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Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems
Engel, Gregory S.,Calhoun, Tessa R.,Read, Elizabeth L.,Ahn, Tae-Kyu,Manč,al, Tomá,š,Cheng, Yuan-Chung,Blankenship, Robert E.,Fleming, Graham R. Nature Publishing Group 2007 Nature Vol.446 No.7137
Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke ‘hopping’ of excited-state populations along discrete energy levels. Two-dimensional Fourier transform electronic spectroscopy has mapped these energy levels and their coupling in the Fenna–Matthews–Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy ‘wire’ connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre. The spectroscopic data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses—even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted and indirectly observed. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.
Re-engineering of Rotary Draw Bending Machines: a Survey of Manufacturers and Users
Bernd Engel,Sara Salman Hassan Al-Maeeni 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.1
Natural resources limitation and new legislative rules for waste reduction prompt the manufacturers of machine tools to be responsible for taking back their obsolete machines of high value-added, and use sustainable disposal methods such as machine retrofitting, rebuilding, or remanufacturing. Re-engineering of machine tools, concerning design development and failure analysis, is a concept enables and facilitates the implementation of the sustainable disposal methods. This paper aims to identify the re-engineering motivations, barriers, and required design modifications. As stated in a survey conducted among users and manufacturers of rotary draw bending machines, as a case study, economic benefits, use of the same tooling, environmental protection are the primary motivations, while spare parts unavailability, old parts wear and damage, and the high price of replacement parts are the most serious challenges make these machines more difficult to reuse. Furthermore, the required design modifications for designing reusable machines were highlighted in this paper. Additionally, measures for improving the accuracy, capacity, and performance of the studied machine are evaluated according to the survey results, and consequently, an investigation approach for mechanical failure analysis was created. In conclusion, it is observed that the results of the studied case confirmed the survey findings.