| 1. |
- Sundberg, Kathrin, et al.
(författare)
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Differences in the catalytic efficiencies of allelic variants of glutathione transferase P1-1 towards carcinogenic diol epoxides of polycyclic aromatic hydrocarbons
- 1998
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Ingår i: Carcinogenesis. - : Oxford University Press (OUP). - 0143-3334 .- 1460-2180. ; 19:3, s. 433-436
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have identified allelic variants of the human glutathione transferase (GST) Pi gene and showed that the two different encoded proteins with isoleucine (GSTP1-1/I-105) or valine (GSTP1-1/V-105) at position 105, respectively, differ significantly in their catalytic activities with model substrates. Moreover, recent epidemiological studies have demonstrated that individuals differing in the expression of these allelic variants also differ in susceptibility to tumour formation in certain organs, including such in which polycyclic aromatic hydrocarbons (PAH) may be etiological factors. In the present study the catalytic efficiencies (kcat/Km) of these GSTP1-1 variants were determined with a number of stereoisomeric bay-region diol epoxides, known as the ultimate mutagenic and carcinogenic metabolites of PAH, including those from chrysene, benzo[a]pyrene and dibenz[a,h]anthracene. In addition, GSTP1-1 mutants in which amino residue 105 is alanine (GSTP1-1/A-105) or tryptophan (GSTP1-1/W-105) have been constructed and characterized. GSTP1-1/V-105 was found to be more active than GSTP1-1/I-105 in conjugation reactions with the bulky diol epoxides of PAH, being up to 3-fold as active towards the anti- and syn-diol epoxide enantiomers with R-absolute configuration at the benzylic oxiranyl carbon. Comparing the four enzyme variants, GSTP1-1/A-105 generally demonstrated the highest kcat/Km value and GSTP1-1/W-105 the lowest with the anti-diol epoxides. A close correlation was observed between the volume occupied by the amino acid residue at position 105 and the value of kcat/Km. With the syn-diol epoxides, such a correlation was observed with alanine, valine and isoleucine, whereas tryptophan was associated with increased kcat/Km values. The mutational replacement of isoleucine with alanine or tryptophan at position 105 did not alter the enantio selectivity of the GSTP1-1 variants compared with the naturally occurring allelic variants GSTP1-1/I-105 and GSTP1-1/V-105. Since the amino acid at position 105 forms part of the substrate binding site (H-site) the effect of increasing bulkiness is expected to cause restricted access of the diol epoxide and proper alignment of the two reactants for efficient glutathionylation. In conclusion, the present study indicates that individuals who are homozygous for the allele GSTP1* B (coding for GSTP1-1/V-105) display a higher susceptibility to malignancy because of other factors than a decreased catalytic efficiency of GSTP1-1/V-105 in the detoxication of carcinogenic diol epoxides of benzo[a]pyrene or structurally related PAH.
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| 2. |
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| 3. |
- Albinsson, Bo, et al.
(författare)
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Seroprevalence of tick-borne encephalitis virus and vaccination coverage of tick-borne encephalitis, Sweden, 2018 to 2019
- 2024
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Ingår i: Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin. - : European Centre for Disease Control and Prevention (ECDC). - 1560-7917 .- 1025-496X. ; 29:2
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundIn Sweden, information on seroprevalence of tick-borne encephalitis virus (TBEV) in the population, including vaccination coverage and infection, is scattered. This is largely due to the absence of a national tick-borne encephalitis (TBE) vaccination registry, scarcity of previous serological studies and use of serological methods not distinguishing between antibodies induced by vaccination and infection. Furthermore, the number of notified TBE cases in Sweden has continued to increase in recent years despite increased vaccination.AimThe aim was to estimate the TBEV seroprevalence in Sweden.MethodsIn 2018 and 2019, 2,700 serum samples from blood donors in nine Swedish regions were analysed using a serological method that can distinguish antibodies induced by vaccination from antibodies elicited by infection. The regions were chosen to reflect differences in notified TBE incidence.ResultsThe overall seroprevalence varied from 9.7% (95% confidence interval (CI): 6.6-13.6%) to 64.0% (95% CI: 58.3-69.4%) between regions. The proportion of vaccinated individuals ranged from 8.7% (95% CI: 5.8-12.6) to 57.0% (95% CI: 51.2-62.6) and of infected from 1.0% (95% CI: 0.2-3.0) to 7.0% (95% CI: 4.5-10.7). Thus, more than 160,000 and 1,600,000 individuals could have been infected by TBEV and vaccinated against TBE, respectively. The mean manifestation index was 3.1%.ConclusionA difference was observed between low- and high-incidence TBE regions, on the overall TBEV seroprevalence and when separated into vaccinated and infected individuals. The estimated incidence and manifestation index argue that a large proportion of TBEV infections are not diagnosed.
