Background: Seroprevalence studies of coronavirus disease 2019 (COVID-19) from many countries have shown that the number of undiagnosed missing cases is much larger than that of confirmed cases, irrespective of seroprevalence levels. Considering the strategy of Korea entailing massive testing and contact tracing from the beginning of epidemic, the number of undiagnosed missing cases in Korea may be negligible. This study was conducted to estimate the seroprevalence of COVID-19 among individuals who were never diagnosed with COVID-19 in Daegu, the epicenter of COVID-19 epidemic in Korea. Methods: Serologic testing for immunoglobulin G antibody based on immunochromatographic assay was conducted in 103 patients and 95 guardians aged 18 to 82 years without any history of COVID-19 diagnosis, who visited outpatient clinics of a single university-affiliated hospital from May 25 to June 5, 2020. Results: The estimated seroprevalence was 7.6% (95% confidence interval, 4.3%-12.2%) with 15 positive cases. Among them, only one had a polymerase chain reaction (PCR)-confirmed case among their close contacts and 13 did not experience COVID-19-related symptoms. Seroprevalence was similar between patients and guardians. Based on this figure, the number of undiagnosed missing cases in Daegu was estimated to be a dozen times more than the number of confirmed cases based on PCR testing. Conclusion: Despite the limitation of a small and unrepresentative sample, this is the first study on seroprevalence of COVID-19 in Korea. Our study suggested that the number of undiagnosed missing cases was substantial even with the stringent strategy adopted in Korea, similar to that of other countries.

Terahertz time‐domain spectroscopy has been used to study the optical and dielectric properties of three chalcogenide glasses: Ge30As8Ga2Se60, Ge35Ga5Se60, and Ge10As20S70. The absorption coefficients α(ν), complex refractive index n(ν), and complex dielectric constants ɛ(ν) were measured in a frequency range from 0.3 THz to 1.5 THz. The measured real refractive indices were fitted using a Sellmeier equation. The results show that the Sellmeier equation fits well with the data throughout the frequency range and imply that the phonon modes of glasses vary with the glass compositions. The theory of far‐infrared absorption in amorphous materials is used to analyze the results and to understand the differences in THz absorption among the sample glasses.

Rationale: Several case reports about the diagnostic and therapeutic approaches of hemarthrosis after total knee arthroplasty using angiogram have been reported, owing to the probability of bleeding caused by vascular injuries. However, there were only few cases of spontaneous hemarthrosis of the knee joint in the elderly patient that have not undergone total knee arthroplasty that have been previously reported. Patients concerns: An 82-year-old male presented to our outpatient department with acute left knee pain. He had no history of trauma. The patient had under gone several times of therapeutic arthrocentesis for treatment of left knee joint effusion at a local clinic. Diagnosis: Arthroscopic examination was performed at the local clinic and was not able to reveal any focus of intra-articular bleeding. We consulted this case with the department of radiology to angiographically find out abnormalities of the genicular arteries. Angiographs showed hyper vascularity of the superior and inferior lateral genicular artery, and superior medial genicular artery. Intervention: One-step embolization using micro-catheter and 50 to 150 μm gelfoam particles was conducted. The hypervascular findings shown on angiogram were markedly subsided after embolization. Outcomes: Until 1 year after embolization, there were no signs of recurrence on outpatient follow-up sessions Lessons: Degenerative changes of the genicular arteries may be a cause of spontaneous knee joint hemarthrosis in the elderly patients. Angiographic diagnosis and treatment may be effective for such cases.

This study reviewed terahertz technologies of time domain spectroscopy, T-ray imaging, and high rate wireless data transfer. The main topics of the terahertz research area were investigation of materials and package modules for terahertz wave generation and detection, and setup of the terahertz system for time domain spectroscopy(TDS), T-ray imaging and sub-THz wireless communication. In addition to Poly-GaAs film as a photoconductive switching antenna material, a table-top scale for the THz-TDS/imaging system and terahertz continuous wave(CW) generation systems for sub-THz data transfer and narrow band T-ray imaging were designed. Dielectric properties of ferroelectric BSTO(BaxSr1-x TiO3) films and chalcogenide glass systems were characterized with the THz-TDS system at the THz frequency range. Package modules for terahertz wave transmitter/receiver(Tx/Rx) photoconductive antenna were developed.

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