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Mn3+ eg Configuration and Electron Transfer in Na-Incorporating α-MnO2 to Improve Electrochemical Supercapacitor: An In Situ and Ex Situ X-ray Absorption Spectroscopic Investigation

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ACS applied Energy Materials 2023年第12期6卷 6443-6455页

作者： Yadav, Priyanka L. Shelke, Abhijeet R. Wang, Hsiao-Tsu Chen, Kuan-Hung Lin, Wei- Xuan Li, Chin-Wei Chen, Mei-Yu Yeh, Ping-Hung Dong, Chung-Li Qorbani, Mohammad Huang, Yu-Cheng Chiou, Jau-Wern Tsai, Huang-Ming Kadam, Prakash M. Chen, Kuei-Hsien Chen, Li-Chyong Pong, Way-Faung Department of Physics Tamkang University New Taipei City251301 Taiwan Department of Electronics Smt. Kasturbai Walchand College Maharashtra Sangli416416 India Bachelors’s Program in Advanced Materials Science Tamkang University New Taipei City251301 Taiwan Center for Condensed Matter Sciences National Taiwan University Taipei10617 Taiwan Center of Atomic Initiative for New Materials National Taiwan University Taipei10617 Taiwan Department of Electrophysics National Yang Ming Chiao Tung University Hsinchu300 Taiwan Department of Applied Physics National University of Kaohsiung Kaohsiung811 Taiwan National Synchrotron Radiation Research Center Hsinchu30076 Taiwan Institute of Atomic and Molecular Sciences Academia Sinica Taipei10617 Taiwan Department of Physics National Taiwan University Taipei10617 Taiwan

Cryptomelane-type α-MnO2 has a high specific capacitance and cyclic stability because of its combination of 1 × 1 and 2 × 2 tunnel structures that are formed from the edge- and corner-sharing octahedra. It, therefore, has the potential to host various cations, which improve its electrochemical properties. The Na incorporation provides an opportunity for charge compensation by forming mixed-valence Mn3+ and Mn4+ states in α-MnO2. This study shows that the incorporation of Na results in superior electrochemical properties by enhancing the specific capacitance and capacity retention of α-MnO2 to 234.4 F g-1 and ∼96%, respectively. The electrochemical performance is improved following Na incorporation by the induced phase competition between α-MnO2 and the induced β-MnO2, while the charge neutrality between Jahn-Teller (JT) active Mn3+ and Mn4+ ions is maintained. The formed Mn3+/Mn4+ mixed-valence species increase the strength of the redox reaction at the electrode-electrolyte interface, as observed from the in-situ Mn K-edge X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure. Ex-situ Mn L3,2-edge XANES analysis further reveals that the introduction of eg from the Mn3+ 3d orbitals causes electron transfer via O 2p states by establishing the double-exchange (DE) Mn3+-O-Mn4+ interaction. This study suggests that the electron exchange also involves the super-exchange (SE) Mn4+-O-Mn4+ interaction, based on field-dependent magnetization (M-H) measurement, which accelerates the redox reaction in α-MnO2. This work demonstrates that JT active Mn3+ eg configuration is responsible for the great improvement of electrochemical properties that are induced by the incorporation and insertion/extraction of Na+ ions with the charge/discharge process, which causes electron hopping between Mn3+/Mn4+ and Mn4+ through oxygen ligand by DE/SE in the α-MnO2 © 2023 American Chemical Society

关键词： Electrolytes

Evanescent wave spectral singularities in non-Hermitian photonics

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Physical Review B 2024年第4期109卷 L041405-L041405页

作者： Huan He Zhaoxian Chen Huanan Li Cheng-Hou Tu Jingjun Xu Andrea Alù MOE Key Laboratory of Weak-Light Nonlinear Photonics School of Physics Nankai University Tianjin 300071 China College of Engineering and Applied Sciences Collaborative Innovation Center of Advanced Microstructures and National Laboratory of Solid State Microstructures Nanjing University Nanjing 210023 China Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10016 USA

Spectral singularities (SSs) emerge at isolated real frequencies when the scattering coefficients of a system diverge, producing scattering anomalies in non-Hermitian systems. Here, based on parity-time symmetry, we introduce SSs for evanescent waves, and explore their exotic features. We show that evanescent wave SSs can realize highly reconfigurable unidirectional lasers and absorbers, and offer the opportunity to observe extreme scattering anomalies associated with SSs in fully passive platforms, decoupling their extreme scattering responses from energy considerations. More broadly, our study opens avenues for non-Hermitian wave engineering, showcasing a link between non-Hermitian physics and structured waves, with implications in nano-optics for extreme wave-matter interactions and functional devices.

