| 1. |
- Patel, Riyaz S., et al.
(författare)
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Association of Chromosome 9p21 With Subsequent Coronary Heart Disease Events : A GENIUS-CHD Study of Individual Participant Data
- 2019
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Ingår i: Circulation. - 2574-8300. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Genetic variation at chromosome 9p21 is a recognized risk factor for coronary heart disease (CHD). However, its effect on disease progression and subsequent events is unclear, raising questions about its value for stratification of residual risk.METHODS: A variant at chromosome 9p21 (rs1333049) was tested for association with subsequent events during follow-up in 103 357 Europeans with established CHD at baseline from the GENIUS-CHD (Genetics of Subsequent Coronary Heart Disease) Consortium (73.1% male, mean age 62.9 years). The primary outcome, subsequent CHD death or myocardial infarction (CHD death/myocardial infarction), occurred in 13 040 of the 93 115 participants with available outcome data. Effect estimates were compared with case/control risk obtained from the CARDIoGRAMplusC4D consortium (Coronary Artery Disease Genome-wide Replication and Meta-analysis [CARDIoGRAM] plus The Coronary Artery Disease [C4D] Genetics) including 47 222 CHD cases and 122 264 controls free of CHD.RESULTS: Meta-analyses revealed no significant association between chromosome 9p21 and the primary outcome of CHD death/myocardial infarction among those with established CHD at baseline (GENIUSCHD odds ratio, 1.02; 95% CI, 0.99-1.05). This contrasted with a strong association in CARDIoGRAMPlusC4D odds ratio 1.20; 95% CI, 1.18-1.22; P for interaction < 0.001 compared with the GENIUS-CHD estimate. Similarly, no clear associations were identified for additional subsequent outcomes, including all-cause death, although we found a modest positive association between chromosome 9p21 and subsequent revascularization (odds ratio, 1.07; 95% CI, 1.04-1.09).CONCLUSIONS: In contrast to studies comparing individuals with CHD to disease-free controls, we found no clear association between genetic variation at chromosome 9p21 and risk of subsequent acute CHD events when all individuals had CHD at baseline. However, the association with subsequent revascularization may support the postulated mechanism of chromosome 9p21 for promoting atheroma development.
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| 2. |
- Bader, Thomas K., et al.
(författare)
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A nano to macroscale study on structure-mechanics relationships of archaeological oak
- 2013
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Ingår i: Journal of Cultural Heritage. - : Elsevier BV. - 1296-2074 .- 1778-3674. ; 14:5, s. 377-388
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical properties of wood at different length scales of its hierarchical structure are governed by structural and compositional properties on smaller length scales. This opens up the possibility to use microstructural data for estimating mechanical properties, which are difficult to assess by conventional, destructive testing but are nevertheless of high relevance for conservation practice. Herein, we investigate such microstructure-mechanics relationships for a particular example, namely the load bearing archaeological oak of the Oseberg Viking ship, displayed at the Viking Ship Museum in Oslo, Norway. In order to identify the effects of degradation on the mechanical behavior and their relations to the microstructure, recent oak specimens of different geographical origin (Norway and Austria) are investigated as well. Wood exhibits a cellular structure. Its cell walls are composed of an amorphous polymer matrix consisting of lignin and hemicelluloses and embedded, stiff cellulose fibers. At the cell level, experimental studies comprised microscopic investigations of the cellular structure, chemical analyses of the composition of the cell walls, as well as nanoindentation tests on single cell walls. The same samples were also analyzed on the macroscopic level, where additionally mass density and annual ring data were measured together with ultrasonic stiffnesses. The chemical data clearly indicate deterioration in the archaeological oak, affecting mainly hemicelluloses and amorphous cellulose. At the cell wall scale, however, this does not necessarily lead to a weaker material behavior. The nanoindentation modulus, as a measure of the cell wall stiffness, was found to even increase. This is counterintuitive to our understanding of the effects of chemical degradation. It might be due to possible modification of lignin in the Oseberg oak, and thus have a stronger effect on the indentation modulus than the concurrent weakening of the interfaces between the load-carrying cellulose fibers and the connecting cell wall matrix when analyzing wood at the microscopic level. A similar effect is also observed for the transversal stiffness of macroscopic samples, which increases. In tension-dominated loading modes, however, the degradation of the interfaces is the dominant effect, resulting for example in a considerable reduction of the macroscopic stiffness in longitudinal direction. This underlines the utmost relevance of the loading condition on the remaining load-carrying capacity of degraded wood. On the macroscale, effects of the geographical origin (i.e. growth conditions) on ring characteristics of the oak tissues override the effects of degradation on the mechanical behavior. They have to be carefully extracted in order to come up with conclusions on the effect of degradation from macroscopic test results. The identified microstructure-mechanics relationships provide the basis for–in further research steps–building mathematical models describing the relations between microstructural characteristics and macroscopic mechanical properties and, thereon, for structural analyses of historical wooden objects.
