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Background: Acute asthma exacerbation in children is often caused by respiratory infections. In this study, a coordinated national surveillance system for acute asthma hospitalizations and causative respiratory infections was established. We herein report recent trends in pediatric acute asthma hospitalizations since the COVID‐19 pandemic in Japan. Methods: Thirty‐three sentinel hospitals in Japan registered all of their hospitalized pediatric asthma patients and their causal pathogens. The changes in acute asthma hospitalization in children before and after the onset of the COVID‐19 pandemic and whether or not COVID‐19 caused acute asthma exacerbation were investigated. Results: From fiscal years 2010–2019, the median number of acute asthma hospitalizations per year was 3524 (2462–4570), but in fiscal years 2020, 2021, and 2022, the numbers were 820, 1,001, and 1,026, respectively (the fiscal year in Japan is April to March). This decrease was observed in all age groups with the exception of the 3‐ to 6‐year group. SARS‐CoV‐2 was evaluated in 2094 patients from fiscal years 2020–2022, but the first positive case was not detected until February 2022. Since then, only 36 of them have been identified with SARS‐CoV‐2, none of which required mechanical ventilation. Influenza, RS virus, and human metapneumovirus infections also decreased in FY 2020. In contrast, 24% of patients had not been receiving long‐term control medications before admission despite the severity of bronchial asthma. Conclusion: SARS‐CoV‐2 was hardly detected in children with acute asthma hospitalization during the COVID‐19 pandemic. This result indicated that SARS‐CoV‐2 did not induce acute asthma exacerbation in children. Rather, infection control measures implemented against the pandemic may have consequently reduced other respiratory virus infections and thus acute asthma hospitalizations during this period. However, the fact that many hospitalized patients have not been receiving appropriate long‐term control medications is a major problem that should be addressed. [ABSTRACT FROM AUTHOR]

Liquid propellants are commonly used in rocket engines due to their high energy density. In this study, we focused on the use of liquid ethanol and liquid nitrous oxide as propellants in a cylindrical rotating detonation engine (RDE) for practical applications, and examined the effects of various conditions on the bipropellant RDE performance. We varied the vapor quality of nitrous oxide in a mixture of liquid and gaseous nitrous oxide due to the flash boiling. In addition, we varied the liquid ethanol temperature, the injector stiffness, and momentum angle of the propellant. We then analyzed the effects of these changes on the propagation mode of the RDE under atmospheric pressure conditions. The results showed that a rotating detonation wave was observed under the combination of high vapor quality of nitrous oxide, high injector stiffness, high liquid ethanol temperature, and high momentum angle. The propagation velocity was obtained as 73∼83 % of the Chapman-Jouguet velocity. Long-duration combustion tests were also conducted, and the internal combustion structure was confirmed from the erosion of the carbon-carbon (C/C) composite material. The detonation wave was considered to propagate near the bottom of the RDE with liquid propellants from the erosion heights of the C/C composite. The erosion height was confirmed to be consistent with the fill height calculated using the sound speed of the nitrous oxide. In addition, characteristic exhaust velocity efficiencies of more than 85 % were achieved in all combustion tests. [ABSTRACT FROM AUTHOR]