检索结果-内蒙古大学图书馆

Thermally activated dynamics of annealed glasses near the yielding transition under cyclic shear

学校读者我要写书评

暂无评论

arXiv 2024年

作者： Graham, Ian R. Arratia, Paulo E. Riggleman, Robert A. Department of Physics and Astronomy University of Pennsylvania PhiladelphiaPA19104 United States Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania PhiladelphiaPA19104 United States Department of Chemical and Biomolecular Engineering University of Pennsylvania PhiladelphiaPA19104 United States

While experiments and simulations have provided a rich picture of the dynamic heterogeneity in glasses at constant temperature or under steady shear, the dynamics of glasses under oscillatory shear remain comparatively less explored. Recent work has shown that oscillatory shear protocols can embed a "memory" into a glass’s structure, whereby the material will exhibit dynamics that are encoded by the oscillatory shear protocol applied. However, most of the computational work studying the memory effect has been performed in the zero temperature limit, and the effects of thermalization are poorly characterized. In this work, we use nonequilibrium molecular dynamics simulations to study the dynamics of a model two-dimensional glass former at low, nonzero temperatures under oscillatory shear. While we show that the systems’ dynamics are independent of sample preparation for either small or larger strain amplitudes, the dynamics become distinct near the yield point when the deformation is applied at finite temperature. We then characterize the dynamic heterogeneity using two metrics, one derived from the vibrational modes and one that exploits machine learning to identify regions prone to rearrangement. This analysis provides evidence that the dynamics below and above yield emerge from distinct structural origins that may be important for developing improved constitutive models that can predict memory in disordered solids. © 2024, CC BY.

关键词： Vibration analysis

Experimental Demonstration of Coupled Learning in Elastic Networks

学校读者我要写书评

暂无评论

arXiv 2023年

作者： Altman, Lauren E. Stern, Menachem Liu, Andrea J. Durian, Douglas J. Department of Physics & Astronomy University of Pennsylvania PhiladelphiaPA19104 United States Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania PhiladelphiaPA19104 United States

Coupled learning is a contrastive local learning scheme for tuning the properties of individual elements within a network to achieve desired functionality of the system. It takes advantage of physics both to learn using local rules and to "compute" the output response to input data, thus enabling the system to perform decentralized computation without the need for a processor or external memory. We present three proof-of-concept mechanical networks of increasing complexity, and demonstrate how they can learn tasks such as self-symmetrization and node allostery via iterative tuning of individual spring rest lengths. These mechanical networks could feasibly be scaled and automated to solve increasingly complex tasks, hinting at a new class of smart metamaterials. © 2023, CC BY-NC-SA.

关键词：

GBEC: Geometry-Based Hand-Eye Calibration

学校读者我要写书评

暂无评论

GBEC: Geometry-Based Hand-Eye Calibration

IEEE International Conference on Robotics and Automation (ICRA)

作者： Yihao Liu Jiaming Zhang Zhangcong She Amir Kheradmand Mehran Armand Department of Computer Science Johns Hopkins University Baltimore MD USA Department of Mechanical Engineering Johns Hopkins University Baltimore MD USA Department of Neurology and Department of Neuroscience Johns Hopkins University Baltimore MD USA Department of Mechanical Engineering Department of Computer Science Department of Orthopaedic Surgery Applied Physics Laboratory Johns Hopkins University Baltimore MD USA

