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Transfer Learning for Keypoint Detection in Low-Resolution Thermal TUG Test Images

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arXiv 2025年

作者： Chen, Wei-Lun Hsieh, Chia-Yeh Kao, Yu-Hsiang Liu, Kai-Chun Peng, Sheng-Yu Tsao, Yu Research Center for Information Technology Innovation Academic Sinica Taiwan Graduate Institute of Electrical Engineering National Taiwan University Taiwan Bachelor’s Program in Medical Informatics and Innovative Applications Fu Jen Catholic University Taiwan Department of Electrical Engineering National Taiwan University Taiwan College of Information and Computer Sciences University of Massachusetts AmherstMA01003 United States Department of Electrical Engineering National Taiwan University of Science of Technology Taiwan

This study presents a novel approach to human keypoint detection in low-resolution thermal images using transfer learning techniques. We introduce the first application of the Timed Up and Go (TUG) test in thermal image computer vision, establishing a new paradigm for mobility assessment. Our method leverages a MobileNetV3-Small encoder and a ViTPose decoder, trained using a composite loss function that balances latent representation alignment and heatmap accuracy. The model was evaluated using the Object Keypoint Similarity (OKS) metric from the COCO Keypoint Detection Challenge. The proposed model achieves better performance with AP, AP50, and AP75 scores of 0.861, 0.942, and 0.887 respectively, outperforming traditional supervised learning approaches like Mask R-CNN and ViTPose-Base. Moreover, our model demonstrates superior computational efficiency in terms of parameter count and FLOPS. This research lays a solid foundation for future clinical applications of thermal imaging in mobility assessment and rehabilitation monitoring. Copyright © 2025, The Authors. All rights reserved.

关键词： Thermography (imaging)

Scalable, nanoscale positioning of highly coherent color centers in prefabricated diamond nanostructures

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arXiv 2025年

作者： Kim, Sunghoon London, Paz Yang, Daipeng Hughes, Lillian B. Ahlers, Jeffrey Meynell, Simon Mitchell, William J. Mukherjee, Kunal Bleszynski Jayich, Ania C. Department of Physics University of California Santa Barbara Santa BarbaraCA93106 United States Nanofabrication Facility Department of Electrical and Computer Engineering University of California Santa Barbara Santa BarbaraCA93106 United States Department of Materials Science and Engineering Stanford University Palo AltoCA94305 United States

Nanophotonic devices in color center-containing hosts provide efficient readout, control, and entanglement of the embedded emitters. Yet control over color center formation – in number, position, and coherence – in nanophotonic devices remains a challenge to scalability. Here, we report a controlled creation of highly coherent diamond nitrogen-vacancy (NV) centers with nanoscale three-dimensional localization in prefabricated nanostructures with high yield. Combining nitrogen δ-doping during chemical vapor deposition diamond growth and localized electron irradiation, we form shallow NVs registered to the center of diamond nanopillars with wide tunability over NV number. We report positioning precision of ∼ 4 nm in depth and 46(1) nm laterally in pillars (102(2) nm in bulk diamond). We reliably form single NV centers with long spin coherence times (average T2Hahn = 98 µs) and 1.8× higher average photoluminescence compared to NV centers randomly positioned in pillars. We achieve a 3× improved yield of NV centers with single electron-spin sensitivity over conventional implantation-based methods. Our high-yield defect creation method will enable scalable production of solid-state defect sensors and processors. © 2025, CC BY.

关键词： Color centers

Small Polaron-Induced Ultrafast Ferroelectric Restoration in BiFeO3

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Physical Review X 2025年第2期15卷 021046-021046页

作者： Wenfan Chen Tian Wang Chun-Chieh Yu Yuancheng Jing Xiaosong Li Wei Xiong Materials Science and Engineering Program University of California San Diego La Jolla California 92093 USA Department of Chemistry University of Washington Seattle Washington 98195 USA Department of Chemistry University of California San Diego La Jolla California 92093 USA Department of Electrical and Computer Science Engineering University of California San Diego La Jolla California 92093 USA

