arXiv subjects

Yongjun Wu

Publications and source records attributed to Yongjun Wu.

At least 19 recordsLinked to original sources

arXiv2026

Dynamic resolution switching for live streaming

Conventional adaptive bitrate (ABR) streaming systems typically rely on static bitrate ladders to optimize Quality of Experience (QoE). While operationally simple, this "one-size-fits-all" approach neglects content-specific characteristics, often compromising streaming efficiency. Per-title optimization methods address this by predicting the rate-distortion convex hull directly from the source content, but their reliance on pre-encoding source analysis can limit their applicability to live streaming. Moreover, the objective video quality metrics (VQMs) they rely on are optimized for overall correlation with subjective scores rather than cross-over accuracy, often yielding inaccurate cross-over predictions and suboptimal ladder construction. To overcome both limitations, we introduce a Dynamic Resolution Switching (DRS) framework for live streaming that remains fully compatible with existing streaming protocols. Our approach augments static ladders with strategically selected representations guided by user bandwidth distributions and cross-over regions. The quality of these representations is then analyzed in real time to construct dynamic ladders. Central to this framework is a lightweight, bitstream-based VQM that ensures computational efficiency while maximizing the accuracy of subjective resolution cross-over prediction through training on Pairwise Comparison (PC) datasets. At each bitrate, the VQM evaluates all candidate representations to identify the resolution maximizing the quality score. This decision process, operating at a configurable granularity (e.g., per segment), drives the dynamic resolution switching mechanism specifically optimized for the metric. Experimental results validate the approach, demonstrating a significant performance gain (approximately 9% BD-rate reduction under the proposed VQM) while maintaining practical feasibility for live streaming.

eess.IV↗

arXiv2026

Thermally Configurable Multi-Order Polar Skyrmions in Multiferroic Oxide Superlattices

Polar topological textures in low-dimensional ferroelectrics have emerged as a versatile platform for high-density information storage and neuromorphic computing. While low-order topological states, such as vortices and skyrmions, have been extensively studied, high-order polar topological families remain largely unexplored due to their higher energy requirements and limited stabilization methods. Here, using a BiFeO3 (BFO)-based multiferroic superlattice as a model system, we demonstrate a thermal-modulation strategy that stabilizes multi-order polar skyrmions and enables reversible tuning of their topological order through phase-field simulations. It was found that temperature modulation drives the system from polar solitons through 1{\pi}-, 2{\pi}-, 3{\pi}-, and 4{\pi}-skyrmion states, with closed heating-cooling path analyses revealing the widest thermal stability window for 2{\pi}-skyrmions (up to 600 K). Leveraging this robustness, 2% Sm doping in BFO lowers the transition temperatures, enabling room-temperature stabilization of 2{\pi}-skyrmions. These findings enrich the fundamental understanding of multi-order polar topologies and establish a tunable strategy for realizing variable-order topological configurations in practical memory devices.

cond-mat.mtrl-sci↗

arXiv2025

Harnessing the polar vortex motion in oxide heterostructures

Polar topology, an analogue of the magnetic topology, serves as a large playground for exotic physical phenomena with a wide range of multifunctional applications. Polar vortices and skyrmions are representative polar topologies that have been predicted to significantly enhance the functionality and information density of nanoelectronic devices due to their ultrasmall dimensions. Despite these advantages, the practical realization of polar topologies in devices is impeded by the intrinsic challenges associated with their controlled motion and manipulation. Therefore, harnessing vortex manipulation-such as motion, on demand creation, annihilation, and shape transformation-is essential for practical device integration. However, vortex motion is often challenged by intrinsic physical limitations in collective lattice distortions and strong pinning effects from the surrounding environment, which remains elusive. In this study, we present real time observation of vortex motion in PbTiO3/SrTiO3 heterostructures, achieved through the application of localized pulsed electric fields and trailing bias fields from a conductive tip. Notably, the vortices exhibit reversible motion in response to the field direction. Furthermore, by precisely manoeuvring the conductive Atomic-Force-Microscopy tip along specific trajectories, we achieved controlled vortex reshaping, with reconfigured vortices showing remarkable stability over extended periods. This underline physical mechanism is further pinpointed by phase-field simulations, which revealed that the motion of the vortex boundary is controlled through the switching of the zigzag patterns of the vortex core. This study highlights the feasibility of harnessing vortex dynamics through external stimuli, advancing the fundamental physical understanding and prospects for next-generation polar vortex-based nanoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