ISBN: (数字)9798350384574

ISBN: (纸本)9798350384581

Hand-eye calibration is the problem of solving the transformation from the end-effector of a robot to the sensor attached to it. Commonly employed techniques, such as AXXB or AXZB formulations, rely on regression methods that require collecting pose data from different robot configurations, which can produce low accuracy and repeatability. However, the derived transformation should solely depend on the geometry of the end-effector and the sensor attachment. We propose Geometry-Based End-Effector Calibration (GBEC) that enhances the repeatability and accuracy of the derived transformation compared to traditional hand-eye calibrations. To demonstrate improvements, we apply the approach to two different robot-assisted procedures: Transcranial Magnetic Stimulation (TMS) and femoroplasty. We also discuss the generalizability of GBEC for camera-in-hand and marker-in-hand sensor mounting methods. In the experiments, we perform GBEC between the robot end-effector and an optical tracker’s rigid body marker attached to the TMS coil or femoroplasty drill guide. Previous research documents low repeatability and accuracy of the conventional methods for robot-assisted TMS hand-eye calibration. Applying GBEC to repeated calibrations, we obtain transformations with standard deviations of 0.37mm, 0.65mm, and 0.40mm (translation) along x, y, and z axes of the end-effector, respectively. The tool alignment experiments after using GBEC achieve a mean accuracy around 0.2mm in Euclidean distance. When compared to some existing methods, the proposed method relies solely on the geometry of the flange and the pose of the rigid-body marker, making it independent of workspace constraints or robot accuracy, without sacrificing the orthogonality of the rotation matrix. Our results validate the accuracy and applicability of the approach, providing a new and generalizable methodology for obtaining the transformation from the end-effector to a sensor.

关键词： Geometry Accuracy Transcranial magnetic stimulation Stimulated emission Flanges Robot sensing systems End effectors

Enhanced fast charging capabilities in natural graphite/iron cross-linked pectin electrodes for lithium-ion batteries

学校读者我要写书评

暂无评论

Materials Advances 2024年第17期5卷 6820-6829页

作者： Chung, Chin-Yi Chen, Wei-Ming Chen, Yan-Ruei Chen, Liang-Yu Su, Yu-Hsuan Chi, Po-Wei Wu, Phillip M. Chang-Liao, Kuei-Shu Tang, Hong-Yi 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 College of Science National Chung Hsing University 145 Xingda Road South District Taichung402 Taiwan Department of Applied Chemistry National Chi-Nan University 1 University Road Puli Nantou545301 Taiwan

Rapid charging capabilities are required for the broader adoption of lithium-ion batteries in emerging technologies such as electric vehicles. Although commercial graphite anodes provide a high energy density, their limitations in quick charging warrant the exploration of novel materials. This study extends prior research on the use of pectin, a natural polysaccharide, as an organic binder for graphite anodes. By introducing iron into pectin, we propose a unique ion-crosslinking mechanism that causes the graphite anode to exhibit pseudocapacitive Li storage. Our findings, corroborated by 3D Bode analysis and AC impedance spectra, revealed a positive correlation between the iron ion and the pseudocapacitive vertex in the graphite reaction. Compared with conventional binders, graphite electrodes utilizing iron-doped pectin demonstrated superior initial and stable capacities, reaching 450 mA h g−1 after 100 cycles at 1C. This study highlights the synergistic effect of pectin and iron ions, offering a new avenue for high-performance, rapid-charging, and environmentally sustainable lithium-ion batteries. © 2024 RSC.

关键词： Lithium-ion batteries

Experimental Characterization of the Thermal Properties of Thin Polypropylene Plates Reinforced with Residues and Fibers from the Borassus Wood (Rônier) of Chad

学校读者我要写书评

暂无评论

Open Journal of applied Sciences 2025年第2期15卷 517-529页

作者： Abakar Malgnan Kimtangar Ngargueudedjim Bruno Bassa Hinpere Wedjou Bianpambe Guy Edgar Ntamack Laboratory of Studies and Research in Industrial Technology Faculty of Exact and Applied Sciences University of NDjamena NDjamena Chad Department of Mechanical Engineering National Higher Institute of Sciences and Technology of Abch Abch Chad Group of Mechanics Materials and Acoustics (GMMA) Department of Physics Faculty of Science University of NGaoundr Ngaoundr Cameroon

