Materials Science
Surface Properties of Ga-Cu Based Liquid-Metal Alloys: Impact of Cu Dilution Topography and Reaction Conditions
Tzung-En Hsieh, Michael S. Moritz, Andreas Mölkner et al. (+10 more)
We studied the surface properties of Ga-Cu based
liquid metal
alloys, a promising material system for supported catalytically active
liquid metal solutions (SCALMS). The impact of Cu dilution in the (
liquid) Ga
matrix is in-detail investigated by X-ray and UV photoelectron spectroscopy (XPS/UPS) and Machine-Learned-Force Field (ML-FF) calculations. With decreasing Cu content, microscopic and macroscopic Ga-Cu model samples exhibit a shift of the Cu 2p core level line to higher binding energies (Eb) as well as a correspondingly shifted and narrowed d-band with respect to pure Cu, which we ascribe to site isolation. To study the property
evolution of Ga-Cu at SCALMS reaction conditions, i.e., where Cu is present in
liquid Ga, additional XPS measurements were performed between 100 and 500 oC. The observed Cu 2p shift to lower Eb is tentatively ascribed to changes in the local environment with increasing temperature, i.e. bond elongation, which is corroborated by ML-FF simulations. The increased Cu surface content at low temperatures is attributed to the presence of crystallized Cu-rich intermetallic compounds, as evidenced by transmission electron microscopy images. In an attempt to generalize the findings for filled d-band transition metals (TMs) in
liquid Ga also Ga-Ag and Ga-Au model systems were investigated. The observed insights may be another step of paving the way for an insight-driven development of low-temperature melting
liquid metals for heterogeneous catalysis.
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All authors Tzung-En Hsieh, Michael S. Moritz, Andreas Mölkner, Christoph Wichmann, Johannes Frisch, Julien Steffen, Caiden J. Parker, Vaishnavi Krishnamurthi, Torben Daeneke, Hans-Peter Steinrück, Andreas Görling, Christian Papp, Marcus Bär
Materials Science
Colossal Cryogenic Electro-Optic Response Through Metastability in Strained BaTiO$_{3}$ Thin Films
Albert Suceava, Sankalpa Hazra, Aiden Ross et al. (+14 more)
The search for thin film electro-optic (EO) materials that can retain superior performance under cryogenic conditions has become critical for
quantum computing. Barium titanate thin films show large linear EO coefficients in the tetragonal phase at room temperature, which is severely degraded down to ~200 pm V$^{-1}$ in the rhombohedral phase at cryogenic temperatures. There is immense interest in manipulating these phase transformations and retaining superior EO properties down to
liquid helium temperature. Utilizing the thermodynamic theory of optical properties, a large low-temperature EO response is designed by engineering the energetic competition between different ferroelectric phases, leading to a low-
symmetry monoclinic phase with a massive EO response. The existence of this phase is demonstrated in a strain-tuned BaTiO$_{3}$ thin film that exhibits a linear EO coefficient of 2516 +/- 100 pm V$^{-1}$ at 5 K, which is an order of magnitude higher than the best reported performance thus far. Importantly, the EO coefficient increases by 100x during cooling, unlike the conventional films, where it degrades. Further, at the lowest temperature, significant higher order EO responses also emerge. These results represent a new framework for designing materials with property enhancements by stabilizing highly tunable metastable phases with strain. Copyright 2025 The Author(s). Advanced Materials published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. (A. Suceava, S. Hazra, A. Ross, et al. "Colossal Cryogenic Electro-Optic Response Through Metastability in Strained BaTiO3 Thin Films." Adv. Mater. (2025): e07564. https://doi.org/10.1002/adma.202507564)
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All authors Albert Suceava, Sankalpa Hazra, Aiden Ross, Ian Reed Philippi, Dylan Sotir, Brynn Brower, Lei Ding, Yingxin Zhu, Zhiyu Zhang, Himirkanti Sarkar, Saugata Sarker, Yang Yang, Suchismita Sarker, Vladimir A. Stoica, Darrell G. Schlom, Long-Qing Chen, Venkatraman Gopalan
Materials Science
Towards Universal Material Property Prediction with Deep Learning and Single-Descriptor electronic Density
Feng Chen, Shu Li, Xin Chen et al. (+3 more)
Owing to its high scalability and computational efficiency, machine learning methods have been increasingly integrated into various scientific research domains, including ab initio-based materials design. It has been demonstrated that, by incorporating modern machine learning