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| 3. |
- Wagner, Leopold, et al.
(författare)
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A combined view on composition, molecular structure, and micromechanics of fungal degraded softwood
- 2015
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 69:4, s. 471-482
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Tidskriftsartikel (refereegranskat)abstract
- Fungal decay alters the composition, microstructure, and mechanical properties of wood cell walls. To understand better the structure-function relationships during fungal decay, selected annual rings of fungal deteriorated Scots pine sapwood were analyzed in terms of their composition, microstructure, and micromechanical properties. The datasets were acquired separately for earlywood and latewood concerning the S2 cell wall layer and the cell corner middle lamella (CCML) and analyzed by means of principal component analysis and partial least squares regression analysis. Links between cell wall stiffness and hardness and the composition and microstructure could be established. Increased mechanical properties in the CCML, as obtained by nanoindentation, were correlated to the degradation of pectins. In the S2 layer, the altered data were related to the degradation of hemicelluloses and lignin modification during fungal decay.
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| 4. |
- Wagner, Leopold, et al.
(författare)
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Cell wall properties of softwood deteriorated by fungi: combined chemical analyses, FT-IR spectroscopy, nanoindentation and micromechanical modelling
- 2013
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Ingår i: Proceedings IRG Annual Meeting. - Stockholm : The International Research Group on Wood Protection.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mechanical properties of wood are determined by its inherent hierarchical microstructure, starting at the nanometer scale, where the elementary components cellulose, hemicelluloses, and lignin build up the wood cell wall material. Fungi cause degradation and decomposition of these components and, thus, alter the mechanical properties of wood. The aim of this study is to gain new insight into these relationships at the cell wall level, particularly at early stages of degradation, characterized by a mass loss of less than 10 %. Early detection of deterioration is essential during monitoring of timber structures as it may help avoiding subsequent larger scale damages. This contribution presents results of an ambitious experimental programme covering the determination of earlywood/latewood specific compositional data with consistent microstructural and micromechanical properties. Scots pine (Pinus sylvestris L.) sapwood was studied in reference condition and after degradation by brown rot (Gloeophyllum trabeum) and white rot (Trametes versicolor), respectively. Ultrastructural and compositional data were acquired by means of FT-IR spectroscopy and wet chemical analyses. Micro-structural features, such as the microfibril angle, were determined by X-ray diffraction. Mechanical properties of sound and degraded wood cell walls were determined using nanoindentation, yielding the (anisotropic) indentation modulus of the S2 cell wall layer and the cell corner middle lamella of Scots pine tracheids. Aiming at the identification of relationships between ultrastructural and micromechanical characteristics, two different approaches were followed. On the one hand, multivariate data analysis was applied. On the other hand, a multiscale micromechanical model was used to derive causal relationships between structure and (mechanical) function for deteriorated wood. Anisotropic indentation theory allows calculating model predictions for the indentation modulus of the S2 cell wall layer based on measured chemical compositions resulting from the degradation process. Comparing these predictions with the experimental results enables to test hypotheses on possible scenarios of wood cell wall deterioration during fungal attack. Identified relationships between ultrastructural, microstructural, and micromechanical characteristics will be discussed as well as the potential of micromechanical modelling in the analysis of fungal degradation strategies and their effect on the mechanical behaviour.
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| 5. |
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| 7. |
- Bader, Thomas K., et al.
(författare)
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Micromechanical modeling of Common yew and Norway spruce
- 2013
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Ingår i: Proceedings in Applied Mathematics and Mechanics. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1617-7061. ; 13:1, s. 185-186
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, a micromechanical modeling approach in the framework of poromechanics is adopted to study structure-stiffness relations of two quite different species, namely spruce and yew, in detail. In particular, microstructural specialties of yew and spruce are assessed. A dominant influence of the cellulose content and its orientation on the stiffness of the cell wall is revealed, while on the macroscopic scale, density is found to be the governing microstructural characteristic for elastic properties.
