| 1. |
- Tabassum, R, et al.
(författare)
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Genetic architecture of human plasma lipidome and its link to cardiovascular disease
- 2019
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1, s. 4329-
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Tidskriftsartikel (refereegranskat)abstract
- Understanding genetic architecture of plasma lipidome could provide better insights into lipid metabolism and its link to cardiovascular diseases (CVDs). Here, we perform genome-wide association analyses of 141 lipid species (n = 2,181 individuals), followed by phenome-wide scans with 25 CVD related phenotypes (n = 511,700 individuals). We identify 35 lipid-species-associated loci (P <5 ×10−8), 10 of which associate with CVD risk including five new loci-COL5A1, GLTPD2, SPTLC3, MBOAT7 and GALNT16 (false discovery rate<0.05). We identify loci for lipid species that are shown to predict CVD e.g., SPTLC3 for CER(d18:1/24:1). We show that lipoprotein lipase (LPL) may more efficiently hydrolyze medium length triacylglycerides (TAGs) than others. Polyunsaturated lipids have highest heritability and genetic correlations, suggesting considerable genetic regulation at fatty acids levels. We find low genetic correlations between traditional lipids and lipid species. Our results show that lipidomic profiles capture information beyond traditional lipids and identify genetic variants modifying lipid levels and risk of CVD.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Rivas, Manuel A., et al.
(författare)
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A protein-truncating R179X variant in RNF186 confers protection against ulcerative colitis
- 2016
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Ingår i: Nature Communications. - London, United Kingdom : Nature Publishing Group. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Protein-truncating variants protective against human disease provide in vivo validation of therapeutic targets. Here we used targeted sequencing to conduct a search for protein-truncating variants conferring protection against inflammatory bowel disease exploiting knowledge of common variants associated with the same disease. Through replication genotyping and imputation we found that a predicted protein-truncating variant (rs36095412, p.R179X, genotyped in 11,148 ulcerative colitis patients and 295,446 controls, MAF=up to 0.78%) in RNF186, a single-exon ring finger E3 ligase with strong colonic expression, protects against ulcerative colitis (overall P=6.89 × 10(-7), odds ratio=0.30). We further demonstrate that the truncated protein exhibits reduced expression and altered subcellular localization, suggesting the protective mechanism may reside in the loss of an interaction or function via mislocalization and/or loss of an essential transmembrane domain.
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| 6. |
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| 7. |
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| 8. |
- Baud, Patrick, et al.
(författare)
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The Brittle-Ductile Transition in Porous Limestone : Failure Mode, Constitutive Modeling of Inelastic Deformation and Strain Localization
- 2021
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Ingår i: Journal of Geophysical Research: Solid Earth. - 2169-9313. ; 126:5
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of the mechanics of the brittle-ductile transition (BDT) in porous limestone is significantly more challenging than for sandstone because of the lack of consistent acoustic emission activity in limestone, meaning that one must rely on alternative techniques. In this paper, we investigate systematically the failure modes in Indiana limestone using X-ray microComputed Tomography imaging (μCT) and Digital Volume Correlation (DVC). Our new mechanical data show that the envelope for the onset of shear-enhanced compaction can be well approximated by an elliptical cap. The DVC analysis revealed the development of shear bands through the BDT, but no evidence of compaction bands. The shear band angles were between 29° and 46° with respect to the maximum principal stress. Compiling these new results with published data on Purbeck and Leitha limestones, we showed that inelastic compaction in each of these dual porosity allochemical limestones was in a good agreement with the normality condition, as defined in plasticity theory. Comparison of the observed failure modes with predictions based on bifurcation analysis showed that the shear band angles are consistently smaller than the theoretical predictions.
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| 9. |
- Baud, Patrick, et al.
(författare)
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The Brittle-Ductile Transition in Porous Limestone Imaged by X-Ray Computed Tomography and Digital Image Correlation
- 2017
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Ingår i: Poromechanics 2017 - Proceedings of the 6th Biot Conference on Poromechanics. - Reston, VA : American Society of Civil Engineers. - 9780784480779 ; , s. 1782-1788
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Konferensbidrag (refereegranskat)abstract
- We studied the brittle-ductile transition in three porous carbonates, Indiana, USA, Majella, Italy, and Leitha, Austria, with porosity ranging between 16 and 31%. A series of triaxial experiments were performed at room temperature, constant strain rate, and at effective pressures ranging from 5 to 150 MPa. Several sets of X-ray Tomography images were acquired before and after deformation. 3D digital image correlation (DIC) was performed on the images of the intact and deformed samples. The use of 3D-volumetric DIC allowed us to map out the subtle development of strain localization associated with the transition from brittle faulting to cataclastic flow in the three limestones. Our observations showed that strain localization may develop at relatively small axial strains of ~1%, in both the brittle faulting and transitional regimes. In Majella limestone (porosity = 31%), the localized deformation involved both shear and compaction. Compaction bands were only observed in less cemented samples of Leitha limestone.
