arXiv subjects

Yong Yan

Publications and source records attributed to Yong Yan.

8 recordsLinked to original sources

arXiv2026

Open-MOPD: Diagnosing and Fixing Capability Imbalance in Multi-Teacher On-Policy Distillation

Multi-teacher on-policy distillation (M-OPD) has emerged as a promising paradigm for consolidating domain-specialized reinforcement learning (RL) experts into a single generalist student via dense, token-level reward supervision. Despite its practical success, the optimization dynamics governing multi-teacher capability integration remain poorly understood, and open, rigorously reproducible recipes are conspicuously lacking. In this work, we establish a controlled M-OPD benchmark on SmolLM3-3B-Base with oracle routing, isolating capability integration from routing ambiguity. Our investigation reveals a pronounced capability integration gap: standard M-OPD captures only 35.6% of the available headroom relative to a domain-routed oracle ensemble, with concise tasks such as instruction following suffering severe degradation and premature stagnation. Crucially, we show that this failure stems not from gradient conflict, but from a severe misallocation of the token-level optimization budget. This pathology is driven by three orthogonal factors: structural sequence-length disparities across domains, dynamic convergence drift due to non-uniform learning rates, and multi-step reward staleness from asynchronous policy updates. To resolve these imbalances, we introduce Open-MOPD, a principled framework incorporating token-share balancing, gap-aware dynamic budget allocation, and student reward refresh. Together, these mechanisms systematically restore cross-domain balance, elevating headroom recovery from 35.6% to 83.4% in a single deployable student. We fully open-source our end-to-end post-training recipe, training trajectories, and evaluation suites on an academically accessible hardware budget.

cs.LG↗

arXiv2025

Progress of the TianQin project

TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about $10^5$ km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ``0123" technology roadmap. In step ``0", the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ``1", the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ``2", the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ``3", i.e., the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based gravitational wave detector, TianQin, and to start gravitational wave detection in space.

gr-qc↗

arXiv2024

Origin of Pressure-Induced Structural Instability in CsPbX$_3$ Photovoltaic Perovskites

Under external stimuli, lead halide perovskites exhibit large atomic fluctuations, impacting optical and electron transport properties that affect device performance in operational settings. However, a thorough understanding of the atomic basis for the underlying structural instability is still absent. Focusing on the model material CsPbBr$_3$, the inherent lattice softness of halide perovskites is elucidated at the atomic level through in-situ single-crystal X-ray diffraction measurements under pressure complemented by atomic level simulations. We identify and explore the nature of the first-order phase transition to a distorted P21/c phase at 1.3 GPa, induced by the sudden Cs-Br bonds breaking. Unlike classical transition metal oxide perovskites, where the internal energy term dominates, we show explicitly that pressure primarily influences the Gibbs free energy for halide perovskites through the pressure-volume term. As such, strategically mitigating bond strains from volume shrinkage is the key to suppressing the first-order behavior for maintaining the coordinates of PbX$_6$ polyhedral upon external perturbation. Our thermodynamic calculation reveals the demand for high entropy in the -T*del-S term, which can be achieved by exploring a broader spectrum of doped A site and B sites in ABX$_3$ systems, enabling continuous structural changes that facilitate recovery from mechanical damage in practical applications.

cond-mat.mtrl-sci↗

arXiv2023

Transverse spin selectivity in helical nanofibers prepared without any chiral molecule

In the last decade, chirality-induced spin selectivity (CISS) has been attracting extensive interest. However, there still exists a large gap between experiments and quantitative theoretical results, and the microscopic mechanism of CISS, especially transverse CISS where electrons are injected perpendicular to the helix axis of chiral molecules, remains elusive. Here, we address these issues by performing a combined experimental and theoretical study on conducting polyaniline helical nanofibers which are synthesized in the absence of any chiral species. Large spin polarization is measured in both left- and right-handed nanofibers for electrons injected perpendicular to their helix axis, which is comparable to the value of parallel electron injection in other chiral molecules, and it will be reversed by switching the handedness between two enantiomers. We develop a theoretical model with extremely weak spin-orbit coupling arising exclusively from electron propagation between neighboring polyanilines and the numerical results are quantitatively consistent with the experimental data. Our results demonstrate that the supramolecular handedness is sufficient for spin-selective electron transmission in chiral molecules assembled from achiral monomers and the mechanism of transverse CISS is revealed.