PTST: A polar topological structure toolkit and database

Ferroelectric oxide superlattices with complex topological structures such as vortices, skyrmions, and flux closure domains have garnered significant attention due to their fascinating properties and potential applications. However, progress in this field is often impeded by challenges such as limited data-sharing mechanisms, redundant data generation efforts, high barriers between simulations and experiments, and the underutilization of existing datasets. To address these challenges, we have created the Polar Topological Structure Toolbox and Database(PTST). This community driven repository compiles both standard datasets from high throughput phase field simulations and user submitted nonstandard datasets. The PTST utilizes a Global Local Transformer (GL Transformer) to classify polarization states by dividing each sample into spatial sub blocks and extracting hierarchical features, resulting in ten distinct topological categories. Through the PTST web interface, users can easily retrieve polarization data based on specific parameters or by matching experimental images. Additionally, a Binary Phase Diagram Generator allows users to create strain and electric field phase diagrams within seconds. By providing ready-to-use configurations and integrated machine-learning workflows, PTST significantly reduces computational load, streamlines reproducible research, and promotes deeper insights into ferroelectric topological transitions.

cond-mat.mtrl-sci↗

arXiv2025

Video Quality Assessment for Resolution Cross-Over in Live Sports

In adaptive bitrate streaming, resolution cross-over refers to the point on the convex hull where the encoding resolution should switch to achieve better quality. Accurate cross-over prediction is crucial for streaming providers to optimize resolution at given bandwidths. Most existing works rely on objective Video Quality Metrics (VQM), particularly VMAF, to determine the resolution cross-over. However, these metrics have limitations in accurately predicting resolution cross-overs. Furthermore, widely used VQMs are often trained on subjective datasets collected using the Absolute Category Rating (ACR) methodologies, which we demonstrate introduces significant uncertainty and errors in resolution cross-over predictions. To address these problems, we first investigate different subjective methodologies and demonstrate that Pairwise Comparison (PC) achieves better cross-over accuracy than ACR. We then propose a novel metric, Resolution Cross-over Quality Loss (RCQL), to measure the quality loss caused by resolution cross-over errors. Furthermore, we collected a new subjective dataset (LSCO) focusing on live streaming scenarios and evaluated widely used VQMs, by benchmarking their resolution cross-over accuracy.

cs.MM↗

arXiv2024

Machine learning assisted screening of metal binary alloys for anode materials

In the dynamic and rapidly advancing battery field, alloy anode materials are a focal point due to their superior electrochemical performance. Traditional screening methods are inefficient and time-consuming. Our research introduces a machine learning-assisted strategy to expedite the discovery and optimization of these materials. We compiled a vast dataset from the MP and AFLOW databases, encompassing tens of thousands of alloy compositions and properties. Utilizing a CGCNN, we accurately predicted the potential and specific capacity of alloy anodes, validated against experimental data. This approach identified approximately 120 low potential and high specific capacity alloy anodes suitable for various battery systems including Li, Na, K, Zn, Mg, Ca, and Al-based. Our method not only streamlines the screening of battery anode materials but also propels the advancement of battery material research and innovation in energy storage technology.

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arXiv2024

Encoder-Quantization-Motion-based Video Quality Metrics

In an adaptive bitrate streaming application, the efficiency of video compression and the encoded video quality depend on both the video codec and the quality metric used to perform encoding optimization. The development of such a quality metric need large scale subjective datasets. In this work we merge several datasets into one to support the creation of a metric tailored for video compression and scaling. We proposed a set of HEVC lightweight features to boost performance of the metrics. Our metrics can be computed from tightly coupled encoding process with 4% compute overhead or from the decoding process in real-time. The proposed method can achieve better correlation than VMAF and P.1204.3. It can extrapolate to different dynamic ranges, and is suitable for real-time video quality metrics delivery in the bitstream. The performance is verified by in-distribution and cross-dataset tests. This work paves the way for adaptive client-side heuristics, real-time segment optimization, dynamic bitrate capping, and quality-dependent post-processing neural network switching, etc.

