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- Al-Abdalla, A, et al.
(author)
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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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In: Journal of Chemical Physics. - : Springer Science and Business Media LLC. - 0021-9606 .- 1089-7690. ; 108, s. 2005-2014
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Journal article (peer-reviewed)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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| 7. |
- Kifetew, G, et al.
(author)
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The effect of drying on wood fracture surfaces from specimens loaded in wet condition
- 1998
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In: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 32:2, s. 83-94
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Journal article (peer-reviewed)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.
(author)
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Influence of tip geometry on fractal analysis of atomic force microscopy images
- 1998
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In: 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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Journal article (peer-reviewed)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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- Ratkevicius, A, et al.
(author)
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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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In: 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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Journal article (peer-reviewed)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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- Rodushkin, Ilya
(author)
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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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In: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 362:6, s. 541-546
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Journal article (peer-reviewed)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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- Thuvander, F., et al.
(author)
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A multiple fracture test for strain to failure distribution in wood
- 1998
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In: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 32:3, s. 227-235
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Journal article (peer-reviewed)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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