Unraveling the pH-Dependent Oxygen Reduction Performance on Single-Atom Catalysts: From Single- to Dual-Sabatier Optima

M-N-C single-atom catalysts (SACs) have emerged as a potential substitute for the costly platinum-group catalysts in oxygen reduction reaction (ORR). However, several critical aspects of M-N-C SACs in ORR remain poorly understood, including their pH-dependent activity, selectivity for 2- or 4-electron transfer pathways, and the identification of the rate-determining steps. Herein, analyzing >100 M-N-C structures and >2000 sets of energetics, we unveil for the first time a pH-dependent evolution in ORR activity volcanos from a single-peak in alkaline media to a double-peak in acids. We found that this pH-dependent behavior in M-N-C catalysts fundamentally stems from their moderate dipole moments and polarizability for O* and HOO* adsorbates, as well as unique scaling relations among ORR adsorbates. To validate our theoretical discovery, we synthesized a series of molecular M-N-C catalysts, each characterized by well-defined atomic coordination environments. Impressively, the experiments matched our theoretical predictions on kinetic current, Tafel slope, and turnover frequency in both acidic and alkaline environments. These new insights also refine the famous Sabatier principle by emphasizing the need to avoid an "acid trap" while designing M-N-C catalysts for ORR or any other pH-dependent electrochemical applications.Comment: 24 pages, 5 Figure

Optimal scheduling of microgrid with distributed power based on water cycle algorithm

Microgrid, taking advantage of distributed power generation technology, plays an important role in maximizing the utilization of renewable energy. Based on the problems of the energy crisis, environmental contamination and the high operating cost of the microgrid, the microgrid model can effectively ease energy pressure.We can dispatch the output of each part in the microgrid to obtain the optimal economy. Since many traditional optimization algorithms have limitations of local optimization, multiple iterations, and slow convergence speed, this paper proposes a method that applies the Water Cycle Algorithm (WCA) to optimize the dispatch of the microgrid to minimize the operating cost. The mathematical model of each distributed power is established. The interactive power between the microgrid and large grid is also considered. The lowest generation cost considering environmental benefits is taken as the objective function. Water cycle algorithm is implemented to obtain the optimal solution under various constraints. Some optimization algorithms such as Genetic Algorithm (GA), Interior Search Algorithm (ISA), and Differential Search Algorithm (DSA) were used for results evaluation. By comparing the results obtained from four different algorithms, a case study shows the WCA possesses the advancements of better convergence performance, faster calculation and higher precision compared to the other algorithms. The results demonstrate that the WCA applied to determine the optimal scheduling of the microgrid can achieve a better result than some other algorithms with an acceptable accuracy and efficiency

Preparation of Broad-Spectrum Polyclonal Antibody and Development of an Indirect Competitive-Enzyme Linked Immunosorbent Assay for Multi-Residue Detection of Biphenyl Tetrazolium Sartans in Antihypertensive Health Foods

An indirect competitive-enzyme linked immunosorbent assay (ic-ELISA) was established to detect the multi-residue of biphenyl tetrazolium sartans in antihypertensive health foods. Candesartan was coupled with bovine serum albumin to obtain immunogen. New Zealand white rabbits were immunized and a broad-spectrum antibody was obtained by an antibody screening assay. The half maximal inhibitory concentrations (IC50) for candesartan, losartan carboxylic acid, losartan potassium, olmesartan, olmesartan medoxomil, irbesartan, valsartan and valsartan methyl ester were 0.2, 0.2, 0.7, 0.04, 0.6, 0.3, 0.9 and 2.4 ng/mL, respectively. The samples were extracted with methanol and the matrix effect was eliminated by diluting the extract with standard solutions. The average recoveries of the eight target compounds were in the range from 80.6% to 120.0% with coefficients of variation equal to or below 14.0%. The results of ic-ELISA were highly correlated with those of liquid chromatography-tandem mass spectrometry (LC-MS/MS) (r > 0.97), indicating high accuracy and good reliability of ic-ELISA

Analysis and Design of A PMQR-Type Repetitive Control Scheme for Grid-Connected H6 Inverters

There exist several challenges in the implementation of proportional multiple quasi-resonant (PMQR) control strategies in single-phase grid-connected H6 inverters, such as high computational costs and design complexity. To overcome these challenges, this paper proposes a proportional multiple quasi-resonant (PMQR)-type repetitive control (PMQR-type RC) scheme for single-phase grid-connected H6 inverters. In the control scheme, a repetitive controller and a proportional controller run in parallel. The repetitive controller is to improve the steady-state harmonics compensation ability, while the proportional controller can enhance the transient performance of the system. Both theoretical stability analysis and detailed design steps regarding the proposed control scheme are introduced. Finally, comparison results on a typical single-phase grid-connected H6 inverter with LC filter under a variety of control methods verify the capability of suppressing harmonics and the robust performance of the proposed control strategy against grid disturbances

Optimal Scheduling of Microgrid with Distributed Power Based on Water Cycle Algorithm

