227 research outputs found

    Spin signatures of exchange-coupled triplet pairs formed by singlet fission

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    We study the effect of an exchange interaction on the magnetic-field-dependent photoluminescence in singlet fission materials. We show that, for strongly interacting triplet exciton pairs (intertriplet exchange interaction greater than the intratriplet spin-dipolar interaction), quantum beating and magnetic-field effects vanish apart from at specific magnetic fields where singlet and quintet levels are mixed by a level anticrossing. We characterize these effects and show that the absence of a magnetic-field effect or zero-field quantum beats does not necessarily mean that fission is inoperative. These results call for a reconsideration of the observations that are considered hallmarks of singlet fission and demonstrate how the spin coherence and exchange coupling of interacting triplet pairs can be measured through magneto-photoluminescence experiments.Engineering and Physical Sciences Research Council (Grant ID: EP/G060738/1)This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.94.04520

    Strongly exchange-coupled triplet pairs in an organic semiconductor

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    From biological complexes to devices based on organic semiconductors, spin interactions play a key role in the function of molecular systems. For instance, triplet-pair reactions impact operation of organic light-emitting diodes as well as photovoltaic devices. Conventional models for triplet pairs assume they interact only weakly. Here, using electron spin resonance, we observe long-lived, strongly-interacting triplet pairs in an organic semiconductor, generated via singlet fission. Using coherent spin-manipulation of these two-triplet states, we identify exchange-coupled (spin-2) quintet complexes co-existing with weakly coupled (spin-1) triplets. We measure strongly coupled pairs with a lifetime approaching 3 µs and a spin coherence time approaching 1 µs, at 10 K. Our results pave the way for the utilization of high-spin systems in organic semiconductors.Gates-Cambridge Trust, Winton Programme for the Physics of Sustainability, Freie Universität Berlin within the Excellence Initiative of the German Research Foundation, Engineering and Physical Sciences Research Council (Grant ID: EP/G060738/1)This is the author accepted manuscript. The final version is available from Nature Publishing Group at http://dx.doi.org/10.1038/nphys3908

    Gaze following in multiagent contexts: Evidence for a quorum-like principle

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    Research shows that humans spontaneously follow another individual’s gaze. However, little remains known on how they respond when multiple gaze cues diverge across members of a social group. To address this question, we presented participants with displays depicting three (Experiment 1) or five (Experiment 2) agents showing diverging social cues. In a three-person group, one individual looking at the target (33% of the group) was sufficient to elicit gaze-facilitated target responses. With a five-person group, however, three individuals looking at the target (60% of the group) were necessary to produce the same effect. Gaze following in small groups therefore appears to be based on a quorum-like principle, whereby the critical level of social information needed for gaze following is determined by a proportion of consistent social cues scaled as a function of group size. As group size grows, greater agreement is needed to evoke joint attention

    The patient-provider relationship is associated with hepatitis c treatment eligibility: A prospective mixed-methods cohort study

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    Hepatitis C virus (HCV) treatment has the potential to cure the leading cause of cirrhosis and hepatocellular carcinoma. However, only those deemed eligible for treatment have the possibility of this cure. Therefore, understanding the determinants of HCV treatment eligibility is critical. Given that effective communication with and trust in healthcare providers significantly influences treatment eligibility decisions in other diseases, we aimed to understand patient-provider interactions in the HCV treatment eligibility process. This prospective cohort study was conducted in the VA Pittsburgh Healthcare System. Patients were recruited after referral for gastroenterology consultation for HCV treatment with interferon and ribavirin. Consented patients completed semi-structured interviews and validated measures of depression, substance and alcohol use, and HCV knowledge. Two coders analyzed the semi-structured interviews. Factors associated with patient eligibility for interferon-based therapy were assessed using multivariate logistic regression. Of 339 subjects included in this analysis, only 56 (16.5%) were deemed eligible for HCV therapy by gastroenterology (GI) providers. In the multivariate logistic regression, patients who were older (OR = 0.96, 95%CI = 0.92-0.99, p =.049), reported concerns about the GI provider (OR = 0.40, 95%CI = 0.10-0.87, p = 0.02) and had depression symptoms (OR = 0.32, 95%CI =0.17-0.63, p = 0.001) were less likely tobe eligible. Patients described barriers that included feeling stigmatized and poor provider interpersonal or communication skills. In conclusion, we found that patients' perceptions of the relationship with their GI providers were associated with treatment eligibility. Establishing trust and effective communication channels between patients and providers may lower barriers to potential HCV cure

