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| 3. |
- Al-Abdalla, A, et al.
(författare)
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Ab initio model potential embedded-cluster study of the ground and lowest excited states of Cr3+ defects in the elpasolites Cs2NaYCl6 and Cs2NaYBr6
- 1998
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Ingår i: Journal of Chemical Physics. - : Springer Science and Business Media LLC. - 0021-9606 .- 1089-7690. ; 108, s. 2005-2014
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present the results of an ab initio model potential (AIMP) embedded-cluster study of the ground and lowest excited states of Cr3+ defects in the elpasolites Cs2NaYCl6 and Cs2NaYBr6; complete active space SCF (CASSCF) and averaged coupled-pair functional (ACPF) calculations are performed on CrCl63- and CrBr63- clusters embedded in ab initio model potential representations of the surrounding lattices Cs2NaYCl6 and Cs2NaYBr6. The experimental structural data are revisited and some new results are found which differ significantly from those available in the literature. The calculated local structure parameters and electronic transition energies which can be compared to experiments are found to be very good; new structural and spectroscopic results are produced which have been neither measured nor calculated, which are complementary to the available ones, and whose quality is expected to be high as well. In particular, the question of the competition of the excited-state absorptions with the potential vibronic laser emission has been adressed: A considerable overlap between the broad E-2(g) –> (2)A(1g) excited-state absorption and (4)A(2g) <– T-4(2g) emission bands is predicted in both materials, which must result in a reduction in the emission efficiency. Finally, it is shown that the quantum mechanical embedding effects due to the fact that the external Cs+, Na+, Y3+, Cl-, and Br- ions are not point charges, are non-negligible; lacking of these effects must be one of the reasons which make previous Density Functional Theory calculations show significantly larger discrepancies with the available experiments.
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- Kifetew, G, et al.
(författare)
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The effect of drying on wood fracture surfaces from specimens loaded in wet condition
- 1998
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Ingår i: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 32:2, s. 83-94
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Tidskriftsartikel (refereegranskat)abstract
- The study describes the effect of drying on fracture surfaces of Scots pinePinus silvestris L. Microtomed specimens of isolated and combined early-and latewood, in green and oven-dried/resoaked state were loaded to failure in uniaxial tension parallel to the grain. The fracture surfaces were studied using scanning electron microscopy (SEM). Both green early- and latewood samples showed rough fracture surfaces, which in latewood was dominated by intrawall failure. In the resoaked state, transwall failure dominated and fracture surfaces were more flat, indicating a more brittle fracture process. Although variation in the data was large, the strength of the resoaked samples were generally lower than those of paired green samples. The observations support irreversible cell wall damage formed during drying which severely affects the failure mechanism.
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| 8. |
- Mannelquist, Anders, et al.
(författare)
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Influence of tip geometry on fractal analysis of atomic force microscopy images
- 1998
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 66:Supplement 1, s. S 891-S 895
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Tidskriftsartikel (refereegranskat)abstract
- Fractal analysis of data from atomic force microscopy (AFM) is often necessary for studying surfaces with scale-invariant roughness. However, the fractal parameters are influenced by the finite-sized tip geometry of the AFM stylus. We make an extended study of such little-known effects. The so-called successive random algorithm is used to generate by computer ideal fractal surfaces with known fractal dimensions and varying height magnitudes. Tip-distorted AFM images are simulated from the ideal surfaces for the case of a strictly geometrical interaction between surface and tip. The AFM-induced error, taken as the difference in estimated parameters between ideal and distorted images, is shown to be largest for small scan sizes and high fractal dimensions. The dependence on AFM tip radius and surface height magnitude is analyzed by the structure function, variance and a Fourier method. The latter is shown to be unreliable for analyzing AFM images. We exemplify how the results can be applied to AFM images of real surfaces.
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| 11. |
- Ratkevicius, A, et al.
(författare)
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Effects of contraction duration on low-frequency fatigue in voluntary and electrically induced exercise of quadriceps muscle in humans
- 1998
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Ingår i: European Journal of Applied Physiology and Occupational Physiology. - : Springer Science and Business Media LLC. - 0301-5548 .- 1439-6319 .- 1439-6327 .- 1432-1025. ; 77:5, s. 462-468
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Tidskriftsartikel (refereegranskat)abstract
- The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise.
