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Reanalyzing the relationship of tropical cyclone frequency and intensity affecting South Korea with the Pacific Decadal Oscillation
No full textTwo-Step Sequential Blade-Coating Large-Area FA-Based Perovskite Thin Film via a Controlled PbI2 Microstructure
Get PDFSolar cells, which are excellent alternatives to traditional fossil fuels, can efficiently convert sunlight into electricity. The intensive development of high-performance photovoltaic materials plays an important role in environmental protection and the utilization of renewable energy. Organic??? inorganic hybrid perovskite materials, with a formula of ABX3 (A = methylammonium (MA) or formamidinium (FA); B = Pb or Sn; X = Cl, I, or Br), have exhibited remarkable commercial prospects in high-performance photovoltaic devices owing to their long carrier diffusion length, excellent light absorption properties, high charge carrier mobility, and weak exciton binding energy. Recently, perovskite solar cells, fabricated using halide perovskite materials as light-absorbing layers, have achieved remarkable results; their certified power conversion efficiency has continuously improved and reached 25.7%. However, high-performance devices are usually fabricated using spin-coating methods with active areas below 0.1 cm2. Hence, long-term research goals include achieving a large-scale uniform preparation of high-quality photoactive layers. The current one-step preparation of perovskite films involves the nucleation-crystalline growth process of perovskite. Auxiliary processes, such as using an anti-solvent, are often required to increase the nucleation rate and density of the film, which is not suitable for industrial large-area preparation. Additionally, the large-area preparation of perovskite films by spin-coating will result in different film thicknesses in the center and edge regions of the film due to an uneven centrifugal force. This will cause intense carrier recombination in the thicker area of the film and weak light absorption in the thinner area, which will reduce the performance of the device. To address these problems, the development of a large-area fabrication method for high-performance perovskite light-absorbing layers is essential. In this study, a two-step sequential blade-coating strategy was developed to prepare the FA-based perovskite layer. In general, PbI2 easily forms a dense film; therefore, formamidinium iodide (FAI) cannot deeply penetrate to completely react with PbI2. The PbI2 residue is therefore detrimental to charge transportation. To fabricate the desired porous PbI2 film, tetrahydrothiophene 1-oxide (THTO) was introduced into the PbI2 precursor solution. By forming PbI2??THTO complexes, PbI2 crystallization is controlled, resulting in the formation of vertically packed PbI2 flaky crystals. These crystals provide nanochannels for easy FAI penetration. The 5 cm ?? 5 cm modules fabricated through this strategy achieved a high efficiency of 18.65% with excellent stability. This indicates that the two-step sequential blade-coating strategy has considerable potential for scaling up the production of perovskite solar cells
Achieving Both Ultrahigh Electrical Conductivity and Mechanical Modulus of Carbon Films: Templating-Coalescing Behavior of Single-Walled Carbon Nanotube in Polyacrylonitrile
Get PDFPromoting the feasibility of carbon films as electrode applications requires sufficient performances in view of both electrical and mechanical properties. Herein, carbon films with ultrahigh electrical conductivity and mechanical modulus are prepared by high temperature carbonization of polyacrylonitrile (PAN)/single-walled carbon nanotube (SWNT) nanocomposites. Achieving both performances is ascribed to remarkable graphitic crystallinity, resulting from the sequential templating???coalescing behavior of concentrated SWNT bundles (B-CNTs). While well-dispersed SWNTs (WD-CNTs) facilitate radial templating according to their tubular geometry, flattened B-CNTs sandwiched between carbonized PAN matrices induce vertical templating, where the former and latter produce concentric and planar crystallizations of the graphitic structure, respectively. After carbonization at 2500 ??C with the remaining WD-CNTs as microstructural defects, the flattened B-CNTs coalesce into graphitic crystals by zipping the surrounding matrix, resulting in high crystallinity with the crystal thicknesses of 27.4 and 39.4 nm for the (002) and (10) planes, respectively. For comparison, the graphene oxide (GO) containing carbon films produce a less-ordered graphitic phase owing to irregular templating, despite the geometrical consistency. Consequently, PAN/B-CNT carbon films exhibit exceptional electrical conductivity (40.7 ?? 104 S m???1) and mechanical modulus (38.2 ?? 6.4 GPa). Thus, controlling the templating???coalescing behavior of SWNTs is the key for improving final performances of carbon films
Reduced Potential Barrier of Sodium-Substituted Disordered Rocksalt Cathode for Oxygen Evolution Electrocatalysts
No full textCation-disordered rocksalt (DRX) cathodes have been viewed as next-generation high-energy density materials surpassing conventional layered cathodes for lithium-ion battery (LIB) technology. Utilizing the opportunity of a better cation mixing facility in DRX, we synthesize Na-doped DRX as an efficient electrocatalyst toward oxygen evolution reaction (OER). This novel OER electrocatalyst generates a current density of 10 mA cm(-2) at an overpotential (eta) of 270 mV, Tafel slope of 67.5 mV dec(-1), and long-term stability >5.5 days' superior to benchmark IrO2 (eta = 330 mV with Tafel slope = 74.8 mV dec(-1)). This superior electrochemical behavior is well supported by experiment and sparse Gaussian process potential (SGPP) machine learning-based search for minimum energy structure. Moreover, as oxygen binding energy (O-BE) on the surface closely relates to OER activity, our density functional theory (DFT) calculations reveal that Na-doping assists in facile O-2 evolution (O-BE = 5.45 eV) compared with pristine-DRX (6.51 eV)
A conceptual framework for designing blockchain technology enabled supply chains
No full textDespite the growing popularity of blockchain technology (BT) applications in a supply chain (SC), the academic literature has failed to offer a complete picture of BT embedded in SC, hereafter referred to as BT-enabled SC, while focusing on BT???s specifics. Against this backdrop, this paper aims to develop a conceptual framework by identifying BT???s multifaceted features and clarifying their roles in designing BT-enabled SCs. Specifically, we delve into BT???s extant definitions in business disciplines as a basis for identifying BT???s key attributes and elucidate how these attributes can be incorporated into the design of BT-enabled SCs by introducing the framework that encompasses the strategic, configural, and operational spheres. This paper contributes to clarifying BT???s conceptual boundary by framing BT as a stack of technologies and applications ??? seven dimensions. Based on seven dimensions, the proposed framework offers guidance on how to design BT-enabled SCs
Roslingifier: Semi-Automated Storytelling for Animated Scatterplots
No full textWe present Roslingifier, a data-driven storytelling method for animated scatterplots. Like its namesake, Hans Rosling (1948--2017), a professor of public health and a spellbinding public speaker, Roslingifier turns a sequence of entities changing over time---such as countries and continents with their demographic data---into an engaging narrative telling the story of the data. This data-driven storytelling method with an in-person presenter is a new genre of storytelling technique and has never been studied before. In this paper, we aim to define a design space for this new genre---data presentation---and provide a semi-automated authoring tool for helping presenters create quality presentations. From an in-depth analysis of video clips of presentations using interactive visualizations, we derive three specific techniques to achieve this: natural language narratives, visual effects that highlight events, and temporal branching that changes playback time of the animation. Our implementation of the Roslingifier method is capable of identifying and clustering significant movements, automatically generating visual highlighting and a narrative for playback, and enabling the user to customize. From two user studies, we show that Roslingifier allows users to effectively create engaging data stories and the system features help both presenters and viewers find diverse insights
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No full textDepartment of Electrical Engineeringclos
Ammonia synthesis by mechanochemical method under ambient conditions
No full textSchool of Energy and Chemical Engineering (Energy Engineering)clos