| 1. |
- Lakhwani, Girish, et al.
(författare)
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Intensive Chiroptical Properties of Chiral Polyfluorenes Associated with Fibril Formation
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 113:43, s. 14047-14051
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of chiral poly {9,9-bis[(3S)-3,7-dimethyloctyl]-2,7-fluorene} (1) were studied using circular dichroism (CD) spectroscopy. Films spin coated from chloroform solution, show CD with a degree of polarization g(abs) (= +4 x 10(-4) at 400 nm) that is independent of film thickness (50-290 nm). This implies that gabs is an intensive property of the material and related to the chiral organization of the molecules on a length scale less than 50 nm. Atomic force microscopy (AFM) on the films reveals fibrils. Addition of nonsolvent methanol to a solution of 1 in chloroform leads to fibril formation in solution and results in CD similar in band shape to that of the pristine spin coated films from chloroform solution and a g(abs) comparable in magnitude. Thus the chiral molecular arrangement leading to circular dichroism is part of the internal structure of these fibrils.
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| 2. |
- Sandri, M, et al.
(författare)
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Signalling pathways regulating muscle mass in ageing skeletal muscle : The role of the IGF1-Akt-mTOR-FoxO pathway
- 2013
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Ingår i: Biogerontology (Dordrecht). - : Springer Science and Business Media LLC. - 1389-5729 .- 1573-6768. ; 14:3 SI, s. 303-323
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Tidskriftsartikel (refereegranskat)abstract
- During ageing skeletal muscles undergo a process of structural and functional remodelling that leads to sarcopenia, a syndrome characterized by loss of muscle mass and force and a major cause of physical frailty. To determine the causes of sarcopenia and identify potential targets for interventions aimed at mitigating ageing-dependent muscle wasting, we focussed on the main signalling pathway known to control protein turnover in skeletal muscle, consisting of the insulin-like growth factor 1 (IGF1), the kinase Akt and its downstream effectors, the mammalian target of rapamycin (mTOR) and the transcription factor FoxO. Expression analyses at the transcript and protein level, carried out on well-characterized cohorts of young, old sedentary and old active individuals and on mice aged 200, 500 and 800 days, revealed only modest age-related differences in this pathway. Our findings suggest that during ageing there is no downregulation of IGF1/Akt pathway and that sarcopenia is not due to FoxO activation and upregulation of the proteolytic systems. A potentially interesting result was the increased phosphorylation of the ribosomal protein S6, indicative of increased activation of mTOR complex1 (mTORC1), in aged mice. This result may provide the rationale why rapamycin treatment and caloric restriction promote longevity, since both interventions blunt activation of mTORC1; however, this change was not statistically significant in humans. Finally, genetic perturbation of these pathways in old mice aimed at promoting muscle hypertrophy via Akt overexpression or preventing muscle loss through inactivation of the ubiquitin ligase atrogin1 were found to paradoxically cause muscle pathology and reduce lifespan, suggesting that drastic activation of the IGF1-Akt pathway may be counterproductive, and that sarcopenia is accelerated, not delayed, when protein degradation pathways are impaired.
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| 3. |
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| 4. |
- Di Nuzzo, Daniele, et al.
(författare)
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Evidence for space-charge-limited conduction in organic photovoltaic cells at open-circuit conditions
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:8
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Tidskriftsartikel (refereegranskat)abstract
- The ac admittance of solar cells under illumination is investigated under open-circuit conditions. Open-circuit conditions are imposed by inserting a probe capacitor into the circuit. The capacitance and conductance of the cells are investigated as function of frequency and continuous illumination intensity. Results are compared with numerical and analytical modeling of charge recombination and transport. In bulk heterojunction solar cells with [6,6]-Phenyl-C-61(C-71)-butyric acid methyl ester as acceptor and poly(3-hexylthiophene) or poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] as electron donor, the high-frequency capacitance C and conductance G follow a power-law dependence on intensity of white light I, with G(I) proportional to I-3/4 and C(I) proportional to I-1/4. The modeling shows that these dependencies can be explained in terms of space-charge-limited current in combination with Langevin type recombination of carriers. For poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b]dithiophene-2,6-diyl]] the capacitance shows a weaker dependence on intensity, indicating fast recombination of photogenerated carriers. Results indicate that the fill factor of relatively well performing polymer solar cells can still be limited by space charge effects and can be improved by enhancing the charge carrier mobility or by reducing the bimolecular Langevin recombination. DOI: 10.1103/PhysRevB.87.085207
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| 5. |
- Duan, Chunhui, et al.
