AbstractA simplified physically based model has been developed to simulate the breaching processes of homogenous and composite earthen embankments owing to overtopping and piping. The breach caused ...by overtopping flow is approximated as a flat broad-crested weir with a trapezoidal cross section, downstream connected with a vertical drop (headcut) and a straight slope for cohesive and noncohesive homogeneous embankments, respectively. For a composite dam with a clay core, the downstream becomes two straight slopes after the core is exposed. The breach by piping is assumed to be a flat pipe with rectangular cross section until the pipe top collapses and overtopping takes place. Sediment transport and morphology changes on the breach top flat section and downstream slopes and inside the pipe are calculated using a nonequilibrium total-load sediment transport model, whereas the time-averaged headcut migration rate is determined using an empirical formula. Stabilities of the side slope, pipe top, headcut, and clay core are analyzed by comparing the driving and resistance forces. The breach side slope is set as the average of the steepest stable slope and its corresponding failure plane angle. The model is able to handle dam and levee breaching by adopting various routing algorithms for headwater and tailwater levels and allowing embankment base erosion. It has been tested using 50 sets of data from laboratory experiments and field case studies. The calculated peak breach discharges, breach widths, and breach characteristic times agree generally well with the measured data.
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Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed Pd nanoparticles of ...about 3-6 nm in diameter are immobilized in the metal-organic framework (MOF) UiO-66(NH₂) via a facile one-pot hydrothermal method. The resulting Pd@UiO-66(NH₂) nanocomposite exhibits an excellent reusable and higher visible light photocatalytic activity for reducing Cr(vi) compared with UiO-66(NH₂) owing to the high dispersion of Pd nanoparticles and their close contact with the matrix, which lead to the enhanced light harvesting and more efficient separation of photogenerated electron-hole pairs. More significantly, the Pd@UiO-66(NH₂) could be used for simultaneous photocatalytic degradation of organic pollutants, like methyl orange (MO) and methylene blue (MB), and reduction of Cr(vi) with even further enhanced activity in the binary system, which could be attributed to the synergetic effect between photocatalytic oxidation and reduction by individually consuming photogenerated holes and electrons. This work represents the first example of using the MOFs-based materials as dual functional photocatalyst to remove different categories of pollutants simultaneously. Our finding not only proves great potential for the design and application of MOFs-based materials but also might bring light to new opportunities in the development of new high-performance photocatalysts.
Metal-organic frameworks (MOFs) have been arousing a great interest owing to their unique physicochemical properties. In this work, Zr-benzenedicarboxylate (UiO-66) and its derivative, ...Zr-2-NH2-benzenedicarboxylate (UiO-66(NH2)), are successfully prepared via a facile solvothermal method and applied to photocatalytic reactions. Powder X-ray diffraction (XRD) confirms the isoreticular nature of UiO-66 and UiO-66(NH2), while Fourier transformed infrared spectra (FTIR) prove the effective presence of amino group. UV-vis diffuse reflectance spectra (DRS) show the photoabsorption edge of UiO-66 could be shifted to the visible light region by simply introducing the amino group (-NH2) on the organic ligand. Importantly, UiO-66(NH2) is proved to perform as an efficient multifunctional visible-light-driven photocatalyst with high stability and considerable recyclability in both the photocatalytic selective oxidation of alcohols to aldehydes using molecular oxygen as oxidant and catalytic reduction of aqueous Cr(VI) to Cr(III) under ambient conditions. Furthermore, the possible reaction mechanism has also been investigated in detail. This work makes a systematic attempt to understand the reaction of photocatalytic selective oxidation of alcohols over MOFs and represents the first example to report the identification of MOFs as promising visible-light photocatalysts toward reduction of aqueous Cr(VI). More significantly, our finding also provides a new way to design MOFs-based photocatalysts, that is, by tuning the predesigned ligands with specific functional groups, the optical absorption properties of MOFs can be flexibly modulated, and then the effective solar energy conversion can be expected.
•A 3-D numerical model has been developed to simulate dam-break flows over uneven beds.•The model adopts an explicit finite-volume method based on collocated mesh that fits on solid boundaries.•The ...application of the model revealed the robustness and accuracy of the model.•Comparisons with depth averaged 2-D and other 3-D models, available in the literature, have been presented.•Application of the model on large computational domains can be computationally expensive.
A 3-D numerical model has been developed to simulate dam-break flow over uneven beds in irregular domains. The model solves the Reynolds-Averaged Navier–Stokes equations (RANS) using a finite-volume method based on collocated mesh that fits the solid boundaries such as bed and walls. The velocity and pressure coupling is achieved using the PISO algorithm and the Rhie and Chow’s momentum interpolation. The Smagorinsky eddy viscosity model is used for turbulence closure of the RANS equations. The movement of water surface is captured using the Volume-of-Fluid (VOF) method with the Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM) to solve the VOF advection equation. The accuracy and robustness of the model has been tested using several small- and large-scale laboratory experiments of dam-break flow. Some comparisons between the calculated results by the present model and those calculated by depth-averaged 2-D and 3-D models in the literature are presented.
