Switchable tribology of ferroelectrics

Artificially induced asymmetric tribological properties of ferroelectrics offer an alternative route to visualize and control ferroelectric domains. Here, we observe the switchable friction and wear behavior of ferroelectrics using a nanoscale scanning probe where down domains having lower friction coefficient than up domains can be used as smart masks as they show slower wear rate than up domains. This asymmetry is enabled by flexoelectrically coupled polarization in the up and down domains under a sufficiently high contact force. Moreover, we determine that this polarization-sensitive tribological asymmetry is universal across ferroelectrics with different chemical composition and crystalline symmetry. Finally, using this switchable tribology and multi-pass patterning with a domain-based dynamic smart mask, we demonstrate three-dimensional nanostructuring exploiting the asymmetric wear rates of up and down domains, which can, furthermore, be scaled up to technologically relevant (mm-cm) size. These findings establish that ferroelectrics are electrically tunable tribological materials at the nanoscale for versatile applications.Peer ReviewedPostprint (author's final draft

Risk of fracture according to temporal changes of low body weight changes in adults over 40years: a nationwide population-based cohort study

Background Low body weight is associated with an increased risk of fractures. However, the effect of temporal changes in the low body weight status on the risk of fracture remains unknown. This study aimed to evaluate the relationships between temporal changes in low body weight status and the risk of fractures in adults over the age of 40 years. Methods This study included data on adults over 40 years old who underwent two biannual consecutive general health examinations between January 1, 2007 and December 31, 2009 extracted from the National Health Insurance Database, a large nationwide population database. Fracture cases in this cohort were monitored from the time of the last health examination to the end of the designated follow-up period (from January 1, 2010 to December 31, 2018) or the participant's death. Fractures were defined as any fracture resulting in hospitalization or outpatient treatment claim after the date of general health screening. The study population was then separated into four groups based on the temporal changes in low body weight status as follows: low body weight to low body weight (L-to-L), low body weight to non-low body weight (L-to-N), non-low body weight to low body weight (N-to-L), and non-low body weight to non-low body weight (N-to-N). The hazard ratios (HRs) for new fractures, depending on weight changes over time, were calculated using Cox proportional hazard analysis. Results Adults in the L-to-L, N-to-L, and L-to-N groups had a substantially increased risk of fractures after multivariate adjustment (HR, 1.165; 95% confidence interval [CI], 1.113–1.218; HR, 1.193; 95% CI, 1.131–1.259; and HR, 1.114; 95% CI, 1.050–1.183, respectively). Although the adjusted HR was greater in participants who changed into having a low body weight, followed by those with consistently low body weight, those with low body weight remained to have an elevated risk of fracture independent of weight fluctuation. Elderly men (aged over 65 years), high blood pressure, and chronic kidney disease were significantly associated with an increase in fractures (p < 0.05). Conclusion Individuals aged over 40 years with low body weight, even after regaining normal weight, had an increased risk of fracture. Moreover, having a low body weight after having a normal body weight increased the risk of fractures the most, followed by those with consistently low body weight

Definitions of unfavorable surgical outcomes and their risk factors based on disability score after spine surgery for lumbar spinal stenosis

