Infrared spectra in amorphous aluminaLuigi Giacomazzi
, Nikita S Shcheblanov
, Mikhail E Povarnitsyn
, Yanbo Li
, Andraž Mavrič
, Barbara Zupančič
, Jože Grdadolnik
, Alfredo Pasquarello
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Abstract: We present a combined study based on experimental measurements of infrared (IR) dielectric function and first-principles calculations of IR spectra and vibrational density of states (VDOS) of amorphous alumina (am-Al₂O₃). In particular, we show that the main features of the imaginary part of the dielectric function ε₂(ω) at ~380 and 630 cm-¹ are related to the motions of threefold coordinated oxygen atoms, which are the vast majority of oxygen atoms in am-Al₂O₃. Our analysis (involving three model structures) provides an alternative point of view with respect to an earlier suggested assignment of the vibrational modes, which relates them to the stretching and bending vibrational modes of AlOₙ (n = 4, 5, and 6) polyhedra. Our assignment is based on the additive decomposition of the VDOS and ε₂(ω) spectra, which shows that: (i) the band at ~380 cm-¹ features oxygen motions occurring in a direction normal to the plane defined by the three nearest-neighbor aluminum atoms, i.e. out-of-plane motions of oxygen atoms; (ii) Al-O stretching vibrations (i.e. in-plane motions of oxygen atoms) appear at frequencies above ~500 cm-¹, which characterize the vibrational modes underlying the band at ~630 cm-¹.
Keywords: amorphous alumina, infrared spectra, first-principles calculations
Published in RUNG: 15.09.2023; Views: 129; Downloads: 3
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Urban Conservation System in China and Its Improvement by Using Historic Urban Landscape ApproachChen Shujie
, 2018, doctoral dissertation
Abstract: In the last few decades, the Modern Conservation Movement has developed from European-limited practices into a global movement with universal common views and practical measures for managing heritage resources in different cultural contexts. As an innovative idea of this movement, the Historic Urban Landscape approach aims to protect and manage historic urban environments with respect to both the fundamental principles in the international doctrines and the local social/cultural/historical contexts. It recommends local authorities to use the HUL toolkit to identify, conserve and manage the overall landscape of their historic cities.
In the case of China, who is an old civilization, a modern nation and a socialist country at the same time, the conservation practice needs to follow the basic and common conservation principles in the international doctrines, and meanwhile, it shall make its initiatives based on the actual social, cultural and political situations. The establishment of Historically and Culturally Famous City (HCF City in short) system is a positive attempt for such a purpose. The system manages various urban elements relating to the city’s historical and cultural features under a comprehensive notion of HCF City. However, the system is not prefect because it depends excessively on the top-down management of local governments, and also because it overlooks the spatial and spiritual relationships among the protected elements...
The thesis provides a big picture of architectural and urban conservation practices in China. It introduces the forming process and the characteristics of historic urban fabric, as well as the history of urban conservation. Then, it takes a deep look at the existing HCF City system, including its basic ideas, structures and mechanism. It analyses the system’s initiatives and deficiencies. Finally, it provides feasible advices to improve the current system by using the HUL toolkit.
Keywords: Urban, History, Heritage, Conservation, Management International Principles, Modern Conservation Movement, Globalization, Localization Historic Urban Area, Historically and Culturally Famous Cities, Conservation System, Historic Urban Landscape Chinese Architecture, Chinese Urban Planning, Conservation History, Policy
Published in RUNG: 11.02.2019; Views: 3524; Downloads: 46
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