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| 3. |
- Kesteloot, N., et al.
(author)
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Deformation and mixing of coexisting shapes in neutron-deficient polonium isotopes
- 2015
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:5
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Journal article (peer-reviewed)abstract
- Coulomb-excitation experiments are performed with postaccelerated beams of neutron-deficient Po-196,Po-198,Po-200,Po-202 isotopes at the REX-ISOLDE facility. A set of matrix elements, coupling the low-lying states in these isotopes, is extracted. In the two heaviest isotopes, Po-196,Po-198, the transitional and diagonal matrix elements of the 2(1)(+) state are determined. In Po-196,Po-198 multistep Coulomb excitation is observed, populating the 4(1)(+), 0(2)(+), and 2(2)(+) states. The experimental results are compared to the results from the measurement of mean-square charge radii in polonium isotopes, confirming the onset of deformation from Po-196 onwards. Three model descriptions are used to compare to the data. Calculations with the beyond-mean-field model, the interacting boson model, and the general Bohr Hamiltonian model show partial agreement with the experimental data. Finally, calculations with a phenomenological two-level mixing model hint at the mixing of a spherical structure with a weakly deformed rotational structure.
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| 5. |
- Balgoma, D, et al.
(author)
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Linoleic acid-derived lipid mediators increase in a female-dominated subphenotype of COPD
- 2016
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In: The European respiratory journal. - : European Respiratory Society (ERS). - 1399-3003 .- 0903-1936. ; 47:6, s. 1645-1656
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Journal article (peer-reviewed)abstract
- Chronic obstructive pulmonary disease (COPD) is a leading cause of mortality; however, the role of inflammatory mediators in its pathobiology remains unclear. The aim of this study was to investigate the influence of gender in COPD on lipid mediator levels.Bronchoalveolar lavage fluid (BALF) and serum were obtained from healthy never-smokers, smokers and COPD patients (Global Initiative for Chronic Obstructive Lung Disease stage I–II/A–B) (n=114). 94 lipid mediators derived from the cytochrome-P450, lipoxygenase, and cyclooxygenase pathways were analysed by liquid chromatography-mass spectrometry.Multivariate modelling identified a 9-lipid panel in BALF that classified female smokers with COPD from healthy female smokers (p=6×10−6). No differences were observed for the corresponding male population (p=1.0). These findings were replicated in an independent cohort with 92% accuracy (p=0.005). The strongest drivers were the cytochrome P450-derived epoxide products of linoleic acid (leukotoxins) and their corresponding soluble epoxide hydrolase (sEH)-derived products (leukotoxin-diols). These species correlated with lung function (r=0.87; p=0.0009) and mRNA levels of enzymes putatively involved in their biosynthesis (r=0.96; p=0.003). Leukotoxin levels correlated with goblet cell abundance (r=0.72; p=0.028).These findings suggest a mechanism by which goblet cell-associated cytochrome-P450 and sEH activity produce elevated leukotoxin-diol levels, which play a putative role in the clinical manifestations of COPD in a female-dominated disease sub-phenotype.
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| 6. |
- Araujo, Rafael B., et al.
(author)
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Assessing the electrochemical properties of polypyridine and polythiophene for prospective applications in sustainable organic batteries
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:4, s. 3307-3314
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Journal article (peer-reviewed)abstract
- Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, the key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.
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| 7. |
- Araujo, Rafael B., et al.
(author)
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Designing strategies to tune reduction potential of organic molecules for sustainable high capacity battery application
- 2017
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 5:9, s. 4430-4454
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Journal article (peer-reviewed)abstract
- Organic compounds evolve as a promising alternative to currently used inorganic materials in rechargeable batteries due to their low-cost, environmental friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of the density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, and pi bonds, as well as carboxyl groups on the formal potential, have been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.
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| 8. |
- Bood, JR, et al.
(author)
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Urinary excretion of lipid mediators in response to repeated eucapnic voluntary hyperpnea in asthmatic subjects
- 2015
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 119:3, s. 272-279
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Journal article (peer-reviewed)abstract
- Exercise-induced bronchoconstriction displays refractoriness manifested as a decreased response to repeated exercise challenge within hours. The refractoriness may be attenuated by inhibition of the biosynthesis of prostaglandins (PG). The aim of the study was to determine which PGs and other lipid mediators are excreted during the refractory period. First, 16 subjects with mild stable asthma performed two repeated 4-min challenges with eucapnic voluntary hyperpnea (EVH) 1 and 3 h apart. There was a similar degree of refractoriness in both protocols (∼15% protection). The 1-h interval was too short to study mediator excretion because the urinary levels did not return to baseline before the second challenge. With the 3-h protocol, there was increased urinary excretion of cysteinyl-leukotrienes and metabolites of the mast cell product PGD2after both challenges. Next, another eight subjects performed two 6-min challenges with EVH 3 h apart, which produced a greater bronchoconstrictor response than the 4-min protocol (30.0 ± 5.4 vs. 17.7 ± 1.5%; P = 0.0029) and a greater degree of refractoriness (∼30%). Analysis by ultra-performance liquid chromatography triple quadrupole mass spectrometry confirmed excretion of the bronchoconstrictor cysteinyl-leukotrienes and PGD2during both challenges. In addition, there was increased excretion of the bronchoprotective PGE2, and also of the main metabolite of PGI2. This is the first report of excretion of PGE2and PGI2during the refractory period to EVH challenge, suggesting that they may mediate the refractoriness. Maintained excretion of PGD2and leukotriene E4following the repeat challenge argues against mast cell mediator depletion as the mechanism of refractoriness.
