatial distribution of small fishes. The Shannon-Wiener diversity index in the MS, TB and NV habitats were 1.28, 0.56 and 0.54, respectively. The total density and biomass of small fishes were significantly higher in the MS habitat （13.68 ind/m^2 and 4.44 g/m^2） than in the TB habitat （1.41 ind/m^2 and 0.54 g/m^2） and the NV habitat （1.08 ind/m^2 and 0.40 g/m^2）, and were not significantly different between the TB habitat and the NV habitat. Water depth had no significant effect on spatial distribution of the small fishes. It was suggested that vegetation type played an important role in habitat selectivity of small fishes, and the presence of submersed vegetation should be of significance in the conservation of small fish diversity.

Interaction between Topographic Conditions and Entrainment Rate in Numerical Simulations of Debris Flow

Debris flow simulations are useful for predicting the sediment supplied to watersheds from upstream areas. However, the topographic conditions upstream are more complicated than those downstream and the relationship between the topographic conditions and debris flow initiation is not well understood. This study compared the use of several entrainment rate equations in numerical simulations of debris flows to examine the effect of topographic conditions on the flow. One-dimensional numerical simulations were performed based on the shallow water equations and three entrainment rate equations were tested. These entrainment rate equations were based on the same idea that erosion and the deposition of debris flows occur via the difference between the equilibrium and current conditions of debris flows, while they differed in the expression of the concentration, channel angle, and sediment amount. The comparison was performed using a straight channel with various channel angles and a channel with a periodically undulating surface. The three entrainment rate equations gave different amounts of channel bed degradation and hydrographs for a straight channel with a channel angle greater than 21° when water was supplied from upstream at a steady rate. The difference was caused by the expression of the entrainment rate equations. For channels with little undulation, the numerical simulations gave results almost identical to those for straight channels with the same channel angle. However, for channels with large undulations, the hydrographs differed from those for straight channels with the same channel angle when the channel angle was less than 21°. Rapid erosion occurred and the hydrograph showed a significant peak, especially in cases using the entrainment equation expressed by channel angle. This was caused by the effects of the steep undulating sections, since the effect increased with the magnitude of the undulation, suggesting that a debris flow in an upstream area develops differently according to the topographic conditions. These results also inferred that numerical simulations of debris flow can differ depending on the spatial resolution of the simulation domain, as the resolution determines the reproducibility of the undulations.

Temporal and spatial distribution of virioplankton in large shallow freshwater lakes

Virioplankton dynamics at seven sample sites(from two freshwater lakes) with different trophic states were monitored over the period of a year.Water was sampled monthly from August 2004 to July 2005,and the abundances of viruses and bacteria were measured using direct epifluorescence microscopy counting.Results indicated that both natural and anthropogenic factors could influence the distribution of virioplankton.Temporally,viral abundance was significantly correlated to bacterial density and water temperature.Spatially,viral abundance was significantly correlated to trophic state.This in turn indicated that viral abundance was directly dependant on host abundance in eutrophic lakes,while trophic state and temperature could drive the distribution of virioplankton.The virus-bacteria ratio was significantly lower in less productive water-bodies.The result implied that the control of virioplankton on their hosts may change according to the host density.

Finite Volume Multilevel Approximation of the Shallow Water Equations

The authors consider a simple transport equation in one-dimensional space and the linearized shallow water equations in two-dimensional space, and describe and implement a multilevel finite-volume discretization in the context of the utilization of the incremental unknowns. The numerical stability of the method is proved in both cases.