In this report, we apply a suite of ultrafast spectroscopic techniques and advanced calculations to reveal the interplay between electronic and lattice degrees of freedom in ferroelectric BiFeO3. Using transient sum frequency generation spectroscopy, which is sensitive to electronic polarizations, we observe a transient electronic dipole reduction upon optical excitation which recovers at 0.5 and 10 ps timescale. The time-dependent density functional theory calculation reveals that both ligand-metal charge transfer and local excitation transition occurred upon photo excitation. To reveal the nature of electronic dipole restoration, we employ transient extreme ultraviolet (EUV) spectroscopy—an element-specific ultrafast technique that follows charge dynamics of Bi, Fe, and O altogether. The transient EUV dynamics observed both ultrafast free charge carrier relaxation to excitons, as well as polaron formation. However, a timescale comparison suggests that only the polaron formation is responsible for the 0.5 ps electronic dipole restoration, whereas the faster electronic relaxation does not contribute to the ferroelectric property changes. Multireference configuration interaction calculation further corroborates this result by showing both Fe and Bi atoms shift from the ground state equilibrium—leading to the polaron formation. Our result disentangles the multidegrees of freedom in ultrafast ferroelectric modulation and identifies the pivotal motion—a local polaron formation—for the fast ferroelectric recovery. It provides crucial insights on the specific lattice distortion that could modulate properties or phase transitions of condensed matter materials.

关键词： Light polarization

Large Spin-Orbit Torque with Multi-Directional Spin Components in Ni₄W

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Advanced materials 2025年 e2416763页

作者： Yang, Yifei Lee, Seungjun Chen, Yu-Chia Jia, Qi Dixit, Brahmdutta Sousa, Duarte Odlyzko, Michael Garcia-Barriocanal, Javier Yu, Guichuan Haugstad, Greg Fan, Yihong Huang, Yu-Han Lyu, Deyuan Cresswell, Zach Liang, Shuang Benally, Onri Jay Low, Tony Wang, Jian-Ping Department of Electrical and Computer Engineering University of Minnesota Minneapolis 55455 MN United States Characterization Facility University of Minnesota Minneapolis 55455 MN United States Department of Chemical Engineering and Materials Science University of Minnesota Minneapolis 55455 MN United States

Spin-orbit torque (SOT) offers an efficient mechanism for manipulating the magnetization of ferromagnetic materials in spintronics-based memory and logic devices. However, conventional SOT materials, such as heavy metals and topological insulators, are limited by high crystal symmetry to generating and injecting only in-plane spins into the ferromagnet. Low-symmetry materials and symmetry-breaking strategies have been employed to generate unconventional spin currents with out-of-plane spin polarization, enabling field-free deterministic switching of perpendicular magnetization. Despite this progress, the SOT efficiency of these materials has typically remained low. Here, a large SOT efficiency of 0.3 in the bulk Ni₄W at room temperature is reported, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni₄W, unconventional SOT from the out-of-plane and Dresselhaus-like spin components are observed. Notably, a large SOT efficiency of 0.73 is observed in W/Ni₄W (5 nm), potentially resulting from additional interfacial contributions or extrinsic effects. Furthermore, field-free switching of perpendicular magnetization has been achieved using the multi-directional SOT of Ni₄W, highlighting its potential as a low-symmetry SOT material for energy-efficient spintronic devices. © 2025 The Author(s). Advanced materials published by Wiley-VCH GmbH.

关键词： epitaxial growth field-free switching spin-orbit torque spintronics unconventional spin Hall effect

Metal-organic chemical vapor deposition of MgGeN2 films on GaN and sapphire

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APL materials 2025年第4期13卷

作者： Hu, Chenxi Thirupakuzi Vangipuram, Vijay Gopal Chae, Christopher Turan, Ilteris K. Hoven, Nichole Lambrecht, Walter R. L. Hwang, Jinwoo Ijiri, Yumi Zhao, Hongping Kash, Kathleen Department of Physics Case Western Reserve University ClevelandOH44106 United States Department of Electrical and Computer Engineering The Ohio State University ColumbusOH43210 United States Department of Materials Science and Engineering The Ohio State University ColumbusOH43210 United States Swagelok Center for Surface Analysis of Materials Case Western Reserve University ClevelandOH44106 United States Department of Physics and Astronomy Oberlin College OberlinOH44074 United States

