Intelligent optimization design of electron barrier layer for AlGaN-based deep-ultraviolet light-emitting diodes

AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) are widely used in sterilization, sensing, water purification, medical treatment, non-line of sight (NLOS) communication and many other fields. Especially it has been reported that the global novel coronavirus (COVID-19) can be effectively inactivated by the DUV light with a wavelength below 280 nm (UVC) within a few seconds, which has also attracted great attention. However, the external quantum efficiency (EQE) of UVC LED is still at a low level, generally not more than 10%. As an important component of EQE, internal quantum efficiency (IQE) plays a crucial role in realizing high-performance DUV-LED. In order to improve the IQE of AlGaN-based DUV-LED, this work adopts an electron blocking layer (EBL) structure based on InAlGaN/AlGaN superlattice. The results show that the superlattice EBL structure can effectively improve the IQE compared with the traditional single-layer and double-layer EBL structure for the DUV-LED. On this basis, the optimization method based on JAYA intelligent algorithm for LED structure design is proposed in this work. Using the proposed design method, the InAlGaN/AlGaN superlattice EBL structure is further optimized to maximize the LED' s IQE. It is demonstrated that the optimized superlattice EBL structure is beneficial to not only the suppression of electron leakage but also the improvement of hole injection, leading to the increase of carrier recombination in the active region. As a result, the IQE of the DUV-LED at 200 mA injection current is 41.2% higher than that of the single-layer EBL structure. In addition, the optimized structure reduces IQE at high current from 25% to 4%. The optimization method based on intelligent algorithm can break through the limitation of the current LED structure design and provide a new method to improve the efficiency of AlGaN-based DUV-LED. © 2023 Chinese Physical Society.

[Epidemiological characteristics of two local COVID-19 outbreaks caused by 2019-nCoV Omicron variant in Guangzhou, China].

Objective: To understand the epidemiological characteristics of two local COVID-19 outbreaks caused by 2019-nCoV Omicron variant in Guangzhou, such as incubation period, serial interval, basic reproductive number (R0) and the influence of gathering places on R0, and provide evidence for the prevention and control of Omicron variant infection. Methods: The data of daily confirmed cases of Omicron variant infection from April 8 to May 8, 2022 in two COVID-19 outbreaks in Guangzhou were collected for model fitting. Weibull, Gamma and lognormal distribution were used to estimate incubation period and serial interval. Exponential growth method and the maximum likelihood estimation were used to estimate R0. Results: The median of incubation period was 2.94 (95%CI: 2.52-3.38) days and median of serial interval was 3.32 (95%CI: 2.89-3.81) days. The estimated R0 in small-size place was 4.40 (95%CI: 3.95-4.85), while the estimated R0 at airport was 11.35 (95%CI: 11.02-11.67). Conclusion: The incubation period of Omicron variant in two local COVID-19 outbreaks in Guangzhou is significantly shorter than that of delta variant. The higher the gathering degree in a place, the larger the R0. Due to its rapid transmission, COVID-19 epidemic is prone to occur. Therefore, the COVID-19 prevention and control strategy should be dynamically adjusted in time.

Discovery of a novel SARS-CoV-2 main protease inhibitor by a simple and optimized colorimetric screening assay

For rapid discovery of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro) inhibitors from a natural product library, a novel colorimetric screening assay was developed. According to the colorimetric principle, the synthetic peptide TSAVLQ-para-nitroanilide (pNA) was used as the Mpro hydrolysis substrate. Subsequently, the working concentration of pNA substrate, Mpro working concentration, hydrolysis time and DMSO tolerance were optimized for the development of a simple and robust colorimetric screening assay. Through these systematic optimizations, we selected 0.4 mumol.L-1 Mpro and 100 mumol.L-1 pNA substrate as the optimal working concentrations in this colorimetric screening assay, and a high Z' factor of 0.9 was achieved. Using this screening assay, natural product ginkgolic acid C13: 0 (GA13: 0) was identified as a novel competitive Mpro inhibitor in vitro. Taken together, we have successfully developed a simple and optimized colorimetric screening assay, which will be vital for the discovery of novel SARS-CoV-2 Mpro inhibitors. Copyright © 2022, Chinese Pharmaceutical Association. All rights reserved.

Aerosol generation from tear film during non-contact tonometer measurement

Aerosols, generated and expelled during common human physiological activities or medical procedures, become a vital carrier for the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). During non-contact intraocular pressure measurements, aerosols can be produced from the tear film on eyes and potentially convey the SARS-CoV-2 in tears, creating a high risk for eye care practitioners and patients. Herein, we numerically investigate deformation and fragmentation of the tear films with various thicknesses and surface tensions that are impinged by an air jet. Evolution of the tear films manifests several types of breakup mechanisms, including both the bag breakup and ligament breakup of tear film on the eyeball, the ligament breakup of tear film on the eyelid margin, and the sheet breakup near the eyelid margin. The sheet near the eyelid margin is critical for generating large droplets and can be formed only if the jet velocity is high enough and the film is sufficiently thick. A criterion based on Weber number and capillary number is proposed for the breakup of tear film into droplets in which three regions are used to classify the film evolution. Our results indicate that eyes with excessive tears have a greater probability of generating aerosols than eyes under normal conditions. We recommend that enhanced protections should be adopted upon measurement for the patients with watery eyes, and the time interval between two adjacent measurements for the same individual should be also prolonged during the COVID-19 pandemic. Published under an exclusive license by AIP Publishing.

