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Fine particulate concentrations over East Asia derived from aerosols measured by the advanced Himawari Imager using machine learning
No full textFine particulate matter with a diameter below 2.5 lim (PM2.5) is deleterious to the cardiovascular and respiratory systems. It is often difficult to assess the effects of PM2.5 on human health over regions with limited ground monitoring sites, especially in East Asia. As an alternative, we estimated near-surface PM2.5 concentrations by analyzing Advanced Himawari Imager (AHI) Yonsei Aerosol Retrieval (YAER) products. This study incorporates daytime data for East Asia covering the Korean Peninsula, China, Japan, Southeast Asia, and southern Mongolia. We collocated AHI YAER product pixels with meteorological, land-cover, and other ancillary data for the period from March 2018 to February 2019. To estimate PM2.5 concentrations over wide areas spanning many countries displaying various relationships between aerosol optical depth and PM2.5, monthly models were developed by considering both the spatial and temporal characteristics of ground-based PM2.5 measurements. Random forest machine learning model estimated ground-level mass concentrations of PM2.5; subsequent 10-fold cross vali-dation (CV) yielded a CV R-2 value of 0.81 and a CV root mean squared error (RMSE) of 12.3 lig m(-3). We investigated the spatial pattern of PM2.5 concentrations over multiple countries and seasonal variation in PM2.5 concentrations. Diurnal variation of a severe PM2.5 event in the Korean Peninsula was investigated as a case study. The model captured the extremely heterogeneous spatial distribution of PM2.5 concentrations peaked around local noon. To measure the capability of the developed model to estimate PM2.5 concentrations in areas with few in-situ data, its predictive performance was evaluated using a dataset independent of the training process with an R-2 of 0.60 and RMSE of 8.18 lig m(-3). This study demonstrates the potential for satellite-based PM2.5 estimation for areas with insufficient measuring stations
Rapidly Changing East Asian Marine Heatwaves Under a Warming Climate
No full textThe East Asian marginal seas (EAMS) are one of the fastest-warming ocean regions globally. This study presents the long-term trends (1982-2020) of extreme ocean warming events called "marine heatwaves" over the EAMS and examines the relationships between marine heatwave trends and mean SST warming trends. We focus on five subregions with different influences from atmospheric perturbation and ocean currents: the northern East Sea (N-ES), southern East Sea, Yellow Sea, Korea Strait (KS), and East China Sea (ECS). During the past four decades, marine heatwave duration and intensity in the EAMS have increased to approximately +4 days and +0.3 degrees C per decade on average, respectively. In summer, the positive trend of marine heatwaves is the highest in the ECS, primarily due to the rapidly increasing mean sea surface temperature (SST). In winter, the N-ES reveals remarkably rapid increases in marine heatwave properties in the last two decades, with increasing rates of approximately 6.2 (4.9) times longer total duration (stronger intensity) than the global average changes. Beyond the impact of the rapid increase in mean SST, the N-ES marine heatwaves can be further extended due to the northward shift of the East Korea Warm Current. In general, mean SST changes are critical to the increasing trend in marine heatwave duration and intensity. This study further emphasizes that the changes in ocean circulation may expedite more rapid changes in extreme ocean events, which can produce more vulnerability in some places, such as the N-ES, to marine heatwaves under continued global warming.Plain Language Summary Extreme warming events of the ocean occurring from several days to weeks significantly impact marine ecosystems. This study investigates the increasing trends of extremely high ocean warming, namely "marine heatwave," over East Asian marginal seas. During the past four decades, marine heatwave duration and intensity have increased to approximately +4 days and +0.3 degrees C per decade on average, respectively. Comparing the earlier period (1982-2000) and the recent period (2001-2020), the most dramatic changes in marine heatwave properties, including frequency, duration, and intensity, occur in the northern East Sea in winter, significantly increasing 763.33% in duration. During summer, the East China Sea reveals the most significant increasing ratio of marine heatwave properties, with change rates of 227.07% in duration. Marine heatwave characteristics have a statistically increasing trend in both seasons in most regions due to global warming. Beyond the impact of the change in mean SST, we find the change in SST variance via shifting ocean current leads to the excessive trend of marine heatwaves