Risk factors for unfavorable surgical outcomes are dependent on the definitions of the unfavorable surgical outcomes. The aims of this study were to compare risk factors for each unfavorable surgical outcome according to two different definitions of unfavorable surgical outcomes after surgery for lumbar spinal stenosis (LSS) as well as compare the clinical course from the preoperative period to 3 years postoperatively between cases with favorable and unfavorable outcomes according to the two different definitions. Overall, 295 patients who underwent spine surgery for LSS and a follow-up evaluation at 3 years postoperatively were enrolled and divided into favorable and unfavorable groups, based on two different definitions for unfavorable surgical outcomes, as evaluated at 12 months postoperatively: the patient-reported outcome (PRO) and minimal clinically important difference (MCID) methods. In the PRO method, patients with a postoperative Oswestry Disability Index (ODI) score > 22 were considered as having an unfavorable outcome, whereas in the MCID method, those with a postoperative ODI score that changed < 12.8 points from the preoperative value were classified as having an unfavorable outcome. As a primary outcome, risk factors for unfavorable surgical outcomes according to each definition were investigated at 12 months postoperatively. In the PRO method, female sex (P = 0.011; odds ratio (OR): 2.340), elementary school attainment (vs. university attainment; P = 0.035; OR: 2.875), and higher preoperative ODI score (P = 0.028; OR: 2.340) were associated with higher odds for an unfavorable surgical outcome. In the MCID method, a higher preoperative ODI score was associated with higher odds (P < 0.001; OR: 0.920) of a favorable surgical outcome. In the PRO method, the favorable outcome group demonstrated significantly lower visual analog scale for back and leg pain and lower ODI scores than the unfavorable outcome group at 3 years postoperatively, whereas in the MCID method, clinical outcomes were not different between the two groups at 3 years postoperatively. A higher preoperative ODI score may be a risk factor for postoperative ODI > 22 after surgery for LSS. It may also be associated with higher odds for improvements in the ODI score of > 12.8.This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2016R1A2B3012850)

Reducing time to discovery : materials and molecular modeling, imaging, informatics, and integration

This work was supported by the KAIST-funded Global Singularity Research Program for 2019 and 2020. J.C.A. acknowledges support from the National Science Foundation under Grant TRIPODS + X:RES-1839234 and the Nano/Human Interfaces Presidential Initiative. S.V.K.’s effort was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division and was performed at the Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), a U.S. Department of Energy, Office of Science User Facility.Multiscale and multimodal imaging of material structures and properties provides solid ground on which materials theory and design can flourish. Recently, KAIST announced 10 flagship research fields, which include KAIST Materials Revolution: Materials and Molecular Modeling, Imaging, Informatics and Integration (M3I3). The M3I3 initiative aims to reduce the time for the discovery, design and development of materials based on elucidating multiscale processing-structure-property relationship and materials hierarchy, which are to be quantified and understood through a combination of machine learning and scientific insights. In this review, we begin by introducing recent progress on related initiatives around the globe, such as the Materials Genome Initiative (U.S.), Materials Informatics (U.S.), the Materials Project (U.S.), the Open Quantum Materials Database (U.S.), Materials Research by Information Integration Initiative (Japan), Novel Materials Discovery (E.U.), the NOMAD repository (E.U.), Materials Scientific Data Sharing Network (China), Vom Materials Zur Innovation (Germany), and Creative Materials Discovery (Korea), and discuss the role of multiscale materials and molecular imaging combined with machine learning in realizing the vision of M3I3. Specifically, microscopies using photons, electrons, and physical probes will be revisited with a focus on the multiscale structural hierarchy, as well as structure-property relationships. Additionally, data mining from the literature combined with machine learning will be shown to be more efficient in finding the future direction of materials structures with improved properties than the classical approach. Examples of materials for applications in energy and information will be reviewed and discussed. A case study on the development of a Ni-Co-Mn cathode materials illustrates M3I3's approach to creating libraries of multiscale structure-property-processing relationships. We end with a future outlook toward recent developments in the field of M3I3.Peer reviewe

Surface enhanced electron correlation on the trivial quasi-two-dimensional bulk insulator 1T-TaS2

© 2022 American Physical Society.While the prototypical quasi-two-dimensional charge density wave system of 1T-TaS2 has been known as a Mott insulator with a possibility of quantum spin liquid, recent band-structure calculations and spectroscopic works in parallel suggested a metallic system or a spin-singlet insulator due to the interlayer coupling. Here, we carefully reinvestigate the out-of-plane electron dispersion, which reflects the interlayer electronic coupling, with angle-resolved photoelectron spectroscopy. We identify two distinct branches for the topmost valence band, which can be unambiguously related to the surface and the bulk layers with different band gaps. Density functional theory calculations clearly indicate a trivial band insulator due to the interlayer coupling for the bulk but the surface band gap affected substantially by the electron correlation. The surface-bulk electronic dichotomy consistently incorporates most of the theoretical and spectroscopic results reported so far and has wide implications for van der Waals materials with nontrivial interlayer interactions.11Nsciescopu

