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arXiv 2023年

作者： Wu, Ziyou Zhao, Dan Revzen, Shai Robotics University of Michigan United States Mechanical Engineering University of Michigan United States Electrical Engineering and Computer Science University of Michigan United States Ecology and Evolutionary Biology University of Michigan United States Applied Physics Program University of Michigan United States

Multi-legged robots with six or more legs are not in common use, despite designs with superior stability, maneuverability, and a low number of actuators being available for over 20 years. This may be in part due to the difficulty in modeling multi-legged motion with slipping and producing reliable predictions of body velocity. Here we present a detailed measurement of the foot contact forces in a hexapedal robot with multiple sliding contacts, and provide an algorithm for predicting these contact forces and the body velocity. The algorithm relies on the recently published observation that even while slipping, multi-legged robots are principally kinematic, and employ a friction law ansatz that allows us to compute the shape-change to body-velocity connection and the foot contact forces. This results in the ability to simulate motion plans for a large number of contacts, each potentially with slipping. Furthermore, in homogeneous environments, this kind of simulation can run in (parallel) logarithmic time of the planning horizon. © 2023, CC BY.

关键词： Friction

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Peak thermal conductivity measurements of boron arsenide crystals

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Physical Review Materials 2022年第6期6卷 L061601-L061601页

作者： Yuanyuan Zhou Chunhua Li Pawan Koirala Geethal Amila Gamage Hanlin Wu Sheng Li Navaneetha K. Ravichandran Hwijong Lee Andrei Dolocan Bing Lv David Broido Zhifeng Ren Li Shi Walker Department of Mechanical Engineering The University of Texas at Austin Austin Texas 78712 USA Department of Physics Boston College Chestnut Hill Massachusetts 02467 USA Department of Physics The University of Texas at Dallas Richardson Texas 75080 USA Department of Physics and Texas Center for Superconductivity University of Houston Houston Texas 77204 USA Department of Mechanical Engineering Indian Institute of Science Bangalore 560012 India Materials Science and Engineering Program Texas Materials Institute The University of Texas at Austin Austin Texas 78712 USA

Recent experiments have validated prior theories of unusual high thermal conductivity (κ) in boron arsenide (BAs) and revealed large κ variation associated with extended and point defects in the samples. The peak κ provides valuable insights into the competition between intrinsic phonon-phonon scattering processes and extrinsic boundary and defect scattering processes in BAs. However, prior measurement methods have not been able to measure the peak κ because of fundamental and technical limitations. Here, we report peak κ measurements of BAs crystals synthesized under different conditions with source materials of different purities via a vapor transport method. For three representative samples, the measured κ peak appears at temperatures between 120 and 150 K and varies from 410±60Wm−1K−1 to 830±100Wm−1K−1. The measured thermal conductivities agree with theoretical calculations across the full temperature range. The similar calculated and measured peak temperatures helps to narrow down the boundary scattering mean free path to be around 4 μm in two samples and 5 μm in another, while the variation of the peak magnitude reveals a one-order-of-magnitude difference in the strength of point defect scattering. The phonon-defect scattering behavior correlates well with the measured electronic Raman scattering background, the impurity concentrations revealed by secondary ion mass spectroscopy, and the Hall concentration and mobility of the p-type samples except for an anomalously high hole concentration that appears in one sample, which indicates nonuniform impurity distribution. The observed correlation clarifies the origins of extrinsic phonon scattering mechanisms in BAs crystals.

关键词： Crystal defects Hall effect Heat transfer Impurities Phonons Thermal conductivity Thermal properties

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Advanced TiO2/Al2O3 Bilayer ALD Coatings for Improved Lithium-Rich Layered Oxide Electrodes

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ACS Applied Materials and Interfaces 2024年第10期16卷 13029-13040页

