Search

In order to improve the backward-facing radar stealth capability of the engine exhaust system, five coating schemes for afterburner, which is radar wave strong scattering source, are formulated. The influence of afterburner coating absorbing materials on the horizontal polarization and vertical polarization RCS distribution pattern of the exhaust system in the range of -30°~+30° azimuth of the typical frequency point in the S-band and X-band is analyzed by using the shooting and bouncing rays, also SAR imaging of typical frequency points in the X-band at an azimuth angle of 0° is simulated.The results show that the distribution of strong scattering sources in S-band and X-band is basically the same, and the influence of different coating schemes of absorbing materials on the RCS reduction effect of two bands is similar. The flame stabilizer is the strongest scattering source of radar characteristic signal, and coating it with radar absorbing materials has the greatest benefit on reducing the radar characteristic signal of the exhaust system. Coating absorbing materials in the four parts of afterburner inner cone, flame stabilizer, lobe mixer and afterburner cylinder is the best absorbing material coating scheme for the reduction effect of RCS in the two wave bands. The average RCS reduction effect of horizontal polarization and vertical polarization in S band is 92.3% and 92.0%, and the average RCS reduction effect of horizontal polarization and vertical polarization in X-band is 90.2% and 88.4%.

The urban water environment, an integral component of the terrestrial hydrosphere, is closely linked to human activities and serves as a fundamental resource for industrial and agricultural development. Sedimentary organic matter in water bodies contains rich biological, physical, and chemical information, playing a central role in nutrient cycling and serving as a primary reservoir for nutrient accumulation. This study assesses the water quality, chemical indicators, and sediment productivity of four typical urban water bodies (Canal, Pond, Lake, and River) in Shaoxing City, eastern China. The results show that artificial water bodies, particularly canals, have higher dissolved oxygen (DO) compared to natural water bodies. Stationary water bodies, such as lakes and ponds, generally have higher total dissolved solids (TDS) and electrical conductivity (EC) than flowing water bodies like rivers and canals. All four urban water body types slightly exceed China's Class-V water quality standard for total nitrogen (TN), with canals, lakes, ponds, and rivers averaging 1.29, 1.22, 1.23, and 1.23 times the standard, respectively. Ponds exhibit the highest total dissolved nitrogen (TDN) content, while ammonium (NH4+–N) and nitrate (NO3−–N) levels are relatively consistent across the bodies, except for lower NO3−–N in lakes. Higher organic matter in canals and lakes, indicated by chlorophyll-a (Chl-a) and permanganate index (CODMn), suggests greater eutrophication compared to ponds and rivers. Sediment total organic nitrogen (TON) content is relatively uniform across all water bodies, with slightly higher values in lakes and rivers. Total organic carbon (TOC) content is highest in lake sediments, 1.51 times that of canals. Carbon/nitrogen (C/N) ratios vary, with ponds and lakes showing the highest averages. Source quantification using isotopic analysis (δ13C and δ15N values) indicates that phytoplankton is the primary sedimentary organic matter source in rivers and canals, while terrestrial sources are significant in lakes and ponds. Sewage notably contributes to rivers and canals. These findings highlight the need for targeted pollution control strategies, focusing on phytoplankton and sewage as key sedimentary organic matter sources to mitigate eutrophication and enhance water quality in urban environments. [ABSTRACT FROM AUTHOR]

