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Background After the detection of the first case of coronavirus disease 2019 (COVID-19) in South Korea on January 20, 2019, it has triggered three major outbreaks. To decrease the disease burden of COVID-19, social distancing and active mask wearing were encouraged, reducing the number of patients with influenza-like illness and altering the detection rate of influenza and respiratory viruses in the Korea Influenza and Respiratory Viruses Surveillance System (KINRESS). We examined the changes in respiratory viruses due to COVID-19 in South Korea and virological causes of the high detection rate of human rhinovirus (hRV) in 2020. Methods We collected 52 684 oropharyngeal or nasopharyngeal swab samples from patients with influenza-like illness in cooperation with KINRESS from 2016 to 2020. Influenza virus and other respiratory viruses were confirmed using real-time RT-PCR. The weekly detection rate was used to compare virus detection patterns. Results Non-enveloped virus (hRV, human bocavirus, and human adenovirus) detection rates during the COVID-19 pandemic were maintained. The detection rate of hRV significantly increased in 2020 compared with that in 2019 and was negatively correlated with number of COVID-19-confirmed cases in 2020. The distribution of strains and genetic characteristics in hRV did not differ between 2019 and 2020. Conclusions The COVID-19 pandemic impacted the respiratory virus detection rate. The extremely low detection rate of enveloped viruses resulted from efforts to prevent the spread of COVID-19 in South Korea. The high detection rate of hRV may be related to resistance against environmental conditions as a non-enveloped virus and the long period of viral shedding from patients.

Since a novel beta-coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in December 2019, there has been a rapid global spread of the virus. Genomic surveillance was conducted on samples isolated from infected individuals to monitor the spread of genetic variants of SARS-CoV-2 in Korea. The Korea Disease Control and Prevention Agency performed whole genome sequencing of SARS-CoV-2 in Korea for 1 year (January 2020 to January 2021). A total of 2,488 SARS-CoV-2 cases were sequenced (including 648 cases from abroad). Initially, the prevalent clades of SARS-CoV-2 were the S and V clades, however, by March 2020, GH clade was the most dominant. Only international travelers were identified as having G or GR clades, and since the first variant 501Y.V1 was identified (from a traveler from the United Kingdom on December 22nd, 2020), a total of 27 variants of 501Y.V1, 501Y.V2, and 484K.V2 have been classified (as of January 25th, 2021). The results in this study indicated that quarantining of travelers entering Korea successfully prevented dissemination of the SARS-CoV-2 variants in Korea.

Objectives Coronavirus Disease-19 (COVID-19) is a respiratory infection characterized by the main symptoms of pneumonia and fever. It is caused by the novel coronavirus severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2), which is known to spread via respiratory droplets. We aimed to determine the rate and likelihood of SARS-CoV-2 transmission from COVID-19 patients through non-respiratory routes. Methods Serum, urine, and stool samples were collected from 74 hospitalized patients diagnosed with COVID-19 based on the detection of SARS-CoV-2 in respiratory samples. The SARS-CoV-2 RNA genome was extracted from each specimen and real-time reverse transcription polymerase chain reaction performed. CaCo-2 cells were inoculated with the specimens containing the SARS-COV-2 genome, and subcultured for virus isolation. After culturing, viral replication in the cell supernatant was assessed. Results Of the samples collected from 74 COVID-19 patients, SARS-CoV-2 was detected in 15 serum, urine, or stool samples. The virus detection rate in the serum, urine, and stool samples were 2.8% (9/323), 0.8% (2/247), and 10.1% (13/129), and the mean viral load was 1,210 ± 1,861, 79 ± 30, and 3,176 ± 7,208 copy/μL, respectively. However, the SARS-CoV-2 was not isolated by the culture method from the samples that tested positive for the SARS-CoV-2 gene. Conclusion While the virus remained detectable in the respiratory samples of COVID-19 patients for several days after hospitalization, its detection in the serum, urine, and stool samples was intermittent. Since the virus could not be isolated from the SARS-COV-2-positive samples, the risk of viral transmission via stool and urine is expected to be low.