algorithms, one can predict material properties with practically acceptable accuracy. However, one of the most significant limitations that restrict the widespread application of machine learning is its lack of transferability, as a given framework is typically applicable only to a specific property. The origin of this limitation is rooted in the fact that a material's properties are determined by multiple degrees of freedom – and their complex interplay – associated with
nuclei and electrons, such as atomic type, structural
symmetry, and the number and
quantum states of the valence electrons, among others. The inherent complexity rules out the possibility of a single machine learning framework providing a full description of these critical quantities. In this paper, we develop a universal machine learning framework based solely on a physically grounded and theoretically rigorous descriptor – electronic charge density. Our framework not only enables accurate prediction of eight different material properties (with R$^2$ values up to 0.94), but also demonstrates outstanding multi-task learning capability, as prediction accuracy improves when more target properties are incorporated into a single training process, thereby indicating excellent transferability. These results represent a significant step toward realizing the long-standing goal of a universal machine learning framework for the unified prediction of all material properties.
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All authors Feng Chen, Shu Li, Xin Chen, Dennis Wong, Biplab Sanyal, Duo Wang
Materials Science
The nature of polar distortions in ferroelectrics
Hong Jian Zhao, Laurent Bellaiche and Yanming Ma
Polar distortion, the collective off-center displacements of atoms, is a fingerprint of a ferroelectric that governs its properties and functionalities. Since the 1970s, the concepts of proper, improper and triggered ferroelectrics have been established to shed light on a diversity of polar distortion mechanisms. Such concepts assign a single nature to polar distortion and are helpful to interpret how polar distortions occur in conventional ferroelectrics such as barium titanate. However, applying these concepts to complex ferroelectrics (e.g., polar orthorhombic hafnia) is notoriously challenging and can yield highly controversial arguments. Here we resolve this issue by developing a tailor-made graph theory for clarifying the nature of polar distortions in complex ferroelectrics, which emphasizes that polar distortions in such ferroelectrics usually exhibit multiple natures among proper, improper and triggered characteristics. We demonstrate the robustness of our theory by working with perovsktie superlattices and polar orthorhombic hafnia (i.e., two representative cases). We successfully identify the mixed proper-improper nature in perovsktite superlattices and reconcile the controversy on polar orthorhombic hafnia by confirming its mixed trigger-improper nature. Our work will definitely lead to a revisitation of concepts in ferroelectric physics and provide opportunities for discovering novel ferroelectrics and related phenomena.
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Disordered Systems and Neural Networks
Symmetry Transitions Beyond the Nanoscale in Pressurized Silica Glass
Zhen Zhang, Zhencheng Xie and Walter Kob
Silica is the paradigmatic network glass-former and understanding its response to pressure is essential for comprehending the mechanical properties of silica-based materials and the behavior of silicate melts in the Earth's interior. While pressure-induced changes in the short-range structure - particularly the breakdown of tetrahedral
symmetry - have been well documented, structural transformations on larger length scales, important for many material properties, remain poorly understood. Here, we numerically investigate the three-dimensional structure of silica glass as a function of compression up to $P \approx 100$~GPa. Using a novel many-body correlation function, we reveal a complex medium-range order: While for $P \lesssim 10$~GPa, one finds tetrahedral, octahedral, and cubic
symmetries, the structure at higher $P$s exhibits alternating cubic and octahedral particle arrangements. The $P$-dependence of the corresponding structural correlation length displays two distinct maxima, which permits to rationalize the anomalous compressibility of silica. The identified complex structural organization on intermediate range scales is the result of a pressure-and scale-dependent interplay between directional bonding, packing efficiency, and network stiffness. Since these competing effects are common in network glass-formers, the identified three-dimensional medium-range order, and hence the physical properties of the glass, are expected to be universal features of such materials under extreme conditions.