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| 12. |
- Rodushkin, Ilya
(författare)
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Capabilities of high resolution inductively coupled plasma mass spectrometry for trace element determination in plant sample digests
- 1998
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 362:6, s. 541-546
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Tidskriftsartikel (refereegranskat)abstract
- The analytical performance of inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of plant sample digests was evaluated using double focusing sector field ICP-MS (ICP-SMS). Instrumental detection limits of ICP-SMS are superior to those obtained by quadrupole systems (ICP-QMS) and reach the fg mL-1 range for elements with high m/z ratios. Matrix effects caused by a plant digest after sample preparation resulting in 200-fold dilution were found to be negligible. The usefulness of high mass resolution for overcoming some spectral interferences is demonstrated. Mathematical correction possibilities could be necessary to improve accuracy. The concentrations of more than 20 elements can be determined in 5 min and only one internal standard is necessary to correct for instrumental drift.
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| 13. |
- Thuvander, F., et al.
(författare)
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A multiple fracture test for strain to failure distribution in wood
- 1998
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Ingår i: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 32:3, s. 227-235
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Tidskriftsartikel (refereegranskat)abstract
- The tensile strain to failure of small wood samples is a desirable property in studies where the effect of small differences in microstructure on failure is of interest. However, the scatter in data is usually significant and only one data is obtained per specimen. For this reason, a new multiple fracture test for measurement of the strain to failure distribution was designed. Wood samples were bonded between two transparent PVC layers with higher strain to failure than the wood. Multiple fractures were then observed in single wood samples during tensile loading. This behavior is already utilized in tests in the field of synthetic composite materials. It was possible to conveniently register multiple fracture events as a function of strain by visual observation through the transparent PVC layers. The data were used to compare two different wood materials and to determine their Weibull distribution functions
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| 30. |
- Schulze-Osthoff, Klaus, et al.
(författare)
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Apoptosis signaling by death receptors
- 1998
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 254:3, s. 439-459
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Tidskriftsartikel (refereegranskat)abstract
- Death receptors have been recently identified as a subgroup of the TNF-receptor superfamily with a predominant function in induction of apoptosis. The receptors are characterized by an intracellular region, called the death domain, which is required for the transmission of the cytotoxic signal. Currently, five different such death receptors are known including tumor necrosis factor (TNF) receptor-1, CD95 (Fas/APO-1), TNF-receptor-related apoptosis-mediated protein (TRAMP) and TNF-related apoptosis-inducing ligand (TRAIL) receptor-1 and -2. The signaling pathways by which these receptors induce apoptosis are rather similar. Ligand binding induces receptor oligomerization, followed by the recruitment of an adaptor protein to the death domain through homophilic interaction. The adaptor protein then binds a proximal caspase, thereby connecting receptor signaling to the apoptotic effector machinery. In addition, further pathways have been linked to death receptor-mediated apoptosis, such as sphingomyelinases, JNK kinases and oxidative stress. These pro-apoptotic signals are counteracted by several mechanisms which inhibit apoptosis at different levels. This review summarizes the current and rapidly expanding knowledge about the biological functions of death receptors and the mechanisms to trigger or to counteract cell death.
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| 32. |
- Akerberg, C, et al.
(författare)
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Modelling the influence of pH, temperature, glucose and lactic acid concentrations on the kinetics of lactic acid production by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour
- 1998
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 49:6, s. 682-690
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Tidskriftsartikel (refereegranskat)abstract
- A kinetic model of the fermentative production of lactic acid from glucose by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour has been developed. The model consists of terms for substrate and product inhibition as well as for the influence of pH and temperature. Experimental data from fermentation experiments under different physical conditions were used to fit and verify the model. Temperatures above 30 degrees C and pH levels below 6 enhanced the formation of byproducts and D-lactic acid. By-products were formed in the presence of maltose only, whereas D-lactic acid was formed independently of the presence of maltose although the amount formed was greater when maltose was present. The lactic acid productivity was highest between 33 degrees C and 35 degrees C and at pH 6. In the concentration interval studied (up to 180 g l(-1) glucose and 89 g l(-1) lactic acid) simulations showed that both substances were inhibiting. Glucose inhibition was small compared with the inhibition due to lactic acid.
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| 33. |
- Alfredson, Håkan, et al.
(författare)
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High thigh muscle strength but not bone mass in young horseback-riding females
- 1998
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Ingår i: Calcified Tissue International. - : Springer. - 0171-967X .- 1432-0827. ; 62:6, s. 497-501
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate whether the type of weight-bearing loading subjected to the skeleton during horseback-riding was associated with differences in bone mass and muscle strength of the thigh, we investigated bone mass and isokinetic muscle strength in 20 female horse riders (age 17.9 +/- 0.6 years) who were riding 7.0 +/- 3.4 hours/week, and 20 nonactive females (age 17.8 +/- 1.1 years). The groups were matched according to age, weight, and height. Areal bone mineral density was measured in total body, head, lumbar spine, right femoral neck, Ward's triangle, and trochanter, the whole dominant and nondominant humerus, and in specific sites in the right femur diaphysis, distal femur, proximal tibia, and tibia diaphysis using dual X-ray absorptiometry. Isokinetic concentric and eccentric peak torque of the quadricep and hamstring muscles were measured using an isokinetic dynamometer. There were no significant differences in bone mass between the horseback riders and nonactives at any site measured. The horse riders were significantly (P < 0.05-0.01) stronger in concentric hamstrings strength at 90 degrees/second and 225 degrees/second and in eccentric quadricep and hamstring strength at 90 degrees/second. Horseback riding in young females is associated with a high muscle strength of the thigh, but not with a high bone mass.