Memristive switching with digital set and multistep analog reset characteristics were demonstrated in tantalum oxide (Ta2O5)-based resistive random access memory (RRAM) devices using Ti and Ag top ...

OBJECTIVES: Following reports of patients with unexplained pneumonia at the end of December 2019 in Wuhan, China, the causative agent was identified as coronavirus (SARS-CoV-2), and the 2019 novel coronavirus disease was named COVID-19 by the World Health Organization. Putative patients with COVID-19 have been identified in South Korea, and attempts have been made to isolate the pathogen from these patients. METHODS: Upper and lower respiratory tract secretion samples from putative patients with COVID-19 were inoculated onto cells to isolate the virus. Full genome sequencing and electron microscopy were used to identify the virus. RESULTS: The virus replicated in Vero cells and cytopathic effects were observed. Full genome sequencing showed that the virus genome exhibited sequence homology of more than 99.9% with SARS-CoV-2 which was isolated from patients from other countries, for instance China. Sequence homology of SARS-CoV-2 with SARS-CoV, and MERS-CoV was 77.5% and 50%, respectively. Coronavirus-specific morphology was observed by electron microscopy in virus-infected Vero cells. CONCLUSION: SARS-CoV-2 was isolated from putative patients with unexplained pneumonia and intermittent coughing and fever. The isolated virus was named BetaCoV/Korea/KCDC03/2020.

As the coronavirus disease 2019 (COVID-19) pandemic continues, reinfection is likely to become increasingly common. However, confirming COVID-19 reinfection is difficult because it requires whole-genome sequencing of both infections to identify the degrees of genetic differences. Since the first reported case of reinfection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the Republic of Korea in April 2020, four additional cases were classified as suspected reinfection cases. We performed whole-genome sequencing of viral RNA extracted from swabs obtained at the initial infection and reinfection stages of these four suspected cases. The interval between initial infection and reinfection of all four suspected cases was more than 3 months. All four patients were young (10-29 years), and they displayed mild symptoms or were asymptomatic during the initial infection and reinfection episodes. The analysis of genome sequences combined with the epidemiological results revealed that only two of the four cases were confirmed as reinfection, and both were reinfected with the Epsilon variant. Due to the prolonged COVID-19 pandemic, the possibility of reinfections with SARS-CoV-2 variants is increasing, as reported in our study. Therefore, continuous monitoring of cases is necessary.

This study investigated the infectivity of severe acute respiratory syndrome (SARS-CoV-2) in individuals who re-tested positive for SARS-CoV-2 RNA after recovering from their primary illness. We investigated 295 individuals with re-positive SARS-CoV-2 polymerase chain reaction (PCR) test results and 836 of their close contacts. We attempted virus isolation in individuals with re-positive SARS-CoV-2 PCR test results using cell culture and confirmed the presence of neutralizing antibodies using serological tests. Viral culture was negative in all 108 individuals with re-positive SARS-CoV-2 PCR test results in whom viral culture was performed. Three new cases of SARS-CoV-2 infection were identified among household contacts using PCR. Two of the three new cases had had contact with the index patient during their primary illness, and all three had antibody evidence of past infection. Thus, there was no laboratory evidence of viral shedding and no epidemiological evidence of transmission among individuals with re-positive SARS-CoV-2 PCR test results.

A real-time reverse transcription polymerase chain reaction (RT-qPCR) assay that does not require Emergency Use Authorization (EUA) reagents was tested and validated for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the early stages of the outbreak of coronavirus disease 2019 (COVID-19) in the Republic of Korea. Early diagnosis of COVID-19 enables timely treatment and the implementation of public health measures. We validated the sensitivity, specificity, precision, linearity, accuracy, and robustness of the RT-qPCR assay for SARS-CoV-2 detection and compared its performance with that of several EUA-approved kits. Our RT-qPCR assay was highly specific for SARS-CoV-2 as demonstrated by not amplifying 13 other viruses that cause respiratory diseases. The assay showed high linearity using a viral isolate from a patient with known COVID-19 as well as plasmids containing target SARS-CoV-2 genes as templates. The assay showed good repeatability and reproducibility with a coefficient of variation of 3%, and a SARS-CoV-2 limit of detection of 1 PFU/mL. The RT-qPCR-based assay is highly effective and can facilitate the early diagnosis of COVID-19 without the use of EUA-approved kits or reagents in the Republic of Korea.

