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Singular vectors of sums of rectangular random matrices and optimal estimation of high-rank signals: The extensive spike model

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Physical Review E 2023年第5期108卷 054129-054129页

作者： Itamar D. Landau Gabriel C. Mel Surya Ganguli Department of Applied Physics Stanford University Stanford California 94305 USA Neuroscience Graduate Program Stanford University Stanford California 94305 USA

Across many disciplines spanning from neuroscience and genomics to machine learning, atmospheric science, and finance, the problems of denoising large data matrices to recover hidden signals obscured by noise, and of estimating the structure of these signals, is of fundamental importance. A key to solving these problems lies in understanding how the singular value structure of a signal is deformed by noise. This question has been thoroughly studied in the well-known spiked matrix model, in which data matrices originate from low-rank signal matrices perturbed by additive noise matrices, in an asymptotic limit where matrix size tends to infinity but the signal rank remains finite. We first show, strikingly, that the singular value structure of large finite matrices (of size ∼1000) with even moderate-rank signals, as low as 10, is not accurately predicted by the finite-rank theory, thereby limiting the application of this theory to real data. To address these deficiencies, we analytically compute how the singular values and vectors of an arbitrary high-rank signal matrix are deformed by additive noise. We focus on an asymptotic limit corresponding to an extensive spike model, in which both the signal rank and the size of the data matrix tend to infinity at a constant ratio. We map out the phase diagram of the singular value structure of the extensive spike model as a joint function of signal strength and rank. We further exploit these analytics to derive optimal rotationally invariant denoisers to recover the hidden high-rank signal from the data, as well as optimal invariant estimators of the signal covariance structure. Our extensive-rank results yield several conceptual differences compared to the finite-rank case: (1) as signal strength increases, the singular value spectrum does not directly transition from a unimodal bulk phase to a disconnected phase, but instead there is a bimodal connected regime separating them; (2) the signal singular vectors can be partiall

关键词： Stochastic inference Data analysis Random matrix theory Statistical methods Stochastic analysis methods

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Accuracy of DFT computed oxygen-vacancy formation energies and high-throughput search of solar thermochemical water-splitting compounds

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Physical Review Materials 2023年第6期7卷 065403-065403页

作者： Bianca Baldassarri Jiangang He Xin Qian Emanuela Mastronardo Sean Griesemer Sossina M. Haile Christopher Wolverton Graduate Program in Applied Physics Northwestern University Evanston Illinois USA Department of Materials Science and Engineering Northwestern University Evanston Illinois USA

The enthalpy change involved in metal oxide reduction is a key quantity in various processes related to energy conversion and storage and is of particular interest for computational prediction. Often this prediction involves the simulation of a high-temperature reduction process with a 0-K methodology like density functional theory (DFT), and it is not infrequent for the high temperature and 0-K stable crystal structures to differ. This introduces a conundrum with regard to the choice of crystal structure to utilize in the computation, with approaches in the literature varying and experimental validation remaining scarce. In this work, we address both the crystal structure conundrum and the experimental validation, and then apply the insights we gain to guide a high-throughput search for new materials for solar thermochemical water-splitting applications. By computing the DFT+U oxygen-vacancy formation energy (ΔEvf) of a selection of ABO3 compounds and comparing different crystal structures for each composition, we highlight the issues that arise when the structure utilized in the computation is dynamically unstable at 0 K, namely the presence of an artificial lowering of ΔEvf, and the lack of convergence of ΔEvf with cell size. We solve these limitations by identifying and employing a suitable surrogate dynamically stable structure. We then validate the predictive power of our calculations against appositely generated experimental measurements of reduction enthalpy for a series of Hubbard U values, finding an accuracy ranging between 0.2–0.6 eV/O. In light of such conclusions, we revise and expand a previous a high-throughput DFT study on ABO3 perovskite oxides. We provide a list of candidate STCH materials, highlight trends with redox-active cation and structural distortion, and identify Mn4+, Mn3+, and Co3+ as the most promising redox-active cations.

关键词： Energy applications First-principles calculations Hydrogen energy

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Incommensurate broken helix induced by nonstoichiometry in the axion insulator candidate EuIn2As2

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Physical Review B 2025年第8期111卷 L081109-L081109页

作者： Masaki Gen Yukako Fujishiro Kazuki Okigami Satoru Hayami Max T. Birch Kiyohiro Adachi Daisuke Hashizume Takashi Kurumaji Hajime Sagayama RIKEN Center for Emergent Matter Science (CEMS) Wako 351-0198 Japan Institute for Solid State Physics University of Tokyo Kashiwa Chiba 277-8581 Japan RIKEN Cluster for Pioneering Research (CPR) Wako 351-0198 Japan Department of Applied Physics University of Tokyo Tokyo 113-8656 Japan Graduate School of Science Hokkaido University Sapporo 060-0810 Japan Materials Characterization Support Team RIKEN Center for Emergent Matter Science (CEMS) Wako 351-0198 Japan Department of Advanced Materials Science University of Tokyo Kashiwa 277-8561 Japan Division of Physics Mathematics and Astronomy California Institute of Technology Pasadena California 91125 USA Institute of Materials Structure Science High Energy Accelerator Research Organization Tsukuba 305-0801 Japan