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Soft Condensed Matter
Demon's variational principle for informational active matter
Kento Yasuda, Kenta Ishimoto and Shigeyuki Komura
The interplay between information, dissipation, and control is reshaping our understanding of thermodynamics in feedback-regulated systems. We develop the informational Onsager-Machlup principle, a generalized variational framework that unifies energetic, dissipative, and informational contributions within a single formalism. This framework introduces a conditioned Onsager-Machlup integral to quantify path
entropy under specified
memory states and enables the derivation of cumulant generating functions for arbitrary observables in systems with measurement and feedback. Our formulation is consistent with
stochastic thermodynamics and information thermodynamics. To demonstrate the utility of the IOMP, we apply it to an information swimmer and show that it systematically reproduces the analytical expressions for the mean velocity and higher-order cumulants obtained by a direct approach, while also enabling the calculation of
entropy production in the single-measurement case. For repeated measurements and the steady state, we derive approximate analytical expressions by using a Gaussian closure for the distribution of measured velocities. Our analytical results show good agreement with numerical results, except for cases of extreme drag asymmetry.
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Materials Science
Thermal and Electrical Properties of (Cr,Mo,Ta,V,W)C High-Entropy Carbide Ceramics
Ali Sarikhani, Steven M. Smith, Suzana Filipovic et al. (+2 more)
The synthesis and characterization, along with the resulting properties, of fully dense \((\mathrm{Cr, Mo, Ta, V, W})\mathrm{C}\) high-
entropy carbide ceramics were studied. The ceramics were synthesized from metal
oxide and carbon powders by carbothermal reduction, followed by spark
plasma sintering at various temperatures for densification. Increasing the densification temperature resulted in grain growth and an increase in the
lattice parameter. Thermal diffusivity increased linearly with testing temperature, resulting in thermal conductivity values ranging from approximately \(7~\mathrm{W\,m^{-1}\,K^{-1}}\) at room temperature to \(12~\mathrm{W\,m^{-1}\,K^{-1}}\) at \(200~^\circ\mathrm{C}\). Measured heat capacity values matched theoretical estimates made using the Neumann–Kopp rule. Room-temperature electrical resistivity decreased from \(137\) to \(120~\mu\Omega\cdot\mathrm{cm}\) as the excess carbon decreased from \(5.4\) to \(0.1~\mathrm{vol\%}\), suggesting an enhanced electronic contribution to thermal conductivity as excess carbon decreased. All specimens exhibited a Vickers hardness of approximately \(29~\mathrm{GPa}\) under a \(0.49~\mathrm{N}\) load. These results underscore the tunability of this high-
entropy carbide system.
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All authors Ali Sarikhani, Steven M. Smith, Suzana Filipovic, William G. Fahrenholtz, Gregory E. Hilmas
Materials Science
Melting phase relation of seifertite and pyrite-type SiO2 determined by machine learning potentials
Doyoon Park, Xin Deng and Jie Deng
Silica (SiO2) is fundamental to both industrial technology and planetary science, yet the phase relations of its high-pressure polymorphs remain poorly constrained. Here, we develop two machine learning potentials (MLPs) for SiO2 that faithfully represent the SCAN and PBEsol exchange-correlation functionals over a wide temperature (1000-10000 K) and pressure (100-400 GPa) range using deep neural networks. With large-scale two-phase simulations powered by these potentials, we determine the melting curves of seifertite and pyrite-type SiO2 and infer the solid-solid phase boundary between these two phases. The SCAN functional, which captures intermediate-range van der Waals interactions, reproduces structural and thermodynamic properties with high fidelity, predicting melting temperatures 6-10 % higher and a seifertite to pyrite-type transition pressure 22 % higher than the PBEsol. The strongly negative Clapeyron slope (-6.1 MPa/K) of this transition suggests that mantle convection could be highly layered in super-Earth
exoplanets, potentially affecting their long-term thermal
evolution and habitability.
