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Fang Yuan

Publications and source records attributed to Fang Yuan.

At least 19 recordsLinked to original sources
arXiv2026

Cascade coalescence dynamically sustains bubble retention near gas-evolving surfaces

Bubble detachment from solid surfaces governs heat, mass, and charge transport across technologies vital to clean energy, including high-current-density water electrolysis and boiling thermal management. At high gas fluxes, however, bubbles remain trapped at active surfaces despite immense buoyancy, severely restricting mass transfer and increasing energy losses. Here, we show that this unexpected surface retention originates from cascade coalescence between unequal-sized bubbles. High-speed observations around microelectrodes demonstrate that when a rising bubble merges with a smaller surface-attached successor, its trajectory abruptly reverses, accelerating toward the substrate at nearly two orders of magnitude above its rising speed. Direct numerical simulations and scaling analysis reveal that asymmetric interfacial retraction during merging generates non-canceling viscous stresses, producing a net downward impulse toward the smaller bubble. Repeated cascade coalescence events accumulate these transient impulses into a steady, time-averaged retaining force capable of opposing buoyancy three to four orders of magnitude beyond quasistatic limits. Our findings establish bubble coalescence as a previously unrecognized mechanism that dynamically sustains bubble retention under high gas flux.

physics.flu-dyn↗
arXiv2026

Chiral, Electronically Decoupled Layers of 1T'-WS2 Topological Insulator via Neutral-Molecule Intercalation

Monolayer 1T'-WS2 is predicted to be a two-dimensional topological insulator, but its intrinsic electronic properties are masked by strong interlayer coupling in its metallic and superconducting bulk parent phase, 2M-WS2. Isolating monolayers by mechanical exfoliation is also hindered by this coupling, preventing experimental examination of monolayer properties. Here we show that 2M-WS2 undergoes amine intercalation through a simple wet-chemical reaction, yielding superlattices in which the 1T' layers are structurally preserved but electronically decoupled by neutral molecular spacers. Intercalation expands the interlayer spacing from 0.5 to 1-4 nm and reconstructs the stacking while preserving the intralayer 1T' framework. Controlled (de)intercalation reversibly switches the system between a superconducting metal and an insulator with an activation gap matching that of the isolated monolayer. Density functional theory indicates that the electronically decoupled layers retain the nontrivial Z2 topology of the monolayer. Chiral amine intercalation further induces chiroptical activity in WS2 electronic transitions. Overall, the successful intercalation challenges the long-held view that group VIB dichalcogenides are inert toward neutral-molecule intercalation and demonstrates molecular intercalation as a general chemical route for realizing monolayer-like topological-insulator physics and enabling chiral van der Waals superlattices in bulk single crystals.

cond-mat.mtrl-sci↗
arXiv2026

Bridging the Post-discharge Gap: A Traceable Multi-agent Framework for Safe and Continuous Care

Post-discharge clinical follow-up is critical for maintaining continuity of care and mitigating long-term health risks. However, traditional follow-up paradigms suffer from shortage of health workforce, fragmented patient histories, and information silos across clinical departments. While large language models have demonstrated potential in medical question-answering, their deployment in continuous care is hindered by hallucination risks and a fundamental inability to reason over longitudinal, patient-specific constraints. Here we present Healink, a memory-enhanced multi-agent framework to support AI-assisted post-discharge follow-up by generating prescription-grounded, traceable responses that improved completeness and perceived clinical utility in retrospective and physician-blinded evaluations. The architecture seamlessly integrates a triage routing mechanism, a unified memory enhancement module utilizing a robust relational database for optimal latency, and a strict constraint-based retrieval-augmented generation engine. By vectorizing historical clinical records and employing weighted similarity functions across diverse phenotypic and intervention dimensions, Healink ensures precise inter-patient and intra-patient case matching while actively preventing cross-departmental drug conflicts. We evaluated Healink on a dataset comprising 400 continuous and 85 highly complex real-world follow-up cases, alongside the webMedQA benchmark. In a rigorous single-blind evaluation conducted by clinical experts, the framework outperformed human physician baselines in both authoritativeness and clinical safety. By generating a traceable, white-box evidence chain, Healink provides a scalable, safe, and highly effective paradigm for intelligent patient management, ultimately enhancing societal healthcare outcomes.