作者： Chen, Wei-Ming Hsieh, Hsin-Yu Wu, Dong-Ze Tang, Horng-Yi Chang-Liao, Kuei-Shu Chi, Po-Wei Wu, Phillip M. Wu, Maw-Kuen Institute of Physics Academia Sinica 128 Section 2 Academia Road Taipei11529 Taiwan Nano Science and Technology Program Taiwan International Graduate Program Academia Sinica and National Tsing Hua University 128 Section 2 Academia Road Taipei11529 Taiwan Department of Engineering and System Science National Tsing Hua University 101 Section 2 Kuang-Fu Road Hsinchu300044 Taiwan Graduate Institute of Energy and Sustainability Technology National Taiwan University of Science and Technology 43 Keelung Road Sec 4 Taipei10607 Taiwan Department of Applied Chemistry National Chi Nan University 1 University Road Puli Nantou545301 Taiwan College of Science National Chung Hsing University 145 Xingda Rd. South Dist. Taichung City402 Taiwan

Surface modification is a highly effective strategy for addressing issues in lithium-rich layered oxide (LLO) cathodes, including phase transformation, particle cracking, oxygen gas release, and transition-metal ion dissolution. Existing single-/double-layer coating strategies face drawbacks such as poor component contact and complexity. Herein, we present the results of a low-temperature atomic layer deposition (ALD) process for creating a TiO2/Al2O3 bilayer on composite cathodes made of AS200 (Li1.08Ni0.34Co0.08Mn0.5O2). Electrochemical analysis demonstrates that TiO2/Al2O3-coated LLO electrodes exhibit improved discharge capacities and enhanced capacity retention compared with uncoated samples. The TAA-5/AS200 bilayer-coated electrode, in particular, demonstrates exceptional capacity retention (∼90.4%) and a specific discharge capacity of 146 mAh g-1 after 100 cycles at 1C within the voltage range of 2.2 to 4.6 V. The coated electrodes also show reduced voltage decay, lower surface film resistance, and improved interfacial charge transfer resistances, contributing to enhanced stability. The ALD-deposited TiO2/Al2O3 bilayer coatings exhibit promising potential for advancing the electrochemical performance of lithium-rich layered oxide cathodes in lithium-ion batteries. © 2024 The Authors. Published by American Chemical Society.

关键词： Cathodes

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Quantum simulation of an extended Dicke model with a magnetic solid

Communications Materials

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Communications Materials 2024年第1期5卷 42页

作者： Marquez Peraca, Nicolas Li, Xinwei Moya, Jaime M. Hayashida, Kenji Kim, Dasom Ma, Xiaoxuan Neubauer, Kelly J. Fallas Padilla, Diego Huang, Chien-Lung Dai, Pengcheng Nevidomskyy, Andriy H. Pu, Han Morosan, Emilia Cao, Shixun Bamba, Motoaki Kono, Junichiro Department of Physics and Astronomy Rice University HoustonTX United States Department of Physics California Institute of Technology PasadenaCA United States Applied Physics Graduate Program Smalley–Curl Institute Rice University HoustonTX United States Division of Applied Physics Graduate School of Engineering Hokkaido University Hokkaido Japan Department of Electrical and Computer Engineering Rice University HoustonTX United States Department of Physics International Center of Quantum and Molecular Structures and Materials Genome Institute Shanghai University Shanghai China Department of Physics and Center for Quantum Frontiers of Research and Technology National Cheng Kung University Tainan Taiwan Department of Chemistry Rice University HoustonTX United States Department of Physics I Kyoto University Kyoto Japan The Hakubi Center for Advanced Research Kyoto University Kyoto Japan PRESTO Japan Science and Technology Agency Saitama Japan Department of Physics Yokohama National University Yokohama Japan Department of Materials Science and NanoEngineering Rice University HoustonTX United States

The Dicke model describes the cooperative interaction of an ensemble of two-level atoms with a single-mode photonic field and exhibits a quantum phase transition as a function of light–matter coupling strength. Extending this model by incorporating short-range atom–atom interactions makes the problem intractable but is expected to produce new physical phenomena and phases. Here, we simulate such an extended Dicke model using a crystal of ErFeO3, where the role of atoms (photons) is played by Er3+ spins (Fe3+ magnons). Through terahertz spectroscopy and magnetocaloric effect measurements as a function of temperature and magnetic field, we demonstrated the existence of a novel atomically ordered phase in addition to the superradiant and normal phases that are expected from the standard Dicke model. Further, we elucidated the nature of the phase boundaries in the temperature–magnetic-field phase diagram, identifying both first-order and second-order phase transitions. These results lay the foundation for studying multiatomic quantum optics models using well-characterized many-body solid-state systems. © The Author(s) 2024.