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| 9. |
- Busse, Christian, et al.
(author)
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Evaluation of the crystallographic fatigue crack growth rate in a single-crystal nickel-base superalloy
- 2019
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In: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 127, s. 259-267
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Journal article (peer-reviewed)abstract
- Cracks in single-crystal nickel-base superalloys have been observed to switch cracking mode from Mode I to crystallographic cracking. The crack propagation rate is usually higher on the crystallographic planes compared to Mode I, which is important to account for in crack growth life predictions. In this paper, a method to evaluate the crystallographic fatigue crack growth rate, based on a previously developed crystallographic crack driving force parameter, is presented. The crystallographic crack growth rate was determined by evaluating heat tints on the fracture surfaces of the test specimens from the experiments. Complicated crack geometries including multiple crystallographic crack fronts were modelled in a three dimensional finite element context, The data points of the crystallographic fatigue crack growth rate collapse on a narrow scatter band for the crystallographic cracks indicating a correlation with the previously developed crystallographic crack driving force.
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| 10. |
- Busse, Christian, 1989-, et al.
(author)
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Prediction of crystallographic cracking planes in single-crystal nickel-base superalloys
- 2018
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In: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 196, s. 206-223
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Journal article (peer-reviewed)abstract
- The inherent anisotropy of single-crystal nickel-base superalloys brings many difficulties in terms of modelling, evaluation and prediction of fatigue crack growth. Two models to predict on which crystallographic plane cracking will occur is presented. The models are based on anisotropic stress intensity factors resolved on crystallographic slip planes calculated in a three-dimensional finite-element context. The developed models have been compared to experiments on two different test specimen geometries. The results show that a correct prediction of the crystallographic cracking plane can be achieved. This knowledge is of great interest for the industry and academia to better understand and predict crack growth in single-crystal materials.
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| 11. |
- Ewest, D., et al.
(author)
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A modified compliance method for fatigue crack propagation applied on a single edge notch specimen
- 2016
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In: International Journal of Fatigue. - London : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 92, s. 61-70
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Journal article (peer-reviewed)abstract
- Crack length measurements with high accuracy are often difficult to achieve during fatigue crack propagation testing under non-isothermal conditions. In this work a modified approach to the compliance method defined in e.g. ASTM E647 is described, which is better suited for high loads, varying temperatures and for taking the scatter in Youngs modulus into account. A numerical finite element study is performed for a single edge notch specimen, to investigate the influence of initiation locations on the accuracy of the method. The change in cracked area versus change in stiffness for three different cases are numerically shown to collapse to one curve, i.e. the result is not significantly affected by how the crack is initiated. The numerical study is compared to results from two experiments using different materials, with heat tinting during the tests for extracting snapshots of the crack fronts. A good agreement between the experiments and the numerical study is shown. A new compliance curve and a new geometry function for the stress intensity factor is proposed for the single edge notch specimen. (C) 2016 Elsevier Ltd. All rights reserved.
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| 12. |
- Ewest, Daniel, et al.
(author)
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Fatigue crack propagation in a ductile superalloy at room temperature and extensive cyclic plastic flow
- 2015
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In: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 80, s. 40-49
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Journal article (peer-reviewed)abstract
- Fatigue crack propagation experiments under both force and displacement control have been performed on the wrought superalloy Haynes 230 at room temperature, using a single edge notched specimen. The force controlled tests are nominally elastic, and the displacement controlled tests have nominally large plastic hysteresis at the beginning of the tests, but saturates towards linear elastic conditions as the crack grows. As some tests are in the large scale yielding regime, a non-linear fracture mechanics approach is used to correlate crack growth rates versus the fracture parameter Delta J. It is shown that crack closure must be accounted for, to correctly model the crack growth seen in all the tests in a unified manner. For the force controlled small scale yielding tests the Newman crack closure model was used. The Newman equation is however not valid for large nominal cyclic plasticity, instead the crack closure in the displacement controlled tests is extracted from the test data. A good agreement between all tests is shown, when closure is accounted for and effective values of Delta J are used.
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| 13. |
- Ewest, Daniel, et al.
(author)
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Isothermal and thermomechanical fatigue crack propagation in both virgin and thermally aged Haynes 230
- 2019
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In: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 120, s. 96-106
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Journal article (peer-reviewed)abstract
- Fatigue crack propagation tests under both isothermal and non-isothermal thermomechanical fatigue conditions have been performed on wrought Haynes 230, a ductile combustor material. A number of specimens were thermally aged by pre-straining and subsequent furnace exposure for 3000 h at 600 degrees C. The tests were performed both under load and strain control, between room temperature and 600 degrees C. The thermally aged notched specimens show a decrease in the crack initiation life, similar to results previously reported for smooth test specimens at room temperature. For the crack growth rates, the effects of thermal ageing were less pronounced than for crack initiation. Further, the tests have been simulated using the finite element method to calculate the crack driving force, where the plasticity induced crack closure is handled with a full history description. A temperature dependent linear kinematic hardening plasticity law has been adopted for describing the material behaviour between room temperature and 600 degrees C. A post-processing tool was used in which the plasticity induced crack opening level was calculated, followed by a calculation of the effective Delta J range for each crack length. The adopted procedure yields good correlation between the different tests, under both isothermal and non-isothermal conditions.
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