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Observation of switchable polar skyrmion bubbles down to the atomic layers in van der Waals ferroelectric CuInP2S6
No full textPolar skyrmions are topologically nontrivial polarization textures that demonstrate exotic physical phenomena and novel memory applications. Thus far, these textures have primarily been reported in oxide-ferroelectric-based epitaxial heterostructures because their stabilization requires an elastic energy penalty from the epitaxial strains. Here, without the epitaxial-strain engineering, we discover polar skyrmion bubbles in stand-alone van der Waals ferroelectric CuInP2S6 crystal through the combination of piezoelectric force microscopy, high-resolution transmission electron microscopy, and phase-field simulations. In a thick CuInP2S6 flake of over −100 nm, skyrmion bubbles feature an elliptical hedgehog-like state with center-divergent or center-convergent configurations. Progressively thinning the flake thickness to −8 nm allows a topological transition from elliptical to circular skyrmionic patterns. Interestingly, the skyrmions can be switched with the change in helicity by probe-applied electrical and mechanical stimuli, which is distinct from the creation and annihilation of other reported skyrmions. Both theoretical and experimental data proves that the formation and thickness-dependence of skyrmion textures primarily stem from charge-related energy penalty. This work opens up a new material system (i.e., two-dimensional layered ferroionic materials) for exploring uncharted polar-topology physics and prospective neuromorphic devices.This work was supported by the National Key Research and Development Program of China (grant no. 2021YFA1500800 to H. T.), the National Natural Science Foundation of China (grant no. 62304202 to F. X., 12272338 to J. W, 12432007 to J. W., 12125407 to H. T., and 92163210 to X. G.), the Zhejiang Provincial Natural Science Foundation of China (grant no. LDT23F04013F04 to F. X.), and the Joint Funds of the National Natural Science Foundation of China (U21A2067 to H. T.). X. Zhang acknowledges the support from King Abdullah University of Science and Technology (KAUST), Office of Sponsored Research (OSR) under the Award Nos. ORA-CRG8-2019-4081 X. Z. and ORA-CRG10-2021-4665 X. Z. The authors thank Dr. Lingyuan Gao for the helpful discussion
Ultrathin graphite-encapsulated Y<sub>2</sub>Co<sub>17</sub> nanostructures with good structural stability and switchable microwave absorption
No full textAbstract: It is crucial to improve the antioxidant ability and structural stability of high-performance rare earth (RE) metal nanoalloys for their potential wide applications. In this work, an efficient functional surface carbon modification method has been provided to fabricate high-stability RE alloy/carbon nanostructures as high-performance electromagnetic materials. Specifically, graphite-encapsulated Y2Co17 nanoalloys constructed with high-purity Y2Co17 nanoparticles entirely coated with dense ultrathin N-doped graphite carbon (NGC) nanolayers to form antioxidative Y2Co17@NGC nanostructures are fabricated by a precisely controlled calcium thermic reduction of well-designed crystalline CoO-Co-Y2O3/C precursors. Another similarly structured Y2Co17@defect-rich graphite carbon (DGC) nanostructure is obtained by replacing NGC in Y2Co17@NGC with DGC by the same calcium thermic reduction but adjusting the carbon sources in the precursors. The excellent oxidation resistance and stable structures for these graphite-encapsulated Y2Co17 nanostructures facilitate the formation of ultrapure magnetic planar-anisotropy Y2Co17 phase, which results in their good soft magnetism with ultrahigh saturation magnetization values of 112.1–113.3 A m2 kg−1. Y2Co17@NGC nanostructures exhibit a favorable C band microwave absorption with a high minimum reflection loss (RLmin) value up to −80.16 dB at 4.30 GHz with a 4.03-mm-thick and Y2Co17@DGC nanostructures show a typical Ku band absorption with a RLmin value of −52.59 dB at 16.71 GHz with a 1.34 mm thickness. The good switchable electromagnetic properties of these graphite-encapsulated Y2Co17 nanostructures are demonstrated to arise from their different surface carbon defects. This work provides a surface carbon treatment strategy for fundamentally improving the oxidation resistance and structural stability of the easily oxidized RE nanoalloys and further constructing novelly structured functionalized RE alloy/carbon nanostructures.This work was supported by the National Key R&D Program of China (No. 2021YFB3501304), the Academic Excellence Foundation of BUAA for PhD Students, the National Natural Science Foundation of China (Nos. 52473227 and 52171150), and the Beijing Natural Science Foundation (No. 2132039)
Real-Time Tracking of Cation Vibrational Dynamics in MAPbBr<sub>3</sub> and FAPbBr<sub>3</sub> Perovskite Films