Zintl phase EuIn2As2 has garnered growing attention as an axion insulator candidate, triggered by the identification of a commensurate double-Q broken-helix state in previous studies, however, its periodicity and symmetry remain subjects of debate. Here, we perform resonant x-ray scattering experiments on EuIn2As2, revealing an incommensurate nature of the broken-helix state, where both the wave number and the amplitude of the helical modulation exhibit systematic sample dependence. Furthermore, the application of an in-plane magnetic field brings about a fanlike state that appears to preserve the double-Q nature, which might be attributed to multiple-spin interactions in momentum space. We propose that the itinerant character of EuIn2As2, most likely induced by Eu deficiency, gives rise to the helical modulation and impedes the realization of a theoretically predicted axion state with the collinear antiferromagnetic order.

关键词： X ray scattering

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Analysis of neutron monitor count rates and timing distributions from latitude surveys 18

Analysis of neutron monitor count rates and timing distribut...

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18th Siam physics Congress, SPC 2023

作者： Yakum, P. Khamphakdee, S. Nuntiyakul, W. Sáiz, A. Ruffolo, D. Evenson, P. Bangliang, C. Seripienlert, A. Jiang, P. Chuanraksasat, P. Munakata, K. Madsen, J. Soonthornthum, B. Komonjinda, S. Graduate Program in Astronomy Department of physics and materials Faculty of science Chiang Mai University Chiang Mai50200 Thailand Department of physics and materials Faculty of science Chiang Mai University Chiang Mai50200 Thailand Department of Physics Faculty of Science Mahidol University Bangkok10400 Thailand Department of Physics and Astronomy University of Delaware NewarkDE19716 United States Department of Physics Faculty of Science and Technology Rajamangala University of Technology Thanyaburi Pathum Thani12110 Thailand Chiang Mai50180 Thailand Polar Research Institute of China Shanghai Pudong200136 China Physics Department Shinshu University Nagano Matsumoto390-8621 Japan Wisconsin IceCube Particle Astrophysics Center University of Wisconsin-Madison WI53703 United States

Neutron monitors continuously record the hadronic part of secondary atmospheric radiation on the ground, which originates from primary cosmic rays. In Thailand, we developed a mobile neutron monitor housed inside a standard-size shipping container named "Changvan." It contains three neutron-sensitive proportional counters set up in the typical NM64 layout. However, the central counter doesn't have the lead producer, leading us to refer to it as a "semi-leaded" neutron monitor. We examined cosmic ray spectral variations on two latitude surveys during 2018-2019 and 2019-2020. This work examines the ratio of count rates between leaded and unleaded setups, which shows notable variation based on geomagnetic cutoff rigidity, suggesting a sensitivity to the cosmic ray spectrum. This measurement could be implemented at stationary stations. The unleaded counter, shielded by the reflector with a higher count from nearby lead, may have advantages over a bare one. Furthermore, we explore alternative techniques to identify spectral changes in Galactic cosmic rays using Changvan data. We analyze using time delay histograms to determine the leader fraction (L) of neutrons that are not preceded by another neutron from the same primary cosmic ray. We also examine other parameters, including the alpha (α) parameter and pulse rate (PR), which can be compared with count rates (CR). Our findings indicate that the ratios of L and α are not significantly affected by geomagnetic cutoff rigidity. In contrast, CR and PR exhibit significant dependency and show opposite trends. © 2023 Institute of physics Publishing. All rights reserved.

关键词： Cosmic rays

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Topological orders with classical Lie group symmetries from coupling electron wires

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Physical Review B 2025年第16期111卷 165140-165140页

作者： Pak Kau Lim Michael Mulligan Jeffrey C. Y. Teo Department of Physics and Astronomy University of California Riverside California 92521 USA Department of Physics University of Virginia Charlottesville Virginia 22904 USA Theoretical Sciences Visiting Program Okinawa Institute of Science and Technology Graduate University Onna 904-0495 Japan

We study the topological order that arises from chiral states with SU(N) or SO(N) edge-state symmetry. This extends our previous study of topological orders that descend from the bosonic E8 quantum Hall state. We use exactly solvable models of coupled electron wires to construct states with SU(m)n, SO(m)n, or Sp(m)n topological order for various levels n. We use our constructions to write down string operators for various non-Abelian anyons. We thereby provide a systematic, model derivation of quantum Hall states, topological superconductors, and spin liquids with emergent non-Abelian quasiparticle excitations, including those of Ising, metaplectic, and Fibonacci type.