(författare)
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Improving Performance of All-Polymer Solar Cells Through Backbone Engineering of Both Donors and Acceptors
- 2018
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 2:12
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Tidskriftsartikel (refereegranskat)abstract
- All-polymer solar cells (APSCs), composed of semiconducting donor and acceptor polymers, have attracted considerable attention due to their unique advantages compared to polymer-fullerene-based devices in terms of enhanced light absorption and morphological stability. To improve the performance of APSCs, the morphology of the active layer must be optimized. By employing a random copolymerization strategy to control the regularity of the backbone of the donor polymers (PTAZ-TPDx) and acceptor polymers (PNDI-Tx) the morphology can be systematically optimized by tuning the polymer packing and crystallinity. To minimize effects of molecular weight, both donor and acceptor polymers have number-average molecular weights in narrow ranges. Experimental and coarse-grained modeling results disclose that systematic backbone engineering greatly affects the polymer crystallinity and ultimately the phase separation and morphology of the all-polymer blends. Decreasing the backbone regularity of either the donor or the acceptor polymer reduces the local crystallinity of the individual phase in blend films, affording reduced short-circuit current densities and fill factors. This two-dimensional crystallinity optimization strategy locates a PCE maximum at highest crystallinity for both donor and acceptor polymers. Overall, this study demonstrates that proper control of both donor and acceptor polymer crystallinity simultaneously is essential to optimize APSC performance.
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| 6. |
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| 7. |
- Melianas, Armantas, et al.
(författare)
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Nonequilibrium site distribution governs charge-transfer electroluminescence at disordered organic heterointerfaces
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 116:47, s. 23416-23425
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Tidskriftsartikel (refereegranskat)abstract
- The interface between electron-donating (D) and electron-accepting (A) materials in organic photovoltaic (OPV) devices is commonly probed by charge-transfer (CT) electroluminescence (EL) measurements to estimate the CT energy, which critically relates to device open-circuit voltage. It is generally assumed that during CT-EL injected charges recombine at close-to-equilibrium energies in their respective density of states (DOS). Here, we explicitly quantify that CT-EL instead originates from higher-energy DOS site distributions significantly above DOS equilibrium energies. To demonstrate this, we have developed a quantitative and experimentally calibrated model for CT-EL at organic D/A heterointerfaces, which simultaneously accounts for the charge transport physics in an energetically disordered DOS and the Franck-Condon broadening. The 0-0 CT-EL transition lineshape is numerically calculated using measured energetic disorder values as input to 3-dimensional kinetic Monte Carlo simulations. We account for vibrational CT-EL overtones by selectively measuring the dominant vibrational phonon-mode energy governing CT luminescence at the D/A interface using fluorescence line-narrowing spectroscopy. Our model numerically reproduces the measured CT-EL spectra and their bias dependence and reveals the higher-lying manifold of DOS sites responsible for CT-EL. Lowest-energy CT states are situated similar to 180 to 570 meV below the 0-0 CT-EL transition, enabling photogenerated carrier thermalization to these low-lying DOS sites when the OPV device is operated as a solar cell rather than as a light-emitting diode. Nonequilibrium site distribution rationalizes the experimentally observed weak current-density dependence of CT-EL and poses fundamental questions on reciprocity relations relating light emission to photovoltaic action and regarding minimal attainable photovoltaic energy conversion losses in OPV devices.
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| 8. |
- Meng, Xiao, et al.
