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Aerosol Layer Height Retrieval Over Ocean From the Advanced Himawari Imager Using Spectral Reflectance Sensitivity
No full textAerosol layer height (ALH) has been retrieved using multi-angle observations or the O2???O2 and O2???A/B absorption bands. This study attempted to retrieve ALH using the Advanced Himawari Imager (AHI), a single passive imager onboard Himawari-8 and -9. ALH retrieval using geostationary Earth orbit (GEO) satellites is advantageous for monitoring diurnal changes in ALH and understanding long-range transport. Before retrieving the ALH, the aerosol optical properties (AOPs) are retrieved using the green-near infrared (NIR) band, which is relatively insensitive to aerosol height. The retrieved AOPs are used as input to the radiative transfer calculation to compute the top-of-atmosphere (TOA) reflectance of a highly sensitive band (the blue band in this study). Then, the ALH is retrieved using the observed and calculated TOA reflectances. Since the retrieval accuracy of the aerosol optical depth (AOD) is better over the ocean, the retrieval was performed only over the ocean during the Korea???United States Air Quality Study (KORUS-AQ) campaign period. The retrieved ALH was validated using the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and high-spectral-resolution Lidar (HSRL)
Chemistry-informed machine learning: Using chemical property features to improve gas classification performance
No full textChemical recognition using machine learning based on detection by gas sensors relies on the accuracy and sensitivity of the sensors at capturing the key features of target classes. In some cases, however, the electronic signal transduced from the detection of analytes does not completely represent the key attributes, resulting in inaccurate classification results when trained from signal data alone. To overcome this shortcoming, we propose a novel ???chemistry-informed??? machine learning framework composed of two modules. From available sensor response data, Module 1 identifies and predicts the chemical properties of the analytes that give rise to the sensitivity and selectivity of the sensors, and Module 2 performs final classifications using the dataset concatenating predicted chemical properties and raw sensor responses. To evaluate the performance and generalizability of our methodology, we conducted experiments with three gas sensor array datasets for gas detection. In all the cases, the performance of gas species classification was improved when the raw features were combined with the predicted chemical property features. The main contribution of our framework is that it bridges the gap between the gas sensor signals and the target analytes, thereby improving classification performance beyond that of models trained exclusively on sensor response data
Synthesis of polyfunctional amines as curing agents and its effect on mechanical property of epoxy polymers
No full textA curing agent is required to cure an epoxy resin, but a few curing agents also improve the mechanical properties of the resin. In addition, it is rare to find hardeners containing multiple amines, which can be used to form high crosslink densities. In this study, two different curing agents with six amine functional groups each were synthesized via a two-step reaction. In the first step, isophorone diamine (IPDI) was reacted with two equivalents of pentaerythritol triacrylate (PETA). The resulting IPDI-PETA2 was reacted with ethylene diamine and 4,4 '-diaminodiphenyl sulfone to form two amine curers with six amines each-IPDI-PETA2-ED (ED) and IPDI-PETA2-DDS (DDS). Both amines were added in varying amounts to an epoxy composition consisting of dicyandiamide and 2-methylimidazole to improve the mechanical properties compared with a reference epoxy composition. Mechanical studies showed that an epoxy composition containing 5% IPDI-PETA2-DDS improved the flexural strength by 34% and impact strength by 36.7%. Furthermore, adding 5% IPDI-PETA2-ED to the epoxy composition increased the flexural strength by 39.7%, to 197 MPa and the impact strength by 38.8% to 68 J/m. These results highlight the potential of curing agents containing multiple amines for improving the mechanical properties of epoxy resins
Perovskite/Silicon Tandem Solar Cells: Choice of Bottom Devices and Recombination Layers
No full textPerovskite/silicon tandem solar cells have been intensively studied in recent years, and their efficiencies have rapidly increased owing to the numerous efforts in this field. A question about which type of silicon solar cell is the most suitable subcell in tandem devices emerges. Herein, three attractive silicon solar cells are summarized, including passivated-emitter rear-cell (PERC), tunnel oxide passivated contact (TOPCon), and heterojunction (HJT) cells. Their structures and features are elucidated for a clear understanding of the mechanism and potential of optimum performance. Moreover, the characteristics and performance of perovskite/ silicon tandem cells with PERC, TOPCon, and HJT subcells are contrasted and discussed. The significant contribution of the passivation layer and structure design on both sides to photovoltaic properties of tandem devices is emphasized. Especially, the recombination layer between two subcells is analyzed in depth in terms of material chemistry, light absorption, and charge transport with a review on preparing the optimized structure
Evolution of Zr Nodes in Metal-Organic Frameworks
No full textNew secondary building units (SBUs) in metal???organic frameworks (MOFs) open opportunities for the rational design of new MOF structures and their emerging properties.
