| 1. |
- Blösch, Günter, et al.
(author)
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Twenty-three unsolved problems in hydrology (UPH) - a community perspective
- 2019
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In: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 64:10, s. 1141-1158
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Journal article (peer-reviewed)abstract
- This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come.
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| 2. |
- Heindel, Jerrold J., et al.
(author)
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Parma consensus statement on metabolic disruptors
- 2015
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In: Environmental Health. - : BioMed Central (BMC). - 1476-069X. ; 14
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Journal article (peer-reviewed)abstract
- A multidisciplinary group of experts gathered in Parma Italy for a workshop hosted by the University of Parma, May 16-18, 2014 to address concerns about the potential relationship between environmental metabolic disrupting chemicals, obesity and related metabolic disorders. The objectives of the workshop were to: 1. Review findings related to the role of environmental chemicals, referred to as "metabolic disruptors", in obesity and metabolic syndrome with special attention to recent discoveries from animal model and epidemiology studies; 2. Identify conclusions that could be drawn with confidence from existing animal and human data; 3. Develop predictions based on current data; and 4. Identify critical knowledge gaps and areas of uncertainty. The consensus statements are intended to aid in expanding understanding of the role of metabolic disruptors in the obesity and metabolic disease epidemics, to move the field forward by assessing the current state of the science and to identify research needs on the role of environmental chemical exposures in these diseases. We propose broadening the definition of obesogens to that of metabolic disruptors, to encompass chemicals that play a role in altered susceptibility to obesity, diabetes and related metabolic disorders including metabolic syndrome.
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| 3. |
- Maggio, Marcello, et al.
(author)
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SHBG and endothelial function in older subjects
- 2013
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In: International Journal of Cardiology. - : Elsevier BV. - 0167-5273 .- 1874-1754. ; 168:3, s. 2825-2830
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Journal article (peer-reviewed)abstract
- Background: Endothelial dysfunction is predictor of cardiovascular diseases that have different prevalence in men and women before menopause. Sex hormones and sex hormone binding globulin (SHBG), novel risk factors for diabetes and cardiovascular diseases even in older individuals, might explain this difference. However, the relationship between these hormones and endothelial function has never been addressed in the elderly. Methods and results: 430 men and, 424 women 70 years older of Prospective Study of the Vasculature in Uppsala Seniors study, with complete data on SHBG, testosterone(T), estradiol(E2), endothelium-independent vasodilation (EIDV), endothelium-dependent vasodilation(EDV), flow-mediated vasodilation (FMD) and the pulse wave analysis (reflection index, RI) were evaluated. Multivariate regression analysis adjusted for confounders was used to assess the relationship between T, E2, SHBG and endothelial function. In men we found a positive relationship between SHBG and EDV (beta +/- SE 3.60 +/- 0.83, p < 0.0001), EIDV (2.42 +/- 0.58, p < 0.0001) but not with FMD. The relationship between SHBG and EDV and EIDV was maintained after adjustment for sex (1.64 +/- 0.47, p < 0.001 and 1.79 +/- 0.35, p < 0.0006, respectively). After adjustment for confounders, the relationship between SHBG and EDV and EIDV was still statistically significant (2.63 +/- 0.90 and 1.86 +/- 0.63, p = 0.004 for both). In women SHBG and EIDV were positively associated (1.58 +/- 0.46; p = 0.0007), and this relationship was independent of sex (1.79 +/- 0.35; p < 0.001). No significant interaction SHBG * SEX was found for EIDV (p = 0.72). In a combined analysis in two sexes, SHBG and EIDV were positively associated (1.13 +/- 0.45; p = 0.01). SHBG was not associated with EDV, FMD and RI. No significant relationship was found between T or E2 and EDV, EIDV, FMD or RI in both sexes. Conclusions: In older men SHBG, but not T and E2, is positively and independently associated with EDV in resistance arteries. In both sexes, SHBG was positively and independently associated with EIDV.
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| 4. |
- Rolland, Nicolas, et al.