No full textIn this study, the ultrafast vibrational dynamics of MAPbBr3 and FAPbBr3 perovskite thin films are investigated experimentally using femtosecond mid-infrared (fs-MIR) spectroscopy and theoretically using density functional theory (DFT) calculations. Specifically, distinct vibrational modes associated with the organic cations─methylammonium (MA+) in MAPbBr3 and formamidinium (FA+) in FAPbBr3─are examined to elucidate how cation size and hydrogen bonding with the inorganic framework influence optical behavior, lattice distortion, material stability, and overall perovskite performance. Experimental results reveal that MAPbBr3 exhibits stronger cation–lattice coupling, as indicated by faster vibrational relaxation and broader spectral features, reflecting greater lattice distortion. In contrast, FAPbBr3 shows weaker coupling, resulting in slower vibrational decay, narrower peaks, and reduced structural distortion─features associated with enhanced material stability and superior charge transport. Notably, this study represents the first instance of using DFT for calculating excited-state vibrational frequencies in these hybrid perovskites, offering new insight into their photoinduced lattice dynamics. The calculations closely reproduce the experimental trends, capturing the vibrational modes, structural distortions, and lattice parameters of both systems. The larger FA+ cation in FAPbBr3 gives rise to a more symmetric lattice with reduced octahedral tilting and lower dynamic disorder compared to the smaller MA+ cation in MAPbBr3. Upon excitation, both materials exhibit lattice expansion; however, the distortion is more significant in MAPbBr3, which aligns with experimental observations. Overall, this study provides critical insight into organic cation dynamics in hybrid perovskites, establishing a direct link between cation–lattice coupling, vibrational behavior, and optoelectronic properties. These findings deepen our understanding of perovskite structure–function relationships and offer guidance for improving material stability and performance in next-generation optoelectronic devices.The authors thank King Abdullah University of Science and Technology (KAUST) for the financial support and the Super-Computing Laboratory at KAUST for the computational and storage resource
A review of flow-induced vibration in wind and oceanic flow: Mechanisms, applications, optimizations, and challenges
No full textThis paper provides a comprehensive review of the latest advancements in flow-induced vibration (FIV) and its two primary applications: vibration suppression and energy harvesting. The focus is on the interrelationship between the underlying mechanisms and these applications. First, key factors such as mass ratio, damping ratio, Reynolds number, and stiffness are examined for their influences on vibration response, with attention to recent advancements in the understanding of vortex-induced vibration (VIV), galloping, buffeting, and flutter. Second, the paper reviews modeling methods for FIV, with particular emphasis on the non-conformal mesh method and the integration of machine learning. The latest optimization strategies for both vibration suppression and energy harvesting are then explored, alongside the challenges associated with each. FIV energy harvesters are categorized based on the working fluid—wind (FIVEHW) and oceanic flow (FIVEHO)—highlighting the effects of flow density (mass ratio) and the unpredictability of flow direction and velocity on the selection of energy transducers, energy evaluation criteria and output scales. Optimization methods for vibration inhibition and energy harvesting are divided into two main categories: (1) direct methods, which directly modify the dynamic behavior governed by the FIV motion equation through the alteration of structural parameters (e.g., stiffness and damping), and the introduction of nonlinearity and multi-stabilities; (2) indirect methods, which regulate flow separation and vortex shedding to control vibration amplitude via geometric modifications (e.g., cross-sectional shapes, surface attachments, and surface roughness), jetting and blowing techniques, and the optimization of multiple oscillators for wake stabilization or wake interference. The paper concludes with a summary and discussion of the current state of the field, identifying existing capabilities and limitations and recommending areas for future research to address remaining gaps.The authors gratefully acknowledge the support provided by Prof. Bassam Dally's baseline funding from King Abdullah University of Science and Technology (KAUST). The authors have obtained necessary permissions for all reproduced figures and materials from the respective copyright holders through the Copyright Clearance Center or other relevant authorities. All reused content is cited appropriately, and permissions are documented as per journal requirements
Age-associated differences in mucosal and systemic host responses to SARS-CoV-2 infection