关键词： Evanescent waves Wave scattering Non-Hermitian systems

Low-Loss, Nonvolatile Tuning of Bragg Structures with Sb2Se3

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Low-Loss, Nonvolatile Tuning of Bragg Structures with Sb2Se3

Conference on Lasers and Electro-Optics (CLEO)

作者： Nicholas A. Nobile Chuanyu Lian Hongyi Sun Yi-Siou Huang Brian Mills Cosmin Constantin Popescu Dennis Callahan Juejun Hu Carlos A. Ríos Ocampo Nathan Youngblood Electrical & Computer Engineering Department University of Pittsburgh Pittsburgh PA USA Department of Materials Science & Engineering University of Maryland College Park MD USA Institute for Research in Electronics and Applied Physics University of Maryland College Park MD USA Department of Materials Science & Engineering Massachusetts Institute of Technology Cambridge MA USA Draper Scholar Program The Charles Stark Draper Laboratory Inc Cambridge MA USA The Charles Stark Draper Laboratory Inc Cambridge MA USA

Sb 2 Se 3 is used to switch between broadband transparency and enhanced index contrast in two device types leveraging Bragg gratings for tunable stop-and pass-band functionalities. Experimental results highlight fabr... 详细信息

ISBN: (纸本)9798350369311

关键词： Bragg gratings Waveguide transitions Phase change materials Optical filters Optical switches Refractive index Fabry-Perot Indexes Passband Optical waveguides

CORNN: Convex optimization of recurrent neural networks for rapid inference of neural dynamics

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arXiv 2023年

作者： Dinc, Fatih Shai, Adam Schnitzer, Mark J. Tanaka, Hidenori Department of Applied Physics Stanford University StanfordCA94305 United States CNC Program Stanford University StanfordCA94305 United States Howard Hughes Medical Institute CNC Program Stanford University StanfordCA94305 United States Physics & Informatics Laboratories NTT Research Inc. SunnyvaleCA94085 United States Center for Brain Science Harvard University CambridgeMA02138 United States

Advances in optical and electrophysiological recording technologies have made it possible to record the dynamics of thousands of neurons, opening up new possibilities for interpreting and controlling large neural populations in behaving animals. A promising way to extract computational principles from these large datasets is to train data-constrained recurrent neural networks (dRNNs). Performing this training in real-time could open doors for research techniques and medical applications to model and control interventions at single-cell resolution and drive desired forms of animal behavior. However, existing training algorithms for dRNNs are inefficient and have limited scalability, making it a challenge to analyze large neural recordings even in offline scenarios. To address these issues, we introduce a training method termed Convex Optimization of Recurrent Neural Networks (CORNN)1. In studies of simulated recordings, CORNN attained training speeds ∼100-fold faster than traditional optimization approaches while maintaining or enhancing modeling accuracy. We further validated CORNN on simulations with thousands of cells that performed simple computations such as those of a 3-bit flip-flop or the execution of a timed response. Finally, we showed that CORNN can robustly reproduce network dynamics and underlying attractor structures despite mismatches between generator and inference models, severe subsampling of observed neurons, or mismatches in neural time-scales. Overall, by training dRNNs with millions of parameters in subminute processing times on a standard computer, CORNN constitutes a first step towards real-time network reproduction constrained on large-scale neural recordings and a powerful computational tool for advancing the understanding of neural computation. © 2023, CC BY.