An Incentive Based Road Traffic Control Mechanism for Covid-19 Pandemic Alike Emergency Preparedness and Response

The Covid-19 pandemic has hit hard on the highly-organised yet risk-vulnerable modern societies, and has introduced new characteristics to large-scale emergencies, which feature long persistence in duration, high frequency in occurrence, large sensitivity to individual behaviours, and extreme high hazard propagation rate owing to the highly-efficient transport networks. This has raised new challenges on long-term emergency preparedness of urban transportation systems in terms of safety, efficiency, robustness and sustainability. Non-cooperative behaviours of transport participants could result in severe performance degradation in emergency preparedness, and mandatory restrictions in human activities can be economical costly and difficult in operation. In addition, current arrangement models for the disaster financial assistance have not been elaborately designed for civilian behaviour optimisation although with great potential as an economical instrument. Hence, in this paper, we propose a reward based traffic control mechanism to generate cooperative behaviours and optimise resource allocation in an urban transportation system for emergency preparedness via distributing credit coins, which can also be treated as a financial assistance approach during long-term disasters. A queueing theory based analytic model is employed to mimic the behaviours of civilians in the transportation system under the emergency preparedness state and a probability choice model is utilised to optimise the emergency preparedness strategies of the system. The experimental results show that the introduction of the incentive based traffic control mechanism can significantly reduce hazard response time, travel delay as well as the energy usage of the urban transportation system at the expense of monetary rewards.

COVID-19 Sources of Primary Care Nurses’ Work Disengagement in Malawi

Drawing on the conservation of resources theory, the study documents sources of primary care nurses’ work disengagement in a low-income country (Malawi) during the COVID-19 pandemic. The study utilized a qualitative approach that recruited 46 primary care nurses between the age of 21 to 53 years. Data were collected using in-depth telephone interviews from April 1st to May 17th, 2020. The interviews generated a total of 276 statements which were analyzed using the open and axial coding technique. Analysis of the interview statements established that sources of primary care nurses’ work disengagement in Malawi during the COVID-19 pandemic fall under three broad categories namely: threat of losing central resources;actual loss of central resources;and failure to gain central resources. The threat of losing central resources was manifested through respondents’ anticipated family-member COVID-19 contagion and conviction about the presence of asymptomatic workmates. Actual loss of central resources manifested as work-overload, workmates COVID-19 diagnosis, and public stigmatization. Last, failure to gain central resources was evident through inadequate personal protective equipment, low professional risk allowances, and minimal government funding allocation. Findings from this study have practical significance as they reveal to hospital management which causal sources are more prevalent in underlying the work disengagement of primary care nurses. In this way, the findings can guide hospital management to focus on mitigating the most prevalent sources of work disengagement to yield a far-reaching impact in heightening primary care nurses’ work vigor, dedication, and absorption. Copyright © Behavioral Science Research Institute

[Epidemiological characteristics of imported COVID-19 cases in Guangzhou].

Objective: To understand the epidemiological characteristics of imported COVID-19 cases in Guangzhou and provide scientific basis for the prevention and control of the disease. Methods: The data of imported COVID-19 in Guangzhou reported as of April 1, 2020 were collected from National Notifiable Disease Report System of China. The software Excel 2010 and SPSS 19.0 were applied for data cleaning and statistical analysis. Results: As of April 1, 2020, a total of 103 imported COVID-19 cases had been reported in Guangzhou, in which 92 were confirmed cases and 11 were asymptomatic infection cases. The number of the confirmed imported cases accounted for 11.4% (92/806) in of the total in China at the same time. The male to female ratio of the cases was 1.58∶1 (63∶40). The median age of the cases was 31 years (P(25)-P(75):22-40 years), range of age was 11-63 years. The main occupational distributions of the cases were business services (41/103, 39.8%) and students (36/103, 35.0%). The imported cases whose destinations were 19 provinces and municipalities rather than Guangdong after entering the country accounted for 43.7%. The main source countries of infections were the United Kingdom (27/103, 26.2%), the Philippines (13/103, 12.6%), the United States (13/103, 12.6%) and Nigeria (7/103, 6.8%). There were 34 inbound flights from which the imported COVID-19 cases were detected, in which 10 flights (10/34, 29.4%) were found to carry more than 3 cases, with an average voyage time of (11.14±0.53) hours. A total of 29 imported cases(28.2%) showed symptoms before entering the country, and 65 cases (63.1%) had been isolated before the onset of the disease. The mean free activity time of the isolated cases after the onset was (6.76±0.79) days. The average number of the imported cases' close contacts was 53. There were 13 clusters of COVID-19 caused by the imported cases, involving 36 cases (including 1 imported associated case). Conclusions: The sources of the imported COVID-19 cases in Guangzhou were widely distributed, and no cases had been found to be infected on the flights. In the early stage of the imported epidemic, there was high risk for the spread of the epidemic. Strengthened prevention and control of imported COVID-19 effectively reduced the of transmission risk of COVID-19 in communities.

[Expanding the pandemic influenza preparedness framework to the epidemic of COVID-19].

On March 11, 2020, WHO officially declared that COVID-19 had become Pandemic. As of March 31, the epidemic had affected more than 178 countries and regions, with more than 780 000 confirmed cases. The Pandemic Influenza Preparedness Framework for the sharing of influenza viruses and access to vaccines and other benefits (the 'PIP Framework' or 'Framework') is an international arrangement adopted by the World Health Organization in May 2011 to improve global pandemic influenza preparedness and response. Since the transmission route and transmission capacity of COVID-19 are similar to that of influenza A (H1N1) in 2009, which conforms to the basic elements of "human pandemic", and the epidemic scale has exceeded that of influenza A (H1N1)， it is probable to incorporate COVID-19 epidemic response into PIPF, and at the same time to verify and improve PIPF in practice. It is recommended that WHO, other international organizations and relevant countries make full use of the PIPF system to respond to the epidemic and better coordinate national actions at the global level. At the same time, China should also make the planning and deploy of domestic epidemic prevention and control and international epidemic cooperation under the framework.