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| 10. |
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| 11. |
- Darmawan, Herlan, et al.
(författare)
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Hidden mechanical weaknesses within lava domes provided by buried high-porosity hydrothermal alteration zones
- 2022
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Catastrophic lava dome collapse is considered an unpredictable volcanic hazard because the physical properties, stress conditions, and internal structure of lava domes are not well understood and can change rapidly through time. To explain the locations of dome instabilities at Merapi volcano, Indonesia, we combined geochemical and mineralogical analyses, rock physical property measurements, drone-based photogrammetry, and geoinformatics. We show that a horseshoe-shaped alteration zone that formed in 2014 was subsequently buried by renewed lava extrusion in 2018. Drone data, as well as geomechanical, mineralogical, and oxygen isotope data suggest that this zone is characterized by high-porosity hydrothermally altered materials that are mechanically weak. We additionally show that the new lava dome is currently collapsing along this now-hidden weak alteration zone, highlighting that a detailed understanding of dome architecture, made possible using the monitoring techniques employed here, is essential for assessing hazards associated with dome and edifice failure at volcanoes worldwide.
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| 12. |
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| 13. |
- Harnett, Claire E., et al.
(författare)
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Large-scale lava dome fracturing as a result of concealed weakened zones
- 2022
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Ingår i: Geology. - : Geological Society of America. - 0091-7613 .- 1943-2682. ; 50:12, s. 1346-1350
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Tidskriftsartikel (refereegranskat)abstract
- Mechanically weakened alteration zones in lava domes are thought to jeopardize their stability. Such zones can be hazardous when concealed within the dome, either because they formed by subsurface hydrothermal circulation or because they formed on the surface but were subsequently buried by renewed lava extrusion. We present a new suite of computa-tional models showing how the size and position of a weakened brittle zone within a dome can affect large-scale fracture formation, displacement, and the collapse mechanism. By combining recent laboratory data for the mechanical behavior of dome rocks with discrete element method models, we show (1) the presence of a weak zone increases instability, which is exacerbated when the size of the zone increases or the zone is positioned off-center; (2) the position of the weak zone changes the deformation mechanism from slumping-type slope de-formation when the zone is positioned centrally, compared with deep-seated rotational slope failure when the zone is positioned toward the dome flank; and finally, (3) dome-cutting tensile fractures form in the presence of a small weak zone (60 m diameter, -14% of dome width), whereas large weak zones (120 m diameter, -27% of dome width) promote the formation of longer and deeper fractures that jeopardize larger dome volumes. Our results corroborate previous field observations at lava domes and indicate that large fracture formation, which greatly influences dome stability and outgassing, can be explained by the presence of con-cealed alteration zones. This improved understanding of the mechanisms responsible for dome instability enables better hazard assessment at volcanoes worldwide.
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| 14. |
- Heap, Graham A., et al.
(författare)
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HLA-DQA1-HLA-DRB1 variants confer susceptibility to pancreatitis induced by thiopurine immunosuppressants
- 2014
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 46:10, s. 1131-1134
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatitis occurs in approximately 4% of patients treated with the thiopurines azathioprine or mercaptopurine. Its development is unpredictable and almost always leads to drug withdrawal. We identified patients with inflammatory bowel disease (IBD) who had developed pancreatitis within 3 months of starting these drugs from 168 sites around the world. After detailed case adjudication, we performed a genome-wide association study on 172 cases and 2,035 controls with IBD. We identified strong evidence of association within the class II HLA region, with the most significant association identified at rs2647087 (odds ratio 2.59, 95% confidence interval 2.07-3.26, P = 2 x 10(-16)). We replicated these findings in an independent set of 78 cases and 472 controls with IBD matched for drug exposure. Fine mapping of the H LA region identified association with the HLA-DQA1*02:01-HLA-DRB1*07:01 haplotype. Patients heterozygous at rs2647087 have a 9% risk of developing pancreatitis after administration of a thiopurine, whereas homozygotes have a 17% risk.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Heap, Michael J., et al.