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Materials Science
Energetic Origins of Competing Deformation Modes in Metastable Titanium Alloys
Ganlin Chen, Deepak V Pillai, Yufeng Zheng et al. (+1 more)
Metastable
alloys, such as $\beta$-phase titanium (Ti)
alloys with a body-centered cubic (BCC)
lattice, can exhibit exceptional mechanical properties through the interplay of multiple deformation mechanisms – diffusionless phase transformations, deformation twinning, and conventional dislocation slip. However, understanding how these mechanisms compete or cooperate across a wide range of metastable
alloys and loading conditions remains a fundamental challenge. Here, we employ molecular dynamics (MD) simulations to investigate the nucleation behavior of competing deformation modes in metastable $\beta$-Ti
alloys as a function of temperature, composition, and loading conditions. We reveal that twinning pathways emerge through reversible transformations between the $\beta$ phase and the orthorhombic $\alpha"$ phase, in agreement with crystallographic theories. Quantitative analyses demonstrate that the dominant deformation mechanisms and preferred twinning-plane orientations are governed by two key energetic parameters: the free energy barrier for homogeneous $\beta \leftrightarrow \alpha"$ transformations and the misfit strain energy along specific phase boundaries. These energetic quantities vary systematically with thermodynamic and mechanical conditions, thereby rationalizing the deformation mode transitions observed in both simulations and experiments. These energetic metrics offer a physically grounded and computationally tractable basis for designing next-generation metastable
alloys.
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All authors Ganlin Chen, Deepak V Pillai, Yufeng Zheng, Liang Qi
Materials Science
Large-gap quantum anomalous Hall insulator in two-dimensional pentagonal TiN$_8$ monolayer
Zheng Wang, Linda Sophie Reitz, Beichen Ruan et al. (+4 more)
Discovering the
quantum anomalous
Hall (QAH) effect in two-dimensional magnets is a central goal of topological condensed matter physics, yet candidate materials combining a sizable gap with a well-defined Chern number remain scarce. We report a new material platform that realizes emergent magnetism and nontrivial band
topology within the largely overlooked family of two-dimensional MN$_8$ monolayers. Through first-principles calculations, we reveal that these systems exhibit out-of-plane
magnetic ground states and nontrivial topological features driven by the localized $d$-orbitals of the embedded transition metals. Remarkably, we identify TiN$_8$ as a
quantum anomalous
Hall insulator characterized by a Chern number of $C=-1$ with a large topological gap of 223 meV. As a companion system, MoN$_8$ is predicted to be a rare high-Chern-number QAH
insulator, with a Chern number of $C=2$, although its much smaller gap of 12 meV renders it more fragile. These findings establish the penta-MN$_8$ family as a versatile and promising platform to realize exotic topological
quantum states. This work not only broadens the material landscape for
magnetic topological
insulators but also lays a solid theoretical foundation for the development of next-generation spintronic and
quantum computing devices.
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All authors Zheng Wang, Linda Sophie Reitz, Beichen Ruan, Zhuoheng Li, Shu-Shen Lyu, Richard Dronskowski, Kaixuan Chen
Superconductivity
Flat bands in condensed-matter systems – perspective for magnetism and superconductivity
Hideo Aoki
There is a recent upsurge of interests in flat bands in condensed-matter systems and the consequences for magnetism and superconductivity. This article highlights the physics, where peculiar
quantum-mechanical mechanisms for the physical properties such as flatband ferromagnetism and flatband superconductivity that arise when the band is not trivially flat but has a strange
Hilbert space with non-orthogonalisable Wannier states, which goes far beyond just the diverging density of states. Peculiar wavefunctions come from a
quantum-mechanical interference and
entanglement. Interesting phenomena become even remarkable when many-body interactions are introduced, culminating in flatband superconductivity as well as flatband ferromagnetism. Flatband physics harbours a very wide range physics indeed, extending to non-
equilibrium physics in
laser illumination, where Floquet states for topologcial superconductivity is promoted in flatbands. While these are theoretically curious, possible candidates for the flatband materials are beginning to emerge, which is also described. These provide a wide and promising outlook.