(författare)
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Ferroelectric Switching and Electrochemistry of Pyrrole Substituted Trialkylbenzene-1,3,5-Tricarboxamides
- 2017
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Ingår i: Journal of Polymer Science Part B. - : WILEY. - 0887-6266 .- 1099-0488. ; 55:8, s. 673-683
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Tidskriftsartikel (refereegranskat)abstract
- We explore a new approach to organic ferroelectric diodes using a benzene-tricarboxamide (BTA) core connected with C10 alkyl chains to pyrrole groups, which can be polymerized to provide a semiconducting ferroelectric material. The compound possesses a columnar hexagonal liquid crystalline (LC) phase and exhibits ferroelectric switching. At low switching frequencies, an additional process occurs, which leads to a high hysteretic charge density of up to similar to 1000 mC/m(2). Based on its slow rate, the formation of gas bubbles, and the emergence of characteristic polypyrrole absorption bands in the UV-Vis-NIR, the additional process is identified as the oxidative polymerization of pyrrole groups, enabled by the presence of amide groups. Polymerization of the pyrrole groups, which is essential to obtain semiconductivity, is limited to thin layers at the electrodes, amounting to similar to 17 nm after cycling for 21 h. (C) 2017 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc.
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| 9. |
- Ramsey, KA, et al.
(författare)
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The Physical Activity and Nutritional INfluences in Ageing (PANINI) Toolkit: A Standardized Approach towards Physical Activity and Nutritional Assessment of Older Adults
- 2022
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Ingår i: Healthcare (Basel, Switzerland). - : MDPI AG. - 2227-9032. ; 10:6
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Tidskriftsartikel (refereegranskat)abstract
- Assessing multiple domains of health in older adults requires multidimensional and large datasets. Consensus on definitions, measurement protocols and outcome measures is a prerequisite. The Physical Activity and Nutritional INfluences In Ageing (PANINI) Toolkit aims to provide a standardized toolkit of best-practice measures for assessing health domains of older adults with an emphasis on nutrition and physical activity. The toolkit was drafted by consensus of multidisciplinary and pan-European experts on ageing to standardize research initiatives in diverse populations within the PANINI consortium. Domains within the PANINI Toolkit include socio-demographics, general health, nutrition, physical activity and physical performance and psychological and cognitive health. Implementation across various countries, settings and ageing populations has proven the feasibility of its use in research. This multidimensional and standardized approach supports interoperability and re-use of data, which is needed to optimize the coordination of research efforts, increase generalizability of findings and ultimately address the challenges of ageing.
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| 10. |
- van der Hofstad, Tom G. J., et al.
(författare)
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Carrier Recombination in Polymer Fullerene Solar Cells Probed by Reversible Exchange of Charge between the Active Layer and Electrodes Induced by a Linearly Varying Voltage
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 117:7, s. 3210-3220
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Tidskriftsartikel (refereegranskat)abstract
- The use of a voltage pulse that varies linearly with time and that is symmetric in time around t = 0 allows for simultaneous determination of (photo)capacitance and (photo)conductance of polymer solar cells. From the measured capacitance, an average density of reversibly extractable carriers is determined, and the result is compared to numerical drift-diffusion simulations. Results are in agreement with large charge densities near the contacts that can be exchanged with the electrode in a thermodynamically reversible manner upon changing the voltage. The combined determination of capacitance and conductance yields a relaxation time tau(rel) for photogenerated charge carriers. Results on thermally annealed poly(3-hexylthiopene):fullerene bulk heterojunction solar cells indicate tau(rel) similar to 2 mu s, limited by extraction and not significantly affected by bimolecular recombination under intensities up to 1 sun. In contrast, for small bandgap poly(diketopyrrolopyrrole-alt-quinquethiophene)-fullerene solar cells with similar to 5% power conversion efficiency, tau(rel) is limited by bimolecular recombination. This illustrates the need for very fast charge transport rates to avoid losses due to bimolecular recombination in solar cells with high charge generation rates. Conclusions from the charge exchange experiments are confirmed by time domain measurements using pulsed illumination.
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