| 1. |
- Izzo, M. G., et al.
(författare)
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Rayleigh scattering and disorder-induced mixing of polarizations in amorphous solids at the nanoscale: 1-octyl-3-methylimidazolium chloride glass
- 2020
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 102:21
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Tidskriftsartikel (refereegranskat)abstract
- Acousticlike excitations in topologically disordered media at mesocale/nanoscale present anomalous features with respect to the Debye's theory. The so-called Rayleigh scattering manifests in a strong increase of the attenuation of the acousticlike excitations and a softening of the phase velocity with respect to its continuum limit value. Mean field models developed in the random media theory framework can successfully predict the occurrence, at the proper length scale, of Rayleigh scattering. The overall attenuation in the Rayleigh region is, however, underestimated. In the framework of random media theory we developed an analytical model, which permits a quantitative description of the acousticlike excitations in topological glasses in the whole first pseudo-Brillouin zone. The underestimation of the Rayleigh scattering is avoided and, importantly, the model allows to account also for the polarization properties of the acousticlike excitations. In a three-dimensional medium an acoustic wave is characterized by its phase velocity, intensity, and polarization. Rayleigh scattering emphasizes how the topological disorder affects the first two properties. The topological disorder is, however, expected to influence also the third one. In common with the Rayleigh scattering, hallmarks possibly related to the mixing of polarizations have been traced in different classes of amorphous solids at nanoscale. The quantitative theoretical approach developed permits to demonstrate how the mixing of polarizations generates a distinctive feature in the dynamic structure factor of amorphous solids. The modeling capability of the proposed mean field theory is tested on glassy 1-octyl-3-methylimidazolium chloride, whose spatial distribution of the elastic moduli is well assessed and can be experimentally characterized. Contrast between theoretical and experimental features for the selected glass reveals an excellent agreement. The mean field approach we present retains a certain degree of generality and can be possibly extended to different stochastic media or different wave fields.
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| 2. |
- Izzo, Maria G., et al.
(författare)
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The Mixing of Polarizations in the Acoustic Excitations of Disordered Media With Local Isotropy
- 2018
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- An approximate solution of the Dyson equation related to a stochastic Helmholtz equation, which describes the acoustic dynamics of a three-dimensional isotropic random medium with elastic tensor fluctuating in space, is obtained in the framework of the Random Media Theory. The wavevector-dependence of the self-energy is preserved, thus allowing a description of the acoustic dynamics at wavelengths comparable with the size of heterogeneity domains. This in turn permits to quantitatively describe the mixing of longitudinal and transverse dynamics induced by the medium's elastic heterogeneity and occurring at such wavelengths. A functional analysis aimed to attest the mathematical coherence and to define the region of validity in the frequency-wavector plane of the proposed approximate solution is presented, with particular emphasis dedicated to the case of disorder characterized by an exponential decay of the covariance function.
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| 3. |
- Åström, Fredrik, et al.
(författare)
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Conceptualising dimensions of bibliometric assessment: From resource allocation systems to evaluative landscapes
- 2019
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Ingår i: Proceedings of the 17th Conference of the International Society for Scientometrics and Informetrics : ISSI 2019 with a Special STI Indicators Conference Track - ISSI 2019 with a Special STI Indicators Conference Track. - 9788833811185 ; , s. 1256-1261
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to discuss the conceptualisation of bibliometric analyses in terms of the levels on which they are performed, adding contextual factors to the dimension where the size of the unit being analysed is considered. Based on empirical investigations of resource allocation systems and research evaluation practices, as well as the previous literature conceptualising bibliometric analyses, a framework based on Whitley’s (2000) notion of research fields as ‘reputational work organisations’, is discussed. The results suggest adding a contextual ‘reputational dimension’ to the size-based dimension distinguishing between micro-, meso- and macro-level analyses. Furthermore, we propose that ‘evaluative landscapes’ (Brandter, 2017) might be a fruitful approach for further analysing how complex and multifaceted landscapes of research assessment affects the individual researcher.
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