Background/Aims: Type 2 autoimmune pancreatitis (AIP) has been considered extremely rare in East Asia. This study aimed to clarify the prevalence, clinical characteristics and radiological findings of type 2 AIP highlighting patients presenting as acute pancreatitis in a single center. Methods: Type 2 AIP patients were classified according to International Consensus Diagnostic Criteria. Radiological findings were compared between type 2 AIP presenting as acute pancreatitis and gallstone pancreatitis. Results: Among 244 patients with AIP, 27 (11.1%) had type 2 AIP (definite, 15 [55.5%] and probable 12 [44.5%]). The median age of patients with type 2 AIP was 29 years (interquartile range, 20 to 39 years). Acute pancreatitis was the most common initial presentation (n=17, 63%) while obstructive jaundice was present in only one patient. Ulcerative colitis (UC) was associated with type 2 AIP in 44.4% (12/27) of patients. Radiological pancreatic imaging such as delayed enhancement of diffusely enlarged pancreas, homogeneous enhancement of focal enlargement/mass, absent/minimal peripancreatic fat infiltration or fluid collection, and multifocal main pancreatic duct narrowings were helpful for differentiating type 2 AIP from gallstone pancreatitis. During follow-up (median, 32.3 months), two patients (2/25, 8%) experienced relapse. Conclusions: In South Korea, type 2 AIP is not as rare as previously thought. Overall, the clinical profile of type 2 AIP was similar to that of Western countries. Type 2 AIP should be considered in young UC patients with acute pancreatitis of uncertain etiology. (Gut Liver 2019;13:461-470)

Background: As of February 21, 2021, 86,992 cases of coronavirus disease 2019 (COVID-19) were confirmed in the Republic of Korea, with 1,557 deaths and 85,435 cases discharged from isolation. This study investigated the infectivity of individuals with COVID-19 who were retested and found to be severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA-positive after recovering from their primary illness. Methods: We investigated 295 individuals with recurrent SARS-CoV-2 positive results, and 836 of their close contacts. We attempted virus isolation in 108 individuals with recurrent SARS-CoV-2 positivity using cell culture and confirmed the presence of neutralizing antibodies by means of serological tests. Findings: The average age was 45·2 years (range, 1–95 years) and 64% were female. At the time of retesting, 55·6% were asymptomatic, and symptoms included cough (18·0%), expectoration (11·2%), sore throat (10·8%), and fever (9·2%). The reasons for retesting were screening (46%), persistent symptoms (37·6%), and new contact with a confirmed COVID-19 case (9·5%). Virus isolation was attempted in 108 individuals with recurrent SARS-CoV-2 positivity, and all tested negative. Three new cases were identified among household contacts based on SARS-CoV-2 polymerase chain reaction testing. Two of the three new cases had had contact with the index patient during their primary illness, and all three had antibody evidence of past infection. Interpretation: There was no laboratory evidence of viral shedding and no epidemiological evidence of transmission among individuals with recurrent positivity. Funding Statement: This study was funded by the Korea Disease Control and Prevention Agency (No. 4800-4837-301). Declaration of Interests: The authors declare no conflicts of interest related to the study. Ethics Approval Statement: The study was approved by the KDCA Institutional Review Board (2020-03-01-P-A). The board waived the requirement for written informed consent.

