Study on the breakdown characteristics of multiple-reignition secondary arcs on EHV/UHV transmission lines

A long-gap AC arc with a length of more than ten meters (secondary arc) are normally generated at the short-circuit arc channel after a single-phase-to-ground fault. In previous studies, arc breakdowns of secondary arcs have mainly been considered as electrical breakdowns, ignoring the role of heat in the arc channel. Besides, the extinction-reignition theory of secondary arc, i.e., dielectric strength recovery theory, still lack the support of experimental data. In this study, based on the equivalent experiments performed in the laboratory, the influences of compensation degree of transmission lines, initial recovery voltage gradient of air gap, test current, wind speed, and wind direction on the breakdown characteristics of secondary arcs are studied and statistically analyzed. The laws of the transient recovery voltage (TRV) and of the rate of rise of recovery voltage (RRRV) also studied by considering the influencing factors mentioned above. The results of this study will provide a more complete experimental basis for the theory of extinction–reignition of secondary arcs and a deeper understanding of the transient characteristics of arc breakdow

Robotic‐assisted bronchoscopy for the diagnosis of peripheral pulmonary lesions: A systematic review and meta‐analysis

Abstract Robotic‐assisted bronchoscopy (RAB) is a newly developed bronchoscopic technique for the diagnosis of peripheral pulmonary lesions (PPLs). The objective of this meta‐analysis was to analyze the diagnostic yield and safety of RAB in patients with PPLs. Five databases (PubMed, Embase, Web of Science, CENTRAL, and ClinicalTrials.gov) were searched from inception to April 2023. Two independent investigators screened retrieved articles, extracted data, and assessed the study quality. The pooled diagnostic yield and complication rate were estimated. Subgroup analysis was used to explore potential sources of heterogeneity. Publication bias was assessed using funnel plots and the Egger test. Sensitivity analysis was also conducted to assess the robustness of the synthesized results. A total of 725 lesions from 10 studies were included in this meta‐analysis. No publication bias was found. Overall, RAB had a pooled diagnostic yield of 80.4% (95% CI: 75.7%–85.1%). Lesion size of >30 mm, presence of a bronchus sign, and a concentric radial endobronchial ultrasound view were associated with a statistically significantly higher diagnostic yield. Heterogeneity exploration showed that studies using cryoprobes reported better yields than those without cryoprobes (90.0%, 95% CI: 83.2%–94.7% vs. 79.0%, 95% CI: 75.8%–82.2%, p < 0.01). The pooled complication rate was 3.0% (95% CI: 1.6%–4.4%). In conclusion, RAB is an effective and safe technique for PPLs diagnosis. Further high‐quality prospective studies still need to be conducted

STRUCTURAL CHANGES OF BAMBOO CELLULOSE IN FORMIC ACID

The structure of cellulose from bamboo fiber before and after treatment in formic acid was investigated in comparison with microcrystalline-cellulose by solid state NMR, FTIR, and X-ray diffraction diagrams. Differences of molecular structures among two kinds of celluloses were validated and expatiated. Results from the experiments indicated notable differences in the crystalline or amorphous region of microcrystalline-cellulose and bamboo fiber. CP-MAS 13C-NMR, and FTIR spectroscopy revealed the presence of Iα and Iβ forms in all of the samples. The effect of acid solution was achieved simultaneously both in the crystalline region and the amorphous region, but there was a more intensive effect on the crystalline region for bamboo fiber. All of the cellulose samples revealed the same chain conformation but a different hydrogen bonding pattern. The absorbency of hydrogen bonds shifted to a high wave number and gradually decreased during treatment. The intermolecular hydrogen bond of 6-OH…O-3′ decreased first, and then increased gradually, which indicated that the cellulose bundled together during hydrolysis

Enhanced Energy-Storage Performances in Sodium Bismuth Titanate-Based Relaxation Ferroelectric Ceramics with Optimized Polarization by Tuning Sintering Temperature

Energy-storage capacitors based on relaxation ferroelectric ceramics have attracted a lot of interest in pulse power devices. How to improve the energy density by designing the structure of ceramics through simple approaches is still a challenge. Herein, enhanced energy-storage performances are achieved in relaxation ferroelectric 0.9 (0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-0.1NaNbO3 (NBT-BT-NN) ceramics by tuning sintering temperature. The original observation based on Kelvin probe force microscopy (KPFM) presented that the sintering temperature has a key effect on the electrical homogeneousness of the ceramics. It is found that a high electrical homogeneousness can induce quick and active domain switching due to the weakening of the constraint from built-in fields, resulting in a big polarization difference. This work provides a feasible strategy to design high-performance energy-storage ceramic capacitors