(författare)
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Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behaviour
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Dome-forming volcanoes are among the most hazardous volcanoes on Earth. Magmatic outgassing can be hindered if the permeability of a lava dome is reduced, promoting pore pressure augmentation and explosive behaviour. Laboratory data show that acid-sulphate alteration, common to volcanoes worldwide, can reduce the permeability on the sample lengthscale by up to four orders of magnitude and is the result of pore- and microfracture-filling mineral precipitation. Calculations using these data demonstrate that intense alteration can reduce the equivalent permeability of a dome by two orders of magnitude, which we show using numerical modelling to be sufficient to increase pore pressure. The fragmentation criterion shows that the predicted pore pressure increase is capable of fragmenting the majority of dome-forming materials, thus promoting explosive volcanism. It is crucial that hydrothermal alteration, which develops over months to years, is monitored at dome-forming volcanoes and is incorporated into real-time hazard assessments.
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| 19. |
- Heap, Michael J., et al.
(författare)
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Imaging strain localisation in porous andesite using digital volume correlation
- 2020
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 404
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Tidskriftsartikel (refereegranskat)abstract
- Strain localisation structures, such as shear fractures and compaction bands, are of importance due to their influence on permeability and therefore outgassing, a factor thought to influence eruptive style. In this study, we aim to develop a better understanding of strain localisation in porous volcanic rocks using X-ray tomographic images of samples of porous andesite (porosity = 0.26) acquired before and after deformation in the brittle and ductile regimes. These 3D images have been first analysed to provide 3D images of the porosity structure within the undeformed andesite, which consists of a large, well-connected porosity backbone alongside many smaller pores that are either isolated or connected to the porosity backbone by thin microstructural elements (e.g., microcracks). Following deformation, porosity profiles of the samples show localised dilation (porosity increase) and compaction (porosity reduction) within the samples deformed in the brittle and ductile regimes, respectively. Digital volume correlation (DVC) of the images before and after triaxial deformation was used to quantify the tensor strain fields, and the incremental divergence (volumetric strain) and curl (used as an indicator of shear strain) of the displacement fields were calculated from the DVC. These fields show that strain localisation in the sample deformed in the brittle regime manifested as a ~ 1 mm-wide, dilatational shear fracture oriented at an angle of 40–45° to the maximum principal stress. Pre- and post-deformation permeability measurements show that permeability of the sample deformed in the brittle regime increased from 3.9 × 10−12 to 4.9 × 10−12 m2, which is presumed to be related to the shear fracture. For the sample deformed in the ductile regime, strain localised into ~1 mm-thick, undulating compaction bands orientated sub-perpendicular to the maximum principal stress with little evidence of shear. Taken together, our data suggest that these bands formed during large stress drops seen in the mechanical data, within high-porosity zones within the sample, and within the large, well-connected porosity backbone. Pre- and post-deformation permeability measurements indicate that inelastic compaction decreased the permeability of the sample by a factor of ~3. The data of this study assist in the understanding of strain localisation in porous volcanic rocks, its influence on permeability (and therefore volcanic outgassing), and highlight an important role for DVC in studying strain localisation in volcanic materials.
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| 20. |
- Heap, Michael J., et al.