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CdS nanorods have been successfully decorated on the surface of MOF (metal-organic framework) UiO-66(NH sub(2)) viaa facile room-temperature photodeposition technique in a controlled manner. ...Electrochemical measurements indicate that the CdS photodeposition proceeds viathe preferential reduction of Cd ions to Cd super(0) followed by chemical reaction with S sub(8). The photocatalytic performances of the obtained CdS-UiO-66(NH sub(2)) nanocomposites have been evaluated by selective oxidation of various alcohol substrates using molecular oxygen as a benign oxidant. The results show that such CdS-UiO-66(NH sub(2)) nanocomposites exhibit considerable photocatalytic activity and stability, which may be due to the large specific surface area and the charge injection from CdS into UiO-66(NH sub(2)) leads to efficient and longer charge separation by reducing the recombination of electron-hole pairs. This work represents the first example of using MOFs not only as supports but also as electron providers to trigger the reaction for coupling MOFs with metal sulfides, thus fabricating novel MOF-CdS nanocomposite systems and improving their photocatalytic activity. It is hoped that our findings could offer useful information and open a new window for the design of novel MOF-semiconductor nanocomposites as efficient visible light driven photocatalysts.
•The paper reviewed the progress in rice root genetic research.•A number of genes associated with root growth or functions have been identified.•It provides an opportunity to further improve rice ...based on MAS.
Rice is one of the most important cereal crops, feeding more than 50% population of the world. To meet the demand of increasing population, rice production has to be improved continually. As a very important part of rice plant, root system plays multiple roles in rice growth: anchorage of the plant, acquisition of water and nutrient elements, and biosynthesis of amino acids and hormones, etc. Almost all of the hot spots about rice research are associated with rice root: drought tolerance, lodging resistance, and efficient use of nutrition, the goal is to increase the grain yield with desirable seed quality. Although the understanding about rice root has been expanded in the last decades, there remain much to be done about root morphology and physiology, especially in root genetics. Rice root research is an exciting and focusing field in recent years. More and more researches on rice root genetics have been made. There is a close relation between above ground traits and underground roots, providing an alternative approach for rice genetic improvement. A number of genes associated with root architecture and physiological functions have been identified, or cloned. It provides an opportunity to further improve rice based on molecular assisted selection. Root traits improvement should be taken into account in future breeding programs in rice. However, root research is still a consuming and difficult work, because it was largely influenced by the complex underground environment. This paper reviewed the progress in rice root genetic research, and discussed its prospects.
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A Ternary composite UiO-66/CdS/1% reduced graphene oxide (RGO) was successfully prepared, with a photocatalytic hydrogen evolution rate 13.8 times as high as that of pure commercial CdS. It shows ...great advantages over the perfect composite photocatalyst-P25/CdS/1%RGO.
Due to the unique structures and properties of graphene and graphene-analogous two-dimensional (2D) nanosheets, numerous methods were developed to prepare these 2D nanosheets; however, it is still ...changeable to fabricate high-quality 2D nanosheets cost-effectively in large scale. Electrochemical exfoliation has emerged as an efficient and mild technology for the preparation of 2D nanosheets, and this paper reviewed the recent development of this strategy. Electrochemical exfoliation was divided into two main categories, anodic and cathodic exfoliation. The merits of each category were summarized and analyzed as well as drawbacks in detail. It provides an avenue to design and fabricate different kinds of high-quality 2D nanosheets cost-effectively in large scale for energy storage and conversion, catalysis, sensors, electronics and so on.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•A 3-D RANS model has been developed to simulate wave attenuation by vegetation.•Wave-induced drag and inertia forces on vegetation are added to the RANS equations.•Wave attenuation by vegetation ...located on sloping bed has been simulated accurately.•Vegetation motion neglected in this study can influence the model accuracy.•Wave conditions and vegetation properties affect strongly the wave attenuation.
Vegetation has been recognized as an important natural shoreline protection against storm surges and waves. Understanding of wave–vegetation interaction is essential for assessing the ability of vegetation patches, such as wetlands, to mitigate storm damages. In this study the wave attenuation by vegetation is investigated numerically using a 3-D model which solves the Reynolds-Averaged Navier–Stokes equations (RANS) by means of a finite-volume method based on collocated hexahedron mesh. A mixing length model is used for turbulence closure of the RANS equations. The water surface boundary is tracked using the Volume-of-Fluid (VOF) method with the Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM) to solve the VOF advection equation. The presence of vegetation is taken into account by adding the vegetation drag and inertia forces to the momentum equations. The model is validated by several laboratory experiments of short wave propagation through vegetation over flat and sloping beds. The comparisons show good agreement between the measured data and calculated results, but the swaying motion of flexible vegetation which is neglected in this study can influence the accuracy of the wave height predictions. The model is then applied to one of the validation tests with different vegetation properties, revealing that the wave height attenuation by vegetation depends not only on the wave conditions, but also the vegetation characteristics such as vegetation height and density.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The critical shear stress for erosion of sand and mud mixtures is theoretically investigated and expressed as a function of the critical shear stresses of pure sand and mud, mud content, and sand ...diameter. The proposed formula accounts for different structures and behaviours of the mixtures with low and high mud contents. The critical shear stress of pure mud is related to the solid/void volume ratio, and this relation is extended to the mud component in the mixture to consider the effect of compaction. It is found that the mud dry density, not the mixture dry density, is a direct factor affecting the mixture erosion. The developed formula has been calibrated and tested using four sets of experimental data collected from the literature. It reproduces the variations of the critical shear stress and mud dry density well.
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