Control over a Wide Phase Diagram of 2D Correlated Electrons by Surface Doping; K/1T-TaS2

We demonstrate the systematic tuning of a trivial insulator into a Mott insulator and a Mott insulator into a correlated metallic and a pseudogap state, which emerge in a quasi-two-dimensional electronic system of 1T-TaS2 through strong electron correlation. The band structure evolution is investigated upon surface doping by alkali adsorbates for two distinct phases occurring at around 220 and 10 K by angle-resolved photoelectron spectroscopy. We find contrasting behaviors upon doping that corroborate the fundamental difference of two electronic states: while the antibonding state of the spin-singlet insulator at 10 K is partially occupied to produce an emerging Mott insulating state, the presumed Mott insulating state at 220 K evolves into a correlated metallic state and then a pseudogap state. The work indicates that surface doping onto correlated 2D materials can be a powerful tool to systematically engineer a wide range of correlated electronic phases.11Nsciescopu

Simulation Model for Prediction of Gas Separation in Membrane Contactor Process

The purpose of this study is to establish a practical simulation model based on mass balance, mass transport equations and equilibrium equation between gas and liquid phases across a porous membrane in membrane contactor process in order to predict the separation behavior by the gassing process of gas mixture in membrane contactor. The established simulation model was verified by comparison between the simulated values and real process values in the separation of CH4/CO2 mixture, showing an excellent agreement between them. The parameter R-value in the model, which is a kind of the permeability of permeant across porous membrane, has been determined by fitting a numerical solution of the model equation to the experimental data to obtain a practical value of the parameter. A parametric study on the gassing process of N2/CO2 mixture in membrane contactor was made with the help of the practical simulation model to investigate the effects of operation parameters on separation performance and to characterize the separation behavior of membrane contactor process. A series of simulations of the separation of N2/CO2 mixture in membrane contactor were conducted, and the optimization on the membrane process was discussed to maximize the separation performance in terms of N2 recovery percent in retentate and CO2 permeation rate. It was observed from the analysis of the result of the simulation that liquid flow rate has a negative effect on N2 recovery percent in retentate but a positive effect on the separation of CO2, while R-value affects the separation performance in the other way. It is confirmed in this study that the developed simulation can be used as a tool to optimize the parameters, i.e., feed gas pressure, liquid flow rate and R-value to maximize the separation performance

DDX3 Upregulates Hydrogen Peroxide-Induced Melanogenesis in Sk-Mel-2 Human Melanoma Cells

DDX3 is a DEAD-box RNA helicase with diverse biological functions through multicellular pathways. The objective of this study was to investigate the role of DDX3 in regulating melanogenesis by the exploring signaling pathways involved. Various concentrations of hydrogen peroxide were used to induce melanogenesis in SK-Mel-2 human melanoma cells. Melanin content assays, tyrosinase activity analysis, and Western blot analysis were performed to determine how DDX3 was involved in melanogenesis. Transient transfection was performed to overexpress or silence DDX3 genes. Immunoprecipitation was performed using an antityrosinase antibody. Based on the results of the cell viability test, melanin content, and activity of tyrosinase, a key melanogenesis enzyme, in SK-Mel-2 human melanoma cells, hydrogen peroxide at 0.1 mM was chosen to induce melanogenesis. Treatment with H2O2 notably increased the promoter activity of DDX3. After treatment with hydroperoxide for 4 h, melanin content and tyrosinase activity peaked in DDX3-transfected cells. Overexpression of DDX3 increased melanin content and tyrosinase expression under oxidative stress induced by H2O2. DDX3 co-immunoprecipitated with tyrosinase, a melanogenesis enzyme. The interaction between DDX3 and tyrosinase was strongly increased under oxidative stress. DDX3 could increase melanogenesis under the H2O2-treated condition. Thus, targeting DDX3 could be a novel strategy to develop molecular therapy for skin diseases