Diagnosis of atrial fibrillation based on AI-detected anomalies of ECG segments.

Early detection of atrial fibrillation (AF) is crucial for its effective management and prevention. Various methods for detecting AF using deep learning (DL) based on supervised learning with a large labeled dataset have a remarkable performance. However, supervised learning has several problems, as it is time-consuming for labeling and has a data dependency problem. Moreover, most of the DL methods do not provide any clinical evidence to physicians regarding the analysis of electrocardiography (ECG) for classification or detection of AF. To address these limitations, in this study, we proposed a novel AF diagnosis system using unsupervised learning for anomaly detection with three segments, PreQ, QRS, and PostS, based on the normal ECG. Two independent datasets, PTB-XL and China, were used in three experiments. We used a long short-term memory (LSTM)-based autoencoder to train the segments of the normal ECG. Based on the threshold of anomaly scores using mean squared error (MSE), it distinguished between normal and AF segments. In Experiment A, the best score was that of PreQ, which detected AF with an AUROC score of 0.96. In Experiment B and C for cross validation of each dataset, the best scores were also of PreQ, with AUROC scores of 0.9 and 0.95, respectively. To verify the significance of the anomaly score in distinguishing between AF and normal segments, we utilized an XG-Boosted model after generating anomaly scores in the three segments. The XG-Boosted model achieved an AUROC score of 0.98 and an F1 score of 0.94. AF detection using DL has been controversial among many physicians. However, our study differentiates itself from previous studies in that we can demonstrate evidence that distinguishes AF from normal segments based on the anomaly score.

Low-Index Facet Polyhedron-Shaped Binary Cerium Titanium Oxide for High-Voltage Aqueous Zinc-Vanadium Redox Flow Batteries.

Aqueous zinc-vanadium hybrid redox flow battery systems are an efficient strategy to address the problems of low voltage and high cost of conventional all-vanadium redox flow batteries. However, the low electrochemical activity of carbon-based electrodes toward a vanadium redox reaction limits the performance of redox flow batteries. In this study, polyhedral binary cerium titanium oxide (Ce2/3TiO3, CTO) is synthesized using molten salt synthesis. CTO is fabricated by adjusting the temperature and composition. Notably, the prepared CTO obtained at 1000 °C shows the highest catalytic activity for a VO2+/VO2+ redox reaction. Further, CTO is prepared as a composite electrocatalyst and applied to a high-voltage aqueous zinc-vanadium redox flow battery. The cell adopts an alkali zinc electrolyte containing a Zn/[Zn(OH)4]2- redox pair and exhibits a high operating voltage of 2.26 V. Remarkably, a zinc-vanadium redox flow battery using the composite electrocatalyst exhibits a high energy density of 42.68 Wh L-1 at 20 mA cm-2 and an initial voltage efficiency of 90.3%. The excellent cell performance is attributed to structural defects caused by A-site deficiency in the perovskite oxide structure as well as oxygen vacancies resulting from the low valence state of the metal ion, which enhance the catalytic activity of the vanadium ions.

Facile one-pot synthesis of biomass-derived activated carbon as an interlayer material for a BAC/PE/Al2O3 dual coated separator in Li-S batteries.

Lithium-sulfur batteries (LSB) are an attractive alternative electrochemical energy storage device compared to conventional lithium-ion batteries due to their higher theoretical capacity and energy density. Despite these advantages, it is still difficult to commercialize LSB because of poor electrochemical performance caused by the dissolution of soluble lithium polysulfides (LiPS). To solve these critical issues, a multi-functional separator was prepared using biomass-derived activated carbon (BAC) and a ceramic layer on the polyethylene (PE) separator. For this purpose, BAC was synthesized by a facile one-pot synthesis method by a specifically designed furnace using various forms of milk waste. The multi-functional separator suppresses the effect of LiPS dissolution and increases the Li+ diffusion kinetics. BAC was able to absorb the LiPS shuttle, as confirmed by UV-vis measurements and X-ray photoelectron spectroscopy (XPS). LSB cells assembled using this multi-functional separator show a higher discharge capacity of 1092.5 mA h g-1 at 0.1 C-rate, while commercial PE separators deliver a specific capacity of 811.8 mA h g-1. These novel separators were also able to suppress lithium dendrites during cycling. This work offers a novel and simple approach for streamlining the synthesis process of BAC and applying it to LSB, aiding in the development of sustainable energy sources.