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| 4. |
- Arnell, Henrik, et al.
(författare)
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The genetics of primary nocturnal enuresis: inheritance and suggestion of a second major gene on chromosome 12q
- 1997
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Ingår i: Journal of Medical Genetics. - : BMJ. - 0022-2593 .- 1468-6244. ; 34:5, s. 360-5
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Tidskriftsartikel (refereegranskat)abstract
- Primary nocturnal enuresis (PNE), or bedwetting at night, affects approximately 10% of 6 year old children. Genetic components contribute to the pathogenesis and recently one locus was assigned to chromosome 13q. We evaluated the genetic factors and the pattern of inheritance for PNE in 392 families. Dominant transmission was observed in 43% and an apparent recessive mode of inheritance was observed in 9% of the families. Among the 392 probands the ratio of males to females was 3:1 indicating sex linked or sex influenced factors. Linkage to candidate regions was tested in 16 larger families segregating for autosomal dominant PNE. A gene for PNE was excluded from chromosome 13q in 11 families, whereas linkage to the interval D13S263-D13S291 was suggested (Zmax = 2.1) in three families. Further linkage analyses excluded about 1/3 of the genome at a 10 cM resolution except the region around D12S80 on chromosome 12q that showed a positive two point lod score in six of the families (Zmax = 4.2). This locus remains suggestive because the material was not sufficiently large to give evidence for heterogeneity. Our pedigree analysis indicates that major genes are involved in a large proportion of PNE families and the linkage results suggest that such a gene is located on chromosome 12q.
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| 5. |
- 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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| 6. |
- Azhdar, Bruska, et al.
(författare)
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Determination of dynamic and sliding friction, and observation of stick-slip phenomenon on compacted polymer powders during high-velocity compaction
- 2006
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Ingår i: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 25:8, s. 1069-1080
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic friction, sliding friction, and the stick-slip phenomenon have been studied on compacted polymer powders during high-velocity compaction. It is particularly important from a practical point of view to distinguish the stick-slip mechanism and the sliding mechanism which occur concurrently. A practical experimental system has been successfully developed to study the dry frictional force and to measure the sliding coefficient between the polymer powder particles and the die wall during high-velocity compaction. Two new components have been introduced as relaxation assists to improve the compaction process by reducing the frictional forces. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form with less change in dimensions. The subsequent movement of the particles can be reduced and the powder bed attains a higher density with a minimum total elastic spring-back. The relative time of the stick-slip phenomenon during the compacting stage is also reduced so that the time needed to transfer from an intermittent stick-slip state to a smooth sliding state is reduced and the powder bed slides smoothly. It was found that the dynamic, dry frictional force is intermittent (stick-slip mechanism) at low compaction rates but that at high compaction rates is becomes more smooth (sliding mechanism). Both mechanisms depend on the nature of the powder and on the compaction conditions. At the beginning of the compaction stage, the sliding coefficient decreases due to an increase in the radial to axial stress ratio until the maximum pressure has been reached. During the reorganization stage, more time is needed for large particles to move, rotate and slide due to their relatively large diameter and mass. As a result, the reorganization stage is extended and the stick-slip phenomenon is observed more with increasing particle size. Much better transfer of the pressure throughout the powder bed and less loss of pressure lead to a higher sliding coefficient due to the overall friction during the compaction process. It was found that the sliding coefficient is proportional to the density. A more homogeneous density distribution in the compacted powder and a smaller pressure loss during compaction has a major influence on the sliding coefficient and on the quality of the compacted material
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| 7. |
- Azhdar, Bruska, et al.
(författare)
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Determination of springback gradient in the die on compacted polymer powders during high-velocity compaction
- 2006
-
Ingår i: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 25:1, s. 114-123
-
Tidskriftsartikel (refereegranskat)abstract
- A uniaxial high-velocity compaction process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with various heights. The influences of the relaxation assist device on the process characteristics are discussed. Two bonded strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. It is shown that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. The delay times between the pressure waves are also strongly dependent on the strain rate. If the height of the relaxation assist device is increased, the first gross instantaneous springback, and the total elastic springback, are reduced. In addition, the density of the powder bed is increased. The relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be also controlled by altering the height of the relaxation assist.
