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Toward an adaptable deep-learning model for satellite-based wildfire monitoring with consideration of environmental conditions
No full textAs the majority of active fire detection algorithms have been developed for worldwide applications using only satellite data without considering observing conditions and environmental factors, their performance varies regionally. This study investigates the viability of an adaptable active fire detection model that is applicable to diverse environmental and observing conditions by fusing numerical model data and satellite images. The model was developed for various land cover and climate types using commonly utilized brightness temperature-related variables (key variables) and supporting variables (sub-variables), including solar zenith angle, satellite zenith angle (SAZ), relative humidity (RH), and skin temperature. A dual-module (DM) convolutional neural network (CNN) structure was adopted to consider the different properties of key variables and sub-variables, and a control without sub-variables was used to assess the impact of observing and environmental variables. The proposed model was further evaluated using existing polar-orbiting and geostationary satellite-based active fire products. The recall and precision of the control model were 0.80 and 0.98, respectively, and the standard deviation of recall for the five focus sites was 0.140. However, the DM CNN model was notable for its higher recall and robustness compared to the control model (recall of 0.84, precision of 0.97, and standard deviation of recall of 0.126). High RH and SAZ, and the day-night transition period contributed to the poor performance of the control model which was mitigated by the DM CNN model. In particular, the use of RH improved the recall of the model, and SAZ contributed to the reduction of performance variation. Our model also outperformed the two geostationary satellite-based active fire products in terms of detection capacity, resulting in a spatial distribution of active fires similar to that of polar-orbiting satellite-based active fire products
Scaling Design of Refrigerant-cooled Thermal-Hydraulic Integral Effect Test Facility for OPR1000
No full textThis study presents the design and preliminary verification of URILO-II, an experimental facility developed for integral effect test of nuclear safety technologies, while also providing a platform for thermal-hydraulic training through experimentation and observation. URILO-II was modeled on the OPR1000 power plant, the most commonly operated in Korea, scaled down to 1/8 height and 1/10 diameter. The refrigerant R134a was utilized to simulate two-phase flow of OPR1000 under 26.5 bar pressure.
Scaling analysis indicated that similarity for the two-phase flow was secured, but distortion in single-phase flow heat transfer and temperature distribution was identified due to the refrigerant???s low single-phase heat transfer rate. Adjustments in power or flow rate were deemed necessary for accurate accident simulations. To check scaling design values, Comparative and CFD analyses were conducted, with resulted in an 8.5 % lower pressure drop. Further research will extend preliminary verification through system code analysis
Ultrathin Self-Powered Heavy-Metal-Free Cu-In-Se Quantum Dot Photodetectors for Wearable Health Monitoring
No full textMechanically deformable photodetectors (PDs) are key device components for wearable health monitoring systems based on photoplethysmography (PPG). Achieving high detectivity, fast response time, and an ultrathin form factor in the PD is highly needed for next-generation wearable PPG systems. Self-powered operation without a bulky power-supply unit is also beneficial for point-of-care application. Here, we propose ultrathin self-powered PDs using heavy-metal-free Cu-In-Se quantum dots (QDs), which enable high-performance wearable PPG systems. Although the light-absorbing QD layer is extremely thin (similar to 40 nm), the developed PD exhibits excellent performance (specific detectivity: 2.10 x 10(12) Jones, linear dynamic range: 102 dB, and spectral range: 250-1050 nm at zero bias), which is comparable to that of conventional rigid QD-PDs employing thick Pb-chalcogenide QD layers. This is attributed to material and device strategies-materials that include Cu-In-Se QDs, a MoS2-nanosheet-blended poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer, a ZnO nanoparticle electron transport layer, Ag and ITO electrodes, and an ultrathin form factor (similar to 120 nm except the electrodes) that enable excellent mechanical deformability. These allow the successful application of QD-PDs to a wearable system for real-time PPG monitoring, expanding their potential in the field of mobile bioelectronics
Versatile layered double hydroxides and derived compositionally complex metal oxides for enhanced catalysis
No full textA general and facile approach to flower-like ZnO fabrication
No full textZnO nanosheets with nanograin distributions, high mesoporosity, and ultrathin thickness have garnered considerable attention owing to their intriguing properties, such as high surface-to-volume ratio and chemical reactivity. Although various methods for fabricating two-dimensional structures have been reported, the surfactant-assisted method is advantageous as it produces nanosheet structures at the water-air interface without affecting the crystal structure of the material. This study developed an innovative surfactant-assisted synthesis method to fabricate flower-like Zinc Oxide (f-ZnO) nanostructures. The synthesis, performed at a mild temperature of 70 degrees C, yields f-ZnO with high surface area-to-volume ratios and porous morphology. The f-ZnO demonstrates photoelectrochemical (PEC) performance due to increased interfacial contact with electrolytes and the formation of a wurtzite ZnO crystal structure. Additionally, f-ZnO exhibits sensitivity and selectivity as a hydrogen sulfide (H2S) gas sensor. This facile synthesis method opens new avenues for developing functional oxide nanostructures for sensors, catalysts, and energy storage systems
Rapid and selective actuation of 3D???printed shape???memory composites via microwave heating
No full textThree-dimensional (3D) printing allows the fabrication of complex shapes with high resolutions. However, the printed structures typically have fixed shapes and functions. Four-dimensional printing allows the shapes of 3D-printed structures to be transformed in response to external stimuli. Among the external stimuli, light has unique advantages for remote thermal actuation. However, light absorption in opaque structures occurs only near the sample surface; thus, actuation can be slow. Here, we propose and experimentally demonstrate the rapid and selective actuation of 3D-printed shape-memory polymer (SMP) composites using microwave heating. The SMP composite filaments are prepared using different amounts of graphite flakes. Microwave radiation can penetrate the entire printed structures and induce rapid heating. With sufficient graphite contents, the printed SMP composites are heated above their glass transition temperature within a few seconds. This leads to rapid thermal actuation of the 3D-printed SMP structures. Finally, dual-material 3D printing is demonstrated to induce selective microwave heating and control actuation motion. Our experiments and simulations indicate that microwave heating of SMP composites can be an effective method for the rapid and selective actuation of complex structures
The microstructural evolution of sputtered ZnO epitaxial films to stress-relaxed nanorods
No full textEpitaxial ZnO thin films and nanorods were grown on c-sapphire substrate by reactive sputtering of Zn in Ar-O2 atmosphere at substrate temperatures ranging from near room temperature to 700 degrees C. Scanning electron microscopy showed that with increase in substrate temperature, the morphology transformed from columnar films to vertically aligned ZnO nanorods. High resolution x-ray diffraction revealed improvement in crystalline and epitaxial quality with increase in substrate temperature, along with the decrease of edge dislocation density from 5 x 1012 cm-2 to 8 x 1010 cm- 2. The films grown near room temperature showed large hydrostatic strain (-6 x 10-3) and compressive intrinsic biaxial stress (-0.8 GPa), which decreased substantially with increase in substrate temperature, due to the desorption of excess oxygen and reduction in edge dislocation density. Above the substrate temperature of 500 degrees C, the intrinsic biaxial stress reversed from compressive to mildly tensile in the case of nanorods, due to the intrinsic tensile stress, originating from crystallite coalescence. Raman measurements correlate well with the changes in biaxial stress and confirm the improvements in crystallinity and epitaxial quality of nanorods grown at higher temperatures. Room temperature photoluminescence of the ZnO films showed weak near-band-edge emission, which enhanced drastically in the case of nanorods due to their superior microstructure and epitaxial quality