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| 2. |
- Aasmundtveit, K.E., et al.
(author)
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Structural anisotropy of poly(alkylthiophene) films
- 2000
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 3120-3127
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Journal article (peer-reviewed)abstract
- The structural anisotropy of various poly(alkylthiophene) films have been studied by X-ray diffraction, using both conventional methods and synchrotron radiation at grazing incidence. Solution-cast films orient with the side chains preferably normal to the film surface, whereas spin-cast films of nonstereoregular material orient with both the main and the side chains in the film plane. For thick (10-50 µm) solution-cast films, the degree of orientation depends strongly on the solvent used for casting, and on the stereoregularity of the polymer, films of stereoregular materials being more oriented than those of nonregular materials. The most oriented nonregular films are those cast from mixtures of chloroform and tetrahydrofuran. Thin (50-500 nm) solution-cast films are more oriented than the thicker ones, and the effects of different stereoregularity or different casting solvents are small. For spin-cast films, the degree of orientation is independent of substrate and solvent. Spin-cast films of stereoregular material have two different phases: One with the side chains normal to the substrate, and another where they are parallel to the substrate. The diffraction peaks of spin-cast poly(octylthiophene) narrow considerably upon heating.
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| 3. |
- Aasmundtveit, K.E., et al.
(author)
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Structural aspects of electrochemical doping and dedoping of poly(3,4-ethylenedioxythiophene)
- 2000
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In: Synthetic metals. - 0379-6779 .- 1879-3290. ; 113:1, s. 93-97
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Journal article (peer-reviewed)abstract
- Electrochemical dedoping and redoping of p-toluene sulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been studied with in situ grazing incidence diffraction with water used as an electrolyte. The diffraction peak positions and integrated intensities do not change significantly during doping and dedoping, while the peak widths increase upon dedoping and decrease upon doping. This implies that the lattice parameters and the relative positions of the polymer chains and the p-toluene sulfonate ions remain unchanged, the redox processes being carried out by the motion of smaller ions between the polymer and the electrolyte, and that the structural order decreases upon dedoping and increases upon doping in a reversible manner.
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| 4. |
- Abramavicius, Vytautas, et al.
(author)
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Carrier motion in as-spun and annealed P3HT:PCBM blends revealed by ultrafast optical electric field probing and Monte Carlo simulations
- 2014
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:6, s. 2686-2692
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Journal article (peer-reviewed)abstract
- Charge transport dynamics in solar cell devices based on as-spun and annealed P3HT:PCBM films are compared using ultrafast time-resolved optical probing of the electric field by means of field-induced second harmonic generation. The results show that charge carriers drift about twice as far during the first 3 ns after photogeneration in a device where the active layer has been thermally annealed. The carrier dynamics were modelled using Monte-Carlo simulations and good agreement between experimental and simulated drift dynamics was obtained using identical model parameters for both cells, but with different average PCBM and polymer domain sizes. The calculations suggest that small domain sizes in as-spun samples limit the carrier separation distance disabling their escape from geminate recombination.
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| 5. |
- Admass, Muluneh
(author)
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3-D numerical modeling of flow and sediment transport in rivers
- 2005
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Licentiate thesis (other academic/artistic)abstract
- The fully integrated 3-D, time dependant, hydrodynamic and sediment transport numerical model ECOMSED was used to simulate flow and sediment transport in rivers. ECOMSED was originally developed for large water bodies such as lakes and oceans and solves the primitive equations of RANS along with a second order turbulence model in an orthogonal curvilinear σ- coordinate system. The availability of the model as an open FORTRAN source code made modifications and addition of new models possible. A new bed load transport model was implemented in the code as well as improvements in treatment of river roughness parameterization, bed form effects, and automatic update of flow depth due to bed evolution. The model was applied to 1- km long reach of the River Klarälven, Sweden, where it bifurcates into two west and east channels. The water surface and the flow division in the channels were made in agreement with field data by spatially varying the roughness. However, the spatial distribution of the bed shear stress was not realistic. Improvements were made in the bottom boundary condition to represent the variable effects of bed forms on roughness depending on the flow regime and the flow depth. The improved model realistically reproduced the flow field as well as the sediment transport processes in the river Klarälven.
