Methane adsorption and dissociation mechanism on the WC(001) surface: a first-principle calculation

The conversion of methane in catalysis fields has aroused much attention for its abundant distribution in nature and it is environment-friendly. However, the C–H chemical breaking is a major challenge and requires proper catalysts for methane activation. Using first-principle calculations, we systematically explore the atomic configuration, interaction strength, dehydrogenation process and electronic properties of methane on noble metal Pt(111) and isoelectronic transition metal carbide WC(001) surface. The adsorption strength of methane activation on the WC(001) surface is stronger and the barrier of C–H bond breaking is smaller than that of the Pt(111) surface. Moreover, the oxygen concentration ranging from 40% to 60% coverage on the WC(001) surface benefits the methane activation and the energy barrier decreased to 0.26 ∼ 0.57 eV. The larger charge transfer emerges at the interface between methane and the WC(001) surface with or without oxygen coverage comparable to the Pt(111) surface. Our theoretical results can provide vital guidance for experimental synthesis conditions of methane activation and the transition metal carbide application in catalysts.</p

A virtual inertia control strategy of interlinking converters in islanded hybrid AC/DC microgrid

In an islanded hybrid AC/DC microgrid, the existing intermittent distributed generations (DGs) and local loads variation frequently cause power fluctuation. And the DC bus voltage is sensitive to it. A virtual inertia control strategy of interlinking converters (ILCs) in an islanded hybrid microgrid is proposed in this paper, which restrains the DC bus voltage fluctuation and enhances the inertia of the hybrid microgrid. Traditional droop control methods of ILCs mostly only focus on power sharing. The proposed control strategy can not only maintain proportional power distribution between DC and AC subgrids, but also regulate the DC bus voltage directly. It can improve microgrid stability during DC-side loading transitions or distributed energy fluctuations. Moreover, no additional energy storage or inverters are required in a cost-effective manner. The validity of the proposed control method is verified by offline time-domain simulation in MATLAB/Simulink and real-time experiment in OPAL-RT digital platform

A virtual inertia control strategy of interlinking converters in islanded hybrid AC/DC microgrid

In an islanded hybrid AC/DC microgrid, the existing intermittent distributed generations (DGs) and local loads variation frequently cause power fluctuation. And the DC bus voltage is sensitive to it. A virtual inertia control strategy of interlinking converters (ILCs) in an islanded hybrid microgrid is proposed in this paper, which restrains the DC bus voltage fluctuation and enhances the inertia of the hybrid microgrid. Traditional droop control methods of ILCs mostly only focus on power sharing. The proposed control strategy can not only maintain proportional power distribution between DC and AC subgrids, but also regulate the DC bus voltage directly. It can improve microgrid stability during DC-side loading transitions or distributed energy fluctuations. Moreover, no additional energy storage or inverters are required in a cost-effective manner. The validity of the proposed control method is verified by offline time-domain simulation in MATLAB/Simulink and real-time experiment in OPAL-RT digital platform

Density Functional Theory Study of Bilayer Borophene-Based Anode Material for Rechargeable Lithium Ion Batteries

The bilayer borophene has been successfully fabricated in experiments recently and possesses superior antioxidation and robust metallic properties, which holds great promise for the future anode materials of Li-ion batteries. Herein, using first-principles calculations, two bilayer borophenes including P6/mmm or P6̅m2 symmetry groups with or without vacancy defects are comprehensively explored and acted as electrode materials with high performance in Li-ion batteries. The charge density difference, adsorption energies, and Bader charge analysis are calculated and discussed for single lithium adsorbed on bilayer borophene. The results shown that with the increase of lithium concentration, the adsorption energies are rapidly decreased due to the repulsion of boron atoms except for the P6̅m2 systems with double side adsorption and corresponding energies remain the narrow range. Meanwhile, the partial density of states shows metallic character after lithium adsorption and indicates good conductivity for the charge–discharge process. Furthermore, small diffusion barriers, low average open-circuit voltage, can be achieved, and large storage capacity is up to 930.2 mA h/g at the lower lithium content of 0.375. These results propose that bilayer borophene might be a good choice for anode material applications in future Li-ion batteries with fast ion diffusion and high power density

Structural Characterization of Boron Sheets beyond the Monolayer and Implication for Experimental Synthesis and Identification

The successful synthesis of quasi-freestanding bilayer borophene has aroused much attention for its superior physical properties and holds great promise for future electronic devices. Herein, we comprehensively explore six boron sheets beyond the monolayer and structurally characterize them via various methods using first-principles calculations for experimental references. On the basis of atomic models of borophenes, simulated scanning tunneling microscope (STM) images show different morphologies at different bias voltages and are explained by the partial densities of states and the height differences in the vertical direction. Simulated transmission electron microscope images further probe the internal atomic arrangement of boron sheets and compensate for the shortcomings of STM images to better distinguish different phases of boron sheets. The interlayer coupling strength is stronger in bilayer borophenes than in the three-layer system via the electron localization function and Mulliken bond population. In addition, simulated X-ray diffraction and infrared spectra show different characteristic peaks and corresponding vibrational modes to further characterize these boron sheets. These theoretical results can decrease the prime cost and provide vital guidance for the experimental synthesis and identification of boron sheets beyond the monolayer

Characterizing Human Collective Behaviors During COVID-19-Hong Kong SAR, China, 2020

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: People are likely to engage in collective behaviors online during extreme events, such as the coronavirus disease 2019 (COVID-19) crisis, to express awareness, take action, and work through concerns. WHAT IS ADDED BY THIS REPORT?: This study offers a framework for evaluating interactions among individuals' emotions, perceptions, and online behaviors in Hong Kong Special Administrative Region (SAR) during the first two waves of COVID-19 (February to June 2020). Its results indicate a strong correlation between online behaviors, such as Google searches, and the real-time reproduction numbers. To validate the model's output of risk perception, this investigation conducted 10 rounds of cross-sectional telephone surveys on 8,593 local adult residents from February 1 through June 20 in 2020 to quantify risk perception levels over time. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: Compared to the survey results, the estimates of the risk perception of individuals using our network-based mechanistic model capture 80% of the trend of people's risk perception (individuals who are worried about being infected) during the studied period. We may need to reinvigorate the public by involving people as part of the solution that reduced the risk to their lives