| 1. |
- Adediran, Gbotemi, et al.
(författare)
-
Micro and nano sized particles in leachates from agricultural soils: Phosphorus and sulfur speciation by X-ray micro-spectroscopy
- 2021
-
Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 189
-
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.
|
|
| 2. |
- Afshar, Reza, et al.
(författare)
-
Creep in oak material from the Vasa ship: : verification of linear viscoelasticity and identification of stress thresholds
- 2020
-
Ingår i: European Journal of Wood and Wood Products. - : Springer Nature. - 0018-3768 .- 1436-736X. ; 78:6, s. 1095-1103
-
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.
|
|
| 3. |
- Almkvist, Gunnar, et al.
(författare)
-
Distribution of iron and sulfur and their speciation in relation to degradation processes in wood from the Swedish warship Vasa
- 2011
-
Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 35, s. 1491-1502
-
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
|
|
| 4. |
- Almkvist, Gunnar, et al.
(författare)
-
K-edge XANES analysis of sulfur compounds: an investigation of the relative intensities using internal calibration
- 2010
-
Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 17, s. 683-688
-
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.
|
|
| 5. |
- Almkvist, Gunnar, et al.
(författare)
-
Prediction of tensile strength in iron-contaminated archaeological wood by FT-IR spectroscopy - a study of degradation in recent oak and Vasa oak
- 2016
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 70:9, s. 855-865
-
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.
|
|
| 6. |
- Almkvist, Gunnar
(författare)
-
The Vasa experience with polyethylene glycol: A conservator's perspective
- 2012
-
Ingår i: Journal of Cultural Heritage. - : Elsevier BV. - 1296-2074. ; 13, s. 175-182
-
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.
|
|
| 7. |
- Almkvist, Gunnar, et al.
(författare)
-
Vasa: the state of deterioration
- 2014
-
Ingår i: McGraw-Hill Yearbook of Science & Technology. - 9780071831062
-
Bokkapitel (populärvet., debatt m.m.)
|
|
| 8. |
- Ausén, Birgitta, et al.
(författare)
-
Personality Features in Subjective Cognitive Impairment and Mild Cognitive Impairment - Early Indicators of Dementia?
- 2009
-
Ingår i: Dementia and Geriatric Cognitive Disorders. - Basel : Karger AG. - 1420-8008 .- 1421-9824. ; 28:6, s. 528-535
-
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.
|
|
| 9. |
- Ausen, Birgitta, et al.
(författare)
-
Self- and Informant Ratings of Personality in Mild Cognitive Impairment, Reviewed
- 2011
-
Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 32:6, s. 387-393
-
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
|
|
| 10. |
- Bjurhager, Ingela, et al.
(författare)
-
State of degradation in archeological oak from the 17th century vasa ship : Substantial strength loss correlates with reduction in (holo)cellulose molecular weight
- 2012
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; :8, s. 2521-2527
-
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.
|
|
| 11. |
|
|
| 12. |
- Boye, Kristin, et al.
(författare)
-
Quantification of chemical sulphur species in bulk soil and organic sulphur fractions by S K-edge XANES spectroscopy
- 2011
-
Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 62, s. 874–881-
-
Tidskriftsartikel (refereegranskat)abstract
- A new data treatment method for fitting spectra obtained by sulphur (S) K-edge X-ray absorption near-edge structure (XANES) spectroscopy was used to quantify the chemical S speciation at three experimental sites with arable soils receiving the same long-term field treatments. Two treatments, crop residue (CR) incorporation and farmyard manure (FYM) application, with equal applications of mineral nutrients were included in the study. In the new data treatment method, internally calibrated spectra of dilute solutions (30 mm) of model compounds were used to fit the sample spectra. This greatly enhanced the reliability of quantitative determination of contributing S species in soil samples and soil extracts. The results indicated that long-term FYM application shifted S species composition from highly oxidized towards intermediate oxidization in two of the soils, but in the third soil the opposite trend was observed. Sulphur XANES spectroscopy of acetylacetone extracts of physically protected and unprotected organic S in two of the soils revealed that physical protection was not related to S speciation; however, intermediate forms of oxidized S species appeared to accumulate in the residual S pool (not extractable by acetylacetone)
|
|
| 13. |
- Chiotis, Konstantinos, et al.