(författare)
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The tensile strength of hydrothermally altered volcanic rocks
- 2022
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 428
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Tidskriftsartikel (refereegranskat)abstract
- The tensile strength of volcanic rocks is an important parameter for understanding and modelling a wide range of volcanic processes, and in the development of strategies designed to optimise energy production in volcanic geothermal reservoirs. However, despite the near-ubiquity of hydrothermal alteration at volcanic and geothermal systems, values of tensile strength for hydrothermally altered volcanic rocks are sparse. Here, we present an experimental study in which we measured the tensile strength of variably altered volcanic rocks. The alteration of these rocks, quantified as the weight percentage of secondary (alteration) minerals, varied from 6 to 62.8 wt%. Our data show that tensile strength decreases as a function of porosity, in agreement with previous studies, and as a function of alteration. We fit existing theoretical constitutive models to our data so that tensile strength can be estimated for a given porosity, and we provide a transformation of these models such that they are a function of alteration. However, because porosity and alteration influence each other, it is challenging to untangle their individual contributions to the measured reduction in tensile strength. Our new data and previously published data suggest that porosity exerts a first-order role on the tensile strength of volcanic rocks. Based on our data and observations, we also suggest that (1) alteration likely decreases tensile strength if associated with mineral dissolution, weak secondary minerals (such as clays), and an increase in microstructural heterogeneity and (2) alteration likely increases tensile strength if associated with pore- and crack-filling mineral precipitation. Therefore, we conclude that both alteration intensity and alteration type likely influence tensile strength. To highlight the implications of our findings, we provide discrete element method modelling which shows that, following the pressurisation of a dyke, the damage within weak hydrothermally altered host-rock is greater and more widespread than for strong hydrothermally altered host-rock. Because the rocks in volcanic and geothermal settings are likely to be altered, our results suggest that future modelling should consider the tensile strength of hydrothermally altered volcanic rocks.
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| 21. |
- Heap, Michael J., et al.
(författare)
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The tensile strength of volcanic rocks : Experiments and models
- 2021
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 418
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Tidskriftsartikel (refereegranskat)abstract
- The tensile strength of volcanic rock exerts control over several key volcanic processes, including fragmentation and magma chamber rupture. Despite its importance, there is a paucity of laboratory data for the tensile strength of volcanic rocks, leading to an incomplete understanding of the influence of microstructural parameters, such as pore size and shape (factors that vary widely for volcanic rocks), on their tensile strength. To circumvent problems associated with the variability of natural samples, we provide here a systematic study in which we use elastic damage mechanics code "Rock Failure Process Analysis" to perform numerical experiments to better understand the influence of porosity, pore diameter, pore aspect ratio, and pore orientation on the tensile strength of volcanic rocks. We find that porosity and pore diameter exert a first-order control on the tensile strength of volcanic rocks, and that pore aspect ratio and orientation also influence tensile strength. Tensile strength is reduced by up to a factor of two as porosity is increased from 0.05 to 0.35 or as pore diameter is increased from 1 to 2 mm. Small, but systematic, reductions in tensile strength are observed as the angle between the loading direction and the major axis of an elliptical pore is increased from 0 to 90 degrees. The influence of pore aspect ratio (the ratio of the minor to major axis of an ellipse) depends on the pore angle: when the pore angle is 0 degrees, a decrease in pore aspect ratio, from 1 (a circle) to 0.2, increases the tensile strength, whereas the same decrease in pore aspect ratio does not substantially change the tensile strength when the pore angle is 90 degrees. These latter numerical experiments show that the tensile strength of volcanic rocks can be anisotropic. Our numerical data are in broad agreement with new and compiled experimental data for the tensile strength of volcanic rocks. One of the goals of this contribution is to provide better constrained constitutive models for the tensile strength of volcanic rocks for use in volcano modelling. To this end, we present a series of theoretical and semi-empirical constitutive models that can be used to determine the tensile strength of volcanic rocks, and highlight how tensile strength estimations can influence predictions of magma overpressures and assessments of the volume and radius of a magma chamber. (c) 2021 Elsevier B.V. All rights reserved.
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| 22. |
- Heap, Michael J., et al.
(författare)
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The thermal properties of porous andesite
- 2020
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Ingår i: Journal of Volcanology and Geothermal Research. - : ELSEVIER. - 0377-0273 .- 1872-6097. ; 398
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Tidskriftsartikel (refereegranskat)abstract
- The thermal properties of volcanic rocks are crucial to accurately model heat transfer in volcanoes and in geothermal systems located within volcanic deposits. Here we provide laboratory measurements of thermal conductivity and thermal diffusivity for variably porous andesites from Mt. Ruapehu (New Zealand) and variably altered basaltic-andesites from Merapi volcano (Indonesia) measured at ambient laboratory pressure and temperature using the transient hot-strip method. The specific heat capacity of each sample was then calculated using these measured values and the bulk sample density. Thermal conductivity and thermal diffusivity decrease as a function of increasing porosity, but specific heat capacity does not vary systematically with porosity. For a given porosity, saturation with water increases thermal conductivity and specific heat capacity, but decreases thermal diffusivity. Measurements on samples from Merapi volcano show that, compared to the unaltered samples from Mt. Ruapehu, hydrothermal alteration deceases thermal conductivity and thermal diffusivity, and increases specific heat capacity. We use an effective medium approach to parameterise these data, showing that when the porosity and pore-fluid properties are scaled for, the measured values agree well with theoretical predictions. We find that despite the microstructural complexity of the studied andesites, porosity is the principal parameter dictating their thermal properties. To understand whether the measured changes in thermal properties are sufficient to influence natural processes, we model heat transfer from magma to the surrounding host-rock by solving Fick's second law cast in 1D Cartesian (dyke geometry) and cylindrical (conduit geometry) coordinates. We provide models for different host-rock porosities (0-0.6), different initial magmatic temperatures (800-1200 degrees C), and different levels of host-rock alteration. Our modelling shows how the cooling of a dyke and conduit is slowed by a higher host-rock porosity and by increased hydrothermal alteration. The thermal properties provided herein can help improve modelling designed to inform on volcanic and geothermal processes. (C) 2020 Elsevier B.V. All rights reserved.
