910 research outputs found

    Emotional responses to world inequality

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    Drawing on discussions with Kenyan, Mexican and British teachers, this paper reports on emotional responses to international socio-economic inequality. Emotional regimes are explored to identify what ā€˜appropriateā€™ responses to inequality are in a variety of local and national contexts. These include rural and urban settings, and social milieus ranging from elite to deprived. Politeness, hand-wringing and humour can create a protective distance; while sadness, anger and hope for change connect with the issue of inequality and challenge the associated injustices. Distancing and connecting emerge as central themes in the analysis. The spatial patterns of emotions align with participants' socio-economic positions, in more disadvantaged settings unapologetic anger about inequality was expressed, as was humour in the face of group or national misfortune. These emotional regimes can be understood within the wider context of participants' socio-economic position; their senses of injustice; and their views on the possibility of social change. I argue that social norms surrounding justice and distribution can influence levels of inequality, and vice versa. This is of particular importance given the societal damage caused by inequality, which is now widely acknowledged.This research was funded by the ESRC and Dudley Stamp Memorial Trust

    Relaxation energies and excited state structures of poly(para-phenylene)

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    We investigate the relaxation energies and excited state geometries of the light emitting polymer, poly(para-phenylene). We solve the Pariser-Parr-Pople-Peierls model using the density matrix renormalization group method. We find that the lattice relaxation of the dipole-active 11B1uāˆ’1^1B_{1u}^- state is quite different from that of the 13B1u+1^3B_{1u}^+ state and the dipole-inactive 21Ag+2^1A_g^+ state. In particular, the 11B1uāˆ’1^1B_{1u}^- state is rather weakly coupled to the lattice and has a rather small relaxation energy ca. 0.1 eV. In contrast, the 13B1u+1^3B_{1u}^+ and 21Ag+2^1A_g^+ states are strongly coupled with relaxation energies of ca. 0.5 and ca. 1.0 eV, respectively. By analogy to linear polyenes, we argue that this difference can be understood by the different kind of solitons present in the 11B1uāˆ’1^1B_{1u}^-, 13B1u+1^3B_{1u}^+ and 21Ag+2^1A_g^+ states. The difference in relaxation energies of the 11B1uāˆ’1^1B_{1u}^- and 13B1u+1^3B_{1u}^+ states accounts for approximately one-third of the exchange gap in light-emitting polymers.Comment: Submitted to Physical Review

    Theory of singlet fission in carotenoid dimers

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    We develop a theory of singlet fission in carotenoid dimers. Following photoexcitation of the ā€œbrightā€ state (i.e., a singlet electronā€“hole pair) in a single carotenoid, the first step in the singlet fission process is ultrafast intramolecular conversion into the highly correlated ā€œdarkā€ (or 2Ag) state. This state has both entangled singlet triplet-pair and charge-transfer character. Our theory is predicated on the assumption that it is the singlet triplet-pair component of the ā€œdarkā€ state that undergoes bimolecular singlet fission. We use valence bond theory to develop a minimal two-chain model of the triplet-pair states. The single and double chain triplet-pair spectra are described, as this helps explain the dynamics and the equilibrated populations. We simulate the dynamics of the initial entangled pair state using the quantum Liouville equation, including both spin-conserving and spin-nonconserving dephasing processes. By computing the intrachain and interchain singlet, triplet, and quintet triplet-pair populations, we show that singlet fission critically depends on the interchain coupling and the driving potential (that determines endothermic vs exothermic fission)

    Large scale numerical investigation of excited states in poly(phenylene)

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    A density matrix renormalisation group scheme is developed, allowing for the first time essentially exact numerical solutions for the important excited states of a realistic semi-empirical model for oligo-phenylenes. By monitoring the evolution of the energies with chain length and comparing them to the experimental absorption peaks of oligomers and thin films, we assign the four characteristic absorption peaks of phenyl-based polymers. We also determine the position and nature of the nonlinear optical states in this model.Comment: RevTeX, 10 pages, 4 eps figures included using eps
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