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| 8. |
- Azhdar, Bruska, et al.
(författare)
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Development of a High-Velocity Compaction process for polymer powders
- 2005
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Ingår i: Polymer testing. - : Elsevier BV. - 0142-9418 .- 1873-2348. ; 24:7, s. 909-919
-
Tidskriftsartikel (refereegranskat)abstract
- The High-Velocity Compaction (HVC) process for powder polymers has been studied, with a focus on the compactibility characteristics and surface morphology of the compacted materials, with and without relaxation assists, by increasing compacting quantity and direction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomena during the decompacting stage. Polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. Scanning electron microscopy (SEM) and image computer board camera, (IC-PCI Imaging Technology) have been used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. The relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). The pressure and density distribution differences between the upper and lower surface are not uniform. Projectile supports or 'relaxation assists' are presented as a new technique to reduce pull-out phenomenon. Experimental results for different compaction profiles are presented showing the effect of varying the opposite velocity during the decompacting stage, and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists.
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| 9. |
- Azhdar, Bruska, 1965-
(författare)
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Novel Technique to Improve High-Velocity Cold Compaction : Processing of Polymer Powders and Polymer-Based Nanocomposite High Performance Components
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Compaction of polymer powders and polymer-based nanocomposites by uniaxial high-velocity cold compaction (HVC), by high-energy ball milling (HEBM) and using a novel technique, relaxation assists, was investigated with a focus on the process parameters, the compactibility characteristics, surface morphology and friction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain the pull-out phenomenon, springback gradient, delay time, relative time of the pressure wave, and stick-slip phenomenon during the compaction process. Experimental results for different compaction profiles, different particle size distributions and different milling system for polymer-based nanocomposite are presented, showing the effect of varying the process parameters on the compacted material; the compactibility in the compacted bed, the uniformity of the compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state. It was found that the high-velocity compaction process is an interruption process and that the opposite velocity and pressure loss during the compaction process have a major influence on the quality of the compacted material. The relaxation assist device is a novel technique that has been successfully developed to improve the compaction process. The relaxation assists are parts of the piston and they are regarded as projectile supports. They are constructed of the same material as the piston, and the diameters are the same but the lengths are different. The relaxation assist device leads to an improvement in the compaction of powders, polymer powders and polymer-based nanocomposites by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form during the compaction process with less change in dimensions in the case of both homogeneous and heterogeneous materials. If the movement of the particles is restricted the powder bed attains a higher density and the total elastic springback is minimized. In addition, there is a more homogeneous dispersion of nanoparticles in the case of a heterogeneous material. A much better transfer of the pressure through the powder bed and a smaller loss of pressure lead to a more homogenous stick-slip of the particles and a higher sliding coefficient due to the overall friction during the compaction process.
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| 10. |
- Azhdar, Bruska, et al.
(författare)
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Polymer-nanofiller prepared by high-energy ball milling and high velocity cold compaction
- 2008
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 29:3, s. 252-261
-
Tidskriftsartikel (refereegranskat)abstract
- High-energy ball milling using comilling in a solid state by low-temperature mechanical alloying to prepare nickel-ferrite (NiFe2O4) nanopowders and ultrafine poly(methyl methacrylate) (PMMA), dispersing nanoparticles in a polymer matrix, and a uniaxial high-velocity cold compaction process using a cylindrical, hardened steel die and a new technique with relaxation assists have been studied. The focus has been on the particle size distributions of the nanocomposite powder during the milling and on the surface morphology of the nanocomposite-compacted materials after compaction with and without relaxation assists. Experimental results for different milling systems are presented showing the effects of milling time and material ratio. It was found that a longer mixing time give a higher degree of dispersion of the nanopowder on the PMMA particle surfaces. Furthermore, with increasing content of NiFe2O4 nanopowder, the reduction of the particle size was more effective. Different postcompacting profiles, i.e. different energy distributions between the upper and lower parts of the compacted powder bed, lead to different movements of the various particles and particle layers. Uniformity, homogeneity, and densification on the surfaces in the compacted powder are influenced by the postcompacting magnitude and direction. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by reducing the expansion of the compacted volume and by reducing the different opposite velocities, giving the compacted composite bed a more homogeneous opposite velocity during the decompacting stage and reducing the delay time between the successive pressure waves.