No full textAge is among the strongest risk factors for severe outcomes from SARS-CoV-2 infection. Here we describe upper respiratory tract (URT) and peripheral blood transcriptomes of 202 participants (age range of 1 week to 83 years), including 137 non-hospitalized individuals with mild SARS-CoV-2 infection and 65 healthy individuals. Among healthy children and adolescents, younger age is associated with higher URT expression of innate and adaptive immune pathways. SARS-CoV-2 infection induces broad upregulation of URT innate and adaptive immune responses among children and adolescents. Peripheral blood responses among SARS-CoV-2-infected children and adolescents are dominated by interferon pathways, while upregulation of myeloid activation, inflammatory, and coagulation pathways is observed only in adults. Among SARS-CoV-2-infected individuals, fever is associated with blunted URT immune responses and more pronounced systemic immune activation. These findings demonstrate that immune responses to SARS-CoV-2 differ across the lifespan, from distinct signatures in childhood and adolescence to age-associated alterations in adults.We offer sincere gratitude to the children and families who participated in this research. We additionally thank Dr. Nicolas Devos, Dr. Devjanee Swain Lenz, Sarah Clarke, and the staff at the Sequencing and Genome Technologies core facility at Duke University for sample processing, library construction, and genome sequencing. We thank Dr. Alejandro Berrio Escobar, John Bradley, Hilmar Lapp, and Dr. Gregory Wray for analysis of SARS-CoV-2 genome sequences and variant calls. This research was supported by a Merck Investigator Studies Program Grant (MISP #60495 to MSK), through funding provided by the Department of Pediatrics in the Duke University School of Medicine, and through funding from the National Institute of Allergy and Infectious Diseases (R01-AI161008 to M.S.K.). SARS-CoV-2 genome sequencing and analysis were supported by funding from the Office of the Provost at Duke University and the Duke Center for Genomic and Computational Biology. M.S.K. and J.H.H. were supported by the National Institutes of Health Career Development Awards (K23-AI135090 to M.S.K., K01-AI173398 to J.H.H.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Dynamic and Periodic Operations for Enhancing CO2 Hydrogenation to Methanol over Cu/ZIF-8 Catalyst
No full textThe catalytic hydrogenation of CO2 to methanol is crucial for a sustainable chemical industry. This work investigates the dynamic behavior of a previously developed Cu/ZIF-8 catalyst to optimize its activity beyond steady-state operation. While it was previously shown that this catalyst demonstrates higher steady state selectivity (~90%) compared to the commercial Cu-Zn-Al (CZA), this study shows how periodic operation strategies can provide valuable insight into active site dynamics and the mechanisms underlying catalytic performance.
It was found that temperature cycling is an effective in-situ conditioning method, accelerating the achievement of high methanol selectivity. Furthermore, dynamic pulsing experiments revealed a promotion mechanism. Pulsing CO into the CO2:H2 feed revealed a critical mechanistic difference between the tested catalysts. On CZA, CO pulses acted as inhibitors, competitively occupying active sites and negatively impacting both selectivity and yield, similar to the inhibitory effect of water observed during CO₂ pulses. In contrast, on Cu/ZIF-8, CO pulses uncovered a dynamic promotional mechanism driven by interactions between CO molecules and the catalyst’s 2-methylimidazolate ligands. These interactions removed surface oxygen species and regenerated active Cu sites, significantly enhancing CO₂ hydrogenation into methanol. These findings highlight the importance of investigating catalysts under dynamic conditions rather than steady-state alone, providing actionable insights such as controlled CO co-feeding strategies to optimize the catalytic performance of Cu/ZIF-8
Copper halide-based portable personal dosimeter for real-time X-ray monitoring
No full textWith an increasing demand for radiation detection devices in diverse sectors such as healthcare, industrial safety, and environmental monitoring, there is an urgent need for portable and affordable personal dosimeters. We demonstrate a Mn-doped Cs3Cu2I5 metal halide portable personal dosimeter for X-ray detection. The device is specifically tailored for individuals working in medical and security environments, providing a crucial safety measure when exposed to scattered X-ray beams. The portable dosimeter has a compact size of 20 × 20 mm and is highly sensitive to X-ray radiation. Equipped with photocurrent readout circuitry and advanced signal processing, our device ensures precise real-time monitoring of X-ray radiation, achieving a low-dose detection capability of 0.1 nGy/s. The device surpasses state-of-the-art personal dosimeters with its fast low-dose detection and easy readout using a mobile phone app, ensuring accurate measurements at minimum radiation levels. The device’s compact size and low power consumption make it ideal for dosimetry applications.The authors acknowledge funding support from the KAUST research translation grant and NEOM Ocean Science and Solutions Applied Research Institute grant 5476
Rare Earths Enrichment: Scaling Up Chromatographic Separation
No full textThe growing global demand for rare earth elements (REEs) has driven
advancements in their extraction and separation processes. This work explores
scaling up chromatographic techniques for REE enrichment, focusing on
challenges in extractive chromatography. The current REE separation
technologies possess some environmental concerns highlighting the need for
novel technologies. Extractive chromatography was proposed as an effective
solution to enhance separation in a more sustainable approach that is more viable
for recovery and separation of REES from non-traditional sources like recycling
of neo-magnets.