Spin-phonon interactions and magnetoelectric coupling in Co-4 B2O9 (B = Nb, Ta)
No full textIn order to explore the consequences of spin-orbit coupling on spin-phonon interactions in a set of chemically similar mixed metal oxides, we measured the infrared vibrational properties of Co B-4 O-2(9) (B = Nb, Ta) as a function of temperature and compared our findings with lattice dynamics calculations and several different models of spin-phonon coupling. Frequency vs temperature trends for the Co2+ shearing mode near 150 cm(-1) reveal significant shifts across the magnetic ordering temperature that are especially large in relative terms. Bringing these results together and accounting for noncollinearity, we obtain spin-phonon coupling constants of -3.4 and -4.3 cm(-1) for Co4Nb2O9 and the Ta analog, respectively. Analysis reveals that these coupling constants are derived from interlayer (rather than intralayer) exchange interactions and that the interlayer interactions contain competing antiferromagnetic and ferromagnetic contributions. At the same time, beyond-Heisenberg terms are minimized due to fortuitous symmetry considerations, different from most other 4d- and 5d-containing oxides. Comparison with other contemporary oxides shows that spin-phonon coupling in this family of materials is among the strongest ever reported, suggesting an origin for magnetoelectric coupling
Boosting the interfacial superionic conduction of halide solid electrolytes for all-solid-state batteries
No full textDesigning highly conductive and (electro)chemical stable inorganic solid electrolytes using cost-effective materials is crucial for developing all-solid-state batteries. Here, we report halide nanocomposite solid electrolytes (HNSEs) ZrO2(-ACl)-A(2)ZrCl(6) (A = Li or Na) that demonstrate improved ionic conductivities at 30 degrees C, from 0.40 to 1.3 mS cm(-1) and from 0.011 to 0.11 mS cm(-1) for Li+ and Na+, respectively, compared to A(2)ZrCl(6), and improved compatibility with sulfide solid electrolytes. The mechanochemical method employing Li2O for the HNSEs synthesis enables the formation of nanostructured networks that promote interfacial superionic conduction. Via density functional theory calculations combined with synchrotron X-ray and Li-6 nuclear magnetic resonance measurements and analyses, we demonstrate that interfacial oxygen-substituted compounds are responsible for the boosted interfacial conduction mechanism. Compared to state-of-the-art Li2ZrCl6, the fluorinated ZrO2-2Li(2)ZrCl(5)F HNSE shows improved high-voltage stability and interfacial compatibility with Li6PS5Cl and layered lithium transition metal oxide-based positive electrodes without detrimentally affecting Li+ conductivity. We also report the assembly and testing of a Li-In||LiNi0.88Co0.11Mn0.01O2 all-solid-state lab-scale cell operating at 30 degrees C and 70 MPa and capable of delivering a specific discharge of 115 mAh g(-1) after almost 2000 cycles at 400 mA g(-1). Compositional tuning is a standard procedure to improve the ionic conductivity of inorganic superionic conductors. Here, the authors report (electro)chemical stable composite halide solid electrolytes applying a nanostructure approach that promotes interfacial superionic conductivity
Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance
No full textThe non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs. Non-fullerene acceptors with large quadrupole moments strongly affect thin-film energetics. Here, the authors show a significant energetic shift (>200 meV) of Y6 upon changing its orientation from face-on to more edge-on using different solvents and its critical impact on organic photovoltaics
A fluoroalkyl iodide additive for Li???O2 battery electrolytes enables stable cycle life and high reversibility
No full textLi???O2 batteries attract extensive attention because they exhibit the highest theoretical energy density among the rechargeable batteries reported so far. However, most studies have focused on improving the cyclability and efficiency of Li???O2 batteries under low-capacity conditions instead of under practical conditions. Here, we increase the capacity range of Li???O2 batteries to a practical condition of 5 mA h cm???2 by introducing CF3(CF2)2I as a dual-functional additive. An electrolyte comprising 1 M LiNO3 in N,N-dimethylacetamide and CF3(CF2)2I provides stable cycle retention and high reversibility even at high areal capacity. Ab initio molecular dynamics simulations demonstrate that the reaction between CF3(CF2)2I and Li metal is spontaneous and leads to the simultaneous formation of LiF as a protective layer on Li metal and LiI as a redox mediator for the oxygen evolution reaction. This study provides new insights for the development of electrolyte additives toward practical Li???O2 batteries