(author)
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Understanding morphology-mobility dependence in PEDOT:Tos
- 2018
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In: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 2:4
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Journal article (peer-reviewed)abstract
- The potential of conjugated polymers to compete with inorganic materials in the field of semiconductor is conditional on fine-tuning of the charge carriers mobility. The latter is closely related to the material morphology, and various studies have shown that the bottleneck for charge transport is the connectivity between well-ordered crystallites, with a high degree of pi-pi stacking, dispersed into a disordered matrix. However, at this time there is a lack of theoretical descriptions accounting for this link between morphology and mobility, hindering the development of systematic material designs. Here we propose a computational model to predict charge carriers mobility in conducting polymer PEDOT depending on the physicochemical properties of the system. We start by calculating the morphology using molecular dynamics simulations. Based on the calculated morphology we perform quantum mechanical calculation of the transfer integrals between states in polymer chains and calculate corresponding hopping rates using the Miller-Abrahams formalism. We then construct a transport resistive network, calculate the mobility using a mean-field approach, and analyze the calculated mobility in terms of transfer integrals distributions and percolation thresholds. Our results provide theoretical support for the recent study [Noriega et al., Nat Mater 12, 1038 (2013)] explaining why the mobility in polymers rapidly increases as the chain length is increased and then saturates for sufficiently long chains. Our study also provides the answer to the long-standing question whether the enhancement of the crystallinity is the key to designing high-mobility polymers. We demonstrate, that it is the effective pi-pi stacking, not the long-range order that is essential for the material design for the enhanced electrical performance. This generic model can compare the mobility of a polymer thin film with different solvent contents, solvent additives, dopant species or polymer characteristics, providing a general framework to design new high mobility conjugated polymer materials.
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| 5. |
- Sousa, Leonardo, et al.
(author)
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Mobility field and mobility temperature dependence in PC61BM: A kinetic Monte-Carlo study
- 2017
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In: Chemical Physics Letters. - : ELSEVIER SCIENCE BV. - 0009-2614 .- 1873-4448. ; 689, s. 74-81
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Journal article (peer-reviewed)abstract
- A study of electron mobility in a PCBM system is performed by means of analytical considerations and Kinetic Monte Carlo simulations. Orbital energies are calculated at the ZINDO level of theory and successively corrected considering contributions from permanent charges and polarization interactions. The relative importance of these environmental effects is analyzed in details, furthermore the predicted mobilities are compared with experimental results and similar simulations performed in C60. (C) 2017 Elsevier B.V. All rights reserved.
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| 6. |
- Volpi, Riccardo, et al.
(author)
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Charge-transfer state dynamics at C60-anthracene interfaces : a kinetic Monte Carlo approach
- 2015
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Other publication (other academic/artistic)abstract
- The morphology of organic interfaces plays an important role in charge-transfer (CT) state splitting, and therefore has a significant impact on the efficiency of organic solar cells. In this article, we use our kinetic Monte Carlo (KMC) method on molecular dynamics-simulated anthracene-C60 interfaces to study the relation between interface morphology and CT state splitting. These KMC simulations were performed at a range of applied electric fields, and with the fields applied at a range of angles to the interface. The results show that depending on the relative orientation of the anthracene and C60 molecules, CT state splitting shows different behavior with respect to both applied field strength and applied field angle. Different orientations may be better suited for different applications. The inclusion of polarization in our model is shown to increase CT state splitting for both orientations studied.
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| 7. |
- Volpi, Riccardo
(author)
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Charge Transport Simulations for Organic Electronics : A Kinetic Monte Carlo Approach
- 2015
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Licentiate thesis (other academic/artistic)abstract
- In this thesis we focus on the modelling and simulation of organic electronic devices, investigating their structural and electronic properties. Organic devices have attracted great interest for their innovative properties, but their functioning still represent a theoretical and technological challenge. They are composed by one or more organic materials depending on the particular application. The morphology of organic devices in the single phase or at the interface is known to strongly determine mobility and efficiency of the devices. The structural disorder is studied through molecular dynamics (MD) simulations. Marcus formula is used to calculate the hopping rate of the charge carriers and the model developed is tested by simulations in a Kinetic Monte Carlo scheme. The dependence of the transfer integrals on the relative molecular orientation is achieved through a weighted Mulliken formula or through a dimer projection approach using the semi-empirical Hartree Fock method ZINDO. Electrostatic effects, have been included through atomic charges and atomic polarizabilities, calculated at the B3LYP level of theory. The inclusion of electrostatic effects has been shown (through simulations in 4PV and C60) to be crucial to obtain a good qualitative agreement with experiments, for both mobility field and temperature dependence in the single phase. In particular the external reorganization energy, calculated through the polarization of the environment, has been shown to have a great impact on the conduction, shifting the inverse Marcus region and helping CT state separation at the interface (between C60 and anthracene).
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| 8. |
- Volpi, Riccardo, et al.