Zr-based MOFs are one of the representative classes of MOFs, featuring high chemical stability, various topological structures, and practical applications. Recently, the number of new Zr SBUs is rising, while the first type of Zr SBU (Zr6) has been exclusive for a long time. Several new Zr SBUs exhibit higher performance than that of Zr6 in catalytic and adsorptive properties.
Before the discovery of several new Zr MOF SBUs, their molecular counterparts (Zr molecular clusters) have been reported. A survey on unlooked Zr molecular clusters unveils their diverse structural types. Understanding Zr molecular clusters will provide important clues to access future Zr-based MOFs.
The predefined geometries of metal???organic framework (MOF) building blocks, which consist of secondary building units (SBUs) and organic linkers, are integral to the rational design of new structures. In contrast to that of organic linkers, access to new SBUs is a daunting challenge because of their complex chemistry during MOF synthesis. Here, we present novel opportunities for molecular clusters to bring future SBUs in MOF chemistry. This opinion article summarizes recently emerging structural types of Zr SBUs and provides an understanding of Zr molecular clusters, suggesting them as new SBU candidates. A structural library of Zr molecular clusters will accelerate the discovery of new Zr-based MOFs and motivate similar analysis on various classes of MOFs
Feasibility of moxifloxacin and proflavine dual fluorescence imaging for detecting gastrointestinal neoplastic lesions: A prospective study
No full textObjectivesHigh-contrast and high-resolution imaging techniques would enable real-time sensitive detection of the gastrointestinal lesions. This study aimed to investigate the feasibility of novel dual fluorescence imaging using moxifloxacin and proflavine in the detection of neoplastic lesions of the human gastrointestinal tract. MethodsPatients with the colonic and gastric neoplastic lesions were prospectively enrolled. The lesions were biopsied with forceps or endoscopically resected. Dual fluorescence imaging was performed by using custom axially swept wide-field fluorescence microscopy after topical moxifloxacin and proflavine instillation. Imaging results were compared with both confocal imaging with cell labeling and conventional histological examination. ResultsTen colonic samples (one normal mucosa, nine adenomas) from eight patients and six gastric samples (one normal mucosa, five adenomas) from four patients were evaluated. Dual fluorescence imaging visualized detail cellular structures. Regular glandular structures with polarized cell arrangement were observed in normal mucosa. Goblet cells were preserved in normal colonic mucosa. Irregular glandular structures with scanty cytoplasm and dispersed elongated nuclei were observed in adenomas. Goblet cells were scarce or lost in the colonic lesions. Similarity analysis between moxifloxacin and proflavine imaging showed relatively high correlation values in adenoma compared with those in normal mucosa. Dual fluorescence imaging showed good detection accuracies of 82.3% and 86.0% in the colonic and the gastric lesions, respectively. ConclusionsHigh-contrast and high-resolution dual fluorescence imaging was feasible for obtaining detail histopathological information in the gastrointestinal neoplastic lesions. Further studies are needed to develop dual fluorescence imaging as an in vivo real-time visual diagnostic method
Buoyant heat transfer of nanofluids in a vertical porous annulus: a comparative study of different models
No full textPurposeThis study aims to numerically study the buoyant convective flow of two different nanofluids in a porous annular domain. A uniformly heated inner cylinder, cooled outer cylindrical boundary and adiabatic horizontal surfaces are considered because of many industrial applications of this geometry. The analysis also addresses the comparative study of different porous media models governing fluid flow and heat transport. Design/methodology/approachThe finite difference method has been used in the current simulation work to obtain the numerical solution of coupled partial differential equations. In particular, the alternating direction implicit method is used for solving transient equations, and the successive line over relaxation iterative method is used to solve time-independent equation by choosing an optimum value for relaxation parameter. Simpson's rule is adopted to estimate average Nusselt number involving numerical integration. Various grid sensitivity checks have been performed to assess the sufficiency of grid size to obtain accurate results. In this analysis, a general porous media model has been considered, and a comparative study between three different models has been investigated. FindingsNumerical simulations are performed for different combinations of the control parameters and interesting results are obtained. It has been