With increasing penetration of the renewable energy, the grid-tied PWM inverters need to take corresponding responsibilities for the security and stability of future grid, behaving like conventional rotational synchronous generator (RSG). Therefore, recognizing the inherent relationship and intrinsic differences between inverters and RSGs is essential for such target. By modeling the typical electromechanical transient of grid-tied PWM inverters, this paper first proves that PWM inverters and RSGs are similar in physical mechanism and equivalent in mathematical model, and the concept of static synchronous generator (SSG) is thereby developed. Furthermore, the comprehensive comparison between RSG and SSG is carried out in detail, and their inherent relation is built. Based on these findings, the rationality and feasibility of migrating the concepts, tools, and methods of RSG stability analysis to investigate the dynamic behaviors and stability issues of SSG is therefore confirmed. Taking stability issues as an example, the criteria of small signal and transient stability of a typical grid-tied PWM inverter is put forward to demonstrate the significance of the developed SSG model (including synchronizing coefficient, damping coefficient, inertia constant, and power-angle curve), providing clear physical interpretation on the dynamic characteristics and stability issues. The developed SSG model promotes grid-friendly integration of renewable energy to future grid and stimulates interdisciplinary research between power electronics and power system.

Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre -including this research content -immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

Benzotriazole ultraviolet stabilizers (BUVSs) are high-production-volume chemicals with ubiquitous occurrence in the aquatic environment. However, little is known about their bioconcentration and biotransformation, and physiologically based toxicokinetic (PBTK) models for BUVSs are lacking. This study selected six BUVSs for which experiments were performed with zebrafish (Danio rerio) exposed to two different levels (0.5 and 10 μg·L–1). Higher kinetic bioconcentration factors (BCFs) were observed at the lower exposure level with environmental relevance, with BCF of 3.33 × 103 L·kg–1 for 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-327). This phenomenon was interpreted by a nonlinear adsorption mechanism, where binding with specific protein sites contributes to bioconcentration. Muscle exhibited the lowest accumulation, in which depuration half-life of UV-327 was 19.5 d. In kidney, muscle, ovary, gill, and skin, logBCF increased with increase in log K OW of the BUVSs until log K OW was ca. 6.5, above which logBCF decreased. However, the trend was not observed in the liver and intestine. Six biotransformation products were identified and mainly accumulated in the liver and intestine. Considering the nonlinear adsorption mechanism in the PBTK model, the prediction accuracy of the model was improved, highlighting the binding of xenobiotics with specific protein sites in assessing the bioconcentration of chemicals for their risk assessment.

Here we report novel multi-channel AlGaN/GaN MOSHEMTs with high breakdown voltage (VBR) and low ONresistance (R ON). The multi-channel structure was judiciously designed to yield a small sheet resistance (R s) of 80 Ω/sq using only four 2DEG channels, resulting in an effective resistivity (ρ eff) of only 1.1 mΩ•mm. The major limitation of highconductivity multi-channel devices is their limited V BR. This work shows that while conventional field plates (FPs) are not suited to increase VBR in high-conductivity multi-channels, slanted tri-gates offer better electric field management inside the device. With a gate-to-drain separation (L GD) of 15 µm, the device presented a low RON of 2.8 Ω•mm (considering the full width of the device (wdevice)) and a high VBR of 1230 V, rendering a small specific R ON (R ON,SP) of 0.47 mΩ•cm 2 and an excellent figure-of-merit of 3.2 GW/cm 2. This work also shows the feasibility of E-mode multi-channel MOSHEMTs with a threshold voltage (V TH) of +0.9 V at 1 µA/mm by tuning the tri-gate geometry. These results significantly outperform conventional single-channel devices and demonstrate the enormous potential of multi-channel power devices.

Nanometer-scale transistors based on III-V compound semiconductors, such as GaAs, InAs, and InP, are at the heart of many high-speed and high-frequency electronic systems 10. Due to their high electron mobilities, these devices exhibit very high small-signal cutoff frequencies, in the terahertz range 11. However, the high-frequency large-signal performance of transistors is still a challenge, since it is severely limited by the output capacitance Cout, electron saturation velocity and critical electric field 12. The maximum switching speed of a transistor (Fig. 1a) with saturation current Imax is limited to performance semiconductor materials. GaAs and InP are limited to the JFOM, while Cout-limited rise-rate of 1 V/ps restricts the performance of SiC, GaN, and Diamond.