(author)
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Effect of Polarization on the Mobility of C60: A Kinetic Monte-Carlo Study
- 2016
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In: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 12:2, s. 812-824
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Journal article (peer-reviewed)abstract
- We present a study of mobility field and temperature dependence for C60 with Kinetic Monte-Carlo simulations. We propose a new scheme to take into account polarization effects in organic materials through atomic induced dipoles on nearby molecules. This leads to an energy correction for the single site energies and to an external reorganization happening after each hopping. The inclusion of polarization allows us to obtain a good agreement with experiments for both mobility field and temperature dependence.
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| 9. |
- Volpi, Riccardo
(author)
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Modelling Charge Transport for Organic Solar Cells within Marcus Theory
- 2017
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Doctoral thesis (other academic/artistic)abstract
- With the technological advancement of modern society, electronic devices are getting progressively more integrated in our everyday lives. Their continuouslygrowing presence is generating numerous concerns about costs, efficiency and the environmental impact of the electronic waste. In this context, organic electronics is finding its way through the market, allowing for potentially low-cost, light, flexible, transparent and environmentally friendly electronics. Despite the numerous successes of organic electronics, the functioning of several categories of organic devices still represents a technological challenge, due to problems like low efficiencies and stabilities (degradation over time).Organic devices are composed by one or more organic materials depending on the particular application. The conformation and electronic structure of the organic molecules as well as their supramolecular arrangement in the single phase or at the interface are known to strongly a affect the mobility and/or the efficiency of the device. While there is consensus on the fundamental physics of organic devices, we still lack a detailed comprehensive theory able to fully explain experimental data. In this thesis we focus on trying to expand our knowledge of charge transport in organic materials through theoretical modelling and simulation of organic electronic devices. While the methodology developed is generally valid for any organic device, we will particularly focus on the case represented by organic photovoltaics.The morphology of the system is obtained by molecular dynamics simulations. Marcus theory is used to calculate the hopping rate of the charge carriers and subsequently study the possibility of free charge carriers production in an organic solar cell. The theory is then compared both with Kinetic Monte Carlo simulations and with experiments to identify the main pitfalls of the actual theory and ways to improve it. The Marcus rate between two molecules depends on the molecular orbital energies, the transfer integral between the two molecules and the reorganization energy. The orbital energies and the transfer integrals between two neighbouring molecules are obtained through quantum mechanical calculations in vacuum. Electrostatic effects of the environment are included through atomic charges and atomic polarizabilities, producing a correction both to the orbital energy and to the reorganization energy. We have studied several systems in the single phase (polyphenylene vinylene, C60, PC61BM) and at the interface between two organic materials (anthracene/C60, TQ1/PC71BM).We show how a combination of different methodologies can be used to obtain a realistic ab-initio model of organic devices taking into account environmental effects. This allows us to obtain qualitative agreement with experimental data of mobility in the single phase and to determine whether or not two materials are suitable to be used together in an organic solar cell.
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| 10. |
- Volpi, Riccardo, et al.
(author)
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Modelling charge transport of discotic liquid-crystalline triindoles: the role of peripheral substitution
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 19:35, s. 24202-24208
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Journal article (peer-reviewed)abstract
- We have performed a multiscale approach to study the influence of peripheral substitution in the semiconducting properties of discotic liquid-crystalline triindoles. Charge carrier mobility as high as 1.4 cm(2) V-1 s(-1) was experimentally reported for triindoles substituted with alkynyl chains on the periphery (Gomez-Lor et al. Angew. Chem., Int. Ed., 2011, 50, 7399-7402). In this work, our goal is to get a deeper understanding of both the molecular electronic structure and microscopic factors affecting the charge transport properties in triindoles as a function of the spacer group connecting the central cores with the external alkyl chains (i.e., alkyne or phenyl spacers groups). To this end, we first perform Quantum Mechanical (QM) calculations to assess how the peripheral substitution affects the electronic structure and the internal reorganization energy. Secondly, boxes of stacked molecules were built and relaxed through molecular dynamics to obtain realistic structures. Conformational analysis and calculations of transfer integrals for closed neighbours were performed. Our results show that the insertion of ethynyl spacers between the central aromatic core and the flexible peripheral chains results in lower reorganization energies and enhanced intermolecular order within the stacks with a preferred cofacial 60 degrees staggered conformation, which would result in high charge-carrier mobilities in good agreement with the experimental data. This work allows a deeper understanding of charge carrier mobility in columnar phases, linking the structural order at the molecular level to the property of interest, i.e. the charge carrier mobility. We hope that this understanding will improve the design of systems at the supramolecular level aiming at obtaining a more defined conducting channel, higher mobility and smaller fluctuations within the column.
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