The resistive switching characteristics of MnO and CeO2 layers with a large resistance ratio (> 105) were demonstrated. The Ag/MnO/CeO2/Pt devices with heterostructures were fabricated. The bipolar resistive switching behaviors were caused by the formation and disruption of conducting filaments in the switching layers. In CeO2 layer, the formation and rupture of conducting filaments was attributed to the reduction-oxidation reaction of CeO2 and CeO2 − x. The conduction mechanisms of ohmic conduction and Schottky emission had been investigated for resistance switching mechanism.

The prevalence of eight respiratory viruses detected in patients with acute respiratory infections (ARIs) in Korea was investigated through analysis of data recorded by the Korea Influenza and Respiratory Viruses Surveillance System (KINRESS) from 2013 to 2015. Nasal aspirate and throat swabs specimens were collected from 36 915 patients with ARIs, and viral nucleic acids were detected by real-time (reverse-transcription) polymerase chain reaction for eight respiratory viruses, including human respiratory syncytial viruses (HRSVs), influenza viruses (IFVs), human parainfluenza viruses (HPIVs), human coronaviruses (HCoVs), human rhinovirus (HRV), human adenovirus (HAdV), human bocavirus (HBoV), and human metapneumovirus (HMPV). The overall positive rate of patient specimens was 49.4% (18 236/36 915), 5% of which carried two or more viruses simultaneously. HRV (15.6%) was the most predominantly detected virus, followed by IFVs (14.6%), HAdV (7.5%), HPIVs (5.8%), HCoVs (4.2%), HRSVs (3.6%), HBoV (1.9%), and HMPV (1.6%). Most of the ARIs were significantly correlated with clinical symptoms of fever, cough, and runny nose. Although HRV and HAdV were frequently detected throughout the year in patients, other respiratory viruses showed apparent seasonality. HRSVs and IFVs were the major causative agents of acute respiratory diseases in infants and young children. Overall, this study demonstrates a meaningful relationship between viral infection and typical manifestations of known clinical features as well as seasonality, age distribution, and co-infection among respiratory viruses. Therefore, these data could provide useful information for public health management and to enhance patient care for primary clinicians.

Drop structure is a key hydraulic structure used in river improvement projects for flood control purposes. However, as demand for riparian construction techniques with environmental considerations is increasing both domestically and internationally, discontinuation of aquatic organisms as a result of high head is raised as a serious issue associated with the existing drop structures. Accordingly, it has become necessary to install a drop structure with a mild slope rather than the existing drop structures with high head, so that the structure can function as a migration channel for fish, which is severed by the existing drop structures, and also improve surrounding landscapes. In this study, which was initiated based on the necessity as such, a drop structure of mild slope was defined as sloping weir and flow characteristics under different conditions were analyzed through a hydraulic experiment. Focusing on efficiency according to energy dissipation that takes place according to different gradients of sloping weir, particle sizes of riverbed materials and the effect of hydraulic jump occurring at the downstream of a structure, this study aimed at identifying flow characteristics according to the conditions of sloping weirs. Thehydraulic experimentwas carried out on a variable-slope channel measuring 0.6 m in width and 20.0 m in length. As for riverbed materials, materials with two particle sizes (16 mm and 25 mm) were selected. For the experiment, models with different slope ratios to the structure, such as 1V:2H, 1V:3H and 1V:4H, were created. For flow conditions and hydraulic jump locations, an amount of water satisfying four water level conditions by stage was flown according to water level at the inlet area. Then, eight points were selected from inlet area, drop area, jet flow area and downstream area by controlling water level at the downstream area and adjusting the location of hydraulic jump occurrence. Water level (y), flow velocity (V), length of hydraulic jump (Lr) and distance of hydraulic jump occurrence (Lj) were measured at the eight points.

Recent development of computing power and theoretical advances in computational fluid dynamics have made possible numerical simulations of water waves with full Navier-Stokes equations. In this study, an internal wave maker using the mass source function approach was combined with the level set finite element method for generation of waves. The model is first applied to the two-dimensional linear wave generation and propagation. Then, it is applied to the three-dimensional simulation of the same problem. To effectively utilize computational resources and enhance the speed of execution, parallel algorithms are developed and applied for the three-dimensional problem. The results of numerical simulations are compared with theoretical values and good agreements are observed.