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| 23. |
- Heap, Michael J., et al.
(författare)
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Whole-rock oxygen isotope ratios as a proxy for the strength and stiffness of hydrothermally altered volcanic rocks
- 2022
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Ingår i: Bulletin of Volcanology. - : Springer Nature. - 0258-8900 .- 1432-0819. ; 84:8
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Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal alteration is considered to increase the likelihood of dome or flank collapse by compromising stability. Understanding how such alteration influences rock properties, and providing independent metrics for alteration that can be used to estimate these parameters, is therefore important to better assess volcanic hazards and mitigate risk. We explore the possibility of using whole-rock delta O-18 and delta D values and water contents, metrics that can potentially track alteration, to estimate the strength (compressive and tensile) and Young's modulus (i.e. "stiffness") of altered (acid-sulphate) volcanic rocks from La Soufriere de Guadeloupe (Eastern Caribbean). The delta O-18 values range from 5.8 to 13.2 parts per thousand, delta D values from - 151 to - 44 parts per thousand, and water content from 0.3 to 5.1 wt%. We find that there is a good correlation between delta O-18 values and laboratory-measured strength and Young's modulus, but that these parameters do not vary systematically with delta D or water content (likely due to their pre-treatment at 200 degrees C). Empirical linear relationships that allow strength and Young's modulus to be estimated using delta O-18 values are provided using our new data and published data for Merapi volcano (Indonesia). Our study highlights that delta O-18 values can be used to estimate the strength and Young's modulus of volcanic rocks, and could therefore be used to provide parameters for volcano stability modelling. One advantage of this technique is that delta O-18 only requires a small amount of material, and can therefore provide rock property estimates in scenarios where material is limited, such as borehole cuttings or when sampling large blocks is impracticable.
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| 24. |
- Jun, B, et al.
(författare)
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Elovanoids are novel cell-specific lipid mediators necessary for neuroprotective signaling for photoreceptor cell integrity
- 2017
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Ingår i: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1, s. 5279-
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Tidskriftsartikel (refereegranskat)abstract
- Docosahexaenoic acid (DHA, 22:6 n-3) is abundant in the retina and is enzymatically converted into pro-homeostatic docosanoids. The DHA- or eicosapentaenoic acid (EPA)-derived 26 carbon fatty acid is a substrate of elongase ELOVL4, which is expressed in photoreceptor cells and generates very long chain (≥C28) polyunsaturated fatty acids including n-3 (VLC-PUFAs,n-3). While ELOVL4 mutations are linked to vision loss and neuronal dysfunctions, the roles of VLC-PUFAs remain unknown. Here we report a novel class of lipid mediators biosynthesized in human retinal pigment epithelial (RPE) cells that are oxygenated derivatives of VLC-PUFAs,n-3; we termed these mediators elovanoids (ELV). ELVs have structures reminiscent of docosanoids but with different physicochemical properties and alternatively-regulated biosynthetic pathways. The structures, stereochemistry, and bioactivity of ELVs were determined using synthetic materials produced by stereo-controlled chemical synthesis. ELVs enhance expression of pro-survival proteins in cells undergoing uncompensated oxidative stress. Our findings unveil a novel autocrine/paracrine pro-homeostatic RPE cell signaling that aims to sustain photoreceptor cell integrity and reveal potential therapeutic targets for retinal degenerations.
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| 25. |
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| 26. |
- Kurzawa-Akanbi, M., et al.