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| 34. |
- Alfredson, Håkan, et al.
(författare)
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Long-term loading and regional bone mass of the arm in female volleyball players
- 1998
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Ingår i: Calcified Tissue International. - : Springer Science and Business Media LLC. - 0171-967X .- 1432-0827. ; 62:4, s. 303-308
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, we compared the bone mineral content (BMC) and bone mineral density (BMD) in the arms of 11 female volleyball players (mean age 22.0 +/- 2.6 years) training for about 8 hours/week, and 11 nonactive females aged 24.6 +/- 3.1 years (mean +/- SD) not participating in regular or organized sport activity. Using dual X-ray absorptiometry (DXA), BMC was measured in the proximal and distal humerus, and BMD in the distal radius. Isokinetic concentric peak torque (highest value attained during 5 or 10 repetitions) of the rotator muscles of the shoulder and flexor and extensor muscles of the elbow were measured using an isokinetic dynamometer. The volleyball players had significantly higher BMC (P < 0.05) at the proximal humerus of the dominant arm compared with the nonactive group, but there were no differences between the groups in BMC of the distal humerus and BMD of the distal radius. In the volleyball players, BMC was significantly higher at the proximal humerus, at the distal humerus, and at the distal radius in the dominant compared with the nondominant arm. In the nonactive group, there were no significant differences in BMC and BMD between the dominant and nondominant arm at any site measured. Except for shoulder internal rotation strength and elbow flexion strength at 90 degrees/second that was higher in the dominant arm in the volleyball players, there were no significant differences in muscle strength of the rotator muscles of the shoulder and flexor and extensor muscles of the elbow between the dominant and nondominant arm in the volleyball players and nonactive controls. In the volleyball players, but not in the nonactive controls, there were several significant relationships between shoulder and elbow strength and BMC at the distal humerus of the dominant and especially the nondominant arm. These results show that young female volleyball players have a higher bone mass in the proximal humerus, distal humerus, and distal radius in the dominant compared with the nondominant arm, and a higher bone mass in the proximal humerus compared with nonactive controls. Muscle strength of the rotator muscles of the shoulder is not related to the higher bone mass in the proximal humerus of the dominant arm. Theoretically, the observed differences in bone mass can be related to the type of loading the skeleton undergoes when playing volleyball.
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| 35. |
- Alfredson, Håkan, et al.
(författare)
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Prolonged progressive calcaneal bone loss despite early weightbearing rehabilitation in patients surgically treated for Achilles tendinosis
- 1998
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Ingår i: Calcified Tissue International. - : Springer. - 0171-967X .- 1432-0827. ; 62:2, s. 166-171
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Tidskriftsartikel (refereegranskat)abstract
- We prospectively evaluated areal bone mineral density (BMD) of the calcaneus and calf-muscle strength (concentric and eccentric plantar flexion peak torque in Nm) in 10 recreational athletes (5 males and 5 females), mean age 40.9 years (range 26-55), who were selected to undergo surgical treatment for chronic Achilles tendinosis localized at the 2-6 cm level. Surgery was followed by immobilization in a plaster cast for 2 weeks, followed by flexibility training and slowly progressing strength training and weight-bearing activity. One patient was excluded after week 0 because of a new injury. Seven patients were back to their preinjury activity at the 26-week control, and eight patients at the 52-week control postoperatively. BMD in the calcaneus and calf-muscle strength on the injured and noninjured side was measured preoperatively (week 0) and postoperatively (weeks 2, 6, 16, 26, and 52). There were no significant differences in BMD between the injured and noninjured side at weeks 0, 2, and 6, but at weeks 16, 26, and 52, BMD was significantly (P < 0.05) lower (11.5%, 18.4%, and 16.4%, respectively) in the calcaneus of the injured side. Concentric and eccentric plantar flexion strength were significantly lower on the injured side preoperatively. Eccentric, but not concentric plantar flexion strength had recovered compared with the noninjured side 1 year postoperatively. Calf-muscle strength was not related to bone mass in the calcaneus. As a comparison, we used a group of 11 recreational athletes (10 males and 1 female), with a mean age of 46.1 years (range 28.9-58.5) who had been surgically treated for chronic Achilles tendinosis at the 2-6 cm level 39.5 +/- 11.8 months ago. In this group, there was no significant difference in BMD of the calcaneus between the injured and noninjured side. It seems that there was a delayed and prolonged calcaneal bone loss despite early weightbearing loading in patients surgically treated for chronic Achilles tendinosis at the 2-6 cm level. Around that time, when the Achilles tendon had healed (4-6 months) and the athletes returned to their sports, the calcaneal bone had a relatively low BMD and might possibly be vulnerable to heavy loadings. There were no signs of recovery 1 year postoperatively, but in a comparison group there were no significant side-to-side differences 39.5 months postoperatively.