(författare)
-
Imaging in-vivo tau pathology in Alzheimer's disease with THK5317 PET in a multimodal paradigm
- 2016
-
Ingår i: European Journal of Nuclear Medicine and Molecular Imaging. - : Springer Science and Business Media LLC. - 1619-7070 .- 1619-7089. ; 43:9, s. 1686-1699
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose The aim of this study was to explore the cerebral distribution of the tau-specific PET tracer [F-18]THK5317 (also known as (S)-[F-18]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 [F-18]THK5317, [C-11] Pittsburgh compound B ([C-11]PIB), and [F-18]FDG were used to assess tau pathology, amyloid-beta deposition and cerebral glucose metabolism, respectively. The MCI patients were further divided into MCI [C-11]PIB-positive (n=11) and MCI [C-11]PIB-negative (n=2) groups. Results Test-retest variability for [F-18]THK5317-PET was very low (1.17-3.81 %), as shown by retesting five patients. The patients with prodromal (MCI [C-11]PIB-positive) and dementia-stage Alzheimer's disease had significantly higher [F-18]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 >98 %. Focal negative correlations between [F-18]THK5317 retention and [F-18]FDG uptake were observed mainly in the frontal cortex, and focal positive correlations were found between [F-18]THK5317 and [C-11] PIB retentions isocortically. One patient with corticobasal degeneration syndrome and one with progressive supranuclear palsy showed no [C-11]PIB but high [F-18]THK5317 retentions with a different regional distribution from that in Alzheimer's disease patients. Conclusions The tau-specific PET tracer [F-18]THK5317 images in vivo the expected regional distribution of tau pathology. This distribution contrasts with the different patterns of hypometabolism and amyloid-beta deposition.
|
|
| 14. |
- Chiotis, K., et al.
(författare)
-
Longitudinal changes of tau PET imaging in relation to hypometabolism in prodromal and Alzheimer's disease dementia
- 2018
-
Ingår i: Molecular Psychiatry. - : Springer Science and Business Media LLC. - 1359-4184 .- 1476-5578. ; 23:7, s. 1666-1673
-
Tidskriftsartikel (refereegranskat)abstract
- The development of tau-specific positron emission tomography (PET) tracers allows imaging in vivo the regional load of tau pathology in Alzheimer's disease (AD) and other tauopathies. Eighteen patients with baseline investigations enroled in a 17-month follow-up study, including 16 with AD (10 had mild cognitive impairment and a positive amyloid PET scan, that is, prodromal AD, and six had AD dementia) and two with corticobasal syndrome. All patients underwent PET scans with [F-18]THK5317 (tau deposition) and [F-18]FDG (glucose metabolism) at baseline and follow-up, neuropsychological assessment at baseline and follow-up and a scan with [C-11]PIB (amyloid-beta deposition) at baseline only. At a group level, patients with AD (prodromal or dementia) showed unchanged [F-18]THK5317 retention over time, in contrast to significant decreases in [F-18]FDG uptake in temporoparietal areas. The pattern of changes in [F-18]THK5317 retention was heterogeneous across all patients, with qualitative differences both between the two AD groups (prodromal and dementia) and among individual patients. High [F-18]THK5317 retention was significantly associated over time with low episodic memory encoding scores, while low [F-18]FDG uptake was significantly associated over time with both low global cognition and episodic memory encoding scores. Both patients with corticobasal syndrome had a negative [C-11]PIB scan, high [F-18]THK5317 retention with a different regional distribution from that in AD, and a homogeneous pattern of increased [F-18]THK5317 retention in the basal ganglia over time. These findings highlight the heterogeneous propagation of tau pathology among patients with symptomatic AD, in contrast to the homogeneous changes seen in glucose metabolism, which better tracked clinical progression.
|
|
| 15. |
- Darreh-Shori, T., et al.
(författare)
-
Inhibition of acetylcholinesterase in CSF versus brain assessed by 11C-PMP PET in AD patients treated with galantamine
- 2008
-
Ingår i: Neurobiology of Aging. - : Elsevier BV. - 0197-4580 .- 1558-1497. ; 29:2, s. 168-184
-
Tidskriftsartikel (refereegranskat)abstract
- The relationship between acetylcholinesterase (AChE) activity in the CSF and brain of patients with Alzheimer's disease (AD) was investigated in 18 mild AD patients following galantamine treatment. The first 3 months of the study had a randomized double-blind placebo-controlled design, during which 12 patients received galantamine (16-24 mg/day) and six patients placebo. This was followed by 9 months Galantamine treatment in all patients. Activities and protein levels of both the "read-through" AChE (AChE-R) and the synaptic (AChE-S) variants in CSF were assessed in parallel together with the regional brain AChE activity by C-11-PMP and PET. The AChE-S inhibition was 30-36% in CSF, which correlated well with the in vivo AChE inhibition in the brain. No significant AChE inhibition was observed in the placebo group. The increased level of the AChE-R protein was 16% higher than that of AChE-S. Both the AChE inhibition and the increased level of AChE-R protein positively correlated with the patient's performance in cognitive tests associated with visuospatial ability and attention. In conclusion, AChE levels in CSF closely mirror in vivo brain AChE levels prior to and after treatment with the cholinesterase inhibitors. A positive cognitive response seems to dependent on the AChE inhibition level, which is balanced by an increased protein level of the AChE-R variant in the patients.