Objectives To monitor antiviral drug resistance among seasonal influenza viruses isolated in Korea during the 2008–2009 influenza season, we examined influenza isolates collected through Korea Influenza Surveillance Scheme for antiviral drug susceptibility. Methods For genetic analysis of antiviral drug resistance, the matrix (M2) and neuraminidase (NA) genes of each isolate were amplified by reverse transcription-polymerase chain reaction and followed by nucleotide sequencing. For phylogenetic analyses, the sequences of hemagglutinin (HA) and NA genes of each isolate were aligned using multiple alignment program. For phenotypic analysis of antiviral drug resistance, drug susceptibilities against M2 inhibitor (amantadine) and NA inhibitors (oseltavimir and zanamivir) were determined by virus yield reduction assay and fluorometric NA inhibition assay, respectively. Results In Korea, the resistant influenza viruses against oseltamivir were first detected in sealsonal influenza A(H1N1) viruses on Week 48 of 2008. Since then, the number of oseltamivir-resistant A(H1N1) viruses was continuously increased and had reached the highest peak on Week 52 of 2008. 533 (99.8%) of 534 A(H1N1) viruses were resistant to oseltamivir and all of them harbored the H275Y mutation in the NA gene during the 2008–2009 season. The oseltamivir resistance identified by sequencing was confirmed by NA inhibition assay. Genetic analysis based on HA gene of the resistant A(H1N1) viruses revealed that the viruses were identified as A/Brisbane/10/2007-like strain which was vaccine strain for the 2008–2009 season. Conclusions The oseltamivir-resistant A(H1N1) viruses were first emerged in Europe in November 2007 and then circulated globally. One year later, the oseltamivir-resistant A(H1N1) viruses were first detected in Korea in November 2008 and continued circulating until the Week 7 of 2009 during the 2008–2009 season. Considering the pandemic preparedness, it should be continued to monitor the emergence and the characterization of antiviral drug resistant influenza viruses.

A wetting and drying(WAD) scheme was introduced in KU-RLMS which is a two-dimensional depth-averaged unsteady model, and applicability tests for wetting and drying were performed in this study. WAD scheme in the model uses a mathematically less elegant but numerically easier method to test for dry or wet cells at each time step, then to apply blocking conditions for fluxes at cells` interfaces. WAD scheme introduced in the model was verified against an analytical solution in a frictionless parabolic basin. It was found that there occurs a little phase difference between analytical and numerical solution and little decrease of amplitude of numerical result. I used three test channels having a linear sloping bottom topography, a stepwise bottom topography, and a stepwise, a bumpy and bowl-shaped bottom topography. It could be found that numerical simulation results in test channels have similar shapes of Balzano[4] and Oey[15].

The fabrication of a manganese oxide and cerium oxide bilayer structure with a 5 × 5 crossbar array was demonstrated. The resistive switching characteristics of Ag/MnO/CeO2/Pt devices were investigated. The devices showed stable forming-free bipolar resistive switching properties with high resistance ratio (>105–6). Resistive switching phenomena were ascribed to the formation and rupture of oxygen-deficient conductive filaments. The mechanisms of ohmic and Schottky conductions were investigated to determine the resistance switching mechanism.

Tri-state resistive switching characteristics of bilayer resistive random access memory devices based on manganese oxide (MnO)/tantalum oxide (Ta2O5) have been studied. The current–voltage (I–V) characteristics of the Ag/MnO/Ta2O5/Pt device show tri-state resistive switching (RS) behavior with a high resistance state (HRS), intermediate resistance state (IRS), and low resistance state (LRS), which are controlled by the reset process. The MnO/Ta2O5 film shows bipolar RS behavior through the formation and rupture of conducting filaments without the forming process. The device shows reproducible and stable RS both from the HRS to the LRS and from the IRS to the LRS. In order to elucidate the tri-state RS mechanism in the Ag/MnO/Ta2O5/Pt device, transmission electron microscope (TEM) images are measured in the LRS, IRS and HRS. White lines like dendrites are observed in the Ta2O5 film in both the LRS and the IRS. Poole–Frenkel conduction, space charge limited conduction, and Ohmic conduction are proposed as the dominant conduction mechanisms for the Ag/MnO/Ta2O5/Pt device based on the obtained I–V characteristics and TEM images.

