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.

[Characteristics of SARS-CoV-2 Omicron infection in children imported from Hong Kong].

Objective: To understand the clinical characteristics of children with SARS-CoV-2 Omicron infection imported from Hong Kong Special Administrative Region. Methods: This retrospective study was conducted to collect the data including clinical manifestations, outcomes and vaccination of 107 children with SARS-CoV-2 Omicron infection imported from Hong Kong Special Administrative Region to be admitted to the designated referral hospital in Shanghai from February to March 2022. According to the occurrence of clinical symptoms, the cases were divided into asymptomatic group and symptomatic group. According to the age of diagnosis, the cases were divided into <3 years group, 3-<6 years group and 6-<18 years group, and the clinical manifestations in different age group were analyzed with t-test and Mann-Whitney rank-sum test. Besides, to analyze the effectiveness of vaccination against SARS-CoV-2 Omicron infection in different age group, the cases aged 3-<18 years were also subdivided into unvaccinated group, 1-dose group and 2-dose group, and the relative risk (RR) was used to demonstrate the effectiveness. Results: Among the 107 cases, 66 were male and 41 were female, with infection age of 10 (5, 14) years. There were 29 cases in the asymptomatic group, and 78 cases in the symptomatic group, and no significant difference in the age of infection was observed between the 2 groups (11 (6, 14) vs. 10 (5, 14) years, Z=0.49, P>0.05). And there were no severe cases in symptomatic group. The length of hospitalization was (18±6) days, and was longer in symptomatic group than that in asymptomatic group ((19±6) vs. (16±7) d, t=0.17, P=0.030). Eight-two cases (76.6%) had a history of epidemiological exposure and, among whom, 81 cases (75.7%) were associated with household transmission. Among symptomatic group, 57 cases (73.1%) had fever and 20 cases (25.6%) had cough. Of the 74 cases undergoing chest CT examination, 17 cases (23.0%) showed mild abnormalities. Of the 83 cases who received the lab tests, 23 cases (27.7%) had white blood cell counts<4×109/L, 3 cases (3.6%) had C-reaction protein >8.0 mg/L, and 6 cases (7.2%) had slightly elevated aspartate transaminase and alanine aminotransferase. Among the 92 children aged 3-<18 years, 31 cases were unvaccinated, 34 cases received 1 dose, and 27 cases received 2 doses. The interval between the last vaccination and infection was 2.2 (0.6, 6.0) months; the interval between the last vaccination and infection in the 2-dose group was longer than that in 1-dose group (6.0 (4.5, 7.3) vs. 0.7 (0.3,2.0) months, Z=3.59, P<0.001).The risk of symptomatic infection was reduced by 45% (RR=0.55, 95% CI 0.35-0.87) with two-dose vaccination compared to non-vaccination in cases aged 3-<18 years. All these cases recovered completely. Conclusions: Children infected with SARS-CoV-2 Omicron are usually mild or asymptomatic. Household transmission is the main pattern of infection with SARS-CoV-2 Omicron in children. Two-dose SARS-CoV-2 vaccination in children aged 3-<18 years can provide partial protection against disease caused by SARS-CoV-2 Omicron.

Decreases in Near-Road NO and NO2 Concentrations during the COVID-19 Pandemic in California

The COVID-19 pandemic and resulting shelter-in-place measures led to widespread adoption of remote work policies and temporary business closures or operation curtailments, disrupting typical commuting patterns. This study investigates how these sudden shifts in traffic patterns affected near-road NO and NO2 concentrations in California. We used (1) near-road air pollution data from the U.S. Environmental Protection Agency's AirNow database, (2) passenger and heavy-duty traffic data from the Caltrans Performance Monitoring System, and (3) weather data from MesoWest between January 1 and April 30 during the years 2017-2020 to model NO and NO2 concentrations as functions of highway traffic and meteorology. We then simulated NO and NO2 under business-as-usual traffic conditions and compared modeled data to observed values. Weekday passenger traffic significantly declined in Northern and Southern California by 29% and 24%, respectively. As a result, Northern and Southern California near-road locations experienced statistically significant declines in NO concentrations of 35% and 32% and in NO2 concentrations of 15% and 29%, respectively, compared to modeled estimates. As a natural experiment, our findings demonstrate that reduced vehicle activity significantly improved air quality, contributing to the body of evidence linking shelter-in-place measures and cleaner air.

Predictors of mechanical ventilation for COVID-19: combined data from three designated hospitals.

OBJECTIVE: Whether patients with COVID-19 require invasive mechanical ventilation (MV) is not yet clear. This article summarizes the clinical treatment process and clinical data of patients with COVID-19 and analyzes the predictive factors for mechanical ventilation for these patients. MATERIALS AND METHODS: A retrospective study was carried out from January 5, 2020, to March 23, 2020, including 98 patients with COVID-19 treated at three designated hospitals in Huangshi City, Hubei Province. Data collection included demographics, previous underlying diseases, clinical manifestations, laboratory examinations, imaging examination results, diagnosis, and prognosis. This study presents a summary of the patients' overall clinical characteristics and clarifies the predictive factors for MV in patients with COVID-19. RESULTS: There were 56 males and 42 females included in this study. The mortality rate was 26.53% (26/98). Fever, cough, and chest tightness were the most common symptoms (64.3%, 37.8%, and 12.2%, respectively). Thirty cases required MV, 30.61% of the total cases, and the mortality rate was 73.33%. The univariate comparison showed that dyspnea, acute physiologic assessment, chronic health evaluation (APACHE II) score, and the ratio between arterial blood oxygen partial pressure (PaO2) and oxygen concentration (FiO2) (P/F) were statistically different between the MV group and the non-MV group (p < 0.05). CONCLUSIONS: Results showed the following: dyspnea; increased white blood cell count; decreased platelets; lowered albumin levels; increased urea nitrogen; increased levels of myocardial enzymes Creatine Kinase (CK), Creatine Kinase, MB Form (CKMB) and lactate dehydrogenase (LDH); increased lactate, and lowered blood calcium tests. These findings may indicate that the patients have an increased probability of needing MV support. A cutoff value for the initial APACHE II score of >11.5 and the initial PaO2/FiO2 ratio of <122.17 mmHg should be considered for MV support for patients with COVID-19.