| 1. |
- Bellander, Martin, et al.
(författare)
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No Evidence for Improved Associative Memory Performance Following Process-Based Associative Memory Training in Older Adults
- 2017
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Ingår i: Frontiers in Aging Neuroscience. - : Frontiers Media SA. - 1663-4365 .- 1663-4365. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Studies attempting to improve episodic memory performance with strategy instructions and training have had limited success in older adults: their training gains are limited in comparison to those of younger adults and do not generalize to untrained tasks and contexts. This limited success has been partly attributed to age-related impairments in associative binding of information into coherent episodes. We therefore investigated potential training and transfer effects of process-based associative memory training (i.e., repeated practice). Thirty-nine older adults (M-age = 68.8) underwent 6 weeks of either adaptive associative memory training or item recognition training. Both groups improved performance in item memory, spatial memory (object-context binding) and reasoning. A disproportionate effect of associative memory training was only observed for item memory, whereas no training-related performance changes were observed for associative memory. Self-reported strategies showed no signs of spontaneous development of memory-enhancing associative memory strategies. Hence, the results do not support the hypothesis that process-based associative memory training leads to higher associative memory performance in older adults.
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| 2. |
- Bellander, Martin, et al.
(författare)
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Behavioral correlates of changes in hippocampal gray matter structure during acquisition of foreign vocabulary
- 2016
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 131, s. 205-213
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Tidskriftsartikel (refereegranskat)abstract
- Experience can affect human gray matter volume. The behavioral correlates of individual differences in such brain changes are not well understood. In a group of Swedish individuals studying Italian as a foreign language, we investigated associations among time spent studying, acquired vocabulary, baseline performance on memory tasks, and gray matter changes. As a way of studying episodic memory training, the language learning focused on acquiring foreign vocabulary and lasted for 10 weeks. T-1-weighted structural magnetic resonance imaging and cognitive testing were performed before and after the studies. Learning behavior was monitored via participants' use of a smartphone application dedicated to the study of vocabulary. A whole-brain analysis showed larger changes in gray matter structure of the right hippocampus in the experimental group (N = 33) compared to an active control group (N = 23). A first path analyses revealed that time spent studying rather than acquired knowledge significantly predicted change in gray matter structure. However, this association was not significant when adding performance on baseline memory measures into the model, instead only the participants' performance on a short-term memory task with highly similar distractors predicted the change. This measure may tap similar individual difference factors as those involved in gray matter plasticity of the hippocampus.
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| 3. |
- Bellander, Martin, et al.
(författare)
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Lower baseline performance but greater plasticity of working memory for carriers of the val allele of the comt val158met polymorphism
- 2015
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Ingår i: Neuropsychology. - : American Psychological Association (APA). - 0894-4105 .- 1931-1559. ; 29:2, s. 247-254
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Little is known about genetic contributions to individual differences in cognitive plasticity. Given that the neurotransmitter dopamine is critical for cognition and associated with cognitive plasticity, we investigated the effects of 3 polymorphisms of dopamine-related genes (LMX1A, DRD2, COMT) on baseline performance and plasticity of working memory (WM), perceptual speed, and reasoning. Method: One hundred one younger and 103 older adults underwent approximately 100 days of cognitive training, and extensive testing before and after training. We analyzed the baseline and posttest data using latent change score models. Results: For working memory, carriers of the val allele of the COMT polymorphism had lower baseline performance and larger performance gains from training than carriers of the met allele. There was no significant effect of the other genes or on other cognitive domains. Conclusions: We relate this result to available evidence indicating that met carriers perform better than val carriers in WM tasks taxing maintenance, whereas val carriers perform better at updating tasks. We suggest that val carriers may show larger training gains because updating operations carry greater potential for plasticity than maintenance operations.
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| 4. |
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| 5. |
- Akhlaghi, Shahin, et al.
