Modelling the Linkage Between Landscape Metrics and Water Quality Indices of Hydrological Units in Sihu Basin, Hubei Province, China: An Allometric Model

AbstractStudying quantitative relationships between landscape pattern and water quality is a fundamental step to assess the impacts of non-point source pollution. Many hydrological models with multi-functionality have been developed as useful tools to study several key mechanisms in non-point source pollution. In landscape ecological studies, however, the empirical modelling approaches have been dominated with emphasis on the relationships between the landscape metrics and water quality indices. The main techniques for developing those models of landscape-water quality are statistical regression analysis based on linear models. In this article, Allometric models and the traditional multiple linear regression models for estimating the linkage between landscape metrics and water quality were tested in Sihu Basin, Hubei Province, China. The models at patch class level were established in 24 hydrological units of the basin, which took nine water quality indices (EC, pH, SS, DO, COD, TN, TP, NO3--N, NH4+-N) as the dependent variables and eighteen landscape metrics calculated in FRAGSTATS 3.3 as independent variables. The results suggested that, compared with the traditional multiple linear regression models, Allometric models were more suitable for SS, DO, TP, TN, NH4+-N, in which landscape pattern metrics could explain the 80.5%, 77.7%, 58.2%, 43.9%, 67.6% of total variation, respectively. There had little difference between multiple linear regression models and Allometric models for EC and NO3--N. The coefficients of determination in Allometric models were not as strong as that obtained in the multiple linear regression models for pH and COD. The above results indicated that using Allometric model may potentially provide a new way to study the linkage between landscape metrics and water quality indices, which will help protect our regional water resources

Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures

Numerical modelling for reactive transport due to the water-dependent activities within building materials

International audienceReactive transport is a critical issue in building materials because it is closely related to the durability of building materials, especially for the porous material with functional connectivity. When building material exposes to the aggressive environment during its service life, the microstructure will be altered because of water-dependent activities, such as salt precipitation/dissolution. This paper establishes a mathematical model for transport problems and chemical reactions intended to characterize the process of precipitation/dissolution in the porous medium. The main algorithm is implemented by the sequential iterative approach (SIA), which is based on two sets of equations. The transport problems are described by a set of partial differential equations based on mass conservation, and the chemical processes, under the assumption of equilibrium, are represented by a set of nonlinear algebraic equations based on the law of mass action. To simplify the problem, this paper focuses on a material perspective of the porous medium, i.e., the development computes the chemical species and water as a function of time only. By adopting our model, transport properties such as ionic concentration and mass of chemical components were implemented. The porosity and the water saturation degree were also considered and examined in our work. Finally, the convergence rate of this numerical model was discussed based on two simulated cases. Such a method could be used as the extra reference when controlling experimental conditions is difficult, in refining the durability-related issues, such as salt intrusion and water transport. © Proceedings of the 2020 Session of the 13th fib International PhD Symposium in Civil Engineering. All rights reserved

Determination on pore size distribution by a probabilistic porous network subjected to salt precipitation and dissolution

International audiencePore system strongly affects durability of building materials. Therefore, representative models for pore system and evolution of the pore system during aging are important for understanding physical processes that affect durability of building materials. In this study, a porous network model was developed based on a probabilistic method to describe pore size distribution, and three transformation laws were employed to establish relationship between the initial pore sizes and modified pore sizes (after salt precipitation and dissolution) regarding the waterfront. Proposed model illustrated evolution of pore size distribution due to salt precipitation and dissolution based on overall porosity and water saturation degree. Moreover, the model can be used to implement the filling/emptying ratio of pores at vicinity of waterfront. Successive transformations were introduced into the model to illustrate evolution of pore size distribution due to long-term salt intrusion. Lastly, parametric studies on the model were performed to further elucidate the modifications on pore size distribution due to salt precipitation and dissolution. © 2021 Elsevier B.V

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