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| 36. |
- Andersson, H O
(författare)
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Relevant elements of laboratory competence
- 1998
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Ingår i: Accreditation and Quality Assurance. - 0949-1775 .- 1432-0517. ; 3:7, s. 281-283
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 39. |
- Annas, Anita, et al.
(författare)
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Induction of ethoxyresorufin O-deethylase (EROD) and endothelial activation of the heterocyclic amine Trp-P-1 in bird embryo hearts
- 1998
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Ingår i: Archives of Toxicology. - : Springer Science and Business Media LLC. - 0340-5761 .- 1432-0738. ; 72:7, s. 402-410
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Tidskriftsartikel (refereegranskat)abstract
- The xenobiotic-metabolizing activity of avian heart was investigated in chicken and Eider duck embryos exposed to aryl hydrocarbon (Ah) receptor agonists in ovo. Both beta-naphthoflavone (BNF) and 3,3',4,4',5-pentachlorobiphenyl (PCB 126) induced 7-ethoxyresorufin O-deethylase (EROD) activities in chicken embryo hearts whereas Eider duck embryos only responded to BNF. The differential responses of chicken and Eider duck embryos were used to examine the involvement of Ah receptor-mediated enzyme induction in the activation of the environmental and food mutagen 3-amino- 1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1). As determined by light microscopic autoradiography, there was a highly selective binding of non-extractable 3H-Trp-P-1-derived radioactivity in endothelial cells of large vessels and capillaries in hearts of BNF- and PCB 126-treated chicken embryos. No binding occurred at these sites in vehicle-treated controls. There was also a strong endothelial binding of 3H-Trp-P-1 in hearts of BNF-treated Eider duck embryos whereas no binding occurred in hearts of PCB 126-treated Eider duck embryos. A positive correlation between induction of EROD activity and covalent binding of 3H-Trp-P-1 to protein in heart homogenates from BNF- and PCB 126-treated chicken and Eider duck embryos was also observed. The results suggest a cytochrome P450 1A (CYP1A)-mediated activation of Trp-P-1 in avian heart endothelial cells although involvement of other Ah receptor-regulated enzymes is also possible. We propose that heart endothelial cells may be targets for bioactivation and toxicity of environmental contaminants in birds exposed to Ah receptor agonists.
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| 44. |
- Bemark, Mats, et al.
(författare)
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Conserved sequence elements in K promoters from mice and humans : Implications for transcriptional regulation and repertoire expression
- 1998
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Ingår i: Immunogenetics. - : Springer Science and Business Media LLC. - 0093-7711 .- 1432-1211. ; 47:3, s. 183-195
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Tidskriftsartikel (refereegranskat)abstract
- Promoter region sequences of human and mouse Igk-V genes were aligned and found to be conserved for about 200-300 base pairs (bp) within subgroups/families. No promoter similarity was found between IGKV promoters from different human subgroups. Related mouse Igk-V gene families were conserved in the promoter region but no similarity was evident when promoters from unrelated Igk-V gene families were compared. Most of the human IGKV promoter subgroups were shown to have mouse counterparts with a similarity region that extended about 150 bp upstream of the translational start codon. All promoters contained an octamer sequence element. The consensus octamer/decamer sequence was favored but only seven residues within the octamer element were strictly conserved. Furthermore, there was also sequence conservation immediately 3' of the octamer where either an A or a G residue was conserved. In addition, other DNA elements were also conserved both within the Igk-V subgroups/families and between mouse and human promoters from related subgroups/families. In several of the subgroups/families an E box of the E2A type was conserved 5' of the octamer and a CCCT element was conserved within the IGKV subgroup II and its related mouse Igk-V families. We conclude from this study that conservation of additional sequence elements besides the octamer is a common feature in Igk-V promoters but that distinct elements are conserved only within a given subgroup/family. Thus, the conservation appears to have operated at the level of function rather than at the level of recognition sequence for defined transcription factors.
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