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Disordered Systems and Neural Networks
Optimization of Transferable Interatomic Potentials for Glasses toward Experimental Properties
Ruoxia Chen, Kai Yang, Morten M. Smedskjaer et al. (+3 more)
The accuracy of molecular simulations is fundamentally limited by the interatomic potentials that govern atomic interactions. Traditional potential development, which relies heavily on ab initio calculations, frequently struggles to reproduce the experimentally observed properties that govern real material behavior. To address this challenge, we present a machine learning-driven, active-learning optimization framework for optimizing classical interatomic potentials to reproduce experimental properties. Our method, here showcased on soda-lime borosilicate glasses, targets both global (density) and local (boron coordination) structural features across a wide range of compositions. By combining a surrogate model with iterative active learning, the framework efficiently explores a five-dimensional parameter space using only 400 molecular dynamics simulations over 17 iterations, making it highly data-efficient and eliminating the need for extensive simulation campaigns. Two transferable parameter sets are identified, each demonstrating good agreement with experimental measurements, including glass density, fraction of four-fold boron, and X-ray structure factor. The framework effectively captures and manages inherent trade-offs between structural objectives and compositional regimes, providing insights into the coordination behavior of boron in complex glass networks. The resulting classical force fields are generalizable and do not require reparameterization for individual compositions. Altogether, this work offers a scalable and experimentally grounded approach for developing transferable interatomic potentials suitable for a broad range of materials, including multi-component glass systems, and beyond.
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All authors Ruoxia Chen, Kai Yang, Morten M. Smedskjaer, N. M. Anoop Krishnan, Jaime Marian, Fabian Rosner
Quantum Gases
From elastic to inelastic deformation of a dipolar supersolid
Qiaomei Zhao, Xingdong Zhao and Jieli Qin
Due to its peculiar superfluid-
crystal duality feature, supersolid has received great research interest. Recently, researchers have paid much
attention to its elastic response properties; however, the inelastic deformation has barely been explored. In this work, we study the transition from elastic to inelastic deformation of a dipolar supersolid Bose-Einstein condensate trapped in a box potential (i.e., a dipolar supersolid with finite size). We obtained the stationary supersolid states (both ground and excited) of the system, and examined the relation between the supersolid size and the number of unit
cells it can accommodate, which can essentially help us to understand the dynamical responses of the supersolid during a dilation or compression process. We found that within a certain dilation or compression extent, the supersolid can retain its original
crystal structure, that is, it endures an elastic deformation; however, when the extent exceeds a critical threshold, the original
crystal structure of the supersolid will be disrupted, which signifies an inelastic deformation. Furthermore, we both analytically and numerically determined the critical point of the transition from elastic to inelastic deformation, and mapped out a phase diagram. These results open up new territory in the research of supersolid mechanical properties, and may find applications in
quantum material science and
quantum-based technologies.
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Quantum Gases
Static and dynamical properties of quadrupolar quantum droplets in quasi-2D condensates
Wei-qi Xia, Xiao-ting Zheng, Xiao-wei Chen et al. (+1 more)
Quantum droplets, stabilized by beyond-mean-field effects, represent a novel state of matter in
quantum many-body systems. While previous studies have focused primarily on dipolar and contact-interacting systems, quadrupolar condensates remain relatively unexplored. In this work, we explore the formation, structural properties, and dynamical behaviors of
quantum droplets in a two-component quadrupolar Bose-Einstein condensate confined to a quasi-two-dimensional geometry. Analytical results obtained via the Thomas-
Fermi approximation predict flat-topped density profiles and linear scaling between effective area and particle number. These predictions are corroborated by numerical simulations, which also reveal the saturation of peak density and chemical potential at large norm. Furthermore,
vortex quantum droplets exhibit anisotropic elliptical morphologies due to the directional nature of QQIs, with their aspect ratios significantly tunable by varying the particle number and quadrupolar interaction strength. Collision dynamics demonstrate rich behavior modulated by velocity and
topology: ground-state droplets transition from inelastic merging to quasi-elastic scattering and
quantum penetration, while
vortex droplets exhibit phase-induced repulsion, fragmentation, and topologically protected tunneling. These findings offer a comprehensive understanding of how higher-order interactions and
quantum fluctuations govern the formation and stability of quadrupolar droplets. This work lays a theoretical foundation for experimental realization and opens new directions for exploring anisotropic
quantum fluids, topological excitations, and applications in
quantum sensing and simulation.