The resistive random access memory (RRAM) devices with heterostuctures have been investigated due to cycling stability, nonlinear switching, complementary resistive switching and self-compliance. The heterostructured devices can modulate the resistive switching (RS) behavior appropriately by bilayer structure with a variety of materials. In this study, the bipolar resistive switching characteristics of the bilayer structures composed of Ta2O5 and Ag2Se, which are transition-metal oxide (TMO) and silver chalcogenide, were investigated. The bilayer devices of Ta2O5 deposited on Ag2Se (Ta2O5/Ag2Se) and Ag2Se deposited on Ta2O5 (Ag2Se/Ta2O5) were fabricated for investigation of the RS characteristics by stacking sequence of Ta2O5 and Ag2Se. All operating voltages were applied to the Ag top electrode with the Pt bottom electrode grounded. The Ta2O5/Ag2Se device showed that a negative voltage sweep switched the device from high resistance state (HRS) to low resistance state (LRS) and a positive voltage sweep switched the device from LRS to HRS. On the contrary, for the Ag2Se/Ta2O5 device a positive voltage sweep switched the device from HRS to LRS, and a negative voltage sweep switched it from LRS to HRS. The polarity dependence of RS was attributed to the stacking sequence of Ta2O5 and Ag2Se. In addition, the combined heterostructured device of both bilayer stacks, Ta2O5/Ag2Se and Ag2Se/Ta2O5, exhibited the complementary switching characteristics. By using threshold switching devices, sneak path leakage can be reduced without additional selectors. The bilayer heterostructures of Ta2O5 and Ag2Se have various advantages such as self-compliance, reproducibility and forming-free stable RS. It confirms the possible applications of TMO and silver chalcogenide heterostructures in RRAM.

Electrical properties of silver selenide (Ag 2 Se) thin film, which is a thickness of 500 nm, were studied using conducting atomic force microscopy (c-AFM). A resistive switching was observed in the sweep voltage range from −7 to +7 V at room temperature. In addition, the Ag/Ag 2 Se/Au structure was compared with the Ag 2 Se/Au structure. It was considered that the resistive switching behavior may cause Ag filaments. The typical resistive characteristics of the Ag 2 Se thin film were presented, and the mechanism was discussed.

ObjectivesWe aimed to evaluate the pathogenesis and chronologic localization of human influenza A (H1N1) virus in experimentally infected cotton rats.MethodsThe animals were intranasally inoculated with 107 plaque-forming units of A/Solomon Islands/3/2006 (H1N1) influenza virus and evaluated for pathogenicity for a period of 28 days. Virus replication kinetics and pathological properties were assessed chronologically. Acute antiviral responses were evaluated by mean of real-time polymerase chain reaction.ResultsCotton rats infected with A/Solomon Islands/3/2006 virus lost weight until 6 days post-inoculation (DPI) and showed decreased activity until 3 DPI. At necropsy, focal areas of redness and consolidation of lungs were evident at 1, 2, and 3 DPI. Lung histopathology showed moderate to severe interstitial pneumonia, alveolitis and bronchiolitis. Influenza A specific viral protein was detected in bronchiolar epithelial cells, alveolar septa and pneumocytes. Influenza viruses were recovered from the lungs during the early period of infection and the titer peaked at 1 DPI. Viral proteins were detected from 4 hours to 6 hours DPI. These trends correlate with the up-regulation of mRNA expression of the IFN-α, Mx1, and Mx2 genes that play critical roles in the anti-influenza response at the early stage of infection.ConclusionOur results provide evidence that supports the use of cotton rats for the study of influenza virus pathogenesis and the immune response.