cs.MA↗
arXiv2026

PACE: Parameter Change for Unsupervised Environment Design

Unsupervised Environment Design (UED) offers a promising paradigm for improving reinforcement learning generalization by adaptively shaping training environments, but it requires reliable environment evaluation to remain effective. However, existing UED methods evaluate environments using indirect proxy signals such as regret, value-based errors, or Monte Carlo, which suffer from bias, high variance, or substantial computational overhead and fail to reflect agent realized learning progress. To address these limitations, we propose Parameter Change Environment Design (PACE), which evaluates an environment through the policy parameter change induced by training on that environment, directly grounding environment selection in realized learning progress. Specifically, PACE assigns environment value using a first-order approximation of the policy optimization objective, where the improvement induced by an environment is proportional to the squared L2 norm of the corresponding parameter update, enabling low-variance and computation-efficient evaluation without additional rollouts. Experiments on MiniGrid and Craftax show that PACE consistently outperforms established UED baselines, achieving higher IQM and smaller Optimality Gap on OOD evaluations, including an IQM of 96.4% and an Optimality Gap of 17.2% on MiniGrid.

cs.LG↗
arXiv2025

NL2GenSym: Natural Language to Generative Symbolic Rules for SOAR Cognitive Architecture via Large Language Models

SOAR, a classic symbol-based cognitive architecture, has been fostering the development of general, human-like intelligent agents. Nevertheless, its practical adoption is hindered by the laborious manual rule coding. Emerging Large Language Models (LLMs) present the immense potential for efficient rules generation. However, there is a critical gap that current research predominantly focuses on conceptual frameworks and lacks robust experimental validation. To bridge this gap, we propose \textit{N}atural \textit{L}anguage to \textit{Gen}erative \textit{Sym}bolic Rules (NL2GenSym), a novel framework that integrates LLMs with SOAR to autonomously produce generative symbolic rules from natural language. Specifically, our framework introduces a novel Execution-Grounded Generator-Critic mechanism. The LLM-based Generator, guided by a Retrieval-Augmented Generation-accessed self-evolving domain knowledge base, proposes rules from natural language. Subsequently, these rules are immediately executed within the SOAR environment to rigorously validate their correctness. Based on this execution-grounded feedback, a reflective LLM-based Critic drives the iterative refinement of these rules. Experiments on our specialized Water Jug Problem (WJP) dataset, utilizing both Gemini and Qwen series models, validate the efficacy of our framework. It achieves a success rate over 86\% in generating rules from natural language. Crucially, the framework also generates novel heuristic rules, reducing average decision cycles for solving the WJP to 1.98 times the optimal solution and 1/1000 of baseline methods. Additionally, our initial experiments show that NL2GenSym enables smaller-parameter models to achieve better performance than larger counterparts.

cs.CL↗
arXiv2025

Comparative Study on the Discourse Meaning of Chinese and English Media in the Paris Olympics Based on LDA Topic Modeling Technology and LLM Prompt Engineering

This study analyzes Chinese and English media reports on the Paris Olympics using topic modeling, Large Language Model (LLM) prompt engineering, and corpus phraseology methods to explore similarities and differences in discourse construction and attitudinal meanings. Common topics include the opening ceremony, athlete performance, and sponsorship brands. Chinese media focus on specific sports, sports spirit, doping controversies, and new technologies, while English media focus on female athletes, medal wins, and eligibility controversies. Chinese reports show more frequent prepositional co-occurrences and positive semantic prosody in describing the opening ceremony and sports spirit. English reports exhibit positive semantic prosody when covering female athletes but negative prosody in predicting opening ceremony reactions and discussing women's boxing controversies.