关键词： Medical applications

Increasing the mobility and power-electronics figure of merit of AlGaN with atomically thin AlN/GaN digital-alloy superlattices

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arXiv 2022年

作者： Pant, Nick Lee, Woncheol Sanders, Nocona Kioupakis, Emmanouil Applied Physics Program University of Michigan Ann ArborMI48109 United States Department of Materials Science and Engineering University of Michigan Ann ArborMI48109 United States Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109 United States

Alloy scattering in random AlGaN alloys drastically reduces the electron mobility and therefore the power-electronics figure of merit. As a result, Al compositions greater than 75% are required to obtain even a two-fold increase of the Baliga figure of merit compared to GaN. However, beyond approximately 80% Al composition, donors in AlGaN undergo the DX transition which makes impurity doping increasingly more difficult. Moreover, the contact resistance increases exponentially with increasing Al content, and integration with dielectrics becomes difficult due to the upward shift of the conduction band. Atomically thin superlattices of AlN and GaN, also known as digital alloys, are known to grow experimentally under appropriate growth conditions. These chemically ordered nanostructures could offer significantly enhanced figure of merit compared to their random-alloy counterparts due to the absence of alloy scattering, as well as better integration with contact metals and dielectrics. In this work, we investigate the electronic structure and phonon-limited electron mobility of atomically thin AlN/GaN digital-alloy superlattices using first-principles calculations based on density-functional and many-body perturbation theory. The band gap of the atomically thin superlattices reaches 4.8 eV, and the in-plane (out-of-plane) mobility is 369 (452) cm2 V-1 s-1. Using the modified Baliga figure of merit that accounts for the dopant ionization energy, we demonstrate that atomically thin AlN/GaN superlattices with a monolayer sublattice periodicity have the highest modified Baliga figure of merit among several technologically relevant ultra-wide band-gap materials, including random AlGaN, β-Ga2O3, cBN, and diamond. Copyright © 2022, The Authors. All rights reserved.

关键词： Aluminum gallium nitride

Revealing the core-periphery structure of cities

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arXiv 2024年

作者： Fanelli, Federica Melo, Hygor P.M. Bruno, Matteo Loreto, Vittorio Sapienza Univ. of Rome Physics Dept Piazzale A. Moro 2 Rome00185 Italy Sony Computer Science Laboratories - Rome Joint Initiative CREF-Sony Centro Ricerche Enrico Fermi Via Panisperna 89/A Rome00184 Italy Via Panisperna 89/A Rome00184 Italy Postgraduate Program in Applied Informatics University of Fortaleza CE Fortaleza60811-905 Brazil Complexity Science Hub Josefstädter Strasse 39 A 1080 Vienna Austria

The distribution of urban services reveals critical patterns of human activity and accessibility. Proximity to amenities like restaurants, banks, and hospitals can reduce access barriers, but these services are often unevenly distributed, exacerbating spatial inequalities and socioeconomic disparities. In this study, we present a novel accessibility measure based on the spatial distribution of Points of Interest (POIs) within cities. Using the radial distribution function from statistical physics, we analyze the dispersion of services across different urban zones, combining local and remote access to services. This approach allows us to identify a city’s central core, intermediate areas or secondary cores, and its periphery. Comparing the areas that we find with the resident population distribution highlights clusters of urban services and helps uncover disparities in access to opportunities. Copyright © 2024, The Authors. All rights reserved.

关键词： Population statistics

Exploring the non-Hermitian topology of exceptional points in lasers and fiber loops

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Exploring the non-Hermitian topology of exceptional points i...

2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023

作者： Schumer, Alexander Nasari, Hadiseh Liu, Yuzhou G.N. Lopez-Galmiche, Gisela Leshin, Jason Lopez-Aviles, Helena E. Ding, Lei Alahmadi, Yousef Hassan, Absar U. Zhong, Qi Rotter, Stefan LiKamWa, Patrick Christodoulides, Demetrios N. Khajavikhan, Mercedeh ViennaA-1040 Austria Ming Hsieh Department of Electrical and Computer Engineering University of Southern California Los AngelesCA90089 United States CREOL The College of Optics & Photonics University of Central Florida OrlandoFL United States Center of Excellence for Telecomm Applications Joint Centers of Excellence Program King Abdul Aziz City for Science and Technology Riyadh11442 Saudi Arabia Department of Physics & Astronomy University of Southern California Los AngelesCA United States

