We present first‐principles simulations of single grain boundary reflectivity of electrons in noble metals, Cu and Ag. We examine twin and non‐twin grain boundaries using non‐equilibrium Green's ...function and first principles methods. We also investigate the determinants of reflectivity in grain boundaries by modeling atomic vacancies, disorder, and orientation and find that both the change in grain orientation and disorder in the boundary itself contribute significantly to reflectivity. We find that grain boundary reflectivity may vary widely depending on the grain boundary structure, consistent with published experimental results. Finally, we examine the reflectivity from multiple grain boundaries and find that grain boundary reflectivity may depend on neighboring grain boundaries. This study raises some potential limitations in the independent grain boundary assumptions of the Mayadas–Shatzkes (MS) model.
We investigate the upper‐crustal seismic velocity structure in the Seoul metropolitan area, where about 20 million people live. The Chugaryeong fault zone (CFZ) is placed in this area, but the ...seismic hazard potential remains unclear. We conducted ambient noise tomography to illuminate the high‐resolution upper‐crustal structure in the Seoul metropolitan area. We analyzed continuous vertical seismic records for ∼5 months from a dense seismic array with 77 broadband stations. Group velocity dispersion curves and tomographic maps were extracted between 0.5 and 10 s periods. We inverted 3‐D group velocity tomography models up to a depth of ∼10 km from the group velocity maps. The shear‐wave velocity model is consistent with the geological features. High‐velocity anomalies at shallow depths are correlated with the surface topography and geology. The CFZ is located at a low velocity below the 5 km depth and presented as the simplified model. The large VS contrast regions are located beneath NS‐trending faults. The cross‐sections coincide with the near‐vertical strike‐slip faults in this area. In the southern region of the Seoul metropolitan area, low‐velocity anomalies correlate with high heat flow regions. Our results effectively suggest high resolution upper‐crustal structures and subsurface hidden faults in the urban area.
Plain Language Summary
The Chugaryeong fault zone (CFZ) runs across the Seoul metropolitan area, where more than 20 million people live. The Chugaryeong fault system was repeatedly reactivated in the Quaternary. This study investigates the upper crustal structures in the Seoul metropolitan area using ambient seismic tomography based on densely deployed seismic stations. The seismic velocity structures are correlated with surface topography and geology. Low velocities are present in the southern Seoul metropolitan area of high heat flows. Vertically consistent low shear‐wave velocity anomalies are observed at depths of 5–10 km in the CFZ. Lateral variations in seismic velocities reveal the fault structures, which is consistent with seismic activities. The lateral gradients of shear‐wave velocities illuminate the near‐vertical fault geometry. The upper‐crustal shear‐wave velocity model may provide information to assess seismic hazard potentials in the Seoul metropolitan area.
Key Points
High‐resolution upper‐crustal structures in urban region are derived from ambient noise tomography based on dense seismic stations
Ambient noise tomography reveals near‐vertical strike‐slip fault zones with low velocity anomalies in the Seoul metropolitan area
The fault zones run across the Seoul metropolitan area, producing earthquakes
Quaternary faults run across the Seoul metropolitan area that is the highest population region in the Korean Peninsula. Active fault identification and seismic hazard potential assessment are crucial ...for public safety. Densely deployed permanent and temporal seismic stations enabled us to detect micro to small earthquakes, allowing us to identify earthquake‐spawning faults in Seoul metropolitan area. The source parameters of 455 earthquakes in 2004–2020 are refined. The Gutenberg‐Richter b value is 0.94. Dominant focal depths are 4–15 km. The focal mechanism solutions of 64 earthquakes are determined using seismic‐wave polarities and amplitude ratios. Strike‐slip earthquakes are dominant in the region. Earthquakes are clustered around the Chugaryeong fault system. The dominant strikes of fault planes range from N20°E to N45°E in the northern and southern Seoul metropolitan areas, suggesting branch fault development locally. The earthquakes in middle‐northern Seoul present N‐S directional strike‐slip motions at depths ∼7.5 km along the Chugaryeong fault, suggesting seismically active near‐vertical faults subparallel with Chugaryeong fault.
Plain Language Summary
The Seoul metropolitan area is the largest population region in the Korean Peninsula. More than 20 million people live in the area where Quaternary faults run across. Historical literatures presented high seismic damages in the region. Active fault identification and seismic hazard potential assessment are crucial for public safety. Dense seismic stations were deployed to investigate the seismicity and earthquake‐spawning faults in the Seoul metropolitan area. We refined the source locations of 455 earthquakes in 2004–2020. The focal mechanisms solutions of 64 earthquakes were determined using the seismic‐wave polarities and amplitude ratios. Strike‐slip earthquakes are dominant in the region. The strikes of fault planes range from N20°E to N45°E in the northern and southern Seoul metropolitan areas. Branch faults appear to develop locally according to the ambient stress field. Microseismicity are clustered locally. The earthquakes in middle‐northern Seoul present N‐S directional strike‐slip motions at depths ∼7.5 km along the Chugaryeong fault. The Chugaryeong fault system appears to be seismically active.