Atomic Layer Deposition of Defective Amorphous TiOx Thin Films with Improved Photoelectrochemical Performance.

A proper control of defects in TiO2 thin films is challenging work for enhancing the photoelectrochemical (PEC) efficiency in water splitting processes. Additionally, a deep understanding of how defects affect the PEC performance of TiO2 thin films is of great interest for achieving better performance. With these aims, we prepared defective amorphous TiOx thin films at various growth temperatures by atomic layer deposition using tetrakis(dimethylamido)titanium as the Ti precursor. Careful X-ray photoelectron spectroscopy and electron spin resonance spectroscopy analyses revealed that the defect concentration in the TiOx thin films can be controlled by adjusting the growth temperature during the ALD process. We also evaluated the light absorption properties of the deposited TiOx thin films using ultraviolet-visible absorption spectroscopy. And it was found that the TiOx thin film deposited at a growth temperature of 200 °C exhibited the highest defect concentration and the highest photocurrent density of 0.051 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) compared to those of the other films. The light absorption efficiency, photogenerated charge separation efficiency, and charge transfer efficiency of defective amorphous TiOx thin films were carefully studied to understand the correlation between the defect concentration in the prepared TiOx thin film and its PEC activity. This study provides insight into the PEC properties of defective amorphous ALD-TiOx thin films.

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation.

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO2 and WO3 (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O2, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O2 removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO2•/O2•- pair in the dark. The WO3 fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight.

Anisotropic Silicification of Nanostructured Surfaces by Local Liquid-Phase Deposition.

Exploration of the bioinspired silicification of artificial scaffolds is crucial to understanding and engineering the hierarchically complex and elaborate three-dimensional (3D) frustules of diatoms, which have high porosity and mechanical stability with related gas diffusion and storage properties. Herein, we report on the bioinspired silicification of the nanostructured surfaces of hexagonally close-packed silica bead (hc-SB) arrays using a liquid-phase deposition (LPD) method. This process, governed by the kinetics of silicification, was controlled using the concentration of the reactants and the reaction temperature and monitored in real time using a quartz-crystal microbalance, which allowed the investigation of the silicification on the surface during the LPD reaction. These heterogeneous LPD reactions on hc-SB arrays were optimized to mimic natural 3D hierarchical structures. Anisotropic silicification of the nanostructures occurred owing to differences in the energy and local concentration of silicic acid on the nanostructured surface. A 3D hierarchical pore network was realized via a heterogeneous LPD reaction by controlling the size, location, and arrangement of the SBs. We believe that our silicification process on nanostructured surfaces can lead to great improvements in the bioinspired morphogenesis-based engineering of 3D hierarchical structures.

Nanotopography-based engineering of retroviral DNA integration patterns.

Controlling the interactions between cells and viruses is critical for treating infected patients, preventing viral infections, and improving virus-based therapeutics. Chemical methods using small molecules and biological methods using proteins and nucleic acids are employed for achieving this control, albeit with limitations. We found, for the first time, that retroviral DNA integration patterns in the human genome, the result of complicated interactions between cells and viruses, can be engineered by adapting cells to the defined nanotopography of silica bead monolayers. Compared with cells on a flat glass surface, cells on beads with the highest curvature harbored retroviral DNAs at genomic sites near transcriptional start sites and CpG islands during infections at more than 50% higher frequencies. Furthermore, cells on the same type of bead layers contained retroviral DNAs in the genomic regions near cis-regulatory elements at frequencies that were 2.6-fold higher than that of cells on flat glass surfaces. Systems-level genetic network analysis showed that for cells on nanobeads with the highest curvature, the genes that would be affected by cis-regulatory elements near the retroviral integration sites perform biological functions related to chromatin structure and antiviral activities. Our unexpected observations suggest that novel engineering approaches based on materials with specific nanotopography can improve control over viral events.