关键词： Atoms

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Emulating complex synapses using interlinked proton conductors

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Physical Review Applied 2025年第1期23卷 014027-014027页

作者： Lifu Zhang Ji-An Li Yang Hu Jie Jiang Rongjie Lai Marcus K. Benna Jian Shi Department of Materials Science and Engineering Rensselaer Polytechnic Institute Troy New York 12180 USA Neurosciences Graduate Program University of California San Diego La Jolla California 92093 USA Department of Mathematics Purdue University West Lafayette Indiana 47907 USA Department of Neurobiology School of Biological Sciences University of California at San Diego La Jolla California 92093 USA Department of Physics Applied Physics and Astronomy Rensselaer Polytechnic Institute Troy New York 12180 USA

In terms of energy efficiency and computational speed, neuromorphic electronics based on nonvolatile memory devices are expected to be one of most promising hardware candidates for future artificial intelligence (AI). However, catastrophic forgetting, networks rapidly overwriting previously learned weights when learning new tasks, remains a pivotal obstacle in either digital or analog AI chips for unleashing the true power of brainlike computing. To address catastrophic forgetting in the context of online memory storage, a complex synapse model (the Benna-Fusi model) was proposed recently [M. K. Benna and S. Fusi, Nat. Neurosci. 19, 1697 (2016)], the synaptic weight and internal variables of which evolve following diffusion dynamics. In this work, by designing a proton transistor with a series of charge-diffusion-controlled storage components, we have experimentally realized the Benna-Fusi artificial complex synapse. Memory consolidation from coupled storage components is revealed by both numerical simulations and experimental observations. Different memory timescales for the complex synapse are engineered by the diffusion length of charge carriers and the capacity and number of coupled storage components. The advantages of the demonstrated complex synapse for both memory capacity and memory consolidation are revealed by neural network simulations of face-familiarity detection. Our experimental realization of the complex synapse suggests a promising approach to enhance memory capacity and to enable continual learning.

关键词： Nonvolatile storage

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Geotechnical Investigations in Lignite Open pit Mine Using Electrical Tomography (2D&3D) and Seismic Reflection Methods 11

Geotechnical Investigations in Lignite Open pit Mine Using E...

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11th Congress of the Balkan Geophysical Society, BGS 2021

作者： Andronikidis, N. Kritikakis, G. Vafidis, A. Hamdan, H. Agioutantis, Z. Steiakakis, C. Economou, N. Technical University of Crete School of Mineral Resources Engineering Applied Geophysics lab Greece University of Sharjah Petroleum Geosciences and Remote Sensing Program Department of Applied Physics and Astronomy United Arab Emirates University of Kentucky Mining Engineering GEOSYSTA Corporation

ISBN: (纸本)9789462823938

The application of seismic reflection and electrical resistivity methods (2D and 3D) in geotechnical investigations is explored through a case study in Northern Greece. These methods were employed to Mavropigi lignite open pit mine and the surveyed area is the next step in mining expansion. The main aim of the geophysical survey was to map the bedrock, the contact between the Neogene and Schist/Carbonate formations as well as to estimate the thickness of the carbonate rocks on top of the Schist formations in order to study the stability of the final mine slopes. These geophysical data provides a geotechnical model which will be used in mine planning from Greek Public Power Corporation. © 2021 11th Congress of the Balkan Geophysical Society, BGS 2021. All rights reserved.