cond-mat.mes-hall↗

arXiv2023

Higher-order topological and nodal superconducting transition-metal sulfides MS (M = Nb and Ta)

Intrinsic topological superconducting materials are exotic and vital to develop the next-generation topological superconducting devices, topological quantum calculations, and quantum information technologies. Here, we predict the topological and nodal superconductivity of MS (M = Nb and Ta) transition-metal sulfides by using the density functional theory for superconductors combining with the symmetry indicators. We reveal their higher-order topology nature with an index of Z4 = 2. These materials have a higher Tc than the Nb or Ta metal superconductors due to their flat-band and strong electron-phonon coupling nature. Electron doping and lighter isotopes can effectively enhance the Tc. Our findings show that the MS (M = Nb and Ta) systems can be new platforms to study exotic physics in the higher-order topological superconductors, and provide a theoretical support to utilize them as the topological superconducting devices in the field of advanced topological quantum calculations and information technologies.

cond-mat.supr-con↗

arXiv2023

Lightweight High-Performance Blind Image Quality Assessment

Blind image quality assessment (BIQA) is a task that predicts the perceptual quality of an image without its reference. Research on BIQA attracts growing attention due to the increasing amount of user-generated images and emerging mobile applications where reference images are unavailable. The problem is challenging due to the wide range of content and mixed distortion types. Many existing BIQA methods use deep neural networks (DNNs) to achieve high performance. However, their large model sizes hinder their applicability to edge or mobile devices. To meet the need, a novel BIQA method with a small model, low computational complexity, and high performance is proposed and named "GreenBIQA" in this work. GreenBIQA includes five steps: 1) image cropping, 2) unsupervised representation generation, 3) supervised feature selection, 4) distortion-specific prediction, and 5) regression and decision ensemble. Experimental results show that the performance of GreenBIQA is comparable with that of state-of-the-art deep-learning (DL) solutions while demanding a much smaller model size and significantly lower computational complexity.

eess.IV↗

arXiv2015

Uniform regularity and vanishing viscosity limit for the compressible Navier-Stokes with general Navier-slip boundary conditions in 3-dimensional domains

In this paper, we investigate the uniform regularity for the isentropic compressible Navier-Stokes system with general Navier-slip boundary conditions (1.6) and the inviscid limit to the compressible Euler system. It is shown that there exists a unique strong solution of the compressible Navier-Stokes equations with general Navier-slip boundary conditions in an interval of time which is uniform in the vanishing viscosity limit. The solution is uniformly bounded in a conormal Sobolev space and is uniform bounded in $W^{1,\infty}$. It is also shown that the boundary layer for the density is weaker than the one for the velocity field. In particular, it is proved that the velocity will be uniform bounded in $L^\infty(0,T;H^2)$ when the boundary is flat and the Navier-Stokes system is supplemented with the special boundary condition (1.21). Based on such uniform estimates, we prove the convergence of the viscous solutions to the inviscid ones in $L^\infty(0,T;L^2)$, $L^\infty(0,T;H^1)$ and $L^\infty([0,T]\timesΩ)$ with a rate of convergence.

math.AP↗

arXiv2014

Theoretic Insight into CO2 Reduction at Active Sites of Molybdenum and Tungsten Enzymes: a π Interaction between CO2 and Tungsten Bis-Dithiolene Complexes

Active sites of molybdenum and tungsten enzymes, particularly mononuclear tungsten formate dehydrogenase (FDH) have been theoretically investigated towards their interaction with CO2. Obvious π interaction has been found between the 2e reduced metallodithiole moiety and the molecular CO2. This weak π bonding is predicated both at gas phase, noted as -6.0 kcal/mol and aqueous solvation level, -3.6 kcal/mol. Such interaction is not only limited to CO2, but also to the CO2 reduced product, i.e. formate, in the form of anion- π interaction, noted as -6.8 kcal/mol and -4.1 kcal/mol respectively in gas and aqueous solvation model. The Bailar twisted angles from 60o to 0o, governing structure preference of tungsten dithiolene from octahedron to triangle prism in their restricted structures, has been explored to evaluate such π in-terrelations with CO2 and formate. An octahedral structure with 3 kcal/mol energy lower is preferred over the triangle prismatic when such interactions are concerned.

physics.chem-ph↗