Facile thermochemical conversion of FeOOH nanorods to ZnFe2O4 nanorods for high-rate lithium storage.

We successfully prepared ZnFe2O4 nanorods (ZFO-NRs) by a simple thermochemical reaction of FeOOH nanorods with Zn(NO3)2 to use as an anode material in lithium-ion batteries. The FeOOH nanorod shape was well maintained after conversion into ZFO-NR with the formation of porous structures. The nanorod structure and porous morphology facilitate Li+ transport, improve the reaction rates owing to the larger contact area with the electrolyte, and reduce the mechanical stress during lithiation/delithiation. The ZFO-NR electrode exhibited a reversible capacity of 725 mA h g-1 at 1 A g-1 and maintained a capacity of 668 mA h g-1 at 2 A g-1; these capacities are much higher and more stable than those of ZFO nanoparticles prepared by a hydrothermal method (ZFO-HT) (216 and 117 mA h g-1 at 1 and 2 A g-1, respectively). Although ZFO-NRs exhibited high, stable capacities at moderate current densities for charging and discharging, the capacity rapidly decreased under fast charging/discharging conditions (>4 A g-1). However, carbonized ZFO-NR (C/ZFO-NR) exhibited an improved reversible capacity and rate capability resulting from an increased conductivity compared with ZFO-NRs. The specific capacity of C/ZFO-NRs at 1 A g-1 was 765 mA h g-1; notably, a capacity of 680 mA h g-1 was maintained at 6 A g-1.

Molecular interaction-dependent surface potentials of sequentially polymerized alucone films.

Here, we investigated the relationship between the surface potentials and molecular interactions in the alucone films grown by molecular layer deposition. Varying the C-C bond order of the organic precursors induced variations in inter-molecular interactions, resulting in variation in the surface potential, associated with the work function of the films.

Size-Dependent Surface Migration of Au Alloys on Si Nanowires at Different Cooling Rates.

Understanding metal alloy migration in metal-catalyzed nanowires growth is a prerequisite for improving its potential applications in the field of nanodevices. Here, we explored the surface migration of Au alloys in vertically aligned Si nanowires with different cooling rates. We varied the diameter of Au alloys by controlling the thickness of Au film as a catalyst for SiNW growth, and found that the behavior of Au alloys migration is dependent on size of Au alloys. In addition, the size-dependent migration mechanism of Au alloys was investigated at different cooling rates, which is related to different Au-Si eutectics.

Solar-rechargeable battery based on photoelectrochemical water oxidation: Solar water battery.

As an alternative to the photoelectrochemical water splitting for use in the fuel cells used to generate electrical power, this study set out to develop a solar energy rechargeable battery system based on photoelectrochemical water oxidation. We refer to this design as a "solar water battery". The solar water battery integrates a photoelectrochemical cell and battery into a single device. It uses a water oxidation reaction to simultaneously convert and store solar energy. With the solar water battery, light striking the photoelectrode causes the water to be photo-oxidized, thus charging the battery. During the discharge process, the solar water battery reduces oxygen to water with a high coulombic efficiency (>90%) and a high average output voltage (0.6 V). Because the reduction potential of oxygen is more positive [E(0) (O2/H2O) = 1.23 V vs. NHE] than common catholytes (e.g., iodide, sulfur), a high discharge voltage is produced. The solar water battery also exhibits a superior storage ability, maintaining 99% of its specific discharge capacitance after 10 h of storage, without any evidence of self-discharge. The optimization of the cell design and configuration, taking the presence of oxygen in the cell into account, was critical to achieving an efficient photocharge/discharge.