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| 11. |
- Carlson, Marie, 1950, et al.
(författare)
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Transnational mobility of higher education within Asia – Strategies and educational conditions among young people related to gender, ethnicity and class
- 2012
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Ingår i: GEA – Gender and Education Association Conference April 11-13, Göteborg. Theme: Gender and Democracy: Gender Research in times of change.
-
Konferensbidrag (refereegranskat)abstract
- Transnational mobility in higher education within Asia – Strategies and educational conditions among young people related to gender, ethnicity and class. This workshop mainly invites to a methodological discussion within an ongoing interdisciplinary project focusing on inter-Asian education mobility – a theme that so far has been given little attention even though access to education has long been the reason for migration and mobility. Many Asian youths travel abroad and study in their neighbouring countries - however, the interest has most often been on the increased numbers of young people from Asian countries who obtain higher education in Western countries. By taking a perspective that situates individuals at the centre this study investigates young people’s strategies, experiences and visions in different Asian contexts. Particular interest is paid to power hierarchies based on class, ethnicity, gender, and religion. Theoretical the project employs the concept of social transnational fields and draws inspiration from cultural, migration, global, and gender studies, as well as postcolonial theory. Six researchers are involved in the project and carry out fieldwork among students who study in India, Indonesia, Malaysia, Middle East, Thailand and Turkey and the students come from neighbouring Asian countries. The research group collaborates in the development of theory and methodology. Disciplines represented in the study are Islamic studies, sociology, anthropology and history. The students’/the subjects’ experiences are in the centre of the research and through the use of life stories as its research methodology, the research group approaches transnational mobility in a unique way. Furthermore a so-called soft comparison is used, contrasting the material in order to generate mutual interpretative advantages. The academic importance of the project lies in its theoretical and methodological approach, but also in the empirical data it generates. The overall aim of the project is dealing with the transnational space and values that govern the various study options and strategies – how students regard the “homeland” and “host” country – the importance of gender, ethnicity and how students are affected by mobility as part of the their own social, political and religious context. At the workshop all six researchers in the project will present some preliminary results based on recent field data and discuss what kind of themes and intersecting aspects we are trying to involve when approaching the students in using life stories. Likewise discuss possibilities/difficulties in conducting a multi-sited interdisciplinary study. In addition to the researchers in the project we hope for at least 10-20 persons to participate in the discussion.
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| 12. |
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| 13. |
- Elmståhl, Sölve, et al.
(författare)
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Behavioral disturbances and pharmacological treatment of patients with dementia in family caregiving : A 2-year follow-up
- 1998
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Ingår i: International Psychogeriatrics. - 1041-6102. ; 10:3, s. 239-252
-
Tidskriftsartikel (refereegranskat)abstract
- Behavioral disturbances are common in dementia. Polypharmacy due to progression of disease and fluctuation of symptoms among patients might increase risk of overtreatment and/or undertreatment. Drug prescription habits were studied in relationship to symptoms of dementia after relocation of patients to group-living care units (GC). Seventy-six demented patients (mean age 81 years) were assessed before, 12 months after, and 24 months after relocation to GC. Vascular dementia was found in 47%, Alzheimer's dementia in 46%, and other dementias in 7%. Medications, regular or as required, were recorded from medication lists. Repeated observations of symptoms like depressive mood and lack of vitality were made with validated scales. Eighty percent of the patients were prescribed drugs; 40% were given neuroleptics and 9% were given antidepressants. During the 2-year follow-up, polypharmacy increased; patients with five drugs or more increased from 15% to 35%; usage of neuroleptics or sedatives, as required, increased from 8% to 25%, p < .01. Depressive mood was noted in 86% after 2 years and 74% showed aggressiveness and anxiety, but only 12% of the patients with depressive symptoms were on antidepressants. Analgesics were prescribed to 26% of patients. In conclusion, a high proportion of patients with dementia had depressive mood and undertreatment of depressive disorder might be suspected. Polypharmacy increased during the 2-year follow-up; this finding calls for careful monitoring of adverse drug reactions, because of the deteriorating cognitive function of these patients.