(författare)
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Altered ceramide metabolism is a feature in the extracellular vesicle-mediated spread of alpha-synuclein in Lewy body disorders
- 2021
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Ingår i: Acta Neuropathologica. - : Springer Science and Business Media LLC. - 0001-6322 .- 1432-0533. ; 142, s. 961-984
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Tidskriftsartikel (refereegranskat)abstract
- Mutations in glucocerebrosidase (GBA) are the most prevalent genetic risk factor for Lewy body disorders (LBD)-collectively Parkinson's disease, Parkinson's disease dementia and dementia with Lewy bodies. Despite this genetic association, it remains unclear how GBA mutations increase susceptibility to develop LBD. We investigated relationships between LBD-specific glucocerebrosidase deficits, GBA-related pathways, and alpha-synuclein levels in brain tissue from LBD and controls, with and without GBA mutations. We show that LBD is characterised by altered sphingolipid metabolism with prominent elevation of ceramide species, regardless of GBA mutations. Since extracellular vesicles (EV) could be involved in LBD pathogenesis by spreading disease-linked lipids and proteins, we investigated EV derived from post-mortem cerebrospinal fluid (CSF) and brain tissue from GBA mutation carriers and non-carriers. EV purified from LBD CSF and frontal cortex were heavily loaded with ceramides and neurodegeneration-linked proteins including alpha-synuclein and tau. Our in vitro studies demonstrate that LBD EV constitute a "pathological package" capable of inducing aggregation of wild-type alpha-synuclein, mediated through a combination of alpha-synuclein-ceramide interaction and the presence of pathological forms of alpha-synuclein. Together, our findings indicate that abnormalities in ceramide metabolism are a feature of LBD, constituting a promising source of biomarkers, and that GBA mutations likely accelerate the pathological process occurring in sporadic LBD through endolysosomal deficiency.
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| 27. |
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| 28. |
- Witcher, Taylor, et al.
(författare)
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Development of permeable networks by viscous-brittle deformation in a shallow rhyolite intrusion. Part 1: Field evidence
- 2024
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 454
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Tidskriftsartikel (refereegranskat)abstract
- Efficient outgassing of shallow magma bodies reduces the risk of explosive eruption. Silica-rich magmas are too viscous for exsolved gas bubbles to escape the system through buoyant forces alone, and so volatile overpressure is often released through deformation-related processes. Here we present a case study on magma-emplacement-related deformation in a shallow (500 m depth) rhyolite intrusion (the Sandfell laccolith, Eastern Iceland) to investigate the establishment and evolution of degassing and outgassing networks in silicic sub-volcanic intrusions. We observe viscous and brittle deformation features: from vesiculated flow bands that organized into 'pore channels' in the ductile regime, to uniform bands of tensile fractures (‘fracture bands’) that grade into breccia and gouge in the brittle regime. Through field mapping, structural analysis, and anisotropy of magnetic susceptibility (AMS), we show that the deformation spectrum, observed all over the laccolith, represents stages of degassing (viscous processes) and outgassing (brittle processes) that resulted in the formation of interconnected permeable networks through the growth and linkage of fracture bands. Areas with concentrations of higher degrees of brittle deformation are proximal to abruptly changing AMS fabrics and point to laccolith-scale strain partitioning in the magma linked to different stages of laccolith growth. The establishment of intrusion-scale permeable networks through the cumulation of discrete magma fractures would have profoundly assisted the outgassing of the entire laccolith. Therefore, fracture banding captures viscous and brittle processes working in tandem as an efficient outgassing mechanism, and should be considered in sub-volcanic intrusions elsewhere.
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| 29. |
- Witcher, Taylor, et al.
