Creep in oak material from the Vasa ship: verification of linear viscoelasticity and identification of stress thresholds

Creep deformation is a general problem for large wooden structures, and in particular for shipwrecks in museums. In this study, experimental creep data on the wooden cubic samples from the Vasa ship have been analysed to confirm the linearity of the viscoelastic response in the directions where creep was detectable (T and R directions). Isochronous stress-strain curves were derived for relevant uniaxial compressive stresses within reasonable time spans. These curves and the associated creep compliance values justify that it is reasonable to assume a linear viscoelastic behaviour within the tested ranges, given the high degree of general variability. Furthermore, the creep curves were fitted with a one-dimensional standard linear solid model, and although the rheological parameters show a fair amount of scatter, they are candidates as input parameters in a numerical model to predict creep deformations. The isochronous stress-strain relationships were used to define a creep threshold stress below which only negligible creep is expected. These thresholds ranges were 0.3-0.5 MPa in the R direction and 0.05-0.2 MPa in the T direction

The chemistry of the Vasa

Analyses of wood from the Swedish warship Vasa revealed a complex chemical composition with increased acidity and depolymerisation of hemicellulose and polyethylene glycol (PEG). Pronounced depolymerisation and acidity were found in ferriferous segments below the surface region with high iron-sulfur-ratios. Decomposition products such as low molecular acids, xylan and PEG oligomers were identified by NMR and MALDI-TOF mass spectrometry in aqueous wood extracts. The concentrations of low molecular acids (formic, glycolic and oxalic) were enhanced compared to unconserved waterlogged wood and recent oak. The highest concentration of formic acid was found at sites with PEG depolymerisation shown by changes in the molecular weight distribution (MWD). Statistical simulations of degradation and model experiments on PEG and holocellulose with Fenton's reagent support degradation initiated by hydroxyl radicals. Multi-elemental analyses were performed by scanning electron microscopy showing different patterns in relation to depth and degradation. The surface region (0-5 mm) was characterized by the presence of particles in the lumina (gypsum, elemental sulfur, iron sulfur compounds) and a background of evenly distributed sulfur and iron compounds. Below the surface, in segments with depolymerisation, crusts of iron compounds were found in the lumina, and ferriferous particles (10-100 nm) were frequently observed in the cell walls. EXAFS analysis of the iron speciation showed that iron is present as hydrated iron(II) ions and iron(III) compounds and complexes. Sulfur K-edge XANES analysis of extracted wood showed that reduced organic sulfur compounds (ROSC) and intermediate oxidized sulfur species bind to macromolecules. The conclusion of the Vasa wood analyses is that degradation processes in the wood are initiated by the presence of iron compounds in regions low in sulfur. In the presence of significant amounts of ROSC the degradation patterns are less common indicating antioxidant properties, i.e. an opposite effect with regard to iron. Full-scale iron extraction experiments with iron chelators on conserved wood artefacts were efficient but time-consuming (years). Minor effects of the extraction treatment were observed on the MWD of oak holocellulose analysed by size-exclusion chromatography

Micro and nano sized particles in leachates from agricultural soils: Phosphorus and sulfur speciation by X-ray micro-spectroscopy

Colloids and nanoparticles leached from agricultural land are major carriers of potentially bioavailable nutrients with high mobility in the environment. Despite significant research efforts, accurate knowledge of macronutrients in colloids and nanoparticles is limited. We used multi-elemental synchrotron X-ray fluorescence (XRF) microscopy with multivariate spatial analysis and X-ray atomic absorption near-edge structure (XANES) spectroscopy at the P and S K-edges, to study the speciation of P and S in two fractions of leached particles, >0.45 and <0.45 mu m respectively, collected from four tile-drained agricultural sites in Sweden. P K-edge XANES showed that organic P, followed by P adsorbed to surfaces of aluminum-bearing particles were the most common forms of leached P. Iron-bound P (Fe-P) forms were generally less abundant (0-30 % of the total P). S K-edge XANES showed that S was predominantly organic, and a relatively high abundance of reduced S species suggests that redox conditions were adverse to the persistence of P bound to Fe-bearing colloids in the leachates. Acid ammonium-oxalate extractions suggested that P associated with Al and Fe (Al-P and Fe-P) in most cases could be explained by the adsorption capacity of non-crystalline (oxalate-extractable) oxides of Al and Fe. These results improve our understanding of particulate P and S speciation in the vadose zone and helps in developing effective technologies for mitigating colloidal driven eutrophication of water bodies near agricultural land. (C) 2020 The Author(s). Published by Elsevier Ltd