关键词： Lignite

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Local and global measures of the shear moduli of jammed disk packings

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Physical Review E 2023年第5期107卷 054903-054903页

作者： Shiyun Zhang Weiwei Jin Dong Wang Ding Xu Jerry Zhang Mark D. Shattuck Corey S. O'Hern Department of Physics University of Science and Technology of China Hefei Anhui 230026 China Department of Mechanical Engineering and Materials Science Yale University New Haven Connecticut 06520 USA Benjamin Levich Institute and Physics Department The City College of New York New York New York 10031 USA Department of Physics Yale University New Haven Connecticut 06520 USA Department of Applied Physics Yale University New Haven Connecticut 06520 USA Graduate Program in Computational Biology and Bioinformatics Yale University New Haven Connecticut 06520 USA

Strain-controlled isotropic compression gives rise to jammed packings of repulsive, frictionless disks with either positive or negative global shear moduli. We carry out computational studies to understand the contributions of the negative shear moduli to the mechanical response of jammed disk packings. We first decompose the ensemble-averaged, global shear modulus as 〈G〉=(1−F−)〈G+〉+F−〈G−〉, where F− is the fraction of jammed packings with negative shear moduli and 〈G+〉 and 〈G−〉 are the average values from packings with positive and negative moduli, respectively. We show that 〈G+〉 and 〈|G−|〉 obey different power-law scaling relations above and below pN2∼1. For pN2>1, both 〈G+〉N and 〈|G−|〉N∼(pN2)β, where β∼0.5 for repulsive linear spring interactions. Despite this, 〈G〉N∼(pN2)β′ with β′≳0.5 due to the contributions from packings with negative shear moduli. We show further that the probability distribution of global shear moduli P(G) collapses at fixed pN2 and different values of p and N. We calculate analytically that P(G) is a Γ distribution in the pN2≪1 limit. As pN2 increases, the skewness of P(G) decreases and P(G) becomes a skew-normal distribution with negative skewness in the pN2≫1 limit. We also partition jammed disk packings into subsystems using Delaunay triangulation of the disk centers to calculate local shear moduli. We show that the local shear moduli defined from groups of adjacent triangles can be negative even when G>0. The spatial correlation function of local shear moduli C(r⃗) displays weak correlations for pnsub2<10−2, where nsub is the number of particles within each subsystem. However, C(r⃗) begins to develop long-ranged spatial correlations with fourfold angular symmetry for pnsub2≳10−2.

关键词： Jamming Packing & jamming problems Granular materials

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Controlling assembly and oscillations of elastic membranes with an active fluid

arXiv

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arXiv 2024年

作者： Berezney, John Ray, Sattvic Kolvin, Itamar Bowick, Mark Fraden, Seth Dogic, Zvonimir Department of Physics Brandeis University WalthamMA02454 United States Department of Physics University of California at Santa Barbara Santa BarbaraCA93106 United States School of Physics Georgia Institute of Technology 837 State St NW AtlantaGA30332 United States Kavli Institute of Theoretical Physics University of California at Santa Barbara Santa BarbaraCA93106 United States Biomolecular Science and Engineering Program University of California at Santa Barbara Santa BarbaraCA93106 United States

We use the chaotic flows generated by a microtubule-based active fluid to assemble self-binding actin filaments into a thin elastic sheets. Starting from a uniformly dispersed state, active flows drive the motion of actin filaments, inducing their bundling and formation of bundle-bundle connections that ultimately generate an elastic network. The emerging network separates from the active fluid to form a thin elastic sheets suspended at the sample midplane. At intermediate times, the active fluid drives large in-plane and out-of-plane deformations of the elastic sheet which are driven by low-energy bending modes. Self-organized sheets eventually exhibit centimeter-sized global spontaneous oscillations and traveling waves, despite being isotropically driven on micron lengths by the active fluid. The active assembly generates diverse network structures which are not easily realizable with conventional paradigms of equilibrium self-assembly and materials processing. Self-organized mechanical sheets pose a challenge for understanding of how a hierarchy of structure, mechanics, and dynamics emerges from a largely structureless initial suspension of active and passive microscopic components. © 2024, CC BY.