Microgrid, taking advantage of distributed power generation technology, plays an important role in maximizing the utilization of renewable energy. Based on the problems of the energy crisis, environmental contamination and the high operating cost of the microgrid, the microgrid model can effectively ease energy pressure. We can dispatch the output of each part in the microgrid to obtain the optimal economy. Since many traditional optimization algorithms have limitations of local optimization, multiple iterations, and slow convergence speed, this paper proposes a method that applies the Water Cycle Algorithm (WCA) to optimize the dispatch of the microgrid to minimize the operating cost. The mathematical model of each distributed power is established. The interactive power between the microgrid and large grid is also considered. The lowest generation cost considering environmental benefits is taken as the objective function. Water cycle algorithm is implemented to obtain the optimal solution under various constraints. Some optimization algorithms such as Genetic Algorithm (GA), Interior Search Algorithm (ISA), and Differential Search Algorithm (DSA) were used for results evaluation. By comparing the results obtained from four different algorithms, a case study shows the WCA possesses the advancements of better convergence performance, faster calculation and higher precision compared to the other algorithms. The results demonstrate that the WCA applied to determine the optimal scheduling of the microgrid can achieve a better result than some other algorithms with an acceptable accuracy and efficiency

Experimental Study of the Concrete Cracking Behavior of an Immersed Tunnel under Fire

This study investigates the impact of fire on the cracking behavior of immersed tunnels. A reduced-scale (1:5) model of an immersed tunnel was constructed to conduct fire tests in both traffic tubes using the HCinc curve as the applied fire. Temperature field changes were carefully monitored during the test by thermocouples and infrared thermography on the outer surface of the tunnel’s ceiling. The continuous temperature field and temperature changes in the concrete cracks were recorded by infrared thermography. By integrating the temperature field distribution in concrete and the behavior of concrete cracking, an analysis of the depth of concrete cracking in the immersed tunnel under fire was conducted. The concrete cracks exceeded 150 mm at 95 min of the fire test. The results indicate that the inner concrete exposed to fire undergoes thermal expansion, leading to tensile cracking of the outer concrete. Additionally, the fire-exposed surface of the tunnel is vulnerable to cracking due to a temperature decrease. Thus, the design of fire resistance of immersed tunnels should take into consideration the potential for concrete cracking caused by thermal strain

Community Structure and Soil Mineral Concentration in Relation to Plant Invasion in a Subtropical Urban and Rural Ecotone

Alien species invasion affects local community biodiversity and stability considerably, and ecosystem services and functions will accordingly be dramatically changed. Many studies have reported a correlation between invasibility and the chemical nature of soil, but the influences of understory plant community structure and soil trace element concentrations on invasibility have not been fully explored. Landscape heterogeneity in the urban and rural ecotone may alter the invasion process, and assessing the invasibility of different types of native forests may lead to a better understanding of the mechanisms by which native species resist invasion. We compared the composition, structure, diversity and stability of the understory community in abandoned fallows, severely invaded by Mikania micrantha and Borreria latifolia, and adjacent natural and planted forests in the urban and rural ecotone of Eastern Guangzhou, China. Additionally, we quantified mineral element concentrations in the topsoil (0–25 cm) most influenced by the root system of understory communities in the forest stand types. Abandoned fallows had the highest concentrations of available ferrum (Fe) and available boron (B) and the lowest concentration of total mercury (Hg) Hg among the three stand types. In contrast to various species diversity indices, the understory structure of the three stands better explained differences in community invasibility. Average understory cover significantly differed among the three stand types, and those types with the greatest number of stems in height and cover classes 1 and 2 differed the most, indicating that seedling establishment may deter invasion to a certain extent. CCA (canonical correspondence analysis) results better reflected the distribution range of each stand type and its relationship with environmental factors, and available Fe, available B, exchangeable calcium (Ca), exchangeable magnesium (Mg), cover, available copper (Cu) and total Hg , were strongly related the distribution of native and exotic understory species. Invasion weakened community stability. The stability index changed consistently with the species diversity index, and abandoned fallows understory community stability was lower than the other stand types. According to our results, both soil mineral element concentrations and community structure are related to alien species invasion. Against the backdrop of urbanization and industrialization, this information will provide forest management and planning departments with certain reference points for forest protection and invasive plant management

Temporal Changes in Community Structure over a 5-Year Successional Stage in a Subtropical Forest

In the context of global warming, the changes of forest structure, diversity, and productivity along with forest succession have always been a topic of interest for many researchers. Studying the changes in community structure, biomass, and diversity of different diameter at breast height (DBH) classes in subtropical mountainous forests during forest succession can provide data in support of future forest succession predictions and forest management. We analyzed the changes of three DBH classes in a 10-ha plot while studying subtropical mountainous forest succession in 2012 and 2017. The results showed that during forest succession, the community abundance and richness significantly decreased while biomass increased slightly. Among the three DBH classes, changes were the greatest in small trees, followed by large trees, and then medium-sized trees. The abundance, biomass, richness, and Shannon–Wiener index of small trees all decreased significantly. In forests with medium-sized trees, biomass decreased significantly and abundance did not change significantly. In large trees, abundance and biomass increased significantly. Changes were observed in environmental driving factors during forest succession. In 2012, driving factors with significant effects included total phosphorus, transmitted direct solar radiation, organic matter, and capillary water capacity. In 2017, two driving factors were total phosphorus and total potassium while the main driving factor was still total phosphorus. The results showed that during forest succession the abundance and diversity of small trees were principal components of community abundance and diversity. A reduction in small-tree abundance and diversity will decrease community abundance and diversity. Large-tree biomass was a principal component of community biomass; accumulation of large-tree biomass will increase community biomass. Schima superba Gardner and Champ. and Castanopsis carlesii (Hemsl.) Hayata are the main dominant species in this area, which can quickly form stable communities. S. superba is also a fire-resistant tree species. Therefore, in natural forest management, planting of S. superba and C. carlesii in the secondary bare land can be considered. In addition, the evergreen broad-leaved forest can be recovered to the forest structure and productivity level before selective cutting, which provides important inspiration for forest management in the region