eess.IV↗

arXiv2023

A molecular Ferroelectric thin film of imidazolium perchlorate on Silicon

Molecular ferroelectric materials have attracted widespread attention due to their abundant chemical diversity, structural tunability, low synthesis temperature, and high flexibility. Meanwhile, the integration of molecular ferroelectric materials and Si is still challenging, while the fundamental understanding of the ferroelectric switching process is still lacking. Herein, we have successfully synthesized the imidazole perchlorate (ImClO4) single crystals and a series of high-quality highly-oriented thin films on a Si substrate. A high inverse piezoelectric coefficient (55.7 pm/V) is demonstrated for the thin films. Two types of domain bands can be observed (in the size of a few microns): type-I band tilts ~60° with respect to the horizontal axis, while the type-II band is perpendicular to the horizontal axis. Most of the domain walls (DWs) are 180° DWs for the two bands, while some 109° DWs can also be observed. Interestingly, the DWs in type-I band are curved, charged domain walls; while the 180° DWs in type-II band are straight, noncharged domain walls. After applying +20 V for 5 s through a PFM tip, the 180° DWs in type-I band shrink first, then disconnect from the band boundary, forming a needle-like domain with a size of ~100 nm. The needle-like domain will extend toward the band boundary after an inverse bias is applied (-20 V), and expand along the band boundary after touching the boundary. Whereas for the type-II domain band, the 180° DWs are more mobile than the 109° domain walls, which displaces ~500 nm after applying +20 V. While such displacement is much shorter after the application of a negative bias for the same duration, starting from the positively poled sample. We hope to spur further interest in the on-chip design of the molecular ferroelectrics based electronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Dynamic motion of polar skyrmions in oxide heterostructures

Polar skyrmions have been widely investigated in oxide heterostructure recently, due to their exotic properties and intriguing physical insights. Meanwhile, so far, the external field-driven motion of the polar skyrmion, akin to the magnetic counterpart, has yet to be discovered. Here, using phase-field simulations, we demonstrate the dynamic motion of the polar skyrmions with integrated external thermal, electrical, and mechanical stimuli. The external heating reduces the spontaneous polarization hence the skyrmion motion barrier, while the skyrmions shrink under the electric field, which could weaken the lattice pinning and interactions between the skyrmions. The mechanical force transforms the skyrmions into c-domain in the vicinity of the indenter center under the electric field, providing the space and driving force needed for the skyrmions to move. This study confirmed that the skyrmions are quasi-particles that can move collectively, while also providing concrete guidance for the further design of polar skyrmion-based electronic devices.

cond-mat.mtrl-sci↗

arXiv2023

HDR-ChipQA: No-Reference Quality Assessment on High Dynamic Range Videos

We present a no-reference video quality model and algorithm that delivers standout performance for High Dynamic Range (HDR) videos, which we call HDR-ChipQA. HDR videos represent wider ranges of luminances, details, and colors than Standard Dynamic Range (SDR) videos. The growing adoption of HDR in massively scaled video networks has driven the need for video quality assessment (VQA) algorithms that better account for distortions on HDR content. In particular, standard VQA models may fail to capture conspicuous distortions at the extreme ends of the dynamic range, because the features that drive them may be dominated by distortions {that pervade the mid-ranges of the signal}. We introduce a new approach whereby a local expansive nonlinearity emphasizes distortions occurring at the higher and lower ends of the {local} luma range, allowing for the definition of additional quality-aware features that are computed along a separate path. These features are not HDR-specific, and also improve VQA on SDR video contents, albeit to a reduced degree. We show that this preprocessing step significantly boosts the power of distortion-sensitive natural video statistics (NVS) features when used to predict the quality of HDR content. In similar manner, we separately compute novel wide-gamut color features using the same nonlinear processing steps. We have found that our model significantly outperforms SDR VQA algorithms on the only publicly available, comprehensive HDR database, while also attaining state-of-the-art performance on SDR content.

eess.IV↗

arXiv2023

HDR or SDR? A Subjective and Objective Study of Scaled and Compressed Videos

We conducted a large-scale study of human perceptual quality judgments of High Dynamic Range (HDR) and Standard Dynamic Range (SDR) videos subjected to scaling and compression levels and viewed on three different display devices. HDR videos are able to present wider color gamuts, better contrasts, and brighter whites and darker blacks than SDR videos. While conventional expectations are that HDR quality is better than SDR quality, we have found subject preference of HDR versus SDR depends heavily on the display device, as well as on resolution scaling and bitrate. To study this question, we collected more than 23,000 quality ratings from 67 volunteers who watched 356 videos on OLED, QLED, and LCD televisions. Since it is of interest to be able to measure the quality of videos under these scenarios, e.g. to inform decisions regarding scaling, compression, and SDR vs HDR, we tested several well-known full-reference and no-reference video quality models on the new database. Towards advancing progress on this problem, we also developed a novel no-reference model called HDRPatchMAX, that uses both classical and bit-depth sensitive distortion statistics more accurately than existing metrics.