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| 8. |
- Bader, Thomas K., 1980-, et al.
(författare)
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Micromechanical Modeling of Wood : Multiscale Modeling and Model Validation
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to its natural origin and its inherent heterogeneities, mechanical properties of wood are highlyanisotropic and show a broad variability, not only between different wood species, but also within a tree [1].Similar to other biological materials, the wood microstructure is well organized and hierarchically structuredfrom the annual rings visible to the naked eye down to the wood polymers cellulose, hemicellulose, andlignin at the nanometer-scale. The aim of the research conducted at the Institute for Mechanics of Materialsand Structures is a deeper understanding of the role of different hierarchical levels and their correspondingphysical and chemical characteristics in relation to mechanical properties of softwood and hardwood. This isachieved by means of micromechanical modeling and experimental analyses at various length scales.A micromechanical model provides the opportunity to predict poroelastic properties of softwood andhardwood tissues at different hierarchical levels from microstructural and compositional data [1,2]. Thehierarchical organization of wood is mathematically represented in a multiscale model. Effective poroelasticproperties are predicted by means of continuum micromechanical approaches (self-consistent method andMori-Tanaka method), the unit cell method, and laminate theory. These approaches are extended to accountfor water-induced eigenstresses within representative volume elements and repetitive unit cells, which aresubsequently upscaled to the macroscopic wood level.Verification of the micromechanical model for softwood and hardwood with a comprehensive experimentaldataset, shows that it suitably predicts elastic properties at different length scales under the assumption ofundrained conditions [3,4]. Moreover, Biot tensors, expressing how much of the cell wall water-induced porepressure is transferred to the boundary of an overall deformation-free representative volume element (RVE),and Biot moduli, expressing the porosity changes invoked by a pore pressure within such an RVE can bestudied at different length scales. Consequently, the relevance and the contribution of specificmicrostructural characteristics to the load transfer and the deformation characteristics in case of moisturechanges in wood can be studied. Besides the scientific interest in structure-function-relationships, theseinvestigations are motivated by the growing importance of wood as building material.
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| 9. |
- Bader, Thomas K., 1980-, et al.
(författare)
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Poroelastic properties of hardwood at different length scales
- 2013
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Ingår i: Poromechanics V. - Reston : American Society of Civil Engineers (ASCE). - 9780784412992 ; , s. 1830-1836
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Hardwoods show a very complex, hierarchically organized microstructure. Slight structural differences at various length scales bring about a huge variety of hardwood species. This motivates the development of a micromechanical model for hardwood. Since differences in the microstructure of the material can be considered in the model, it offers the opportunity to explain the variability of mechanical properties of the whole class of hardwood. The micromechanical model is formulated in the framework of poroelasticity. In this contribution, poroelastic properties at different length scales of the material are discussed. Validation of the micromechanical model is based on an extensive experimental database covering elastic properties and microstructural characteristics of different temperate and tropical hardwood species. Exemplary parameter studies demonstrate the ability of the model to study the contribution of specific microstructural characteristics to the load transfer and the deformation characteristics of wood.
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| 10. |
- Bader, Thomas K., et al.
(författare)
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Shear stiffness and its relation to the microstructure of 10 European and tropical hardwood species
- 2017
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 12:2, s. 82-91
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Tidskriftsartikel (refereegranskat)abstract
- In this study, shear stiffness properties of 10 different hardwood species and their relation to the corresponding species-specific microstructure are investigated. For this purpose, shear stiffness of 10 different hardwood species is experimentally measured by means of ultrasonic testing. In addition, a micromechanical model for hardwood is applied in order to illustrate the influence of certain microstructural characteristics such as mass density and volume fractions of vessels and ray cells on the shear stiffness. Comprehensive microstructural and mechanical data from previous investigations of the same hardwood material support the interpretation of the microstructure–shear stiffness relationships. Mass density was confirmed to be the dominant microstructural characteristic for shear stiffness. Also, ultrasound shear wave propagation velocity increases with density, particularly in the radial-tangential (RT) plane. In addition to density, comparably higher shear stiffness GLR can be explained by comparably higher ray content and lower vessel content. As for GLT, a ring porous structure seems to lead to higher shear stiffness as compared to a diffuse porous structure. For this shear stiffness, vessel and ray content were found to have a less impact. Also, the rolling shear stiffness GRT was found to be higher for a diffuse porous structure than for a ring porous one. Moreover, the data supports that ray cells act as reinforcements in the RT plane and lead to higher GRT
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