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| 14. |
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| 15. |
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| 16. |
- Ivarsson, Ylva, 1976-
(författare)
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Evolutionary Analysis and Posttranslational Chemical Modifications in Protein Redesign : A Study on Mu Class Glutathione Transferases
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glutathione transferases (GSTs) constitute a family of multifarious enzymes that conjugate glutathione (GSH) with a wide range of electrophiles. GSTs are grouped into different classes based on protein sequence similarities. Despite high sequence identities between GSTs of the same class they often display different substrate specificites. Human GST M1-1 is efficiently catalyzing the conjugation of GSH and various epoxide substrates, whereas the 84% sequence-identical GST M2-2 has low activities with the same substrates.Evolutionary rate analysis was used to identify hypervariable amino acid positions among GST Mu class sequences. A Thr to Ser conversion of the variable residue 210 in GST M2-2 elicited a drastic increase in catalytic activity with epoxides, which is the characteristic activity of GST M1-1. This provides support for the usefulness of evolutionary analysis in identifying functionally important residues, although the additional mutations of two other variable residues did not confer any noteworthy changes in activity.To further investigate the functional importance of residue T210 in GST M2-2 it was replaced by all other commonly occurring amino acids. The replacements caused marked changes in substrate specificity, stability, and expressivity, indicating how functionalities of a duplicated Mu class GST may easily be altered by point mutations. The stereo- and regioselectivity in epoxide-conjugation catalyzed by GSTs M1-1 and M2-2 was investigated. The results show that a serine in position 210 is beneficial for high enantioselectivity with trans-stilbene oxide. However, an alanine in position 210 is more favorable for stereo- and regioselectivity with the smaller epoxide substrate styrene-7,8-oxide. The low enantioselectivity of GST M1-1 was improved 10- and 9- fold with styrene-7,8-oxide and 1-phenylpropylene oxide, respectively, through different combination of site-specific mutations and posttranslational chemical modifications. The approach can be employed in more extensive screening experiments where a large variety of modifications easily can be tested.
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| 17. |
- Jacobson, K., et al.
(författare)
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Chemiluminescence as a tool for polyolefin oxidation studies
- 2004
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Ingår i: Advances in Polymer Science. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0065-3195 .- 1436-5030. ; 169, s. 151-176
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Forskningsöversikt (refereegranskat)abstract
- The oxidation of polymers such as polypropylene and polyethylene is accompanied by weak chemiluminescence. The development of sensitive photon counting systems has made it comparatively easy to measure faint light emissions and polymer chemiluminescence has become an important method to follow the initial stages in the oxidative degradation of polymers. Alternatively, chemiluminescence is used to determine the amount of hydroperoxides accumulated in a pre-oxidised polymer. Chemiluminescence has also been applied to study how irradiation or mechanical stress affects the rate of polymer oxidation. In recent years, imaging chemiluminescence has been established as a most valuable technique offering both spatial and temporal resolution of oxidation in polymers. This technique has disclosed that oxidation in polyolefins is non-uniformly distributed and proceeds by spreading. This review is the result of several investigations performed by the authors and other research groups where chemiluminescence has been used to study oxidative degradation of polyolefins, either as the main technique or as a complement to other techniques.
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| 18. |
- Johannisson, Bengt, 1942-, et al.
(författare)
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Organizing Societal Entrepreneurship : A Cross-Sector Challenge
- 2015. - 1
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Ingår i: Handbook of Entrepreneurship and Sustainable Development Research. - Cheltenham : Edward Elgar Publishing. - 9781849808231 - 9781849808248 ; , s. 130-154
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Bokkapitel (refereegranskat)abstract
- Allying and expanding the diverse fields of entrepreneurship and sustainable development research is a modern day imperative. The Handbook of Entrepreneurship and Sustainable Development Research cuts through the different approaches and perspectives of the two fields to point the way ahead for research on sustainable entrepreneurship, outlining the motivation, intentions and impact of ecopreneurs in a local, national and global context.This Handbook paints an illuminating picture of the historic and current understanding of the bond between entrepreneurship and sustainable development. The authors explore the basic contradictions between the two fields and outline the transformative role entrepreneurship can play in achieving sustainable development. 45 expert researchers and their research communities from 16 countries across Europe, Africa, Australia and North America provide original and informative contributions on a variety of issues, from women’s empowerment to climate change and organic farmers to ecotourism.With current and authorative contributions spanning the globe, this Handbook will inspire researchers, teachers and policy-makers to compose their own understanding and contribution on the fast expanding field of entrepreneurship and sustainable development.
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| 19. |
- Johansson, Ann-Sofie, et al.