(författare)
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Degradation of fluoroelastomers in rapeseed biodiesel at different oxygen concentrations
- 2017
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 136, s. 10-19
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of fluoroelastomers (FKM) based on different monomers, additives and curing systems was studied after exposure to rapeseed biodiesel at 100 °C and different oxygen partial pressures. The sorption of fuel in the carbon black-filled FKM terpolymer was promoted by the fuel-driven cavitation in the rubber. The bisphenol-cured rubbers swelled more in biodiesel than the peroxide-cured FKM, presumably due to the chain cleavage caused by the attack of biodiesel on the double bonds formed during the bisphenol curing. With any of the selected types of monomer, the FKM rubbers absorbed biodiesel faster and to a greater extent with increasing oxygen partial pressure due to the increase in concentration of the oxidation products of biodiesel. Water-assisted complexation of biodiesel on magnesium oxide and calcium hydroxide particles led to dehydrofluorination of FKM, resulting in an extensive fuel uptake and a decrease in the strain-at-break and the Young's modulus of the rubbers. An increase in the CH2-concentration determined by infrared spectroscopy, and the appearance of biodiesel flakes in scanning electron micrographs of the extracted rubbers, were explained as being due to the presence of insoluble biodiesel grafted onto FKM on the unsaturated sites resulting from dehydrofluorination. The extensibility of the GFLT-type FKM was the least affected on exposure to biodiesel because this rubber contained less unsaturation and metal oxide/hydroxide particles.
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| 6. |
- Akhlaghi, Shahin, et al.
(författare)
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Deterioration of automotive rubbers in liquid biofuels : A review
- 2015
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 43, s. 1238-1248
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Forskningsöversikt (refereegranskat)abstract
- Concerns over the fast depletion of fossil fuels, environmental issues and stringent legislation associated with petroleum-based fuels have triggered a shift to bio-based fuels, as an alternative to meet the growing energy demand in the transportation sector. However, since conventional automobile fuel systems are adapted to petroleum-based fuels, switching to biofuels causes a severe deterioration in the performance of currently used rubber components. The degradation of the rubber materials in biofuels is complicated by the presence of different additives in biofuels and rubber compounds, by oxidation of biofuels and by the effects of thermomechanical loadings in the engine. This paper presents a comprehensive review of the effects of different types of biofuels, particularly biodiesel and bioethanol, on the physical, mechanical, morphological and thermal properties of elastomers under different exposure conditions. In addition, the literature data available on the variation of rubbers' resistance to biofuels with the changes in their monomer type and composition, cure system and additives content was also studied. The review essentially focuses on the compatibility of biofuels with acrylonitrile butadiene rubber, fluoroelastomers, polychloroprene rubber and silicon rubber, as the most commonly used automotive rubbers coming into contact with fuels during their service. The knowledge summarized in this study can help to develop a guideline on the selection of rubber for automotive parts designed to withstand biofuels.
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| 7. |
- Akhlaghi, Shahin, et al.
(författare)
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Effects of ageing conditions on degradation of acrylonitrile butadiene rubber filled with heat-treated ZnO star-shaped particles in rapeseed biodiesel
- 2017
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321.
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of acrylonitrile butadiene rubber (NBR) after exposure to biodiesel at different oxygen partial pressures in an automated ageing equipment at 80 °C, and in a high-pressure autoclave at 150 °C was studied. The oxidation of biodiesel was promoted by an increase in oxygen concentration, resulting in a larger uptake of fuel in the rubber due to internal cavitation, a greater decrease in the strain-at-break of NBR due to the coalescence of cavity, and a faster increase in the crosslinking density and carbonyl index due to the promotion of the oxidation of NBR. During the high-temperature autoclave ageing, less fuel was absorbed in the rubber, because the formation of hydroperoxides and acids was impeded. The extensibility of NBR aged in the autoclave decreased only slightly due to the cleavage of rubber chains by the biodiesel attack. The degradation of NBR in the absence of carbon black was explained as being due to oxidative crosslinking. The dissolution of ZnO crystals in the acidic components of biodiesel was retarded by removing the inter-particle porosity and surface defects through heat treating star-shaped ZnO particles. The rubber containing heat-treated ZnO particles swelled less in biodiesel than a NBR filled with commercial ZnO nanoparticles, and showed a smaller decrease in the strain-at-break and less oxidative crosslinking.