This study focuses on the thermophysical characterizations of composite materials made from polypropylene reinforced with residues and fibers from Borassus wood from Chad. These properties are experimentally determined at different temperatures using the hot wire method of the “FP2C” machine, where the hot wire probe is inserted between two specimens. The values of the thermal conductivity in powdered Borassus wood range from 0.170 W/mK to 0.182 W/mK for female wood (FNTF) and from 0.169 W/mK to 0.173 W/mK for male wood. For the female and male fibers, the thermal conductivity values range from 0.137 W/mK to 0.157 W/mK for the female and from 0.138 W/mK to 0.168 W/mK for the male. The thermal effusivity of the residues and fibers of Borassus wood varies from: 509.6 Ws1/2/m2K to 543 Ws1/2/m2K for the powder of female wood and from 524.6 Ws1/2/m2K to 547 Ws1/2/m2K for the powder of male wood. For the fibers of Borassus wood, the values range from 410.6 Ws1/2/m2K to 523.6 Ws1/2/m2K for the female wood fibers and from 420.3 Ws1/2/m2K to 480.3 Ws1/2/m2K for the male wood fibers. These results are important for the applications of Borassus wood residues and fibers in construction works regarding the thermal insulation of habitats.

关键词： Composite Materials Residues and Fibers of Rônier Wood from Chad Thin Sheets Thermal Properties Characterization

Entanglement-Enhanced Neyman-Pearson Target Detection

学校读者我要写书评

暂无评论

arXiv 2024年

作者： Ward, William Hariri, Abdulkarim Zhang, Zheshen Applied Physics Program University of Michigan Ann ArborMI48104 United States Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48104 United States

Quantum illumination (QI) provides entanglement-enabled target-detection enhancement, despite operating in an entanglement-breaking environment. Existing experimental studies of QI have utilized a Bayesian approach, assuming that the target is equally likely to be present or absent before detection, to demonstrate an advantage over classical target detection. However, such a premise breaks down in practical operational scenarios in which the prior probability is unknown, thereby hindering QI's applicability to real-world target-detection scenarios. In this work, we adopt the Neyman-Pearson criterion in lieu of the error probability for equally likely target absence or presence as our figure of merit for QI. We demonstrate an unconditional quantum advantage over the optimal classical-illumination protocol as benchmarked by the receiver operating characteristic, which examines detection probability versus false-alarm probability without resorting to known prior probabilities. Our work represents a critical advancement in adapting quantum-enhanced sensing to practical operational settings. © 2024, CC BY.

关键词： Quantum entanglement

The effect of stereochemical constraints on the radius of gyration of folded proteins

学校读者我要写书评

暂无评论

arXiv 2025年

作者： Logan, Jack A. Sumner, Jacob Grigas, Alex T. Shattuck, Mark D. O'Hern, Corey S. Department of Mechanical Engineering Yale University New HavenCT06520 United States Graduate Program in Computational Biology & Biomedical Informatics Yale University New HavenCT06520 United States Integrated Graduate Program in Physical and Engineering Biology Yale University New HavenCT06520 United States Benjamin Levich Institute and Physics Department The City College of New York New YorkNY10031 United States Department of Applied Physics Yale University New HavenCT06520 United States Department of Physics Yale University New HavenCT06520 United States

Proteins are composed of linear chains of amino acids that fold into complex three-dimensional structures. A general feature of folded proteins is that they are compact with a radius of gyration Rg(N) ∼ Nν that obeys power-law scaling with the number of amino acids N in each protein and ν ∼ 1/3. In this study, we investigate the internal scaling of the radius of gyration Rg(n) versus the chemical separation n between amino acids for all subchains of length n. We show that for globular proteins Rg(n) ∼ nν1,2 with a larger exponent ν1 > 1/3 for small n and a smaller exponent ν2 g(N) ∝ Nν. To describe this scaling behavior for Rg(n), we carry out folding simulations for a series of coarse-grained models for proteins beginning with the freely-jointed and freely-rotating chain models composed of spherical monomers and varying degrees of stereochemical constraints. We show that a minimal model, which coarse-grains amino acids into a single spherical backbone atom and one variable-sized spherical side-chain atom, and enforces bend- and dihedral-angle constraints, can recapitulate Rg(n) for x-ray crystal structures of globular proteins. In addition, this model predicts the correct average packing fraction and size of the hydrophobic core, which are two key physical features that can be used to distinguish between computational 'decoys' and correctly folded proteins in protein design applications. © 2025, CC BY.