(författare)
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Structure-activity relationships and thermal stability of human glutathione transferase P1-1 governed by the H-site residue 105
- 1998
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Ingår i: Journal of Molecular Cell Biology. - : Elsevier BV. - 1674-2788 .- 1759-4685 .- 0022-2836. ; 278:3, s. 687-698
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Tidskriftsartikel (refereegranskat)abstract
- Human glutathione transferase P1-1 (GSTP1-1) is polymorphic in amino acid residue 105, positioned in the substrate binding H-site. To elucidate the role of this residue an extensive characterization of GSTP1-1/Ile105 and GSTP1-1/Val105 was performed. Mutant enzymes with altered volume and hydrophobicity of residue 105, GSTP1-1/Ala105 and GSTP1-1/Trp105, were constructed and included in the study. Steady-state kinetic parameters and specific activities were determined using a panel of electrophilic substrates, with the aim of covering different types of reaction mechanisms. Analysis of the steady-state kinetic parameters indicates that the effect of the substitution of the amino acid in position 105 is highly dependent on substrate used. When 1-chloro-2,4-dinitrobenzene was used as substrate a change in the side-chain of residue 105 seemed primarily to cause changes in the KM value, while the kcat value was not distinctively affected. With other substrates, such as 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and ethacrynic acid both kcat and KM values were altered by the substitution of amino acid 105. The constant for formation of the sigma-complex between 1,3, 5-trinitrobenzene and glutathione was shown to be dependent upon the volume of the amino acid in position 105. The nature of the amino acid in position 105 was also shown to affect the thermal stability of the enzyme at 50 degrees C, indicating an important role for this residue in the stabilization of the enzyme. The GSTP1-1/Ile105 variant was approximately two to three times more stable than the Val105 variant as judged by their half-lives. The presence of glutathione in the incubation buffer afforded a threefold increase in the half-lives of the enzymes. Thus, the thermal stability of the enzyme and depending on substrate, both KM values and turnover numbers are influenced by substitutions in position 105 of GSTP1-1.
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| 20. |
- Kari, Leif, et al.
(författare)
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Dynamic stiffness of natural rubber cylinders in the audible frequency range using wave guides
- 2001
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Ingår i: Kautschuk und Gummi, Kunststoffe. - 0022-9520. ; 54:3, s. 106-
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Tidskriftsartikel (refereegranskat)abstract
- This paper applies a wave guide model to analyze the temperature influence on the dynamic stiffness of a cylindrical vibration isolator of natural rubber in the audible frequency range; covering 20 to 20 000 Hz and - 60 to + 60 degreesC. A nearly incompressible material model is applied with shear modulus based on a fractional derivative model, thereby reducing the parameter number needed to accurately fit measurement results. Employing the method of reduced variables enlarges the frequency range available from measurements. Of particular interest are the stiffness peaks and troughs, the low-frequency stiffness, the propagating and nonpropagating modes, and their dependence on temperature.
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| 21. |
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| 22. |
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| 23. |
- Kari, Leif, et al.
(författare)
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Structure-borne sound properties of isotropic magneto-rheological rubber
- 2002
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Ingår i: Kautschuk und Gummi, Kunststoffe. - 0022-9520. ; 55:12, s. 669-673
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic properties of isotropic magneto-rheological rubber are examined through experiments within an audible frequency range covering 100 to 1250 Hz while applying an external magnetic field of 0 to 0.8 T. The shear modulus for this manufacturer convenient material, consisting of dispersed irregular, micrometer sized iron particles in a nitrile rubber matrix, is found to depend strongly on both frequency and magnetic field, while the loss factor is almost independent of those factors. Magneto-rheological rubbers applied to vibration isolators promise to have more functionality than conventional isolators while rapidly and reversibly change rigid body and stiffness peak frequencies.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
- Lokander, Mattias, et al.
(författare)
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Improving the magnetorheological effect in isotropic magnetorheological rubber materials
- 2003
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Ingår i: Polymer testing. - 0142-9418 .- 1873-2348. ; 22:6, s. 677-680
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Tidskriftsartikel (refereegranskat)abstract
- Magnetorheological (MR) rubber materials are the solid analogue of magnetorheological fluids; i.e. their theological properties can be controlled by an applied magnetic field. However, the use of a crosslinked matrix allows larger particles to be used than in fluid matrices, and when large irregular particles are used alignment of the particles is not necessary for obtaining a substantial MR effect. We show that the absolute MR effect of isotropic MR rubber materials with large irregular iron particles is independent of the matrix material, and that the relative MR effect can be increased by the addition of plasticisers. Other ways of increasing the MR effect are to increase the magnetic field, although the materials saturate magnetically at high fields, or to use small amplitude strains. Finally, we show that the damping of isotropic MR rubbers is to some extent increased by an applied magnetic field, but that the increase is too small to be of any practical importance.