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| 8. |
- Austrell, Per Erik, et al.
(författare)
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Survey of Design Methods and Material Characteristics in Rubber Engineering
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff structures. Examples of these are shock absorbers, vibration insulators, flexible joints, seals and suspensions.The development of computers and of analysis programs in this area has given engineers a new tool for the design of elastomeric components. Computer simulation by finite element analysis has become increasingly important, allowing the mechanical behavior of products with for complex geometries, as well as loading cases of different kinds to be evaluated. Computer simulations enable both static and dynamic aspects to be analyzed. These matters have been recognized by the manufacturers of rubber products and by their customers. The benefits are shorter time for product development and also quality improvements.However, the possibilities available for finding less complicated technical solutions at lower cost with the use of elastomers, has not been fully utilized. Rubber components could be employed more frequently in design if engineers were more familiar with materials of this sort.Part of the problem lies in education and in the dissemination of information. Engineers working in the design area tend to not be very familiar with elastomeric materials and their properties. The offerings of courses on the mechanics of polymers at schools and universities are very limited. Skillful engineers in this field have usually acquired their knowledge through many years of experience and not formal education.Moreover, the complicated nature of the material behavior involved makes it difficult to devise general design rules and design tools. Only recently have computers and analysis programs become powerful enough for the analysis of nonlinear elastic problems involving large strains.It is essential, if one is to become competitive in high-tech applications, to possess a thorough knowledge of computer methods, material models and test methods available.There has likewise been a lack of relevant data for the computer analysis of elastomeric materials. The design tools employed rely on the material models available and on the test data required for the calibration of these models. In many cases, the only information available for analysis is a value for the hardness of the rubber in question. The wide variety of rubber compounds is also a problem. The characterization of different materials is costly and time-consuming. There is thus a need for simple and reliable methods to characterize the different vulcanizates.
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| 9. |
- Bellander, Martin
(författare)
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High pressure vulcanization : crosslinking of diene rubbers without vulcanization agents
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High pressure vulcanization (HPV) is defined in this thesisas crosslinking of rubber materialsat elevated pressure andtemperature, without the use of any vulcanization agents. Thisis atotally new vulcanization technique, not used in theindustry today. The HPV technique,however, has an interestingpotential since no hazardous chemicals need to be handled,thematerial does not contain any additives. The phenomenon thatcertain rubber materials can be crosslinked in this way wasobserved already in the 1960s, but there has been a lack ofknowledge of the underlying reaction mechanisms, kinetics, theresulting network structure and also the correlation betweenthe molecular structure and the physical properties ofthesematerials. The purpose of this thesis is to increase theknowledge of high pressurevulcanization, with respect toreaction kinetics and mechanisms, network structure andphysical properties.A low cis-polybutadiene was used as a model material forcrosslinking at high pressure (10-290 MPa) and temperature(240-250°C), and comparisons were made withperoxidevulcanizates. Both unfilled and carbon black filledsamples were studied. Nitrile- and styrene-butadienerubber werealso crosslinked successfully. Crosslink density is a centralconcept inthis thesis and was evaluated by swellingmeasurements. The microstructural changesoccurring duringvulcanization were studied by Fourier Transform InfraredSpectroscopy(FTIR) and 13 C solid state nuclear magneticresonance (NMR). The mechanical propertieswere investigated bydynamic mechanical thermal analysis (DMTA), tensile testing,and permanent set and stress relaxation measurements.Theprogress of the reaction proved to be well controlled by thetreatment time, temperature and pressure, resulting inmaterials with widely different properties within onesinglecompound due to the possibility of controlling thecrosslink density during the vulcanizationprocess. The reactionmechanism was shown to