关键词： Spheres

Dark Current and Noise Characterization of InGaAs/GaAsSb T2SL Photodetectors 22

学校读者我要写书评

暂无评论

Dark Current and Noise Characterization of InGaAs/GaAsSb T2S...

Optical Components and Materials XXII 2025

作者： Gil, Armando Phillips, Jamie Ettenberg, Martin H. Kurdak, Cagliyan Applied Physics Program University of Michigan Ann ArborMI48109 United States Department of Electrical and Computer Engineering University of Delaware NewarkDE19716 United States Princeton Infrared Technologies Inc. 7 Deer Park Dr. Ste. E Monmouth JunctionNJ08852 United States Department of Physics University of Michigan Ann ArborMI48109 United States

ISBN: (纸本)9781510684720

We investigate the dark current and dark current noise spectra of a short-wavelength infrared based blind photodiode as a function of temperature. We designed and built a custom cryogenic system with a slow temperature relaxation time to perform measurements. The measured device uses a type-II superlattice (2.9 nm InGaAs / 2.9 nm GaAsSb) absorption layer with an effective bandgap of 580 meV that is lattice-matched to InP. At temperatures above 150 K the dark current activation energy was found to be 140 meV, which rules out diffusion- or GR-limited currents and explains that large magnitudes of dark current when compared to similar devices. When normalized to current, we find that 1/f noise grows with temperature, reaches a maximum at about 200 K, then reduces as the temperature goes to 300 K. © 2025 SPIE.

关键词： Indium arsenide

First principles investigation on half metallic ferromagnetism properties of cubic VLaO3 compound

学校读者我要写书评

暂无评论

Materials Today: Proceedings 2023年

作者： Jain, Ekta Behera, Debidatta Agrawal, Yogesh Yugbodh, Kshitij Abraham, Jisha Annie Sharma, Ramesh Mukherjee, Sanat Kumar Department of Applied Science Sagar Institute of Research Engineering and Technology Excellence Bhopal-462016l Madhya Pradesh India Department of Physics Birla Institute of Technology Mesra-835215 Ranchi Jharkhand India Department of Mechanical Engineering Sagar Institute of Research Engineering and Technology Bhopal-462016l Madhya Pradesh India Department of Mechanical Engineering Sagar Institute of Science Technology and Engineering Bhopal-462044 Madhya Pradesh India Department of Physics National Defence Academy Khadakwasla Pune-411023 Maharashtra India Department of Applied Science Feroze Gandhi Institute of Engineering and Technology Raebareli-229001 Uttar Pradesh India

In this investigation, we thoroughly examined the equilibrium structural, electrical, magnetic, elastic, thermodynamic, as well as thermoelectric behavior of the vanadium lanthanum oxide perovskite VLaO3. The computations were executed with the FP-LAPW method, as in cooperated in the WIEN2k package that rely on the first principles method, using generalized gradient approximation (PBE-GGA). The explored compound has been observed to be ferromagnetically stable i.e., in FM phase as it has lowest energy in FM state than in paramagnetic phase i.e., in NM phase. The thermodynamical and mechanical stability of the studied VLaO3 compound is also assured by evaluating its formation energy, cohesive energy and second order elastic constants. Furthermore, our computed findings reveal that the studied compound belongs to half metallic perovskites with an energy gap of 2.56 eV in the majority spin and possesses a total magnetic moment of 3.99μB/unit cell. Additionally, the thermal as well as pressure dependence of volume, specific heat capacity, and bulk modulus are also examined with the aid of GIBBS which rely on quasi harmonic Debye theory. Finally, the thermoelectric transport properties are also evaluated as a function of chemical potential in the range extending from -2.0 eV to 2.0 eV for different temperatures at 300 K, 700 K and 1200 K to explore budding possibility of this compound for energy harvesting applications. © 2023 Elsevier Ltd. All rights reserved.

关键词： Electronic properties