Key Points
Earthquake‐spawning faults run across the Seoul metropolitan area
Chugaryeong fault behaves as a single continuous fault, producing earthquakes
Branch faults develop locally by the ambient stress field
The development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have ...been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness.
Fiber‐based implantable electronics are one of promising candidates for in vivo biomedical applications thanks to their unique structural advantages. However, development of fiber‐based implantable ...electronic devices with biodegradable capability remains a challenge due to the lack of biodegradable fiber electrodes with high electrical and mechanical properties. Here, a biocompatible and biodegradable fiber electrode which simultaneously exhibits high electrical conductivity and mechanical robustness is presented. The fiber electrode is fabricated through a facile approach that incorporates a large amount of Mo microparticles into outermost volume of a biodegradable polycaprolactone (PCL) fiber scaffold in a concentrated manner. The biodegradable fiber electrode simultaneously exhibits a remarkable electrical performance (≈43.5 Ω cm−1), mechanical robustness, bending stability, and durability for more than 4000 bending cycles based on the Mo/PCL conductive layer and intact PCL core in the fiber electrode. The electrical behavior of the biodegradable fiber electrode under the bending deformation is analyzed by an analytical prediction and a numerical simulation. In addition, the biocompatible properties and degradation behavior of the fiber electrode are systematically investigated. The potential of biodegradable fiber electrode is demonstrated in various applications such as an interconnect, a suturable temperature sensor, and an in vivo electrical stimulator.
A biodegradable fiber electrode with high electrical conductivity and strong mechanical robustness is fabricated using a surface‐embedding of Mo microparticles into a biodegradable fiber scaffold. The fiber electrode shows excellent biocompatibility and dissolution properties against biofluids. This study also provides several demonstrations of the fiber electrode such as an interconnect, suturable fiber temperature sensor, and in vivo electrical stimulator.
Germicidal ultraviolet light (GUV) systems are designed to control airborne pathogen transmission in buildings. However, it is important to acknowledge that certain conditions and system ...configurations may lead GUV systems to produce air contaminants including oxidants and secondary organic aerosols (SOA). In this study, we modeled the formation and dispersion of oxidants and secondary contaminants generated by the operation of GUV systems employing ultraviolet C 254 and 222 nm. Using a three-dimensional computational fluid dynamics model, we examined the breathing zone concentrations of chemical species in an occupied classroom. Our findings indicate that operating GUV 222 leads to an approximate increase of 10 ppb in O3 concentration and 5.2 μg·m–3 in SOA concentration compared to a condition without GUV operation, while GUV 254 increases the SOA concentration by about 1.2 μg·m–3, with a minimal impact on the O3 concentration. Furthermore, increasing the UV fluence rate of GUV 222 from 1 to 5 μW·cm–2 results in up to 80% increase in the oxidants and SOA concentrations. For GUV 254, elevating the UV fluence rate from 30 to 50 μW·cm–2 or doubling the radiating volume results in up to 50% increase in the SOA concentration. Note that indoor airflow patterns, particularly buoyancy-driven airflow (or displacement ventilation), lead to 15–45% lower SOA concentrations in the breathing zone compared to well-mixed airflow. The results also reveal that when the ventilation rate is below 2 h–1, operating GUV 254 has a smaller impact on human exposure to secondary contaminants than GUV 222. However, GUV 254 may generate more contaminants than GUV 222 when operating at high indoor O3 levels (>15 ppb). These results suggest that the design of GUV systems should consider indoor O3 levels and room ventilation conditions.
Background: Acupotomy is a type of acupuncture where a scalpel-shaped needle (miniscalpel needle) is used instead of a normal acupuncture needle to exfoliate adhesion sites or to relax entrapped ...regions. This study aimed to identify the descriptive characteristics of patients who received acupotomy treatment at a single Korean Medicine Clinic.Methods: This retrospective review analyzed the medical charts of patients who had received acupotomy at least once from August 2017 to December 2019 at a single Korean Medicine Clinic. The demographic characteristics, chief complaints, acupotomy treatment sites, and principal diagnosis codes were analyzed.Results: We identified 551 outpatients; the average age was 52 ± 14.26 years and 49.9% were male. The patients underwent an average of 8.47 sessions of acupotomy. Altogether, 35.91% of the acupotomy treatments were administered to the spinal regions, of which 60.01% were in the lumbar region. The codes related to the lumbar spinal condition/disease which were used most frequently. The chief complaints were dizziness, lumbar spinal stenosis, and Dupuytren’s contracture in patients over 60 years of age.Conclusion: This is the 1st analysis of acupotomy treatment patterns in Korea to date. Acupotomy is primarily administered in the treatment of spinal conditions/diseases, especially for those involving the lumbar region. Future studies are necessary to determine the clinical outcomes of patients who receive acupotomy treatment and the safety of this treatment.
The commercialization of graphene-based products is challenging, because many engineering and economical aspects have to be taken into consideration. A stronger collaboration between academia and ...industry would be beneficial for accelerating the process.The commercialization of graphene-based products is challenging, because many engineering and economical aspects have to be taken into consideration. A stronger collaboration between academia and industry would be beneficial for accelerating the process.
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