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| 28. |
- Lokander, Mattias, et al.
(författare)
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Magnetorheological devices
- 2006
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Ingår i: Elastomers and Components: Service Life Prediction - Progress and Challenges. - : Woodhead Publishing Limited. - 9781845691004 ; , s. 165-169
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The mechanical properties of magnetorheological materials can be changed and controlled by an applied magnetic field. This makes the group of materials interesting for damping applications and vibration control. Most of the work done so far has been performed on magnetorheological fluids, which are suspensions of magnetically polarizable particles in a carrier liquid. For some applications it would be preferable to use a rubber or a gel instead of the liquid. Such magnetorheological solids would not have any problems of sedimentation of particles, the devices could be made smaller and cheaper since there would be no need of a container for the fluid, and the changes in the mechanical properties could be expected to be faster than in a liquid. However, magnetorheological solids work only in the pre-yield region while the fluids typically work in the post-yield region, so the two groups of materials are therefore more complementary than competitive. Examples of rubbers that are interesting for magnetorheological applications are silicone, natural rubber and nitrile rubber. The addition of iron particles to the rubber will influence the service life of these rubber devices. For optimal function of the devices, prediction of service life is necessary. Such predictions are also necessary for magnetorheological devices to become commercially successful.
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| 29. |
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| 30. |
- Lokander, Mattias, et al.
(författare)
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Oxidation of Natural Rubber based Magnetorheological Elastomers
- 2004
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 86:3, s. 467-471
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Tidskriftsartikel (refereegranskat)abstract
- The Theological properties of magnetorheological (MR) materials can be changed continuously, rapidly and reversibly by an applied magnetic field. Solid MR materials consist of magnetically polarisable particles, generally iron, in an elastomer matrix. The high iron concentrations required (about 30% by volume) in order to get a substantial magnetorheological effect should influence the long-term stability of the materials. In this paper, the oxidative stability of natural rubber-based magnetorheological elastomers has been studied by chemiluminescence and oven ageing. The results show that the oxidative stability of natural rubber decreases dramatically when large amounts of iron particles are incorporated in the matrix. This is probably due to the large amounts of oxygen on the surface of the particles. Conventional antioxidants can be used to prolong the lifetime of magnetorheological elastomers, but in order to get acceptable lifetime of the materials a careful selection of the antioxidant system has to be made.
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| 31. |
- Lokander, Mattias, et al.
(författare)
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Performance of Isotropic Magnetorheological Rubber Materials
- 2003
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Ingår i: Polymer testing. - 0142-9418 .- 1873-2348. ; 22:3, s. 245-251
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Tidskriftsartikel (refereegranskat)abstract
- Magnetorheological (MR) rubber materials are the solid analog of magnetorheological fluids; hence, their theological properties can be controlled by an applied magnetic field. If the particles embedded in the matrix are carbonyl iron, they have to be aligned by a magnetic field before the curing of the rubber, in order to achieve a substantial MR effect. However, the use of a crosslinked matrix allows larger particles to be used. We show that MR rubber materials with large irregular particles have a large MR effect although the particles are not aligned within the material. This is explained by the low critical particle volume concentration of such particles. A similar effect can be obtained for materials with carbonyl iron, if the particles are badly dispersed and thereby behaving like larger irregular particles. Besides the achieved level of dispersion, the theological properties of the matrix material do not influence the MR effect.
