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- Cao, J. S., et al.
(författare)
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Quantum biology revisited
- 2020
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:14
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthesis is a highly optimized process from which valuable lessons can be learned about the operating principles in nature. Its primary steps involve energy transport operating near theoretical quantum limits in efficiency. Recently, extensive research was motivated by the hypothesis that nature used quantum coherences to direct energy transfer. This body of work, a cornerstone for the field of quantum biology, rests on the interpretation of small-amplitude oscillations in two-dimensional electronic spectra of photosynthetic complexes. This Review discusses recent work reexamining these claims and demonstrates that interexciton coherences are too short lived to have any functional significance in photosynthetic energy transfer. Instead, the observed long-lived coherences originate from impulsively excited vibrations, generally observed in femtosecond spectroscopy. These efforts, collectively, lead to a more detailed understanding of the quantum aspects of dissipation. Nature, rather than trying to avoid dissipation, exploits it via engineering of exciton-bath interaction to create efficient energy flow.
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| 2. |
- Mangnus, Astrid C., et al.
(författare)
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Envisioning alternatives in pre-structured urban sustainability transformations: Too late to change the future?
- 2022
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Ingår i: Cities. - : Elsevier BV. - 0264-2751. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- In the governance of urban sustainability transformations, participatory futures practices are increasingly popular. Yet there is a rising awareness that the success or failure of these practices depends on how they are staged and the context in which they are conducted. These contextual factors are often less than ideal, and futures practices take place at the crossroads of many pre-determined agendas and priorities. We distinguish four factors that shape the effects of participatory futures practices: 1) how the institutional landscape constrains or enables a project aimed at urban sustainability transformations; 2) the participatory culture surrounding the project; 3) the project design; and 4) the futures methods applied. We assess these factors in three cities within the European H2020 IRIS Smart Cities project. In each city, project members participated in sessions where they designed citizen engagement using a futures methodology: the novel Scope and Ladder models. Each city reflects a different combination of the four contextual factors. We find that space for exploration and re-imagining can be found and optimized under imperfect conditions. Drawing on the results of the three cases, we conclude with a set of recommendations for the funders, project members and futures organizers of urban sustainability transformation projects.
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| 3. |
- Messinger, Johannes, 1963-, et al.
(författare)
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S-3 state of the water oxidase in photosystem II
- 1997
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Ingår i: Biochemistry. - : AMER CHEMICAL SOC. - 0006-2960 .- 1520-4995. ; 36:23, s. 6862-6873
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the reductant hydrazine on the flash-induced oxygen oscillation patterns of spinach thylakoids was used to characterize a new super-reduced redox state of the water oxidase in photosystem II. The formation of a discrete S-3 state is evident from the shift of the first maximum of oxygen evolution from the 3rd flash through the 5th flash to the 7th flash during a 90 min incubation of dark-adapted thylakoids with 10 mM hydrazine sulfate at pH 6.8 on ice. A distinct period four oscillation with further maxima on the 11th and 15th flashes is still observed at this stage of the incubation. The data analysis within the framework of an extended Kok model reveals that a S-3 state population of almost 50% can be achieved by this treatment. A prolonged incubation of the S-3 sample with 10 mM hydrazine (and even 100 mM) does not lead to a further shift of the first maximum toward the 9th flash that could reflect the formation of the S-5 state. Instead, a slow oxidation of S-3 to S-2 takes place by an as yet unidentified electron acceptor. A consistent simulation of all the measured oxygen oscillation patterns of this study could, however, only be achieved by including the formal redox states S-4 and S-5 in the fits (S-4 + S-5 up to 35%). The implications of these findings for the oxidation states of the manganese in the tetranuclear cluster of the water oxidase are discussed.
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