|
|
| 16. |
- Engler, Henry, et al.
(författare)
-
Two-year follow-up of amyloid deposition in patients with Alzheimer's disease
- 2006
-
Ingår i: Brain. - : Oxford University Press (OUP). - 0006-8950 .- 1460-2156. ; 129:Pt 11, s. 2856-2866
-
Tidskriftsartikel (refereegranskat)abstract
- Beta amyloid is one of the major histopathological hallmarks of Alzheimer's disease. We recently reported in vivo imaging of amyloid in 16 Alzheimer patients, using the PET ligand N-methyl[11C]2-(4'-methylaminophenyl)-6-hydroxy-benzothiazole (PIB). In the present study we rescanned these 16 Alzheimer patients after 2.0 +/- 0.5 years and have described the interval change in amyloid deposition and regional cerebral metabolic rate for glucose (rCMRGlc) at follow-up. Sixteen patients with Alzheimer's disease were re-examined by means of PET, using PIB and 2-[18F]fluoro-2-deoxy-d-glucose (FDG) after 2.0 +/- 0.5 years. The patients were all on cholinesterase inhibitor treatment and five also on treatment with the N-methyl-d-aspartate (NMDA) antagonist memantine. In order to estimate the accuracy of the PET PIB measurements, four additional Alzheimer patients underwent repeated examinations with PIB within 20 days (test-retest). Relative PIB retention in cortical regions differed by 3-7% in the test-retest study. No significant difference in PIB retention was observed between baseline and follow-up while a significant (P < 0.01) 20% decrease in rCMRGlc was observed in cortical brain regions. A significant negative correlation between rCMRGlc and PIB retention was observed in the parietal cortex in the Alzheimer patients at follow-up (r = 0.67, P = 0.009). A non-significant decline in Mini-Mental State Examination (MMSE) score from 24.3 +/- 3.7 (mean +/- standard deviation) to 22.7 +/- 6.1 was measured at follow-up. Five of the Alzheimer patients showed a significant decline in MMSE score of >3 (21.4 +/- 3.5 to 15.6 +/- 3.9, P < 0.01) (AD-progressive) while the rest of the patients were cognitively more stable (MMSE score = 25.6 +/- 3.1 to 25.9 +/- 3.7) (AD-stable) compared with baseline. A positive correlation (P = 0.001) was observed in the parietal cortex between Rey Auditory Verbal Learning (RAVL) test score and rCMRGlc at follow-up while a negative correlation (P = 0.018) was observed between RAVL test and PIB retention in the parietal at follow-up. Relatively stable PIB retention after 2 years of follow-up in patients with mild Alzheimer's disease suggests that amyloid deposition in the brain reaches a plateau by the early clinical stages of Alzheimer's disease and therefore may precede a decline in rCMRGlc and cognition. It appears that anti-amyloid therapies will need to induce a significant decrease in amyloid load in order for PIB PET images to detect a drug effect in Alzheimer patients. FDG imaging may be able to detect a stabilization of cerebral metabolism caused by therapy administered to patients with a clinical diagnosis of Alzheimer's disease.
|
|
| 17. |
- Forsberg, Anton, et al.
