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arXiv 2023年

作者： Jasra, Ajay Maama, Mohamed Ombao, Hernando Applied Mathematics and Computational Science Program Computer Electrical and Mathematical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia Statistics Program Computer Electrical and Mathematical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia

In this paper we consider the filtering of partially observed multi-dimensional diffusion processes that are observed regularly at discrete times. We assume that, for numerical reasons, one has to time-discretize the diffusion process which typically leads to filtering that is subject to discretization bias. The approach in [16] establishes that when only having access to the time discretized diffusion it is possible to remove the discretization bias with an estimator of finite variance. We improve on the method in [16] by introducing a modified estimator based on the recent work of [17]. We show that this new estimator is unbiased and has finite variance. Moreover, we conjecture and verify in numerical simulations that substantial gains are obtained. That is, for a given mean square error (MSE) and a particular class of multi-dimensional diffusion, the cost to achieve the said MSE falls. Copyright © 2023, The Authors. All rights reserved.

关键词： Mean square error

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Viscosity in water from first-principles and deep-neural-network simulations

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npj Computational Materials 2022年第1期8卷 1318-1327页

作者： Cesare Malosso Linfeng Zhang Roberto Car Stefano Baroni Davide Tisi SISSA—Scuola Internazionale Superiore di Studi Avanzati 34136TriesteItaly Program in Applied and Computational Mathematics Princeton UniversityPrincetonNJ08544USA DP Technology Beijing100080PR China Department of Chemistry Department of Physicsand Princeton Institute for the Science and Technology of MaterialsPrinceton UniversityPrincetonNJUSA CNR Istituto Officina dei Materiali SISSA Unit34136TriesteItaly

We report on an extensive study of the viscosity of liquid water at near-ambient conditions,performed within the Green-Kubo theory of linear response and equilibrium ab initio molecular dynamics(AIMD),based on density-functional theory(DFT).In order to cope with the long simulation times necessary to achieve an acceptable statistical accuracy,our ab initio approach is enhanced with deep-neural-network potentials(NNP).This approach is first validated against AIMD results,obtained by using the Perdew–Burke–Ernzerhof(PBE)exchange-correlation functional and paying careful attention to crucial,yet often overlooked,aspects of the statistical data ***,we train a second NNP to a dataset generated from the Strongly Constrained and Appropriately Normed(SCAN)*** the error resulting from the imperfect prediction of the melting line is offset by referring the simulated temperature to the theoretical melting one,our SCAN predictions of the shear viscosity of water are in very good agreement with experiments.

关键词： viscosity Strongly ambient

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Bayesian Spectral Graph Denoising with Smoothness Prior

Bayesian Spectral Graph Denoising with Smoothness Prior

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Annual Conference on Information sciences and Systems (CISS)

作者： Sam Leone Xingzhi Sun Michael Perlmutter Smita Krishnaswamy Program for Applied Mathematics Yale University Department of Computer Science Yale University Department of Mathematics Boise State University Department of Genetics Yale School of Medicine Wu Tsai Institute Yale University FAIR Meta AI Computational Biology and Bioinformatics Program Yale University

Here we consider the problem of denoising features associated to complex data, modeled as signals on a graph, via a smoothness prior. This is motivated in part by settings such as single-cell RNA where the data is very high-dimensional, but its structure can be captured via an affinity graph. This allows us to utilize ideas from graph signal processing. In particular, we present algorithms for the cases where the signal is perturbed by Gaussian noise, dropout, and uniformly distributed noise. The signals are assumed to follow a prior distribution defined in the frequency domain which favors signals which are smooth across the edges of the graph. By pairing this prior distribution with our three models of noise generation, we propose Maximum A Posteriori (M.A.P.) estimates of the true signal in the presence of noisy data and provide algorithms for computing the M.A.P. Finally, we demonstrate the algorithms’ ability to effectively restore signals from white noise on image data and from severe dropout in single-cell RNA sequence data.

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Unified Variational Approach Description of Ground-State Phases of the Two-Dimensional Electron Gas

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Physical Review Letters 2024年第26期133卷 266504-266504页

作者： Conor Smith Yixiao Chen (陈一潇) Ryan Levy Yubo Yang (杨煜波) Miguel A. Morales Shiwei Zhang Center for Computational Quantum Physics Flatiron Institute New York New York 10010 USA Department of Electrical and Computer Engineering University of New Mexico Albuquerque New Mexico 87131 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

The two-dimensional electron gas (2DEG) is a fundamental model, which is drawing increasing interest because of recent advances in experimental and theoretical studies of 2D materials. Current understanding of the ground state of the 2DEG relies on quantum Monte Carlo calculations, based on variational comparisons of different Ansätze for different phases. We use a single variational ansatz, a general backflow-type wave function using a message-passing neural quantum state architecture, for a unified description across the entire density range. The variational optimization consistently leads to lower ground-state energies than previous best results. Transition into a Wigner crystal (WC) phase occurs automatically at rs=37±1, a density lower than currently believed. Between the liquid and WC phases, the same ansatz and variational search strongly suggest the existence of intermediate states in a broad range of densities, with enhanced short-range nematic spin correlations.