This study focuses on extractive chromatography technique and its scalability for
REEs enrichment. Experiments include the impregnation of adsorbents,
measuring adsorption equilibrium and the optimization of column
chromatography setups, examining key factors influencing separation efficiency.
Results demonstrate potential improvements in scalability of the separation
techniques, paving the way for more sustainable and economically viable process
of rare earth separation
Advances in ORR Catalysis Promoted by Graphene-Supported Low-Cost Metal Clusters: A DFT Study.
No full textThe oxygen reduction reaction (ORR), which converts molecular oxygen (O2) into water (H2O), is critical for renewable energy transformation processes. However, its industrial application is hindered by long conversion times. Recent studies suggest that transition metal clusters deposited on graphene are promising candidates for ORR catalysis. In this work, we employed density functional theory (DFT) calculations to explore the thermodynamically most stable energy profile of the ORR on pentamer metal clusters (Fe5, Co5, and Pt5) supported on undoped graphene and nitrogen-doped graphene (for Fe5), under standard electrochemical conditions (pH = 0 and U = 0). Both the "standard" intermediates (*OOH, *O, *OH) and the "unconventional" intermediates (*O*OH, *OH*OH) were studied, analyzing thermodynamic stability, adsorption energies, and the influence of the implicit water solvent. Our results reveal that the inclusion of "unconventional" intermediates significantly alters the reaction thermodynamics, presenting a new pathway that is energetically more favorable than the classical one. Catalytic performance predictions, based on the theoretical overpotential (ηORR), indicate that the four catalysts exhibit good stability and high activity in both reduction mechanisms. In particular, Fe5@NGr shows the best catalytic performance in the "unconventional" mechanism, with an ηORR close to zero. This study, for the first time, demonstrates how the metal cluster and the support's electronic and structural properties influence the stability of ORR intermediates and catalytic performance. The improved performance of Fe5@NGr in the "unconventional" mechanism highlights the importance of selecting the right metal and engineering the graphene support, particularly through N-doping, for the rational design of low-cost, high-performance catalysts.The authors thank the KAUST Super-Computing Laboratory (KSL) at KAUST and the CINECA award under the ISCRA initiative for the availability of high-performance computing resources and support. The Italian MUR through PRIN 2022 projects “MATISSE - 2022K5SX27” is kindly acknowledged for financial support to L.C
CCB79 is a primate-specific cilium initiation factor essential to maintain neural progenitor diversity in developing brain tissue
No full textAbstract
Identifying the genes that regulate the accurate spatiotemporal diversity of neural progenitor cells (NPCs) helps to understand the mechanisms of human neocortex expansion. In primate brains, an additional intermediate progenitor layer, the outer subventricular zone (oSVZ), facilitates the expansion of the neocortex. Here, we identify an uncharacterized gene, KIAA0408, and show that its expression is enriched in intermediate progenitors. Removing KIAA0408 in human-induced pluripotent stem cell (iPSC)-derived brain organoids results in an impaired cortical organization characterized by abnormal cell fate and patterning defects, including the depletion of intermediate and ventral progenitors. Molecularly, KIAA0408 codes for a 79-kilodalton centriolar distal appendage protein (DAP) that controls cilium biogenesis (hereafter CCB79). CCB79 forms a complex with other DAP components and specifically localizes in the DAP at the onset of ciliogenesis, and its absence blocks ciliogenesis. Mechanistically, progenitors in 3D brain tissues are unable to form cilia, which induces aberrant hedgehog signaling and causes premature differentiation. Finally, human CCB79, rather than the mouse ortholog, rescues cilia defects, suggesting that CCB79 has undergone rapid evolution from rodents to primates to fine-tune ciliogenesis for proper brain development.</p