    Disability weights for comorbidity and their influence on Health-adjusted Life Expectancy

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    BACKGROUND: Comorbidity complicates estimations of health-adjusted life expectancy (HALE) using disease prevalences and disability weights from Burden of Disease studies. Usually, the exact amount of comorbidity is unknown and no disability weights are defined for comorbidity. METHODS: Using data of the Dutch national burden of disease study, the effects of different methods to adjust for comorbidity on HALE calculations are estimated. The default multiplicative adjustment method to define disability weights for comorbidity is compared to HALE estimates without adjustment for comorbidity and to HALE estimates in which the amount of disability in patients with multiple diseases is solely determined by the disease that leads to most disability (the maximum adjustment method). To estimate the amount of comorbidity, independence between diseases is assumed. RESULTS: Compared to the multiplicative adjustment method, the maximum adjustment method lowers HALE estimates by 1.2 years for males and 1.9 years for females. Compared to no adjustment, a multiplicative adjustment lowers HALE estimates by 1.0 years for males and 1.4 years for females. CONCLUSION: The differences in HALE caused by the different adjustment methods demonstrate that adjusting for comorbidity in HALE calculations is an important topic that needs more attention. More empirical research is needed to develop a more general theory as to how comorbidity influences disability

    Inequitable Gains and Losses from Conservation in a Global Biodiversity Hotspot

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    A billion rural people live near tropical forests. Urban populations need them for water, energy and timber. Global society benefits from climate regulation and knowledge embodied in tropical biodiversity. Ecosystem service valuations can incentivise conservation, but determining costs and benefits across multiple stakeholders and interacting services is complex and rarely attempted. We report on a 10-year study, unprecedented in detail and scope, to determine the monetary value implications of conserving forests and woodlands in Tanzania’s Eastern Arc Mountains. Across plausible ranges of carbon price, agricultural yield and discount rate, conservation delivers net global benefits (+US8.2Bpresentvalue,20yearcentralestimate).Crucially,however,netoutcomesdivergewidelyacrossstakeholdergroups.Internationalstakeholdersgainmostfromconservation(+US8.2B present value, 20-year central estimate). Crucially, however, net outcomes diverge widely across stakeholder groups. International stakeholders gain most from conservation (+US10.1B), while local-rural communities bear substantial net costs (-US1.9B),withgreaterinequitiesformorebiologicallyimportantforests.OtherTanzanianstakeholdersexperienceconflictingincentives:tourism,drinkingwaterandclimateregulationencourageconservation(+US1.9B), with greater inequities for more biologically important forests. Other Tanzanian stakeholders experience conflicting incentives: tourism, drinking water and climate regulation encourage conservation (+US72M); logging, fuelwood and management costs encourage depletion (-US$148M). Substantial global investment in disaggregating and mitigating local costs (e.g., through boosting smallholder yields) is essential to equitably balance conservation and development objectives

    The entangled triplet pair state in acene and heteroacene materials

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    Entanglement of states is one of the most surprising and counter-intuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which mediates the spin-conserving fission of one spin-0 singlet exciton into two spin-1 triplet excitons. Despite long theoretical and experimental exploration, the nature of the triplet-pair state and inter-triplet interactions have proved elusive. Here we use a range of organic semiconductors that undergo singlet exciton fission to reveal the photophysical properties of entangled triplet-pair states. We find that the triplet pair is bound with respect to free triplets with an energy that is largely material independent (∼30 meV). During its lifetime, the component triplets behave cooperatively as a singlet and emit light through a Herzberg–Teller-type mechanism, resulting in vibronically structured photoluminescence. In photovoltaic blends, charge transfer can occur from the bound triplet pairs with >100% photon-to-charge conversion efficiency.The authors thank the G8 Research Councils Initiative on Multilateral Research Funding (EPSRC EP/K025651; US National Science Foundation CMM1-1255494; Japanese Society for the Promotion of Science), JC thanks the University of Sheffield for a VC fellowship. AJM and SLB thank EPSRC (EP/M01083X and EP/M025330). The work in Mons is supported by BELSPO through the PAI P6/27 Functional Supramolecular Systems project and by the Belgian National Fund for Scientific Research FNRS/F.R.S. DB is a Research Director of FNRS
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