关键词： Wave functions

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Field driven cluster formation in two-dimensional colloidal binary mixtures

arXiv

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arXiv 2022年

作者： Qian, Dingwen de la Cruz, Monica Olvera Applied Physics Program Northwestern University EvanstonIL60208 United States Applied Physics Program Departments of Materials Science and Engineering Chemistry and Physic and Astronomy Northwestern University EvanstonIL60208 United States

We study size- and charge-asymmetric oppositely charged colloids driven by an external electric field. The large particles are connected by harmonic springs, forming a hexagonal-lattice network while the small particles are free of bonds and exhibit fluid-like motion. We show that this model exhibits a cluster formation pattern when the external driving force exceeds a critical value. The clustering is accompanied with stable wavepackets in vibrational motions of the large particles. Copyright © 2022, The Authors. All rights reserved.

关键词： Binary mixtures

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Correlation between noncollinear spin orientation and lattice distortion in Ni0.4Mn0.6TiO3

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Physical Review Materials 2024年第12期8卷 124410-124410页

作者： Shang-Hsien Hsieh Surajit Ghosh Yu-Hui Liang Hsiao-Tsu Wang Chao-Hung Du Jau-Wern Chiou Chun-Ming Wu Chin-Wei Wang Yu-Cheng Shao Department of Physics Tamkang University New Taipei City 251 Taiwan National Synchrotron Radiation Research Center Hsinchu 300 Taiwan Bachelor's Program in Advanced Materials Science Tamkang University New Taipei City 251 Taiwan Department of Applied Physics National University of Kaohsiung Kaohsiung 811 Taiwan

This work studies the correlation between noncollinear spin orientation and lattice distortion in XY-like spin-glass (SG) Ni0.4Mn0.6TiO3 (NMTO) using neutron diffraction and synchrotron-radiation-based spectroscopic techniques such as resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). The neutron study reveals a shorter spin-spin correlation length along the c axis than in the XY-plane, which is typical of XY-like SG. It also reveals that the NiTiO3 matrix dominates the shaping of the low-temperature complex magnetic structure of NMTO. A local lattice distortion in the form of a large increase in the nearest-neighbor Ni-O bond length along the c axis was observed from temperature-dependent extended x-ray absorption fine-structure measurements close to the SG transition temperature, TSG. The Ni L3-edge RIXS spectra at around TSG indicate a possible magnon excitation with various d−d interactions and charge-transfer excitation. The Ni L3,2-edge XMCD measurement shows ferromagnetic-/ferrimagneticlike behavior at the temperature near TSG, closely matching the opening of hysteresis curves that are recorded below TSG. These findings compellingly demonstrate that at low temperature, Ni2+ ions in the XY-plane of NMTO exhibit a noncollinear spin alignment, that facilitates Dzyaloshinskii-Moriya-type exchange interactions, elucidating the complex spin dynamics of this SG system.

关键词： Spin glass

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Plasmonic BICs as Biosensors with Better Detectivity

Plasmonic BICs as Biosensors with Better Detectivity

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Conference on Lasers and Electro-Optics (CLEO)

作者： Zhichao Li Ciril S. Prasad Xielin Wang Gururaj V. Naik Applied Physics Graduate Program Smalley-Curl Institute Rice University Houston TX USA Department of Electrical and Computer Engineering Rice University Houston TX USA

Plasmonic sensors exhibit high sensitivity due to enhanced local fields. But, their detectivity is poor because of their poor Q-factors. Using a plasmonic BIC, we experimentally demonstrate enhanced Q-factors in a pla... 详细信息

ISBN: (纸本)9781957171258

关键词： Absorption spectroscopy Field enhancement Optical sensing Plasmonic sensors Q factor Sensor performance

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Characterisation of Hβ spectra from EXO 051910+3737.7 X-rays binaries

arXiv

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arXiv 2025年

作者： Nuchvanichakul, Pornisara Irawati, Puji Rittipruk, Pakakaew Gandhi, Poshak Knigge, Christian Charles, Phil Wannawichian, Suwicha M.S. Program in Applied Physics Department of Physics and Materials Science Faculty of Science Chiang Mai University Chiang Mai50200 Thailand Department of Physics and Astronomy University of Southampton Southampton United Kingdom National Astronomical Research Institute of Thailand Chiang Mai50180 Thailand Department of Physics and Materials Science Faculty of Science Chiang Mai University Chiang Mai50200 Thailand

We investigate the spectral characteristics of the Be/X-ray binary system, EXO 051910+3737.7, in which Be/X-ray systems are the largest sub-class of high-mass X-ray binaries. Spectroscopic observations are taken by the Thai National Telescope (TNT) with a Medium-RESolution spectrograph (MRES) instrument for seven nights spanning from 2020 to 2021. Our primary focus is directed towards the analysis of two Balmer lines, namely Hα and Hβ, given that Be stars typically exhibit emission features in at least one of these hydrogen Balmer lines during certain phases. Our observations reveal split Balmer emission lines throughout the entire duration of our monitoring. Double Gaussian profiles were employed for line fitting to characterize these lines. The presence of double peaks in the Balmer lines indicates the presence of asymmetries within the circumstellar disc. We then analyze V/R variations and the changes in Hβ spectra. Our analysis of V/R variation which Violet (V) and Red (R) peak intensity components, revealed rapid fluctuations occurring within a single day, although determining the precise periodicity was constrained by instrumental limitations and the duration of observability. Furthermore, employing observed the wavelength differences (∆λ) in conjunction with typical Be star parameters allowed us to estimate the radius (rβ) of the Hβ emitting envelope. The average value was calculated to be 2.585r∗, with a standard deviation of 0.050r∗ © 2025, CC BY-NC-ND.