关键词： Lie groups

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Degradation of Organic LEDs Characterized with Algebraic Decay Relaxation Function 15

Degradation of Organic LEDs Characterized with Algebraic Dec...

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Advances in Display Technologies XV 2025

作者： Aygen, Can Richards, Michael Yazdaanpanah, Ramin Kulkarni, Sachin Tanriover, Ibrahim Onsager, Claire Lin, BoYen Lee, Jiun-Haw Aydin, Koray Grayson, Matthew A. Department of Electrical & Computer Engineering Northwestern University EvanstonIL United States Department of Opto-Electronic Engineering National Dong Hwa University Hualien Taiwan Graduate Institute of Photonics and Optoelectronics Department of Electrical Engineering National Taiwan University Taipei Taiwan Program in Applied Physics Northwestern University EvanstonIL United States

ISBN: (纸本)9781510685246

Lifetime studies of organic light emitting diodes are necessary to both understand and mitigate causes of degradation. Here, electroluminescence (EL) studies of green organic light-emitting diode (OLED) pixels are measured continuously using three different dc currents over a period of one week, and their slow EL degradation is accurately fit to an analytical expression with only two fit parameters. The slower-than-exponential EL decay is fit to an empirical unified heavy-tail function that can interpolate between power-law algebraic decays (AD) and stretched-exponential decays (SE). Whereas SE and AD are largely indistinguishable down to 50% of the initial luminance, here we report degradation down to 10% of the initial luminance which most closely fits an AD function with remarkable precision over the entire duration of the experiment. All relaxations share the same characteristic exponent β = 0.53 in the power law decay, whereas the characteristic time-scale τ for degradation decreases with a power-law exponent B = 1.9 as the current increases. The high degree of accuracy in the fit allows asymptotic predictions at time scales that are orders of magnitude longer than the duration of the data collection. The voltage across the OLED is simultaneously monitored under constant-current degradation and reveals an early-onset time scale where the voltage reaches a minimum before degradation runoff. © 2025 SPIE.

关键词： Organic light emitting diodes (OLED)

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Plasma broadening of autoionizing resonances

arXiv

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arXiv 2023年

作者： Pradhan, Anil K. Department of Astronomy Chemical Physics Program Biophysics Graduate Program Ohio State University ColumbusOH43210 United States

A general formulation is developed to demonstrate that atomic autoionizing (AI) resonances are broadened and shifted significantly due to plasma effects across bound-free continua. The theoretical and computational method presented accounts for broadening mechanisms: electron collisional, ion microfields (Stark), thermal Doppler, core excitations, and free-free transitions. Extrinsic plasma broadening redistributes and shifts AI resonance strengths while broadly preserving naturally intrinsic asymmetries of resonance profiles. Integrated oscillator strengths are conserved as resonance structures dissolve into continua with increasing electron density. As exemplar, the plasma attenuation of photoionization cross sections computed using the R-matrix method is studied in neon-like Fe XVII in a critical range Ne = 1021−24cc along isotherms T = 1 − 2 × 106K, and its impact on Rosseland Mean opacities. The energy-temperature-density dependent cross sections would elicit and introduce physical features in resonant processes in photoionization, (e + ion) excitation and recombination. The method should be generally applicable to atomic species in high-energy-density (HED) sources such as fusion plasmas and stellar interiors. © 2023, CC BY.

关键词： Photoionization

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R-matrix calculations for opacities: III. Plasma broadening of autoionizing resonances

arXiv

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arXiv 2023年

作者： Pradhan, A.K. Department of Astronomy Chemical Physics Program Biophysics Graduate Program Ohio State University ColumbusOH43210 United States

A general formulation is employed to study and quantitatively ascertain the effect of plasma broadening of intrinsic autoionizing (AI) resonances in photoionization cross sections. In particular, R-matrix data for iron ions described in the previous paper in the RMOP series (RMOP-II, hereafter RMOP2) are used to demonstrate underlying physical mechanisms due to electron collisions, ion microfields (Stark), thermal Doppler effects, core excitations, and free-free transitions. Breit-Pauli R-matrix (BPRM) cross section for the large number of bound levels of Fe ions are considered, 454 levels of Fe XVII, 1,184 levels of Fe XVIII and 508 levels of Fe XIX. Following a description of theoretical and computational methods, a sample of results is presented to show significant broadening and shifting of AI resonances due to Extrinsic plasma broadening as a function of temperature and density. Redistribution of AI resonance strengths broadly preserves their integrated strengths as well as the naturally intrinsic asymmetric shapes of resonance complexes which are broadened, smeared and flattened, eventually dissolving into the bound-free continua. © 2023, CC BY.

