Search

Agricultural nonpoint source pollution (ANPS) can cause systemic pollution of the ecological environment, directly threatening sustainable agricultural development and human health and safety. Accurate estimation of ANPS loads, clarification of the sources and spatial distribution patterns of ANPS, and effective control and management of ANPS in the watershed require identifying critical source areas. This case study focuses on the Danjiang River basin, a critical water source for China's South-to-North Water Division and demonstrates the efficiency of ArcGIS's spatial statistical analysis methods in discovering the hidden spatial pattern of ANPS and extracting the causes associated with the spatial pattern, as well as the accuracy of identifying critical source areas of ANPS. In this study, two spatial statistical analysis methods, Anselin local Moran's I and hot-spot analysis (Getis–Ord Gi*), are applied to propose a method for accurately identifying critical source areas of ANPS based on the spatial distribution of ANPS loads. The results of the study are as follows: (1) based on the MIKE LOAD model, the annual ANPS loads of chemical oxygen demand (COD), ammonia nitrogen (NH4), total nitrogen (TN), and total phosphorus (TP) in the Danhan River basin are calculated as 182,530.15, 16,137.39, 58,285.92, and 2,962.84 t/yr , respectively. (2) Clusters are mainly distributed in the southwestern part of the watershed, and the spatial pattern is directly related to land use and rural population; the spatial pattern of outliers is related to agricultural modes and geographical characteristics. (3) Hot spot clusters are concentrated in the hinterland of Hanzhong Plain; the regional specialty of agriculture is the dominant factor in determining the spatial pattern of cold-spot and hot-spot clusters. (4) Based on these findings, seven critical subbasins and one critical source area of ANPS that need to be prioritized for control in the study area are identified. Agricultural nonpoint source pollution (ANPS) is a significant cause of ecosystem pollution, which directly threatens the sustainable development of agriculture, human health, and safety. The Dan–Han River Basin is a crucial water source in China for the South-to-North Water Diversion Project and provides water to 140 million people. It is essential to ensure that the water quality of the Dan-Han River remains unpolluted. The ANPS as a major source of water pollution in the watershed is difficult to identify and control. Accurately identifying the sources and spatial distribution patterns of ANPS pollutants is a prerequisite for maintaining water quality and controlling ANPS. Our study offers a new perspective on methods to reveal the hidden spatial pattern and identify critical source areas of ANPS in watersheds. This research demonstrates the effectiveness of ArcGIS's spatial statistical analysis methods in discovering the hidden spatial pattern of ANPS, extracting the causes associated with the spatial pattern, and accurately identifying critical source areas of ANPS. These methods can also be applied to study nonpoint source pollution in other watersheds. [ABSTRACT FROM AUTHOR]

It is well known that in the process of thermal oxidation of silicon, there are Pb-type defects at amorphous silicon dioxide/silicon (a-SiO2/Si) interface due to strain. These defects have a very important impact on the performance and reliability of semiconductor devices. In the process of passivation, hydrogen is usually used to inactivate Pb-type defects by the reaction Pb + H2 → PbH + H. At the same time, PbH centers dissociate according to the chemical reaction Pb H → Pb +H. Therefore, it is of great significance to study the balance of the passivation and dissociation. In this work, the reaction mechanisms of passivation and dissociation of the Pb-type defects are investigated by first-principles calculations. The reaction rates of the passivation and dissociation are calculated by the climbing image-nudged elastic band (CI-NEB) method and harmonic transition state theory (HTST). By coupling the rate equations of the passivation and dissociation reactions, the equilibrium density ratio of the saturated interfacial dangling bonds and interfacial defects (Pb, Pb0, and Pb1) at different temperatures is calculated. [ABSTRACT FROM AUTHOR]

The structural evolutions and electronic properties of AulPtm (l + m ≤ 10) clusters are investigated by using the first-principles methods. We use the inverse design of materials using the multi-objective differential evolution (IM2ODE) package to globally search the equilibrium structures and investigate the evolving trend from a two-dimensional structure to a three-dimensional structure on horizontal extension and vertical extension for AulPtm (l + m ≤ 10) clusters. The three-dimensional stable geometry of Au8Pt and Au8Pt2 is discovered for the first time in our work. We also notice that the equilibrium structures of AulPtm (l + m = 10 and l ≤ 8) tend to form a tetrahedral geometry and can be obtained by replacing the Au atom in the most stable structure of Aul+1Ptm−1 with the Pt atom, where Pt atoms assemble together and occupy the center of clusters and Au atoms prefer to lie on the vertex or edge position. The average binding energy (Eb) is mostly decided by Pt–Pt bond numbers, namely the numbers of Pt atoms, followed by Au–Pt bond numbers. The second-order energy difference (Δ2Ev and Δ2Eh) and the nearest-neighbor energy difference (Δ4Enn) show that Au6Pt, Au4Pt2, Au3Pt3, Au2Pt4 and AuPt7 clusters exhibit high relative physical stability, so we suggest that these clusters could be defined as the magic number clusters for AulPtm (l + m ≤ 10) clusters. The HOMO–LUMO energy gap (Eg), adiabatic ionization potential (AIP) and the adiabatic electron affinity (AEA) are also investigated to elaborate the relative electronic stability of all the clusters. [ABSTRACT FROM AUTHOR]