关键词： Stars

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Green synthesis of CuO/Fe₂O₃/ZnO ternary composite photocatalyst using grape extract for enhanced photodegradation of environmental organic pollutant

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Chemosphere 2024年 351卷

作者： Jansanthea, Pongthep Inyai, Nattha Chomkitichai, Weerasak Ketwaraporn, Jiraporn Ubolsook, Putthadee Wansao, Chaowarit Wanaek, Aimon Wannawek, Atit Kuimalee, Surasak Pookmanee, Pusit Program in Chemistry Faculty of Science and Technology Uttaradit Rajabhat University Uttaradit 53000 Thailand Program in Environment Faculty of Science and Technology Uttaradit Rajabhat University Uttaradit 53000 Thailand Program in Physics Faculty of Science and Technology Uttaradit Rajabhat University Uttaradit 53000 Thailand Department of Science Faculty of Science and Agricultural Technology Rajamangala University of Technology Lanna Lampang Lampang 52000 Thailand Program in Industrial Chemistry Innovation Faculty of Science Maejo University Chiang Mai 50290 Thailand Program in Applied Chemistry Faculty of Science Maejo University Chiang Mai 50290 Thailand

This research delves into fabricating a CuO/Fe2O3/ZnO (CFZ) ternary composite photocatalyst, employing grape extract for its eco-conscious synthesis. The method intricately integrates copper acetate, ferric nitrate, a... 详细信息

This research delves into fabricating a CuO/Fe₂O₃/ZnO (CFZ) ternary composite photocatalyst, employing grape extract for its eco-conscious synthesis. The method intricately integrates copper acetate, ferric nitrate, and zinc acetate as precursor compounds, harmonizing them with grape extract serving as a green reducing agent. Meticulous microwave treatment and controlled calcination orchestrate the nuanced formation of the desired composite material. The extensive characterization, involving X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, ultraviolet–visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence (PL) spectroscopy, unveils an array of favorable physical, chemical, and optical attributes conducive to proficient photocatalysis. Notably, CFZ–10mc showcases a narrower bandgap of 1.91 eV, which is pivotal for bolstering electron–hole separation, thereby enhancing its photocatalytic efficacy. Assessment of CFZ's performance in degrading Rhodamine B (RhB) under UV irradiation highlights an impressive 88.8% degradation efficiency within 120 min, accompanied by a kinetic rate constant of 1.81 × 10⁻² min⁻¹. Deliberation upon crucial parameters, including photocatalyst dosage, initial RhB pH, and reactor energy consumption, introduces the electrical energy per order (E_EO) as a notable efficiency metric. CFZ manifests a substantial reduction in operational costs, estimated to be 18.10 times lower than conventional photolysis, signifying an E_EO value of 509.17 kWh m⁻³ order⁻¹. Optimal operational conditions propose a photocatalyst content of 1.5 g L⁻¹ and an initial RhB pH of 7, fostering the prevalence of the primary active species, •OH. These findings illuminate CFZ's potential in mitigating organi

关键词： CuO/Fe2O3/ZnO Grape extract Green synthesis Organic pollutant Photodegradation Ternary composite photocatalyst

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Multilevel Particle Filters for Partially Observed McKean-Vlasov Stochastic Differential Equations

arXiv

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arXiv 2024年

作者： Awadelkarim, Elsiddig Jasra, Ajay Applied Mathematics and Computational Science Program Computer Electrical and Mathematical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia School of Data Science The Chinese University of Hong Kong Shenzhen China

In this paper we consider the filtering problem associated to partially observed McKean-Vlasov stochastic differential equations (SDEs). The model consists of data that are observed at regular and discrete times and the objective is to compute the conditional expectation of (functionals) of the solutions of the SDE at the current time. This problem, even the ordinary SDE case is challenging and requires numerical approximations. Based upon the ideas in [3, 12] we develop a new particle filter (PF) and multilevel particle filter (MLPF) to approximate the afore-mentioned expectations. We prove under assumptions that, for ϵ > 0, to obtain a mean square error of O(ϵ2) the PF has a cost per-observation time of O(ϵ−5) and the MLPF costs O(ϵ−4) (best case) or O(ϵ−4 log(ϵ)2) (worst case). Our theoretical results are supported by numerical experiments. © 2024, CC BY.

关键词： Mean square error

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