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Author Correction: Thermodynamic optical pressures in tight-binding nonlinear multimode photonic systems

Communications Physics 2024年第1期7卷 1页

作者： Nikolaos K. Efremidis Demetrios N. Christodoulides Department of Mathematics and Applied Mathematics University of Crete Heraklion 70013 Crete Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology-Hellas (FORTH) Heraklion 70013 Crete Greece CREOL/College of Optics University of Central Florida Orlando 32816 FL USA

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Local viscoelastic properties and shear stress propagation in bulk and confined polymer melts and low-molecular weight liquids

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Physical Review research 2024年第2期6卷 023161-023161页

作者： Alireza F. Behbahani Petra Bačová Patrycja Polińska Craig Burkhart Manolis Doxastakis Vagelis Harmandaris Institut für Physik Johannes Gutenberg-Universität Mainz Staudingerweg 7 D-55099 Mainz Germany Institute of Applied and Computational Mathematics Foundation for Research and Technology - Hellas Heraklion GR-71110 Greece Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica Facultad de Ciencias IMEYMAT Campus Universitario Río San Pedro s/n. Puerto Real Cádiz 11510 Spain Goodyear S.A. Avenue Gordon Smith Colmar-Berg L-7750 Luxembourg The Goodyear Tire & Rubber Company 142 Goodyear Boulevard Akron Ohio 44305 USA Department of Chemical and Biomolecular Engineering University of Tennessee Knoxville Tennessee 37996 USA Computation-based Science and Technology Research Center The Cyprus Institute Nicosia 2121 Cyprus Department of Mathematics and Applied Mathematics University of Crete Heraklion GR-71110 Greece

Through the analysis of the spatial correlations of local stress, we detect the propagation of long-ranged liquid-elasticity-mediated shear stress waves in polymeric and low-molecular weight liquids. The propagation of shear waves is effectively planar; i.e., σαβ propagates in the αβ plane. The autocorrelation functions of the local stress of a region are affected by both the relaxation of stress in that region and the propagation of stress from the region to the rest of the sample. However, due to the planar propagation of shear waves, the transfer of σαβ from those slices of the simulation box that are periodic in the αβ plane is negligible. This allows direct probing of the position-dependent local stress relaxation modulus of liquid in the vicinity of a confining surface.

关键词： Confinement Non-Newtonian fluids Physisorption Polymer behavior Polymer conformation & topology Rheological properties

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Asymptotic approximations for the phase space Schrödinger equation

arXiv

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arXiv 2021年

作者： Karageorge, Panos D. Makrakis, George N. Department of Mathematics and Applied Mathematics University of Crete Voutes Campus Heraklion700 13 Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology 100 Nikolaou Plastira Heraklion700 13 Greece

We consider semi-classical time evolution for the phase space Schrödinger equation and present two methods of constructing short time asymptotic solutions. The first method consists of constructing a semi-classical phase space propagator in terms of semi-classical Gaussian wave packets on the basis of the Anisotropic Gaussian Approximation, related to the Nearby Orbit Approximation, by which we derive an asymptotic solution for configuration space WKB initial data. The second method consists of constructing a phase space narrow beam asymptotic solution, following the Complex WKB Theory developed by Maslov, on the basis of a canonical system in double phase space related to the Berezin-Shubin-Marinov Hamilton-Jacobi and transport equations. We illustrate the methods for sub-quadratic potentials in R. © 2021, CC BY-NC-ND.

关键词： Gaussian beams

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Interspecies spin-noise correlations in hot atomic vapors

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Physical Review A 2023年第5期108卷 052822-052822页

作者： K. Mouloudakis F. Vouzinas A. Margaritakis A. Koutsimpela G. Mouloudakis V. Koutrouli M. Skotiniotis G. P. Tsironis M. Loulakis M. W. Mitchell G. Vasilakis I. K. Kominis Department of Physics University of Crete Heraklion 71003 Greece Institut de Ciències Fotòniques The Barcelona Institute of Science and Technology 08860 Castelldefels (Barcelona) Spain School of Applied Mathematical and Physical Sciences National Technical University of Athens 15780 Athens Greece Institute of Electronic Structure and Laser Foundation for Research and Technology 71110 Heraklion Greece Física Teòrica: Informació i Fenòmens Quàntics Departament de Física Universitat Autònoma de Barcelona 08193 Bellaterra Spain Departamento de Electromagnetismo y Física de la Materia Universidad de Granada 18010 Granada Spain Institute of Theoretical and Computational Physics University of Crete Heraklion 70013 Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology 70013 Heraklion Greece Institució Catalana de Recerca i Estudis Avançats 08010 Barcelona Spain Quantum Biometronics Heraklion 71409 Greece