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All authors Wei-qi Xia, Xiao-ting Zheng, Xiao-wei Chen, Gui-hua Chen
Quantum Gases
Macroscopic Self-Trapping and Dynamical Phase Transition in Momentum Space Bose-Einstein Condensates
Colby Schimelfenig, Federico Serrano, Corey Halverson et al. (+3 more)
Self-trapping is a hallmark phenomenon of nonlinear dynamics. It has significant applications in modern physics, including band structure engineering, phase transition dynamics,
quantum metrology, and more. Dilute-gas Bose-Einstein condensates (BECs), in which self-trapping can arise from interatomic interactions, are a
prime testbed for probing nonlinear dynamics. In this Letter, we report the observation of self-trapping in a
spin-orbit coupled BEC subjected to a stationary optical
lattice. We employ Raman-induced
spin-orbit coupling, complemented by a matching optical
lattice that facilitates coupling between momentum eigenstates of the
spin-orbit coupled system. By ramping the Raman detuning, we probe atomic current flow between these eigenstates and identify a clear distinction between a delocalized mixed state and a self-trapped regime. Following a quench of the Raman detuning, the time-averaged atomic current exhibits non-analytic behavior across the transition between these two regimes in certain parameter ranges, signaling a dynamical phase transition in the system.
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All authors Colby Schimelfenig, Federico Serrano, Corey Halverson, Annesh Mukhopadhyay, Qingze Guan, Peter Engels
Materials Science
Reciprocal Space Attention for Learning Long-Range Interactions
Hariharan Ramasubramanian, Alvaro Vazquez-Mayagoitia, Ganesh Sivaraman et al. (+1 more)
Machine learning interatomic potentials (MLIPs) have revolutionized the modeling of materials and molecules by directly fitting to ab initio data. However, while these models excel at capturing local and semi-local interactions, they often prove insufficient when an explicit and efficient treatment of long-range interactions is required. To address this limitation, we introduce Reciprocal-Space
Attention (RSA), a framework designed to capture long-range interactions in the
Fourier domain. RSA can be integrated with any existing local or semi-local MLIP framework. The central contribution of this work is the mapping of a linear-scaling
attention mechanism into
Fourier space, enabling the explicit modeling of long-range interactions such as electrostatics and dispersion without relying on predefined charges or other empirical assumptions. We demonstrate the effectiveness of our method as a long-range correction to the MACE backbone across diverse
benchmarks, including dimer binding curves, dispersion-dominated layered phosphorene exfoliation, and the molecular dipole density of bulk water. Our results show that RSA consistently captures long-range physics across a broad range of chemical and materials systems. The code and
datasets for this work is available at https://github.com/rfhari/reciprocal_space_
attention
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All authors Hariharan Ramasubramanian, Alvaro Vazquez-Mayagoitia, Ganesh Sivaraman, Atul C. Thakur
Statistical Mechanics
Adiabatic Elimination in Relativistic Stochastic Mechanics
Tao Wang and Yu Shi
We investigate the adiabatic elimination of fast variables in relativistic
stochastic mechanics, which is analyzed by using the equation of motion and the distribution function, with relativistic corrections explicitly derived. A new dimensionless parameter is introduced to characterize the timescale. The adiabatic elimination is compared with the path integral coarse graining, which is more general yet computationally demanding.
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