3,995 research outputs found

    Quantum chemical investigation on iodine oxides and their role in the formation of atmospheric aerosols

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    En esta contribuci贸n se presenta un estudio te贸rico de diferentes reacciones qu铆micas entre 贸xidos de iodo y agua que pueden contribuir a la formaci贸n de part铆culas en la atm贸sfera. Mediante el uso de c谩lculos quimicocu谩nticos ab initio con tratamiento de la correlaci贸n electr贸nica se han obtenido propiedades termodin谩micas para caracterizar esas reaccione

    Rapidly convergent quasi-periodic Green functions for scattering by arrays of cylinders---including Wood anomalies

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    This paper presents a full-spectrum Green function methodology (which is valid, in particular, at and around Wood-anomaly frequencies) for evaluation of scattering by periodic arrays of cylinders of arbitrary cross section-with application to wire gratings, particle arrays and reflectarrays and, indeed, general arrays of conducting or dielectric bounded obstacles under both TE and TM polarized illumination. The proposed method, which, for definiteness is demonstrated here for arrays of perfectly conducting particles under TE polarization, is based on use of the shifted Green-function method introduced in the recent contribution (Bruno and Delourme, Jour. Computat. Phys. pp. 262--290 (2014)). A certain infinite term arises at Wood anomalies for the cylinder-array problems considered here that is not present in the previous rough-surface case. As shown in this paper, these infinite terms can be treated via an application of ideas related to the Woodbury-Sherman-Morrison formulae. The resulting approach, which is applicable to general arrays of obstacles even at and around Wood-anomaly frequencies, exhibits fast convergence and high accuracies. For example, a few hundreds of milliseconds suffice for the proposed approach to evaluate solutions throughout the resonance region (wavelengths comparable to the period and cylinder sizes) with full single-precision accuracy

    On the evaluation of quasi-periodic Green functions and wave-scattering at and around Rayleigh-Wood anomalies

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    This article presents full-spectrum, well-conditioned, Green-function methodologies for evaluation of scattering by general periodic structures, which remains applicable on a set of challenging singular configurations, usually called Rayleigh-Wood (RW) anomalies (at which the quasi-periodic Green function ceases to exist), where most existing quasi-periodic solvers break down. After reviewing a variety of existing fast-converging numerical procedures commonly used to compute the classical quasi-periodic Green-function, the present work explores the difficulties they present around RW-anomalies and introduces the concept of hybrid 鈥渟patial/spectral鈥 representations. Such expressions allow both the modification of existing methods to obtain convergence at RW-anomalies as well as the application of a slight generalization of the Woodbury-Sherman-Morrison formulae together with a limiting procedure to bypass the singularities. (Although, for definiteness, the overall approach is applied to the scalar (acoustic) wave-scattering problem in the frequency domain, the approach can be extended in a straightforward manner to the harmonic Maxwell's and elasticity equations.) Ultimately, this thorough study of RW-anomalies yields fast and highly-accurate solvers, which are demonstrated with a variety of simulations of wave-scattering phenomena by arrays of particles, crossed impenetrable and penetrable diffraction gratings and other related structures. In particular, the methods developed in this article can be used to 鈥渦pgrade鈥 classical approaches, resulting in algorithms that are applicable throughout the spectrum, and it provides new methods for cases where previous approaches are either costly or fail altogether. In particular, it is suggested that the proposed shifted Green function approach may provide the only viable alternative for treatment of three-dimensional high-frequency configurations with either one or two directions of periodicity. A variety of computational examples are presented which demonstrate the flexibility of the overall approach

    Research Findings on Empirical Evaluation of Requirements Specifications Approaches

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    Numerous software requirements specification (SRS) approaches have been proposed in software engineering. However, there has been little empirical evaluation of the use of these approaches in specific contexts. This paper describes the results of a mapping study, a key instrument of the evidence-based paradigm, in an effort to understand what aspects of SRS are evaluated, in which context, and by using which research method. On the basis of 46 identified and categorized primary studies, we found that understandability is the most commonly evaluated aspect of SRS, experiments are the most commonly used research method, and the academic environment is where most empirical evaluation takes place

    Reflections on a Fellowship and Time as a DEI Coordinator with Oscar Fernandez

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    In this episode of PDXPLORES, Dr. 脫scar Fern谩ndez, a contingent faculty member in University Studies at Portland State University, discusses his work during a diversity fellowship at UC Irvine. That work resulted in the forthcoming essay, Queering a Coordinator\u27s Diversity, Equity, and Illusion (DEI) Work in Academe: Disappointments, Self-Deceits, and Hopes Disclosed, to be published by the University of California Humanities Research Institute\u27s journal Foundry. Fern谩ndez opens up about his experiences as a DEI officer for University Studies, how that experience informed his essay, and thinking about DEI efforts within the context of higher education