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| 32. |
- Lokander, Mattias, 1973-
(författare)
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Performance of Magnetorheological Rubber Materials
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnetorheological (MR) rubber materials are the solid analogue of magnetorheological fluids; i.e. their rheological properties can be controlled continously, rapidly, and reversibly by an applied magnetic field. They consist of magnetically polarisable particles in an elastomer matrix and they can be made to respond to changes in their environment; hence, they are considered as "smart" materials. Examples of potential applications for these materials are adaptive tuned vibration absorbers, stiffness-tuneable mounts and suspensions, and automotive bushings. The purpose of this work was to increase the knowledge relating to magnetorheological materials for damping applications. The materials should exhibit a large response to an applied magnetic field, and have good mechanical and long-term properties. MR rubber materials were made from nitrile, natural and silicone rubber, with irregularly shaped iron particles several micrometres in size. The particles were not aligned by a magnetic field prior to the vulcanisation; hence, the materials can be considered to be isotropic. These materials show a large MR effect, i.e. an increase in the shear modulus when a magnetic field is applied, although the particles are not aligned within the material. This is explained by the low critical particle volume concentration (CPVC) of such particles. Similar behaviour can be obtained with materials containing carbonyl iron, if the particles are aggregated so that they behave like large irregular particles. The iron particle concentration must be very close to the CPVC in order to obtain a large MR effect without alignment of the particles. The absolute MR effect (MPa) in an isotropic MR rubber material with large irregular iron particles is independent of the matrix material, and the relative MR effect (%) can thus be increased by the addition of plasticisers. However, the obtainable effect is limited by the reinforcement of the particles and by friction between the particles. Therefore, it is very difficult, if not impossible, to achieve an MR effect larger than 60%. Other ways of increasing the MR effect are to increase the strength of the magnetic field, although the materials saturate magnetically at high field strengths, or to use small strain amplitudes. The strong strain amplitude dependence of the MR effect suggests that MR rubber materials are most suitable for low amplitude applications, such as sound and vibration insulation. Measurements at frequencies within the audible frequency range show that this is a promising application for MR rubber materials. The incorporation of large amounts of iron into the rubber matrix decreases the oxidative stability dramatically. This is probably due to iron oxides on the surface of the particles, and to the fact that the oxidation rate is enhanced by iron ions, which are able to diffuse into the matrix. Standard antioxidants do not provide sufficient stabilisation for MR rubbers. Thus, proper stabilisation systems have to be found in order for these materials to be successful in applications.
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| 33. |
- Shanks, David, et al.
(författare)
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Improved Antioxidant Formulations for Polymeric Materials : Synergistic Protective Effects in Combinations of Organotellurium Compounds with Conventional Phenolic Antioxidants or Thiols
- 2003
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 81:2, s. 261-271
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Tidskriftsartikel (refereegranskat)abstract
- As judged by differential scanning calorimetry experiments at 190 °C and chemiluminescence measurements at 150 °C, addition of 0.10–0.30 wt.% of certain organotellurium compounds to polypropylene caused a notable protection against oxidation of the material. The best stabilizers (diaryl telluride 3 and alkyl aryl telluride 4), offered a similar degree of protection as commercial stabilizer formulations comprising a mixture of Irganox® 1010 and Irgafos® 168 (0.1 wt.% of each). The protective effect of the organotelluriums was substantially improved in combinations with sterically hindered phenols or thiols. The protection was often much better than the added effects of the individual components and, thus, can be considered as synergistic. Evaluation of a series of stabilizers where tellurium had been exchanged for selenium and sulfur (compounds 2) showed that the synergistic protective effect was unique for tellurium.
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| 34. |
- Stenberg, Emelie, et al.
(författare)
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Continuing professional development in general dentistry-experiences of an online flipped classroom
- 2024
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Ingår i: European journal of dental education. - : John Wiley & Sons. - 1396-5883 .- 1600-0579.
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Continuing professional development is a lifelong learning process. One pedagogical approach that can be used is active learning. Flipped classroom is a method that has been shown to improve deeper conceptual understanding. In an online setting, the method saves travel, time, and costs. To our knowledge, flipped classroom is rarely used in continuing professional education. This study in general dentistry explored experiences of an online flipped classroom course in continuing professional development.Materials and Methods: Fifteen dental hygienists, clinically active in general dental care, were interviewed. They were recruited from an online course on the latest classification system for periodontal diseases. The course had been conducted using an active learning and flipped classroom model. The interviews were semi-structured. Data were extracted using qualitative content analysis.Results: The experiences of the dental hygienists could be summarized in three themes: Stimulation of knowledge gain through self-paced studies, The ease of virtual networking among colleagues, and Fostering of direct practical application through collaboration.Conclusion: New and emerging communication technology seems to open new possibilities for continuing professional development in general dentistry. Study participants felt that, in an online environment, mixing asynchronous and synchronous communication in a flipped classroom model facilitated learning in continuing professional development. Online active learning seems to work well in continuous professional development in general dentistry. After the course, the participating dental hygienists stated that they were able to use their new knowledge clinically and felt confident doing so.
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| 35. |
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