cs.CL↗
arXiv2024

Directionally Locked Heteroepitaxy with a Structurally Modulated van der Waals Material

Precise orientation of symmetry-mismatched epilayers on van der Waals (vdW) substrates via heteroepitaxy has commonly been achieved through surface treatment processes to accommodate weak interlayer registry and bonding strength, thereby limiting the range of material combinations for heterostructure design. In this study, we investigate the influence of lattice instabilities in a structurally modulated vdW TaCo2Te2 substrate on the growth and alignment of a symmetry-mismatched bulk CoxTey epilayer using in situ heating in a transmission electron microscope (TEM). We show that a Peierls-like lattice instability occurs in TaCo2Te2 at a transition temperature of ~523 K, which was corroborated by phonon calculations. Post-heat-treated samples reveal a thermally induced surface diffusion process and the dominant lateral growth of the CoxTey epilayer on the TaCo2Te2 vdW layers, as observed in cross-sectional TEM images. Temperature-dependent selected area electron diffraction (SAED) patterns reveal that the quasi-vdW CoxTey/TaCo2Te2 heterointerface acquires directional locking by aligning larger interlayer lattice mismatch along the lattice instability axis of TaCo2Te2, while preserving a strong lattice matching along the orthogonal direction. This heterostructure exhibits precise interlayer registry with one-dimensional lattice incommensuration along the lattice instability axis, resulting from structural distortion to accommodate lattice-mismatch strain. Moreover, the interfacial reconstruction of TaCo2Te2 back to the distorted phase stabilizes the lattice-locking of the quasi-vdW heterointerface at elevated temperatures. These findings encourage the expansion of material diversity for designing and predicting novel multi-dimensional heterostructures by leveraging lattice instabilities to guide epitaxy.

cond-mat.mtrl-sci↗
arXiv2024

$Mesiri$:Mephisto Early Supernovae Ia Rapid Identifier

The early time observations of Type Ia supernovae (SNe Ia) play a crucial role in investigating and resolving longstanding questions about progenitor stars and the explosion mechanisms of these events. Colors of supernovae (SNe) in the initial days after the explosion can help differentiate between different types of SNe. However, the use of true color information to identify SNe Ia at the early-time explosion is still in its infancy. The Multi-channel Photometric Survey Telescope (Mephisto) is a photometric survey telescope equipped with three CCD cameras, capable of simultaneously imaging the same patch of sky in three bands (\emph{u, g, i} or \emph{v, r, z}), yielding real-time colors of astronomical objects. In this paper, we introduce a new time-series classification tool named Mephisto Early Supernovae Ia Rapid Identifier (\emph{\texttt{Mesiri}}), which for the first time, utilizes real-time color information to distinguish early-time SNe Ia from core-collapse supernovae (CCSNe). \emph{\texttt{Mesiri}} is based on the deep learning approach and can achieve an accuracy of $96.75\pm0.79$\%, and AUC of $98.87\pm0.53$\% in case of single epoch random observation before the peak brightness. These values reach towards perfectness if additional data points on several night observations are considered. The classification with real-time color significantly outperforms that with pseudo-color, especially at the early time, i.e., with only a few points of observations. The architecture of BiLSTM shows the best performance than the others that have been tested in this work.

