| 1. |
- Adediran, Gbotemi, et al.
(författare)
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Micro and nano sized particles in leachates from agricultural soils: Phosphorus and sulfur speciation by X-ray micro-spectroscopy
- 2021
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 189
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Afshar, Reza, et al.
(författare)
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Creep in oak material from the Vasa ship: : verification of linear viscoelasticity and identification of stress thresholds
- 2020
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Ingår i: European Journal of Wood and Wood Products. - : Springer Nature. - 0018-3768 .- 1436-736X. ; 78:6, s. 1095-1103
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Tidskriftsartikel (refereegranskat)abstract
- 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 confrm 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 ftted 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 defne 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.
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| 3. |
- Almkvist, Gunnar, et al.
(författare)
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Distribution of iron and sulfur and their speciation in relation to degradation processes in wood from the Swedish warship Vasa
- 2011
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Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 35, s. 1491-1502
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Tidskriftsartikel (refereegranskat)abstract
- Wood samples from the Swedish warship Vasa were analysed by scanning electron microscopy and X-ray absorption spectroscopy with the focus on speciation and distribution of iron and sulfur compounds in the wood matrix. Both these elements were found at high concentration (10–100 mg/g) in the surface region as a result of former accumulation of iron sulfides, elemental sulfur and reduced organic sulfur species (ROSS). Below the surface region, iron was the dominating element (1–10 mg/g) present both as iron(II) and iron(III) compounds, which diffused into the wood matrix from corroding iron bolts and other iron items during the time in the sea (1628–1961). Electron microscopy results revealed that iron and sulfur are present in a variety of particles of different sizes and compositions in the surface region, in contrast to the interior where few particles were found. Here, the presence of iron compounds of nano-particle size inside the cell walls enables a close contact between the wood polymers and reactive oxygen species originating from reactions with iron compounds. The presence of ROSS seems to have played an important role as scavengers of reactive oxygen species. Samples with high iron : ROSS ratio displayed evident signs of degradation as indicated by depolymerisation of wood components accompanied by increased acidity due to low molecular organic acids. The observations strengthen the hypothesis of the pro-oxidative and antioxidant properties of iron and ROSS compounds, respectively, and that the chemical activities of these elements play crucial roles in the long term preservation of wooden maritime artefacts
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| 4. |
- Almkvist, Gunnar, et al.
(författare)
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K-edge XANES analysis of sulfur compounds: an investigation of the relative intensities using internal calibration
- 2010
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 17, s. 683-688
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur K-edge XANES (X-ray absorption near-edge structure) spectroscopy is an excellent tool for determining the speciation of sulfur compounds in complex matrices. This paper presents a method to quantitatively determine the kinds of sulfur species in natural samples using internally calibrated reference spectra of model compounds Owing to significant self-absorption of formed fluorescence radiation in the sample itself the fluorescence signal displays a non-linear correlation with the sulfur content over a wide concentration range. Self-absorption is also a problem at low total absorption of the sample when the sulfur compounds are present as particles. The post-edge Intensity patterns of the sulfur K-edge XANES spectra vary with the type of sulfur compound, with reducing sulfur compounds often having a higher post-edge intensity than the oxidized forms. In dilute solutions (less than 0.3-0.5%) it is possible to use sulfur K-edge XANES reference data for quantitative analysis of the contribution from different species The results show that it is essential to use an internal calibration system when performing quantitative XANES analysis Preparation of unknown samples must take both the total absorption and possible presence of self-absorbing particles into consideration.
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| 5. |
- Almkvist, Gunnar, et al.
(författare)
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Prediction of tensile strength in iron-contaminated archaeological wood by FT-IR spectroscopy - a study of degradation in recent oak and Vasa oak
- 2016
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 70:9, s. 855-865
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Tidskriftsartikel (refereegranskat)abstract
- Oak from the Swedish warship Vasa and recent oak that was aged after impregnation with iron(II) chloride has been analyzed by FT-IR spectroscopy and submitted to tensile strength testing. The aim was to investigate correlations between FT-IR bands in the fingerprint region, chemical degradation, and tensile strength in iron contaminated oak. The concentration of carboxylic functions increased and the acetyl groups in the hemicellulose fraction were decreasing as a function of degradation time. These changes are accompanied by reduced tensile strength and elevated content of oxalic acid (OA) in both Vasa wood and the impregnated recent oak samples. To evaluate the possibility to predict tensile strength from spectral data, chemometric modeling by partial least-squares (PLS) regression was applied. The strategy of repeated double cross validation (rdCV) allowed a realistic prediction of tensile strength. Overall, chemical changes and mechanical performances of iron contaminated wood are strongly correlated and thus FT-IR spectroscopy is suited to predict the strength properties of the degraded wood.