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arXiv2023

Making Video Quality Assessment Models Robust to Bit Depth

We introduce a novel feature set, which we call HDRMAX features, that when included into Video Quality Assessment (VQA) algorithms designed for Standard Dynamic Range (SDR) videos, sensitizes them to distortions of High Dynamic Range (HDR) videos that are inadequately accounted for by these algorithms. While these features are not specific to HDR, and also augment the equality prediction performances of VQA models on SDR content, they are especially effective on HDR. HDRMAX features modify powerful priors drawn from Natural Video Statistics (NVS) models by enhancing their measurability where they visually impact the brightest and darkest local portions of videos, thereby capturing distortions that are often poorly accounted for by existing VQA models. As a demonstration of the efficacy of our approach, we show that, while current state-of-the-art VQA models perform poorly on 10-bit HDR databases, their performances are greatly improved by the inclusion of HDRMAX features when tested on HDR and 10-bit distorted videos.

eess.IV↗

arXiv2022

Mechanical configurable nanopatterning of polar topological states and formation of post-skyrmion

The controllable phase transition and nanopatterning of topological states in a ferroelectric system under external stimuli are critical for realizing the potential applications in nanoelectronic devices such as logic, memory, race-track, etc. Herein, using the phase-field simulations, we demonstrate the mechanical manipulation of polar skyrmions in ferroelectric superlattices by applying external local compressive stress through an atomic force microscopy (AFM) tip. Different switching pathways are observed: under small to moderate force (<1 uN), the skyrmions coalesce to form a long stripe; while increasing the applied load (e.g., above 2 uN) leads to the suppression of spontaneous polarization, forming a new metastable topological structure, namely the post-skyrmion. It is constructed by attaching multiple merons onto a center Bloch skyrmion, showing a topological charge of 1.5 (under 2 uN) or 2 (under 3 uN). We have further designed a mechanical nanopatterning process, where the stripes can form a designed pattern by moving the AFM tip (write), which can also be switched back to a full skyrmion state under an applied electric field (erase). We believe this study will spur further interest in mechanical manipulation and nanopatterning of polar topological phases through mechanical forces.

cond-mat.mtrl-sci↗

arXiv2022

Subjective Assessment of High Dynamic Range Videos Under Different Ambient Conditions

High Dynamic Range (HDR) videos can represent a much greater range of brightness and color than Standard Dynamic Range (SDR) videos and are rapidly becoming an industry standard. HDR videos have more challenging capture, transmission, and display requirements than legacy SDR videos. With their greater bit depth, advanced electro-optical transfer functions, and wider color gamuts, comes the need for video quality algorithms that are specifically designed to predict the quality of HDR videos. Towards this end, we present the first publicly released large-scale subjective study of HDR videos. We study the effect of distortions such as compression and aliasing on the quality of HDR videos. We also study the effect of ambient illumination on perceptual quality of HDR videos by conducting the study in both a dark lab environment and a brighter living-room environment. A total of 66 subjects participated in the study and more than 20,000 opinion scores were collected, which makes this the largest in-lab study of HDR video quality ever. We anticipate that the dataset will be a valuable resource for researchers to develop better models of perceptual quality for HDR videos.

eess.IV↗

arXiv2022

Subjective and Objective Quality Assessment of High-Motion Sports Videos at Low-Bitrates