The catalytic properties of the magic gold–platinum bimetallic clusters (Au4Pt2 and Au6Pt) for the reduction of SO2 by CO, without or with preadsorbing CO molecules, are firstly investigated using density functional theory calculations. We find that the catalytic activities improve effectively with the preadsorption of CO onto the catalysts and that the catalytic activities of Au6Pt(CO)n are better than those of Au4Pt2(CO)n as more CO molecules are adsorbed onto the catalysts. During the reaction process, the Au4Pt2(CO)n clusters always keep two-dimensional morphologies except for when n = 5 and the Au6Pt(CO)n clusters have three-dimensional geometries except for when n = 0. The most stable adsorption site for SO2 molecules on the catalysts is the site of preadsorbing the next CO molecule on the corresponding catalysts. The largest activation energy (Emaxa) is related to the metal 5d (M-5d) band center and the charge transfer (Ct) as well as the bond length (Rb) between COS and the catalyst contribute to the desorption energy (Ed) of COS corporately. We propose that Au6Pt(CO)6 is a cost-effective gold–platinum bimetallic catalyst for the reduction of SO2 by CO. [ABSTRACT FROM AUTHOR]

The structural evolutions and electronic properties of AulPtm (l + m ≤ 10) clusters are investigated by using the first-principles methods. We use the inverse design of materials using the multi-objective differential evolution (IM2ODE) package to globally search the equilibrium structures and investigate the evolving trend from a two-dimensional structure to a three-dimensional structure on horizontal extension and vertical extension for AulPtm (l + m ≤ 10) clusters. The three-dimensional stable geometry of Au8Pt and Au8Pt2 is discovered for the first time in our work. We also notice that the equilibrium structures of AulPtm (l + m = 10 and l ≤ 8) tend to form a tetrahedral geometry and can be obtained by replacing the Au atom in the most stable structure of Aul+1Ptm-1 with the Pt atom, where Pt atoms assemble together and occupy the center of clusters and Au atoms prefer to lie on the vertex or edge position. The average binding energy (Eb) is mostly decided by Pt-Pt bond numbers, namely the numbers of Pt atoms, followed by Au-Pt bond numbers. The second-order energy difference (Δ2Ev and Δ2Eh) and the nearest-neighbor energy difference (Δ4Enn) show that Au6Pt, Au4Pt2, Au3Pt3, Au2Pt4 and AuPt7 clusters exhibit high relative physical stability, so we suggest that these clusters could be defined as the magic number clusters for AulPtm (l + m ≤ 10) clusters. The HOMO-LUMO energy gap (Eg), adiabatic ionization potential (AIP) and the adiabatic electron affinity (AEA) are also investigated to elaborate the relative electronic stability of all the clusters.

The catalytic properties of the magic gold-platinum bimetallic clusters (Au 4 Pt 2 and Au 6 Pt) for the reduction of SO 2 by CO, without or with preadsorbing CO molecules, are firstly investigated using density functional theory calculations. We find that the catalytic activities improve effectively with the preadsorption of CO onto the catalysts and that the catalytic activities of Au 6 Pt(CO) n are better than those of Au 4 Pt 2 (CO) n as more CO molecules are adsorbed onto the catalysts. During the reaction process, the Au 4 Pt 2 (CO) n clusters always keep two-dimensional morphologies except for when n = 5 and the Au 6 Pt(CO) n clusters have three-dimensional geometries except for when n = 0. The most stable adsorption site for SO 2 molecules on the catalysts is the site of preadsorbing the next CO molecule on the corresponding catalysts. The largest activation energy (E) is related to the metal 5d (M-5d) band center and the charge transfer (C t ) as well as the bond length (R b ) between COS and the catalyst contribute to the desorption energy (E d ) of COS corporately. We propose that Au 6 Pt(CO) 6 is a cost-effective gold-platinum bimetallic catalyst for the reduction of SO 2 by CO.