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| 6. |
- Almkvist, Gunnar
(författare)
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The Vasa experience with polyethylene glycol: A conservator's perspective
- 2012
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Ingår i: Journal of Cultural Heritage. - : Elsevier BV. - 1296-2074. ; 13, s. 175-182
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Tidskriftsartikel (refereegranskat)abstract
- It is now fifty years since the raising of the Swedish warship Vasa, one of the first wooden shipwrecks and certainly the largest to have been conserved with polyethylene glycol (PEG). Now a standard material for waterlogged wood conservation, PEG has since been used on a number of other shipwrecks, thanks largely to the Vasa experience. As the second generation of conservators at the Vasa Museum in Stockholm, we are often asked our opinions about PEG, and whether we would still use the same materials and techniques should another ship like Vasa be raised today. What have we learnt and what would we do differently this time? In this paper, we examine the Vasa experience from the initial conservation decisions, through to the most recent research projects and examine how PEG has fared over the last fifty years. Finally, we take the lessons learned and apply them to the future, both for Vasa material and for newly found wrecks. (C) 2012 Elsevier Masson SAS. All rights reserved.
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| 7. |
- Almkvist, Gunnar, et al.
(författare)
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Vasa: the state of deterioration
- 2014
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Ingår i: McGraw-Hill Yearbook of Science & Technology. - 9780071831062
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Bokkapitel (populärvet., debatt m.m.)
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| 8. |
- Ausén, Birgitta, et al.
(författare)
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Personality Features in Subjective Cognitive Impairment and Mild Cognitive Impairment - Early Indicators of Dementia?
- 2009
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Ingår i: Dementia and Geriatric Cognitive Disorders. - Basel : Karger AG. - 1420-8008 .- 1421-9824. ; 28:6, s. 528-535
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: The purpose of the present study was to investigate patterns of personality in patients with subjective cognitive impairment (SCI) and mild cognitive impairment (MCI), compared to healthy controls. Methods: We assessed24 patients with SCI, 35 patients with MCI and 26 healthy controls with the self-report questionnaire Swedish Universities Scales of Personality measuring aspects of neuroticism/anxiety proneness, extraversion, and aggression-hostility. Results: Patients with SCI and MCI showed significantly more Somatic Trait Anxiety, Psychic Trait Anxiety and Stress Susceptibility than healthy controls. Moreover, there was a significant increase in Detachment in patients with MCI and a significant decrease in Adventure Seeking in patients with SCI, relative to healthy controls. Conclusions: Patients with SCI and MCI presented specific patterns of personality alterations with higher scores in traits related to anxiety proneness and aggression-hostility and lower in traits of extraversion. In most subscales differences followed a sequential pattern with gradually increasing scores from healthy controls, to patients with SCI and further to MCI. The groups differed in amount and type of symptoms, suggesting that patterns of personality may be related to degree of cognitive impairment.
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| 9. |
- Ausen, Birgitta, et al.
(författare)
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Self- and Informant Ratings of Personality in Mild Cognitive Impairment, Reviewed
- 2011
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Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 32:6, s. 387-393
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Tidskriftsartikel (refereegranskat)abstract
- Aims: To examine the degree of agreement between self-and informant ratings of personality in relation to cognitive function in patients with mild cognitive impairment (MCI), subjective cognitive impairment (SCI) and healthy controls (HC). Methods: Thirty-two patients and informants with MCI, 23 with SCI and 22 HC completed the Swedish universities Scales of Personality (SSP). Correlations and incongruence between self-and informant ratings were calculated. The Mini Mental State Examination (MMSE) was used to assess cognitive function. Results: The correlations between self-and and informant ratings were fair-to-moderate on a majority of SSP scales and significant in 44%. The incongruence between patients and informants was significantly larger in MCI than in HC across SSP scales. There was a significant negative correlation between the incongruence index and the MMSE for all subjects. Conclusions: Self-informant agreement on ratings of patients' personality was reasonable. Incongruence between patients and their informants was associated with MCI but not SCI or HC. Disagreement between patients and informants indicates cognitive impairment. Copyright (C) 2012 S. Karger AG, Basel
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| 10. |
- Bjurhager, Ingela, et al.
(författare)
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State of degradation in archeological oak from the 17th century vasa ship : Substantial strength loss correlates with reduction in (holo)cellulose molecular weight
- 2012
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; :8, s. 2521-2527
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Tidskriftsartikel (refereegranskat)abstract
- In 1628, the Swedish warship Vasa 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 Vasa museum. Chemical investigations of the Vasa 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 Vasa 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 Vasa 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.
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