关键词： Self assembly

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Spectroscopic investigation and local structure of Eu3+ ions in lead phosphate glasses for optical device applications

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Optik 2024年 300卷

作者： Basavapoornima, Ch. Masthanaiah, E. Vijaya, N. Depuru, Shobha Rani Kaewkhao, J. Pecharapa, Wisanu Jayasankar, C.K. Department of Physics Sri Venkateswara University Tirupati517 502 India Institute of Aeronautical Engineering Hyderabad500 043 India Physics Program Faculty of Science and Technology Nakhon Pathom Rajabhat University Pathom Nakhon73000 Thailand Nakhon Pathom Rajabhat University Pathom Nakhon73000 Thailand College of Materials Innovation and Technology King Mongkut's Institute of Technology Ladkrabang Bangkok Ladkrabang10520 Thailand

Phosphate-based glasses are promising materials which are being employed for broad range of applications whereas Eu3+ is an efficient activator due to its predominant 5D0 →7F2 emission (red region). In this direction, an attempt has been made to investigate the effect of Eu3+ ions doped lead phosphate glasses (PPbKANEu: P2O5+PbO+K2O+Al2O3+Na2O+Eu2O3) to explore possible photonic device applications. Optical absorption, excitation, photoluminescence and decay rates are used to characterize the PPbKANEu glasses. The photoluminescence spectrum of Eu3+:PPbKAN glasses exhibit emission channels from the first excited (5D0) to the ground (7FJ (J =0–4)) multiplets. To determine the local site symmetry of surrounding Eu3+ ions, the relative fluorescence intensity ratio of 5D0→7F1 versus 5D0→7F2 emission channels has been analyzed. The emission spectrum of PPbKANEu glasses exhibits a comprehensive lifting of degeneracy of 5D0→7F2 and 5D0→7F1 emission channels. By considering C2v symmetry for Eu3+ ions, the second (B02= −406 and B22=−158) and fourth (B04=980, B24=297 and B44=926 cm–1) rank crystal–field (CF) characteristics were estimated along with CF strength factor (S= 402 cm–1). The lifetime of 5D0 state is estimated to be 2.09, 2.23, 2.21 and 2.21 ms for 0.1, 0.5, 1.0 and 2.0 mol% of Eu3+ ions, respectively. The analysis of the decay times reveals that the lifetime of 5D0 state is less affected by the concentration of the Eu3+ ion. The results are compared and discussed with reported values and confirm the potentiality of the PPbKANEu glasses for optical device applications in visible regions. © 2024 Elsevier GmbH

关键词： Ions

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Development of a Speed-Limiting Braking Mechanism for Baby Walkers Using a PI Controller

Development of a Speed-Limiting Braking Mechanism for Baby W...

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Smart Mechatronics (ICSMech), IEEE International Conference on

作者： Islamiyati Islamiyati Riza Muhida Muhammad Riza Arko Djajadi Sadiman Sadiman Yoga Tri Wijayanti Kusumawardhany Airlangga Rijanti Huminsa Ranto Morison Panjaitan Dandi Efendi Program Studi Kebidanan Metro Poltekkes Kemenkes Tanjung Karang Lampung Indonesia Department of Mechanical Engineering Universitas Bandar Lampung Bandar Lampung Indonesia Department of Engineering Physics Universitas Multimedia Nusantara Tangerang Banten Indonesia RSUD Jendral A. Yani Metro Lampung Indonesia RSUD Sukadana Lampung Timur Indonesia

ISBN: (数字)9798350368918

ISBN: (纸本)9798350368925

Baby walkers are commonly used to support infants in developing motor skills and walking abilities, yet their uncontrolled movement poses significant safety risks, such as falls and injuries. This study addresses these risks by developing a speed-limiting braking system that prevents baby walkers from exceeding a safe speed limit of 0.3 meters per second, thereby enhancing safety. The system integrates a Proportional-Integral (PI) controller, a speed sensor, and a servo motor-driven braking mechanism. Methodology involved MATLAB simulations to fine-tune controller parameters and physical testing for validation. Results showed the braking mechanism engaged promptly when the speed limit was reached and disengaged when speed decreased, confirming effective regulation without impeding natural infant movements. This study demonstrates a reliable solution to enhance baby walker safety while promoting safe motor development for infants. MATLAB simulations and physical tests confirmed the system's efficiency in real-time speed monitoring and automated braking. The results highlighted rapid response times and seamless braking, providing controlled deceleration without interfering with the infant's natural movements.

关键词： Pediatrics PI control Real-time systems Safety Time factors Reliability MATLAB Servomotors Monitoring Testing

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