MgGeN2 films were synthesized using metal-organic chemical vapor deposition on GaN/c-sapphire templates and c-plane sapphire substrates. Energy-dispersive x-ray spectroscopy was used to estimate the cation composition ratios. To mitigate magnesium evaporation, the films were grown at pyrometer temperature 745 °C with a wafer rotation speed of 1000 rpm. Growth rates were determined by fitting energy-dispersive x-ray spectroscopy spectra to film thicknesses using NIST DTSA-II software. The thickness estimates determined by this method were consistent with scanning transmission electron microscopy measurements done for selected samples. Scanning electron microscopy images revealed faceted surfaces indicative of a tendency toward three-dimensional growth. X-ray diffraction spectra confirmed that the films were highly crystalline and exhibited preferential orientation in alignment with the substrate. Atomic force microscopy measurements show that film thicknesses are consistent across samples grown on both GaN templates and sapphire substrates, with typical roughnesses around 10 nm. Transmittance spectra of films grown on double-side-polished sapphire substrates yielded band gaps of 4.28 ± 0.06 eV for samples exhibiting close-to-ideal stoichiometry. Comparison of the measured spectra with ab initio calculations are in good agreement both near the bandgap and at higher energies where excitation is into higher-lying bands. These findings provide insight into the growth and characterization of MgGeN2, contributing to the development of this material for potential applications in optoelectronics and power electronics. © 2025 Author(s).

关键词： Metallorganic chemical vapor deposition

Hybrid Josephson Rhombus: A Superconducting Element with Tailored Current-Phase Relation

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Physical Review X 2025年第1期15卷 011021-011021页

作者： L. Banszerus C. W. Andersson W. Marshall T. Lindemann M. J. Manfra C. M. Marcus S. Vaitiekėnas Center for Quantum Devices Niels Bohr Institute University of Copenhagen 2100 Copenhagen Denmark Department of Physics University of Washington Seattle Washington 98195 USA Department of Physics and Astronomy Purdue University West Lafayette Indiana 47907 USA Birck Nanotechnology Center Purdue University West Lafayette Indiana 47907 USA School of Electrical and Computer Engineering Purdue University West Lafayette Indiana 47907 USA School of Materials Engineering Purdue University West Lafayette Indiana 47907 USA Materials Science and Engineering University of Washington Seattle Washington 98195 USA

Controlling the current-phase relation (CPR) of Josephson elements is essential for tailoring the eigenstates of superconducting qubits, tuning the properties of parametric amplifiers, and designing nonreciprocal superconducting devices. Here, we introduce the hybrid Josephson rhombus, a highly tunable superconducting circuit containing four semiconductor-superconductor hybrid Josephson junctions embedded in a loop. Combining magnetic frustration with gate-voltage-controlled tuning of individual Josephson couplings provides deterministic control of the harmonic content of the rhombus CPR. We show that, for balanced Josephson couplings at full frustration, the hybrid rhombus displays a π-periodic cos(2φ) potential, indicating coherent charge-4e transport. Tuning away from the balanced configuration, we observe a superconducting diode effect with efficiency exceeding 25%. These results showcase the potential of hybrid Josephson rhombi as fundamental building blocks for noise-resilient qubits and quantum devices with custom transport properties.

关键词： Parametric amplifiers

Small-Scale Testbeds for Connected and Automated Vehicles and Robot Swarms: Challenges and a Roadmap

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arXiv 2025年

作者： Xu, Jianye Alrifaee, Bassam Betz, Johannes Mokhtarian, Armin Mittal, Archak Cai, Mengchi Mangharam, Rahul Shehata, Omar M. Elias, Catherine M. Zaech, Jan-Nico Scheffe, Patrick Jahncke, Felix Ulhas, Sangeet Sankaramangalam Arfvidsson, Kaj Munhoz Department of Computer Science RWTH Aachen University Germany Department of Aerospace Engineering University of the Bundeswehr Munich Germany Professorship of Autonomous Vehicle Systems Technical University of Munich Germany Department of Civil Engineering Indian Institute of Technology Bombay India School of Vehicle and Mobility Tsinghua University China Department of Electrical and Systems Engineering University of Pennsylvania United States Mechatronics Engineering Department Faculty of Engineering and Materials Science The German University in Cairo Egypt Department of Computer Science Engineering The German University in Cairo Egypt INSAIT Sofia University "St. Kliment Ohridski" Bulgaria School for Engineering of Matter Transport and Energy Arizona State University United States Division of Decision and Control Systems KTH Royal Institute of Technology Sweden

This article proposes a roadmap to address the current challenges in small-scale testbeds for Connected and Automated Vehicles (CAVs) and robot swarms. The roadmap is a joint effort of participants in the workshop "1st Workshop on Small-Scale Testbeds for Connected and Automated Vehicles and Robot Swarms," held on June 2 at the IEEE Intelligent Vehicles Symposium (IV) 2024 in Jeju, South Korea. The roadmap contains three parts: 1) enhancing accessibility and diversity, especially for underrepresented communities, 2) sharing best practices for the development and maintenance of testbeds, and 3) connecting testbeds through an abstraction layer to support collaboration. The workshop features eight invited speakers, four contributed papers [1]–[4], and a presentation of a survey paper on testbeds [5]. The survey paper provides an online comparative table of more than 25 testbeds, available at https://***/testbeds-survey. The workshop’s own website is available at https://***/iv24-workshop. Copyright © 2025, The Authors. All rights reserved.