High-Performance Infrared Photodetectors Driven by Interlayer Exciton in a Van Der Waals Epitaxy Grown HfS2/MoS2 Vertical Heterojunction
No full textThe van der Waals (vdW) heterojunctions of transition metal dichalcogenides (TMDCs) provide an advanced platform for interlayer exciton generation to detect the exceeding cutoff wavelengths of individual TMDCs. Herein, the first demonstration of high-performance infrared (IR) photodetectors driven by interlayer excitons and based on HfS2/MoS2 vdW heterojunctions grown by chemical vapor deposition is presented. HfS2 exhibits selective growth only on MoS2, establishing a vertical heterojunction that effectively generates interlayer excitons. The synthesized HfS2/MoS2 vertical heterojunction with type-II band alignment exhibits a low interlayer bandgap and a significantly large interface area, enabling highly efficient IR detection. Moreover, the built-in potential in HfS2/MoS2 plays a pivotal role in the outstanding photoresponse by suppressing the dark current and providing gradient band bending for the interlayer exciton-induced photocarriers to drift toward each electrode. The HfS2/MoS2 photodetector exhibits remarkable performance, achieving a detectivity (D*) of approximate to 7 x 10(13) Jones at 1550 nm, D* of approximate to 2 x 10(14) Jones at 980 nm, and fast response time of 60 mu s, surpassing previously reported 2D photodetectors. Overall, the successful demonstration of a photodetector based on vdW epitaxial HfS2/MoS2 paves the way for the advancement of large-scale high-performance IR sensors
Investigation of Hole-Transfer Dynamics through Simple EL De-Convolution in Non-Fullerene Organic Solar Cells
No full textIn conventional fullerene-based organic photovoltaics (OPVs), in which the excited electrons from the donor are transferred to the acceptor, the electron charge transfer state (eECT) that electrons pass through has a great influence on the device's performance. In a bulk-heterojunction (BHJ) system based on a low bandgap non-fullerene acceptor (NFA), however, a hole charge transfer state (hECT) from the acceptor to the donor has a greater influence on the device's performance. The accurate determination of hECT is essential for achieving further enhancement in the performance of non-fullerene organic solar cells. However, the discovery of a method to determine the exact hECT remains an open challenge. Here, we suggest a simple method to determine the exact hECT level via deconvolution of the EL spectrum of the BHJ blend (ELB). To generalize, we have applied our ELB deconvolution method to nine different BHJ systems consisting of the combination of three donor polymers (PM6, PBDTTPD-HT, PTB7-Th) and three NFAs (Y6, IDIC, IEICO-4F). Under the conditions that (i) absorption of the donor and acceptor are separated sufficiently, and (ii) the onset part of the external quantum efficiency (EQE) is formed solely by the contribution of the acceptor only, ELB can be deconvoluted into the contribution of the singlet recombination of the acceptor and the radiative recombination via hECT. Through the deconvolution of ELB, we have clearly decided which part of the broad ELB spectrum should be used to apply the Marcus theory. Accurate determination of hECT is expected to be of great help in fine-tuning the energy level of donor polymers and NFAs by understanding the charge transfer mechanism clearly
Experimental Robust Spontaneous Synchronizations in Coupled NbOx Oscillation Neurons for Unconventional Computing
No full textIn this brief, we demonstrate experimentally achieved oscillation dynamics in coupled NbOx thresholds witch (TS)-based oscillation neurons (ONs). We first show the challenges in observing oscillation caused by devicevariability, which is further validated through HSPICE simulations. To obtain robust oscillation response, a reliable TS developed via atomic layer deposition for conformal NbOx is introduced. By developing coupled NbO(x )ONs using acoupling resistor (RC), the out-of-phase synchronizationis demonstrated owing to the weak connection. Moreover,we achieve a transition to in-phase synchronization as the coupling strength increases, showing an inverse relation-ship with the magnitude of R-C. Based on these results,oscillatory neural networks, where multiple NbO(x )ONs arefully connected, are examined to execute pattern recognition via MATALB simulation