关键词： Iron

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Oil-source correlation and Paleozoic source rock analysis in the Siwa Basin,Western Desert:Insights from well-logs,Rock-Eval pyrolysis,and biomarker data

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Energy Geoscience 2024年第3期5卷 313-327页

作者： Mohamed I.Abdel-Fattah Mohamed Reda Mohamed Fathy Diaa A.Saadawi Fahad Alshehri Mohamed S.Ahmed Petroleum Geosciences and Remote Sensing Program Department of Applied Physics and AstronomyCollege of SciencesUniversity of SharjahSharjah27272United Arab Emirates Geology Department Faculty of ScienceSuez Canal UniversityIsmailiaEgypt Faculty of Science Geology DepartmentAl-Azhar UniversityP.O.Box 11884Nasr CityCairoEgypt Abdullah Alrushaid Chair for Earth Science Remote Sensing Research Geology and Geophysics DepartmentCollege of ScienceKing Saud UniversityRiyadh11451Saudi Arabia

Understanding the origins of potential source rocks and unraveling the intricate connections between reservoir oils and their source formations in the Siwa Basin(Western Desert,Egypt)necessitate a thorough oil-source correlation *** objective is achieved through a meticulous analysis of well-log responses,Rock-Eval pyrolysis,and biomarker *** analysis of Total Organic Carbon across 31 samples representing Paleozoic formations in the Siwa A-1X well reveals a spectrum of organic richness ranging from 0.17 wt%to 2.04 wt%,thereby highlighting diverse levels of organic content and the presence of both Type II and Type III *** of the fingerprint characteristics of eight samples from the well suggests that the Dhiffah Formation comprises a blend of terrestrial and marine organic ***,a significant contribution from more oxidized residual organic matter and gas-prone Type III kerogen is ***,the Desouky and Zeitoun formations exhibit mixed organic matter indicative of a transitional environment,and thus featuring a pronounced marine influence within a more reducing setting,which is associated with Type II *** analysis of five oil samples from different wells—SIWA L-1X,SIWA R-3X,SIWA D-1X,PTAH 5X,and PTAH 6X,it is evident that terrestrial organic matter,augmented by considerable marine input,was deposited in an oxidizing environment,and contains Type III *** scrutiny confirms the coexistence of mixed terrestrial organic matter within varying redox *** is the uniformity of identified kerogen Types II and III across all samples,known to have potential for hydrocarbon *** discovery presented in this paper unveils captivating prospects concerning the genesis of oil in the Jurassic Safa reservoir,suggesting potential links to Paleozoic sources or even originating from the Safa Member *** revelations mark a substantial advancement in understanding source

关键词： Biomarker data Oil-source correlation Rock-Eval pyrolysis Source rocks Siwa Basin

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Vibrational entropies of oxygen vacancy formation in metal oxides

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Physical Review Materials 2024年第5期8卷 055407-055407页

作者： Bianca Baldassarri Jiangang He Christopher Wolverton Graduate Program in Applied Physics Northwestern University Evanston Illinois 60208 USA Department of Materials Science and Engineering Northwestern University Evanston Illinois 60208 USA

Oxygen vacancies play a key role in many energy-related applications, and the investigation of the thermodynamic forces driving their formation across different materials can be tackled through the use of ab initio methods. In this context, however, computational studies targeting finite-temperature properties such as entropy remain scarce. Wider-ranging studies are of interest to deepen the understanding of the role of the entropy of oxygen vacancy formation and its different components in processes like the ones involved in solar thermochemical hydrogen (STCH) production, and to investigate the existence of common trends and differences between materials. In this work, we use density functional theory and harmonic phonon calculations to compute the vibrational entropy of oxygen vacancy formation (ΔSvib) for 10 different metal oxide compounds. The computation is carried out by taking the difference between the vibrational entropy of a vacancy-containing and a pristine structure, while the entropic contribution from the final gaseous state of the oxygen lost from the material is accounted for separately with a gas entropy term. We first examine the temperature dependence of ΔSvib and highlight the presence of an initial peak around room temperature, followed by a steady decrease resulting from the presence of an additional O atom (the one becoming vacant) in the defect-free structure. We then inspect the atomic contributions to ΔSvib, and highlight similarities and differences between compounds. Finally, we consider other significant sources of entropy, and find ΔSvib to provide a smaller, yet non-negligible, contribution to the total entropy of vacancy formation. We also compare the temperature dependence of ΔSvib to that of the gas entropy, and show that the two largely counterbalance each other at high temperatures.

关键词： Entropy Hydrogen production Density functional theory

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