Harnessing and storing visible light using a heterojunction of WO3 and CdS for sunlight-free catalysis.

CdS and WO3 (CdS/WO3) bilayer film electrodes are fabricated to harness solar visible light (λ > 420 nm) and store photogenerated electrons for possible use during periods of unavailable sunlight. The overall film thickness is approximately 50-60 µm, while the CdS underlayer is slightly thinner than WO3 owing to a packing effect. The energetics of CdS and WO3 determined by optical and electrochemical analyses enables cascaded electron transfer from CdS to WO3. The open circuit potential (EOCP) of CdS/WO3 under visible light (approximately -0.35 V vs. SCE) is nearly maintained even in the absence of light, with a marginal decrease (∼0.15 V) in ∼20 h of darkness. Neither CdS nor WO3 alone exhibits such behavior. The electron lifetimes (τ) of CdS and WO3 are each less than 100 s, whereas coupling of the two increases τ to ∼2500 s at the EOCP. In the absence of dissolved O2, τ further increases, suggesting that O2 is the primary electron acceptor. In spite of oxic conditions, CdS/WO3 is capable of continuously reducing Cr(6+) to Cr(3+) and Ag(+) to Ag(0) after removal of visible light. The number of utilized (i.e., stored) electrons in the reductions of Cr(6+) and Ag(+) are estimated to be ∼1.08 × 10(17) and ∼0.87 × 10(17), respectively. The primary role of CdS is to be a visible-light absorber in the 420-565 nm wavelength range, transferring the photogenerated electrons to WO3. The electrons stored in WO3 are gradually released to electron acceptors with suitable redox potentials.

Location-Controlled Growth of Vertically Aligned Si Nanowires using Au Nanodisks Patterned by KrF Stepper Lithography.

The location-controlled epitaxial growth of vertically aligned Si nanowire (v-SiNW) arrays over large surface area was investigated with Au nanodisks (AuNDs) patterned by KrF stepper lithography. There are two steps for synthesizing v-SiNWs from an AuND pattern: annealing and growth. The annealing process induces the formation of a single Au nanoparticle (AuNP) from an AuND pattern, which consists of several cracked AuNPs. Here, the oxide layer between the AuNDs and Si substrate is necessary for impeding the diffusion of Si atoms into the AuNPs. However, the oxide layer must be removed for properly aligned epitaxial SiNW growth. These SiNW arrays in large area can contribute highly to improve a nanowire-based engineering by controlling the location of SiNWs with consistent pitch.

Intramolecular and Intermolecular Interactions in Hybrid Organic-Inorganic Alucone Films Grown by Molecular Layer Deposition.

Investigation of molecular interactions in polymeric films is crucial for understanding and engineering multiscale physical phenomena correlated to device function and performance, but this often involves a compromise between theoretical and experimental data, because of poor film uniformity. Here, we report the intramolecular and intermolecular interactions inside the ultrathin and conformal hybrid organic-inorganic alucone films grown by molecular layer deposition, based on sequential and self-limiting surface reactions. Varying the carbon chain length of organic precursors, which affects their molecular flexibility, caused intramolecular interactions such as double reactions by bending of the molecular backbone, resulting in formation of hole vacancies in the films. Furthermore, intermolecular interactions in alucone polymeric films are dependent on the thermal kinetics of molecules, leading to binding failures and cross-linking at low and high growth temperatures, respectively. We illustrate these key interactions and identify molecular geometries and potential energies by density functional theory calculations.

Fine-Tunable Absorption of Uniformly Aligned Polyurea Thin Films for Optical Filters Using Sequentially Self-Limited Molecular Layer Deposition.