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| 6. |
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| 7. |
- Admassie, Shimelis, et al.
(author)
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A polymer photodiode using vapour-phase polymerized PEDOT as an anode
- 2006
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In: Solar Energy Materials & Solar Cells. ; 90:2, s. 133-141
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Journal article (peer-reviewed)abstract
- We report the photovoltaic properties of devices made using a highly conducting polymer electrode, from vapor-phase polymd. poly (3,4-ethylenedioxy) thiophene (VPP PEDOT) on glass substrate as an anode and a polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2thienyl-2',1'3'-benzothiadiazole)] (APFO-3) mixed with [6,6]-phenyl-C61-butyric acid methylester (PCBM) in the ratio of 1:4 as the active layer. The device performance was compared with that of devices made with PEDOT-PSS on glass substrates. The surfaces of VPP PEDOT were imaged using at. force microscopy (AFM). [on SciFinder (R)]
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| 8. |
- Admassie, Shimelis, et al.
(author)
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Charge storage properties of biopolymer electrodes with (sub)tropical lignins
- 2014
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 16:45, s. 24681-24684
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Journal article (peer-reviewed)abstract
- The electrochemical and charge storage properties of different lignins inside biopolymer electrodes were studied and correlated with the chemical variations of the lignins as indicated from the nuclear magnetic resonance (NMR) spectroscopic data. The varying fractions of monolignols were found to correlate with charge storage properties. It was found that as the sinapyl to guaiacyl (S/G) ratio increased both the specific capacitance and charge capacity increased considerably. This indicates that quinones generated on S-units can contribute more to charge storage in the biopolymer electrodes.
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| 9. |
- Admassie, Shimelis, et al.
(author)
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Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
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In: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 156:7-8, s. 614-623
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Journal article (peer-reviewed)abstract
- The electrochemical and optical properties of a series of alternating polyfluorene copolymers with low band gaps were determined. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor-acceptor-donor (DAD) sequence to achieve the lowering of band gaps. The polymers were solvent-casted on platinum disk electrode and the band gaps were estimated from cyclic voltammetry (CV). These values were compared with values obtained from optical absorption measurements. Although the electrochemically determined band gaps were found to be slightly higher than the optical band gap in most cases, values are well correlated. The values of the band gaps determined range from 2.1 to 1.3 eV. © 2006 Elsevier B.V. All rights reserved.
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| 10. |
- Aikio, S, et al.
(author)
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Seed bank in annuals: Competition between banker and non-banker morphs
- 2002
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In: Journal of Theoretical Biology. - : Elsevier BV. - 1095-8541 .- 0022-5193. ; 217:3, s. 341-349
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Journal article (peer-reviewed)abstract
- Seed bank is a plant life history strategy against the unpredictability of the biotic and the abiotic environment. We simulated competition between a seed banking and a non-banking morph of an annual plant. A constant fraction of the banker morph seeds was allocated to the seed bank, where they had a constant mortality and germination rate. All surviving seeds of the non-banker morph germinated in the next generation. The seedlings of both morphs experienced similar density-dependent mortality. Whether one of the morphs wins or the morphs coexist was evaluated from parameter space plots and statistically with logistic regression analysis. All parameters of the model had a significant, nonlinear effect on the persistence of the morphs, supporting our approach of numerically covering a wide range of parameter values. The seed production of a focal morph increased its survival and decreased the survival of the other morph. Otherwise, the morphs showed opposite response to changes in the model parameters. The banker morph was usually the winning strategy when it had a higher seed production than the non-banker morph. The banker morph benefitted from high germination probability, while the non-banker benefitted from high allocation to seed bank and high seed mortality. The coexistence of the morphs was inhibited by high banker morph seed production and seed mortality and promoted by high values of all other parameters. The system showed complex dynamics when banking was the winning strategy or the morphs coexisted. In addition, a part of the parameter space where the non-banker morph wins showed complex dynamics. Our results suggest that seed banking is a beneficial strategy if seed number is increased consequently, e.g. due to a decreased seed size. If banking decreases seed number, the non-banker morph wins or the two morphs coexist. (C) 2002 Elsevier Science Ltd. All rights reserved.
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