astro-ph.IM↗
arXiv2024

Anomalous Superconductivity in Twisted MoTe2 Nanojunctions

Introducing superconductivity in topological materials can lead to innovative electronic phases and device functionalities. Here, we present a new strategy for quantum engineering of superconducting junctions in moire materials through direct, on-chip, and fully encapsulated 2D crystal growth. We achieve robust and designable superconductivity in Pd-metalized twisted bilayer molybdenum ditelluride (MoTe2) and observe anomalous superconducting effects in high-quality junctions across ~ 20 moire cells. Surprisingly, the junction develops enhanced, instead of weakened, superconducting behaviors, exhibiting fluctuations to a higher critical magnetic field compared to its adjacent Pd7MoTe2 superconductor. Additionally, the critical current further exhibits a striking V-shaped minimum at zero magnetic field. These features are unexpected in conventional Josephson junctions and indeed absent in junctions of natural bilayer MoTe2 created using the same approach. We discuss implications of these observations, including the possible formation of mixed even- and odd-parity superconductivity at the moire junctions. Our results also demonstrate a pathway to engineer and investigate superconductivity in fractional Chern insulators.

cond-mat.supr-con↗
arXiv2024

Superconductivity from On-Chip Metallization on 2D Topological Chalcogenides

Two-dimensional (2D) transition metal dichalcogenides (TMDs) is a versatile class of quantum materials of interest to various fields including, e.g., nanoelectronics, optical devices, and topological and correlated quantum matter. Tailoring the electronic properties of TMDs is essential to their applications in many directions. Here, we report that a highly controllable and uniform on-chip 2D metallization process converts a class of atomically thin TMDs into robust superconductors, a property belonging to none of the starting materials. As examples, we demonstrate the introduction of superconductivity into a class of 2D air-sensitive topological TMDs, including monolayers of Td-WTe2, 1T'-MoTe2 and 2H-MoTe2, as well as their natural and twisted bilayers, metalized with an ultrathin layer of Palladium. This class of TMDs are known to exhibit intriguing topological phases ranging from topological insulator, Weyl semimetal to fractional Chern insulator. The unique, high-quality two-dimensional metallization process is based on our recent findings of the long-distance, non-Fickian in-plane mass transport and chemistry in 2D that occur at relatively low temperatures and in devices fully encapsulated with inert insulating layers. Highly compatible with existing nanofabrication techniques for van der Waals (vdW) stacks, our results offer a route to designing and engineering superconductivity and topological phases in a class of correlated 2D materials.

cond-mat.mes-hall↗
arXiv2024

Mixed-halide perovskite alloys $\text{CsPb}(\text{I}_{1-x}^{}\text{Br}_x^{})_3^{}$ and $\text{CsPb}(\text{Br}_{1-x}^{}\text{Cl}_x^{})_3^{}$: New insight of configuration entropy effect from first principles and phase diagrams

Stability is one of the key issues in mixed-halide perovskite alloys which are promising in emergent optoelectronics. Previous density-functional-theory (DFT) and machine learning studies indicate that the formation-energy convex hulls of these materials are very shallow, and stable alloy compositions are rare. In this work, we revisit this problem using DFT with special focus on the effects of configuration and vibration entropies. Allowed by the $20$-atomic models for the $\text{CsPb}(\text{I}_{1-x}^{}\text{Br}_x^{})_3^{}$ and $\text{CsPb}(\text{Br}_{1-x}^{}\text{Cl}_x^{})_3^{}$ series, the partition functions and therewith thermodynamic state functions are calculated by traversing all possible mixed-halide configurations. We can thus evaluate the temperature- and system-dependent configuration entropy, which largely corrects the conventional approach based on the ideal solution model. Finally, temperature-composition phase diagrams that include $α$, $β$, $γ$ and $δ$ phases of both alloys are constructed based on the free energy data, for which the contribution of phonon vibrations is included.

cond-mat.mtrl-sci↗
arXiv2024

Coalescence induced late departure of bubbles improves water electrolysis efficiency

