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The creation of ordered collective vacancies in experiment proves challenging within a two-dimensional lattice, resulting in a limited understanding of their impact on catalyst performance. Motivated by the successful experimental synthesis of monolayer molybdenum borides with precisely ordered metal vacancies [Zhou et al. Science2021, 373, 801–805] through dealloying, the nitrogen reduction reaction (NRR) in monolayer borides was systematically investigated to elucidate the influence of such ordered metal vacancies on catalytic reactions and the underlying mechanisms. The results reveal that the N-containing intermediates tend to dissociate, facilitating the NRR process with reduced UL. The emergence of ordered metal vacancies modulates the electronic properties of the catalyst and partially facilitates the decomposition of N-containing intermediates. However, the ULfor NRR in Mo4/3B2and W4/3B2exhibits a significant increase. The compromised electrochemical performance is explained through the development of a simple electronic descriptor of the d–p band center (ΔdM–pB). Among these materials, Mo4/3Sc2/3B2exhibits the most superior catalytic activity with a ULof −0.5 V and favorable NRR selectivity over the HER. Our results provide mechanistic insights into the role of ordered metal vacancies in transition-metal boride for the NRR and highlight a novel avenue toward the rational design of superior NRR catalysts.

The continuous frequency tuning of a second-harmonic (SH) 800-GHz gyrotron is experimentally studied. The influence of the electron pitch factor on harmonic mode competition and frequency tunability has been thoroughly examined. By controlling the pitch factor, the competition from the fundamental parasitic mode can be effectively suppressed. The stable oscillations of the SH mode were achieved with an output power of up to 150 W and a continuous frequency tuning range of 0.8 GHz around 800 GHz. Similarly, the gyrotron operating in the fundamental mode can achieve wideband continuous frequency tuning range of 8.71 GHz around 385 GHz.

Pulsed high-field magnets are important tools for modern scientific research. Given the current state of material development, stress-optimized design is a primary approach to achieving high magnetic fields. Nevertheless, the analysis and optimization of the structural mechanics for pulsed magnets are highly complex, involving various factors such as multi-physics coupling, elastic–plastic analysis, and conductor-fiber laminate structures. Traditional manual design methods are inefficient and unable to achieve the global optimal solution. Therefore, the development of automated optimization methods is important. However, magnet optimization involves hundreds of parameters, making intelligence optimization challenging. This article proposes a simplified analytical mechanical model for the reinforcement structure design of pulsed magnets, which reduces the number of variables to approximately ten and enables the application of heuristic optimization algorithms. Thus, this article proposes a hybrid optimization architecture based on the multi-objective particle swarm optimization (MOPSO). The analytical model and finite-element analysis (FEA) are deeply embedded in the MOPSO algorithm as a calculation module to achieve efficient and effective optimization. The obtained results show that the proposed method is valid and efficient for optimizing high-stress magnets.

The misalignment issue is not only an engineering challenge but also a problem of academic interest for the development of high-frequency gyrotron oscillators. In this article, the linear and saturated behavior of beam–wave interaction in gyrotron oscillator with an arbitrarily misaligned electron beam is studied in a general form. Misalignment causes eccentricity between the electron beam center and the resonator, resulting in the coupling strength loss and additional phase variation, which in turn affects the beam–wave interaction. The coupling strength loss leads to an increase in the starting current and the saturated current and a decrease in the saturated efficiency, while the additional phase variation modulates the cyclotron resonance condition and the electron bunching process, regulating the linear and nonlinear behavior of the gyrotron. The general analysis reveals that the diverse behaviors of misaligned gyrotron highly depend on the azimuthal mode index and the frequency cyclotron mismatch. The findings of this study offer valuable insights into the effects of misalignment on gyrotron operation and provide useful guidance for the design and alignment process of gyrotrons.