(författare)
-
PET imaging of amyloid deposition in patients with mild cognitive impairment
- 2008
-
Ingår i: Neurobiology of Aging. - : Elsevier BV. - 0197-4580 .- 1558-1497. ; 29:10, s. 1456-1465
-
Tidskriftsartikel (refereegranskat)abstract
- It is of great clinical value to identify subjects at a high risk of developing AD. We previously found that the amyloid positron emission tomography (PET) tracer PIB showed a robust difference in retention in the brain between AD patients and healthy controls (HC). Twenty-one patients diagnosed with MCI (mean age 63.3 ± 7.8 (S.D.) years) underwent PET studies with 11C-PIB, and 18F-fluoro-deoxy-glucose (FDG) to measure cerebral glucose metabolism, as well as assessment of cognitive function and CSF sampling. Reference group data from 27 AD patients and 6 healthy controls, respectively, were used for comparison. The mean cortical PIB retention for the MCI patients was intermediate compared to HC and AD. Seven MCI patients that later at clinical follow-up converted to AD (8.1 ± 6.0 (S.D.) months) showed significant higher PIB retention compared to non-converting MCI patients and HC, respectively (ps < 0.01). The PIB retention in MCI converters was comparable to AD patients (p > 0.01). Correlations were observed in the MCI patients between PIB retention and CSF Aβ1-42, total Tau and episodic memory, respectively.
|
|
| 18. |
- Henrik-Klemens, Åke, et al.
(författare)
-
Iron extraction from archaeological wood with diethylene triamine pentaacetic acid (DTPA): application and optimization.
- 2016
-
Ingår i: Proceedings of the 13th ICOM Group on Wet Organic Archaeological Materials Conference, Florence May, 2016. ICOM, Committee for Conservation, Working Group on Wet Organic Archaeological Materials.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Since the redox catalytic activity of iron may be detrimental for archaeological wood under aerobic conditions, treatments for the extraction or passivation of iron are of interest. This study was conducted to further explore the use of extraction treatments with the high performance iron chelator diethylene triamine pentaacetic acid (DTPA). The concentration of DTPA which would suffice for an effective iron extraction was experimentally investigated, . Of additional interest was whether the treatment responds differently to non-conserved and polyethylene glycol (PEG) impregnated archaeological wood. Extraction experiments with the concentration of DTPA as a variable were carried out on untreated waterlogged oak from the recently excavated the Skaftö Wreck (late mediaeval) and on PEG impregnated dry oak from the warship Vasa (1628). Iron distribution before and after extraction was scanned using X-ray Fluorescence (XRF) and the amounts of extracted iron were analysed with Atomic Absorption Spectrometry (AAS). In conclusion, there was no difference in extraction efficiency between the different concentrations of DTPA used in this study, which would imply that it is only useful to increase the concentration to a certain level. The treatment was effective on both untreated and PEG impregnated wood with extraction rates within the same range (percent extracted 63-78 %).
|
|
| 19. |
- Leuzy, Antoine, et al.
(författare)
-
Longitudinal uncoupling of cerebral perfusion, glucose metabolism, and tau deposition in Alzheimer's disease
- 2018
-
Ingår i: Alzheimer's & Dementia. - : Wiley. - 1552-5260 .- 1552-5279. ; 14:5, s. 652-663
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Cross-sectional findings using the tau tracer [F-18] THK5317 (THK5317) have shown that [F-18]fluorodeoxyglucose (FDG) positron emission tomography (PET) 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 PET 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.
|
|
| 20. |
- Norbakhsh, Shahin, et al.
(författare)
-
Impact of iron(II) and oxygen on degradation of oak - modeling of the Vasa wood
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:6, s. 649-655
-
Tidskriftsartikel (refereegranskat)abstract
- In the wood of the Swedish 17th century warship Vasa, iron (Fe)-catalyzed chemical degradation has taken place after the salvation in 1961, which is manifested in increased acidity accompanied by cellulose degradation and reduced strength in the oak hull. Model studies on fresh oak impregnated with Fe(II) also led to tensile strength (TS) reduction in the same order of magnitude as observed in the wood of the Vasa. In the present study, further experiments have been performed concerning the Fe-catalyzed wood degradation. Namely, the degree of wood degradation was monitored quantitatively by measurement of the O-2 consumption of Fe(II)-impregnated oak, kept in closed vials with different relative humidities (RH), as a function of time. The initial O-2 consumption was high and declined with time. After 200 days, the accumulated O-2 consumption was 0.3-0.4 mmol g(-1) wood. Degradation products with low molecular weight were analyzed. The release of CO2 and oxalic acid (OA) was positively correlated with RH (0.235 and 0.044 mmol g(-1), respectively, at RH98% after 200 days). Samples kept for 1500 days at RH54% had accumulated 0.044 mmol OA g(-1) wood, which is equal to the average OA content in the interior of Vasa oak (corresponding to 4 mg g(-1)). Oak samples, from which extractives had been removed prior to Fe(II) impregnation, did not change their O-2 consumption or TS reduction compared to the nonextracted samples, indicating that extractives are not essential for cellulose degradation in this context.
|
|
| 21. |
- Norbakhsh, Shahin, et al.