ISBN: (纸本)9798350345995

When non-Hermitian eigenvalue surfaces form intertwined Riemann surfaces, the corresponding non-Hermitian singularities, also know as exceptional points (EPs), are located at the center of this specific topology. Various experimental platforms have recently been presented in which interesting new physics associated with these branch point singularities can be explored. In particular, it has been shown that dynamically encircling EPs may lead to a so-called chiral state transfer. The chirality in this context refers to the fact that in such an encircling protocol, the final state at the end of an EP-enclosing loop solely depends on the encircling direction (clockwise or counterclockwise), but not on the initial state. Such a chiral behavior is intrinsically linked to the state vector deviating from adiabatically following the system's eigenstates associated with the eigenvalue surfaces;instead, due to the non-Hermitian violation of the adiabatic theorem, non-adiabatic jumps let the system undergo transitions from lossy eigenstates to eigenstates with gain. Here, we present two experiments that implement concepts that go beyond this established paradigm. © 2023 IEEE.

关键词： Topology

Cavity-coupled telecom atomic source in silicon

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arXiv 2023年

作者： Johnston, Adam Felix-Rendon, Ulises Wong, Yu-En Chen, Songtao Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Smalley-Curl Institute Rice University HoustonTX77005 United States

Atomic defects in solid-state materials are promising candidates for quantum interconnect and networking applications. Recently, a series of atomic defects have been identified in the silicon platform, where scalable device integration can be enabled by mature silicon photonics and electronics technologies. In particular, T centers hold great promise due to their telecom band optical transitions and the doublet ground state electronic spin manifold with long coherence times. However, an open challenge for advancing the T center platform is to enhance its weak and slow zero phonon line emission. In this work, we demonstrate the cavity-enhanced fluorescence emission from a single T center. This is realized by integrating single T centers with a low-loss, small mode-volume silicon photonic crystal cavity, which results in an enhancement of the fluorescence decay rate by a factor of F = 6.89. Efficient photon extraction enables the system to achieve an average photon outcoupling rate of 73.3 kHz at the zero phonon line. The dynamics of the coupled system is well modeled by solving the Lindblad master equation. These results represent a significant step towards building efficient T center spin-photon interfaces for quantum information processing and networking applications. © 2023, CC BY.

关键词： Silicon photonics

Human Fall Prediction and Detection Using Low Price IMU Sensor

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Human Fall Prediction and Detection Using Low Price IMU Sens...

IEEE Eurasia Conference on IOT, Communication and Engineering (ECICE)

作者： Chanasorn Nutsathaporn Sakchai Chomkokard Wiwat Wongkokua Noparit Jinuntuya Somchoke Ruengittinun Siriporn Sasimontonkul Department of Physics Metrology Program Faculty of Science Kasetsart University Bangkok Thailand Department of Computer Science Faculty of Science Kasetsart University Bangkok Thailand Faculty of Sports Science Kasetsart University Kamphaeng Saen Campus Nakhon Pathom Thailand

ISBN: (纸本)9781665482097

In this project, we develop a device to warn the elderly when they are unsteady and at a risk of falling, based on a low price IMU sensor. From our preliminary study we find that during the sway, the body vibrates violently in all frequencies. This is different from the body at stationary posture, where the vibration is small, or when a person moves in a regular manner where the body vibrates with some definite frequencies. From these results, it is possible to use the mean amplitude of the Fourier spectrum of the body acceleration to distinguish the vibration state of the body, which can be used in the warning system. We then designed the device using the low price MPU6050 sensor to measure the body acceleration. This device will be attached to the body (hip) for collecting the acceleration data. An ESP8266 board is used to collect and control the sensor operation. Another ESP8266 board is used to receive and send the data to a Raspberry Pi unit. All data transmission is performed wirelessly via ESP NOW protocol, which is a low power consumption 2.4GHz wireless communication with a data package of up to 250 bytes at a time with 100-200m transmission range, which cover the living space area of typical wearer. When the mean amplitude of Fourier spectrum is greater than the warning criteria, the Raspberry Pi will send a signal to the warning unit wirelessly through the ESP8266 board. There are 3 types of alarms in warning unit which are sound alarm, light alarm, and LCD display alarm. We have tested our system with many volunteers. The mean amplitude of Fourier spectrum in the steady, walking, and sway condition can be clearly distinguished. In all cases the state of risky from falling can be detected correctly. We are now in the process of maximizing the data sampling and analyzing time to make the falling prediction as fast as possible.

关键词： Vibrations Wireless communication Performance evaluation Protocols Power demand Measurement units Alarm systems