关键词： Testbeds

A skin-mimicking multifunctional hydrogel via hierarchical, reversible noncovalent interactions

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science Advances 2025年第20期11卷 eadv8523页

作者： Guo, Xingkui Zhang, Songlin Patel, Shubham Sun, Xiaolu Zhu, You-Liang Wei, Zechang Wang, Rongguo He, Xiaodong Wang, Zuankai Yu, Cunjiang Tan, Swee Ching Department of Materials Science and Engineering National University of Singapore Singapore 117574 Singapore State Key Laboratory of Molecular Engineering of Polymers Department of Macromolecular Science Institute of Fiber Materials and Devices Laboratory of Advanced Materials Fudan University Shanghai 200438 China The Grainger College of Engineering Department of Electrical and Computer Engineering Department of Materials Science and Engineering Department of Mechanical Science and Engineering Departments of Bioengineering The Grainger College of Engineering Beckman Institute for Advanced Science and Technology Materials Research Laboratory Nick Holonyak Micro and Nanotechnology Laboratory University of Illinois Urbana-Champaign Urbana 61801 IL United States National Key Laboratory of Science and Technology on Advanced Composites in Special Environments Harbin Institute of Technology Harbin 150080 China State Key Laboratory of Supramolecular Structure and Materials College of Chemistry Jilin University Changchun China Department of Mechanical Engineering The Hong Kong Polytechnic University Hong Kong Shenzhen Research Institute of The Hong Kong Polytechnic University Shenzhen China

Artificial skin is essential for bionic robotics, facilitating human skin–like functions such as sensation, communication, and protection. However, replicating a skin-matched all-in-one material with excellent mechanical properties, self-healing, adhesion, and multimodal sensing remains a challenge. Herein, we developed a multifunctional hydrogel by establishing a consolidated organic/metal bismuth ion architecture (COMBIA). Benefiting from hierarchical reversible noncovalent interactions, the COMBIA hydrogel exhibits an optimal combination of mechanical and functional properties, particularly its integrated mechanical properties, including unprecedented stretchability, fracture toughness, and resilience. Furthermore, these hydrogels demonstrate superior conductivity, optical transparency, freezing tolerance, adhesion capability, and spontaneous mechanical and electrical self-healing. These unified functions render our hydrogel exceptional properties such as shape adaptability, skin-like perception, and energy harvesting capabilities. To demonstrate its potential applications, an artificial skin using our COMBIA hydrogel was configured for stimulus signal recording, which, as a promising soft electronics platform, could be used for next-generation human-machine interfaces. Copyright © 2025 The Authors, some rights reserved.

关键词： Fracture toughness

Flexible Full-Stokes Polarization engineering by Disorder-Scrambled Metasurfaces

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arXiv 2025年

作者： Cheng, Zhi Zhou, Zhou Wang, Zhuo Wang, Yue Yu, Changyuan Department of Electrical and Electronic Engineering The Hong Kong Polytechnic University China Department of Electrical and Computer Engineering NUS Graduate School National University of Singapore Singapore117583 Singapore Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices School of Optoelectronic Science and Engineering South China Normal University Guangzhou510006 China The Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen China

The ability to arbitrarily and flexibly control the polarization of light, including both the state of polarization (SoP) and the degree of polarization (DoP), is highly important for quantum optics, polarization imaging, and coherent optical communications. Although metasurfaces have shown promise in polarization control, the few studies focusing on the DoP often lack flexibility in manipulation. Here, we propose a novel approach using a disordered metasurface to flexibly convert natural light into partially polarized light, enabling independent and flexible control over all Stokes parameters. The metasurface is composed of two types of meta-atoms, uniformly distributed with specific quantity ratios, decoupling the design parameters in the process of polarization control, and allowing a one-to-one correspondence between metasurface and polarization spaces. The azimuthal and elevation angles of the SoP on the Poincaré sphere are independently controlled by the meta-atom rotation and size, while the DoP is governed by the quantity ratio. A developed algorithm determines the disordered metasurface arrangement, with theoretical calculations showing an average error of less than 3° for both the azimuthal and elevation angles and a control accuracy of ±0.05 for the DoP. Copyright © 2025, The Authors. All rights reserved.

关键词： Quantum optics