Development of methods enabling the preparation of uniformly aligned polymer thin films at the molecular level is a prerequisite for realizing their optoelectronic characteristics as innovative materials; however, these methods often involve a compromise between scalability and accuracy. In this study, we have grown uniformly aligned polyurea thin films on a SiO2 substrate using molecular layer deposition (MLD) based on sequential and self-limiting surface reactions. By integrating plane-polarized Fourier-transform infrared, Raman spectroscopic tools, and density functional theory calculations, we demonstrated the uniform alignment of polyurea MLD films. Furthermore, the selective-wavelength absorption characteristics of thickness-controlled MLD films were investigated by integrating optical measurements and finite-difference time-domain simulations of reflection spectra, resulting from their thickness-dependent fine resonance with photons, which could be used as color filters in optoelectronics.

Wetting behavior on hexagonally close-packed polystyrene bead arrays with different topographies.

Herein, we investigated the wetting behavior of hexagonally close-packed polystyrene bead arrays with different bead diameters and surface flatness. The contact angle was found to be influenced by the surface roughness as well as the contact area of the polystyrene bead array with a water droplet.

Axon-First Neuritogenesis on Vertical Nanowires.

In this work, we report that high-density, vertically grown silicon nanowires (vg-SiNWs) direct a new in vitro developmental pathway of primary hippocampal neurons. Neurons on vg-SiNWs formed a single, extremely elongated major neurite earlier than minor neurites, which led to accelerated polarization. Additionally, the development of lamellipodia, which generally occurs on 2D culture coverslips, was absent on vg-SiNWs. The results indicate that surface topography is an important factor that influences neuronal development and also provide implications for the role of topography in neuronal development in vivo.

Hybrid Cu x O-TiO2 Heterostructured Composites for Photocatalytic CO2 Reduction into Methane Using Solar Irradiation: Sunlight into Fuel.

Photocatalytic CO2 conversion to fuel offers an exciting prospect for solar energy storage and transportation thereof. Several photocatalysts have been employed for CO2 photoreduction; the challenge of realizing a low-cost, readily synthesized photocorrosion-stable photocatalytic material that absorbs and successfully utilizes a broad portion of the solar spectrum energy is as yet unmet. Herein, a mesoporous p-type/n-type heterojunction material, Cu x O-TiO2 (x = 1, 2), is synthesized via annealing of Cu/Cu2O nanocomposites mixed with a TiO2 precursor (TiCl4). Such an experimental approach in which two materials of diverse bandgaps are coupled provides a simultaneous opportunity for greater light absorption and rapid charge separation because of the intrinsic p-n heterojunction nature of the material. As detailed herein, this heterostructured photocatalyst demonstrates an improved photocatalytic activity. With the CO2 reduction of our optimal sample (augmented light absorption, efficacious charge separation, and mesoporosity) that utilizes no metal cocatalysts, a remarkable methane yield of 221.63 ppm·g-1·h-1 is achieved.

Annealed Au-assisted epitaxial growth of si nanowires: control of alignment and density.

The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vapor-liquid-solid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl4 as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.

Local liquid phase deposition of silicon dioxide on hexagonally close-packed silica beads.

Liquid phase deposition (LPD) is a useful method for the production of oxide film with low reaction temperature and production cost. With the report that the LPD of oxide films is conformally processed with uniform thickness and composition, there has been significant attention given to investigating its kinetic controls and growth mechanism on the flat surface. In this work, we explored the LPD of silicon dioxide on the hexagonally close-packed silica beads array as a nanostructured surface. The deposition and etching reactions of SiO2 occurred locally and simultaneously on silica beads, and were distinguished from the amount of fumed silica added in LPD solution. From locally competitive reactions, we obtained the anisotropic morphology of close-packed silica beads, and proposed a mechanism for the local LPD of SiO2 driven by nanostructured surfaces. This work contributes highly to improve metal oxide-based engineering, and also provide greater insight into the topography-driven LPD.