Videos often have to be transmitted and stored at low bitrates due to poor network connectivity during adaptive bitrate streaming. Designing optimal bitrate ladders that would select the perceptually-optimized resolution, frame-rate, and compression level for low-bitrate videos for adaptive streaming across the internet is therefore a task of great interest. Towards that end, we conducted the first large-scale study of medium and low-bitrate videos from live sports for two codecs (Elemental AVC and HEVC) and created the Amazon Prime Video Low-Bitrate Sports (APV LBS) dataset. The study involved 94 participants and 742 videos, with more than 23,000 human opinion scores collected in total. We analyzed the data obtained and we also conducted an extensive evaluation of objective Video Quality Assessment (VQA) algorithms and benchmarked their performance, and make recommendations on bitrate ladder design. We're making the metadata and VQA features available at https://github.com/JoshuaEbenezer/lbmfr-public.

eess.IV↗

arXiv2022

Dynamics of the lithium metal electrodeposition: Effects of a gas bubble

Rechargeable lithium metal batteries have been widely investigated recently, driven by the global trend for the electrification of transportation. Understanding the dynamics of lithium metal electrodeposition is crucial to design safe and reliable lithium metal anodes. In this study, we developed a grand potential-based phase-field model to investigate the effect of a static gas bubble, which forms due to the complicated internal side reactions, on the dynamics of the dendrite growth during electrodeposition. It is observed that with the presence of a gas bubble, the dendrite growth is largely accelerated, due to the accumulation of lithium ions on the far side of the bubble away from the anode surface, which could serve as an ion "reservoir" for the dendrite growth, leading to the bending/tilting of the lithium dendrites toward the bubble. Meanwhile, the effects of the bubble size and distance to the anode are further studied, demonstrating that the larger the bubble size and the closer to the anode, the longer the lithium dendrites grow. We hope this study could serve as an example to exploit the effect of extrinsic factors on the dendrite growth dynamics.

cond-mat.mtrl-sci↗

arXiv2022

Surface engineering for ultrathin metal anodes enabling high-performance Zn-ion batteries

Zn metal battery has been considered a promising alternative energy storage technology in renewable energy storage and grid storage. It is well-known that the surface orientation of a Zn metal anode is vital to the reversibility of a Zn metal battery. Herein, the (101)-oriented thin Zn metal anode (down to 2 μm) is electrodeposited on a Cu surface by adding dimethyl sulfoxide (DMSO) electrolyte additive in ZnSO4 aqueous solution. Scanning electron microscope (SEM) observation indicates the formation of flat terrace-like compact (101)-oriented surfaces. Insitu optical observation confirms that the (101)-oriented surfaces can be reversibly plated and stripped. DFT calculations reveal two mechanisms for the nucleation and growth of the Zn-(101) surface: (1) formation of Zn(101)//Cu(001) could lower the interface energy as compared to Zn(002)//Cu(001); (2) large reconstruction of the Zn (101) surface with DMSO and H2O absorption. Raman, XPS, and ToF-SIMS characterizations indicate that adding DMSO in ZnCl2 could facilitate the formation of ZnO-based SEI on Zn metal surface, while OH- and S-based SEI can be obtained with DMSO in ZnSO4. The electrochemical testings are performed, which demonstrates a higher cyclability for the (101)-oriented Zn in the half cell as well as a lower charge transfer barrier with respect to the (002)-dominated surface of the same electrode thickness. Zn||V2O5 full cells are further assembled, showing better capacity retention for the (101)-Zn as compared to the (002)-Zn with the same thickness (5 μm, 3 μm, and 2 μm). We hope this study to spur further interest in the control of Zn metal surface crystallographic orientation towards ultrathin Zn metal anodes.

cond-mat.mtrl-sci↗

arXiv2021

Order-disorder transitions in a polar vortex lattice

Order-disorder transitions are widely explored in various vortex structures in condensed matter physics, i.e., in the type-II superconductors and Bose-Einstein condensates. In this study, we have investigated the ordering of the polar vortex phase in the (PZT)n/(STO)n superlattice systems through phase-field simulations. An antiorder state is discovered for short periodicity superlattice on an SSO substrate, owing to the huge interfacial coupling between PZT and STO as well as the giant in-plane polarization in STO layers due to the large tensile strain. Increasing the periodicity leads to the anti-order to disorder transition, resulting from the loss of interfacial coupling and disappearance of the polarization in STO layers. On the other hand, for short periodicity superlattices, order-disorder-antiorder transition can be engineered by mediating the substrate strain, due to the delicate competition between the depoling effect, interfacial coupling, and strain effect. We envision this study to spur further interest towards the understanding of order-disorder transition in ferroelectric topological structures.

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