We report an experimental and theoretical study of spin-noise correlations in a Rb87−Cs133 unpolarized alkali-metal vapor dominated by spin-exchange collisions. We observe strong unequal-time interspecies correlations and account for these with a first-principles theoretical model. Since the two atomic species have different spin precession frequencies, the dual-species vapor enables the use of an additional experimental handle, the applied magnetic field, for untangling various subtypes of spin correlations. In particular, the measured cross-correlation and autocorrelation spectra shed light on a number of spin-dynamic effects involving intra-atom, interatom, intraspecies, and interspecies correlations. Cross-correlation coefficients exceeding 60% have been observed at low magnetic fields, where the two spin species couple strongly via spin-exchange collisions. The understanding of such spontaneously generated correlations can motivate the design of quantum-enhanced measurements with single or multispecies spin-polarized alkali-metal vapors used in quantum sensing applications.

关键词： Atomic & molecular collisions Atomic & molecular processes in external fields Atomic & molecular structure Atomic spectra Collective effects in atomic physics Effects of atomic coherence on light propagation Fine & hyperfine structure Light-matter interaction Magneto-optical spectra Optical pumping Quantum optics Zeeman effect Atomic ensemble Atomic systems Atoms Magnetic moment Correlation function measurements First-principles calculations Optically detected magnetic resonance Stochastic differential equations

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A semi-continuum multiscale model of graphene-based polymer nanocomposites: Mechanical characterization

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computational Materials Science 2025年 257卷

作者： Barakat, Malak Reda, Hilal Harmandaris, Vagelis Lebanese University Faculty of Engineering Branch III Hadat Beirut Lebanon Computation-based Science and Technology Research Center The Cyprus Institute Nicosia Aglantzia2121 Cyprus Department of Applied Mathematics University of Crete Crete HeraklionGR-71409 Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology-Hellas FORTH Crete HeraklionGR-71110 Greece

This paper describes a hierarchical multi-scale scheme that aims to efficiently predict the mechanical behavior of graphene-based polymer nanocomposites with continuum models using data from detailed atomistic molecular dynamics simulations. First, the structure of graphene is modeled using linear beam finite elements that resemble interatomic interactions occurring at the level of the nanofiller's microstructure. The mechanical properties of graphene are then computed for several sizes to eliminate size effects. Next, the graphene/polymer interphase is represented by non-linear spring finite elements, which resemble interactions occurring between atoms of the nanofiller (graphene) and the polymer matrix. With the matrix represented as a continuum solid, its nodes are connected to those of graphene using interfacial springs. We then compute Young's modulus and Poisson's ratio of the designed polymer nanocomposite by performing tensile tests in all three Cartesian directions. The semi-continuum three-phases multi-scale model traversing nano up to macro scales is compared against other models in the literature and is found to achieve comparable accuracy with atom-based simulations. At the same time, its computational efficiency allows the study of large-scale graphene-based polymer nanocomposites in the engineering scale. © 2025 Elsevier B.V.

关键词： Tensile testing

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The Anisotropic Gaussian Semi-Classical Schrödinger Propagator

arXiv

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arXiv 2021年

We present a construction of the Anisotropic Gaussian Semi-Classical Schrödinger Propagator, emblematic of a class of Fourier Integral Operators of quadratic phase kernels related to the Schrödinger equation. We deduce a set of algebraic relations of the variational matrices, solutions of the variational system pertaining to single Gaussian wave packet semi-classical time evolution, representing the symplectic and other invariances of the dynamics, which are subsequently used to derive the Van Vleck formula from the semi-classical propagator, as an argument for the practical importance of the later relations in the relevant wave packet calculus. © 2021, CC BY-NC-ND.

关键词： Riccati equations

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Cumulant gan

arXiv

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arXiv 2020年

作者： Pantazis, Yannis Fasoulakis, Michail Paul, Dipjyoti Stylianou, Yannis Katsoulakis, Markos Institute of Applied and Computational Mathematics Foundation for Research & Technology Hellas Greece Institute of Computer Science Foundation for Research & Technology Hellas Greece Computer Science Department University of Crete Greece Department of Mathematics and Statistics University of Massachusetts at Amherst United States

In this paper, we propose a novel loss function for training Generative Adversarial Networks (GANs) aiming towards deeper theoretical understanding as well as improved stability and performance for the underlying optimization problem. The new loss function is based on cumulant generating functions giving rise to Cumulant GAN. Relying on a recently-derived variational formula, we show that the corresponding optimization problem is equivalent to Rényi divergence minimization, thus offering a (partially) unified perspective of GAN losses: the Rényi family encompasses Kullback-Leibler divergence (KLD), reverse KLD, Hellinger distance and χ2-divergence. Wasserstein GAN is also a member of cumulant GAN. In terms of stability, we rigorously prove the linear convergence of cumulant GAN to the Nash equilibrium for a linear discriminator, Gaussian distributions and the standard gradient descent ascent algorithm. Finally, we experimentally demonstrate that image generation is more robust relative to Wasserstein GAN and it is substantially improved in terms of both inception score and Fréchet inception distance when both weaker and stronger discriminators are considered. Copyright © 2020, The Authors. All rights reserved.