found that the an increase in Darcy and Rayleigh numbers enhances the thermal transport rate and strengthens the nanofluid movement in porous annulus. Also, higher flow circulation rate and thermal transport has been detected for Darcy model as compared to non-Darcy models. Thermal mixing could be enhanced by considering a non-Darcy model. Research limitations/implicationsThe present results could be effectively used in many practical applications under the limiting conditions of two-dimensionality and axi-symmetry conditions. The only drawback of the current study is it does not include the three-dimensional effects. Practical implicationsThe results could be used as a first-hand information for the design of any thermal systems. This will help the design engineer to have fewer trial-and-run cases for the new design. Originality/valueA pioneering numerical investigation on the buoyant convective flow of two different nanofluids in an annular porous domain has been carried out by using a general Darcy-Brinkman-Forchheimer model to govern fluid flow in porous matrix. The results obtained from current investigation are novel and original, with numerous practical applications of nanofluid saturated porous annular enclosure in the modern industry
Pollution characteristics of PM2.5 during high concentration periods in summer and winter in Ulsan, the largest industrial city in South Korea
No full textHigh PM2.5 episodes frequently occur in Northeast Asia, and the source-receptor relationship for PM2.5 in megacities is a critical issue. As the largest industrial city in South Korea, Ulsan suffers from frequent high PM2.5 episodes. However, studies on the long-range atmospheric transport (LRAT), local emissions, and secondary formation of PM2.5 in Ulsan have been limited. In this study, the characteristics of high PM2.5 episodes in Ulsan were interpreted using hourly data for PM2.5 components. The periods with the highest PM2.5 concentrations in winter 2014 (February 24-26; 99.3 +/- 18.6 mu g/m(3)) and summer 2014 (June 24-27; 49.9 +/- 12.3 mu g/m(3)) were designated as Pollution Periods 1 and 2, respectively. In general, secondary inorganic ions (SO42 , NO3- and NH4+; SNA) were generated by the liquid phase reaction of water-soluble materials during winter, and sulfate and secondary organic aerosols were mainly formed via photochemical reactions during summer. During Pollution Period 1, the concentrations of sulfate, organic carbon, and elemental carbon sharply increased, and three major sources were identified: (1) LRAT from fossil fuel and biomass burning in eastern China and North Korea, (2) the influence of petrochemical and non-ferrous industrial facilities in Ulsan, and (3) enhanced secondary formation of ammonium sulfate and organic aerosols due to air stagnation. During Pollution Period 2, the concentration of SNA and heavy metals sharply increased, and three pollution sources were identified: (1) the influence of local industrial facilities and ship emissions, (2) external inflow from thermal power stations and national industrial facilities in southern coastal cities, and (3) secondary organic and inorganic formation. In this study, the reasons for the high winter and summertime PM2.5 events in Ulsan were more clearly understood, which can be the basis for the establishment of PM2.5 management policies that consider LRAT, local primary emissions, and secondary formation
Semi-mechanistic analysis of emergency planning zones for 20 MWe lead-cooled fast reactor by hypothetical accidents during Korea's arctic exploration
No full textSmall modular reactors or micro modular reactors have been considered as an alternative power source for merchant ships because of minimal carbon emission and a long lifecycle without refueling. Ahead of the operation, however, their emergency planning zones (EPZs) should be optimally set and approved to ensure both radiological safety and cost efficiency in case of nuclear accidents. Thus, the required size of EPZs was analyzed based on semi-mechanistic assumptions for hypothetical accidents with MicroURANUS, a micro modular fast reactor type of 20-MW lead-bismuth-cooled, used to power an icebreaker during Korea's Arctic missions. For meteorological data, actual icebreaker data acquired in 2020s Artic exploration were utilized. The results showed that EPZ sizes, rationalized in terms of stability class, wind directions, and inherent radioprotection design, ranged within the assumed icebreaker boundary. When comparing various regulations among countries and the International Atomic Energy Agency, dose criteria of Korea (10 mSv/2 d) were found to be strictest. Since major contribution to the whole-body dose was from noble gases (over 96%), a high-quality air filtration system in addition to external shielding would significantly reduce hazards. The emergency situation could be successfully controlled without evacuation and sheltering, avoiding overestimated socioeconomic costs