Amorphous silicon quantum dots (a-Si QDs) were grown in a silicon nitride film by plasma enhanced chemical vapor deposition. Transmission electron micrographs clearly demonstrated that a-Si QDs were formed in the silicon nitride. Photoluminescence and optical absorption energy measurement of a-Si QDs with various sizes revealed that tuning of the photoluminescence emission from 2.0 to 2.76 eV is possible by controlling the size of the a-Si QD. Analysis also showed that the photoluminescence peak energy E was related to the size of the a-Si QD, a (nm) by E(eV) = 1.56+2.40/a(2), which is a clear evidence for the quantum confinement effect in a-Si QDs.

Several studies have attempted to identify factors associated with longevity and maintenance of health in centenarians. In this study, we analyzed and compared the gut microbiota of centenarians in longevity villages with the elderly and adults in the same region and urbanized towns. Fecal samples were collected from centenarians, elderly, and young adults in longevity villages, and the gut microbiota sequences of elderly and young adults in urbanized towns of Korea were obtained from public databases. The relative abundance of Firmicutes was found to be considerably higher in subjects from longevity villages than those from urbanized towns, whereas Bacteroidetes was lower. Age-related rearrangement of gut microbiota was observed in centenarians, such as reduced proportions of Faecalibacterium and Prevotella, and increased proportion of Escherichia, along with higher abundances of Akkermansia, Clostridium, Collinsella, and uncultured Christensenellaceae. Gut microbiota of centenarians in rehabilitation hospitals were also different to those residing at home. These differences could be due to differences in diet patterns and living environments. In addition, phosphatidylinositol signaling system, glycosphingolipid biosynthesis, and various types of N-glycan biosynthesis were predicted to be higher in the gut microbiota of centenarians (corrected p < 0.05). These three metabolic pathways of gut microbiota can be associated with the immune status and healthy gut environment of centenarians. Although further studies are necessary to validate the function of microbiota between groups, this study provides valuable information on centenarians' gut microbiota.

The effects of indium segregation and hydrogen on the optical and structural properties of InGaN/GaN multiple quantum wells, grown by metalorganic chemical vapor deposition were investigated. Photoluminescence and high-resolution transmission electron microscopy analysis showed that two types of indium-rich regions can be formed in the InGaN well layers. Self-assembled quantum dot-like indium-rich regions were found in the well layer grown at a normal growth temperature. These regions behaved as luminescent centers, showing a maximum indium content at the center of indium-rich region. However, randomly-distributed indium-segregated regions, which formed near the upper interface of the InGaN well layers during the subsequent high-temperature annealing process led to the degradation of the optical properties by generating defects such as misfit dislocations. The use of hydrogen during the growth interruption was found to be very effective in suppressing the formation of indium-segregated regions in the InGaN well layers.

Few population-based studies have focused on the epidemiology and comorbidities of chronic urticaria (CU) or chronic spontaneous urticaria (CSU). The objective of this study was to obtain information on the epidemiology and comorbidities associated with CU and CSU in Korea. We conducted a cross-sectional analysis using a national health insurance database. An algorithm based on the International Classification of Diseases, 10th revision, was used for the identification of patients with CU and CSU, and an age-sex adjusted logistic regression model was used to assess the risk of comorbidities in these patients. The average annual prevalence rates of CU and CSU during the 4-year period between 2010 and 2013 were 3.08% and 1.40%, respectively. The prevalence rates of CU and CSU were higher in women than men (1:1.39 and 1:1.34, respectively) and peaked at 0-9 and 70-79 years, respectively. After adjustment for age and sex, the patients with CU and CSU were found to have a significantly higher prevalence rate of CU/CSU-related diseases, compared with those without CU (mean adjusted odds ratio, 8.46; 95% confidence interval, 8.10-8.83). Allergic rhinitis, drug allergies, asthma, thyroid diseases and cancers were the most common comorbidities. Stomach, thyroid, liver and prostate cancers were the most prevalent cancers. This study provides large epidemiological data on the prevalence rates of CU and CSU, and their comorbidities, in Korea. Patients with CU and CSU impose a higher burden, in terms of specific comorbidities, than those without CU.

IMPORTANCE Narrowband UV-B (NBUVB) phototherapy has been the mainstay in the treatment of vitiligo, but its long-term safety in terms of photocarcinogenesis has not been established.OBJECTIVES To investigate the risks of skin cancer and precancerous lesions among patients with vitiligo undergoing NBUVB phototherapy, based on the number of NBUVB phototherapy sessions. DESIGN, SETTING, AND PARTICIPANTS This nationwide population-based retrospective cohort study enrolled 60 321 patients with vitiligo 20 years or older between January 1, 2007, and December 31, 2017. Patients and outcomes were identified through nationwide cohort data from the Korean national health insurance claims database, and frequency matching by age and sex was performed. EXPOSURES The number of phototherapy sessions each patient received between 2008 and 2017. Patients were classified into 5 groups according to the number of phototherapy sessions (0 sessions, 20 105 patients; 1-49 sessions, 20 106 patients; 50-99 sessions, 9702 patients; 100-199 sessions, 6226 patients; and Ն200 sessions, 4182 patients). We also identifed patients who underwent at least 500 phototherapy sessions (717 patients). MAIN OUTCOMES AND MEASURES Primary outcomes were the development of actinic keratosis, Bowen disease, nonmelanoma skin cancer, or melanoma after enrollment. RESULTS Among the 60 321 patients with vitiligo in this study (33 617 women; mean [SD] age, 50.2 [14.9] years), the risks of Bowen disease (<50 sessions of phototherapy: hazard ratio [