In water electrolysis, bubbles form on the electrode and interact through processes such as collision and coalescence. However, the impact of bubble coalescence a fundamental process governing electrolytic bubble behaviour-on electrolysis efficiency remains unclear. Here, we show that enhancing bubble coalescence improves electrolysis efficiency by more than 30% compared to systems where coalescence is inhibited. One key feature is the continuous coalescence of a newly detached bubble with microbubbles on the electrode, which delays the former from departing. Experimental observations and numerical simulations reveal two key benefits of bubble coalescence for electrolysis efficiency: (1) it liberates surface bubbles from the electrode at much smaller sizes, reducing their diameter from approximately 60-80 um to less than 10 um, thus freeing the active sites of the electrode from bubble coverage; (2) it induces strong agitation, with velocities reaching 1m/s in a small region near the electrode (at a depth of 10-5 m), thereby significantly improving the heat/mass transfer locally. Importantly, the chaotic agitation effect lasts for approximately 10 ms, two orders of magnitude longer than the coalescence process, which occurs in around 0.2 ms. This work provides valuable insight into bubble management in water electrolysis and other gas-evolution electrochemical reactions.

physics.chem-ph↗
arXiv2023

Purely anharmonic charge-density wave in the 2D Dirac semimetal SnP

Charge density waves (CDWs) in two-dimensional (2D) materials have been a major focus of research in condensed matter physics for several decades due to their potential for quantum-based technologies. In particular, CDWs can induce a metal-insulator transition by coupling two Dirac fermions, resulting in the emergence of a topological phase. Following this idea, here we explore the behavior of three different CDWs in a new 2D layered material, SnP, using both density functional theory calculations and experimental synthesis to study its stability. The layered structure of its bulk counterpart, Sn4P3, suggests that the structure can be synthesized down to the monolayer by exfoliation or chemical means. However, despite the stability of the bulk, the monolayer shows unstable phonons at {\Gamma}, K, and M points of the Brillouin zone, which lead to three possible charge-density-wave phases. All three CDWs lead to metastable insulating phases, with the one driven by the the active phonon in the K point being topologically non-trivial under strain. Strikingly, the ground-state structure is only revealed due to the presence of strong anharmonic effects. This, underscores the importance of studying CDWs beyond the conventional harmonic picture, where the system's ground state can be elucidated solely from the harmonic phonon spectra.

cond-mat.mtrl-sci↗
arXiv2023

Cosmological Distance Measurement of 12 Nearby Supernovae IIP with ROTSE-IIIB

We present cosmological analysis of 12 nearby ($z<0.06$) Type IIP supernovae (SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise photometry, we present a new image differencing technique that is implemented for the first time on the ROTSE SN photometry pipeline. With this method, we find up to a 20\% increase in the detection efficiency and significant reduction in residual RMS scatter of the SN lightcurves when compared to the previous pipeline performance. We use the published optical spectra and broadband photometry of well studied SNe IIP to establish temporal models for ejecta velocity and photospheric temperature evolution for our SNe IIP population. This study yields measurements that are competitive to other methods even when the data are limited to a single epoch during the photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and optical spectra, we apply these models to the respective photometric epochs for each SN in the ROTSE IIP sample. This facilitates the use of the Expanding Photosphere Method (EPM) to obtain distance estimates to their respective host galaxies. We then perform cosmological parameter fitting using these EPM distances from which we measure the Hubble constant to be $72.9^{+5.7}_{-4.3}~{\rm kms^{-1}~Mpc^{-1}}$, which is consistent with the standard $ΛCDM$ model values derived using other independent techniques.

astro-ph.HE↗
arXiv2023

Surface-Confined Two-Dimensional Crystal Growth on a Monolayer

Conventional vapor deposition or epitaxial growth of two-dimensional (2D) materials and heterostructures is conducted in a large chamber in which masses transport from the source to the substrate. Here we report a chamber-free, on-chip approach for growing a 2D crystalline structures directly in a nanoscale surface-confined 2D space. The method is based on a surprising discovery of a rapid, long-distance, non-Fickian transport of a uniform layer of atomically thin palladium (Pd) on a monolayer crystal of tungsten ditelluride (WTe2), at temperatures well below the known melting points of all materials involved. The resulting nanoconfined growth realizes a controlled formation of a stable new 2D crystalline material, Pd7WTe2 , when the monolayer seed is either free-standing or fully encapsulated in a van der Waals stack. The approach is generalizable and highly compatible with nanodevice fabrication, promising to expand the library of 2D materials and their functionalities.