Background: To explore the effect of non-pharmacological interventions (NPIs) on respiratory pathogen profiles among hospitalized infants aged 0–3 months in Beijing during the coronavirus disease 2019 (COVID-19) pandemic. Methods: Respiratory specimens were collected from 1,184 infants aged 0–3 months who were hospitalized for acute respiratory infection at the Children's Hospital affiliated with the Capital Institute of Pediatrics from January 2018 to December 2023. The data were divided into three groups—the pre-epidemic (January 2018 to December 2019), epidemic prevention and control (January 2020 to December 2022), and post-epidemic (January 2023 to December 2023) groups—based on the outbreak of COVID-19 and the implementation and termination of NPIs. The specimens were tested for 14 respiratory pathogens, including influenza virus A (Flu A), influenza virus B, respiratory syncytial virus, parainfluenza virus (PIV), adenovirus (ADV), human metapneumovirus (HMPV), human bocavirus, human rhinovirus (HRV), coronavirus, Chlamydia trachomatis, Chlamydia pneumoniae (C.pn), Mycoplasma pneumoniae, Bordetella pertussis, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Results: A total of 1,184 infants, including 649 males and 535 females, with acute respiratory infections were admitted. The positive detection rate for respiratory pathogens was 51.77% (n = 613). In 2023, the proportion of infants with respiratory infections after the epidemic was 19.4% (319/1646), the positive detection rate of respiratory pathogens was 68.3% (218/319), and the mixed infection detection rate of respiratory pathogens was 16.1% (35/218). Prior to the epidemic, these rates were 11.9% (431/3611), 37.1% (160/431), and 5.0% (8/160), respectively. During the epidemic prevention and control period, these rates significantly increased to 12.4% (434/3486), 54.1% (235/434), and 11.1% (26/235) (P < 0.05), respectively. Post-epidemic, the proportion of newborns testing positive for respiratory pathogens decreased, while the number of infants aged 29–90 days significantly increased. The proportion of admission weight and contact history with respiratory patients increased significantly compared to before and during the epidemic, with statistical significance (P < 0.05). After the epidemic, a total of 13 respiratory pathogens were detected throughout the year. There were statistically significant differences in the detection rates of Flu A, PIV, SARS-CoV-2, HRV, HMPV, ADV, and C.pn before, during, and after implementation of the NPIs during the COVID-19 epidemic (P < 0.05). Post-epidemic, the detection rates of Flu A, PIV, and SARS-CoV-2 were significantly higher than those before and during the epidemic (P < 0.017). The detection rates of HRV, HMPV, and ADV significantly increased after the epidemic compared to those before the epidemic (P < 0.017). Before the epidemic, the positivity rate of respiratory pathogens was high in the first and fourth quarters. After the termination of NPIs, the positive detection rate decreased in the first quarter but increased in the second, third, and fourth quarters, with a statistically significant difference (P < 0.05). Conclusion: The implementation and lifting of COVID-19 NPIs have caused significant changes in the detection and seasonal distribution of respiratory pathogens in infants aged 0–3 months in Beijing. NPIs temporarily reduced the detection rate of respiratory pathogens in infants during the prevalence of COVID-19. Understanding the prevalence of respiratory pathogens before and after the epidemic is particularly important for the prevention and control of respiratory diseases in infants. [ABSTRACT FROM AUTHOR]

We report a catalytic late‐stage bromination strategy for the α‐C−H functionalization of aryl acetic acid. The aryl acetic acid was transformed into enediolate in the presence of an (AcO)4B2O with the combination of DBU, and consequently underwent an electrophilic bromination reaction with pyridinium tribromide. A wide range of α‐bromo aryl acetic acids were isolated in yields of 19–65 %. In addition, the reaction could be performed on a gram scale, and several transformations of the products were carried out. [ABSTRACT FROM AUTHOR]

In this study, the effect of electric field on the component dissolution and gel properties of silver carp surimi was investigated. The optimal process for electric field-assisted water-saving washing of surimi was obtained through response surface experimental design. The results showed that the electric field technology could effectively promote the solubilization of fat, ash and water-soluble proteins and the enrichment of salt-soluble proteins in surimi. Moreover, this technology significantly reduced gel degradation and increased the gel strength by inhibiting protease activity and activating transglutaminase (TGase). The optimal process parameters for electric field-assisted washing of surimi were as follows: Electric field voltage 56 V, fish-water mass ratio 1:3, washing time 3 min. The salt-soluble protein content was 8.67 g/ 100 g surimi, while the protease activity was 6.48 U/mg protein under these conditions. Meanwhile, this technology significantly increased the whiteness, elasticity, gel strength and water holding capacity of surimi gels (P<0.05), while reducing water consumption by 40%. This provides a new idea for the application of electric field in water-saving washing of surimi. [ABSTRACT FROM AUTHOR]

Understanding the effect of environmental factors on population characteristics of amphibians is crucial for their conservation and management. This is especially pertinent in regions vulnerable to climate change, such as the Qinghai–Tibetan Plateau (QTP). Here, we investigated the underlying environmental factors affecting the occurrence and abundance of Tibetan frogs (Nanorana pleskei) in the Three-River-Source region (TRSR) on the QTP. We found that N. pleskei is predominantly located in the headwater region of the Lancang River, with an increasing population size from northwest to southeast across the TRSR. Temperature oscillation acts as an ecological filter to determine the occurrence pattern, whereas the abundance is jointly influenced by maximum monthly temperature and precipitation and precipitation variability. Our study presents up-to-date information on the distribution and population status of N. pleskei in the hinterland of the QTP, which can assist conservation practitioners in developing effective management plans. Furthermore, our findings can contribute to the understanding of the distribution and abundance of amphibians within challenging high-elevation and plateau environments, offering insights that are valuable for the conservation and management of other amphibian species inhabiting similar high-elevation regions. [ABSTRACT FROM AUTHOR]