be of a radical type, and vinylunsaturations inthe polybutadiene are consumed concurrentlywith the crosslink formation. The effect ofpressure on thereaction is a decrease in molecular mobility, which results inhighercrosslinking reaction rate due to a decrease intermination reactions. When a carbon black filleris introduced,the number of polymer-filler interactions is increased due tothe ability of thepolymer to penetrate the carbon blackstructure under pressure. The mechanical properties areas goodas those of peroxide vulcanizates, and especially theresistance to deformation inservice-use at elevatedtemperatures suggests that the resulting material may be usedin gasketand seal applications. In spite of the difficulties ofmould sealing that arise at elevatedpressures, it was possibleto obtain vulcanized samples by common injection mouldingwithproperties comparable to those obtained by traditionalvulcanization.Keywords:High Pressure Vulcanization, Vulcanization,Crosslinking, Pressure, Elevated Temperature, Polybutadiene,Carbon Black, Rubber-Carbon Black Interactions, CrosslinkDensity, Peroxide Vulcanization, Injection Moulding,Nitrile-Butadiene Rubber.
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| 10. |
- Bellander, Martin
(författare)
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Plasticity of memory functioning : genetic predictors and brain changes
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human cognitive functions are not determined from birth, but are plastic and can be altered by environmental factors. The promising idea of a cognitive intervention that would improve memory functioning has attracted a lot of attention over the last decades. By taxing memory functions through repeated training, researchers try to demonstrate improvement in the trained or other functions. However, people do not profit equally from these training regimes and their effect on brain integrity also differs between persons. In this thesis, I explore factors related to individual differences in cognitive training response, and their effects on the brain. The first part of the thesis concerns training of working memory (wm), and whether training-induced performance increases are influenced by certain genetic variations. The genetic variations studied are confined to genes related to the neurotransmitter dopamine (da), which is related to cognitive performance. In Study I, we investigated the effect on wm training gains of single nucleotide polymorphisms (snps) in the lmx1a gene, previously linked to Parkinson’s disease (pd). This gene is important for the development of da neurons. For one of the snps, we found that over the course of four weeks of wm training, the two genotype groups showed a differential pattern of gain, such that those participants carrying the allele associated with a lower risk of pd showed larger gains. In Study II, we examined if three da related snps were associated with gain in several cognitive abilities, after 100 days of broad cognitive training taxing wm, episodic memory (em), and perceptual speed (ps). The first one was the lmx1a snp that was found to be linked to wm training gains in Study I. The second was a snp in the drd2 gene, important to striatal da availability. The third was a commonly studied snp in the comt gene, coding for the enzyme that degrades da cortically. We found that only the comt snp had an effect on training gains, and only for wm. The second part of this thesis focus on em function, more precisely associative memory; if it could be trained, and what effects training may have on brain structure. In Study III, we explored process-based associative-memory training for older adults. Participants underwent six weeks of training on several different associative-memory tasks, with transfer tasks administered before and after training. An active control group underwent the same training, but practiced only on item memory tasks. No intervention effects were found for associative memory or the far transfer measures; however, the associative-memory training group showed larger gains than the controls on an item memory task. In Study IV, we used vocabulary learning as a way of studying associative-memory training. Participants studied a new language and their knowledge, effort, and cognitive capacity were measured. Before and after training, participants underwent structural magnetic resonance imaging (mri). We found that, compared to a control group, language learners showed increased grey matter (gm) volume in hippocampus. Furthermore, this volume increase was predicted by baseline capacity on a task measuring short term memory. Collectively, these studies show that the variability in training gains is not only noise, but rather meaningful variations that could be used to further our understanding of what factors determine the capacity for plastic change, both in brain and in behavior.
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