(författare)
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Development of permeable networks by viscous-brittle deformation in a shallow rhyolite intrusion. Part 2: Microstructural analysis
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Volcanic and magmatic outgassing mechanisms can determine eruptive behavior of shallow silicic magma bodies. Most outgassing mechanisms proposed take place along conduit margins, where highest strain rates drive ascending magma to brittle failure. However, these mechanisms do not account for outgassing large volumes of magma away from the conduit walls. Here, we present a continuum of porosity preserved in the microcrystalline rhyolitic Sandfell laccolith, Eastern Iceland. Three stages in the continuum are described: porous flow bands, pore channels, and fracture bands. These deformation features are present throughout the entire exposed volume of the Sandfell laccolith in meter-long band geometries, ranging from mm- to dm-scale thickness, and interlayered with coherent, undeformed rhyolite. Using microstructural analytical methods, we show that emplacement-related deformation induced strain partitioning around a crystal content of 45% that resulted in the segregation of melt-rich and melt-poorer flow bands. Subsequent deformation induced by continued magma emplacement caused strain partitioning in the melt-rich flow bands. Depending on strain rate, different types of deformation features developed, through dilation or porosity redistribution (porous flow bands), cavitation (pore channels), or tensile fracture (fracture bands). Porous flow bands have permeability values ~4 orders of magnitude higher than undeformed rhyolite. Pore channels and fracture bands have much larger length scales, and so permeability increase dramatically in those systems. Hence, the abundance and interconnectivity of deformation features preserved in the Sandfell laccolith provided an efficient outgassing mechanism for the bulk of the intrusion. Outgassing due to viscous-brittle magma deformation during magma emplacement should therefore be considered for crystal-rich magmas, e.g., during effusive lava dome extrusion.
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| 30. |
- Witcher, Taylor, et al.
(författare)
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Experimentally produced shear fabrics in partially melted rhyolite
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The rheology of magma largely dictates its ability to release pressurized volatiles through outgassing. Degree of outgassing governs explosive potential of silicic magma in the shallow crust. Rheological studies have been conducted to constrain the outgassing mechanisms in magmas with one, two, or three phases (pure melt, crystal or bubble suspensions, and crystal and bubble suspensions). While synthetic materials reduce uncertainties of results, applying the same methods to natural material allows for comparison to deformation textures preserved in nature. Here we deform natural rhyolite from the Sandfell laccolith, Eastern Iceland in torsion, in an attempt to recreate tensile fracture arrays that have previously been created on synthetic HPG8 melt by the same method. We used a Paterson-type torsion apparatus to deform partially melted (3-phase) rhyolite at 900 and 850 degrees C at controlled twist-rates (constant strain rate). We performed 9 successful experiments at strain rates between 2.92 x 10-5 and 1.87 x 10-3 s-1 and reaching a final strain of ~1. Mechanical results show steady-state viscous deformation took place in all experiments, with apparent viscosity decreasing and maximum stress generally increasing with increasing strain rate. Preliminary sample imaging has shown strain partitioning between bubbly melt and ‘stiff’ clusters of microlites, and approximate crystal and bubble fractions of 0.26 and 0.03, respectively. We compared our results to rheological models of crystal suspensions, and crystal + bubble suspensions. Relative viscosity is higher than crystal suspension models at 0.26 crystal fraction, which may be explained by the influence of bubbles. The microlite clusters ‘rolling’ through melt channels may have also contributed to the apparent viscosity being higher than expected at 0.26 crystal fraction. We propose future work to simulate natural rhyolite fracturing by lowering deformation temperature to increase melt viscosity, increasing crystal fraction, and running experiments to higher final strain values.
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| 31. |
- Witcher, Taylor, et al.
(författare)
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Metal liberation by magma fracturing
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Demand for metals is increasing with the advancement of technology. Silicic magmas contain metals of interest in trace quantities which need to be released from the magma and concentrated by many orders of magnitude to form economically viable mineral deposits. Mechanisms that can act on such large volumes of magma and allow metal-rich fluids to move through the magma are keenly debated. Here we present evidence from the Sandfell laccolith, an exposed rhyolitic magmatic intrusion in Eastern Iceland. Sandfell hosts a rarely-preserved magmatic fracture network that contains extensive mineralization of hydrous Fe-silicates, hydrous Mn-oxides, and La-oxides. The bands of tensile fractures are pervasive throughout the exposed intrusion and have, remarkably, survived 11 Ma of weathering processes post-emplacement. Their excellent preservation and exposure have allowed the first thorough documentation of what role magmatic fractures play in a metal-partitioning process. We propose that small-scale yet extensive fracturing of silicic magma during emplacement provides essential pathways for vapor-rich volatiles to decouple fluid-mobile elements from the melt, and sufficiently localize them for later transport into high-grade veins. Understanding the processes behind metal partitioning and fluid transport in the magmatic environment will increase the efficiency of mineral exploration, contribute to geothermal applications, and shed light on degassing mechanisms occurring at depth under active and hazardous volcanoes today.
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