关键词： Generative adversarial networks

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Inference of stochastic dynamical systems from cross-sectional population data

arXiv

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arXiv 2020年

作者： Tsourtis, Anastasios Pantazis, Yannis Tsamardinos, Ioannis Computer Science Deptartment University of Crete Heraklion Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology - Hellas Heraklion Greece

Inferring the driving equations of a dynamical system from population or time-course data is important in several scientific fields such as biochemistry, epidemiology, financial mathematics and many others. Despite the existence of algorithms that learn the dynamics from trajectorial measurements there are few attempts to infer the dynamical system straight from population data. In this work, we deduce and then computationally estimate the Fokker-Planck equation which describes the evolution of the population’s probability density, based on stochastic differential equations. Then, following the USDL approach [22], we project the Fokker-Planck equation to a proper set of test functions, transforming it into a linear system of equations. Finally, we apply sparse inference methods to solve the latter system and thus induce the driving forces of the dynamical system. Our approach is illustrated in both synthetic and real data including non-linear, multimodal stochastic differential equations, biochemical reaction networks as well as mass cytometry biological measurements. Copyright © 2020, The Authors. All rights reserved.

关键词： Dynamical systems

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Enhancing speech intelligibility in text-to-speech synthesis using speaking style conversion

arXiv

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arXiv 2020年

作者： Paul, Dipjyoti Shifas, Muhammed P.V. Pantazis, Yannis Stylianou, Yannis Computer Science Department University of Crete Greece Inst. of Applied and Computational Mathematics Foundation for Research and Technology Hellas Greece

The increased adoption of digital assistants makes text-to-speech (TTS) synthesis systems an indispensable feature of modern mobile devices. It is hence desirable to build a system capable of generating highly intelligible speech in the presence of noise. Past studies have investigated style conversion in TTS synthesis, yet degraded synthesized quality often leads to worse intelligibility. To overcome such limitations, we proposed a novel transfer learning approach using Tacotron and WaveRNN based TTS synthesis. The proposed speech system exploits two modification strategies: (a) Lombard speaking style data and (b) Spectral Shaping and Dynamic Range Compression (SSDRC) which has been shown to provide high intelligibility gains by redistributing the signal energy on the time-frequency domain. We refer to this extension as Lombard-SSDRC TTS system. Intelligibility enhancement as quantified by the Intelligibility in Bits (SIIBGauss) measure shows that the proposed Lombard-SSDRC TTS system shows significant relative improvement between 110% and 130% in speech-shaped noise (SSN), and 47% to 140% in competing-speaker noise (CSN) against the state-of-the-art TTS approach. Additional subjective evaluation shows that Lombard-SSDRC TTS successfully increases the speech intelligibility with relative improvement of 455% for SSN and 104% for CSN in median keyword correction rate compared to the baseline TTS method. Copyright © 2020, The Authors. All rights reserved.

关键词： Speech intelligibility

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Speaker conditional WaveRNN: Towards universal neural vocoder for unseen speaker and recording conditions

arXiv

引用

arXiv 2020年

作者： Paul, Dipjyoti Pantazis, Yannis Stylianou, Yannis Computer Science Department University of Crete Greece Inst. of Applied and Computational Mathematics Foundation for Research and Technology Hellas Greece

Recent advancements in deep learning led to human-level performance in single-speaker speech synthesis. However, there are still limitations in terms of speech quality when generalizing those systems into multiple-speaker models especially for unseen speakers and unseen recording qualities. For instance, conventional neural vocoders are adjusted to the training speaker and have poor generalization capabilities to unseen speakers. In this work, we propose a variant of WaveRNN, referred to as speaker conditional WaveRNN (SC-WaveRNN). We target towards the development of an efficient universal vocoder even for unseen speakers and recording conditions. In contrast to standard WaveRNN, SC-WaveRNN exploits additional information given in the form of speaker embeddings. Using publicly-available data for training, SC-WaveRNN achieves significantly better performance over baseline WaveRNN on both subjective and objective metrics. In MOS, SC-WaveRNN achieves an improvement of about 23% for seen speaker and seen recording condition and up to 95% for unseen speaker and unseen condition. Finally, we extend our work by implementing a multi-speaker text-to-speech (TTS) synthesis similar to zero-shot speaker adaptation. In terms of performance, our system has been preferred over the baseline TTS system by 60% over 15.5% and by 60.9% over 32.6%, for seen and unseen speakers, respectively. Copyright © 2020, The Authors. All rights reserved.

关键词： Speech synthesis

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