Imaging in-vivo tau pathology in Alzheimer's disease with THK5317 PET in a multimodal paradigm

PURPOSE: The aim of this study was to explore the cerebral distribution of the tau-specific PET tracer [(18)F]THK5317 (also known as (S)-[(18)F]THK5117) retention in different stages of Alzheimer's disease; and study any associations with markers of hypometabolism and amyloid-beta deposition. METHODS: Thirty-three individuals were enrolled, including nine patients with Alzheimer's disease dementia, thirteen with mild cognitive impairment (MCI), two with non-Alzheimer's disease dementia, and nine healthy controls (five young and four elderly). In a multi-tracer PET design [(18)F]THK5317, [(11)C] Pittsburgh compound B ([(11)C]PIB), and [(18)F]FDG were used to assess tau pathology, amyloid-beta deposition and cerebral glucose metabolism, respectively. The MCI patients were further divided into MCI [(11)C]PIB-positive (n = 11) and MCI [(11)C]PIB-negative (n = 2) groups. RESULTS: Test-retest variability for [(18)F]THK5317-PET was very low (1.17-3.81 %), as shown by retesting five patients. The patients with prodromal (MCI [(11)C]PIB-positive) and dementia-stage Alzheimer's disease had significantly higher [(18)F]THK5317 retention than healthy controls (p = 0.002 and p = 0.001, respectively) in areas exceeding limbic regions, and their discrimination from this control group (using the area under the curve) was &gt;98 %. Focal negative correlations between [(18)F]THK5317 retention and [(18)F]FDG uptake were observed mainly in the frontal cortex, and focal positive correlations were found between [(18)F]THK5317 and [(11)C]PIB retentions isocortically. One patient with corticobasal degeneration syndrome and one with progressive supranuclear palsy showed no [(11)C]PIB but high [(18)F]THK5317 retentions with a different regional distribution from that in Alzheimer's disease patients. CONCLUSIONS: The tau-specific PET tracer [(18)F]THK5317 images in vivo the expected regional distribution of tau pathology. This distribution contrasts with the different patterns of hypometabolism and amyloid-beta deposition

State of Degradation in Archeological Oak from the 17th Century <i>Vasa</i> Ship: Substantial Strength Loss Correlates with Reduction in (Holo)Cellulose Molecular Weight

In 1628, the Swedish warship <i>Vasa</i> capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the <i>Vasa</i> museum. Chemical investigations of the <i>Vasa</i> were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of <i>Vasa</i> oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the <i>Vasa</i> oak and the average molecular weight of the holocellulose, where the load-bearing cellulose microfibril is the critical constituent. The mean tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies

Longitudinal uncoupling of cerebral perfusion, glucose metabolism, and tau deposition in Alzheimer's disease.

INTRODUCTION: Cross-sectional findings using the tau tracer [18F]THK5317 (THK5317) have shown that [18F]fluorodeoxyglucose (FDG) positron emission tomography data can be approximated using perfusion measures (early-frame standardized uptake value ratio; ratio of tracer delivery in target to reference regions). In this way, a single positron emission tomography study can provide both functional and molecular information. METHODS: We included 16 patients with Alzheimer's disease who completed follow-up THK5317 and FDG studies 17 months after baseline investigations. Linear mixed-effects models and annual percentage change maps were used to examine longitudinal change. RESULTS: Limited spatial overlap was observed between areas showing declines in THK5317 perfusion measures and FDG. Minimal overlap was seen between areas showing functional change and those showing increased retention of THK5317. DISCUSSION: Our findings suggest a spatiotemporal offset between functional changes and tau pathology and a partial uncoupling between perfusion and metabolism, possibly as a function of Alzheimer's disease severity