(författare)
-
Mimicking of the strength loss in the Vasa : model experiments with iron-impregnated recent oak
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:6, s. 707-714
-
Tidskriftsartikel (refereegranskat)abstract
- Previous studies of the oak wood of the 17th century warship the Vasa have shown significant changes in the chemical and mechanical properties compared with recent oak. The most important factors contributing to these changes are the incorporation of iron compounds during waterlogging and the uptake of polyethylene glycol (PEG) in the course of the 17 years of preservation treatment. To investigate the effect of iron-dependent oxidative degradation reactions, recent oak wood samples were impregnated with aqueous iron(II) chloride solution (0.1 M) and thereafter exposed to air or pure oxygen at controlled relative humidity in long-term experiments followed by tensile strength (TS) measurements. The iron-impregnated samples exposed to oxygen displayed significant effects already after 1 week and the reduction in TS was similar to 50% after 1 year. The samples treated with additional PEG displayed less TS reduction, whereas the addition of cysteine had no effect. The size exclusion chromatography of treated samples showed that the average molecular weight of holocellulose had decreased. The results confirm that iron compounds have a detrimental effect in wood and indicate that PEG might act as an antioxidant for the degradation processes. Concerning the Vasa, it may be concluded that most degradation related to iron compounds and oxidative processes have taken place during the first period of conservation when the wood was exposed to oxygen in a still very humid state. Thus, the current rate of oxidative degradation under the present relatively dry museum conditions should be relatively low.
|
|
| 22. |
- Vorobyev, Alexey, 1985-, et al.
(författare)
-
Relations of density, polyethylene glycol treatment and moisture content with stiffness properties of Vasa oak samples
- 2017
-
Ingår i: Holtzforschung. - : Walter de Gruyter GmbH. ; 71:4, s. 327-335
-
Tidskriftsartikel (refereegranskat)abstract
- Treatment with polyethylene glycol (PEG) is the preferred method for conservation of waterlogged archaeological wooden objects. However, PEG impregnation leads to softening and increased hygroscopicity of the material. The present study compiles experimental results concerning the full elastic properties of PEG impregnated archaeological wood from the Vasa ship in relation to its basic density, PEG content (PEGC) and moisture content (MC). The results show a correlation between a more porous microstructure and high PEGC, and consequently, higher MC. The PEG and moisture contribute to the mass of the wooden object as well as to softening of the material, which are undesired properties in a larger load-carrying wooden structure. A compromise between the improved dimensional stability and degradation of mechanical properties should therefore be considered in the conservation of wooden object treated with PEG.
|
|
| 23. |
- Wagner, Leopold, et al.
(författare)
-
The influence of chemical degradation and polyethylene glycol on moisture-dependent cell wall properties of archeological wooden objects : a case study of the Vasa shipwreck
- 2016
-
Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 50:6, s. 1103-1123
-
Tidskriftsartikel (refereegranskat)abstract
- Cell wall measures allow for direct assessment of wood modification without the adverse effect of varying density and microstructure. In this study, cell wall properties of recent and archeological oak wood from the Vasa shipwreck were investigated for cell wall stiffness, hardness and creep with respect to effects of chemical degradation, impregnation with a preservation agent, namely polyethylene glycol, and moisture. For this purpose, nanoindentation tests were performed at varying relative humidity, leading to different moisture contents in the wood samples. Concurrently, microstructural and chemical characterization of the mate- rial was conducted. Impregnated and untreated recent oak wood showed a softening effect of both moisture and preservation agent at the wood cell wall level. On the contrary, increased stiffness was found for non-impregnated Vasa oak, which can be explained by aging-related modifications in cell wall components. These effects were counteracted by the softening effect of polyethylene glycol in the impregnated Vasa material, where a lower overall stiffness was measured. The reverse effect of the preservation agent and moisture, namely increased indentation creep of the cell wall material, was revealed. The loss of acetyl groups in the hemicelluloses explained the decreased hygroscopicity of the Vasa oak. In the impregnated Vasa oak, this effect seemed to be partly counteracted by the presence of low-molecular polyethylene glycol contributing to higher hygroscopicity of the cell wall. Thus, the higher overall sorptive capacity of the impregnated Vasa material, with respect to the non-impregnated material, was detected, which has resulted in a sorptive behavior similar to that of recent oak wood. The proposed approach requires only small amounts of material, making it especially suitable for application to precious historical wooden artifacts.
|
|