cond-mat.mes-hall↗
arXiv2022

Atomically Sharp Internal Interface in a Chiral Weyl Semimetal Nanowire

Internal interfaces in Weyl semimetals (WSMs) are predicted to host distinct topological features that are different from the commonly studied external interfaces (crystal-to-vacuum boundaries). However, the lack of atomically sharp and crystallographically oriented internal interfaces in WSMs makes it difficult to experimentally investigate hidden topological states buried inside the material. Here, we study a unique internal interface known as merohedral twin boundary in chemically synthesized single-crystal nanowires (NWs) of CoSi, a chiral WSM of space group P213 (No. 198). High resolution scanning transmission electron microscopy reveals that this internal interface is (001) twin plane and connects two enantiomeric counterparts at an atomically sharp interface with inversion twinning. Ab-initio calculations show localized internal Fermi arcs at the (001) twin boundary that can be clearly distinguished from both external Fermi arcs and bulk states. These merohedrally twinned CoSi NWs provide an ideal material system to probe unexplored topological properties associated with internal interfaces in WSMs.

cond-mat.mtrl-sci↗
arXiv2021

Harvesting the triplet excitons of quasi-two-dimensional perovskite toward highly efficient white light-emitting diodes

Utilization of triplet excitons, which generally emit poorly, is always fundamental to realize highly efficient organic light-emitting diodes (LEDs). While triplet harvest and energy transfer via electron exchange between triplet donor and acceptor are fully understood in doped organic phosphorescence and delayed fluorescence systems, the utilization and energy transfer of triplet excitons in quasi-two-dimensional (quasi-2D) perovskite are still ambiguous. Here, we use an orange-phosphorescence-emitting ultrathin organic layer to probe triplet behavior in the sky-blue-emitting quasi-2D perovskite. The delicate white LEDs architecture enables a carefully tailored Dexter-like energy-transfer mode that largely rescues the triplet excitons in quasi-2D perovskite. Our white organic-inorganic LEDs achieve maximum forward-viewing external quantum efficiency of 8.6% and luminance over 15000 cd m-2, exhibiting a significant efficiency enhancement versus the corresponding sky-blue perovskite LED (4.6%). The efficient management of energy transfer between excitons in quasi-2D perovskite and Frenkel excitons in organic layer opens the door to fully utilizing excitons for white organic-inorganic LEDs.

physics.optics↗
arXiv2021

TaCo$_{2}$Te$_{2}$: An air-stable, magnetic van der Waals material with high mobility

Van der Waals (vdW) materials are an indispensable part of functional device technology due to their versatile physical properties and ease of exfoliating to the low-dimensional limit. Among all the compounds investigated so far, the search for magnetic vdW materials has intensified in recent years, fueled by the realization of magnetism in two dimensions (2D). However, metallic magnetic vdW systems are still uncommon. In addition, they rarely host high-mobility charge carriers, which is an essential requirement for high-speed electronic applications. Another shortcoming of 2D magnets is that they are highly air sensitive. Using chemical reasoning, we introduce TaCo2Te2 as an air-stable, high-mobility, magnetic vdW material. It has a layered structure, which consists of Peierls distorted Co chains and a large vdW gap between the layers. We find that the bulk crystals can be easily exfoliated and the obtained thin flakes are robust to ambient conditions after four months of monitoring using an optical microscope. We also observe signatures of canted antiferromagntic behavior at low-temperature. TaCo2Te2 shows a metallic character and a large, non-saturating, anisotropic magnetoresistance. Furthermore, our Hall data and quantum oscillation measurements reveal the presence of both electron- and hole-type carriers and their high mobility.

cond-mat.mtrl-sci↗